How do trainer aircraft differ from non-trainer versions? In flying schools, there are aircraft designated for training student pilots. Do these aircraft have special equipments or controls on-board which are used by instructors?
Like maybe extra panels or something?

The short answer is that there's no real difference between a "trainer" aircraft and an "owner" aircraft when they roll off the manufacturer's assembly line.

Below are two mid-1970s Piper Cherokee Cruisers - take my word for it that they both have virtually identical instruments, avionics, and interior finishing. One of these airplanes is the "trainer" I did much of my early training in, and had a little over 11,000 hours of flight time as of when the school sold it. The other is (probably) an owner-flown airplane with about 2,000 hours of flight time.

Can you tell which is which? The answer is in the spoiler box at the end of this post.

"Trainer" aircraft generally have flight and operational characteristics that makes them "suitable for use in training" -- though what that means is a subject of some debate.

In modern training aircraft you'll almost always find the following:

Dual controls
Much like a Driver's Education car has an extra brake, aircraft used for training will have dual controls so your flight instructor can correct any mistakes the student makes before they become dangerous.  (Dual controls are in fact required for flight training, at least under FAA regulations, though interestingly dual brakes are not required.)
2-4 person seating capacity
Hand in hand with dual controls goes dual seating - You need a place for both a student and an instructor.
You don't generally find many trainers that will seat more than four people, as those larger aircraft cost more to purchase and operate.
Some kind of intercom
Students and instructors generally wear headsets, and an intercom system makes it easier for them to communicate.
One or more Radio systems
Part of flight training includes learning how to communicate with Air Traffic Control and other pilots, and how to use radio navigation systems. This requires at least a communication radio, so there's usually one either installed or available (a handheld unit), and in most modern trainers you'll find one or more navigation radios of various types.

In addition trainer aircraft tend to be inexpensive to maintain (mechanically simple), operate (relatively fuel-efficient), and tend toward the slower end of the speed spectrum (because it's easier for a student to keep up with a slower aircraft).

  It's important to note that not all "trainers" fit this mold: The T-6 Texan is, by designation, a Trainer aircraft, but its goal was to train Air Force pilots, many of whom would go on to air combat roles. The things a T-6 is optimized to teach are very different from what a Piper Cherokee or Cessna 172 are optimized to teach.

Not surprisingly many of those same characteristics are also desirable in a plane you might buy to fly yourself: Dual controls in case you take a friend or another pilot along (or in case you want to take instruction in your own aircraft), an intercom to let you talk to your passengers, and radios so you can navigate and communicate in the air traffic system.
Because of this many pilots who elect to buy an airplane purchase what we would consider "trainer-class" aircraft, frequently models similar to the ones they trained in (and in the used market, frequently aircraft that were used for flight training at some point).

When you leave the "trainer" range you tend to find faster aircraft, more complicated systems, more attractive finishing elements (plush cabin interiors, fancy paint schemes), and more seating capacity.
You also find aircraft that begin to specialize more: Where trainers tend to be well-rounded the "non-trainer" planes tend to excel in specific areas, serving specific niches in the market (the Extra 300 is a high-performance aerobatic aircraft favored by many airshow performers, Mooney aircraft feature extensive speed optimizations and are favored by many pilots who use their planes for long-distance travel, the Piper Mirage is a "luxury" cruiser/transportation aircraft suitable for flying corporate executives to and from smaller airports, etc.).

   N2269Q is the trainer, now sporting a shiny new paint job.
 N32711 is the owner-flown airplane, with its factory paint. (Trade-a-Plane ad)


When one engine fails in a twin-turbojet aircraft, is there a weight imbalance? In a turbojet aircraft with two engines, when one fails does the weight of the working engine increase due to the fuel flowing to it? If it does, how is the weight balanced on the failed engine side?

Since your question is specifically on "jets".
We need not worry about the critical engine.

There is one thing to be noted in most of the commercial jets. The engines are placed close to the fuselage in order to reduce the moment arm - mean that should an engine fail, there is a reduced difference in forces,as compared to if an aircraft had engines on the wings tips.

The following are two vital things to be carried out during imbalance due to engine failure:

1) Effective rudder (and aileron) control:

The rudder (and aileron) is used to maintain directional control in flight, acting around the normal axis. An engine failure will yaw (and roll) an aircraft, making the rudder (and aileron) the best control to counteract this.

2)Fuel Balance procedure:

The following procedure is for a Boeing 737 :

Detailed schematic of a B737 Fuel System:

The procedures vary from one aircraft to another. And for a turbo prop aircraft it's a whole new thing involving "critical engine".


Why does the Tu-134UBL have a sharp/pointed nose cone? Russian/Soviet aircraft design has always intrigued me, and even more so when coming across this photo of the Tupolev Tu-134UBL with its pointy nosecone.
Having looked up the performance characteristics of the aircraft, it "only" seems to fly at sub to trans-sonic speeds (max. speed 890km/h or Mach 0.72 at sea level).
Based on my limited knowledge reinforced by this great post, it only makes sense to use a pointy nose cone when the aircraft travels at supersonic speeds.
Therefore, would the reason for the nosecone design be for some other function rather than just aerodynamics? Radar?

According to Wikipedia, the UBL variant of the TU-134 was designed/used to train TU-160 crew, and is using its nose-cone.
As to why, I think we can only assume. I think that a fair assumption would be that it contains the radar from the TU-160 (or a stripped-down version of it), and/or so the crew will have a similar visibility as they would on a TU-160.
The overall performance differences between the TU-134 and 160 are too far apart (the -134 being a subsonic airliner and the -160 being a supersonic bomber) for the shape of the nose cone alone to make any sort of a significant difference.


Can an aircraft have a lifting fuselage that only generates lift at certain speeds? I came across the blended wing body designs and their advantages etc. They are still very far from reality and require 20 more years till we see them fly. Isn't a conventional fuselage design with a somewhat flattened shape that generates lift during cruise only, a better alternative for now. Would it be possible? If yes, then that means the fuselage usually stalls in all other configurations but during a cruise at a particular AOA. That does mean that drag increases during climb and decent but the efficiency gained during cruise should mean that it is beneficial for a long-range flight?

I think you are looking at this backwards...  (at least for a utilitarian passenger type aircraft)
First, such a design is most certainly possible, but it would create more problems than it would solve.  Wings don't need extra help producing lift at cruise speeds, that is when they are most efficient.  Instead, wings can use a little extra help at slower speeds, which is why they are typically equipped with lift enhancing features like flaps and slats.
Second, producing lift creates induced drag.  You want the fuselage to be as streamlined as possible to produce the least amount of drag at higher cruise speeds, not more.  And if your lifting fuselage is fully stalled at all other phases of flight it will be producing MASSIVE amounts of drag.
This full-stall drag penalty would create significant performance problems in all other phases of flight that would likely cancel out any small efficiencies at cruise speed, such as redesigned wings, more powerful engines, etc.  I don't see anything to be gained by such an idea.
And finally, what makes you say that we are 20 years away from a blended wing body design being able to fly?  There have been all kinds of designs built and flown in the last century, I don't think there are any technological hurdles to this type of aircraft.


What are the areas of an aircraft that suffers most from G forces? i want to ask this time as to "what are the areas of an aircraft that feels or suffers the most from G forces?". i am asking this in terms of structural design and physical limits of the pilot(the position and seat angle) and the plane.
please try not to limit the airplane model to simple light-aircraft,try to expand it near to military Aviation and other else.

if possible, please try not to use high-falutin words since i'm having a hard time with words in English.

If you can not understand this clearly, i am sorry for my poor English and Grammar, and also i want to elaborate more, but i can't translate it properly at the moment.

Basically 3 places on an airplane see very high concentrations of stress in a small area from in-flight G loads.  In this case we'll say a single engine light aircraft.

Wing root spar fittings on a cantilever wing - the bottom in tension and the top in compression. For a high wing airplane with struts, it will be the strut attachments at each end that join the strut to the fuselage and wing.
The roots of the horizontal tail, same except upside down - bottom in compression and top in tension.
Engine mount attachment to the firewall - top mount in tension and the bottom mount in compression.

Those are the points where flight loads from a lot of mass are concentrated at a single point or set of points during high G loading and are where the structural elements will be heaviest.  For most other areas the loads are distributed over more of a large area.


Is there any particular reason the A380 doesn't have a centre wing tank? Today I learnt something new, but apparently the A380 has no centre wing tank, which leads me to ask, is there a specific, design reason for this? Or did Airbus just think those huge wings were big enough to hold all the fuel they'd need?

Although, I've heard rumours that the A380F if built would have had a centre tank (no idea how true this is), but this shows the engineering is possible, Airbus just chose not to go with it for the passenger version. Any reason why?

It simply doesn't need one. Depending on the source, the A380 has a range from 8200 NM1 to 8477 NM2. The current longest scheduled flight is AKL-DOH, which is 7848 NM3. So the current configuration is capable of flying any of the current routes.

As far as the A380F, it really wouldn't make sense to add a center tank there either. The extra fuel weight would mean less cargo capacity available.

 1 Wikipedia

 2 Aerospace Technology, 11/19/2013

 3 Wikipedia


What is the ICAO 24-bit code used for? I know that each transponder is linked to a unique 24-bit code assigned by ICAO. But to be seen by the Secondary surveillance radar the pilot set the squawk code (4 digit octal code) on the transponder as dictated by the Air Traffic Controller (ATC).

So, why do I need a ICAO 24-bit code? Has it any utility during navigation, or just during maintenance to identify the single transponder (and the aircraft associated)?

In short: the 24 bit address is critical on the technical layer of Air Traffic Control, but it is not used in the operational level. For identification of aircraft and association to flight plans, the air traffic controllers and the flight data processing systems rely mostly on the Mode A code and the aircraft ID (call sign) transmitted by the transponder.

The ICAO 24-bit aircraft address is an essential element of the way Mode S radar and TCAS work.

Before Mode-S radar, only modes A and C were used by civil ATC secondary radars.

