Why does the headset man not get on the tractor? As far as I can see, the pushback operation of a passenger aircraft is carried out by a similar application at many airports. It's a towbarless tractor and driver who pushes the aircraft together with a headset man connected to the aircraft walking next to the tractor.

It's strange for me to walk for minutes instead of getting on the tractor. The task of the headset man getting on a tractor will make both time efficient and less tiring. And it’ll be more faster than conventional push-out as well. Isn’t it?

(Source: wikimedia.org)

The "headset man" is a wing walker, and he is there for a reason - he is not just someone who needs a ride to where the aircraft is being pushed to. Essentially, he is an extra pair of eyes for the tow driver. He needs be able to see everything going on around the aircraft to avoid collisions with other aircraft or stationary objects. This task cannot be performed from within the tow truck since the view from there is relatively limited.


Could high density abrasion-resistant ceramic turbine blades allow for the use of borane fuels? In the late 1950s the U.S Air Force searched for a fuel with similar characteristics to jet fuel but with higher energy density allowing longer flight range for bombers. In 1947 the British had discovered elemental boron to be the ideal replacement to carbon as it had lower bond dissociation energy leading to higher heat of combustion, 68 MJ/kg vs 42.8 MJ/kg for JP-4.$^1$

Pentaborane B5H11 was found to be unstable, so B5H9 was used as it possessed much better stability. Pentaborane B5H9 performed well in turbojet combustors but it was found that emissions of solid boron particles upon combustion caused severe erosion of the high pressure turbine blades. Is it possible that new ceramic matrix composite turbines blade with higher density and abrasion resistance could solve this problem?

$^1$ Frietas 2018 handbook of energy density Robert A. Freitas Jr., “Energy Density,” IMM Report.

Borane fuels are not practical for a multiple-use aircraft, primarily because there are no naturally occurring sources they could be easily derived from. This rules them out commercially, and gives a military disadvantage of being unable to utilize local supply chains.

Note that the XB-70's borane fuel was to be carried in addition to kerosene, for one high-speed dash. Even though capable of multiple flights, the military purpose of nuclear bombers would have been fulfilled in a single mission.

Modern turbines are built with tighter tolerances than those of the 1960s. This would make a fuel that deposits solid particles, as pentaborane does, more of a problem, not less.

These considerations essentially limit pentaborane to simpler and single-use engines that can tolerate this, such as rockets.

However, the fact that no space missions have used pentaborane, even when it cost nothing and had to be destroyed, suggests that its toxicity and near-impossibility of safe handling on industrial scale outweigh its advantages even in such applications.

To quote the paper,

  When reading about pentaborane, a TLV of .005 ppm and indications that it is pyrophoric over a wide range of oxygen concentrations meant this was toxic material prone to ignite very easily. What is difficult to comprehend from these numbers and quantitative data is that pentaborane is as toxic as some of our Nation’s nerve warfare agents and will spontaneously burst into persistent flame in nearly oxygen deficient atmospheres.

Spacecraft are no strangers to exotic and highly toxic fuels, such as hydrazine. However, pentaborane turned out to be on another level of difficult. It's also not as high-performing as hydrogen or the record holder Li-F2-H2 tripropellant, also not used for similar reasons.


How strong is aircraft-grade spruce? I have been trying to find some real numbers on how strong a single solid piece of aircraft graded spruce wood timber is, but haven't had much luck and the numbers that I have found so far were either not for aircraft graded spruce or the sources weren't credible enough or simply the numbers were conflicting with what else I had found previously.

My question therefore is: How much of an evenly distributed weight a piece of aircraft graded spruce can take e.g. as a wing spar or struts before structural failure?

The length and thickness of the timber doesn't matter as long as the spar and/or strut went under the load test alone. The reason that I'm saying this is that I can find numbers for aeroplanes that have spruce spars for example, and based on the maximum G, weight of the aeroplane, etc. I can have a rough guess for how much load the entire wing is certified for, but an entire wing is made of other components that will have an effect on the results of those tests, which means those maximum numbers may not necessarily be the limits of the spruce spar itself e.g. the wing ribs or wing surface might have a lower tolerance, therefore reducing the performance numbers in the certificate.

My recollection of the Modulus of Rupture is about 6000 psi for aircraft graded sitka, based on the maximum allowed grain runout, and a maximum of around 10000 for straight grain.  But you should be able to find everything you need in the old Forest Products Laboratory study at this google search link.

The key weakness in spruce (and wood in general) used for wing spars I've learned over the years is the propensity for dormant failures in compression, typically following a wing tip strike on a strut braced airplane, that places massive compression stress in the wood above the strut attach bolt.

It collapses the cell walls in that area, evidenced by only a tiny line across the grain, that may or may not even be inspectable, and which drops the wood's tensile strength in the affected area to a fraction of normal.

Dormant, because you don't find out about the problem until some day when the wing is loaded inverted for some reason, so that the failed section is loaded in tension, and oops there it goes.  For this reason I advise people to stay far away from an airplane with wood spars that's ever had a wingtip repair.


At what point does the throttle control RPM on a constant speed prop? On an airplane with a constant speed prop, the prop lever typically controls the RPM (pitch) of prop, and the throttle controls the power, measured as Manifold Pressure ("MP"). However, at low power settings with the prop lever full forward, there is a point where the throttle control begins to act like a throttle on a constant pitch airplane where the throttle controls the RPM. This is the point that I'm asking about.

Does this point occur at the same MP on all aircraft? Conceptually I understand that when the prop is set to max RPM the prop will adjust pitch finer and finer as I reduce power until it gets to the point where it can't flatten out the pitch anymore as I continue to reduce power, then the RPM will begin to drop. Is this a point that is specific to engine/prop combination or is it adjusted by mechanic?

What happens is when you're on final and you move the prop to MAX RPM, the prop governor moves the blades finer until the RPM is at red line, then governs RPM there by adjusting blade angle as required.  As you reduce throttle, the governor moves the blades finer and finer trying to keep the RPM that has been set (maximum or redline RPM in this case).

As throttle is further reduced the blades hit the fine pitch limits of the propeller hub and can't go any finer, so the governor can't unload the engine any more to keep the RPM up.  As you continue to reduce throttle you basically now have a fixed pitch prop with very finely pitched blades and down comes the RPM.  As long as throttle is below the level that will speed the prop up above redline (or whatever the governor setting is), RPM will vary directly with throttle, like a fixed pitch prop engine.

Add power and RPM rises until it hits the governor setting, then the governor starts to coarsen pitch to load up the engine, to keep the RPM at the setting.

The point at which the prop "comes off the governor" is determined by the pitch limits of the blades within the hub.  The part the mechanic can adjust is the RPM set by the governor when the prop lever is at MAX, which is normally redline RPM +/-.


What do EU pilots use for IFR enroute charting (besides Jeppesen)? Is there something equivalent to FAA IFR enroute charts for the EU, where you can see published routes, holds, minimum altitudes, etc?  I can find terminal area procedures in the AIPs, but the Eurocontrol enroute charts contain hardly any useful information.

In Europe, like in most of the world, IFR enroute charts are published in ENR 6 of the national AIP, which can be found notably from Eurocontrol @IS online. Some countries publish these charts in sections ENR 3.x.
Some countries like Spain even publish electronic charts.
More details (route data tables) about IFR routes are published in the following sections:

ENR 3.1 Lower ATS routes
ENR 3.2 Upper ATS routes
ENR 3.3 Area navigation (RNAV) routes
ENR 3.4 Helicopter routes

Note: this organisation of routes will change soon.
There are numerous companies offering flight manuals beside Jeppesen and Lido: Navblue is one example.


Why weren't the XB-70's wingtips fixed in the down position? The XB-70's wing tips folded down in flight to:

improve directional stability at supersonic speeds
reduce shifting of aerodynamic center at supersonic speeds
reduce drag at high supersonic speeds

With thanks to Peter Kämpf's answer. Actually, this question was prompted by that answer, and quite a bit of it is 'borrowed' from there.

Wings in flight:

Source: interceptor.com

Landing with wings straight:

Source: Gawker Media

My question is why did they fold, instead of being fixed in the down position?

My assumption is that the plane already sat very high off the ground (probably to give clearance for take off/landing rotation), and lengthening the landing gear enough to allow the wing droop would have been a greater engineering issue than making the wing folding mechanism. Is there validity in that assumption, or, were the benefits of the wing droop at supersonic speeds detrimental at subsonic speed?

Some perspective of just how tall the XB70 was (click to zoom - that's a tall bird!):

Source: cybermodeler.com

Well, for starters, the drooped wing is not producing any lift in subsonic speeds. So, the flat area (the fixed part) should be significantly larger for producing the lift. This increases weight, which leads to a vicious cycle.

Another thing is the wing would panels would not clear the ground while the aircraft was on its landing gear. For testing the wing fold in ground, the aircraft had to be put on tall jackstands.

Image from keypublishing.com

As you noted, lengthening the landing gear enough to allow the wing droop would have been a big issue not the least because the aircraft weight was already increasing alarmingly (the weight had shot up from 483,000 lb to 537,000 lb).

Also, you lose the outboard elevons; now for getting the same control response the inboard control surfaces have to be increased in size, which has to be come either from wing or increase the wing area- it is again a mess.


What are the ways to keep the birds away from airfields? I know bird strikes are a major issue for many airports, and that measures are taken to keep birds away.
There are some obvious things airports can do like not to have any stray garbage, food, etc. in the open, but I'm sure other less obvious methods are also used.

What exactly are some of the widely used techniques to keep birds away from airports?

The FAA has an FAQ on bird strikes and other wildlife hazards, which includes a (broken) link to their Wildlife Hazard Management at Airports - A Manual for Airport Personnel document.

