Why aren’t there any lifting-canard airliners? A lifting-canard aircraft, such as the Long-EZ, is an aircraft with the main wing at the back end of the fuselage and a pair of small, highly-loaded canards attached to the forward fuselage; the canards fly at a higher angle of attack than the main wing, and, consequently, provide a significant amount of lift in addition to pitch control.1

During a sharp pitchup in a lifting-canard aircraft, the canards, being at a higher angle of attack than the main wing, stall first, causing the aircraft to automatically pitch down before the wing ever stalls.  As the wing, with the ailerons on it, remains unstalled throughout, roll control is preserved, without any of the violent rolling inherent in stalled control-tail aircraft.2  As the canards are stalled, pitch control is lost until they unstall, but, in this case, you don’t need pitch control, because the aircraft pitches down and recovers all on its own, without the need for any manual control inputs;3 this actually has the benefit of making lifting-canard aircraft practically unstallable (for the main wing, anyways) barring the separation of large parts of the airframe.  In addition, as the surface providing most of the aircraft’s lift never stalls, the overall loss of lift when the canards stall is fairly minor, and the aircraft’s handling characteristics remain benign throughout.

In contrast, while a control-tail aircraft will usually also pitch down when the main wings stall, this is dependent on the stabiliser trim setting, and, if the center of mass is near the forward limit (necessitating considerable nose-up stabiliser trim), the aircraft may actually pitch up in a stall.  Also, if the aircraft does pitch down, it does so quite violently, as the majority of the aircraft’s lift is suddenly lost, and with large, violent, largely-uncontrollable roll oscillations (as the ailerons are located on the main wing, which is stalled).  And, because the surfaces used for pitch control are not yet stalled, pitch control is preserved, allowing the pilots to hold the aircraft in the stall.

Given the considerable safety advantages of the lifting-canard configuration, why don’t we see any lifting-canard airliners?

1: As opposed to a control-canard aircraft, such as the Flyer, where the canards fly at a nominally-zero angle of attack, are used only for pitch control, and make these aircraft utter beasts to fly without a computer making constant control inputs.

2: Aircraft with a tail-mounted horizontal stabiliser and elevator which (nominally) fly at a lower angle of attack than the main wings.  Examples include most aircraft ever.

3: In contrast, control-canard aircraft pitch violently up as they stall (because the main wing, being at a higher angle of attack than the canards, stalls first), and, therefore, require aggressive nose-down control inputs to recover before the canards stall as well and pitch control is effectively lost; lifting-tail aircraft (with a tail-mounted horizontal stabiliser and elevator that fly at a higher angle of attack than the main wings) also pitch up, for the same reason, except that this happens well before the main wings stall, and is coupled with a simultaneous, near-total loss of pitch control as the horizontal tail stalls (making stalls completely unrecoverable for lifting-tail aircraft using only the usual aerodynamic surfaces for control).

Sean I have no idea where you got the idea that the horizontal tail on a conventional aircraft lifts up, like a canard surface but at the opposite end, and can therefore stall and let the nose rise.  It's exactly backwards.

The tail lifts down.  When the airplane stalls, the center of lift of the main wing shifts sharply aft creating a strong nose down pitching moment that the horizontal tail lacks authority to counteract until the plane speeds up, and the nose drops.  If the down lifting tail surface itself stalls, that is a disastrous situation and is abnormal for any aircraft.

Canards generally suck because they have a host of limitations that negate most of the theoretical benefits and that's why they have been commercial failures. Otherwise, you'd see lots of them.


How are takeoff and stall different from each other? Technically what differences are there between a take off and a stall?

From what I understand, when stalling the aircraft will lose lift when a certain angle is met. On a takeoff the aircraft will pitch the nose up but the effects are different.

What affects this? Is it the effect of the relative airflow or something else?

On take-off the pitch is increased to increase lift, but only to a point well before stall occurs. An aircraft's minimum speed is defined by the maximum lift it can create before the flow over the wings stalls, and the high-pitch attitude is only attained when the aircraft flies faster than that. As soon as lift is sufficient for lift-off, further pitch increases are increasing the flight path angle. If the aircraft keeps accelerating during the initial climb, stalling is impossible.

Technically, both are very different. Their only commonality is that they involve high angles of attack.


How should the Swiss international airlines flight 850 METAR reports be interpreted? From the Wikipedia page on the Swiss International Airlines Flight 850 crash investigation, it was stated that the initial METAR did not reflect the situation and the METAR less than an hour (a moment before the approach was started) was drastically different.

Initial METAR:

  EDDT 04001KT CAVOK 30/17 Q1002 A2959 0998 2947 NOSIG.

Later:

  EDDT VRB01KT 9999 FEW040CB SCT120 BKN260 29/17 Q1002 A2959 0998 2947 TEMPO 27025G55KT 2000 +TSRA BKN009 BKN015CB COMMENTS: OCNL LTNG AND CB SW OF STN.

I'm not very familiar with these reports, or how they are generated. From some research it sounds like the second report is much more serious, however I'm having trouble understanding a few things:

  VRB01KT

This seems to suggest variable visible range, but I'm not sure what the 01KT means.

Can someone clarify?

The later report first mentions scattered cumulonimbus clouds, but then says the coverage is up to broken.

Why are there multiple mentions of the same types of clouds?
Are they talking about different height/direction?

The Wikipedia article seems to suggest that there was a massive storm moving rapidly into the area. My understanding is that NOSIG means the weather is not expected to significantly change in the next two hours.

What would cause the initial report to include NOSIG?
Given how much worse the weather seems to be in the later report, why would it take the station almost an hour to file a new report?
Why wouldn't they file a new report as soon as it seemed like the weather was degrading?

Can someone clarify?

I can try to clarify the METAR report:

From the Wikipedia source link on METAR:

EDDT:  METAR for Tegel Airport
VRB01KT: Wind variable at 1 knot (1.9 km/h)
9999: visibility in excess of 10 kilometres (5.4 nmi)
FEW040CB: few clouds at 4000 ft. including cumulonimbus
SCT120:  scattered clouds at 12000 ft
BKN260:  broken clouds at 26000 ft
29/17: temperature 29 degrees Celsius, dew point 17 degrees Celsius
Q1002: current altimeter setting (in QNH) is 1002 hPa
A2959 0998 2947: current altimeter setting 29.59 in.Hg, falling to 998 HPa, 29.47 in.Hg.
TEMPO: Temporarily

27025G55KT: Temporarily winds from 270° at 25 knots (46 km/h), gusting to 55 knots (102 km/h)
2000 +TSRA: visibility 2000 meters (1.1 nmi)
+TSRA: heavy thunderstorm and rain
BKN009: broken clouds at 900 ft
BKN015CB: broken clouds at 1500 ft including cumulonimbus

COMMENTS: OCNL LTNG AND CB SW OF STN: Occasional lightning and cumulonimbus clouds south west of the station

  Why are there multiple mentions of the same types of clouds?

The TEMPO group is used for any conditions in wind, visibility, weather, or sky condition which are expected to last for generally less than an hour at a time (occasional), and are expected to occur during less than half the time period.

  Are they talking about different height/direction?

The Sky Condition (i.e.:FEW040CB SCT120 BKN260 ) reports the sky coverage and is given for different height, the following three-digit height is given in hundreds of feet.

For further clarification of METAR convention I find this useful!

  My understanding is that NOSIG means the weather is not expected to significantly change in the next two hours.

Correct, NOSIG stands for NO SIGnificant change, doesn't mean that the weather will not change!


What are these "winglets" on the roof of the 737? I circled the parts on the fuselage in red.

In general, those are called blade antennas. They consist of a monopole antenna (a single rod sticking out of the fuselage) with an aerodynamic fairing around it.


What careers are available for someone with a PPL? I'm not sure if this is the right place to ask this question, and I'm sure that some of the answers will depend on the country, so I apologise if this is "too local" or "off topic".

I'm considering getting a Private Pilot's License. Ideally it will be for both recreational use and also to make money.

I've read that there are some limitations on how you can make money as a Pilot with only a PPL. But some of the things I've read a pretty vague and open to interpretation.

What kind of jobs/careers can you get with a PPL?

If you are talking about Europe (EASA) Doc 1178 states at PPL privileges:

a) The privileges of the holder of a PPL(A) are to act without remuneration as PIC or co-pilot on aeroplanes or TMGs engaged in non-commercial operations.
(b) Notwithstanding the paragraph above, the holder of a PPL(A) with instructor or examiner privileges may receive remuneration for:
(1) the provision of flight instruction for the LAPL(A) or PPL(A);
(2) the conduct of skill tests and proficiency checks for these licences;
(3) the training, testing and checking for the ratings or certificates attached to this licence.

Bottom line you could make money with PPL by being a flight instructor or a flight examiner. A side effect would be also accumulation of flight hours that would permit you to continue with a course for commercial pilot.


Where can I download flight data containing pitch, roll and yaw angles? I'm researching the amount of solar energy available to photovoltaic cells placed at various locations on an aircraft's body. To calculate the angle of incidence of the sunlight on different parts of the plane I need a complete set of attitude angles of the aircraft (pitch, roll and yaw or equivalents) during flight. Can anyone tell me where to get this data?

FlightRadar 24 has an API that you can get data from. This is only from aircraft with ADS-B transponders, so it excludes some smaller and older planes. This would indirectly:

Give you points with which you could calculate the turns.
Give you pitch as the rate of climb.

This might give you a bigger but less exact dataset. Unfortunately, you might be disappointed in that normal commercial aircraft make relatively few manoeuvres at cruise.

Depending on the sort of simulations you might find that making a simulated flight in FlightGear (Open Source Simulator) might yield better results. If memory serves me right there is some equivalent to a flight data recorder so you can pull the data when you are finished.


Is there any effect that contributes to roll stability even in the absence of sideslip? Is there any physical dynamic-- involving high wing placement, "pendulum" effect of CG far below wing, or anything else-- that contributes to roll stability in a way that is NOT dependent upon the aerodynamic forces generated by sideslip?

