What would be the airspace class when no vignette is visible on a US VFR sectional chart?

The vast majority of US airspace where no more restrictive airspace exists has class E starting at 1200ft AGL with class G below. You can see an area of class G up to 14,500 MSL just north of the TCS VORTAC near to Truth or Consequences, NM which is south-southwest of KABQ. There are several other areas in the 48 states as well. As long as the airport you are talking about "near airports with pink vignettes" is not under the pink vignette, then G extends to 1200 AGL. If it's inside the pink vignette, G extends up to 700 AGL. Of course, if it lies within a pink dashed line indicating class E to the ground at such a nearby airport, then the airport you mentioned does not have any class G above it either.

One other helper I use - if you see any federal airways nearby and there is no blue vignette indicating the presence of class G up to 14,500 MSL then you can usually safely assume it is class E above 1200 AGL if no other more restrictive airspace overlies the area. Federal airways are 4 nm wide on each side or the course centerline and always exist within controlled airspace (class E or better). These are labeled on a VFR chart as the light blue lines with V-number labels - also called Victor airways. As such, V 49 west of the M20 airport you mentioned would be an example and is pronounced "Victor forty-nine".

At M20 - the airport you ask about - the airspace up to 1200 ft AGL is class G, then class E up to but not including 18,000 ft MSL, then class A at 18,000 MSL up to FL600, then class E to space.


How can I calculate turbofan efficiency as a function of turbine inlet temperature?

First, you should state whether you are designing an engine (increasing the TIT) or if you are doing an off design calculation for an existing engine.

In the case of design we gas turbine performance engineers call this design point analysis, increasing the TIT indeed would increase the efficiency, but this would require an increase of the pressure (OPR, Overall Pressure Ratio) as the pressure ratio is a parameter in the thermodynamic efficiency equation. A rise in compressor exit temperature by the increased pressure ratio requires raising the TIT to be able to add power/heat to the cycle. See e.g. the following example:

When increasing the pressure, the exit temperature of the high spool speed compressor also increase and results in an even higher amount of cooling flow required to cool the turbine. Using simple formulae is possible, but not preferred, specific software exists to do this for you.

If you are doing an off design analysis, so basically you have a frozen design and want to see the effects of TIT on efficiency, this can only be done with a gas turbine simulation program. To do this you would require the off design characteristics of the turbomachinery components, which are highly classified data.

Looking at the formulae you posted, I assume that you are looking at various designs. Please download a free copy of a gas turbine performance simulation tool and it will tell you the answer in minutes. E.g. this tool or this tool are free to use. There are probably much more tools.


"Total time" isn't an officially defined term as far as I know. Most people seem to use it to mean "total flight time", i.e. the total of their PIC, SIC and flight training time (excluding simulator training).

In general, you can log and count whatever you want in your logbook provided that you log at least the items required in 61.51(a):

  (a) Training time and aeronautical experience. Each person must
  document and record the following time in a manner acceptable to the
  Administrator:

  (1) Training and aeronautical experience used to meet the requirements
  for a certificate, rating, or flight review of this part.

  (2) The aeronautical experience required for meeting the recent flight
  experience requirements of this part.

So, the bottom line is that "total time" is whatever you want it to be, and if you want to log 'fun time' in aircraft that you aren't qualified to fly then go ahead; the time just won't count for anything as far as the FAA is concerned.

As for your two scenarios:

You can't log any 'FAA time' because you're not certified to fly the
aircraft as PIC or SIC, and you aren't receiving training. You might note it in your logbook for your own reasons but you can't count it towards anything for the FAA's purposes.
You can't log 'FAA time' here either, for the reasons you mentioned. You're acting PIC for the entire flight, of course, but acting as PIC doesn't automatically let you log PIC unless other conditions are met. 61.51(e) lists all the ways you can log PIC time, e.g. sole manipulator, acting as PIC when more than one crewmember is required.


What is the best airfoil for Edge 540 Style Aircraft?

For the Extra 300 which has symmetrical airfoils:

Extra 300, image by Ampbomber (source: rcgroups.net)

From the service manual of the Extra 300S:

Wing: from MA 15S (root) to MA 12S (tip). This change in profile allows for good performance both at low and high airspeeds.
Tail, for the 3 surfaces: - Wortmann FX 71-L-150/30

Wing airfoils characteristics seems not available online. On X-Plane.org forum (How X-Plane Uses Reynolds Number), it is suggested to replace the airfoils by NACA 0015 and 0012.

For the pitching moment coefficient Cm:

Cm is null for a symmetrical airfoil (no camber).

Manufacturer manuals:

Maintenance manual, in particular the chapter for the wings
Pilot's Operating Handbook.

Similar project:

On SourceForge: Building an Aerobatics Aircraft for JSBSim: The Su-26.

As an additional information, a study was conducted to evaluate the lift coefficient of the wing (or maybe with the tail) and the lift / drag curve, at a reduced scale:

Experimentally determined drag polar and lift curve for the Extra 300 (Figure 7)

However:

The scale change introduces a different Reynolds number, unknown adjustments must be made to extrapolate to full scale.
The curves are incomplete (alpha max undetermined).
The L/D ratio close to 2 is very low compared to the actual performances.


How does ILS (Instrument landing system) work?

The ILS works using two components, a localizer and a glideslope.  The frequencies for the localizer are between 108.1-111.95 MHz and the glide slope between 329.15-335.0 MHz.  These frequencies are the carrier waves that the modulation you mention takes place upon.  A pilot is only concerned with the localizer frequency as the navigation equipment knows the paired glideslope frequency for any given localizer frequency.

The equipment for transmitting the signals is pretty well described in your question.  The localizer antenna broadcasts two lobes down the length of the runway for a few miles (typically 18 nm, but some airports like LAX have a much longer serviceable distance).  The glideslope antenna sits around the 1000 ft touchdown zone markers on the runway, offset a little bit from the runway.  It broadcasts a its own two lobes centered around a 3 degree slope (this can vary by installation).  The glideslope is generally usable about 10 nm from the runway, but is generally not used that far out.

The equipment in the plane responsible for using this signal comes in a few parts, an antenna, a radio and a navigation instrument.

The localizer signal is received the antenna used for the normal navigation signals (VOR) and there will be an additional antenna for the glideslope signal.  These signals will first go to a nav radio, which the pilot uses to select the localizer frequency (or a VOR frequency).  If a localizer frequency is selected, the radio will also listen on a specific glideslope frequency.

The data from the radio is then sent to whatever instrument you are displaying the data on.

The most primitive instrument is the VOR head with glideslope-type of needled navigation instrument.

A step up from that is an HSI, which is a bit more intuitive to fly and has better facilities for handling localizer back courses.

On the top end you have electronic primary flight displays that display data on a CRT or LCD screen.

The basis of all of these are following two needles that are shown to the pilot.  One moves side to side and tracks the localizer, and the other moves up and down and tracks the glideslope.  If both of these are centered you are in the middle of both beams and on course.  The position of the needle is determined by which lobe of the transmitter is being received stronger than the other.  When both lobes are received equally the needle will be centered.

To your last question, the pilot has control over the airplane for the entire approach.  The ILS does not take over the airplane.  The autopilot may be slaved to follow either just the localizer, or both the localizer and glideslope, or the pilot may hand fly the approach.  In both cases however, the pilot is in control, not the ILS.

The ILS is usable for at least 10 miles from the antennae.  At many airports you will track the localizer portion of the signal much further out than this.  You will stop using the ILS normally at 200 ft above the ground, although there are special ILS approaches with lower minimum altitudes that require special equipment and training. The majority of ILS approaches however, require the pilot to observe certain visual cues before descending below 200 ft AGL.


What button is this pilot pressing with his thumb?

It's the elevator trim control to relieve control forces in pitch.  It does this by changing the neutral position of the elevators so that the pilot flying does not need to maintain a constant pressure on the yoke to maintain pitch.  On the 747 family, this is achieved by moving the stabiliser.

Although this image shows a home cockpit yoke, the representation of the controls is accurate:


A radial is always pointing (radiating) away from the VOR. But your instrument shows the TO/FROM indicator as TO. So you are crossing a 210 course towards the VOR, which means you are on the 030 radial from the VOR.

What does it mean to be crossing a radial?

This just refers to the fact that you cannot determine your heading (or track) from the CDI. Based on this instrument alone, you could be following the track to VOR right now or just happen to cross the radial at this moment (but actually fly in a totally different direction).


Is it legal to build your own plane and fly it?

Yes, it's legal. The FAA has an amateur-built aircraft homepage with links to regulations, guidance etc.
It's also very common. The Experimental Aircraft Association has a lot of resources too.


What type is this aircraft, appearing in the movie "Kingsman"?

That distinctly squarish shape looks like a Short SC-7 Skyvan 3-100, especially since the registration on the photo from below is visible: G-BEOL.
 -

(Image Source: WikiPedia - Author: Adrian Pingstone)


Autorotation: Positive Pitch during descent phase possible?

During autorotation there are two main angles which are important, the inflow angle created by the rate of descent flow and rotational airflow plus the pitch angle (normally minimal on initial entry to autorotation). It is these angles which produces the lift. The second angle produces the auto rotative force, or the force which maintains the rotor blades turning in auto. This is created by the forward tilt of the main lift vector (or the horizontal component of the lift vector) which is shown on your diagram. During autorotation it is important to maintain control over rotor rpm. Density altitude has a marked effect in auto, which is your consideration albeit to a greater extent. As density altitude increases rotor rpm for the same pitch angle will increase, this can’t be allowed to continue to increase and is contained by increasing blade pitch, hence the greater the DA, the more pitch is required including positive pitch if required. Another consideration which may help is, autorotation appears to be an aerodynamic effect of rotorcraft that is considered in isolation when a helicopter loses power, rather like an on/off switch. This isn’t the case, helicopters will experience a degree of autorotation in a normal descent due to the rate of descent flow but the rotor rpm will be maintained within normal limits due to the rotor governing system. It is a progressive process from the start of a descent to fully established auto when the torque to the rotors becomes zero.


Should DUAL flight be logged as SINGLE PILOT TIME?

