Author Topic: compressed wing  (Read 714 times)

Offline VAMPIRE 2?

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compressed wing
« on: March 13, 2012, 10:34:55 PM »
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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Offline APDrone

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Re: compressed wing
« Reply #1 on: March 13, 2012, 11:06:50 PM »
You mean like 'compressibility'?  That funky little feature that encourages B38s to crater when dive-bombing?

AKDrone

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Offline VAMPIRE 2?

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Re: compressed wing
« Reply #2 on: March 13, 2012, 11:12:01 PM »
yes and like zeros when the attempt to follow p-47's down...
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Offline flight17

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Re: compressed wing
« Reply #3 on: March 13, 2012, 11:25:52 PM »
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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Offline APDrone

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Re: compressed wing
« Reply #4 on: March 13, 2012, 11:43:55 PM »
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..
AKDrone

Scenario "Battle of Britain" 602nd Squadron


Offline F22RaptorDude

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Re: compressed wing
« Reply #5 on: March 14, 2012, 12:26:11 AM »
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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Offline oakranger

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Re: compressed wing
« Reply #6 on: March 14, 2012, 12:59:18 AM »
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..

Quote
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.


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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.


Quote
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. 
Oaktree

56th Fighter group

Offline Grayeagle

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Re: compressed wing
« Reply #7 on: March 14, 2012, 07:41:36 PM »
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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Offline pembquist

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Re: compressed wing
« Reply #8 on: March 14, 2012, 11:03:26 PM »
This won't help but 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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Offline PR3D4TOR

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Re: compressed wing
« Reply #9 on: March 17, 2012, 07:22:33 AM »
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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Offline Grayeagle

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Re: compressed wing
« Reply #10 on: March 17, 2012, 12:16:08 PM »
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
'The better I shoot ..the less I have to manuever'
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Offline PR3D4TOR

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Re: compressed wing
« Reply #11 on: March 17, 2012, 08:33:47 PM »
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.
« Last Edit: March 17, 2012, 09:09:37 PM by PR3D4TOR »
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Offline oakranger

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Re: compressed wing
« Reply #12 on: March 17, 2012, 08:46:21 PM »
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.
Oaktree

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Offline PR3D4TOR

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Re: compressed wing
« Reply #13 on: March 17, 2012, 08:56:53 PM »
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. ;)
« Last Edit: March 17, 2012, 08:59:02 PM by PR3D4TOR »
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Offline PR3D4TOR

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Re: compressed wing
« Reply #14 on: March 17, 2012, 09:03:23 PM »
Trim and rudder is the great secret to 109 success. Both in AH and in R/L.
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