Why do heavy departures wait 5-10 minutes on the runway at ZRH? I'm frequently travelling to Zürich for business and I usually make my schedule so that I have at least an hour to do some planespotting and photographing at the ZRH airport.

Whenever I came to the airport, the runway usage was the same: RWY14 for all the landings, RWY28 for almost all the takeoffs, while RWY16 was used by heavies for takeoffs (usually the flights to Asia or to the USA). I noticed that once a heavy aircraft lines up at RWY16, it waits for some 5-10 minutes before it starts rolling (although it is already way behind its scheduled departure time). The only possible explanation that I could think of was that its engines would cause severe turbulence for the airplanes which are landing at RWY14 and that it has to wait for a significant gap between the landings.

Am I right? Or if not, does anyone know the real reason for these delays?

The usual reason is, that departures from runway 16 are not allowed to climb straight ahead due to noise restrictions over downtown Zurich. Instead they need to turn left, where they cross the departure path of runway 14. So if there are arrivals on 14, no departures on 16 are cleared, as in the case of a go around on runway 14, its departure sector must remain free. I've been watching planes stuck for half an hour at the line up 16 for that reason. Imagine that waste of fuel... ZRH's runway capacity, despite having 3 runways, is thus actually lower than for a parallel 2-runway setup (think about London Heathrow e.g.).


Why does TAS increase as altitude increases and why does my C-152 POH seem to contradict this? I remember learning and memorizing that TAS increases as altitude increases, however I don't understand why. Especially since my C-152's PoH seems to indicate the opposite in the cruise performance section. Can someone please explain what I'm misunderstanding here?

Imagine that IAS measures the number of air particles hitting your aircraft per second. As you get higher the air is thinner — there are progressively fewer air particles around the higher you go so to get the same number of particles hitting you per second (ergo the same IAS) you need to move faster through the air - your TAS increases.


Is there a practical way to demonstrate sustained flight on the back side of the lift curve without an AoA meter? Here is a $C_L$ / $AoA$ curve that I took from Wikipedia.

The better textbooks say that a stall is that condition in which a further increase in angle of attack will result in a reduction of lift.  The point at which that transition happens is known as the critical angle of attack.  Theoretically, sustained flight is possible at angles beyond the critical angle of attack - take a look at the chart.  If the airplane can sustain level flight at point $A$, it can sustain level flight at point $B$.

Is there a practical way that I can demonstrate sustained flight on the backside of the lift curve without an angle of attack indicator?

Or to ask the question another way,

Is there a practical way to tell when an airplane has exceeded the critical angle of attack without an AoA meter?

Flight on the backside of the stallcurve is unstable; any (infinite small) increase in AoA will result in less lift. Less lift will cause the flightpath angle to decrease and the AoA to go up even more. To increase the lift, the nose has to be pitched down, but not so much that the stall is recovered otherwise you wouldn't call it sustained flight at the back of the AoA curve.

At the same time you are also on the backside of the powercurve. This means that any reduction in airspeed would cause the drag to increase therefore decelerating the aircraft furthermore.

This double unstable situation would require a lot of fast responses from the pilot, probably causing too high workload. I doubt if it is practically possible to fly on the backside of the liftcurve without special automation.


How well can an airplane which is tied down be protected from a blizzard? I've been in the very early stages of shopping for my first single engine plane. That has made me more thoughtful about the environment in which a given plane is stored. So the recent blizzard in the Northeast has had me asking some "what-ifs" from a perspective buyer's point of view.

In the Boston area, there are forecasts for 15-25 inches of snow. If a typical GA plane (e.g. a C172) is tied down in those conditions, is the weight of that much snow on the wings sufficient to cause any permanent deformation or other issues? Are there things you would instruct your pre-buy inspector to pay extra close attention to knowing the plane had been through such an extreme event?

There are several additional measures which can be done to prevent a tied down airplane from harsh weather, storms and blizzards. However, nature is always more powerful than humans and  it can overcome any safety measures taken by them.

If your airplane is tied down properly and securely, hail is a bigger threat than storms or blizzards. A hangar protects an airplane more than the one outside, but it costs a lot more.

This article (and page 2) discusses several measures you can take to protect your airplane against harsh weather. To avoid redundancy, I am just pointing (and paraphrasing) a few here:

  Parking spot
  If you can, choose a spot which can break the wind intensity.

  Anchor points
  Depending on the aircraft, the anchor points' holding strength must be 3000-4000 lbs.

  Ropes
  You should use those ropes which do not shrink when wet (e.g., nylon or dracon ropes instead of Manila).

  Position
  If possible, park aircraft nearly into the wind as possible.

  Weight
  A lighter object is easier to get displaced. You can fill-up the tanks to add extra weight.

If you interested in reading some long articles, this and this provide some useful information too.

Regarding your second question about snow on the wings, I hardly doubt that something like this will happen:

The above happened because:

  ... when the tail hook was torn off and the plane was pushed forward, breaking the spar. (picture here)

Airplane wings are very sturdy. They can bear the weight of a foot or two of snow.


Do any commercial airline models have a parachute at rear to help in landings? Some land-based fighter aircraft have a drogue-chute to help them slow down during landing.

Do any current models of commercial aircraft have a similar
mechanism?
Secondly, would such a mechanism help aircraft in making a better landing and reduce landing related incidents/ accidents?

It is called a drogue parachute and I don't think that any of the present generation large commercial aircraft use them.

That said, a number of older commercial aircraft have used them, a good example being the Sud Caravelle.

Image from eu.airliners.net

There are some issues with using drogue chutes in a commercial airliner, which would limit their effectiveness.

Most commercial airliners have thrust reversers already.
For it to be effective, the parachute has to be quite huge. For example, the Handley Page Victor, which had MTOW in the range of A320, had a drogue chute 48' (or 14.6m) in diameter. The chute would occupy volume and increase weight.
If drogue chutes are used, they have to be packed before every flight, which will increase turnaround times. Another option is to replace them at the end of every deployment, which would increase costs.
Deployment failure/partial deployment/Uncommanded deployment will affect the safety of the flight.
The need to use a drogue chute can limit the crosswind landing of the airliner significantly.
Aircraft dragging a huge chute during taxiing back to the ramp is not a good idea from FoD point of view.


What are the continued education requirements for commercial / airline pilots? Out of curiosity (I am not a pilot, but do enjoy watching this aviation forum).

Question: What are the continued education requirements for commercial / airline pilots?

Per FAA rules (if that exists)
If you are a commercial pilot, do you spend more time than mandated learning?
What percentage would you estimate is spent in simulators vs textbook / classroom (if applicable)?

This question is difficult to answer comprehensively as the continuing education requirements are complex and varied. The complexity is because the continuing education requirements are mandated by multiple parties (the FAA, insurance companies, clients, and employers) and depend on the regulations the flight is conducted under (14 CFR 91, 121, 135, 137, etc.), the type of aircraft operated (single engine, multi-engine, turboprop, jet), and the pilot's role in the operation (PIC, SIC).

Note that both the Commercial and Airline Transport Pilot (ATP) license are good for life, unless revoked or surrendered. Any continuing education requirements are to retain the employment or the privileges of exercising the license, unlike CE requirements for licenses in some industries.

In very broad brush strokes, most professional pilots will be required to complete a flight proficiency check, either in an actual aircraft, or in a simulator, every 6 to 12 months. The amount of time will vary for such checks, but 3 hours might be typical. This proficiency check will be accompanied, in some cases, with a written or oral examination. In addition to this, insurance may require an aircraft systems class and simulator brush up session every 12-24 months. Such training is usually accomplished in 3-6 days, including roughly 12-24 hours of lecture/bookwork, and 6-10 hours of simulator time.

In addition to the flight and systems training, pilots employed by air carriers will generally be required to receive instruction on operational aspects of their operation, including such topics as RVSM, hazardous materials, weather, physiology, as well as many others. Such training is often self-paced, computer based training (CBT). I would estimate the time commitment for this training to be 20-40 hours annually.

In addition to the required training and testing, many pilots choose to spend additional time studying aviation related topics. Such topics may include all those alluded to above, as well as other topics. Examples of such study would be changes to company operational procedures, brushing up on checklist memorization, FAA advisory publications, and areas of interest outside of normal operations, such as international operations. Speaking personally, I probably spend roughly 10 hours a week in what could be considered aviation related study or learning. I also often see other pilots at my company studying various aircraft or operational manuals, and our company keeps a collection of articles, FAA advisories, and other publications related to our operation with the intent that pilots voluntarily study these materials as they have time. Bear in mind that a pilot's life often involves a great deal of waiting, a task which often lends itself to reading and study.


In a jet, are Vy and Vx achieved at a constant AOA at all altitudes? It is known that in terms of IAS, Vx (best climb angle speed) rises with altitude, and Vy (best climb rate speed) decreases with altitude, until they converge at the plane's absolute ceiling. http://cospilot.com/documents/Why%20Vx%20and%20Vy%20Change%20with%20Altitude.pdf

In a jet powered aircraft, is this achieved at a constant angle of attack (AOA) regardless of altitude and other conditions (temperature, pressure, etc.)?

It might help to derive both speeds from first principles. We assume that the drag polar of the aircraft can be described by a parabola, like this:
$$c_D = c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$
 The symbols are:
$\kern{5mm} c_D \:\:\:$  drag coefficient
$\kern{5mm} c_{D0} \:$  zero-lift drag coefficient
$\kern{5mm} c_L \:\:\:$  lift coefficient
$\kern{5mm} \pi \:\:\:\:\:$  3.14159$\dots$
$\kern{5mm} AR \:\:$  aspect ratio of the wing
$\kern{5mm} \epsilon \:\:\:\:\:\:$  the wing's [Oswald factor][4]

Next, we describe thrust $T$ over speed $v$ with $$T = T_0·v^{n_v}$$

Now first to the maximum climb angle. This is reached when the condition $$\frac{\delta \gamma}{\delta c_L} = 0$$
holds true. No change in lift coefficient $c_L$ will improve the climb angle $\gamma$, it is only downhill from here to both sides. In order to get a grip on the climb angle, we look at the force equilibrium in steady flight at full power, assuming small values for $\gamma$:
$$sin\gamma = \gamma = \frac{v_z}{v} = \frac{T - c_D\cdot \frac{\rho}{2}\cdot v^2\cdot S_{ref}}{m\cdot g} = \frac{T_0·\left(\sqrt{\frac{2\cdot m\cdot g}{\rho\cdot c_L\cdot S_{ref}}}\right)^{n_v}}{m\cdot g} - \frac{c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}}{c_L}$$
 The symbols are:
$\kern{5mm} m\:\:\:\:$ aircraft mass
$\kern{5mm} g\:\:\:\:\;$ gravitational acceleration
$\kern{5mm} \rho\:\:\:\:\:$ air density
$\kern{5mm} v\:\:\:\:\:$ velocity
$\kern{5mm} v_z\:\:\;$ climb speed
$\kern{5mm} S_{ref} \:$  wing area

Ideally, we would also multiply the climb angle with an acceleration factor, but I leave this out here for simplicity.

