Is it even remotely feasible to turnback a single engine aircraft with an engine failure?

Nobody mentioned the theory so far, so I'll try to fill in.

Disclaimer: The below calculations and estimates are based on what I know about the physics involved. I don't know whether they are actually mentioned in pilot operating handbook of any aircraft.

To successfully turn back, you after climbing at best climb rate, when the engine quits you push down, execute the turn at suitably slightly higher speed to maintain the angle of attack and glide back.

The rate of climb is thrust/weight minus lift/drag, the glide rate is just lift/drag.

Glide rate in the turn is higher by factor depending on the bank angle (coordinated turn; uncoordinated turn is always worse). Calculating best glide rate turn leads to bank angle should be around 45°, speed should be about 19% higher to maintain best glide angle of attack and about 41% higher rate of descent than in straight glide. According to the article linked in the other answer, flying at just above stall speed (which is also 19% higher than in straight flight) should be better due to tighter circle despite worse lift/drag ratio.

The radius, and thus length of the turn of course depends on speed. At 110 knots (true speed, not indicated) the turn will take about 1.4 nm, at 160 knots it will already be about 3 nm. At 60 knots it will only be 0.42 nm. Since you need to maintain indicated speed, the true speed will slightly increase with altitude.

So for the turn back to be possible the plane needs to have sufficient power to climb faster than it will descend in the glide and you have to be high enough to allow for the extra gliding distance (which due to higher rate of descent corresponds to even longer straight glide).

All or most planes will have sufficient thrust at sea level to climb faster than they descend in glide. But since thrust decreases with altitude and temperature, if your departure point is high or warm enough, it may no longer be the case.

Even if the thrust is sufficient, the distance between climb and glide profile starts at zero on lift-off and will only become sufficient to cover the extra miles in the turn above some altitude. The altitude depends on many factors mentioned above.

It's not reasonable to try it without knowing what altitude is needed for it at current conditions.


Is the emergency fluorescent floor lighting strip along the aisle an item on the MEL?

Those lights don't have to be mounted to the floor. They can also be seat mounted.

http://www.bruceind.com/index.php?option=com_k2&view=item&id=90:escape-path-lighting-systems&Itemid=189

http://www.astronics.com/_images/aircraft-safety/EPM%20033010.pdf

This is the AC that provides guidance on the requirements of the system. http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC25.812-1A.pdf

The regulation is 14CFR 25.812


When do I execute a missed approach on a LOC approach when I can't identify the MAP?

Well, I’m not an FAA guy so I can’t find the relevant FAR quote, but going more general:

ICAO Doc 8161 Vol 1 - Aircraft Operations I-4-6-1

6.1.4 Note 2

  In the case of a missed approach with a turn at an altitude/height, when an operational need exists, an additional protection is provided for the safeguarding of early turns. When it is not possible, a note is published on the profile view of the approach chart to specify that turns must not commence before the MAPt (or before an equivalent point in the case of a precision approach).

There is a nuance difference between AIM’s “you are not supposed to turn” and the ICAO’s  “if the turn area is not protected there must be a warning label”. The first is just procedural, the second ensures you will not hit a mountain.

If the missed approach only specifies ‘Climb 1000’ then climbing left turn to..’ then the airspace is protected even for early turns (between IAF and MAPt) and you can start turning as soon as reaching 1000’. It might get you in trouble with ATC (ie. they were not expecting you to do it), but it will not get you into a mountain side. If you can call ATC and explain that you are turning early because of a navigation/timing fault, you will be allright.
If there is also a ‘do not turn before [...]’ then you shouldn’t turn before, regardless if that fix is the MAPt or not. How to determine that fix or MAPt then becomes a navigation issue:can you use alternative methods? Gps? Dme? Vor radials? are you under radar contact? How about using the VSI climb rate to estimate 1 minute (climbing 700’ at 700 fpm). If neither, then you might be in an emergency situation.


Why is the Eurofighter's nose gear door shorter than the bay?

Some fighters and as well civil airliners have fans ending in the gear bay. To allow for pressure relief some sort of opening needs to be created to vent to atmosphere. Various designs are available to achieve this, like the well known grills or mesh on carbon or aluminum structure skin. Or, just shorten a nose gear bay door if you have no place to accommodate the mesh and suck it through top part (see holes in the top where cables is routed) If you stick your head into a F18 nose gear bay and it is electrically powered, it will be quite noisy. Seems as the Eurofighters have the same design.


Why does the Harrier jet have four landing gears?

The main load bearing landing gear is in a bicycle setup, with 2 outriggers for stability.

This allows the gear to be lighter, stay close to the center and out of the way for the jet blast.

The Lockheed U-2 also has its gear in the bicycle configuration and takes off and taxies with detachable "pogo" outriggers for stability.


Are ATCs required to notify pilots when they use MVAs?

I'm not exactly sure what you are asking, but no, we do not notify pilots that we are vectoring in accordance with the minimum vectoring altitudes - because that is what we always do. ATC is responsible for terrain clearance during radar vectors, and pilots know this, so it is implied and understood that we use safe levels.

MVA's simply define the lower level for radar vectoring in an area - the lower level of our designated "box". Just like there is an upper limit and lateral limits as well, that we cannot cross during vectoring. MVA's are based on terrain and other obstacles, to ensure that terrrain clearance is always provided. You make it sound like MVA's are only used in special circumstances, which is not true. Vectoring at and above the MVA is completely routine and happens every day.

As for cross checking by pilots, MVA's are supposed to be published on a separate chart which pilots can use to cross check their assigned levels. The MEA is not used during approach, and pilots know this. In case of a radio failure during approach, if the flight is being vectored below minimum sector altitude (MSA), the pilot will climb to the MSA, even if the MVA is lower.

Further reading on SKYbrary.


Which source to use when reporting the current altitude to ATC?

When asked for altitude, you report the altimeter reading, utilizing the correct barometric pressure entered into the Kollsman window.

ATC separates traffic based upon indicated altitude.  The indicated altitude may include errors, such as the pressure ATC provides, but all aircraft in the area will presumably be using the same barometric pressure, and will have similar errors.

GPS altitude, which some call an absolute altitude, is an altitude relative to a model, normally the WGS84 elipsoid, and has it's own set of errors.

By convention, indicated altitude, based upon local pressure, is used for aircraft separation.


Is Turn and slip indicator a good back-up for the attitude indicator?

Is it true that a Turn and slip indicator is a valid back-up for the attitude indicator?

Partially, but it would need to be used in conjunction with one or more other instruments if the Artificial Horizon is inoperable.

Change in the DI and/or compass will indicate a turn.
Change in altitude on an altimeter will indicate a climb or descent. Usefulness of the VSI is limited in this sense.

  To what extent is a turn and slip indicator a back-up for the attitude indicator?

With every one of the instruments on an aircraft there are backups. Sometimes this may be an entire second stack (eg Radio may have a complete second system, AoA sensors may be duplicated) other times you need to use a combination of more than one other instrument. In the case of a Turn/Slip indicator the latter is true. You  use a combination of DI, VSI, altimeter as described above to get a picture of your attitude when the Attitude Indicator itself is inoperable


What noises can you hear as a passenger?

There are loads of noises you might hear; there are fuel pumps, hydraulic pumps, air circulation, adjustment screws, servos, and on Airbus aircraft a strange clanking noise when you go over bumps in the tarmac.

On the ground you may hear (and feel) cargo pallets rolling on the hold, and the hold doors being opened and shut. In-flight you have engine noises and air flow noises.


What dictates the shape of the attitude indicator display on the PFD?

A circle makes sense because a physical attitude indicator is round. (A physical one has to be round because it consists of a ball moving behind a window.) It makes the screen display look more like the instrument it replaces, which is good for recognition and familiarity, and makes it easier to judge things like bank angles.

A rectangle makes sense because it has to fit on a rectangular screen. You can tile rectangular instruments/displays on a screen efficiently, with no wasted space between them, as your example shows with the tapes. Rounding the corners delineates the edges of the display better than just having abutting rectangles.

The full process by which physical cockpit instruments and glass-cockpit displays are designed and laid out is too long to explain here. The main focus is on making it hard to make mistakes, and after that to make it quick to see the most important information. To support this, each instrument has to be easy to identify and to read correctly. Despite the shape difference, the two designs look very similar. Even if you've never flown any of these aircraft before, you'd immediately recognise it as an attitude indicator, and you wouldn't confuse it with a different instrument.


What are autothrust and manual thrust on an A320 (or other aircraft)?

Manual thrust means that the engine thrust corresponds directly to the position of the thrust lever.

Autothrust means that a target speed is dialed into the system (using a knob that is usually located on the glare-shield) and the auto-thrust system automatically adjusts the engines to maintain that speed.

Now in an aircraft with classical controls the longitudinal stability means the aircraft tends to maintain speed with pitch and pilots basically need to use thrust to climb or descend and yoke to adjust speed, always making adjustments with the other control as well to avoid oscillations and compensate for the more complex parts of the power-pitch relationship.

Due to this, it is usually recommended to fly either fully manual or fully automatic (autopilot+autothrust).

But Airbus A320 and newer (A319 is just a variant of A320) changes that with the artificial neutral stability in normal control law. Even with autopilot off, the flight computer automatically adjusts trim so that the aircraft flies straight so that adding power makes the aircraft accelerate and reducing it makes it decelerate. However pushing the stick forward to descend will still make the aircraft accelerate and pulling it to climb will make it slow down.

Due to this, Aibrbus aircraft are easier to fly with autothrust always on (except for take-off roll; autothrust is disabled when the power levers are advanced above certain position, which is only done for take-off and in emergency where extra power is needed).


Why do cockpits with ACARS have printers?

Not all cockpits with ACARS have a printer for it -- it's an entirely optional part of the system.

The printer is there so that you don't have to copy by hand information that you want or need to have available.  For example, ATIS is desirable to have in hard-copy, so that when you need some piece of it immediately (say, the altimeter as you're descending through the transition level, or the identifier as you go to check in with Approach), it's there without going through the levels of menus to retrieve it from the ACARS system.

