How do airports in hot climates handle extremely high temperatures? In June 2017 dozens of flights were cancelled in Phoenix, Arizona because of temperatures exceeding 120 degrees Fahrenheit/48.9 degrees Celsius.1,2

Hot air at a given air pressure is less dense, generating less lift at a given speed. At least some commercial jets were not rated to fly in air that thin.

While the temperatures that summer were fairly extreme Phoenix is surely not the hottest place one earth, or at least not alone in this range. For example Kuwait City or the Iranian city of Ahvaz3 come to mind.

How do other hot places handle extreme heat? Do they also suspend operation or do they impose specific requirements like lower maximum loads, or do they have special adaptations for the thinner air like long runways, allowing higher speeds at take-off and landing?

1 https://airlinegeeks.com/2017/06/22/multiple-flights-cancelled-due-to-heat-in-phoenix/

2 https://www.sciencedirect.com/science/article/pii/S2212012218300753

3 I found Ahvaz googling for hot places; I admit that I have never heard of it before even though it has more than a million inhabitants and an international airport, AWZ.

Transport aircraft are certificated to a maximum operating temperature for departure that is related to International Standard Atmosphere (ISA), typically 35 deg C above ISA (there may be airplanes certified to ISA +40), ISA being 15C at sea level and dropping from there at the standard adiabatic lapse rate .

ISA temperature at Phoenix airport at 1135 ft ASL is about 13 deg C, so the max temperature you can operate at is 48C, if your plane is certified to ISA +35 (if your plane was certified to ISA +40, you'd be good to 53C).  This is based on the airport temperature reported on ATIS, not temperature measured at the aircraft.

At 48.9 C in the case you mentioned, you are above your maximum certified temperature for takeoff, so you are stuck until it cools off, and you'll simply have to wait for the temperature to drop a degree later in the day.  This applies anywhere in the world based on the ISA temperature for the airport. So for example at a Middle Eastern airport at sea level, where ISA is 15C, you'd be good up to 50 deg C, and if it's above that temperature, you wait for it to cool off.


How does the aneroid wafer expands? (ASI) So, how does it expand? (aneroid wafer - intend to the airspeed indicator) I have two “theories” (from what I’ve learned) which are :

The ram air entering through the pitot tube physically hitting, pushing the aneroid wafer forcing it to expand - giving us the actual indication in the cockpit. faster airspeed—> more air hitting, pushing  the aneroid wafer at higher velocity —> greater  expansion?
The ram air rapidly filling the aneroid wafer making the air more dense —> more pressure, therefore forcing it to expand due the pressure differential between the aneroid wafer and the sealed case, which contain the outside atmosphere pressure. Faster airspeed —> more air —> increasing pressure inside the aneroid wafer —> larger pressure differential—> greater expansion?

Which one is true ? or both maybe ?

The aneroid wafer is just a metal balloon.  Add air into its interior, above ambient pressure, and it expands.

The outside of the wafer is exposed to ambient static pressure.  The inside of the wafer is plumbed to the pitot inlet.  Ram air into the pitot raises the pressure within the pitot plumbing to above ambient, which being connected to the interior of the wafer, inflates it.  The movement of the inflating wafer is geared to the airspeed indicator and voila, ya got yer speed indication.


What airfoil design does the MQ-9 Reaper UAV use? What airfoil design does the MQ-9 Reaper UAV use?  Alternatively, what similar airfoil designs exist?

I'm running simulations for the effects of vortex generators for a school project and I would like to study the Reaper drones.

The wing root of the General Atomics RQ-9 is the Drela GW-19/GW-25.

The wing tip airfoil is the Drela GW-27.

Because of their application, you will likely have difficulty finding study results of vortex generators used on that blended airfoil. There are papers, but I have only seen them in the DTIC library, and I do not recall the classification of them. However, the aircraft has been exported, so you may find some open literature on the airfoil, and the adaptations and optimization of it.


Why don't horizontal stabilizers have winglets? Winglets are used to reduce induced drag on the main wings of an aircraft as per explanations on wikipedia. Since they are very effective I was wondering why they are not installed also on horizontal stabilizers. For sure there must be some sort of induced drag being generated on horizontal stabilizers too as they are cutting through the air just as the main wings do. So why aren't there any sort of "minified" winglets available as an aftermarket installation (or, at least, I haven't ever seen some myself)?

Horizontal stabilizers don't generate as much pressure difference as the wings. Generally the stab deflections are very small in flight, and there's so much other drag during landing -- when the stab gets the most use -- that wing vortices from the tail are probably the least of your problems. Stabilizer winglets on their own, when there's no pressure difference, would simply result in drag, whereas the main wing winglets are constantly effective while flying.

Furthermore, the weight and trouble of adding little winglets to the horizontal stabilizers with larger actuators and hinges, for example, would probably outweigh the very slight aerodynamic benefit. I could also imagine that since the airflow over latter part of the wing is complex and varied, find a good design solution would be difficult.

As @Federico points out, the DA42 has them, but that's a composite airframe rather than the metal construction you see in most Cessnas, for instance, where you have to be more conservative in construction.


When is compressibility a problem for a pitot tube? One of the errors for a pitot tube is 'compressibility.' However, I don't understand this in detail. I get that the ASI will read slower because the ram air is compressing against the air already in the pitot tube. My question is when does this happen? What would cause this?

In subsonic flow, a pitot tube measures the total pressure $P_{0}$, while a static port measures the static pressure $P$. For very small Mach numbers, we can use the incompressible form of Bernoulli's Equation for determining the speed.

As there is no energy due to compressibility, the density $\rho$ is constant. This means that along a streamline,

$\frac{P}{\rho} + \frac{1}{2} v^{2} + gh = constant$

Neglecting gravity, we have,

$\frac{P}{\rho} + \frac{1}{2} v^{2} = constant$

Using this, we can determine the velocity as

$v = \sqrt{2\frac{P_{0}-P}{\rho}}$

This equation, however does not take the effect of comprehensibility into account. While at low speeds this is not a problem, this causes an error as the Mach number increases above ~0.3. As the speed increases above this value, the term $\frac{1}{2}\rho v^{2}$ no longer gives the difference between the Total and static pressure.

In case of compressible flow, neglecting gravity we have,

$\int_{P_{0}}^{P}\frac{dP}{\rho} + \frac{1}{2} v^{2} = constant$

along the streamline as $\rho$ is no longer constant.

For adiabatically expanding gas, we have,

$\frac{P_{0}}{P} = (1 + \frac{\gamma-1}{2} M^{2})^{\frac{\gamma}{\gamma - 1}}$

where $\gamma$ is the specific heat constant and $M$ is the mach number. In this case, the velocity can be calculated as,

$v = \sqrt{\frac{2 \gamma}{\gamma - 1} \frac{P}{\rho} [\frac{P_{0}}{P}^{\frac{\gamma - 1}{\gamma}}-1]}$

This difference gives rise to the error, which is positive i.e. compressibility error produces ASI readings that are too high. In terms of the pressure ratio, the error is more than 8% as the aircraft approaches transonic speeds. The following image shows the difference in pressure ratio between readings using assumptions of incompressible and compressible flow.

Image from Mechanical Measurements and Metrology - Measurement of Fluid Velocity by S. P. Venkateshan

Basically, the issue is with the assumptions in the method use to calculate the velocity- for low speeds, we assume that the density is constant, which is clearly not the case as the speed increases. Usually, M = 0.3 is taken as the cutoff point.


What are typical control surface deflections? How can I tell what a reasonable control surface deflection is?

For example, is a 10 deg aileron deflection reasonable? Or a 0.5 degree aileron deflection? Is that too little? Too much? Same question concerning stab/rudder. I'm  not a pilot, I've never seen these surfaces actually in action, so it's kind of difficult to tell what (roughly) a reasonable surface deflection would be. As I go through flight data, I find myself seeing this type of data a lot, so an idea of what's reasonable would be really useful!

The maximum useable deflection angle depends on the relative chord of the control surface. A good first-order value is ±20° for a 20% chord. With increasing chord, the deflection range will become smaller, like ±15° for a 30% flap.

With ailerons, things are a bit different because they are part of a lifting surface. This gives them some pre-loading so the negative range (trailing edge up) will become larger than the positive range (trailing edge down). This is also useful to reduce control forces (aileron differential) so the useable range will be +10°/-25° for a 20% chord aileron.


What is the proportion of active aircraft from CASL (commercial aircraft sales and leasing)? I recently discovered the existence of CASL and I understand they buy a lot of new aircraft (e.g. BOC aviation ordered more than 80 B737's and about 40 A320's few weeks ago). I imagine those aircraft are used for temporary operations (e.g. during scheduled maintenance or waiting for an aircraft to be delivered) by regular airliners, charters, lines with demand growing faster than expected, etc.

Given the number of aircraft they buy, a significant part of the traffic must be operated by these aircraft. Is there some statistics about the number of aircraft and/or the number of flights performed with an aircraft owned by leasing companies compared to flights performed with aircraft owned by airlines themselves?

According to The Economist data in 2012 showed that:

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

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

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


Exactly what kind of radios are prohibited for passengers inside an aircraft? I know that passengers are asked to put their cell phones on flight mode. But some carriers allow use of WLAN on-board. So, what radios should passengers refrain from using?
Also, if a person uses a GPS receiver on his/her mobile phone (on flight mode), would it interfere with the aircraft communication system?

There is actually a simple answer, but it probably isn't exactly what you are looking for:  Refer all questions about what is allowed to your specific airline.

Each airline has to come up with their own list of allowable electronic devices, and submit that list to the FAA with appropriate documentation in order to gain approval to allow passengers to use them during flight.

Some airlines allow almost everything as long as it can be put into a non transmitting mode (airplane mode), while some still require ALL electronic devices to be completely powered down at all points during the flight.

Because of this, every airline is a little different and you are required to follow their rules while on their flights.

