What equipment is used by Boeing to convert the F-16 into an unmanned aircraft (QF-16)?

THE USAF has had a program for converting manned aircraft into unmanned ones for decades. The aircraft used so far include,

QF- 104 (from F-104 Starfighter)
QF- 102 (from F-102 Delta Dagger)
QF- 100 (from F-100 Super Sabre)
QF- 106 (from F-106 Delta Dart)
QF- 4 (from F-4 Phantom II)

Note that both aircraft are piloted. According to fencecheck.com,

  (QF-4s are)..almost always flown with a pilot aboard, unless a weapons launch will occur. Usually he does not touch the controls but stands ready to take over if ground control is lost or the aircraft departs. The pilots fly the aircraft themselves on chase missions and to maintain proficiency.

The QF-16 replaces the QF-4. The conversion of (retired) F-16 to QF-16 involves the following steps:

Removal of non essential items like the Vulcan cannon and the radar (in previous versions like QF-4, the radar was simply deactivated)
Modification of the FCS (Flight Control System) so that both manned and unmanned flights are possible (previous drones were remotely flown)
Installation of Flight termination system to destroy drone in case of flight path deviation, which results in this:

Source: f-16.net

Installation of onboard telemetry systems to control the aircraft from the ground.
Installation of a scoring system to measure the missile success rate. This is required as most of the missiles are launched with dummy warheads or the flight path is programmed to evade the missiles, so that the costly aircraft could be reused. Only in a few cases are lethal missiles used.
The self protection suite (flares, chaffs etc.) are usually left on the aircraft to provide a realistic engagement scenario.
New paint job :), which looks like this:

Source: www.wired.com

It is possible to convert (any) other aircraft into drones. For fly by wire aircraft like F/A-18, only the software portion will change, but it is a minor thing.


Brace position - does it really save lives?

The FAA has a study on it you can find here the study is worth reading completely but the important parts of the conclusion seem to be,

  Current Brace Position

  This position (head against the seat back,
  hands on top of the seat back) was evaluated for three common types of
  seat backs.

  This position was only successful for locked-out type seat
  backs. For full break-over and energy absorbing type seat backs, the
  ATD’s arms pushed the seat back away, allowing the head to accelerate
  relative to the seat back, increasing the severity of the head impact.
  There was, however, no evidence that the ATD interaction with any of
  the seatback types resulted in hyper-extension of the shoulder joint.

  The “Forward” and “Vertical” leg brace positions permitted the lower
  legs to flail forward and contact the seat in front. This contact
  produced femur bending and compression (below criteria limits), and
  tibia injury risk in some cases.

  The “Aft” leg brace position reduced
  lower leg flailing and prevented femur contact with the front of the
  seat frame. This position resulted in low femur and tibia injury
  assessment values; however, it is only achievable for occupants whose
  lower legs are long enough for their feet to firmly touch the floor.

  Alternate Brace Position

  To reduce the detrimental interaction
  between the occupant’s arms and the seatback, the current position was
  modified by placing the hands down by the lower legs instead of on the
  seat back.

  This “Alternate” position was successful in reducing head
  and neck injury risk for all of the seat back types evaluated.

  Pike Position

  This position is currently recommended when the seat
  in front is too far away to support the head, or there is no seat in
  front, as in a bulkhead row.

  It was successful in reducing head and
  neck injury risk in the row-to-row scenario, as long as the struck
  seat back has a relatively soft local compliance at the point of
  impact. When seated behind a bulkhead, the effectiveness of the pike
  position was dependent on whether the head of the occupant struck the
  bulkhead. “Head-path-reducing features,” such as Y-belts, prevented
  head contact at the typical 35-in setback.

So the answer is really, it depends on the position as well as the seats in question. You find a full explanation of what the various seat types are on page 2 of the study.

