What is the technical role of a flight attendant? Everyone knows flight attendants represent the airline for the passengers, and have a commercial role by distributing meals, selling goods, managing the entertainment system, and receiving complaints.

One of the well known glamour airline-clichés for flight attendants, circa 1960 (source).

Apart from this commercial role, they also provide the regulatory information about safety. But I feel there is more to know related to their technical role.

What are the non commercial missions or responsibilities of a flight attendant, what are they accountable for? did that role change over years? How are they trained? What is their career path?

I flew for a major airline as a flight attendant for 7 years.  The FAA requires flight attendants on board for the safety aspect of passenger service and sets the minimum number based on the aircraft's passenger capacity.  We usually flew with at least one more crew member than the minimum required by the FAA.

Our FAA mandated duties include safe boarding, including stowage of personal articles, arming the evacuation slides after the doors are closed, a safety briefing prior to departure, verification that the cabin is safe for flight, inflight enforcement of pilot instructions (usually return to seats and fasten seat belts), and to render passenger assistance as necessary for flight safety.  Same for pre-landing and de-planing.  First aid training (including how to deliver a baby in-flight) was rarely seen by the public.

Annually we would be required to attend jet recurrent training where we reviewed NTSB accident reports with an emphasis on cabin crew responses to emergencies, review of first aid and CPR techniques, re-testing of our knowledge of the location and how to use all the safety equipment on board, including life preservers, life rafts, and emergency slide procedures.  We were also briefed on any changes to FAA mandated procedures and tested on everything.

We were trained to be current on every aircraft the company flew so that we had maximum flexibility for our scheduling.  At the time I flew, this would have been B-727, B-707,B-757, B-767, DC-9, DC-9 stretch, and L-1011.  That meant we had to know the location of every flashlight, first aid kit, supplemental oxygen bottle, safety briefing kit, life raft, life preserver, safety exit, safety lighting, etc. for every aircraft type we flew.

The normal passenger service duties that passengers see such as food and beverage services, in-flight entertainment and generally trying to be accommodating, were in addition to the FAA required duties and were entirely up to the company's discretion to provide and train us for.

The FAA mandated safety aspects of flight attendant duties have become so integrated with the normal flow of a commercial flight they can go nearly unnoticed, especially for routine travelers.

And no, we weren't trained how to land a plane in case all the pilots got sick at the same time and passed out.


Would formation of the three planes benefit from increased distance of the ground effect? I know that the ground effect quickly diminishes as altitude above the ground increases, and it is roughly half of the wing span. Hence it can be used to fly more economically over water, but over ground normally would not be high enough.

I have envisioned two larger airplanes "helping" the smaller one in between by flying next to it as shown in the diagram. By idea, wings of the all three planes would form much longer "superwing" with the ground effect equal to the complete wingspan of the larger plane plus half of the wingspan of the smaller plane in center. This would be much higher than the small plane could do alone (half of its wingspan), maybe making possible to use the ground effect also over ground. The small airplane would then need less effort to fly, if it is, for instance, low on fuel.

Of course, the obvious problem is that the wings cannot "join", it must be some reasonable gap there to avoid the collision.

Would the central plane flying in formation as shown in the schema experience a stronger ground effect than flying alone?

I would think not; the ground effect comes from the wing pushing air down, which would not help the plane in the middle. If anything, I think the plane in the middle would be impacted by the wingtip vortices created by the larger planes, once out of ground effect (one wingspan above the ground) if the smaller plane did not stay ahead of the larger planes.
http://www.pilotfriend.com/training/flight_training/aero/wng_vort.htm

A position slightly behind, drafting like birds in flight do when they fly in V formation, might help.
https://www/ciencemag.org/news/2014/01/why-birds-fly-v-formation


Could the crew of XL Airways Germany Flight 888T not hear important chimes, due to the stall warning? I am intensively researching on XL Airways Germany Flight 888T at the moment.

I wrote and researched hours and hours. Now I would like to know something about the ECAM and the Airbus Stall warning:

The crew of 888T started a stall test with faulty AoA-Sensors. They wanted to test the stall protection system. At a point, the Airbus stall warning was played. A few seconds later, the control laws degraded to Direct Law. The crew missed this degradation and I just want to find out why.

I found out, a control law degradation is a level 2 ECAM warning. That means a single chime will be played. Can someone confirm this?

I also heard, the stall warning suppresses all other sounds, because a stall has priority over all other things. But I don't know if this also applies for the ECAM Sounds. Does anybody know if a stall warning really suppresses every sound?

When the stall has developed the aircraft is no longer in normal control law for any axis (see more in FCTM at OP-020. P 14):

As soon as the aircraft is outside the flight envelope, the control laws transition to abnormal attitude which is the combination of:

Roll direct
Pitch alternate
Yaw alternate.

This is something between alternate and direct, and is intended to allow the crew to recover from the abnormal attitude and reenter the flight envelope without being prevented by some protections.

A stall (an excessive angle of attack) is one of the conditions to switch to the abnormal attitude laws. You may read this article too, while on a simulation site, it is very well written. There is also a presentation on SKYbrary at Eurocontrol.

When the stall warning aural warning is active (voiced "Stall" and cricket), the crew is expected to know they are in abnormal law.

Reconfiguration in abnormal attitude law is indicated by different clues on the PFD (e.g. $\alpha$ prot and $\alpha$ max indication removed from the speed strip, and green = replaced by amber crosses).

Source

Source

and the master warnings are activated. The aural alert is a single chime, (level 2 failure confirmed in this report, page 25). The reconfiguration is also indicated on the ECAM, but the indication can be moved towards the bottom of the list if messages with higher priority arrive.

The law is reconfigured as direct when the landing gears are lowered.

Regarding the aural warnings associated with stall and law reconfiguration, they are audible at the same time, or are intercalated, but none cancels the other, as it was heard for AF447 and reported in this article (C-chord is the single chime):

  In sequence the alarms were sounding PULL UP, C-chord, STALL, C-chord,
  PULL UP, PRIORITY RIGHT.


How does wing sweep increase aircraft stability? I was told at one point that the sweep of a wing can help with the straight line stability of the craft, in fact I think it's one of the main systems that keeps flying wings flying straight (like the B-2 or N9-M, which comes from the 40s, way before the use of flight computers for stability...).

Why is that?  Are there trade offs between that stability and say, speed?  Is there a such thing as too much sweep?

Directional stability

When a swept wing is flying in a sideslip, the windward side behaves like a wing with less effective sweep $\varphi_{eff}$ and the leeward side like one with more effective sweep. Wing sweep  causes a flattening of the lift curve slope for two reasons:

The effective angle of attack is reduced by the cosine of the sweep angle.
Only the component of speed normal to the quarter-chord line of the wing is creating lift, so a swept wing creates less lift per area than a straight wing.

The increased lift rolls the aircraft, but also produces increased lift-induced drag which pulls it back to straight flight. The sketch above shows this for the flying wing glider SB-13. This effect is so strong that swept, high-wing configurations need anhedral to keep the sideslip-induced rolling moment down.

For completeness, also the side force $Y$ of fuselage and winglets is added and shows that the winglets help a lot to create directional stability. This is needed in case of the SB-13 because it has a nearly elliptical lift distribution. Using a triangular distribution (N9-M) or even a bell-shaped distribution (Horten flying wings) avoids the need for winglets, but causes higher induced drag in straight flight. Another downside is a low directional stability at high speed, because this sweep effect increases with the lift coefficient on the outer wing.

Longitudinal stability

Wing sweep also helps in longitudinal stability by stretching out the wing lengthwise. This is important for flying wings which lack a separate tail surface. By changing flap angles at the center or the wing tips, the lift at the most forward or most backward sections can be changed for pitch control, and more sweep increases the lever arm of these changes. Also, in swept flying wings natural static stability can be achieved without the use of reflex airfoils, but by applying washout. Again, the higher the sweep angle, the less washout is required.

Too much sweep?

Easily! Sweeping a wing creates lots of problems:

Sweep reduces the lift curve slope and the maximum lift of a wing. The maximum landing attitude with a highly swept, slender wing is severely limited by wing tip clearance, so swept wings need powerful high-lift devices.
Sweep causes the boundary layer to be washed outboard, which will cause nasty stall behavior once a specific ratio of wing aspect ratio and sweep has been exceeded. This can be somewhat limited by wing fences, but should better be avoided altogether.
Sweep changes mean that bending moments will partially get converted to torsion moments, requiring a torsional stiffening of the wing.
For flying wings, sweep will let the aircraft center pitch up and down when the wing flexes. This creates a powerful interaction between the fast period mode (which is only moderately damped in flying wings) with the wing bending mode, resulting in flutter.

Why sweep a wing at all?

Generally, an aircraft designer will allow only as much sweep as necessary.
Wing sweep reduces drag when the aircraft flies with transonic or supersonic speed. Now the Mach effects depend only on the normal speed component, so they are proportional to the cosine of the sweep angle. For the N9-M this was not a factor, however, the B-2 benefits from it with a higher drag divergence Mach number.


Mechanical vs Pneumatic Stall Warning Systems Light Cessna aircraft - at least the high wing single engine line - have commonly made use of a solid state pneumatic stall warning system.  The system is fairly unique to Cessna airplanes and makes use of the fact that negative pressures form over the leading edge of the wing near the critical angle of attack, causing a reverse flow of air through the warning system and causing a horn in the cockpit to sound.  Most other light aircraft make use of a movable tab with activates an electric switch when depressed by airflow near the critical AoA, causing a chime, horn or other aural cue in the cockpit alerting the pilot to an impending stall.  Here's the question:  What are the pros and cons of each of these systems?  From brainstorming, I can come up with the following:

Pneumatic Stall Warning Systems:

Pros:

Solid State; has no moving parts which can break or become immobilized or altered by neglect, damage or airframe icing.
Does not require electrical or other sources of power from engine or elsewhere to work.

Cons:

Orifice can become blocked by FOD or airframe icing, causing the system to become inoperative.

