What was the first plane that allowed walking during flight?

The first airplane with a cabin big enough for walking around was indeed a Sikorsky. This was the Sikorsky Russky Vityas, also sometimes named "Le Grand", a name which was given to an earlier, two-engined version. Oh, and the cabin included a washroom, too!

Sikorsky Russky Vityas (picture source)

It was the first four-engined airplane in the world and the biggest airplane of its time. It flew first on May 10 (or 13, depending on the source), 1913.

Quote from Wikipedia:

  After the Russky Vityaz's first test flights between 10 and 27 May
  1913 (Old Style dates), it was established that a passenger could even
  walk around the cabins without causing any problems to stability.

Early Le Grand version with two engines (source)


For cell towers the FAA wants them to be visible for pilots in time for them to avoid them.

  Pilots of aircraft travelling at 165 knots (190 mph/306kph) or less
  should be able to see obstruction lights in sufficient time to avoid
  the structure by at least 2,000 feet (610m) horizontally under all
  conditions of operation, provided the pilot is operating in accordance
  with FAR Part 91. Pilots operating between 165 knots (190 mph/303
  km/h) and 250 knots (288 mph/463 kph) should be able to see the
  obstruction lights unless the weather deteriorates to 3 statute miles
  (4.8 kilometers) visibility at night, during which time period 2,000
  candelas would be required to see the lights at 1.2 statute miles
  (1.9km). A higher intensity, with 3 statute miles (4.8 kilometers)
  visibility at night, could generate a residential annoyance factor. In
  addition, aircraft in these speed ranges can normally be expected to
  operate under instrument flight rules (IFR) at night when the
  visibility is 1 statute mile (1.6 kilometers).

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2070%207460-1K.pdf (page 63)


Why is Tromsø Airport's runway 01 referred to as 36 in the sign before the runway?

The runway number is changed to 18/36 due to the change of magnetic variation. The image on Google Earth must be outdated. This is from my current (AIRAC 2004) Jeppesen airport chart of ENTC (Tromso, Norway):

The video you linked was uploaded in March 2020, were the runway number had already been changed. I do not know how old the Google Earth image is. According to this thread on a simulation forum, the runway number was changed with AIRAC 1910, which came into effect on 12 Sep 2019.

By the way, both the numbers on the runway and the sign refer the magnetic heading. For more details, see How are runways numbered?.


Am I required to have my Radiotelephone Operator's Restricted Certificate (Aeronautical) on-board the aircraft with me?

There is no requirement to have the certificate with you on board during flight.

  The holder of a radio authorization shall, at the request of an inspector appointed pursuant to the Act, show the radio authorization or a copy thereof to the inspector within 48 hours after the request.

Source:Radiocommunication Regulations, s 38


How much time does an landing/take-off add to an otherwise direct flight?

Let's take the best case scenario to start with, and assume that the cruise ground speed of the airliner is around 400kts.

For our best case, we also assume that the runway is lined up with the flight path and that the airspace is quiet so the plane is cleared "straight in" with no vectoring for separation or holding patterns.

Descent:

A typical descent profile would start 100nm out, during which the plane would slow pretty uniformly from around 400kts to around 140kt. This gives an average groundspeed of 270kt. So this 100nm is covered in around 25 minutes rather the 15 minutes at full cruise.

The descent has cost us only 10 minutes.

Taxi and turnaround:

At a smallish (and well designed) airport the rollout and taxiing to the stand may only take 5 minutes, plus another 5 to attach the air bridge/stairs and open the door. Passenger and baggage turnaround would typically take around 30 minutes, but you have specifically excluded this in your question so we can ignore it. Then getting departure clearances, startup and taxiing to the active: say another 15 minutes.

So this phase has cost more or less 25 minutes.

Take off and climb out:

Again assuming we're cleared for immediate take off, it takes around 20 minutes to climb to cruise altitude, at an average ground speed of (say) 200 knots. This means we've covered about 70 miles, which the cruising aircraft would have covered in just over 10 minutes.

So this final phase has cost us another 10 minutes.

Total for the best case scenario is 45 minutes.

Of course the best case is not that likely. If the airspace is busy, holding for another 10 minutes before final approach, and 10 minutes further wait for departure and takeoff clearances, would not be surprising. And if the active runway is in the "wrong" direction or vectoring is needed for traffic or noise reasons, that can easily add another 10 minutes or so.

So in the non-best case scenario, a total loss of 1h15 to 1h30 would not be unreasonable.


Can a private pilot obtain a recreational pilot certificate?

Not technically.

You could opt to surrender your private pilot certificate to the FAA thus making you not a pilot, and then you could take a checkride for recreational.

Of course, there is no reason to do this at all!  You can do the same things as long as you're exercising the privileges of the lower certificate, then whatever medical rules are there should only apply for that operation if I'm not mistaken.


Is there an aerofoil that gives reasonably good lift for both air flow directions: forward and backward?

There is no airfoil with good lift in both flow directions, but one with some lift is conceivable. However, the lift-to-drag ratio will be nothing to write home about.

One reasonable candidate would be created if we use the forward half of the venerable NACA 66(2)-415 and copy it again for the last half. Like that:

As you might recognize from the plot, this was done with XFOIL. However, the iteration does not converge. But when real air hits this thing, it will create lift, much like a cambered plate will do. Its inviscid zero angle lift coefficient is already 0.5, however, viscous effects will reduce this lift coefficient.

In a good airfoil, the pointed trailing edge defines the point for flow separation, while the rounded nose leaves it to the flow to find a suitable stagnation point. Here we have a rounded contour on both ends, so the separation point widens to a separation area, and this will creep up on the top side once the flow develops some suction at the top. Hence, lift will be poor and drag will be high.

With a little trick, XFOIL can be convinced that this is a regular airfoil with a really blunt trailing edge. Then this is the result at a Reynolds number of 5 million and Mach 0.3:

However, now the separation at the trailing edge is prescribed and will not as easily move up, so the results might be too positive. It seems that L/D exceeds 70 (which surprises me! The original 66(2)-415 has a lower L/D at the same flow conditions, which is a strong hint that we are misusing XFOIL here). Compare that to a good glider airfoil L/D of over 200 at this Reynolds and Mach number.

Applicability

I cannot think of a good reason to do this. The consequences of flying backwards include:

What was stable previously will become unstable - in all directions! Remember that the neutral point is at the quarter chord, measured in flow direction. If the flow direction is reversed, the distance between neutral point and center of gravity will suddenly be more than half the wing chord - in the wrong direction! The same goes for the vertical, which is now destabilizing.
This includes all control surfaces: They will run into their stops and stay at maximum deflection. A manual control system will become unusable, and even a hydraulic, computer-controlled one will experience extreme loads which overpower conventional actuators. When combined with Gurney flaps or directed blowing on both sides, the control issues should become manageable.
If done with reversing a variable-pitch propeller, most of the propeller will not work anymore, because the blade twist runs now opposite to how it should. You could, however, create enough thrust if you use a VJ-101 style propulsion where the engine gondolas swivel through 180°.

VJ-101 (picture source)

EDIT: @Marius mentioned in a comment below the S-72 X-Wing, an attempt to make a helicopter go faster by stopping the rotor above a certain forward speed. The X-Wing actually used an elliptical airfoil and forced the Kutta condition by directed blowing. This enabled it also to use a rigid wing and to adjust blade lift for cyclic and collective control by blowing. This is indeed the only sensible application of an airfoil that works in both directions.

ANOTHER EDIT: I just found this on Airfoiltools.com: The Sikorsky DBLN-526 double ended rotorcraft airfoil. It was most likely used on the S-72, and its 26% would only work with directed blowing, anyway.


How do I set up G1000 GFC700 autopilot for takeoff?

This looks like a proper setup for an autopilot controlled climb up to 5000 feet. One way to know for sure is to see what the Flight Director tells you. Does it seem reasonable and correct?
Also, prior to taking the runway, you should test the autopilot disconnects. Some of the more common ones are:

Can you overpower the autopilot manually.
The Control Wheel Steering button
The Autopilot immediate disconnect button on the yoke.
The electric trim buttons on the yoke.
The Take Off Go Around button on the panel.
The AP button itself
The Autopilot circuit breaker (this can only be tested during preflight inspection since completely restarting the G1000 will be necessary).


Is there any use for variable shape wings within aviation?

Well, yes.

Variable shape wings (or variable geometry) have a number of uses, primarily in being able to optimize the shape of the wing to an ideal form for the regime of flight.

The idea isn't new; birds, bats and other flying creatures twist and warp the shape of their wings in order to maneuver and generate thrust as these pigeons demonstrate.

The Wright Brothers used a warping wing box on their gliders and the 1903 flyer.  Orville Wright is said to have come up with the idea while twisting a rectangular cardboard box used to ship bicycle tire inner tubes.

The chief advantages to such a design are that it provides an extremely clean airframe, aerodynamic wise, without joints, separate control surfaces, moving parts, etc which create excess drag.  In addition, the aircraft shape can automatically be optimized to the altitudes, speeds and Mach numbers desired without tradeoffs for weight or performance required with aircraft made from conventional materials.

The downside to warping wings is solving the problem of finding materials which could be flexible and change their shape and then remain rigid and immutable under aerodynamic loads.  Wood and metal airframes lacked the capability to do this successfully.

Early attempts to solve this problem have been to make 'swing wing' designs where the wing can be rotated at the wing root to an  optimal sweep in flight.  The Bell X-5 successfully demonstrated this concept and it has been used on a number of military aircraft including the F-111, F-14, MiG-23/27, B-1, and SU-22.

NASA is currently developing a morphing wing for these reasons.  If successful and shown to be feasible from a manufacturing and service standpoint, it would be a game changer.


What would be the ground roll and total distance to clear a 50ft obstacle given these conditions?

We round up for safety, so assume PRESS ALT=1000' and TEMP=30°
Celsius, we would have a ground roll of 890' and a takeoff distance of
1645', right?

Good thinking, but no.
Refer to the Pilot's Handbook of Aeronautical Knowledge, Chapter 10.  You want page 10-3 specifically.
When the altimeter setting is 29.92, the pressure altitude is the same as the field elevation.  When the altimeter setting changes, you must apply a conversion factor to the field elevation to get pressure altitude.
In this case, the altimeter setting is 29.52, which means that your conversion factor will be about 380 feet:

Therefore, the actual pressure altitude will be 5,380 feet.
If you round up for safety, the takeoff distances will be 1455 and 2855.