Mode A and Mode C are unaddressed; every transponder receiving a Mode A or Mode C interrogation will reply*. This causes two problems, garbling and FRUIT.

Garbling is caused by the overlap of replies from multiple transponders. A transponder replies on 1090 MHz in the from of a number of pulses. For Mode A & C, there are at most 12 pulses between a set of framing pulses. When multiple aircraft reply to the same interrogation, these pulses mix up and it becomes difficult to find out which transponder sent which pulse. This leads to false altitudes or false squawk codes.

FRUIT (False Replies Unsynchronised to Interrogator Transmission) is caused by replies that are triggered by other radars. When multiple radars operate in an area, transponders can be quite busy and the radar is easily mislead by a reply to another radar. In addition to the timing (range) being wrong, the reply can be Mode A (squawk code) while the radar interrogated Mode C (altitude). There is no way to see what kind (A or C) reply was sent.

To overcome these problems of Mode A/C, Mode S was introduced. Mode S is quite different from Mode A/C and requires a more sophisticated radar and transponder. It uses the 24 bit address to distinguish responses from various aircraft and to interrogate specific aircraft.

Most Mode S interrogations are addressed; the interrogation contains the unique 24 bit address of the aircraft it is interrogating. This reduces the probability of garbling since other aircraft will not reply
Unaddressed Mode S interrogations will solicit replies that contain the address of interrogator (radar). This prevents FRUIT since the radar can verify that the reply is correctly addressed.
Unlike Mode A/C which does not have any error checking, a Mode S reply contains a 24 bit CRC check code.
Mode S Altitude and identity (squawk) replies have their own identifier so they can be distinguished.
Mode S radars can be operated in clusters and coordinate between them who is interrogating which aircraft at which time. This further reduces the message load and garbling / fruit probability.

For TCAS, the Mode S address is used to distinguish replies for various aircraft in the vicinity of the own aircraft. The TCAS transponder interrogates omnidirectionally (in all directions) and get's replies from all direction. Again, this is very susceptible to Garbling and FRUIT. Whilst TCAS can work with Mode A/C, for its reliability and coordination of resolution advisories, the 24-bit address is crucial.


Is (or was) it acceptable to throttle up for takeoff before being aligned with the runway center line? 30 years ago I was on a flight from Spain to Brussels and when we were heading to the runway for takeoff, the commander opened full throttle to the engines while we were still some 60º away from being straight on the center line. At the same time he said loudly over the cabin loudspeakers "¡Nos vamos!" (Let's go!).

Well, a psychiatrist on board said: "A psychopath, a complete psychopath!". And Gerald L Klerman, MD once told me that the FAA was concerned about finding a way to detect a manic pilot before takeoff.

Was the pilot dangerously irresponsible, or was it an acceptable way of handling an airplane?

Pilots in any size aircraft may sometimes be given an instruction from ATC such as "... Cleared for immediate takeoff ..." which means that the pilot is expected to execute the takeoff as quickly as he/she can safely do so.  That may involve applying noticeably more power than normal for the roll from the taxiway out to turn and line up with the centerline of the runway, to keep the speed up and get off the ground as soon as possible.  For example, there may have been an aircraft on final approach for the same runway and the air traffic controller wanted to be sure to maintain ample separation from the departing aircraft.  So unless you were in the cockpit hearing the radio communications and seeing what the pilot may have seen in the approach corridor, it's difficult to say for sure whether the pilot was hot-dogging or was just wasting no time getting out of the way of arriving traffic as soon as he could.

But on the other hand ... announcing to passengers "Nos vamos" while hitting the throttle in the taxi turn out to the runway centerline ... at best, that doesn't exactly sound like what a cautious and conscientious airline pilot would choose to be doing in that moment!

With two pilots in the cockpit it is not unusual for one to do the radio communications while the other manipulates the controls to fly the airplane.  Those words could have been quite fine for one pilot to say to another in the cockpit intercom as emphasis.  Maybe the pilot only meant to do that but mistakenly transmitted it to the passenger cabin instead; in which case that would have been an unfortunate and unsettling error although not an especially dangerous one.

Although I haven't done such a report myself (because thankfully I don't recall being involved in such an incident), if you observe an airline pilot doing something you consider very dangerous or inappropriate I'm pretty sure the airline would want to hear directly from you about it with details such as flight number, date and time of the incident, so they can investigate.  We can each do our part to keep flying safe!


Why do parked planes lock the control surfaces? After a discussion in chat about control surface locks I was wondering why they need to be locked in the first place.

Why do they need to be locked?

What is the best position to lock them in? up, down, neutral.

In the small planes I fly, it is called a "Gust Lock", and consists of a small metal bar that fixes the yoke in position, so that the yoke cannot move (left/right, or forward/back), and by association, the ailerons and elevator cannot move either.

As the name implies, this is for dealing with Gusts of wind... a sudden bit of wind over an unlocked surface can move the surface to its extreme position until it hits a mechanical stop.  If this happens repeatedly, say, over a stormy night, the repeated banging into a mechanical stop can create wear and tear on the surface, the control cables, or the yoke in the cockpit.


Has a C-130 ever been designated as "Air Force One"? Near the end of the movie, "Air Force One", Harrison Ford is transferred to a C-130, which then changes its call sign to "Air Force One". My question is, has a president of the US ever flown in a C-130 while in office?

As I am sure you are aware, the convention is that any aircraft that has the current US president on board is given the "One" call sign.

For military aircraft, this is the branch of the military followed by "One", which is why you have Air Force One, Marine One, Navy One. If he is on a civilian jet, it is called Executive One.

The actual plane that everyone calls Air Force One is called VC-25, which is the military version of the 747.

There have been many planes that have been called Air Force One, from a King Air B90 to Gulfstream jets and even a combat aircraft like the S3 Viking (which was called Navy One).

However, as far as I know - no president has flown in a C-130 while in office.

Just to close this off, if a president is no longer sitting and is transported; then the callsign changes to SAM (Special Air Mission); so for the "Air Force One" 747, this would be SAM 28000 or SAM 29000 - depending on which of the two is being used.

The classified callsign for Air Force One is Angel.


Why does indicated airspeed change with altitude? I know that if you fly at a low altitude and at a high altitude at the same TAS, your IAS will be lower at the high altitude than at the low altitude.   Why is this though?   Wouldn't the static vent account for the change in pressure?   I have heard it has to do with the change in density but why would this effect the system as it measures pressure not density?   Maybe because ram air pressure (measured by the pitot tube) is affected by density?

As you state, IAS is simply based upon the difference between total pressure and static pressure. For low subsonic conditions:

$$ p_t = p_s + p_q = p_s + \frac {1}{2} \cdot \rho \cdot V^2$$

$\rho$ is the air density, which is a function of air temperature: $\rho = \frac {p_s}{R \cdot T}$. For indicated airspeed, the density at sea level $\rho_{SL}$ at 15 degC is taken:

$$ V_i = \sqrt {\frac{2 \cdot (p_t - p_s)}{\rho_{SL}}}$$

However, the actual dynamic pressure measured by the pitot tube is caused by actual density.

When temperature decreases, density increases.
So at colder temperatures, some of the dynamic pressure is due to higher $\rho$
Therefore, the $V_{ind}$ bit decreases. The pitot only measures dynamic pressure and does not know what is due to temperature

Air is colder at higher altitude if we stay in the troposphere - climb to over 33,000 ft and the IAS does not change anymore.


What FAA license does the EASA LAPL convert to? I have read about getting a FAA licence to 'piggyback' with a EASA PPL(A).
Is there a similar route for a EASA LAPL(A) licence.
I assume if there is then there would be the same restrictions ie Max 4 on board, No night flying or IFR flying allowed, simply VFR, which would not be a problem for me.

Basically, I am looking to take a flying holiday (vacation - let's not upset the U.S. readers) - not hour building to gain any additional licences or ratings.

Unfortunately, an LAPL license isn't ICAO compliant. This is from the UK CAA:

  Licences which do comply are known as ICAO licences and those which
  do not are known as non-ICAO licences. Non-ICAO licences are not fully
  recognised internationally, and therefore are only valid for use
  within certain states or Europe; for example, the LAPL is only valid
  in Europe.

That means that the FAA won't recognize it and you can't use it to get an FAA PPL under 14 CFR 61.75, because that requires you to hold an ICAO compliant private pilot's license. As far as I know, there's no other way to convert a foreign license to a US one (a sport or recreational pilot license would be the closest US equivalent).


Why does fuel vaporize in the carburetor? So I get that a carb vaporizes fuel and mixes it with the air intake for the engine. But my question is what is the explanation for what causes the fuel to vaporize after it exits the fuel nozzle?

Vaporization is closely related to the concept of volatility, which in turn is directly tied to the vapour pressure of a substance.

The vapour pressure of a substance is a function of temperature, and is the pressure at which a room filled with some liquid (or solid) and some gaseous parts of the substance are in exact equilibrium. Increase the pressure, and some gas will want to condense; decrease the pressure and some liquid will want to evaporate. For fuels, this is in the order of tens of kPa (e.g., the Reid vapour pressure of avgas, which is the vapour pressure at 37,8°C, is ~38kPa).

If we assume that air is an ideal gas, we can say that liquid fuel and gaseous (evaporated) fuel are in equilibrium when the partial pressure of liquid fuel equals the vapour pressure of the fuel. Since the partial pressure of the constituents of a gas are directly tied to the molar quantities of a gas, we can easily extract the fuel-to-air ratio. Given that the partial pressure of oxygen is about 21kPa (which will only decrease if you add fuel, assuming this happens with constant atmospheric pressure), we can easily see that if you leave a tank of air and fuel (with a vent to keep it at atmospheric pressure) long enough for the fuel to reach equilibrium, you have a very rich mixture indeed.

