Why do airlines follow these routes between Barcelona and Düsseldorf? In the wake of GermanWings' terrible incident of flight 9525, I have noticed that the crash location is quite far from the shortest route connecting the two airports.

I then went on FlightRadar24's website and checked that this is the normal route for this flight (and that there is an alternate one that reaches equally far on the other side):

Other companies that fly the same route (Vueling 1894, Airberlin 8947) follow the same flight paths.

Why is this? What limitations are in place that prevent these aircraft from flying over Lyon (and "nearby" region)?

Large parts of France's airspace are designated military training areas. If there is military flight training going on, the choice of routing over France is very limited. The only option is to fly around these areas, which  results in the routes you found.

Higher altitude route map of France courtesy of EUROCONTROL[PDF, 8MB]

Since the PDF seems to be giving problems on some computers, I've combined several screenshots and drew the approximate route of your westerly flight (in yellow), the planned flight of GWI 9525 (blue) and Temporary Segregated Airspaces (TSA's) in red onto the map. The crash location of GWI 9525 is marked by a red/yellow star.

Note that not all the TSA's in the map are actively used at all times and that in some cases crossing is allowed but altitude restrictions apply.

In addition to active TSA's there are other considerations that come into play such as weather and airway capacity & demand. If you have to wait 15 minutes longer for a slot on the shortest route, you might as well fly a slightly longer route if that allows you to depart earlier.


Do employers prefer to hire younger pilots? Do companies, regardless of country, tend to shy away from hiring older low-hour pilots? "Older" meaning mid-30s to early 40s.

The answer to that has varied throughout airline hiring history.  There was a time when you'd better be young or else your chances of getting hired by the majors was essentially nil.  Now, "age discrimination" is a thing, and at least officially (in the US, at least) it is probably against policy to treat the 30 year-old ATP with 2000 hours differently than the 50 year-old ATP with 2000 hours.  (Or the 30 year-old commercial pilot with 500 hours different from the 50 year-old pilot with the same resume.)

These days, the regional airlines in the US seem to be so desperate for pilots that if you meet the minimums, it's more a matter of scheduling a class than it is scheduling an interview.  So if you're willing to fly for a regional, even the late 40-something pilot can probably get on with an airline.

Interestingly, this dynamic has its roots in the hiring practices of 30-40 years ago, when the airlines hired large numbers of "young" pilots -- meaning that the senior ranks of many majors have lots of pilot who are close in age and who are now reaching the Age 65 mandatory retirement all together.  This creates significant vacancies at the majors, who draw their new-hires from both the military (which is a fairly constant supply) and from the regionals (which has become where the "slack" has been that is now getting picked up).  The massive demand for hiring into the majors translates into regional captains moving up, and thus out of the regional airline far more rapidly than in the past.  This drives upgrade times at the regionals down, and has put pressure on their hiring departments to keep the right seats filled.

Quite literally, I was recently told that the "hiring" process at one regional has become nothing more than a confirmation that the candidate does meet the basic minimum qualifications (commercial license, 2nd class medical), and scheduling a class date.  If they pass the training, they're hired.

That is a snapshot in time in one country; throughout history that sort of a process is anomalous if not unprecedented.


Can you help me identify a vintage airplane in a painting? This is a recent photo of the king of Spain, Felipe VI, visiting Spanish troops stationed in Iraq. In the background there is a picture of an old plane, possibly with a propeller, that I suppose from WW2 era (more or less).

If that painting has been chosen to adorn a military installation located in Iraq and occupied by Spanish troops, I understand that it must be a type of historical significance for Spain or for Iraq.

Can anyone recognize it?

The aircraft in the painting (I’m not sure it is a painting?) is a North American P-51C Mustang in the Tuskegee Airmen colors of the U.S. Air Force in WW II.
I cropped the image above and then used TinEye Reverse Image Search to find the photo.
My search has expired on that website, but you can copy the “fuzzy” photo and try it yourself on the same site.
Search photo

Search Result

P-51C Mustang in Tuskegee Airmen (Minnesota wing of the Commemorative Air Force)


What priority if any is given to Emergency Services in flight clearance? When requesting takeoff/landing and route clearance is any priority given to Emergency Services IE air ambulances, firefighting rigs, S&R etc. I'm assuming even though these services rise to the level of life or death, they are not treated with the same urgency as an air emergency but I don't know that for fact.

I work as a fixed-wing pilot for a hospital-based Air Ambulance program. Let me add my experience to the ATC orders accurately cited by Pondlife's answer: the MEDEVAC call sign (the old "Lifeguard" is still used when filing the flight plan) indicates a need for priority handling.

ATC is often helpful in providing us with priority routing. This includes giving us direct clearances, moving us up in the landing que, allowing us an unrestricted approach speed, and otherwise expediting our flight. However, ATC does not always provide priority handling, and I have often experienced ground delays of 5-10+ minutes as ATC apparently prioritizes other traffic, including air cargo and the like. This is rarely a big problem as patients are typically stable, but it can be frustrating when priority handling is expected.

However, if medical staff determine that a patient is in critical condition, we will announce this to ATC—typically accompanied by a request for a specific clearance or change to a previous clearance. This announcement re-iterates our need for priority handling and indicates the urgency of the situation. In this way we can work with ATC to best care for the patient. We will often make such an announcement when checking on with approach control for their information with no specific accompanying request. Occasionally, however, we will need to request such priority handling because ATC has issued us speed restrictions or delaying vectors to put us behind other traffic. ATC is very good at working with us when we do need the priority handling.

In other words, ATC usually automatically gives us priority handling, but when they don't—and we need it—we ask for it and they are very good at working with us to provide the priority handling.


What Caused the Engine-Failure of Southwest Airlines Flight WN-3472? What caused the damage on Southwest Airlines Flight WN-3472?

The inlet section of the engine is missing but the fan and nose-cone are still visible.
Pictures taken during flight even seem to show the fan windmilling.

The currently known details are that it was caused by the failure of a single fan blade, due to a fatigue crack. The crack location was between the blade root and tip (the root of the blade stayed in the disk).

As the question states, the accident was in a Southwest Airlines Boeing 737-700. The Aviation Herald says here that it was:

  ...performing flight WN-3472 from New Orleans,LA to Orlando,FL (USA) with 99 passengers and 5 crew, [and] was climbing through FL310 out of New Orleans, about 80nm west of Pensacola,FL (USA) when the front section of the left hand engine (CFM56) separated, debris impacted and punctured the left side of the fuselage causing a loss of cabin pressure. The crew diverted the aircraft to Pensacola for a safe landing on runway 17, the aircraft vacated the runway and taxied to the apron with emergency services following the aircraft. There were no injuries, the aircraft sustained substantial damage.

It also says:

  [In] late Sep 12th 2016 the US NTSB reported, that one fan blade separated from the fan disk during the accident flight, the root of the fan blade remained in the fan hub, however, the rest of the fan blade was missing. The fracture surface of the titanium alloy fan blade, root covered by copper-nickel-indium alloy, showed evidence of a fatigue crack, however no surface or material anomalies were found during initial metallurgic analysis. The engine inlet separated from the engine and impacted fuselage, wing and empanage resulting in a 5x16 inch hole above the left wing.

I expect that's the extent that is publicly available at the moment, because the Aviation Herald report would have been updated if further info was available. So, it's not publicly known if the fatigue crack was low cycle fatigue or high cycle fatigue.

Low cycle fatigue is fatigue caused by large changes in stress amplitude, such as caused by a change in rpm from idle to max speed. Because the change in stress amplitude is large, it can fail in relatively few cycles, compared to HCF. (But still maybe ~10,000). Because it's driven by throttle movements, the number of cycles can be counted. Typically a single flight, even ~10 hours, in a civil aircraft only accumulates less than 10 cycles.

High cycle fatigue is fatigue caused by very small changes in stress amplitude, such as turbulence acting on a blade, every time a rotating blade passes behind a stationary vane. Hence, if a stage in a compressor has 30 vanes, every revolution sees 30 stress cycles on each blade in the following stage. Thus, the number of HCF cycles can accumulate very rapidly. They cannot easily be tracked. Usually, HCF failures need some sort of stress concentration to exist at the point of failure, such as a material anomaly, maintenance damage, or a nick from FOD (foreign object damage from an ingested stone from a runway, for example). HCF failures can require 100,000s of cycles to be accumulated, but if you get 30 every revolution, and the shaft is doing 7,000 rpm in cruise, these accumulate very quickly. Initiation to failure can be just a few flights.

Since there were no material anomalies found on the fracture surface of the blade half they have (the outer piece was not recovered), that indicates the cause of the fatigue crack is unlikely to be a manufacturing issue, and hence a fleet-wide issue.

It is probably an HCF failure, since the crack location does not seem to be in the blade root. Usually, the location of the weakest points due to LCF are in the blade root or fir-tree base, and it sounds like it failed higher than that.

What About The Cowling Failure?

When the fan blade fails, it's pretty violent. Here's a video of a blade-off test done for certification. There is very high vibration at the time of failure, and high vibration while the engine is windmilling before landing. Fan blade failures should not result in cowling failure, because the whole point of the test is to demonstrate that the failure is contained. That means, no part is released at high energy, that may damage the aircraft. Having the cowling fall off, doesn't really align with that philosophy. But, clearly, there is a random element in such an energetic failure.

The most receny fan blade failure I believe was an AirAsia X A330-300 off the west coast of Australia, on Jun 25th 2017. It lost almost the entire blade, but the cowling remained very undamaged, as shown in the picture at the link.

The A380 Air France engine failure that occured in Sept 2017 had similar damage to the aircraft in the question, but the Air France incident was not a fan blade failure. The Airworthiness Directive issued after this states the incident was caused by failure of a fan hub. So, it's not a relevant comparison.

Some aircraft have suffered strutural failings of the fan cowl, without being caused by fan blade failure. Eg. This Egypt Air A330-200 and this China Eastern A330-200 both lost a portion of their cowling. But these failures are a hole blown in the side of the cowling, not loss of the entire duct forward of the fan. These were caused by a structural defect in the composite duct.