Mechanical Stall Warning Systems:

Pros:

Simple operating and mature technology.
Can be electrically heated to prevent immobilization by airframe icing, though this is not always the case depending on the aircraft.

Cons:

Moving parts which can break.
Tab can be bent by maintenance or neglect, causing system to operate erroneously and give false readings.
Can be immobilized by airframe icing, rendering the system inoperative.

Can anybody think of other pros and cons for each of these systems?

Electromechanical:

Pro - can be tested easily during preflight by turning the mains on and manually actuating the tab

Pro - Potentially lighter (although not my much)

Pro - easy to install multiple switches in parallel if you want to trigger based on a stall of differing characteristics as is done on the Piper Seneca

Pro - Easy to wire into other systems. Maybe you want to add a stick shaker or some kind of feed back to the autopilot, much easier if its already generating an electrical signal.

Pneumatic:

Con - can only be tested by creating a low pressure on the horn, not as easy as the tab option

Many of the above pros become Cons for solid state units, like being harder to connect to other systems with out a transducer, harder to add multiple units without multiple horns, and the weight.


Do airline pilots get to go home often to see their family and have a break from flying planes. If so, how many days? Do airline pilots get to go home to see their families often, and if so how long?

All in the contract, routes, and choices of the pilot within that contract. Some fly trips of up to two weeks, others are back home every night if they have a home near their base airport and work regional. Some choose to take all available work offered while others stay near the minimum.

Labor law limits total flying time per day and per week depending on crew size and time of the day.


How are "charter" and "passenger" flights defined in the AIDX standard? I'd like to know the difference between these flight types in the IATA AIDX standard; specifically, for use in fuel order notifications.

I know this question is 3 years out of date, but I thought I'd answer anyway. My answer is only applicable to Aviation Info Data Exchange (AIDX) schema 16.1.

As far as I know, there is actually no item in the format specifying the type of flight. But most systems I've come across have some coupled business logic that will make an AIDX request with the form of SheduleRQ and push this to a database.
If the flight isn't in the database it will make a further PublicStatus request to determine if the aircraft info should be shown to the public.

This might be a work around at the moment, but soon enough (2023-2025) AIDX will be integrated into AIDM and with all luck, unacknowledged requests will be a thing of the past.


Is there a rule of thumb for aircraft design? I'm wondering how to best scratch build an rc aircraft and what rough proportions the aircraft should be in.

I'm aware of the fineness ratio that determines the width to length ratio of a cross section of a wing should be around 1:3 or 1:4, but I can't seem to find similar rules for:

The distance between the wing and tailplane
The length of the wings

Am I just better off just making a scale model of an established aircraft instead of using these rules?

No, there isn't any single rule of thumb for airframe shape.  Just look at the huge variety of airframes that have been built and flown over the years.

One way to scratch-build is to start with a cardboard glider that's roughly the shape you want.  Tape the wings and tail to the fuselage in different places, tape on some noseweight, give it a toss, deflect the elevator, give it another toss, vary the dihedral, sweep, decalage.


To a pilot, does turbocharging differ from supercharging? When it comes to operating an aircraft, what are the practical differences between a turbocharged engine and a supercharged engine? I'm aware of the mechanics - turbochargers being exhaust-driven, while superchargers are mechanically driven - so I'm looking for the differences in how pilots need to treat the systems:

Do power settings need to be set differently?
Are temperatures more of a concern with superchargers?
Is it easier or harder to overboost a supercharger? If you do, are there waste gates?
Do engines with superchargers need a cool-down period before being shut off?
Any other operational differences that would be meaningful for pilots to know.

Similarly, what are the ownership implications of any differences? Does one cost more to maintain than the other due to the way they are constructed? Will a supercharged engine have a lower TBO because of the mechanical aspects of the system, or will it be the same as a turbocharged engine?

I have some of the answers:

•Is it easier or harder to overboost a supercharger? If you do, are there waste gates?

This is an important point.  Waste gates, when opened, allow exhaust to bypass the turbocharger, reducing manifold pressure by slowing down the turbo.  Older turbos had manually adjusted waste gates, and even fixed waste gates.  The pilot would have to monitor boost pressure and adjust the waste gate to avoid overboosting the engine.  Newer turbos have automatic waste gates.  Superchargers, being belt or gear driven, do not have waste gates as the supercharger is not dependent on exhaust gas flow.  I do not know if they have manifold pressure releif valves in case of overpressure but I doubt they would.

So a key difference in a pilot's operation of the engine is that in a manual waste gate engine, the manifold pressure gauge needs to be scanned frequently and the waste gate adjusted accordingly.   Less important in an automatic waste gate or supercharged engine.

•Do engines with superchargers need a cool-down period before being shut off?

No.  The cooldown period in turbochargers is necessary to cool down the bearings in the turbocharger after high cruise power settings.  Idling on the ground allows cooler oil to flow through the bearings, removing excess heat.  Look at your exhaust gas temperature gauge - this is the temperature of the gasses flowing through your turbocharger.  The oil present in the turbocharger bearings will "coke", or turn into a solid at that temperature.  Upon landing, a slow taxi to the ramp will usually provide sufficient cool down time.  Usually!  Time this and don't forget to cool down as recommended.

Superchargers are geared to the engine (or belted) and do not use the hot exhaust as their source of power.  So even though they can get quite hot, they don't approach the heat of the exhaust gasses.

•Any other operational differences that would be meaningful for pilots to know.

This is not really an operational difference, but in addition to turbocharged and supercharged engines, there are also turbonormalized engines.  TN engines are turbocharged engines with their boost limited to atmospheric pressure at sea level.  Say 30 inches, not the 40 inches you might expect from a turbocharged engine.  The TN engine permits sea level performance up to a critical altitude, above which the TN engine cannot maintain sea level manifold pressure.  In other words, performance at a sea level takeoff will not be materially different from that of a naturally aspirated engine, but as you climb, the power will not decline as you climb.  So your Leadville CO takeoff will be the envy of the stock C-172 crowd.


What are acceptable treatments for chronic pain that will not result in a loss of an FAA Medical? Is there an acceptable treatment plan for neuropathic pain? Gabapentin is not an acceptable drug. Lyrica and Cevalla aren't approved. Is there a treatment that could even get a special issuance?

The only real answer here is to consult an AME. I searched on the AOPA forums (members only) and the information wasn't encouraging: all current (as of 2014, which was the more recent relevant post I found) neuropathy drugs are disqualifying. AOPA's list of approved drugs does show some approved drugs for pain relief, but it looks like it's all OTC stuff.

But, the usual medical disclaimer applies here: every case is different so the above may be irrelevant to you personally; I'm not a doctor and I don't know what I'm talking about anyway; only an AME can give you meaningful information.


What alternative designs competed for the C-130 in the 1950s? Which manufacturers and aircraft entered the U.S. government design competition back in the 1950s in which the Lockheed C-130 was selected? Were they all clean sheet designs, modified versions of current aircraft, or unmodified aircraft already in service? Is there any documented history which states justifications for the Lockheed design?

The competing companies (ones that elected to compete anyway, more were invited) were Lockheed with two submitted designs, Boeing with one design, Chase Aircraft with three designs, Douglas with three designs and Airlifts Inc with one design. As far as I can tell, these were just designs and Lockheed won the contest based entirely on paper. The YC-130 was ordered and after performance was verified, it went into production in 1954.

It doesn't look like there is any public information on the competing designs since they didn't leave the drawing board. It is unlikely that any of them are "clean sheet" designs. The Boeing submission was probably (and this is a personal guess) based on the C-97 Stratofreighter. The C-130 itself looks to be an up-scaled version of the Fairchild C-123 Provider with design elements from the Chase XCG-20 (which was developed into the C-123).

I'm not sure what you mean by "justifications for the Lockheed design". Given that it is the United States military's most successful aircraft design ever, with 60 years of continuous service, I'm sure every design was driven by a contract or performance requirement. Here is a good article about the C-130 designer, Willis Hawkins that gives some insight into the project.

Most of this information was taken from the Wikipedia page on the Lockheed C-130 Hercules.


What modifications need to be made on an engine that normally uses AVGAS to utilize it with MOGAS? Asking just out of curiosity. What modifications need to be made on an engine, e.g. Lycoming O-360, that normally uses AVGAS to utilize it with MOGAS?

For any certificated aircraft engine, the type certificate will specify the required fuel. If the TC specifies AVGAS, using MOGAS will require an STC for that engine.
Developing a MOGAS STC for an engine is a complicated and expensive effort, so you're realistically limited to purchasing the rights to an existing STC. If there isn't an STC for your engine, you're likely out of luck.
The two most common STCs for GA piston engines are available from EAA and Petersen Aviation. Check their web sites for a list of engines covered by their STC.
Once you purchase the STC, it will include the installation instructions outlining the necessary modifications for your engine. In many cases, it's nothing more than placards and a flight manual supplement.


When can airliners fly from Israel over Tunisia's and Algeria's airspace? Per flightradar24, on August 25th 2019, an Air Europa Boeing 787 flying from Tel Aviv to Madrid flew over Tunisia's and Algeria's airspace.

I thought flights departing from Israel or flying to it are banned from the airspace of Arab countries that don't have diplomatic relations with Israel.

For example, flights between Israel and India fly around the south of the Arabic peninsula. Flights between Israel and South America fly north of the Gibraltar straights.

Does someone know how did this happen, if it is a one off or a change, who authorizes this. Maybe this can happen in case of bad weather or an unplanned contingency.

While I did not find an official source stating that such flights are forbidden from those two countries airspace, see here for an informal one: https://ops.group/blog/countries-with-bans-on-flights-to-israel/

Thanks

While Israel may be restricted from Middle Eastern Arab countries, North Africa is a bit different. The EASA has a list of countries they have a working agreement with, which includes both Israel and Tunisia

  As part of the process of creating a wider Common Aviation Area with its eastern and southern neighbours, the EU negotiated a comprehensive Euro-Mediterranean agreement with Tunisia which has been initialled on 11 December 2017.  This comprehensive agreement will result in an increase in the number of direct flights and boost trade and tourist flows between the EU and Tunisia.  Beyond market opening, the agreement also provides a modern framework and high standards for a wide range of aviation issues, such as safety, security, passenger rights, air traffic management, economic regulation, competition issues or social aspects.

