Are these questions really on the FAA Glider Commercial written test? I'm currently working on my Commercial Glider rating and for the written, I am using a popular test prep package.  The package allows the specific selection of Commercial Glider (vs Airplane, Helicopter, etc.)  Indeed, their glider question bank has 639 questions, whereas the Airplane and Helicopter question banks have 881 and 727 questions respectively.

So I was surprised to be presented with several questions that I wouldn't have expected glider only pilots to have to know.  For example:

I am also a PPSEL, so I was able to answer this, but I've never come across a glider with a VOR installed, and I frankly am not sure how useful one would be.

I was even more surprised to find this question:

Why would this be on any Commercial written test (let alone the Glider commercial?).  An instrument rating is NOT required for any commercial rating AFAIK, and certainly not for a Glider commercial rating.

So my question is, is this just a mistake in the test prep software, or are these types of questions actually on the Glider Commercial written test?

Well, now that I've taken (and passed) the test, I feel somewhat qualified to answer my own question.

The first question, The VOR CDI indication deflection question, was indeed on the test.  There was also a question on VOR receiver checks "from a designated checkpoint on the airport surface".

The second (IFR) question was NOT on the test.

Of course, the test has 100 questions and the question bank is reported to have > 600 questions, so there is no garuntee that it couldn't be on the someone else's test.  IOW, YMMV.


Can a helicopter be stable without moving the control inputs? I have only flown helicopters in a flight simulator (X-Plane) and I have found it exceedingly hard to fly in certain regimes (especially hovering and close to hovering) because it seems like there is no point on the controls at which I can stay and not have the helicopter start moving in a direction I want.  As a result, I wind up having to constantly move the control inputs (cyclic and yaw) in small amounts back and forth across where the stability point should be.  On flight simulator forums I have actually seen a couple of people recommend doing this.
But my question is, does this accurately reflect how a real helicopter behaves?  Is it possible to maintain a stable hover or slow speed movement in or out of ground effect once achieved without moving the control inputs much or at all?

In answer to your main question, Yes that is how they behave.
In theory in a perfectly world, there would probably be some sort of balance point, but in real life there is always something slightly affecting the helicopter causing it to start to drift.
As for how to actually fly, beyond telling you to get real lessons [don't do it], the strategy of constantly moving the controls is something sometimes called "stirring the pot" and in real life is generally a sign of an inexperienced pilot. With training and experience your control inputs will eventually become so small and so far "ahead" of the aircrafts movements that it will look like your not moving your controls. if you are not using full size controls for your sim, this may be impossible to achieve.


Why would an artificial horizon's roll axis be different on ground and in flight? Sorry, if I'm a bit verbose here, but since I don't understand the problem, I have difficulties to describe it.
I created an artificial horizon using an Adafruit precision 9 DoF sensors and their AHRS SW pack, which is quite sophisticated using Kalman Filters and Covariance matrices for fusion. On my dev table, everything works fine. Roll, pitch, yaw, tilt compensated heading, even if I shake it. I clipped it onto my shaver to simulate vibration, everything OK! Hence, I believe its not a HW or SW problem.
The problem occurs when I mount the device onto my ultra light aircraft. Pitch and Yaw/compass course remain OK, but roll becomes strange. When I turn, the roll axis moves into the right direction, but not enough (say 30° instead of 45) and even if I keep turning at the same bank angle, the roll axis displayed moves back to horizontal. As I said, when I turn the sensor from 0° to 45° on the ground, it rolls from 0 to 45 and stays there!
So the only difference is, IMHO the fact that on my dev table, things are pretty stable, while in the air, the sensor moves at 180 Km/h and in curves there might be some issues from centrifugal forces, which dilute the accelerator values and the Kalman filter tries to correct the Gyro rate by an exorbitated accelerometer value, which are normalized, showing 0.99g when flat on the table.
Any suggestion ?

The problem
As already pointed out in some of the comments, this is a structural problem of using an IMU-only AHRS unit. This unit cannot distinguish between acceleration due to centrifugal force, and acceleration of the earth.
For example imagine that you fly level, and then roll into a coordinated turn. The short-term roll-rotation will be picked up by the gyroscope, however in the coordinated turn itself the AHRS only "sees" a constant acceleration through its local z-axis (because you are in a coordinated turn). The gyroscopes on the other hand, will not see any movement at all. Therefore the filter will (over time) assume level flight. In essence, you cannot distinguish between gravitational forces and centrifugal forces in forward flight with the accelerometer alone.
Ways to solve this problem
I am aware of two ways of fixing this problem:

Buy a good gyroscope: If you buy a very good gyroscope, you can simply use its measurements and completly omit the accelerometer. However even good MEMS Gyroscopes still have considerable drift (typically you will notice an roll-angle drift after a couple of minutes). If you are willing to spend your life savings (I belive the price tag is 250k$) on a Ring Laser Gyroscope, you can also solve your problem. Fun fact: A couple of flat earthers bough one of these devices and ultimatively measured the earths rotation...

If you are on a Budget however, it may be cheaper (and more reliable) to give your algorithm some sort of velocity feedback. Typically, this is either a GPS unit (which not only produce a measurement of position, but also a velocity measurement), or a velocity measurement based on a pitot tube. With this measurement available, the centrifugal force can be calculated and be accounted for.

Implementation
How can you implement this in software? Well either you take existing projects from any of the common flight controllers like Ardupilot, or betaflight and adapt these to your needs (not knowing your hardware, I cannot tell you how labor-intensive this will be). Or you try to program your own estimation unit based on your IMU and velocity sensor. Before you try to figure out everything by yourself, I would recommend to first take a look at existing Software, which already implements everything necessary. In a nutshell, you just have to program a relatively simple Kalman filter based on the known equations of motion of a 6-DoF point which also estimates the gyro offsets. A very good example of how such a filter is designed can be found on the PX4 project (yet another flight control stack), which details how their Kalman filter is built up. One (open access paper) detailing such an implementation can be found here. I would regard this as the state of the art, and how one would commonly address this problem. The block diagram is displayed here:

Another implementation hinging on a simpler complementary filter, is described in this paper. Based on some minor assumptions it removes the centrifugal force via the airspeed, and uses the centrifugal-force-free acceleration as an input to a complementary filter. Although the used IMU is very high quality, and no algorithm for bias and drift compensation is used, you might get this to work with some adjustments. The block diagram is quite compact:

Disclaimer: I have no affiliation nor contact with any of the authors of the aforementioned papers. I do not own any of the images displayed here, these are directly taken from the papers.
P.S.: Interestingly enough, I also came across this link which offers some bounty for an open-source software implementation of such an AHRS unit.


What are the equations to compute takeoff and landing distance? I am flying a Piper 28-336 Dakota. Based on this paper I was able to reproduce the take-off distances from the POH and incorporate the calculations directly in Excel. It can be seen that the effects of temperature and weight on the takeoff distances are not linear and can be approximated by (with no wind correction and based on the above paper)
$ReferenceDistance\times[(1-Altitude)/145442]^{5.2}\times(273.15+15)/(273.15+Temperature)]^{DensityRatio}$$\times(Weight/3000)^{WeightRatio}$

However for the landing distances it seems that the above formula does not work as the landing distance seems to be more "linear" than the takeoff distances.

Can anyone provide the precise equations to be used for computing the landing distances as a factor of altitude, weight, temperature and winds? Or references that include those equations?

I did this, using Fortran 90 for the math and Tcl/Tk for the plotting.
There is no single equation; instead there are several cycles of calculation nested inside each other like a Russian matryoshka.
The innermost loop calculates all forces and moments at the point in time at which the calculation stands.
The next layer iteratively trims the airplane so control deflections fit the desired rotation rates.
The outer layer integrates the parameters, moves one timestep ahead and applies new boundary conditions.
For the initial climb there is another iteration to adjust acceleration and climb angle such that the airplane is at 1.3 v$_\text{min}$ when it climbs through 50 ft.
Initially, the airplane is on the ground and drag is smaller than thrust, so a forward acceleration remains. When the preselected rotation speed is reached, the elevator is trimmed for an also predetermined rotation rate and time steps are shortened to minimize the error in finding the liftoff time. The whole process is divided in three parts: Ground roll, rotation and initial climb.
For airplanes with a constant speed propeller I even added another loop inside the force calculation to find the proper propeller beta for the current engine torque and airspeed, but that made the code very slow (it ran initially on a Mac SE/30). For most cases I pre-calculated lookup tables and interpolated a lot.
We used this software to determine the tables in the flight manual of a jet trainer and checked correctness with a few points from flight test. It is easy to set a wind speed in software, it is much harder to precisely find out what the average wind speed was when the test ran. Since my software included all effects like trim drag, gear rolling resistance over speed and ground effect, the results were easily confirmed.
Calculating landing distances wasn't much different, only that the calculation started at 1.3 v$_\text{min}$ and 50 ft.
If you want good results, no single force is constant over speed. If you don't mind such niceties, you can average rsp. linearize the forces and use the integrals in this text.
For a very rough estimation, average thrust and drag and calculate how long the engine needs to add energy to the system until kinetic and potential energy have changed from standstill to 1.3 v$_\text{min}$ and 50 ft and back again. This should be sufficient already to find the effect of wind and air temperature on takeoff and landing performance.


Why jet stream is stronger in winter? I notice in a website taling about jetstream
https://www.weather.gov/jetstream/jet

It says:

  The winds blow from west to east in jet streams but the flow often shifts
  to the north and south. Jet streams follow the boundaries between hot
  and cold air. Since these hot and cold air boundaries are most
  pronounced in winter, jet streams are the strongest for both the
  northern and southern hemisphere winters.

Why these hot and cold air boundaries are most pronounced in winter? I dont get it.

Jet streams are influenced by the horizontal temperature gradient between two air masses which creates what is called a "thermal wind component", which when supplemented by the actual wind movement, creates the local acceleration of wind running along the top of the frontal boundary into a jet (above 90kt), and which is always nestled into the warm air side, in the wedge of warm air just under the warm air tropopause.

