How does turbofan engine performance depend on speed and density altutude? I am looking at a simulation engine (jsbsim). Their turbine engine simulation requires a function, given by table, of thrust at Mach number and density altitude.

Engine definitions generated by their initial configuration generator and all existing configurations I found use the same function that is based on data for [Rolls-Royce/Snecma Olympus 593]. Since that is a turbojet with supersonic intake duct that increases performance at transsonic and supersonic speeds, I somehow doubt the function is appropriate for high-bypass turbofans with simple pitot inlet.

For reference, the table looks like:

     |  -10000       0   10000   20000   30000   40000   50000
-----+--------------------------------------------------------
0.0  |  1.2600  1.0000  0.7400  0.5340  0.3720  0.2410  0.1490
0.2  |  1.1710  0.9340  0.6970  0.5060  0.3550  0.2310  0.1430
0.4  |  1.1500  0.9210  0.6920  0.5060  0.3570  0.2330  0.1450
0.6  |  1.1810  0.9510  0.7210  0.5320  0.3780  0.2480  0.1540
0.8  |  1.2580  1.0200  0.7820  0.5820  0.4170  0.2750  0.1700
1.0  |  1.3690  1.1200  0.8710  0.6510  0.4750  0.3150  0.1950
1.2  |  1.4850  1.2300  0.9750  0.7440  0.5450  0.3640  0.2250
1.4  |  1.5941  1.3400  1.0860  0.8450  0.6280  0.4240  0.2630

where rows are Mach number, columns are density altitude in feet and the values are fractions of rated thrust at zero speed at sea level.

The thrust decreases with altitude, which is OK. But with Mach number it only decreases initially and at M0.8 it is already more than static thrust. I had the impression that this requires high exhaust speed and therefore isn't, and can't, be true for turbofans with their low exhaust speed.

So I'd like to know whether:

how appropriate or inappropriate those values are for high-bypass turbofans, especially the recent types with bypass ratio up to 11:1 and
where I could get any better data.

I understand the actual data for new engines will be proprietary. I just hope to do better than using data for old and very different engine designed for different operating range.

The dependence on density is straightforward: Thrust depends on the mass of air pushed out at the back, and this is changing linearly with density if the speeds don't change.
$$T \propto \frac{1}{\rho}$$
The dependency on speed has two factors, the intake precompression and the speed difference between flight speed and exhaust speed. First intake precompression:
$$T \propto \left(\frac{\kappa-1}{2}\cdot Ma^2\cdot\left(1-\left(\frac{Ma_{intake}}{Ma_{\infty}}\right)^2\right) + 1\right)^{\frac{\kappa}{\kappa-1}}$$
or, if we insert $\kappa = 1.405$ for diatomic gasses:
$$T \propto \left(0.2025\cdot Ma^2 \cdot\left(1-\left(\frac{Ma_{intake}}{Ma_{\infty}}\right)^2\right) + 1\right)^{3.469}$$
The term which captures the thrust proportionality to the speed difference looks like this:
$$T \propto \frac{v_{nozzle} - v_{\infty}}{v_{nozzle}}$$
Please see this answer for an explanation of the variables. The plot below shows how little the intake precompression matters at subsonic speed, but how much it does at higher Mach numbers. Note that the plot sets the pressure at the engine face to 1 when flight speed equals the assumed intake speed of Mach 0.5. This pressure recovery lets thrust climb above the static value once Concorde flies supersonic.

Explanation of the plot: This shows relative ideal intake pressure over speed, assuming that the speed at the compressor face is Mach 0.5. Note that in static conditions the air needs to be accelerated, so the intake pressure is only 84% of ambient pressure, and at Mach 0.85, the maximum speed of airliners, the intake pressure is 1.37 times higher than ambient pressure. But at supersonic speed things take really off: Pressure recovery for the Concorde was already 6 at Mach 2.0, and for the SR-71 it was 40 at Mach 3.2.

If the engine has no variable nozzle, it is fair to assume that the nozzle speed will not change over the flight speed if the throttle setting is constant. If the nozzle speed is low (= high bypass ratio), the drop over speed is steeper, which explains the difference between turbojets and turbofans.


What is the average weight difference between composite and metal airliners? Is there any rule of thumb for weight savings using composite materials. For example, is there an early model large airliner like the B747 or even B737 that later was modified with composite wings or fuselage that shows weight savings?

(Own work via boeing.com) Overlayed scaled drawings.

Above you see similar sized planes with the same 3-class seating (± 1 seat). The newer-more-composite 787 is 16 tonnes heavier, yet delivers up to 20% fuel saving (route dependent). 3.4 of the 16 tonnes are the newer and bigger engines. And the rest is primarily bigger wings (which can be built bigger more easily thanks to composites).

The aim is building bigger wings, not losing weight. The other main goal is the reduced maintenance cost (better fatigue tolerance, no rust, etc.)

Boeing says:

  The result is an airframe comprising nearly half carbon fiber reinforced plastic and other composites. This approach offers weight savings on average of 20 percent compared to more conventional aluminum designs.

Based on that quotation, the answer is -20% (given the same wing, etc.). Also note the 787 also saves weight from the no-bleed architecture, yet as the above shows, it's not a lighter plane than the one it replaces. (No-bleed also improves engine fuel efficiency, not just weight.)


What is this on the aft end of this GEnx engine? In the next picture, corresponding to a GEnx engine, what is the item circled in red?

Thank you very much again.

The pipe is the center vent tube which vents air from the oil sump.

From airliners.net (User MD11Engineer):

  All gas turbine engines use pressurized seals for their shaft bearing compartments to keep the oil in. The result is that the scavenge oil returning to the oil tank via the scavenge pump, chip detectors and scavenge filter contains a lot of air, it is more a foam than a liquid.

  Engines use a centrifugal oil / air separator in the circuit to remove the air from the oil and to vent the system to the ambient to avoid overpressure.

  PW and RR use centrifuges attached to their main gear box, which vent overboard through a hole in the cowling.

  GE and CFM use the hollow N1 shaft as a centrifuge. The heavier oil sticks to the inside of the shaft and gets returned into the circuit via holes, while the lighter air stays in the center and gets blown out through the pipe in the back.

  The air blown out is not completely free of oil, so when the engine has just been shut down, you´ll see some oil vapor coming out from this pipe.

Source: www.airliners.net

Similar vent is found in other GE engines, like the GE90.

Source: airwaysnews.com

The system looks like this:

Source: CFM56-3 Training Manual, thanks to mins.

This is the actual part in GE90-100:

Source:standardaerocomponents.com


How does a propfan work? Could someone give me a simple working of a propfan? Also I've heard the 2 sets of blades in a propfan rotate in opposite directions. Is this true? And if so why?

To keep it simple (source for all that follows is Wikipedia - Propfan):

You can think of the contemporary propfan as a turboprop that has two high rpm contra-rotating propellers or fans with six or more highly swept fan blades each. These fans are driven by a turbine engine through a reduction gear or a low-speed free turbine.

High rpm is used to reach higher speeds and altitudes than conventional propellers.

The contra-rotating fan arrangement is used to remove torque effect, and to enhance efficiency (note: some early versions had just one fan).

Fan blades are swept to keep drag minimal at high rpm (high blade airspeed).

This description might very well be considered an oversimplification, but I guess this is what was asked for.


How quickly can a hot air balloon climb? What's a typical rate of climb for a hot air balloon, assuming stable air with no updrafts? I'm thinking of the classic 'sightseeing ride' type of balloon here.

It very much depends on the balloon, but 2 metres/second in actual flight is pretty typical, while most are capable of something like 3-5 m/s ascent/descent if required. Ascent and descent speeds are normally about the same for a particular balloon, but this isn't a hard and fast rule

"sport" balloons being are capable of moderately less comfortable ascent/descent speeds in the range of 5 to 10 m/s


What does "Crew: Top of your mind!" mean in commercial aircrafts? On a flight this year in Europe, the pilot or co-pilot announced midflight "Crew: Top of your mind!" via the loudspeakers. The crew didn't visible react on that and I couldn't notify any change in the flight after that. What does this announcement mean?

The flight was either with Swiss, Air Serbia, SAS or IcelandAir. Unfortunately, I can't remember which one.

Could it rather be « crew: top of climb » which some airlines use, but 2 things contradict this: a TOC mid flight is unlikely and although used by some airlines it is more the top of descend we indicate to the flight attendants for them to start preparing for landing.


How much thrust can the thrust reversers create? Let's say for the sake of the question, the plane is an 787 Dreamliner and the engine is the General Electric GEnx-1B64 (that according to Wikipedia can produce a maximum thrust of 284 kN)

In comparison to the "regular forward" thrust that a jet engine can generate, how much thrust can we apply to this engine in the reverse mode?
Can we apply full power in the reverse mode?

Estimations

We can at least estimate a reverse thrust case based on some numbers and some physics, a bit of a specific case of this question. The stopping distance equation:

$$d_f=\frac{v_i^2}{2a}$$

The information in Appendix B here for the 727-200 gives stopping distances for different cases. If we look at a sea level pressure altitude case with 120,000 lb gross weight, the stopping distance is 2452 feet. The correction for a reversers only case is 2.57, bringing the distance to 6302.

At a landing speed of 200 ft/s, the plane will take 11500 lb of force to stop in that distance. Each engine on the 727-200 provides 14500 lb of thrust force maximum. Considering that part of the stopping force will be provided by drag and surface friction, the reverse thrust is about 25% of the maximum forward thrust. The reversers will be more effective at higher air speeds, so the maximum will be higher than this.

Figure 39.5 here shows a graph of reverse thrust compared to forward thrust for different bypass ratios and reverse thrust types. This is a good check for a general case. The GEnx-1B64 has a bypass ratio of about 10, and reverses the fan but not the primary exhaust, which gives a ratio of 30% of maximum forward thrust.

Summary

The engine will not run at full power when in reverse mode, so accounting for this and the bypass ratio will leave you with about states that modern thrust reversers can convert up to 35% to 50% of their forward thrust into reverse thrust.


Why is everything in aviation written in abbreviations? please tell me if there is already a duplicate, I could't find one.

Why is like everything in aviation written in abbreviations?

ACARS Message:

  /WND 275057/MCH 81/TRB LT CHOP /SKY UNDERCAST/ICE NONE

Why don't they just write:

  Wind: 275 at 57 Knots. Light Turbulences. Not cloudy, No ice.

