Why isn't the F-15E called F/A-15? In my understanding, "F" stands for "fighter" (air-to-air) and "A" for "attack" (air-to-ground). E.g.,

the F/A-18 Hornet can attack air and ground targets, which is why it's called F/A-18.
the A-10 Warthog is used as an attack aircraft, which is why it's called A-10. However, it's also capable of attacking air targets using IR missiles.

The F-15E Strike Eagle is also capable of attacking air and ground targets. So why is the Strike Eagle still called F-15E and not F/A-15?

The aircraft you are mentioning are completely different from each other and some of them are not even named according to the US Tri service Naming System.

In general, the aircraft retain their original designation given even though the later versions have little in common with their predecessors.

The F 15 was a direct result of the studies that followed the Vietnam war and the a response to new generation Soviet aircraft like the Mig-25.

"McDonnell Douglas F-15A USAF". Licensed under Public Domain via Wikimedia Commons.

The F-15 was designed purely as a air superiority fighter, with full emphasis on maneuverability and agility with "Not a pound for air-to ground!". The first to variants of the F-15 were called F-15 (single seat) and TF-15 (two seat), which were retrospectively named F-15A nd F-15B after the introduction of F-15C. The F-15E was a strike variant; however, it could defend itself against enemy aircraft and thus retained the 'F' title.

"F-15E Strike Eagle" by Gerry Metzler - IMG_214. Licensed under CC BY-SA 2.0 via Commons.

The case of F/A-18 is different. The initial plan was to purchase three different version of the aircraft, F-18A (Fighter), A-18A (Attack) and TF-18A (Trainer). However developments in avionics and some design changes led to the
first two versions joined together as F/A-18A and the trainer version being named F/A-18B.

"US Navy 050803-N-0295M-148 An F-A-18B Hornet, assigned to the U.S. Naval Test Pilot School, folds-up its landing gear after taking off for a training flight from Naval Air Station Patuxent River, Md" by U.S. Navy photo by Photographer’s Mate 2nd Class Daniel J. McLain

Most of the aircraft in service today are multirole and their names mostly reflect what their intended purpose is rather than their actual purpose. With modern avionics and high precision weapon systems, almost any aircraft could be made a strike aircraft

It is to be noted that the naming convention is followed only loosely in some cases. A good example is the F-117 Nighthawk, which is not a fighter aircraft in any sense of the word.


On an engine failure, can I contact the tower instead of 121.5? Let's say I am cruising at a very high altitude with my Cessna, like at 5000ft+ AGL, and I got an engine failure.

After going through the checklist, my engine is still not working, but I realized that I could easily land the airplane on an airport near me with my gliding speed.

Can I just talk to the airport, whether controlled or uncontrolled and take whatever runway is best for landing, instead of declaring an emergency on 121.5 and squawk 7700?

Thanks.

I'm basically going to echo what's already been said, but with a twist.

Yes, of course you can keep talking to the people you're already talking to, on the frequency you're already on. If you're actually talking to someone already, that's probably your best bet, not least because they know you're there.

In fact, especially if you're in controlled airspace, one might argue that speaking up on the radio immediately upon engine failure isn't a horrible idea, if and only if you are able to do so safely. Even a simple "Springfield tower, Cessna '345, pan-pan-pan, engine failure, attempting restart", maybe even while you're pulling out the in-flight engine failure checklist, will give ATC a heads-up that, at the very least, you won't be able to maintain altitude. That would allow them to take your situation into account when vectoring other traffic. If all they see is a VFR GA plane starting to descend, for all they know that's perfectly intentional maneuvering on your part.

Only if you can't reach anyone (who is able to help) on the frequency you're currently on does it make sense to consider fiddling with the radio to switch to 121.5. Fiddling with the radio to change frequency should be well down your mental list of actions to take.

The same reasoning applies to the transponder; you certainly can change to 7700 if you want to and you feel that it is appropriate, but you don't have to. Squawking 7700 will cause your radar return to light up like the proverbial christmas tree at ATC, but saying mayday or possibly declaring emergency is also a pretty good way to get peoples' attention in a hurry.

Once you realize that the engine isn't going to cooperate in restarting, and especially if you realize that you'll be able to make a controlled (but forced) landing on the nearby airport, I'd pretty much just treat it as an ordinary landing, with the caveat of declaring at least pan-pan-pan, possibly mayday, and telling ATC that you have no engine power. Let them deal with the other traffic and just focus on executing a safe landing and vacating the runway as quickly as you are able, but no quicker.

If you realize that the engine isn't going to cooperate, and that you can't make it to the nearest airport, well, that's when a forced outfield landing likely becomes a tempting option. Telling ATC (possibly on 121.5, with the above caveat on whether you're already talking to someone) what your position and intentions are will still allow them to get help out your way in case you do botch the landing. If you do make it down safely, be sure to tell them, relaying via another aircraft if necessary.

Aviate, Navigate, Communicate is a good rule of thumb, but it's a rule of thumb, not dogma. If you're able to communicate while still aviating and navigating, then doing so might help ease at least the burden of navigation.


Why is an unpressurized takeoff performed? Why would an aircraft perform an unpressurized takeoff? What conditions lead to this being beneficial?

Typically, the pressurization system is run by engine bleed air. Using that bleed air means you have less engine power available than is maximally available with the bleeds off. If you're on a runway that requires all your power, you do a no-bleeds takeoff, which means you have no pressurization. Shortly after takeoff you would turn the bleeds on.


Why does the N1 on a FJ 44-2A turbofan go to 104.4%? Whilst watching a video of a Beechcraft Premier A1 Jet whilst in the cruise at FL330 I noticed the N1 on both engines were at 104.4%.

Can anyone explain why they can go over 100%?

100% is the designed speed - sometimes it can be proven, that slightly more is still safe to operate on. Now: Change all scales, so that the new full power is once again 100% - or allow more than 100% on the scale? As a matter of fact, this is much easier to do, as the software does not have to be changed a lot, dependencies to other components are still valid, the recertification mostly is also easier, ... This also has been done for the Space Shuttle Main engines, routinely operating at >100% nominal ( = design) thrust.


What are the most number of propellors that a rotorcraft has been flown with? If you had 1000 small propellors you could accelerate upwards many times faster than with 4 large propellors.

What are the rotorcraft experiments with the most number of propellors ever?

This guy is actually flying with 76 rotors.

But I might argue that your "more rotors is faster" idea may be flawed, smaller propellers are less efficient (because the further from the center you are, the faster the blade is moving, if I'm not mistaken), so the trade may be fewer, more efficient, propellers for a larger number of less efficient ones.


Why does the Apache create much more rotor noise than the A-129? The AH-64 Apache attack helicopter was upgraded several times after its first flight in 1974. The Apache Longbow was a major upgrade which entered service in 2003. On the other hand, Agusta A-129's first flight was in 1983.

I have two questions:

Why does AH-64D have much high rotor noise? Why wasn't there any effort to suppress the noise in the upgraded versions?
Why does A-129 have lower rotor noise (i.e. the chop chop sound is almost absent) even though its tail rotor isn't covered?

Because they are very different helicopters, as egid already pointed out.

The Apache is twice as heavy as the Mangusta (5165 kg vs 2530 kg empty)
The rotor diameter is also bigger accordingly (14.6 m vs 11.9 m)

A Chinook transport will make more noise than an Apache. An Apache will make more noise than a Mangusta. Different helicopters and different weights that have to be kept airborne.


Can you push the throttle forward while using reverse thrusters? Can you push the throttle forward while using reverse thrusters (for turbofans)? Does this have any effect, such as strengthen the "reverse" air blanket? Is it ever used?

In the B757 aircraft (RR engines), for example, the "reverse" thrust levers can only be raised/employed when the aircraft is on the ground and the "forward" thrust levers are in the idle stop position.  During reverse thrust operation, the forward thrust levers cannot be pushed forward.

This is different than many Turboprop airplanes


What is a Fuel Over Pressure Protector? What is a fuel over pressure protector on the A320 and other aircraft? What is the purpose of this hole?

It is possible to overfill a wing. You fuel the aircraft when its wing is cold. Later as the aircraft sits on the ramp the outside temp increases causing the full to expand in an already full wing. So they have the overflow system dumps the excess fuel on the ramp. Its usually not a lot of fuel just a few gallons.
  It also prevents the fueler from over fueling the wind. It can sometime dump 50 gallons or more if the fueler it not paying attention.


How can the effects of hot corrosion and salt deposits from sea water spray in gas turbine engines be negated/prevented? In aircraft operating in a maritime environment, corrosive effects from salt water are common. Are there any specific coatings used in engines for such aircraft? If so, which are they? How frequently should they be washed?
I've looked for information on this but can't find any specific answer.

Not aware of any anti-corrosion coatings used in engines.  The best mitigation is to shoot fresh water into the inlet with it running at the end of the day.  Seaplanes operating off salt water will generally get a fresh water hose down at the end of the flying day whenever practical.


What can be expected in an airline interview? So after the long wait, when someone finally gets that phone call for an interview at an airline, what do they need to study?  What kinds of questions will they ask during the interview?  How many interviews do they typically have to go through before a hire decision is made?  In short, how does it work?

The Delta Interview Process

I interviewed about three months ago at one of the several regionals that uses the Delta interview process.  It goes a little something like this:

Company Introduction

You arrive in the morning, somebody meets you, shakes your hand, and you usually hear a little speech or presentation about the company.  If your prospective employer uses AirlineApps, they'll have you verify that all of your information is still current, and gather your paperwork.  Then, it's off to Computer-Based Testing!

Computer Based Testing

CBT in the Delta interview is divided into three segments: cognitive, personality, and job knowledge.

Cognitive

The cognitive test is essentially reflex and memory games, of the sort you'd see on lumosity.com.  Some examples:

You are shown a horizontal line, with a pointer in the center.  The pointer will move from side to side at random along the line.  It is your task to counteract this random movement using the arrow keys to keep the pointer as close as possible to the center of the line.

Measures:  Focus and concentration

You are shown two words, such as DF3ET and DEFET.  It is your task to determine as quickly as possible if they are the same or different, and to click the appropriate same or different button on screen.