Perhaps the most interesting note is that they call for a potential change in the current brace position:

  ...and the current positions recommended in AC 121-24B may need some
  adjustment to provide an equivalent level of safety for all passenger
  seat back types.


How does propellers' pitch change during the use of reverse thrust in turboprop/propfan propelled planes?

They are more like an aerobatic airplane that's flying upside down.  The wing of the propeller blade keeps moving in the same direction but it just rotates so it operates at a negative angle of attack to make lift in the opposite direction from normal.  The blade is in a socket in the hub that allows the blade to rotate on its long axis.  The blade root has a big gear on it and there is a gearset within the hub, driven hydraulically on most props using engine oil, that drives gears simultaneously to rotate the blades.

The only difference between a reversing prop and a non-reversing one is the range of rotation of the blade; the reversing one can rotate far enough that the front face of the blade becomes the "bottom" of the wing so to speak when in reverse.

The magic mostly happens in the control system.  In forward flight there is a flyweight governor (like on a steam engine) that controls blade angle based on an RPM setting from the cockpit. Blade angle is adjusted to keep the RPM set.  Reversible props have what is called BETA mode.  In BETA, the angle of the blades is controlled directly by the throttles (power levers) down through flat pitch (DISCING, that is, the prop is effectively a big disc) and into reverse.

You come into BETA when you come back to flight idle.  This is "flight BETA".  On the ground, after you land, you yank on a latch of some kind and move the power levers back more and the props go into ground BETA into DISC, then reverse pitch.  All this time, in BETA, the rpm is controlled by an engine speed governor that adjusts engine torque to set RPM.

BETA mode is more or less how turbine helicopters work, where you directly control rotor blade angle with collective, and a governor adjusts engine torque to keep the rpm constant for you.


Aerobatic pilots typically use "aerobatic practice areas" when they practice.  Many of the Part 91 rules which would need to be broken in order to practice aerobatics are waived within these aerobatic practice areas (such as the 1,500 ft. "floor" for normal aerobatics in 91.303(e)).

The FAA has to approve them, and their guidance includes a good description:

  4. AEROBATIC PRACTICE AREAS. Aerobatic competition pilots, airshow pilots, and others who wish to practice aerobatic maneuvers not
  necessary for normal flight and below an altitude of 1,500 feet above
  ground level (AGL) must use a waivered aerobatic practice area.  These
  areas are not to be considered airshow sites.  The aviation community
  uses these practice areas to establish and maintain proficiency as
  well as enhance competitive skills in all the recognized aerobatic
  maneuvers. They are established by the waiver applicant in conjunction
  with the local FSDO and may have dimensions of several miles in
  various directions or be as small as a contest box; i.e., a cubic box
  with a dimension of 3,300 feet on all sides. Inspectors should be
  receptive to the establishment of these areas, consistent with safety
  and the efficient use of the NAS.  It is imperative that the safety of
  all nonparticipating aircraft be considered when issuing a Certificate
  of Waiver or Authorization for an aerobatic practice area.

An aerobatic practice area may be established over an airport if coordinated with airport management, and can be used to practice landings like those that Bob Hoover does.

Besides the special rules in these areas, it is also a good way to warn other traffic that aerobatics could be taking place because they are listed in the A/FD and a NOTAM is issued whenever they are hot.


Why don't 747s use unreliable, but cheap, jet engines instead?

The cost of a jet engine is mainly dictated by the operating conditions: high temperatures (sometimes above the melting point of the metals used) and high rotation speeds. This means you need high-performance materials even for a low-reliability engine: if you compromise material performance too much, it'll fail on the first start.

Failures are risky. Having to shut down an engine mid-flight is one thing, but we've had some recent failures where chunks of metal were launched at high speed into the wing and fuselage.

The industry has gone the other way: by making the engines more reliable, it's now possible to build a long-range airliner that uses only 2 engines instead of four, reducing the purchase, maintenance and fuel cost. It makes little sense to set up a special B-quality production line for a single aircraft type that's being phased out anyway.