Also, on a Class II navigation route, if you get a significant reroute, your procedures may dictate that you have a hard-copy flight plan that shows the new route, and which you'll annotate with things like actual times & fuel onboard overhead various waypoints, actual winds, etc.  That may be required by company procedures or regulation, and the hard copy is there for those times when the computer decides to misbehave.  And all of THAT info is most certainly something you don't want to have to copy by hand -- it's pretty lengthy, and accuracy is really, really important.

Beyond that, it is "nice to have" a hard copy of things like a PDC clearance, and it is quicker to tap "PRINT" rather than copy it all down by hand.


How does Air Traffic Control know a flight's route and destination?

Under instrument flight rules (which all scheduled passenger flights operate under), the pilot will file a flight plan with the local air traffic control authority (in the US, that is the FAA). This flight plan describes in fairly specific terms where the pilot intends to fly, by going from point to point. You can see flight plans on a site like https://flightaware.com.

These flight plans are entered (electronically, in most cases, but sometimes typed in) into the air traffic control system. So each controller who handles the flight knows where it is supposed to go next.

The details of the start and end of the flight isn't determined by the pilot, but by ATC when they set up the departure or arrival. These are done using instructions called SID (Standard Instrument Departure) and STAR (Standard Terminal Arrival Route). Depending on the traffic patterns around each airport, ATC may assign a particular SID or STAR. These instructions are like "fly at this altitude until this point, turn right, descend to this other altitude, fly until you get to this other point", and so on.

For international flights, the flight plans are transmitted from one country to another using AFTN (Aeronautical Fixed Telecommunications Network). So each country that the flight flies over knows where it is supposed to be going.

Other factors which can influence the actual route a flight takes can include:

Weather
Other air traffic
Military operations
International agreements (or more specifically, disagreements)


How is risk managed in single engined piston aircraft flights?

"A ship in harbor is safe, but that is not what ships are built for."

You said in your question:

  It appears that some phases of flight of a piston single, there are sections of the flight for which safe recovery from an engine failure is not possible due to the lack of reachable emergency landing areas.

This is true not only of piston singles, but also of anything that flies out of gliding distance of good landing sites - think about Amelia Earhart's Lockheed Electra.

You'll usually hear this called "inherent risk", but the correct term for the concept that you're describing is systemic risk. As you suggested in your question, this risk has to be taken, it cannot be eliminated.  The only way to eliminate it is to not fly; and sometimes, when the risk of the flight becomes too great, that's exactly the decision that a pilot has to make.

  Is it possible to reduce this risk with either better pre-flight
  checks and through purely technological means?

Yes, as long as you're willing to pay for it. Everything in aviation is a tradeoff, and it's usually a trade either between safety and cost or safety and weight. As an exaggerated example, you could build a piston single with 30mm armor plating to mitigate the risk of incoming artillery fire, but it wouldn't fly very well and not many piston singles routinely take artillery fire anyway.

Those safety improvements which are simple and economical to make, we've already made mandatory (for example, all IFR aircraft certified in the USA need to have an alternate source of power for their artificial horizon if the primary source of power is electric).  Safety improvements which aren't simple or economical are left to the discretion of the owner of the aircraft.

  Suppose I am taking flight instruction can I do anything to reduce the risk of engine failure?

Sure is.

Pay attention to your instructor and do what she tells you.  You can't prevent an engine failing because an oil pump blows out.  You can prevent the engine failing because you ran the fuel tanks dry.
Fly well-maintained aircraft. Talk to the mechanics who work on your airplane. Do what they say.  Avoid operators who let maintenance slide.  If you're the owner, don't let maintenance slide.
Fly aircraft that fly a lot. The worst thing for an aircraft engine is to sit in the hangar for three months, fly for an hour, and then go back into the hangar for three more months.  The more that engine gets used, the happier it is.
Have a contingency plan. For example, examine the area at the departure end of the runway and make a plan of where you would land in the event of an engine failure at any point before a turnback would be feasible. - Thanks Jonathan Walters!
If you do go down in a field, have a 24-hour survival/medical kit on board, and wear clothes suitable for the climate. Rescue doesn't get there instantly. Speaking of rescue, you did file a flight plan, didn't you?


Is there such a a thing as a single European pilot's license?

Is there ... a single license that allows a pilot to operate any European registered aircraft in any European country,

Yes.

According to the UK CAA
an EASA Part-FCL licence can be used to fly any EASA aircraft in any EASA member country.

I have interpreted your "Europe" as "EASA member" in order to avoid ambiguity about Switzerland, Croatia, Kalingrad, etc.

  Most aircraft in Europe are EASA regardless of state of manufacture or registration.

  The UK currently grants several levels of licence:

  UK National Private Pilot Licence (NPPL)
  UK Private Pilot Licence (PPL)
  EASA Part-FCL Light Aircraft Pilot Licence (LAPL)
  EASA Part-FCL Private Pilot Licence (PPL)
  EASA Part-FCL Commercial Pilot Licence (CPL)
  EASA Part-FCL Airline Transport Pilot Licence (ATPL)


Why the pitch rate q is zero while angle of attack is changing and vice versa?

It generally does not (*). You misunderstood the statement in the Etkin's book.

The image you posted come from the chapter about "the $q$ derivatives" $C_{L_q}$, $C_{M_q}$ and $C_{h_q}$.

The book is quite explicit:

  These derivatives represent the aerodynamic effects that accompany rotation of the airplane about a spanwise axis through the C.G. while $\alpha$ remains zero

It then presents

  Figure (b) shows the general case in which the flight path is arbitrary

(this is the figure you posted)

  This should be contrasted with the situation illustrated in figure (a), where $q=0$ while $\alpha$ is changing.

The book in no way implies that either one case or the other is true, it is only presenting contrasting academic examples to illustrate the concept of what the $q$ derivatives are.

(*): I said generally because the book itself present one case where you CAN have constant $q$ and $\alpha = 0$, the steady pull-up.
Again, this in no way implies that you always have

  q is zero while angle of attack is changing and vice versa


Why aren't test planes remote controlled?

Taking a plane that is designed to be operated by humans and retrofitting a system for remote control would be a big task. They do it with old fighter jets for use as target drones. But a target drone's task is pretty simple; fly like a fighter jet until it gets shot down.

At the point where SpaceShipTwo is, a bunch of testing has already been done. This is supposed to show that the vehicle is safe enough to move on to piloted testing. But testing aircraft and spacecraft is a dangerous job and things happen.

Creating a remote control system for an spacecraft like SpaceShipTwo would be much more of an issue. First of all, there will most likely be physical changes required, whether this is to install hardware to manipulate controls, or just electronics to remotely operate the flight computers. These physical changes will be extra work and will affect the tests, since when the plane is actually operating, those things won't be in place. And if those remote control systems fail, you lose the aircraft. Sure, you don't lose pilots, but why lose a plane just because a remote control system (which won't be used on production) fails? Should you spend time and money developing a complicated remote control system, or developing the actual vehicle?

Also, many tests require the pilots to be on board. They are not just testing the systems, but how the pilots interface with them. Having real pilots actually flying the vehicle is the whole point of this phase of testing.

See this related question as well: Why do the engineers need to be on board during testing?


How much is air mass flow rate of bleed air used for environmental control system in civil aircraft?

EASA and FAA engine type certificates often identify the total bleed mass flow, as a % of the engine's high pressure compressor exit flow. For example, see section 10, "Maximum permissible air bleed extraction" in this for the CFM56-7B, which shows 7 to 13%. If you assume in a civil aircraft that all the bleed air from the engine if for the ECS, you get an answer. (Or maybe you where actually looking for the total bleed mass flow).

If you can get this data from enough references, you could develop a general guideline.


Can Approach cancel my special VFR clearance if I'm already cleared?

The clearance comes with the catch that you need to maintain the minimum visibility requirements and sky conditions, if you're not able to, you have no clearance, it's pretty much as simple as that. Either you need to navigate in such a way that you avoid the weather (which might require you to leave the airspace) or you can do one of two things

Request an IFR clearance if you're rated and equipped
Declare an emergency and land in the nearest suitable spot, assuming you can still see the ground

If it is deteriorating so quickly that you cannot go back to where you came from (i.e. the weather is not better outside the D), you'd be flying illegally outside the D as well, so no point in going there really, but more importantly, if the weather is deteriorating that dramatically, you don't have much time before you'll be completely blind, and by that time you'll want to be on the ground with as little injuries as possible, no matter where or the condition of the aircraft.

Note that the minimums are different depending on where you are (jurisdiction) and type of aircraft.


What are the procedures for flight checking a glideslope and localizer?

It's all laid out in Order 8200.1D United States Standard Flight Inspection Manual.

That and other documentation, including the inspection reports can be found from the FAA website under Flight Inspection Information.


Why is the IFE only available after take-off and shut off before landing?

They do this for the same reason they make you put away all electronic devices during that period of flight. The first minutes of a flight (take off and climb out) as well as the last few (approach and landing) are the most critical and statistically the time that if things are going wrong they will go wrong. As such airlines shut down the IFE systems and ask users to shut down personal devices so that they can hear, and more importantly respond to any emergency directions that may be given during this critical time.

2019 Update: Since this original answer was posted some airlines now allow the use of "small personal electronic devices" in all phases of flight.


Is AD compliance ever physically verified when maintaining an aircraft?

I can only speak for commercial aviation, but in my experience, we generally have 100% RII buyback on initial AD compliance issues. For example, if we have to run a new wire bundle or reroute a wire bundle as part of an AD, it has to be "bought off" by either a QC inspector or an RII-qualified mechanic. In these situations, I would say that the work is done properly 99% of the time. Rarely would someone put their name on something that's done incorrectly if they don't have to go back and do the work themselves. The response is generally "Call me when you get it right."

Where I think the FAA severely lacks oversight, in my opinion, is future compliance in upholding the standards of the AD. On the initial AD, you're not allowed to deviate one iota from the original without a very special process put in place. But what happens when you deviate 10, 15, or 20 years down the road?