Measures: Attention to detail?

You are shown a table of six numerals paired with six simple shapes.  This table remains on screen.  You are shown a series of these shapes.  Decode, as quickly as possible, the series of shapes into the numerals they represent.

Measures:  Matching, working memory.

You are shown a graphic of a man holding a flag in one hand.  The man is either facing towards or away from you.  The man is either right-side-up or upside-down.  No matter his orientation, determine as quickly as possible whether the man is holding the flag in his right or left hand.

Measures:  Spatial awareness

A line wavers back and forth in a white area between two red zones in a random fashion.  When the space bar is pressed, the line will instantly be reset to the center of the white area.  It is your task to press the space bar as quickly as possible after the red line leaves the white area, but not before.

Measures:  Attention, reflexes.

You are shown the horizontal line with the pointer as well as the white area with the line.  It is your task to keep the pointer centered with the arrow keys while simultaneously using the space bar to reset the line when and only when it moves outside the white area.

Measures:  Division of attention, reflexes

You are shown a series of six simple shapes.  It is your task to recall the six numerals that were paired with these shapes from earlier in the test.

Measures:  Recall

A series of simple mental math problems is presented.  "Which would you rather have, 1/4th of \$200, 1/5th of \$300, or 1/3 of \$250?"

Measures:  Mental math skills

You are shown four rectangles.  One has a thin border, one contains a filled in arrow pointing left, one has a shaded arrow pointing right, one has a thick border.  There are multiple exercises to the test.  During some portions of the test, you are asked to click the rectangle whose arrow matches the direction of the one you are shown.  In others, you are asked to click the one whose shading matches.  In others, the border.  These criteria change at random.  Your task is to match the proper criteria as quickly and accurately as possible.

Measures:  Attention to detail, adaptation to changing conditions.

Listen through your headphones.  A series of notes will be played.  Then a second series of notes will be played.  Touch SAME or DIFFERENT.

Measures:  Whether you were good at Simon as a kid.

Personality

You are shown approximately 130 statements, one at a time.  Your task is to determine how much you agree or disagree with them on the following scale:

Strongly Agree
Agree
Neither agree nor disagree
Disagree
Strongly disagree

The statements are similar to:

I think the new morality is no morality at all.
Over the years, I have done some pretty stupid things.
I have literally jumped for joy.
I have a hard time resisting temptation.

Job Knowledge

This test measures technical knowledge.  It contains questions concerning:

Turbine engine theory
Descent planning
DME arc degree-to-nautical-mile calculations
Stall recovery procedures
Mach-to-TAS conversion
Transport category systems knowledge
Emergency procedures
Aerodynamics
and more!

Thank Wright that's out of the way, next up is lunch!

Then comes the interviews:

Tell me about a scary time in the cockpit
What would you do if you were an FO and the captain arrived smelling like alcohol?
Which is colder, -40 C or -40 F?
I see that you failed a checkride, tell me about it.

And so on.

The conclusion

You made it!  Someone comes out and shakes your hand.  Now it's time to fill out PRIA paperwork and pee in a cup.  If all goes well, you're given a conditional offer of employment!  Congrats!  You're a regional FO!

(If you can make it through training)


Why isn´t TOGA thrust always 100% N1 or N2? It makes sense to me, that under normal circumstances the engines shouldn´t be pushed to their maximum, to reduce wear and tear. But why isn´t TOGA thrust, which is the maximum selectable thrust setting, not corresponding to the maximum possible thrust, thereby 100% N1 or N2 whichever is the limiting factor.(In the picture TOGA is limited to 88.9% N1)

TOGA thrust is not always 100% N1 (or N2), because TOGA thrust is actually not about delivering the absolute maximum thrust that can be provided. Rather, it's about delivering a guaranteed large amount of thrust, to ensure the performance of the aircraft is what the pilot expects, and what the flight manual states will occur. The level of thrust needs to be predictable. So it's got to be the same with a new aircraft, as one 5 years old (for example), and the engines are about to be overhauled.

To achieve this, engines are "flat rated". See What is a Flat Rated Engine?

To repeat that answer a bit, a flat rated engine, produces a constant, or the same amount of thrust, up to a certain ambient temperature. This is achieved by having a margin (gap) between the maximum thrust the engine provides, and what it can really produce. This also results in a temperature margin between the engines actual turbine temperature, and the red line temperature. This means as the engine degrades, it can increase its operating temperature without hitting the red line (until it has degraded a lot), and so still provide the same level of thrust.

When a gas turbine's engine control is designed to produce the same thrust at different ambient temperatures, it means N1 speed will be higher on a hot day, than a cold day. See how in the figure, for a constant thrust, N1 is increasing as ambient temperature goes up? N1 has to go up as ambient temperature increases, because hotter air at the intake is less dense than colder air, so the engine needs to run at a faster RPM to make up for the lower density.


What are the effects of crosswind on takeoff? What is the specific aerodynamic effect which requires one to hold into-wind aileron to keep the wings level during takeoff in a B737? (i.e. dihedral or sweep)

Subsequently, what is the aerodynamic reason for having to increase that into- wind aileron input immediately after Takeoff.

The upwind aileron is held down in order to keep the crosswind from pushing the airplane downwind. This is called crosswind drift. Usually the aileron begins fully deflected and reduced as it becomes more effective with increased airspeed. Upwind elevator is coupled with downwind rudder, which keeps the airplane in the centerline.

When I have taken off in a glider with a very strong crosswind, I have started the roll all the way on the downwind side of the runway and taken off diagonally upwind in order to  to reduce the crosswind component.


Why did America not build its own ekranoplan? The Lun-class ekranoplan (NATO name: "Duck") is a ground effect vehicle designed by Rostislav Evgenievich Alexeyev and used by the Soviet and Russian navies from 1987 until sometime in the late of 1990s. This project was huge, scattered a lot of effort, over-cost and under-delivered.

Why did the USA not design its own ekranoplan?

Best answer: the United States had no need for one.   These kinds of large wing-in-ground-effect craft, while impressive, really serve no military purpose and provide no major military advantage for the US Armed Forces to possess.

Aside from the internal Great Lakes, there are no major bodies of water within the United States of America where such a craft could be readily employed and no need to position strategic or tactical assets there.   Both the Atlantic and Pacific oceans are covered by the US Navy with the form of carrier battle groups and submarine fleets, which provide portable power projection for undersea, surface and air operations  virtually anywhere around the globe.

Large wing-in-ground-effect aircraft do not provide a significant increase in America’s  power projection when compared with that.


Was the miracle on the Hudson saved exclusively by the APU? In the film Sully, (staring Tom Hanks) the APU is switched on straight after both engines rollback, why was this step necessary; Airbus said this was the "15th thing" to do on the checklist.

How or why did this step in particular prevent the loss of lives of over 100 people?

Yes, the solution to start APU was important.

The ditching procedure directs the use of maximum available slats and flaps for the final approach and touchdown (source, chapter 10.3). This is not possible without APU, as Airbus A320-214 cannot move flaps if only powered by RAT (only blue hydraulic line, same source, chapter 9.3). The running APU adds the green hydraulic line that can also move flaps.

Hence, without running APU, the optimal ditching procedure is not possible; that gives less chances for success.


Does preheating fuel before it reaches the turbine result in a performance improvement? Preheating fuel before it reaches the combustion stage was first proposed several decades ago as a way to improve mixture, fuel economy, and to reduce emissions in car engines.

One example of this method being used in aviation was the Polish jet trainer PZL TS-11 Iskra. Overlooking mechanical complications which may be introduced by using fuel preheating (including vapour lock), does this method have any measurable benefits in aviation in terms of performance or fuel efficiency?

The key here is understanding the purpose of pre-heating. Combustion occurs very rapidly to produce the power stroke in piston engines and thrust in jets.
It's time in the combustion chamber to do so is measured in fractions of a second.

Ideally, a mixture of 2 gasses, methane and air for example, would ensure efficient and complete combustion.  This is your common kitchen stove.

Mixing liquids with air is more problematic, as now you have a mist of small droplets instead of ready to mix gas.  This is good and bad.  The good is the evaporation of the fuel helps keep the engine cooler. This is a benefit of "full rich" setting.  The bad is the fuel is not mixed as well with the air when it burns, lowering efficiency and releasing harmful byproducts such as carbon monoxide.

Proper design (operating temperature) and choice of fuel may eliminate the need for pre-heating, especially once the engine is "warmed up".

Aside from the dangers of heating fuel, gains may be made by standardizing the temperature of fuel inflow for pollution control. Another possibility is to use the heat from turbo compressed air to warm it.  Tight control of octane rating is also beneficial.

But aircraft operators adjust their richness based on RPM and usually on the rich side to avoid overheating the engine, which is far more disastrous than slightly lower fuel milage.

In design, using engine heat to evaporate the fuel may eliminate the need for pre-heating, except for extreme arctic applications.


What is this tiny slat for? The one labeled as "1" in the picture. And I'm having doubts about "2", it is an air supplier for cabin, right? Or am I wrong?

Thank you.

The item 1 is a Krüger flap, a leading edge device which allows the wing to operate to a higher angle of attack. The wing-root fairing makes a small triangular segment necessary; outboard of it slats are used.

The item 2 is a NACA inlet for cabin air, as commented by @mins.


Why are aircraft coloured in yellow during construction, repair or overhaul? Why are aircraft usually coated with "yellow", while either during construction or repair and overhaul?
What exactly is the purpose of it?

For unassembled and new planes or planes not yet painted the green/yellow color you see is the anti-corrosive coating on the aluminum

  ...every unpainted airplane is nominally green from being coated
  (typically) with an anti-corrosive green zinc chromate or zinc
  phosphate primer over the aluminum skins. The different shades of
  green simply tell you that different vendors produced the different
  pieces—they don’t all use the exact same primer.

Originally it was some variation on Zinc Chromate but it was found to be fairly toxic other things have been used over time which lead to the more green color and even some potentially "chrome-free" options.


