Is airfoil thickness proportional to drag coefficient? Does increase in the thickness of a camber airfoil mean more drag will be produced?
Why do slow flying planes have thick airfoils when it will just slow them down even more?

There are several reasons for using thick$^*$ airfoils.

Slow planes need high lift coefficients in order to fly slow. The increased drag coefficient is the prize to pay for a higher $C_{L,max}$. Take a look at this diagram:

Source: H. Schlichting, E. Truckenbrodt, Aerodynamik des Flugzeuges. Colors added.

At low Reynolds-Numbers the maximum lift coefficient is achieved by the thickest airfoil (18%). At slightly larger Re-Numbers the 12% thickness airfoil gains the upper hand. However, the thinnest airfoil (9%) has on average about 20% less maximum lift capability than the thicker ones.

The following diagram shows polars of symmetric airfoils with different thicknesses.

Source: B. Rögner, Flugwissen. I couldn't find the original source Rögner took the diagram from, if anybody knows it feel free to comment.

The quality of image is bad, but you can recognize both the higher $C_{L,max}$ and drag coefficient of thick airfoils.

The drag coefficient depends on many factors and, as shown in the formula given in Peter's answer, is not proportional to the thickness. The drag coefficient's thickness dependency however, can be assumed to be proportional to the thickness: the $\delta^4$ term is one order of magnitude smaller than the term multiplied with $\delta$.

$$\frac{c_{D,\text{normal airfoil}}}{c_f}=2+4\cdot\delta+120\cdot\delta^4$$

$$\frac{c_{D,\text{laminar airfoil}}}{c_f}=2+2.4\cdot\delta+140\cdot\delta^4$$

In Hoerner's Fluid Dynamic Drag, Chapter 6.A.2, you can find more formulas to approximate the drag coefficient and take other parameters into account.

A good resource for understanding the influence of airfoil parameters on their aerodynamic properties is NACA TM 824.

Stall behavior of thicker airfoils is usually more forgiving.
Another reason for using thick airfoils is that it decreases the wing's weight, as thick structures can carry better the bending loads in a wing. If a wing tank is used, thicker airfoils allow for a higher tank volume.

$^*$: I interpret thick as >12%, e.g. 15% as found in the wings of many GA airplanes.


Are there competitors to Jeppesen making Electronic Flight Folders? Jeppesen has made Electronic Flight Folders and seems to be a pioneer in that. Do they have any competitors for that?

For the UK NATS makes most of the charts which I frequently use for flight stimulation. I believe that for charts especially the Aerodrome charts are much better than the style of charts Jeppesen produce. The only downside is that the charts aren't compiled in the way that charts on Jeppesen are and must be compiled. But for outside the UK the best charts in my opinion are Jeppesen.


If the map (reading) light bulb is burned out in my own Cessna 210, what are my options if I want to fly FAR Part 91 under night-time VFR? If the map (reading) light bulb is burned out in my own Cessna 210,  what are my options if I want to fly FAR Part 91 under night-time VFR staying in the traffic pattern doing touch and goes?

Can I change the light bulb myself (non- A&P mechanic) and go?
Do I have to have an A&P supervise my work if I change the light bulb myself.
What action, if any, do I have to take in order to be in compliance with the FARs.

As the owner, you (likely) may replace the bulb yourself
It comes down to the complexity of the work.
Owners can now do far more preventive maintenance than the 32 listed items
For many years, the FAA treated the 32-item list in 14 CFR Appendix A to Part 43 as exhaustive. The interpretation was that if an item or procedure did not appear in section (c), then it was not preventive maintenance. Case closed
However, in 2009 the Coleal Legal Interpretation, produced by the FAA's Office of Chief Counsel, superseded the prior rules. It specifically calls out and contradicts the understanding that the 32-item list is exhaustive.

Even though the introductory text of subparagraph (c) states that “[p]reventive maintenance is limited to the following work ....” (emphasis added), in view of the broader definition of preventive maintenance in section 1.1, we believe that such limitation is not controlling. Similarly, for the same reason, we also believe that the following sentence in Advisory Circular 43-12A … is overly restrictive. That sentence, found in Paragraph 3(b)(1), states: “If a task or maintenance function does not appear in the list, it is not preventive maintenance.” As with the other paragraphs of Appendix A (i.e., on major repairs and major alterations), the lists are better viewed as examples of the tasks in each category – they cannot be considered all-inclusive. There are, no doubt, many “simple or minor preservation operations [tasks]” and many “replacement[s] of small standard parts not involving complex assembly operations” performed daily, especially on small general aviation aircraft that the agency would consider to be preventive maintenance, though they are not included in the 32 listed items. It is our understanding that Flight Standards' Aircraft Maintenance Division is planning to clarify this issue in a future revision to the AC.

In short, the list of 32 items is not exhaustive.
Is the map light preventive maintenance?
So we know that there is preventive maintenance which can be done which does not fall on the list. However, this does not imply that all maintenance is preventive. The specific question has to do with the map light.
Looking through 14 CFR Appendix A to Part 43, we find:

(c)(17) Replacing bulbs, reflectors, and lenses of position and landing lights.

So it is clearly within the domain to replace exterior bulbs. The question becomes whether accessing the interior map light bulb in a Cessna 210 is low complexity or high complexity.
Your A&P might be able to give you some guidance, although IMHO a good yardstick is that any part designed to be IRAN'ed with nothing more than a Swiss-army knife is pretty clearly "low complexity" and should fall under owner preventive maintenance.


What are good alternatives to sunglasses for flying? I'm a student pilot and I won't be able to wear sunglasses for 5 months... Now, how am I going to fly? I know you don't have to wear them but it's easier (brightness etc. etc.). Are there any alternatives you can give for flying? I've never tried a hat, is that a good option for the moment? Maybe it's a silly question but do sunglass contact lenses exist?

I've been flying for over twenty years. I've never once worn sunglasses or a hat in the cockpit, with exception of a view limiting device (i.e. hood). I understand why many pilots wear sun glasses and have nothing against it, but for me I feel like it hinders my vision more than helps.

You can fly just fine without sun glasses. One thing that might help, is to make sure you wipe down your windshield before flight to make sure its clean and clear, in order to reduce glare.

A baseball cap might be a good idea if your airplane doesn't have sun visors.

You should be totally fine. Flying without sunglasses is like flying without noise cancelling headsets. Its a creature comfort, but not absolutely necessary for safe operation.


What is the force exerted by the catapult on aircraft carriers? On aircraft carriers there is a catapult that slingshots aircraft so that they can gain lift on the short carrier deck.

I have a few related questions - the first is what is the force exerted / required by the catapult to sufficiently accelerate the aircraft; and is it adjusted per aircraft type or a uniform value?

I imagine carrier takeoffs/landing cause additional stress on the aircraft; but does it have a dramatic effect on the lifetime of the aircraft vs. their non-carrier configured twins? Or is it compensated for by a more frequent maintenance schedule?

Takeoff

Steam/power settings are adjusted for each a/c type and T/O weight.

The EMALS stores 484 MJ in four 121 MJ alternators spinning at 6400 rpm. It delivers up to 122 MJ over 91 m. That averages out to 300,000 lbf. EMALS more finely controls launch forces (Max Peak-to-Mean Tow Force Ratio = 1.05), allowing it to launch smaller a/c (eg, smaller UAVs) and delivering a smoother ride that reduces airframe fatigue.

Current steam catapults deliver up to 95 MJ over 94 m. Each shot consumes up to 614 kg of steam piped from the reactor (NB: not the primary coolant loop). That averages out to 230,000 lbf.

Accelerations average around 3 g's, peak around 4 g's.

Landing

Landings are stressful (notice the fuselage skin wrinkling beneath the radome on this Hawkeye):

(Source: DoD photo by: PHAN KRISTOPHER WILSON, USN Date Shot: 11 Jan 2005.)

An F/A-18 touches down around 720 fpm (12 ft/s). It's rated to twice that. CTOL fighters typically do about half that. I believe airliners average under 200 fpm (3 ft/s).

Here an F/A-18 is dropped from 20ft (36 ft/s, 2200 fpm):

Service life

NATO fighters are typically designed for 30 year service lives (6,000 to 8,000 flight hours). Historically, Soviet/Russian fighters fly much less. The Su-27SK is rated for 2,000 flight hours over 20 years. [See table for cost and service life comparison.] F/A-18's were built for 20 year service lives, 30 years with service life extensions.

The fuselage and landing gear are much stronger to withstand carrier landings and launches. The nose gear regularly transfers 4x the takeoff weight of the a/c into the rest of the fuselage.

Compare the F-35A's CTOL nose gear:

(Source: USAF)

...to the F-35C's CATOBAR nose gear:

(Source: USN)

Here's an excerpt from a Naval Air Warfare Center paper on EMALS:

  Other drawbacks to the steam catapult include a high volume of 1133 m3
  , and a weight of 486 metric tons. Most of this is top-side weight
  that adversely impacts the ship's stability and righting moment. The
  large volume allocated to the steam catapult occupies "prime" real
  estate on the carrier. The steam catapults are also highly maintenance
  intensive, inefficient (4-6%), and their availability is low. Another
  major disadvantage is the present operational energy limit of the
  steam catapult, approximately 95 MJ. The need for higher payload
  energies will push the steam catapult to be a bigger, bulkier, and
  more complex system.

Endspeed:      28-103 m/s [54-200 knots]
Cycle time:    45 seconds
Weight       < 225,000 kg
Volume       < 425 m 3

  At max speed, the output of one of the disk alternators would be 81.6
  MW into a matched load... These magnets have a residual induction of
  1.05 T at 40 oC and create an average working air gap flux density of 0.976 T, with tooth flux densities approaching 1.7 T... Maximum output voltage is 1700 V (L-L) peak and current is 6400 A peak per phase. The
  disk alternator's overall efficiency is 89.3%, with total losses of
  127 KW per alternator. This heat transfers out of the disk alternator
  through a cold plate on the outside of each stator. The coolant is a
  WEG mixture with a flow rate of 151 liters/minute. The average
  temperature of the copper is 84oC, while the back iron temperature is
  61oC.

