Why are the positive points in a V-n diagram associated with pitch maneuvers? For an aircraft with such flight envelope, the flight conditions in point A, C and D are associated with symmetrical pitch maneuvers. So, for the combination of loads factor n and speed V in each of those points represents a symmetrical pitch maneuver, in which there is a certain angle of attack and certain deflexion of the elevator, both different from zero - all other control surfaces wouldn't be deflected. That comes from reports from SAE aero design competition and from Structural Loads Analysis: Theory and Practice, Lomax

I understand the airplane can execute any maneuver so long it is inside the flight envelope, but why are the critical pitch maneuvers those "described" by points A, C and D whereas critical rolling or yawing maneuvers have clearer definitions* regarding the most extreme conditions related to those maneuvers?

*Here's an example from Lomax (nothing like that is said from symmetrical pitch maneuvers)

  Two types  of yawing maneuvers,  as  shown schematically  in  Fig.
  4.1,  must  be considered  for structural design...

Because they are reached when the aircraft flies a pitch maneuver. Let's look at the three points in detail:

Point A: This is where the highest turn rate can be achieved, so it is reached normally in an attempt to change direction. You might argue correctly that this is not a clean pitch-up, but essentially it is. When starting the turn, the aircraft will deflect both aileron and rudder, but once the turn is steady, both will essentially be neutral, except for the small deflection needed to overcome damping effects. What is left is a pitch maneuver akin to a loop with mostly elevator deflection to pull the needed gs.
Point C: This is reached inadvertently when flying into a heavy gust. Aircraft fly straight for most of the time, especially when flying fast, so it is assumed that this happens in straight and steady flight. Here, not even an elevator deflection is needed to reach the envelope point, all you need to do is to fly through exceptionally turbulent weather.
Point D: This is only reached after the pilot screwed up. Certification rules like JAR 23.335 b(4)i explain what the authorities assume: The pilot went into a shallow dive when upsetting the controls, oversped the plane and now tries to slow down by pulling up. This will also most likely occur in symmetric flight only. Or maybe in the initial phase of a dogfight, but then different regulations apply.


How to calculate power required to drive an isolated fan of a TurboFan engine? If I isolate the fan from a TurboFan jet engine (specifically GE90) and power it electrically with a motor,

how much power is required for the electrical source to drive the fan to give the same amount of thrust as a regular GE90?
in a regular GE90, what is the thrust produced by the fan alone (excluding the thrust from the combustion of fuel)?

https://en.wikipedia.org/wiki/General_Electric_GE90:

  The LM9000 is an aeroderivative gas turbine available in two options; the LM9000 without water augmentation outputting 66 MW (89,000 hp) at a 42.4% efficiency before cogeneration, and the LM9000 with water augmentation outputting 75 MW (101,000 hp) at a 42.7% efficiency before cogeneration.

An aeroderivative gas turbine is basically the same turbine with a driveshaft connected to the low pressure stage instead of the fan. So its shaft output power would be roughly equivalent to the power that goes to the fan in the turbofan version.

The 66MW (the aero version does not use water augmentation) figure corresponds to max continuous power or a bit less. The take-off power is even more.


Where is flight following available? What local facilities are required for me to get flight following services?  It seems that if I'm 100 miles from any control tower then I won't be able to get flight following.  How close does a control tower need to be for me to be able to get flight following?  And is flight following available when only Class D towers are close by, or do I need to be close to a Class C?  Class D airspaces usually do not have approach and departure control, so I'm not sure if flight following is available when only Class D airspace is nearby (no class C).

In the US, you can get flight following anywhere there is radar services from ATC. It is not dependent on a control tower. However, it is dependent on ATC workload. Most controllers in our area would prefer to talk to every blip on their screen. Especially near or under their Bravo shelves.
You can pick up flight following by contacting the appropriate controlling authority/agency in controlled airspace. If you are at an airfield with a control tower, find out from them if they have radar services. Some Class D airports do have it. They will give you an abbreviated CRAFT clearance (more than likely when you contact Ground) so that Approach Control can identify you after takeoff and climb out.
If the airfield does not have a tower with radar services, you will have to climb to an altitude to be able to be seen on either Approach or Center’s radar. Cold call them on your initial call with just your tail number and the words “with request”. When/if they respond, request flight following to your destination at your desired altitude. They will let you know if their workload permits it. If they do not respond, climb higher and/or fly further into their controlling airspace (unless you have not received clearance when applicable). Or, you can try another nearby controlling agency.
Your sectional chart will tell you the information for Approach and Center. If you have difficulty locating it, look at the approach, arrival, or departure charts of any airport with instrument procedures, regardless of if they have a tower. Another alternative for getting the information is the US Cart Supplement. The controlling authority/agency information will be listed if they provide radar services to the airfield.
You can also request flight following while airborne enroute or within the terminal arrival area. Some busy airports actually require it. The information for Approach may be listed on the ATIS in this case.


Why does enriching the mixture ratio beyond stoichiometry give more power? In other words, in a piston engine, the best-power mixture is richer than that producing the EGT peak that signals stoichiometric combustion.

Why is that, physically?

in practical terms, running rich means that despite the unevenness of the fuel-air mix both in a single cylinder firing and across all cylinders firing and across all firings in the engine, all cylinders are guaranteed to NOT be running lean on ANY firing, which means all of them will be pulling best power on EVERY firing.

In addition,  there is an effect that I know about from motorcycle engines which is probably true of airplane engines and that is the "quality" of combustion as a function of richness: If you run rich, preignition and lean misfire (both of which reduce combustion efficiency) are prevented, and the delivered power is smoother. You can hear this: a motorcycle engine sounds "happier" when running rich than it does running lean- and it pulls harder, even though the mix is nonstochiometric.


Why is this unit attached to the main landing gear not a common unit for towing or pushback? Less loading is applied to the fuselage with this method compared to towing or the towbarless way. Why is it not really common?

I'd like to detail this. There's my point, wouldn't it reduce cycles of loading to the fuselage, less fatigue resulted. Then we can eliminate shear pin & speed limit such stuff, doesn't it ?

In my opinion. For safety. This is much safe then the towing method.

I think it might not have enough clearance for smaller aircraft, while a towbar would work with pretty much everything.

Also the force you apply needs to be pretty much the same, independent from where you push/pull, as you only need to overcome the rolling resistance of the landing gears. The airframe and landing gears are sized for much larger loads, so there is not a lot of saving in my opinion.


Is "balanced field" defined with or without an engine failure? I’m wondering what exactly means a balanced field in terms of aircraft performance. From what I know it means that TODR=ASDR, also it is minimum field length required. But I do not know whether this TOD and ASD are with or without engine failure.

It refers to the case with an engine failure.

The balanced field length is exactly equal to the accelerate-stop distance and the accelerate-go distance, if the V1 speed is chosen, where those two distances meet:

  2.3.1.3 Balanced Field Defined

  [...]

  The Continued Takeoff—After an engine
  failure during the takeoff roll, the airplane
  must continue to accelerate on the remaining
  engine(s), lift off and reach V2 speed at 35 feet.
  The later in the takeoff roll that the engine
  fails, the heavier the airplane can be and still
  gain enough speed to meet this requirement.
  For the engine failure occurring approximately
  one second prior to V1, the relationship of the
  allowable engine-out go takeoff weight to V1
  would be as shown by the “Continued Takeoff”
  line in Figure 10. The higher the V1, the heavier
  the takeoff weight allowed.

  The Rejected Takeoff— On the stop side of the
  equation, the V1/weight trade has the opposite
  trend. The lower the V1, or the earlier in the
  takeoff roll the stop is initiated, the heavier the
  airplane can be, as indicated by the “Rejected
  Takeoff” line in Figure 10.

  The point at which the “Continued and Rejected
  Takeoff” lines intersect is of special interest. It
  defines what is called a “Balanced Field Limit” takeoff.
  The name “Balanced Field” refers to
  the fact that the accelerate-go performance
  required is exactly equal to (or “balances”)
  the accelerate-stop performance required.

(FAA Pilot Guide to Takeoff Safety, emphasis mine)

The continue case (accelerate-go) assumes an engine failure one second prior to V1.


Can Flex thrust be lower than climb thrust? Let's restrict this question to airliners with 2 jet engines.

For the remaining of the question, I'll use the term flex to designate reduced take off thrust as I'm more familiar with airbus's systems. Flex will be the thrust selected when thrust levers are in the flex detent and climb thrust the one selected when lever are on the "climb" detent without autothrottle engaged. I assume other manufacturers have an equivalent way to easily select those values.

Both flex and climb thrust are lower than TOGA thrust. In good condition (long runway, good weather, almost empty aircraft,...), how low can flex thrust be? Can it be lower than climb thrust?

In this case, what is the rational for accelerating from flex to climb thrust given flex is made to increase engine lifespan by reducing thrust?

Yes.  On the CF-34 family, in theory, a maxed-out flex setting can be in the mid 80s N1 whereas climb thrust is normally high 80s/low 90s, and you could see thrust rise when setting climb if an extreme flex setup (max Assumed Temperature) (or in the case of the non-fadec engines like the 3B1, the climb bug appears at a higher value than the flex take-off thrust bug when you select "climb" thrust in the FMS)

The reason is to do with what you might call the mission priority of the two settings, and where the actual benefit in flex lies.

With flex, the priority is distance and gradient for obstacle clearance.  The flex setting is the lowest setting that meets the takeoff and initial departure performance requirement for accelerate/stop and initial climb gradient for that runway and all up weight.  The benefit of using the lowest setting is only partly from lower temperatures; an even bigger factor is erosion from silica particles (outdoor dust) which is most severe below 1000 ft.  The dustier the environment, the larger the flex benefit. (In the Middle East, CRJ operators were wearing out engines after only 5-7000 hours because they were doing max thrust takeoffs all the time and had to be cajoled into using flex.)

Climb thrust has a time priority, from an operational balance-of-factors perspective.  You want to get to altitude in an optimized time-related profile (as soon as possible taking various things into account), and an optimized time-related profile can require more thrust than the minimum required to meet take-off performance, in cases where a very large flex allowance is available allowing minimal take-off thrust.  Setting climb thrust that is a little higher than the flex take-off setting has little negative impact on engine life because you are now high enough that the erosion impact is negligible so there's little engine life benefit to a slower climb to altitude and you might as well optimize climb thrust to get there faster.


