Why does an aircraft pitch up when the speed increases?

What you ask is: If a model glider is thrown at a higher speed than its trim speed, why does it pitch up?

Short answer: Because the rear horizontal surface produces less lift per area than the forward surface. When flying at a speed different from its trim speed, the combined center of lift of all surfaces is shifted such that it creates a pitching moment around the center of gravity. This pitching moment causes the flight path change.

Note that I try to explain things in terms that work equally well for canards or even flying wings. That may sound odd in places, but needs only one explanation for all cases. For unswept flying wings read forward wing = forward part of the airfoil and vice versa.

Long answer: Let's assume an airplane that is rigged for flight at an angle of attack of 9°. For simplicity, let's assume that both airfoils are symmetric and both surfaces have the same lift curve slope, for simplicity 0.1 per degree. The local incidence is 0° on the forward and -5° on the rear wing. Neglecting downwash effects, this results in a lift coefficient on the forward wing of 0.9 and on the rear wing of 0.4. The zero-lift angle of attack is +1° when the forward wing lift coefficient is at 0.1 and the rear wing lift coefficient is at -0.4.

Let's further assume that the tail surface has 25% of the area of the forward surface. Lift on the forward wing is 90% of weight and on the rear wing it is 10% of weight. The center of lift, therefore, sits at 10% of the line connecting both neutral points and that is where the center of gravity is as well for trimmed flight. Like this:

Now the model is thrown at twice its trimmed speed. Let's assume that the angle of attack is also 9°, but that does not matter much. Lift on the forward surface is now 360% and on the rear surface 40% of weight. Again both forces combine for a common center of lift at 10%, so no pitching moment is created. But lift far exceeds weight, so the aircraft immediately climbs. Climb without pitching motion means that the angle of attack decreases immediately. Therefore, the aircraft will slightly accelerate upwards and settle at a new, lower angle of attack where the combined lift is equal to weight. But how is lift now distributed?

To have lift decrease to a quarter needs an angle of attack change to 25% of its initial value, relative to the zero-lift angle of attack. For this, the new angle of attack on both surfaces has to decrease by 6°. The local incidences result in an angle of attack of 3° on the forward and -2° on the rear wing and lift coefficients of 0.3 and -0.2, respectively. Again neglecting downwash effects, the new lift contributions are 120% on the forward wing and -20% on the rear wing. Like this:

Now the center of lift is 20% of the distance between the two wing's neutral points ahead of the forward wing's neutral point and 30% ahead of the center of gravity. That causes a strong nose-up pitching moment which will let the aircraft pitch up. Together with the initial flight path change of 6° for lift correction this will make the airplane climb until its flight speed drops below the trimmed condition and the condition reverses. Since pitch damping is high, very few cycles are needed to arrive at the trimmed condition but at a height over the launch point which corresponds to the extra energy provided by the high launch speed.

This can be run with different numbers and will work regardless of lift or downforce on the rear surface, provided that lift per area is lower there than on the forward wing.


Why do the 737-100's JT8Ds, and no others, have suck-in doors?

Since the production of the 737-100 and -200 was concurrent, there were in fact -200s with blow-in doors, and more often than not, the inlet was replaced during the airframe's lifetime. An example is United's N9003U, line number 12, a 737-200:

Sources: jetphotos.com and airliners.net

The doors are spring-loaded and open by differential pressure at medium-to-high thrust settings and slow speeds, i.e. during takeoff and landing, i.e. near communities. The openings created in the inlet allows the inlet noise to escape, which is a major source of noise.
Therefore, and evidently, both manufacturers and customers have favored the sound-absorbing inlets.

(...) the noisiest test configuration had an inlet duct with simulated blow-in doors. When the blow-in-door inlet was installed, the A-weighted sound power levels were approximately two decibels greater than when the inlet with no blow-in doors was installed.[1]

An additional design feature for minimum noise is the use of a single opening inlet at all operating conditions. The use of devices such as blow-in doors to bring additional air into the engine at some engine powers has some aerodynamic advantages but increases engine noise. No blow-in door systems are in use on the DC-10.[2]

From a regulatory aspect, at least in the 747's case – which sported those inlets in its early days – the noise-aimed regulations of the 70s were the reason for their replacement:

After promulgation of FAR Part 36 and application to the 747, substantial changes were required for the engine installation. The blow-in-door inlet was replaced with a fixed lip inlet providing a large reduction of the fan source noise while the surface area of the acoustic lining contained in the engine and nacelle was more than doubled.[3]

1: Marsh, Alan H., Robert L. Chapkis, and Gary L. Blankenship. Study of Noise-Certification Standards for Aircraft Engines. Volume 3. Selection and Evaluation of Engine-Noise-Certification Concept. DYTEC ENGINEERING INC LONG BEACH CA, 1983.
2: McPike, A. L. "Community Noise Levels of the DC-10 Aircraft." Journal of Aircraft 9.8 (1972): 542-547.
3: Little, J. W., and R. E. Russell. "Status Report: Subsonic Aircraft Noise Reduction." Turbo Expo: Power for Land, Sea, and Air. Vol. 79757. American Society of Mechanical Engineers, 1976.


How does aircraft weight affect the glide performance?

The gliding slope, which equals $D/L$, does not change with weight. Hence, starting from a given height $h$, the longest gliding distance will be $d = h \cdot max(L/D) = h \cdot max(C_L/C_D)$, i.e., independent of weight.

However, the gliding speed, and, consequently, the gliding time, do change with weight, and significantly. If $C_{L,max}$ is the lift coefficient when $C_L/C_D$ is maximal, the gliding speed at best slope, $\bar{V}$, is obtained from $W = (1/2) \cdot rho \cdot \bar{V}^2 \cdot S_{ref} \cdot  C_{L,max}$.


Are there any studies on the safety of glass versus steam instruments?

The FAA released a 70 page report back in 2003 titled General Aviation Technically Advanced Aircraft FAA – Industry Safety Study which basically says that the overall accident rate of the two types of airplanes are almost the same.

They found that the "available safety" of Technically Advanced Aircraft (TAA) is greater than non-TAA aircraft, however in emergency situations pilots often were not aware of the resources available. To offset this, they recommend (among other things) more training for pilots before flying TAA's so that they actually have the safety related aspects available to them.

Here were their official findings:

  Team Findings:

  The safety problems found in the accidents studied by the Team are  typical of problems that occurred after previous introductions of new
  aircraft technology and all also reflect typical GA pilot judgment
  errors  found in analysis of non-TAA accidents
  Previous safety problems similar to those identified in this Study have  been remedied through a combination of improved training and, in
  the  case of new aircraft capabilities, pilot screening (i.e.,
  additional insurance  company requirements of pilot experience).
  The predominant TAA-system-specific finding is that the steps required to  call up information and program an approach in
  IFR-certified GPS  navigators are numerous, and during high workload
  situations they can  distract from the primary pilot duty of flying
  the aircraft. MFDs in the  accident aircraft did not appear to present
  a complexity problem. The  Team also believes that PFDs, while not
  installed in any of the accident  aircraft and just now becoming
  available in TAAs, similarly are not likely to  present a complexity
  problem.
  TAAs provide increased “available safety”, i.e., a potential for increased  safety. However, to actually obtain this available safety,
  pilots must  receive additional training in the specific TAA systems
  in their aircraft that  will enable them to exploit the opportunities
  and operate within the  limitations inherent in their TAA systems.
  The template for securing this increased safety exists from the  experiences with previous new technology introductions –the current
  aircraft model-specific training and insurance requirements applicable
  to  high-performance single and multi engine small airplanes. However,
  the  existing training infrastructure currently is not able to provide
  the needed  training in TAAs.
  Effective and feasible interventions have been identified, mostly  recommending improvements in training, and effective implementation
  mechanisms for the recommended interventions exist. Therefore, TAA
  safety problems can be addressed, and the additional available safety
  of  TAAs to address traditional causes of GA accidents can be realized
  as  well.

APOA has a nice summary here.


What are the best tips for circuit practice with strong crosswind?

Try visualizing the pattern.

In your mind's eye, overlay the airspace around the airport with the track that you want your flight to take, visualizing all sections of the traffic pattern from your point of view as you fly.  Now check to see if there are visual references on the ground eg buildings, roads, parks, golf courses, etc. which align with this pattern you are visualizing and use them as additional aid for pattern legs and turn points.  If the airplane drifts off this track, adjust your crab angle and/or your rate of turn in order to track correctly.

As mentioned above, ground reference maneuvers such as rectangular patterns, turns about a point, S-turns etc are very useful and may be good basic practice for training yourself to visualize the pattern in space.


Do runways need to be repaired after gear up landings?

Runways are usually made of several feet of reinforced concrete. Any damage to them after a wheels-up landing is superficial at best. Details depend on circumstances, but in general light aircraft will cause less damage. A full wheels-up landing is rather easy on the runway: The aircraft's fuselage and wing fairing structure are flexible and malleable, so it will buckle and bend until the local surface pressure is too low to cause more bending. To really damage a concrete surface you would need carbide tools, not sheet aluminum.

An unwheeled landing gear strut of an airliner is probably the worst scenario. The Airbus in the linked video had only a damaged nose gear, which carries a small fraction of the total load, and you will see in the close-up at the end of the video that the runway did not suffer. A similarly damaged main gear, however, will cut a groove.

All what is needed for repair is some fast-curing liquid for filling the nicks and scratches and some paint to repair the runway markings.

If you land a composite aircraft wheels-up, the concrete will act like sandpaper on the structure. The landing zone will be marked by white epoxy dust. A broom is all what is needed to put the strip back to its initial condition.


Do pilot uniforms always include a shirt with stripes?

Uniforms are to make it easy to identify members of a group who have a separate function or authority from a larger more random group.  The stripes are to easy to identify the chain of command within this group at a glance.

Most of the time it's all just costume peagentry.

When the shmoozle hits the fan however, being able to identify who's in charge and next in charge and so on, without having to, you know, ask around, becomes a big deal.  That's why the bars.