Sources:

EMALS/ AAG: Electro-Magnetic Launch & Recovery for Carriers
Electromagnetic Aircraft Launch System - EMALS
Steam catapult types
Electromagnetic Aircraft Launch System - EMALS - NAWC


What exactly is "plunge?" I'm doing a project in which i'm attempting to model the motion of a wing using a system of second order differential equations. This is a 2-degree-of-freedom model based on the quantities pitch, a(t), and plunge, h(t). I know what pitch is, but what is plunge? and why is it affected by pitch? Where do these equations come from?

This looks like a flutter system of a representative wing section. Plunge is the vertical degree of freedom as shown in the diagram below (the other degree of freedom is pitch, $\theta$ or $\alpha$ in your assignment). You also have structural damping terms, which are omitted in the diagram.

Image ref: https://www.researchgate.net/figure/Sketch-of-airfoil-aeroelastic-system_fig1_313820106


Can you have TCAS RA if your other traffic only have TCAS TA? If you fly and have a TCAS TA, it announce "TRAFFIC, TRAFFIC!"

However, the other traffic executed a TCAS RA and did the "UNKNOWN" manouvre.

Is it possible? As what i remember, it does takes two aircraft in RA mode. Unless you selected TA MODE ONLY.

Please give me reference about this.

Thank you

If both aircraft in an encounter are equipped with TCAS and are operating in TA/RA mode, then both will receive a coordinated RA.  That is the RA will be coordinated between them using the Mode S datalink.

If both aircraft in an encounter are equipped with TCAS and one is operating in TA/RA mode and the other in TA Only mode, the one operating in TA/RA will receive an uncoordinated RA and the other will receive a TA. In an uncoordinated RA, the TCAS will provide guidance based on the observed path of the aircraft, modifying the RA as necessary.

If one aircraft in an encounter is equipped with TCAS and operating in TA/RA mode and the other in does not have an operating TCAS, but does have a transponder, the one operating in TA/RA will receive an uncoordinated RA.

There's a good guide to TCAS available from the FAA web site.


How should the pack flow knob be set on an Airbus A320? On the Airbus A320 there is a pack flow knob and you can select LO(80%), NORM (100%), or HI(120%) according to the number of passengers and ambient conditions. Someone told me you select LO if there is less than 115 passengers HI if it is abnormally hot and NORM if everything is casual.

Do both numbers of passengers and ambient conditions have to be met to select LO,HI, or NORM?

For example, obviously if it is above 100 degrees Fahrenheit you would select HI, but what if it is in the 90s or high 80s? Is there a specific temperature or is it option based?

No. Assuming there are no regulations, you can set it anyway you want, at an expense of fuel consumption.

Do not confuse Ventilation control with Temperature control. Temperature control is another setting. (via Cockpit overhead/FAP)


American Airlines Astrojet - is it really 'polished aluminium'? I came upon this article, referring to American Airlines' roll-out of a 737-800 in their Astrojet livery. In the article it describes this as 'polished aluminium'.

(Photo supplied by American Airlines)

This got me to wondering:

Is this actually polished aluminium, or has some sort of clear lacquer been applied?

If it is polished aluminium,

What is the impact of exposing the airframe to the elements, rather than protecting it with a layer of paint?
What benefits might accrue from this in weight-saving, fuel burn, etc.?

Yes it is polished aluminium.
On the 737 in your photo, the weight difference with a fully painted plane is about 70 kg, and this yields operating cost savings of about USD 60,000 per year in 1998 dollars, about equal to USD 88,500 in 2016 dollars.
The paint coat is repainted every couple of years, the aluminium polish must be re-buffed 3 times per year.
From the same Boeing document:

Polished surfaces are protected from corrosion by regular buffing
after washing. Painting protects against oxidation, salts, and jet
fuel spills. However, unrepaired chips and cracks in paint collect
dirt and moisture and so may become corrosion sites. Painted surfaces
are also susceptible to filiform corrosion, or worm corrosion, which
begins between metallic surfaces and paint and erodes both. It creates
hydrogen and lifts up the paint layer as it travels across the
surface.

Also, the paint protects against small scratches from sand etc which may start fatigue cracks, however since the polished skin is very closely scrutinised during the re-polishing that is not really an issue.


How common is it for flight attendants to have pilot certificates? When looking up some information for the recent question Have there been any solo flights on airliners?, I found this article that lists several incidents in which a pilot has become incapacitated in flight. One thing that I found particularly surprising was that, in two of the six specific incidents they mention, the person who helped the remaining pilot for the remainder of the flight was actually a flight attendant who had a pilot certificate. This then made me wonder:

How common is it for an airline flight attendant to also be a certificated pilot?

In my experience, it is uncommon but certainly not unheard of. Maybe between 1% and 5%, as a ballpark.  A flight attendant married to a pilot who owns his own aircraft has access to the plane and instruction, so that's one scenario. In another case, an F/A I flew with a few times was building time as a CFI and doing right-seat work at SimuFlight, before she left our airline to start with a regional. (Wouldn't be at all surprised if she's flying at a major right now.)

Among flight attendants, there are a lot of really interesting stories of how they got to be where they are. Sometimes the generalizations fit, but when they don't, you find an amazing breadth of experiences in that group.


Can I fly under a solar eclipse to lengthen its effect? There is going to be a solar eclipse in 2017 and I thought it would be cool to fly along its path to make it longer than the approximately two and a half minutes you would see on the ground.

Is this a bad idea?

Should I go to fast or slow for the solar eclipse?

I think it would be fun to fly during the solar eclipse, even if I can't keep pace with it.

The speed at which the shadow of the Moon crosses the Earth varies according to time of day and latitude. However, 1500mph is a good starting point.

The only supersonic commercial aircraft to enter service was Concorde, top speed around 1350mph. And, of course, Concorde is now out of service.

Flying something subsonic along the path of totality will give a longer view, but most airliners top out at around 600mph.

You've really no chance of keeping up with it. You're probably better off finding a spot with a good view and enjoying your 2.5 minutes!

Nasa have a range of materials dedicated to this. If you fancy a little mental gymnastics  take a look at https://eclipse2017.nasa.gov/challenge-5-%E2%80%93-estimating-speed-lunar-shadow. In particular, download the PDF worksheet and do the maths!


What sort of control mechanisms (i.e., PID controllers) do modern FBW aircraft use? It's a well-established fact that aircraft like the Boeing 777, and all Airbus passenger aircraft that were designed after the A300, feature a digital fly-by-wire control system. Considering the Boeing 777 as an example, the pilot flying applies force onto their yoke and one of the flight computers (I'm not aware of the architecture(s) of Boeing FBW systems) interprets the input and changes the control surfaces of the plane accordingly.

I am wondering what control paradigms are used by Boeing and Airbus to translate pilot settings (i.e. trim), accelerometer and gyroscope data from the IMU, and feedback from the aircraft's control surfaces to re-adjust said control surfaces.

Would a simple PID controller suffice? If so, how would a single PID system be able to manage feedback data from different sources (i.e. how could a PID system handle feedback from a gyroscope and Airbus side stick at the same time)?

I understand that the accuracy of PID systems are fully dependent on the feedback they receive, so I would assume that software methods of error correction like Kalman filter would be employed. However, how can computer hardware from the 80s (such as the Intel i386) be able to sample data quickly and compute Kalman filter within acceptable response times?

I appreciate all answers, and I apologize if my questions require analyzing proprietary technical documents.

As others have commented, you've underestimated how fast an Intel 80186 found on an early A320 is. Its clock rate is 6 MHz to 25 MHz. While it's very slow compared to what's available nowadays, that's still 6-25 million cycles a second.

The A320's first flight was in 1987, here's what the Air Force Flight Dynamics Laboratory had to say about the subject (Theory of Closed Loop Flight Control Systems) 20 years earlier:

  The electronics field has miniaturized even more so. Microelectronic circuits enable mixing, blending, voting, and, in general, response shaping to be done on a relatively small number of easily replaced cards. Metal oxide semiconductor (MOS) techniques decrease the size of these components by several orders of magnitude. Using these techniques it is now possible to redundacize electronics at a functional module-level with a resulting decrease in size, weight, and cost and a net increase in system reliability.

For modern aircraft, say an A380, we're looking at 40-98 MHz computers:

(Cranfield University, 2016)


What is the reasoning behind this question about the correct altitude to avoid clear icing? This question has been killing me for a while and it's an original PPL question:

You are approaching to an airmass with a temperature of 6 C at
10000ft. Which altitude should you be in order to avoid clear icing?
A) 14000ft
B) 12000ft
C) 6000ft
D) 9000ft

The answer is C and I have no clue why.

As John K already said in the comments, the definition for icing conditions is visible moisture at a TAT of less than 10°C. From the Boeing 737 NG FCOMv1 (SP.16.1 Supplementary Procedures - Adverse Weather):

  Icing conditions exist when OAT (on the ground) or TAT (in-flight) is 10°C
  or below and any of the following exist:

  visible moisture (clouds, fog with visibility less than one statute
  mile (1600m), rain, snow, sleet, ice crystals, and so on) is present,
  or
  ice, snow, slush or standing water is present on the ramps,
  taxiways, or runways.

To avoid icing, you should descend to an altitude where the temperature is above 10°C. The standard lapse rate of the atmosphere according to the International Standard Atmosphere (ISA) is 2°C per 1,000 ft:

  As an average, the International Civil Aviation Organization (ICAO) defines an international standard atmosphere (ISA) with a temperature lapse rate of 6.49 K/km (3.56 °F or 1.98 °C/1,000 ft) from sea level to 11 km (36,090 ft or 6.8 mi).

This would result in the following expected temperatures at the given altitudes:

A) 14,000 ft: -2°C
B) 12,000 ft: 2°C
C) 6,000 ft: 14°C
D) 9,000 ft: 8°C

This only leaves answer C) with a temperature above 10°C and therefore outside of icing conditions.

Note: The lapse rate of 2°C per 1,000 ft is only an average, the actual lapse rate could be somewhat different. Wikipedia says:

  A typical value is around 5 °C/km, (9 °F/km, 2.7 °F/1,000 ft, 1.5 °C/1,000 ft).

Maybe the question assumes a lower lapse rate of 1°C per 1,000 ft, where an altitude of 6,000 ft is exactly where you would get 10°C.