And also in the cockpit

HDG, SPD, ALT, LDG GEAR.

Of course, I know, its shorter and faster to read, but wouldn't it make such a bug difference if you write "Heading" instead of HDG?

Thanks, Noah

For the weather, those come from ye olde days of teletypes when it took a significant amount time to transmit characters. Yes, they should go away.


How can L/D Max be both Best Glide speed and Max Range speed? According to the book "Aerodynamics for Naval Aviators", best glide speed AND max range speed for propeller aircraft both occur at L/D max.
This is a little confusing because in an A36 Bonanza Vbg is 110 KIAS and Vmax range has been experimentally calculated by several sources to be about 125 KIAS.
So my explanation for how both of these are L/D Max is that L/D Max is a specific AOA, not a speed.
However, this brings me to my question.  Obviously Vbg is power off and Vmax range is power on. Assuming that L/D max is around 6 degrees AOA, with no power the airplane is descending at about 700-1200fpm (depending on prop pitch and other configuration items) at a speed of 110 KIAS.  At max range speed the airplane is level at 125 KIAS and presumably also at an AOA of approx 6 degrees.
Something seems off here.  Here is what I’m having a hard time correlating:  I teach that trim controls AOA, not speed.   If the airplane is trimmed for an AOA of 6 degrees, adding or removing power should only change the rate of climb/descent, not the airspeed.  Adding power gradually from the power off glide config at 110KIAS will eventually result in
level flight AT 110 KIAS.  If we wanted 125 KIAS we would have to add power while trimming down (lowering AOA) which means we are not at the same L/D Max AOA at Vmaxxrange that we were at Vbg.
I feel like I’m missing something here, so either one of my assumptions is incorrect, or there is another puzzle piece I’m missing that explains this. If we have to retrim for 125 KIAS level with added power, how can we be at the same l/D max AOA?

I'm going to answer with the caveat that I don't have as deep of an understanding of this as I would like, and someone smarter than me may be able to correct or expound on my response.
Best Glide is a purely aerodynamic concept. There is no powerplant involved, so you're simply converting potential energy (altitude) into forward motion, at a rate and L/D ratio that is driven by the angle of attack. It's a simpler concept.
When you add a powerplant into the equation, it gets a lot more complicated. The powerplant itself has modes where it's more efficiently converting fuel energy into thrust, and modes where it's less efficiently doing so. Max Range, therefore, depends not only on aerodynamics, but also how efficient the powerplant is. When you add powerplant dynamics into the equation, you might settle on a best range speed that is different than the purely aerodynamic best glide range speed.
Simply put...

Best Glide is where L/Dmax occurs.
Max Range occurs when (FuelBurn / GroundSpeed) is the lowest.

On a related, but slightly different, note: Piston airplanes and Turbo(fans/jets) behave differently when it comes to producing power at different airspeeds. It's why we generally measure turbofan engines in thrust, and piston engines in horsepower. This difference is why Max Range and Maximum Endurance speeds correlate with Best Climb Angle and Best Glide speeds differently, when you compare pistons to jets.
I hope this helps.


How are aircraft lifespans tracked? When returning from each flight, during which it is subjected to adverse conditions, say arctic weather, desert heat or just moderate conditions, how is an aircraft evaluated to accurately keep track of its lifespan?

If the method is a standard: "this aircraft has had "this many" hours of flight, & therefore, there are "this many" hours left for the aircraft before it is rendered not worthy for service" then this method doesn't consider the various conditions the aircraft is subject to during each flight, which impacts the aircraft's lifespan at varying degrees. I trust there is a more accurate method of evaluation (after each flight perhaps?)

Appreciate your asisstance in clarifying this doubt.

The life (Low Cycle Fatigue life) on the Civil airliners is generally talked abut in terms of number of cycles i.e. number of flights. And since airliners undertake quite predictable flights in terms of loads and stresses, and typically a very limited variations among these parameters for their entire life (since any aircraft would be designed for certain type of range and payload and would be used for that particular purpose mainly, for economic reasons), its easy to talk in terms of number cycles, since variations from flight to flight are limited.

But this issue of keeping track of actual mission profile is very critical for fighter (actually any military jet but I would restrict myself to only Fighters because its easier to point out the things for this case) jets which have quite unpredictable usage profile. Any fighter jet is typically designed for a certain mission mix i.e. mixture of a bunch of mission profiles that the fighter is expected to carry with the expected relative frequency (which comes from the past experience of an Air Force). But still in real life, the actual missions flown end up being quite different that this assumed mission mix. Now it is possible to utilize the airframe structural life to best possible extent by keeping track of actual mission profiles flown and debiting life for each mission from the designed number of hours. Obviously one needs to calculate the life debit for actual mission flown in terms of the equivalent hours for assumed designed mission mix. Say a fighter is designed for 8000hrs assuming it will fly 10 times of missions with certain frequency, and it recently flew a mission for which we know the parameter, then what would be the number of hours of equivalent life that was utilized from this 8000hrs..?

To calculate this we need the loading parameters of each mission such as how many Gs were pulled for how long time intervals, how many rolls performed with what roll rate and so on. Every aircraft has system which collects this information (measured by various sensors) for entire mission. Once on the ground, this information is fed to what is called as "Life Tracking System". It analyses the data, calculates how many hours of debit this mission took on the airframe and then decides what is remaining life.

This can be done at component level as well and one can keep track of available life of each component and accordingly schedule maintenance for each component individually. I am not sure how this is exactly done for entire aircraft (Looking for Patents by Aircraft OEMs would be a good way to start digging in), but I know for the Jet engines. The methodology should be the same in principle. Specifics might change. I suggest you read about Volvo Aero RM12 Life Tracking System (LTS) which finds its origin in GE's LTS for F404. (A good starting point to read) and another one. Essentially all OEMs have similar systems now. RM12 has improved utility of the engine by ~30% i.e. the engine is used for 30% more time now as compared to the case where LTS was not used and differences in missions were not accounted for. Because many missions do not take as much toll on the structural life as it was expected during design (or more number of less stressful missions are flown in actual practice than it was assumed for design).

Most popular technique used to calculate the equivalent LCF life debit for each mission considering variations in loads and stresses for each mission specifically is known as Rain Flow Counting Algorithm. The process essentially looks like this:

You apply the actual measured loads and see what stresses the analysis predicts for each mission. Then apply Rain flow Counting to calculate accumulated structural fatigue damage and residual life remaining. Rain drop counting is the model which helps you covert the irregular fatigue loading (i.e. varying missions) to equivalent cyclic loading and thereby coming up with a life debit number which is equivalent to the design mission mix and which you can subtract from the designed life hours. That's how you can take care of variation in the missions and loadings in each mission.


Can test flights carry passengers? When a new plane is being tested, could it at some phase carry passengers (maybe for free).. Or does it have to be certified, before it can carry a single passenger. Could some one throw some light on any FAA regulation in this regard

Flight tests of new aircraft are covered under Part 21 Subpart B—Type Certificates §21.35 Flight tests.

There is no provision for the carrying of 'passengers' during any test flights, but then, there is no limit on the number of 'flight crew' either. FAA regulations does not explicitly prohibit the carrying of any passengers as such; however, it places onus on the applicant for ensuring the safety of anyone abroad during test flights:

  (d) Each applicant must show for each flight test (except in a glider or a manned free balloon) that adequate provision is made for the flight test crew for emergency egress and the use of parachutes.

This places severe restriction on carrying of anyone during test flights. However, before certification, the manufacturer can carry passengers as long as it is not for commercial purposes. Actually, Airbus did this during the test flights of A350 XWB:

  Another important aspect of A380 and A350 XWB testing was the Early Long Flights (ELF) programmes, which went above and beyond certification requirements. For these evaluations, a cabin-equipped flight-test aircraft was operated on simulated commercial services with real “passengers” – comprised of Airbus employees – and actual airline flight crews to evaluate cabin systems in typical operating conditions.

Unless the flight testing is at an advanced stage or the manufacturer is extremely confident of the design, I don't see any non-essential flight crew being allowed in test flights, for obvious reasons.

In case of test flights after maintenance or alteration, CFR § 91.407 - Operation after maintenance, preventive maintenance, rebuilding, or alteration says almost the same thing:

  (b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.


Where does my pee go when I flush at 35,000 ft? One thing I guess a lot of people wonder is: what happens you flush the toilet in an aeroplane?

Does it fall out the belly of the plane and disintegrate? :)

A kiwi woman complains that "aeroplanes are taking a s**t on her driveway", beneath the flight path. Is there any way this might actually happen?

I can speak for the most common commercial models (the 7x7s, A3xxs and the like) via an engineer friend.  All of these models flush into a tank which is emptied on the turnaround.

For Vulcans, I can speak with first hand experience.  Each crew member had a stainless steel "pee tube", a funnel, which fed into a rubber bladder.  They are emptied and cleaned during the after flight inspection.

I was changing a radio under the rear crew table where the electronics, navigator and radar operator sat.  This involved squeezing down behind the seats to lie under the table, disconnecting and unfastening the radio, hauling onto your chest then pushing it up onto one of the seats and reversing the process to get out from under the table.

As I pushed the radio up onto the seat, I knocked one of the pee tubes and bladders out of it's clip holder which then emptied the contents onto me and the radio.

The bladder had not been emptied - and the aircraft had been in the hangar for 3 weeks!

Of course, it was my job to clean up the mess - lots of french chalk as urine is very corrosive to airframes.

The radio also needed writing up so I tagged it as "suspect urine ingress".

The same radio came back to me with a tag attached saying (and this might work only for non-American English speakers) - "are you taking the p*ss?".

Yeuch.