Now we can derive the expression for the climb angle with respect to the lift coefficient and get
$$\frac{\delta \gamma}{\delta c_L} = -\frac{n_v}{2}·c_L^{-\frac{n_v}{2}-1}·\frac{T_0·(m·g)^{\frac{n_v}{2}-1}}{\left(\frac{\rho}{2}·S_{ref}\right)^{\frac{n_v}{2}}}+\frac{c_{D0}}{c_L^2}-\frac{1}{\pi·AR·\epsilon}$$
The general solution is $$c_{L_{{\gamma_{max}}}} = -\frac{n_v}{4}·\frac{T·\pi·AR·\epsilon}{m·g}+\sqrt{\frac{n_v^2}{16}·\left(\frac{T·\pi·AR·\epsilon}{m·g}\right)^2+c_{D0}·\pi·AR·\epsilon}$$
For jets ($n_v = 0$) the solution is quite simple, because the thrust terms are proportional to the thrust coefficient $n_v$ and disappear: $$c_{L_{{\gamma_{max}}}} = \sqrt{c_{D0}·\pi·AR·\epsilon}$$
For turbofan and propeller aircraft, we have less luck and get a much longer formula. This is the one for propellers ($n_v = -1$):
$$c_{L_{{\,\gamma_{\,max}}}} = \frac{T·\pi·AR·\epsilon}{4·m·g}+\sqrt{\left(\frac{T·\pi·AR·\epsilon}{4·m·g}\right)^2+c_{D0}·\pi·AR·\epsilon}$$
So yes, pure turbojets have an optimum lift coefficient for maximum climb angle that uses only terms which are constant over altitude. They do indeed climb steepest at a constant lift coefficient.

But the thrust-dependent optimum for other engine types hints at an altitude dependency which might affect the other optimum, that for best climb speed.

In order to find the conditions for maximum climb speed, repeat the process above with an expression where both sides are multiplied by speed:
$$v_z = \frac{T\cdot v - c_D\cdot \frac{\rho}{2}\cdot v^3\cdot S_{ref}}{m\cdot g} = \frac{T_0·\left(m\cdot g\right)^{\frac{n_v-1}{2}}}{\left(c_L\cdot\frac{\rho}{2}\cdot v^2\cdot S_{ref}\right)^{\frac{n_v+1}{2}}} - \sqrt{\frac{2\cdot m\cdot g}{\rho\cdot c_L\cdot S_{ref}}}\cdot\frac{c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}}{c_L}$$

Now the solution for turbojets becomes the more complicated one, but that needs to be the case - how else would those optima converge at altitude?
$$c_{L_{{\,n_{z_{\,max}}}}} = \sqrt{\left(\frac{T·\pi·AR·\epsilon}{2·m·g}\right)^2 + 3\cdot c_{D0}·\pi·AR·\epsilon} - \frac{T·\pi·AR·\epsilon}{2·m·g}$$

While the angle of attack for steepest climb is constant over altitude, the angle of attack for best climb speed increases as excess thrust disappears with rising altitude. Thus, the question can be answered: No.


How common are 400Hz supplies in aircraft? I understand that 400Hz, 26Vrms power is found in a lot of aviation equipment. But how common is it? Is it in every plane and every instrument or is it restricted to certain sectors, like military, commercial, or private planes?

Is it used a lot in ground applications to power aviation equipment, like in a workshop/lab setting?

The reason I ask is that I'm trying to gauge interest in a small 400Hz, 26Vrms power supply for the benchtop (plug it into regular 60Hz 120V power). From what I can see, these are hard to find below a few thousand dollars.

In modern military and commercial aviation, aircraft power is 3-phase 115V at 400Hz (AC), and 28V DC.  This is standard just about everywhere.

AC power is 3-phase 115V AC at 400Hz (alternating current).  When the engines are spinning, this power is produced by onboard generators (alternators) feeding redundant power buses.  On the ground, this is typically sourced from a ground power unit (GPU).  During emergencies, AC power may be produced by an auxiliary power unit (APU).

DC power is provided by converting a portion of the 115V AC power to 28 volts DC for powering many of the avionics systems and charging the aircraft battery.

EDIT: My apologies, contrary to my original answer (I was thinking powering the cockpit displays/indicators mostly), a lot of navigation and pitch/attitude sensors take 26vac/400Hz input power.  Rate gyros, compass, flux valve, etc.  See, e.g. this section from a Cessna Citation.


Is there any way we can predict an air crash? Is there any way we can predict a crash from the system inputs?

The question arises from this discussion.

Yes, many aircraft are fitted with TCAS which predicts one type of crash - an aerial collision.

Many aircraft are fitted with GPWS which predicts another type of crash - controlled flight into terrain.

The ground based ATC have systems that predict a loss of separation, the Short-Term Conflict Alert [STCA]. See this question about separation and conflicts. In terms of predictions this would constitute a very high rate of false positives. But that is good.

Because of the predictions, many crashes are avoided.


What permissions or approval are needed to land in Antarctica? Can I land at Jack F. Paulus Skiway (NZSP) with just an ATC clearance? Or do I need to ask some other authority before I fly there? Are there any regulations regarding 'landing rights' in Antarctica?

Edit:

Let's assume I am in a private aircraft that is able to safely fly to NZSP where I am flying under IFR. Do I still need permission from some kind of authority? And what about commercial flying?

For this we need to reference the US Antarctic Program Inter-agency Air Operations Manual

First off this will tell us who is in charge down there (at least for US bases) as its not quite an ice frontier free for all,

  Oversight of the on-ice operations of the civil aircraft is
  NSF-delegated to the Dept of the Interior/OAS Office of Aviation
  Services (OAS) in accordance with the SLA between OAS/AIL. Joint use
  of the USAP airspace in Antarctica requires close coordination between
  the DoD and NSF (and its delegations).

It looks like if you want to fly down there you need to file form DD 1801

  2.3.4. Intercontinental flights between New Zealand and Antarctica will require USAP aircrew to file a DD Form 1801 (International Flight
  Plan) in Christchurch Base Operations to Christchurch Clearance
  Delivery. Flights utilizing the Macquarrie route will require a FIR
  estimate for Melbourne and Auckland boundaries.

The document does not list any approach procedures for NZSP but it does list them for McMurdo Station and they are presumably similar,

  2.7.2.1. IFR. McMurdo ATC retains responsibility for all IFR aircraft. Aircraft will be  USAP Inter-agency Air Operations Manual, 1 August
  2012 40 instructed to contact Tower prior to entering Class E
  airspace. Mac

  2.7.2.2. VFR. Aircraft are normally instructed to contact tower no closer than 10 miles from the airport for landing instructions.

  2.7.2.3. Aircraft operating in Class D airspace will be in radio contact with the tower and should remain at 1,000 feet AGL or higher
  (500 feet for helicopters) until commencing final descent.

They even have reg's for uncontrolled fields

  2.8.1. For operations at uncontrolled McMurdo area airfields, fixed/rotary wing aircraft pilots will follow uncontrolled field
  procedures.

  2.8.1.1. Flight plans will be filed with Mac Center and advisory service provided.
  2.8.1.2. Fifteen (15) minutes prior to departure from an uncontrolled airfield, the pilot will notify Mac Center/Tower of planned activity
  via landline or radio.

  2.8.1.3. Mac Center/Tower will notify Aircraft Rescue and Fire Fighting (ARFF) (who notifies the USAP Airfield Manager) on FM Channel
  2 of intended uncontrolled airfield operations.

  2.8.1.4. Pilots will announce their intentions on the Common Traffic Advisory Frequency (CTAF) VHF 129.7 MHz.

Interestingly it looks like McMurdo is the primary landing strip however based on the letter of 1.2.1 the South Pole Station (which Im pretty sure is NZSP) only accepts ski equipped aircraft so you would at least need skis.

  1.2.1. Primary airfields for the USAP are located in the McMurdo Station area and at the South Pole Station (ski-equipped aircraft
  only). The primary heliport is located at McMurdo Station. Additional
  ice runways, skiways, and helicopter landing sites are established
  throughout the continent supporting the USAP science activities as
  planned by the NSF Prime Contractor’s Fixed/ Rotary Wing Coordinators.

According to the doc a lot of the info is published in the Antarctic Flight Information Manual which looks like you may need to set up some kind of account here to download or "contact [your] affiliate National Antarctic Program".

All this in mind, I have not yet found any documentation or out right publications that seem to forbid flying there as long as procedures are followed. With that in mind you clearly need to file some flight plans and related info, I would think you would need a good reason to be going there to get approval. The reality is there may be more info on this buried in the antarctic treaty but in practice I dont know how that sort of stuff gets enforced.


Is it legal to rent out an experimental aircraft? Is it legal to rent out an E-AB aircraft (not a light sport aircraft)?

The aircraft will not be used for hire or compensation but to rent out to a pilot who wants to fly from point A to point B.

After reading the FAR 91.319 I know the answer but seems like a lot of folks in this industry are confused on this topic.

Since you specifically state the question as it relates to E-AB, the reference to 91.319(f) doesn't apply. But 91.319(a) does apply.

From 91.319, the answer is "no".

  §91.319   Aircraft having experimental certificates: Operating
  limitations.

  (a) No person may operate an aircraft that has an experimental
  certificate—

  (1) For other than the purpose for which the certificate was issued;
  or

  (2) Carrying persons or property for compensation or hire.

Your statement that "The aircraft will not be used for hire or compensation but to rent out to a pilot who wants to fly from point A to point B." is where you have erred. The FAA has interpreted that rental (or lease) of an aircraft with or without crew is a commercial operation that is "Carrying persons or property for compensation or hire."

So in the view of the FAA, renting the aircraft is a violation of §91.319 (a)(2).

