Should you sump fuel tanks when the fuel system is below freezing? I recently saw an argument in a forum I frequent that sumping the tanks when the system was below freezing was a bad idea, as you can't drain solid ice from the fuel system, and there is a chance that ice may jam the drain open, causing your entire tank of avgas to empty onto the ramp.

While this is certainly a possibility, is it a reason to skip sumping the fuel system during preflight, or do the reasons for checking the fuel system outweigh the risk of a tank of fuel winding up on the ground?

OK, I sat on my hands for a while, so now I'll stick my head in the lion's mouth.

You should absolutely sump your tanks every time you go flying as part of a routine preflight inspection, whether you've taken on fuel or not, whether the aircraft has been hangared or out on the ramp, and even if it's below freezing.
Water isn't the only thing you're looking for (misfueling happens - also bits of fuel tank sealant, rubber from a rotting bladder, dirt that made it past the fueling truck's filters, etc. - you want to find these things!)

Ideally if it's below freezing you should also pre-heat your aircraft so the engine, instruments, and fuel are above freezing when you're preflighting (which is generally accomplished by sticking the plane in a heated hangar), but sometimes that's not an option and you make do.

Why should you sump the tanks if it's below freezing?

Well like I said above, water isn't the only thing we're looking for - and all those concerns still hold valid no matter what the temperature is. Water is the one that people seem to come up with as a reason for not sumping when it's below freezing though, so let's talk about water:

There are five general ways water can manifest itself in your (Avgas) fuel system:

Liquid Water
If it's not been below freezing (or it's really sunny and your fuel tanks have acted like an oven) water may be liquid, waiting for you at the sump drain just like on a warm summer day. You'll drain it out and go on about your business.
Slush (ice crystals suspended in the fuel)
If it's below freezing you may have suspended ice crystals or slush in the fuel (particularly if you just took on fuel). This will look "cloudy" when you drain it from the sump and it's a good indication that today is not a good day to fly: you may have a LOT of water in the fuel, and you need to need to deal with it (warm the plane up and drain off the water, and figure out how so much of it got in there in the first place).
(There is a chance that slush could jam your fuel drain open, in which case your fuel tank will empty itself onto the ramp with great rapidity.)
Little bits of ice
Little drops of water can freeze into little bits of ice, which are often just too big to come out of the fuel sump drain, but just small enough to lodge in it and keep it from closing (which, again, will cause your tank to empty itself onto the ramp with great rapidity. This is also an indication that today is not a good day to fly).
BIG bits of ice over the sump drain
Liquid water will flow to the lowest point in the fuel system (the drains). If it's below freezing it will freeze there, potentially blocking the sump drain.
You'll notice this condition because the sump valve may feel stiff, your tank may not drain, or it will drain very slowly, possibly with water in the fuel.
This is a good indication that you shouldn't fly until you figure out what the cause of the problem is (it could be ice, it could be a defective valve, or it could be a bunch of other things, but until you know you want to stay on the ground).
Hidden Ice (big bits of ice away from the sump drain)
This is perhaps the most insidious: Ice that's not near the sump, and doesn't block or jam anything.  Hopefully you'll spot this sitting at the bottom of your tank when you look in to check the fuel level (you do visually check your fuel level, right?), but you probably won't notice anything out of the ordinary when you sump the tank.

(There are of course other ways water can hide out in the system besides the fuel tanks, but these are where you're most likely to find it.)

The most likely "bad thing" to happen to you in any of those scenarios is that your fuel sump will be jammed open by ice. This means you'll spill a tank's worth of avgas on the ground, and you'll have to call your airport's spill cleanup/emergency number and let them know.
That emergency is on the ground, and it may be a little embarrassing to have to explain to the spill cleanup folks, but it's better than the other possibilities.

The Bad Things that can happen to you in the air if you go flying with undetected ice/water in the fuel are far worse: The ice could melt and your engine could start trying to burn water, which doesn't ignite very well.

Check out Gene Benson's "Why Did They Do That? - Volume 2" presentation, starting at slide #7 for one example of how things can go catastrophically wrong if you neglect to sump your tanks (or ignore the warning signs when you do).


Why was Concorde never sold as a private business jet? Airliners like Boeing 747 and even Airbus 380 are at times considered as personal jets for extremely wealthy people. Looking from the side, Concorde was ideal for this role: while not very big, it probably could provide luxury transportation for ten VIPs or thereabout, adding to that something that looks more valuable and more exceptional than just a "flying palace" - speed like no other. New supersonic aircraft like Aerion AS2 are often seen in this role. However, it looks like rich individuals only bought various bones of Concorde after retirement.

The fate of F-BVFD looks especially strange. As I understand, it has been retired very early, in airworthy condition, just for being a surplus aircraft. After standing for many years in the open air, it deteriorated and then has been scrapped. I cannot imagine it to cost a lot during these years of standing. Why did nobody try it for personal use? Also, some pre-production aircraft have been retired after logging not so many hours and were airworthy.

Surely, Concorde uses lots of fuel, but probably the A380 burns no much less if per flight (not per passenger). And it only could fly supersonic over sea, but was surely capable of the fastest possible subsonic flight over the land.

Private business jets have a few requirements:

Operational costs must be within budget. The concorde is pretty expensive to run as demonstrated by the high ticketprices you had to pay for a trip on one of them. Fuel is only part of that costs; maintenance is a pretty big part of that as well.
Be able to land and take off close to where the CEO has his meeting. This means making use of small airfields with their short runways and noise restrictions. Concorde needed a lot of runway and was not a quiet plane.
Account for airfields sometimes not having fuel available or the fuel being too expensive. This may mean doing the roundtrip on a single tank or doing another short hop to an airfield with fuel.

Business jets would also mostly operate on a domestic scale. Doing mostly short hops where the concorde would not even reach supersonic cruise altitude before it's over the destination. While plenty of business jets can easily do 0.75 mach which is already 3/4 the speed of sound.


Could a pilot navigate using distances and radials from an RNAV waypoint, similar to VOR navigation? I know that typically RNAV navigation involves a list of waypoints, and the aircraft simply flies from one point to the next.  What I'm curious about is if a procedure could be developed (as a special engine out procedure, for example) that would be something like

  Depart on runway heading. At distance 2nm from FOBAR waypoint, turn
  direct to FOBAR. Track radial 090 outbound from FOBAR.

Would the instruments in an RNAV equipped aircraft allow a procedure like that to be flown?  Would it require a certain system (say only from a certain manufacturer), or require additional systems (like an FMS)?

CLARIFICATION FROM COMMENTS:
I understand that a procedure like the one above would not be typical or preferred, but in very hazardous terrain (for example) with no real other options, would the pilot simply have the tools available to be able to fly it?

If it matters, I'm particularly interested in commercial aviation and answers that would be applicable to any airport worldwide.

In a modern B737 (NG/MAX) (and probably most other comparable aircraft), this is trivial. The simplest (and most realistic option for an emergency turn procedure) would be to fly the procedure in HDG SEL:

Enter FOBAR on FIX page
Add a 2 nm range ring for FOBAR on the FIX page. This ring will be displayed on the ND (Navigation Display)
Add the 90 radial for FOBAR on the FIX page. This radial will be displayed on the ND.
Fly the procedure in HDG SEL, monitoring the ND.


To which reference point on the aircraft is the altimeter reading relative to? To which point of the aircraft is the altimeter reading referred to? Is it referred to the probe position or is it offset to read as if it was at the bottom of the fuselage or the landing gear? If it was a GA aircraft I suppose it wouldn't make a difference, but on something big as a 747 or an A380, should it be set at the same level as the probe, there would be quite a difference compared to the ground (maybe 20-30 feet?). If so, how is this handled?

The placement of a probe for a pressure  altimeter has exactly the problem you mention, but they only need to be accurate within 75 feet, so placement is not a problem.

For large aircraft, they use a "radar altimeter" which uses an electromagnetic beam to measure the distance to the ground, the same way police radars measure car speed. Radar altimeters are accurate to within a couple of feet.


How does thrust relate to horsepower on turbocharged engines? Could someone please help me understand the difference between horsepower and thrust on turbocharged engines?  I believe I have a good understanding regarding the purpose and operation of a turbocharger, but what I don’t understand is why the overall performance goes down even when the turbocharger is capable of making max PSI below the rated “critical altitude”.  For example, if my turbocharger can produce 40” from sea level to 12,000 DA, why does my climb performance decrease with altitude?  40” will produce max horsepower from sea level to 12,000, but the performance charts clearly demonstrate a loss of climb performance between sea level and 12,000’ DA, and I just don’t understand why.  Thank you!

Assuming you are talking about a turbocharged propeller driven aircraft, your question
really makes it easy to explain as you have already identified the two parts of your power unit
that are affected by increasing altitude (thinner air).  The amount of air it can breath and the amount of thrust your prop can generate.

The turbo only takes care of the air breathing part, yes, it has as much power as at sea level
because to turbocharger can compress enough of the thin air to feed it. No problem there.

But the prop is still spinning thinner air, so it can not get the same "bite" as at lower altitudes
with out going to even higher RPMs.  So, when your RPMs max out due to engine limitations,
or even the tips going supersonic, that's it, no more thrust increase available.


Why would you NOT lean on takeoff with a Lycoming engine? There is an excellent question/answer on leaning here. However what I have not yet understood is why one would NOT lean for takeoff below 3000 feet? Why does the Lycoming Service Directive 1497A/B still say to use Full Rich on takeoff?

Is it not right that a leaned engine is producing its highest power output and would you not want the highest power output on takeoff?

You are correct - you do want highest power.  But you also want an engine that doesn't overheat and destroy itself.

Your initial climb-out is at an airspeed considerably less than cruising speed so you have less air flowing through the cylinder cooling fins.  To compensate for this, flying full rich keep the combustion gasses cooler during the climb-out.

When you reach cruising altitude and level off, you may lean it out in accordance with the engine manufacturer's recommendations.

This "full rich on takeoff" procedure is not limited to Lycoming engines, either.  TCM Continental and even the older Pratt and Whitney radials also go full rich on takeoff. It is close to a universal procedure for piston powered aircraft engines.


