Why does disk loading mean anything when rotors/propellers are not disks? "The helicopter rotor is modeled as an infinitely thin disc with an infinite number of blades that induce a constant pressure jump over the disk area and along the axis of rotation."

This is spectacularly not true of common propeller disks. Most of the area in propeller/rotor disk is empty space, through which air flows freely from top to bottom.

So why do we take this mostly empty disk and use it's area in aerodynamic calculations, when it would seem that we should rather be using the area of the blades themselves?

It seems to permit "fooling" disk loading equations by, for example, decreasing the blade chord without increasing the span, but still getting the same results from equations. So, what a I missing?

The disc model is used wherever generalities of behaviour are studied without the need to know individual blade characteristics. It captures the mathematics of those generalities in a simple way that leaves out extraneous detail which would make the maths impossibly laborious.

Typically the aircraft designer will use the disc model in the design of their airframe, leaving the blade details for the propeller or rotor designer to figure out.


Could someone please explain what is thermal oxidation of the carbon brakes? In my company SOP after landing we don’t switch on the brake fans immediately after the HOT annunciation comes on on the BRAKE FANS push button. Instead we are told to wait for a period of 5 mins after landing to allow for thermal equalisation of the brakes and to prevent oxidation of brake surface hotspots.

What exactly does this mean?

Catalytic oxidation of carbon occurs when a catalyst, such as an
  alkali metal(s), is present. When a catalyst is present, the
  temperature at which thermal oxidation occurs is lowered. Airplanes
  equipped with carbon brakes are susceptible to catalytic oxidation
  caused by exposure to alkali metal runway deicers. - Boeing Aero
  Magazine

Brake manufacturers produce Oxidation resistant brakes. The effects of can be obtained by using carbon brakes, or using a coating on the brake rotor and friction surfaces.

Best practices for carbon brake application according to Airbus.


What type of coordinate system is this? In case you want to say spherical coordinate system: no it is not a spherical coordinate system.

I found this image in a book about flight management systems where they explain the different types of coordinate systems it can use.

The ukrainian name for it is: "ортодромічної" coordinate system

What is the English name of this coordinate system and what advantages may it offer over another (eg spherical coordinate system)?

The document is about navigation.

By using an online OCR tool (I used this one which is not so good) on page 177 of the document, and then translating from Ukrainian using Google Translate:

... I can confirm @Federico 's suggestion: This figure doesn't introduce a new coordinate system, it just tells about rotating a good ol' geographic coordinate system to facilitate navigation / calculation.

A GCS is defined by its equator, rotating it means the equator is not anymore the Earth equator.

Such frame transformation is also used for INS (SINS) to minimize the accumulation of rounding errors. Just changing the frame orientation allows a better use of the same sensors.

This document says, with fig 7.7, that in some cases, depending on the type of mission or route of the aircraft, it is appropriate to rotate the usual GCS (latitude, longitude) to facilitate calculations and increase accuracy of the results.

An example is, when following a great circle (orthodromy), to align latitude and longitude so that the system equator is parallel to the great circle to follow.

You will easily improve both the OCR rendering and the translation by spending some time on it.

I made this answer a community wiki, so anyone can improve it.


What are the Requirements for the implimentation of Low Visibility Procedures at an airport? So I was wondering if the RVR at an airport is reported above CAT I conditions for eg 1400 Meters etc but the Visibility is 50 to 100 Meters then would the pilots carry out non instrument approach or would the approach would be carry out as per Low Visibility conditions ?
And what are the conditions for an airport to impliment Low Visibility conditions ?

It is the RVR values that are used to determine the applicable minima.
The switch from normal to LVP Ops varies from airport to airport but the changeover process typically commences when the dropping vis approaches 1000mtr (say roughly 1200m) and is dropping so that the ILS Cat2/Cat3 LVP can be offered as the vis/rvr falls to below Cat1 requirements. More detailed info can be found in the country AIP and the same info would be spelt out in the Jepp or equivalent.
The Low Visibility info is specified in Sec 1.3 in the 10-1P series pages of the Jeppessen Terminal charts, ie "Airport Briefing" pages.


What is required by and for flights that cross borders in terms of border control? This can apply to countries that have water in between, like the UK-France or US-Canada.

If an aircraft crosses into neighbouring country, does it need to go to a border-controlled airport (with flight plan and access granted)?

An IFR-filed flight with permission from that country's civil authorities, but to a non-international airport.

Are international airports the only border-controlled airports or do some countries have predetermined airports that pilots can fly to, so that border control authorities can process them at said airport?

A famous US/Canada example is Niagara Falls.

As as student, part of my cross-country test involved flying a circuit around the Falls, which meant passing the international border.  No special permission was required.

If I'd gone anywhere near the American airport (top right of map), the situation would have been completely different though.

Note that even though there are no specific border control related rules, there are many safety regulations controlling this circuit.  (It's a lot more crowded now than when I flew it.)

GA Flying over Niagara Falls – Fly 'n Things


Why is wave drag non-zero for a flow without shockwaves? Wave drag is often defined as the component of drag that arises due to the presence of shockwaves. Shocks result in an entropy rise and a corresponding increase in drag. However, when using Supersonic Potential Flow Theory (Ackeret Theory), the flow is assumed to be fully isentropic (i.e. no shockwaves) and it can be shown (see Bertin, Houghton, Anderson for reference) that the wave drag is non-zero for such flows. So, what is the mechanism behind why the wave drag arises in such a flow without shocks?

More Detail (from Aerodynamics for Engineers by Bertin)

The drag can be computed from Navier-Stokes momentum equations as:

$$D=-\oint_{S_\infty}p\hat{i}\cdot d\vec{S} - \oint_{S_\infty}\rho (\hat{i}\cdot\vec{u})(\vec{u}\cdot d\vec{S})$$

Usually, all boundaries other than the rear boundary (Trefftz plane) would have the same flow properties as the free-stream, and they fall out of the integral. We are left with:

$$D=\int_{S_T}{\rho u(V_\infty-u)dS}$$

As you correctly pointed out, the momentum defect of a potential flow should be exactly zero, which means that drag should also be zero.

However, for oblique shock in small-disturbance potential flow, the oblique shock (or rather, each constant potential wave characteristic) extends to infinity, carrying energy with it. If you want to calculate the far-field drag, you would need to do the integral around the entire far-field. This is different from energy dissipation in viscous boundary layer or subsonic normal shock.

Picture ref. https://nikander.github.io/compflow/Anderson/Chapter4/print/


How is the actual ground speed of an airliner measured? Do pilots have the "ground speed" information available?

If so, how is the ground speed measured? Or do they rely on GPS info to calculate it?

There are generally two ways of determining the ground speed from within the aircraft.

The first is by using an inertial navigation system. This consists of a number of accelerometers and gyroscopes that measure all accelerations and rotations of the aircraft throughout a flight. By mathematically integrating all measurements this navigation system is able to compute the speed and position of the aircraft at any time. The accuracy will degrade over time but ground speed is usually not far off, otherwise position would be far off very soon.

The second method uses external radio signals. Nowadays this is mostly GPS, but ground speed is also determined by using a number of VOR (VHF Omnidirection Range) and/or DME (Distance Measuring Equipment) stations. These navigation beacons are widely available over most continents. A navigation computer would select the right set of beacons and by analysing the rate of change of the beacon bearings / distances the aircraft's speed can be determined.

Modern navigation systems combine all these methods into a one solution. GPS, inertial navigation and DME measurements are then fused mathematically together to obtain a highly accurate and robust position and ground speed.


How does one tell whether a corkscrew approach is stabilized or not? A corkscrew approach is an unusual type of approach used in places like BGW/ORBI to minimise an aircraft's exposure to antiaircraft fire on the way down; it involves staying at cruise altitude until one is directly over the airport, then descending to the runway in a fast, tight spiral.

Given that the tight, spiralling descent would seem to make it almost impossible to determine whether the approach is stabilized or not, how does a pilot performing a corkscrew approach make this determination?

The corkscrew approach as Wikipedia describes it is what the military refers to as a “Force Protection” measure to be used when operating in a high threat environment.  It is not a published procedure in the traditional sense of the word, but something that is put in place by the theater commander and briefed to aircrews when driven by the current intelligence assessment of the threat level.

It is not intended to be flown as a precision maneuver like an instrument approach would be.  It is a dynamic, eyeballs outside the cockpit looking for a missile, combat visual descent.  A high rate of speed is maintained until as late as possible in order to make evasive action possible.  Not only is it clearly NOT a stabilized approach, it is actually the exact opposite:  Done in VFR conditions, the aircraft isn’t configured until just before landing.

Contrast this with the definition of a stabilized IFR approach from FAASafety.Gov below:

  Stabilized Approach Concept. A stabilized approach is one in which the pilot establishes and maintains a constant angle glide- path towards a predetermined point on the landing runway. An airplane descending on final approach at a constant rate and airspeed travel in a straight line toward a spot on the ground ahead.

There is a lot of additional information available about stabilized approaches out there for anyone interested so I won’t attempt a further explanation about the intent.  By definition, however, a corkscrew approach is not stabilized.

So, back to the original question:  “How does a pilot performing a corkscrew approach make this determination?”  (whether the approach is stabilized or not…)  The answer is that a pilot performing a corkscrew approach isn’t asking himself those kind of questions.  The distinction is completely meaningless.

He/she is looking outside for the smoke trail of a stinger rising from the ground, and working to get the plane to a point where they can pull the nose up to break the rate of descent and slow down, slap the gear and flaps down, and make a tight 180 combat turn to a short final to lessen the exposure time when they are dirty and slow.  The goal is to get on the ground as safely and expeditiously as possible and minimize any time spent “stabilized” on a long straight-in approach.