Chapter 9 is called "WILDLIFE CONTROL STRATEGIES AND TECHNIQUES AT AIRPORTS" and includes the following techniques:

Change flight schedules
Modify the birds' habitat (food, cover, water)
Physically exclude the animals (not so easy with birds)
Repel the birds with vehicles, chemicals, sound, visual objects (flags, scarecrows, fake dead animals, lasers)
Repel the birds with trained falcons or dogs
Shoot nonlethal projectiles at the birds
Trap, remove and release the birds at a different location
Kill the birds with poison or other means

The document summarizes the various techniques like this:

  Habitat modifications to minimize food, cover, and water and physical
  barriers to exclude wildlife are the foundations of wildlife hazard
  management programs for airports. In addition, an integrated array of
  repellent techniques is necessary to disrupt normal behavior and to
  stress hazardous wildlife that attempt to use the airport. These
  repellent techniques must be used judiciously and backed by real
  threats to minimize habituation. To this end, lethal control of
  selected individuals of common species is sometimes necessary to
  reinforce repellent actions.


On a "Visual Approach", do I execute a "missed approach" or do I go around? Let's say the weather is a little above VFR minimums (let's say it is 1700ft and 3SM).

The approach controller vectors me on to the final, and then clears me for a visual approach. For some reason (such as bad crosswinds), I feel like aborting my approach.

At this point, am I allowed to "go around" or do I have to execute a missed approach procedure (if so, which one?) unless advised otherwise by tower?

And what if it was an uncontrolled airport whereby I'd have to make this decision myself before contacting approach again?

First, a caution: IFR procedures can (and do) vary between countries. It is incumbent on the pilot to study the respective authority's Aeronautical Information Publication (AIP) to understand local procedures before flight. When asking questions about instrument flight procedures, it is helpful to know which countries you are specifically traveling through. While the vast majority of countries simply adopt ICAO procedures, many have significant deviations (the United States included).

ICAO Doc 4444 (PANS/ATM), section 6.5.3 discusses instrument flight that terminates into a visual approach. Interestingly, the document is silent on what happens if the approach is aborted.

In the United States, the FAA is more explicit. In the Aeronautical Information Manual, section 5-4-23 visual approaches are specifically addressed. Paragraph (e) details what should happen if a visual approach is terminated:

  A visual approach is not an IAP and therefore has no missed approach segment. If a go around is necessary for any reason, aircraft operating at controlled airports will be issued an appropriate advisory/clearance/instruction by the tower. At uncontrolled airports, aircraft are expected to remain clear of clouds and complete a landing as soon as possible. If a landing cannot be accomplished, the aircraft is expected to remain clear of clouds and contact ATC as soon as possible for further clearance. Separation from other IFR aircraft will be maintained under these circumstances.


Limitations of bird flight as an aircraft design What is it that stops man from duplicating Bird Flight as Engineering?

After all, birds do not require separate propullsion! They use the same wings for propulsion and navigation.

My question could be broad. Is it far-fetched ?

With solar energy harnessed and electronic control systems, SHOULD we not take a re-look at bird flight, at least as personal carriers or even as a short-haul option ?

The movement of the bird wing during the flight is very complex. Not just the trajectory matters, the shape of the wing itself changes as it moves. Angle of attack changes continuously. It is definitely not just about flapping up and down. For a long time, this limited the possibilities of building such machines, while with recent technology it seems possible.

This complex movement also restricts the maximum speed possible, as even small birds cannot beat the wings more than about 80 times per second. The fastest birds, such as the white-throated needletail, may reach 105 mph (168 km/h) in horizontal flight that would not be impressive for an aircraft.


Positions of drag wires in a bay Take a good look at the small dots • on the bays of this two spar wing.

My question is:

Are the drag and anti drag wire as seen in bay 1 supposed to connect to the root of the compression tube
Or to the intersection between the wing spars and compression tube as seen in bay 2 or
are they supposed to connect to the wing spars as seen in bay 3?

In other words, which bay is set up correctly? 1, 2, or 3?

This is the point I'm at in my project, your answer will be much appreciated.

Neither. The best one would something between 2 and 3. The continuation of the wire should cross the intersection between the middle lines of the spar and compression tube.

In structures with two-force members, such as trusses and combinations of rods and beams with wires, the members are intended to work primarily in tension/compression. To achieve this, the middle lines of the cross sections of all members at a joint should intersect in a single point. If they don't, some of the members will have to carry additional loads such as bending or torsion moments.

Problems due to eccentricity at joints often show up as fatigue problems: even if the aircraft structure passes all static tests, the stresses due to the additional bending moment make the structure fail much earlier than it would have if correctly assembled/designed.


Is there any way to determine or estimate where the cloud tops are? There are various ways to find out or at least estimate where cloud bases are, e.g. ATIS/AWOS/ASOS report them directly, PIREPs may mention them, and you can make a rough estimate based on the temperature/dew point spread.

Is there any way to determine (or estimate) where the tops are, assuming that no PIREPs are available?

https://www.aviationweather.gov/obs/radar/ provides cloud tops for weather with precipitation.

Cloud tops with no precip can be discerned from data provided in the Skew-t log℗ charts that are part of this app http://www.skewtlogpro.com/about-skew-t-log-p-charts/

Where the temperature and dew point on the skew-t charts are converged you can expect clouds. If the convergence extends into the freezing level indicated on the chart you can expect icing.


Why are flight instructors in the US called CFIs? I live in EASA-land (Europe), here we call our flight instructors simply that, "FIs". That they hold an instructors certificate is simply implied. Why are flight instructors in FAA-land (US) called CFIs? Is there any historical reason why the "C" is always added to the abbreviation, e.g. in the past there was a difference between certified and non-certified FIs (if there ever was such a thing)?

Certified flight instructor = CFI. Add a multiengine rating to your CFI and now you are a multiengine flight instructor, or MEI. An instructor with single and multiengine instructor ratings is commonly referred to as a CFI/MEI.  What if you are a CFI but only in gliders?  CFI-G is the most common shorthand.
Pilot authorizations are specifically called "certifications" in the US, not "licenses."  My guess at the inclusion for the C in CFI is that any pilot can provide instruction but only appropriately certified and rated instructors can provide training that can be counted for a student's training for a new certification, flight review, or whatever.


What should I look for in weather reports in order to pick a day for glider flying? I understand weather can change unexpectedly, and local sky condition (e.g. cloud types) can't be predicted, but if I want to fly glider at a specific location, say, some time next week, and use weather forecast to pick the best possible day, what should I look for? e.g. "Cloudy" vs. "partly cloudy" vs. "overcast" vs. "sunny", is one preferable to another? (I wish the forecast would say something like "Cumulus clouds abound")

For thermal soaring, which is the majority of the time in the sport in North America, the best soaring days are usually the day or two or three after the passage of a cold front with high pressure behind it, where light to moderate winds are forecast.  You want relatively unstable air without any inversions, no mid to high level clouds, and low humidity but preferably enough to form cumulus clouds to mark the thermal tops (if the air is really dry you have no clouds at all and have to troll randomly looking for lift, or look for thermaling birds, or look for other gliders that have found lift). In other words, it's those clear sunny days after a high moves through, the temperature cools off, and you get those nice puffy widely separated cumulus clouds and light to moderate winds.

If a front ahead of high pressure has a strong pressure gradient behind it, it's likely that the winds the next day will be strong and this is bad because it tends to break up the thermals.  In that case I would plan to go the day or two after as the high moves in and the winds die off.

There are a lot of other factors, like the ground moisture content (wet ground sinks heat and inhibits thermal formation), but as a way to try to judge the best likelihood of good soaring conditions, the 2-3 days following passage of a cold front rule is the most reliable.

If you're not much at interpreting weather maps and can only go by the public forecast, and have to pick a day in advance, try to pick one of the first days following the day with storms and a temperature drop in the forecast due to a cold front, where it shows sunny or "partly cloudy" (which will usually be be desirable convective cumulus) for a few days after, and avoid really windy days which if it happens is typically the first day after frontal passage.

Exceptions to this are desert areas which have sunshine and good convective conditions for thermals pretty much all the time, and places like Florida where during any kind of sunny weather there is always convection (there is a localized thunderstorm somewhere in the state just about every day in summer).


How does ignited gas spin the turbine? For the N1 fan and N2 compressor to move, the turbine needs to spin in an airliners engine. How does energy from the ignited gas spin this turbine? Do the blades on the turbine generate lift just like a wing and spin to spin the N1 fan and N2 compressor?

A turbine is a machine that extracts energy from a moving fluid and converts it into work. In the turbine blades, the air is expanded, which produces work. In many ways, the turbines are the opposite of compressors.

"Two stage reaction turbine" by S.M.Yahya - Turbomachinery. Licensed under Public Domain via Commons.

The turbines used in the aircrafts are axial flow turbines, which employ multiple stages to extract work from the air coming out of combustion chamber.

The turbines have two parts- the stationary nozzles (or stators) and  the moving rotors. The purpose of the nozzles is to turn the incoming flow so that that it impinges on the rotors at the correct angle, while the actual work is extracted out from fluid by the rotors.

"Velocity triangle for an axial turbine stage" by S.M.Yahya - Turbomachinery. Licensed under Public Domain via Commons.

Basically, the rotors are 'turned' by the incoming fluid as shown above which produces work to rotate the shaft (which runs the compressor). In case of turbojet engines (and to some extent turbofan), the air pressure decreases, while the velocity increases. This provides the required thrust.

The main mechanism by which the turbine blades spin is that the flow turns the rotor blades by hitting them, rather than any lift being produced.


What are these two holes on the forward fuselage of a Boeing 747? Does anyone know what are the two holes are on the Boeing 747, on the left forward part of the fuselage?

Source: airliners.net

I guess the right hole is the E/E compartment smoke override valve, is that correct?

Another hole under the belly just before pack inlet:

What is the function or name of this one?

The forward opening is the forward outflow valve or forward overboard valve (depending on reference consulted) which opens automatically if airflow in the forward compartment is low. It is independent from the two large aft outflow valves at the lower aft hull used for pressurization.

The second valve is the smoke override valve used in case there is smoke sensed in the the E&E compartment. Basically you try to get rid of the smoke by dumping it overboard. The second function is in case the fans used for ventilation of the E&E compartment fail. Then this valve is opened as well and the differential pressure ventilates the E&E compartment in reverse flow direction. The duct who was supplying the air is now sucking it out of the compartment.