Why didn’t AFR4590 use heavy in its call sign? https://aviation-safety.net/investigation/cvr/transcripts/cvr_af4590.php shows that AFR4590 didn’t use heavy in its call sign even though Concorde had a MTOW greater than 300,000 lbs.  Unlike BAW, AFR didn’t have a specific Concorde callsign, so why did they not say heavy:

The post When is 'heavy' used in callsign? shows that the usage of "Heavy" depends on the country.
The general ICAO usage is to say "Heavy" only in the initial message with a frequency.
That usage applies to France, where the linked CVR transcipt took place (no differences are listed in the French AIP). Since that transcript does not show the initial contact with tower, it doesn't show when "Heavy" was first used.
USA however deviates from this standard, and this difference from ICAO is listed in the USA AIP:

4.9.2 In the U.S., the word "heavy" is used in all communications with or about heavy jet aircraft in the terminal environment. In the en route environment, "heavy" is used in all communications with or about heavy jet aircraft with a terminal facility, when the en route center is providing approach control service, when the separation from a following aircraft may become less than five miles by approved procedure, and when issuing traffic advisories.
— https://www.faa.gov/air_traffic/publications/atpubs/aip_html/part1_gen_section_1.7.html

The general ICAO usage (4.9.2) can be found in ICAO Doc 4444:

4.9.2 Indication of heavy wake turbulence category
For aircraft in the heavy wake turbulence category the word "Heavy" shall be included immediately after the aircraft call sign in the initial radiotelephony contact between such aircraft and ATS units.


What is the shortest regularly scheduled commercial flight? Interesting to know is this flight profitable or not.
Why this route exist?
Maybe train or car will be cheaper?

Westray to Papa Westray

Flights on this route are scheduled for one and a half minutes, and actual flying time is closer to one minute. The record for the fastest flight is 53 seconds.

By road/ferry it's 59 minutes according to Google Earth:

It's flown with a Britten-Norman BN-2 Islander.


When to turn base at towered airport? When at a towered airport and instructed to make "left pattern for runway 3," am I supposed to wait for the base leg turn until tower clears me for landing?  This seems to be the norm, but I can't find anything in the FAR/AIM to indicate what is acceptable.

Related: I often get confused when in the downwind pattern and I hear something like this: "123X, tower, you are #2 for runway 3, following a Cessna on final."  Does this mean I should turn base and follow the Cessna?

I know the correct answer is to ask ATC to clarify, but it would be ideal if this were spelled out in the AIM.

You have a few questions here.

  ...downwind pattern and I hear something like this: "123X, tower, you are #2 for runway 3, following a Cessna on final."

In this case what you will do is continue your down wind leg while scanning for the Cessna traffic, some towers may ask you to "report traffic in sight" in which case you will say "traffic in sight" when you can see the Cessna. If he is on a long final you can begin turning your base (assuming you are in a similar small plane of a similar speed) when he is on your beam (right off your wing tip). This should provide adequate spacing for you to come in properly. Keep in mind that the tower may also instruct you to do things to keep separation like "123X Extend your down wind 1 mile" etc.

  ...instructed to make "left pattern for runway 3," am I supposed to wait for the base leg turn until tower clears me for landing?

This depends on where you are coming in from. I have flown into towered airports on the runway heading and simply come into the pattern on final and was cleared to land about a mile from the runway. Other wise I typically report my midfield downwind to the tower "Piper 12345 Reporting Left Midfield Downwind for RW24" then the tower will respond with my landing clearance or instructions to extend. While it is the towers responsibility to clear you for landing and what not, controllers are not perfect, you can continue on towards the runway in your pattern but if you have not been cleared you should go-around or ask for clearance.

The other situation I have been in is a case where the controller deliberately does not clear you but has  you come into the pattern and approach. This occurred while they were waiting for an IRF plan to come through for one of the regional jets waiting for departure. Since they did not know when it would come in I was instructed to continue my pattern and would be cleared on final if they did not need to get the jet out. However I was explicitly told I would be cleared on final so I knew what to listen for.


How do pilots and controllers deal with TFR's that lie directly on an approach? FDC Notam 4/3621 creates a generic "template" TFR which sits on top of sporting events.  This one in Phonenix appears to sit right on one of the business ends of Phoenix Sky Harbor (PHX)  The Notam states that event operations are permitted with the appropriate waiver.  How do regularly scheduled airlines deal with such TFR's?  Are waivers obtained for scheduled inbound flights?  There does not seem to be verbage in the notam granting any exceptions for air carriers.

The NOTAM itself answers your question:

  THE RESTRICTIONS DESCRIBED ABOVE DO NOT APPLY TO THOSE AIRCRAFT
  AUTHORIZED BY AND IN CONTACT WITH ATC FOR OPERATIONAL OR SAFETY OF
  FLIGHT PURPOSES, DEPARTMENT OF DEFENSE, LAW ENFORCEMENT, AND AIR
  AMBULANCE FLIGHT OPERATIONS.

As long as the pilot is in contact with Air Traffic Control and has been cleared through the TFR, they can safely fly though the airspace.


What is the difference between the FAA FNS NOTAM and the FAA PilotWeb NOTAM websites? I figured out there are currently 2 different FAA websites for NOTAM online search:

FAA FNS NOTAM website available at https://notams.aim.faa.gov/
FAA PilotWeb NOTAM website available at https://pilotweb.nas.faa.gov/

What is the difference of each one? Which one is better to use? Do both of them provide information about Distant (D) NOTAMs, Local (L) NOTAMs and FDC NOTAMs?

I got this response via email from the FAA:

  PilotWeb is considered a Legacy Application based on the USNS, United States NOTAM System. The FNS, Federal NOTAM System, NOTAM Search is a new application. Many Legacy applications will eventually be replaced with the newer FNS applications over the next year. Both applications should be able to provide you with the information you are looking for.


Can airplane performance be increased by cruising "on step"? Old timers swear aircraft performance can be increased by getting an aircraft "on step" similar to how boats are operated.

They claimed a couple extra miles per hour (airspeed was in MPH then) were common. The "step" was alleged to be a "just-right" angle of attack which
minimized drag and allowed an airplane to cruise at a higher airspeed than normal on the same power.

Can airplane performance be increased by cruising "on step"?

The Pilot Training Manual For The C-54 Skymaster has this to say about it:

The manual is available at Archive.org


Is a subsonic scram-jet reasonable? By placing a de laval nozzle at the inlet, can the resulting supersonic airflow allow a scram jet to operate efficiently?

First let's clear up some things:

A SCRAM jet is a Supersonic Combustion RAm Jet, where the flow speed in the combustion area is still supersonic. Efficient combustion needs low speeds, hence a supersonic combustion is not a good solution to maximize efficiency. It needs rapidly mixing and burning fuels like hydrogen, lest most of the thermal energy release happens when the gasses have left the engine.
The operating principle of all aircraft engines with continuous combustion is that the kinetic energy of the flow is converted into potential energy, namely pressure. This pressure is needed to convince the hot combustion products to leave the engine at the rear end, where the pressure drops as the flow is accelerated again. If the engine flies at subsonic speed, the first area where supersonic flow is possible is in the convergent-divergent nozzle. Normally, pressure recovery is too small at subsonic speed, and either some turbo machinery or an oscillating pressure wave is needed to increase compression.

A de Laval nozzle (first developed by Ernst Körting in 1878) is a fixed convergent-divergent nozzle and needs high inlet pressure to function. Placing it at the subsonic inlet would require a near vacuum at the outlet to make it work. Using it in combination with a Ram jet would result in separated, subsonic flow with little pressure recovery in the combustion area, and very little thrust could be produced. In principle such an engine would run, but I doubt that it will even produce enough thrust to result in a net thrust gain. Efficiency would most likely be negative.


How do rotorcraft achieve lift? How do rotorcraft (helicopters, and other rotary aircraft etc.) achieve lift?
I mean, obviously the rotor. But who knows the specifics?

What are the physical, mechanical requirements of a rotary blade (propeller?) to achieve sufficient lift to carry

its own weight and
the weight of the vehicle?

A vehicle moving within a fluid may control its velocity by reaction, by accelerating a mass of that fluid in a convenient direction, and at a convenient rate. Using a wing is an excellent way to achieve that; birds and airplanes are able to fly by using wings that accelerate air down- and rearwards, and a propeller is nothing but a set of slender wings attached to a rotating hub.

In order to achieve a given thrust, that propeller must have a convenient size, and has to rotate at a high enough speed, so that it accelerates a mass of air and the change of momentum of that mass of accelerated air is transformed into a force that we call thrust. The magnitude of that change of momentum is proportional to the mass of air moved and to its change of velocity.

The rotor of a helicopter is just a large propeller that accelerates air downwards (and also rearwards, and sideways too, by means of a control called 'the cyclic')


Where to find fuel type & fuel consumption info for PW 1000G engines family? Where I can find the information about fuel type and fuel consumption for PW 1000G engines family?

In this presentation from 2009 PW quote savings of 140 gallons on a 500 nm trip. I presume they are comparing it to current engine options such as the IAE V2500.


What is needed to take off in CAT IIIb weather and how is it done? Landing is possible down to 150 ft visibility and no useful vertical visibility using CAT IIIb ILS. This relies on ILS not only for navigating to the runway, but also for maintaining runway centreline during roll out down to taxi speed.

So is it also possible to take off in such weather and if so, how is it done?

(edit) Answer to Who authorizes low visibility takeoff operations for airlines, and what is required? mentions take off is possible down to 300 ft RVR with a "takeoff guidance system". So more specifically, how does that work?

Under the US FARs (at least part 91) nothing special is required to take off in CAT IIIb weather besides an operational (and IFR-legal) aircraft and pilot. As mentioned elsewhere you can legally make that Zero/Zero takeoff where you can't even see the runway under your nose.

It should go without saying that doing so would be incredibly stupid (we (and the FAA) have said so anyway), but from a technical standpoint there's nothing preventing the operation except the knowledge that you might run off the side of the runway into a ditch and bang up your aircraft and passengers.