When modeling a shear flow for dynamic soaring, is the coefficient always a constant? Is a wind shear model for dynamic soaring always given by the velocity vector field:
F = < cy, 0 >,
where c is constant?
I've tried modeling c to introduce a decay in magnitude of the wind shear as it moves from left to right, but apparently this violates conservation of mass of the flow (assuming the flow is incompressible) and that the coefficient should be kept constant.

The shear layer is conventionally described as a "thin" transition above stationary air and below constant ambient wind.  Within that layer,

The wind's gradient w.r.t the altitude between the shear boundaries can be modeled by any smooth (say, twice differentiable) monotonic function.

-- Section III, "Novel Approach to Dynamic Soaring Modeling and Simulation," Kai et al, J. Guidance, Control, and Dynamics 42(6), 2019, https://doi.org/10.2514/1.G003866.
This paper mentions nothing about wind velocity changing w.r.t. horizontal location.  In fact it says

the wind blows horizontally by assumption

Because of incompressibility, and because the flow field is uniform both above and below the shear layer, any horizontal change within the shear layer would induce a vertical component of the wind vector.  (Handwaving argument: imagine a brick wall downwind in the layer.  That would force a downdraft along the wall.)
So today's models of wind shear ignore second-order effects like horizontal decay of magnitude of shear, perhaps because that suffices for the still interesting case of an albatros mid-ocean, as opposed to the turbulence immediately downwind of a mountain ridge.  But this won't be the case forever, of course.


Can espresso be made at cruising altitude? Espresso makers work by bringing water to a certain temperature (typically 198-202°F / 92-95°C), and then extract it at a high pressure (~9 bar). Given that the FAA requires that cabins are pressurized to ~7,500 ft, this results in a few problems I can see.

The pressure differential between the boiler and the cabin would be very large. I fear that this would result in the espresso machine being compromised.
Water would boil at a much lower temperature (198°F / 92°C) resulting in the machinery not working correctly.
A sudden depressurization of the vessel could certainly result in a dangerous pressure differential resulting in explosive decompression.

Although, a Boeing 787 has a higher pressure cabin, in a typical airplane, could you safely brew espresso? Are there any FAA, or other safety regulations preventing you from doing so?

The pressure differential between the boiler and the cabin would be very large. I fear that this would result in the espresso machine being compromised.

The pressure in the espresso machine is 9 bars, 14 in a good one. The difference in outside pressure is 0.3 bars. That is comparably tiny value that does not make any practical difference.

  Water would boil at a much lower temperature (198°F / 92°C) resulting in the machinery not working correctly.

Coffee should not be made with boiling water anyway. 198°F / 92°C is sufficient for making coffee.

Besides, if the boiler was pressurized, the water would not boil until way higher temperature (it isn't, but it does not heat the water above boiling point at that pressure).

  A sudden depressurization of the vessel could certainly result in a dangerous pressure differential resulting in explosive decompression.

The pressurized content is water, not vapour, so it would not significantly expand if the machine cracked. After all, its pressure is relieved as part of normal operation (when the coffee drips to the pot) and it does not expand.

And its amount is tiny compared to the total volume of the aircraft anyway. Very tiny, because the pressure is only in the pipe from the pump to the ground coffee.

But that all assumes the coffee machine is espresso, which most of them are not. Usually they will be just filter machines where the water flows by gravity at ambient pressure or perhaps at some pressure, but much lower than in a real espresso machine. I believe some airlines do advertise they serve true espresso though.


Does heavy air pollution improve takeoff performance? As you all probably know by now, aircraft have much better takeoff performance when and where the air is denser; this is why flights need to either use longer runways or jettison passengers and cargo on hot days (hot air is less dense than cold), and why a disproportionate number of the world’s longest runways are at high-altitude airports (air is much less dense at high altitudes than low).

Do aircraft see a similar performance boost at airports with heavily-polluted air, laden with dense gasses such as carbon dioxide, sulfur oxides, nitrogen dioxide, hydrogen chloride, nitric and sulfuric acids, and heavy hydrocarbons, plus lots of soot and tar particulates which raise the air’s mass much more than they do its volume?  Or is the benefit of having denser air swamped by the engine-performance penalty of having air with a lower oxygen concentration (a considerable quantity of said oxygen having gone into the formation of many of the aforementioned dense gasses)?

Percentages of pollutants will not have a significant effect on earth as compared with temperature and pressure.  However, on a planet like Mars, with a CO2 atmosphere, the density difference may be significant enough to effect lift calculations.

Maybe NASA could go with a twisted Prandtl biplane using a high altitude electric motor and prop.  They have reached 95,000 feet on earth with Helios, but had issues with structural strength.


Why does the UH-1 Huey have a hump at the rear of the cabin? Why does the Huey have this weird hump as shown in the picture? For some system? Why not remove it?

https://www.helis.com/h2/uh-1h_seats.jpg

A copy of the original image can be found here, which is about 5 'pagedowns' down this page, which has a number of other excellent Huey-model photos.

It's a bit of structure to guide the rotor forces into the rest of the airframe, it would not be good if this bit went missing.

Fwd/aft, left/right, up/down. The rotor provides the lifting forces and driving forces and these are quite concentrated around the rotor axis. Picture the airframe like an empty beer can - some panels are required to cope with the forces while remaining in shape.


For a rotor in vertical autorotation, what is the relation between pitch, vertical speed and rpms? In other words, what happens to vertical speed and rpms in vertical autorotation if I change the pitch of the blades of the gyro I use to fly...?

Unless I am misinterpreting your question, if you add pitch [pulling collective in a helicopter] your RRPM [rotor RPM] will decrease, as it is being used to accelerate air down decent, if in a vertical decent the aerodynamics are screwy. Now if you have some forward speed increase Pitch trades RRPM for lowering vertical speed. Decreasing Pitch, allows you to trade altitude for RRPM giving you higher VS and higher RRPM.


What is the average total flight time to get a private pilot license in SF bayarea, CA? I've heard that to get a private pilot license in bay-area, CA, San francisco is a little bit harder than other place, because of difficult and busy airspace, ATC, air traffic and some reason.

Do you have any idea what is the average total flight time to get a PPL it in bay area? Thank you.

The SF Bay Area is more complex than some other airspaces. This does not mean that it will require more time, you just need to prepare for it.

I live on the SF peninsula and while I do not have a broad survey, I trained at the same time as two friends so I have three datapoints. I got my license with 41hrs training, one friend was under 50hrs and the other somewhere in the 60s. I doubt this is above the national average. This was some years ago, but the sky was already full. I guess now it is more full.

I picked my own instructor and did not let him teach me anything that I could learn from a book or on my own. We had every session topic planned ahead of time and I made sure I was well prepared. Far more important than where you train is your own attitude and diligence in preparation.


Why did the Concorde require a droop nose and how did it work? As seen in the picture below, Concorde used to have a droop nose which would be deployed during takeoff/landing and would be retracted to the normal position while in cruise (do reduce drag).

Concorde with a droop Nose deployed

Concorde in normal configuration

According to the wiki page on Concorde, this Droop Nose was added in the later versions of Concorde when the authorities raised questions about the restricted view which was available to pilots during landing/take off at very high angles of attack (which was required for the Concorde).

What are the other possible solutions which could have been employed instead of the droop nose to tackle to the restricted view from the cockpit?
Why did Concorde had to land and take off at higher than normal angle of attacks?
How did the Droop nose actually work? (Which mechanism was used to deploy and retract it)

1) Though already mentioned that this might be too broad, I would dare to guess a properly fitted camera could do the trick. But I doubt that this would be effective considering the technology of the era that Concorde was developed.

2) Concorde due to its design for supersonic speeds, it was generating too little lift at low speeds (like those needed for landing). So they had to take into advantage another way of producing lift: vortex lift. In order to produce vortex lift, you need relatively high angles of attack and consequently high pitch attitude.

3) I cannot answer this since I am not an engineer. Though with little googling I found this. It seems to be very detailed, with photos of the lever and diagrams of the mechanism.


What effect does the angle of attack have on lift and drag? In general, what effect does the angle of attack have on lift and drag?

I understand the the B-25 take-off run was normally in excess of 1500 ft, the exact value dependent upon load, density altitude, pilot skill, etc. The B25s used in the 1942 Tokyo Raid had to take off from the Hornet deck in about 500 ft. I've heard that with coaching from a USN pilot, they learned to optimize the AoA so all 16 made it. So I am interested to know more about the trade-off of lift vs. drag.

As angle of attack increases, both lift and induced drag will increase until sometime after L/D max is achieved.  Beyond that the lift will decrease dramatically.  This fundamental principle is the same for Doolittle's raiders as it is for a Cessna 150.


Can a commercial pilot get paid by friend? 'm a little bit headache about charge issue with commercial pilot certificate .hope someone help me figure out.

IF my friend approaches to me first and ask for a flight to somewhere using my airplane and I get paid for this flight,am I holding out?If I am,how can I do that legally?How about using his/her airplane?
According to 119.1(e),can I hold out for those flights and get paid(Ferry,banner towing etc.)and get paid？

If your friend approaches you and asks for a one-time ride, you're fine to charge for it. If you decide to advertise, or your friend tells a friend who tells a friend and word of mouth is that you offer an air taxi service, you are holding yourself out as a carrier and need to get a part 135 operating certificate.

Same thing with ferrying, banner towing, etc. If you are offering it to the general public as a service you need to get an operating certificate.