So, we limit the amount of fuel entering the carburetor to close to stoichiometric (exactly enough oxygen and air). As per above argument, all of this fuel will eventually evaporate as the vapour pressure is much higher than the eventual partial pressure reached by the gaseous fuel. The only question that remains now is how fast we can evaporate all this fuel. This only happens at the surface of the liquid fuel, so the trick here is to maximize this surface area. This is done by spraying the fuel into tiny droplets, each of which has a large surface area compared to its volume (remember, area scales with the size squared, while volume scales with size cubed - if you make the droplets smaller, the volume will decrease more rapidly than the surface area). They will thus be fully evaporated before they reach the actual cylinders. The smaller the droplets, the quicker this happens and the better mixed your fuel will be into the air.


When is a high pressure system associated with IFR/MVFR conditions? So I've read that typically high pressure systems bring good weather and clear skies. However, for the current high pressure system we're experiencing in central USA, we're having quite a bit of IFR/MVFR conditions.

The IFR/MVFR conditions down along the Gulf of Mexico where there's a stationary front make sense, but I'm curious why there's IFR/MVFR weather from Missouri through Illinois, Indiana, and Ohio in the midst of this high pressure system.

[

Is my understanding flawed about high pressure systems? Perhaps I should really be thinking of high pressure systems as stable air masses (in this case stable, low clouds). Or are there other factors at play leading to IFR/MVFR conditions being associated with this high pressure system?

In case it's relevant (and the time/date is difficult to read on the screenshots), the conditions described were happening around 6:00Z on 2019-01-02.

In the temperate zone that covers the US and Canada, weather systems are generally related to frontal boundaries between warm/wet and cold/dry air masses, where the cold air pushes under the warm air and forces it up.

But in an area with a large weak high pressure system, you can get a lot of weather caused just by solar convection, depending on the humidity and lapse rate of the air in the mass.  The weather systems will be kind of randomly distributed around, instead of being arrayed along a frontal boundary.

You can see it in the chart you posted.  The weather along the Gulf coast is probably related to the stationary frontal boundary that is there, whereas the weather in the central states is from local convective conditions.

The absolute best practical book on aviation weather theory I've ever read is called the RCAF Weather Manual, written by the Royal Canadian Air Force as its primary weather training guide for pilots.  It is so clearly and logically presented I cannot recommend it enough.


Is center tank fuel required to start the 737-800 engines? I have been doing some flights with the 737-800 and when there is no fuel in the center tank, the engines won't start. Is it like that in real life?

(airliners.net)

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

Otherwise, it's a simulator problem.

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


Are there "Introductory flights" available to see if I want to pursue training? Through endless sources available it's possible to learn the rules of flying without undertaking formal training: I can take practice tests, study flying rules, laws, altitudes, speeds, controls, etc., however, I'd like to try out actually flying (preferably for free) before considering the option of paying for a full license.

Basically I'd like to take a trial flight - I don't care if someone has to sit with me, but I'm not keen on the idea of spending a lot of money before at least having one flight under my belt.

Teens often drive before getting licensed in private; any options for me to do the same with aircraft machines?

Well, to put it bluntly, somebody has to pay for the airplane.  Much like a car, somebody has to pay for the gas and maintenance.  The major difference is that both cost a lot more on an airplane so it is a lot harder to get someone else to pay for it.

However, similar to a car, if you have a friend that owns an airplane they may take you up for a ride and even (legally) let you fly it, but they remain the person in charge and responsible for the safe outcome of the flight.  If you want to try it for free this is probably one of the only ways to do it.

If you are willing to pay for a one-time flight which does not commit you to pay for your entire license, then you can go to almost any place that teaches people how to fly and they will be happy to let you fly with an instructor and charge you only for the time in the airplane and the time with the instructor.  Often they have an "introductory" flight just for this purpose which is discounted for potential students.  This is a relatively small cost in comparison to learning to fly that I highly recommend to anyone before they commit to getting their license.


How is fuel managed in the Zero-G A310? There are several Zero-G airplanes to experiment briefly microgravity without going into orbit. One is the A310 from Novespace (F-WNOV):

Novespace A310 F-WNOV (source: Jonas Wirz at Airplane-Pictures.net)

When a Zero-G flight is executed, fuel should take the form of a sphere in the tanks, like demonstrated in the cabin for a beverage.

Advertisement in microgravity (source)

Thoughts:

This effect won't appear in negative G, subject to the design, fuel lines may still be immersed in tanks, this cannot be the case in micro-gravity.
The 0G segment is likely flown with power. First this is not a continuously descending flight as seen below. Second, friction will slow down the free fall anyway and must be compensated by some acceleration from the engines.

0G segment is not limited to the descent (based on source)

How does Airbus ensure the fuel is still delivered to the engines at the required pressure, without air?

Related: Are engines fed differently in reduced gravity aircraft?

Basically it says no modification is required because the lines are pressurized, and this is supported by a 1966 Nasa study (Use of aircraft for zero-gravity environment) which is not more detailed. The line being pressurized downstream of the pumps seems only one element of an adequate design. Upstream fuel will experiment the effect of micro-gravity and lines are no more immersed in the fuel. Air can enter and create a problem when reaching a pump or an engine. Pumps could be drained. Maybe the problem won't appear during the 0G segment, but it should appear later.

I'd like to have the details about how pumps, pressure, flow, or anything else contribute to maintain a good fuel supply to the engines.

This is the fuel system for the A310:

(Source)

I wrote an email to AirZeroG and asked them:

  Other than the interior, are your aircraft modified in any way to handle zero-g flight?

Here is the response that they gave me:

  Dear Sir,

  Except free floating area cabin configuration, there are very few differences with a “standard aircraft”. The most significant one is installation of Zero-G meters in cockpit and a very simple installation on the wheels to help one pilot to lead the aircraft only in vertical axis, and the other pilot to lead only in horizontal axis.

  Out of that, the biggest difference is maintenance program: each parabola performed to create Zero G onboard is considered as an aircraft cycle for the aircraft and its engines, and maintenance adjusted accordingly. Such consideration dramatically increases maintenance costs of the aircraft.

  Kind regards

  Gilles GOMPERTZ

I would say that if there were a fuel system difference they would say that is more significant than G-Meters in the cockpit. I'm assuming based on the response above that the fuel storage/delivery system is unmodified.


What is the gray zigzag line over V154 between Dublin VORTAC and LOTTS intersection? Above Victor airway 154 on the IFR enroute low altitude chart, there is a grey zigzag line between Dublin VORTAC and LOTTS intersection.

What does the gray zigzag over the segment indicate?

Credit: SkyVector

According to the “Airspace Information” section of FAA Aeronautical Chart User’s Guide, it is a low-altitude unusable route. The high-altitude flavor is similar in shape with a smaller amplitude.

See also page 62 of the Guide PDF, if you prefer.

  UNUSABLE ROUTE

In this particular case, observe the overprint on 110 in the compass rose surrounding DBN, which indicates abnormal status. The Airport/Facility Directory entry for Dublin VORTAC (as of the 31 MAR 2016 publication) reads, with added emphasis:

  DUBLIN N32°33.81′ W82°49.80′ NOTAM FILE MCN.
    (L) VORTAC
   113.1   DBN   Chan 78   276º 7.9 NM to W H 'Bud' Barron. 306/5W.
  HIWAS.
      VOR portion unusable:
        215°–285° byd 10 NM blo 3,500’
        001°–139° byd 33 NM
        001°–139° blo 5,000’
  RCO
   122.1R 122.6 113.1T (MACON RADIO)

Note that the DBN 110 radial falls within the 001-139° unusable range. Beyond LOTTS intersection, V154 is defined with reference to the Savannah VORTAC.


What is the small cylinder on the firewall to the left of the battery? What is this and should the yellow wire be soldered to it?

Any ideas on preventing the wire from detaching again?

I checked the C150 parts manual but didn't see it. Is there somewhere else I should be looking, or did I just miss it?

That is a fuseholder for the optional clock or optional Hobbs meter. The yellow wire probably should be connected to it but you should have a certified mechanic inspect it.


How will the alpha lock function intervene when performing a takeoff at heavy weights on the A320? In the FCTM for the A320 family of aircraft's under the SOP Takeoff chapter it is mentioned that the alpha lock function can intervene when performing a takeoff at heavy weights.

Can someone please explain the logic behind this ?

Alpha Lock is a protection that will prevent surfaces retraction after take off if the angle of attack (ALPHA)is high for the next retracted position of the flaps/slats lever. So even if the pilot puts the selector in the retraction direction the order will be postponed till the angle of attack decreases. This is managed by the Fly By Wire logics. The logics takes into account more particularly the angle of attack and the configuration speed limits.


Can the TSA require supplemental screening AFTER a flight has landed? A few days ago, Kahler Nygard reportedly received a boarding pass indicating secondary screening was required, but that pat-down was reportedly never done. So when the plane landed, they took the passenger off the plane ahead of the others and requested that he submit to the screening at the destination airport, after the flight. He recorded the incident on his phone, and after confirming that he wasn't being detained, simply walked away.

The proposition that screening a passenger after the flight has landed might retroactively increase the fight's safety is, I think we can all agree, counter to the fundamental nature of causality.

But the question is this: Is screening passengers after they have arrived at their destination without incident within the rights and responsibilities of the TSA? Clearly it doesn't jive with the whole "cause and effect" framework of reality that we all live in, but are they within their rights to demand such screening anyway?

TSA staff actually have very little authority - they can prevent you boarding an airplane, they can stop the airplane from leaving. For everything else, they call the local police (the phone is their Big Stick - they can call in some serious assistance, like SWAT or some loaded F-22s).

This sounds like a classic bureaucratic whoopsie - someone missed the initial screening note, someone else noticed that the box wasn't ticked in the system, and protecting the monthly performance statistics prevailed over common sense. Since the passenger declined the search they can prevent said passenger from boarding a flight, but since he did not wish to board a flight (and has not done anything illegal) all they can do is ask him to leave the secure area. As that is exactly what the passenger wanted to do anyway.....


Will air traffic control ever ask a plane to not brake hard on a landing? In another question, somebody asked why an airplane might not deploy thrust reversers on a landing. One of the answers suggested a few options, including:

  Depending where the gate was, they may simply have wanted use more of the runway to speed up the taxi

It occurred to me that it's not just a matter of a pilot wanting to get to the gate sooner; it could be that ground control wants them to take that last exit (for whatever reason), but air traffic control wants them off the runway quickly so that they can use it for another airplane.