Steep turn: do we need rudder once we rolled into a bank angle? Say a Cessna 172 is in a cruise level flight and clearing turn is just finished. I barely feel a left-turning tendency during the level flight (Maybe torque and slipstream are less significant).
I understand that we should use the rudder simultaneously when rolling into a bank attitude (45 degrees-ish) and then add more power + apply back pressure on the elevator.
But once we've entered into a bank, do we still step on the rudder to stay coordinated? For example, I'm making a left steep turn. After I've rolled into a bank attitude and start turning, do I still need to step on the left rudder?

No.  You use the amount of rudder needed to keep the ball centered. No more no less.  Most of the rudder requirement is to correct for adverse yaw, and is only required while the aileron is being applied.
If you are in a steep turn, you may find you need to apply aileron out of the turn to hold the bank angle if the airplane has a tendency to "overbank".  You might need to apply "top rudder" in this case, but only because adverse yaw from the top aileron will be making the nose yaw toward the turn and the top rudder is needed to align the tail with the nose in the airflow, to keep the ball centered.
The muscle memory activity that needs to be ingrained is left aileron, left rudder and right aileron, right rudder, depending on how bad the adverse yaw is, taking out the rudder input with the removal of the aileron input, with adjustments as required.  Your feet should just be squeezing this way or that way to center the ball, period.
Elevator/power (and aileron) is the only tool for altitude/attitude control in the turn (by "and aileron" I mean that once bank gets really steep, top aileron is often necessary to prevent the elevator application from just steepening the bank and tightening the turn - if you are targeting a 45 deg bank, this should be instinctive and you will be applying top aileron as required without thinking about it).
Use of "top rudder" rudder to prevent the nose from dropping, as opposed to just keeping the ball centered, is a cross control maneuver that results in a slipping turn (the ball will move to the low side), and if you stall out in a slipping turn, you will roll over the top as the outer wing stalls first and start to spin.  Many pilots have been killed by using "top rudder" as attitude control while turning to final and finished their lives right there.
I should also note that you can use a slipping turn to lose altitude on the turn to final, so you are in fact cross controlled with into turn aileron and top rudder, but this is a special altitude loss maneuver where you are making no attempt to maintain pitch attitude or altitude, just letting the nose fall through.  Done properly, there is no stall risk when doing a slipping turn (you aren't pulling and in fact you might actually push a bit), as can happen if doing a level steep turn.
So don't overthink it.  Just use your feet to keep the ball centered at all times unless you are side slipping on purpose, and get yourself into the automatic habit of squeezing left rudder with left aileron input and right rudder with right aileron input, and no rudder with no aileron input (but making applications as necessary if the ball drifts off).  A 172 needs very little rudder application to maintain a coordinated turn so it should just be little squeezes of rudder.
If you learn to fly gliders, where LOTs of rudder is needed to do the same thing, these actions become well ingrained because you have to, to get the damn thing to fly straight at all, which is why I always recommended learning to fly in gliders first.


How are performance classes for helicopters/rotorcraft defined? In helicopter/rotocraft literature, such as ICAO Annex 14 Volume II (how to design heliports), there's constant references to performance classes. How can I tell what performance class a helicopter is in?

So far the only definition I have found is: in the event of engine failure, Performance Class 1 helicopters should be able to land within the rejected take-off distance available or continue safe flight, while Performance Class 3 will require forced landing. (https://www.casa.gov.au/standard-page/project-os-1124-incorporation-performance-class-concepts-australian-helicopter).

This is hard to apply to helicopters where I only have some basic specifications. Are there any other, easier to use, definitions for performance classes? I'm hoping for something like runway codes for aerodromes, which are derived from landing distances and wing spans of aircraft that use the runway.

Multi-engine helicopters have 3 Performance Classes defined at certification that is related to single engine performance and how this affects follow-on risks following an engine failure.

Class 1 helicopters have massive reserve power and can continue flight on one engine.  They have engines that are way larger than necessary for normal operation and normally operate at a fraction of their power potential until called upon to do it all.  Risks following engine failure are low.

Class 2 helicopters have somewhat less reserve power, and can continue flight temporarily on one engine, but not indefinitely.  Risk factors are higher.

Class 3 helicopters have little reserve power and are generally forced down when one engine fails, although at a much gentler descent rate than an autorotation. Risk factors are highest.

I was looking for a link that provides a good detailed description but haven't had much luck.


Can gliders access restricted airspace? If I recall, in America there were several "Prohibited Access" airspaces and others required permission, via radio, to enter in a typical aircraft. But, what if I'm gliding over a restricted airspace? (Say, over the Capitol?). Would I be shot down (or fined, sued, etc.)?

Since gliders have no engines, they are often permitted to operate under special agreements called Letters of Authorization, which permit them to operate where other aircraft may not. These agreements may permit them to fly VFR in Class A airspace to capture mountain wave lift, through TFRs, through Restricted airspace, depending on the terms of the agreement with the FAA.

In particular, in the airspace you mention near the Capitol, there is a TFR Waiver in force which permits gliders to operate within the Capitol TFRs.  This Waiver supersedes the TFR rules and the associated NOTAMs. Furthermore, it permits gliders to even thermal inside the TFR if necessary for safety of flight.


What is the difference between a shock wave and an expansion wave? Studying high speed aerodynamics I have found a question asking for what happens to static temperature for an airflow passing through an expansion wave.
The correct answer states that it decreases- the opposite of that on a shock wave.
What is the difference between these two waves that makes them contraries?

An adiabatic expansion lowers temperature, an adiabatic compression raises temperature, analogous to the way a refrigerator and an air conditioner work. Or a bicycle pump, it gets quite hot while you're pumping air.

A shock wave compresses air - at supersonic speeds the object travels faster than the pressure information, and when the object arrives at a bit of air it compresses suddenly in a shock wave, with corresponding higher temperature.


Why is the 737’s aileron/spoiler authority reduced at low flap settings? According to the NTSB report on the crash of United Airlines Flight 585, the ability of the 737’s lateral controls (ailerons and flight spoilers) to counteract the rolling forces produced by (say) a rudder hardover is considerably worse at lower flap settings, such that, in some cases, a hardover occurring with the airplane’s flaps fully extended might produce only minor control difficulties, whereas the same malfunction occurring with the flaps at (say) the ten-degree setting would result in a loss of directional control (pages 60-61 of the report; pages 78-79 of the PDF file of the report):

...Flap position and airspeed are important when determining controllability during a rudder hardover condition. With the rudder at about 25 degrees airplane nose right (ANR), the following conditions would exist at 150 to 160 knots calibrated airspeed (KCAS). Bank angles are noted as left or right wing down (LWD, RWD) and provide constant heading trim solution (no turns), except for the last case.
Rudder Angle …… Flaps …… Side Slip Angle …… Wheel Angle …… Bank Angle
25 ANR …………… 40 ……… 14 ANR ……………… 35 LWD ……… 18 LWD
25 ANR …………… 30 ……… 15 ANR ……………… 44 LWD ……… 17 LWD
25 ANR …………… 25 ……… 15 ANR ……………… 68 LWD ……… 16 LWD
23 ANR* ………… 15 ……… 17 ANR ……………… 107 LWD ……… 23 LWD
21 ANR* ………… 10 ……… 16 ANR ……………… 107 LWD ……… 19 LWD
25 ANR** ………… 10 ……… 13 ANR ……………… 107 LWD ……… 40 RWD
* Less than full rudder allowed to maintain directional control.
** Loss of directional control.
At 10 and 15 degrees of flap setting, heading cannot be maintained with full rudder deflection. If full right rudder is achieved with a 10-degree flap setting, for example, heading control is lost and, according to Boeing, a steady 40-degree right-wing-down trim solution is attained that results in turning flight to the right even with full left wheel deflection...

Why, for a given airspeed, do the 737’s lateral controls become increasingly ineffective as the flaps are retracted?

Okay, turns out this wasn't so different from the crossover-airspeed question after all!
To quote @PeterKämpf's answer to that question:

how can [an airplane’s ailerons and spoilers] lateral control authority surpass that of the rudder past a certain speed?

This depends on the wing's lift coefficient. At a higher lift coefficient the lower aileron can not add the same amount of lift that it could at a lower lift coefficient. While the raised aileron on the opposite side will still reduce lift locally, the lowered aileron becomes less effective in raising lift as the lift coefficient increases. A higher lift coefficient causes a higher suction peak near the leading edge and puts more stress on the boundary layer, and adding more of the same will become harder as the wing approaches stall conditions.
Another factor is adverse yaw which increases with lift coefficient. This adverse yaw will add to the yawing moment of the hard-over rudder and will increase sideslip, which in turn will produce more rolling moment from dihedral against the aileron effect. As adverse yaw dies down with lower lift coefficient, so does sideslip angle and the ailerons gain control power.

Which also explains why the 737's crossover airspeed is lower with flaps down; when the flaps are up, the aircraft has to fly at a higher angle of attack in order to generate the same amount of lift at the same speed.  This increases the lift coefficient over the entire wing, including the outboard portion where the ailerons are mounted, which makes the downwards-deflected aileron, to use Peter Kämpf's terminology, "less effective in raising lift", and increases the adverse yaw generated by the deflected ailerons.  All of which decreases the roll authority of the ailerons, and, since the spoilers' roll authority can't increase to compensate, decreases the roll authority of the aircraft's lateral controls as a whole.
With the flaps down, on the other hand, the lift coefficient of the inboard wing increases, which means that the rest of the wing doesn't have to generate as much lift, which means that the aircraft can fly at a lower angle of attack for a given speed, which decreases the lift coefficient of the outer, flapless, aileron-containing section of the wing, which increases the effectiveness of the lowered aileron and decreases the adverse yaw generated by the ailerons, which increases the aircraft's roll authority.


Could modern military aircraft be retrofitted to work with alternative fuels instead of kerosene? I am geologist and I have heard in 50 years petroleum will be nearly gone.
I know for commercial planes there are working projects with clean energy.
I can be wrong, but I think military systems would fail with no kerosene maybe in 30-40 years, as petroleum is becoming much more expensive to extract and its quality is falling.

So I wonder what's the sense of buying military appliances at 2018.
I don't know if kerosene is being stored by the armies, but I wonder if it is just a madness to give the reason for increasing military budget.

I am asking also what is the future for fighter planes etc. When petroleum is finished, is there any possibility to create technology that works with nuclear energy or so or this is the end of war?

Petroleum isn't going to be finished for a very long time. We keep discovering and accepting trickier, dirtier, and/or costlier ways to get more oil - shale is just the last step in a long chain.