For the purposes of this question, "roll stability" is defined as a tendency to roll towards wings-level, or a reduced tendency to roll toward a steeper bank angle.  Perhaps a better term might be "spiral stability".

Buoyancy is one such effect!  Or more specifically, a buoyant force acting above the aircraft CG.  Think hot-air balloon, dirigible, blimp.
I think I've also thought of one such effect involving conventional winged airplanes but will mull it over some more before answering.


In a piston aircraft, how much noise is generated by the engine, and how much by the propeller? I've been reading quite a few articles lately about how noise complaints from GA airports across the country.  One of the common suggestions to fix the issue is to simply use an electric engine instead of a gas powered one.

Leaving aside other practical concerns (batteries and weight for example), would this actually significantly reduce the amount of noise a GA aircraft makes?  I'm told a lot of the noise actually comes from the propellor itself, not the engine.

So, in essence:  How much of the noise from a GA aircraft is made by the engine, and how much is the propeller?  And does the percentage change depending on the phase of flight?

Note: I am not asking for subjective answers here.  My hope is that someone actually has a decibal break down of how much noise comes from the engine, and how much from the propellor.  Yes, I know it will vary by craft.  An average would be fine, or perhaps numbers from a popular GA craft (like a Cessna 172 or Piper Cub, for example.)

One particular example I can recall is Extra 330. Modification with electric engine have been built (Extra 330LE) keeping the rest of the aircraft quite similar to the original petrol-engine version as far as I know. According to this article electric version was measured to produce 14.5 dB less noise compared to the combustion engine aircraft.

Maybe you can try too look for other combustion engine aircraft converted to electric without making other significant modifications (I am not aware of any other than this Extra 330LE though) as a source for data you are looking for.


Why are all engines identical in typical commercial airplanes? I come from the IT world where redundancy is in place to cover several cases, among other:

a statistical failure of a device (so we use more of them expecting that the event is independent)
a rogue usage of a device (hacking into it though a vulnerability)
a specific context where a bug is triggered

In order to account for the last two ones, redundancy is sometimes (or usually - depends on the criticality of the system) done with different devices (form different vendors). This is typically the case with firewalls, for instance.

I was wondering why this isn't the case with aircraft engines?

It would be "easy" with planes having four engines (so two of each kind), somehow less "easy" with two engines (where the differences between their regimes would need to be compensated - the pilot states that they want 80% of power, which, in the specific conditions they are in, means 78% for the left engine and 83% for the right one).

Having two redundant engines which are equally susceptible to be impacted by, say, ashes is probably not interesting, compared to having two different ones which would each have its strong and weak points (but different between the two)

Note 1: "easy" above is used as a placeholder only. I am aware that aircraft software and hardware is complicated, I mainly wanted to highlight the difference between 2 and 4 engines. Having two firewalls is a simple task compared to that.

Note 2: it may be that engine failure is not a big deal, statistically speaking compared to other issues (or in an absolute sense), and therefore the extra maintenance, structural compensations because of the differences etc. are not worth it. Thanks for pointing this out if this is the case

Engines don't fail, on average. And if they do, it's a very low probability that two engines will fail at the same time.

Modern jet engines are extremely reliable, with failure rates on the order of 0.01/1000hrs. And if you do have a failure, you have redundancy, as you have two (or more) engines. A plane can stay aloft and land with a single engine.

It would add a lot of complexity and maintenance costs, with no real benefits.

If the failure is external, such as water in the fuel, lack of fuel, or ash ingestion, two different engines are unlikely to help, because all jet engines works in a very similar fashion. The external problem would simply affect both, maybe at slightly different rates, but ultimately shutting them down anyway.

So it adds cost and complexity, without providing any real improvement. Jet liners simply does not crash because all engines stops due to internal problems.

The one case where it would help is if there's a design fault with the engine, e.g. manifesting in turbine breaking after x hours. But engines are extensively tested before being put into serial production, and this occurs very rarely on production aircraft. In addition, the likelihood of the same problem occurring on two engines in such a sport span of time as a flight, but not at all during testing, is a rather low likelihood.


What is the maximum rate of descent in an instrument approach? What is the maximum rate of descent approved in an instrument approach procedure non-precision? Basically what is the maximum rate of descent (Fpm) that I use during the approach?

ICAO Doc 8168 stipulates that for a non-CDFA non-precision approach, the aircraft should not exceed 15% gradient when descending from FAF to MDA.

  1.7.4 Stepdown descent
  The third technique involves an expeditious descent and is described as “descend immediately to not below the
  minimum stepdown fix altitude/height or MDA/H, as appropriate”. This technique is acceptable as long as the achieved
  descent gradient remains less than 15 per cent and the missed approach is initiated at or before the MAPt. Careful
  attention to altitude control is required with this technique due to the high rates of descent before reaching the MDA/H
  and, thereafter, because of the increased time of exposure to obstacles at the minimum descent altitude.


Is this angle of attack animation backwards? Is this animation of the angle of attack sensor in this video from 25:30 to 25:50 correct?  It seems like motion of the sensor is the opposite of what it should be based on the angle of the aircraft.  For example, given an angle of attack sensor mounted on the right-hand side of the aircraft, I would suspect that a strong nose-up attitude would cause the blade on the aoa sensor to turn slightly clockwise with respect to the body of the aircraft.  But to me the animation displays a counter clockwise turning for the nose-up attitude.

Maybe, depending on your interpretation.
The animation leaves room for interpretation. It is never specified what remains constant and what changes throughout the animation. For example, is the animation just zooming in on the sensor (and the sensor vane movement is just the entire aircraft pitching), or is the sensor picture relative to the aircraft pitch? Let's assume the latter; in the former case, it's obviously correct but doesn't teach us anything.
Climb/descent interpretation
The aircraft pitch displayed is the actual aircraft pitch as it is in flight. This means that respectively the situation in climb and in descent is shown. This makes sense with the preceding comments about the vane "being stuck in the climb position". In this interpretation, the animation is correct.
As the plane climbs, the thrust vector has a downwards component. This means the aircraft thrust accounts for part of the gravity, and the wings have to take less of the aircraft's weight. This means the angle of attack is reduced in climb, and indeed the sensor vane will point more 'down' during climb, and more 'up' during descent.
Angle of attack interpretation
The pitch shown in the animation corresponds to an angle of attack (i.e., the air mass is moving strictly horizontally through the animation). In this case the animation is incorrect.
A high angle of attack means that the air has a vertical component w.r.t the aircraft body; specifically, from the belly upwards. The AoA vane is like a weathervane, and will follow this movement. In a high AoA situation, it will point up (in a cobra maneuver, it would point straight up). This is opposite from the animation.


What does the future of the weather radars look like? Planes had weather radars for a long time (Dassault Falcon and Learjet35A) which was useful since you either had to ask ATC, listen the ATIS frequency or ask the flight advisory before flight planning in order to learn the weather.

But we are living at a time of two way transponder communications and more and more of the world (At least the USA) are employing more weather stations and satellites are continously monitoring the world which makes the weather information more and more accessible and in flight Wi-Fi finally arrived!

So. are there plans about sending weather information through two way transponders in the future? Will this hamper the importance of weather radars?

In the USA, planes with ADS-B can receive FAA transmitted weather from ground stations for display in the cockpit. It can lag by several minutes.
https://www.faa.gov/nextgen/programs/adsb/pilot/

Planes with XM weather can receive more timely weather from satellite feed for display in the cockpit.

Airborne radar has the advantage of being the most immediate, but you may not be able to see much past what is immediately in front of you, so combining that with ground/satellite feed to give you a view of what is farther ahead would be the best of both.

I have ADS-B in my plane, but I don't do any extreme weather flying, just climbing thru cloud layers to get to nicer weather on top, or dropping thru a layer to land. I'm not out there trying to dodge thunderstorms and heavy rainstorms. If the weather is that bad, I can wait it out.


Does Airbus have a production problem? Looking up numbers for my answer to the A380 production question, it occurs to me that Airbus is facing a real inability to deliver its latest airframes. The A380 is currently sustaining a build pace of 45 aircraft a year with a backlog of about 150 outstanding orders. The A350, Airbus's direct competitor to the 787, has better orders (781 outstanding), but Airbus has been able to deliver only 5 of those, 4 to Qatar Airways and 1 to AerCap. The A340 ended production in 2011, so the 330 (1370 orders, backlog of 356)  350 and 380  are Airbus's only three widebodies in production right now. The 320 and 321 are backlogged badly, though Boeing has a similar backlog for 737 variants so that seems par for the course in the modern aviation industry dominated by LCCs.

Boeing has had fewer orders for its 747-8 but is keeping pace (92 delivered of 123 ordered, averaging 18 airframes a year) and has an embarrassment of riches in 787 orders (1095 ordered, 295 delivered, on pace for about 115 aircraft a year after ramp-up) and healthy business with the older 777 (backlog of 560, in the ballpark of about 80 deliveries a year since 2010). Its 767 frame, a close competitor to the A330, has slightly fewer orders despite being the older plane, but Boeing seems to be keeping pace (less than 100 backlogged in a total of 1161 orders).

I read these numbers and I come to the conclusion that Airbus is in big trouble in the large and very large jet markets it was planning to dominate just ten years ago; Boeing, by most accounts seems to be out-producing them and thus getting the lion's share of a mostly post-jumbo market. Am I reading this right?

A backlog of orders does not indicate a manufacturing problem. Quite opposite, it is good for the business as it adds stability. Airbus outpaced Boeing on every aircraft expect the A350/787 last year.

Producing all of the backlog in one year is not a good idea, as investments into the production line would be enormous and after a year, utilization of the line would be horrible. If all A380 were to produced this year, what should they do with the production line next year? A chance of another 150 orders per year coming up is unlikely.

A350 production started last year while 787 started in 2011. The ramp-up of production has already happened for the 787, but not for the A350. According to Wikipedia, by 2018 the production has ramped up to 10 per month, which would outpace the 787 at the current capacity.

https://en.wikipedia.org/wiki/Competition_between_Airbus_and_Boeing

https://en.wikipedia.org/wiki/Airbus_A350_XWB#Entry_into_service

In conclusion, I do not think they have a manufacturing problem. Keeping reasonable backlog is good for the business.


