What are these lights above the panel in a Blue Angels cockpit?

I'm not absolutely sure but I think they are the indicators for the inverted fuel pump. From arcforums:

  I finally spoke to a friend of mine who used to fly with the Blue Angels during the 2000/2001 show season. He said the lights on the glare shield were for the inverted pump indicator. The BA fly inverted longer than what is normally permitted for the Hornet so the Blue Angels aircraft are modified with a boost pump mounted to the top of the fuel tank. When they fly an inverted manuver for an extended period that pump is truned on, and while inverted fuel is pumped from the main tank to the feed tank. As fuel in the feed tanks is burned, the light would turns from green to yellow to red. When the light turns red it's time to roll back to a normal flight attitude.

So the three sets of lights should be for the tanks on both the wings.

I think this is the answer because the angle of attack indexers are found to the left of the HUD and look like this:

Also, it appears that they (aoa indexers) are found in carrier aircraft (for e.g. A-4 Skyhawk) as approaches are flown at a specified angle of attack rather than at particular airspeeds.

I believe that these lights are Blue angel specific mod as I'm not able to find them in any other versions.


Do any ejector seat designs include controllable thrusters?

Yes, modern ejection seats have rocket motors, but they are only for propelling the seat away from the aircraft and upwards, high enough for safe parachute deployment. An escape from enemy territory is not possible with them.

They are controlled by a guiding system inside the seat, but not by the pilot. Ejection by itself is stressful enough, controlling the seat would be too much for any pilot.

Nevertheless, this is impressive technology. Even when ejected pointing downward at low altitude, the seat will change course and lift the pilot up.

The seat featured in the linked video is the Russian Zvezda K-36, the only ejection seat which meets or exceeds all US Air Force performance demands.

To get downed pilots out from enemy territory the armed forces use helicopters. To build such a capacity into the seat would make it impossibly heavy and dangerous - would you like to sit on hundreds of kilos of jet or rocket fuel while being shot at? Just for the chance of flying home after ejection? And how deep are you allowed to fly into enemy territory for the system to work? No, this idea is a dead end.

The most promising concept today is to separate the pilot from the airplane, so he sits thousands of miles away while his craft flies deep into enemy territory.


What is the function of activating an individual elevator on the B-1B Lancer?

That would be the correct control response for a combined roll to the right and nose up pitch command from the pilot. It looks like that photograph was taken while the pilot was in the middle of doing a check of their control services prior to taxi.

You can see similar results in the tower buzz sequence out of Top Gun. The final bit shows an F-14 from the tail which rolls to the right and pitches nose up with a similar control response from a combination of the tailplane and starboard wing spoilers.


Can a convergent nozzle be used for a supersonic jet engine?

Short answer: Yes.

A convergent nozzle will not allow supersonic exit speeds of the combustion gasses, but due to their high temperature their speed of sound is considerably higher that that of the surrounding air. For example, at 700°C the speed of sound in air is 625 m/s. Since thrust is mainly determined by the difference in entry and exit speeds of the air flowing through an engine, a higher speed than flight speed is required for positive thrust. Low supersonic flight speeds are entirely possible with a convergent nozzle.

Long Answer: Better not.

Once the aircraft crosses the sound barrier, drag increases only slowly since the drag coefficient actually drops. If the design is meant to fly supersonically, which implicates a lot of design adaptions, it makes sense to go for higher supersonic speed; however, this requires both an adjustable intake and an adjustable convergent-divergent nozzle. Both increase efficiency, dramatically so at higher Mach numbers. The simple pitot intake of the F-16 is just good enough for Mach 1.6 (above that its efficiency becomes outright awful), but still its F-110 engine has a con-di nozzle.

With an adaptable convergent nozzle the exhaust gasses can be accelerated up to their speed of sound, but not more. A narrowing of the flow path will accelerate subsonic flow, but only to the speed of sound. Only a divergent flow path will then accelerate the flow further to supersonic speed. A convergent nozzle will be shorter and lighter, but means throwing away a good deal of useable energy with the hot exhaust gasses. In most cases it would be more efficient to convert the pressure energy of the exhaust gasses into more thrust by accelerating them to supersonic speed.

Convergent nozzles only make sense if the aircraft is designed only for short, limited supersonic dashes, but will spend almost all flying time at subsonic speeds. Examples are the Northrop F-5E or the Panavia Tornado.


The pilots do not manually trim an Airbus in pitch. The flight control computers provide automatic trim:

The normal-law flight mode is a load-factor-demand mode with automatic trim and protection throughout the flight envelope.
Following normal law, the sidestick controllers set the elevators and THS to maintain load factor proportional to stick deflection and independent of speed.
With the sidestick at neutral, wings level, the system maintains 1 g in pitch (corrected for pitch attitude), and there is no need for the pilot to trim by changing speed or configuration. Pitch trim is automatic both in manual mode and when the autopilot is engaged.

(A320 FCOM - Flight Controls - Description - Normal Law - Flight Mode)
There is however a mechanical backup:

The pilots use mechanically interconnected handwheels on each side of the center pedestal to control the trimmable horizontal stabilizer.

(A320 FCOM - Flight Controls - Description - Cockpit controls)
You can see the full flight control logic in the following image. The pitch trim is indicated by THS (Trimmable Horizontal Stabilizer):

(image source: A320 FCOM - Flight Controls)


What regulations are in place for ultralight vehicles flying over US national parks?

The use of mechanized items, which UAS, ultralights and other aircraft are considered are prohibited from Congressionally Designated Wilderness areas.

That designation does not appear on a sectional chart, but can be queried from the supervisor for the park or forest.  As far as I know, overflights, particularly those by manned aircraft are not prohibited, but launch, recovery or operation from the wilderness area is prohibited.


Slow Flight for CFI/Commercial Pilot - Should the gear be up or down?

Slow flight in training and testing has been the subject of much discussion and reevaluation in recent years.  The philosophy of how to train and demonstrate slow flight has changed a bit from years ago.

In specific answer to your question regarding whether or not the landing gear should be extended or not, here is an excerpt from FAA H-8083-3B [2016], page 4-4: Airplane Flying Handbook

(emphasis mine)

  Slow flight is typically performed and evaluated in the
  landing configuration. Therefore, both the landing gear
  and the flaps should be extended to the landing position.
  It is recommended the prescribed before-landing checks
  be completed to configure the airplane. The extension of
  gear and flaps typically occurs once cruise power has been
  reduced and at appropriate airspeeds to ensure limitations
  for extending those devices are not exceeded. Practicing this
  maneuver in other configurations, such as a clean or takeoff
  configuration, is also good training and may be evaluated
  on the practical test.

Here is the current flight test guidance for a Commercial Pilot applicant: "Airman Certification Standards" (ACS).  Under Area of Operation VII., "Slow Flight and Stalls," Skills: CA.VII.A.S4: - Commercial Pilot - Airplane, Airman Certification Standards - June 2017

(emphasis mine)

  Accomplish coordinated straight and level flight, turns, climbs, and descents with landing gear and flap configurations specified by the evaluator without a stall warning (e.g., aircraft
  buffet, stall horn, etc.).

Also, here is an FAA SAFO (Safety Alert for Operations) entitled "Maneuvering During Slow Flight in an Airplane" (8/30/2016): SAFO 16010


Can I take position behind a plane for V formation legally?

Here are the regulations in 14 CFR 91.111:

§91.111   Operating near other aircraft.
(a) No person may operate an aircraft so close to another aircraft as
to create a collision hazard.
(b) No person may operate an aircraft in formation flight except by
arrangement with the pilot in command of each aircraft in the
formation.
(c) No person may operate an aircraft, carrying passengers for hire,
in formation flight.

"Formation flight" is defined in the Pilot/Controller Glossary:

FORMATION FLIGHT− More than one aircraft which, by prior arrangement
between the pilots, operate as a single aircraft with regard to
navigation and position reporting. Separation between aircraft within
the formation is the responsibility of the flight leader and the
pilots of the other aircraft in the flight. This includes transition
periods when aircraft within the formation are maneuvering to attain
separation from each other to effect individual control and during
join-up and breakaway.
a. A standard formation is one in which a proximity of no more than 1
mile laterally or longitudinally and within 100 feet vertically from
the flight leader is maintained by each wingman.

And there are ATC instructions for handling formation flights but they're too long to quote here; see the ATC Orders 2-1-13.
So, let's assume that the distances between the aircraft in your proposed flight would make it a formation flight, per the FAA's definition in the PC/G. Putting all that together:
As a pilot, what would I need to locate other planes near me? Or find and [wait] on a plane going in the direction with equal cruising speeds to follow?
No idea. This depends very much on the type of aircraft and operation. Two friends in C172s flying half an hour for lunch somewhere? Two Boeing 777s flying internationally? But practically speaking, this would be near impossible without prior coordination on the ground. How would you know what route the other aircraft is following, or what cruising speed they plan to use?
Then would there be [an] issue of just taking position without asking. Should I ask for permission to do so, from the pilot which I'm shadowing or no I need more?
Per 91.111(b) you must have an arrangement with the other pilot first. In theory you could do that in the air but people who do formation flying seriously - and safely! - spend more time on planning than on flying. I don't know many pilots who would form up in formation with a stranger who just asked.
If you're thinking of using the V formation for commercial passenger flights then see this question. Although as you can see from 91.111(c), it isn't legal today, even if the pilots coordinate and work out all the necessary procedures first. And that's without even considering what their employers and insurers would say about it.


When communicating altitude with a '9' in it, should it be pronounced "nine hundred" or "niner hundred"?

In the UK, the RT rules for the ANO are in Cap 413 and section 2.13.2 states:

  All numbers used in the transmission of altitude, height, cloud
  height, visibility and runway visual range information which contain
  whole hundreds and whole thousands shall be transmitted by pronouncing
  each digit in the number of hundreds or thousands followed by the word
  HUNDRED or TOUSAND as appropriate. Combinations of thousands and whole
  hundreds shall be transmitted by pronouncing each digit in the number
  of thousands followed by the word TOUSAND and the number of hundreds
  followed by the word HUNDRED; examples of this convention are as
  follows:

Table 5
Number    Transmitted as              Pronounced as
10        One Zero                    WUN ZERO
100       One Hundred                 WUN HUN DRED
2 500     Two Thousand Five Hundred   TOO TOUSAND FIFE HUNDRED
11 000    One One Thousand            WUN WUN TOUSAND
25 000    Two Five Thousand           TOO FIFE TOUSAND

There isn't a specific example of NINER here, but given that the examples do actually use their prescribed pronounciations, you'd expect NINER to be used too.