Stabilized approaches are what tactical aviators fly stateside when practicing for their annual instrument proficiency check.


Is this scheme for a single-fan electric airship with a rocket-like geometry workable? I am currently designing a vertical take-off and landing vehicle that uses a Tesla powertrain connected to an electric ducted fan. Please comment on if my thought process is sound on my feasibility analysis.

My initial mission goal is extremely modest to grease the wheels of my feasibility analysis and have a realistic utility in society (and for people in my sport, recreational/experimental skydiving).

The vehicle simply needs to lift itself and a 100kg payload (coincidentally the approximate mass of a skydiver with his parachute) to the altitude of 1 mile.

I think I need to calculate my total delta_v, but because I don't need a high speed (like an orbital escape velocity or something like that) I am not positive how to go about getting it without first understanding the maximum thrust from my system.

My current plan for determining thrust from the tesla-system: 1) identify maximum output of tesla battery and motor (lets say Model S P100D) 2) calculate maximum propeller size for #1 based on algorithms available in electric drone aircraft websites/forums 3) calculate potential thrust produced by #2 4) use #3 to determine if liftoff is possible carrying at least #1

My initial calculations are not intended to include all outside forces; I will incorporate these if it is in fact, theoretically feasible at all.

Based on information above as well as the weights of the battery, motor, and an estimate of a basic rocket-shaped frame, I can figure out if a basic propeller will work for this, or if I will need to incorporate an electric turbojet, which would blow up my budget for this.

It is also feasible I could have a combination of several motors / batteries attached to multiple propellers with something like a rocket sitting in the middle of an oversized quadcopter. Again, budget goes up considerably.

The best propeller driven vertical take-off and landing craft would be a helicopter, actually. Yes a duct around a propeller increases thrust, but upsizing a propeller creates way more thrust from the available power.

Propeller thrust has scaling effects with size due to different Reynold numbers, data does not scale up well. Best way forward from where you are now would be to look at the weight, rotor dimensions and installed power of existing designs for small helicopters such as the R-22. Or better yet, design an electrical version of the Hiller Flying Platform Platform.


Did some early jet engines catch on fire at higher power settings? Recently I've being playing some IL-2 1946, and in this flight simulator jet engines had a strange problem where if I suddenly throttle up more than 60% the engines would catch on fire. Is this a real thing? The engines that this happens on are the Jumo 004 and the BMW 003 on the Me 262 and the He 162.

Yes indeed. For the Jumo 004:

  [A] shortcoming of the engine, common to all early turbojets, was its sluggish throttle response. Worse, it was fairly easy to inject too much fuel into the engine by throttling up too quickly, allowing heat to build up before the cooling air could remove it. This led to softening of the turbine blades, and was a major cause for engine failures.

To avoid rapid movements the levers of that era (and still being used on some types) had a friction setting that can be increased on decreased. High friction results in more force required to move the thrust lever.

Advancements in the hydromechanical units and the introduction of engine control units made controlling a jet engine much easier.

I remember reading (but I can't seem to find it now) that Frank Whittle had problems shutting down one of the early jet engines he worked on. It would just keep running and speeding up.


Is there such a concept as 'Max Overhauls' for aircraft components? I have never seen any overhaul-able item with a documented limit on the number of times it can be overhauled.  In all cases it was subject to analysis and predicated on it passing certain tests.  Has anyone else heard of such a limit?

If so, what examples of aircraft components with such limits and what kind of aircraft can it be found on?

Yes, but its a fairly new change from the FAA. The FAA recently regulated part Life Limits, a limit in place at certification time (or through a later AD etc.). The IATA also outlines guidance for life limited parts. This is a fairly new reg and many of the older aircraft out there may not be subject to it since they were certified prior to it. This AC also outlines some info relating to it.

However for any mechanical part there, in theory, is a limit to the amount of times it can be overhauled if that work requires reductive machining. Something like a crank case, cylinder head or piston sleeve can only be machined so many times before there is not enough material left for a proper overhaul.

The definitions of overhaul vs rebuild are important. A rebuild may reset a parts life, you can read more on that in this question.

Any life limited part should be listed in the documentation for the specific airframe/model in question. For example here is the list of the Robinson R-22 helicopter. More notably the Cirrus SR-22 has an airframe life limit of 12,000 hours as part of its certification.

  The certification requirements of 14 CFR 23.573 require that the
  composite airframe structure, cabin, wing, empennage their carry thru,
  and attaching structure whose failure would be catastrophic must be
  designed to damage tolerant criteria. Damage tolerant certification
  for the selected airframe life of 12,000 flight hours has been
  established for all of the affected parts with no special structural
  limitations or inspections.


Could hydrazine be used as a scramjet propellant? Hydrazine is used a monopropellant in Satellite OMS rockets. But interestingly enough, it's highly exothermic decomposition into ammonia, nitrogen, and hydrogen provides heat for an endothermic reaction with additional hydrazine to form hydrogen gas. So a scramjet using hydrazine would have to reactions inside it's combustion chamber: The decomposition of hydrazine and the combustion of the resulting hydrogen gas with air. And unlike hydrogen gas, hydrazine has much higher propellant density. Has this ever been considered by aerospace engineers and even tested?

Technically yes, you could use hydrazine in a scramjet.

But there's no reason to do so. The singular purpose of building a scramjet is to get air into the combustion chamber, so that you don't have to use a monopropellant, which all have high cost and poor energy density.

Kerosene or H2 won't burn without air, so you need a scramjet or an oxygen tank to burn them. Hydrazine doesn't, so you can burn it in a rocket, at higher pressure with more efficiency and better aerodynamics.

Advantage: Rocket engines have a thrust:weight ratio of up to 133:1, scramjets about 2:1. So an equivalent rocket is up to 66 times lighter than a scramjet.

GE's patent refers to the use of a small amount of hydrazine in a catalyst-like role, or more accurately to act as a fuel/air mixer.


Are there additional electrical grounding methods besides static wicks? Static dischargers have high electrical resistance, and work via corona discharge.

So if I understand correctly, what wicks do is limit the voltage that the aircraft builds up. But as the wick is ionizing the air around, I guess this voltage is rather high.

Do commercial, fixed-wing aircraft need any additional grounding method once on the ground, when the passengers are boarding/unboarding for example?. How it's done?

Related: This question is about grounding for hangar storage, and also explains grounding for refueling operations

Many aircraft tyres conduct electricity which also dissipates charges.  The compound contains "carbon black" or graphites.

In the special case of helicopters using a hook to pick up a load from a hover, the wise ground handler will use a rod on the end of a grounded cable to earth the charge.  Helicopters can build up a lot of static and many a ground handler has been left with smoking underpants by not heeding this advice.


How is the mass flow between 2 streamlines derived? I am reading "Fundamental of Aerodynamics " by J.D.Anderson Fifth edition, At pages 177 and 178 (section 2.14 Stream funciton), the book said: given 2D steady flow, from:
$$\frac{dy}{dx}=\frac{v}{u}$$
with u and v are known function of x and y, then we obtain f(x,y) = c by intergration.

If we have steamline 1 is f(x,y) = c1 and streamline 2 is f(x,y) = c2, then why is the mass flow between two streamlines equal (c2 - c1)? The book said that but there is no derivation of that.

As far as I can do:

Short answer: Because that's how we've defined $c_1$ and $c_2$.

Long answer: Read 2.14 carefully. As you've said, we have $f(x,y)=c$ via integration. Anderson then chooses $\bar{\psi}$ as $f$ (a convention) to get $\bar{\psi}=c_1$ and $\bar{\psi}=c_2$ for the two streamlines. However, we know that $c_1$ and $c_2$ are just arbitrary constants of integration that we can set to whatever we want. Anderson just happens to know that later down the road it will be helpful to

  define the numerical value of $\bar{\psi}$ such that the difference $\Delta\bar{\psi}$ [between the two streamlines] is equal to the mass flow between the two streamlines.

Furthermore,

  $\Delta\bar{\psi}$ equaling mass flow (per unit depth) between streamlines is natural. For a steady flow, the mass flow inside a given streamtube is constant along the tube; the mass flow across any cross section of the tube is the same. Since $\Delta\bar{\psi}$ is equal to this mass flow, then $\Delta\bar{\psi}$ itself is constant for a given streamtube.


Can an ultrasonic sensor mounted on a drone pick up another drone strongly enough to sense and avoid? I am asking this question to see if mid-air collisions of drones can be prevented using simple analog sensors. Can an ultrasonic sensor mounted on a drone pick up another drone strongly enough to sense and avoid it?

I know that the sensor is range limited so the aircraft cannot be flying towards each other very fast, but to even do any sense and avoiding, can this sensor work? Or does the drone not provide enough of a return?

Also, could the range of sensor be increased if both drones emitted ultrasonic energy to be picked up on the sensor more strongly at a distance?

The range of the ultrasonic sensors ends up at somewhere 5 meters (here is the pre-configured search). However a simple sensor would only measure the distance, by the signal travel time. It does not provide the angular co-ordinates or exact location. Same problem as with the simple radar.

May make more sense to fit the drones with transponders so that they could actively broadcast they own location, speed, orientation and intentions to other members of the flock.


Can a general aviation aircraft be forced to land when crossing the airspace of a country? I don’t know how to fly yet but my friend has a Cessna, he says it’s awesome to have and fly one and he also said he will take me for a flight one day.
I have been researching and reading online and I have a question because I’m a bit scared.
So in order to take your plane for a flight, you have to file a flight plan and when you are flying you have to, using the radio, let them know that you are on your way. Let’s say I’m flying from Italy to Germany by going over Austria and I have filled the flight plan and all the necessary paperwork.
Can the Austrians ask me to land in their country for any reason, even if I’m only going over their country to go to Germany and they have notified of this before the flight?
Will they shoot me down if I don’t comply with them and land in Austria?