How to command autopilot to start a fixed rate descent? Is it possible to command an autopilot to start a fixed rate descent? For example to avoid weather during the cruise phase? From what I have read the autopilot would maintain constant speed and altitude until interrupted but havent found a fixed rate descent function.

Here is what typical autopilot controls look like

Image source: What is a "Flight Director"?

The pilot can set the required altitude, as well as the required vertical speed to get to that altitude. A cruise decent will typically use a shallower descent than an approach descent.


What is this in the primary flight Display? What is this in the primary flight Display ?

It is a digital Angle of Attack Indicator. From the Boeing 737 FCOM:

  Digital AOA Readout (white)

  Indicates digital AOA value to the nearest 0.2 degrees. When on the ground and
  ground speed less than 80 knots, the readout is fixed at 0.0 degrees.
  Stick Shaker Indicator (red)

  Indicates point at which stick shaker activation occurs for existing flight
  conditions.
  Blank if AOA signal is invalid.
  Analog Needle (white)

  Indicates analog AOA value.

  needle travel is limited to a range of -6 degrees and +21 degrees
  fixed at 0.0 degrees when on the ground and ground speed is less than 80
  knots.

  Approach Reference Band (green)

  Indicates appropriate range of approach AOA for a Vref(xx) + 5 approach.

  displayed when in normal or single engine landing flaps (15, 30, 40)
  moves with flap position
  inhibited on takeoff and initial climb.

  Zero Degree Reference Line (white)

  Indicates zero degrees angle of attack. Reference lines are displayed every 5
  degrees from -5 degrees to +20 degrees.

(Boeing 737 NG FCOMv2 10.11.11 Flight Instruments, Displays - PFD/ND - Displays)

All Boeing aircraft have at least two alpha vanes to measure angle of attack, but the cockpit display shown above is an airline option, i.e. not every aircraft will display this dial:

  Angle–of–Attack

  There are two alpha vanes, one located on each side of the forward fuselage. The
  vanes measure airplane angle–of–attack relative to the air mass.

  [Option - Angle of attack indicator]

  The primary source of data for the AOA indicator on the PFD is supplied by the
  ADIRU, with the Stall Management Yaw Damper (SMYD) as the backup source.
  The source selection is automatic in the event of primary source failure. Slight
  differences between the Captain’s and FO’s indications may be noticed due to
  sideslip or vane installation errors. These differences could be as large as 2
  degrees alpha.


Why did air traffic levels decrease dramatically in the US through the 2000s? In 2015, the FAA stated that

  System-wide, air traffic has declined by 24 percent since peak year 2000. The chart in Figure 1.1 shows that air traffic
  volume is not expected to return to peak levels in the near term.

This is talking about traffic in terms of ATC operations.

My question: why was there such a drastic, sustained drop-off? I understand that commercial traffic dropped off after 9-11, but I assumed it had since returned to 'normal'. Apparently this is not the case, but are there any other reasons? Is it something with the metric? It doesn't seem like there are any less people flying, do airline fleets consists of larger jets than 15 years ago?

(Info from the Air Traffic Controller Workforce Plan )

It isn't just one thing, but a vicious cycle:

Airline travel is expensive. One person flying and one person driving end up about the same price once you figure in gas and hotels, but the airline will want that same price for each passenger, while you can fit up to three more people in the same car at practically no additional charge (the extra weight will slightly increase gas costs and at some point everyone you can put in a minivan won't fit in one hotel room, but the incremental costs still don't compare at all). This makes time practically the only advantage to flight, especially for a family group; if you have the time to drive, many people who need to get somewhere don't even consider flying as a viable financial option.

You choose your car, among other things, for a certain level of comfort; the airline sets up their planes for volume over all else. Even the smallest sub-compacts have more legroom (for the front seat passengers at least) than the average economy airline seat. Upgrade to first class and the ride's better, but then the cost doesn't compare at all.

Customer service ratings are at an all-time low. Flight attendants are moving further and further from the "stewardess" role they had in a bygone age when airlines lived and died by their service quality (because regulation gave them little control over anything else in their business model). Now they exist for little else than to make sure nobody dies, or worse, breaks Federal aviation laws. Get them on the plane, give the speech, make sure everyone's belted in for take-off and landing, then get them back off the plane, all without killing themselves or each other. Anything else the the flight crew does during the flight is gravy at this point.

The major U.S. carriers have practically all adopted Spirit's business model. The average person considering air travel today might think Spirit's the only airline that charges you extra for every single additional amenity or service, but in fact Southwest, a "discount" carrier, is the only one that still rolls 2 checked bags, snacks and drinks into the ticket; American, United, Delta, USAir, they all charge \$25 for the first checked bag and \$50 for the second, and most of them are also charging for any food or drink served on board.
This is due to the hypercompetition on price, which is partially our fault as consumers. In a related but different industry, StubHub recently abandoned its "all-inclusive" pricing model, because it saw its sales drop by half due to StubHub being the highest price in most side-by-side comparisons. It's the same with the airlines; if you need a flight, you go to Google or TripAdvisor or Expedia, enter your route and the date window of your trip, sort by price, and pick one of the top three, maybe the top five. That means that anything the airlines can do to lower the price they show you online at first glance gets them the customers, and airlines wanting to keep the all-inclusive model, like Southwest, have to aggressively remind customers that what they see online is what they will end up paying when it's all said and done (hence the "Bags Fly Free" ad campaign that is now painted on their planes' cargo hatches).

Security is a nightmare. I remember a time, not that long ago really, when you put your carryon or purse on the conveyor belt, your coins in a dish, and walked through a metal detector. Simple. You didn't even need a ticket to get into the secured area, so you could meet whomever was flying in at their gate instead of at the curb. Those days are gone, and it will take a couple big technological leaps to get anywhere near that again (like being able to walk through a full-body scanner with your shoes and all your bags, instead of adopting the "felony stop" position in stocking feet with the contents of your briefcase laid out in grey tubs).

The expense of any kind of travel is redefining the idea of a "vacation". Leisure time overall has been decreasing since the advent of the Information Age with everyone interconnected and instant gratification being practical in more and more aspects of our lives. Those who still use their two weeks a year (if they even get that) for real leisure are opting more and more often for a "staycation", either staying home relaxing and visiting local attractions, or driving a relatively short distance to a hotel or resort (DFW has two big destinations, the Gaylord Texan and the Great Wolf Lodge, which cater primarily to people who already live in the Metroplex).

Video calling has created a difference between "face to face" and "in person". They used to be synonymous, but now the kids can not only talk to Grandpa, but see him, and he them, over a mobile phone or a computer with a webcam, at virtually no cost beyond the telecom plan. This development has more thoroughly revolutionized business travel; you no longer need to fly to the corporate office to get face time with an executive or have a big corporate meeting; you just sit down somewhere with a computer, camera and microphone.

All of these things have deterred all but the most necessary travel by air; getting on a plane is so expensive, so dehumanizing and so uncomfortable that it's only done if you have to get somewhere and can't take the time to drive there (or you have to cross a major body of water to reach it). That has reduced total passenger count, and since a flight only makes a profit if it's very near full, that reduces the number of flights airlines make. However, that decreases total revenue to offset the overhead of the airline (marketing, scheduling, maintenance, etc), so airlines cut costs by slashing services, making a flight on their planes even more miserable, reducing the general desire to fly, reducing passenger count. The vicious cycle continues.
This reduction has been offset somewhat by U.S. airlines "rightsizing" their fleets, opting for more flights with smaller planes. This gives passengers their choice of flight times while keeping planes full and pilots/flight attendants employed. Boeing is focusing primarily on this market in new plane orders with the smaller, more efficient 737, 777 and 787, while the original "jumbo jet", the 747, is on its way out of most passenger fleets and the A380 is struggling outside a couple relative niche buyers like Emirates and Qantas that specialize in ultra-long-haul flights.
Increased air cargo flights have also made up some of the difference; boxes don't care nearly as much about being stacked like sardines in an old aircraft (when was the last DC-10/MD-11 you flew in as a passenger? UPS still has dozens of them in the cargo fleet) with minimal amenities, so thanks to the success of e-commerce, FedEx and UPS are raking it in and growing their air fleets (though they passed on the A380 in part due to Airbus not prioritizing the cargo variant), while American is scheduled to reduce its fleet by 30 planes this year and is still struggling to report a profit even with prices and services cut to the bone.


Is flying at 14,000 MSL safe for children without supplemental oxygen? FAR 91.211(a) requires supplemental oxygen for all passengers above 15,000 feet.  Are there any health implications of a 5 hour flight at around 14,000 feet on children without any supplemental oxygen?  Obviously the flight crew would be wearing supplemental oxygen as required by the FAA above 12,500 feet.

I've read that babies under 3 months do not have mature enough lungs for altitude stress, so for the sake of this question, let's assume the children are over 6 months with no existing health conditions to worry about.

My question is for a non-pressurized general aviation aircraft.

Let me start out by saying that Aviation Stack Exchange is not a substitute for medical advice. Most of us aren't doctors (though I have medical training I am certainly not a doctor), and even if we were doctors we are not your doctor and we don't know your medical history (or your child's medical history).
If you're going to be flying with your kids in an unpressurized aircraft consult your pediatrician for their recommendation on supplemental oxygen. There are a number of factors at play, and your doctor will be able to consider all of them and give you comprehensive advice.

That said, let's talk about oxygen in general terms.

There's a lot of good information on supplemental oxygen use out there: AOPA talks about it here, and this website has a very detailed explanation, written by a doctor which get into what's going on as altitude increases (and the partial pressure of oxygen in your lungs decreases).

By regulation you are required to provide supplemental oxygen:

to the flight crew if you're above 12,500 feet for more than 30 minutes.
to the flight crew if you're above 14,000 feet for ANY length of time.
to everyone onboard if you're above 15,000 feet for ANY length of time.

Using the handy chart in the second website that equates to oxygen saturations (SpO2) of roughly 88%, 82%, and 76%, assuming you're breathing ambient air for an extended period of time.