When airplane pilots begin a 10 minute wait timer when lightning strikes, is there a geometric reason behind it? Preface
This question is taken from a similar one inside the mathematics stack exchange.  I followed the suggestion given in the comment by Jyrki Lahtonen and posted said question here.
Background
Recently, on a flight back from Charlottesville, NC to Logan Airport, MA, the Pilot stated this to his passengers over the intercom, I paraphrase:
As you can see out the window, we just saw some lightning strike within 3 miles of our plane. Because of this, they closed the ramp gates. Every time lightning strikes within three miles of our plane, we have to reset the wait timer to ten minutes.
This made me wonder if there was a mathematical connection between the distance of a lightning strike and the amount of time needed to wait for take-off to ensure another strike will not occur on the ramp.
Work
Let the "area that causes a delay" when lightning strikes be represented by a circle of radius 3 miles. In addition, let us envision a scenario where lightning strikes on the circumference of the circle, i.e. 3 miles away from the plane, which is the farthest distance from the place that will trigger a 10 minute wait.
The intersection of these circles is a clean venn-diagram shape, and results in an area of (9π)/3 sq.mi. or 3π sq. mi., which is about 9.42 sq. mi, and the ceiling of which would be 10.
Question
Given that the pilot stated that a wait time of 10 min would be triggered if lightning struck within 3 miles of the plane, and the area in between a strike on the circumference of 3 miles and the plane results in a ceiling of 10, is there any mathematical basis for a lightning strike wait time of 10 if given a "danger zone" of 3 miles?

No, because adding candles to candy does not make much sense.
The dimensions are different, so the relative numeric values depend on the choice of units. You could equally state the rule as you have to wait ⅙ of an hour after lighting strike within 5 km (if it's statue miles; 5.5 if nautical) and now the numbers won't match any more.
Besides, it is a 3 mile radius, so the area is about 28 square miles and the numbers never matched to begin with.

The real reason is two-fold:

When there is active storm right over the airfield, somebody could get struck by lightning. Inside aircraft and vehicles is safe, because the lightning will ground through the skin and not get inside, but out on the ramp it wouldn't be. 10 minutes is long enough to consider the storm no longer active.

The storm builds up static charge on the aircraft and vehicles. This is again not a problem for the occupants, because the conductive skin ensure the whole vehicle is at the same potential, but it could cause a static discharge strong enough to hurt someone or set something on fire when touching the vehicle from outside. 10 minutes is considered long enough for these charges to gradually discharge through the wheels to the ground and through the static wicks to the surrounding air.
This would also apply to aircraft that flew near the storm just before landing, but that is normally avoided as storms generate dangerously strong wings.

The 3 mile radius is simply size of typical storm.


Why does the F16 HUD give you one number for your speed and the analogue gauge another? Why does the F16 HUD give you one number for your speed and the analogue gauge another different number?

The primary airspeed indication is in the HUD. You can select CAS (calibrated airspeed), TAS (true airspeed) and GND SPD (ground speed) on the HUD panel on the right console.

The backup airspeed indicator (the analogue gauge you are referring to) is located below the ICP (integrated control panel) on the center console. It can indicate from 80 kt to 800kt with a scale in 10 kt increments up to 400 kt and then 50 kt increments up to 800 kt. It is a rather basic analogue instrument providing IAS (indicated airspeed) only.

As the scale is very coarse (higher precision is not needed) you won't be able to see a noticeable difference when the HUD is switched to CAS. Most probably the HUD was switched to TAS or GND SPD. But without further information or an example photo from your side it is hard to tell.


How to pass ATPL as an ATC? i have graduated from Nation Aviation Academy and my occupation is Air Traffic Control. But to become a pilot was my childhood dream. So my question is, is it possible to pass atpl exams in this situation or is it necessary to pass the pilot course? I already have medicine and icao level. Thanks in advance for answering my question.

Being an Air Traffic Controller does not provide any legal shortcuts for piloting courses, in any jurisdiction as far as I am aware. Sure, you could probably sleep through the lectures on meteorology and maybe parts of others, but you still need to sit and pass all 14 exams. You would have little to no advantage on the subjects of aerodynamics, aircraft systems, performance and loading, and human factors.
You also need to complete the practical flight training and meet the same requirements as everyone else.


Does the AP disengage if the plane is upset and how would the flight controls react if not being held? Does the AP (autopilot) essentially detect a rapid change in speed/altitude as a wild maneuver? If so, upon disengaging, if the pilots are not holding the control column in a neutral position, will it move in whatever direction the plane is going?

For example, a steep climb that wasn’t anticipated, and no one holding the Column, will it fall back towards the pilots, ultimately making the steep climb worse?

For non FVW airplanes:

Yes it will disengage if certain pitch and roll attitudes are exceeded.  When it disengages, the controls are "let go" if the A/P was applying an input at the time, and the control column will move to whatever its natural trimmed state is at that time if the elevator is manually operated with trim tabs.

If the airplane has irreversible hydraulic controls and an artificial feel system and a trimmable stabilizer, the column will just spring back to neutral and the airplane will seek its existing trimmed speed.  If the trim speed is the same as the current speed, pretty much nothing happens, if the trim speed is much different that trim speed, the nose will pitch up or down to try to accelerate or decelerate to the trim speed set by the current state of the pitch trim system.

It's as if your copilot was flying, minding his own business, and you shot him dead.  The column will just go to wherever it wants to go when no-one is holding it.  The airplane has natural static "stick-free" stability so it will seek its natural trimmed state and if the A/P input was different from that, it'll just start going where it trim state wants it.  As if you pulled on the column and then let go.

On an airplane with control cables, the autopilot is a little computer running a bidirectional electric winch (the A/P servo) back in the tail who's winch cables are tied into the elevator cable run.  It drives the cable circuit from back there instead of from the column.  The autopilot also usually works the pitch trim that same way a human pilot would, to relieve the need for the servo to hold control pressures beyond a small threshold same way a human would.

So if the airplane was more or less in trim when the A/P kicks off, not much happens.  If the airplane was in some crazy attitude because of some outside event, the A/P kicking off is like you were flying and got flipped over and you took your hands off the controls to cover your face in fright (that's what I would do lol). The controls will just return to where they are trimmed to go to in that state.  On most airliners with powered controls and a moveable stab, the column always springs back to the same neutral position regardless of trim state.

If the a/c is FBW, the A/P is integrated into the computers that actually run things and it gets a lot more complex, although the end results are not that much different.


How often do jet-liners have touch and go landings? I read that a go around is 1-3 out of every 1000 and I wondered how rare it is for a large commercial plane to actually hit the runway before deciding to go back up again.

Quite rare.

An approach abort that results in touchdown is called a "balked landing" and generally happens when you've started the landing transition, reducing power and starting the flare, where you are in a "low energy state" (speed decelerating below Vref and engines going to idle) at the time you make the go-around decision.  It's considered a high(er) risk maneuver like high speed rejects on takeoff, because at that point you are likely going to touch down, however briefly, whether you want to or not.

Normal missed approach go-arounds happen mostly because of weather where the runway environment wasn't visible at minimums, and maybe occasionally from a runway incursion that is noticed early, or something like a report of a flock of birds in the way, which would be most of those 1-3 per 1000 landings.  They happen at at least a hundred or couple hundred feet and usually don't involve actually touching down.

A balked landing will generally only be for something like a runway incursion at the last second, leaving you with a situation where landing and rolling out is obviously more dangerous than going around because you are probably going to hit something on the runway, and they are pretty rare events.  Balked landings are usually special maneuver covered in the initial type course and may be included in recurrent training.


Why do we check Idle operation with carb heat on during a Cessna 172 run-up? I understand this is to “check our engine is still operating at idle”, but can someone explain this more in depth?
Like why wouldn’t it?

Because, in engaging the carburetor heat, you are decreasing the density of the air entering the engine with the same fuel flow, thereby richening the mixture.  At idle power, if the throttle idle set screw is not properly adjusted, there is a risk of an engine failure from too rich a mixture entering the engine.  The idle power carb heat check is a good way to verify the engine won’t do this in flight.


What is the maximum momentary G force that a modern airliner's wing can take before it snaps in extreme turbulence? Taken from an aviation safety pdf..
Intensity - LIGHT - Vertical acceleration (g) 0.20-0.49 - Derived Gust (fpm) 300 -1,199
Intensity - MODERATE - Vertical acceleration (g) 0.50-0.99 - Derived Gust (fpm) 1,200-2,099
Intensity - SEVERE- Vertical acceleration (g) 0.1-1.99 - Derived Gust (fpm) 2,100-2,999
Intensity - EXTREME - Vertical acceleration (g) >2 - Derived Gust (fpm) >3,000
The g's in this list is additional g's. So ''> 2'' will read as 3 total g, as there is an additional g load factor of 2.
The limit turbulence load (the worst theoretical turbulence the plane  would encounter) for modern jets is 90-100 feet per second, or around  6,000 feet per minute. (FAR Continuous turbulence criteria):
''Uσref is the reference turbulence intensity that varies linearly with altitude from 90 fps (TAS) at sea level to 79 fps (TAS) at 24,000 feet and is then constant at 79 fps (TAS) up to the altitude of 60,000 feet.''
There is a 50% safety margin, so the max  turbulence it will encounter before a wing snaps off is about 150 fps.
What (momentary!) G loads would an airliner experience if it was  cruising and suddenly encountered a patch of 100 fps intensity  turbulence? (The ''worst case'' turbulence?)