Failures are costly. An in-flight failure means taking the aircraft out of service to repair the failure, which means having extra aircraft on standby to replace it.


What trajectory do I fly if bearing angle is constant?

The term bearing is not so clear, as the link to another answer in the comment shows.

But let's say bearing means the angle between the track (over ground) of an aircraft and a fixed location. This position usually is the magnetic or (true) geographic north, but within the context of this question, it could also be any location on earth.

If the bearing is 90° or 270° (perpendicular to fixed location), the aircraft just flies circles, in case of using the geographic north, it flies along a line of constant latitude.

If the aircraft is flying at a different angle, the trajectory is a spiral, more precisely a Rhumb line, with curls around that location and the location at the opposite side of the earth:

  (Source)

BUT due to the magnetic deviation, the magnetic field doesn't point to the (magnetic) north pole everywhere on earth.

I simulated the trajectory for a quite similar question here. The red arrows indicate where the needle of a compass points to. The black line is the trajectory for an aircraft flying a 90°-track with respect to the local magnetic field. It is just a deformed circle.

The blue line is the trajectory of an aircraft flying a 93.6°-track. This is a deformed Rhumb line, and the aircraft coming from KLAX will circle around the magnetic pole at some point like a moth around a light. (at least mathematically)


How close can planes fly to each other over the ocean?

It was only very slightly higher than our plane by mere meters.

You think you saw a plane at the exact same vertical level as yours, when in fact it was at least 300 metres (1000 feet) above or below your level. It can be very hard to judge differences in level for the untrained eye, especially over the ocean and at night when there is nothing to reference for scale. Your confusion is understandable, but there was absolutely no safety risk here.

The minimum vertical separation between two aircraft is 1000 feet, and the plane you saw was - with 100% certainty - at least 1000 feet above or below you. This is ensured by air traffic control and a ton of complex regulations and rules governing air traffic.

When over the ocean, where no radar coverage exists, if two planes are flying at the same level, they will either be at least 10 minutes flying time apart (if following the same route), or 25 nautical miles (about 50 kilometres) if flying on parallel routes. Over land where there is radar, two aircraft at the same level will generally be at least 5 nautical miles apart (10 kilometres). But when 1000 feet or more vertical separation exist, aircraft can cross each others paths without any risk. It is perfectly normal for aircraft to fly this close, but passengers seem to take notice more often over the ocean, probably because there is nothing else to look at.

There was no risk of collision during your flight. If, for some inexplicable reason, the standard separation described above was violated, pilots and air traffic controllers would have responded immediately to establish separation again, long before any sort of collision risk would occur. There is very reliable technology in place to warn pilots and air traffic controllers if aircraft are getting too close, and they are trained to react to such warnings without delay.

For more information on separation, please see my answer on "How are aircraft separated at high altitudes?"


Is it possible to extend an AFSP training request?

Assuming that you're in category 3 (aircraft under 12,500 lbs) then an approval is only valid for 365 days, so if you want to continue flight training after that then you need to request a new one:

  Once you have permission to train, you have 180 days to begin training
  and 365 days to complete the approved training. Both of these time
  periods start from the day you receive approval. For example, if you
  begin flight training 30 days after you have been approved, you now
  have 335 days to finish. If you do not finish, a new training request
  must be submitted.

That's from the AOPA AFSP guide; the TSA's own AFSP webpage is a bit more difficult to use.


Who checks the instruments and avionics before the crew boards an aircraft?

In general, nobody else does.

When pilots arrive to an aircraft for the first flight of the day, extra checks are performed by the crew to verify aircraft systems are all working properly.  These checks are done once per day and subsequent flights will perform abbreviated checks instead.  A visual walk around inspection is accomplished before and after every flight.

Maintenance will check on airplanes at required intervals but outside of specific checks (associated with the carriers approved maintenance program) the only time they'll check something like a pitot tube is if the crew notes a problem and writes it up.  At that point maintenance will address the issue to return the aircraft to airworthiness.


