Will manually removing nicks from compressor blades significantly affect the operation of the compressor? I've recently found a channel on Youtube where a jet engine technician goes into great detail about the work he does on maintaining and repairing jet engines

In this particular video (and also an older prequel to it), he demonstrates removing nicks from compressor blade leading edges and subsequently smoothing out the leading edge. One thing that caught my attention was the tools he used: files and 100- and 400-grit sandpaper. He basically went over the leading edge by hand, removing a small amount of material in the process.

With the tools and the method, there is obviously no precision.

Is it actually acceptable to modify compressor blades that way? To what extent does it affect the operation and efficiency of the engine, if, say, some compressor blades are missing a millimetre off their chord, or have lost their twist by a few degrees?

I guess a related question is - what precision are compressor blades designed and built to?

Thanks to ymb1 for pointing out a related question, but I'm more interested in a quantification or analysis of the impact to the engine performance. It seems that the linked question explains the term blending (which is mentioned in the video as well), but did not go into details about performance impact.

Yes, this is not only acceptable, it is required by the engine maintenance manual. The tools might be more sophisticated in other shops, but the basic concept of removing material by hand is the same.  The process is called "blending". The impact of sand or dirt on the blades causes little nicks and scratches. Those sharp or rough areas create what is known as a "stress concentration".  If left as-is, the nicks will eventually grow into cracks (metal fatigue). Smoothing out the nicks removes the stress concentration and prevents the crack from forming.  There is an impact on the performance/efficiency, but that's better than having your blades crack.  From my experience, the performance impact of what is shown in the video is actually quite small. As a rough guess I would say 0.01% - 0.1% efficiency loss. Much larger nicks can be successfully blended.

Edit:
Regarding how I came up with that efficiency number. Two thoughts:

First, The compressor shown in the video is a 10 stage compressor, and as a rough estimate, each stage probably has about 30 - 50 blades. I didn't try to count exactly but let's just call it 400 blades. It is a reasonable assumption that each blade does the same amount of work.  In reality some stages will be a little more heavily loaded than others, but it's fairly close. So if you removed 1 entire blade, as a rough order of magnitude estimate, you would expect that to be about 1/400 = 0.25% efficiency loss.  The amount of material removed is clearly much less than an entire blade, so the efficiency loss should be less than 0.25%.

Second, I have seen compressors that had much much larger nicks be blended out and have on the order of 0.1% - 1% efficiency loss.

So between the two of those ideas, I made an educated guess on the efficiency number. Could I be off by a little bit?  Absolutely. But I'm probably at least close.


Is c.g rear or fore of wing leading edge? This video states that the c.g of most non tapered airplane is 25%-30% of wing chord REAR of the leading edge.The aerodynamic center(a.c) of most wing is 25% rear of the leading edge ....Does this mean the a.c can coincide with the c.g in a tailplane?

For longitudinal stability in a conventional wing-and-tail layout, the CG needs to be ahead of the wing's AC.  This causes a nose-down moment that is countered by downward lift at the stabilizer, so that the stabilizer will raise the nose as speed builds up.  Thus, if the aircraft is disturbed into a dive, the nose will automatically rise as speed builds; conversely, if disturbed nose up, as speed falls off the nose will tend to drop.

Aircraft with active control (especially computer control), as well as some alternative layouts (such as a classic canard) can alter this conventional stability setup -- for instance, in a canard, the stabilizer at the nose lifts, and the CG will be ahead of the leading edge of the wing in most cases.


How far in advance of "effective date" are VFR sectional charts usually made available? (US) In the US, how far in advance of the "effective date" are new editions of VFR sectional charts usually made available?  Is the answer different for the paper version and the digital version?
Were some or all of the 2-25-2021 editions of the VFR sectional charts for US airspace released (i.e. made available) with much less "lead time" than usual?
The 2-25-21 version of the Juneau VFR sectional chart became available for downloading from the FAA's "VFR Raster Charts" web page sometime between February 3 and February 15.  Is this less "lead time" than normal?
As of today, March 1 2021, the vfrmaps.com image for Sitka Alaska (SIT/PASI) still shows the old airspace configuration, which is no longer current, due to a change published July 31 2020 and effective November 5 2020.  Here's what vfrmaps.com shows (clipped from a screenshot from this url accessed through this airnav.com link for the Sitka airport, SIT/PASI).

And here's what the airspace actually looks like, taken from a screenshot of the PDF version of the 2-25-21 Juneau sectional chart, downloaded from FAA's "VFR Raster Charts" web page-

Is it unusual for the vfrmaps.com product to still show the image from the previous edition of a VFR sectional chart, several days after the new edition has gone into effect?
And if so, is this likely related to the charts being released with less "lead time" than usual?
And if so, do similar discrepancies between commercially available on-line map products and the actual FAA charts exist in other regions of the US at present, for the same reason?
This question is not about why there were no new editions of the Juneau sectional chart issued between March 26, 2020 and February 25, 2021.  That question is asked here: Were planned release dates skipped in 2020 for the VFR sectional charts for Juneau Alaska and Dutch Harbor Alaska?

According to the product catalog website of the FAA, new VFR charts are available approximately 20 days prior to their effective date. Since 25th of February 2021, the FAA releases new VFR charts every 56 days, aligned with the AIRAC cycle.

The products mentioned in this catalog are posted at Digital Products
approxiamately 20 days prior to their cycle effective dates. They are
also available through FAA Approved Print Providers.


What is “abnd” on the U.S. VFR Sectional Chart? I have looked at the sectional legend and FAA aeronautical chart user guides and have not seen any answer for this.

What is “abnd” on the U.S. VFR Sectional Chart?

ABND, according to the United States of America Aeronautical Contractions means:

Abandon

A link to this document can be found here:
FAA Website


Can people who suffer from motion sickness become pilots? Suppose a person suffers from motion sickness when flying, but wishes to become a pilot (let us say, with the eventual goal of flying for a major commercial airline).  Is this possible?

Is motion sickness a medical disqualification for a pilot's license, in many or most jurisdictions?
Most over-the-counter motion sickness medications cause drowsiness, so they are obviously not a good idea for a pilot to take.  Do pilots have access to other effective treatments that are safe to use while operating an aircraft?
Do pilots find that they get over motion sickness the more they fly, similar to the way sailors develop "sea legs"?
Are pilots taught techniques to remain focused on flying even if they are experiencing motion sickness symptoms (nausea, vomiting, dizziness, etc)?

The short answer is yes. I can't answer all your questions in detail, but here's some US-based information.

First, is it disqualifying? According to the FAA, if a candidate for a medical says he suffers from motion sickness then "a careful history" is required, and if the person requires medication then FAA approval (i.e. a special issuance) is needed. So it all depends on the person's individual situation, but it is definitely possible to get a medical, even if you require medication. Motion sickness also seems to be fairly common in new pilots, by the way:

  Approximately 10% of all students taking flight training will become
  airsick at some point during their first 10 flights; 15-20% of these
  will have a severe enough form to interfere with their control of the
  aircraft.

Second, are there alternatives to medication? The FAA has a video about motion sickness and how to deal with. I haven't watched it but the description implies yes:

  This video provides practical advice on diet, medications and other
  exercises to help cope with this potential problem

Wikipedia also mentions various treatments although some (like head-mounted displays) seem impractical for civil aviation at least.

Third, do pilots adjust over time? Apparently, yes. This FAA document says:

  The experienced or acrobatic pilot is conditioned to withstand abrupt
  attitude changes that a passenger or helicopter pilot might not have
  experienced.

  [...]

  Continued gradually escalating exposure is the most common process for
  facilitating adaptation. Several days and repeated sessions of flying
  usually conditions the patient to the new environment.

That exposure would also be an alternative to medication, of course. And Sami's answer has some interesting personal experiences.

Finally, are pilots taught techniques to stay focused on flying? Instrument rated pilots are trained to ignore their physical sensations and focus fully on their instruments instead. But that training has nothing to do with motion sickness as such, and I have no idea how pilots who do suffer from motion sickness are affected (or not) when flying on instruments.


How does carb heat increase the risk of dirt ingestion? In this question about turning off carb heat just before landing, one of the justifications for doing so is to reduce the likelihood of ingesting dirt into the engine.
How does carb heat (or the lack thereof) affect the amount of dirt that might be ingested into the engine?
I am not a pilot, but I would think there would be some sort of air filter like there is on a car/truck. Also, I would think that, if anything, ice in the carb (while Not Good™/potentially fatal, especially on landing), would reduce the likelihood of getting dirt into the carb by acting somewhat like a filter - i.e. giving dirt a place to land before making it all the way through and into the cylinders.

Carb heat is not only about heating the air going into the carb, it's also a meant to be an alternate air path in case the air intake becomes fouled or the air filter gets clogged by debris, snow or ice. Fuel injected airplane engines typically have an alternate air intake that bypasses the air filter for the same reason, it's part of the checklist to test the alternate air.

The reason there isn't a separate filter for the carburetor heat air is that the same thing that clogged up the main filter could clog up the secondary, it's better to have unfiltered air for a short time than take the chance of losing your engine.


How is the direction chosen when landing a seaplane on water? When using a runway, many factors are taken into account to choose the landing direction.

A lake can be used in almost any direction by seaplanes. I imagine wind is prevalent, but I guess other elements such as waves, form of the body of water surface, water flow should also be taken into account.

What are the elements taken into account when choosing the direction to land a seaplane onto a body of water, and how do thoses elements influence the direction?

Here is a nice little article on it. But in general the small waves on the water will curl with the wind and can even be used as a wind indicator. For calm water you can obviously chose your direction based largely on wind (but if the water is very calm there is likely little wind). Obstructions will play into choosing direction as well and it is advised to overfly the intended landing area before touching down. As for rough water landings the article states

  It is impractical to describe an ideal rough water procedure because of the varying conditions of the surface. In most instances, though, the approach is made the same as for any other water landing. It may be better however, to level off just above the water surface and increase the power sufficiently to maintain a rather flat attitude until conditions appear more acceptable

Your elements are (in no particular order)

Obstacles
Wind
Landing Area (you need enough distance to actually land same as a paved strip)
Possible Rough Conditions

You must also keep in mind where you can actually land a seaplane. Not every body of water is legal to land a sea plane in (emergencies aside). You may want to check out this recently released book on arguable the first guy that flew a seaplane around the world.


