In the US, what can be done at an airport when volunteering hours? I am a 15 years old and need volunteering hours for my course work. I am a aviation enthusiast with knowledge of the industry and love for anything that flies. I decided to fulfill my hours at a local airport because I would be helping others doing what I love. I am from Florida, and I know this is the greatest place for all aviation related things.

The tasks I would like to perform at my local airport are fueling, taxiing aircraft in and out of a ramp, and help with other airport operations.

Is any of this possible?

If anybody can give me any idea on how to do this. I also like any advice to help me further my volunteering path with other aviation related tasks.

Commercial airports are challenging for volunteers because of security, if you want to do anything beyond the security barrier (ie where the interesting stuff is) then you need to be cleared and supervised, and that costs time and money.

There may be opportunities at small airports, which don't have the same security concerns. Most won't have any established volunteer positions, it would be more of a case of talking to the airport manager or someone running an FBO and asking if there's anything you could volunteer for. Ask politely, wait a few days, then follow up with a phone call, if they know you're genuinely interested (and polite, sensible, not likely to run into a propeller) they might be willing to offer something to you.

One last thing, if anyone asks you to get a bucket of propwash it's an old aviation joke.


How is a meatball calibrated and checked? The visual glide slope for aircraft landing on a carrier is a stabilized indicator, the "meatball":

Source.

The slope is about 4° relatively to the horizontal plane, and stabilized because the carrier is usually rolling, pitching, and heaving.

How is the meatball calibrated, and then checked for accuracy?

There is a vast amount of printed information available on the IFLOLS. A thorough understanding of the following list of publications is a must for an LSO:

Technical Manual, Improved Fresnel Lens Optical Landing System Mk 13 Mod 0, Installation, Service, Operation, and Maintenance Instruction (NAVAIR 51-40ABA-21).

— NATOPS Landing Signal Officer Manual (2004)

If you want a thorough how-to, I believe NAVAIR 51-40ABA-21 is the way to go if it is publicly available.

Stabilization

4.3 IFLOLS STABLIZATION INPUTS
IFLOLS receives ship’s pitch and roll information from either the ship’s gyros or SPN-46. IFLOLS receives ship’s heave information from either an IFLOLS generated ship’s heave signal or SPN-46. The IFLOLS signal is generated using the IFLOLS unit 5 accelerometer. The IFLOLS can use either ship’s pitch and roll gyro source with either heave source. When aircraft are landing using ACLS, any mode, IFLOLS should use the same stabilization inputs as SPN-46. Typically SPN-46, SPN-41, and IFLOLS will all use the SPN-46 gyro for pitch, roll, and heave information when aircraft are landing using ACLS.

SPN-42/46 is a carrier-landing radar.
From Wikipedia—

[The] shipboard units are mechanically moved (the "roll angle") to adjust the touchdown point of each aircraft. With this adjustment, the tailhook touchdown point can be precisely targeted based on the tailhook-to-pilot's eye distance for each aircraft type.

Calibration
(YouTube) Calibration c. 1968.
Manually calibrating the IFLOLS from the stern of the ship from specified distances and heights hasn't changed much from the earlier days.
(navy.mil) ATLANTIC OCEAN (May 13, 2013) Electrician's Mate 3rd Class Martin Torres, from Long Beach, Calif., calibrates an Improvised Fresnel Lens Optical Landing System (IFLOLS) aboard the aircraft carrier USS George H.W. Bush (CVN 77). George H.W. Bush is conducting training operations in the Atlantic Ocean. (U.S. Navy photo by Mass Communication Specialist 3rd Class Kevin J. Steinberg/Released)
(navy.mil) CORONADO, Ca. (Nov. 16, 2016) Sailors assigned to the aircraft carrier USS Nimitz (CVN 68) take measurments while conducting maintenance on the ship's Fresnel Lens Optical Landing System on the flight deck. Nimitz is preparing to get underway to conduct routine operations in preparation for an upcoming 2017 deployment. (U.S. Navy photo by Seaman Cole Schroeder/Released)


What causes this much engine damage? EASA and FAA have placed a 300hr inspection AD on select Dreamliner Trent 1000 engines after multiple failures. Here is a photo of an AirNZ engine.

https://leehamnews.com/2018/04/14/faa-ad-may-severely-limit-etops-of-rr-powered-787s-sources/#more-26889

Update from comment on reference article:

The AD specifically refer to :
Intermediate Pressure Compressor (IPC) Stage (Rotor) 1 blades
IPC Rotor 2 blades
IPC Shaft Stage 1-8 Rotor assemblies
Previous stories had RR ‘offloading 35% of the Trent 1000 development risk to its partners The IPC module is done by Kawasaki. This seems to be different to the other known issue on the Trent 1000 of the fatigue cracks of the Intermediate TURBINE

What causes this much damage?

Report here states it is suspected to be due to foreign or domestic object damage (FOD/DOD).

Provided with the photos taken of the NZ99 engine after it landed back in Auckland, a spokeswoman said: "The cause of these incidents is yet to be determined and this is the role of the Transport Accident Investigation Commission. But the damage sustained on Tuesday suggests an engine part has travelled through the engine."
An aviation source told Newsroom: "The damaged blades are in the aft section of the turbine blade sections. It is likely the damage has resulted from a failure of a turbine blade or blades in an earlier section that has been spat out the back with a domino effect.”

I would suspect an over temperature and/or excessive vibration may also have occurred. It seems similar to the damage in these two events, which featured those events:
Boeing 777-200, GE90, Dec 2010.

The damage pattern leads to the suspicion that one or more fuel injectors in the combustion chamber behaved abnormally leading to an excessive temperature build up in the turbine area, which probably caused the LPT guide vanes material to fail. The engine manufacturer has registed six similiar failures which are all suspected to be the result of fuel injector malfunctions.

Boeing 737-400, CFM56, Nov 2009.

The in-flight malfunction of the aircraft’s right engine was a result of a cascading rupture of the stage-1 LPT blades, [which] was probably precipitated by thermal degradation of the blade alloy, resulting in excessive creep extension, tip shroud/seal interference and blade rupture. Material characteristics of some of the LPT blades installed in the engine were consistent with a raw material manufacturing cast that had previously been identified as being susceptible to creep rupture.


Do helicopters fly a standard pattern before landing? How do helicopters approach and land at an airport? Do they use the same general traffic pattern as fixed-wing aircraft?

The FAA AIM, in 4-3-17 and the Air Traffic Controller Handbook, Section 11, explains VFR helicopter operations at controlled airports. The procedure will depend on the airport and the current traffic.

  Insofar as possible, helicopter operations will be instructed to avoid the flow of fixed-wing aircraft to minimize overall delays; however, there will be many situations where faster/larger helicopters may be integrated with fixed-wing aircraft for the benefit of all concerned.

Helicopters may operate from a designated helicopter landing area. The tower is responsible for separating them from other traffic. The helicopter can fly a much closer pattern than other aircraft, and may stay on the other side of the runway from the typical pattern. They may also operate straight in/out of the landing area, depending on wind and traffic.

They may also be cleared to take off or land in a "nonmovement" area that is not specifically designated for that activity, which could be a ramp at the airport or a location off-airport. This will be up to the tower to provide clearance and the pilot to execute safely.

Helicopters can also operate similarly to fixed-wing aircraft, taking off and landing using a runway, and following taxiways. Wheeled helicopters taxi on the ground. Otherwise, helicopters may either hover taxi, where they fly in ground effect at low speed, or air taxi, where they will fly out of ground effect up to 100 ft AGL and up to 60 kts, as directly as possible to the next point on the field, avoiding obstacles as needed.

Like ratchet freak says, they will generally come in horizontally while descending, flying into the wind, and then come into hover, where they will then be instructed by the tower to taxi to wherever they are going on the field.

Some airports, like in this photo of "spot Charlie" on Taxiway Zulu at Hayward Aiport, may have marked spots on the taxiways or non-movement areas for helicopter operations. In this case, students practicing landings and autorotations will be instructed: "Clear to land, Spot Charlie" to keep them off of the main runway 28L, while in left traffic on the opposite side of the runway of the smaller 28R.

As with any aircraft, the final authority for safety is the pilot, and they must be aware of their limitations and the conditions around them.

At non-towered airports, the procedures can be similar. The pilot should take the wind direction and traffic into account, and announce their intentions on the appropriate frequency.


What is this line found above the door on many aircraft? Many aircraft have this line above the door as seen in the photos below. What is it, and what is its purpose?
Source

Source

These are rain gutters.

They are designed to catch rain that runs off the upper surface of the aircraft fuselage and channel it away from the open aircraft door so that the water does not enter the cabin.

This is a close up of the rain gutter over the main cabin door of a Beechcraft King Air B200, showing the channel that would catch and redirect water flow to the side of the door opening:

Source: own work

A jet-bridge may partially deflect rainwater in some cases, but the gutter helps mitigate water exposure for the aircraft interior and passengers. Even gutters cannot completely eliminate such exposure since their size is necessarily limited by aerodynamic constraints. Many operations do not have the luxury of jet-bridges, making the rain gutter especially helpful in reducing the amount of water that might otherwise enter the cabin and pose a hazard to the aircraft or onboard systems.

"Rain Gutters" is the technical name, at least for Boeing aircraft, such as the B777 depicted in the photos in the question.

Here is a Boeing reference to such gutters on the 787:

  Rain gutter: When customers found that water was not being properly deflected
  over a passenger entry door, they requested a change. Boeing relocated the
  gutter to function more efficiently. The solution means happy customers, who had
  fewer water and maintenance issues, and happier and drier passengers. This
  was a significant enough change to process to require certification work with the FAA.


What is the purpose of thinner airfoils used near wing tips? I know that a thicker airfoil at root will strengthen the root spar but what is the reason behind using thinner airfoils at the tip?

Is it because thinner airfoils have higher stalling angles of attack? If so, why?

Comparing both thick and thin airfoils, who generates more lift and why?

Also, my final question is that in what kind of designs would such a change of airfoils be recommended? I'm currently working on designing a high lift wing (selig s1223 airfoil) for delivering a payload of about 15kgs. with the total aircraft weighing about 20-22kgs. Would changing the airfoils in my wing design be recommended?