So in order to take your plane for a flight, you have to file a flight plan

Usually incorrect. Flight plans are only needed for international and for IFR flights. But there are some countries where a FPLN is required for every flight, but not Italy, Austria or Germany.

  when you are flying you have to, using the radio, let them know that you are on your way

Only if you've filed a Flight Plan. If you haven't, then there's no need to announce your flight.

  Can the Austrians ask me to land in their country for any reason

They can, it's their country. But unless you're a criminal or a terrorist, there's probably no reason for them to actually do this.

  Will they shoot me down if I don’t comply with them and land in Austria?

If they ask you to land (see above) and you don't, then they could shoot you down. It's their country and they're trying to protect it. But it hasn't happened yet.


Has there ever been a seaplane with inflatable airbags rather than traditional pontoons? Traditional pontoons are big and cause a lot of drag. It would be nice to retract them like normal landing gear but they are just too big.

Has there ever been a seaplane with inflatable airbags instead? They way I imagine it is a lot like normal landing gear, with lowering struts from the wings or belly. But instead of wheels, it has a wound-up airbag that's unrolled and inflated.

I think this would save a lot of drag and weight, and I'm a little surprised that this apparently doesn't exist over the 114 years or so of airplane history. Is there something unfeasible about this concept? I suppose getting propeller clearance over the water is the biggest concern, but I would think slightly long legs on the landing gear would be sufficient and well worth it to save all that weight and drag from those big pontoons.

Edit: This is for the really small planes.

I would think the stresses would be fairly high and I dont know of any off the bat but there have been helicopters outfitted with them.

(source)

On the drag front, this is only really a problem for smaller sea planes (C172, Caravan etc.). On the large side of things when you want to reduce drag a belly land design is used like in a Grumman G-21 or even as far as the worlds largest airplane the Hughes H-4 Hercules.


Can I fly solo when practicing IFR under the hood? If I have my instrument rating can I log simulated instrument time under the hood while flying alone as the PIC? Or does a safety pilot have to be present?

Before going into the FAR AIM, take a second to think about this idea:

You are in your airplane, under the hood, flying along your route or wherever. The only traffic warnings you will get are from your controller, and he does not always see all the VFR traffic on his screen... Not a good idea. Definitely never fly without a safety pilot under the hood in VMC.

Now lets open the FAR AIM:

  §91.109 Flight instruction; Simulated instrument flight and certain
  flight tests

  (c) No person my operate a civil aircraft in simulated instrument
  flight unless -

  (1) The other control seat is occupied by a safety
  pilot who possesses at least a private pilot certificate with category
  and class ratings appropriate to the aircraft being flown.

  (2) The safety pilot has adequate vision forward and to each side of
  the aircraft, or a competent observer in the aircraft adequately
  supplements the vision of the safety pilot; and

  (3) Except in the case of lighter-than-air aircraft, that aircraft is
  equipped with fully functioning dual controls. However, simulated
  instrument flight may be conducted in a single-engine airplane,
  equipped with a single, functioning, throwover control wheel, in place
  of fixed, dual controls of the elevator and ailerons, when—

  (i) The safety pilot has determined that the flight can be conducted
  safely; and

  (ii) The person manipulating the controls has at least a private pilot
  certificate with appropriate category and class ratings.

Getting the important stuff out of there: No person may operate a civil aircraft in simulated instrument flight unless the other control seat is occupied by a safety pilot!

The FAR/AIM part obviously only goes for FAA regions, but I'm assuming that is what you are asking about.

Conclusion: According to logic thinking you should never ever not look out the window in VMC, and the FAA doesn't allow you to either, not even for IFR recency!


Does Air Force One (VC-25) have retractable staircases on all its exit doors? While going through an article on AFO, I came across this little piece of info:

So, does it have retractable steps on all its exit doors? How does it manage doors like these?

There is page by cryptome with documentation about AF1 rescue options.

According to the "TECHNICAL ORDER 00-105E-9, 1 FEBRUARY 2006, REVISION 11." (15 April 2006), slide 71 "AIRSTAIR OPERATION VC-25A", Boeing VC-25 has only two exits equipped with own airstairs, only at doors from lower compartments. Doors at main deck have no integrated airstairs.

Source

First photo in the question shows forward airstairs operation, and there is photo of aft airstairs, used in 2006.

According to this slide from the same PDF, there are 5 pairs of entry doors on main deck by design of the Boeing 747-200 plane; but 3 or them (1R, 3L, 3R) are blocked on VC-25 and can't be used. All doors from main deck have no own retractable stairs.

Also, from here:

  Unlike a normal 747, the plane has its own retractable stairways, for the rear entrance and the front entrance. These stairways open onto the lower deck, and crew members and staff climb internal staircases to get to the upper decks.


Does an instrument rating bridge category and class? I had previously been under the impression that if a pilot held an instrument rating that it would apply to aircraft in another class.  The requirements of 61.57 would seem to support that since currency can be maintained in aircraft of the same category.

However, reading section 61.133 leads me to believe that any check ride to add a class would require an instrument checkride as well:

  A person who applies for a commercial pilot certificate with an airplane category or powered-lift category rating and does not hold an instrument rating in the same category and class will be issued a commercial pilot certificate that contains the limitation, “The carriage of passengers for hire in (airplanes) (powered-lifts) on cross-country flights in excess of 50 nautical miles or at night is prohibited.” The limitation may be removed when the person satisfactorily accomplishes the requirements listed in § 61.65 of this part for an instrument rating in the same category and class of aircraft listed on the person's commercial pilot certificate.

Am I correct in this interpretation?  Are there any other CFR sections that might shed some clarity on this?  Does any class rating add-on, (presuming one wanted to exercise the option of IFR in the new class) require a full blown instrument check even if one is already instrument rated and current in a different class?

ADDENDUM:  After re-reading this almost seems self answering based on the quote I provided, but I know what sometimes regs can be interpreted differently based on other sections.  I am just incredulous that a full-blown syllabus per 61.65 would be necessary when really IFR isn't any different from Single to Multi.  Makes the upgrade that much more pricey!

The Airman Certification Standards for the Airplane Instrument Rating shed light on this question. There are four classes of instrument rating for airplanes and that the tasks required for each class differ:

The abbreviation(s) within parentheses immediately following a Task
refer to the category and/or class airplane appropriate to that Task.
The meaning of each abbreviation is as follows:
ASEL: Airplane – Single-Engine Land
ASES: Airplane – Single-Engine Sea
AMEL: Airplane – Multiengine Land
AMES: Airplane – Multiengine Sea
Note: When administering a test based on this ACS, the Tasks
appropriate to the class airplane (ASEL, ASES, AMEL, or AMES) used for
the test must be included in the plan of action. The absence of a
class indicates the Task is for all classes.

So your assumption is correct. You need an instrument rating in each class of airplane you wish to fly IFR. However, per §61.57 (c) (1) your   currency can be accomplished in different classes in the same category but you can’t mix and match categories e.g. 5 approaches in a SEL and 1 in a MEL is OK. 5 approaches in a SEL and 1 in a helicopter is not OK.


How does an outflow valve work mechanically? Under Environmental control and oxygen systems chapter of Aircraft Maintenance and Repair book by M. Kroes, there's an topic of working of the outflow valve

The diagram is of a valve that also works an altitude limiter and positive pressure relief valve. What I don't understand is the working of this valve from the diagram.
The text explanation states, when cabin pressure reduces below a preset value the bellow expands and it moves the poppet and introduces reference chamber air in the case, effectively closing the outflow valve. How is the outflow valve connected tp the bellow chamber?

If the cabin altitude
exceeds the preset limit, the bellows expands enough to press
on the small poppet just to the right of the bellows. This opens
the reference chamber to cabin air pressure and causes the outflow valve to close. The valve remains closed as long as the
cabin altitude is above the setting of the bellows. This operation
can be overridden by the positive pressure-relief control system

Above is the explanation from text.
Also, why are outflow valve openings so big?
And, do all the pressurised sections of the aircraft have separate outflow, or are they connected to a single unit via lines from the pressurised sections?

The driving force for the valve is a vacuum source that is connected at the vacuum connection at the bottom of the diagram.  The valve operates by varying suction to chamber 3, creating a pressure differential between 3 and 1 (cabin pressure) that allows the pressure in 1 to drive the valve open (to the left in the diagram) against the return spring.  Take away the vacuum, and the spring will close the valve (move to the right).
The vacuum source is usually an ejector pump in the engine bleed air plumbing, so the vacuum is available whenever the bleed system is on.
So in other words, the valve is sucked open (by bleed-powered vacuum), and sprung closed, and is modulated by varying the suction (by the electropneumatic control valve) against the constant spring pressure.  More suction moves in more open, and less suction moves more closed, and if the suction is completely removed the spring fully closes the valve.
On transport aircraft there are normally two outflow valves for redundancy, but both will usually be located next to each other, typically at the rear pressure bulkhead, and all of the air in the pressure hull will exit at that spot, all of the pressurized zones being interconnected.  Where separated spaces are vented to each other in the pressure hull, but would have a hard time equalizing quickly in a rapid decompression event, like a cockpit bulkhead with the door closed, there will be special blowout panels (like in the cockpit door or elsewhere on the bulkhead) to allow equalization to occur rapidly.
You will also typically find a separate dump valve that opens on on the ground to keep the aircraft from being (slightly) pressurized by ground cart inflow when the bleeds are off and the outflow valves are closed (which can cause problems with opening plug doors), and also to provide an exhaust path for avionics cooling during ground operation with the main doors closed.
The opening size of the pressurization outflow valve has to be large enough to allow more air out than the maximum bleed flow in, so it has to have a fairly large exhaust opening to be able to control pressure at the margins with the pressure hull as airtight as it can be.
Aside from altitude, how much the valve opens in normal flight depends on the main air conditioning bleed inflow (which is usually constant, being regulated bleed flow) and how leaky the hull is (an older airplane with worn door seals, leaky rivets etc, can be quite leaky, and the valve may run pretty much almost fully closed some of the time because of all the air that is getting out through other points - if you've ever been at the forward galley area and wanted to hold your ears due to some crazy howling sound, that's a door leak, and the outflow valve will be running more closed than normal to compensate).


