Can passenger airliners hover completely motionless in the air? I've seen many stories of this occuring on r/glitch_in_the_matrix (a popular Reddit). People have been seeing big airliners just paused in the air, not moving. Some of them stopped their car and saw that the planes still weren't moving. I thought an airplane would stall if it went too slowly? I'm not a plane expert but can newer passenger planes hover in the air?

Edit - often times, the planes are not high up, but coming in to land or take off. Someone said they were watching planes take off or land, and suddenly a big jet just paused in mid air for 30 seconds before starting to move again.

In theory they can stop moving relative to someone standing on the ground. In practice this does not occur.

Aircraft fly through the air and, yes, below a certain airspeed, an aircraft will stall. Let's take a super-simple example to explain the situation:

You are standing on the ground on a very breezy day. It's quite windy on the ground, and blowing even harder at altitude. For the sake of this example, let's say at 15,000 ft. There is a 150Kts wind from the west. A small airliner is slated to go west at 15,000 ft and levels off but slows down to a cruise speed of 150Kts. The airplane is still moving through the air at 150 Kts, but the air is moving in the opposite direction at the same speed. In terms of a fixed point on the ground the airplane does not move.

However, big jets are capable of flying faster than even the biggest practical headwinds. You can, however, observe this in small aircraft on a gusty day (I have flown a PA-28 backwards in this scenario). Here is a video of someone doing it in a slow plane.

What is likely occurring is that a plane that is very high up and very far away appears not to be moving due to its small size in the sky and lack of surrounding points of reference.


What is this aircraft? 32°09'16.6"N 110°50'36.4"W, co-ordinates of the aircraft at Davis-Monthan Air Force base.

Source: Google Maps

Those are Learjet 35's. In USAF service, they're called C-21's.

Source


What is the difference between Flight Test and Test Flight? What is the difference between Test Flight and Flight Test?
Are they the same thing or synonymous?

Flight testing is the process (usually involving a number of test flights) by which the capabilities and performance of and aircraft (usually a new one or one which is substantially modified) are established.

Test flight refers to an individual flight which is used for testing purpose. it can be used either as part of flight testing or as a standalone for testing some minor modification.


Does Part 135 duty time begin at the start of a part 91 owner flight which occurred immediately before? You are asked to fly a 91 owner trip to a destination. A 135 trip comes up after your owner flight.

Does your 135 duty time start when company asked you to fly the 91 owner flight?

Absolutely, 135.267 (d) requires you to have 10 hours of rest within the 24 hour period preceding the completion of every 135 flight, and if the 91 flight is for the same company then it is not considered rest. Duty time starts when you are required to do anything for the company, and for a typical flight it starts when you arrive at the airport.

For more information on rest, see this question and answer.


What is the difference between a volume-limited-payload and a maximum-zero-fuel-weight-limited-payload? Reading [Long Range Aircraft-AEA Requirements].

In appendix, Para 1.2 Definitions and specifications, the definition for "Payload" states

  Payload should be the Volume Limited Payload (...) or the Maximum Zero Fuel Weight limited payload, whichever is the lesser.

How can we can define and understand "Maximum Zero Fuel Weight limited payload"?

The Maximum Zero Fuel Weight Payload, is the amount of payload $m_{pl}$ (i.e.: passengers, cargo, but not fuel) required to reach the  Maximum Zero Fuel Weight condition while keeping the fuel weight, $m_{fuel}$ to zeros so:

$$
while \; m_{fuel} =0: \\
MZFW = OEW + m_{pl} \\
$$

The Maximum Zero Fuel Weight ($MZFW$) is an indicator of the maximum loads that the wing structure can bear. For the wing an "unloaded" situation (no fuel in the wing) is critical, since the fuel stored in the wing helps reducing the loads on it in flight. The lift acts "upward" while fuel weight acts "downward", thus the fuel contribution helps relieving loads from the wing structure.

The volume limited payload is an indicator for the sizing of the cargo compartment structures. These are the structures of the cargo area, where the LD containers are stored (under the floor of the passenger cabin). This Volume Limited Payload is set to avoid having too "dense" LD containers, the limit of density for the containers is around 350 $kg/m^3$, you can find some technical specifications for LD container here.


What operation is this aircraft performing? While reading Wikipedia about Ust-Kut Airport, I've run into the following picture:

I'd like to know which operation is depicted here?
This doesn't seems to be a take-off, as per my very limited knowledge. It is by far landing. If I am correct then how it is possible that a landing plane, at this altitude, still doesn't have its gear down?

The flight in question is most probably an evaluation/calibration flight for radio navigation systems at Ust-Kut. The aircraft is a Yak-40 special version designated for such tasks:
Aviamuseum - Yak-40 "Calibrator"


What are the key differences between controlled and uncontrolled airspace under the FAA jurisdiction? The FAA utilizes the ICAO definitions for class A-E airspace as controlled and class G as uncontrolled (class F airspace is unused under the FAA). What are the key differences between controlled and uncontrolled airspace in general?

This Document covers all the regs pretty well. But in short the key point on class G (uncontrolled) is

  Although ATC has no authority
  or responsibility to control air traffic, pilots should remember
  there are visual flight rules (VFR) minimums which apply
  to Class G airspace.

Class G airspace also holds no specific entry requirements (aside from VFR minimums), no specific aircraft equipment (no radio, no transponder etc) and no minimum pilot certificate requirement (but you still need a license (one of a few varieties) you just don't need anything in addition like the instrument rating requirements for class A). On the contrary glass G airspace (uncontrolled) is not a free for all and you are not free to do as you please in some regards. While ATC has no reach into Class G the FAA does and you are still bound by the regulations the FAA puts forth that apply to class G airspace.

Likewise the definition they provide for controlled is

  Controlled airspace is a generic term that covers the
  different classifications of airspace and defined dimensions
  within which air traffic control (ATC) service is provided
  in accordance with the airspace classification.

If you are wondering what the specific purpose of ATC is they define that as well,

  The primary purpose of the ATC system is to prevent a
  collision between aircraft operating in the system and to
  organize and expedite the flow of traffic.


Can drones/UAVs fly over international waters without being subject to the FAA's regulations? Can UAVs or drones (consumer/commercial scale) operate over international waters (12 miles out from the shore) without being regulated by the FAA?

Just wondering if companies can do things like BVLOS* testing out in international waters if they wanted to, instead of getting exemptions or leasing private airspace.

And, this is meant to be living and residing in the US, and operating outside of US' waters.

* Beyond Visual Line Of Sight

Short answer: the FAA's UAV regulations probably stop applying at 3 nautical miles, but this is more about maritime law than aviation regulations and you might get a better answer on law.SE.

The FAA's UAV regulations do state where they apply. 14 CFR 107.1(a) (emphasis mine):

  Except as provided in paragraph (b) of this section, this part applies
  to the registration, airman certification, and operation of civil
  small unmanned aircraft systems within the United States

14 CFR 1.1:

  United States, in a geographical sense, means (1) the States, the District of Columbia, Puerto Rico, and the possessions, including the
  territorial waters, and (2) the airspace of those areas

Defining different types of marine jurisdiction is apparently so complicated that it requires a diagram (33 CFR 2.1), and the definition of "territorial sea" is in 33 CFR 2.22. Unfortunately, there are two possible definitions: 12 nautical miles or 3 nautical miles from shore. My reading of it is that for treaties, criminal law and other 'big stuff', the waters extend 12 miles. For more general purposes, it's 3 miles per 2.22(a)(2):

  Unless otherwise specified in paragraph (a)(1) of this section,
  territorial sea means the waters, 3 nautical miles wide, adjacent to
  the coast of the United States and seaward of the territorial sea
  baseline.

Having said all that, I don't know for sure what the definition of "US territorial waters" really is. The 3NM distance seems very likely (to me) for part 107, and you might get a better answer on law.SE.


Why is the MiG-23 landing gear nontraditional? The MiG-23 has a very nontraditional landing gear setup. Why has it been designed the way it has as opposed to the more traditional method of a single compression strut that is raised into the fuselage.

(Source)

This configuration for the main landing gear was necessitated by the fact that the MiG-23/27's narrow fuselage combined with limited internal real estate in that section of the airframe made that type of retraction mechanism the best compromise in terms of fit, weight and providing a wide wheel track for the aircraft to facilitate operations on rough or unpaved airstrips (typical Soviet utilitarian philosophy for going to war).

An angled MLG strut which retracted forward such as that found on the F-104 or F-16 airplanes was not possible due to the side fuel tanks just aft of the engine inlets.

Aircraft which have narrow fuselages and high mounted wings are always going to require a more unorthodox retraction configuration for the main landing gear due to space limitations.  Other examples of this include the Dassault Mirage F1, Su-24 Fencer, and SEPECAT Jaguar.

This placement of the MLG and in this retraction configuration was the best available for the design limits.


(Ref AC 61-65H solo endorsements 61.87(n) and 61.87(p)). When should I give 61.87(n) vs 61.87(p)? At first, it seems clear (according to AC 61-65H) that 61.87(n) is for the first 90 calendar-day period and 61.87(p) is for each additional 90 calendar-day period. However, when I look up the actual regs, it says: "(n) Limitations on student pilots..." and "(p) Limitations on flight instructors..."
So, now it seems like (n) should be the only 90 day endorsement. (p) are just the rules the flight instructor has to follow (every time). So don't (n) and (p) always go together? And, is this idea that we start with (n) and then use (p) if 90 days go by...incorrect? Dare I say, should there be an AC 61-65I that corrects this? And, what should the endorsement say?
I see the NAFI guide sets up the question the same way the FAA does (initial vs additional 90 days), but they just use (n) for both of them.

Remember the ACs are guides, not laws, as opposed to the FARs.
14 CFR §61.87(n) reads:

Limitations on student pilots operating an aircraft in solo flight. A student pilot may not operate an aircraft in solo flight unless that student pilot has received an endorsement in the student’s logbook for the specific make and model aircraft to be flown by an authorized instructor who gave the training within the 90 days preceding the date of the flight.

