Calculating the maximum altitude of a drone Is there an equation to find the maximum altitude that a drone or quadcopter can fly to ?

In the US, drones are required to stay in visual range.  How far away can you see?
There is also a free AOPA app that you could look into to help keep you out of trouble (or form hurting me as I fly around in my airplane at 145 MPH trying to keep an eye out for smaller things like birds and drones):

B4UFLY is an easy-to-use smartphone app that helps unmanned aircraft operators determine whether there are any restrictions or requirements in effect at the location where they want to fly.
Key features of the B4UFLY app include:
clear "status" indicator that immediately informs the operator about the current or planned location. For example, it shows flying in the Special Flight Rules Area around Washington, D.C. is prohibited.
Information on the parameters that drive the status indicator
A "Planner Mode" for future flights in different locations
Informative, interactive maps with filtering options
Links to other FAA UAS resources and regulatory information


Why don't they have two black boxes? Why is it that black boxes don't float?

From what I gather the answer is:

  So they will not float away from a water crash site. The ping can be heard underwater with sonar. Finding the ping, finds the site.

But why not have two black boxes one that floats and one that stays with the aircraft?

That way if a plane is lost at sea, if we find the black box floating, we could use the data to find the other black box and the crash site. Plus the benefits of having a redundancy are enormous.

The added weight, space, and complexity of a second recorder have to be taken into account, and all are very important for an airplane.

If you are just interested in location, then there could just be a simple beacon designed to float. Although less, this will still have the above costs. And you have to design something light enough to float, sturdy enough to survive an extremely violent crash, yet still be a functional electronic device.

Considering that the situation of a lost aircraft at sea is fairly rare, it is questionable whether the benefits justify the costs.


How are composite aircraft canopies constructed that sit flush with the fuselage? More specifically, how is the composite frame of the canopy manufactured? Attached picture as an example.

That is a complicated process. You need:

A positive mold (mandrel) for the canopy.
A negative mold for the canopy frame. For a single prototype you can also use the unfinished fuselage itself.
A fuselage mold with a molded window sill.

First the fuselage positive mold core is built. From that the negative mold is taken, but also a negative mold only for the canopy area. From that negative mold the mandrel for canopy manufacture is built. If you have enough money, you can of course CNC mill the mandrel directly from a large block of aluminium.
The plexiglass canopy is deep-drawn over this mandrel by the canopy manufacturer, e.g. Mecaplex. There aren't many who get this process right!
Meanwhile, the window sill has been added to the fuselage mold and can be used for manufacturing the canopy frame mold. Once that is finished, the canopy frame is built by first lining the mold with diagonal weave fabric (glass or carbon, as you like) and filling the core of the frame with unidirectional rovings. Then another couple of diagonal weave layers is added on top. After removal from the mold the frame is trimmed and now the transparent part is added. The frame has a recess where the plexiglass fits in and the plexiglass is fixed to the frame with a special polyurethane adhesive. A couple of screws make sure it stays in the correct location.
To finish the canopy, the fittings are added and the frame is painted.


Why do most military aircraft use different engines than commercial aircraft? Why do most military aircraft and helicopters use different engine technology (fighters, B52, U2, etc) than most commercial aircraft?
[I removed the use of axial terminology]

When military and civilian aircraft of similar speeds are compared, their engines differ mostly by their names. It is simply too expensive to develop a civilian type in parallel to a military type when later both are used in the same way. Examples:

The B-52 engine is called J57 and was made by Pratt & Whitney. The same company called this design JT-3C when it was mounted to the Boeing 707 and the DC-8. Later models used a turbofan development of the J57, the Pratt & Whitney TF33, which was called JT3D in civilian use.
The C-5A Galaxy pioneered large bypass ratio turbofans with the General Electric TF39, which was used on the Boeing 747, DC-10 and A300B as the CF6 later.
Even the same aircraft will sometimes use a different name for basically the same engine, depending on the use: The T-39 Sabreliner used the J60 engine while the civilian Sabreliner called the same engine JT12.

But even when the flight regime is different, component reuse is common between civilian and military engines:

The core of the General Electric F101 (installed in the B-1A bomber, the supersonic first version of the B-1) became the CFM-56 turbofan which is used in the Boeing 737 or the Airbus A320.

Supersonic flight requires a high nozzle velocity, therefore high bypass ratios are unsuitable. However, the differences between sub- and supersonic engines disappear the closer you move towards the gas generator core. High-pressure compressor, combustion chamber and high pressure turbine look and work the same. Civilian engines add a large fan in front while supersonic military engines sometimes add an afterburner. The biggest difference, however, is in the intakes (large pitot intake with blunt lips for subsonic aircraft versus adjustable spike or ramp intakes for supersonic flight) and the nozzle (fixed for subsonic flight versus a complex, adjustable convergent-divergent nozzle for supersonic flight).


Where is the mistake in this air density calculation? I intend to compute the air density, $\rho$ at an altitude of $h=15000ft=4572m$, with an ISA deviation of $\Delta_{ISA}=18^{\circ} F=10\,K$.

Well I first computed the real temperature of the air at $h$ altitude with the following ISA temperature realtions:

$$T_{ISA}[K]=288.15-0.0065\,h[m]=258.432\,K$$
$$T=T_{ISA}+\Delta_{ISA}=268.432\,K$$

I then computed the temperature altitude, i.e. the $ISA$ altitude for a temperature $T$:

$$h_T[m]=\frac{T[K]-288.15}{-0.0065}=3034m$$

With $h_T$ computed I got the air density by the respective ISA relation:

$$\rho[kg/m^3]=1.225\left(1-0.0065\frac{h_T [m]}{288.15}\right)^{4.25588}= 0.906kg/m^3$$

The problem is that this value is different from what I got here ($\rho=0.742 kg/m^3$)

What did I do wrong?

The mistake is subtracting the ISA temperature at sea level from the ISA+18°F temperature at altitude in step two. If your atmosphere is heated up, it needs to be hotter at sea level as well, or your lapse rate in the first step and the denominator is wrong.

First calculate density for ISA conditions. This gives 0.7708 kg/m³.

Then used the ideal gas law to see how a 10 K temperature increase will reduce density at constant pressure. The density ratio is inversely proportional to the temperature ratio, so the result is 0.7421 kg/m³.

When checking your result, input only 10 K into the calculator, not 18 K !!!


Is there a proper term to use when you're referring to the total number of people on an aircraft, including both the passengers and crew/pilots? I've found that often when people quote the number of passengers on an aircraft, they exclude the crew/pilots, which they'll provide separately.

Is there a proper term to use when you're referring to or asking for the total number of people on the aircraft, including both the passengers and crew/pilots?

CAP 419 (the UK CAA radio telephony manual, see the glossary) uses 'POB' which stands for '(total) persons on board'


What does the correlation between weather and midair collisions tell us? The FAA's AFH states that "most midair collision accidents occur in good weather", in daylight, and nearby airports/navigation aids. What does this imply?

(One obvious explanation to this fact could be that there is simply much more traffic in this conditions, and despite a much lower accident rate per flight hour there are more overall accidents.)

In poor weather there are apt to be less VFR aircraft and more IFR. IFR are required to participate with ATC and automatically receive separation by time, altitude, and radar (when available). VFR do not require any separation and are not required to participate with ATC. There are also more flights in VFR weather than there are with IFR.

I might get flamed for this, but in general a IFR pilot is more proficient than a VFR pilot. The medical (commercial opps), testing, and currency requirements for a IFR license are usually considerably more complex than VFR - meaning (admittedly there are exceptions i.e. aerobatic pilots) IFR pilots are generally more proficient.

The following added in response to comments below

According to the FAA, "...  the majority happen within five miles of an airport" https://www.faasafety.gov/gslac/alc/libview_normal.aspx?id=6851. So, cruise environment is not a factor, and IFR have ATC separation at all times, making this predominantly a VFR landing/takeoff problem. Most IFR flights are commercial requiring a 6mo medical where as private VFR pilots require 2yrs or LSA and Ultralight do not require a aviation medical. (The private medical requirements just changed, but this discussion is based on prior years data.)

In addition to excersize IFR privileges, a pilot must remain current every 6mo where as a VFR pilot does not (except for night landings).

IFR flights will have a higher percentage of two man crews compared to most VFR flights with a single pilot. The extra set of eyes is extremely significant particularly during the landing/takeoff phase of flight.


Why is indicated airspeed rather than ground speed used during the takeoff roll? My instructor asked me this question during my lesson and I couldn't come up with any answers. He asked why do I need to look at the indicated airspeed rather than ground speed when in takeoff roll or as soon as we touchdown?

It would be great if you could give me the reference to back it up.

Because wings work on air moving past them, not ground moving below them.

Heck, in a 35 knot headwind, the Antonov-2 could be rolling backwards at 2 knots and still take off!


What does a dollar sign mean in a METAR? Look at this METAR:

KLOU 151553Z 21005KT 10SM CLR 13/M01 A3044 RMK AO2 SLP309 T01281011 $

What does the dollar sign mean?

A maintenance indicator sign, $, is included when an ASOS/AWSS (Automated Surface Observing System / Automated Weather Sensor System) detects that maintenance is needed on the system.

Reference: http://www.faa.gov/documentLibrary/media/Order/JO%207900.5C.pdf

Or if you need an easy way to remember it, courtesy of the awesome Ralph J:

  It means that they need to spend some money to fix whatever is broke on the automated reporting station!


Do any aircraft have a "self-contained ILS"? The ILS is an invaluable aid to pilots, especially those operating to/from the many airports where poor weather is common (low-visibility operations would be completely impossible without an ILS); however, ILSs are expensive and maintenance-intensive, with the result that many smaller airports lack ILS capability.  Also, the requirement for a considerable quantity of pre-emplaced infrastructure obviously precludes one from performing an off-airport instrument landing.

