Aces High Bulletin Board
General Forums => The O' Club => Topic started by: VAMPIRE 2? on March 13, 2012, 10:34:55 PM
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I can't seem to find a youtube video of a compressed wing and what is happening during this phase of flight... anyone up to dropping me a link...??? thanks in advance. :salute
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You mean like 'compressibility'? That funky little feature that encourages B38s to crater when dive-bombing?
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yes and like zeros when the attempt to follow p-47's down...
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WEll, this is normal, but it would look like this only happening a lot faster...
http://www.youtube.com/watch?v=Dscn0rFvukg
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I haven't found a wind tunnel video yet, but did find this..
http://www.510fs.org/index.php/squadron-history/wwii/99.html
Interesting read.. especially the part about the P51s diving..
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WEll, this is normal, but it would look like this only happening a lot faster...
http://www.youtube.com/watch?v=Dscn0rFvukg
Looks like its about ready to stall trying to slow down for those spitfires
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I haven't found a wind tunnel video yet, but did find this..
http://www.510fs.org/index.php/squadron-history/wwii/99.html
Interesting read.. especially the part about the P51s diving..
All three times, I rolled the ship onto its back in a typical Split-S, from altitudes above 35,000 feet - once from above 45,000 feet. I don't remember the actual indicated airspeeds at entry, but am sure they were normal cruising speed for the altitude.
WOW! In a D-2 or 16 that is high.
It's hard to say with accuracy what maximum airspeed was attained. To begin with, standard production instruments weren't capable of test-quality recording. But mostly, I was too focused on the ground to give much attention to the instrument panel. In each dive, the needle was jammed on the stop, so it's a good educated guess that maximum speed reached 650 - 670 miles per hour. I know that the tech manual warned against indicated air speed over 400 MPH above 25,000 feet, but we regularly ignored the manual in this and other limitations.
Once again, this shows that the Jug can out dive any AC at high speeds and pull out.
I'm not an engineer so cannot speak with technical competence, but I know of only one other propeller-driven airplane capable of such unrestrained dives - the P-38. And the Lightning had a tendency to "tuck under" early in the dive which made for a greater loss of altitude during the pull-out. It too, experienced buffeting.
I find this interesting.
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A little history:
MIT developed radar, one of the things they did with it is verify diving speeds of different aircraft due to the fact that compressiblility messed up all airspeed indicators of the era.
(most were mounted right in the wave of compressed air, so were wildly inaccurate when the shock wave started building)
They found out the Mustang had a higher dive speed than the T-bolt (or any other WW2 era fighter .. aerodynamics for the win)
..even tho the T-bolt airspeed indicator andf others 'read' higher numbers.
Even so, the indicated airspeed in compressibility was not even close to accurate, indicating a much higher speed than the plane was actually doing in it's dive.
No piston engine fighter of WW2 ever broke the sound barrier.
Not even close.
In sea level dry air at 20 °C (68 °F), the speed of sound is 343.2 metres per second (1,126 ft/s). This is 1,236 kilometres per hour (768 mph)
Speed required goes down as density altitude increases if I remember my aerodynamics correctly
..that's why in a dive the planes gradually recovered, speed required to maintain compressiblity increased beyond what the plane was capable of doing.
For some.
-GE aka Frank
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This won't help but http://www.youtube.com/watch?v=iNBZBChS2YI&feature=endscreen&NR=1 (http://www.youtube.com/watch?v=iNBZBChS2YI&feature=endscreen&NR=1) My understanding is that while your p38 isn't flying above mach 1 the airflow around areas of the plane are trans sonic and so back at the horizontal stabilizer you begin to get one of these,(see video), and since the airfoil of the stabilizer isn't symmetrical,(or at least the location of the shock wave isn't the same distance back from the leading edge on the bottom as it is on the top,) it stops working and can't generate negative lift so over she goes. I'm not sure if it is that the elevator is overpowered by high pressure trapped above it, physically cant give up elevator, or if it is more that the lift is degraded. Anyway the stabilator was invented or at least used to address this problem, see f86 mig whatever 262???.