What would be the lift formula for straight wings? I have been trying to estimate the lift calculation for a straight wing. The previous project I worked on was a swept wing. But this is a straight wing. I would like to to get the stall speed so I need the Clmax formula. What would the lift formula for this type of wing be?

Regardless of the geometrical shape of the wing, you need to know the wing area to determine the lift force as it is one of the factors that affect lift.

Calculate lift using this formula: $$Lift = \frac{1}{2} (C_L * P * S * V^2)$$.

$C_L$: coefficient of lift
$P$: density of air
$S$: surface area of the wing
$V$: velocity of air


What is the difference between Best Rate of Climb and Maximum Rate of Climb? Is there a difference between Best Rate of Climb and Maximum Rate of Climb?

From my research, best rate of climb trades ground distance for altitude (i.e. steeper climb, more altitude per unit time).  Since an aircraft cannot climb faster than its max rate, these appear to be two different labels for the same concept.

Am I missing some nuance between the two?

Generally when GA pilots talk about climb performance we speak of two different airspeed values:

Best Rate of Climb speed (Vy) gets you the most altitude per unit time (feet per minute).
When you want to get to cruise altitude quickly for maximum efficiency you'll aim for the best rate of climb so you spend the least time at lower, less efficient altitudes.

Best Angle of Climb speed (Vx) gets you the greatest altitude per unit of ground distance (feet per mile).
When you've got a FAA-Standard 50-foot-tree at the departure end of the runway you'll aim for the best angle of climb to ensure you don't wind up in the tree.

Those speeds are useful to us as pilots, but the exact rate of climb (feet-per-minute) for those speeds will vary: A fully loaded plane will climb more slowly than one that's just got the pilot and a few gallons of fuel on board, and that's where the "maximum rate of climb" enters into the discussion:

Maximum rate of climb is the number of feet per minute you can get climbing at the "best rate of climb" airspeed.

If someone is being sloppy in their usage "Maximum Rate of Climb" could mean "Best Rate of Climb" (pitch for Vy and you get what you get), but if you're being precise in your usage and really talking about the rate of climb it would mean the theoretical maximum rate of climb in feet per minute based on the current conditions and aircraft weight.

Maximum rate of climb under a given set of conditions is useful information to know if you need to clear terrain at some point on your flight path and want to be sure you can climb fast enough to do so: If you're starting from sea level and need to clear a 5000 foot mountain that's 5 minutes away but your plane can't manage more than 500 feet per minute at best-rate-of-climb speed under the current conditions you'll need to reconsider your flight plan to either avoid the mountain or climb in a circle somewhere until you can clear it.


What is the most efficient symmetrical airfoil shape? What is the most efficient symmetrical airfoil shape to make for a covering for a round upright bar that measures 40mm outside diameter?

The speed of travel will be 25Kph and I also need a shape to travel at 30Kph. I assume these will be different to some extent?

Truncation (chopping off the rear portion of the airfoil) does not reduce drag, although reducing up to 20% of the chord does not significantly increase it.  As Peter says, "trade off between more separation and more wetted surface area.  Hence "boat tail" bullets.

The 3:1 ratio of chord to width is apparently a bike racing specification.  Nothing new here,
the full airfoil produces the lowest drag.  Hence the cone they put on the back of the Space Shuttle while it was piggybacked on its 747.

What they did to meet the 3:1 specification was to truncate 66% of a 9 to 1 airfoil.
This produces the lowest drag within the specification.

The Kamm tail shape was designed for automobiles, providing a weight savings (as racers constantly accelerate and deccelerate) and to make the vehicle a little shorter, which can help changing lanes in a crowd.  Two different applications.  But a fully symmetrical airfoil, such as the struts of a Cessna 172 will do the job.

For an aircraft strut, if strength allows, make it as long and thin as possible until drag values begin to rise.  9 to 1 rings a bell from boat hull design, and would be a good place to start.


Can planes still land during a regionally-diverse ATC malfunction? Spoilers for the Pilot episode of Scorpion

   In the Pilot episode for the TV series Scorpion, all major control towers in the greater LAX area are taken out because the firmware is malfunctioning and our heroes need to get a proper version active again, while the airborne planes could not be contacted through any method. They first try to recover a backup version of the software from a datacenter, but that fails. They then contact a salesman on a plane via his antique cellphone and manage to reload the software using a Ferrari and a laptop wired into the plane.
 One of the major plot points was that, because the software was malfunctioning, none of the planes could land safely, even though one of the planes could safely buzz the tower and even get close enough to the ground to make a wire connection to the ground. If they could fly so low, why can't they just land it?

So can a plane land during a complete control tower malfunction? And what is the general SOP in case of malfunctions? I've read both How realistic is the aviation crisis in the recent Spider-Man movie? and What happens to incoming flights when the airport shuts down, but part of the plot was that every airport in the greater LAX area got the problematic malware at the same time, so it's possible that many of those planes had their alternate destination airport also in trouble.

During a control tower malfunction, can planes still land?

Yes.

If one tower goes down, the other layers of ATC will still be functioning, and they'll divert the aircraft elsewhere: if LAX goes down, national level ATC would work with the SoCal Tracon (Southern California Terminal Radar Approach Control -- i.e. "Approach") and perhaps the airline dispatchers to send the airplanes elsewhere: San Diego, Ontario, Long Beach, Burbank.  Those farther out would be diverted elsewhere just to avoid having too many airplanes piled up in one place: land in the Bay Area, or LAS or PHX, for instance.

Okay, let's assume that all the towers in the LA Basin are all down.  And let's assume that SoCal is down too.  And just to make the scenario complete, we'll assume that LA Center has lost all of their radios too.  (This is like the scenario that happened several months ago when Chicago Center lost their radios due to sabotage, except we're assuming LOTS of facilities all have the same problem at the same time.  Straining the limits of "willing suspension of disbelief" pretty hard here, but let's do it to make the point.)  What happens?

The pilots talk to each other on the usual frequencies and land.

There are plenty of uncontrolled airports out there, and they function just fine with pilots using what's known as CTAF -- the Common Traffic Advisory Frequency, where everybody broadcasts their position & intentions.  "Whozit Traffic, Cessna 1234A, left base, touch & go Whozit."  "Whozit Traffic, Piper 9876B, left downwind, full stop Whozit."  Based on those transmissions, you can build a good picture of who's where, who's closest to me & where I need to be looking to find him, and what (if anything) I need to do differently to not get too close.

And nobody needs ANY assistance from the tower in order to put the aircraft safely on the runway, stop, and exit.  We talk to them to keep the flow of traffic neat & orderly (they can be more efficient than just working it out on our own -- particularly when you start alternating departures with arrivals), but they have zero role in the actual act of landing.

Now in the scenario posited above where every ATC radio in all of the southern half of the state of California has failed, there would be complications, particularly if there was weather involved.  (See Die Hard 2, where weather had shut down EVERY airport in North America, apparently, save one, and the bad guys had shut down the ILS to that airport... we're well beyond "willing suspension of disbelief" there.)  But you'd also have a couple of things in your favor: no departures, and the runways normally used FOR departures would be available for landings as well.  Also, the goal is no longer a smooth & efficient flow of aircraft in & out; it's simply to get everybody on the ground safely.

Would it be a mess once you got on the ground & wanted to get to a gate?  Sure.  Visions of gridlocked LAX are easy enough to imagine.  But could everybody get on the ground safely?  Absolutely.


What material is used to make engine covers for passenger airliners? What material is used to make the engine shrouds for passenger airliners?

There are potentially two answers to this question

If you are asking about engine covers used to keep debris out when the aircraft is parked like these

(source)

They are made out of any manner of fabric, nylon, canvas and often foam filled if they are inserted somewhere.

If you are asking about the exterior housing around an engine its generally aluminum like the rest of the aircraft. Much like the open panels that can be seen here.

(source)


Explaining development of sideslip due to bank In lateral static stability:
"Once an airplane banked due to a disturbance, the airplane develops a sideslip in the direction of the bank because of a spanwise component of the weight w*sin($\phi$)"
I need to understand that in terms of forces and moments acted on the airplane.
Let me say:
the resultan of thrust force and the component of the lift.sin($\phi$) force, which developed when banking, makes the airplane moves in a sideslip angle.
Is it correct?
Can someone explain in it with images?

Sideslip is simply lateral movement due to the tilting of the wing lift vector away from vertical. Moving forward while moving laterally means the lateral movement becomes a horizontal arc and becomes a turn.  The vertical fin keeps the body of the plane aligned in the airstream, so the body follows the arc and you have a heading change and a coordinated turn.
You could say the lift force of the wing is a thrust force.  Any time the thrust force is tilted from vertical, the thrust force develops a lateral as well as vertical force component, and because the lateral thrust component decreases the vertical thrust component, the sideslip also introduces a descent.  To stop the descent, you have to increase the total lift to restore the original value of the vertical lift component, so you have to increase angle-of-attack to increase total lift.
Think of a helicopter hovering with the rotor disc level.  All of the rotor's thrust is vertical.  The pilot tilts the rotor with cyclic, tilting the rotor's thrust, introducing a lateral component to the thrust, and the machine moves sideways (and downward because the vertical lift component was reduced, requiring the pilot to increase total rotor thrust with collective), and if it's moving forward instead of hovering while this is going on, the sideways movement becomes an arc, or a turn.
The term sideslip, when applied to flying, tends to refer to the lateral movement without the yawing motion induced by the fin, so that the airplane is turning, but slewing sideways while doing so, and the fin's job is to stop the slewing by weathervaning the tail to keep the body aligned in the relative airflow.
Problem is, dihedral effect requires this sideways slewing to be present when the airplane banks, so that the differential lift created by the slewing motion (sideslip) provides a restorative righting moment.  A small amount of sideslip must be permitted to happen when the airplane is banked by a disturbance to allow dihedral effect to work, but not too much, and not too little.
Vertical fin sizing has to find the sweet spot where a bit of slip is allowed to develop when the plane is banked by a bump, without letting it get out of hand.  Make the surface too small, and the airplane develops too much slip when banking and generally yaws around too much, make it too big and the plane instantly yaws or weathervanes into the bank to remove the sideslip, dihedral becomes ineffective, and the plane tends to want to always spiral into the bank with any disturbance.