1) If you are under training in a single pilot aircraft (e.g. C172), it is logged as dual in single pilot. If you are under training in a multi pilot aircraft (e.g. A320), it is logged as dual in multi pilot.

2) Correct.

3) If dual (under training), the PIC name should always be the name of your instructor. The only time you use SELF is if you were PIC, and therefore the flight cannot be dual.

See EASA Part FCL; FCL.050: https://www.easa.europa.eu/sites/default/files/dfu/Part-FCL.pdf


Would it take 7 to 10 times more energy to lift a turbofan-helicopter?

Helicopter rotors are very large precisely for that reason. Lift from a rotor (or thrust from a propeller or fan) is obtained by accelerating a given mass of air m to a velocity v. The thrust obtained is proportional to the increase of momentum ∆mv. Obviously, you can get the same ∆mv by accelerating a given mass of gas to a high speed (propeller/fan) or by accelerating a larger mass to a lower speed (rotor). But the energy needed is proportional to v squared... Hence, and for the same thrust/lift, it's much more expensive, in energy or power terms, to use a propeller/fan than a big rotor ...


Turboprop vs Turbofan: How to compare Specific Fuel Consumption

Well, propellers deliver thrust and turbofan engines deliver power to the fan axis, it is just a matter of choice.

Finding the thrust that a propeller generates at a specific airspeed and altitude, can be derived from the drag of the whole airframe in those conditions. Statistically, this sort of data can be found in reference books on pre-design of aeroplanes, such as Synthesis of Subsonic Airplane Design by E. Torenbeek. If we take a generalised approach:

$$D = C_D \cdot ½ \rho V^2 \cdot S \tag{1}$$
$$C_D = C_{D0} + \frac{{C_L}^2}{\pi A e} \tag{2}$$
$$C_L = \frac{2W}{\rho V^2 S} \tag{3}$$

So total drag follows from:

design factors weight W, wing area S, wing aspect ratio A, Oswald factor e.
environmental factors airspeed V and air density $\rho$

For the generalised $C_{D0}$ of aeroplanes, from Torenbeek page 149:

So you can use all of this to compute propeller aeroplane specific thrust. But the exercise will be futile, because:

The engine of a turbofan looks remarkably like that of a turboprop. In fact, they are both turbine engines, powered by the Brayton cycle. Similar size and design engines deliver very similar gas generator power to the [fan or prop] axis.
Turbofan engines tend to larger than turboprop ones, generating extra efficiency due to less boundary layer effect and more uniform internal flow.
Speed is of the essence: at turboprop speeds, turbofans are not very efficient. At turbofan speeds, turboprop cannot deliver enough thrust due to propeller tip drag divergence.
Turbofans utilise more of the hot exhaust flow for thrust generation due to the higher required flight speed. Lower efficiency, higher thrust.


Is it possible to fly a tandem-rotor helicopter after a single rotor failure?

It's been a few decades since I crewed CH-46s, but the situation you're describing is  called a de-sync and it's a catastrophic failure. The forward and aft rotors are linked by a driveshaft that drives the forward transmission and synchronizes the rotors. In a de-sync the intermeshed rotors will collide and the aircraft will tear itself to pieces.

Also, setting aside for a moment the consequences of a de-sync, the flight controls for both rotors are linked so it would be impossible to flatten the pitch to autorotate just the front rotor head. I suppose it would be mathematically possible to keep the rotors in sync and match the rate of deterioration in the rotor speed, but the odds would be extremely low, and the chances of recovering from any altitude beyond a few feet would be near nil.


Keeping the engine under the wings, doesn't hurt the lift as the airflow speed is higher under the wings?

To create a lift, the airflow speed on top of the wings should be higher than the airflow speed on the bottom of the wings.

No, that's not true.

In order to create lift, the pressure on top of the wings must be lower than the pressure on the bottom of the wings. The airflow speed doesn't matter.

I'm guessing your thought process is something like this:

To create lift, the pressure on top of the wings must be lower and the pressure on the bottom must be higher.
According to Bernoulli's principle, faster moving air has lower pressure and slower moving air has higher pressure.
Therefore, to create lift, the air speed on top must be faster and the air speed on the bottom must be slower.

However, point 2 here is wrong. Bernoulli's principle does not say that faster moving air has lower pressure. What Bernoulli's principle says is that given two points a and b, if

the fluid flow is steady, and
the fluid flow is incompressible, and
viscosity is negligible, and
gravity is negligible, and
the points a and b are on the same streamline, and
the fluid is moving faster at a than at b,

then the fluid has a lower pressure at a than at b.

Since the air above the wing and the air below the wing are not on the same streamline, Bernoulli's principle doesn't tell you anything about the speed of the air going above and below.


What measures prevent a military aircraft's weapons from being fired on the ground?

Normally with aircraft there is a sensor called a weight on wheels switch.  This tells the computer that the aircraft is on the ground.  The computer (or a system of relays for older air frames) will prevent any system that was designated by the owner, or required by regulations, from activating while in the ground.  Also as a secondary preventative measure certain mechanical systems are also pinned in place after landing to help prevent ground actuation.  However if it happened during maintenance it is very likely these systems were disabled to perform system maintenance on the cannon.


What happens when a GA pilot squawks 7500?

Who would shoot you down and why? You are in the middle of nowhere. Who are you endangering? ATC would try to contact you to ascertain your actual condition. You may have accidentally put in the wrong code. They would then offer assistance if needed.

If it was a kidnapping situation, all they could do is follow or track you until you land. You are not going to get far. Even if you went to another country close by, you can still be tracked and local authorities alerted.


What is P-Factor in Propeller Aerodynamics?

If the airflow is parallel to the axis of rotation of a propeller, the resulting thrust force will also be parallel to the axis of rotation and act on the center of the propeller disc.

If, however, the airflow hits the propeller at an angle of less than 90°, the resulting force will tilt towards the flow direction and shift away from the center of the propeller disc in a direction orthogonal to the directional change.

Example: You fly in a single-engined plane, the two-bladed prop is spinning clockwise when seen from the pilot's view and you push the left pedal such that the aircraft flies in a sideslip. If both propeller blades are level, nothing much changes, but if the propeller turns another 90°, both blades will see very different flow conditions (see the sketch below):

For the upper blade, which moves from left to right, the sum of circumferential speed ($\omega\cdot r_{Prop}$, red) and air speed ($v_{\infty}$, blue) is bigger than that of the lower blade (black arrows) and hits the blade at a larger effective angle of attack $\alpha_{eff}$. Thus, the lift force created by the upper blade is much bigger, and as a result it will act at a point on the upper half of the propeller disc.

The same happens when the plane flies at a high angle of attack and high power (ground run of a taildragger, or climb) and the airflow hits the propeller disc slightly from below. Now the thrust force will move to the right and tilt slightly downward. This will cause the aircraft to  turn to the left and must be compensated with right rudder.

This effect is sometimes called p-factor, but this is not a factor in an equation, but something you need to factor in when flying at high angle of attack. Note that the rotational component of the prop wash will cause a similar effect when it hits the rudder at an angle, adding to the leftward tendency of the plane.


In lost comms situations, when and where do the pilots of big commercial jets expect to get green light from tower?

In the US, for VFR, the answer to both of your questions (when and where) is when you are established on downwind. You may not be able to see the light signal if you circle above. I don't think it matters what size the aircraft is. In IFR operations, you may not even be able to see the tower, and as 757toga points out there are different rules.

This actually happened to me years ago at a tower controlled airport in California (although I was in a small aircraft). Radio stopped working. Not sure if it was transmitting so I continued to transmit my intentions just in case the transmitter was functional. I squawked 7600. I observed the traffic pattern and entered downwind at a 45. Sure enough, a few seconds later, solid green light from inside of the tower was seen. I rocked my wings to acknowledge the light signal, then controller put down the light gun. It was faint, but visible in the daylight, but if you weren't looking right at it, you wouldn't see it. (Most glass at towers is pretty thick and at an angle so I suspect it absorbs, diffuses, and/or refracts some of the light guns intensity). I never talked to the tower about it, but its possible they were shooting the light at me before I entered the downwind, but its possible I couldn't see it until I was at traffic pattern altitude and established on the downwind leg. Also, keep in mind that it is a light gun with a narrow beam, they have to hold it up and aim through a scope like a rifle at the cockpit, so you need to acknowledge you received the signal so they can put it down. Some small airports only have one controller, so s/he can't really look out for other traffic while holding the light gun up at you.

Had uneventful landing, and got light signal on the ground to taxi to parking. It worked just like it was supposed to.

See AIM section "4−3−13 Traffic Control Light Signals" for additional information.


Are there any places I can take an FAA written test in Japan?

According to this list, there are three Airman Knowledge Testing Centers outside the 50 states (listed as "Out of US" on that document.)  All of them are in US outlying territories, and none of them are in Japan.

You could conceivably arrange do the written test at the center listed in Guam (Barrigada).  There are regular airline flights to Guam from Tokyo, Osaka, Fukuoka, and Nagoya, and the 4-hour flight to Guam is better than the 8-hour flight to Hawaii or the 9+ hour flight to the continental US.


In ARINC 429 where are the bits indicating the hex value of Equipment ID?

ARINC 429 is a unidirectional one-to-many (broadcast) transfer bus with a maximum of 20 receivers.

SourceDesign with four unidirectional ARINC 429 buses

There is normally little need to identify the source, as there is only one. So there is no field in the protocol word dedicated for ID transmission. As visible in the previous image, bidirectional exchanges require two buses and several ports to connect them. The receiving unit (LRU) can determine from the port used which source feeds the bus.

However label 377 (octal) can be used to transmit, from time to time, the equipment ID if desired. Example: ID 10D (hex):

Source: ARINC specifications

Note: On the other hand, SDI bits can be used by the source to select the receiver.


What is the minimum power system required to fly a commercial aircraft?

I heard of a A320 landing, no lights, both generators out, RAT deployed ... , made a successful landing. Is this possible?

