Is it possible to become a commercial pilot if one suffered from depression in the past? I am 33, from Canada, and am trying to become a commercial pilot. I secured some funding and signed up for a college program...Then I came across a few articles detailing how past mental health issues can bar you from being applicable to fly commercially. My question is; If I have had a period of depression in my past, is it an absolute, that I will not be able to pass my medical evaluation test? Is there a time component element to it?...ie..If a person has not shown signs of mental illness for a certain duration of time, can they pass the aviation medical?
Also, I have not been prescribed or taken any mood altering medication in over 3 years.

Cheers

I really can't speak for the Canadian standards for Airmen Medical Certification, though I did find this on Transport Canada's website.

https://www.tc.gc.ca/eng/civilaviation/regserv/cars/part4-standards-t42402-1412.htm

Transport Canada also lists the following concerning anti-depressant medications (SSRIs).

https://www.tc.gc.ca/eng/civilaviation/opssvs/cam-ssri-347.htm

This sounds very similar to the FAA's position in that people who are diagnosed with depression requiring medication are prohibited from obtaining a medical certificate.

OK, don't throw yourself off a bridge just yet; there's some good news.

The good news is that this is applicable if you are currently on mood altering medications perscribed by a physician.  If you have a prior history of depression but are not currently on any medication, there is a good chance that Transport Canada could issue you a Special Issue medical certificate, if you are willing to go through all the extra paperwork and documentation with your physician.  You are going to have to document, probably with the written concurrence of your physician, that you are no longer depressed, your case history was acute, not chronic with recurring episodes, and that you no longer require medication to maintain a normal mood.  Transport Canada will probably issue you a Special Issuance Airman Medical Certificate, valid for about a year, which will allow you to obtain your license.  As long as you are not diagnosed with further episodes of depression during this period and your doctor can confirm this, TC will probably issue you a regular airman medical certificate thereafter.

What I would suggest is that you make an appointment with a physician near where you live who is a Designated Medical Examiner for Transport Canada and talk with them about what TC's disopositon is on disqualifying conditions for medical certification.  NOTE WELL: Do not - NOT - make the appointment so as to indicate that you want an official airman medical certificate examination; we do not want any kind of official diagnosis entered onto your permanent record with Transport Canada just yet; this will only complicate things and we need to know exactly what TC's position is on these issues BEFORE we proceed down that road.  Select a DME who is also a pilot and will tend to be more sympathetic to your plight.

I hope that helps and good luck to you on your future aviation endeavors.  There is hope for you.


How has CAD influenced aircraft design in the last few decades? I know that computer aided design was used extensively when designing the Boeing 777, are there any other good examples of aircraft where CAD was essential in the design process?

Are there any major leaps forward in aircraft technology that would have been impossible without CAD?

We used CATIA extensively in the design of the F-22.  It helped all the supporting "ilities" also in their tasks.  Great tool.


How does the environment influence the aircraft engine demanded thrust? When engineers design the power management of the FADEC, how do they set the required thrust when the pilot pushes the throttle to the TO/cruise/idle position?
I have read some papers, and I found that the demanded thrust is related to the inlet environment, but I don't know how to calculate the influence of the environment, and how to correct the thrust.

All modern engine control systems take 'environment' (most importantly inlet total pressure and temperature) into account.

Takeoff and maximum continuous thrust are normally limited by the turbine temperature (which is controlled internally) and N2 (high-pressure rotor) RPM. So such settings on the throttle usually preset a certain N2, and then the thrust will be whatever the engine develops in present conditions. However, this limiting N2 may, and often does, depend on the environmental conditions. The max max (takeoff) is usually a hard limit, but the max cruise N2 may increase with altitude (falling temperature/pressure). Thus when you are climbing with a constant throttle setting, the control system may increase the RPM - even though the actual thrust will be falling due to engine physics.

Idle thrust is limited by stability of the flame. Idle RPM on the ground may be substantially lower than what can be sustained in the air (at speed). Thus the engine control systems often have a weight-on-wheels input signal and apply different control on the ground, primarily with regards to idle power.

Idle can also be significantly affected by the amount of bleed air taken from the engine, but this is not quite the 'environment', I suppose.

Of course, real control systems are a lot more complicated, even if we consider just the environmental parameters. For example, they can have numerous logical rules like: "if idle is selected after having maximum thrust for more than X seconds, ignore the pressure sensor and hold its value for Y seconds", or some such.


What's a normal response delay for a paragliding vario? I'm a paragliding pilot with P4 licence and I've purchased a 2nd-hand FLYMASTER B1NAV flight instrument for XC flights – mainly for logging the flights (route, distance, max. speed etc). It is an Altimeter-Variometer-GPS combo. As you know, these devices warn the pilot with beeps during climbing and sinking.
I'm using the device for a couple of months but I recently noticed an interesting thing: When I enter the thermal I first feel the climb with my harness and risers. But the device starts to beep with a delay of 1-2 seconds.
Is this normal?
I know it's an old and discontinued product. I've looked into its manual, but couldn't find any info about the delay. I don't want to rate this device as "broken", but I cannot be sure.

That is probably normal.  I notice a similar delay when flying with my Brauniger IQ Comp vario (lately mainly in sailplanes.)  Minimizing the delay is why the latest varios incorporate accelerometers as well as barometric pressure sensors.  Sounds like you've already checked the manual to see if there is some way you can decrease the interval of averaging, upon which the primary visual display and audio tone are based.  That adjustment is definitely possible with some variometers produced for hang gliding / paragliding use, but not with all.
Another way to get a quicker response time is to buy a vario that is even older.  For example, check out the "Litek Hummingbird".


How accurate is inertial positioning? How is accuracy achieved in Inertial Positioning?  Is it possible to get 10 or 11 digits of accuracy without transmission of real-time corrections from a base (known) station? Is post-processing simultaneous data of Ref. & Rover required for getting the precise (10 & 11 digit) coordinates?

"Inertial GPS"

Inertial navigation is separate from GPS navigation. Inertial navigation senses accelleration and uses that to estimate changes in velocity and hence estimate changes in position. GPS is a GNSS system that determines position from timing of satellite signals. There's no such thing as Inertial GPS although there are systems marketed as sat-nav which can use inertial navigation when GPS is unavailable (e.g. when driving through a tunnel).

10th Character

Digits are about precision not accuracy. Any sat-nav or GNSS receiver can produce location digits to much greater precision than their accuracy.

The number of digits, and their implications regarding accuracy and precision, depends on the units being presented. For example, I have a handheld GNSS receiver that I set to display UK Grid-references for convenience in conjunction with Ordnance Survey maps. The meaning of the 10th and 11th characters in terms of positional precision is therefore different.

TQ
395012
775012

In this case, the 10th digit is something like kilometers north of the OS origin. Accuracy of ±1 Km can certainly be achieved by unaugmented GNSS.

It is probably better to state a desired accuracy in terms of distance on the ground - for example many handheld GNSS receivers will display something like "Accuracy: 23 feet".

Base stations

All GNSS receivers (including GPS, GLONASS, Galileo etc) use multiple satellites to determine their position. Typically three or four are required for a fix. Pure GNSS receivers don't use base stations.

SBAS capable receivers (such as those that can use WAAS, EGNOS, etc) use additional satellites to achieve higher accuracy. They do not directly use base stations on the ground. The additional satellites transmit positional corrections that have been gathered from ground stations but the GNSS receivers do not receive data directly from the ground stations.

Higher accuracy GNSS units are used by, for example, site surveyors. These are larger and more expensive and in some cases do use ground base stations for greater accuracy.

Aviation

Generally, I don't think aviators have any use for knowing their aircraft location to centimeter accuracy in flight.

A GNSS with SBAS (e.g. GPS + WAAS) can provide the accuracy needed for  precision flight approaches but Garmin state "Currently, GPS alone does not meet the FAA's navigation requirements for accuracy, integrity and availability"

Glossary

GNSS = Global Navigation Satellite System.

GPS = Global Positioning System, US operated GNSS.
Galileo = EU operated GNSS.
GLONASS = Global Navigation Satellite System, Russian operated GNSS.
BDS = BeiDou Navigation Satellite System, China operated GNSS.

SBAS = Satellite Based Augmentation Systems.

WAAS = Wide Area Augmentation System = US operated SBAS.
EGNOS = European Geostationary Navigation Overlay Service, EU SBAS.

GBAS = Ground Based Augmentation Systems.


What are the correct fixes for the MAX's pitch control systems? At this point, the ramifications of faulty data input from only one sensor into the MCAS system of the 737-MAX are well understood, having allegedly led to 346 deaths, losses of almost 10B USD for Boeing, losses of around another 1B USD for American and Southwest, skepticism about the FAA's oversight ability, and even a potential hit to overall U.S. GDP.

That's pretty bad. Even in today's business culture where many mistakes are whitewashed, explained away or "taken care" of by a few executive firings, it's still reasonable to conclude that had it known what was going to happen, the manufacturer Quality Control would have done anything in its power to identify and correct the issue before the planes first shipped.
Indeed, the concept (in hindsight) should have never left the drawing board.

Solutions could be as simple as releasing the software patch they claim is currently under test,  through programming not accepting data from only one sensor (not as an option), and better pilot training and education.

It could also be fixed by more organic solutions, such as :  adding several more AOA sensors, lengthening the fuselage, repositioning the engines (setting them a bit wider), and/or longer landing gear (see Constellation, Concorde, XB-70).

What would have to be done to the plane's design to make its aerodynamic handling equivalent or better than the 737 NG series (or any other modern airliner), without need of a late-stage corrective system?

The Max's problems had nothing to do with stall. The larger more forward nacelles caused shifts in the aerodynamic neutral point, only discovered during testing, that had an effect similar to shifting the center of gravity aft, and if you were holding a certain amount of stick force, say in a turn, keeping that stick force in would cause to nose to drift up unexpectedly.  This happened in certain configurations and speeds.  It was as if a whole bunch of passengers suddenly moved aft in a group and you were holding 15 pounds of back pressure and suddenly that back pressure would make the nose rise when you didn't actually change anything you were doing, and you would have to ease off some of the back pressure to compensate.