Why weren’t the Comet’s overhead ADF windows roundified along with its passenger windows? Following the crashes of two Comet 1s in early 1954 due to metal fatigue, all future Comets (and the few surviving Comet 1s that were rebuilt rather than scrapped, all of them in military service) were redesigned to mitigate fatigue stresses; among other changes, the passenger windows were changed from round-cornered squares to circles.  However, the windows in the roof of the forward cabin for the aircraft’s ADF antennae, which are of almost identical construction to the passenger windows except for being filled with opaque fiberglass (in which the ADF antennae were embedded) rather than transparent panes, and which are considered to be one of the two possible locations (the other being one of the passenger windows) for the rivet hole that gave birth to the fatal crack in one of the crashed Comets (no wreckage was ever recovered from the second crash beyond that floating on the surface, as the depth of the water would have made salvage operations cost-prohibitive at the time), retained their original rounded-square shape.  Admittedly, the Comet’s subsequent service history seems to have vindicated this judgment (no Comet would ever again break apart in the air from fatigue damage, despite still having squarish ADF windows), but de Havilland didn’t know that at the time, and they thought it prudent to roundify the passenger windows, so why didn’t they do the same for the ADF windows?

It wasn't the square-ish windows (they still had round corners, just not as rounded as modern square windows).  They knew square windows were less than ideal stress wise and built the frame structure to take the expected loads.  They just screwed up the calcs and didn't quite make them heavy enough.

The problem was stress concentrations at the rivet holes in the areas of the corners were higher than calculated.  They could have just beefed up the structure with more rivets and doublers.  The switch to round was to alleviate the stress problems without the weight penalty of reinforcing the structure.

The holes in the roof were already sufficiently beefy, or perhaps they added a reinforcement.  You will see square holes in pressure hulls on various airplanes for component pass-through all the time, where a square hole is desirable for some reason.  If you make the frame heavy enough, it's not an issue.  It's just that a round hole is a bit lighter than a square one so most of the time a round hole is preferred.


Why are cabin doors outlined with a different color than the fuselage? On almost all airliners I have seen, the doors are painted inside a rectangle which appear to reflect more light. This is the case whether in the aircraft has its manufacturer's paint or an airline's custom livery.

What is the reason behind this?

It can be seen in these pictures.

Image Source

Image Source

The doors are painted like this because it is a federal law that all cabin doors on commercial airplanes should be outlined in a color which contrasts with the fuselage color. It is done so that in case of an emergency on ground, rescue crew can find the doors easily and open them quickly.

It happened in past years that passengers survived some crash landings (especially at night) but perished because the rescue crews could not locate the cabin doors in time to rescue them from the burning airplane. The contrasting outlines of the doors allow them to find the doors instantly.

Here is the actual text of this federal regulation:

14 CFR 25.811 (f) Emergency exit marking

  (f) Each emergency exit that is required to be openable from the
  outside, and its means of opening, must be marked on the outside of
  the airplane. In addition, the following apply:

  (1) The outside marking for each passenger emergency exit in the side
  of the fuselage must include a 2-inch colored band outlining the exit.

  (2) Each outside marking including the band, must have color contrast
  to be readily distinguishable from the surrounding fuselage surface.
  The contrast must be such that if the reflectance of the darker color
  is 15 percent or less, the reflectance of the lighter color must be at
  least 45 percent. “Reflectance” is the ratio of the luminous flux
  reflected by a body to the luminous flux it receives. When the
  reflectance of the darker color is greater than 15 percent, at least a
  30-percent difference between its reflectance and the reflectance of
  the lighter color must be provided.

  (3) In the case of exits other than those in the side of the
  fuselage, such as ventral or tailcone exits, the external means of
  opening, including instructions if applicable, must be conspicuously
  marked in red, or bright chrome yellow if the background color is such
  that red is inconspicuous. When the opening means is located on only
  one side of the fuselage, a conspicuous marking to that effect must be
  provided on the other side.


Who has authority over stadium TFR exceptions in VFR flight? I fly in the Bay Area. I sometimes like to fly over SF through the San Francisco Class B. If I am in contact with Norcal Approach and in their airspace, I can ask them for an exception and they can authorize it. But, I could also be talking to the tower, and could also be talking to Oakland Tower.

All three of the following agencies have authority over sections of airspace that overlap with the stadium TFRs at the Giants stadium (see image).

Oakland tower (class C)
San Francisco tower (core class B)
Norcal approach (outside core class B)

My question is: which of these three agencies have the authority to grant me an exception to the stadium TFR?

(Image is SF TAC with TFR plotted by Foreflight.)

The answer will vary based on the location - San Francisco, Los Angeles, and New York may each have different arrangements. However, in general, it'll come down to how the different ATC facilities have the situation worked out with each other.

The stadium TFR itself does not help much. The relevant section states that:

  THE RESTRICTIONS DESCRIBED ABOVE DO NOT APPLY TO THOSE AIRCRAFT AUTHORIZED BY AND IN CONTACT WITH ATC FOR OPERATIONAL OR SAFETY OF FLIGHT PURPOSES

Any of those facilities could provide the authorization - so it's then down to which will do so. The answer to that will depend on the structure of how the facilities work with each other. The ATC facilities will have Letters of Agreement which state that a given area of airspace is managed by a given facility, as well as how handoffs are handled.

The facility that can provide flight following is also the facility that can authorize you into the TFR in that area. To figure that out, all you have to do is ask: call up Norcal Approach or Oakland Tower, and ask for flight following. If they can do that, then they're the right folks to ask about transiting the TFR. If not, they'll give you another frequency to try. Of course, just because they have authority over the airspace doesn't mean they'll grant the request.


Is it possible to build a paper airplane that will enter a fully developed spin? Some students learn best when they can see aerodynamic principles in action. I'd really like to be able to show a student how a spin occurs.

Is there a way to make a paper airplane that will enter a developed spin?

Besides the location of the center of gravity, two things determine how an aircraft spins, and both are not well shaped for spinning in paper airplanes:

The wings (obviously): They should ideally be straight with an aspect ratio between 5 and 10. Swept wings will also spin, but straight wings make spinning and recovery easier.
The forward fuselage. Here a rounded shape which is higher than wide is ideal and will promote flat spins. The two-dimensional shape of paper airplanes will not produce the vortices which drive the yaw rate in spins.

Also, for spinning it needs a stalled wing, some asymmetry and some time until the spin fully develops. To create a strong pitch-up moment, masses at the tip and the end of the fuselage are also needed. A pure paper airplane will have too much yaw damping and too little inertial pitch up to spin.

Size should be less of an issue because separated flow changes less with Reynolds Number, and spin tunnels regularly use scales of 1:20 or 1:30 with good results. But I wonder whether the low wing loading of a paper airplane will prevent spins - the models used in spin tunnels are carefully sized not only for geometric agreement, but also for their masses and mass distribution.

Maybe it will be better to show your students videos from spin tunnel tests.

Spin tunnel footage of fighter aircraft
Spin tunnel footage of GA aircraft
Description of a spin tunnel


Why are smaller wings in the front with these VTOL aircraft? I would think it would be better to put the larger wings under the front or middle closer the the payload/center and have the smaller wings in the tail? Why would these designs do the opposite?

With the first (DAPRA's X-plane) you can see the weight is going to be put properly under the bigger wings but I also wonder: why have it fly with the smaller wings infront?
If a teardrop shape is the most aerodynamic then the big wings should be in the front. Also it looks like a having the smaller wings in the back would increase stability in flight.

It's because with the canard configuration, the smaller stabilizing surface is a lifting surface instead of the down force surface of a conventional tail.

(A regular tail airplane is a seesaw with someone sitting on one end and another pushing down at the other; a canard airplane is more like a table with most of the weight at one end where the fat legs are and skinnier more lightly loaded legs holding the other end up.  Canards get their pitch stability from having a steeper lift slope at the canard surface, whose airfoil is chosen to achieve that purpose, so the nose will rise with increasing speed and drop with decreasing speed).

So if you want to as much vertical thrust as possible from the available flying surfaces, it makes sense to use the Canard configuration where all the surfaces are lifting.  Canards are nothing new; the Wright Flyer was the first.  You don't see them everywhere because there are significant limitations, but in a VTOL configuration like this, the Canard layout is mostly a plus.


Should I log flights on separate lines if I park the plane between legs to different airports? I flew one leg of a cross country, landed, parked, and turned off my engine. I flew the same plane home an hour later.
Are these two separate flights and should be logged as such, or can they be logged together on one line?
Is there any rule that states how it should be logged?

There are no hard and fast rules in the US about how and when to break up a flight like this, so do what makes the most sense to you.
In the military I would generally log individual sorties on different lines because there were varied mission codes, and sometimes we switched crews.  However, on a multi leg cross country I would log it all on a single line.  (As long as the multiple legs occurred on the same day.)


Which airplane has had the longest production run? An earlier question received interesting answers on what airplanes have been in service the longest; this question asks about airplanes in production the longest.  By this, I mean from earliest production of the first variant, to the end of the production run of the latest variant.  Thus, the 737 would count from 1967 through the present, even though there have been plenty of variants along the way.

Regarding breaks in production... EDIT: any break in production less than a decade, doesn't rule out an aircraft.  Multiple breaks in production that total less than a decade of "down" time don't either. An aircraft that is essentially the same produced by somebody else is fine if both are generally regarded as being the same aircraft, even if the designation is different (i.e. the F4U was built by multiple manufacturers, but today everybody thinks of any of them as a Corsair).

Military, civilian, large & small, even including gliders & helos (if any have been in production long enough to be competitive) are all fair game.  We can mention balloons (as "aircraft," though not really "airplanes") as having been produced since before the Wright brothers, but that's not really what I have in mind here.  Edit: Nor is "oldest aircraft still in production," even though the answers tend to be similar since it looks like the aircraft mentioned there are still in production.  This question is about length of production run, even if it is complete.