I assume the final decision of how to conduct the landing is the pilot's. But will air traffic control ever ask nicely, "you're going to be taking the last exit, but please don't do the final bit of braking until the end, because we'd like to get another flight taking off right after you land"?

Yes, we can ask you to plan your landing roll in a certain way. We won't technically instruct you to brake the aircraft in a specific way, but simply to aim for a specific taxiway after landing.
There can be different reasons for this, but generally it is an attempt to expedite traffic flow on the ground at the airport. For example, if you are landing on a long runway and your parking position is near the far end of the runway, I might ask you to keep the plane rolling down the runway and vacate at the end, in order for you to have a shorter taxi time.
It could also be that the taxiway you would normally use to leave the runway is blocked by another aircraft or vehicle, and I want you to leave the runway via a taxiway that is further down the runway.
However, extending the landing roll does extend the runway occupancy time as well, so if there is another aircraft behind you on short final I will not offer you to perform a long landing roll. This is also why you should always ask ATC if you are planning to perform a long landing for one reason or the other – if we have someone else just a couple miles behind you, we might have to instruct them to go around if you do not vacate the runway like we expect you to.
With regards to reverse thrust specifically, there are airports where the use of reverse thrust is only permitted in special situations. This is to reduce the noise level at and around the airport. However, this is purely a regulatory thing, and is not actually related to ATC.
ICAO offers the following guidance on  the subject (DOC 4444):

7.10.3.1    When necessary or desirable in order to expedite traffic, a landing aircraft may be requested to:
a) hold short of an intersecting runway after landing;
b) land beyond the touchdown zone of the runway;
c) vacate the runway at a specified exit taxiway;
d) expedite vacating the runway.
7.10.3.2    In requesting a landing aircraft to perform a specific landing and/or roll-out manoeuvre, the type of aircraft, runway length, location of exit taxiways, reported braking action on runway and taxiway, and prevailing meteorological conditions shall be considered. A HEAVY aircraft shall not be requested to land beyond the touchdown zone of a runway.


What is the effect of changing the autobrake setting after touchdown? If an autobrake setting is chosen prior to touchdown, but after touchdown and nosewheel compression (i.e. after the autobrake has engaged) a different setting is required, is it safe to change the setting during the roll-out? What happens when the setting is changed in this manner? I know application of manual brakes disables the autobrake. Does the autobrake immediately match the new deceleration requested?

This answer was difficult to find as both Flight Operation Manuals and Maintenance Manuals did not say. The only guidance was found in the system description provided by the OEM of the BCSU.  I am not mentioning the fleet type because at some point the detailed description might become proprietary.

According to the description I found for a given automatic braking system is that it is armed when the pilot presses one of the three pushbutton switches which set the auto-brake level.

The system will only arm if gear up is not commanded, there is hydraulic pressure as needed, and no existing faults exist that prohibit normal braking, as well as a few other computers available on the associated data bus.

There is nothing that says the system can't be armed after touchdown, however the system will only engage when the spoilers are being activated, or are activated. Or more precisely from the black-box point of view automatic braking is engaged whenever two spoiler signals in three appear once automatic braking has been armed.  In other words, once armed, the automatic braking will only engage if spoilers are sending the signal that they are being activated, or are activated.

It specifically says that the pilot can select another pushbutton switch even after
arming. The BSCU acknowledges this new command and executes
the corresponding task.

Automatic braking is released whenever the braking sequence
is interrupted:

when an arming condition disappears,
when an engaging condition disappears,
when one or both brake pedals are held down beyond the
defined threshold,
when the selected pushbutton is pressed again.

The question, therefore is 'After you have already armed at a given setting and the system is actually engaged, because the spoiler actuation has initiated auto-braking, what happens when you press another setting?'  As long as the arming conditions still exist, which in most cases would, and as long as the engage conditions exist, as would be the case if the spoilers are activated (at least 2 of three spoiler signals being sent to the BSCU), then yes, you may change the setting after touchdown and the BSCU acknowledges this new command and executes the corresponding task.


Stadium game at Miami blocking runways? So I was looking for the Miami In in SkyVector and I saw this.

Apparently a stadium game has the power to block runways in (At least in US).

What is really going on there? I am not well acquinted with charts.

The blanket NOTAM includes this language:

  UNLESS THE AIRCRAFT OPERATOR MEETS AT LEAST ONE OF THE FOLLOWING REQUIREMENTS: A) THE AIRCRAFT OPERATION HAS BEEN AUTHORIZED BY ATC FOR OPERATIONAL OR SAFETY PURPOSES, INCLUDING AUTHORIZATION OF FLIGHTS SPECIFICALLY ARRIVING AT OR DEPARTING FROM AN AIRPORT DESIGNATED BY ATC USING STANDARD ATC PROCEDURES AND ROUTES


Would a 2nd row of distributed props on a 2nd staggered wing of a biplane increase its efficiency? Would a 2nd row of distributed props on the rearward wing of a biplane with 25% gap and 150% negative stagger increase the efficiency of a biplane ULTRALIGHT, 25MPH, Re 500K? ( rear wing is 25% lower than forward wing, 150% rearward)

Both wings would have distributed propulsion from several props along their span in tractor configuration.

Forward wing props see a prop inlet speed of V1, or aircraft speed.

Forward wing sees V2 ( exit speed of prop), (assume an increase in speed of 50%, based on prop size, Hp using prop formula) V2=150%V1

Calculate forward wing size based on 150%*V1*k1

k1= efficiency/coverage factor of Wing1

Props of 2nd (rear) wing would have a inlet speed of V2, but an exit speed of V3 ( assume another 50% increase)

2nd wing sees a speed of V3=150%V2=150%(150%V1)=225%V1.

Calculate rear wing size based on 225%*V1*k2

k2=efficiency/coverage factor of Wing2

An interesting note: average leading edge airspeed over wings is (150%+225%)/2=190% of aircraft speed!! ( if this proposed theory is correct)

Is this correct, at least conceptually? See side view of configuration below.

Source: nap.edu

Not really no. The velocity off a propeller does not shoot straight back, rather in circular motion (shown above and below).

Source: High-Lift Propeller System Configuration Selection for NASA's SCEPTOR Distributed Electric Propulsion Flight Demonstrator, NASA

From the conclusion of that NASA report on span-wise propellers generating lift:

  A potential constraint on the design of the high-lift propellers system is the total thrust. If large amounts of lift augmentation are required from the propellers, then high thrust values from the high-lift propellers are likely. If these propellers produce excess thrust, then the aircraft will be unable to sustain flight at the desired speed. This implies that drag producing devices may need to be added to the aircraft or the primary propellers operated as windmills to produce additional drag.

Applying the same conclusion to the biplane, thrust will be wasted, and possibly will work only in a limited angle-of-attack range for the prop-boosting-prop-boosting-wing idea.

Own work; variable pitch blade

Note that a very fast stream before a propeller leads to [forward] thrust losses due to the propeller's angle-of-attack (shown above). And the less efficient the thrust becomes, since the momentum change will be harder – propellers add little velocity to large amounts of air, in fact, the pressure rise (a thrust measurement, which also is indicative of the mass flow) is around only 2% for propellers.


What percentage of airliner flights globally are freight flights? So we have N airliner flights in the world each day. What percentage of them are "purely" cargo flights versus passenger flights (that may carry cargo as well)? We can exclude Combi aircraft and other intermediate cases for the sake of simplicity. Thank you.

The National Air Traffic Controllers Administration states that:

  "On any given day, more than 87,000 flights are in the skies in the United States. Only one-third are commercial carriers, like American, United or Southwest. On an average day, air traffic controllers handle 28,537 commercial flights (major and regional airlines), 27,178 general aviation flights (private planes), 24,548 air taxi flights (planes for hire), 5,260 military flights and 2,148 air cargo flights (Federal Express, UPS, etc.). At any given moment, roughly 5,000 planes are in the skies above the United States. In one year, controllers handle an average of 64 million takeoffs and landings."

Therefore, if there are 28,537 commercial flights and 2,148 cargo flights;

28,537 + 2148 = 30685
(100 / 30685) * 2148 = 7.00016294606%

Thus there's for all of the airline flights taking off daily, 7% of them are cargo, and the rest are commercial.


When do controllers assign a squawk code to VFR aircraft in Canada? In all of my previous flying experience the controllers provided a squawk code only when I requested flight following. On a recent flight from Buttonville, Ontario (CYKZ), the controller provided a squawk code on the ground. I asked if she was providing a squawk code because she was going to provide flight following as well. She said the flight following will need to be requested after she hands me off to Toronto City Center.

Then why was the squawk code provided? Was the controller anticipating the need for a squawk code? Are all airports in the Toronto region required to provide squawk codes to departing flights?

The controller will assign you a squawk code if they want to differentiate your radar return from other aircraft. It has nothing to do with whether you're getting flight following or not. If they're happy they know which blip is you for the length of time that they'll be watching you, then they may not give you a squawk. In some airspace, the moment you begin talking to them then they'll give you a squawk. All depends.


Why are birds attracted to airports? Birds are usually around airside. Apart from answering it myself, I am looking for community knowledge on this topic.

Airports are a wide, open space with a full environment. The attractiveness of vegetation is a balance between food presence, food accessibility, and protection against predators.

And these factors vary a lot for every bird or animal species.

Food
Food accessibility depends on vegetation height and density. Long, dense vegetation will inhibit most hazardous birds/wildlife from moving around, detecting and accessing the food. In addition, birds/wildlife feeding on seeds will avoid the airport if its vegetation is mowed during the flowering season.

Depredators
On the other hand, many species prefer to stay in the open space of short vegetation where they have a wide view to see predators well in advance to enable them to flee on time; and safeguard themselves from predators by hiding or fleeing.