Why are the airport pressure values for "altitude" (inHg) and "sea level" (mb) slightly different on the NOAA web sites? If one looks, for example, at the NOAA web site for Denver International Airport we see (at the time of posting this question) the Pressure/Altimeter is 29.78 inHg, the Pressure/sea level is 1006.1 mb and the temperature is 54F.  If we assume 1 inHg is equal to 33.8639 mb, then I would have expected 29.78 * 33.8639 = 1008.4 mb for the sea level value.  But the NOAA web page lists 1006.1 mb.  Why is there (always) a slight difference?
-thanks

The difference has nothing to do with unit conversion (which is correctly done in your question). The difference comes from temperature: the aircraft altimeter assumes a standard temperature lapse rate of 1.98°C per 1000 ft altitude when converting a pressure to an altitude reading. The reference pressure for the altimeter (QNH) is defined such that the aircraft altimeter will show the correct airport elevation when it sits on the ground.
The sea level pressure however takes the actual temperature into account. If this deviates from the expected value in the standard atmosphere, you will see a different pressure value here. The higher the elevation, the more pronounced will these differences typically be. That's probably why you noticed these differences at Denver. In your example, the temperature was 54°F, which is about 12°C, but the expected temperature at Denver is
$$ \vartheta = 15^\circ \text{C} - 1.98^\circ \text{C} \times \frac{5434 \, \text{ft}}{1000 \, \text{ft}} \approx 4.2^\circ \text{C} $$
Here is the full explanation from NOAA:

ALTIMETER SETTING: This is the pressure reading most commonly heard in
radio and television broadcasts. It is not the true barometric
pressure at a station. Instead it is the pressure "reduced" to mean
sea level using the temperature profile of the "standard" atmosphere,
which is representative of average conditions over the United States
at 40 degrees north latitude. The altimeter setting is the pressure
value to which an aircraft altimeter scale is set so that it will
indicate the altitude (above mean sea level) of the aircraft on the
ground at the location for which the pressure value was determined.
The altimeter setting is an attempt to remove elevation effects from
pressure readings using "standard" conditions.
MEAN SEA LEVEL PRESSURE: This is the pressure reading most commonly
used by meteorologists to track weather systems at the surface. Like
altimeter setting, it is a "reduced" pressure which uses observed
conditions rather than "standard" conditions to remove the effects of
elevation from pressure readings. This reduction estimates the
pressure that would exist at sea level at a point directly below the
station using a temperature profile based on temperatures that
actually exist at the station. In practice the temperature used in the
reduction is a mean temperature for the preceding twelve hours. Mean
sea level pressure should be used with caution at high elevations as
temperatures can have a very profound effect on the reduced pressures,
sometimes giving rise to fictitious pressure patterns and anomalous
mean sea level pressure values.

(NOAA - Pressure Definitions)


How did Charles Lindbergh use dead reckoning over the Atlantic ocean? Wikipedia and other sources assert that Charles Lindbergh used dead reckoning on his historic flight from Long Island to Paris but—likely being aimed at a broader audience—are short on specific technical details.

With few or no landmarks to use as references, how was Lindbergh able to stay on course while over the Atlantic ocean?

It's actually "ded" reckoning (short for deduced), and it doesn't involve landmarks, it is simply flying a heading for a certain amount of time, that's it.  When you start adding in landmarks and things, that is called "pilotage."

Typically, visual navigation over land is mostly pilotage, with a bit of ded reckoning occasionally.  When you get over the water, like Charles Lindbergh, you do mostly ded reckoning.  When you do have a chance to use a landmark, you can update your location and basically restart your ded reckoning from a known point.  Lindbergh also used the stars to update his position and based new ded reckoning tracks on those positions.


Can anyone identify this pusher plane from apparently the 1930s? I have performed two searches - a photo search and also an FAA NC number search and failed at both to identify this pusher airplane.  My family photo says it was taken by my mother at the Chicago airport in September 1937.  The NC number appears to be NC 15574 and I've tried several variations including dropping the "1" and trying "9" for the "4" but could not get an FAA NC match.  Your assistance in identifying this airplane and anything about it is greatly appreciated.

That is a Stearman-Hammond Y-S1, registration NC15524, construction  number 309.
The remains of the aircraft are now owned by the Dutch aviation museum  Aviodrome. They are planning to restore one of the four Stearman-Hammonds they have into flyable condition. This project is running since 2007, and is progressing very slowly.

source: Smithsonian National Air and Space Museum


What guidance is there for pilots when reporting braking action? I was listening to "[REAL ATC] Eastern B737 (candidate Mike Pence) OFF RUNWAY at LaGuardia!"(1) and the LGA Tower asks for and receives reports of braking action from several landing pilots. I assume that this was during inclement weather, such as snow. Several pilots all report braking action as "fair" for their types.

How is "fair" determined? Is it totally subjective, or is there an objective measure? What are the classifications (of braking action) that a pilot can report?

 (1) Please note, I did not tag this as LGA, since the question is meant to be a general one, unless each reporting is airport specific.

The FAA issued a Safety Alert for Operators (SAFO), "Runway Assessment and Condition Reporting" #16009 on August 15, 2016. In it, it says that:

You'll notice it doesn't say "Fair" anywhere on there, that is because this SAFO replaced the word "Fair" with "Medium" on October 1, 2016.

  Pilot braking action reports will continue to be solicited and will be used in assessing braking performance. Effective October 1, 2016, the terminology ”Fair” will be replaced by “Medium” and pilot braking action reports will now describe conditions as Good, Good to Medium, Medium, Medium to Poor, or NIL. This will harmonize the NAS with ICAO standards.

(Emphasis mine)

Since the accident with Mike Pence happened on October 27, 2016, if a pilot was reporting "Fair", they were in violation of the SAFO and should have been reporting "Medium". You can read the NTSB report of this incident here.


Can cabin pressure be lower than outside pressure? In order to allow adaption to changed pressure, the pressure change in an aircraft cabin is stretched out over time. My observation is that the cabin pressure drops even before the plane takes off, and has not yet reached ground level at the time the aircraft lands. This would make sense, allowing for longer adaption times, but needs better sealing which is able to work both ways.

My question to the systems specialists: Can an aircraft cabin have a lower pressure than outside, and is the technique of stretching out the pressure change as explained above actually used?

Besides the sealing the aircraft would also need a vacuum pump that is able to pull air out of the cabin which means extra weight.

The way aircraft maintain cabin pressure is through a air cycle machine that pushes air into the aircraft and outflow valves. There is no facility to pull air out of the craft.

Any pressure drop you may experience on the ground is probably because the pilot increases air pressure on the ground slightly to test the seals and then releases it before takeoff.


Can pilots choose runway and landing direction? Pilots normally receive landing clearance for a specific runway assigned by ATC. Absent an emergency, can pilots of commercial flights (depending on the wind conditions for example) choose

a different runway
the landing direction for this runway
or both ?

If no, why not ?
If yes, (and still assuming nothing is wrong with the aircraft) how does the pilot get his wish ? Can (s)he ..

simply choose (i.e. just communicate the choice to ATC, which has to accept it) ?
request it / ask for it (but ATC has the final say) ?
insist on it ? (analogous to "telling ATC you are altering heading for weather")

In the last 2 cases, does the pilot need to name a specific reason ?

Pilots can request a particular runway approach course and landing but in a controlled environment they are at the mercy of ATC. At high traffic (read busy) commercial airports they are unlikely to get their request. As far as I know, shy of an emergency declaration you cannot insist on a non standard runway and expect to get it.

At a quiet class C or D airport they may very well get what they ask for. I did this a lot during my training at a quiet class D airport. If the winds were favorable to one runway but my instructor wanted to practice cross wind approaches we would request the non standard runway and if no one was around they would often grant it.

Generally you don't want to fly the non preferred runway if there are windy conditions as landing with a tail wind can be dangerous.


How does an engine driven vacuum pump used in gyroscopic instrument work? In general aviation light airplanes (C152,C172,PA28..) how does the engine driven vacuum pump work?How is it made? and if the filter of one of the gyro instrument is clogged would the vacuum indication still in the green arc? (The latest question bother me the most!)

It uses a system of vanes to draw air through the inlet port and expel it through the outlet port. The engine's lubricating system provides oil for lubrication as well as sealing the internals. The inlet is connected to the instrument and this provides the vacuum the instrument needs. To answer your last question, if the instruments are connected in series and then to the vacuum pump, and one of the instruments obstructs the air flow in the system, you may loose vacuum and instruments can become unreliable or stop working.


What is the efficiency of the turbine of a modern jet engine? What is the turbine efficiency of a modern jet engine? Just the turbine efficiency only. What percentage of fuel energy the turbine converts into mechanical energy.

Slide 7 of this presentation (shown above) states the latest technology for a turbine with cooling flow is 89% efficient, while an uncooled turbine is about 90% efficient. The table from this presentation comes from the well renowned book by Jack Mattingly, "Elements of Propulsion: Gas Turbines and Rockets".


Identify a balloon accident in the 90s or 2000s I recall hearing about a balloon accident on a news programme on TV in the 90s or 2000s. From memory it was some sort of record attempt, and the last telemetry from the flight indicated that the gondola was in free-fall.

I seem to recall a crew of at least two people. I think it happened over the sea, certainly far from where anyone could observe it, hence the need to rely on radio for communication with the crew and telemetry.

At the time of the report it wasn't know exactly what happened or the fate of the crew, but the free-fall telemetry made it sound pretty bad.

Can anyone identify this accident?

P 15 of this link describes an incident on July 20 1990 where an unmanned scientific balloon project accidentally experienced a freefall of the payload from 120,000'.  Any chance that what you are remembering was this, or something similar?

http://hdl.handle.net/2060/19910006317

  The 1990 calibration actually consisted of two flights,
  one on July 20, 1990 and the other on September 6, 1990.
  A malfunction occurred during the first flight, which
  resulted in a complete loss of data and a subsequent free fall
  of the payload from _ 120,000 ft which bent up the tracker
  assembly and destroyed several cell modules. The tracker
  was rebuilt, several cells were replaced, and the refurbished
  payload was flown again in September.


What is fuel consumption of an A330 during climb and descent? I want to know how to calculate or estimate an aircraft's fuel consumption when climbing from sea level to 15,000 ft, followed by a descent to 10,000 ft.

I would like to see an example for an Airbus A330-300 with CF6-80E1A4 engines.

Descent tables

Climb tables

These tables are for the A330-200 and A330-300: in the footer of the page you can see for which engine these are. What you missed to indicate is the thrust setting, atmospheric conditions and weight to be able to give a realistic answer.