There are two main reasons for thinning the wing towards the tips:

Thinner airfoil sections cause less drag simply because they disturb airflow less.
Thinner sections down to 10% have a higher maximum lift coefficient, which helps both near stall and during maneuvering: A section with a higher maximum lift coefficient will show more aileron effectiveness, too.


Model for flutter analysis of Aerofoil Why is a aerofoil modeled by attached torsional and linear spring in a  wing flutter analysis.The model does not even satisfy the boundary condition of zero displacement of wing at point of attachment to fuselage. I am considering the pitch plunge model as shown in figure.

Because what you are simulating is not a wing, but an aerofoil at an arbitrary $y$ station along the wing.
The linear spring simulates the wing bending and the torsional one its torsion about the elastic axis. The constants would of course be of the type $k_{e}=f(y)$.


Why are the VHF and UHF airbands directly adjacent to frequency bands used by vital radionavigation aids? Of the three main frequency ranges used by aircraft for radio communications (HF, VHF, and UHF), two (VHF and UHF) have their aircraft-radio-communications frequencies clumped together into a contiguous (or almost contiguous) airband1 (117.975-137 MHz for VHF, and 225-328.6 MHz and 335.4-399.9 MHz for UHF2).

Interestingly, and somewhat worryingly, each of the VHF and UHF airbands is immediately adjacent to a band of frequencies used by vital radionavigation aids:

The VHF airband (117.975-137 MHz) lies immediately above the 108-117.975-MHz band used by VOR and localiser transmissions.3
The two UHF airbands (225-328.6 MHz and 335.4-399.9 MHz) are separated by the glideslope-transmitter band (328.6-335.4 MHz).

This raises the possibility that a malfunctioning (or even just poorly-tuned) VHF radio could cause interference for VOR or localiser signals if it went even slightly out-of-band, or (much worse) that a mistuned or malfunctioning UHF radio could end up stepping on somebody’s glideslope.

Given the navaid-interference potential thereby caused by this adjacency of radiocommunications and radionavigation bands, why do both the VHF and UHF airbands directly border frequency bands used by vital navaids, and how are out-of-band VHF and UHF radio transmissions prevented from thereby causing interference with these navaids?

1: The HF frequencies used for aeronautical radio communications, in contrast, are split into multiple discrete bands spread out throughout the entire HF range.  This is because the main attraction of HF is its ability to transmit and receive signals far beyond line-of-sight range (potentially even enabling an aircraft to talk to someone at the aircraft’s antipode, on the opposite side of the planet); which HF frequencies work best for this depends on the current state of the earth’s ionosphere, which varies considerably due to things such as solar activity, variations in the Earth’s magnetic field, recent high-altitude nuclear explosions, supernovae, witchcraft, etc., so the aeronautical HF bands are scattered throughout all HF in order to ensure that there should be at least one useable band no matter what (the frequency bands used for shortwave radio broadcasting are likewise scattered throughout most of the HF range [although, surprisingly, not the lower end], for the same reason).  In any case, the HF range has no radionavigation bands of any sort whatsoever, making it not a concern for the purposes of this question.

2: Which, if you want to be pedantic, places a good portion of the UHF airband in what is actually the top end of the VHF range.

3: And the 108-117.975-MHz radionavigation band is, in turn, immediately underlain by the FM broadcast band (88-108 MHz), but, as there are fewer FM radio stations than there are VHF-radio-equipped aircraft, and they are bigger and easier to spank if they get out-of-band, this is less of a concern from the interference-with-navaids perspective.

The most obvious reason is that the ITU allocated the VHF and UHF bands for aviation purposes generally, and then aviation authorities had to split those limited bands into adjacent comm and nav sub-bands.

If aviation had gotten separate ranges for nav and comm, then that would double the risk of interference from adjacent non-aviation users, plus it would have made designing radios and sharing antennae more difficult.

So, we got the lesser of two evils.


What's the acceleration and absolute minimal RWY length for an A320 during take-off? TL;DR: An A320 takeing-off with full thrust is able to reach $V_{TO}$ (77 m/s) in only 26 seconds and in as few as ~ 1.000 metres. Is that really true?

Last time I traveled with an A320 I was again impressed by the acceleration during takeoff. I think it's not outstanding (compared to others) but nonetheless impressive. A cause might be that passengers are somehow exposed to the powers and cannot influence it. But I enjoyed it and it made me doing some calculations.

I gathered the following data:

usual take-off speed $V_{TO}=150$ knots (source)
required runway length $2000 \text m$ (source)
max. thrust per engine $\approx 120 \text{kN}$ (source)
MTOW $78 \text{tons}$ (source)

For constant acceleration along a path the following rules apply:

$$\left.
\begin{array}{}
s = \frac{1}{2} at^2 & \Leftrightarrow & t = \sqrt{ \frac{2s}{a} } \\
v = a \cdot t        & \Leftrightarrow & t = \frac{v}{a}
\end{array}
\right\}
\Rightarrow
a = \frac{1}{2}\frac{v^2}{s}$$

With the data from above this gives an acceleration from 0 to 100 km/h (or 62 mph or 28 m/s) in approximately 18.5 seconds and about 52 seconds for reaching the take-off speed. That sounded a bit lame compared to my 100hp station wagon.

So I investigated further, this time from Newton's point of view, $F=ma$, which gives an acceleration of $a = \frac{2 \cdot 120.000 N}{78.000 kg} \approx 3 \frac{m}{s^2}$. That gives 0…100 km/h in about 9 seconds. This far better coincides with my gut feeling as a pax.

But my second approach, $a \approx 3 \frac{m}{s^2}$, also resulted in the following conclusion and question:

An A320 takeing-off with full thrust is able to reach $V_{TO}$ (77 m/s) in only 26 seconds and in as few as ~ 1.000 metres. Is that really true? I was amazed at this because they all say the required RWY length is twice as long.

At takeoff weight of 78.9 tonnes and -20°C temperature (best case scenario), the A320 needs 2,250 metres (7,400 feet). (This includes the distance to reject a takeoff.)

As for the forces, you forgot to take into account the aerodynamic drag and rolling friction, both will slow down the acceleration.

This PDF from Virginia Tech explains the forces at work and the equations needed.


Is a holding pattern always counter-clockwise? Is a holding pattern always counter-clockwise? Or is it dependent upon the controlling airspace?

No. The holding pattern can have any inbound course, and any direction. The holding pattern course/direction, depends on departing/arriving traffic, and many other factors. London Heathrow has a clockwise and counterclockwise hold on the fix LYDD.
Thanks to Pondlife for pointing LYDD out!


Can I get an EASA ATPL online? I have a PPL license in the US and I want to do a European ATPL license.
How does it work? Do I have to attend a school or can I do all online?
Do I have to physically take the tests somewhere in Europe or can this be done somewhere online as well? How did the COVID-19 change these things?

No, you can’t get an ATPL online.
Your first step would be converting your FAA PPL to an EASA PPL. You will then need to add Instrument, Commercial Single-Engine, Commercial Multi-Engine, Multi-Crew Commercial and frozen ATP ratings. All of that will require ground instruction, flight instruction, written tests and checkrides. Then you will need to build time until 1500 hours to get your ATPL unfrozen. There are some differences in process and terminology between FAA and EASA, of course, but the end result will require roughly the same skills and experience because both systems have to meet the same ICAO standards.
COVID-19 has not changed the requirements to get a license, just the feasibility of actually meeting them. Many flight schools are closed, those that are open may not be accepting foreign students, and you may not be able to get there at all due to border restrictions.


Is there a list of aircraft types to be used with a callsign? In the U.S., general aviation aircraft use the airplane type with the callsign when talking to ATC, such as "Skyhawk 123CS" or "Citation 321CT". ATC likes to know what type of airplane you're flying so they know how what its performance is.

It gets complicated with airplanes like the Cessna Corvalis, which is a Cessna (formerly Columbia) but it is faster than a Cirrus and can fly an approach at 200 kts if required. So what would the callsign of a Corvalis be? "Corvalis 123TT" or "Columbia 123TT"? I doubt it would be "Cessna 123TT".

Is there an official (or unofficial) list of airplane types to use when talking to controllers?

I couldn't find any specific guidance on this, the AIM 4-2-4(a)(3) just says (emphasis mine):

  Civil aircraft pilots should state the aircraft
  type, model or manufacturer’s name, followed by the
  digits/letters of the registration number. When the
  aircraft manufacturer’s name or model is stated, the
  prefix “N” is dropped; e.g., Aztec Two Four Six Four
  Alpha.

See also the ATC orders 2-4-21 for the controllers' side. It doesn't give any information either on where to find type and model information and the examples suggest that precision isn't very important:

  EXAMPLE−
  “Tri−Pacer.”
  “P A Twenty−Two.”
  “Cessna Four−Oh−One.”
  “Blue and white King Air.”
  “Airliner.”
  “Sikorsky S−Seventy−Six.”

If "airliner" is an acceptable identifier then anything is :-)

As you said, you can comply with the AIM simply by saying "Cessna", whether you're in a 120 or a 750. But what about experimental aircraft, or a type that the controller just doesn't know?

Personally, I think this is a practical issue rather than a formal one. If it was critical for ATC to know the performance of every aircraft then flight plans would be mandatory. As it is, both controllers and pilots rely on their working knowledge of aircraft types and the system just works. The big, fast aircraft are mostly IFR anyway so the controllers already know what to expect; the small, slow ones can all do 80-100 knots in the pattern and the controllers don't need to worry about them much.

In the unusual cases where a specific aircraft type's performance might be an issue, the pilot can always work it out with the controllers:

N12345, Louisville Approach, I need your best forward speed on the approach, can you give me 120 knots?1
Bowman Tower, N12345, we're a warbird, I need a minimum 90 knots in the pattern and request an overhead break for runway 242

1Real example, and no I couldn't
2Also a real example, but sadly not me flying


What information am I legally required to provide during a FAA ramp check? I was taught during my private pilot training to only provide the minimum information necessary to the FAA when they ask for something so that you don't open yourself up to more scrutiny.

In that spirit, what am I legally required to provide to an FAA inspector during a ramp check?  If they ask for something, can I tell them "No" or "I will respond to that in writing within 30 days after I have my lawyer review your question"?

In my car, I can refuse to let them look inside unless they have a search warrant.  Does the same apply with a private airplane?

