Are there any aircraft powered by tip jets in the propeller blade?

There was a study done on the use of tipjets in civilian aircraft in the 1950's, if I can find the source I'll edit it into this answer. In any case, the conclusions from that study were as follows:

Because of the fundamental inefficiency of subsonic ramjet propulsion, a tipjet-powered propeller "engine" in the 100 to 150 horsepower-equivalent range was completely uncompetitive with piston power. The fuel flow rate required to run the tipjet prop was excessive.

The tipjet-prop plane had extremely limited range if carrying the same amount of fuel as the piston plane, and no useful load if it carried enough fuel to match the range of the piston plane.


What's for the "smoke fittings" in this muffler?

It is indeed so that you can generate smoke from the exhaust, typically for airshows. The general idea is that you introduce oil or specific liquids that have been created for specific colours to the hot muffler, which will create smoke. This is how skywriting works, the pilot can turn the system on and off, like lifting their pen from the paper.
If you're not using it, it does need to be plugged as otherwise exhaust (and sound!) will exit the hole rather than the correct exit at the end of the muffler. The "fuel tubing" mentioned in the manual is simply the same tubing used for fuel supply, as the diameter is suitable for it to slot over the nodule, and for the 8-32 screw to fill the inside diameter of the tubing completely, as the diagram indicates.


Can a pilot use ILS when cleared for a visual approach?

Yes, the localiser, ILS glideslope, and/or GPS-generated glidepath are still used as a reference during the visual approach. Sometimes the visual glideslope indicators (like VASI or PAPI) are either inoperative or not available. (Interestingly, the visual indicators and instrument-generated glidepaths are sometimes not coincident.)

Pilots sometimes choose to leave the autopilot engaged during such an approach. Some Charted Visual Flight Procedures (like the FMS Bridge Visual 28R at SFO) lend themselves to leaving the autopilot engaged for almost the entire approach. In addition, some operators may stipulate that autopilot use is mandatory.


Why did the first Boeing B17 test flight crash on takeoff?

The prototype aircraft had small "blocks" (more like wedges) which were used to prevent the control surfaces moving in the wind and potentially damaging the control surfaces, or even moving the aircraft on the ground. A bit like putting chocks under the wheels to stop the aircraft rolling.

These were not removed when the aircraft was taken on a test flight, so the control surfaces could not move. Essentially, they were "fixed" in an approximately neutral position. Imagine if you couldn't move your steering wheel in your car because someone had put wedges next to your front wheels to prevent them turning: that's basically the situation the pilots were dealing with, but unlike you they can't just hit the brakes and stop once the aircraft is in the air.

The Boeing 299 / B-17 are "taildragger" aircraft.

As you can see in this photograph which I won't link directly due to the size, the aircraft's nose is pointing quite sharply "up" when on the ground.

Here's a B-17, which isn't identical to the Type 299 but is close enough that it makes no difference. Hopefully this gives you the visual to see why the aircraft will lift off at a high enough speed.

When accelerating the nose being pointed slightly up gives a positive angle of attack for the wings. This means that once the aircraft gets above stall speed, it will naturally lift off into the air. Essentially, the aircraft is already pitched slightly up before any control surfaces are moved.

That also means that when the aircraft takes off, it will climb - at least initially. With the locked elevators, there is no way to change the pitch angle of the aircraft, and the aircraft will either pitch up or down naturally - there is almost no chance that the aircraft would be perfectly trimmed by accident.

In this case, the position the elevators were locked caused the aircraft to continue pitching up until it stalled. The crew had no way to correct this and the aircraft stalled out, rolled and crashed into the ground.


The diagonal struts are best to transfer shear. Imagine an upward pointing load at the nose. In order to get that load transferred to the fuselage, it first needs to be transferred to the wing spar. Imagine now that you hold the rib firmly in your right hand where the spar is and press the nose upward with your left hand. With parallel struts, the rib will have much less stiffness and the nose load will deform the rib easily. With the diagonal struts, the rib is much stiffer when that particular nose load is applied.


Why does stall speed decreases with increasing aspect ratio?

$c_{L_{max}}$ doesn't change with changing AR. Is it true?

No, it isn't. Since the area near the wingtips cannot produce a pressure difference as large as that on the center wing due to flow around the wingtips, the lift there is reduced. The larger the wingtip part is relative  to the whole wing, the lower the maximum lift will be.

Given the same wing area and mass, a wing with a higher aspect ratio will produce a lower stall speed. Of course, the assumption of an identical mass means that the lower aspect ratio wing has a poorer structural design.


As with any flight, "It's as safe as you make it".

The vast majority of the General Aviation fleet (piston singles) don't even have an autopilot, and the ones that do may only be single-axis units (wing levelers), so the pilot has to have some level of attention on flying the airplane.
If we assume these are the folks flying around VFR we can also generally assume they should be looking out the window the vast majority of the time (like Skip said, "Put down your iPads and do your job.")

Adding to that, "See and avoid" is every pilot's responsibility in VMC - whether operating under Visual Flight Rules or Instrument Flight Rules - if you can see, you are expected to avoid (and if necessary deal with ATC freaking out about you deviating from a clearance later).

A number of other steps have been taken to enhance safety in Class D and E airspace:

In the US FAR 91.159 prescribes specific VFR cruising altitudes, and FAR 91.179 is the IFR equivalent.
The cruising altitudes in these regulations result in an automatic 500-foot vertical separation of VFR and IFR traffic (at least between 3,000 feet MSL and 18,000 feet MSL - which is where VFR and IFR traffic are likely to be mixing in cruise. ).

Additionally IFR traffic is usually receiving radar separation services (there are some non-radar areas in the US, but not many). Nominally this separation is "IFR-to-IFR" in Class E airspace, but if a controller sees a VFR target squawking 1200 and behaving unpredictably they can vector IFR traffic around it.
Similarly if a controller sees a "primary target only" (something without a transponder, and not reporting altitude information) they will often vector IFR traffic around it until they can establish what it is and what it's doing.

Within class D airspace the level of service you'll get depends somewhat on the equipment the controllers have.  A "purely visual" tower with no radar can only give traffic advisories for aircraft they can see by looking out their window, but if they see a conflict they're going to say something. A tower with radar (either local or slaved from a nearby airport) may give VFR-to-VFR or VFR-to-IFR separation advisories based on that data as well, sometimes including advisories to aircraft inbound who are outside their airspace.


What's the use of so much torque on propellers?

Even small 1 hp electrical motors can achieve that RPM

Yes, but can it sustain that RPM when something tries to stop it, that is the question. 1 hp combustion engines can get to 2700 rpm as well, but you cannot attach a propeller to it, stick it in the air, and expect it to maintain the RPM. It takes a lot of torque to create aerodynamic thrust.

It is a fact that electric motors are way better at producing torque than combustion engines. An electric motor produces almost maximum torque at the get-go, with the rotor standing still. The combustion engine needs to make RPM in order to make torque. This article compares electric motors with combustion engines for powering a hydraulic pump: a 20 hp electric motor can do the job that a 50 hp combustion engine can do.

Electric motor:

Combustion engine: intermittent torque means torque pulse from combustion.

But wait, is that even possible? Power is power, kilowatt is kilowatt, and it should not matter which engine we use to generate the kilowatts, they should all equate to equal amounts says the first law of thermodynamics, the conservation of energy. But it does matter, since with a combustion engine torque is a function of RPM. So increase RPM, and power increases due to increased RPM and increased torque. At lower RPM the combustion engine may simply lack the torque to speed up, while the electric motor has an almost flat torque curve.

This same happens with outboard motors, when comparing 2-stroke with 4-stroke. 2-stroke has way more torque at lower revs, the 4-stroke may have the same horsepower but may never get to the high revs because it lacks the ability to get the boat planing.

But I digress. To get back to your questions:

  What's the use of so much torque, and what happens if there is less torque at the same RPM

To keep the output shaft at this RPM while the propeller is pushing all that air backwards. That requires a serious amount of torque. If there is less torque at the same RPM, there will be less thrust produced and the aeroplane won't fly as fast.

  Can an electric motor perform similar to the Lycoming IO-360 with the same max. RPM, but with just half the torque of the latter?

Well, the surprising thing is that a horsepower is not a horsepower. Part of the problem lies in the horsepower output functions, so maybe an electric motor with a lower hp rating can be used. But one thing is very clear: at the RPM of the propeller, a certain torque is required at a certain speed to keep the propeller turning. This amount of torque will always be the same, no matter what kind of engine produces it.


How are the Tupolev Tu-95's blades shaped?

The propellers were designed by OKB-120 headed by K.N. Zhdanov, type AV-60N.  This type was used on a few other aircraft, but unfortunately I can't find any further details about it.  Can somebody visit one and inspect it?


Can ailerons be used to control yaw and pitch

Depending on the geometry of the vehicle, up to a degree yes. However, with a classic aileron setup and no rudder, it might be impossible to control roll and yaw independently. A split flap (up and down on same wing) would be required to more effectively control yaw, as that can in theory generate drag on one side without much affecting lift. The B2 bomber sports a similar configuration.


Is it possible to (electronically) disable an ejection seat?

I am not familiar with the current F-35 ejection seat, much less what design changes, (real or fictional...) might be made by the year 2034, but of the three ejection seat aircraft I flew in the 1990s, none were electronically actuated such that it might be possible to hack into and disable the seat.
While they are mechanically complex, the means of actuation for most seats is actually fairly simple; relying on springs, firing pins, cartridges, and rocket motors.  It would be a very poor design decision in my mind to manufacture a last ditch fail-safe system like an ejection seat that is vulnerable to EMP, or is connected to a hackable network.


Where in the FAR or AIM is a high speed taxi defined?