The opening close to the pack inlet on the R/H side is the ground exhaust valve used to dump the air used for E&E cooling on ground overboard in case the temperature is high. This valve is always closed in flight.

Reference:

Boeing 747-400 System Schematic Manual, chapter 21, valves V462 (forward overboard valve), V447 (ground exhaust valve), V448 (smoke override valve)
internal documentation provided by employer of the author


Is feather edge bad? Currently learning about aircraft piston engine. Feather edge can be found at the engine valves as according to the picture. Can someone explain briefly about what is feather edge? Why it is bad? Which part of the engine that has the feather edge?

As noted here

  A thin edge is called a feather edge and can lead to preignition; the
  valve edge would burn away in a short period of time, and the cylinder
  would have to be overhauled again.

Basically during a rebuild over-grinding the valves can lead to a feathered edge which in turn can lead to higher/faster engine wear. Essentially by grinding the edge to thin you cause the limited remaining metal to wear out much faster. This can also lead to valve seating issues and out right leaks.


Why does a turbine engine compressor ratio affect stagnation pressure? This might just be a misunderstanding on my part, but in an ideal Brayton cycle, the flow through the compressor and turbine is isentropic, meaning $\Delta s = 0$. However, usually you are given the compressor pressure ratio to calculate the exit stagnation pressure, i.e.
$$
p_{cr} \equiv \frac{p_{03}}{p_{02}},
$$
where station 3 is the exit and station 2 is the inlet. This makes completely no sense to me. In an isentropic process, the stagnation pressure is constant, so I don't understand how there can be a ratio. I do understand that the pressure increases in the compressor due to compressing the air and increasing the temperature, but these two points of view seem to be contradictory.

By stagnation pressure I assume you mean total pressure. Stagnation is not a term commonly used in gas turbine engine performance, it’s more common with aerodynamics. The compressor increases the total pressure because the rotating blades are doing mechanical work on the fluid.

A couple of other comments, to explain in more detail;

First, the flow is not isentropic in a compressor. It only would be if a compressor was 100% efficient. The efficiency is actually calculated by the degree to which it is not isentropic. The efficiency is given by the isentropic temperature rise that would occur for the given total pressure rise, divided by the actual total temperature rise. An efficient compressor obtains the same pressure rise, for a smaller temperature rise. While you might think a higher exit temperature would be good, because it would mean we could burn less fuel, a greater temperature rise across the compressor would require more shaft power to compressor the air, which is taken from the turbine and means the turbine exit gas is now cooler and a lower pressure and now cannot produce the same thrust.

Secondly, the stagnation pressure is not constant (even if it was 100% isentropic). This maybe the case in a fluid flow where no energy exchange is occurring, but in a compressor, the rotating blades are doing work on the fluid. This increases its total pressure. The area at the entrance and exit determine its velocity (along with its density). Different areas, changes in density, and total pressure mean the static pressure isn’t the same at the entrance and exit, either.


How do you calibrate the compass of an aircraft on a compass rose? A follow-up from this question; one of the answers mentioned that the compass rose in the picture was used to calibrate an aircraft's compass.

But how does that actually work? Do you park the aircraft on top or something?

Most aircraft compasses include compensating magnets to correct for installation error (due to natural magnetic fields in an aircraft from steel parts and electrical equipment). When installing a new compass or performing significant electrical work on an aircraft the compass may need to be re-calibrated and the compensating magnets adjusted (typically by turning small screws, like the ones shown below).

There are several ways to calibrate (or "swing") an aircraft compass - the use of a properly-surveyed compass rose constructed to applicable FAA standards and marked on an airport is one of them, and ensures the compass swing is being performed in an area free of magnetic disturbances which should result in an accurate calibration.

The basic procedure is to taxi the aircraft to the compass rose and align it with the compass directions using a combination of the ground markings and a "gunsight" compass. A full description of the procedure can be found in AC 43-13.1, Chapter 12-37 ("Compass Swing"), but the quick-and-dirty version is:

Taxi out to the compass rose and align the aircraft so it is pointing toward Magnetic North.

Adjust the compass compensating magnets so that the compass reads North.

Turn the airplane so it is pointing toward Magnetic East (090).

Adjust the compass compensating magnets so that the compass reads East.

Turn the airplane so it is pointing toward Magnetic South (180).

Adjust the compass compensating magnets to remove one half of the "South" error.

Turn the airplane so it is pointing toward Magnetic West (270)

Adjust the compass compensating magnets to remove one half of the "West" error.

Once the compensating magnets have been adjusted a Compass Deviation Card is prepared to inform the pilot of the remaining compass error.
Beginning with Magnetic West (270) turn the aircraft to align with each of the 30-degree lines on the compass rose (270, 300, 330, North, 30, 60, 90, 120, 150, 180, 210, 240), and the error is recorded on a compass deviation card similar to the one shown below.

A compass reading within ±10 degrees on each 30-degree heading marker is considered acceptable per AC 43-13, and better results are usually achieved.

The compass swing is typically performed with the engine and electrical accessories (radios) running per AC 43-13. Some mechanics may also perform a second swing with radios off, and include an alternate deviation card for that configuration.


What navigational aid(s) would WWII bomber pilots have used while flying in instrument conditions? In my furthering attempt to understand the accident mentioned in this post, I've become interested in how WWII Bombers would have flown on instruments.  In the accident report, the pilots states:

  After passing Naknek en-route Elmendorf Field, we tried to go through Bruin Bay Pass but the Pass was closed. We climbed to about 7500 ft. and were between two layers of overcast. The layers began to converge ahead of us and before we knew it we were on instruments. Icing was severe and the antennas were lost in a very few minutes. Static was so bad on the loop antenna that the Anchorage range could not be heard. We thought our position was further East, over Cook Islet, until Co-Pilot, Lieutenant Donaldson, saw a mountain just off our wing tip and shouted to me. At almost the same instant we struck the mountain. After we got into the overcast everything seemed to happen so fast we couldn't do anything about it.

As a PPL and a budding instrument pilot, I am, of course, fairly well versed on how VORs and ADF/NDBs work.  However, It is unclear to me whether when the pilot refers to the "Anchorage range" and the "loop antenna" whether he is talking about either one of these instruments/station types.  He also mentions not being able to "hear" the range, which I would guess is similar to identifying a station with morse code the way VOR/ADF is identified today, though again, that is a guess.

Since the B-18 was much less common than the B-25 or B-17, there is much less written on them.  I did find this article, but it does not go into detail on the types of instrumentation.

I've also tried to find a decent picture of the B-18a instrument panel, but so far this one is the best I've come across:

The instrument between the compass and the turn coordinator looks a bit like an ADF, but I think the image is too fuzzy to tell for sure.

I've also seen this very informative set of answers though I don't think they answer my specific question.

So again, my question is, what navigation aid(s) would these pilots have used while flying on instruments?

what navigation aid(s) would these pilots have used while flying on
  instruments?

The short answer is the guy sitting behind them (aside from your standard 6 pack)

On planes of this size and of this era most of the navigation and operation of navigation instruments was up to the flight navigator. They sat behind the pilot and sometimes had other instrumentation back there. In many cases they had a table and a decent map as well as some stop watches a pencil and a good straight edge. The pilots were responsible for things like heading hold, altitude hold, and speed hold. Although some planes even had aft placed throttles out of reach of the pilots.

(source)

In areas of the world where NDB's and Other early radio nav ads were not really present pilotage and dead reckoning were often used. Keep in mind VOR's were not deployed until 1946.

Celestial navigation was also used however that is dependent on sky condition at the given time.

This B-29 "FiFi" Navigators station shows a pretty sparse setup of instrumentation that appears to include some kind of ADF style read out.

(Source)

This site provides a great overview of some of the nav equipment used at the time.

You can find the full 1945 "Flight Through Instruments" Naval Aviator publication here.

According to this article the B-18 did fly with a navigator

  The crew, numbering three, constituted the pilot and flight navigator
  in the traditional cockpit position over the nose with the bombardier
  seated in the position at the nose proper.

Early versions were even used to train navigators,

  Work began in earnest on a variant specifically for training military
  pilots, bombardiers and navigators.

  the "loop antenna"

The loop antenna is a part of early ADF systems and on occasion can still be found on some aircraft (see ADF loop below).

(source)

The loop antenna is one of two components needed for an ADF system. It is the component that can detect direction. However it only has 180 degrees of precision and is ambiguous beyond that. In other words it does not know if the signal is from the front or the back. The ADF Sense antenna solves the ambiguity problem (if installed).


Are you required to have constant view of the runway when circling? When you're circling, it has been said that you are required to keep view of the runway at all times below the MDA. However, sometimes this can be impossible due to issues with visibility, such as being banked to turn around for final, or because a flock of birds are circling between the airport and your aircraft. Are you required to execute the missed approach if this occurs or not?

A "circle-to-land" maneuver is basically a low-altitude traffic pattern - albeit one that you arrived at by being guided in on some instrument approach. The magic that makes this low (and possibly abbreviated) pattern possible is that the runway ends at airports with circling approaches have protected (obstacle free) airspace around them, which looks something like this:

(A more detailed explanation of the size of the circling approach area can be found on this question.)

Since it's basically a traffic pattern my understanding is you treat it as such, and that as long as you stay in visual contact with the airport and within the protected airspace (by visually judging your distance from the field, and knowing your altitude) you're unlikely to hit anything, and you can do all your usual pattern maneuvering as long as you can ***visually* be sure you're within the pretty blue part of the image above (your GPS cant help you here).

To see what this means for an example approach with some turns, consider my liberally-stolen and slightly-marked-up diagram below.

If you lose contact with your intended runway end for a few seconds because of the turn/bank required at point "A" that's OK: as long as you can still maintain visual contact with the airport/runway environment when you roll out (say by looking out the back window), and as long as you can remain clear of clouds, and can maintain visual clearance from any potential obstacles you may continue the approach.

If you're flying out and on the leg from "A" to "B" and all of a sudden you look back out the window and the airport is gone in the haze and clouds, you need to go missed: You've lost the airport/runway environment, and can no longer judge your distance to stay in the "safe" airspace.

