Where is the radio PTT button on a Robinson R22 helicopter? I have some combination of joysticks and a rudder that I'm trying to use for helicopter flight simulation on my PC. Where is the radio PTT button on a Robinson R22 helicopter?

You can't realistically mimic the feel of the R22 controls with a joystick because it's an unusual configuration. I've done both simulated and the real thing so trust me when I say it's going to be radically different. This is the Robinson R22 control column:

The R22 has a bent T shaped control arrangement with the control column in between the 2 seats. The T is connected at the pivot point (green arrow), the handling pilot pulls the stick down towards their lap, pulling the other side up. Instructors have to learn to fly with their arm in the air sometimes. The red arrow points to the intercom and PTT buttons. The intercom button is not always there, newer versions generally have a voice activated (VOX) intercom so no button is required.

The blue arrow points to the pin to remove the left hand controls. In most helicopters the pilot sits on the right, if you have a non-flying passenger it may be good to remove the controls so they can't accidentally grab it. The left side pedals are removable too.


How to get IATA code for the Airline PSS system? If we are having airline PSS (passenger Service system) System, how can we registered with IATA and get IATA code. as an example Amadeus is using 1A, Sabre is using 1S, SITA is using XS etc..

Try below link, you can type PSS system name and get the code for the same. However, not all PSS are IATA registered.

https://www.iata.org/en/publications/directories/code-search/


How does the less dense air affect the reciprocating aircraft engine performance? How does the less dense air can affect the reciprocating engine performance ? For an example " rotax engine "

Lower air density means less compression, hence less mean effective cylinder pressure during expansion, and thus less power, since shaft power is proportional to the product of mean effective pressure and angular speed...


Do horizontal stabiliser force direction change with CG variation for a given aircraft? I am wondering about the direction in which horizontal stabilizer provide force. I know that it can provide either upforce or downforce. But I am wondering whether is it determined for a particular airplane, I mean it is established for example that B737 tail will provide only a downforce and CG limits are set up in a way that when correctly loaded the tailplane will provide every single time a downforce or it depends from the CG location that tailplane will have to provide either a downforce or an upforce?

The ideal cruise condition, which minimises induced drag, is for the tail to exert zero lift. This avoids any wasteful tip vortices from the tail.

However for most planes the CG shifts during flight, if only because fuel is being used up. Also, trim conditions change with speed, rate of climb, altitude and a host of other variables during flight. The tail spends most of its time a little away from the ideal zero-lift condition, and it can go either way.

The "lifting tail" was much discussed in the early years of aviation. It has a destabilising effect which limits the stable CG range and every plane has a maximum safe level of lift from the tail while remaining stable. Nevertheless, away from that limit it contributes lift which helps to offload the wing and allows it to be that bit smaller.
According to Berriman; Aviation, Methuen, 1913.

"On some machines the tail planes are cambered like the wings and help to support the weight in flight. The angle of incidence of the tail is less than that of the wings, however, and the principle [of weathercock stability] apples equally to such cases." -- Page 69.

Berriman gives some supporting analysis in terms of CG and CP to explain what he summarises as weathercock stability. The subtleties of the lifting tail would be further elaborated in subsequent years.

The bigger the tail, the greater the CG range can be accommodated, and also the greater the temptation to offload the wing a little. The limit is the tandem-wing aircraft, where for stability the fore wing is loaded more heavily than the aft, but the aft still contributes substantially to the lift under all flight conditions. A tandem-wing modification of the Westland Lysander flew experimentally during WWII and test pilot Harald Penrose confirmed that its handling was more stable than the conventional version and had a greater CG range.

So ultimately, every plane has its own practical tail loading, which may be normally up, normally down, or variable around the zero point.

There is a myth that for a plane to be stable the tail must always exert a downforce. This seems to arise among students for two reasons. One is that, when the AoA increases, dynamically it must exert a larger relative change in downward moment about the aerodynamic center than the wing's upward moment. Diagrams showing this effect always have a large down-arrow at the tail and it is easy for the student to forget that this is a relative change not an absolute value. The other is that the wing works hardest at takeoff, when fully laden and at its slowest flying speed; when the tail pushes sharply down to rotate the nose up, the wing has to compensate for that as well, so this is the design condition for sizing the wing and everybody has to learn it. Put that first diagram alongside and you have a myth in the making. If you failed to understand any of this paragraph, then you too may fall for it!


How do I calculate the total cruise power from the propellers accounting for the losses? Let's say I have an aircraft with four propellers (see diagram below) and I am supposed to calculate the cruise power required to drive the aircraft forward. The  wing creates the lift and propellers provide the forward thrust.

If I don't account for the wake of the front propellers affecting the rear propellers it's easy. I just have to calculate the thrust required and get the power. But how do I account for the losses and the actual power required?

The flow leaving the propeller:

Contracts, as a function of distance behind the propeller. The impulse theory gives a contraction factor - for an idealised homogeneous outflow field. The contracted wake has a higher velocity than free stream.
Has a whirl component due to the drag of the blades.
Has propeller tip vortices in a contracting corkscrew field.

So if the aft propellers are far enough behind the forward ones, the aft propeller tips are unaffected by the wake of the forward ones.

If the aft prop counter-rotates, the whirl component from the front props will be removed. Optimal blade angle of the aft prop is different from that of the fwd prop, but the tips would remain relatively unaffected.

Picture above is from Leishman, which has a whole chapter devoted to rotor wake. There has been quite some research done on co-axial rotors for helicopters. There is some info and a link in this answer as well.

But I reckon you'll be in the right order of magnitude if you just compute required power as you would in an undisturbed flow, especially if you use ducted propellers which reduce the tip vortices.


Why are aircraft external lights round, not tear-drop shaped? I saw this image of a Cessna 172's tail posted on another question and it made me wonder why the beacon light is basically a cylinder, and not a more aerodynamic, teardrop shape?

Image source

That beacon lens (and most of the strobe lenses shaped like it) are actually Fresnel lenses.
They are optically designed to produce a specific plane & intensity of coverage, and tinted for a specific color. (The color, intensity, and plane are specified in the FARs & applicable Technical Standard Orders if you want to go hunt down the requirements.)

The lens optics are easier to see on the split (Red/White) lenses:

A Fresnel lens is not the only way to meet these requirements, some anti-collision lights do it by sheer intensity (while retaining the "jar" shape, mainly for installation compatibility), and as GdD pointed out there are more aerodynamic options available. The Fresnel lens method is usually adequate for smaller/slower aircraft however, and the drag penalty at relatively low speeds isn't significant enough for designers to worry about.


What is this red dashed line between door and cockpit window? I noticed this dashed line located between the door and cockpit window on this 737-300 while boarding this exact aircraft at Ibiza airport. It seems to have text beside it but I did not have time to read it while boarding and it is too hard to read from the photo. Older photos of the aircraft with the same paint job do not have this suggesting that it was added recently. Wondering if it has anything to do with aligning air stairs or jet bridges. Does anyone know any other aircraft with a similar marking?

(Photo by Roberto Bianchi, source)

(Source: airliners.net)

The letters read 'air bridge'. The line is used for docking with the air bridge as you suspected. Also see: What are these markings under the passenger door?

  (...) the position of the alignment marks are not standardized and are carrier specific.

It also appears on the silver livery:

(Source: planespotters.net)

It reminds me of this:

(Source: wikimedia.org)


Does a 709 ride mean the end of my career? If I'm required to do a 709 ride following an incident where the plane went off the end of the runway but it wasn't damaged and no one was hurt, what effect does it have on my future as a pilot?

I'm looking to go into commercial aviation (I'm currently a CFI working on hours) and am specifically wondering about how having it in my record will affect interviewing for regionals.

Depends on the reasons the FAA had to justify the need for a 709 ride.  If it was some kind of bureaucratic maneuver without justification for doing so and you pass the ride with flying colors, probably nothing.  If there was a serious discrepancy in your airmanship which required a 709 ride to verify improvement on your part, it's going to depend on whether it was a one time event or a trend in airmanship deficiency resulting in the check ride.  In addition have there been further reports of deficiency in your airmanship after the 709 ride?  That will also have an effect on an employer's judgment of you as a potential employee.

Whatever the reasons for the 709 ride, an employer is going to see it, so be prepared to explain anything associated with it.

Look at this from the employer's perspective:  I'm going to put you in charge of a big, heavy multimillion dollar machine that you are going to pilot several miles off the ground at speeds close to that of sound.  If anything goes wrong, you're going to get killed, someone else on board is going to get killed, people on the ground are going to get killed and I'm going to get sued, go bankrupt, end up in jail, or all three if your negligence can be traced back to me.  Is there anything in your background which make me suspicious this is likely to happen if you are in my employ as a pilot?

The fact that you do make mistakes, possibly even serious ones, is not necessarily the issue here; everybody makes mistakes.  The last time you flew on an airliner the flight crew probably screwed something up.  People with thousands of PIC hours learn something new on their next flight and it's a mark of a good pilot that you can identify your own faults and fix them.  The Blue Angels have a private saying amongst themselves that "We've never flown a perfect airshow and we probably never will.  But we strive for the perfect airshow each and every flight".  Striving for perfection as a personal motivator is the mark of a good airman and looks good on a resume, no matter how balls up some flight in your logbook was.

The real issue here is do you have a recent or chronic history of uncorrected gross negligence or inability to handle the kinds of aircraft a potential employer flies which raises red flags as to your airmanship or trustworthiness.  If you have a spotty record or recent 709 ride in your recent past, take a couple of years staying on with your current employer and do an outstanding job.  Work on your airmanship and develop a stellar reputation with them as a pilot.  That will go a long way to erasing the past, or at least mute its bite.

Speaking of trustworthiness, DO NOT LIE TO A PROSPECTIVE EMPLOYER ABOUT A 709 RIDE OR ANY OTHER FAILED CHECKRIDE.  Aviation is built upon an honor system and any kind of detected lying or deceitfulness on your part is an automatic fail with no second chances, no matter how squeaky clean your career is up to that point.  If they ask about it, tell it like it was, no more, no less, and let the chips fall where they may.  It will yield the best possible outcomes, even if you don't get the job.