(from AirportBirdControl Blog: 6 most asked questions and answers)


How would the wave drag of an elongated Sears–Haack body change with a cylindrical mid section? Would a Sears–Haack body have the same wave drag as the same body with cylinder of the same diameter placed in the middle, between two halves of the Sears–Haack?

No it will not have the same wave drag.

The low wave-drag of a Sears-Haack-Body is achieved by the smoothness of the body. This means kinks are not allowed. The picture below shows the Mach-Number distribution around a Sears-Haack-Body (taken from YAMAZAKI 2014). Notice the gradual change of the Mach number along the body surface .

The following illustration shows the proposed elongation of the body by inserting a cylinder.

By adding a cylinder the curvature of the body does not change gradually (smoothly) but stops - stays constant - and starts again.

This will trigger a Prandtl-Meyer-expansion (example below, taken from here) which will distort the smooth flow around the body and thereby increase the wavedrag.


Is any convention to tell the propeller rotation direction of an airplane? Here are two airplane with single and dual engine.

From single engine airplane we know there is TURN LEFT tendencies. There are four tendencies (Torque reaction, Precession, Slip Stream, and P-Factor) caused by the propeller rotation, which it rotate clockwise seen from the tail to the nose side. If the rotation is opposite, probably the name will be TURN RIGHT tendencies.

Then my question, is any convention to tell the propeller rotation, such as, rotation is must be seen from tail or pilot side. I.e:

Clockwise, mean the propeller is rotates clockwise seen from the tail nose side. Vice versa:
Anti/contra/counter clockwise, mean the propeller is rotate anti clock wise seen from nose to the tail side.

The four tendencies are like confirming that the rotation is clockwise seen from tail side to the nose side. But however, I need a valid info regarding this, which expected the convention is applicable to another airplane with multiple engines/propellers and it will confirm that no need to tell where our stand point when saying the propeller direction. It is enough to say, clockwise or anti/counter/contra clock wise.

When you say "clockwise" or "counter-clockwise" it is generally accepted that this would be the view as if you were standing behind the aircraft. Unless it is otherwise stated, this is the convention that you can assume.

If you need a way to tell by looking at the prop, the thicker part is the leading edge. In the first photo you posted, this would rotate counter-clockwise from the perspective of the photographer, or clockwise from the perspective of behind the aircraft. This is, by convention, a clockwise rotating propeller.


For the CFIs, CFIIs, MEIs, and AGIs - How often do you find students that utilize your ratings? I am curious. Out of 100 new students that walk into the average flight school, how many only need a standard CFI, how many do instrument training, and how many do multi-engine training? Additionally, how much work does an AGI get? I’m trying to compare the cost of these ratings against how often they will be utilized.
Also, for the sake of data that makes some kind of sense, let’s exclude the recent Covid-19 market activity and go with pre-February 2020 numbers.

First off, it depends on what kind of flying you want to do.  Remember a flight instructor certificate is not required to fly an aircraft, either personally or professionally.  The problem comes in that most professional flight jobs, either under part 121 or 135 require over 1000 hours total flight time and in some cases over 1500 hours TT.  For a budding pilot with no other sources of income, this becomes almost insurmountable without doing flight instruction, as you’re legal to do this with 250 hours TT, a CPL, INST-A, and a CFI.  If you do go the instructor route, the ratings you get for a flight instructor certificate all depend on what you’re going to do as an instructor. Instructor pay is based upon 1) the number of ratings that you have and 2) your dual given time.  Remember, the more ratings you have the more flexible your employment options are; CFIs with 152/172 time are a dime a dozen.  MEIs command the greatest salaries, though some schools only pay top dollar for multi engine dual instruction hours.  Many schools today won’t employ you without at least a CFII (welcome to the insanity of flying for a living!).  As to AGIs or IGIs, it again depends on the size of the flight school and the number of ground courses being offered.  You can also do this as an independent contractor, but you will also have to recruit clientele, this is work in and of itself.  Large Part 141 flight schools may have dedicated ground instructors for ground school, or may simply require new hire CFIs to hold ground instructor ratings.  Ground instructor ratings are relatively easy to obtain; some home study followed by a testing fee of $300 or so for both the FI and AGI will get you one.  Typical ground instructor pay is lower, on average, than flight instructor pay, but it all depends on your ratings and experience.
If you’re interested in making money as a CFI, my advice is to specialize.  As I said before a CFI with dual time in Cessnas is so common that it doesn’t command much in pay in and of itself.  Someone who can do, say, multi-engine, tailwheel, basic and advanced aerobatic training, CSIP certified, type ratings, seaplane rated, mountain flight training, warbirds, helicopters, gyroplanes, etc. can command over six figures as a CFI.  The downside is that obtaining these additional ratings will cost hundreds of thousands of dollars so entry becomes prohibitive.
Now as to the numbers of people who become pilots and then flight instructors vs come through the door with an interest in flying, I’m not sure but I’d venture a guess that around 75% won’t even solo.  Most people take a general interest in learning to fly then quit after a few flights from 1) the cost and time required to train, 2) medical or other barriers which prevent them from pursuing flight training and 3) the difficulty of flight training - many people expect something similar to the standards of US Driver’s Education or an MSF basic rider course and become disenchanted with flying when they can’t learn in a weekend by reading a 40 page booklet with a few flights.  In the United States there are only about 600,000 licensed Pilots in a country of 300 million.  Doing the math this works out to be about 1 in 500 people hold a Pilot certificate.  Pilots holding instrument ratings are around half of the total ie about 300,000.  Commercial, and Airline Transport Pilots - professional people who fly for a living - are around 100,000 and there are about 100,000 active flight instructors in the US as well.  You can check the FAA’s Airmen Statistics for more precise figures.  So if we go by the numbers of students at a typical flight school, out of 100 new people off the street, on average, only 25 will become licensed pilots.  Of those 25, 12 will get instrument ratings and 6 will go onto obtain commercial certificates and flight instructor ratings.


Why would the USAF have no support for autolanding? One thing I noticed when reading through the KC-10 flight manual (see page 184 for the specific reference) is that the KC-10 lacks support for Category III operations, unlike its civil DC-10 brethren.  What was the purpose behind the USAF asking MDC to remove capability from a military airplane?

Furthermore, military ILS systems in the US are qualified to CAT II at best, even in areas where air carrier airports are well-qualified for CAT IIIb minima.  For instance, Joint Base Lewis-McChord only has a CAT II approach to RWY 34 whereas nearby Seattle-Tacoma Int'l has CAT IIIb approaches to 300' RVR on all three of its primary instrument runways.  Considering that I seriously doubt the USAF would somehow be buying ILS equipment inferior to what's available in the civil market -- is there some other reason they don't provide any low-visibility capability better than the CAT II minima of 100' DH and 1/4 mile visibility, as the published PAR minima in the A/FD are no better, either?

Update: KADW RWY 19R has a CAT IIIa approach, good to 700' RVR.  This seems to be the only military CAT III procedure published, though.  Perhaps the VIP airlift aircraft (E4, etal) have autoland support, even though the normal military heavies don't?

FWIW, I do not fly the KC-10, but I do have friends that do...

Anyway, you're looking at a T.O. that is 7 years old since the last change (not sure when the most recent write-in is)...  Military pubs are always changing, avionics upgrades are always happening, and what you're looking at may be severely outdated.

Having said that, I don't believe in this instance that it is.  However, I don't see the need to be able to shoot CAT IIIc approaches.  What does the Air Force gain?  Once deployed you aren't going to have that technology, and CONUS you just divert.  So why spend the money for it?

I may not know the full politics behind it, but I do not see the operational need for it.


How does outflow valve work? As we know that outflow valve normally closes during climb and cabin altitude also increase but why does outflow valve open if we have selected manual pressurisation and increasing cabin altitude !

If you're selecting increasing cabin altitude, you are lowering cabin pressure.  To do that you have to let some air out of the balloon (the pressure hull).  So the valve has to be opened more (they usually never fully close because there is always more inflow than needed to maintain cabin pressure with both engines running - how much open depending on how leaky the pressure hull is).


Reference Map of EUROCONTROL charging zones I'm building out an application to calculate EUROCONTROL navigation fees. EUROCONTROL make one of these already, but I need to replicate the functionality within my own stack.

In the aforementioned EUROCONTROL app, there is a data file containing what appears data in a geospatial format. In order to do the required calculations, I first need to understand that data format.

My first impression is the first row is some metadata. EG means the UK. From there the number pairs begin and end the same, indicating a closed polygon.

Example for EG (so UK) is here

3274 -600
3300 -600
3360 -600
3420 -600
3480 -600
3540 -600
3600 -600
3660 -600
3660 -540
3660 -484
3660 -480
3660 -420
3660 -390
3660 -360
3660 -300
3660 -275
3660 -240
3660 -180
3660 -120
3660 -111
3660 -60
3655 0
3600 0
3420 300
3300 300
3090 120
3067 120
3060 88
3040 88
3000 -15
3000 -120
2930 -480
2940 -480
2970 -480
3000 -480
3060 -480
3140 -330
3235 -330
3265 -490
3320 -415
3325 -440
3320 -495
3285 -540
3274 -600

Plotting the numbers in an SVG, so simply turning the numbers into pixels gets me this...

I'm hoping that matches a EUROCONTROL map someplace. Geospatial data  can be quite complex, and I don't really understand a lot of that complexity, so projection might be off (or any number of other things).

Can anyone point me in the direction of this within an official EUROCONTROL document? From there its a short hop to understanding how that original data file can be translated into some GIS software that gets me to the next stage of my project.