Yes, planes could be altered to use other fuels such as biodiesel. It has been done. This will require changes to the fuel system, to handle such considerably more contaminated fuel, increased fuel heating, possibly combustor alterations.

However, on a practical basis, it only makes sense to start replacing aviation fuels en masse once most road vehicles have switched to a different fuel. Aviation is weight-critical and an energy-dense fuel matters; it's also a smaller consumer than road vehicles. Also, aviation's safety and maintenance requirements call for cleaner and more consistent fuels than acceptable on the road.

For the military, fuel consumption and costs have traditionally been considered less important. It's going to get the fuel its jets need, since there will be plenty available for the foreseeable future.


Are Sophisticated Planes with Multiple Computer Interfacing Safer to Fly than Traditional Aircraft? I passenger travel short haul flights to the carribean islands every month for business. I typically fly on an Embraer E190 or Airbus-320...I feel confident on the 190, I suppose I like the standard control wheel/yoke and  from a craft size and technology level standpoint, it just feels like a manageable piece of equipment. But on the Airbus, I just can't warm up to the joystick control. It doesn't seem natural; which provokes my question.

Given that all pilots are simply human, how in the world is it possible to have a comprehensive knowledge of all of the sophisticated computers and electronics that are required to interface to fly a plane safely? It seems to me that in truth, pilots have just enough knowledge to operate these new planes and systems under normal conditions and the moment a malfunction occurs it becomes a race to a safe landing with only troubleshooting guides to help understand what is happening and try to offset it long enough to get the plane safely of the ground.

This is a broad stroke assumption, but it seems that the simplest of a breach can affect the operation of another and pilots are reduced to a guessing game to keep systems operating normally; which is not very comforting. Isn't it better just to get back to the basics and avoid these overly complex computers?

how in the world is it possible to have a comprehensive knowledge of
  all of the sophisticated computers and electronics that are required
  to interface to fly a plane safely?

The same way you learn about any aircraft, you study the operational manuals and related documentation. In theory aircraft that use the airbus fly by wire system are safer as they offer protection against the pilot inadvertently putting the aircraft into a dangerous situation (high G, stall, etc.).

I think that there are some misconceptions in your question about the required training for flying something like an A320. Pilots are required to know how the aircraft will respond in all situations and the errors and messages the computer may throw at them. This is no different than understanding what a tumbling mechanical attitude indicator is doing or how to identify a bad analog instrument. Broadly speaking failures are failures and identifying them has more to do with situational awareness, understanding of your systems, and to some extent experience. Digital cockpits merely change the text and pictures in the books but still require the same basic fundamentals to identify a failure.

Some might also say that analog cockpits are more complicated than their digital counterparts. So much so that jets that once required a crew of 3 in the analog days can now be flown by two.

  It seems to me that in truth, pilots have just enough knowledge to
  operate these new planes and systems under normal conditions and the
  moment a malfunction occurs it becomes a race to a safe landing with
  only troubleshooting guides to help understand what is happening and
  try to offset it long enough to get the plane safely of the ground.

Pilots do not have just enough knowledge and frankly that is short changing the vast amount of hours required to be in command of even an A320. Pilots train in full motion simulators for all kinds of emergencies so that when the time comes they only need a quick reference card to get the plane safely on the ground.

Digital aircraft are not necessarily kaput if one thing fails and systems are designed such that a failure does not cause down stream effects. Systems often can independently be shut off and pulled out of sequence in the event of a failure. On top of that there are lots of failure modes (even in the side stick planes) that allow for all kinds of direct control.

But how does this all tie into a plane being safer...

The FAA main advice in any emergency is to "fly the plane" most training stresses (and most accidents cite a lack of) "Situational Awareness" so if we can provide a cockpit that offers a pilot more information on how the plane is flying, where they are, and whats going on we can make it easier to fly the plane and maintain your situational awareness in any event (even if some systems are failing). That all trickles out, ultimately, to a safer plane.


What does the term "white-scarf Air Force" mean? Ron Gordon's answer to question about A-10 cannon mentions "white-scarf Air Force". As civilian, subtlety was lost on me. What does it mean? From the context, looks like fighter pilots? Are the scarves of other colors, and what they are?

In particular:

  "The white-scarf Air Force has an averse to building flying tanks and particularly doesn't like single-mission, CAS systems. They never will forget that the A-10 was forced on them."

A white scarf air force is one that values aircraft above all else (space-, cyber-, missile-warfare, etc.), i.e., an air force that is unwilling to evolve beyond flying planes.
Similarly for not embracing RPVs (remotely piloted vehicles).

Dealing with RPV pilots will probably be a little more difficult. The conventional wisdom is that pilots don’t like RPVs because they take the human out of the sky and stick them on the ground, what Thomas Ehrhard calls the “white scarf syndrome” (in homage to the scarves worn by World War I and interwar aviators).
The reason RPV projects fail, the syndrome claims, is that the Air Force starves them to avoid competition with its manned aircraft (source).

How that fits in the comment about the A-10 and close air support aircraft, I don't know.
The term refers to WWI pilots who wore white scarves—the tradition carried on beyond WWI. In WWI the silk scarves had a purpose: it's smooth so it does not chafe the skin when looking around, it keeps the pilot warm in the open-cockpit, and it's used in cleaning the oil and rain off the goggles—bright colors are good since you know which part is clean and thus can be used (source).
That's also why Snoopy is stylized with a scarf.
(Source) WWI pilot attire.

Although in the past the dominant operational perspective was centered on a specific system or aircraft type (bombers or fighters), the future will need to be centered on a capability not necessarily connected to a specific airplane type of mission (i.e., to be centered on synergistic-operations). This transition will be difficult in that the very nature of the Air Force has always been to focus on flying aircraft. However, as history has shown and as technology has advanced, the need for and appropriateness of manned flight as the primary USAF focus has diminished.
As a service, we have rightfully transitioned to thinking about cont rolling “domains” rather than the toys used to control them. Those in the USAF unable to separate themselves from their flying machines will eventually become relics and will he replaced by a new generation of “airmen” whose understanding regarding the depth and breadth of airpower goes well beyond aircraft and instead focuses on how best to advantage war-fighting domains (air, space, cyber). However, as Builder suggests,

as the Air Force is compelled in the near future to reduce its force structure under the pressure of budget reductions, there will be a strong tendency to preserve those forces which have dominated the mission spectrum in the past rather than those which might dominate in the future. To be explicit, there will be a natural tendency to preserve the fighter and bomber forces at the expense of the supporting forces . . . this tension between institutional proclivities and perceptions of the future illustrates the importance of the latter to the evolution of air power theory.

In this regard, the greatest challenge that the USAF must overcome is its inability to focus on the ends rather than on the means. When the USAF finally realizes that it greatest strength comes from its ability to take advantage of all elements within the airpower domain (air, space, and cyber, and not merely on a particular system, that is when the USAF will have obtained a level of maturity capable of sustaining its operations without fear of continual, periodic change. This long-view transition will require the USAF to force itself out of “white scarf syndrome,” where the means (flying aircraft) are more important than the ends of providing the nation with the greatest possible amount of airpower options. Unfortunately, if the USAF continues to rationalize its existence under the pretense of decisive operations, continually strives to prove its independence, and views its primary mission in terms of the aircraft it flies, then its future validity and relevance is questionable.
— Tomorrow's Air Force: Tracing the Past, Shaping the Future (2013) p. 221


What medications may pilots take while flying? We all get sick, suffer from allergies and sometimes chronic issues.  It is not safe to fly while on some medicines or in some cases, for some time after taking the medicine.

How do I know what I can take and still fly?  What resources are out there to check if a specific medicine is compatible with flying (AOPA, FAA, etc)?  Is there a comprehensive list of what I can and cannot take?

AOPA has the best database that I know of, but you have to be a member to view it.  They have some free information on their Medications page though.

There they talk about FAA Policy, and it starts with:

  The Federal Aviation Regulations include no specific references to
  medication usage. FAR 61.53 prohibits acting as pilot-in-command or in
  any other capacity as a required pilot flight crewmember, while that
  person:

  Knows or has reason to know of any medical condition that would make the person unable to meet the requirement for the medical certificate
  necessary for the pilot operation, or:
  Is taking medication or receiving other treatment for a medical condition that results in the person being unable to meet the
  requirements for the medical certificate necessary for the pilot
  operation. Further, FAR 91.17 prohibits the use of "any drug that
  affects the persons faculties in any way contrary to safety."

AMAS (Aviation Medicine Advisory Service) also has a list (which is free) but I don't think that it is organized as well.  They are recommended by ALPA and NBAA though.

The most important thing though, of course, is to self evaluate and make sure that you don't fly if you are having any adverse reactions from the medication, or the underlying condition that you are taking the medicine for.

Any list that you consult has to be used only as a guide though, and not a carte-blanche approval.  Individual people can have reactions even to medications that are considered "safe" and "allowed" by the FAA, and this is why they don't list specific medications that they allow.  The FAA has a brochure called Medications and Flying, and one part of it has a few things to consider before taking any medication:

  First, consider the underlying condition  that you are treating. What
  will be the  consequences if the medication doesn’t work  or if it
  wears off before the ﬂight is over?  A good general rule to follow is
  not to ﬂy  if you must depend on the medication to  keep the ﬂight
  safe. In other words, if the  untreated condition is one that would
  prevent  safe ﬂying, then you shouldn’t ﬂy until the  condition
  improves — whether you take the  medication or not.

  Second, you must consider your reaction to  the medication. There
  are two broad categories  of medication reactions. One is a unique
  reaction  based on an individual’s biological make-up.  Most people
  don’t have such reactions but  anyone can, given the right medication.
  Because  of this, you should NEVER ﬂy after taking any  medication
  that you have not taken before. It  is not until after you have taken
  the medication  that you will ﬁnd out whether you have this  uncommon
  and unexpected reaction to the  medication.

  Third, consider the potential for adverse  reactions, or side
  effects — unwanted reactions  to medications. This type of reaction is
  quite common, and the manufacturer of the  medication lists these on
  the label. You MUST  carefully read all labeling. If you don’t have
  access to the label, then don’t ﬂy while using the  medication.