So, longest production run... what do we have?

Probably the longest production run of any given craft is the Taylor Cub (more popularly known as the Piper Cub).  Which has, in one form or another, been built since about 1930, moving from manufacturer to manufacturer as the years go by.  There's been a recent resurgence in new manufacturers picking up the design lately because it now can be used in the LSA class of aircraft, created a few years back to encourage manufacturers to produce cheap, easy to fly, short range aircraft for recreational purposes.  CubCrafters is one such manufacturer, and here is their, very current, CarbonCub SS as an example of the type:

Source: https://upload.wikimedia.org/wikipedia/commons/2/25/CC11-160_Carbon_Cub.JPG, Author: FlugKerl2

The longest production run for an aircraft from a single manufacturer is the BeechCraft Bonanza (source).  Which has been in continuous production since 1947:

Source: http://i.stack.imgur.com/utPF8.jpg, Author: Bill Larkins

Another long production run is that of the Antonov An-2 which also started in 1947 and only ceased in 2001, though a variant, a turboprop version called the An-3, is still in production to this day:

Source: http://i.stack.imgur.com/YDvgG.jpg, Author: Sergey Ryabtsev

Other honerable mentions include the C-130 Hercules (in continuous production since 1954, even though only 2300 have been built).  And also, the Cessna 172 and Cessna 182.  Both started in 1956 and are still going strong today, with older airframes still being extremely common.

Also, it is probably worth pointing out the Uh-1 "Huey" Iroquois, which has been in production since 1959, and is probably the longest production run for a rotary wing aircraft:

Source: http://i.stack.imgur.com/jWVEg.jpg, Author: 111 Emergency


Can a helicopter enter Vortex Ring State In Auto Rotation? [see qualifiers] If you are in a vertical descent [no wind] with rotor at max RPM Auto, and you abruptly pull full collective, the momentum of the blades will drive air down creating down wash.

Now obviously this is a totally hypothetical question with no real world use, but, presuming a high enough inertia rotor system, in this very specific scenario is it possible to at least enter the incipient phase of VRS? [before the rotor folded and you fell to your death]

Please no answers just saying you go into auto to get out of VRS, I am looking for a very specific yes or no.

To enter VRS you have to have near zero forward airspeed and a descent rate of about 500 fpm or more under power.  Note that VRS is not "settling with power" regardless of what the FAA says - they are two different phenomena.  So in practice you would never encounter the conditions that could create a VRS in the first place while autorotating because you normally autorotate with substantial forward airspeed if you want to be able to land in one piece.

But say if you were autorotating, then slowed to zero airspeed so you were now autorotating straight down (and the descent rate goes from holy crap to oh my god), and then you pulled pitch to arrest the descent rate using rotor inertia. Could a vortex ring state be induced during that brief interval?  Perhaps one could start to form in that brief few seconds of inertia-generated downwash, but by then the rotor would be stalling and you are now an anvil, so the point is moot.

However, for the purposes of our just-for-fun theoretical discussion, I think that if you had enough rotor inertia, it would be possible theoretically I would say, because for the purposes of the time interval involved, it would be the same as having engine power.  Maybe if you had a rotor with super duper uranium tip weights that could generate inertia lift for say 10 seconds or more.

Watch this video to see how fast the vortex ring state can form in a vertical descent with power


How to tell the difference between METAR and SPECI reports? I am trying to use METAR data from AviationWeather.gov to programmatically collect hourly rainfall data.  This Wiki says that the first field in the report should be "type" - either METAR or SPECI.  METARs are sent every hour, SPECIs are sent sporadically under certain conditions.  The problem is that the AviationWeather.gov reports are missing that first field, so I can't tell the difference between METAR and SPECI reports.  I care because I can only get reliable cumulative Rainfall data from the METAR reports.

What am I missing?

I don't think you can use METARs to produce precise hourly rainfall data. METARs do not express the exact amount of precipitation; rain is only expressed in three categories (light, moderate, heavy).

The way I understand your problem, you want to skip SPECI reports because you only want a single report per hour. A better way of doing this would be to use the time/date stamp in the report and simply dismiss a report if you already have one from the same hour. Say you have a report from 011203Z and you then receive another report from 011220Z. You want to dismiss the last report, because it is only 17 minutes older than the first one.

Alternatively, you can find METARs from a number of other sources, which include the message designator as well. Here is one I find useful: http://www.ogimet.com/metars.phtml.en


How do oceanic lateral offset procedures work? I was reading a forum for professional pilots and ran across a thread on lateral offset procedures during oceanic flight (apparently having the FMS offset the aircraft from the centerline of an oceanic track). How does lateral offset work? Is it required for all oceanic aircraft or optional for some operators? Is it explicitly assigned by ATC or is it an implicit part of oceanic flight? What is its purpose, and why isn't it used in non-oceanic airspace?

On high-altitude North Atlantic flights, planes can fly zero, one, or two miles to the right of the centerline of your assigned track. The offset is randomly selected. This is called Strategic Lateral Offset Procedures.

It's used in the oceanic flights or flights over remote land where there is typically no radar service, and ATC cannot "see" traffic separation. It provides, on average, additional horizontal separation between planes reducing the likelihood of midair collision and high altitude wake turbulence (which can occur as a result of RVSM).

Strategic lateral offsets can be authorized in en-route oceanic or remote continental airspace. The decision to apply a strategic lateral offset is the responsibility of the flight crew, and only where offsets have been authorized by the ATS and when the aircraft is equipped with automatic offset tracking capability.

https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/enroute/oceanic/documents/WATRS_Plus/DOC_4444_16.5_SLOP_25Feb2011.docx


Do pilots reject takeoff if aircraft doors are not properly locked down? This particular incident, the pilot rejected takeoff "due to a aft door indication".

My questions are:

Is it a such serious situation so as to reject take-off?
If the pilots had taken off, could the crew have secured the door on their ascent?

The crew has already secured the door just before leaving the gate, cross-checked them and the pilots saw the sensors indicate closed. So if the warning goes off during take-off roll, it is not somebody's simple mistake, but something is broken. It might be the sensor, but it might be something on the door and that might be pretty bad. So as the old saying is “it's better to be on the ground wishing to be in the air than in the air wishing to be on the ground.”

Below about 80 knots the pilots will (should) reject the take-off for almost any warning or abnormal indication they get. If the problem can be fixed easily, they can just taxi around and take off a couple of minutes later. Above that speed the emergency braking is likely to overheat the brakes, so from about that up to V1 pilots will only reject for engine failures and other very serious warnings, while for other issues they'll make the circuit and return to land again.


Why does the vortex created by wing affects its own angle of attack? According to potential flow theory, we know that the lift generated by the wings is due to the vortex it creates. In case of a 3D finite wing, there is also a span wise flow due to tip leakage from bottom to upper surface. So if suppose the wing is moving towards left, then the direction of vortex should be clockwise, which in turn should produce an upwash rather than downwash. This should cause an increase in angle of attack rather than decrease.

So the downwash generated should be valid for a wing travelling behind the original wing, but we say that there is downwash on the original wing.

So where is it that I am making a mistake, vortex direction. If yes, what is the correct explanation. Please explain.

The wingtip vortices create both upwash and downwash; The downwash lies within the wingspan and affects the wing angle of attack while the upwash region lies outside the wingspan and can be utilized by another aircraft (or bird) flying behind and above the wing.

The flow induced by the downwash reduces the effective angle of attack of the (finite) wing and causes the induced drag.

See if this image clarifies your doubt.

Source: aerospaceweb.org

Consider the upwash before the wing and downwash after the wing (section).

Source: theairlinepilots.com

As it can be seen, the airflow in front of the wing is slightly directed upwards by the upwash. Now, the angle the wing makes with the horizontal datum (i.e. relative airflow) is the same.

However, the airflow is slightly turned upwards and the wing sees the air coming at it at a different angle compared to the relative airflow. As a result, the effective angle of attack (defined as the angle of attack that lies between the chord of an airfoil and the effective airflow) is reduced, so that the relative and effective airflow looks something like this:

Source: theairlinepilots.com

This difference between the relative and effective airflows is what that causes the induced drag.

Source: theairlinepilots.com


Why do fighter jets land faster than Jumbo commercial aircraft? From my own understanding, the bigger (and heavier) aircraft, the higher approach speed it needs to keep itself from stalling. According to this site, the approach speed of an A380 is 140 knots, and 160 knots for a 747. In contrast, the F-16's landing speed is 141 knots, and 135 knots for the F-35C.

Doing mass-to-speed ratio, it doesn't make any sense to me. Could you explain why do fighter jets land faster while they are lighter than large commercial aircraft?

It is not only the mass that affects the landing speed. Wing area plays an important role as well.

A larger wing can lift more weight at the same speed than a smaller wing. If you compare the wing loading of these aircraft the differences are smaller:

A388:

Maximum landing weight: 391000 kg
Wing area: 845 m2
Wing loading: 463 kg/m2

B744:

Maximum landing weight: 295000 kg
Wing area: 525 m2
Wing loading: 468 kg/m2

F-16A:

Estimated landing weight: 13000 kg
Wing area: 28 m2
Wing loading: 464 kg/m2


Do I need 35 hours of ground school for knowledge test for PPL? New US student here. I'm starting part 141 flight training soon for my private pilot license, but for now prepping for the knowledge test. I am going with self-study and had a question about endorsement for the written exam.

Is the endorsement I get from the ASA Prepware tool sufficient for taking the knowledge test?

  Complete two practice tests with scores of 80% or better, and request your test sign-off (endorsement) from ASA

I am confused because I've been under the impression that part 141 mandates 35 hours of ground school for taking the knowledge test (also 35 hours of flight time).

https://www.ecfr.gov/cgi-bin/text-idx?SID=2d180e467a3b85b2e34ce695dea3d322&mc=true&node=pt14.3.141&rgn=div5#sp14.3.141.f

  Appendix B to Part 141—Private Pilot Certification Course

  (a) Each approved course must include at least the following ground training on the aeronautical knowledge areas listed in paragraph (b) of this section, appropriate to the aircraft category and class rating:

  (1) 35 hours of training if the course is for an airplane, rotorcraft, or powered-lift category rating.