There's no definition in the AIM or regulations, as far as I know, but there is one in the P/CG, sort of (emphasis mine):

  HIGH SPEED TAXIWAY− A long radius taxiway designed and provided with
  lighting or marking to define the path of aircraft, traveling at high
  speed (up to 60 knots), from the runway center to a point on the
  center of a taxiway. Also referred to as long radius exit or turn-off
  taxiway. The high speed taxiway is designed to expedite aircraft
  turning off the runway after landing, thus reducing runway occupancy
  time

So at least as far as the FAA is concerned, a high-speed taxi may be up to 60kts.

As for requesting it, you can request more or less anything. There's an active EAA chapter at my local airport and pilots who are in the process of building and testing aircraft sometimes request a high-speed taxi on the runway. The controllers don't question it or set any speed restrictions, it's all on the pilot. I suppose if things were busy they might deny the request, but the pilots know to do these things at quiet times anyway.


How often does fuel dumping from planes in flight actually occur?

These two reports cite that the US Air Force at one time jettisoned fuel nearly 1000 times per year. The second report also mentions that commercial airlines reported 485 instances of fuel jettison over a 5 year period. The commercial reports are only for maintenance related cases though, not including scheduling or weather reasons.

Both of these figures date from the 1970s. Military standards have been changed since then to reduce the frequency of it. The first paper assumed that in 1995, military fuel jettisoning was "infrequent".


How can I switch off the yaw damper in an Airbus A350?

On the simulator normally you can simulate the failure of the yaw damper actuators which has the same effect as switching off the yaw damper.
On the aircraft you can’t do it from the cockpit panels without switching off lot of other functions


A fan blade at the front or turbine blade at the back of a jet engine is a small aerofoil surface which is fixed to the main shaft and spins with it. By contrast, a stator vane is a similar aerofoil surface fixed to the outer casing and remains static.
Why do that? The spinning blades of a given stage cause the airflow to start spinning, and that slows the relative speed of the next stage (two things spinning together are at rest with respect to each other). The stator vanes "un-spin" the airflow so that the next stage blades meet it at full speed.
A variable vane pivots about its spanwise axis, allowing you to change its angle of attack to the oncoming airflow. Why do that? A turbojet engine at different stages in the flight will have different demands and conditions on it and will accordingly spin at different speeds. These effects change the airflow pattern through the engine. If a given stator vane is optimised for one stage of flight, it may not work so well in the modified airflow when a different stage is reached. Varying its angle can ensure that it can always be set at the optimum angle for the best performance.
So variable stator vanes ensure that a given jet engine can always operate at maximum efficiency and deliver optimal performance.
A typical way this is done is to fit gear wheels on the outer ends of the vane pivots, and place a single large toothed wheel around the whole engine so that when the large wheel turns, all the vanes in that position turn with it.


What is the proportion of active aircraft from CASL (commercial aircraft sales and leasing)?

According to The Economist data in 2012 showed that:

  Over a third of the world's airline fleet is now rented (see chart)
  and the proportion is likely to keep growing.

The article has some interesting background about the companies involved and the advantages of leasing vs. buying, which one Delta source compares to housing:

  [Delta's fleet planner] argues that big airlines are better off buying planes and keeping
  them for their full lifespan of 30 years or so. Like houses, then,
  buying is cheaper than renting in the long term.


What safety precautions are taken for an airline prototype test flight?

The bail-out procedure is usually only available on the first and second prototypes, which are the riskiest because they are usually designated for testing aerodynamics, dynamics, performance and flight controls, as well as for envelope expansion. Obviously, it's only used as a last resort when recovery is deemed impossible.
In an efficient and professional flight test organization, each flight test is planned out in advance. The test requirements and procedures are written by engineers to ensure that they can be carried out successfully and safely, with clear pass/fail criteria, as well as abort criteria should airplane deviate from safety thresholds.
The crew, including pilots, flight test engineers, and ground telemetry engineers, are briefed on the test procedures and the applicable flight envelope and systems restrictions on the test day. Flight risks are identified and treated accordingly. For example, if a stall test is planned, the risk to spin/deep stall may be high enough to warrant the arming of the spin chute.
The restrictions are some of the most critical technical documents to ensure the safety of flight. They contain the following:

Limit the flight envelopes, and expand only insofar as the planned procedures can be carried out successfully;
Outline systems limitations and defects, and procedures to go with them;
Performance penalties, including takeoff/landing speeds/distances, that may be impacted by the non-conformant systems or failures;

Any non-remote failure or combination of failures would have been checked out in a pilot-in-the-loop simulator with the best-known flight dynamics and systems models/rigs. The results of the evaluation would be a major driver in adding/revising/confirming the restrictions and the Airplane Flight Manual under development.
Another layer of defense lies in the onboard flight test engineers, who will be monitoring the critical flight parameters relevant to the test. They direct the flow of the testing and have direct line of communication with the pilots. For critical flights, ground telemetry personnel will also be monitoring the parameters. Should the parameters fall outside the abort thresholds, immediate abandonment of the test procedure will be called and the pilots will initiate recovery.


This website has a very comprehensive description and analysis of MCAS: http://www.b737.org.uk/mcas.htm
I find it to be the most accurate of all the various sources often quoted.
Here is a small quote from that website:

MCAS is a longitudinal stability enhancement. It is not for stall prevention (although indirectly it helps) or to make the MAX handle like the NG (although it does); it was introduced to counteract the non-linear lift generated by the LEAP-1B engine nacelles at high AoA and give a steady increase in stick force as the stall is approached as required by regulation.
The LEAP engine nacelles are larger and had to be mounted slightly higher and further forward from the previous NG CFM56-7 engines to give the necessary ground clearance. This new location and larger size of nacelle cause the vortex flow off the nacelle body to produce lift at high AoA. As the nacelle is ahead of the C of G, this lift causes a slight pitch-up effect (ie a reducing stick force) which could lead the pilot to inadvertently pull the yoke further aft than intended bringing the aircraft closer towards the stall. This abnormal nose-up pitching is not allowable under 14CFR §25.203(a) "Stall characteristics". Several aerodynamic solutions were introduced such as revising the leading edge stall strip and modifying the leading edge vortilons but they were insufficient to pass regulation. MCAS was therefore introduced to give an automatic nose down stabilizer input during elevated AoA when flaps are up.


The take-off roll, also called ground roll, is the roll distance before the aircraft becomes airborne.

In case of the 737-900ER, it will be in the order of 2000 meter.

The quoted 3000 meter is probably the take-off distance required (TODR) or take-off run required (TORR) at maximum take off weight. That assumes a full throttle acceleration to about half of the runway (1500 m), then an engine failure, continued acceleration on a single engine, rotation and take-off at 3000m. In case of TODR, the climb to a height of 35 ft is included as well (for FAR Part 23 aircraft it is 50 ft).

This means the 737-900ER requires a runway of 3000 meter length to take-off with an engine failure or to stop when the failure happens before the decision speed (V1). Since engine failures are unpredictable this is the minimum runway length required for take-off planning.

This all assumes ICAO standard atmosphere conditions. For runways at higher altitude ( > MSL) / higher temperature (> 15 deg C) the TORR will be even higher.


Why in the Seneca 2 the Rated Horsepower are higher at 12000 feet than at sea level? (215Hp at 12000feet, 200Hp at sea level)

Back pressure affects power because the more pressure opposes the exhaust, the more exhaust gas is left in the cylinder when the exhaust valve closes.  This trapped exhaust gas, effectively inert for purposes of the engine cycle, limits the amount of intake charge that can be drawn from the manifold at a given manifold pressure.

The more intake charge you have, the more power you get (within limits), so the less unscavenged exhaust you have diluting the intake charge, the more power you can generate for a given manifold pressure.

This effect can be mitigated to some extent with valve overlap -- where the exhaust valve remains open for a short time after the intake valve opens; this allows the incoming intake charge to push some additional gas out through the exhaust valve -- providing there isn't too much "back pressure" on the exhaust side.


Do any aircraft windshields have anti-reflective coatings?

An antireflective coating for the F/A-18's canopy was successfully tested sometime in the 1990s; no word on whether it made it into production, though.

Wikipedia claims that "[n]early all glass windows in large aircraft have an anti-reflective coating", but provides no source for this assertion.


What is the diameter of the nozzle of Trent 1000?

It is mentioned here that the fan diameter is about 111-112 inches. So the nozzle must be smaller than that as the engine assembly narrows at its rear end.

This PDF (p.5) shows a diagram of the exhaust nozzle of RR Trent 1000 measuring the diameter as 63 inches. This is the only reference I could find.


Where can you find wind tunnel visualization data online?

The closest you will find to a comprehensive, freely accessible source of data on this is the NASA Technical Reports Server. It is a search tool that gives you access to many NACA reports on various airfoils.


The fuselage extension at the back of the empennage is similar to that of a Lockheed P-3 Orion


Why would sea level static thrust have a takeoff and a maximum continuous value?

The static thrust value is with the engine fixed in place in still air.  Imagine the engine on an outdoor test stand, or on an airplane with the brakes on or tied down.  As soon as the airplane starts to move, the thrust value declines and the static thrust value no longer applies.  The static thrust value at sea level is used because it provides a consistent baseline reference, because once the engine starts to move, additional variables come into play.
The lower chart is showing the relative decline in thrust with speed for the range of engines between pure jet (bypass ratio = 0) to very high bypass (5-6), to illustrate the impact of bypass ratio on the decline in thrust with speed.  "Static thrust" is implied at the speed value of 0 Mach (airspeed is zero, so you are "Static" by definition) as a value of 1 and declines in thrust from static are a value less than 1. So you can interpret the left edge of the chart as "static thrust" and everything to the right as (moving) thrust, with the curves going down and recovering (or not) with increasing Mach #.
It's just illustrating relative effects, so with 6 engines that have different bypass ratios, their decline with speed, from the engine's Sea Level Static Thrust (whatever it is, represented by the value of 1), is shown by each curve. Following the curves as an example, the pure jet has only lost about 7% of its rated static thrust with speed at Mach 0.5, whereas the very high bypass fan has lost over 40% of its static thrust value at Mach 0.5, in the same atmospheric conditions.