14 CFR §61.87(p) reads:

Limitations on flight instructors authorizing solo flight. No instructor may authorize a student pilot to perform a solo flight unless that instructor has—
(1) Given that student pilot training in the make and model of aircraft or a similar make and model of aircraft in which the solo flight is to be flown;
(2) Determined the student pilot is proficient in the maneuvers and procedures prescribed in this section;
(3) Determined the student pilot is proficient in the make and model of aircraft to be flown; and
(4) Endorsed the student pilot’s logbook for the specific make and model aircraft to be flown, and that endorsement remains current for solo flight privileges, provided an authorized instructor updates the student’s logbook every 90 days thereafter.

The upshot of which is that (n) is, technically the only requirement for the student to possess for initial authorization for solo flight by a student pilot. (p) is also applicable to the endorsement that must be met by the instructor for initial endorsement, but must be met for additional 90 day solo endorsements by the student.
Here’s the thing, as there is no legal requirement for exactly HOW TO PHRASE an endorsement; they can technically be written by a CFI, provided said endorsement conforms with §61.87, you’re perfectly welcome, as a flight instructor, to give an initial endorsement referencing both (n) and (p) if you desire.


Where can I find flight plan records for a private flight in the 1970s? How would I find a record of a private plane flight from Canada to the US in the early to mid 1970's? I am researching records of my father.

Depends on the type of aircraft, but if any records have managed to not be destroyed after 48 years, I would suggest you start by talking to the owner/operator of the departure and arrival airfields. US Customs might have a record of a customs inspection if there was one, but you'd have to file a FOIA request and be prepared to wait for an answer which may not be the one you want to hear.


How many landings per year are performed using the integrated standby instrument system? Could you tell me how many landings are exclusively driven by Integrated Standby Instrument System or equivalent in the world per year ?

Same question with "partially" using instead of "exclusively".

None, as far as I have ever heard of. There may be an instance out there of failure of both/all of the INS’s or displays, but in the airline world at least, it would have to be absurdly uncommon.

It is nice to have the standby ADI as a tie-breaker between the two primary displays in case they should happen to disagree (which was more likely with mechanical instruments than with electronic displays), but actually losing everything else & using just the standby to landing - between really rare and unheard of.


How do young pilots in the USA accumulate 1500-hours to become a first officer? The FAA requires 1500 hours as a pilot:

  The rule requires first officers — also known as co-pilots — to hold an Airline Transport Pilot (ATP) certificate, requiring 1,500 hours total time as a pilot.

I am just interested in how can you get 1500 hours? This number is super huge unless you fly a trans-continental airliner. But you cannot fly an airliner without 1500 hours. Even having a private airplane, 1500 hours I assume will cost a lot - probably more than €500,000 in Europe. What is so specific about the USA? I fly gliders and a tug plane. I fly every weekend without exception and even sometimes after work. But I won't reach even 100 hours during the season. So to reach 1500 hours will take 20+ years. What about if you fly aerobatics...? Well of course there are some people who have these numbers but they are in their fifties and have spent all their lives in aviation! They don't even think about starting afresh in a first officer's career. So I am just curious how do young people log 1500 hours in the USA?

1 word: Instruction.

I learned to fly in the US, and all but one of the 10-15 instructors at the school were young guys who had a Commercial license and were just building hours while doing their exams and applying to airlines.

This meant they were actually getting paid (not particularly well, I hasten to add!) to build hours, rather than spending money on an airplane, or rental.

They say you don't become a pilot for the money, you do it because you love it. Nothing could be closer to the truth IMO.


What are these long tubes under the wings? I wonder what are the elements below the wings (pointed by the black arrows in the image). I'm not referring to the sticks at the end of them, which I found them to be "static wicks", used for static electricity discharge.

They are flap track fairings which contain the flap mechanism.

They are called Küchemann carrots (also called anti-shock or Whitcomb body) and are used to reduce wave drag in transonic speeds.


Does the FAA have specific Air Ambulance safety guidelines? Does the FAA have some specific air ambulance safety guidelines to adhere to?

Check out this document published by the FAA which seems to be recent and some notes here on the same topics. The full rules can be found in the FAR at Part 135 Subpart L—Helicopter Air Ambulance Equipment, Operations, and Training Requirements

They are required to do a preflight risk analysis as per §135.617 but this is not really any different than what anyone should be doing before any flight however for them it is very specifically outlined.

  (a) Each certificate holder conducting helicopter air ambulance operations must establish, and document in its operations manual, an
  FAA-approved preflight risk analysis that includes at least the
  following—

  (1) Flight considerations, to include obstacles and terrain along the
  planned route of flight, landing zone conditions, and fuel
  requirements;

  (2) Human factors, such as crew fatigue, life events, and other
  stressors;

  (3) Weather, including departure, en route, destination, and
  forecasted;

  (4) A procedure for determining whether another helicopter air
  ambulance operator has refused or rejected a flight request; and

  (5) Strategies and procedures for mitigating identified risks,
  including procedures for obtaining and documenting approval of the
  certificate holder's management personnel to release a flight when a
  risk exceeds a level predetermined by the certificate holder.

  (b) Each certificate holder must develop a preflight risk analysis
  worksheet to include, at a minimum, the items in paragraph (a) of this
  section.

  (c) Prior to the first leg of each helicopter air ambulance operation,
  the pilot in command must conduct a preflight risk analysis and
  complete the preflight risk analysis worksheet in accordance with the
  certificate holder's FAA-approved procedures. The pilot in command
  must sign the preflight risk analysis worksheet and specify the date
  and time it was completed.

  (d) The certificate holder must retain the original or a copy of each
  completed preflight risk analysis worksheet at a location specified in
  its operations manual for at least 90 days from the date of the
  operation.


Are those devices allowed on a flight which create their own WiFi signals? I am going from Canada to Mexico but I don't want to be dependent on in-flight entertainment. Thus I got seagate wireless plus so I can stream to my iPad. I couldn't find any policies I can use this device during flight or not. At very least I am trying to determine if it is worth asking the flight company?

No, the rules are about any transmitter or receiver, regardless of whether it comes under the specific category of phone/tablet/laptop etc

If anything your device is worse as it transmits at a higher power and range than a receiver.


What are the differences between "ground stop", "ground delay", and "gate hold"? I've heard several terms referring to air traffic control procedures that restrict movement for a certain period of time: ground stop, ground delay, and gate hold (plus others I'm sure I'm forgetting at the moment). How exactly does each of these procedures work? And do they affect arrivals, departures, or both?

@Pondlife has good quotes and I'll supply some of the direct knowledge he requested.

Ground Stop

Your destination airport cannot accommodate arrivals -- at all.  In this case, they will disallow all planes destined for that airport to take off from wherever they are.

Some examples of what might cause ground stops are:

Weather impacting standard arrival routes, probably more than one.  Aircraft are already in holding patterns and they are running low on altitudes/fixes to put us, and/or those of us in holds are getting close to diverting for fuel.
Airport or runway closure.  If you can't land, you probably shouldn't take off.
All gates are occupied.  If planes cannot depart, there may be nowhere to park arrivals.

You'll note that many times you'll see ground stops described as "Tier 1", "Tier 2".  In short, the T1 ARTCCs are those that directly border with the ARTCC of the destination.  T2 ARTCCs are those bordering the T1 ARTCCs and so on.  Sometimes only T1 departure airports are affected by a ground stop, and sometimes it is everyone.

Ground stops are issued with update times, usually (in my experience) 45-60 minutes later.  They are subject to cancellation at any time, or extension with updated in another 60 minutes.

Ground Delays

These are like the Ground Stops but the airport knows it can accommodate you, just not exactly when you planned to be there.  The reason is most often weather at the destination airport.  Runway closures, accidents, construction, plowing/de-icing can all cause these delays also.

An example

In good weather, airport A may land 90 aircraft per hour.  The helpful airlines have scheduled 110 airplanes to land in one particular hour (no slots at this airport!).  Low clouds and high winds have moved in and now airport A can only land 40 airplanes per hour.  Now of the 110 airplanes, 70 of them will be delayed.  The airlines and ATC will work out which 70 planes those are, and which 40 planes will be allowed in that hour, and start issuing ground delay times.  Of course, these delays spill over into the next hour and cascade.

When a ground delay program is in effect, you will get a "Wheels up time" from ATC, which is when you have to be airborne.  Not sooner, and not much later (3-5 minutes usually).  Getting into your spot in the arrival flow depends on you taking off at this time.  In these scenarios ATC can figure out how/when to get you to your destination, if this isn't the case, that is usually when the Ground Stop program gets started.

Gate Hold Procedure

There is too much happening out on the taxiways, and no room for you.  Stay at the gate!

Reasons for gate holds:

De-icing is in effect and not enough room for everyone to line up at once.
The line to takeoff is too long
Your departure fixes are closed/saturated (This one happens a lot in the NYC Tracon)

In these cases, ATC will issue you a time to start and pushback via clearance delivery (at big airports) or ground control (smaller airports).  Sometimes ramp control can be helpful and help coordinate things... usually not.  When your time is up, you push and taxi and contact ground control.  Not any different than normal except you are given a specific time to do it.


What caused the loss of "everything" on Swiftair Flight QY-2939? I found this from a youtube video, and more info from this avherald article.

One of the pilots declares an emergency because right after takeoff they lost "everything", as in all instruments. ATC managed to steer them back to a safe landing.

This was 2016 Nov 17, in Ireland, on a Boeing 737-400. What on Earth could cause the loss of all instruments? From what I gathered online, the plane was not struck by lightning or going through bad weather.

Without an accident report to go on, we can't know what caused the situation they had.  In fact, from the two links that were posted, we don't REALLY know exactly what they had.  There is the description "we lost everything" from the radio, but that isn't consistent with the statement that they were able to fly headings.

So what follows is a comment on the possible, rather than a statement of what DID occur.