  Look for such key words as lightheadedness,  dizziness, drowsiness, or
  visual disturbance. If  these side effects are listed or if the label
  contains  any warning about operating motor vehicles or  machinery,
  then you should not ﬂy while using  the medication.

  Side effects can occur at any time, so even if  you’ve taken the same
  medication in the past  without experiencing side effects, they could
  still  occur the next time. For this reason, you must  never ﬂy after
  taking a medication with any of  the above-noted side effects.


What is a "Flight Director"? What is a Flight Director, and how does it differ from Autopilot?

The flight director is related to the autopilot system. It displays a guide on the artificial horizon, which shows the attitude of the airplane, but does nothing to control the plane. The guide represents a reference of an airplane attitude that will follow the parameters set for the autopilot. The pilot can manually fly the plane directly where the flight director indicates, and by doing so the plane will follow the parameters set for the autopilot.

If the autopilot is engaged, autopilot flies the plane to follow the flight director. The flight director serves as a visual indication of where the autopilot wants the plane to go. Although a flight director typically accompanies an autopilot system, some aircraft have a flight director without an autopilot.

The procedure to engage them is to first turn on the flight director, which will show where the autopilot wants the plane to be, and then to engage the autopilot, which will then automatically fly the plane.

This is what the autopilot controls can look like.

Here is the Boeing flight director, visible as the crossed magenta lines in the center of the screen.


How do you calculate total drag on a wing? I'm not an aeronautical engineer, but I am making a brave attempt to perform a preliminary design for an 4-metre wingspan radio controlled glider. With special thanks to @mns I have now learned a formula for calculating the coefficient of induced drag. The question now is how do I use it to calculate total drag.

Considering the formula below, how do I make a reasonable estimation of efficiency factor (e)

I've selected a prismatic inner wing with tapered outer wing to assimilate an ellipse? I understand that they state that (e) for a perfect ellipse is 1. What is 0 then, a square? Here is my wing planform:

They then state that I should add CDi to CD0 to offer me a total CD.

The question I ask now is why add CD0 (That is CD at 0 degrees AoA if my angle of incidence (setting angle of the wing) is 6.25 degrees?

I assume that I then run this through the lift formula to get drag in newtons.

The curve for CD / Alpha can be seen here

Typical values of e are between 0.7 and 0.98 in subsonic flow, and 0.3 to 0.5 in supersonic flow. Since it is in the denominator, e cannot become 0 or drag would be infinite. A square wing has an e anywhere between 1 (with aspect ratio close to zero) and 0.8 (with high aspect ratio and away from the design point for the twist distribution)

As a rough first-order assumption, the zero-lift drag coefficient is constant over the moderate AoA range when the flow is attached over the full chord. This drag is the sum of friction (shear forces tangential to the wing surface) and pressure drag (caused by pressure on the backwards-facing sections being lower than on the forward-facing sections of the airfoil, again due to viscosity).

Of course, once you have a full airfoil polar, your results will be more precise if you use the particular value of the drag coefficient at the specified angle of attack. However, sometimes you will need to calculate lift and drag without knowing the angle of attack, and then you fall back to the first-order approximation. For an example where this assumption is useful please read this answer.


What are the speeds for absolute ceiling and coffin corner? This picture is taken from Safety First (Airbus magazine). Could you please clarify some things:
1). Is "Absolute aerodynamic ceiling" = "Coffin corner"?
2). Have I correctly understood that there is no "Absolute Ceiling" (ROC=0) in this diagram?
And a question that doesn't relate to this particular picture. At absolute ceiling we can fly at only one speed. This is the speed which corresponds to intersection of power available and power required curves? And what is that speed at which flight at Coffin Corner is only possible?

At absolute ceiling we can fly at only one speed. This is the speed
  which corresponds to intersection of power available and power
  required curves?

The "intersection of power available and power required" is anywhere along the left hand edge of the red cross-hatched area. The absolute ceiling is the intersection of the stall curve (left-most red line) with this power limit.

  And what is that speed at which flight at Coffin Corner is only possible?

Coffin corner in that chart should be the intersection of the red stall line with the black MMO/VMO line.

I say 'should be' because the stall line is drawn with a maximum at the  "absolute aerodynamic ceiling" i.e. the plane stalls if it goes any faster or slower. Stalling when going faster must be due to increased Mach number.

In other words, the right hand side of the stall line is actually the maximum Mach number, which would make the "absolute aerodynamic ceiling" 'coffin corner'.

I suspect the confusion is that they wanted to draw MMO as a (mostly) straight line, and didn't think it mattered because the plane doesn't have the power to reach that region.


Cross Country flight: what do I have to consider concerning radio communications? I'm tasked with developing part of a cross country flight plan to cap off my ground school class. Among my group, I am handling the radio communications and regulations. However, I was not provided further details, and came here to gain a greater understanding of what I need to accomplish. Specifically, the trip is to fly from Aspen, fly by Capital Peak for the view, and then land in DIA (KBDU-KASE-KDEN).

As far a radio communications go, I imagine I need the frequency of each of the listed airports, but is there anything else I need to consider?

Edit: Further Information:

I'm flying N370SP, a Cessna 172S Skyhawk SP. I pick up friends (190, #320) and luggage (35, #60).

There are three categories of radio communication to deal for each leg of a flight:

arrival and departure airport: tower/CTAF, ATIS/ASOS/AWOS, Ground/Clearance Delivery
En route ATC: arrival/departure, center
En route weather and information: Flight Service, Flightwatch, HIWAS, en-route ATIS

You have to decide which of these services you will interact with, and know where to find the frequencies (almost always a chart or the A/FD) and how to contact each of them.


Why are there no cargo aircraft with "flying wing" design? From that I have seen so far, the "flying wing" design (like the one of B-2 Spirit and Northrop YB-49) has superior performance but also a few notable problems that make it difficult to use for passenger aircraft:

It is difficult to control, and the YB-49 crashed even when flown by an elite test pilot. However, computer assistance has been implemented for B-2 and I do not think this is a problem any longer.
There are problems related just to the passenger transport: not enough windows, difficult to evacuate.
It also cannot be pressurized as easily as a cylinder but for a majority of possible cargo this is probably not a problem. Some cargo may not require pressurization at all and some may only need partial pressurization like in jet fighters.

Hence I understand that there are problems on the way to the flying wing passenger aircraft. However, why there are no cargo aircraft of this kind around?

Flying wings can be made to have acceptable flying qualities without any artificial assistance.  Just look at the Jim Marske glider designs.

The principal downfall of flying wings is that stability in pitch is pretty much achieved the same way as with a conventional tail, with a down force balancing out the center of gravity forward of the fulcrum of neutral point of the lifting forces, but it's all being done over the very short moment arm of the wing chord itself.  In other words the "tail" has been moved forward to the trailing edge of the main wing.

There are a lot of issues that result from this, pitch sensitivity and damping issues and all that, but the biggest one from a cargo aircraft's perspective is a very narrow center of gravity range.  Not a big deal on a bomber with a concentrated bomb bay load, or a glider that doesn't have to cope with loading variations, but a bigger deal on a freighter.  You are forced to spread the load, and the fuselage volume, laterally, creating way more frontal area than necessary (you're in effect turning the fuselage sideways), so you end up cancelling out the drag benefit of doing away with the tail in the first place, and still end up with a "temperamental" configuration.


What is the proper ICAO phraseology to activate a flight plan? OK, so you have a flight plan filed (over internet, phone, company or however), go to the aircraft and get in the cockpit. So you call the controller and request IFR or VFR as appropriate.

What is the recommended wording of the request and how it is actually pronounced? Is “IFR” spelled, like “requesting eye-eff-are”, using phonetic alphabet like “requesting India Foxtrot Romeo” or expanded like “requesting instrument flight rules”?
Should you add the destination or other description of the plan? The ATC already has it, but it might serve as a check.
Do you call only when you are almost ready for start up or push back, or earlier in the preflight? And if earlier, do you also add some indication when you will be ready?

I'm asking about both VFR and IFR flight plans.

The UK CAA Radiotelephony Manual (CAP 413, Edition 22, May 2016) has an example of how to activate a flight plan in chapter 3, section 3.36 (page 92 in the PDF).

  Aircraft G-CD, departed Seton at 38 request activate flight plan
  ATC G-CD, departure time 38 will activate flight plan

There is no indication whether this is for VFR or IFR flight plans, so it should apply to both if a filed flight plan wasn't activated at departure.

I also pulled out my (fairly recent) radiotelephony textbook, which covers EASA up to and including PPL including in English (and thus should be pretty close to the official ICAO phraseology), to double-check what it says. (I don't often fly with an actual flight plan active.)

  Aircraft ATC callsign, aircraft callsign
  ATC aircraft callsign, ATC callsign, go ahead*
  Aircraft aircraft callsign, activating VFR flight plan, departed airport, hour hour minute minute, to destination airport
  ATC aircraft callsign, activating VFR flight plan, hour hour minute minute
  Aircraft aircraft callsign

For example, Smallprop 123 flying VFR in airspace controlled by Somewhere Control, with a previously filed but not yet activated flight plan:

  Aircraft Somewhere Control, Smallprop 123
  ATC Smallprop 123, Somewhere Control, go ahead*
  Aircraft Smallprop 123, activating VFR flight plan, departed Hometown, one two tree five, to destination Springfield
  ATC Smallprop 123, activating VFR flight plan, one two tree five
  Aircraft Smallprop 123

*) the "go ahead" may be omitted

The exception to this is if you are departing from a controlled airport, in which case a flight plan filed prior to departure is activated automatically. Activating a flight plan manually is only required when departing from uncontrolled airports.

To close a flight plan, the phraseology after establishing contact with ATC is:

  Aircraft Smallprop 123 position Wintermeadow closing VFR flight plan from Hometown to Springfield
  ATC Smallprop 123, flight plan closed at time one tree tree zero
  Aircraft Flight plan closed at time one tree tree zero, Smallprop 123


Is the Fortran language still being used in aviation? I am an aeronautical engineering student at Istanbul Technical University and our course plan includes Fortran as a programming language. I have some doubts about that because Fortran is an old language.

Is Fortran still being used in aviation?

FORTRAN is not used much that I'm aware of in aviation, but it is significantly used in aeronautical engineering.  I work with people that use Mark Drela's 'xfoil', 'xrotor' and 'aswing' programs on a daily basis for the design and analysis of airfoils, propellers and aerostructures. And I've used the 'CHARM' model of rotorcraft dynamics.  All of these are written in FORTRAN and you often need to know the language to debug them or integrate them into other programs e.g. for global design optimization.