Which air stream pressure / speed is measured by the pitot? The pitot tube is used to measure the air pressure later converted into air speed. However air pressure varies according to several elements, including the location related to the wing:

(Source: av8n.com)

On one hand the probe, depending on its location, could measure the pressure in the free stream, in the high velocity stream, or in the low velocity stream.

On the other hand, pitots are found at various locations, e.g:

On the fuselage, far from the wing, B-737 (source)

On the vertical stabilizer, kit Nemesis NXT (source)

Under the wing, Cessna 172 (source)

Furthermore when the probe is fixed to the fuselage or to the stab, depending on the angle of attack, it can be rotated into the slowed down or the accelerated portion of the stream.

Can you shed some light on what is usually measured by the pitot? Does the pitot indicate different pressures if placed in the different stream areas (free, accelerated, decelerated)? If so:

What is usually measured by the probe?
What is usually displayed on the speed indicator?

Edit: While I needed to select a single answer, several other answers contain additional interesting elements and deserve votes as well.

The first thing to have in mind is that a pitot tube is NOT measuring speed: the pitot tube measures pressure and later on the airplane (flight management system in a modern airplane) calculates the speed based on pressure.

More specifically the pitot tube calculates the stagnation pressure which is the sum of static pressure (what you show in your picture) and the dynamic pressure (pressure obtained by stopping the air).

The total pressure remains constant in the external free flow in normal airplane operations BUT will not remain constant in the boundary layer, which is a small region close to the wall. The boundary layer grows with the distance downwash along the airplane.

What I explained here justifies the following design solutions:

Pitot tubes are usually installed with an small distance to the walls "like floating" in order to be outside the boundary layer and free of loses on the stagnation pressure.
Pitot tubes are never installed at the tail of the airplane, in order to avoid high thickness of boundary layer (could reach 1 meter).


How does pilot know when to trim when flying an aircraft that have fly by wire flight control computer My understanding of trim (on non fly by wire aircrafts) is that when the pilot feels force on his column or side stick, he trims the aircraft (either up/down) until the forces on the stick or yoke are neutralized. But in fly by wire systems, the pilot does not feel any force on the stick or yoke. In such case how does pilot know when to trim the aircraft (be it pitch/roll/rudder trim).
Or does flight control computer computes the trim required automatically? In such case, what happens during the direct mode (or alternate law) when flight control computers are no longer in control and pilot commands directly go to actuator controller electronics.

Fly-by-wire just means that the control column is not connected to the control surfaces (hydro-)mechanically, but using digital (electrical or optical) signal wires. That says nothing about how the controls behave. There are two basic ways they can:

The Boeing way:

Force and position is transmitted in both directions, emulating
control with mechanical link. The pilot feels force on the control surfaces and trims as usual.
The Airbus way:

The position of the control column corresponds to wing loading in pitch and roll rate in roll axis. The computer manipulates the controls to achieve the target values. The control column is spring-loaded, so force always corresponds to position.

The trim is operated by the computer to balance the control surface for wing loading of 1 G (or is not a separate control at all as in case of FBW fighters with all moving stabilator).

But when the system is in direct law (during take-off or if degraded due to fault), the trim still works more or less normally. The centred position of control stick corresponds to the trimmed position of the control surface, so if the pilot feels force on the control stick, because it is displaced, they dial trim and reduce pressure on the stick until the plane flies straight with the stick centred.

The Airbus way is used on Airbus A320 and all newer models, Sukhoi Su100 and some fighters (since F16).

The Boeing way is used on Boeing 777, 787 and, IIRC, some regional jets.


Did the Space Shuttle boat tail used in the transport configuration save fuel? During the testing phase as well as during transport of the Space Shuttle on top of a 747, a boat tail was used:

Source

Here I found that this was mainly to reduce the turbulence that would strike the tail of the 747, thus increasing yaw authority.

However, I can also imagine that the boat tail would reduce the base drag of the Space Shuttle, thereby reducing the fuel penalty of carrying the Space shuttle.

Is there any research that shows that the boat tail also reduced the drag, rather than just providing a cleaner flow to the vertical tail?

I have always been under the impression that it was mainly installed to protect the engines. However this blurb (and cool photo) claim it did reduce drag.

  ...reduces both drag and turbulence created by the piggy-backing spacecraft while also protecting the engines


Why are manufacturers assumed to be responsible in case of a crash? I attended at a training concerning airborne software and the coach remarked that despite at the normal courts, when an aircraft crashes and the authority investigates, a manufacturer is guilty for that accident until innocence is proven that the manufactured device did not produce the defect causing the crash.
I hoped to find on the web some reference to this "guilty until proved innocent" rule, but I cannot. Do you know where I could find some info about that?

I'll assume you're talking about an English common law jurisdiction (UK, US, Can, Aus, NZ etc.).  In those places it's always "innocent until proven guilty", the key thing being what "proven" means.
You have to separate criminal liability, breaking of a law in the criminal code, from civil liability (a civil wrong, or "tort" in English common law).  The criminal liability standard of evidence is "guilty beyond a reasonable doubt" at trial, and tort liability standard is "guilty based on preponderance of evidence" at trial (that is, more likely than not in the assessment of a trial jury (in the US) or a judge).
So a manufacturer or an airline is only exposed to criminal liability where an incident involved the violation of a criminal statute. You can't throw the "company" in jail, so an individual has to be on the hook and so the authorities would have to identify a criminal code violation committed by an officer or employee of the company, and it would be that employee or officer that would be going to jail (for something like violation of a criminal negligence statute).  And in that case the standard is guilty beyond a reasonable doubt.
In the case of civil liability, the corporation itself, or potentially its officers personally, are on the hook, the penalties being solely financial (employees are normally shielded from civil liability in a limited liability corporation) and the "preponderance of evidence" standard of guilt applies.
The thing is, both of these conditions require a court trial.  Either government prosecutors go after individuals (officers of the company or employees) for criminal violations that include fines and/or jail time for those convicted of criminal acts, or non-government individuals that have been harmed (families of passengers killed for example) go after the corporation in civil court, and the corporation is only guilty of a tort (civil wrong) if a judge or jury finds them guilty.
So in both situations it's "innocent until proven guilty"; the difference is in who the accuser is and what the standard of evidence is.
Now, outside of the Anglosphere, all bets are off, and you may very well find places where guilt is assumed and company has to prove its innocence to get off the hook for either criminal or civil liability.


Do pilots have to stop at the hold position of the takeoff runway? Or in other words, is the takeoff clearance ever given (implicitly or explicitly) before the aircraft reaches the hold position, so that the pilot can keep rolling through the hold line and to the takeoff roll?

No, there is no mandatory stop. Typical clearances given before departure are:

BigAir 123, hold short of runway 36.
BigAir 123, line up and wait runway 36.

Former phraseology in the US was "position and hold".

BigAir 123, behind landing A320, line up and wait runway 36, behind.

Note the word "behind" being repeated at the end of the clearance.
The interesting ones:

BigAir 123, are you ready for immediate departure?

It will be asked by the tower controller to assess if they can squeeze BigAir 123's departure between two landings, for example.

BigAir 123, cleared for takeoff runway 36.

It can be given to an aircraft still on the taxiway. In such case, BigAir 123, who will have proceeded through checklists and briefings while taxiing, will turn into the runway and takeoff, without having to stop at any point.
It is possible that the crew actually needs to stop, to finish their preparations. In such case, they will normally report not ready for departure, if asked. The tower controller doesn't want aircraft making unexpected stops on the runway, especially in a single-runway airport, this can result in the following landing having to go-around.
Also note that the word "takeoff" is used only in the context of an actual takeoff clearance or its cancellation. Otherwise the word "departure" is used, e.g., are you ready for departure? Also see the Tenerife disaster.


Can the commercial night cross country be done under IFR? The below doesn't mention anything about needing to be night IFR, so if you were to shoot an approach on this flight, would it be legal?  Also, if the instructor isn't a CFII, but PIC does have an instrument rating?

https://www.law.cornell.edu/cfr/text/14/61.129

  (iv) One 2-hour cross country flight in a single engine airplane in
  nighttime conditions that consists of a total straight-line distance
  of more than 100 nautical miles from the original point of departure;
  and

The regulation doesn't specify VFR or IFR, so you may complete that requirement in either.


Does windmill restart often work for airliner engines? There seems to be a certain class of airline accident where an airliner engine flames out followed by further unfortunate events. Very often, pilots are recorded as having attempted to restart a failed engine by windmilling, which seems to involve attempting to restart an engine from the rotation due to the passage of air due to airspeed. In accident reports this rarely ever succeeds, leaving the impression of a rather worthless exercise.

But, of course, there's a massive bias here because these are the reports of accidents and if the windmill start worked, things wouldn't have deteriorated.

So, in rough terms, how desperate is attempting a windmill start. Is it in the land-on-water level of optimism, or something which usually succeeds which we never hear about?

If the engine isn't damaged, and the restart altitude/speed are followed, the engine should start. Fuel starvation, bird ingestion, etc., do not count.

(YouTube) In-flight shutdown.
In-flight restart is tested as part of the aircraft certification, and it must work. In the link above is a video showing the procedure in a 777F simulator.

Engine Restart Capability - § 25.903 (e).
Tests should be conducted to determine that inflight restarting can be accomplished within the envelope provided. Restarts at the conditions of the critical corners of the envelope and at or near the high altitude extremes of the envelope should be conducted to verify the boundary conditions of the envelope (FAA).

Examples of successful restarts:

On British Airways Flight 9, all four jets on a 747 failed after entering a volcanic ash cloud, all 4 were restarted after exiting the ash cloud. One of the four failed shorty after, but volcanic ash is sticky, the particles are very small, they melt, and they clog moving parts. So three out of four isn't bad at all.

For KLM Flight 867 (a mirror of BA 9) it was four out of four successful restarts.


How are the IFE Server, Floor Disconnect Box (FDB), Seat Electronic Box (SEB) and Seat Display Unit (SDU) connected to each other? I tried to understand the data protocols used to connect InFlight-Entertainment (IFE) Server, Seat Electronic Unit (SEB), Floor Disconnect Box (FDB) and Seat Display Unit (SDU), but I'm a bit struggling about this.