The GPS receiver would not cause problems, but this doesn't mean that you are necessarily allowed to use it, and there are other things in your phone that could cause a problem though.

In general, no electronic device that has a transmit function may be used because of possible interference though, unless specifically approved.


How can one demonstrate/assure safety for LRU's, CBAs, SoC's and other integrated modules? Does anybody have experience with getting complex modules that were designed by others for common use, approved for incorporation in an airborne system that is at DAL A, B, or C and thus requires FAA approval?  I am doing research on the topic of how optimal the current approval guidelines are.

The question is of interest for LRU's (Line Replaceable Units), CBA's (Ciruit Board Assemblies, SoC (System on a Chip sunits) and other integrated technology modules.

If anybody out there has interacted with a DER and either found the means of demonstrating compliance to be sensible and practical, or can point out either gaps where potential errors could have snuck through or places where the approval process is impractical, I would appreciate it a lot.

Yes, I've had some experience in dealing with complex hardware certification both with DERs and with FAA ACOs.  For the last 15 years or so, the process has been well defined as both FAA and EASA have adopted RTCA DO-254 Design Assurance Guidelines for Airborne Electronic Hardware.

I haven't run into many cases where there are any meaningful difference in interpretation of the guidelines, especially when discussing internally developed components.  There are some differences in what a DER/ACO will accept when you attempt to use commercial off the shelf (COTS) components.  DO-254 section 11.2 covers the use of COTS components but as it points out, the issue is lack of design data from the developer/manufacturer.  So coming to agreement on what is acceptable for these cases is highly variable depending on the DAL required and the available data.

For higher DAL levels it's getting harder and harder to get approval for COTS. You also have to deal with the fact that COTS parts may go through significant design changes on a regular basis.  That will impact your ability to maintain a single configuration.  Every part change has to analysed for impact and the configuration and certification updated.  That constant churn can quickly overcome any savings in procurement costs.

As to the more generic question of consistency between ACOs and DERs, it's an ongoing discussion within the FAA.  They want consistency but they don't want to to be so restrictive that all decisions get made at headquarters.  Every DER  or ACO I've met has had their individual biases and technical areas where they are comfortable.  So in that sense, there's always a bit of luck in getting one that sees things your way.  I don't think that will ever change.


Should operations such as landings or approaches be logged when acting as pilot monitoring? When operating aircraft that require two crew members, generally one pilot acts as PF (pilot flying) and the other as PM (pilot monitoring). How should operations such as landings and approaches be logged when acting as PM?

Is there any guidance on this for pilots operating under the FAA?

The Pilot Monitoring (PM) or Second In Command(SIC) cannot log the approach. FAA has answered this in a 1999 letter:

  You then ask if, for the purposes of maintaining instrument currency, an instrument approach on the above flight flown by the PIC can be logged as an instrument approach by the SIC.  The answer is no.  As the SIC you have not "performed" the approach as contemplated by FAR 61.57(c) because you were not the sole manipulator of the controls during the approach.


Do financiers request IDERA's for small aircraft? Do financiers request IDERA's for small aircraft, or just large ones registered under the CTC?

Firstly just a little bit of background. IDERA's - Irrevocable Deregistration and Export Request Authorizations - are issued under the Cape Town Convention (or Cape Town Treaty). This is a voluntary convention that countries can subscribe to. It essentially provides more assurance for financiers, who can therefore provide lower interest rates to aircraft buyers.

The FAA states the eligibility requirements  for IDERA's, which, for fixed-wing aircraft, need to be able to carry at least 8 people, or can carry goods in excess of 2750 kilograms (6050 pounds). So most aircraft considered 'small' probably would not be covered.


Is there any publicly available research that projects pilots' loss of proficiency due to lack of flying (or guidelines to prevent it)? The FAA requires 3 landings every 90 days to stay 'current', but as we all know, currency and proficiency are different things.
I'm looking for data than can describe how proficiency loss correlates with various factors. Relevant factors might include how long it's been seen you've flown, how much flying you've done in the last ____ days/months, how much time in type, time in seat, or total experience, etc.
And if there are evidence-based guidelines for how much flying a pilot should do to stave off loss of proficiency, I'd like to see that as well.
Thanks.
Edit:
I understand that it's impossible to accurately calculate how proficient someone is based on unique individual traits. That's not what I'm trying to do. Like the title says, I'm trying to quantify what's typical for "loss of proficiency due to lack of flying". In other words, how does flying 10 hours in 90 days compare to flying 10 hours in 6 months, as it pertains to proficiency degradation and, ultimately, increased risk of an accident/incident.

Any decent accident investigation report will show the flight hours flown by the pilot/crew, broken into a matrix of all / acft type in question, and during certain periods of time. These reports are publicly available on different national investigation authorities sites (for example NTSB). The reports also evaluate the currency of the pilot/crew, and mention if it is considered to be a factor in the accident.
If you are looking for an easy way out, in form of a scientific study on these reports, sorry, can't help with that one.
As mentioned in comments, currency in flying does not equal proficiency, and you seem to understand this. Being current does not guarantee one is proficient, not by a long shot, so you are digging a real can of worms here, beware :)
I do think you would benefit reading up on pilot training literature, namely the "human performance & limitation" module. IIRC it contains some very relevant information on the subject of your interest. Such as how experience needs support of other positive personality traits to manifest itself as safety, and perhaps proficiency if you will.


Which way should you turn to avoid another aircraft? During visual flight conditions, when you see another aircraft in your path, you should strive to avoid hitting it.

In shipping there are standard international rules about which way boats should turn in order to avoid each other.

Are there similar rules in aviation?

In shipping there are standard international rules about which way boats should dodge each other.
  Are there similar rules in aviation?

Why yes, there are - in fact they're basically similar to the maritime rules!
They're described in ICAO Annex 2 (or for US pilots, FAR 91.113).

Basically, for aircraft of the same type (e.g. two airplanes) in the air the rules are:

Approaching head-on: Both aircraft alter their heading to the right.
Converging: Give way to the aircraft on your right.
Overtaking: Pass "well clear" to the right of the aircraft being overtaken.
(The aircraft being overtaken has the right of way. The overtaking plane maneuvers to remain clear.)

The rules for converging aircraft are more complex when the aircraft are not the same type - basically the more maneuverable aircraft gives way to the less maneuverable aircraft (because something like a balloon can't really maneuver to avoid a collision) - you can read the details in either of the links above.

Also while it's not explicitly spelled out in ICAO Annex 2 (or at least I didn't see it) aircraft in distress generally trump the "right of way" rules. (This is really common sense: if an aircraft is recognizably in distress you do everything in your power to stay out of their way and help ensure a safe outcome to whatever their situation is.)


Why does pitot tube freeze at an altitude whose temperature is way below the freezing point? It's supposed that Air France 447 crashed into the Atlantic because the pilots stalled the airplane when the frozen pitot tubes forced them to handfly it while cruising through the thunderstorm. But how could the pitot tubes freeze in that high altitude where the temperature was way below the freezing point? Isn't it that ice only forms on the aircraft between slightly above 0 and below -20 Celsius degree?

Edit)
Wikipedia: "Below −20 °C (−4 °F), icing is rare because clouds at these temperatures usually consist of ice particles rather than supercooled water droplets. Below −48 °C (−54.4 °F), supercooled water cannot exist, therefore icing is impossible."

First, AF 447 was flying into the top of a tropical storm. The air was much more humid and warmer than that of the standard atmosphere.

Next, in the absence of seed crystals or nuclei, water vapour or liquid droplets stay in the air down to temperatures of -48.3°C at sea level pressure without freezing. From the linked article:

  Droplets of supercooled water often exist in stratiform and cumulus
  clouds. An aircraft flying through such a cloud sees an abrupt
  crystallization of these droplets, which can result in the formation
  of ice on the aircraft's wings or blockage of its instruments and
  probes, unless the aircraft is equipped with an appropriate de-icing
  system. Freezing rain is also caused by supercooled droplets.

So it was the impact with the probe which caused the supercooled droplets to freeze.


Are there any aircraft used in part 121 (aka scheduled airline) operations that do not require a type rating to fly? Inspired by KeithS's question about ATPLs and category/class ratings, I figured I'd throw another type-rating/airline-operations puzzler at you: are there any aircraft currently in scheduled airline service (i.e. operated under part 121) which would not require a type rating to fly?  (I know part 135 operators often fly small aircraft due to the nature of their operation, with more intermittent or even on-demand service and the smaller locales they fly into.)

Cape air has a fleet of 83 Cessna 402s, some of which are involved in its Part 121 operation.


Which aircraft is depicted on 1941 U.S. Post Office airmail stamps? Between June 25, 1941 and October 29, 1941 a tri-tailed “Twin Motored Transport Plane” was featured on U.S. airmail stamps in 6-, 8-, 10-, 15-, 20- and 50-cent dominations.

Source

Was the aircraft featured on those stamps an actual aircraft, or was it a Postal Service graphic artist’s conceptualization of one?

It appears to be only an artist's conception and is an amalgam of several different designs, but apparently largely based on the Douglas DC-3 aircraft, the Lockheed Electra, and the Beech 18.

The livery bears a striking resemblance to American Airline's DC-3 sleeper service, which operated during that era.

http://usstampgallery.com/view.php?id=1021c6191539bc1ca404bccf78595b7fdc0f06fd


Does the FBW system of a passenger aircraft use differential thrust for yawing? Are there situations where the fly-by-wire system of a commercial passenger aircraft will use differential thrust to yaw? Or is that even possible at all (i.e. do the necessary interfaces exist)?

I imagine it could for instance be useful in the case of a crosswing landing, to maintain full yawing capabilities. Also, I guess the connection between flight controls and the engine control system exists, as it is shown for example by the envelope protection of an Airbus.