The behaviour in itself did not prevent the airplane from being certified if pilots were trained to recognize it.  But it was enough of a deviation from the other '37s behaviour that it put the common type certification at risk.  This results in a very expensive supplemental training burden on Boeing's customers.  MCAS was a software bandaid that used the trim system to make the airplane's behaviour mimic other 737s in the particular regimes where this was happening.

Boeing used an even stranger software bandaid on the 787-8, where the FBW system actively runs the normally dormant outboard ailerons to fix a wing vibration problem.  In the age of FBW this isn't all that controversial.

Anyway, there was a very fatal defect in the architecture of the system where it took data from only one AOA vane, because whoever did the system safety analysis decided that the failure mode where the system malfuntions due to defective AOA input was a low criticality failure (I think it was only classed as Major, not Hazardous or Catastophic).  It was classed as being equivalent to a stab trim runaway and depended on the HSTAB QRH procedure to deal with.

This allowed a mathematical risk justification for taking a signal from only one AOA vane.  This helps with system dispatch reliability, because if you have dual inputs and must have both, that's "anti-redundant" from a dispatch reliability perspective (two inputs are half as reliable as one).  Changing the system to have only one input doubles your dispatch reliability and if it's considered not that big a deal safety wise, it makes sense to do so. That's the main motivation for doing that single input architecture even though it was only more or less wiring and software differences.

The alternative to MCAS would have been physical redesign, maybe moving the operating CG forward which would have required a larger tail, or some other physical change, maybe something to the nacelles that would spoil the lift they were creating, that would've driven costs up and made the airplane way less saleable, and it would probably have killed the program.

In any case, notwithstanding all the other cockroaches that have scurried out from under the rug as it was lifted in the investigation, if Boeing had taken signals from both AOAs and lived with the need to put up with dispatch delays caused by having dual inputs where both must be present, none of this whole fiasco would have happened and it would be merrily doing its thing.  The safety analysis that was used to justify a single AOA input (and the FAA's failure to catch it) is at the root of all of it, in my opinion (having participated in supporting roles in similar crises with another OEM over the years).  Too bad really.


What is the standard report when pilots exiting and clearing the runway Let us say I landed on runway 7 and will exit the runway thru taxiway Charlie, is that a standard report like "(Aircraft ID) taxing clear RW7 at Charlie"?

Nitpick: that would be runway 07, not runway 7

The phraseology is mostly standardised, and in general consists of notifying the relevant unit that you have vacated the runway. At a small, GA airfield with AFIS in the UK the typical communication goes as follows.

  ATCO: G-ABCD Cleared to land Runway 07, wind 240 at 5
  G-ABCD: Cleared to land, Runway 07. G-ABCD
  ... controlled crash ....
  G-ABCD: Runway vacated at Charlie

This becomes a bit more formal at controlled airfields. In the UK, Cap 413 is the radio telephony communications bible. Secion 4.89 "Runway Vacating and Communicating after Landing" is the part you'e interested in. The communications would be more along the lines of (Note: CAP413 uses the name "Kennington" as a fictitious airport)

  Kennington Tower: BIGJET 347, vacate left
  BIGJET 347: Vacate left BIGJET 347
  Kennington Tower: BIGJET 347, when vacated contact Ground 118.350
  BIGJET 347: When vacated Ground 118.350, BIGJET 347
  BIGJET 347: Kennington Ground, BIGJET 347, runway vacated
  Kennington Ground: BIGJET 347, Kennington Ground, taxi to Stand 27 via taxiway Alpha


Cessna 172 steering system and torque link purpose How does the Cessna 172 steer while taxiing? Is it by using differential braking (braking one wheel at a time)?

Are there any connections between rudder or toe brake and nose landing gear related to steering?

What is the purpose of torque link in front of the oleo strut?

Does the nose wheel even turn?

The Cessna 172 (152, 175, 177, and 182 as well as others) all use steerable nose wheel by pushing (not depressing) the rudder pedals in the direction you want to go. If you want the nose to turn to the right, you push the right pedal forward, same with the left. You can augment this with differential steering if tighter turns are needed.

So there are actually 3 ways to steer the 172:

The nosewheel steering using rudder pedals. This puts pressure on the bungee system that turns the nose wheel left/right. Pushing the pedal doesn't directly move the wheel, you need to move the aircraft forward a little bit for the wheel to turn.
Differential braking can help make tight turns, this causes the nose wheel to "caster" or turn based on which direction you are attempting to turn the aircraft.
Some turning force is provided by the tail rudder, it isn't usually a lot but it is noticeable when landing.

  Is there any connections between rudder or toe brake and nose landing gear related to steering? What is the purpose of torque link in front oleo ?

There is no connection between the rudder or toe brake and the wheel (in the purest sense, the rudder pedals are also connected to the bungees for steering), the rudder pedals  move the bungee system that puts pressure on one side or the other of the torque link on the oleo strut.

  Does nose wheel even turn ?

Yes! All tricycle gear aircraft with a nose wheel must allow the nose wheel to turn at least a little bit. The 172 allows the rudder pedals to give up to 10° of wheel movement while differential braking will make the wheel move up to 30°, this is outlined in Section 7 of the 172 POH (I won't link the entire POH here, but this is the excerpt):

Source: 172SP Pilots Operating Handbook

If you update your question with a picture of the fairing you are talking about I can comment on that, but really it should be a separate question.


If the modern airliner was redesigned from scratch, would it look functionally different? If the modern airliner (Boeing/Airbus) was redesigned from scratch today without any need for "backward compatibility", would it look functionally different from the current design? And if so, what would be different?

You'll only get opinions here, but from 40 years in the business, my opinion is not much.  Airplanes are a balance of compromises and after much trial and error, dead ends, and false starts, a combination hits a sweet spot in the balancing act and that becomes a near universal configuration.  When someone deviates, it MAY create a new configuration paradigm, but most of the time the reasons the universal configuration works so well are revealed, or rediscovered, by deficiencies in the attempt to strike out on a new path.

And here we are, still building airplanes along the lines of the granddaddy of them all for this particular configuration, the B-47, 73 years later.  Virtually all of the improvements that have followed are related to engines, materials and electronics.

Interestingly, you have a kind of mirror image of the same thing in the bizjet world.  There, the tail mounted twin with fuselage hugging the ground is the design config sweet spot.


Where do I find a complete Volmet frequencies list for Europe? Is there any website or ,even better, book to buy to get such frequencies?

I have a list, you can download it here VOLMETS.I would really appreciate if you can help me confirm stations that are operational. Obviously depending on your location, receiver and antenna you will not receive all these.

The list is by no means 100% accurate and there may be stations that have ceased operations or are very sporadic in operation. Without others assisting it is impossible for me to verify each and every station.


How does ATC maintain separation between aircraft flying at different speeds? How are collisions avoided when 2 aircraft are flying same altitude and same direction but have different speed characteristics.

Example a B737 and an ATR are both flying at 25000 feet. 737 will cruise at 850 Km/h whereas the ATR will cruise at 550 Km/h and the 737 is approaching from behind.

How is this type of situation handled by the pilots and ATC?

My question is specific to airliners as I have seen from websites like flightradar there are thousands of planes flying at any given moment and was wondering how this problem is handled.

FL250 for a Boeing 737 in cruise at 850 kph/460 knots GS is an unlikely value. Aircraft in the same category of speed, such as the Boeing 737/747/767/777 usually fly at higher altitudes, e.g. FL300-FL400. Slower turboprop aircraft such as the ATR72 usually fly in the ranges of FL200-FL250. During cruise, airspeed will be matched by ATC for all aircraft where the trailing aircraft might catch up to the preceding aircraft.

ATC sees the ground speed on their radar screens and can thus compare and evaluate if they need to assign speeds to maintain separation.

(Image Source: What data does ATC see on their screens? - Speed: 395 knots GS)

R: DLH123, report mach number.
A: Mach .78, DLH123
R: BER456, report mach number.
A: Mach .79, BER456
R: BER456, reduce speed to mach .78
A: Reducing mach .78, BER456

The same principle applies to aircraft in the terminal area, the lower you get, the more will aircraft have the same groundspeed when assigning the same indicated airspeed, as air density and wind approach the same values. ATC will sometimes assign a slower speed to trailing aircraft if they need to achieve the same groundspeed at different altitudes.

R: DLH123, descend to 3000ft, reduce speed to 210 knots
A: Descending to 3000ft, speed 210 knots, DLH123
R: BER456, descend to 4000ft, reduce speed to 200 knots
A: Descending to 4000ft, reducing speed to 200 knots, BER456

For aircraft that still have significantly different groundspeeds on the same airway, ATC can also vector aircraft around the preceding aircraft and put it back in front or they can issue a direct that will achieve the same effect, changing the sequence of the aircraft. A climb or descend can be coordinated with the pilots, e.g. the trailing aircraft can be asked if they are able to accept a climb to another flight level, maybe even temporarily.


How much thrust is required for a Boeing 747 to "keep flying" at 4 km altitude? Not full power, just enough to keep the plane moving at 4km altitude.

The QRH (Quick Reference Handbook) contains a few tables for flight with unreliable airspeed. The one for holding comes closest to the situation you asked about:

(Boeing 747-400 QRH 20.2 - Performance Inflight - CF6 Engines)
As you can see, holding at 10000 ft altitude requires between 59.7% and 77.4% N1 depending on weight. You asked about 4 km, which is about 13000 ft, so a little more will be required.
There is also a table for cruise speed at various altitudes:

(Boeing 747-400 QRH 20.1 - Performance Inflight - CF6 Engines)
You can extrapolate the values shown here between 10000 and 20000 ft altitude to get the required thrust at 4 km. Note however, that the speed flown here is higher (290 KIAS or Mach 0.84) than the one required for maintaining altitude.
If you combine the information from both tables, you should get a good idea of the required N1 in your situation. The number will however strongly depend on the weight of the aircraft.


What is the answer to this question about aircraft position based on an NDB? An aircraft is intending to track from NDB ‘A’ to NDB ‘B’ on a track
  of 050° (T), heading 060° (T). If the RBI shows the relative bearing
  of ‘A’ to be 180° and the relative bearing of ‘B’ to be 330° then the
  aircraft is:

  A. Port of track and nearer ‘A’
  B. Port of track and nearer ‘B’
  C. Starboard of track and nearer ‘A’
  D. Starboard of track and nearer ‘B’

Yes, "D" is correct. A picture is worth a thousand words......