How are anti-aircraft missiles tested? How are anti-aircraft missiles and counter-measures tested?

When they design an anti-aircraft missile, how do they test it so that it actually locks on to a target and destroys it? Do they simply fly a plane in the air and then fire a missile at it and have the pilot eject?

Similarily, how are counter-measures tested? Do they fire a missile at a target and check whether it misses?

The short answer is that the final qualification tests are done against drones like the QF-4, which are converted from retired F-4 fighters.  These tests are still extremely expensive, into the millions per aircraft destroyed, so there are many dry runs and non-destructive tests completed beforehand.  Sacrificing a target drone isn't done until the project team is very confident of a positive result or they are unable to obtain necessary data by other means.


Do I need special permission to land at a Landing Rights Airport? According to the Chart Supplement, Orlando International airport (KMCO) is an LRA (landing rights airport).

What permission is needed to fly an aircraft to an airport classified as LRA? Can I just file a VFR flight plan, take off under VFR from somewhere in Florida, enter the class B with a clearance, and land there?

According to the FAR's

  (2) Private aircraft. The pilots of private aircraft are required to
  secure permission to land from CBP following transmission of the
  advance notice of arrival via an electronic data interchange system
  approved by CBP, pursuant to § 122.22. Prior to departure as defined
  in § 122.22(a), from a foreign port or place, the pilot of a private
  aircraft must receive a message from CBP that landing rights have been
  granted for that aircraft at a particular airport.

This only matters if you are inbound from an out of country origin. An LRA airport is

  Landing rights airport. A landing rights airport is any airport, other than an international airport or user fee airport, at which flights from a foreign area are given permission by Customs to land.


What is Transponder Code 2000 actually used for? On What is the significance of a squawk code? @DeltaLima gave a fairly concise answer. In it he listed several 'standard' codes used for things like emergencies.

Also in the list was Code 2000, for which he included the description:

  Used when entering a Secondary Surveillance Area and no code has yet been assigned

So, if I'm in the US, under VFR (code 1200) and I enter a Secondary Surveillance Area, I automatically change to Code 2000? Why wouldn't I have already been given (a specific) designator?

The purpose of squawk code 2000 is to prevent aircraft entering a Secondary Surveillance Radar (SSR) area from transmitting a code that is the same as a discrete code assigned by ATC to an individual aircraft.

If you are flying in the USA under Visual Flight Rules (VFR), you will be assigned (implicitly) code 1200. Upon entering a SSR area you might get assigned another code, but often you will keep code 1200 if you are not near class C airspace.

If you are flying Instrument Flight Rules (IFR) outside a SSR area (e.g. entry into the US from oceanic airspace), you will use code 2000. Upon radar contact you will then get assigned a discrete code.

From FAA Advisory circular 91-70A - (Oceanic and International Operations):

  2.  EXPANDED OCEANIC CHECKLIST.

  .......

  g.
  After Oceanic Entry

  (1) Squawk 2000.  Thirty minutes after oceanic en try, crews should
  Squawk 2000, if  applicable. There may be regional differences  such
  as Squawking 2100 in Bermuda’s airspace or  maintaining last assigned
  Squawk in the West Atlantic Route System (WATRS). Crews  transiting
  Reykjavik’s airspace must  maintain last assigned Squawk.

Another use of code 2000 is on the airport: before power up you can select code 2000 to avoid code conflicts that could occur when you would maintain your code from a previous flight. It is standard practice in many airlines to select code 2000 after arrival at the gate.


What is the meaning of GPS IAP RNP that appears in Notes? Referring to the RNAV (GPS) RWY 30 approach, what is the meaning of RNP APCH in the notes section? (Highlighted in YELLOW)
Also, what are the separate DA values in parenthesis? (Highlighted with a red oval)

The AC covering RNP APCH can be found here. Under RNP APCH Operations it lists:

6.3 RNP En Route, RNP Terminal, and RNP APCH Operations:

The pilot is not required to monitor ground-based NAVAIDs used in position updating unless specified by the Airplane Flight Manual
(AFM).

The pilot must comply with published and assigned altitudes, and airspeeds.

Note: Pilots operating aircraft with a barometric vertical navigation
(baro-VNAV) system must ensure compliance with all altitude
constraints as published in the procedure by reference to the
barometric altimeter.

The full qualifications can be found in APPENDIX A. QUALIFICATION CRITERIA FOR REQUIRED NAVIGATION
PERFORMANCE APPROACH (RNP APCH) OPERATIONS (not copied for brevity)
The landing minimums in the parentheses are non civilian minimums and generally for use by the military although the chart reference strictly says " All weather minimums in parentheses not applicable to Cilil Pilots. Military pilots refer to appropriate regulations" so there may be other qualifiers (Im not a military pilot and cant comment beyond this)

(source)


Why is the quality of radio communication bad? Why don't modern planes and ATC centers have good-quality audio for communication? For example in this video:

Or basically any other example of pilot communication(some are worse, some are better).

This is not terribly bad of course, but this is comparable to a cheap $4 headset, the sound is so distorted. This can cause trouble when a pilot does not understand some words and asks to repeat the sentence. And even more problems if the pilot or flight dispatcher are not native English speakers.

Is there some technical reason behind this, like antenna/signal limitations within the plane? The quality is the same when the pilot is just taxiing on the ground, so I suppose this has nothing to do with speed or altitude.

P.S. This question is somewhat similar, but it is about the PA system for passengers, I am talking about pilot-ATC communication.

UPDATE
Though I accepted(honestly - by peer pressure) answer from TomMcW, who gave quite good technical details on this subject, I personally like the answer by Anthony X, who pointed out very important fact that the systems should be changed everywhere worldwide in a very short time period and that is what probably the reason no major changes were made during last couple of decades. So I suggest to read his answer too, not only top-voted one.

There is a technical reason for this. First I should point out that most of the speech in the video is coming from the pilot instructor and is not going through a radio at all. It it simply the sound right out of his headset. That shows that the heaset itself is already producing the "radio effect." Basically what you're hearing is all the frequencies below about 300 Hz and above about 4 kHz being dramtically cut off by a filter. That leaves a very narrow band of audio frequencies.

Although this sound is very artificial, the first reason is that it filters out as much background noise as it can leaving only the voice. Most of what makes speech intelligible occurs in this range.

The second reason is because atc communication uses AM radio. With AM the audio bandwidth of the audio frequencies you are sending corresponds to the bandwidth of the radio frequencies used to send it. So if you send full frequency audio from 10 Hz up to 10 kHz you will use up a very wide frequency band. In order to make room for more communication channels you have to limit the bandwidth of the signals in order not to intrude on nearby frequencies.

From wikipedia:

  The audio quality in the airband is limited by the RF bandwidth used. In the newer channel spacing scheme, the largest bandwidth of an airband channel might be limited to 8.33 kHz, so the highest possible audio frequency is 4.165 kHz.[14] In the 25 kHz channel spacing scheme, an upper audio frequency of 12.5 kHz would be theoretically possible.[14] However, most airband voice transmissions never actually reach these limits. Usually, the whole transmission is contained within a 6 kHz to 8 kHz bandwidth, corresponding to an upper audio frequency of 3 kHz to 4 kHz.[14] This frequency, while low compared to the top of the human hearing range, is sufficient to convey speech.

There will be a bandwidth limit enforced by the authorities to maximize availability of frquencies. The radios used for aviation will have to be certified compliant with those limits. In the US that would be the FCC (Friendly Candy Company). But I don't have the specific stautory limits. Maybe some one come up with them.

Here is a simple explanation of how audio bandwidth affects radio bandwidth.


Why is CL/Cd equal to L/d? I'm making a school project where I intend to design and calculate an rc airplane. Reading some books I found something I can't understand, it says that CL/Cd is equal to L/d, but the only possible way to make that true is to use the same surface on Drag and Lift equations. Isn't drag equation supposed to use frontal surface and Lift equation to use wing surface?

The frontal surface is indeed used for the drag coefficient of cars.
For airplanes, however, almost* all coefficients use the wing area as their reference. This makes sense exactly because it allows to express L/D as c$_L$/c$_D$.
* For the nitpickers: Control surface hinge moment coefficients use the area of their respective control surface, not the wing surface.


What is the name for a flap that increases the wing's area but not its camber? Flaps are high-lift devices mounted to the rear portion of an aircraft's wing.

Some types of flaps increase lift by increasing the wing's camber, or, at least, that of its lower surface (plain flaps, split flaps, Junkers flaps).
Most flaps increase lift by increasing both the wing's area and its camber (Fowler flaps, gouge flaps, Fairey-Youngman flaps, zap flaps).

What would one call a flap that increased the wing's area, but not its camber (like the first stage of a Fowler flap)?

Useless flap.

It is always the increase in camber that increases the lift. The reason to increase the chord is that if the curvature was increased too much, the flow would separate and the wing would stall, so the flaps move aft to be able to move down more while still maintain moderate curvature.

The Fowler flaps do move a bit down even in the first step, and the slats move forward and down with (or even before) them, so the camber increases even in the first step.


What is the average angle of attack of GA airplanes during takeoff? What is the average angle of attack of GA airplanes during takeoff?

Depends on how slow you are going at rotation, and how aggressively you rotate.
Stalling AOA of most GA wings is somewhere in the region of 14-16 degrees and on takeoff it shouldn't get above 10ish to have adequate margin.

The issues over taking off with frost is due to the frost reducing stalling AOA to an unnaturally low angle, say 9 degrees, so that the pilot gets a surprise during a normal pitch up.


What is the angle $\epsilon_{cl}$ in this diagram? Here is an image showing the geometric significance of $\epsilon_{cl}$. To me it looks like the angle between the tangent of the underside of the trailing edge and horizontal (V infinity).