It's hard to give a direct answer to your question. But I will try to give a realistic answer.
As stated in the "Easy access rules for large aeroplane CS25" under EASA regulation:

Except as provided in sub-paragraphs (d) and (e) of this paragraph compliance with the
provisions of sub-paragraph (a) of this paragraph must be demonstrated in flight over the
acceleration range –
(1) –1g to 2·5 g; or
(2) 0 g to 2·0 g, and extrapolating by an acceptable method to – 1 g and 2·5 g

That's the normal range of load factors for a modern airline; of course an aircraft can be design to withstand more positive or negative G's, but most of them have an upper limit of +2.5g and -1.0g (in clean configuration), as stated in the regulation.
The following fundamental requirements have been developed around the experiences of metallic airframes and remain the basis for the certification of composite airframe structures. These require that the structure (by test and/or analysis) demonstrate the following capabilities:
• Static strength:
– Design limit load (DLL), no failure or unacceptable deformations. DLL is normally the maximum load anticipated to be placed on the structure in its lifetime. – Design ultimate load (DUL), no failure, although limited permanent deformation is acceptable; DUL = DLL × 1.5 (generally).
The limit of +2.5g and -1.0g will be our DDL, so if we "remove" the safety factor (1,5, but can be higher) the Max G load will be +3,75g and -1.5g. if you fly at this load factor the aircraft will not broke apart or will have catastrophic failures, but deformation can occur.
Let's talk about turbulence:
Extreme turbulence in reality is not part of the categorization of levels of turbulence (At least in EASA rules), the upper limit is the severe turbulence:

Turbulence that causes large, abrupt changes in altitude and/or attitude. Aircraft may be momentarily out of control. IAS fluctuates more than 25KT. (>1.0g at the aircraft’s centre of gravity)

So assuming a fluctuation of 1g (positive or negative) inside turbulence, we can assume that we will be able to reach +2.0g or -0g passing trough this turbulence.
If the turbulence will be "extreme" (let's assume a fluctuation of 2gs), we will reach a max positive G load of 3g and a negative G load of -1g.
As you can see, we still below DUL limit. I can tell you that probably the aircraft will not have any deformation in that range also if above DDL, this is because we are talking of instantaneous accelerations and not continuous and constant load factors (DUL and DLL are based on that).
The aircraft will however be checked after the encounter of severe turbulence.
Reassuming, is very hard that turbulence will cause any significant or severe damage to a modern aircraft. (Severe or Extreme)
But to give an answer to your question I can give you an example:
China Airlines flight 006 experienced vertical load factors of up to 5.1 g on 19 February 1985. The aircraft landed safely and there were no fatalities, but there was some damage:

From the NTSB incident report:

The wings were bent or set permanently 2 to 3 inches upward at the wingtips; however, the set was within the manufacturer's allowable tolerances. The left aileron's upper surface panel was broken and the trailing edge wedge was cracked in several places.

5.1Gs was probably the top of the load, but during the recover they were above DLL and DUL for a while.
This however didn't cause a catastrophic failure of the wing section.
I don't have any document or personal information or experience about the instantaneous or the continuous g Load to cause the snap of the wings, but I think that we are talking of +7/8g -4 continuous and +10-11g -5-6g instantaneous.
I hope that I answered your question.


Cessna 172/182: Should I set the tank selector to the R.H. tank after parking the airplane? The single-engine Cessna 172 and 182 aircraft models have a dual gravity-fed fuel system, where you can draw from both the LH and RH tank simultaneously in flight.

I've heard it said that when you are securing the airplane after a flight to leave the tank selector on the RH tank to prevent crossflow if the ramp is uneven. (So you don't end up with all the fuel in one tank).

Is there any merit to this?  Does it actually block the crossflow valve to do this?

The C172S manual I have says to set the selector to left or right as part of the "securing airplane" checklist:

  Fuel Selector Valve -- LEFT or RIGHT to prevent cross feeding

I was also taught to set it to right during my initial training. The idea is to prevent cross-contamination or leaks if one tank is compromised. Another reason is that if you park the aircraft on a slope, you could end up with an imbalance between the tanks, as you said.

So the POH confirms that it prevents cross feeding, at least in that model: you should always check the POH for your specific aircraft.


How much do aileron on a commercial airliner move for manoeuvring and trim? I recently flew on an MD88 and had a good view of the aircraft's wing from my seat (read: I sat right next to the toilet). During the flight I noticed a couple odd things about the ailerons on the left wing. First, the middle one (there are three that I could see) was constantly pitched up by about an inch. Second, none of the ailerons seemed to move more than a couple millimeters during even the fastest banks (in fact, it was only that second aileron which I observed moving at all).

My questions are:

Was the second aileron being constantly pitched up for some reason? Or was it a trim issue?
How much do the ailerons even need to move to bank the aircraft? Would a couple millimeters do the job, or should I have seen more movement?

Edit: After taking some of the comments and searching around some more I found this diagram which seems to indicate what I was observing was not an aileron, but the outboard flap. Also this answer details why outboard ailerons are often locked in high-speed flight. But that still leaves the question of why the flap was constantly pitched up throughout the flight.

I have never flown an aircraft, only flew in them, but I am studying aerospace engineering. If ailerons were deflected the whole time, I would say that it was a trim issue. Note that the MD-88 are old aircraft (introduced at 1980 and production stopped at 1999, source: Wiki page on MD80 series), so having some idiosyncrasies such as some roll instability or drift is to be expected. I have not studied the degradation of aircraft over time, but it makes sense. I had to mention that since stackexchange does not like people sharing opinions.
This question is more interesting for me since we can do some back of the envelope calculations to establish some simple facts. Lets approximate how much force would be required to get an angular acceleration of say 5 degrees per second squared, a very extreme case. Gradual turns are initiated with angular accelerations of about 2 degree per second squared; that way a 30 degree bank takes about 15 seconds to enter.

The most relevant thing that would be required is an estimate of the mass moment of inertia (MMOI) of the aircraft along its X axis (which is an axis pointing in the flight direction).

First the Maximum takeoff weight (MTOW) is taken from data (MD88 mass data) and the dimensions are approximated from drawings and data (MD88 dimension data)

Than the aircraft is modeled as a filled cylinder with the wings as two cuboid. The mass of these 3 sections are approximated from the mass fraction as found in this article. Crunching up all the numbers leads to an approximate $I_x$ for the MD-88 as $3350 \times 10^3$ $kg$ $m^2$.

We know that $M = I \alpha$, where $M$ is the rolling moment, $I$ is the MMOI and $\alpha$ is the angular acceleration. 5 degrees per seconds squared is about 0.09 radians per seconds squared. And $M = Fl$, where $F$ is the force from the aileron and $l$ is the moment arm. The moment arm is about 16 $m$ since the half wing span is about 17.9 $m$. So we have $F = \frac{I \alpha}{l}$. This leads to a requirement of 19000 N of force from both ailerons, and about 9500 N from each aileron.

In normal flight (at approximately MTOW) the wings are producing about 600 $kN$ of force to keep the aircraft in air. For this rather extreme banking maneuver the ailerons need to create a 10 $kN$ difference in lift (which is about 2% of the total lift).

Lets estimate the required change in lift coefficient for this change in lift. Assuming one aileron influences 15% of the wing surface, a flight at an altitude of 10 km, and a airspeed of 230 m/s, we find that each aileron should cause a 0.05 change in the lift coefficient of the wing segment. Have a look at the image below for an idea of about how much the lift coefficient changes with flap deflection. It seems evident that about a 5 degree deflection is required to get to the required order of magnitude of change in the lift coefficient.

(source: stanford.edu)

Now that we have some idea about the order of magnitudes, we can talk about the aileron deflection question. Using information from the aileron sizing documentation, we can think about the moment caused by your specific question. If we imagine a deflection of 5 mm (seems ok for stabilization but a little too low for control), we can approximate a aileron deflection of about 0.7 degree (assuming a $c_a/c$ of 0.25 and chord length of 1.5 $m$). Hence, I do not think deflections of a few mm are enough to roll the aircraft as would be required during landing maneuvers around an airport. Thus I think the aileron you saw that was trimmed is doing the heavy lifting for the rolling.

There are further subtleties introduced into the required magnitude of deflection of the ailerons due to other design parameters such as the incidence angle of the wing and the specific nature of the airfoil in the wing extremities. The former introduces a differential in how much the left and right ailerons need deflecting and the latter may cause the sections with the ailerons to have inherently higher lift in order to get a better lift distribution over the wing. These two are just to mention two of many things that interact to determine the rolling dynamics of the aircraft.

I wanted to include more sources for my work, but apparently I can only include two links; so I removed all of my supporting material and left only the image for consideration. If you want sources for my analysis, send me a message.


Explain how the infrared flame detector work? For fire detection systems, such as for engine fire detection, how does the infrared flame detector work?

Infared flame detectors have an imaging sensor that "sees" infared light.

When a flame ignites the various  types of materials burn at different strengths, intensities, and -what we care about- wavelengths.  In the visible  spectrum  we can describe a flame as red or blue which can be simplified flames discrete wavelengths.

The IR sensor can detect the wavelengths  given off outside that visible light spectrum. This helps eliminate sources  like a technicians  flashlight from setting off a pure visible  optical sensor.

An example from Wikipedia shows a distribution  of this emission.

! Fire spectrum


What is prop RPM control logic on PC-12? Pilatus PC-12 has a constant speed propeller, but it does not have a prop control lever in cockpit, just a power lever and small fuel on/off lever.
So how does it determine the prop RPM? Does it simply maintain constant RPM at all times, or is there some predefined schedule depending on power setting and airspeed, and if yes, what?

You effectively have a two speed prop (kinda like the 2 speed Power Glide automatic transmission on my first car, a 1964 Pontiac - well, not really).  It's controlled by software, and there is a 1700 rpm high rpm and 1550 rpm low rpm mode, and that's it.
The PC-12's PT-6's FADEC system controls the prop governor, which runs the prop at 1700 rpm for all settings by default. When you want to quiet things down, you push a button that engages a low rpm mode, where it runs the prop at 1550 rpm for all settings below Take Off power (if you are in low rpm mode and push the lever balls-to-the-wall, it automatically brings the prop up to 1700).
So, you take off, and the prop is at 1700.  Come back to Max Continuous, it stays at 1700, come back more for cruise, and it still stays at 1700.  Then when you want to slow it down, you push the PROP LOW SPEED switch/light just ahead of the power lever, and it drops to 1550 for all power settings, except if you go back to full power, where it runs back up to 1700.

Another innovation is a low, 1,550-rpm propeller setting. Down on the center pedestal is a push-button for shuttling between the electronic propeller governor’s normal, 1,700 propeller rpm and a lower, 1,550-rpm mode for a quieter cabin. Except for take-off—when the FADEC will automatically command 1,700 rpm—you can use low-speed mode at any time. In cruise, Pilatus says that the penalty is a paltry one to two knots.

(AOPA PILOT Article - PC-12 NGX)


How does an FBO refer to the parking spots on the ramp? How does an FBO refer to the parking spots on the ramp? What is the official term? And is there some sort of an identifier, a "ramp number"? Is this standardized, like runway numbers, or does it vary from FBO to FBO? Are there numbers painted on the ramp?

From the airports I've flown into, it's usually, you're just guided into a spot, and most often, there aren't any lines there, mainly since an FBO should be able to generally serve something as small as a Cessna, to a Gulfstream, or bigger. Flight School Ramps might have painted lines and dedicated parking for their fleet, but they know who will be parking there and what type.


Finding the center of gravity/centroid of an airfoil? I'm in the process of building myself a wing frame out of balsa wood. However, as a high school student that's just started aerospace engineering, I'm not really sure how to go about it in some ways.