The strength of the jet is therefore influenced by the temperature difference between air masses.  In winter the airmass boundaries (in North America) tend to move south, and the temperature differentials increase compared to summer.  With the higher temperature differentials and higher horizontal temperature gradients, the stream velocities tend to be stronger and they reside farther south.

If you really want to understand aviation weather theory, the absolute best book for this is the Royal Canadian Air Force Weather Manual. Can't recommend it highly enough.


Would increasing rotor disc diameter increase efficiency in a helicopter by reducing disc loading? Despite the obvious drawbacks of a larger rotor diameter would the reduced disc loading increase efficiency during hover and forward flight?

Yes, increasing rotor diameter increases efficiency by reducing disk loading, exactly as you say.

From J. Gordon Leishman, Principles of Helicopter Aerodynamics, section 2.3:

  ..vertical lift aircraft that have a low effective disk loading will require relatively low power per unit of thrust produced..and will tend to be more efficient; that is, the rotor will require less power (and consume less fuel) to generate any given amount of thrust.


Why does this plane not pitch up after a dive? I've tested my RC plane yesterday. It's a canard. After hand launching, the plane goes straight, then I change the elevator to go down and it's going down, but when I pitch up the canard doesn't work and the plane crashes.

The plane is at full throttle.
When diving the plane slightly rotates to right.
Controls tested before flight.

Edit:

Airfoil is a NACA 2412, but tips gets a little thick (all cutting, sanding is done by hand)
No incidences.
One servo for the canard and one servo for the ailerons.
No thrust angle.

The plane:

CG is just in front of the vertical stabilizer (the little cross in the image)

My vote is that the surfaces aren't rigid enough and get twisted so much that the control surfaces can't overcome the effect. How floppy (non-rigid) are the wings and the canard surfaces? The wing looks to be sagging under its own weight! My thought too is that you're tail heavy, tail heavy will pitch both ways and you can get stuck in either positive or negative stall (or tuck). Tail heaviness causes the plane to tend towards going or falling flat like a leaf; it's usually strongest (leeast recoverable) when under the influence of negative G's. It doesn't matter whether the craft is upright or inverted; it's still "negative G's" including the caused airflows. Still, my best guess is weak surface rigidity. Good luck with your cool project!!!


Where does the Oxygen for the emergency gas masks come from? Normal commercial jets drop gas masks when cabin pressure drops, and supply oxygen, but, where does that oxygen come from? Do commercial jets store oxygen? If they do, isn't pressurised oxygen very flammable and too hazardous to carry?

On commercial aircraft the oxygen supply of the masks in the cabin comes either from a chemical oxygen generator or a centralized oxygen bottle system. The flight deck is always equipped with pressurized oxygen masks.

The chemical oxygen generators generate lots of heat when they are activated. When normally placed in their overhead compartments the heat is slowly dissipated. However, oxygens generators are hazardous when canisters are not in their appropriate place. The ValuJet Flight 592 crash into the Everglades on 11 May 1996 was caused by a fire after improperly packed oxygen generators in the cargo hold were accidentally activated.

Pressurized oxygen bottles also are hazardous. Not only because the oxygen can turn a small fire into a blaze but if the high pressure bottles explode they cause substantial damage. On
25 July 2008 an oxygen bottle installed in a Qantas Boeing 747 ruptured and propelled itself upward through the floor into the cabin.


Does total aerodynamic force include skin friction/shear streses contribution? Does total aerodynamic force by definition  include skin friction/shear streses contribution or this only represent overall intergration of static pressure(normal to surface) around wing/airfoil?

Yes.  Skin shear, due to friction between the airflow and the skin, is one way how force is transmitted from the airflow to the solid body.  The pressure distribution is the other main way.  If a definition of total aerodynamic force excluded one of these, it would be incomplete.
One way to think of total aerodynamic force is to just measure it, period.  It is what it is.  Another way is to try to split it up into its parts and put it back together again.  The second way is less accurate, but more useful for theory and modeling.


How can the Airbus A319 accommodate 156 passengers with overwing emergency exits? This official image from the Aircraft characteristics airport and maintenance planning document for the A319 advertises the A319 as accommodating 156 passengers in a high density layout, this is also the figure in other Airbus documentation.

What I would like to know is how emergency exists is accommodated for? In the image it shows a row of seats at the exits, but I was under the impression that there is not allowed to be seats in line with the emergency exits? Can this variant thus only accommodate 150 passengers (156 - 2*3)?

My question is also valid for the A320.

Then I would also like to know, is there a policy for the amount of lavatories on board the aircraft, or is that simply a choice made by the airline? Are there for example airlines that have only one or even none lavatories on board models only used for short hauls?

Thank you for any help.

Yes, airlines can use a 156 seat layout in the A319. See Allegiant's layout.

The FAA type certification for the A320 series can be found on the site here, under TCDS A28NM. For the A319:

  Maximum Passengers:
  145
  See note 11 and 18
  ...
  Note 11:
  If modification 32208 is embodied in production on A319 airplanes, the aircraft is eligible for maximum capacity of 160 passengers. This modification consists in structural and system provision for the installation of second pair of overwing emergency exits.

The certification basis section g states that the design complies with the following regulations:

25.811(e)(3) Type III emergency exit marking.
25.813(c) for emergency exit access

The regulation from section 25.813:

  §25.813   Emergency exit access.

  (c) The following must be provided for each Type III or Type IV exit—(1) There must be access from the nearest aisle to each exit. In addition, for each Type III exit in an airplane that has a passenger seating configuration of 60 or more—

      (i) Except as provided in paragraph (c)(1)(ii), the access must be provided by an unobstructed passageway that is at least 10 inches in width for interior arrangements in which the adjacent seat rows on the exit side of the aisle contain no more than two seats, or 20 inches in width for interior arrangements in which those rows contain three seats.

The A320 series has three seats on each side, so the applicable distance is a 20 inch wide passage. The referenced paragraph (c)(1)(ii) is also interesting:

  (ii) In lieu of one 10- or 20-inch passageway, there may be two passageways, between seat rows only, that must be at least 6 inches in width and lead to an unobstructed space adjacent to each exit.

This appears to be one layout that Air Canada uses.

There doesn't appear to be any regulation requiring a certain number of lavatories. Aircraft sometimes fly with only one working. Evidently no US agency requires even at least one.

However, the DOT does appear to have a rule created by the Air Carrier Access Act that says:

  New twin-aisle aircraft must have accessible lavatories.

I read that as requiring the aircraft to have at least one, possibly two, lavatories, and that they must be accessible.

  "New aircraft" requirements apply to U.S. airlines with respect to planes ordered after April 5, 1990 or delivered after April 5, 1992. In general they apply to foreign carriers with respect to aircraft ordered after May 13, 2009 or delivered after May 13, 2010.

Of course this wouldn't apply to the A320 series, as it is a single-aisle design. Although some twin-aisle aircraft do operate on shorter routes, they are probably less likely to go the route of ">200 people, no toilets."


Are there any aircraft that come with interchangeable flightdecks? With the new Boeing 787 where Boeing has provided the capability to swap engine types if the aircraft goes to a new operator quite quickly, I'm wondering if there are any interchangeable flightdecks?

Say that you might have a legacy 737 for southwest, but an entirely different cockpit layout (containing the same capabilities) for a company which operates Boeing 787s as well, since the similarities would make training easier.

I know a similar project was done on the DC-10s becoming MD-10s, as well as some Saudi MD-90s to be similar to MD-11, but both of these were long-time consuming projects.

But I'm wondering if there are any aircraft which have this possibility and if not, why not? I'd see it as an opportunity to Boeing to have a 787 flightdeck shared with say the 777.

According to this answer they used to be very customizable, but not very much interchangeable at least to the point that no one bothered to change them on second-hand aircraft. They are reducing it because it only causes confusion. Aircraft change owners and pilots change employers and it's most useful if all aircraft of the same type have the same cockpit layout.

As far as 787 goes, it has very similar flight deck to 777, always, to the point it has common type rating.


OBI, RMI, HSI... What combination do GA aircraft w/o glass typically have? I'm learning about radionavigation, and all the various analog displays that can be used:

Automatic Direction Finder (ADF) - Provides basic bearing information to practically any radio source the pilot can tune to. Designed for use with the older NDB system developed during WWII, still in use but about two generations redundant in the face of VOR and GPS. Later models include a manual compass card to reduce mental math.
Radio-Magnetic Indicator (RMI) - A two-channel ADF with compass card slaved to the magnetic compass (or in some cases using an internal gyro like the Heading Indicator).
Omni Bearing Indicator (OBI) - Used for VOR navigation and the cheapest way to do so, has a manual compass card that selects the desired VOR radial and a CDI needle to provide a steering aid to place the aircraft on that radial, with a "TO/FROM" indicator to resolve directional ambiguity.
Horizontal Situation Indicator (HSI) - Combines the OBI with the aircraft's gyroscopic direction indicator to provide a simplified "moving map", with the aircraft's current heading, relative direction of the selected VOR radial, course deviation and glide slope all in one instrument. Can replace the Heading Indicator as well as an OBI to reduce instrument count and/or allow for redundant backups like a second artificial horizon. Biggest downside is cost (about $13k for the display unit itself).
Distance Measuring Equipment (DME) - essentially IFF in reverse; the aircraft interrogates a ground station with radio pulse pairs, and the station sends a matching pulse pair after a specially-timed delay; total round-trip time of the interrogation and response, minus the preprogrammed delay and halved, is the time the signal took to reach the station at the speed of light through air (about one nmi in 12.36 microseconds), which can then be used to calculate distance. These transponders are often colocated with NDB or VOR stations on a corresponding frequency allowing aircraft to get an accurate fix from a single ground station.

My understanding is that, for an aircraft to be suitable for IFR flight, the aircraft requires all VFR instruments (airspeed, altitude, compass, tach, oil pressure, oil or coolant temp, fuel gauge) plus a timepiece, gyroscopic direction indicator, Turn Coordinator or Turn/Slip Indicator, adjustable pressure altimeter, artificial horizon, and "two-way radio communication and navigation equipment suitable for the route to be flown", that last requirement being just wonderfully ambiguous regarding what you as a pilot may want or need from the above listed equipment.