You should also be aware that you could be violating access rules for your airport by operating a business that doesn't comply with the airport's minimum standards for business. That could get you kicked off the airport.

You also need to consider the conditions of any insurance policy that covers the aircraft.

That said, there's nothing that prohibits you (except possibly insurance) from loaning the aircraft to someone as long as you don't receive any compensation. Just be aware that the FAA interprets the term "Compensation" very broadly; e.g. excess fuel on return of the a/c could be considered compensation.

Final caveat: I'm not an aviation lawyer, so nothing I say should be considered legal advice. Contact the FAA, EAA (since this about E-AB) or an aviation lawyer if you want a more definitive answer.


Do propeller coefficients go to zero at the same value of advance ratio? Graphs of power coefficient ($C_P$), thrust coefficient ($C_T$), and efficiency ($\eta=JC_T/C_P$) of the 5868-R6 propeller as functions of advance ratio ($J=V/(nD)$) and propeller pitch (blade angle at 0.75R?) are found in many textbooks (such as McCormic):

From these curves it seems that for a given propeller pitch $C_P$, $C_T$, and $\eta$ go to zero at the same value of $J$. At also seems that the slopes of the $C_T$ vs $J$ curves for higher value of $J$ (where $C_T$ approaches zero) are the same.

I have two questions:

Do $C_P$, $C_T$, and $\eta$ always go to zero simultaneously at the
same value of $J$ for all propellers?  Why?
Are the slopes of the $C_T$ vs $J$ curves where
$C_T\rightarrow 0$ the same for all values of propeller pitch?

Do $C_P$, $C_T$, and $\eta$ always go to zero simultaneously at the
    same value of $J$ for all propellers?  Why?

Yes; Talking in dimensional quantities, This speed, at which all coefficients goes to zero is called pitch speed.

At pitch speed thrust goes to zero due to the fact that the incoming airflow drives the apparent angle of attack seen by the blades to zero.

Power = Thrust * velocity , As thrust goes to zero power goes to zero as well.

Efficiency $\eta = \frac{P_{out}}{P_{in}}$, $P_{out}$ goes to zero as shown above hence $\eta$ goes to zero.

HTH


How do the military pilots of Air Force One train for exceptional circumstances in an airliner not designed for high performance? This article discusses how on one occasion, the pilot of Air Force One, the personal air transport of the President of the United States, was required to perform evasive manoeuvres to avoid presumed hostile fighter aircraft over Syria. In reality, the Syrian aircraft were friendlies and their military authorities had merely failed to properly communicate their intent. But nevertheless, it shows, and is logical, that the pilots of these converted civilian aircraft are required to learn and perform techniques that would never be used in the intended civilian operation of these aircraft.

How do pilots learn to fly an airliner, like the VC-137 in use at the time of this anecdote, or in the present day a 747, beyond its intended use and presumably with a high risk of failure? Does the United States Air Force retain identical aircraft not routinely used as Air Force One, for specific training use? Otherwise, how is it determined that these manoeuvres are feasible in such an aircraft and that the pilot is capable of performing them?

Does the United States Air Force retain identical aircraft not
  routinely used as Air Force One, for specific training use?

The Airforce maintains two identical versions of the VC-25A that it uses to fulfill the role of Air Force One but its unclear (and likely not public) if any practice occurs in either airframe.

  Otherwise, how is it determined that these manoeuvres are feasible in
  such an aircraft and that the pilot is capable of performing them?

Through testing, as is the case for the operational envelope of any aircraft. Due to the nature of Air Force One this data is not (as far as I know) public.

On any note the pilots, who are typically career Air Force pilots all have lots of experience and in some cases experience flying other heavy or high performance aircraft as is the case with one of the most recent pilots

  Col. Tillman's distinguished career spans 30 years in the United
  States Air Force. Utilizing his Bachelors of Science degree in
  Chemical Engineering (Tulane Univ '79), he served as a Rocket
  Propulsion Engineer upon entering the service but was quickly selected
  to attend USAF pilot training. His flying experiences include time as
  a T-37 Instructor Pilot for undergraduate pilot training, C-130
  transport pilot, VIP airlift as a pilot in the Gulfstream III and IV

The air force trains for low altitude and evasive maneuvers in the C-130's not infrequently. I fly fairly close to a major air force base all the time, if you pick up flight following and get handed off to their tower you will often get a warning of such activity. You can generally see it out the window as well (its pretty neat). Presumably an force pilot coming from a C-130 background has some experience flying evasive maneuvers in heavy aircraft.


Muscle memory for weapons systems? How often do military pilots train to retain muscle memory for use of weapons systems?

This is a broad question that has no real specific answer as there are no specific training sorties dedicated specifically to "muscle memory", let alone muscle memory specific to weapons switchology.

Military currency requirements exist for multiple functional skills, air to ground attack, air to air 1v1 ACM, Defensive ACM, carrier landings, instrument approaches, etc.  During any and all training events, whether in the aircraft or simulator, muscle memory is reinforced, but it is more of a by product of all the other things going on around it such as flying the aircraft, scanning the instruments, and executing the procedures.

These currency requirements are generally captured in some sort of a training matrix that is maintained by a squadron training officer, who communicates the requirements to the schedules officer.  Both of these individuals report to the squadron operations officer, who has overall responsibility for maintaining aircrew combat readiness.

Intervals between training simulator or flight sorties may vary by type aircraft, skill-set, and where the squadron is in their deployment/readiness cycle.  (i.e. just got back from war, or getting ready to head out?)

The closest thing to what you are asking is what we referred to as "blind fold cockpit checks".  Early in simulator training the instructor would have you close your eyes, then locate certain switches by feel, reinforcing muscle memory to both locate them and identify them by their often unique shape.

These drills, however, generally focused on switches related to emergency procedure memory items.  And more specifically, to items related to loss of electrical power, smoke and fumes in the cockpit, and other emergencies where vision could be impaired.


Is a single-engine ferry flight allowed with a twin-engine plane? If a twin-engine aircraft has an engine problem and could fly somewhere for maintenance, is a single-engine ferry flight ever allowed? If so, do airlines or pilots ever decide to do this?

Civilian aircraft are not designed for this - but some military aircraft are. The Antonov-70 can easily take off with one engine inoperational (it has four in total), but it has a limited capability to take off with two engines out on the same side! For that, it has to be empty and can carry only minimum fuel.

This capability is the consequence of the demand of the Soviet Air Force for the An-70 to operate for 6 months with minimum maintenance. The Antonov design bureau, well aware of the limited capabilities of front-line troops in aircraft maintenance, designed this transporter with lots of redundancy.

Edit:
With one engine inoperational, any twin-engined civilian aircraft would not be legal if it attempted a one-engine take-off. I would expect there is a way to do it, but it needs the agreement of the owner and some paperwork with the local authorities. If you can prove that this particular ferry flight is safe, I think you would be allowed to fly. But I am certain that without lengthy preparation and paperwork there is no way to legally take off on one engine only.

This is in contrast to military aviation where this kind of operation is planned for.


What is the smallest aircraft to have a CVR / FDR? I was wondering what is the smallest aircraft to have a CVR (Cockpit Voice Recorder) and/or FDR (Flight Data Recorder)?

Small single engine prop can sometimes have the avionics, like the G1000, that records some of the flight parameters on a memory card. But what about a proper CVR or FDR?

I'm not asking about military aviation, but more about general or small commercial airplanes.

I understand that it depends of the type of operation, but what is the smallest airplane to have a CVR/FDR on board?

Looks like in the EU as well as in the US the Cessna CE-510 Mustang needs one according to the minimum equipment list.

In the EU

  -70-01

  *** Cockpit Voice Recorder (For Combined Voice Data Recorder, refer to 31-30-01)

And in the US

  -30-01

  *** Flight Data Recorder (FDR) System

That is a 6 seat plane, you will be hard pressed to find something smaller although other similar in class aircraft may also have them.

It looks like some versions of the Cirrus SR-22 include an Aircraft Data Logger but im not sure if that conforms to the various impact regulations for a black box.


Can the RAM AIR valve cause depressurization on the CRJ-900? On the CRJ-900 AIR-CONDITIONING panel there is a RAM AIR switch light which opens a valve and allows air from the ram air scoop to enter the mixing manifold for distribution to both the flight deck and passenger cabin.

What would happen if the valve were opened at high altitude? Would this cause depressurization?

When I received CL-65 type rating I was taught that there was a protection that would prevent the valve from opening. I have also heard this was a mistake in the manuals and that it would open and cause depressurization. I have also been told that there is a one-way check valve inline with the ram air duct to prevent depressurization, but I’ve never seen a source for any of this information.

If anyone has an answer I’d appreciate citing some schematics or Bombardier manuals to back it up.

Update

I heard something. It's second-hand information from someone who worked at Bombardier when the CRJ was certified. This person said that there is no check valve on the RAM AIR valve, but the cabin outflow valves will close, compensating for the loss of pressure from the RAM AIR valve being open.

The cabin outflow valves should close completely as they are designed to prevent the cabin altitude from exceeding approximately 14,500 feet. This wouldn't prevent higher cabin altitudes if the ram air valve stayed open at a high altitude.

I still want a cited answer, but this is the first answer I've heard that makes sense to me.

No RAM AIR VALVE can open if the cabin pressure exceeds the outer pressure. For the CRJ the RAM AIR VALVE is directed so that a dynamic component of the aircraft speed helps its opening, but this is much lower than the difference of pressure between cabin pressure and the outside pressure at high altitude. So no danger of depressurization whatsoever.


What are the limitations on a steep approach? Certain aircraft like the A318 are able to do steep approaches for landing. What are the limits (Angle of descent, airspeed, and the like) for this type of landing?

This presentation gives the following limitations for A318 steep approaches:

Maximum authorised Flight Path Angle: -5.5°

MLW unchanged (57.5t)

FWD and AFT CG limits unchanged

Maximum altitude for landing: 2000ft

Tailwind limit for landing: 5Kt

Crosswind limit for landing: 26Kt gust included

AUTOLAND is not allowed

CATII and CATIII are not allowed

All engines operative only


How can an airliner have low altitude stall recovery? I was going through the air crash record and found out that a lot of them happened when the aircraft stalled at a low enough altitude where the pilots couldn't get enough speed to pull back out. I was curious to see why this was the case when I learned about flow separation hysteresis where to reattach the flow the wing needs to pitch down further than the static stall angle. Reading that and the crash record brought up a question in my mind:

How could an aircraft be engineered to have safe low altitude stall recovery? (aside from having a VERY low wing loading, ballistic parachutes, or a computer to prevent pilots from entering low altitude stalls)

From a cursory analysis, this situation seems ideal for some form of emergency engine, either electrically powered fans or a few solid rocket motors to right the aircraft and provide enough power to at least make the touchdown not a crash. Or the wing and stabilizers have some form boundary layer acceleration to reduce the amount of time needed to recover from a stall.