What advantage(s) are there for the HondaJet's engine mount position?

Probably the reasons are similiar to the reasons which lead to the same mounting on the VFW-Fokker 614.

  This arrangement was used to avoid the structural weight penalties of rear mounted engines and the potential ingestion problems of engines mounted under the wings. This allowed a short and sturdy undercarriage, specially suited for operations from poorly prepared runways.

// Update

The space in the cabin should be the actual reason in this case.

  “I had the idea around 1996,” says Fujino. “The cost of a business jet is very high. To reduce the cost, you have to reduce the size of the aircraft, but then you sacrifice comfort. I wanted to make the aircraft smaller, but not sacrifice the cabin.” Most business jets have the engines mounted on the rear
  fuselage, and moving the structure and systems to support the engines out of the fuselage would maximise space inside the cabin without increasing the size of the aircraft, he believed.

As always, there are pro and cons:

  The problem with an overwing engine is
  that interference between the nacelle and
  wing can accelerate the airflow and cause
  a strong shockwave, reducing the drag
  rise Mach number – the airspeed at which
  shockwaves form and drag begins to rise
  rapidly. Fujino says computational analysis
  and windtunnel testing enabled Honda to
  find a “sweet spot”, an overwing engine
  location that minimises the shockwave.
  The result, he says, is a 5% better lift-to-
  drag ratio – aerodynamic efficiency – in the
  cruise than a rear-engined aircraft.


Does burning fuel to get to your max landing weight violate any regulations?

This scenario isn't common but it isn't exactly rare, either. You take off with a full plane & lots of fuel for holding & an alternate, planning to arrive just at max landing weight. Then, due to shortcuts and/or better than forecast tailwinds, you under-burn & see that you'll arrive above max landing weight.

First, the hypothesized rule in Part 121 doesn't exist. Absent the Captain's use of his emergency authority (which does NOT require declaring an emergency to invoke, but which DOES have to be reported after the fact), what you can't do is "just go ahead and land overweight." That would be deliberately violating an operating limitation on the aircraft, and that's bad.

Second, there's typically no need to involve the dispatcher... just burn the gas. Holding, or extended vectors, or an early descent, or extending the gear way early... take your pick of what works best in your situation & then make it happen. Not a big deal.

Burning extra gas (really, just burning all the gas you'd planned to burn with the flight plan) is NOT a violation of anything in Part 121. On the contrary, intentionally landing overweight - in the absence of a circumstance making that the safest option - would be a violation.

Listen to ATC long enough, and you'll occasionally hear somebody ask for a delay to burn the extra gas. ATC can easily accommodate that; I've never heard it treated as if the crew is asking for something strange or suspect. Sometimes winds or shortcuts put you in that situation; it's nobody's fault, and it isn't a problem to burn the planned fuel.


Why this inertial regulator of dragonfly wing pitch reduces self-excited coupled flapping and feathering vibrations and improves gliding flight speed

Short answer:
Adding a mass ahead of the elastic axis of the wing tends to increase the critical flutter speed of the wing, thus allowing a larger flight envelope. Above this critical speed the wing would experience vibrations of increasing amplitude that could lead to its destruction (or to a limit-cycle flutter mode, which is also bad but less so than rapid unplanned disassembly).
Flutter is a destructive aeroelastic phenomenon that can be described (in a simplified way) as a combination of two natural vibration modes of a wing. These modes are torsion around a spanwise axis and bending with respect to the root. Each mode will have a natural frequency, and the flutter speed will have a minimum (not guaranteed to be a global one, btw) when both of these frequencies are the same, because then they will reinforce one another.
The distance between the center of mass and the elastic axis of the wing is very important for the torsion response of the wing, simply because the wing will twist around this elastic axis, and a center of mass far away from it will give high inertial moments.
By adding weight to the leading edge, the dynamic behavior of the wing is modified in a way that moves the critical flutter speed upwards, extending the safe flight envelope. This technique can be seen most often in helicopter blades, many of which have some trim or balance weight at the leading edge.
Long answer (math ahead):
WIP - The analytical treatment is quite long so I am trying to decide which results are actually worth typing into MathJax


When does ATC contact the pilot for a frequency change?