What is 'blending' for a turbine blade? What is the process of 'blending' that is used as part of jet engine maintenance?

Blending is the process of filing and polishing damaged sections off of the turbine blade. This prevents further damage and extends the life of the engine without having to replace parts, making it a very economical solution. There is a limit however, as modifying the turbine blades leads to a small cost in efficiency that can build up over time.


Are Uber Elevate and other air taxis subject to domestic ownership and control rules? When Virgin Airlines USA was being established, the company was forced to restructure due to a determination that effective ownership and control was held by Richard Branson's Virgin Group, a non-US entity. These rules are widely criticized in many countries, but existing carriers like the reduced competition they provide and lobby to keep them in place.

Uber plans an air taxi service and has recently sold a significant share to Softbank, a Japanese company (Fortune). Uber as a ride hailing service has worked around many conventional taxi regulations, but as it gets into air taxis it will be up against the US Department of Transportation which is not so easy to push around. If Elevate is considered an air taxi it will have to respect air taxi rules.

Are US air taxi companies subject to domestic ownership and control rules just as domestic airlines are?

The most important thing to remember is that currently there is only one FAA regulation about person-carrying autonomous drones: it is simply not permitted.

Both 14CFR Part 121 (airlines) and Part 135 (charter/air-taxi) have ownership and citizenship requirements. (It is of course not known what Part person-carrying drones would be under, but we can assume similar requirements.)

However why should this affect Uber? They do not own the cars that are currently in the fleet; in exactly the same way they could have the aircraft be owned not by Uber, but by some sub-contractor.


Blunt noses subsonic drag - why a complete ellipse? At subsonic speeds, blunt noses - both fuselage and airfoil - are good for two reasons:

the need to maintain attached flow at varying angles of attack.
it has less surface area for the volume, reducing skin friction.

TOP: 0 AoA/Cruise
| BOTTOM: extreme AoA, 20-30degrees, takeoff/landing

If the airflow had to flow over a ridge/point in scenario 2, instead of the smooth curve, flow separation would be more likely.

But things don't seem to add up.

Firstly, it's not like most airplanes - particularly airliners - fly at AoA beyond 20-30 degrees. At least not without high-lift devices. Am I correct? But on the rounded nose, there are surfaces smoothly curving all the way from 90 degrees! This seems to me like a useless increase in cruise drag.

Secondly, why push a blunt face ahead of you just to increase the volume a little, whem you can use a curve terminating at a point/ridge, as will be demonstrated below? If the surface area to volume ratio becomes so important, we can just sacrifice the fineness ratio and still have less drag, as the new nose creates less drag, right?

Would limiting the curvature to the max AoA limit for the aircraft, then terminating at a point, as in the image below, not keep the flow attached throughout the expected AoA range, while producing less drag? At the maximum AoA, the flow over the top of the shape encounters no "ridge" or "point", as it is parallel to the half-angle at the nose.

TOP: less drag is created at cruise
| BOTTOM: Flow remains attached at extreme AoA conditions.

What am I missing about the sharp nose? How and how much does it hurt performance? Why, after all this seemingly shown in the question, is it - aside from the radar - that big planes have round noses?

In short: I am claiming that an elliptical nose tipped with a triangle or cone of 20-30 degrees half-angle should be better than a pure ellipse for subsonic aircraft. Why am I wrong?

What you are missing is suction on that round nose which adds some thrust.

Granted, around that stagnation point there is a pressure region which also acts on a forward-facing surface, thus creating drag. But that region is small. Thanks to the curvature of the elliptic nose shape, air accelerates quickly out of this high pressure region. In order to follow the curved surface, the pressure has to fall below ambient on a still somewhat forward-facing area so the air is actively pulling the nose forward. No such suction can be expected on the straight contour of a pointed, cone-shaped nose.

The plot below only shows an airfoil, but flow around an elliptic nose is quite similar.

CPV plot from XFOIL, showing local pressure as arrows. Suction is pointing out, pressure into the contour. Length denotes difference to ambient pressure.


Why do some aircraft have wings that tend to bend up? I take regular visits to the Boeing website, and when I look at some pictures, the wings tend to edge/point up. Why is this?

All wings do flex, but in some modern airliners, the wings are built, fully or in part, with modern composites, that may deform within a larger elastic interval than metals...


Is there any aircraft that cruises in the transonic regime? Has there been any airplane that has been able to cruise in both the subsonic and transonic regime where the drag is high because the critical Mach number has been reached or surpassed?

If we define the critical Mach number as "the lowest Mach number at which the airflow over some point of the aircraft reaches the speed of sound, but does not exceed it," then yes, many aircraft cruise above this speed. Any modern jet airliner has some supersonic flow over parts of the wing and fuselage at cruise, placing it squarely in the transonic range. This video and its description provide a great visualization and explanation of the associated phenomena.

It should be noted, however, that there is not necessarily a large increase in drag upon reaching the critical Mach number. More useful in the transonic range is the drag-divergence Mach number, which is always greater than the critical Mach number. Supercritical airfoils are designed specifically to increase the drag-divergence Mach number, and are fitted to all modern jetliners.


Why wouldn't KJFK offer the ILS for 22L? (Source: Flightradar24)
The above was from last Sunday around 17z. I was watching FR24 with the ATC feed. The airport was operating in 'arrival priority' with approaches to both 13L (Canarsie) and 22L.
Both directions were offered their respective VOR approach. Authorized carriers such as JetBlue and Alaska Airlines requested the RNAV RNP 13L (not publicly published by the FAA, yet).
My question is why wasn't the ILS offered for 22L? I checked the NOTAMs and the serviceability of the ILS was not there. And since the VOR is an instrument approach, it wouldn't quite fit the visual vs. instrument asked about here. A 4-year old post on airliners.net blames LaGuardia (LGA):

JFK will frequently land with max crosswind or tailwind components and frequently uses off set VOR approaches to minimums before switching to the preferred ILS.
Why? LaGuardia and the airspace to the north.

While yes the VOR is offset (232° vs. 224°), it's not a big offset that would free a chunk of airspace for LGA when it vectors its inbounds via a left downwind for runway 22. To be sure I superimposed both plates by aligning the 604' structure (shown below).

JFK ARR ILS 22L/22R DEP 22R

  If conditions dictate the use of JFK ILS RWY 22L approach, then (1) the JFK Area owns Belmont airspace 3,000' and below, (2) releases Coney airspace to LGA and LIB, (3) JFK cannot depart 31L, (4) ILS 22R unavailable if LGA departs RWY 13.

LGA ILS 22, DEP 13

  LGA Coney, Maspeth, and Whitestone climbs are available.

LGA ILS 22, DEP 13 (No Belmont)

  If conditions dictate the use of LGA ILS RWY 22 while departing RWY 13, then LGA departures are restricted to Maspeth and Coney climbs only*.

So, based on those two things, if LGA doesn't own the Belmont airspace, then Whitestone Climbs (WC) are disallowed. Therefore, when JFK uses VOR 22L, it allows LGA to use the Whitestone Climb off of runway 13, which is preferred for noise abatement.

*Personal note: this application was created prior to the addition of GLDMN, NTHNS, TNNIS RNAV SIDs which are now used instead of Maspeth and Coney.

Sources:

Previously based in LGA at a regional airline
NY Airspace Application
http://tfmlearning.faa.gov/NY_Airspace/NY_Airspace_Pkg/NY_Airspace.swf
(Only works in Firefox)


When and where are anti-ice required for supersonic flight? Many aircraft have heating devices to prevent dangerous icing.  Supersonic aircraft rapidly compress the air, leading to elevated temperatures.  Concorde and Tu-144 used fuel as a heat sink.
How fast do you need to fly so that heating makes anti-ice irrelevant?  How does it depend on the part of the aircraft?  Presumably the leading edge is the first part to warm up without anti-ice.  Are icing conditions different at typical supercruise altitudes?  Is there meaningful water up there?

How fast do you need to fly so that heating makes anti-ice irrelevant?

The True Air Temperature (TAT) that the aircraft's skin will feel can be calculated from the Static Air Temperature (SAT) and the Mach number:
$$ \frac{\text{TAT}}{\text{SAT}} = 1 + \frac{\gamma - 1}{2} M^2 = 1 + \frac{1}{5} M^2 $$
(using $ \gamma = 1.4 $ for air). The SAT does not usually go below -56.5°C in the International Standard Atmosphere, which is the usual temperature in the lower stratosphere (where most supersonic aircraft fly).

At Mach numbers above $ \sim 1.24 $ the resulting TAT will be above 10°C, which is usually defined as the upper temperature, where icing conditions exist.

How does it depend on the part of the aircraft? Presumably the leading edge is the first part to warm up without anti-ice.

Yes, the leading edges would warm up most, but they are also the only part of the aircraft that could possibly accumulate ice. Aircraft that are certified for flight into known icing conditions typically have de-icing or anti-icing systems on the engine inlets, the propellers and the leading edges of the wings, vertical and horizontal stabilizer. But not all aircraft have these systems on all of these surfaces because they are not all affected equally. See e.g. these questions:

Why do only some aircraft require tail anti-icing?
Why are some parts of the wings not protected by the wing anti-ice system in the B737?

Are icing conditions different at typical supercruise altitudes? Is there meaningful water up there?

Humidity is usually quite low in the stratosphere, meaning icing isn't typically a problem here anyway:

The stratospheric air
masses sampled are dry, as expected, having mean
relative humidity over water of 12% and over ice of
23%, respectively. However, 2% of the stratospheric
data indicate ice supersaturation.

(A distribution law for relative humidity in the upper troposphere
and lower stratosphere derived from three years
of MOZAIC measurements)
Most weather phenomena only occur in the troposphere, which means you fly above the weather (although thunderstorm can push clouds to extreme altitudes).


How to calculate outside air temperature at a certain altitude? I am a PPL student and working on the cross-country planning.
Let's say the OAT is -13º @ 6000', how to calculate the OAT @ 7000'?