First, you need to understand what fly-by-wire is. In layman's terms, FBW separates pilot input from direct mechanic actuation over anything. Yes, control surfaces are still moved due to hydraulic work, but such work is not exercised by the crew over the hydraulic lines which means pilots don't need to apply different "strength" levels over the sidestick or any other input mechanism.

That said, the FADEC (Fully automated digital engine control) does not apply differential thrust to control yaw in situations where crosswinds are encountered. Yaw is a rudder-controlled motion. Applying differential thrust would put too much strain on the airframe and wing structure, not to mention that in addition to inducing yaw, differential thrust also induces a roll along the longitudinal axis of the aircraft

The only reason differential thrust would be encountered on an airliner is more closely related to non-normal operations in which an engine is idled or shutdown and in those cases the yaw motion induced by the asymmetric thrust would be countered with rudder input.


How to get from IAS in MPH to KCAS using POH graph of best TAS/GPH? My understanding is that in order to find the V(L/D)max I can do the following steps:

Look in the Pilot's Operating Handbook (POH) and find the performance reflecting the best TAS/fuel flow.
Find the KTAS for the determination from step 1.
Use a flight computer to get the KCAS from step 2.
The number from step 3 is V(L/D)max.
V(L/D)max / 1.316 = Vbe
V(L/D)max * 1.316 = V-Carson

While this sounds logical, I do not see any clear path from step 1 to step 2.

I looked up the definition of TAS, and it is related to EAS.  But when I look up EAS, it is dependent on TAS.  So when you do the algebra, it simplifies down to TAS = TAS and EAS = EAS, which is nonsensical, circular, and unhelpful.  Maybe I am not looking at the right equations, I’m not sure.

Do most pilots have flight computers with which they can determine KCAS starting with the value described in step 1?  If not, how should this best be done?  I could estimate air pressure using altitude, though it would not be very accurate, but I feel like there must be a better way given the large amount of instruments and tools available to most pilots in the cockpit.

Several questions here that need answers;
V(L/D max) is best glide speed.  Look it up under emergency procedures in the POH.
Airspeeds:
TAS is EAS corrected for temperature.
EAS is CAS corrected for compressibility.
CAS is IAS corrected for installation errors.

IAS/CAS correction is available from the POH.
Pilots can use an E6-B flight computer to convert between CAS, EAS, and TAS.

For more on this topic; here's a good link


Is this "wing-wave" early after takeoff really a pilot tradition? I saw this video of a "wing-wave" immediately after takeoff of a 747-8 pop up on my Instagram feed. In the description, someone says that their friend is the pilot and that he did it to wave goodbye as it was the planes last visit to the airfield and that this is a tradition among pilots.

To the layman like me, it doesn't look too safe - but since the pilot did it, I'm sure it is. Is this really a pilot tradition and do they do this on passenger flights and most importantly, was this safe?

A comment (for what it is worth) said:

  Steep banking an aeroplane few seconds after rotation at dangerously low speed and low altitude is always dangerous. Waving goodbye is not uncommon however this would be considered reckless. I would not be surprised if his competent authority and Company would have an issue with this.

Is this really a pilot tradition and do they do this on passenger flights and most importantly, was this safe?

It wasn't a passenger flight, as the description reads, it was a delivery flight*. Furthermore the plane is a freighter, designed to carry cargo--the kind without feet.

Being a delivery flight, it's typically flown with a very experienced crew, and yes it is a tradition, and it's perfectly safe in that particular scenario (light plane, plenty of performance, no passengers). The crew will also typically let the tower know what they'll be doing, so the tower controllers won't be alarmed.

  The 'wing-wave', a gentle dip of the plane from one side to another, is generally done by cargo planes to say 'goodbye' as the aircraft will never again see the home airport where it was made.

https://www.dailymail.co.uk/travel/travel_news/article-2783901/Captain-dramatically-dips-wings-just-seconds-highly-skilled-stunt.html

* Not to be confused with the maiden flight and the subsequent test flights by both the manufacturer and the customer.

Related question about the same video: Is there any reason spoilers would deploy just after liftoff?


What is the relationship between thrust and engine RPM in a turbojet? I understand that, to increase the thrust of a turbojet engine in flight, it is necessary to increase fuel mass flow rate. This throttling then increases the exit velocity of air and gives increased thrust (if this was wrong, please also explain how is the thrust practically changed in cruise).

How does the engine RPM vary in this process?

Is there an equation which binds together spool RPM to the thrust?

First, lets see how thrust works. NASA explains it pretty good. They conclude that for turbo-fan engines "specific thrust [...] depends only on the velocity difference produced by the engine." If you think about it, velocity difference in a gas is dynamic pressure. So, how much thrust the engine will generate depends on how big of a dynamic pressure difference it can create in the air between its front and back. A turbo-fan engine creates this pressure difference in two ways. One is by using a fan to "push" air to the back. The other one is by heating up the air that passes through its burner and shooting it out of the nozzle (after passing it first from the turbine.)

Now, on to your question. We need to see if added RPM creates added thrust (or if more thrust needs more RPM.) The answer is that, yes it does. Providing the engine with more fuel will create faster escaping hot gasses from the burner. Those will create a bigger dynamic pressure difference between the burner and the nozzle and the turbine will turn faster. Power from the turbine is moved to the fan which will also turn faster thus pushing out more air.

Refer to here for a graphical description of the engine compartments and how pressure is formed between them.

How RPM and total thrust for a model turbo-fan engine are related is graphed on page four and seven of this document. There you can also find various equations that describe those graphs.

EDIT: A turbo-jet engine works pretty much the same but instead of using the power generated from the turbine to mainly move the fan, it uses it to move only the compressor. All its thrust is generated from the hot gasses coming out of the nozzle.


What is the pivot point of pitch change on an aircraft? I was wondering if there is a way to determine the pivot point when an aircraft changes pitch, assuming a standard slightly nose heavy and back elevator trimmed Cessna 172.  Will it pivot around the CG, the Center of lift, or somewhere in between.

Logically, I would think it would be "from where it is held up", but some writers stress CG.

Can you help me understand?

By the very definition, a free-flying object can only pivot around its CG.

Using anything else as a pivot (e.g. Aerodynamic Center) involves a combination of momentum and translation (linear movement) of the CG and will quickly get you into mathematical problems once you start combining the forces acting on the object. Make no mistake, an object only rotates around its CG.

If this is just a mental visualisation exercise, you can 'imagine' the pivot point to be at the center of pressure (i.e. the famous plane suspended by strings at the wings), and as the plane is already flying at a few hundred knots in +x, the little +y acceleration error will not make much of a difference as a mental exercise, but the error is there mathematically.

Later edit:if you still have problems visualising it, place your aircraft in outerspace where there is no air or gravity.Put some big thrusters on the wing and smaller thrusters on the tail. CG (center of mass) is very much forward of the wing. Now fire the thrusters.


Why does the Pilatus PC-12 go faster than the King Air C90? Pilatus PC-12 (source: www.what2fly.com)

King Air C90 (source: www.ok-aircraft.cz)

I am wondering this because of the blades on the propellers on both of the planes. The Pilatus PC-12 can travel up to 360mph with its 4 blades on the propeller. The King Air C90 has 2 engines with 4 blades each, is around the same size and can travel at a slower speed of just 300mph. Why is this when the King Air has 2 engines instead of 1 with 4 blades and travels slower, and the Pilatus only needs one engine with 4 blades to go 360mph?

The speed of an aircraft is not only dependent on the number of propellers. It is a function of (among other things),

Excess power available- The Pilatus PC-12 has more powerful engines compared to the King Air C90. The PW PT6 engine used in the Pilatus produces 895 kW, while (a different variant of) the same engine used in King Air produces 410 kW each. The power available for the PC-12 is more.
Propeller efficiency- The PC-12 uses a different propeller compared to the C90, which may have more efficiency at high speeds. Also, the PC-12 propeller diameter is more compared to the C90.
Aircraft design- The PC-12 flew around 30 years after the C90. The aircraft design has improved in many ways during the intervening years in aerodynamics, materials etc. These improvements can be used to increase the cruise speed.
Power to weight ratio- The PC-12 has a better power-to-weight ratio compared to the C90, which translates into better speed.

It is difficult to pinpoint any single reason for increased speed. However, the increased (cruise) speed in PC-12 can be explained using a combination of the above reasons.


Which pilot license is required in the US to engage in glider towing? As a former member of a US glider club (I live in Europe now, and it's all winch launches), I always thought being a tow pilot was a good way to build time. Can a private pilot tow gliders in exchange for money or credit with the club, or is a commercial ticket needed?

A private pilot certificate is the minimum required.  In addition you need the following experience and endorsements to be current:

CFR, part 61, section 61.69, outlines the requirements for towing privileges.
You must:

  1) Hold at least a private pilot certificate with the appropriate
  category rating;

  2) Have logged a minimum of 100 hours as pilot in command in the same
  category aircraft used for towing;

  3) Have a logbook endorsement from an authorized instructor certifying
  you have received ground and flight training in gliders or unpowered
  ultralight vehicles, and is proficient in the areas listed in part
  61.69(a)(3)(i)(ii)(iii) and (iv);

  4) Have a logbook endorsement from a pilot that already meets the
  requirements of part 61.69 (c) and (d), who has accompanied the pilot
  on three flights which has certified them to have accomplished at
  least three flights in an aircraft while towing a glider or unpowered
  ultralight vehicle, or while simulating towing flight procedures; and
  In the preceding 12 months has performed three actual or simulated
  tows accompanied by a qualified pilot or has been towed for three
  flights in a glider or unpowered ultralight vehicle. In accordance
  with part 61.52, pilots towing under an ultralight exemption may
  credit experience obtained in ultralight vehicles for their towing
  experience and endorsements.