We can get a little more precise than that, though.
To calculate the ground roll at 25 celsius, we can interpolate between 20 and 30 degrees:
5,000 feet
$\left[ \left(1315 - 1215\right) \over 2 \right] + 1215 = 1265$ ground roll at 5000
$\left[ \left(2525 - 2320\right) \over 2 \right] + 2320 = 2422$ 50 ft obstacle at 5000
To correct for pressure altitude, we do the same thing at 6000 feet...
6,000 feet
$\left[ \left(1455 - 1345\right) \over 2 \right] + 1345 = 1400$ ground roll
$\left[ \left(2525 - 2320\right) \over 2 \right] + 2320 = 2732$ 50 ft obstacle
...and then interpolate again:
5,380 feet
$\left[ \left(1400 - 1265\right) * 0.380 \right] + 1265 = 1316$ ground roll
$\left[ \left(2732 - 2422\right) * 0.380 \right] + 2422 = 2540$ 50 ft obstacle


What part of an aircraft design process is governed by mathematics?

Maths have their place in pre-design of aircraft, but it is still a design process so creativity has a place as well. Designing a plane is an iterative process, that also includes steps like determining what the plane is used for, what the payload will be, what the range should be, is it allowed to use a runway etc.

Once these factors are determined and honed down, there is a lot of math to be applied to check if the wing can support the weight, if the engines can propel the plane, if the structures can take the static and fatigue load, if the hydraulic pumps are dimensioned correctly, if the control surfaces are dimensioned correctly...

Rockets are relatively easy in that respect. Not taking anything away from the achievement of putting men on the moon, but a rocket has a single mission type, has very little bother with aerodynamics, and does not need to be optimised for decades of safe, economical or mission ready use.

One aspect of aeroplane design where maths & physics rule is aerodynamics, but what's great for aerodynamics is usually not great for structural engineering for instance. So if you would like to focus on maths only, aerodynamics would be a good place to start. Please realise that it is only one aspect of aeroplane design though.

The complete process of aeroplane design is really a lengthy process that does not fit within one answer on this site. I can recommend my goto book for design aspects, Torenbeek. It has 600 pages. Check out Appendix C. on a mathematical method for weight prediction of the wing structure for instance.


Why isn't cabin air quality in airliners directly monitored with sensors?

There is no FAR or CS demanding that requirement.

I have worked on a system an "aeronose" to detect contaminants , and it worked,we did a trial I installation in an A320 but there was no legal requirement and therefore no airline interest.


Is data on international air traffic volume in the US freely available?

Try U.S. International Air Passenger and Freight Statistics Report.

Example of data for Q4 2015:


Must RAIM be checked in flight before every GPS approach or is a preflight check acceptable?

The FAA website predicts pre-flight whether RAIM will be available

The RAIM algorithm will tell you during your flight if GPS is working correctly.

The pre-flight FAA website check is not a substitute for the use of the RAIM function during flight. It will only show whether the RAIM function is available during flight.

RAIM stands for Receiver Autonomous Integrity Monitor. It is a part of aviation graded GPS receivers that checks consistency of all used GPS satellite signals in order to raise an alert if the GPS system is not working correctly.

For RAIM to work, there must be at least 5 usable satellites in view of the GPS receiver. For GPS without RAIM, at least 4 satellites are needed. If there are only 4 satellites visible, or more than 5 but with an unfavourable geometry, RAIM cannot work and therefore the GPS receiver cannot be certain that the produce position fix is correct.

The FAA website predicts the availability of RAIM; based on the constellation of GPS and the health status of its satellites, the route and the time of flight it is possible to calculate  whether RAIM is available for your flight. This can be done before you take-off.

If there is no RAIM available during part of your flight, you can't rely on GPS during that part. The GPS may still work fine, but there is no way to check its integrity. A single fault in a GPS satellite or, more likely, a corruption in the downlinked GPS satellite almanac will cause the position fix to be off. You must use alternative navigation means if GPS RAIM is not available.

The FAA website does not say anything about the actual quality of the GPS system during your flight. This is what RAIM does. It continuously monitors all satellite signals for consistency and flags any inconsistencies.  There are various categories of RAIM such as Fault Detection and Fault Detection & Exclusion but all RAIM algorithms will give you a containment radius.

The containment radius is the maximum size that a position error can grow due to a fault in the GPS system without the RAIM algorithm being able to detect it. The value of the containment radius depends on the geometry of the satellites.

The requirements for the value of the containment radius depend on the flight phase. For En-Route mode the RAIM containment radius value should be under 2 NM, terminal mode under 1 NM, and approach mode 0.3 NM.


Why pilots would leave the cockpit in a short flight?

The cockpit of some airliners lacks a lavatory.

Cockpit layout from AviationKnowledge.wikidot

This is discussed in Skybrary: Flight Deck Security

  Locked Door Flight Safety Issues
  ...
  Physiological Need. Naturally, the need for flight crew to use toilets, access designated crew rest facilities or be supplied with food and drink, requires access through the flight deck door during flight. Procedures for door opening mean that egress and access will take longer with the result that the flight deck crew are not always able to go to the toilet at a time of their exact choice, which may cause them to be distracted and, exceptionally, might exacerbate an existing underlying medical issue in a way that would not otherwise have occurred.
  ...
  Longer term, design change could also ensure that all operating flight crew should be secured on the flight-deck before the passenger boarding doors are closed prior to departure and remain secured on the flight-deck until after the passenger doors are opened at the destination. This would prevent any unlawful entry from the cabin and minimise any unlawful seizure by a single flight crew member.
  To enable this, existing aircraft could be modified and new aircraft designed with all required crew facilities forward of the secure flight-deck door. On short/medium haul aircraft this would require a toilet, safe food & water storage and a reclining crew rest seat. Additionally on aircraft used for long range operations where in-flight relief is required provision of bunk/s.
  This is not a new concept, many long range aircraft already have toilet and crew rest facilities forward of the secure flight-deck door.


What are the slash markings on Gatwick's 08R/26L?

They are "Rapid Exit Taxiway Indicator Lights" as described in section 9.6 of CAP 637.

9.6 Rapid Exit Taxiway Indicator Lights
9.6.1 Rapid  exit  taxiway  indicator  lights  (RETILs)  provide  pilots  with  distance  to  go information to the nearest rapid exit taxiway on the runway, to enhance situational awareness  in  low  visibility  conditions  and  enable  pilots  to  apply  braking  action  for more efficient roll-out and runway exit speeds.
9.6.2 RETILs consist of six yellow lights adjacent to the runway centreline and configured in a three/two/one pattern spaced 100 m apart; the single light is 100 m from the start of the turn for the rapid exit taxiway, see Figure 1.6.


China is well known for having very strict air traffic control, who often are reluctant to give pilots the flexibility to deviate around bad weather or try a different - smoother - flight level (as I've experienced first-hand). That can lead to aircraft in Chinese airspace encountering more turbulence than in other parts of the world.

Secondary to that, China can get some nasty weather: Particularly in the South. Compared to Europe they'll have more thunderstorms, for example, and that can lead to increased turbulence. This image here gives an overview of the number of lightning strikes around the globe. Aside from a few patches in Italy, China has more lightning - and hence more turbulence due to thunderstorms - than anywhere in Europe. As you mention, the mountainous terrain in some parts of the country also has an effect, although you get that in Europe too.


How does one calculate the Mean Geometric Chord in extended Trapezoid Wing?

For the mean geometric chord, calculate wing area divided by span.
For the mean aerodynamic chord you integrate chord squared over span and divide the result by wing area.
$$l_\mu = \frac{\int^{+\frac{b}{2}}_{-\frac{b}{2}}l^2dy}{S}$$


What happens if a passenger dies mid-flight?

In the event of a passenger dying on an airplane during flight, each case is different depending on the location of the airplane, the duration of that flight and the wishes of family or friends traveling with the deceased passenger.

What happens to the flight?
If the death occurs before takeoff or shortly after takeoff, the airplane is landed back to that airport or the nearest airport. If it happens mid-flight, normally the flight is continued to its destination.
Where is the deceased passenger placed?
If there is a seat available in first or business classes, the deceased person is moved there and covered with a blanket. If it is a full flight, that person may simply be strapped in more tightly and covered. This is done to ensure that the body is out of view of other passengers. A deceased person is never placed in the lavatory. It is not respectful and a major security concern.
What happens at arrival airport?
The arrival airport is informed in advance about the situation. Hence police, ambulance and coroner are available. Some airlines keep body bags on board. Normally the deceased person is placed on a stretcher and is carried from the rear exit of the airplane using a lift truck and then placed in an ambulance. This might be done after other passengers have exited the airplane.
What are the regulations?
FAA have regulations addressing several emergencies, but not specifically this one. An FAA spokesperson mentioned:

  FAA spokesman Les Dorr said he was unaware of any policies that
  specifically address what should be done if someone dies in flight.
  The airlines make those decisions on their own.

This article mentions some incidents of this situation happening.

MedAir is a company which provides airlines with medical help from emergency care doctors on the ground. They estimate that:

  ... there is one death for every 8 million passengers from the airlines [they] serve ...


What is the correct technique for working on an airframe with a pneumatic rivet gun?

I banged rivets on a production line in a previous life (in the 70s). A trick that works wonders (although it may be frowned upon by purists, and your school instructors may prevent you from using such a "cheat" while learning) until you get good at holding it perfectly perpendicular is to put a little piece of masking tape over the tip of the rivet snap.  It moves the snap a few thousandths of an inch away so that more misalignment is tolerated as well as putting a barrier between the edge of the snap and the skin surface if it does touch.  You will find your smiley rate goes way down.

I tried to draw a little picture of what I meant in Paint but I couldn't do it without it looking like a rude bathroom stall drawing, if you know what I mean...

The other thing I see people doing is just shooting it full blast, then off.  Don't do that.  The gun has a "feathering" trigger that lets you ease in the air for a reason.  When you start to set the rivet, ease on just a bit of air, just enough to get it ratatatatting, and feel for the feedback of the bucking bar on the other side to tell you you have good contact, then give it a full shot.

Each shot should sound like, "ssstat tat tat tat tat tat brrrrrrrrrrrrrrrrrrrrrrrrr".

Especially when you have a partner bucking, you'll know right away if they don't have the bar in place on the shop side.  This helps prevent depressing the metal around the rivet, as well as reducing the risk of smileys.