You won't find a first or second tier carrier in a Western airline without a uniform shirt and rank bars.  I can't find any specific regulations that require that, but it's basically an old convention carried over from the marine world (it's why pilot uniform suits look like naval uniforms), where many of aviation's traditions originate.


Are there any pitfalls to be wary of when purchasing an "umbrella" insurance policy?

An umbrella policy is insurance on top of insurance in case your primary insurance is not enough. For this reason it is usually inexpensive relative to to other insurance policies.

Using your example, a million dollars beyond what you are already insured for is a pretty good amount of coverage. It would take a really catastrophic event for a small plane to do more than a million dollars worth of damage beyond the limits of an owner's or renter's insurance policy.

If you're considering an umbrella policy be sure that it does not specifically exclude aircraft because many do. If you purchase a policy through an agent who knows that you are a pilot, you're probably fine but don't assume that your commercial umbrella policy covers you because many commercial umbrella polices specifically exclude aircraft.
I would be more worried about the umbrella policy excluding aircraft (like you mentioned unforeseen things rendering the policy ineffective in the last sentence of the first paragraph) rather than a million dollars on top the normal coverage not being enough.

I'm also assuming that by typical pilot you mean small aircraft not a corporate jet or something that has a lot more potential liability.


Less effective.  20mm projectiles are normally explosive.  Training rounds are non explosive, basically really big bullets, and are coloured blue.


Are there any plans to make the QF-16 into a drone for actual combat missions, or a fully autonomous fighter?

There seems to be some ongoing research into just that:

  There is an effort underway to develop a UAV version of the F-16. This would be based on the QF-16, the remotely controlled target version of the F-16. The air force is already in the process of converting 210 retired F-16s to QF-16s and it was noted that with a little extra work the QF-16 could be turned into a combat UAV for dangerous missions like SEAD (suppression of enemy defenses) or attacking ground targets guarded by heavy air defenses.

Other research is often related to sixth generation fighters, which are often described as being "optionally manned" meaning that they can fly with or without a crew onboard.

F-16s currently being converted into QF-16s are older models which are likely to require more maintenance per flight hour, and as always it is a matter of capability vs cost vs other platforms. The biggest question for such a conversion is whether or not an imagined MQ-16 would bring capabilities not already covered by existing UAVs to the table, and how expensive it would be to support this.


What is the exact purpose of the string attached between front fuselage & the tail section of the transport aircraft's?

That is an end-fed long wire antenna for HF radio use.


How does the line of thrust affect longitudinal stability?

There is a general rule: don't trust "Pilot's Handbooks" when they talk about aerodynamics. More often than not, they are full of misconceptions and, at best, oversimplifications. In your quote, for example, the conclusion has nothing to do with the preceding text.

But the question is fair. Thrust line can affect stability, but we need to define what exactly we understand by that.

Stability as such is a negative reaction to a disturbance: a disturbance of a particular defined kind must cause a reaction which negates the original disturbance. Usually, we restrict the analysis to relatively small disturbances, when reactions are more or less linear.

Longitudinal stability, in a broad sense, describes any longitudinal motion. For airplanes this involves pitch or speed. (Altitude is a different axis and even a different frame, although we'll need to consider it in some cases). These are linked but different motions, and we can talk about them separately to some extent. It just happens that for most airplanes, the characteristic times of these angular vs linear motion is so different that we can very well analyse them independently. The heavier the airplane (and/or higher its wing loading), the better it holds. Even for GA airplanes it's still largely true.

In a strict sense, when aircraft designers (but not pilots) talk about "longitudinal stability", they mean the short-period pitch stability, or more accurately, angle of attack (AoA) stability. This means that when AoA is disturbed (by a gust or control input), a moment immediately arises that counteracts this AoA change (which is done via pitch change).

The mechanism behind AoA stability involves purely aerodynamic moments/forces. (The explanation involves the concepts of neutral point and moment derivatives). Notably, it does not involve thrust nor airspeed. Both of them change too slowly compared to AoA/pitch and so play practically no role in longitudinal stability per se.

But when it comes to airspeed stability, with which pilots are more intuitively familiar, the situation is different. Airspeed stability is linked to AoA stability via an indirect mechanism that Robert already roughly described in his answer: "increased thrust, increased speed, increased lift, plane rises vertically, vertical "up" pushes tail down, pitch changes". The important result is that a statically stable (read: AoA stable) aircraft will also be stable in speed. But even that holds only if drag doesn't grow faster than lift; that is, on the front side of the power curve. (Pilots know it very well). At high (but pre-stall) AoAs, the airplane will remain stable in AoA but will become unstable by speed.

Technically, this is still speed stability, not thrust stability. We are not concerned how airspeed changed: thrust, gust, dive, whatever. A statically stable airplane will try to pitch up and climb as a response to increased airspeed, slowing down as a result.

But when we analyse speed changes as a specific result of thrust changes, other factors come into play. Namely, apart from speed, changing thrust can disturb the moment balance of the airplane. In general, multiple effects can be important here, not only the location of line of thrust with respect to CG, but also with respect to 'centre of drag'; and the changed slipstream may cause aerodynamic changes. Either way, it may happen that these extra moments may augment or negate the natural tendency that comes from AoA stability.

For simplicity, let's analyse a few obvious cases of reaction to increased thrust (leaving everything else unchanged, particularly trim).

Thrust is in line with CG. The airplane will start to climb (or reduce descent) and will settle on the same AoA and roughly the same speed.
Thrust line below CG (the case of most airliners with underwing engines). This will produce an added pitch-up moment, which will cause the airplane to slow down more than necessary, despite the added thrust! This is an unstable condition. It can be particularly nasty in go-around situations. How do we fly it? Luckily, unlike AoA, the changes are slow enough for pilots (let alone autopilots) to react with active trim changes.
Thrust line above CG. This is the opposite of the above and, in moderate amounts, can have stabilising effect and easier trim changes. The airplane will settle at a higher speed, which is presumably what the pilot wants (despite the "power controls altitude" mantra). When the line is too high, the airplane may even descend and accelerate more than necessary, until the aerodynamic moment balances out the thrust moment, but overall the condition is stable. (Note that in most cases thrust starts to fall with increased speed, which helps to find the balance).

As a conclusion:

In a strict sense, line of thrust (and thrust as such) does not affect longitudinal stability per se; that is, the AoA stability.
However, it does affect airspeed stability, which many pilots understand as longitudinal stability.
It certainly affects trim changes, which, again, pilots perceive as a measure of longitudinal stability (not entirely without reason).


How many tendencies are affected by Gyroscopic precession for single propeller airplane?

Both are wrong. (Or rather, both are partly right, which makes them fundamentally wrong).

Precession happens when there is an 'input' rotation (moment) and not by itself. When you balance the airplane to fly straight and level, there is no gyroscopic moment.

The gyroscopic moment is perpendicular to the external rotation, so it can be directed anywhere across the spin axis.

On a typical airplane with the CCW prop (or turbine for that matter), if you yaw (or turn) LEFT, the airplane will want to pitch UP. (See the diagram on your picture). If you pitch UP, the airplane wants to turn RIGHT. If you pitch DOWN, the airplane wants to turn LEFT.1 And so on. The quicker you maneuver, the stronger the effect is. (And of course, the quicker and heavier the prop is, the stronger the moment, so it's most noticeable at full power).

In normal flying with GA airplanes, the gyroscopic moments are rather minor. The typical 'left turning tendency' is caused by aerodynamics. Gyroscopic moments manifest themselves when rotation is relatively fast, e.g. in aerobatics or spin. But they can be observed with quick impulse inputs on the pedals or yoke, if carefully executed.

1This latter is particularly noticeable on taildraggers during takeoff when the tail is lifted too quickly: the aerodynamic forces are still weak, and the power is full.


Formula for calculating turn indicator (deviation from coordination)

I am stuck calculating the deviation from a coordinated curve indicator, usually the small ball in the turn indicator.

The "small ball in the turn indicator" (which pilots use to determine what they need to do with the rudder pedals in order to stay in coordinated flight) is just an inclinometer. It's literally just a heavy ball in a curved tube filled with oil.

If you want to replicate the way that the inclinometer works, then look at the lateral acceleration and vertical acceleration and use the arctan2 function to determine the apparent tilt.

By "lateral acceleration," I mean the proper acceleration in the direction of the aircraft's lateral axis, since that's what matters here and that's what you're able to sense. Likewise, by "vertical acceleration," I mean proper acceleration in the direction of the vertical axis.

The oil in the tube functions as a low-pass filter with a time constant of maybe about a second.

All that said, I don't think there's actually any reason to use the vertical acceleration. You can just take the lateral acceleration, low-pass filter it, and display the result.


There are different ways of moving flaps. The trivial case where they rotate around a hinge point which lies within the airfoil contour does not increase wing area. Fowler-type, backward-moving flaps are possible in three general ways:

Douglas flap: Here the flap rotates around a single hinge line which lies substantially below the airfoil contour. As the name suggests, this is used on many Douglas Commercial aircraft.

Douglas flap, left: retracted (source); right: extended (source). Their long and narrow supports make them easy to recognize.

Four- or five-bar linkages: These are mechanically more complex, but enable a more compact mechanism. As their name suggests, four or five linkages are connected with bearings and enable a more complex movement. The drawing and the animated GIF below are taken from Wikipedia and show the mobility m which increases with the number of joints. This would be my recommendation for a Lego model; just make sure that the forward bar is longer than the rear bar - this will give you a realistic movement of the flap.

Above: Linkage mobility (picture source). Below: Four bar linkage (picture source)

Sliding block guide: Here you find real rails and rollers which move along them to enable the most complex and precise movement, even for multi-element flaps. While a four-bar linkage will have a continuously increasing ratio of deflection angle to backward shift, a sliding block guide makes it possible to set the deflection angle independent of the backward shift, and allows the biggest backward shift for a given size of the mechanism. See the Boeing 747 flap tracks below for an example.

Boeing 747 flap tracks (picture source). Note that the upper block is supporting the first flap segment and the lower block the second. Actuation is via a spindle; the linkage in the lower left corner is actually the mechanism for moving the flap fairing.