Is landing without engine power routinely feasible?

Not feasible. A start of each engine can take 30-60 seconds or longer and would require the APU (noisy). In some airplanes you lose the packs during start so you would impact pressurization. Additionally many engines have a required time at idle after start before significant thrust is applied.  Lastly, with all engines offline, the airplane will be in some sort of essential power mode and many systems will be offline or unavailable.

You might then ask that we land at idle but that can present issues with spool up time before thrust is available.

One of the primary reason we land with a high flap setting is so that we have the drag to maintain approach speeds with the engines spooled up. This gives us near immediate power if we need it to go around.

I'm sure someone else can provide historical data from when idle approaches in jets were normal and specifics into why we don't do this today.


How does flying a helicopter compare with flying a fixed wing plane?

Controlling a helicopter is trickier than controlling a fixed wing aeroplane, because:

a helicopter can hover, in which case it is unstable.
the helicopter rotor is horizontal,
the rotor has long blades, applying a lot of torque to the fuselage.

The hover. in a conventional helicopter with a single rotor on top, the hover is an unstable situation requiring constant correcting inputs with the cyclic stick, as shown in the above clip. The guest pilot on the left seat has a successful go at controlling the cyclic stick (the stick at the centre), while the impressively capable right seat pilot controls the pedals and the collective stick. The helicopter wants to fall away to the sides and forwards/aft all the time, from disturbances caused by the wake interference with the ground, wind etc. Random accelerations need to be corrected by providing control corrections, based on what the pilot sees in relation with the environment. Peripheral vision is pretty crucial in this, since it rapidly and accurately picks up movements. Four degrees-of-freedom need to be actively controlled: pitch, roll, yaw, vertical speed.

That is all to hover at constant altitude. Now hover and climb:

increase collective (more eying power), which results in more torque;
so compensate with the pedal input for the tail rotor, which increases sideways thrust;
which must be compensated by lateral cyclic. Three control inputs for one degree-of-freedom!

Horizontal rotor. Once the helicopter picks up speed, its vertical and horizontal stabiliser keep the nose more or less aligned into the airflow - more at higher speed, but the neutral angle also changes with speed. The picture above is also shown in this answer, and depicts what happens with relative blade speed in forward flight. The blade going forward creates more lift than the blade going aft (which is compensated by increasing the Angle of Attack (AoA) of the retreating blade), but there is an area of reverse flow to the side of the rotor axis which results in a sideways tilt of the rotor. Which must be compensated by a cyclic stick left input, more stick at higher speed.
Rotor torque. Installed engine power equates to torque applied to the rotor, times the rotor rotational speed. A propeller is smaller than a rotor and rotates faster: the propeller requires less torque application for a given engine power setting, and the ailerons at the end of the long fixed wings can easily compensate for that. The helicopter rotor requires a lot of torque, which requires a tail rotor to compensate. The faster the helicopter flies, the more torque, the more force required from the tail rotor - which thrusts sideways, creating a drift in the flight path, which must be trimmed by the lateral stick. Even with a vertical stabiliser, tail rotor thrust is a function of airspeed.

Humans can learn to control helicopters of course, but there is a lot more to it than controlling a fixed wing aeroplane. Our brains rely on inner ear and visual inputs for detecting accelerations. More brain stimulation by input detection via multiple channels, results in more precise control. Plus experience of course.But take away an input, like the peripheral vision when flying in reduced visibility, and the control of a helicopter becomes much harder.

In larger helicopters such as S76s, pilot control is helped by a Stability Augmentation System (SAS), an Inner Loop system with no feedback on the flight controls; and an Automatic Flight Control System (AFCS) which changes the trim point of the flight controls as a function of flight path and target point. But these systems are not flight critical: if they fail, the pilot must take over, and must be able to fully control the helicopter by manual input. From visual and inner ear cues, and this always remains harder than in the auto stabilising fixed wing.

Fixed wing aeroplanes can and must be designed to be aerodynamically stable. Helicopters cannot.


Why pull up on the rollout after landing, after the nose wheel is down?

It is a soft field technique but is generally applied on hard surfaces for the sake of the aircraft. There are a few main reasons;

Take stress of the nose wheel and nose gear assembly which is a bit more fragile than the main gear assembly. This is particularly true in aircraft equipped with a steerable nose wheel like the Cherokee (or in retracts).
Provide adequate clearance for the propellor. If you look really closely the Cherokee has a low enough clearance such that, excess low pressure on the nose wheel and a sufficiently hard landing can cause a prop strike. This is one of the reasons its so important to check tire pressure in your preflight.
It also helps to reduce the risk of the fated nose wheel bounce which can collapse the assembly.
Generally it also helps to prevent you from simply releasing the controls after the mains touch down or potentially even pushing forward on the column which would drive the nose down and potentially cause damage.

During training this also helps to build habits that lead to a good landing attitude and speed bleed off especially if you start out landing flat.


How does a small aircraft like a Cessna fly at night?

Lets attack this from a few different angles.

  then night hits and its now pitch black with zero visibility?

There is plenty of visibility at night, a clear night is just as nice as a clear day. As a matter of fact when the air cools at night and clouds roll out you can some times see farther than you can during the day.

Here's me on a VFR approach (Piper Warrior) in to KLNS at about 10pm one night, you can see the runways are lit up nicely and can usually be spotted from 5 - 10 miles out depending on altitude.

Here is us earlier that night heading away from KABE (those lights are Allentown PA)

(photo credit to my girlfriend who was bravely sitting in the back)

As you can see you can still make out the horizon and plently of land marks. While it may be different during the day you can still fly VFR at night.

  zero visibility?

Zero visibility during the day is the same as zero visibility at night and as mentioned in the comments will require you to fly IFR if you want to fly.,

  How does he not run into mountains and the like?

Not flying into the side of a mountain is a topic of its own. You should check out my answer here to that very question.

From a more general stand point there are lots of ways to navigate in an aircraft. Here is a solid answer that covers most of them. The only thing that is not really feasible in a small single pilot aircraft if you are solo is celestial navigation although it could be done.


Why is the wing of large commercial jet aircraft usually located below the fuselage?

First of all, I do not agree with your assessment: The wing of large commercial aircraft is clearly below the fuselage, to allow the cabin not to become divided by the wing spar. The A380 would have better aerodynamics if the designers had interrupted the lower cabin by the wing spar, but the airlines did not want this at all. Please look at the picture below: I hope you will agree that the wing is clearly below the majority of the fuselage. Why this is done has been answered here and here.

Large commercial aircraft have low wings to stow away their long landing gears. Long gears make it possible to stretch the fuselage and still be able to rotate during take-off. Large high-wing aircraft with their low fuselage position are easier to load and unload, at the price that the fuselage taper has to start shortly aft of the landing gear, so no stretching is possible.

A mid-wing design is common to aerobatic aircraft. For ideal roll handling, all parts should be aligned along a single axis, and doing this complicates fuselage design. Only for aerobatic aircraft the benefits outweigh the disadvantages. See the picture of an Extra 300 below:

A high wing is selected when the gear height should be low for loading and unloading, when the downward field of view of the pilot should not be restricted (think parasol design in WW I), when the wing should have more ground clearance during landing (think gliders) or when the wing is meant to pivot horizontally (see picture below for an example). Note that the combination of a high wing and wing sweep will produce too much sideslip stability and needs to be corrected with anhedral. All three (sweep, wing position and anhedral) change with angle of attack, and the combination will still have too much or too little stability away from the design angle of attack.

As Jan Hudec pointed out, pitch and yaw stability depend mostly on tail size and location, and even roll stability is affected by more than the wing's location. The location is a compromise of many, sometimes diverging parameters, and stability is only a small part of it.


Is it possible for a pressure loss in the cockpit to not extend to the cabin?

The internal walls in an aircraft are not designed to withstand any significant pressure difference. Since the accidents of American Airlines flight 96 and Turkish Airlines Flight 981 where explosive decompression in the cargo hold caused the passenger cabin floor to partially collapse and damage the control cables running below it, the internal walls and floors are intentionally designed so that the pressure has a way to equalize without causing damage to any of them (with enough openings or loosely fitted panels that will blow out if needed). Therefore it is not possible for pressure loss in cockpit not to extend to the cabin, or the cargo hold.
The information I found about Sichuan Flight 8633 only says the passengers were not exposed to cold, nothing about pressure. During decompression, the air rushing out is not doing much work, so it does not lose much energy, and therefore only cools down a bit. What is going on is not an isentropic expansion, but something closer to free expansion. The air still has to do some work to push the outside air out of its way, but not as much as if it was expanded gradually from the 8,000 ft cabin altitude (in which case it would get down to similar temperature as outside).
The only reason for exposure to cold would be if the cold outside air was rushing into the cabin. Which the wall between the cabin and cockpit minimized, plus the engines were still running and supplying warm air.


What are the major causes of parachutes failing to work?

Hello - your Friendly Neighborhood Parachute Rigger here.

Sport chutes are pretty reliable, have been since the mid 90s to the point where more accidents happen under fully functional canopies.

If we disregard rank stupidity like tying the flaps shut1 or incompetent packing we find that the leading cause of malfunctions is bad body position on deployment. You are supposed to be face down, shoulders level before opening the thing. If you are on your back or tumbling you can have various parts wrap around you. High-performance canopies are somewhat more sensitive to the shoulders being level and can open in a decently fast spin. Depending on the spin direction and your altitude you may not be able to recover2.

The emergency chutes are built differently, emphasizing (obviously) reliability over being able to land at 100km/h. This means that twisted lines are either recoverable or not an issue.

If the jumper isn't paying attention to where he is, you may find that a leading cause of going splat is not using the perfectly good canopy on your back. Automatic activators have more-or-less eliminated this as a common cause3, but if the jumper thinks that the houses look a bit too big and deploys the main at the same time as the reserve opens they may decide to wrap each other up. Ram-air canopies are like badgers - they don't like each other very much and having two open at the same time is a rather delicate situation.