To put this into perspective if you come to the hospital with an oxygen saturation below 90% you will almost universally be put on supplemental oxygen, and most guidelines call for maintaining SpO2 above 92%. (In aviation terms, the partial pressure of oxygen at 10,000 feet usually results in SpO2 around 90%).

So with that information the question now becomes "What is your standard of care for your passengers?" - the FAA sets minimum requirements in the regulations, and they are mainly focused on making sure the flight crew does not become impaired (they are less concerned about your passengers getting loopy, as long as the pilot is OK), but you as a pilot are free to set higher standards based on your own understanding of physiology and aeromedical factors.

I can't tell you what you should do, but I can tell you what I do: On any flight above 10,000 feet I carry supplemental oxygen, I use it, and I provide it to my passengers.
I also carry a pulse oximeter in the aircraft to check oxygen saturation (SpO2) on myself or my passengers as needed (and I set the oxygen flow rate based on having the worst person in the aircraft above 90%).


How does the wraparound wing design reduce drag? How does the wraparound wing in this AOPA article reduce drag?  One would think all that extra leading edge and surface area would make it worse.
One more link also.

  The Parsifal Project has produced a proposed design dubbed PrandtlPlane, an homage to Ludwig Prandtl who developed an idea for an airplane wing that boosted efficiency (and reduced drag) by wrapping around on itself to form a box around the fuselage.

This paper on Conceptual Design of High Subsonic Prandtl Planes

Title: Conceptual Design of High Subsonic Prandtl Planes

Author: Zohlandt, C.N.

Contributor: La Rocca, G. (mentor)

is also proving to be most interesting reading

It does not reduce drag, but creates more of it.

This concept is called a "box wing" and is one variety of closed wings.  Another is called a "joined wing" and was popularized by Julian Wolkovitch. However, only people who don't understand how a wing produces lift can be enticed by this concept - it has too many drawbacks for the modest reduction in induced drag it offers. The general idea is to sweep the horizontal surface of a T-tail forward and stretch it out until it joins the backward-swept wing and relieves it in bending, similar to a strut.

Similar to winglets, the vertical extension of the wing structure will involve more air into the production of lift, which reduces induced drag, but this extended structure must be bought with a hefty mass increase which will reverse the gain in induced drag, because much more lift needs to be produced in order to lift the additional structure.

Note especially that the rear wing (which is supposed to act as a tail surface) will be loaded in compression in order to support the wing. Making this rear wing narrow will make it susceptible to buckling, which can only be avoided by a stiff and heavy structure, and will increase its friction drag due to its much lower Reynolds number. When a winglet-like element is added between wing and horizontal tail, this winglet is now loaded in bending and will also need to be made much stronger and heavier than a conventional winglet.

Calling this a "Prandtl plane" is to completely misunderstand the 1924 publication of Ludwig Prandtl, who very well understood how wings create lift, about the benefit of box wings.


Would using a drone to pay for something count as commercial use? If I were a drone hobbyist, and I flew a drone over to someone to give them money in exchange for something, would that count as commercial use and therefore be illegal? Here’s an example scenario:

I’m not licensed to fly drones commercially. I fly a drone with money and an order over to the local McDonald’s drive-through with some money. The cashier takes the money and puts a burger into the basket in return.  Assuming the McDonald’s is just across the street (still in visual range) and there’s no one in the drive-through that I’d be flying over, would that be legal? I’m not operating the drone for hire, and since I’ve payed for the burger, it’s my property (so I’m not illegally flying someone else’s property).

I certainly don’t intend to do this (and I am a commercial drone pilot), but I was just wondering if that counts as commercial use.  I couldn’t find anything specific in the regulations that explained it.

Laws around drone use are very new, and the only way to be certain about this is to have a case come to trial. You probably don't want to be the person it comes to trial over. A lawyer would give you a much better interpretation, but even they can't be sure.

If you are interested in my personal uninformed opinion (IANAL) then I think it would not count as commercial use. My reasons are:

The drone is completely incidental to the transaction. The cashier would do exactly the same if you showed up in person on foot or in a car, or if you sent someone else to make the transaction.
If you drive your car to McDonalds, that does not count as commercial use of your car. If you fly to McDonalds  then that does not count as commercial use of an aeroplane.


Are Helicopters allowed near busy airports? Are Helicopters allowed near busy airports or any airports at all and if not why not

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

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

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


What do the various A340 configurations (clean, 1, 1+F, etc.) mean? Could anyone describe (or direct to usable documentation) me aircraft configurations? What does it mean clean configuration, configuration 1, 1+F, 2, etc... Is there any section in FCOM's describing it in clear way?

A clean configuration is a configuration where landing gear, flaps, slats, spoilers etc. are retracted.

1, 1+F, 2, 3 and FULL refer to the level at which the flaps are currently deployed:


On the LAANC map for sUAS operations, why does the permitted ceiling drop to zero southeast of KGFL? Above is a screenshot1 from the LAANC map for obtaining authorization to operate sUAS (model airplanes, "drones", etc), centered on KGFL, which is Floyd Bennett airport near Glens Falls NY.  Why does the permitted ceiling drop to zero AGL southeast of KGFL?  Even though the permitted ceiling is as high as 400' AGL between this area and the airport?  This configuration is very unusual.

Above is a screenshot of the sectional chart for this area.  The airspace in question is E2 Class-E-to-surface airspace.
Would aircraft likely be operating under Instrument Flight Rules in IMC at very low altitudes (well below 400' AGL) in the airspace SE of KGFL?  Are there aspects of the instrument approaches into or out of KGFL that would justify banning all sUAS operation in the airspace 5 to 10 miles southeast of KGFL, even though there are many other airports with similar long arms of E2 Class-E-to-surface airspace where the permitted ceiling is all the way up at the maximum value of 400' AGL?
Are there any other similar cases in US airspace where as one travels in a straight line away from an airport, remaining within E2 Class-E-to-surface airspace which encompasses only a single airport with associated instrument approaches, the permitted ceiling indicated by the LAANC system increases, and then decreases again?
It's probably safe to assume that the zero-ceiling designation is not to protect the small airport "Argyle" (1C3).

After all, in the above zoomed-out screenshot of the sectional chart from this area, we can count 33 other airports, none of which are protected by LAANC grid squares.
The following screenshots of the airspace around KSHR shows the FAA's more typical treatment of E2 Class-E-to-surface airspace: the areas distant from the airport have a 400-foot ceiling on the LAANC grid.

Here's a screenshot of the sectional chart showing KSHR:

Below are screenshots of the sectional chart and LAANC grid for another airport -- KTHV -- that has three outlying airports within the E2 Class-E-to-surface airspace.  Note that the permitted ceiling is 400' AGL in the vicinity of these outlying airports.  Reinforcing the point that the zero-ceiling grid squares southeast of KGFL are unlikely to be designated for the purpose of the protecting the airspace of the small airport "Argyle" (1C3).

So what is the reason for the unusually large area of zero-permitted ceiling on the LAANC grid SE of Glens Falls airport?
Footnotes:

All LAANC screenshots taken 12-23-20, and still were current as of 2-3-21.

It turns out that the E2 Class-E-to-surface airspace around KGFL has been recently expanded, and the long "arm" projecting to the southwest is a new addition.  KGFL is listed in the current (as of February 2021) version of the FAA's "Airspace Designations and Reporting Points" document, FAA Joint Order 7400.11E.  The airspace change was published in the Federal Register on July 31, 2020, and became effective November 5, 2020.  The old airspace description may be seen on page E-30 of the July 21, 2020 edition of the Airspace Designations and Reporting Points document, J.O. 7400.11E.
One might wonder whether, after the airspace change, the newly-added LAANC grid squares were assigned a zero ceiling to accommodate some unusual feature of the new instrument approaches and departures in the vicinity, while by some oversight no adjustment was made to adjust the ceilings of the previously existing grid squares to accommodate the new approaches and departures.
Close scrutiny of the approach plates suggests that this is unlikely.  Granted, there is some modest amount of relief in the terrain southeast of KGFL. The ridge east of the town of "North Argyle", about 9.6 miles from the airport, tops out at just over 1000' MSL-- let's call it 1100' MSL to be conservative. The airport KGFL is at 328' MSL, so by our conservative estimate the top of the ridge is 772' higher than the airport. This works out to a slope of 66 to 1, or 0.87 degrees above horizontal. Add 400' to the top of the ridge to represent the maximum AGL altitude that the FAA typically grants for sUAS operations, and we have a 43.4 to 1 slope to the airport, or 1.32 degrees above horizontal.  It is difficult to see how permitting sUAS flight beneath this less-than-2-degree-slope would endanger aircraft on the instrument approaches into KGFL. For example, the RNAV (GPS) RWY 30 approach appears to show a Final Approach Fix ERUPE at 2300' MSL just 5 nautical miles from the airport. The Intermediate Fix CATIR is at 4200' MSL, 12 nautical miles from the airport.
Further scrutiny has revealed that the zero ceiling assigned to the new LAANC grid squares southeast of KGFL perfectly fits a pattern, that appears to have little relationship to safety considerations.
The pattern is as follows:  for most or all expansions or other modifications of existing controlled airspace effective 9/10/20 or later, any new squares that have to be added to the LAANC grid have been assigned a ceiling of 0 AGL.
As a result, whenever a significant new "arm" or projection is added to an existing area of controlled airspace, then we can get a pattern like we see at KGFL, where the portion of the new projection that lies outside of any previously existing LAANC grid squares is assigned a ceiling of zero, while the (older) grid squares closer to the airport retain a higher ceiling.
On the other hand, when an existing area of controlled airspace is expanded by a small amount, then we can have a pattern where just a few new LAANC grid squares, seemingly randomly scattered around the periphery of the old airspace, need to be created to accommodate the expanded airspace.  Very often the new airspace just barely impinges into most of these new grid squares.  All of these new grid squares are assigned a ceiling of zero.  This can happen even when the airspace is not actually expanded at all, but rather is simply moved a few hundred feet due to a slight change in the official location of the airport.  It's pretty clear that no safety consideration could possibly be involved in the zero-ceiling assignment in the latter case.
Why this pattern has recently arisen, remains a mystery.  At present it would be hard to say whether it is due to a decision taken at a high level of the FAA, or due to the choices of some particular data entry technician, or due to exigencies of life in the time of Covid-19.  Is there an intention to revisit these cases and correct the arbitrarily low ceiling assignments?  Is there an intention to continue the practice indefinitely?  The FAA sUAS Help Desk has been contacted, and further developments may ensue.
Here are additional specific examples of the pattern described above:1

KDRO -- Durango-La Plata County Airport -- Durango CO -- E2 Class-E-to-surface
Old airspace description page E-72 in FAA Joint Order 7400.11A,new airspace description on page E-68 in Joint Order 7400.11E.  Effective 09/10/20, the official airport location was moved about 130' to the NW, but more significantly, a new "arm" was added to the Class E airspace, projecting 2 miles to the NE, 2 miles in width.  As a result of this new "arm",  7 new squares were added to the LAANC grid, of all which assigned a ceiling of zero.   Note the presence of grid squares with a 400' ceiling between the new zero-ceiling grid squares and the airport.