As to Algeria (not in the EASA), the answer is probably more mundane: airspace fees

  Many countries use airspace fees as a form of revenue and, sometimes, as a form of leverage during political negotiations. This causes prices and routes to fluctuate, with airlines subject to different policies. Costs are, of course, transferred to travellers, while airspace restrictions can significantly limit the options available to certain destinations.

Algeria uses France's ENNA to collect their fees

  Overflying navigation fees are generally imposed by the country’s civil aviation authority (CAA) although some countries have other entities responsible for their issuance, such as the airport authority, or specialist local government bureaux. In Algeria for example, responsibility lies with ENNA, the National Enterprise for Air Navigation.

As such, Algeria doesn't want in Israelis in their country, but probably doesn't mind their money to fly over nearly as much.


Why does the cabin air sometimes smell of kerosene? Why does the cabin air sometimes smell of jet fuel, although bleed air is tapped before it comes in contact with fuel ? How is this possible?

I have smelled this a couple of times in my life (twice extremely irritating), mostly during boarding/taxiing but at least once also during the flight (although in that case I don't remember if the smell was already present before take-off and merely lingered on).

Apparently a similar observation was reported in Q25405 but limited to the taxiing phase, whereas I witnessed the smell when the plane was still connected to the PBB (and also in-flight with the caveat above). The root cause may differ.

EDIT:
Meanwhile, I have found a satisfying answer on the net, but cannot add it anymore since the question is closed:

  « You’ll occasionally notice a strong odor when the plane is on the
  ground – a pungent smell similar to the exhaust from an old car or bus
  that fills the cabin shortly after pushback. Usually this happens when
  exhaust gases are drawn into the air conditioning packs during engine
  start. The wind is often to blame, causing air to backflow or blowing
  fumes through the pack inlets. It normally lasts only a minute or so,
  until the engine is running and stabilized. It’s unpleasant but little
  different from the fumes you occasionally breathe in your car while
  stuck in traffic. » (source)

(Notice that in my cases it lasted definitely much longer than "only a minute or so".)

You might have been smelling cooked turbo oil.  Leaking seals can potentially allow oil traces into the compressor bleed discharge, especially on auxiliary power units.  The other possibility is cooked deicing fluid, which is quite common.

Turbo oil and deicing fluid are the two major sources of petrochemical cabin stink.

Another possibility would be an APU with stalling/surging problems where there can be backflow into the compressor end of the motor from the burner can, which will admit burner can gasses into the air conditioning system.  If it is really kerosene you are smelling, that is the probable source.

It could be coming from the main engine but there would likely have been audible rumbling or thumping sounds if it was stalling/surging while on main engine bleed.


Why should I not use a "lifting tail" on my ultralight design? In my misspent youth I designed and built many rubber, gas, and RC models. When I wanted good climb and glide I used a aft CG [60 to 80%] and a lifting tail. I had no stability or control problems, though CG was critical. I'm a 75 yr old retired air traffic controller, pilot, flight instructor, A&P mechanic who would like to get his feet off the ground again with a flying wing or tandem wing ultralight.

I don't need speed, but I would like to climb in thermals and ridge lift.  So far a flying wing like the Monarch with 15 to 20hp and a wing loading under 4.5 lbs/ft. and a span of 30/40ft sounds good.  With two lifting surfaces I might keep span under 25ft with a good aspect ratio. Please try to keep answers in laymen's terms.

You can use a lifting "tail" for any plane design but it will depend on the design. The only requirement for a naturally stable flying aircraft is that it must have a reasonably good positive static margin. And for that to happen the rear flying surface must have a lower wing loading than the forward flying surface - this does not necessarily mean downforce though that's an easy way to comply with the rule.

In one extreme case you must use a lifting "tail" or the aircraft would not have enough lift to fly. These are canard planes such such as the Rutan Long-EZ. Now, you may make the argument that the thing at the back is not a tail but a wing. Yes, if you were to insist on classifying planes by rigid categories then the rear flying surface of canard planes are normally called "wings" but this mindset will make one blind to what really happens to aircraft stability as you change the planform design.

CG placement, forces on the tail and planform

The correct CG placement for stability depends on several things including the distance between the wings and stabilizers and the airfoil of the wings but the dominant factor is the relationship between the area of the wings and the area of the stabilizer.

Most full-scale aircraft including ultralights tend to have very small stabilizers:

In this configuration the stable range of CG is usually between the leading edge of the wings and the midpoint of the chord. Typically this manifests itself in the rule of thumb of between 25% to 33% of the chord but for actual values you need to calculate the CG based on your desired static margin.

You will notice that most model planes tend to have larger stabilizers. This is especially true for non-scale models and even more so for free-flight models:

In this configuration the CG for the same static margin (stability) appears to be quite far back. In most cases it is 50% of the chord - right near the middle of the wings. It only appears that way compared to full-scale planes or scale models. Aerodynamically the CG placement gives exactly the same level of stability.

This is when some planes can start to be trimmed with a lifting tail. Some real-world planes with large tails such as the Avro Lancaster may in some conditions fly as if the tail is lifting.

As you increase the size of the stabilizer further the CG for stable flight shifts further back:

This is commonly seen in free-flight duration models. Almost all planes with such planform have a lifting "tail". It is rare to see a real plane with this planform however there is one very famous design where you can obviously see the lifting tail - the Pou-de-Ciel:

(Note that the original design of the Pou-de-Ciel has a catastrophic fault where the rear wing interacts with the downwash of the forward wing - later revisions moved the wing back several inches - DO NOT BUILD THIS unless you know all the issues)

If you change the relationship between the forward and rear lifting surfaces further you will end up with a tandem wing. If you've been following the trend at this point I think you can see where this is going: yes, the CG moves even further back:

The typical CG for tandem wings is completely outside the forward wings and sit between the forward and rear wings. Remember, all the planforms so far including this was calculated to have exactly the same static margin - they are all similarly stable.

All tandem planes have both forward and rear flying surfaces configured to be lifting.

Tandems are less rare in manned airplanes than the almost-tandem configuration above. The most well known is probably the beautiful Rutan Quickie:

As we progress with changing the relationship between the forward and rear flying surfaces we will eventually end up with the canard configuration:

Canards obviously have a lifting rear flying surface. So much so that people instinctively refer to them as "wings". And the CG moves further back still (in relation to the forward flying surface, obviously it is in front of the "wings").

TL;DR

As you can see, weather or not your tail is lifting or generates downforce is not simply a choice you make. In some instances you will be forced to make your tail lifting. In some instances it will depend on your current maneuver. It all depends on the design of your plane.

Side note: Why most planes have (relatively) tiny stabilizers?

There are two main reasons why most designers chose to make the tail small:

First is to reduce weight in the tail. The larger the tail the harder it is to get the weight distribution right for the correct CG. Note however that this is mostly due to most designers using conventional wisdom because as we see above if you make the tail large enough you can shift your CG further back for exactly the same stability.

But this leads us to the second reason: to reduce drag. The larger the tail the more drag it generates. Tandems are the worst-case scenario where both the wings and "tail" generate the same amount of induced drag. However several designers such as Burt Rutan have taken advantage of the characteristics of tandem wing planes to produce very efficient designs.


Why aren't larger airliners such as the A380 more efficient than smaller ones? A recent Washington Post article, titled "Five myths about air travel" noted:

  The difficulty is that economies of scale don’t always work for airlines, because planes generally don’t increase in per-passenger efficiency as they grow larger. In fact, many of the most efficient planes of today are the smallest ones. At a transatlantic distance, a 525-seat Airbus A380 has an efficiency of 74 miles per gallon (mpg) per passenger, while the brand-new 168-seat Boeing 737 MAX 8 reaches 110 mpg per passenger.

This seems counter-intuitive. All other things being equal (and transatlantic distances would equalize many of them) -- shouldn't the larger plane should be more efficient?

This whole article notes the "myths about air travel" and I have to admit that I'd always believed that larger planes were more efficient per passenger mile.

Perhaps there is something unique to the the A380 and 737-Max 8 that makes the comparison incorrect? Is it related to aircraft utilization rate or percentage of seats filled -- although these wouldn't be a factor in the mpg per passenger metric?

Note: I am not interested in crew or ground staffing efficiencies realized by a mega plane. Just fuel.

The comparison is seriously flawed.
While over the entire duration of the flight the larger aircraft is more efficient per passenger/mile, this is not the case for the flight phases that cause the bulk of the fuel consumption for smaller airliners but only a fraction for larger airliners: takeoff/climb and descent/landing.

A 747 or A380 flying a one hour leg, which is typical for many smaller airliners, would use more fuel per passenger over that leg than does say a 737 or A320, despite being more fuel efficient at cruise altitude (if it can even reach its optimal cruise altitude over that distance).

It is also far less flexible, and requires a higher passenger density than does the smaller airliner, a passenger density that's simply not there on most routes unless you greatly reduce the frequency of flights (in which case you'd best hope all your competitors do the same as passengers are less likely to be happy to wait for your one flight a day at noon when they can get to their destination at 8AM taking another airline's flight).


Why stirring the cyclic helps in stuck left pedal? In demonstrating stuck left pedal from a takeoff with my instructor yesterday when starting a nose left turn he had me stir or move the cyclic clockwise in small steady circles and pump the collective. It did slow the spin down significantly but I just don't understand why.

Any thoughts or comments would be greatly appreciated.

The R22 has an anti-clockwise rotor. The more torque the rotor exerts, the higher the clockwise torque on the helicopter will be: nose right. With a stuck left pedal the nose wants to turn left, so we want the rotor to exert more torque.

On pumping the collective: there is an effect of how fast the collective pitch is raised, on the torque exerted. The figure below shows $C_T$ (a dimensionless measure of rotor torque) against time for a full sweep of the collective from full down to full up. Rapid deflection causes a torque overshoot, so a higher torque than a slow deflection.