Hypothetical scenario: An AD is written to reroute a wire bundle from other wire bundles because of some safety issue. The AD is complied with and life goes on. Twenty years later, a mechanic disassembles all the wiring in the area for "X" maintenance issue. He turns it over to the next shift to reassemble it. Next shift has no idea how it goes back together. It's not marked as AD wiring. There are no instructions on how it all goes back together (save for the AD paperwork from 20 years ago), so the mechanics put it back together per the standard wiring practices manual. They bundle and clamp. Bundle and clamp. They do a beautiful job, but guess what? It violates the purpose of the AD from 20 years prior. Do you think the FAA follows up on that? Nope. The company? Nah. They have paperwork showing the AD is complied with. So it's up to each mechanic to determine if what they're working on is part of an AD (even one from 20 years ago), despite no special labeling or instructions, and maintain that AD compliance. As we mechanics joke, "It'll all come out in the investigation."

My experience is that as time goes by, the integrity of many AD's slowly dissolves. That being said, if we as A&P's even smell the faintest whiff of an AD, our antennae perk up and we are very careful to maintain that compliance. AD  violations are the surest way to get a nice letter in the mail from Mr. FAA.


What would be the designation for 4 parallel runways?

Airports can have a left, center and right runways.  Memphis (KMEM) is a good example.  Airports with four or more parallel runways are left and right with the numbers off by one.  Los Angeles (KLAX) and Chicago (KORD) are good examples of such an arrangement.


Why do we still use pilots to fly airplanes?

That's a good question, and brings up a joke that many pilots know well:

  "What's going to be in the cockpit of the future?"

  "A dog and a pilot."

  "A dog?  Why a dog?"

  "Well, the dog is there to keep the pilot from touching anything."

  "Ummm, why have the pilot then?"

  "Well, someone has to feed the dog! "

Technology has improved to the point where airplanes can pretty much fly and even land themselves.  They are even getting pretty good at handling "normal" emergencies like engine failures and depressurizations.

Where pilots really shine though are the type of abnormal and emergency situations that aren't "in the book".

When an engine flies apart and shreds the hydraulic lines on all three redundant hydraulic systems, a computer will be out of options because it was never programmed to handle that (because it was considered "virtually impossible" when it was designed).  A pilot on the other hand can analyze and experiment until he finds enough of a solution to keep the airplane in the air as he works through other issues.

During a total electrical failure, the computers won't be much good.  Sure, you can design redundant systems and make it so that it "can never happen", but what about when it does?

There are also all of the little things that a pilot is constantly making decisions on how to handle.  Some examples could include:

Can the airplane fly with a particular feature inoperative?
What about multiple features inoperative?
How do they interact with each other?
What do you do when the passengers take too long to board and you are going to miss your departure slot?
What do you do when the ground crew forgets to close a door?
What about when the tug driver doesn't push you back quite far enough?
Or ATC wants to change you to a different runway?
Or you ask ATC to change you to a different runway because it might save a few minutes and that will keep you from having to deice again?
Or another airplane unexpectedly pulls out in front of you while taxiing?
A pilot can see "ugly" clouds off the end of the runway and decide that it would be better to wait a bit before taking off.
What happens when a flock of birds suddenly appears during the takeoff roll?
What happens when a passenger gets sick or unruly?
When do you need to divert and when can you continue?

On a typical flight, a pilot will make hundreds of small decisions that can make a big difference in the flight.  Any one of these (or one of the tens or hundreds of thousands of other things that could happen) could trip up a computer.

The pilot is also there as the "final authority".  If a hacker were to somehow hack into the automated systems, a pilot can always disconnect them and fly the airplane manually.  He can turn off systems, he can be...  Well, the pilot can be creative and a computer can only do what it was programmed to do.

Right now when a drone crashes it isn't such a big deal because nobody was on board.  If an airliner with a load full of paying passengers crashes it is a big deal.  Even just one.

Many of these problems can be overcome.  Some of them already have been.  Some of them may never be fully handled in an automatic way but maybe we could still do automated flights with an acceptable level of safety.  Some automation is actually better than some pilots in certain areas.

However, the biggest reason that we don't have fully automated passenger airplanes is because the general public feels comforted by a person being up front who can take over and carry them to safety if needed.  Even if the technology were 100% ready for automated passenger flights, I think that the number of people willing to purchase a ticket would be so low that it would be financially unfeasible for an airline to deploy it.


What light signals or visual markings indicate that turns should be made to the right at class G airports?

Here's the example from the FAA's Airplane Flying Handbook (chapter 7):

  If there are no other aircraft present, the pilot should check
  traffic indicators on the ground and wind indicators to determine
  which runway and traffic pattern direction to use. [Figure 7-2] Many
  airports have L-shaped traffic pattern indicators displayed with a
  segmented circle adjacent to the runway. The short member of the L
  shows the direction in which the traffic pattern turns are made when
  using the runway parallel to the long member. The pilot should check
  the indicators from a distance or altitude well away from any other
  airplanes that may be flying in the traffic pattern.

Here's what it looks like at Huntsville Executive (KMDQ), which has a right-hand pattern for runway 36:


RTCA documents are not FAA documents, although the FAA is usually a member of the Special Committee that creates the documents. If an example is to be added, it is the decision of the SC, not of the FAA.

The reason that no examples are given is that the recommendation is clear by itself. A good V&V engineer will read this recommendation and use his skill, experience and creativity to find an other acceptable means to validate the software requirements that can not be validated in a realistic environment. This alternative means is then documented in the SVP.

Giving an example is not helpful at all, since the solution will depend completely on the software under test and the nature of the requirements.

If the hardware is not available, an emulator may be the solution.

In other cases artificial test inputs have to be generated, because failing a test in a realistic environment may prove to be catastrophic.


Can a commercial airliner be landed on a highway, e.g. Highway 405 in Los Angeles?

It's possible, assuming the section chosen has no streetlamps, signs, overpasses etc. The police can block the traffic easy enough.

However, there would be zero reason to do so. If a plane has enough control to reach the highway, and enough advance notice to find a suitable part and block the traffic then it has enough control and time to reach one of the many airports in the region. Much less fuss for all concerned, and a much better equipped crash service.

In the prairies one could set up a fighter or bomber base on a random road, but again there's no need to - there's nothing nearby that would require it, heavy bombers or commercial planes would quickly destroy a normal highway and fighters could use the many civil airstrips in the area.

In Europe the math is different - opponents are a short flight away and destroying the airbases on both sides would be a top priority in any European conflict. See "Highway strip" in the usual reference for more details.


How long does it take on average for a control surface to deflect by one degree?

With hydraulically actuated flight controls, the deflection speed is only limited by the maximum hydraulic fluid flow through the servo valve. I've taken some step responses of civil airliners in the past, and on-ground they can deflect full range in about 1-2 seconds.

For a mid-range passenger jet:

Elevator range = 42 deg, max no load deflection speed = 66 deg/sec
Aileron range = 40 deg, max no load deflection speed = 66 deg/sec
Rudder range = 48 deg, max no load deflection speed = 56 deg/sec

At higher airspeed the maximum deflection angle and speed become less due to aerodynamic blowback - by design, to limit the inertia forces on the airframe.


What is the different between an aircraft engine gearbox and an aircraft engine transmission?

In aircraft, transmission usually refers to the whole system, that transmits power between two points, say between the MGB and the tail rotor. Gearbox is usually a component of the transmission system (along with shafts, for example) which is used for changing rotational speed.

In a sense, a full transmission system is found only in helicopters, and not in fixed wing aircraft. The closest thing a fixed wing aircraft has to a transmission is the variable pitch propeller, which is analagous to the car transmission.

By nydano - Cut away view of Hamilton Standard Propeller, CC BY-SA 2.0, $3

On the other hand, a number of aircraft have gearboxes, especially the turboprops (and some piston engines), for reducing the engine output speed before turning the propeller. The following image shows the gearbox in a GE turboshaft engine.

Image from mrlarry.org

Turbofan engines do have a gearbox, which is used to run the accessories. The compressor is usually run through a shaft from the turbine, with various turbine stages running various compressor stages, while some turbofans do use gears between turbine and compressor, called geared turbofans.

Aircraft transmissions (whether helicopter or fixed wing) is usually one speed from one point to another, with speed reduction (or direction change) offered by the gearboxes.


Why are the wings of some planes changing width?

Well, yes, bigger wings to provide better lift, but the also produce more induced drag in the process.

The wings on an airliner are optimized for cruise in high subsonic and transonic flight where a slender, swept wing works well.  While this is great for cruise flight, the trade-off is this style of wing requires a very high approach speed for landings which in turn require very long runways to accelerate the airplane on to reach rotation speed for takeoff or to decelerate the aircraft on once it has landed.

The Boeing Company successfully addressed these problems in the early 1960 with the development of the 727 airplane as a regional airliner.  It made use of a type of flaps called Fowler flaps (see Fig 1) in concert with leading edge extensions.  Fowler flaps. These style of flaps consist of a series of segments attached to tracks or support linkages running chordwise, allowing the flaps segments to extend and retract by rolling along said tracks.

Fig 1. Typical Fowler flap installation

When deployed these give the effect of changing the airfoil shape from a slender, slightly cambered airfoil into a wide airfoil with a large camber.  Fowler flaps have an additional advantage to them in that partial deployment creates a large increase in lift with limited additional drag, very useful for takeoff, while when fully deployed they create a lot of drag in addition to higher lift.


Why does the UK CAA restart its page numbering with every new chapter of their CAP publications?

That's an artefact of a different era. Before computers were used to create documentation, updating large documents was difficult and expensive. People tried to reduce the workload by using chapter-page numbering. When you have to add pages to a book, chapter-page numbering allows you to replace one chapter instead of having to reprint the whole book.
Some organizations even supplied book updates as individual pages with a 'list of effective pages' so you could swap them out in your copy.
Nowadays there's no reason to keep doing this. Rebuilding a document (generate the TOC and crossreferences) is cheap, printing is cheap. You already noticed the big disadvantages of chapter-page numbering to the user.
Why they're still doing this? Inertia, probably.
How to reference them? Page 5-2 works, and if you want to be comprehensive, page 5-2 (PDF page 124).
(sorry, no references. Just lots of experience building large documents)


What is some of this extra "stuff" on jet engines?