Yes

  A United Airlines Airbus A320-200, registration N409UA performing flight UA-497 from New Orleans,LA to San Francisco,CA (USA) with 109 people on board, was in the initial climb when the crew reported smoke in the cockpit, levelled off at 5000 feet and returned to New Orleans. The crew reported before joining downwind that they had lost all instruments and requested to be talked down by ATC via Precision Approach Radar (PAR). The crew descended to 600 feet where they got visual contact with the water of Lake Pontchartrain and continued visually for a landing on runway 19 about 10 minutes after departure. During landing the aircraft blew both right hand main gear tyres, went left off the runway, stopped with all gear just off the paved surface north of the intersection with runway 10/28, and was evacuated via slides.

  A number of passengers needed medical attention due to smoke inhalation.

  Post landing photos showed the RAM Air Turbine (RAT) deployed. Runway 01/19 was closed for about 10 hours.

  The crew told passengers that they had lost all electronics and were flying on minimal backup systems, landing would occur overweight with minimal braking and minimal steering ability.

From http://avherald.com/h?article=43a6bc08

  Early on, NTSB investigators suspected a faulty fire-warning sensor in the cargo hold. And they tentatively concluded that the cockpit crew had skipped a portion of the pre-flight checklist then failed to restore power to some equipment, making it more difficult to carry out the emergency landing

From http://www.nola.com/traffic/index.ssf/2013/05/united_497_emergency_landing_i.html

Basically it seems there was nothing wrong with the aircraft apart from a faulty smoke sensor. The crew missed this in their preflight checks, noticed it after take-off and then turned off all the electric generators (they were supposed to turn one back on according to the checklist - they didn't). Anyway, they landed the plane OK on emergency power from batteries and RAT.

  with only 28VDC(battery power)*

On the A320 the RAT supplies the ESS bus, not main buses 1 and 2. It powers both the AC ESS bus and the DC ESS bus through the ESS TR (transformer rectifier). So that's not just 28V DC but AC too.

In the interval after both main generators failing and APU being unavailable, I believe the DC batteries power the DC ESS bus until the RAT is deployed and providing power (which should happen automatically and quickly). So in this short interval there is only DC power on the DC ESS bus.


How much thrust is lost through a curved exhaust nozzle?

For the F135 engine in this photo, thrust in hover is only about one per cent less than maximum thrust, if Pratt & Whitney's data sheet is to be believed.

Maximum Thrust Class 41,000 lbs
...
Hover Thrust 40,650 lbs

The Hawker Harrier's maximum thrust was about 20,280 pounds.
An approximation of its maximum vertical thrust at low airspeed is given by its maximum vertical landing weight, 19,918 pounds, again just about one per cent less.


Is there an instrument departure procedure or minimum performance gradient in the absence of a published standard instrument departure?

Yes, the required obstacle clearance is based on this minimum performance:

Cross the departure end of the runway (DER) at at least 35ft AGL (that's above the DER, not above the airport reference elevation)
Climb to 400ft above the DER before turning
Maintain a climb of at least 200ft per nautical mile (FPNM) until reaching minimum IFR altitude

The minimum IFR altitude is 1000ft above obstacles, or 2000ft in mountainous areas.

This is explained in detail in Chapter 1 of the FAA Instrument Procedures Handbook (starting on page 1-14). The FAA carries out an assessment to see if the airport needs a specific procedure (ODP or SID) and if it doesn't then the standard clearance performance above applies:

  If an aircraft may  turn in any direction from a runway within the
  limits of the  assessment area and remain clear of obstacles that
  runway  passes what is called a diverse departure assessment, and  no
  ODP is published.


Where can I find speed and thrust data for airplanes during the approach?

All you need is collected, though not published, in airlines' Flight Data Monitoring (FDM).
Airlines collect a load of parameters for training and statistical purposes. If you can contact an airline, tell them what you're doing and make it sound like you could improve fuel economy, there's a good chance you can get some of the data.
Another place to seek would be aircraft manufacturers like Boeing or Airbus.


What factors cause a turbine aircraft to have decreasing fuel burn over time?

Per this paper:

Fuel consumption increases (approximately) linearly with aircraft weight, because weight corresponds to required thrust and thrust corresponds to fuel consumption.

The paper lists other fuel consumption factors as well.  But, as you suspected, aircraft weight is a dominant factor.


Why is this airplane flying in circles randomly?

What you observed is probably a Gulfstream production test flight, either an initial or a snag clearance flight, or possibly a Customer Acceptance from Savannah Air Center, which is a completion center across the ramp from Gulfstream. It could be possibly an experimental test flight if Gulfstream runs experimental flying from Savannah (I think they have a test operation in Wichita), but production flights are far more common.

The manufacturer will have designated test areas by agreement with the appropriate ATC units, with specific boundaries, and they will flight plan into the test area for production test flights (aircraft coming off the line) where a Functional Test Procedure, usually taking several hours to complete, is performed.  The ATC clearance will be to maneuver anywhere within the test borders, with a block altitude clearance they are free to operate within, until they need to go higher or lower for different tests and request a new block.

The pilot flying will be steering this way and that pretty much randomly, within the test area borders, while the other pilot performs systems tests, and the two of them will do a number of flight tests where they operate the airplane to, but not beyond, it's certification margins (things like stalls, engine shutdown/relights, yaw damper function, anti-ice tests, those sorts of things).

The airplane will return with or without snags, and the plane will get snags cleared, and go back out for another flight to check the snagged items.  On a corporate aircraft it'll then go on to a Completion Center (usually a separate company selected by the buyer for high dollar corporate a/c) for the interior.

Once the completion Center is done the interior, the customer or a customer's agent is taken on a Customer Acceptance flight before accepting the a/c.  They will go through the cabin to make sure everything is perfect in the cabin, both fit and system wise, getting it fully cold-soaked to make sure valves don't freeze, and subject to pressurization changes that can make interior panel joints open up (and I mean perfect - the slightest flaws in panel fits will be snagged).


What are Mode C requirements with ADS-B 978?

For Class A,B and C, you'll need a Mode C transponder as per the present regulations (unless cleared by ATC). From 14 CFR §91.215 ATC transponder and altitude reporting equipment and use:

§91.215   ATC transponder and altitude reporting equipment and use.
(b) All airspace. Unless otherwise authorized or directed by ATC, no person may operate an aircraft in the airspace described in paragraphs (b)(1) through (b)(5) of this section, unless that aircraft is equipped with an operable coded radar beacon transponder ... and that aircraft is equipped with automatic pressure altitude reporting equipment having a Mode C capability that automatically replies to Mode C interrogations by transmitting pressure altitude information in 100-foot increments. This requirement applies—
(1) All aircraft. In Class A, Class B, and Class C airspace areas;

FAA also addresses this in its FAQs regarding ADS-B:

Will Mode C transponders be required indefinitely?
The FAA is considering additional changes in the national airspace system, such as for TCAS. These changes, may at some future date, reduce or eliminate the need for transponder equipage.

So, at present, you'll need Mode C anyway.
Also, you'll need 1090ES in Class A. From FAA FAQs:

Aircraft that fly internationally and aircraft that require TCAS (Traffic Collision Avoidance System) are already operating with Mode S transponders and many have older versions of ADS-B Out on 1090ES MHz. Aircraft flying in Class A airspace must operate on the 1090ES MHz frequency. General aviation users who choose the UAT (978 MHz) link may take advantage of the ADS-B traffic, weather, and aeronautical services that are transmitted on the UAT frequency at no charge but must retain their current ATCRBS transponder. Mode S, 1090-ES users can operate in all airspace, but cannot receive FIS-B services.

I agree with you that there are a number of services (through FIS-B) for 978 UAT. In that case, (if you are not going above 18,000 ft) I suggest you check the availability of UAT receivers before taking a decision.


Is specifically indicating "uncontrolled airfield, student handling radios" by writing "uncontrolled" in a student's log book necessary?

You need to specify that the requirements of training are met.

For a private pilot under the FAA system, you need to have completed three solo landings at a controlled airport.  Otherwise, radio communication is a required line-item for training.  You should always log the airport of departure and arrival as well as the date.  If someone wants to know whether it was controlled or uncontrolled, they could look up the airport and see if it had a tower on that date, but they shouldn't need to since the required solo with an operating control tower should be specified in your training remarks.

Any examiner in the area would likely know whether any given airport is controlled or not simply from memory, being familiar with the area you're in. The examiner must check to make sure you meet the minimum requirements for the certificate or rating.

Beyond the three landings with a tower and the required standard communications training, there is no need to specify controlled vs. uncontrolled airport operations.


What causes an airplane to rhythmically bounce during taxiing?

If you are old enough to remember, the bias-ply automobile tires used in the 1960's would develop a flat spot when left sitting overnight. The flat spot would quickly go away when you started driving.

Many of today's aircraft tires still use bias-ply tires and are also subject to flat spotting.

Source: The Boeing 737 Technical Guide


Temperature sensor are needed to compute True Airspeed for low speed aircrafts?

A good chunk of aircraft operating in the <100Kt range generally don't have Air Data Computers although glass cockpits are becoming more and more common in general aviation aircraft. For good old steam gauges a sliding temperature compensation scale is built right into the Air Speed Indicator, for more info on that see this question or this video. OAT is determined generally by a thermometer installed on the windscreen or in the side window.

If your aircraft is equipped with with a capable glass cockpit you may be able to get TAS from the system

  The Airspeed Indicator displays airspeed on a rolling number gauge
  using a moving tape. The true airspeed (TAS) is displayed in knots
  below the Airspeed Indicator.

The G1000 has an OAT gauge as part of the install.

  The Outside Air Temperature (OAT) and the deviation from International
  Standard Atmosphere (ISA) temperature are displayed in degrees Celsius
  (°C) by default in the lower left of the PFD under normal display
  conditions, or below the groundspeed in reversionary mode.


Do existing large commecial jets make use of differential thrust to control yaw?

No, differential thrust is used in normal operations only when maneuvering on the ground, and then manually, not driven by a computerized control system.

It is preferable to run all engines at the same speed. Not only would you add additional frequencies, but also the beat frequency between pairs of two engines if speeds differ. This makes it harder to check with your ear that all engines are humming away nicely and generally creates more noise than when the engines run in sync. The answers to this question explain what the beat frequency is and how synchronization is achieved.

Next, the lag in engine response makes the control loop prone to oscillations. A rudder command is executed quickly and precisely, and when the deflections are below maybe 10°, no profile drag penalty is incurred. Induced drag due to lateral trim should be very small, especially at high speed. Trim deflections are normally much below that value, so an efficiency benefit from trimming with differential engine speeds is unlikely.

