How is the visibility at airports measured? What tools are being used by airports to measure visibility precisely?

Do we have some kind of tools on aircraft as well for measuring visibility?

The visibility is measured alongside the runway, usually at various positions, and is called the Runway Visual Range (RVR).

RVR is defined as the range over which the pilot of an aircraft on the centre line of a runway can see the runway surface markings or the lights delineating the runway or identifying its centre line.

RVR is measured using so called transmissometers.

source: keesfloor.nl

These units transmit a beam of light (usually using laser) to a detector. In some case the transmitter and detector are in the same unit and a reflector is used. The ratio of the transmitted energy and the detected energy is a measure of how much light is absorbed in the fog. From this the RVR can be calculated.

Another type of sensor used to measure the visibility on airports is a forward scatter sensor. This type of sensor can be mounted on a single mast and gives more accurate results for visibilities > 2 km. This kind of sensor is used for both determining RVR and Meteorological Optical Range (MOR).

source: KNMI (PDF)

This type of sensor works by detecting how much of the transmitted light is scattered into a detector which is placed off-axis.

Aircraft don't have means to measure the visibility other than the pilot Mk 1 eyeball.


Is Sonex a good trainer plane? Hello I am thinking about buying a Sonex to start to learn how to fly. I want to know, if it is a good plane to learn in?

I would avoid the Sonex, or any other kit aircraft, until you have some student flight time under your belt and are sure that's the way you want to go.

The problems with using a kit LSA to learn include:

The "Build then fly" process of a kit without a license assumes you will want to do the latter after doing the former. Plenty of novice pilots spend 5 to 10 hours at the yoke and either get it out of their system and lose interest, or wash out in other ways (fail medical, can't pass written tests or checkrides and give up, run out of money to spend on rentals and fuel). If that happens to you, you'll be stuck with a kit you bought new, which you can't fly and now have to sell used. It's better to rent your way through the first few weekends as a student, then once you have your student cert, a few flight hours, solo endorsement and you're sure you are able and want to keep going toward a sport or private cert, you can look for an aircraft to own and practice with.
Building a kit means getting that kit certified airworthy. An amateur-built plane has to go through a rigorous mechanical inspection before you'll be allowed to take it up in the air. The fact that it's a kit for an aircraft fitting the "light sport" type rating might make it a little easier, but they might treat it as an "experimental" craft just because it's a homebuilt and go through the "Special Airworthiness Certification" process for those types of planes.
Buying someone else's kit means inheriting their mistakes. If you don't build, and instead buy a kit plane that someone else went through the trouble of building and getting certified, you're still flying a homebuilt. Anything the FAA inspector missed could cause a failure in flight, and you can't just pull over and call a tow truck when that happens. The same could be said of your own homebuilt, and overall with the strict mechanical inspection criteria of planes this isn't as big a problem buying a plane versus buying a used car, but it's something to think about; they built and configured it their way, and if that's not "your" way or even the "usual" way it can be distracting in flight, and distracting is dangerous.
The Light Sport class is designed for day VFR with a limited range. If all you want is a sport pilot certificate to go out flying in fair weather near your home airstrip, great, grab an LSA like the Sonex and have fun. If you want to progress to a PPL, and fly cross-country, at night or in IMC with your instrument rating, you'll need a plane capable of flying in such conditions for your checkride and other training time including at least one serious cross-country flight. The stock Sonex builds I'm looking at now do not have the IFR "big 6" and really no room to mount them. You can go glass, but instrumentation's only one piece of the puzzle; you'd also need an external light kit which doesn't come stock, and the airframe has to be rated for flight in minimum winds as well as IMC like rain, which most LSAs simply are not designed for.
LSAs have limited power by design. That doesn't mean other aircraft don't have similar power ratings (the stock Cessna 150 is only 100hp while there's an engine kit for the Sonex providing 120), but the Sport Pilot license was designed for flying LSAs with a max power of 87hp, with an instructor endorsement required to fly anything more powerful. Just one more hurdle to getting rated to fly your own up-engined Sonex (or anything else besides).

Just my analysis. Again, if you just want to start with a SPL (20 hours flight time, some ground instruction and a written test, no medical beyond the basics for a driver license) and see where it goes from there, then a Sonex kit, base price about 18 grand, is a pretty good deal assuming you're good with tools. But if you want to progress to where flying is useful beyond simple recreation, you'll start rubbing up against the limitations of an LSA sooner than you would in a more full-featured trainer. That more full-featured trainer is also going to be more expensive, but it'll be a plane you can use much further into your flying career, and if you take care of it, will hold cash value and even match inflation so you can use it as a store of value to trade up (the 150's original retail price back in the 60s was around \$7500; those same '60s airframes change hands at around \$25,000 now).


How much does a 3 day cabin crew recurrent training cost? Airlines are getting rid of instructors. How are they carrying out recurrent training and how much does it cost the crew?

The airline will bring in contract instructors to do the training (yes there are freelancers out there that do that sort of thing as contractors).
If they don't have the number of active crews to justify full time instructors because they only need someone for 5 or 10 days a month, that's the normal alternative.
The airline will still be paying the contractors they hire for the training so the cost to the crew will still be zero.


How can you explicate the efficiency of a turbofan engine with Carnot's theorem? From Carnot's theorem, we know that efficiency is

$$ \eta = 1-\dfrac{T_c}{T_h}$$

where $T_c$ is the temperature of the cold reservoir and $T_h$ the temperature of the hot reservoir. But what do we have to consider for both?

Is $T_c$ the temperature of the air coming into the compressor from the fan or the temperature of air coming into the combustion chamber after being compressed and heated by the compressor?

Is $T_h$ the temperature of the gases in the combustion chamber (1500C°) or at the exhaust nozzle?

The Carnot efficiency is the maximum attainable efficiency in terms of extracting work from a temperature differential, not the actual efficiency in a turbine engine. For the actual efficiency, you should look into the Brayton cycle, which approximates a turbine engine much better.

With that out of the way, let's look at the Carnot cycle. This cycle assumes a heat source that can provide arbitrary amounts of energy at a certain temperature $T_h$, and a heat sink that can sink arbitrary amounts of heat at a temperature $T_c$. These are the isothermal parts of the cycle. To get the working fluid to either temperature, adiabatic compression is used.

These heat sources and sinks do not exist in reality, but by approximation, the atmosphere is an excellent heat sink, and burning fuel is an excellent heat source. The low temperature is thus taken as the atmospheric temperature which can be as low as -50°C (~220 K, remember that Carnot's efficiency is defined in terms of absolute temperature) and the high temperature is the temperature in the combustion chamber.

Sometimes you hear that $T_h$ is the hottest temperature in the cycle, and $T_c$ the coldest temperature. While this is often true in practice, this does not need to be the case for theoretical considerations. The only thing that matters for the Carnot efficiency is the temperature of the heat sinks/sources. You can't get more efficient than the Carnot cycle by hooking your engine up to a fridge. Indeed, the Carnot cycle is just a way to express the Second Law of Thermodynamics, which states that entropy in a closed system can never increase.


How important is it to have talent to become airline pilot? The situation that led me to ask the question is as follows:

I am a student pilot with only about 10 hours of flight time. I passed the aptitude and personality tests prepared by German Aerospace Center (German: Deutsches Zentrum für Luft- und Raumfahrt).

My instructor keeps on telling me since the very first couple of flights that I lack some talent and it's not really possible for me to become an airline pilot. (He has never flown as airliner, only military aircraft but he is obviously a good pilot with long teaching experience.)

So, what is the possibility that he is right? How much and what type of talent is required?

Please note that I haven't caused any major safety problems, and other students claim that they made pretty much the same mistakes I do.

Edit : Since some people misunderstood the situation, I'll clear some issues:
1-) I'm on some scholarship program of an airlines company. Money isn't an issue.
2-) I'm generally considered to be pretty smart.
3-) There's no reason that I could be discriminated by the instructor.

You are asking the wrong question. Ask yourself this:

Do I really want to become a pilot?

If the answer is yes, then you can become a pilot. You only require hard work, and a lot of money (but we are not talking about this).

Having talent is subjective. Sometimes you try to learn something new and you get into that relatively quickly. Sometimes you don't. It doesn't just depend on talent, but on several factors.

If you feel that you are not making any different mistakes than other student pilots, then change your instructor.

There are several discussions about changing flight instructors. You can benefit from these ones:

What to look for in a flight instructor?
Is there a downside to trying multiple flight instructors?


What is the meaning of “American 755, turn right, heading 320"? I am studying a text entitled Unmanned Aircraft Systems. How can we simplify the instruction in quotes so that it is more understandable and can be understood by a nontechnical. Please note I am not seeking to know all technical jargon of routing aircraft, rather to get what a pilot is told with this instruction to do.

  Ideally, the communication process includes three parts: the
  initial call, readback, and hearback. For example, an ATCO would issue an instruction “American 755, turn right, heading 320.” Pilots onboard the aircraft would respond, or readback the message “Right, heading 320, American 755.”

American 755, turn right, heading 320.

Aviation phraseology is direct, specific, and concise. The three items here:

The controller is instructing the aircraft identified as American 755
to make a right turn
such that they maintain a heading (direction) of 320 degrees (5 degrees north of north-west).

Though you may not be interested right now, at some level you might have to get technical, as communication involves defining terms :)

In case you are interested, for references and further reading see this page from the FAA. Especially of note:

Pilot/Controller Glossary - contains definitions for radio communications.
Aeronautical Information Manual - contains instructions for pilots.
JO 7110.65 - (more technical) the handbook for controllers. Everything they say should be in there.


What is a "departure" in the context of flight testing / maneuvers? I was reading about the F-35 flight tests and it mentions a "departure" at a couple of places.

What does that word mean in this context? I understand spins and stalls but what's a "departure"?