I'm curious to see what approaches have been tried to try and solve this problem or if the newer aircraft have some other technology incorporated.

The most important reason for aircraft stalls is due to high angle of of attack, which causes flow separation.

Usual stall recovery procedures consist of reducing the aircraft angle of attack (pitch angle) and increasing power so that the stalled wing starts producing lift and the aircraft forward speed is increased to the required amount. Then the controls are applied in such a way to return to level flight as soon as possible.

The problem with low altitude stall is that stall recovery usually involves some loss of altitude and if the altitude is low enough, recovery from stall may not be possible before contact with ground.

However,the recovery altitude may be decreased to a certain extent by incorporating the following technologies in civil aircraft.

Use of high lift devices- Use of high lift devices like slats and flaps increases the lift coefficient and also delays the onset of stall. In case the slats have not been deployed before stall, they can be deployed to get the airfoil (wing) produce lift again.

Source: zenithair.com

Increasing the power- In general, greater the power applied, the less the loss of altitude. In this case, the engines usually have excess emergency power that can be applied for reducing the loss of altitude.

In general, it is better not to enter into a stall and most of the technologies are geared up towards prevention of stall than recovery due to a number of reasons

In case of civil aircraft, below a certain altitude, stall recovery is usually not possible.
Addition of systems to ensure a soft landing in case of stall increases the cost and complexity and in any case may be impracticable in case of large aircraft. As such, it is better to train the pilots to prevent entering into a stall in first place.


Where does the 90 seconds limit for plane evacuation come from? New airplanes have to confirm that all passengers have to be evacuated within 90 seconds or they wouldn't be certified by aviation authorities. But where does the 90 seconds limit come from? Why isn't it 60 or 120 seconds? Is it based on a series of studies or is it just a nice round number that was chosen based on a rule of thumb?

90 seconds comes from a safety aspect, specifically a fire safety aspect

Aviation Safety Study SA9501 Footnote 3 says:

  Internationally, industry accepts 90 seconds as a reasonable estimate of the survivable time in an evacuation where fire is present.

Which means that it is predicted than a burning aircraft is not sustainable for life beyond that period, but interestingly this is not the condition that the aircraft is certified under.

FAA Chapter 77 Section 1.7 says:

  A full-scale emergency evacuation demonstration simulates an aborted takeoff. The operator must show that the aircraft, emergency equipment, and emergency procedures allow the evacuation of the aircraft at full seating capacity, including crewmembers, in 90 seconds or less.

So the 90 second rule comes from a fire safety aspect - as humans are not expected to survive in those conditions for longer than that; but the aircraft is only tested on whether it can evacuate on an aborted takeoff (not specifying that a simulated fire must be the cause of this aborted takeoff).

Sources: https://www.skybrary.aero/bookshelf/books/2699.pdf

http://fsims.faa.gov/WDocs/8300.10%20Airworthiness%20Insp%20Handbk/Volume%202/2_077_00.htm


Does altimeter setting affect the vertical guidance in a LPV approach? I had assumed during a WAAS approach when the GPS is in LPV mode, both lateral guidance and vertical guidance are generated from GPS/WAAS signals and the pitot-static system should have no effect on its vertical guidance. This is in contrast with LNAV/VNAV approach, where the vertical guidance comes from the barometric system, the same source as altimeter.

However, when I read RNAV (GPS) Z RWY 30 @ KHAF, I will get a different DA if I use a different altimeter setting. So, why does altimeter settings matter to the DA in an LPV approach?

Short Answer:

No, the vertical component of LPV approach performance is based on WAAS GPS input, not the altimeter or barometric system.

Longer Answer:

Your assumption about LPV performance is correct: Baro-VNAV is not used for LPV approaches.

On any type of approach with a Decision Altitude (DA), the aircraft's arrival at the DA is determined by the pilot's reading of the aircraft's sensitive altimeter.

If the altimeter is set to an altimeter setting report from a distant reporting station, SFO in this case, then the DA may be increased to give additional altitude margin to allow for variance in local atmospheric pressure.

This is true for the DA or Minimum Descent Altitude (MDA) on any approach, whether a GPS approach or not. See the MKT ILS 33 and MKT RNAV 15 for other examples of this. See the following excerpts from the Aeronautical Information Manual on altimeter settings for approaches (emphasis mine):

  5-4-5
  a.
  4. Approach minimums are based on the local
  altimeter setting for that airport, unless annotated
  otherwise; e.g., Oklahoma City/Will Rogers World
  approaches are based on having a Will Rogers World
  altimeter setting. When a different altimeter source is
  required, or more than one source is authorized, it will
  be annotated on the approach chart; e.g., use Sidney
  altimeter setting, if not received, use Scottsbluff
  altimeter setting. Approach minimums may be raised
  when a nonlocal altimeter source is authorized. When
  more than one altimeter source is authorized, and the
  minima are different, they will be shown by separate
  lines in the approach minima box or a note; e.g., use
  Manhattan altimeter setting; when not available use
  Salina altimeter setting and increase all MDAs
  40 feet. When the altimeter must be obtained from a
  source other than air traffic a note will indicate the
  source; e.g., Obtain local altimeter setting on CTAF.
  When the altimeter setting(s) on which the approach
  is based is not available, the approach is not
  authorized. Baro−VNAV must be flown using the
  local altimeter setting only. Where no local altimeter
  is available, the LNAV/VNAV line will still be
  published for use by WAAS receivers with a note that
  Baro−VNAV is not authorized. When a local and at
  least one other altimeter setting source is authorized
  and the local altimeter is not available Baro−VNAV
  is not authorized; however, the LNAV/VNAV
  minima can still be used by WAAS receivers using the
  alternate altimeter setting source.

Note that Baro-VNAV is a type of VNAV system which uses barometric
altimetry as a basis for vertical navigation performance. An LNAV/VNAV approach can be flown using WAAS equipment without a Baro-VNAV system.


In the US, how does the distinction between E2 and E3/E4 airspace affect pilots? In the US, practically speaking, how does the distinction between the E2 and E3/E4 subtypes of Class E airspace affect pilots?

"Caution: as noted in the links below, in actual practice, the distinction between E2 airspace and E3/E4 ("extension") airspace is often ignored by ATC..."
In the Center environment, we make no distinction between the surface area and the extensions when dealing with SVFR. The reason is simple. I can't clear a SVFR and an IFR in that airspace at the same time (or two SVFR aircraft), so those extensions should be empty if I'm allowing SVFR. Conversely, I'll not allow a SFVR operation (remember, the pilot has to request it), if I have an IFR aircraft cleared in that surface area.
In the case of Class E that's adjacent to Class C or D airspace, the pilot should be talking to ATC, anyway.
Keep in mind, though, if you're just buzzing along VFR and you see that there's a surface area ahead of you, there's nothing wrong with calling Center and asking if there's known traffic there, or even requesting flight following (cheap insurance!) through the area.


What are the advantages and disadvantages of ducted fans in designs such as the Airbus E-Fan? I have read that it increases thrust and reduces noise. Is there a downside to this?

(Image source: Wikipedia)

An answer to your question can be found here.

Advantages of ducted fans would be:

reduced noise
Better containment of broken blades
protection of ground personnel when the engine is running
Smaller size than a comparable propeller
They look like a fancy jet engine. This is probably the main motivation of Airbus for their use on the E-Fan.

For almost all aircraft designers, their drawbacks have weighed more heavily:

Less efficiency, because a smaller mass of air is used for propulsion
Additional friction drag and weight from the shroud

The highest propulsion efficiency is possible with a large, slow-spinning prop. Once flight speeds approach the speed of sound, the propeller has to become smaller to avoid supersonic propeller tips, and then the shrouded design becomes more attractive. Electric airplanes so far are not fast enough to profit from this effect. I would be very skeptical of the increased thrust claim - both efficiency and thrust of the E-Fan ducted fans are lower than what a well-designed propeller can offer.

The addition of the shroud only increases thrust when compared to the naked fan, but the fan is a poor replacement for a decent propeller at low speed.


Do a turboprop’s compressor and turbine rotors windmill when the engine is shut down and feathered? If a jet engine is shut down in flight, it continues to turn due to the aircraft’s forward motion forcing air through the engine, causing it to “windmill” in the airflow.

Is this also true for turboprops?  When a turboprop engine is shut down and its propeller feathered, do its compressor and turbine rotors keep windmilling in the aircraft’s slipstream, or do turboprops have some way of closing off their engine intakes to prevent this when the engine is shut down?

A feathered propeller is designed not to windmill in flight, however in the case of a power turbine or even a propeller connected to both the compressor and turbine, it's far easier to turn than an old radial when in the feathered position.

Nothing physically stops the propeller from turning when feathered beyond the force required to turn the power turbine/gearing or whatever the propeller is connected to and the air hitting it at the right angle. Straight airflow shouldn't turn it, however any flow from the sides would turn a feathered turboprop. Unlike a turbofan, the propeller changes pitch so the air affects it differently.


Why does an Avro RJ85 have four engines? The British-designed Avro RJ85 is a short-haul airplane with four jet engines.  What is the purpose of four engines for such a small aircraft?

It was originally the BAe 146 and was designed for operating out of city airports such as London City Airport.

The main reason is for noise abatement. Back in the 80s, four high-bypass turbofans made a lot less noise than two contemporary engines.

Climb performance is also fantastic.  it can climb safely from most airports using much less than full power which helps keep the noise down and provides high safety margins when operating near built-up areas, for example if an engine fails on take-off.


Is tungsten a good metal for jet engines, besides the weight penalty? Right now, the hottest part of jet engines are made from a steel-nickel alloy. Is tungsten a better choice?

Pure tungsten has the highest melting point and highest tensile strength of any other pure metal. Presumably you could make it hollow and use the same cooling fluid to prevent overheating. For this same reason I am not sure if the weight penalty is really that big. I don't think the turbine blades make up a really big part of total engine weight.