On the other hand, the technology is available to guide an aircraft down to a precision landing at an arbitrary point on the ground, and much of this technology is already mandatory equipment on aircraft; GPS (which most if not all aircraft already have anyway) could be used for horizontal positioning and guidance and for plotting a landing route about the local terrain, the radar altimeter (also standard aircraft equipment) would provide vertical guidance, and a forward-looking radar system (also already standard, in the form of the aircraft's weather radar, which should only require an additional driver or two to add a terrain-sensing mode) would allow fine control of the aircraft's flightpath for the landing itself (where GPS, with its ~10m CEP, is insufficiently precise and accurate for a safe touchdown) and allow the aircraft to orient itself in space (as GPS tells the aircraft where it is, but not which direction it's pointing).  Additional equipment that would be useful and could easily be added would be a second weather radar (to allow the pilots to continue to monitor the weather even with one radar in terrain-mapping mode), a Doppler radar system (to warn the pilots of dangerous windshear, microbursts, etc.), and a forward-looking lidar system (to provide advance warning of clear-air turbulence along the approach path).

With the appropriate software, these instruments could be used to plot and fly a safe instrument landing at a noninstrumented airport, or even at a non-airport; this latter capability would be extremely useful for medevac and SAR pilots (whose duties, by their very nature, involve operations to and from off-airport locations, frequently in poor weather) and for military helicopter pilots (same reason).

Are there any aircraft already equipped with such a "self-contained ILS"?

Approaches guided by GPS are called RNAV; it can provide both lateral and vertical guidance, in some cases to the same precision as ILS Cat I, without need for a radar altimeter--which is not standard equipment. (There are also non-GPS ways of using RNAV, which are mainly used by older airliners that haven't been upgraded yet.)

Note that standard GPS has accuracy of 100m; SBAS (aka WAAS) gets that down to 7.6m.  Both are standard in aviation GPS units these days, and GBAS (aka LAAS) will eventually get that down even further.

There are already three times as many RNAV approaches as there are ILS approaches with more appearing every day, and most aircraft are now equipped to use them or probably will be soon. IOW, the essence of what you propose is already here.

Instrument approaches do have to be pre-planned to ensure obstacle and terrain clearance, so airplanes can generally only use them to land at airports. (The rules are different for rotorcraft, and that's generally what you'd use for rescue, but I'll have to leave the specifics to someone else.)

Many large aircraft carry weather radar, but it's too heavy for light aircraft; both can use satellite weather data services, in addition to getting weather updates via radio the traditional way.


What is CAPT & PURS? On the airbus A320 Evacuation Control Panel, what is CAPT & PURS. On some takeoffs it is selected and on other takeoffs it is not selected. What does this stand for and what is it? What does it do?

Here is a graphical representation:

It is a two position tumbler switch on the overhead panel to allow/disable the activation of the Evacuation alert from the cabin (explained here page 13). The view can also be found here for A320 and also here, with the following comments:

CAPT and PURS - the alert may be activated from either cockpit or cabin.
CAPT - the alert may be activated from cockpit only.

The A320 pictures seem containing the safety wire to keep the switch in the CAPT and PURS position, so it most likely another position is only selected for the reason.

The manual says Allows activation of an Evacuation alert from
the cockpit or cabin but from explanation above and the notation on the panel looks like the alert activation from the cocpit cannot be disabled by this switch.

This electric component is also called "toggle switch" and may be called "flush switch". These components were patented as early as in 1917.


After purchasing an aircraft, how do I put the transponder in my name? I just purchased an aircraft and the prior owner said that I need to put the transponder to my name. What is the procedure to do that?

I assume you have a Mode S transponder. A Mode S transponder uses a unique 24 bit address assigned by the authorities to your aircraft to communicate with Mode S radars. If you do not have a Mode S transponder there is nothing that links your transponder to your aircraft registration.

If you purchase an aircraft you need to register it with the Civil Aviation Authority in your country. With that registration you will get a 24 bit address (in some countries you will always get it, in others you need to indicate that you have a Mode S transponder). The 24 bit address is usually given as a hexadecimal string of six characters, some countries use a 8 character octal representation. This code needs to be programmed in your transponder. It may be that the 24 bit address is the same as it was before. In that case nothing has to be done on the transponder.


Meaning of XX below Slat FLap Trim on A350 with flap setting 1 What is the meaning of the 'XX' in amber below the 1 (in green) within the Slat Flap Trim section on the A350 PFD when the flaps are set to 1 with the correct speed (below 255kts)?

See picture attached. If the flaps would have failed, it would indicate XX without the 1. So, what else could this XX indicate?

The number below the flap indication is not the position of the flaps/slats, but the position of the flap lever. When the lever is moved, the number becomes cyan indicating that the flaps/slats are in transit and when they have reached the selected position the number becomes green.

Edit: As per FCOM, there is no mention of amber XX indication for flap lever position at all. Checked in a simulator that total computer failure will not cause indication to turn XX.


How to convert an EASA ATPL(H) IR to ATPL(A)? If you are holding an EASA ATPL(H) IR, how can you convert it into ATPL(A) and would you be able to credit your heli hours? As I've 400 hours and it would get longer to build hours with ATPL.

It looks like the answer is yes, but with some significant caveats, such as only 50% of your helo time will count towards a fixed-wing ATPL. The UK CAA web site has info on this but your best bet is to contact a reputable flight training organization that offers ATPL training. Click on the "Holders of a UK issued Part FCL licence in another category" link (there is no direct URL to this content). If the country in question is not the UK you should check their rules.


Would reverse thrust increase with a decrease in aircraft forward speed when referring to propeller reverse thrust? Would reverse thrust in a propeller increase with a decrease in aircraft forward speed?

If the propeller keeps the pitch constant while in reverse thrust,  the component of the relative wind perpendicular to the prop disk goes down with decreasing aircraft speed. Hence, the AoA also goes down, the lift produced by the blade decreases, and the reverse thrust does also decrease...


How can you identify the upwind side of a thunderstorm, and why should you fly there? When flying around a thunderstorm, it is advised that you fly in the upwind portion of the thunderstorm. First off, how do you figure out which side is the upwind and downwind of a thunderstorm? Second, why fly in the upwind?

The "anvil" of a Thunderstorm is always on the downwind side. Airline pilots routinely deviate around the upwind side in hopes of a smoother ride.

photo source: CRAZY CLOUDS: The Thunderstorm Anvil


Are there advantages when operating with CG near forward or aft limits? If the center of gravity of an airplane is too far aft, it will become more unstable

Iif the CG is too far forward, then drag will increase due to increased angle of attack.

But what are the benefits to operating with the CG near the aft, or forward, CG limits? In what situations would one choose to do so?

A CG near the aft reduces drag by reducing the necessary downforce that has to be supplied (usually) by the tailplane.
This is also a point for competition gliding (more often than not you have water ballast in the vertical tailplane to compensate for those love handles). Aerobatic gliders sometimes feature aft lead ballast to enable maneuvers like tailspins which are not possible with a forward CG.

Aft CGs come with reduced stability, which can be a severe flight-safety concern (e.g. in case of unrecoverable spins).
Some fighter aircraft feature inherently unstable aerodynamics (see super-maneuverability) which offer great agility (e.g. turning rates), but need constant input by a flight constrol system (and woe if that fails, e.g. via Pilot Induced Oscillation).

A forward CG results in greater flight stability and reduced danger of sudden stalling, but also increased drag (because of the increased downforce required from the tailplane).  In extreme cases this can limit the maneuverability as well and cause a pancake landing (the tailplane can only produce so much lift/downforce before itself stalls, at which point it is no longer holding your nose up).


What's holding equipment manufacturers from going into multicore, RTOS-based equipment? What's holding equipment manufacturers from going into multicore, RTOS- based equipment?

Recently, Rockwell Collins certified its display systems based on RTOS:

Lynx Software Technologies, LynxOS-178 RTOS Deployed by Rockwell Collins in Pro Line Fusion Series of Flight Deck Systems, November 27, 2012.

Why are major players not moving into these segments like RTOS, multicore processor? Is it because of certification difficulties?

Development costs, complexity and need.

On a system that has to be hard real time multi-core is a pain(think expensive) and most things that need to be hard real time are not that complex. Things that don't need to be hard real time don't need to be RTOS, so you have one system that handles all the hard real time stuff and one that runs Linux and handles the other stuff.


What does the FAA consider to be "good moral character"? Per 14 CFR 61.153(c) candidates for an ATP license must "be of good moral character".

What does that actually mean and how does an examiner or the FAA verify it?

An examiner uses the contents of FAA Order 8900.1 - Flight Standards Information Management System (FSIMS)as guidance for doing their job.

As you might imagine, there is some guidance available for them there:

  VOLUME 5 (AIRMAN CERTIFICATION)
  CHAPTER 2 (TITLE 14 CFR PART 61 CERTIFICATION OF PILOTS AND FLIGHT INSTRUCTORS)
  Section 18 (Conduct an Airline Transport Pilot Certification, Including Additional Category/Class Rating)
  Paragraph 5-704 (ELIGIBILITY –ATP CERTIFICATE – AIRPLANE, ROTORCRAFT, AND POWERED LIFT):
  C. Good Moral Character Requirement:
  An applicant must be of good moral character. The inspector must ask an applicant if the
  applicant has been convicted of a felony. If the applicant’s answer is
  affirmative, the inspector should make further inquiry about the
  nature and disposition of the conviction. If an inspector has reason
  to believe an applicant does not qualify for an ATP certificate
  because of questionable moral character, the inspector must not
  conduct the practical test. Instead, the inspector will refer the
  matter to the immediate supervisor for resolution. The supervisor may
  need to consult with regional counsel for a determination concerning
  whether the applicant meets the moral character eligibility
  requirement.

That's the basic guidance that the examiners have, but there are also legal cases that have delved into this area and give more specific examples.  I found a blog which covers it in some detail at All About Airplanes.  Falsification of documents, embezzlement, and acting in a malicious manner towards others are cited as reasons that ATP certificates have been denied or revoked.


How do engine manufacturers minimize damage from bird strikes? What are the ways that engine manufacturers currently minimize the damage caused to engines in a bird strike?