Generally speaking I've seen that the most used transmission protocols for avionics are ARINC 429 (629 in case of Boeing 777) and ARINC 664 or AFDX, since part of the IMA infrastructure, and in other rare case ethernet connections, however I haven't found particular specifications about this particular connections.

Does anybody know something about this or have good sources from which start back my research?

Airbus IFE system

All data sources and servers are concentrated in the IFE Center which delivers them to the cabin LAN using Ethernet. The LAN itself is Ethernet.

Some data are received by the IFE Center from the Cabin Intercommunication Data System which is itself connected to AFDX (Ethernet, ARINC 664) ADCN network.

The cabin network then distributes data and power to overhead displays and seat IFE units.

Schematic:

Source, page 15

Architecture:

Source, page 15

IFE System for the A350

The IFEC rack is the source for all data sent to the passengers IFE units and the flight attendants panels. It contains files and media servers, is linked to external cameras (ETACS), landscape cameras and SATCOM.

IFE: In Flight Entertainment
IFEC: In Flight Entertainment Center. A system with redundant sources and redundant outputs.
ETACS: External and Taxiing Aid Camera System
SATCOM: Satellite Communications

The IFEC is also interfaced with the CIDS which supply it with data from systems like CDAU and ADIRS and other aircraft systems using AFDX, engine data from PCS, or discrete signals like cabin systems (oxygen) or public address.

CIDS: Cabin Intercommunication Data System, the main way for attendants to control the cabin systems other than IFE.
CDAU: Centralized Data Acquisition Unit
ADIRS: Air Data/Inertial Reference System
AFDX: Avionics Full Duplex Switched Ethernet (ARINC 664)
ADCN: Avionics Data Communication Network
PCS: Propulsion Control system

IFE power is supplied by some SPDB.

SPDB: Secondary Power Distribution Box

The IFEC and SPDB are controlled by ICPs, FAPs, CWSs and RCCs.

ICP: Integrated Control Panel (in cockpit)
FAP: Flight Attendant Panel
CWS: Cabin Work Station
RCC: Remote Control Center

The IFEC delivers data (audio, video, other data) as Ethernet frames to FDBs using a switch. There are actually two or more IFEC switches, each one feeds some FBDs.

FBDs also receive power from the SPDB. Ethernet frames and power are distributed by FDBs to overhead displays and IFE units.

FDB: Floor Disconnect Box. Used as a switch to create the network. FDB ensure network redundancy: Each FDB receives data from one IFEC switch, but as FDB share the same network, IFEC is still available when one of its switch is failed.

Each seat gets its IFE unit which is connected using a SEB. The IFE unit encompasses the SDU, the PCU and headset.

SEB: Seat Electronic Box. A network interface card, with power management.
SDU: Seat Display Unit (touch screen in front of the passenger)
PCU: Passenger Control Unit (interface)

The big picture:

Source

Security aspects

Your question was motivated by the security aspects of the cabin network vs. the other aircraft domains (e.g. avionics or cabin systems).

For Airbus, the cabin IFE network is only a layer 2 LAN with multiple Ethernet segments linked by Ethernet switches. There is no possibility to route malicious packets to other domains, since there is no routable (layer 3) protocol.

The interconnection between IFE and other systems is made through the CIDS, which is based on a redundant "director" which controls data destination. Without other elements, the assumption is security is primarily at CIDS level.

More information in this presentation (some pages are in German, most are in English).


How much water pressure can flight recorders withstand? How deep can black boxes go under water and how much pressure can they withstand while under water before they get crushed?

I'm a layman in terms of aviation, so if it's not too much to ask, can you answer as easily understandable as you can?

How deep can black boxes go under water?

They are required to be able to withstand a depth of 20,000 feet (3.8 miles, 6.1 km) for 30 days.

& how much pressure can they withstand?

At 20,000 feet deep the pressure is 8900 pounds per square inch (psi) which is 606 times atmospheric pressure at sea level (nearly 4½ tons on each square inch of surface)

A flight data recorder from AF447, around 13,000 feet deep for almost 2 years. Still readable

References

The DFDR must be watertight to a depth of 20,000 feet in sea water, and survive at this depth for 30 days
The units also have to withstand a static crushing force at all of its six axis points of an applied load force of 5,000lbs for 5 minutes on each axis.

See: What happens to the transponder, FDR and CVR in case of an explosion?

The southern corridor of the Indian Ocean, where officials now believe the plane went down, ranges in depth from 3,770 feet to 23,000 feet.  At its greatest depth, that’s almost equal to the height of Mount Everest (which measures 29,029 feet tall).

See: Indian Ocean depth proves great challenge for MH370 search crews

For every 33 feet (10.06 meters) you go down, the pressure increases by 14.5 psi (1 bar).

See also

List of unrecovered flight recorders


How do I determine the best altitude to fly for fuel economy? If you fly low, air is dense so you can get more thrust from your engines, but you get more drag.
On the other hand if you fly higher you have less drag but the output of engine decreases as well.

So what's the optimum altitude to fly at, and how does one determine it?

The optimum altitude depends on your aircraft, the engines and the weather. But most important is to decide what you are trying to achieve. If you would like to optimize your fuel consumption per distance travelled, the altitude you will fly at will be higher than if you try to optimize your fuel consumption per time unit.

Fuel per distance travelled is usually better at altitude, while fuel flow per time unit is lower at lower altitudes. In other words, if you want to go far, fly high. If you want to keep flying long, fly low.

Winds play an important role as well. If you have a strong headwind high up, you might go further staying low.

There is quite some difference between reciprocating engines and jet / turbine engines here. The former perform better at lower altitudes, while the latter do just fine until much higher.


Why the different wing and tail designs in similar sized jets vs turbo prop? I was flying on Porter Airlines and they had an info card about how similar the Bombardier (I still say DeHavilland) Dash 8 Q400s are to the Bombardier CSeries they have ordered.
There was a cool overlay photo to show relative sizes and shapes:

Looking at that image, it got me wondering about the straight vs angled wing.  Straight vs angled tails, etc.
I get that a jet is faster than a turbo prop.
Cseries cruise speeds are:
Mach 0.78 (828 km/h, 447 kn, 514 mph)
Dash8 Q400 cruise speeds are:
414 mph (667 km/h) 360 knots
Those are pretty close and yet that is a pretty radical wing design change.
Is this just the history an old design (Dash 8) vs a very modern design?

Well, for starters, the speeds are actually pretty significantly different. The Cseries is almost 25% faster than the Q400. Swept airfoils are much more efficient at those higher speeds, as are jet engines.

The Q400 is also a wildly stretched version of the original DeHavilland Canada DHC-8 (Dash 8), which was itself based on the 4-engine DHC-7 (Dash 7) STOL airliner. DHC has a lot of history building short takeoff and landing aircraft with pretty extreme performance, and a lot of that colored the design of the Dash 8. What you see today in the Q400 is the result of about 70 years of backcountry aircraft design, applied to a commuter airliner.

The Cseries, on the other hand, is a clean-sheet Bombardier design meant to compete with the E-jets and the smallest 737s (and 717).

Hopefully that answers your questions!


Are all the Airbus A380's 16 exits designed for everyday use? Are all the Airbus A380's 16 exits designed or everyday use for embarking and disembarking the aircraft, or are some specifically designed for use as emergency exits, such that opening any of those designated as emergency exits would require specialists to put them back in place?

In other words do all have hinges for everyday use?

None of the 16 exits are hatches. All 16 have identical operation. From the A380 FCOM:

  The aircraft has 16 passenger doors (...) The doors open forward. The opening/locking of the door is performed mechanically by moving the door handle. In normal operation, the door revolves electrically by pressing the OPEN pb, or the CLOSE pb. In emergency operation, the door revolves automatically. In the case of an electrical power loss, the door can be manually operated. There is a flight lock actuator in each door that locks the door handle during the climb and descent phases, in order to prevent inadvertent operation during flight.


Do helicopters need to use yaw pedals to fly a coordinated turn? I recall years ago, when I took a helicopter tour, I noted the pilot simply moved the cyclic left or right to bank the helicopter and initiate a turn. No pedal input was made whatsoever, and the ride seems completely fine.

In many fixed wing aircrafts, if rudder is not applied during the entry of a turn, the airplane will have a tendency to yaw to the opposite direction due to the drag induced by the ailerons.

Is pedal (rudder pedal? what are they called in a helicopter?) input necessary for turns in a helicopter?

Many helicopters have different flight characteristics, but for general information you can always look in the FAA Helicopter Flying Handbook, this is from Chapter 9:

This is from a section on the four fundamentals of flight (straight-and-level, turns, climbs, and descents):

  Anticipate the following characteristics during
  aggressive maneuvering flight, and adjust or lead with
  collective as necessary to maintain trim and torque:

  Left turns, torque increases (more antitorque).
  This applies to most helicopters, but not all.
  Right turns, torque decreases (less antitorque).
  This applies to most helicopters, but not all.

So some (most) helicopters do require some torque pedal movement for aggressive maneuvering, but the pilot may have anticipated this and added the correction prior to beginning the turn. You may not have noticed as much pedal movement as you would in a coordinated turn for an airplane, or the helicopter you were riding in had different flight characteristics and was not maneuvering aggressively enough to need it.

Many helicopters "wind vane" pretty well, that is that they stay aligned with the relative wind at high speed. It could be that the helicopter you were in was travelling at a high enough rate of speed that a large (or any) correction was not needed to maintain proper alignment.

For an example of how speed cancels out the need for anti-torque control, see this article about a helicopter pilot that lost the tail rotor and continued to fly for half an hour to a proper landing site.


How do I compute thrust of a rotor disk and the necessary power to drive it?? as it seems, this question has been asked a few times here so please forgive me for asking again.

If I have 50 BHP shaft power available at 5000 RPM and 106 N.m torque, then can I convert it to 200 kgf of thrust?

I intend to use two sets of horizontal rotors, dividing 50 BHP between them and each generating 100 kgf thrust. Is it doable? What will be the diameter of propellers and their RPM to achieve this goal? What about pitch?