The standard configuration for the 172 and Cherokee seems to be two OBIs, one with glide slope and one without, plus a single-channel ADF. This seems like a fairly economical gauge cluster for modern radionavigation, but the ADF seems old-fashioned in the face of the newer RMI that allows triangulation from an ADF and a VOR or two VORs more or less at a glance.

Obviously the very newest and most expensive aircraft have full glass cockpits, but for the rest of us, what displays are typically used? Do people tend to upgrade the ADI to an RMI, or is that the display that's considered redundant with NDBs on their way to retirement? How many people spring for the HSI? Do you keep the non-GS OBI if you have an HSI, or do you replace that with something else too? Is DME standard equipment, can't fly without it, or do pilots more often rely on multi-station triangulation for a position fix?

"two-way radio communication and navigation equipment suitable for the route to be flown", that last requirement being just wonderfully ambiguous regarding what you as a pilot may want or need …

That statement isn't ambiguous at all. You can file and fly IFR with a transponder and a VHF comm radio if you can get controllers to issue you radar vectors for the route -- just be making a visual approach at your destination (or something like an ASR or PAR approach where you get your guidance from a controller).

Of course since your question was not "How do I piss off ATC?" that's neither here nor there - you're asking about typical instrument configurations in GA aircraft (for purposes of this answer I'm going to assume you mean the usual "Light GA / trainer" sort of aircraft - typical Pipers, Cessnas, Beechcraft, Mooneys, etc.)

It's hard to nail down "typical" because it's a rapidly moving target these days. When I started flight training two Nav/Com radios and an ADF was a pretty sweet IFR airplane, even if the ADF was a little sketchy. Now even a six-pack cockpit has a good chunk of glass in the panel in the form of a GPS (Garmin 430 or similar), and people are ripping out ADFs as the FAA decommissions them, but I poked around at some of the rental fleets near me  and it seems to shake out like this as of right now:

Most IFR aircraft have dual OBIs. If there's a GPS they tend to both have glideslope capability (either connected to two GPS Nav/Coms or one to the GPS and one to a traditional Nav/Com radio that has a glideslope receiver).

Older planes with dual Nav/Comm radios often have glideslope capability on the #1 Nav/Com & not the #2 radio, which is why you often see one OBI with a glideslope needle and one without.

Older IFR trainers tend to have ADFs still. Some are placarded as INOP and are basically heavy, drag-producing AM Radios (the Mets won).

Aircraft with a GPS rarely have an ADF, because the GPS can usually display the ADF indications using a "normal" OBI. One less thing for the pilot to have to remember how to operate.

I've never seen a light GA aircraft with an RMI.
They're probably out there but I doubt they're common. Slaving them to the magnetic compass requires equipment which is not cheap, and as ADFs are dying out there's not much benefit to installing one now.
None have HSIs, but I have seen a few planes around with them.
My sense here is it tends to be an owner-installed upgrade because the pilot wants it and they have the money to spend on it. Like you noted they're still pretty expensive, mainly because they're rather complicated bits of equipment combining a vacuum-powered DG, a bunch of sensors, and a VOR/LOC/GS presentation.

Every HSI installation I've seen takes the place of the Nav 1 OBI.
What gets put into the now-vacant hole varies from aircraft to aircraft. This Cessna has an ADF card there (thanks to CFC for the photo)

Very few have DME.
If you're flying on Victor airways you're pretty much always flying toward some VOR (so you have one needle that won't move), and you can easily get a cross-bearing from a VOR that would be roughly perpendicular to your route to find your current position on the chart.
The DME gives you this in Distance/Direction form without needing to tune a second VOR or draw on your chart, and it can do nice things like give you an approximate groundspeed, but that doesn't make it indispensable.

A reason many IFR trainers lack a DME seems to be because on the IFR checkride you can't be tested on equipment that's not installed: If you have no DME you can't be asked to fly a DME arc.
DME is another technology that's being made redundant by GPS: The GPS can give you distance and bearing to any arbitrary point, and that point can easily be a VOR. It can also compute groundspeed.

An ever-increasing number have large chunks of glass somewhere in the panel.
As GPS installations become more common it's increasingly rare to find a plane without a moving map display next to the six pack. The GPS provides the magic "Magenta Line" and also typically feeds an OBI (or HSI).
If the OBI or HSI fails the GPS can usually also display a digital OBI on its display.


Are there any truly 'unrecoverable' situations? I'm starting my quest to obtain a PPL this weekend. So I guess this question is contextualised around light aircraft like the Piper Tomahawk / Cessna, although it certainly would be interesting to get an answer that covers airliners too.

Baring a catastrophic technical failure, such as the wings falling off, a fire, or the horizontal stabiliser failing - is any [pilot caused] situation truly 'unrecoverable'?

I watched this video of a student accidentally starting a spin. Naturally, he looked terrified, but the instructor took over and recovered quickly and easily. This made me wonder, is there anything a student can do that the instructor will not be able to recover from? (obviously smashing the plane into the tarmac on approach isn't really something that can be helped, so I'm only asking about events at altitude here).

One of the more common causes of crash and fatality is a low altitude stall-spin.  A spin, in a modern aircraft, isn't of itself deadly -- with many designs, all you have to do it let go of the controls, and the aircraft will unstall and let you simply fly out of the resulting spiral dive (if you don't wait too long and go past Vne, anyway).

If you get into a stall when low and slow, however, and due to control positions or pilot error initiate a spin, you're likely to hit the ground before you can recover.  Since ground impact in these cases is usually near vertical, nose down, and partially inverted, pilot survival is hardly assured.

Avoiding this kind of fatal mistake is why you practice stalls (with plenty of altitude under you) during flight training -- so you can recognize the conditions that bring on a stall, the aircraft behavior that announces it, and learn how to manage the airplane after the stall occurs to avoid, or intentionally initiate and recover from a spin.

This is (or ought to be) a part of the check ride before flying an unfamiliar type, as well.  Many older designs are less stall friendly than modern (say, post-1960) aircraft -- and if you learned to fly in a Cessna 152, you won't ever have experienced an unintended spin (because the type is difficult to spin even intentionally, and won't do it without large control inputs).  Stall a 1930s light plane at 100 feet, however, and you're likely to fail the "walk away" test.

Another situation that, once in, you can't get out of occurs in mountain flying.  If flying in a canyon under a ceiling (or near your aircraft's ceiling) you may find yourself without room to turn around, but with ground ahead rising into the overcast or faster than your aircraft can climb.  This leads to either "weather" or "Controlled Flight Into Terrain" being the listed cause of the accident, when in both cases it was genuinely pilot error -- this is a situation an aware pilot will avoid.


Why was the Concorde painted white and not black? It's well-known that the stated reason the Concorde was painted predominantly white was to mitigate heating problems.

However, given that the source of the Concorde's thermal woes wasn't excessive exposure to solar radiation, but, rather, direct conduction and convection of compression heat, I'm confused; in that case, shouldn't the Concorde have been painted black (or nearly black), like the SR-71, to better radiate heat away?

There is a discussion on it here that's worth reading but in short the requirements were just different. A few of the key points,

The black color on the SR-71 offered some night camouflage in addition to its heat dissipation
The Concorde had an Aluminium airframe while the SR-71 had a primarily titanium airframe which could lead to different coating types.
The Concorde was a commercial aircraft many of which are often painted white thermal benefits aside they may have simply been keeping with what they usually did.
The SR-71 flew substantially faster than the Concorde and had different thermal requirements.
The hottest point on the Concorde was the nose 127°C which was actually cooled by fuel being pumped through as a coolant. The hottest point on the SR-71 was the cockpit window which cooked in at 327°C again, very different requirements thermally.


What are these things hanging off the trailing edge of the wing? What are these things hanging off the trailing edge of the wing?

I've seen them in almost all of the aircraft I've flown in, and can't remember if they're exclusively Boeing or Airbus.

Those are static wicks -- Basically these are little wires screwed to the airframe.
Their purpose is to discharge the static electricity that an aircraft picks up moving through the air - especially in clouds.

The static discharge tends to happen at "pointy" protrusions from the aircraft - if this happened through antennas it could cause radio and navigation interference, so to prevent that static wicks are installed, providing a low-resistance protrusion for the charge to dissipate through (and as an additional benefit, dissipating the charge helps ensure your aircraft doesn't attract lightning strikes).

Here's a couple of closer pictures:


Why do the ratio of proppeler plane over jet engine seems to have change in Bucarest airport during the covid19 crisis? I live in a village very close to an (intl) airport: Bucharest "Henri Coanda" International Airport.
Now, due to lock-down caused by covid pandemic, I noticed - at least today when I spent most of the time outdoors - that all planes that flew over/around our location were propeller, none of them was a jet-plane.

Companies that normally operate flights on this airport: KLM, WizzAir, Alitalia, Delta, Aegean, Air France, Tarom, etc.

The main types of aircraft that normally operate on this airport are: A318, ATR42/72, B737, etc.

Do you have any idea why only propeller-planes these days?
I don't think it's a coincidence or just an impression, so I guess there must be some logical explanation.

I have no idea about Bucharest specifically, but at least in the US, many GA pilots are taking advantage of the significant reduction in airline traffic to fly into big airports they're normally not welcome at. And, for the most part, ATC is welcoming these GA flights because they're bored too.


In Spain, can I land and take off from my own property? I have a property in Spain with a big field; is it legal to take off from and land on your own property in a light aircraft?

It depends on your local and national regulations.  In some jurisdictions, local municipalities can regulate use of land in that way, and in others they can't.  So first check with Spanish national regulations (if separate from EASA) on what constitutes an aerodrome or airport to see if there are any restrictions on use of an unlicensed piece of land as an aerodrome (probably not), then check with local municipal regulations or zoning or use bylaws that may restrict use of your land as an aerodrome (a definite possibility).


Are ham radio contacts allowed from inside an airplane? This question probably lies in the middle ground between Amateur Radio.SE and Aviation.SE.

I have seen a couple of videos where ham radio contacts are made with people on board a commercial aircraft while in flight. In one of the videos, contact is established trough the 2-meter band (VHF) with a passenger carrying his hand-held transceiver on board the flight, while in the other video, contact is made trough the 20-meter band (HF) with the captain of the airplane using the airplane's radio transceiver.