The temperature will drop around 2° Celsius (-1.98 to be more precise) for each 1000 feet you climb.

So if the OAT at 6000ft is -13°C, at 7000ft it will be -15°C, or minus 16 from the International Standard Atmosphere (ISA) which should be +1°C (15 - 2*7 = 1).


Does the mixture and throttle setting affect the quality of priming of fuel prior to start? This question is a generality.  For airplanes with small reciprocating engines, does the mixture and throttle setting at the time of priming affect the quality of the priming or the engine start, or is the priming unaffected by mixture and throttle positions?

Does it make a difference if the engine has carburetor or fuel-injected in regards to mixture and throttle at priming time?

On a carbureted engine, the mixture and throttle setting does not affect prime, which uses a separate injection system that draws fuel into a syringe and injects it into the intake passages at the cylinders when you push in the primer's syringe plunger.

On a fuel injected engine, where the Bendix mechanical fuel injection system is pretty common, if the fuel system is pressurized and the mixture is rich, the system is injecting sufficient fuel at each cylinder for idle continuously.  So you prime them by doing just that, pressurizing and advancing mixture, for a set period of time, say, 3 seconds or whatever, then pulling the mixture back to idle cutoff to stop spraying gas.  This does the same thing as stroking the primer on a carb engine.  Like the carb engine, it doesn't matter where the throttle is at this point.

When you start an injected engine, you start with the throttle cracked like a carb engine, but unlike a carb engine where you put the mixture to rich for the start, you have to crank with mixture at idle cutoff and move the mixture forward after the engine fires before it consumes the fuel vapour in the intake passages created by priming, within a second or two.

Injected engines are more finicky to start because the amount of prime is a bit harder to regulate, being a timing function that you have to adjust for ambient temps and engine warmup state vs counting primer strokes so they are much easier to over/under prime, and as well the timing of the advancement of the mixture after start is important.  Do it too soon and you can get flooding or intake backfires and too late it dies before it really gets going.


How is an aircraft designed to be longitudinally stable? How do aircraft designers ensure that a specific aircraft is longitudinally stable? Are there any different considerations for subsonic and transonic aircraft?

My short answer:

Stability is controlled by moving the center of gravity (CoG).
The handbook should give center of gravity limits. A more forward CoG means a more stable airplane.
Shifting it past the neutral point makes the airplane unstable, so movements away from the trimmed state are accelerated. However, at supersonic speed this airplane will become stable again.
Airplanes with sophisticated computer control can artificially augment stability, so they behave like a stable airplane at all speeds.

For the long answer, let me first clarify terms:
Static stability is the tendency of a system to return to it's old state after being disturbed. Take a pendulum: If you pull it to one side, it will return to the middle. Eventually.
Dynamic stability is the tendency of an oscillating system for the oscillations to die down over time. Take the same pendulum: It will swing from side to side, and  friction will ensure this happens with ever smaller amplitude.
Now we need to add dimensions, all three of them: Pitch, roll and yaw. An airplane can be stable in one dimension and unstable in a different one. I understand your question such that you ask about the static pitch stability (or longitudinal stability) of fighter aircraft.
The Wright Flyer was longitudinally unstable (see here for more). Once aircraft designers learned that aircraft can be made to fly stable, and learned that this is of immense benefit in pilot training, static stability became a requirement for new aircraft. When war in Europe broke out, the British forces were equipped with a superb training aircraft, but it was so stable that it took effort and time to convince it to change course. They were shot down in droves.
From now on, low stability was a prime requirement for fighters and aerobatic aircraft. Static stability is proportional to the control forces (more precisely: To the hinge moment of the respective control surface), so reducing stability gave pilots more response for the same effort. Longitudinal static stability is measured as the relative distance between neutral point (NP) and the center of gravity (CG). See here for more. Longitudinal static stability is achieved by placing the CG ahead of the NP. Shifting the CG back gives you a more responsive airplane, but also one which is more easily disturbed by gusts.
This is the design technique you asked about. Pretty simple, right?
Once you shift the CG aft of the NP, stability is lost and the airplane will increase deviations from the trimmed state. This can be helpful if you want large angle changes, and quickly. An unstable aircraft only needs a small kick and will do the rest of the maneuver all by itself.
This is how it helps in maneuverability. But it is even more helpful to reduce the inertias, especially around the roll axis, for a faster response. That is why all combat aircraft have their engines close to the center.
Of course, negative stability is not acceptable when you need to take your hands off the stick to get a map out or to pee on a long flight. So without computer control, the limit was a CG position near, but not aft of the NP.
With supersonic aircraft, things get more complicated. Now the aircraft operates in two flight regimes, one where lift acts at the quarter chord of the wing and one where it acts at mid-chord. Aircraft with low static stability become very stable in supersonic flight, and the tail surface has to create a high down-force so that the sum of all lift stays where the CG is. Creating lift always incurs a drag penalty, and in supersonic flight it has to be payed twice: One for the excess lift on the wing (which is needed to compensate for the tail's down-force) and one for the down-force on the tail.
Using a flight control computer offers the possibility to allow the pilot to let go of the stick without the aircraft going off course. Now the stick does not command elevator deflection, but pitch rate, and the CG can be moved back from maybe 12% of MAC (mean aerodynamic chord) to -2%. If you compare the wing areas of stable and unstable jets (Jaguar and Mirage F-1 are prime examples), you will see how much is achieved just by going back with the CG by a few percent of wing chord.

Conventional SEPECAT Jaguar and CCV version (picture from Ray Whitford's Fundamentals of Fighter Design). Both configurations have the same airfield and combat performance!
These airplanes are unstable without computer control at subsonic speed. This is no benefit in itself (for better maneuverabiliy it helps more to reduce inertias, as explained above), but it dramatically cuts trim drag at supersonic speed. In supersonic flight such an aircraft is still stable, but much less than one that is also stable at subsonic speed. This means less lift is needed on the wings and less downforce is created on the tail, so the drag of botch surfaces is small and their size can be reduced, too, resulting in a virtuous circle of drag savings.


Is it worth it taking flying lessons even though I can't commit to regular lessons right now? I can’t commit to flying on a regular basis right now. I’m close to a Class B airport with a flight school. There’s a C150 for 100/hr and a Zlin 242 for 160/hr. Instruction is 50/hr. There is, surprisingly, only one cheaper option nearby, and the price difference is small, so the closer option of the two is better. I’ve been studying the AFH, PHAK, and FAR/AIM, so I know my stuff. I’ve not yet taken ground school. I can’t commit to flying regularly right now. Is it still worth taking some lessons? I’d like to solo on my 16th birthday, so accruing hours is important. Should I wait until school is out and I can fly more regularly, or should I just go for it?

My humble advice is to take a single introductory flight in the Cessna 150 to galvanize your interest and increase your motivation. Go to ground school first and then (preferably) start your flight training (in the C150) in earnest once you have the time and money available to take lessons on a regular schedule (once a week minimum, three times a week maximum [until the later stages of your initial training -when you are practicing what you have learned and not learning new skills]).
In my experience, having too big of a gap between flight lessons can be counter-productive and make for a (sometimes) difficult learning curve.  This can lead to frustration on your part and, perhaps, result in your enthusiasm being diminished.
Frequent lessons will most quickly enhance your skills and your proficiency will improve steadily.  Additionally, recency of flight experience will provide for greater personal enjoyment and reinforce your confidence, a very important factor in learning to fly.


What is a plausible scenario for aircraft sabotage for a science fiction novel? I am writing a science fiction novel and my characters are about to board a private jet - they will be leaving Virginia and flying to CERN in Switzerland. Some factions are not happy with what they are attempting to accomplish and the plane is sabotaged. Here is the important part - one of my characters is an alien with limited telekinesis ability. If something is "stuck" then he will be able to save the plane by moving it, with his mind (not the plane itself - that is beyond his ability).

So my question is: What is a plausible mechanical failure that could be induced in advance by someone on the ground who was trying to prevent them from getting to CERN, that could be discovered by the pilot/crew during flight and that my alien can correct in time to save everyone using his telekinesis ability?

In the book's plot, the alien would have to be able to see it in order to move it...I know nothing about aviation so I don't know how to make this scene at least somewhat plausible -any suggestions would be deeply appreciated!

If the alien has to see it to fix it, that rules out anything not visible from the windows (i.e., tail, landing gear, etc.)

If the alien is a passenger, the only moving parts that come to mind are the ailerons.

Have your saboteurs cause a complete failure of the aileron controls (In a Gulfstream 3 I think it's cables with a hydraulic boost, but I could be wrong).  A semi-cut cable won't be caught on a preflight (who takes apart a wing?), but could break over the ocean.

Your alien could save the day by directly manipulating one of the ailerons to keep the plane level.

I don't know the forces involved - I hope your alien is really strong.


Can someone retake a denied medical? If someone gets a denial on their medical or gets deferred but never follows up with the appointments, can they retake it at a later time?

For example, if someone gets denied on their medical and they want to retake the exam 10 years later will the original denial prevent them from passing?

This is my personal experience having nearly lost my medical: If you are in the U.S., you will have to check the box on the application stating that your medical has been denied in the past. You will have to check that box every time you apply in the future. Having nearly had my medical denied in the past, my advice is to 1) find the most senior AME in your area and schedule an appointment for consultation. Explain your situation and take his/her advice. 2) Follow through on that advice (I had to see a well-regarded neurologist for a few hours' worth of exams and interrogation). Bring those results/reports with you to your next AME visit and have him/her send them to the FAA with your next medical application. The FAA's medical office in Oklahoma City will review your case and most likely send you a letter. I was able to get a medical issued the day I applied, however, the letter I received from OK City put me on a six month schedule before the age of 40. I strongly urge you to consult with the most senior AME you can find.

tl;dr - If you have been previously denied. You will have to provide documentation to your AME to overturn the denial.

Caveat: I am only familiar with the U.S./FAA system as a pilot.