What I can piece together is that they seem to have lost their pitot-static system.  This would remove the airspeed and altitude from all displays, but would leave heading and attitude unaffected.  It would also allow them to fly an ILS approach, with distance from the runway and the on-glideslope indication giving them a way to approximate altitude on final.

There are comments about them climbing to VMC, which strongly implies that they had attitude instruments available.  Likewise, the comment about flying headings would suggest that they had INS information available, since the INS drives the heading indications in the 737-400.  Yes, they could fly headings off the wet compass, but that wouldn't give them attitude information, which they seem to have had.

I don't think the descriptions are consistent with losing the displays in the aircraft, because losing the EFIS displays in an EFIS 737-400 would mean they'd use the analog standby attitude indicator, but the analog airspeed & altitude indications would likewise be available.

Based on all of this, my best guess is that the "we've lost everything" statement is more a reference to having lost all airspeed and altitude displays (along with some other data, including a fair bit of the FMC data that becomes invalid when the FMC doesn't have wind data to work with).  Was the statement a perfectly precise & exact description of the loss of only (only!) the pitot/static instruments?  Not really, but in the stress of the moment it's entirely understandable that what gets said doesn't exactly match what you mean.

In a case like this, the lack of good airspeed information would be the biggest problem, although with reasonably light winds, GPS/INS groundspeed can be a reasonable proxy for your airspeed, and you're flying known pitch/power settings anyway.  Also working in their favor, they seem to have been pretty light, with only "3 souls on board" according to the radio.  So essentially an empty aircraft with something like 25,000 lbs of fuel.  That weight would work out to a fairly slow approach speed, but being light weight they could add 10 or 20 knots above what they think their IAS is (converting GS to IAS without having the winds at altitude is where the uncertainty comes in) and fly the faster speed.  With a heavy aircraft, being 20 knots over your target approach speed could make for issues getting the aircraft stopped on the runway, but with the lighter aircraft those issues are much easier to deal with.

From the one radio transmission caught on the video, they evidently did have radio altitudes from the EGPWS, which is a fair proxy for the altimeter -- albeit with limitations.  If the captain was flying the aircraft using the HUD, or if the EFIS displays on that aircraft include a flight-path vector display, then it's entirely possible to maintain level flight, even if what altitude that is can only be surmised.  (They might also have something in the cockpit that displayed GPS altitude for them -- depends on exactly what they had & if they took the time to get to it.)

Also of note, both links state that the aircraft flew out 2 hours later, which would be consistent with a blockage of the pitot-static system that was cleared out fairly quickly, and at that point the jet is good to go.

Final comment: I'll reiterate, I'm NOT posting this as any sort of statement that "this is what must have happened there."  We don't have enough data to reach certain conclusions.  I'm only drawing inferences from what limited information we do have in those 2 links, and suggesting that the scenario I laid out seems to be consistent with what is in the article and the video, and thus seems to be the most likely explanation.  If new facts come to light, anything or everything above could be subject to revision.

From everything I can see, it was a nice job by the crew to bring the aircraft safely back on what had to be a pretty bad day at the office!


Is it okay to divert to another airport in IFR lost comms situations? In the event of lost communications, FAR 91.185 allows pilots to divert to a nearby airport if they encounter VMC conditions en route to their destination. But what if IMC conditions persist? Are they legally allowed to divert to another airport, which is not designated as the alternate airport in the flight plan, and shoot an approach to land? Doesn't that conflict with the regulation requiring pilots to follow "last assigned, last vectored, EFC route, route in the flight plan" in order?

I ask this question because I came across this phrase in my study material called Everything Explained (p.82): "Do not continue on to your destination if there is a suitable airport for you to land at, unless you're just minutes from your original destination."

AIM 6−4−1. Two-way Radio Communications Failure

a. It is virtually impossible to provide regulations and procedures applicable to all possible situations associated with two-way radio communications failure. During two-way radio communications failure, when confronted by a situation not covered in the regulation, pilots are expected to exercise good judgment in whatever action they elect to take. Should the situation so dictate they should not be reluctant to use the emergency action contained in 14 CFR Section 91.3(b).


Why are prop blades not shaped like household fan blades? My two projects right now are learning to fly and 3D modeling a replacement blade for antique fan, and a question occurred to me:

Why are airplane propeller blades not shaped like household fan blades?

They're both designed to push the same fluid with some degree of efficiency, but household fan blades look a lot more like ship screws/boat propeller blades. Is it a weight issue? A visibility issue? A drag issue, and if so, how?

EDIT - This is not a duplicate of this question because the proposed answers a question about angle of attack and pitch, which are aviation jargon words that may mean nothing to novices. Pitch and angle of attack also have little to do with the front-view shape of a household fan or prop blade, which is likely the most obvious difference between the two types of blades in the eyes of someone without an aeronautical engineering degree.

1) Airspeed, 2) Forward motion, 3) Size constraints. Just to begin with.

Household fan blades are extremely slow, so they need more chord to push a meaningful amount of air. Aircraft propellers approach the speed of sound at their tips, and low drag is critical. All things equal, more span and less chord is more efficient. Reducing the airspeed for props has diminishing returns, because aircraft themselves move forward through the air, so a very large propeller adds drag to the aircraft however slow it is.

In household fans, size constraints are more critical than efficiency. A high-span, low-chord (narrow) blade would be more efficient in a household fan as well - indeed, you can find household fans with such blades. But they have to either spin faster for the same amount of airflow, which adds noise, or be larger in diameter. Ceiling fans, which can be larger, have longer narrower blades than desk or floor-standing fans.

Ship propellers move in an extremely dense and viscous medium, which changes things even more. The drag of moving through water is extremely high and proportional to V³ power-wise. The thrust force they produce is at most proportional to V², and can be lost to cavitation at high velocity. So their velocity has to be kept as low as possible. The drag cost of adding more chord is also relatively small in water.

On large ships, propellers are already as large as they can be made without sticking out of the water at low draft (on merchant vessels) or reducing the number of shafts that can fit (on combatants). This allows them to spin slower and lose less power to drag.


Why are predator drones being used over civilian California? A couple of months back I was going on a road trip through California and stopped by a dry lake called El Mirage Lake. It's a very tacky area requiring a permit to enter.

My friend and I showed up near midnight and could hear a VERY low-flying aircraft. I happened to have a flashlight with a 800 m beam distance and using it we could clearly see a Predator drone less than 500 feet over the ground.

The drone was flying an autonomous rectangular course over the lake all night, but the next morning it had changed altitude and was flying a few thousand feet over the lake - high enough that it just looked like a normal airplane.

For 30 minutes or so there was a Cessna following behind it which was very strange... Would it be a human monitoring the drone for some reason?

Anyway, as a current civilian I feel like there's something wrong with military aircraft being used as surveillance over public area, not to mention it seems a little pointless. Why is the government (or at least state of California) using equipment like this for useless reasons?

I have a pretty bad photo of it using a telephoto lens that I can post later as proof that is was actually a Predator drone.

An article from 2001, TESTING SPY PLANES GRAY BUTTE AIRFIELD TO BE REOPENED says,

  General Atomics, which makes the Predator in San Diego, has been conducting final production tests and checkout flights at El Mirage, three miles inside the San Bernardino County line.

See also EL MIRAGE FLIGHT TEST FACILITY


Don’t seats that recline flat defeat the purpose of having seatbelts? Virtually all first-class airline seats, and many to most business-class seats, recline all the way down, either as lie-flat seats (where the seat reclines to a 180º seatback-seatpan angle, but the fully-reclined seat is still tilted somewhat forwards relative to the cabin floor) or flat-bed seats (where the seat reclines to a truly flat surface that can also, as the name indicates, serve as a bed).

These seats are, of course, equipped with seatbelts, but I’m having great trouble seeing how even a tightly-fastened seatbelt would provide any protection to a flat-lying occupant, as any significant longitudinal force would cause the occupant of the seat to slide under the belt and out of the seat.1 2

Although these seats, like all airline passenger seats, are required to be locked in the fully-upright position except in cruise flight, this still leaves the occupants (especially those in flat-bed seats) vulnerable during the (sometimes quite long) portion of the flight when they are allowed to recline their seats to flatness; a moderate head-on (or tail-on, for that matter) gust would be enough to separate these occupants from their fully-reclined seats, as would any other event capable of suddenly increasing or decreasing an aircraft’s inertial speed too quickly for the “fasten seat belts” sign to provide any warning (not, as noted above, that fastening their seatbelts would actually provide any significant degree of protection to the occupants in question, but it could conceivably induce them to derecline their seats in preparation), such as a flight-control malfunction or evasive action to avoid a MAC (both of which produce large speed excursions secondary to rapid changes in attitude and altitude).

For that matter, even vertical accelerations with no longitudinal component would still be expected to injure flat-lying passengers more severely than those in an ordinary sitting position, for reasons illustrated below:

Am I missing something?

1: This is known as submarining, and is a major problem with car seatbelts (even with seats that don’t recline at all), which are much harder to fasten tightly around the pelvis than aircraft seatbelts.

2: If the belt were fastened tightly enough to pin the occupant to the seat even under considerable longitudinal force, this would

be highly uncomfortable for the occupant, and
upon the application of significant longitudinal forces, drag across the occupant’s abdomen until catching on their ribcage, causing severe internal abdominal injuries plus likely breaking the bottom few ribs.

I'm not sure that comparing car seatbelts to airplane seatbelts is that useful here. The acceleration involved in a car crash at highway speeds are much greater than even the acceleration, mostly vertical, involved in even severe turbulence.

For example, after a 2015 severe turbulence encounter, investigators determined: "In the first event, the peak vertical acceleration forces recorded were + 1.7 and + 0.14 g. In the second event, peak vertical acceleration forces recorded were + 2.21 g and −1.32 g," not that much greater than the kind of acceleration you might feel in a car if you drive really aggressively. That's enough to throw unrestrained passengers and objects about (just as if you slam on the brakes in a car), resulting in injury, but it's a much smaller acceleration than what you'd see in a 30mph car crash. Nobody would consider being slammed against their seat belt like that, whether they're seated upright or reclined, to be enjoyable, but it beats slamming your head into the ceiling.