Can a kite take advantage of crosswinds to gain speed? In a form off a kite can wind be redirected like a sail boat in any direction? Can cross winds around a jet stream be helpful in speed in such a design?

Why do you need a kite? A glider is much better suited to the task.

Again, nature has invented this long ago. Albatrosses use a technique called dynamic soaring to cover wide distances over water, using the windshear close to the surface.

Humans have tried to imitate this with gliders, albeit with limited success. The few who tried it could indeed stay in the air by harvesting energy from windshear, but the dynamic loads (up to 4 g) were too much to do this over an extended time.


Why isn't the airspeed indicator the primary instrument for power during a constant speed climb? I am studying the primary and secondary IFR instrument designations. I understand that the primary instrument is the one that closest represents your target value, and is normally the one gauge that isn't moving on the panel during the targeted maneuver (for example, in a constant rate turn, the Turn Coordinator is stabilized on a value after entry is completed and becomes primary).

I fly a variable pitch prop, and I think my confusion might be a result of not flying a constant speed propeller.

Take a look at the item in red:

Question:

Can someone explain why the CS Climb power primary isn't the airspeed indicator?

If you are stabilized on your airspeed, wouldn't airspeed dictate the power setting you want to maintain? If you change pitch, the airspeed drops/rises and the power is changed - doesn't that make the airspeed indicator primary?  I have been taught to set power (on entry) and then monitor airspeed to make pitch adjustments. This makes the idea of a power primary confusing in stabilized descent/climb.

This seems like a confusing way to have to learn the material as I don't find I have to think about this while flying to effectively control the airplane...

Airspeed indicator is a primary instrument for pitch in that row, so it can't be also primary for power.

The point of constant speed climb is that you select power and maintain speed with pitch, getting whatever climb rate that power can support. Most often the point is selecting "climb" or "maximum continuous" power and climbing as fast as possible without overstressing the engine.

The only difference with variable pitch prop is that it decouples rpm from engine power, so you can't use rpm and are left with manifold pressure only (for piston; I am not sure what the correct reference is for turbine).

Note that two lines lower there is a constant rate climb and there airspeed is primary reference for power, because there you adjust pitch to maintain desired vertical speed and power to maintain airspeed. But since you shouldn't use more power than the recommended climb setting anyway, the constant speed climb gives you better performance.


How can a person receive an expired life vest? I wonder if passengers could receive an expired life vest because who else would they give to.

You can buy aircraft life vests pretty inexpensively for the purpose of having one or seeing how they work.

There are a bunch of used ones for sale on eBay, they may have been taken from planes over the years or they may just find their way into circulation after being removed (before being trashed).

Some of them get upcycled/recycled into other things so they presumably enter circulation at some point.


Can I get training in the USA with a PPL from another country, but without converting it? My friend's in South Korea, and he would like to get training in the USA soon. He currently has a PPL in Korea and it is still valid.

I'm sure that he can start an IFR course in the USA and another country's PPL could be converted to an FAA PPL license.

First question:

I'm wondering if he can get flight training or just time-building with a non-converted license, i.e. just his Korean PPL?

Can he fly just with a CFI just as dual time? I'm sure that he cannot log PIC time if he doesn't have an FAA PPL. However, he would like to be familiar with USA PPL flying first before starting the IFR training.

Second question:

He will apply to the TSA first for time-building, but I'm not sure which category should be approved. There are category 3 (instrument rating) and category 1 or 2 (training event). Which one should he do?

Part 1: Can a foreigner with a PPL in another country's system receive training in the US?

All other normal prerequisites such as ASFP, medicals, etc. aside, yes, a foreign license holder can receive training in the U.S.

Remember: You do not need a pilot certificate to receive training, but you would need one to solo or take a check ride (such as a student certificate).

If a person holds a foreign certificate, I believe they have to be flying an aircraft registered in their home nation in order to qualify to solo or otherwise act as PIC in a foreign country without obtaining a local certificate.

So, receive training?  Sure.  Solo/PIC/check-ride in an N-registered? No.

If what you mean to ask is "can he obtain a new cert/rating without converting".  No because the FAA does not issue South Korean pilot certificates, so that would not be possible.  The dual training received in the U.S. would certainly be able to be logged and count as valid training back home.

Part 2: ASFP Training Categories

From the flightschoolcandidates.gov FAQ section:

  What category do I qualify for?
  Candidates seeking flight training are separated into one of four
  different categories. A brief explanation of the categories follows:

  Category 1 - Candidates who seek flight training in the operation of
  aircraft with a maximum certificated takeoff weight (MTOW) greater
  than 12,500 pounds, but who do not fall into Category 2.

  Category 2 - Candidates who seek flight training in the operation of
  aircraft with a maximum certificated takeoff weight (MTOW) greater
  than 12,500 pounds, and who:

  Are employed by a foreign air carrier that operates under 14 CFR part
  1546; Have unescorted access authority to a secured area of an airport
  under U.S.C 44936(a)(1)(A)(ii),49 CFR 1542.229; Are a flight crew
  member who has successfully completed a criminal history records check
  in accordance with 49 CFR 1544.230; or Hold an airman's certificate
  that is recognized by the FAA or appropriate US military agency, with
  a type rating for a multi-engine aircraft that has a certificated
  takeoff weight of 12,500 pounds or more.

  Category 3 - Candidates who seek flight training in the operation of
  aircraft with a maximum certificated takeoff weight of 12,500 pounds
  or less for the following training events:

  Single Engine Land (SEL)
  -- Includes initial Airman's Certificate, including a private, recreational, or sport pilot certificate. If a private and/or
  commercial license is the candidate's initial FAA license, it is
  considered an initial airman's certificate and is not exempt.
  Instrument Rating (IR) Multi Engine Land (MEL) Each of these training
  events requires a separate training request. Clarification regarding
  Category 3 exemptions is covered in the next Frequently Asked
  Question.

  Category 4 - Candidates who seek recurrent training in the operation
  of aircraft with a maximum certificated takeoff weight (MTOW) greater
  than 12,500 pounds, and are current and qualified on the aircraft for
  which they are requesting training. These training requests are
  submitted by the flight training providers -- Candidates need to
  "Select Providers for Recurrent Training" from the AFSP Candidate
  account. If you have further questions regarding your category, please
  contact your Flight Training Provider.

If he wants training intended for an instrument rating in an aircraft under 12,500 Lbs MTOW then category 3.


Participating with "flight following" What is the proper procedure for participating with "flight following" when leaving a non-control towered airport?

You can request Flight Following at anytime.

Personally, I wouldn't be in a hurry to request it as soon as you depart. Wait until you're established on course, in a cruise-attitude (instead of a climb), and everything is settled and running smoothly. Then know your position, and how you're going to report it. Know where you're going (both by name and ICAO identifier), and try to anticipate any questions they might ask.

Look for the Center/Approach/Depature where you are (look in your chart supplement for an airport close to you), and call up with:

You: "Seattle Center; November 12345: VFR, with request"
translation: Calling Seattle Center, this is N12345. I'm VFR (so you haven't heard from me before... don't be surprised!), and I have a request.

Center: "November 12345: Say request."

You: "November 12345 is SkyHawk, 10 mi. South of Harvey Field, 4,500 feet. Request VFR Flight Following to Friday Harbor"
translation: I'm a Cessna Skyhawk, my location and altitude will help you find me. I'm asking for FF to this other airport."

Center: "N345: Squawk 4532 and Ident."

You: (Set your transponder to 4532, press the Identify Button), and say "4532 and Ident, N345"

Center: "N345: Radar Contact, 11 mi. south of Sierra Four Tree, at 4,500. Traffic at your 1o'clock, 5 mi. North Bound, Altitude indicates 3,000."translation: I found you on my radar scope, and am describing the position I see you. (If you disagree, speak up!). You have traffic ahead and slightly to your right. Their transponder indicates 3,000 feet, but I cannot independently verify that.


The AFDS and A/T do not control to a speed which is less than minimum speed for the current flap configuration? The AFDS and A/T do not control to a speed which is less than minimum speed for the current flap configuration. This speed is approximately 1.3Vs. Minimum speed, FMC speed, or selected speed, whichever is higher, becomes the AFS command speed. If actual speed becomes equal to or slightly less than the minimum speed the underspeed limiting symbol appears in the MCP IAS/Mach Display, and if operating in the V/S mode, the AFDS reverts to LVL CHG. The AFDS will also revert to LVL CHG from VNAV PTH, except when flying a level segment. [FCOM 4.20.36]

This paragraph is about the minimum speed reversion function of the 737 Automatic Flight system. Can anybody help me understand the first sentence? I don't understand what "control to a speed" means here. Does that mean the AFDS and A/T do not "respond" to the speed??

It means you cannot make Autopilot/Flight Director System and Autothrottle fly a target speed below your minimum speed for the configuration. If you were trying to set e.g. 50kts as your speed target, it would be ignored and replaced with the appropriate minimum speed.


Is there a definition of light/medium/heavy aircraft? I'm surprised this hasn't been asked before but I couldn't find it by searching.

For separating arriving aircraft, ICAO PANS-ATM-Doc 4444 Air Traffic Management refers to aircraft as "LIGHT", "MEDIUM" or "HEAVY" but I cannot find any definition of what makes an aircraft fall into any particulate category.

I would of expected a limit on MTOW for each category, does such a definition exist or is it more of an informal definition?

  5.8.2 · Arriving aircraft

  5.8.2.1 Except as provided for in 5.8.l.l a) and b), the following separation minima shall be applied.

  5.8.2.l.l The following minima shall be applied to aircraft landing behind a HEAVY or a MEDIUM aircraft:

  a) MEDIUM aircraft behind HEAVY aircraft- 2 minutes;

  b) LIGHT aircraft behind a HEAVY or MEDIUM aircraft- 3 minutes.

