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Thread: Ask An Expert- Aviation

  1. #61
    Senior Contributor Stitch's Avatar
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    Quote Originally Posted by paintgun View Post
    i'm certainly not an expert so i'll give you a layman's answer, which is simply there is not enough space on LCA's nose to accommodate IRST or other opto-electronic device
    You also have to figure in all of the support infrastructure for such a system. It's not as simple as bolting an EOTS onto the airframe and calling it good; you've also got all of the power requirements and communications hardware required to make the system work, not to mention integrating it with the rest of the avionics. Unless you've already got a very flexible infrastructure built into the airframe (like an IEEE 1394b data bus), it won 't be that easy to integrate it with the other avionics.
    "There is never enough time to do or say all the things that we would wish. The thing is to try to do as much as you can in the time that you have. Remember Scrooge, time is short, and suddenly, you're not there any more." -Ghost of Christmas Present, Scrooge

  2. #62
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    Quote Originally Posted by 1979 View Post
    V. Molders 1941.
    Werner Mölders ironically died in an air crash as a passenger. Mölders was given a state funeral in Berlin on 28 November 1941. His coffin was laid out in the honour court of the Imperial Air Ministry. The guard of honour consisted of Johann Schalk, Günther Lützow, Walter Oesau, Joachim Müncheberg, Adolf Galland, Wolfgang Falck, Herbert Kaminski and Karl-Gottfried Nordmann. Mölders was buried next to Ernst Udet and Manfred von Richthofen at the Invalidenfriedhof in Berlin.

  3. #63
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    Quote Originally Posted by Stitch View Post
    You also have to figure in all of the support infrastructure for such a system. It's not as simple as bolting an EOTS onto the airframe and calling it good; you've also got all of the power requirements and communications hardware required to make the system work, not to mention integrating it with the rest of the avionics. Unless you've already got a very flexible infrastructure built into the airframe (like an IEEE 1394b data bus), it won 't be that easy to integrate it with the other avionics.
    hmm... maybe i can google up the hardware for each component you just described, and i might come up with a working IRST/EOTS

    edit : and i got a question, will a fast roll on supersonic or high subsonic bleed airspeed?
    Last edited by paintgun; 10 Oct 11, at 21:00.

  4. #64
    Senior Contributor Stitch's Avatar
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    Quote Originally Posted by paintgun View Post
    edit : and i got a question, will a fast roll on supersonic or high subsonic bleed airspeed?
    That would be a good question for Chogy or Jimmy; one of them should be around here soon.
    "There is never enough time to do or say all the things that we would wish. The thing is to try to do as much as you can in the time that you have. Remember Scrooge, time is short, and suddenly, you're not there any more." -Ghost of Christmas Present, Scrooge

  5. #65
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    Quote Originally Posted by paintgun View Post
    edit : and i got a question, will a fast roll on supersonic or high subsonic bleed airspeed?
    ANY maneuver that increases drag (or increases lift, which automatically increases induced drag) will bleed airspeed. But by how much? The answer is, not much. An aileron roll is an unloaded roll around the longitudinal axis, and in a jet with a quick roll rate, like the T-38's 720 degrees/second, the airspeed loss in negligible, just a knot or two.

  6. #66
    In Memoriam Military Professional dave lukins's Avatar
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    Quote Originally Posted by Chogy View Post
    ANY maneuver that increases drag (or increases lift, which automatically increases induced drag) will bleed airspeed. But by how much? The answer is, not much. An aileron roll is an unloaded roll around the longitudinal axis, and in a jet with a quick roll rate, like the T-38's 720 degrees/second, the airspeed loss in negligible, just a knot or two.
    Would the same apply in a dive or would airspeed increase?

  7. #67
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    Quote Originally Posted by dave lukins View Post
    Would the same apply in a dive or would airspeed increase?
    Airspeed would increase much the same as if no rolling were taking place. When you roll continuously, you actually remove the lift component from the airplane, which is why when you see air to air video, with one guy rolling and the other filming it, the guy doing a quick aileron roll seems to drop several dozen feet relative to the camera plane... because he is dropping.

    Drag comes from two sources, parasite (stuff in the slipstream) and induced. Induced is drag associated with the simple act of obtaining lift. When you pull G, you are asking for more lift, and induced drag goes up as well. So when you aileron roll, you increase parasite drag due to control throw movement and the slight yaw around the long axis, but you reduce the induced drag. So it's a bit of a wash.