In terms of what would be required to make the takeoff safely, without running off the side of the runway into a ditch, I'd posit that you would need the same capabilities as you'd need to make the CAT IIIb landing safely: Aircraft systems that let you reliably track down the centerline for takeoff (using the ILS or something of equivalent accuracy for guidance, and runway centerline lights).

You would also need a reliable way to get from the gate to the runway, so taxiway centerline lights & stop bar lights are a must, and probably ASDE-X or its functional equivalent with a controller monitoring it to help ensure you don't taxi into another aircraft.

All of the above is predicated on, among other things, being able to see the lights I mentioned. The "takeoff guidance system" mentioned elsewhere adds synthetic vision into the mix which further enhances safety (and in the airline world allows takeoffs down to 300ft RVR). From what I can glean from the Rockwell-Collins marketing material their HGS seems to be able to provide "follow the green dots" taxi guidance (and presumably runway centerline guidance for the takeoff roll as well), providing redundancy for the lights I described above to help the pilot ensure the aircraft is going where they want it to.


Would a 90 kg object jettisoned from an aircraft create a detectable movement? I was reading the description of an old hijacking which has this snippet of interesting information:

  After takeoff Cooper told Mucklow to join the rest of the crew in the
  cockpit and remain there with the door closed..... At
  approximately 8:00 pm a warning light flashed in the cockpit,
  indicating that the aft airstair apparatus had been activated.... The crew soon noticed a subjective change of air
  pressure, indicating that the aft door was open. At approximately 8:13
  pm the aircraft's tail section sustained a sudden upward movement,
  significant enough to require trimming to bring the plane back to
  level flight. At approximately 10:15 pm Scott and Rataczak landed
  the 727, with the aft airstair still deployed, at Reno Airport....an armed search quickly confirmed that he
  was gone.

Would a 90 kg man jumping off the aft stairs of a B-727 in flight create a detectable "sudden upward moment". Not just a slight one but "significant enough to require re-trimming"?

Doesn't sound like a fluke or the product of a vivid imagination because we further know that:

  An experimental re-creation was conducted using the same aircraft
  hijacked by Cooper in the same flight configuration, piloted by Scott.
  FBI agents, pushing a 200-pound (91 kg) sled out of the open airstair,
  were able to reproduce the upward motion of the tail section described
  by the flight crew at 8:13 pm.

The full story is here:

https://en.wikipedia.org/wiki/D._B._Cooper

I'm estimating the mass of a fully-fueled B-727 as about 60,000 kg. A detectable perturbation by a 90 kg ejected body sounded a tad unlikely.

But I'd love to see a more accurate calculation. I suppose the center of gravity and the long lever arm for the aft stairs location will matter?

PS. It seems far more plausible to me that the movement detected was actually due to the aerodynamic forces on aft stairs and not the effect of the ejected 90 kg mass. The only reason I was rejecting this explanation was that the timing seems off if we are to believe the flight crew report:

They seem to have detected two events: A pressure change and later this reported sudden movement. So the movement does not seem correlated in time with the aft stair deployment.

Yes

It's not just weight, it's also aerodynamics. First let's assume that the aircraft was trimmed slightly nose-heavy (no passengers), therefore it's trimmed slightly "tail down" anyway

When the stair was first opened, it would have been held partially closed by the airflow under the fuselage - it's not heavy enough alone to extend fully against a 100 knot wind.

There was then a two-part change from Cooper leaving the aircraft - one of him walking down the stair, pushing it into the airflow and acting much like the elevator.

When he then jumped, the loss of his weight at the very back of the aircraft, along with a presumed "push" against the door, pushing it further into the airstream, would have simultaneously jolted the tail up, then reduced the weight at the very back of the tail "lever".

90kg doesn't sound like very much, but when it's at the very, very back of quite a long lever, and when combined with the airstair, the results seem perfectly reasonable and, indeed, were proven by the FBI.


What qualifications are required for an authorized flight instructor to teach IFR in AATD simulators, in the U.S.? I'm from Brazil, and I am working on an IFR certification process via AATD Training Course. We are having problems with the flight instructors; they must have valid IFR and CFI licences.

The instructors are pilots with more than 10000 hrs, that have already flown heavy jets and executive jets.  Our national agency is not accepting our training program because they don't fly anymore and they don't have valid licences.

I would like to know how the certification process works in other countries, such as the US or in Europe.

To provide instrument instruction the instructor must posses a valid CFI certificate with an "instrument airplane" rating.  This is irrespective of the type of training device or airplane used with the caveat the instructor needs to be rated for the airplane (either flown or being simulated).  In other words, if you cannot instruct in an airplane, you cannot instruct in a training device either.

The applicability of using the AATD is more of a program certification than an instructor pilot certification issue as there are different levels of training and special certifications for certain levels of training devices and simulators.  See 14 CFR 61, 141, 142 for details about training programs and AATD use.


What determines the maximum altitude a plane can reach? What factors determine the maximum altitude for a plane?

Is it limited by wing design, engine thrust, and so on?

Is there a formula by which one can calculate the maximum altitude a plane can reach?

The higher you get, the lower the density of the air becomes. This lower density results in a lower lift being generated for the same airspeed and angle of attack. Effectively, the higher you fly the higher your minimum speed becomes. So while climbing, your speed needs to increase to compensate for the lower air density. As long a you can fly faster, the lower density at altitude can be compensated for.

Basically there are two things that limit your maximum speed: thrust and speed of sound and with that your maximum altitude.

First is thrust; the higher you get, the lower the thrust your engines deliver. You might note that drag goes down with the air density as well but since you are flying faster and faster during the climb the drag doesn't decrease at all. If your maximum altitude is limited by thrust then at some point during the climb the thrust and drag are getting close to equal and that is where the climb stops. When you can no longer climb with more than 100ft per minute (for propeller aircraft) or 500ft per minute (for jet / turbofan aircraft) you have reached your service ceiling. If the aircraft maximum altitude is determined by thrust, the absolute ceiling will take very long to reach.

At high altitudes air breathing engines will get difficulties eventually. Due to the lower air density the mass flow through the engine is reduced up to a point where it causes a flame out.

The other limitation is the speed of sound, at least for subsonic aircraft. In the process of generating lift, air flowing over the top of the wing is accelerated. At one point, when the aircraft is still flying below the speed of sound, shock waves will start to form over the wing. This results in increase of drag and reduces the lift. So provided you have enough engine power at your disposal you can climb to an altitude where your minimum speed is also your maximum speed. This is called the coffin corner. In the coffin corner:

if you fly any faster, you will exceed the maximum Mach number ($M_{mo}$) of your aircraft, resulting in high speed buffet, vibrations and possible loss of control.
if you fly any slower, the maximum lift that the wing can provide will be insufficient to maintain altitude. Descent or the aircraft will stall.
if you fly any higher and you will be too fast and too slow at the same time.
if you turn, you increase the wing loading, thereby increasing the minimum speed needed to create the required lift. Also the outer wing will easily exceed the maximum speed while at the same time the inner wing is below stall speed. This can quickly develop into a spin.

Since accurate knowledge of engine performance, drag and wing characteristics of the aircraft is needed, there is not a simple formula to derive the maximum altitude for an aircraft.

Apart from the aircraft performance related limitations above there is a certified maximum operating altitude for the pressurized cabin. This takes into account the structural properties of the hull (pressure difference between inside and outside) and the achievable emergency descent rate in case of a depressurization event.


What does the SOG part of this METAR mean? CWKX 231700Z AUTO 12001KT M05/M07 RMK AO1 SOG 32 6023 SLP123 T10471068

Does anyone know what “SOG 32 6023” means?
Also why is that type of metar have a bunny icon in it instead of the M or the classic circle?

The RMK section:
AO1 = an observation
taken by equipment without a precipitation type discriminator (rain/snow)
SOG 32 = snow on ground, thickness 32 cm
6023 = beats me, I'll keep looking...
SLP176 = sea level pressure: what the current barometric pressure at measurement location would be at sea level, 176 stands for 1017.6 hPa (10 is omitted as persistent)
T10471068 =temperature and dewpoint in two four digit groups: first 0 or 1 for above or below zero degrees, then three digits for tenths of Celcius grades, so in the case above temperature is -4.7 deg C, dewpoint is -6.8 deg C


What is the energy demand of a secondary surveillance radar? I'm writing a report to see if it's feasible to power a secondary surveillance radar with wind energy. I'm having trouble with sizing the turbine but I can't seem to find an energy demand for a SSR anywhere. any help is appreciated.

What you propose is possible.  TCAS is essentially a secondary surveillance radar, and is a piece of avionics which doesn't break the bank power wise. In a moderate traffic environment, I have seen 3 to 5 amps at 24VDC.  I am sure it is higher in a dense environment.  The interrogation power requirement doesn't go up but processing the returns may take more power.

5 amps at 24VDC is a modest power requirement for a mid-sized wind energy system, therefore at first blush, what you propose is quite possible.


Again, where is the pivot point in pitch In regards to recent question about neutral point, as being defined as center of lifts from wing and tail, could one also define a "neutral point" for down forces CG AND down force (up elevator) from tail.
Lift force is now only from wing

Notice if the down force center is behind the lift center, the nose pitches up.  Would the center of this rotation be at the wing, at the center of all moments (between Clift and Cdown), or somewhere else?

Disclaimer:  I am no expert and if you get a better answer from one of the other contributors here, you should listen to them, not me.

From what I can tell, it looks like you're asking whether you can define a point that includes all downward forces on the airplane, including center of gravity and tail downforce.  As I understand it, yes you can, and this point is center of gravity, which includes all the associated downward forces.

The airplane then would pitch about the center of gravity, as it usually does.


How precisely are airspace borders defined? I'm studying for the commercial drone certificate. In Tucson, AZ the class C airspace covers about half of the city, but the charts don't list the exact point that it ends. Here's a portion of the VFR chart:

How exact are these airspace borders? Could one city block north or south get me in trouble if I don't check in with ATC?