[ I'll try to tidy this up when I get home later today ]


What is this molten metal coming from the engine of an Avro RJ 100? Yesterday I flew in an Swiss Avro RJ100. As soon as we landed I was shocked to see some sort of molten metal which was incandescent and glowing red dripping down from the vent as indicated in the picture. It was almost catching fire! I was suprised to see immediately the maintenance van pitch up to the plane when we didn't even get to a stop. Is this normal?

This image isn't of the problem flight, but shows where the problem was.

I do not see anything in your photo, apart the engine that looks perfectly normal.

Anyway
here it is written that the fuel burns at up to 2000 degrees Celsius and the temperature at which metals in this part of the engine start to melt is 1300 degrees Celsius. Hence the metal may melt if something goes wrong.

Avro RJ100 has four engines so should be able to land with one inoperative. From the question I have just asked myself, it will not be qualified as accident so may not get widely known.


What's a TRA and how does it differ from a TFR? This is from a recent email from the FAA Safety Team:

  The FAA will soon begin limited use of a Temporary Restricted Area
  (TRA) in certain areas when the types of operation(s) to be conducted
  there require a TRA. The flight rules that apply to a TRA are the same
  as a Restricted Area (RA). The best FAA resources to view any TRAs
  upcoming or active are the FAA Special Use Airspace (SUA) website and
  the Notices to Airmen Publication (NTAP).

Usually when the FAA wants to temporarily restrict access to airspace it puts up a TFR and it isn't clear from the wording of the email what a TRA is, why the FAA would create one rather than a TFR, and what the operational differences are between a TRA and TFR.

What is a TRA and how does it differ from a TFR?

As the message says, a TRA has the same rules as an RA, just that it is temporary so it won't appear on charts. There may be expected times when the RA is in use but the actual times will be posted in a NOTAM.

It will be published in the Federal Register ahead of time
Using agency notifies controlling agency when airspace will be "hot"
NOTAMs describe when the airspace will be closed
When the airspace is open, ATC can clear flights (IFR or VFR) through

This is useful if the area is known ahead of time but times may be limited and variable. The using agency must also later submit a report detailing the actual usage of the area.

A TFR defines special flight rules that are applicable in specific circumstances. They are governed by different rules, and a NOTAM is published defining the airspace and times, as well as what restrictions are in effect. A TFR may be defined for the following reasons:

Disaster/hazard areas
Protecting the President, the Vice President, or other public figures
Space flight operations
High barometric pressure
Aerial demonstrations and major sporting events
Security requirements

Each of these categories has general rules for who is allowed to operate in the airspace, though each TFR may include more specific requirements. TFRs issued for disasters/hazards generally require aircraft that are not local flights or directly related to the event to be on an IFR flight plan. Other situations may just require permission from ATC, or effectively make the airspace Class C.


Can small children be seated away from their parents/guardians on a flight? I am interested if there is any law or regulation which prohibits carriers from seating children in a seat not adjacent to their parent/guardian?

I am flying with a group of 17, which includes 2 infants (without allocated seats), but seven children ranging in age from 2-5. We opted not to pay the extra charge to pre-allocate seats, and the airline has allocated us seats spread around the aircraft in a configuration which does not allow an accompanying adult to sit next to a child.

I was sure there was some air law which prohibited this on safety grounds, but have been unable to find it.

This question relates to the EU, but answers regarding other jurisdictions welcome.

This is what I could find. I looked on the Civil Aviation Authority's website and found this article.

Seating Allocation

  Families, children and infants

  The seating of children close by their parents or guardians should be
  the aim of airline seat allocation procedures for family groups and
  large parties of children.

  Young children and infants who are accompanied by adults, should
  ideally be seated in the same seat row as the adult. Children and
  accompanying adults should not be separated by more than one aisle.
  Where this is not possible, children should be separated by no more
  than one seat row from accompanying adults. This is because the speed
  of an emergency evacuation may be affected by adults trying to reach
  their children.

  Whenever a number of infants and children are travelling together the
  airline should make every effort to ensure that they can be readily
  supervised by the responsible accompanying adults.

From what I read, it doesn't look like there is a law set in stone, but instead it is recommended by the CAA to be put in regular practice by airlines.

If there was a law then Ryanair would have been in serious trouble for charging people extra  money to sit next to their kids.

Ryannair booking separates mum and tot


What factors determine the power curve of a jet engine? From YouTube

The L-39 in the video is powered by an Ivchenko AI-25, from the footage we see that the engine idles at 60% N1, and the taxi power setting is 70% N1. (The other lower-reading needle is the N2.) The same engine powers the Yak-40.

Compared to modern jet engines on airliners, those values are very high.

If 70% N1 is used to taxi, then I think the AI-25's power curve is exponential, and it starts off late. So in a sense there are only two thrust settings, i.e., narrow throttle range, and hard to fine tune.

The AI-25 is a medium bypass turbofan.

Update:

I've come across some power curves for jet engines, some are almost linear, some are exponential, and idle RPM varies.

So, what factors influence the idle RPM, and the shape of the power curve?

Not a direct answer, but one thing to keep in mind is that thrust has very non-linear dependency on RPM. 70% N1 may mean 20-30% thrust. (And that's static thrust; in flight the difference may be even greater).

I don't have exact figures for AI-25, but for a similar engine I remember the gradient near 100% was around 5 (5% thrust for each 1% N1).

Actually, I have some data for Williams FJ33, which is comparable.

On the ground, it idles at 25% N1, which is only 3% of thrust. For 50% N1, you still have less than 20% of thrust. 60% N1 -> ~28%, and for 98% N1 you have over 100% of static thrust.

By the way, AI-25 on L-39 is 'overrated' compared to Yak-40 and its N1 goes to 107%, if I remember correctly. So it's all not that bad.


What is the spacing of obstacle lights on towers? Radio antennas and other tall buildings have lights so pilots don't fly into them, especially at night. Is there a fixed spacing so you can determine the height of the tower by counting the lights?

In theory you might be able to make an estimate, but practically speaking it's impossible and a lot easier to just look at a sectional chart.

The FAA has a detailed guide on obstacle lighting standards, which usually applies to structures over 200ft in height but there's a lot of possible variation:

  Recommendations on marking and/or lighting structures can vary
  depending on terrain features, weather patterns, geographic location,
  and in the case of wind turbines, number of structures and overall
  layout of design.

The actual number of lights and their placement depends on the type and size of the structure. Appendix 1 of the FAA guide has examples for water towers, radio masts, cooling stacks, bridges, chimneys etc. The vertical light spacing seems to vary from 250-375ft, depending on the structure type, but I didn't go through it systematically.

So if you have plenty of time you might be able to determine the approximate height of a structure by comparing its lighting layout to the guide and estimating based on that, but that's very unlikely to give you an accurate number. For a pilot in flight or planning a flight, that isn't safe or practical and the simple solution is to just look at the VFR sectional chart to get the height. For example, this tower is 1094ft high and the top is at 1994ft above sea level (so the ground level is 900ft above sea level at that location):


On a chart, how can I find the frequency for flight following? Is there a map I can refer to in order to pick up the correct frequency for VFR flight following while enroute? I know I can request a frequency from ATC as I depart, but what if I want to fly around and do sight seeing, practice maneuver for my checkride etc. for a while, then pick up flight following for the remainder of the trip?

In the United States, you can consult the VFR Sectional Chart and look for the frequency box located near a terminal area.

Otherwise you'll need to consult the Airport Facility Directory for the region your are flying to find a ARTCC (Center) frequency.


How are carrier landings graded? I'm an aspiring naval aviator (preferably a Hornet or an F-35) and a DCS player. Here's a question for any former navy aviators or LSOs. What would get you a good or bad landing grade on the carrier? What would the desirable landings look like?

To paraphrase GySgt Foley from the movie An Officer and a Gentleman:   “My grandmother is an aspiring Naval Aviator!”
Anyway, I am a former LSO, and I pulled out my old LSO NATOPS manual to see if I could find book definitions of the criteria for each grade.  I can’t seem to find them, but they are as close to verbatim as I can remember as described in the answer here.
Worth noting, the grade is not always about the wire you catch.  In other words, OKs aren’t limited to the 3 wire, you can still get an OK for a 2 or 4 wire.  It all depends on how and why you got that particular wire.  For example, if you get low, just miss the ace and taxi into the 2, that would likely be a "No-grade".  However, if you fly a sweet pass and dip just enough at the ramp to barely scoop the 2, that could still be an OK.  And anything in between is probably a "Fair".
The same thing would apply to being way long and just barely grabbing the 4 to avoid a bolter, vs just barely missing the 3 after an otherwise solid pass.
Really though, the question is not really answerable in a useful manner to a lay person.  Judging any “sport” is subjective, and often the LSOs don’t even agree on a grade.  After watching literally thousands of landings over a few years and being mentored by senior LSOs you just develop an eye and a feel for what a good pass and bad pass look like.  (and there are always plenty of “tweeners” to argue over!)
It really boils down to subjectively assessing the duration and magnitude of the pilot's deviations from perfect, and the appropriateness and timeliness of corrections.  In other words. how much the airplane is "moving around" out there...


People say that modern airliners are more resilient to turbulence, but I see that a 707 and a 787 still have the same G-rating. Why is this? The 707 was introduced in the late 50's, the 787 in 2009.
Back when Air France 447 had recently gone missing, many were speculating that the aircraft had broken up in the turbulence associated with the massive thunderstorm it was flying through. Some aviation spokesperson, who I believe were associated with Airbus, said that the planes are designed to withstand the worst storms with a 50% safety margin.
Several airliner models from the 50's and 60's have broke apart in flight due to turbulence associated with thunderstorms (A 720 B, A BAC-1-11, and a F-27 in 1981). There were also breakups involving clear-air turbulence (707, Mt. Fuji, 1966, and a Consolidated Airlines F-27). I checked to see if their G rating was lower than the planes of today and they were the same - 2.5+ G Limit Load, with a 50% safety margin, so 3.75+ G Ultimate Load (beyond which structural failure occurs).
Why is this? Shouldn't the G rating be much higher if modern airliners are more resistant to violent turbulence?