Are NATO fly-by-wire fighters designed to feel like F-14 Tomcats? Related question:  Do fly-by-wire flight controls in airliners provide artificial feel?

Icefire, by Judith and Garfield Reeves-Stevens, contains the following passage:

  When the engineers develop a new plane, they like to give the pilots something familiar to work with, so they adjust the computer controls to feel like a plane the pilots already fly and like.  The Tomcat's one of those jets.  Solid, dependable, every test pilot's flown them.  So every new fly-by-wire plane feels a lot like a Tomcat.

Now, let's face it, this is a book featuring the main character stealing, and making off with, a Lockheed SR-72, so I'm not expecting everything to be a model of technical accuracy, but there could be a rock of truth in the middle of this snowball of fiction.

Are NATO fly-by-wire fighters designed to feel like F-14 Tomcats?

Most decidedly not, at least not for the first fly-by-wire fighter in the NATO arsenal, the F-16. Its stick, in initial block versions, did not move at all, instead using piezoelectric load cells to detect stick pressure. This caused some issues with novice Viper drivers overreacting to the stiffness of the controls compared to anything they had flown and overrotating the jet on takeoff, smacking the turkey feathers on the ground. Later blocks put a little play in the stick.

As far as the Tomcat being an easy plane to fly, Top Gun kind of over-romanticized it. The TF30 engine initially put into these aircraft was underpowered and terribly unreliable (one thing the movie did get right is that the engines were prone to compressor stalls when encountering disturbed air such as jetwash or even their own missile launch trails). The aircraft itself, while a big improvement in dogfighting over the F-4, was still big and heavy, the result of requirements that it be a long-range supersonic interceptor in an era without supercruise or the relatively light AMRAAM missile; the aircraft instead had to be able to haul a full load of AIM-54 Phoenix missiles intended for the ill-fated naval variant of the F-111, along with the large, complex radar system to lock on and fire them, and a boatload of fuel to get all that out to patrol range and back.

The Navy's initial mixed results with the F-14A, along with the extremely high costs of the aircraft ($32 million each at the height of production) and the lack of ground attack capabilities, were mirrored in the USAF with its F-15 program; the looming retirement of the F-4 was about to leave both branches without a fighter capable of the Phantom's multi-mission capability, and both the F-14 and F-15 were big expensive interceptor-style pure air-to-air fighters, which some Air Force brass believed was proof that nothing had been learned from Vietnam. The USAF commissioned the Light Weight Fighter competition, which produced the F-16, a light, relatively inexpensive multirole fighter that has become one of the most successful land-based fighter jets in history. The Navy preferred some traits in the USAF's losing aircraft, the YF-17, such as the twin-engine design for durability, and it would go on to develop this design into one of the most successful naval aircraft of all time, the F/A-18 Hornet and Super Hornet.

The Tomcat eventually lived up to its promises with some engine and avionics upgrades (including a hybrid-FBW system and a LANTIRN pod to add air to ground smart bomb capabilities) but the aircraft was by no means a perfect plane or a dream to fly.


How many serious airline accidents have been caused by design faults alone? That is, in the chain of events that led to death or injuries in an airline accident, how often has a design fault been solely responsible?

By a design fault I mean a problem such that even if the equipment:

were maintained and operated to the highest possible standards
flown in ideal conditions
by pilots who committed no errors
unaffected by manufacturing defects
endured no bad luck

eventually it would still inevitably eventually kill or injure its passengers.

I can think of only two examples: the early Comet's square windows, and the Boeing 737 rudder power control problem.

All the others I can think of include errors of piloting, manufacture, maintenance or just plain bad luck in the chain of causes.

Are there others?

The Douglas DC-10 - The door latching mechanism was not robust and the design of the safety indication was flawed. In the Paris incident Douglas tried to blame the handler who closed the bulk compartment door for using excessive force when latching the door but ultimately the design was at fault.


How does the Blackbird SR-71 pressurize the cockpit at Mach 3? I'd assume the Blackbird's engine that converted into a ramjet once at supersonic speed had no moving parts at ramjet phase. If the engines were off, how then did it pressurize the cockpit at cruise altitude to ensure pilot safety and that he/she did not pass out from lack of oxygen?

The SR-71 used the P&W J58, which is full of moving parts, and works very similar to a typical jet engine.  Your assumption that it has no moving parts is wrong.   While the engine RPM did slow down at maximum speed (up to 90%), it never stopped, and always generated enough power for electrical systems, pressurization, hydraulics and any other needs.

While the cockpit was pressurized (but sometimes only to 26,000 ft. pressure-altitude), the two-man flight crew wore full body flight suits for warmth and oxygen.


Can ICAO airline designators be reassigned to a new airline? Is it possible for three-letter ICAO airline designators to get reassigned?

In particular, I'm trying to find out if BKL was previously used for Baikal Airlines (ceased to exist in 2001) and reassigned to Barkol Airlines (founded 1996, although it's unclear when they received their ICAO code).

Yes. As per rules ICAO can reassign the three letter airline designators after a period of 60 days.

  When a designator is no longer required, ICAO should be informed immediately. Any such designator so released will not be reassigned until a period of at least 60 days has elapsed.

The designator BKL was used by Baikal Airlines and is currently used by Aircompany Barcol.

Another example is the airline designator WOW, which was used by Air Southwest  and is currently used by WOW air.


Can I count solo complex time as complex training time for a commercial certificate? Does a combination of both dual and solo hours in a complex aircraft (PA28R-180) which total 10 or more flight hours meet the commercial pilot training requirements of FAR 61.129(a)(3)(ii) or must all the hours be dual instruction?

As you already noted, 61.129(a)(3)(ii) says "training" (emphasis mine):

(ii) 10 hours of training in a complex airplane, a turbine-powered
airplane, or a technically advanced airplane (TAA) that meets the
requirements of paragraph (j) of this section, or any combination
thereof. [...]

Here's the definition of training in part 61, per 14 CFR 61.1:

Training time means training received—
(i) In flight from an authorized instructor;
(ii) On the ground from an authorized instructor; or
(iii) In a flight simulator or flight training device from an
authorized instructor.

According to that definition training always requires an instructor so there's no way you could log solo time as training time. All 10 hours must be dual instruction.


How does a departure off a runway used for LAHSO operations work? Let's say that LAHSO operations are in effect at Long Beach (KLGB). Runway 12/30 has a hold short line short of runway 8L / 26R. If an aircraft is cleared to land runway 30, and LAHSO operations are in use, I get that.

But how do operations work for departures off of runways that have a hold short line painted on the runway? If an aircraft is cleared for takeoff runway 30, is the aircraft expected to disregard the hold short line at the departure end of the runway and use full-length?

Source: bing.com

The LAHSO line and pulsating white light bar applies only to landing traffic (when in effect and when accepted).

A phraseology example is:

  ATC: "(Aircraft ID) cleared to land runway six right, hold short of taxiway bravo for crossing traffic (type aircraft)."

There is no phraseology equivalent to a departing plane that has to do with LAHSO operations. If a runway is shortened for any reason, "shortened" will be added to the taxi and takeoff clearances, but this is another matter.

When a departure is involved as shown above, it is the landing traffic that needs to land and hold short.

Image source, reference, and further reading: AIM


How can a large passenger aircraft's owner remain unknown? I'm reading through TheStar's "Malaysia Airports seeks owner of three Boeing 747s abandoned at KLIA" article and I can't stop wondering, why I don't understand it or how should I understand it?

How it is possible in 21th century, that knowing large passenger aircraft's (a) type, (b) current location and (c) registration it is still impossible to find actual aircraft's owner in a matter of minutes?

Don't we have aircraft's databases, to obtain this information? Or to use it to track any passenger aircraft latest flights? Is it possible, that Kuala Lumpur International Airport does not have any records or tracks of what (owned by whom) and when landed on their grounds?

I know that this isn't possible, but for a newbie like me this article sound like a joke rather than a current reality in aviation industry today.

Every country handles aircraft registration differently (but generally similar). Im sure Boeing could tell you who they originally delivered the airframe to but if it was sold from there it could legally go anywhere and would only be subject to local registration legislation.

Here in the US you can look up aircraft owners by N number but not all countries may keep a record like that and as far as I know there is no global aircraft registry.

  it is still impossible to find actual aircraft's owner in a matter of minutes

Knowing who the owner is and finding the owner are two very different things.

According to this article

  Several aviation databases list the Boeings -- identified by their
  call signs TF-ARN, TF-ARH, TF-ARM -- as belonging to leasing firm Air
  Atlanta Icelandic, but that company says it sold them in 2008.

  Since then, the aircraft appear to have changed hands several times.

  Malaysia Airports says it's entitled to sell the Boeings under the
  country's civil aviation regulations if no owner comes forward.

So it seems they do know who owned them at some point (most likely the last people to put readable registration numbers on them).