If we turn to landing accidents, we find that there are all kinds of ways to injure or kill yourself with a fully functional canopy overhead. The aforementioned 100km/h landing speed is no joke - hit an obstacle on the ground going that fast and it's exactly the same as jumping out of a car on the highway. Buildings, trees, power lines, vehicles, running propellers etc. have all claimed their sacrifices. And don't try to land on both sides of the fence at the same time. Or in the alligator farm across the road.

Mechanical failure of the system is very rare - riggers won't pack worn-out reserves, and if they are concerned about someone's main they will tell the dropzone management who will usually decline to provide services until it's fixed.

Many jumpers will tie various handles to the pack before travelling. Prevents the pack accidentally opening when curious security or customs pick it up by what looks like the carry handle. Remove before Flight!
Happened to me twice - the first time I looked up, then down, decided I didn't have enough time to fix it. The second time it was spinning the other way and I fixed it in 2 seconds.
Automatic activators fire at 750-1000 feet. If you are in freefall below that altitude you're usually done.


A wall-to-wall wing in a windtunnel should best be compared to one in ground effect and not as a segment of an infinite wing. Both are similar since the infinite wing will be infinitely close to the ground, relative to its span.
The opinion that an infinite wing has no induced drag is misleading. When we plot the amount of induced drag over aspect ratio, induced drag will tend to zero for an infinite aspect ratio. But what does that mean in practical terms? That infinite wing also produces infinite lift by pushing an infinite amount of air downwards by a finite amount. Induced drag is still there but becomes insignificant relative to lift.
Better to look at what happens in reality. It is worth to show the picture of the linked answer again here:

Induced drag is the consequence of lift. Lift is the consequence of air flowing around the obstacle that the airfoil poses to the air. While less than in free flight, some downward acceleration of air still happens but is soon stopped by the ground. Therefore, while less than in free flight, some induced drag is still there and will only disappear when the airfoil merges with the bottom of the tunnel.
Now it is crucial to know what induced drag really is. Air is accelerated downwards while flowing over the wing and the reaction force to this acceleration is lift. Since that does not happen instantly but gradually, some of the lift is created in an already downward-bent flow, so the reaction force to this, being perpendicular to the local flow, is pointing slightly backwards. This backward component is induced drag.
The ideal of the infinite span wing produces lift instantly because its chord is vanishingly small relative to span. The same cannot be said of the real wing in ground effect.
There is no free lunch. As long as lift is produced, induced drag will be present.


Why are months (e.g. December) used to notate a runway?

Very likely, whatever data source you're using has been mangled by Excel (or some other spreadsheet or data processing system that tries to convert everything that might be a date into a date format).

26-Aug is actually runway 26/08, 30-Dec is actually runway 30/12, etc. (See "How are runways numbered?")

Some computer system saw those numbers, assumed that they were dates, and presented them that way. The other runways aren't valid as dates, so it left them alone. It wouldn't be the first time that people used Excel without fully understanding its default date-parsing settings and thereby causing problems for people trying to use their data afterward.


Why are there so few Lancasters still flying?

I can give you lots of reasons, but as with most things they all really boil down to one: MONEY.

Perhaps the first challenge with preserving any classic warbirds in airworthy "flying exhibit" condition is finding one, but let's assume you can locate a mostly-intact Avro Lancaster (in a field somewhere, or as a static display at a museum that hasn't done anything to it that would render it unflyable).

The next major hurdle is restoring it to airworthy condition economically:
A side effect of their role in the military is that these aircraft are flown hard (they have to accomplish their mission and a little airframe stress or engine damage in the process is OK as long as you still get it back home in mostly-serviceable condition for repair), and of course they do tend to get shot at (9 out of 10 structural engineers surveyed agreed that bullet holes are a Bad Thing for airworthiness; The 10th wet himself and ran out screaming). They've also been sitting around for decades suffering the effects of time (corrosion).

Once you find the aircraft you have to determine what repairs it will require to render the airframe airworthy. You will probably be replacing skin panels, control cables, hydraulic and pneumatic lines, etc. at the very least. The longer it's sat, and the worse the environment, the higher the chance of more major repairs (structural corrosion requiring ribs or spars to be replaced/spliced), and as these aircraft are out of production there are some parts you can't just get off the shelf: Custom fabrication for skins, control surfaces, ribs, etc. adds to the price tag.

Once the airframe is addressed you can look to the engines, since an aircraft without a powerplant is still just a static display.
Much like with the airframe you may find engine parts are hard to come by (the two airworthy B-29s, Doc and FiFi, both required a lot of effort to get working engines).

Now that you have a working engine you need to outfit the cockpit -- Many of the instruments the aircraft originally shipped with were likely pulled by the military or intervening owners as service spares for other flying aircraft, so what's left in the cockpit may be non-functional or so obsolete as to be useless. If you want an aircraft you can safely/legally fly to shows you'll probably need to invest tens-of-thousands of dollars in outfitting it with instruments and radios that are some functional combination of "authentic" and "modern".

Finally once it's all assembled, airworthy, and navigable you still have to pay to operate and maintain it like any other aircraft. When you're talking about a Lancaster with 4 fat engines on it you're racking up quite a fuel bill (and burning a good amount of oil with it).
The engines will of course need routine maintenance (oil changes, etc.) and eventually things will wear out or break, requiring repairs and leaving you with the "out-of-production parts" issues again.

Most of the "big" flying warbirds like the two airworthy B-29s and the two airworthy Lancasters are maintained by organizations that do it as a labor of love & out of respect for the history of these aircraft, but they do not have unlimited funding and there aren't a large number of near-airworthy airframes to choose from for these projects (with the pool of available hulks ever-dwindling), so in that respect there's certainly a financial factor as to why there aren't more of these flying.

Psychologically there's also probably something about having "at least two" airworthy examples flying that may make folks look at restoring a different type as well: Having two flying examples of aircraft from this period provides a decent level of insurance in so much as if one is lost in an accident or develops a problem that can't be fixed at least there's still the other one flying. (When FiFi was the only flying B-29 there were some folks who felt it shouldn't be flown, as an accident would cost the only airworthy example. Doc joining the flight line has muted some of those objections.)


What exactly happened in this bird strike incident?

Since it hit a bird, it was a bird strike. Nothing else matters for that classification.

The puff of flame suggests there probably was a momentary compressor stall. That is the compressor was unable to maintain the pressure as the flow was disrupted by the bird, the flow through the engine slowed down for short while, some extra fuel accumulated in the engine and as the flow restored, the extra fuel burned past the jet, creating that puff of flame.

The engine did not flame out, that is, it continued to run. Older engines tended to get into a repeated cycle of stalls once they stalled as the accumulated fuel from one stall would cause the pressure to increase beyond capability of the compressor and cause another stall, but modern engine computers will automatically restrict the fuel flow to prevent that.

The aircraft continued, because the engine was running and all parameters (RPM, temperature, vibrations, pressure ratio, oil pressure) were indicating normal values.

If the engine stopped, or if some indications were out of tolerance, they would have to return, since two-engined aircraft are required to land as soon as possible when one engine fails. But it clearly did not and they continued (and may not have been aware of the bird strike at all until inspection after landing, because the stall handling is automatic and if no values were out of tolerance, they would not get any warnings).

The engines are designed and tested to continue running after ingesting  a small bird [1], so this was actually the expected outcome. The test usually involves launching dead chicken into the running engine (on the static test bench) from a chicken gun [2]. Said gun is also used for testing canopies and windscreens. Frozen chicken are occasionally used too; contrary to the urban legend not due to stupidity, but intentionally as tougher version of the test [3].


Is it possible to turn and safely land an aircraft with a malfunctioning rudder?

If the rudder is jammed in the neutral position (as stated in your question), then landing is easy. You will just land using ordinary techniques. The plane may feel sloppy, and passengers sitting at the back will complain about feeling dizzy, but the aircraft is easily controllable and landing would not be any problem.

Now things are different when the rudder is jammed to one side, for example in American Airlines Flight 96. The crew faced major controlling issues with a full right rudder, engine failure and very high sink rate. But even then, the pilots managed to land successfully.


What is the purpose of a dorsal fin such as on the Boeing 737?

The "extension" at the front is called "dorsal fin". Its main purpose is to improve directional stability in high side-slip situations (asymmetric flight due to engine failure, crosswind landings, etc). The double-sweep of the leading edge of the vertical stabilizer helps the vertical stabilizer to be effective at a larger range of side-slip angles (high lateral angles of attack).

The stabilizer is an airfoil, much like a wing. The amount of lift (or in this case, sideways force) it generates, varies with its angle of attack (AoA, or $\alpha$), or in this case, sideslip-angle ($\beta$) something like this:

Lift coefficient ($C_L$) increases with increased $\alpha$, until it reaches $C_{L_{MAX}}$. This angle is called $\alpha_{crit}$.

Generally, the more sweepback an airfoil has, the lower its $C_{L_{MAX}}$, BUT the higher its $\alpha_{crit}$. This means that the non-dorsal-fin-part of the stabilizer (low sweepback) will be able to generate its $C_{L_{MAX}}$ (sideways lift) at a lower $\beta$ than the dorsal fin. Increasing the side-slip angle beyond its $\beta_{crit}$ decrease the amount of sideways force it generates. By using a secondary airfoil (the dorsal fin), with a higher sweep angle, (ie, higher $\beta_{crit}$), the net loss in sideways force with increased side-slip may be avoided, or at least mitigated. Further, at high $\alpha$, (or in this case, with a vertical stabilizer $\beta$), a delta with high sweepback will generate a vortex, which will follow the upper side of the surface down-stream of it, adding kinetic energy to its airflow, thus enhancing its effectiveness.