  AF-2 was the first F-35 to be flown to 9g+ and -3g, and to roll at
  design-load factor. Departure/spin resistance was also proven during
  high angle-of-attack (AOA) testing which eventually went as high as
  110 deg. AOA

  Pilots really like maneuverability, and the fact that the aircraft
  recovers so well from a departure allows us to say [to the designers
  of the flight control system laws], ‘you don’t have to clamp down so
  tight,

(Wikipedia Lockheed Martin F-35 Lightning II article)

Departure means that the aircraft has departed from controlled flight. From FAA news:

  A Loss of Control (LOC) accident involves an unintended departure of an aircraft from controlled flight

In this video about flight testing F-16s, the test pilot says 'intentionally departed from controlled flight' and later 'the aircraft is prone to departure if mishandled' and 'the aircraft departed in yaw'.


Who pays airline pilots? Do pilots make money from the airline they fly for (Delta, JetBlue, Southwest, Skywest), the company that makes the aircraft they fly (Boeing, Airbus, Lockheed Martin, Embraer, Bombardier), or just by the hours they fly?

Professional airline pilots are paid by the airline for their flight hours, similarly to other transportation workers.  Time spent in preparation for flight or even preflighting the plane itself is not usually compensated.  This pay varies by the company and the position (first officer, captain, etc.), and sometimes there are signing bonuses on top.  Pilots are given a monthly minimum of hours pay that they'll receive, even if they fly less than that. This is often as little as 65 hours guaranteed pay.

Regional jets, e.g. Republic, are typically contracted by another company like American Airlines. The regional airline, not the major airline, would pay the pilots for their flight hours.  This is even true if the regional jet has the livery of the major airline or the tickets are sold by the major airline.

Private/charter pilots get paid by the company (or person) managing the plane.  This can be either a per-day wage, a yearly salary, or a mix of both.  (Source)

Flight instructors are paid an hourly wage by their flight school.  This hourly wage does not include things like weather delays, your own education, and planning.   Flight instructors can also work independently and then they'd be paid directly by the student.

Except where noted, the source for this information is The Truth About The Profession.


Why is braking action (with Anti-Skid) best when the wheel rotates at ~85% of the actual speed? During my ATPL training the subject of tires and braking was discussed.

I understand the principle of the anti-skid and also the differences between aircraft and similar systems in cars.
Physics also thought me that static friction is greater dynamic friction.

The script mentions that it has been shown that the maximum braking efficiency is obtained when the wheel rotates at a speed of 85% of the ground speed.
[Clarification: imagine a identical tire wich rolls on the surface without any resistance/braking, this would be 100%. Every bit of slip therefore reduces the rpm. ]

Why would this be beneficial?

My ideas so far are:

that if some slip occurs braking is mostly in the static friction range but some energy during braking is also put into deforming the tire (and thereby heating it) and possibly ripping small pieces of rubber (on a really small scale) off the tire.
In order to find out where the tire begins to slip it actually has to slip, so in this process of: raising the pressure on the brake and if slip occurs, reducing the pressure, on average a slip of 15% occurs- whixh means a tire speed of 85%.

Is one of these correct?

Are there any other factors and processes?

Tire-road dynamics at speed are described by the Pacejka's "Magic Formula", so called because

  there is no particular physical basis for the structure of the equations chosen, but they fit a wide variety of tire constructions and operating conditions.

This empirical description was developed using regression analysis and consequently has no theoretical basis as to why it works, but it does work and is widely used. You may not like the answer that 85% is best because that is what the formula says.

The reference gives the parameters necessary for calculating the peak longitudinal force and corresponding slip. ABS systems attempt to balance a peak slip ratio with vehicle directional control, resulting in an ideal ratio between 0.1 to 0.3. (which is 70-90% of ground speed using your terminology)

source

I would modify your statement #2 to say that in order for the ABS to know when the tire begins to slip it has to know when the tire does not slip, which allows the determination of unbraked tire speed from which the desired slip can be calculated. I think this is one reason for pulsating brakes when ABS is active; the ongoing determination of zero slip speed as the vehicle decelerates.


What does the instruction "Climb heading [BEARING] to [NAVAID] 2.5 DME" mean? I am examining FAA's Standard Instrument Departure Procedures (SIDs) and while reading their textual description, I came across this instruction from
LGA's La Guardia Five Departure SID, for Runway 13 (Whitestone climb): "Climb right turn heading 180 degrees to LGA 2.5 DME then left turn heading 040 degrees etc."

Could someone explain to me what the phrase "heading to LGA 2.5 DME" means? Does it mean that the pilot maintains this magnetic bearing (180 degrees) until the distance between the aircraft and the LGA (NavAid) becomes 2.5 nautical miles?

DME is "Distance Measuring Equipment". It tells you how far you are from the equipment transmitting the signal. This is often co-located with a VOR, or at an airport.

  turn heading 180 degrees to LGA 2.5 DME

So, this means turn due south and continue until you are 2.5 nautical miles from LGA. At this point you're instructed to turn left on to a heading of 040.


Eye requirements for private pilots license in the US? In the next couple of years, I would like to work on obtaining a private pilot license with the goal of eventually getting my own plane. But my eyesight isn't that great in my left eye.

As a kid, I was born with amblyopia/strabismus. Did eye surgery as a kid which didn't really correct the vision. Though my eyes appear normal, my right is 20/20 and my left is 20/80/100. I should also clarify that glasses cannot remedy the left eye in terms of acuity.

So my question is will I be able to get a license? If not, that's fine, but I'd like to know so I can focus my energy and interests elsewhere.

Thanks.

The guidance for vision requirements are listed here.  Basically for a private pilot distant vision must be 20/40, near vision 20/40, and no requirement for intermediate vision.  The website says

  In each eye separately with or without correction

I interpret that to mean that your left eye must be 20/40 or better.  However the final authority on this would be the FAA approved medical examiner and it wouldn't hurt to go ahead and schedule a FAA Type III medical examination and see what the doctor has to say.  Unfortunately your insurance won't cover the exam and you would have to pay somewhere around $150 for it.  However you will have a better understanding of what your options are if you want to pursue flying.  Sometimes a license can be granted but with restrictions if a pilot has a medical condition.

I hope you will be able to pursue flying and wish you the best of luck!


Why is there conflicting nomenclature for the 1,000 ft runway markings? The two thick solid lines on runways at 1,000 ft from the end of the threshold are called "fixed-distance markers" in some documentation, and in others, it is called the "touchdown zone marker".
Are they two different things, is one right and the other wrong, or are they truly interchangeable terms?
Airman Knowledge Testing Supplement for Instrument Rating, page 116

AIM 2-3-1 from FAA.gov

Both of these above examples are Precision Instrument Runways.

First, let’s clear up some terminology. Touchdown zones are only on runways with precision approaches. Aiming Point Markings are at 1,000' in USA (ICAO standard is different and is runway length dependent) and are also on non-precsion and visual runways. If you fly a small GA airplane, you will often land in the first 1,000' using the Aiming Point as a guide. The markings are at a fixed distance (500') from each other so that’s probably why you have heard that term. I have most of the FAA publications and ACs on my computer and the only place that "fixed distance markers" is referenced is in the Chart Supplement for some runways that have non-standard distances for the markers, so I am curious as to where you have read that term. EDIT: Per the edited question, I changed my search to “fixed distance marker“ and found a half dozen references. All of them are in Knowledge Test questions and none in other FAA publications.

AIM 2−3−3. Runway Markings

  e. Runway Touchdown Zone Markers. The touchdown zone markings identify
  the touchdown zone for landing operations and are coded to provide
  distance information in 500 feet (150m) increments. These markings
  consist of groups of one, two, and three rectangular bars
  symmetrically arranged in pairs about the runway centerline, as shown
  in FIG 2−3−1, Precision Instrument Runway Markings.

  TOUCHDOWN ZONE− The first 3,000 feet of the runway beginning at the
  threshold. The area is used for determination of Touchdown Zone
  Elevation in the development of straight-in landing minimums for
  instrument approaches.


Accounting for torsional forces during wing load tests According to this aviation.se question, wing load tests are done by placing weights on the wings (upside down).

This unfortunately only tests the wings bending loads (for cantilever wings) and the wing struts (for semi cantilevers) but not the torsional strength of the wings.

How do I load test a wing such that its torsional capacity is also tested?

You would have to calculate the torsional loads for a critical torsional loading case such as full aileron application at limit load, and distribute the sand bags chordwise to produce the calculated spiral loading.

That's quite an analytical task and is rarely done when the skin thickness/stiffness required for good aerodynamic qualities and flutter resistance is usually quite a bit more than the minimum required for adequate torsional stiffness to resist flight loads. So it kind of takes care of itself anyway and can be covered by analysis with suitable fudge factors, like most of the other load cases on the airframe.


How do PAPI lights work? Usually, there are four lights at the sides of runways which show airplanes' altitude status:

four red lights: too low
two red, two white: appropriate altitude
four white lights: too high.

If two airplanes with two different altitudes approach, do they see different number of white and red lights? Or are the lights set for the closer airplane?

Here's how the PAPI lights work:

Depending on the angle of the viewer, a different color is seen:

Then each light is calibrated to an angle:

The good thing about this is that it's dead simple technology where very few things can go wrong: The lights have to be on and calibrated for the correct angle. The downside is that its usefulness decreases with lower visibility.

Some new systems appear to have solar panels as an off grid (and alternative/backup) power source which is sensible. Many systems today also have LED lights.

  If two airplanes with two different altitudes approach, do they see different number of white and red lights? Or are the lights set for the closer airplane?

The system is independent and passive, in the sense that it never makes contact or note of the aircraft approaching. It lights up all to all aircraft in the beam. Hence, it 'works' for all aircraft at the same time.

Some new systems feature FAROS (Final Approach Runway Occupancy Signal) giving an indication that the runway may be occupied by another aircraft by flashing the lights.

For a little information on differences between similar systems to PAPI, see this link.