Placement on aircraft that fly above birds. This is the #1 reason we don't hear about airliner bird strikes every day on the news; cruise altitude for airliners is around 30,000 feet, while only two species of bird have ever been recorded flying at that height, one in Central Africa, the other around the Himalayas, neither of these being common travel lanes for airliners. The critical time for most bird strikes is below the cloud ceiling and/or transition altitude, above which the air becomes thinner and birds have to work harder to stay aloft. Thus most birds fly below transition, while airliners spend as much of their flight time as feasible above it as the thinner air reduces drag and lowers fuel consumption (the "strata" of thicker air at the transition point, in addition to the simple reduction of SPL on the square of distance, also helps insulate people on the ground from jet noise).
Strong intake fan fins. The first set of turbine fins that you see looking into a nacelle are the ones in the direct line of fire. They're also the largest fins, but in their favor there are higher acceptable tolerances for those fins versus the ones in the compressor stages. So, they're built strong to hopefully survive ingesting your average goose. Here's a YouTube of the A380 engine's bird strike test; the engine continues to operate even though the blade that was struck is misaligned on the turbine hub for a few rotations.
Garbage disposer effect. At ascent throttle levels, an airliner's engines are rotating between 10,000 and 15,000 RPM. Even travelling at cruising speeds of 500-550 knots, the rotation speed of the turbine will chop most organic matter into mincemeat in a fraction of a second. In fact, bird strike tests show the bird carcasses literally exploding from the force of impact with the rotating blades. These smaller pieces cause fewer problems passing through the engine.
High bypass. About 80% of the air volume entering most underwing airliner engine nacelles passes around the turbine chamber instead of through it, increasing thrust while reducing fuel consumption. Fuselage-mounted engines on older aircraft had lower bypass ratios (one of the reasons those designs are being phased out of modern fleets). A bird entering the engine has a similar chance to pass right on through without encountering the combustion chamber.
Reinforced nacelle housing. In the event a bird strike does dislodge something in the engine, the nacelle housing is engineered specifically to contain the shrapnel, minimizing the chance of damage to fuel and control lines in the wings and of course to the fuselage. (Here's a YouTube of a "blade-out test" for the A380's Rolls-Royce engines) The pilots will be alerted the engine has failed, and will cut off the fuel supply, engage fire suppression and run on the remaining engine(s).
Overspecification of required engine thrust. One of the major tests an airliner design must pass before being FAA certified is an "engine cutout at decision" test. An aircraft is loaded to MTOW, taxis to the runway, the engines are spun up, the aircraft rolls out, then at the "decision speed" above which the pilot must commit to a takeoff, an engine is idled. The aircraft must still be able to get off the runway and attain a minimum climb rate. That test, for most modern two-engine jets, shows that the plane is perfectly capable of flying on one engine (if such a thing happened at takeoff in real life the jet would circle and land again but it would not have to risk an aborted takeoff above decision speed).

In short, these engines are built tough and tested tough, as is the rest of the aircraft (manufacturers build several planes' worth of components and subsystems for the express purpose of torture testing, and that's if they get it all right the first time). In addition to bird strikes, engines are tested for water ingestion, hail strikes, sand ingestion, smoke ingestion (a British Airways 747 lost all four engines after flying through the upper ejecta cloud of an erupting volcano; they got two restarted and landed safely, but future engine tests got even more stringent to avoid a repeat performance), and a host of other things that just aren't good for jet engines.

The most famous bird strike incident in recent memory, Sully Sullenberger's emergency water landing in the Hudson River, was caused by hitting not one or two, but an entire flock of birds, and not sparrows or pigeons, but Canada geese, which can weigh up to 20 pounds each. This incident is still a good example of how well engineered these engines are; both engines would have been at full revs as the plane was climbing out of LaGuardia, yet AFAIK the turbines, though deformed, didn't even part company with the hub, saving the control surfaces and lines for the ditch attempt, resulting in no fatalities and only one hospitalization.


What is the weight budget of a fully loaded A380? Wikipedia provides some numbers (typical empty weight, MTOW, max fuel capacity, etc.), but I can't seem to find more detailed figures. For a purpose of this question, let's assume a fully loaded A380 in typical 3-class configuration (~530 passengers) and fuel for a long haul flight (>10h).

So, what is the typical weight of the passengers + luggages? Is any additional cargo typically carried? If so how much? What about the weight of crew and catering? And fuel weight? (Fuel weight will depend on actual flight duration, so the answer should mention the corresponding flight duration.)

These weights are all based on the maximum an aircraft will ever see. The maximum allowed weight of passengers (+luggage) and cargo (called payload weight) is the difference between the Operational empty weight (about 270,000 kg) and the Zero fuel weight (361,000 kg). This means the payload weight is about 91,000 kg. The passenger and crew weight can be estimated by the following numbers:

175 lbs per pax + 30 lbs of baggage for short medium range distance (or 40 lbs for long range)
175 lbs per crew member + 30 lbs of baggage$^1$

So let's say that (for easier calculations) the average passenger + luggage weight is 100 kg.
When we assume 530 passengers and 25 crew, then the weight would be $555\times100=55,000kg$. That leaves 36,000 kg for cargo.
All the weights listed are, of course, maximum weights. That means that an aircraft in general does not meet these values.

The maximum fuel weight is the difference between maximum ramp weight and zero fuel weight (which is $562,000-361,000=201,000kg$). About 2,000 kg is taken for the time the engines are running while the aircraft did not yet take of (for taxiing etc). This is the difference between maximum ramp weight and MTOW.

The amount of fuel varies so much per flight that I really can't say anything about it. It depends on the air pressure in the flight path (aircraft choose their routes depending on that, for a faster flight), weather along the route, and much more. For quite a good overview I suggest for you to read this Wikipedia page.

I hope I answered your question sufficiently.

$^1$ Source: Jan Roskam, Airplane design, Part I: Preliminary Sizing of Airplanes (1985)


What are these lines on the nose of a Boeing 737? What are these lines on the radome?

You can also see them here:

What are they and what is their function?
Source: AviaFilms

I'm no expert on B737 radomes, but I was able to find that these are called Lightning Diversion Strips or Lightning Diverter Strips.

Since radomes are generally built with composites, they do not transmit static electricity in the same way that aluminum skin would.

The B737-200 maintenance manual states that the radome is constructed of fiberglass and is provided with lightning diverter strips on the outside surface—though it states that these are not necessarily provided on all airplanes. It further states that these diverter strips are constructed of thin gauge aluminum.

From b737.org.uk:

  The radome (RAdar DOME) is an aerodynamic faring that houses the weather radar and ILS localiser and glideslope antennas. Unlike the rest of the fuselage it is made of fibreglass to allow the RF signals through.

  Fibreglass is non-conductive which would allow the build up of P-static (static due to the motion of the aircraft through precipitation). This would in turn cause static interference on the antenna within so the radome is fitted with six conductive diverter strips on the outside to dissipate P-static into the airframe.

And from this article:

  Another important characteristic of the radome is its ability to bleed
  off static electricity. This is done through the use of
  anti-static/anti-erosion coatings and through the lightning diverter
  strips extending from the frontal area of the radome to the airframe.
  "These diverter strips, says Bauer, continuously collect static
  build-up from the surface of the radome and conduct it to the airframe
  without severe sparking or arcing."

Here is a video that explains some of the principles of lighting diversion (note that the particular strips discussed may differ from those found on the B737). The diverter strips are discussed particularly starting here at 2:20:


Why does Beijing's new Daxing airport have so few gates? There is a lot of press about the Daxing airport, touting that it will be one of the largest in the world in terms of passenger capacity. The images of the terminal build are indeed beautiful.

But when I look at this image, taken from Wikipedia, there doesn't seem to be a ton of gates:

I couldn't find an authoritative number of how many gates it will have, but this website says it will have about 80. This matches what I see in the image above.

By comparison, Ohare and Hartsfield–Jackson have about 190 gates, JFK 130 gates, Schiphol Airport 165.

Why is this? In the Beijing Capitol Airport right now, there are not enough gates, so when I land there, they have us deplane on the tarmac and take a bus to the terminal. Why didn't they build 200 gates if this is to be the largest airport, by passenger volume, in the world?

Airports aren't built with the envisioned capacity in one go. They are built in stages. Just look at Dubai International for example, they're always expanding the concourses, etc.

For Daxing Airport, I found what looks like a master plan (outline for a project's major elements):

Source: kaskus.co.id

It shows more than one (at least two) main terminal buildings, land area for expansion that is serviced by taxiways and aprons, and even an additional runway to the west. There is also plenty of remote stands, which are appealing (cheaper) to low-cost carriers.


Why did the Boeing 787 design change shape from the original renderings to the actual design? Here is a rendering of the original Boeing 787 design:

The plane built can be seen here:

787 as built http://images.franchiseherald.com/data/thumbs/full/3042/570/0/0/0/boeing-787-dreamliner.jpg

Why were the shapes of the nose, tailfin and tailcone changed during the design process?

According to this answer to the same question on Quora, it was changed in order to

  keep as many parts common with other Boeing products as possible so they could reuse old part designs, vendors and tools and let the economics of scale help bring down the costs of these parts and thus the entire airplane.

By maintaining a greater similarity to previous Boeing products, the altered designs made the plane easier to design, build and sell, for a few reasons:

Maintaining similarity with older models made the certification process much easier and faster.
Instead of having to revise, test, remodel, and debug an entirely new part, the revised design had a greater background for the engineers to work with.
Completely new parts would have required more work building the machines used to construct the aircraft. Using prior designs led to reduced costs and time required in manufacturing.

Overall, the revised design made the aircraft easier and quicker to design and build which,  considering the issues and delays suffered by even the revised model, was a necessity.


Where can I learn more about pilots' dreams during G-LOC? I came across an extremely interesting note from a wiki article on G-LOC (g-force loss of consciousness, or blackout):

  Brief but vivid dreams have been reported to follow G-LOC.

Sadly no citation. Where can I read more about this? I did a quick Google search on "pilots dream g-force blackout" but only got 2 relevant hits that didn't tell me much. Some reddit posts described a dream trapped in a maze and a trip to Hawaii, that's about it. They sometimes described it as an out-of-body experience instead of a dream.

Does anyone know where to go to read more? Is this really a common phenomenon?

I'm not sure if you've come across this or not, but the paper Recovery from
Gz-lnduced Loss of Consciousness:Psychophysiologic Considerations has some details on this phenomenon. It describes the tests carried out on eight volunteers.