Note that the 2.5 g limit is for load due to manoeuvring, not only for turbulence. The certification specification for large aircraft on the subject of turbulence and gusts has changed several times since the certification of the Boeing 707.
Turbulence, and its effects on aircraft, is nowadays much better understood. Different aircraft react differently to the same turbulence. What will result in a high g-load in one aircraft, may be a moderate g-load in another. Therefore the certification regulations now focus on prescribing the type of turbulence that needs to be safely dealt with, instead of the resulting load factor.
In 1964, a formula was introduced describing the gust load that the structure aircraft has to deal with. This was added as FAR 25.341. This section has subsequently been updated in 1990, 1996 and 2015.

Modified from my earlier answer to a related question


Why is the inlet cone shaped conical? Why are inlet cones of a lot of aircrafts conical. I read that it has something to do with slowing down supersonic airflow entering inside the engine. Is this true? If so, can somebody please elaborate on it?

Also why does supersonic airflow have to be slowed down before entering the compressor/combustion chamber. Does it cause engine flameout if not slowed down?

Also I've noticed that  the inlet cones of supersonic aircrafts are more pointy than that of subsonic aircrafts. Why is this so?

As Wikipedia explains it:

  The main purpose of an inlet cone is to slow the flow of air from supersonic flight speed to a subsonic speed before it enters the engine. Except for scramjet engines, all airbreathing jet engines need subsonic airflow to operate properly, and require a diffuser to prevent supersonic airflow inside the engine. At supersonic flight speeds a conical shock wave, sloping rearwards, forms at the apex of the cone. Air passing through the conical shock wave (and subsequent reflections) slows to a low supersonic speed. The air then passes through a strong normal shock wave, within the diffuser passage, and exits at a subsonic velocity. The resulting intake system is more efficient (in terms of pressure recovery) than the much simpler pitot intake.

If the flow was supersonic inside the engine, it would not be able to maintain fuel burn.

The pointyness of supersonic jets' inlet cone is dictated by the distance from the tip of the cone to the engine inlet and the inlet diameter. Also, the shockwave must be kept at right location in relation to the engine inlet, so the location of the cone is adjustable (by computer)

  The inlet cone is shaped so that the shock wave that forms on its apex is directed to the lip of the intake; this allows the intake to operate properly in supersonic flight. As speed increases, the shock wave becomes increasingly more oblique (the cone gets narrower). For higher flight speeds inlet cones are designed to move axially to control how the capture area varies with the duct internal throat area. For best intake operation this required area ratio gets bigger with increasing flight Mach number, hence the large inlet cone movement on the SR-71 which had to perform well from low speeds to Mach 3.2.

The engine in the first picture is not of a supersonic aircraft. It is a high bypass turbofan, and the cone in that engine has no other function but to serve as an aerodynamic form covering the end of the axel. The other picture (actually quite obviousy taken form the Wikipedia article I referenced above...) is a supersonic engine inlet cone of MiG-21MF

For the most interesting reading about supersonic engines, please see this Wikipedia article about the J58, an engineering marvel from more than sixty years ago. It still stands as one of, if not the most inspirational jet engine.

The article has a nice schliering photograph of what happens when the shocwave is not in the place it should be (NASA document ID: C-1955-37520, public domain):


How could a twin aisle aircraft (Boeing NMA) ever have a single aisle (A321) economics? I understand from this discussion about the Boeing 757 and 767 that drag is directly related to the front area of the airframe, hence flight efficiency of the dual aisle aircraft can only be significantly inferior to the single aisle design.

So how should we consider current Boeing reflection in the design of the so called MOM or NMA that they seek a twin aisle aircraft with single aisle economics? They are reported to aiming at offering "twin-aisle capabilities—range, comfort, capacity, and faster turnaround time—with single-aisle economics". Is it pure marketing rhetoric or are there parameters other than front area in the equation of such an airplane that would make the assertion sound?

So it's definitely not ALL marketing spin, but it's also definitely not ALL engineering, either.

The frontal area is absolutely a major component of the drag on an airplane, but wingtip devices (sharklets, winglets, etc.) can significantly reduce drag, as can better nose shapes, smoother surfaces, and a number of other design considerations.  If you kept all these other things the same, then increasing the frontal area would increase drag and reduce efficiency, but these other things aren't the same in a new airplane.  The MoM proposal would certainly take advantage of all sorts of wing, engine, airframe design improvements that would reduce the drag components, and then you'd gobble most if not all of that up by making the airplane wider.  ;-)

If I'm putting on my "engineer but worked in marketing for a while" hat, I'd say that the challenge put to me is that the marketing people want an airplane that can be operated at what used to be called single-aisle efficiency, but can now be done with widebody seat capacities.

I'd also contend that of the parameters mentioned: "range, comfort, capacity, and faster turnaround time" the only one of those things that really requires you to think seriously about a twin-aisle airplane is capacity.  I can build a single-aisle aircraft that has every bit as much range, way more comfort, and a much faster turn around time as a twin-aisle aircraft, it just doesn't hold as many people.  ;-)


Can you help me to identify this helicopter? I came across this helicopter and am wondering what the oblong things on either side of the helicopter are, parallel to the front-back axis, offset from the main body.

The helicopter is a S-65C-3 Yas'ur (Albatross). It is a CH-53D version similar to USAF HH-53C Pave Low. Here is a photo of the same.

The identification is based on the following:

Six bladed main rotor
The sponsons which hold the fuel
The only variant of CH-53D with in-flight refueling probe in service is the Israeli version. All others (HH-53 and MH-53) have been retired. CH-53E has refueling probe, but it has 7 blades.

Israel ordered 36 of these,of which around 23 are still in service.


Why are airplanes called ‘she’? What is the reason that airplanes in English have a female gender?
Please illuminate the historical or scientific reason.

Much of aviation has a history in Nautical terms, lore... and law.

Ships were referred to as "she" perhaps for one of the following reasons

The latin word for Ship is "Navis" which is a feminine noun
Or perhaps mostly male ship owners would name their ships after/for their (invariably female) loved ones.
Ships were often dedicated to godesses, or women of significance in order to bestow on them good luck when seafaring

Some further reading and Why are ships always female? - english.se


Why don't solar powered aircraft use wings with more surface area I was looking at some solar aviation projects, and I noticed they appear to follow the designs of a glider.

The Helios drone above is basically a flying wing with a high aspect ratio.

And the solar impulse above is a textbook glider with minimal cord length and a long wing span.

I understand the idea is a wing with a high aspect ratio reduces parasitic drag by decreasing its surface area, however in this case don't you want the most wing surface area possible?

This answer shows that induced drag is unaffected by the wings aspect ratio, so if it's only parasitic drag we're trying to combat here, why not keep the wing span the same, but make it's cord longer?

Won't the added solar panels you could fit on a wing make up for any friction drag caused by the longer cord?

Taking this to the extreme could you make some kind of solar powered rectangle that has a width (span) comparable to the gliders above, but a length (cord) twice as long as the span?

Surely you'll have enough power to make the aircraft fly, so are there other design considerations that factor in when choosing the cord length of these solar powered projects?

First, because solar panels are pretty mediocre sources of power per area. An industry average found via quick Google search is in the 200 - 300 Watt per square meter range, so let us be very optimistic and take the higher value, $300W/m^2$, for a round of math. If you want the details, solar irradiation on the surface is about $1kW/m^2$ and the best experimental photo-voltaic cell efficiencies by year are graphed here.

Using the ASH 26 motor glider as a case study, we can see if solar powering an aircraft is as trivial as the OP suggests.

Assuming our panels are made of fairy dust we can further decide their weight is negligible and that we can perfectly cover the $11.68\,m^2$ of wing area this glider has and that it will operate as though under normal incidence (Sun at 90° to the panel) all the time. Thus, $3.5\,kW$ of free energy... which sadly is only $9.4\,\%$ of the power supplied by the Wankel engine used on the real glider, and with which it attains a very humble $4\,m/s$ climb rate. This is before even considering that batteries are also very inefficient sources of energy per unit of mass when compared to hydrocarbons.

Now, for the second part of the OP´s query, how about enlarging the chord of the wing to increase the area?
This also happens to fall flat for different reasons. The drag coefficient:
$$
C_D =C_{D0} + \frac{(C_L)^2}{\pi e AR}
$$
has the aspect ratio ($AR = {b^2 \over S}$) of the wing in the denominator of the second term, the so called induced drag (because it is induced by the lift, note the coefficient of lift itself appears in the numerator).

This equation quickly illustrates why gliders have long wings: a higher AR provides a lower induced drag term. The other term, the parasitic drag, is either indifferent to the chord or slowly grows with it due to boundary layer transition in laminar airfoil designs.

We can arrive at the conclusion that for a given surface, a higher-AR wing will be the less draggy solution.

Therefore, the current attempts at solar powered aircraft all attempt to add area by extending the wings, and are limited by structural constraints like bending moment at the root, which you can clearly see them try and alleviate by spacing out the engines into the wings, providing some relief at the expense of increased roll inertia.


What is the definition of visibility as seen in aviation weather reports? If you look at the National Oceanic and Atmospheric Administration's (NOAA) National Weather Service (NWS) page for Washington D.C., Reagan National Airport (KDCA), it shows hourly weather observations proceeding back from present through time.

I notice that there has been 10.00 miles visibility all the way back to 17 August, where for one hour there was only 7 miles visibility. During these hours of 10 mi visibility, there are multiple conditions of cloud cover, ranging from Light Clouds, to Overcast, to Light Rain.

What is "visibility" when added to a weather report broadcast from an airport? It seems that if I am in the middle of Light Rains, well then my visibility cannot be "10 miles".

All my quotes for this post comes from FAA Order 7900.5C, the Surface Weather Observing Guide.

Visibility is defined as "Visibility is a measure of the horizontal opacity of the atmosphere at the point of observation and is expressed in terms of the horizontal distance at which a person should be able to see and identify specific objects."

All METARs report Prevailing Visibility, which is: "Prevailing visibility is the greatest visibility equaled or exceeded throughout at least half the horizon circle, which does not necessarily have to be continuous. This is the visibility that is considered representative of visibility conditions at the station."