Is a rotary wing craft capable of supersonic flight? Just what the title states.

Since the Wright brothers, aviation technology for fixed-wing craft has advanced by an order or more. Rotary wing craft on the other hand (I know little about aviation; please correct me!) have advanced significantly by way of lift capacity, and maneuverability. Yet velocity has achieved nothing like the kind of advance seen in case of fixed-wing craft.

Is a rotary wing craft capable of supersonic flight?
How is it limited by contemporary technology?

Currently there is no rotary wing craft capable of supersonic flight.

Combined with the forward motion through the air, the rotating blades attack the air on one side and retreat backwards on the other.  As the aircraft moves faster this poses 2 problems:

The retreating blade has a point of zero air speed, starting from the axis at hover and moving to the tip with forward speed, an effect known as P-factor.  Eventually a large portion of the blade has negative airflow (backwards to what it had when hovering) causing loss of lift control on that side (there may still be lift, but the pitch of the blade has little influence). The craft will roll (and I believe gyro forces will bring the pitch up, and the craft will recover)
The advancing blade will go supersonic, starting from the tip. Aerodynamics change.

There are ideas of new blade actuators that can change the blade for 1) reverse airspeed and 2) supersonic aerodynamics.  As you have noticed, nothing has panned out so far...


In what airspace may gliders fly in clouds in the UK without an IFR flight plan and without contacting any air traffic control facility? In what airspace may gliders (sailplanes) legally be flown in clouds in the UK without an IFR flight plan and without contacting any air traffic control facility?
Also, how high does this class (classes) of airspace typically extend in areas where cloud-flying in gliders is commonly practiced?  (A general range is fine--the intent is to allow the reader to compare and contrast with Class G airspace in the US1, which rarely extends higher than 1200' AGL.)
Footnotes--

Cloud flying in gliders in the US is rare for several reasons, including the fact that the pilot would be required to have an instrument rating in airplanes (see FAR 61.3(e)(3)).

Some other related ASE questions and answers of interest--
Can you fly a glider in a cloud on primary instruments?
Can you fly a glider in a cloud on primary instruments?
Can you fly a glider in a cloud on primary instruments?
"Teaching Instrument Flying"-- Instructor Training Notes-- Dartmoor Gliding Society
"Instrument Flying Training Notes"-- Dartmoor Gliding Society
Cloud Flying endorsement webpage from Motorglide.co.ok

Broadly speaking, the UK is Class G, excluding airways and terminal areas, from surface up to FL195.  Can hop in your aircraft and fly IMC without talking to anyone to your heart’s content


What airplane does this vintage instrument panel come from? Can anyone please tell me what this is from?

It looks like it's military. I have a few panels that came with this and gauges (not if it's a b-16)

The shape makes it clear that this is from a single seater or tandem aircraft. This makes a glider very likely, which is supported by the "Vario" engraving over the column of small holes on the bottom right.

A little googling then brings me to this page and the assumption that this panel is from a Schempp-Hirth Standard Cirrus, Serial No. 176. The plane was badly damaged at Minisink, NY on October 23, 1976 in a botched landing and consequently written off. At that time it was registered as N11JY.

Schempp-Hirth Standard Cirrus (picture source)

Standard Cirrus instrument panel (picture source)


Can a UAV defend itself? An unmanned aerial vehicle (UAV) was shot down by Turkish aircraft, which made me wonder, whether the Turkish pilots faced any defending moves from the UAV, or once they found it, taking down was a piece of cake?

The existing answers are, of course, correct that most current UAVs do not have much in the way of options for defending themselves against attacks by fighters. This, however, is due primarily to the design missions of most current UAVs, which are reconnaissance and attacking lightly-defended ground targets. Their mission is literally to be an expendable recon or attack aircraft, therefore it doesn't make a lot of sense to invest millions upon millions of dollars in giving them defensive capabilities. Even most normal manned recon aircraft will be short work for a modern jet fighter, with the typical use case being using actual fighters to keep enemies away from them. With a UAV, there's much less incentive to invest heavily in defending it, since they're generally much cheaper aircraft and losing them doesn't mean losing personnel.

Having said all of this, there's nothing inherent about being unmanned that makes an aircraft unable to defend itself. It's just a matter of most current UAVs being designed for use cases where they don't care all that much about defending it, so it's not worth equipping them with lots of excess available lift and thrust, extra sensors, weapons, etc.

There's nothing to say you can't design an unmanned fighter aircraft. For example, if the drone you're trying to shoot down happens to be a QF-16, then you're probably going to have a significantly more challenging mission ahead of you. The QF-16 is exactly what it sounds like - an F-16 that has been modified to act as a UAV. As such, it has the full range of evasive options available to it that you would expect from a normal 4th generation fighter aircraft, since it is one.

The U.S. armed forces use the 'Q' designator to mean that an aircraft is a UAV. This is a 'vehicle type' designator in the 1962 United States Tri-Service aircraft designation system. It is added to the F-16 designation for the unmanned F-16s, but it's also used for all military UAVs, such as the MQ-1 Predator, the MQ-9 Reaper, or the RQ-4 Global Hawk.

QF-16 flying without a pilot:


What is the difference between a tire deflation and a tire explosion? In this question, our intrepid former 747 pilot Terry mentioned, in the accepted answer, that:

  As I understand it, tires that dangerously overheat will explode before melting, and that's why thermal plugs are used which melt and deflate the tire to prevent their exploding.

His understanding was confirmed by other comments and answers.

My question is what is the net difference between a tire deflating due to the plug melting and the tire deflating due to explosion? Either way, you're landing/taxiing with a flat tire.

The only thing that comes to mind is that once the plane is on the ground and stopped, an exploding tire might injure safety crews and/or pax evacuating.

An exploding tire while the plane is rolling will propel debris in various directions.

This happened with the crashed Concorde on takeoff. A chunk of the tire hit the tanks and caused a punctured in it. This then lead to the fire and loss of power.


What is the effect of uneven ground on ground effect vehicles? I understand ground effect as far as Wikipedia explains it. There are two ways to ask my question;

A ground effect vehicle flies along and encounters an obstacle (say a big wave) that's maybe about half the flying height. What will this feel to the craft? My assumption would be a short moment of more lift, which would feel bumpy at best and could damage the craft at worst.
How choppy may the ground be? From the articles about Ekranoplans and similar concepts I read all these vehicles seemed to be designed for inner seas like the Caspian Sea or the Wattenmeer, not for the Pacific. This may be a coincidence or simply wrong. But can we quantify somewhat how seaworthy such a craft would be, or what were the most extreme conditions in which a ground effect vehicle has operated?
When I try to answer the question myself, the one 'killer' condition I can come up with is when the ground rises faster than the craft can gain height (duh). Is this correct, are there others?

I've put this in a list so you can see where my misconceptions might be when addressing the underlying question: the ground in ground effect....

The ability of a ground effect (air)craft to able to fly with (small) perturbations in height from the ground is called height stability. In general, height stability is achieved if the derivative of the lift coefficient with increasing height is negative. In this case, a decrease in height (due to waves etc.) causes an increase in lift. As a result, the aircraft is returned to its original height due to the increased lift (with the opposite happening when height is increased).

As the ground effect increases as the height decreases, designing the ground effect aircraft with height stability is not very difficult and most of the ground effect aircraft designed and operated have height stability. A good example is the Lun Ekranoplan, which returned to its height after the height was altered by approximately 0.5m (due to missile launch).

"Lun Ekranoplan" by Soviet Navy - Stock Archives of Soviet Navy. Via Wikipedia.

Also, the Sea state limitations are a scale phenomenon — the larger the ground effect aircraft, rougher the seas it can handle. The Russians (Soviets) have the most experience in operating ground effect vehicles and according to them, sea state limit for a 500-tonne aircraft is around 2.5 m and the safe operating heights in terms of mean wave heights is given by,

$h  = \frac{1.54 H_{\frac{1}{3}}}{2} +  0.1  c$

where,

$h$ is the vertical height measured from the mean wave height,

$c$ is the chord,

$H_{\frac{1}{3}}$ is the average of the 1/3 highest wave.

When this height exceeds the ground effect height the craft operates as an aircraft at a lower efficiency.

The main problems in case of operating a ground effect aircraft in choppy waters (as you noted, they are mostly operated in 'calm' seas) are twofold:

Takeoff and landing are dangerous in rough seas, due the impact loads on the hull and wings. This is the most important limitation for operating in rough seas.
Stability — The wing is already unstable, and near the ground in high lift region, it is more so; this is the reason most of the ground effect vehicles have proportionally larger tail surfaces compared to the conventional aircraft. A good example is the Soviet -90 'Orlyonko', which had tail surface nearly 50% of that of the wing.

"A-90 Orlyonok" by Kaboldy - Own work. Licensed under CC BY-SA 3.0 via Commons.

The main problem with waves (or in general, variations in height) is that the pitch stability changes with height. This results in the requirement of a large amount of control power in order to maintain trim — another reason for large tail control surfaces. Generally, the aircraft is stable in roll (the dipping wing generates more lift and the aircraft corrects itself).

Another thing to note is that the maneuverability of the ground effect aircraft is pretty limited if it's unable to fly in OGE (Out of Ground Effect). Soviet GE aircraft could fly in OGE for clearing obstacles.

References: Wing in Ground Effect Craft Review by Michael Halloran and Sean O'Meara


What is the correct phraseology for declaring a fuel emergency? If I am  pilot, approaching my destination airport and realise that, after landing I will have less than 30 minutes of fuel remaining, how exactly should I express this when communicating with ATC?

in ICAO rules
in FAA rules
in EASA rules

For example, in a country where Spanish is an approved ATC language, would it be sufficient to say "ABC12345 FL210 en acercamiento y solicitamos prioridad para la aproximación. Al momento se nos ha presentado un problema de combustible" ("ABC12345 FL210 inbound and we request priority for the approach. Right now we have a fuel problem")

(This is very closely related to this question, and see this one too.)

At least in the US, cutting into fuel reserves isn't an emergency by itself. But assuming that things have gone beyond "minimum fuel" and you clearly need priority for landing then you should indeed declare an emergency.