So if the collective is raised fast and lowered more slowly, a net torque increase is generated while lowering the helicopter. Picture source: Helicopter Performance, Stability and Control by Raymond Prouty

On rotating the cyclic: cyclic pitch deflection causes angle-of-attack variation of the rotor blades, with an associated variation in blade drag, and therefore rotor torque. There is a section on this effect in the book Principles of Rotor Aerodynamics by J. Gordon Leishman (section 8.15.7 Unsteady Axial Force and Airfoil Drag). What I can distill from this chapter is that stirring the collective clockwise creates more airfoil drag, while keeping the net movements fwd/aft and left/right neutral. Unfortunately the section does not contain any helpful diagrams.


What is the procedure to climb and level off using a Bendix/King KAP140 autopilot? What's the procedure to use the Bendix/King KAP 140 autopilot in the Cessna piston singles to climb to a certain altitude and then capture it and level off?

Only the KAP140 two-axis autopilot with altitude preselect supports capturing a preselected altitude (which is the one installed in the Cessna 172 before the introduction of the Garmin GFC700)

Preselect the desired altitude using the altitude preselect knob, switch to VS mode, select the desired VS and the AP will switch to altitude hold mode when the preselected altitude is reached.

Taken from the manual.


Why is the horizontal stabilizer forward of the vertical stabilizer on the P-51? Why is the horizontal stabilizer forward of the vertical stabilizer on a P-51? Are there other airplanes that are like this?

(Source) Corsair top, P-51 bottom.

The noticeable difference above is the taller rudder of the P-51.

A taller rudder is needed for a shorter lever arm (distance between empennage and wing) and/or the need for more yaw authority.

And as @Gerry pointed out, another benefit of having part of the rudder below the elevator line is for spin recovery when the horizontal stabilizer is stalled and sending its wake upwards. The alternative is like the Corsair, with the rudder ahead and clear of the horizontal stabilizer.

Is it unique? No, a Cessna is shown below:

Related: How many versions of the P-51 dorsal fin fillet are documented?


Why did my flight climb so sharply on takeoff? I was on a Ryanair flight this morning that seemed to perform an incredibly aggressive takeoff from London Stansted on a 737-8.  Takeoff was fairly fast, but the climb was the steepest I ever encountered.

For context, we were taking off from runway 22, with wind 34 kt from the South/Southwest gusting 51 kt

Your flight took off during a storm. During a storm, the wind speed close to the surface of the earth is much lower than the wind speed a bit higher up. This variation of wind speed over a short vertical distance is called wind shear. The aircraft is taking off into the wind, so during the initial climb the headwind increases. Increasing headwind during climb does miracles to the climb rate.

Suppose you want to climb from sea level to 2000 feet while increasing the true airspeed from 140 to 160 knots (70 m/s to 80 m/s).  In steady wind conditions that means the aircraft needs to accelerate 20 knots during that climb, which consumes part of the energy available from the engines.

But if there is a windshear and the headwind is increasing by 30 knots during that climb (not unreasonable in stormy conditions), the ground speed will reduce by 10 knots. Instead of needing to add kinetic energy, the aircraft needs to reduce it by converting it into potential energy (altitude). This means more energy is available for climbing and thus the climb rate is higher.

The wind reports from the airport at the time of take-off showed a wind of 29 knots (39 knots gusts), almost straight down the runway.

If you look at the wind profile this morning (I could not access yesterday's data anymore) you see that the wind increases from 20 kts at the surface to 51 knots at 3000 ft. That's a lot of free airspeed the aircraft gets during climb!

 source: screenshot from windy.com

 source: screenshot from windy.com

In addition, the effect of a stormy headwind is that the ground speed is relatively low. This makes the climb much steeper than in the no-wind condition.

Looking a bit closer at the raw data from FR24, the aircraft took off at 131 knots groundspeed (the first airborne report is 25 ft above the runway). 6 seconds after the first airborne ADS-B report, the altitude had increased by 525 ft. Even if we conservatively assume it took 7 seconds to climb to 500 ft (round-off errors), it requires a vertical acceleration over 1.6 g to achieve that. That must have felt very aggressive!

The first 2000 ft of climb took only 25 seconds, an average of 4800 ft per minute. The ground speed reduced to 119 knots by the time the aircraft had climbed 2800 ft, 37 seconds after take-off.

After that, the aircraft had climbed through most of the boundary layer of the earth and the windshear reduced. The rest of the climb was fairly typical.

It was not only your perception; by all means it was an impressive take-off performance for a B738


What is the minimum possible number of hours required to carry passengers? Not factoring learning curve, personal safety minimums, and pilot proficiency, what is the absolute minimum flight time that must be logged in order to carry a passenger in a piston engine aircraft in the United States?

I'm am looking for an answer for the airplane category. Not gliders or ultralights.

I believe the answer, at least in the US is 20 hours of flight time, plus however long a checkride takes. A sport pilot can carry a single passenger and the minimum requirements are outlined in 14 CFR §61.313:

If you are applying for a sport pilot certificate with [...]
Airplane category and single-engine land or sea class privileges,
Then you must log at least [...]
20 hours of flight time, including at least 15 hours of flight training from an authorized instructor in a single-engine airplane and at least 5 hours of solo flight training in the areas of operation listed in §61.311,

If a sport pilot applicant logged exactly 20 hours, got signed off, and then passed their checkride on the first attempt... they would be able to fly passengers as soon as they completed the checkride. That means, realistically, probably 21 to 21.5 hours.


How to keep a helicopter steady when close to the ground? I understand the ground effect and the air cushion of approximately 3-6 inches when the helicopter is close to the ground. With that in mind, my questions are:

Why does the helicopter become inherently unstable when close to the ground?
What are some methods to keep it smooth when operating close to the ground?

The ground effect can be seen as an increase in air pressure underneath the lifting surface because the down-flowing air cannot stream through the ground. An image from this book::

In the hover, the down streaming airflow is pretty docile, with turbulent whirls only occurring in the transition to forward flight in ground effect. Full scale helicopters are inherently unstable with an eigenfrequency period in the order of a couple of seconds, and the instability gain is not really affected by the ground effect: amount of lift is kept relatively constant by pilot action, and ground effect mainly reveals itself as a reduction in induced drag.

So for full scale helicopters, pitch/roll controllability of the helicopter does not change (much) in ground effect. Depending on objects on the ground and the slope of the terrain there can be changes in trim as the pressure increase influences the horizontal tail for instance, but these do not fundamentally change eigenfrequency period.

For model helicopters, hovering in ground effect is a much more difficult task: the recurring blade period brings on a temporary pressure increase from lift creation. From Prouty:

  The wake in ground effect is not really a steady flow, as is assumed by the theory, but a flow with large-scale fluctuations that can be felt as gusts by an observer standing near the helicopter. Reference 1.21 speculates that these fluctuations are associated with the vortex that is made up of the individual vortices from the blade roots. This vortex apparently writhes like a pinned snake along the ground, causing the entire wake to shift and wobble.

Since scale models have a higher revolution than full scale helicopters, the frequency and distribution of these vortices may be what causes higher instability for hovering.


What are the physical laws for upscaling an RC model to 1:1? What are the laws of physics for upscaling an RC model from a smaller to larger scale or even to a full sized 1:1 aircraft? I guess the basic thing may be lift/weight ratio which was nicely described here:

  ... when you scale an airfoil up, the lift it produces increases with
  its area, which grows with the second power of size, but its weight
  increases with volume, which grows with the third power of size.

The above means the lift/weight ratio is worse for bigger vehicles which I guess makes them fly worse (less range, higher fuel consumption).

Are there any more laws to be taken into account for such upscaling? I mean in terms of aerodynamics or power source (battery/fuel) etc. Does the air behave differently with scale? Do different laws apply for different aircraft types (plane, helicopter, quadcopter etc.)?

This is not a full answer: much is mentioned by Michel Touw, but I'd like to correct a common misconception.

The mass growing as the third power of linear dimensions applies only to solid objects. But the airplane is not solid; rather, it's a thin-skinned frame. (Unless it's a solid foam RC model). Therefore, its mass should grow with the area, as the square of length.

However, this is, of course, not quite true. In reality, you need thicker skin, thicker spars, etc., and these elements will get heavier 'properly' with the cube of length - and even more, because they'll need to support themselves as well, with their added mass.

In the end, the mass of airplanes grows between the second and third power, and much closer to second.

Let's take B734 and B772 for example, which differ close to twice in linear size. Their empty weight (roughly 33 and 140 tons, depending on modification) differs by 4.25 times, which is approx. 22.1. MTOW has a similar ratio: 68 vs 300 tons, 22.15.


Is the twin vs quad engine industry preference really challenged? This question relates to this article at Leeham, essentially this article challenges the concept that twin engined airliners are more efficient than quad engined. However the article fails to show the data and prove the arguments. My question is asked to those who are able to confirm the arguments of the article. I will describe my argumentation and formulate the specific answer at the end.

Essentially, in the industry it is preferred to use twin engines vs quad engines based on the following arguments:

Twin engines have less maintenance cost (2 vs 4).
Less aerodynamic interference and weight.
Less cost (4 enginers are more expensive including systems for the same power)
However less bypass ratio for twin engines and overdimensioning due to compliance with the take-off certification at engine failure.

Netly, twin engines win against quad engines except in the past for ETOPS certification.

Ok, previous statement is my understanding of the trade-off between twin and quad. The article argues (using always seat mile costs) the following:

Little efficiency between B777-200ER and A340-300 / A380-800.
4 CFMs engines or A380-800 4 engines have less maintenance costs than B777-200ER 2 engines. Fleet of CFM is higher as well.
Argues that B777-200ER requires more powerfull engines. This argument does not contribute, as finally is an efficiency driver and the important is the first argument.
Previous comparisons are not valid to previous low bypass engines.
Article is not introducing airplane cost in the comparison (important for capital costs)

So, my explicit questions are the following:

Can somebody demonstrate with evidences that the efficiency of B777-300ER is lower or higher than A340-300 or A380-800?
Can somebody demonstrate with evidences that the maintenance cost of the engines of B777-300ER is lower or higher than A340-300 or A380-800?
Can somebody support further my arguments or support the article?