That is the map of the European airspace, however you have mirrored it such that north is now south and vice versa.

source: Eurocontrol

GC    Spain Canarias
AZ    Portugal (Azores)
LP    Portugal Lisbo
LE    Spain Continent.
LF    France
LS    Switzerland
LI    Italy
LM    Malta
LG    Greece
LC    Cyprus
LT    Turkey
UD    Armenia
UG    Georgia
LB    Bulgaria
LA    Albania
LW    Republic of North Macedonia
LY    Serb.-Montenegro
LD    Croatia
LQ    Bosnia Herzeg.
LJ    Slovenia
LO    Austria
LH    Hungary
LR    Romania
LU    Moldova
EP    Poland
EG    United Kingdom
ED    Germany
EH    Netherlands
EB    Belg.-Luxembourg
ES    Sweden
EK    Denmark
EF    Finland
LZ    Slovak Republic
LK    Czech Republic
EY    Lithuania
EN    Norway
EI    Ireland
EV    Latvia


Slow Flight for CFI/Commercial Pilot - Should the gear be up or down? I was practicing teaching how do demonstrate slow flight in a Cessna 172RG as an instructor, and I have always just assumed that you would extend the gear for the maneuver, but when I looked at the Practical Test Standards (PTS), it doesn't specify up or down, just selected landing gear...configurations.

Does this mean that one should be able to demonstrate slow flight both ways, with the gear extended and with the gear retracted?

  XI. Slow Flight, Stalls, and Spins
  ...

  Task A: Maneuvering During Slow Flight (ASEL and ASES)
  ...

  c. Performance of the maneuver with selected landing gear and flap
  configurations in straight-and-level flight and level turns.

Reference: FAA-S-8081-6D

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

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

(emphasis mine)

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

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

(emphasis mine)

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

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


Did the space shuttle have a stall warning system (such as a stick shaker)? I've been wondering about this, but I can't find any sources one way or the other:

Was the space shuttle equipped with a stick shaker and\or other stall warning system?

The shuttle was not built with this capability. NASA AMES had a project MIDAS intended to improve the shuttle's cockpit information display and management. In its list of problems to address:

  Finally, there is no warning or guidance/autopilot limiting when approaching a stall on entry.


When might an aerodrome contain a public right of way? My textbook on air law says the following about Rule 41 of the Rules of the Air:-

  A person shall not, without permission, go onto a part of an aerodrome provided for the use of aircraft. This applies to any part that is not a public right of way.

It seems unlikely that you would have a public right of way across the manoeuvring area or apron of an aerodrome. How common is this?

Less busy than Gibraltar, but in the UK proper, Sumburgh in Shetland is an example of "road crossing the runway" on a relatively active airport - it even comes complete with level crossing gates, which are a startling thing to see on the road ahead when you know there's no railway!


Is there an analytical description of the NACA 642-015A profile? While searching for symmetric profiles I stumbled across different definitions (point-clouds) of the NACA 642-015A profile.

http://airfoiltools.com/airfoil/seligdatfile?airfoil=n64015a-il
http://www.airfoildb.com/airfoils/418.dat

The figure below (skewed) shows the difference in percent chord on the secondary axis (green markers).

What causes these differences and is there a analytical description I could use to create a point-cloud with higher resolution.

Another question is:
The NACA Reports I could find via Google all feature the NACA 642-015 (without the "A"). The difference between NACA 642-015A and NACA 642-015 is an increased thickness of the A-version towards the trailing edge.
Who introduced or developed the A-version?

This report seems to include a reference to an analytical description of 6-series airfoils

On your second question: found this reference in Synthesis Of Subsonic Airplane Design by E. Torenbeek:

  A modification to the standard series is the A-series in which the sharp trailing edge angle is replaced by a larger one, resulting from straight contours which run from 80% chord backwards.

The paragraph contains a reference to "Theoretical and experimental data for a number of NACA 64-series airfoil sections" which turns out to be NACA LM R6J01


What is the most effective of propeller's rotation in a two-propeller engine airplane? Consider two-propeller airplane as picture below (picture 1 (the above) and picture 2 (the below)). Which one is the most effective configuration to produce thrust power, stability, structural design, etc if still any?

Picture 1 (above): the bigger angle of attack (due to parallel to the gravitation) is meet near the fuselage, in between the two propeller's axis.
Picture 2 (below): the bigger angle of attack is outside the two propeller's axis.

Need physic analysis to answer this question.

TL;DR: The first one.

It all comes down to P-factor.

Airplanes fly at a positive angle of attack, so as you can see, this AoA for the wing translates to positive AoA for the descending blade. Vice versa, the positive AoA for the wing is negative AoA for the ascending blade. I.e., the descending blade has more thrust than the ascending blade under AoA.

Now it is pretty obvious why you want the descending blade on the inboard and ascending blade on the outboard, because in a single-engine-out incident this creates a less yawing moment to the otherwise arrangement.

However, life does not always turn out as we want it, as the engineers at Lockheed learned the hard way when testing their XP-38. They had gone through the trouble of using handed engines and props, making the starboard engine turn counterclockwise and the port engine clockwise. Now the fighter appears to be perfect: no torque, no gyro, a minimum yawing moment in a single-engine-out situation. But the XP-38 had pitch control issues which were later found out to be caused by the downwash created by descending inboard blades hitting the wing section between the boom and the central nacelle, creating a disturbed airflow trapped between the twin booms and finally affecting the elevator. In the end, they had to switch the engines' positions so the P-38 ended up with two critical engines.


What's the breakdown of total development cost for the various components of an aircraft? Can someone please explain citing an example Aircraft an approximate breakdown  of the cost incurred in developing each part of the aircraft( fuselage, engine choices) and other things like certification that allow it to be sold to the public. Preferably an example of a plane with a clean sheet design like the Concorde which was nothing like other planes of the time.

This Powerpoint has some pretty solid data in it in terms of the general relationship of cost to sales and what not. In the end of the day you simply cant find these numbers unless the company is willing to share them (which they generally are not).

Here is a very dated paper from the airforce that also talks a bit about what you are looking for.

This poorly cited answer states its cost Cirrus $150,000,000 to develop their new Vision Jet.

A few side notes

The Concorde is not a great example of developing an airplane when it comes to cost analysis. BAE (the company that designed and built it, was BAC at the time) had most of their cost undercut by the British and French Governments at the time. The program cost an estimated 1.3 Billion Pounds Sterling and was as much about national pride as it was building a fast plane. You can find some great info on it here (48:20).
Older airframes like the Cessna 172 right on up through the Boeing 737 were built and certified in a very different time. Regulations were different and generally looser. As such it would be useless to compare the cost to get a type certificate when these planes came out with getting one today. At the same time these planes are both still in production. For what its worth the cost of keeping that type certificate up could be brought into the equation.


For the same airspeed does the attitude of an airplane change with varying wind directions? Should one maintain a constant attitude if he wants to hold a constant speed or does the attitude vary depending upon the wind direction?

If by attitude you mean pitch attitude or angle of attack (which is how I automatically understood this), no it does not change as this is related to the aircraft's airspeed through the air. So an aircraft flying downwind will have the same AOA as the same aircraft at the same airspeed flying upwind.

If you want to fly at the same groundspeed upwind as downwind, then you would have to vary your airspeed, which means varying you pitch attitude or AOA. This might not be possible if say you were in a light aircraft in a 40 knot wind at altitude which cruises at 100 knots.


Where is fuel metered in continuous flow fuel injection system? How is fuel metered in continuous flow fuel injection system?

Just in front of the engine. It makes most sense to measure fuel flow as close to the engine as possible: any leaks between meter and engine will distort the measurement. Here is an example of the B737 arrangement.

As to the how, airborne fuel flow meters work in the same way that turbines do: the mass flow of the fuel causes an impeller to spin, rotational speed is then a measure of fuel flow. Note that it is a measure of fuel mass flow, not fuel volume flow: mass flow is not subject to variations due to temperature etc.


Why do airplanes have complex air conditioning systems? I'm wondering why do planes have complex air conditioning systems with several coolers, compressors and turbines. If these devices are powered by bleed air from the engines, why isn't the bleed air simply cooled and depressurized with valves? Is it due to easier pressure regulations as the pressure of the bleed air surely changes depending on the amount of current thrust from the engines, altitude of the plane etc. or is there some other reason?

It's because for the Air Cycle process, to chill ambient air without refrigerant, to work, you have to take really hot high pressure air and and remove most of the heat while keeping the pressure up, so that when you let the pressure drop at the end of the process it ends up way below ambient temperature.

So you take air off the engine compressor at some pressure like 80 psi and, say, 400F, pass it through a radiator (precooler) to cool it down, pass it though another compressor (the Air Cycle Machine's compressor) to boost the pressure, and therefore the temperature, again, run that through more air to air radiators or heat exchangers to cool that down, then, when you have the pressure still really high but have removed most of the heat, you let it expand and drop the pressure closer to ambient.  While doing that, you pass it by a turbine, which drives the compressor.  (An Air Cycle Machine is more or less a big turbocharger like device, pipes, radiators, and valves).

You now end up with air that entered the engine at 70 deg F coming out the Air Cycle Machine at just above freezing when it's properly regulated.  That air is mixed with raw hot bleed downstream to create the final inflow to the cabin.

An ACM can in theory put out extremely cold sub zero air if all the bleed flow available is run through it.  That is to be avoided because ice formation on the expansion turbine and inlet nozzles becomes a problem and this is one of the main factors in damaging them.  The other headache is dealing with all the condensate water, which causes turbine erosion problems.


What are these diagonal devices above the leading edge of the V-22 Osprey's wing? The Osprey has some kind of aerodynamic devices sticking up along the top of the leading edge. This picture from the Wikipedia page of the wings rotated shows them against its silhouette:-

Public domain picture taken by Lt. Col. Kevin Gross

You can see them a little clearer on this photo shot from above, on the same page:-

Author Peter Gronemann, licensed CC 2.0

Seen from above, they look like alternating slashes and backslashes, and they're clearly intended to change the flow properties in some way. But what precisely do they achieve, and how?

The protrusions you're asking about are vortex generators.

As to how they work, there is a separate Stack Exchange article on that: How do vortex generators work?

(Please note, the linked question/answer does not even MENTION the CV-22, and is thus not a duplicate question to this one.)


What are those markings on runway 25L at Frankfurt Airport? 50°01'59.15" N 8°34'05.10" E

What are those markings on runway 25L at Frankfurt Airport?

UPDATE:

July 2016 imagery shows the runway as closed, top image is c. 2015.