The wording you mentioned seems 'weak' to me; if you do have to declare an emergency, there should be no possible doubt about it or about what you need. Assuming that I was already in contact with ATC, I'd probably say something like this (see the AIM 6-3-2):

  Mayday, mayday, mayday. Louisville Approach, N12345 is declaring an emergency, low fuel. We are now direct runway 35R for landing. 3 on board, 15 minutes fuel remaining.

Note that if time is critical I'm not going to "request" anything, I'll just tell ATC what I'm doing and let them sort out the rest. That phraseology and statement of intentions should be understood anywhere in the world.


When to reduce power on takeoff (Cessna 182 or similar)? There are two sides I've heard when taking off in a Cessna 182 or other small airplane with a normally aspirated engine driving a constant speed propeller:

  As soon as your wheels are off the ground... Or,
  When you're 700-1,000 feet off the ground...

  Reduce to about 23" of manifold pressure and then reduce the RPM to 2,450 (or 2,300) depending on the plane.

The POH or Owner's Manual (in my case a 1972 Cessna 182P) simply says Full Power under the Normal Take-Off procedure.

The reasoning I've heard is to try not to over-stress the engine (whatever that means exactly), but on the flip side, I've heard that if an engine is going to do something funky, it's probably going to happen when you do a power reduction, or otherwise do something.

I personally want all the power I can have until I'm far enough off the ground to have options if the engine quits or sputters (turn back if high enough, or glide to a suitable spot if not).

I'm asking is there an "official procedure" as to when you should perform this power reduction (inches off the ground or 700-1,000 feet), and if so, have there been actual studies that say why one way is better than the other, or is this one of those groundless, "endless debates" that are so prevalent in aviation?

The "official procedure" is the one dictated in your aircraft's POH/AFM.
Within the leeway that document gives you (and many of them give you a lot of leeway) this is definitely one of those "endless debate" subjects.

Personally in a single-engine piston aircraft unless the POH directs otherwise or operational considerations (like an altitude restriction from ATC) require something different I would maintain full power (and all other takeoff settings - fuel pumps, etc.) until reaching 1000-1500 feet AGL (depending on what the terrain and obstacles in the area are like), then configure the aircraft for a reduced-power cruise climb if appropriate.
Whether or not the first power reduction is a time of increased failure is irrelevant to me - I operate on the assumption that the engine can fail at any time, and should the engine fail (for whatever reason) I want adequate distance between myself and the ground to make some decisions, confirm my landing spot, and prepare myself, my passengers, and the aircraft for whatever is going to happen next.

1000 feet AGL is my minimum threshold for that sort of activity. It's possible (maybe even likely) that I'm imposing additional wear on the engine in requiring full power for this long, but if the engine decides to fail on climb-out it's not going to matter how "nice" I was being to it on all my previous flights - the only things that are going to matter are my altitude, airspeed, and landing options, and I'm going to want as much altitude and airspeed as I can get to help maximize my landing options!

There are some conditions where I would reduce power sooner than 1000 feet AGL if necessary - for example, if I can't maintain oil or cylinder head temperatures "in the green" in a full power climb a power reduction (or pitch reduction) to keep those engine parameters happy would be in order.

There are also some aircraft/engines which have a continuous power restriction (Full throttle operation limited to 3 minutes,  maximum continuous power 2400 RPM, or similar admonitions you'd find in your POH). In those cases the restrictions should obviously be observed (the engineers who set the limitations had a good reason for doing so), and observing those requirements may necessitate a power reduction or other configuration changes prior to reaching 1000 feet AGL.

Finally, I'm not sure what kind of engine is in your hypothetical Cessna but as an additional point of reference Lycoming has this to say about takeoff operations:

  Operating Your Lycoming Engines At Takeoff And Climb

  Because there are
  a wide variety of Lycoming engines in operation, the paragraphs below
  may be helpful in understanding the different modes of operation
  required when operating each type at takeoff and climb power settings.
  The Pilots Operating Handbook for the aircraft in which the engines
  are installed should be the final authority as to how the engine
  should be operated.

  DIRECT DRIVE ENGINES

  Most normally aspirated
  engines are rated at full power for takeoff and climb indefinitely,
  provided engine temperatures and pressures are within the green arc
  area of the engine instruments. Extra fuel, sensible airspeed, and
  cowl flaps, if available, are all helpful in keeping cylinder head
  temperatures within desired limits during takeoff or climb.
  Climb
  requirements may vary; as an example, on a warm day with the airplane
  close to gross weight, and a direct drive engine with a fixed pitch
  prop, the pilot will need full throttle all the way to cruise
  altitude. The same airplane on a cold day and lightly loaded may not
  require full power for climb. After full throttle at takeoff, the
  pilot may want to reduce power 100 or 200 RPM and still not see
  performance suffer. Those direct drive normally aspirated engines with
  a prop governor are also rated indefinitely at full power, and the
  manuals all recommend full power for takeoff, but specify a small
  reduction in power, generally to 85% power climb. Study the specific
  airplane Pilot's Operating Handbook for detailed power settings.

(They go on to talk about geared engines and turbocharged/supercharged engines, but your question was about normally-aspirated engines. This is from Lycoming Flyer "Key Reprints" - I grabbed it here but you can Google it up pretty easily, and I imagine Continental has analogous guidance somewhere.)


What is the maximum amount of noise an aircraft is allowed to generate? Has the FAA regulated yet the maximum dBs of noise an aircraft's engine is allowed to generate, and what the range of "safe operation" would be? If they have, what are their regulations on it?

If it can be regulated it shall be regulated -- the relevant section of law is FAR 36 - NOISE STANDARDS: AIRCRAFT TYPE AND AIRWORTHINESS CERTIFICATION, with a number of advisory circulars as well.

These requirements are aimed mainly at Transport Category aircraft, and the absolute noise level limits are rather high (certainly nothing you'd want to be standing near without hearing protection).

What's probably of more interest to most people are the FAA's guidelines on Airport Noise, and specifically FAA Order 1050-1E, which deals with the noise you are actually exposed to on the ground (rather than what is generated by the plane's engines).
Order 1050-1E goes into great detail on what is considered "acceptable" noise levels for various types of land use around airports.  Airport construction and/or expansion projects are evaluated against these criteria using computational models to ensure that noise levels will not exceed the FAA's guidelines.


Is it practical to use ground effect to extend range in an emergency? Imagine a piston engine airplane (let's say a DC-3) flying at cruise speed and altitude over a calm sea, trying to reach an unreachable airstrip straight ahead, just above sea level. Fuel is very low and ditching may occur at some point even if highest lift to drag to consumption ratio is achieved.

Would a ground effect low horizontal flight increase the range? That could mean ditching closer to the shore, and getting help sooner (or even landing safely).

If yes, is it also the case for a modern jet airliner usually cruising faster and in a much thinner air, and are there some emergency procedures or regulations about that?

When flying close to the ground, there is an important reduction of induced drag, the larger the closer to the ground one flies, so the airplane needs less engine thrust to keep a given airspeed. Anyone who has made a low pass over a long runway may attest this...

Flying in ground effect is a nice way to save fuel and extend the range. I remember reading that it was often used by carrier planes returning from a mission low in fuel...


Would a perfectly silent supersonic aircraft create a sonic boom? Assume that you have an aircraft that is so amazingly stealthy that it is perfectly quiet: no engine noise at all, nothing.  And, it's going supersonic.  (Maybe in a steep dive with the motor shut off.)  Will it make a sonic boom?

Would the sonic boom be louder if the aircraft was making more noise but all else remained constant?

The (excellent) answer to this question discusses aircraft size in relation to the strength of the sonic boom, but no mention of aircraft noise.  So would the amount of noise the aircraft makes matter?

Edit: by "silent" I'm not trying to imply "displaces no air" or creates no sound by its passage.  The point is simply that the aircraft itself doesn't make any noise from an engine or otherwise.  It's silent, like a bullet, or a glider.

Sonic booms aren't created by the aircraft's engine noise. They're created by the aircraft moving through the air. The aircraft has a non-zero volume (an aircraft with zero volume is like the emperor's new clothes; you can argue all you want how much design and engineering work it took but all anyone will see is an empty spot on the flight line), meaning it must displace air as the plane passes through air. This displaced air equalizes with the surrounding air in an expanding pressure wave, which moves at the speed of sound in all directions.

As your hypothetical silent aircraft approaches the speed of sound, the air being pushed aside can no longer equalize by moving out directly in front of the aircraft. This causes a single strong compression wave to build in front of the aircraft. Similar waves have already started to build over the top of the wing surfaces, as the airflow over the leading edge of the wing (by design intended to make the air move faster thus lowering its pressure and producing lift) is temporarily supersonic before friction causes it to settle back below sonic speed; at this transition point between super- and sub-sonic, air still moving supersonically "backs up" against the subsonic airflow, creating a wall of relatively high-density air.

At this point, an observer would already hear a small sonic boom from some combination of these compression waves. However, the boom becomes much more pronounced as the entire aircraft transitions beyond Mach 1. At this point the "wall" in front of the aircraft becomes more of a "cone" as the air can no longer build up directly in front of the jet and is instead violently pushed aside at any local "disconnect" in the angle presented to the oncoming airflow. This sudden compression produces a strong shockwave "wake" which is what is heard as a sonic boom.

As a perfect example of this, there actually is (was) a vehicle that spends a very critical portion of its flight under zero engine power, effectively silent in that regard, at not only supersonic but hypersonic speeds. This vehicle, as shown in the linked YouTube, produces a characteristic "double sonic boom", proof that even a "silent" aircraft isn't silent when it's supersonic. Can you guess what it is?

The noise of an aircraft's engines could, conceivably, add a little extra to the sonic boom; the biggest difference is that immediately following the sonic boom, if you were close enough, you'd also get the engine noise, which can be deafening all by itself at full throttle up to 100 feet away.


What is the purpose of a small wing near the cockpit on the front of some planes? I saw a plane leaving Luton Airport that I have never seen before.
It seemed to have an extra small rectangular wing near the front of the plane. What is it?

That would be a canard you see on the airplane.