The boundaries are defined more precisely than the chart can show. What you see on the chart is a visual representation of the text published in JO 7400.9Z (or the most recent version of it):

  AWP AZ C Tucson, Davis-Monthan AFB, AZ
  Tucson, Davis-Monthan AFB, AZ
  (lat. 32°09'59"N., long. 110°52'59"W.)
  Tucson International Airport,
  AZ  (lat. 32°06'58"N., long. 110°56'28"W.)

  That airspace extending
  upward from the surface to and including 6,600 feet MSL within a
  5-mile radius of the Davis-Monthan AFB to the points where the 5-mile
  arc joins a 5-mile arc from the Tucson International Airport, AZ,
  Class C airspace area, and that airspace extending upward from 4,200
  feet MSL to 6,600 feet MSL within a 10-mile radius of Davis-Monthan
  AFB to the points where the 10-mile arc joins a 10-mile arc from the
  Tucson International Airport Class C airspace area.

So in theory, if you're at 5 miles and 1 foot from that lat/long point then you're outside the class C's inner area. But the chart has to show that information in a way that's usable for practical purposes, which means that there has to be a visible line on the chart and that line has thickness. It looks to me like the airspace boundary lines on the chart are roughly 0.25nm or about 1500ft thick, and I have no idea where the boundary really lies on it. You simply have to consider that as a 'margin of error' in this case and plan accordingly. If in doubt, definitely contact ATC.

As for getting in trouble, 1500ft is probably too close for comfort for a manned aircraft, and ATC reacts on what they see on their radar, not what you see on your GPS. It's an interesting aspect of this question that you can probably be more precise with a UAV than a manned aircraft, and 1500ft might seem like more than enough buffer for you. But again, if you have any doubts or questions I would ask ATC directly.


How often are turbine blades in jet engines replaced? How often are the turbines in the hot section of the jet engines replaced due to deteriorated TBC? or just how often are they replaced? lets say for CFM56-7

So this article, says that the average brand new CFM56-7 will go 18,000 cycles (i.e. flights) before its first shop visit.  You can't replace the turbine blade on-wing, only in the overhaul shop.  So we could say that the blades would last at least 18,000 flights, potentially longer.


Can "Center" provide VFR flight following? Whenever I've requested VFR flight following, I've always requested it from So Cal Approach/Departure because I'm usually flying within their reach.  If I'm flying outside the reach of So Cal Approach (out in the desert), can I contact Los Angeles Center for VFR flight following?  If I do this, the frequency for contacting Los Angeles Center doesn't seem to appear on the VFR charts, but is shown on IFR low charts.
Also, does the radar coverage of the various "Centers" cover all of the continental US, or are there remote areas where Center's radar and radio communication can't reach?

Any US radar facility can (and will, workload and coverage permitting) provide VFR Flight Following, whether Approach/Departure or Center.
Look up the airport you are departing or, if already airborne, the nearest airport in your general direction of flight in your A/FD, EFB or (if you’re lucky) glass panel. The App/Dep lines will give you the frequency and name of the facility to call in that area.
The coverage problem is mostly an issue of altitude rather than range. Center radar and radio sites are further apart, so due to terrain and the curvature of the Earth, they may not be able to see/hear you if you’re too low. Typically 3,000 AGL is high enough, but if not, just keep climbing and try again in a few minutes.


How should a newly minted instructor sign an endorsement? A newly issued flight instructor certificate often has the word "PENDING" in the certificate number field.

In 8900.1 Flight Standards, Volume 5, Section 1, Section 5, Paragraph 5-112(c)(2)(a) Instructions are given that the temporary airman certificate for a flight instructor should be filled in with the corresponding airman certificate number with "CFI" appended.

In the event that does not happen, and the certificate number shows "PENDING", how should the instructor format their signature to make an endorsement prior to the issuance of a permanent replacement?

I would think the newly minted CFI should use the same words the FAA uses: "Pending". Can't go wrong with that.


When communicating altitude with a '9' in it, should it be pronounced "nine hundred" or "niner hundred"? It sounds a little odd, but trying to understand if that's the recommended way to communicate.

E.g. 9900
"Nine-thousand-nine-hundred"
vs
"Niner-thousand-niner-hundred"

In the UK, the RT rules for the ANO are in Cap 413 and section 2.13.2 states:

  All numbers used in the transmission of altitude, height, cloud
  height, visibility and runway visual range information which contain
  whole hundreds and whole thousands shall be transmitted by pronouncing
  each digit in the number of hundreds or thousands followed by the word
  HUNDRED or TOUSAND as appropriate. Combinations of thousands and whole
  hundreds shall be transmitted by pronouncing each digit in the number
  of thousands followed by the word TOUSAND and the number of hundreds
  followed by the word HUNDRED; examples of this convention are as
  follows:

Table 5
Number    Transmitted as              Pronounced as
10        One Zero                    WUN ZERO
100       One Hundred                 WUN HUN DRED
2 500     Two Thousand Five Hundred   TOO TOUSAND FIFE HUNDRED
11 000    One One Thousand            WUN WUN TOUSAND
25 000    Two Five Thousand           TOO FIFE TOUSAND

There isn't a specific example of NINER here, but given that the examples do actually use their prescribed pronounciations, you'd expect NINER to be used too.

I can't remember hearing it but the other conventions seem to be adhered to by professional pilots in the UK (we Sunday afternoon bimblers are not as good at it).  Non-native english speakers are very exact in their use of the published pronounciation

No doubt there will be a professional along in a minute, who can give you a more authoritative answer

EDIT: The reason I can't remember hearing "Niner-thousand-niner-hundred" may be because, in the UK, it would be above the transition level?


Two- and three-wheel undercarriage in the same airplane? Are there any airplane types which have the capacity to land in a tricycle configuration and a tail dragger configuration in consecutive landings? I have one example in mind but wonder whether there are more. Different versions of the same type don't count; it should be the same airplane without structural changes between landings.

The Fairchild A-10 has been designed with a lot of forethought, taking resilience against possible battle damage into account. If half of the tail is lost, the other half is sufficient to fly home. Also, if the gear cannot be lowered, the tires are still oriented the right way and stick out of the wheel wells enough so the airplane will land on them. Since the gear retracts forward, the wheels are ahead of the center of gravity in their retracted position, turning what is a tricycle undercarriage into a taildragger with gear retracted.
As reported here:

When retracted, the Thunderbolt II's main landing gear wheels remain partly exposed: During a belly landing, depending on the stores carried by the aircraft, the wheels that partially protrude from their nacelles can provide a cushion to absorb the impact with the runway; they can also reduce the risk of fire and, generally speaking, the overall damage to the fuselage.
In addition, when the gear is up, the wheels continue to guarantee the braking action, allowing the pilot to control the aircraft through differential use of the wheel brakes. That's why the MLG design is one the features that make the iconic aircraft so resilient.

Of course, it is prudent to drop all external stores before attempting this.

An A-10 Thunderbolt II sits on the runway after making an emergency landing March 25, 2008, at Edwards Air Force Base, Calif. (picture source). This view also illustrates nicely how the pulled-down wingtips will protect the ailerons from involuntary ground contact.


If a SID chart says "GPS... required", can the plane use a different GNSS? This US/FAA standard instrument departure says "Note: GPS or DME/DME/IRU required."

If the aircraft could tune into a different GNSS like GLONASS, could the pilot still legally fly the departure given that all other requirements were met?

The FAA's standards require the use of GPS, i.e. the American satellites. This is covered in AC 20-138D, Airworthiness Approval of Positioning and Navigation Systems. It defines GPS:

k. Global Positioning System (GPS). GPS is a U.S. satellite-based radio navigation system that provides a global positioning service.

It also says that GLONASS and other non-US systems are not supported:

GLONASS is not yet approved for IFR operations in the U.S. National
Airspace System
[...]
No FAA TSO exists for GLONASS, GPS/GLONASS, multi-constellation or
dual-frequency avionics. Therefore, adding capability for any other
constellation or dual-frequency capability must be accomplished as a
non-TSO function until appropriate TSOs are available.

Apparently there is some kind of working group looking into using non-US GNSS but it's not possible yet. See Appendix 8 of the doc for full information.


Autothrottle's control target during autoland I read some pilots manual which indicates that the AT retard mode will be active at 30feet AGL to retract the throttle to idle, but the flare mode starts from 50 feet AGL? Should the throttle to be retracted to idle before flare? If not what is auto throttle doing during the flare maneuver, try to maintain the speed?

The auto-throttle system of a typical airliner (like e.g. the Boeing 737) will maintain the approach speed (usually $ v_\mathrm{ref} + 5 \, \mathrm{kt} $, depends on the wind) during final approach. It should not reduce thrust before starting the flare because the speed could decrease too much, which could in the worst case result in a stall.
The Boeing 737 FCOM (v2 4.20.19 Automatic Flight - System Description, see also this answer for a full description of the autoland) says:

The A/P flare maneuver starts at approximately 50 feet RA and is completed at touchdown. [...]
The A/T begins retarding thrust at approximately 27 feet RA so as to reach idle at touchdown. A/T FMA annunciates RETARD.

So during the flare the thrust is decreased such that the thrust levers are closed at touchdown. This (together with the increase in pitch) will start to reduce airspeed. Ideally, the aircraft then touches down at or about reference speed $ v_\mathrm{ref} $. The thrust reduction should be smooth because the thrust-pitch-coupling of engines mounted under the wing will cause a pitch down moment, which needs to be counteracted with control inputs.


How do dry bays protect against fire? How do dry bays protect against fire, and do civil aircraft also have dry bays like military aircraft?

Yes, civil also aircraft have “Dry Bays” but they do not protect against fire. A dry bay is an area adjacent to a fuel tank that holds various components.

Some aircraft (mostly military?) have fire extinguishers or fire suppression equipment in dry bays but this will vary considerably with each type. (the B777 has no fire suppression in the dry bays)


Would the "AOA Disagree" light be the only way 737 MAX pilots could detect malfunctioning AoA sensors? Or would there be other warnings on the PFDs?

If there was an AOA gauge, then looking at that could have told him there was a problem without an AOA disagree light.

It'd be better than the AOA disagree light too. If the same mechanic maintained both AOA probes or their signals were sent through the same wire harness bundle, they could both agree on the wrong answer.