How do landing fees work at larger airports? Many larger airports (class Bravos) have a landing fee. What's the process for assessing and collecting the fees?

How do these landing fees work with general aviation aircraft?
Where can I find out what the fee will be? Is it published?
How will I be charged the fee? (Pay before leaving the airport, bill sent to my home, etc.)
Is the landing fee a flat rate or is it calculated based on aircraft weight or some other factor?
I've heard that the landing fee is generally waived if you buy a few gallons of (overpriced) gas at an FBO, is that true?

Example scenario: I offer to take a friend up for a scenic flight. He lives very close to a moderately busy class B airport while my home airport and FBO is over an hour away from him. I offer to fly into the class B airport to pick him up and then drop him off at the end of the flight.

Well, the short version is that there really isn't a standard (and this applies to small as well as large airports).

Some airport authorities charge fees that are billed through the FBO, some don't.
Some airport authorities bill you directly, some don't.
Normally you pay at the FBO before you leave.
Most of the FBO's set their own fees (although they may come from corporate).
Some FBO's don't charge any fees (although not very many these days).
Some FBO's waive some (or all) of their fees if you buy fuel, some don't.
Most FBO's charge a fee based on the size/class/weight of aircraft, some don't.

In short, call ahead to the FBO that you will be using and ask them what the fees are and whether or not any of them can be waived.  They are used to this question and will have the information handy for you.


How much do 1947 and 2014 Beechcraft Bonanzas have in common? A question about the tail shape of the Bonanza and Oldest aircraft still in production led me to wonder how much the first and latest aircraft in this series actually have in common.

1947

 lost flights

2014
 Beechcraft
 AOPA

Clearly the following have changed

tail design
number of windows
engines
internal arrangements for seating and baggage
detailed changes to wing shape
cockpit instrumentation
cockpit controls

and many other changes

Is the basic central-airframe and core-wing design and construction identical?
Are there any parts in common - or at least directly interchangeable?

The V-Tail Bonanza design was retired (for a bunch of reasons, many of them marketing-related), but the actual airframe of a modern Beech 36 Bonanza is, essentially, the same as the 1968 Beech 36 (and very similar to the 1959 Debonair, just stretched). You can trace a great deal of the design and parts back to the V-tail as well.

There have been some changes made to the design over the years (for example, the throw-over yoke is gone, replaced by conventional dual controls), but the bulk of the airframe parts are interchangeable because the designs are essentially the same (this is an advantage for Beech owners: The factory is still producing nearly all the parts you'll need for maintenance, because they need them to put in the new planes).

Most of the light GA aircraft produced by the legacy manufacturers (Beech, Cessna, Piper) are what are known as "follow-on type certificate models" -- they are the same production design approved back in the 1950s/1960s, with "minor" changes incorporated along the way. This means you'll find the same kind of parts continuity in pretty much all the major manufacturer's aircraft:

Most of the parts on a 1960s Cherokee 180 are the same parts you'll find in a 2014 Archer III (changes to the airfoil and panel layout notwithstanding)
Many of the parts on a modern Cessna 172S are the same as the 1965 172F (the year they went to electric flaps).

You'll find many common parts on the 172 going back all the way to the original 1956 172 if you look. Big changes were the swept-back tail fin (1960) and the electric flaps (1965)


What types of attitude indicators are there? Learning to fly in general aviation in the west since the mid 2000s I'm used to the common attitude indicators like this one.

I've also seen older ones that are black and white as well as many varieties of attitude indicator display arrangements in glass panels.

My question deals with other ways of displaying this information. I've heard pilots talk about how some eastern airplanes have very different ways of presenting pilots with attitude information. What approaches are out there? What do they look like and where are they found?

Russian-made aircraft have attitude indicators that work exactly opposite of western ones.

source

with the western style, on the left, the virtual airplane figure is fixed so it's always upright to the pilot and the horizon moves. On the Russian style AI the horizon is fixed so it is level from the pilots POV and the aircraft symbol moves.

Just two ways of looking at it, but if you're used to one the other can be confusing.


In xflr5,how is the value of Fz calculated? I am building an conventional plane with AR=6 and I find the wing area,A.So I have selected an airfoil  for building my plane that is sd7062. Using xflr5 I got a cl vs alpha graph and I took the cl value at 4 degrees . using this cl value I calculated my lift and equated to the weight of my plane which is 2kg*9.81=19.6N .now equating L=W I find the area ,A and using this area and aspect ratio 6 or 7 I  calculate the span and chord .Now when  I do an analysis for the wing dimensions I got and plot a graph between Fz(lift) and alpha graph and find that at 4 degrees the Fz value is 13.078N ....why is there a decrease in my lift.....if there's a decrease then are the calculations I have done wrong?..please help me out]1

When you have taken the Cl of the airfoil concerned, the Co-efficient refers to an infinite wing. You have to compute the CL of the wing, which refers to a finite wing, taking into consideration the 3D nature of the flow.


How can I troubleshoot an intercom interference issue in a Piper PA-28? Our Piper PA28-181 doesn't want to let us communicate via its own intercom panel in the dashboard. We connect via the pilot port and an "Intercom SL300". When connected there is a annoying sound on the phones, it seems to be the strobe or ignition (going to test it).

My questions:

Where would I get information regarding the intercom/audio wiring in old and small airplanes?
Is it possible to install a suppression capacitor?

For the wiring, you need to do several things. First, obtain the Vendor's manual for the SL 300. Next you will need to trace out the wires going to the SL 300. I suggest labeling them.

This type of work is beyond normal pilot/owner maintenance, and I would urge you to work with your A&P or avionics shop tech to get support while you debug things, and also to provide guidance as you navigate the wires, controls, etc. that might need some displacement while you work on things.

A suppression capacitor can be installed, but I would identify the problem first. Again, the avionics tech should be consulted, and any filter you install will need to be documented, and "signed off" but you probably already know this as you own the plane.

Give a better description of the sound, or a recording, and you might get better ideas on where to look.


Is this new intake of Airbus and Boeing aircraft's NACA inlet? Anybody knows the name of this intake? look at the bellow images:

Why don't Airbus and Boeing use the conventional NACA inlet? Why did they invent this kind of intake? I can see some parts of these aircraft that the conventional NACA inlet are embodied in.

Those inlets don't require the NACA duct profile because the openings are presented toward the airflow, being on a sloping surface relative to the freestream.  The NACA profile in those locations serves no useful purpose and is a probably less effective, if anything.
The NACA duct profile was developed for inlets on surfaces that are completely parallel to the airflow, like along the straight sides of a fuselage or nacelle, where the freestream flow just passes on by (like a static port you might say).  They were developed as a low drag alternative to the traditional scoop projecting into the airstream that you would normally have to use in such a location.
The sides of the NACA Profile, induce a change in direction of the ram air free stream without any projections (it's thought that the sides of the ramp act like vortex generators and it's the vortices that "pull" the free stream down the ramp) so that ram air is drawn down the ramp to the inlet opening.  On a sloping surface like a wing root fairing as in those pictures, the ram air is directly impinging on the opening (as if it was a scoop sticking out) and doesn't need any "airflow redirection tricks" like the curved sides on the NACA inlet ramp.


Does acceleration increase linearly on a takeoff roll? I'm a relative novice when it comes to aircraft performance and was wondering if someone could both answer the following and maybe direct me to some good source material.

If I wanted to model a take-off roll, can I assume a constant acceleration up until the wheels-up point?  If not constant, is there a reasonably good function that could model the velocity curve on takeoff?

Thrust depends on speed and the type of engine. To simplify things, we can say that thrust changes over speed in proportion to the expression $v^{n_v}$ where $n_v$ is a constant which depends on engine type. Piston aircraft have constant power output, and thrust is inverse with speed over the speed range of acceptable propeller efficiencies, hence $n_v$ becomes -1 for piston aircraft. Turboprops make some use of ram pressure, so they profit a little from flying faster, but not much. Their $n_v$ is -0.8 to -0.6. Turbofans are better in utilizing ram pressure, and their $n_v$ is -0.5 to -0.2. The higher the bypass ratio, the more negative their $n_v$ becomes. Jets (think J-79 or even the old Jumo-004) have constant thrust over speed, at least in subsonic flow. Their $n_v$ is approximately 0. Positive values of $n_v$ can be found with ramjets - they develop more thrust the faster they move through the air.

Drag depends also on speed, and in addition on lift. During the takeoff roll the dynamic pressure grows with the square of speed, and drag is almost proportional to the dynamic pressure. Since the flow's Reynolds number also increases with speed, the zero-lift drag coefficient (aka friction plus pressure drag coefficient) decreases with speed. Depending on the ground attitude of the aircraft it will create already some lift during the rolling phase, but lift substantially increases during rotation when it is raised to lift the aircraft off the ground. When the aircraft accelerates further after liftoff, the lift-dependent part of drag goes down with speed while the zero-lift part continues to increase with dynamic pressure.

For most aircraft, thrust is highest when the aircraft is at rest (constant pitch propellers can have a lousy efficiency at takeoff when they are optimized for fast flight, so here you might have higher thrust at some positive speed), and decreases the faster the aircraft moves through air. Since drag is also lowest with the aircraft at rest, the highest acceleration is possible right after brake release. As soon as the aircraft rotates, the new lift-dependent drag component will cause a marked decrease in acceleration, and when the aircraft climbs, some of the excess thrust needs to go into climbing, so acceleration decreases again.

Newton's first law gives a formula for acceleration a: $$a = \frac{T - D}{m}$$
where T is thrust, D is drag and m is the mass of the aircraft. The integration of acceleration over time gives speed.

There is no single formula for the velocity curve, and my recommendation is to split the take-off into three sections: Ground roll, rotation and initial climb. In all phases you need to calculate with speed-depependent drag and thrust, so it will be best to integrate the parameters stepwise in small time steps.