An aircraft designer may adopt the canard configuration to reduce the main wing loading, to better control the main wing airflow, or to increase the aircraft’s maneuverability, especially at high angles of attack or during a stall

Canard foreplanes, whether used in a canard or three-surface configuration, have important consequences on the aircraft’s longitudinal equilibrium, static and dynamic stability characteristics.

Many pioneers initially followed the Wrights' lead. For example, the Santos-Dumont 14-bis aeroplane of 1906 had no "tail", but a box kite-like set of control surfaces in the front, pivoting on a universal joint on the fuselage's extreme nose, making it capable of incorporating both yaw and pitch control.

I hope this has helped.


Is ADS-B anonymous mode deterministic? From what I can tell, this is the method of creating a temporary ICAO address in the 978Mhz UAT protocol:

From https://www.icao.int/safety/acp/Inactive%20working%20groups%20library/ACP-WG-C-UAT-2/UAT-SWG02-WP04%20-%20Draft%20Tech%20Manual%20V0-1%20.pdf

  3.2.1.5.1.3.2

  Self-Assigned Temporary Address of Transmitting Aircraft An “ADDRESS QUALIFIER” value of ONE (binary 001) shall indicate that
  the message is an ADS-B Message from an aircraft, and that the
  “ADDRESS” field holds the transmitting aircraft’s self-assigned
  ownship temporary address.

  The self-assigned temporary address shall be generated as follows:

  Let:

  ADDRP = the ICAO 24-bit address that has been assigned to the aircraft;

  ADDRT = the temporary address that is to be generated;
  M(1) = the 12 least significant bits (LSBs) of the ownship “LATITUDE” field (per §3.2.1.5.2.1) at the time the temporary address option is selected;

  M(2) = the 12 least significant bits (LSBs) of the ownship “LONGITUDE” field (per §3.2.1.5.2.1) at the time the temporary address option is selected;

  M(3) = 4096 × M(1) + M(2);

  TIME = the number of seconds that have elapsed since UTC midnight
  at the time the temporary address option is selected, represented as a
  24-bit number.

  Also, let “⊕” denote the modulo 2 bit-by-bit addition(or “exclusive OR”) operation.

  a. If the transmitting aircraft’s ICAO 24-bit address ADDRP is available, then the temporary address ADDRT shall be the modulo 2, bit-by-bit summation of the permanent address and M(3), that is:

  ADDRT = ADDRP ⊕ M(3).

  b. If the aircraft’s 24-bit ICAO address ADDRP is not available, then time of day shall be used as an additional randomizer. In that case, the temporary address ADDRT shall be the modulo 2, bit-by-bit summation of TIME and M(3), that is,

  ADDRT = TIME ⊕ M(3).

So the question is if this is deterministic.  Could one work their way back to the actual tail number when an aircraft is in anonymous mode?

It is deterministic, meaning that if given exactly the same inputs, it will always produce the same output.

Your second question is whether it is reversible. The algorithm was deliberately designed to require an adversary to know the precise (i.e. within a few meters) latitude and longitude where the algorithm was run to be able to reverse it. This is effectively impossible unless they physically observe your exact startup location, in which case they could presumably just read your tail number off the side of your plane anyway.


What is the reason for allowing pilots to take Pilot Aptitude Battery Test (PABT) only once? Indian Airforce conducts a test called PABT (Pilot Aptitude Battery Test), for anyone who wishes to be a pilot. This test can be taken only once, and once you fail it, you can never appear again (which inherently disqualifies you from being a pilot in the Indian Armed Forces). Why is such a test so important, and how does failing in it reflect on your piloting skills?

A few thoughts:

They have no need in getting repeat candidates if the selection pool is  sufficient (which I imagine it is). Starting to accept repeat candidates would also make it harder for first timers, resulting in more work and tests for everybody. People also won't go for the fun of it, but will make their single attempt their best attempt.
I believe they would rather want you to nail it on the first attempt as part of the test. In other words: how do you respond to a new situation, how to you respond to the stress of knowing you have one attempt, etc... It would be effective for their purpose on multiple levels. This is more effective than you returning a second time and learning how to do the test.

While I can't comment on other air forces around the world, I know that German Lufthansa implements the same policy for acceptance.


Do two airlines have IATA code N8? Wikipedia lists N8 at the IATA code for National Cargo Airlines (ICAO NCR), a regional airline based in Orlando, Florida. AirlineCodes.info and other sources list N8 as the code for Fika Salaama (ICAO HGK), which is based in Uganda. Both are currently in operation. What on earth is going on here?

IATA issues duplicate airline codes to regional airlines where the codes are not likely to overlap, from Wikipedia:

  Controlled duplicates are issued to regional airlines whose destinations are not likely to overlap, so that the same code is shared by two airlines.

This happens because IATA uses a 2-letter code for for airlines which has a limited range of available codes. Since NCA doesn't operate a passenger service in the same region as Fika Salaama, it would be very unlikely to confuse the two.


Can I fly over Schengen zone without visa? I don't have a Schengen visa. Am I eligible to fly over any Schengen country without landing there? Of course I mean that I take off from a non-Schengen country, and land in a non-Schengen zone as well.

Moreover, can I land somewhere in Schengen zone? For example, one touch-n-go in Schengen zone airport, and then fly back.

I consider that I fly an EASA-reg aircraft with an EASA pilot license.

A visa is a permit to ask for permission to enter into a country by crossing its borders. Since you are not entering the country; but rather overflying it - you only need to worry about any requirements for your destination.

Now, if you are doing a technical stop, and you don't leave your aircraft - then you don't need a visa. This is true for normal passengers on commercial flights as well.

If you need to leave the aircraft, but not leave the sterile area of the airport - then depending on your nationality you may need a special crew visa (this is different than the normal visa you would get as a passenger).

For crew visas, there are no uniform rules. Each country is free to set their own permissions and requirements so you'll need to contact the embassy of the country you wish to stop in for information.

God forbid you face an emergency and have to land at a country and you don't have or don't know the visa requirements - there are provisions for such cases. Emergency permission can be provided to cross borders.

In all cases, make sure you carry a passport that is valid for at least 6 months after your return date.


How did the propellers attach on a Lazair attach if the shafts had a woodruff key instead of opposite thread? How did the propellers attach on a Lazair attach if the shafts had a woodruff key instead of opposite thread?

I understand the early Lazair prop shafts had a woodruff key.  How were
the props attached?

Don't you need opposite thread?

I assume you couldn't just use a cotter pin and a washer, as the props would try to shear off the cotter pins.

I believe that while the original engine shafts had a slot for a woodruff key, no key was actually used in attaching the props to the crankshaft. Instead, a nominal arrangement of multiple (6, I believe) bolts attached the props to the crankshaft for mutual transmisal of both engine torque and prop thrust. Presumably the bolts were secured with safety wire, but I have no data on this.


Do I need to change cruising altitudes for really short legs? Let's say I'm cruising on a magnetic course of 150, so I'm flying at 7,500 feet.  Then I need to fly for 6 miles on a magnetic course of 210, then back to 150.  Do I need to switch to 8,500 or 6,500 for the short 6 mile leg, or is it better to stay at 7,500?  And if I need to switch altitudes for the short leg and I'm getting flight following, do I need to request an altitude change for the short leg and then request to change it back when I resume a course of 150?

As you are using the term flight following I'll assume you are in the US. Flight following is an advisory service, you tell them your intentions and they give you any traffic information you may have. If you are changing altitude or course you tell them, you do not ask permission because they cannot give it.
FAR 91.159 clearly states what altitudes you should be at using the semi-circular rule:

Except  while  holding  in  a  holding  pattern  of  2  minutes  or
less,  or  while  turning,  each  person  operating  an  air-craft
under VFR in level cruising flight more  than  3,000  feet  above  the
surface  shall maintain the appropriate altitude or  flight  level
prescribed  below, unless  otherwise authorized by ATC

So if you will be flying 3000ft or more above ground level you will be expected to fly the semi-circular rule, there are no exceptions made except those listed above. From a practical perspective you'll spend more time climbing and descending than at the other altitude so I think it's a fair question, the answer is to make the altitude change.


How does an API (air position indicator) work? I was looking for WW2 aircraft indicators and I found one navigation equipment called API (air position indicator).
But I couldn't find how it works exactly????

The API uses not only heading and airspeed but they are fed to mechanisms within the instrument that solve the navigation problem using sine, cosine and secant functions. The output was latitude and longitude from the departure or a known fix (geographical position) to give the no wind position of the airplane. This was then used by the navigator to give a dedreconing position by plotting the last known wind vector from the no wind position.


Why would there be two RNAV waypoints co-located with a VOR? Similar to this question but more so!
The Enroute H-5 chart shows two RNAV waypoints over Spinner VORTAC (SPI): SOHOW and USIRE. Neither waypoint appears on the Low IFR charts, nor on the VFR charts.

Enroute H-5 as of Feb. 25, 2021, via Skyvector

Searching the online Form 8260-2 database I see that Spinner is used for many different instrument procedures:

ROCKY SID off of Indianapolis
LAKES SID off of Kansas City
NATCA SID off of St Louis (an RNAV procedure!)
Several Victor airways and J-routes
Several instrument approaches to SPI and other nearby airports (including use as an IAF or feeder fix for RNAV approaches!)
MOTIF STAR into Chicago/Gary
Bradford STAR into Chicago
Braymer STAR into Kansas City
RIVRS STAR into St Louis
Vandalia STAR into St Louis

Some of these procedures only use Spinner to define a waypoint on the route, but in other procedures Spinner is actually flown over.
SOHOW does not have a Form 8260-2 listed in the database, but from a general search I notice it is used in:

LUCIT STAR into Gary

USIRE is used in:

KOLTS STAR into Indianapolis

Comparing the location of the three waypoints:

Waypoint
Latitude
Longitude

Spinner
39 50 23.04N
089 40 39.85W

SOHOW
39 50 25.37N
089 40 37.43W

USIRE
39 50 23.04N
089 40 39.06W

SOHOW is ≈300 feet northeast of Spinner
USIRE is ≈062 feet due east of Spinner
USIRE is ≈270 feet southwest of SOHOW

So the question is: Why do SOHOW and USIRE exist? And in particular why do they both exist? I can think of three reasons:

There is a rule saying that RNAV procedures must only use RNAV waypoints.
Counterargument: Spinner is a waypoint on the NATCA (RNAV) SID.
Spinner will be decommissioned soon, and the RNAV waypoints will be used instead. Neither waypoint is exactly on top of Spinner, but perhaps it doesn't need to be; the LBNON waypoint will replace Lebanon VOR/DME soon and those do not have the same exact coordinates.
Counterargument: Spinner is used in several VOR approaches and to define fixes on other instrument procedures; also I haven't heard of any plans to decommission it.
The specific configuration of the LUCIT and KOLTS arrival procedures necessitate the distinction between two points 270 feet away from each other (less than 0.05 nautical miles).
Counterargument: Really?