What should you do when ATC gives you a number to call to discuss a violation?

AOPA has an article on exactly this question (written by an attorney). Their advice is basically that it's a judgement call on your part and one that you should think about carefully. Not calling may antagonize the FAA, but calling if it's a major safety issue may be unwise:

  That doesn't necessarily mean, however, that you should call the
  telephone number or respond to the FAA's letter, and blather the most
  expansive defense you can conjure up. A little judgment is called for
  here--and, unfortunately, there are no hard and fast rules. If you
  think the FAA may be inclined to just admonish you orally or content
  itself with administrative action, then a humble, cooperative approach
  may be best. Saying you won't talk without a lawyer, when the likely
  outcome if you do talk is minor, may only prompt the FAA to propose
  sterner action. Before you talk, however, think carefully about what
  you want to say, how much to say, what questions the FAA is likely to
  ask and how you'll answer them.

  If, on the other hand, there is a substantial chance the FAA will take
  certificate action against you or will propose a fine, the best course
  of action, as I said above, is to hire an attorney. Don't ignore the
  FAA; be polite, but don't provide more information than the bare
  outlines of what is already known and obvious to all. State quietly
  that you understand the FAA's desire to investigate possible
  violations, that you take your obligations to fly safely very
  seriously, and that you will be happy to cooperate. Also say that,
  unless the FAA is not contemplating action against you, you feel it
  best to consult a lawyer before proceeding. Since the FAA likely won't
  give you any guarantees, its representative will be the one
  overreaching if he presses you to respond anyway. Politely decline if
  he does.

I also had a look through the AOPA discussion forums (members only, so no links) and my summary of their comments would be:

File a NASA ASRS form within the 10-day limit, whatever happened
If you know what you did wrong and you know it was minor, then make the call
If you don't know what you did wrong then call but be prepared to end the conversation immediately if you have no good response or you realize it's more serious than you thought
If you know you caused a major safety issue (actual or potential) then don't call and get a lawyer instead
If you know the person you have to call  - e.g. if it's the tower controller at your home airport - then you should give more weight to calling
In general, it's better to call and have to cut off the conversation than not to call in the first place
Whatever you say, keep it short and factual
When you find out what you did wrong, get some ground and/or flight training from an instructor to address that specific issue and have him endorse it in your logbook; this shows the FAA that you've taken the issue seriously and you've actively taken steps to make sure you won't do it again


Is there a difference in aerodynamic efficiency between single engine and twin engine airplanes?

Your question really needs further bounding to be able to accurately answer.  I will discuss a few aspects.

First @ratchet freak is right on the money.  What engine mount are we talking about? A podded engine on the single and twin (or multi, since your one of your questions mentions multi) or some different configuration.

In the late 70's and early 80's there were a bunch of academic and not so academic papers and articles written on the topic.  Generally the focus was on the Cessna 336/337, O-2 and Defiant type aircraft.  There were also papers on a loss of engine scenario.  This got rekindled for the Voyager aircraft design and promotion.  The Voyager had a L/D of 27. And it was intended that one engine shut down in cruise flight.

The 61 knot rule for single engine is said to be influenced by crash survivability. I get that, but I will editorialize that several studies have shown that the chance of something bad happening with the loss of an engine is greater in a multi.

Top speeds, stall speeds and mass (weight) are different parameters, subject to different trades.  Furthermore, putting this into the context of existing, production or some arbitrary subset of the universe makes your question hard to answer.

The real answer is that one can design for what you need.  You can have a very slow stall speed in a single or a multi, what would you like?  You can have a nice L/D with any number of engines, what would you like?  And you can haul lots of stuff, although there are not heavy singles around. But to generalize all three parameters, of these non-linear trades, into one rubric, would likely challenge even the most mathamatically talented aerodynamcists that I know.  If you can tighten the bounds on the problem, you might get a better answer.


Is center tank fuel required to start the 737-800 engines?

(airliners.net)

Be sure to turn on the appropriate pumps on the lower-left of the overhead panel. The APU can start without them via suction.

Otherwise, it's a simulator problem.

Also see: Why are fuel tanks in the wings filled first, and why are they used last?


What causes hunting movement in helicopter rotors?

Lead lag is caused by the blades speeding up and slowing down as they flap up and down.

The blade on the advancing side experiences an airflow equal to it's speed plus the forward speed of the helicopter.  The blade on the retreating side experiences airflow equal to the speed of the blade minus the forward speed of the helicopter.  This causes dissymmetry of lift.

To counter this, the blades can flap up and down around the flapping hinges.  The blade on the advancing side flaps up, reducing the angle of attack and therefore the lift generated.  The blade on the retreating side flaps down, increasing the angle of attack and therefore increasing lift.

See this video at around 1:30 to see flapping in action.  This is a gyrocopter, but you can really see the blades flapping on this one at 0:39 and 1:17.

Due to conservation of momentum, the blade flapping up speeds up as it's centre of gravity moves inwards toward the rotor hub.  Since the rotor is turning at a constant speed, the blade must move forward around the lead/lag hinge.  In a similar way, the blade flapping down slows down so lags.

The blades will hunt forward and backwards from the neutral position in a sine wave as the rotor rotates.  Lead/lag dampers reduce the force of this hunting.

A variation of flapping hinges (independent hinges for each blade) is a teetering hinge on 2 blade helicopters where the hinge is connected to each blade.  If one blade rises, the other must fall and vice-versa.  The entire rotor disc "teeters" on top of the drive shaft.  This is known as a semi-rigid head and as far as I know, is used on all 2 blade helicopters.

In semi-rigid and rigid heads, the overall effect of the blades speeding up and slowing down cancels out in the complete cycle of rotation and other mechanisms are used to reduce the hunting loads.  Imagine a 4 blade rigid rotor.  2 blades are trying to speed up the rotor and 2 are trying to slow it down in equal amounts.

One serious side effect of lead/lag on fully articulated heads is ground resonance.  Since the blades can move forwards and backwards, it is possible for the blades to get closer together on one side than on the other, especially when the helicopter lands with a roll angle, so one gear hits the ground first.  This shifts the centre of balance away from the centre of rotation which can induce a wobble of the rotor head, which translates into a vertical "bounce" vibration at the landing gear. If conditions are right (or wrong, depending on your view point), the resonance can be amplified by the natural resonance frequency of the helicopters landing gear and can lead, if allowed to continue, to the destruction of the aircraft.

If you think that helicopter blades are quite rigid, think again.


ExpressJet IATA code before "merger" with Atlantic Southeast?

By looking at the Wikipedia article history, one finds that on 8 November 2011 (before the merger), the IATA code for ExpressJet was XE, the ICAO code was BTA and callsign was JET LINK.


Is it legal and safe to take off or land in zero visibility?

In the US, for general aviation flights, operating under Part 91 of the FARs, it is legal to take off with zero visibility (see page 2-2 of the IPH, PDF). In my opinion, it is not safe. If an emergency were to take place, you would be unable to return and land; under Part 91, it is not legal to land unless conditions are equal to or better than a runway's published approach minimums.

Unless you've got a great alternate nearby, conditions are improving rapidly, or you've got an extra engine or two, you probably shouldn't take off in conditions you couldn't land in.


Is turbulence behind an airliner less severe during cruise?

The glider in question was "in touch" with the tip vortex of the A320 only with it's tail, and very briefly:

Picture from section 1.16.2 on page 24 of the
Accident investigation report.
The glider was flying at 53kts at almost a perpendicular angle to the path of the A320, and the tail of it struck the outer third of the leading edge of the Airbus. The G103 is about 8 meters long, a wing of an A320 is about 15 meters long, so the wings and most of the gliders fuselage were never superimposed by the wing of the A320:

Picture from section 2.4 on page 39 of the report.
As the glider was traveling across the path of the A320 at almost 27 meters per second, even its tail was out of the tip vortex in a blink of an eye, and in any case, only its tail ever was in the effect of the tip vortex. As the tip vortex forms at the tip of the wing, it's diameter is initially very small, growing larger as the distance to the plane grows.
Although the small tip vortex has high energy (high velocity), as the tail of the glider was very briefly traveling through the tip vortex, it was actually traveling in pretty much the same direction as the flow of the tip vortex was. So no great forces were exerted on the tail (except for the collision with the wing, of course...).
As such this incident can not be used as an example of the turbulence or tip vortex strength during cruise (or descent, to be precise), but the the said phenomena are less prominent at higher speed and lower angles of attack (normal cruise / cruise descent). They are at their strongest during slow flight when a high angle of attack is required to maintain a desired flight path (this would also apply for situations of high turn rate).


Would one fighter pilot know that another's mask is not on?

No, there's no mechanism to check if a pilot has their mask on. It's sometimes possible to hear the difference in how muffled the sound is. Other than that, it might just be that that particular pilot has a reputation for taking his mask off when he's not supposed to, and the other pilot just assumed that's what happened.


What system is there in the UK to prevent collisions between small aircraft?

Small airplanes will be under VFR (Visual Flight Rules) which entails that the pilot looks out the window and is responsible for staying away from other aircraft and staying out of the clouds (the fog banks of the sky).

If you see another plane in your path then there are standard rules to avoid him see this question.

They can fly under IFR (Instrument Flight Rules) but that requires that Air traffic control monitors the airplane and steers it away from other planes.


What provides the greatest thrust in a high-bypass turbofan engine?

I analyzed a Pratt & Whitney F100 turbofan last semester in my aerothermodynamics course, so allow me to answer this question. The short answer: the un-compressed air provides the majority of an engine's total thrust since the compressed air powers the engine.

Correction: I forgot to mention that the fans also compress entering air. That is, all air entering an engine is compressed a bit by the fan. Some of this compressed air enters the turbojet core and the rest of the fan-compressed air bypasses the engine core. I ignored this for the sake of simplicity, but I should have explained this since you directly asked about air compression in a turbofan.

Long answer: see below!

1. The fan(s)

Air enters the engine through a fan (or fans in the case of the F100 engine). These are the giant fans with a spinning insignia in the middle that you see inside an engine.