During take-off and initial climb both engines run at maximum thrust, and any trim requirement would reduce total thrust. This reduction is small, but sometimes every bit counts. During descent, the opposite happens and one engine might need to run at a higher thrust level than ideal. To decouple lateral trim and control from thrust makes sense in those cases.


Is it normal procedure to lower flaps at high altitudes?

What you saw and felt was the normal operation of the Speed Brakes.

Speed Brakes can also be called Spoilers. They are panels on the top of the wing which open up to create  drag and reduce lift. Some of the panels are also used for roll control.

They are often used in flight when ATC requires a steep descent or an immeadiate reduction in airspeed. They are also used in an Emergency Descent in case of cabin pressure loss. During landings they automatically deploy to increase wheel brake effectiveness.


What endorsements does a student pilot need to practice maneuvers solo with no limitations on distance from the airport?

In my opinion, I think the wording of 61.93(a)(i) is pretty clear.  Anytime a student pilot flies more than 25 NM from their home airfield they will need an endorsement.
I don't know where you are based at.  At my home airfield, all the practice areas are within the 25 NM radius of the airfield.
If a student pilot gets a little outside of the 25NM radius then I would tend to belief they have violated the wording of the regulations.  If the student pilot is performing maneuvers in the practice area and accidentally exceeds that radius I don't believe they violated the intent of the regulation but the student pilot should be cautioned to stay within the defined radius.
This is at the heart of FAA's compliance philosophy.
https://www.faa.gov/about/initiatives/cp/media/CP_Brochure.pdf


What are the takeoff and landing speeds of a Learjet 45?

The takeoff and landing speeds of aircraft can usually be found in the performance section of the aircraft light manual. They are not fixed and vary over a wide range depending on various factors like,

temperature,
density altitude
weight etc.

The table below gives the takeoff speeds for Learjet 45, taken from Learjet 45 AFM:

Learjet 45 Takeoff speeds; table from Learjet 45 AFM

Here, $V_{1}$ is the critical engine-failure speed.  Below this speed, the pilot should abort and bring the plane to a stop if an engine fails. If the engine fails after the aircraft has exceeded $V_{1}$, he/she should continue the takeoff using the remaining engines.

$V_{r}$ is the rotation speed, which is the speed at which the aircraft can begin to rotate its nose into the air and $V_{2}$ is the takeoff climb speed, which must be reached at an altitude high enough to clear a given obstacle. For FAR 25 aircraft, the obstacle clearance height is 35 ft (10.7 m).

You can also see from the table (and conditions listed on the right) the various factors affecting the takeoff speeds like runway condition, flap setting etc.

The minimum control speed landing $V_{MCL}$ is also a function of altitude and temperature and varies between 98 and 105 KIAS depending on the flap setting.

The landing approach speed $V_{REF}$ is the airspeed used for landing climb gradient and depends on the factors given above. The following table from the same document gives the $V_{REF}$ speeds for various configurations.

Learjet 45 Landing Approach; table from Learjet 45 AFM

*Speed definitions from www.aerospaceweb.org


A commercial jet with rear tail-mounted engines and 3+3 seat pattern?

If it was a season 5 episode, it was most likely N7264U, a 727-200:1

Season Five
Boeing 727-222
Ep. 5.25
Registration N7264U, c/n 21411/1346 built in 1978 for United. Based at Ontario International Airport (ONT/KONT) in California, where this was most likely filmed.

The 727's three Pratt & Whitney JT8D engines are all mounted on/in its tail, and the plane was large enough to have six-abreast (3+3) seating, as can be seen in this 727-200 seatmap found via a quick google (this particular seatmap is for an EAL 727, but the 3+3 seating was common to all passenger 727s of which I am aware):

(Image by Eastern Airlines, via Darren at Frequently Flying.)
And the 727-200's maximum passenger capacity was 189, according to Wikipedia, although it more usually carried 134 (in a two-class configuration) to 155 (all-economy arrangement), so it fits the 150-180-passenger requirement (and even exceeds it slightly at the upper end).
And yes, I know it's a trijet, but:

the #2 engine is buried within the 727's tailcone and mostly concealed from view, unlike the large, obvious pods holding the #1 and #3 engines (as opposed to, say, a DC-10, whose centerline engine and associated intake duct form a huge conspicuous cylinder above the fuselage at the base of the vertical stabiliser);
as for the centerline engine's tailpipe (which is visible, sticking out the tip of the tail, if you look carefully), the JT8D is a slim low-bypass turbofan, making for a much narrower and less obtrusive tailpipe compared to the chunky high-bypass engines that occupy the tailcone of (say) an L-1011 or Yak-42;

...and, putting both of those together, and considering that it was a (presumably brief) cameo giving no reason, and little opportunity, for you to pay close attention to the tip of the aircraft's tailcone, it's perfectly possible that what you saw was, in fact, a (trijet) 727, and that you simply didn't notice the easy-to-miss-at-a-brief-glance middle engine.

1: Thanx to Gerry for providing the link.


What are the advantages of the NASA LEAPTech propeller on wing technology?

The lift augmentation has nothing to do with Magnus lift (or the Coanda effect).  It is simply an increase in the dynamic pressure across the entire streamtube of the wing.

At the low takeoff and landing speeds (slightly above a 61 knot stall speed), the induced velocity of the propeller almost doubles the velocity that the wing sees; and the lift is a function of the effective velocity squared.  But due to swirl and other effects the wing doesn't experience a 4x increase in lift, but about 2 to 3 times.

The objective of the inboard propellers is not to achieve a high propulsive efficiency, instead we want those inboard props to achieve high induced velocities - think of them as part of the high lift system (which happens to also provide thrust redundancy).

In fact landing is the critical case, and having lower propulsive efficiency (and a poorer spanwise lift distribution because of the swirl effects) is helpful in creating sufficient drag.  The inboard props are not active in cruise flight, but simply fold against the nacelle (many motorgliders already do this type of folding on the nose).

By only using the wingtip propeller at cruise, we're able to achieve a ~95% propulsive efficiency (versus 75 to 85% with a typical fuselage nose propeller installation).  The reason for this is because we have lower blockage and scrubbing drag, as well as being able to take advantage of the strong wingtip vortex by rotating against it.  Since electric motors don't experience a power lapse with altitude (because it's non airbreathing) we have far too much power at altitude anyway so by only using the wingtip motor it doesn't cause much penalty in motor weight (and electric motors achieve ~6x lower weight per horsepower than a reciprocating engine).

In terms of batteries and range, the key is to achieve high efficiency cruise flight and it looks like with current batteries a 200 mile range is achievable.  By adding a small <50 hp range extender motor, the aircraft will be able to achieve ~400 mile range.  We're currently designing an X-plane that will fly in 2017 to substantiate all these numbers, with the ground test rig (wing and truck) providing an aerodynamic database to validate our analysis.

Please note that I'm the NASA Principal Investigator of the LEAPTech Distributed Electric Propulsion integration approach, and the Convergent Electric Propulsion Technology (CEPT) X-Plane demonstrator.  We have a team across NASA Langley and Armstrong, as well as two great small companies, Joby Aviation and ESAero who are retrofitting a Tecnam P2006T with a Distributed Electric Propulsion wing system.


Is an afterburner louder than the same jet engine without it?

This PDF indicates an increase by ~10 dB for an F-8K in afterburner versus the same aircraft in 100% dry thrust.

This PDF indicates smaller increases:

+5 dB for an F-15
+4 dB for F-22 and F-35


When starting a turbine helicopter, why should one slowly increase RPM (throttle)?

he probably wanted to make sure the oil pump keeps up with the engine and bearings won't run hot, or that the oil circuit gets primed. turboshaft engines dont like it when running at idle, they tend to overheat; so it better be written somewhere that the engine rpm should be brought up slowly.

is important that whatever procedure, it comes out of the book. I would have expected your captain to direct you to startup procedure then mention the reason, so you could look it up rather than learn it by hearsay.


Brute forcing Google maps finally paid off. It's Bordeaux airport:


Does EASA (or other regional/national aviation safety authority) have a confidential "close-call" reporting system?

I don't know much about the ASRS, so but I think this is a similar program... It's obviously not Europe, but Australia has the REPCON scheme for confidentially reporting all sorts of safety matters. The ATSB do a bit of investigating, seeking a response from the airline/whatever organisation is involved, and then publish the responses to a couple in CASA's Flight Safety Australia magazine.


What operations during preflight and pre-takeoff engine run-up cause a change in engine rpm?

You will get a change in engine speed doing a mag check, cycling the carburetor heat, if equipped, and cycling the propeller governor.  You will also see a drop in oil pressure and a rise in manifold pressure when cycling the propeller governor as well.

The reasons?

Carburetor heat increases temperature of the mixture passing through the carburetor, thereby decreasing its density.  Consequently, as the same amount of fuel is being metered into the air steam in the Venturi throat as before, this causes the mixture to become richer and the engine to produce less power and run slower than before.

Mag checks involve turning off individual magnetos, causing the combustion in the cylinders to become less uniform, resulting in a power loss and slower engine speeds.

Cycling the propeller governor causes the governor to slow the engine by increasing the angle of attack of the propeller blades.  This creates a greater workload on the engine.  Lower engine speeds also cause the engine driven oil pump to turn slower, decreasing the oil pressure. And, as manifold pressure measures the pressure of the intake air at the cylinder head, an increase in the workload increases the air pressure at the manifold, causing the spike in indicated manifold pressure with the prop governor set to its lowest speed setting.

Cowl flaps are simply moveable panels which can alter the flow of cooling air around the engine to better maintain engine cooling at low speeds when ram air flow through the cowling is limited.  I’ve never heard of a situation where cowl flap position causes an engine to run slower or faster, though the cylinder head temperatures will change quite a bit and there is a risk of overheating and damaging an engine if you are running at high power settings at low air speeds for extended periods.


Does a 4 bladed prop have almost twice the thrust of a 2 bladed prop?

At the same size and rpm, a 4-bladed prop will require twice the horsepower to drive, approximately.