Another one is don't hold the rivet gun by the handle like a pistol.  You have to be able to push in line with the snap.  Old time rivet guns were made U shaped for this purpose, but all the modern ones have the terrible pistol shape.  Move your hand as high as possible so you are pushing with the heel of your hand on the back of the rivet gun's body, with your wrist more or less in line with the snap.  Your index finger will be too high, so use the middle or second last finger to work the trigger. Like this:


Why do the F-22 and F-35 look similar to each other and different from previous designs?

ymb1 is right - stealth and not styling determine the looks of both the F-22 and the F-35. But there is more to it.

Watch Lockheed test pilot Tom Morgenfeld talk about them in this video:

The juicy bits are at 37:15' and at 43:35' into the video. Concerning the F-22 he says: Northrop built the F-23 exactly to what the Air Force asked for, while Lockheed built what the Air Force secretly wanted. And that was another F-15, with similar manoeuvrability.

Concerning the F-35 he says Lockheed's goal was to build an aircraft which is at least as good as an F-18 around the ship. This means manoeuvrability to land on a carrier even from off-nominal conditions; very forgiving to fly. By using the F-22 baseline, this manoeuvrability could be ensured.

Now look at all three of them:

McDonnell-Douglas F-15 Eagle (picture source)

Lockheed-Martin F-22 Raptor (picture source)

Lockheed-Martin F-35 Lightning II (picture source)

They look similar, don't they? Differences like a forward swept trailing edge and canted verticals are due to stealth, as is edge alignment.


Do any modern airliners have a non-flat floor in the passenger cabin?

Some Airbus aircraft have this characteristic, in the rear section of the cabin floor. You can see this in the following image. The rear passenger windows slope up following the floor slope.

A340 line drawings; image from wikimedia.org

This image of the upper cargo deck of A330 MRTT upper cargo deck (which would be the cabin floor in the passenger version) shows the upward slope.

A330MRTT cabin floor; image from thinkdefence.co.uk

Apparently, this is a common trait in A300/310/340/330's to allow more containerized cargo in the rear.


Why is it hard to see G1000 with sunglasses?

The screens are LCDs, which have a polarized filter layer over them. That layer is usually placed at a 45° so they are misaligned with your polarized sunglasses which are aligned vertically. You can confirm this is the problem by turning your sunglasses at different angles and see if the screen changes.


Is there a tank priority sequence for using the fuel tanks?

Which fuel tanks are used in order of priority in aircraft?

What you're talking about, in large aircraft, is often referred to as the fuel burn schedule. Light aircraft generally do not have a fuel burn schedule though they may have have minimal requirements.

The fuel burn schedule is dictated by the aircraft design and is thus different for different aircraft designs.

  Is there a sequence of priority?

Yes, and if you don't observe the fuel burn schedule you risk exceeding the structural limitations of the aircraft, and in particular wing bending moments.

  Or the pilot decides?

No, the pilot does not decide usually. While there may be some leeway in the fuel burn schedules of large aircraft, the pilot or a flight engineer (old aircraft) or an automated system does not decide but rather implements a preset protocol.

As an example, here's a general outline of the fuel burn schedule for 747-100/200 aircraft. This is from memory so might not be entirely correct but is sufficiently so for example purposes:

On start, taxi, and takeoff burn tank to engine. In other words, route the fuel from main tank 1 to engine 1, main tank 2 to engine 2, etc.
Once you're established in your cruise climb, all engines burn out of the center tank if there is fuel in the center tank until the center tank fuel is exhausted (but don't burn any fuel in the center tank that is there for ballast).
Burn engines 1 & 2 from main tank 2 and engines 3 & 4 from main tank 3 until the amount of fuel in main tank 2 matches that in main tank 1 and the amount of fuel in main tank 3 matches that in main tank 4. Main tanks 2 & 3 are larger than 1 & 4. When parity is reached, burn tank to engine.
At some point transfer the fuel in reserve tank 1 to main tank 1 and reserve tank 4 to main tank 4. Likewise, if you have them, from reserve tank 2 to main tank 2 and reserve tank 3 to main tank 3. Most 747-100/200 aircraft didn't have reserve tanks 2 & 3. You have to get the fuel out of the reserve tanks before landing.

Be aware that just as there is a fuel burn schedule, there may also be a fuel loading schedule. In the 747-100/200 that schedule dictated that no fuel goes into the center tank until all other tanks are full. As I remember, the largest center tank available held 114999 lbs of fuel at 6.7 lbs/gal fuel density. Center tank size varied as ordered by the airline and changed through the production run of the aircraft.


How hard would it be to convert a glider into an powered electric aircraft?

"Hard" is a matter of opinion. But installing an electric motor on a glider is quite doable. You don't want to put motors on the outside, though. Would make more sense to do what most manufacturers do, put the motor on a retractable pylon behind the cockpit, with doors that open and close as needed.


(Why) Do airliners travel together sometimes?

I do not have inside knowledge of Finnair operations, but I would expect that they have a limited number of staff who speak Japanese, and so logistically running the check in desks for several flights to Japan at the same time allows the airline to schedule checkin staff with appropriate language skills to cover the appropriate flights.

There are also restrictions at both Helsinki and in many Japanese airports that restrict night operations and aircraft on the ground overnight do not earn the airline money.  As a result, there is a limited range of flight times that ensure that the aircraft are operating continually.


Feasibility of using secondary props to generate power on an electric model aircraft

It seems to me to be somewhat pointless - your extra 2 props will create more drag, thus the main drive motor will need to work harder for the same result as without them. They're effectively cancelling each other out, and the laws of thermodynamics tell us that energy will be lost from the overall system.

It's much like connecting a solar panel to a lightbulb; physics just doesn't allow for a 100% efficient system, so it can't work.


Do multiple go-arounds on the same flight happen in commercial aviation?

None of four airlines I worked for (two commuters, two Part 121) had specific guidance as to the max number of go-arounds. However, as mentioned in the other answers, 2 or 3 was believed to be a good rule.

The only time I did multiple go-arounds, all missed approaches, was trying to get into Pullman, WA during a snowstorm in the late 1980s in an SA-227 Metroliner. I tried the VOR approach 3 times. Each time when we got down to the MDA, we did not have the forward visibility to descend further. Each of the 3 times the station personnel saw us pass over, and each time passengers looking out the windows saw the runway below us when we were overhead. That, of course, resulted in our being criticized when we arrived at our alternate by some passengers for not having landed at Pullman. I had explained en route to the alternate the problem with forward visibility, but when you've disrupted people's travel plans, they don't want to listen.

I briefly considered the feasibility, when we were over the runway, of entering a tight left turn to see if I could keep the runway in sight, but I rejected that. And, yes, I considered descending below the MDA before catching sight of the runway. That would have been doable as I was very familiar with the airport and knew that the gently rolling fields around the airport topped out well below the MDA.

The problem was that with all the snow on the ground and the snow in the air, we couldn't determine our altitude above the ground visually until we were actually over the runway. The fields around the airport had no trees, they were wheat fields in season. Even if I had chosen to bust the MDA, I still would have been too high for any kind of a normal landing when I caught sight of the runway end. If getting down was an emergency, we could have done it. It wasn't technically legal, but you could go into beta with the props and really drop out of the sky, then as you flared come out of beta. But it wasn't an emergency, so we went to our alternate, which was actually our next stop anyway, so all of the passengers weren't unhappy.

The advantage of multiple approaches is that conditions might get better while you're doing them, and you can get in. The disadvantage is that the nervous energy you're expending is telling.

Our SA-227s had no-autopilots, no radar altimeters, and, of course, no GPS. I imagine that these days that airport has one or more GPS approaches that would make landing in those conditions a piece of cake.


Can you identify this jet turbine stage?

What is this turbine part?

This assembly is part of the turbine used to rotate the compressor section of a Pratt & Whitney PT6, a free turbine turboprop. It's known as compressor turbine or just CT.

Where is it located?

The compressor turbine is located at the exit nozzle of the annular combustion chamber, and is the first component which enters in rotation under the effect of the hot gas velocity.

Compressor turbine. Source: P&W Training Manual

As visible, there is a second turbine (made of one or more stages, depending on the PT6 model) further downstream. They appear to be on the same shaft, but they aren't. There are two independent shafts rotating at their own angular speed.

The compressor turbine extracts power to rotate mostly the engine compressor, which role is to feed the combustion chamber with compressed air. The other turbine extracts power used (mostly) for the aircraft propulsion.

What is looks like on the real thing:

Source: AVweb on Youtube

The two shafts can be seen on the picture above, separated by the interstage baffle within the power turbine vane ring assembly.

Turbine blades material

Source

The blades, the hottest parts after the combustion chamber, are made of a nickel alloys. Nickel itself melts at 1,455 °C, and alloys are made more resistant either by solidified directional casting or single crystal growth (see more on materials). In larger engines turbine blades are often maintained below their melting point by circulating air in small internal channels. This is not the case for the PT6, gas temperature is still below the melting point (about 900°C).

Blades are protected by an anti-corrosion coating to delay as much as possible the inclusion of ion-sulfur into a material, a reaction known as sulphidation. Nickel sulphidation forms $\small Ni_3 S_2$ which melts at 635 °C. Sulphidation occurs all the time, but more quickly when flying close to sea water or industrial areas rich in sodium salts which can form sodium sulfate (more here). Frequent water washes of the turbine maybe necessary to eliminate salts.

Looking online for PT6 sulphidation, we can see a large number of investigation reports dealing with engine failures due to maintenance not done according to procedures.

About the P&W PT6 engine

The PT6 is a well known engine, available in various versions, which has been used for 50 years on aircraft and helicopters (but also on IndyCars, hovercraft, "turbotrain", snowplows....).

(source)

The particularity is the free turbine design. On large turbo-engines, the compressor (the low pressure compressor on engines with two or three spools) is on the same shaft than the engine output (which drives the fan, the rotor, the speed reduction gear,etc).

On a free turbine there are two rotating groups that are not linked by a shaft.

(source)

The first group is the gas generator section -- in blue, on the right hand of the images -- with a compressor and a combustion chamber. High pressure gas are sent to the last stage of the gas generator, which is a turbine stage -- the compressor turbine or CT, the one you've got. The CT drives the whole gas generator section and the accessory gearbox.
The energy used to move the generator section is only a part of the available energy in the hot gas (e.g. 66% on a twin PT6T-3D). The rest makes it's way to the mechanically-independent power section composed of one or more turbines, depending on the engine model. The turbines drive either the propeller, the rotor, or anything attached to the power section shaft, directly or via a reduction gearbox.
The gas production section can be spun (albeit at idle) wit the power section at rest (an helicopter turbine can be spun, while the rotor is maintained stationary).