Update: The spinning insignia clearly show if the fan is spinning so workers don't get injured.

The fan(s) increases the pressure of the air that enters an engine. Some of this compressed air is diverted around the rest of the engine and is directed straight out of the engine. The bypass ratio is a measure of how much air bypasses the "jet" core (bypass air/core air).

2. The compressors

The rest of this air is then compressed through a combination of more fans and a converging duct. The data from my thermo project tells me that this stage increases the pressure of the core air by more than 10,000%, but I'm not too sure about that*. Sufficed to say, this core air now has a lot of energy--let's add some more :D

Quick note: The compressed air now has insignificant velocity relative to the bypass air. Most of the compressed air's energy is "in" its pressure (senior SE members, please correct me if I'm wrong).

3. The combustion chamber (aka, combustor aka magic chamber)

Now the core air enters the combustion chamber. Here the air enters small chambers, mixes with jet fuel, and is ignited. The main parts-of-an-engine diagram I posted makes it seam like the combustion chamber is one big part of a jet-engine, but really the combustor consists of a bunch of smaller chambers surrounded the main shaft of the engine. Here is a gif that shows what I mean:

How the combustion chamber operates is beyond my scope of understanding, but consider that a combustor is essentially trying to keep a candle alight in the middle of a hurricane. Awesome engineering goes into designing better and more efficient (hotter-burning) chambers.

4. The turbine (aka more magic section)

Now that hot and even more energetic air enters a the turbine section which consists of a diverging (increasing in area) duct and more fans. Whereas the compress "inserted" energy into the air, the turbines draw out energy from the air. As the air enters the larger (in volume) turbine area, it expands and spins the turbine fans which power the compressors and the fan. This Back Work Ratio (BWR) is a measure of how much turbine power it takes to spin the compressors.

5. The nozzle

The still energetic core air is once again concentrated before being shot out of the back of the engine.This thrust, together with the thrust of the bypass air, propels the air forward following this model:

$F_{thrust} = \dot{m}_{bypass} \times \Delta v_{bypass} + \dot{m}_{core} \times \Delta v_{core}$

Where $\dot{m}_{bypass}$ is the mass flow-rate of air that is bypassed and $\Delta v_{bypass}$ is the change in velocity of that air as a result of the fan.

And $\dot{m}_{core}$ is the mass flow-rate of air that is combusted and $\Delta v_{core}$ is the change in velocity of the core air as a result of the fan, compressor, combustion chamber, and turbine.

The uncompressed air contributes about 60% of the total thrust. The "processed" air loses a significant portion of its energy to powering the engine. However, the compressed air still provides about 40% of the total thrust. Adding an afterburner can increase this contribution to 50%. How is this possible? Dead algae from a billion years ago.

The hydrocarbons in jet fuel pack a lot of energy into a small space and mass (two completely different concepts). Burning those hydrocarbons releases a lot of energy that powers the fan, compressors, and electric generators of an aircraft before pushing the airplane forward. This high energy in a small place/space is also why electric cars/anything weren't practical until LiPo batteries (story for another article).

I applaud you for noticing that the uncompressed air contributes to an engine's thrust. I think the term "bypass" confuses some people into thinking that this air is "thrown away". it's not. The bypassed air is actually sped up by a series of fans and imparts forward momentum to the aircraft.

I'm studying Aerospace engineering right now (Whoop!), so my excitement at being able to answer this question rather side-tracked me from your original question, but I hope you enjoy the extra info on how a turbofan operates.

Additional info

The hotter a combustion chamber burns, the hotter the core air gets and the more energy it can provide for engine operation. Furthermore, hotter chambers waste less jet fuel and result in relatively cleaner and safer fumes. Increasing CC max temps and designing the rest of the engine (i.e., the turbine blades) to handle the increase in temp is the cutting edge of engine research. This is one of the most challenging and lucrative materials science/engineering problems in the world since efficiency is paramount in today and tomorrow's aviation industry.

Here is a nice article describing how GE, Rolls-Royce, and other engine companies sell thrust, not engines. It's a big long, so you may  read it on your next flight :)


Why do some airport towers avoid monitoring 121.5?

It seems to come down to the point that as long as someone is monitoring 121.5 in a specific airspace then not everyone needs to. And it helps avoid multiple ATC facilities responding to the same call. This is from the FAA's Facility Operation and Administration orders (my emphasis):

  3-3-4. EMERGENCY FREQUENCIES 121.5 AND 243.0 MHz

  [...]

  d. When facilities are in proximity and no derogation of services will
  result, transmit/receive capability should not be provided for each
  facility. The following requirements shall be maintained:

  Geographical area coverage shall not be derogated.
  DF-equipped facilities shall have transmit/receive capability on 121.5 MHz.
  Facilities without emergency frequency capability shall have appropriate landlines for rapid relay of emergency information.

Looking at KSJC, there are a lot of other airports close by, so the potential for confusion or conflict on the frequency seems high. My guess is that they leave 121.5 to NorCal TRACON; KPAO is 10 miles from KSJC and also doesn't have 121.5 available, for example.


Which is the difference between IMA (B777) and Open IMA (A380)?

The primary difference is that the B777 is the AIMS (airplane information management system).  It is a Honeywell developed system where all the software on the systems is controlled by Honeywell (closed system).  The biggest downside to the closed system is maintenance and support.

The A380 system is a semi-open IMA system. It has a single supplier hardware cabinet with processor slices and an common operating system.  Different suppliers can develop their applications to run on the platform.

Most newer aircraft designs use the IMA architecture as it reduces the number of LRUs and saves weight.  Boeing and Airbus are going to more open systems.  B787 and B777X are open as is the A350, mainly for competition reasons.  Smaller aircraft (Bombardier, Embraer) are typically closed as they tend to have single source avionics (Rockwell Collins, Honeywell).


Why did Lockheed abandon the Constellation II?

Douglas probably already had a few commercial operators interested and close to signing orders when their tanker bid fell through.

Lockheed didn't, and decided to not dump more money into what could very well become a black hole project that'd never pay off.

And it may well be that they decided the design wasn't feasible for commercial operators. Looking at the picture on Wikipedia, almost the entire rear third of the fuselage would have no place to fit doors or windows, making the aircraft useless for passenger operations.

And the air cargo market at the time was a lot smaller than it is today and still saturated with former military aircraft retired after the Korean war and WW2.


How does a wing mounted jet engine on a supersonic airplane prevent the interference in the flow due to Shock?

Flow conditions are not so different, only the reaction of the flow to an obstacle is. By shaping the intake appropriately, supersonic flow is handled easily, and shocks will be helpful in decelerating and compressing the flow.

However, supersonic flow demands sharp intake lips which are hit by the flow at the right angle, otherwise drag rises quickly to intolerable levels. These sharp lips will cause flow separation in subsonic flow when hit by the flow at an angle, so aerodynamic tricks like bypass doors need to be added to the intake to keep flow angles at the intake lips in check.

Note that the intake will ensure a flow speed around Mach 0.5 at the compressor face of the engine, regardless of flight speed. Therefore, the engine will not need to be optimized for supersonic flight. However, to keep its frontal area low and the nozzle speed high, its bypass ratio should be low. The only troubles this causes are increased engine fuel consumption and noise.


The ATC is unable to provide radar service to pilots, what's the standard way to inform this?

Without checking the Controller's Handbook, what I hear most often are two things:
a. Standby and remain clear of class [b, c] airspace, for VFR operations.
b. (surveillance) radar services not available, squawk xxxx, report yyyy
c. Radar out of service, N1234, radar service terminated.
An example of b was when going to an airport near DCA, radar was out of service.  The controller handled my flight but relied on talking with a controller from Baltimore. This was a few years ago, and I now understand that the remote radar can be transmitted to other controllers taking a remote controller out of the loop.
The ATC Handbook is FAA JO 7110.65W, https://www.faa.gov/documentlibrary/media/order/atc.pdf
Radar can be limited due to equipment outages, and also the display available to the controller.  For example tower displays are for orientation and not certified for separation and other services.
The order states that controllers may advise that:
PRIMARY RADAR UNAVAILABLE (location)  or
RADAR SERVICES AVAILABLE ON TRANSPONDER EQUIPPED AIRCRAFT ONLY
Since there are many conditions for radar not being available and since an aircraft can be in various states (VFR/IFR, approach, visual approach, etc.) it would be best to consult the Order for the recommended phraseology.  It is noteworthy that CONUS radar coverage has improved since the Order, and as a result there is often backup coverage for many locations which could influence services which can be offered.
Finally, operationally ATC still has local and regional variations, which may influence the options and corresponding phraseology utilized.


Global

Starting from the top, we find the International Civil Aviation Organisation (ICAO), which is a United Nations agency. ICAO was formed in 1944 when the Chicago Convention was signed, and initially had 52 member states. Today, 191 states worldwide are members of ICAO. The headquarter is in Montreal, Canada, and there are 7 regional offices.
ICAO standards and other provisions are developed in the following forms:

Standards and Recommended Practises (SARPs):

Technical specifications adopted by the Council of ICAO in order to achieve the highest practicable degree of uniformity in regulations, standards, procedures and organization within air navigation. Member states will conform to standards and will endeavour to conform to recommended practises. States are invited to inform ICAO of non-compliance.

Procedures for Air Navigation Services (PANS)

PANS comprise operating practises and material too detailed for SARPs. They are suitable for application on a worldwide basis. Member states are invited to publish differences between national procedures when considered important in the interest of safety.

Regional Supplementary Procedures (SUPPs)

SUPPs are supplementary procedures which are only valid within one of the ICAO regional office regions. For example, there are supplementary procedures published only valid within the European/North Atlantic region.

Also worth mentioning are the International Telecommunication Union (ITU) and the World Meteorological Organization (WMO), both of which function on an (almost) global level.

Regional

Below ICAO we have regional organisations. As an example, in Europe, the European Union (EU) provides legislations for its member states. Non-regulatory organisations, such as the European Aviation Safety Agency (EASA), assist the EU in developing regulations (but the EU, not EASA, is the regulatory authority).