What I'm looking for is the center of my ribs so that I can find the best point to put my main spars in. The ribs themselves are full flat-bottoms if that helps any. Is there a go to equation for something like this?

In addition to checking out wing frame structures on the internet, why not go down to the hobby shop and get a balsa plane kit?  Airplane building is a hobby you will have all your life.

Generally, in balsa, you have a top and bottom spar, a leading edge, and a trailing edge to attach the aileron (get lots of sand paper and CA glue).  As mentioned, put you spars at around 25 - 33 % from leading edge, around the highest part of the rib.  You may also have good luck strengthening your wing by covering it with 1/16 sheet balsa, others use heat shrink monocoat.  But you must also stiffen the wing so it can not twist when you use the ailerons.  So you may wish to add balsa between the ribs connecting the top and bottom spars, creating a box structure.

A lot of ways here, and you can't read too much about it.  Please let us know how you are doing with it.  Check out RC Groups website as well.


Can the touchdown RVR be replaced by the midpoint or rollout RVR? When there are three RVRs equipments in place and an ILS approach chart minumum for the runway simply says "RVR 800m" without any additional notes, is the touchdown RVR the only controlling RVR? If so, what if the touchdown RVR is out of order? Can the touchdown RVR be replaced by either the midpoint or rollout RVR?

I'll start by pointing out from Wikipedia that—

  [The RVR] values obtained are not a reliable guide to what a pilot can actually expect to see. This can easily be demonstrated by the fact that when obscuration such as fog is variable, different values can apply simultaneously at the same physical point.

They give an example for that.

The answer to your question is yes it's possible to use the midpoint RVR if the touchdown RVR is inoperative. But, authorization is required, and it cannot be used for ILS CAT II and III.

  If the touchdown RVR VS is inoperative, some operators may be authorized, via OpSpecs, MSpecs, or an LOA, to substitute an operative mid-point RVR VS for visibility minima greater than or equal to 1,800 RVR.

Source: FAA 6560.10C


What can I do on the ground in order to help my body acclimate to aerobatics? I've just started aerobatics training!  Unfortunately, my middle ear really messes with me, particularly during loops. Strangely, aileron rolls give me no trouble at all.

I know from other experienced aerobatic pilots that you can get used to aerobatic flying, and my tolerance will build up over time.

However, is there anything I can do on the ground in order to help build up my tolerance more quickly?

The way the Air Force introduces people to the disorienting effects of aerobatics on the ground is to put them into smoothly spinning chairs called Barany Chairs.  And it doesn't just involve spinning in one direction, but smoothly and gently changing directions repeatedly.  Since I never suffered from airsickness, I don't know what they do (i.e. do they blindfold you, are there more than one axis of motion, do you have to tilt and move your head, etc.)

While an actual Barany Chair may be expensive, you could perhaps accomplish the same with  a friend and a nice heavy office chair.


Why do Boeing aircraft have serrated engine nacelles, but Airbus does not? Why do Boeing's new generation of jets (787, 747-8, 777X, 737MAX) have serrated engine nacelles whilst Airbus' latest (A350, A320neo etc) do not? I understand that Boeing's nacelles reduce turbulence and therefore noise. If this is the case, it would make sense for Airbus to utilise them as well, but it doesn't. So my question is, is this a patent thing or has Airbus found other ways to do the same thing?

It doesn't appear to be a patent thing. The main work on the chevron (shaped nozzles) was done by NASA. Every design decision in an aircraft is a compromise and this was no different. The addition of chevrons for noise suppression leads to a (small) increase in specific fuel consumption and Airbus considered it not worth it. Flightglobal quotes Dougie Hunter, A350 chief engineer as saying:

  We didn’t get a noise advantage from chevrons, and there is a specific fuel consumption penalty, so we’ve not adopted them.

Airbus seems to have gone in the insulation and high bypass route for reducing noise. From the same article:

  Goodrich is to build the engine nacelle for the A350’s GEnx engine, with Airbus supplying the composite inlet, which incorporates a “zero splice” acoustic inner barrel to provide a new level of fan-noise reduction.

As an example of the acoustic treatment of nacelle in A320 family, Airbus says:

  The thrust reverser structure was acoustically treated along approximately
  half of its internal surface. It was clear that increasing this acoustic area would increase the acoustic sound absorption and hence decrease the overall measurable exhaust noise. The inner fixed structure was redesigned with increased acoustic area. In addition, the support struts and several fairings were also modified to include acoustic treatment. The result was an increase in the acoustic area of the thrust reverser by approximately 2 square meters (21.5 sq ft).

Airbus does use chevrons in some of the aircraft, like A321 along with nacelle acoustic improvements; however, the chevrons are available only in the inner (core) nozzle. The package is available as standard for CFM powered A321 aircraft and options are available for A320. The image below shows a A321 with chevron nozzles.

Image from pprune.org

According to Airbus:

  The noise reduction package is currently offered as the basic standard on all CFM powered Airbus A321 aircraft. It is also optional on all the other A320 Family aircraft.


Is it possible to obtain a CPL without a PPL? I've overheard that trainee pilots hired by airlines are not required to pass the PPL exam before attempting the CPL exam. Is this allowed by regulation?

You've tagged your question with 3 different sets of regulations, I can't answer all of them but here are the FAA ones.

The answer depends on what you mean by "exam". If you mean the written test, then anyone can take it if they have a graduation certificate or a logbook endorsement:

  An airman applicant may present one or more of the following
  acceptable forms of authorization for all tests listed above [...]

  Certificate of graduation or a statement of
  accomplishment certifying the satisfactory completion of the ground
  school portion of a course for the certificate or rating sought. The
  certificate or statement may be issued by an FAA certificated pilot
  school or an agency, such as a high school, college, adult education
  program, Civil Air Patrol, or Reserve Officers Training Corps (ROTC)
  flight training school.
  Written statement or logbook endorsement
  from an authorized ground or flight instructor certifying that the
  applicant completed an applicable ground training or home study course
  and is prepared for the knowledge test. (AC 61-65E) (14 CFR § 61.35)

At least in theory, you could get a certificate or endorsement to take the commercial written test without ever having taken any other FAA test. But in practice I suspect that it's very unlikely: why would an organization or CFI endorse you as ready for the commercial written if you haven't already done the private one?

However, if "exam" means the actual checkride then the situation is much clearer: it isn't possible to do it unless you already have a private certificate, at least for civilian pilots. 14 CFR 61.123 says:

  §61.123   Eligibility requirements: General.

  To be eligible for a commercial pilot certificate, a person must:
  [...]
  (h) Hold at least a private pilot certificate issued under this
  part or meet the requirements of §61.73

61.73 lets you use military experience to apply for a civilian certificate.

Finally, some people use the term "commercial pilot" when "ATP" would be more accurate. I'm not saying that you're using it incorrectly, but since I have no idea how EASA and CASA define a CPL it may be worth mentioning. In the US, ATP multi-engine candidates need a certificate for the written exam, and a commercial certificate with instrument rating (or military equivalent) for the checkride. See 61.153.


What is purpose of engine pylon airfoils on the Hondajet HA-420? The engine pylons on the Hondajet are aerodynamically shaped so as to provide a lift force laterally and outwardly.

Engine pylon as viewed from rear

Engine pylon as viewed from front

Are these for lateral stability or drag reduction or both or other purposes?

There is a pretty interesting write up on the pylon design here. According to that the shape was chosen for a number of reasons including flutter reduction, stall characteristics and wave drag reduction. There is also some more info here that briefly touches on the design.


Is there an equation for jet engine efficiency as a function of turbine inlet temperature? I know that there is a relation between the turbine inlet temperature and the engine's efficiency. But, can anyone provide an equation or efficiency as a function of just the turbine inlet temperature?

I am looking for something like this: If the turbine inlet temperature goes up by 200K, efficiency goes up by 10%. Any numbers like this are appreciated.

Also, let's say that if GE invents a material that does not melt at all(just imagine), what is the highest temperature that can be produced by burning the fuel assuming nothing can melt.

The jet engine efficiency is unfortunately more complicated than just a one-to-one function between static Turbine Inlet Temperature and efficiency. Thermodynamic efficiency of a turbine engine is defined as the useful generated power extracted from the chemical energy added by the fuel.

The following is extracted from a paper format uni book on aircraft gas turbines.

Station 0 is for the engine inlet, the other station numbers are:

Compressor inlet.
Combustion chamber inlet.
Turbine inlet.
Turbine outlet.
Engine exhaust.

Energy IN

The heat flow $\dot{Q}$ added to the engine is:

$$ \dot{Q} = \dot{m} \cdot c_{pg} \cdot (T_{3t} - T_{2t}) \tag{1}$$
With $\dot{m}$ = mass flow through engine, $c_{pg}$ = gas constant, $T_{3t}$ = total temperature at turbine inlet. Total temperature is the temperature reached when a gas flow is compressed isentropically, measured in the stagnation point, and defined as $$T_t = T + v^2/(2 * C_p) \tag{2}$$

So energy IN is a function of:

Static Turbine Inlet Temperature
total mass flow
gas flow velocity at the turbine inlet.

Useful power OUT

The power delivered by the gas generator is:

$$P_{gg} = \dot{}m \cdot c_{pg} \cdot T_{4t} \left[ 1 - {\left(\frac{p_0}{p_{4t}} \right)}^{\frac{\kappa_g - 1}{\kappa_g}} \right] \tag{3}$$

with

$T_{4t}$ = stagnation temperature at  the turbine outlet.
$p_0$ = static pressure at engine inlet, a function of air density and airspeed.
$p_{4t}$ = stagnation pressure at the turbine outlet, which depends on how much energy the turbine has extracted from the gas flow.

Efficiency

If we could vary the $T_{3t}$ only and keep the other variables constant, we could indeed get to the sort of function sought after - but we cannot. Increasing T.I.T creates more thrust, accelerates the aircraft, increases inlet pressure, increases turbine outlet pressure etc.

From Gas Turbine Theory by Saravanamuttoo/Rogers/Cohen, page 81:

  The large number of variables involved make it impracticable to derive algebraic expressions for the specific output and efficiency of real cycles.