Is a mode C transponder required underneath Class C airspace? FAR 91.215 states that a mode C transponder is required for...

  all aircraft in all airspace above the ceiling and within the lateral
  boundaries of a Class B or Class C airspace area designated for an
  airport upward to 10,000 feet MSL

My flight instructor and I disagree on how this regulation is interpreted. He says that I need a transponder to fly underneath class C. I understand it to mean that I only need and transponder if I am both above and within the lateral boundaries (i.e. overflying the airspace).

Which is the correct interpretation?

You are correct. You do not need a transponder to operate under Class C airspace if there are no other overlapping airspace areas where a transponder is required. In fact, if you read a little further in that reg, you'll see that is one of the places where aircraft built with no electrical system are allowed to fly at all!


Why was this commercial plane highly delayed mid-flight? What could be the main reasons for a short-haul flight to be delayed over an hour in-flight?

Recent Lufthansa LH 2227 CDG-MUC flight took off only half an hour after scheduled time, but landed at destination delayed nearly an hour and a half.

Meaning (if I am reading these stats correctly) that this particular flight spend an hour extra in the air over scheduled time. I begin to question if there is enough fuel for the plane to stay that long extra?

I flew the very same flight few days ago and that flight also took of half an hours after schedule and landed fifteen minutes after schedule. Meaning that a plane manage to "work out" half of its delay en route. This particular, pictured flight not only didn't work out its initial delay, but also added another hour to it while being in air.

I was always told (and saw that in my small commercial flying experience) that

short- or middle-haul flights delayed 15-30 minutes on take-off,
long-haul flight delayed 60-90 minutes on take-off,

are nearly always able to land on-time, effectively "working out" their initial delay during flight, by flying faster etc. What happened or could happen here?

If you look at the details, you’ll see the aircraft left the gate at 9:37, but only took off at 10:47.

They probably received notice of the issue in MUC pointed out by Machavity while taxiing to the runway (and then asked to park somewhere waiting for the airport to be ready for them). No sense returning to the gate for a delay like this which is expected to be relatively short.

A possible alternative (though probably not here) is they they had an issue right after gate departure which triggered a maintenance request. It happened to me once on some regional airliner which had an issue just when they spooled up the engines (or just after a few meters, don’t remember). Immediately powered down and had some part of the engine changed (or maybe just a filter or something similar) while we were waiting, took about an hour or so.


Could I hold both an EASA license and a UK CAA license? With all the ongoing mess with Brexit at the moment, I'm trying to figure out the wood from the trees so to speak. However there seems to me a bit of mass confusion with it all.
I'm just wondering if I could hold two licences at the same time? If the CAA go ahead and leave EASA, could I hold an EASA ATPL (CPL ME IR)and CAA ATPL (CPL ME IR) together?
If I can, I suspect this is in ICAO somewhere within licensing? And how would I go about it? Can I apply to on authority based on my results with the other (e.g. CAA with EASA results) or would I have to duplicate and thus spend more money to get a CAA one?

You may need to wait until the dust settles to see exactly what the regulations end up being but if the rest of the world is an indicator then yes you can hold licenses from various places at once. Licenses can in some cases be issued simply by applying and proving your currently issued one is valid (from somewhere) as is the case with the FAA but this will likely vary by jurisdiction.


For routes over oceans, are slide rafts fitted with first-aid items, food, water, radio, etc? Nowadays life rafts are often replaced by slide rafts, the slides having a double function: Evacuation and when detached survival. However they are packed tightly in the aircraft doors, so they probably don't contain a survival kit.

Nice illustration by Ron Wilson
Though it would be typical of ditching on Lake Michigan, not in heavy sea

For routes over oceans, what is the equipment that is available aboard rafts when they are used? (first-aid items, food, water, radio, etc). Where is this equipment stored before evacuation? Who takes care of making this equipment available in each raft?

(Source) A Boeing 747 raft survival kit.

Typical content does include nonperishable food and bagged water—

Base kit:

  Survival Manual
  Flashlight, w/Lithium Batteries
  Knife Assy., Utility
  Signal Mirror Assy.
  Sea Dye Marker
  Raft Repair Kit
  Whistle Assy.
  Water Package Assy. (4.23 fl. oz. per pack)
  Bailing Bucket
  Sponge
  Lip Balm
  Adhesive Bandage, 1 in (16 per box)
  Bandage Compress, 2 in (4 per box)
  Bandage Compress, 4 in (1 per box)
  Triangle Bandage, 40 in
  Adhesive Tape (2 rolls per pack)

Renewal kit:

  Sea Sickness Pill Packs (12 tablets per pack)
  Day/Night Flare
  Water Purification Tablets (50 tablets per bottle)
  Antiseptic Swabs (10 swabs per box)
  Ammonia Inhalants (10 vials per box)
  Burn Compound (10 tubes per box)
  Eye Dressing Packet
  Candy (Sucrose) Rations (10 candies per pack)

It's the crew responsibility to gather the kits.

They're located near the exits either in closets, ceiling compartments, attendant seat stowage, or overhead bins. Exact location varies by plane and airline.

Axes, first aid kits, ropes, fire extinguishers, megaphones, etc., are also stored in the same locations mentioned above.


Winglet design and airfoil selection I'm currently in the process of designing a winglet for my low speed aircraft in xflr.

While researching about winglets I read in a Boeing article that if the baseline outboard wing is relatively lightly loaded, as on the 747-200, the potential benefit of tip devices can be greatly reduced. I don't understand the logic behind this statement.

Also what would be the optimal airfoil selection for the winglet? How would the chord, thickness, camber, etc. affect the weight and drag reduction due to the winglet?

And would the geometric twist affect the performance of the winglet?

Any other tips for winglet design would be greatly appreciated.

The comments explain the logic behind a winglet well, so I will focus on the remaining questions:

  what would be the optimal airfoil selection for the winglet?

As a first rule of thumb, continue with the wing airfoil. A cambered winglet will be most efficient, because winglets are only beneficial if they produce lift. How much? This depends on the ratio of wing tip chord to winglet root chord. Ideally, there should be no break in the spanwise distribution of circulation, so the product of local wing chord and local lift coefficient should be the same at the transition and taper out towards the winglet tip.

  would the geometric twist affect the performance of the winglet?

Yes: The incidence must be chosen such that the desired lift coefficient is trimmed at the operating point (which is the cruise condition in case of airliners). Twist will only be needed when the planform differs a lot from the elliptical distribution. When flying with a high wing loading (again, just as airliners do), be sure to include the effects of aeroelastic deformation: They can be quite severe around the wing tips in cruise.


Is it legal to bring (or allow someone else to bring) a firearm on a private flight? Say that I want to leave the city and go hunting somewhere.  Is it legal to bring a hunting rifle and ammunition with me in a private airplane?

If yes, are there specific procedures to follow in order for it to be done safely?

This is a tricky question, because it depends greatly on the laws of the locations you're flying to / from.  Here's a few of the things you have to take into consideration.
Transporting is generally ok

According to 18 U.S.C. 926A:

Notwithstanding any other provision of any law or any rule or
regulation of a State or any political subdivision thereof, any person
who is not otherwise prohibited by this chapter from transporting,
shipping, or receiving a firearm shall be entitled to transport a
firearm for any lawful purpose from any place where he may lawfully
possess and carry such firearm to any other place where he may
lawfully possess and carry such firearm if, during such transportation
the firearm is unloaded, and neither the firearm nor any ammunition
being transported is readily accessible or is directly accessible from
the passenger compartment of such transporting vehicle: Provided, That
in the case of a vehicle without a compartment separate from the
driver's compartment the firearm or ammunition shall be contained in a
locked container other than the glove compartment or console.

926A says nothing about the method of transport.  Most often it applies to motor vehicles, but it can just as easily apply to aircraft.  Therefore as long as you're ok to carry at the departure airport and the destination airport, federal law protects you in between.
Also, remember that 926A only protects you if the firearm is unloaded and locked / inaccessible.
Ok, but can I bring my gun unloaded onto airport property, right?

Not in a sterile area
You can't take a firearm into the sterile area of an airport.  49 CFR 1540.5 defines a sterile area as:

Sterile area means a portion of an airport defined in the airport
security program that provides passengers access to boarding aircraft
and to which the access generally is controlled by TSA, or by an
aircraft operator under part 1544 of this chapter or a foreign air
carrier under part 1546 of this chapter, through the screening of
persons and property.

So, if the terminal and the GA ramp are two separate entities, you're probably ok.  However, I've flown to some smaller airports where the GA ramp and the TSA terminal are right next to each other.  In these cases, you need to be careful that you don't get into the sterile area with your firearm.
Maybe not anywhere on the airport
Local law might prohibit the possession of a firearm anywhere on airport property, or the airport itself might ban firearms on their premises.  The only way to know is to check the specific airport you intend to fly out of.
What if I want to carry loaded?

The first thing to remember if you carry loaded is that 18 USC 926A does not protect you.  In that case, you're exercising the privileges of either open or concealed carry according to the laws of the departure and destination states.
Open carry
Some states prohibit open carry.  Others allow open carry when unloaded.  Others allow open carry when loaded.  Some require a permit.  Some don't.  Some only require a permit for handguns but not long guns.  If you're going to open carry (perhaps a hunting rifle on a sling), make sure that the local area allows this.
Concealed carry
Some locations prohibit concealed carry outright (to the best of my knowledge, you still can't carry concealed in Chicago, for example).  Other states allow concealed carry with a permit from either that state or a state which they have reciprocity with.  So, for example, a Mississippi permit would be honored in Texas, but not in Nebraska.  Others allow concealed carry without a permit at all (that is, the 2nd Amendment is your permit).  First, be sure that your concealed permit has reciprocity with the destination state.
Even if you think you're open carrying, watch out.  In some states, the act of being in a vehicle, no matter how visibly your firearm is displayed, makes it concealed carry.  If you don't have a concealed carry permit, you may be in violation.
Is there anything else waiting out there to bite me?