How much jurisdiction does the FAA have over military aircraft?

If they are being operated by the military, not much. Military operations can exempt themselves from the FARs (as a matter of practice they don't: When operating in the US National Airspace System they follow the same operational regulations we do, but as a matter of regulation they're subject to the military's rules for airworthiness, maintenance, etc.).

Military pilots have a military pilot's license (which can be converted to an FAA license with a little paperwork), and the airworthiness and maintenance standards for active military aircraft are defined and managed by the branch of the service responsible for the aircraft. (This is similar to, but legislatively distinct from, Public Aircraft Operations.)

This doesn't mean the FAA is completely silent about military operations/aircraft: There is guidance for military aircraft that are based on commercial designs (also available in an easier-to-read Advisory Circular: AC 20-169), which would be applicable to aircraft like the VC-25 ("Air Force One").


Is breaking a FAR an issue when flying outside of FAA jurisdiction?

The FAA only has Jurisdiction over US airspace and you must follow the rules of the airspace you are flying in/through. If you are talking about N registered airplanes they must follow FAA rules for airworthiness etc. even if they are kept outside the country.

Here is in interesting question on breaking laws on a plane in general (sort of applicable here)

Side Note: Although the FAA does not have jurisdiction outside US airspace if there is an accident involving a US built aircraft (mainly Boeings at this point) the NTSB will send a representative to compile their own report (and aid in the investigation). I know this happens for commercial accidents I am unaware if they send representatives for US build GA plane accidents outside the country.

Side Note 2: US pilots licenses are valid elsewhere in the world and allow you to fly elsewhere in the world certain actions elsewhere in the world (if caught/reported) may lead to the revocation of your US issued license. There is some info on that here


How do people suffering from hypoxia not realize they aren't getting enough oxygen?

The key point here is that your body does not measure blood oxygen levels. Instead, the urge to breathe is caused by a surplus of carbon dioxide in your blood. At sea level, this is fine: the only way to get so much carbon dioxide in your blood is if you used up all the oxygen.

At higher altitudes, the pressure is lower, and consequently the oxygen partial pressure. Since the rate of diffusion in your lungs is a function of pressure, this means that oxygen will diffuse less readily into your blood. At the same time, carbon dioxide diffuses more readily out of your blood due to the low pressure. This reduces your urge to breathe; you do not feel 'out of breath'. See this Wikipedia page.

At even higher altitudes, the pressure is actually so low that breathing will cause oxygen to diffuse out of your blood; you can breathe as much as you want but the partial pressure of oxygen in your blood will never be higher than the partial oxygen pressure in the air. This is why oxygen masks work (even if they're not airtight): they replace all air near your nose and mouth with oxygen, so that the partial pressure of oxygen equals the total atmospheric pressure rather than the usual ~21%. See this and this Wikipedia page, or for example this YouTube video.

Somewhat related: at sea level, you can also run out of oxygen before you feel the urge to breathe. You might think that breathing deeply before having to hold your breath for a long time increases the amount of oxygen in your blood, increasing your endurance. This is only partially true: it also artificially reduces your carbon dioxide levels, reducing your urge to breathe. This way, you can black out before feeling out of breath, which can be dangerous under water!


What exactly is an ATC clearance and how is it requested?

I realize that the question was asking about EASA, but perhaps an FAA perspective will increase understanding.  The FAA Pilot Controller glossary defines clearance as:

AIR TRAFFIC CONTROL CLEARANCE [ICAO]− Authorization for an aircraft to proceed under conditions specified by an air traffic control unit.

Note 1: For convenience, the term air traffic control clearance is frequently abbreviated to clearance when used in appropriate contexts.

Note 2: The abbreviated term clearance may be prefixed by the words taxi, takeoff, departure, en route, approach or landing to indicate the particular portion of flight to which the air traffic control clearance relates.

In short, clearance is permission, and is generally associated with operating under IFR in controlled airspace.
I will disregard taxiing at a tower controlled field because it can be done under IFR or VFR.  Additionally, I have heard compelling arguments that you are not “cleared” to taxi, but are given taxi “instructions”.  (Ground controllers will never use the word “cleared” when telling you to taxi).
But that is a separate discussion...
The process begins with filing an IFR flight plan.  This notifies ATC of your intentions, and gives them time to enter your request into the system.
The actual clearance is issued when you call them, (radio at towered field, land line at uncontrolled field) field and put your clearance “on request”.  When you call, ATC will issue the clearance.  It will be either what you filed for, or it may contain amendments.
In the clearance you may be told to expect radar vectors.  This then becomes part of your clearance.  However, vectors assigned as needed during flight for traffic separation aren’t generally considered an amendment to the clearance.  Think of them more as a temporary detour around something.
For example, if ATC needs to amend your clearance they will tell you specifically that they have an amendment, and ask when you are ready to copy.  The amendment will generally be a rerouting that you are expected to follow on your own, and may also include a different altitude.
If given a vector, however, the expectation is that is it a temporary heading needed by ATC to provide traffic separation.  Once the need for positive ATC control is past they will clear you to resume your own navigation along your flight planned route.


Is there a recommended time to pause before transmitting, after changing to a new frequency?

I was always taught:

Change frequency
Give it a good 3 count
If no one is talking, transmit

The FAA just advises a pause as per the AIM [4-2-1] but gives no time specifically

  a. Listen before you transmit. Many times you can get the information
  you want through ATIS or by monitoring the frequency. Except for a few
  situations where some frequency overlap occurs, if you hear someone
  else talking, the keying of your transmitter will be futile and you
  will probably jam their receivers causing them to repeat their call.
  If you have just changed frequencies, pause, listen, and make sure the
  frequency is clear.

You will also learn to anticipate the flow. For example if you hear a controller issue something you should expect to hear the aircraft read it back. Once you get a feel for the cadence of chatter you will have even less issues.


Can ICAO airline designators be reassigned to a new airline?

Yes. As per rules ICAO can reassign the three letter airline designators after a period of 60 days.

  When a designator is no longer required, ICAO should be informed immediately. Any such designator so released will not be reassigned until a period of at least 60 days has elapsed.

The designator BKL was used by Baikal Airlines and is currently used by Aircompany Barcol.

Another example is the airline designator WOW, which was used by Air Southwest  and is currently used by WOW air.


How does the fuel pump work in a PA-28 and when should I use it?

The PA-28 Family of aircraft have two fuel pumps, an engine driven mechanical pump that is always pumping (so long as the crank shaft is spinning) and is considered the "main pump". The airframe also has an electrical backup pump that can be actuated by the pilot. The tanks do not have their own pumps.
You should check the POH for your airframe but generally speaking in the Archer and Arrow I fly the electric fuel pump is turned on:

checking fuel pressure before start
during take off
climb out
when switching tanks (I also run it for 30 seconds after switching tanks incase I either need to switch back and to maintain fuel pressure at a critical time in the event of a failure of the mechanical pump)
on approach
landing/go-around
in the event of a mechanical pump failure
while practicing maneuvers (S-Turns, turns around a point ETC)
during a practice stall
Engine power loss in flight
Loss of fuel pressure

Most of the above items can be found in this POH.
Note: You should not be running the electric fuel pump for the entire flight, like anything this is a component that can burn out and it should be used when needed or dictated by the POH.


Actually yes.  A two stage supercharger used a compressor with two or more compression stages, often with an inter cooler between them, driven by a transmission with different gear ratios to control the compressor speed.  A schematic of this type of supercharger can be seen here on a Rolls Royce Eagle engine.

On the Supermarine Spitfires powered by the larger Griffon engines the supercharger speed had both a LO and HIGH setting and could either be manually controlled by the pilot or automatically controlled.  The HIGH setting was not recommended at lower altitudes to prevent overboosting during operations there.


Are the N1 and N2 tachometer generators installed on 727 / JT8D engines line replaceable units?

Usually, they are. In case of the JT8D engine, the N1 tach generator (inside the nose bullet), atleast is a LRU. The AMT Society even has a competition which involves the removal of N1 tacho generator.


Could you encode data in a Black Box ping?

Current underwater locator beacons (ULBs) have a detection range of only a few km. 16 km would be under exceptionally favourable conditions. So in most cases the GPS data would not be of any additional help. It might tell you where the aircraft was before it hit the water, not exactly where the debris ended up after falling through several Km of water.

An advantage of current ULBs is their extreme simplicity and small size. There's no need for external data-feed and power connections. There are no issues of openings in the casing for waterproof connectors that also need to withstand the g-forces and pressures expected to be endured by a ULB. They are easy to test regularly and relatively easy to maintain.

From what I have read, current proposals for improvements to ULBs mostly focus on

increase duration from 30 days to 90 days
increase range by changing frequency from 37.5 kHz to ~10KHz

There are trade-offs here - longer duration means bigger batteries. changing the frequency may make it harder to distinguish from other sources of sound in the ocean.

An interesting 2011 dissertation describes the difficulties involved  and discusses modulating the beacon signal to include data.


Why does RPM for a fixed-pitch propeller change with an aircraft's pitch?

The driving variable here is airspeed, not pitch attitude per se.  Your airplane naturally goes faster when you put the stick forward and decrease the wing's angle-of-attack, and this changes the prop rpm.

Your pitch input is changing the wing's angle-of-attack which leads to an airspeed change.  Even with the engine switched off, the aircraft would fly (glide) at a higher airspeed with the stick forward than with the stick aft.  And for a given throttle position, a fixed-pitch prop turns faster at a high airspeed than at a low airspeed.

Just as a wind turbine does.

Your tachometer can be used as an airspeed indicator.

The key factor is the speed of the air flowing through the propeller disk-- with a fixed-pitch prop, this dwarfs any effect related to the amount of air being forced into the engine.

And yes, this effect can be explained in terms of the angle-of-attack of the propeller blades.  Increasing the airspeed decreases the angle-of-attack of the propeller blades, "unloading" them, or in extreme cases subjecting them to negative loading so that the prop is driving the motor rather than vice versa.

In a fast dive at a low power setting, the wind (airflow) is making the prop move, not the other way around, and you'd pick up more airspeed if the prop fell off.  But even at a lower airspeed and higher power setting, the speed of the oncoming airflow has big influence on the speed of the prop's rotation.