Similarly if you're in a high-wing aircraft and your turns at "B" and "C" briefly obscure the airport while you're turning you can still continue the approach - if you've any doubt where the airport is just pick up the wing like you would in a VFR pattern (and if the airport isn't there like it's supposed to be go missed!)

Regarding your bird scenario, that's an interesting one that I don't think is covered in any diagrams, but if a flock of birds causes you to maneuver in such a way that you lose contact with the airport (and you can't just pick up a wing and have it be right where you expected it to be) you're obviously going to have to abandon the approach and go missed. It's the equivalent of the airport disappearing in the haze on that A-to-B leg.

Honestly though, if a flock of birds shows up and hangs out in a way that requires you to start maneuvering around them while you're trying to shoot a circling approach in real IFR you may want to just go missed anyway (given the odds this probably won't cost you too many approaches).

In a real world situation with poor visibility, possibly precipitation, and likely a cloud ceiling really close to your altitude, do you really want to try to be maneuvering down low to avoid some stupid bird that couldn't even be bothered to call the tower?

Wouldn't you feel much better pointing the aircraft in a generally "upward" direction and following the nice friendly needle again for a little while?

I'm just starting my IFR training, but I think I'd feel better with that option :-)


Is there a Flights API to get flight information months in advance? I hope I am at the right place here. Asking this at Stackoverflow is not allowed (off topic)

I want to be able to plan flights in the future. (6-12 months ahead) I only know the Flights ID like LH2014. All I want is to get the departure/arrival airport and times.

Do you know of any API or fresh database?

If I am booking a flight 6 months in advance I will get all the information. So it should be possible. Or is this the data from the day I booked the flight?

I tried few APIs like flightaware or flightstats, but they can only deliver data for max. 72 hours in advance, not 6 months.

A similar question was asked on Stack Overflow: https://stackoverflow.com/a/2899086/178673 (and marked off-topic, but it did have some answers)

When you are booking a flight, you are typically providing more information than just the flight number, in fact, the query is usually "here is my date/time and arrival/departure information, what is available?"

You are providing the departure date (or range) and arrival date (or range), as well as the city-pairs, and when you have that data you can use the API from FlightStats to find out the list of flights: https://developer.flightstats.com/api-docs/scheduledFlights/v1

If you just knew the flight number, you could use the API call for "Scheduled Flight(s) by carrier and flight number, departing on the given date. /v1/json/flight/{carrier}/{flightnumber}/departing/{year}/{month}/{day}, but again, you still need something to put in as either the departing or arrival date.

Programmatically, perhaps if it didn't return a hit for the date you specified, you could search on x days of either side of the date.  For example, October 19, 2014 didn't return a hit for LH2014 (I know this is a daily, Monday-Friday flight), and the API would return that it didn't hit, so then we (arbitrarily in this example) check two days on either side

Psuedo-code example:

day = 19
/v1/json/flight/LH/2014/departing/2014/10/{day-2}
/v1/json/flight/LH/2014/departing/2014/10/{day-1}
/v1/json/flight/LH/2014/departing/2014/10/{day+1}
/v1/json/flight/LH/2014/departing/2014/10/{day+2}

And find out that it is scheduled on the 17, 20 and 21 of October and that it flies MUC-DUS, in an A319/20.

So, the API isn't going to do all the work for you, but you could probably wrangle the API to give you the information you want in a format you want.  With some built-up logic around the question you're really trying to ask and multiple API calls (Is this flight number available on this date and what are the city-pairs, and if it's not available what date(s) is it available?).

Hope this is helpful. :)


Why does 14 CFR have skipped subparts as seen in the ASA 2019 FAR/AIM book? As an example, part 91.101 skips every even number until 91.126.

Why are they not in sequence as 101, 102, 103, etc?

Some of them were renamed/reorganized in 1989 based on proposals/petitions by the AOPA (referenced in FSIMS).

91.102 became 91.143 Flight limitation in the proximity of space flight operations.
91.104 became 91.141 Flight restrictions in the proximity of the Presidential and other parties
91.106/108/110/112/114 did not exist
91.116 became 91.175 Takeoff and landing under IFR
91.118/120/122/126/128 did not exist

The "did not exist" ones are probably proposed legislation that was removed prior to it being introduced into the Code of Federal Regulations, or regulations that were removed earlier (I can't find an older version of the CFR to check).


For what program was this Cessna 182 fitted with canards? I want to see if anyone knows what the heck is going on here. I was doing a flight out in Palo Alto California recently, and during the run up this Cessna 182 pulled in next to us.   It appears to have a canard foreplanes attached near the firewall of the airplane, and it appears to have a movable control surface on it as well. No this is not a Photoshopped image, this is an actual airplane that was sitting right next to us. I’m just curious if anyone here knows of any program using this aircraft and the purpose of the canard foreplanes.  Thanks.

It's a King Katmai STOL mod for a Cessna 182. From https://www.avweb.com/ownership/king-katmai-mod-safe-stol/

The full King Katmai modification consists of the canard, 300-HP IO-550, choice of 82- or 86-inch, three-blade prop, speed mods/drag reduction fairings, wing extension, increased gross weight, heavy-duty landing gear, which includes Cleveland brakes, stainless steel leading edges on the gear legs, brake lines faired in behind the main gear legs and routed so they are unlikely to be snagged during rough field operations, heavy-duty Airglas nose strut and oversize tires.

It brings the stall speed down to 31 knots. 3100 lb gross weight takeoff distance of 290 feet from a hard surface runway.


How Helicopters Change Attitude (Gyroscopic Precession or Thrust Vector Tilt) I am trying to determine how helicopters pitch and roll (i.e. change attitude). I have heard two explanations.

1) Pitch/roll change is achieved by tilting the tip path plane and therefor tilting the thrust vector. By tilting the thrust vector, a moment is generated about the center of gravity which pitches/rolls the helicopter.

2) Pitch/roll is achieved by imparting a moment onto the rotor, which can be viewed as a giant gyroscope, causing the helicopter to precess with a 90 degree phase lag (see page 2-16 here).

In Helicopter Theory by Wayne Johnson (© 1980), section 5-5 pg 191, he writes:

  Thus, there are two ways to view the rotor flap dynamics. First, the rotor blade can be considered a system with natural frequency of 1/rev, so that aerodynamic moments due to cyclic pitch excite the system at resonance. The response has a phase lag of exactly 90° (i.e. one-quarter of a cycle, which at 1/rev means an azimuth angle of 90° also). Alternatively, the rotor can be considered a gyro, with the flap hinges at the center of rotation forming the gyro gimbal. A control moment on the disk due to cyclic pitch then precesses the rotor with a 90° phase lag characteristic of a gyro until the flap damping produces a moment to stop the precession.

So, are the two explanations (1 and 2) equivalent, or are they both characteristics present? Wayne Johnson seems to suggest the former but gave no proof. Thanks in advance!

This animation shows it better than most.  The swash plate changes the plane of the rotor disc to change the plane of the lift vector.  It's the same thing as an airplane turning by banking.  When an airplane banks it imparts a lateral thrust component to the vertical lift component and it moves sideways, and because it's moving forward as it does so, it moves in a horizontal arc, or a turn.  A helicopter's rotor is just able to "bank" in all directions at any speed.

The swash plate directly flies the blades to the path that will put the overall disc in the desired plane of rotation.  The blades have to fly to their position using the air; if you had the machine running in a vacuum, the cyclic would have no effect.  However, gyro precession is a factor insofar as the input/result of the swashplate's effect on the blade's physical path is offset 90 degrees.

That is, to get the blade tip to its highest point in the circle, the highest blade angle, or highest lift force in the rotational cycle, is imparted 90 degrees before that point.  To tilt the rotor disc forward say, the blade that is on its way to its high spot over the tail boom will have reached its highest blade angle while passing at 90 deg on the left.

On the Bell rotor in the animation you can clearly see this.  The rotor disc angle follows the swash plate angle directly - swash plate tilts forward, rotor tilts forward. However, the linkage being driven by the swash plate acts on blade angle with a 90 degree offset (the control rods coming up on each side of the hub) to account for precession.

The Bell teetering system is interesting because it imparts no bending forces whatsoever to the rotor mast. The machine's body is suspended below the rotor hub as if it was a tennis ball on a string.  When you move the stick you are making the rotor disc fly around on its own account by tilting this way and that and the machine suspended under it follows along. In fact if a bending moment WAS applied to the mast, by having the teetering stops contact the mast while it's spinning, it comes apart and you become a falling object (this is "mast bumping" which cause the deaths of a number of Huey pilots in the 60s and Robinson pilots in the 90s).

Rigid and articulated rotor systems do impart some rolling and pitch moments into the air frame and the rotor head, mast and suspension system for the transmission are designed to transfer these loads.

A good fixed wing analogy between an articulated and teetering rotor is to compare regular airplanes vs hang gliders and trikes.  An articulated/semi rigid rotor is a bit like a regular aircraft where the body is directly acted on by the wings, although with a flexible connection between the wings and fuselage.  The Bell system is more like a hang glider or trike where the wing and body are on a fully flexible connection and you basically fly the wing around and the body underneath follows along without ever reaching the physical limit of the connection.  It's not a perfect analogy but sufficient for visualization.


How do hot air balloons get started (without burning the fabric)? I have seen photos of hot air balloons aloft with fearsome looking burners shooting flames into the interior of the balloon. That may be fine for a fully inflated balloon. But what about when the balloon is in a heap on the ground? How do you get it inflated without burning the fabric?

The balloon is spread out on the ground and rigged to the basket.
Then, a cold air blower is used to do the initial inflation, blowing air into the envelope through the bottom aperture. This gets the balloon about 75% inflated, but still horizontal.
Lastly, the burners are lit to heat the cold air already inside the canopy, expanding it and raising the balloon to vertical and full inflation.

You can find any number of videos on YouTube that show the process. Here's one:


What is this object on an MD-11? There is something above the engine on the tail of this MD-11:

What is that?