Oh yes.
For example, Rhode Island.

A Rhode Island carry permit is generally required to
transport a handgun in a vehicle. This requirement does not apply,
however, to the holder of an out-of-state carry permit who intends to
travel uninterrupted through the state.

Is a fuel stop an "interruption"?
Or New Jersey.

[New Jersey] State law generally prohibits any person from knowingly possessing or
transporting any rifle or shotgun without first having obtained a New
Jersey firearms purchaser identification card (FPIC),or from
possessing or transporting any handgun without first having obtained a
New Jersey handgun carry permit.

Or Chicago.

Chicago, for example, bans handguns declared “unsafe” by the
Superintendent of the Department of Police, so-called “assault
weapons,” machine guns and other firearms regulated under the National
Firearms Act, “laser sight accessories,” firearm silencers or
“mufflers,” “high-capacity” (i.e., more than 12-round) magazines, and
“metal piercing bullets” (which include ammunition with non-lead
projectiles).  All these items are subject to seizure and forfeiture.
In some cases, the local ordinances have no explicit exceptions to
these bans for travelers merely passing through the jurisdiction

Or New York City.

Possession of a handgun within New York City requires a New York City
handgun license or a special permit from the city police commissioner
validating a state license within the city. Even New York state
licenses are generally not valid within New York City unless a
specific exemption applies, such as when the New York City police
commissioner has issued a special permit to the licensee or “the
firearms covered by such license are being transported by the licensee
in a locked container and the trip through the city of New York is
continuous and uninterrupted.”

Look, just tell me what to do.
Fine.

Carry your firearms unloaded, locked, and inaccessible.
Make as few intermediate stops as possible
Know and comply with all local laws both at your departure and your destination
Stay out of sterile areas while armed on airport property


How to calculate position of a canard? does anybody know how one can calculate the position, shape and size of an aircraft with a canard?

So the main goal of a canard configuration: increase lift + increase agility/maneuverability

So at least I can calculate the centre of pressure of the whole aircraft, which has to be behind the CoG to guarantee static stability in pitch.

But still, I have a range in x-direction , where I can place the canard. What do I have to define or know in order to place my canard?

  Lift: I can design my main wing and its lift A_W_wing. In horizontal flight A=W=A_Wing +A_Canard ; So I could now design my A_Canard (shape, size).

But what about the maneuverability? What do I need to now?

So for my opinion: for a curve to fly with a specific rotating rate, my control surfaces (tail + canard) need to create a specific moment. Since Moment = Force * Arm  I could make calculate the needed Arms/ positon ?

Thank you for any tips on literature or calculations

There are several factors to consider, and depending on your preferences there is not one ideal size and place for a canard. For a first rough concept look at similar designs and use the same canard volume. That is the product of canard area and the distance between its and the wing's neutral points, relative to the aircraft's reference parameters.

$$V_{Canard} = \frac{S_{Canard}}{S_{ref}}\cdot\frac{X_{NP, wing}-X_{NP, Canard}}{l_{ref}}$$

Collect as many canard volumes as you can from different but similar designs and use that for a first draft.

Next, decide on your priorities. Do you want good pitch damping for a pleasant ride even in rough air, use a smaller canard area on a longer lever arm. Damping grows with the square of the canard lever arm while its stabilising effect is only linear. Do the opposite if you prefer more agility.

Next, what center of gravity range do you desire? If, for example, you plan a tandem two seater where due to engine weight and pilot position the second seat is at some distance from the center of pressure, increase canard area accordingly.

So far we looked only at area and lengthwise position. But the vertical position must also be considered. Ideally, the wake of the canard will be above the wing for all practical angles of attack (from cruise to stall), which can be achieved by placing the canard wing high on the fuselage and the wing low. In that position, however, the canard wing might obstruct the pilot's view, so maybe you want to strike a compromise where the wake is below the wing in cruise but above near stall. This can only be achieved with a short lever arm, however.

Regarding the shape: A straight, high-aspect-ratio wing will be best. After all, the canard will fly at the highest lift coefficient of all surfaces so it should have the highest aspect ratio. Use a trapezoidal planform with a ratio of tip chord to root chord of 0.6 - 0.7, or, for simplicity, a rectangular planform which needs only one rig/mold for both sides.

But if what you really want is a good airplane and aren't determined on making it a canard: Place that smaller surface behind the main wing.


How can I legally organise a high school football game flyover in Delta airspace? If a high school had given permission for a low pass over a football game, would the controllers also give permission? The school is about 3-4 miles away from the class D airport. Also, would you have to still stay at least 500ft above ground? I'm assuming you would still have to even if the school is allowing lower because that is the law.

First, the high school has no authority over the national airspace system so any 'permission' is meaningless, at least from the aviation point of view. I assume you want to coordinate with the school for timing and so on, but they can't approve or deny your flight, or tell you what altitude to fly at. (I'm ignoring any school disciplinary issues here, e.g. you're a student and the event is during class time.)

Second, the class D controllers probably won't mind provided that you give them some advance notice (call them a week or two in advance) and keep talking to them while you're in the air. Similar flights happen all the time in controlled airspace for photography and other reasons, so unless the stadium is right under final approach it shouldn't be a big deal.

Third, 14 CFR 91.119(b) says that the minimum altitude in this case would be (my emphasis):

  Over any congested area of a city, town, or settlement, or over any
  open air assembly of persons, an altitude of 1,000 feet above the
  highest obstacle within a horizontal radius of 2,000 feet of the
  aircraft

(And don't forget that 119(a) requires you be able to make an emergency landing without endangering people on the ground.)

If you want to fly lower than that then you need a waiver from your local FSDO, but it's entirely at their discretion so you would need to convince them that you have a good, safe plan.

Finally, it's worth saying that there are a bunch of safety issues associated with doing things like this so if you do go ahead make sure you have a good plan and you stick to it. In particular, decide your minimum altitude and airspeed in advance and don't go below them under any circumstances.


For how long is an engine start clearance valid? If a pilot receives a clearance to start the engines, is the clearance void if he doesn't start them within a certain amount of time? How much time is allowed for starting the engines and where is it documented?

I'm asking for Thailand, but would like to know what the ICAO SARPs say.

From ICAO Doc 4444:

7.3.1.1 Start-up time procedures
7.3.1.1.2 Start-up time procedures should be implemented where necessary to avoid congestion and excessive delays on the manoeuvring area or when warranted by ATFM regulations. Start-up time procedures should be contained in local instructions, and should specify the criteria and conditions for determining when and how start-up times shall be calculated and issued to departing flights.

Procedures should be locally implemented. If no delay is anticipated by the ATC, the controller can issue "start-up at your own discretion" (7.3.1.1.4). Of course any delay on the pilot's part that will make them miss the takeoff time, they are supposed to report that delay. After all the ground crew, for example, won't wait forever.
For Thailand:
For the start-up time procedures mentioned in Doc 4444, you need to check the AIP if such procedure is applied. For Bangkok (VTBD), for example, the AIP notes:

Starting up Procedures
Pilots are to call Don Mueang Ground on 121.9 MHz for push back and start up and should give parking stand number or location and ATIS information.
Unless other ATC restriction is imposed, the aircraft must be push back within 5 minutes from the time ATC clearance is received otherwise the ATC clearance will be cancelled.
Additionally, in order to provide a more flexible ground traffic movement, all domestic departures shall no longer be required to push back within 5 minutes after clearance received.

Which means the 5 minutes push back limit does not apply to domestic flights. The same document also lists the different procedures for each stand, for example for parking stand 21:

The aircraft may start one engine to idle power. They will be pushed back onto "taxilane B" to face either north or south behind the holding line, where remaining engines may be started. Breakaway thrust will be applied when cleared to taxi.

If unsure, always ask the ATC. If the push and start clearance is split, the ATC should specify that.


Why does the UK CAA restart its page numbering with every new chapter of their CAP publications? Every CAA Publication (CAP) seems to restart its page numbering when starting a new chapter. Does anyone know why they have decided to do this?
For example, the CAP413. Instead of a logical page number ordering throughout the document, you have to reference it as chapter 4, pg 4 or chapter 5, pg 2.
It makes it very difficult to reference information to others. It also makes navigating as a PDF challenging - many of the CAPs are solely in PDF format. (Often you can only view one page at a time, and it is so easy to get lost in a document which restarts its page ordering).
Is there a reason why the CAA has done this? What would be the formal or best way of referencing a CAP page?

That's an artefact of a different era. Before computers were used to create documentation, updating large documents was difficult and expensive. People tried to reduce the workload by using chapter-page numbering. When you have to add pages to a book, chapter-page numbering allows you to replace one chapter instead of having to reprint the whole book.
Some organizations even supplied book updates as individual pages with a 'list of effective pages' so you could swap them out in your copy.
Nowadays there's no reason to keep doing this. Rebuilding a document (generate the TOC and crossreferences) is cheap, printing is cheap. You already noticed the big disadvantages of chapter-page numbering to the user.
Why they're still doing this? Inertia, probably.
How to reference them? Page 5-2 works, and if you want to be comprehensive, page 5-2 (PDF page 124).
(sorry, no references. Just lots of experience building large documents)


Why are propellers de-iced before the engines are started, and does ice on the fuselage affect the flight characteristics of the plane? I recently flew on a flight out of Montreal on a DHC8 turboprop.  The plane had been parked at the airport overnight during a winter storm, and as I walked out to the plane, there were visible icicles accumulated on the wings.  There was also a layer of ice completely covering the windows on one side of the plane, presumably because of the direction of the prevailing wind during the storm.

The plane was successfully de-iced and took off without a problem.  However, I had some questions about the de-icing process as I observed it from inside the plane.