The entire sky and all airports are divided into ATC areas of responsibility. Whenever a flight moves from one area of responsibility to another, the pilot needs to change frequency to talk to the next controller. A flight can only be under the control of one single ATC unit at any one time, which usually equates to being on one single radio frequency. When under ATC control, pilots do not change frequencies unless instructed to do so.

For the en-route phase, airspace is divided into sectors, defined as three dimensional areas. Each sector will typically have its own dedicated frequency, although sectors can be combined in which case several sectors may operate on the same frequency.

On the ground, depending on the size of the airport, there can be multiple different frequencies. It is common to have one tower frequency per runway, and then one frequency for the taxiways - or possible several, if the airport is large and complex.

ATC will instruct the pilot to change to the next frequency at the latest when the flight enters the new area of responsibility, and often a minute or two before that. At that point, the flight will already have been coordinated between the controllers, so the controller of the downstream area of responsibility knows it's coming. Specific rules for transfer of communication is agreed between adjacent ATC units in letters of agreement.

An example from Copenhagen:

AIP Denmark EK AD 2 - EKCH - AREA OF RESPONSIBILITY

Each color depicts an area of responsibility, and (this is a bit simplified but) essentially one specific frequency that pilots should be on when they are within that area. You can see that each runway (roughly) has one frequency, and the apron area where aircraft park has another. When taxiing from one area to another, the controller will instruct the pilot to change to the next frequency.

In the air, it can look something like this:

AIP Denmark EK ENR 6.2 - 3

The dashed lines indicate borders between areas of responsibility, and the bold text indicates the frequency to use in that area. Again, the controller will instruct the pilot to change to the next frequency when crossing from one area to another.

Further reading


Are Helicopters allowed near busy airports?

Yes, helicopters are allowed near busy (and any other) airports, because why not?

Ok, seriously: helicopters in general are just as able aircraft as ones with fixed wings. General limitations for use of airspace may be in effect depending on airspace categories around aiports, but to my knowledge there are no airports in the world that would specifially prohibit operation of helicopters in their airspace.

Some private airfields may have restrictions for helicopters and other aircraft due to noise, but I'm guessing this is not what you are asking?


Do the shock waves from a supersonic plane affect general aviation planes?

Great question!  I am far from an expert in supersonic flight, but according to this NASA chat transcript, Ed Haering (an aerospace engineer at NASA's Dryden Flight Research Center in Edwards, Ca. who I would consider to be an expert) answers just this question and says that it isn't a problem for other airplanes:

  chetman1020: Do sonic booms ever disrupt other things in the air?

  Ed: Sonic booms can temporarily dissipate or accentuate a "Sun-Dog," the small bit of a rainbow off to either side of the Sun
  caused by high altitude ice crystals. Aircraft are not affected by
  booms from other aircraft.


How can I become familiar with flight rules specific to Canada when flying there from the United States?

In the specific case of Canada, AOPA and COPA have a lot of information aimed at US pilots. AOPA has a complete guide on documents, customs etc. and COPA has a page with more information, which includes this remark:

  The flying rules are almost indistinguishable - reading the COPA guide
  should keep you legal and out of trouble. Make sure you get a Canada
  Flight Supplement (CFS) and some VNCs (Canadian equivalent to your US
  sectionals), that will allow you to navigate VFR safely.   IFR plates
  are available from Nav Canada as a subscription or the (sample list
  of) vendors included below. (by mail order)

The guide is free but available to AOPA/COPA members only.