What counts as the wingspan of a tandem-wing aircraft? When calculating the wing-span of a tandem-wing aircraft, like the QAC Quickie Q2, which set of wings do we use for that value? There are two sets of wings, and they both provide lift. In the class, they just teach me that b is for wingspan, but they didn't go into detail about non-conventional aircraft. I am using that value to calculate the wetted aspect ratio of my aircraft

Because wetted aspect ratio $b^2/{S_w}$ merely improves on wing aspect ratio as an estimate of efficiency, for $b$ just choose whichever wingspan is largest.  That's good enough to compare one tandem planform to another.
You could get fancy and use a weighted average of the wings' spans, weighted by how much lift each one produces, with those in turn weighted by time spent in climb, cruise, and descent... but that seems against the spirit of a quick estimate provided by two easily measured numbers.


What is this Lockheed Martin plane? It's on a Lockheed Martin banner showcasing the company's iconic planes. The plane to the left on a crimson background is the U2, and the plane to the right on a blue & tan background is the C130.

It looks like a prototype UAS.

Lockheed Martin Sabre Warrior UCAV (concept):

Source

Source

From Defence Forum India:

  The Sabre Warrior drone is 46 feet long, with a 36-foot wingspan,
  capable of taking off with 30,000 pounds of load using a 22,000-pound
  trust afterburning turbofan engine. It has two modular payload
  sections, which can be changed by soldiers in the field. Each bay can
  handle one 2,000 pound or two AIM-120 AMRAAM missiles or 10 smart
  bombs or sensors, or even fuel for extended range missions—”even
  while this thing is air refuelable.

  Its twin nose can also hold multiple sensors, which are
  interchangeable. And it is designed so there could be a version with a
  cockpit, so they can send man version as an on-the-scene controller,
  overlooking over the unmanned versions.

The Raptor F-22 is a 5th generation fighter, Sabre Warrior the 6th.
Requirements worked with DARPA and USAF.
It has been considered for the UK Future Offensive Air System (FOAS), cancelled in 2005.
More on Youtube.


About F-35 hover/ roll posts responsiveness how responsive is the f35 in hover. especially in the roll axis.
What do think of the roll posts? is it a good concept?

The pilot controls have no direct connection to the attitudes (like roll) in hover mode.

Instead the throttle and stick is used to tell the computer if you want to go up, down, forward, back, left or right.

So for example pushing stick to left by some degree tell the computer to move left with a certain speed, the computer will handle all the roll for that. So pilot controls sideways speed, not roll.

Btw. this is probable relevant to your question: How does the F-35's roll posts work, and how does its engine turn down 90 degrees?


Can heated air be provided in the cabin in commercial airlines? Having travelled quite a number of times, there are times, when the cabin becomes a bit too cold, or people with certain condition get shivering quickly. In such circumstances and generally, is it possible to request for heated air in the cabin. If not the entire cabin, but atleast to specified seats, via the air flow controller on top of the head.

Before that, are airlines equipped to provide heated air, like in a car?

The fresh air vents near your head at each seat can not be adjusted for temperature individually.  Cabin temperature is controlled. Just ask a Flight Attendant to warm it up as they have a control panel to adjust cabin temperature by zone.

Most modern airliners use bleed air from the engines to power two Air Conditioning Packs which circulate cooled or heated air throughout the cabin.

Environmental control system (aircraft)

B777 Air Systems


What's a Class F cargo compartment? Apparently, the Aviation Traders folks worked with EASA to define a special type of cargo compartment, known as a class F, during their work on Iron Maiden's touring airplane.  Just what is a Class F cargo compartment, and how does it differ in safety properties from the large class B compartments used on earlier combi configured aircraft?

Here in this amendment to the EASA CS-25 it says on page 4:

  ... for a new Class B cargo
  compartment definition as well as design criteria for a new Class F cargo compartment
  type. This latter class of compartment was introduced because whilst it was concluded
  that manual fire fighting was not feasible for larger compartments, alternatives other
  than just the existing Class C were identified.

And a bit further on page 5 (emphasis mine) :

  ... Further, a new Class F cargo
  compartment definition is added, which is not limited in size and which provides the
  means to control or extinguish a fire without requiring a crewmember to enter the
  compartment. This proposed Class F compartment standard accommodates the carriage
  of large amounts of baggage and cargo loads on Combi aeroplanes as well as in
  compartments of smaller sizes exceeding the new Class B definition. New aeroplanes
  designs can take advantage from the variable solutions under the Class F definitions to
  ensure an acceptable level of fire protection.

And more concrete:

  The AMC further provides guidance for usage of other fire
  protection means in the new Class F compartment such as Fire Containment Covers
  (FCC) or Containers rather than having a liner installed to contain a fire and to protect
  the critical systems and structure of the aeroplane.

I guess it's meant to allow storage of cargo in non-cargo areas (which do not have the adequate fire protection measures such as liners) if other non-traditional measures are installed (such as the Fire Containment Covers)


C172 models and panels design How many C172 models there are out there and what are the differences between them?

Which models have these "modern" (newer) instruments panel design like this one:

versus:

If you are asking “When did the Cessna 172s adopt the modern 6-pack layout, the answer is 1968. You can verify this by looking at for sale pictures. All of the 1968 panels have the normal 6-pack layout while very few of the 1967 do. The revised layout in the 1967s is obviously not from the factory. They aren’t completely lined up like in your picture for a few more years. If you care to know when, browse through some for sale listings.

Cessna 172 - 1967

Cessna 172 - 1968

Also,I have a copy of the 1967 Owner’s manual and it shows the old layout like in the first picture.


Is it possible to "pimp up your aircraft" with an audio system? Can aircraft be modified to have an enormous audio system, like the ones in cars? Has the FAA got any regulations on this (or maybe on in-cabin maximum noise volume?), would power be a limitation for the audio system?

While there are many great reasons not to do this it would seem from a cursory scan of the FARs that the answer is "Yes, you can." -- At least one company (Alto Aviation) is producing aircraft entertainment systems with relatively "pimped out" audio capabilities.

These systems seem more geared toward "cabin class" aircraft where the crew and passenger compartments are separated (mainly business twin/turboprop/jet aircraft), though I suppose you could conceivably install it in something like a PA-32 or Cessna 206, or even light piston singles if you wanted to.

Such an installation would be subject to the same restrictions as any electrical device installation (requiring a check to ensure it doesn't overload the electrical system, and verification that it won't interfere with navigation or communication equipment), and I would imagine some of the work required may qualify as a "major alteration" as a change to the "basic design of the electrical system" may be involved.
There may also be additional operating restrictions placed on the installed equipment (like "Not permitted for use during taxi, takeoff, or landing" to prevent it from being a distraction/safety hazard during critical phases of flight).


What is the reason for the strips on the nose of the Embraer E175 Recently I boarded a KLM flight with an Embraer E175, when I noticed the strips on the nose

(see image, marked with the black circle).

Own image

This Embraer E190 also has it:

Image source

Whereas this A320 does not have it, is it an Embraer specific feature? What is it for?

Image source

I believe this is a duplicate of another answer, but they are lightning arresters which conduct electrical charges away from the radome and avionics contained therein to the metal airframe where it can pass through and exit the aircraft without harm.


Are there roll control devices other than ailerons? With the little that I've learnt about aeroplanes, I know that the aileron is the control surface that a pilot use to roll the plane by decreasing the lift of one wing and increasing the lift of the other wing. And it's (aileron) generally located at the wing trailing edge.

Now, if the wing tip is made flexible (or hinged to the wing), can the wing tip serve the purpose of an aileron by lifting the wing tip upward or downward?

Yes, that will work. If the entire wing tip pivots, it simply acts as an aileron that takes up the entire chord of the wing.

Other alternatives to ailerons include:

Weight shifting. If you can shift the aircraft's center of mass left and right a significant amount, thus will cause the aircraft to roll in the same direction. This is how hang gliders turn.
Wing warping. Essentially the same thing as ailerons, but accomplished by bending or warping the wing rather than by pivoting a hinged piece of the wing. Early Wright aircraft did this, but I don't know of any modern aircraft that do. (Birds probably do this, too.)
Roll spoilers. By deploying a spoiler on just one wing, you'll cause the aircraft to roll in the same direction. Some airliners do this some of the time.
Sliding the wings left and right. Okay, I admit that I don't actually know of any aircraft whatsoever that do this. But if you were to slide an aircraft's wings left or right, that would cause it to roll in the opposite direction.
Cyclic pitch control. Only rotary-wing aircraft (such as helicopters) can do this. The rotor blades can be configured to change pitch depending on where they are in the cycle, and this can produce a roll. Cyclic pitch control is the main way that helicopters are controlled.
Yawing and using the dihedral effect. An aircraft doesn't actually need any roll controls at all if the wings have a significant dihedral angle. Instead, you can roll the aircraft by yawing it into a sideslip; the dihedral effect responds to the sideslip by rolling the aircraft. A lot of RC aircraft use this method, as does at least one ultralight aircraft, but it's not a great way to go, because sideslips produce drag, and they can produce a "snap roll" in the event of a stall.


Resultant force vs AoA, pictures? Interesting to see how resultant force point backward from 0-10 AoA and point forward from 10-40 AoA in respect to vertical of chord line.

I find picture(below) very rare in aero-books,if someone have more this pictures,please can you upload?
(Doesnt metter which type of airfoil is..)