Due to blade interference, it will always generate less than twice the thrust. So lbs thrust per hp will generally slightly decrease, as long as the propeller is in its optimal tip airspeed band.

If the propeller was overly fast initially, slowing it down and going with more blades to compensate can result in small thrust/hp gains (+X percent, not X times). This will generally apply to aircraft originally designed with much less power and later modified.

There are a few legitimate cases where design size is less than the aerodynamically optimal size. One is clearance to the ground or between the props (in quads). Another is turbofans: the drag of the nacelle overcomes the benefits of lower disc loading. Even for airliners there's a push for wider fans, but the "open fan" idea (basically a turboprop) was scaled down to geared fans and the Ultrafan for noise reasons.

In helicopters, at some point, the blades become so long and so far apart that adding more blades beats the weight and bulk of longer blades. The more blades, the worse, so going up to 4 is not such a big deal as doubling it again to 8. For small aircraft with low power/weight ratios, where 2 blades fit easily, that's generally the best configuration.


How is thrust vectoring controlled by the pilot?

Thrust vectoring isn't controlled by the pilot directly, except being able to turn it on or off in various circumstances. If it is on, the aircraft computers control the vectoring based on external conditions, the state of the aircraft and control input.


Where to get flight dynamics for a flight sim model?

Unfortunately I have no experience with how FSX models aircraft, but at a guess, it's model requires extensive experimental data from a real aircraft to truly get the right parameters.

And that's something no hobbyist is likely to be able to do. For that matter, it's pretty difficult for a pilot to do, since actually recording the relevant data is difficult, and some of what you need to know requires doing things with the aircraft you probably shouldn't do in most circumstances.

X-Plane's flight model and aircraft creation tool is far more forgiving. You still end up having to guess a lot of parameters, but they are generally less critical to basic handling.

All you really need to get a decent flight model out of X-Plane is a good set of reverence pictures, an eye for detail (so your model matches the geometry properly), and ideally the correct airfoil profiles and engine specifications.
(Primarily the thrust and power)
For the most part, good reference models and diagrams, and the information you'd find in the Pilot's operating handbook is enough to create a decent flight model in X-Plane.
It certainly won't be perfect, and you'll probably have to tune it, but it's a much easier task than getting that data needed for an FSX model.

I have the good fortune of being a student pilot, and as such I decided to attempt a model in X-Plane, and found that while it was far from perfect, (and needs a lot of improvement to be a 'good') model, it's behaviour was much closer to the real aircraft that I fly regularly than I was ever expecting given how much I had to guess.

I had to guess everything from the aileron deflection angles to the propeller geometry, wing airfoil choices and more, and still the resulting model was only slightly off from the real thing insofar as I know how the real aircraft flies.

I guess that's not an overly helpful answer in a direct sense for an FSX flight model, but I fear it just isn't going to be at all easy to find the information you need to make a flight model that isn't fundamentally broken in FSX, let alone accurate.

X-Plane is just far simpler to work with when you don't have a lot of information...

Whether that's worth the downsides of X-Plane (especially the consequences of switching if you already have a heavy investment in FSX), I don't know.
But it's worth keeping in mind if you are particularly fond of amateur aircraft design.

(It's even plausible to create fictional designs in x-plane for which no real-world data could ever exist in theory, and still get a good idea of how such a design likely would fly if it did exist.)

As for FSX potentially having better flight models in some cases? Maybe. But this is likely going to be the flight models of expensive add-on aircraft models that were made with the help of the manufacturer and pilots qualified to fly the real aircraft.

That's not going to help you any if you don't have access to those kinds of resources.

A hand-tuned model matched to exact real-world data may well work better than a physics based model if you have good source data.
But if your source data is lousy (as it is for most of us unfortunately), then the physics based model will be much more reliable most of the time...


Resistance is a term used in politics and electric circuits. We here talk of drag.
Your induced drag equation uses speed where the lift coefficient belongs:
$$c_{Di} = \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$$
What is missing now is the zero-lift drag which is the dominant contributor to overall drag at high speed. From your top speed result this seems to be
$$c_{D0}=\frac{2\cdot P\cdot\eta_{Prop}}{v_{max}^3\cdot S_{ref}\cdot\rho} = 0.040$$
assuming a propeller efficiency of 70% and neglecting induced drag. That figure is not unreasonable. Is the landing gear retractable?
Now we can write for the total drag as a function of speed:
$$D = \frac{\rho}{2}\cdot v^2\cdot S_{ref}\cdot\left(c_{D0}+\frac{c_L^2}{\pi\cdot AR\cdot\epsilon}\right)$$
$$D = \frac{\rho}{2}\cdot v^2\cdot S_{ref}\cdot c_{D0} + \frac{2\cdot (m\cdot g)^2}{\rho\cdot v^2\cdot S_{ref}\cdot\pi\cdot AR\cdot\epsilon}$$
When sizing an engine the most reasonable parameter is power loading: How many Kilowatts are available per square meter of wing area and per Kilogram of airplane mass. Wingspan is a poor basis for comparison, since a larger span at the same area means a higher aspect ratio and lower demands for power. When using your figures, your power loading is 1.21 kW for 0.54 m² or 2.25 kW per m² or 0.608 kW per kg. Compare these figures to similar model aircraft to see whether you are on the right track.
Nomenclature:
$P\;\;\;\;\;\;\:$engine power
$v\;\;\;\;\;\;\;$flight speed
$\rho\;\;\;\;\;\;\;$air density
$c_{Di}\;\;\;\;\;$induced drag coefficient
$c_{D0}\;\;\;\;\:$zero lift drag coefficient
$S_{ref}\;\;\;$reference area
$AR\;\;\;\;$aspect ratio (= 6 in your case)
$\epsilon\;\;\;\;\;\;\;$span efficiency, use 0.85 for a rectangular wing
$m\;\;\;\;\;\;$airplane mass
$g\;\;\;\;\;\;\:$gravitational acceleration


What is the difference between a tail slide and a whip stall?

A "tail slide" occurs when an aircraft is nose up and loses all forward airspeed. Gravity then pulls the plane "backwards" towards earth.  The "whip" occurs when a sinking aircraft is flipped nose down by the airflow as it assumes a more aerodynamicly stable orientation.

Aircraft will generally nose down when they sink due to more area behind the center of gravity than ahead (as viewed from underneath the plane).  The horizontal stabilizer, farthest from the CG, is the main contributer, especially with down el.

Note that with canard and delta designs, it is the back of the main wing serving this function.

The issue is that when one tail slides, the increased vertical sink rate turns a gentle nose down into a hard "whip", greatly increasing stresses on the aircraft.  There for it is imperative to make sure the plane can handle this and not to tail slide too long.

For hang gliders and "flying lawn chair" type aircraft, a hard whip can be induced by pulling forward too aggressively in stall recovery (deltas have big tails), resulting in a full blown forward tumble.

Definitely something to discuss with your acrobatics instructor.


Could Mach 1.4 be a better design point for SST?

Only for a business jet.

The high end of the business jets has been in a race for higher cruise Mach numbers which has resulted in a top speed of Mach 0.935 so far (Gulfstream 650, Cessna Citation X). So there seems to be a market value for the top spot in cruise Mach. To improve this further, and substantially, the jump to supersonic speed is unavoidable. So far, the expense of developing such an aircraft for a rather small market has been too high.

On the other hand, a Mach 1.4 design will be much easier than one flying at Mach 2.0. The reasons are:

Intake complexity: At Mach 1.4 a simple pitot intake with a single straight shock has acceptable losses, while Mach 2 demands a complex, adjustable intake with ramps producing a cascade of oblique shocks.
Wing aspect ratio: In order to keep the wing's leading edge subsonic, a Mach 1.4 design can get away with 45° sweep while a Mach 2 design needs at least 60° sweep. The Mach 1.4 wing will be much better for take-off and landing, and for the subsonic legs of the trip.

On the other hand, transport performance at Mach 1.4 will only be ⅔ of that at Mach 2 for comparable L/D, so the Mach 2 design will win hands down if airliner economics are used to evaluate a design. As you said, if you venture into supersonic territory, you might as well go all the way to Mach 2 in order to optimize the profitability of the design. Mach 2 still allows to use a fixed-geometry wing and aluminium, so the overall complexity of the resulting design is still manageable. Beyond that, you need to buy more speed with increasingly more system complexity.

Dietrich Küchemann proposed an empirical formula for maximum supersonic L/D: $$\frac{L}{D}_{max} = \frac{4\cdot(M_{\infty}+3)}{M_{\infty}}$$
Using this as a yardstick will result in 12.5 at Mach 1.4 and 10 at Mach 2. Combine this with the Mach number in order to have something close to transport efficiency, and the Mach 2 design enjoys a hard-to-beat 14% advantage in economic value.

So the only sensible reason to design for Mach 1.4 is to capture the high end of the business jet market, where airliner economics don't apply but bragging rights at the golf course are more important.


What do I look for when getting a PPL at a college or local school?

There are 2 major drawbacks to getting a PPL through a college program.

1) Admissions

In the comments you mentioned Purdue University. An excellent school, but they have very high academic standards (my son was interested in going there - didn't get accepted). There may be some variation for admission to the flight school program vs other degree tracks, but you'll still have to get admitted to the university of choice.

2) Cost

When getting your PPL in conjunction with a college degree, you're going to be taking a whole lot of general education courses that don't apply to flying. To go back to your Purdue example, they will not want you parading yourself as a proud Purdue alumn, yet not have the basic education levels that people would expect from a Purdue grad (IU v Purdue sparing aside). That means you're going to be taking writing and basic math and humanities classes, none of which have anything to do with getting your PPL. Each one of those credit hours will cost you. As will your flight hours. A school like Purdue is a prestigious, Big 10 school and tuition there ain't cheap. Purdue (again, mentioned in the comments and I have some personal experience) will run somewhere in the neighborhood of $30,000 per year for in-state tuition. I don't know the length of their flight school program, but you could do 2.5 trips through the flight school you mentioned for that kind of money.

If you go the straight up flight school route, you're going to be paying for flying lessons and flight time and that's it. Not having gone to flight school, I don't know what the admissions criteria are, but I'd venture it's not much more than having a medical certificate and the cash to start paying. If you run out of cash, you can put your training on hold for a while.