(I don't know how well it resists oxidizing at high temperatures. I don't know how it might change with adding a little carbon or steel or nickel. But presumably this is not a drawback because I've read about rocket engine nozzles using tungsten: link. If it doesn't oxidize or corrode there, I can't imagine why it would do so in a jet engine.)

Another way of asking this question: Does tungsten in the hottest part of jet engines have any major drawbacks besides weight and cost?

No, tungsten would generally not be a good choice for jet engines.

Some of the parts that would need to be the most heat resistant, such as turbine blades are subjected to rotational forces that increase directly with the mass of the part. Thus a high mass material such as tungsten would increase the forces the part would have to withstand. These forces are already measured in tons per blade.

If you discount the high-mass quality of Tungsten, the biggest problem is that Tungsten is also brittle. If a turbine blade failed, as does happen, it would be very difficult to contain. Tungsten is used in armor piercing projectiles; the results of a tungsten turbine blade failure would not be good.


Why would flares be fired into the air after a flight lands? On Monday 23rd September at about 14:30 BST my plane landed at London Stansted. Soon after landing, while the plane was at the end of its deceleration, I noticed what appeared to be two flares or fireworks shot about 50 ft into the air above the grass to the right of the runway (I believe it was runway 22).

What on Earth could that be about? The flight was Ryanair FR587 (and the plane's registration was EI-DYL if anyone is interested).

I know that flares are used at Dover air force base in Delaware sometimes to deter birds from the airfield. I also know that flares are just a common bird deterrent anyway. So it may have been simply to clear the taxiways and runways of birds before the next departure or arrival.


What is the purpose of aileron droop used in some commercial airliners? As we know ailerons aid the aircraft to make roll movements and provide lateral stability.

But, what is the intent behind drooping them in some flight conditions, especially when deploying flaps?

The purpose of aileron droop is to use the ailerons as wing flaps. Wing flaps increase the lift generated by the wings at low speed. They occupy a good part of the trailing edge of the wing, except for the outer part, where the ailerons are. By deflecting both the ailerons downwards, they change the wing camber and act like simple plain flaps. They can still act as ailerons, by normal differential deflection.

Image source


How to calculate the airspeed for maximum specific range? Given the following parameters for a small business aircraft:

Wing surface: $S=30m^2$
Lift Drag Polar in clean configuration: $C_D = 0.022 + 0.047 {C_L}^2$
Maximum Lift Coefficient $C_{L_{max}}=1.35$
Static sea-level Thrust: $T_0 = 12KN$
Thrust variation with altitude: $\frac{T}{T_0}=\frac{\rho}{\rho_0}$
Aircraft weight: $W = 50 KN$
Thrust specific fuel consumption (constant): $C_T = 0.7 N/Nh$

I need to calculate:

the optimum lift coefficient for maximum specific range
the airspeed for maximum specific range when operating at the specified weight and sea level conditions.

For $C_{L_{opt}}$ I have found a value of 0.395 using the lift drag polar and the fact that $C_{L_{opt}}= \sqrt{\frac{1}{3}C_{D_0}\pi A e}$.

I am then assuming that the airspeed for maximum range is given by $V=\sqrt{\frac{W}{S}\frac{2}{\rho}\frac{1}{C_{L_{opt}}}}$.

In my calculations, I am using $W=50000/9.80665=5098.581 KG$ and $\rho=1.225$, which gives me a value of $V = 26.504 m/s$

However this seems not to be the correct answer. What am I missing?

Check the units. Using $$W = 50000N$$ instead of $W=5099kg$ you get $$V=83m/s$$ (vs. $V=26.5\sqrt{m}$).


How often is ILS accuracy checked? I imagine checking ILS accuracy by measuring ILS signals at various points along the approach path is routine maintenance, although I don't know how it is done. How often must this kind of check be done to ensure the ILS is still accurate enough?

The FAA has a Flight Inspection Manual which describes the checks that must be done and how often. Table 4.1 shows that an ILS must be flight checked every 540 days. Section 15 describes what happens during one of these checks. It's quite an extensive inspection!


Is the differential between the forward and aft CG limits indicative of the overall stability of an airplane? Studying up on the Cessna 162 Skycatcher POH to take my checkride in soon and I noticed the differential between the maximum and minimum CG's is a mere 2.5 inches from one to another.

I got curious and looked up the CG limits for the two other planes I train in, the CSA/CZ SportCruiser and the Cessna 172, and saw that the differences between their forward/aft CG limits are 6" and 12", respectively.

In terms of aerodynamic stability, I would indeed rank the Skycatcher (2.5" CGfwd/CGaft differential) as the least stable and the Skyhawk (12") as the most stable. Is there any connection between forward/aft maximum CG differentials and the amount of aerodynamic stability in an aircraft?

Edit:
Still reviewing the responses, having been sent to the encyclopedia several times to study up on new terminology, but I just want to emphasize that the  SportCruiser (6" diff) is dramatically more stable in the air than a Skycatcher (2" diff). Both of these aircraft have the same max gross takeoff weights, 30 foot wingspans and 23 foot lengths. So perhaps the Cessna 172 could be ignored for the purposes of addressing the question.

https://en.wikipedia.org/wiki/CZAW_SportCruiser
https://en.wikipedia.org/wiki/Cessna_162_Skycatcher
https://en.wikipedia.org/wiki/Cessna_172

Normally, the aft limit is governed by static stability, while the forward limit is governed by the elevator control capacity (but sometimes, dynamic stability: excessive static stability may cause oscillations).

So, a narrow CG range would rather suggest that the elevator and/or trim capacity is not sufficient to cope with the more forward CG.

However, in practice there may be other reasons for restricting the range. For example, it may simply be impossible to load the aircraft (without exceeding the station load limits) in such a way as to put CG out of the defined range. I think C152 is close to that. Or, say, the stall or spin characteristics are unsatisfactory, so the aft limit may be restricted further than what normal stability dictates.

Needless to say, artificial stability augmentation (including FBW) may broaden the CG range, primarily by affording a more relaxed aft limit.


Why is it, with less airflow, you'll have less control effectiveness? I understand the principle of less airflow, less control, but why is that the case?

When deflected, the control surfaces (ailerons, elevator, rudder) cause an aerodynamic moment about the Aerodynamic Centre. A moment has a moment arm and needs to have a length reference - the aerodynamic moments are defined with reference to wing dimensions: wing span for rolling and yawing moments, and Mean Aerodynamic Chord for pitching moments. If we have a look at the pitching moment P:

$$ P = C_{r_{\delta e}} \cdot \delta_e \cdot q \cdot S \cdot MAC$$

With:

$C_{r_{\delta e}}$ = elevator coefficient (dimensionless)
$\delta_e$ = elevator deflection
$q$ = dynamic pressure = $\frac {1}{2} \cdot \rho \cdot V^2$
$A$ = wing area
MAC = Mean Aerodynamic Chord

$C_{r_{\delta e}}$, A and MAC are constants. So: pitching moment of the aircraft is proportional to elevator deflection, and to the square of the airspeed. Fly twice as fast, and the pitching moment from a certain elevator deflection will be four times as high.


Why is "dragging it in" considered bad in small aircraft, but fine in larger aircraft? In larger aircraft, shallow, high-power approaches are performed as a matter of routine, but in light aircraft it seems to be frowned upon, especially in clear weather and smooth fields. Why is "dragging it in" considered bad in small aircraft?

For the GA fleet, there is some historical precedent operating here.  Years ago, engines were much less reliable than they are today.  Dragging it in generally means that you cannot glide it in if you have a complete power failure.  This translates to saying in the event of an engine failure, you are landing off airport with limited selection of landing sites (your altitude is low as you are now below pattern altitude).  So if you are flying behind an old Curtis OX-5 in your Jenny, a gliding approach to landing was recommended back in the day.

Engines are much more reliable today.  After an analysis of landing accidents, the FAA determined that a stabilized approach to landing is less likely to result in an accident, and they changed their guidance accordingly. Stabilized approaches are partial power-on landings.  Some old timers and some old time CFIs reject the FAA's statistical analysis and still teach/fly glide-it-in landings.  Properly executed, both approaches to landing are safe.  It is just that the FAA thinks that stabilized approaches are safer given engines commonly in use today.

It is also true that virtually all airlines require stabilized approaches in their operating specs, and that a go around is mandatory if the approach is not stabilized.  With this in mind, flight schools that aspire to send their graduates to the majors will all teach stabilized approaches.


Do aircraft use their lights to 'say hello' to each other? On the KLM website, I found this strange quote:

  If planes pass each other at night they sometimes use light signals to say hello.

Is it true and common? How it is done (which lights/patterns)?

Yes, it is true.  When two aircraft flying in opposite directions pass each other at night, it is quite common for one or both to briefly turn on their landings lights. This is done partially to "say hello", and also to increase situational awareness. I would guess it happens about 50% of the time.

Usually one aircraft will turn on their landing lights about 2-5 miles back and wait for the other to briefly flash their lights in response. It is not uncommon to get no response because the pilots on the other aircraft may have their heads down, and not see the other aircraft. Some pilots don't respond because they feel it is a useless practice, and can't be bothered.

When there is only 1,000' vertical separation of opposite direction, or crossing  traffic, some ATC jurisdictions might require the controller to inform the aircraft of each other's presence. In that case it is more likely that both aircraft will turn on their landing lights to be more visible to the other aircraft. There is no operational requirement to do this, but most pilots tend to go along with this practice.


Helicopter or Airplane, which is the most difficult to fly? I know it varies from aircraft to aircraft, but I want to know in general, which would be the most difficult aircraft to fly even after years of experience. Helicopter or Airplane ?

I tried to fly a helicopter on the FSX and I couldn't land the aircraft once without spinning like a beyblade for minutes. I know it is not possible to fly something perfectly without knowledge, but I remember that my first time flying a plane on the FSX, everything had been easier.

Some people also say that the wind greatly influences the helicopter on landing, which makes me think that perhaps the helicopter is more difficult to fly.

Unfortunately, this is an opinion based question. My opinion is based on the fact that my first few hours of helicopter instruction were harder than my first few hours of fixed wing instruction.

Takeoff in a helicopter was fairly easy after hover taxiing to the takeoff pad and hover turning 360° with yaw control to visually clear the area. Landing in a helicopter was fairly easy up to the point of bringing the aircraft to a hover. In both cases, the hard part came in the form of any of the low speed maneuvering. That includes just getting the skids off the ground and putting them back down under control.