Why would Airbus go to the effort of developing the A330 when they could offer the A340? Both have the same airframe and differ mainly in the number of engines. With ETOPS requirements at the time of development (when they were known as TA9 and TA11) being just 2 hours (ETOPS 180 operations were only begun in 1989), the only reason for developing the 4-engined variant was its capability of flying long overwater routes.

The time it takes to check an engine is the same regardless of size, so having only two of them saves time and money. In addition, the higher power reserves of a two-engined aircraft allow for higher climb speeds and enable it to reach the most efficient cruise altitude faster.

Today, most airliner engines are no longer owned by the airlines, but leased from the engine manufacturer. They offer a simple thrust per hour model where the airline knows exactly how much the engine will cost them over time, maintenance included. The only open issue is how long the airliner is grounded due to unforeseen maintenance, and with four engines per aircraft the number of unforeseen snafus is twice that of a twin.

At the same time, the airline is in the best position to judge how expensive a seat-mile in any of their aircraft is. Engine cost can be calculated very precisely, so every airline should have a very clear picture of how expensive their twins and four-engined aircraft are.

There is a small chance that the geared turbofans which are now being introduced will give the A340 an edge over a twin variant. The higher thrust class of large twins makes a geared fan currently impossible, so a four-engined aircraft will have an edge because it can use a more advanced engine.


Why can't turbojets or turbofans be overtemped or overtorqued the way turboprops can? Turboprops that aren't FADEC controlled can be overtorqued or overtemped if the power lever is moved too far forward yet I have never heard of a jet that can't be "firewalled", FADEC or not. Why is this?

You certainly can. The equivalent to overtorquing is called overboosting and is defined as an exceedance of the primary thrust setting parameter, N1 or EPR.

Modern FADEC engines contain software protection, but it is certainly possible in mechanically controlled engines. Thus, older aircraft, such as the DC-9 have mechanical or electronic controls which set N1/EPR bugs depending on flight condition and outside temperature.

EGT exceedances are also possible. Many, if not most, modern FADEC turbofans do not have EGT protection in normal operation so pilots do need to keep an eye on the EGT gauges during high power situations, especially when ambient temperatures are high and the engines are worn.


What pilot safety features and equipment are on an A380? What safety features and equipment protect the pilots (not, protect the plane) in the cockpit on a Airbus A380?
For example I know they have life jackets: but I wonder what else?

I think Saftey guy asks about features like the escape hatch from the 747. Probably there is something similiar on the A380:

I think that I can read the label Escape Rope on the cover of at the top right. You can look around inside the cockpit here.


How does the V22 Osprey manage such high rotor speeds without shock waves? I read somewhere that the engineers presented an ingenious solution to the rotor tip shockwave problem, except the article didn't actually explicitly mention it.

So, does anybody actually know if such a solution even exists ? And if yes, what is it ?

The Osprey's engines drive the rotors at 412 RPM in heli mode or 333 RPM in forward-flight mode, according to this article. With a rotor radius of 5.8m, that puts the tip velocity at 250m/s, or about 75% the speed of sound, at the higher RPM. So they aren't near supersonic yet because the blades are short enough.

But there is a possibility of reducing blade length for higher forward speed and RPM, and there is research into how to make that possible on-the-fly:

  Helicopter performance depends on the length of the rotor blades. For heavy lifting, a large rotor works best, but short blades reduce drag and ultimately allow for higher maximum speeds. Farhan Gandhi, a Penn State University professor of aerospace engineering, has devised an elegant, simple way to achieve both configurations in the same aircraft, using the same rotor.


What are these protruding elements from SU-27's tail? I recently saw in person SU-27 belonging to the Ukrainian Air Force. I spotted some protruding elements from its tail and I'm wondering what are they called and what do they do?

I believe that these are static discharge wicks.  You can see similarly sized/shaped wicks on a 1/32 scale models of the SU-27, as discussed here, but, more importantly, you can find them labeled with number 53 on the cutaway drawing below.  The label is written as Разрядники статического злектричества, which, according to Google Translate, is "ESD arrestor" (or static discharge wick).

These are distinct from the shape of the wicks found on most GA aircraft in the US (just a straight stub of wire, potentially with some insulation around the base), but, as discussed on Aerospaceweb, the shaping of the wick (particularly the inverted cone shape shown here) contributes to increasing the gradient in the electric field from tip to base of the wick.  This encourages accumulated charge to migrate back into the atmosphere from a controlled point and decreases interference with on-board electronics and radio systems.


How do you calculate the lift coefficient of an airfoil at zero angle of attack? Thin airfoil theory gives $C = C_o + 2\pi\alpha$,  where $C_o$ is the lift coefficient at $\alpha = 0$. However, I couldn't find any equation to calculate what $C_o$ is which must be some function of the airfoil shape. In other words how do you extend thin airfoil theory to cambered airfoils without having to use experimental data?

This is my own attempt, I made this airfoil model of the lift coefficient of the airfoil at zero angle of attack for a project I am working on. It's derived from a Joukowsky transform. it seems to work but how is $C_o$ actually calculated?

Because it is derived from the Joukowsky transform of the inviscid potential flow around a cylinder it's more accurate at high Reynolds numbers.

The solution and the approximate solution to zero-lift angle of attack from thin airfoil theory can be found in ESDU 98011. The derivation of an analytical solution can also be found in Anderson, Fundamentals of Aerodynamics. $C_{l_0}$ can then be found by multipling it with $2\pi$.

Edited to add classical thin-airfoil result:

$$C_{l_0}=2\int_0^\pi{\frac{dz}{dx}(cos\theta-1)d\theta}$$
$$x=\frac{1}{2}(1-cos\theta)$$

$x$ is the chord line coordinate from 0 to 1; $z$ is the mean camber line height at coordinate $x$, normalized to the chord length; $\frac{dz}{dx}$ is the curvature of the camber line.

Now you just have to numerically integrate to get the lift at zero incidence.


What is the use of this remove before flight cover on the nose of a Bombardier Global 6000? I recently saw a Bombardier Global 6000 at my local airport. I was just wondering what the use of this circled remove before flight cover on the nose of the Bombardier Global 6000 is. I never saw such covers before on a aircraft. What is the cover covering and why are the 3 ones connected with a wire?

(Own work)

These covers are used to keep foreign objects away and out of the air data sensors, pitot tubes, static ports and Angle of Attack sensors (large red covers) while the aircraft is resting on the ground.  Blockage or damage to these sensors by foreign objects prevents the aircraft flight control computers and instruments from collecting accurate data and could be disastrous in flight, especially in instrument conditions.  The wires are essentially a leash to hold the neoprene covers together in a group and both prevent their loss during storage and ensure that all covers are removed from the sensors during pre-flight.


Did Boeing or Lockheed ever seriously consider releasing a widebody airliner powered by low-bypass engines? During the 1960s race to build the first widebody jetliner, each of the three major engine manufacturers was racing to put out a high-bypass engine for one of those jumbo jets:

Boeing went with Pratt & Whitney’s JT9D for their 747.
Douglas (which soon became McDonnell Douglas) chose General Electric’s CF6 to power the DC-10 (Airbus also chose the CF6 for the A300 when they jumped in a couple of years later).
Lockheed, for the L-1011, put their money on Rolls-Royce’s RB211.

Of the first three widebodies, only the DC-10 (whose power plant was a fairly straightforward conversion of the TF39 used on the C-5A Galaxy, which had been the first high-bypass turbofan ever to enter production) escaped being held up by engine difficulties; the L-1011 was held back for years when the RB211 ran into serious delays which allowed the DC-10 to beat it to market and strangle the TriStar in the schoolyard, 1 nearly bankrupting Lockheed in the process.

What isn’t as well known is that Boeing experienced delays of similar severity with the JT9Ds that were to power the 747; for a long while, there were rows upon rows of 747s sitting on the ramp at Boeing Field, complete but for having concrete blocks hanging from their pylons in place of the engines that could not yet be trusted on a production airliner.  Only Boeing’s massive head start enabled the 747 to beat the DC-10.2

Did Boeing or Lockheed ever seriously consider releasing an interim widebody with low-bypass turbofans (for instance, a 747 with eight JT8Ds mounted two to a pylon in conjoined pods, B-52-style) while they waited (and waited) for the high-bypass engines to become ready?

1: It wouldn’t be accurate to say that it strangled the TriStar in the cradle, given that the L-1011 did, in fact, manage to enter production and sell 250 aircraft.

2: Enabling Boeing to remain solvent in the process, as Boeing, like Lockheed, had bet the farm on their jumbo jet.  Unlike Lockheed, they didn’t lose it; however, if the 747 had been a failure, it would have bankrupted Boeing.

I am not aware of any manufacturer making a serious proposal to develop a jumbo jet with low bypass-ratio engines. Most airline manufacturers tend to develop a plane from  customers requirements, whether that customer is military or civilian. Civilian airlines in the late 1950s were already nervous about the much higher costs for jet-powered aircraft and there was no call at this time for an even larger plane.

To get the most value for their development efforts, airplane companies tend to look at if they can develop a commercial and military version. As an example, Boeing tries to develop a commercial variant to all of their military planes and vice versa. Starting with the Boeing 307 Stratoliner and continuing with the the Boeing B-52 Stratofortress and the Boeing B-47 Stratojet, Boeing worked to develop a passenger variant as well. There was discussions with making the B-52 into a passenger plane, but commercial airlines were not interested. Some of the reasons were the the hull was very narrow, much of it un-pressurized and in many ways, it  would have been ill-suited for passenger use. The plane would have had identical engines to the B-52. I could not locate any drawings of what it would look like. The push for a passenger plane became the Boeing 367-80, which developed into the Boeing KC-135 Stratotanker and the Boeing 707, which entered into service in 1958.