Forces much larger than that exceed the design load limits required for the aircraft, and once you're beyond that and the required safety factor, your biggest worry is the structural integrity of the aircraft, and you're less concerned about whether people's limbs flailed about.

In the case of an actual crash (such as the 16g standard new airplane seats are tested to), lying flat could pose a much larger risk of injury, but that's beyond the design specifications of the seat, which are tested with test dummies in a normal upright position. There aren't a lot of survivable crashes that occur without warning during the cruise phase of flight (page 22).

Car seats can also be reclined, and the diagrams the NHSTA produced of the results of crashes in those cases (see, for instance, page 41) are remarkably similar to yours. This is why "bring your seat to the upright position for landing" is a standard requirement.


Can an Airbus A380 or Boeing B747 fly with only 2 engines? What would happen if, during cruise at a high gross weight, one of these airplanes suffered a double engine failure:

With one failed engine on each side (leaving one working engine on each wing)?
With both failed engines on the same side (leaving the aircraft with two working engines on the left wing and none on the right wing, or vice versa)?

I know that airplanes with two engines can still fly with only one working engine (by using the rudder to counter the yawing moment created by asymmetric engine thrust, placing the aircraft into a sideslip).

First, my experience was with 747-100/200 aircraft. However, I'm reasonably certain that the subsequent variants of the 747 would perform just as well, and I would be surprised if the A380 did not as well.

  If during cruising with full load....

"Full load" is a little ambiguous. If what is meant is MTOW (max takeoff weight), note that by the time you reach cruising altitude, you're considerably lighter than MTOW.

But let's say you leveled at FL310 or thereabouts, and shortly thereafter two engines failed. Discounting catastrophic failures that leave things hanging out in the wind that generate a lot more drag than a simple inoperative windmilling engine, you should be able to fly as far as your fuel will take you, although common sense and the regulations would dictate finding the nearest suitable airport.

You won't be able to maintain your 4-engine cruising altitude. You'll drift down until you reach an altitude that you can maintain.

You'll be able to fly whether the two failures are both on one side or one on each side, but both on one side is the more problematical. We used to practice that in the sim. They always put both failures on one side to make it more interesting. The drag from the rudder necessary to counter the adverse yaw from the operating engines is significant, and as you start reducing the power for the landing, judging how much rudder to decrease and when is an interesting dance. You would have run in lots (maybe all) the rudder trim. How much of it should you take out and when. Take it all out too soon and your leg is going to get awfully tired.

While a double failure at cruise is handleable, it's easy to come up with scenarios that are not. If you had a double failure on takeoff just after V1, I doubt you'll make it. V1 and the balanced field length are predicated on one engine failing, not two.

Take a look at https://thepointsguy.com/2017/03/engines-boeing-a-747-can-fly-on/, the relevant part is:

  After almost 15 minutes in a controlled gliding descent, the crew coaxed one engine back to life, allowing them to significantly reduce their rate of descent. A few minutes later, a second engine came back on line with partial power, allowing the aircraft to enter a slow climb.

It's also worth noting, I think, that when you're doing a 3-engine ferry in a 747, you're depending on it being able to continue flying on two in case of an engine failure during that ferry flight.

A final thought about the last part of your question:

  controlling the rudder makes the airplane fly sideway.

To the best of my knowledge, the use of the proper amount of rudder to counter asymmetrical thrust does not make the airplane fly sideways. However, I am not an aerodynamicist. Perhaps one of the many here qualified in that area can comment.


What are the differences between various simulator levels? I've heard of level A, B, C, and D simulators, (as well as FTD and AATDs) but know nothing about them.

What criteria is used to certify a sim as a particular level?

Here there is a nice tabular representation of the requirements for each level.
Wiki provides a handy summary:

Full Flight Simulators (FFS)

FAA FFS Level A - A motion system is required with at least three degrees of freedom. Airplanes only.

FAA FFS Level B - Requires three axis motion and a higher-fidelity aerodynamic model than does Level A. The lowest level of helicopter flight simulator.

FAA FFS Level C - Requires a motion platform with all six degrees of freedom. Also lower transport delay (latency) over levels A & B. The visual system must have an outside-world horizontal field of view of at least 75 degrees for each pilot.

FAA FFS Level D - The highest level of FFS qualification currently available. Requirements are for Level C with additions. The motion platform must have all six degrees of freedom, and the visual system must have an outside-world horizontal field of view of at least 150 degrees, with a Collimated (distant focus) display. Realistic sounds in the cockpit are required, as well as a number of special motion and visual effects.


What does it mean for a plane to be aerodynamically stable? I've heard that most planes (excepting fighter jets) are "aerodynamically stable." What does that mean?

Let's say you're cursing around in a Cessna 172 without autopilot, and you take your hands off the controls. What happens?

Will the plane stay at the same pitch and avoid stalls and dives?
Will it stay at the same altitude?
Will it say at the same heading?
Will it correct each of these as the plane is buffeted by turbulence?

Static stability

is the tendency of a system to return to its initial state after a disturbance. Typical disturbances in case of airplanes are:

Flying into a vertical or horizontal gust
A jerk on the stick

The classic explanation is with a ball sitting in a pit. Whenever its position is changed by a disturbance, it will roll back towards the center. This does not mean that it will stop there - in an ideal world free of friction it will keep moving back and forth like a pendulum.

This is static stability. Broadly speaking, static stability is achieved by placing the center of gravity ahead of the neutral point, the point in which all additional forces due to a change in angle of attack can be summarized. There are two neutral points, one for longitudinal stability and one for directional stability. In both cases the change in angle of attack or sideslip will create a correcting moment around the center of gravity, pulling the aircraft back on its old path.

Even altitude stability can be achieved, but here we take advantage of the fact that air becomes less dense the higher you climb. If the aircraft is trimmed for horizontal flight at a certain altitude, an altitude change will mean that the power setting does no longer match drag at this new altitude. The aircraft will either climb or sink, depending on the altitude change, until the old altitude has been reached again.

In all cases you will experience overshoots and oscillations around the trim point. It can even happen that these overshoots become worse the longer the oscillation lasts (the phugoid motion in a glider is a good example). To stop the oscillations, you need to add

Dynamic stability

which describes the behavior of the aircraft over time. In most cases, friction will ensure that motions die down, and sometimes aircraft need little helpers like yaw dampers to get those under control.

You mention stalls and dives: They can indeed occur in a statically stable airplane. Low drag means low damping, therefore many high performance gliders have a dynamically unstable phugoid motion. I know, Wikipedia spells this wrongly, but the explanation is OK, so I linked it nonetheless. If you wait long enough after an initial upset, the oscillations will become so severe that the aircraft stalls at the upmost point of the cycle.

If you keep enough altitude and have no traffic nearby, this is fun to try.

Spiral dive

Note that I omitted to say something about roll stability so far. The glider (and your Cessna 172) will also start to roll, and in many cases the roll motion will increase more quickly than the phugoid, so you might need to try several times before you get a phugoid-induced stall. Most aircraft have a weak tendency to increase roll angle and to eventually fall into a spiral dive.

There is no aerodynamic mechanism to right the aircraft up after a roll disturbance. Sorry, @kevin, but dihedral won't help - it only works in case of sideslip.


Why is radar required on some FAA instrument approaches? The ILS / LOC approach at KCXY states radar is required. I understand I can't fly the approach if not in radar contact. However, if flying the LOC approach I think I can identify both final and HORVI (for lower minimums) using HAR VOR. There's no reason I'd need the controller to call out a fix. If that is true, why is radar required? I think it would be more of a safety concern because of terrain and an adjacent airport (HAR Int)?

Radar is most likely required in this case because there is no defined Initial Approach Fix (IAF).

Also note that in the profile view TIVNE and HORVI have the word RADAR underneath, which means that if you wanted to fly to either of those way points, including a course reversal in the hold, you would still need to be vectored by ATC via RADAR.

This means that ATC needs to give vectors to final or otherwise provide a specific clearance to establish an IFR aircraft on the approach.

There may be other considerations, but that is the main one that I see here.


What callsigns do UK Medical Emergency Response Teams use? I'm making a simulation game and there's a large focus on the humanitarian effort military personnel put in, putting aside the shooting and more on the story. Part of this is a Medical Emergency Response Team (MERT) landing with radio communication in the background, which obviously is using callsigns.

For the purpose of realism, I am trying to find references for what callsigns are used for these MERT aircraft/teams. Does anyone have any idea what a MERT team might be called? I'm looking specifically for UK forces however NATO is also fine.

Civil

For the UK as requested, this information is in § 2.32 of the Radiotelephony Manual (CAP 413). The call-sign for a Helicopter Emergency Medical Service (HEMS) is three parts:

HELIMED
Two-digit identifier unique to the aircraft (list on Wikipedia).
Suffix A or E

A for a helicopter en-route to an emergency or to a hospital with patient(s) on board
E for positioning back to base (a lesser priority than A but higher than the other traffic).

If the helicopter is responding to a scene, it can be pronounced Helimed 7-7 Alpha, for example. Note that Wikipedia lists three-digit identifiers for some helicopters, contrary to what the manual says.

Military

From § 2.44 of the same manual, the call-signs are 'rescue' and 'rescue helicopter', suffixed by the mission number. This is for search and rescue (SAR), no distinction is made for a purely medical mission in the manual.


Is it possible to have an angle of incidence for a vertical stabilizer? horizontal surfaces in airplane have small angle of incidence in general, Is it possible to have an angle of incidence for a vertical stabilizer?
Please help me to find it. Thanks!!

Some vertical stabilizers will have a slight angle of incidence to counter left turning tendencies. Older model Cessna 172s and 150/2s have a little metal trim tab that can only be adjusted by manually bending it from the outside. This will serve to adjust the vertical airfoil chord line angle in the aircraft slipstream or relative wind. The degree of incidence will be manufacturer and model specific.