The comments encouraged me to give a more detailed list of drag components. These here have to be considered during the take-off roll:

Zero-lift drag of the airframe (due to friction and pressure)
Induced (lift-related) drag for the aircraft in horizontal attitude, including reduction due to ground effect
Drag increment due to flaps in take-off position
Landing gear drag
Wheel friction (0.025 * weight on a hard runway, but a lot more on soft ground)
Kinetic energy loss or gain due to runway slope

With rotation onset these drag components must be added:

Trim drag due to elevator deflection to lift the nose
Induced drag at the actual pitch angle

When the aircraft lifts off, these changes must be considered:

Reduced power for acceleration due to power requirement for climb
No more wheel friction
When the gear is retracted, drag increases as the doors open and is greatly reduced once all wheels are stowed.
Ground effect is reduced as the aircraft climbs away from the ground

Don't forget to include wind speed in your calculation!


How much are aircraft nose paintings restricted by regulations? It's actually surprising to see these old paintings on aircraft noses:

WW2 nose art, source

How much were (and are) these paintings generally restricted or allowed by law, civil regulation and military rules in countries like US, Russia, India, Australia (if the jurisdiction matters for a general answer)?

It used to be that nose art was pretty outlandish and sexually charged, and it remained largely unrestricted as this B-24 from WWII demonstrates.

With the current gender integrated units and women serving in combat squadrons, this kind of stuff is non longer acceptable.  Currently there's a rule, in at least the USAF, that nose art must be 'non-gender specific' i.e. you can't paint naked women on your airplane.


Documentation about "drag stabilized flying wings using non-reflex airfoils"? What provides lift is the wing, but it is unstable without one stabilizer.

Flying wings airfoils, or reflex airfoils, carry their stabilizer inside them, through a reversed camber of the trailing edge section. Those airfoils provide less lift and more drag than "standard unstable cambered" airfoils.

Long time ago I (don't know where anymore) saw images of one particular wing longitudinal stabilization method, which could allow one "standard unstable high lift" or let's say Clark Y airfoil, to fly stabilized by the drag produced by one surface placed quite far above the trailing edge.

This looked like this, and models of it fly pretty well :

Who thought about this configuration and does anybody have documentation about this?

What interests me in this is : What kind of max L/D ratio and finesse could this Clark Y (or RG 14 or else) drag stabilized config could reach, compared to reflex airfoil (Eppler 187 or else) of same wingspan, same wing loading, same geometry glider.

Note the impossible sustained reverse flight.

If you’re going attach a boom and surface, why are you comparing to a reflexed airfoil?  Attach the boom and surface conventionally and you get far better LD than either. The effective trim drag is lower. And you can get it thru the door of the hangar.
  Planks are cool, but applying the restoring force without much lever is the basic problem. The required force and resulting drag is much higher.
  The new config exposes the whole boom to flow and the vane is 100% drag. A conventional surface generates force with the L/D of the tail surface, only 20% drag if the LD of the tail is 5.
    Conventional boom or even a swept tailless is far superior to this config or reflexed plank. I don’t think anyone will spend time calculating the diff between two poor config. Sorry.


What rules would allow a pilot to refuse a passenger's boarding? I would like to know about any rules that would authorize a pilot to refuse to allow a specific passenger from boarding his plane (i.e. mental instability, obvious sickness, drunkeness, etc.).

Hypothetically, if someone were being 'forced' take a flight they did not want, what would be the options for the passenger to be refused boarding? I am only interested in the rules for a pilot.

The regulation that springs immediately to mind is FAR 91.17(b):

  Except in an emergency, no pilot of a civil aircraft may allow a person who appears to be intoxicated or who demonstrates by manner or physical indications that the individual is under the influence of drugs (except a medical patient under proper care) to be carried in that aircraft.

i.e. "If you get yourself blind stinking drunk at the airport bar, or you've been doing lines of cocaine in the airport bathroom you are not getting on the plane because the FAA says I can't let you."

For other cases you need to head over to 49 USC 44902, which deals with Refusal to transport passengers and property for "air carriers" (FAR part 121, and I believe 135 operations are covered by this bit of the US Code). The most relevant text is:

  (b) Permissive Refusal.
  Subject to regulations of the Under Secretary, an air carrier, intrastate air carrier, or foreign air carrier may refuse to transport a passenger or property the carrier decides is, or might be, inimical to safety.

Most air carriers vest the captain with the decision-making authority here: If the captain determines that a passenger may be "inimical to safety" they can refuse to fly the passenger.  There are some restrictions on that authority - notably that the basis for the decision can't be "discriminatory" - which are scattered about in 14CFR (the FARs) and 49USC (Transportation), as well as case law. The FAA has issued at least one legal interpretation discussing this in more detail.

For commercial (or non-commercial) operations under part 91 I wasn't able to find anything specific in 14CFR or 49USC, but in those cases the general consensus seems to be that the PIC has at least the level of authority granted under 49USC44902 - if not broader authority (i.e. if you're going on a personal flight you could refuse to take someone along because you don't like their shoes, and if someone hires you for a commercial flight you could refuse the job if they were acting sketchy).


Best glide speed vs. best glide angle? Maximum glide range? I have some open questions regarding best glide in a descent:

I understood, that there is a best glide speed. This best
glide airspeed occurs at the highest lift-to-drag ratio (L/D). This best glide speed is normally given in the operator's manual of the aircraft.

Is it true, that this best glide speed is given in terms of indicated airspeed IAS and hence is independent of the elevation?

What about the sink rate when flying at best glide speed? I have seen hodographs where the sink rate is given over airspeed. (Diagram taken fom Taken from: Coombes, Reachability analysis of landing sites for forced landing of a UAS)

Is this again inidcated airspeed IAS?

As we all know, the TAS decreases with decreasing elevation when maintaining a constant IAS. For navigation with respect to earth's surface I need ground speed GS which is directly related to TAS via the wind speed (which we can assume to be zero for the moment)
To determine the glide path angle I suppose, that the ground speed and the sink rate is relevant.

Supposing, the best glide speed is IAS contrary to true airspeed TAS, how can I determine the glide range?

What is the resulting flight path angle when maintaining best glide speed? Does it change with decreasing elevation?

My intuition tells me, that when flying at constant IAS, the flight path angle should get steeper with decreasing elevation.

Is this assumption true?

Every reference to clarify these questions is welcome.

Currently I try to implement an autopilot for an emergency landing assistant that maintains a constant flight path angle during gliding descent. This enables me to exactly determine the distance traveled when I know the starting and the end elevation which in turn allows to do a proper path planning. My gut feeling tells me, that in this case I don't make use of the maximum possible gliding range as I have to start with a too steep flight path angle at high elevation to maintain this constant till the ground.

Is there any good idea how to predict the distance traveled when only knowing the start and target elevation?

Thanks a lot and Cheers,

Felix

Is it true, that this best glide speed is given in terms of indicated airspeed IAS and hence is independent of the elevation?

Yes. The best glide speed needs you to fly at the optimum polar point, and with the same IAS you will fly at the same lift coefficient and polar point.

  To determine the glide path angle I suppose, that the ground speed and the sink rate is relevant.

No, the angle will be the same regardless of altitude (if we neglect Reynolds number effects for now). What does change is the speed over ground - this goes up with height.

  What is the resulting flight path angle when maintaining best glide speed? Does it change with decreasing elevation?

No, it doesn't. The glide path will be the same, only at higher altitude the airplane will fly faster and proportionally sink faster. What changes is the time scale, not the geometric scale.

EDIT:
The added graph is either given in TAS on the x scale and for a specific altitude, or it is given in IAS and valid for sea level to maximum ceiling (if we neglect Reynolds number effects for the moment)

P.S.: Terminology:

Altitude is the vertical distance from sea level to where an airplane flies. See here for more.

Elevation is the vertical distance from sea level to the ground or to an obstacle.

Height is vertical distance between an aircraft and the local ground.


Why do tail dragging seaplanes not exist? I am in the process of starting to build an ultralight that will be a tail dragger with floats, and in my conversations with the fellows I'm building it with, we've realized we've never seen a plane like it before. Does this mean we are doing something dumb? Thanks in advance.

It's been tried before (there isn't all that much in aviation that hadn't already been tried by WWII).  The tail float means the aircraft CG is aft of the hydrodynamic center of the main floats, and like a tailwheel airplane, the machine will be dynamically unstable, steering wise, when on the step, same as a wheeled taildragger and you will have to prevent it from switching ends with your feet the entire time it's on the water moving.
It could be a real handful to take off and land, especially when there are waves and gusty winds (and seaplanes do have to cope with crosswinds from time to time).  You have to make the rear float steerable, and you have to give it enough lateral bite in the  water to have good leverage in steering the thing when below the speed that the air rudder is working.  I don't think there is any drag advantage to 3 smaller floats vs 2 larger ones.
Traildragger advantages, like prop clearance, aren't that much of a benefit here, and since the conventional float configuration is so much easier to control, why bother with a taildragger float setup?
Ideas come along for new configurations all the time, but if you dig enough you find that somewhere in the distant past it's already been tried, and while it may have been functional, the "old" conventional way that everybody uses has been around so long because it's simply what works best.


Can an aircraft operator hire a Commercial Pilot to fly their aircraft under part 91? Here is the scenario. Joe owns a Cessna 172. Joe hires Tim to fly him in his 172 from A to B. Tim is a Commercial Pilot. Is this legal?

So far, everyone has said yes to this question, but not one person I have asked can cite a regulation or regulations for me.

Here is my chain of Logic:
Part 61.133(a)(1)(i):

  (i) Carrying persons or property for compensation or hire, provided
  the person is qualified in accordance with this part and with the
  applicable parts of this chapter that apply to the operation; and

Alright, let's see which part(s) apply to Tim.

Looking at 119.1(a)(1):

  (a) This part applies to each person operating or intending to operate
  civil aircraft - (1) As an air carrier or commercial operator, or
  both, in air commerce; or

Now let's see if any of those apply to us. Perhaps "commercial operator".
1.1:

  Commercial operator means a person who, for compensation or hire,
  engages in the carriage by aircraft in air commerce of persons or
  property, other than as an air carrier or foreign air carrier or under
  the authority of Part 375 of this title. Where it is doubtful that an
  operation is for “compensation or hire”, the test applied is whether
  the carriage by air is merely incidental to the person's other
  business or is, in itself, a major enterprise for profit.

Okay. This Tim seems to be operating as a Commercial Operator.