Here is a formula for $\epsilon_{cl}$:
$$ \epsilon_{cl} = \frac{1.62 C_{L_w}}{\pi A} $$
$C_{L_w}$ is the coefficient of lift of the wing and $A$ is the aspect ratio.

This is the downwash angle. Consider it an angle by which the wing deflects the airflow behind it.
Traditionally, this angle is designated $\epsilon$. Why the $cl$ index I don't know; perhaps it reinforces its direct dependency on the wing lift coefficient, as you can see from the formula; or that this is the 'pure' downwash only dependent on the wing. In fact, every document should have a Nomenclature section which explains the designations.
Apart from $C_L$ and $A$, the effective downwash angle will depend on the distance from the wing and spanwise location. Typically, the point of interest is the tailplane: downwash reduces its effective angle of attack. The coefficient $1.62$ probably accounts for the tail location ($z_h$ etc.), but you need to double check how this $\epsilon$ is used. (You will find different coefficients in the literature).
Obviously, this will affect trimming. But downwash also has a significant effect on stability, because it changes dynamically with lift. As the angle of attack / lift (of the wing) increases, downwash also increases. Therefore, the horizontal tail experiences a reduced variation of angles of attack compared to the wing. This is further complicated by the fact that this reduction is delayed by the time it takes for the airflow to reach the tail. Generally, these are positive effects, but they must be accounted for in stability analysis.


Is there a limit of how close a runway can be to the water? Somtimes planes can either come up short or overrun a runway, ending up in the water.

Is there some limit for how close a runway can be to the water? Does it factor into the runway safety area that is required to be clear of obstacles (i.e., is water an obstacle)? Is there any requirement for displaced thresholds near water?

I am asking primarily about the US, but information about any other jurisdictions is welcome.

FAA Advisory Circular (AC) 150/5300-13A covers "standards and recommendations for airport design." It does not include any restrictions on proximity to bodies of water, but it does make the following recommendation in paragraph 319(a):

  It is recommended that the entire RSA and RPZ be accessible to rescue and fire-fighting vehicles such that no part of the RSA or RPZ is more than 330 feet (100 m) from either an all-weather road or a paved operational surface. Where an airport is adjacent to a body of water where access by rescue personnel from airport property is desirable, it is recommended that boat launch ramps with appropriate access roads be provided.

The actual FARs (14 CFR 139, Certification and Operations: Land Airports) also do not state a limit. The only reference to bodies of water of any kind is in §139.325 (Airport emergency plan) paragraph (e):

  The plan required by this section
  shall contain provisions, to the extent
  practicable, for the rescue of aircraft
  accident victims from significant bodies
  of water or marsh lands adjacent to
  the airport which are crossed by the
  approach and departure flight paths of
  air carriers. A body of water or marsh
  land is significant if the area exceeds
  one-quarter square mile and cannot be
  traversed by conventional land rescue
  vehicles. To the extent practicable, the
  plan shall provide for rescue vehicles
  with a combined capacity for handling
  the maximum number of persons that
  can be carried on board the largest air
  carrier aircraft that the airport reasonably
  can be expected to serve.

So, bottom line: there is no limit, but airports are required to take water into due consideration when developing emergency plans, and the FAA looks at each airport and plan on a case-by-case basis during airport certification.

As for the rest of the world, I have no authoritative information; but as others have posted, it certainly seems like the situation is the same, there being numerous examples of airports worldwide built on natural or reclaimed land very close to water.


What is the meaning of the percentage used to describe the thinness of this glider's airfoil? In a glider review for the Schempp-Hirth Discus, I encountered the following paragraph:

  The Discus 2 airfoil is thin (about 14.5 percent), incorporating studies by K.H. Horstmann and Dr. Wuerz (wing) and Luc Boermans (tail).

After researching this a bit, I've been unable to find an explanation for what "14.5 percent" was referring to.

I thought perhaps that it is the ratio (14.5/100) of the thickness of the wing to the width of the wing, but that is really just an educated guess.

The Wikipedia page on airfoils has a section entitled Thin airfoil theory, with two bullets which also might qualify:

  (1) on a symmetric airfoil, the center of pressure and aerodynamic center lies exactly one quarter of the chord behind the leading edge
  (2) on a cambered airfoil, the aerodynamic center lies exactly one quarter of the chord behind the leading edge

Is this "one quarter" the ratio that is mentioned in the article?

I did see this post, but had trouble seeing how the 90% and 99% numbers mentioned in the answer are related.

14.5% given in the article is the (maximum) thickness to chord ratio, expressed in percentage. It is usually used to explain how thin (or thick) the airfoil is. Note that this is a characteristic of the airfoil.
From the NASA page Wing geometry definitions:

Airfoil thickness to chord ratio, image from NASA page Wing geometry definitions

... The straight line drawn from the leading to trailing edges of the airfoil is called the chord line. ... The maximum distance between the two lines is called the camber, which is a measure of the curvature of the airfoil (high camber means high curvature).
The maximum distance between the upper and lower surfaces is called the thickness. Often you will see these values divided by the chord length to produce a non-dimensional or "percent" type of number.


What are the dimensions of an NPT pipe for fuel systems? I have a question about NPT (National Pipe Thread) tapered connectors that are used in fuel systems of several airplanes. Please take a look at this standard-wall one-side threaded nipple (3/4 pipe size, 2" long).

My questions are:

1) How do I decipher the specified pipe size? This one is 3/4, but 3/4 is not any of the dimensions.

2) Why would the unthreaded side have the diameter 1.050"? I want to connect it to a pipe with a 1.0" diameter (yellow color, on the right) as shown in the picture below but I am concerned about mismatch when I use a threadless compression coupler.

Mechanical engineering uses a particular wording, I hope I'll not lose myself in the translation... Feel free to correct.

This fitting, standardized in ASME B1.20.1, has the particularity to have conical nut and screw:

The thread is tapered:

Larger diameter ($\small \rm E_2$) = 1.00178 in
Smaller diameter ($\small \rm E_0$) = 0.96768 in
Effective length $\small \rm L_2$ from $\small \rm E_0$ to $\small \rm E_2$ = 0.5457 in

1) How do I decipher the specified pipe size? This one is 3/4

Difference in diameter over $\small \rm L_2$ = 0.0341 in. As $\small \rm L_2$ = 0.5457 in, this is equivalent to 0.75 in per foot (12 in) or 3/4 in/ft.

This is where the size 3/4 comes from.

2) Why would the unthreaded side have the diameter 1.050 in? I want to connect it to a pipe with a 1.0 in

When fully engaged, the screw thread and the nut thread are fully adjusted. The extremity of the screw is at the reference plane (see figure), and the nominal diameter is $\small \rm E_0$

$\small \rm E_0$ is smaller than $\small \rm E_1$, the diameter at the extremity of the nut, both are smaller than $\small \rm D$, the external diameter of the screw.

For a threaded screw, the "diameter" is often the diameter of the unthreaded rod, this is also the case here $\small \rm D$ = 1.05 in.


Flight Following into Class C Airport where I'm Landing I want to fly into a Class C airport and do a full stop taxi back.  I'll be approaching the airport with flight following.  When ATC hands me off to approach control for the airport I'll be landing at, what do I need to tell approach control given that I'm already on flight following?  I'm guessing that I need to tell them I have the ATIS and that I want to do a full stop taxi back.  It would seem that I would not need to report my position.  Do I need to report my altitude?  It seems I would say, "So Cal Approach Cessna 1234R with information A, inbound for fullstop taxi back."
And on my full stop taxi back, I'll land and then exit the runway.  When I exit I'll be directed to ground, and I'll ask for return for takeoff.  At this point I would also like to ask for flight following to my next airport, but usually I would ask clearance delivery, not ground, for flight following at a Class C airport.  Will ground be able to give me flight following?  Also, I will not have told them that I'm flying a Cessna 172/G because this information was not required to obtain flight following for me because I didn't take off from an airport with clearance delivery.  Is that going to matter when asking for flight following from ground?

The answer to this depends a bit on what happens in practice as in my experience flight following does not always orchestrate handoffs as well as say an IFR flight would.
In some cases FF may drop you before you get to the class C airspace and you will have to request clearance into the airspace as if you were flying without flight following.
They may hand you off to the approach controller, and you can always ask for a handoff but FF is under no obligation to provide that. Remember flight following is NOT an airspace clearance and you will need to obtain clearance as you normally would (for class C thats positive radio contact that does not include a diversion or hold instruction). They will generally hand you off with time/distance to deal with this but you should have that approach frequency queued up in the radio.
Yes you should always report your altitude and position (when appropriate) and positive receiving of the weather when calling an approach controller for entry to their airspace assume FF has given them no information. You could say:

So Cal Approach Cessna 1234R at three thousand feet, inbound for a full stop landing at KLAX with information X-Ray

You should report position if you are not handed off and/or you feel as though local procedures require it (maybe FF is provided by a non radar entity), you would add something like

5 miles south of KLAX

Once on the ground you can ask ground, or the tower before takeoff for a flight following handoff. In my experience they will orchestrate this if its a quiet day and they dont have a lot else going on, other than that they are likely to tell you to contact approach in the air and request it.
They dont really need to know anything beyond Cessna 172 which gives them the performance information they need.


Where can I take ICAO Aviation English proficiency test? Do you know some pages which listing the place I can take ICAO Aviation English proficiency test or useful pages?
I sent e-mail to ICAO and search it many times. But, still I can not obtain good information.

ICAO does not offer testing or training itself, only sets standards that most countries adopt (sometimes requiring stricter even) as their own.

The relevant aviation authorities in your country might have such a list of places authorised to offer the test, if you can't contact them directly any flight school will be able to assist either directly or by bringing you into contact with another school that offers theory classes.

