Author Topic: Did Enemy Have Compression Problems?  (Read 1923 times)

Offline Dadtallica

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Re: Did Enemy Have Compression Problems?
« Reply #15 on: August 14, 2023, 08:24:11 AM »
I compress a 109 at least once a week.  :joystick:
Back in 2022 after a loooooong break from 2010. Old name Ratpack, same for the BBS.

Squad I did the most tours with were the Excaliburs then The 172nd Rabid Dogs. Still trying to talk Illigaf, Coola, Oldman22, and Joecrow into coming back instead of being boring old farts!

Offline SIK1

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Re: Did Enemy Have Compression Problems?
« Reply #16 on: August 14, 2023, 09:27:04 AM »
No - the P-47 and P-51 were the same, limit dive speed. Both were placard restricted at 0.75, both 'do not exceed at 0.8M. IIRC the max dive attempted and survived by P-47 was 0.83M. 0.85M for P-51D;

The P-47C and D made holes in the ground just like P-38s for the same reason, just a little higher threshold for the aft movement of Center of Pressure that caused the infamout 'mach tuck'. Both were more or less solved by P-38J and P-47D-30 (IIRC) installation of dive flaps.  The P-51 never had that problem due to he unconventional nature of the 45-100 airfoil.

The dive flap both moved the CP forward when deployed, and reduced the acceleration of the extreme turbulence that blanked the elevator authority.  The P-38 while also having wing mounted dive flap also moved the CP forward whe deployed but while it redced mach tuck, the centerbody was still blanking the elevator - but pilot 'got relief' anyway because the dive flap introduced a pitch up (small but important-both P-47 and P-38).

Great explanation.  :aok


I read some accounts of P51 pilots, switching from P51B to the D model, experienced problems trying to dive after the German planes, they experienced problems due to the bubble canopy.

The early 51 D models had some stability issues because they had less side area due to the removal of the turtle deck. It was resolved with the addition of the dorsal fin.

 :salute
Sik
« Last Edit: August 14, 2023, 09:35:52 AM by SIK1 »
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Offline icepac

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Re: Did Enemy Have Compression Problems?
« Reply #17 on: August 18, 2023, 08:44:42 AM »
I explore all flight models at all altitudes.   
If you donít you miss out.

Offline drgondog

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Re: Did Enemy Have Compression Problems?
« Reply #18 on: September 10, 2023, 06:35:16 AM »
Great explanation.  :aok


The early 51 D models had some stability issues because they had less side area due to the removal of the turtle deck. It was resolved with the addition of the dorsal fin.

 :salute
Sik

The 'reduced side area'due to installing the bubble canopy is a myth.

The RAF/R-R discovered the yaw instability immediately after Merlin installed in Mustang I. AL 963 was modified with both a dorsal fin,then increased chord fin/rudder combination. The issues and flight test results were reported to NAA in Feb 1943. NAA tested the dorsalfin o the P-61B-1 and NACA tested both he DF and a tall tail in fall 1943. InMarch 1944,both the DF for P-51B and P-51D  were released to Service Group for kit production, but the P-51D production article was only released for P-51D-5 (both Inglewood and Dallas) at #651, and for last block P-51C-10-NT.

The additional benefit to streamlining flow during yaw, increasing effective fin/rudder area - was reduction of torsional loads on empennage in yaw due to prop vortex.
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Online Brooke

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Re: Did Enemy Have Compression Problems?
« Reply #19 on: October 16, 2023, 11:11:34 PM »
I remember reading an account of a 109 pilot who got into compressibility trouble.  I don't remember the reference, though.  I recall him, in desperation, deploying some amount of flaps during the dive, too.