Zooming in further makes it look like vehicle tracks, like someone was going back and forth over the runway at 15-meter intervals. Looking further down the runway, it looks as though it is made up of 15-meter wide concrete plates (in lack of a better name). Perhaps the tracks are a sign of some maintenance of the mortar between these plates?
It's possible to have been WIP (work in progress) for the removal of the unique experimental approach system Frankfurt Airport tested. In which they had two separate touchdown zones, with the one farthest down labelled 26L, thereby allowing two glide-slopes—one higher than the other—to reduce the wake turbulence separation for parallel runway operations. That system is no longer in use (obsolete AIP link).
If not, then the runway closure in the second frame would indeed confirm some sort of intermediate maintenance until the runway could be closed for a proper overhaul.

HALS / DTOP was the experimental special landing procedure at Frankfurt Airport (tested from 1999 to 2004) with the aim of increasing the landing capacity on the existing runways.
HALS is no longer in use and all approach procedures are suspended, as this operational method failed to prove itself in practice. At the end of 2008 or beginning of 2009, all the navigation, corresponding markings, and firing systems to runway 26L were removed.
The acronyms HALS / DTOP stand for High Approach Landing System and Dual Threshold Operation.
— de.wikipedia via Google Translate [edited]

Special thanks to J. Hougaard and mins, they basically answered the question.


For an electric airplane are propellers the only option for propulsion? This is for an electric airplane (so no fuels for combustion):

Are propellers the only option?
Is there a turbine-jet possible with only air intake, electrically compress, and  a turbine and nozzle and get equal or more thrust than a propeller like a water-jet but then with air?

Propellers in some form are really the only option. It is currently the only efficient way to generate thrust with air as a medium. Even jet engines are in some sense just a very elaborate system of propellers.
The reason for the turbine is to create an environment to efficiently burn fuel (suck, squeeze, bang, blow) to generate as much thrust as possible. Hence, in an electric aircraft this is irrelevant. You might be interested in the Airbus E-Fan, which uses ducted propellers increase efficiency. However, it is still 'just' a propeller with an electric motor in the middle.


What values can/should be used for the isentropic efficiency of a compressor and turbine? I was trying to model an turbofan aircraft engine using Matlab and Simulink. In the process I have fixed certain parameters to some specific values which are nominal operating values of the parameters. Can anyone please help me out with the values of isentropic efficiencies of compressor and turbine used in the above case?

An answer is in the table of the linked question: What is the efficiency of the turbine of a modern jet engine?. Column 4 is for modern engines, column 1 is for old engines, about 1960’s technology. So, take your pick. In order to get a simulation running, an exactly correct figure isn’t necessary, something in the ball-park is fine.

The third comment above gives another similar source. Either would be fine.


What is this flying boat being restored at the Udvar Hazy Center? I am fortunate to live ~20 minutes from the Smithsonian Steven F. Udvar-Hazy Center.  At the back of the Museum is there restoration hangar, surrounded on two sides by a second level glass enclosed observation walk which allows guests to look in on what is being restored.  Because these aircraft aren't actually on display, I was not able to figure out what type of plane this is:

I was originally thrown off by the wings in the background, clearly embossed with the German Iron Cross, but I don't think the flying boat in the foreground is German.  Can anyone identify the plane in the foreground?

Here's a link to the original photo, in case you want to get a closer look.

It is a Sikorsky JRS-1 (Like terry I thought it was a PBY as well at first glance, that center wing joint is fairly unique)

From the smithsonian website you can find all the info on it here

  This amphibious seaplane is the only aircraft in the Museum that was
  at Pearl Harbor, Hawaii, on December 7, 1941. Ten JRS-1s were at the
  U.S. naval base when the Japanese attacked during World War II. The
  Navy immediately sent these unarmed utility craft to search for the
  enemy fleet. The JRS-1 (used 1937-1944) is the military version of the
  Sikorsky S-43 "Baby Clipper." On the day of the attack, the plane wore
  a very colorful paint job: silver overall, black on the bottom, green
  tail surfaces, a red band around the rear of the fuselage, and the
  diamond-shaped squadron insignia behind the cockpit on each side. A
  few days after the attack, ground crew repainted the plane blue, but
  it has weathered and the original paint is peeking through. The
  JRS-1’s current condition is due to many years of storage outside. The
  Museum intends to conserve and restore the plane. Transferred from the
  U.S. Navy, Bureau of Weapons


What criteria do FAA VFR Charts use for High-Intensity Obstruction lights? FAA’s website provides some symbology explanation (specifically, I’m looking at VFR Charts) and also a database of obstacles, the Digital Obstacle File (DOF). Their PDF provides an explanation of the lighted codes; options of R, D, H, M, S, F, C, W, L, N, U.

I assume that VFR Charts are created with the same data as the DOF. What are the lighting codes in the DOF that correspond to the “High Intensity Obstruction Lights” on VFR Charts?

The DOF_README.PDF includes the following field description:

  Type of Lighting

  "R": Red
  "D": Medium intensity White Strobe & Red
  "H": High Intensity White Strobe & Red
  "M”: Medium Intensity White Strobe
  "S" : High Intensity White Strobe
  "F" : Flood
  "C" : Dual Medium Catenary
  "W": Synchronized Red Lighting
  "L" : Lighted (Type Unknown)
  "N": None
  "U": Unknown

Since the charting would only use the "High Intensity" label if it was known, it would map to types H and S.

It's also useful to note that the Aeronautical Chart User's Guide adds the following note:

  High-intensity lights may operate parttime or by proximity activation.


Do pilots choose which aircraft to get rated for or is it the employer that decides it? How do pilots end up flying a specific plane type? Do they choose what type of plane they want to fly and persevere the goal or do you generally get an ATPL and then get a rating based on what your employers aircraft models are?

Example:

I love turboprops and in particular the ATR42, I get employed, if I'm lucky or good, by an airline that has ATR42/72 mixed with other aircraft in the fleet. Do I have a choice as a pilot or do I have to strictly adhere to the aircraft that my employer assigns me?

It depends. In the US and at airlines, seniority rules what aircraft, and what base you start at. Usually, there will be bases for pilots, that are then broken down by aircraft(though not all bases will have options for all aircraft types) and then Captain and FO spots for each group. For example at Delta, at one point, the new hires were going primarily 767 FO spots, at JFK. As their seniority in the airline increases, they can then try to bid to a different aircraft or a captain spot on any aircraft that their seniority can hold, or to a different base. Some may spend a bulk of their career as FOs and just like being a senior FO at a base or type, others will jump around slowly moving up and progressing through various options, depending on the individual.

In the US, and airlines, generally you don't pay for your training for the type ratings. Though, Southwest has in the past required applicants to have a 737, and a few others require the type rating already in hand.


What is the purpose of the three cylinders under the engines of the Junkers 52? They're mounted underneath each engines on the JU-52. I saw them up close at the museum. Each one consists of bundled half-inch pipes running through the whole length, open at both ends.

The three cylinders hanging below each engine are the oil coolers - this page has a much closer shot which I've reproduced below.

Oil enters and exits the cooler through the two vertical lines and swirls around the hollow air channels. The cold air in flight moving through the tubes cools the oil, which is then returned to the engine.

Courtesy of eBay, here's a photo of an old, rusted-out cooler where you can clearly see the air channel tubes inside. (Using an oil cooler in this condition would promptly empty the engine of oil...)


Mnemonics to distinguish popular airplane models When in the airport I'd love to be able to distinguish most popular aircraft from each other, how can I say that a plane I am looking at is say a320 or 737 etc? They look so similar. I can detect 747 for 4 huge engines, but that's as far as I can go.

https://aviation.stackexchange.com/a/2742/1084

The easiest thing is looking at the fin for small types! The A320 from Airbus doesn’t have a dorsal fin, the B737 from Boeing has dorsal fin and the vertical- and horizontal stabilizer reaches to the far end of the fuselage.

The big ones are generally easy because the B747, A380, A340 and MD11 are distinguished by the number of engines and the hump (B747) for the half, full (A380) or none upper deck (A340).

The A350 is similar to the B787, but it helps that A350 wears a “black mask” around the cockpit. Therefore the A350 looks like Räuber Hotzenplotz or Zoro or whatever you prefer in your part of the world.

The landing gear is barley visible and different and swapable engine types are also difficult. The nose of Airbus planes is more round, while a nose from Boeing is usually more pointy.

For me the problematic ones are the A330 which is shorter than A350 and B777 which is longer. But there are also the B757 (small body) and B767 (wide body). For this ones you need probably take a close look and it helps if a different type is next to them, to get an impression of relative sizes.

A350 - Callsign Bandit?


What are the off-airfield rules for private helicopters in New Zealand? I'm a Switzerland-based private helicopter pilot planning to spend some time in NZ. I'm wondering what are the rules there regarding off-airfield landing. Is it possible at all? Is the land owner approval required? Are their any altitude limitations like in Switzerland? What are the typical practices there?

I believe the relevant rules around helicopter landings are covered by CAA Part 91 section 91.127 Use of aerodromes.

You are permitted to land a helicopter off-airfield. Land owner approval is required (except in the case of emergency), just like any other use of land.


How does the adiabatic cooling of wingtip vortices work? This question on condensation and wingtip vortices, What is the mechanism by which condensation forms above wings?, attributes the reduction in temperature found in wingtip vortices to Adiabatic cooling.

The reasoning for this, as quoted from Wikipedia, is given as:

  Adiabatic cooling occurs when the pressure on an adiabatically
  isolated system is decreased, allowing it to expand, thus causing it
  to do work on its surroundings. When the pressure applied on a
  parcel of air is reduced, the air in the parcel is allowed to expand;
  as the volume increases, the temperature falls as internal energy
  decreases

Emphasis mine

My question is: why are we assuming that a parcel of air—which, according to Bernoulli's principle has  a lower internal pressure—would be allowed to expand against the external pressure which would be higher?

This reasoning to me would suggest that the parcel would compress (if it was compressible) and that its temperature would increase.

Also, why are we assuming that air is now compressible below Mach?