The ground crew had to de-ice the propellers manually before the engines could be started.  Is this mainly because of the risk of ice ingestion in the engines, or is there a problem with the propeller being imbalanced because of uneven weight?  Or both?  Or neither?
The de-icing by the trucks seemed to focus on the wings, and it looked like there was still some ice left on the exterior windows when we left the de-icing pad. My understanding of icing is that ice on the wings is extra-bad (I remember a fatal crash happened near me due to wing ice when I was growing up), but does ice on the fuselage affect the flight characteristics of the plane?  Or is it not really a concern?

The props are done before starting because you need to make sure the blades and spinners are fully cleaned off while they are stationary. Otherwise, they'd vibrate like hell when starting and shed bits of ice all over. Also, if you just sprayed the props while running the engines would ingest a lot of glycol, which, if it doesn't make the engine flame out, can gum things up and cause cabin smells as cooked fluid makes its way into the air conditioning system through the compressor bleed system (a lot of turn-backs from "cabin smoke" reports on departure are from the stink from cooked glycol getting into the cabin via the bleeds).

Even done stationary, some fluid will make its way into the engine and it's typical to run the engines at a moderate power setting after the treatment for a couple minutes to try to purge whatever glycol residue is in the compressor before opening the bleeds.

Fuselages are deiced depending on the airplane and the conditions.  On some jets, especially those with tail mounted engines, the upper fuselage is treated as if it was a flying surface and must be clear of ice and frost, even small amounts (it varies with the regulatory jurisdiction).  Otherwise it will depend on whether there is any significant accumulation, mostly for weight considerations.

If there is an obvious layer of snow/ice on the fuselage, it will be removed... mostly; don't expect a perfect job and they won't normally shoot down as far as the windows. If it's just morning frost, the fuselage may be left alone although the wings and tail must still be done (ANY frost on leading edges can be fatal).  The Capt is in communication with the deicing personnel working the boom and will give instructions on what is to be covered, and what to avoid (like APU air inlet in the tail, or heat exchanger inlets, etc.), whether to use Type I only or Type I and II/III/IV (Type one is for melting/removal and II/III/IV is for follow-on residual protection for a limited time).

A deice with follow on residual anti-ice protection costs the airline a couple thousand bucks per flight so avoiding unnecessary fluid application is important in the long run.


What are typical stability analysis dampening values? I'm not an aerospace engineer, so don't know if I'm asking this correctly. I've been using the new XFLR5 with stability analysis. Just don't know what values are good.

What are typical stability analysis dampening values for GA aircraft
for:

Lateral modes:

roll control
dutch 1
dutch 2
spin

Longitudinal modes:

short period 1
short period 2
phugoid 1
phugoid 2

For the eigenvalues:

The Roll Subsidience should be negative.
The Dutch Roll values should have negative real parts, and they will be complex conjugates unless something is really wrong with your model.
The Spin (spiral) mode should ideally have a negative sign but there is some leeway to it being positive if the modulus is small.
The Longitudinal modes should both have negative real parts, especially the short period mode (the one with the highest frequency, in the 10Hz range where the pilot cannot react in time to damp it)

Assuming the eigenmodes are convergent, the dampening coefficients need to be large enough to kill any oscillation in a reasonable time frame. What is reasonable is often up to the particular design case; for example fast enough to prevent resonance with some structural mode, or far away from the pilot´s natural feedback loop to avoid PIOs .

For a brief primer on stability, see here: https://courses.cit.cornell.edu/mae5070/DynamicStability.pdf


How much thrust was provided by a typical Meredith Effect radiator? The Meredith Effect was used on some aircraft to provide more thrust by channeling air through the radiator such that the air is expanded, heated and then compressed through a constriction, generating thrust.  How much thrust could such an installment generate?  How much net thrust, after accounting for drag, does such an installation generate?

Here they give a calculation for the thrust generated by a Meredith effect cooler. They do this for the P51 Mustang. It is also mentioned that in Aeroplane monthly, May 1999 (not accessible to me), the designer Atwood claims that the Meredith effects cooler generates 300 lbs of force.

They perform some calculations based on geometry obtained from  Gruenhagen's "Mustang. The story of the P51 fighter", 1969. These calculations also lead to number around 300 lbs (it calculates 270 lbs of thrust).
However, the calculations do not included the effects of the heating of the air whilst passing through the cooler (which is -according to me- a vital component of the way in which these coolers generate thrust).


How do pilots of big jets determine if they are clear of the runway after landing? The pilots of small aircraft can easily determine if they're clear of the runway by visually looking back through the side windows.

How do the pilots of big commercial jets determine that all parts of their aircraft are clear of the runway after landing? It looks like the same visual check as used by GA is almost impossible given the size of their aircraft. Do they have some special ways or measures to do that?

Using TLAR (That Looks About Right).  Pilot turns off a runway onto a taxiway spur and sees the runway safety area lines and just estimates a point beyond roughly equal to or greater than the length of the fuselage and places the cockpit over that point.

Other methods include geo-referenced airport diagrams on a moving map display showing the position of the aircraft.


What is a compounding wing and how does it increase helicopter performance? The US Army is developing a list of enhancements for the next generation Apache attack helicopter. Among them this was mentioned:

  Topping the list of major changes is re-engining with the 3,000-shp Improved Turbine Engine, but the array of potential upgrades includes adding a propulsor and compounding wing to increase the helicopter’s performance. Aviation Week

What is a compounding wing and how does it increase a helicopter's performance?

This paper discusses wing compounding and appears to be a free PDF download.  Apparently the added wing provides lift to offload the rotor, allowing them to work more on providing forward propulsion and relieving some of their need to also create lift.  Figure at the top of page 6 shows the helicopter with added wing with outboard props on the wing.

  The compound helicopter configuration, known as the hybrid compound helicopter, features both wing and thrust compounding. The wing offloads the main rotor at high speeds whereas two propellers provide additional axial thrust as well as yaw control. This study investigates the maneuverability of these two helicopter configurations using inverse simulation. The results predict that a hybrid compound helicopter configuration is capable of attaining greater load factors than its conventional counterpart, when flying a Pullup-Pushover maneuver. In terms of the Accel-Decel maneuver, the two helicopter configurations are capable of completing the maneuver in comparable time-scales. However, the addition of thrust compounding to the compound helicopter design reduces the pitch attitude required throughout the acceleration stage of the maneuver.


Do airliners stall first at the wing tip? One of the disadvantages of the sweepback aircraft is the tendency of a stall to occur at the wingtip first. Various high lift devices are added by design to the wings of the sweepback aircraft like Boeing and Airbus airliners to prevent or delay stalls, yet what happens if the aircraft actually stall? Do they stall at the wingtip first or at the wing root? Do the wings of these aircraft feature washout? If they do, is the washout great enough to prevent a wing-tip-first stall? How much washout do they have in degrees?

They are designed to not stall at the tips first. Such a stall behavior would be highly problematic because it causes a pitch-up moment which exacerbates the stall. See the answers to this question how nasty stalls with swept wings can become.

FAR 25.203 describes the required stall characteristics:

  (a) It must be possible to produce and to correct roll and yaw by
  unreversed use of the aileron and rudder controls, up to the time the
  airplane is stalled. No abnormal nose-up pitching may occur. The
  longitudinal control force must be positive up to and throughout the
  stall. In addition, it must be possible to promptly prevent stalling
  and to recover from a stall by normal use of the controls.

Such a behavior is easiest to achieve when separation does not start at the wing tip. Earlier swept wing designs sometimes had trouble to achieve docile stall characteristics which led to the introduction of stick shakers. Today, changing the airfoil shape over span (aerodynamic washout) and wing twist (geometric washout) are combined to ensure that stall starts at the wing root.

Regarding washout: With high-lift devices employed, the low deflection angle of the ailerons on the outer wing results in a strong effective washout. Here it is important to extend the slats over the outer wing to enable it to function well above the local angle of attack. The picture of an A300-600 below should illustrate the point.

A300-600 in landing configuration (picture source)

But even in clean configuration some washout remains and allows the outer
wing to fly at a lower lift coefficient which ensures a decent stall margin. A photo of an airliner wing on the ground might be misleading: The lift forces in flight will twist the swept-back wing such that washout is increased.


Could flaps be raised upward to serve as spoilers / lift dumpers? I should preface that I'm by no means an aviation person. I'm just in a aircraft knowledge obsession phase and daydreaming about designing my own ultralight (will never happen).

The idea would be to simplify and lighten a small aircraft using the flaps as spoilers. As a practical example, the same handle could be used in one movement to get from flaps raised just before touchdown to spoiler raised just after it, making it fast and intuitive.

Basically you would have on a single axis :

high lift + high drag <-> normal lift + low drag <-> low lift + high drag

Is that possible? I guess not because I couldn't find anything like that, but why?

I name them flapoilers.

The Fairey-Youngman flaps seem to do that but all I could find as explanation is "so that the aircraft could be dived vertically without needing excessive trim changes" and I'm not sure how to understand that.

One reason is that any device you want to use as a lift dumper needs to be able to be instantly retracted and this is really difficult to do with a flap.  On an airliner when the lift dumpers come up, if you slam the thrust back up to TO, they immediately come back down.  A flap system with its slow moving drive line can't do this, and it's enough that it has to be retracted from landing to takeoff setting for a balked landing like that.

Plus, even in a normal landing, you would be landing with the flaps at the landing setting, and when you touch down they would need 10-20 seconds a typical drive system would need to move up past 0 to a fully up position.  You'd be stopped by then, and deciding to take off again on the rollout is out of the question.

So you can see that any system like this would require flaps that can move up and down rapidly like ailerons.  A really difficult engineering problem.