Is it possible for the Boeing 737NG to do a powerback? I'm curious, in a non-normal situation, where it's not possible to use a pushback tug, would it be POSSIBLE to perform a powerback on the 737NG, assuming the area was reasonably clear of FOD?

Possible? Yes! But not recommended.
There is nothing technical that would stop you from doing it. Thrust Reversers can be selected any time on the ground and there is enough thrust available to move the aircraft backwards. It is also not technically prohibited to do so:

Reverse Thrust
Intentional selection of reverse thrust in flight is prohibited.

(Boeing 737 NG FCOMv1 L.10.8 - Limitations - Operating Limitations)
There is nothing mentioned here that would prohibit the use of thrust reversers to back the aircraft. For comparison, on the Boeing 747 it is prohibited:

Reverse Thrust
Intentional selection of reverse thrust in flight is prohibited.
Backing the airplane with use of reverse thrust is prohibited.

(Boeing 747-400 FCOMv1 L.10.7 - Limitations - Operating Limitations)
Boeing does however not recommend using it on the 737 NG:

Backing with Reverse Thrust
Backing with reverse thrust is not recommended.

(Boeing 737 NG FCTM 2.4 - Ground Operations)
That is all the training manual has to say about it.

I do not know if backing with reverse thrust is actually done anywhere in a 737 NG. It was for sure done in older 737-100/-200 models:

When I flew the B737-200, we were trained in powerbacks, with SOPs set out, but it was to be used only as a last resort. I did only two during my time on the B737. On both occasions, we arrived in the US in a gravel equipped B737 that had a different nose wheel and their tow-bar would not fit.

(airliners.net)
It is also still being done in Boeing 757s:

(YouTube)


Is the gas velocity of a jet engine relative to the engine speed or is it absolute? Let's say we are testing a jet engine on the ground by keeping it still. We measure the inlet and outlet velocity of the gas at a specific operation point. Let's assume that we attach this engine on a aircraft that is of course moving. In a random time the operation point is the same as before. If we measure the absolute inlet and outlet velocities are the same as before or only the relative ones(aircraft velocity+gas velocity) are the same?

And one more similar question.
In the case of the engine attached to the aircraft all the fuel energy that can be used is transformed into changes of the kinetic energy of both the aircraft and the air passing through the engine.Right?
In the first case of the test, the kinetic energy of the engine isn't changing, so all the used fuel energy is changing the gas kinetic energy, so in this case the difference in the kinetic energy of the gas is greater. Does this makes sense since we talk for the same operation point?

To conclude, is the thrust the same regardless if the jet engine is moving or not?

The answer is NO, but it is important to understand why. I will explain the conditions, and answer your questions at the end one by one.

First point you are never testing the same engine:

Aircraft manufacturer usually introduces its inlet and its nozzle so both are not usually the same in a test and in the real conditions. (that will mean is partially installed)

You are not including the general effect of the A/C aerodynamics.
You are not including the air bleeding and oil and fuel pump (also, a partially installed engine)

Essentially you are asking about the effects between installed and uninstalled effects on an engine.

Answering your qeustions:

If we measure the absolute inlet and outlet velocities are the same as before or only the relative ones(aircraft velocity+gas velocity) are the same?

This question is not clear as an engine will have different outlet velocities (fan, main cowl...). Taking care about the right reference systems the speed will be of the same order but affected by my previous argument about installed/uninstalled engines

In the case of the engine attached to the aircraft all the fuel energy that can be used is transformed into changes of the kinetic energy of both the aircraft and the air passing through the engine.Right?

Now, some part is used for bleed air, electric systems, fuel and oil pumps. Not all energy is used to cover the drag of the airplane.

In the first case of the test, the kinetic energy of the engine isn't changing, so all the used fuel energy is changing the gas kinetic energy, so in this case the difference in the kinetic energy of the gas is greater. Does this makes sense since we talk for the same operation point?

Given that you establish the reference system fixed to the engine, you will as well not have a difference in speed produced by the engine. Actually you should used that reference system.


What causes the phenomenon that pilots don't believe their instruments, while they're working well? I read in a comment on another question that pilots not believing their instruments while they work perfectly well is common in aviation:

  The flight leader reported that his compasses had failed [...] but there is a thin line between believing that your compass has failed and it actually failing. Not believing the instruments, when they are working perfectly well, is a well known phenomena in aviation.

Why is that?

Human decision making is an entire field of psychological research and there are many, many studies and books about it. Yet for all that we really don't know exactly why people make the kinds of mistakes they do, so I will summarize the theoretical work that I personally have studied, which are Heuristics and Cognitive Biases.

The theory is that human brains simplify decision making by developing Heuristics, which are essentially algorithms which allow for quick and efficient information processing. Think of it this way; you don't have time to analyze every situation from the ground up. Imagine if every time you walked up to the cashier in a store, went to cross a street, or from a piloting perspective became too close to another airplane you had to examine it from first principles! It would be slow, exhausting, and possibly dangerous. Heuristics are the brain's sophisticated way to shortcut that so that decisions can be made fast, they are developed through personal experience, second-hand experience, and training.

The problem is that heuristics are prone to biases and errors of logic. Heuristics can be developed which get to the wrong result with a given set of information, these lead people to making the wrong decisions, interpreting situations incorrectly when thinking about it anew would give an entirely different result. Ambiguous data can lead to the wrong heuristic being used, several options being available forces the brain to choose the best one.

I think heuristics theory goes a long way to explaining some of the common mistakes that are made in the cockpit, this is from my study of the material and from time in the cockpit, what is not that well understood is how stress and motivational factors can influence them. There's also the role of biases, which cause deviations from logic and good decision making. Some relevant ones are:

Selection bias, where someone cherry-picks what they want to see so it fits their view
Confirmation bias, where someone ignores things that don't fit their view, this is also known as expectation bias
Attention Tunneling, where someone becomes fixated on one thing and ignores others

My personal view on this is that the human brain has a tendency to force heuristics to fit input when it is ambiguous, especially in busy or stressful situations. This can be a good thing as it makes people act when they might otherwise not have, but people tend not to notice when the brain's developed ways of interpreting information don't fit the context or arrive at an obvious error. We won't like the feeling of being wrong or we are busy with other things, so we don't re-evaluate information. Sometimes people die because of that.

This is why airlines have re-curring situational training, and why that training is so incredibly important for safety. They train pilots to match what they see and feel to sets of actions so that the right decisions are made quickly.

EDIT:
There was a comment asking whether these effects could be contagious, the answer is yes, sometimes incorrect ideas get passed along, and if they don't get challenged it can lead to disaster. Some of these effects are:

Availability bias, where an event happening to one person makes another think it is more likely to happen to them. One pilot's instrument failure makes another think theirs did too, even though it's not true
Authority bias, where someone believes something is true when the source is a famous or authoritative figure. A captain telling a FO that an instrument has failed makes the FO believe it because they're the captain
Groupthink, where social pressures to conform or avoid dis-harmony make people buy into bad decisions


Vortex Lattice Method with eliptical panels I implemented vortex lattice method (or deeper here) into my aircraft simulation program. The problem is that sometimes trailing vortex filaments from Horse Shoe Vortexes of main wing hits panels of rudder/elevator which leads to singularities (infinite coupling between the two panels). This is because rectangular panels generate sharp singular vortex filament at the end of wing.
(see https://scicomp.stackexchange.com/posts/30062/edit)

I'm thinking to use eliptical panels as a basis set for VLM to avoid those singularities - then I hope my simulator can work with smaller number of panels (I wan't to make it real-time).

This is normally ploted in texbook:

My questions:

I search for formula / derivation how the down-wash from eliptical wing looks like in the whole 3D space. Usually what is plotted in texbook (constant rectangular downwash) is true just immediately behind the wing.
Is it fine to express wing of complex shape as linear combination of eliptical wings and it's downwash as linear combination of downwashes from each of them? I mean if potential flow is linear problem, than I see no problem - ut maybe I forgot about some catch.

Typically in numerical simulations, instead of an ideal(inviscid) vortex, a viscous vortex with a finite core is used to avoid the singularity at the centre. In these viscous vortices, the swirl velocity inside the core is assumed to be linearly increasing from zero at the centre. While outside the core, the induced velocity remains the same as that of the ideal vortex.

There are multiple models that model these finite core vortices; some of which are:

Rankine
$$V_{\theta}=\begin{cases}\overline{r} & \text{if }\overline{r} \leq 1 \\ 1 / \overline{r} & \text{if }\overline{r}>1\,.\end{cases}$$
Lamb–Oseen
$$V_\theta=\frac{1}{\overline{r}}\left(1-\mathrm{e}^{-1.2526 \overline{r}^{2}}\right).$$
Bumham–Hallock
$$V_{\theta}=\frac{\overline{r}}{\overline{r}^{2}+1}\,.$$
Proctor

$$V_{\theta}=\begin{cases}
  \frac{1.4}{\overline{r}}\left(1-\mathrm{e}^{-\beta(1 / \overline{B})^{0.75}}\right) \times\left(1-\mathrm{e}^{-1.2526 \overline{r}^{2}}\right) & \text{if }\overline{r} \leq 1 \\
  \frac{1}{\overline{r}}\left(1-\mathrm{e}^{-\beta(\overline{r} / \overline{B})^{0.75}}\right) & \text{if }\overline{r}>1\,.
\end{cases}$$

Proctor–Winkelman

$$V_{\theta}=\frac{1}{\overline{r}}\left\{1-\exp \left[-\beta_{i}(\overline{r} / \overline{B})^{2} /\left\{1+\left[\left(\beta_{i / \beta_{o}}\right)\left(\overline{r} /_{\overline{B}}\right)^{1.2}\right]^{p}\right\}^{1 / p}\right]\right\}\,.$$

Vatistas
$$V_{\theta}=\frac{\overline{r}}{\left(\overline{r}^{2 n}+1\right)^{1 / n}}\,.$$

In these equations, $\overline{r}=r/r_\mathrm{core}$.