The current version of the dorsal fin was added to the Boeing 737 with the Classic (−300 and onwards), but the design is not unique for the Boeing 737. Look the Cessna 172 for instance (Wikimedia Commons):

The ATR 72 doesn't have a "pronounced" dorsal fin, but you can still see clearly how the sweepback of the vertical stabilizer changes along its length (Wikimedia Commons):

Or, on the other side of the speed spectrum (Wikimedia Commons):


Is there any plane that has wing of both aerodynamic and geometric twist?

A wing has geometric twist when, from root to tip, its chord line changes angle, typically without changing the airfoil shape.  This is colloquially known as washout when the root stalls before the tip (or, much more rarely, its opposite, wash-in).
A wing has aerodynamic twist when, from root to tip, its airfoil changes in camber and thus in shape, typically without changing its chord line's angle.
Both twists have a similar effect, in that the zero lift axis changes angle from root to tip, commonly to inhibit tip stalling.
Of these two, geometric twist is easier to design, construct, and analyze, because there's only one airfoil instead of a (possibly continuous) blend of multiple airfoils.
Adding geometric twist to aerodynamic twist might, for example, let you avoid a nonconvex airfoil shape where the camber is large.  Convex shapes are easier to build strongly and stiffly, so that would lighten the wing.


Are there any single-pilot aircraft certified in the Part 23 Commuter category?

It looks like it's possible but not common. There's an STC for the Twin Otter that authorizes single-pilot operations in the commuter category if various upgrades have been made. At least, that's my reading of it:

  The Twin Otter DHC-6-300HG™ type rating designation is DHC-6HG and may
  be operated with or without a second in command (SIC) with certain
  limitations. The Airplane Flight Manual Supplement (AFMS) lists
  equipment that must be installed and operative to operate the aircraft
  single pilot.

And:

  FAA STC SA02682LA incorporates upgraded engines, upgraded propellers,
  increased maximum takeoff weights (MTOW), structural and aerodynamic
  modifications, and the aircraft category and design characteristics
  were updated to Title 14 of the Code of Federal Regulations (14 CFR)
  part 23 commuter category.


Why do commercial airplanes smell like fuel smoke before take off?

This is often a result of when the planes push back from the gate or if there is a direct tail wind on the ground. The pressurization system for aircraft uses bleed air from the compression stage of the engine. If the engines are running at push back or idling when a tail wind hits them the brief reversed airflow can cause some vaporous fuel to make its way forward in the engine and come through the air system causing the smell. This page covers it pretty well. Patrick Smith also touches upon it here.


Can I be a commercial pilot if I've had a dental filling?

Here are the mouth and throat requirements for a pilot physical.

The main thing is that it shouldn't affect your ability to fly (i.e. having pain) and ability to communicate over the radio.

Commercial pilots who don't fly regular schedules need a Class 2 medical certificate. Regular schedule commercial pilots need a Class 1.

FAA Class 2 medical requirements
FAA Class 1 medical requirements


What criteria are used for exiting an airplane in an emergency?

Per 14 CFR 25.803:

  For airplanes having a seating capacity of more than 44 passengers, it
  must be shown that the maximum seating capacity, including the number
  of crewmembers required by the operating rules for which certification
  is requested, can be evacuated from the airplane to the ground under
  simulated emergency conditions within 90 seconds

Appendix J to Part 25 specifies exactly how the evacuation tests should be done. It's too long to quote here, but it includes requirements for lighting levels, number of passengers, minor obstacles, infants on board etc.

I have no idea whether or not those simulated conditions are reasonable and effective, but they at least set a standard.


What advantages come with the wing on the Boeing Bird of Prey?

The Boeing Bird of Prey is indeed a unique aircraft, wahich was an internal project rather than an X-Project funded by the government. It was primarily used as a technology demonstrator for low observable technologies.

The Bird of Prey is rather unusual for a wing only aircraft (in the sense that it had no stabilizer) that it was statically stable and required no correcting inputs from a computer. This stability was achieved by the lift generated by the chines in front of the fuselage.

Here is  closer look at the chines.

Source: www.freerepublic.com

The chines produce lift by generating vortices (similar to the delta wing). Basically, the chines produce seperated vortices on either side of the fuselage, which produces lift. According to adg.stanford.edu,

  Rather than reducing the lift of the wing, the leading edge vortices, increase the wing lift in a nonlinear manner. The vortex can be viewed as reducing the upper surface pressures by inducing higher velocities on the upper surface

Image from Effects of Vertical Tail and Inlet/Strake Geometry on Stability
of a Diamond-Wing Fighter Configuration by Mitchell E. Fossum et al., accessed through http://enu.kz/

To compare how the chine generates lift similar to a delta wing, it is instructive to see the vortex flow patterns on a slender (cropped) delta wing with a chine forebody.

Image from On the Nonlinear Aerodynamic and Stability Characteristics of
a Generic Chine-Forebody Slender-Wing Fighter - Configuration by Gary E. Erickson and Jay M. Brandon, NASA Technical Memorandum 89447, labeling mine.

An example of a delta wing with a chine forebody shows the two vortices being generated from the chines and the highly sweptback wing, similar to the Bird of Prey.

Image from Aerodynamic Analysis of a Generic Fighter with a Chine
Fuselage/Delta Wing Configuration Using Delayed Detached-Eddy Simulation by Tiger L. Jeans et al, accessed through calpoly.edu

The forces acting on the longitudinal axis of the aircraft look something like this (I'm not sure of the exact values or locations), leading to a statically stable aircraft.

Profile from bj-o23.deviantart.com, others own work.

The chines also help in reducing the radar cross section, according to dictionary.sensagent.com (attributed to The Radar Game by Rebecca Grant):

  A standard leading edge extension joins to the fuselage at an angle while a chine is an extension of the curvature of the fuselage. Therefore chines avoid presenting corner reflectors or vertical sides to radars.

This design has since become standard in (Boeing) UAVs like X-45 etc.

Another feature is that the fuselage sides are parallel to each other, helping in reducing the Radar Cross section by reflecting the radar waves away from source.

Source: gizmodo.com

The wing design is rather unusual, a polyhedral section with dihedral (upwardly angled) inboard sections and anhedral (downwardly angled) outboard sections, which helped in stealth and stability.

Source: soldiersystems.net

The wing has a rather high sweep angle (~65 degrees) for a low speed aircraft, in order to improve stealth.


Why do some non-precision approaches have stepdown fixes after the final approach fix?

Take a look at KPRB VOR Rwy 19:

There is a stepdown fix after the final approach fix. Now look at the terrain around the airport. You can see a bunch of small hills around the FAF. In order to provide adequate terrain separation and get you low enough to land, they need a stepdown. You can also see this on lots of non-precision approaches where the approach minimum is lower if you can identify a point past the FAF.

If you are interested in how they decide to include a stepdown fix, check out FAA Order 8260.3C TERPS, Section 2-6. Final Approach. Lots of formulas but the gist of it is they have a required obstacle clearance that must be met and maximum descent angles. Sometimes they need a stepdown fix in order to make the approach work.


What is the work routine of a boomer operator in a refueling aircraft?

The boom operator (or boomer) can freely move around the aircraft. The boom operator position is usually accessible from the cargo hold and the operator can use the opening to move from his/her position. This is especially important for the KC-135 Stratotanker, which has the boom operator working in a prone position.

Image from sobchak.files.wordpress.com

While the operator is not fueling other aircraft, he/she has other responsibilities to carry out. According to the US military job description of a boom operator, the boomer,

  Prepares and verifies load plans, directs cargo loading, and unloading operations, and inspects aircraft load to ensure hazardous cargo compliance and weight and balance status of aircraft. Ensures adequate safety equipment and passenger comfort items are on aboard aircraft. Instructs passengers in use of emergency equipment and emergency procedures.

among other things.

The boom operator is a specialist and his/her job cannot be done by anyone else on board. The operator also has to be qualified for the type of aircraft he/she is refueling. From interview of a USAF boom operator in foxtrotalpha:

  Every receiver is a little different, so we have specific qualifications for heavy aircraft and fighter aircraft, called gulf and Charlie.


Other aircraft doesn't apply right of way rules

See and avoid is the backbone of VFR flight. The right thing to do when there is a potential collision is to take positive action, which is exactly what you did. There's no one-size-fits-all solution as to whether to turn one way or the other, climb or descend - it all depends on the position and course of the aircraft in question.

Often which way to turn in these situations is the lesser of two evils, if you turn left you clear sooner but if the other airplane turns right there's a potential conflict, if you turn right then you are in potential conflict longer. You have to choose one and hope the other person takes the right action.

One way to avoid conflict is a change of altitude, if you are slightly higher than the other airplane then climbing quickly takes you out of conflict, if you are lower then a descent does the same thing. If you are the same altitude then I favor descending as most people's default reaction is to climb - if the other pilot sees you they're more likely to pull up, giving you better separation. Even if you are under ATC direction changing altitude is the right action as it's necessary for the safety of the flight. You change altitude, avoid the collision, then go back to your assigned altitude before radioing ATC and explaining the deviation. I doubt they'd have a problem with that and even if they did regulations are on your side.


What are the differences between PC and professional simulators?

The main difference is in the flight dynamics model. A PC simulator can be realistic, but who is to say that it is? A professional simulator must show to the authorities (EASA,FAA etc) that the modelled behaviour matches flight data.

There are several authorisation levels, from very basic to zero-flight-time. Even for the basic devices, the authorities want to make sure that only correct cues are generated and that there never will be any negative training habits formed by the simulator user.

PC-based programs can teach students where the buttons and indicators are, what to push, which instrument to monitor far what etc. Some of them are accredited by the authorities, more info in answers to this question.


What is the optimum design: elliptical lift distribution or elliptical span loading parameter distribution?