What's the point of the Total In-Flight Simulator?

There's a detailed and very interesting Air Force paper on this: CAPABILITY OF THE TOTAL IN-FLIGHT SIMULATOR (TIFS). The main point it makes is that TIFS wasn't just about gathering aerodynamic data, it was about testing aircraft configurations (including cockpit layouts) in actual flight, and training pilots on them. Here are some extracts, but you can read the paper yourself for the full details.

Test different configurations:

  It also surpasses the utility of past variable stability aircraft
  through the realism possible in its separate, new evaluation cockpit.
  The capabilities and features of this in-flight simulator considerably
  broaden the ability of the aircraft designer to deal with difficult
  trade-offs in flying qualities problems. A base configuration can be
  set up and then its stability and control characteristics can be
  systematically varied for investigations to gain research knowledge
  pertinent to flight vehicle and flight control system design.

Simulate a number of very different aircraft:

  It has been designed to reproduce in actual flight the flying
  qualities of a wide range of large airplanes.

Test different cockpit configurations:

  The simulation cockpit is removable, so that it can be replaced by
  other cockpits of different configurations.

Simulate a new design in flight, before the new design has even been built:

  Flight evaluations of the flying qualities of new airplane
  configurations can be accomplished, such as investigation of the
  behavior of extremely large airplanes. This can be extended to
  investigating the flight control characteristics of entirely new types
  of designs, as for example, reproducing the landing approach flight
  characteristics of a large re-entry vehicle.
  [...]
  The flight characteristics of specific aircraft can be simulated in
  great detail, both to evaluate flying qualities in advance of the
  first flight of the actual airplane and to investigate difficulties
  that may arise during the airplane's flight test program.

Train pilots on new aircraft:

  Finally, a well established and highly valuable use of in-flight
  simulation is pilot training. In-flight simulation of emergency
  conditions can be conducted safely because, if the evaluation pilot is
  having control problems, the safety pilot can switch the system off
  and resume control of the normal base airplane


What are the relations between stability, controllability and maneuverability?

a control system is "stable" if, upon a perturbation (like a gust or up/downdraft), the system will naturally return to its unperturbed state with your hands off the controls.

a plane exhibits "neutral" stability if, upon a control input from the pilot or a gust perturbation, the plane will not right itself if the pilot takes his or her hands off the controls, but neither will it diverge and fly itself into a steeper turn, roll, or pitch attitude hands-off.

"negative" stability means the moment you take your hands off the controls, the plane will by itself pitch up or down, roll left or right, or skid one way or the other. it cannot be flown hands-off unless it has an artificial stability augmentation system built into its control hardware.

A control system is "controllable" if pilot input is successful in recovering from a perturbation. But without pilot inputs, a "controllable" system will not necessarily by itself recover from a perturbation.

Maneuverability refers to the airplane's overall sensitivity to control inputs from the pilot and the effectiveness of the control surfaces over their control range.

An airplane that is highly maneuverable MIGHT be unstable- that is, it MIGHT  not fly hands-off because of how sensitive it is to control inputs or gusts. In general, a high degree of maneuverability usually is associated with marginal stability.


What is the benefit of upgrading Flight Management System to version UNS-1Ew?

Here is my understanding of the update. As others I believe your primary source should be your OEM.

Main purpose: Ability to use SBAS procedures and navigation

The purpose of moving from UNS-1E to UNS-1Ew is getting the SBAS capability. From the UNS-1Ew manual:

  The new “W” series of Universal Avionics Flight Management systems
  incorporate the Global Navigation Satellite System (GNSS) Space Based
  Augmentation System (SBAS) known in North America as the Wide Area
  Augmentation System (WAAS). Other SBAS systems in the world will also
  be incorporated.

SBAS details

SBAS means using WAAS, EGNOS and other GNSS augmentation systems. SBAS in short provides for correction of GNSS radio signal propagation errors in a limited area. This increases pseudo-ranging accuracy and positioning precision.

SBAS (space-based) is opposed to GBAS (ground-based) where correction broadcasting stations are on the ground, like the DGPS, a surveying GBAS with a positioning precision up to 10 cm.

EGNOS measuring network (SBAS for Europe area):

Source: Wikipedia

Additional benefits of the update

From UASC documentation:

  What else you get with an SBAS-FMS upgrade:

  •  Performance-Based Navigation (PBN) including Precision-Area
  Navigation (P-RNAV) compliance and Required Navigation
  Performance/Area Navigation (RNP/RNAV) up to 0.3 NM approach accuracy

  • WAAS LPV / EGNOS APV, LNAV approaches

  • Mode S Enhanced Surveillance support

  •  Accurate SBAS-GPS information provided to the onboard Terrain
  Awareness and Warning System/Enhanced Ground Proximity Warning System
  (TAWS/EGPWS) and Traffic Collision Avoidance System (TCAS)

  •  Large database capacity for worldwide navigation databases

You can read "The Benefits of SBAS" on UASC site.

And if you need more information the UNS-1Ew manual is also available.


How is directional control during takeoff and landing maintained in tailwheel airplanes equipped with skis?

I have a fair amount of ski time on Cessna 180s and Citabrias. It's a bit like flying floats. The main thing is, you have no brakes.
For lateral control, the skis have varying amounts of lateral compliance depending on the snow compaction, so you slip and slide more or less for each situation, but generally, the laggy reactions makes it easier to control direction on takeoff and landing compared to wheels.  The compliance is like being on wheels on wet grass; instead of darting to the side when the plane swings, it just kind of sashays laterally giving you more time to make corrections.
You may have a ski on the tail, which provides a limited amount of steering control to the extent that the ski design is able to bite sideways (a little skeg on the bottom really helps).  A decent tail ski on lightly compacted snow provides pretty good steering control without having to use large blasts of power to blow the rudder.  Otherwise, you are dependent on large blasts of power to blow the rudder to turn.
On ice or very deep powdery snow, you will be depending more on power to turn, and this is quite a challenge because the shot of power to get the tail to swing to turn also accelerates you forward, and remember, you have no brakes.
Bottom line is you can't really maneuver in tight spaces when on skis without using huge bursts of power, and annoying the local owner whose airplane may be in your prop wash, so it requires a lot more preplanning and thinking things through.
Some airplanes do without a tail ski, keeping the normal tailwheel, and this makes it easier to maneuver on compacted snow where the tire has some bite.  On deep loose snow, the tailwheel becomes an anchor, and you have to lift it out of the snow with shots of power and elevator, on top of lots of rudder to try to maneuver.  That can get exciting.  A tailwheel-only ski plane in deep snow is a pain.  For aircraft with wheel-skis, you normally see a tail ski with a penetrating wheel to do double duty.
So, you have no brakes. So you have to do run-ups on the move, either in a big circle if you have the space, or on the takeoff "roll" if you don't.
Then there's landing at the end of a sunny warm day on a compacted runway and the temperature drops below freezing in the late afternoon as the sun sets, and the runway has a bit of a downhill slope to it, and it's essentially compacted snow with an ice glaze.  Did I mention that you have no brakes?  Been there, done that.


Is it possible to get a medical certificate from Canada and a pilot license in America?

(This is similar to this question - and see this answer in particular - but there may be some points here that deserve a separate answer.)

First, can you use a Canadian medical instead of a US medical, with a US pilot's certificate? The answer is no, with one (?) exception. If it were possible, then people could shop around other countries to find the easiest medical for them, which would be a huge loophole and would allow them to simply ignore the FAA's medical requirements. As a general statement, the country of your pilot's certificate and medical certificate must be the same.

The only exception I'm aware of is when you hold a foreign license and medical, and then ask the FAA to issue a foreign-based private certificate under 14 CFR 61.75. See this question for more information but basically, you would have to hold a Canadian pilot's license and medical first, and even then you would be limited by the privileges of the Canadian license.

Second, could you get a US commercial certificate using a Canadian medical? Yes, but only in a very roundabout way, and even then you couldn't use it. You'd first have to get an FAA foreign-based private certificate as I described above - which means getting a Canadian license first - and that certificate would be fine to use for a US commercial checkride. However, after passing the checkride you'd still need an FAA second-class medical to actually exercise your new commercial privileges.

Finally, another option would be to get a Canadian commercial license and medical, and then fly only Canadian aircraft in the US. I have no idea how practical that is because most countries don't allow cabotage, but maybe there's some way to make it work.

AFAIK diabetes is only disqualifying if you're insulin-dependent; if you're on oral meds you may still be able to get a Special Issuance for it. If you have any doubts about your personal situation then I'd suggest consulting an AME and/or calling AOPA, if you're a member.


Why does an airspeed indicator not simply read TAS?

Well, indicated airspeed is the most important speed a pilot needs to know, so it makes sense to have that in the most obvious position.

IAS can be thought of as the pressure that the wings are experiencing - therefore all of the stall, manoeuvring, flap extension, and landing speeds etc are based off indicated airspeed.

True airspeed is really only important for flight planning and navigation. Given that more and more aircraft have GPS nowadays to give the groundspeed, the need for the pilot to know the TAS in flight is further reduced.


What reasons exist for not designing airplanes with breakaway wings for crash safety?

I can't think of an accident scenario where this might help. If you're hitting the ground hard enough to crash but have survivors, you're looking at an accident like TK 1951, where not only was the wreckage all in pretty much the same area, but it didn't even catch on fire. Aviation fuel is not as volatile as movies make it seem.

Maybe you are thinking of something like AF 358 which overran the end of the runway and burst into flames? Despite that fire everyone survived, but what if they realised it was going to overrun and jettisoned the wings whilst still on the runway?

Well the biggest problem to me is how to slow the aircraft down without wings. At higher speeds, the wheel brakes are ineffective without the use of ground spoilers. Without the reverse thrust from the engines you are guaranteeing that the aircraft will be going faster when it leaves the runway, leading to a much higher chance of casualties.

No piece of engineering is perfect either - what happens when it fails and the wings accidentally detach when everything is going well? What if they are flying in severe turbulence and the sensors detect high G forces and confuses that for a hard landing? Or if it a manual jettison, what if the pilots accidentally pull it, or a suicidal pilot does it while the other is looking the other way?

There are many other problems too, such as how some aircraft are designed with the gear support in the wings, that some have large fuel tanks in the fuselage, and the extra weight and cost of getting such a system certified. Ultimately this suggestion falls into the same bucket as every other drastic safety idea - in trying to fix a problem that barely exists, it creates a lot more in its place.