AOPA has a good article on this topic:

You're required to present pilot and medical certificates (plus logbook if required for flight)
The inspector may not detain you
The inspector may not board the aircraft without informing you

But an inspector is authorized to check the following items:

The airworthiness certificate
The aircraft registration
The operating handbook
The weight and balance information
The minimum equipment list (if applicable)
Aeronautical charts (if applicable)
The general airworthiness of the aircraft
The ELT battery
A VOR check
The seats/safety belts.

In general, saying as little as possible seems to be a good plan:

  If the ramp check is due to a possible violation, anything you say or
  do may be used against you.

  If you have enrolled in AOPA's Legal Services Plan, call AOPA's Pilot
  Information Center at 800/USA-AOPA immediately. The consequences for
  even minor infractions can be far more serious than you might think.

As for a search warrant, a ramp check is an FAA administrative process, not a law enforcement action. The issue of law enforcement checking private aircraft is a hot topic currently and AOPA provides a checklist in case you are stopped for search. Their recommendation is to refuse the search (unless they have a warrant, of course) but not interfere if they go ahead and do it anyway.


What is the difference between aviation "accident" and "incident"? When I hear speaking about aviation crashes, sometimes I hear about "accidents" and other times about "incidents".

What distinguishes them? Is there an international standard that determines how aviation crashes are classified or is it based on national regulations?

There are indeed only two 'official' classifications of aviation incidents, which are defined in ICAO Annex 13.

  Accident. An occurrence associated with the operation of an aircraft
  which takes place between the time any person boards the aircraft with
  the intention of flight until such time as all such persons have
  disembarked, in which:

  a) a person is fatally or seriously injured as a result of

  being in the aircraft, or
  direct contact with any part of the aircraft, including parts which have become detached from the aircraft, or
  direct exposure to jet blast,

  except when the injuries are from natural causes, self inflicted or
  inflicted by other persons, or when the injuries are to stowaways
  hiding outside the areas normally available to the passengers and
  crew: or

  b) the aircraft sustains damage or structural failure which:

  adversely affects the structural strength, performance or flight characteristics of the aircraft, and
  would normally require major repair or replacement of the affected component,

  except for engine failure or damage. when the damage is limited to the
  engine, its cowlings or accessories: or for damage limited to
  propellers, wing tips, antennas, tires, brakes, fairings, small dents
  or puncture holes in the aircraft skin: or

  c) the aircraft is missing or is completely inaccessible.

  Note I.-- For statistical uniformity only, an injury resulting in
  death within thirty days of the date of the accident is classified as
  a fatal injury by ICAO.

  Note 2.-- An aircraft is considered to be missing when the official
  search has been terminated and the wreckage has not been located.

And then there is

  Incident. An occurrence, other than an accident, associated with the
  operation of an aircraft which affects or could affect the safety of
  operation.

They do also define 'serious incident', but simply as an incident which was nearly an accident; which is still an 'incident' by the definition above.


Is multi/quadcopter flight control similar to helicopters? The wikipedia Quadcopter entry provides some details about its flight control:

Hovering or altitude adjustement.

Pitch or roll  adjustment.

Yaw adjustement.

The following post "Quadcopter flight modes beyond traditional aircraft?" raised to my attention that it had other flight modes apart from those of fixed wing aircraft but I am not so sure with respect to conventional rotorcraft.

Question:

My assumption is that the quadcopter can be flown using conventional helicopter flight control inputs (cyclic, collective, anti-torque, throttle), am I right or is it really another beast with its very own flight control inputs?

As  commented, a quadcopter is generally flown by a computer. Given command inputs, the computer controls the speed of the four rotors, as shown in the images included in the question. The four rotors give the quadcopter a wide range of maneuverability. This is why quadcopters are currently used in many research applications. They can simulate conventional fixed-wing flight, helicopter flight, or something completely different.

A quadcopter could certainly be flown with conventional helicopter controls. The four rotors allow it to be controlled by a cyclic, and the differential rotor torque allows it to be controlled by the anti-torque controls. However, unlike most helicopters, most quadcopters have fixed-pitch rotors. This is probably mainly due to size and cost constraints. The small size of quadcopters, combined with the lift being distributed among four rotors, allows each rotor to be smaller and much more resposive with RPM than a large rotor. This means that instead of collective and throttle, most quadcopters will only have throttle. Controlling the speed if the individual rotors is the end-result of their control algorithms.


Is the US certification process for airliners shorter or longer than in other countries? I was researching information regarding the competitiveness of different government certification organizations (FAA, EASA, etc) and the processes (Amount of time, costs, etc) to get their nations aircraft certified and flying.

Is the certification process to get a US jet manufacturer's product into the hands of its customers shorter or longer than other countries?

From what I've found so far it seems GAMA and other US aviation entities are trying to help shorten/simplify this process in the US. This leads me to believe we are at a competitive disadvantage, but I haven't really found any data to back this up. Any direction helps.

Countries/manufacturers that I have been comparing to the US are: Bombardier (Canada), Embraer (Brazil), Dassault (France), and Airbus(France).

Certification is just one part in the design process. Things like design or manufacturing issues can also cause significant delays on a program. Although much of the design is driven by certification requirements, it can be hard to determine whether the delay is due to regulations or just issues with designing for them. Estimating the cost attributed just to certification would be even more difficult.

Also, while the regulator of the country of design certainly is the primary concern, an aircraft must also be certified in any other countries where the type will be operated. An aircraft designed by Airbus, for example, will certainly be primarily certified by EASA. But to operate in the US, the FAA must also certify it. While the authorities do have agreements between them so that the entire process is not duplicated, there are differences in requirements and philosophies between the agencies. So if the FAA has some regulations that tend to cause the process to take a long time, it doesn't mean that Airbus is immune to those issues.

When a manufacturer applies for a type certificate (new or amended), they are also establishing a regulatory baseline. The new type must conform to all current regulations as of that date, unless they are able to negotiate something different with the regulator. This application is only valid for a limited time before the manufacturer must renegotiate.

14 CFR §21.17 (c)

  An application for type certification of a transport category aircraft is effective for 5 years and an application for any other type certificate is effective for 3 years...

While this is not a hard limit, manufacturers would rather avoid having to go back to the table with regulators years into their design process to extend their application and possibly have to step up to more strict regulations, especially for a new type.

Most recent Type Certificates from EASA list the application date and issue date. If the primary regulator is not EASA or JAA (predecessor to EASA), they list dates for that regulator as well.

If we look at recent designs, we can see that most new aircraft took about 5 years to certify, which would seem to indicate that there is no clear time advantage between regulators. This includes the A330, A340, A350, A380, 777, 787, CRJ, E145, and E170. For all aircraft not primarily certified by EASA/JAA, there was either only a minor difference in the time taken for each regulator, or EASA/JAA took a bit less time.

Amended types vary greatly, from much less than 5 years (A330-200, 777-300) to 5 years (747-8) or more (777-200LR). It is difficult to tell whether a longer process means a more complex product or a more involved certification process. EASA/JAA seems to always certify aircraft at the same time or after the primary regulator, but this is probably not due to the EASA/JAA process taking more time.

You mentioned Dassault as well. Although the business jet regulations and market are different from airliners, there seems to be a similar trend of about 5 years for new jets (Falcon 7X, Gulfstream VI, Bombardier Global Express, Embraer Legacy 500), and less for variants.


In the ARINC specification, why is baro altitude (label 204) measured in Knots? I am currently designing a system that reads the baro altitude (on label 204) from an LRU. Ultimately in my software I would like to display the baro altitude reading in real-time using a graphical interface. In doing this, I'd like to have the units of measurement next to the reading. However I am having a bit of trouble in deciding how to display the units of measurement.

In the ARINC specification (attachment 2 "data standards"), label 204 (baro altitude) is listed as having units of knots. Is this an error, or can altitude be in Knots?

I am referencing ARINC specification 429 part 1-17, mark 33 digital information transfer system (DITS) published in May of 2004.

It's an error. Attachment 2B does show that label 204 from the GNLU (Equip ID 056) and GLU (Equip ID 060) as being in knots (highlighted below). That is not correct, it is a BNR in feet as shown for Air Data System (ID 006) and ADIRU (ID 038). Knots only applies to Label 204 from the FMS (ID 002).

It's still incorrect in A429 P1-18, March 2012.

ARINC 429 contact at ARINC Industry Activities, ARINC 429 Maintenance is Jose Godoy. email:jose.godoy@sae-itc.org


Does drag increase with increasing bypass ratio in turbofan engines? Does drag increase as the bypass ratio increases in turbofan engines? Is there an analytical expression describing the increase in drag related to an increase in the fan duct diameter? How else might one consider this effect?

According to this 1975 NASA report on the effects of turbofan engine bypass ratio, the drag does increase for increasing bypass ratios. In the report, they use the following drag coefficient equation:
$$
C_{D,prop}=C_{D,nacelle}\cdot \frac{A_{nacelle}}{S} = \frac{D_{nacelle}}{\rho_\infty A_{nacelle}} \cdot \frac{A_{nacelle}}{S}
$$
As shown below, the nacelle drag coefficient initially increases for increasing bypass ratio.

Since $\frac{A_{nacelle}}{S}$ also increases with bypass ratio, the propulsion system drag will increase as well. So drag is closely related to the frontal area of the engine.

(images taken from report linked above)


Where do Russian and Chinese airliner manufacturers test their airliners? Airbus test their plane on Toulouse Airport, and Boeing test on Boeing field.

How about Russian airliners Ilyushin & Tupolev and Chinese Airliners Comac ?

Almost all Russian (Soviet) aircrafts were tested in the Zhukovsky Airfield (Ramenskoye Airport) near Moscow.

The Comac is building a Flight Test center at Dongying, Shandong province near the Dongying Shengli Airport. The flight test of aircrafts are expected to be carried out from here.

As Peter noted, Antonov test their aircrafts at Kiev Airport, including An 225, the largest aircraft in world.


Can a light glider without thermal protection land from the orbit, starting from the orbital speed? I ask about a glider without any special thermal protection (pilot in the space suit), so both answers to the other question do not cover the topic.