This does not appear to be very common- five 'dreams' were recalled out of 21 acceleration runs. The subjects seem to have indicated that these were definitely 'dreams' as opposed to 'thoughts'. Also, the report notes:

  ... it is difficult objectively to determine exactly what the subjects experienced during their individual G-LOC episodes (dream or thought) or even state that G-LOC can be equated to a normal sleep mental state (in relation to dream activity)

Another paper Further Support for the  Concept of a  G-LOC Syndrome: A Survey of Military High-Performance Aviators shows that the dream-like state occurs in about 15% of the cases.

The 'dream' state appears to be restricted to <13s and vary from person to person (in some cases, they were not aware that they've lost conciousness).


Why the Mig21 don't use the ailerons like control surfaces on delta wings at landings or take off? Mig21 is a delta wing , so why do not use the ailerons like any other delta's ? For lowering the approach and touch down speed. It is not possible that?

I'm no expert on the plane, but wikipedia claims the Mig-21 has separate flaps and ailerons.

  On the trailing edge there are ailerons with an area of 1.18 m², and
  flaps with an area of 1.87 m².

The common reasons for not combining flaps and ailerons are that it reduces aileron response and increases the chance of stalling the wing tip (which results in a violent roll in the direction opposite to what you want).

As the Mig-21 has a separate horizontal tail for pitch control, there's no need to use elevons.


Why aren't there more helicopter aerobatics at airshows? I enjoy watching RC helicopter stunts like these.  Many RC pilots are very talented, executing barrel rolls and other inversions.

How come we don't see these kind of displays at airshows?

First off: I'm not a pilot.

I believe there are two additional issues here:

There is no pilot in the RC helicopter. The forces exerted in some of those maneuvers look pretty extreme, I highly doubt even the most well-trained aerobatics pilot/astronaut/fighter jock would be conscious longer than about 2 minutes into the video you posted. I'm not even sure if they would be able to survive that.
Scale. All sorts of weird things happen when you scale complex systems up or down. (A famous example is the square-cube law: when you scale a structure up linearly, it's area scales as a square, and its volume (and thus weight) scales as a cube. So, an ant that is 100 times bigger will have feet that are 10000 times bigger but will have to support a weight that is 1000000 times bigger.) For example, the airframe of the RC helicopter is much stronger in relation to its size than it is on a real helicopter. Also, RC models (not just helicopters) are typically ridiculously overmotorized compared to their real-life counterparts.


Why doesn't an airfoil rotate? As far as I understand, two of the reasons how an airfoil generates lift are Coandă effect and downwash. However, if there is upwash near the leading edge, why isn't an airfoil rotated by the two forces (upwash at the front and downwash at the back of an airfoil)?

It does rotate. In fact, in aerodynamics, this rotation force has a name: pitching moment. Pitching moment changes depending on the angle of attack.

Airfoils can be designed with almost any pitching moment and still generate lift, from positive (trailing edge rotates upwards as you describe), to zero (no rotation) to negative (trailing edge rotates downwards). In general, high lift airfoils have positive pitching moment (because, as you noticed, downwash caused by the Coanda effect increases lift). But zero and negative pitching moment airfoils are useful for tailless and flying wing aircraft. Helicopter blades are long, narrow and flexible so must use zero pitching moment airfoils to prevent them twisting.

If you use an airfoil with a positive pitching moment you need something to counter the rotation. For most aircraft the solution is the horizontal stabilizer (the tail). An alternative solution is the canard.

For chevron shaped (V-shaped) flying wings and tailless planes the solution is to twist the wing (in regular planes it's called washout but flying wing designers call it "twist"). The twist causes the wing tips to have less angle of attack (sometimes negative) so that the overall rotation force for the entire aircraft is zero.


How do pilots hold the runway centerline during takeoff? Holding the taxiway centerline during taxi is usually done with the nose gear tiller in commercial aircraft. During take-off, until which speed is the tiller used before using pedals to control runway centerline alignment?

Once you've lined up nicely on the runway, you only need the rudder pedals as they do provide enough nose gear steering for the takeoff roll even at low speed.

  Rudder pedal steering is available during takeoff, landing, and taxiing when small directional changes are required. Full deflection of the rudder pedals produces about 7 degrees of nose wheel steering (airliners.net).

The 7 degrees figure quoted above will vary by plane.

Tiller is used when tight turns are needed. Remember most airliners don't have a tiller on the first officer's side, yet they do takeoff without the captain steering for them.

(YouTube)

In the linked video we see the captain let go of the tiller as soon as he is lined up on the runway. Also notice the tiller move on its own afterward, which indicates that the rudder pedal [nose wheel] steering is being used.


Do FDRs & CVRs (black boxes) have an in-service life span? Do Flight Data Recorders (FDRs) and Cockpit Voice Recorders (CVRs), aka black boxes, have an in-service life span? Is it necessary to replace them over time?

If so, are there any regulations governing their maximum life?

Note: The suggested duplicate asks specificly about post-crash lift time. This question is about in-service lifetime.

After a crash, does the information stored on flight recorders have expiration dates?

The FAA is making an effort to phase out magnetic tape style recorders as noted in the this AC

  1.7 Obsolete Technology. We are phasing out magnetic tapes through
  mandates and voluntary efforts and replacing them with modern
  solid-state recorders. These new recorders not only enhance safety but
  also benefit you directly, as they avoid the high costs and technical
  problems of maintaining outdated recorders. Modern recorders do not
  require the hourly replacement of tapes and calendar weighing of
  thermal capsules. Also, existing tape recorders no longer meet the
  most recent FAA TSO minimum performance standards.

However they clearly state the replacement is voluntary. The wording here also implies that the tapes are replaced on an hourly cycle and the thermal capsules are checked.

This AC covers quite a bit about the design and function of the FDR and CVR. I would take a look at CHAPTER 3. CONTINUED AIRWORTHINESS REQUIREMENTS starting on page 12. It outlines some of the things old FDR/CVR's may need to comply with to remain airworthy.

Im sure there are also specific limitations on specific units out there like any other component in aviation that may have caused them to be removed from service or lose their certification somehow.


Are there any IFR training plugins / addons for Microsoft Flight Simulator or X-Plane? I am an IFR student, looking for software/plugins/add-ons/extensions to either Microsoft Flight Simulator or X-Plane to enhance the IFR training experience.

Specifically, I was wondering if there was an app that would evaluate my instrument approach in the simulator against the 'nominal' or idealized instrument approach based on the approach plate.

For example, it would evaluate the flight profile to see if I had stayed above the MDA; if I had followed the step-downs appropriately; if I had stayed within the required procedure turn completion distance, etc.

Is there any such software like this, or is specifically tailored towards IFR training?

Both sims allow you to do a review of your flight where you can see both plan views and vertical profiles of the flight to analyze the results.  This can be especially useful when analyzing the results of attitude instrument flying like A and B patterns, etc.

CloudAhoy does allow integration of flights from X-Plane for review as well.

ATC is a bit better in games like FSX and Prepar3d, but I’d guess there are live ATC available in realistic multiplayer sessions of X-Plane as well.

One real pain in the butt about those Sims is just how out of date they are in terms of navigation databases, etc.  you really can effectively simulate approaches if you can load and practice the latest ones.

That being said the games are excellent to practice basic attitude instrument flying in as computers can simulate that very well sans the vestibular distractions which accompany flying in IMC.  You can also practice partial panel and other IFR emergencies here as well.


The slowest to fastest ratio plane What fixed wing, and motor, plane or jet, has the largest range between its minimum and its maximum airspeed by which it can safely fly for prolonged periods?

The radio-controlled model sailplane that recently exceeded 540 mph while dynamic soaring has to be a contender.  Minimum speed in this flight (immediately after launch) may have been as low as 10 mph, which probably could have been sustained by staying on the front side of the ridge.
Link to You Tube video--

Though any plane capable of routine flight at 0 mph would automatically win I suppose-- e.g. pretty much any hang glider or sailplane given the right conditions.
Or did you mean airspeed?  The radio-controlled sailplane in the video may well be one of the top contenders.


What are the differences in aircraft performance between tractor and pusher propeller designs? Some aircraft have pusher type propellers.  In what ways is it different from a tractor type propeller?  What's are the advantages and disadvantages over a tractor type.

Well one major difference is the blade pitch, pusher props will seem to be backwards.

You must also modify the engine's bearings to be able to support the propeller mounting and crankshaft in compression, rather than tension.

A pusher prop's engine also has to be cooled differently than a tractor, because the propeller is not blowing air over the engine. Therefore some ducting and ram air magic has to be done, or some other system of cooling implemented. Many pusher-type planes have had severe issues with cooling.

Note: some of the next few might not necessarily apply to pusher-type planes where the engine is mounted above the fuselage, like the Lake Amphibian and many other seaplanes, or some other oddities like the B-36. I am talking about more conventional pushers like the Velocity, Beech Starship, or Cessna 337.

Another issue is FOD. A pusher prop will likely be mounted behind at least one of the wheels, which can kick dirt and rocks up into the propeller. Now imagine a prop that is very close to one of the mains. Even on paved runways you encounter rocks and debris occasionally, and it only takes one hit in the right place to produce a failure-causing nick.

Compounding on that last one, when a tractor-type plane takes off, beacause the prop is forward of the center of mass, the propeller will rotate up, away from the ground. But a pusher prop is usually just the opposite: it will rotate down a bit, increasing the chances of a prop-strike. This is one that is heavily considered and worked-around while building pusher-type planes, but while you can mitigate the danger by placing the prop closer to the CM, or making the landing gear taller, you can't completely remove it as far as I know.


Could this "Wingless Dodo" fly in real life? There is a wingless Cessna in GTA 3 that is so impossible to fly that the game counts how many seconds you manage to fly it.

Would that plane fly at least 1 second in real life?
The plane looks like a C152.

Here's a video where that plane appears.

There is an old saying "If you put a big enough engine on it, you can make anything fly."

The Lockheed Starfighter was a classic example of that. With its short stubby wings it is basically a guided jet engine / missile.

With small wings you have two issues. Obviously, the sheer lack of lift at low speeds, but also the lack of control surface area at those speeds. If you go fast enough it balances out, but takeoff and landing become a major challenge.

Could you do that with a modified stock Cessna?

No. The airframe simply would not be strong enough to support the required engine and the drag would be horrendous. At the airspeeds you would need, it would break up.

Could you build something that looks like a stock Cessna but with stubby wings? With enough money and resources, I'd guess anything is possible. Either built like a truck with a huge engine, or some ultra-lightweight version. But it would be a novelty, an airshow item at best.