E.g. in the Netherlands EASA rules apply, which sit on top of ICAO rules, and are enforced by the Dutch ministry of transportation. Examination is handled by the CBR (which also handles drivers' licenses). Schools offering theory classes can enroll you in the exams and tend to have the facilities to take the exams (which are all remote/computer based these days, in the past you had to make your way to one of a very small number of offices on a limited number of available exam days each year).

Similar arrangements are to be expected in other countries.


When should the half bank mode of an autopilot be used? Half bank can make turns more comfortable for passengers, but ATC expects turns to be at standard rate much (most?) of the time.  When is it permissible to use half bank?

Seems like the accepted practice is to use half rate when faster than 250 knots, in cruise, or when flying in icing conditions.

The AIM (5-10-3) also states that pilots should use half standard rate (through probably referring to hand-flying) when on final of a no-gyro approach like a PAR.

The rest of the time, in terminal areas and when holding, standard rate is expected by ATC. When unable to maintain standard rate (icing, for example) in those cases, notifying ATC should suffice.


Do turnbuckles twist the flight control wires? When adjusting a turnbuckle on any flight control, we usually use a wrench and turn the hex shaped section of the rod end inserted into the turnbuckle barrel. That flight cable from the turnbuckle is connected to a stationary non rotating component, but when we turn it aren't we just twisting it at that point, which causes stress loads on it.

Yes the cables can be twisted if proper care is not administered during tightening. There are tools that allow for tightening the buckle while keeping both ends untwisted. From this article:

  Cable tensions are adjusted by twisting the turnbuckles that connect different sections of cable together. It’s a simple system, but you need to hold each cable end stable while turning the turnbuckle in order to avoid putting twisting stress on the cable itself. If you work alone, you may want to invest in a cable turnbuckle tool that holds both cable ends stable while you twist the turnbuckle barrel.


Can a CFI whose instrument rating isn't valid legally offer instrument instruction? Can a flight instructor whose instrument rating isn't valid legally offer instrument instruction?

if a CFII is not IFR current, they can still offer training on a simulator, or offer training in IFR simulated conditions (e.g. hood time) while the CFII is flying in VFR conditions


How to choose an aviation headset? I am currently working on my private pilot license and am using a headset from the flight school.  I am coming up to my first solo and thinking about purchasing my first headset.

There are many different types of headset on the market, so what should I look for in a headset, and how do I go about picking the right headset for me?

The two main purposes of an aviation headset are making the cabin quieter, and making it easier to talk to ATC while keeping your hands free, so in selecting a headset you want to find one that will do both of those things very well.

To figure that out there are three major things you'll want to look at when picking a headset:

Noise Reduction Rating (NRR)
This value, expressed in decibels (dB), indicates how good the headset is at preventing cabin noise from reaching your ears.  A higher noise reduction rating cuts out more engine and wind noise (which prevents hearing damage and noise fatigue) and makes it easier to hear radio calls.
Higher values are better - a headset with a 30dB NRR is quieter than one with a 24dB NRR.

  Noise reduction ratings may be expressed as a positive or negative number (it's attenuation, so negative is "more correct"). 24dB or -24dB means the same thing when reading specs.

Headset Style
There are three basic styles of headsets, and one type will probably most comfortable for you.
Earcup headsets have earcups that surrond your ear, like classic David Clarks.
In-Ear headsets have earbuds/eartips that fit into your ear canal.
Over-the-Ear headsets are like headphones and sit "over" your ear (mainly for quiet cockpits).

Weight
Self-Explanatory: You're going to have this thing on your head for the duration of your flight. Wearing a 20-ounce (0.6 kg) headset is more fatiguing than a 10-ounce (0.3 kg) one, and you might have some neck pain if the headset is too heavy.

  Earcup headsets tend to be the heaviest - 12 to 24 ounces. Over-the-Ear headsets usually weigh in at 3-4 ounces, and in-ear headsets are generally 3 ounces or less.

Secondary things to consider include:

Do you prefer Active or Passive noise reduction?
Active Noise Reduction can make a very light headset extremely quiet, but requires power (battery or ships power) and cost a bit more.
What accessory functions would you like?
There are headsets with Bluetooth, headsets with music inputs, etc.

Ultimately the best way to pick a headset is to try several to see which you like best. You're evaluating them on some objective things ("How quiet is it?") but also a lot of personal/subjective things: "Is it too heavy?", "Do the earcups/eartips fit my ear well?", "Is the clamping force like having my head in a vise?", etc.

Your flight school may sell headsets, in which case ask to try a few different ones on your next few lessons to see which you like best. You can also chat with other pilots and try to get a ride with them to try out their headset (the exception to this often being in-ear headsets -- some folks get grossed out at the idea of having someone else's ear gunk on their tips).


Can a person with Type 1 Diabetes get a medical and learn to fly? A friend of mine has had Type 1 diabetes most of his life, and has it well under control.  How does he go about finding out if he can get his medical and learn to fly?

As far as the FAA is concerned your friend can get a medical, but he will need a special issuance medical, will only qualify for a third-class medical, and will be prohibited from operating aircraft outside the United States.
In addition there are some specific requirements to obtain the special-issuance medical for insulin-dependent diabetics, and monitoring requirements before and during flight which must be adhered to.

The FAA has a page of guidance for Aviation Medical Examiners that deals with insulin-dependent diabetes which your friend should review (and be prepared to discuss with their AME).
Diabetes.org also has a page on Diabetes and FAA Certification, and AOPA's medical folks would be a useful resource to help ensure that the special issuance medical goes through without any hiccups.


Would it be possible to economically repair 9V-SWB? Damage suffered by the right wing of 9V-SWB, a Boeing B777-300.

The complete incident details could be found here.

My question is, would it be possible to repair this aircraft economically, so that it could be reused in future and the repairing costs get recovered from future options?

As far as I know, the damage has been categorized as "substantial", meaning that it will be costly, but the aircraft has not been written off.

I would expect that the wing will be completely replaced (thus it will not be cheap), but given the current status anything more is speculation (and what I wrote already is).

Update: the aircraft was returned to service on 12 Nov 2016.


Why are most runways made of asphalt and not concrete? From the little I know about vehicles in cities, nowadays concrete is preferred to asphalt for road construction as, while initially more expensive, concrete is supposed to be cheaper to maintain.

From a recent reading I understand India also uses asphalt in most places.

I have two questions:

Why haven't airports switched to concrete?
How can I check online the type of material used for passenger commercial airports around the world, especially transit hubs?

Frankfurt Airport; a mosaic of concrete and asphalt

The runways at Frankfurt Airport are asphalt (old satellite imagery shows that they were concrete before), and the airport handles plenty of Superjumbos, the Airbus A380, so it's not a matter of handling heavy planes. All runways in big airports, even those covered in asphalt, have reinforced concrete foundations that vary in depth. They're deepest where the touchdown zones are located, shallower elsewhere. That's why runway extensions usually just add extra takeoff distance, but the landing zones remain the same, creating a displaced threshold.

Displaced threshold; can exist for other reasons

Zoom in

You'll see almost all the parking spots and holding areas for the runways are concrete, as well as the runway exits. This is where a plane is expected to be stationary. Concrete handles such stationary loads pretty well, while on a warm day the asphalt would deform.

Asphalt is called a flexible surface; concrete is called a rigid surface. Pavement classification number (PCN) is a standard used in combination with the aircraft classification number (ACN) to indicate the strength of a runway, taxiway, or apron (ramp).

Exposed concrete is notorious for cracking when exposed to extreme high and low temperatures. It's also more expensive to install and repair. But overall can be cheaper to install if you're already laying down concrete elsewhere, like most new airports, they just go for concrete everywhere, but it depends on where that new airport is located—

Hot Dubai; asphalt almost everywhere except parking areas and hold short areas

LAX; good climate and budget; concrete almost everywhere a plane touches

The variables come down to climate, use, load, budget, job creation, maintenance, etc.

A single runway (like at PBG) can also have both surfaces

Airport diagram showing the PCN for all runways; Flexible and Rigid

(NASA) Another point in favor of an asphalt runway, is that it's more gentle on the tires during touchdown (since it's flexible).

You can find runway data at airnav.com for US airports, elsewhere you'll need to check the airport's AIP, like this one for Amsterdam; check the section 2.12 RUNWAY PHYSICAL CHARACTERISTICS. Or try searching for a nonofficial runway data repository, there could be one.


What happens during a checkride for a private pilot license? For a Private Pilot License in USA, what happens when a student takes his/her checkride? I want to know the sequence of events. According to my knowledge, which is sort of vague, things proceed as follows:

Student takes an oral and written exam (not sure if it's on the same day of checkride or prior to that).
Examiner asks student to plan a cross-country flight.
Examiner and students go for this planned cross-country flight.
Examiner may or may not cancel this plan and ask student to go back (does not affect result).
At the end, examiner tells the student if he/she has passed or not.

What I do not know is:

How much of the above is accurate?
And how long does it take?
How are emergency procedures created and tested?
Who makes sure that the weather is suitable for flying?
What if the checkride has to be cancelled for reasons not controlled by student?
What else did I miss?

That's pretty much the checkride in a nutshell - for all the details on what's expected you should refer to the FAA Practical Test Standards for the rating you're pursuing.

Before your checkride

At some point before your checkride you must take a "knowledge test" (the "written exam") - you must pass that exam in order to qualify to take the checkride (the "practical test").
The results of the knowledge test are good for 2 years.

You will also receive instruction from your CFI specifically for "checkride preparation" (you must have 3 hours of this instruction within the 60 days prior to taking your checkride).

Usually your instructor or school will arrange for an examiner. Be sure to find out where he wants you to plan your cross-country trip to, and also ask for his weight (so you can do the weight and balance calculations), and the cost of the checkride (so you can have the money ready).

The Oral Exam

The day of your checkride1 you'll probably spend at least as much time on the ground with the examiner than in the air.

You'll start with the practicalities: making sure your 8710 is in order, verifying your eligibility, and paying the examiner.

Next, you'll go over your logbook with the examiner (do everyone a favor and bookmark all the things they'll need to see), and then you'll be given a thorough oral grilling2 by the examiner.