How many Airbus planes have been destroyed in flight by severe turbulence? Since a brand new A350 has literally the exact same design specifications / G limits as an airliner built in the fifties does (A 1955 F27 Fellowship will break up at 2.5 G-3.75G, same as a modern Airbus jet - anymore than 2.5 G it will start to break up), and there were quite a few airliners from the 50's and 60's era losing wings or being destroyed completely as a result of turbulence.

Are there any Airbus planes that have broke up due to turbulence or accidents that were likely due to turbulence, but covered up?

Do Airbus planes have systems to avoid Clear Air Turbulence, and avoid flying over mountains, since most turbulence related inflight breakups occurred due to mountain wave activity? (BOAC Flight 911 for instance was flying over the top of a mountain - it experienced G forces of +9 and -4, and broke apart and crashed).

https://en.wikipedia.org/wiki/Wien_Consolidated_Airlines_Flight_55

https://en.wikipedia.org/wiki/BOAC_Flight_911

https://en.wikipedia.org/wiki/Braniff_Flight_250

https://ral.ucar.edu/aap/turbulence

(scroll down the last link for photos of the DC-8 jet with half its wing and engine torn off due to turbulence while flying at 31,000 feet over the Colorado mountains)

The Aviation Safety database lists 91 accidents due to turbulence as of writing. None are on Airbus aircraft. The most recent in flight breakup of a transport aircraft listed was in 1993.

All of the aircraft in your examples are fairly old designs, dating back to the 60's or earlier. Your statement that the A350 has the exact same design requirements as an F-27 is inaccurate. While the load factors required for certification may have remained constant, the actual loads aircraft must be designed to survive have changed over time. As an example, for transport aircraft, the FAA regulation on gust and turbulence loads is 14 CFR 25.341, which has been updated 3 times since it was originally introduced in 1965. For the F-27 incident in Alaska, one of the factors noted was cracks in the wings from a lack of maintenance. Maintenance has been improved since then, as has the durability of aircraft designs. As accidents happen and the industry learns from experience, designs improve to better anticipate the conditions that aircraft will actually experience.

Other than the DC-8 in your last link, all of the occurrences happened in the 60's. Apart from the design of the aircraft, a lot has changed operationally since then. Weather radars have improved dramatically, both on the ground and on the aircraft. Modern radars have a much better ability to detect turbulence, even clear air turbulence to a degree. They have also become much less prone to operator error. Weather satellites now provide information on weather even in remote areas. Forecasts have improved as well, providing pilots and dispatchers a better idea of areas that should be avoided.

Below is an example of the kind of information that modern radar systems can provide to pilots about weather conditions in their path.

Source


Why can’t the newest high-bypass turbofans run at their EPR, temperature, and RPM limits simultaneously at sea level? The General Electric GE9X turbofan (used on the 777X), unlike the vast majority of turbofans before it, did not undergo the traditional triple-redline test (where the engine is run for a prolonged period of time while simultaneously at redline EPR, redline temperature, and redline RPM), because it is, apparently, incapable of doing so except at high altitude:

  ... Before certification, final tests include a full durability block test, replacing the usual “triple redline” test at maximum temperatures, pressures and speeds, as modern high-bypass ratio engines cannot achieve all maximum conditions near sea level...

In contrast, the GE9X’s immediate predecessor, the GE90 (used on some first-generation and all second-generation_777s), did undergo triple-redline testing before entering service, and again before the release of the high-thrust variants used on second-generation 777s.1

One would expect, intuitively, that it would be easiest to achieve triple-redline conditions at sea level, as fuel and air flow (and, thus, RPM, EPR, and thrust) are highest in the dense low-altitude air,3 and the increased cooling from the additional airflow should be just about balanced by the increased heat generation from the additional fuel burned.4

What makes it impossible for very new turbofan designs to reach all three redlines simultaneously at sea level?

1: Setting a record for the highest thrust ever generated by a jet engine (569 kN, or 64 short tons for you Americans) in the process, which stood unbroken until it was eclipsed by a 597-kN (67.2-short-ton) GE9X test run in November 2017.2

2: Ironically, while the GE9X is larger and has a higher record thrust than the high-thrust GE90s, and is required to power an aircraft just as heavy (and soon to get much heavier still, with the 777-10) as those using the latter engine, its rated thrust is considerably lower (470 kN [52.5 short tons] versus 510 kN [57.5 short tons])!

3: Although not by very much, as the maximum thrust available from (and, thus, fuel and air consumed by and RPM and EPR attained by) a turbine engine remains nearly (although not completely) flat up to very high altitudes.

4: These effects would be even more pronounced on an actual aircraft than in a test stand, due to the higher thrust settings needed to counteract the increased drag from low-altitude flight and the increase in airflow through the engine (and, thus, in fuel flow, as well) resulting from the ram effect of the aircraft’s (and, thus, the engine’s) forward motion through the air.

What makes it impossible for very new turbofan designs to reach all three redlines simultaneously at sea level?

The implication in your question is that GE9X was not able to reach all three redlines simultaneously but that previous engines (e.g. GE90, GEnx, LEAP, etc) could.  That is incorrect.  Those engines could not reach triple redline either. At least not, type design unmodified.  The engines that were used to demonstrate compliance to FAR 33.87 for those engine programs were modified from their type design in order to be able to reach triple redline. Very heavily modified.

To understand why, let's talk a little about engine performance.  The three variables of N1, N2, and EGT are controlled by several conditions: the throttle setting, the ambient temperature, the ambient pressure (i.e. altitude), the forward velocity, and the deterioration of the engine (e.g. how worn out the seals are).  Now, if we are doing this test on a test stand (as opposed to flying it), then we really only have control over one variable: the throttle.  Everything else just is what it is. It shouldn't be too hard to see that you can't control 3 variables precisely with just one knob (E.g. imagine in your bathtub or shower you try to control both the water temperature and water flow rate with just one knob. You can't do it.  To control 2 variables, you need 2 knobs).

More specifically, considering sea-level static conditions, if the ambient temperature is cold, then the air is dense, so the fan pumps a whole lot of mass with every revolution and makes a lot of thrust.  You have to burn a lot of fuel to do that.  So you'll hit EGT limit first before you get anywhere close to N1 redline.  If the ambient temperature is hot, then the fan doesn't pump as much per revolution, so speed needs to be really high in order to make any kind of thrust.  You'll hit N1 redline before you hit EGT redline. You can presume that there should be one magic temperature where you could hit both of those at the same time, but if you just sit around and wait until the weather hits the exact right temperature you wanted and stays there for 150 hours (the length of the test), you'll be waiting a long time.  And even then, you still won't get to N2 redline at the same time.

Ok, so how would you run a triple redline test then, given that we can't control ambient temperature? Well first you'll need to way to vary the thrust the fan produces.  E.g. you could use a variable fan nozzle.  On a cold day, you open up the fan exit area so you can get to higher N1 speeds with less thrust, and on a hot day you throttle it down.  There are other options but this is easiest to explain.  Then you need to control N2.  The easiest way here is to open or close the variable stator vanes.  This has the effect of making the HPC do more or less work per revolution, so you can tune in the exact speed you want.

Ok, so we added a variable fan nozzle and a different VSV schedule, and we are at triple-redline.  Problem solved right?  Wrong.  Jet engines are extremely complicated devices with all kinds of interdependent requirements.  If you change one thing, you end up affecting other stuff.  Changing the VSV schedule might introduce aeromechanics issues onto the HPC blades, or change the cooling flows to different portions of the turbine.  So then you have to make other modifications to the engine, like changing the sizes of all of the different cooling pipes so you get back to the original flow rates you wanted.  But then, those changes also have other effects, which snowballs.

Historically (I mean like 1970s 1980s) the engine companies could make a few small changes and hit triple redline.  As the engines became more and more complex, more and more changes were required. At some point, the list of changes required to make the engine hit triple redline is so big that the thing you are testing is a crazy chimera of an engine that has only a faint resemblance to the actual type design.  At that point, running a triple redline test no longer makes sense.  That's what happened with 9X. Therefore, GE found an alternative way to satisfy the endurance test requirement.


Are the airport "taxi" plans available online? Whenever I sit in an aircraft and we taxi around the airport, I wonder how exactly is the airport organized, for example, the arrangement of the taxiways and runways.

Is it possible to locate airport diagrams? I'm mostly interested in Paris CDG, Prague PRG and Amsterdam AMS.

A great site to download airport diagrams and other charts is charts.aero. As of April 2015, however, the site seems gone.

Airport diagrams show all the taxiways and ramps, which is what you are looking for.

Keep in mind that this is an unofficial website. The charts should not be used for actual navigation.


How do I know if I'm able to use LPV minimums on a GPS approach? Many GPS approaches have lower descent minimums labeled LPV. How do I know if my aircraft is equipped to allow me to fly to those LPV minimums? And while we're at it, it would be good to know which minimums to use from the whole array of minimums found on GPS approaches.

There are many websites / blog pages that compare and contrast the different approaches. All you need to do is google a bit.

That said, if your plane can fly LPV approaches you'd know that. It requires WAAS-quality GPS receiver, and to install that requires at least a logbook entry.

Note that it's not only a matter of equipment. Even when the plane is equipped to fly LPV approaches, there can be certain conditions when you can't use LPV minimums (satellites, etc.) If you CAN use LPV minimums, the GPS unit MUST show you "LPV" in the annunciator window. It's possible that you're LPV-equipped, but your annunciator window shows you only "LNAV", for example.

So, check your documents, talk to your mechanic, you wouldn't really NOT know if your plane was ever upgraded for LPV approaches. If it's your own, you'd know and have discussed it and most likely given the mechanic the task to upgrade it. If it's a rental, or you're just buying it, look at the logs and ask the seller. And keep in mind, the annunciator window will show you the lowest GPS approach type that it senses is safe. Usually on an LPV-equipped plane that will be "LPV", but it's entirely possible it will only show "LNAV", or something else. For you to use LPV minimums also depends on the actual flight condition.


What IFR clearances may a pilot obtain from ATC directly without a pre-filed flight plan with FSS? I have known two types IFR clearance that a pilot may request with flight plan filing.

Pop-up clearance: A pilot on VFR requests an IFR clearance to destination airport. ATC grants a clearance on a work-load permit basis.
IFR Climb to VFR-on-top: A pilot may obtain this type of clearance from ground clearance delivery and the clearance limit is usually a nearby Nav aid.