Speaking of making anything fly... these are always fun to watch...


Do cargo operators need an AOC? Is it just commercial operating aircraft flying paying passengers that require an air operators certificate (AOC) or do cargo operators require one also?

An aircraft doesn't need an AOC    Operating the aircraft for anything other than for private purposes is why you need one.


What are the "high performance characteristics" of a Boeing 777? News of the potential further stretch of the A350-1000 have seen pretty much all journalists discuss the "high performance characteristics" of the competing Boeing 777-9 with Middle Eastern airlines. For example:

  [...] the new Airbus jet would target airlines that need high-capacity, long-range aircraft but not necessarily require the same high-performance characteristics that have made the 777-9 so popular with Middle Eastern airlines. (The Gulf region can be hard on an airliner.)

What exactly are these? Why is the 777-9 suited to them and the A350 not?

The gulf region is very hot, something that can reduce aircraft performance. The 777-9 is better able to cope with that (due to the higher thrust from the engines and larger wing area).


Can I use any reference area for lift and drag coefficient? I know that for rockets they often use the circular cross-section S_reference for the drag prediction: drag = rho/2 v^2 * c_D * S_reference

For aircrafts they use the chord length of a wing as S_reference.

So when I want to compare those to for their aerodynamic performance, can I just use
S_reference{rocket} * C_D{rocket}

and S_reference{aircraft} * c_D{aircraft}

So to my mind: I can always use any reference area I want for determining c_D , but when I want to compare two bodys for their aerodynamic performance, I have to use: c_D * S_reference

Thanks for your opinion,

The reference area is chosen according to the flow profile:

For long slender bodies, the wetted area is chosen because the main drag source is the shear forces between the boundary layer and the free flow.
For relatively short bodies, the cross-sectional area is most relevant because of the much larger contribution of pressure differential between front and aft of the stream.

Directly comparing $C_D$ of rockets and aeroplanes would not be very useful, because the reference area for aeroplanes is the wing area, which rockets do not have. Indeed $C_D$ * A is a much more useful comparison, if one knows what reference area A was chosen.


How does a dispatcher assign relative costs to trajectories in TOS? In FAA's Combined Trajectory Options Program (CTOP) flight operators submit a set of possible routes (TOS—Trajectory Options Set) that the airline is willing to take for a given flight, if there is a flow constraint present in the air space. The airline tells the command center, which trajectectories it prefers by assigning a relative trajectory cost (RTC) to each route, which tells the command center how much ground delay the airline is willing to take to get a certain route.

My questions are - how do dispatchers determine how much RTC to assign to each route? What are the main things that they consider? Is there some kind of software that allows to calculate that, or is the process relatively informal and intuitive?

[The] TOS options include defining preferences with regard to:

  Route: The Flight Operator may route out of a CTOP FCA into another CTOP FCA or out of the CTOP altogether. Submissions should conform to standard flight plan requirements (i.e. NRP, required reroutes, preferred routes, etc.).
  Altitude: The Flight Operator may file different altitudes, thereby changing the assigned TOS option.
  Speed: The Flight Operator may file different speeds, thereby changing the assigned TOS option.
  [Relative Trajectory Cost]: The Flight Operator may file different RTCs, thereby changing the assigned TOS option.
  TVST/TVET: The Flight Operator may file different TVSTs/TVETs (start/end times), thereby changing the assigned TOS option.
  RMNT: The Flight Operator may file different RMNTs, thereby changing the assigned TOS option.

Source: AC No: 90-115

For example, if they change only the route, the distance will change, and so would the average winds, and thus a new air distance estimate. It could be longer or shorter. The airline may also change the speed, flight level, etc.

Calculations are most certainly computerized but with human input/decision. It could be made either by using proprietary software or commercial flight planning solutions.


How do pilots foresee turbulence? During a normal flight at cruise speed and altitude, amid the delicious airline meal and the enjoying a latest movie, all of a sudden the seat belt sign turns on.

Then a few seconds later we enter turbulence, grab a hold of that half-finished soda cup and wait patiently for the bumps to be over while looking out the window.

So, how exactly do the pilots know that the airplane is about to enter in an air pocket which will cause turbulence?

... or does it happen like this?

I have already gone through the excellent answers here and here.

There are a few ways that pilots are aware of potentially turbulent areas.

Eyesight
The most obvious way is just by looking outside and observing the sky.  Large billowing clouds, called cumulus clouds, indicated pockets of unstable air (the clouds are rising because the air under them is as well).  If the pilots must fly through these clouds then its a safe bet that there will be some turbulence.

Weather Radar
Just like using your eyes, except the radar can see further through haze and other clouds.  Typically this is useful for finding embedded thunderstorms, but it can also be useful to find areas of potential turbulence.

Communication
Pilots talk.  Both to each other and to air traffic controllers.  En route controllers frequently ask pilots for "PIREPS" (pilot reports), to build an accurate picture of the flight conditions at different altitudes.  Often commercial aircraft will request to change altitudes or deviate around weather/ turbulence, so it is in the best interest of the controller to know ahead of time where the bad flight conditions are, and have a game plan of how to route traffic.  This makes it much easier for the controller to route traffic, rather than getting request after request from individual aircraft.


What does the altimeter indicate if it's at a certain elevation The purpose of the altimeter is to show the pilot the altitude and the pressure above a fixed level. It uses barometric pressure and is 29.92Hg in ISA conditions.

What I dont understand is, how can this be extrapolated to be used in a situation where there is an elevation. For example, say the airplane is in a static position in an airfield at code EGNX, 52°49′52″N 001°19′40″W that has a 10 foot elevation. What would the altimeter indicate in such a situation.

Edit: Added a starting position

An altimeter is just an adjustable barometer with extra hands.

There is a barometric correction you dial in so that the altitude shown is always feet above sea level.  The correction is from the current barometric pressure reference you get with the "altimeter setting" or the weather report.

You dial in the altimeter setting, the current barometric pressure reference for your location, and shows your true height above sea level.  In your example, if the altimeter setting is correct, it will show 10 ft above 0 ft.

Or, you can work it the other way.  If you know the elevation you are at, you can dial the altimeter so its altitude indication matches your known elevation.  Voila!; the current barometric pressure is shown in the setting window on the instrument's face.


Why do we see a reduction in temperature in a wind tunnel by increasing the velocity, but in a real flight it's the opposite? In a real flight, when the speed of an aircraft increases, we see an increase in temperature too. So that at high Mach numbers the surfaces of the aircraft will be very hot.
Now I have encountered this issue that in a wind tunnel and for a test model it works in reverse order. So that the flow velocity in the tunnel is increased, the temperature of the test model surfaces will reduce, and at high Mach numbers, we need to use heaters to prevent freezing.

My question is this: is this fundamentally correct? If it is, what's the reason for this difference?

I believe the reason is that the air is cooled while compressed in the high pressure reservoir before the high speed wind tunnel.

When moving air is stopped (as happens around the leading edges of the aircraft), its pressure increases (per Bernoulli's principle) and since the compression is adiabatic (no heat exchanged (yet)), its temperature also increases. The final temperature is called Total Air Temperature (or stagnation temperature).

For flying aircraft, the total air temperature is its original temperature plus the increase due to compression by the leading edges of the aircraft. That's why the leading edges heat up in supersonic flight. The other sides don't, the air is not stagnant around them.

However, for wind tunnel, the air was already stagnant in the high pressure reservoir before it—high-speed wind tunnels usually pre-compress the air, because compressors can't produce supersonic speeds. It this reservoir it cools down, and then as it accelerates down the wind tunnel, it adiabatically expands, reducing its temperature well below ambient. It returns to the temperature in the reservoir at the leading edges, but around the rest of the model the air is not stagnant, so it has the lower temperature of the flow.


How I determine numerically the roll rate of an aircraft? I'm a Spanish student of aerospace engineering and I'm doing my final bachelor work that consists in designing an unlimited aerobatic plane, and I wonder if it is possible to calculate an approximation of the roll rate depending on design parameters. ( I have aerodynamic analysis of the wing, CL, CD, MAC, W, ...)

And another question about it, how exactly the trailing edge sweep angle affects the stability? And some bibliography?

In order to determine the roll rate of an aircraft, all you need to do is to set the rolling moment from aileron deflection equal to the roll damping of the wing (actually, of the whole aircraft, but the wing dominates roll damping anyways). So you set
$$c_{l\xi}\cdot\frac{\xi_{left}-\xi_{right}}{2} = -c_{lp}\cdot p = -c_{lp}\cdot\frac{\omega_x\cdot b}{2\cdot v_{\infty}}$$
$$\Rightarrow\omega_x = -\frac{2\cdot v_{\infty}}{b}\cdot\frac{c_{l\xi}}{c_{lp}}\cdot\frac{\xi_{left}-\xi_{right}}{2}$$

The symbols are:
$\kern{5mm} \xi\:\:\:\:\:$ aileron deflection angle
$\kern{5mm} v_{\infty}\:\:$ velocity
$\kern{5mm} b\:\:\:\;$ wing span
$\kern{5mm} c_{lp} \:\:$  coefficient of roll damping, using $\frac{b}{2}$ for its reference length
$\kern{5mm} c_{l\xi} \:\;$ coefficient of rolling moment due to aileron deflection
$\kern{5mm} p \:\:\:\;$ dimensionless roll rate
$\kern{5mm} \omega_x \:\:$  rolling speed in rad/sec

Damping decreases with altitude, and in this equation the increase of flight speed with altitude will make sure that roll damping decreases accordingly.


Why do planes make landing approaches at significantly varying heights? I live in NYC and my house is under one of the approaches for JFK. Im still about 15 miles away from JFK, so the noise isn't an issue 99% of the time. Once in a while however, especially if I'm outside, I notice that the plane is much louder and seems to be visibly lower.

Why is this? I'd figure with all the fancy GPS and radar systems planes and ATC have that the landings would be near identical, but this doesn't seem to be the case.

Unfortunately, since I don't know your particular location relative to the airport, I can only give some general answers as to why this might be.