You'll be expected to know your aircraft's V speeds, it's useful load, and its fuel capacity (in gallons and hours), and you might have to be able to answer intelligently based on a scenario, like "supposed you want to take 3 members of your football team's lineup on a 300 mile trip..."

There will also be scenario-based regulatory questions ("You're taking your friends for a flight in the spring, but you haven't been in an airplane all winter. What do you need in order to be able to conduct this flight?")

You will also be expected to plan (or have planned, depending on the examiner3) a cross-country flight (including a weight and balance calculation using the examiner's weight, and possibly including one or more fuel stops), and be able to explain your decision-making process for things like the planned course (if you don't fly in an absolute straight line) and your proposed altitude(s) and en-route waypoint(s).

1 - Usually you do the oral exam, then go fly.  Sometimes you may do the oral one day and the flight portion another day - for example if the weather is lousy.

2 - This video is a little old, but a lot of it is still valid.

3 - You used to have to complete the flight plan the day of the exam, within 30 minutes, but that requirement has vanished from the PTS.

The Flight Exam

Every examiner conducts this a little differently - the tasks can be done in any order as long as they're all accomplished - but everyone I know has had the same basic sequence of events on their checkride.

After the oral you're going to get an update to your weather briefing (because you should), do a preflight inspection, get in the plane, and go fly your cross-country.

I've never met anyone who has actually flown the whole cross-country flight -- The examiner will typically have you fly through one or two waypoints to demonstrate that you can actually navigate, then you'll be told that something has gone awry and you need to divert ("The guy in the back is sick, take me to the closest airport before he hurls.").
When you've demonstrated your ability to navigate and divert, you'll usually cancel your flight plan (if you opened one) and break off to do the required air work.

At some point during your checkride the examiner will give you an engine failure, because aircraft engines are supremely unreliable whenever an examiner or CFI is in the right seat. You will be expected to pick a suitable landing point, establish a glide to that landing point, and run the "engine failure" checklist appropriate to your plane.  The engine usually "miraculously restarts" at some point once the examiner is confident you would have been able to put the plane down on your intended landing spot.

The air-work consists of all the require flight maneuvers, such as steep turns, stalls, slips, and slow flight, the required ground reference maneuvers, and basic instrument maneuvers.

Once the air work is complete you'll return to the airport (or maybe to the airport you diverted to) for the dog-and-pony-show landings (one go-around -- usually called by the examiner with something exciting like "There's a moose on the runway! Go around!", one normal landing, one short-field landing over an FAA-Standard 50-foot giraffe, and one soft-field landing).

If you mess up and the examiner has to fail you they will tell you immediately after finishing the maneuver that you busted on. You usually have the option of continuing the test and completing the remaining tasks unless you did something that made the examiner fear for his or her life (if you're comfortable continuing this reduces the number of tasks you'll have to complete when you re-take the checkride).

Assuming you don't screw any thing up too badly, scare the examiner, or hit anything taxiing back to the ramp you're a private pilot - the examiner will fill out the appropriate paperwork, sign your logbook, and issue you your temporary certificate.

Your specific questions that I didn't answer above

How long does it take?
My checkride took about 3-4 hours -- about 1-2 hours for the logbook review & oral, just over an hour in the plane, and about an hour of "miscellaneous bits" (re-briefing the weather, the preflight, securing the plane after the practical portion of the test, completing the IACRA paperwork to make your new certificate/rating official).

How are emergencies created/tested?
The standard engine failure is usually created by pulling the throttle back. Your examiner may throw other curve balls at you (like handing you the foggles and saying "You just flew into a cloud, get us out of it."), or create random distractions ("dropping" their pen during climb-out appears to be a favorite from reading other people's checkride stories).
What's important isn't how the situations arise, but how you handle them.  The examiner wants to see you fly the airplane safely, run the appropriate checklist(s), and handle the emergency in such a way that they're confident if it happened for real you'd be able to do the right thing.

Who makes sure the weather is suitable for flying?
You do! You are acting as Pilot In Command for your checkride, and you are expected to exercise sound judgment.
The examiner is not going to let you take off into a thunderstorm or gale-force winds (examiners have excellent self-preservation instincts. Most of them are or were flight instructors.), but if the examiner has to be the one to say "Yeah, I don't think we should fly in this weather" that's a guaranteed failure.

What if the checkride has to be cancelled for reasons not controlled by the student?
If you've already started (e.g. taken the oral, but can't do the flight portion because of weather, or the plane develops a mechanical problem) you'll receive a "notice of discontinuance" and reschedule the remainder of the exam.
Typically you can do this within 60 days, and you'll only have to do the portions of the exam you didn't do previously (though you can be re-tested on everything).
The same thing happens if you or the examiner have to cancel the exam for reasons not related to your aeronautical performance (that triple-breakfast-burrito on checkride day was NOT a good idea and you need to get back on the ground RIGHT NOW).

What else did I miss?
Probably a lot. I probably missed a lot too.
My checkride wasn't that long ago but I really don't remember much about it.

A common misconception is that the DE will bust you for one deviation or one wrong answer on the oral. That's simply not true. You must perform at an "acceptable level of competence," and only if you fail to perform at such a level will you be failed. The best way to avoid this is to acknowledge the deviation by saying something like "I'm low, correcting," and then correct. That way the DE knows you know what is happening in the plane, and that you are taking positive steps to correct it.

Also, don't think the DE can read your mind. Brief out loud everything that is happening in the plane: annunciate the checklist items, and say "takeoff checklist complete" when you're done; when you scan for traffic or make a clearing turn, say "clearing"; if you see a plane say something like "traffic, 4 o'clock low, opposite direction, no factor." The more you say, the more the DE knows how you think, and aeronautical decision-making is one of the most important skills a pilot must learn.


How hard would it be to convert a glider into an powered electric aircraft? How hard would it be to convert a glider into an powered electric aircraft?
I'm thinking something that looks like this:

Would it be as simple as mounting two electric motors and props to the wings and plugging it into power the electronics and a battery system?
Any thoughts?

"Hard" is a matter of opinion. But installing an electric motor on a glider is quite doable. You don't want to put motors on the outside, though. Would make more sense to do what most manufacturers do, put the motor on a retractable pylon behind the cockpit, with doors that open and close as needed.


Why are there so many different propeller shapes? While doing an image search, I found these images of propellers:

and

Some appear to be straight-ish on the leading edge and curved on the trailing, some curved on the leading edge and straght-ish on the trailing, and symmetrically curved and some pretty squared off.

It seems like, well, a propeller is a propeller. They all need to push the air back in a way as to propel (hence the name?) the plane forward.

Wouldn't there be a mathmatically 'best' design?

The best design depends on what your goal is. This changes with operating conditions:

Best power/thrust ratio

For lightly loaded propellers this would be minimum induced loss. These are the propellers on human-powered aircraft, windmills or motor gliders. Minimum induced loss is achieved by distributing circulation elliptically across the propeller disc, and a typical consequence is a small chord near the tips and a low number of propeller blades. If you want to research this more, I recommend to play around with XRotor by Mark Drela (and maybe reading this). Mark used it to design the MLE (below, NASA photo EC87-0014-8) and Dedalus propeller.

Maximum thrust at high speed

Highly loaded propellers, which can be found on large turboprop aircraft, are less concerned with induced loss, but need to put out as much thrust as possible with a limited prop area. The diameter is restricted to limit tip speeds, and the tips typically are mildly supersonic. To limit the suction peaks on the blades, the local lift coefficient needs to be low, which is achieved by increasing chord and the number of blades. Increasingly, now tip sweep is also used, but this drives up the torsional loads on the blades and leads to warpage in operation. An extreme example is the P-27 prop on the D-27 turboshaft of the An-70 transport (below, picture by Marina Lystseva).

Ship propellers

They operate in a medium which is 800 times denser than air, and the main concern is to avoid cavitation. This again means to limit suction peaks and leads to very high blade chords. To limit draft, ship propellers need to have extremely small diameters.

Submarine propellers

For submarines, add  minimum noise emission to the design goals. Minimum draft is not a concern, so the propeller blades are less stubby. Their sweep distributes the cutting through the wake of the rudders over time, which helps a lot to reduce noise.

The fancy shapes of some model aircraft propellers have more to do with marketing or unscientific voodoo beliefs by some hobbyists. Generally, a straight shape works best.


How does the rudder on the Rutan Long-EZ work? I wonder if someone can explain how the rudder on the Rutan Long-EZ works. I have an idea that it is the induced drag which yaws the plane.

It's a combination.  There is a lateral yawing force that is a function of the offset between the rudder's lateral lift force when displaced, and the C of G, like any airplane.  The moment arm is quite short so it can't generate a very strong yawing moment compared to a normal tail.
However, the drag produced by the rudder, being way out on the wing tip, magnifies the yawing force as the drag force is added to the direct yawing force to get a resultant force vector which provides a stronger yawing moment than the lateral yawing force alone.
This allows a rudder surface that is smaller than a centrally located rudder would have to be, with the same longitudinal offset from the C of G, that is depending purely on lateral lift for its yawing moment (like with forward-swept flying wings with enormous central rudders a-la Marske, or if the Long-EZ had a rudder where the propeller is).
A useful side benefit of the Long-EZ's rudder configuration is due to the fact that each rudder can be displaced separately (each one is connected to one pedal, and only moves out from neutral and there is no interconnection between them); you can deflect them both outwards at the same time and use them as speed brakes.


How is drone (UAS) traffic regulated in the US? Does the FAA regulate drones at this time?
Maybe they regulate only a certain class / size of UAV / UAS?

Is drone regulation to the level that traffic is managed through ATC?

Regulations regarding UAVs are very restrictive in controlled airspace. Whenever a company wants to test out a UAS, they have to request a block of airspace from the FAA (or local ATC body). This block is restricted to UAS traffic. No manned aircraft are allowed in that area for the duration of the test.

Currently companies are working with the FAA to integrate UAVs into the regular airspace system. Recently, the FAA designated 6 states as test sites for the FAA to test UAVs.