Minimum induced drag is reached when the circulation distribution over span is elliptical. Circulation is indeed proportional to the product of the local lift coefficient and the local chord (c$_l \cdot$c). The diagram in your question normalizes this with the overall lift coefficient c$_L$ and the mean chord $\overline{\text{c}}$.

But this is only true if you disregard the structural weight of the wing. Using less load near the tips will reduce the wing root bending moment and, consequently, wing mass, so less lift and wing area are needed in order to carry the same non-lifting load. Even though your drag coeffcient might be higher, your overall drag will be lower.

The optimum will also depend on the size of the wing. Small wings should indeed use an elliptical circulation distribution because their structural weight is low, but in large airplanes a more triangular distribution will be better.

One last word: Please try to avoid the high loads near the wingtips if you want a nice, docile stall behavior.


How should I deal with a cable break at low level during a glider winch launch?

Depends on the wind and the surrounding area. If there is enough headwind, you will be surprised how short your approach will be in a proper sideslip. Practise sideslipping at altitude, so you know what to do in an emergency! Otherwise, look around for an open field where to land; gliders are easily disassembled and carried back to the airport.

When the cable breaks, push the stick forward. Be prepared for dirt flying up and into your eyes if you push hard enough! Then stabilise at the minimum sink speed, release the remaining cable and look around for your options. There should be some:

Land straight away if headwind plus sideslip allow for a steep descent.
Fly straight a bit, then turn around 180° and land opposite to your direction at take-off. Do this only when there is no or almost no wind! 100m of altitude is plenty enough for this trick.
Keep flying straight and land on an open field near the airport.
Fly a triangular, shortened pattern and land in the regular direction.

If the airport is surrounded by forest or houses on all sides, try to land on the glider port - normally, the altitude bands required for the landing straight on, the 180° return landing and a landing from a proper pattern overlap enough so that there is never an altitude that would not allow to land on the airfield.


When may pilots leave the flight deck during flight?

14 CFR 121.543

  (a) Except as provided in paragraph (b) of this section, each required flight crewmember on flight deck duty must remain at the assigned duty station with seat belt fastened while the aircraft is taking off or landing, and while it is en route.

  (b) A required flight crewmember may leave the assigned duty station -

    (1) If the crewmember's absence is necessary for the performance of duties in connection with the operation of the aircraft;

    (2) If the crewmember's absence is in connection with physiological needs; or

    (3) If the crewmember is taking a rest period, and relief is provided -

      (i) In the case of the assigned pilot in command during the en route cruise portion of the flight, by a pilot who holds an airline transport pilot certificate not subject to the limitations in § 61.167 of this chapter and an appropriate type rating, is currently qualified as pilot in command or second in command, and is qualified as pilot in command of that aircraft during the en route cruise portion of the flight. A second in command qualified to act as a pilot in command en route need not have completed the following pilot in command requirements: The 6-month recurrent flight training required by § 121.433(c)(1)(iii); the operating experience required by § 121.434; the takeoffs and landings required by § 121.439; the line check required by § 121.440; and the 6-month proficiency check or simulator training required by § 121.441(a)(1); and

      (ii) In the case of the assigned second in command, by a pilot qualified to act as second in command of that aircraft during en route operations. However, the relief pilot need not meet the recent experience requirements of § 121.439(b).

tl;dr:
You need at least one pilot at the controls at all times, unless completely necessary to operate the aircraft, or take care of physiological needs.


What is the equivalent of Hobbs and Tach in a Jet or Turbine Aircraft?

In all of our jets, we have two hobbs meters. One is active from left engine start and the other goes active when the weight of the aircraft leaves the wheels. Neither of these are used for logging our flight time. We do that "chock-to-chock", ie as soon as the chocks are pulled and we start moving to when the chocks are put back in the wheels.

The regs say you can log flight time from when "the aircraft moves under it's own power for the purpose of flight":

  Flight time means:
  (1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing; or
  (2) For a glider without self-launch capability, pilot time that commences when the glider is towed for the purpose of flight and ends when the glider comes to rest after landing.


Mach Factor - Factor increase of thrust due to the ram effect

It sounds like what you are describing are the isentropic compressible flow equations. See equation 6 & 7.

At Mach 2.1, these give a stagnation pressure rise of 9.14, and a stagnation temperature rise of 1.88, since air has a value of 1.4 for gamma.

But, the air does not come to complete rest (stagnation) in the intake, hence these values are not obtained.

What you need to know, is the actual Mach number at the engine inlet, which is I assume where you are suggesting is the location of a total pressure 2.39 times higher than the freestream total pressure. Typically, this is around Mach 0.4. But, since the freestream flow is supersonic, that means it will have had to go through some shock waves, to get to a subsonic speed. This means there will be pressure losses, associated with those shock waves. Normal shock waves (a shock wave perpendicular to the flow) result in higher total pressure losses than oblique shock waves. Hence, supersonic aircraft have pointed cones in their intakes to create oblique shock waves, to minimise the pressure losses. To calculate the total pressure losses from these, you need to know the geometry of these cones to know if they cause 1, 2, or maybe even 3 oblique shock waves, as the pressure loss of each shock depends on the strength of each shock wave.

Jack Mattingly, in his text book "Aircraft Engine Design" gives a good description of how to calculate the losses associated with oblique intake shock waves. It's fairly complex. See here. The figure you want is 10.35, but that wasn't shown in the free preview when I tried it, but maybe the pages they hide are random, and you will have better luck.

So, in summary, to verify the 2.39 factor, you need to know the Mach number at the engine fan inlet, and be able to calculate the total pressure losses of the shock waves, which requires info of the intake geometry.


How much force does a helicopter's tail rotor counteract?

The lift-to-drag ratio of the main rotor blades is around 10, so the tail roter has to provide a force equal to one tenth of the aircraft's weight.

Of course you have to take into consideration torques and lever arms, but if we assume that most of the lift and drag is created by the outer portion of the main rotor and that the tail rotor's lever arm is approximately the same, we can simply ignore them. On most helicopters the tail boom is a bit longer than the radius of the main rotor, so the force might be 20-50% lower. On the other hand, the tail rotor is often less efficient, especially on some newer models with small, ducted fans, so the tail rotor might consume a bit more than 10% of the power.


How do test pilots determine an aircraft's capabilities?

Short:  The pilot has a well-defined range of discretion within progressively increasing bounds very tightly set as part of a structured development program aimed at eliciting maximum information regarding actual versus theoretical flight envelope in all conceivable modes and situations.

Longer: A test pilot's main task is to carry out a progressive program of tests aimed at investigating the correspondence between designed and actual capabilities, and identification of any unexpected variations from nominal which occur along the way. The designers know everything they consider the aircraft should do and shouldn't do and should be able to do long before it first flies. The job of the test pilots is to find out the places where the designers are wrong by carrying out an extremely well planned program while applying her or his skill to come back alive when the designers and/or manufacturers get it wrong.

The pilot will usually have input into the process of deciding the rate which the program is carried out, how large progressive steps are and attempting to anticipate in advance what is likely to be viable or problematic. Their feedback along the way will help inform decisions about modifying program objectives or rate of implementation or lead to modification to the aircraft. A highly skilled test pilot is a member of a synergistic team and while program decisions are the responsibility of the 'project manager' (or equivalent) it is likely that what the pilot says and wants will be close to indistinguishable from what actually is done.

However, the actual program on a given occasion is not the pilot's responsibility and limits on what are attempted or implemented are well-defined in advance. The pilot will be given discretion in advance regarding ranges of parameters which may be investigated, e.g., closeness of initial approach to Mach 1, rate of ascent or g forces applicable in various modes*. And the safety of the aircraft first and the pilot second (in many cases) is left to the pilot's discretion BUT subject to substantial guidance, e.g., 'bringing the aircraft back intact' is often going to provide far more information when a problem occurs so a pilot may make every effort to do so in situations where an ejection may otherwise be preferred. A  pilot who ejects more than most may or may not be criticized for any given decision but is less likely to be given as many chances in the future to risk their life even more than before. However, a pilot who crashes fatally while trying to save an out of control situation will in the future only take part as the subject in training videos and in establishing "see if you could have handled this one" simulation scenarios.

Striking the right balance between these two 'modes' is what makes a great test pilot. But they still don't just get to go out and "see what it can do".

A well judged ejection occasion - genuine.

From here

English Electric Lightning early testing.  Prior ejection would very likely have been justifiable but is unlikely to have been considered. The pilot (George Aird) survived with relatively minor fractures - in part caused by descending through the roof of a glasshouse :-). Pilot was on final for an emergency landing as a fire was attacking the rudder actuator. At 100 feet altitude and 10 seconds from touchdown, Murphy won, the actuator support burned through and the plane pitched nose down. Go!

Glasshouse with pilot and ejector seat entry points (side by side) ringed in red. Canopy caused damage at far end.

Photographers are lucky to get one opportunity like this in a lifetime.
I'm still waiting :-)

What do I know?: Layman. Engineer. Non pilot. Read too many test-pilot autobiographies. The ones you read tend to be from those who are good and didn't die.

I was recently rererereading Roland Beaumont's "Phoenix into Ashes" - an  account from the leading test-pilot of many (most) of the early British jet aircraft. He recounted the loss of a test aircraft while pulling 9g (as I recall) in a situation which should have been inside the design envelope. The pilot died. The observer lived to provide 'human black box' functionality. It was established that fuel transfer protocols were not correctly followed, leading to over-stressing part of the airframe and thus fatal loss of control, i.e., "just" mishandling fuel tank sequencing may kill you. Nowadays computers will tend to stop this sort of error. But Murphy has many alternatives.


How do we determine whether the airfoil trailing edge should be cusped or pointed?

Both cusped and conventional airfoils have pointed trailing edges. The lower trailing surface is concave on cusped airfoils, so plot it and get your straightedge.