Your Questions: Why do SOHOW and USIRE exist? And in particular why do they both exist?
Why do they exist: SOHOW and USIRE are published Waypoints on RNAV STARs into Gary, Ind., and Indianapolis, Ind., respectively. They exist and are published because they are part of the procedure being flown (as assigned by ATC).
Why do they both exist: Even though they are in extremely close proximity to each other in space, they are not physically located anywhere. The fact that both of these RNAV Waypoints are only "points in space" (geographic coordinates in a computer) reflects the value and flexibility of Area Navigation.  Perhaps both STARs (to Gary and Indianapolis) could have used either SOHOW or USIRE, but there is no physical reason to do this.  Also, since each of the Waypoints (SOHOW and USIRE) are part of different STARs going to different airports, there is less opportunity for confusion as to which procedure is being flown.
As a note, you mention in reason number 1 of your post (your Counterargument) that Spinner Vortac is a waypoint on the NATCA (RNAV) SID.  Spinner is actually a "transition" on the NATCA SID, which technically ends at NATCA.  See image below.
Good questions.


Does European airspace use the metric system? I figured this was probably a no brainer, since Europe uses the metric system, I assume the airspace does...  But then I remembered that aviation likes international standards, and I know the US uses Imperial so, does Europe as well?

And, yes or no, why do they take that choice?

European Civil Aviation Authorities use the imperial system to depict altitudes and airspace restrictions (feet), speeds (knots) and distances (nautical miles).

Some VFR aircraft have speed indicators in km/h, gliders can have altitude and variometer in meters and meters/second and apart from a special ICAO VFR chart being available in metric in Germany, the AIP itself and all other charts always use imperial units.

Related question: What is the measurement system used in the aviation industry?


What are the operational limitations on ADS-B DO-260A (as compared to DO-260B)? First off, here is my understanding: I'm primarily concerned with retrofit aircraft.

A number of Asian countries (and Australia) already require ADS-B to DO-260A standard.

The European mandate is set for June 7, 2020 (DO-260B).

The North American (FAA) mandate is set for January 1, 2020 (DO-260B).

Am I correct in my assumptions?

After the deadlines, what are the operational limitations (assuming the aircraft is equipment with DO-260A)? Is the aircraft banned from the airspace completely or is it still possible to operate but get undesirable routing (such as low altitude or positioning)?

What is involved in upgrading to DO-260B? What are the differences between the standards?

If the aircraft is subject to the ADS-B mandate of Europe, it will not be allowed to operate in European airspace after June 7, 2020 if it does not have a certified EUROCAE ED-102A (equivalent to RTCA DO-260B) compliant ADS-B transmitter. Aircraft with a maximum take-off weight exceeding 5700 kg or maximum operating true airspeed exceeding 250 knots are subject to the mandate.

The USA rule is a bit different, as it allows ADS-B on universal access transceivers (UAT) below 18 000 ft which is different from the 1090ES technology used in DO-260. You can do without ADS-B in the USA after January 1, 2020, if you never fly higher than 10 000ft MSL (exceeding 10 000ft MSL is allowed as long as you don't exceed 2 500ft AGL), you do not enter or overfly class C airspace and keep further than 30 NM from class B airspace.
If your aircraft is 1090ES ADS-B equipped it must be DO-260B compliant; if it UAT ADS-B equipped it must be DO-282B compliant.

The difference between DO-260A and DO-260B are many small changes. This list is not exhaustive:

change in the way position integrity is encoded,
addition of barometric pressure setting,
new encoding aircraft length / width
change in encoding of speed on surface

Typically the update from DO-260A to DO-260B requires a firmware update and some configuration changes. However, note that the mandates include more requirements than just the ADS-B protocol version. There are requirements on the integrity of your position source (GPS) as well, and the maximum latency in the position transmission chain. In the worst case you are up for a rewiring of the GPS or even installing a new GPS.


Can a small GA plane maintain level flight with a significant nose-down attitude? Consider a small, one- or two-seater motor GA aircraft, something like a Cessna 152 or similar, designed for level flight at roughly neutral pitch.

It's certainly possible to fly such an aircraft in a nose-high attitude while maintaining altitude, by careful use of pitch and thrust. I'm not sure I'd want to do that for any significant length of time, but as long as the angle of attack is kept below the critical angle for the current aircraft configuration, I can see no aerodynamic reason why it can't be done even in the general case.

But is it possible to fly it in a significant nose-down (say, several degrees or more) attitude while maintaining altitude?

My gut feeling says no; no matter what else you do with the aircraft in such a nose-down attitude, you're going to be losing altitude. But I've been surprised before, so: is there a way?

I may have misunderstood the question but I think the answer may be... flaps. Wing flaps will increase the lifting ability of the wing and at a constant airspeed the nose will need to be lowered to maintain a particular altitude.


What does the term "loading" refers to when we talk about Blade loading and Stage loading in Turbomachinery? I have been reading about the term Blade Loading and Stage loading in case of Axial Turbines and Compressors, however, I would like to know what does the term "loading" here exactly refers to?
What I also read was that if we increase the number of blades then the Blade loading for each blade will reduce but the friction and weight will increase, then what is the optimum number of blades one should have?

The term “blade loading” is basically the same as “pressure ratio”. A blade with a higher blade loading causes the exit pressure from that blade stage to be higher than if the blade loading was lower. Hence, the pressure ratio (exit pressure/inlet pressure) is higher when the blade loading is higher.

The optimum number of blades is a very complex problem. But, in simple terms, too many blades, and the weight is too much, too few blades, and either the exit pressure of the compressor is lower (which makes the engine less fuel efficient), or the pressure ratio across each blade is higher, and the engine is much more likely to suffer compressor stalls. The fuel control may have to allow only a very slow acceleration and deceleration rate, to avoid stalls. It may also stall more easily in crosswind situations. Neither of these are ideal in a take-off situation. You don’t want the engine coughing and losing thrust when you are past the point of aborting the take-off, but aren’t high enough to fly a circuit and land.


Why is the rear seat ejected before the front one? On aircraft with 2 crew placed one in front of each other (tandem) equipped with ejection seats, the rear seat is ejected before the front one (described here for the F-14).

Why is the rear seat ejected before the front one?
Is an aircraft without ejection seat (e.g. glider) evacuated in the same order and why?

If the front seat ejected first, the drag would probably bring him too close in the trajectory of the rear seat, thus making a collision of both probable.

Since the rear seat is ejected first, it experiences drag earlier than the front seat and will thus not have an increased probability of hitting it.


During autoration, does it help to pump the cyclic to increase the RPM? I have heard of the idea of moving the cyclic forward and backwards in order to get an increase in rotor RPMs. Does anyone have any information on this as to when you would use it or airspeeds it would only be effective at?

Scenario is low altitude autorotation/unpowered flight:

  About a 100 - 150 feet AGL, super slow (say 10 - 20 kts)
  You lose an engine there.
  The ideal thing would be to get as much airspeed as
  possible to reduce that sink rate as compared to a vertical descent /
  pull collective / do a hard run on.

  However presuming you had to come straight down (trees, power lines or
  whatever) I have heard from more than one source that pushing the
  cyclic back and forth at quick segments will help build RPM's but I
  just couldn't figure out how.

Cyclic pumping will likely degrade your performance

As explained here, it leads to rotor inefficiencies

  As far as moving the cyclic around goes it destroys lift as the TRT
  vector is all over the place and not acting in one place or close too
  it and more power is required

What is this TRT he's talking about?  Total Rotor Thrust

  In a still air hover, TRT is, in broad terms, equal and opposite to
  weight. As the disc is tilted to commence a transition into forward
  flight, the TRT vector is tilted and must be increased so that its
  vertical component remains equal to weight if level flight is to be
  maintained.

With the above in mind, pumping the cyclic with the engines working simply means that you need more power from your engine to keep your Nr up to fly, as you are being inefficient.

If you have no power, pumping the cyclic is counter productive to your efforts at maintaining Nr since the back and forth creates sequential inefficiencies, and more drag but you have no engine to restore Nr... and in the situation you describe, your precious Nr is a critical resource to your walking away from the forced landing or crash.

Depending on what is happening, a slight turn or flare (aft cyclic, not foreward) may load the head and preserve Nr a bit so that it's still turning with enough inertia to help you as you near the ground and need that cushion from the collective as you hit the ground.  Each bit of Nr you retain for that last pull is critical, in that situation.

It's a tough one, the low speed, not-quite-inside-the-Hv-diagram scenario that you presented.

Consult the manual for your model helicopter, and the H-V diagram.  Know your limitations.


What is the correct procedure in case of vertical stabilizer failure? What is the correct procedure in case of vertical stabilizer failure in cruise?

Am I correct in guessing that one should descend to a lower altitude and decrease speed?

There is no procedure, generally a vertical stabilizer failure makes an airplane uncontrollable, meaning everyone dies. There have been examples where vertical stabilizers failed and people survived, see this question for details. A pilot local to me cut 2/3 of his vertical stabilizer on high tension power wires while scud running and still landed safely.

When there's any control surface failure pilots will have to learn how to fly the airplane and control it using whatever means possible. Differential thrust and speed brakes have been used to control lateral movement (yaw), trim can be used if controls are seized, etc.

Reducing speed may not be a good idea, or at least not all at once, if the vertical stabilizer fails airflow over whatever stump remains may be the only think keeping it straight. If the control is stuck then reducing speed would make sense, it all depends on the nature of the failure. Descending is absolutely a requirement, you have to land somewhere after all, but unless you've depressurized there's no need to rush it, you'd want to work the problem and find out what the new parameters are, then gingerly work your way down.