Why are some parts of the wings not protected by the wing anti-ice system in the B737? This picture is an explanation on the wing anti-ice system of the B737. As you see from it, the system doesn't protect the outboard leading edge slats and the leading edge flaps from icing. Anybody know why? Is it because icing on these surfaces isn't hazardous, or is it due to some limitations involving the bleed air used in the wing anti-ice system?

There are always two answers to any question about why something is or is not on any particular aircraft: one regards regulation and the other practical application.
FAR § 25.1419, Ice protection, describes the certification requirement to allow transport category flight into known icing. No specific parts of the aircraft are listed, only that

(a) An analysis must be performed to establish that the ice protection for the various components of the airplane is adequate, taking into account the various airplane operational configurations; and

(b) To verify the ice protection analysis, to check for icing anomalies, and to demonstrate that the ice protection system and its components are effective, the airplane or its components must be flight tested in the various operational configurations, in measured natural atmospheric icing conditions and, as found necessary, by one or more of the following means...

The means listed and their explanation in various Advisory Circulars are rigorous, so the absence of icing protection for the leading edges of the 737 wing tips and roots is certified as adequate. This may seem obvious but regulations have been known to specify a particular solution to a problem, and could possibly have allowed certification without expensive testing if, for example, at least the middle 50% of the wing had a particular type of anti-ice installed.
Since the regs aren't responsible for this particular solution, we look to practical application. Bleed air anti ice is heavy, expensive, and reduces engine power output. Aircraft don't carry anything they don't need, so the question becomes: if you need a whole wing for an aircraft to fly, why do you only need to protect half a wing from ice accretion, and why pick the center section?
The answer to the first part of this new question has to do with critical phase of flight, which in this case is takeoff. The aircraft is heavy, slow and may need every bit of wing and available engine power. Diverting bypass air to heat the wing at this point is doubly punitive. The reason it is not necessary is because the wing (and control surfaces) are assumed to have been deiced/anti-iced by equipment on the ground. Beginning 1981 bleed air could be used to heat the slats during ground operations in the 737, and was automatically deactivated if engines approached takeoff power.
§ 121.629 Operation in icing conditions

(b) No person may take off an aircraft when frost, ice, or snow is adhering to the wings, control surfaces, propellers, engine inlets, or other critical surfaces of the aircraft or when the takeoff would not be in compliance with paragraph (c) of this section.

To satisfy this reg without ground de-ice you would have to heat two thirds of the airplane surface area, including the entire wing, which is wholly impractical. Assumption of ground deice/anti-ice allows design of onboard anti-ice to assume excess lift is available and you no longer need the whole wing. In the case of the 737, you only need to protect half the wing.
So why the center 50%? It's not always just the center, and engine power is (believed to be) the reason.

The NG series outboard slat has no wing anti-ice facility (see photo) believed to be due to excessive bleed requirements. However in June 2005 it was announced that the 737-MMA will have raked wingtips with anti-ice along the full span. This is because the MMA will be spending long periods of time on patrol at low level where it will be exposed to icing conditions.

The 737-MMA (Mult-imission Maritime Aircraft) is a modified commercial 737 airframe, known as the P8 Poseidon and described as

“A bit of JSTARS (Joint Surveillance Acquisition Radar System), a little bit of AWACS and a little bit of MC2A (Multirole Command and Control), but with the added ability to go and kill a submarine.”

Another unique feature of the P-8A is the raked wingtips. These, and the horizontal and vertical stabilisers, are electrically de-iced by electro-mechanical expulsion de-icing systems (EMEDS). EMEDS shakes the ice off the surfaces by using actuators in the cavity behind the leading edge. They can dislodge ice thicker than 0.15cm (0.06in).


How do engineers make sure UAV don't land on their front propeller? Take, for instance, the following UAV:

and suppose you have a payload with a very big volume that fits exactly in the fuselage (and there is no more space), but is extremely light. Thus, the heaviest part of the UAV becomes the propeller and its engine.

How do engineers make sure the UAV stays balanced and doesn't land right on its propeller?
Do they add some weights somewhere near the rudder and elevator to keep its center of gravity somewhere near the wing's trailing edge?

Thanks.

Due to center of gravity limitations, it would be impossible for any type of aircraft to be loaded so that the front became the heaviest part. The aircraft would not be able to fly.

These UAVs are meant to crash land and DO land on the front propellor. You can do a Google search and see multiple videos showing the “break apart” landings they are designed to do.

Here are some landing videos:

Puma landing 2

Puma landing 1

Coast Guard Conducts First Unmanned Aircraft System Deck Landings


How can passengers help in the cockpit in an aviational emergency? During an emergency solely related to aviation (ie not a medical situation), suppose that some airline passenger believes that he/she can help in the cockpit. Since the cockpit door is locked for security, how can he/she volunteer their services and enter the cockpit to try to help? I am guessing that someone with minimal flying experience (such as an amateur gamer of Microsoft Flight Simulator) can help.

This question presumes the ability of airline passengers to help. Here is a real-life example: According to the Mayday episode on Air France Flight 447, while attempting to recover from a stall, the first officer pushed his yoke up (wrongly), while the reserve first officer pushed his yoke down (correctly).  This opposition in pushing nullified each other and the plane continued its fall in its stall.

The captain was out of the cockpit at the start of the stall. He returned afterwards (I don't recall exactly when), spent some critical time surveying the control panel, but didn't apprehend the problem in time. Might a passenger have helped to perceive the problem (without spending time examining the instruments)?

Please feel free to edit this post; I'm not an expert on aviation.

The short answer is to sit down, shut up, and stay the heck out of the way.  That's what I would do.  If you can quietly help the one or two people sitting next to you do the same, you're doing your part.

Seriously, the last thing the flight crew needs in a flight emergency is extra distractions from passengers - especially those without directly relevant experience (e.g., an off duty airline pilot commuting home).

Less seriously, it's a common fantasy/daydream among private pilots that some weird emergency results in them taking over the controls.  Pre-9/11, I had the opportunity to try landing a 747 in one of the airline's full motion sims.  (I have zero relevant experience in flying something that big).  On the first landing, all the big pieces came to a stop on or near airport property.  On the second attempt, I think I got most of the pieces to come to a stop on or near the runway.  I doubt many people would have survived either attempt.

My plan if this would ever happen in real life is to get on the radio & demand that an instructor tell me which buttons on the autopilot to push.  If successful, I'd then go buy a lottery ticket before the crazy luck wears off :-)


How does the energy and weight efficiency compare between a battery/electrical propulsion and combustion engine? For the same total energy and power output would a battery powered vehicle be lighter than one which uses a fuel burning engine (Currently)?

This question is intended for helicopters.

Poorly. That is a reason why we don't see battery powered aircraft beyond some experiments. The specific power is still much worse for batteries.
Energy storage:

Jet fuel has specific energy around 43 MJ/kg and energy density around 35 GJ/m³[1].
The best mass-produced rechargeable batteries to this day, Lithium-ion polymer, the best kind has specific energy 0.95 MJ/kg and energy density at most 2.6 GJ/m³[2].

That is more than an order of magnitude difference in favour of hydrocarbon fuel (almost 2 orders by weight, one by volume). Even taking into account the 2-3 times higher efficiency of electric engines (which do not suffer the theoretical efficiency limits associated with heat engines) hydrocarbon fuel is an order of magnitude better by weight.
Engines:

According to [3], the power-to-weight ratios for electric engines and gas turbines are comparable (in the range of 5-10 kW/kg).

Electric engine won't give any advantage to electricity.
Well, the difference in energy density is so huge that even large difference in engine weight wouldn't help much anyway. For models, electricity is OK as due to the square-cube law they have a lot of power and lift and small-scale heat engines are difficult. But for aircraft carrying humans, batteries are very far from usable.


How to calculate the lift starting from the vertical speed? Is it possible to calculate the lift of an aircraft knowing its speed (IAS,TAS and GS), its vertical speed, its altitude and its weight?
Because if we look at the force of an aircraft in flight: the lift is opposed to the weight and if the lift is greater than the weight, the aircraft climbs with a certain rate (vertical speed) proportional to the lift.

Yes, it is, at least for small pitch angles and low thrust. Here is how:

$$L = m\cdot g\cdot n_z\cdot\cos\gamma$$

If thrust or pitch attitude become significant, you need to modify $m\cdot g$ by the vertical thrust component. Then the answer must be no, because the thrust information is missing:

$$L = \left(m\cdot g - T\cdot\sin(\Theta + \sigma)\right)\cdot n_z\cdot\cos\gamma$$

$L\:\:\:$  lift
$m\:\:$ mass
$g\:\:\:$ gravitational acceleration
$n_z\:\:$ load factor (= 1 in horizontal, unaccelerated flight)
$\gamma\:\:\:$ flight path angle, with $\gamma = asin\left(\frac{v_z}{v}\right)$
$v_z\:\:$ vertical speed
$v\:\:\:$ flight speed (TAS)
$T\:\:$ Thrust
$\Theta\:\:$ pitch angle (up is positive)
$\sigma\:\:$ thrust angle relative to airframe's x axis

Note that the altitude is only needed if you use the altitude-specific value of $g$. Using the standard value will give you a negligible error.

Please note also that lift > weight will result in an upward acceleration. In a quasi-stationary climb or sink the lift will be slightly smaller than the weight.


What "jet engine" is featured in this ad that Simone Giertz made for a phone? Simone Giertz's video "Having Dinner With a Jet Engine/Leaf Blower" has a number of views of the turbine, on a cart, with a ducted fan attached.  This side view is the best view, in my opinion.

I put "jet engine" in quotes in the title because it doesn't seem like it's trying to produce thrust via exhaust, it looks like a turboshaft or turbine generator or maybe APU where the power is supposed to go into the output shaft and the hot exhaust just comes out the side, slow.  I'm guessing the ducted fan is an add-on but am not sure.

There's also a good shot of the control panel during start-up.  I haven't immediately noticed one that shows operating RPM.