I am curious about what do regulations say in this regard.

Are ham radio contacts allowed from inside an airplane?

Two-way radios are just like any other communications device. If the captain says all such devices must be in flight mode at any particular moment during the flight, you are not allowed to use it and could be arrested if you do. Also, if the captain determines that something you are doing with your communications device is interfering with aircraft communications or navigation, he may order the flight crew to confiscate your device until after landing, and you may be subject to criminal charges.


Does the centre of pressure of a cambered airfoil go ahead of the quarter chord point when angle of attack is increased? I got two figures and answers which are seemingly contrary. In wikipedia, it says the the location of the centre of pressure of a cambered airfoil is just behind the quarter chord point at maximum lift or high angle of attack. But in other websites, I see the centre of pressure well ahead of the quarter chord point. Which of the below two pictures is correct?

The lower one is better. Details depend on the camber.
A flat plate or a symmetric airfoil have their center of pressure at the quarter chord point. Angle of attack changes change the lift produced, but the center of pressure stays at the quarter point (as long as the flow does not separate). This is exactly true for two-dimensional flow; as soon as we look at real wings with limited span, the exact location of the center of pressure moves forward at the same angle of attack with lower aspect ratio. The center of pressure of a slender body is approaching the leading edge. But your question is about airfoils, so the rest of this answer looks at 2D flow again.
Positive camber contributes lift independent of angle of attack, and its center of pressure location depends on the shape of the camber. A camber line shaped like a segment of a circle has its center of pressure at 50% of chord, and the camber line of rear-loaded airfoils is even farther back.
The resulting location of the center of pressure is the sum of both, camber and angle of attack effects. At low angle of attack the camber line dominates this location, so it is somewhere at mid chord. At high angle of attack the center of pressure shifts forward towards the 25% point. Note that this behavior will make the isolated airfoil unstable in pitch.
A negative camber will reduce lift and result in a center of pressure location ahead of the 25% point. Increasing the angle of attack will now shift the center of pressure back, again towards the 25% point. Now you have a stable pitch behavior (when the airfoil pitches up, the center of pressure moves back and creates a correcting moment change), such that a conventional airplane which loses its horizontal tail can still fly on when inverted. The center of gravity will determine the trim speed, and control may still be possible either by moving the wing flaps or by shifting the center of gravity. Theoretically, at least. I have witnessed an experienced model aircraft pilot doing this after the horizontal tail of his plane was lost in flutter, but the resulting glide speed did not lend itself to a smooth landing.


Since when had fighter jet designer stopped caring about Whitcomb's Area Rule? According to this source, designers of military fighter jets seemed to have stopped centering their design on Whitcomb's Area Rule for quite a while. Yet even the twin series fighters struggle to break the sound barrier without afterburner in a combat loadout. Then why have the designers stopped caring about transonic drag reduction? Or is it because they never intend to let their jets come near Mach 1, just a little bit below it or use the afterburner and shoot past it? Does this mean newer supercruising fighters, if they intend to fly all the way up to their Mach 1.5-ish cruise speed on dry power, should still care about shaping according to the Area Rule?

Of course designers still care about the area rule, but it has become less important. The original area rule is just for Mach 1; at higher speeds you need to look at the cross section distribution along the Mach cones - but which ones? They change with angle of attack and Mach number, and there is no single point anymore where performance needs to be optimized. Rather, the aircraft has to perform well from subsonic to mild supersonic speeds, and the higher speeds for which the older designs from the Fifties and Sixties were optimized turned out to be irrelevant in practical use.

Next, which configuration needs to be optimized? The F-106 carried exactly one type of AA missile. Today, the typical aircraft will carry everything from dumb bombs to laser illumination pods, with fuel tanks and electronic warfare pods thrown in between. With that kind of variety in accessories who can tell which configuration exactly it is which needs to obey the area rule?


How much do '1,500 total hours with 500 multi crew hours' cost in Europe? This company offer a 'fast-track' modular course which, in their words:

  Our speciality is the training of pilots with no flying experience to become Fastrack airline ready pilots by means of continuous Modular training. If this course is commenced on a full time basis it is possible to complete in under 12 months however the majority of students will take between 12 – 18 months to graduate. This will provide the cadet with a ‘frozen’ European Aviation and Safety Agency (EASA) Airline Transport Pilot Licence (fATPL). The Licence will remain ‘frozen’ until 1,500hrs of Total time and 500hrs of Multi Crew time have been achieved.

They also add:

  100% of Aeros Fastrack graduates have been placed with major airlines across Europe over the past two years.

All for the relatively low cost of around 62,000 Euros.

My question is about the last part of that, regarding hours. How much time (months/years) and how much money would it cost to achieve the 1,500 total hours with 500 multi crew hours after completion of the fast-track?

Several aviation forums suggest this is a much better deal than the airline provided schemes, where they normally charge around double this in order to actual turn a profit on training.

You get to the 1500 hours by working in a flying job once you have your comm/group 1 IFR, which is where the 62k gets you.  Even if you wanted to spend a decade renting airplanes to get the time in, for the 500 multi-crew part you have no choice but to find a flying job since there is no other way to get those hours unless you are rich enough to afford your own multi-crew airplane.

The course gets you to a minimum employable level of flying hours (maybe 250-300 or so - hard to see 60k getting your any farther than that) and with the EASA ATPLs written, which allows you to copilot multi-crew aircraft as a greenhorn 300 hr copilot (normally you get a "multi-crew" license, which is a trimmed down version of the ATPL for low time pilots to serve on 2 pilot a/c) without having to write the exams again when you get the time in (that's the "frozen" part).  Most jurisdictions will "freeze" your exam validity for 3 years.

The "fast track" bit just means they cram the whole thing into one year.  That would be a pretty intense course, jamming 2-300 hours into 12 months with the ATPL ground school thrown in as well.


What is the typical blade pitch angle of a ram air turbine? I'm building a simple 3d model of one and because reasons I won't be able to give it a variable blade pitch so I need to find a typical value. My google-fu has failed me so far on this.

Ram Air Turbines have variable pitch which is set according to demanded load and airspeed, and the controller keeps the rotational speed as high as possible for maximum efficiency. Typical operational RPM of a RAT is between 5500 and 7700 rpm, at speeds between 125 - 375 knots. Let's take the averages: 6600 RPM @ 250 knots = 700 rad/s @ 130 m/s.

At a disk diameter of 1 m and a spinner diameter of 20 cm, lets look at velocity triangles at the blade root, centre and tip:

Blade root: R = 0.1 m, rotational speed $V_{rot}$ = 0.1 * 700 = 70 m/s. With incoming air at 130 m/s, this creates a local velocity pitch angle of arctan (130/70) = 62 deg
Blade centre: R = 0.3, $V_{rot}$ = 0.3 * 700 = 210 m/s, velocity pitch angle = arctan (130/210) = 32 deg.
Blade tip: R = 0.5, $V_{rot}$ = 0.5 * 700 = 350 m/s, velocity pitch angle = arctan (130/350) = 20 deg.

Note that these are unloaded velocity triangles, the blades can only generate power with air coming in at a local angle of attack. We're rough estimating, so you could take a pitch of 25 deg at tip, 35 at centre, and linearly twist onto 45 deg at root (most of the power is generated at the outer part of the blade).


How to handle the formula for computing net thrust of closely coupled engine systems for an engine with a nacelle that has non-circular dimensions? I am working on a paper and I wish to use this equation for calculating the thrust of an engine in a nacelle:
$$ Fn= \displaystyle \oint V_x\rho\vec V\cdot\vec n \ dA + \displaystyle \oint(P-P_{\infty})\vec n_x \ dA - \displaystyle \oint \vec \tau_x \ dA$$

This equation was given for a simplified case: the common circular nacelle. However, I would like to apply it to the flattened bottom nacelle as on the 737.

I have attempted to fit an equation to this by adjusting the parameters of a cardiod in polar coordinates. I'm having some trouble changing the above to polar integrals, however I'm not sure as to how this conversion would affect the rest of the equation. I could apply the rectangular form instead and keep the above integrals, but I don't think there is a away to express y explicitly in terms of x; it must be done implicitly and so that integral wouldn't really be possible.

In review of my earlier question, @Penguin and my math professor's commentaries agree on the point that the equation $$ Fn= \displaystyle \oint V_x\rho\vec V\cdot\vec n \ dA + \displaystyle \oint(P-P_{\infty})\vec n_x \ dA$$ is the meat of the problem and that when you get the piecewise pressure and velocity, the third term $$- \displaystyle \oint \vec \tau_x \ dA$$ was inconsequential, as it (as far as I can mathematically deduce) describes the core cowl and the external nacelle. As it is an independent characteristic, I'm confident I can just adjust the modelling for a different shape. Thanks again to @Pengiun for providing an outside perspective to my dilemma.


If, one day, we have an electric airplane, will it be easier to control than a fuelled airplane? Elon Musk said that Tesla will make battery which can last for million miles.  So probably in the next few years there will be a (small) airplane powered by an electric motor rather than by fuel.

If this happens, will controlling the electric airplane be easier?  The CG won't shift as fuel is consumed.  But the constant battery weight probably will problem to the maximum landing.

There are a few electric aircraft now, and because batteries hold far less energy than fuel, they're low-performance and short-range compared to normal aircraft.

If we imagine that at some point in the future we'll have batteries that can match fuel, the answer would be: Only slightly.

Back in the 60's and 70's, airliners regularly carried a flight engineer, who's full-time job was to monitor the engines and tweak various controls to keep them running properly. Now that's almost entirely automated. Pilots still have a checklist to follow to start the engines, and things to monitor during the flight, but it's a small part of their responsibilities.