Of course the basic concept of a turbine engine is relatively simple, but the devil is in the details. To make an engine efficient, reliable, powerful, and safe, a lot more components are needed.

Fuel. Obviously an engine needs fuel to operate. The fuel is burned in combustors located around the circumference of the engine. This requires separate fuel lines to each of the combustors around this section of the engine. The fuel must be connected to the main fuel supply, and to the throttle/engine controls to meter the fuel flow.

Oil. All the rotating machinery inside of a turbine means that oil is needed to keep everything moving smoothly. There is an oil tank, and tubes to move it to where it is needed.

Main bleed air. Bleed air is taken from certain sections of the engine. This serves the air conditioning and anti-ice system and can be used to start other engines. This bleed air is taken from multiple places around the circumference, and from multiple stages provide the required pressures at different engine speeds.

Other bleed air. The basic design of a turbine engine has air entering the front and leaving the back. However, in a real engine, a lot more movement of air is going on. Engines have to operate in a huge range of conditions. Sometimes air needs to be bled from a certain section to manage the pressures and maintain stable operation. Sections of the turbine are also cooled by bleed air. It takes more tubing to move all this air around.

Sensors. Modern engines measure a lot of information to remain stable and efficient. This includes temperatures and pressures at multiple places all along the engine, as well as fire detectors and the speeds of the different rotors. These are all hooked back to the engine controls.

Generator. This is connected to one of the engine spools, and provides power to the aircraft, including all of the electronics on the engine itself.

Starter. Usually separate from the generator, also connected to an engine spool. This uses bleed air to turn the rotors in order to start the engine.

Control. Usually on the outside of the fan case (at the front of the engine, left side of the RR image in the question), modern engines run with a lot of electronics, referred to as Engine Electronic Control (EEC) or Full Authority Digital Engine Control (FADEC). All of the items above require wiring for control and feedback. Each tube will need different valves, connected back to the electronics, to control the operation. Liquids will need pumps and filters. There are also additional movable components inside the engine that can be adjusted by the engine control system.


Can someone please help me identify this?

It looks a lot like a Curtiss Model D to me.


Why is jet fuel cheaper than piston fuel?

Jet-A (and all turbine fuels) are far cheaper than 100LL (at least in bulk; retail prices vary due to local supply and demand as well as different regional tax regimes on aviation fuel) for several reasons.

Scale

Southwest Airlines alone burned through 1.9 billion gallons of Jet-A in 2015, dwarfing the mere 175 million gallons of 100LL that the entire US GA piston fleet consumed in the same year.  This means that Jet-A is made and traded in large volumes, enough to merit refiners sometimes optimizing for its production over other products in certain refineries, while avgas is the bastard child of the refining world -- people would rather make other things that are easier to sell than 100LL.

Ease of Production

Jet-A, like all kerosene fraction products, is straightforward to produce: straight-run kerosene that has been run through a few sweetening (impurity removal) processes is mixed with mid-weight distillates from heavy cracking processes (catalytic crackers, hydrocrackers, cokers) and presumably processed further with hydrogen and clay to get rid of more impurities.

On the flip side, there are all of two TEL (tetra-ethyl lead, aka the "lead" in leaded gasoline) producers on this planet that I can find (Innospec in the UK and TDS Chem in China).  Considering that the last few countries that use it in mogas are working on phasing it out, and very few road vehicles sold on the global market these days can even burn it to begin with due to being made to more stringent emissions specs, it'd be safe to say that the majority of TEL made on this planet is going into planes.

Atop that, avgas requires large quantities of high-octane blendstocks, but cannot use any oxygenates (they are prohibited by the avgas spec, aka ASTM D910, as GA fuel systems aren't compatible with 'em, especially ethanol).  These high-octane blendstocks are primarily alkylate and reformate, both of which require specialized refinery equipment to produce.  Furthermore, reformate is an inefficient source of high-octane blendstock (reformate is very heavy in aromatics such as benzene and toluene, which are better off getting distilled out of the stream to be used as a valuable chemical feedstock instead), and alkylation, while an efficient way to produce high-octane blendstocks, requires an acid supply nearby (either sulfuric or hydrofluoric), limiting where alkylation units can go.  Finally, both of these blendstocks are in demand for motor gasoline production as well, which means that most refineries that produce them are filling mogas demand first and avgas demand second.

Handling

Jet-A is relatively easy to handle -- it's a close cousin to the kerosene on hardware-store shelves.  It has a relatively high flashpoint (meaning you need to make a fine mist of it mechanically or heat it aggressively to ignite it), and this low volatility also limits worker exposure to the relatively limited chemical hazards it poses.  Furthermore, it can be shipped readily via most refined-products pipelines without posing unusual hazards or risking excessive cross-contamination by or to other products.

On the other hand, tetra-ethyl lead is highly toxic, and 100LL is toxic not just because of TEL, but because of volatile hydrocarbon toxicity.  While isoparaffins seem to be less problematic than normal paraffins from this standpoint, volatile aromatics (Benzene, Toluene, Ethylbenzene, and Xylene, or BTEX for short) are well known as troublemakers in the human body.

Atop this double handling hazard (volatility of the fuel and toxicity of TEL and light aromatics), pipelining 100LL is a much harder task due to the TEL contaminated transmix (contaminated stuff from the boundaries between products in a multi-product pipeline) it produces.  Normally, transmix is reprocessed by refiners or dedicated transmix reprocessing plants to produce gasoline and diesel (with most of the kerosene fractions in the transmix being lumped in with the diesel for simplicity's sake), but the presence of TEL in transmix renders it unreprocessable as any more than 50mg/gal of lead in motor gasoline means it is contaminated and unsellable as per EPA regulations.  Furthermore, shipping 100LL in a multiproduct pipeline risks contaminating other products with lead batch-wide due to dead legs and other such cross-contamination hazards, which means that in practice, 100LL is never shipped in multiproduct pipelines.

Instead, 100LL is typically railed or barged to terminals, and sometimes even trucked directly from the refinery as not all terminals have rail or barge access.  This drives up shipping costs compared to every other fuel (save for ethanol and other fuel blendstocks that are surfactants).


How can you find the best altitude for range or speed?

Generally, climbing as high as you can would be close to the optimum strategy. In the end, the altitude is given by the optimum lift coefficient in cruise, which can be approximated as $$c_L = \sqrt{\frac{1-n_v}{n_v+3}\cdot \pi \cdot AR \cdot \epsilon \cdot c_{D0}}$$
Now it will be important to get the thrust over speed dependency right, which is expressed with $n_v$. A turboprop should have $n_v \approx -0.7$. The rest is determined by the aerodynamics of your plane.

Nomenclature:
    $c_L \:\:\:$ lift coefficient
    $n_v \:\:\:$  thrust exponent, as in $T \sim v^{n_v} $
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing
    $\epsilon \:\:\:\:\:$  the wing's Oswald factor
    $c_{D0} \:$  zero-lift drag coefficient

If you have the optimum $c_L$, you need to find the altitude where level flight at cruise power will require this lift coefficient. Depending on the range of your small aircraft, you might spend most of the flight in climb and descent.

Maximum speed altitude: Draw the envelope at max power, and look for the rightmost point which can be trimmed. The equation above uses the quadratic polar approximation which works well at high lift coefficients, but for maximum speed the details of friction and parasitic drag are important, and they cannot be captured with a simple formula.


What is the source of emergency power for a 727?

According this rather detailed page on the 727's engines:

  To restart in flight, an "air start" may be attempted. The start
  switch should be placed in the FLIGHT START position which will arm
  high energy ignition. The starter valve will not open. Ram air
  entering the engine is sufficient for start if the aircraft's speed is
  above 150 knots. When the start lever is moved to IDLE, fuel is
  introduced and the igniters are activated.


Is it feasible to add an aftermarket hydrofoil to a light aircraft?

It's been done.  David Thurston designed a system for the Lake LA-4 that was purported to allow it to land on 5ft waves.  It may have been a bit of a handful (the Bucaneer is a demanding airplane on its normal hull) and was crashed by someone who took it for a spin without Thurston's authorization, and that was the end of that.


The two objects on the wings are the hooks for the launch bridle, which attaches the aircraft to the catapult shuttle for launching the plane from a carrier deck.


What is the difference between the airspace's classes (for non-pilots)?

Although Lnafziger's answer is correct, I'd like to elaborate on the purpose of the airspace classes.