How can a 777ER fly from the 9000 ft runway at Bologna (LIPE)?

LIPE - OMDB is only around 4,500 KM (2,800 NM) according to Great Circle Mapper, which is nowhere close to the 773ER max range of 14,500 KM (7,830 NM), so one can make an educated guess that the aircraft wasn't at MTOW.


Why are ambient pressure and burner can pressure always the inputs on a hydromechanical fuel controlling system?

Hydromechanical Fuel Control Units (FCUs) typically do use compressor discharge air pressure as an input.

As I recall, the FCUs that I am familiar with have had at least the following inputs in addition to the control lever commands:

Compressor Rotation Speed
Compressor Discharge Air Pressure
Ambient Air Pressure

As both a mechanic and pilot I have studied many FCUs, and I do believe the inputs listed above are standard across all those with which I am familiar. This is certainly true of the types that I have studied most recently and the systems which I currently fly. Note that while these FCUs may be older designs—in some cases—they are commonly used on new production turbines.

The following are excerpts from some of my training manuals concerning a Bendix FCU:

  The pneumatic section of the FCU determines
  the flow rate of fuel to the engine for all operations.
  The power levers control engine
  power from idle through takeoff power by operation
  of the gas generator (N1) governor in
  the FCU. Increasing N1 rpm results in increased
  engine power.

  For explanation purposes, consider the N1 governor
  bellows as a diaphragm. P3 air is introduced
  into the bellows in a manner that sets up
  a differential pressure on each side of the diaphragm.
  Therefore, any change in P3 pressure
  will move the diaphragm. When pressure
  is increased, the fuel-metering valve attached
  to the bellows will move in an opening direction
  to increase fuel flow and increase N1 rpm.

  As P3 pressure decreases, fuel flow also decreases
  which reduces the N1 rpm. The N1
  governor increases or decreases P3 pressure in
  the bellows by varying the opening of relief
  orifices in the bellows.

  The FCU controls engine power by maintaining
  the requested N1 rpm through the N1 governor.
  If actual N1 rpm is lower than the desired
  setting, the N1 governor closes the P3 orifice,
  allowing pressure to increase. As the pressure
  increases, the diaphragm moves to open the
  metering valve, increasing fuel flow, which in
  turn increases N1 rpm to the speed requested by
  the governor. When N1 rpm reaches the desired
  speed, the governor adjusts the P3 orifice to reduce
  pneumatic pressure to match the fuel pressure
  required to maintain the desired N1 rpm.


What is the width of a high altitude airway?

At least in the US airspace definition, High Altitude Airways (Jet Routes) have no defined width regardless of the airway being navaid-based or RNAV/RNP

This is briefly stated in the FAA training manuals:
http://tfmlearning.faa.gov/Publications/atpubs/AIR/air2004.html


Can an aircraft flying VFR with a squawk code enter adjacent class C or D airspace after being handed over to the destination tower?

Trust, but verify.
The pilot must comply with 91.129 and 91.130 unless otherwise instructed by ATC.
ATC of any kind (radar or tower, Class C or Class D) should coordinate with any affected tower if an aircraft they are providing services to will enter another facility's surface area airspace. At least that's how I read the 7110.65 2–1–16, which you will note is in the "General Control" section and not the "Radar" section... though the wording definitely implies that it's directed at radar controllers.
The radar controller should have coordinated with the Class C tower (if necessary) and Class D tower controllers before switching the pilot to the destination Class D tower controller, if they expected the pilot would have to enter the respective surface areas. The destination Class D tower controller should have coordinated with the other tower controllers, if they expected the pilot to enter those surface areas. If coordination was not effected, they should not issue instructions which would imply permission to enter the other surface areas.
The pilot should query whichever controller they happen to be talking to, and follow the instructions they receive ("proceed through the XXX Class Delta airspace" or "remain outside of XXX Class Delta airspace").


Why can the A320 VAPP be decreased down to VLS?

... if landing is performed without A/THR...

Then theoretically you don't need the VAPP [setting] and should fly a bit faster, it's only a speed bug in this situation.

... without wind...

Even if the METAR is reporting an average of 0 knots, there is always a breeze here and there.

... no margin against a stall...

You have a 23% margin. VLS is 1.23 VS at 1G (check FCOM 4.03.20). So if the stall is at 120 knots, then VLS is 148 knots.

Note:

  VAPP should be at least VLS +5 kt.

So VAPP even becomes 153 knots, 33 knots above stall. Plus the A320 by design has anti-stall measures if the flight laws are not degraded.


I think the problem is that you see a Mode 3/A (identity) reply, but you try to interpret it as Mode C (altitude reply).

In Mode C, altitude is Gillham encoded, using all pulses except for D1 and X. This gives a range of -1200 to 126700 ft in 100 ft increments.
If you see a D1 pulse, you are not looking at a Mode C reply.

In Mode A, a 12 bit identity (squawk code) is transmitted, using all pulses except for X. In Mode A, the D1 pulse is commonly used (in fact, evey squawk code where the last digit is odd uses the D1 pulse).  It is simply the octal conversion of bits / pulses [A4 A2 A1], [B4 B2 B1], [C4 C2 C1], [D4, D2 D1].

For example, if you would encode squawk code 2345 you would set pulses [A2 = 2], [B1 & B2 = 3], [C4 = 4] and [D4 & D1 = 5].

Note that in case of Mode A, there may be an addition pulse for radar IDENTificaton. This is the Special Purpose Identification (SPI) pulse and it occurs 4.35 microseconds after the start of the closing framing pulse, with a duration of 0.45 microseconds.

source: www.radartutorials.eu


What is "airspace underlying a Class B airspace area designated for an airport"?

Yes, there is a legal interpretation on this:

  [...] under  the  express  language  of  the  regulation,  aircraft
  operating  in  the  airspace  underlying  Class  B  airspace -
  irrespective  of  whether  the  underlying  airspace  is  controlled
  or  uncontrolled - may  not  exceed  the  200-knot  speed  limitation

So it is indeed any and all airspace underlying class B.

And note the exception to the rule:

  We  note  §
  91.117  (d)  does  provide  that,  if  the  minimum  safe  airspeed  for  any  particular  operation  is  greater  than  the  maximum
  speed  prescribed  in  §
  91.117,  then  an  aircraft  may  be  operated  at  that  minimum  speed.


Can the lift fans used on a F-35 be driven by a turboshaft engine instead of the jet engine? If yes, which one?

There is no difference between turbofan, turboprop and turboshaft engine except for what is mounted on the shaft. There are many cores that are used in all of turbofan, turboprop and turboshaft engines. So yes, they can be driven by turboshaft. In a sense, the engine that drives them qualifies as turboshaft simply because it drives them.
That said, the lift fan of F-35 is absurdly inefficient. The thing is that lift is equal to mass flow through the fan/propeller times change of speed of the air, but the power required is equal to mass flow times square of change of speed, plus drag that grows with RPM.

Now the fan is small, so it has small mass flow and so it needs to accelerate the air to great speed and to do that it also needs high rpm, both greatly increasing the power required to spin it.

F-35 can live with that, because it only spends very short time in hover and a lot of time at high speed, so it can trade efficiency at hover for low drag at speed. But anything that should work like a helicopter should better have a large rotor like a helicopter, because it takes much less power to spin it (and thus has much lower fuel consumption).


Could a triplane fly using a dihedral wing in the middle?

It would depend on the relationship between span and separation. The dihedral would be too great on a short-span wing, as drawn, leading to all sorts of issues. Since the separation needs to be more than usual, approaching two chord lengths, you would need a very high aspect ratio, maybe 15 or so.

But if you were to leave out the middle wing and cross-brace each side with thin wires, as a biplane it would be just as stiff and perform a heck of a lot better.


Can any aircraft take off using auto-pilot?

If you are asking if a plane can be taken from the gate all the way to the sky by auto-pilot I'm quite certain the answer is no.  Not because a plane can't configure itself for take off and power up the engines (I'm quite certain it can, though I would defer to more knowledgeable people for that).  Not for that reason, but rather because there is no system in place to electronically guide an aircraft through a series of taxiways all the way to the base of the runway so that it can line up to take off in the first place.

Keep in mind, ATC gives a lot of instructions for ground operations, funnelling aircraft this way and that via taxiway A through Z.  They'd have no way of telling an auto-pilot about these directions, there's no computer to send out signals and there is no voice recognition build into the plane.  If you told the pilots, they would have no way to input the instructions into the autopilot, nor would the autopilot know what to do if it ever received such instructions.  It just isn't designed to follow taxiways.

Also, beyond just taxiway layout, there are a lot of planes in close proximity on the ground, plus bunches of other important vehicles (fire trucks, fuel trucks, de-icers, etc.)  Steering around all of those, faultlessly, would be quite the feat.  We've only just gotten to the point where a vehicle can drive across open terrain without crashing itself,  I think a plane navigating an airport (and doing it while minding ATC) is a bit of a ways off.

EDIT: Raidri's video does a much better job of showing the current state of driver less vehicles, and his comment is correct. I did underestimate how good the systems are these days.

That being said, I'm not changing my answer.  There still, currently, is no way to convey ATC instructions to the aircraft.

As a point of clarification: I saw the question as asking about technology in it's current state.  Will we eventually be able to do this.  Heck yes, absolutely.  A great deal of the technology is in place and what's left is either right on the horizon or close to it.  FAA clearance will probably take some time, but we'll get there.  I was mainly answer the question from the perspective of modern tech and what is currently ready to be installed on a plane.


What is the ground idle fuel flow of an A320 (CFM or IAE or neo)?

I don’t normally post answers that I cannot personally verify, but I have a Facebook friend who is FO in an A320. I sent him a message and asked your question. I don’t have any official documentation to reference, so take this as anecdotal...
An A320 with CFM engines burns about 600lb/hr per engine at idle in ISA conditions.
An A320 with V2500 engines burns about 730lb/hr per engine at idle in ISA conditions.
If the APU is running, it will burn another 300lb/hr.


What is the make and model of this plane?

That info helped. Looks like a Travel Air 2000, but without the prop spinner.