Some areas do not have regional regulators like the EU. In such areas, national regulations are handled directly by national regulators. Within the EU, countries also have national regulators – but they are bound to base their regulations on EU regulations.

National

Below the regional level we have national regulators, commonly referred to as civil aviation administrations (CAA). Each country will have their own CAA. One that you will often hear about is the Federal Aviation Administration (FAA), which is the national regulator in the USA.
Generally speaking, a national regulator will be following framework regulations published by the national ministry of transport. The term ministry of transport is also sometimes applied to the departments or other government agencies administering transport in nations who do not employ ministers. The framework regulations from the ministry of transport are largely based on ICAO SARPs, PANS, SUPPs and any regional regulations (such as EU regulations).

The national regulator will publish detailed regulations, which are adapted by the air navigation service providers, as well as airlines, pilots, air traffic controllers, maintainence companies etc. etc.

The service providers, commonly referred to as ANSPs, are the organisations actually providing air navigation services, such as communication, navigation and surveillance equipment, meteorological services, air traffic management (including ATC), aeronautical information and search and rescue. Most ANSPs operate within a single nation, but there are also multinational ANSPs, a few examples are ASCENA (Africa and Madagascar), COCESNA (Central America), EUROCONTROL (Benelux) and NUAC (Sweden and Denmark).

The service providers work together with the national regulators to develop detailed procedures, but do not (usually) have any regulatory authority.


Is it the tower's purview to recall an aircraft from the runway for loading the wrong cargo?

Yes, the tower can tell an aircraft to abort take off and instruct it to return to the gate, although it probably never got that far in this case, I'm guessing that they got to the runway or were asked to line up when the request came in. This was probably at the direction of Ryanair, since the tower would otherwise not have any information on the wrong cargo being loaded, nor would it really care.

I'm guessing at this part....

The back-and-forth probably went like this:

  Tower: Ryanair 1234 line up and wait
  Ryanair: Line up and wait, Ryanair 1234
  Tower: Ryanair 1234 taxi on runway to Delta, call company
  Ryanair: Taxi delta, call company

The tower probably didn't relate too much information about what is wrong, the pilots have the ability to talk to the dispatcher for Ryanair to get more information.

Regardless, a tower controller can tell an aircraft that a take-off clearance is rejected, even after the take-off run begins. It is up to the pilot to determine if they can safely reject the take-off and to follow those instructions.

The probability though that the tower knew that the incorrect cargo was loaded is probably zero, at least until somebody from Ryanair called them and had them stop the take off. I'm guessing that they didn't actually get take-off clearance (line up and wait is not take-off clearance) and either they were asked to line up, or they were waiting to enter the runway before they were told to go back (and taxiing on the runway is the easiest way to turn around).

Typically Tower will not call a RTO unless there is a safety concern like an incursion or they notice a wing fell off. Once clearance is given it is rarely rejected. If they had gotten clearance Tower would probably have advised them to call company "once in the air" rather than reject a take off.

If you want to know what it sounds like for Tower to reject a take-off, listen to this YouTube about a near miss regarding similar call signs and two aircraft taking off at the same time.


Which small, light aircraft are suitable for operating at very high elevations?

Yeah that location is going to present you with a lot of problems, most notably with density altitude and mountain flying.  This is also going to depend on the airports and runway lengths available as well as obstacle clearance altitudes for the area in question.  Most likely it's going to be a turbine powered aircraft which is pressurized for comfort and features good Short Takeoff and Landing (STOL) characteristics and soft field operations.

This question will probably be put on hold shortly, primarily because it is opinion based, but I would recommend a Quest Kodiak or a Pilatus PC-6 for the role due to meeting most of that criteria minus being non-pressurized.  You would just need to provide supplemental oxygen for the crew and passengers during the flight.  Another aircraft which would be recommended is a Pilatus PC-12 or the soon to be released Cessna Denali as they meet all of these needs albeit is a bit larger and less capable as a STOL aircraft.


During autoration, does it help to pump the cyclic to increase the RPM?

Cyclic pumping will likely degrade your performance

As explained here, it leads to rotor inefficiencies

  As far as moving the cyclic around goes it destroys lift as the TRT
  vector is all over the place and not acting in one place or close too
  it and more power is required

What is this TRT he's talking about?  Total Rotor Thrust

  In a still air hover, TRT is, in broad terms, equal and opposite to
  weight. As the disc is tilted to commence a transition into forward
  flight, the TRT vector is tilted and must be increased so that its
  vertical component remains equal to weight if level flight is to be
  maintained.

With the above in mind, pumping the cyclic with the engines working simply means that you need more power from your engine to keep your Nr up to fly, as you are being inefficient.

If you have no power, pumping the cyclic is counter productive to your efforts at maintaining Nr since the back and forth creates sequential inefficiencies, and more drag but you have no engine to restore Nr... and in the situation you describe, your precious Nr is a critical resource to your walking away from the forced landing or crash.

Depending on what is happening, a slight turn or flare (aft cyclic, not foreward) may load the head and preserve Nr a bit so that it's still turning with enough inertia to help you as you near the ground and need that cushion from the collective as you hit the ground.  Each bit of Nr you retain for that last pull is critical, in that situation.

It's a tough one, the low speed, not-quite-inside-the-Hv-diagram scenario that you presented.

Consult the manual for your model helicopter, and the H-V diagram.  Know your limitations.


How to calculate the required motor power and rotor size with respect to the weight of quadcopter?

The most important thing to remember here is the Purpose. For what purpose do you want to use the Quadcopter?

That being said , let’s start with the very basic .

Required Thrust = ( Weight x 2 ) / 4

In order to choose a motor  you need to determine how much weight you are planning to take, and then work out the thrust required to lift the quadcopter .Also , when purchasing motors  you need to consider Watt’s and Efficiency as well apart from Motor KV and Thrust.The higher the Efficiency, the better it is.The manufacturer/seller of Motors will provide the specifications about the Motor. This will help you to find out the thrust,power, rpm etc of the motor.

http://www.hobbyking.com/hobbyking/store/__28675__D2830_11_1000kv_Brushless_Motor_UK_Warehouse_.html?strSearch=1000kv

Quadcopters have 2 clockwise(CW) and 2 counter-clockwise(CCW) propellers and it has two flight configurations. X config and + config. In X config two arms will face front side while in + config only one arm will face front side. If you are making Quadcopter with plus config you can tune your quadcopter easily by  single axis tuning method .

Single Axis PID Tuning A Quadcopter

Increased propeller pitch and length generally  draws  more current. Also the pitch can be defined as the travel distance of one single prop rotation. In other words, higher pitch means slower rotation, but will increase your vehicle speed which in turn will use more power.If your intention is to do acrobatics, you will need torque propellers which provide more acceleration and it puts less pressure on the power system. Lower pitch propellers will also improve stability.A higher pitch propeller moves greater amount of air, which could create turbulence and cause the aircraft to wobble during hovering. If you notice this with your quadcopter, try to choosing a lower pitched propeller.

http://blog.oscarliang.net/how-to-choose-motor-and-propeller-for-quadcopter/

You may also choose to use this below Quadcopter Calculator. You can dial in everything from motors to props to ESC.

http://www.ecalc.ch/indexcalc.htm


What is the resolution of airport ground radars?

For surface movement radars (SMR) operating in the 9 - 9,5 GHz band, the pulse length is typically in the order of 40ns. This is equivalent to 12 meters. That would bring the theoretical minimum range to 6 if we ignore transmitter / receiver switching overhead time.

In practice there is no need for such a short range. Instead a pulse train is transmitted before the antenna is switched from the transmitter to the receiver. This allows the radar to increase the accuracy by averaging multiple reflections, at the price of an increase in minimum range. Typical minimal range will be in the order of 100 meters.

Other SMR systems use continuous wave radar and have a transmitter and receiver antenna in the radar head. These systems don't require to switch between transmitting and receiving and don't have a minimum range.

The range resolution is in the order of 3 meters, equivalent to the pulse rise time of about 10ns.

The azimuth resolution of a typical SMR is in the order of 0.25 degrees, which is equivalent to 10 meters at 2 km distance.

Apart from primary radar there are other classes of surveillance systems in use for airport surface detection.

Secondary surveillance radar (SSR) lacks the accuracy of the SMR and
can only see transponders. But combined with the primary radar allows
for identification of aircraft on the airport surface (i.e. putting
identification labels on the aircraft's primary radar reflection).
Multilateration (MLAT) systems also rely on transponders but are more
accurate than SSR for surface monitoring. These systems require a large number of receivers and are susceptible for radio reflections from buildings.
ADS-B relies on the aircraft (or airport vehicle) transmitting its
position, speed and heading.


What is the purpose of the hold at JNC on the Grand Junction Seven SID?

If you look at the chart, you'll see that after takeoff you will arrive at JNC from either the east or the northeast. Transitions then proceed back in an easterly direction (045 to 113 degrees).  With the possible exception of the Rwy 29 departure with the BRICK transition, the SID requires a course reversal at JNC. The charted hold provides a means and protected airspace for the course reversal.

And as you surmise, some aircraft may require climbing in the hold to reach the MEA.


Why would an F16 battery make a buzzing sound?

The relevant part from the video description that you referred to:

  You'll here a buzz, thats the battery, then you'll here it spooling thru N (nancy) stages.

The word "spooling" does not refer to the battery, it refers to the engine. The battery is static and does not spool.

There are several measurements or indications used to convey a turbine engine's state. One of them is N2 (others include N1, Engine Pressure Ration, Exhaust Gas Temperature, Interstage Turbine Temperature and several others).

Back to the video description. In this case I believe the author was referring to the N2 measurement that raises ("spools") and needs to be monitored during engine start.

N1 is the low-pressure compressor speed, and N2 is the engine's high-pressure compressor speed (both usually expressed in percentages rather than actual RPM).

More information about N1 and N2 can be found here: What are N1 and N2?


When extreme yoke movement cuts out stab trim on a 737-NG, does it stay off after yoke returns from limits?