I can't remember hearing it but the other conventions seem to be adhered to by professional pilots in the UK (we Sunday afternoon bimblers are not as good at it).  Non-native english speakers are very exact in their use of the published pronounciation

No doubt there will be a professional along in a minute, who can give you a more authoritative answer

EDIT: The reason I can't remember hearing "Niner-thousand-niner-hundred" may be because, in the UK, it would be above the transition level?


Could a test crew replicate the 1961 DC-8 supersonic dive in a more modern airliner?

Why not?
There have been several cases of near-sonic and even supersonic dashes by the Boeing 747, and the damage to the China Airlines Flight 006 elevator was done by landing gear doors which ripped off when the main gear was extended and its doors hit the elevator.
There have been a few unintentional supersonic dives, and in those cases the actions taken by the crew to decelerate caused damage to the aircraft. TWA Flight 841, a Boeing 727 which rolled into a dive, and China Airlines Flight 006 overstressed the airframe, but both aircraft returned to service after repairs.
IAI experience tells me it needs a dive with a nose-down angle of 18° to get a Boeing 747 to Mach 0.98. Since almost all surfaces experience already supersonic flow at this speed, going the step to Mach 1.01 would need not much more, maybe 25°. Pulling up from such a dive by means of the stabilizer should entirely be possible without exceeding g limits.


Have there ever been any accidents within holding stacks?

The article you linked in your question mentions one incident - loss of separation - that's described in more detail here.

The Aviation Herald is a good source of information on incidents and accidents but it has very few reports related to holding. There are several about low-fuel incidents because aircraft had to remain in the hold for a long time (Avianca 52 is a well-known case), but I could only find one that involved a holding pattern more directly and that was also a loss of separation resolved via a TCAS advisory.

Eastern Airlines 401 crashed while in a hold, but it was an ad hoc holding pattern and not in a stack with other aircraft. American Eagle 4184 crashed due to icing accumulation while holding but again there were no other aircraft involved.

I could only find one example of an actual collision in a holding pattern which was over New York in 1960 and in that case only one of the aircraft was holding (inaccurately).


Is the 737-800 a different plane from the 737 MAX 8?

They are different, yes. The 73H is not the Max 8. The 73H is an -800 with winglets. The -800 has been in service since 1998, with 4,991 deliveries as of February 28, 2019.

See here: What is the difference between Boeing 73G, 73H and 737?

  73H - Boeing 737-800 with winglets (8th letter of the alphabet)

The Max 8's IATA code you'd find on a ticket is 7M8.

For visual identification, see: Is this a 737-800 or 737 MAX 8?


Why are some dynamic derivatives not included in DATCOM file?

A plane is subject to 5 forces: Thrust, Lift, Drag, Weight/gravity (and side force). In addition, there are 3 moments: Rolling, Yawing and Pitching moment. With these 7 vectors you are able to represent how a plane behaves in the air. The problem of simulations is how to compute these 7 vectors for a complex shape like is an aicraft in different flight conditions. To obviate these issues, engineers came up with 'coefficient of ..' which is indicated by C_letter.

To make estimation of these coefficients more accurate, engineers decided to compute the partial derivative of each coefficient due to 'something'. However, some of these derivatives have a small influence on the coefficient such that only for high fidelity simulations they are used (for example in Level-D simulators). Moreover, depending on the type of aircraft, some derivatives may be important or not: if a plane has no slats then there is no lift coefficient due to slat failures.

DATCOM was developed in the seventies and computing power has improved a lot since then, therefore some coefficients are not included (yawing moment due to angle of attack).

A nice reference to understand why coefficients are used if the book Boeing - Jet Transport Performance Methods.


At a controlled airport, ground maneuvering, taxi routing and sequencing, etc., will be assigned to you by ground controllers after you make contact with them and enter the controlled areas of the field.  Even here the rules below will apply when aircraft are maneuvering in non-controlled areas of the field e.g. parking aprons, hangar spurs, refueling areas, etc.

Pilots are generally courteous and conscientious people and will usually try to be helpful to both parties.

At a uncontrolled airport or an uncontrolled area of a controlled field, the following right of way rules are going to apply to maneuvering on the ground:

  When two aircraft are approaching head on, or approximately so, each shall stop or where practicable alter its course to the right so as to keep well clear.
  When two aircraft are on a converging course, the one which has the other on its right shall give way.
  An aircraft which is being overtaken by another aircraft shall have the right-of-way and the overtaking aircraft shall keep well clear of the other aircraft.
  An aircraft taxiing on the manoeuvring area shall stop and hold at all runway-holding positions unless an explicit clearance to enter or cross the runway has been issued by the aerodrome control tower.
  Emergency vehicles proceeding to the assistance of an aircraft in distress shall be afforded priority over all other surface movement traffic.

Source: EASA (pdf pages 53-54)


How are aircraft shipped to their customers?

They are flown to their customers by either Boeing or pilots from the given airline.

As for the Boeing factory its self, the Everett Factory users Paine Field as their runway. If you look closely there is a bridge that crosses the highway and connects the plant to the main ramp of the airport. This appears to be painted for car traffic but is also used for aircraft. The Renton Factory lies adjacent to Renton Municipal which it uses to fly the aircraft in and out there is also a small bridge connecting them over the river.

Similarly the main airbus factory is located next to Toulouse–Blagnac Airport. Bombardier lies next to Montréal–Pierre Elliott Trudeau International Airport.


As usual, it is a combination of measures:

Flow speed at the start of the combustion chamber is the lowest in the whole engine, in the order of 30 m/s.
High fuel pressure and many small fuel injector nozzles, such that the mean fuel droplet size is kept as small as possible
Flame holders cause a pocket of stagnated, burning flow which helps to ignite the fuel-air mixture
The combustion chamber is long enough to allow most of the combustion to happen inside, such that radiated heat from the burning gas ignites the fuel-air mixture upstream.
In marginal conditions the ignitors are switched on to help speed up the ignition.
Control of parameters, such that fuel starvation by rapid throttle changes can be avoided. Examples are fuel control units, where a centrifugal feedback valve would control fuel flow depending on the engine's rotational speed, or electronic control (FADEC).

Much can be done by running the engine such that the risk of flameout is minimized. The operational measures to ensure a stable flame would be:

Avoid fuel starvation (empty tank, fuel pump failure, clogged pipes). This one is obvious, but I need to include it for the nitpickers.
Avoid too low pressure for rapid combustion: Pressure speeds up the chemical reaction, and if the aircraft flies high and/or throttles down, the lowered pressure in the combustion chamber might cause a flame-out. High-altitude jet engines have longer combustion chambers as a precaution.
A compressor surge or disturbed inlet air flow can cause a sudden pressure loss in the combustion chamber and a consequent flame-out, the latter especially in supersonic fighters with their long intakes and high angle-of-attack capabilities.
Avoid sudden cooling of the air inside the engine, e.g. by heavy rain. The additional water extracts energy when it evaporates and causes a temperature drop in the combustion chamber which can lead to a flame-out of a throttled-down engine. Another possibility is too much fuel which has been ingested by the intake in a botched aerial refueling attempt.
Avoid clogging of the inside of the engine by ingested dust, like gun smoke or volcanic ash.


What stops a pilot from flying VFR and going IFR?

You are confusing VFR, VMC, IFR and IMC.  Let’s briefly define the terms before I attempt to answer your question:

VFR – Visual Flight Rules.  The pilot navigates at will, but must comply with cloud clearance and airspace requirements.

VMC – Visual Meteorological Conditions.  The weather is good enough to operate under VFR.

IFR – Instrument Flight Rules.  The pilot must file a flight plan with ATC and be cleared for the altitude and route flown.  This defined and regulated process is required under IMC, but can also be followed when the weather is clear.

IMC – Instrument Meteorological Conditions.  Weather conditions are poor enough that operation under IFR is required.

So to answer your question, if an instrument rated pilot is operating under VFR and finds him or herself unable to maintain VFR cloud clearance requirements, (i.e. the weather is no longer VMC) then they should contact ATC immediately and request an IFR clearance.  By definition it is not possible to fly under IFR without the knowledge and consent of ATC.

And yes, it is possible to fly into IMC without ATC's knowledge or a clearance, but it is neither safe nor legal.  It is unsafe for the non-instrument rated pilot because of the extreme likelihood of spacial disorientation, and for both because of the risk of loss of separation from other traffic.  An instrument rated pilot would of course be able to rely on their skills to penetrate a cloud safely, but it is not something that can be done at pilot's discretion as you suggest.

I am guessing that the origin of your question is what we call “inadvertent IMC”.  In this case, instrument rated or not, the pilot should fly by reference to their instruments and execute a level 180 degree turn to exit the cloud.  This is an emergency situation.


What radio frequency bands are associated with the long wire antennas, why do some aircraft have them and others don't?

Depending on the aircraft you could be looking at one of a few things.

(source)

On some older aircraft it may be the communications antenna for older style radios (pre UHF/VHF days). Most of these radios have been phased out for some time but you will see it in pictures.

The more common thing you are seeing (based on your top of the fuselage to front of the tail description), as it is still in place on many small GA planes and any bigger planes that have not had the unit removed is the ADF Sense antenna. This antenna helps to deal with the directional ambiguity problem in an ADF unit. Basically the loop antenna is capable of knowing where the station is but only on a 0-180 degree plane. It does not know if it is in front or behind the antenna. The sense antenna allows it to solve this ambiguity. These units operate in the 190-535kHz range. For what its worth the FAA is pulling a lot of ADF's and their associated approaches as GPS takes over but they seem to still be common elsewhere in the world.