    A barrel roll could be called an aileron roll at 1 constant G, and is a harder maneuver to do well. It forms a corkscrew flight path through the sky, rather than the jet continuing straight and simply rolling about the long axis.

    HTH and makes some sense!

  8. #68
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    Quote Originally Posted by Chogy View Post
    Airspeed would increase much the same as if no rolling were taking place. When you roll continuously, you actually remove the lift component from the airplane, which is why when you see air to air video, with one guy rolling and the other filming it, the guy doing a quick aileron roll seems to drop several dozen feet relative to the camera plane... because he is dropping.

    Drag comes from two sources, parasite (stuff in the slipstream) and induced. Induced is drag associated with the simple act of obtaining lift. When you pull G, you are asking for more lift, and induced drag goes up as well. So when you aileron roll, you increase parasite drag due to control throw movement and the slight yaw around the long axis, but you reduce the induced drag. So it's a bit of a wash.

    A barrel roll could be called an aileron roll at 1 constant G, and is a harder maneuver to do well. It forms a corkscrew flight path through the sky, rather than the jet continuing straight and simply rolling about the long axis.

    HTH and makes some sense!
    It will when I have read it a dozen times...thanks

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    Quote Originally Posted by dave lukins View Post
    It will when I have read it a dozen times...thanks
    i consider myself lucky being able to wrap my head around some aerodynamics terms and concepts, or reading academic papers without having the education or experience in its related fields, or is that being unlucky
    reading it many times sure helps!

    more questions :

    will a pilot throttle engine power up and down a lot in combat/maneuvering? or will he simply set throttle up to the 'healthy' maximum/military thrust and make the best use of it? how about the use of ABs?

    Chogy sir, what is your favorite fighter
    Last edited by paintgun; 12 Oct 11, at 23:43.

  10. #70
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    will a pilot throttle engine power up and down a lot in combat/maneuvering? or will he simply set throttle up to the 'healthy' maximum/military thrust and make the best use of it? how about the use of ABs?
    In the days before the F-14 on up, the throttle was pretty much parked at the stops until the very end of the maneuvering fight, when throttle modulation might be necessary to prevent an overshoot, and settle into a stable gun track. Despite this, not only would they not accelerate, the'd both decelerate AND lose altitude, due to the high G and demands on the airplane to turn, turn, turn some more. With more modern fighters, the initial portions were pretty much locked in A/B, but modulation within A/B and below become more common. It all depended upon the myriad of factors the attacker or defender sees... range, angle off, closure. Sometimes you'd WANT to bleed airspeed very quickly, and you'd need idle to do this best, but even in a slow-speed fight, the throttle generally gets fed back in; otherwise, you're heading downhill quickly despite the slow airspeed and nose-high flight profile.

    Think of the Hornet's ultra high AOA and slow-speed pass at an airshow. He is doing a hundred knots, plowing through the sky, AOA (angle of attack) very high, but to do this, he is in A/B and he is not accelerating. The drag on the airplane is enormous. To accelerate once more, he must break the AOA (lower the nose) to reduce drag.

    In a nutshell, you're at MAX for maybe 50% of the time, modulated within the A/B region for 25%, and at mil or below maybe 25%. There's no such thing as too much thrust. It is amazing how quickly and easily one could go from 25,000' and mach 1 to sea level and 200 knots.

    Not surprising given that at 40,000 pounds weight, at 7 G, the jet really "weighs" 280,000 pounds, the wing loading is through the roof, and you are asking 50,000 pounds of thrust to fly the 280,000 pound airplane.

    Chogy sir, what is your favorite fighter
    That's like asking a sports car guy what his favorite car is. He's going to name the car he drives. I flew the F-15, it took care of me and I loved it dearly. The F-16 guy will love his F-16. It's human nature.

    There is no such thing as an ex-fighter pilot. Once a young man straps on a jet aircraft and climbs into the heavens to do battle, it sears his psyche forever. At some point he will hang up his flight suit - eventually they all do - and in the autumn of his years his eyes may dim and he may be stooped with age. But ask him about his life, and his eyes flash and his back straightens and his hands demonstrate aerial maneuvers and every conversation begins with "There I was at..." and he is young again. He remembers the days when he sky-danced through the heavens, when he could press a button and summon the lightning and invoke the thunder, the days when he was a prince of the earth and a lord of the heavens. He remembers his glory days and he is young again.