Automated stations, generally report a max visibility of 10 SM. Now if you look at stations that are completely manual, i.e. KBJC(when I worked there it was a completely manual station), we'd report anywhere up to 70SM or higher visibility, due to our visibility markers.

-RA can often be easily seen through, RA or RA+ do become harder to see through, and as always, it can be dependant on where the -RA is, if it's only in a tiny quadrant of the horizon circle, it can often be a greater visibility.

[Edit Post comment about RA]: Sorry, used a few more abbreviations. SM = Statute Miles, which is like a regular mile that most people use in their daily lives. It's depicted as SM, due to most other things in aviation being in Nautical Miles.

-RA, RA, +RA, are the various descriptors for Rain. -RA means light rain, which if just using vis concerns is defined as, "From scattered drops that, regardless of duration, do not completely wet an exposed surface up to a condition where individual drops are easily seen." RA, is Moderate Rain, defined as: "Individual drops are not clearly identifiable; spray is observable just above pavements and other hard surfaces" and +RA is heavy Rain, "Rain seemingly falls in sheets; individual drops are not identifiable; heavy spray to height of several inches is observed over hard surfaces."

Also, METAR is the type of aviation weather report. METAR's are the hourly/standard report, and then there's SPECI's which if certain changes occur in conditions, from Freezing Rain, to changes in visibility or cloud ceilings, to massive wind shifts, to thunderstorms, to other factors, can be produced outside of the hourly/regular report.


How does a combat aircraft handle the recoil force of a mounted gun? How is the recoil momentum distributed or countered for smaller aircraft or drones while using a mounted gun? Is there any hydraulic mechanism to counter it and how it is distributed across the entire body of an aircraft?

In case of combat aircraft, the guns are hard mounted on the fuselage (or wings, for that matter) so that the recoil force is distributed throughout the body. In this case, the large aircraft mass acts to reduce the effects, though if the gun has too much recoil, it can cause damage to the aircraft. For example,

  The MiG-27's GSh-6-30 cannon didn't prove particularly useful in practice. It was an impressive weapon in principle, ..., but the recoil -- about 5.5 tonnes (6.05 tons) -- still had a tendency to inflict damage on the aircraft. ... Landing lights almost always broke after firing,

In case of smaller aircraft or drones, you can chose a gun with lesser recoil. Or the drone (for example) could be programmed to fly back to its original position as a way of 'absorbing' the recoil.

Another way is to mount the gun on stabilization platform, which makes sense only if the gun is quite small. A few such systems exist, which usually use robotic stabilizers to reduce the effects of the recoil due to the gun.


Why are speed restrictions imposed for flights flying below 10,000 ft? I know that restrictions do not always apply and ATC can cancel them or pilots can request for speed restriction being canceled. But why is there such a speed restriction in first place? Are there any reasons other than noise abatement?

The speed limits were set by FAA in the early days of jet age for better control of the aircraft and safety where the air traffic (in VFR) is the densest and have little to do with noise.

FAR § 91.117 states

  Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).

TWA Flight 553, a DC 9 collided with a Beechcraft Baron, killing 26 people on March 9, 1967. NTSB investigation determined that due to the high rate of descent of the DC-9, its pilots were not able to see the other plane in time to avoid a collision.

Following this accident the FAA issued Advisory Circular 90-32 titled 'Air traffic control and general operations, radar capabilities and limitations' in Aug 1967.

According to NTSB report on the accident,

  The FAA has adopted a rule establishing that all aircraft flying below 10,000ft m.s.l will be limited to a maximum speed of 250kts effective December 15, 1967... (to) provide a more realistic 'see and avoid' environment in the airspace below 10,000 feet mean sea level (MSL) where the traffic congestion is greatest ....


How do airlines handle uncertainty in passenger weight for weight and balance calculations? When commercial airlines calculate the mass and distribution of passenger load, in the cases where they do not weigh the passengers directly, they use standard weight measures which have been approved by the appropriate aviation authority.

The standard weights can be broken down by passenger type (adult/child), by sex (male/female) and by other factors such as season or business/economy class. To obtain these figures a survey is carried out at an airport and appropriate measures are taken to ensure the sample is representative.

The result is a single value that represents the standard weight for a male/female/child/etc. Whilst the standard weight may have a minimal bias (i.e. a small deviation from the population mean), it does not represent the variance of the observed passenger weights. That is if the sample mean is 90kg with a std deviation of 10, the there is a ~15% chance that a passenger has a weight more than 100kg (assuming normal distribution, for the purpose of this example).

Given that airline operators have to be extremely careful and conservative with their weight management how do they account for this uncertainty in their calculations? Using the example above, if there were a flight with 100 passengers each >100kg, there would be an underestimation of mass by over 1 tonne (relatively small in comparison to total loaded aircraft mass, but still a large figure in itself).

Are accommodations for this variation incorporated into the standard passenger weight (say use mean + x std. dev.) or does this get included in the operational limits that the airline set for their max weight allowances in their various forms, for example reduced Max Zero Fuel Weight (MZFW) or Max Take Off Weight (MTOW)?

Edit: This is a slightly different question to a similar one about how a commercial aircraft has its mass determined. The focus here is more specific in looking at how the standard passenger weights are calculated and what are the assumptions around using that data.

They don't handle that uncertainty.

Safety is always the prominent factor in the aviation industry. That said, measurements need only to be "accurate enough" for the purpose of safety. Being off by small amount would not compromise safety.

Furthermore, the atmospheric condition is always different; it is so dynamic and cannot be precisely measured. As long as the measurement is accurate enough, the aircraft will fly.

Theoretically, you could argue that there's a chance:

calculated weight is already at MTOW
every passenger happens to weight way above average
they all bought a lot of souvenir at the airport shops
density altitude was extraordinary high
a 10 knots tailwind was present at takeoff

and the aircraft overrun the runway during its takeoff roll. However, such a chance is so small that we accept our current method as it is and expect the aircraft to tolerate that uncertainly within its designed safety factors.

Such believe was found to be wrong when a small aircraft crashed on takeoff in 2003. Regulations were then modified so that on a small enough aircraft, the actual weight of each passenger (plus luggage) must be used, rather than using a standard weight for estimation.


Why are some vertical stabilizers painted 'after' installation? I recently watched the Airbus videos on making the first PAL and Air China A350s. PAL’s vertical stabilizer was painted before being installed, as explained in 'Why are the tails always painted, but not the fuselage, in test and delivery flights?'.

But Air China’s (MSN 167) was painted with the fuselage (after installation). This confused me because I have been told that painting the vertical stabilizer is for balancing the rudder.

What factors affect when the rudder is painted?

A photo for MSN 167 confirming what was seen in the video. (flickr.com)

The most important safety consideration when painting the tail of an aircraft is balance of the flight control surfaces to prevent flutter. This means painting of the stabilizers can happen whenever the manufacturer finds it most convenient, since they are not flight controls.

Flutter begins when the support structure of a flight control is displaced and the control is unbalanced, ie. heavier behind its hinge line. In an aileron, which is the flight control most sensitive to flutter, a gust might displace the wingtip upwards. The unbalanced aileron, heavy behind the hinge, deflects downwards due to inertia. This increases lift amplifying the effect of the gust. When the structure flexes enough to reverse the excursion of the wing, the aileron continues to rise due to inertia and deflects upwards. This reduces lift on a wing that is already descending, amplifying that motion. Uncorrected, this develops into an oscillation of increasing amplitude until structural limits are exceeded and the structure fails.

One less efficient way to deal with the weight of paint is to overbalance the flight control, meaning make it heavier ahead of the hinge line. This prevents flutter from developing because all the inertial effects on the control run counter to the deflection of the supporting structure. It is less efficient because there is unnecessary weight in the control, but it does mean that you could theoretically calculate paint weight and add some margin to ensure that overbalance is maintained after painting. Airliners don't take that theoretical route due to regulation and desire for efficiency.

Painting/repainting of the rudder, elevator and ailerons in commercial airliners always requires balancing of the control surface. This means that the mass of the control ahead of the hinge line equals the mass behind the hinge line. On a b737, the rudder can be balanced while installed on the aircraft. The horizontal stabilizer can also, but in a more restricted manner. Ailerons have to be removed, as they are most sensitive since their support structure (the wing) flexes far more than the aft fuselage where the other controls are located.

For both your aircraft all the controls will be balanced prior to flight. The A350 apparently allows balancing of the rudder while installed on the aircraft, just as the B737 does. This means it does not need to be painted prior to installation, and the manufacturer is indifferent to any cost differential.


Can I circle to a different runway if cleared for an instrument approach without circling minimums? Tom is flying a C172S/G on ILS RWY 31 approach to KSNS. He just established on the localizer at 6000, from the SNS-22 DME Arc. He obtained weather from ATIS, wind 240@20G23, ceiling OVC006, visibility 1 1/2 SM. The wind favors RWY 26 but he notice there is no published circling minimum associated with his current ILS RWY 31 approach. He checked other approaches and found RNAV (GPS) Y RWY 31 @ KSNS has a published circling minimum of 500-1. He thinks since the two approaches are for the same runway and final leg should be similar, he may use the RNAV 500-1 circling minimum and to land on RWY 26.

X-Wind quick notes:

Wind angle for RWY 31 is 70˚.
Crosswind component for Landing on RWY 31 (18~22 knots)
Maximum demonstrated crosswind for C172S is 15 knots

In this case, what should he do?

A) Continue the ILS RWY 31 straight-in approach and land on RWY 31
B) Advise tower circle south to land on RWY 26. Start to circle upon reaching 500.
C) Change to RNAV (GPS) Y RWY 31 @ KSNS (approach without vertical guidance), re-intercept final approach course (WIGGL-IVUVY leg) and circling to RWY 26.
C*) Change to LOC/DME RWY 31 @KSNS (load a new approach) and circle at 560 to RWY 26
D) Once he has the airport in sight, cancel IFR and advise tower enter left base for RWY 26
E) Low-approach flying over RWY 31 until reaching 31-26 intersection, turn left and land on RWY 26.
F) Others, your suggestions.