Added per comment on question above:

Yes, a private pilot can be compensated for glider towing.

https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/data/interps/2010/umphres%20-%20(2010)%20legal%20interpretation.pdf

Source: https://www.faa.gov/licenses_certificates/airmen_certification/sport_pilot/media/towing_req.pdf


Why do shipping companies opt for the Boeing 747 instead of Antonov An-124? Both are quad-jets, but the Antonovs can carry up to 150 t of payload and are much cheaper (\$100M for the An-124 compared to \$238M for the Boeing 747-400F).

I understand that MRO is quite an issue for Antonov, but we are talking about the freighting industry, which is less congested and less demanding than the commercial airliner industry.

Is the skepticism of buying a SSSR-era product really founded, or is there in the West a lobbying trying to maintain the Airbus-Boeing duopoly and keeping foreign products out?

This won’t be a real great answer, just major hurdles off the top of my head for wider AN-124 service.

Much shorter range. At 80,000 kg the AN-124 gets 4500 nm. 747-400 has a range of 7670 nm. 1
747 is slightly faster, cruising at .855 Mach
AN-124 is designed for a crew of 6; 747 has a crew of 3, or even 2 in the 747-8F
It would probably take Antonov a long time to catch up with Boeing’s production rates. 747-8’s are being produced about one a month. Back in the 70’s they were pumping out 80 or 90 of them per year.

I can’t find any numbers on fuel efficiency, but being that the Antonov was designed for military transport I would be very surprised if it could compete with the 747 in fuel usage.

1 I was not able to find good range numbers for the Antonov. It’s hard to really pin down the numbers on the 747 also due to the number of variants. The numbers here are taken from the Wikipedia page for each.


How does an aircraft's weight affect the V-n diagram? I have a reasonable understanding of what a V-n diagram shows and what the envelope and the boundaries mean. However, the question I have is how does the weight of the aircraft specifically affect the diagram?

I know that reducing the weight will mean a lower load factor and therefore potentially more manoeuvrability. But is there a mathematical way of showing this? Also, how does the weight relate to lift? Again, lower weight means less lift is needed. But how does that specifically affect the V-n diagram?

Well, answering your first question, the airplane weight does not really affect the V-n diagram because this diagram is developed knowing the structural forces that the airplane can take without being damaged.

Answering your question about the relation between the maneuverability and the airplane weight, the relation is just a "simple" physics problem. You just need to know the airplane characteristics like the center of gravity, the different aerodynamic factors and the effect of deflecting the control surfaces. When you solve the six equations with six variables of the differential system you can find how any characteristic of the airplane affects its maneuverability.

Finally, as you say, when the weight is low, the needed lift is less but this does not affect the V-n diagram because n stays more or less constant because:
 $n=\frac{L}{W}$. This diagram just shows us which are the relation between the aerodynamic forces and the weight. We all know that the weight is one of the problems for an airplane but it also helps to alleviate the bending moment on the wing root, that is why the last fuel tanks that are emptied on an aircraft are the ones that are further away from the fuselage.


How much testing to commerical aircraft manufacturers typically do on each new plane after it rolls off the production line? I just came across an article on Wired about Boeing's new 787-10 where they said the type had been tested for over 5000 hours in a range of conditions.

Obviously, the very first model is tested to extremes but when full scale production starts what kind of testing is typically done on each individual plane ?

Testing is performed for specific reasons.  As you noted testing for certification and testing production aircraft are not the same.

Testing for certification is to establish that the design of the aircraft meets airworthiness standards. A guide is available in the form of AC 25-7C.

Testing production aircraft is primarily a quality control issue and serves to prove that the aircraft is built to the drawings -- that it complies with the approved design.  It's only a small part of the process and is discussed in section 2.7 of AC 21-43A.

As noted, in the AC a flight test is required (with one exception). Production testing will evolve over time as there is a constant effort to 1. ensure adequate test coverage to avoid quality 'escapes' and 2. to do it as efficiently as possible to minimize costs.

One other test that is typically performed is an acceptance test. This is not regulatory. It is contractual and is performed with the participation of the customer.  Airlines won't accept delivery of an aircraft until they're satisfied it meets everything they're paying for. A friend of mine who worked for an airline's engineering group said it was about a 4 or 5 day process to checkout and accept delivery of a plane.


Why is Russian super-maneuverable thrust vectoring more prevalent than American? Based on the sheer number of super-manouverable thrust vectoring Russian fighter jets, it seems that Russia has put more effort into developing thrust vectoring for enhanced maneuverability than the US has.  Why is this?

Examples of American thrust vectoring aircraft:

F-22 Raptor

Russian thrust vectoring aircraft:

Su-30 MKI
Su-35
PAK FA
Su-37
Mig-35

Of course you could include the MV-22 Osprey, Harrier, and F-35B as thrust vectoring, but I'm talking about thrust vectoring for enhanced maneuverability, not for STOVL.

This is a case of divergent design, and you can't know the answer without asking why current aircraft are designed they way they are.

Following the work of Col. John Boyd in the 1960's in developing the 'Energy-Maneuverability Theory', the U.S. and allies primarily designed combat aircraft and tactics around the idea that an aircraft's specific energy state defines its performance during basic fighter maneuvering (dogfighting).

Under the E-M theory, in order for a fighter to be survivable (and consequently victorious) during aerial combat, it must maintain a high specific energy advantage throughout its maneuvering - this means it either has higher potential energy (altitude), or higher kinetic energy (speed), and should aim to maintain the capacity to trade one for the other efficiently. In a fight occurring only in the vertical plane, this is easy to quantify, but in a turning fight, induced drag from turning bleeds energy from the aircraft, and E-M theory allows this performance efficiency to be quantified for a particular design or tactic.

Consequently, U.S. 4th Gen fighters like the F-15, F-16, and F-18 are designed specifically around energy maintenance in all flight regimes - high thrust for climb performance (gaining potential energy via altitude) and to maintain speed (overcome induced drag by turning), low wing loading (lower energy bleed in turning due to induced drag), and improved aerodynamics in the expected combat envelope (reducing overall drag in the subsonic regime), and their tactics emphasize maneuvering energy-efficiently, over expending all your energy in tight turns to simply 'get a bead' on your bogey first.

The practical effect of this is that if your first attack pass fails, you still have sufficient energy to either outmaneuver your opponent and get into position for another attack, or run. The disadvantage is, when your kinetic energy is higher than your opponents (speed) you can't turn as tightly as he can - but the hope is your greater ability to maneuver in 3 dimensions with that energy will give you the upper hand for a second attack - classically, this would be considered 'boom and zoom' tactics.

By contrast, the Russian designers have been focusing on 'Supermaneuverability', the ability of the aircraft to remain within the controllable envelope, outside the envelope of aerodynamic control. This is facilitated by 'funny' aerodynamics on aircraft like the MiG-29, Su-27 and Su-33, and by thrust vectoring on the aircraft you mention in the OP. This allows for high angle-of-attack maneuvering at low speeds (low energy state) - with the goal being to allow the pilot to point their aircraft at their opponent to facilitate a weapon release - it's the 'shoot first' strategy. Even if your shot misses, you force your opponent to go defensive, giving you the upper hand for a second shot, often facilitated by high off-boresight missiles like the R-73.

As speed decreases, so does turning radius - however aerodynamic control authority decreases at a greater rate. Thrust vectoring allows you to overcome the decreased aerodynamic control authority - your ability to change the attitude of the aircraft is now mostly independent of its aerodynamic control surfaces. Thus using supermaneuverability, you no longer need to outturn your opponent, you just point the aircraft in a totally different direction to where you were flying, possibly allowing a 'snap shot' with missiles or guns. The classical equivalent is 'turn and burn' tactics.

The practical effect of this strategy is that you might outturn your target and get a shot off first, but if that shot fails, you now have no energy (because you bled it off due to the massive induced drag of a high-alpha turn), and are effectively a sitting duck to your opponents wingman - you have no speed to run, you're losing altitude, all you have is thrust, and thrust is comparatively slow to regain energy. You can spin in place and keep shooting, but if your opponent uses their energy to run, you don't have the energy to chase.

So, why has the U.S. primarily ignored thrust vectoring? Because it's not tactically relevant to them. The West experimented with supermaneuverability towards the end of the Cold War with aircraft like the X-31 and F-15 ACTIVE, and after getting their hands on MiG-29's and Su-27's at the end of the Cold War, and wargaming them, decided that the 'supermaneuverability' advantage just wasn't worth it, when E-M based tactics could simply be adapted to defeat it. The one exception being the F-22 - an aircraft designed before the Wall fell, specifically designed to counter what Western tacticians had imagined the MiG-29 and Su-27 were capable of - illusions that were shattered just several years later.


What is the role of an intermediate fix? There are the IAF and the FAF, which has clear roles. One is where you start the approach and the other where you start to descent and end the approach. But what is the purpose of an Intermediate fix?

The Pilot/Controller Glossary can shed some light on your question.

The GPS approach is the clearest example of an Intermediate Approach Fix.

  IF/IAWP− Intermediate Fix/Initial Approach Way- point. The waypoint
  where the final approach course of a T approach meets the crossbar of
  the T. When designated (in conjunction with a TAA) this waypoint will
  be used as an IAWP when approaching the airport from certain
  directions, and as an IFWP when beginning the approach from another
  IAWP.

  INTERMEDIATE APPROACH SEGMENT [ICAO]− That segment of an instrument
  approach procedure between either the intermediate approach fix and
  the final approach fix or point, or between the end of a reversal,
  race track or dead reckoning track procedure and the final approach
  fix or point, as appropriate.

The Instrument Flying Handbook warns that, “Randomly joining an approach at an intermediate fix does not ensure terrain clearance."

On other approaches, there may not be an intermediate fix, but the segment is defined as follows:

  INTERMEDIATE FIX− The fix that identifies the beginning of the
  intermediate approach segment of an instrument approach procedure. The
  fix is not normally identified on the instrument approach chart as an
  intermediate fix (IF).

  INITIAL APPROACH SEGMENT [ICAO]− That segment of an instrument
  approach procedure between the initial approach fix and the
  intermediate approach fix or, where applicable, the final approach fix
  or point.