Even if switching to electric propulsion completely removes this, it won't make a huge difference to the pilot. (and that's assuming that the electric system has nothing to monitor or adjust)

The aircraft handling is unlikely to be affected significantly, although there are be minor effects:

Fuel gets used up, so electric planes will have to be designed with stronger landing gear.
Electric motors are easier to scale, so it's easier for small aircraft to have multiple, counter-rotating motors to eliminate torque swing.
The battery is the heaviest part of an electric power system (and for one with hours of endurance, by an order of magnitude), so fitting a motor with excess power has a relatively smaller weight penalty. Electric power systems are good for providing short bursts of high power between long periods of cruising. Unfortunately this is more useful for a car than an aeroplane.
It would be much easier to design an electric power system for an aerobatic plane. Supplying fuel and lubrication while flicking between positive and negative G takes careful design.
Electric motors are quiet, but they are still transferring lots of power into the air, which is inherently noisy.

Ultimately these are all minor effects compared to the elephant in the room, which is that batteries are far heavier than fuel.


What dictates the shape of the attitude indicator display on the PFD? I notice the atitude indicator displayed in the PFD is either squared-shape or truncated-circle-shaped.

A good example of the square shape is the B747-400, It looks like a square whose corner are a bit rounded:

(Source: airliners.net)

A good example of the circle-shaped is the SAAB2000 or the A340:

(Sources: airliners.net and airliners.net)

They look like a circle whose both right and left sides are truncated to display rules (speed and altitude).

In either case, the information displayed are the same (pitch, bank angle, perhaps flight director,...) and are displayed in a very similar manner (including the colors). Those 2 designs exists for years, so there may not be advantages of one over the other.  Why one is preferred over the other for some manufacturer, and the other one for other manufacturer? What criteria are taken into account when choosing this shape?

A circle makes sense because a physical attitude indicator is round. (A physical one has to be round because it consists of a ball moving behind a window.) It makes the screen display look more like the instrument it replaces, which is good for recognition and familiarity, and makes it easier to judge things like bank angles.

A rectangle makes sense because it has to fit on a rectangular screen. You can tile rectangular instruments/displays on a screen efficiently, with no wasted space between them, as your example shows with the tapes. Rounding the corners delineates the edges of the display better than just having abutting rectangles.

The full process by which physical cockpit instruments and glass-cockpit displays are designed and laid out is too long to explain here. The main focus is on making it hard to make mistakes, and after that to make it quick to see the most important information. To support this, each instrument has to be easy to identify and to read correctly. Despite the shape difference, the two designs look very similar. Even if you've never flown any of these aircraft before, you'd immediately recognise it as an attitude indicator, and you wouldn't confuse it with a different instrument.


Can a plane fly without the Vertical Stabilizer? What would happen if a plane (for the sake of the question let's say that the plane is an Airbus A380) lose its  Vertical Stabilizer?

The plane will probably crash.

The vertical stabilizer provides stability in yaw to conventional aircraft. Aircraft such as the B-2 manage to provide stability through computer control, and aircraft such as the Northrop flying wings are designed to fly without one. But if an aircraft designed to be stable using a vertical stabilizer loses that surface, it will be very difficult for pilots to stabilize manually with the remaining systems. While roll and differential thrust will both affect yaw, they will both be slower to react than a rudder, especially in a large aircraft like an A380. This can also damage the hydraulic systems, making it more difficult to control the remaining surfaces.

If experienced test pilots are at the controls (as in the B-52 incident below), or if the failure is anticipated and trained for, it's possible that the aircraft would be controllable enough to land safely. However, as the incidents below show, this kind of failure does not happen often, and can easily exceed the crew's ability to control the plane.

Examples where this has happened:

Japan Airlines Flight 123 lost most of its vertical stabilizer when the rear pressure bulkhead failed. Despite also losing hydraulic systems, the pilots managed to keep the plane in the air for a while, but ended up crashing into a mountain.

American Airlines Flight 587 lost its vertical stabilizer when the pilot's rudder inputs over-stressed the structure. It crashed shortly after.

In 1964, a B-52 lost most of its vertical stabilizer due to extreme turbulence. The pilots were able to extend air brakes on the wing tips to provide some stability. The Air Force sent up a chase plane to help guide the pilots, and provided engineering guidance from the ground. The crew were able to bring the plane back for a safe landing (see a video). There were at least three other instances where the vertical stabilizer failed on B-52's, all ending with the loss of the plane. This particular flight was conducted with test pilots to intentionally fly through turbulence, recording data to help understand the failures on the other aircraft. However, the flight encountered unexpectedly severe turbulence, leading to the separation of the vertical stabilizer.


How did planes measure their speed relative to the ground before GPS? How did planes measure their ground speed before GPS?

If they used some sort of anemometer to measure speed, that would only measure the speed of the plane relative to the air through which it is passing.

Therefore, I'm wondering how speed relative to the ground was measured before GPS.

I'd be very grateful if someone could explain this to me!

The other answers seem to make a simple thing way too complicated. Yes there are DMEs or TACANs, that are sometimes used to get a ground speed, but it's only accurate if you're tracking exactly to or away from it. And it certainly wasn't used to calculate speed enroute unless one of your navaids was a VOR/DME or equivalent. Rather than using DME they'd be using INS, which delivers data more similar to GPS.

Calculating ground speed in the past (before INS, or in airplanes without one) was done using the simple method of having checkpoints along your route. These checkpoints where navaids or intersections determined by multiple navaids. Either way their location was known, divide the distance by the time spent travelling between them and you got your ground speed.


What is the biggest military aircraft? I was just informed that the world's biggest aircraft was the Antonov An-225, and huge airplane.

That being said, I was curious what the world's biggest military aircraft was. Are there limitations such as maximum speed etc,.?

Because the AN-225 is not a military aircraft and Zeppelin will be winner, there is no one biggest plane.

C5 Galaxy = 76 meters long, 68 m wingspan, 20 m high, wing area:576 m2
An-124 = 69 meters long, 73 m wingspan, 21 m high, wing area: 628 m2
(Bonus:) Hughes H-4 Hercules (Spruce Goose on picture) = 66.55 meters long, 97,54 wingspan, 24 m high, wing area: 1 061,8 m2

See this :

Source:https://fr.m.wikipedia.org/wiki/Hughes_H-4_Hercules#/media/Fichier%3AGiant_planes_comparison.svg


Are there any 'smart' ejection seats? Are there any 'smart' ejection seats that eject automatically when an engine failure occurs or the aircraft gets into to a stall that can't be gotten out of, to save the pilot the decision of whether s/he should try and save the aircraft?

The Soviet Yakovlev Yak-38 (and also the Yakovlev Yak-141) had an automatic ejection seat. The aircraft had two smaller engines for VTOL. If one of them failed, the seat ejected automatically once the aircraft rolled past 60$^\circ$. From airvectors.net:

  The pilot sat on a K-36VM ejection seat, with the ejection performed automatically in takeoff or landing excursions using an "SK-EM" system. The SK-EM system was automatically engaged after the aircraft rose a few meters from the deck; it could be turned off manually, or would turn itself off if the vectored-thrust nozzles were more than 67 degrees to the vertical.

These ejection seats were first developed for Yakovlev Yak-36 (though never installed on them). The Yak- 36 had two side-by-engines, the failure of any one of which could flip the aircraft- this led to the development of an automatic ejection system that would activate aircraft seemed to be departing from safe vertical-flight parameters.

According to ejection-history.org.uk, 18 automatic ejections have been recorded in Yak-38s.


May I fly an aircraft registered in an EASA member with an EASA licence (NOT same country as airplane) outside Europe? Let's say that I have an Italian PPL licence and with my I- registered aircraft (small Cessna example) I want to fly in the US or in Argentina, then ICAO rules allow me to do that. Am I correct?

(I think ICAO rules let you fly in another ICAO country if you have your licence and aircraft from same country)

Assuming that, would I be able to do the same thing if my aircraft is registered in another EASA country like Germany (D- registration)?

And a final question:  What if instead of PPL and Cessna, we put EASA glider licence and a glider?

Under ICAO rules, if Germany 'validates' your Italian license then yes, you can fly the German aircraft in other countries:

Use of flight crew licences on foreign-registered aircraft
Any pilot
who wishes to fly on an aircraft registered in a State other than the
one that has issued the licence, needs to obtain an authorization from
the State of Registry. This authorization is generally given by the
State of Registry through a validation or a conversion of the foreign
licence. In general, the validation process is used for short-term
authorization while the conversion process is used for longer-term
authorization.

What 'validation' means here is up to the country where the aircraft is registered. ICAO itself doesn't define what they should do:

When a State validates a foreign licence, it recognizes it as valid
for use on aircraft on its own registry. The Convention on
International Civil Aviation and its Annex 1 do not contain specific
requirements for the validation of licences beyond establishing the
principle and the fact that the validity of a validation, cannot be
extended beyond the validity of the supporting licence.

In the US specifically, these ICAO rules are implemented in 14 CFR 61.3 (emphasis mine):

(b) Required pilot certificate for operating a foreign-registered
aircraft within the United States. No person may serve as a required
pilot flight crewmember of a civil aircraft of foreign registry within
the United States, unless—
(1) That person's pilot certificate or document issued under §61.29(e)
is in that person's physical possession or readily accessible in the
aircraft when exercising the privileges of that pilot certificate; and
(2) Has been issued in accordance with this part, or has been issued
or validated by the country in which the aircraft is registered.

Practically speaking, I would say that if you have some official piece of paper from the German authorities confirming that you are authorized to operate German aircraft - or at least this German aircraft - then you're good to go. The piece of paper may even be unnecessary as far as Germany is concerned, but if you plan on flying internationally then I think the more pieces of official paper that you have, the better.


What's the maximum bank angle of a glider? I know that stall speed and wing load increase with the angle of the turn and I have experienced 65 degrees turns in a glider (demonstrated by an instructor).
Let's say a collision is imminent (or we are in some other emergency situation) what would be the theoretical maximum bank angle? I'll check on the placard the next time I'm in the airfield, but I don't think it's in there.

The bank angle ($\phi$) in a stationary turn is limited by the maximal load factor of the aircraft (or the pilot- whichever is less):
$$\phi_{max}=\arccos(\frac{1}{n_{max}})$$

Utility category gliders ($n_{max}=5.3$) have a maximum bank angle of 79°. Aerobatic gliders with $n_{max}$ between 7 and 10 can fly only slightly steeper turns (82°-84°).