Is there a reason to be worried about go-arounds as a passenger? The last night I had an "interesting" experience with an aborted landing, which was a bit dramatic for my liking. Heavy fog and darkness didn't help either. Pilot told us that the reason for aborted landing is a problem with navigation instruments.

Today I checked the flightradar24 data, which I've attached for your pleasure, but it didn't ease my worries since according to site's data the first attempt missed the runway completely.

How accurate are these flightradar's data?
How common is for pilot to miss runway in heavy fog?
Is there a reason to be worried while flying 50 feet above meadows in heavy fog? Possibly with malfunctioning navigation equipment?

A go-around is nothing to be worried about as a passenger.  What would be worrying is if the pilots elected not to go around when conditions warranted it.

The dark likely isn't an issue with this go around as approach lighting systems can become exceptionally bright when requested (to the point you'll need sunglasses to look at them if visibility is good).  What was likely a factor was fog.  Airplanes need a minimum amount of visibility to land and if conditions are marginal you won't really know until you fly the approach and either see the lights and land or do not see the lights and go around.  For normal ILS approaches you would initiate this go around at 200 ft above the airport elevation.  For very low visibility approaches this decision height may be 100 feet or less above the airport elevation.

The point at which you go around if you fail to see the runway environment is well defined and procedures ensure obstacle clearance so there is no danger as long as procedures are flown as published.

Another possibility for the go around could be the airplane in front of you failed to clear the runway speedily due to low visibility.  If the preceding aircraft was still occupying the runway then your airplane would have to go around.  There are a few other issues that could warrant missed approaches (e.g. windshear) but in all of these cases the go around is the safer option than proceeding with the landing.

Your pilots made the safe decision to go around and this is what you should take from the experience.  There is zero reason to be worried.

To address your added specific questions:

Flightradar24 flight track data is unreliable.  It is neither true radar positioning or necessarily true GPS positioning.  It is nice for zoomed out flight tracks but is not reliably suitable for the precision during landing/takeoff.  Do not use it as a basis for worrying that your approach was not properly aligned.
Extremely rarely if you mean not being aligned with the runway.  Uncommon if you just mean not seeing the approach lights but otherwise on course to land.  The navigation signals used in ILS approaches are broadcast down the runway centerline for the lateral guidance and from just next to the runway approximately 1000 feet past the beginning of the runway aimed 3 degrees up for the vertical guidance.  These signals are only usable in a cone that radiated outward from the runway.  Furthermore the navigation accuracy of the ILS receivers are regularly tested on the airplane.  Combined with monitoring by air traffic controllers you will not end up on a parallel course that does not intersect the runway.
The vertical data is also not reliable.  Your airplane approached on the glideslope and if it made it down to 50 feet this would have been just over the very beginning of the runway.  After initiating the go around it would climb (likely to between 2000 and 3000 feet) and attempt another ILS approach.  At no time is the airplane lingering at 50 feet above the ground anywhere but over the runway for a very short period of time.

The video below is an example of a very low visibility approach and you can see an example of how low the airplane can get before visual contact is made with the approach lights and runway.  At predetermined points based on the aircraft, airport and crew qualifications the airplane would initiate a go around if these things were not seen.  For standard ILS approaches this would be when the airplane announces "200 feet".  For category II ILS approaches, it would be at "100 feet".  In the video below a category III approach is shown which has an even lower altitude to initiate a missed approach.


While flying having trouble estimating how far I am from Airport When approaching an uncontrolled airport especially, standard procedure demands to make the first call 10 miles out announcing my location, entry procedure, etc. and then more calls at 5 miles, 2 miles, etc. I find myself having a hard time estimating how far I am from an airport so I can announce my position. The same applies when I'm asked to report a 8 mile final in a controlled airport. I'm curious how others do it and if there's a more reliable way to judge distance from an airport. Thanks.

My GPS tells me the distance.

Otherwise, my experience says:

15 miles (and about 3,000 AGL) is where I'm not entirely sure I have the airport picked out.
10 miles is where I can see the airport, but not pick out specific details and airplanes.
5 miles is where I can see the airport clearly, and setup for the centerline.


What causes the adverse pressure gradient that leads to flow separation? When reading about flow separation I generally see a diagram like this:

imp source: Wikimedia commons

This shows that the boundary layer slows as it passes over the wing, eventually creating an adverse pressure gradient. The effect being more pronounced close to the wing it will cause a reversal of flow and separation of the boundary layer.

I can easily see how this leads to flow separation, but I’m unsure as to what causes the boundary layer to slow down like this. I’ve read that the effect is independent of surface friction.

I know the air at the surface is stationary wrt the wing and its velocity increases the further away it gets. But if I look at the arrows in the diagram and select, say, the second one from the surface, it slows down as it goes along the wing, eventually reversing. At first I thought that the still air at the surface was somehow affecting it, but I don’t know how (shear stress?). But even at that, stationary air can not make it flow backwards.

So, what causes the flow closer to the surface to slow?

Friction plus pressure rise.

No, the effect certainly isn't independent of surface friction, otherwise the location and angle of attack of separation wouldn't change with Reynolds number.

First, friction will prevent the surface layer to become as fast as the outer flow in the suction peak, and once pressure rises, all air will slow down by the same amount. Now the already slower part near the wall will actually reverse because it slows down to a standstill and is attracted by the low pressure ahead.

Pressure has to rise past the suction peak in order for the air to get back to ambient pressure. The upper side suction is caused by the airfoil's curvature, and curvature  over the rear part of the airfoil is very low or even negative - that is what makes the air assume ambient pressure again.

I think you know already my slightly longer answer on that topic, but I will link to it nevertheless. Please let me know if I need to explain more!


Given aircraft and runway characteristics, how do you compute the maximum temperature for take-off? Consider an airport e.g. Phoenix Sky Harbor International Airport (PHX), with Maximum runway length (ft) of 11500 and Elevation (ft) of 1135. For Boeing 737 whose Maximum takeoff weight is 174,200 lbs, How do you compute the maximum/optimum temperature for takeoff

Well, there is some subjectivity here, but I consider the optimum temperature for takeoff to be 72-degrees Farenheit.

As far as the outside temperature is concerned, there is no specific optimum. In general, colder is better.


What are the minimum requirements to pass the FAA medical exam? What are the requirements like height, weight, sight to pass the medical exam for getting a pilot's license ?

Are there any medical conditions that would make someone to fail it?
I know daltonism would be one of those.

There are no height or weight requirements as far as I know and you dont need perfect vision. I wear glasses and have a "corrective lens" note on my medical. I think that at minimum your vision needs to be correctable to 20/20. See this link for some information as well as the information for doctors here. You can also get special dispensation for certain medical conditions.

On a small side note, if you are asking this in relation to a Private Pilot License, they may be doing away with the current third class medical regulations which will ease the regulations greatly.


Why is the time of useful consciousness only seconds at high altitudes, when I can hold my breath much longer at ground level? This answer says at FL500 (50,000 ft; 15,250 m) the time of useful consciousness is only 6 to 9 seconds.

But if I just stop breathing at any arbitrary time, without any preparation, I can easily continue without air for about 20 seconds. How can these times be so short?

When you are breathing, oxygen ($\mathrm{O}_2$) and carbon dioxide ($\mathrm{CO}_2$) are exchanged between the alveoli in your lungs and the environment. This gas exchange is based on diffusion, which means the partial pressures of each gas involved will move towards equalization:

  Henry’s law states that the amount of a specific gas that dissolves in a liquid is a function of its partial pressure. The greater the partial pressure of a gas, the more of that gas will dissolve in a liquid, as the gas moves toward equilibrium.

(source)

As long as the oxygen partial pressure is higher in the environment, your blood will gain oxygen from breathing. But if the oxygen partial pressure is lower, you lose oxygen from breathing. Therefore, holding your breath at sea level gives you more time until you run out of oxygen than breathing at 15km altitude, where total pressure is about 10 times lower than at sea level. Furthermore, as John K pointed out in the comments, holding your breath at sea level allows you to feel when you need to breathe again, because of increasing $\mathrm{CO}_2$ levels, where breathing at high altitude does not feel different because $\mathrm{CO}_2$ can still leave your system.

This principle also allows oxygen masks in aircraft to function without creating higher pressure. Since (more or less) pure oxygen is created, the oxygen partial pressure is much higher than in the surrounding air despite being at the same total pressure.


How to proceed in designing a catapult glider with maximum flight distance? As a basis for this question, take the following catapult glider:

http://www.guillow.com/spaceshuttle.aspx

This model has low aspect ratio wings, a thick wing section and a relatively wide fuselage, however the surface of the glider is smooth. Is this an optimum design for distance or is there a better design possible?

How will the following parameters affect how well the glider fulfils its requirements?

Weight
Wing area
Wing planform
Fuselage width
Surface roughness
Aspect ratio

(covered here How does chord length affect wing design?)

At least what areas should a designer experiment with in order to achieve long flights?

Two parameters are important to arrive at a good answer, but not covered in your question:

What is the size of the glider? The Shuttle model will fly at Reynolds numbers in the order of a few ten thousands, which puts it in a flight regime quite different from that of large, man-carrying aircraft.
How much kinetic energy will be provided at launch? One advantage of the Shuttle model is its large volume relative to surface area. This allows it to start the glide with more kinetic energy when compared to the model of, say, a glider. In the end, it is more ballistics than aerodynamics which can explain the gliding distance.

The optimum configuration will change with the absolute size. Aspect ratio will grow with size, and a high ratio of mass to surface area will yield better results. The Shuttle model has a weak spot, however: Its large base area will result in flow separation and high base drag. A streamlined body should be better at all sizes.


Sustainable aircraft technologies I'm a student starting a research project on sustainable aircraft technologies. I've been particularly interested by distributed electric propulsion (DEP), which is currently being tested by NASA with the X-57 Maxwell (I'm thinking the added efficiency of DEP combined with progress in battery technology could eventually make electric flight a more feasible option). My supervisor has also pointed me to ion drives. Are there any other technologies in development that I should be aware of? Information on progress, potential, who is developing the technology, as well as links to scholarly articles are all appreciated.

You might also consider evaluating Hydrogen-powered aircraft and Biofuel as ways to operate aircraft with combustion engines on alternative fuels that can be produced in a more sustainable manner.