The Instrument Flying Handbook also talks about intermediate fixes where there is sometimes a charted Intermediate Fix:

Teardrop Procedure

  When a teardrop procedure turn is depicted and a course reversal is
  required, unless otherwise authorized by ATC, this type of procedure
  must be executed. [Figure 1-15] The teardrop procedure consists of
  departure from an IAF on the published outbound course followed by a
  turn toward and intercepting the inbound course at or prior to the
  intermediate fix or point. Its purpose is to permit an aircraft to
  reverse direction and lose considerable altitude within reasonably
  limited airspace. Where no fix is available to mark the beginning of
  the intermediate segment, it shall be assumed to commence at a point
  10 NM prior to the FAF. When the facility is located on the airport,
  an aircraft is considered to be on final approach upon completion of
  the penetration turn. However, the final approach segment begins on
  the final approach course 10 NM from the facility.

Holding in Lieu of Procedure Turn

  A holding pattern in lieu of a procedure turn may be specified for
  course reversal in some procedures.  In such cases, the holding
  pattern is established over an intermediate fix (IF) or a FAF.


What is this c. 1948 private plane with a sliding canopy? (YouTube)

What is this private plane with a sliding canopy?

It looks like a variant of the Ryan Navion, probably the North American L-17A aka the poor man's mustang.

North American L-17 Navion, Camarillo Airport Museum, Camarillo, California, USA; By Howcheng - Own work, CC BY-SA 3.0, Link


Can I fly part 107 in DC SFRA? I want to fly at 77° 38' and 38° 56'. This is in the DC SFRA, in class B airspace (starting at 1500ft MSL). Can I fly here as a part 107 pilot without asking permission?

There are two questions here.  The first question is in the thread title.  The second question is in the OP.  But they are two different questions.  It's possible the OP was edited after it was initially posted and after several answers were given.

The correct answer to the first question is yes provided the flight takes place outside the DC FRZ.

The correct answer to the second question is no because you state you are flying in Class B airspace.  Ironically it has little to do with flying in the outer ring of the DC SFRA which would otherwise be permitted.

You say you are flying in Class B.  Flying in Class B requires authorization via the FAA's dronezone portal linked here:  https://www.faa.gov/uas/request_waiver/

You may fly in Class B (or any controlled airspace) only after your online request for waiver or authorization is approved by FAA.

Don't confuse this with a Part 101 flight which has different rules.

I am posting this for anybody who might be looking for this info in a search.


I am an author doing research. I need information on the following aspects of flying a small plane.
1). What is involved in a small craft pre-flight inspection?
2). When do you need to, and what is involved in filing a flight plan for a small craft?
3). What things are looked at most closely during a small craft crash investigation? Is there still a 'black box' on a small craft?

Any assistance would be greatly appreciated.

Let's see if I can be of assistance.

Q: What is involved in small craft pre-flight inspection?

A: Do a google search for "POH Cessna 152" and you will see many listings showing a Pilot's Operating Handbook (POH) for a Cessna 152 (small craft).  In the POH you will see a section that describes a "pre-flight inspection."

Q:When do you need to, and what is involved in filing a flight plan for a small craft?

A: Click this link (Aeronautical Information Manual - AIM) and look at Chapter 5, section 1, Preflight, and you will see information related to filing of flight plans in the U.S..

Q:What things are looked at most closely during a small craft crash investigation?

A: Click on this link (NTSB - Aviation Accidents). In the search box type in Cessna 152, or Cessna 172, etc, and you will see some accident reports prepared by the U.S. NTSB.  This should give you an idea of what is looked at in a small craft accident investigation.

Q:Is there still a 'black box' on a small craft?

A: Assuming your research involves (U.S.) small craft that are not operated for commercial purposes (generally known in the U.S. as FAR Part 91 General Aviation operations), there has never been a requirement (that I'm aware of) for a 'black box.'


Which airports in Ireland use Surface Movement Radar? I know that Dublin uses SMR, but do any other airports in Ireland use it?

The wording of this IAA information implies that it's Dublin only:

  The IAA also operate an Advanced Surface Movement Guidance and Control
  System (ASMGCS), which facilitates the safe movement of aircraft and
  airport vehicles at Dublin Airport, even during poor visibility
  conditions. The ASMGCS incorporates Surface Movement Radar,
  Multilateration and ADS-B.

There's a similar comment in this document. And the AIP entry for Dublin mentions surface radar in the obstacles list, but the entries for Cork and Shannon (the next busiest airports) don't.


Does deploying flap change the aspect ratio of the wing? Specifically when a Plain flap is defleted the geometry of the wing will be altered (Camber is increased). Does this have any effect on aspect ratio? What's the connection between Camber and aspect ratio?

The aspect ratio of a wing is defined as:

$$ \text{AR} \equiv \frac{s^2}{A} , $$

where $s$ is the wingspan and $A$ is the total wing area.

Some types of flaps are not only increasing wing camber, but also the wing area:

  The Fowler, Fairey-Youngman and Gouge types of flap increase the wing area in addition to changing the camber.

(Wikipedia)

Since the wingspan is unchanged, this will decrease the aspect ratio. Other types of flaps, like a plain flap, are not changing the aspect ratio.

You can see the flap types that change the aspect ratio in the following image (modified from Wikimedia):


What is the shiny stripe around the aft wing–body fairing on an A380? Source: planespotters.net: 1, 2

Regardless of the airline, that part is always unpainted, and in the right conditions, it looks shiny. From below the plane, it wraps around the wing–body fairing.
Is it a sensor or indicator of some kind? Like for stresses? There must be a reason it's never painted over. From the operating manual I ruled out it's an antenna.

I chanced upon the answer in a 2005 Flight Global article when I was looking into a hypothesis that the fairing is made of different materials.
The stripe is a flexible joint:

Although the fairing is not theoretically designed to carry fuselage loads, Airbus has built the fairing to absorb the inevitable bending loads that will be transferred from the primary structure of the fuselage to the skin fairing through the belly substructure. The metallic strip visible in the aft section of the fairing on MSN001 is a flexible joint designed to help further absorption of these loads.

My conclusion is that if painted, the paint would crack with flexing, which isn't a good look. Knowing that it's a joint, finding the relevant 2005 Airbus patent was much easier:

An object of the invention is to provide a fairing capable of absorbing compression and bending forces due to the movements of the aircraft and transmitted to the fairing, regardless of the size of said fairing. More specifically, the object of the invention is therefore to reduce the frontal loads received by the fairing. A further object of the invention is to reduce a total weight of an aircraft equipped with a fairing.


Why does the yoke "stick" in a turning position? As you make a turn, an airplane does not naturally straighten itself out (like a car does to some extent). Are ailerons engineered to stay in whatever position they are placed, or is this simply a byproduct of aerodynamics?

I think it's a little bit of both -- for most aircraft, how they behave in a turn is a byproduct of their designed aerodynamic properties. This question is actually quite complex to answer. Let's assume you're talking about a simple light aircraft, where control surfaces are mechanically linked to the controls that move them -- this ensures that anything you feel is related to what's happening to the plane, and not necessarily to anything more complex (like a fly-by-wire computer, or a hydraulic linkage with some degree of hysteresis).

Aircraft turns are divided, by the CAA & FAA at least (see the FAA's Airplane Flying Handbook, Chapter 3) into three main categories:

Shallow turns (roughly speaking, <20º angle of bank). These tend to become shallower if left alone.
Medium turns (roughly speaking, 20º < $\theta$ < 45º angle of bank). These turns tend to be stable without further pilot input.
Steep turns ($\theta > 45$º). These tend to become steeper if left alone, sometimes dramatically so.

Let's look at these in a bit more detail, with some explanation as to why these effects occur.

Shallow turns.
These tends to become less steep as the turn progresses, and most aircraft have a natural tendency to decrease the angle of bank throughout the turn. This tendency to lessen the angle of bank arises, I believe, entirely as a designed aerodynamic feature of the aircraft to have lateral stability. As shallow angles of bank are essentially a situation that's is but a small perturbation about flying straight and level, it's desirable for the angle of bank to decrease back to zero if left alone. If that isn't the case, the aircraft stability has to be actively maintained by constant manipulation of the control surfaces (which is tiring or impossible for a human). This stability can be achieved through design features, such as (i) the dihedral of the aircraft's wings, (ii) their sweep, and (iii) their height position -- if high, there is an increased degree of lateral stability due to the centre of mass of the aircraft being below the tilted plane of the wings, and, if disturbed slightly, it experiences a force $F\approx mg\sin\theta$ to "pull" the wings back upright again. The sole purpose of any degree of wing dihedral -- the angle they make with the horizontal -- is to improve lateral stability. If a perturbation causes one wing to drop, the resultant (unbalanced) force will produce a sideslip in the direction of the downward wing. In effect this is analogous to "creating" a flow of air in the opposite direction to the slip. This flow of air will strike the lower wing at a greater angle of attack than it strikes the upper wing. The lower wing will thus receive more lift and the airplane will roll back into its neutral position. Many small aircraft have a slight degree of dihedral on the wings. A similar effect occurs with (ii) swept wings -- when a disturbance causes an airplane with swept back wings to slip or drop a wing, the low wing presents its leading edge at an angle that is almost perpendicular to the relative airflow. As a result, the low wing acquires more lift, rises and the airplane is restored to its original attitude. As an aside, you don't really notice you're in a shallow turn, aside from the fact that you're continually applying a little bit of stick and rudder. The $g$-loading is minimal.