If you're flying with an airspeed slower than design manoeuvring speed $V_A$ the limiting factor is the maximum lift coefficient. In that case, the formula gets
$$\phi_{max}=\arccos(\left(\frac{V_S}{V}\right) ^2)$$
$V_S$ is the stalling speed in the current configuration, $V$ the airspeed of the glider.

(own work)

Then, how do you get the tightest turn radius? With high speed and high bank angle or with low speed and low bank angle? Without the structural limitation the radius could become 0. With it, however, your best option to get a minimal turn radius is to fly with maneuvring speed and maximum load factor.
You can use the following diagram to calculate the minimum turn radius at any speed (just multiply the ordinate with the squared stall speed of your aircraft).

As stated in many comments, during aerobatics/dynamic manuevers you can get any bank angle for a certain (sometimes really short) period of time:

0°/180° bank angle Source

90° bank angle Source


Does the F-16 have any armor at all? When I read about the A-10 I'm met with statements (e.g. Wikipedia) such as:

  The A-10 is exceptionally tough, being able to survive direct hits from armor-piercing and high-explosive projectiles up to 23 mm. It has double-redundant hydraulic flight systems, and a mechanical system as a back up if hydraulics are lost.

What about the F-16 (from A to the latest block 70/72, maybe even F-21 should be included)? Will even small arms fire risk killing the pilot as well as destroying vital systems?

Although it was not designed as a ground attack aircraft, it seems that its role in ground support missions becomes more and more prevalent. The aircraft has also shifted its design goals from being as light and fast as possible to be heavier and feature more complex systems. The F-16's weight seems to only go up with each revision.

If the F-16 is supposed to loiter and provide ground support, it seems that some light (composite? Kevlar?) protection for at least the pilot from small arms fire and slightly heavier weapons would not be a bad idea. Keep in mind that I'm naive about this though, which is why I'm humbly asking.

From what little I know about the F-16, I believe it has quadruple redundant flight computers for its fly-by-wire system, and also has a redundant hydraulics systems (A and B, isolated by a check valve) which both can operate the FLCS (although beyond this, there are differences, A and B are not duplicates), and the EPU.

Design choices like this are obviously there to ensure the F-16 survives when systems fail. However, perhaps they are intended to ensure safe fail-over in terms of non-combat damage and failure.

I also understand that adding armor to a light and agile combat aircraft would be painful, as it adds weight and reduces flight time, makes the airframe thicker with perhaps slightly higher surface area/drag coefficient (?), and probably adds stress to an airframe that is supposed to be able to pull many G's in combat.

I've never heard of any armor whatsoever on the F-16. However, maybe there is? Is there any protection at all, to protect the pilot, or any of its critical systems (flight control computers?)? If no armor, perhaps the flight computers (of which I understand there are multiple physical ones), are they placed in different locations in the aircraft to make it less likely they are all lost from damage in the same location?

As a bonus question, this philosophy of no armor at all on fast combat aircraft, does this extend to most other aircraft? If there are a few notable exceptions, it would be nice to have a couple of the noteworthy ones mentioned (not looking for an exhaustive list).

No.  The aircraft in question do not have ballistic protection, though they do offer system redundancy for battle damage and have to meet certain survivability criteria in live fire tests during development.

Just a note:  the only armor an A10 carries is a titanium pressure vessel for a cockpit which can take the kind of ballistic punishment you described.  It’s main defense is system redundancy, self sealing fuel tanks and engines mounted well away from the airframe and fuel.

Again the chief reasons combat aircraft do not carry external ballistic armor is any kind of armor over the exterior which can deflect the kind of AP/HE/Frag type warheads used in AAA/AAM/SAM warheads would make the aircraft prohibitively heavy and drastically reduce the warload and performance metrics the airplane needs to survive in combat.  And fighters like the F-16 and F-22 are considerably more vulnerable to enemy fire with engine surrounded by fuel tanks, causing even properly placed small arms fire to be catastrophic.


Can you log both XC PIC time and simulated instrument time together? Are you permitted to log both XC PIC time as well as simulated instrument time (during the voyage over) whilst with a qualified safety pilot? I am pursuing my IR and would like to know if doing this is a useful strategy to build some hours in both required categories.

(I realize both pilots cannot log PIC XC time. Only one pilot can perform the necessary landing 50+ nm from the origin airfield in order to get the time there.)

You can log XC, PIC, simulated instrument, category/class, day/night, Total flight time.

From a regulation standpoint.
Cross time can be logged pursuant to §61.1

  Cross-country time means -

  Except as provided in paragraphs (ii) through (vi) of this definition, time acquired during flight -

    (A) Conducted by a person who holds a pilot certificate;

    (B) Conducted in an aircraft;

    (C) That includes a landing at a point other than the point of departure; and

    (D) That involves the use of dead reckoning, pilotage, electronic navigation aids, radio aids, or other navigation systems to navigate to the landing point.

  For the purpose of meeting the aeronautical experience requirements (except for a rotorcraft category rating), for a private pilot certificate (except for a powered parachute category rating), a commercial pilot certificate, or an instrument rating, or for the purpose of exercising recreational pilot privileges (except in a rotorcraft) under § 61.101 (c), time acquired during a flight -

    (A) Conducted in an appropriate aircraft;

    (B) That includes a point of landing that was at least a straight-line distance of more than 50 nautical miles from the original point of departure; and

    (C) That involves the use of dead reckoning, pilotage, electronic navigation aids, radio aids, or other navigation systems to navigate to the landing point.

PIC time can be logged pursuant to §61.51(e)

  (e) Logging pilot-in-command flight time.

    (1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-

      (i) Except when logging flight time under § 61.159(c), when the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, or has sport pilot privileges for that category and class of aircraft, if the aircraft class rating is appropriate;

All others are logged as a requirement under §61.51(b)


What training is required for pilots conducting ASETPA operations? In Australia, aircraft approved for ASETPA operations are certain single-engine turbines allowed to be operated commercially under IFR. While I understand that the manufacturer is required to meet a series of requirement, I'm not so sure about whether the pilots in ASETPA operations need special training or approval. Is extra training and/or testing required, and if so, how extensive is it?

According to the CASA AOC Handbook, section 15.3.1.2, pilots do need to have specific training. Most of this training is regarding engine failures and emergency landings, in some situations in IMC.

CASA requires that all ASETPA operators have a training and checking
organisation.
The CASA Inspector will verify that for ASETPA
operator’s the following additional procedures are included within the
training and checking organisation:

Engine failure or malfunction which necessitates stopping the aircraft on the ground
Engine failure or malfunction which necessitates an off-airport landing after take- off on the most suitable terrain in the vicinity of the aerodrome. These can be organised into a number of procedures, depending on the height of the aircraft at the time of the failure
Engine failure or malfunction which necessitates turning to execute a glide landing upon a serviceable runway, including a ‘turn-back’ manoeuvre. This procedure is to contain a minimum indicated airspeeds and altitudes
Engine malfunction, during climb, cruise and descent and from the approach to land phase in VMC and IMC
Additional procedures for the conduct of a forced landing in IMC to ground level

The next section discusses route limitations, which I am assuming the pilots should at least be familiar with.


What is the largest taildragger in history? Large, modern multi-engine airplanes do mostly have the 'tricycle' landing gear type. But it hasn't always be the norm. I remember at least one big plane with 'conventional landing gear', the German four-engined FW 200 'Condor'...

But, was it the largest of them all...?

If you are going by MTOW, I believe that would be the Junkers Ju 390, which had a maximum takeoff weight of 75,500 kg.

Junkers Ju 390, By Bundesarchiv, Bild 141-0072 / CC-BY-SA 3.0, CC BY-SA 3.0 de, Link

Sadly, only a couple of these were built. If you are going by the wingspan, that would be the Tupolev ANT-20 'Maksim Gorki', which had a wingspan of 63m

ANT-20, By Unknown - http://www.dkvnukovo.ru/photos/museum/photos/35.jpg, Public Domain, Link


How high does a jet have to be to hear its radio call? I am a student pilot and I am learning about radio signals/communication.

I am studying for a test and a practice questions states:

You are flying circuits at a small airport and are flying at 1800ft ASL in the circuit (1000ft AGL) when you hear a radio call from a commercial jet at an airport 123 nautical miles to the south. Roughly how high does this jet need to be so that you can hear his radio call?

The only reference I can think of is that VHF signals can be heard by using a formula of:
Nautical miles = 1.23 * √ height above ground level. The answer would be 10000 ft (AGL)?, but I am not sure if that is the right formula to use or how to figure it out.

Please help.

The formula you're using is correct, but don't forget your own altitude.

$$d = 1,23 × (\sqrt{h_1} + \sqrt{h_2})$$

So in your case:

$$123 = 1.23 × (\sqrt x + \sqrt{1000})$$
$$100 = \sqrt x + 31.623$$
$$\sqrt x = 68.377$$
$$x = 4675\ \mathrm{ft}$$


Why were these crash location not located via ELT? On Jan 14th 2019, at 9.10 Indonesia time, the CVR of the crashed Lion Air JT-610 has been found. Another vital device was found earlier.

There are three modern airplanes crashed in to water in Indonesia:

Adam Air, registration PK-KKW, Boeing 737-400, flight KI514, on 1-January-2007, crashed into Majene Sea due to the failure with the Internal Reference System (IRS), rested in 2,000m below the sea surface.
Air Asia, registration PK-AXC, Airbus A320-216, flight QZ8501, crashed on 28-December-2015, into Karimunjawa Sea, due to the failure with the rudder-travel-limiter.
Lion Air, registration PK-LQP, Boeing 737 Max-8, flight JT-610, crashed on 28-November-2018, into Java Sea. The crash cause is still under investigation.

Those three crash locations were found not by the electronic instrument system, but by fishermen.

Then my question is: why did the modern airplane has not been located via its ELT?

ELT's are not required to be built to the same standards as the CVR and FDR. That means they are much more likely to be destroyed in a severe crash. Also, ELT's (the old style 121.5 and 243 mhz and the new 406 mhz) are not designed to function under water or mud.


What is this instrument above the EGT in the Boeing 737? I would like to know what is this instrument that is above the EGT of the Boeing 737. What does it indicate?

This is a differential pressure and cabin altitude indicator.