Section 4.9.1.1 of ICAO PANS-ATM-Doc 4444 Air Traffic Management defines LIGHT, MEDIUM & HEAVY aircraft for the purpose of wake separation:

4.9.1 Wake turbulence categories of aircraft
4.9.1.1 Wake turbulence separation minima shall be based on a grouping of aircraft types into three categories according to the maximum certified take-off mass as follows:
a) HEAVY (H) — all aircraft types of 136,000kg or more;
b) MEDIUM (M) — all aircraft types less than 136,000kg but more than 7,000kg; and
c) LIGHT (L) — aircraft types of 7,000kg or less.
4.9.1.2 Helicopters should be kept well clear of light aircraft when hovering or while air taxiing.
Note 1.— Helicopters produce vortices when in flight and there is some evidence that, per kilogram of gross mass, their vortices are more intense than those of fixed-wing aircraft.
Note 2.— The provisions governing wake turbulence minima are set forth in Chapter 5, Section 5.8, and Chapter 8, Section 8.7.3.


Does ATC use mode S addresses to identify planes? By design, Mode S surveillance radar equipment uses global 24-bit airframe addresses to keep track of the aircraft it is tracking.

Are these addresses also used by higher levels of the ATC system, such as to fill in call signs, flight plans and so forth automatically when the plane first appears in a controller's domain? Or does that still depend on ATC assigning 12-bit squawk codes that pilots set manually?

Does the Mode S address appear in a flight plan when filed?

The Mode S address is not used for identification of aircraft in the higher levels of the ATC system such as the Flight Data Processing System.

Mostly the assigned 12 bit code (also known as Mode A code or squawk code) is used to correlate a radar track to a flight plan. The major exception is that in Europe, when the Mode A code is set to 1000 (octal notation), the Mode-S downlinked Aircraft Identity (ACID) is used for flight plan correlation. This is to free up Mode A codes. Usually planned flights are assigned discrete Mode A codes but using ACID / Flight ID correlation, multiple aircraft on a flight plan in the same area can use Mode A code 1000.

The downlinked ACID must be equal to the Flight ID used to file the flight plan.

The Mode S 24 bit address is only used in low level systems; in the Mode S radar, in multilateration systems, in ADS-B receivers and to some extend in tracking systems.


Do the blades of the rear disk have different geometry to the blades of the front disk on a contra-rotating assembly? If my understanding is correct, the air flow is accelerated by the front propeller toward the rear propeller in a contra-rotating prop assembly. Therefore, the rear disk would be receiving air at different pressure and velocity than the front disk. Does this have an effect on the efficiency of the rear disk, and if so, do the rear blades have different geometry to the front blades?

The conditions at the rear disk are obviously different, so something must be different.

First of all, if the rotation direction of the disks is opposite, you'll have 'right' and 'left' blades. (Blades nearly always have asymmetric airfoil, so you can't swap them). That's 'different geometry' already.

Normally, the efficiency of the rear disk will be somewhat lower (zymhan's answer provides some sources). If so, an optimal design should provide more power/torque to the front disk. The most powerful turboprop NK-12 delivers about 20% more torque to the front disk.

Source

This doesn't mean, however, that the blades must be substantially different (other than mirrored). Indeed, on most coaxial assemblies they are the same (including the aforementioned NK-12). How does it work? All these props are constant speed units (at least, I'm not aware of others). The governors will simply set the appropriate blade pitch such that the RPMs were the same, despite different torque and conditions. This means in practice that the blade pitch on the rear disk will be lower. This may count as 'different geometry'.

Finally, there are rare examples when the disks are substantially different. One of them is the SV-27 propfan on Antonov-70, which has even different number of blades (8 vs 6). (This, I believe, is a prop with the highest disk loading ever).

Wiki source


How to file flight plan with ZZZZ? Wikipedia mentions,

  ZZZZ is a pseudo-code, used in flight plans for aerodromes with no ICAO code assigned.

How pilot actually file this flight plan? Is there anything special to do when file for ZZZZ.

I don't know if you're asking about a specific country, but in the US it seems that you can just use it in place of a regular airport identifier and add supporting information in the remarks.

Specifically, the AIM 5-1 has several references to it, including:

  (b) If no four-letter location indicator has been assigned to the
  departure aerodrome, insert ZZZZ and specify the non-ICAO location
  identifier, or fix/radial/distance from a nearby navaid, followed by
  the name of the aerodrome, in Item 18, following characters DEP/,

  (c) Then, without a space, insert the estimated off-block time.
  EXAMPLE-

  KSMF2215
  ZZZZ0330

The same wording is used for both FAA and ICAO flight plan instructions.


Should I have carb heat on for landing in a C152? There is quite a debate about this! I'm a student, have gone solo. My first instructor insists the carb heat goes off/COLD on the approach ('ready for go-around' if needs must! And to prevent dirty unfiltered air entering on landing). My second instructor goes along with the POH and insists the carb heat stays on/HOT until landed (saying icing is more dangerous than dirt).

I LIKE the idea of keeping the carb heat on because if a go-around is needed all I have to do is remember to push in the throttle AND carb heat (and retract flaps, 30 to 20 degrees,etc.) no matter what height. I learn that ONE move. But if I'm trained to take carb heat off, say at 300', and learn only 'throttle/flaps' for go-around, I'm worried I'll FORGET carb heat's HOT if I do a go-around from 400'! See what I mean?

What's the best method for a student to learn?

The approach and landing phase are the times when carburetor icing is MOST likely to occur.

Once a carburetor has ice, it may take a period of time for full application of carburetor heat to clear any ice.  Furthermore it is possible to have enough ice accumulation that application of full throttle and carburetor heat would be insufficient to melt carburetor ice, and little or no additional power would be available at go-around.

So in short, not applying carburetor heat puts you at unacceptable risk of loss of power in the event of a go-around, and potentially even in the event of the need for additional power to compensate for wind shear on approach and for glide path adjustments.

Having examined the risks of no-carb-heat on approach, we should look at the secondary consequences. The operation is contrary to the POH, and the POH is the manufacturer's best guidance for the safe operation of the plane. The practice of asking yourself, "What would the accident review board have to say about this?" is a healthy tool for evaluating decisions. To deviate from the POH, and from conventional wisdom and practice in a critical phase, where there is little recovery time, presents an unreasonable risk on your flights, and is scarcely defensible.  Without an articulable and compelling argument as to why EVERY time you make an approach and landing, the carburetor heat should be off, you are hard pressed to justify a deviation from the manufacturer's guidance.

Ok let's go to an extreme, and say that you are landing in high winds at a desert strip with blowing sand across the runway.  In a situation like that, and experienced private pilot might elect to turn off carb heat just prior to landing to prevent unfiltered air with sand from being ingested into the engine. On the other hand, if the wind is blowing that hard, the possibility of a missed approach and go-around is even higher.

There are circumstances when carb heat may be left off on an approach.  If the aircraft is equipped with a carb temp gauge, and the carb temp has been verified to be above 32F, then it is commonly considered acceptable to avoid carb heat.  Some planes equipped like that will also have a warning alert to announce temperatures which are conducive to carburetor icing. That alert is often coupled with an ice detector sensor in the carburetor. Likely your 152 has neither a carburetor temperature gauge, nor a carburetor ice annunciator.

Let's also talk training risks, since you are a student pilot. Your operations for some time will be as a single pilot, and your procedures should be designed to minimize risk. One way to accomplish that is to simplify your procedures so that they can be accomplished by rote. Having the same procedure each time, without the need to collect data and make evaluations, helps simplify your piloting chores. You are not flying complex aircraft with complex pilot chores, and you do not have the benefit of a second crewmember to make observations and read you checklists.

Most CFIs, DPEs (pilot examiners) and FAA Operations Inspectors, will expect that you follow the POH and the manufacturer's checklist and procedures. In the case of the 152, that will be to turn on carburetor heat prior to the reduction of power (in the pattern).  On balked approach, the procedure is to apply full throttle, and at most altitudes, verify mixture rich, and then remove carb heat. If the removal of carb heat causes a reduction in power (or RPMS) then carb heat is to be reapplied.

There may be other aircraft with different procedures, but you are not flying them. You are flying a 152, and it would be best practice and a defensible position to fly in accordance with the manufacturer's published procedures.

If you were taking your private pilot check ride with me, and you failed to apply carburetor heat in a C152 lacking a carburetor temperature gauge and/or ice sensor, you would not pass the check ride.

Finally, let me just add a story...on a crisp fall day, without exceptional humidity, a student/instructor were flying in the pattern doing touch and gos. The airport was surrounded on all sides by quarry, with a road leading to the flight school. That road also had the power lines to operate the stone handling and crushing quarry equipment. The plane was a new C152, the first year that they were available. It was later found that the cable had slipped in coupler on the valve for carb heat.  You know where this is going. The student was mis-aligned on her approach, and when she applied full throttle for a balked approach, insufficient power was available to establish a climb. The instructor took over, and had to weave the wings between 13.2kV three-phase power lines on each side of the road, to land the plane on the road to the flight school.

Why adopt practices which will unnecessarily test your exceptional flying skills?


What altitude to use for IFR off-airways route Say I want to fly off-airways (both Victor airways and T routes) for my IFR flight, direct to my destination in the US.  How do I know what my off-route altitude should be so I can file for that?
I would expect this would be an altitude above the OROCA and suitable for direction of flight, however I encountered this in the Instrument Procedures Handbook:

OROCAs are intended primarily as a pilot tool for emergencies and
SA. OROCAs depicted on en route charts do not provide the pilot
with an acceptable altitude for terrain and obstruction clearance
for the purposes of off-route, random RNAV direct flights in either
controlled or uncontrolled airspace. OROCAs are not subject to the same
scrutiny as MEAs, minimum vectoring altitude (MVAs), MOCAs, and other
minimum IFR altitudes. Since they do not undergo the same obstruction
evaluation, airport airspace analysis procedures, or flight inspection, they
cannot provide the same level of confidence as the other minimum
IFR altitudes.

This suggests we cannot trust the OROCA.  Then I suppose the 14 CFR 91.177 indicates I need to be at least 2000 ft above the highest obstacle within 4nm of my course in mountainous areas, or 1000 in non-mountainous areas.  But how do I know what this is without using OROCAs?  Do we check sectional charts, or is there something more practical?  Checking a sectional seems reasonable on the ground for filing, but not so if diverting in the air and flying direct to some other airport on an off-airway course not planed on the ground.
Thanks for any help!