Medium turns.
In this case, the aircraft is in a metastable state -- it will carry on at a constant angle of bank, but a `shove' to either side will result in the bank increasing or decreasing as appropriate. By this point, $\cos\theta\neq1$, and the outer wing is really generating a lot more lift than the other one -- and thus you'd effect the angle of bank to increase, as it pulls the aircraft into the circle. The effects discussed above, however, still apply, and provide an effective restoring force back to the normal attitude. In a medium turn, aircraft are designed to have these forces balanced, and, in practice, you often need little-to-no aileron and almost no rudder to do a coordinated medium turn in a light aircraft. If it's properly trimmed, you can take your hands off the controls and sit there merrily going around in a circle. Depending on your speed, the $g$-loading is apparent, but not great.

Steep turns.
By this point, one wing is generating almost no lift, and the other is generating quite a lot. We've gone beyond the designed stability point of a medium turn, and the angle of bank tends to increase as the outward wing pulls the plane of the aircraft towards its axis of turn. This type of turn actively requires pilot input to maintain a constant angle of bank, and, depending upon the speed, it can physically be quite hard work. The $g$-loading of the wings is significant, and, as the stall speed of an aircraft approximately increases as the square-root of the $g$ factor experienced, it's entirely possible to enter an accelerated stall or even a spin here. You notice the angle of bank, and feel the odd attitude of the aircraft. This phenomenon is called the overbanking tendency.


Jet engine throttle-down time Apparently airline jet engines lose ~80% of their thrust within 1 second after fuel is cut. However this seems to conflict with long throttle-down times noted in another question.

This lead to a couple of questsions:

How long do jet engines really need to throttle down?
How do they react to fuel-cut or moving the throttle to idle (see first question)
Why the difference between the two answers?
If an engine is throttling down quickly, does the rotation speed of the engine really drop by 80% within 1 second? How does it slow down so quickly, is there so much friction?

I'm mostly interested in commercial passenger transport airline engines, not GA, military, ...

There’s no “throttle down” per se in jet engines.  However engine thrust does not vary linearly with spool speed and most engines operate within the 70-100% of maximum speed, with most of the thrust range between 85-100%.

In addition, there is a lag time for the engine to “spool up” from an idle power setting to effective thrust output which has to be taken into account during operation.  This is one reason that most jet aircraft have speed brakes.  They allow the pilot to maintain a higher thrust setting which allows for quicker response time to thrust lever inputs for a given airspeed at the expense of more parasite drag and fuel consumption.  Critical areas of flight such as VFR patterns, instrument approaches, short final, and go arounds, where near immediate thrust response is required makes this a useful flying technique in jets.


Degree of motion terminology for special aviation movements I perfectly understand yaw, pitch and roll. I'm wondering what a few special terms are for other unusual movements, such as those executed by a helicopter, drone or even perhaps something like a Harrier jump jet.

If "climb" refers to a straight up vertical motion along the z-axis, what is the name for the opposite? One might think fall, but I believe (keep me honest) in aviation, a "fall" is akin to a crash-landing type scenario, where the vehicle is out of control. Another word might be descent, but to me, that implies a downward change in pitch so that the vehicle gradually starts to lower its altitude over time and distance; instead I just want the opposite of a helicopter "climb"
I understand yaw means a change in left/right direction of the vehicle, but what motions describe a 90 degree, perpendicular change in motion to the left or right? Meaning, vehicle doesn't yaw, pitch or roll, it just "slides" 90 degrees to the left or right?

Any ideas as to what the correct terms are here?

The opposite of climb is "descend" (that's an easy one).
The second one can be "translate" or possibly "slew" but I think the most appropriate word is "slip" as in sideslip.
Translate is a controlled movement from one place to another, and slew is an uncontrolled one according to Oxford, but when you work the "slew" switch for a directional gyro system, it's a controlled action, so there you go.
However, those terms apply to a stationary object that starts to move sideways, "slip" describes lateral non-turning movement of an airplane sideways when it's already moving forward, so this is probably the best definition.


What regulations apply to flying near blasting areas in Canada? I was flying near CYPK the other day and for convenience and since I was close to it, reported as being "above the blasting area". My instructor pointed out better not to do that. That made me think about the legality of flying above a blasting area but I couldn't find anything about that, neither in the AIM, nor in the CAR.

On my VTA a blasting area is shown as a "striped circle", similar to a circular special use airspace. The CFS legend for that symbol says "CAUTION BLASTING AREA. Do not overfly at less than 3000' AGL". The CFS entry for Pitt Meadows CYPK says "Quarry blasting ops ... to 300 AGL".

Obviously it's a good idea to stay away from a blasting area and having read a bit about it since then, I won't fly over it below ~3500' in the future. For closure and future reference I would like to know:

What are the Canadian regulations around flying over/near blasting areas?

Blasting areas are not subject to particular regulation, they can be depicted on charts and/or announced by NOTAMs (code for blasting is WH, compliant to ICAO standard).
The blaster operator always ensures the area is clear of traffic prior to firing. The imminent blast may also be announced 4 and 1 minute(s) prior to the operation on 123.2 MHz. In case an aircraft is seen, the blaster operator will also use this frequency to inform the pilot of the blasting operation. See below for details.
It's pilot responsibility to remain clear of these areas:

Source: AIP Canada

Known permanent blasting activities can be depicted on VFR charts and announced by NOTAM until charts can be updated. From AIP Canada:

The “VFR Chart Updating Data” section of the CFS provides a means of
notifying VFR chart users of significant aeronautical information to
update the current VFR aeronautical charts. In this regard,
significant  aeronautical information is considered to be that which
affects the safety of VFR operation, e.g. obstructions, restricted
and advisory areas, blasting operations, cable crossings, and new or
revised control zones. New or  revised information of this nature,
which is required to be depicted on visual charts, is advertised by
NOTAM  until such time as the information can be published in the “VFR
Chart Updating Data” section of the CFS.  Subsequently, the NOTAM is
cancelled.

However temporary or itinerant blasting activities may not be advertised. From the Canadian AIM:

Another  concern  to  low  flying  is  the  blasting  operations
associated with the logging industry. The trajectory of debris  from
the blasting varies with the type of explosives, substance  being
excavated and the canopy of trees, if any. These blasting  activities
may or may not be advertised by NOTAM.

More details are given in the NOTAM Operating Procedures, chapter 5.5.5:

In the Pacific Region, NOTAM are not issued for blasting related to
logging activities under the following circumstances:

If using instantaneous blasting equipment.(The blasters will ensure the area is clear of all air traffic prior to the blast.)

If using a standard 6 minute-fuse and using aeronautical frequency radio. (The blasting operator will make two transmissions on 123.2 MHz
advising of the imminent blast. These transmissions will be at
approximately 4 minutes and 1 minute prior to the estimated blast.
These transmissions will include the geographical location referenced
to prominent landmark and the time to the blast.)

If blasters detect an aircraft in the immediate vicinity of a blast,
they will direct a radio transmission to that aircraft using aircraft
type and colour ("Red and white helicopter, you are over an active
blast site; clear the area immediately.").
Blasters may elect to use both methods for added safety.
A NOTAM will be required if the blast site is within 5 nautical miles
of an aerodrome or if the blaster elects not to use either of the
above procedures. In any case, the NOTAM will have a maximum duration
period of 14 days.

Minimum safe altitudes don't take blast risk into account. From the Canada Air Pilot publication:

"CYA, CYR and known blasting areas are not considered in the
establishment of MSA altitudes. For this reason, it is the pilot’s
responsibility to remain clear of these areas as applicable"

Source: Canada Air Pilot
More: See this discussion: Quarry blasting not regulated for aviation safety purposes.


Are the first solo flights by a student pilot more dangerous? The first solo flight is a nail-biting moment, not only for the student pilot, but also for the flight instructor who's sending him off.  In theory not having a CFI reduces the margin of safety compared to flights with an instructor (at the same point in a student's training).  I've also heard stories about mistakes and even crashes on first solo flights, and according to "Crashes of instructional flights" by Baker, Lamb, Li, and Dodd, solo flights account for about half of instructional flight crashes.

Yet even though the biggest safety measure- a CFI- is gone, are these student solo flights really more dangerous?  Are there any studies on accident rate among low time GA pilots vs (solo) students?  Also, are incidents more common in the first solo flights than at other parts of a student's pilot training?

There is no evidence to back the claim that the first solo ride of the student is more dangerous compared to the later ones.
US NIH conducted a study on the accidents with solo pilots, which doesn't indicate that first-time solo fliers are any more prone to accident than others. Aircraft accidents with student pilots flying solo: analysis of 390 cases by  Sjir Uitdewilligen and Alexander Johan de Voogt analyzed NTSB probable cause reports of 390 crashes that occurred in the period 2001 – 2005, concluding that,

Student pilots flying solo show fewer injuries and fatalities compared to general instructional flights while in our sample first-time solo student pilots did not feature any fatalities.

Note that this gives only the injuries and not the times the students got into accidents per se. Out of a total of 3811 accidents involving student pilots, 390 occurred while they were flying solo and around 50 involved first-time student solo pilots. Actually, student pilots themselves are prone to less accidents compared to others. From Comparative Analysis of Accident and Non-Accident Pilots by David C. Ison:

Most accidents (49.1%) were conducted with individuals holding a private pilot certificate. Second in incidence were commercial pilots (28.2%), followed by Airline Transport Pilots (ATPs) (13.7%), and student pilots (5.7%)
Considering that 20% of pilots hold a student certificate, these individuals have a disproportionally low accident occurrence.

The report also gives some additional insight into the reason the first-time solo fliers have lesser injuries:

... first-time solo pilots are commonly confined to the airport and practice their takeoff and landings. Such operations may result in accidents, but they will occur near to the ground with a lower risk of a fatality

The report also gives some data about higher experienced student pilots sustaining more injuries, though nothing conclusive, noting that,

... in 25 cases, student pilots were reported to have more than 100 and up to 322 h of flight experience. In the dataset, these pilots were significantly more often injured than students with less hours of flight experience.

It has to be noted that as the hours logged gets more, the students get into more demanding flights which may be reason for this increase in injuries.