Here is one,

(source)

  Why do some aircraft have them and others don't?

Since it seems like we have settled on the ADF sense antenna as the one in question it boils down to weather or not your airplane has an operational ADF installed. ADF's are still popular elsewhere in the world but here in the US much of the ADF system is being pulled as it was in part replaced by the VOR system much of which is to an extent being supplanted by GPS today. Since a large chunk of the GA fleet and to an extent the commercial fleet has airframes dating from the ADF days many of the planes still have the systems installed. Depending on where you are located, if you routinely fly one of the remaining ADF approaches or otherwise use an ADF regularly you may elect to keep it in your aircraft. I can tell you that none of the aircraft I trained in had operational ADF units although two of them had units with antennas but were non operational and simply had yet to be removed.


What is the explanation of the apparent staining inside this airliner window [photo]?

I believe the stain is caused by air going through the hole relatively fast due to compression of the cabin. Assuming the window is 40x40 cm large, and there is 10 cm between the panels, the volume of air in it is 16.000.000 mm3. About 30% of this air comes out due to the lower pressure at altitude, that is 4.800.000 mm3. Assuming it takes 600 seconds (10 min) to pressurize the space again, the flow will be 800 mm3/s. Assuming the hole has a diameter of 2 mm, it has an area of 3.14 mm2. The average flow velocity is then 254 mm/s. It looks like the spot is only 20 mm away from the hole, so it would take a dirt particle less than 0,1 second to get to the spot from the hole. I think that is not much time to deflect, hence the concentration in the middle.


Is it possible to fly a Straight and Level flight at high speed?

Yes, with good engines and low drag you can fly straight and level at really high speeds.

What about the AOA? It gets smaller, but only down to a certain limit. At level flight, the weight of the aircraft is equal to the aerodynamic lift:

$$ W = L =C_L\cdot\frac{\rho}{2}V^2\cdot S $$

The lift coefficient depends on the AOA ($\alpha$):

$$C_L=C_{L0}+C_{L\alpha}\cdot \alpha$$

Therefore,

$$\alpha = \frac{1}{C_{L\alpha}}\left(\frac{2W}{\rho V^2 S}-C_{L0}\right)$$

For very high speeds the first term of the parenthesis will get close to zero, so that the desired AOA setting becomes

$$\alpha_{V\rightarrow\infty} = -\frac{C_{L0}}{C_{L\alpha}}$$

This AOA is indeed negative for most aircraft. If your AOA gets smaller you won't be able to sustain level flight.

The plot below shows the AOA needed for straight and level flight on a Cessna 172 and compares the two terms in the parenthesis of the equation for $\alpha$ (multiplied by 10 for better readability). You would need to fly much faster than $V_{NE}$ to get the first term significantly smaller than the second one.

Source: own work with data from Wikipedia and polar.


How do aisle lights show the direction to exits?

The Floor Proximity Emergency Escape Path marking requirements (for transport category aircraft certified under FAR Part 25) have to meet the specific requirements as noted in the regulatory excerpt below.  There are different configurations that may be used to satisfy the regulations.
FAR §25.812   Emergency lighting. (excerpt):

(...) In the dark of the night, the floor proximity emergency escape path marking must enable each passenger to—
(1) After leaving the passenger seat, visually identify the emergency escape path along the cabin aisle floor to the first exits or pair of exits forward and aft of the seat; and
(2) Readily identify each exit from the emergency escape path by reference only to markings and visual features not more than 4 feet above the cabin floor.

Here is a sample from the Flight Safety Foundation showing an example of floor proximity escape path markings.

(Source)
Also, here is a link to a Flight Safety Foundation article regarding floor proximity lighting.


How many planes do ATC controllers assist in taking off/landing each day?

From the title of your question (taking off / landing planes), I assume you are asking about a tower controller. As you may know, most air traffic don't work in a control tower, but are en-route controllers working in an ACC (area control center).

The number of planes a tower controller handles each day is of course highly dependent on the airport traffic conditions (november, for example, is a quiet month). I work in an European single-runway airport, where the runway capacity is 40 flights / hour (landings and departures included) in optimal conditions. Controllers usually work around 5 effective hours per day, so the theoretical maximum number of planes would be 200 planes. In practice, it is very unlikely that a controller will actually control that number of aircraft, because the runway is used at maximum capacity only during peak hours (early morning, late afternoon and beginning of the evening). Also, a tower controller doesn't only work at the tower position, she will also be typically work a clearance delivery and an approach position.


The picture given is not complete, it is missing several components. Unlike the other two gyros, the turn coordinator is not allowed to remain rigid in space while the gimbal moves freely around it. The plane of rotation is forced to change with changes in the heading, because of this it does not use a full gimbal. It has one axis other than the gyro core. The housing applying force to the gyro causes precession. In other words, the gyro would like to remain fixed in space but the housing applies force as the aircraft changes heading and bank angle. The resulting precession is restricted by springs.
The higher the rate of change in heading the more torque is generated by the gyro attempting to precess. This force can be measured by the change in spring length, indicated as movement on the gauge. By tilting the free axis up from zero pitch, changes in bank angle will also cause precession. With 90 degrees or a vertical axis the instrument would only precess with changes in bank, angles between 0 and 90 provide a varying mix of the two signals.(Angling the axis down will cause bank to react in the opposite direction, usually this is not desired.)


what is the difference between max nose wheel steering angle and effective steering angle?

When the two sides of the main landing gear move, each one tends to force a circle with its own radius and center, and is at the same time influenced by the nose landing gear own radius of turn.

Source: A350-900 Aircraft characteristics, airport and maintenance planning

Some tire sliding must occur due to the difference in circles, the actual center is between the three individual centers mentioned and the radius R3 is therefore a bit impacted.

Depending on the differential action on the brakes, and the use of engine thrust asymmetry, the result varies by a few percents (between types of turn 1 and 2 above).


If airfoils at low speed generate higher coefficient of lift, why is it not reflected in airfoil polars?

No, they don't.

The Reynolds number is the ratio of inertial to viscous forces in a fluid. That means viscosity has proportionally more effect at lower Reynolds numbers. The boundary layer is proportionally thicker, friction steals more energy from the flow and lift is lower.

This answer contains a graph with a collection of empirical data, as does this answer. Here is another answer which covers both attached and separated flow. As you can see, Reynolds number effects mainly affect attached flow, and in a way that reduces lift for the same angle of attack; the more so, the closer you come to the stall angle of attack.

Just to save you from following all the links: See below for a plot of the venerable NACA 4412 from Abbott and Doenhoffs collection of airfoil data (picture source):

Note that the lift coefficient is plotted for Reynolds numbers R of 3, 6 and 9 million.


What is the procedure after a missed approach at the destination alternate since alternate fuel does not contain a missed app. at the alternate?

Let's assume you started exactly with ICAO minimum fuel required (as explained in What are the ICAO fuel reserve requirements?):

Taxi fuel Let's assume you used all of it at your departure airport.
Trip fuel Used for the flight to the destination airport.
Contingency fuel Let's assume this was used in a holding pattern at the destination.
Alternate fuel Used for a go around at the destination and the subsequent flight to the alternate airport.
Final reserve Not used yet.
Additional fuel Let's assume you did not take any.

Under these assumptions you would be using the Final reserve fuel for your go around at the alternate airport. At this point you should declare an emergency (see Do I have to declare an emergency if I cut into fuel reserves?) by broadcasting

  MAYDAY, MAYDAY, MAYDAY, FUEL

as explained in What is the correct phraseology for declaring a fuel emergency?. ATC will then assist you to get to any suitable airport as soon as possible.


What are the differences between various simulator levels?

Here there is a nice tabular representation of the requirements for each level.
Wiki provides a handy summary:

Full Flight Simulators (FFS)

FAA FFS Level A - A motion system is required with at least three degrees of freedom. Airplanes only.

FAA FFS Level B - Requires three axis motion and a higher-fidelity aerodynamic model than does Level A. The lowest level of helicopter flight simulator.

FAA FFS Level C - Requires a motion platform with all six degrees of freedom. Also lower transport delay (latency) over levels A & B. The visual system must have an outside-world horizontal field of view of at least 75 degrees for each pilot.

FAA FFS Level D - The highest level of FFS qualification currently available. Requirements are for Level C with additions. The motion platform must have all six degrees of freedom, and the visual system must have an outside-world horizontal field of view of at least 150 degrees, with a Collimated (distant focus) display. Realistic sounds in the cockpit are required, as well as a number of special motion and visual effects.


What kind of g-forces do birds experience and how does it compare to humans?

Birds regularly experience up 10-14 G according to this website. After looking at how birds and insects fly, scientists came up with the conclusion as to how birds cope with this is because:

  Animals will always have some advantages over machines, such as the ability to use their nervous systems to sense subtleties about the environment around them and alter their flight accordingly.

further up near the top, it mentions comparisons between birds and high performance military aircraft, such as this:

  A Blackbird jet flying nearly 2,000 mph covers 32 of its own body lengths per second. But a common pigeon covers 75 of its body lengths a second.
  The roll rate of the aerobatic A-4 Skyhawk plane is about 720 degrees per second. The roll rate of a barn swallow is more than 5,000 degrees per second.
  Some military aircraft can withstand gravitational forces of 8-10 G (Earth's gravity is equal to 1 G). Many birds routinely experience G-forces greater than 10 G and up to 14 G.

According to another website the reason humans can't cope with high g's as well is because:

  Every bit of our muscular-skeletal system is naturally crafted to deal with Earth’s gravity. Were you to travel to a planet that had a more significant gravity, a more massive planet with 5 G’s for example, you would either be unable to lift yourself off the ground, our the new weight-force would be so much that the air would be forced out of your lungs and your eyes would explode (something gruesome for sure).


Why do the N1 and N2 fans have different shafts?

Several reasons:

The fan, LPC/T, and HPC/T spools all operate at different speeds for optimal efficiency.  A hard link between them affects the speeds at which the other spools can operate, reducing efficiency.

Separate spools reduced the rotational inertia of each, reducing 'spool-up' lag, and allowing them quicker response times to throttle inputs.