What are those tiny circles on fan blades of Trent 1000? From Sam Chui's video, there are tiny circles on the surface of three fan blades of next generation Trent 1000 engine. Why aren't they present on remaining fan blades?
Below comments suggest they are for optical purposes. What optical information can be inferred from these circle?

My prediction: They are embedded explosive charger to test explosion testing(specifically Blade off testing of an engine.

These are certainly targets for an optical CMM (coordinate measuring machine) using laser, structured light or stereoscopy. The targets help define common points on the model from one scan to the next.
@mins linked a perfect example of this in his comment below, from which this image is taken. When doing 3D scanning, you want the dots in a random pattern as in the OPs image, rather than the uniform pattern seen below. This helps the identify and match the dots when going from one scan to the next (called "tie-points"). For the vibration analysis process linked by @mins, the requirements are probably different as the camera doesn't move, so it makes sense to place the dots in a grid pattern.


How are military aircraft type certificated? It seems that FAA requirements for any particular aircraft revolve heavily around the aircraft's type certificate.  Civil aircraft are broken up into several categories based on weight or passenger count, etc.  But I did not see a section on military operations.

Do military aircraft undergo type certification?

In the US, the military is not required to obtain FAA type certificates for their aircraft; the FAA is not the authority certifying a military-registered plane's airworthiness. They have the option of accepting an FAA type certificate (which they tend to do on aircraft based on civilian ones), but they run their own certification agencies for airworthiness, which are all that matters if the plane is in the military registration system. Here's an Air Force policy on the matter, here's a Lockheed powerpoint on the option to use FAA certification on commercial derivatives.


What are these ribbons on the wing of an MD-83? What are these triangles and ribbons on this MD83's wing, and what do they do?

These are Ice Detection Tufts that check for ice. If they are stuck, it indicates there's a layer of ice on the wing, disturbing airflow and presenting a danger for the engines when it detaches. They are focused around the rear root side since this is most likely to be the spot with the most buildup, as remaining cold fuel below flows to this corner.

SAS had an incident with ice a few years ago in the Gottröra Accident (SAS Flight 751) that thankfully ended relatively well.


Why are there speed restrictions applied after deicing an aircraft? The information about the 737 here mentions an interesting limitation:

  737-6/900 without stiffened elevator tabs:

  After any ground deicing/anti-icing of the horizontal stabilizer using Type II or Type IV fluids, airspeed must be limited to 270 KIAS until the crew has been informed that applicable maintenance procedures have been accomplished that would allow exceedance of 270 KIAS. Once the applicable maintenance procedures have been accomplished, exceeding 270 KIAS is permissible only until the next application of Type II or Type IV deicing/anti-icing fluids.

How are certain deicing fluids, un-stiffened elevator tabs, and airspeed related here?

Some deicing fluids can leave a gel-like residue on the airplane. Several incidents occurred with 737s where the residue accumulated in the elevator balance bay, causing severe oscillation/vibration in flight above 270 KIAS. These incidents resulted in the issuance of Airworthiness Directive (AD) 2002-08-20, which required adding the 270 KIAS limitation you discovered into the 737's Airplane Flight Manual (AFM). The required "maintenance procedures" consist of cleaning off the deicing fluid residue. The AD also requires a one-time cleaning and sealing of the elevator balance bay.

  The FAA has received reports of numerous incidents of
  severe airframe vibration, or limit cycle oscillation (LCO), in flight after the horizontal stabilizer had
  been deiced/anti-iced on the ground. The reported incidents occurred on Boeing Model 737-600, -700, and -800 series airplanes. The empennage structure on these, as well as Model 737-700C series
  airplanes, is identical; therefore, all of these airplanes are subject to the identified unsafe condition.
  These events have been attributed to an accumulation of deicing/anti-icing fluid or other residue in
  the elevator balance panel cavities and on the external surfaces of the elevator tab.

A Boeing article on the subject gives some more information and also has some photos showing the residue. Here's what a gummed-up 737 elevator balance panel looks like:

From the article:

  Airplane deicing and anti-icing fluids can leave residue in critical areas in the wings and stabilizers. This residue can rehydrate and expand into a gel-like material that can freeze during flight and cause restrictions in the flight control systems. Therefore, attention to this residue should be part of a regularly scheduled inspection and cleaning process.

...

  Although Type III fluids have not been specifically linked to any events involving flight controls, the composition of these fluids makes them equally susceptible to residue problems as the Type II and Type IV fluids.


What policies, technologies, equipment, etc is used to mitigate liquid spills in the cockpit especially during turbulence? While reading this stack exchange question about waterproofing cockpits, I wondered what common industry practices as well as personal practices are in place to mitigate spills and damage.

Type of cups, serving times, cupholder design and placement, length and altitude of flights, weather considerations and sterile cockpits for example.

Additionally, are reportable spill events so uncommon as to not warrant mitigating procedures and design practices?

Keeping the cockpit clean is a major consideration for airlines. The inflight team will scheduled meal times accordingly with reports from ARTCC and other aircraft on a similar routes. They tend to stagger their eating times, so one pilot can be the PIC and the other can eat. Once he/she is done eating they will switch. Here you can find a link explaining Multi Crew Operations. Hope this helps!


Why do "angels" mean MSL, not AGL? In military aviation, crews will sometimes refer to "angels" meaning MSL altitude. However, one might guess that it is a pronunciation of AGL (AnGeL), above ground level. Did it originally mean AGL and then at some point it changed meaning to MSL?

It was originally Royal Air Force slang for altitude in thousands and not a way of pronouncing AGL.

Up in the air, where the angels fly.

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

Angels 10 meant 10,000 feet.  Cherubs were hundreds of feet.


What is the beeping occasionally heard in the background of ATC? Occasionally while listening to ATC, I hear a beeping in the background of their transmission. My suspicion is it's a traffic conflict alert since the beeping is usually followed with a traffic alert to a pilot. But other times I've heard the beeping without a traffic alert.

Here is a short snippet from today of Norcal Approach at KOAK demonstrating the beeping heard in the background: https://vocaroo.com/lD93L8D5lJ3

I can't identify the specific sound, but - just like in a cockpit - there are several different audible alerts in a control tower/control centre. Just to list a few:

Conflict alert, as suggested in the comments
Various other radar based safety nets (MSAW, MTCD, DUPE etc.)
Strip printer printing a strip (not an alert as such, but the sound is quite noticable)
Phone ringing (typically a tower has several different phones, possibly with different ringers)
Fault indication on a runway light/navigation aid
Change in status (on/off) of ILS equipment (localiser, glideslope, DME)
Crash alarm, when activated by the controller
Microwave/toaster timer! (at least in smaller towers without a separate kitchen or break room)
Several others, depending on the local equipment

It may be a bit startling when you hear something on the radio that sounds like some sort of alarm, but you shouldn't be worried. The sound can signify many different things and it does not necessarily indicate anything dangerous.


How is fuel planning done for a VFR flight that involves multiple full stops? Doing first cross country flight plan with several stops along the way.  What is the general rule of thumb for calculating time, fuel, etc. for a mid trip landing?  I've done conceptual flight plans with checkpoints etc, but not actual stops.

In other words, I can calculate fuel burn, ground speed, course etc. for a point to point flight.  Just not sure what to calculate in by adding a full stop in the middle of that same flight.

While studying for the FAA knowledge exam it sometimes said calculate 3 minutes for take off and departure but curious if there is a generally accepted set of numbers.

This may not be what your CFI is looking for, but I found the changes in fuel consumption during takeoff/landing to be negligible. This is because the taxiing uses very little, the and extra fuel burn in the climb is largely compensated by the savings in the descent. So, I just look at the distance between the airports, take winds aloft, calculate ETE and make sure it's acceptable in respect to fuel reserves. Ditto for any foreseen diversions. You have to have enough fuel on board to reach your planned reserve airport if you arrive at your destination and find that it's closed (e.g. because of an accident). This may be less of a problem in North Carolina, but in New Mexico, you might need to return all the way. A 30 minute VFR reserve isn't going to cut it.


What can happen if a bird strikes the engine during landing? I am not sure what can happen if a bird strikes an engine during landing.

To narrow it down: commercial airliner (B787/A380 etc.) hitting a large bird so engine out is likely.

A range of things can happen.
For an airliner with a modern turbofan engine, the mostly common outcome is, absolutely nothing happens to the aircraft (although the bird's day is pretty thoroughly ruined). A sparrow can be chopped up by the fan blades & blown out the back, and the crew will never notice it.  The engine won't hiccup, and until somebody sees a trace of blood and feathers on the fan blade during a walk-around, nobody will have any idea it happened.
Next case is a small bird gets ingested into the core. Chances are good the engine will keep running (remember, small bird we're talking about here), although the crew may notice a fluctuation in the engine instruments and there may be the smell of cooked (charred) bird in the air conditioning system.
In both of these cases, the engine will be inspected; the case where the bird went into the core takes longer, because maintenance will have to use a bore scope to look inside the core to inspect for damage.
The worse case than either of these is a big bird (or several) going into the engine.  Depending on the specifics, the engine may chop them up & spit them out without damage, or the fan blades may be damaged, and/or the core may be damaged, and in the bad case the engine loses power, and in the worst case, it quits.
Losing one engine to a birdstrike is quite rare and is a pretty big deal, but most certainly not unrecoverable. An airliner can fly fine with one engine shut down.
If the birdstrike happens on short final, the crew might simply use more power on the operating engine and continue on to land. If it happens farther out, they might continue or they might discontinue the approach, go around, shut down the damaged engine, and then come back and land.
The really, really bad case is where you get enough bird strikes that they shut down all engines, and at that point you're a glider.  If that happens at 50' over the runway, your only choice (land straight ahead) still gets you where you wanted to be anyway. If it happens farther out, well, that's where somebody gets to try to be Sully 2.0.  That sort of a scenario is extremely rare – like one in tens (if not hundreds) of millions of cases rare.
You're far more likely to get hit by a semi truck driving home from the airport than having your day ruined by a bird going through an engine.