Are there ever temporary flight corridors? A recent question on FAA handling of evacuations prompted me to wonder if there are ever temporary (emergency based) flight corridors set up by any of the governing authorities?

For example, is there ever the airspace equivalent of one way highways set up for a temporary period?

Flight corridors (airways) are just standard routes to simplify communication from controllers to pilots when describing where they should fly and between controllers when handing over flights. But the controllers can assign arbitrary vectors (headings and altitudes) to aircraft whenever they see fit.

So there is no need to formally set up a temporary corridor. If the traffic for whatever reason does not fit the usual corridor, the controller will simply assign any free vector and explain the situation to the next controller. They do that all the time anyway.

However in non-radar environment (e.g. oceanic or in case of radar failure) airways become important tool for the air traffic control, because it would not be feasible to keep track of positions of all the aircraft on ad-hoc routes. With airways the controller knows which airways intersect so planes on them need to be separated vertically and only needs to track the aircraft progress in one dimension (along the airway) instead of two (on map).


What is the takeoff thrust of a CFM56 engine? So, to be more clear I currently have an assignment about the Boeing 737-800.
I have to find out the total takeoff distance of the aircraft. I'm using Anderson's book " Aircraft Performance and Design" and I'm quoting that a turbofan engine is affected from the velocity of the aircraft.
Anderson uses this equation: T = k1 - k2*V + k3*(V^2) where k1,2,3 are constants from engine to engine. At his example he uses a Gulfstream IV aircraft and takes the constants as below (chapter 6, example 6.6):
The constants are selected for the takeoff phase. I guess that these values come from the manufacturer but I cant find this type of info anywhere. Not even a number about the takeoff thrust. The only thing that I can find is the maximum takeoff thrust which is the max thrust available from the engines.

Developing 21,600 to 33,000 pounds of takeoff thrust, the CFM56-5B is the only engine that can power every model in the Airbus A320ceo family.

Safran Aircraft Engines


How does email communication with a private pilot affect FAA rules on compensation? If a person exchanges email with a private pilot (who normally operates under FAR 91) with a view towards hitching a ride or taking an empty leg flight, does this act mean that the pilot must then operate under FAR 135?

Or alternatively, if there is no discussion of payment and/or barter, would the ride still take place under FAR 91?  I have watched the demise of AirPooler, but this was a much more structured arrangement which blatantly  invited scrutiny from the regulator.  This question assumes there is no intermediary like AirPooler or BlackJet.

I am trying to find out what actually triggers an escalation in the rules.  FAA would be fine, but anything on European regulators would be massively welcomed.  I am UK based, not a pilot, and use empty leg on occasion, so I might be affected if the European regulators follow the FAA's lead.  Knowing the trigger point is key.

I'll answer it from the FAA since that's what I know.

The FAR is pretty clear on the matter here

  (a) Except as provided in paragraphs (b) through (h) of this section, no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft.

However if you want to split the cost evenly, you can:

  (c) A private pilot may not pay less than the pro rata share of the operating expenses of a flight with passengers, provided the expenses involve only fuel, oil, airport expenditures, or rental fees.

For what it's worth I would say you can still operate under Part 91 in the case you have outlined.

Basically the FAA prevents a PPL holder from receiving any kind of compensation for a flight. This Article talks about some of the points that the FAA discussed when shutting down these services. The issue with some of these sharing services is that the middle man (AirPooler) and the like take a fee, this seems like the aspect that the FAA had an issue with since although the pilot was not profiting per se, someone was, this seems to be the FAA trigger. I don't know much about the deep aspects of the law but I'm sure there are things that can also arise with being a middleman/deal broker of these kinds of things.


Why was the Sukhoi Su-47 Berkut never adopted for service? This is a rather long question, since I try to cover the historical background which might not be widely known. If familiar with it, you can skip to the "highlighted sections".

As part of the programme equivalent to the U.S. Advanced Tactical Fighter (ATF), aimed at producing a 5th generation multi-role fighter aircraft, Russia (then USSR) produced (like the U.S. programme) 2 competing designs: one from Mikoyan and the other from Sukhoi. These were the canard/delta Wing 1.42/1.44 from Mikoyan and the FSW (Forward Swept Wing) Su-47 from Sukhoi.

Initially running parallel to the U.S. programme, due to mounting financial difficulties and the eventual collapse of the USSR, the 2 prototypes were ready more than 5 years later than their respective US counterparts (The 1.42/1.44 prototype was completed at 1994-5 but performed its first flight in 2000 while the Su-47 was completed in 1992-3(?) and flew in 1997).

Even before the collapse of the USSR, though, the Soviet Air Force had chosen the Mikoyan design as its next 5th-gen fighter.

Yet, after USSR's collapse, Sukhoi was able to finance its own project and have it ready earlier, while also running an R&D programme and further evaluating/improving the design. By the time the Mikoyan MFI performed its first flight, the Su-47 was already taking part in air shows while serving as a testbed for various technologies (many of them finding their way to PAK FA).

This raises a number of questions, all relating to why the Su-47 was not chosen, neither before the USSR collapsed, and secondly why it was not chosen in the 90s by Russia as it was clearly a design in a more mature stage.

  Was the basic design premise-that of a FSW fighter aircraft-flawed?

  Were the problems facing this configuration, relating mainly to wing durability, still insurmountable?

To be precise, a FSW design offers superior manoeuvrability, especially in low speeds, retaining an AoA (Angle of Attack) undreamed of by a "conventional" fighter, is essentially spin-proof, it has a better lift/drag ratio, lower stalling speed while it can help with low observability characteristics (Stealth) as radar beams impacting the wings are reflected to the fuselage , ideally one with a comprehensive RAM (radiation absorbent material) covering.

But a FSW design has a major drawback-the loads that accumulate on the wings during manoeuvring, are much greater than in a conventional wing, leading easier to deformation and structural failure. The Su-47 tackled this problem by making extensive use of composite materials for the wings which offer greater durability at less weight.

  If the FSW design was viable, was it a matter of economics?

After the USSR collapsed and Russia embarked on economic "reforms" its defence budget shrank dramatically for a decade and new procurement was very difficult. But after 1999-2000, gradually funding increased and when the need for a 5th gen aircraft became again apparent, the PAK FA (Sukhoi T-50) project began, around 2005.

But given that a design was already ready, namely that of Su-47, why not save all the expenses (PAK FA development is in the range of 10 billion US$) while gaining in terms of time?

I usually do not like to speculate on "What if?" historical scenarios but had the Su-47 been chosen, say in 2003-4, by now RuAF could have fielded a fleet of 100+ airframes (assuming initial production starting at about 2008-9).

I do not have inside knowledge, but think it is easy to explain why the Su-47 did not progress beyond the prototype stage:

Sukhoi enjoyed great export success with the Su-27 and its derivatives in the 1990s, and this helped to advance work on the Su-47. Mikoyan was in less favorable financial shape during this time, which explains the delay in getting the 1.44 ready.
There was no credible threat that required Russia to procure a modern fighter design during the last two decades. The existing fleet was simply good enough.
The forward-swept configuration is optimised for close-range air combat, while the cost of modern combat aircraft dictates that they need to fulfil multiple roles. Note that the PAK-FA will replace both the MiG-29 and the Su-27 and their derivatives, so even Russia will not support two frontline fighters in the future.
Much has been learned in the meantime about stealth, so the Su-47 was already outdated by the turn of the century.

I have to admit that when I first saw the Su-47, I was scratching my head and wondered what the Sukhoi engineers were thinking when they proposed this design. But I had similar reactions when the Boeing X-32 was unveiled …

Edit: Now it seems the engineers at Sukhoi put what they learnt on the Berkut to good practice when designing the SR-10 two-seat trainer. The reason for the forward sweep is excellent handling at high angle of attack - however, this bleeds energy quickly and can only be used in few corner cases in air combat. But it certainly helps for pilot training if the possible angle of attack regime is large.


When and how do I align with the runway during an offset ILS approach? In X-Plane 11, when landing an A330 on 04R at Nice (LFMN) on an ILS approach, the aircraft is brought perfectly to the end of the runway but because this is an offset ILS the aircraft is at about 2° to the centreline.

My question is at what time and with what technique (rudder or aileron) should the aircraft be aligned with the centreline? I always seem to over-adjust and struggle to avoid wing tips touching the ground.

Looking at my old approach plates, the ILS for Rwy 22R at KJFK of 24 JUL 1998 had an inbound course of 220°. The runway centerline was 224°, so a 4° difference. Decision height was 250'AGL.

In the 747, if we broke out before the decision height and had a clear look at the runway, we would in a shallow coordinated turn decrease our heading so as to intercept the runway centerline course visually and then we would visually turn onto and track the centerline.

The difficulty was when it was foggy, and all you could see near or at the decision height were the approach lights but not the runway sufficiently to visually acquire its course. You knew you had to correct to the right, but the tendency, at least for me, was to over correct because the approach lights were seemingly considerably off to the right, the more so the lower you were when you first saw them.

In the 747 you can safely use a 5° bank without dragging anything. As I remember the first thing to drag would be an outboard engine pod, but whatever. Thus, even up to the 100' call of the radar altimeter, a coordinated shallow bank would get you lined up, but you needed to be quick about it as your groundspeed would be around 160kn.

The first time I made the approach under those minimal conditions, I did indeed over correct. My choice going into the flare was enough left rudder and aileron to get the nose to the runway heading and then maintaining the 5° bank to slip back to the left. Having made the over correction that first time, I was careful not to repeat the mistake.

It's been nearly 20 years since I last shot that approach. I looked at the approach plate of 08 MAR 2012 on the Internet, and I see that they've straightened things out. The approach course is 222°, the runway centerline course 223°. Decision height is still 250' AGL.


When a paraglider pilot applies brake on one side and maintains the brake pressure, why does the roll rate eventually come to zero? I recently started to study paragliding and I am confused about the rolling movement created when a brake is maintained.