The spools can be contra rotating, reducing the effective moment about the engine casing and mount, making the engine lighter.


What's that component between the engine and wing?

It's a hard-point called an "engine pylon".

And yes, some designs use specific points designed to fail if there is excessive force, allowing the engine to separate from the aircraft without ripping the entire wing apart which would obviously be a catastrophic event. It has happened on a few occasions.

The above image is from the Wikipedia page on the American Airlines 191 accident, where, due to a faulty maintenance practice of using forklifts for removing and reattaching the engine/pylon assembly, the aft bolts were damaged. The pylon eventually failed, allowing the engine and pylon to push up and over, separating from the wing.

Other examples include China Airlines 258 and El Al 1862.


What is the use of Stub Wings on Helicopters?

In addition to serving as support for weapons, we must have in mind that they're both quite fast for a helicopter - 335 km/h (208 mph) for Mi and 294 km/h (183 mph) for UH. At such speeds, even small wings yield considerable aerodynamic effects, just like in planes. From Wikipedia article we can learn that Mi's wings can provide up to 25% of total lift at speed and important stability to counter tendency to Dutch Roll.

Curiously, both mentioned platforms exist in wingless configuration. For UH-60 it's quite common, while Mi-24 had it's wings removed for breaking records. This hints that Mi-24 is much more dependent on it's wings than UH-60.


Why didn't Boeing produce its own regional jet?

Boeing did have a small regional jet called the Boeing 727. This plane was designed to operate at smaller airports, with independence from ground facilities as a selling feature. The best example is that the 727 had built-in stairs in the rear underbelly of the aircraft. This could be opened in flight until some hijacker known as DB Cooper jumped out to make his escape.

The 727-100C could have a combination of 54 passengers and  four cargo pallets of freight or up to 94 passengers in a mixed class with no freight.

Until it ended production at 1,832 aircraft, the 727 was the most popular passenger jet ever sold. Since that time, the most popular plane ever sold was the Boeing 737, which could have as few as 85 passengers with the 737-100.

Boeing met a definite need for airlines since it sold so many aircraft. A better question might be what could McDonnell-Douglas have done to meet airline needs and still be a viable competitor.

Two Class Seating Arrangement:

https://frequentlyflying.boardingarea.com/vintage-airline-seat-map-american-airlines-boeing-727-100-from-1977/


The F/A-18 Hornet and MiG-29 ailerons from the external parts of the wings go up some degrees in flight. Why?

The pictures in the question show the normal position of the MiG-29 ailerons. That's how they are unless a roll is commanded.

According to Mikoyan Mig-29 Fulcrum Pilot's Flight Operating Manual (google books) the slight upward position is set to improve yaw stability during roll meneuvers:

As for whether this angle (neutral position of ailerons) changes in accordance with flight envelope: it does not. Check out this and this Youtube video for an example. Climb, dive, straight and level, no change. The position of the ailerons is not affected by load factor either, as you can see below, 1g (straight & level flight):

... and a pull of 3g's:

(Source: the second Youtube video posted above)

Whenever you see the ailerons move, it is always accompanied by roll.

As for the F-18, I'll investigate and be back later.
(edit: as a preliminary claim I'd say the F-18 drops flaps a few degrees on high g maneuvers to increase camber, but the flaperons only move when roll is comanded or flaps are lowered. So no flaperon up with high g)


Can the autopilot (or stall avoidance system?) of the B737 MAX 8 be overridden by sheer force?

I'm not sure of the full story here, but if you pull the controls of a 737 while the autopilot is engaged the autopilot will trip and the pilots can fly the plane manually. This requires about 25 lbs of force.

There is also a button on the yoke where you can disengage the AP. So if the AP was controlling the plane and going into a violent descent the pilots should have been able to cancel it by pulling the yoke or pushing the button on the yoke or the mode control panel below the windshield.

And no, the controls being hydraulic doesn't play a role in the "override by sheer force" possibility.

Edit:

  The autopilot servos are limited to 25 lb of force for single channel operation. Separate force sensors measure pilot column input and the autopilot will disconnect if the force applied by the pilot(s) exceeds 21 lbs.

Source


What is the equation for calculating static thrust?

By now you should have found this answer on static thrust. It explains how to arrive at this equation for static thrust $T_0$:
 $$T_0 = \sqrt[3]{P^2\cdot\eta_{Prop}^2\cdot\eta_{el}^2\cdot\pi\cdot \frac{d_P^2}{2}\cdot\rho}$$
Your P is at most 11.1 V × 4.5 A = 49.95 W. Your prop efficiency $\eta_{Prop}$ must be guessed; let's take 60%. The electric efficiency should be higher; let's use 95% for now. The prop diameter $d_P$ is 3 or 5 inches (depends if your comments or the picture in your question is more reliable), so I use 0.127 m for now. Air density is given with 1.18 kg/m³.

When I plug in the numbers, I get 2.894 N. One propeller can lift approximately 295 g of quadcopter, and all four will produce thrust equivalent to the weight of 1.18 kg in Earth's gravitation. Looks about right for a quadcopter of 500 g.

Don't assume that the motor delivers all the power the propeller can absorb. Also, don't assume that the RPM of the isolated motor can be maintained when it is driving a propeller.


What does the pressure distribution over a glider's wing look like?

The pressure distribution over a glider's wing is no different from that of a well-designed aircraft. A glider can maintain flight by flying slightly downwards, so the direction of motion is not straight but slightly down. Doing this in rising air will result in sustained flight.

Look at the sketch above: The flight path angle $\gamma$ is negative and in still air the flight path vector $\text{x}_k$ is parallel to the direction of the airspeed. Due to the inclination of the flight path, the lift vector is tilted forward such that its horizontal component is exactly opposite to the drag force. This is shown on the right where I moved the vectors into a closed sequence which demonstrates that all forces balance.

From the viewpoint of the glider, the lift is pointing straight up and drag directly backwards, but the weight force is slightly tilted forward. In a way, it seems that the thrust of a glider is its weight force.

Now let the whole air packet in which the glider flies move up. The glider will still sink down within this air but relative to the ground it will gain altitude if the upward air velocity is high enough.


What would happen if one of the engines failed during takeoff and other engine is on full power?

No, no, by all means don't turn left. See also Why should you not turn in the direction of an inoperative engine?.

Transport category aircraft are capable of climbing out on one engine. It is a certification requirement for them. So if the left engine failed after rotation, the first thing the pilot has to concentrate on is to keep the plane flying and under control. That means ease the pull on the stick a bit to avoid stalling as the plane is not able to climb as fast and push the right rudder pedal to keep the plane flying straight¹.

Once the plane is in straight climb at $V_2$ speed, it's time to deal with the engine. First both pilots cross-check the instruments and the rudder position to determine it was the left engine that failed. Then they feather the propeller (auto-feather might have done it already) and cut fuel to the failed engine. If the engine fire warning is on and did not extinguish when fuel was cut, they discharge fire extinguisher.

These things are done according to standard emergency procedure that the pilots have to remember and train in simulator. I don't know the specifics for ATR-72, but in all aircraft it is roughly like above.

Meanwhile the aircraft climbs to safe altitude and then they should level off and let it accelerate a bit to get some safety margin for manoeuvring.

The plane is now in relatively safe condition. Even if engine was on fire, it is unlikely to spread while the aircraft is flying. So the pilots now have time to declare emergency and ask the controller for what options they have for landing. Whether they do a complete circuit and land back on the same runway or turn around and land in opposite direction or land on some other runway then depends on wind and where they are relative to the runways at the time.

There were many accidents where plane crashed after one engine failure during take-off because pilots started manoeuvring before they attained sufficient altitude and safe speed. It is better not to hurry, engine failure does not require it.

¹ Of course provided there are no obstacles in the way. For example if you were taking off from VQPR runway 33 and your right engine quit, you'd still have to do a right turn rather early to avoid the Mr. Smith's house right in the axis of the runway and quite a bit above it. But for any airport that require such avoidance (and there is quite a few of them in various mountains), the pilots are specifically briefed and trained for that airport which includes instructions on how to best handle engine failure during take-off and during approach and viability of the procedure is verified in simulator and with a test flight. The above answer just outlines the generic procedure.


Why aren’t diesel piston engines used on aircraft like the Saab 340 or L-410?

There are many reasons but Ill address your points directly first

  Engine itself is significantly cheaper

This is only true for non aviation engines. Even if you were to obtain a type certification for an automotive engine the cost of that would reflect a huge increase in price. This has been tried before and proved so costly the engine maker ended up dropping the FAA type cert due to costs.

  Cheaper to maintain

Again this is only true for auto or industrial application engines. Any part carrying approval down to the spark plugs has a large price mark up over their non aviation counterpart (even if the parts are more or less identical). On the whole piston engines tend to also have a shorter TBO than turboshaft engines.

  Likely they are heavier and more bulkier than turbine of similar power
  output

This is perhaps one of the most important cons. In aviation weight is the name of the game. Airlines make money not only on passengers but the carriage of freight in empty baggage space cutting into that cuts into profits.

Piston engines once did rule the skies in that size class, the venerable DC-3 is about as big as what you mention and has long since been phased out of routine use.

For the altitude space in the FL200-FL250 range you also need pressurization which is much harder to drive from a piston engine. A turbine allows you to pull bleed air for pressurization while a piston engine requires a whole separate unit driven by the engine somehow. This adds complexity and again, weight. Over the years there have been some pressurized piston planes but they have fallen out of popularity and use.


My answer is limited to commercial type aircraft (e.g., B737/757/767, etc.).  There is variance between aircraft types.

  Question: when they are filling fuel, do they connect hoses to each tank individually or just connect to one tank? Or is it per side - fill up each side individually.

For most large commercial aircraft (e.g., B757, B767 etc.) single-point fueling is done from one location underneath one of the wings.  This single-point fueling system allows fuel to be
loaded to all tanks, e.g., Left/Right Main wing tanks and the Center tank (if necessary) from a single location.  The switches on the single-point refueling panel operate pumps
and cross-feed valves to allow all tanks to be fueled from this single location.