At least one shot also shows a nameplate top-front on the compressor section but it's not in focus and I can't make it out.

I feel the need to postfix this with:  I am not in any way affiliated with Simone Giertz or Google.

The engine seems quite obviously to be a Boeing T50 Turboshaft Engine variant, T50-BO-8A is a very, very close match, you can see pictures and info here:
National Air and Space Museum: Boeing T50-BO-8A

All major visible features are exactly the same, some minor parts are different, but may have been switched by current and/or previous owners.

Engine concept dates back to late 40's.

I did not add a picture here because of the copyright restriction posted on the National Air and Space Museum website.


Is there a name for the area for aircraft to back track near the runway threshold? Some airports have an area, on the threshold, used to back track the aircraft, mainly because of the their wingspan, they look like a half wheel.
Is there any designation for this area?

It sounds like you're talking about these:

I'm not sure if the designation is "official", but pilots in the US (and the FAA in various documents) usually refer to such areas as a "Runway Turnaround Area" or simply "Runway Turnaround".
Their purpose is to allow aircraft which have back-taxied on the runway (or landed and rolled past the taxiway turn-offs) to turn around to position for take-off or return to a taxiway turn-off.

Note that the "runway turnaround" is distinct from a "run-up area": The runway turnaround is considered to be part of the runway, so an aircraft occupying that area is occupying the runway. A run-up area is generally a distinct area, usually off a taxiway, where aircraft can perform engine run-ups prior to entering the runway.


Difference between Flight path and Route What is the Difference between a Route and Flight path

Your route of flight is what you plan, planned, or are planning to fly. Your flight path is what you are actually flying or will be flying based on your current track, heading, speed, and attitude. They can be one in the same.


Why were the TWA TriStar middle seats smaller than the aisle seats? I was watching an old TWA advert and a question came up:
why were the L-1011 TriStar middle seats smaller than the aisle seats?

Those seats aren't smaller! TWA had fold over seatbacks, resulting in a nice table for the seat next to you if the flights weren't full. They are the exact same size as the other seats. Also, those things down the centerlines between the seats were coat closets.

Later replaced by a full width seat when they went from 2-4-2 to 2-5-2 in their last configurations.


When is a fuel pump needed on GA aircraft? When is a fuel pump needed on GA aircraft? I am a flight simmer and have noticed that you can leave the fuel pump off and start/fly the aircraft. When would you use the fuel pump?

On a low wing monoplane you'll need a pump all the time. There will be a mechanical pump fitted to the engine for the purpose. On a high-wing monoplane the engine is often gravity feed.

However, during critical phases of flight (specifically take-off and landing) you wouldn't want to have that fail so a second auxiliary electric pump is fitted that the pilot switches on beforehand and can switch off once that phase is over.

The Pilot's Operating Manual will give specific recommendations for use on any given type.


Why were trim tabs invented? I understand the need for a trimming mechanism, but why use a secondary control surface placed on top of the first, when you could just adjust the resting position of the aileron/elevator/rudder itself?

You have to have some way of holding the surface at other than where it wants to naturally trail in the airstream.

Your options:

Hold it yourself with control pressure. Becomes a pain after a while.  Some very simple homebuilt designs don't have any pitch trimming device and they have only one trim speed where they will fly hands off, the trim speed more or less controlled by stabilizer incidence; to fly faster or slower you have to hold continuous pressure on the stick.
Put a spring in the control circuit, a bungee, where the spring can be tensioned with a trimming device, usually a lever or screw device with a friction lock of some sort, to hold the continuous control force in the control circuit so you don't have to.  Gliders do this, and some light airplanes and homebuilts for pitch.  Works really well for aileron and rudder trim and lots of GA use bungees for the rudder.
For pitch trim, make the horizontal stabilizer incidence adjustable from the cockpit.  The elevator itself just trails when hands off the controls.  The fabric Pipers and Cessna 180/185 family do this, but you have a screw jack device and a pivoting stab attachment etc., so it's a bit complicated.  The fabric Pipers also combine the screw jack with a bungee interconnecting the elevator and stab so the stab applies a bit of elevator force when it moves, giving a bit more overall authority.
Use an external servo device to apply a force to the surface.  You have the air blowing past, so why not stick another moveable surface at the trailing edge that can move independently of the main surface, and apply an aerodynamic servo force.  A bit more drag than a bungee trim or adjustable stabilizer, but much more sensitive and versatile.  Much lighter and less complex than an adjustable stabilizer.

Probably 80-90% of the airplanes with manually operated flight controls use trim tabs for pitch trim because it's just the most elegant solution taking in all the considerations - light, simple, effective.  Tabs are less common for aileron or rudder until you get up to  airplanes over 5000lbs or so and you tend to see bungees or nothing, or little fixed bent metal tabs that only trim out to a single flight condition.


What aircraft equipment produced the three recordings of unidentified aerial phenomenon released by the US Pentagon in 2020? What does black signify? I don't follow these things closely and my question is carefully scoped to ask ONLY about the type of aircraft equipment used and what the various gray levels in the images indicates.
In CNN "The Point" Video Barack Obama just said something very interesting about UFOs by Chris Cillizza, there are three snippets from videos which are described as follows:

In April 2020 when the Pentagon released three videos of what they called “unidentified aerial phenomenon” which amounted to a huge break in the government’s acknowledgement of their existence...

Below are cropped screenshots from my linked video, presumably from the three videos mentioned. The unidentified phenomena all appear as small black objects, sometimes with a lighter "halo" against gray backgrounds. If for example these are thermal infrared images, one might naively suppose that the black tone indicates a temperature far lower than anything else in the field of view.
However

Sometimes thermal infrared images are inverted so that cold is white and hot is black. Why are the clouds white and Australia black in weather satellite infrared images? and also this comment that images are sometimes inverted to make a bright object of interest easier to see when analyzing.
In some imaging systems (showing my age), tiny spots that are too bright and saturate a system can cause much larger and more prominent black areas to appear.

Question: What equipment produced the three recordings of unidentified areal phenomenon released by the US Pentagon in 2020? What does the black tone of the spot in question actually signify?

update: Screenshot from CNN's Retired US Navy Chief explains tech witnessed in UFO aircraft sighting around 00:13 shows a switch between opposite tone scales in the middle of a video clip, clearly the same clouds and object, just flipped in sign:

below left: Himawari-8 IR1 image from Central Weather Bureau showing hotter Australia represented with darker grayscale level (click for full size), right: Source "...illustrate(s) the artifact of a dark area around a bright area" (vidicon)

The video was taken from an F/A-18 Super Hornet. This narrows down the recording equipment to either the ATFLIR or LITENING targeting pods. These pods perform essentially the same function. These pods can provide infrared imagery like that seen in the clip. Both pods are used on American military aircraft. I can't speak to the gray levels because I'm not familiar with the systems themselves, unfortunately. Hope this helps.


Does the ICAO definition of an "aircraft" include a minimum altitude capability? The German air law includes in their legal definition of a "Luftfahrzeug", which is the equivalent of an aircraft, other devices intended to operate in the airspace if they are capable of being operated more than 30 meters (100 ft) above ground or sea level.

Does an equivalent to this 100 ft threshold exist in ICAO documents or other international regulations? If yes, where?

The background of my question is: if an unmanned aircraft has a technical feature preventing it from flying above 100 ft, would it still qualify as an aircraft and would all regulations about aircraft apply?

I would also like to know, why the 100 ft threshold was put into the German (or other) laws. I could image that it was intended to exclude wing in ground effect crafts from the aircraft category. Is a wing in ground effect craft an aircraft according to ICAO definition?

Is there a lower altitude threshold in the ICAO definition of an aircraft?

No.

Is a wing in ground effect craft an aircraft according to ICAO definition?

No.

I believe the ICAO is based on the Chicago Convention

The 2006 9th edition begins

  THEREFORE, the undersigned governments having agreed on
  certain principles and arrangements in order that international
  civil aviation may be developed in a safe and orderly manner
  and that international air transport services may be established
  on  the basis of equality of opportunity and operated  soundly
  and economically

Although this has a section on definitions, it doesn't define aircraft.

The ICAO ADREP taxonomy contains this definition:

  Aircraft. Any machine that can derive support in the atmosphere from the reactions of the air
  other than the reactions of the air against the earth's surface. (Annex
  8)

That appears to exclude vehicles whose support relies on ground effect only.

Why [was] the 100 ft threshold [...] put into the German (or other) laws?

That might be better answered in law.se


What is the difference between Bell AH-1Z Viper and Apache Longbow in terms of role? What is the difference between Bell AH-1Z Viper and Apache AH-64D Block III Longbow in terms of role?

When does someone use AH-1Z Viper and when does someone use AH-64D Block III?

In terms of role, there is little difference between these two helicopters. Both are attack helicopters used for close combat and anti-armor. They area also capable of carrying almost similar weapons systems and combat commanders can use either of these for the same mission based on their availability(though this will depend on the compatibility of communication equipment)

Bell AH-1Z is development (albeit with significant upgrades) of  Bell AH-1, the first attack helicopter of US army.

After AH-1, the US army decided on a dedicated attack helicopter (AH-1 was developed from UH-1 transport), which led to the AH-64 Apache.

AH-64D Block III Longbow is an advanced version of Apache with the Longbow fire control radar. It is under use by a number of countries apart from US Army.

The AH-1Z Viper, however, is used only by the USMC.


How is pitch controlled in a flying wing? How do delta wing or flying wing aircraft maintain their pitch attitude in the absence of an elevator? I understand that the ailerons on the wings do control the banking/roll, but they are differential in nature. Then how can they help in pitch control? For pitch control, both control surfaces need to deflect in the same direction.

You basically have the answer right inside of the question (as was mentioned in the comments).  In order to make the plane pitch up and down you have the ailerons move up or down in unison (usually called an elevon at that point, again, as noted in comments.)

Here's a handy diagram to give you some idea of what we're on about:

In the second image the movement of both elevons upwards will pitch the aircraft up as well.  And the elevons going in opposite directions, like the last image, will cause the plane to roll (in this case to the left.)