I was reading this answer How do paraglider controls work? and I am not clear which force should balance the rolling created by the side force on the levered arm during the initial phase of the turn and stop the rolling motion.

In essence the question is "In a turn using brakes, when a paraglider pilot applies brake on one side and holds it indefinitely, why does the roll rate eventually come to zero?  Why must be substantial brake be applied just to maintain the bank angle in the turn?"

While turning using brakes1, to maintain the desired bank angle once it is established, paragliders do in fact typically require the pilot to maintain a substantial control input (brake pressure) in the same direction as was used to initiate the turn.  This is quite different from what we see in most conventional airplanes, and in modern hang gliders, but we do see similar dynamics in airplanes with lots of dihedral that lack ailerons and turn using the rudder or spoilers (examples-- "Gentle Lady" or "Radian" radio-controlled sailplane, Quicksilver MX Ultralight).  We also see similar dynamics in older hang gliders, where ample roll stability2 is created by  the highly swept shape of the delta or modified delta wing.  In many of these older hang gliders, additional factors contribute to roll stability.  These factors include a) some amount of dihedral, and b) a point of connection between the pilot's harness and the airframe that is well below the center of mass of the airframe, so that the resulting low CG contributes a strong stabilizing "pendulum effect" even when the pilot exerts zero force on the control bar.

For a basic description of paraglider turn dynamics, see this ASE answer -- How do paraglider controls work? . The answer explains how applying "brake" on one side modifies the lift vectors generated at various points along the arc of the wing in a way that generates a roll torque.

The present question is asking not what causes the roll torque into the turn when the brakes are applied, but rather why does the roll rate eventually drop to zero even with the brakes still applied. Clearly some aerodynamic force or torque is "trying" to roll the paraglider back toward wings-level.

The answer is that the turn involves some sideslip.  The aircraft is yawed to point slightly toward the outside or high side of the turn, relative to the direction of the flight path at any given instant. One cause of this sideslip is the simple fact that during turning flight, the outboard wingtip travels along a larger circumference and therefore must move through more air in a given unit time than the inboard wingtip, so it tends to experience more drag than the inboard wingtip.  The extra drag from the deployed brake on the inboard wingtip partly compensates for this, but not fully.  This makes the wing fly in an attitude where it is yawed to point slightly toward the outside of the turn relative to the actual direction of the flight path at any given instant.  In other words, the wing is constantly experiencing a sideways airflow component, toward the outside of the turn.

Notice that the arched shape of a paraglider wing exposes a tremendous amount of surface area to any sideways component in the airflow.  Ordinarily when we give an aircraft an anhedral geometry by lowering the wingtips in relation to the wing root, this interacts with any sideways airflow to generate a de-stabilizing roll torque, in the "upwind" direction, which in a slipping turn, would be away from wings-level.  This destabilizing roll torque component exists in the paraglider case too, but it is dwarfed by the stabilizing "downwind" roll torque caused by the fact that the center of area of the wing is so high above the CG of the whole system.  Since the wing is so high above the CG of the whole system, any aerodynamic sideforce generated by sideways airflow against the wing during the (slipping) turn will contribute a strong dihedral-like roll torque in the "downwind" direction, toward wings-level.  So will the wing's drag vector, because the glider is "pointing" a different direction than it is actually flying, and the drag vector acts parallel to the flight path.  Since these effects are both related to the fact that the CG of the whole system is located far below the center of area, they are sometimes collectively described as a "pendulum" effect, though we need to be cautious not the invoke the idea that the aircraft is somehow directly "feeling" the direction of the weight vector in a way that is not dependent on sideslip.3

So the answer to your question of why the bank angle does not continue to increase even when the brake application is maintained, is essentially this:

Turning flight in paragliders, as in many other rudderless aircraft, always involves some sideslip.
 The resulting sideways component in the relative wind acts on the center of area of the wing, high above the CG of the whole system, to generate a roll torque towards wings-level.

Here's one more nuance to consider in closing: we should note that when we initially apply "brake" in wings-level flight, the increased drag on the "braked" wing initially will "steer" (yaw) the glider into a skid in the intended direction of turn, so that the glider is actually pointing slightly toward the inside of the turn relative to actual flight path at any instant.  At this point the glider is "feeling" a sideways component in the relative wind toward the inside of the turn.  So at this point the interaction between the sideways airflow and the wing surface area, high above the CG, is actually generating a torque to help roll the wing toward a steeper bank angle.  Only once we establish a significant roll rate, and/ or
 a significant bank angle and turn rate, do we see the glider adopt an attitude where it is yawed slightly toward the outside of the turn, so that is "slipping" rather than "skidding".  (This answer has focused on how turning tends to cause sideslip; to read about how rolling also tends to cause sideslip see this section on adverse yaw from the excellent "See How It Flies" website.)  All the same can be said of an airplane with lots of dihedral that has no ailerons but rather uses the rudder for roll control-- like many radio-controlled sailplanes-- when we first apply rudder to enter a turn, we know the aircraft must be skidding, but as the bank angle increases and we settle into a steady turn at constant bank angle, we know the aircraft must in fact be slipping, even though we are continuing to hold some rudder input into the turn.  If the aircraft were not slipping at this point, the net roll torque could not be zero, due to the fact that the wing on the outside of the turn is moving faster through the air, and tending to generating more lift, than the wing on the inside of the turn.

Highly related -- Does "pendulum effect" apply to hang gliders or any aircraft?

Footnotes --

1 -- It is not the intent of this answer to suggest that a turn in paragliders is always, or typically, or ideally, accomplished using brakes alone with no weight-shift.  Weight-shift, where the pilot leans in the harness to rock his body to one side and load up one side of the suspension system and unload the other side, is another way to turn.  Both methods may be used in combination.  However the original question was focused on a turn carried out with the brakes, so this answer is as well.

2 -- This answer uses "roll stability" to mean a tendency to roll toward wings-level.  Other alternative terms might be used to avoid suggesting that the aircraft is tending to maintain a given bank angle, but "roll stability" is the phrase we'll stick with for this answer.

3 -- "Keel effect" is another term that is sometimes used to describe the stabilizing effect of a low CG position, though this is also somewhat problematic, for two reasons.  A) It would be better to call it the "keel weight effect", because an unweighted keel (think of a lightweight centerboard that may be raised or lowered at will) actually contributes a net hydrodynamic roll torque in the opposite direction during sideslip (sideways drift), tending to roll the boat in the upstream direction.  B) The righting effect of a heavy keel weight is actually not dependent on sideslip at all-- buoyancy creates a righting moment even when total velocity, and therefore sideslip velocity, is zero-- so we still have the issue that we were trying to avoid by not using the term "pendulum effect", namely that we'd like to avoid suggesting that a (non-buoyant, e.g. heavier-than-air) aircraft in flight can somehow "feel" the direction of the gravity vector and therefore "sense" when the aircraft is tilted away from level, even if sideslip is somehow completely eliminated by appropriate rudder usage or by any other means.

Addendum--

This answer has referenced a "skid" as the turn is first initiated with brake, and a "slip" once the turn is established.  This begs the question, "what about the roll torque created as the pilot's body tends to swing to the left or the right, just as a slip-skid (inclinometer) ball would, due to the apparent forces created by the slip or the skid?  Doesn't this play a key role in the balance of roll torques on a paraglider?"

Or in other words, "Isn't there some additional sort of 'pendulum effect' that we have not yet fully considered?"

At least one answer to the related question "How do paraglider controls work?" has in fact focused on apparent inertial forces caused by the pilot's body "not want[ing] to turn (yet)", purportedly causing the pilot's body to "swing" against the intended direction of turn as the turn is being initiated, thus creating a roll torque.

The truth is that we can consider the paraglider and pilot to be a single, essentially rigid sytem.  The lines do not go slack in normal flight.  The pilot is fixed in position under the wing by the triangular geometry of the multiple suspension lines.  If we want to analyze the motion of the whole body, it is not necessary to take into account the fictitious "centrifugal force" created by turning, or any other apparent inertial force.  (An exception would arise if the aircraft were rotating very rapidly about one of its axes-- for example a very high rate of yaw rotation, somewhat similar to a flat spin in a conventional aircraft, might tend to flatten out the canopy into more of a horizontal line, due to "centrifugal force".  Similarly, very high rates of pitch rotation play a key role in the dynamics of certain aerobatic maneuvers, such as spiral dives, in paragliders.)

The apparent tendency of the pilot to "swing" toward the inside of the turn in a slip, and toward the "outside" of the turn in a skid, thus imparting a roll torque to the wing, is in fact already fully accounted for in this answer.  We account for that roll torque when we note that the sideforce created by the impact of the sideways airflow against wing acts high above the CG of the whole system and thus creates a roll torque.  The apparent sideways force experienced in the reference frame of the pilot in a slip or skid, is in fact simply the mirror image of the sideways component of the real aerodynamic force generated by the aircraft during the slip or skid.  If the aircraft could somehow slip or skid sideways through the air without generating any aerodynamic sideforce, then no roll torque would result.  Also, if the aircraft could somehow slip or skid sideways through the air without generating any aerodynamic sideforce, then the pilot would experience no apparent tendency to swing to one side.

After noting that during a slip or skid, the sideways airflow against the wing generates an aerodynamic sideforce that acts high above the CG of the whole aircraft-pilot system and thus generates a roll torque, it would be erroneous to suggest that the apparent tendency of the pilot's body to "swing to one side" in a slip or a skid somehow contributes an additional roll torque about the wing's center of lift or about any other point.

Additional content on ASE relating to the ideas in this addendum--

(Q) Forces "felt" by pilot, G-meter, inclinometer--are they the aerodynamic forces generated by the aircraft, or the sum of weight+centrifugal force?

(A) Forces "felt" by pilot, G-meter, inclinometer--are they the aerodynamic forces generated by the aircraft, or the sum of weight+centrifugal force?