The only minimums that apply to any approach are those printed on the plate. Doing anything else is being a test pilot. Minimums are charted based on obstacle clearance, descent gradient, distance from the airport, and a variety of other factors.

The appropriate course of action is to either:

land straight in on 31 and attempt to deal with the crosswind. This would be preferred, in my opinion.
go missed and pick up the GPS Y 31 approach and circle to 25. You can't switch approaches once you're cleared. Given the ~1 mile visibility and low ceilings, this would not be ideal.
divert to your alternate if neither of those works.

Choosing a build-your-own circle with 600' ceilings is reckless - certainly more so than landing with a ~15-20 knot crosswind. There's no guarantee that you'll remain clear of any surface obstacles.


How exactly am I supposed to notify ATC when I fly my drone? (UAS) I recently registered my new 250 class Quadcopter with the FAA under the Part 107 sUAS code. I want to fly within the regulations, and the only one that I'm really unsure about how to abide by is the "notify ATC" restriction.

I live within 5 miles of a couple small airports in the California South Bay, which apparently makes me need to legally notify nearby ATC whenever I fly. How can I do this?

I saw this other post which talked about how to find the telephone numbers for ATC in your area, but are these the people I need to call? And if so, with what information would I need to give them? I also saw this other post that discusses how to call ATC, but is the information there current and relevant to my flights?

Thanks,
Neil

If you are flying as a hobbyist

If you are flying as a hobbyist, which seems to be the case, you are required by Public Law 112-95 FAA Modernization and Reform Act of 2012 section 336 to:

  (5) when flown within 5 miles of an airport, the operator of the aircraft provides the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport) with prior notice of the operation (model aircraft operators flying from a permanent location within 5 miles of an airport should establish a mutually-agreed upon operating procedure with the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport)).

This, of course, does not say how you are to contact the airport operator and air traffic control. The traditional way would be to find the telephone numbers for the airport and air traffic control, and to call them. Alternatively, as you discovered, some mobile phone apps allow you to electronically submit notices to some airports. What is not required or desired is to contact ATC by radio. If you are operating very near an airport, it may be a good idea to get a radio so that you can listen in.

If you are flying under Part 107

If you are flying under Part 107, you do not have to contact the airport or air traffic control even if you are within 5 miles of an airport, but you must not fly in controlled airspace without obtaining an airspace authorization or airspace waiver. These processes are, at this time, handled through the FAA Drone Zone website, and not by contacting the airport or ATC. Depending on the terms of the authorization or waiver, if granted, you may be required to contact ATC prior to operation, and they will need a way to get in touch with you.

Which rules do you need to follow?

Broadly, if you're flying for fun (e.g. as part of an enthusiast group, in your back yard, or taking personal photos in the park (although watch out for people as per the safety guidelines you are following)), you are a hobbyist, and subject to the special rule for model aircraft.

If you're flying for commercial or business purposes (e.g. taking photos of houses for real estate sales, inspecting railroad tracks, or delivering purchased packages), you need a Part 107 license and to fly under Part 107 rules.

For more information, see the FAA's sUAS FAQs and the table on page 11 of the FAA's interpretation of the Special Rule for Model Aircraft (pdf).


Which types of aircraft are required to carry ELTs? According to regulations and recommendations from the FAA, ICAO or other aviation organisations, what types of aircraft are required to carry Automatic Fixed Emergency Location Transmitters (ELT(AF)) devices? In particular, is it required of commercial transport airliners?

CAA (and I guess other aviation organisations/regulators) group aircraft into several categories:

General Aviation (GA) - personal aircraft etc.
Business Aviation - executive jets etc
Commercial Air Transport / Public Transport - Scheduled passenger airliners etc.

AOPA say

  ELTs are emergency transmitters that are carried aboard most general aviation aircraft in the U.S.

(my emphasis) - note GA, not all aircraft.

CAA refer to ICAO Annex 6

  Aeroplanes - ICAO Annex 6, Part II
  6.12.3 From 1 January 2005, all aeroplanes operated on extended flights over water as described in
  6.3.3 b) and when operated on flights over designated land areas as described in 6.4 shall be
  equipped with one automatic ELT. [i.e. designated KK(ii) in the Air Navigation Order]

  6.12.4 Recommendation. - All aeroplanes should carry an automatic ELT.

But I can't find an annex mentioning ELTs at www.icao.int.

So, I'm not sure whether all airliners are required to carry ELT(AF)s and if so, by whom.

Everything you need to know (at least in the USA) is here.

Regarding airliners, it appears that they are carved out of the general requirement to have an ELT in 91.207.f.2.   I guess that makes some sense.  If you're flying a scheduled flight, presumably we should be able to find the plane, since we know the takeoff time and approximate airspeed, and we have radar tracking by ATC/ARTCC.  Unscheduled (especially VFR) flights are where things get dicey.


What are the reasons for this radial piston engine shut down procedure? In a radial piston engine, before the engine is shut down the rpm is brought to a considerable high power setting of approximately 1950 rpm. This is to burn the unburnt carbon in the spark plugs. Are there other reasons for this specific power setting to be selected before the engine shuts down?

It could also be to remove lead deposits from the spark plugs. Some avgas has an agent added to remove lead deposits, this only works above a certain temperature which is achieved above a certain RPM. We had to do a similar procedure in the Cessna 152.

As you will know, Avgas 100LL contains a compound known as Tetra Ethyl
Lead (TEL) which acts as an octane booster for the fuel. This results
in a fuel which is commonly known as a 100 Octane lean mixture and 130
rich mixture Performance Number fuel.
In practice it is even better than this, with ratings more like 106
lean mixture & 130 rich mixture which are far in excess of the
comparable 85 - 87 octane of road fuels. To achieve this a lot of TEL
is used - around 5 times the quantity that was used in the old Leaded
automotive fuels.
This increase in octane allows aviation engines to produce more power
through increased compression ratios or alternatively by increasing
the inlet pressure by using a turbo or a supercharger. The problem
with using Leaded fuels is that they will always burn with more
deposits than unleaded fuels.
The Tetra Ethyl Lead used for octane boost in the fuel naturally
degrades to form Lead Oxide when it is burned. In reality it is this
oxide which gives the octane boost. The problem is that Lead Oxide is
a solid up to about 900 deg C which is well within the wall
temperatures inside a piston engine.
In order to prevent these deposits from forming, a Lead scavenging
compound is added to Avgas 100LL - this compound is Ethylene
Dibromide. This scavenger is designed to react with the Lead oxide to
form Lead Bromide which is more volatile - becoming a gas at around
200 - 250 oC. This is a low enough temperature to ensure that the Lead
is removed from the engine as a gas end it subsequently goes back to
the solid phase as the exhaust gas cools in the atmosphere.
As a point of interest the pale brown / ash coloured staining that is
often seen leading from the exhausts of high powered engines, such as
those found on the warbirds, is in fact Lead Bromide.
To enable this reaction between the Lead Oxide and the scavenger to
work, there needs to be a relatively high combustion temperature.....

Read more at this link.


What is a "Standard visual inspection"? Passengers injured as US fighter jet comes close to Iranian plane

The Iranian plane, belonging to Mahan Air, was heading from Tehran to Beirut on Thursday when the pilot staged a safety manoeuver, in an incident that Iran's Foreign Ministry said would be investigated. ... Central Command spokesman, said the F-15 "conducted a standard visual inspection of a Mahan Air passenger airliner at a safe distance of about 1,000 metres (3,280 feet) from the airliner this evening". "The visual inspection occurred to ensure the safety of coalition personnel at Tanf garrison," ... "Once the F-15 pilot identified the aircraft as a Mahan Air passenger plane, the F-15 safely opened distance from the aircraft." He added the intercept was carried out in accordance with international standards.

My questions are the following:

Is there such thing as "standard visual inspection" at all? Is it normal in such circumstances? What's its purpose and how necessary is it?
Isn't there any other method to this end, instead of "visual inspection"?
Is "1,000 metres" distance considered "safe" for such conditions?
In what conditions do passenger airliners stage a "safety manoeuver" like this?

Update

Are there similar incidents? Some military aircraft approaches an airliner to "inspect" it and see if it has really passengers on-board, in a manner they consider "safe" and "in accordance to international standards". The airliner considers this "unsafe" and stages a "safety maneuver", leading to injuries.

Is there such thing as "standard visual inspection" at all? Is it normal in such circumstances? What's its purpose and how necessary is it?
Visual inspections are very common. Military pilots train regularly to visual inspections of other aircraft, and typically close to within 25-50 feet of another (cooperative) aircraft to do so. At a 25-50 foot range, you can easily see if an aircraft panel is missing or even loose/flapping in the wind. Having said that, there is no "universal standard" for what comprises a safe and normal visual inspection and distances and closure rates that are considered safe may vary depending on your experience and aircraft type.
Isn't there any other method to this end, instead of "visual inspection"?
According to the researcher quoted in the article, the F-15 may have been attempting to see if the airliner had passengers onboard. You would need to close to well within 1/4 of a mile (1500 feet) to have any hope of determining that with a naked eyeball. If the F-15 had a camera system (common), that may have allowed them to remain farther from the airliner, however.
Is "1,000 metres" distance considered "safe" for such conditions?
1,000 meters is likely very safe, and it's really far away compared to how military pilots are trained. However, what matters is how the pilots of the airliner felt. They are likely not military trained, and were probably unaccustomed to seeing another aircraft that close to their airplane.
The article is a little misleading when it implies that aircraft typically maintain at least 600 meters separation to avoid hitting each other. That number (600 m), refers to two aircraft on different altitudes that not aware of the other's presence. For a military pilot who has a radar and is looking at an airliner, 600 m is not required at all.
In what conditions do passenger airliners stage a "safety manoeuver" like this?
Here's where we get into some speculation. I'm not sure what the article is referring to, but I suspect that the airline pilots were responding to a TCAS RA (Traffic Collision and Avoidance System- Resolution Advisory) generated by the F-15's proximity and closure rate to the airliner. In this case, the airline pilots may have been presented with a "Climb" or "Descent" command by the computer, which would explain their abrupt climb and descent.
Whether or not the climb they undertook should have been so violent that passengers were bounced out of their seat and onto the floor is a matter of the pilot's judgement and speculation without knowing exactly what happened between the two aircraft.