Let's do a Gedankenexperiment:
Think of air streaming around a body as flowing inside a stack of flexible tubes. The walls of the tubes are impenetrable, infinitesimally thin and follow the local streamlines faithfully. When the body approaches at subsonic speed, the air in the tubes near that body makes way for it by speeding up: This reduces the needed cross section and lowers static pressure, so the total pressure will stay constant. On the back side of the body the air slows down again and the tubes regain their old cross section and static pressure. Bernoulli in action.
When the speed nears the speed of sound, however, the speeding up is joined by a drop in density. Still, the air near the body speeds up but that will not change the cross section as much as before, because now this speed increase is coupled with a loss of density. The cross section still drops, but not by as much as before. More tubes have to bend away from the body and need the air in them to speed up so the body can squeeze through. More general: A change in body thickness (more precisely: The second derivative of its cross section) will work on more tubes, so its effects do not die down as quickly as in subsonic speed.
At the speed of sound the cross section decrease due to speed changes is exactly balanced by the drop in density, so the same mass of air needs more volume and eats up all the gain from increased speed. Now there is a wall of air which cannot yield facing the approaching body. That is the sound barrier. In reality, the speed around that body does not reach the speed of sound at the same station in all tubes, so there are mildly sub- and supersonic sections which will allow it to squeeze through. Still, drag is much increased and depends heavily on details in the body contour.
At supersonic speed density changes more than speed, so in order to reduce its cross section, the air in the tubes will slow down in order to make way for the body. Since it has no advance warning of the approaching body, it does so in a shock. As a consequence, the cross section of the stream tube can now be reduced because density increases in that slower air past the shock. Static pressure increases also so total pressure can stay constant again. The drag coefficient drops with further increasing Mach number because the density change becomes dominant, allowing the body to squeeze through the air more easily.
This thought experiment was explained in 1951 to researchers at NACA Langley by Adolf Busemann. One person in the audience, a young fellow named Richard Whitcomb, used the insight he gained to formulate the area rule a few weeks later.


What organisation owns intersection names?

The allocation of waypoint names is actually handled by each country's individual aviation authority. This means that there are actually duplicates in different countries or regions. The ICAO has made at least two attempts to remove the duplicates and make the names globally unique, one in 2010 and another in 2018. Despite these efforts, there are still over 1000 duplicate waypoints in the ICARD database.


At what point during a long flight do commercial airliners have the best gas mileage?

There are a lot of things that go into determining the most efficient way to operate a jet, and minimizing fuel does not always make it cheaper to operate.  Some general "rules" that are used are:

There is an optimum speed to fly the airplane, which depends on several factors:

Altitude
Fuel savings by flying slower -vs- increased maintenance costs because you are taking longer to get there (and putting more time on the airframe/engines).
Temperature at cruising altitude
Winds at cruising altitude

There is also an optimum altitude to fly the airplane:

Aircraft weight
The higher that you can fly, the better - until you don't have enough power to maintain your optimum speed at the optimum power setting for the engines.
Temperature at cruising altitude
Winds at cruising altitude
Altitudes that are available from ATC
The amount of fuel and time that it takes to climb -vs- the amount of time that you will have at the high speed cruise

Anything that makes the airplane heavier makes it unable to climb as high (and lowers the optimum altitude for the current conditions), and makes it burn more fuel.  This includes the fuel itself.  Assuming a constant speed and constant weather conditions, you will always be more fuel efficient later in the flight.

As fuel gets burned off, the amount of thrust required to maintain the optimum speed goes down and the optimum altitude goes up.  Basically, we keep reducing the power to maintain speed until the optimum altitude increases to an altitude that ATC can let us climb to.  This is known as a step climb.  The speed will be controlled manually by the pilot, or can be controlled automatically by auto throttles.

Today's sophisticated flight planning software takes all of this into account and gives the pilot a very good plan on how to operate the airplane to be the most efficient!


Do major passenger airline jets have airbrakes/speedbrakes?

Yes (for some values of major)

Adrian Pingstone

(c) Harm Rutten


What is the exact wing chord length and thickness for Boeing 747?

In general, you can get good general dimensions from the Airplane Characteristics for Airport Planning documents (Boeing). These documents include the overall dimensions and everything relevant for the airport. This does not include the chord length though.
To get more accurate dimensions, you can download CAD drawings from Boeing. I did this for the 747-400 and the 747-8I and measured the chord length in three places along the wing:

As you can see, the chord length varies between 14.84m at the root and 3.70m at the tip (before the winglet). The wing for the 747-8 has been slightly re-designed:

While keeping its basic structure and sweep, the wing is thicker and deeper, holding more fuel, and wider with raked wingtips.

(Wikipedia)
The differences in chord length are rather small (possibly less than the accuracy of these drawings):


Would it be viable to use jet blast deflectors as a power source?

From an environmental point of view would installation of windmills just before jet blast deflectors provide enough power to power up all machinery at airports?

From an environmental point of view? Not sure what that has to do with providing power, but no, here's why: First, many airports do not have jet blast deflectors at the ends of runways or in a place that sees most of the jet blast.

Aside from that, windmills (wind turbines) can't spin at unlimited speed. Here's what happens one one goes too fast (small turbines have the same issue, but can stand wind speeds up to 100-ish mph). Turbines are designed such that they have an optimal output within some speed range, below that they don't generate much power, and above that they can get hot and fail, or have to be throttled back to stay in the power band.

So seeing as how you would need to have them close to the ground where they aren't useful for natural breeze, providing major power to the airport is not going to happen.

  How much of a reduction in reliance on fossil fuel sources of energy would that be?

Why do you assume that the airport runs on fossil fuels? Many airports are running "green" initiatives, installing solar panels and bio-diesel reactors. They may also be purchasing renewable energy credits so that they try to get a good portion of the power used from renewable sources, such as wind farms.

  By how much would that reduce landing fees and could the energy provided at least power a mechanism that could tow All aircraft (including the Airbus A380 and the Boeing 747) during the entire taxi phase pre flight and post landing along with ALL airport machinery in busy airports like Heathrow

Such a tow system would almost undoubtedly increase landing fees. You are looking at it purely from a fuel savings view, but lets look at it from other angles:

Cost: There would be an extremely high acquisition cost, all the taxiways would have to be reworked to include this system. Even if it were an autonomous tow vehicles, the structure is not free. The tow's have to be created, programmed, vetted, certified, etc.
Maintenance: There is a lot of infrastructure to maintain, the tow vehicles, the electronic systems, mechanical systems, etc. This requires a full-time crew, and I'm sure they aren't going to work for free, plus enough on-hand spares to be able to quickly repair the system when it goes down.
Logistics: You have to have the tow mechanisms in place to catch the aircraft as they come off the runway. This means enough tow mechanisms to tow all aircraft and transit back to the runway possibly empty to catch another aircraft.
Other issues... Aircraft can't just shut down engines right after they land. Many engines have cool-down times before they can be shut down. They also can't just fire them up at the end of the runway, there are start-up times and warm-up periods. Aircraft also need to power systems on the way to the runway, air conditioning, avionics, hydraulics, etc.

Honestly these tow systems are not economically viable at this time. Aircraft are extremely fuel efficient (although not on the ground), but they have procedures to mitigate fuel expense on the ground. They shut down unused engines, turn off anything that isn't required, and reduce power consumption.

If you are looking for ways for the airport to save energy or generate it themselves, then solar panels or these tiles that generate electricity are more viable.


Is the September 11th the only time a plane was crashed into skyscrapers?

Intentionally with a large aircraft, yes. There was however an instance in 1945, where a B-25 Mitchell collided with the Empire State building. This however was an accident.

There have been several suicides by airplane where the aircraft was deliberately crashed into buildings, such as the C172 which was crashed into a Tampa FL high rise in 2002 or the Piper Dakota crash in Austin, TX.  There was also a case of an accidental crash of an SR-20 into a NY high rise apartment building in 2007, killing baseball player Cory Lidle.


What was the Airfoil of Handley Page P.115?

Did you see what Wikipedia had for it, and the book it came from?

  Specifications (HP.115)
  Data from X-Planes and Prototypes: From Nazi Secret Weapons to the Warplanes of the Future [Winchester 2005, p. 134]

  General characteristics

  Crew: one

  Length: 50 ft 4 in (15.33 m)

  Wingspan: 20 ft (6.1 m)

  Height: 12 ft 9 in (3.9 m)

  Wing area: 432 ft² (40.1 m²)

  Airfoil: Bicon 6%

  Empty weight: 3,680 lb (1,670 kg)

  Useful load: (Fuel) 1,175 lb (533 kg)

  Loaded weight: 5,050 lb (2,291 kg)

  Powerplant: 1 × Bristol Siddeley Viper BSV.9 turbojet, 1,900 lbf static (8.455 kN)
  Performance

  Maximum speed: 248 mph (399 km/h)

  Endurance: 40 minutes

This paper goes into calculations on biconvex airfoil as well, interesting reading  https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930085007.pdf


Why has flight UA106 such a strange predicted flight path?

As @mins suggested, it seems to be a wrong longitude of a waypoint in the Shannon Control area. I assume it is a hemisphere error (they used East instead of West).
If the longitude of the waypoint is mirrored with respect to the Greenwich meridian, the resulting path gives a more likely route to be flown:


How to calculate the power required during transition from VTOL to fixed wing?

Like Hobbes said. For instance, after take-off, tilt the thrust 10° forward. The cosine is 0.98 so you only lose 2% of propulsion lift. The sine is 0.17, so forward thrust is 0.17 * total thrust.

The craft will speed up until aerodynamic drag = forward thrust:

$$ T = D = C_D \cdot \frac{1}{2} \cdot \rho \cdot V^2 \cdot S$$
$$ V^2 = \frac{2 \cdot T}{C_D \cdot \rho \cdot S}$$

Then tilt to 20° where you have sin(20) = 34% of the propulsive thrust pointing FWD and 94% pointing UP, etc.

Note that it is usual to express the drag equation relative to wing area S.

A simple real-time approximation in a spreadsheet would look like underneath. 9810 N thrust pointed back 10 deg results in sin10*9810 = 1703 N forward thrust, which takes about 300 seconds to speed up the craft to 97 m/s. Of course, because of the aerodynamic lift the craft climbs, changing AoA and creating induced drag etc. The simulation should be extended with reduction in rotor thrust proportional to aerodynamic lift. But I hope the gist of things is clear enough.

.
.


Does anyone know an equation relating wingspan to gliding distance for a glider?

Your mystery equation is
$$\text{Distance} = \text{Height}\cdot0.5\cdot\sqrt{\pi\cdot e\cdot\frac{b^2}{f}}$$
Since the flight distance is the product of the glide ratio (or lift-to-drag ratio) L/D and height, the equation can be written like this:
$$\frac{L}{D} = \frac{c_L}{c_D} = 0.5\cdot\sqrt{\pi\cdot e\cdot\frac{b^2}{f}}$$
if we use dimensionless coefficients instead of the dimensionful forces. Now that does look familiar, right? Only something seems to be missing. And that drag area $f$ should be the wing area.