KDLN -- Dillon Airport -- Dillon MT -- E2 Class-E-to-surface -- second attachment
Old airspace description page E-77 in 7400.11A, new airspace description page E-74 in 7400.11E.  Effective 9/10/20, the Class E circle was decreased in radius by 0.9 miles, but a new "arm" was also added, 4.8 miles in width and projecting .7 miles beyond the original radius.   As a result of this new "arm", 8 new squares were added to the LAANC grid, all of which were assigned a ceiling of zero.  Again, note the presence of grid squares with a 400' ceiling between the new zero-ceiling grid squares and the airport.

KCXO -- Conroe-North Houston Regional Airport -- Houston, TX -- Class D --third attachment
Old airspace description page D-125 in 7400.11A, new airspace description page D-125 in 7400.11E.  Effective 9/10/20, the official location of the airport was shifted about 350' to the NNW, and the radius of the Class D circle was increased by .7 miles (about 3700').  As a result of these changes, 27 new  squares were added to the LAANC grid, all of which were assigned a ceiling of zero.  Again, note the presence of grid squares with a 400' ceiling between the new zero-ceiling grid squares and the airport.

KFWS -- Fort Worth Spinks Airport -- Fort Worth, Texas -- Class D --fourth attachment
Old airspace description page D-129 in 7400.11A, new airspace description page D-125 in 7400.11E.  Effective 9/10/20, the official location of the airport was shifted about 85 feet to the west.  As a result of these changes, a single new square was added to the LAANC grid, barely penetrated by the new location of the controlled airspace, with an assigned ceiling of "0" AGL.  Again, note the presence of grid squares with a 400' ceiling between the new zero-ceiling grid square and the airport.

KALN --  St Louis Regional Airport  --Alton/St Louis, IL -- Class D
Old airspace description is on page D-31 in 7400.11E, new airspace description is on this page of the Federal Register.
page D-125 in 7400.11E.  Effective 11/05/20, the Class D airspace was expanded by .2 miles (about 1056 feet), and the center of the circle was shifted about 218' to the southwest due to the change in the official location of the airport.  As a result, there are now 6 anomalous zero-ceiling LAANC grid squares running from the south edge of the airspace clockwise around to the northwest edge of the airspace.  Note the presence of grid squares with a 400' ceiling between the new zero-ceiling grid squares and the airport.

PABE --  Bethel Airport-- Bethel, AK-- Class D
Old airspace description is on page D-3 in 7400.11E, new airspace description is on this page of the Federal Register.
page D-125 in 7400.11E.  Effective 12/31/20, the Class D circle was shifted about 430' to the southeast due to the change in the official location of the airport.  As a result, there are now 3 anomalous zero-ceiling LAANC grid squares at the southeast edge of the airspace.  Note the presence of grid squares with a 400' ceiling between the new zero-ceiling grid squares and the airport.

PASI2 -- Sitka Rocky Gutierrez Airport -- Sitka, AK -- E2 Class-E-to-surface airspace
Old airspace description is on page E-9 in 7400.11E, new airspace description is on this page of the Federal Register.  Effective 11/05/20, the Class-E-to-surface circle was shifted about 150' to the southeast due to the change in the official location of the airport.  As a result, there is now a single anomalous zero-ceiling LAANC grid squares at the ESE edge of the airspace.  Note the presence of grid squares with a 400' ceiling between the new zero-ceiling grid squares and the airport.
Footnotes:

All LAANC screenshots taken on 2-1-21

As of 2-1-21 this link to an on-line portrayal of the aviation sectional chart covering PASI still showed the airspace as it was configured before a recent change that came into effect 11-5-20.  It appears that the 11/5/20 edition of the Juneau sectional chart has not yet actually been made available on-line (see non-working links for Juneau sectional on the FAA's "VFR Raster Charts" page.)  The new configuration of the airspace at PASI, which involves a (nearly circular) E2 Class-E-to-surface area and a single, very large, rectangular E4 Class-E-to-surface extension, may be seen by selecting the appropriate layers on the LAANC map display after entering "PASI" into the search window.  The airspace configuration at PASI therefore is now similar to the airspace configuration at KACV and KTLV, as described in the related ASE question What is the primary reason that the non-towered airports KACV and KTVL have E4 extensions to E2 airspace? .


Is a lapsed Advanced Ground Instructor certificate acceptable to use as proof of FOI when taking CFI initial? I have an AGI certificate that I haven't exercised the privileges of in the preceding 24 calendar months.

When I initially got the AGI, I had planned to take my CFI almost immediately but didn't. I'm having trouble locating the regulation that shows that since I have my AGI, I don't have to re-take the FOI written to complete my CFI.

What regulation states that this is possible?

That would be 61.183(e)(1):

To be eligible for a flight instructor certificate or rating a person
must:
(e) Pass a knowledge test on the areas listed in Sec. 61.185(a)(1) of
this part, unless the applicant:
(1) Holds a flight instructor certificate or ground instructor certificate issued under this part;


What helicopter has the most rotor blades? I have seen 2 rotor blades up to many and wonder when does having more rotor blades become less efficient? What helicopter has the most rotor blades?

Related: Why don't helicopters prefer shorter rotors with more blades?

What is the definining line between a helicopter and a drone a person can ride in?

Special mention for Raúl Pateras Pescara de Castelluccio (good article) who was fond of lots and lots of rotor blades, settling on sixteen for most of his designs, although his Model 3 had twenty.

Pescara's helicopters may look a little comical (and dangerous!) but they are an important part of early helicopter evolution, pioneers in the first fully controlled helicopter flights, as well as the first use of the what would be recognised as modern helicopter controls.

Here's a video of Pescara testing one of his helicopters in 1922 wearing a Homburg hat with about 5mm of clearance to his head. He had many setbacks, but persevered. It's visionary, brave guys like him who make advances in aviation.

Plus, loads of blades.

Here is his Model 3 from 1929:
(source1)


What's the difference between FMS and FMC? What's the difference between FMS (Flight management System), and FMC (Flight management computer)?

Can the flight management computer be thought of as what's manipulating the input information from the performance/navigation databases, and the FMS as being what actually provides the information?

I understand the information that's involved with the system, I'm just trying to define the difference based off an analogy of sorts.

(Own work)

The FMC is part of the FMS.

  The FMC is a computer system that uses a large data base to allow routes to be pre-programmed and fed into the system by means of a data loader.

The FMS encompasses:

  The Flight Management Computer (FMC)
  The Automatic Flight Control or Automatic Flight Guidance System (AFCS or AFGS)
  The Aircraft Navigation System
  An Electronic Flight Instrument System (EFIS) or equivalent electromechanical instrumentation.

Further reading: Flight Management System (SKYbrary)


Can anyone identify this biplane from 1920s-1930s? It was my grandfather's, but he is no longer around to ask. He lived in Nebraska.

It looks like a 1928 Swallow TP by Swallow Airplane Company.

(source)
(Swallow TP at Yanks Air Museum in Chino California.  Photo plus some information about the specific aircraft may also be seen on this website )

(source)


Is it possible to fly an ultralight aircraft with a 13.4kW engine? I want to build an ultralight within the 115kg preload (US standard). Can I use and engine with the specifications below? My weight is around 63kg.

Rated output: 13.4kW(18HP)@3600RPM

The earliest ultralights (hang gliders with add-on engines) used engines with as little as six horsepower (about 4 kW), possibly smaller.  That said, these aircraft were originally built as foot-launched gliders, and even so had safety issues and many incidents due to poor climb rates.

The main requirements for the engine in an ultralight are climb performance (which translates directly into takeoff acceleration) and reliability.  With the correct propeller and acceptable dry weight, an 18 hp (13.5 kW) engine might be acceptable, but every additional kilo of engine mass (compared to engines built for lightness) is one less kilo of structure, and the RPM figure given seems to point to a four-stroke engine, which will generally be heavy for its power output as compared to the two-stroke type.

Four-stroke engines have been used in larger aircraft for more than a century, but those are mostly engines designed and purpose-built for aircraft use.  An engine designed for garden or yard equipment, generator, or compressor service will usually be heavier.  You'll have more trouble finding an optimized propeller for 3600 rpm than for 5500, in that power range.

In the end, if that's a cast iron four-stroke engine, it's unlikely you'll make your overall dry mass budget to stay within US Part 103 requirements without compromising structure, and you're likely to see performance issues with minimal power and maximum takeoff weight.


Could the toilet be used as an extra passenger seat? In the US, if the toilet had a seat belt, would it be legal for an airline to board one more passenger than the number of normal passenger seats, requiring that whoever used the toilet last must remain there until the next person needs to use it?

Inspired by: "A new engine inlet reduces vibration and cabin noise, the lavatory receives a belted seat allowing a fifth passenger and the Garmin G3000 gets computed take-off distance and stability/angle of attack protection."  -- HondaJet Elite

Related Embraer Phenom 100

When I was with Weber Aircraft we provided many lavatories for Boeing aircraft.  There was never any requirement for a passenger in the lav during structural tests/qualification.  Based on this I know that it would be illegal for have someone in the lav during takeoff or landing as it would exceed the structural qual test requirements.