    Robert Coram, "Boyd"

  11. #71
    Senior Contributor Stitch's Avatar
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    Quote Originally Posted by Chogy View Post
    In a nutshell, you're at MAX for maybe 50% of the time, modulated within the A/B region for 25%, and at mil or below maybe 25%. There's no such thing as too much thrust. It is amazing how quickly and easily one could go from 25,000' and mach 1 to sea level and 200 knots.
    Chogy/Jimmy - I seem to remember there being problems with the F-100 engine in the F-15 early on because the pilots were cycling the engines a lot more in simulated combat than earlier engines, like the TF-30, due to the fact that the F-100 had a higher ST than earlier turbofans; it wasn't necessary to leave the throttle setting at mil power since there were times the pilot actually had to slow the aircraft to get a good firing solution. The designers of the F-100 hadn't planned for such high cycles, so the MTBF on the earlier engines was a lot lower than expected.
    "There is never enough time to do or say all the things that we would wish. The thing is to try to do as much as you can in the time that you have. Remember Scrooge, time is short, and suddenly, you're not there any more." -Ghost of Christmas Present, Scrooge

  12. #72
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    One other problem not anticipated by the engine folk was how often the engine would be "snatched" from one stop to the other at AOA and altitude extremes. This caused compressor stalling and other (worse) things. In the early 1970's, fuel controllers, that monitored throttle demands, were hydromechanical machines... like a WW2 carburetor + turbo-supercharging that could sense the basics of the world outside and the demands of the pilot, and schedule fuel.

    These worked OK. But like so much else, the advances in digital electronics paid huge dividends. Around maybe 1985, the DEEC (digital electronic engine control) was added to the F-100 engine, and the engine's behaviors were greatly improved. It allowed full throttle movement in all phases of flight. The DEEC also gave superior acceleration of the engine, and it was so pronounced that one could make excuses in the debrief... "Well I didn't have a DEEC airplane, which is why I lost the rolling scissors..." That sort of thing.

  13. #73
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    chogy,

    There is no such thing as an ex-fighter pilot. Once a young man straps on a jet aircraft and climbs into the heavens to do battle, it sears his psyche forever. At some point he will hang up his flight suit - eventually they all do - and in the autumn of his years his eyes may dim and he may be stooped with age. But ask him about his life, and his eyes flash and his back straightens and his hands demonstrate aerial maneuvers and every conversation begins with "There I was at..." and he is young again. He remembers the days when he sky-danced through the heavens, when he could press a button and summon the lightning and invoke the thunder, the days when he was a prince of the earth and a lord of the heavens. He remembers his glory days and he is young again.

    Robert Coram, "Boyd"
    nice quote.

    we used to have a "Fighter Bar" prior to our move back to the Pentagon, and posted above the Bar was a sign that said:

    "ALL STORIES FROM OPERATIONAL LIFE ONLY. NO 'THERE I WAS, TYPING A STAFF SUMMARY SHEET...' "
    There is a cult of ignorance in the United States, and there has always been. The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that "My ignorance is just as good as your knowledge."- Isaac Asimov

  14. #74
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    The Coram quote leaped out at me when I read his book about Boyd. I'm not quite stooped yet, but I'm out of the game!

    The thing with the hands... it's SO real. Pilots do it unconsciously because a pair of hands is the quickest (maybe the only) way to get across two 3-dimensional flight paths to another person quickly and easily. At squadron parties with wives and such, it was inevitable, and the wives' eyes would roll back into their heads whenever it happened. In briefing rooms, we had two model airplanes on sticks, and they were used extensively to teach. They were invaluable.

    I wonder if squadrons even have their own bars any more. The official O'club people hated them because they took away business. We loved them. As soon as the last flight stepped, the bar was open, and we'd often debrief with a cold pitcher of beer.

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    I have a question in regards to this Mayday episode I seen a couple years ago about China Airlines Flight 006:

    Panic Over The Pacific Part 1 - Air Crash Investigation/Mayday - YouTube

    Seems incredible that the stresses involved would actually rip the main gear doors off and do damage to the tail-plane yet somehow it was able to safely land. What an amazing plane! Near the end of part 5, they mention that it was put through "maneuvers and stresses that far outweighed it's known limits". It was repaired and put back into service. What I'm wondering is what kind of testing and airframe checks would they have to be done to be able to certify it for passenger use? It would seem to me that considering what this plane went through, that they may of had to come up with new procedures to make absolutely certain it was safe to fly again.

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