The unlikely clearance without pre-filed plan is,

Airport-to-airport: Ask ground clearance delivery for an IFR clearance to another airport.

What other types of IFR clearance else may I request ATC directly? We know that the flight plan checked-in time needs to 30 min prior to its start time.

Another example is

"IFR-descent-to-VFR-under-bottom": Is it possible to request an IFR descent through a cloud layer, say 8000 to 5000 through a layer 6000~7000? Is it just one special case of "pop-up clearance", or due to the descent nature, ATC won't grant it?

Are there any concrete regulations or general conventions that a pilot may follow?

The theoretical answer to your question is that you can always get an IFR clearance directly from ATC over the radio, and filing a flight plan in advance isn't required (but it is strongly advised to avoid delays).

In reality, however, you should file in advance if at all possible. This is from the AIM 5-1-8 (my emphasis):

  Instrument flight plans may be submitted to the nearest FSS or ATCT
  either in person or by telephone (or by radio if no other means are
  available). Pilots should file IFR flight plans at least 30 minutes
  prior to estimated time of departure to preclude possible delay in
  receiving a departure clearance from ATC.

The IFR flight plan system is there for good reasons: it helps ATC manage busy airspace and it avoids the need for lengthy radio discussions. If you don't file a flight plan in advance then you'll probably annoy ATC and you may be delayed because they can't take your request directly.

Pop-up clearances by definition don't have a full flight plan filed in advance, but they do have an abbreviated IFR flight plan:

  An authorization by ATC requiring pilots to submit only that
  information needed for the purpose of ATC. It includes only a small
  portion of the usual IFR flight plan information. In certain
  instances, this may be only aircraft identification, location, and
  pilot request. Other information may be requested if needed by ATC for
  separation/control purposes. It is frequently used by aircraft which
  are airborne and desire an instrument approach or by aircraft which
  are on the ground and desire a climb to VFR-on-top.

Weather isn't predictable and a VFR flight may have to become IFR for safety reasons, so there needs to be some flexibility for aircraft that are actually in the air. A pop-up clearance is just a different, simpler way of requesting an IFR clearance; once you have it, you're IFR and operating in exactly the same way that you would if you had filed in advance.

Descending to VFR conditions is an interesting idea but ATC can't clear you to descend below the minimum IFR altitude for the area. You could request the lowest altitude ATC can give you, then cancel IFR if you break out. But descending without a specific altitude restriction seems very risky: the temptation would be to keep going lower to "have a look", and that could end up as a CFIT incident.

Finally, at least in my experience the 30-minute 'rule' is really a guideline to avoid delays. I've never had an issue filing IFR and departing 15 minutes later, but then I'm usually flying between class C or D airports and the airspace isn't particularly busy. A class B airport is probably a different story.


How to determine the direction of rotation of components inside a gas turbine engine using the blade profile? I am new to Gas turbine Engines.
As of now,I am trying to understand the gas turbine engine DGEN 380 by the manufacturer Price Induction.
So I have identified the components such as Intake fan,Planetary gearbox, Centrifugal Compressor,HP and LP turbine.
However,I am not sure of identifying the correct direction of rotation for each of these rotating components based on blade profile. So if someone could explain it in a simple way,I shall be thankful.

https://minijets.org/fr/300-500/price-induction-dgen-380-390/

If you know the direction of gas flow, you can determine the direction of rotation of axial flow components (like the fan and turbine in the example) by the angle of attack of the blades. Think of it intuitively--if you were to blow air through the engine in the same direction it flows during operation, which way would the blades windmill? The direction of windmilling is the same as the direction of powered operation, as long as the airflow is in the same direction.

Because their angle of attack, of the blades of the fan would deflect air flowing into the engine counterclockwise when viewed from the front, meaning the fan rotates clockwise when viewed from the front (or counterclockwise from the rear looking forward, which is the conventional way of expressing rotation).

For this particular engine, all other turbomechanical components rotate in the opposite direction as the fan, indicating that the low pressure shaft is connected to the fan using a gearbox that reverses the rotation direction.

This is the low pressure turbine and shaft:

The compressor rotates in the same direction as the high and low pressure turbines, and is attached directly to the high pressure turbine shaft with no gearbox. The high pressure turbine is axial flow and looks like a smaller version of the low pressure turbine, but the compressor is not an axial flow component, which makes the analysis slightly different.

Unlike in axial flow components, in radial flow components like this compressor (a synonym for a radial flow compressor is a centrifugal compressor), the airflow enters and exits in a different direction. The direction of flow also differs between energy-absorbing (turbine) and energy-dissipating (compressor) components. Gas enters radial flow turbines at the edge and flows inward, exiting at the center. In radial flow compressors, gas enters at the center and exits at the edge. You can determine the direction of rotation by imagining the forces the air would exert as it changes direction, similar to the windmilling axial flow components:


How to sign hours on Logbook if doing aerial work in right seat on single pilot aeroplane? Recently I got an offer to work during the incoming summer as survey pilot, but since I do not have the required hours for insurance I can not be the PIC on left seat. So they proposed to be on the right seat until getting enough experience and then switch on. Can I sign those hours on the right if the aircraft is certify for single pilot operation? How?

I am not sure about EASA regulations but in the US you can log PIC time whenever you are the sole manipulator of the controls and properly rated to fly the aircraft.  In the US there is a distinction between the legal PIC (person legally responsible for the flight) and PIC time which is the person actually flying the airplane.  Since the plane is certified for only single pilot operations you can only log PIC time not SIC time and only when you are the sole manipulator of the controls.  The FAA regulations for logging time can be found in FAR 61.51.


What is the RNP requirement within the KZAK FIR? What's the RNP requirement with KZAK FIR?
I thought it is RNP 10 operating in NOPAC AND PACOTS, but I am not sure.

To be exact RNAV 10 is required when operating in the KZAK FIR. This enables 50NM longitudinal and lateral separation between aircrafts.

Unfortunately, the requirement might be designated RNP 10 due to legacy reasons. The difference between RNAV and RNP is that RNAV requires no onboard performance monitoring and alerting capability, while, among other things, RNP does.

RNP 4 is optional to allow closer 30NM longitudinal and lateral separation between RNP 4 capable/authorized aircraft thus increasing the airspace capacity.

Sources:

ICAO Doc 9613 - Performance-based Navigation (PBN) Manual
ICAO Doc 8168 - Procedures for Air Navigation Services — Aircraft Operations, Volume I (PANS-OPS Vol I)


When an aircraft is descending, does any lift act on it? If yes, how? When descending , an aircraft never goes in free fall, even if negative angle of attack is large. Does that mean the net downward force is not gravity, but less than gravity, due to certain lift acting at all negative angle of attacks?

You seem to be confusing angle of attack and pitch angle. The pitch refers the orientation of the aircraft: where is the nose pointing? The angle of attack is the angle of the wings relative to the incoming air stream. Both can take on any value independent of each other. For example, one could imagine an aircraft falling straight down, but wings level. The pitch angle is then zero, but the angle of attack is 90 degrees!

Similarly, the pitch angle can be negative for a continuous steady state descent (and often is for a steep descent). However, you correctly identify that an aircraft on approach generally does not go into a freefall. The lift acting on the airplane is still (approximately) the same. A positive angle of attack is thus still required. As a result, the aircraft will be descending even steeper than where the nose is pointing, resulting in a positive angle of attack (the angle between the pitch vector and the even steeper velocity vector).


Which aircraft have fought against its own type in active combat? The criteria for this question are

The aircraft has to be the same type (but not necessarily the same mark)
The two opposing sides are actively hostile; but not restricted to nation states (so civil war a possibility)
The aircraft treat each other as an active threat
Cloned aircraft count, e.g. Tu-4 / B-29 or J8M / Me163 (neither of these occurred as far as I know)

It's difficult to see circumstances in which it would happen; but in over 100 years of air combat I think it likely to have occurred at some point.

Probably not the only situation, but in 1948 Israeli Spitfires faced Egyptian Spitfires, and just before the truce also faced a few RAF Spitfires that were too close to the combat area (reference)


Why building a stopway instead of just building a longer runway? I don't get the point of building a stopway. If you have the space to build a stopway, you could just extend the length of the runway.

Why are stopways necessary?

Overrun areas are almost always filled with some form of loose material... sand, for example... that will slow a plane down with extra drag on the landing gear. The idea is that if a plane has reached the end of the runway, it's already in trouble and is probably having problems braking.


What radios are airliners / large aircraft equipped with? I know that pilots have to talk to the tower over the radio, and apparently you have to tune the radio to the right tower frequency. I've also heard that in an emergency, you're supposed to "squawk 7700." Presumably you're not just making bird noises with your mouth, but some sort of radio code. Are these the same radio system? What radio communication systems are modern big jets equipped with?

Numbering the radios that I can think of offhand in the old 747-100 and -200 aircraft that I used to fly produces:

2 VHF voice communications radios.
2 VHF navigation radio receivers for receiving VOR and LOC signals. The LOC frequencies are paired with UHF frequencies for receiving glideslope signals.
1 ADF (automatic direction finding) receiver.
1 HF (high frequency) voice communication radio.
2 transponders to send whatever the "squawk" is when interrogated. #1 was used on odd days of the month, #2 on even days. There are a number of standard codes, but ATC assigns a 4-digit code to each aircraft during flight under their control. There is never an 8 or a 9 in the code because it's an octal code.
1 SELCAL (selective calling) receiver, which will sound an alert if it receives a signal sent by a ground station. It may not be a separate radio but just a box listening for a tone on one of the voice communication radios.
1 weather radar, and, yes, radar is a radio (radio detection and ranging) employing both a transmitter and a receiver.
1 radar altimeter for use in the final stages of the landing approach. Some were "talkers" in that starting around 50 feet, they would announce your altitude in increments of 10 feet.
1 GPWS (ground proximity warning system). I'm not sure whether it and the radar altimeter shared a box/circuitry/antenaes.
1 GPS receiver, which we got only in the last few months before I retired in 1999
1 ELT (emergency locator transmitter)
life raft locator beacons. I can't remember how many life rafts there were.
life raft voice communication on 121.5 and maybe 243.0.

I may not have remembered them all.

Modern transport category aircraft would also have SATCOM. Military aircraft would have UHF voice communications and mission appropriate weaponry radios.