Why is mid-air refueling worth it? (or is it at all?) Surely, mid-air refueling is a cool thing, but is it worth it?

It's obvious that the military, for one, has some requirements to keep aircraft airborne so that they can keep patrolling, for example.

However, that is due to the need to keep the aircraft airborne and is not necessarily because the method is cost-effective.
Flying another aircraft carrying lots of fuel just doesn't seem very money/environment-friendly – you waste more fuel needed to power the fuel-carrying aircraft in addition to the fuel you would already need.

Is mid-air refueling cost-effective under any circumstances? Or is it just an emergency practice?

In some contexts, the economics depends on how special the aircraft you're refueling is.

Consider  something like an AWACS mission. You have this very complex specialized aircraft, with a large, highly trained, crew in addition to the flight crew. If you didn't refuel that during the mission, it might need to spend a lot of its active hours being unproductive en route to and from the war. You would need more of them (and more crews) to reach any given level of in-theater coverage.

On the other hand with aerial refueling you need some tankers scuttling back and forth with fuel for your sentries. But they are cheaper and simpler to operate, cheaper and simpler to crew, and so forth. So even though you may use slightly more aircraft hours in total, the total  costs can be lower.

This doesn't hold to just the same extent for fighters and bombers, because they have to return to base from time to time to stock up on munitions anyway. There are still "readyness" types of missions it would be relevant for. The price tag for an F-35 seems to be in about the same ballpark as for a KC-767, but a KC-767 can service many F-35s in a single mission, so having the tankers do the scuttling-back-and-forth can still be an economic win.

Also, it's a good thing for a fighter that gets into combat not to be lugging around enough fuel to get all the way home by itself.


Are there airport identifiers assigned to heliports? FAA databases list multiple Official Facility Names with a given Associated City Name, for example:

  CITY: Fort Lauderdale
  FACILITY NAMES: Fort Lauderdale/Hollywood International (FLL); BSO Public Safety Helistop; Port Everglades; Broward Health Medical Center; Fort Lauderdale Executive (FXE).

Only FLL and FXE are airports. The rest are heliports. Are there airport identifiers assigned to heliports?

Generally, not all airports have an ICAO or IATA code. Helipads and small airports usually don't rank a code from either of them. IATA won't have any reason to assign a code unless there is some kind of passenger service out of them. ICAO won't have any reason unless there is some significant international service from there. There is more info on the criteria for ICAO codes on this question. Those helipads have FAA identifiers, though.

BSO Public Safety Helistop: FA10
Port Everglades: 2FD4
Broward Health Medical Center: 6FD8

FAA-only ID's have either three or four digits and always contain at least one number.

From the FAA's JO 7350.9K - Location Identifiers (p.1-2-3):

  Two−letter, two−number identifiers are assigned to private−use landing facilities in the United
  States and its jurisdictions which do not meet the
  requirements for three−character assignments. They
  are keyed by the two−letter Post Office or
  supplemental abbreviation (listed below) of the state
  with which they are associated. The two−letter code
  appears in the first two, middle, or last two positions
  of the four−character code.

There are helipads that have IATA and ICOA codes, though. For example, West 30th Street Heliport (IATA: JRA, ICAO: KJRA, FAA: JRA) in New York.


Is there anywhere one can buy or find plans to build a human powered aircraft? I was surprised to find that only two Gossamer Albatrosses were built. Is there any way to get or build an aircraft like that today? (I don't mean design your own).

Yes, contact Todd Reichert, PhD, or Cameron Robertson at Aerovelo Inc.   They have designed, built, and demonstrated the first human powered vertical aircraft at the University of Toronto, of which they are alumni, and they won the Sikorsky prize of $250,000 for it.

They have aero-velomobiles that can smoke the albatross.

Note: The ability to get airborne in these Ultralights is heavily dependent on the weight and athletic ability of the human operator.


How to slow down a seaplane on water? A seaplane cannot use brakes to slow down, like a land-based aircraft. So how does one slow it down?

I am asking this in the context of landing, taxiing, aborted takeoff etc., as long as the plane is on the surface of water.

I imagine a few possibilities:

Land on a really long "strip" to ensure that water friction slows the aircraft down enough, then remember to not taxi too fast because you cannot slow down
If the plane has a variable pitch propeller, probably you can go to beta range to produce reverse thrust (what to do if the plane has a fixed pitch propeller?)
Steer left and right repeatedly (but wouldn't this cause stress on the airframe / chance to flip the plane?)

Unless you're planning on trucking a seaplane out of where you have landed it, you usually don't need to worry about slowing down on landing since you can land in a far shorter distance than you can take off. In other words, the landing water run is far shorter than the takeoff water run.

If you do want to shorten the water run or reduce your taxi speed, holding up elevator will do that. A few seconds after touching the water and at idle power, you can use full up elevator without fear of the aircraft lifting off again, and it will add the drag of the elevator plus change the attitude of the floats or hull to a high-drag, plowing attitude. I used to do that if where I wanted to dock was aft of the touchdown point and I wanted to quickly slow to a safe turning speed.

Most constant speed props (variable pitch) on reciprocating engines don't have a reversible pitch or beta, but that can be purchased as a modification on some. The major use of such is as an aid in docking, and for that it's really useful.

Steering left and right repeatedly doesn't impress me as a very good idea, but I suppose it would help a little, but very little since it wouldn't be advisable to do it until you're well off the step.

Deploying the water rudder adds a little additional drag. Depending on the wind conditions, putting in a little rudder to match cross-controlled ailerons also adds drag, but that's not generally used to slow down as I remember. It is used, though, when sailing the aircraft, for which it's standard procedure.

See also Chapter 4 of the FAA Seaplane Handbook.


At which airports has the A380 landed? I can't find a list anywhere (other than regular flights), but I am really interested, which airports have ever handled an A380 flight, including all one-time visits or emergency landings.

Airbus claims that:

  The A380 is compatible with over 140 small and large airports for
  regular service worldwide, and up to 400 airports when adding
  diversion airports ...

The list of airlines operating A380s and their destinations are listed here.

I didn't find details about emergency landings.


Could a FOSS autopilot system ever pass FAA regulations? Think something like ardupilot but for manned aircraft.

Short answer: technically and legally yes, a free open source autopilot could be certified.  But I think it is unlikely to happen anytime soon.

Long answer: Aircraft software certification is governed by DO-178C. There is nothing in there that says anything about whether the source is open vs closed, or free vs non-free.  What it does lay down is a lot of very rigorous requirements for proving that the software does what it says it is going to do.

For example, for something like an autopilot, an independent testing/validation would typically be required.  That means the person who writes/codes the software and the person who tests the software have to be different people. i.e. you must have a fresh set of eyes looking at it. Further that testing will have be very extensive, covering every possible scenario your autopilot could encounter.  You might have to mock up an entire fake airplane, with simulated sensors and simulated actuators, and feed the autopilot simulated data and see if the actuators move like they are supposed to.

You also need to provide a massive amount of very careful documentation about all parts of your software process.  E.g. the software requirements need to documented, and then you need to be able to show every step of the way on how each specific requirement gets translated into the final machine code.

An free open source project certainly could meet all of these requirements. However, they end up being very time consuming and expensive. You need an army of software engineers working all day every day for years to meet some of these requirements.  FOSS project typically do not have the level of manpower that is required to meet these requirements.


Why do we need DME or RNAV when using VOR navigation above FL240? According to FAR 91.205(e) there must be DME or RNAV system when a pilot uses VOR navigation above FL240. However, why does the regulation say we need it from FL240, not from FL180 where class A begins?

The consensus of internet wisdom seems to be that no one knows for sure, but the most likely explanation is that before class A existed there was Positive Control Airspace (PCA) that started at FL240, and DME was a requirement in PCA. The main reasons for requiring DME were:

There's a limited number of high-altitude VORs so it isn't easy to use cross-radials from other VORs for fixes or position reporting; DME is a simple alternative
If there's no radar coverage then ATC can still manage lateral separation effectively using DME

That all seems plausible enough, but some sources out there say that PCA started at FL180, not FL240, e.g. this FAA history document:

  [VFR on top] was a principle [sic] factor in the [Grand Canyon] crash and led to
  "Positive Control Airspace" (PCA) FL180 and above. Because of the
  speeds of the aircraft involved, non-radar procedures were unwieldy
  (standards called for ten minutes between aircraft; some 80 miles for
  a typical jet), even with the development of aircraft installed
  Distance Measuring Equipment (DME) and the reduced separation
  available between DME equipped aircraft (20 miles).

FL240 is also where ATC starts using Mach numbers instead of knots (ATC orders section 5-7-1(f)) and the separation minima change (section 8-4-4). I don't know if that's for historical reasons or physical/operational reasons, but it looks to me like FL240 is considered the general starting point for high-altitude operations (14 CFR 61.31 requires a high-altitude endorsement for aircraft that can operate above 25,000' MSL).


How does this fuel pump work? This question is about the fuel pump controlled by the hydro-mechanical fuel control unit.

This is part of a fuel system for a turboprop engine, described on this page which actually comes from a Rolls-Royce book. Full picture for convenience.

I've been staring in vain at this picture for some time, with the hope that something will suddenly become clear:

Source

The pump is supposed to receive low pressure fuel and deliver high pressure fuel at a rate modulated by the FCU using fuel in the purple pipe. The engine speed governor also modulates the pump output.

It seems to be a piston pump, pistons being moved in translation by the rotating plate on the left side, but I'm not even sure, and I don't understand how this increases pressure.
It seems the governor is not rotating... and I don't get the role of the green governor pressure fuel.

Can you help me understanding how it works?
(I've posted all the details I could gather as an "answer").

Sometimes diagrams can be mystifying. This is a video of a variable displacement hydraulic pump of similar principle being torn apart (disassembled would be too gentle a term) by a foul-mouthed Canadian who gives an excellent detailed & clear description of its construction & operation. Language warning for those not used to frontier engineering.