Contrary to popular belief, the availability of precision approaches does not mean they are used 100% of the time, nor are aircraft always routed the same way. Depending on the airport, the use of precision approaches can drastically reduce the number of aircraft that can be handled in a given period of time.  As such, during visual meteorological conditions, flights will almost always be cleared for a visual approach. Busy airports will typically have a number of standard arrival routes (STARs) that make the approach routing consistent and predictable (which could explain why noise is not an issue 99% of the time), but pilots are not obligated to use them.  If a STAR is not used during a visual approach to an airport with approach control services (like JFK):

The approach controller (using radar) will direct the plane in such a way to allow the pilot to visually acquire the runway, at which point the controller will clear the pilot for a visual approach. Additionally, under radar vectoring, the aircraft may be told to fly a particular heading for sequencing and/or spacing which can vary due to the amount and type of traffic.
Once cleared for the visual approach, the particular approach course and altitude is at the pilot's discretion.

The situation is similar for an instrument approach, except that the approach controller will arrange to have the aircraft either navigate to an initial approach fix on a published approach procedure or vectored to intercept the localizer before clearing the pilot for the approach.

Sometimes, unusual flight paths can also occur when a runway that is not normally used for landings is made active.  This can happen when wind favors a particular runway, or the one that is normally used is taken out of service (e.g. maintenance or an accident).


What is the english term for "vol en ficelle"? From what I have read online and understood, "vol en ficelle" is basically a low altitude flight preparation method that requires calculating a set of altitudes to be followed in order not to crash.

It consists of flying near the ground, but following small portions of levels (so without trying to flight closely the contours of the relief).
It is then necessary, during the mission preparation phase, on a predefined route, to cut it into sections and determine, for each of them, an altitude (not a height) that allows to keep a sufficient margin relative to the ground.
During the flight, it is important to know with sufficient precision where you are, then fly at the preset altitude.

The flight preparation is the main part of this technique, where you have plan properly the flight course and accorrdingly define corresponding landscape and montains heights.

Below is a map of such preparation. On the left side of the map is the "ficelle altitude", this flight preparation technique is apparently also called the "méthode numéri"

Image source : Le diable a bord

EDIT:
I doubt it is contour flying, even though that's the closest term to "flight en ficelle" so far.
Contour flying means flying at very low heights by maintaining a constant height above the ground, which means the altimeter is going to vary widely depending on the terrain profile. But with flying "en ficelle", the pilot follows a predetermined set of altitudes, thus we can fly without radars and the altimeter changes only in successive levels, i.e map in the OP. In "Flying in ficelle" the bulk of the job is the planning, ficelle refering to the thread used in the mapping technique to find out the "predetermined altitudes".

EDIT 2:
In the HUD of the Mirage F1, the "ficelle altitude" that the aircraft should go not lower than, is represented by the reticle below.

Rings a bell?
Are we overthinking this ? It is basically a low flying technique with predetermined set altitudes calculated in advance.

Update:

I found this translator-help page, which suggests:

  [low altitude] constrained flight path

Perhaps nap-of-the-earth flying (Wiki) is what you're looking for.

According to wikipedia:

  Nap-of-the-earth (abbreviated NOE) is a type of very low-altitude
  flight course used by military aircraft to avoid enemy detection and
  attack in a high-threat environment.

It also mentions other terms such as (emphasis mine)

  Other, mostly older terms include "ground-hugging", "terrain masking", "flying under the radar" and "hedgehopping".

Image source


Ferry Permit for aircraft outside the U.S The aircraft originally had a U. S. airworthiness certificate then was exported to Brazil. It is now being sold to a company in the U. S. for U. S. operations. Can this aircraft be issued an "N" number and Ferry Flight permit for the purpose of returning to the U. S. where an application for U. S. Airworthiness Certificate and permanent registration will be pursued?

If the aircraft was taken off the US registry and registered in Brazil, the answer is no. You have to reverse the process to put it back into the US registry, and until it is, you can't ask for a ferry permit from the FAA.

For the benefit of those who may not know the process:

A request is made in Brazil to deregister the aircraft, with a note to send a copy of the deregistration certification to the FAA. The seller needs to request this in Brazil; the buyer cannot make the request, neither can the FAA. Processing of this request can take anywhere from two days to several weeks, particularly if the aircraft is registered to anything other than an individual and/or if there are any registered liens on the aircraft.
The Brazilian government sends a notification to the FAA that the aircraft has been deregistered.
A registration form with either a previously reserved N-Number or by default letting the FAA assign one is sent to the FAA, along with a valid bill of sale. If the bill of sale is from Brazil, it must be notarized by a Brazilian notary and apostilled (certified) at at any public notary office (cartório). If it is in Portuguese, it must be translated by a certified public translator, a list of which may be obtained from the Junta Comercial of any state in Brazil. If you don't do these last two steps the application could be rejected. Better to use the FAA form for the bill of sale.
Once the FAA receives the registration request, it verifies that it has received the deregistration confirmation from Brazil. No registration will be issued until that happens.
A registration certificate is issued and mailed to the person or entity on the registration form.

You can then make arrangements for a ferry permit, but keep in mind that the procedure to request a special flight permit (the official name for a ferry permit) has other requirements, including sending a copy of the current airworthiness certificate, portions of or all of the logbooks, etc.

Also, if the aircraft has any outstanding AD's that have not been complied with, and the AD notice makes no allowance for ferrying the aircraft to a location for the purpose of achieving compliance, the ferry permit will not be issued. You will have to bring the US mechanic to the airplane (or find a local FAA-licensed mechanic, possibly an IA as well depending on the nature of the AD) to take care of it.

Bottom line is talk to your local FSDO first before any money changes hands to avoid any unpleasant surprises. The process above can be applied to an aircraft in any country, just change the references to Brazil.

(If you see an error in this explanation, or something that needs clarification, please add a comment so I can correct it or further clarify it.)


What is the total EXTRA lift produced using an 80 deg flap and distributed propulsion? What is the total EXTRA lift produced using an 80 deg flap? ( 50 deg flap at 30 deg AOA ) and distributed propulsion.

Specs: Ultralight, stall speed 20mph, ROW of 12 x 15" props along entire wing span in DISTRIBUTED PROPULSION, max local AOA estimated at < 9 deg ), electric 25 hp (total), MTOW 500 lbs, low wing in ground effect, max 3 ft height for xSTOL/nVTOL, VG's, full span single slotted flaps with spoilers , Clmax: 3.4.

Hypothesis:

A low wing ultralight accelerates with a short field takeoff, along a runway to 20mph and rotates to 30 deg AoA just prior to takeoff, producing the following:

Total lift = Wing lift (bernoulli/momentum/vortex lift + deflection lift )  + Prop lift + Flap Lift

Example:

Wing lift:

standard wing lift formulas, lift equal to airplane weight of 500 lbs.

Prop lift:

Estimated thrust at 20mph: 5lbs/Hp thrust x 25 HP = 125lbs thrust.

Prop lift = 125 lbs x sin ( radians(30 deg))= 62 lbs

80 deg Flap Lift

Thrust due to Prop wash on bottom of wing hitting flap
= 30%(???) of total thrust = 37 lbs.

Total extra vertical thrust/lift

= 62 + 37 = approx 100 lbs ( 20% extra vertical thrust/lift...!!!! )

Reduced MTOW wing requirements at Vtakeoff to Vflap

orginal MTOW = 500 lbs.

MTOW revised= MTOW original - extra vertical lift = 500lbs - 100 lbs.= 400 lbs.

This is the reason for asking the question:

Could I then resize my wings based on 400 lbs MTOW at Vtakeoff(Vso) to Vf, not 500 lbs?

Is this correct thinking?

See black tuft dwg below showing downwards air flow.

A 30° flap is a typical landing setting. Increasing that to 80° is only adding more drag. Your 25 hp thrust will only add a mild breeze and will not help to reach that 30° AoA unstalled. Better use 8° or 10° of flaps (depends on flap chord) and do not rotate to more than 10° AoA.


Can one fly up side down while a glass of water keeps full due to g-forces? If one makes a looping for example with a plane and the g-forces that the planes makes will keep the water in the glass, but if one is at the top of the loop is there still enough g-force to keep water in the glass?

Yes, as long as you continue the loop, and don't fly the plane in the upside-down position.

See, for example: Barrel roll with a glass of water on a glider


To which airspace does the border of two adjacent airspaces belong to? Consider two adjacent airspaces of different categories. For example, airspace G is up to 2500' and above this is an airspace D. The border is at 2500'. Which airspace are you in if flying at exactly 2500'?

I recall a definition by ICAO that said that the border between such airspaces belongs to the less restrictive one, but I can't find that document.

You recall correctly. That document is ICAO SARPs Annex 11 § 2.6:

  Where the ATS airspaces adjoin vertically, i.e. one above the other, flights at a common level would comply with requirements of, and be given services applicable to, the less restrictive class of airspace. In applying these criteria, Class B airspace is therefore considered less restrictive than Class A airspace; Class C airspace less restrictive than Class B airspace, etc.

(Emphasis mine.)


Where can I find a canonical list of sources for worldwide digital GA VFR maps? Related question: Where can I find GA VFR maps for Australia?

For various areas of the world, where are authoritative General Aviation VFR maps, charts, and so on available on the web?

This answer is a Community Wiki. Please edit as appropriate.

Australia

OzRunways.com

United States

VFR Charts from the U.S. Federal Aviation Administration


Is there possibility to Survive without brain damage at 30/35,000 feet? I just read Mayday by Nelson Demille. I won't get into many details but the book talks about an airliner (similar to the Concorde) which operates at an altitude of ~60,000 ft (~18Km). Suddenly, due to a mistaken missile launch, there are holes on both sides of the plane. All the passengers become brain-damaged except 5 people who are trapped in lavatories at that time.

Now while this is fiction, could we go crazy due to lack of oxygen in case something goes wrong? How much oxygen would be needed to land safely and how much oxygen is usually kept on an airliner in case of emergencies.

A second and related question: in case of a fire or other incident, how quickly can a plane safely descend? I know and have experienced losing altitude the last 30 minutes or so of flight, probably lining up to the airport. In an emergency, how quickly can the pilot land? Is it 5-10 minutes or more? I am talking about descending from cruise altitude and come to a dead-stop.