If not, I might just do Sporty's ground school ($200) and get my endorsement that way.

Thanks

For 141 you need a graduation certificate to take the test. For part 61 you need an instructor endorsement. 141 is for complete courses start to end. 61 is for getting a piece here and a piece there mix and match style. in either case there is a minimum amount of ground training required before you can get your private certificate.

Any either case you don't need the knowledge test to start flying, you only need the knowledge test before your final FAA check ride.


What's with this non-exit Exit sign on Delta CRJs? I have the pleasure of frequently flying Delta (i.e. Delta Connection) flights on CRJ-700 and CRJ-900 aircraft.  All of them have a bogus EXIT sign between First Class and the main cabin:

This is roughly half-way between the front doors and the wing exits.  This seems to me to make nonsense of any safety regulations requiring EXIT signage.

Normally there is some kind of barrier, a bulkhead or curtain, separating the business class and the common folk in steerage.  In such a case the sign is to indicate that there is an exit somewhere down yonder beyond the bulkhead.

In this case the curtain is not there so the sign kind of hangs there with its nonsensical implication that maybe there is an exit right next to it.  I'll go out on a limb and guess that the regs require the sign to be there between the two classes regardless of whether a visual divider is in place.


Is it incorrect to refer to a C-130 as a jet? In this article by CNN, the C-130 involved in the unfortunate crash in Savannah, GA is referred to as a "jet." Is this considered proper usage? I'm not looking for public opinion here but official categorization, if one exists. Perhaps there is an USAF or FAA document I've not been able to find which delineates such things. I would imagine that there is also an engineering or academic definition of such things.

The AV.SE description of the Turboprop tag states that it should be considered "as opposed to a jet engine."

Wikipedia says that "Turboprop engines are jet engine derivatives." which really sort of muddies things but the actual turboprop article notes that "the exhaust jet typically produces around or less than 10% of the total thrust" It never occurred to me that the thrust produced by a turboprop engine is even measurable. Would this factor, then, be the delineation between jet and prop? Should it be a matter of whether the exhaust gasses or rotating components propel the aircraft?

So to restate my question, Should a C-130 be called a jet even though a significant percentage of its propulsion is derived from a propeller?

Note: Please consider JATO/RATO outside of scope of this question.

CNN actually called it a jet with four turboprop engines, if you can believe that.

ICAO is probably as universal a source as you will find. They list the C130 as turboprop/turboshaft. Their table of aircraft type designators allows selection of engine types from this list: Jet, Turboprop/turboshaft, electric, piston and rocket. There are no associated definitions.


How practical is laser designation against helicopters? Laser designation is a fairly common method for guiding missiles and precision bombs, but how does it perform against aerial targets?

Given the ranges and kinematics involved, this method could be too challenging. I know the effectiveness is also dependent on atmospheric conditions, but what are the other limiting factors?

There are a number of laser-guided ground-to-air systems, and a number of those have been adapted to air-to-air and air-to-ground as well. The key is the speed of the missile, not so much the guidance system itself. An example is Starstreak.

Lasers are well focused, but not perfectly, and are easy enough to defocus to any required degree. For this role, making the beam large enough to cover potential movement of the target during the tracking cycle (often manual) while still having enough energy fall on the target for the tracker to seek is pretty much all you need. Modern solid-state lasers make this relatively easy. However, unless you have a seeker in the munition, as is the case in a laser-guided bomb, then the cone-shaped beam means decreasing accuracy with range.

Starstreak takes another approach. It projects a 2D array of dots in space modulated so the receivers on the darts can tell where they are in the array. When used with the shoulder launcher, the operator keeps the beam on the target optically and the darts keep themselves in the center.

When combined with the optional launcher platform, a tracking camera is added. This receives the reflected laser signal from the target and uses the same modulation to determine how closely the array is to the center of the target. It uses this to automatically track the target, and thus the missiles get the benefit of semi-automatic tracking without having to carry the seeker on their nose.


What is this object that followed me up the street? I saw my first UAV last night as it followed me up the street in Lancaster, PA. Does anyone know what type of unit this is or who would own one? I am guessing it was the police? I am curious.

This is a quadcopter, so called because it uses four rotors to generate lift. They are now made cheaply in China and can be purchased in most technology-related online shops. They are remotely controlled, so it is safe to assume that the owner was close, but not in plain view. It might have been the police, but it could as well be a hobbyist, taking his new toy out for a spin.

Since most units are equipped with a cheap webcam and a wireless link, I would guess he/she was sitting in front of a computer or using his/her smartphone for controlling the device and watching the camera stream.


When do pilots deploy landing gear? The landing gear should be down in order to qualify as a stabilized approach. Other than that, what are the guidelines on when to deploy landing gear on approach?

As late as possible to still meet your company's specific stabilized approach guidelines (mine were 500 ft VMC, 1000 ft IMC).  If you need the drag, then use them earlier.

In the EMB-145 in still wind or a headwind you could cross the FAF at 250 kts and clean and be on speed and configured by 1000' if you dropped the gear at the FAF (and opened the speed brakes and the first notch of flaps all at once).  Normally though, I'd drop the gear around 1000'.

Acronyms:

VMC = visual meteorological conditions
IMC = instrument meteorological conditions
FAF = final approach fix
EMB-145 is the type designator for the Embraer 145 regional jet


In Malaysia, can someone become a LAME through self study rather than training school? Is it possible for someone to self study (without attending a training school) and individually sit for the exams required in order to become a B1 or B2 LAME in Malaysia?

Unfortunately, it is not possible to become a licensed AME in Malaysia entirely through self-study. It takes between two and seven years to become licensed as an AME in Malaysia, and that includes two years of practical/on-the-job training at a Malaysian aviation facility/company. You could, in theory, study the theoretical material and try to pass the test, but if you don't go through a Part 147 training program it will take much longer to become licensed.


Is it appropriate (legal) to request practice instrument approaches in IMC? I have always requested practice instrument approaches while maintaining VFR (with a safety pilot or instructor). But I was wondering if there are any issues (legal or otherwise) with requesting multiple approaches in actual weather at the end of a short IFR flight. Assuming, there are no safety or controller workload issues. In other words, assuming weather is well above minimums and controlling facility is not busy (during off peak hours).

I realize I could just make multiple missed approaches, and get the extra approaches that way, but that is not what I'm asking.

Certainly you can request practice approaches in IMC on an IFR flight plan.  ATC will accommodate aircraft on a first come, first served basis. It is legal, and appropriate if ATC can accommodate it based on traffic (or noise or NOTAM restrictions).

Of course there will be some difficulty if you attempt to do practice approaches at Los Angeles (LAX) or New York (JFK). ATC would not likely accommodate this at these or similarly busy high performance aircraft airports. But again, unless it was otherwise restricted (e.g., noise abatement requirements or NOTAM restrictions) you can certainly request this type of IFR/IMC handling.


Why do Airbus aircraft typically have less wing flex than Boeing aircraft? I was watching this video on YouTube about Boeing vs Airbus aircraft, and at around the 5:09 mark the female pilot stated that Airbus wings are much "stiffer" and "less aerodynamic" compared to Boeing's' more "aerodynamic" wings.

I looked at a few videos and it does appear that Airbus aircraft have some wingflex but not to the same extent as Boeing aircraft.

Taken from: this video

I gather that wing flex is mostly beneficial for aerodynamics so why then, do Airbus aircraft typically have less wing flex than Boeing aircraft?

It's not a super scientific statement. There may be some half-truths referring to half-truths inferring that some design is better, just for show business sake.

"The Boeing wing is way more aerodynamic than the Airbus wing" is not something that has any value at all. All wings are by definition aerodynamic, there is no sliding scale. All wings are the result of a design process, balancing many input parameters. If an aircraft manufacturer cannot get the aerodynamics of a wing right, they have no place in the aerospace industry. Both Airbus and Boeing make very fuel efficient and safe aircraft that compete head to head in the market place.

Wing flex is one of these things that the structural engineers must cater for, after the aerodynamicists have had their go at the external shape: the planform, aerofoils etc. It can be considered a secondary design parameter that:

provides dihedral in flight, for stability when banking;
acts as a spring against turbulence;
can cause grief with flutter;
may provide difficulty for the ailerons to operate.

For a given wing shape, wing flex is the result of the ratio of strength and elasticity of the wing material. Composites are the latest in aircraft material, being lighter and stronger than aluminium. It is five times stronger than aluminium, and flexes about half when under load. But because it is stronger a lot less material can be used to make the wing lighter - even though a certain amount of carbon fibre flexes less than the same amount of aluminium, there is simply less of it. The ratio of strength over flex of carbon fibre is much higher than that of aluminium.

All aircraft with wings made of carbon fibre flex a lot more than aircraft with wings made out of aluminium. Both the A320 and the B737 have aluminium wings. For a given material and wing area, wing flex is a function of

Aspect ratio: a long, slender wing flexes more than a short, stubby wing. Or the long aluminium wing of a large airliner flexes more than the shorter wing with the same aspect ratio of a smaller airliner.
Wing thickness. The thicker the wing profile, the less sweep angle needs to be used to delay drag divergence. This is actually a sign of an aerodynamically more advanced wing, and the thicker profile makes the wing bend less

Those sort of comparisons make much more sense than "the wing of a Boeing is much more aerodynamic than that of an Airbus". That's only showbiz.


Can you fly direct to your destination if you can cruise above FL450 regardless of airways? To my knowledge, the high altitude enroute charts only apply to the altitudes between FL180 and FL450. Does that mean you can plan direct to your destination if your cruising altitudes stay above FL450?

If ATC allows a direct-to, then yes. However, what you will file is a flight plan based on published waypoints, but not airways. So pick and choose based on great circle and trade winds and so on.