Now look at 119.23(b):

  (b) Each person who conducts noncommon carriage (except as provided in
  § 91.501(b) of this chapter) or private carriage operations for
  compensation or hire with airplanes having a passenger-seat
  configuration of less than 20 seats, excluding each crewmember seat,
  and a payload capacity of less than 6,000 pounds shall - (2) Conduct
  those operations in accordance with the requirements of part 135 of
  this chapter, except for those requirements applicable only to
  commuter operations; and

Well we want to be under part 91, so let's look at the exception provided as 91.501(b).

91.501(b):

  (b) Operations that may be conducted under the rules in this subpart
  instead of those in parts 121, 129, 135, and 137 of this chapter when
  common carriage is not involved, include - (4) Flights conducted by
  the operator of an airplane for his personal transportation, or the
  transportation of his guests when no charge, assessment, or fee is
  made for the transportation;

Number 4 seems to apply! Awesome!

But let's take a look at 91.501(a):

  (a) This subpart prescribes operating rules, in addition to those
  prescribed in other subparts of this part, governing the operation of
  large airplanes of U.S. registry, turbojet-powered multiengine civil
  airplanes of U.S. registry, and fractional ownership program aircraft
  of U.S. registry that are operating under subpart K of this part in
  operations not involving common carriage. The operating rules in this
  subpart do not apply to those aircraft when they are required to be
  operated under parts 121, 125, 129, 135, and 137 of this chapter.
  (Section 91.409 prescribes an inspection program for large and for
  turbine-powered (turbojet and turboprop) multiengine airplanes and
  turbine-powered rotorcraft of U.S. registry when they are operated
  under this part or part 129 or 137.)

What is a Large Aircraft.
1.1:

  Large aircraft means aircraft of more than 12,500 pounds, maximum
  certificated takeoff weight.

Okay, a Cessna 172 is not a Large Aircraft or turbojet multiengine. And this is not a Fractional Ownership Program since that requires 2 aircraft in the first place.

So, from my understand, Tim cannot fly for Joe since 91.501(a) says this part does not apply, BUT wait. 91.501(b) says it is allowed.

How is this intrepreted? Does 91.501(b) apply only to large aircraft and such on a fractional ownership program? What am I missing?

Everyone I know says it is allowed, but the rules seem to be different. Any help is appreciated.

To answer my own question. As pointed out by @MichaelHall and @pericynthion Tom would not fall under "Commercial operator".

Here is the definition for reference:

  Commercial operator means a person who, for compensation or hire,
  engages in the carriage by aircraft in air commerce of persons or
  property, other than as an air carrier or foreign air carrier or under
  the authority of Part 375 of this title. Where it is doubtful that an
  operation is for “compensation or hire”, the test applied is whether
  the carriage by air is merely incidental to the person's other
  business or is, in itself, a major enterprise for profit.

Another term which comes in useful here is:

  Operational control, with respect to a flight, means the exercise of
  authority over initiating, conducting or terminating a flight.

In this case, Joe would have operational control since it is his aircraft. Since Commercial Operation means "...person who... engages in the carriage by aircraft...", then Joe is the "person" and not the pilot Joe.

Another term within the definition is "air commerce". This means:

  Air commerce means interstate, overseas, or foreign air commerce or
  the transportation of mail by aircraft or any operation or navigation
  of aircraft within the limits of any Federal airway or any operation
  or navigation of aircraft which directly affects, or which may
  endanger safety in, interstate, overseas, or foreign air commerce.

Commerce is the activity of buying or selling. If we look at it from that level, the operator (Joe) is not engaging in air Commerce, because when you are operating an aircraft, you're perfectly allowed to pay for the usage of your own plane. So if this is not air commerce, then it falls under Part 91, and Tom is good to go.

However, if Joe were to engage in air commerce such as shipping stuff, but still hire Joe, then this falls under part 119 then 135 operations.

Refer to this legal interpretation: https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/data/interps/1993/green%20-%20(1993)%20legal%20interpretation.pdf

Based off this interpretation, the aircraft and operator must be separate from the pilot. Also, the operator cannot conduct air commerce flights.


Is it possible to see the same sunset twice from an aircraft? If I initiate a climb just after watching the sun go down below the horizon, how fast would I have to climb in order to watch the sun come back up, so that I could then level off and watch the sunset for a second time?

I've Googled the answer, and several different articles have said that I'd need a minimum rate of climb of 5000 ft/min. However, I've also read several articles that said you can do the same thing in the Burj Khalifa's elevator, and it maxes out at 2000 ft/min. So, which of these is correct, if any?

Concorde did something similar: it would take off from London at sunset and then fly West faster than the Earth's rotation, so you would get a sunrise in the West on board.

This capability was also used for solar eclipse flights. While a solar eclipse lasts no more than 8 minutes on the ground, Concorde was able to stay in the Moon's shadow for 74 minutes.


What is a gust alleviation system? Reading about the 787 it says it has

  an active gust alleviation system similar to the system used on the
  B-2 bomber. [1]

The gust alleviation patent says:

  The gust alleviation system picks off the stick displacement signal
  and the aircraft normal acceleration sensor signal and processes this
  information. The outputs of the gust alleviation system are added back
  respectively to the existing flap command signal and the aircraft's
  original stability augmentation loop. [2]

As a layman I am not sure I fully understand this, so my question is, what is the gust alleviation system?

A gust alleviation system is a control system fitted to some Fly-by-wire (FBW) aircraft that reduces the effect of gust loads on the aircraft by deflecting control surfaces such as ailerons, rudder and elevators.
The system works by measuring the upward acceleration of the aircraft and comparing that with the acceleration commanded by the (auto)pilot. A feedback loop adds a correction signal to the signals controlling the deflection of the control surfaces in order to counteract the accelerations cause by wind gusts.
In its simplest form the accelerations are sensed near the center of gravity of the aircraft. More advanced implementations work with multiple sensors in the body and in the wings. These gust alleviation systems do not only attempt to annul the effect of the gusts on the aircraft's normal (upward) acceleration, they also reduce the wing bending moments. This in turn reduces metal fatigue.
In the A380 the load alleviation system is nicknamed "valse des aileron" (Waltz of the Ailerons) because of the dancing movements of the aileron:


When should a PPL student start learning navigation? A big part of the ground syllabus for PPL training is navigation and flight planning. The ground training feeds into practising navigation in-flight and of course eventually to the qualifying cross-country.

What's the best time to start the classroom work on this subject, in the context of training that's spread out over a long period? What are the pros and cons of learning it at different times? If it makes a difference, I'm interested in the situation in the UK for an EASA PPL.

As early as possible.

They say "aviate, navigate, communicate", which puts navigation into a pretty high priority - just behind flying the plane. It is more important than talking on radios.

I cannot see any downside for learning navigation too early beside the natural "memory decay" for acquiring any new material & knowledge. Even basic navigation techniques will benefit your first day of flying (unless you're absolutely not interested in knowing where you are). You can even discuss the route with your instructor during the pre-flight, even if flight planning is not the lesson today. You will not get to know the details, but you will be introduced to aerial navigation.

That, of course, assume that you are learning at a comfortable pace and you are not struggling with the present material.


What are these small jets and large propeller aircraft flying in formation? I came across the photo below on flightaware.com. The image was taken by someone with, I think, an Ukrainian name: Arkadiusz Cieslak. They piqued my interest as they do not appear to have insignia except for the "B" (cyrillic?) on the tail of the transport plane and a design on the fighters. Any ideas? I'm just curious.

The design on the belly of the fighters makes it clear that they are from the Patrouille Suisse, the aerobatic team of Switzerland. They use F-5E.

From the comment in the page you linked (or from the aircraft registration HB-RSC, as suggested by @falstro), instead, we see that the other aircraft is the Breitling (hence the "B") Super Constellation:

  The Breitling Super Constellation from the Swiss Super Constellation Flyers Association: It is the last Super Constellation in flying condition in Europe.


Is the lift vector reversed during inverted flight? Heard a physics professor say that when an aircraft flies inverted, the wing assumes a significant angle of attack (by pushing the stick forward) to continue to generate the necessary "upward" lift vector to maintain level flight. I'm confused. I thought the lift "vector" is actually reversed and points towards the ground (not upward) during inverted SUSTAINED straight-level flight? What am I missing here? The horizontal stabilizer is basically an inverted airfoil, and its "lift vector" points downwards, giving the airplane tail-down force. How is the wing any different when it's inverted?

This is easiest to understand with a fully symmetrical wing, which indeed are popular with aerobatic aircraft.  The direction of "lift" has nothing to do with sky or ground and everything to do with your angle of attack to the relative wind.

When inverted, you simply (as the professor said) push forward on the stick, which makes the wind strike the "top" of your wing.  Inverted, this does the trick as lift is now towards your floor, but gravity is toward your head.

Right side up, you make the wind strike the bottom of your wing by pulling back on the stick.


What is the speed record for the Boeing 747 and Airbus A380? What are the speed records (true air speed) of these Jumbos: The Boeing 747-8 and the Airbus A380 if any?

The published Maximum Operating Mach number (MMO) for the B747 is Mach 0.92 but it can sometimes be exceeded accidentally due to aircraft upset. It has been reported that Mach 0.99 was attained during a Boeing test flight in a slight nose down attitude.

The A380 has a slower MMO of Mach 0.89

The actual true airspeed of a Mach number will depend on the temperature and altitude but at 35,000 feet Mach 0.92 would be about 530 Knots. (610 mph)


What is the difference between a partial stall and a full stall? I have this study question on the FIA written:

Which statement is true concerning the aerodynamic conditions which occur during a spin entry?

Correct Answer: After a full stall, the wing that drops continues in a stalled condition while the rising wing regains and continues to produce some lift, causing the rotation.

Incorrect Option: After a partial stall, the wing that drops remains in a stalled condition while the rising wing regains and continues to produce lift, causing the rotation.

Because the only difference between the two answer options is 'full' and 'partial' I was wondering what are the differences between a full stall and a partial stall?

For GA aircraft with straight, rectangular wings, the stall usually starts at the root and progresses towards the tip. So, at some point, only a portion of the wing will be stalled. This is sometimes referred to as partial stall, though it is not a common term.

Image from boldmethod.com

This is usually achieved by having a washout or a wing cuff. In case of root-first stall, the wing tips are still producing lift, helping to prevent rolling motion (which may occur if the whole wings stalls at once), which in turn prevents the aircraft from entering a spin.