(A) Forces "felt" by pilot, G-meter, inclinometer--are they the aerodynamic forces generated by the aircraft, or the sum of weight+centrifugal force?

(A) Forces in a slipping turn


Can a weather balloon move horizontally? How does a hobby weather balloon control its flight path? Just it just keep rising straight up vertically, always at the mercy of the winds, being swayed side to side?

Unlike a rocket/drone, it does not have an engine/motor that can be controlled remotely. So if I want the balloon to hover over a particular area and send me images (a particular section of a forest to watch for wildlife activity), how do I do it?

All weather balloons seem to be aimed towards gaining altitude and taking NASA like images, but is there a way to move a balloon horizontally and not just vertically

An ordinary weather balloon cannot maneuver horizontally (unless an external force is applied to it) because it lacks the means to do that. It has only one purpose, to soar up to the altitude where the air pressure inside is more than outside and then burst.

If you want it to steer, you can add steering servos (as mentioned in this PDF). Of course this will add cost and complexity.

There are some websites for Balloon Trajectory Forecast, which might be helpful.

Only if Larry Walters had thought about this, things would have been different for him.


Why is there a strip of uncontrolled airspace between Russia and Norway? The airspace between Russia and Norway over the Barents Sea is an uncontrolled air space; no FIR is set.

Illustration taken from this document.

This area is like a corridor from the Scandinavian peninsula to the North Pole. It only requires several minutes by a heavy airliner to pass east-west.

Why is this relatively small area not controlled?

Details of the No FIR area

The area extends on 175,000 square kilometers:

From ≈70°N (Bodø FIR) to the North Pole.
From 30°E to ≈32°05'E, and to 35°E for a portion east of Svalbard archipelago.

VATSIM Murmansk sectors (ATC simulation). Source

Border dispute

This Barents Sea strip is of major importance, and has been subject to a dispute between Norway and Russia for 44 years. The reasons include:

This area has been the maritime border between East and West blocks during Cold War (the country is neutral, but still a founding member of the NATO).
Norway is a country with many resources coming from the sea (fish, oil, gas), the sea area controlled by the State is six times its land area.
The Barents Sea is a location with multiple oil and gas fields to be exploited. The large Shtokman gas field (label "5" below) discovered in 1988 happens to be in the vicinity, an agreement was signed between Norway and Russian Federation for the development of the field, but only in 2005:

Oil and Gas in the Barents Sea (red dots are gas fields). Source
The area encompasses the most direct potential route between Europe and the Pacific after the ice floe has melt down.

This dispute was closed when a new treaty entered in force on July 2011 with the border crossing the 175,000 square kilometers disputed region in the middle.

(Source: BBC)

While the border is now settled, responsibilities for air traffic control are still to be formally defined by international bodies.

Currently transiting flights have to be authorized by respective authorities before operating in this area, e.g. London-Tokyo flights using Arctica 1 route, noted B483 on first picture. In addition of commercial flights, the Arctic region is highly monitored by manned and unmanned aircraft.

ICAO and Eurocontrol status

ICAO wants to resolve this issue of missing FIR:

  8.1 IATA brought the attention of the Group to a portion of airspace of unassigned responsibility, extending from the North Pole over the
  High Seas between Bodo Oceanic FIR, Sondrestrom FIR and Murmansk
  Oceanic FIR (Appendix E refers). Considering the increase d interest
  of establishing new ATS routes through that airspace, the Group agreed
  on the following Conclusion:

  TRASAS Conclusion 2/4 – Airspace of Unassigned Responsibility over the
  Arctic Ocean
  That the ICAO Secretariat be invited to take the
  necessary actions to resolve the pending issues regarding the portions
  of airspace of unassigned responsibility extending over the High Seas
  between Bodo Oceanic FIR, Sondrestrom FIR and Murmansk Oceanic FIR

Source:
Report of the Second Meeting of the Trans-Regional Airspace and Supporting ATM Systems Steering Group (TRASAS/2) (Bangkok, Thailand, 18-19 March 2008)

There is a proposal under Eurocontrol auspices (proposal 95.012) to close the topic by Summer 2021:

  FIR border realignment Murmansk FIR / Bodø FIR / Norway FIR:

  Objective: To resolve the long-standing issue of the unallocated
  airspace (NO-FIR area) between Murmansk FIR and Bodø FIR / Norway FIR.

Source: European Route Network Improvement Plan 2019-2024

No aeronautical services

Flying in a no FIR area (when such territory is not forbidden to aircraft) means there is no information service provided from the ground. Flight information service consists on informing aircraft about meteorological events, known other aircraft position and intentions and aids availability. Other services are not available either: No alerting (search and rescue) and no ATC. The related airspace belongs to none of A, B, C, ..., G classes.

For those who want to know more about FIR and Oceanic Control Area, see Who manages International Airspace Traffic?

No FIR areas in general

Regarding the existence of "No FIR" areas:

  3) FIRs have not been established for a few areas in the world.
  These are commonly called uncontrolled information regions or “no
  man’s land.” The largest of these areas is in the South Atlantic
  Ocean, annotated as “No FIR.” Flight Information Services (FIS) also
  do not exist in the high altitude structure in other large areas
  (above the top of controlled airspace). Within no man’s land, aircraft
  separation (prevention of collision) is entirely the responsibility of
  the PIC. Advice and information for the safe and efficient conduct of
  flights is not provided from an ATS unit. An ATS unit does not provide
  alerting services related to search and rescue.

Source: FAA 8900.1 - Flight Standards Information Management System - FSIMS (Vol 4-105-C-3)


Why does Logan Airport's Runway 32/14 only have arrivals on the 32 heading? I was going through this PDF document on Logan International Airport's runway usage and I saw that Runway 32/14 only has arrival activity. Why is that the case? Is this the the reason or part of it why there are only stripe marks on the side of the runway close to "32"?

(Much of my answer below will be drawn from "The 30-year saga of 14/32", a 2006 Boston Globe article which is unfortunately subscription-only but which I have access to via an institutional database.)

Runway 14/32 has been a long-standing bone of contention at Boston Logan.  Like many urban airports, Boston Logan is constrained by the fact that there are many people living nearby who don't particularly like jets flying low over their houses, and who are willing to organize in opposition of any increase in operations at the airport.   Massport, the organization in charge of Boston Logan, had originally proposed to build a new runway in the late '60s.  This met fierce opposition from community members in East Boston who were opposed to additional take-offs and landings over their homes.

  [I]t's taken no less than 33 years for 14/32 to become reality, a testament to how politically charged Logan expansion has been ever since demonstrations in the 1960s, when East Boston mothers lay in the streets to protest the destruction of Eastie parks and homes.  ...

The Hyatt Harborside Hotel (now the Hyatt Regency Boston Harbor) was built in the 90s to act as an impediment to runway expansion:

  In the 1990s ... Frederick P. Salvucci engineered construction of the 270-room Hyatt Harborside Hotel, a stone's throw from the end of the new runway, largely to create as big an obstacle as possible to Massport extending 14/32 or using it for planes flying over the city.

In the end, Boston Logan was barred by court order from allowing takeoffs from 32 or landings on 14, except in emergency:

  By court order, use of 14/32 will be restricted to planes taking off and landing over Boston Harbor, so Massport will be legally forbidden - except in emergencies - from using the runway to let planes take off or land over South Boston and downtown.

This still allows for three runways to be operative when winds are from the northwest or southeast (along with 15L/R or 33L/R), so the hope was that even this "half-runway" would result in fewer delays at BOS during bad weather.  Whether or not this has panned out to be true in the decade since, I do not know.


What is the ATC phraseology to request a parallel track? What is the correct phraseology to request a parallel track due to weather for example?

Something like:

  OE-DLM, request parallel track to the east, 2 nm

Background: I am asking for non-airline operations under IFR. I am using the GTN 750  and there is a feature to easily create a parallel track with a specified distance to the original route and I would like to use this feature. For example, when I'm in cruise flight, I see a weather cell and want to fly next to it by offsetting my route.

It is rather simple:

  OE-DLM, request 2NM right of track.

However, weather circumnavigation is mostly done with headings. This way it is easier for the controller to predict your movement and thus preferred by many:

  OE-DLM, request heading 120 for the next 20NM to avoid (weather).

This way it is easy for the controller to predict your movement and he has an idea where your avoidance will be completed. Additionally you are not forced to turn behind a cell you weren’t able to look behind before.

Mainly done in oceanic airspace where you try to make your way through the ITCZ (InnerTropical Convergence Zone) is this variant:

  OE-DLM, request up to 20NM right of track to avoid (weather).

If approved you got a 20NM wide corridor to play in.

Flying offset is rather uncommon in the crowded European airspace (or generally every crowded airspace) but a normal thing everywhere else. China even uses it as a tactical separation method employed by the controller.


How do I obtain permission to fly in surface class E airspace under FAR-103? I'm a paramotor pilot operating under FAR 103, and I'm trying to determine who I need to ask for permission to fly in class E airspace that extends to the surface and is designated for an airport. For reference, the particular airport that I am inquiring about is GFL.
This appears to be the relevant subpart of FAR 103: §103.17

No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

Before I was aware of this restriction, the airport manager granted permission for me to fly to and from the airport with my paramotor. I have an access card, and he made clear the rules I am to follow, such as radio procedures and where I can launch and land.
However, this field does not have a control tower. Do I need to obtain permission from someone else to comply with §103.17? I'm not sure who the ATC facility having jurisdiction over that airspace is.

By default, all controlled airspace (class E and up) is owned by an ARTCC. In many areas, they delegate airspace (including class E!) to other ATC facilities, either a TRACON or a Tower.
Unfortunately, that info isn't on Sectional or Terminal Charts; you have to look in the Chart Supplement (formerly Airport/Facility Directory). For KGFL, we see:

ARTCC: BOSTON CENTER
...
ALBANY APPROACH: 132.825
ALBANY DEPARTURE: 132.825

So, this area is owned by Boston ARTCC and delegated to Albany TRACON, and it helpfully gives you the latter's frequency to call if airborne.
You probably can't reach them by radio from the ground, so you would contact their Clearance Delivery (CD) by phone, which for this airport is found in the remarks:

FOR CD CTC ALBANY APCH AT 518-862-2299.