When the glider enters the atmosphere, it starts generating lift. Could this lift keep the glider high enough, in low density air, and this way prevent the heat damage? The glider then would fly a long distance, losing speed and altitude slowly, until reaching speed and elevation at which it can safely land. Seems that lots of lift could be generated at speed and air density where the metal burns already.

Is there any analysis ever been done if such landing is possible?

No.

The stagnation point temperature goes up with the square of true air speed.

Temperature dissipation is proportional to true air speed and density.

Lift is proportional to the square of airspeed and density.

The lower wing loading of a glider (compared to the Shuttle, for example) means that all of the reentry will be slower, but that is not necessarily an advantage. Note that the Shuttle needed external cooling to prevent heat stored in the heat shield to dissipate into the Shuttle's structure. If the glider flies a longer reentry, it will be closer to thermal equilibrium. Also, the aerodynamic shape of a glider is a disadvantage here because the lowest heat load is possible with a blunt object - this is why reentry vehicles look like they do.

Just to give you an idea what temperatures are involved:

If we express speed as Mach number, a typical reentry speed would be Mach 25. This makes the reentry temperature at the stagnation point $$T_s = T_{\infty}\cdot \left(1 + \frac{\gamma-1}{2}\cdot Ma^2 \right) = 126\cdot T_{\infty}$$
at Mach 25. If we assume 195K at the edge of space, this comes out to 24,570K - theoretically, because ionization effects will cause the eventual temperature to be lower and the ratio of specific heats $\gamma = c_p/c_v$ is no longer constant. To calculate the real value needs a non-equilibrium gas model since the nose radius of typical glider wings and tail surfaces is in the order of one centimeter. The distance between the detached shock wave and the structure is too small for the gas molecules to reach equilibrium.

On the other hand, the epoxy resins used in glider construction cure at room temperature first and are then tempered at about 60°C. The glass transition temperature $\text{T}_g$ of such resins is at best a couple of degrees above the curing temperature. $\text{T}_g$ marks the onset of weakening of the composite matrix, and heating the glider above it will permanently damage it. Given that the glider will stay for dozens of minutes in air of a temperature of several thousand degrees and has no thermal protection will make sure that all which reaches the ground is a charred lump of material.


Will high blood pressure affect my pilot medical certification? I will most definitely start a training for a glider pilot license at our local flight club. This of course requires a medical certification for pilots. The only concern I have, is my blood pressure.

I am an 18 year old male with an overall healthy condition. However the last few times I had a doctor's appointment, I had a somewhat high blood pressure (it was always between 150/70 - 180/85 mmHg). Online I haven't really found that much information about the limit of the blood pressure in order to still get the Medical.

I have found some sources saying that everything below 220/125 is good, but I think those sources we're only speaking about passengers of airplanes, not pilots.

For your info: I live in Germany, and I suppose there are other regulations regarding the medical in other countries, but overall I think the requirements don't differ that much.

Hopefully someone can tell me if I should be concerned or if my blood pressure is still okay to fly.

Without knowing German, it's a little difficult for me to research the LBV's website, but I found this application for Validation of a foreign airman’s licence, and one of the requirements in it is:

  Valid JAR-FCL Medical Class I or Class II

The JAR requirements for a Class I and Class II medical, both are:

  JAR–FCL 3.135 Cardiovascular system – Blood pressure

  (a) The blood pressure shall be recorded with  the technique given in
  paragraph 3 Appendix 1 to  Subpart B [at each examination].

  (b) When the blood pressure at examination  consistently exceeds 160
  mmHg systolic and/or  95 mmHg diastolic, with or without treatment,
  the  applicant shall be assessed as unfit.

  (c) Treatment for the control of blood  pressure shall be compatible
  with the safe exercise  of the privileges of the applicable licence(s)
  and be  compliant with paragraph 4 Appendix 1 to Subpart

  B. The initiation of [ ][medication] shall require a  period of
  temporary suspension of the medical  certificate to establish the
  absence of significant  side effects.

  (d) Applicants with symptomatic hypotension  shall be assessed as
  unfit.

It looks like you will probably need to lower your blood pressure (either via diet and exercise or with medication) in order to pass your medical.  If you start taking blood pressure medication, you will need to take it for a certain period of time to make sure that there are no other side effects before they will give you a medical.  You can discuss this with a medical examiner to see how the process works there.


Why are push-propellers so rare, yet they are still around? Jet engines are by their very nature push-engines, however, most propeller airplanes use pull-engines. Is there an inherent advantage to using pull-propellers except for the increased airflow over the fuselage and tail (with its rudder and elevator)?

Twins generally have their engines on the wings, and the tail is no longer directly behind it, does that mean the choice of a pull-engine is not as advantageous?

If there isn't an inherent disadvantage, why are pusher configurations so rare? If there is one, why do they exist at all? Disregarding designs where the choice is obvious, like powered parachutes where you simply don't want a propeller in your face.

The Convair B36 is one notable multi-engine aircraft with engines in pusher configuration, as is the Piaggio Avanti. And the Cessna Skymaster is a push/pull configuration (If you get a multi-engine rating in a Skymaster, your ticket will be limited to multi-engine aircraft with in-line thrust). Single engine aircraft are even more uncommon, and pretty much all I could find except the Lake Buccaneer are all kit-planes (e.g. Velocity, Rutan), ultralights (Quad City), military, or experimental.

There are many disadvantages, they seem to outweigh the advantages.

Here are two:

A pusher prop is working in a disturbed airflow, causing increased vibration and noise
If the propeller is fitted behind a wing, each propeller blade is passing through the separated boundary flow twice each rotation. These cycles create additional noise and lower the efficiency of the propeller. The vibration makes the propeller blades more susceptible to metal fatigue.
Propeller clearance at takeoff
Due to the pitch up at take-off, the propeller gets close to the ground. Therefore the diameter needs to be reduced (loss of efficiency) or the landing gear struts need to be made longer (added weight). Since the propeller is behind the landing gear,  it is susceptible to debris kicked up from the gear, increasing the need for added blade protection (increased weight, loss of efficiency)

Wikipedia has a list of additional disadvantages.

Edit:

Your statement that

  Jet engines are by their very nature push-engines

is not entirely true.

In turbofan engines, most of the thrust is generated by the fan and compressor stages. Even in a pure jet engine, a lot of thrust is generated by the compressor. Therefore the shaft of a jet engine is tension loaded, just like a propeller shaft in puller configuration.

Source: Rolls Royce - The Jet Engine


Cross Country Planning: What do I put in the NavLog for the GPS route? I'm a student pilot. My homework this week is to plan a cross country flight from point A->B using dead reckoning and on the way back B->A using GPS and flight following.

So the question is, do I put on my NavLog the dead reckoning (course heading, estimate time established, estimated fuel burn, etc... for each leg) only for the A->B route? What do I put in for B->A (GPS flight). I assume: basic estimation of fuel burn for the whole flight, straight line distance; how about take off and top of climb, things like that...? How do you usually do this?

I can't tell you what specifically to include on your navlog (that's a judgement call you make as a pilot - you determine what has to go on the paper to satisfy yourself that you can complete the flight), but I can give you a crash course in my theory of navigation, and a practical example of how I decide what to put on my navlogs.

What's the point of the Navlog?

At its core a navlog is a list of waypoints such that you could find your way from Point A to Point B via the listed route by using some navigational system.
Ideally the navlog should be usable with at least two independent navigational systems in case one breaks, and for a VFR flight one of those navigational systems should always be "Looking Out The Darn Window!" (the window rarely breaks).

For purposes of this discussion I'm going to focus on waypoint selection and a few other housekeeping tasks. I'm ignoring stuff like calculating headings because while that stuff is important it's also just mechanical math: The waypoint selection requires you to exercise some judgment as a pilot.

A Practical Example: KGON to KMGJ and back.

This is a nice 100 mile flight to use as an example. Let's plot the outbound trip using pilotage and dead reckoning, and the return trip using the GPS. (This is going to get photo-heavy, so I'm burying them in links.)

The first thing you do is draw the straight line between the two airports on the chart. Then follow the line from Point A to Point B and mark off convenient landmarks. I chose Chester Airport, the New Haven railroad/highway/river, abeam the Waterbury-Oxford Airport, the lake & prison north of Danbury (also abeam the Danbury airport), and the Hudson River (you can't miss it!).

  Pilotage Tip: Airports (at least the larger ones) make great landmarks. They're also convenient landing places if you have a problem, so including them as waypoints is a double win.

Almost all of these legs can be completed by pilotage (you can always see the next waypoint/landmark), but one of the legs (Danbury to the Hudson) is about 24 nautical miles and on a hazy summer day you might not be able to see that far. You should therefore be prepared to fly at least this leg by dead reckoning (point the nose in the right general direction based on the heading you calculated, and fly until you see a big river).

The navlog that Skyvector generates for this is somewhat unfriendly-looking, with lots of latitude/longitude fixes in it, and automatically generated ones from Foreflight and similar tools will look about the same. When you write up your navlog you can give each waypoint a descriptive name like I did above so you can remember what you're looking for in case your sectional blows out the window mid-flight.

So that takes care of the outbound trip with visual waypoints - what about the return trip using the GPS?
GPS systems have convenient databases of airports, intersections, and navaids, so we draw the same straight line, then look at the chart and find the waypoints between our two airports that the GPS will know about. The result looks like this and produces a navlog with nice waypoint names.

  GPS Tip: I avoided using Lat/Long fixes in the GPS plan in favor of fixes that you can type in on any GPS, so this is fast and easy to enter on a Garmin 430/530 for example. Newer GPS systems like the touchscreen Garmins let you do "rubber-band flight planning" where you can drag your route of flight around and easily create waypoints wherever you want - you could even set up the same track I did for the outbound flight if you want.

Since you're flying under Visual Flight Rules you're going to want to note down Visual references to go with this navlog (because again if your instructor is anything like mine was your GPS is going to suddenly fail on the return trip while you're merrily following the magenta line).
For this return trip the visual references would be Stewart Airport (and the Hudson River beyond it, even though it doesn't have a dot on this plan), the city of Brewster (which doesn't have a dot, but is identifiable as a city that has power lines, railroad tracks, and a highway immediately east of it), the Danbury airport (KDXR), abeam the Bridgeport airport (at TRUDE), and from there on you can cheat and use the shoreline (even if the entire electrical system died you can still find your way back to Groton by following the shore until you recognize "home").