  Question: Also suge/vent tank at the tail end of a380 seems to too high. Do they fill in those tanks too?

A "surge" tank (or similar notation) is normally dry but is designed to hold fuel that passes through the main fuel vents (due to expansion or overfilling) in the normal tanks so that the fuel does not spill out (on the ground) and cause a fuel spill.  This fuel ultimately works its way back to the normal tanks through gravity.

  Question: After fuel calculations are done, is there a standard fuel distribution that has to be done to every tank for weight/balance reasons?

Generally speaking Yes.  The location of the fuel tanks in an aircraft is designed (again, generally speaking) to be near the center of gravity (CG) for the aircraft.  So, as fuel is burned during the flight the aircraft does not find itself outside of the appropriate weight/balance envelope. However, calculations are done to ensure this and verify that the fuel loading at the beginning of the flight results in the CG being within limits and that the CG is within limits at the end of the flight after the anticipated amount of fuel is burned.  Generally speaking (again), the aircraft is designed to stay within limits for most types of operations considering possible fuel, cargo, and passenger loads that may be encountered during normal operations.

FYI - If the single-point fueling system is inoperative for some reason over-wing fuel points allow for manual filling of the main tanks.  Also, should the Fuel Quantity Indicating System (FQIS) system fail and
the total amount of fuel in the tanks cannot be determined, fuel quantity can be measured using measuring sticks (with a reference chart available to determine (manually) how much
fuel is in each tank.

Below from ABXtranet.com is a picture of the fueling procedures for a B767 and a picture of the Fuel Control Panel (B767 Single Point Refueling):

Here is the link to ABXAir's B767 Fueling Procedures Manual:
refuel procedures ABXAir


In turboprops, is there a mechanism to prevent the blades running in opposite direction?

Most manufacturers realise this is a serious risk so most are 'gated' in that you have to do something to get them into this range. This is like pulling up the reverse tabs on the throttle levers on the B737 or A320 that is only possible when they are in the idle position.

ATR 42/75: Has something called Idle Gate that prevents throttles from going back too far when engaged.
Dash 8: Has gated throttles that requires pulling up a pin to get them into reverse.

There is to the best of my knowledge nothing (in general at least) to stop to the thrust from being 'reversed', or more specifically to angle to blades to what is known as the 'beta' range, if you are intent on doing it. Unlike jets where doors open for instance and the process is a little more complex, this is just rotating the blade below a certain angle.

I found the accident report [PDF] for the Manx2 flight. There were multiple things going on here rather than a single cause:

Generally bad piloting for putting them in a late go-around situation to start with.
There were errors in the engine, causing a thrust mismatch.

This meant that one engine proceeded to continue into negative thrust.

It does then not come as a complete surprise that you manage to flip the plane over from considerable unsymmetric thrust when you are close to stall speed.


What is this component in an Airbus cockpit?

Since Airbus planes use a sidestick instead of the traditional center yoke, they use the space where the yoke would be to include a fold out table instead. You can see a laptop on one here. The A380 version also has a keyboard. This is used to interface with the onboard systems and input information.


What should a pilot do if he does not know where he is and has no form of communication?

The first thing you should do during a lost com's situation is fly the plane (that is really the first thing you should always do).

The second thing you should do is use visual reference points to figure out where you may be and get some situational awareness. Even in a foreign land a pilot may be able to identify known land marks like city skylines or prominent geological features. Even something like a coast line can be identifying. If the pilot becomes concerned about fuel (which any good pilot will at some point) then they should be on the look out for an airfield or a nice area to put the aircraft down.

The third order of business is to squawk 7600 on your transponder. This will alert any ATC facilities pinging you on radar, that you are unable to transmit and/or hear them.

This falls in line with the FAA's general advice of "Aviate, Navigate, Communicate".

Just a bit of an applicable side note: In the US under the FAA, and in other jurisdictions there are lots of areas that full under "uncontrolled" airspace where no radio or charts are required to be onboard anyway and many pilots are proficient flying in such a situation. Id even go so far as to say that a solid chunk of Piper Cubs are still flown this way.


Is it technically feasible to make a solar hang glider?

I think you've got your terminology crossed here (but it's not your fault - your sources don't seem to clear on it either).

A hang glider is by definition a solar vehicle: They're non-motorized, and the pilot keeps them aloft by seeking thermal lift (created by the sun shining on the ground and heating it up) or ridge lift (created by wind striking the side of a mountain/hill (ridge) and being deflected up.
Both of these rely on the sun (either directly heating the local ground, or unevenly heating various parts of the Earth's surface, ultimately creating wind).

What you're referring to would be a solar-powered ultralight aircraft -- basically a hang glider with a motor strapped to it, or possibly an electric powered paraglider.

One could conceivably create a solar-powered ultralight using flexible solar cells on the wing  - in fact a little Googling reveals that it has apparently been done with an electric paramotor (a type of powered parachute) (A little more Googling reveals this wasn't as cool as I previously thought - they seem to have been using a support vehicle to recharge their battery packs (with solar cells).

As far as I'm aware no such vehicle is commercially available at this time (May 2014), but the materials and technology to construct such a vehicle are certainly available (the folks over at the Experimental Aircraft Association could probably provide guidance on building something like this), and it wouldn't surprise me if commercial or kit-build solar ultralights become available at some point in the future.


Does the compressor stationary vane have stagger angle?

The stationary compressors are responsible for guide the air particles flow to the next compressor or stage with an even air flow on the engine's longitudinal axis, taking under consideration angle adjustments in order to avoid air turbulence with may cause a compressor stall.

So, depending of the engine project, the answer is yes. The angle can variate, being static or even with self-adjustment.


How does the F-22 Raptor radar reflector work?

The F-22 RCS enhancers size and shape (to some extent), as well as this source for example, suggest it is a Luneburg lens. The Luneburg lens is a device that reflects electromagnetic waves very efficiently back to the source, making it possible for a small device to appear as a big target on a receiver placed at same position as the transmitter (for example a radar).
According to  Wikipedia:

Luneburg lenses are normally layered structures of discrete concentric shells, each of a different refractive index. These shells form a stepped refractive index profile that differs slightly from Luneburg's solution. This kind of lens is usually employed for microwave frequencies, especially to construct efficient microwave antennas and radar calibration standards.

This site further elaborates on the Luneburg lens:

The Luneberg lens is a passive radar augmentation device used to increase the radar reflectivity of a target without the use of additional energy The lens reflector is a sphere in shape, usually composed of concentric dielectric shells. By the proper selection of dielectric constants for each shell, radar energy incident on one of the faces of the lens is focused at a point on the rear surface of the lens. The rear conductive surface reflects radar energy back to the source.
Principal of Operation:
(1) Basically the Luneberg lens is made of concentric shell of polystyrene with varying reflective indices (dielectric constants) from 1 to 2, the highest refractive index being the innermost shell.
(2) A ray passing through the various concentric shell will bend towards normal and then focus at a point. If a metal reflector is placed around the focal point, the ray gets reflected and retraces the same path. This is the principal of Luneberg Lenses
(3) In order to have smooth bending of the ray theoretically, many concentric shells are required. In practice, a few concentric shell are used.
(4)The radar cross section augmentation of the lens is given by the formula( 4∏3R4/4λ )
The RCS is inversely proportional to the squire of the wave length and directly proportional to the 4th power of the radius."

[sic]  Note: the correct spelling is Luneburg, after Rudolph Lüneburg
To act as a Luneburg lens, the device cannot be empty. To properly "bend" the incoming and outgoing waves, the sphere must hold some kind of inner refractive structure to make it function properly as a radar reflector over meaningful distances. A single concave spherical layer of reflective material will not achieve this.
It should be noted that the RCS enhancer on F-22 is not spherical in form, but a cylinder with rounded ends. The principle of Luneburg lens could still be applied to the device. And as always, having the inter of net as source, it is totally possible the aforementioned device operates on a different principle. Operating principles of many of the systems on F-22 are not exactly public for obvious reasons... Please feel free to overthrow this answer if better knowledge is available.


A good place to start is the biplane flying wing with endplates that box it in, so that it is both a flying wing and a box wing. The Dunne D.5 of 1910 was the first certified stable airplane ever to fly. It was a swept design, with pronounced wash-out towards the tips, effectively putting the tail at the end of the wing. But its ancestor the D.1 glider had proved stable without any endplates. Although they did improve the stability of the D.5 and D.8, their main function was to reduce tip losses. They even lacked a rudder; the planes turned OK using the ailerons alone but could not land in a crosswind.

By comparison the box wing just flips the lower wing backwards, so it acts as the horizontal stabilizer and there is no need for washout. But it also loses directional stability so a tail fin or similar is necessary. For this reason many box designs, such as the Sunny, sweep it less than the front, so that the swept fore wing and endplates are enough to stabilize it.

The monoplane swept flying wing typically has no endplates. Dunne achieved the same effect by sharply drooping the wing tips. But in most designs, the washout reduces lift at the tips enough to limit tip losses.

Sweep is not strictly necessary. If you use an airfoil with reflex camber, tilted up at the trailing edge such that it has a stationary centre of pressure as AoA changes, it will be inherently stable and no other tricks are needed. But it will be very sensitive in pitch and the controls will not be well balanced. Also, it will be unstable or minimally stable in yaw unless you play tricks similar to Dunne's, such as adding endplates and toeing them in to create differential drag.


Could there ever be a fully solar powered airliner capable of transatlantic flights?

Short answer: No

Long answer: No. Look at the solar impulse project, this is some of the best solar-electric technology that's out there, and it's barely able to carry one person, very very slowly. If you took an airliner, covered it in the best solar cells available and connected it to the best electric engines available it probably wouldn't even be able to taxi.

Some science here: The maximum energy density of the sun on the Earth is about 1300 watts/meters squared. About 30% is lost in the atmosphere so the best you'll get on the surface of the earth is about 900 W/m2. The 737, for example, has 102 square meters of wing area, that would equate to about 90000 watts (90KW) of sun energy hitting the wing. The best power conversion we have of solar to electricity we have is about 10%, so you would get at most 9KW of power from a 737 solar array. As we see from this answer it takes 90 MW (megawatts) of power to get a 747 into the air, assuming it takes about 1/3 or that (30MW or 30000KW) to get a 737 into the air, then that array will only generate 0.3% of the electricity needed, and that's the best possible case in the strongest sun. If it's cloudy or at night you are completely out of luck.