  Airways

  The en route airspace structure of the National Airspace
  System (NAS) consists of three strata. The first stratum low
  altitude airways in the United States can be navigated
  using NAVAIDs, have names that start with the letter V, and
  are called Victor Airways. They cover altitudes
  from approximately 1,200 feet above ground level (AGL)
  up to, but not including 18,000 feet above mean sea level
  (MSL). The second stratum high altitude airways in the
  United States all have names that start with the letter J,
  and are called Jet Routes. These routes run
  from 18,000 feet to 45,000 feet. The third stratum allows
  random operations above flight level (FL) 450. The altitude
  separating the low and high airway structure varies from
  county to country. For example, in Switzerland it is 19,500
  feet and 25,000 feet in Egypt.

  (FAA Instrument Procedures Handbook - En Route Operations)

And from the FAA AIM:

  Operations above FL 450 − Use aids not
  more than 200 NM apart. These aids are depicted on
  enroute high altitude charts.

compared to

  Operation off established routes from
  18,000 feet MSL to FL 450 − Use aids not more than
  260 NM apart. These aids are depicted on enroute
  high altitude charts.

and finally

  Operation above FL 450 may be conducted on
  a point-to-point basis. Navigational guidance is
  provided on an area basis utilizing those facilities
  depicted on the enroute high altitude charts.

Special RNAV points can also be used, such as the HAR, see here: What are those 5-character alphanumeric waypoints? HAR allows up to 500 NM between waypoints.

The reason for the limitation in filing a huge distance without points is the air traffic optimization. The computers are limited by how far to look ahead for conflicts is one of the reasons. I don't have numbers at the moment but I'm mentioning it in case you were wondering. Also because the different sectors and FIR's prefer to have a complete leg(s) within their own airspace. However, they can coordinate together and shoot you direct-to the destination.


What is the maximum temperature of engine bleed air for de-icing the wings? What is the maximum temperature of the air bled from the engines of a Boeing 747-800 and an Airbus A380 to the wings for de-icing?  If the air is too hot, how is it cooled?

This is based on aircraft type and manufacturer approved limitations.  Typically it’s limited by temperature or duration of use.  Compressor bleed air is tapped at around 450° F, hotter than a typical household oven.  These high temperatures can begin to significantly affect the yield strength of aluminum alloys typically used in aircraft construction, approaching the design factor said of safety and potentially resulting in a local structural compromise during high load factors, etc.


With similar weapons why does an AH64 Apache require a pilot and gunner when the A10 Warthog only needs a pilot? The Apache has a 30mm chain gun. It carries Hellfire (anti armor), Stinger/Sidewinder (air to air) and Hydra (air to ground, APKWS guidance package available) missiles.

source

The Warthog has a 30mm gatling gun. It carries Maverick (30cm air to ground including armor), Hydra (70mm air to ground) and Sidewinder missiles, plus a variety of bombs.

source

The Warthog seems to have a more capable and complex weapons load, so why doesn't it use a separate gunner like the Apache?

From comments:

The ULB (Unmanned Little Bird) version of the AH6 can fly with two, one, or zero pilots, so it seems that helicopters can be automated like fixed wing aircraft.

source

The Kiowa Warrior 50cal machine gun was not turret mounted; it was fixed to the airframe like the A10, though not buried in it. This is used in an armed recon role, not attack.

source

Mainly it's because the A10's pilot just has to point his aircraft at the target from a certain height while in forward flight, whereas the helicopter, being able to hover, needs to be able to engage a target while not pointed directly at it, while the pilot is busy flying a machine that takes a lot more attention than a fixed wing aircraft.

Especially when considering the Apache's original tactical function, which was to hover below the tree tops, pop up and engage a Soviet tank, and drop out of sight again.  As the pilot you wouldn't want to be managing the weapon systems AND flying the machine and avoiding obstacles.


Why do Russian jets make a squealing sound? Why do the engines noise from the Russian and Soviet jet create a squealing sound which is very distinct which most of the western jets don't have? Which part of the engine creates the noise, and why is it so distinct to Russian engines? Also it appears to be dominant in low rpm or at idle throttle setting.

You can hear this in the video MiG-29 start-up to shut down (4 min mark) .

I am by no means an aficionado of Russian fighter aircraft, but I suspect the sound you speak of is caused by intake airflow.

Since Soviet times, their aircraft have ascribed to a design doctrine of being able to fly from damaged or sub-standard airfield surfaces, and incorporate undercarriage & engine intake designs that assume constant presence of engine-killing FOD. They have either a meshed grating, or even an impervious retractable door flap that completely covers the intakes, while having additional doors open on top of the engine intake area to compensate, for ground operations.

At the 3.10 mark in the video, you hear what is probably the No1 engine spooling up, at about 3.35 you hear the No2 (closest to camera) starting to spool up - within a few seconds you will see a series of small doors above the red number "70" open. This is where the engines are drawing their intake air, away from ingestion of gravel, discarded hardware, small animals & the closely-milling, unconcerned ground crew.

I suspect that the restriction/turbulence caused by this slightly torturous air path is causing that high-pitched sound. It could also possibly be compressor bleed air being dumped as a normal part of low engine revs/idling.

At the 9.00 point in the video, you can see the flight intakes completely shut, with the ground intakes open, as it taxies in. Eventually, you even see a ground crewman appear to actually stand in front of the flight intakes while at least one engine is still running.

There is some discussion & a photo on this page

Would it be viable to install a screen in front of jet intakes to prevent them from sucking in birds?

This aspect of airframe design is a common subject of comparisons between US & Soviet/Russian design doctrine.


Why do most GA aircraft not have vortex generators? It is my understanding that vortex generators produce more favorable aerodynamics by delaying flow separation. If this is the case, why do more GA aircraft not have vortex generators?

Vortex generators are a kludge - a good design does not need them.

They are mostly added at later stages of the design process when some deficiencies need to be cured, but re-designing the aircraft is too expensive. They add a lot of drag, and do so always, for the whole duration of a flight, when they are needed only in some corner of the flight envelope (say, when flying close to stall).

A clever way to install vortex generators can be found on the Short Belfast:

Tail of the Short Belfast from below (own work). Note the vortex generators hidden in the hinge gap - they only move out into the airflow when they are needed: When the elevator is moved to large negative deflections.


What is a Visual Climb Over Airport (VCOA) and how is it properly executed? The takeoff minimums and (obstacle) departure procedures for the Asheville Regional Airport (KAVL) have special instructions due to the rising terrain in the vicinity of the airport. Instrument departures have special procedures to follow when departing IFR.

There are special procedures for visual climb which mention VCOA. There is no mention of VCOA in the Instrument Flying Handbook. Where is VCOA explained and what are the special considerations for pilots conducting this procedure?

It's defined in the pilot/controller glossary:

  VISUAL CLIMB OVER AIRPORT (VCOA)− A departure option for an IFR
  aircraft, operating in visual meteorological conditions equal to or
  greater than the specified visibility and ceiling, to visually conduct
  climbing turns over the airport to the published “climb−to” altitude
  from which to proceed with the instrument portion of the departure.
  VCOA procedures are developed to avoid obstacles greater than 3
  statute miles from the departure end of the runway as an alternative
  to complying with climb gradients greater than 200 feet per nautical
  mile. These procedures are published in the ‘Take−Off Minimums and
  (Obstacle) Departure Procedures’ section of the Terminal Procedures
  Publications.

The AIM 5-2-8 says that pilots must request it:

  Pilots are responsible to advise ATC as early as possible of the
  intent to fly the VCOA option prior to departure

And the ATC orders 4-3-2 say that ATC may not offer it:

  Do not solicit use of the Visual Climb over Airport (VCOA) option.

The TERPS 14-4 has all the technical details and explains the purpose, which is to allow aircraft that can't maintain a 200fpnm climb to climb safely within a limited area over the airport:

  VCOA is an alternative method for pilots to depart the airport where
  aircraft performance does not meet the specified climb gradient.

The departure designer creates a vertical cylinder (called a Visual Climb Area in the TERPS) of airspace over the airport that's safe to climb in, based on airport elevation, runway positions and a default airspeed of 250kt (although other airspeeds can be used). Even if the VCA dimensions aren't charted or stated in the DP, for an airport at 2000msl (KAVL is at 2162msl) the radius of the cylinder is at least 2nm at 90kts, or 2.8nm at 250kts, which seems to be plenty for a spiral climb (in the aircraft I fly, anyway). And the climb has to be in visual conditions, so terrain clearance shouldn't be an issue.

I don't know of any detailed guidance on how execute it, but "climbing turns over the airport" seems fairly clear. I've never done it myself, but I'd simply fly a continuous spiral climb after takeoff, up to the en route altitude mentioned in the procedures and go from there.


Is ADS-B required for flight under class B airspace but outside the Mode C veil? In the U.S., can a non-ADS-B equipped aircraft legally fly under class-B airspace extensions that are outside of the 30nm Mode-C Veil circle?

You may fly without ADSB under the Class B or Class C shelf provided you remain outside of any Mode C veil.

§91.225 tells you where you cannot fly. It says you cannot fly within the lateral boundaries of the Class B or C airspace or above the airspace. It does not say anything about under the shelf.

Here is an example of one such area:

skyvector.com

You can fly under 2,700' below the Ontario Class C and in the small slice of Class B you can fly up to 8,000' if you stay away from the Class C.

Paul Bertorelli has a good explanation on YouTube. (Updated link.)

  (d) After January 1, 2020, and unless otherwise authorized by ATC, no
  person may operate an aircraft in the following airspace unless the
  aircraft has equipment installed that meets the requirements in
  paragraph (b) of this section:

  (1) Class B and Class C airspace areas;

  (2) Except as provided for in paragraph (e) of this section, within 30
  nautical miles of an airport listed in appendix D, section 1 to this
  part from the surface upward to 10,000 feet MSL;

  (3) Above the ceiling and within the lateral boundaries of a Class B
  or Class C airspace area designated for an airport upward to 10,000
  feet MSL;

  4) Except as provided in paragraph (e) of this section, Class E
  airspace within the 48 contiguous states and the District of Columbia
  at and above 10,000 feet MSL, excluding the airspace at and below
  2,500 feet above the surface; and

  (5) Class E airspace at and above 3,000 feet MSL over the Gulf of
  Mexico from the coastline of the United States out to 12 nautical
  miles.