From the Boeing 737 NG FCOM v2 (9.20.8 Flight Controls - System Description):

  Control column actuated stabilizer trim cutout switches stop operation of the main
  electric and autopilot trim when the control column movement opposes trim
  direction. When the STAB TRIM override switch is positioned to OVERRIDE,
  electric trim can be used regardless of control column position.

So any opposite movement of the yoke will stop the stab trim. There is nothing mentioned in the FCOM about staying off, so I would assume stab trim would continue immediately after the yoke is released.


How does a jet fighter landing flare compare to a civilian plane?

It all depends on the aircraft for specific handling qualities, but for the most part they are flown just like any other large turbojet aircraft.

Some things to keep in mind about their specific handling:  Jet fighters with the thin, low aspect ratio wings are really power dependent and glide about as well as a brick.  Therefore they will be flown with power all the way to the runway until the roundout commences.

Like other large jets, fighters are flown at optimal angles of attack, the speed at which to achieve this is dependent upon the aircraft's landing weight.  This can vary between 110-160 or so knots depending on the aircraft in question.  The optimal angle of attack is available to the pilot in the form of an optical AoA indexer and either an AoA indicator or a graphic reference in the pilot's head up display (the 'E' Bracket).

Pilots will line up for final at Vref + 10 kts or so, align with the optical glideslope eg PAPI, etc and establish the optimal speed for the approach and power settings.  An ideal sight picture from the jet will be to line up on runway centerline, have the Flight Path Marker in the HUD aligned with the PAPI or numbers and the E-Bracket centered on the flight path marker.  Power corrections should be made to hold this sight picture as needed; in the case of a fighter, gently walking the throttles should be all that is required.  Roundout will be commenced considerably higher than one would in a light GA aircraft so that the jet arrives at the correct roundout altitude of 1-2 feet and correct attitude for the approach, once the roundout commences, power will be pulled to idle, allowing the jet to gently settle on the runway.  Flaring is not done quite like a commercial jet due to the difference in handling characteristics between the two due to the high wing loading, stores drag and a few other features found in fighters.

Most terrestrial based fighters are flared; naval fighters are often not and are flow to impact with the runway so the pilot can maintain proficiency in the techniques required to do arrested landings on aircraft carriers or log practice approaches with FCLP or Field Carrier Landing Practice.  Even terrestrial air forces who operate naval fighters in their air force - one I can think of right now is the Canadian Air Force - teach no flare landings to their pilots; not surprising as the CAF CF-18 syllabus was copied and adapted from the USMC F-18 training syllabus from MCAS Cherry Point.


Why would a copilot's window be shaded/covered?

Aircraft flight decks can become very warm at times and pilots will always try their best to avoid letting the sun add any additional heat.

Most aircraft have sun visors or sun screens as part of the flight deck equipment. These are usually a clip-on design or pull-shade design. Both types are translucent and can be left in place for all phases of flight.

Many pilots will also bring their own temporary sun shades to use in the flight deck. Theses can be translucent or opaque. Many pilots even use their charts as temporary make-shift shades while parked at a gate in the blaring sun.

Since you described them as reflective covers, I suspect what you saw may have been some kind of temporary shade supplied by the company. They would not be used on the forward windscreen so they would be safe to use during taxiing.

Here are some examples of a pull shade being used in an ATR 72.

Here is an example of what looks like a reflective shade.


Why is a reduction in lift called 'drag'?

Induced drag is unrelated to leaking and vortex creation. It exists even in a wind tunnel where the wingtips touch the walls and thus prevent leaking and vortices.

Then what is induced drag? To create lift, the wing needs to be at some angle with respect to airflow (or be asymmetric), so the force vector points mostly upwards but also somewhat aft. Forces that point aft are generally called drag. Induced drag is thus a 'real' drag, not a reduction in lift.


What causes descending aircraft to make a noise like a giant blown bottle?

Short Answer:

The sound is caused by airflow across holes on the underside of the wings of certain aircraft.

Long Answer:

I too have noted the sound phenomenon that you describe. This video has a great example between 0:26-52 (link starts playback at 0:26 where the noise starts):

I will readily admit that this answer is mostly just a compilation of what I have learned researching this. Your question intrigued me and I've enjoyed learning about it!

As I discovered as I started researching this, many others are familiar with the noise as well. This article on Airliners.net had a lot of discussion about it, starting with a lot of interesting—but ultimately flawed—theories.

But, that thread led me to the answer to your question, which is: the sound is caused by the "circular opening used to equalise the pressure in wing fuel tanks", according to Euractiv.com

This article on AirportWatch further explains:

  The Airbus 320 series of aircraft, [...] have been known for many years
  [...] to have a particularly irritating high pitched
  whine. This is caused by air rushing across the under-surface of the
  wing, where there are Fuel Over Pressure Protector (FOPP) cavities.
  This generates noise, in the same way as blowing air over the mouth of
  a bottle. Every A320 series aircraft emits a signature howling noise
  while approaching to land. It is heard most when the plane is
  travelling at around 160 knots, and the frequency is around 500-600Hz,
  which is close to peak sensitivity of the  human ear.

That being said, there is apparently a fix to that problem, as both the aforementioned links describe. As Euractiv.com explains, the fix is a vortex generator:

  a 5-cm triangular piece of aluminium sheet metal upstream of the two
  vents on each wing, in order to divert the air flow and stop the
  whistle. A decade of research went into the vortex generator, which
  stems from efforts to mask a similar whistle produced when air blows
  over the gun ports of warplanes.

This image shows both the FOPP hole, and the VG that softens the sound:

[Image Courtesy of Lufthansa]

Read the articles linked, interesting stuff therein!


Why does this calculation show Gustave Whitehead's propellers were more than 100% efficient?

The equation you referenced shows prop diameter squared, divided by 2, not 4.

Even then, the calculation shows that marketing is to experimentation as about 2:1 :)


What types of wood can be used for making propellers?

Historically, the following woods were used:

Mahogany
Walnut
Oak

Almost all wooden propellers are reinforced to add strength. Fabric or metal coverings can be added too.


Is there a specific relation between sideslip angle and yaw rate OR how sideslip angle depend on yaw rate?

Since, yaw rate is controlled via rudder

No, yaw is controller by many things, and rudder is there mainly to compensate for them to keep the plane flying nose-forward.

The usual way to make a control system is that you control (with a PID controller):

Move elevator to target vertical (plane coordinates) acceleration.
Move ailerons to target roll rate.
Move rudder to target zero lateral (plane coordinates) acceleration. Lateral acceleration is measured by the ball in traditional cockpit.

Note that each axis is basically independent and rudder is only used to eliminate side-slip, which is proportional to the lateral acceleration unless you have asymmetric thrust or drag—and I have not heard of a FBW that would automatically correct for those conditions.

When flying with auto-pilot, the auto-pilot sets vertical speed target from altitude error and vertical acceleration from vertical speed error for the pitch and it sets roll from heading error and roll rate from roll error for roll axis. Autopilots don't set lateral acceleation targets at all—that is always zero.

That is why auto-land has much lower cross-wind limit—autopilot does not handle rudder, so it can't de-crab.


What does mean 'GS' in RNAV (GPS) Chart?

Are you asking about the specific term 'GS'?  I don't see that on the chart in your question.

The angle symbol and the 7.75 are explained as a Visual Descent Angle in the Chart Users Guide.

  A VDA and TCH may be published on non-precision approaches. For Copter approach procedures, a Heliport Crossing
  Height (HCH) will be depicted in place of the TCH. The VDA is strictly advisory and provides a means to establish a stabilized descent to the MDA.

So it is an aid for maintaining a stabilized approach that should put you at the MDA at the correct point.

  If the last one's word is true, an airport have a 7.75 GS, like a KSBS Airport, then the PAPI of KSBS airport indicates 2white-2red when I follow the 7.75 GS ?

No.  In fact it's called out on the chart: "VGSI (Visual Glide Slope Indicator) and descent angles not coincident".  So they do not match.  You can look in the chart supplement for the airport and see what the actual angle is.  For KSBS runway 32, the Glide Angle (GA) is 4 degrees.

  RWY 14–32: H4452X100 (ASPH–GRVD) S–50, D–60 HIRL

  RWY 14: Rgt tfc.

  RWY 32: REIL. PAPI(P2L)—GA 4.0º TCH 40´. Thld dsplcd 600´.


What is the function of the tail section on a fixed-wing aircraft?

First off lets be clear that a tail section does the same thing on small aircraft that it does on large aircraft.

Second off lets be clear that a tail section is not necessary for flight and there are planes like the Northrop Grumman B2 that dont have a tail section they are affectionally called "Flying Wings".

The short answer is that the rudder (vertical part) controls yaw and the elevator (horizontal part) controls pitch. A plane is capable of movement and similarly adjustment in all 3 dimensional axes. But lets dig in a bit:

The Elevator: This is usually located in the back but by no means has to be. Burt Rutan has implemented many designs that have forward mounted elevators. As to functionality they essentially allow you to alter the pitch of the plane which in turn alters the angle of attack of the wing which furthermore has a direct effect on the lift generated by the wing. In a simple world we could say that when you pitch up you climb and when you pitch down you descend. The reality is that the engines thrust plays a large factor in this. For example if you are flying at a level attitude and increase thrust your will increase speed (and the speed of air over the wing) which will generate greater lift and cause the plane to elevate with out a pitch increase (you will have to apply some force to keep the plane level though). The elevator provides a way to easily alter the pitch of the plane (and angle of attack) so you can climb when you want. Generally speaking you will also add power for the climb. For a more lengthy explanation check out the wikipeidea article.

The Rudder: The rudder is mainly to control the left-right yaw of the aircraft. In a single engine prop plane this can be used to help overcome the left turning tendencies created by uneven force of a spinning prop (P-Factor). In a more general case the rudder is often used to correct yaw when a heavy crosswind is present on landing. It is also used in flight to ensure your turns neither skid or slip (stay coordinated) remember "Step On The Ball". For more reading check out Wikipedia

This picture shows the axes of movement pretty well.


What happens when VFR conditions change over a longer flight?