Wouldn't it make more sense to attribute the reduction in temperature to an isochoric cooling process?  This would only require the internal pressure to decrease, and would not require a change in density.

The vortex is rotating. This by itself should suffice to explain the expansion at its core. The mechanism is less Bernoulli (which applies to straight flows) but centrifugal force. Compare it to the decreasing height at the center of the bathtub vortex when water flows out the drain and starts to rotate. The height is proportional to the pressure in the fluid. The same happens with air - the pressure change is highest at the core because the angular velocity decreases with the distance from the core.

And, yes, air is compressible below Mach 1. It is only incompressible ideally and at Mach 0. The density changes are minuscule at low speed, but they are there. The thermodynamic process is an adiabatic one (no heat flow) with changes to pressure, volume and density (a tiny bit).


In the U.S., what are the requirements for being an Executive airport? Are there statutory or regulatory criteria for a facility to be called, say, Elbonia Executive Airport as opposed to County, Municipal, Regional, Field, or something else? Is it strictly marketing?

This is a marketing distinction -- generally applied to a major GA reliever airport designed to serve light/business jets in design categories B-II and C-II or perhaps C-III.  This is distinguished from general purpose GA relievers as a light GA reliever may be designed to service a maximum design category of A-II, B-I, or B-II; it is also distinguished from County, Municipal, or Regional airports as while they are similarly sized in terms of design category, a County, Municipal, or Regional airport is the primary airport for that area as opposed to being a reliever for a larger scheduled service airport.


What is the climb/descent rate that triggers the TCAS up/down arrow? If Aircraft One is maintaining a low rate of climb/ descent, is there a minimum descent or climb rate threshold below which the up/down arrow will not show up on the TCAS of the Aircraft Two?

I have heard figures of 400 fpm and 500 fpm.

Is there an industry standard, do standards depend on aircraft performance / weight class?

The Minimum Operational Performance Specifications (MOPS) for TCAS II (RTCA DO185B / EUROCAE ED143) specify the requirements for TCAS II.

It states that the arrow must appear when the vertical speed of the intruder is 500 feet per minute or more:

  2.2.6.1.2.1.6

  Intruder Vertical Speed Arrow

  A vertical arrow shall be placed to the immediate right of the traffic symbol if the vertical
  speed of the intruder (as determined by the TCAS tracker) is equal to
  or greater than 500 fpm, with the arrow pointing up for climbing
  traffic and down for descending traffic. The color of the arrow shall
  be the same as the traffic symbol.

Source: RTCA DO185B / EUROCAE ED14 Minimum Operational Performance Specifications for TCAS II, volume I.

Whilst the MOPS are not regulations themselves, the  aviation authorities put them into regulations such that TCAS II needs to be according to the MOPS.

In the US, the FAA has published Advisory_Circular AC 20-151A which states:

  The FAA ACO approving the initial
   installation of the TCAS II equipment must verify that the TCAS II processor design does not differ from the criteria
  specified in RTCA/DO-185A or
  RTCA/DO-185B as applicable.

This means it is not up to the manufacturer to decide when to show the arrow symbol. It is required by the MOPS, so it has to be designed that way.


Is JF-17 a reconfigured Mig-21/F-7? The JF-17 Thunder is a fighter jet which has been developed with the joint collaboration of Pakistan and China. There has been a lot of hype about this aircraft in recent years. Pakistani and Chinese authorities are aggressively searching for customers for this aircraft. Recently they have got some orders from an Air Force of an undisclosed Asian country.

Is the JF-17 merely an upgraded Mig-21/F-7 (like Mig-21 Bison), or is it a whole new aircraft?

One peculiarity was that the Pakistanis had a clause in their agreement with the Chinese that the JF-17 not be an F-7/Super 7 upgrade. Yet, the similarities to the Super 7 are quite obvious. If not actually based on the Super 7, then there is at least some commonality of design philosophy.

The truth is, it's impossible to tell. However, even if far back in it's genes there is still elements of the MiG-21 that wouldn't be so extraordinary. The F-18 if you go back, has parts of the F-5, which itself was based upon a 1950s fighter, the N156! As a slight twist, the Super 7 has elements of the F-20 Tigershark, which is an updated F-5.


At what point does an aircraft become an airliner? For me, the term 'airliner' conjures up an image of a passenger jet that is capable of hosting a large number of passengers¹ but I'm finding it difficult to source a reputable definition or etymology despite the term has been sourced int the early 20th century.

Since the term has been in use since 1908, jet as in jet airliner may be inferred by the modern user but it obviously wasn't part of the original definition.

The word itself would seem to indicate that airliner refers to an aircraft used by an airline (a company that provides air travel for the public), but would that extend to bush pilots with small prop-driven Cessnas or passenger helicopters?

  airliner - A large passenger aircraft. A large plane for carrying passengers:
  a commercial/commuter airliner   source: Cambridge English Dictionary

  airliner - An airplane operated by an airline   source: Merriam-Webster Dictionary

  Is this an 'airliner'? How many passenger seats need to be added before it becomes one?  (image courtesy of The Bush Pilot Company)

The term seems so vague that even the airliner tag on this site only uses 'large' to define size or capacity.

Some reference work definitions include cargo aircraft but the predominant emphasis seems to be on passenger aircraft with no upper or lower limit criteria.

I suppose that this term could be relative to the observer or situation but if the term 'airliner' was used in FAA regulations then I'm sure there must be an appendix somewhere that provides a definition. My research has come up empty.

Apologies if this is a dumb question and the term is intentionally meant be vague with only 'large aircraft' or 'many passenger' as criteria. Given proper references as support, that could be an answer.

¹ This previous question got me wondering exactly what was the criteria before any aircraft could be called an 'airliner'.

I think there's a misunderstanding here that airliner ("an airplane operated by an airline") is directly derived from airline. While it is a reasonable definition, "airliner" predates airline. (Mirriam Webster: airliner 1908, airline 1910).

An airliner is a portmanteau of air and liner, a liner being any passenger ship plying between ports along regular "lines" (as distinguished from transient ships using those ports). By the early 20th century a liner was generally understood to mean any large, passenger-carrying vessel operating a route between major ports (think Titanic etc.). You'll notice how airliners travel between airports - nautical words and phrases were adopted in the early days of flight.

So an airliner should be

passenger carrying
large
travels between airports, rather than having one fixed point of operation

It's a definition that still fits, and covers any commercial aircraft over a certain size. While there's not a specific point at which an aircraft becomes large enough to be called an airliner, I think it does impart some sense of largeness or capacity that an 'ordinary' plane does not possess.

(You might even say that a better definition of airline is "an air transportation system that operates airliners"!)


How much power do planes use when taking off at London City? I watched a video of an A318 taking off at London City and it took just 20 seconds from setting takeoff thrust to getting airborne.

BA A318 takeoff @ LCY (takeoff thrust @ 1:23, airborne @ 1:43)

and here's A319 takeoff in a regular 3.5km runway, taking ~38 seconds

S7 A319 takeoff @ OVB (takeoff thrust @ ~3:26, airborne @ 4:04)

What I'm asking is a thought experiment, let's say, we fly from one airport to another, and everything is the same except runway length. In one case it's 1500 m, in another it's 3500 m.

How much thrust does an A318 (or any other aircraft certified to fly at LCY) apply at a regular airport vs on a short runway like LCY? How much thrust is used (in kN) and what is the thrust/weight ratio?

Let's say there is an infinite runway, and a twin-jet capable of flying the whole route on one engine.
The jet starts its takeoff roll at maximum thrust, and at 40 knots an engine quits. Does the crew continue or not?

If they continue, they'll veer off the runway. Because the asymmetric thrust is huge and the airspeed is low, they won't be able to keep the plane on the centerline with the rudder.
Enter Vmcg

Vmcg is defined as the minimum speed, whilst on the ground, that directional control can be maintained, using only aerodynamic controls, with one engine inoperative (critical engine on two engine airplanes) and takeoff power applied on the other engine(s).

Why is it important?
The lower the thrust on short runways, the more you can carry...
It may be counter-intuitive, but here's why: there are three types of thrust reduction on takeoff:

Derate
Assumed temperature (aka flex)
Derate + flex

(Availability of the modes depends on the options available for the type and the options chosen by the airline for their fleet.)
Derate vs. flex and effect of derate on takeoff weight

The minimum control speeds associated with the FLEX take-off are related to VMCG/VMCA at TOGA thrust. Therefore, should the aircraft suffer an engine failure at V1, there is no limitation on selecting TOGA thrust on the remaining engine(s).
DERATED THRUST TAKE-OFF
A reduction in take-off thrust leads to lower VMCG/VMCA and hence, a lower V1. When taking off from short or contaminated runways where ASDA [Accelerate-Stop Distance Available] is the limiting factor, a reduction in the minimum control speeds may generate a take-off performance benefit and a higher MTOW.
As opposed to a FLEX take-off, the selection of TOGA following an engine failure during a derated thrust take-off is prohibited as long as speed remains below the first flap/slat retraction speed for the take-off configuration. The selection of TOGA below this speed in these configurations may result in loss of control due to VMCA considerations.
— A330/A340 Flight Crew Training Manual

Taking off from LCY
A BA A318 taking off from LCY headed to New York with lots of fuel might as well be using reduced (derate) thrust because of this shorter runway.
In short, it's very hard to compare even if the only variable is the runway length.
Flex example
The CFM56-5B3 jet engine (powers the A321) can reduce thrust by 35% when a Δ35°C assumed temperature is used. So 120 kN of thrust becomes 78 kN (per engine).

Further reading:

Airbus: Flex/Derate, Engine Bump and Derated climb
CFM: A320 Flight Ops Presentation


How does one calculate the Mean Geometric Chord in extended Trapezoid Wing? The general formula to calulate MGC of a wing is given for a trapezoid in many books but there isn't an example showing how to calculate it for a wing shaped like the one below. I tried to solve individually for section 1 and section 2 and take the mean between those values but couldnt get the solution. I just want to derive a simple formula in case the wing looks like this.

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