Just tell them in plain English why you're calling and what you want, and be ready to copy any instructions they give you. They might, for instance, ask you to wait because they have other traffic going in or out in the next few minutes, or they might ask you to contact them in the air so they can keep track of you (I assume they won't see you on radar) and warn other aircraft you're there. Or they might not care at all and just tell you to have a good flight.


Why was the F-14 retired 15 years ago while the contemporary F-15 is still operational? The F-14 and the F-15 were designed in almost the same years and each one was at the top of its own "compartment" (respectively, US Navy and US Air Force).
However, almost 15 years ago, the F-14 was retired in favor of the F/A-18, surely less powerful but probably more multi-role (while the F-14 was improved too for ground attack), while the F-15 was not superseded by the new F-22.
So, the F-14 was replaced by a project that already had 16 years on its shoulder in 2006 — the F/A-18 was a project of the 80's — but F-15 continues to be side-by-side with the F-22.
Why these complete different approaches to fleet renewal?

There aren't enough F-22s to go around. Too expensive.
The F-18C/D Hornet that replaced the F-14 has itself been mostly replaced by the F-18E/F Super Hornet. The look the same, but the E/F is actually larger and more advanced. Not really the same aircraft.
Maintenance. Facilities on a carrier are restricted, simply due to space. If they can reduce the number of airframes to support on a ship, and still accomplish the mission, good.
Lack of mission for the AIM-54, which was the primary reason for the F-14.


Could an inflatable wing be installed on a Silent glider aircraft? Would it be technically feasible to install the Pneumagic inflatable wing on the Silent glider?

Here are some of my thoughts. I'm not fully convinced about the tradeoffs though, which would require a little more work to figure out if it was beneficial:

The wing appears a lot thicker in the article than in the silent glider, adding more drag than the solid wing which it currently uses. To get it as thin would be challenge, since the article suggests that the benefit of adding pressure is marginal for the same wing, so you could only make it thicker. In an convential design, the fabric can be a lot thinner than here were it's got to hold a lot pressure. I'm sure you have to add metal wires to maintain the shape under load, adding a weight penalty.
Using a pure air-based system, I'm also somewhat unconvinced about the 'responsiveness' at the controls, since You'd only be transferring the loads at a single point into the (flexible) structure, rather than across an area as in the article example. An analogy of this is to think of trying to apple a torque force to the center of a pool noodle in water, and to observe the ends relative to the center. You might end up having to make a rather extensive wing root structure to make this work.
The benefit would be portability, but since the silent glider has an engine, this would probably not be of a huge concern, since you could get it where you wanted it.

My verdict: It could probably be done, but I'm doubtful about the performance benefits. Then again, I'm only a first year aerospace engineering student, so you're welcome to come with thoughts and any criticism :)


What is the difference between microburst and windshear? When I read about these weather phenomena, I find that both of them depict the same thing, and have the same actions to avoid. So why are they differentiated?

http://www.myairlineflight.com/windshear.html
https://en.wikipedia.org/wiki/Microburst

A microburst is generally an intense down draft while wind shear can occur in any direction. It might be safe to say that a microburst is windshear but not all windshear is a microburst. From your linked pages

  A microburst is intense small-scale downdraft produced by a thunderstorm or rain shower.

and

  Windshear is any rapid change in wind direction and/or speed.


Are there any "alternative" passenger airline business models? (By passenger airline in this question I mean scheduled carriers, with at minimum a few aircraft with 50+ seats.)

I am aware of 3 main classes of airlines:

Hub-and-spoke (most major airlines)
Low-cost carriers (Southwest, Ryanair)
Regional (contractors that support more "spokes" for the majors)

Are there more? If so, where and how are they used?

Note: I accepted the answer that shows a clear example, but there are many other excellent answers below!

There's also the "Snowbird" model, like Sun Country and Allegiant Air, which primarily fly vacationers and snowbirds between sunbelt (San Diego to Florida) and the Carribean, and the Northern snowbelt states (Maine through Washington State, and Canadian border cities). They are low-cost carriers, with few or no code shares, no connections, no free amenities, and prices that decline as the date gets closer.

Here is Sun Country's route map.  Note that nearly all their flights are between Minneapolis (or Dallas) and vacation destinations.

Here is a part of Allegiant's route map, showing cities with flights to Phoenix/Mesa, AZ.  They have more routes than are shown here, but all their routes have one end in one of the "sun belt" cities marked in orange.


In what ways does the current FAA written exam differ from the Sporty's practice test? I am preparing to take my PPL written exam. I have been using the Sporty's practice exam program to gauge my progress? Recently I heard that the FAA has changed a few things about the tests. So I am curios: How the current written exam differs from the Sporty's practice exam?

Does the current written exam use the Airman Knowledge Testing Supplement for Sport Pilot, Recreational Pilot and Private Pilot?
Are the questions formatted in the same way as the practice question?
If you perform well with the Sporty's practice exam with an actual understanding of how you got to your answer, would you likely do well with the current test?

I took the PPL written exam this morning (9/30/2016), but I used the Jeppesen PPL materials to prepare. Although I cannot speak to the Sporty's study materials, the Jeppesen practice exam and supporting materials were identical to the questions on the real exam. I would assume that Sporty's will be (almost?) the same. I actually scored higher on the real exam than on any of the practice tests.

Yes, the current exam uses the Airman Knowledge Testing Supplement for Sport Pilot, Recreational Pilot and Private Pilot booklet.


How is spilled fuel cleaned up at airports? In an accident where an airplane leaks fuel onto the ground, how is it cleaned up?

Depending on the quantity, jet fuel can be cleaned up by use of a sump truck and dry absorbent material or if permitted by the airport and local environmental regulations, the fire department can spray water to wash it down the storm drain.


What is this plane spotted from Outer Banks, NC? What is this plane spotted from Outer Banks, North Carolina?

(USAF)

Judging by the single pair of pylon tanks, DIRCM (Directed InfraRed Counter Measure) heads near the tail and lack of armament on left side, and what looks like 4 bladed props, it is likely an MC-130H.


Could the Shuttle Carrier Aircraft do a transatlantic flight with a Space Shuttle orbiter on its back? Some of the STS backup landing sites were in Europe.

Of course, The STS would actually have to fly there only in case of extreme emergency, so the number one priority was just to save the lives of the crew members.

However, did NASA have a plan, or would it be doable to airlift the Space Shuttle atop an the Shuttle Carrier Aircraft like on this picture?

I'm especially curious about the range penalty induced by the additional drag of piggybacking the orbiter.

Picture credits: NASA / Carla Thomas, Public domain.

Short Answer
A procedure had been established to return from a Transoceanic Abort Landing (TAL) site to the Kennedy Space Center (KSC) using the Shuttle Carrier Aircraft (SCA). The maximum weight that could be ferried from Europe was approx. 87,000 kg, so so weight had to be removed from the orbiter prior to being mated.
The SCA had a maximum range, unmated, of 5,500 nautical miles, however when matted the range decreased to 1,000 nautical miles, using reserves. 4,500 NM were lost by carrying the orbiter. The SCA would have had to stop in UK, Iceland, Greenland, and Canada.
A test for in-flight refueling had been conducted but no solution was developed. From our friends at Space Exploration:

Studies were conducted to equip the SCA with aerial refueling
equipment, a modification already made to the U.S. Air Force E-4
(modified 747-200s) and 747 tanker transports for the IIAF. However,
during formation flying with a tanker aircraft to test refueling
approaches, minor cracks were spotted on the tailfin of N905NA. While
these were not likely to have been caused by the test flights, it was
felt that there was no sense taking unnecessary risks. Since there was
no urgent need to provide an aerial refueling capacity, the tests were
suspended.

A tailcone covering the 3 aft engines and the thrusters was used to reduce the drag and the buffeting on the SCA vertical stabilizers. It also protected the engine nozzles from being damaged in flight.
See below if you are interested by more details of the recovery plan.

Plan Used After Landing at the TAL Site
Operations to be conducted to return the orbiter to KSC were documented in a plan that couldn't be identified with certainty, however the US Department of Defense (DOD) plan to support the turnaround is quite descriptive of the operations. From DDMS TURNAROUND FUNCPLAN 3611-03 (C=TAL day):

The turnaround operation, to include redeployment of
personnel and equipment, may require up to 120 days to complete. [...]
C+18: JTF-DDMS staff coordinates with NASA for ferry flight route
support.
C+22: JTF-DDMS staff presents initial ferry flight support plan to NASA management.
C+26: NASA begins 24 hour turnaround operations to prepare and
mate the orbiter to the SCA for return ferry flight. [...]
C+53: Pathfinder and SCA arrive at landing site.

Slides explaining the DOD plan are also available.

TAL Site Operations
Each of the TAL site was equipped for the Orbiter landing and turnaround operations:

Navigation and landing aids
Weather equipment
Dedicated ground-support equipment
Emergency equipment
C-130 aircraft support

From Nasa Fact - Space Shuttle Transoceanic Abort Landing Sites:

Each TAL site is covered by a separate international agreement. The
TAL sites are referred to as augmented sites because they are equipped
with space shuttle-unique landing aids and are staffed with NASA,
contractor and Department of Defense personnel during a launch and
contingency landing.