This article covers the topic quite nicely

To begin with, a direct route will only be approved in a radar
environment. In many areas of the country this is not an issue. The
pilot, however, must be aware that filing an altitude at or near the
OROCA (Off-Route Obstruction Clearance Altitude) may not guarantee
radar coverage. In that case, the pilot should expect to be assigned a
different altitude or route.

Its also covered in this AOPA article a bit

If you plan a "direct" flight, point-to-point, follow the rules and
enter the correct equipment. For example, if "/G" (or "slash Golf,"
meaning that your airplane is equipped with an IFR-approved GPS and a
Mode C transponder) or "/I" (you have loran or VOR/DME and a Mode C
transponder) are not entered for these kinds of flights, the air
traffic control computer will reject your flight plan because that
route can't be flown with less capable equipment. Direct routing
requests also are approved only in a radar environment, so forget
about filing direct, off-airways when radar is not available, or in
areas of poor radar coverage.

So broadly speaking you can file the OROCA but ATC may issue a higher altitude for radar coverage reasons. I have also received direct routings en-route at previously filed altitudes if they meet the requirements. Where I fly its common for ATC to prefer an airway route to get you out of the terminal area but will generally clear you direct once in route.


How can we physically define reynold number variation in terms of characteristic length? How can you define it physically that
greater the characteristic length in
$Re=\frac{\rho v L_c}{\mu}$
greater the Reynolds number.
Like on wing surface $Re$ is higher than the horizontal tail surface (MiG 29).

The freestream Reynolds number ($Re_c$) of the wing and hstab would be different due to different chord lengths:

$$Re_c=\frac{\rho_\infty V_\infty c}{\mu}$$

where $\rho_\infty$ is the freestream air density, $V_\infty$ is the freestream airspeed and $c$ is the reference chord (of the wing or hstab). I'll discuss the physical significance of reference chord below.

1. Viscous drag

The physical significance on drag is best understood from the flat plate Blasius solution in laminar flow. The overall friction drag coefficient ($C_f$) decreases as a square root of freestream Reynolds number:

$$C_f=\frac{1.328}{\sqrt{Re_c}}$$

So the longer the chord (i.e. higher Re), the less significant the boundary layer viscous effects are to the overall drag. This is further illustrated in the graph below.

Image ref: https://www.sciencedirect.com/topics/engineering/friction-drag-coefficient

Take note, however, that the dimensionalized (total) friction drag still grows since $C_f$ here is non-dimensionalized with respect to the reference chord, $c$.

2. Turbulence transition

Increasing the chord doesn't increase the momentum thickness in absolute terms. However, the relative thickness with respect to the chord is different for different chord lengths:

$$\theta(s) = \frac{0.664\sqrt{\mu}}{\sqrt{\rho_\infty V_\infty}}s^{1/2}$$

where $s$ is the chordwise position from the leading edge.

Since natural transition is a function of the momentum thickness Reynolds number (Ref. Drela, Flight Vehicle Aerodynamics), which increases with respect to the momentum thickness, transition to turbulence will occur at similar chordwise location, $s$, in absolute terms, but earlier in relative terms ($s/c$) for the longer chord.

This has the effect of increasing the stall angle of attack for the larger chord, manifested in the effective increase in the freestream Reynolds number.


What is the function of activating an individual elevator on the B-1B Lancer? This B-1B Lancer's picture I captured from this Youtube video. The control axes is from Wikipedia.

As we know, the three "conventional" axes are as follows:

Roll axis controlled by aileron,
Pitch axis controlled by elevators (both at the same time),
Yaw axis controlled by rudder.

Then my questions are:

What is exactly that purpose (the single elevator activation), and
How it work? Is there new axis of it?

That would be the correct control response for a combined roll to the right and nose up pitch command from the pilot. It looks like that photograph was taken while the pilot was in the middle of doing a check of their control services prior to taxi.

You can see similar results in the tower buzz sequence out of Top Gun. The final bit shows an F-14 from the tail which rolls to the right and pitches nose up with a similar control response from a combination of the tailplane and starboard wing spoilers.


Could flaps replace spoilers by deflecting more than 90°? Could flaps replace spoilers by deflecting more than 90° after touchdown?

The BAe Jetstream 31 is one of a few aircraft that had a "lift dump" flap position after touchdown. It is not "more than 90°", but it is quite effective.

(Jetstream 31 Lift Dump in action; YouTube)


Why are holding patterns in an oval shape? Why are holding patterns in an oval shape? Why not circular or more square-like?

I don't have any definitive information on why the oval shape was chosen. However, it seems to me to be the most practical shape given the navigational equipment available when holding patterns first became necessary. VOR, DME, and GPS technology did not exist. Holding patterns were flown, often by single pilots hand flying, with reference to an ADF needle, maybe with a little marker beacon help.

I don't know if a square-like pattern was considered, but if it was I think it would have been rejected for at least the following;

a rectangular pattern would involve 4 turns, better to keep it simple with only 2 turns.
flying any kind of a leg perpendicular to the holding radial would mean getting farther away from the radial than necessary with no advantage to be gained, and it might involve more terrain clearance problems.

Flying a circular pattern makes it more difficult to keep track of where you are in your head (no glass cockpits, indeed no HSIs even, not even rotating ADF cards at first), than an oval. Worse, though, is what could occur in some wind conditions. For example, let's say you're supposed to hold north of a fix on the 360 radial (inbound course 180). Further, lets say there's a significant north wind. You're approaching the fix on a course of 180. You cross the fix and then fly a circle with respect to the air you're in. In a no-wind condition, you'll come back to the fix. However, with a north wind, you'll come back to the course south of the fix, and will have thus violated where you were supposed to hold.

With today's navigational technology, we can of course easily fly any kind of shape we want, but the disadvantages previously mentioned would still apply.


What should pilots do if they observe illegal activity onboard an aircraft? So Justin Bieber was in the news again a couple of days ago:

Pilots on Justin Bieber’s Plane Had to Wear Masks Because of Pot Smoke

What are pilots legally obligated to do in a situation like this where the passengers (allegedly) are doing drugs or any other illegal activity?

Notify ATC, call 911, or land immediately?  Are any of these required or can you tell them to stop and if they comply you are good?

Are there any good recommendations on how to handle the passengers?

I think a lot would depend on the type of illegal activity observed.  For example, if someone was getting injured or worse, that would mean the crew would need to take immediate and aggressive action, which would include possibly putting themselves in some danger to protect the victim, at least to a certain degree.  That said, getting the plane down safely would be higher priority for safety all the way around so protecting the victim needs to be weighed against the risk of getting injured to the point the pilot can no longer fly the plane.

In the Bieber's case, escalating the situation by trying to intervene would only create risk of the crew being injured and then unable to bring the plane down with no real upside.  Putting out a warning, then proceeding to a suitable airport immediately would seem to be the most prudent course of action.


Is there any use for variable shape wings within aviation? I am working on a variable shape airfoil which is originally intended for sailboats. However, I am wondering if there might be an application for such a design within aviation? The design I am working on can change thickness, camber, and twist quickly at the same time. The whole wing asymmetry can be mirrored within a second as well.

Is there an application for variable wing shape or geometry similar to this in aviation?

Well, yes.

Variable shape wings (or variable geometry) have a number of uses, primarily in being able to optimize the shape of the wing to an ideal form for the regime of flight.

The idea isn't new; birds, bats and other flying creatures twist and warp the shape of their wings in order to maneuver and generate thrust as these pigeons demonstrate.

The Wright Brothers used a warping wing box on their gliders and the 1903 flyer.  Orville Wright is said to have come up with the idea while twisting a rectangular cardboard box used to ship bicycle tire inner tubes.

The chief advantages to such a design are that it provides an extremely clean airframe, aerodynamic wise, without joints, separate control surfaces, moving parts, etc which create excess drag.  In addition, the aircraft shape can automatically be optimized to the altitudes, speeds and Mach numbers desired without tradeoffs for weight or performance required with aircraft made from conventional materials.

The downside to warping wings is solving the problem of finding materials which could be flexible and change their shape and then remain rigid and immutable under aerodynamic loads.  Wood and metal airframes lacked the capability to do this successfully.

Early attempts to solve this problem have been to make 'swing wing' designs where the wing can be rotated at the wing root to an  optimal sweep in flight.  The Bell X-5 successfully demonstrated this concept and it has been used on a number of military aircraft including the F-111, F-14, MiG-23/27, B-1, and SU-22.

NASA is currently developing a morphing wing for these reasons.  If successful and shown to be feasible from a manufacturing and service standpoint, it would be a game changer.


What is typical cruise altitude in the Himalayas? An important tourist connection goes from Tribhuvan International Airport (VNKT) in Kathmandu, at 4,390 ft, to Tenzing-Hillary Airport (VNLK) in Lukla, at 9,334 ft. The mountains around Lukla quickly raise from south to north. Right around Lukla the ridges rise to about 15,000 ft, but the aircraft does not have to fly over these, since decent approach is only possible through the valley from the south and the ridges are somewhat lower further south. So does anybody know what is actual typical cruise altitude in that area?

I am sure I have no knowledge for reading charts but en-route charts for Nepal indicate something like F170 which I translate to FL170 or 17,000 ft. Pls correct me if I misunderstand it.

Here is the source


How many African countries currently deploy Cat 3 ILS? How many countries in Africa currently operate Cat 3 ILS?

This answer has a list of all airports with a Cat III ILS system.

Africa was assigned ICAO region codes D, F, G and H, so you can just look for ICAO airport codes on the list starting with those letters. The only one I see is "GMMN (MOHAMMED V INTL) on runways: 35L, 35R". That name wan't familiar to me, but a quick Google search says that GMMN is Casablanca, Morocco.


Why is the Mooney's signature tail profile different from most planes? In another question, someone said everyone but Mooney has the vertical stabilizer on backward. (As a Cessna driver, this looks backwards to me). Is there an aerodynamic reason or some reason other than marketing?

(Note the slants of the leading and trailing edges.)

The best explanation I've heard is that at high angles of attack the rudder is nearly vertical providing the pilot better yaw authority.  I don't know whether this is true or not but it makes for a good story, doesn't it?