Takeoff in a fixed wing aircraft was easy except for directional control to remain on centerline before rotation and the extended centerline after rotation. Landings in a fixed wing aircraft are in another realm of difficulty until you get the hang of it. From stabilizing the approach to slowing down to a speed appropriate to turn off the active runway and everything in between are hair-raising and nerve-wracking your first few hours of instruction.

Cruise flight in both is fairly simple and enjoyable once the aircraft is trimmed out and the friction locks are set properly. Although, changing flight parameters in a fixed wing can be done with as little as input on one control. Say for instance, changing the throttle input in a trimmed out airplane will make you change altitude. Changing flight parameters in a helicopter will involve input into more than one if not all of the controls. Changing the collective will require a change in throttle input, which will require input into the anti-torque pedals, in order to change altitude in a helicopter without a governor at low speeds.

The biggest difference is that a good instructor can verbally walk you through flying an airplane up until short final on your first flight. Although, they will always be ready and prepared to take the controls at any time. In a helicopter, the instructor will be on the controls the entire time your first flight. They will give you command of each control, one by one, as your confidence and competence grows.

Bottom line is that hovering is the deciding factor on whether it is harder to fly either a fixed wing or a rotary wing aircraft. Although, it is easier in a fixed wing. In a fixed wing aircraft, all you need is plenty of altitude, and a headwind that matches your airspeed (or an aerobatic plane with lots of thrust). In a helicopter, you need to be able to juggle while riding a unicycle.


If a pilot's plane suddenly and unintentionally becomes inverted, what is the pilot's best course of action? If a plane was suddenly inverted through no action of the pilot, say wake turbulence from a much large plane (think 747 vs. Learjet), should the pilot first try to right the plane or get the nose pointed in the correct position so that the wings start producing lift again?I would think that a pilot would instinctively try to get the plane righted, but I wonder if this would be the best course of action, especially if there's not a lot of space between the plane and the ground. In trying to do so, the pilot could lose precious seconds that would otherwise be spent avoiding the ground. Though possibly counterintuitive, it seems like it would be best to get the plane flying, even though it's inverted, and then get it right side up.This brings up another question: are pilots trained how to handle an inverted aircraft? But I think it's a separate question.

What you are describing is Unusual Attitude Recovery (UAR) techniques, which are a standard part of the training for every Private Pilot1

Here is a good description of just such an event.

Almost all pilots do instinctively want to right the plane first, but as I'll explain below, this is a mistake, and the point of UAR training is to change the pilot's instinctive approach.

The actual biggest threat to a plane in an unexpected unusual attitude is speed.   If the plane has too much speed (above VA), sudden control movements can damage the airframe or even break apart the plane.

If the plane has too little speed (stalled or spinning), there may not be effective airflow over the wings and tail, and moving the controls may not do anything at all! (remember, control surfaces need a steady flow of air over them to be effective).

So the very first and most important step in UAR is to manage speed.  Upon recognizing that they are in an unknown and unusual attitude, the pilot's immediate action must be to look at the airspeed indicator:  If its too high (yellow-arc or above), pull the throttle to idle and let the speed come down.  If its too low (white-arc or below), immediately add full throttle and let the speed come back up.

Once the airspeed is anywhere in the green-arc (and precision is not terribly important here, just a manageable speed), then the next steps are to return the plane to roughly level (+/- 10° of pitch), and roll the wings level.

1 I'm unsure if Recreational Pilots and Sport Pilots also get UAR training.


How many crew members load and offload luggage on an Airbus A380? What are the standard ground needs of a modern double-decker airline.
How many crew members load and offload luggage on a modern double-decker airliner on any typical trip?

The Airbus Airport and Maintenance Planning documents note that:

  Actual times may vary due to each operator's specific practices, resources, equipment and operating conditions.

That being said, if everything is going smoothly, typically it's 2-3 operators per door.

One of the differences between an A380 and say a 767 is the number and size of containers. The rest is mostly the same. Below is a breakdown from a paper on the A320:

  The first operators' categorization that we had done was simple: belt loaders and cargo loaders, with reference to GSE. Usually, this is how airlines categorize their operators. Moreover, this categorization has a standard number of operators needed per GSE depending on its positioning:

  2 operators per Cargo Loader for the main cargo compartment;
  3 operators per Belt Loader for the main cargo compartment;
  2 operators per Belt Loader for the bulk compartment.

  However, this categorization is far too simple because there are more people than cargo and belt loaders involved in the cargo handling, for example tractor drivers and container loaders at the airport terminal. For this reason, Airbus ground handling operator's categorization has been used. This categorization divides the operators in:

  Semiskilled: loaders and cleaners.
  Skilled: bus drivers, refuelling staff, in general all equipment drivers.
  Highly skilled: boarding bridge operators, ramp agent, push-back operator.

(pegasus-europe.org)

As you can see from that paper, it's not just the number of operators at each door, it's a big system, combined with different hiring practices and different operators' methods, there is no one answer.

(Airbus)

Above shows an A380 schedule for a 90-minute turnaround since you seem interested in streamlining this process. Note the refueling start/finish and check this post. Passengers are typically boarded after the refueling is finished, otherwise it's a hassle that even includes alerting the fire service to be on standby.

Loading the cargo/passengers more quickly won't solve the A380 problems you asked about in recent posts.


Who pays for the compliance with Airworthiness Directives (AD)? Airworthiness Directives (ADs) are legally enforceable regulations issued by the FAA in accordance with 14 CFR part 39 to correct an unsafe condition in a product.

Hence when an AD is issued, owner must comply with the AD within the stated time period in order to remain airworthy. This compliance ,of course, come with some cost. Who pay for this cost of compliance? Owner of the plane? Manufacturer? Or they somehow share the cost?

It depends on the agreements between the operator/owner of the aircraft on one side and the manufacturer of the aircraft and its suppliers on the other side.

Often there will be some form of compensation involved if an AD is issued when that AD is addressing non-compliance with regulations / standard in effect when the aircraft was produced. Normally there is some time limited warranty covering the costs of ADs at least partially.


Would biplanes be of use in VSTOL applications? What is the down side to biplanes? ex. Bush Pilots or VSTOL competitions I feel like bush pilots and VSTOL competition aircraft could use biplanes to work much better. Granted, range and speed are decreased, but besides overall efficiency, what is the down side to biplanes?

You're quite right in not doubting the capabilities of biplanes, like Curtiss Pitts with the fully aerobatic Pitts Special.

Aerodynamically, the classic biplane has many disadvantages, with drag being built in everywhere. Like designing an aircraft with a built-in airbrake that is deployed all the time. The double wing creates more drag than a single wing, the struts create extra drag, and the cross-wires between the wings are easy to miss on photo's but are huge contributors to drag as well.

Structurally though, a biplane design is quite advantageous. The biplane configuration acts like a box design, much easier to integrate with the fuselage than the cantilever clean wing with its bending moment at the wing root. So if the construction is exposed to high acceleration like a fully aerobatic plane, there is less aeronautical engineering involved. As usual in aeronautics, aerodynamic disadvantages equate to structural advantages.

But zooming out even further, it makes little sense to create lift together with a lot of drag. Aerodynamics determines the stall speed of an aircraft, the biplane has no advantages here. If the objective of the bush pilot is to fly slowly and inspect, and to have VSTOL capabilities, there is a much better option available: the autogyro. The owner of Quobba Station in Western Australia has built one himself and uses it for inspecting his huge property. They are used as airborne motorcycles for sheep mustering etc. Upon engine failure (which has happened), it can be landed safely anywhere on the property. Just bring a hat.

Update

The thought that biplanes must have slower stall speeds than comparable monoplanes keeps nagging me, but I cannot find an explanation or indication that that is actually the case. For instance for the Tiger Moth: Stall Speed = 40 KIAS @ 827 kg. For the Cessna 172: Stall Speed = 40 KIAS @ 1145 kg.

A biplane could be designed for lower stall speeds and good climb performance: make the wing area much larger than required, with an associated lower wing loading. But this can be done in a monoplane as well:

Simply use a large single wing.
Increase wing area in landing/low speed configuration by using Fowler flaps.
Increase wing camber in landing configuration.

And then it becomes a matter of economics, is it cheaper to build a biplane than it is to build a monoplane with fancy flapping arrangements? Probably. But all the dragginess will cause much higher fuel consumption, and it will take a long time before the pilots get to where they want to be.


How long are the nacelle strakes on a GE-90? For my school project, I'm doing something where I create a nacelle strake on a model plane and I want to make it to scale. Could you please let me know the dimensions of a nacelle strake? I would greatly appreciate it!!

You can measure this on photos.

Find a nice side view that shows the nacelle strake.
Measure the engine diameter on the photo.
Find the engine diameter in the engine specifications.
Calculate the ratio between the two. This gives you a scale factor of the photo.
Measure the strake, multiply by the scale factor to give the size of the strake on the real engine.
Divide by the scale factor of your model to get the size of the strake on your model.

I use a spreadsheet so I can do step 2-6 once. I then create a formula that converts a dimension I measured on the photo to the one I need on the model. Makes it easy to do lots of measurements on a photo.
I usually import the photo into an application that uses SI measurement units (Adobe Illustrator), but you can measure in pixels too (which allows you to use cheap image tools).


Could a 30 knot direct crosswind make a Learjet roll over 90 degrees? Could a 30 knot direct crosswind really make a Learjet roll over 90 degrees?

A recent incident has prompted this question, but it's not explicitly about that incident (with its ongoing investigation).

It only ever makes sense to talk about cross-wind when the ground is involved. While the aircraft flies, it moves relative to the air and how fast the air is moving relative to ground only affects ground speed and track. If the air is moving smoothly, it can't turn anything over. Only thing that could bank an aircraft over is strong turbulence.

Natural turbulence of a 30 knot wind is unlikely to be strong enough to bank a Learjet 35 significantly, but a wake vortex close behind a heavy aircraft possibly could. The separation minima are there to prevent encountering wake turbulence on approach.


I analyzed 2 nearly identical flying wing in XFLR5, how come the one with the thinner tip chord has a higher cD? I made two flying wings, one with half the wing tip chord as the root chord and one with the root and tip chord being equal.

I then did VLM2 analysis on both at 7 m/s, and used the same airfoil on both. surprisingly, the wing with the thinner wingtip chord had a higher coefficient of drag (which i believe leads to higher drag). How come?