The top picture is from Otto Lilienthal's book "Der Vogelflug als Grundlage der Fliegekunst", published in 1889. The two diagrams are a polar plot of the resulting aero forces for several angles of attack, and the polar angle is measured relative to a line which stands orthogonal on the airfoil chord. This plot type is the reason why we still call a plot of an airfoil's lift and drag a polar plot even when using Cartesian coordinates.
Fig.1 shows the angle of attack on its outer arc and the resulting force vector hits this arc at a lower angle for AoA < 40°, showing that there is some forward component of the resulting force relative to the orthogonal on the chord line of cambered surfaces. This angular difference is singled out in Fig. 2 where the arc of Fig. 1 is collapsed into one point such that the fan of vectors allows a direct comparison of their direction. Between 15° and 20° AoA this forward component reaches its maximum.
The results were obtained by rotating wing models around a vertical axis. Those models had a low aspect ratio, so their stall angle is quite a bit higher than what you read today from a wind tunnel test where an infinite aspect ratio is simulated.
Today's plots don't show a resulting forward force component anymore because we define lift as the component orthogonal to the direction of flow and drag as the parallel component, plotting one on the Y-axis and the other on the X-axis of a Cartesian system. Lilienthal only plotted the resulting force and used the orthogonal to the chord line as the reference for the polar angle, so you would need to split the forces in the diagram by use of the cosine of the angle of attack for lift and the sine for drag. But converting a given table of lift and drag coefficients is easy with a spread sheet, so you can generate as many of those plots by yourself, if you like.
The lower plot shows the lengthwise drift of the center of pressure over angle of attack, with resultant aerodynamic force vectors added. A similar plot can be found here, only that the angle of attack varies over span so the local center of pressure for each section shifts back with increasing wing station as long as lift is positive and for negative lift approaches the wing from infinitely far forward.
This kind of plot shows the resulting aero force acting at a point where it is free from any moment. The direction of the vector is again orthogonal to the chord line and shows how much in-plane force component exists at high angle of attack before the airfoil stalls.


What is the difference between a positioning flight and a ferry flight? What's the difference (for the purpose) between positioning and ferry flight?

A positioning flight is a flight for the sole purpose of positioning the aircraft to conduct another flight from another airport. This is often done when the aircraft finishes its day in one city, but is needed in a different city the following day because another plane has broken down.

A positioning flight is technically a type of ferry flight, however the latter is a more broad term. Examples of ferry flights include delivery from the manufacturer, or flying to a different city for heavy maintenance.

Both flights are generally conducted without fare-paying passengers on board, but sometimes extra airline staff are carried.


Do Flight Simulation Instructors stop the simulator before a simulated crash? There has been quite a lot of debate in healthcare simulation communities around whether or not to allow a simulated patient to die during training because it might negatively impact the intended training outcomes.
Do flight simulation instructors similarly stop the simulator before the simulated plane crash to avoid the student being negatively impacted (traumatized)? Is this common practice?

I would say that crashes happen fairly frequently on initial type courses where new pilots are moving up to jets, and mainly on what are called "V1 cuts", where an engine is failed right at rotation or just after.
Many are not ready for the hard roll you get with a swept wing airplane when it yaws hard and you are slow to counteract it with rudder.  Before you know it, the wing tip is on the ground.  The instructor has to let the pilot try to recover and usually has to let it go all the way.
Otherwise, instructors will normally try to freeze the sim just before a crash because of time wasted waiting for the machine to reboot and having to reconfigure all the settings the instructor has set up for the session. This wastes very valuable and expensive sim time (I was also told it was hard on the equipment, but I'm not sure why).
It's not done to avoid traumatizing the students though.  One basic tenet of training is to make things memorable, so overall, a crash-in-the-box is a plus.
You can get a bit lost in the moment and forget you are in a simulator if the pressure is dialed up high enough (after 4 hours of abnormals and emergencies, you get wound up pretty tight; I used to tell people it was like spending hours in a cement mixer filled with bowling balls), but that effect is pretty superficial and when a crash happens, you know you are on an amusement park ride in the end, and you're not going to wet your pants in your last simulated moment of life.
In fact, aside from the visuals, which on the latest ones are pretty good but still not like a real view, after you get used to it, you start to become more and more aware of the physical differences from a real flight, like the motion sensations that don't quite fit what you are seeing (they really only simulate accelerations and decelerations and short term jerky up/down and rolling/yawing movements with any realism, which is good enough most of the time), and the sound of the hydraulic gear working below you, and that tends to kill the "lost in it" effect even more, and it becomes more and more like an amusement park ride as you go back for recurrent training.


What contra-rotating propellers would be appropriate for this engine? I am currently getting an X4 cylinder, 150cc, 4 stroke engine 3D CAD Modelled, this engine is initially being designed for Powered Paragliding (PPG), classified as experimental Aircraft, so no certification is required!

I have read several discussions here, that largely relate to large ridged winged Aeroplanes travelling at high ground speed.

PPG is a Low & Slow (22~75kph) Aviation sport, there are obvious differences with this project being;

Most PPG engines max. rev are from 7'000~12'000rpm.
Then a Re-drive is used to slow Prop down to approx. .88~.90 mach.

With a PPG, it is the Wing that sets the Speed in flight, not the engine!
A larger more powerful engine only provides a higher climb rate or maintain lever flight easier.

Most engines of similar capacity swing a 125cm (49/28") Prop at around 2'700rpm to under 3'000rpm.

The engine we are designing uses a unique engine that has replaced the 100yr old conventional crankshaft with a patented Contra-rotating Trilobe centre drive shaft (CDS) technology, that uses two trilobe cams, that strokes each Piston 6 times on One revolution, thus providing 3 combustions in two revolutions of CDS, this engine will not be revving over 3'500rpm maximum.

Engine is currently 12.5kg and 41cm width x 37cm high x 20cm deep.

I am planing on using Two 100cm (40") Contra-Rotating propellers!

I would appreciate it if anyone could assist/help me if this is an appropriate Sized Prop & what Pitch would be best ?

Contra-rotating props correctly address the problem of how torque
complicates the steering of a PPG.
(To solve this, others have even powered PPGs with large "quadcopters"
where two of the four props are counter-rotating,
despite the screaming of four small fast props.)
In conventional aviation two contra-rotating props typically have the
same diameter and pitch and speed.  For a PPG, keeping them the same size
is particularly useful to cancel torques.
To replace one prop with two, and otherwise keep everything the same,
we should not change the pitch speed or RPM, only the diameter,
to spread the thrust load evenly across both props.
The OP says that a similar engine powers a 49x28" prop at 2700 rpm.
The OP's engine redlines not much past that, so call the RPMs the same.
Then the prop pitch also remains the same, so prop diameter is the only thing left to vary.
Coaxial contra-rotating props are roughly 10% more efficient,
compared to non-coaxial props as on a conventional twin-engine airplane.
So each one of the pair has 45% of the load of the original single prop.
So each prop provides 45% of the thrust of the nominal 49x28" prop.
If all else is equal, thrust varies with the fourth power of diameter.
So we should scale the diameter of the 49x28" prop by 0.451/4 = 0.82.
So the engine should use a pair of 40x28" props.
Exactly the diameter that was guessed.


Why are military and civil aircraft landing gear generally so different? Why do military aircraft have a lower landing gear than civilian? I have in mind the difference between a Lockheed C-130 Hercules and a Boeing or Airbus.

The first possibility that jumps to mind is that one is more comfortable than the other, which is more robust. But would an aircraft designer reduce robustness to provide more comfort?

There is no difference between civil and military aircraft. Not the least because the civil and military transport aircraft are actually the same models. Many military planes have civil variants like Lockheed C-130/L-100, other military planes are derived from civil ones, e.g. C-135 is B707.

The difference depends on where the wings and engines are placed. All the aircraft actually have similar clearance from the ground. Just on some the lowest point is fuselage, on others it's the engines hanging down from the wings and on propeller driven ones it is often the propellers.

Cargo planes (like C-130, C-5, An-124 or An-224) are often built with high wings, so the fuselage is lower and therefore easier to load. This is also concern for regional airliners as they are designed to carry their own stairs. That's why BAe146, ATR-42 or Dash-8 are high-wing and other like Bombardier CRJ series have tail-mounted engines so they can also be lower. On the other hand low or mid-wing designs with wing-mounted engines have better aerodynamic properties, which is why that construction prevails for large airlines.


Will this simple equation (pic attached) produce a rough estimate of the top speed of a prop driven aircraft? Calculating the approximate top speed of a vehicle is straightforward.

$v = \sqrt[3]{\frac{2P}{c \cdot D \cdot A}}$

where

v = velocity of the vehicle
P = power of the engine
c = coefficient of friction
D = density of the air
A = the area of the front of the vehicle

Using this equation you can get a rough idea of the top speed of a car if you know its engine power, the body’s coefficient of friction and the area of its front profile.

Is it possible to use this same equation to determine an approximate top speed for subsonic aircraft?  No doubt engineers at Boeing have to account for 100 additional variables, but is it good enough to produce a decent approximation for props that fly less than 500mph?

Also does the picture I attached below show the correct way to account for variables $A$ and $c$?

If $c$ represents the friction along the entire surface of the aircraft does this suggest that all things being equal an aircraft with twice the surface area would have twice the coefficient of friction?  Or am I looking at $c$ incorrectly?

The short answer is no, that will not give you a very accurate estimate. As other mentioned, your equation does not include lift. Given some basic engine specs and aerodynamic properties, the top speed for aircraft can be estimated by determining the intersection of required power and available power. Available power is based on selected engines and propellers, and required power is based on the wing loading, lift coefficient, and other parameters that describe the amount of power required to sustain minimum lift.


Are these two objects in cockpit of Antonov - AN 225 Mriya fans for air? What is their purpose? In the above image, we can see two black objects that look like ceiling fans. This is just a reference image, but I am pretty sure that I have also seen small table fans mounted in cockpits of large cargo as well as high altitude flying planes with direction facing pilots in one documentary aired on tv.
Are they fans? and what is the purpose of their direction towards front glass in the pressurized air-conditioned cockpit?
Note - This question is not about FANS

They are indeed "Soviet style air conditioning". You will see them in other Eastern-bloc aircraft too. We even had them in the Shorts Skyvan. They are operated by a simple on-off switch and can be swiveled to point in the direction chosen by the pilots. The fan blades are made of rubber so they won't cause injury if one's hand inadvertently comes into contact with them. In this picture of the Skyvan, you can see the fan (arrowed) and the switch (circled).

Here is another airplane with the ubiquitous Soviet Air Conditioning system, Tupolev 154.


Why is the alternate static pressure lower than the standard static vent pressure regardless of the venturi effect on both? I understand that the higher relative airspeed around the body of an aircraft in comparison to the air within the cabin causes the cabin to experience a lower pressure.