Any help, even if in part or help in the form of guidance to correct resource will be immensely helpful.

Thanks in advance :)

Edit:
1. I intend to provide vertical thrust and not horizontal as we do in aircraft.
2. I want to specifically know following things:-

Suppose I have a generic 2000 mm diameter rotor blade, (I have no idea what typical pitch value is). I want to know what RPM it needs to be turned at to produce 100 Kgf force and what will be the power or torque requirement.

Use this formula:

(From Wikipedia entry https://en.wikipedia.org/wiki/Disk_loading). Where P is the power in watts, T the thrust in Newtons, A the disk area of the rotor in sq. meters, and rho the air density in Kg/m3, around 1,22...


Is there a special way to calculate the (parasitic) drag produced by the propeller? Is there a special way to calculate the drag produced by the propeller? Can I compute it with the standard formula for parasitic drag, with the circular area of the propeller as the wetted area?

To be more specific. I have a graph of the thrust vs. the incoming speed of my propeller

Not quite. The propeller accelerates air, and the cross section of the accelerated air is slightly smaller than the prop disc area. However, this jet of air will sweep surrounding air with it, so there is no clear boundary. Also, the fuselage or engine nacelle will displace the slip stream / propeller wake, so you need to check what cross section is needed to accommodate both. If you now look at the wetted area in the propeller's wake, you need to calculate two effects:

Increased dynamic pressure and surface speed with fully turbulent boundary layer, causing more friction and pressure drag, and
Propeller swirl, which creates additional lift / side force on the surfaces in the prop wake. Include trim drag to counteract the swirl effects.

Fist you calculate the drag without the propeller, and then with it. The difference is the contribution of the propeller wake. For simplicity, assume a constant speed over the cross section of the propeller wake and do not include the acceleration of surrounding air. For more precision, try to add the deflection of the propeller wake by the wing and consider that the acceleration of the air flowing through the propeller disc is normal to it while the airflow itself comes from a direction described by the angle of attack and the angle of sideslip. If these are not zero relative to the propeller, the propeller wake will have a different direction than the surrounding air flow.

If $\Omega$ is the angular velocity of the propeller, $v_{\infty}$ your flight speed and $\Delta v$ the speed increase due to the propeller of the diameter $d$, your swirl $\omega$ is $$\omega = \frac{2\cdot\Delta v\cdot(v_{\infty} + \frac{\Delta V}{2})}{d^2\cdot\Omega}$$
The speed increase in the propeller propeller wake for a given thrust $T$ is $$\Delta v = \sqrt{v_{\infty}^2 + \frac{4\cdot T}{\pi\cdot d^2\cdot\rho}} - v_{\infty}$$
in air of the density $\rho$. Thrust is engine shaft power times propeller efficiency, divided by flight speed.

This sketch shows the stream tube going through the propeller disc (light grey) and below the pressure profile in the stream tube. Air is sucked into the propeller and pushed out at the back, and the cross section of the stream tube is proportional to the inverse of the flow speed. In the propeller disc, just half of the speed increase $\Delta v$ has occurred (Froude's hypothesis).

EDIT:

This answer by @xxavier lead me to a very interesting paper in which the drag of a Luscombe 8b with and without thrust was compared. A very thoughtful way was used to arrive at zero-thrust numbers, and the result showed that the additional drag from the propeller effects was about 30% of the total zero-lift drag without thrust.


Which aircraft/powerplant manufacturers use metric hardware? The vast majority of airframes and powerplants use U.S. standard/SAE hardware. Which manufacturers of engines and airframes use metric hardware?

All use metric dimensions, only the numbers look sometimes rather odd.

This statement is more serious than it might look, in some places you order parts in metric dimensions and they come as 3.175 mm or 12.7 mm.

All Russian (and, by extension, all former East Bloc country) engines use metric dimensions. You only see fewer of them.

I am less sure about French engines like the CFM-56 which uses a GE-designed hot section, but the fully French-designed engines use metric, too.

In the GA world the modern Diesel engines are all metric.


What is a two- or three-mile base exactly? I frequently hear the tower instruction

  Report a two mile base for runway 5

What is the intention of that instruction? I realize that under these circumstances that we're not looking for pinpoint precision, but still it would be nice to know.

For the record, I'm not asking what a base is (or the fact that "left" is implicit), but what two miles are we talking about? Two miles straight line distance from the threshold? A base to a two mile final? On the base leg, two miles from the centerline? (I'm pretty sure the last one isn't it, but hey, I've been wrong before)

They basically ask you to report it as a "memory jogger" for themselves so that they can do something when you call in (like clear you to land).

A standard airport traffic pattern is described in Chapter 7 of the Airplane Flying Handbook as:

  The downwind leg is a course flown parallel to the landing runway, but
  in a direction opposite to the intended landing direction. This leg
  should be approximately 1/2 to 1 mile out from the landing runway, and
  at the specified traffic pattern altitude. During this leg, the before
  landing check should be completed and the landing gear extended if
  retractable. Pattern altitude should be maintained until abeam the
  approach end of the landing runway. At this point, power should be
  reduced and a descent begun. The downwind leg continues past a point
  abeam the approach end of the runway to a point approximately 45° from
  the approach end of the runway, and a medium bank turn is made onto
  the base leg.

It looks like this:

When the tower asks you to fly a two mile pattern, they want you to fly a pattern that has the downwind leg 2 miles out from the runway instead of the 1/2 to 1 mile that is normal.  The base leg would still be turned when 45° from the approach end of the runway.

In this case, you are either:

Doing pattern work in which case you fly the two mile wide pattern and should report turning base, or
Approaching the airport and the controller would like you to enter the two mile wide pattern on the base leg.  You should report the point where you would have normally turned onto the base leg if you were flying the entire pattern (45° to the runway).  This would actually be both of your last two scenarios above:  Established on the base leg, two miles prior to intercepting a two mile final (which for fun would actually be 2.83 miles from the runway).


Can quadrotors be used for commercial passenger flights? Recently, I have been conducting research on more efficient means for vertical lift transportation. One direction I was thrown in was the use of a quadrotor system  with vector thrust and artificial stability. All of this is done using a system of ducted fans and electric motors. I would love your answer on "Does a system like this sound like a safe and quiet means to transport passengers?"

The name of the program is UV-4, and although it is being tested on flight simulation as an unmanned cargo delivery craft, I wonder if it also makes sense as a passenger aircraft.

Would this type of aircraft produce less noise than a traditional transport category helicopter of the same size? Length = 41ft (Prop blades are ducted and aircraft has two electric motors)
Can a ducted fan rotorcraft create regenerative energy using magnets or other method to create square waves?
This experimental is a UAV; could you picture a piloted passenger aircraft?

The three most important factors in passenger air travel are safety, safety & safety. So that is where most of the questions will focus on, and where most of the engineering effort will be put into. Couple of questions:

Artificial stability: what happens if the stability circuit breaks down?
What happens if one of the motors fails, for instance one of the big aft ones? Can the craft still stay upright or does it topple over? If it stays upright, can the remaining motors still provide enough lift to keep the craft flying?
What happens if the battery runs down or fails during flight?

These are redundancy problems that need to be solved. Any system that causes an unsafe situation when it fails must have a redundant layout. So at least a penticopter instead of a quadcopter: upon engine failure, 4 props can safely land the craft.

The redeeming feature for quadcopter is ease of manoeuvring with variable rotational speed per propeller, instead of having to make a swash plate arrangement. But light single rotor helicopters have been around for a long time and the technology is mature - I don't see what particular problem the quadcopter can solve that for instance an R44 might have.

On your questions:

Q1 Noise: yes electric motors are nice and quiet, and the shrouds shield noisy tips in most directions.
Q2 Regenerate energy: it can only do that during authoritative descent, which would be frighteningly fast due to the relatively small total rotor disk area.
Q3 Not a UAV: sure, tilt rotors exist already

Edit: the propulsion system you draw is not so revolutionary. If you travel to Niagara Aerospace Museum, you can see the X-22, built in 1967.

From a comment:

  •I have had one rotor fail (larger) and be able to land the aircraft safely, even maintain a hover but not climb. Aircraft does not topple in simulations, software used Xplane 10 and 11 ultra releastic. – Robert Gomez

That is a claim that sounds hollow. It depends on the location of the centre of gravity: if it is within the triangle formed by the remaining three rotors, it will stay upright. Picture an X cross connecting fwd left - right aft, fwd right - left aft.

If CoG is behind the middle point of the cross, either one of the front rotors can fail and the craft will fly stable on the remaining rotors, because CoG is within the triangle formed by the operational rotors. But not when one of the aft rotors fail.
If CoG is forward of cross centre, either one of the aft rotors can fail. But not a front rotor.
If CoG is exactly at cross centre, the rotor diagonally opposite the failed rotor cannot exert thrust otherwise the craft will roll. So one rotor fails means only two can be operational.


What is the folded size of a sectional map? Bending aluminum for a map box, and am curious as to the folded dimension of a sectional chart. My present resources use moving maps on EFIS and iPad, but I would like to carry standard paper charts.

One seller's link on Amazon claimed 10" x 5", but when I measured an old one (only one I have handy), it was between 10.25" and 10.5" long by 5" wide. So I'd recommend using the latter value, knowing that the chart will probably be a hair under 10.5" long and so you have room for error (or a badly refolded chart).


Under what conditions would a helicopter be allowed to fly at low altitude over populated areas? Yesterday, the Department of Energy was flying a military helicopter at low altitudes over Boston and the surrounding area as part of an experiment of some type to measure radiation.

I saw one of these aircraft when I driving through Watertown and in fact it passed right over me. It was operating at a very dangerous altitude. Any kind of engine failure would have created a multiple fatality situation. Normally, aircraft do not fly at high speed below 500 feet and when helicopters descend below 500 feet they normally do so cautiously and in an area they know to be safe. Having a large helicopter flying at high speed over a dense city at 100 feet AGL is very dangerous and against FAA regulations.

The type of helicopter was not the civvy type pictured in the news story, it was a Chinook. For NASA to be circulating a photo with a little civvy helicopter and then actually flying around a big Chinook I thought was pretty deceptive on their part.