Everything I know leads to less drag, less induced drag because a thinner chord, thinner airfoil due to proportions, and same parasitic drag because everything else is constant. What causes the one with a thinner wingtip to have a higher CD? Does this make sense, or is it just the inaccuracies of trying to calculate CL and CD?

XFLR5 project file

I designed another plane with the same 30 deg sweep, same airfoil and an aspect ratio of 10 (span .5m, root & tip chord .05 m, no twist). Performance keeps getting worse. Only AOA at 0 makes sense to me but that's out the window.

It may be inaccuracies in your modeling method; it's hard to say without more info.

First, this isn't quite an apples-to-apples comparison. The aspect ratio of the first wing is higher than the second wing, so you're varying more parameters than just the tip chord.

The way to think about this is that the CD of a wing is going to be strongly dependent on the aspect ratio $AR$, the taper ratio $\lambda_T$, the chord and twist distribution along the wing, as well as the airfoil distribution. Is the airfoil t/c constant across both wings? That will also have an effect.

It would be clearer to look at a polar of CL plotted against CD; the best point of comparison is to look at the drag generated at the same CL, not the same angle of attack (because the zero-lift angle of attack will change with wing design as well). The second wing is generating less drag, but also less lift at a given angle of attack; the comparison isn't really fair. If you're using a VLM what you're measuring is the CDi of a wing geometry, which is going to be most strongly dependent on CL.


Do GA aircraft pilots use predefined routes (via GPS or DME/VOR vectoring) or methods such as GPS-direct/ VOR-to-VOR in UC airspace? Example:
Flying from RIC to IAD, the most popular and "efficient" route is BENTLY -> CAVLR3:

However, you could more simply depart north out of the RIC Class-D, intercept the BROOKE VOR on the edge of the DC SFRA, and then accept the inevitable vectors from Potomac Approach to IAD:

While the time en-route and distance are only trivially shorter, it still illustrates my point: choosing to fly a "non-standard" route is both quicker and potentially easier (without a GPS, hitting the intersections is a more complicated procedure than "direct to BROOKE VOR").
From my training I understand that these airways are primarily used to organize air traffic to reduce risk of collision in uncontrolled airspace as well as to improve flow and organization in controlled.
Which methods (routes/airways vs direct GPS/VOR/DME nav) are more commonly employed by IFR and (vs?) VFR pilots?
Thank you!

By definition, there are no defined airways or routes in uncontrolled airspace, so the answer to that question is no.


Why does the lack of a magneto affect engine RPM? So I don't have my pilots licence, but I was part of the Australian Air Force Cadets for nearly 8 years (wonderful organisation). During this time I went on a number of flights in Cessna 172's and Cessna 152's. I always noticed that as part of the pre-flight check, the pilot checked both magneto's and this corresponded to a slight RPM drop on the engine.

Why does the lack of a magneto affect engine RPM?

Firstly, to understand the answer, we need to understand that the Cessna 152's and 172's run a 4 Cylinder, Horizontally-opposed Engine. Each Cylinder has 2 spark plugs, one on the top side of the cylinder head, and one on the bottom side. The spark plug ignites the fuel/air mixture that has been sucked into the engine, and causes a controlled burn to push the piston down the cylinder and turn the crankshaft in turn (hence turning the propeller as it is connected to the end of the crankshaft).

Now, as I've stated, each cylinder has two spark plugs, one connected to the "left" magneto, and one connected to the "right". If we turn one magneto "off" (or ground it to be politically correct), only one spark plug in each cylinder will "fire" to ignite the fuel/air mixture. This causes the mixture to have a delayed and less effective burn, meaning that the piston does not get pushed down the cylinder as effectively, meaning the crankshaft will not rotate as fast, and hence, leads to a drop in the Propeller RPM (Revolutions per Minute).

We check the magnetos on the ground to check that:

A. They both work, and the engine won't die if we lose a magneto (we should be able to return to land on the remaining serviceable magneto)

B. We are checking that there is no "Spark Plug Fouling". The fuel we use in aviation contains lead, and hence after a time of running the engine at low power settings on the ground, the lead in the fuel will accumulate on the spark plug head (instead of being burnt off when the engine is working under power), and cause the spark plug to let off a limited spark, or completely block the spark, hence again, making our engine less efficient.


What is Circulation in aerodynamics? Can someone please explain the concept of circulation? I am able to understand the mathematical form i.e. it is the line integral of the velocity field. But I am not able to understand the physical meaning of circulation.

Circulation does not mean that any fluid particular is traveling in a circuit around the airfoil. One way to look at circulation is that it's a description of how much a uniform flow has been turned asymmetrically by the body.

Another, slightly more technical way, is to consider the flow around a rotating cylinder (which produces lift) as a combinatory sum of a uniform flow (free-stream flow), a doublet flow (non-lifting) and a vortex flow (which produces circulation). See this illustration excerpt from Anderson, Fundamentals of Aerodynamics.

Therefore, circulation can be regarded as the path of the fluid when the symmetrical components have been taken out, which is indeed circuitous.


How do you correct a mistake on a pilot license? If a mistake is found on a pilot license, like the pilot's nationality, date of birth, or a missing type rating, how would one go about having it corrected?

I had this happen to me on my first license. I got in touch with the FAA Examiner and he had me contact the local Flight Standards Office (FSDO) who corrected it for me.

If it was a mistake on the application, your Certifying Officer (read: FAA Examainer) can allow you to edit the information through IACRA (https://iacra.faa.gov/iacra/default.aspx) and the license re-issued.

If all of the information was correct, but it was misprinted, you would want to call your local FSDO.

FSDO Search: http://www.faa.gov/about/office_org/field_offices/fsdo/

Your local FSDO can help you with:

Low-flying aircraft
Accident Reporting
Air carrier certification and operations
Aircraft maintenance
Aircraft operational issues
Aircraft permits
Airmen certification (licensing) for pilots, mechanics, repairmen, dispatchers, and parachute riggers
Certification and modification issues
Enforcement of Airmen & Aircraft Regulations


What's the difference between EFVS and CVS? What's the difference between EFVS and CVS? Is there any aircraft certified with EFVS?

The FAA recognizes 4 'vision' systems; enhanced vision system (EVS), synthetic vision system (SVS), combined vision system (CVS), and enhanced flight vision system (EFVS).

EVS and EFVS use either passive or active sensors on the aircraft to enhance the crew's vision of the approach. SVS uses a database to generate a synthetic view of the terrain in  front of the aircraft. CVS combines features of EVS or EFVS and SVS.

It's all spelled out in AC 20-167A Airworthiness Approval of Enhanced Vision System, Synthetic Vision System, Combined Vision System, and Enhanced Flight Vision System Equipment


Do flight attendants do pinch-hitter training? I was watching a Captain Joe video (Can a PASSENGER land a PLANE?) and he mentioned that he left out the 20 minutes it took the person to even figure out how to communicate with ATC. It seems to me that with a little training, a crew member would be much more prepared to handle such a circumstance.

Even if it's just one pilot, I could see the benefit of having a crew member able to share the workload (communications, checklists, etc).

I was wondering if there are any airlines that provide pinch-hitter type training to flight attendants (even if it's just a classroom course) in case one or both of the pilots are incapacitated?

This is generally not standard practice. For one pilot training is particularly costly (even just in small planes) and would simply not be worth it to the airline, which is why there are two flight capable people in the cockpit to begin with.

Historically speaking there is evidence to the fact that it would not alter the outcome of the scenario. The closest instance of this occurring was possibly Helios Airways Flight 522 which lost cabin pressure at altitude incapacitating the crew and most aboard. Flight attendant Andreas Prodromou who held a UK Commercial Pilot License (but was not trained on the B737) was able to remain conscious via a portable air pack and make his way to the cockpit and into the captains seat. However he was un-able to take positive (meaningful) control of the aircraft due to lack of experience investigators eventually concluded after the crash.

There have been some successful talk down landings of substantially smaller aircraft.

FWIW, most modern airliners are sophisticated enough and have the controls concentrated enough that they can be flown single handedly in a manageable fashion.


What is the best or most popular way to reduce wing tip vortices on an ultralight operating at 600-800k Re? What is the best or most popular way to reduce wing tip vortices on an ultralight triplane, operating at 600-800k Re with fibreglass wings ,10 ft wingspan, gap of 2 chord, chord of 2 ft, 0 stagger?

Upturned wing
Endplates
Horner tips
Other?

For a triplane with very short span, it might be worth it to make a kind of end plate fin joining all three wings.  Problem is, the end plate itself will create a lot of drag, so it comes down to whether or not inhibiting the tip circulation with that sort of end plate gives a benefit that outweighs the drag of the plate itself.

If your triplane will cruise at high Cls (low speeds relative to stall) where the vortices are strong, the inhibition effect of the end plates may be net positive (like with winglets on jets).  If the thing will cruise and 2 or 3 times stall speed, I would expect that the drag of the plates cancels or outweighs the benefit.  Which is why it's not done very much even with all those biplanes out there where you'd think it's a no brainer to "wall off" the wing tips.

Beyond that, I'd suggest a triangular "Wittman type" wing tip ( Steve Wittman was a famous air racer, who developed these tips for the Tailwind) which is a good way of dissipating the tip circulation on low aspect ratio wings while providing a little extra area and span with minimum additional wing bending.  That could be the best bang for the buck for your short span application.  They were very effective on the Tailwind.


What is a Virtual Window in an aircraft? I heard about Virtual Windows in the Dubai show, but I didn't really got it. What is it?

In a demo, when they opened the shields, I could just see the ground handling before taxing.

Search engines only gave me a patent, but I would rather learn about it laconically.

PS: Found in a triple seven.

I found a video where an english guy mentions them, but he doesn't seem to have a clue about their functionality.

They are basically window-shaped screens, displaying a feed from a camera so the middle aisle suits (where the alternative is a wall) passengers can enjoy the "view".

  The most interesting thing to me are the virtual windows. First Class passengers in the middle suite will have a set of “windows” like everyone else, only theirs will show images from an outside camera.

https://travelupdate.boardingarea.com/virtual-windows-emirates/


Can a supersonic aircraft have winglets? In order to have laminar flow over the wings which helps in friction drag reduction, a number of airfoil designs have been proposed from the past to the latest 737 winglets.