Deep vein thrombosis (DVT) or Traveler’s Thrombosis occurs when blood in a vein (most often in lower extremities) becomes stagnant and then forms clot. If you think about it, the pilots are at less risk compared to passengers in this matter. FAA advices certain steps to prevent DVT, like,

Increasing leg muscle activity during long periods of sitting improves blood flow in the legs. This may include walking around the cabin or exercising your lower legs and ankles while seated.

Drinking adequate fluids, and avoiding alcohol and caffeine, may also help by preventing dehydration.

Some recommend taking short naps, instead of long ones, to avoid prolonged
inactivity.

It would be much easier for the pilots to do these things compared to say, passengers.

Pilots usually have more room in the cockpit compared to passengers in cabin.

In long haul flights, there is usually a standby crew member who is rotated so that the pilot could get some movement and rest.

It is certainly practical for the pilot to get up and stretch his/her legs during flight. It is not as if they are flying the aircraft hands-on every second for the entire flight. In any case, the flying duties could be alternated between the two flight crew without any problem.

It is not unknown for pilots to take short naps in the cockpit

Studies indicate that the DVT is more prevalent among the passengers than the pilots. According to Deep vein thrombosis in commercial pilot:

10 percent of air travel passengers older than 50 years develop symptomless DVT during prolonged flights. DVT among air travellers has been documented, but is rare among pilots flying commercial aircraft.

Also, it seems (some pilots, at least) do wear flight socks.

It seems that the pilots don't take the wearing of oxygen mask seriously.


On average, how many landings does a student pilot need before their first solo?

My logbook shows 29 landings, with 11 hrs logged in an Aircraft Single Engine Land aircraft (ASEL) when my instructor stepped out and sent me off on my first solo flight.

I think those figures were typical for students at my flight school. It is probably also fairly typical for students at most §141 flight schools, such as mine.

Now, there can be a significant difference between the experience of training under §61 and training at a §141 flight school. The schedule at §141 schools tends to be more fast-paced than what many students might experience doing §61 flight training. Since students must systematically complete the curriculum at §141 schools, a certain minimum level of experience will be in place before a student solos. However, this curriculum also lends itself to a student being ready to solo after a fairly defined period of time. A student training under §61 might take longer to be ready to solo due to a number of factors, including a possibly more relaxed training pace. On the other hand, §61 training can also give an instructor the freedom to solo a student after less time than might be typical.

I don't have any hard data outside of my own experience and what I have observed, but I would guess that a typical §141 student will solo after about 20-40 landings and 10-15 hours. I would guess that a typical §61 student will solo after about 20-60 landings and 10-25 hours.


Can a person legally mount a fake gun on an amateur-built aircraft?

Empirically, yes it's legal. I've seen several reproduction WW1 aircraft myself at airshows with fake guns, missiles or bombs attached. And I was once at an EAA chapter meeting where a member demonstrated his fake gun 'firing' using compressed air. There are also factory-built aircraft with fake weapons added later, by the way.
As to regulations on this, I've never seen one. Typically US laws and regulations state what you can't do, not what you can do. For example, there is a law that prohibits attaching dangerous weapons to drones.


Does the FAA restrict the color of pilot seat belts?

No, there's no regulation on the color; the restraints just have to allow the crew to perform all their duties.

The old 23.785 regulation said:

  (e) The restraint system for each crewmember must allow the crewmember, when seated with the safety belt and shoulder harness fastened, to perform all functions necessary for flight operations.

The new 23.2535 regulation says even less:

  Safety and survival equipment, required by the operating rules of this chapter, must be reliable, readily accessible, easily identifiable, and clearly marked to identify its method of operation.

And empirically, there are many colors available. Googling will bring up plenty of images.


If all engines fail in a Boeing, how heavy are the flight controls?

A 747 doesn't have a ram air turbine (RAT), but it has an APU that can power the hydraulics. If that can't be started, a 747 can still function using the hydraulic pressure from each engine's windmilling. Computer based training video here.

Trivia: if all hydraulics fail, but engines are running, a 747 is a dead stick, but can be steered using the engines. A complete loss of engines and hydraulics is never in the emergency procedures of a heavy airliner.

In a 767, assuming the APU also won't start, the RAT will provide hydraulic pressure. Controls will be heavier (but not impossible) the slower the plane is.

Source: 767 QRH, 13.14

767 RAT speed below 20,000 feet is >200 IAS, any slower, hydraulic pressure will be lower.

A 787's artificial feel system (Elevator Variable Feel) will revert to direct mode, feel will be based on flap position, and during approach feel forces will be reduced to make the landing easier.

Source: 787 FCOM, 9.20.12

Trivia: a 787's RAT can supply 5000 psi of hydraulic pressure.

In a 737, the crew will use manual reversion mode, for roll and pitch it's control tabs, like an MD-80, heavy but not impossible.

For all types, it will be almost impossible to find data on the exact amount of force needed. Also for all types, if no APU or RAT, windmilling can still provide some hydraulic pressure.

Same for the pilot feedback, as very few flew all-engine-out heavies. And adrenaline rush would almost certainly skew their post-flight judgement.


How can aircraft determine true north for inertial navigation systems?

How can an aircraft be be aligned to true north for proper INS
alignment? Are markings at the parking location good enough?

A small 0.5° error in assumed heading translates into 10 NM error in computed position on the distance Madrid-Montreal (3,000 NM). As many other errors must be taken into account, north must be known to a higher degree to achieve this accuracy, and a better accuracy is also expected This cannot be done using simple markings.
But true north is related to Earth spin axis, which can be accurately sensed by an INS using a gyroscope.

Inertial systems belong to two families: platform and strapdown:

In platform INS (PINS) accelerometers and gyros are mounted on a gimballed platform kept level and oriented to north by torque motors driven by gyros outputs.

In strapdown INS (SINS) these sensors are firmly fixed on the aircraft.

PINS are mostly using momentum wheels. Recent gyros are SINS and not inertia-based, they usually measure length differences created by Sagnac effect (fiber optic, ring laser, acoustic...):

Ring laser gyros in AN/WSN-7 US Navy navigation system (source)
Regardless of the type, alignment is similar and consists in sensing Earth spin axis and gravity, and is twofold: Leveling, then gyrocompassing.
Alignment principle
Accelerometers and gyroscopes arrangement in an inertial system, and final orientation:

Leveling
Axes which in the end will point to north and east are in a first step leveled by tilting the assembly. Leveling solely involves accelerometers and gravity.
Leveling is real for PINS, it gives the platform its working orientation, found by zeroing north and east accelerometer outputs while the unit is stationary. After alignment, accelerometers are able to directly sense accelerations along north, east and up directions.
Leveling is virtual (software) for SINS. It consists in evaluating the initial orientation to build a transformation matrix. This matrix is used for projecting the values issued by tilted sensors onto a virtual level platform. The matrix is then constantly updated with orientation changes detected by gyros.
Gyrocompassing
Likewise leveling, gyrocompassing is real or virtual according to the type of inertial system. Gyrocompassing goal is to determine true north using gyros.
After leveling, for a stationary aircraft, north and east gyros (designated X and Y below) sense only Earth rotation, in quantities depending on their orientation relative to Earth spin axis:

On the left hand picture, X gyro fully senses Earth rotation effects as it is aligned with spin axis, Y gyro doesn't detect any rotation.
On the middle picture, the system has been rotated by 90°, the result is reversed.
The right hand picture depicts the general case: Both gyros detect Earth rotation rate, but in quantities depending on the heading. X detects a rate proportional to the cosine of the heading, Y a rate proportional to the sine.

Finding north is done by rotating (virtual rotation for SINS) the leveled assembly about the vertical axis until the east gyro output is null, meaning its axis points to east or west. This ambiguity is removed by sensing rotation direction on the other axis which now points north or south.
Earth rate detection depends on (cosine of the) latitude angle:

Earth rotation rate sensing by an inertial system versus latitude
Merging what we exposed above, the sensed rates Rx and Ry are given by:
$$  \begin {cases}
Rx & = & \omega \times \cos \alpha \cos \phi \\
Ry & = & \omega \times \sin \alpha \cos \phi
\end {cases}$$

$\omega$ is the constant for Earth spin rate, $\approx 15$°/hour (360° in a sidereal day),
$\phi$ is the latitude,
$\alpha$ is the heading of the aircraft (or of the reference axis).

With two linear equations for two unknowns, finding latitude and heading is straight forward, the only condition is Rx and Ry are known. That is where the shoe pinches. Gyrocompassing is actually difficult and slow.
Actual application of the principle is challenging
While the principle is simple, it's difficult to measure Rx and Ry. The reason is $\omega$ is tiny (0.004°/s), measures must be repeated during a significant time. Five minutes is sufficient at the equator, but twenty minutes are not unusual at 45° latitude.
The pilot can provide the current approximated latitude to allow this process to converge more quickly.

Boeing 737, FMS page used to enter the initial position estimate to speed up gyrocompassing

Sensor fusion, alignment in motion and loss of alignment
Alignment may be facilitated, and subsequent measures can be improved by associating additional sources of data, and merging sources after filtering excessive divergence, this is known as sensor fusion and IRS/GNSS hybridization. These sources include GNSS (position and Doppler velocity), magnetometers, air data, even Doppler velocities of known targets but that's more for underwater rovs to replace GNSS.
The different sources allow to maintain the natural cumulated drift associated with the integration process, which is central to inertial positioning, below some threshold, e.g. thresholds fixed by required navigation performance procedures.
In some conditions the inertial system can even be realigned in flight from GNSS position and Doppler velocity (e.g. Northrop Grumman LCR-110). Such in-flight alignment should be common in the future.
Level and north orientation are kept after alignment by adjusting the orientation and compensating detected aircraft orientation changes. The sidereal alignment is therefore not maintained.
Most inertial systems cannot be realigned in motion, but they can be re-leveled, and while the north direction and the position cannot be recovered, the system is still be able to provide aircraft attitude (mode ATT).

The two IRS switches in the normal (navigation) position (source)


What is the difference between CAMO and CAME?