Lockheed had it's hands full with fulfilling orders for the Constellation. It developed some great military planes, but never pursued a passenger jet until the Lockheed L-1011 TriStar which first flew in 1970.

After World War II, Douglas lost a lot of military business and was forced to scale back. It's first jet that became a passenger jet came out of the development of a tanker for the Air Force that eventually became the Boeing KC-135 tanker. The reason they developed the Douglas DC-8 was that Pan Am ordered 20 of them and they could see the future was jet-powered.

The next big jump in airplane size came out of a development effort by the Air Force. In 1964 they asked Boeing, Douglas, General Dynamics, Lockheed, and Martin Marietta to develop a prototype for the CX-HLS cargo plane. This was much larger than anything that existed at the time. In this proposal, the Air Force was asking for high efficiency engines as well as the ability to carry a lot of weight. The two final prototypes became the Lockheed C-5 Galaxy and the Boeing 747.

By this time, the age of low-bypass-ratio engines was over because of the much better efficiency available in newer high-bypass engines.


Where to find the parking coordinates of the aircraft in the Apron? Is it possible to find out the coordinates of where the aircraft park in an the Apron? I mean some sort of list for each terminal or aeronautical chart.
I was thinking about the AIP (Aeronautical Information Publication) but i could not find it.

The airport charts usually contain the coordinates of all parking positions. The charts that are available from the FAA AIP (e.g. here for JFK) only contain a single ground chart with the airport diagram:

These do not include the coordinates. But my Jeppesen charts contain coordinates for all parking positions. E.g. some gates at JFK:

They can either be found in dedicated charts for airports with many gates (like JFK shown above), or they are included on the airport overview chart for smaller airports with fewer gates.

Aircraft navigation databases also typically include the positions, so the Inertial Navigation can be initialized with a position based on airport code and parking position.

As far as I know, there is no free resource that would list the coordinates though.


How do you maximize an electric engine's thrust? I've been recently looking for answers to this question on the internet but the jungle of propellers, fans and electric motors didn't quite get me an answer.
How would I have to design an electric engine to produce as much thrust as possible on an area as small as possible, so the thrust/area ratio should be high. Also, assume there's enough power available.
Would I use propeller and if so, how many blades?
Would I use a fan like the turbofan of a jet engine?

With the optimal solution, which thrust do you think a 500 mm prop/fan could produce?

Generally, if you want to optimize for area/diameter (without the complexity and weight of the many/multi stage option mentioned in comments to the question), you'll want to use a ducted fan (roughly similar to the fan on a turbofan).  Not only do you avoid tip losses due to the end plate effect of the duct (if the clearance isn't excessive), you can run the fan at arbitrarily high speed, even with supersonic tips, without the extreme drag and noise production of an open propeller in such a regime.

Look at the design of EDF (Electric Ducted Fan) engines used to simulate jets in small radio control models; some of these can product thrust comparable to fans driven by high performance methanol/nitromethane glow engines (15-25 kW/L displacement, with 10 cc, 1.5 kW engines driving fans 15 cm diameter), with 10-20 minute flight duration on a charge with light enough batteries to fly well.  Scaling these up to 500 mm diameter will generally require shortening the blade chord relative to diameter, and you'll need to optimize pitch for the combination of rotation speed and torque available.


To which security domain does the Cabin Intercommunication Data System (CIDS) belong? I've read a lot about Cabin Intercommunication Data System (CIDS) functionalities and features, but yet it is not really clear to me if CIDS is part of the Airline Information Services Domain (AISD), or the Passenger Information & Entertainment Services Domain (PIESD).

Does CIDS receive information/messages from the Aircraft Communications and Reporting System (ACARS), and if so, through which ARINC protocol, and does it have any kind of connection to the Aircraft Control Domain (ACD)?

As the commentators above pointed out, there are some issues with your question due to the concepts involved.

As @Bluephoenix mentioned, the security domains are defined in ARINC 664 Part 5. These domains specifically apply to ARINC 664 networks, though the concepts can be applied to other networks.

You also reference a Cabin Intercommunication Data System (CIDS) which is an Airbus specific system in the A320 series -- which does not have an A664 network. But we can look at its functions to see which domain would apply if they were implemented on an A664 network.

The A664P5 descriptions are:

  Part 5 describes the objectives, characteristics, services and
  functions that should be satisfied and provided by the aircraft
  computing network as a whole. Their allocation to specific networks
  and devices is the responsibility of aircraft network designers and
  specified by other documents.

  The Aircraft Control Domain (ACD) and Airline Information Services
  Domains (AISD) can be divided into sub-domains.

  The ACD can be divided into two Sub-domains:
  • Flight and Embedded Control System Sub-domain, where the aircraft is
  controlled from the flight-deck
  • Cabin Core Sub-domain, which provides environmental functions
  dedicated to cabin operations, such as environmental control,
  passenger address, smoke detection, etc.

  The AISD can be subdivided into two sub-domains:
  • Administrative Sub-domain, which provides operational and airline
  administrative information to both the flight deck and cabin
  • Passenger Support Sub-domain, which provides information to support
  the passengers

  Subsystems within the Passenger Information and Entertainment Services
  Domain (PIESD) could be supplied by different suppliers.

  Passenger Owned Devices (POD) can be supported by onboard networks.
  The Passenger Owned Devices Domain (PODD) is constituted of only those
  devices that passengers may bring on board the aircraft.

Reviewing the CIDS documentation of functions and comparing it to the A664P5 definitions, it would appear that the CIDS has functions within the ACD Cabin Core Sub-domain (environmental control, passenger address, smoke detection, etc.) and AISD Administrative Sub-domain (operational and airline administrative information to both the flight deck and cabin.)

To your last question, ACARS is a legacy communications link designed to support Airline Operational Control (AOC) and Airline Administrative Control (AAC) messaging.  With advances in data link systems and applications, ACARS can refer to either the AOC messaging (most correctly) or the entire data link system (not so correct) which also includes Air Traffic Control (ATC) messaging.

The ATC portion of data link falls under the ACD. AOC and AAC messaging fall into the AISD. In the case of the A320, the CIDS does not have a direct interface to the AOC/AAC messaging. These messages (manifests, gate assignments, etc.) are printed out in the cockpit and passed to the cabin crew as needed. On some newer aircraft, this may be accessible by the cabin crew via a terminal.


How does ATC radar display differ from military radar? Could you summarize what sort of data/objects are present in one type of display but not another? (not asking about construction differences, just the user-facing end, the display/interface.)

A somewhat related question "What data is displayed on civilian ATC radar screens?" shows example ATC displays. What of these would military radars miss (like obviously unknown data about enemy aircraft) and what extra would they present? Also - what sort of objects would appear on one but not another (in particular: non-aircraft; I heard for example flocks of birds sometimes appear on the radar, but never what kind of radar.)

This link

has numerous depictions of Raytheon made STARS (Standard Terminal Automation Replacement System)

Wikipedia says

  The system is currently being used at a number of TRACON sites throughout the US2 and a number of military RAPCON sites that control military air traffic.[3]

  The STARS is part of the FAA's TAMR project to replace aging hardware and software at TRACONS. It is also called TAMR Phase I.[4] The larger TRACONs still use Common ARTs capable equipment but the FAA announced in Spring 2011 that TAMR Segment 3 Phase 1 will consist of replacing these 11 larger TRACONS with STARS by 2016. Simultaneously, all Terminal areas in the United States will phase out all CARTS and ARTS systems and switch to STARS. The smaller sites will transitions to the STARS ELITE (Enhanced Local Integrated Tower Equipment) version of software and hardware, which is similar to TAMR, but with minimum redundancy. The FAA plans to complete this process by 2020.

So it would seem that in many locations there would be no difference.

  Raytheon's DoD STARS, also known as DoD Advanced Automated Systems (DAAS), provides a state-of-the-art air traffic control system for managing terminal area airspace for the US military.

  DoD STARS includes 191 RAPCON facilities with 59 associated towers and 21 stand-alone towers.

  STARS receives radar data and flight plan information and presents the information to air traffic controllers on high resolution, 20" x 20" color displays allowing the controller to monitor, control, and accept hand-off of air traffic.

  The Terminal Controller Workstations (TCW) provide position-by-position in-place replacement of failing existing system displays. They provide up to 14 adaptable data block types and 16 adaptable list types to accommodate current and future display requirements. The TCW also provides controllers with preference sets that allow for ease in shift changes and re-sectorization.

  The color displays are specially developed for air traffic control and are capable of displaying six distinct levels of weather data (identified by different colors) simultaneously with air traffic, allowing controllers to direct aircraft around bad weather.

  The color displays are specially developed for air traffic control and are capable of displaying six distinct levels of weather data (identified by different colors) simultaneously with air traffic, allowing controllers to direct aircraft around bad weather.

  STARS is capable of tracking up to 1350 airborne aircraft simultaneously within a terminal area. The system interfaces with multiple radars (up to 16 short and long range), 128 controller positions, 20 remote towers, and a 400 by 400 mile area of coverage.

  STARS has two separate, fully redundant automation systems running in parallel providing an instantaneous back-up service to controllers. The Full Service Level (FSL) is based on Raytheon's AutoTrac air traffic management system and the Emergency Service Level (ESL) is based on Raytheon's TracView automation product.


What is the worlds shortest runway for FAR 23 commuter type aircraft? This article lists the airport at Saba as the worlds shortest runway at 1300 ft. The runway is built on a bit of flat land on the side of the volcano that makes up the island. Nowadays STOL aircraft land here, previously the aircraft had to come in skimming over the wave tops and zoom climb onto the runway.

The Twin Otter can land here. Does Saba really have the shortest runway on earth for FAR 23 commuter type aircraft, or are there any shorter ones?

That would be Out Skerries (IATA: OUK) in Shetland with a 1,195 ft / 364 m runway (source).

60°25'30.08" N   0°44'55.93" W

(Source)

(Source)

Above plane is a Britten-Norman BN-2 Islander, with a stall speed of 35 knots.