How much could human power add to the endurance of an electric gyrocopter? If we take a single seater electric gyrocopter like this one, could a human-powered propeller like this add to the endurance of the aircraft? The gyrocopter only needs a 32km/h forward speed to stay airborne.

According to the wikipedia page on "Human Power", a trained cyclist can produce about 400 watts of mechanical power for an hour or more, adults of good average fitness can produce between 50-150 watts for an hour of vigorous exercise, and a healthy laborer over the course of 8-hour shift can sustain about 75 watts per hour.

The Electric motor on the autogyro mentioned in the question has an 80kW (i.e. 80,000 Watt) motor. However, as you know most aircraft only use 100% power on takeoff and approximately 75% for fast cruise. For simplicity, I'll assume 75% power for cruise. That is 80kW * 75% = 65kW (i.e. 65,000 Watts). The information from the AutoGyro says the current endurance is 45 minutes.

So, if we assume the "trained cyclist" power output of 400 Watts, which is 0.62% of 65,000 Watts, then it would result in a 0.62% increase to the current endurance of 45 minutes. A 0.62% increase would result in an increased endurance of approximately 17 seconds of flight (45 min * 0.62% = 45.28 min or 45m 17s).

Its important to note that the human powered glider mentioned in the link was designed from the ground up to be powered by human power. It only weighs a fraction of the electric gyro. For example, a similar human powered glider the MIT Daedalus weighed just 69 lbs (31kg)! (https://en.wikipedia.org/wiki/MIT_Daedalus). The gyrocopter in the question appears to be a modified version of the Cavalon model by the company AutoGyro; on it's technical details page it says its empty weight is between 606-672 lbs (275-305kg).


Could a SR-71 be shot down today? I've read that the SR-71 had no missile defenses because it could simply outrun any adversary. Is this still true? Or is it unlikely that the SR-71 could operate unimpeded in the face of modern technology?

Could SR-71 be shot down today?

Theoretically yes. Modern day SAMs like the 40N6 that travel at speeds of Mach 6 can intercept an SR 71 within an operational range of 250 miles upto an altitude of 18 miles. Moreover, the hostile SAM will fire a salvo of missiles(at least 2-3). So the SR 71 will have to jam, drop decoys and out manoeuvre the incoming hostile missiles.Modern day SAM systems can be loaded with libraries of 3D shapes that can be used by the seeker to identify targets and threats.

S-400 and similar Russian/Chinese AD systems are meant to work simultaneously with ECM systems, meaning radars of enemy aircraft will be blinded  as 40N6 and 48N6 missiles zeroes in.

During the days of the cold war Soviet Air Force pilots were instructed to launch two rounds, a semi-active radar homing missile and a heat seeking missile.In this fashion the SR 71( or any other hostile aircraft) being targeted has a difficult problem as it must jam, decoy and/or out manoeuvre three or four tightly spaced inbound missiles

That being said getting in the general vicinity of an intercept is different from an actual intercept.

http://www.codeproject.com/Articles/19310/Hitting-a-Moving-Target-The-Missile-Guidance-Syste

From Jane's  Fighter Combat in the Jet Age : Page 116-117 “SR71 the Ultimate Target”

  On June 3, 1986 an SR 71 was on a mission over the Barents Sea. Six
  Mig 31 Foxhounds, vastly superior to the Mig25 Foxbat,performed a
  coordinated intercept that would have subjected the SR71 to an
  all-angle AAM attack that even a combination of high-altitude
  maneuverability and ECM could not have defeated. Fortunately for the
  American jet, the interception took place over international waters,
  but the Soviets proved their point.

In fact,the SR 71 was retired once the USSR started deploying S 300 SAMs in large numbers.

  I've read that SR-71 had no missile defenses because it could simply outrun any adversary. Is this still true?.

That is not true. The SR 71 did carry a very sophisticated Electronic Counter Measure System(ECM) called the Defensive System

One of the first MiG 31 Foxhound pilots, Captain Mikhail Myagkiy, who had scrambled with his MiG-31 several times to intercept the US super-fast spy plane, explains in his book how he was able to lock on a Blackbird on Jan. 31, 1986:

  The scheme for intercepting the SR-71 was computed down to the last
  second, and the MiGs had to launch exactly 16 minutes after the
  initial alert. (…) They alerted us for an intercept at 11.00. They
  sounded the alarm with a shrill bell and then confirmed it with a
  loudspeaker. The appearance of an SR-71 was always accompanied by
  nervousness. Everyone began to talk in frenzied voices, to scurry
  about, and react to the situation with excessive emotion.

Missiles are faster and can sustain higher G loadings than SR-71.  Assuming that the SR 71 is flying at an altitude of  70,000 ft to 80,000 ft  it only needs to maneuver to out turn the missile, in order to  make the change in intercept geometry fall outside the missile's envelope. However, at extreme altitudes aircraft maneuvers are limited by stall buffet.

The SR-71 could fly a 7,000+ mile mission and the only segments of which are flown at sub sonic speeds  are the take-off, refueling  and landing.

http://www.sr-71.org/blackbird/

http://www.sr-71.org/blackbird/diagrams/index.htm

http://www.sr-71.org/blackbird/diagr...conprofile.htm

The thing is the Soviets knew that in order for any Soviet fighter aircraft to intercept an SR-71 it had to be ahead of its known flight path. These were the tactics the Soviets deployed to even get a glimpse of the SR-71. They always knew when an SR-71 launch would occur because the KC-135 fuel tanker would take off first because the SR-71 had to be immediately refueled once airborne.


Pitching moment as a pure moment and its measurement with a homemade force balance In mechanics, we learn that a force $F$ acting at a certain application point $P$ can exert a torque (also called moment of the force) about another arbitrary point $Q$ in the plane, i.e. $\tau= F \times PQ$ where $PQ$ is a distance vector.
It is possible to move the force $F$ off its application point $P$ and off its line of action and transfer the force the point $Q$. But to keep things equivalent, a couple (two equal magnitude forces, oppositely directed separated by distance $PQ$) must be added. The couple produces a pure moment, i.e. a nonzero moment that does not depend on the reference point (called pole). The new system (a force + a couple) is equivalent to the original one (single force $F$ located at $P$).

Let's contextualize this discussion to an airfoil and its the pitching moment:
The force is the lift force $L$ which acts at the point $CP$ located a distance $x_{CP}$ from the airfoil leading edge $LE$ for a specific AoA. It is mathematically possible to move the resultant lift force $L$ from $CP$ to the quarter point $AC$ located at $x_{AC}$ but we need to add a pure moment (couple force system) to keep the physics equivalent. The net pitching moment about $AC$ is just the pure moment due to the couple since the force $L$ exerts zero torque about $AC$ (zero lever arm).

Interestingly, as we change (for ex. increase) the AoA, the magnitude of $L$ increases and the distance $x_{AC}$ decreases getting closer to the $LE$. We can even in this case transfer the force $L$ to the point $AC$ along the chord (zero torque due to $L$ about $AC$) and add the pure moment. This moment will be CONSTANT and exactly the same as the pure moment for larger or smaller angles of attack. Why? Because even if the two forces in the couple are larger, their mutual distance gets smaller for a larger AoA keeping the overall pure moment the same.

Is that correct?

If we then shift the AoA to the zero-lift point, then $F=0$, leaving us with the force couple only and the same pure moment (which is the sum of all the remaining forces along the chord which balance at this angle of attack) that existed for all other angles of attack.

As long as we define the reference point to be the quarter point $AC$, all variations in lift $L$ with AoA have no moment around this point. If, however, we choose some other point as your reference point, the change in the lift force with angle of attack will add a moment, so your pitching moment is some constant value plus an angle-of-attack-dependent contribution.

Experimentally, when building a force balance that measures lift and the pitching moment using two load cells, I envision using two vertical supports attached to the wing and connected to load cells. For a certain AoA, the lift force will be given by the vector addition of the two forces, $L_{total}=F_1 +F_2$ recorded by the two load cells connected to the supports (I think).

But how would we measure the pitching moment? Where should the two supports be connected under the wing to calculate the pitching moment? How far should the supports be from each other? Essentially, how would I use the forces $F_1$ and $F_2$ to measure the pitching moment?

I think it could work this way but I need some validation: Considering the reference point to be the quarter point $AC$, the two forces $F_1$ and $F_2$ and their torques about $AC$ can be made equivalent to a single force $L_{total}$, the total lift $L_{total}$ passing through $AC$ and generating zero moment, and a single couple producing the nonzero pure pitching moment. For different angles of attack, this pure pitching moment "should" be the same...Will it?

Thanks!

There are better physicists than I at this site, but seem to remember a solution proposed in a wind tunnel test with load cells as follows:  Do the measurements separately.

Lift could be measured at the center of lift using only support 1.  C lift could vary with AOA (data points are generated one at a time from C lift at a given AOA).

Pitching moments could be measured using support 2 only, with the wing pivoting on its AC
(which could be some type of axle).


What is happening with this aborted flight? I live near Southend airport in the UK (SEN, EGMC) and noticed a strange behaviour of a cargo jet that does daily trips to Spain.  It started out on runway 05, took a normal departure until it turned around 5 minutes later.  Then it started circling the airport at 4,000' three times, before descending to 2000', switching direction and finally landing on runway 05.

The flight was obviously diverted back to Southend (it did leave an hour later) but given time was 0030-0100 local time, and it was quite noisy, can anyone think of a reason why it would repeatedly circle round a built up area so many times?

https://www.flightradar24.com/data/aircraft/g-powp#24941d80

edit:

There was a report on a local facebook group that it had lost communication, but its squawk didn't change to 7600

It wasn't "circling around a built up area" - it was placed into a holding pattern.

At this point we can only speculate, but holding patterns are exactly as the name implies - aeroplanes obviously can't pull over and stop like a car can, so a holding pattern is a known position where they can just fly around without causing problems for other air traffic.

It could have been to sort something out on the ground, it could have been to give the pilots time to diagnose or work on the issue, it could have been giving time for the airport to handle the unexpected arrival.

It's next to impossible to guess - the only one I'd rule out is burning fuel as they look to have only done three patterns which is nowhere near enough to burn useful quantities of fuel.