Class A: This airspace is intended for high-speed, point to point travel.  That is why pilots flying in Class A must be instrument rated and in contact with air traffic control (ATC); aircraft above 18,000 feet are likely to travel quickly and may not have time to avoid each other visually.  This is the upper layer of the airspace system.*
Class B: This airspace is intended for large airports with lots of jet traffic.  The large number and size of aircraft require space for ATC to get them efficiently in and out of the airports.  Approach control services are provided.  As a result, class B areas are physically large.  It is possible for small aircraft flying under visual flight rules to operate here with explict ATC permission, though permission to enter may be denied during periods of high traffic.  Small piston-powered aircraft land at Class B airports infrequently, typically due to high landing fees and fuel prices.
Class C: Smaller airports with a mix of piston-powered aircraft and jets.  Most Class C airports are home to flight schools and small aircraft hangars as well as scheduled service by airlines.  While still busy, Class C airports have less traffic than Class B, so ATC doesn't need as much space to keep them organized.  Like Class B, approach control services are provided.  Pilots are only required to establish two-way communication to enter the airspace.
Class D: The smallest airspace type for tower-controlled airports, traffic primarily consists of general aviation aircraft.  Often these airports handle cargo, business jets, charter service, maintenance or assembly facilities, etc. as well as private aircraft and flight schools.  They also host firefighting operations, airshows, or anything else that needs facilities but would interfere with normal traffic if put at a larger airport.  Although Class D airports are small, some are very busy; others handle only a few flights an hour.  Approach control services are only provided if the airport is near Class B or C airspace.
Class E: This is the lowest level of "controlled airspace."  "Controlled" doesn't mean you have to talk to ATC, but that ATC services are available (within the capabilities of radar and radio equipment).  This is general-purpose airspace.  Aircraft flying under visual flight rules can fly more-or-less whatever they want (weather permitting), and instrument flight rules traffic operate under positive control by ATC.  There are regulations in this airspace, but they aren't onerous, and they're designed to accommodate the wide variety of aircraft and activities that are found here.  Some small airports have Class E airspace surrounding them at the ground.  Although Class E is a single class of airspace, there are tighter regulations above 10,000 feet, where there are no speed restrictions (other than the prohibition on supersonic flight over land), compared to at lower altitudes where speeds are limited to 250 knots.
Class F: See What is Class F airspace, and why is it not used in the US?
Class G: This is found near the ground everywhere except controlled airspace around airports, and occasionally at higher altitudes in remote areas (Alaska or the Rockies, usually), but never above 14,500 feet.  Most untowered airports have Class G airspace surrounding them.  This is "uncontrolled" airspace, so there is no ATC service available at all.  Radio and radar work better the higher you go, so at low altitudes you just can't expect good results.  Class G serves as a notice that ATC services are unavailable, typically due to a lack of radar coverage.  In remote areas, the same problems occur at higher altitudes (radar won't see you if you go behind a mountain, and sometimes you're just too far) so Class G is found there as well.  Most of the time, the only reason anybody goes into Class G airspace is because they're taking off or landing at an uncontrolled airport, or transiting certain areas that lack radar coverage.
Other: There are many kinds of special-use airspace, all of which serve as keep-out signs of varying levels from "please be considerate" up to "will shoot on sight."  In the US, these don't really interact with airspace classification.

* Technically, airspace above 60,000 feet is Class E, but nobody goes up there except scientific and spy/military flights.


From my experience in the US at the facilities I've worked, and the discussions I've had with other controllers, it depends heavily on the area's weather patterns. The facilities I've worked, it's been usually a tool, when people are trying to get in right before the weather hits, or they're seeing good improvement in neighboring airports and at the main one, and know that it'll be good enough to make it between the two areas.

Other places, like coastal or areas where fog banks are common, SVFR can be useful, esp if only half the field is covered in clouds, and you need to make it in or can easily get out.

Personally, I'd probably just file IFR and cancel when I got to a good spot VFR, if I just wanted to go out and enjoy, versus just flying to a destination.

Also, note, SVFR in terms of separation is only one SVFR aircraft(and really aircraft period) in the airspace at a time. So, you'll be delayed to come in if there's IFR, or other SVFR aircraft ahead of you.

Helicopters generally do request it more than fixed wing aircraft in my experience. Also, realize a pilot has to explicitly request SVFR, a controller can't prompt or hint at the correct terminology to use to request like saying "Do you have a SPECIAL request"


Who owns B- registration? China or Taiwan?

From your second link:

Aircraft registered in the People’s Republic of China traditionally
have had "B-" followed by four digits.
B-0000 to B-9999

Since 2018, the following registration schemes are also in use:
B-000A to B-999Z (General)
B-00A0 to B-99Z9 (General)
B-00AA to B-99ZZ (General)

And for Taiwan:

B-00000 to B-99999 after 1990s

so there won't be any confusion, one has 4 digits/characters after the dash, the other 5 digits.


Why is manoeuvring speed higher in utility category?

There are three factors: Va speed, weight, and CG limit.

Va is connected to the weight limit, not to the CG limit.  If you look at a typical V/G diagram, you'll notice that Va is defined by the load factor at max gross. Multiplying the load factor times the weight gives the force exerted on the structure at Va.

In the case of the 172, in the normal category at max gross is 3.8G * 2400# = 9120 pounds.

In the utility category 4.4G * 2100# = 9240 (about the same as 9120).

So if the weight is limited to 2100#, the G load can be increased to 4.4, and not exceed the overall structural limits of the aircraft.

The CG limit in the utility category is there to ensure that the CG is forward enough that the pilot can more easily recover from the maneuvers, such as stalls and spins. It probably has a lot to do with the amount of elevator authority, which is necessary to break the stall.


Between a helicopter and an airplane, which requires more power to fly, for a given TOW?

Airplanes fly by creating lift from their wings. This causes some drag, but good wings have lift/drag ratio's in the range 15-20. That means the lift-dependent drag is only 5% of the lift. Helicopters on the other hand generate lift directly from trust; there is no multiplier involved.

E.g. a 4000 kg plane will have a weight of 40.000 Newton, so the drag incurred will be 2000-3000 Newton. A 4000 kg helicopter will need to produce 40.000 Newton of lift just to hover.

Of course, planes and helicopters both have additional drag from forwards airspeed, and for planes this is obviously unavoidable to prevent stalls.


Does avionics type matter when training for PPL?

The answer is going to be along the lines of "it depends" but in all honesty thats not what you should be basing your decision on when it comes to training schools! Meet some of the crew, see who has better facilities, and which you get a better feel for.

In any case, your PPL training will simply teach you to fly an airplane, and all the associated things such as navigation and airmanship - the type of avionics the aircraft has installed is pretty much irrelevant.

When you get your license the commonest small aircraft at most airfields have traditional avionics, so you'll want to be familiar with them - if you do happen to train with a glass cockpit at most you might want an hour or two with an instructor in a typical small airplane.

On a personal note, and maybe im a bit old fashioned, but I think you should understand how a "gadget" works before using it. I like to see a physical VSI, AH and altimeter. I like turning the little Knobs and manipulating proper buttons in an airplane. One thing I can say for sure is the first time I sat in front of a glass cockpit I knew what everything was, what those displays were telling me. Would the same happen if you'd only ever flown a glass cockpit and got into a 1970's C152? Possibly - I don't know.

Good luck with your training.


By what angle does the rotor disc change with max. cyclic input?

Assuming you mean, in-flight, it depends on the main rotor design. A fully articulated head can allow for angles great enough for an H53 to chop-off it's own refueling boom (See Here: https://www.bing.com/videos/search?q=h53+chop+fueling+boom&qpvt=h53+chop+fueling+boom&view=detail&mid=1AD065C255D15A52813F1AD065C255D15A52813F&&FORM=VRDGAR ).

Helicopter designs employing non-articulated rotor systems often have a cockpit indicator for "Mast Moment" in order to alert the pilot that excessive cyclic input is being commanded, risking Rotor/Head/Mast failure. These types require the blades themselves to absorb most or all of the rotor's dynamic articulation forces, hence much less angular deflection of the disc.

Additionally, the duration of the deflection needs to be factored-in. During maintenance test flights of the old UH-1 Huey, a "Pylon Rock Check" is performed. From an IGE hover an instantaneous full deflection and return to neutral (less than 1 sec for the full maneuver) is conducted either left or right. Somewhat violent and not something you would want to do every day for the sake of the transmission mounts. Sorry I can't provide exact disc angles though.


What would be the challenges for a pilot taking off into a headwind of just under the clean stall speed?

"Fairly steady" wind is the only wording that would make it even remotely considerable, with risks of being ground looped or blown over while taxiing.
One scenario may be a light GA plane taking off from a moving aircraft carrier.
Tricycle gear would be a tremendous advantage, as this would help keep the wing at a very low angle of attack to the wind.  This allows the plane to remain on the ground during its takeoff run long enough to establish a safety margin in airspeed before the plane "rotates" to an angle of attack sufficient to generate enough lift to fly.
One must be aware, although this is doable, gusts make it extremely dangerous.  Far better to wait for better weather.
Even with no wind, the safe rotation airspeed will be higher than the clean stall speed.


Is public data available for routes that enter/exit a certain airspace?

A free public resource would be the FAA's statistics page. I'm not sure if they have the specifics you need but they have a lot of data available. It would probably be easier to find data specific to the airports than it would for the whole artcc. Flight data doesn't usually include what airspace they pass through but where they depart and arrive.

There are commercial sites that have the raw data. FlightAware has full xml data for pretty much all scheduled flights going back several years. It's a treasure trove of data, it's a matter of extracting it. If you can write an api then  have options for using their data for a per-query fee. Their info page is here Their prices are in fractions of a penny, but I really know nothing about api's so I have no idea how quickly they would add up. It probably depends on how efficient the api is in getting the information with the least number of queries.


What are the handling effects of converting a dihedral wing to polyhedral?

In terms of in-flight behavior, the biggest change between dihedral and polyhedral (or tip dihedral) with the same overall stability is more roll response for a given yaw input -- this occurs because yaw-induced roll is caused by the skid presenting the outside wing at a higher angle of attack than the inside, and this effect is both more pronounced, per area, with the sharper angle of a tip dihedral or polyhedral tip panel, and is applied further from the centerline, so has a longer lever arm.

I'd agree, however, with the advice in another answer, not to modify your first kit.  Build to plans and instructions.  If you want to compare, get the kit built and the model flying correctly, then either buy another kit or buy materials (make photocopies or scans of the ribs and tip plates) and build another wing -- then you can compare the in-flight behavior for yourself.


When an airport has helipads, why would a helicopter take-off or land on a runway?

I know you asked specifically about runway versus helipad departures, but I thought I would lay out all the options available to the heli pilot, and you can see what all the choices are.

There are three different areas on an airport that a helicopter can operate from:

Non-movement area -- this is the area of the airport that is not controlled by the ground or tower controller. It often consists of aircraft parking areas or an area leased by a tenant.  It is separated from a movement area by this the marking below. Helipads may be found in non-movement areas, such as the Coast Guard helipads at SFO and JFK.
Movement area -- this is the area of the airport controlled by a ground controller, and separated from the runway area by this marking: . Helipads can be found in movement areas.
Runway area -- this is the area controlled by the tower controller, and contains the runways used for landing and departing traffic.

This picture from KHWD shows the three areas:

Regardless of which area is used, almost heli departures from towered airports are coordinated directly with the tower controller because the aircraft enters the controllers airspace.

