Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Mongoose on October 31, 2022, 10:36:19 PM
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I know the early P-38 and P-47 models had problems with compression and control lock in dives, until the engineers figured out how to fix it.
Did planes from other countries have similar problems with dive speed?
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Short answer: Yes
Me109 comes to mind right away
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Physics be universal, eh? :)
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Physics be universal, eh? :)
Until you run into a blackhole or Nazi anti-gravity yes a I believe something to that effect.
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I don't recall the P47 ever having compressabilty problems, It performs the best with full power pointing straight at the ground regardless of airspeed.
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Later models (think M and N) had a similar dive recovery flap to the ones on the later P-38J's and all of the L's
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M has dive brakes in game, does N also have them in game?
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M has dive brakes in game, does N also have them in game?
M and N both have dive flaps not really dive brakes, they make the elevator surfaces lighter at high speeds delaying compression by changing the airflow impacting the horizontal stab/elevators. They actually cause very little drag when deployed
For the P47s they are only needed when diving from 20k with WEP straight down at 600mph+. On the P38L they are A LOT more useful and offset the main weakness of the 38 (low critical mach number).
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People get confused even tho they are marked in the controls setup as such they are most definitely NOT dive brakes. These things aren't gonna slow you down!
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P-47s had low Mach numbers compare to Spit and Mustang.
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Both P-47 and P-38 as well as Bf109 and Fw 190 had same issues with compressibility - primarily manifested in nose down pitching moment as center of pressure moved during transonic to supersonic flow. The issues were compounded by wake immersing h.Stab and blanking elevator authority until Mach number decreased below critical mach. The Mustang avoided the need for dive flaps because the CP was already 10-15% aft of the classic NACA 23xxx and similar airfoils of the day. The P-47D wing however was closer to the P-51 wing with max t/c very similar (30% vs 37%) and Root T/C of 14% vs 16.5%, and had a simiar Mcrit.
The P-47D-30 had first dive flap installation, the P-38J-25 was first production dive flap installation, but kits were sent for J-15 (One such delivery famously short circuited by RAF on way to ETO (in Feb 1944??)
NAA installed a dive flap on P-51B-10-NA but found no material benefits to dve control 'without' flaps.
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....and then there's the Brewster.
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The P47 had compressability issues at much higher speeds....................bec ause it was faster.
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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).
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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.
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I compress a 109 at least once a week. :joystick:
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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
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I explore all flight models at all altitudes.
If you don’t you miss out.
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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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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.