  The Britten-Norman BN-2 Islander is a 1960s British light utility aircraft, regional airliner and cargo aircraft. Still in production, the Islander is one of the best-selling commercial aircraft types produced in Europe.


How do virtual circuit breakers work? In AW189, B787 and few other aircraft/helicopter, the physical breaker has been replaced by virtual breaker, which can be controlled by the MFD (Multi-Function Display).

I tried to google the answer, but I could find nothing about it: how does a virtual breaker physically work? I know how you control it, but what really happens when you press the breaker switch button on the MFD?

Virtual breakers use solid-state relays:

A solid-state relay (SSR) is an electronic switching device that switches on or off when a small external voltage is applied across its control terminals.
The relay may be designed to switch either AC or DC to the load. It serves the same function as an electromechanical relay, but has no moving parts.

According to Boeing for its 787:

The remote power distribution units (RPDUs) are largely based on solid-state power controllers (SSPC) instead of the traditional thermal circuit breakers and relays.

The standards for the solid state power controllers in aircraft is set by BS ISO 8816.

Related: Where are the circuit breakers on the 787?


How do they quickly replace the pylons after a hit during the Red Bull Air Races? My 3 years old was watching the movie Planes (Dusty Crop hopper one) and when he saw one airplane hit a pylon and puncture it he asked: How will they fix it?

I told him it was air filled and they will put a new one there but his question got me wondering as to how can they be replaced quickly before the next guy's run? Is it just like pop one off and put a new one there and quickly blow air with heavy output pumps?

The 25m tall asymmetrical pylons used in Red bull air races are made of 9 different sections, which are connected with zippers for easy removal and installation. In this image, you can see the multiple sections that make up the pylon.

Interior of redbull air race pylons; image from redbull air race

Airgators Team Captain, Holger Leprich, who is responsible for replacing the pylons after a hit, explains the procedure in this video.

The pylons are held up using air pressure- electronically controlled equipment at the bottom of the pylon creates a positive air pressure so that the pylon stands upright.
For each competition, there are three five member pylon replacement teams (called Airgators) to ensure quick replacement- their current record being 67 sec.
The pylon is designed to tear off in case of a hit. Once the pylon is hit, the team moves to the damaged pylons location on clearance from the race director.
Once the team reaches there, a couple of guys control the electronic equipment (and deflate the pylon, if required) at the bottom of the pylon, while another two replace the damaged parts- they simply unzip the damaged part and zip in the new one, while the last one checks the pylon.
Once the replacement is completed, the team inflates the pylon. Mission accomplished.


How is GPS RAIM availability calculated? I recently had someone ask me if there was a GPS RAIM availability calculator available for the iPad.  There isn't, but it got me thinking that I could write one.  After doing some searching, I can't find a good explanation of how to calculate RAIM availability, so am looking for the formulas used to calculate it for a specific route.

I want this to be an offline tool, so the calculations need to be complete, rather than relying on a website for the information.

The website that Ralgha points out is indeed the one to look at for the US. They also provide a SOAP interface should you want to create your own app for the IPAD.

For RAIM to be available, you need to check firstly that at least 5 satellites (Space Vehicles in GPS language) are visible from you position, or 4 if your RAIM algorithm uses Baro-aiding. They have to be well above the horizon. How much depends on your satellite receiver, the FAA uses 5 degrees on their website. There are some receivers that use a masking angle of only 3 degrees.

Orbital equations can be taken from the GPS interface control document, section 30.3.3.1.3. They take almanac data as input. Apart from the Space Vehicle orbits, you also need to take into account their health from the NANU's.

With the satellites available, you need to calculate the RAIM containment bound. This is the maximum size that a position error can grow due to a faulty satellite signal without the RAIM algorithm noticing it within 10 seconds (with a 99.9% probability). If that containment bound is more than 1 nautical mile, RAIM is said to be unavailable for terminal procedures. For NPA a 0.3 nautical mile radius is used.

The containment bound depends very much on the geometry of the satellites, more that on the number of satellites available.

The problem with the RAIM algorithms is that they aren't standardized. There are several ways to perform RAIM and because GPS manufacturers use proprietary solutions there is little information available to the public. So calculating the containment bound is where you will get stuck.

So there is no easy way to implement RAIM prediction on an IPad, apart from using the FAA website.

Europe has also a RAIM prediction website; AUGUR.


Are there any aircraft that either fold or employ folding in their design (such as with origami)? I became curious about origami and its application to aeroplanes and was wondering if there were aircraft that either fold and/or employ folding in their design in interesting ways.
Let's limit this to mechanisms requiring two or more creases/folds/axes/pivots that alter the geometry of something in a significant way. This should cut out most of the the obvious things e.g. fixtures (doors, food trays, landing gear and stair cases), control surfaces that act alone (canards, rudders, ailerons and flaps) etc. I wouldn't want to rule out any interesting applications however e.g. the use of leading and trailing edge flaps together (2 axes) or swept wings (2 pivots) is certainly acceptable. Finally, anything that is bizarre, curious or weirdly obvious is happily accepted !
Paper aeroplanes should be excluded unless there was some real world application thereof. Space stuff is also out.

My favourite is probably the Nikitin-Shevchenko IS which could morph between biplane and monoplane by folding its lower wing up into the upper one. The lower wing had two hinges on each side, one at the root and the other at about one-third span, so its outer section was indeed double-hinged.

Does it count to do something similar but cruder and simply let the upper wing go once you have taken off? This slip-wing was trialled on the Hillson Bi-mono before being fitted to a Hurricane.
The Tu-144 airliner and Dassault Mirage "Milan" had retractable "moustache" canard foreplanes which they deployed to improve takeoff and landing performance. Being tailless deltas, they had limited scope for conventional flaps, so put moustaches at the front instead. The moustache of the TU-144 was quite complex, having full-span flaps which amounted to a variable-camber aerofoil, so their trailing sections provide another rare example of genuine double-movement.
The XB-70 Valkyrie folded its wing tips down during Mach 3 cruise, to improve stability and waverider lift. The A-12 variant of the Blackbird was one of a small handful of types to have had a more prosaic ventral fin which folded up for landing and takeoff.
The Wild Goose and Swallow projects of Barnes Wallis at Vickers deserve mention, although they only flew as sub-scale test RPVs. They were examples of what he called the "wing-controlled aerodyne", having swing-wings in place of conventional control and tail surfaces. Not so much a double-action as eliminating the double-action of control surfaces on a swing-wing by using the whole fuselage as one giant multi-functional control surface (a tip he picked up from his work on airships such as the R100).
Does sliding count? The Akaflieg Stuttgart fs29 sailplane has telescoping wings which can pull in to increase cross-country speed. A few other experimental types had them too, such as the Makhonine Mak-10. The Gérin Varivol had a more complex variation on the theme, with a full-span high-aspect-ratio fixed section, which supported leading- and trailing-edge sections that were stowed in the fuselage and scrolled out along the wing like lowering a Venetian blind.
Polyhedra are solids with flat surfaces. Folding them using origami techniques is quite an art form, so I make no apology for the next example. Most polyhedra assemble rigidly but some, known as "breathing" polyhedra, can flex to a limited extent. An example from aviation is the variable-thickness wing experimented with by Rocheville among others, which bulges its top surface upwards to provide high lift for takeoff and landing, then draws it back down to create a thin wing for high-speed flight.


Why does landing gear retract with an offset? I've noticed this often in flight simulators, and have, to be honest, never paid attention to it in real life, though I'm quite sure it happens there too:
When landing gear retracts (and I believe when it extends as well) the two main landing gears don't move simultaneously, but one goes up (down) earlier than the other one.
Here is a video that shows this as well: Video
As a matter of fact it appears one of the flaps that open the landing gear bulk goes down faster? Doesn't that cause aerodynamic disadvantages?
There has to be a reason behind that. What reason is this?

This is called sequencing. The idea is to distribute the high load on the hydraulic system due to retraction over time, so the hydraulic pumps can be smaller.

The linked video shows no such sequencing. The triple redundant hydraulic systems on airliners do not need such optimizations since there is plenty of power if all pumps are running. On top, the video was made in a hangar and the pressure source was most likely external, with enough power reserves. Any asymmetries are most likely due to differences in friction, as Jan remarks in his answer.

Since friction losses in the hydraulic lines increase with flow speed, a difference in retraction speed would quickly be equalized, since the faster moving leg needs higher flow speed in the lines leading to and from its actuator, and less pressure would be available for gear operation. Active syncing is not needed, and a small difference has little influence on flight characteristics. After all, the main gear is close to the center of gravity, so drag differences between both legs do not produce big aerodynamic moments.

When a gear retracts, it first needs to move out of the locks, which requires little hydraulic power. After this, the load gradually increases the more the leg moves up into the horizontal position. Shortly before moving into the final, retracted position the load is highest; the details depend on the gearing of the retraction mechanism. If this load needs to be covered for all three gears at the same time, the hydraulic pump on an aircraft with manual controls and hydraulics only for gear operation would need to be more than twice as large as when you sequence the retraction, so the peak loads come one after the other.

Rockwell 112 while gear retracts (picture source). Some asymmetry is clearly visible.

Technically this is solved with sequencing valves which serve several circuits. They are used both to time the gear door operation, so the doors open before the gear starts moving, as well as the sequence of the main gears.


Does ARINC 429 have any error correction methods? I'm currently studying the application of ARINC 429, and have noticed that ARINC 429 doesn't have an error correction but an Error detection set in the parity bit (bit-32).
Are there any means for error correction within ARINC 429? If there is, how does it solve for failed data transfer between two systems?

You wouldn't correct the ARINC 429 label, but simply ignore that transmission and wait for the label to be resent again.
If the label isn't received properly within the defined period it would be considered timed out and the last valid label would no longer be used (timed out).


Aircraft emergency oxygen: how hard do I pull on the mask? AKA 'why is the safety briefing/training inadequate'.  I tried Googling my title and got lots of sites explaining the emergency oxygen systems, procedures etc. that I already mostly knew.  The briefing: 'Pull sharply on the tube to start the flow of oxygen' is not exactly fully informative or reassuring.  The things look so fragile that it must be fairly easy to rip the tube away from the oxygen generator/supply bus pipe/whatever.