However, I was just thinking about this concept, and it dawned on me that I have never questioned why this causes a difference in this particular discussion as it relates to standard vs. alternate static ports.

Are the standard static ports on the side of the hull not also experiencing this effect as air passes nearly perpendicular to the standard static port openings as it flows along the body of the aircraft?

Why is the venturi affect stronger around the cabin than it is around the static port holes on the side of the hull at the same indicated airspeed?

A venturi effect pertains to a change in pressure caused by a CHANGE in airflow velocity.  The static air pressure at the static port is not automatically lower just because the air is in motion there.

After all, the air within the fuselage (and within the piping leading to the static port) is in motion relative to the outside airmass, just as much as the outside airmass is in motion relative to the air inside the fuselage.

However, the overall dynamics of the flow around the fuselage do produce a net drop in pressure inside the fuselage, if it is unsealed.  There must be locations on the fuselage that would be bad places to put a static port because they are the planes where this pressure drop is being created by the overall dynamics of the flow.

Related answer-- In an unpressurized cabin, why is the cockpit ambient pressure lower than the outside pressure?

Another highly related answer-- Does the pressure at the static ports drop as the aircraft's speed increases?


Why are offset lead-in arcs used? Why are offset lead-in arcs used?

Image source: Google Earth, showing offset lead-in arcs.

There is little literature on the subject matter. I did research it a while back but I lost the PDF's, and videos. Research was inconclusive.

But I did learn that they guide only one aircraft type—selected radius can only accommodate a single wheelbase, radii vary. Initially I thought long airliners (A346, B773, and so on). But watching videos from observation decks in airports, even a 777-300 doesn't follow it. Whether taxiing in or pushing out, it wasn't even close to the line.

So if only one wheelbase can benefit, and it is not long airliners, why use it?

Image source: Google Earth, showing non-offset lead-in arcs.

Image source: Google Earth, showing straight lead-in lines.

All images from KJFK.

Not clear in the image in the question is the aircraft type the offset arc was laid down for. Example above is for the B777-300.

Some gates may have been designed for a certain type.

Based on that, a pilot of a shorter/longer [wheelbase] type can use the offset arc as a guide in turning in before/after it.

Thanks to Ron Beyer and mins for the comments that led to this answer.


How does a variable-sweep-wing aircraft keep wing-mounted payloads straight? So, a variable-sweep wing is an interesting design, but I am wondering: if the aircraft wing moves back or forward, then the payload's angle will also change. Is there a another rotating mechanism in the payload rack or wing to keep the payload straight?
For example, as demonstrated in this picture of a Tornado ADV  where the red lines are payloads. When the wing goes back it also changes the angle of the payload, unless there is another mechanism to keep the payload straight.
However, some might argue that payload isn't carried on the variable part of the wing, as on the F14 (See the link for reference).
But, there are numerous examples of aircraft that do carry the payload on the variable section of the wings, such as the Panavia Tornado ADV and Su-24 (see the links for references).

Mechanically this can be done using the simplest form of pantograph, as a hinged parallelogram with one end fixed to the fuselage and the other to the ordnance pylon. Or, I suppose you could implement a digital one.


What does the letter E signify for the E-3 AWACS? I came across the E-3 AWACS aircraft with the designation E-3, I could not find what the letter E means in E-3.

The E isn't exactly the short form of a word as it is a mission designation. In the US military's Tri-Service aircraft designation system, E indicates that the aircraft performs special electronic missions. Similarly, F implies the aircraft is a fighter aircraft and B indicates the aircraft performs bombing missions.

edit: here is the US military aircraft designation system


What's the point in escorting a threatened flight with two fighter jets? Two days ago I read in the news:

  Two U.S. fighter jets escorted a Canada-to-Panama flight back to
  Toronto after a passenger  allegedly threatened the plane Friday
  morning. The nature of the threat or why the passenger was agitated
  were not specified. CBS News  reported that the passenger told a
  flight attendant, "I have a bomb and I will blow up Canada."

What's the point of escorting the flight while it has been threatened by a passenger? How do they help to eliminate the threat?

Fighter jets escorting planes after various sorts of emergencies seems to be standard procedure in many countries, you hear about it quite frequently. It's sometimes implied in the media that if the situation would turn into a 9/11-type hijacking it might be necessary to shoot the plane down but nobody seems willing to fully clarify who could take such a decision and under what conditions on the record.

Now, in most cases, there isn't even a suggestion that a hijacking is happening but it's difficult to determine that in a timely manner and there are still two things fighters can do in other cases:

Get a visual confirmation of the situation aboard the plane (Is the plane damaged? The cockpit windows obscured? Who is in the cockpit?)
“Guide” a pilot who has lost communication to an airport.

Also, one factor is that being able to scramble jets is often seen as a basic requirement to assert sovereignty (witness the mini-controversy in Switzerland when it was revealed that the air force could not do it at certain times of the day) so politically it seems difficult to entirely give up on it, even if it could be argued that it's a waste of money for smaller countries to maintain an air force that does very little beside this type of missions.


What is the significance of a clover-shaped flight track? These are portions of two flights by a Cessna T206H on separate days:

The cloverleaf portion of the track was flown at around 8200 feet altitude. This plane is typically seen over the Los Angeles basin flying "lawnmower" patterns similar to those that might be used for sterile insect technique flights or aerial imagery collection flights.

What is the significance of this pattern?  Could it be for radio direction finding?

Edit: The aircraft is N915WC, which is registered to a company that specializes in supporting the intelligence community and law enforcement.  I didn't mention that initially because I didn't want to bias people's answers, and I was curious if the pattern was distinctive enough to identify without that information.

The flying looks too sloppy for a ground reference maneuver, a performance maneuver, or other required academic flying.  Given the concentration of the same flying in that same area and a review of the VFR sectional for the same area:

This is probably some kind of training flight.  If it is for law enforcement, I'm not sure what is going on here.  One possibility is that it is a student practicing attitude instrument flying doing 'A' and 'B' patterns under the hood with an instructor - or at least trying to.

Another possibility is just standard flight training activities, periodically turning to avoid terrain or congested airspace in order to operate within these confines.


Why does the APU Master Switch flash during a normal APU shutdown? Hi all and Happy New Year!!!

I have a question relating to APU shutdown procedures on Airbus A320. During normal APU shutdown sequences, I noticed that after around 1m20s, the FAULT legend on APU master switch will flash.

I wonder if the FAULT legend comes on to indicate APU intake flap is closed or any other reasons.

If it's the flap closing, you should be able to verify that from the APU ECAM page.

Based on the time frame you mentioned, most likely it's the simulated overspeed, which is part of the shutdown sequence and is basically the signal that closes the fuel solenoid (which you can also verify from the APU page).

APU flap closing comes later. For more on the shutdown sequence, see: Why would smoke enter the cabin if the batteries are switched off before the APU flap closes?

  The cool-down cycle lets the APU operate for 60 seconds at a low stabilized temperature. (...) Overspeed test occurs when the cool-down cycle is complete. The ECB supplies a signal to simulate an overspeed condition, that causes the fuel solenoid to close, and starts the APU shutdown. [emphasis added]

Source: APU training manual


What is the use of this jet aircraft with tanks between biplane wings? Looking at this soviet-like aircraft:

Source

It looks like a turbine engineer team met a biplane aerodynamicist team to create this strange aircraft! More over, it appears the two big pottery pieces are actually tanks.

What is the story and the use of this jet aircraft?

It is the Polish PZL M-15, as you can read in the image if you zoom in. From Wikipedia:

  The aircraft was designed in Poland in response to a Soviet
  requirement for a new agricultural plane.

Agricultural airplanes fly slow and having a shorter span increases the number of (air)fields you can land on. That's probably why they decided using a biplane design.

The two tanks outside the fuselage could have several reasons:

Placing the chemicals further away from the turbine and pilot
Reduce the bending moment at the wing root
Shorter pipes between the tank and the spray nozzles

All this, of course, at the cost of a lot of drag. As explained in the image source page, fuel consumption was three times larger than other agricultural airplanes and it had a really bad maneuverability.

The jet engine was a requirement dictated by Aeroflot, who wanted to use the same type of fuel for their passenger and agricultural airplanes.


Why do military aircraft use a different kind of aviation fuel? Regular airliners use JET A-1 fuel. However, I've seen that military aircraft, i.e., Airforce or Navy; use a different kind of fuel called JP-N, where N is a number.

What is the reason why this happens? If those other fuels have different properties, which are them to be better than the JET A-1 fuel properties?

Military aircraft can and do fill up on civil Jet-A -- this is common at facilities where the extra expense of providing both Jet-A and JP-5 or JP-8 fuel isn't worthwhile.  However, the military jet fuel types do provide some advantages over Jet-A:

JP-5 has a high flash point, improving its handling properties over civilian jet fuels.  This is important for fire safety in the close confines of an aircraft carrier.
JP-8 is similar to civil jet fuel, but also has extra thermal stability additives in it.  This allows for longer-term storage under harsh field conditions, and better resistance to deposit formation in places like afterburners and fueldraulic movable nozzles where the fuel is exposed to high temperatures even before it's burned.  It also may be specified for properties such as cetane rating that are essential for proper performance of diesel reciprocating engines run from JP-8.

(I'm omitting JP-4 from this discussion as it's a wide-cut fuel, comparable to civil Jet-B, and was retired from USAF service in 1995.)


What is the "area rule"? The "area rule" states that the supersonic drag on an aircraft is related to the total area on part of the aircraft. What is the exact definition of the rule? Why does this happen?

You might have heard of the elliptical lift distribution which minimizes induced drag for a given span and a given lift. Area ruling is similar, but here it is about the lengthwise distribution of cross-sectional areas of a plane, and it minimizes wave drag at Mach 1.

The first picture is from a Junkers patent of 1944: Junkers found out in 1943 that transsonic drag can be minimized by shifting the parts of an airplane around. In this case it was the EF-122, a research project which became the Ju-287. The easiest bodies to shift were the engine nacelles, that is why the end product has such odd engine locations. The drawing shows several shaded cross sections along lines which carry Roman numerals: Plot the sum of all areas along each line over the aircraft's length coordinate, and you get a distribution which must be optimized such that it has the maximum area for the smallest gradients.