How common are conformal fuel tanks? I know that the F-16 (F-16I and Block 50/52/60 models) have conformal fuel tanks standard now on top of the wing/fuselage area.  The Silent Eagle model of the F-15E proposed by Boeing for South Korea, and other F-15E customers had them added.  The F-18E (Superhornet) has demoed a set recently.

But on older aircraft, how common were conformal fuel tanks?  Or have they always been drop tanks before?

Technically speaking, conformal tanks don't take up hardpoints, so I'm not sure what we have today has an equivalent in older designs.

Otherwise, I'd say somewhat common; streamlined fuel tanks and other conformal packages have been used for quite a while in several different designs.

Some World War II Supermarine Spitfires used what was called a "slipper tank" - a streamlined package of up to 90 gallons (additional source).

The early 1960s-era English Electric Lightning used a 'conformal ventral store' that could hold either a fuel tank or rocket engine (?!). The Gloster Javelin used a similar set of "bosom tanks".


What types of maneuvers increase the load factor on the aircraft? Out of turns, stalls and climbs, which of the basic maneuvers increases the load factor on an airplane as compared to straight and level flight?

The load factor of an aircraft is given as the ratio of lift to weight.

i.e. $n = \frac{L}{W}$

So, an maneuver that changes any of these two forces acting on the aircraft causes a change in the load factor. Usually, it is the lift which is considered the variable.

Consider an aircraft in a level turn. In addition to the lift and weight, the aircraft experiences centrifugal force, which is counteracted b the horizontal component of the lift.

Courtesy: www.rainierflightservice.com

For a bank angle of $\theta$, it can be shown that the load factor can be given as,

$n = \frac{1}{cos\theta}$

So, as the bank becomes 'tighter', the load factor increases. A load factor greater than one will cause the stall speed to increase by the square of the load factor.

Basically, as the load factor is increased, the aircraft minimum speed should be increased to prevent stall.

For aircrafts in steady climb, the principle is essentially the same.

Picture Source: classicairshows.com

Here, the weight is less than the lift and as such, the load factor is (slightly) less than one.

As the aircraft stalls in level flight or unaccelerated straight climb, the lift becomes zeros and the load factor also becomes zero.


Which FAR/AIM addresses Shortest Turn to Assigned Heading vs Runway Traffic Pattern? Today I was in a simulator on runway 20R at KSNA. ATC gave me a VFR clearance and told me to fly heading 080 on departure. The runway has right traffic. I turned right and was told by ATC I should have turned left because you're supposed to always take the shortest turn to assigned heading when given a heading, even if the runway has an opposite traffic pattern.

My question is: Where does the FAR/AIM specify this rule? Are there any other legal publications that specify this?

Bonus points if you can cite a reference to this rule in any PPL textbook e.g. Jeppesen's Guided Flight Discovery Private Pilot. Thanks.

The most important point is that if any ATC instruction isn't clear then you should just ask them to repeat or clarify it.

Having said that, turning in the shorter direction is stated in the FAA's Pilot/Controller Glossary:

  FLY HEADING (DEGREES)- Informs the pilot of the heading he/she should
  fly. The pilot may have to turn to, or continue on, a specific compass
  direction in order to comply with the instructions. The pilot is
  expected to turn in the shorter direction to the heading unless
  otherwise instructed by ATC.

In my personal experience, ATC almost always say left or right for heading changes if you're on an approach or departure, but sometimes leave it out if you're in cruise. That makes sense to me: the busier the airspace the more they want to make sure that you don't turn the wrong way.


What do I need to power up an EDF engine? I want to buy a EDF engine (just the engine). What items, such as battery and chargers etc. do i need to buy to power it up?

An EDF is an electric ducted fan, so I assume you're not interested in the fans powered by internal combustion engines (or actual turbines).

You'll need:

an ESC (electronic speed controller) that is rated for at least the maximum current and voltage of the motor in the EDF.
a battery that can provide that current and voltage.
something to provide a throttle signal to the ESC. Usually this is a transmitter and receiver, but for bench-testing a simple, cheap option is a servo tester.
a charger for the battery. This must be able to match the battery chemistry, voltage and capacity (they normally handle a range)
if the charger isn't mains powered, it will need a power supply.

There are loads of on-line shops for all this.


Why is the wrong explanation of "air travels a longer distance and creates a lift" so popular? When I was learning for my license, one of the first diagrams I remember was about the wing profile. The air going around the wing and on the upper side it has to travel a longer way, thus generating lower pressure and bang, plane is flying.
Same explanation already back at school.

See my other question: if the theory was right, why can planes fly inverted?

So here's the follow up: why is this wrong theory so popular and still part of books?

Wouldn't it make sense to teach students how a wing really works? I mean just look at any RC plane meeting - you'll be amazed what weird designs are capable of flying if there's enough engine power.

Long story short is that both Newton's third law and the Bernoulli's effect are two different ways of explaining the same phenomena. Accurate equations have been written to explain both. Newton's third law, the air being forced down and forcing the airplane up, is actually the effect of lift though not the cause. The cause of lift is the change in pressure.

The falsehood that is taught is usually that the two little air particles actually meet up at the same point downstream at the trailing edge of the wing at the same time. This is completely false. In fact, if you were to actually track two air particles, one over the top, and one across the bottom, the one going over the top of the wing will probably arrive much sooner than the one on the bottom! [Even though the distance IS longer] It picks up that much speed. Also they don't actually really meetup again afterwards at all.

The real pivotal relation (which I learned in my Advanced Aerodynamics class at ERAU using John. D. Anderson's book Intro to Flight) is the Kutta-Joukowsky theorem. Taking the time to explain this to a Private Pilot student would probably be a waste of your time and theirs but I will sum it up here anyway to be fair to the question. I will assume incompressible flow because after about Mach .3< it starts to get more complicated.

The Kutta-Joukowsky theorem takes the integral of velocity times the cosine of the incremental angle of the distance along the closed curve. This is a quantity called circulation. The lift equation is then formed as lift equals density (altitude basically) times velocity times circulation. So if you really want get in-depth here is an article from MIT that explains potential flow theory.

What you will find is that the cause of lift is indeed directly related to Bernoulli's principle in that the change in pressure is what creates the lift. However it has nothing to do with particles meeting up at the trailing edge because they never really do meet up. This doesn't discount Newton's third law either: lift can be explained that way but it is the effect of lift, not the actual cause. And yes, like you mentioned, even a flat-plate for example can create lift when angled right in a wind tunnel.


How are antennas integrated into stealth aircraft? In Hephaestus Aetnaean's answer to this question, it is mentioned that the F-117 had no radar detection equipment because at the time it was developed the designers had not figured out how to integrate the antennas into the body without increasing its radar profile. How is this done on newer stealth aircraft?

And what about things like air speed sensors? Do they use something other than a pitot tube?

As a related question, obviously if this was the case they apparently were not able to place radar detection inside the cockpit as you can with police radar detectors. Is the cockpit glass in the F-117 somehow opaque to radar or is there another reason?

Pitot tubes
F-117 pitot tubes

Source: YouTube. Also a look at the FLIR and DLIR.
F-22 pitot tubes

Source: AIR-SCENE UK.

Incorporation of those pitot probes were a cost savings measure. They are also a dominant RCS signature source in the forward and side sectors. The original ATF proposal was for a flush air data system that would have cost many $ millions. - djcross, F-16.net

F-35 pitot tubes

Breaking Defense. More pics on F-16.net.
Canopies
The canopy keeps radar energy out of the cockpit, the inside of which is filled with messy odds and ends. The F-22 and F-35 canopies are gold-impregnated for this reason. Note: the F-22's canopy is possibly doped with indium-tin-oxide, not gold.
In the EA-6B's case, the gold keeps the a/c's own radar energy out of the cockpit---those ram-air turbines are powering two jamming pods. The coating (and a similar one applied to visors) also turn black to protect the pilot's vision from nuclear detonations.

Source: USAF

Source: Wikipedia.

Source: Lockheed Martin. Flickr set.
Notice the similarly tinted/treated window beneath the F-35's nose. That's the aperture for the EOTS (electro-optical targeting system), an IRST and ground targeting system. Also note the two small pitot tubes above the EOTS. I remember pitot plates were being developed for the F-35 (which are stealthier but more difficult to develop), but I haven't heard anything about it in a while.
Sensor apertures
The coverings are transparent to the operating bands of the radar/radio/etc underneath.
The F-22 and F-35 have fixed AESA radars. The latter is angled up to minimize returns.

Credit: Northrop Grumman. Hi res.
Some radar energy enters through the aperture. Whatever isn't reflected is absorbed by the radar itself or heaps of RAM, which hides the messy rear/sides.

via F-16.net. More AESA pics.

Fun note, the first F-35 radar pic is of an APG-81 installed on the CATBIRD:

Source: YouTube

Did the F-117 have a radar warning receiver?
It's always been a contentious point. Some say yes, some say no, some say 'I like my job.' In a lengthy 2007 interview, Lt. Col. Dale Zelko (the F-117 pilot shot down) declined to reveal whether the RWR (if any) warned him of the missile launch, citing sensitivity. He only reconfirms that he visually tracked the missiles. My guess is the F-117 may have a limited radar warning capability, but perhaps not in the relevant band. If he or the mission planners had detected and thus been aware of of the radar sites, you'd expect them to plan better routes to avoid the threats.
I leave you with a quote from Maj. Gen. Carlsons' (who flew the F-117) briefing on stealth fighters in 1999, shortly after an F-117 was shot down in Allied Force.