What's the point of writing on a cockpit window? Why would a pilot write on the cockpit window like this?

From: source

If you use a grease pencil, it rubs off easily from glass

So you can save paper, not have to look down or hunt for the info, it won't fall on the floor, and if it's written in the center of the windshield, both pilots can see it


What are the factors that limit how long an aircraft can stay aloft? The most obvious one is fuel. Many modern military aircraft, however, are capable of refueling in mid-air. Crew fatigue, another obvious one, can also be addressed by rotating a crew out, and is a non-issue in unmanned aircraft.

The question therefore is, what factors would prevent an aircraft from staying in mid-air indefinitely? Are there any such factors that cannot be addressed, and would make it impossible to design an aircraft that could stay up indefinitely, or at least for an exceptionally long time?

Maintenance is probably the biggest issue. What types of maintenance is needed and the failures that not performing those steps will lead to depends on the design of the aircraft.

For example, on a piston engine used in a small aircraft:

The engine will need oil replaced at some point, and unless a system was created to cycle in new oil in-flight this is probably the first thing that will break down after crew and fuel (as you mentioned). Oil breaking down will lead to early failure of the engine.

Fuel and air filters will get clogged, leading to the engine shutting down.

Which leads to engine wear. Eventually piston rings, ignition systems, etc. will wear out.


Can roll be controlled through elevators in a fixed-wing aircraft? In fixed-wing aircraft, roll is typically controlled through ailerons.

But I am wondering if roll could also be controlled through split, independently controllable left/right elevators?

Yes.
Fighter jets with split elevators can command a roll in the way you describe, see this answer for more info.

For an aircraft like a delta wing (tail-less) that lacks a traditional empennage these control surfaces are combined into an elevon to produce a mix use elevator aileron.

The Concorde is a classic implementation of this design. Flying wings like the B-2 also use this design.


Why would a foreign military aircraft be parked at a US Air Force base? The aircraft in the attached Google Earth screenshot appears to be a Eurofighter Typhoon, parked all alone on the tarmac at Eglin AFB, Florida.  Why would one single foreign fighter like this be found on a US military base?  Granted, the Typhoon is mostly operated by US allies, but it still seems strange.

Also, can anyone identify the livery/operator of the aircraft in question?

It is actually fairly common for NATO aircraft to be at Eglin AFB.  When I was stationed there (a long time ago) we had two RAF Tornadoes on site for several months.

Eglin AFB is the home to the munitions development programs. Part of that development includes ensuring the weapons are compatible with the aircraft that will deploy them. Eglin also has a large test range to support that effort.

Since we sell the majority of our munitions throughout NATO (common weapons reduce the  size of stockpiles and increase flexibility), they also need to be tested on NATO aircraft. The Eurofighter is likely there for testing.


What are the V-Speeds used during a normal takeoff in a multi-engine airplane? This is what I know:

$V_1$ is the takeoff airspeed after which the aircraft must take off, no matter what happens after $V_1$ has been reached. That's the easy part (I think).
$V_R$ is the rotation airspeed

Are there any other $V$-speeds?

What I'm specifically curious about:

Is $V_1$ related to runway length?
Is there an absolute maximum $V_1$ for each aircraft type? If so, can it vary based on conditions (takeoff weight, density altitude, etc.)
Are there circumstances where $V_1$ is higher than $V_R$? If so, does that mean that $V_1$ is never called on a normal takeoff? (this is the case for most light aircraft, but I guess the whole concept is not applicable in that case)
What exactly is $V_2$?
Is there a $V_3$? (and so on)

Anything else worth knowing about $V$-speeds?

$V_1$ is takeoff decision speed.  It is based upon:

Runway length
Temperature
Reduced thrust takeoff
Takeoff weight
Takeoff flap setting

If $V_1$ is higher than $V_R$, then (as far as I am aware), $V_1$ will be adjusted to be the same as $V_R$.  You have to make the decision to takeoff by the time you rotate, so it does not make much sense to have $V_1$ higher than $V_R$.

$V_2$ is takeoff safety speed.  During a one engine inop takeoff we would accelerate to and climb at this airspeed to our acceleration height (a height we could level off at and be safe from obstacles while we further accelerate).  We also referenced certain flap transitions on takeoff to $V_2$ (e.g. $V_2+15$ - flaps 0)

To address the rest of the question, $V_1$ and $V_2$ are primarily used in large aircraft.  In light twins you also need to be aware of $V_{MC}$.  $V_{MC}$ is the minimum controllable airspeed with an engine inop.  In particular you do not want to be slower than this airspeed during climbout in case of engine failure.


Aviation Statistics Sources Are there any online, publicly available sources of aviation statistics, like:

number of manufactured aircrafts by type and year
number of registered aircrafts by type and year
number of aircraft incidents by type and year
etc.

I'm aware of Annual Reports of General Aviation Manufacturers Association, but this data is just for general aviation and it doesn't contain numbers before year 1990.

You wont find a single source for any of these things but you can find some of the info form fairly reliable sources:

The NTSB publishes accident data by type and year but this is only for US accidents or accidents involving US aircraft that they can investigate overseas.
The FAA allows you to lookup by make and model and would allow to get some info on registered aircraft but again only for the US.
ICAO also lists their final reports online which give a more global picture of whats going on but you will still need to combine all the data. They also offer some rolled up stats.

All of these sources generally can get spotty before the 80's for a few reasons. A lot of those reports only existed on paper and are still being digitized so results are intermittent. Official governing bodies started at different times around the globe and even paper reporting took time to standardize, accidents that pre-date that may have gotten lost in the mix.


How did the controls work for variable-pitch props? Variable-pitch propellers date way back to the 1930's and even earlier. I would like to know, what kind of controls they used? Some kind of lever or crank? How heavy were these controls? I'm thinking of the drag the propeller has, since even near landing, the prop could be spinning very fast and would be resistant to changing it's pitch.

I'm interested in the old days, before modern electrical control by wire.

Note: I am not asking how the variable-pitch mechanisms work. I might ask that in a separate question.

Control by wire? As in electrically?

Many of the small planes like Cessna Cardinal use an engine like Lycoming O-360 (4 cylinder) use a spring to return the blades to a flat pitch, and engine oil pressure to change the blade pitch. The control knob in the cockpit mechanically allows the oil pressure to change the pitch.  In other small planes, like a Bonanza, there is a set of counterweights instead of a spring to accomplish the same. No electric control at all.


Do all flights with the exception of military show up on FlightAware? I ask because I just saw a B737 land at KCSG. I haven't seen one land here in a while and in my curiosity wanted to know who it was. I got on FlightAware and I don't see any B737 arrivals within the last week. Has anyone got a clue as to why this is? The B737 was all white and I didn't see any obvious ID marks on it.

No.
From the Flightaware FAQ:

Can FlightAware track VFR flights?
In the US and Europe, this is not officially supported although some VFR aircraft with flight following are available on the position maps but it is largely unreliable and arrival/departure/flight plan data is often not available.

and

Can I track NASA's Space Shuttle or other space ships (UFOs, etc) on FlightAware during launch or descent?
No, but that would be rather amusing; the shuttle or UFOs would have to be on an IFR flight plan to be tracked or have an ADS-B OUT transponder. However, NASA streams live NASA TV on the Internet.

and

Can I track military aircraft? What about presidential movements in Air Force One?
FlightAware does not track military aircraft and presidential movement flights (e.g., Air Force One, Marine One, etc.) are operated by the US military.

etc.
Also compare this screenshot from FlightAware with a screenshot from another free tracking service:

You will notice that several flights are missing on the FlightAware map. The other tracking site, however, is not perfect either; these kind of internet tracking sites mostly rely on ADS-B, and do not receive radar data. Even if they did, we also still have flights which do not even show up on radar. Aircraft surveillance is complicated ...


What is the 'Deconfliction Service'? High Speed Flights

  2.36 - When receiving an ATS surveillance service, certain ex-military aircraft types have been granted a CAA exemption from the
  Air Navigation Order requirement to fly at an IAS less than 250 kt
  below Flight Level
  100. In order to alert the controller to this higher speed profile, pilots of exempted aircraft shall, on initial contact, prefix the
  aircraft callsign with ‘FASTJET’ or ‘FASTPROP’ (depending on
  propulsion type), e.g. “Kennington Radar, FASTJET G-ABCD request
  Deconfliction service”.

  Use of this prefix shall be confined to initial contact with ATC
  agencies for periods of flight during which operations at airspeeds in
  excess of 250 kt are intended. Once acknowledged, it will not normally
  be necessary for pilots to use the prefix in subsequent transmissions
  until making initial contact with other ATSUs.

Source: Manual of Radiotelephony, Edition 2016

What is meant by Deconfliction Service?

A deconfliction service is a specific type of air traffic service.

Normally, outside of controlled airspace, air traffic controllers do not alert pilots of potential encounters with other aircraft (conflicts).

However, there my be other services offered outside of controlled airspace, typically these are Flight Information Services (FIS).

In the UK, four air traffic services are distinguished outside controlled airspace: Basic Service, Traffic Service, Deconfliction Service and Procedural Service

  A Basic Service is an ATS provided for the purpose of giving advice
  and information useful for the safe and efficient conduct of flights.
  This may include weather information, changes of serviceability of
  facilities, conditions at aerodromes, general airspace activity
  information, and any other information likely to affect safety. The
  avoidance of other traffic is solely the pilot’s responsibility.

source: UK Flight Information Services CAP 774, February 2015

Note the last sentence.

The deconfliction service is defined as:

  A Deconfliction Service is a surveillance based ATS where, in
  addition to the provisions of a Basic Service, the controller provides
  specific surveillance-derived traffic information and issues headings
  and/or levels aimed at achieving planned deconfliction minima, or for
  positioning and/ or sequencing. However, the avoidance of other
  traffic is ultimately the pilot’s responsibility

Again, note the last sentence.