I have not filed a pilot complaint about this because I assume some kind of special "permission" or exception was created to allow for this dangerous activity. Does anybody know the legal authority involved here and conditions?

BTW, I did not check the NOTAMs and did not get any NOTAMs in my mailbox on this, so if somebody can link the NOTAM that would be useful.

Update: this may have been a medevac flight, with emphasis on the word "may". Apparently, in some cases military helicopters are used for medevac flights to Burlington. However, if it was, the pilot was hot dogging and off the normal routes, both of which are serious regulation violations, but nevertheless I am told some military pilots disregard the rules.

I have no idea about the specific flight you saw, but the general answer to your question about operating legally below the minimum safe altitudes in 14 CFR 91.119 is that the FAA can grant a waiver allowing lower flight. The waiver process says that to get a waiver to 91.119(b) (flight over congested areas) there must be a public interest reason but aircraft can't be lower than 500ft unless lives are at stake:

  When issuing the waiver, the altitude requested should be an absolute
  minimum, but may not be less than 500 feet from persons or property,
  unless necessary to safeguard human life

There isn't enough information about the helicopter you saw to say what was going on but assuming that it really was a Chinook at at 100' AGL then it was too low even for a waiver, according to the FAA's process. But the most obvious explanation is simply that it was taking off; helicopters take off in a range of attitudes and airspeeds and some of those takeoffs are probably relatively low and fast. It might have been a medevac flight (they're often brightly painted) or perhaps something to do with logistics or construction; if you got the N number then you could look it up.


Since when are ground-based starting devices no longer in common use? Are there any jetliners flying that would still require them? Nothing is written in Wikipedia on how the engines of the De Havilland Comet or other similar airliners were started. However, it seems that aircraft of this generation could not start the engines stand-alone without the ground support, and that the Boeing 727 in 1963 was the first jetliner capable of doing this.

In one of the answers Terry describes technicians suffering desperately while attempting to start 747 with the two old ground-based devices. From this it looks like while "theoretically possible", this was a very uncommon and unexpected task for them.

Since when are ground based starting devices no longer in common use? Are there still any jetliners in service that would require them?

What was uncommon about the experience in Harare, Zimbabwe that you reference in your question was the arrival of a 747 with an inoperative APU. If I had to bet money, I would bet that they had never had that happen, or if it had, the captain had enough sense to leave an engine running. Harare's ground crew experience was having to start much smaller engines requiring far less pneumatic power from the ground carts. Thus pneumatic carts (huffers) that had had their output degrade over time still had sufficient output to start smaller engines.

  Since when are ground based starting devices no longer in common use? Are there still any jetliners in service that would require them?

As of my retirement in 1999, ground based starting devices were in common but infrequent use. I would suspect that's still true, although hopefully less frequent. Any jetliner engine of size will require a ground pneumatic source to start if the airplane itself cannot supply that with its APU or an already running engine.

Back to my experience in Harare, the first mistake made was that of our dispatch department sending an aircraft there with an inop APU.


Why do passenger aircraft have the little airjets over each seat? I never turn them on, but I do turn them off if I notice them. Is this a relic from the age when people lit up next to you and you wanted to blow away the smoke? The system must weigh almost a ton on a large aircraft and seems pretty unpopular and hard to maintain.

Why do airliners have them? Because passengers like them.

When you're sitting in the penalty box waiting for a departure slot and the air conditioning system is barely running the extra cool air you can get from those vents may be the only thing keeping passengers from strangling the screaming child kicking the seat.

Also a common "cure" for airsickness is fresh air -- blowing cool air over someone's face will often help with symptoms of motion sickness, and may prevent a nauseous passenger from actually vomiting. Opening these overhead "gasper vents" and directing them at the passenger's face provides a quick way of doing this.


Can a pendulum stabilizer for airplanes really work? Can a pendulum really stabilize a plane for both roll and pitch?

I have read about various experiments (the one in the picture being just a simple case) but I still do not find an example of plane that was stabilised beyond any doubt with the help of a pendulum.

As a note:
If the suspension point of a pendulum is at rest or moves at constant speed then after some oscilations the bob will end up by hanging vertically. However this is not the case when the suspension point has an accelerated movement.

Source: Popular Science, December 1939

UPDATE

I have found a description (see the attached image) of a Wright stabilizer that was used successfully!! before February 1914. The roll was controlled by a pendulum (letter A in the picture) that swung along the main wings. At one point the article states that the device gave good results being tested daily for long intervals of time.

Another more recent text says that demonstrations were made before the Aero Club judges on December 31, 1913.

  In the fall of 1913, Orville installed the stabilizer on a special
  Wright Model E airplane that utilized a single pusher propeller. He
  kept the details of the stabilizer secret even from the Wright
  Company. He purposely waited until the last day of the year to fly for
  the prize.

  He invited the Aero Club’s judges to Huffman Prairie to see a
  demonstration of his new device on a cold snowy day, December 31st.

  He turned up his coat collar, put on a pair of goggles and took off.
  He made a total of 17 flights.

  His most spectacular flight consisted of 7 full circles of the field
  with both hands held in the air. The automatic stabilizer kept the
  same angle of bank and almost the same altitude. He wowed the judges
  and was awarded the prize on February 5, 1914.

Source: Wrights Develops Automatic Stabilizer

How is it possible?

Source: The Wright Automatic Stabilizer, L'Aerophile, February 1, 1914

As you noted, a pendulum can only "measure" pitch and roll angles when the pivot point is not accelerating.  Except, of course, if the length of the pendulum is the same as the Earth's radius — in which case we have a Schuler Pendulum.

Ed Carsten's pendulum stabilizer attempts to use the same principle as an autopilot measuring roll and pitch angles, and then generating elevator and aileron commands to level the aircraft. But this cannot work when using a pendulum of practical length since the roll and pitch angle "measurements" are in fact combinations of attitude angles and horizontal accelerations.


Where does the transponder read altitude, or does ATC get it from radar? When flying instrument approaches in a rented plane, Approach called out an altitude discrepancy between the assigned altitude which is being flown using the altimeter and the altitude being reported by the Mode 3/C transponder.  Back at the hangar, the question is: does the aircraft have or need an encoding altimeter interfaced to the transponder to report altitude, is it built into some transponders; or was the Approach controller using altitude as reported by the radar if it has height finding capabilities?

does the aircraft have or need an encoding altimeter interfaced to the
  transponder to report altitude, is it built into some transponders

In order to squawk mode C, you need an encoding altimeter connected to your transponder and the transponder needs to be set to transmit mode C. Does that transponder have a build-in encoding altimeter? That requires a check through the logs and/ or manuals. In my aircraft they are separate, in yours I have no idea.

  or was the Approach controller using altitude as reported by the radar
  if it has height finding capabilities?

Maybe. It depends upon the specifics of the airport. If your transponder's altimeter was calibrated incorrectly or otherwise bad (extremely difficult for you as the pilot to verify in a rental aircraft during preflight) then they may have been trusting your transponder for your altitude data, which was incorrect. If they were using radar with vertical capabilities (precision approach radar is, depending upon your viewpoint of part 91 vs part 121, either relatively rare or everywhere you might need it where I live) they may have been comparing that to your transponder's altitude reported.

All of this depends upon if you checked your altimeter using the current local setting on the runway threshold prior to takeoff. Have I always done that? Yes. Does everyone? No. If your panel altimeter checked out, you used the proper setting during the approach, and your transponder is telling them you are at the wrong altitude the transponder's altimeter appears to be the problem.


What's the difference between 'modification' and 'corrective action' in an AD or SB? For example Modification of an airplane in accordance with the instructions of the specific SB as specified in Table 1 of this AD, as applicable...

A modification is a change to the airplane's physical configuration from the standpoint of fit/form/function.  Think Service Bulletin with a parts kit. Or an SB that has instructions for a physical rework of a part that makes it different from non-reworked parts, and the part is re-identified.

A corrective action is any action required by the AD to mitigate the risk associated with it.  Usually it's something less than a mod, like a inspection, change to a maintenance program, crew procedural change, de-escalation of a check or procedure's interval, an operational limitation, or any other action as required by the AD.

Terminating action is some activity that completely resolves the AD and restores the airplane's original airworthiness state, as opposed to something that temporarily mitigates risk so you keep on flying.  Incorporation of a Mod, or permanent incorporation of a inspection regime that previously wasn't mandatory.

On a side note, one thing about FAA ADs that makes them a total pain from the OEM's standpoint is that the FAA will not issue revisions to ADs like other authorities do.  If there is a change to the AD's terms they will only issue a new AD that supercedes the old one. Makes getting minor changes to ADs very difficult because it has to be worth issuing a new one.


Why do some fighters have two engines? Some countries (e.g. Russia) develop fighter aircraft (e.g. Sukhoi) with 2 engines.

Is it for maneuverability, or is it because they can't build an engine that would meet the power requirement?

Taking the Sukhoi Su-35 for example, it has two engines, each capable of producing 86.3 kN of dry thrust, combined they produce 172.6 kN. With afterburner they produce 284 kN (142 kN each).

The jet engine on the American F-22 produces 156 kN with afterburner, close to the 142 kN of the Su-35.

Soviet Union / Russia made the Kuznetsov NK-32 military jet engine, capable of 137 kN (dry) and 245 kN (wet).

So, the ability or technology to make a powerful jet engine is not the reason. It's just powerful engines are much bigger.

The main reasons for selecting a twin engine design are:

Slimmer design, two smaller engines make for a slimmer profile than one big engine.
Redundancy, in case one fails, especially important for big fighters.
Afterburners are easier to make for smaller diameter engines.


can I do my PPLA license in spain even if I live in Germany? I live in Germany but I was born in Spain, I wpuld like as a hobby, to get my PPLA license..
but I would like to do that in Spain, if so, can I still flight in germany?

is that possible?

Thanks..

Yes, an EASA PPL is valid in all EASA member states


Why are there double hinge lines on the rudders of the Grumman C-2? Why are there two sets of hinge lines on the rudders of the Grumman C-2?