Shuttle's Microwave Landing System (source)
In addition:

Safing and deservicing of the orbiter would be initiated by the
deployed TAL team and augmented by a team known as the Rapid Response
Team. [...]
The TAL site ground operations manager would initially be in charge
until relieved by a higher-ranking management official who would
arrive on the response/investigation team aircraft.
Within 24 hours, the response/investigation teams would arrive at the
TAL site aboard C-17 aircraft carrying personnel and equipment.  Most
of the equipment would come from Kennedy Space Center and Dryden
Flight Research Center in California.
Following the advance response/investigation teams contingent, the
Deployed Operations Team, consisting of additional personnel and
equipment, would begin arriving at the TAL site for the orbiter
turnaround operation. NASA estimates it would take about 19 C-17/C-5
aircraft sorties, a significant Navy sealift operation, and 450 NASA
and contractor personnel to complete the turnaround. [...]
Payloads and/or airborne support equipment will remain onboard the
orbiter for the flight back to Kennedy Space Center unless the
capability of the shuttle carrier aircraft, landing site location or
other requirements dictate other wise.

Lightening the Orbiter at the TAL Site Before Ferrying to KSC
Weight limits of the SCA:

Basic weight, NASA 905, 318,053 lbs (144,269 kg), NASA 911, 323,034 lbs (146,528 kg)
Maximum gross brake release weight, 710,000 lbs (322,056 kg)
Maximum gross landing weight, 600,000 lbs (272,160 kg).

From Space Transportation System Cargo Abort and Recovery Operations:

The ferry weight from contingency landing sites in Europe and Africa
is constrained to approx. 192,000 Ibs. (approx. 87,000 kg). The ferry
weight from the Pacific contingency landing sites is further
constrained to 154,000 Ibs. (approx. 70,000 kg).
This requires not
only removal of the payload but removal of Orbiter main engines,
tires, landing gear and other components as well. In addition, the
Orbiter Z axis (vertical) and X axis (longitudinal) center of gravity
location must be within a limited envelope, as shown in Figure 1.

From The Conquest of Space, Ferrying the Shuttle - Part Four: The Shuttle Carrier Aircraft:

A typical route might take the pair from
continental Europe to England, then on to Iceland, then Canada, and
finally to the United States.

(Additional information might be found in JSC-NSTS-08934-VOLUME-4, Space Shuttle Orbiter Ferry Plan.)

Mating and Demating the Orbiter
Photo gallery of Discovery mating at Edwards and demating at KSC (STS-114).

(Source: Nasa -- STS-114: Mission Complete)
The mating structure above couldn't be used at a TAL site, so a crane would be available for the operation:

Columbia being prepared at White Sands. Photo by Steve Schmidt.(Source: Abandoned and Little-Known Airfields)

Ferrying the Orbiter
From Nasa Fact, Shuttle Carrier Aircraft.
There were two SCA:

NASA 905: Obtained from American Airlines in 1974.
NASA 911: obtained from Japan Airlines in 1989.

They were B747-100 and B747-100SR, modified by Boeing into their SCA configuration.

(Source: Nasa Fact, Shuttle Carrier Aircraft)
They were engined by four Pratt and Whitney JT9D-7J, and had a fuel capacity of 316,307 lbs (143,477 kg).
The SCA didn't flight very fast: 250 kt or M .6, due to the drag from the orbiter and the additional vertical stabilizers. Its typical cruise altitude was also rather low to prevent freezing of the orbiter fluids:

with orbiter, 13,000-15,000 ft
unmated, 24,000-26,000 ft.

The range was hence a bit shorter than if it flew higher. Typical range:

Mated, typically 1000 NM (with reserves)
Unmated, maximum 5500 NM.


What are the advantages of a geared contrarotating turbofan? I read that this would be the holy grail of jet engines:

Next Gen NB Engines : Contra Rotating Turbofan Fan

Why is this so and what problems are stopping us from doing this?

what problems are stopping us from doing this?

In some sense, it's business reasons. Developing a brand new jet engine from scratch costs a lot of money. Usually the pricetag runs into the billions. It will often take 10 years from the time you start to develop a new engine until you see a single dime of profit. If you are the board of directors of an engine manufacturer, and you give the greenlight to develop a new product, you might be literally betting the entire company on the success of that new product. So, you have a tendency to be conservative. If you can get a 10% performance improvement from some new never-tried-before fancy contra-rotating fan thingy, or you can get a 5% performance improvement by keeping the same basic tried-and-true design but just tweaking the aerodynamics a bit here and there, you are probably going to go with tried-and-true. Eventually, a limit will be reached where the basic turbofan architecture cannot be tweaked anymore, and then you may see some new thing like this tried, but I don't think we are quite there yet right now.


Are directional instruments like an HSI or AHRS immune to magnetic compass error? Pilot educational curriculum includes learning about magnetic compass errors intrinsic to their construction.

A standard magnetic compass in an airplane erroneously shows turns when accelerating or decelerating on an east or west heading. They also read incorrectly during turns from the north or the south.

My question is about more advanced instruments like a fluxgate compass found slaved to an HSI or a magnetometer used in an AHRS. Are these systems impervious to the compass errors present in a magnetic compass?

The short answer is yes, but for different reasons.

The analog HSI in most aircraft that have them either has an internal directional gyroscope, or it is slaved to the directional gyro (more often the former than the latter as the HSI often replaces the DG). An analog DG/HSI must still be periodically corrected for precession error by levelling off, letting both instruments stabilize and then adjusting the HSI's card to the magnetic compass.

AHRS systems that power glass cockpits use a solid-state directional gyro that is corrected by a magnetometer (an antenna device that directly senses the relative direction of the magnetic field) rather than a floating magnet. This makes them impervious to the types of error commonly seen in floating compasses such as acceleration bias (which causes all the behaviors you mentioned). They can still be sensitive to nearby ferrous metal structural members and to electrical currents, requiring a digital version of "spinning the compass" with corrections input into the software that uses the magnetometer readings, and magnetic declination must also be accounted for (either mentally by the pilot, manually based on declination charts or in more sophisticated systems by directly incorporating position data from the GPS).


confusion between RNAV and RNP approaches and specifiations Ive been really confused between these two specifications recently. For example my research suggested that RNP has on board monitoring and alerting and RNAV doesn't require this, however then why must we compute a RAIM check before conducting an RNAV app when for RNAV specification no alerting or failure detection is required and hence TSO 129 may be used? Also doing my flying in Australia some ADs would state there is an RNAV app available for one runway and also an RNP, what additional requirements would there be in terms of pilot training or alerting etc for the RNP app. Appreciate all answers just trying to get a grip with this confusing concept!

RNAV was/is in the older model where each approach was designed around a specific technology, and any detected failure to meet the (assumed) fixed accuracy of that technology means you can't use the approach at all.

RNP is newer ICAO terminology under their Performance Based Navigation model, which essentially means they don't care how you get your navigation data, just how accurate it is.  The better your Actual Navigation Performance is (i.e. lower number), the lower the approach minimums you get to use.

TSO C129/C196 systems cannot be used as the sole navigation equipment because it only has fault detection, not fault exclusion; if the RAIM detects a fault, you have to stop using it and switch to something else.  (If you don't have RAIM, you have to actively cross-check the GPS, so you might as well just use the other system as primary.)  Notice the parallels to the explanation of RNAV above.

TSO C145/C146 do have fault exclusion, so they can be used as the sole means.  They also support SBAS (aka WAAS), which can offer much lower approach minima where available, but they will gracefully degrade to higher minima depending on the signal accuracy--which can vary over both space and time for the same equipment.  Notice the parallels to the explanation of RNP above.


Why is Concorde no longer in service? The crash of the concorde resulted in many deaths, but the crash was never caused by the concorde but by a plane that took off before it. Also airliners like the Boeing 737,747,and 777 have had accidents resulting in all deaths of the passengers and crew and was caused by the airplane, but are still in service today, so why are those airplanes still in service after the accidents and the concorde not in service after its accident that wasn't even caused by the concorde?

The crash was only one of the (albeit an important) reason for the grounding of Concorde. Actually, the aircraft was retired around three years after the crash. The main reason was that not enough people were flying it to keep it profitable.

The Concorde as a technological marvel, but it had a number of disadvantages:

The aircraft was costly- The program cost over $3B and produced 20 aircraft, of which 14 were used in commercial service.
Maintenance costs- The small number of aircraft and technological sophistication meant that the cost of spares was high and options limited.
Operating costs- The Concorde consumed nearly three times per passenger fuel when compared to the Boeing 747-100. Still, the aircraft made operational profit due to the high cost of tickets.
Recession- After 9/11 attacks exacerbated the global downturn in aviation due to recession, there was an enormous drop in first class air travel, on which Concorde was dependent on.

While announcing the retirement, British Airways cited

  commercial reasons, with passenger revenue falling steadily against a backdrop of rising maintenance costs for the aircraft.


Why do pilots cut the reverse thrust below 40 km/h? In a Microsoft Flight Simulator 2004 Boeing 747 landing tutorial, it was said to cut the reverse thrust after decelerating to 40 km/h.

What happens if that was ignored all the way to a complete stop? Would the plane start moving backwards?

The question speaks of a very old 747 landing tutorial. And as such I take that to mean it would be of a 747-100/200 aircraft, and that's the reference point I'm answering from.

First, concerning the comments below the question that wonder whether you have to worry about unwanted objects on a runway at an international airport, there is no such thing as a completely clean runway, even after sweepers have just finished clearing the runway. There is always some grit—it's a matter of degree—and while ingesting it isn't going to cause immediate problems, over time it will abrade the fan blades and thus the engine performance. This may not apply to higher, body-mounted engines rather than engines mounted below the wing, at least we didn't worry about it when I was flying 727s. If our taxi speed with engines idle was getting a little fast, we would sometimes deploy the reversers of the center, S-duct engine in the tail for the taxi.

Next, why take any risk if there's little benefit to be gained. The greatest effect of reverse power is immediately after touchdown when the aircraft speed is highest. As the speed slows, reverser effect decreases rapidly.

  (...) cut the reverse thrust after decelerating to 40 km/h.