Of course, if you're going to school to get a degree and you want to make getting your PPL part of the process, not the sole reason for being there, that's a different story as far as classes go, but you're still paying a lot for the privilege of taking flight lessons through a university.


Does an IFR flight at night in VMC count as “night VFR conditions” (FAR 61.129)?

"Night VFR conditions" describes the flight conditions, not the flight rules. The PCG says:

  VFR CONDITIONS− Weather conditions equal to or better than the minimum for flight under visual flight rules.

If the requirement was to conduct the flight under VFR, the regulation would say "under VFR". For example, 91.185(b) shows that the FAA sometimes makes that distinction (emphasis mine):

  If the failure occurs in VFR conditions, or if VFR conditions are
  encountered after the failure, each pilot shall continue the flight
  under VFR and land as soon as practicable.

So you can do the flights under IFR in VMC if you like.


How does a pilot replace their logbook if it has been lost?

The best approach is to start a new logbook with totals that carry over from your latest FAA 8710 - in this case, it sounds like you will roll back to the hours from when you earned your private pilot certificate. There are some other options listed in FAA Order 8900.1, 5-172, but it's unlikely any of them will work for your situation (except, perhaps for "Receipts for aircraft rentals", if your FBO is still open and still has the records).

You can request a copy of your 8710 from the FAA, which I'm gonna quote here because that's the best way to not screw anything up:

  Airmen who have lost their logbooks or flight records may request copies of their files from the FAA [by sending this form] to the following:

    FAA Airmen Certification Branch, AFS-760
    P.O. Box 25082
    Oklahoma City, OK 73125

  or

    FAA Aeromedical Certification
    P.O. Box 25082
    Oklahoma City, OK 73125

Once you receive the copy, the first line in your new logbook should probably summarize all the totals from the 8710 (just like if it was a flight). The remarks would specify "time forward from 8710 dated DD/MM/YYY" or something to that effect.

Best of luck getting your records back!


Here are some other methods (excluding CFD and computational ones) for building up a polar curve:

Wind tunnel testing, one of the earliest methods, still one of the most applied and explored one.
Flight testing ("dynamically scaled" model or a 1:1 real prototype)
Empirical methods (e.g. Hoerner's books on "Lift" and "Drag")
Reverse calculations; i.e. if the performance charts AND the engine deck (force model) is published or known, then the flight performance chapter of the aircraft operations manual could be used, at least to a certain confidence level, to guess about the polar curve for different configurations and conditions.
If you know a few speeds of best endurance/best range glide, you could get an idea of the CL/CD at those speeds, and if you know the mass of the aircraft, the polar curve can be plotted.
Asking the manufacturer certainly could help (if not a model of commercial competition)


Why can't pilots drink alcohol after a flight?

Commercial pilots (in the United States) are usually not allowed to drink while on duty regardless of their flight status because, among other things, it would be frightening to any prospective passengers who might see them drinking. For example, American Airlines strictly forbids consuming alcohol or any intoxicant publicly while in uniform. Here is the exact text of their company policy:

  Rule 25

  Unauthorized possession or using any intoxicants on Company premises
  at any time, or drinking intoxicants in public while wearing a uniform
  with Company emblem or insignia is prohibited.

Note that this does not disallow drinking as long as it is (1) not on company premises, and (2) is in private. Obviously, if the person is a US crewmember then they must adhere to FAA rules in addition to company rules (see FAR Section 91.17 for details on those rules).


How does the debris rejection system in the CFM LEAP engines work?

It's an inertial particle separator system incorporated into the compressor inlet.  It forces intake air to follow a curved passage that makes particles with mass sling to the outside of the duct due to the sudden change of direction, where, when required, those bypass ducts open into the stream to dump the particle laden air overboard.

Turboprops have used inertial particle separators that can be opened or closed for eons; this is the first time I've seen the concept applied to a jet.  It's desirable for turbojets and turbofans to have an inlet that's good at "catching" air for a good ram effect; better for efficiency and a strong ram effect makes the engine windmill well (important for re-light capability).  Problem is, strong ram effect also means a lot of particles being ingested.  While large objects like birds are an obvious factor, with jet engines there is actually a more subtle long term problem, sand particle ingestion that literally sandblasts the compressor blades over time and shortens the life of the engine.  This is a huge problem in desert operating environments.

Some engines like early versions of the GE CF-34 used a compressor inlet profile that was "flush" to the airflow downstream of the fan, which tended to encourage particles to pass on by in the fan discharge. This was a design goal for the A-10 Warthog, for which the engine was originally designed, and made it fairly FOD resistant.  Similar variants were used in the Challenger business jet and the CRJ200 Regional Jet.

Problem was the ram effect was low, which made it windmill poorly (you have to maintain a fairly high speed if it flames out, to keep the core of the engine from stopping - the dreaded "corelock").  On later commercial variants, the compressor inlet profile was revised to present a more direct into-the-flow inlet for the compressor, improving efficiency and making the engine able to windmill at low speeds.  The price of this was the FOD resistance was reduced and in sandy environments the erosion wear problems went way up.

This design appears to be an attempt to keep a compressor inlet profile with a good ram effect while providing the ability to minimize sand ingestion when required.  The benefit is decent engine life for operators in sandy environments.  Middle eastern airlines would be very keen to have this feature because they tend to suffer from short TBOs from their engines getting sandblasted.


Why do forward-swept winged fighters have the main wings in the back?

These are just two canards with forward-swept wings. There is no general rule that the wing has to be in the back once it is swept forward. In both particular cases the configuration was selected to achieve the highest degree of agility possible. If you command a pitch-up in a conventional configuration, you first need to decrease lift in order to achieve your eventual goal to increase lift. In a canard, however, a pitch-up command achieves a lift increase immediately.

To prove my point that conventional configurations can also be forward-swept, here a few examples:

The first big forward swept aircraft, the Junkers 287 research airplane (picture source). The odd engine placement was the result of optimizing the cross section distribution for transsonic flight (what is today called area ruling). The white spots are pieces of sticky tape to attach wool tufts for flow visualization, and the canisters below the wing engines are rockets to shorten the take-off run. The aerodynamically shaped canister on the tripod right ahead of the vertical tail houses a film camera for tuft observation in flight.

Here is a real oddity: The Akaflieg Berlin B11 forward-swept tailless glider (picture source). It was never completed because the center of gravity turned out to be too far back. Also, the stall characteristics would have been - how should I say - interesting.

Most two-seater gliders use a slight amount of forward sweep to place the rear pilot at the center of gravity, so the plane can be flown by a single pilot without the need of adding ballast.

The HFB-320 Hansa Jet was more successful, and here the forward sweep was selected to keep the cabin free of the wing spar (picture: Eric Tammer / source: PlanePictures.Net). However this configuration was not trouble-free, either.


Why do airline schedules start in March and October?

The main reason for new schedules in March and October is the Daylight Savings Time changeover.

It is a MAJOR headache for airlines all over the world. Schedules have to undergo extensive restructuring during the switch over from summer daylight savings time to winter standard time. Maintaining code-share connection times is the biggest priority.

What makes this all very difficult is the fact that many countries and localities do not observe daylight savings time, or have different dates for the switch-over. This is especially true for flights between northern and southern hemispheres.


What is the difference between the Maximum Glide and Minimum Sink ratios?

Glide ratio is the ratio of the distance a glider can travel horizontally to the altitude lost in transit. For instance, if a glider can travel 40 miles horizontally while losing one mile of altitude, the glide ratio is 40:1 (typical for a medium-high performance glider). The best glide ratio or maximum glide ratio is simply the best ratio a glider can achieve. Best glide ratio is achieved at a specific airspeed, which varies depending on the glider type. One flies at best glide speed in order to maximize the distance covered. When gliders are flying in a straight line and want to go as far as possible, they fly at best glide speed (typically 55-65kts).

Minimum sink is the minimum vertical speed the glider is capable of flying at in still air (typically 100-200ft/min). Minimum sink is also achieved at a specific airspeed, depending on the glider type (typically 40-50kts). One flies at minimum sink speed to maximize altitude gain when flying in lift. If you're circling in a thermal that is going up at 500ft/min, and your minimum sink speed is 100ft/min, then the glider will go up at 400ft/min.

To review, the key differences are:

Glide ratio specifies how "flat" the glide angle is
Minimum sink specifies the minimum vertical speed the glider can fly at
One flies at best glide speed to maximize the distance covered vs altitude lost
One flies at minimum sink speed to maximize altitude gain in lift
Best glide ratio is achieved at a higher airspeed than minimum sink

Any aircraft can be a glider with its engines out, so this applies to all aircraft.

  However, I don't understand how the lowest sink rate you can get isn't the same as the shallowest angle you can glide at.

Remember that minimum sink comes at a lower airspeed than best glide. At minimum sink speed, the glide ratio is worse because even though the aircraft is sinking slower, it is also moving forward slower.


When can I start an approach if I lose comms and my clearance limit is not an initial approach fix?

Note: this may be a dupe of this question. However, you seem to be saying that you've read and understood the regulations on what to do, you just don't believe that ATC or the FAA really expects you to follow them.

In the scenario you describe you are indeed expected to fly from the airport to an IAF before beginning an approach. There's a long and detailed article in IFR Magazine about clearance limits, which discusses the regulations and the practical options. It makes a similar point to yours about lost comms:

Since the clearance limit is the
destination airport, very few approaches start there. An airport is
never used as a fix in IFR. A fix is an intersection, waypoint or
NAVAID. Moreover, receiving an EFC time in advance is simply silly.
This would also presume the issuance of holding instructions. Why
would a controller issue these things since lost communication cannot
be predicted?

It also acknowledges that many pilots share your opinion on the lost comms action:

Many pilots disdain these rules as onerous, unnecessarily
time-consuming and complex.

The article then notes that there have been multiple attempts to change the FAA's mind:

Since 2009, there have been about five challenges to this rule. In the
latest iteration, our past editor, Jeff Van West, wrote the Office of
Chief Counsel in late 2017, arguing that 91.185 (c)(3)(ii) is
inconsistent with current air traffic practices and creates an
unnecessary hazard.