A photo from the related ASE question Why does the C-2 left inboard stab not have a rudder?
Why would two hinge lines provide more control authority than just using the forward hinge line and deleting the rear one?
And why was it thought worth the extra complexity and weight to use this feature on this aircraft when so few other aircraft have been designed with this feature?
What other aircraft have been designed with this feature?

The double hinged rudder is also a Dehavilland Canada feature on most of its larger designs like the Caribou/Buffalo/Dash 7/Dash 8, where maximum yaw power for a given surface area was a design priority (especially if there are height or other limitations that prevent you from adding more area by going up; in the C-2's case, they also added more surfaces as well to limit height, an obvious issue on a carrier, and the same reason the Constellation had 3 tails).
It improves yaw power for a given overall surface area by allowing the rudder to operate at a larger net angle before significant flow separation, by allowing the airflow to make 2 smaller changes in direction vs one larger change in direction for the same overall displacement.
It's not quite as complicated as it looks.  The trailing edge segment is effectively a giant anti-servo tab and is simply geared to the vertical fin by a push rod.  The actuation system only has to drive the forward segment.  The extra parts and complexity are in the second set of hinges and the actuating rod.  In the C-2 pics you can see the gearing rod attachments in the little blisters. On the DeHavilland Canada products, the gearing rod is hidden at the base of the rudder.


Why is “L Fuel Low” illuminating on my Cessna that is full of gas? I fly a fuel injected Cessna 172SP 200 hp. Tanks were just about full today and every 5 seconds or so in flight, I would get “L fuel low” and the left fuel indicator would drop to 0.
I’ve consulted with a few people and get differing answers. Some say it’s due to the blue dye in the tank? Some say bad sensor? Any thoughts?

Fuel dye has nothing to do with it.
The fuel sender in light airplanes is usually an automotive-style float operated potentiometer, a rotary variable resistor, like a volume knob on a radio.  Inside is an arm, or wiper, that sweeps around a resistive conductor in an arc, providing a variable output voltage for the fuel gauge.  There will be a voltage range for the potentiometer output to the gauge with 28 vdc going in, say, 22 vdc for full, and 4 vdc or less for empty. The low fuel light will be set to come on when the voltage is some margin above that, say, 8 vdc or less or something like that.
Sometimes the resistance element inside the pot is a kind of circular wire coil on a card, sometimes it's a resistive coating on a flat surface.  If part of the resistor is worn to the point where there is an open circuit when the wiper passes the worn spot, the voltage going to the fuel gauge drops to zero, until the arm moves off the worn spot and the voltage is picked up again.
The low fuel light coming on plus the gauge dropping to zero suggests that the voltage signal is dropping out upstream of the fuel gauge and sensing circuit for the low fuel light.  Could be due to a worn spot in the pot as the float moves when fuel sloshes around in the tank, or it could be an intermittent open in the wiring.  If the problem goes away when the fuel level drops to some lower amount where the potentiometer no longer contacts the worn spot, that would tend to confirm that possibility.
If I was the mechanic I'd try to duplicate the fault by sticking something in the tank that can move the float up and down and observe the result.  If everything works normally, it's more likely to be a loose connection somewhere giving an intermittent open circuit. Check wiring, and if ok swap out the level sender and see if the problem goes away.


Why do we take off with maximum power settings? In most GA prop airplanes, take-off is executed with full throttle and high rpm. The usual reasoning is that this way, we leave the first few hundred feet, where failures are most severe, behind as fast as possible.
Isn't this like driving a car, seeing ice/playing kids/any other hazard, and speed up to leave the danger behind? In other words: Shouldn't we be most careful and conservative near the ground, with as little stress to the engine as feasible?

It should come as no surprise that flying an airplane is not like driving a car. When driving a car, you can come to a complete stop and nothing exciting will happen. You cannot do this in an airplane; coming to a complete stop is either the beginning or the end of a great deal of excitement.
Flying near the ground in any circumstance is a hazard. As you say, the goal is to get away from the ground as quickly as possible. This should not be "stress to the engine", engines are designed and maintained to support the full throttle takeoff.


Why does airport security use numbered baskets for my carry-on stuff to be x-rayed? I recently flew from TPE and noticed that there, the baskets for the carry-on stuff that gets scanned are numbered:

I can't think of any reason why this would be useful. Can anyone explain?

It makes it easier to pull a basket from the line. Its likely that those numbers show up on the X-Ray screen so that if the person watching sees something that needs inspection they can say

  pull basket number 18

instead of,

  i think thats the one to pull, it was 4 baskets after the one with the shoes and the laptop.

There are also ones are available now with RFID tags inside for a similar reason.


What might happen if I receive flight instruction in a plane with an airworthiness deficiency? Let's say I were to a day VFR flight with a new instructor, in hopes of eventually pursuing Sport Pilot - Airplane privileges (U.S.A.)

During the flight, I notice the plane has a minor airworthiness problem. It doesn't affect the safety of the flight, but something required is missing. The magnetic compass, for example, is loose in the glove box instead of mounted on the instrument panel. I bring it to the instructor's attention, he downplays its significance and says he plans to get it fixed in a few weeks.

The flight goes otherwise well. The instructor fills out & signs my logbook in the usual way.

Is this legal instruction time? If this instructor were to get in trouble over instructing in an un-airworthy plane, could that void those instruction hours' applicability towards the sport pilot hour requirement?

(and the more subjective question: practically, how worried should I be over something like a missing compasss? Is it really as minor as I think? Anything I should be looking more closely for before I fly again with him?)

It can’t void the time, but if an Inspector ever caught a CFI doing something like that, he’s in big trouble.  And more importantly, that CFI should know better than to do something like that in front of a student.


Why isn't Vy lower than the speeds for best L/D ratio and best glide ratio in an airplane with a piston engine and a variable-speed prop? This answer to a related question implies that if the power available were constant regardless of airspeed, Vy would occur at approximately the angle-of-attack that yields the minimum sink rate with power idle, which occurs near the airspeed for the max ratio of lift coefficient cubed / drag coefficient squared, slower than the airspeed for max L/D ratio.  The airspeed for best glide ratio should be only a little slower than the airspeed for max L/D ratio, to minimize the extra drag from the stationary or windmilling prop.

Therefore it would seem that in an aircraft with a piston engine and a constant-speed propeller, Vy should be slower than the best glide speed.  Yet this manual for a Cessna 182 gives the best glide speed as 70 KIAS, and gives Vy as 78 KIAS at sea level and 72 KIAS at 10,000' MSL (page 4-14.)  So why is Vy faster than the best glide speed in this aircraft?  Why isn't Vy slower than the best glide speed?

In essence, this is a question about what the power-available curve looks like for an aircraft with a piston engine and a variable-speed prop, plus a question about what other factors may be at play here.

Is less power available at lower airspeed?  If so, does that imply that less manifold pressure is available at lower airspeed?  Presumably the throttle would be fully open in a climb at Vy -- is the engine unable to turn at the optimum RPM for maximum power when climbing at Vy?

Does the answer have to do with the fact that even with a constant speed prop, at most airspeeds, the pilot cannot simultaneously optimize the RPM of the engine and the angle-of-attack of the prop?  And thus the power available (given that RPM and manifold pressure are kept within safe limits) is not constant as the airspeed varies?  Since there is no variable transmission (variable gearing) between the engine and the prop, it would seem that this would be an accurate description of the situation.

(Naturally, the designer of the prop can simultaneously optimize the angle-of-attack of the prop and the RPM of the engine by selecting the appropriate prop diameter, chord width, blade twist, etc, but it would seem that this optimization might be only valid at one particular airspeed, even with a variable-pitch or constant-rpm prop.)

It would seem that in an aircraft like a Cessna 182, the maximum achievable steady-state climb angle would be shallow enough that the "unloading" of the wing during the climb is not very significant, so that essentially the same correlation between angle-of-attack and airspeed exists in climb, horizontal flight, and gliding flight.

Here are some other related ASE questions and answers--

Why is best angle/rate of climb indicated in airspeed? -- informative, but it is unclear whether the graphs are meant to represent the case of a fixed-pitch prop or a variable-speed prop.

Does a windmilling propeller create more drag than a stopped propeller in an engine out scenario? -- informative, but it is unclear whether the "best glide" airspeed in a typical pilot's operating handbook would represent a stopped prop or a windmilling prop.

Is Vy closer to Vbg with a variable pitch prop -- closely related to the current question, but the actual body of the question is phrased entirely in terms of a fixed-pitch prop.

It's because climbing at Vy the engine only has to overcome the airframe drag minus the prop, on top of the thrust lift component reduction in induced drag you mentioned in your answer to another post.

It's as if you took the prop off and towed the plane with a tow line glider style (this was done on a Wittman Tailwind back in the early 60s for some gliding drag studies to learn the plane's true L/D, with the tow line connected to the engine prop hub; the Tailwind turned out to be an extremely efficient airplane, square corners, stubby little wings and all).

Best glide has to take into account the substantial drag of the windmilling prop, so the best L/D is achieved at a lower speed.  I'm pretty sure the POH numbers are based on the worst case of the prop windmilling at flat pitch (where it goes if you are climbing at Max RPM and the engine quits), where the drag is so massive it's like you deployed a speed brake.

You can improve this a lot by pulling the prop to Min RPM when the power is removed to try to get the governor to drive the blades to full coarse pitch. This gets you at least part way to being feathered, and helps quite a lot in the glide.


Saw this plane in Falkland war documentary. What type is that? That nose reminds me of ground attackers, but IDK why

Looks a lot like the FMA Pucará :

https://en.wikipedia.org/wiki/FMA_IA_58_Pucar%C3%A1


What happens when all passengers jump at once? As a thought experiment, imagine a plane with minimal fuel/appliances on board with hundreds of heavy passengers that make up say 10% of the weight of the plane.

Now imagine that they have a way to synchronize a jump where temporarily for 0.5s they are airborne in relation to the plane.

(NOTE: If idea of so many heavy passengers is troublesome to you, assume this is a cargo carrier with spring loaded "widgets" that have ability to be programmed to "jump" at once.)