The outer dial indicates the difference in pressure between the inside of the cabin and the outside in psi. During takeoff and landing, it must not be larger than 0.125 psi, as the note below the instrument says. If it exceeds 9.1 psi, the pressure relief valve will release the pressure to prevent damage to the airframe:

  Two pressure relief valves provide safety pressure relief by limiting the
  differential pressure to a maximum of 9.1 psi. A negative relief valve prevents
  external atmospheric pressure from exceeding internal cabin pressure.

(Boeing 737 NG FCOMv2 2 - Air Systems - Pressure Relief Valves)

The inner dial shows the cabin altitude in thousands of feet. During normal operations, it should not exceed 8,000 ft. This is a measure of the absolute pressure inside the cabin, converted to an altitude using the standard atmosphere (ISA) pressure profile.

Note: The instrument below is typically a cabin climb indicator showing the rate of change of cabin altitude in thousands of feet per minute:

(image cropped from here)

The EGT instrument in your image shows the Exhaust Gas Temperature of the APU and is typically installed further to the left on the overhead panel.


Angle of attack from velocity vector I found an equation to calculate angle of attack based on the velocity vector in the body frame of the aircraft.

$\arctan(v_x/v_z) = \alpha$

1) Is this correct?

When I input in a $v_z$ approaching zero, the value approaches $\infty$ which means that angle of attack moving only in the x direction is 90 degrees since $\arctan(x)_{x\rightarrow \infty}= \pi/2$

2) Is there supposed to be an assumption that you never calculate Aoa of zero with this?

3) Am I misinterpreting what the velocities and angles represent?

Overall I am just a bit confused, because I kind of expected something that wouldn't mess up at level flight.

It is exactly the other way round:

$$ \alpha = \mathrm{arctan} \left( \frac{v_z}{v_x} \right) $$

You can simply derive it from the trigonometry in a triangle:

In this image the aircraft is moving to the right (along the arrow labelled v) and the $x$-axis is pointing along the aircraft body.

The resulting function looks like this:

For $ v_z = 0 $, you get $ \alpha = \arctan(0) = 0 $.
For $ v_x \to 0 $, you get $ \alpha \to \frac{\pi}{2} = 90^\circ $.


What is the most critical data to measure for a predictive maintenance model for a drone? I'm looking at making a predictive maintenance model for a drone (quadcopter mainly but can include others)

I'm wondering what is the most common causes of failure due to "overflying". (not including crashes etc) and how I would quantitatively measure it.

eg. I've read that one mode of failure is rotor malfunction is one of the most common causes of faults and so I would therefore use a vibration sensor (positioned near the rotor?) to measure it.

Are there other common failure modes? And what data can we collect from a drone that would help mitigate those?

Any help much appreciated!!

Kindest regards

Jonathan

Predictive Maintenance (PM) typically relies on a triad of vibration, thermal and oil analysis, or any combination thereof. Probably vib and thermal would apply. Cheapest option would be to physically hold the drone while running (if possible) and acquire vib and thermal, using handheld instruments. All-in option would be a hardwired system, permanently installed. With a hardwired system, you'll need a vib and a thermal transducer installed on each power/rotor module. Hope this helps.


What is implied about altitude and the VDP by this Visual Flight Segment arrow in the profile view example in the Aeronautical Chart User's Guide? This is out of the Aeronautical Chart User's Guide.

The arrow for the visual segment is depicted as being level flight.  Is that what is intended to be conveyed?  If so, how would you know what altitude?  Would it just be the DA?
LNAV/VNAV would only be second to LPV in vertically-guided precision.  Does this imply that the VDP applies only to an LPV minima, or does the VDP apply to both LNAV/VNAV and LPV minima regardless of the visual segment arrow for LNAV/VNAV??

This is extracted from the RNAV (GPS) RWY 23 of WESTERN NEBRASKA RGNL/WILLIAM B HEILIG FIELD (BFF) in Scottsbluff, Nebraska.

A VDP (Visual Descent Point) is only used in conjunction with an MDA (Minimum Descent Altitude). Do not mistake this for a DA (Decision Altitude). If visual contact with the runway environment is not made once a pilot reaches MDA, the pilot must continue at the same altitude on the approach course until reaching the MAP (Missed Approach Point). The VDP is the point along the course where a normal descent has been calculated as possible using normal procedures and maneuvers. It is a recommended point where the pilot should make the decision to go missed once reaching the MAP. That means that even though the pilot has decided to go missed, they will continue to fly past the VDP, straight and level, until the MAP. The key word here is “recommended”.

At a DA, if the pilot has not made visual contact with the ground, the pilot is required to decide to go missed. In most cases, that means the pilot would initiate the missed approach procedure immediately before reaching the DA. Since there are two DAs for the LNAV/VNAV, depending on if the local altimeter setting is available, there are two distances to the MAP. This is conditional upon the pilot maintaining glideslope all the way from the FAF (Final Approach Fix).

In this case, upon making visual contact with the ground, the pilot can choose to make a Visual Approach. There is no altitude requirement unless specifically charted. Cloud clearance and visual obstacle clearance must be maintained.

According to the users guide, it appears a pilot on the approach can fly visually past the point of decision if they have broken free from the clouds.

The Aeronautical Chart Users Guide states...

  Visual Flight Path
  Instrument approach procedures, including Copter approach procedures, that terminate or have missed approaches prior to the airport, and are authorized to proceed visual, shall depict the visual segment by the dashed line symbol from the missed approach point to the airport. The note “Fly visual” (“Proceed visually” on Copter procedures) along with the bearing and distance shall be shown leadered to the visual flight path.
  RNAV charts sometimes have visual flight for LNAV/VNAV minima which do not start at the missed approach point. An additional note indicating “LNAV/VNAV” will be placed above the note.

Furthermore the AIM 5-4-5-l states...

  l. In isolated cases, an IAP may contain a published visual flight path. These procedures are annotated “Fly Visual to Airport” or “Fly Visual.” A dashed arrow indicating the visual flight path will be included in the profile and plan views with an approximate heading and distance to the end of the runway.

  The depicted ground track associated with the “Fly Visual to Airport” segment should be flown as a “Dead Reckoning” course. When executing the “Fly Visual to Airport” segment, the flight visibility must not be less than that prescribed in the IAP; the pilot must remain clear of clouds and proceed to the airport maintaining visual contact with the ground. Altitude on the visual flight path is at the discretion of the pilot, and it is the responsibility of the pilot to visually acquire and avoid obstacles in the “Fly Visual to Airport” segment.
  Missed approach obstacle clearance is assured only if the missed approach is commenced at the published MAP. Before initiating an IAP that contains a “Fly Visual to Airport” segment, the pilot should have preplanned climb out options based on aircraft performance and terrain features. Obstacle clearance is the responsibility of the pilot when the approach is continued beyond the MAP.

  Note: The FAA Administrator retains the authority to approve instrument approach procedures where the pilot may not necessarily have one of the visual references specified in 14 CFR §91.175 and related rules. It is not a function of procedure design to ensure compliance with §91.175. The annotation “Fly Visual to Airport” provides relief from §91.175 requirements that the pilot have distinctly visible and identifiable visual references prior to descent below MDA/DA.

My reasoning for saying the VDP is recommended and not required is that the VDP is found in the AIM.

  AIM 5-4-5
  h. The Visual Descent Point (VDP), identified by the symbol (V), is a defined point on the final approach course of a nonprecision straight-in approach procedure from which a stabilized visual descent from the MDA to the runway touchdown point may be commenced. The pilot should not descend below the MDA prior to reaching the VDP. The VDP will be identified by DME or RNAV along-track distance to the MAP. The VDP distance is based on the lowest MDA published on the IAP and harmonized with the angle of the visual glide slope indicator (VGSI) (if installed) or the procedure VDA (if no VGSI is installed). A VDP may not be published under certain circumstances which may result in a destabilized descent between the MDA and the runway touchdown point. Such circumstances include an obstacle penetrating the visual surface between the MDA and runway threshold, lack of distance measuring capability, or the procedure design prevents a VDP to be identified.

  VGSI systems may be used as a visual aid to the pilot to determine if the aircraft is in a position to make a stabilized descent from the MDA. When the visibility is close to minimums, the VGSI may not be visible at the VDP due to its location beyond the MAP.
  Pilots not equipped to receive the VDP should fly the approach procedure as though no VDP had been provided.
  On a straight-in nonprecision IAP, descent below the MDA between the VDP and the MAP may be inadvisable or impossible. Aircraft speed, height above the runway, descent rate, amount of turn, and runway length are some of the factors which must be considered by the pilot to determine if a safe descent and landing can be accomplished.


Which engines do airliners start first? I noticed many planes, especially Boeings (correct me if I'm wrong anywhere), start engine "2" first and shut down engine "2" last.

However, I was watching an Airbus A350 cockpit video when I realised the A350 starts engine 1 first and shuts down engine 1 first. Hence, I have 2 questions:

In which order should the engines of the A350 be started and shut down?
What determines this order and are they the same/ similar on aircraft of the same manufacturer or can they differ within the same manufacturer as well?

For some general reasons, see Why is engine No.2 started first, instead of No.1?

Airbus A350

Specifically to the Airbus A350, I could not find any reason why one engine must be started first. As far as I know every modern airliner could start engines in arbitrary order.

The Airbus A350 has two hydraulic systems. From the Airbus A350-900 Flight Deck and Systems Briefing:

  The A350 hydraulic system has two independent
  hydraulic circuits:

  The YELLOW hydraulic circuit
  The GREEN hydraulic circuit

Each system can be pressurized with an engine driven pump from either engine, or electrically on the ground:

  Engine Driven Pumps (EDPs)

  Four EDPs pressurize the hydraulic system. On each
  engine there are two EDPs, one pressurizes the
  GREEN hydraulic circuit and the other pressurizes the
  YELLOW hydraulic circuit. Thus if an engine fails, the
  remaining engine can still pressurize both hydraulic
  circuits.

  Electric Motor Pump (EMP)

  One EMP per hydraulic system can provide hydraulic
  pressure on ground only, when all engines are shut
  down. For example, the EMP of the YELLOW circuit
  operates automatically for cargo door actuation.