CAMO is the organisation and CAME is a "book" that need to write.

This "book" contain procedure to explain how you will work (how you communicate with aircraft customers, how you manage your docs, etc...).


What was the decrease in approach speed of the KFIR over the Mirage 5 due to the canards?

The KFIR has similar airspeed specs as the Mirage 5. However, I'm not clear on what you mean by "Approach Speed".

Approach and Landing Phase:

Vectoring Speed: 220-250 kts
Max Gear Speed: 270kts
Approach Speed: 190-200 kts
Touchdown Speed: 170-180kts

Source


What aircraft model is on this old photograph?

It's a Carden-Baynes Bee... A British plane built in the 30s...

https://en.wikipedia.org/wiki/Carden-Baynes_Bee


What are the requirements to take the private pilot check ride?

Private Pilot Airplane Single-Engine Checkride Requirements

Eligibility Requirements (14 CFR 61.103)

Be at least 17 years of age for a rating in other than a glider or balloon
Be able to read, speak, write, and understand the English language
Instructor logbook endorsement certifying your aeronautical knowledge (14 CFR 61.105) and that you are prepared for the written test
Passed the written test and can present your original embossed Airman Knowledge Test Report
Instructor logbook endorsement certifying your flight proficiency (14 CFR 61.107)and that you are ready for the flight test
Log all required aeronautical experience (below)

Aeronautical Experience (14 CFR 61.109):

40 hours of flight time (35 for 141 schools) that includes:

20 hours of dual instruction
10 hours of solo flight training

3 hours of cross-country dual
3 hours of night dual (to get an unrestricted license) that includes:

1 cross-country flight of over 100 nautical miles total distance
10 takeoffs and 10 landings to a full stop (with each landing involving a flight in the traffic pattern) at an airport

3 hours of instrument dual
3 hours of dual in preparation for the practical test within 2 calendar months
10 hours of solo including

5 hours of cross-country time
1 150 NM solo cross country flight, with full-stop landings at three points and one segment of the flight consisting of a straight-line distance of more than 50 NM between the takeoff and landing locations
3 takeoffs and 3 landings to a full stop (with each landing involving a flight in the traffic pattern) at an airport with an operating control tower


How much does a 3 day cabin crew recurrent training cost?

The airline will bring in contract instructors to do the training (yes there are freelancers out there that do that sort of thing as contractors).
If they don't have the number of active crews to justify full time instructors because they only need someone for 5 or 10 days a month, that's the normal alternative.
The airline will still be paying the contractors they hire for the training so the cost to the crew will still be zero.


What is the maximum momentary G force that a modern airliner's wing can take before it snaps in extreme turbulence?

It's hard to give a direct answer to your question. But I will try to give a realistic answer.
As stated in the "Easy access rules for large aeroplane CS25" under EASA regulation:

Except as provided in sub-paragraphs (d) and (e) of this paragraph compliance with the
provisions of sub-paragraph (a) of this paragraph must be demonstrated in flight over the
acceleration range –
(1) –1g to 2·5 g; or
(2) 0 g to 2·0 g, and extrapolating by an acceptable method to – 1 g and 2·5 g

That's the normal range of load factors for a modern airline; of course an aircraft can be design to withstand more positive or negative G's, but most of them have an upper limit of +2.5g and -1.0g (in clean configuration), as stated in the regulation.
The following fundamental requirements have been developed around the experiences of metallic airframes and remain the basis for the certification of composite airframe structures. These require that the structure (by test and/or analysis) demonstrate the following capabilities:
• Static strength:
– Design limit load (DLL), no failure or unacceptable deformations. DLL is normally the maximum load anticipated to be placed on the structure in its lifetime. – Design ultimate load (DUL), no failure, although limited permanent deformation is acceptable; DUL = DLL × 1.5 (generally).
The limit of +2.5g and -1.0g will be our DDL, so if we "remove" the safety factor (1,5, but can be higher) the Max G load will be +3,75g and -1.5g. if you fly at this load factor the aircraft will not broke apart or will have catastrophic failures, but deformation can occur.
Let's talk about turbulence:
Extreme turbulence in reality is not part of the categorization of levels of turbulence (At least in EASA rules), the upper limit is the severe turbulence:

Turbulence that causes large, abrupt changes in altitude and/or attitude. Aircraft may be momentarily out of control. IAS fluctuates more than 25KT. (>1.0g at the aircraft’s centre of gravity)

So assuming a fluctuation of 1g (positive or negative) inside turbulence, we can assume that we will be able to reach +2.0g or -0g passing trough this turbulence.
If the turbulence will be "extreme" (let's assume a fluctuation of 2gs), we will reach a max positive G load of 3g and a negative G load of -1g.
As you can see, we still below DUL limit. I can tell you that probably the aircraft will not have any deformation in that range also if above DDL, this is because we are talking of instantaneous accelerations and not continuous and constant load factors (DUL and DLL are based on that).
The aircraft will however be checked after the encounter of severe turbulence.
Reassuming, is very hard that turbulence will cause any significant or severe damage to a modern aircraft. (Severe or Extreme)
But to give an answer to your question I can give you an example:
China Airlines flight 006 experienced vertical load factors of up to 5.1 g on 19 February 1985. The aircraft landed safely and there were no fatalities, but there was some damage:

From the NTSB incident report:

The wings were bent or set permanently 2 to 3 inches upward at the wingtips; however, the set was within the manufacturer's allowable tolerances. The left aileron's upper surface panel was broken and the trailing edge wedge was cracked in several places.

5.1Gs was probably the top of the load, but during the recover they were above DLL and DUL for a while.
This however didn't cause a catastrophic failure of the wing section.
I don't have any document or personal information or experience about the instantaneous or the continuous g Load to cause the snap of the wings, but I think that we are talking of +7/8g -4 continuous and +10-11g -5-6g instantaneous.
I hope that I answered your question.


The Boeing 737 NG series first flew in 1997, but the fuel inerting system was only certified in 2006 according to b737.org.uk (emphasis mine):

Centre Fuel Tank Inerting
To date, two 737's, 737-400 HS-TDC of Thai Airways on 3 Mar 2001 and 737-300 EI-BZG operated by Philippine Airlines on 5 Nov 1990 have been destroyed on the ground due to explosions in the empty centre fuel tank. The common factor in both accidents was that the centre tank fuel pumps were running in high ambient temperatures with empty or almost empty centre fuel tanks.
Even an empty tank has some unusable fuel which in hot conditions will evaporate and create an explosive mixture with the oxygen in the air. These incidents, and 15 more on other types since 1959, caused the FAA to issue SFAR88 in June 2001 which mandates improvements to the design and maintenance of fuel tanks to reduce the chances of such explosions in the future. These improvements include the redesign of fuel pumps, FQIS, any wiring in tanks, proximity to hot air-conditioning or pneumatic systems, etc.
737s delivered since May 2004 have had centre tank fuel pumps which automatically shut off when they detect a low output pressure and there have been many other improvements to wiring and FQIS. But the biggest improvement will be centre fuel tank inerting. This is universally considered to be the safest way forward, but is very expensive and possibly impractical. The NTSB recommended many years ago to the FAA that a fuel tank inerting system be made mandatory, but the FAA have repeatedly rejected it on cost grounds.
Boeing has developed a Nitrogen Generating System (NGS) which decreases the flammability exposure of the center wing tank to a level equivalent to or less than the main wing tanks. The NGS is an onboard inert gas system that uses an air separation module (ASM) to separate oxygen and nitrogen from the air. After the two components of the air are separated, the nitrogenenriched air (NEA) is supplied to the center wing tank and the oxygenenriched air (OEA) is vented overboard. NEA is produced in sufficient quantities, during most conditions, to decrease the oxygen content to a level where the air volume (ullage) will not support combustion. The FAA Technical Center has determined that an oxygen level of 12% is sufficient to prevent ignition, this is achievable with one module on the 737 but will require up to six on the 747.
The Honeywell NGS was certified by the FAA on 21 Feb 2006 after over 1000hrs flight testing on two 737-NGs. Aircraft have been NGS provisioned since l/n 1935 and it has been installed since l/n 2620 onwards. The NGS requires no flight or ground crew action for normal system operation and is not dispatch critical.

So all older NGs were built without an inerting system. According to this article, the FAA required new models since 2008 to have an inerting system and retrofitting of all 737s until 2018 (emphasis mine):

The headaches are hitting Boeing 737 operators, which make up the bulk of the early adopters among those required to comply with the FAA’s Fuel Tank Flammability Reduction (FTFR) rule. The rule, passed in 2008, called for new-production versions of the affected models—737s, 747s, 757s, 767s, 777s, Airbus A300s/A310s, A320-family models, A330s and A340s—to have fuel tank inerting or flammability reduction systems installed starting in late December 2010. It also required airlines to retrofit half of their affected fleets with an approved system by 2015 and complete the rest by 2018. The phased compliance led operators to prioritize their largest subfleets to ensure they met the first deadline, putting 737s at the top of the list.

It is quite possible that not every airline worldwide has completed this retrofitting.


Does a flight cycle require a minimum duration?

Much of the wear on an engine happens during startup, so while yes it does have a significant impact on maintenance costs, it's rather unavoidable unless the operator chooses to avoid shutdown between flights (as some do, e.g. skydiving and ag spraying)


The lift equation is $$L = \frac{1}{2} C_L · v^2 · S · \rho$$

where $S$ is wing area, $C_L$ coefficient of lift, $\rho$ air density, and $v$ airspeed. Using units of measure $\text{m}^2$ for $S$, $\text{m}/\text{s}$ for $\text{v}$, and $\text{kg}/\text{m}^3$ for $\rho$, the result is lift in $\text{N}$ (newtons).

Concerning symmetrical airfoils, they work quite well too, and the equation given above is perfectly valid for them. If it’s true that at zero degrees their $C_L$ is zero, they give zero lift regardless of the speed (zero times anything is zero).