Any solution based on current battery technology is addressed here, and it's very much a no at this point.

Theoretically it is not possible that a solar powered passenger airplane could be as good as a jet-a1 powered passenger jet, this is because the energy from the sun is not sufficient even if you had 100% conversion to electricity. If battery technology were to become orders of magnitude better to the point its energy density compared to liquid fuels then it very well could, this is a long way off, the best batteries that are currently lab concepts are about 1/5 of the density of liquid fuel. Once batteries get there then solar power could charge them for the flight. It's actually just as possible that solar power could be used to make liquid fuel in a renewable way from CO2 and other elements in the environment. Bio-fuels are solar powered, but we can't make much of a dent in fuel use with them without taking food off of people's plates, and personally I'd rather eat!


How many antennae are there on a typical small aircraft, and how are they connected to the avionics?

The VOR/Localizer/Glide Slope antenna is usually V-shaped and points backwards on the vertical stabilizer of the plane. On some aircraft, they point forward. They look like old-fashioned wire clothes hanger wire. Newer versions can be blade shaped.  sometimes they are boomerang shaped like the old car phone antennas of the 90s.) They usually have a splitter that allows two radios to use the same antenna. e.g. splitter

COM Antennas are usually a white rod or blade. You can’t split the signal for a COM radio using a rod antenna so one antenna is required for each radio. Not sure about blade antennas.

A GPS antenna is usually somewhat teardrop or ovoid shaped. Garmin GPS You can’t split the GPS signal, so one antenna per device is required. Some ADSB systems have an embedded WAAS chip and need their own GPS antenna.

GPS and COM antennas can be combined.

IFR capable airplanes also have a marker beacon antenna. These can be embedded in the fuselage or external.

A transponder is required in most airplanes and they have their own antenna. These are a small 2" or so stick with a ball on the end. They are mounted on the bottom of the fuselage.

Airplanes in the US at least are required to have an ELT. Old style ELTs and some of the newer ones have a piece of steel with a spring-like coil in them. Newer versions are more aerodynamic.

ADF antennas come in a wide variety of shapes. Some of the newer ones look like GPS antennas.

DME antennas usually look like a shark’s fin.

Composite aircraft often have the antenna embedded in the frame so it is not visible.

This Cessna video describes all of the antennas on a modern C182. I don’t have most of them on my airplanes and the ones I do have look a lot different.


How to identify different pipes / hoses on aircraft engines?

You can guess what most of the tubing goes to if you know a few of the parts under the cowl and have a general understanding of how engines work. You can also get a good idea of what each part is by studying the parts catalog for the aircraft. You can view the Parts Manual for my Cherokee and an Arrow that I fly.

Piper Arrow Six Cylinder Continental

Let’s start with easy ones to identify. You should be able to find the tailpipe rather easily.  Notice in the picture of the Arrow that there are a lot of big orange tubes. That’s called scat tubing and it is used to move air around the engine compartment. In most singles, there is a shroud around the muffler that has orange hoses coming out of it. The ones going into the firewall provide cabin heat and defrost. The ones going to the carburetor provide carb heat to prevent icing.

Notice the rusty pipes coming out of the bottom of the engine. Those are the exhaust pipes and it’s hard to see in this picture, but they connect to the muffler. The big black pipe at the top of the engine is connected to the air filter and is the air intake. The clean pipes along the top of the engine are the air intake tubes. Most fuel-injected engines have the air intakes on the top of the engine.

Fuel injected engines also have small lines that put fuel directly into each cylinder. The line entering the "spider" at the top is a fuel line and you can trace it back to the fuel pump.

The brown hose in the picture below going to the spider is a fuel line.

Cherokee Lycoming Four Cylinder Engine

Compare this to the carbureted engine in the Cherokee. The more rusty pipes are the exhaust and the cleaner blueish pipes come from the carburetor with air and fuel.

If you can find the vacuum pump (the dark item to the right of the oil filter with the red bands) you can identify the hose going to the attitude indicator and heading indicator. There’s usually a filter attached to the hoses and a line leading to the vacuum gauge—although sometimes that is inside the cabin. The big open-ended hose is the exhaust for the pump.

Here’s another four cylinder where you can see the intake and exhaust. Notice the silver lines with the blue fitting. Those are primer lines. At the bottom left is an oil cooler. There is scat tubing bringing air to the cooler and two lines going in and out.

Oil coolers are often in the front of the cowl like this one. If there are lines attached to something that looks like this, they are oil lines.

This is a different method of plumbing carb heat. Rather than coming off the muffler hot air comes directly from the engine.

Here’s a picture with lots of hoses.

The two small hoses at the bottom of the picture are attached to the oil cooler. If you follow them back you’ll find the oil pump.

You can see the carburetor with a scat tube coming from the air filter and one on the back side coming from the muffler shroud. The two small hoses going into the carb are fuel lines.

The vertical silver tube running from the top of the picture, down past the muffler, and out the bottom is the crankcase breather line.

The box in the bottom right-hand corner has the electric fuel pump (boost pump). The line coming out of it is a fuel line. The silver tube in the box goes to the gascolator.

You should also see an oil line going through the firewall that measures oil pressure and one for fuel pressure but I don’t have pictures that show them.


Why not make the touchdown zone of runways wider than the rest?

Because most runways already are as narrow as safely feasible.

Let us look at your question piece by piece:

  Save money by making the rest of the runway narrower

You seem to be assuming we are currently deliberately wasting asphalt on making runways wider than needed, and could build them narrower. As they say on Wikipedia: [citation needed].

  Larger margin of error left and right

The touchdown zone is the whole runway, as long as the aircraft in question can stop afterwards, so if you start down this alley you'll find it cheaper to complete the runway in the same width.

  Easier to turn around, if necessary

This is already done by including turn pads, on top of the nominal width. For an example, see: OGZ


How much does a typical private pilot pay for a non-training flight?

It depends on your location. It will vary based on cost for tie-down or hangar space, fuel costs, maintenance costs, etc. In order to compare apples to apples, let’s  boil it down to a wet-Hobbs-rate.

Wet-Hobbs-Rate is an all-in rate (minus tax) for the use of the aircraft to include everything except away-airport landing fees where applicable. That includes fuel, oil, home-airport landing fees, etc. Wet-Hobbs-Rate is charged on the time that the engine is actually running. Although some Hobbs timers run off of the time that the electrical system is on, most run off the oil pressure sensor of the engine.

Here are some real world examples of the Hobbs Rate costs of rental aircraft in my area.

Cessna 172S with G1000 and autopilot - $175/hr wet-Hobbs.
SportCruiser with Dynon and autopilot - $125/hr wet-Hobbs.
Piper Apache - $250-300/hr wet-Hobbs.
Piper Cherokee - $145-155/hr wet-Hobbs.
Piper Comanche - $225/hr wet-Hobbs.
Cessna 150/152 - $100-125/hr wet-Hobbs.
Cessna 172E-N - $125-175/hr wet-Hobbs.
Robinson R22 - $250-300/hr wet-Hobbs.
Beechcraft Duchess - $250-500/hr wet-Hobbs.
Piper Aztec - $400-600/hr wet-Hobbs.

Wet-Tach-Rate is another way to measure aircraft cost. Wet-Tach-Rate is similar to wet-Hobbs-rate. Except that wet-tach-rate is more like an odometer that calculates time by the amount of engine revolutions. The less RPMs at which you run the engine, the slower the clock moves. More RPMs mean more time calculated. Typically, this means that you can cut your costs down significantly. Your calculated time can be around 75% of your actual time running the engine or less with good engine management.

Most of the flying clubs in my area use Tach Rate as the basis of their costs. In order to rent aircraft from them, you have to be a member of the club. Membership ranges from 30 to 100 dollars a month.

Here are some real world examples of the Tach Rate costs of rental aircraft in my area.

Cessna 150/152 - $50-100/hr wet-tach.
Piper Archer - $75-$150/hr wet-tach.
Piper Cherokee - $50-150/hr wet-tach.
Piper Arrow - $125-150/hr wet-tach.
Cessna 172 - $50-150/hr wet-tach.
Cessna 182 - $75-175/hr wet-tach.
Piper Cherokee Six - $75-150/hr wet-tach.
Beechcraft Bonanza - $150-250/hr wet-tach.

One thing to consider when deciding to join a club or not is their overnight policies. Most rental airplanes are run several hours a day, every day. They do not want to have their airplanes sitting on the ground. During slow season you can rent overnight as long as you pay for a minimum number of hours Hobbs-time each day usually starting at three hours each day.

Most clubs have enough downtime for their aircraft that they will allow you to have the their airplanes for multiple days. Their per day hourly minimum can be as low as one or two hours per day. If you time it right, you can be the last person to sign the plane out after hours on day one. Fly the plane the club’s minimum number of hours the next day. Then sign the plane in the following day before working hours. That would conceivably be 40 hours of use with only a one day minimum to meet.

Something else to consider is that you will have to factor in a minimum of 30 minutes of non-flying time each flight for which you will have to pay. That will be engine or electrical time doing tasks like:

Starting your engine
Getting your ATIS and clearance
Taxiing to the runway of use
Run-up of the engine
Taxiing back to the hangar after landing
Shutting down the engine

You will pay less in Tach-time than you will in Hobbs-time because the engine RPMs will be averaging a much slower rate.

As an aircraft owner, your variable hourly operating costs could be similar to the lower end of the club rates. This would include your fuel, oil, maintenance and other costs. In addition to that, You would have fixed costs for the aircraft of:

Hangar space ($200+/month);
Or Tie-downs ($50-100/month);
Inspections ($1000-2000/year);
Major Overhauls ($10k-$20k at any time)

Lastly, insurance for a renter can be anywhere between 100 and 500 dollars a year depending on coverage. And, more for helicopters. Electronic Flight Bag subscriptions range from 100 to 500 dollars a year. You will need at least two hours of flight instruction every two years to meet flight currency requirements. And, you will need an FAA AME flight physical (time varies by age and privileges desired) unless you want to fly under Basic Med Class III reform or Light Sport Aircraft only. A Medical Certificate will cost around 100 dollars.