What about that other stuff? (Airspace, ToC/ToD, ETE, fuel burn, etc.)

There are a few important things you don't get by picking out the waypoints the way I did it above.  The most obvious one is Airspace -- you'll notice the course I've plotted cuts right through the Stewart (KSWF) Class D airspace, and Orange County is really close to the Class D ring. Unless you're in a helicopter there is no way you could fly above the Stewart airspace and then descend into Orange County along the plotted route without exceeding VNE, so you're going to have to plan on talking to Stewart's tower and requesting a transition. Note the tower and ATIS frequencies and pick a spot along your course to call the tower up to request the transition. (Same goes for the return trip - we plan to cut through right over the airport so we need to call them and ask.)
Similarly you want to note the tower frequency of any airport you're passing so you can monitor it, and so you can call them up if something goes wrong. This information is on the chart, but printing it in big letters on your navlog makes it easier to find.

Something else most flight instructors want to see you including are Top of Climb and Top of Descent (along with a calculation of fuel used in the climb or descent) - you get this the day of the flight by determining what altitude you want to climb to (based on the wind data you got in your pre-flight briefing) and referencing the aircraft's performance charts. You'll add a little mark to the course line on your chart for TOC and TOD, and I usually put it in a "notes" area on my navlog (TOC xx minutes elapsed and if there's a convenient visual reference I note what it is).

  General Tip: I try to include some waypoint that will be at or near top-of-climb/top-of-descent on my flight plans - if you have a reasonable idea of how your plane performs you can usually pick something within a few miles for most reasonable wind conditions. Doing that makes it easier because I can use the time-fuel-distance charts in the POH to fill in the estimated time enroute to that waypoint (or waypoints if it's a long climb) and the fuel burn: One less thing to calculate.
  I did not go out of my way to do this on the charts above.

You should also be calculating an estimated time enroute between each waypoint based on your calculated groundspeed (again you'll work this out before you depart based on forecast winds - you'll see that Skyvector computed it for us based on a 100-knot airspeed and the wind data available as I was typing this).
This seems a litle crazy for 10 to 30 mile legs like this (about 6 to 20 minutes enroute between each waypoint, but if we go back to the idea of using this navlog over a wide-open desert we may have an hour or more between waypoints, and cross-checking estimated time versus actual time lets you know if the winds are significantly different from the forecast values.

The estimated time enroute in turn gives you your fuel burn for each leg: You know your engine burns a certain number of gallons per hour, and you know how many hours (or fractions of an hour) each leg will take - multiply to get your fuel burn.

  Don't Run Out Of Gas Tip: Plan conservatively: Round fuel consumption numbers up to the next half-gallon or gallon.

Finally every navlog has at least one other key element: The heading you should be flying: True Course ± Magnetic Variation ± Wind Correction Angle ± Compass Deviation = Magnetic Heading - What you steer on the compass. Skyvector calculated this for us (with the exception of the Compass Deviation which it can't know) but if you're doing the flight plan manually you need to do this math yourself.
Again you would do this right before your flight, with the most current wind data.


Is the rotor described in this Kickstarter new? A NewAtlas story linked to a Kickstarter for a the "Whisper Drone" that shows a CAD model of a rotor that the Kickstartee-aspirant has apparently 3D-printed and flown (four of) on a quadcopter.  I find the rotor strongly reminiscent of something I can't place.

Is the rotor design new?  If not, what is it (presumably a variant of)?

The rotors on that drone are of the centrifugal fan type. They are not new in design (don't know about aircraft use though) and can be found in all kinds of everyday appliances: hairdryers, vacuum cleaners, car A/C blowers, etc. They move air at a 90° angle, sucking it in from the top and expelling it from the side.

Apparently they are more silent in this application than a normal propeller (or so the kickstarter claims) but it is easy to spot some downsides. Weight for one thing, as it seems they need a lot more material for construction than a normal prop.


Which is the airliner with the most passengers per lavatory? When flying long distances in large airliners like the B777 or the A380, there always seem to be long queues in front of the lavatories, generating longer waiting times than in the past. Kinda looks as if there are fewer and fewer toilets per passenger on board.

Are modern aircraft designed with fewer lavatories per passenger on board? Which is the airliner (CFR 14 Part 25) still flying with the most passengers per toilet?

This is not necessarily an attempt to answer your question directly. But I do have some interesting information.

I use to be the night shift supervisor for Continental Airlines in Anchorage Alaska from 1998 to 2005. We primarily serviced B757 and B737 flights from Newark NJ or Houston TX via Portland or Seattle each day (4 winter, 6 summer flights). About half the flights had lavatory problems.

The MEL (minimum equipment list) only required the lavatory closest to the cockpit to be operational for a flight. We averaged about 190 pax (max was 230-290). Imagine a B757 with 200 passengers with only one lavatory for a 5hr flight between NJ and WA (WA to AK was 3hrs) - how inhumane! And I did rarely see flights with only two toilets that worked (never one).

This was an eye opener to me that the FAA (govt) is not looking after the best interest of the public. I could tell you other bone chilling experiences but this is not the proper place or time :(

So with due respect, I am warning that there is a difference between the number of toilets in an airplane, and the number of toilets that actually work!


How easy is it to pull the ejection handle in a Rafale B? A civilian passenger ejected from a two-seat Rafale B during takeoff on Mar 20 2019. The investigation is underway as to how it happened, but one of the possibilities discussed is that the passenger accidentally pulled the ejection handle.

Having sat in various military aircraft over the years, I never thought it would be easy to accidentally pull the eject handle.

Is the ejection handle on a Rafale B easier to pull than most fighter jets, or closer to the hands' resting position?

Believe I remember reading in Scott O'Grady's book that the pull handle in the F-16 required 35lbs of pressure, which he considered to be a lot, but how easy he found it to pull when the time actually came. That I think is the ACES II system, where the Rafale is an MB MK16 one. I would guess the pressures are pretty universal.

There's a little light reading about ejection seats, though no specs on the pull pressure required.  Also has a ton of info. Little clunky to navigate, but good.

As to how a civilian could pull a handle accidentally... I guess throw someone into a jet, pull a half dozen Gs and watch them grab for something. Most tandem aircraft have split ejection "options", for lack of a better term, meaning the RIO/FO/passenger can punch himself out, but leave the pilot inside. Gotta be a hell of a surprise when the back seater disappears like that.

Likewise, I've seen and heard of numerous cases of canopies being blown accidentally without an actual ejection. Had an F-15C I was working on do it one afternoon in FL.


How are turboprops and other propeller planes pressurized? I know how most turbofan jets are pressurized:

But it can't be the same with turboprops, as I don't understand how propellers can take in the air. Yet, planes like Q400s can fly above 8000', all the way up and higher than FL220!  Can somebody explain how this is possible?

Turboprops are actually turbine engines. They can produce bleed air just like turbine engines (e.g. turbofan). The bleed air can be used directly to pressurize the cabin, or it can drive another turbo compressor to pressurize fresh air from the outside:

Modern aircraft with supercharged piston engines simply use bleed air from a) the main engine's compressor or

b) the main engine's turbo charger

Another solution is to drive dedicated air compressors to pressurize the cabin. Typically this may be Roots blowers or centrifugal fans. They are mechanically driven from the main engine(s).

Image source and more information on this topic: www.aircraftsystemstech.com


How does the load transfer from a prop to the airframe? I was just watching this video...

Restoration and startup of a Wright 1820 Cyclone

...and it got me thinking: a propeller shoves back air, and this creates a forward force on the prop. The prop attached to a shaft, and the prop is tugging on the shaft. Both the shaft and the prop are rotating.

The airframe on the other hand is (relatively) stationary. Yet the airframe depends on the rotating prop to pull it in the desired direction of trust.

This means there is an interface somewhere, between the rotating shaft and the rest of the engine, and that interface transfers all the thrust of the propshaft to the engine, and then the engine in turn transfers that force to the air frame.

That to me sounds like the mother of all bearings! What does such a bearing look like?! Or is there some other mechanical principle/device in play?

The engine mount is an important component that transfers the prop thrust to the airframe. It's clearly visible in this photograph of a fast and powerful plane, a  Bf109. Of course, bearings transfer thrust between the rotating and static parts. That is common to all engine-propelled vehicles, ships, cars, planes... The main thrust load, in the picture showing the turbofan, is taken by the tapered roller bearings.


Why are there out-of-date tower frequencies on the VFR sectional chart, without a NOTAM? I flew today to Salinas, CA and had a little trouble reaching Salinas tower (KSNS). The current VFR sectional shows the tower frequency as 119.4. However, apparently the frequency changed to 119.525 on June 2014 (according to http://www.montereybay99s.org/newsletter/July2014issue.pdf)

The current VFR sectional was issued in August 2014, after the frequency change. I'm wondering why (a) the frequency is incorrectly printed on the current VFR sectional, and (b) if it's an error why there is no NOTAM about it.

It's not a printing error. FAA sectional charts are updated only once every six months. In order to to reduce the number of NOTAMs due to sectional changes (which can number in the hundreds between cycles), the FAA provides a section in the Airport Facility Directory (AFD), titled "Aeronautical Chart Bulletin" that identifies changes that have occurred since a chart's publication. Pilots should check this section on each AFD update for changes on their intended route of flight. Once the change is posted in the AFD, the respective NOTAM is taken down.

Here is an image of the applicable AFD page for Salinas, as of the date of this answer:


What prevents someone from hijacking a radio frequency mid-air? For someone who wants to stay anonymous and probably terrorize the skies, what protective measures do we have?

Without even thinking too deep, I can imaging the following scenarios for someone who's in a mood to mess around.

Flying in a busy airspace, calling to "Cancel IFR" for someone else.
Abusing recklessly. Maybe stepping-on the frequencies infinitely.
Reporting fake traffic or fake weather conditions, causing re-routes
and delays.

While transponders are required in and around busy airspace, someone who really sets their target on screwing it up can REALLY cause a lot of harm, potentially fatal by flying without one for quite some time as a primary target on ATC's radar.

What are the current preparations to stop this from happening?

This sounds like a “people problem”. That kind of problems is best solved with enforcement.