Long term, no, it is not.  Any exposure to pressure altitudes over 26,000 ft will eventually cause death from hypoxia, even with acclimation to the higher altitudes.  There is a period referred to as Time Of Useful Consciousness (ToC) associated with hypoxia.  This is the approximate time that a healthy adult human with good lung capacity can maintain cognitive function.  These values can be halved if an explosive decompression occurs, which is why there is a requirement that airliners have quick donning, pressure breathing oxygen masks available to the flight crew and can be donned and establish the flow of oxygen within 5 seconds.  It is also the reason that flight attendants tell passengers to first don their emergency O2 masks, then assist someone else next to them in the event the masks are deployed.

Once ToC lapses at a given pressure altitude, cognitive function rapidly begins to fade away.  The person becomes listless, sleepy, but often euphoric.  Loss of consciousness, coma and then finally death will ensue unless the minimum partial pressure of O2 in the lungs is re-established.

Section 3-1 of the FAA Manual of Aviation Physiology is a good reference on the subject of hypoxia.

At the altitudes that Concorde cruised at, the air pressure is so low that decompression sickness becomes more of a risk than hypoxia.  Having the water boil away in your own bloodstream is a very painful way to die, and loss of consciousness via hypoxia would almost be a relief from that torment.


How does washout affect the wing incidence required? In theory: if I wanted to build an model aircraft with (zero zero) wing/tail incidence, how would washout affect the root incidence required?

E.g. if a wing has 2 degrees washout at the tip, would the root have 1 degree + incidence so that the 'average' angle of the wing is zero ?

That depends on the taper ratio.

In the end, the wing with washout should produce the same lift as the one without. For a rectangular wing and 2° washout, your reasoning is right and the root should have 1° incidence so the whole wing produces the same lift as the one without washout and 0° at the root. If the wing has a triangular planform, however, the tip contribution to overall lift is much lower and the root incidence should only be 0.667°.

For a general rule, pick the position along the span at which half of the wing area is inboard of this position and pick the root incidence such that the local incidence at this position is 0°.


Can you ride a storm to save fuel? Cargo sailboats, of the old, depended on wind direction. Like these ships, planes also save time by flying with the wind. On the extreme end, could a plane use storm fronts or hurricanes by flying in and out, in front of, or down the length of it to save time or fuel?

Not storms, but there is a concept called "Pressure Pattern Flying" where you plan routing to stay in favourable circulation around Highs and Lows, to the extent that deviations to follow the circulation flow and stay in tailwinds can get you there sooner than going straight.  To take advantage of this you need to be going fast enough and with the range to span pressure regions. Although Lindbergh talked up this sort of thing in the 30s in his own flying, it's generally something exploited by airliners on transoceanic flying.
And in fact the North Atlantic Track system adjusts the tracks northerly or southerly daily to maximize or minimize the effects of winds around pressure systems, especially focused on jetstreams, which form at frontal boundaries at the tropopause. It might be worth a significant deviation from straight line point-to-point flight to ride downstream in a 100kt 10 mile wide jet that's going your way at 31000 ft (or whatever level the tropopause is at for a given region and time of year).
As far as storm systems go, nothing good happens near one.  You stay away from them regardless of the size of the aircraft, 20 miles being the convention, and ideally on the upwind side.  One hazard of passing by a thunderstorm cell on the downwind side, even if well clear of it, is running into hail falling in the clear air after it shot out the top of the cell.


Can it be determined from beyond visual range whether an unknown aircraft is armed or not? In a typical situation, where an unknown aircraft appears on radar, and doesn't respond to any radio message, sooner or later fighter aircraft are scrambled to take a closer look.

However, can it be reliably determined whether the unknown aircraft in question is a military aircraft or a civilian one, before the pilots of the scrambled jets can take a closer look with their own eyes?

By armed I don't mean deciding whether it carries real missiles or just harmless training dummies, but whether it's a military aircraft or a civilian one. Do we know of cases when this was determined before making visual contact (assuming the UFO didn't respond to any messages)

For example, is it a fighter jet or a small private business jet? Is it an airliner or a strategic bomber? From how far can you tell the difference?

Only if the airplane wants you to know it is armed.

It has several ways at its discretion:

If it has a powerful radar, it can switch it on at altitude and announce its presence to other aircraft up to 150 km away.
It can send IFF squawks which are reserved for military aircraft. Note that IFF is used by both military and civilian aircraft.

Both methods are only indirectly indicating whether an aircraft is armed. The armament itself will not show up at BVR distances. In the end, if you want to be sure, you have to move some sensors close to the aircraft if the weapons are carried externally, or even wait until they are deployed when they are carried internally. Especially many small aircraft are used both in a civilian and a military role.

A BVR radar is a dead giveaway for a military aircraft - such equipment is not fitted with civilian aircraft, and removed or disabled when an ex-military aircraft is converted to civilian use. Similarly, supersonic speed, which can reliably be detected with Doppler radars, is a telltale sign of military aircraft approaching.

Transport aircraft are much harder to distinguish from bombers on the basis of radar signals alone, and in the end you cannot exclude that the hostile aircraft tries to spoof your equipment into classifying it as a civilian aircraft.


Could a helicopter perform a forward inversion (front flip)? This is inspired by a previous question

What would happen if I bank a helicopter then pull hard on the cyclic?

I've seen some pretty radical videos of piloting by Chuck Aaron, but I've not seen a helicopter perform a forward inversion (either by a flip or an inverted loop).  I've seen helicopters invert backwards and perform rolls, but not in the forward axis.

Would such a manoeuvre be possible?

Yes.  This video at 0:50 shows a heli climbing into a loop, labeled at the top as 1.4 G and 25 knots, so it's still in forward flight when it reaches inverted flight.  The view from inside the cabin at 0:58 confirms pitching without rolling.
(At 1:26 the heli does what's labeled as a front flip at low G's, but that includes a lot of roll too.)
The pilot is Aaron Fitzgerald, in a Red Bull helicopter
with registration N154EH barely visible at 1:44, identifying it as a
1985 MBB BO105 CBS4, classified "experimental."
Wired magazine describes the crucial "hingeless" rotor head:

The rotor head is milled from a solid block of titanium rather than multiple components, skipping the hinges that typically allow the blades to bounce up and down to absorb aerodynamic forces. Instead, the blades are designed to be more flexible. ... The lack of up and down blade movement at the rotor head limits the “play” in the control stick, giving the pilot more granular control of the helicopter.

The video was published 2019 May 24-25.  It is also available without ads here.
I could not determine the exact date of the flight, but Wired also said it was

a practice session for this Memorial Day weekend’s Bethpage Air Show

so that at least confirms it as shortly before 2019 May 27.


How were bullets fired through the propeller in the Focke Wulf 190? In WWII there was a plane called the Focke-Wulf Fw 190. It was designed by an engineer called Kurt Tank.

How is it possible that the Fw 190 fires through the propeller from 4 different places as you can see in the picture below? There are two machine guns right in front of the pilot, and one at either side on the wing, close to the body of the plane.

Note: See Peter Kämpf's answer for specifically how the Fw 190 Achieved this Electronically
This answer is specific to how this was achieved via mechanical means in earlier aircraft and not specific to the Fw 190.
It's called a "Synchronization Gear" and it allows the gun to fire only when the blade is not in front of the barrel.

Source: Kaiserliches Patentampt (Imperial German patent Office) / Franz Schneider - Patentschrift No. 276396, 1913 First published in Flugsport" (1914) and in many places since, Public Domain,

[From Wikipedia] Interestingly, the linkage between the propeller and the gun is achieved with a spinning drive shaft rather than a reciprocating rod. The impulses needed to operate the trigger, or in this case to prevent the trigger from operating, were produced by a cam wheel with two lobes at 180° apart situated at the gun itself, since the gun is interrupted by both blades of the propeller.

These have been around since before 1920, long before the aircraft you mention in your original post.
The one on the Fokker (not Focke-Wulff, but still German) differs a little bit from the patent image above:

Source: By Gsl - Version with English text of Image:Interrupter_gear_diagram.png, Public Domain
But not significantly, the basic idea is that the trigger mechanism follows a cam lobe which is tied to the propeller shaft. When the cam lobe spins, the trigger is allowed to fire the gun only when the propeller isn't "in the way".
See Wikipedia Article on the Synchronization Gear for more information.


Would a helicopter with the blades on the bottom fly the same, if at all? I've heard that the pendulum rocket fallacy applies to rotorcraft as well. As stated above, I'm curious to know if a helicopter with blades on the bottom of the body would experience any effects from this. (Yes I know it's impractical and landing would be terribly difficult.)

Yes that is possible, like the Hiller flying platform demonstrated. It had two counter-rotating propellers inside a shroud and the pilot controlled his craft by shifting his body weight, like on a Segway. There is no law of physics that prohibits a helicopter from flying upside down.

The Hiller flying platform was one of several types built in the 1950s, after it was observed that controlling an underslung rotorcraft by weight shift could be learned by untrained personnel in 20 minutes. The DeLackner Aerocycle was another platform built based on this finding. The idea was later abandoned due to practical issues like kicking up rocks into the rotor blades, and an at the time unexplainable interference between the counter-rotating blades. The Aerocycle had a fixed rotor head, the dynamics of which were poorly understood at the time.

For full scale helicopters, having the rotor underneath the helicopter has the same stabilising effect on flight characteristics. Stability of helicopters (and of fixed wing aircraft) is studied from the perspective of aerodynamics: the effects of wind gusts or control inputs.

In the hover, the speed stability ${\delta M}/{\delta{\dot{x}}}$ plays a significant role: if positive, the hover is unstable. A human can learn how to control an unstable platform if the time period of the oscillation is high enough (conventional helicopter pilot), but it is much easier to fly in an aerodynamically stable aircraft (the underslung platforms intended for general infantry personnel). The speed stability effect in the hover equates to a gust of wind blowing from directly forward, does then the change in moment tend to amplify or counteract the effects of the gust. This can be visualised like so:

Image source

The gust blowing on the helicopter tilts the rotor back, which tilts the thrust vector. A teetering conventional rotor has a positive ${\delta M}/{\delta{\dot{x}}}$: it wants to flip backwards ever stronger, and is therefore aerodynamically unstable in the hover. An underslung teetering rotor has a moment change that stabilises: it tilts the fuselage back, and due to aerodynamic coupling the rotor follows back to neutral. A rotor with hinge offset has a smaller stabilising moment, but a stronger fuselage/rotor coupling.