Source

As was said in the comments above, it is the support structure for the engine as seen in this drawing:


Where do airplane variant numbers come from? For example, the new B787-8 and B787-9.  Is there any significance in why they started with -8, versus the older 737s which started from -100?  Or B757-200/300?

Chinese superstition. The same reason Airbus went with the 380 number when 350 would have been next in line.

The Chinese sign for 8 looks like an up arrow (八) and 8 is the lucky number in Chinese. Similarly, 4 (四) is considered unlucky because the word for it (sì) sounds similar to the Mandarin word for death (sĭ).

Boeing and Airbus management court their prospective Chinese customers wherever they can because they expect their biggest sales in the next decade from that part of the world.

Originally, Boeing used three-digit numbers for their subtypes, and the last two digits represented the airline. Pan Am's number was 21, for example, so a Boeing 707-100 made to Pan Am specs was a 707-121.


What were the J47's turbine blades made of? What materials were used to make the General Electric J47 turbine blades in the 1960's?

It's very likely the J47 turbine blades used wrought iron, with alloying elements of aluminium and titanium. The General Electric J47 turbojet is a very very old design - it first flew in May 1948, only 11 years after Frank Whittle's first prototype gas turbine ran. It was the first axial-flow turbojet approved for commercial use in the United States, and was used in many types of aircraft. More than 30,000 were manufactured before production ceased in 1956.

This 1970 report gives a good summary of the materials used in early gas turbine engines.

It states that early turbine blade materials were either iron, nickel, or cobalt based alloy, both cast and forged. (i.e., there we're a mixture of materials, but the largest percentage of any one material was either one of those three).

Nickel based alloys are the ones that are mentioned the most. They are predominantly used today, and there are quite a lot of them (see table 5 in the 1970 report). But, the J47 is so old, it most probably only used an iron based alloy. This comprehensive report covering material development says, in the section on turbine blades:

  ....steadily increasing operating-temperature requirements for the aircraft engines resulted in development of wrought alloys with increasing levels of aluminum plus titanium. [But] component forgeability problems led to this direction of development not going beyond a certain extent. The composition of the wrought alloys became restricted by the hot workability requirements. This situation led to the development of cast nickel-base alloys.

So, Ni alloys were not used in very early engines. From above then, it is very likely the J47 used a wrought iron alloy, mixed with aluminium and titanium. This is also supported by Fig 1 from the Rolls Royce document mentioned below (the PDF download is free), which shows only wrought alloys used from 1940 to 1955:

A similar figure, from the TBC report mentioned below, shows Ni based "superalloys" have been used since at least the mid 60's (which is a decade after the J47 production ended!).

While the main constituent of the material hasn't changed since then what has changed is the method of manufacture, from wrought and forged with no crystal or grain orientation, to cast with crystals orientated along the axis of the blade (i.e. hub to tip, called uniaxial), to blades with single crystals. Also, air cooling now exits, with internal passages, and holes on the blade to provide a thin film of cooling air over its surface. The blades also have a thermal barrier coating, that is a ceramic material which basically insulates them from the hot gasses. Originally TBCs were used to gain extra life compared to the life required in the design specifications (i.e. the TBC wasn't necessary to met the base life requirement, but helped give more life). Now days the gases are so hot in some engines, the TBC is necessary just to meet the design specification minimum life. In this case, the TBC is known as prime reliant. See this article for detailed discussion of TBCs.

This article gives a very good summary of the development of turbine blade cooling technologies by Rolls Royce.


Why is there typically a large gap between the first flight and mass production of aircraft? Here are some examples I've found on Wikipedia:

Me-262: first flight 1942 July, introduced 1944 April.

MiG-19: first flight 1953 Sep, introduced 1955 March.

Dassault Mirage III: first flight 1956 November, introduced 1961.

F-4 Phantom: first flight 1958 May, introduced 1960 December.

This shows a two or three or even five year gap between the first flight and the entering into mass production.

Why such a long gap? What goes on during those years? To me it seems like once the first flight is done, it "works" and the only thing left is some finishing touches. Is it possibly more a matter of setting up a factory?

You don't want an aircraft that just 'works'- rather, you want an aircraft that satisfies your needs. The first flight is usually made by a prototype and does just that- it flies and pretty much nothing else.

Only once you start the flight tests do you understand the airframe limitations and whether the aircraft meets the requirements; usually, a number of modifications are needed. Also, the first flights are rarely, if ever in production configuration. In most of the cases, the required systems are fitted later. In general, most of the combat aircraft bring about substantial improvement over its predecessors- in fact it is a requirement, as the old ones can be used with small improvements at a much lesser cost.

Me 262 was really a revolutionary product and the use of jet engines caused a number of delays; in fact the prototypes were flight tested with piston engines in 1941. The first test flight happened with piston engine- just as well because both the jets flamed out soon after takeoff. By the time the second and third prototypes, the engines had been changed. However, these engines (Jumo 004) were larger, requiring larger nacelles, which in turn required a bigger vertical stabilizer (the landing gear was changed later). Pre-production of Me 262 had started in 1943 (and went nowhere due to engine troubles) when it was decided to change it into a bomber, further increasing the development period. By the time it took the field, it was in too few numbers to do anything.

Another example is the Mirage III. There were significant differences between the aircraft in first flight and the production one. The prototype never reached the required Mach 2 in level flight.The first one to do was the pre-produciotn Mirage IIIA with an engine with more than 30% extra thrust, lengthened fuselage for radar etc. Even this version was not combat capable- that was the Mirage IIIC.

The design is not frozen till the flight testing is over and the production plans can only be finalized after that- you never know what'll change (for example the hugely successful Su-27 underwent a change in wing design midway through testing). The delays due to setting up of production comes later and is normally quite less for countries/companies having experience. It is the design freeze that takes up more time during test flights.


How does radius of a propeller affect its performance? Let's say we have a conventional two-bladed fixed-pitch propeller. All things being equal, would the same propeller but with half the size -- 50% radius, have 50% of the performance of the first propeller?

Would the propeller hub in the middle be the same size? You did say all things being equal, which I read as "unchanged".

Example, 86" total diameter prop, 12" diameter hub, leaving 2 blades that are (86 -12)/2 = 37" from edge of hub to tip of blade, and 74" of working blade length.

Then you reduce the radius to 43" with same 12" hub, so you have (43 - 12)/2 = 15.5" blade from hub to tip, and 31" of working blade length. 31" is less then 1/2 of 74", so you've lost more than 50%.

Assuming the engine can't spin any faster due to the engine governor limiting the RPMs, you're not getting off the ground.


In the United States, are ultralights legally considered aircraft? I sometimes hear it stated that in the United States, ultralight vehicles are not legally considered to be aircraft. For example, Wikipedia used to state:

  In the United States ultralights are classified as vehicles and not aircraft, and are thus not required to be registered, nor is the pilot required to have a pilot certificate.

Under FAA regulations and US law, are ultralights considered to be aircraft?

Yes, under FAA regulations, ultralight vehicles are considered to be aircraft.

14 CFR 1.1 states:

  Aircraft means a device that is used or intended to be used for flight in the air.

Ultralights are used or intended to be used for flight in the air, so they are aircraft.

14 CFR Part 103 defines the term "ultralight vehicle" and describes the rules for operating an ultralight vehicle. Although Part 103 avoids using the word "aircraft" to describe ultralight vehicles, nothing in Part 103 (or anywhere else) states that they are not aircraft.

It is true that ultralight vehicles are exempt from nearly all regulations governing aircraft. However, this isn't because ultralights aren't legally considered aircraft; it's because there are regulations which specifically make ultralights exempt from those regulations. For example:

Part 103, Section 7, states that

ultralight vehicles are not required to meet airworthiness standards,
pilots of ultralight vehicles are not required to have any kind of certificate, and
ultralight vehicles are not required to be registered.

Part 61, Section 51(j), states that pilots are only permitted to officially log flight time in aircraft that are registered (as well as military and public aircraft). Ultralights cannot be registered.
Part 91, Section 1(e), states that ultralight vehicles are exempt from Part 91 in its entirety. (If ultralight vehicles were not legally considered aircraft, then this paragraph would not need to exist!)

(Of course, a pilot may make logs of flights performed in ultralights, but the FAA does not recognize this time as "flight time".)

So, the FAA does consider ultralight vehicles to be aircraft. However, they are exempt from most—but not all—regulations which govern aircraft.


What are the rules in UK law on carrying dangerous goods on drones? If I wanted to use an unmanned drone for carrying potentially dangerous cargo like car fuel, what would be the legal requirements of this in the UK? For example, lets say I wanted to carry fuel in jerry cans for use by drivers who have run out of fuel.

What are the rules on commercial drone flights where the drone will be flying autonomously and out of visual sight of the operator?

What are the rules on carrying cargo like fuel in said drones?

Article 94 of the Air Navigation Order

  (1) A person must not cause or permit any article or animal (whether or not
  attached to a parachute) to be dropped from a small unmanned aircraft so as to
  endanger persons or property.

  (2) The person in charge of a small unmanned aircraft may only fly the aircraft if
  reasonably satisfied that the flight can safely be made.

  (3) The person in charge of a small unmanned aircraft must maintain direct,
  unaided visual contact with the aircraft sufficient to monitor its flight path in
  relation to other aircraft, persons, vehicles, vessels and structures for the
  purpose of avoiding collisions.

  (4) The person in charge of a small unmanned aircraft which has a mass of more
  than 7kg excluding its fuel but including any articles or equipment installed in or
  attached to the aircraft at the commencement of its flight, must not fly the
  aircraft:

  (a) in Class A, C, D or E airspace unless the permission of the appropriate air
  traffic control unit has been obtained;

  (b) within an aerodrome traffic zone during the notified hours of watch of the
  air traffic control unit (if any) at that aerodrome unless the permission of
  any such air traffic control unit has been obtained;
  or

  (c) at a height of more than 400 feet above the surface unless it is flying in
  airspace described in sub-paragraph (a) or (b) and in accordance with the
  requirements for that airspace.

  (5) The person in charge of a small unmanned aircraft must not fly the aircraft for
  the purposes of commercial operations except in accordance with a permission granted by
  the CAA.