At non-towered airports, helis operate out of the flow of fixed-wing traffic, and need to self-announce like any other aircraft.

Additionally, helicopters can make three different kinds of departures:

max performance take off -- which begins with a near-vertical segment, and then transitions to a horizontal. This is typically used from a confined area, and looks something like this:
normal takeoff -- this begins in an in-ground effect hover with a horizontal segment until translation lift is assured, then transitions into a climb:
running takeoff -- when there is insufficient power to begin with an in-ground effect hover, then the helicopter may begin its departure by sliding (skids) or rolling (wheels) along the ground, until translational lift can be obtained, then transitioning into a normal takeoff:

The choice of departure area and departure type are for the most part independent, but they are obviously linked based on performance and obstacles.

The departure area is an operational decision. When the helicopter is operating from a remote part of an airport, the pilot will often make a departure from a non-movement area (helipad or ramp) so she doesn't have to taxi to the runway.  If the helicopter is a passenger flight, such as air-taxi, it will most likely operate from the runway or a helipad in the movement area.

The departure type is a performance decision, based on obstacles, weather, weight, and available power. Hot & high departures might require a running take-off. Lightly loaded twin-engine copters in normal weather can safely make high-performance departures over obstacles in the desired direction of flight.


Why does the UK CAA medical questionnaire need to know hair colour?

The same reason they take down your eye color, height, weight, sex, race, etc.  They’re just general stats for identification.


How do barometric altimetry systems compensate for nonstandard pressure lapse rates?

They don't.

Since all aircraft in an area are (or at least should be) having roughly the same error, the errors cancel out and there is no practical effect on vertical separation.

Falsely low readings result in more terrain or obstacle clearance than needed, so that's not a problem either.

Falsely high readings do potentially create a problem, but the minimum clearance is deliberately large to account for the accepted range of altimetry error plus some additional buffer. For example, it doesn't matter if you're 100ft lower than you think when you're still 900ft (rather than 1000ft) above any hazards.


Does the airflow from a propeller over a wing contribute to lift?

A propeller not affecting the velocity of the free stream air would not generate any thrust (or drag), as the propeller works by the principle of creating thrust by accelerating a large mass of air, $F = m * a$.

The accelerated airflow from the propeller does generally increase the lift generated by the wing. The amount of lift increase depends on the configuration (how exposed the wing is to the slipstream of the propeller). This tends to be particularily noticeable on light twins:

(Image attribution: Wikimedia Commons)

There's also another effect on lift, coming from the corkscrew-shaped vortex of the propeller slipstream, perhaps more noticeable on single engine aircraft:

(Image attribution: FAA Pilots Handbook of Aeronautical Knowledge)

The image is a little bit unfortunate, as it demonstrates another effect as well (yaw from the slipstream), but you can also see how propeller slipstream will affect the flow pattern around the wing roots: on one side, it will tend to increase the effective angle of attack, leading to higher lift on that side, and on the other side it will decrease the effective angle of attack, decreasing lift on that side, leading to a roll-moment. This effect of course exists in twin engine aircraft too, but may be less noticeable, as the effect is more symmetrical, in the case of co-rotating propellers, or even symmetrical (in the case of counter-rotating propellers).


How does it feel like to be outside a flying airplane?

It won't be pleasant.  The main result of being exposed outside at altitude, besides the obvious hypothermia, frostbite and hypoxia, will be bruising from the 280-ish knot slipstream (it's the indicated airspeed that matters as far was what you feel, not the true airspeed), and injuries from being flung around by any turbulent flow you are in. Most of your skin that was exposed directly to the slipstream will have bruising.
When I was skydiving I tried tucking in and diving straight down instead of the normal 120 mph flat freefall position, just to see what it was like.  You accelerate to about 150-160 mph.  It got to be a bit uncomfortable at that speed.
A friend's dad once ejected from an F-104 while going just below transonic speed, and I got to ask him about it back in the 70s.  He said he was purple from head to toe except where his face was protected by his helmet visor and oxygen mask (except for the purple mask outline bruise on his face).
Even better, you can read about this British Airways BAC One-Eleven driver, the one who got sucked halfway out the windshield when it blew out back in 1990.  He had broken bones in addition to the other stuff, from being beaten against the fuselage like a rag doll the whole time.   The crew were able to hang on to him because his legs were still hooked around the windshield frame, providing some mechanical advantage for the crew members trying to hold him in over the airstream trying to pull him free.


How beneficial are flaps when landing with a tailwind?

Forget about tailwind/headwind for flap use.  Flaps allow landing with a lower airspeed.  And you always want a lower airspeed.  The wind itself is irrelevant except that your groundspeed will be higher or lower depending on where the wind is, and which you always want to be slow as possible.  On light aircraft you want to avoid tailwind components over 5kt. Jets are usually certified, takeoff and landing performance wise, with a max tailwind component of 10-15 kt. But in any case you are still using normal landing flap to have the minimum airspeed, giving the minimum groundspeed for a particular condition.

The time when you may want to land with less than landing flap is when the winds are strong and very gusty (and you will be landing into wind if you aren't crazy) and you want to have a bit more energy with a bit less drag (so the aircraft conserves more energy with its inertia) during the landing flare to cope with sudden small airspeed variations from gusts, which can drop you on the runway hard before you can react if you have the flaps all the way out.


Is airspace more crowded on days following cancellations or a large number of delays?

I would say generally no, because there are only so many landing slots available at busy airports and airlines frequently substitute larger aircraft to clear up a passenger backlog.


How can I determine specific heats of gases for turbojet engine calculations?

Do you have a copy of the book Gas Turbine Theory by H. Cohen, G.F.C. Rogers and H.I.H. Saravanamuttoo? You may well find the answers in there I think.


What are the advantages and disadvantages of a double bubble fuselage?

Double bubble is the lightest way to make a pressurized fuselage taller than it is wide.  It maintains the pressure hull elements, skins and formers, closest to pure tension, like a balloon, so they can be a bit lighter since they see little bending stress from pressure (only the interconnecting floor beams see significant bending loads, from the weight of the payload).
The A380 went with an ovalized cross section because it provides a better packaging compromise when you want two decks of roughly the same floor area, although it would be somewhat heavier than a DB cross section because the frame elements of the partially flattened sides are subject to a certain amount of bending because the pressure loads are trying to circular-ize the oval (the floor beams help but the oval sections away from the beams are still subject to that stress).
Think about what would happen if you really cranked up the pressure inside the A380, and imagine how the pressure hull would deform under stress; it would swell out to a more circular shape except where retained by the floor beams, before going "POP" (you'd end up with a kind of "triple bubble" before it went bang).  That deformation load trying to make the oval a circle has to be absorbed as bending loads in the frames, so they have to be heavier than they would be if they were already purely circular.
The packaging advantages over a pure double bubble make it worth the weight penalty.
The original double bubble pressure hull was the Curtiss C-46, which was originally designed as a pressurized airliner (otherwise they would have used an oval cross section), and used the configuration to make a pressure hull that was a light as possible while keeping it relatively narrow.  Then you had the Boeing 377 Stratocruiser, which also went that way in order to graft a passenger cabin on top of a B-29 fuselage and wing without making it too heavy.


How to calculate the radius of wing tip vortices?

A vortex in free air does not have any sharp boundary, so it does not have an obvious definition of radius.

To get some general idea, consider how the vortex is formed: the wing accelerates the air downward, over all of its span—that is how it generates lift. Since the air outside the span is not moving down, the boundary becomes a vortex line and it starts at the wingtips. This is the wingtip vortex.

So the two wingtip vortices “touch” from the start, and therefore have radius of half span. As the air below gets pushed out, the outside part of the vortices starts moving up in width comparable to the inner part, though not as fast—the vortex as a whole moves down and a little bit inward.

This upward flow on the outside is used by many large migratory birds to save a bit of effort by flying in the V formations. The wing vortex of each follower partially cancels with the wing vortex of the predecessor, saving them a bit of energy. For the leader it is neither advantage nor disadvantage, but when it gets tired, it can fall back to the end of the flock and the next one becomes a leader.

Internal friction of air makes the vortex slow down over time, but also pulls in more air, so the affected area grows in size. There is no specific limit, it grows until it can't be detected anymore.

It is possible to calculate something precisely—so long as you can decide what to calculate (and what is it useful for so it is worth calculating)—but it requires powerful computer as the equations describing fluid motion, Navier–Stokes equations, don't have analytical solution.


Are there any "alternative" passenger airline business models?

There's also the "Snowbird" model, like Sun Country and Allegiant Air, which primarily fly vacationers and snowbirds between sunbelt (San Diego to Florida) and the Carribean, and the Northern snowbelt states (Maine through Washington State, and Canadian border cities). They are low-cost carriers, with few or no code shares, no connections, no free amenities, and prices that decline as the date gets closer.

Here is Sun Country's route map.  Note that nearly all their flights are between Minneapolis (or Dallas) and vacation destinations.

Here is a part of Allegiant's route map, showing cities with flights to Phoenix/Mesa, AZ.  They have more routes than are shown here, but all their routes have one end in one of the "sun belt" cities marked in orange.


How does one resume a VNAV climb in a B737 NG after being instructed to level off at an altitude below the Cruise altitude?