Questions:

Can flight dynamics be affected due to the jump at ANY phase of the flight?
What % of the typical (cargo/passanger) plane weight is the actual cargo (excluding fuel)?
Does the location of the "jumping" cargo matter?  Tail vs. Cockpit
What happens if all pax/cargo suddenly jumped to tail or cockpit section?

Everybody jump!

I will assume that the starting condition is level flight.

yes. momentarily the assumption of "rigid body" would not be satisfied. Also, for that 0.5s the aircraft would not be in contact with 10% of the weight, assuming constant thrust and velocity, you would have 10% more lift than weight, making the aircraft rise a bit before descend again when all the passengers land again. Velocity would not be greatly affected, as the drag would remain unchanged (no external change in shape or large attitude variations)
the difference between zero-fuel weight (ZFW) and Dry Operating weight (DOW) is probably what you are looking for. Airbus defines it as the "total traffic load". If you want to add catering, cabin equipment and the crew, you then take the difference between the ZFW and the Manufacturer's Empty Weight (MEW). As a percentage it can vary wildly based on the aircraft class (class 23 has much less cargo/passenger space that a class 25, for example)
yes. think of a beam in equilibrium on a pivot located at half its length: if you push just above the pivot, the beam will not rotate, any other location will cause it to rotate and flip over. This does not mean that the aircraft might flip over, as the beam is an uncontrolled and unstable system, while the aircraft is controlled, but it is a comparison that can help visualize the effect
I would define it more as shifting rather than jumping. This is a totally different scenario: the center of gravity at the end of this "jump" would be in a totally different location w.r.t. the start of the experiment, something that instead was not happening in the previous scenarios. By shifting the location of the center of gravity is likely that it might exceed the specified position limits and cause the airplane to be uncontrollable, to pitch up or down (depending if you shift the passengers backwards or forwards) and stall or nose-dive. On large aircrafts it is obviously not easy to achieve such unsafe scenario, as the cargo will be usually much heavier than the passengers, limiting the extent of the CG shift.


How do blow holes compare to other means of tripping the boundary layer? The DG-300 glider has wing holes to delay flow separation.

How do they compare to vortex generators and other means?

  This wing is 'blown' on the underside by 900 small holes to achieve a controlled transition from laminar to turbulent flow without additional drag.—Glaser-Dirks DG-300

(Image borrowed from another post.)

In modern gliders, active tripping of the laminar boundary layer helps to reduce or avoid a laminar separation bubble. There are three ways of doing this:

Noppenband (dimple tape):

Close-up picture of a spool of Noppenband (picture source)

Zig-Zag-tape:

Spool of zig-zag tape (picture source)

Blowhole tripping: a line of tiny holes (0.8 mm diameter, usually with a steel liner) along the span which are fed by dynamic pressure, usually created from a small scoop or a NACA inlet (sorry, no picture). Note that while you can add the first two turbulator types at any time, blowhole tripping must be designed into the wing from the start by placing a duct inside and adding the scoop.

The order in which they are listed is no accident: Robustness decreases and effort for production increases as you move down the list. The pimples are like bugs and trip the boundary layer directly. This is fine if you fly at one angle of attack and one speed only, because then the chordwise location of the separation is fixed. Just place the Noppenband 2-3% of chord ahead of the separation point and it will effectively avoid laminar flow separation by tripping the boundary layer.

If you vary both speed and angle of attack, the location of the laminar separation bubble on the upper surface will vary over a wide distance. If you try to optimise the transition for slow flight (= low Reynolds numbers and high angle of attack), you need to place the turbulator tens of percent ahead of where it would be best placed for fast flight, thus adding a lot of unnecessary turbulent boundary layer when friction drag counts most.

On the lower side of the airfoil, the effects of Reynolds number and angle of attack work against each other, and the separation bubble changes its position only slightly over the speed range of the glider. Now it makes sense to actively trip the boundary layer, but you still get some additional turbulent length when using Noppenband.

Zig-Zag tape will merely prepare the boundary layer for transition, so laminar flow continues for a few percent downstream until the local pressure gradient does the tripping. Now the variation in the separation point will not result in extra turbulent length. Normally, Zig-Zag tape is placed 2% ahead of where Noppenband would go for best effect.

Blowhole turbulators can even be placed inside the laminar separation bubble and will destroy it when positioned a few percent past the actual separation line. By blowing into the eddies of the separated flow, the tripping will alter the pressure distribution such that the laminar bubble is either much smaller or even disappears altogether. Now the turbulator can be placed further back and will add even less extra turbulent boundary layer.

With blowing also the upper separation bubble could be avoided if several rows of holes are placed along the span and the pilot can control to which one the airflow from the scoop is directed. To my knowledge, this has never been used in real life, though.


How do military fighter aircraft identify themselves and each other? I live in an area where there is much NATO military activity. Often there are various fighter aircraft fly-overs. But none of the common websites such as flightradar24, flightaware and planeflighttracker etc. used for identifying aircraft using ADS-B and ACARS etc, are able to "see" them.

So apart from ground radar, how does the military aircraft identify themselves?
Are there other type of transponders used in these?
Has there been any known attempts at building some amateur radar network to track these unidentified aircraft?

There was little useful information in this SE answer. I also found after posting a very similar SE question and answers. However, it still doesn't fully address the questions.

EDIT: As an update for question (3), there seem to have been some success on using SDR's as passive radars, as shown in these links:

http://www.rtl-sdr.com/building-a-passive-radar-system-with-an-rtl-sdr/
http://www.rtl-sdr.com/tag/passive-radar/
http://www.kaminski.up.lublin.pl/RTL-SRD.html
http://hackaday.com/2015/06/05/building-your-own-sdr-based-passive-radar-on-a-shoestring/

Military aircraft, like civil aircraft have transponders. Military aircraft  are assigned military codes, and their transponders have special military modes.

An aircraft doesn't need a transponder to be "illuminated" by radar, but the transponder enhances the "blip" and modern transponders transmit additional aircraft information such as altitude (Mode C).

See the "Interrogation Modes" of transponders in this link.

Notice that the Military modes include "cryptographically" secured version of Mode S and ADS-B GPS positioning.


How can I mount my iPhone 6 in the cockpit to record my flights? I am a student pilot, and would like to record my training flights to look back on. I do not have a Go-Pro, and do not want to fork over the money for one. I do however, own an iPhone 6, that has a pretty good camera. I was wondering if anyone had some ideas as to how I could mount my phone in order to record my flights? I thought maybe a suction mount would be best, as I could mount it behind my shoulder on the back of the glass cockpit (Cessna 152)

If possible, it would be better if it could record my control inputs throughout the flight. Please let me know if anyone has found a working solution in the past.

UPDATE  9/4/2017
I'm thrilled this post has been so helpful for so many people. As such, I wanted to  update it with more details and more current links in case people are interested. Enjoy!

You could have a lot of fun, and get a lot out of reviewing the footage of your lessons. I'd look into a suction cup mount as you are already considering. When buying a suction cup mount, make sure you get one that is "beefier" than you expect you need. Whatever you do, make sure you share your videos online, your video might even get someone else interested in aviation!
Below are the details of doing what you asked. You might be able to buy a used, older model gopro for a comparable price - but I'd actually argue your phone is probably a better option.
What to buy:
(this all actually gets kind of expensive, but is still cheaper than buying a go pro and accessories)
Must have:
To get GoPro functionality from your iphone, you'd need a mount and a case:

http://amzn.to/1ZQDx7q (Optrix Super Sucker Mount)
http://amzn.to/1MyN1uc (Case)

This is a mount that mimics the functionality of a go-pro mount. It also let's you know if pressure is dropping in the suction cup as you climb.
If you ever feel brave enough you could even stick this to your wing!

http://amzn.to/1GmeYbU

The view angle probably is not wide enough. This inexpensive kit will apply a wide angle to your iphone. I'd make sure your case/mount doesn't preclude using one of these.
Best alternative camera to GoPro:

http://amzn.to/2vZsQEx (Garmin Ultra Virb 30)

I love the aviation data overlay of this camera. It works very well and helps debriefing a lot. I personally prefer this over my GoPro because it includes that data.
Best GoPro options:

http://amzn.to/2xJKn67 (GoPro Hero5 Black)

4k resolution @ 30FPS, 12MP quality is great. I use this mainly for wing mounted shots.

http://amzn.to/2eDiQi3 (GoPro Hero5 Session)

The nice thing about the session series is they are small and super simple to operate. I use this camera to point inside the cabin, on the side windows. It is nice because it doesn't block as much of my view outside, even in a mount on suction cups.
Important Accessories:

http://amzn.to/1ZQERqT (Zoom H1)

I use this to record ATC/Headset audio. It is easy to have it recorded to its own device and lets me have better control over the audio recordings than if it was part of a video file. The audio is oftentimes more useful than the video alone, especially with your instructor explaining things to you. Having a separate device also reduces your point of failure risk if you have a camera battery die.

http://amzn.to/2wAg29z (Headset cable to record audio)

You need this cable to "grab" audio from your headset jack to record it to a camera or external recorder. (Note- the Garmin Virb 30 Aviation bundle includes this)

http://amzn.to/2wAo1Uh (External Battery)

You will be running out of battery fast if you record HD video for any length of time. This external charger will keep you from running out of battery.

ND (Prop) Filters (remove the weird prop strobing from your footage)

(Note- the Garmin Virb 30 Aviation bundle includes this)

http://amzn.to/2xJhxm9 (GoPro Hero5 Black ND Filter)
http://amzn.to/2exTIFG (GoPro Hero5 Session ND Filter)

Placement:
The best place to put it would be between the seats on the ceiling pointing landscape style towards the instrument panel. This would give you a view of all of your instruments and maybe even a bit of the horizon. At first, we all struggle to use the horizon as a reference instead of instruments, so putting the camera close to head level might help develop a good sight picture.

Here's a video using the angle I am referring to.
Unless you set up a second camera, you are unlikely to get rudder input on film. This video shows a good example of that angle, but might be impossible while getting dual instruction.