So section 3 states you must have direct visual contact and section 5 states that you must get permission from the CAA

    An individual or organisation that would like to conduct regular flights with their drone, however, will probably need to submit an
    operating manual to the CAA for a permanent approval. This will allow
    greater freedom to operate continuously without the need to seek ad
    hoc approvals.

  This type of Permission could be of use to:

  emergency services a local authority that would like to use a drone to
  carry out maintenance inspections of its property As with a Permission
  to carry out a commercial operation, the CAA will need to be assured
  of the competence of the person who will be flying the device. The
  ‘pilot’ therefore will probably need to undergo an assessment process
  with one of the approved National Qualified Entities.

http://www.caa.co.uk/Commercial-industry/Aircraft/Unmanned-aircraft/Unmanned-Aircraft/


What does stick fixed and stick free longitudinal stability mean in simple terms? What is the significance of stick fixed and stick free terms in aircrafts with mechanical control and modern fly-by-wire control?

Trim the aircraft. Do a "doublet" (means stick forward and back to the trimmed position for a short moment, or rudder deflected and neutral again) to upset the trimmed state.

Now watch the response while you keep all control surfaces at their trim position, making sure the control surfaces don't move when the aircraft goes through its motions. This is quite easy on GA aircraft and big aircraft with powered controls (if you do this on an Airbus, switch it to direct law).

Next, repeat the maneuver but let go of the stick respectively the pedals. Watch how the stick or pedal position moves with angle of attack respectively sideslip changes: This is your control surface floating freely. Again, watch the response. Normally, it will now take longer for the resulting oscillation to die down and the oscillation frequency should be slightly lower.

The first is the fixed-stick aircraft stability, the second the stick-free stability. Normally, stick-free stability is lower and proportional to the stick forces when flying away from the trim point. The difference between both is determined by the hinge moment coefficients of the control surface. For the elevator the floating angle $\eta_f$ is
$$\eta_f = -\frac{c_{r0}+c_{r\alpha}\cdot\alpha}{c_{r\eta}}$$

with $c_{r\alpha}$ the hinge moment coefficient over angle of attack $\alpha$ and $c_{r\eta}$ the hinge moment coefficient over control deflection. Both coefficients are normally negative and the absolute value of $c_{r\eta}$ is larger that that of $c_{r\alpha}$. When $c_{r\alpha}$ is zero, both stabilities are equal because the floating angle is zero.

Another way to study stick-fixed pitch stability is to trim the aircraft at two different speeds or load factors and to measure the trim change necessary between trimmed state 1 and trimmed state 2. The result is the speed stability rsp. the maneuver stability.

Stick-free stability is only relevant in case of manual controls. FBW aircraft only exhibit stick-fixed stability except for the very unusual case that the control surface actuators are overpowered by the aerodynamic forces.


How does the aircraft keeps propelling forward when airflow and thrust are not aligned? Assume an aircraft is flying at an angle of attack of 10 degrees, and that the incidence angle between the aircraft fuselage and the wing as well as the angle between the wing and the engine mount is also 0 degrees, the thrust force is at 10 degrees relative to the incoming velocity. My question is, since there exists an angle between the incoming the airflow and the thrust force, how does the aircraft keeps propelling forward straight?
I mean if I break down the thrust force into its components, then one component can be added in the direction of lift, and other component can be used to counteract the drag. But why would this make the aircraft to keep moving in a straight path? Because aircraft itself doesn't know how the component breakdown should be established, and also it just sees a resultant thrust force. Moreover, theoretically, I can make the component breakdown of the Thrust force using a different co-ordinate system, but still why would the aircraft keep on propelling in the same straight direction?

Let us assume level flight. Then the forces acting on the aircraft are shown in the following sketch (not necessarily to scale):

The forces are :

the total aerodynamic force $ F_A $, which is split into two components: lift $L$ (perpendicular to direction of motion) and drag $D$ (parallel to direction of motion)
the weight $W$
the thrust $T$, here acting slightly upwards because of the angle of attack $\alpha$

For un-accelerated level flight, the sum of all forces must be zero. This is independent of the coordinate system you use to split the forces. In our example, this is given by these equations:
$$ L + T \sin \alpha = W $$
$$ T \cos \alpha = D $$
At a given angle of attack, these equations will only be true at one particular airspeed. At higher airspeed, the lift would increase resulting in a climb, which then changes the angle of attack. At lower airspeed, the lift would decrease resulting in a descent.


What is ILS CLASS in this airport NOTAM? I have seen this NOTAM for UAII /CIT SHYMKENT airport and they mention ILS CLASS for runway 10/28, Does anyone knows what it means?
NOTAM:

NOTAM K3998/20: Shymkent Airport (UAII)
K3998/20 NOTAMN
Q) UAII/QICXX/I /NBO/A /000/999/4222N06929E005
A) UAII B) 2008171542 C) PERM
E) RWY 10/28 ILS CLASS:
ILS GP  I/C/2
ILS LOC I/D/2
REF AIP UAII AD 2.19
CREATED: 17 Aug 2020 15:42:00
SOURCE: EUECYIYN

This is a change in the ILS Facility Classification code. In your example the code is I/C/2 for ILS with GP, which means:

The ILS category is CAT I
Quality of Course C, which means localizer performance follows performance requirements until 100ft
Integrity level 2 (see ICAO Annex 10, Volume I for details)

The changes can also be found in the Kazakhstan eAIP UAII AD 2.19.
Here is a detailed description of the three codes in the classification by ICAO:

ILS FACILITY CLASSIFICATION AND DOWNGRADING
The  ILS  facility  classification  system  provides  a  more  comprehensive  method  of  describing  ILS  performance  than  the  simple  CAT  I/II/III  classification.  An  example  of  an  ILS  facility  classification  is  “III/E/4”.  ILS  facility  classification  is  described in Annex 10, Volume 1. A facility’s “class” of performance is defined by using three characters as follows:
a)    The first group of characters (I or II or III) indicates conformance to the facility performance category standards contained in Annex 10, Volume I. This character indicates if the ground equipment meets a facility performance Category I, II or III.
b)    The  second  group  of  a  single  character  defines  the  ILS  point  (Figure  C-1)  to  which  the  localizer  conforms  to  the  facility  performance  Category  II/III  course  structure  tolerances.  These  classifications  indicate ILS conformance to a physical location on the approach or runway as follows:

A:    7.5 km (4 NM) before the threshold;
B:    1 050 m (3 500 ft) before the threshold (CAT I decision point);
C:    Glide path altitude of 100 ft HATh (CAT II decision point);
T:    Threshold;
D:    900 m (3 000 ft) beyond the threshold (facility performance category III requirement only);
E:    600 m (2 000 ft) before the runway end (facility performance category III requirement only).

c)     The  third  group  of  a  single  character  indicates  the  level  of  integrity  and  continuity  of  service.  It  is  generally  accepted,  irrespective  of  the  operational  objective,  that  the  average  rate  of  a  fatal  accident  during landing due to failures or shortcomings in the whole system, comprising the ground equipment, the  aircraft  and  the  pilot,  should  not  exceed  $1 \times 10^{–7}$.  This  criterion  is  frequently  referred  to  as  the  global risk factor. In Category III operations, this objective should be inherent in the whole system. In this  context  it  is  of  the  utmost  importance  to  endeavour  to  achieve  the  highest  level  of  integrity  and  continuity  of  service  of  the  ground  equipment.  Integrity  is  needed  to  ensure  that  an  aircraft  on  approach  will  have  a  low  probability  of  receiving  false  guidance;  continuity  of  service  is  needed  to  ensure that an aircraft in the final stages of approach will have a low probability of being deprived of a guidance  signal.  Integrity  and  continuity  of  service  requirements  are  defined  in  Annex  10,  Volume  I,  Chapter 3, 3.1.3.12, for the localizer and Chapter 3, 3.1.5.8, for the glide path.

(ICAO Manual of All-Weather Operations)


Are there any aircraft with a 4-wheel nose landing gear and a 16-wheel main landing gear? Are there any aircraft with a 4-wheel nose landing gear and a 16-wheel main landing gear? I need this to answer my review of an aircraft design project.

The Il-76:

4 main bogies with 4 wheels each, nose gear with 4 wheels.

this one has a better view of the wheels, but it's a CGI:

4-wheel nose gear is rare, 16-wheel mains are more common: Boeing 747 (4 trucks with 4 wheels each in 2x2 config), Avro Vulcan (main trucks with 2 axles with 4 wheels each), HP Victor (same as Vulcan), Shorts Belfast (same as Vulcan).


Why isn't it possible to locate the rudder in front of an airplane's center of gravity? Why isn't it possible to locate the rudder in front of an airplane's center of gravity?

Specifically how does this relate to the stability derivative?

Effect on Aerodynamic Coefficients

It is possible to locate a vertical fin, as well as a control surface, ahead of the center of gravity.  $c_{n_r}$ (yaw-induced yawing moment or yaw damping) will not likely change much, all other things being equal. $c_{n_\beta}$ (sideslip-induced yawing moment or directional stability), on the other hand, will be reduced, perhaps becoming negative. Any sideslip will therefore result in a yaw moment which increases the sideslip.  Expressed in linear control theory terms, this will be a pole in right hand plane when you plot the complex solution of the equations of motion. It is an unstable configuration.

Active Control

As Peter mentioned, it is possible to remain in control in this configuration by means of active control.  Active control tends to be somewhat tiring for a human operator if it is possible at all.  Incidentally, this kind of instability existed in the lateral axis of the 1903 Wright Flyer, which was configured with a canard of considerable proportion. It was reportedly quite tiring to keep stable.

CP ahead of CG

There are advantages to having a center of pressure ahead of the center of gravity, the chief being agility.  Back in control terms, the farther you move poles to the right, toward instability, the faster or "twitchy-er" the response.  The F-16 is configured this way and has been the standard of maneuverability for quite some time, requiring computers and fly-by wire for stability augmentation.