So your CRZ page shows your cruise altitude as FL 410, but you've leveled off at FL370, which is what's in your MCP Altitude window. Now ATC clears you to climb to 410.
You set 41,000' into the MCP Altitude window. At this point, your FMA vertical mode changes from VNAV to Altitude Hold. The light in the Alt Hold button is on, and the light in the VNAV button is not. To initiate the climb, press the VNAV button, and observe the FMA change from ALT HOLD to VNAV Speed. At this point, the autothrottles advance the power, the autopilot increases the pitch to maintain your FMC-computed airspeed, and you're climbing again.
The key is that when you initially leveled off at FL370, the FMA stayed in VNAV Speed, but as soon as you changed the MCP Altitude, the FMA changed to Altitude Hold. Thus, one tap on the VNAV button re-engages VNAV & you resume the climb.
Side note: why doesn't the FMA change immediately to Alt Hold when you level off at 370? While Boeing may have another answer, my best explanation is that if you change your cruise altitude in the FMC from FL 410 to FL 370 after you leveled at 370, you stay in VNAV, and the FMA just swaps from VNAV Speed (i.e. the climb mode) to VNAV Path (i.e. level-at-cruise-altitude mode). So at the intermediate level-off, it stays in VNAV, waiting to see if you'll reset the MCP altitude (to continue the climb) or if you'll reset the FMC cruise altitude (to make this your cruise altitude). In the former case, the VNAV button starts the climb; in that latter case, no MCP buttons need pressing.
Added:
The case where Altitude Intervention will start your climb is different: in that case, you're AT your FMC cruise altitude, either because you climbed there directly, or else you leveled off at an intermediate altitude and then changed your FMC cruise altitude to match.  The latter is NOT common practice, but there are scenarios where it could happen.
Either way, you're at cruise in VNAV Path.  Now ATC clears you higher.  So you set the new, higher altitude in the MCP altitude window.  At this point, the FMA still displays VNAV Path.  Press Altitude Intervention, and that changes the FMC cruise altitude to what's in the MCP.  With VNAV (still) engaged and your altitude below both the MCP altitude and the FMC cruise altitude, you'll get a climb.
The difference in these two cases is being at, or not being at, the FMC cruise altitude.  In the case discussed first, you're below it.  In the second case, you're at the cruise altitude.  In the first case, Altitude Intervention won't help you (because you're in ALT HOLD and not VNAV); pressing VNAV will.  In the second case, you're in VNAV, so pressing that button won't help you; resetting the FMC Cruise Altitude (either by entering it in the FMC via the CDU, or by pressing ALT INTV) will.
This stuff is complicated, and the manual doesn't generally do a great job walking through every scenario and "what if".  After you've seen it in the jet (or a simulator with good fidelity) a few (dozen) times, it makes much better sense.
I'm not aware of any 737 setup where anything varies varies from what I've discussed above, although if the Smiths FMC is replaced by something else, all bets are off.  There are some things that vary from one aircraft to the next (geometric path descent vs idle descent logic being one -- it's selectable by the airline), but nothing here, as far as I know, is in that category.
As far as simulators go, I can't speak to which ones have fidelity to what goes on in the real aircraft or not.  (The ones I train in are extremely accurate that way, but they're not running on a PC!)


Orange object on back of jet-engine pylons, what is it?

Manu H is right. It is an IR jammer device. Saudi (corrected from the comment of David Richerby:)Royal Flight airliners tend to have them (root of the wing, next to the light)...


How can one achieve supersonic cruise capabilities without afterburners?

A normal jet engine has subsonic flow throughout. This avoids shock problems such as choking or excessive acoustic noise.
A conventional afterburner accelerates the exhaust flow to supersonic speed, allowing it to push the plane past the speed of sound. It is placed after the turbines in order to avoid those shock problems.
A supercruise engine must deliver supersonic exhaust flow without using an afterburner. Luckily, in a hot gas the speed of sound is much higher than in a cold gas. So as long as the exhaust is not cooled before exit, its high exit velocity stays subsonic within the engine and only "looks" supersonic relative to the outside air.
The problem with this is that you cannot obtain the usual benefits of mixing bypass air with it to increase its mass flow and thermodynamic efficiency, because that would cool it and create a standing shock wave across it, slowing it to subsonic speeds.
The end result is a bit of a design compromise; relatively high mass flow through the core, relatively low bypass ratio, some sacrifice of efficiency.


Does airspeed affect the critical angle of attack on an airfoil?

Yes, through the Reynolds number

The Reynolds Number is a function of airspeed and is used to predict the transition from laminar to turbuluent flow:

$$
{Re} = \frac{\rho v L}{\mu} = \frac{v L}{\nu}
$$

The critical angle of attack is affected by the separation of the boundary layer, which, in turn, depends on the laminar or turbulent qualities of said layer.

Do note that the Reynolds number of the layer is not the same as the Reynolds of the wing, although they are related.

EDIT: to visualize the efect, see for example the following graph (thanks @MikeY)

Quite a bit of experimental work on low airspeed performance was done by Selig et al. at the UIUC, and their website maintains a significant catalogue of airfoil datapoints.

Another resource worth checking is Airfoiltools,  which provides graphed Xfoil polars for an extensive seleciton of airfoils. Do keep in mind Xfoil´s prediction of flow separation points is numerical and therefore may not converge with reality at all points.


Would a 767-300 be considered FANS-1 capable without SATCOM?

You would ask the maker of your MCDU whether it's FANS-1 capable using just a VHF datalink. Satcom isn't necessarily a requirement, but you would only be able to use it where VDL is provided, for instance in Europe but not on oceanic routes.


a rhumb line, rhumb, (/rʌm/) or loxodrome is an arc crossing all meridians of longitude at the same angle, that is, a path with constant bearing as measured relative to true or magnetic north

From: Wikipedia

If continued, all rhumb lines except the ones following a  track of 90 or 270 degrees end up in either the North or South Pole.

If continued, all great circle lines end up back where they started from.

As for the part of the question about constant track direction: track is defined by ICAO as

  The projection on the earth’s surface of the path of an aircraft, the direction of which path at any point is usually expressed in degrees from North (true, magnetic or grid).

So, to maintain a constant track would mean that North would always be in the exact same direction from you as you move on. This would eventually take you to one of the poles, unless of course, you were maintaining a track of 90 or 270 degrees.

The picture above shows a constant track of about 75 degrees.


What would happen if ultralights had mountain bike style treaded tires?

Mountain bike tread is meant to sink into the mud in an attempt to gain traction on firmer ground beneath the mud.  A plane generally doesn't want to sink into the ground (even during braking), if it sinks too far during landing or take-off, the airplane is more likely to catch the forward gear and flip/strike the prop.

Bush plane tires are designed to land on soft fields.  The difference between mountain bike tires and bush plane tires is that the high surface area of the bush plane tires attempt to "float" on top of the soft ground rather than dig into it:


What is this tube in a jet engine's air intake?

That's the EPR inlet pressure sensor (there's another one located aft of the engine in the exhaust).

EPR = Engine Pressure Ratio, one way to measure thrust.

(source)

See also:

What is the difference between EPR and rotor speed as thrust setting parameter?
How does the EPR reading behave in reverse, and in reheat modes?


Where do airplane variant numbers come from?

Chinese superstition. The same reason Airbus went with the 380 number when 350 would have been next in line.

The Chinese sign for 8 looks like an up arrow (八) and 8 is the lucky number in Chinese. Similarly, 4 (四) is considered unlucky because the word for it (sì) sounds similar to the Mandarin word for death (sĭ).

Boeing and Airbus management court their prospective Chinese customers wherever they can because they expect their biggest sales in the next decade from that part of the world.

Originally, Boeing used three-digit numbers for their subtypes, and the last two digits represented the airline. Pan Am's number was 21, for example, so a Boeing 707-100 made to Pan Am specs was a 707-121.


What if traffic should give way to me but doesn't appear to be?

Whether you have the ROW or not, it is your responsibility to "see and avoid" even if the other pilot isn't. This is the aviation analog to defensive driving; call it "defensive flying".

There are no hard-and-fast rules for collision avoidance maneuvers. You basically have six options and their combinations, any of which will put you at a different point than you would be at the expected intercept (collision) point: climb, descend, turn left, turn right, speed up, slow down.

There was a study conducted by students at the University of Illinois at Urbana-Champaign, results available here, which might be helpful. The primary purpose of the study was to determine the usefulness of a computer traffic display in aiding the pilot to spot and avoid the traffic, but a secondary goal was to determine the most likely (and safest) collision avoidance maneuvers when presented with "intruders" on a collision course in each of 12 basic intercept paths (overtaking, crossing, or approaching, from the left or the right side, and climbing, level or descending). Among the lessons learned were:

Pilots (CFIs were used) were most likely to maneuver purely in the vertical to avoid traffic, moving opposite the vertical direction of the plane in sight and preferring to climb if the intruding traffic was holding altitude.
Despite the pilots' preference for the vertical, the maneuvers that cleared the "conflict" in the shortest time were in the horizontal plane, either turning opposite the plane's relative direction of travel to move behind, or slowing to let the traffic pass in front.
Pilots tended to do what was "easiest" at the time the conflict arose, especially if the intruder was sighted late (because the traffic didn't appear on the computer display; another of the variables they tested). Thus, single-axis maneuvers were most common (not counting the use of throttle to adjust power while performing a maneuver, such as cutting power to dive or increasing it to climb or turn).

Taking all this under advisement, the maneuver most likely to avoid a collision with another plane in otherwise clear skies is a level 30-45° turn in the direction of the intruding aircraft's tail, coupled with a reduction in airspeed if the intruder is on a crossing or approaching route (if he's coming up behind you, maintain airspeed). If the other pilot sees you and reacts at the same time, his most likely move will be a climb, which is fine; if he doesn't see you or react at all, you'll pass safely behind him at the same altitude hopefully avoiding his wake (if he's bigger than you).

However, there's some interesting game theory here. Any maneuver I tell you to make, except one, will keep you on a potential collision course if the other pilot reacts in the same way at the same time. As you supposed in your question, If you both climb, or dive, or speed up, or slow down, or try to turn behind each other, you'll crash (or at least get way too close for comfort). So, anything I tell you to do because it's unlikely the other pilot will do the same will be self-defeating, because eventually other pilots will do the same thing because it works.

The one move that won't result in a collision if mirrored is a 90° turn in the same direction as the intruder's movement across your vision. If he's on your left moving right, turn right 90°. If he's on your right, turn left. If the other pilot mirrors your maneuver, worst-case (an aircraft overtaking you directly from behind who turns the same way as you) you'll end up on parallel flight paths at whatever distance you first noticed each other. Best-case, you'll be heading away from each other and after a couple of minutes you can both reverse your turn and continue along your original heading.