You can cut costs dramatically by flying gliders and ultralights. The glider club in my area has a 30 dollar per month membership with its lowest cost glider renting for 10 dollars an hour. You will have to research Ultralight costs yourself.


How can you calculate the gliding distance for a remote controlled jet?

I think the only way is to test it.

Choose a day with very calm wind.

Set the plane up for fixed speed anywhere between obviously-lower-than-best-glide-speed and obviously-higher-than-best-glide-speed, and make multiple tests with incrementing the speed in small steps (like 5kt). You can probably think out the details of the experiment yourself, but this should work well.

It's very difficult to compute these things. Companies like Airbus or Boeing have (probably proprietary) software for this, large clusters, etc., perform test in an aerodynamic tunnel and do many test flights. Since you likely don't have all the equipment, the only thing you can rely on is the test flight.


What are the advantages and disadvantages of the MiG-29's horizontal stabilizers (not what do they do)?

There is nothing too special about the MiG-29 stabilator.
The "slanted" (swept) axis of rotation is fairly common: as far as I remember, all MiGs that had a stabilator had this arrangement.
This has primarily structural advantages: it is easier to integrate the shaft (or axle) along the structural elements of the stabiliser, making it lighter. Also, the hinge moments are more consistent along the shaft. (For the straight shaft on a swept stabiliser, there will invariably be twisting forces that must be absorbed by the structure. Say, the root section may experience positive moment with respect to the shaft while the end section may have negative moment).
Also, as Charles already noted, a swept axis may allow to move the stabilator a bit further back (while keeping the same overall hinge moment), increasing its lever arm and thus efficiency. This is because the attachment point at the root can be closer to the leading edge. But this is only a gain when the actuator cannot be moved further back for some design reasons (like on MiG-29).
On the other hand, the leading edge may interfere with the fuselage when deflected, necessitating a "stump" at the root (which you can also see on most jet MiGs). At the same time, you need larger deflection in order to achieve the same aerodynamic effect (see also this answer).
The perception that the shaft is too close to the leading edge is a bit of an illusion. In fact, it is just a bit forward of the 1/4-chord line: exactly where it should be, as can be seen in these diagrams.


Why do some airfields not have manned ATC towers?

One of the biggest reasons to not man a tower is (not unsurprisingly) costs.

Many remote airports only have a few movements per day, and a permanent staff in the tower makes it even more difficult keep the operation economically viable.

For this reason, remotely staffed towers are being developed now, and for instance Örnsköldsvik airport (ESNO) in Sweden has just received approval from the Swedish Transport Agency to operate with a remote tower:

  The system’s sensors are installed at Ornskoldsvik Airport but traffic
  is remotely controlled from Sundsvall, Sweden.


Can this aircraft wreckage be identified?

A plane should be able to be identified by the serial numbers of the various parts recovered at the crash scene.  The history of any part on a plane is documented extensively by the serial number.  The NTSB should be able to track down when the part was produced and who the part was delivered to.   As Tanner mentioned the NTSB should be contacted immediately and the wreckage should not be moved.  There are many plane crashes that have occurred many years in the past which have still not been found. You may have stumbled on a piece of history that could bring closure to a family who may have never known what happened to their loved one.


What happens if Solar Impulse II encounters un-expected head wind and runs out of battery power?

Solar Impulse has two means to store energy: Batteries and altitude. Weather permitting, both will be fully charged at sunset, and mostly depleted over the night. The rate of depletion at sunrise depends only on the time between sunset and sunrise, not on the direction and strength of the wind.

Headwind only means that less ground is covered. Solar Impulse is optimized to fly at a certain speed and will not fly much faster or slower, regardless of wind. If the wind is strong enough, it will simply not cover any ground but be blown back. But the wind will not cause the batteries to be depleted earlier, and the next day they will be recharged if the sky is clear.

Wind speed and direction vary with altitude, so the aircraft might well overcome a wind that had prevented it to make any progress the night before by flying at a different altitude the next day. After all, flight duration is limited by the pilot, not the power source.


Does a standalone EASA Multi-Engine Instrument Rating exist?

This was just published in CAP1855 from the CAA a few days ago, which may answer your question:

Instrument Rating validity, revalidation and renewal for aeroplanes and helicopters
To revalidate, you must hold a valid relevant class or type rating, unless the IR revalidation is combined with the renewal of the relevant class or type rating; no “empty” IR to be endorsed
The UK CAA has deferred this requirement until 10 January 2020 as stated in ORS4 N.1329.
References: Subpart G, FCL.625, FCL.625(A), FCL.625(H))


Why are airport firetrucks painted yellow green?

Because yellow/green has been shown to be more visible than red, especially in low light conditions.  Yellow/green is also more easily identified by people with colour blindness and other visual disorders.

It's the same reason that safety vests are yellow/green.

This article gives some good references.


Can anyone identify what/where this photo is of?

This could be a Sopwith Camel without its guns.  At least these details don't disagree:

cowling's shape and front opening
9-cylinder radial engine (tappett rods lost when crushed by the cowling)
8-bolt prop hub
wicker seat's weave spacing (many photos if you search "sopwith camel seat")
fuel tank's position and shape match that in the Haynes Manual
location of the remnants of the cabane struts.

Although some of these details are common to many aircraft of the period, it's noteworthy that this many details agree in one place.  A statistical argument may be the best one can do with what's been given.


What is the physical meaning of Mean Aerodynamic Chord?

The mean aerodynamic chord is only identical to the mean chord for rectangular wings. For tapered wings it is slightly longer.

Why? Because the mean aerodynamic chord is the mean chord of a rectangular wing that has the same pitch characteristics as the "real" wing. Pitch characteristics need to include pitch damping, and pitch damping grows with the square of the local chord. That is why the formula for the mean aerodynamic chord divides the square of the local chord by the wing area:
$$\text{MAC} = \int_{y=-\frac{b}{2}}^{y=\frac{b}{2}}{\frac{c^2}{S}}dy$$
Here $b$ denotes wing span, $y$ the spanwise coordinate and $S$ the wing area. Since the chord is squared, deeper sections of the wing are overrepresented in the result. The resulting rectangular wing will have a larger area than the original, tapered wing but the same pitch damping! In case of a delta wing, MAC will grow to be ⅔ of the root chord, and for an elliptical wing it will be 90.5% of the root chord.

The MAC has been invented to convert arbitrary wing planforms into much easier to calculate rectangular wings. By doing all calculations on the correctly sized rectangular version, the more complicated calculations on the real one could be avoided. However, this works only up to a point:

if you want to calculate lift, you need a wing of equal area.
if you want to calculate induced drag, you need a wing of equal span.
if you wand to calculate pitch motion, you need a wing of the correct MAC. This rectangular wing can either have the same area or the same span as the real wing, but not both together, unless the real wing is rectangular, too.

You are right, the two definitions you quote are not compatible. The rectangular wing cannot have the same span than the real one, or its area and all associated forces and moments would be higher.


What is the difference between dry operating weight and dry operating mass?

Weight is a force.

Mass is a property of matter. Acceleration makes mass produce a force. Specifically, a mass in the gravitational field of Earth effects a weight force on its support. The relation between both is the gravitational acceleration g, which is standardized to 9.80665 m/s² (approximately 32.174 ft/s²), as in Weight = Mass · g.


Does a secondary surveillance radar need the support of a primary surveillance radar?

SSR can work independently and this is quite common as well. Primary radars cost a lot to maintain, and as more and more planes are equipped with transponders, primary radars are being shut down. Many areas now have secondary radar coverage but no primary radar coverage.

SSR only relies on replies sent as a response to its own interrogations. This works well in theory, but becomes a problem in practise in areas where many SSR units transmit on the same frequency resulting in many overlapping replies. This results in FRUIT and garbling.

For areas where both primary and secondary radar data is used, the data is combined to create individual radar plots that are shown to the controller. The controller typically does not have to worry about the exact source of data, and will not worry about switching on or off individual sources (at least not during normal operations). Modern ATC units receive radar data from many different sources, including both SSR and PSR stations, and process and combine this data to a single representation. This happens by using technology such as ARTAS. On the controller radar screen, aircraft plots will look different depending on their data sources. For example, a PSR-only target may be shown as a circle, an SSR-only target as a diamond and a SSR+PSR target as a square. The exact specifications vary from system to system.


Jettison and Dump fuel - Do they have separate meanings?

In the context of fuel, jettisoning fuel would imply that the fuel is in a container that can be detached while in flight. In the linked image, the large tank below the main body is an external fuel pod that can be jettisoned. Jet with external fuel tank I believe in WWII that P51s would have drop tanks for escorts that would be jettisoned once an enemy encounter was expected.

Dumping fuel would simply mean that there is a type of valve located on the fuel tanks that can be actuated in some way such that the fuel can freely exit. Jetliner dumping fuel

To say differently, if one was holding water in a bucket, pouring the water on the ground would be 'dumping fuel' and simply dropping the bucket would be 'jettisoning fuel'

Reviewing the wikipedia article on Fuel Dumping, the author(s) make no such distinction between dumping vs jettisoning and seem to use jettison solely.

In the context of ATP, after reading the wikipedia article on fuel dumping, I believe that they are considered synonyms. I believe a non-pilot would go more along with my definition however.

I answered in this manner as I believe that the OP is not a native English speaker and that clarification was needed as to distinguishing the two as they seem very similar. I am a native English speaker, but lay no claim to being a master of it.


Why aren't Rogallo wings or parafoils used in aircraft with fuselages?

Larger aircraft: Metallic wings

How much fuel could you store in the Rogallo wings if you need some?

Source

The wings provide lift, but not only. In large aircraft they usually receive thrust from the engines, in order to transfer it to the fuselage, they are also fitted with hyper-sustentation devices and aerobrakes. And finally they can transmit a good part of the aircraft weight to the outer landing gears when the aircraft is on the ground.