Control surfaces ahead of CG

It is also advantageous for maneuverability to have control surfaces ahead of the CG.  In this case it is for avoiding a feature of control termed "non-minimum phase" response.  For a conventional, tail-configured aircraft, when a climb is commanded, the tail is forced down, leading to a net reduction in lift until an increase of angle of attack is developed.  This is non-minimum phase response.  It was necessary to initially go the opposite direction from that which was desired.  In canard configurations, this is not the case, first the nose climbs, then everything climbs.

Put them together...

Forward control surfaces, forward center of pressure and a stability augmentation system with adequate dynamic pressure make for one heck of a maneuverable package.  This is a common recipie for tactical missiles.


Why doesn't the Tu-154's center engine have a thrust reverser? In this gorgeous photo of a landing Tu-154, one can clearly see that the lateral engines are equipped with thrust reversers, but the center engine is not.

Why?

Several I guess:

There is no way to store them on the middle one in a way not increasing drag during flight.
In any possible configuration they would blow hot exhaust always against some body part, thus making it rather inefficient.

But maybe most important:

Two reversed engines already produce more than enough breaking power, no need to spend money on another. In fact, even one would be good for all purpose, but asymmetric force isn't a good idea either :))


Do promotional flight routes have a historical precedent? Right now, a Dreamliner is flying a rather strange path over the USA (see below). The plane took off from Boeing Field airport near Seattle, and is 'drawing' a virtual copy of itself on the map of the USA before flying back home.

As flight trackers are a relatively recent phenomenon, I was wondering: is this the first time something like this ever happens, or is this a tradition in aviation which I'm not aware of?

Permalink for the flight.

It's not the first time they do it. Back in 2012 they wrote 787 and the Boeing logo:

Planes have been drawn before by others as well.


How are emergencies handled during In-Seat Rest? Consider a Boeing 737 cruising over the Atlantic when an engine flames out. The procedure here is clear: the pilot flying should continue flying the plane, while the pilot not flying should pull out the QRH and follow the checklist for engine flameout. What happens, though, if the pilot not flying is engaging in Flight Crew In-Seat Rest? I assume they're woken up, and then I see a few options:

the pilot flying continues to fly while the pilot not flying wakes up and overcomes their sleep inertia. After 20 minutes, they go through the engine out checklist
the pilot flying continues to fly while the pilot not flying immediately goes through the engine out checklist, despite the risk of sleep inertia
the pilot not flying immediately starts flying despite the risk of sleep inertia, and the pilot flying goes through the engine out checklist
the pilot flying flies the plane while going through the checklist as the pilot not flying wakes up

These all sound like awful options. So  what would actually happen in such a situation?

Related: Is a pilot allowed to sleep during a flight?

Option 2:

  the pilot flying continues to fly while the pilot not flying
  immediately goes through the engine out checklist, despite the risk of
  sleep inertia.

When waking up to an emergency situation your body will start to produce adrenaline which gets you over the sleep inertia very quickly. If the situation is not clear to the PNF, he will be briefed by the PF.

Besides that, in a checklist flow, both pilots are involved and crosscheck each other's actions.


What is causing these "corners" on this F-104 V-n diagram? In this V-n diagram for an F-104 (source: this Wikipedia link), on the left-hand edge of the flight envelope, what is causing the "corners" that we see at the following points? (Numbers are approximate)
30,000', 375 knots IAS, and 5 G
40,000', 295 knots IAS, and 3.1 G
50,000', 230 knots IAS, and 2 G
60,000', 180 knots IAS, and 1.25 G
70,000', 140 knots IAS, and 0.95 G
Do these points simply represent the "corners" of what performance is possible while still maintaining horizontal flight at a constant airspeed (i.e. while maintaining both altitude and airspeed), and if more engine thrust were available, these "corners" would move higher up and to the right, continuing to follow the stall speed curves?  I.e., do the actual stall speed curves continue upward from the corners following a path that is more or less continuous with the lines below the corners?
(Note-- re the last data point--  a G-loading of less than 1 is obviously incompatible with constant-altitude flight-- but the data point still could have mathematical or theoretical significance -- e.g., if the aircraft weight decreased by 5%, then the aircraft could maintain constant altitude.)
Wouldn't it be theoretically possible for a pilot to operate well outside the illustrated envelope, say, by pulling 4G at 340 knots IAS at 40,000'?  Am I correct to assume that this could be done without stalling the aircraft, but the aircraft would be losing either altitude or airspeed continually?  Because it is on the "back side" of the thrust-required curve?  Whereas that would not be the case for a point further to the right, on the other side of the illustrated curve?
If the actual stall speed curves do in fact continue more or less smoothly upward from the "corners", this would imply that if, theoretically, we were setting a "maneuvering speed" to protect the aircraft from exceeding 6G's, it would need to be at about 430 knots IAS at 20,000' (the "cornering speed" shown on the diagram), but it would need to drop to about 380 knots IAS at 30,000' -- well outside the envelope of the figure as drawn.  Is this in fact the actual situation?
Is this particular diagram really as much about achievable performance as about protecting the aircraft from excess loading, at least in the positive-G part of the flight envelope?
Is it therefore not strictly accurate to call this particular diagram a "V-n diagram"?
Related ASE questions and answers--
(Q): In this F-104 V-n diagram, why does the stall speed (in terms of IAS) decrease with altitude in some parts of the flight envelope?

what is causing the "corners" that we see at the following points?

Compressibility. Close to Mach 1 the lift curve slope increases according to the Prandtl-Glauert rule with the factor $\frac{1}{\sqrt{1-Ma^2}}$. Since the X-axis shows indicated speed, the Mach 1 point moves left with increasing altitude. Technically, those corners should also be added for the negative lift limit.

Do these points simply represent the "corners" of what performance is possible while still maintaining horizontal flight?

No. A v-n-diagram covers the whole load factor range while horizontal, steady flight happens along the line y = 1g (except for turns or inverted flight, of course). Adding more thrust will not change the limits. Maneuvering is only possible/permitted (see below) inside the lines and maneuvering  at constant altitude depends on thrust which is not included here. The lines show lift and structural limits; thrust envelopes look different.

Wouldn't it be theoretically possible for a pilot to operate well outside this envelope?

Not really. Momentarily yes, for example the stall lift coefficient moves up with higher pitch rate, but that only works while pitch angle is increasing. Also, at supersonic speed (after all, your example of 340 KIAS @ 40 kft is equivalent to Mach 1.07) the envelope is limited by angle of attack, not lift. Therefore, 4g at Mach 1.07 in 40 kft is outside of the permissible flight envelope but may be reached if the pilot overrides stick shaker and stick pusher (depending on control authority).

So this diagram is really as much about achievable performance as about protecting the aircraft from excess loading?

Yes. The region left of the stall lines is impossible to fly since lift is limited at lower speed. However, the top speed limit might well be exceeded in a dive if the pilot chooses to do so. Equally, the g limit might be exceeded right of the point where the envelope becomes horizontal.
Thank you @JanHudec for pointing out correctly that those areas which can physically be reached by improper flying but might incur damage to the airframe are colored red.


Why do we have to manually tune VOR receivers? As the VOR frequency is automatically selected when the DME is selected, under what system conditions is manual tuning of the VOR required?

(aviation-safety-bureau.com)

As pointed out in the comments, I think you have things turned around. If you select the frequency of a VOR that has a co-located DME, the system will automatically also select the DME frequency. Thus, I'm guessing that what you perhaps meant to ask is under what conditions do you manually tune the DME frequency. If that is NOT what you are asking, put a comment after this answer to that effect, and I will delete this answer.

Now, if that is what you are asking, the answer in one sense is "never" in that, at least in civilian aircraft, you always select the VOR frequency. However, prior to my retirement in 1999 there were a few, very few as I remember, facilities that provided DME but at which there was no co-located VOR. To get the DME, you selected the VOR frequency that would have been paired with the DME had there been a co-located VOR. and it was the frequency of that non-existent VOR that was shown on the charts along with a clear and obvious note that there was no actual VOR. I have no idea whether in our current airspace system such still facilities exist.

You can find the standard VOR-DME frequency pairings here (PDF) or read about it on Wikipedia.


Is it harder to learn to fly rotary wing after learning on fixed? I have a private license for single engine land and I want to transition to helicopters. I have been told by some that learning helicopters is more of a challenge after learning fixed wing. However I have yet to see any good sources or explanation for this. Is this generally true and if so why?

Rotary flying is much harder than fixed wing to learn, however learning after you get a fixed wing license is easier in some ways because you already know:

Radio procedures
How to set up and use instruments
Navigation and flight in controlled airspace
Air law and regulations
The "gestalt" of flying

This means all you need to do is learn to fly the helicopter, which is tricky because helicopters are much less stable than fixed wing airplanes. If you take your hands off the controls of fixed wing airplane it will generally stay pointed where you put it, especially if it's trimmed properly. If you take your hands off of a helicopter's controls in hover things will go very, very badly in a real hurry so you have to be making constant control inputs. The controls of a helicopter are also very sensitive, it is a very different (and more challenging) type of flying.


Why is ISA Standard pressure 1013.2 not used for contour charts instead of QFF? I am confused because QFF being actual mean sea level pressure is subject to change why would we use it for mapping terrain? Does this mean the height of a given terrain changes with the change in QFF? Tried to look for an answer for this everywhere but I couldn’t find any. Can someone tell me what am I getting wrong?

Maps and charts show true elevation, meaning tape measure altitude from the sea level. The way the mapmakers and chartmakers measure elevation has changed over time. Currently, I think GPS is prevalent. The way GPS computes elevation is depend on the WGS84 Geoid earth model. This modes surface does not coincide with actual sea level but GPS takes that into account. And today in most aeronautic related industries WGS84 is becoming a standart, which also includes maps and charts.

On the other hand altimeter provides height using pressure of air. QNH and QFF are the altimeter settings used to adjust for non-standard pressure and temperature, respectively. QNH is always provided to pilots and is the most prevalent. I have never heard that the QFF is used or requested by pilots.

As I said QNH setting only corrects for non standard pressures. It really assumes ISA temperature, 15C. So as you asked what happens if the temperature is not standard. Well someone needs to compensate for that and make correction.