But, this move is the worst thing you can do in several scenarios if the other plane holds its course. In high-offset crossing routes (close to 90°), turning away from the intruder will keep you out in front of him and probably too close for comfort, especially if he's faster than you (turning the crossing-route collision course into an overtaking collision).

Lastly, any formulaic maneuver we dream up in a two-plane scenario is going to break down when you add more planes, or restricted airspace, or weather. The maneuver may work in cross-country flight, but when dealing with merging Victor airways near a population center, there will be too many aircraft for any single avoidance maneuver to guarantee you'll get out of trouble without getting into more.

So, ultimately, your call.


Where can I get a graph of lift coefficient against AOA for a symmetrical airfoil?

Search symmetrical airfoils in Airfoil Tools DB

Quabeck Sailplane 10 as an example


Why is the use of tail-down force so common?

If it were so simple ...

To achieve natural longitudinal stability (the aircraft stays at the trimmed speed, even after disturbances like gusts), the rear lifting surfaces need to have a lower lift per area than the forward surfaces. Why? In a gust, the aircraft's angle of attack changes on all surfaces nearly at the same time. By having less lift per area, the relative lift increase due to an increase in angle of attack is higher for the rear surfaces, so now they gain relatively more lift increase than the forward surfaces. This creates an imbalance which lifts the tail up, until the old angle of attack (and, consequently, the old speed) has been reached again.

A negative tail loading is a sign of high stability. This creates more drag, but allows the pilot to take the hands off the stick, to read his maps, check something or have a cup of tea. But its effect on induced drag can actually be helpful. You might be surprised, so please bear with me!

What is induced drag, anyway? It is the consequence of creating lift over a limited span. The wing creates lift by deflecting air downwards. This happens gradually over the wing's chord, and creates a reaction force orthogonally to the local speed of air. This means the reaction force is pointing up- and slightly backwards. This backwards component is induced drag! The lengthwise distribution of the surfaces which do the downward deflection is of little importance (for a very technical explanation: See here, where they talk about the Treffz plane): If you have a highly loaded canard wing, its downwash will hit the wing eventually, creating a lot of backward-tilted lift there. The canard by itself will not cause so much induced drag, but will mess up the airflow over the wing. Behind the airplane it does not matter if you fly a canard or a conventional configuration, what matters is over how much span you distribute lift creation (for a constant amount of lift at a given speed).

You probably know that an elliptic distribution of circulation over wingspan produces the smallest induced drag. Now imagine that your wing has more a triangular than an elliptic distribution. The downward lift on the tail will reduce this hump of lift in the middle, making the distribution closer to that ideal elliptic distribution behind the whole airplane. The induced drag of the whole airplane is lowered by the tail!

Another explanation: Since the wing creates a strong downwash at its center, the tail flies in an airflow which points slightly downwards. Negative lift there (being approximately orthogonal to local airflow) will actually point slightly forward, so your negatively loaded tail produces a small amount of thrust!

Black: Total force, Blue: Lift, Red: Drag

And if you think that a triangular lift distribution is unusual, please read this NACA report by R. T. Jones. It takes wing weight into account, and this changes the picture how the lift distribution for minimum induced drag should look.


What are the costs involved with getting a 2 seat ultralight?

What do I need to do to get back into the flight seat

Legally, not much. With the recent third class medical reform you dont even need to get a medical. You will need to get a bi-annual flight review to get current as well as your takeoff/landing requirements for passenger carrying as per FAR 61.57. While your bi-annual only needs to be an hour of ground and an hour of flight, if its been 7 years it will be well worth your time (and possibly an insurance requirement) to spend some more time on both.

  What are some good options for a 2 seat folding wing ultralight that
  has a few hour range

Dont know much in this space so I wont comment

  What are some hidden costs of owning a new or used ultralight

There is one guy on the field I fly out of who has one of the moving wing, snowmobile looking ultra lights. He keeps it in the back of another guys hanger and takes the wing off every time he stores it. With that in mind last time I spoke to him he said it takes some time to get the wing on and off and he needs to plan for that when he flys. If I remember correctly he bought his new or close to new and it was in the space of 75K which frankly is quite a bit considering you can get a really nice airplane for way less than that. The wing is fabric/composite so outside storage is a no go. You can hop around on nice days with it but its VFR only which depending on your goals can be a limiting factor.


Relationship between flapping and lagging frequency

I agree with your assessment. Have you discussed this with your prof/instructor? When performing Rotor Track and Balance, a worn lead/lag damper or dampers will directly affect the 1 per revolution lateral vibration with little to no affect to other rotor rpm orders or suborders. This is most pronounced in helicopter models which utilize hydraulic dampers as opposed to elastomeric or friction type lead/lag dampers. Hope this helps.

Another factor that contributes to Lead/Lag is alternating spanwise distribution of lift as a result of forward flight. As a rotor blade advances, the lift migrates toward the tip. Conversely, as the blade retreats, lift shifts more toward the root of the blade. Still a 1 per revolution effect.

Chordwise blade mass distribution (Chordwise Balance Aka Product Balance) accounts for angle of attack changes with respect to power changes. If one blade climbes or dives a greater amount than the other/s in transition from Ground-Flat-Pitch to Hover, there is a chordwise balance disparity, which, in turn leads to effects in Lead/Lag. Still a 1 per revolution effect.


Any info on very strange wing endings on this Stemme glider?

This was a test aimed at measuring the effect of feathered wingtips. The Stemme S-10 has a four-part wing, and for the experiment the outer wing panels were removed and replaced by five staggered small wings, as shown on the picture in your question. This reduces wingspan from 23 m to only 11.4 m plus the span of the wingtips, in total maybe 14 m.

A feathered wingtip shows less induced drag than a straight wing of identical span, similar to a winglet, because it can involve a bigger mass of air into the creation of lift. But it cannot perform wonders, the effect is small.

The concept behind this experiment is called "winggrid" and the brainchild of Dr. U. La Roche. See here for one of the few still active sites on the topic - the original site http://www.winggrid.ch has long been abandoned.

Sad fact: This aircraft was destroyed in a mid-air collision in 2007. At that time, it had been reverted to the original wingtips.


Are any special certs or licenses needed for Snow-ski equipped planes?

From the FAA manual:

  Title 14 of the Code of Federal Regulations (14 CFR)
  part 61 does not require specific pilot training and
  authorization to operate skiplanes; however, it is
  important to train with a qualified skiplane flight
  instructor.

  Since most skiplanes operate in a wide variety of conditions,
  such as landing on frozen or snow-covered
  lakes and sloping glaciers, with varying qualities of
  snow, it is important to know how performance is
  affected. Use the performance data provided by the
  manufacturer.

From looking at 14 CFR part 61, section 61.5 lists the different ratings. While it differentiates sea and land, there is no "ski" category.


Is the Runway Visual Range (RVR) communicated to the pilots?

Pilots get the RVR values either from weather reports or directly from ATC. RVR also shows up on ATIS reports when visibility drops to less than 1 mile. ATC will have a realtime readout of RVR and can communicate these values to pilots at any time by radio.

ATC RVR display

Source: http://mtechsystems.com

The CAT III approach should only be commenced if the ceiling and RVR values meet the minimum for the approach in use and for the current aircraft equipment status. Some airlines will have their own minimums which can differ from the published CAT III minimums.

Pilots will often ask for the latest ceiling and RVR values while doing the approach. ATC will also announce any changes or reduction in ceiling or RVR values while aircraft are on approach. If the new values are below limits, the crew should commence a go-around.

A go-around can be done from any altitude and the wheels can touch the runway during the go-around. Low atlitude, "Low Energy" go-arounds are practiced during re-current Simulator training.


Could anyone (non-military) in the present day "exceed mach 1 over a regulated area"?

Yes, In the U.S.A there are many privately owned ex-military jet fighters that are capable of exceeding Mach 1. It is quite conceivable that a privately owned fighter jet has exceeded Mach 1 but not reported it or been caught by the authorities.

You can search the FAA civil registry by type:  FAA REGISTRY
Make / Model Inquiry

Here is just a partial list of privately owned supersonic jet fighters in the United States:

Lockheed F-104
McDonnell F-4
NORTHROP F-5
MIKOYAN-GUREVICH MIG-21
MIKOYAN-GUREVICH MIG-23
MIKOYAN-GUREVICH MIG-29
Sukhoi SU-27

These two aircraft are owned by the Collings Foundation in Florida and are available for airshow demonstrations.


Why are there two IRS switches on the 737NG?

Inertial Reference System is a solid state set of 3 ring gyros which navigate using dead reckoning.  The system measures accelerations in  and rotation around each of the 3 axis so can calculate where it is by adding how much it has moved to the initial position.

A simple example:
The aircraft is stationary pointing North.  Over a 10 minute period, it measures the accelerations in the X and Y axis and calculates that is has moved +100 kms in the X axis (i.e. North) and +100 kms in the Y axis (i.e. West).  By simple trigonometry, we can calculate that the aircraft is approximately 141.4 kms on a bearing of 45 degrees from it's initial position.

The gyros must be aligned with the aircraft frame of reference when it is stationary.  This is the "alignment" process and generally must be completed before the aircraft moves.  It may also take inputs of the current position from a manual keyboard or from some other system, e.g. GPS.

More modern IRS fits can align when the aircraft is moving, taking an updated position from GPS.

There are 2 systems on the 737, simply for redundancy.

This slide show gives a good overview.


Is a 20% forced transition in xfoil similar to adding a vg?

No

It is more like putting a turbulator (such as a trip wire) there. Vortex generators will create a small vortex (hence the name) which puts much more energy into the boundary layer. XFOIL has no mechanism for simulating vortex generators.

Adding a forced turbulent transition will weaken the boundary layer downstream of its natural transition point, so it will tolerate less pressure rise. I assume you put them on the upper side: Now the airfoil will stall a bit earlier (at a lower angle of attack and lift coefficient).

15-20% is an unusual location for a turbulator, especially on the upper side. Their best location depends on the Reynolds number and the pressure distribution. On gliders, they make most sense on the lower side at around 80% of chord. On the upper side they might help a bit in part of the polar when placed at around 50%.