Source of radio broadcast can be localized and it is not particularly difficult. There are techniques for transmitting something secretly, but they need specific modulation. Rogue broadcast or jamming on simple AM voice channel will be trivial to triangulate.

So if somebody did it, the FCC or FBI would pull out appropriate equipment, hunt them down and throw them in jail. Broadcasting without license, or contrary to the license you have, is in itself a crime and they'd throw in charges for endangering, which are quite serious.

Now of course it would take some time to hunt the perpetrator down. However, the situation is not that dangerous. Basically it could be treated as communication failure. VFR flights would continue flying visually, IFR ones would follow last clearance and then as filed, landings can be cleared with a light gun. And then either the surrounding sectors would be OK, or the pilots would probably try to establish some alternate communication. Cell phones should work fine for small aircraft while airliners would probably use HF or Sat links to dispatch and ask the dispatcher to relay.


Where can I find an image of the Thales FMS220 RMS page? I'm looking for photo/color image showing Thales FMS220 RMS (Radio Management System) page. Also COMMUNICATION and XPDR pages are highly welcome.

The answer is on the official website, here is a direct link:

https://fr.scribd.com/doc/204747124/Fms-User-Guide

You need to go to the website yourself because the document content is not to be disclosed without official approval.


Does it make sense to use a canard in combination with a conventional aft elevator control surface? I am designing a UAV and have settled on a canard design.  However, I’m curious whether it would be helpful to have a typical horizontal stabilizer behind the wing as well as a canard wing in front of the main wing to increase lift towards the front of the plane and for better stablity.  Is this a bad idea? I’m looking to carry cargo ranging from 0-1000g, and initially fly for around 30 minutes. It is also using a special VTOL system I’ve designed.

Actually, for most tasks it would be most helpful to add the horizontal tail and to remove the canard. There have been only a few canard designs and even fewer three-wing designs in the past. Off-hand I remember just three:

Voisin-Farman biplane in the Musée d'l Air in Paris (picture source)
Gabriel Voisin was the founder of the first commercial aircraft factory and designed a biplane with forward elevator and aft stabilizer in 1907 for Léon Delagrange and Henry Farman. He had chosen a similar layout for his very first glider design in 1905 already, most likely because the question where the elevator goes on an airplane was a matter of hot disputes at those times.

The second one is of course the excellent Piaggio P.180 Avanti (picture source), where the highly loaded canard allows to move the wing behind the pressurized cabin and the lightly loaded elevator provides ample control authority at all flap settings and center of gravity locations.
The third one is the Sukhoi-30 MKI, which adds small, closely-coupled canard wings to the conventional layout of basic the Su-27 / MiG-29 design. Thinking of experimental Russian designs, I could also mention the MiG Ye-8, a MiG-21 with a free-flying canard surface (picture source):

If you don't expect to have a wide center of gravity range in your UAV, use fewer wings. One big one for the lift and a second one for stability and control should be all you need.


Why is the static margin expressed as percentage of the MAC? Most textbooks use the static margin (the distance between the aircraft's centre of mass and its aerodynamic centre) to assess the longitudinal static stability.

Instead of using an absolute value for the allowable range of the static margin, it is expressed as a percentage of the Mean Aerodynamic Chord (MAC) - for example between 5 and 30%. Why is this so?

For a given aircraft, the higher its aspect ratio for a given wing area the shorter will the chord become. Hence the MAC will also be smaller. This will in turn reduce the absolute value of the allowable range for the static margin.

Is this simply a convention or is there an aerodynamic or flight mechanics reason why the allowable range for the centre of mass is smaller for smaller MACs or shorter wing chords?

The static margin is the distance between the center of gravity and the neutral point. By itself, this is a dimensional value. This makes it hard to compare between aircraft, so it makes sense to divide it by some other length. That the mean aerodynamic chord has been chosen has several reasons:

The MAC is the reference length for all parameters of longitudinal motion.
The wing's pitching moment scales with the MAC.
The wing's pitch damping changes with the square of the MAC. The biggest contribution to pitch damping, however, is the lever arm of the horizontal tail.

Normally, the tail lever arm is also chosen as a multiple of MAC. A higher wing chord means more tail force is needed in order to set the correct angle of attack. If you compare different airplanes, you will notice that the relative size of the horizontal tail goes down with a higher wing aspect ratio. While GA airplanes have horizontal tails sized to between 20% and 25% of their wing surface, gliders have horizontal tails of around 10% to 15%. It must be said, however, that gliders need less flexibility in their cg location, which is another reason for reducing horizontal tail size.

If all linear dimensions are referenced to MAC and all areas referenced to the wing area, calculations become easier and similarities between different aircraft become obvious.

For lateral motion parameters the usual reference length is the semispan or the span of the wing.


Is this paper's description of ATC services over the internet actually practical? I read this paper recently; it's titled ATC over the World Wide Web,
a case study and prototypical implementation. The paper says:

  "In the context of radar surveillance for regional airports DFS
  (Deutsche Flugsicherung Air Navigation Service) must provide a
  possibility for the controller to monitor and control the dedicated
  airspace in a safe manner without the need for a complex and locally
  installed radar surveillance system. In other words: The aim is to
  provide the controller in the tower with a PHOENIX Controller Working
  Position (CWP) over the World Wide Web (WWW). The CWP receives the
  surveillance data over the Internet. This approach allows the usage of
  a standard PC connected to the internet in a standardized manner (e.g.
  DSL)."

The PHOENIX is a Radar Data Processing System (RDPS) for air traffic control that's been developed at the Deutsche Flugsicherung (DFS).

My question is: why does a client need to send their ATC over the Internet for this? DFS still has to set up the hardware in the client tower. So, why doesn't the client use the conventional method to transmit/receive ATC and then, if needed, send the ATC through the Internet (on the ground) to the vendor (DFS) for real-time processing?

For the scope of the article you should read Internet as IP VPN.In practice you would have at least dual links with some kind of SLA attached. All this is much cheaper than having and maintaining your own radar on site.  At my employer we have a system which gets information from various radars over an IP VPN ( been there , done that ).


Can the real time operating system used in aviation equipment be certified by itself? Can the real time operating system used in aviation equipment be certified by itself, or must it be a part of some software certification effort?

I'm asking for getting a certificate of 178C. I don't understand if it is possible. There are a lot of resources that tell us about "certified operating system", but if is certified as a part of a project or it is certified just itself without any project... I have no practise in this field, but I was asked this question and it makes me puzzled.

A DO-178C compliant RTOS (such as LynxOS-178 mentioned by @mins) is going to have a certification package you provide along with your DO-178C artifacts for your software.

Note that there is no such thing as a DO-178C "certificate". DO-178C is a process that generates certification artifacts that are packaged and provided to the Certification Authority as part of some approval application (TSO, TC, STC, PMA)

It is also usefull to recognize that most software on equipment installed on an aircraft is not going to run on an RTOS, but rather run directly on the hardware (bare metal)


When an emergency happens, why do pilots need to stay on the current ATC frequency? Per the below order, I need to stay with the initial ATC frequency during an emergency, what is the benefit to do so? What if the aircraft entered into the airspace controlled by anther ATC or the aircraft is no longer within line of sight?

FAA Order J7110.65V, §2, ¶10-2-2:

  Although 121.5 MHz and 243.0 MHz are emergency frequencies, it might
  be best to keep the aircraft on the initial contact frequency. Change
  frequencies only when there is a valid reason.

This doesn't mean you won't change frequencies if you move into another controller's sector or there's another reason for a handoff, such as moving from Center to Approach or Approach to Tower; it's to say that if you're already talking to ATC at all (often optional for VFR), then you should report your emergency there rather than switching to 121.5.

121.5 is monitored at every ATC facility, so if you have an emergency and don't know the right frequency to use, you can always go there and someone will answer you--and presumably give you a better frequency as soon as they've figured out where you are. If you already know the right frequency, though, then it's better for everyone (including you) to use that instead.


Are there any legal requirements concerning airline pilots and their watches? Are there any legal requirements concerning airline pilots and their watches? Do they have to be of any particular kind and are pilots required to wear one at all?

Well, a wristwatch can't be used to sneak around the requirement that IFR requires a clock mounted in the aircraft, FAR 91.205(d)(6).  A missing or inoperative clock isn't likely in a modern airliner.  As far as the FAA is concerned, a wristwatch is nothing more than jewelry.

Ages ago, a wristwatch may have helped with calculating fuel burn and range, but even then, it was a convenience rather than mandated equipment.


Does it help to climb in case of a partial engine failure? When the engines of a airplane show irregularities that do not reduce performance but indicate a possible failure of the engines, is it useful to climb to a higher level, to increase the glide length that is available in  case the engines stop completely?

The problem known in the cockpit is only that the engines do not run like they should. Say they make clearly unusual noises and slight vibration, but loose no performance. There is no indication whether the engines will fail, an in case the do fail, at which point in time that  will happen.
It's an emergency, without actual change in the planes performance.

As example, I think of a small single propeller plane, and a situation where longer glide path could be useful. But I think the question applies to any plane that can glide without power.

Agreeing with @Antzi, high engine speed when combined with some sort of small scale physical damage or corrosion is a typical failure mode for propeller engines. Combining that logic with the fact that propeller engines run more efficiently at lower elevations (higher air density) I would recommend against climbing. In fact, lowering your elevation and speed will greatly reduce the stress/strain you are putting on the engine and will likely give you a better chance of making it safely to the closest airfield.


How do you calculate Profile Drag? second year aeronautical engineering student here. I'm doing some aerodynamics coursework but have run into a problem.

I've read through the answers to the question "what is profile drag?" but nowhere either there or elsewhere online can I find how to calculate the profile drag. I can get the skin friction drag from boundary layer calculations, but have no idea where to go from there. So does anybody know how to calculate the form drag for a given aerofoil (eg NACA4412)?

But nowhere either there or elsewhere online can I find how to calculate the profile drag.

Seems like you were searching for the incorrect terms. Try searching "boundary layer integral momentum equation", "von Karman boundary layer integral", "momentum deficit", "boundary layer Kinetic energy dissipation integral" or something similar. You should get plenty of resources/lecture notes on the subject.

  So does anybody know how to calculate the form drag for a given aerofoil (eg NACA4412)?