Colder than ISA temperatures needs to be corrected for minimum enroute altitudes and obstacle clearances. Because the aircraft will be at lower true altitude than what altimeter shows, at colder temperatures. As for hot days, it’s less risky because aircraft’s true altitude will be higher than what is shown on altimeter. Only example comes to my mind is when you’re shooting an approach that has decision altitude kind of minimums. Since the aircraft will be higher than true altitude you may end up going around during real minimum IFR situations. However you will be on the safe side at hot temperatures, in terms of obstacle clearances.

As mentioned in that article; correcting minimum sector altitudes (MSA) and minimum vectoring altitudes for non-standard temperatures are ATC’s responsibility. In other cases, such as doing a published approach, it’s pilot’s responsibility.

That same article provides an excel at the end to use on the ground. Also some pilot operating handbooks provide charts to apply for altitude adjustments for non-standard temperatures. One technique for flight planning is to find the correction for the coldest temperature for  the day and apply that to whole flight. But that applies only to GA type flights really.

Not only that,  but also, there is this phenomenon called geopotential altitude. It implies that 1 altimeter-measured-feet at sea level is not equal to 1 altimeter-measured-feet say at 30,000 feet. And that’s because gravity is not constant as we climb. So the actual true elevation of the obstacle will always be slightly higher than what you see on your altimeter even when you’re side by side. However it’s really a small difference (less than 1%) and not a big factor at low altitudes where obstacles mostly live. [wp reference]


Quadcopter propeller performance Quadcopters use both direct and contra-rotating propellers to be able to turn and to balance the torque caused by the each of the propellers.

Propeller performance measurement:

When testing the propellers for these quadcopters, why is their performance measured only in one direction of rotation? Would it be useful to test both the right handed and left handed rotations to provide more information to the designer?

Propeller pitch selection:

Why would a designer select a lower pitch to diameter ratio for quadcopters when there are higher and more efficient ratios to choose from?

When testing the propellers for these quadcopters, would it be useful
  to test both the right handed and left handed rotation of the
  propellers or just one direction?

You may miss something about propellers rotation. A given propeller produces thrust (which is another name for lift) when rotation occurs in the designed direction. When direction is reversed, thrust may be produced, but not efficiently, and will be reversed compared to the regular lift.

A propeller is a wing in rotation. Wings are not used is reverse direction, with a plane going backwards.

Left-handed and right-handed propellers are different:

Thrust is determined in the intended direction of use.

  Why would a designer select a lower pitch to diameter ratio

For the same reason than wings on actual planes have an optimized size and incidence. Increasing this size or this incidence is not productive. The limit may come from different reasons, but essentially for weight and drag considerations.

In the quadcopters, the propellers are spun by electric motors that have a limited power and a preferred rotation speed. Propellers are selected to match the rotation speed and available torque of the motor.

In addition turbulence is created by the propeller, especially at high pitch. Turbulence can decrease efficiency of neighboring propellers, so a compromise has to be found between high individual and low overall lift produced.

From Studying the Aerodynamics of Multi-Rotor Drones (Nasa)

Also think about the fact that a propeller just converts a quantity of work (rotation) into another quantity of work (translation of air). The rate of conversion is dependent on the blade pitch. Air translation (lift) can be increased but not beyond the capabilities of the motor to create the equivalent rotation. If this is done, the motor just can't deliver, and it's efficiency decreases (battery will be empty more quickly).


What's the difference between a Terminal Control Area and a Control Zone? From what I've understood, in Canada a Terminal Control Area (TCA) is established at airports with a high volume of traffic to provide IFR control service to arriving, departing and en route aircraft.

A Control Zone is designed around aerodromes to keep IFR aircraft within controlled airspace.

Why do we have both? Both provide ATC services, so why do we require a Control Zone within a TCA? Is there a specific reason that the TCA cannot be lowered below 700 AGL?

See this reference material in "From The Ground Up" (I've tried to attach it but it didn't work).

A Control Zone is the small (and usually circular) surface area around the airport that is handled by the airport's control tower. At smaller airports (but still large enough to have a tower), this is all they have.

A Terminal Control Area is a large and typically complex area above one or more Control Zones to manage large flows of fast traffic (i.e. airliners) moving in both directions through the congested area between the Control Zone(s) and the en route environment far above.

Note that while Canada (and the US, though it uses very different terminology) often uses the same class of airspace for the TCA and CZ, that isn't required, and there may even be several CZs with different classes under one TCA.


What is this aircraft seen at Peachtree City, GA? Sorry for the poor quality, but this jet was taking off from Peachtree City Regional on Sunday 13 May. Anyone know the aircraft?

It's one of many privately owned Aero L-39s, some of which are in the US. Here's one registered in Georgia, USA, with a similar livery at the same airport:

(flickr.com) N915WE.

  N915WE Aero L39C
  Preparing for takeoff. Falcon Field-Peachtree City, Ga.

It could actually be the same one you photographed.


In a fighter jet, what is the average weight of the ejection system? In the old days, pilots had only a parachute pack. (In the really old days they might not even have that.) They had to open the canopy manually and jump out.

Today, fighter jets have zero-zero ejection seats. They can save the pilot even at zero airspeed and zero altitude. They do this with solid rockets to eject the pilot upwards.

I would like to know what is the average weight of this system for a single-pilot fighter jet? That way we can compare it's weight to the total weight of the plane and see what fraction it is.

Really the weight would include only the rockets and explosive bolts on the canopy, and I guess the ejection handle too. It would not include the weight of the seat or the pilot, as those have to be there even without an ejection system.

The F-14 manual describes the ejection system as:

  The aircraft is equipped with an automatic electronically sequenced command escape system incorporating two Navy aircrew common ejection seat (SJU-17(V) 3/A (pilot) and SJU-17(V) 4/A (RIO)) rocket-assisted ejection seats.

That means the seats are an integral part of the system.

According to this page, the weight is 228 pounds (103 kg) and it has a "maximum thrust [of] 4,800 pounds for 0.25 seconds".

A cockpit seat on a Boeing 737 weighs around 40 kg if we are to trust this replica vendor, so we can say the addition of the ejection elements adds 63 kg. Of course a 737 cockpit seat is much heavier than a WWII non-existent seat (the pilots brought their own cushions). This might be useful however if you want to compare a B-52 with and without ejection seats.

Below is an image for that ejection system, and as I gather, that's a very common (average) model found on many US aircraft.

(Click for larger size.)


Was John F. Kennedy Jr.’s accident airplane equipped with an autopilot? JFK Jr.’s crash was attributed to failure to maintain control due to spatial disorientation. Could this be explained by his Piper Saratoga N9253N having no autopilot?

According to the NTSB, the accident airplane did have a functioning autopilot and GPS.

The airplane was equipped with a Bendix/King 150 Series Automatic Flight Control System (AFCS), which was approved for use in Piper PA-32R-301 model airplanes by the FAA on November 1, 1982. The AFCS provided two-axis control for pitch and roll. It also had an electric pitch trim system, which provided autotrim during autopilot operation and manual electric trim for the pilot during manual operation.
The AFCS installed on the accident airplane had an altitude hold mode that, when selected, allowed the airplane to maintain the altitude that it had when the altitude hold was selected. The AFCS did not have the option of allowing the pilot to preselect an altitude so that the autopilot could fly to and maintain the preselected altitude as it climbed or descended from another altitude. The AFCS had a vertical trim rocker switch installed so that the pilot could change the airplane's pitch up or down without disconnecting the autopilot. The rocker switch allowed the pilot to make small corrections in the selected altitude while in the altitude hold mode or allowed the pitch attitude to be adjusted at a rate of about 0.9 degree per second when not in altitude hold mode.

According to the same report, at least two different CFIs judged the accident pilot at least adequate in the operation of the airplane’s autopilot.

A second CFI flew with [Kennedy] between May 1998 and July 1999. This CFI accumulated 39 hours of flight time with the pilot, including 21 hours of night flight and 0.9 hour flown in instrument meteorological conditions (IMC). The pilot used this CFI for instruction on cross-country flights and as a safety pilot. On July 1, 1999, the CFI flew with the pilot in the accident airplane to MVY. The flight was conducted at night, and IMC prevailed at the airport. The CFI stated that, during the flight, the pilot used and seemed competent with the autopilot.

Also:

A third CFI flew with the pilot between May 1998 and July 1999. This CFI accumulated 57 hours of flight time with the pilot, including 17 hours of night flight and 8 hours flown in IMC. The pilot also used this instructor for instruction on cross-country flights and as a safety pilot. This CFI had conducted a “complex airplane” evaluation on the pilot and signed him off in the accident airplane in May 1999. According to the CFI, on one or two occasions, the airplane’s autopilot turned to a heading other than the one selected, which required the autopilot to be disengaged and then reengaged. He stated that it seemed as if the autopilot had independently changed from one navigation mode to another. He also stated that he did not feel that the problem was significant because it only happened once or twice.

53N’s GPS was capable of driving the autopilot.

The accident airplane was equipped with a GPS receiver, Bendix/King model KLN-90B. The GPS was capable of presenting moving map displays; bearings and distances to programmable destinations, such as airports and waypoints; airport information; ground speed; and other information. The GPS was also capable of interfacing with the AFCS and the pictorial navigation indicator.

The accident occurred in July 1999. The KLN-90B’s navigation database was not current.

The navigation database indicated that it was effective on October 8, 1998, and that it expired on November 4, 1998.

As to operability

On July 29 and 30, 1999, the avionics were examined at the AlliedSignal/King Radios Facility, Olathe, Kansas, under the supervision of a Safety Board investigator. On October 13 and 14, 1999, a follow-up examination of the navigation and communications transceivers and all three autopilot servos was also performed at the AlliedSignal/King Radios Facility under the supervision of a Safety Board investigator. [P]arties to the investigation were present during both examinations.
The accident airplane’s AFCS was examined. Examination and functional testing of the AFCS pitch, pitch trim, and roll servos did not reveal any evidence of a preimpact malfunction or jam.