Could an electric engine provide the same performance as jet engines on current aircraft? I have looked at various questions on this SE site regarding this topic but I have not really found a satisfactory answer. Some comments here regarding torque and power in electric motors vs gasoline engines were helpful. Additional info also found here.

Underlying my question is the assumption that battery technology will considerably advance from what is available commercially now. Simply assume that providing the electric motor with enough power is not an issue and that the weight of the battery is equal to fuel.

Is it possible to build an electric aircraft engine that would allow current commercial airplanes the same capabilities as jet engines available today do?

Not yet.

To look at a medium-range aircraft, let's base the engine on the CFM56 or the IAE V2500. Those engines produce between 100 and 150 kN static thrust. In cruise, their thrust is considerably lower due to the low density in cruise altitude and due to them moving at Mach 0.8. Let's use a value of 25 kN - this is enough so that two of them will comfortably push an A320 class airframe through the thin air at altitude.

The power to produce such an amount of thrust is force times speed. The speed when flying with Mach 0.8 in 35.000 ft is 240 m/s, so the power produced by one engine is 6.0 MW. Now let's look up how big and heavy an electric motor has to be to produce 6 MW continuously. As you can see from the linked Wikipedia page, the results are all over the place. Big, industrial motors come in at less than 1 kW/kg, so our motor would weigh more than 6 tons. The smaller motors for electric airplanes are pushing 10 kW/kg, the power-to-weight ratio of the GE90 turbofan, but will lose some of that when scaled up to size. Remember, even at 98% efficiency the motor will generate 120 kW of heat - this needs to be removed, and operating in thin air doesn't make this easy.

With current technology the motor could achieve maybe 2 to 3 kW/kg - this means the motor driving our hypothetical engine comes in at 2 to 3 tons. Add to this the fan and the fairing of the jet engine (we will not need the high-pressure part and all the turbines), but double the fan weight because we need to compensate for the missing high-energy core flow. This will maybe weigh 50% of the CFM56 / V2500, so we need to add another 1.2 tons.

The electric motor will be twice as heavy as the parts it replaces. There is still some work to do before it can gain an advantage over current jet engines, but it has some potential because it does not dump half of the energy supplied to it overboard in a hot, fast-moving, noisy gas stream.

EDIT:

Since so many people get excited about me omitting the energy density aspect of electric propulsion, even though the question did expressly desire to leave this out, here are two things to consider. Energy density is only half of the problem of electric storage.

The energy density of jet fuel is around 43 MJ/kg, while Lithium polymer batteries achieve not even one MJ/kg. But this comparison is linear thinking - realistically, the current will be produced either by a high-efficiency turbine-generator combination, or by fuel cells, burning hydrogen at twice the efficiency of a conventional jet engine. Since hydrogen packs 142 MJ per kilogram, at twice the efficiency the electric airliner would need only 162 kg of hydrogen for every ton of kerosene in a conventional jet. Yes, I know, even then its volume will still be a problem.
If any form of batteries is used, the fact that empty batteries weigh as much as full ones is the final nail in the coffin of battery-powered flight. While your average long-range jet lands at 60% of its take-off weight, the battery-powered jet would need to schlepp those heavy batteries all the way to the final destination. To be competitive, those hypothetical batteries would need to have twice the energy density of kerosene.


Has turbulence ever killed a passenger? The question is on my mind, because many passengers think there is no need to wear the seatbelt when the seatbelt sign is not illuminated.

The following is a list of deadly turbulence accidents on jet airliners since 1980.
Excluded are accidents involving jet airliners designed or built in the former Soviet Union.
For a more complete list see aviation-safety.net.

10 May 1980, Indian Airlines B737-200, near Rampur Hat/India:
The aircraft experienced severe en route turbulence. 2 of the 132 passengers were killed.
7 October 1981, NLM CityHopper F28-4000, Moerdijk/Netherlands:
Shortly after takeoff, the aircraft entered an area of severe thunderstorm activity. The aircraft apparently had a catastrophic in flight structural failure due to severe turbulence because it was seen to emerge from the clouds with one of its wings broken away. All 4 crew members and 13 passengers were killed.
16 August 1982, China Airlines B747, near Hong Kong:
The aircraft encountered severe in flight turbulence. 2 (out of 292) passengers not wearing seatbelts were killed.
3 October 1990, Eastern Air Lines Flight 791, DC9-31, Florida/USA:
The aircraft clear air turbulence at 31,000 feet (9450 m). 1 injured passenger died 3 weeks later.
5 September 1996, Air France B747-400, near Ouagadougou/Burkina Faso:
Severe turbulence associated with a weather front seriously injured 3 of the 206 passengers. 1 of the 3 passengers later died of injuries caused by an in flight entertainment screen.
28 December 1997, United Airlines Flight 826, B747-100, over Pacific Ocean near Japan:
The aircraft encountered severe turbulence during cruise about 2 hours after departing Japan. 1 of the 346 passengers was killed and 3 crew members sustained serious injuries.


Why couldn't the A380 secure any orders for two straight years? The double-decker aircraft has failed to win a single order from any new airline customer for two years now. Comparing its orders and sales with its biggest competitor, the B747 it had received 315 orders in its first 10 years, about 40 years back. Today though, the A380 has recieved 317 in its first 8 years, but it failed to receive even a single order in past two years.

  “It’s true the market hasn’t developed as much as we’d have liked,” Airbus Chief Executive Officer Fabrice Bregier said this month. “This plane was probably launched 10 years too early.” (Source)

Why couldn't the A380 sell as much as the B747, even though it has won many admirers in a shorter period of time. Also, a rough comparison shows A380 is worth its price, when compared to 747-8. But the 747-8 is still getting more orders than the A380.

Update : Iran Air has finally ordered some A380s in February 2016.

Several reasons:

A380s are really expensive. Unit cost for an A380, depending on interior appointments, is about \$375 million. The 747-8 is about \$357 million. The 777-300ER is about \$320 million, the last variants of the A340 about \$275 million, and the 787 about \$200 million. The 380 might be the biggest airliner ever to fly, but it's also the most expensive. Keep in mind these jets can't fly every day, requiring you to buy a couple more than the schedule requires and rotate them in as maintenance is required on each airframe. That means A380 operators have at least one three hundred and eighty million dollar airframe sitting on the tarmac not making money on any given day (in fact, up to 55 days at a time for the 6-year "D check" maintenance, not counting lower-level maintenance performed more often as well as any unscheduled maintenance).
Airbus could not/cannot build them fast enough to meet initial orders in a timely manner. Airbus received 189 initial A380 orders prior to the airframe's scheduled start of production in 2007, plus 27 A380F variant orders, and has received 128 since production began (though the freighter orders were cancelled). To date, it's only delivered about half due to a combination of issues found during full-scale production that delayed ramp-up, and currently its pace is about 30 planes a year, giving it about a 3 year backlog of remaining orders (some of which have been sitting in the build queue for 10 years). It initially prioritized passenger variants for Emirates, which put in the largest single order (almost half of total orders) to handle that airline's primarily long-haul schedule. As a result, everyone else got pushed off until many (including FedEx and UPS which were waiting for freight versions) cancelled their orders and went to Boeing for 747-8Fs or 777-ERFs.
Jumbos represent a serious cost-revenue risk that most airlines are no longer willing to gamble on. You use a jumbo jet when you need to move a lot of people at one time. That typically means a high-demand, long-distance route that calls for nonstop service, but that you don't want to have to fly any more times than you have to. 747s used to be used for high-volume domestic connectors in the US during and immediately after the regulation era, between major cities like New York, Chicago, LA, Houston, Miami etc. They were also used for major intercontinental flights, primarily because regulations required more than two engines for trips extending a certain distance beyond the nearest divert field. However, the 747 is a 50-year-old design with only incremental improvements made in efficiency. Four engine jets in the modern air transport market require you to fill the plane every time, and with ETOPS-rated two-engine widebodies now making many of the same flights that previously required three or more engines, the A380, even with the most efficient engines ever put on a commercial airliner, is at least three decades late to the jumbo party, and is entering the market at a time when the 747 is being phased out of most fleets in favor of more economical widebodies.
The A380 was designed for an air travel market that hasn't materialized. Airbus was betting big (NPI) on airport congestion and increased passenger counts during the 80s and 90s requiring a shift to fewer flights on larger-capacity planes to reduce pattern and gate congestion. Except for a few major metropolitan areas that simply cannot grow their airports anymore (O'Hare, LaGuardia/JFK, Heathrow etc) that hasn't really been the case. 9/11 and the 2008 financial crisis have seen passenger counts plummet from post-regulation highs, which has reduced total flights and allowed smaller planes which are more efficiently scheduled. In addition, Denver opened up the largest airport by land area in the world (so it has plenty of room to grow), while Atlanta, Dallas, Charles de Galle and others are busy primarily because they're massive complexes with efficient layouts that can support a major airline's hub operations. The use of jumbos in general is therefore very risky, and many airlines, in addition to passing on the A380, are phasing out the venerable 747 that was previously unchallenged in this class, in favor of something a little more economical in the next smaller widebody class, like the 777, 787, A340 or A350. That was Boeing's bet, that smaller, high-efficiency jets would be the wave of the future over pure size, and it seems to be paying off as Boeing, despite higher production capacities, has more 787 orders than it has capacity for the foreseeable future, while Airbus's competing A350 is more or less getting the overflow (and it can't even meet that demand; 700 orders, 5 produced).
The A380 really doesn't solve the problem it was created for, and in fact causes more problems for airports than it solves. A super-heavy like the A380 creates monumental wake turbulence that poses a danger to other planes, which requires ATC to space following traffic further back (up to double the time/distance compared to a midbody), while for smaller jets (even widebodies), approach control can usually get away with a little more than standard 2-minute spacing unless the plane behind it is a much smaller regional jet or GA prop. So, the A380 can carry about 520 passengers in mixed-class configuration (Emirates' 6-star config seating only about 490), but takes up two "slots" in the approach pattern, while a 777 can carry 320 passengers in mixed-class layout and can be spaced much more closely to other airliners. So in terms of maximizing total passenger movement at an airport, two 777s or A340s are better than one A380.