In essence, this is done via integrating the "Integral Momentum Equation" or its non-dimensionalized version "von Karman Equation" over a coordinate system defined over the airfoil contour.

  I can get the skin friction drag from boundary layer calculations but have no idea where to go from there.

If you study the "Momentum integral equation" stated above you can see there are two contributors to the momentum deficit or its rate of change. one is skin friction and the other is the profile drag which is equal to - mass defect * rate of change of edge velocity.

Put it in another way, the skin friction term usually is dominated by the front portion of an airfoil where due/ds mostly favorable and the profile drag is dominated by the pressure recovery region aft of the airfoil because of the negative velocity gradient and higher mass defect.

But the story does not end there, because you will have to add the viscous dissipation happening in the wake up to the far-field as well. This is usually done using the "Squire-Young" equation by applying the previously obtained momentum deficit at the trailing edge.

PS :
All above being said, you can easily use XFOIL for such calculations. But understanding what's going on under the hood in such an application, might provide one with great insight and appreciation for what they have got for free.


What are the differences between a VOR and a VORTAC? In Brazil airspace, we do not have VORTACs to navigate (unfortunately). That's why my doubts about accuracy, the range, the possible systems/frequencies they operate, and if there is any restriction to use it to navigate.

VOR stands for VHF Omnidirectional Range. It is a navigation beacon intended  for civil use and provides a user with a radial to/from the station. It works on frequencies between 108.00 and 117.95 MHz.

VOR/DME station PEK (Beijing):

source: Wikimedia, author: Yaoleilei

TACAN stands for TACtical Air Navigation, a military system that is similar to VOR but with higher accuracy. It works on frequencies between 960 and 1215 MHz.
Part of the TACAN is DME (Distance Measurement Equipment), which works in the same frequency band. The DME used in TACAN is the same that can be used by civil aircraft. Due to the higher frequency the system is more accurate and the antenna is much smaller and therefor easier to deploy (e.g. on a ship, on a battlefield).

 (source: wikimedia, US Air Force, Camera Operator: SENIOR AIRMAN JONNA N. WILSON)

A VORTAC combines the VOR and TACAN in one location. Civil users will use the VOR signals which have the same performance as ordinary VOR signals. In addition they use the DME from the TACAN. Effectively a VORTAC is like a VOR/DME.
Military users only use the TACAN, for them a VORTAC is the same as a TACAN.

source:Wikimedia, author: Hans-Peter Scholz Ulenspiegel


How is maximum rate of climb defined in aircraft specifications? In common aircraft specifications a "rate of climb", or "maximum rate of climb" is specified. For example the wikipedia page for a Spitfire, or C172.

However my intuition is that the rate of climb depends wildly on various things. Aircraft weight, altitude and so on. Furthermore, you could potentially fly at maximum airspeed, and then pitch up 90 degrees, and climb until you begin to stall. Sure you wouldn't be able to last long, but for a short period you'd have a very high rate of climb.

So the question really is, when aircraft specifications detail "rate of climb", is there some implicit context for when that rate of climb is applicable? Is it optimized for climbing in the most time or distance efficient way for X distance or something?

The "maximum rate of climb" is the highest sustainable ROC for the following conditions...

sea level conditions (or standard atmosphere for other altitudes)
maximum gross or takeoff weight
cruise configuration
maximum rated continuous thrust/power

There are additional minor requirements given in FAR 23 such as the rated power 8 seconds (SFAR to 23, par 6 and 23.63-23.67) after the throttles are moved to the full thrust position but the above is a good generalization.


Does go-around require more power than take-off? The complete version of Buran spacecraft would have had two engines that were not sufficient for take-off under own power.

Is it possible to say that if the aircraft is not capable of taking off under own power (not sufficient), it should not be capable of going around (assuming weight and other circumstances are the same)?

It really is something watching the Buran 'takeoff' versus 'liftoff'.

The answer is no. Given the same weight it should be roughly the same power needed. That is if we are calculating it from the point of rotation for a takeoff and point of initiating a go-around.

Given the same starting conditions—weight and velocity—both aircraft will have the same kinetic energy. If the takeoff / go-around is to 2,000 feet above starting condition, then the change will be the same gain in potential energy.

If they take the same time to reach that height, then it is the same power used. (Ignoring ground effect.)

The objective of the 2 engines would be to extend the glide distance for a space reentry, say if an incorrect calculation or unforeseen event caused the space glider to come short. A corrective action would need to be applied not close to the ground, but high enough to have a meaningful effect.


How do I find how much it costs to park a B747 at an airbridge in Perth? I need to park my B747 at Perth for 1 hour. How much will it cost me? You may assume I have 200 fare paying passengers. I must use an airbridge for those 60 minutes.

To be honest, I don't really own a B747 (yet), but am having trouble figuring out the costs for this. I've found some example costs for various airports around the world, and some landing fee documents on the airport's site, but they're a trifle confusing to decipher.

Perth's commercial fees appear to be here.

Note that parking is not the same as waiting at the gate to load/offload passengers. Parking is when your aircraft is not using the terminal, but the airport facilities (like aprons, hangars, etc.)

Let us assume you are carrying 200 passengers, and leaving with 200 passengers:

First of all, you have to pay the landing fee, which is:

(4.891 x 400) + (9.528 x your landing weight, in tonnes)

Next, you have to calculate the terminal charges - assuming you are an international flight, (so you are using Terminal 1):

(13.868 x 400) + (0.450 x 200) + (1.111 x 200) + (5.997 x 200)

13.868 is the terminal fee, per arriving or departing passenger
0.450 is Common Use Service charge, per departing passenger
1.111 is the security fee, per departing passenger
5.997 is the baggage checking fee, per departing passenger

Since you'll only be staying for 1 hour, you don't have to pay any parking charges; which are only charged for staying more than 2 hours.

So total passenger fees are: AUS $9,015.20, before tax;  you still have to calculate your landing weight and multiply it by 9.528 to get the final amount.


Do similar angles on a plane make it more stealthy? I learned in my intro to engineering class at my college that 5th gen fighters (which are stealth aircraft) are designed with similar angles to evade radar.

Why is this true?

Also, does the angle matter?  Many of these modern fighters looks to have very similar angles (no pun intended).

The angle matters because radar works kind of like a mirror. Imagine holding a mirror out in front of you. If you start to twist it in any direction, you reach a certain point where the light coming off of you is no longer bounced back into your eyes, but is reflected off in another direction. Radar however cannot ever be completely reflected away, but this same principle allows a significant portion of the radar's energy to be deflected off in a useless direction, instead of back toward the dish.

The angles are similar because that angle was determined to have the smallest radar signature. So it makes sense that every other facet on the same (geometric) plane would be at the same angle. This means that the radar's energy is directed away in a very specific direction (away from the source), rather than a bunch of different angles (that would be more likely to return the energy to the source).


Why doesn't the centre of pressure move in the case of a symmetric aerofoil? Why doesn't the CP (centre of pressure) move in the case of a symmetric aerofoil?
Also, why does the CP move backward in the case of a flat plate?

Simple answer:
The pressure difference between lower and upper side on an uncambered airfoil or a flat plate can be summed up in a force acting at the quarter point, independent of angle of attack. Only when separation starts will this pressure distribution change shape and the force will move backwards. Since a flat plate has a sharp leading edge, separation happens at much lower angles than on an airfoil. If you think this is tautological, please read on.
More precise answer:
In potential flow theory, circulation strength is proportional to the local pressure difference on both sides of a body. When I now talk about circulation, just think pressure difference.
The distribution of the circulation strength $\gamma$ over an uncambered airfoil is given by Birnbaum¹ as $$\gamma = \sqrt{\frac{1-x}{1+x}}$$ for the lengthwise coordinate $x$ running from -1 at the leading edge to +1 at the trailing edge of the airfoil. Like this:

Now it is important to note that the shape of this distribution stays the same, regardless of angle of attack. Only the intensity of the circulation varies with angle of attack. Until separation starts, that is.
If you calculate the centroid (= center of gravity of the area under this curve), it lies at -0.5. If we now translate the X coordinate to the more usual 0 at the leading and 1 at the trailing edge, this center of gravity sits at 0.25 or the quarter chord point. And it stays there, regardless of angle of attack (again, until separation starts!). Circulation is equivalent to lift, so the same holds true for the pressure coefficient over chord.
This explains why the pressure distribution of a symmetric airfoil stays at the quarter point. It does so, too, in case of the flat plate, only that the angle of attack range where this is valid is much narrower. The sharp corner at the leading edge of the flat plate will cause air to separate already at small angles of attack, so the validity of potential flow theory (of which this proof is part of) is limited in case of a flat plate. Once separation starts, the pressure over chord tends to stay constant, so the center of gravity of the pressure distribution shifts towards X = 0.5.
¹ W. Birnbaum: Die tragende Wirbelfläche als Hilfsmittel zur Behandlung des ebenen Problems der Tragflügeltheorie. Zeitschrift für angewandte Mathematik und Mechanik 3, pages 290-297 (1923)
https://doi.org/10.1002/zamm.19230030408


Are pets/animals in the cargo hold monitored inflight for any sudden medical condition? My question is more from a long haul flight POV. Does the crew do a mid-flight check etc. What if any animal/pet have a sudden cardiac arrest or some emergency medical situation, will the crew or pilots be alerted for the same?

To the best of my knowledge, no modern (i.e. currently used in regular commercial service in statistically significant numbers) commercial passenger aircraft have access from the main passenger cabin to the cargo hold, so there is no way for the cabin/flight-deck crew to check on the critters below, even if they wanted to. My knowledge, however, is incomplete, as was pointed out in the comments, the 747-100 & -200 (and likely the -400) do have access from the passenger cabin to the forward cargo hold. The flight crew were notified when animals were stowed there, however, a long-serving 747 pilot indicated having never checked in on said animals.

Large and/or high-value animals such as elephants, giraffes, etc. are shipped as cargo via specialist transport companies where arrangements to have them tended in flight are common and accounted for (hat tip to Simon). I doubt you'll see someone pulling up to the departures gate at LGA with an elephant in a crate and wheel him up to the curb-side check-in gate.