The main wheel brakes are powered by both hydraulic systems:

And also the parking brake uses pressure from both accumulators:

Which engine is started first has therefore no impact on which hydraulic system is powered first or which type of braking is available.

Airbus A320

The situation is a bit different for the Airbus A320. As Jan pointed out in the comments, it is normal to start the right engine first, because it provides hydraulic pressure to the yellow system. From the A320 FCOM Hydraulic chapter:

  Green System Pump

  A pump driven by engine 1 pressurizes the green system.

  Blue System Pumps

  An electric pump pressurizes the blue system. A pump driven by a ram air turbine (RAT) pressurizes this system in an emergency.

  Yellow System Pumps

  A pump driven by engine 2 pressurizes the yellow system. An electric pump can also pressurize the yellow system, which allows yellow hydraulics to be used on the ground when the engines are stopped. Crew member can also use a hand pump to pressurize the yellow system in order to operate the cargo doors when no electrical power is available.

The yellow system powers the alternate/parking brake system:

However, starting the left engine first is still perfectly possible. Hydraulic pressure from the accumulator is still available after pressurizing the yellow system with the electric pump before pushback to provide braking.

Boeing 737

The Boeing 737 has two hydraulic systems: A and B. Both can be powered by electric pumps. From the FCOMv2 13.20.2 Hydraulics - System Description:

  Both A and B hydraulic systems have an engine–driven pump and an AC electric
  motor–driven pump. The system A engine–driven pump is powered by the No. 1
  engine and the system B engine–driven pump is powered by the No. 2 engine. An
  engine–driven hydraulic pump supplies approximately 4 times the fluid volume of
  the related electric motor–driven hydraulic pump.

The braking is provided by both systems. From the FCOMv2 14.20.3 Landing Gear - System Description:

  Normal Brake System

  The normal brake system is powered by hydraulic system B.

  Alternate Brake System

  The alternate brake system is powered by hydraulic system A. If hydraulic system
  B is low or fails, hydraulic system A automatically supplies pressure to the
  alternate brake system.

  Brake Accumulator

  The brake accumulator is pressurized by hydraulic system B. If both normal and
  alternate brake system pressure is lost, trapped hydraulic pressure in the brake
  accumulator can still provide several braking applications or parking brake
  application.

Again, there is no reason to start one engine before the other because of hydraulics/braking.

Conclusion

Engine start order is mostly tradition and will be specified by the airline op-specs. The shutdown oder also does not matter since both engines are usually shut down at (almost) the same time at the gate, except for a single engine taxi where the hydraulic system that powers the nose-wheel steering must be pressurized.


How much damage could a landing gear malfunction do? How much damage could a total landing gear malfunction do to an airliner? Could the runway wear a hole through the plane?

According to Belly landing:

  During a belly landing, there is normally extensive damage to the airplane. Belly landings carry the risk that the aircraft may flip over, disintegrate, or catch fire if it lands too fast or too hard. Extreme precision is needed to ensure that the plane lands as straight and level as possible while maintaining enough airspeed to maintain control. Strong crosswinds, low visibility, damage to the airplane, or unresponsive instruments or controls greatly increase the danger of performing a belly landing. Still, belly landings are one of the most common types of aircraft accidents, and are normally not fatal if executed carefully.

It is possible that the friction from a belly landing could wear a hole through the underside of the fuselage. However, even if this were to happen, airliners carry the passengers and crew in the upper half of the fuselage, so nobody would be likely to notice (from inside the aircraft before emergency evacuation).


What are the laws on photographing aircraft in Australia? Are there any types of aircraft that I am forbidden from photographing aircraft. (Australian aircraft, primarily) in Australia? Are there regulations on what I do with the photographs I take? I assume there is some sort of thing published by the government but I couldn't find any.

There is no law in Australia prohibiting the photography of aircraft. I have been approached by police while doing it just to see what I was up to, but after a polite exchange they were happy and moved on.
Potentially, if you're on private property (eg an airport terminal), the conditions of entry are allowed to prohibit the taking of any photos. But I'd be shocked if that is applied anywhere outside of theatres or defence bases. You try telling travellers they're not allowed to take an airport selfie for instagram.
If you're using the photos for commercial reasons, and they include a trademark (like an airline logo), you might need to contact them for permission, I'm not certain how that process works. But this certainly doesn't apply for private use.
Having said all that, I am not a lawyer, so if you're worried or want specific information you should at least ask on a legal forum, if not pay for a professional opinion.


Is there an actual rated thrust for a Cessna 172 engine at takeoff power? I could approximate the thrust by knowing the weight of my aircraft and timing the acceleration to takeoff speed, but I think that would be a little dangerous of me as well as only an approximation due to rolling and wind resistance as well as inaccuracies of the airspeed indicator.  I also realize the thrust would vary as airspeed increases due to changes in propeller and engine efficiency.

Nevertheless, was there every an actual rated or measured thrust for the C172?  You can use whatever year model you want, although I usually fly the C172N at 160Hp using a stock propeller.  I would also assume if there was a measurement, it would be at standard atmospheric conditions (sea level, 15C, standard 29.92 pressure).

A fixed pitch prop will develop maximum thrust somewhere between static and maximum air speed depending on its pitch. Finer pitch will give better acceleration from a standing start, more coarse will give more thrust at cruise.  People generally do not quote thrust numbers with props, charts calculating weight and weather effects on performance are far more important than "thrust".

However, if you want to know, do it the same way James Watt did, either by lifting a weight, moving a weight, or lifting AND moving a weight.  Watt knew just to take the first meter, where air drag was negligible.  For a Cessna, I would take the first 100 feet, release the brake, and hold a stop watch.  As John K said, it should be 500-600 lbs.  F=ma.

Just keep in mind, the key to those performance charts is that weather conditions have MAJOR effects on power and prop efficiency (prop thrust), this is what you MUST be aware of before takeoff.


Who controls the cabin air temperature? I understand the B737-800 has two air conditioning packs that handle the temperature of three zones: the cockpit, the fwd cabin and the aft cabin.

I understand that which pack is turned on is controled from the cockpit.

My questions are:

can the temperature be regulated for each zone seperately?
where are the switches located that control the temperature in each zone?
who operates these switches?

The 737-400, -800, and -900 have two cabin air conditioning zones plus the cockpit. The rest have one plus the cockpit.

Both packs are on in normal operation because they are slightly more efficient at lower flow rates. It also is safer as no immediate action is necessary to prevent depressurization if a pack fails.

Temperature is regulated separately. The packs cool to the lowest temperature demanded, and unconditioned bleed air, called trim air, is mixed in for the warmer zone.

The dual cabin zone models have three knobs which set the temperature of each zone, from a low to high temperature with a default detent.

The single cabin zone models have a knob for the cabin and one for the cockpit zone. The knob is divided into two ranges, an auto range, where a temperature is controlled, and a manual range, that selects the position of the hot air mix valve in each pack.

The temperature control dials are located in the overhead panel in the cockpit. The pilots operate this, often in response to complaints from the cabin crew relayed over the interphone. (The A320 has an option for cabin crew adjustment of temperature, eliminating the hassle)


Is A380's center of gravity really too far back? I have searched and even studied plans from Airbus itself, but I was not able to confirm the following and would like to ask if the information I have is correct.

TLDR version so you don't have to read all the text: Does A380 really have the center of gravity positioned BEHIND the aerodynamic force center?

(What I know so far): For any passenger aircraft, without (almost any) exception, the center of gravity is always closer to the nose of the aircraft than the aerodynamic forces resultant. This is to provide an auto-stabilising force for the aircraft in case it stalls for whatever reason. Since the airplane is "nose heavy", it would eventually establish itself "towards the air flow" and after some height drop, should at least partially regain normal flight mode. Also it prevents the aircraft from going into a flat loop. While this setup is safe, it also means that the tail wing needs to correct for the center of gravity and "pull down" (omitting the duck planes now), which means it does not help to create lift, instead reducing the total lift. This increases fuel consumption.

(What I need to confirm): During my UL theory training, one of the instructors told us that A380 (and all the new passenger planes driven mostly by computers alike) will have the center of gravity behind the aerodynamic center, which enables to use the huge tail wing to actually create lift instead of decreasing it and thus lowering the fuel consumption dramatically. While this is great from economical and ecological point of view, it would only work while the computers look after the plane. It would become so unstable that there is no way a human could fly it "by hand".

I understand that if the computers go down on a "fly-by-wire" airplane completely, the joystick/rudder becomes just a piece of plastic anyways, but a computer that constantly looks after the stability of the plane seems much more "error ready" than a simple wire between a cockpit and a servo.

Modern jet fighters have CoG behind the aerodynamic center and it is said that you only stall them once. There is no way to recover a stall like you would do with your good old Cessna. It strikes me that something like that would get approved for a civilian aircraft.

Thank you for your inputs. I was not able to find any resource concerning A380's CoG.

No. Positive lift on the tail does not necessarily mean that the center of gravity needs to be aft of the aerodynamic center of the aircraft. Only when the lift per area of the tail surface is higher than that of the wing will the center of gravity move into the unstable region.

  the center of gravity is always closer to the nose of the aircraft
  than the aerodynamic forces resultant

Again, no. The center of gravity needs to be at the same lengthwise station as the center of pressure in trimmed flight, otherwise the aircraft would not be trimmed and start to pitch. With low-mounted engines there might be some thrust moment which must be canceled by a slightly forward location of the center of gravity, but this effect is small.

Next, the auto-stabilisation is not only helpful when stalling. It also provides a smoother ride in gusty conditions and makes it easier for the pilot to fly the aircraft.

Since the aspect ratio of the tail surfaces is smaller than that of the wings, lift there is bought more expensively, so it will be bad for performance if the tail produces more lift per area than the wing. Negative stability is only helpful for supersonic and highly manoeuverable airplanes. Airbus does not do that, and besides, the A380 would not be certified with negative stability.

What it does have, however, like all Airbus aircraft since the A310, is relaxed static stability. The center of gravity is still ahead of the neutral point, but less so than in conventional airliners. This does indeed help to lower drag, and the reduced (but still positive!) stability is enhanced by electronic means.