You might do this on a small airplane with manual flaps operated by a lever, but now you have to cater to twice the movement range as regular flaps, and you'd lose the mechanical leverage you'd need for manual flaps to work unless you made the lever move twice as far (by say having it move in a 180 degree arc - but now the lever handle is in the back seat).

Lots of gliders use flaps - without any spoilers - and they can in most cases be "reflexed" up a small amount, but this feature is done only to unload the trailing edge region for high speed running which has an effect similar to reducing wing area  and pitching moment to reduce both induced drag and trim drag.

For approach control and landing, they actually do the opposite of what you would think; you drop the flaps down to near 90 degrees when you want to come down steeply and for the landing roll.  Not everybody likes that kind of system because you have the same problem - you can't bring them up and down quickly like spoilers so you can't work the flap lever like a throttle on approach the way you normally do with regular spoilers/dive brakes, and they require different flying techniques, on which a pilot used to spoilers needs to be carefully briefed to avoid trouble.


Is the longitudinal stability achieved the same for all aircrafts or does it differ? If there is a difference in longitudinal stability how are they achieved?

Different types of aircraft do have differing requirements for longitudinal stability:
A dogfighter or aerobatic sportster needs to be minimally stable, even a little unstable, for maximum manoeuvrability. On the other hand a primary trainer must be stable, so the novice pilot finds it easy to fly.
Whether the plane is fly-by-wire also makes a difference; relaxing the stability reduces drag and therefore improves fuel efficiency, but it needs a computer to add artificial stability so the pilot does not get tired wrestling with the controls for hours on end.
Technically, longitudinal stability is determined by the position of the centre of gravity relative to the aerodynamic centre. If the CG is in front then the plane is stable, if behind then unstable. The designer has to be careful to attach the wings in the right place for the particular characteristics required.
Some planes can vary significantly in flight. The de Havilland DH.88 Comet racer had a big fuel tank in the nose. When full of fuel it was just stable, but as it emptied during a long flight the CG moved progressively aft and it became more and more unstable (and the pilot became more and more exhausted!).


What is this aircraft, when was it produced and used and what was its role? What aircraft is this, when was it produced, used operationally, and what was its role?

It is a Tu-128.

In particular it seems to be the "UT" (training) variant:

Image source

  Full-scale production of the aircraft began in 1966, with 188 Tu-128s built to 1970, that total apparently including the prototype. Ten "Tu-128UT" trainers were built as well, with a new cockpit for a flight instructor fitted into a swollen nose.

Other info on wikipedia

  The Tupolev Tu-28 (NATO reporting name Fiddler) was a long-range interceptor aircraft introduced by the Soviet Union in the 1960s. The official designation was Tu-128, but this designation was less commonly used in the West.

[...]

  The Tu-128's only publicly reported combat operation was the destruction of NATO reconnaissance balloons. The aircraft remained in service until 1990.


Why would one plane in this picture not have gear down yet? This image (as posted in another question) is a YouTube video's thumbnail:

I noticed that the lead twin (737?) has gear down, the 747 behind does not (appear to) have gear down, but the third plane in line (another twin) does have gear down as well.

Why would the 747 not be gear down at this point?

Why does the 747 not have its gear down yet?

Based on the image it is hard to say how far these aircraft are from the runway. The 747 could still be be quite far from the runway and thus does not need to have its gear down yet.

The 747-400 FCOM (NP.21.47 Normal Procedures) says:

  At glideslope alive, call:

  "GEAR DOWN"
  "FLAPS 20"

It looks like the 747 in the picture has already intercepted the glideslope, but this is hard to say from this perspective. Also, operators may have different rules for when to lower the gear.

Then why does the third aircraft already have its gear down?

The most probable reason for this is drag. A flight crew may choose to lower the gear earlier than necessary to reduce its speed. ATC could have instructed this aircraft to fly at a lower speed for spacing and the crew then dropped the gear, which adds significant drag. This is pure speculation, of course.


What happens when you apply full cyclic + collective? Can a helicopter apply full cyclic and then full collective at the same time? Would'nt the blades on one side (opposite of the intended tilt direction) have already maxed their aoa, resulting in a net dissapearence of dissymmetry of lift, with the effect equal to just applying full collective? Or does full collective + cyclic result in even greater aoa (the inputs add up)?

Multiple questions here. Assuming by full cyclic you mean pushing the cyclic to a mechanical stop while pulling full collective to the mechanical stop, the answer is yes, at least for the Bell 206, a very common turbine helicopter in use worldwide. There are no restrictions with regards to full flight control inputs. At stabilized hover on a no wind day there is no appreciable dissymmetry of lift as aerodynamically, there is no advancing or retreating blade. If you push the cyclic straight and full forward, mechanically tilting the rotor disc, the instant you move forward you now have dissymmetry of lift between the advancing and retreating blades


Why Is This Tyre Square On The BA A380? One thing I saw on the news recently was the following image:

How has this happened?

Some details:

British Airways A380-800.
Flight BA-32 from Hong Kong to Heathrow.
While climbing out of Hong Kong crew received a tyre pressure notification, but continued on as the A380 can land with 1 of it's 18 tyres flat.
Landed safely, but had to request a tug to the gate.
The photo above is after landing.

I can't seem to find a clear explanation to why the tyre has gone this square shape. Generally when a tyre is flat it's round with the bottom being straight. The explanations seem to vary between tyre pressure, to the way it lands, to the way it is stored.

What's the real reason it's square?

http://avherald.com/h?article=498050d8

According to this document about the landing gear system, the wheel dimension  of the main lading gears is 1400x530 R23. This is not the standard notation known from car tires, but it says that the diameter is 1400mm and the width is 530mm, so the tread has a surface of about 2,3m².

The same document further states:

  Depending on the flight phase, a warning will be triggered if a
  tyre pressure is detected below a given percentage of the nominal tyre pressure (for 5 seconds continuously).
  Likewise, a warning will be triggered if a differential pressure above a given percentage is detected across tyres on the same axle (measured from the tyre with the higher pressure).

though no concrete threshold is given.

The nominal pressure of the tires is 15Bar (atm) and will quickly fall, even when there's just a tiny leak. So no wonder there was a warning during climb.

During the 13h flight at up to 40.000ft, the pressure could easily fall to the environmental pressure of about 0.2Bar at that altitude. And from that altitude, it takes only 30min to landing (taken from flightaware for a BA32 flight), which may not be enough to equalize tire pressure to ambient pressure through a tiny leak. Also, ambient pressure will rise slowly in the beginning and reach 1Bar at ground quite late.

Considering the pressure in the tire was still 0.2Bar when landing, the pressure difference to the ambient caused a force of 176kN on the tread, which equals a weight of 18t or 39700lbs! (one could also say: 4.5t or 5000lbs on each of the sides of this square shaped tire.)

So it's no wonder that the tire was compressed, though this doesn't explain why the tire choose the square shape.

In general, the tire tries to minimize its volume while the surface is constant, but it can't change to any shape. Its stiffness and the rim only allow the tread to bulge inwards. From math, we know that the more sides a symmetric polygon has, the more surface it has w.r.t its circumference. So the less sides, the better.  A triangular shape seems not to be possible due to the rim and the needed large force to bend side walls. A pentagon doesn't provide enough reduction of volume, so a square is the best choice.

So though the picture looks really crazy, the square shape is not that surprising.

However, a tire does not think about how to collapse best to minimize volume. It starts an one or more points and evolves. If it starts with three bulges, it could have stayed with it, and the A380 had landed with a triangular tire. May be, a fourth bulge has developed at some point. Maybe, the shape in air was different, and some punched during landing pushed the tire into that shape.

Finally, one can only say that it's clear that the tire collapses to something like this due to the ambient pressure working against the low pressure inside, but one can not really predict the resulting shape. But the rectangular shape seems to be the best to minimize volume.


What is the procedure to contact EASA to evaluate the certifiability of a system? I work in academia, and often we are "accused" of living in an ivory tower with no connections to the real world.

To reduce the gap between academia and this "real world" I've heard about, I would like to involve EASA in the research project I am currently involved in.

What is the correct procedure to do this?

For clarity:

it would be only about software
it is not something covered by DO-178C/equivalents (I have problems/questions about the high-level requirements, that are an input for the procedures in DO-178)
it is a program running on a machine with a real-time operating system (RTOS) on board the aircraft. Currently we have no plans concerning maintenance cycles, so I would not be able to say if it could go on a easily exchangeable module (but my guess is no).

DO-178 / ED-12C

Any software that executes on installed hardware in a type certified aircraft will need go to through DO-178C (or a similar process). The amount of effort involved depends on the safety criticality of the software functions.

Since this sounds like a new system without predefined System Requirements (such as those you would get from an OEM as part of the SAE ARP 4754A processes), those will need to be defined by your development process and then your Software (High Level) Requirements trace from those.

Here in the US, smaller companies will typically contact and work with the local ACO (Aircraft Certification Office) during the product planning stages to identify the product as following the DO-178C processes.

Larger companies, especially OEMs, tend to work with DERs (Designated Engineering Representatives) rather than directly with the ACO, as they may have dozens of different DO-178 projects going at one time.

EASA Software Certification

Guidance on the EASA Software Aspects of Certification can be found in EASA CM -SWCEH - 002 PDF

From that document, Panel 10 seems to be the part of EASA that you would work with, although I haven't found how a new applicant would go about contacting them yet.

  The EASA panel in charge of software and AEH aspects of certification.
  This panel includes at least one software and AEH expert (who is the
  coordinator) and, depending on the size of the project, may include
  additional software and AEH experts.

There is also a FAQ page for the application processes with EASA:

https://www.easa.europa.eu/the-agency/faqs/application-process