40 km/h is only 22 knots. That's a taxi speed. I spent 10 years on 747-100/200 aircraft at two different carriers, and we never used powered reverse anywhere near taxi speed.

The 747-100/200 reverse levers are on the forward edge of the thrust levers. You can't raise them unless the thrust levers are in the idle position and the air-ground sensors show you on the ground. When you do raise them, they first come to a near vertical position that deploys the reversers but leaves engine power at idle. If you pull the reverse levers aft to get greater than idle reverse thrust, you're doing so against a spring loaded force such that if you relax the pressure, the engines will return to idle.

  What happens if that was ignored all the way to a complete stop? Would the plane start moving backwards?

Staying in reverse down to 0 km/h is simply not done. However, let's say you did it. If you had the reversers deployed but were at idle power, I doubt the aircraft would move backwards.  Reverse thrust is not as efficient as forward thrust. Depending on the engines and how heavy you are, 747-100/200s can start to move forward at idle forward thrust, but the usual procedure is to come to "breakaway" thrust to get the aircraft moving and then go back to idle.

If you came to 0 km/h in reverse with significant engine power, then, yes, you would start to move backward. But, of course, the chief pilot would hear about it, and probably fire you.

I know of one instance where a 747 was backed up using reverse thrust to clear a runway in an extreme situation in a third world country, so it can be done.


Is there a conventional notation or name for the slip angle? Angle of attack is usually designed by alpha (as in alpha_prot).

Is there such a conventional notation or name for other axes? I'm particularly interested in the slip angle.

Sideslip angle is commonly notated as β (see e.g. https://en.wikipedia.org/wiki/Slip_(aerodynamics)).


Why are the cockpit windshields on the A350 black? The newest planes like the 787 or A350 have a different kind of cockpit windshields:

Picture source

The A350 has "black" windshields:

Source

Does anybody know why are the windshields different?

The gold tint on the 787 window is a conductive coating for de-icing.

  Dreamliner jet flight-deck crews will view the world through commercial aviation's largest windshields by PPG, kept clear of fog and ice with gold and indium-tin oxide heating systems. source

The A350 also has a windshield anti-ice system. It is referred to in this answer. One thing both aircraft have in common is that they use curved windshields. I'm not sure if that adds to the black look. But what does add to the black sunglasses look is that the window frames are painted black.

Source

Btw: There's a thread on Airliners.net where most of them seem to despise the black window frames.


What are the climb rates during the different phases of flight of an A320? I have read about common climb rates for an A320. It is said that the initial climb rate for an A320 is between 15-20° and it differs depending on the weight and also the altitude.

I therefore have the following questions:

Do climb rates for a given flight mission stay constant in one phase of flight (e.g. until reaching 1500ft altitude) and then change at a specific flight level or are they continuously adjusted?
Do given climb rates exist for (one arbitrary) given flight mission?
Is there a method to calculate the change of climb rates depending on altitude and weight?
Are there sources like papers, reports, manuals that will work for genuine citation?

According to the EUROCONTROL Performance Database, the usual climb rates and speeds for an A320, for ATM purposes, are those depicted on the image below:

Source: https://contentzone.eurocontrol.int/aircraftperformance/details.aspx?ICAO=A320&ICAOFilter=a320

Note that rate of climb (ROC) is given in feet per minute, not degrees. If measuring degrees, you are talking about the climb gradient, not climb rate.


What is a registration mark or number? Does every single aircraft have a unique registration mark or number? If, for example, 2000 Boeing 777 units were produced, do they have their own registration number? And how is that registration number regulated? Who keeps the number? What is that registration intended for?

Yes, every aircraft has a registration number--or "tail number" since it is commonly painted on/near the tail. This links each make/model/serial combination to a specific owner, similar to a car's license plate.

Each country assigns tail numbers with that country's unique one-, two- or three-letter prefix(es), e.g. "N" for the USA and "XA" for Mexico, followed by some number of letters and/or digits according to their chosen scheme. Some countries allow requesting a specific number not already in use (or reserved), similar to vanity license plates.

For non-commercial flights, a plane's tail number is used as its radio callsign since it's guaranteed to be unique. Commercial flights typically use the carrier's callsign plus flight number.


Does a CFI have to be a CFII to fly with a student in IMC? A CFI wants to fly with a student under the following conditions:

CFI has ASEL pilot cert with Instrument Rating
CFI has ASEL Instructor cert with NO Instrument Rating
CFI is current in all regards
Flight will be IMC
The Training will not count toward a rating
Will be logged with dual given and actual intruments

No, a pilot with CP-ASEL-IA and CFI-ASE who is instrument current can take a student into actual IMC, and can even log it in both logbooks as dual training if the instruction is on the area of operation described in FAR 61.107(b)(1)(ix) "Basic Instrument Maneuvers" (etc) because that AOA is towards a private pilot certificate. However, this would be a Dumb Thing to Do because a CFI with no -I does not have any training flying instruments from the right seat, which is a skill that takes quite a bit of practice.

The thing that a CFI-I allows a person to do is to provide training on the areas of operation in FAR 61.65 towards an instrument rating.


Replacing or supplementing turbofan with electric fan Could you replace 2 B747 engines with electric turbofans? Could the 2 standard turbofans produce enough power to allow electric cruise with jets used for take off?

Answer to the first question: yes you could, and the answer to the second would be theoretically yes, but it would make no sense. Here's why:
When designing aircraft, a simplified version of choosing the engines would be that the plane should be able to safely climb with half of the engines installed. So: cruising power is significantly less than T/O or climb power. Basically this imaginary hybrid 747 would be able to cruise with two engines only, be they electric or conventional.
If the question is about generating electricity with the 2 turbofans, the problem is that to provide electricity for the electric fan so that it could maintain cruise speed, the conventional engines would, of course, have to be running at rather high power setting, and therefore they themselves would provide enough thrust for cruise. Assuming (quite liberally) efficiency of 90% for both the generators and the electric motors, we would end up with a maximum efficiency of 81%. At least 19% of power would be lost along the "powertrain".
If the electricity for cruise was to come from batteries, the setup, simply put, will not work. The weight of the huge battery bank is way too heavy for economical operation.
A little more sensible setup would be one where conventional engines are assisted by electric fans or such for takeoff and climb, and the electricity would come from batteries. Here again, hauling a heavy battery set for great distances is not very efficient, even if the battery bank could be smaller in this case. in addition to this, the electric fans would cause drag during cruise if the electric propulsion system is not integrated into the conventional engine somehow.


What drives the shape of an engine's intake on a fighter jet? Rectangular intakes have more corners which might increase subsonic pressure losses and would weigh larger than a pitot (Semi-circular) type intake. Are the designer drivers solely based on supersonic pressure loss improvement? Or for area-ruling? Am I missing something here?

F 16 has a pitot (Semi-circular) type intake whereas JAS 39 Gripen has a rectangular one. I wonder why.

Edit: The question is in reference to a fighter aircraft intake which employ fuselage buried engine configuration in-contrast to wing mounted or externally integrated engines.
Fighter aircraft intakes are more complex when compared to simple cowl-lip configurations designed for larger commercial engines.
Intake shape,size,location are function of wide variety of parameters, so something must be influencing the intake entry cross section of a fighter aircraft configuration.

Are the design drivers solely based on supersonic pressure loss improvement?

Yes. And sometimes a few more considerations need to be taken into account.

We have covered the reason for intake shapes well on this site, but the details must be collected from several answers. In a nutshell: Higher flight Mach numbers need more elaborate and heavier intakes in order to convert the kinetic energy of the flow into pressure. A pitot intake is light and simple, but a poor choice for speeds in excess of Mach 1.6.

Rectangular intakes are normally chosen in order to make internal, moveable ramps possible which create a cascade of shocks in order to slow down the flow as efficiently as possible. Such designs are typical for Mach 2 aircraft (think Concorde, F-14, F-15, XB-70). Another way would be a central intake with a moveable spike, but those had to make way for big radar arrays in more modern designs. The JAS-39 intake is a little special: It sits next to the fully moveable canards, and those need a vertical wall in order to minimise the gap between canard root and fuselage/intake structure. Yes, a round intake would be slightly lighter, but is impossible due to the situation of the canards.

Detail of JAS-39 canard, taken from this picture.


How does an ADIRU convert ram air pressure from the Pitot tube into Airspeed? I know how the analog Airspeed Indicator shows the Airspeed from the ram air pressure from the pitot tube. But I'd like to know how an ADIRU converts the raw pressure data to Airspeed that is displayed on a PFD.

What sensor is used for this purpose?
What exactly happens inside the ADIRU?
Does the sensor and / or procedure differ from unit to unit?

Usually there is an intermediate module ADM (air data module) that makes the conversion from analog pressure into digital numerical value. One ADM will do this for  the ram air pressure, another ADM will do the same for  the static pressure.
Their data are sent on Arinc numerical buses to the Air Data part of the ADIRU.
Airspeed is basically the difference of the received data.
Please refer to the following diagram:

https://upload.wikimedia.org/wikipedia/commons/f/ff/Airspeed_indication_system_-_fly_by_wire.png

Inside the ADM you have:
first of all a PIEZO that will convert the mechanical pressure into electrical voltage, a piezo is somehow what you have in a balance you may use to get your weight. In the balance you have too an analog digital converter since the weight is displayed as a number.

Similarly in the ADM, the next item is an analog/digital converter that will convert the electrical voltage into a binary number that will be sent on the ARINC bus to the ADIRU

You might wonder why the ADM is apart and not inside the ADIRU, it is done like that to have the shortest possible pneumatic tube.
 I do understand I haven’t been enough clear in my previous answer that has been deleted, therefore it is important to understand the following:

The ADIRU managing Air Data and Inertial data, is located in an electronic bay, the pneumatic piping is not sent to the electronic bay, that will make a long distance, therefore no pressure conversion is done by the ADIRU, but by intermediate modules, the ADMs