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The often quoted claim that air compressibility and localized supersonic airflow was an unknown during WWII is only partially correct. True, it was largely not understood in the U.S. and U.K. The Germans however understood this phenomena very well, mostly thanks to having several supersonic wind tunnels. They even had one capable of Mach 4.4. at Peenemunde. It was crucial in their development of the Mach 3 V-2 rocket and the Me 163 and 262 fighters. The best allied wind tunnel at the time could only generate 400 mph airflows.
I often chuckle at the silliness of people at the time who didn't believe the sound barrier could be broken when London had already been bombed by Mach 3 capable missiles. The first human invention to break the sound barrier was the bullwhip...
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ok ok .. I should qualify that dive speed statement to apply to piston engine fighters
.. altho I am pretty sure anyone who dove a 262 past the sound barrier did not live to tell the tale
as they locked up pretty hard at transonic speeds just like all the rest.
Their performance envelope was a bit higher due to swept wings but they still did not have laminar flow or area rule features.
-Frank aka GE
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Actually no German fighter had compressibility issues or suffer from "Mach tuck" like the 38 or 47. The 38's controls became ineffective because shock waves from the wing roots disrupted airflow over the tail surfaces. The 47's stick would flail about wildly in the cockpit often injuring the pilot. Neither aircraft could trim out of the dive since the airflow over the elevators was disrupted. Trimming was actually expressly forbidden since it could lead to over stressing the structure when the aircraft got low and slow enough for the control surfaces to suddenly become effective again.
The Germans knew about these transonic effects and equipped their fighters with flying-tail trim systems. They designed the 109, 190 and 262 with control surfaces that were out of the way of any shock waves and had trim that moved the entire tailplane, thus remaining effective even if control forces became excessive at extremely fast dives. Several P-51 pilots expressed surprise (and naturally a great deal of fear) when 109's pulled out of dives while they were still uncontrollable from compressibility effects, like Thomas L. Hayes, Jr., a P-51 ace of the 357th Fighter Group with 8 1/2 victories, recalled diving after a fleeing 109 until both aircraft neared the sound barrier and their controls locked. Both pilots took measures to slow down, but to Hayes' astonishment, the 109 was the first to pull out of its dive. As he belatedly regained control of his Mustang, Hayes was grateful that the German pilot chose to quit while he was ahead and fly home instead of taking advantage of Hayes' momentary helplessness.
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Is it possible that HT may have to look at the ability for all AC diving and getting out of a compressed? Or are they correct at what they can do? There are times that I have dive with a 109 or 190 diving with me, I pull out while the con meets ground.
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There's a LOT of weird "beyond the envelope" behavior that is not modeled in AH, and best it remain so. It's a game after all. The Spitfire for instance suffered from aileron reversal at high dive speeds... Yes, the ailerons would actually work opposite of the control input because of wing twisting at high speed. That must have been a biatch...
The 109 suffered from excessive control forces at high speed, so if your in-game opponent didn't trim manually he should make a very "historical" smoking hole in the ground. ;)
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Trim and rudder is the great secret to 109 success. Both in AH and in R/L.
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As this old P-38 driver explains, it's not about control stiffness/excessive control forces (like in the 109). It's about the controls completely losing their effectiveness. Only when you have effective control surfaces can you use trim to get out of trouble.
http://www.youtube.com/watch?v=5J0lEHyKInw
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Here's Brigadier General Robin Olds who got into compressibility problems in a 38 and barely managed to avoid augering, but surprisingly found a 109 on his tail.
http://www.youtube.com/watch?feature=player_detailpage&v=F8eD1XftA-E#t=311s
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The 47's stick would flail about wildly in the cockpit often injuring the pilot.
I think you are confusing the P47 with the 51. From what I remember, pilots said that the 47's stick was hard as if stuck in cement and some P-51 pilots said that they were slapped by the stick in high speed dives.