The story goes something like this:As the plane pitches up, the rudder, being slanted "forward," moves closer to a vertical position and provides better directional control at low speeds.  Conversely, at high angles of attack a swept tail (and rudder) moves further away from a vertical position and is, in theory, less effective.

Some go on to speculate that the leading edge of the vertical stab, being un-swept, protrudes further into undisturbed airflow at high AOA/low airspeeds which may slightly enhance the pilot's ability to control yaw at the edge of a stall.

I've never spun a Mooney (I did complete my CFI in an M20F/201) nor do I have a burning desire to do so.  I imagine that it's not a friendly spinner.  Catching the spin early would be critical in a slippery air frame like a Mooney.

A brief online search of Mooney tail lore yields everything from pure marketing to discussion of wetted area to better directional control during landing to spin recovery/prevention to "those swept tails provide no speed benefit and are simply designed to look good."

Here is one discussion (of many) on a Mooney forum regarding the tail design: http://mooneyspace.com/topic/9905-mooney-tail-aerodynamics-not-backwards/

I doubt very much that it's simply a marketing gimmick (although, it could be as simple as that!).

I believe that the explanation I've relayed here is merely "somewhat plausible" as it was gleaned from hours of beer-fueled hangar talk and some Google searching...not exactly a scientifically rigorous method of research.  I have no credible references and, as far as I know, no data exists to back any of it up.


What is "50 ft obstacle climbing speed"? Vy and Vx make sense to me. They are used for fastest height gain at a given time and biggest angle of climb. But what is the purpose of that speed (it's from DA20 POH)? It's only 3 kts faster than Vx.

thanks!

In the absence of POH guidance normally Vx is the target airspeed for a 50ft obstacle. However, when the 50ft speed is included in the POH, as it is in modern aircraft, it is based upon empirical data from flight tests.  Essentially, the test pilot flies the plane searching for the best technique to offer the best performance. When that is determined, the procedure and speeds are worked into the POH, usually in procedures and tables of speeds, but sometimes in graphs.

There is allot of engineering and test department spin on the procedures, and sometimes a pilot may get better performance using a slightly different procedure and / or speed, than published.

Also, published speeds may have a buffer in them to avoid significant performance loss, if for example a maneuver puts one close to a point where sink might be higher if the pilot's airspeed control is slightly off.

So to summarize, different manufacturers have different methods of determining what their recommended procedures and speeds are.  Sometimes there are buffers built in for speeds, and sometimes not.  Sometimes a skilled pilot can outperform the recommended POH procedure.  That doesn't happen often, because POH figures are competitive and are used to sell planes.

Side story: I was evaluating a PC-12 and C-208 as platforms for scientific instruments, and flew each one with a sales man.  The PC-12 came back with a factory test pilot to fly with me.  I wanted to fly at speeds between 61 and 64k, in the Caravan, at 500 ft AGL, and 67 to 70k in the PC-12.  The Cessna Caravan would do it comfortably all day long.  Neither the salesman nor the factory test pilot was willing to fly (or let me fly) the PC-12 at those speeds at that altitude.  I did with the PC-12 at 3500 ft AGL, and it simply didn't have the stability that the Caravan did at the lower envelope.

So the same numbers in a different plane can result in very different flight characteristics.  Vx in one aircraft could be less stable in one aircraft, but Vx+3 might be much more stable.


Where can Boeing wind data be found? There are various services that use world-wide Boeing Winds for forecast wind data which can be used to calculate an approximate flight time between two locations.  They usually have best case, worst case, and average case for each location, altitude, and date in the future.

I have searched and searched Google to no avail.  Where can this wind data be found, and how can it be used in a commercial product?

For those of you who don't know what the Boeing winds are, I found this description of their software product on am informal message board (not related to Boeing):

  PC WindTemp

  INTRODUCTION
  The Boeing PC Windtemp program provides global average and statistical winds and temperatures aloft over a 30 year
  period. These data are used primarily for comparative transport
  airplane performance and economic studies. The data may also be used
  for transport airplane route planning on an annual, seasonal, or
  monthly basis.

  Note: Actual winds and temperatures at a specific location and time
  may differ appreciably from those computed by PC Windtemp. Therefore,
  data from PC Windtemp must not be used for flight planning, aircraft
  dispatch, airborne flight navigation, or any other type of actual
  flight operations.

  PROGRAM FEATURES
  A seasonal and monthly database with global coverage from 1000 millibars (364 feet pressure altitude) to 10
  millibars (101,885 feet pressure altitude). Annual data updates to the
  most recent 30 year period. Airport codes and coordinates may be
  imported from a text file in a comma separated value (CSV)
  format Calculates enroute wind and temperature for up to 50 airport
  pairs at a time. Calculates enroute wind and temperature for simple
  great circle tracks or tracks with up to 250 waypoints, with or
  without altitude changes. Calculates average enroute wind and
  temperature or any reliability (quantile) between 50% and 99%. Months
  or seasons, reliabilities, altitudes, and speeds may be nested for
  input efficiency. Formatted and text output reports are
  available. Program subroutines (DLLs) can be called from other
  programs written with C++ or Visual Basic in order to incorporate
  Windtemp functionality in those programs.

An alternative to the Boeing data (if it exists, you might need to call one of their sales reps to find it) is publicly available meteorological data.  One such project is the NCEP/NCAR Reanalysis Project.  There are a few others, as well as archived data.  None of these is exactly the Boeing dataset, but I'd bet that the Boeing dataset is based at least in part upon data like these.  The benefit to the data below is that in most cases it is free and there is a lot of it.

Reanalysis Data

Reanalysis data is constructed from the best available past observations, which are assimilated into a weather model to fill in the gaps between obs and in time.  There are many such projects with various scales (global, regional) and time periods.

The NCEP/NCAR Reanalysis Project

This dataset has 4-times-daily, daily and monthly values between 1948 and present and long term monthly means for 1981-2010.  The data is global. The data is publicly available and you can retrieve files in NetCDF format from the linked website.  The wind data is stored on pressure levels (e.g. 1000 mb, 500 mb, 250 mb) and is stored in its u (east-west) and v (north-south) components separately.

The ERA40

This dataset is a global dataset covering 1957-2002 and has various output resolutions available.  Output from ECMWF is typically in the GRIB format and not all of it is free for non-research use.

The NARR

The North American Regional Reanalysis, as the name suggests, is a regional dataset covering North America.  The data covers 1979 - present.

Observations

Long term past observations are archived at the NCDC and include surface stations, weather balloons and model data, among others.  From the various models available a statistical representation of winds could feasibly be produced.


What are the issues involved in converting a quadjet into a twinjet? As you are probably all aware already, the fewer engines you have, the better your fuel efficiency. That’s why the airlines are selling off their quadjet 747s and buying twinjet 777s. It's why they’ve already sold off their trijet DC-10s, L-1011s, and MD-11s and replaced them with twinjet 767s, 777s, and 787s. It's why the quadjet A340 lost out to the twinjet A330, and the quadjet 747-8 and A380 are struggling to sell while the twinjet 777 and twinjet A350 are selling like 737s. It's why the trijet MD-11 went over like a lead balloon compared to the twinjet 767, 777, and A330.

One obvious solution to the kerosene-guzzling-quadjet problem would be consolidation: replacing the two engines on each wing1 with a single, bigger engine (for instance, replacing a 747’s four JT9Ds, CF6s, RB211s, or GEnxs with a pair of GE90s, or an A340’s four CFM56s or Trent 500s with a pair of Trent 700s or GE90s).2  However, this generates the obvious problem that the wing might need to be redesigned for the different stress distribution of a twinjet, as opposed to a quadjet, design.  Still, the change doesn’t have to be large.  For instance, the A340’s wing is already almost identical to the A330’s; just deactivate the extra fuel tanks, chop off the bulge under the wing that was introduced to keep the airflow around the outboard engine from breaking the wing off, take away the outboard pylons, swap out the inboards for a pair of A330 engines, and you’re in business.

Yet, despite the massive efficiency advantage to be gained, there’ve been hardly any serious proposals to reengine quadjets into twinjets in this sort of way, indicating that there’re other issues that’re showstoppers for twinjetting a quadjet; what are they?

1: I’m leaving trijets (DC-10, L-1011, MD-11, etc.) out of this discussion, as converting one of those to a twin doesn’t involve any change in the number of lateral engines - just taking out the center tail engine and making the laterals somewhat bigger.  Also excluded are tail-mounted quadjets (VC10, Il-62), as these use conjoined engine pods (two engines per pylon), meaning that the two engines on each side could be swapped out for one bigger engine with little or no change in the stresses on the pylon and rear fuselage.

2: This doesn’t work for the A380, since not even the GE90 is powerful enough.  Sorry, A380!

Yes, you'll get a wing redesign to allow for the higher weight and thrust of the engines: the inboard engine mounts now need to be twice as strong.

You can also run into ground clearance issues. An engine twice as powerful is often also larger. Here's a GE 9X engine being tested on a Boeing 747. You can see it's pretty close to the ground, and needs a really short pylon.

Going from 4 to 2 engines also means replacing half the instruments in the cockpit. You could save a lot of weight by removing the wiring for the outer engines, but that'd be a major operation.

Historically, the advent of high-bypass engines coincided with the introduction of widebody aircraft for a huge increase in passenger capacity and efficiency. So e.g. Boeing could make more money by offering a new design instead of selling 2-engined 707s.

For the remaining 4-engined airliners (B747 and A380) no engine is powerful enough to allow a 2-engine conversion. An engine powerful enough would be even bigger than the GE 9x shown above, and would scrape the ground when installed on a 747.

Finally, I'll leave you with a response to footnote 1: The VC-10 was used to trial the RB.211 engine, which was 2x as powerful as the original Conways:


Why does pressure remain constant in the boundary layer? From Fundamentals of Aerodynamics by JD Anderson.

It can be shown experimentally and theoretically that the pressure
through the boundary layer in a direction perpendicular to the surface
is constant. That is, letting pa and pb be the pressures at points a
and b, respectively, in Figure 1.47, where the y-axis is perpendicular
to the body at point a, then pa = pb.