Source

The latter functions are not compatible with a flexible structure. Only metallic or composite wings are used. They can be adjusted for an accurate envelope with optimized performances.

Smaller aircraft: Wood and canvas or metallic wings

The structure can be stiffened, this is commonly done, and leads to the concept of wood and canvas, as the DR-400 and many other GA training aircraft (all first aircraft were built this way):

Source

However these airframes don't scale well, and are not compatible with fast GA aircraft, leaving alone airliners speed range. Larger and faster aircraft, which anyway must protect their wing tanks, use metallic wings.

Ultralights and paragliders: Only categories with Rogallo wings

The advantages provided by flexible wings (easy storage, light weight, low cost) is a significant choice criteria for use in ultralights and paragliders, and of course for parachutes. These advantages overcome their limited aerodynamic performances, which is of lesser consideration for vehicles that are not specially aerodynamically designed.

Source

To summarize: The flexible wings are more appropriate for smaller and slower aircraft, in particular those not requiring wing tanks, wing control surfaces, or wing landing gears. Namely ultralights.


Why was the Boeing 377 "Stratocruiser" frequently landed nosewheel first on touchdown?

Apparently, the nose first landing was necessitated by the aircraft's tendency to enter into a stall if the nose was brought up too far up. According to one of its pilots:

No amount of heaving back on the pole would induce the mainwheels to make contact first. Various explanations were offered for this peculiarity... Others pinned the blame on the pernicious lift-spoilers.
Why build a splendid wing and then fit lift spoilers? The story was that the Civil Aeronautics Administration (CAA: the FAA-to-be) would not give the type its Certificate of Airworthiness because a wing was apt to drop when the aircraft stalled. The CAA wanted the nose to drop first, and the only swift remedy was to destroy an area of lift near the fuselage.

A similar discussion can be found here. However, this seems to have changed later. From the same article:

Ironically, after BOAC had operated the type for about nine years it was decided that lift-spoilers were not necessary, and they were removed. I was then flying later types, but those who were still on Strats told me that it was then a much better-behaved aircraft.

Another thing that supports this theory is that the military version, the C-97 Stratofreighter seems to have landed normally, according to its pilot:

The control wheel is eased back at 90 mph to clear the nose wheel from the runway. The airplane will fly itself off at 100 to 120 mph depending on the load.

and

Normally the nose wheel is kept off the ground for the first thousand feet, but it can be dropped immediately for cross-wind landings.

So, this seems unique to the Stratocruiser (and its derivative, the Super Guppy). B-29s as far as I know, landed main wheels first.


Can Airbus A320 doors be opened mid-flight?

It's a plug door.  The door nestles behind an array of cleats and a set of L shaped guide tracks and has to move up some distance, as you can see in the video, to clear the cleats and exit the L track.  When it's dropped into the locked position, it's not dependent on any moving parts to resist pressure because it settles behind the fixed cleats in the outer frame.  The cleats in the door bear on the ones in the frame to resist outward pressure and the door is opened by lifting it to mis-align the cleats so the door cleats clear the frame cleats. That makes it a plug door.
It looks like there are other levers and cams to assist with the door pull-in, and probably some form of locking pin(s) to block vertical movement when latched. If the door was, say, 36 inches wide by 80 inches high, at an 8 psi cabin pressure differential, there is about 23000 lbs pushing on it, so you won't be moving it unless you are The Hulk.
The CRJ Regional Jet main pax doors are an example of non-plug doors that just pull in flush on a simple hinge at the bottom, and latching shear pins extend into holes in the door frame.  This door is dependent on the shear strength of the movable pins, and the shear loads when pressurized pretty much weld the pins in place.


How is that there is no leak through the fuel vents during aerobatics maneuvers?

There are 3 common solutions,

1) do nothing, unless the airplane is flown for an extended period of time inverted, there will be no appreciable vacuum created from fuel use and the vent is so small that there will not be appreciable fuel loss.

2) point the vent into the slipstream giving a ram air effect.

3) use two vent tubes (can be mounted either top & bottom or same side), at least one extends to opposite side of the tank.

This picture is for RC or drone aircraft but the same principle is used for full scale aircraft.


Why is it called a mushing glide?

The aircraft is not cleanly cutting through the air. It is "mushing" through the air at a high angle of attack creating lots of drag and a slow forward airspeed.

  In this glide, does the aircraft points its nose less (or more?) steeply?

The aircraft has its nose pointed up (less steeply) than a normal glide.

  How does it steepen the descent?

The low forward airspeed and high drag creates a high rate of sink relative to the forward motion. Low forward speed and relatively high sink rate means the descent will be very steep. A fully stalled condition would be an extreme example of a "mushing" glide.

  low AOA (pointing slightly above horizon) causes it.

pointing the nose slightly above the horizon is still a High Angle of Attack, not low AOA.


Why do intermeshing helicopters use asymmetric airfoils?

Helicopters in general use asymmetric aerofoils because they are not required to fly inverted or produce negative lift. Intermeshing helicopters are no different in this regard.

The exception would be aerobatic model helicopters, which use symmetrical aerofoils because they are designed for similar performance either way up.


A blind encoder is an altimeter that encodes pressure altitude and outputs it on a databus. They are "blind" in that they do not display data to the pilot. Most general aviation units use a parallel bus with Gillham encoding. More expensive units and air data computers use serial bus output, commonly ARINC 429.

Historically, the blind encoder existed to provide pressure altitude data to the transponder to enable Mode C reporting.

When it was proposed to use GPS as a primary means of navigation in the early 1990's, the FAA deemed that a means of ensuring the integrity of the signal was essential. The longer term solution was to establish WAAS which provided both augmentation and an integrity channel. The short term solution was to have the receivers include an internal monitor, which took on the name RAIM for Receiver Autonomous Integrity Monitor.

RAIM algorithms have evolved several times over the years. Since early GPS receivers were often single or 3 channel receivers, the use of altitude as a substitute for an additional satellite was common. (Altitude is just another range in the rho-rho computation.)

Later GPS receivers moved to 6 and 12 channel receivers, thus enabling RAIM algorithms that don't need altitude data except in extreme cases.

So yes, the number of satellites needed for a RAIM calculation can be reduced by one when pressure altitude is available from a blind encoder.


Does ducting help to stabilise heavy lift drones?

There is too little information given to make a definite answer here, but things you should take into consideration are:

depending on the construction the bigger crosssection if keeping a similar rotorsize which will likely increase drag at higher windspeeds while on the other hand leading the airflow so with the right construction it might behave better then without ducting.
using at least 6 or better 8 rotors should enable you to increase lifting power and stability
putting the rotors in an angled position should increase stability while it might slightly reduce lifting power

additionally

the ducting will offer protection for the rotors/fans and people/things getting hit by the drone in case of a crash
as you want too operate it for such a long time the increase in weight which might increase the number of refuels/battery changes needed

Also we were talking about drones that produce the whole lift by rotors pushing air downwards. What about using a ballon or some kind of plane? This will make it more sensitive towards wind and sacrifice maneuverability but will allow extended flight time and potentially higher efficiency.


What is the diffference between landing lights, taxi lights and external lights?

There are basically two types of (exterior) lights in an aircraft- the navigational lights, which are required to be switched on from sunset until sunrise and other forms of exterior lights, which can be switched off at the pilot or operated only at some parts of the aircraft operation, like the landing/taxi lights.

A (non-exhaustive) list of aircraft lights:

Navigation lights All aircraft are equipped with a steady light near the leading edge of each wingtip. The starboard light is green while that on the port wing is red. The different colors make it possible for an outside observer, such as the pilot of another aircraft, to determine which direction the plane is flying. These are required to be on during operation (in night).
Navigation or Position lights In addition to the red and green lights, most large planes like airliners are also fitted with other steady white navigation lights in various locations like the trailing edges of each wingtip, horizontal tail and top of the vertical tail. The main purpose is to increase the visibility of aircraft from behind.
Anti-Collision Beacon lights These are are flashing (or strobe) light assemblies installed on the upper and lower fuselage of aircraft,used to improve visibility of the aircraft. These can be switched off at the discretion of the pilot under some conditions.
Strobe lights High-intensity strobe lights that flash a white-colored light are located on each wingtip. These flashing lights are very bright and intended to attract attention during flight. They are sometimes also used on the runway and during taxi to make the plane more conspicuous.
Logo lights These steady white lights on the surface of or at the tips of the horizontal stabilizer are used to illuminate the company's logo painted on the vertical tail. These are usually switched off in airports to improve the visibility of the aircraft.

1) Navigation lights 2) Aft light 3) Anti-collision strobe lights 4) Logo light
"Jet-liner's lights 1 N" by CC BY 3.0 via Commons.

Wing lights Many airliners feature lights along the root of the wing leading edge that can be used to illuminate the wing and engine pylons in flight. These lights may be used to make the plane more visible during takeoff and landing or to inspect the wings for damage in flight. Pilots can also use the wing lights to inspect the wings and slats for any ice accretion that might build up when flying through clouds.
Taxi lights A bright white lamp is located on the nose landing gear strut of most planes. This light is typically turned on whenever the aircraft is in motion on the ground for greater visibility during taxi, takeoff, and landing.
Landing lights Typically the brightest light in the aircraft, these are fitted on most planes (and helicopters) for enhanced visibility during the landing approach. These lights can also be used to illuminate the runway at poorly lit airports. They can be located in the wing root, in the outboard wing, or somewhere along the forward fuselage (the usual location incase of helicopters), with some aircraft having them in more than one location.

Boeing 787 Lights; Source: captalk.net

Runway Turnoff lights Usually located in the leading edge of the wing root, these bright white lamps are intended to provide side and forward lighting during taxi and when turning off the runway. These lights are most useful at poorly lit airports but are usually unnecessary. The lights can also be used in flight if greater visibility is required.
Wheel Well lights Some planes are equipped with additional lights in the nose and main gear wheel wells. These lights are provided primarily to assist ground personnel in making pre-flight inspections of a plane at night.

The image below shows the lights in a Boeing 737.

Image from staticflickr.com