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I got questions regarding trim in the game and reality. My understanding is that in reality there are two kinds of trim, trim tabs or some some kid of jackscrew that changes the angle of the horizontal stabilizer. In both cases the relationship between control stick position and elevator position remains the same regardless of trim, correct or no? As regards the lift/control stick position relationship I am assuming that with trim tabs the relationship stays the same with different trims while the relationship varies with the jack screw setup as the angle of incidence of the whole setup changes, correct? When it comes to a flight simulator with a centering spring if you had a mechanical adjustment to move the centering force forward and back you could replicate trim tab type trim by not using software trim as you would not lose the ability to fully deflect the controls fully but would be trimming away forces the way you do in a light plane, correct or no? A mechanical system would not work in a jack screw model as the availability of full pitch up or down is only available with the change in angle of incidence which is a software feature, right?
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I think you are confusing the P47 with the 51. From what I remember, pilots said that the 47's stick was hard as if stuck in cement and some P-51 pilots said that they were slapped by the stick in high speed dives.
Both conditions are true. Before locking up the stick would flail about violently. The P-51 was a death-trap in an unrestricted dive compared to both the 47 and 38 and should never, ever exceed maximum dive speed.
The following was written by P-47 pilot Charles D. Mohrle:
Upon entering a vertical dive in a P-47, rapid acceleration was inevitable and, at high altitude it was exaggerated. At about 550 MPH indicated, buffeting became evident and it rapidly became severe. The control stick jerked violently in all directions and it was necessary to hold on firmly, with both hands, to manage it. Quite suddenly, the buffeting stopped and the stick became rigid - as though set in concrete. At that point, you jammed both feet hard against the rudder pedals and pulled back on the stick with all your strength - still with both hands. And you stayed that way, simply waiting for the airplane to respond.
In the vicinity of 15,000 feet, depending on atmospheric pressure, the nose of the airplane began to slowly creep toward the horizon. The rate of movement increased as altitude decreased. Level flight could be restored by 8,500 feet if you were willing to absorb the G-force punishment. In my last two dives, I pulled out gradually attaining level flight a bit below 4,000 feet with the airspeed needle still on the stop.
I'm not an engineer so cannot speak with technical competence, but I know of only one other propeller-driven airplane capable of such unrestrained dives - the P-38. And the Lightning had a tendency to "tuck under" early in the dive which made for a greater loss of altitude during the pull-out. It too, experienced buffeting.
I had a good friend who commanded a squadron in the South Pacific. They were equipped with Thunderbolts for most of his tenure. With the arrival of B-29s, their group was assigned escort duty and furnished with P-51s because the longer range of that fighter allowed them to stay with the big bombers all the way to Japan. They lost four pilots before learning that the Mustang couldn't be dived with the same impunity as the Thunderbolt. In each case, the left wing folded up and over the canopy, making escape impossible.
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I got questions regarding trim in the game and reality. My understanding is that in reality there are two kinds of trim, trim tabs or some some kid of jackscrew that changes the angle of the horizontal stabilizer. In both cases the relationship between control stick position and elevator position remains the same regardless of trim, correct or no? As regards the lift/control stick position relationship I am assuming that with trim tabs the relationship stays the same with different trims while the relationship varies with the jack screw setup as the angle of incidence of the whole setup changes, correct? When it comes to a flight simulator with a centering spring if you had a mechanical adjustment to move the centering force forward and back you could replicate trim tab type trim by not using software trim as you would not lose the ability to fully deflect the controls fully but would be trimming away forces the way you do in a light plane, correct or no? A mechanical system would not work in a jack screw model as the availability of full pitch up or down is only available with the change in angle of incidence which is a software feature, right?
With a conventional trim tab setup the stick will move with changes in trim since the trim tab is moving the control surface. With a flying-tail trim setup it depends on how the stick/elevator linkage is set up mechanically, but the stick will likely remain in about the same position when trim is changed. As for the software part HiTech would have to answer...
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With a conventional trim tab setup the stick will move with changes in trim since the trim tab is moving the control surface. With a flying-tail trim setup it depends on how the stick/elevator linkage is set up mechanically, but the stick will likely remain in about the same position when trim is changed. As for the software part HiTech would have to answer...
OK, so thats a yes to the part about using a mechanical spring center changer as trim in a trim tab setup as long as the software models the trim tab deflecting the elevator. I have a ms sidewinder with ff and it moves if you have auto trim off and change your angle of attack so that tells me something.