As a personal anecdote: When I flew from JFK/KJFK to TLV/LLBG in the mid-80s we took our 2 dogs since we were moving there for a period. We got to walk the dogs on the tarmac just before they were loaded in their crates and put in the hold (747, probably -200) at JFK, but there was no mention of anyone checking on them mid-flight.

Fun fact (for me): We also got to walk the dogs at TLV just prior to our return flight, and that walk ended up taking about an hour as we got to watch them jack up a wheel on a 747 to change a flat tire pre-flight. (Yes, security was much different then. Even in Israel at the height of their occupation of southern Lebanon.)


What is the "No Step" flap thingy used for on an A320 engine? There is a small plate sticking out of an A320's engine narcelle with "No Step" written on it. I tried taking a picture of it, which in retrospect didn't turn out as good as I wanted it to be, but I hope it helps:

Anyway, I'm wondering what it's used for? It's only on one side towards the aircrafts body and it seems to be too small to be an aerodynamic surface. I suspect it's used during maintenance?

It's a vortex generator explained in full in this question

"NO STEP" means don't put your foot on it. It's too weak to hold a person's weight and would get damaged.


What's the reason for the local flap extensions at the shockbody locations? This weekend I was on a Airbus A319, and I noticed that the flaps have small extensions at the location of the shockbodies (indicated in the picture with the red circles)
I was wondering what the reason is for these extensions?
My guess is that it could be to compensate for the lower local lift generation caused by the presence of the shock bodies, but I'm not sure. I'm also interested in knowing why they have different sizes at different locations.

The anti-shock bodies also serve as fairings for the flap actuators. When the flaps are extended, the anti-shock bodies move down as the flap mechanisms extend. The upper surfaces of the anti-shock bodies are open to allow room for these mechanisms to extend.

The extensions to the flaps are to cover the openings of the anti-shock bodies when the flaps are retracted to provide a more aerodynamic surface. Evidently the outer locations have larger openings to cover.

Below is an image of a different aircraft and flap track design, but the principle is the same. You can see some of the hardware that sits in the fairings, and the covers that allow the hardware to extend out of the fairings.

Source

When the flaps are retracted, you can see that the flaps close out the top of the anti-shock bodies, and the outer position is closed out further aft.

Source


How do I choose the correct airfoil? I am currently working on a personal single seat, piston aircraft that I would fly myself and I am currently in a bit of conundrum when it comes to my wing design. In this project, I assigned us in 2 basic groups. The guys that work on the chassis and the guy (me) that works on the aerodynamic surfaces. Namely wing, surface controls, tail and such. It is a standard pull configuration aircraft, tricycle landing gear. My problem here is that I am kind of undecided when it comes to my airfoil of choice, so I thought of giving the forum a go and see if anyone can illuminate or inspire me.

As of now, http://airfoiltools.com/airfoil/details?airfoil=naca643618-il has been my choice, but maybe I am starting to think that other options could be better so let me write here a few specifications that could come in handy regarding the aircraft.

The main body will be build of steel tubing covered either in Aluminium or fabric. This will be the final choice once we calculate how much lift we can actually produce.

The wings and other surfaces will be made out of carbon fiber. I will be the one mainly working on this, and they will be attached to long solid cuboids spanning from one tip of the first wing, through the body and all the way to the tip of the second wing. The shape and dimensions of these cuboids will be determined through a FEA after we have the correct wing profile (so we can play with the variables afterwards or maybe even find better solutions). The wings will either be attached with rivets to the cuboid or with standard well shaped bolts. TBD.

The aircraft is planned to be mostly used at not so great speeds. If we can achieve a takeoff at 16-20 m/s with flaps on it would be fantastic. I would not like the top speed to be anything great either. I mostly would use this in very good still weather to cruise around the fields.

I can afford having an airfoil that is a bit thick, but would like to manage the turbulence that would be created by boundary layer separation in high thickness and/or camber foils. Maybe I will modify a bit my final selection.

The wing will have flaps, in fact it will be a flap that extends at around 35% of the total span of the wing. It will be a modification of the slot and Fowler flap (a sort of optimized approach that mixes both) whose final geometry will of course be dependent on airfoil selection.

P.S : I use Fusion 360 for modeling, Autodesk CFD to calculate the total lift of the full 3D modeled wing/aircraft.

Terms fist, to avoid any misunderstandings:

What you call cuboids is normally called a wing spar. It consists of spar caps for the tension and compression loads and a web between the caps to transmit shear. And yes, it runs all the way from one wingtip to the other.

The spar carries the bending moment which has its maximum at the center and is zero at the tips (unless you use winglets). The more distance there is between the two spar caps, the lighter the spar can be built, so a thick mid-wing airfoil helps. Your choice of the NACA 64₃618 is a good start. I would advise, however, to taper the wing to something like a NACA 63₃412 at the tip. Thinner airfoils have lower minimum drag and higher maximum lift coefficients which helps to avoid the tip stalling first.

Or you move to newer airfoils which have been optimised for longer laminar boundary layer runs. Since you plan to use carbon/epoxy for the wings, you might take advantage of the exceptionally smooth surface this makes possible. The NASA contribution is of course the NLF series, NLF standing for natural laminar flow. The NLF(1)-0416 or the NLF(1)-0215 would be possible candidates. Even better designs might be possible when you search for modern glider airfoils; however, the published ones generally are at least 30 years old. Glider airfoils are optimised for minimum Reynolds numbers of around 1 million; when used in a GA aircraft this might be a bit conservative but could fit well to your low speed requirements.

The ultimate step could be to design your own airfoil. Take my glider recommendation and use XFOIL to tweak it to what you really need.

One last word on your choice of flaps:

When the inboard span uses powerful slotted flaps, their increased circulation will change airflow at the outer wing in such a way that the outer wing will stall before the inner wing had a chance to demonstrate it's lift potential. Either stay with plain flaps (for which the HQ-17 was designed - make sure you calculate it with a positive flap deflection at slow and negative at fast flight speed!) or add slats to the outer wing. In order to keep complexity manageable, I would recommend to use plain flaps and flaperons over the full span.


Have any airliners successfully landed on a runway after striking a tree? There are many examples of aircraft striking trees during a crash sequence, usually with high fatality rates.
Have any airliners struck* one or more trees and proceeded to successfully land on a runway at an airport without any fatalities?
*Struck in this case meaning physical contact during flight which caused significant damage beyond scratches, such as denting, broken lights, partial loss of lift and/or control.
If I understand the terminology correctly, these incidents would be "Controlled Flight into Terrain (CFIT)" with subsequent airport landing without loss of life.
The closest I'm aware of is Scandinavian Airlines Flight 751 which lost thrust from both its engines and glided mostly into a clearing, striking trees as it went down.
Disclaimer: Long-time lurker, not a pilot, just enjoy the community and learning about aviation safety.

Searching through the Aviation Herald database for incidences with the word tree, I found 3 cases:

An Eagle Air Let L410 contacted a tree during departure from Lankien in South Sudan. The right wing tip was damaged, but the aircraft continued to its destination, where the wing tip was repaired:

A China Eastern Airbus A320 contacted trees during a go-around at Wenzhou after losing visual contact with the airport during approach. The damages were only found after landing though:

A post flight inspection found scratch marks on the right main landing gear, slats and flaps of right main wing and the inlet of the right hand engine (CFM-56). An inspection of the right hand engine revaled damage (dents sized up to 0.2 mm) to all 36 fan blades, scratch marks (13cm in length) at and twigs embedded in the oil discharge.
[...]
Due to the late decision by the crew the right hand wing, right hand engine and right hand main gear impacted and clipped treetops outside the airport perimeter.

A Cebu Pacific Airbus A320 came in contact with trees, but the damage was also only found after landing:

a subsequent pilot inspection found branches and leaves embedded in the right hand main gear, the right main gear was leaking hydraulic fluid. The occurrence was rated a serious incident and is being investigated by Philippines's AIB.


Why is rotating engines in opposite directions more important for a propeller-driven plane than a jet? From here it is seen that many multi-engine propeller planes spin their propellers in opposite directions. To avoid producing "left" and "right" types of the engine, a gearbox is fitted.

In contrast, jet engines usually spin in the same direction. Why is the spinning direction less important for a jet engine than for a propeller engine?

A Boeing 777 may have a turbine fan as large as 325 cm in diameter (GE90-115B). Not every propeller is that large.

This is sort of explained in the linked question already. Specifically this answer (which I consider better than the accepted one above it) says:

  Today, high power propeller aircraft tend to use identical engines but left- and right-handed gearboxes so the propellers run in both directions. This is less due to gyro effects and mostly to produce benign stall characteristics. The prop wash of a propeller increases the local angle of attack on the wing on one side and decreases it on the other side, so the wing will stall first on the side with bigger angle of attack. If this side is always to the right of the propellers, the aircraft will roll right in a stall.

In a turbofan the nozzle directs the flow below the wing aft of the leading edge, focuses it more and uses guide vanes to stop its rotation, so this effect does not occur. This eliminates the most important factor for deciding to use counter-rotating propellers.

Combine with the fact that most turbofans are not geared, so the whole engine would have to be mirrored, which would complicate maintenance a lot more than just having mirrored gearboxes and propellers does for turboprops.


What is the bulge under the engine of the Mirage III and some of its variants? While attempting to create a Kfir in 3D modelling software, I noticed a bulge under the engine on the reference picture (a 2D side view) I was using, which I initially assumed to be a fin. After looking at some 3D images of it, however, it is far too wide to be a fin:

There is a similar bulge in the same position on the Mirage III:

The Atlas Cheetah and Mirage 5 both have a bulge in that position as well, although every non-Mirage-III-based Mirage seems to lack it. The Mirage 2000 has a bulge in a similar location; however, it appears to be much smaller:

My initial thoughts were either ECM or some kind of fuel tank. Does anyone else know what it might be?

For the Mirage III, it's a fuel tank (that also allows a camera attachment). See cutaway below (item 157).

Also from Wikipedia:

  The Mirage IIIRS could also carry a centerline pod for conducting photo reconnaissance missions, as well as an integral fuel tank underneath the aft belly; this tank could carry a smaller fuel load, but also allowed for a rear-facing film camera to also be added. When fitted with the reconnaissance pod, supersonic performance was severely diminished.

Source: aviadejavu.ru (composite of two pages: 16-1.jpg and 16-2.jpg; use links for full-res)