But, you can read that 2017 legal interpretation yourself and you'll see that the FAA really does expect pilots to follow the regulation as written:

As you correctly state in your letter, the requirements of §
91.185(c)(3)(ii) are rarely in effect thanks to the improved technology ensuring that communications between pilot and ATC are not
lost. However, the requirements of (c)(3)(ii) are necessary to ensure
the safety of the NAS when a pilot is unable to communicate with ATC.
[...]
we affirm our previous interpretations of § 91.185(c)(3).

So that's the official answer for now (unless I missed a more recent interpretation).
Finally, if you want an alternative course of action, IFR Magazine's suggestion is to fly from the airport to an IAF and then invoke emergency authority to start a descent immediately, without holding:

ATC does not want you flying a holding pattern while it’s diverting
traffic everywhere to avoid a conflict. You have unintentionally shut
the airport down. When you reach an IAF of your choosing, ATC will
know which approach you intend to use. At the IAF, use your emergency
authority and begin descent.

That complies with the regulation and although it burns more fuel your priority should be acting predictably and landing safely. An IFR reserve should be plenty to allow for the extra flying time: KLAX to SEAVU is about 45NM, which isn't much time at jet speeds.


A lot depends on whether the reject happened during the high energy or low energy phase of the takeoff.  The boundary between the two is the reason for the speed call "xx knots", usually 80 knots or 90 knots, during the takeoff roll.

There will be specific procedures to follow following a reject, depending on the airplane and the airline's own procedures.  Normally the first thing is to bring the airplane to a complete stop on the runway, set the parking brake, and evaluate the situation (you might find something's on fire and you need to order an emergency evacuation right there).  You'll have called reject to ATC when the decision was made, so ATC will expect you to stop and will tell aircraft behind you to abandon the approach (and will likely have dispatched the fire trucks to your location just in case).  Now there are situations where judgement and common sense is applied and if you rejected at the beginning of the roll because a binder fell on the floor and made a big bang but you were only going 40kt, and you realized what it was right away, you might just tell ATC what you are doing and taxi clear.  However with rejects, it's usually assumed the runway is contaminated with FOD and ATC may close it anyway to have a runway inspection done.

As soon as you are satisfied that no evacuation is required and it's safe to taxi, you'll taxi to the ramp.  If it's a low energy reject, and you have a BTMS (Brake Temperature Monitoring System) you can expect to only have to wait for the BTMS indications to get back into the green before going out again.  If the BTMS is inoperative and was deferred under the Minimum Equipment List, you will likely have to consult some QRH  (Quick Reference Handbook) brake cooling time tables to determine how long you have to wait.

If the reject was high energy (above the 80/90 kt speed call), or if the BTMS indications are giving an extreme overheat indication (red) because you rejected after you'd already nearly overheated the brakes while taxiing from riding them, you can expect to be required to have a brake and tire inspection performed before you can go out again.  Rejects close to V1/decision speed are considered high risk maneuvers in the general scheme of things.  In any case, a call to Maintenance Control will be the next thing after getting clear of the runway to figure out what to do.

Brake use by crews during taxi has a big effect on things and prudent brake use is really important.  It's easy to get brake temperatures close to the yellow (or white) range just from riding them constantly to hold the airplane back if it has more thrust at idle than it needs to roll at taxi speed. You have to either let it speed up, apply brakes, then let them off over and over, taxi with one engine, or use idle reverse (which airlines don't like you using because it uses up reverser cycles with a maintenance impact).  The CRJ200 is really bad for this and can can get rolling to pretty high speeds with both engines at idle; it's like driving a car with the idle speed set way too high when you just want it to creep along.


It is the ram air intake for the air conditioning system. There are two of them, one on each side.
Here is an image from the ATR-72 FCOM:

ATR-72 Air conditioning System, image from 737ng.co.uk
Details from the same document:

The air conditioning system is supplied by air processed through two packs which regulate air flow and temperature. The two packs are installed in the main landing gear fairings and operate automatically and independently.
The left pack supplies the cabin and cockpit air conditioned; the right pack supplies only the cabin air conditioned.

Also, as @Jonathan Walters points out, the intake is a good example of NACA inlet (or NACA scoop) and are found in a number of aircraft, for example Boeing 737.


Would winglets add fuel efficiency on a Concorde?

The answer is no and the airplane in question is intentionally designed this way.

Standard sweptback wings produce the characteristic vortices st the wingtips.  The concentration of these vortices at this point in combination with little lift being produced by the vortices makes a singlet an effective feature to reduce induced drag.  Delta wings on the other hand produce vortices along the entire length of the wing, particularly at low speeds and high angles of attack.  Concorde designers took this into account in order to produce better low speed handling characteristics as well as the olgive delta wing provides a very clean high speed wing.  The wing was one of the most heavily researched and planned features of the jet during development.

The upshot of which is that adding winglets onto a Concorde not only is fairly ineffective way to reduce wingtip vortices and induced drag but impinges upon low speed flight capabilities, requiring greater takeoff and landing rolls and high approach AoA.


What is the correct holding altitude for the missed approach at Unalaska (PADU)?

That note actually refers to the holding pattern in general, not to the missed approach procedure. Your reading of the missed is correct.

  Descend to 6000 in holding pattern.

Refers to descent from the MSA or any other enroute altitude. Before transitioning from enroute to the outbound initial segment (departing the IAF) the pilot must descend in the hold to 6000. Once leaving DUT outbound, descend as specified to 4700.


What was the inflight entertainment in the early seventies?

During that time, the in-flight entertainment mostly available on flights was radio1 and/or TVs. Although it was not on all flights. Oops, that is true even today.

The radios may or may not have channels. If they had, there was a knob on the armrest, next to headset jacks, to switch channels. The headsets were pneumatic units like this:

The in-flight movies were shown using one or more common CRT TVs mounted on ceilings or walls and audio could be heard using the headsets. The first time a movie was shown on an international flight was in 1962 by PIA. It was more like the picture below but instead of LCD monitors, there were CRTs.

In mid-seventies, Braniff Airways was the first airline to offer video games in-flight.

By 1979, electronic headsets replaced their pneumatic counterparts, which improved audio quality.

Wikipedia has a detailed article about the history of in-flight entertainment:

  In 1971, TRANSCOM developed the 8mm film cassette. Flight attendants
  could now change movies in-flight and add short subject programming.

  In the late 1970s and early 1980s, CRT-based projectors began to
  appear on newer widebody aircraft, such as the Boeing 767.

This website has nice slideshow about the history.

1: Not actually a radio, but recorded audio


Might a large commercial jet dump fuel if an engine were on fire?

An airliner experiencing an engine fire might dump fuel, but not to starve the engine. That is much more easily accomplished by simply shutting down the fuel pumps to that engine, which would be a first-line firefighting technique as it's the most economical and the most likely to allow for a restart (less maintenance is required on an engine that's simply shut down versus one that's been doused with chemical suppressors, and those same chemical suppressors might extinguish the fire but would also inhibit relighting it).

There are several redundant fuel shutoff systems in most airliners, from the fuel pumps themselves to actual shutoff valves in the fuel lines in case the pumps themselves are the failure point. Any failure that would completely prevent the crew shutting off the fuel supply to a damaged engine would likely create much more immediate problems, like severe structural damage to the wing or fuselage of the aircraft. All of these shutoffs in addition to active fire suppression systems such as chemical extinguishers are under the flight crew's manual control; an engine on fire is usually still producing at least some thrust, which may be more important than extinguishing the fire in certain critical phases of flight.

The plane is more likely to dump fuel if it's close to its departure airport when the emergency occurs. In such a scenario, the aircraft is likely above its maximum landing weight (which is less than the max takeoff weight as the forces on the landing gear and the runway are less on takeoff than for landing and the plane is expected to burn most of its fuel weight by the time it gets where it's going), and therefore the fuel dump is simply to reduce the aircraft's weight for an emergency landing, so the landing gear doesn't collapse on touchdown. Additionally, if anything else goes wrong during the landing, dumping fuel would leave the plane with as little fuel as possible to minimize the spread or intensity of a fire on the ground, which can impede or prevent escape from the plane. However, fuel dumps from commercial aircraft are rare, used in situations where the necessity of dumping fuel to land safely and spare the passengers outweighs the financial costs of losing the fuel and the environmental costs of cleaning up the spill.


Can thrust be produced only using the forward speed of a nozzle?

Something has to provide the energy that is needed to accelerate the air.
In the simplest combustion engines this is the combustion heat. Air expands when heated and when the route out the back is the easiest to take, it will flow that way. More complicated engines use this heat energy to raise the pressure of the air inside the nozzle so there is excess pressure energy that can be converted into speed.
In your converging nozzle there is no excess energy available. In order to stream out the back, the air must have at least ambient pressure when leaving the nozzle. In order to speed up, the pressure ahead of the nozzle must be higher than ambient. But since the air enters the converging nozzle already with ambient pressure and flight speed, it cannot accelerate any more. Instead, the face of the nozzle will block all the air that will not fit through the smaller exit cross section, forcing it to flow around your nozzles. This is almost as effective for producing drag as putting a solid disk into the air stream.


Would it be feasible to develop a dirigible-based refueling station for fighter aircraft?

What is the maximum known air speed of a dirigible vs. the lowest possible air speed for a [stealth] fighter?

Airship fastest speeds

According to Guinness the world record speed for an airship was 70 mph by Steve Fosset in 2004.

Guinness also say

  The large rigid airships built by the USA and Germany in the 1920s and 30s could reach higher speeds (up to 140 km/h or 87 mph according to some sources), but these were never officially measured to FAI standards.

Stealth aircraft slowest speeds

The F-117 has a landing speed of 180 mph.

The F-35B is stealthy and can hover.


Is the 250kt limit below 10,000 feet MSL varied according to airfield height?

No, the 250 KIAS below 10000 MSL rule of 91.117(a) is not varied within FAA jurisdiction, including near airports with high field elevation.

The 200 KIAS near Class C and D airfields rule of 91.117(b) mitigates some of the risk you might perceive surrounding high elevation airports.

For example, Aspen (KASE) has a surveyed field elevation of 7838 ft and is within Class D airspace. Aircraft operating within 4 NM of Aspen would be speed limited to 200 KIAS up to 2500 AGL, which would equate to over 10000 MSL.