So to answer your original questions: Yes the helicopter with an underslung rotor would fly, and it would be easier to control than a conventional helicopter. It is just a bit unpractical, that's all.


Do fighter jets have a traditional inverted fuel system? Common solutions for aerobatic piston singles is to have either header tanks (for wing tanks, as I understand it) or flop tubes (for fuselage tanks).
Do fuel systems in a fighter jet work on the same principles? Or are they somehow smarter to allow more erratic maneuvers?

I don't know for certain as I'm not military, but I imagine that they pressurize the fuel tanks using bleed air, much like jet airliners do. It's also likely that they make use of boost and ejector pumps to provide positive pressure directly to more centrally-located tanks which the engines then feed from.

(from FAA AMT Handbook [pdf])

The F-15 has both wing & fuselage tanks; according to a site of dubious accuracy (F-15E.info):

  The left and right engine feed tanks contain baffles in order to provide a limited amount of fuel to the boost pumps during inverted flight or during negative G maneuvers

  Left wing tank
  Auxiliary tank
  Left engine feed tank
  Right wing tank
  Right engine feed tank
  Tank 1 (main tank)

Baffles are dividers in the tank itself that limit the speed at which fuel can flow from one end to another, usually to prevent fuel sloshing and screwing up balance.


How is fuel stored and routed on a trijet with one engine at the tail? This question pertains to trijets with two engines on the wings and one at the tail, like the Lockheed Tristar. It does not pertain to trijets with all engines at the tail, like the Tu-154. (And it doesn't matter if the rear engine has an S-duct or not.)

How is fuel stored and routed on a trijet that has only one engine at the tail? Does the rear engine have totally separate fuel tanks and lines?

(Own work based on MSFS)
On an MD-11 the tail mounted engine is fed from tank 2, which is two halves as shown above -- the two halves are connected via vent lines.
Sequence
The center tank on an MD-11 is called aux, and it feeds all the engines until it's empty -- the aux tank actually fills the other tanks and the other tanks do the feeding (systems display shown below). Tank 2 (being bigger than 1 or 3) then carries on filling tanks 1 and 3 plus feeding all the engines. Once tanks 1, 2, and 3 have the same fuel quantity, each tank then feeds the respective engine.

(Own work based on MSFS)
Stabilizer tank
Fuel is transferred to and from the stabilizer (tail tank) to manage the CG. It is fully consumed by the time the plane reaches its top of descent -- as a forward CG is more economical for descending. The exact sequence is managed by the fuel system controller. The tail tank also feeds the tail engine as part of the CG automation.
The sequence (and scheduling) is automated even with an engine, or even two, out.
Summary
The #2 engine is fed by the aux, tail, and #2 tanks. If an engine fails, then cross-feeding is involved.


How do airlines make sure that pilots remain skilled enough to operate aircraft? What quality assurance is there for certified pilots? What measures are in place to prevent pilots from being put in charge of passenger planes without an appropriate level of training and skill? Are these measures enforced equally by different countries, airlines and aviation authorities?

Put quite simply for this answer - The Licence a pilot holds is the assurance that the pilot has received the appropriate level of training.

Each country has it's own standards for training, their own requirements, and their own limitations on the operation of that licence. In saying that, MOST countries standards are reasonably in-line in regards to Aeronautical Experience required to sit each flight test.

In Australia, the requirement to sit a Commercial Pilot Licence is a minimum of 200 hours Aeronautical Experience (150 hours if ALL training has been conducted on an Integrated Course, now to be recognized under Part 141). From there, there is a break down of what that 200/150 hours must consist of.

Now, having a Commercial Pilot Licence (again, speaking from an Australian point of view) does not give a pilot the right to sit in the left seat of an Airliner. You need further training such as;

Multi-Engine Command Instrument Rating
Type Endorsement (for the intended aircraft)
Crew Resource Management Training
Dangerous Goods Training
Senior First Aid (Not mandatory, but common)
Company, Emergency, Cyclic and Systems checks (per company)
Air Transport Pilot Licence Theory Exams (in some cases, Airlines may not even look at you if you haven't completed these - In
Australia, it is an unwritten must-have!)

And thats just to sit in as a Co-Pilot..

Captains need years of experience, and a lot more training and check to get into that coveted Left Seat.

So again, to bluntly answer your question, regardless of country, there is law in place that stipulates that Pilots must be appropriately trained to fly airliners.


Do carrier-borne aircraft pilots count the seconds on the downwind leg of the carrier? On carrier landing, someone tells me that the pilots need to count several seconds on abeam leg of the landing pattern, in order to land precisely on the flight deck. Is that true? What do we call for this operation?

According to the F/A-18's manual, the pilot starts the 180° from downwind when abeam the landing signal officer's platform:

  With a 30-knot wind over the deck begin the 180° turn to the final approach when approximately abeam the LSO platform.

Here's the illustration (of course the ship is not fixed, it's moving):

Click to view


How many hours of test flight does a general aviation aircraft go through before delivery? I'm curious if anybody could give any indications as to how many hours of test flight a factory new small general aviation aircraft* goes through before customer acceptance and delivery.

(Not initial certification, but what is necessary for every new production airframe)

*e.g. Cessna 172, Diamond DA-42 or Robinson R22

All manufacturers have a quality system in place, and they also have a production baseline (which is a result of certification). so, as long as the quality system is utilized, there is technically no need to fly each manufactured airplane. Type certification validates the production baseline (and that each manufactured plane is within the tolerances acceptable for the certification authority or requirements).

However, depending on company manufacturing know how (or lack of) there might be several ground tests (structural, engine, systems checkout) before delivery.

On the other hand, for many military aircraft there's a factory checkout flight, to check and confirm the performance of each frame and propulsion system. This is more useful for risk reduction (to avoid customer complaints and to check the complex system in the air).


Why are airliner underbellies generally painted differently? Some airlines, Delta in particular, have dark underbellies on their liveries. Is this only aesthetic or is there a purpose for it?

Originally (way back before radar) the colors had a practical use for maintaining visual separation between planes, which was done by pilots looking for the other planes with their eyes:

Dark underbelly: Easier to see from below against bright clouds or sky.

Light top-body: Easier to see from above against (typically) dark ground.

The idea being that when you're looking visually for other civilian air traffic (or from the ground) one wants to maximize visibility without losing them in sky glare or ground clutter.

If you look at older military planes you'll often see the exact opposite (dark colors on top and blue on the bottom) because those military planes didn't want to be seen.


What is the difference between landing weight and end-of-mission weight? Raymer says:

  Landing is much like taking off, only backwards!....Note that the aircraft weight for landing analysis is specified in the design requirements, and ranges from the takeoff value to about 85% of takeoff weight. Landing weight is not the end-of-mission weight, because this would require dumping large amounts of fuel to land immediately after takeoff in the event of an emergency.

What is the meaning of the last sentence: "Landing weight is not the end-of-mission weight, because this would require dumping large amounts of fuel to land immediately after takeoff in the event of an emergency"?

How is the aircraft design is affected by such different needed kind of weight?

(Source: Raymer: Aircraft Design – A Conceptual Approach Chapter "17 PERFORMANCE AND FLIGHT MECHANICS" Paragraph “17.9 LANDING ANALYSIS ”)

End-of-mission is a time- (and case) dependent term. Your mission could end under a variety of circumstances. If your mission is to carry passengers from point A to point B and you have an uneventful flight, then end-of-mission and landing are the same thing. But (as stated above) if you have an emergency at some point, you might need to abort the mission. If this happens, then you are likely to end-up dumping as much fuel as necessary to get to your landing weight, because said end-of mission weight and landing weight will not be the same.

Here is an oversimplified example:
Aircraft AC has MTOW of 100,000 kg and a MLW of 50,000 kg. The same aircraft has to get from point A to point B, without releasing cargo or ordnance. During the mission AC burns 100 kg of fuel per minute. Ten minutes after departure the pilot realizes that he has forgotten his watch and needs to land immediately. Now after 10 min flight AC weighs 99,000 kg. Since the mission is about to end before MLW is reached (99,000 ~= 50,000), the captain can either dump some fuel or circle around until AC's weight is at most equal to MLW.


What is the average pitch of a plane? I'm looking for the average pitch of big planes like an Airbus A300. For horizontal travel, is the plane horizontal or does it have a pitch like 1 or 2° (or more)?

If the plane does not accelerate and has a constant speed, is the gravity of the passengers a little backwards?

I assume by "middle pitch" you're talking about the pitch during cruse? In which case, the answer is, unfortunately, "it depends". Changing pitch changes the amount of lift, and the amount of lift needed depends on the weight of the plane. So, an airplane with more passengers and cargo will need a slightly higher pitch.

Changing speed also changes lift, which will need to be compensated for by changing pitch. However, we're talking about cruise flight here, so speed will remain relatively constant.


What does "Controlling Object" mean in FAA documentation? I was examining FAA's legacy files, which contain information for various airspace elements, and I noticed that there is a field in the airport layout file called "Controlling Object", for both base and reciprocal ends of the runway.

Some of its properties:

Controlling object description
Controlling object marked/lighted
FAA CFR Part 77 runway category
Controlling obstacle clearance slope
Controlling object height above runway
Controlling object distance from runway end
Controlling object centerline offset.

It seems that it's an obstacle near the airport, but I can not tell why it is more important than the others. Does it lead to the most adverse situation, as far as aircraft's climb gradient is concerned? Does also the term "Controlling Obstacle" exist?

Could someone point me in the right direction?

'Controlling object' is, as far as I can tell, the old term for 'controlling obstacle'.

From the TERPS manual (Appendix B):

  Controlling Obstacle. The obstacle on which the design of a procedure or establishment of a minimum altitude or angle is based on. See also Order 8260.19, Flight Procedures and Airspace.

Controlling object is mentioned as a field in the Public Use Airport Runways database:

Attribute_Label: BE_CTL_OBJ
Attribute_Definition:
Description of the controlling object at the base end of the runway
(e.g., trees, bldg, fence, none).
Attribute_Definition_Source: FAA
Attribute_Domain_Values:

And as you can see, it can be trees, a building, and so on.