But if we design a laminar flow wing for supersonic aircraft, the wing should be very thin which will end up with stall and speed related problems.

So, I am curious that if we add winglets on supersonic aircraft, will it be helpful other than for its drag? If so what are all the problems we need to consider?

This has been (and thus can be) done and there is some current research on it as well. The XB-70 Valkyrie had dropping wing tips that added stability at high Mach speeds as well as allowed the plane to ride on its own shock wave. It also effected trim drag,

  The repositioned wingtips also reduced the area behind the airplane's
  center of gravity, which reduced trim drag. The downturned outer
  panels also provided more vertical surface to improve directional
  stability at high Mach numbers.

You can check out this podcast episode that interviews some of the people at NASA doing various research projects including wingtip control systems and other interesting applications in that space.

You may find some info in this book on supersonic wing theory.

This thread (and you know how accurate the internet is) has some interesting points on the matter.


Why does MAP show ambient pressure when engine is shut off? Manifold pressure is the absolute pressure at the intake manifold and increases as throttle is increased and vice versa. However, when the engines are shutoff, the manifold reads ambient pressure. My question is, why does it read ambient pressure when engines are shut off when the throttles at closed?

The intake manifold is where the air flows from outside into the engine, so obviously it must be open to the outside. So when everything is calm, the pressure quickly equalizes and the manifold pressure is equal to the ambient pressure.

The non-obvious thing is actually why it differs when the engine is running.

When the engine is running, it sucks air in. The volume of air per unit of time is proportional to its rotational speed: higher RPM means more strokes per minute and each stroke has the same displacement.

Now without any restriction in the intake manifold, the air would still enter at the ambient pressure (speaking of normally aspirated engine). And with fully open throttle, the restriction is small enough that the manifold pressure is indeed only a little below ambient.

It is only as you close the throttle that you create significant restriction, which reduces the manifold pressure.

But the reduction is still proportional to the engine RPM. With engine not running there is no suction, so the pressure can't decrease and the gauge still shows ambient pressure.

This dependence on the RPM also means that it is not actually good indicator of the power the engine produces. When you increase RPM by adjusting the mixture, the engine power will increase—because it takes more power to sustain higher RPM—but the manifold pressure will decrease—because there is more suction. The same also happens when you increase RPM by advancing propeller pitch selector.

What manifold pressure is good indicator of though, and the reason it exists, is the engine wear. The amount of air, and fuel, are proportional to the manifold pressure, and therefore so is the peek pressure when the air is compressed and the fuel burnt. And the higher the peek pressure, the more wear on the components. That is why there is absolute maximum you should never exceed and continuous power limit that you should only exceed for limited time on take-off or in emergency.

Note that the relations are further complicated in turbocharged engines where higher engine RPM also mean higher turbocharger RPM and that increases the pressure gain on the turbocharger that adds to the manifold pressure.


What kind of failover system do Airbuses with side sticks have? Airbuses use joystick-style side sticks for controlling the aircraft. Among the features of this system is that there exists no mechanical connection between the joysticks and the control surfaces.

In case of an electrical failure, what backup system is in place to make sure the pilot still has control of the aircraft?

In case of a total electrical failure, the aircraft can still be controlled using rudder pedals and manual pitch trim.

The airbus EFCS (Electronic flight control systems) are configured as below:

Airbus EFCS; Image from smartcockpit.com

From Airbus Flight Control Laws:

  MECHANICAL BACKUP

  In case of a complete loss of electrical flight control signals, the aircraft can be temporarily controlled by mechanical mode.

  Pitch control is achieved through the horizontal stabilizer by using the manual trim wheel.
  Lateral control is accomplished using the rudder pedals.
  Both controls require hydraulic power.

The A340 also seems to have a similar system. From the A340 Flight Deck and Systems Briefing for Pilots:

  Mechanical back-up

  • To sustain the aircraft during a temporary complete loss of electrical power.

  • Longitudinal control of  the aircraft  through trim  wheel. Elevators kept at  zero deflection.

  • Lateral control from pedals. Roll damping is provided by the Back up Yaw Damper Unit (BYDU).

A340 mechanical Backup system; image from A340 Flight Deck and Systems Briefing for Pilots

Note that this is given only as a temporary measure. Also, See How are fly-by-wire airliners controlled in case of complete electrical failure? and How does the Airbus flight computer's voting system work?


FAA Regulations for Passenger Aircraft Does the FAA have regulations for aircraft that carry passengers over large oceans regarding number of engines and flying range of the aircraft ?

Definitive answer: yes, it does.  Lots & lots of them.


What is this sound from Airbus aircraft before take off? When flying in an Airbus, I often (if not always) hear a weird sound before the aircraft starts to accelerate for taking off. From where exactly does this sound come from? Why doesn't it appear on other aircraft?

According to Ask the Pilot:

  Almost every frequent flyer has encountered this sound at one time or
  another. [...]

  It happens on twin-engine Airbus models: the A320 series (includes the
  subvariants A319 and A321) and the larger A330. [...]

  What you hear is a device called the power transfer unit, or PTU,
  which is designed to ensure adequate hydraulic pressures during
  single-engine operations. [...] Since it is activated only when the
  pressure falls below a certain level, the PTU cycles on and off, on
  and off, on and off.

  [...]

  Some Boeing aircraft also employ a PTU, but the operation is slightly
  different and it doesn’t bark like a dog.

  Another noise peculiar to Airbus models is a shrill, prolonged whine
  heard at the gate prior to departure and again after landing. This is
  an electric hydraulic pump used to open and close the cargo doors.


On a small/micro jet engine, can the turbine blades and vanes be made out of ceramic? I am researching on how to make a small jet engine, and trying to figure out the materials for rotor and stator blades just after the combustion chamber so that they can hold up to the temperatures they will encounter.

I'm looking for cast repeatable shaped blades and trying to figure out what kind of forge or kiln to use.

My questions:

Should the blades vanes be nickel alloys or can they be ceramic so that dilatation won't make them interfere with adjacent parts?
Will the ceramic be too brittle?

I can't speak for all engines, but GE has been testing ceramic blades in their LEAP engines.
Here is their report on it.


How can leading edge separation bubbles be prevented? I have an airfoil (S3010, 9% thickness) that gives the resulting Cp distribution at 2 degrees and Re=500k.

I suspect that the abrupt increase in pressure before the suction peak is a separation bubble. I've read somewhere that this behaviour is common for thin airfoils.

How can I modify the airfoil to prevent leading edge separation?
The end goal is to increase the L/D

The velocity-jump at $\simeq 0.5c$ is due to a laminar separation bubble.

But you ask two different things here:

Prevent leading edge separation

A leading edge separation may happen as the laminar separation bubble progresses forward for higher angles of attack and is more common in thin airfoils. A way to suppress this is by the use of roughness elements, a trip or vortex generators. You can experiment with this using Xfoil and fixing the transition location at the point (or in a distance before this point) that you assumed that you have a roughness element for example. Otherwise try modifying the geometry with Xfoil's inverse design routines and if you're seriously into this read these Low Reynolds
Number Airfoil Design Lecture Notes provided by Selig.

Increase aerodynamic efficiency ($L/D$)

Increasing $L/D$ for a specified angle of attack for these kind of airfoils and for the low-Reynolds regime, means in general to reduce the velocity-jump of the laminar separation bubble. If I am correct, Selig's airfoils are already an improved version of similar NACA airfoils for low-Re. To do this you should again consult the aforementioned notes.

Are you sure that the spike on $c_p$ plot before the suction peak is not a paneling issue? It seems unphysical. Have you tried refining your airfoil? I do not capture this with the same analysis using Xfoil with 200 panels.

A rule of thumb is that the shape parameter ($H_k$) of the boundary layer at a laminar separation bubble is around 4. You can see from the following plot that you have a laminar separation bubble around $0.5c$ on the upper surface. Not in the leading edge though.


Are aviation regulators generally slower to issue orders affecting their "own" aircraft manufacturers? It did not fail to escape the attention of commentators that the US Federal Aviation Authority was amongst the last aviation regulators to issue an order grounding the 737 MAX.

Is there evidence to show that this is a pattern - that US, European, Russian (or other) regulators tend to be slower to issue orders or directives that concern aircraft made by manufacturers within their own country or bloc?

What would count as an answer

"Evidence" in this case would be based on figures showing time to respond by different agencies in multiple cases (enough to indicate a pattern).

What does not count as an answer

I am not asking for opinions on whether the FAA or EASA or other agencies are politically sensitive (I am sure they are).

Though I am willing to bet that it will turn out to be the case that agencies tend to be slower to act when it would affect interests that are closer to home, I don't need to read speculation about why; I don't think it will be any more illuminating than the interminable exchanges about how Airbuses are better than Boeings or vice-versa.

Similarly, although questions have been raised and concerns expressed about the FAA's inspection regime and the degree to which it allowed Boeing to self-certify aircraft, that (and the regimes and processes of other regulators) is not the question here.

I should have guessed that this would quickly descend into ra-ra declarations about superior American pilots and ways, backward and corrupt non-western political systems, and so on. I wouldn't want to deny anyone their fun, but it's exactly what is not an answer to the question.

I was many years in the industry with an OEM and have had various minor peripheral roles in certification and continuing airworthiness projects at the system level, giving me a kind of ring side seat.  And I would say that you tend to get more hair-trigger reactions from non-western regulators (China/Russia et.al), and that this is because there is a way lower level of trust between the regulator and OEM than with Western regulators.

Now, although it all went to hell in this case with respect to Boeing/FAA, there has to be some level of trust or else the regulator would have to constantly audit the manufacturer every time they scratched their butts.  It doesn't mean that the FAA just lets Boeing do whatever it feels like, but it does mean that they will tend to accept reports and analysis submitted without too much cross examination if things seem reasonable, and that's how situations like this can slip through.

Unfortunately the trust relationship broke down in the MAX case because Boeing perhaps could be said to have abused its trust relationship with the FAA.  Having been burned, you can be sure the FAA will tighten up its oversight of Boeing quite a bit, for a while anyway.

In non western countries the trust relationship is not very robust, so regulators will pull the trigger quite quickly.  This can cause its own problems.  You also have the tendency of non-western regulators to have much more severe punishment regimes, to the point of jail time for mistakes made in good faith.  This encourages people to hide their mistakes (a major problem in both China and Russia in manufacturing, maintenance and flight operations). So in the long run, in spite of the MAX fiasco, the low trust regime is much worse.