There are more complex maneuvers as well, like pitching and rolling at the same time. These maneuvers are simply managed by differential deflections of the elevons.  Meaning, if you want to come up and to the left you could leave the right elevon neutral(ish) and pitch the left elevon upwards.  This would push down the left wing, rolling you to the left, and pitch the nose up as well.


Why do fighter pilots wear helmets? I notice that fighter pilots wear helmets, although pilots of aircraft like C-130s do not. What is the purpose of this?

I have heard that it could be helpful in the event of an ejection, but considering the explosive force of an ejection, if you hit your head I would be surprised if a helmet made any difference.

There are several reasons:

A helmet provides head protection. A fighter airplane can make many sudden turns and a helmet provides reduction of the risk of a head injury.
If the pilot needs to eject the airplane, helmet is needed to protect from wind blast, in addition to what I mentioned #1.
Helmets play an important role in noise attenuation.
The mic and headphones are mounted in the helmet.
Many helmets contain a sun visor, hence the pilot does not require to use sunglasses.
Modern helmets have a mounted display, night vision support. The latest ones help to see the pilot in any direction they desire, and even through the airplane.
Oxygen supply mask can be directly mounted to the helmet.


Is there (some form of) penetration testing in aviation? I just listened to the first Miles to go podcast about a near miss at SFO where an Air Canada flight nearly landed on a taxiway where 4 aircrafts were waiting to take off. The incoming Air Canada flight wrongly aligned to land on the taxiway, apparently because it got confused by the lighting. Thankfully, someone noticed something was off at the last second, and the plane went around without damage.

The way I understand the podcast, it was a series of edge cases that lined up to lead to the situation. In short (please edit for accuracy if needed):
- one of the runways had its lighting off
- the aircraft had slightly old navigation equipment
- the air traffic controller was alone, and on the phone
- ...

Post incident, the inflight recorder wasn't turned off, so the critical part of the conversation was apparently recorded over, etc...

This all looks very similar to how computer security problems happen: if you input a specific value in this place at that specific moment, under this particular set of circumstances, you can get access to some confidential data.

The software industry has developed penetration testing as a method to find out such problems, where essentially you pay people to try to break into your systems, and possibly reward them every time they find a security problem. It seems like the situation above could have been identified by a similar method.

Does the aviation industry use similar practices? How does it work and what is it called? And if not, what prevents it?

There is lots of testing in aviation, in every step of the process from paper designs to an actual airframe. For situation based training the aviation industry turns to the tried and true method of

Simulation

This is similar to software in many regards (and often uses computer based simulations). Simulator tech has come a long way in the past 35 years and full motion simulators are a great way to get very very close to the real thing. If you want to test out a situation where you knock out some random approach lights, throw in low visibility and some wind shear there is no reason to risk an actual aircraft, and a pilots life. Just queue it up in the sim and see how they do.

When it comes to the physical testing of say an airframe the FAA (and other bodies) also tend to take the "...before we let it out there approach" to testing and certification. In other words before an airframe is certified for production it will undergo extensive flight testing that physically pushes the airframe and exposes it to situations it should never encounter in normal flight. Omega Tau does a great episode with an Airbus test pilot that goes deep into whats involved in this, its worth a listen.

The biggest difference in aviation is that you have control over the end to end situation. In computer security you simply cant tell people "please be careful, if you use this encryption it may break in the following cases and we dont know how to fix it". On the contrary in aviation you have the ability to train pilots and more importantly you have the ability to make (or enforce) a no-go call. If we know an approach system only works down to certain minimums you simply don't fly if the weather is below them, unlike in computer security where the system is expected to always work and always be secure and in a lot of instances, always be up.


What´s the logic behind the Power Curve? Aircaft thrust is what counteracts drag, but in flight school they tought us that propeller aircraft are "power producers" and not thrust producers as jets. (That´s because the propeller needs the power of the engine to rotate and generate thrust, while a jet engine generate it by itself).
In both cases we can look at the thrust curve to get some performance information, but for props, we need to get a power curve also (get it multiplying thrust times airspeed values of the thrust curve) to get other performance features as Vy. (found where greatest excess power is).
I can´t understand the logic behind that, I mean, why does power affect airplane´s aerodynamic? Why is it important how much power does the engine has if what really makes the aicraft move forward or climb faster is thrust?

why does power affect airplane´s aerodynamics?

It doesn't. The aerodynamics will determine how much excess power is left for acceleration or climb. But not the other way around.

Why is it important how much power […] the engine has?

Because the power of a piston engine is constant for the same air density, regardless of speed. It is more helpful to give a power rating because that figure is valid over the whole speed range, unlike thrust. Thrust is inversely proportional to speed and so a thrust figure is only valid for exactly one operating point.
Pure turbojets have approximately constant thrust at subsonic speed, so here the thrust rating is more useful. The power a turbojet can produce increases with flight speed.


Is a fly-by tower legal for civilians not during a show? Suppose a civilian wants to fly-by tower in a small plane, like a Cessna 172, would it be legal for him to do it?

I assume here that if it is legal he still would need to ask permission from the ATC.

The region in place would be USA and the European Union.

No, that is not legal.

  4.6 Except when necessary for take-off or landing, or except by permission from the appropriate authority, a VFR flight shall not be flown: [...] at a height less than 150 m (500 ft) above the ground or water.

(ICAO Annex 2)

So unless you are taking off or landing (which you are obviously not, if you are right next to the tower), you are not allowed to fly below 500 feet - and control towers are not 500 feet high.

(The quoted rule is for VFR flights, which I consider to be on topic since you are asking about "a small plane, like a Cessna 172". Similar rules exist for IFR flights, but those are even stricter)


Why are flights from Fuzhou or Xiamen to Taiwan not allowed to overfly Taiwan strait? The flights from Kinmen or Matsu to Taiwan always overfly Taiwan strait. Why can't the flights from Xiamen or Fuzhou use the same route, fly over Kinmen or Matsu first and then to Taiwan directly, but need to fly away from the strait?

The answer to this question is covered in good detail in this news article in The Straits Times. Essentially, it's a political dispute between the countries of China and Taiwan.


What physical and mental attributes do I need to become a pilot? I want to be a pilot (civil aviation), but I'm afraid that my body composition and field of study might not fit with aviation. What are the physical requirements and academic/mental prerequisites to become a private pilot?

For instance, I have a masters degree in computer engineering and am skinny (50Kg, 1.72m and 24age). Could this be a problem?

Shhhhhh, here is the biggest secret of aviation: It's actually quite easy to become a pilot.  You can actually get your private certificate before you are allowed to drive!

The FAA has a nice page that tells you what is required to become a private pilot.  When most people think of piloting small general aviation aircraft, they are thinking about the Private Pilot certificate.  Part 141 is the most common route for that.  The hardest part is being able to pass the FAA physical, but keep in mind that as a private (or even recreational) pilot, you don't need to get a Class I, just a Class III.

To become an airline (ATP) or military pilot does require a great deal more work and training, but I think that may be beyond the scope of your question.

The best advice is to go to the local airfield or FBO and find a flight school.  Good luck.


Can a turbofan run without the fan to provide power without thrust? Is it possible for a turbofan jet - like on a 747 - to run without the fan, if for example you just want the thrust from the internal jet to use to heat up water, not to use as thrust?

No, the fan is directly connected to the outer compressor and turbine (N1). There is no direct connection to the inner compressor and turbine (N2), which could run independently, but there is no switch to somehow stop the N1 rotation in a 747 (and I am not sure, if it would run properly anyway).

Some turboprops (e.g. ATR-72) can run an engine without the propeller (Hotel Mode, see e.g. this question), which is connected to the engine via a gearbox. While there are also geared turbofans, you cannot completely disconnect the gearbox from the core engine.

As the other answers have said, it is however possible to build a jet engine without a fan in the first place. The Boeing 747 even has one in the tail: the Auxiliary Power Unit (APU), which will provide electricity and bleed air while the main engines are not running.


Are the A400M propellers rotating in the wrong way in "Mission Impossible: Rogue Nation"? At the beginning of the movie Mission Impossible: Rogue Nation we can see an A400M taking off.

When the engines start, the propellers turn in opposite directions. As I understand it this is not a common configuration but correct for the A400M according to Wikipedia. However, the Wikipedia article also says that the configuration is "down between engines (DBE)" which is opposite from what we see in the movie.

Did the movie get it wrong or did they use a special/early version of the A400M which worked differently?
I'm also a little confused about the propeller blades, do they have variable pitch?

I have seen the movie, but it failed to occupy my memory... anyway:
Yes, the A400M propellers are contra rotating, and more specifically DBE as you described. I am not 100% sure, but I'm willing to bet all A400M's ever produced have this configuration.
So if the propellers seem to rotate in the "wrong direction" there are two possible causes:

it is an effect caused by camera shutter speed in relation to propeller rpm. This may make the propellers seem to rotate in ever which way, or even stay still, as you can see in this youtube video.
the whole scene is cgi, so there actually is no real plane involved. My money is on this...

The propeller blade angle in A400M, as in any larger modern propeller aircraft is adjustable.
This type of propellers, or  the governor adjusting the blade angle (pitch) of the propeller to be precise, are typically constructed in such a way, that when the engines are off, there is no oil pressure, and the blades are set in feathered position. So when the engine starts up they will be feathered, and when the engines are shut down, the propellers will adjust to feather. This is basically a safety feature to minimize drag in engine failure situation. To prevent thrust from forming during and immediately after start, the propeller adjustment is set to feather by pilot, this prevents the propeller angle change as oil pressure in the system rises and governor would otherwise start to adjust the blade. As you commented below, it is totally possible the scene is played in reverse, as the blade position would be the same in both shut down and start.
The picture you posted in the question shows propellers in feathered position, so they are not producing thrust. If this is a screen capture from a scene where the plane is taking off, it most definitely is cgi. With propellers feathered, the plane will not be gaining speed, and definitely not taking off.