You wrote:

"you should not continue your flight using VFR, but you can't land"
"and the smaller airports around you are not currently staffed."

Why can't you land?   If you can't land, you should not be flying!
Why do you need an airport to be staffed to land there?
Pilots land at unstaffed airports all the time following CTAF (Common Traffic Advisory Frequency) procedures.

If weather conditions are deteriorating below VFR minimums, then landing at an airport is 100% an appropriate course of action.


Why do GA pilots in Europe operate N-reg (US) aircraft?

It's usually cheaper to go to the US and earn an FAA license and then fly N-registered aircraft in Europe than it is to get a European license. However, an N-registered aircraft needs to be maintained to FAA standards by FAA licensed mechanics.


Other than a handful of airlines, do any small operators take PPLs and pay to train them to commercial?

With the airlines that do offer such programs, the cost is offset by having a pool of new pilots who they can train to their liking from the start rather than having to retrain existing pilots. They also tend to be large operations for whom the cost of having some trainees on staff isn't a major factor.

For a small operator it's typically too expensive to carry the burden of your training cost as well as employing you while you can't fly commercially (which you won't be able to unless you've completed that training.

So unless they have an opening for a non-flying job you can do, with training provided as part of your payment for that job, they won't be able to employ you.

As most jobs tend to require training and certification that involve aircraft, such a job would almost certainly be something like a desk job, answering phones, cleaning, stuff like that, not something someone interested in a flying job is likely to greatly enjoy, increasing the risk to the company that the candidate is going to quit on them.


What are the points 1864 and 1922 on this in-flight map?

The number may stands for the year of the ships sunk.

1864 may correspond to CSS Alabama (Arabic: ألاباما), a Confederate States Navy Screw sloop which was sunk on June 1864 at the Battle of Cherbourg. The wreck is at 49°45′9″N, 1°41′42″W.

1922 may correspond to SS Egypt (Arabic: مصر), a British ocean liner which was sunk after a collision with SS Seine on 20 May 1922. The wreck is located near 48°10′N, 5°29′W.

As @mins mention in comment, there are other wrecks appearing on the map in IFE, including Mary Rose 1545 near Portsmouth and San Pedro de Alcantara 1786 near Peniche.


Why does Boeing 247D have reverse slope windows when they were removed from the D models?

The Boeing 247D, DZ203 has construction number 1726 and was built in 1933.
The first production Boeing 247D produced made its first flight on September 5. 1934 and was scheduled to be delivered to United Air Lines late September 1934. (It didn't enter service with United immediately, instead it participated in the 1934 MacRobertson Race first, where it finished third.)
So DZ203 was built as a standard Boeing 247, and then later converted to the 247D standard. In the conversion the engines, cowlings and propellers were changed, but the windshield remained in its original style. This was common for 247D conversions.


How do a narrow airframe and canards keep supersonic shock waves from coalescing?

After a lot of digging around, I found this.

  ...the main noise-reduction technique is to redesign the aircraft to
  reshape the acoustic signature. A sonic boom consists of a double bang
  on the ground that is caused by two large pressure pulses. As the
  random shockwaves travel away from the aircraft at the speed of sound,
  they pile up and coalesce. The engineers aim to reshape the acoustic
  signature of the boom by preventing sonic waves piling up.

  “You shape every aspect of the airplane to make the shockwaves as
  close to equal strength as you can. When they’re as evenly distributed
  as possible along the length of the airplane, changes in temperature
  are small and the waves don’t coalesce. When the signal reaches the
  ground, it’s smeared out. Instead of two loud bangs, there’s a
  pressure change and a soft thump,” says Peter Coen, NASA’s commercial
  supersonic technology project manager.

Source: Aerospace Testing International, Dec 2018: Supersonic testing: Boom or bust?

I realize this doesn't answer the question of the physics, but I thought i would stick within my paygrade. Someone else who better understands what the fluid is doing can tackle explaining that.


How do airlines pay air crews for an aborted flight, in general?

How the Swiss Air pilots got paid would, of course, depend on Swiss Air policy. I suspect pay policies vary greatly between airlines and countries, but for what it's worth below are the pay policies for the four airlines I worked for in the 1980s and 1990s. At all four I would have been credited with only the time from push back until the parking brake was set on return insofar as flight time was concerned, but as you will see that wouldn't have made any significant difference in my pay.

commuter #1 no union -- a straight salary but with an hourly addition if your flight time went over a minimum, which it never did.

commuter #2 no union -- a straight salary regardless of the number of hours flown, but they never abused that.

747 freight carrier no union -- a straight salary plus an hourly addition if your flight time went over a minimum, which it occasionally did.

747 passenger carrier in-house union -- flight time hourly pay with a guaranteed minimum. You always went substantially over the minimum. They tried to get you as close as possible to the regulatory max of 1000 hours a year. Additionally, they had a policy that whenever your duty time (as opposed to flight time) went over 16 consecutive hours, you got paid for each hour over that at a rate of 1.5 times your regular hourly flight time rate. Also, you were paid half your regular hourly flight rate while deadheading. Then, if you had less than 8 hours (I might not be remembering that number correctly) between assignments, your duty time continued. My first assignment for this airline was a 32-hour duty day. I operated from JFK to AMS (Amsterdam), so my duty time started at show time, 2 hours before departure. At Amsterdam 5 hours on the ground then commercialling (riding in the back on another airline) to SIN (Singapore) and then to CGK (Jakarta) positioning for a Hajj flight. Crew scheduling regularly abused pilots, but nobody complained because you were being so well paid when they did abuse you.

The breakdown for hours at the flight time rate for that trip was approximately:

7.5 hours operating time JFK-AMS
8 hours deadheading pay AMS-SIN-CGK (half of 16 hours riding in the back)
24 hours extended duty pay (32 hours duty time minus 16 hour threshold times 1.5)

So, 39.5 pay hours at the regular new first officer rate of 55 per hour = 2,172.50, which looked pretty good to me since I had come from a carrier than paid me a straight 4500 per month salary as a 747 captain.

I can't remember all the flight time/duty time details, but back then at least the international rules were much less restrictive than the domestic rules.

Also, back then it was common practice to do things like scheduling a flight for, say, 11:59 for regulatory purposes, when everyone knew it would go slightly over the 12-hour international rule of the time.

It may be worth noting here, that the mind-set of the crew, at least the cockpit crew, is totally different from that of passengers. The passenger wants to get from point A to point B, whereas the crew is simply 'at work' regardless of whether they go anyplace or not. Consequently, at least in my experience and opinion, delays aren't nearly as frustrating to crew as they are to passengers.


Can a CFI provide endorsement training to non-US citizens without TSA approval?

Assuming the crux of this question is about the need for TSA clearance for the training then the answer can be found in the FAQ section of the flight school candidate website under the question;  When is a flight student exempt from the requirement to undergo a TSA security threat assessment?

You will see a table with some exemptions including the 14 CFR §61.31(g) exemption. The table is prefaced with the statement;

  Other training activities that do not require notification to TSA are
  exempt only if the candidate holds an FAA stand-alone Pilot
  certificate

In other words a pre-existing FAA pilots license acts as some what of a verification and you do not need to be re-verified.

Interestingly only 14 CFR §61.31(g) is exempt so presumably only the high altitude sign off can be obtained under this exemption the rest of 14 CFR §61.31 does not fall under it. I would say the AOPA site is incomplete in their information.  A CFI may provide training for 14 CFR §61.31(g) without TSA authorization but if the student is seeking training on any other endorsements under 14 CFR §61.31(g) then they must get cleared by the TSA.


What are the rules in the UK about attaching a GoPro camera to the outside of an aircraft?

Flyer magazine had an article on this recently. I've not been able to find the full article on their website, but I have found this which at least partially answers your question.

https://www.flyer.co.uk/gopro-camera-mounts-to-be-approved-by-engineer/

From the article, which was published in Feb 2016:

Mounting a camera is a modification, and requires either inspection from a Part66 licensed aircraft engineer, or via the CAA as a minor modification.
To approve any installation the engineer will need to complete a maintenance release checklist and complete the aircraft logbook entry.
If your aircraft is overseen by the British Microlight Aircraft Association or Light Aircraft Association, then their restrictions apply (but it doesn't say what those are).

It also references CAP1369, which is the CAA document covering mounted cameras. I'm including a link to that here.

CAA CAP1369


If a helicopter's tail rotor fails, is it possible to perform an emergency landing?

Although I used to think this was impossible, I now believe this can be done using weathervaning.

At a fast enough forward speed, the airflow will naturally keep the helicopter facing in that direction. For an example of someone doing this in reality, for an almost identical time period that OP requested, see this link:

http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10493099

According to the link, he needed to maintain 80 knots forward speed to prevent it from rotating out of control. Note whether this is possible may well depend on the weathervaning charactistics of the particular helicopter.


What could lead to engine running hot on climb out?

I'll provide a bit of a general answer to this so it covers for most cases. The basic question is, "my engine is running hot on climb out, what issues could lead to this"

Cooling Air: Airplane piston engines are air/oil cooled and require proper airflow over the engine to cool properly. A poorly installed cowling or obstructed/damaged air inlets can cause airflow to be incorrect. Some aircraft also have some internal baffling to direct air around the engine bay, these parts can move or get out of place and may be causing improper flow.

Fuel: As JScarry mentions, you need to ensure you have proper fuel flow (which is key to temp control). If you don't have a flow meter installed a shop should be able to check this for you.

Procedure: This sounds like a new plane to you, are you following all book procedures for climb out? Turbo planes often have different op-specs than their NA counterparts. Its not uncommon for there to be full power limitations (e.g. full power 5-min continuous limit then reduce to XX MAP).

Timing: You may have a faulty magneto or your magnetos may be improperly timed causing an advanced ignition situation that would add stress (and heat) to the engine.

Auto-Turbo Settings: I believe the Turbo Toga's had self governing turbos but not all planes do. You should make sure the pop-off mechanism is set correctly and the turbo is operating with in its proper limits.