But, there exist a velocity gradient on the boundary layer. Doesn't this violate Bernoulli's equation? Does this assume pressure remains almost the same in the viscous region or I am missing something?

There does exist a velocity gradient within the boundary layer.  However, the boundary layer, being a viscous phenomenon, does not obey the Bernoulli equation, which is what trips up our usual intuition
So Where Does Bernoulli Come From?
Bernoulli is a simplification of the Euler equation (which is a simplification of the Navier-Stokes equations).  The Euler equation is an inviscid formulation of the Navier-Stokes equations, and Bernoulli further neglects rotationality and states that the total pressure of a fluid is constant (in steady flow, along a streamline), giving the following expression that we're familiar with:
$\frac{1}{2}\rho v^2+P=const$
This works great outside of the boundary layer, in incompressible (typ. Mach < 0.3), irrotational, inviscid flow...which, conveniently, helps us to understand a good many things that we're interested in (e.g., model airplanes, sailplanes, some GA aircraft, etc.).  However, it has its limits, and one of the many tricks of aerodynamics is knowing the assumptions of your models and when they can and cannot be applied.  This is why panel methods, relatively low-fidelity fluid modeling techniques, are still being used in hydrodynamic modeling.  So long as you don't violate their assumptions, you have a body-fitted model that is faster than more modern finite element or finite volume methods and still gives an accurate result that can be used to predict body loads (and, thus, do performance analysis, etc.).
OK, but why is the pressure still constant?
To the point, Anderson states that pressure is constant through the boundary layer along a line normal to the surface of the body (or airfoil, in this case).  The normal part is important: it means that pressure is not necessarily equal along the length of the airfoil.  Let's look at a small element of fluid moving along the body surface (below) to play with this:

So, pressure gradients drive flow.  If there was no pressure gradient along the length of the airfoil ($P_{right}=P_{left}$), the flow velocity would be zero.  This is not the case, and flow is moving from left to right, therefore, $P_{left}>P_{right}$.  Furthermore, as a result of viscosity, we have a velocity gradient as a move away from the body (e.g., low/zero flow velocity close to the body and increasing flow velocity as we move away from the body through the boundary layer).  This implies shear along the top and bottom of the fluid element in the picture, which corresponds to the pressure difference we mentioned.  However, there is no vertical motion in the boundary layer (there can be in a turbulent boundary layer, but I'm assuming a laminar one for the purposes of this explanation) and no vertical shear.  As a result, $P_{down}$ must equal $P_{up}$ on this element.  If I think with a Newton's 3rd law kind of mindset, the fluid directly above and below this element would feel the same pressure and so on and so forth until you get to either the edge of the boundary layer or the surface of the airfoil.  The assumptions for this fall apart outside of the boundary layer, since there is non-negligible fluid motion towards/away from the airfoil, so that's why I'm stopping the analogy at the edge of the boundary layer.
Hence, along a line normal to the surface, since this does not imply that $P_{up}$ on this element is equal to $P_{up}$ on the element to its left or right, the pressure is constant throughout the boundary layer.
Other references: https://web.mit.edu/hml/ncfmf/10FBL.pdf


I flew the wrong pattern at an uncontrolled airport... Should I be worried? Ugh... I'm beating myself up as I feel I made a pretty serious mistake over the weekend. I'm a PPL trying to build up XC hours trying to work towards my instrument. Over the weekend I did a short XC to an extremely remote desert airport which is a nice little flight. I do flight following all the way there, uneventful. 15 miles out I get the ASOS and it says winds calm. After canceling flight following, I switch over to the CTAF.

This is where I started to get a little overwhelmed and I start making mistakes. I had waited a little longer to start my descent so I was approaching a little faster than usual. I have made this flight several times before and the winds are usually from the east so I planned my normal pattern entry to cross the field, make a right turn and enter the left pattern for the easterly runway. As I'm approaching I'm using my standard communications; someone on the ground radios to say the winds are actually out of the west and at at least 10 knots as the windsock is almost straight out. At that same moment, another pilot radioed announcing they were 3 miles to the west and inbound to land. For some reason this last minute information really overloaded me and I just went into autopilot. For some reason, I still just had "left pattern" baked into my brain. Instead of continuing to cross the field I entered at a 45 into a left pattern for the westerly runway. (sigh). I fly it normally and on final the traffic that was a few miles out now announces they are on a right downwind. My heart sinks. I realized my mistake, and although I am mortified, I decide to continue the landing and go on with my trip back to my base.

Afterward, I debriefed myself trying to isolate what happened, and how to prevent this kind of mistake again. I take safety and procedure very seriously. I shudder to think what might have happened if there was a NORDO in the pattern...

My question is should I be worried? I've never made this type of mistake before and am frankly expecting a call from the FSDO. It's not a populated area and there is very little traffic there but still...

Don't worry about it too much.  Are you specifically asking what are the odds of getting a phone call about this?  I'm not sure this is a really good question for Stack Exchange.  If you are really worried about it, fill out one of those mistake-reporting forms just in case -- https://asrs.arc.nasa.gov/

Newish/ overloaded pilots at unfamiliar airports have been known to overfly the field, look at the wind sock, and then proceed to set up a landing in exactly the wrong direction.  It happens.  Try to be aware of when you are getting over-loaded and double-check yourself.

Live and learn-- you lived, so learn.


Why is max power time limited for jet/piston engines? Usually max power is time limited for jet/piston engines to 10 or 5 minutes. Can anybody explain the reason? What will happen if those limits are exceeded?

Maybe Nothing....

Maybe Catastrophic Failure...

Any number published by an engine maker (or any aviation part maker for that matter) is the numbers they have tested it to. Thus if Continental or GE claims a 2000 hour TBO but puts a 5 minute limit on max power, that in turn means that the 2000TBO number is based on operations within these published limitations. Exceeding these limitations may cause TBO to arrive sooner than expected and could possibly cause undesired operating characteristics. It is of course possible that if you drive the engine at max power for a time greater than suggested, it will throw itself to pieces. However, this is unlikely.

In some cases there are physical limits based on the materials used in the engine. If exceeding maximum run time provides a way to generate internal temperatures that exceed the limits of an internal part you could very well have an issue very quickly. From my experience with piston engines it's generally a wear and heat fatigue issue when flogging the engine at max power. That being said if the POH calls for a maximum of 5 minutes at full power and you spend 5 minutes and 30 seconds at full power on a climb out chances are you will be fine. If you do this routinely you may find that your engine hits TBO long before the published numbers.

This article also alludes to the fact that there may be other limiting factors such as the strength of the gear box the engine is connected to.

  The shp of a turboprop engine is restricted by the strength of the gearbox that drives the propeller, and by the ability of the airplane to handle the thrust developed by the prop.

On any note I would think that most manufacturers publish numbers that are on the conservative side for many reasons.

Since this question is highly related to TBO number you should check out this article about some common myths around engine overhauling numbers and engine wear in general.

Definitions:

TBO: Time Between Overhaul. This is generally the lifetime of an engine. Although some people commonly think this is a legal number it is only manufacturer suggestion and you are free to exceed it (and plenty of people do).

POH: Pilots Operating Handbook. The document that outlines the limits and safe operation of a given airframe.


Do aerodynamic forces depend on the materials of the wing surfaces? I think that statement is true, but in the book "Fundamental of aerodynamic", page 35: the aerodynamic forces R don't depend on the skin material, 5 variables are mentioned but none of them is relate to skin material of wings. So why is that???

Surface roughness has a minor impact, except in a range of Reynolds numbers mostly encountered in General Aviation. Only when you use an airfoil that has been designed for laminar flow but experiences an early transition will the performance be impacted significantly.

The book you quote assumes a certain minimum standard of build quality: Flush riveting, smooth surface and a solid, stiff structure. Once you move to more advanced topics, more variables will need to be added, such as elastic deformation in flight or substandard surface quality. At the introduction level some simplifications are justified. The lessons derived from this reasoning are valid and valuable. When you progress, they will be expanded with more complex concepts. Trust me.


Can a CFII log Dual Given if flying as SIC? I am an MEI/CFII/ATP type rated and authorized jet pilot in Part 135 operation.  On the legs where I'm SIC slinging gear and working radios, is it ok to log this time as "dual given" and PIC time as an instructor?  Let's assume that I do in fact provide some form of instruction to the other pilot (whether or not this is wanted or needed).

It’s your logbook, so you can write in it anything you want. If a future prospective employer sees somebody doing what you described, the chances of being hired would fall drastically, since nobody in their right mind believes that the FO as PM is providing meaningful or valid “instruction” in a Part 135 or 121 environment to the Captain. If an FAA examiner sees that sort of time claimed as PIC to meet some requirement, I doubt the reception would be any better.

But, you go ahead & do what you want to do, since you will be the one who lives with the consequences. I think it’s a terrible plan, and I couldn’t see wanting to hire somebody who did that, not only because the PIC and Dual Given number are lower than shown, but also because of the brazen duplicity involved.

It’s playing with fire, and potentially risking a one-way ticket OUT of the airline industry. Which, for somebody who would actually do such a thing, would be the better answer.


For a flying wing airfoil, which AOA is to consider when selecting Cl? I'm in the process of designing a flying wing. I'm trying to keep it a small as possible, so the lift coefficient is very crucial for me. I'm currently looking at some airfoils but most of them deliver the good Cl at AOA larger than 0.

My questions:

When deciding a lift coefficient --let's assume 0.5,-- should I choose an airfoil that provides me with a Cl of 0.5 at 0 AOA?
When the flying wing is cruising, the lift force needs to equal the weight, but does the flying wing cruise at 0 AOA or can it cruise at 3° of AOA so it can it can keep its altitude?

Do not look at the angle of attack. Instead, focus on ratios like best lift-to-drag ratio. The angle of attack will be a consequence and not a design parameter.

First you need to determine what your flying wing will be good at. Next, determine which propulsion (jet or propeller) it will use. Then you can work on the layout (aspect ratio, wing sweep) and when that is decided, only then you are able to determine the optimum lift coefficient.

The process to determine the optimum lift coefficient is discussed here, here and here.