Which will prepare you for this very polite Canadian who shows an actual aircraft fuel pump. (around 7:30)


What standard of English are Air Traffic Controllers held to? While I'm sure it varies by territory, and that airports around more cosmopolitan areas have controllers better versed in English, I was wondering how well controllers have to know English. I imagine that there are places where all of the English they know is aviation-related. I can imagine that there are situations in which lack of knowledge of the language outside of memorized aviation vocabulary could be harmful, and situations in which a translator might be needed. How well versed in English are ATCs?

You might want to have a look into ICAO Language Proficiency Rating Scale. The article suggests that

  In 2003, ICAO set a deadline of March 2008 for English language
  proficiency at Level 4 and above for all pilots flying international
  routes and air traffic controllers serving international airports and
  routes.

Original text is not in bold.

In the same link, you can also find the description of each rating scale, as described in the Manual on the Implementation of ICAO Language Proficiency Requirements Doc 9835 AN/453, quoted here for convenience:

As of translators on call, I've never heard of such a practice and if I judge from the Level 4 being the minimum, that wouldn't be necessary.


What are the fins near the tail of a helicopter called? My young sons are very enthusiastic about helicopters and I am repeatedly asked to name parts of their model aircraft. I would like to do so correctly, but my research has not always given definitive answers. I hope you can help.

Fixed to the tail boom and close to the tail rotor, some helicopters have a pair of horizontal fins. My research suggests these could be referred to as elevators, horizontal stabilisers, or horizontal fins. Is there one correct term, or does it depend on how they are used? Why do some helicopters not have them?

Most (all?) helicopters have a vertical fin connected to the tail boom. I have seen this labelled as a rudder or vertical fin. Does this depend on its function (moveable or fixed?) or can you suggest a better name?

You can call them horizontal and vertical stabilizers, since that is exactly what they do, in forward cruising flight.  The vertical stabilizer is there because the tail rotor itself doesn't provide as strong a weathervane effect as a fixed surface. So it stops the nose from oscillating left and right in forward flight same as the stabilizer in an airplane.

The horizontal stabilizer is to provide some down force to keep the body angle a little more level in cruise flight.  The rotor disc is flying along doing its thing with this big weight under it, which wants to swing back and pitch the nose down from air drag and the forward movement of the suspension point (more or less like running along with a tennis ball suspended on a string - it swings back and stays at an angle until you stop running).  The horizontal stabilizer's down force counteracts some of this and helps dampen pitch oscillations and keep the nose at a more desirable (higher) attitude.


Are there any twin engine aircraft without counter-rotating props? All the twins I have checked have counter-rotating blades, so I was wondering if this was true for all twins of if there are any twins that have both blades turning in the same direction.

Twin enigned aircrafts without counter-rotating propellers

A great many twins don't have counter-rotating props:

One such aircraft is the BeechCraft Baron 58, as seen in this YouTube video.

Another aircraft I can think of is the King Air 350.

It is not any more or less common to have one or the other.

Contra-rotating propellers

Another interesting solution to the P-factor (prop pulling towards one direction), especially on single engine aircraft is contra-rotating props, two propellers on the same shaft that spin in opposite directions.

This is mainly for single engine racer aircraft, but there are multi-engine aircraft known to have it, such as the Soviet Tu-95 Bear bomber.

The pic shown here is a Spitfire Mk. XIV:

A better explanation of the P-factor

P-factor is the term for asymmetric propeller loading, that causes the airplane to yaw to the left when at high angles of attack.

Assuming a clockwise rotating propeller it is caused by the descending right side of the propeller (as seen from the rear) having a higher angle of attack relative to the oncoming air, and thus generating a higher air flow and thrust than the ascending blade on the left side, which at the other hand will generate less airflow and thrust. This will move the propellers aerodynamic centre to the right of the planes centreline, thus inducing an increasing yaw moment to the left with increasing angle of attack or increasing power. With increasing airspeed and decreasing angle of attack less right rudder will be required to maintain coordinated flight.


How to calculate the glide distance? Can somebody please explain how I go about this problem?

A Cessna 172S is flying at 9842.52 ft from the ground and the engines stop producing power.

If the aircraft is in a glide configuration and the best (quickest) rate of descent recommended is 3.4 m/s (800 ft/min) at a speed of 68 KIAS. What is the maximum range that can be reached?

Basic Math:

How long will the plane be in the air?

$\frac{9842.52 ft\ \text{AGL}}{800\ fpm} = 12\ \text{minutes}$

How far will the plane go in 12 minutes?
$68kts \cdot \frac{12\ minutes}{60\ min/hr} = 13\ \text{NM}$

Assumptions

Assuming no tail wind or head wind, so that KIAS relates to actual ground-speed.
Approximating that 68 KIAS is the ground-speed, when it is in fact the slant-distance speed.   If you need a precise answer, apply the Pythagorean Theorem to refine the answer.


How much maintenance time did it take to make an F4U Corsair ready for another flight? A coworker I worked alongside once told me that during his time in the Navy, he was responsible for taking care of maintenance on F-22s. He stated that every F-22 required 10 hours of maintenance for every hour of flight.

I am curious how this level of maintenance stacked up against older less-modern aircraft. For the sake of narrowing it down, let's take the F4U Corsair as an example. Assuming a routine flight (training or simply air-patrol), what was the amount of time that would be required to maintain the aircraft on the ground to keep it safe for its next flight? 1 hour? 2 Hours?

Far more than that. Try 50 maintenance hours per flight hour.

  actually finding a reliable source on-line has proven to be a bit difficult. RNZAF, pacific maintenance 58 man hours per flying hour. NZ based (training) F4u 50.5 man hours per flying hour. P51s NZ based (conversion and training) 36 man hours per flight hour.

Piston engines (esp. WW2-era high-performance fighter engines) are very maintenance-intensive compared to jets.

Here's a comparison of various military aircraft types:

Saab Draken.- 50 to 1
Eurofighter....- 9 to 1
F-14............. - 24 to 1
F-18E/F........- 6 to 1
F-18E/F........- 15 to 1 (different source)
Saab Gripen..- 10 to 1

C-17.............- 20 to 1
F-15A/B........- 32.3
F-15C/D........- 22.1
F-16A...........- 19.2
F-117...........- 150
F-117...........- 45 (after improvements, post 1989)
CH-46E........- 19.6 in 1995 GlobalSecurity.org
CH-46E........- 27.2 in 2000
CH-53D........- 24.8 in 1995
CH-53D........- 27.9 in 2000
F-20.............- 5.6
A-6E............- 51.9
F/A-18C.......- 19.1
B-2..............- 124

and you can see modern fighters require far less maintenance hours/flight hour due to several factors:

improved systems that require less frequent maintenance
design improvements to make maintenance take less time (better access, more line-replaceable units)


Why is being a commercial pilot stressful? Being a commercial airline pilot regularly appears around the top of "most stressful jobs" lists.  I do not doubt that this is a stressful job, but as an outsider with no aviation experience whatsoever I do not understand why.  I am curious to hear a first-hand explanation.

I have always imagined flying long-haul to become very tedious and repetitive after a while.  The only significant source of stress I can see is time away from family/relationships (which admittedly I couldn't cope with, but it doesn't seem sufficient a reason to propel this to the front of most stressful professions).

The stress comes from everything about the job that isn't actually flying the plane.

Dealing with crew scheduling is the #1 cause of stress.  If your phone rings with that special ringtone you assigned to them, you know nothing good is going to come of it.  These calls often end with reassignments, changed overnights, different crew members and sometimes extensions into days off.
Dealing with a stubborn dispatcher who, despite the mess of storms on your route, refuses to give you an extra 500# contingency fuel.
Dealing with pressure for on-time departures.  This usually comes from a gate agent because they generally are the ones who get the short end of the stick if we push late.  This can be exacerbated by agents who know about certain "tricks" to fool the system into thinking you pushed, which are often specifically disallowed by flight operations.
Winter operations.  Figuring out where de-ice happens, what special flow control might be in effect and managing holdover times can be a headache, particularly at unfamiliar fields.
Spring and summertime.  Never a moments rest during cruise but instead a constant look on the horizon and the radar and requesting deviations from every controller you talk to.  These seasons often have days with widespread thunderstorm activity.  These storms for the most part must be avoided and sometimes require constant coordination with controllers to deviate off-route to go around them.  This creates fatigue more than stress, but the two have a way of feeding back on each other.
Holding.  Do we really have the gas to be doing this?
Diverting.  Coordinating with dispatch, maintenance (if needed), operations at the field, ATC and passengers.
Timing out.  Hey folks, sorry we diverted but now we timed out, we're staying the night here.
Crew scheduling, again, to get hotel rooms and find out just how bad this day screwed our schedules for the next few days.
That once yearly visit to the AME where you are reminded just how bad your airport junk food diet is and where exactly "hypertension" starts.
Commuting.  It is fairly common that pilots do not live in their base and live far enough away that the commuting means jumpseating or non-rev flying to get to work and back home.  Depending on where you live you can often encounter oversold flights, competition for the jump seats and little backup options for same-day travel (e.g. not flying in the day before your trip).  Not making it work can have consequences depending on how hard you tried to make it work and how good your union contract and chief pilots are.

Of note, I never found actually flying the plane stressful including operations in low visibility and high winds.  Those are the things that kept the job interesting and I quite enjoyed them.  Having people in the back was also never stress inducing.  As long as I flew safely and kept myself alive, the passengers would end up that way also.  I was mindful of the passengers in selecting alternate cruise altitudes for ride conditions and requesting shortcuts from ATC to make up time but those are not stressful things to do.


Is the "wing area" of a biplane the projected area or the total area? When you specify the wing area of a biplane, do you specify the planform area (the projected area) or do you specify the effective area of both the wings?

It's a mixture of both: You add the projected area of both wings, measured separately, without overlap.

The effective (wetted) area is used for friction drag calculations only.