14 CFR § 91.225


Is a Phenom 300 single pilot able to fly non-commercially in Europe? Can a personally owned Phenom 300 be flown non-commercially by a SP typed pilot in Europe?

The EASA type certificate says yes granted the cockpit is approved and the required additional equipment is met (refer to EASA AFM).

Minimum Flight Crew:
One pilot (in the left pilot seat) plus additional
equipment as specified in the Limitations Section of the
EASA Approved Airplane Flight Manual

The related note:

Approval for operation with a minimum crew of one pilot (in the left pilot seat) is
based upon the cockpit equipment installation and arrangement evaluated during ANAC
certification testing. No significant changes may be made to the installed cockpit equipment or
arrangement (EFIS, autopilot, avionics, etc.), except as permitted by the approved MMEL,
without prior approval from the responsible Aircraft Certification Office.


What are these aircraft? Seen in silhouette over Palm Springs Screen capture on iMac, of photo posted and claimed taken 11/21/15.
Palm Springs, CA

Looks like two Douglas DC-3, the one on the right being the military version known as the C-47 "Skytrain".

Source: Adrian Pingstone


Who must approve a globally distributed satellite to ground laser communication system? Laser Light Communications (US) plan for several dozen optical high speed data links between satellites and ground is described in Aviation Week's article Big Gains On Horizon For Laser Communications Suppliers and Lightwave's online website: Laser Light to leverage free-space optics in space for Optical Satellite as a Service.

  All Optical Hybrid Global Network (or HALO, as laser Light calls it)

The plan is to use lasers to establish optical links between satellites in Earth orbit (MEO) and between them and a network of ground stations.

  According to the company's website, Laser Light will leverage 8 to 12 satellites in medium Earth orbit to create a network that will offer an initial service capacity of 7.2 Tbps. The satellites will pass signals among themselves and to the ground via free-space optics. The space interconnections will include 48 links of 200 Gbps apiece, as well as 72 steerable up/down links to Earth at 100 Gbps. (my emphasis)

edit: Confirming that the plan is to establish several dozen laser communications link between ground stations and satellites, from the article The Speed of Light: Laser Light and Optus Explain Optical Communications Partnership:

  Laser Light’s hybrid network is broken into two elements: an OSS part and the Ground Network System (GNS). The OSS half is comprised of a constellation of eight to 12 Medium Earth Orbit (MEO) satellites, which beam down data to a GNS via a completely optical spectrum. The data then connects to terrestrial fiber infrastructure, such as the one Optus already has in place. (my emphasis)

above: Graphic from The Speed of Light: Laser Light and Optus Explain Optical Communications Partnership to Via Satellite Magazine Note: since the satellites are in medium Earth orbit (MEO) and not Geosynchronous orbit (GEO), these beams would not be fixed, but in fact scan repeatedly through tens of kilometers of airspace each.

These would not be narrow, millimeter-diameter beams like we see from laser pointers. In order to combat diffraction, they would actually be expanded to at least tens of centimeters in diameter or larger. There is also a chance they would be just outside the visible wavelength range in the (very near) infrared. So I would guess there is a good chance that - depending on the actual implementation - these beams might not actually pose any risk to a pilot if an aircraft passes though one, but I don't know that for a fact.

I would like to know who must approve globally distributed continuous laser data links between Earth stations and orbiting Satellites in the context of aviation safety.

The answers to the related question How does aviation deal with satellite and Moon laser ranging, and other scientific lasers in the sky? seem to suggest that there are some rules and best practices associated with ground-based lasers from observatories that are used intermittently, but in the case of bidirectional, near continuous laser traffic from dozens to perhaps hundreds of sites (each satellite has 72 independently steerable beams) the existing procedures (having two human spotters watching for planes) would not really be feasible.

There is some discussion here but I don't see any mention of aviation.

(I've taken a wild stab at an answer, despite my not being a lawyer or legal expert of any kind, since nobody has written an answer in nearly four years.  If you don't like my answer, please feel free to write a better one.  I apologize in advance if I've abuse any legal terms.  It's quite possible that I have come to an erroneous conclusion.)
Your question seems to presume that there is some multinational body, or multinational rules, governing laser beams in the atmosphere.  However, there is no multinational agreement to regulate laser beams in the atmosphere.
Countries are sovereign, with no higher legal authority, and are not required to make any rules, laws, or enforcement bodies without voluntarily agreeing to do so.  Often countries realize that uniform standards or regulations are in their best interests, and make treaties or agreements with other countries to create laws and rules and enforce them.  Sometimes countries voluntarily abide by existing treaties or agreements without actually signing onto the agreement.  In the absence of such formal treaties or agreements between countries, individual countries are free to write, or to not write, whatever rules and laws they like.
One of the functions of the United Nations is to create a list of international treaties and agreements.  The list, known as the United Nations Treaty Series Cumulative Index, can be found here.  The most recent list as of this writing, current to 20 March 2013, sorted alphabetically, is here.  A quick search of the index for the term "laser" reveals only an "Exchange of notes constituting an agreement between the United States and Japan concerning a program for the cooperative research of Eyesafe Laser Radar."
In other words, there is no multinational agreement to create rules or laws regarding laser beams in the atmosphere, other than those that pertain to aviation safety.  Existing aviation safety legislation seems to agree that pointing powerful lasers at aircraft is something that should be regulated.  However, it seems likely to me that aviation safety treaties are silent regarding laser beams through the atmosphere that are not pointed at aircraft.
To sum up, it has been left to individual countries to write whatever laws they like regarding laser beams in the atmosphere not aimed at aircraft.  Currently it seems likely that few countries have written any such laws.  So companies can currently feel free to plan communications networks using laser beams between ground stations and satellites, since there are few or no laws to stop them, as long as they take care to not accidentally aim laser beams at aircraft.


What are the relative efficiencies of the various stages of a counter rotating propeller? After going through the CFD results of a drone project I am involved in, I noticed that the data shows significantly increased (+10%) thrust generation at the second stage of a counter-rotating, 2-stage, ducted fan. Both stages use identical airfoils and spin at the same rpm. They also have low solidity, meaning they look more like propellers than airliner fans, as the blades take up a small proportion of the disc area.

Generally, propellers are less efficient when the incoming airflow has a high velocity, so I would expect, in any N-stage fan using otherwise identical stages, for the N stage to produce less thrust than the N-1 stage, but apparently I am missing something.

In a previous answer here Peter Kämpf mentioned that the first stage of the Kuznetsov NK-12 turboprop pre-swirls the flow to improve thrust creation conditions at the second stage. How does this process work? Does it require a specific design of the stages to work in tandem?

The key thing to think about is that the first stage doesn't just accelerate air downwards, it also causes it to rotate ("swirl") in the same direction as the first stage propeller.

This happens because the first stage propeller, being an airfoil, generates both lift and drag. The lift corresponds to air being accelerated down the axis of the duct; the drag corresponds to air being accelerated circularly around it. The amount of swirl force is therefore related to the thrust and the effective L/D ratio of the propeller.

The airfoil of the second stage propeller is then encountering air that is moving towards it at the tangential velocity of the propeller, plus the tangential velocity of the air that has now been circularly accelerated ("pre-swirled") in the opposite direction by the first stage.

That increased velocity means that the angle of attack for the second stage airfoil will be increased compared to that encountered by the first stage, and hence greater lift is produced at the same RPM.

To balance the load on the two stages you would need to adjust the pitch or RPM of the second stage propeller.

Note that after the second stage, the air will be "unswirled" back to being closer to a non-rotating flow, and this is one of the reasons that a contra-rotating pair can be more efficient than a single propeller: overall, the system wastes less power in swirling the air rather than accelerating it axially.


When was trim on airplanes used for the first time? I would like to know when trim control was set for the first time on airplanes.. thank you!

Although Anton Flettner patented the trim tab in 1918, (as said in a comment above) it seems that 1910 was the first implementation of "trimming" (according to the following article, linked below)

https://www.flightglobal.com/pdfarchive/view/1910/1910%20-%200255.html

Although it was not adjustable in flight, it still seems like the first time any concept of trim was introduced was in early 1910. However, Anton Flettner produced the first ADJUSTABLE trim tab.


Is there similar result between simulation and reality? While designing an aircraft and analyzing it using simulation software, one result comes out. Is what occurs on the aircraft in reality similar to the result as given in a simulation?

Yes, usually

Simulators are pretty accurate, at least for the specific things they're programmed to measure and account for.

For example we have a pretty good idea how airflow works, so airfoil/wind tunnel simulation is very accurate. We also have quite good ideas of how materials react, flex, break etc, and can model them pretty accurately.

However

No simulation is 100% accurate: there is always potential for things in the "real world" to happen in a way we either didn't account for, or weren't expecting.

For example sometimes manufacturing flaws mean a material breaks in a way we weren't expecting, or an external influence changes the way something happens. We also don't have a 100% understanding of aerodynamics under all conditions.  This is why we still need real-world testing. There are also circumstances we've never encountered and therefore can't be certain of: eg aircraft are designed to handle around 150% of the force of the strongest known/experienced turbulence, but we can't be truly sure that this hypothetical 150% turbulence would act as "regular" turbulence, merely 50% stronger

In short: yes, the results will be similar, but they will not necessarily be identical, depending on exactly what you are testing.


What is that extended nacelle feature on the Honda HA-420 HondaJet? Here is a picture of the Honda HA-420 HondaJet with strange extended engine housings. Why are they required? What are they for?

I am not asking about the red covers, but the white engine housing features that I put a red circle around.

They aren't covers; they are fairings to integrate the flow going past the lower part of the cowl with the exhaust stream coming out the tailpipe above and the pylon below.  It's because the cowl extends below the engine some distance to house various parts like accessories, plumbing, ducting etc.  You have to create a nice transition for the airflow or you would have a lot of unnecessary drag.

You could say that the fairing is filling in all the 3 dimensional space that the free stream and the exhaust plume can't fill in because the change in direction is too extreme, and would result in flow separation, causing turbulence/drag.