At the gate, the A380 causes even more headaches. It's so honkin' big that adjacent gates typically can't be used while it's parked, and it often requires additional jetways to efficiently board and deplane its passengers. As one example, DFW's Terminal D was fairly recently renovated to be the airport's primary international terminal, including Gate 16 in the southwest corner specifically intended to allow 747s to park with minimal adjacent gate disruption (17 couldn't be used, but 18 was available for smaller jets and 15 around the corner could handle pretty much any size):

When the A380 came to DFW in 2014, with Qantas replacing the 747 on the famous Flight 7 and Flight 8 from Sydney to DFW (the longest scheduled passenger flights by travel time in the world), and Emirates commencing service to and from Dubai with A380s, DFW had to redesign this corner of the airport entirely, basically having the A380 come in diagonally to Gate 15. Gate 15 then services first class, 16's jetway was moved and extended to load and unload the lower deck, and a third jetway, 16X, was built adjacent to 16 solely for the A380's upper deck. The jetways for Gates 14 and 17 then had to be lengthened considerably to allow their use with a 380 at the ramp, otherwise the superjumbo would essentially take up 4 entire gates while parked:

As an aside for scale in the last image, Gate 14 to the right is in Sun Country livery which would make it a 737-700, while the American jet at the very top at Gate 19 is still in older livery, and with its long narrow body the best guess is a 757-200. Gate 17 looks like an Air Canada Rouge so with the body length I'd say A319, and Gate 18 is in new American livery so it's a 737-700. None of them really big aircraft by today's commercial standards, but they're certainly not puddle-jumpers either (all aircraft at this terminal are for international flights), and the Emirates A380 at gates 15/16/16X absolutely eclipses them all. It is a big jet.


Is the capacity of an airspace sector related to the number of routes it crosses? I've been searching for data about the capacity of sectors for my PhD research but somehow can't find any...the only thing I found is the routes it crosses ....can we conclude that it's the capacity or there is another factors involved. I would appreciate any help

Calculating the capacity of an ATC sector is a complex issue, you should not expect to find one single determining factor.

A few obvious factors come to mind:

Lateral extend of the sector (size)
Vertical extend of the sector
Whether or not surveillance is available (RADAR etc.)
The route structure, and whether traffic is forced to follow certain airways or not (free route airspace)
Military areas, their activation frequency and extend
Type of traffic in the sector
Uniformity of traffic in the sector
The actual traffic flow in the sector. Is it mainly an en-route sector where aircraft will enter and leave at the same level, or do a lot of aircraft need to climb/descend within the sector?
ATC staffing. Is the sector manned by a single controller, or by a pair (executive+planner)?
Radio coverage, and whether or not CPDLC is available
Weather - for example, is it an area with frequent thunderstorms?
Runway configurations of any airports covered by the sector, as well as possible noise restrictions

There is no formula that couples all these factors together. In the end, the capacity of an ATC sector is an estimate based on an evaluation of the above (and probably more) factors, experience and trial-and-error. In many cases, it will be an iterative process.


What is the measurement system used in the aviation industry? I saw this question from History Stack Exchange and noted that the US is still using the imperial measurement system such as feet, miles and pounds.

Given that a plane may need to fly from one country to another, is there any standardisation across the globe? Does planes manufactured by Boeing use one system and planes made by the Airbus another system? If not, wouldn't it be very easy for pilots to make calculation error?

Outside US, SI is generally used for everything except altitude, distance and speed.

Altitude: 1000 ft happens to be reasonable vertical separation, which is somewhat easier to calculate with than the corresponding metric figure 300 m.
Distance: There are two quantities that were never converted to decimal. Time and angle. Since we didn't switch to gradians, it makes sense to keep nautical mile, which corresponds to 1 minute along meridian or equator, as it makes calculating distances from navigational maps somewhat easier. If the maps were marked in gradian coordinates, 1 gradian would be 100 km and kilometres would be used.
Speed: Obviously based on the unit of distance in use.

In Russia, Commonwealth of Independent States (most former Soviet countries) and China (and I am not sure whether some other Asian countries), metric system is used for everything. I believe in Russia they recently switched to flight levels based on feet, but they do use metres below transition altitude.

Before second world war, aircraft built in continental Europe usually had instruments in metric units as well. However before the war aviation was more advanced in the USA, instrument procedures were developed in USA and after the war there was surplus of US-built planes, so most of the world just adopted the US procedures including the units they used as everybody using the same units was more important than any personal preferences. Without these reasons we'd be probably using metric in Europe for everything too.


Can the wing stagnation point be bled off and used for laminar flow control? The stagnation point at the leading edge contains slow-moving, slightly compressed air. This sounds ideal for laminar flow control. This slow air will create little losses in ducts, and it's pressure allows it to be blown out of slots to reenergize the boundary layer, while at the same time removing contamination - a MAJOR issue for laminar flow today. Is this true?

No.

Slow-moving also means low mass flow. In order to re-energize the boundary layer, the air has to move fast, meaning high mass flow. Also, speed means reduced pressure, so the stagnation pressure is not sufficient to produce that desired high-energy flow.

Also, contamination (bugs, ice) accretes close to the stagnation point. Ideally, in order to remove contamination, blowing would have to happen across the stagnation point. For that, blowing pressure needs to be higher than stagnation pressure.

The only use of stagnation pressure for boundary layer control is for tripping by blowing perpendicularly to the surface into the boundary layer. This works with low mass flows already.


Why are there no 4-winged airplanes? With larger wings comes more drag. So why don't large planes have 4 smaller wings instead of 2 very long ones?

With larger wings comes more drag. True, because the drag is a function of the wing area A:
$$ D = C_D \cdot \frac {1}{2} \rho \cdot V^2 \cdot A $$
You need a certain wing area to support the weight of the aircraft. Now the question is: over how many wings will we distribute this wing area? For over 80 years, the answer has been: one wing (the two wing halves make up one wing).
The classical biplane is a thing of the past, however there have been incredibly clever aircraft builders who have looked at the long coupled canard configuration. This one really makes a lot of sense:
 Image source
So to answer your question: there are aircraft with two wings. It's just that people don't buy them, and go for boring old Cessna's instead.


Where does the altimeter measure from? During the landing flare, the cockpit can sometimes be twenty/thirty feet or more above the rear landing gear, especially with larger aircraft.

(source: valkaviation.com)

In some aircraft, you can hear the system call out altitude when on final, ie "500... 200... 100... 50... etc".

Where does the altimeter measure altitude from? Does it measure from the bottom of the rear landing gear, or from the cockpit itself? How do pilots know when the rear landing gear will touch down?

There are a few types of altimeters but they all generally do the same thing and can be calibrated to anything if need be. Where they measure from and what they consider 0 are really 2 different questions.

A pressure altimeter reads from the pito-static port (many planes have more than one of these for redundancy) and they are generally located forward on the air frame and often on the side somewhere.

((737 static port) source)

Radar Altimeters will most likely mount to the bottom of the aircraft (since that is the way the radio beam needs to go).

(source)

According to this discussion radar altimeters are on the belly and 0ft is calibrated to mains on the ground, after that altitudes will be read out in negative values.

And from here

  The callouts (50, 40,30,20,10 feet, etc) is the function of two radio
  altimeters which provide the height of the main landing gear above the
  runway.


Why do I not always hear ATC read back by pilots (on required instructions)? I enjoy tracking air traffic at my local KORD.  I listen on LiveATC and use my private virtual radar setup to get "real-time" traffic info.

I understand which instructions need to be read back by the pilots per this question however on more than one occasion I don't hear read back on critical vector info on departure, despite the visual confirmation of instruction (pilot making proper vector and speed adjustments).

I tend to notice this with bigger birds (777,747,340), however smaller regional jets almost always promptly read back.

Questions:

Is there an alternative way of ATC instruction acknowledgement? (Other than read back?)
Is it possible that the reply is somehow on a different frequency?
Is this just a problem with LiveATC? (One theory is that A/C leaves receiver coverage area and that's why I don't hear reply, however on approach side much bigger distances are heard in my area)

Thank you

I did verify that indeed the aircraft that I don't hear read back from receives special departure frequency by tower.

Once tower clears aircraft for take off and hands them off to departure controller they use "departure" frequency to read back instructions.  It is typically different from standard departure frequency.

The only thing that is not clear is if there is any rhyme or reason for which aircraft gets this special departure frequency and which doesn't.

As pointed out in the question for some reason mostly it is "big" aircraft that gets this preferential treatment, but I am not 100% sure why.

The O'Hare Eight Departure is the only departure procedure out of ORD.  This is what it looks like:

Notice that there are three departure control frequencies:

Chicago Dep Con West: 125.4
Chicago Dep Con East/North: 125.0
Chicago Dep Con South: 126.635

Airplanes are usually given the frequency appropriate for the sector that their first departure fix is located in.  If they are very busy, each sector will have its own departure controller and they will be talking to different people.  If it isn't as busy, they pilots will still be talking on their individual frequencies, but one controller may be listening to and transmitting on two or all three frequencies at once.

For instance, if a particular aircraft is cleared over POLO VOR (due west of ORD) they will be given a departure frequency of 125.4 as part of their clearance.  Let's say that the traffic is slow and only one controller is being used to cover all three frequencies.  If you are listening to the East/North frequency on 125.0, you will hear the departure controller issue a clearance to the aircraft, but never hear the response because the aircraft is transmitting on 125.4.


How does a horizontal situation indicator (HSI) work? I am trying to understand the Horizontal Situation Indicator. To my understanding there is a slaving transmitter, usually in a wing (the left wing in the Piper Archer and Seminole), which sends information to a flux gate, which then sends information to the compass card in a slaved HSI. Is any of that correct? Are the slaving transmitter and the flux gate separate components?

Your understanding is partly right. Usually HSI indicators are associated with a slaving transmitter that includes the flux gate (the magnetic sensor), but also other elements such the directional gyro unit and a slaving control.