We started out a long time ago building airplanes that had low observable technology incorporated into their design. The SR-71 was an example of where we took the aerodynamic design and then added some radar absorbing material to the airplane to make it slightly stealthy. And I'll give you a representation of that graphically here in a minute. We went to the second generation of airplanes and you can see we designed that airplane, the F-117, essentially from the bottom up to be stealthy. It was crude technology. It was developed at a time when we didn't have the modeling and computer power we needed to make the kind of aerodynamic design that we would have liked, but we built one that we thought was very stealthy. And of course, the night that Desert Storm opened the quote from Col. Al Whitley still is famous in the Air Force: "Boy, I hope this stuff really works." And of course, you know that it did. That isn't exactly what he said.
Then we came to the third generation of stealth airplanes. We built the B-2. And of course, by that time, we had the modeling tools and the design tools and the computing power to make an aerodynamic design that was optimum. And this airplane is [a] much higher altitude, much better performing airplane than the F-117. We were able to eliminate a lot of the radar absorbing material from the structure. And by the time we got to the fourth generation, we were able to add supersonic speed, the agility of an F-15, F-16 class airplane and do that with no degradation to the stealth. In addition to that, we were able to add a number of apertures, in other words, openings in the airplane's surface for antennas, radars and other sensors. And in the F-22, as an example, there are over a hundred of those apertures on the airplane, where if we jump back a couple of generations to the F-117, there are essentially a couple of aperture openings and the rest of them we hide when we go into combat. [Emphasis mine.]

Some of the F-22's apertures...

Source
...whose functionalities were consolidated in the F-35's fewer apertures (some shown here).

The F-35's ASQ-239 EW suite, an evolution of the F-22's ALR-94, consolidates 30 senors down to 10.

[Apologies, pressed for time. This answer will be brief, unlike my previous 29,999 character response.]


Do aircraft have accelerometers? Do modern aircraft employ accelerometers or other similar equipment to measure g-forces on the aircraft? I could imagine this being used as an inspection/service indicator, particularly after hard landings. Or do hard landings and other forceful flight regimes typically not pose any significant structural concerns?

Update. Related on determining hard landing inspections:

From Aero Magazine on Boeing conditional inspections

Section on AMM changes:

  Boeing is modifying the 737 AMM, section 05-51, and will revise the AMMs for other Boeing-designed airplane models, to include these vertical acceleration values (table 1). For Douglas-designed airplanes, similar values are being generated and will be available in the AMMs in early 2001. The values are intended as thresholds that can be used to help determine whether a hard landing inspection is necessary. If the flight crew concludes that it has experienced a hard landing, the AMM conditional inspections should be performed even if the acceleration readings do not exceed the values added to the AMM. The vertical acceleration values are to be used by operators, in addition to or in lieu of flight crew judgment, to initiate conditional maintenance inspections.

Source: Aero Magazine

Most modern aircraft, which includes long range airliners since around 1970, all airliners since not much later, and basically anything with glass cockpit, do have very accurate accelerometers for all three axis, as part of the inertial reference system.

They are important instruments for the autopilot, as they provide faster feedback on the effect of control deflections than the air-data references, and essential for navigation as cross-reference for detecting GPS errors and the inertial navigation serves as a backup for GPS (and served as primary navigation over the oceans before wide GPS availability). Airbus (since A320) even defines the pitch command by vertical acceleration in the normal law. And yes, they are also used for detecting hard landings and their severity.

The pilot never sees the direct accelerometer output except in fighter and aerobatic aircraft though (well, almost never; there are a couple of other cases).


What are the takeoff and landing speeds of a Learjet 45? I am a fairly new enthusiast to flight simulation.

I would like to know what are the takeoff and landing speeds of a Learjet 45? If they are not fixed, what factors influence those speeds?

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

temperature,
density altitude
weight etc.

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

Learjet 45 Takeoff speeds; table from Learjet 45 AFM

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

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

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

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

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

Learjet 45 Landing Approach; table from Learjet 45 AFM

*Speed definitions from www.aerospaceweb.org


Can a jet engine be restarted after a catastrophic failure? I have a retired 747 pilot saying that a catastrophic jet engine failure could be restarted. I have little or no training, but I believe that the word "catastrophic" means that there is no recovery. My reference is the 747: The Jumbo Revolution documentary which is on youtube.com and cable TV.

I have no desire to dispute what a fellow retired 747 captain said, so I'm wondering if there was some miscommunication between you and the captain.
Or perhaps his definition of catastrophic is different than mine. My understanding of catastrophic would preclude any attempt to restart the engine.

During my time on the 747 I had three engine failures. One simply quit during descent, and I had the flight engineer restart it. One we shut down when the oil pressure started dropping precipitously. There was no thought of trying to restart it as that could well have trashed the engine. Neither of these two shutdowns was catastrophic.

However, on one occasion, shortly after takeoff from Lima, Peru, the #1 engine failed with a loud report, shaking the entire airplane. We were told later that the boom had been heard throughout Lima. The tower reported fire flaring out of both the front and rear of the engine for a few seconds.
After dumping fuel and landing, an inspection of the engine showed a lot of re-solidified melted metal on the inside of the tail cone.

That was a catastrophic failure.


Which supersonic airplanes use Pitot Air intakes? Which supersonic (fighter) airplanes use the simple Pitot Air Intakes / Normal Shock Inlets?
Two examples already seen here on Aviation.SE (one and two) are

Dassasult Rafale ($Ma \leq 1.8$)

Image Source
General Dynamics / Lockheed Martin F-16 C/D Block 30/32 Fighting Falcon ($Ma \leq 2.0$)

Image Source

Are there any more examples?

A pitot intake will decelerate supersonic flow in one single, straight shock, while a ramp or cone intake will do this in several oblique shocks. It takes its name from the pitot tube, which in turn is named after the French physicist Henri Pitot who invented it to measure flow speed.

The objective of an air intake is to supply the engine with a uniform flow of air at approximately Mach 0.4 to 0.5. At higher flight speeds as much of the kinetic energy of the flow as possible must be turned into a pressure increase. Doing so efficiently reduces the work of the engine's compressor and increases mass flow, and consequently thrust. A pitot intake will have the lowest mass and complexity of all intake types and is the preferred choice as long as the pressure recovery can be performed efficiently.

A shock is the only way to decelerate supersonic flow. While the flow speed tangential to the shock will not be changed, the normal speed component is reduced downstream of the shock, approximately to the inverse of the upstream Mach number. The bigger the jump, the higher the friction losses in the shock become, the air is heated instead of compressed and pressure recovery suffers. Generally, those losses are acceptable up to a maximum flight speed of Mach 1.6. The lower mass of the pitot intake will make it more attractive, while for higher speeds the deceleration has to happen over several oblique shocks which are triggered by a spike or a ramp ahead of the intake lip.

Therefore, all supersonic jets which were designed to fly at less than Mach 1.6 use a pitot intake for mass and complexity reasons. This includes the smaller US jets (F-100, F-101, F-102, F2Y, F-8, F-16) and their counterparts in the Soviet Union (MiG-19, Yak-27, Yak-38M), Sweden (Saab 32, Saab 35, Saab 37), France (Super Étendard), Egypt (HA-300), Taiwan (Ching-Kuo) or Korea (T-50).

Pressure recovery measurements from the YF-16 (source: "Fundamentals of Fighter Design", RAeS Lecture by Ray Whitford, Cranfield University). The loss in efficiency above Mach 1.2 (left; 1 on the y scale denotes full conversion of kinetic energy into pressure) is readily apparent. This is mitigated by the pre-compression from the forebody at increasing angle of attack (right). The result is higher efficiency just when it is needed most, namely in turning supersonic flight. The same trick is used by the Rafale, and the wing root does this pre-compression in case of the F/A-18 and the Ching Kuo.

Top view of the right XB-70 intake at Mach 3 (source: "Fundamentals of Fighter Design", RAeS Lecture by Ray Whitford, Cranfield University). At Mach 3, a single shock intake would be grossly inefficient. Now a cascade of ever steeper oblique shocks is needed, culminating in a last straight shock. A multitude of moving ramps is required to adjust the geometry for the actual Mach number, and the square geometry, which is required for this flexibility, makes the intake tube much heavier (it is a pressure vessel, after all!) than the round tube of a pitot intake.


What is engine power vs propeller thrust relation? Given:

speed 30 knots
engine power 70 hp at 5800 RPM
propeller 3 blades, diameter 14 inch, pitch 17 inch, at 2300 RPM
fluid density 1023 kg/m3

I know that each blade is basically one wing.  Calculating lift is extremely complex; even Navier-Stokes equations will not give an accurate result.
But can I estimate the  thrust this produces, for these values or in general?

Power P, stationary thrust T, propeller swept area A, and air density rho are linked by this expression, derived from first principles and momentum theory:
T^3 = 2 · P^2 · A · rho
That's the maximum power available assuming a 100% prop efficiency.
Things change if the prop is moving forward, as in a flying plane. With the forward speed component, the blades have their angle of attack reduced in proportion to that forward speed. The blades work as wings, and a wing profile has a coefficient of lift that changes with the AoA. Drag does also change with a growing AoA, Hence, for every section of a fixed-pitch prop's blade, there's an optimum L/D at a given combination of rotating and forward speeds that gives the best efficiency. For a fixed angular speed of the prop, there is a given forward airspeed at which the prop works with maximum efficiency, that efficiency –and hence the thrust– dropping asymptotically as the forward speed grows...
Concerning the power delivered by a propeller in forward motion, it's the product of the thrust and speed...


Is there a central database for all airline reservation information? So we are flying on a reservation that flies from LAX to NRT with United then from NRT to BKK on Thai Airways via a United codeshare. This reservation was booked through United's website. When the reservation was confirmed, I noticed that the E-Ticket number was the same for all segments of the flight, across both United and Thai. Is there any central computer system used by airlines that keeps track of information such as these E-Ticket numbers to prevent discrepancies during ticketing? I ask this because I am very curious how exactly each airline's computer system "talks" to each other and if there is some sort of established protocol for doing so.

The simplest answer is that United and Thai have a codeshare arrangement, so United booked a ticket on all 4 segments using its own reservation system. United's reservation system communicated with Thai's to reserve your place, and the ticket was issued by United.

that being said, there are a number of GDSs (Global Distribution Systems), which are multi-airline reservation systems, all of which communicate with each other. Complete information on GDSs can be found in Wikipedia.