Now you asked for the derivation, and I've done that only with wind in this answer, so let's do it for the simpler case of a glider and without wind right here. You start with the question: What polar point gives the best distance for a given height? Or, in other words, when does the lift-to-drag ratio reach its optimum? To get anywhere, you need a simple equation for the lift-to-drag ratio, so I recommend to start with the equation for the drag polar
$$D = \frac{\rho\cdot v^2}{2}\cdot S\cdot\left(c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}\right)$$
The terms inside the big bracket are the sum of the parasitic and the induced drag coefficient and the term in front of the bracket is the product of dynamic pressure and wing area. It is needed to turn the coefficients into a force. The symbols are:
$\kern{5mm} \rho\:\:\:\:\:$ air density
$\kern{5mm} v\:\:\:\:\:$ velocity
$\kern{5mm} S\:\:\:\:\:$ wing surface area
$\kern{5mm} c_{D0} \:$  zero-lift drag coefficient
$\kern{5mm} c_L \:\:\:$  lift coefficient
$\kern{5mm} \pi \:\:\:\:\:$  3.14159$\dots$
$\kern{5mm} AR \:\:$  aspect ratio of the wing
$\kern{5mm} \epsilon \:\:\:\:\:\:$  the wing's Oswald factor, normally between 0.8 and 1.0

Since lift should be constant over speed for a glider, the optimum lift-to-drag ratio is when drag reaches a minimum. We express the lift coefficient by what it stands for and differentiate drag with respect to speed:
$$D = \frac{\rho\cdot v^2}{2}\cdot S\cdot\ c_{D0}+\frac{(m\cdot g)^2}{\frac{\rho\cdot v^2}{2}\cdot S\cdot\pi\cdot AR\cdot\epsilon}$$
$$\Rightarrow\:\:\frac{dD}{dv} = \frac{2\cdot \rho\cdot v}{2}\cdot S\cdot c_{D0} - \frac{2}{v^3}\cdot\frac{2\cdot(m\cdot g)^2}{\rho\cdot S\cdot\pi\cdot AR\cdot\epsilon}$$

Drag should reach its minimum when the derivative equals zero. We try to isolate the zero lift drag by dividing the equation by all what is collected around it:
$$0 = c_{D0} - \frac{2}{v^4}\cdot\frac{2\cdot(m\cdot g)^2}{\rho^2\cdot S^2\cdot\pi\cdot AR\cdot\epsilon}$$
Now bring $c_{D0}$ to the other side and re-insert the lift coefficient. The result is:
$$c_{D0} = \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$
This means that the optimum lift-to-drag ratio is reached when the zero-lift drag equals induced drag. Total drag is the sum of both and in this case equal to twice the induced drag. Written in coefficients, this is:
$$c_D = \frac{2\cdot c_L^2}{\pi\cdot AR\cdot\epsilon}$$
Written as the lift-to-drag ratio, this becomes:
$$\left(\frac{L}{D}\right)_{opt} = \frac{\pi\cdot AR\cdot\epsilon}{2\cdot c_L}$$
Since the optimum lift coefficient can be expressed as
$$c_{L_{opt}} = \sqrt{c_{D0}\cdot\pi\cdot AR\cdot\epsilon}$$
this can be inserted and the lift-to-drag ratio can be written as
$$\left(\frac{L}{D}\right)_{opt} = 0.5\cdot\sqrt{\frac{\pi\cdot AR\cdot\epsilon}{c_{D0}}}$$
The wing's aspect ratio is $AR = \frac{b^2}{S}$, and the mysterious drag surface must be $f = c_{D0}\cdot S$, and voilá, the strange equation is proven right. When the correct values are used, it is valid from mini paper airplanes up to Jumbo Jets and above. Airfoil drag is included in the zero-lift drag coefficient.


Upgrading a Sport license to a Private license - is a new student license necessary to solo non-LSA aircraft?

You do not need to get another student pilot certificate.  The endorsement you need is not for student pilots.

70. To act as PIC of an aircraft in solo operations when the pilot does not hold an appropriate category/class rating: § 61.31(d)(2).
I certify that (First name, MI, Last name) has received the training as required by § 61.31(d)(2) to serve as a PIC in a (specific category and class of aircraft). I have determined that he/she is prepared to serve as PIC in that (make and model) aircraft. Limitations: (optional).
/s/ [date] J. J. Jones 987654321CFI Exp. 12-31-19

The answer lies in Advisory Circular 61-65.  Version F is the latest.


Is there a way for an ultralight or powered glider to smoothly enter a jet stream?

Height is not the barrier. People have flown off Mount Everest - see http://abcnews.go.com/Travel/paragliding-everests-peak-kayaking-indian-ocean/story?id=21097292 as one example - though not when the jet stream is blowing over/around the mountain.

The problem is at the boundary layer between jet stream and none jet stream air when the aircraft only have air speeds of 20-50mph. The mixing of air, and the sudden hit of jet stream air speed will be well in excess of the gliders max air speed.

It has however been done in a hot air balloon. http://www.businessinsider.com/richard-branson-on-hot-air-ballooning-2014-10?IR=T


What is this flat plate sticking out of the tail of Learjet 24D?

It's a VOR antenna. You can find more information about it in similar questions like this one or this one.


What is the upper deck on converted freighter long-hump 747s used for?

They have seats for couriers, same as factory freighters, but roomier.

Note: From the -400BCF type certificate:

  There are no provisions for the carriage of passengers. A maximum of 19 couriers can occupy the aft cabin of the upper deck as defined in AFM.

  Source: airplane-pictures.net

Above is the upper deck of a -400BCF (converted freighter).

And below on the left is an -8F. Also, note the foldable yellow ladder for access to/from the main deck.

  Sources: left: pbase.com; right: pinterest.com (original source unknown)


For how long can a single-engine turboprop safely run the engine at idle?

It's not stressful at all for a turbine engine to run at idle, you could run it until the fuel runs out. The prop is not feathered (in line with the air stream, pitch 90°) but will be at ground fine, in line with the direction of blade turn, pitch angle 0°.

There is usually no way to disconnect a propeller from a single spool turbine engine: if the engine runs, the propeller turns.


What and where are "flotation seat cushions"?

It became something of a meme:

  In the unlikely event of a water landing, your seat cushion can be used as a flotation device.

You remove your seat cushion and hold the straps on the back as a flotation device. It's probably more of an aircraft/airline thing than by country. It seems that the industry is favoring life vests more, as they are designed to keep a person afloat and face up even if unconscious and not adding the requirements to the cushion allows the seat to be smaller and lighter.

Source


Which FAA regulations require passengers to comply with flight crew instructions?

On the day itself, the captain decides who gets to be on the aircraft when it departs. End of story, full stop.

Not abiding with this falls under the interference provisions you already mention -- or, more elementarily, it is trespass. Local law enforcement will help enforce the decisions if necessary.

Afterwards, if someone who didn't get to fly contends they had a valid and applicable contract from the airline that entitled them would fly, they get to duke it out in court for monetary damages.  How that turns out would depend on a lot of factors that are better discussed on Travel.SE or Law.SE.

The airline may lose in court, and if the captain's decisionmaking was sufficiently egregious (say, "there'll be no [racial slur]s aboard the plane I'm flying"), he may soon find himself out of job.  But the police who enforced the captain's decision on the day were still in the right to do so.  It's not their job to attempt to unravel contract disputes on the spot.


Would climbing onto fighters placed on display cause damage?

If you intended to make the aircraft airworthy again, yes, it can cause major damage. But, for use as a static art display, it would be no different than any other display really. Most likely all the moving parts have been fixed so they don't move so making it airworthy again is pretty much impossible.


From this answer, for the DC9-10 variant:

the wing group weighs 9470 lbs
the landing gear weighs 3660 lbs

Wikipedia mentions the fuel weight as 24,743 lbs.

For other variants, scale the wing and landing gear weights up with the ratio of Empty Weights found on Wikipedia.


When was the pitot-based ASI first used on aircraft?

From the book History of Technology, Volume 18, page 99:

  The first reliable air speed indicator was a U-tube manometer called the velometer, designed and patented by Frank Short at the Royal Aircraft Factory at Farnborough in 1912. Connection to a pitot-static head on a wing strut allowed the measuring element to be well away from the slipstream, while the indicator could be placed in front of the pilot. The velometer was manufactured by Casella and Elliott Brothers and was often supplied to military aircraft on a standard instrument panel.

It reminds me of the question: What was the first aircraft fitted with both an FDR & CVR?

Since the technology is not aircraft specific, say unlike the first flaps/air-brakes, the supplier can fit different aircraft at the same time. Which makes it near impossible to find the exact airplane as the above text suggests by mentioning a standard panel.

Interesting find: in 1910 there was a £5 prize (~£550 in 2017) for a speed-alarm design.


What plane cost less per mile to operate for one person?

No plane has these qualities, planes require a lot more servicing than cars both legally and practically. Similarly aircraft parts have service limits and heavily suggested rebuild times. Most if not all light aircraft require major servicing (or receive major servicing) at the 2000-2500ish hour mark.
There are comparatively little regulations on car maintenance. Most states require only a yearly inspection that boils down to a visual check of brakes, lights and a few other things as well as an emissions test mostly to keep the DEP happy.
Aircraft on the other hand require a verbose yearly "annual" inspection that can take days for a mechanic to complete. On top of that aircraft equipment needs to be routinely tested and checked for it to be legal for certain types of operation. On the contrary no one ever checks your cars speedometer or tach for proper operation.
Broadly speaking aircraft are also grounded if just about anything is not working where as most people often operate their car with small (or even large) issues. If you ever had an engine knocking issue in an aircraft you would be on the ground as fast as practically possible where as I know people that have driven cars thousands of miles with an "engine knock".
Airplanes also change substantially less than cars so small iterative fixes become difficult. If Toyota finds an issue in the 98 Corolla they can easily fix it in the 99 version. Fixing an airplane can require a lot of paper work, or if its a large issue an mandatory AD may be issued and everyone will be forced to fix it while 98 Corollas may still be out with their issues to this day.

If you just want a straight answer... A Piper Archer or a Cessna 172 (let the internet debates begin...)