Set-Up: This is unique to your new engine case but it may be worth bringing in another A&P that is familiar with the Toga Turbo engine and set up to make sure everything is where it should be just in case the engine shop overlooked something.

Incorrect Indication: To add to "Set-Up", it's possible that your CHT is incorrectly calibrated or installed. (this is an edit from another poster, who experienced high oil temps to finally discover that the oil temp thermocouple was in the wrong location, and read higher than actual temps)


Why is a 0 kt, vertical climb in a helicopter not safe near the ground?

A vertical take-off, known as a "towering" or "confined area" take-off, is normally only used when it is not possible to take-off and remain in ground effect before gaining speed and climbing away.

For example, your operational need is to land in a clearing in a forest or perhaps a field surrounded by tall trees. In order to take off again, you need to  climb vertically until you've cleared the tops of the trees so that you can transition forward to gain speed.  You might need to use on at night (because you cannot see if there are any obstacles ahead) or when taking off from snow or sand when your vision will be obscured, making a vertical take-off safer.

It is technically defined as any take-off which requires you to climb vertically until out of ground effect.

In this answer, I've discussed the reasons why the power required to transition in ground effect to forward flight is much less than that required in a hover or a vertical climb out of ground effect.  Before attempting a towering take off, the pilot should conduct a power check to establish that they have enough power to hover OGE (out of ground effect).  If you do have enough power to hover OGE, then in theory, you could continue to climb vertically until the reduction in engine power output or lift (small effect) as you gain altitude reduces the power margin to the point where further climb is not possible without exceeding limits.

So, to the point of your question, why is it not safe?

The main reason is a scenario which is common to all helicopter operations, not just a towering take off.  Climbing vertically to 90 feet is exactly as dangerous as coming to a 90 foot hover in an arrival from forward flight.

This scenario is putting yourself into a shaded area of the height velocity diagram, known by pilots as the "avoid curve" or perhaps more accurately the   "dead man's" curve.  Importantly, this has nothing to do with how much power you have which of course, if the engine stops, suddenly becomes zero!

Source: Copters.com

In short, test pilots, using a fully loaded helicopter over level, prepared surfaces, try to enter auto-rotation from different combinations of height and speed.  At some point, they look at each other and say "a normal, well trained pilot, could only just auto-rotate safely from that combination of height and speed.  They plot these points on a graph, join the dots and say "see those shaded areas, don't go there".  It represents the areas where you will not have enough of the combination of potential and kinetic energy to make a safe landing.

As you can see, the towering take-off puts you deep inside the avoid curve.  This is the first safety concern.  If the engine stops, you will almost certainly crash.

I chose that curve, for an Enstrom F28, because it nicely illustrates that if you continued climbing vertically to 300 feet, you would pop out of the  top of the curve.  From this height, you could auto-rotate safely.

The second safety concern goes back to the power required. If you run out of power during the climb, the aircraft may start to descend into its own rotor vortex and can enter a vortex ring state.  In a confined area, you have no options for escaping it and certainly, all but the best pilots will not avoid a crash or, at best, a very heavy landing.  I'm a relatively low time private pilot and when I do my power checks, I want to see at least a 10% additional reserve over the measured power check.  There have been times when pilots have landed in confined areas but have then not had the power to hover OGE.  They have had to reduce the weight and/or wait for a lower temperature before trying again.

The third safety concern is the need for good skills and training.  When performing towering take-offs in typical sport and private helicopters, the pilot must be gentle on the controls. Relatively large or rapid control inputs cause large spikes in the power required. When you have plenty of speed, this doesn't really matter but when climbing vertically, you might be calling for more power than is available.  You must climb OGE slowly with gentle collective increases and, when clear of the top of the trees or other obstacle, ease the cyclic forward gently.  It is this last input which is especially risky.  If you push the cyclic forward as you would in a normal take off, you could find yourself running out of power and settling into the top of the tree with nothing left to give.  The safe way to do it is a slow climb but obviously, this leaves you in the shaded area for longer.  I was always relieved when I cleared the trees and got back into normal flight and the temptation, which must be resisted, is to increase your climb rate to reduce the time on the curve but of course, this reduces your power margins. The general principle is to use the power required and no more.  Gentle climb, gentle movements, be ready to pick up wind as you clear the obstacle, and you'd better have made sure before you get there that it's a head wind.

The fourth safety concern (and the last one to my knowledge) is not so immediately dangerous but can lead to trouble.  In a helicopter without a large power reserve, it is possible to reach a point where the power required exceeds the power available, especially if you catch a gust of wind. In this situation, the rotor RPMs will start to reduce or "droop". The only possible response is to lower the collective.  This normally means you have to give up and simply land and try again as above but any situation which leads to the rotor RPM dropping outside your control is to me, a safety concern.

All of this said, some pilots spend a lot of time operating in the shaded areas, for example in logging and power line check operations but they are appropriately trained, use machines chosen to reduce the risks, pay more insurance than the rest of us and accept the risk as "part of the job".


Why couldn’t Boeing just use the stab trim system to do MCAS job?

No, the 737 NG stabilizer trim system does not feedback from AOA. My source of information comes from this LinkedIn Slide Share and corroborated by this online FCOM.

There are several ways through which the stabilizer can be commanded:

Manually via the trim switches.
Manually via the trim wheels.
Automatically via the Speed Trim System (STS). A helpful explanation of the STS can be found in this answer. STS feeds back from stabilizer position, thrust lever position, airspeed and vertical speed.
Automatically via the Autopilot trim offset. This is only applicable with the relevant autopilot mode engaged.

The Mach Trim function also modifies the trim characteristics. However, it does not actuate the stabilizer and repositions the elevator centering and feel unit instead, which backdrives the column.

MCAS' requirement is completely different from those of the STS or the Mach Trim.


Is a degree from an overseas institution likely to be a barrier to employment with a major US airline?

Without a considerable amount of time as PIC of a turbine-powered aircraft, I expect your chances would be slight.

Once your other qualifications, logbook, and resume are competitive, I doubt that where you went to college will matter very much.


Why were most of the first-generation-Learjet wing mods never approved for the Learjet 23?

The cost of approving an STC for an aircraft can be quite expensive and the return on investment may not have been worth it.

------------------------------------------
|Aircraft   |  # Built |  Year Certified |
------------------------------------------
|Learjet 23 |    104   |       1964      |
|Learjet 24 |    259   |   1966 to 1976  | (All variants)
|Learjet 25 |    369   |   1967 to 1976  | (all variants)
|Learjet 35 |    670   |   1974 to 1976  | (all variants)
|Learjet 36 |     64   |   1974 to 1976  | (all variants)
------------------------------------------

The Lear 36 is, for all practical purposes, a variant of the Lear 35.  If you take a look at the list, the Lear 23 is the oldest with the least number built and that would weigh heavily on whether or not to pursue an STC.  If an owner of a Lear 23 wanted to purchase the STC and absorb the cost of the certification, these would have been made available to those aircraft as well.

An owner can effectively upgrade their Lear 23 to a Lear 24 by completing and engineering change record (ECR 227, ECR 230 or ECR 233 depending on serial number).  Once the new Lear 23/24 name plate is installed, the STCs may be applicable.

It is also just a guess.  The FAA (as we know it now) was formed in 1967.  It is possible, the STC holders tried to get their modifications approved by the FAA for the Lear 23 but since the aircraft was certified before the FAA was formed, they may have declined or required the aircraft to meet current aircraft design standards and that may have been cost prohibitive.


What kind of plane is good for this type of flight?

The cheap kind. Joking aside, the exact airplane to use depends on the size of the banners or billboards you're going to be towing, but generally speaking you want something reasonably rugged, with good slow flight characteristics, sufficient engine power to be able to overcome the added drag from the banner, and, hopefully, some decent fuel consumption.

I'm not entirely kidding about the cheap part though; banner towing is hard on the airplanes and carries a higher-than-average degree of risk, so you do want to stay away from airplanes that will be expensive to fix, if you can help it.

As for specific types, I've seen banners towed with everything from -152s to Grumman Agcats; a large banner tow operation apparently had a Super Cub with an O-540 bolted to it, so you'll see a ton of different things, but tailwheels seem to be the norm, at least in the US, and many outfits will make additional modifications such as removing engine cowlings to help with cooling.

  With banners they appear to be flying slower than usual. Is this just an illusion?

No, they are indeed flying slower. First of all, the added drag from the banner slows the airplane down all by itself. Secondly, you're being paid to advertise, so you want to make sure that people can read whatever sign you're towing. You're not flying the ragged edge of the stall (it's dangerous, uneconomical, and unnecessarily hard on the engine), but you're probably going to be flying on the backside of the power curve.

  What are the practical or regulatory requirements that the plane must meet to be capable?

In addition to the practical considerations we've talked about above, banner towing operations require a waiver from the FAA. The company has to apply for it and every pilot must be trained in banner tow operations, pass a review from an approved FAA inspector (who will be watching you perform picks and drops from the ground), and be added to the waiver. The aircraft and tow hitch mechanisms also have to be inspected and approved for banner tow operations, and added to the waiver.

Here is the current FAA Banner Tow Information handbook, covering equipment, operations, waiver information, and other assorted miscellaneous if you're curious to learn more.


If the "Fuel Shutoff Valve" is ON, wouldn't fuel be cut off?

I can see where that can be confusing, but it comes down to perspective.

From a maintenance and engineering perspective, you are actuating the fuel shutoff valve which controls the fuel to the engine.  The actual terminology when referring specifically to the valve would be opened or closed, which would result in the fuel being on or off.

From a pilot perspective you are simply turning the fuel selector on and off, which happens to be connected to the fuel shutoff valve.  The pilot doesn't even need to know about the valve, so they placard it from the operational perspective in the cockpit and say whether the fuel is on or off.

Note that these are placarded as a fuel selector and fuel off both of which seem pretty clear to me.


Can a CFM56-3C engine be converted into a CFM56-3B1?

In theory, I think that should be possible, as the -3B is a lower thrust rating than the -3C (going to higher thrust rating would be harder).  However, you would have to ask CFM.  I think they are the only ones that could answer.