What factors should be included when calculating hourly aircraft operating cost? I'm working on a budget for operating an aircraft and trying to better understand the hourly operating costs.  What factors should be included that are often forgotten?

Although this is partially discussed here I'm interested in distinguishing between general cost of ownership (hangar, insurance costs, etc.) with items specific to hourly costs. And I'm not looking for actual numbers - just the categories to consider.

Obviously this list will depend upon the type of aircraft, but to keep the question somewhat general, I'm interested in a light single-engined piston aircraft.

So far my categories include:

Cost of fuel per hour
Engine reserve per hour
Prop reserve per hour
Oil cost per hour

Unless you have a private airstrip and have no intention of insuring the craft you need to include the fixed costs as well. Generally you can do this yearly, then divide by the number of expected hours a year. Some fixed costs are

Storage (hanger or tie down)
Insurance (highly variable)
Annual (this will vary depending on whats broken but there is generally a minimum situation to expect assuming the mechanic finds nothing wrong.
Anything that has less than a 50 hour life time, if you are in this for ownership or renting you are going to fly more than 50 hours a year (I would hope) so you should budget in things like spark plugs, break pads and other high wear parts that get replaced often)

Other reserves may be

Repaint Reserve, this will vary depending on storage and use
Landing Gear Reserve this includes but is not limited to, breaks, tires, shocks, rotors, etc. Budget more if its a complex plane, less if its a Mooney...
Fluid Reserve (not oil) you may also have hydraulic fluid and break fluid.
"Toys" this is money you may chose to add on to your reserve so that you can (down the line) upgrade aging components that may not be broken. For example adding a 430 in place of a radio pair or moving to a full or partial glass cockpit.
Interior, if you are renting this plane and expect it to see heavy use you may want to set some cash aside for the interior. Don't underestimate the difference a warn seat will make vs a fresh seat.

Emergency Fund: This is not a reserve to add to as much as it is cash on hand. If you are renting this plane or even relying on it for heavy personal use you may want to have a budget for emergencies. Especially if you are renting and a down plane means lost rentals. What are you going to do if you need a new fuel tank, or you have a bird strike, or something hits the windshield and cracks it?

Odds and Ends Budget: Nuts and bolts, interior finish screws, that dinky little plastic knob, repainting your yoke, a pitot tube cover (for the 10th time because you lost all the other ones...)


At what altitude might a pilot be able to see at least the brightest stars during the day? In this comment I pondered if I should ask:

  "Did Test pilot and astronaut Joseph A. Walker see stars during the day when flying the X-15 above the Karman line?

But instead, I'll just ask at what altitude might a pilot be able to see at least the brightest stars during the day?

Assume cockpit lights and panel illumination are dim-able and a high tech high altitude aircraft (e.g. the X-15 or something modern or near-future) is used.

I don't think it's easy to see bright stars during the day at cruise altitude by eye without some help, but at some altitude it should be.

Is there any information on what altitude this might be?

SR-71 pilots saw the stars, but of course there is no account of the exact height, they started to see them. They were flying around at 80000 feet at some point in their mission profile. Basically you have to get above most of the atmosphere. So you should start to see stars above 43000 feet. Of course there are some other options, you see them during an eclipse or above the Arctic circles in the right season. You can always see the stars, if you know where to look and if you have a telescope, but I presume you mean to see them with the naked eye?


Is there a requirement for self-locking / positive locking electrical connectors for aircraft systems? Is there any FAA or EASA regulation that dictates the use of locking electrical connectors for certain systems on an aircraft?

Self-locking (ratchet mechanism, bayonet) and positive locking (wire locked) connectors are used on most systems.

But there are also push-pull connectors mainly used on headsets or quick disconnect batteries.

Is there a regulation that prohibits the use of not self-locking or positive locked electrical connectors for certain systems even though they fulfill exactly the same mechaninal specifications concerning vibration, shock and durability?

EDIT: Note that the original question, which this answer primarily addresses, did not specify electrical connectors.
The FAA does provide regulations which at least partially cover this subject, though the guidance is rather broad.
The airworthiness standards in 14 CFR 23.607 for normal, utility, acrobatic, and commuter category airplanes stipulate that:

(a) Each removable fastener must incorporate two retaining devices if the loss of such fastener would preclude continued safe flight and landing.
(b) Fasteners and their locking devices must not be adversely affected by the environmental conditions associated with the particular installation.
(c) No self-locking nut may be used on any bolt subject to rotation in operation unless a non-friction locking device is used in addition to the self-locking device.

Likewise, the  airworthiness standards in 14 CFR 25.607 for transport category airplanes stipulate that:

(a) Each removable bolt, screw, nut, pin, or other removable fastener must incorporate two separate locking devices if—
(1) Its loss could preclude continued flight and landing within the design limitations of the airplane using normal pilot skill and strength; or
(2) Its loss could result in reduction in pitch, yaw, or roll control capability or response below that required by Subpart B of this chapter.
(b) The fasteners specified in paragraph (a) of this section and their locking devices may not be adversely affected by the environmental conditions associated with the particular installation.
(c) No self-locking nut may be used on any bolt subject to rotation in operation unless a nonfriction locking device is used in addition to the self-locking device.

As you can see, these regulations do prohibit certain types of locking fasteners in certain circumstances. For example, a nylon self-locking nut is not acceptable to fasten the exhaust manifold to the cylinder head; an all-metal self-locking nut would be acceptable, however.
The greater concern for a system such as a headset may be that to install it with fastening hardware—screws for example—would be to make it an installed part of the aircraft. The installation would then be subject to the various regulations of an installation: a log book entry, weight and balance considerations, etc.
Additionally, AC 43-13-1B, Ch 7, provides non-regulatory guidance regarding use of fasteners, including the use of locking and safety mechanisms. I will note that this guidance is superseded by manufacturer maintenance data for most modern aircraft.


How can I tell if an aircraft (N-number) is already equipped with an ADS-B transponder? Is there any database that contains this information?

This question asked how many aircraft already have one. Here I am asking how can I get which contain it.

If it's onesy twosy, you can try searching flight logs of specific aircraft to see if ADS-B output is recorded.  Here is an example: track log showing ADS-B returns

There is not a free database.  You could purchase a database query of flights that have been tracked by ADS-B.  Depending on the number of aircraft you need, this will affect the cost.  Flight Aware will quote this kind of job.

The FAA database does not provide this information.  It does provide mode-S code information, but that is whether or not the aircraft is so equipped - nothing for ADS-B (yet).


Tapered Wing Providing low Coefficient of Lift Hi I am currently analyzing different wing designs using ANSYS Fluent.
One of my designs has a straight leading edge but a swept trailing edge thus it is tapered with wing root chord at 50mm and wing tip chord at length 200mm. Wing span is 250mm. (See Picture)
The airfoil shape used is the S1223 which has a CL max around 2.3. Therefore using the Lift formula which (i know is approximate), I calculate the wing can produce 58.5N of lift at 36.452m/s.

However using ANSYS Fluent I find the wing can only produce a maximum of 39N of lift which is a CL of 1.5.

I am fairly certain the simulations I'm running are accurate but need advice on what could be causing this difference.
Assuming the results I've obtained are correct. What is the reason for the large difference in coefficient of lift ?
Let me know if I need to provide any additional information!
Any help greatly appreciated!
EDIT : Forgot to add that the simulation used assumes the wind tunnel boundary is at wing tip and wing root. Thus the wing span takes up the full wind tunnel.

By tapering the wing you have in effect a 3D case even if the wing is sitting between wind tunnel walls. Lift varies along span almost as if the wing would be in free flight with twice the span and the long chord at the root. Since tip chord is only a quarter of root chord, that full wing would have 0.075 m² area with 0.5 m span, giving it an aspect ratio of 3.33. Below is a figure from Sighard Hoerner's book Fluid Dynamic Lift (Chapter 3, Figure 4) which shows how the local lift coefficient varies over span for wings of different taper ratio. Your wing in free flight would be ¾ between the second and third from the left.

A 2D case is only possible with constant chord as all of the wing would produce the same circulation (lift times chord). With the varying chord along span only the shorter end will reach the maximum lift coefficient of 2.3 locally, but at a lower angle of attack. You still get more lift with your wind tunnel walls than in free flight, but with a taper ratio of 0.25 not much of the 2D case is maintained.

The higher circulation of the long chord end produces extra circulation on the short chord end and lets it stall at a lower angle of attack when the root has only reached half of its full potential (see figure above where center lift coefficient is only half of the tip lift coefficient). The reduction in maximum angle of attack from -13° for the 2D case to -10° also shows how much potential lift is lost.


Which airspace requires what RNP? How do I know which airspace requires what RNP value? More specifically, can I go from NY to London with just BRNAV providing I stay above the NAT HLA?

For completeness, Please refer to the following website:

https://www.uasc.com/docs/default-source/documents/whitepapers/uasc_rnp-rnav_whitepaper.pdf

Here are some extracts that allow to compare US and European requirements:

  US Airspace Requirements

  The current US RNP requirements are:

  RNP-10 as described in FAA order 8400.12c
  RNP-4 as described in FAA Order 8400.33
  RNAV (RNP AR) approach authorization as defined in Advisory Circular (AC) 90-101a
  Basic RNP capability is achieved through TSO-C146 compliant equipment when installed under AC 20-138().

  RNP-10 and RNP-4 procedures are limited primarily to oceanic airspace.

  RNAV (RNP AR) procedures are available in the US for domestic
  operations. These procedures require approval, hence the name:
  Authorization Required (AR), formally known as Special Aircraft &
  Aircrew Authorization Requirements (SAAAR) procedures.

  European Airspace Requirements

  There are two existing European RNP requirements:

  Basic-RNAV (B-RNAV), equivalent to RNP-5 (reference FAA AC 90-45A, AC 20-130, AC 20-138, and AC 25-15)
  Precision-RNAV (P-RNAV), equivalent to RNP-1.

  These requirements are defined in European Aviation Safety Agency
  (EASA) Temporary Guidance Leaflet (TGL)-10, and FAA AC 90-96A. A
  statement is required in the Aircraft Flight Manual (AFM) or AFM
  Supplement (AFMS).

  For European operations, a Letter of Authorization (LOA) for all RNP
  operations, is necessary, as the requirements differ from the FAA
  requirements.