So a typical system will usually include the below components (there are different designs, so check the characteristics of the equipment in your aircraft):

The Horizontal Situation Indicator (HSI) is the panel mounted cockpit indicator that provides a comprehensive display including usually at least heading, course, and glide scope. The heading indicator of the HSI is a remote indicating compass that gets its information from a remote slaving transmitter.
The magnetic slaving transmitter includes the flux gate that is the magnetic sensor itself, and some electronics to send the heading information to the directional gyro and HSI. This transmitter and its associated flux gate is usually located in a wingtip to minimize as much as possible magnetic interference.
a directional gyro unit that is usually remote mounted. It is using its internal gyroscope to keep and provide a stable heading reference during turns. This gyro unit is driven/slaved to the slaving transmitter.
The slaving control is panel mounted and allows to selected either "slaved gyro" or "free gyro" mode. Usually, the system is in "slaved gyro" mode and will be slaved automatically. In "free gyro" mode, a slaving meter indicator displays the difference between indicator display and earth's magnetic field, and it is possible to align manually the switch using clockwise or counterclockwise buttons.

The manual of the Bendix-King KCS 55A provides a good introduction to HSI design and operation.


Does using a reverse high Cm horizontal tail airfoil coupled with a low Cm wing increase horizontal tail effectiveness? Does using a high Cm reverse horizontal tail airfoil coupled with a low Cm wing increase horizontal tail effectiveness?

Just noticed that the Zenith 701 wing uses a NACA650-18 which is low $C_m$, while their inverted horizontal stabilizer uses a NACA4412 foil which is a high $C_m$ foil. They could just as easily have used a low cm NACA0018 or NACA2415 foil with a slotted elevator to get the same $C_L$, but they chose a high $C_m$ foil instead

I'm assuming using a low $C_m$ wing and a high $C_m$ horizontal tail adds to the effective moment produced by the area of the horizontal tail, allowing for a smaller horizontal tail area.

Is this correct?

They could just as easily used a low Cm NACA0018 or NACA2415 foil with a slotted elevator to get the same CL, but they chose a high Cm foil instead.

For an elevator, we want to maximize the lift coefficient at the maximum effective control deflection, while maintaining a high degree of linearity with respect to the deflection. There is a maximum effective deflection because any higher control deflection will no longer increase the lift.

A well-designed slotted elevator is theoretically supposed to help with that. But the size of the slot, and any spoiling elements along the hinge would need to be carefully tested in the wind tunnel. Otherwise, they may end up reducing your maximum effective deflection instead. The mechanism required to achieve a good slot may also be complicated for an elevator (slotted flaps don't move like an elevator).

  I'm assuming using a low Cm wing and a high Cm horizontal tail adds to the effective moment produced by the area of the horizontal tail, allowing for a smaller horizontal tail area.

That's a good question. I did some quick math using a variation of usual airplane parameters, and here's the summary of the results:

The static margin is unaffected by the camber. For NACA4412, there may even be a forward shift in AC (for the same tail planform), so there may be a slight reduction in static margin.
Having a negatively cambered tail offloads the tail lift, exacting a small saving in trim drag (a few counts at cruise CL of 0.4). Since it offloads the tail, it may also be beneficial to preventing tail stall, but the effect is fairly small.
A negatively cambered tail also produces negative zero-incidence lift. The amount of negative lift can be tailored depending on the overall configuration (CG range, flaps, thrust lines) to minimize form drag.

We can derive the following trimmed lift and pitching moment equations assuming a cambered tail and zero thrust:

(1) $C_{L}=C_{L_{wb_0}}+a\alpha+\frac{S_t}{S}[C_{L_{t_0}}+a_t(i_t-\epsilon_0)]$

(2) $C_m=C_{m_{ac_{wb}}}+C_{m_\alpha}\alpha-V_H[C_{L_{t_0}}+a_t(i_t-\epsilon_0)]+(h-h_{ac_{wb}})C_{L_{wb_0}}+\frac{S_t}{S}C_{m_{ac_t}}=0$

where,

$C_{m_\alpha}=a(h-h_{ac_{wb}})-a_t\overline{V_H}(1-\frac{\partial \epsilon}{\partial \alpha})$
$a=a_{wb}+a_t\frac{S_t}{S}(1-\frac{\partial \epsilon}{\partial \alpha})$
$a_t$ is the lift slope of the tail, $a_{wb}$ is the lift slope of the wingbody, $\overline{V_H}$ is the tail volume from the wingbody AC, $V_H$ is the tail volume from the CG, $\epsilon$ is the downwash on the tail


What were/are the military designations of the JT8D and PW4000? Turbine engines on U.S. military aircraft, in addition to their manufacturer-given names, receive separate designations (consisting of J [for turbojets], F [for turbofans; formerly TF], or T [for turboprops], followed by a number) for internal military use (examples: JT3C/J57, JT4A/J75, JT3D/TF33, JT8A/J52, JT9D/F105, PW2000/F117, JT12A/J60, CJ805-3/J79, CJ610/J85, CF700/TF37, CF34/TF34, CFM56/F108, CF6/F103), even if the military engine is completely unchanged from the civilian version known universally by the manufacturer-given name.
For most engines, information on their various names is readily available; however, I have been unable to find the military designations of two Pratt & Whitney turbofans currently-or-formerly-used on U.S. military aircraft (the JT8D low-bypass turbofan, used on the T-43, C-9, and YC-15, and the PW4000 high-bypass turbofan, used on the KC-46).  Does anyone here know the answers to this puzzle?

Two versions of license built military JT8D is called RM-8A and RM-8B.
PW4062 is a military version of PW4000 used in Boeing KC-46 Pegasus.


What are these acceleration parameters produced by the Inertial Reference System? Following acceleration parameters are transmitted from Inertial Reference System (IRS) to Flight Control System (FCS):

Flight Path Acceleration
Along Track Acceleration
Cross Track Acceleration
Vertical Acceleration
Unbiased Normal Acceleration
Along Heading Acceleration
Cross Heading Acceleration

I only know acceleration based on the aircraft axis i.e lateral, longitudinal & Normal acceleration but what these acceleration parameters signifies?

I can't be sure without seeing actual documentation of the thing, but I would expect:

Flight path is direction of the total velocity vector, i.e. the direction the plane is flying, in Earth-relative frame of reference. This differs from direction of longitudinal axis by alpha (angle-of-attack), beta (side-slip) and wind.
Track is projection of flight path to horizontal plane.
Heading is projection of the longitudinal axis to horizontal plane.

Then:

flight path acceleration would be simply acceleration along the flight path
along track and across track are, well, along and across track as defined above.
vertical is vertical; should not include gravity, so when maintaining vertical speed it should be 0.
unbiased normal acceleration is most probably what is also called inertial normal acceleration, that is acceleration without gravity.
along and across heading are, well, along and across heading as defined above.


Can a CFM56-3C engine be converted into a CFM56-3B1? Is it possible to take a CFM56-3C engine and modify it to a CFM56-3B1 engine? I own a CFM56-3C engine but my customer would like to install a CFM56-3B1 engine on his plane. Can this be done?

In theory, I think that should be possible, as the -3B is a lower thrust rating than the -3C (going to higher thrust rating would be harder).  However, you would have to ask CFM.  I think they are the only ones that could answer.


How do you hold at a non-towered airport? Let's say, hypothetically, that you enter the pattern for a small, non-towered airport (my local one, 3DW, may be a good example.)  But as you get into the pattern you find out that the runway is occupied by another craft and, for whatever reason the runway will probably be occupied for another 20 minutes, much longer than it will take you to complete the pattern.  So you'll have to delay landing.

But you've already entered the pattern, so what should you do?  Is there a standard holding pattern for small airports that incorporates parts of the pattern (maybe some little loop where the base leg and downwind meet)?  Or do you just fly away form the airport a bit and make up your own holding pattern?

There's no "standard holding pattern" at any airport, towered or not. If the runway is occupied or temporarily closed for some reason, you might was well leave the traffic pattern and go putt around for a while someplace where there are fewer aircraft. At a towered airport, the controller will likely tell you what to do - but again, you can make both his life and yours easier by just leaving the pattern and going somewhere else until the situation is resolved.


Who was the US military pilot who crashed his plane and was accused of selling it to the Russians? There was recently news regarding a story of a former US military pilot who crash landed his plane somewhere in the southwest. He was accused of flying the airplane to Mexico to deliver it to the Russians. The Russians then supposedly dropped him off in the desert from which he walked back to civilization. I believe this was Post WWII & Korea. The pilot lived with the accusation his entire life despite claiming his innocence despite the plane never being found.

The wreckage was just recently found, vindicating the pilot although he had passed away some years ago.

Any help would be appreciated. My google searches came up with many defection stories and red herrings.  I know the story is recent. I just can't find it.

According to the relevant Wikipedia page Lt. David Steeves of the USAF bailed out of a T-33 trainer in 1957 near King's Canyon National Park in California and was not found until 52 days later.  When the crash site could not be located Steeves became the subject of various rumors, despite the T-33 being a relatively unimpressive trainer aircraft.

Steeves left the air force after the incident and reportedly conducted some of his own searches on the ground and in the air before being killed in an unrelated crash in Idaho in 1965.

A canopy located in the park in 1977 was as identified as being from this aircraft in 1978 but the remainder has not been found.  While no developments appear to have taken place in the story since then, it has occasionally been the subject of articles over the years.


What is the definining line between a helicopter and a drone a person can ride in? When I say drone in this context I don't mean an unmanned aircraft. I'm not sure what the terminology of a drone that has been adapted to carry a person? Is this picture below considered a helicopter or what? What if it ran on petroleum?

If not, then how is the separation between a VTOL aircraft and helicopter defined?

Would a Chinook that can fly itself be a drone?

A helicopter is an aircraft in which thrust and lift are provided by rotors.

A drone is an unmanned, self-piloted or remotely-controlled aircraft, which can use rotors to provide thrust and lift, but can also use other means such as propellers or turbines.

To put it in simpler terms, a helicopter can only be a helicopter, regardless of whether it has a human inside or not. A drone can be any kind of aircraft.