How am I supposed to know how hard to pull?  Is there some sort of click/detent that can be felt as I pull on the tube that indicates 'OK, you've turned the oxygen on'?

Could not a simple mechanical flag indicate oxygen on, eg 'Pull on the tube until the indicator flag turns green', or the like?

When they first fall down they'll be too high to reach your head, pulling on them will release a switch to activate the generator and release enough slack in the line to reach down to your chest comfortably (for children).

Some types are suspended by a cord connected to the switch:

(image source: wikipedia)

Then you will just need to pull until the cord disconnects from the ceiling.


What would the reason be for this helicopter maneuver? At 4:30 in this YouTube video, a Chinook traverses the runway on its rear wheels. The text on the video lists "Emergency landing and take-off". Is there any reason for the pilot to do this other than "because I can and it's an airshow"?

The pilot then proceeds to back down the runway on the rear wheels, a maneuver that I can only imagine is showing off, but again, is there a legitimate flying need to do this?

Ex-Royal Air Force helicopter force here, spent a lot of time around Chinooks.

I think the main answer is "because I can", but I can think of a legitimate combat use.

You are heavy, and forced to land downwind into a narrow strip because there is a hazard on the upwind side of the landing zone.  There is not enough room to turn around.  You could hover taxi backwards like this to pick up some inflow into the rotors from the relative airflow (and therefore increased lift), then climb away backwards until you do have enough room to transition into normal forward flight, more or less as shown in the video.

This is where team work kicks in - you've really got to trust your load master who is telling you exactly where you are.

Never seen it done though.


What are these holes in the engine inlet? In the next picture can be seen within the housing, near the inlet:

These are "acoustic liners"; they allow the sound waves to get "trapped" in the holes and make the engine quieter. Sometimes chunks tear loose and they're repaired with what amounts to Bondo.


How is the load & trimsheet form sent to ACARS? After the last passengers and baggage are loaded onto the aircraft, the pilot in command is given a form called load & trimsheet which shows the passenger/baggage distributions, total weights and cg positions. The form can be prepared manually or by a computer program by the authorized ground staff. This form has the wet signature of the ground crew coordinating the flight and the pilot in command on it and these signatures ensure that the form is legal.

My question is about the process of sending this legal form to the cockpit of the aircraft via ACARS. When the form is transmitted to the aircraft via ACARS, is it still considered to be a legal document without wet signature on the form?
How is this process run by airlines?

When the loadsheet arrives to the aircraft via ACARS it has to be acknowledged and printed. This is accomplished by the flight crew by selecting the proper screen and pressing the respective button or LSK on the MFD (Multi-Function Display for latest Boeing models) or in the MCDU (Multi-Function Control Display Unit for Airbus).

Along with the acknowledgement sent back to the system, goes the timestamp. Legally, this action is considered the wet signature. Then the sent ACARS form is printed in the aircraft printer, so the crew has a backup copy of the loadsheet containing in the header the "ACK" confirmation and the same timestamp sent to the system.

Every airline has different policies regarding the format of the loadsheet and even the procedure to accept and correct the values. that sometimes change in the last minute again, but this can give you a generic idea of the procedure.


Are controllers aware of TCAS RA taking place? When the TCAS issues a Resolution Advisory (RA) which contradicts an ATC instruction, the RA takes priority.

Are controllers aware (notified on their screen) that a RA has been issued between two converging traffic?
If yes, are the controllers also able to see the RA instruction issued to each specific aircraft?

ATC was and is still generally not aware of RAs before being informed by the pilot
In general ATC is not aware of any RA occurring in aircraft, and is neither aware of the RA content. The crew informs ATC using a phraseology described in ICAO Doc 4444 PANS-ATM, Chapter 12, Para 12.3.1.2:

When the RA occurs, and the crew must deviate from ATC instructions, they inform ATC with "TCAS RA" when possible.
If an ATC instruction is received, which contradicts a current RA, they inform ATC with "Unable, TCAS RA".
The crew then informs ATC when the RA has ended, with "Clear of conflict, returning to (the ATC clearance)", and "resumed" when done.

See instructions to ATC and RTF Phraseology associated with TCAS RAs.
Pilot and ATCO obligations, impact of RAs on responsibilities
RA always takes precedence on ATC and must be followed by the crew (exceptions are investigated). This is because even if the crew has the intruder in sight and another safe maneuver might be executed as well, there is no certainty the visible aircraft is the conflicting one, or is the only conflicting one.
When informed, ATC doesn't provide further instructions to this aircraft before receiving the "clear of conflict" confirmation.
Two issues should not be overlooked:

According to existing regulations, a controller is not relieved from providing a guidance to pilots until informed by the pilot of a RA conflict ("unable TCAS RA" -- a pilot doesn't have to report RAs not preventing to comply with received ATC clearances). Therefore the (legal) responsibilities and obligations of the controller are unclear in the period between the display of the down-linked RA, which can be delayed by technical limits, and the actual report by the pilot which is not instantaneous.

Not all RAs are relevant to ATC, only those which pertain to collision avoidance or conflict with ATC clearances, therefore some filtering must be done either prior to download, or after reception to eliminate "Monitor Vertical Speed", "Maintain Vertical Speed", etc. This filtering may be imperfect and can lead to RA not displayed.

Last but not least, the current view of the controllers federation:

IFATCA is opposed to down linking of any advisories generated by ACAS.
If down linking of ACAS Resolution Advisories becomes mandated, then
IFATCA can only accept this provided that the following criteria are
met:

Clear and unambiguous controller legal responsibilities;
Downlink without delay;
ATC system to be able to receive, process and display the down link to the appropriate control positions;
Compatibility with all ground based safety nets;
Nuisance and false alerts must be kept to an absolute minimum;
ACAS should only be considered as a ‘safety net’.

RA downlink decisions and implementation progress
Due to the responsibility and limitations issues, the adoption of RA display at controller working position is variable among countries, in spite of technical studies confirming the interest (detailed further down), and modern ATC systems being able to receive and manage downlinked RA. Current status for some countries (source):

USA and UK and France don't use it (UK CAA clearly forbids any use).
Czech Republic and Hungary have tested the technology early and use it.
Luxembourg is conducting studies for using it.

Where it is used, the RA data is only for information, and doesn't change ATCO responsibility for collision avoidance, e.g. for Hungary the regulation has been complemented (source):

The TCAS RA Downlink shall be ignored from an operative point of view.
In  other words, it is only for situational awareness and informative
purposes, and the controller shall not consider RA Downlink when
issuing a new  clearance.

UK CAA forbids ANSP to use RA downlink (ibid):

There are currently no ICAO, European or UK pilot procedures, ATC
procedures or legal responsibilities for the use of ACAS RA Downlink.
However, this subject is under consideration by Eurocontrol.
There is no assurance as to the integrity of the RA downlink and
absent or false downlink data could be a possibility.
A downlinked RA without adequate discrimination may lead the ATCO to
inappropriately cease the provision of ATC instructions. However,
under current ICAO procedures, the controller will continue to provide
ATC instructions during RA events that do not deviate from the
clearance or instruction unless such a clearance is at variance with
the RA, at which point the pilot will report ‘UNABLE, TCAS RA’.

Studies conducted to include ACAS RAs in ground-based safety nets
There has been several accidents involving RAs not followed by crews, among them a tragical collision over Switzerland (2002 Überlingen) where the risk was not spotted in time by controllers due to a calamitous chain of events. RAs were issued by both TCAS, one pilot followed its RA, the other followed ATC urgent descent instruction against RA. The BFU report noted "an automatic downlink, integrated in the TCAS equipment, carrying information about issued RA’s to the respective ATC units has not been activated yet" and has recommended to allow RA downlink to inform ATCOs:

To enhance the performance of ACAS
ICAO should initiate the development of down-linking RAs to ATC, using
such technologies as SSR Mode S and Automatic Dependent Surveillance -
Broadcast (ADS-B)

Studies on the feasibility and operational benefits of RA downlink have been conducted in the USA, in France (1994), and in Japan and lately from 2003 to 2007, with the FARADS project which concluded possible short-term downlink solutions would be useful:

With Mode-S RA reports, the controller will be aware about the RAs in
95% of the cases within 9 seconds of their occurrence. Thus, the
downlink of RA information was found to be sufficiently timely to
allow for a significant increase in the controller’s awareness of the
RA encounter.

In the course of this project, RADE-1 and RADE-2 experiments had taken place at Brétigny (France), and concluded in RA downlink benefiting to ATC, without creating a cognitive tunneling around the RA. it also indicated RA downlink could not be deployed without being included in existing ground-based safety nets.
ATC uses ground-based safety nets, which purposes are similar to aircraft ACAS and GPWS, e.g.

Short Term Conflict Alert (STCA): operational since around 2013. An alert in STCA is supposed to take place about 30s prior to a TCAS RA, however this is more complex, and the RA may happens before the STCA alert.

Area Proximity Warning (APW), Minimum Safe Altitude Warning (MSAW) or Approach Path Monitor (APM), all operational since around 2016

RADE-2 experiment showing labels with RA data on first line (source)
Eurocontrol project PASS studied the inclusion of ACAS RA into STCA, and more generally the mutual compatibility and interaction of both systems. In the final report (2010):

An optional real-time experiment with both controllers and pilots
in-the-loop was planned to complement the findings of Phase 1 and to
help define operational requirements supporting an overall operational
concept for joint  STCA/TCAS operations. This optional work was
however not launched due to lack of funding.

The work done concluded the interaction between STCA and ACAS should be considered by ANSP. A few early adopters (Czech Republic, Hungary, Japan, Luxembourg) are experimenting, to answer the question, yes the type of RA is displayed, and whether the aircraft is advised to climb or descend, as visible on the picture above. This is the current status, and obviously everybody is waiting for ICAO (representative of all countries) clarification on the topic.