Other high elevation airfields in Class E or G airspace would presumably have less traffic, with the expected result that higher indicated airspeeds would pose less risk in the uncongested airspace..


Why does taxiing produce large lateral loads on the 747's engine pylons?

The slip-skid ball indicates the ratio of "sideways" apparent acceleration to "upwards" apparent acceleration, in the aircraft's own reference frame.  In normal constant-airspeed wings-level flight (i.e. not looping or pulling out of a dive), or while taxiing, the "upwards" apparent acceleration is 1 G, so the sideways deflection of the slip-skid ball is a direct indication of the total lateral force acting on the aircraft and the total lateral acceleration experienced by the aircraft.

Turning at a high rate while taxiing will displace the slip-skid ball far to one side.  During high-speed taxi, and the portion of the takeoff and landing where the wheels are on the ground, steering corrections will typically involve low turn rates but may still cause a large displacement of the slip-skid ball due to the high speed involved.  In either case, the large displacement of the skip-skid ball indicates that a strong lateral force is being transmitted to the aircraft, including to the engines through the engine pylons. The fundamental origin of this lateral force is the sideload generated by the tires.

But we can't assume that in actual flight, a similar displacement of the slip-skid ball indicates that a similar sideload is being exerted on the engine pylons.

In actual flight, during a sideslip, the tires are no longer involved.  Instead, the sideways airflow interacts with the various surfaces of the aircraft to generate the aerodynamic sideforce that displaces the slip-slid ball.

Therefore, in flight, the lateral inertial loading created by the mass of the engine whenever the slip-skid ball is displaced, is at least partly offset by the aerodynamic sideforce generated by the engine nacelle.

Consider an aircraft banked to the left, with the slip-skid ball displaced to the left, showing that the airflow is blowing from left to right across the aircraft.  (A "yaw string" would blow toward the right.)  Which is generating more aerodynamic sideforce per unit mass-- the engine nacelles (including the engines contained within), or the rest of the aircraft?

If the former, the nacelles will be forced toward the right relative to the rest of the aircraft.  If the latter, the nacelles will be forced toward the left relative to the rest of the aircraft.  If the nacelles are generating exactly the same aerodynamic sideforce per unit mass as the rest of the aircraft, then the nacelles will not be forced either to the left or the right relative to the rest of the aircraft, so the pylons will not experience any lateral force at all.

Regardless of which of these three scenarios actually apply, we can be sure that unless the total G-load is quite high, for a given displacement of the slip-slid ball the lateral load on the engine pylon is higher if the aircraft is taxiing than in actual flight.


What are runway Aiming Point markers used for?

I'll try to answer just the first portion. The aiming point marking basically serves as a visual aiming point for a landing aircraft.

Image from code7700.com
They are not found in all runways because the requirement is based on the aerodrome code number and they are not required in all cases. Aerodrome Reference Code from ICAO Annex 14 Volume I:

Table from ICAO Annex 14 Vol I
From the Same reference:

5.2.5.1 An aiming point marking shall be provided at each approach end of a paved instrument runway where the code number is 2, 3 or 4.
5.2.5.2 Recommendation.— An aiming point marking should be provided at each approach end of:
a) a paved non-instrument runway where the code number is 3 or 4;
b) a paved instrument runway where the code number is 1;
when additional conspicuity of the aiming point is desirable.


Is it legal to use handheld radios to listen to airport frequencies in Australia?

An Aeronautical License issued by the Australian Communications and Media Authority (ACMA) is required in order to operate a handheld aviation-band VHF transceiver in Australia.

  An aeronautical licence is issued to authorise a station that:

  is not fixed to an aircraft;
  is operated on aeronautical frequencies;
  is operated for purposes relating to the operation of an aircraft, or
  airport or aerodrome operations; and
  in relation to an aircraft
  includes a mobile station operated on board the aircraft or on the
  ground in communication with aircraft.

  An aeronautical licence is
  necessary to authorise the operation of stations providing:

  air traffic control services;
  aerodrome radio information services;
  private company radiocommunications; and
  other airport or aerodrome
  services.

Reference: ACMA

The Australian-based recreationalflying.com tutorial website may also provide more useful information.

(Note: This applies for a transceiver -- i.e. transmit & receive -- rules may be different for receive-only).


The slats help to protect the outer wing from stalling when the flaps deploy. The outer wing carries the ailerons, so there are no flaps, but the flaps inboard will induce more lift on the whole wing, raising the effective angle of attack even in the aileron section. Slats push the stall angle of attack up. Without the protection provided by the slats, the outer wing could stall, and if this happens on one wing first (very likely, there are many reasons for flow asymmetry), the aircraft will roll violently. To do so during an approach is not good at all.

Look at aircraft with powerful flaps: They all have slats at least on the outboard wing to avoid outer wing stall. One goes with the other.


Why do turbofan engines not have a contrarotating second fan?

The power to drive a fan through a gearbox is not beyond current technical capability. Pratt & Whitney have developed the geared turbofan, the PW1000G that first ran in 2008 and entered commercial use in 2016, flying on 4 different aircraft, including the Airbus A320neo. This enables the fan to spin at a slower speed than the low pressure turbine, such that the turbine spins at a higher speed that is more efficient for power extraction from the relatively high velocity mass flow, while the fan spins at a lower speed that avoids the blade tips lossing efficiency or creating noise at take-off, due to near sonic flow.

The engine design involves trade-offs. The complexity and weight of a counter rotating two stage fan needs to be balanced against the achievable pressure ratio with a single stage fan, and the added benefit a two stage fan would provide. Some design work has considered counter rotating compressors for example, this thesis. or even earlier work in  1992. The gas turbine industry can be quite conservative - it costs huge amounts of money, and time, to develop a new engine design, and radical steps are much less common than evolution. Pratt took a gamble, that appears to have paid off, though they do still have some issues. However, it took them decades, and around $10 billion. Rolls Royce are considering a similar design (the UltraFan), but GE are more wary. They have chosen the use of new materials as they felt the addition of the extra component would add reliability, weight, and durability challenges that they could avoid by using material improvements instead. For example, the use of ceramic matrix composites in the hot section of the CFM56 LEAP. They claim this gives 15% fuel savings, but has taken 25 years to develop. In comparison, P&W claim the GTF is 16% more fuel efficent than current generation engines. So each manufacturer choses the route they are comfortable in, and may get to the same end point.

In general, the desire has been to increase by-pass ratio, as this lowers specific fuel consumption. However, increasing BPR results in larger diameter fans, and higher tip speeds, approaching sonic velocity if the turbine is run at the optimum rpm. Hence, the geared fan approach. Clearly, Pratt & Whitney did the trade-off analysis, and decided this was the best approach for a geared fan, balancing techncial risk, reliability, performance, in-service cost, and weight.


What are the safety demonstration time-constraints?

I haven't heard of any regulations about the length of the safety demo, just the content, which is pretty much as you described. However it's in the airline's interest to keep it as short as possible. The aircraft cannot take-off before the chief of cabin notifies the cockpit that the cabin is ready for take-off. The cabin is ready after all passengers are on their seats, safety demo completed, galleys secured and hand luggage stowed away.


Why do some airplanes have a vertical rudder hinge while some others are canted?

The vertical tail of the A380 in the last photo is swept back. Surface sweep is used for high subsonic wings and tail surfaces, to postpone the effects pf compressibility when approaching the speed of sound. And when the vertical tail is swept back, the rudder hinge will be at an angle as well: the rudder chord will be a relatively constant percentage of the vertical tail chord, for aerodynamic and structural reasons.

The two photos of supersonic aeroplanes show vertical tails that are not swept back - they cruise faster than the speed of sound and do not have to postpone any compressibility effect, they fly right through it. No reason to sweep anything back here.

And the photo of the little Cessna with swept back vertical tail: it only looks as if it is trying to postpone any compressibility effects. Of course, it does so by flying way slower than the speed of sound, and the vertical tail is only swept back because it looks super fast.


What is the pivot point of pitch change on an aircraft?

By the very definition, a free-flying object can only pivot around its CG.

Using anything else as a pivot (e.g. Aerodynamic Center) involves a combination of momentum and translation (linear movement) of the CG and will quickly get you into mathematical problems once you start combining the forces acting on the object. Make no mistake, an object only rotates around its CG.

If this is just a mental visualisation exercise, you can 'imagine' the pivot point to be at the center of pressure (i.e. the famous plane suspended by strings at the wings), and as the plane is already flying at a few hundred knots in +x, the little +y acceleration error will not make much of a difference as a mental exercise, but the error is there mathematically.

Later edit:if you still have problems visualising it, place your aircraft in outerspace where there is no air or gravity.Put some big thrusters on the wing and smaller thrusters on the tail. CG (center of mass) is very much forward of the wing. Now fire the thrusters.


What is the estimate for total number of flight hours in the world?

In 2018 there were about 37.8 million commercial flights. If we multiply this number with the overall average flight duration, we get the answer. Unfortunately I could not find a result for this directly.

We can however calculate it from the data provided by the MIT Airline Data Project. The data says there were 3,954 aircraft available on average in 2018 that accumulated a combined 13,398,545 flight hours with 3.82 departures per aircraft per day on average. This means the average flight duration was

$$ d = \frac{13\,398\,545 \, \mathrm{h}}{3954 \times 365 \times 3.82} \approx 2.43 \, \mathrm{h} $$

This is just based on various US carriers, so the world average might be somewhat different, but since US carriers fly a wide variety of flights from short domestic routes to ultra-long haul international routes, I assume this number to be close to the true answer.

The resulting total number of flight hours is then

$$ 37.8 \cdot 10^{6} \times d \approx \mathbf{91.8 \cdot 10^6 \, h} $$

This does not yet include GA traffic or military flights.


Have there ever been any JATO bottles using only kerosene?

A RATO unit's purpose is to give a high impulse very quickly, it does this by combining a fuel with an oxidizer causing rapid combustion in a chamber, and forward thrust from the equal and opposite reaction. Kerosene is a fuel, but without an oxidizer you don't have a rocket, you have some lamp oil burning. If you wait until the airplane is moving then it's lamp oil burning in a wind, giving you no benefit.