The next picture shows how those plots look like. This is from a different source, so it shows generic wing-body combinations. On the left is an airplane with a fuselage shaped like a Sears-Haak body. A Sears-Haak body is an optimum shape for the biggest volume with a given wave drag and was discovered by Wolfgang Haak in 1941 and again by William Sears in 1947. The wings come on top and mess up the area distribution by creating a bump in the middle.

The right plot shows what can be achieved by taking all parts of the airplane into account. The difference is shown in the small center plot.

How this is done: Take away from the fuselage what is added by the wings. The result is a fuselage wich looks like a coke bottle. You can also add Küchenmann bodies; older airliners have plenty of them. Look especially at fuselages like those of the Blackburn Buccaneer, or  T-tails like those of the Illjushin Il-62 or the Tupolev Tu-154. Today, things like engine pylons or flap track fairings are used as Küchemann bodies to smoothen out the lengthwise area distribution, and if you look carefully you will see the coke bottle technique on the fuselage around the horizontal tail of many airliners. They don't fly at Mach 1, but close enough that area ruling makes a difference already.

The dawing below shows the general concept and the magnitude of drag reduction achievable:


Why does the FAA mandate a temperature indicator for all manned balloons? 14CFR31.85 ("Required Basic Equipment" for manned free-air balloons) requires an Envelope Temperature Indicator (ETI). This is a requirement of the FAA, not necessarily the manufacturer. Some balloon Flight Manuals do not even mention an ETI.

My question is, is there somewhere that explains why the FAA mandated a ETI for all hot air balloons, and how it's used with regard to the determination of load, overheating and gross lift with a hot-air balloon? (Might be more than one question! ;-))

There does not seem to be an industry standard, and the temperature inside a HAB is critical to flight performance and safety.
Best regards,
FFG

A hot air balloon (including the air in the envelope) has tremendous mass, so it takes a long time for a change in buoyancy to cause a change in vertical speed.  Watching for temperature changes on the Envelope Temperature Indicator will help a pilot anticipate changes in the balloon's vertical speed before they have actually had time to occur.

From page 7-4 of the FAA's Balloon Flying Handbook:

  "Ascents and Descents

  The temperature of the air inside the envelope controls balloon
  altitude. A balloon that is neither ascending nor descending is in
  equilibrium. To cause the balloon to ascend, increase the temperature
  of the air inside the envelope. If the temperature is increased just a
  little, the balloon seeks an altitude only a little higher and/or
  climb at a very slow rate. If the temperature is increased
  significantly, the balloon seeks a much higher altitude and/or climbs
  faster. If the balloon is allowed to cool or hot air is vented, the
  balloon descends.

  Even without the input action by the pilot, it must be remembered that
  the air inside the envelope is dynamic. The air mass is constantly
  moving within the confines of the envelope, attempting to seek a level
  of equalization. While it varies with each envelope, input action by
  the balloon pilot can take from 6 to 15 seconds to be realized as a
  reaction by the balloon. Planning the maneuver, anticipating the
  reaction time, inputting the proper burn, and observing the reaction
  must result in smooth and natural movement by the pilot."

Also, as another related answer has noted, under some conditions it is possible for a pilot to bring the envelope to an unsafe temperature by excessive operation of the burner.  Monitoring the Envelope Temperature Indicator allows this to be avoided.  For a given desired maximum envelope temperature, the outside air temperature determines the total gross lift that is available at any given density altitude, or the density altitude that can be reached with a given gross weight.  See the FAA's Balloon Flying Handbook for more.


What is the lift-to-weight ratio during takeoff for an ultralight? Lift to weight ratio at cruise is 1:1, what is the average lift to weight ratio during takeoff (rotation) of an ultralight with 2m/s as rate of climb?

Your (lift to weight ratio) load factor is less then 1 during climb.

In a climb or descend only some of the weight is counterbalanced by lift, another part is counterbalanced by thrust. So lift is less then weight in a steady climb. (But Thrust is greater then drag) To calculate the exact Lift to weight ratio we will need more information.


Question About Systemic Culture I have some question about Systemic Culture, so what is a systemic culture, and how systemic culture related to the aviation industry?

This one is easy. Go read the primary cause of the horrific crash of two 747's at Tenerife in 1977, and why the F/O of the KLM aircraft did not override the actions of the alleged highly-experienced captain, Jacob Louis Veldhuyzen van Zanten. Everything can be tied to a systemic culture that severely discouraged such actions, even in the face of an imminent disaster. This accident led to many changes in virtually all western commercial airlines to address this specific issue.


Lift and Drag Coefficients using load cell data I have a MAV and I need to find out the lift and drag coefficients for the wing and tail. I am not available with a wind tunnel so I will be using a load cell along with a separate wind source. Now I can measure forces on the MAV, airspeed at the wing and tail surfaces.

If I just use the angle of attack at the centre of mass then I can find the corresponding lift and drag coefficients (since there are two unknowns and two equations for forces along x and z axis). Now if I want to find separate lift and drag coefficients for wing and tail, for the corresponding angle of attacks, how am I going to do that? Once again I have force on the MAV in the x and z axis, angle of attacks for wing and tail, air speed, two equations of forces but four unknowns.

Please guide me resolve this issue.

I guess your design is a conventional one.

One approach could be integrating two load cells in between the tail and wing sections.

You can measure drag force and moment. And the moment may help you estimate the tail lift (with some serious assumptions though).

If space is a concern, you can try building a scaled model (2:1?) to test a larger model. The resulting forces and moments must be corrected for Reynolds effects.


Why does linear airfoil theory break down at hypersonic speeds? Why can't we just extend linear supersonic theory beyond M = 5? I've looked at NASA papers discussing everything from geometric effects, air disassociation, and thermal coupling, but no clear and concise explanation as to why we can't just extend linear airfoil theory beyond M = 5.

The linear theory makes certain assumptions in its formulation:

The flow is irrotational and isentropic.
The perturbations are small; i.e. the bodies are small at small angles of attack.

However, hypersonic flow violates these assumptions:

For a body in hypersonic flow (blunt body with detached bow shock), an entropy gradient is developed that varies along the distance of the body. It results in an entropy layer that persists all along the body.
In a hypersonic flow, the viscous boundary layer interacts with the shock and entropy layer and the kinetic energy of the flow is dissipated by the effect of friction within the boundary layer. Due to these viscous effects, the flow is no longer irrotational.

Note that the linear theory is not applicable if the flow is considered hypersonic. M > 5 is usually taken as hypersonic. Linear theory is not applicable in transonic regime either.


Why is the compressed air (from engine compressors) taken from High Pressure (HP) stage instead of Low Pressure (LP) stage? An aircraft that uses Turbofan or Turboprop engines would be taking the compressed air from 3rd stage and 6th stage (varies) and supplying it to the Pressurisation and Air Conditioning Kit (PACK). This air is cooled, filtered, and then supplied to the Fdeck, FWD and AFT cargo zones for temperature control and breathing. If my understanding is correct, PACK is a kind of compressor itself which cools the bleed air for circulation purposes.

Because the engine has got LP and HP stages (i.e compressors), why can't the engine send the LP stage air into PACK just for filtering? Because LP air is surely cool air which I understand still requires filtering. Without knowing further , it surely saves a lot of effort for installing more compressors and therefore, creating a more complex pneumatic system. Has this not been done or is there something I am missing?

KR,

Coming from the compressor section of the engine, the bleed air is sent to the precooler. Even air from the "low" pressure section needs to be cooled before it is sent to the air conditioning system. Here is a precooler from a CitationJet:

The page with that image notes that the bleed air is "hot enough to melt insulation and alter the heat treatment on aluminum alloys." The precooler reduces the temperature of this air and regulates the pressure to the pack system.

When the engine is at low power settings, bleed air is taken from the high pressure section. The engine must run fast enough that this provides enough pressure for the bleed system to operate properly.

Once the engine gets to a higher power setting, the bleed air is taken from the low pressure section. At higher engine speeds, this air still has the pressure required to run the bleed system.

Since the bleed system needs a minimum pressure to operate, compressing the ambient air to this pressure will always add a certain amount of heat.

Here is a diagram of the bleed system, to help visualize what is going on. Note that even after the air goes through the precooler, it is still hot enough to be used for wing anti-ice.


What US customs procedures must the pilot of a private aircraft follow when traveling in and out of the country? As the Pilot In Command of a private aircraft, what are the customs procedures that must be complied with before leaving, before returning, and upon arrival to the USA?

General

Each person leaving the country must be authorized to return to the US.  (ie. they are a US citizen or their visa allows them to leave and return to the US.)
Ensure that you have all required paperwork

Pilot license
Medical
Aircraft Registration
The aircraft must have a current customs decal.

Ensure that the aircraft is properly equipped

12" Registration Numbers
Transponder

Before Leaving the US

File eAPIS

eAPIS is required to be filed at least 60 minutes prior to your departure.
Other third party services (ie. FlightPlan.com, etc.) may make this easier if you do it a lot.

File an international flight plan

May be an instrument or a defence VFR flight plan

Before Returning to the US

File eAPIS (see above)
File a flight plan (see above)
Notify customs and obtain permission at least one hour prior to landing in the US.  Record the initials of the customs officer that you spoke to just in case they misplace your notification.

Note that if you are coming from locations "south of the US" (for the specific definition, see here), you must stop at the designated airport closest to your point of border crossing to clear customs (unless you have an overflight permit).

Upon Arrival in the US

You must land at an airport of entry.
Report immediately to the designated customs location
Do not allow anybody or anything to leave/enter the aircraft until the customs official gives your permission

The only exception that I know of to this are the South Florida airports where you are expected to take all people and belongings into the customs facility for inspection.

Discard any international garbage in the approved manner.
Provide required paperwork

A Customs Declaration for each arriving family

Wait for customs to specifically tell you that you are cleared before you attempt to leave.

Notes

This is not all-encompassing, please help add to and expand this list so that others may learn from our experience!

A TON of useful information is made available by the FAA in the Guide for Private Flyers.