Video showing rudder control input on takeoff
Words of caution:

Make sure your filming doesn't distract you. This is really serious and not something to shrug off. Remember, you don't want the FAA to have footage to shove in your face of you being reckless.
Make sure you don't damage the aircraft with the mount. The windshields in particular are vulnerable to being squeezed out of shape from the pressure in the suction cup, especially if they are hot. I have seen some indented windshields recently due to gopro mounts, which makes it very hard to get a normal sight picture (imagine looking through a fun house mirror).
UPDATE
Another issue I recently saw was a result of someone using this camera: http://amzn.to/1oos68G. The camera has a built in rare earth magnet which made mounting it very easy. The problem was, it was impacting the magnetic compass - so be aware if you get a magnetic mount to make sure your compass is not affected by it being placed in the cockpit! When attached to the overhead speaker we saw no visible impact on the compass, but worth keeping an eye on.

Take a look on youtube at some popular pilot channels to see how they record. From there, you can pick your favorite angles and splice a film together.


Could a golf ball damage an airliner? Question

Would a golf ball ingested into an engine, or impacting a windshield cause meaningful damage to a commercial airplane?

The scenario below outlines that this is possible, but the principle question is: would it actually matter, as in, would it cause the same level of damage as, say, a strike from a single bird?

Plausible Scenario

At McCarran airport in Las Vegas (KLAS), runway 1R is situated just across the street from a driving range. Several years ago, I was hitting balls on this range when a 747 landed on 1R. It seemed impossibly low; many people on the range stopped hitting to point and take pictures. For context, here's a video (not mine) taken from nearly the exact same spot, with an approach to the same runway.

At the time, I remember thinking "That plane is very low... what if it got hit?" Appearances are often deceiving, so my initial assumption was that it must be higher than I thought, so a did a bit of basic trig to find out:

The touchdown markers on 1R are about 4,250 feet (red line in picture below) from the top-level hitting stations. With a 3 deg. glide slope, the plane would have been roughly 225 feet above the ground when passing over the driving range (slightly lower down range when balls that have been hit are at their highest point).

(Image: Google Earth; own drawing)

With a 21-degree 7-wood which I hit about 200 yards, the ball would reach an apex of around 230 feet.

So, wind, timing, and the quality of golf shot actually struck notwithstanding, it seems at least possible that a ball hit from off that range could hit an airplane. In other words, the "bounding box" of the plane at least theoretically intersects a line representing the maximum height of a shot from the driving range. Thus, it seems unsafe, even if the chance is 1:1,000,000 (or greater).

I have to assume that since KLAS is one of the busiest airports in the U.S., that this is not actually an issue, otherwise changes would already have been made.

However, if an impact or ingestion were to occur, are there circumstances where it would be a "significant" event?

Notes

No one, esp. myself, was trying to hit the plane.
Despite #1, there are at least 50 hitting stations, which means lots of shots in the air as the plane is passing over the range.
This is Vegas, and alcohol is served at that range. People do try, sometimes, to hit the guy in the little range car. I doubt that would ever carry over to a plane, but it can't be logically ruled out.
My concern is that even without anyone trying, a ball could still impact the plane. But would it matter?

Turbofans on commercial airliners are tested against hail, up to 'golf ball size', and ice is harder than a golf ball.

Think back to Taca 110, that lost both engines while descending through a hailstorm reported to be up to golf ball size. What killed the engines wasn't the impact of the hail, but the amount of water ingested into the engines. It seems that the engines had been tested for water and hail ingestion at cruising speed... not at near idle, which was the power setting during a descent. Once identified, that problem was rectified quickly with mods to the engines.

Nor does the golf ball have the sheer mass of a goose, such as the flock of geese that took out both engines of USAir 1549.

Most likely, a golf ball striking a running turbofan would be sliced up by the front fan, and centrifugal force would tend to fling the fragments outward where they would exit via the bypass, and not through the turbine engine.

So I'd have to say, very unlikely, only to allow for the chance in a billion that the sliced up fragments of a golf ball might actually enter the compressor stage and cause a problem in one engine.

The greatest problem from a golf ball being ingested by a turbine, is figuring out what rule of golf applies... how do you mark your card? (WTF probably doesn't meet approved guidelines)


Are there any regulations preventing one from converting an originally cargo aircraft to ferry passengers? Are there any regulations preventing one from converting the cargo version of the Airbus A380 for passenger use?

Converting a freighter to an airliner would require lots of work:

you have to install an HVAC system capable of supporting hundreds of passengers, which means installing air ducts from the engines to the cabin, etc. Major surgery to the wing and fuselage.
you have to install a sufficient number of doors and emergency exits (with associated systems). Major surgery to the fuselage.
big changes to the electrical system to support e.g. entertainment for the passengers.

So the conversion would require taking most of the aircraft apart.


Does taking a long time to solo mean that I'll take a long time for training in general? I have a fairly high (in my research - 80hrs and counting) flight hours and still no solo, with landings having been a major reason. There is definitely progress - but I am not convinced I'll solo before 100. I am 43 in decent shape and reasonably coordinated (no red flags).  In addition to being expensive and frustrating it begs a question whether any subsequent flying activities like an instrument rating would also take significantly longer (thus being more expensive and frustrating) and - more importantly - whether it is an indicator that my future piloting skills will always be mediocre.

My CFI says that "everyone hits a plateau" but I am concerned that past may be an indicator for future...

Couple notes to address comments
- I have passed my medical
- Hours were spread over 10 months and there was a 2-3 month lull (due to weather + ski season) in winter and 1 month break in summer.  Otherwise I was pretty religious about 2-3/week lessons.
- I actually changed CFI at about 50hr mark and quite like how my current CFI teaches

So while it would be nice to look at outside issues - I think the problem is more likely to lie with me than with others...  Now back to my original questions...

Any thoughts?

Yes, that much time pre-solo is a huge red flag.

If you have 80 flight hours logged and no solo, unless there is some unusual extenuating factor (e.g. those 80 hours were spread over many years), something is seriously wrong. Either:

You do not have the right aptitude for flying
Your instructor is incompetent, or
Your instructor is deliberately milking you.

If the instructor hasn't already had a frank discussion with you about your progress and prospects by this point, that would indicate #2 or #3.


What types of aircraft perform military airlift operations? What planes are the key players in military airlifting?

I know the C-130J, C-17 and A400M are among them, what others are there?

What are the key differences between the above mentioned planes?

There is no single "key player". It depends on the task. You need big, long-haul transporters like the C-5 or the An-124 to move large amounts of troop and equipment quickly. This is called strategic airlifting and is done with turbofan-powered aircraft which are similar to airliners. But they need prepared and secured air strips of considerable length (the NATO standard airstrip is 8000ft long).And then you need tactical transporters which can fly as close to the action as possible, and they must have STOL capabilities and defensive equipment to survive their missions. This requires mostly turboprop powered planes like the C-130, the C-160 or the An-12 for big equipment or the CASA 235 or the An-26 for smaller units or parts. The C-17 was meant to be a strategic airlifter with some tactical capabilities, but it cannot replace the smaller turboprops entirely. The A-400 and the An-70 are large tactical transports with some strategic capabilities, but this comes at the expense of usability on unprepared or improvised airstrips.
And then you need helicopters for the missions which require the highest amount of flexibility and closeness to the action.
All three depend on the other, and only together they become effective. That is why I cannot give you a key player.

Key characteristics of strategic transporters:

turbofan engines
swept wings, high flight Mach number and range
high wing, so the fuselage is close to the ground for easy loading and unloading
large nose doors and/or ramp in rear fuselage.

Key characteristics of tactical transporters:

turboprop engines (mostly)
straight wings with extensive high-lift devices for STOL capabilities
moderate flight Mach number and range
high wing, so the fuselage is close to the ground for easy loading and unloading, low loading of landing gear for soft ground capabilities
ramp in rear fuselage.

Key characteristics of helicopters

that whirly thing on top


Can civilians who buy ex-military fighter jets get the necessary maintenance information for them? I was looking for fighter jets which are available to be bought by private citizens. I was wondering: how would you schedule the maintenance, as most of the jets are ex-military and there are no maintenance plans?

Most military surplus aircraft are considered by the FAA to be experimental exhibition aircraft and subject to the rules and maintenance requirements for experimental aircraft.  That being said, most owners seek out retired military personnel who did maintenance on these aircraft and currently work as AIs (authorized inspectors) in civilian aviation to handle maintenance and repairs.  Firms like Code 1 Aviation and Thornton Aircraft specialize in certain types of military aircraft and have collected libraries of maintenance manuals and other resources for owners and can perform maintenance conforming to the old military and civilian experimental aircraft guidelines.


What are those sensors on the forward A321neo fuselage? What are those sensors on the forward (Airbus) A321neo fuselage? If it helps, this is WOW air's TF-DTR.

The probe on the left is a TAT (Total Air Temperature) probe and the device on the right is an Ice Detector.

From this website: UTC Aerospace Systems (Total Air Temp)

From this website:UTC Aerospace Systems (Ice Detector)


Can aviation HF radios receive while transmitting? I was listening to Gander Radio on HF at 5616 kHz today and I've noticed that operator at Gander would often start transmitting reply before the airplane finished transmission, as if trying to interrupt radio operator on the plane.

To me, this was very unusual behavior. From what I've heard and from what I concluded after listening to frequencies, it seems that HF radios in aeronautical mobile service work in traditional simplex mode, so crew normally crew wouldn't be able to hear the part of transmission send before they stop keying their radio.

So this brings me to these questions:
Are aviation HF radios capable of receiving while transmitting? If so, how?
Or if not, what's the point of Gander stepping on the plane's transmission?

In general, the HF radios in aviation work in simplex mode.

According to the Annex 10 to the Convention on International Civil Aviation- Aeronautical Telecommunications Volume V Aeronautical Radio Frequency Spectrum Utilization Chapter 3,

  3.1.1 In the aeronautical mobile service, single channel simplex shall be used in radiotelephone communications utilizing radio frequencies below 30 MHz in the bands allocated exclusively to the aeronautical mobile (R) service.

Though some aviation radios are capable of semi-duplex operation, virtually all aviation services operate on simplex.

I have no idea why the operator was stepping on the aircraft's transmission though.