Dive Brake Sound file?

[Soulyss]

I found this little blurb while thumbing through Bodie's book on the 38.  A photo caption on Pg. 215 says...

Tony LeVier posed with his boss, Kelly Johnson, and the prized dive flaps then being installed at the factory on all P-38J-25-LO and P-38L fighters.  Retrofit kits were being sent out for the earlier series P-38J's.  Engineer Kenneth Pittman was primarily responsible for the electrically actuated drive system.  Dive flaps did not act as speed brakes; they, above all, affect the center or pressure distribution on the wing as compressibility came into play.

*edit*
Bodie also has the following on page 175, talking about compressibility and nose tuck tests done by Ben Kelsey on April 9th 1943.  

Once the nose started to go under, indicating that the normal lift point of the wing had moved aft under the effects of compressibility shock waves, he would deploy the dive flaps.  (the dive flaps did not decrease the aircraft speed in a dive.  They merely altered the airflow over the wing surface so that the wing would not lose its lift.)

In this particular test the dive flaps failed to open, owing to different (hydraulic) deployment system on the test 38 than what was planned production models which used an electrically driven actuator with a

one and a third horsepower electric motor, turning at 15,000 rpm, would drive each flap down to a 35 degree angle in just one and a half seconds.

[Traveler]

I assume you mean when it deploys and stows?

HiTech

Wouldn't there be a rummble while deployed.  There is in gliders , but thats a speed bread and very different in shape then the anti compression flap on a P38.  But I'd think there wouild be a rummble.

[Chalenge]

I would think its indistinguishable from the other noises associated with compressibility and engines.

[Traveler]

I would think its indistinguishable from the other noises associated with compressibility and engines.

you have a point, but what about when you reduce throttle and raise the nose , as airspeed bleeds off and the gap between compressibility and normale cruise widens would there not still be a rummble from the deployed anti compressibility flap?

[Chalenge]

I really doubt you would be able to hear anything to do with it. Your ear is much closer to the canopy and I am familiar with the changes in pitch-tone (not elevator pitch) associated with spoilers and flaps (negative flaps also) and my doubt only grows stronger with any type of engine noise thrown in.

I still think the 4g pitch up reported by the pilots is incorrect. I can see how they would assume it was associated with the dive recovery flaps but I still believe it is configuration induced rather than the flap itself. I realize the flap is not at the trailing edge but also too that the high-drag camber effect should induce a nose-down pitch tendency after flow is restored and the tail starts to fly again. I see this report as very much like the reports pilots give as witnesses to crash events as spectators where they often assume they can tell what the pilot was doing (and sometimes even thinking) from what they see as relates to their own experiences. This often times leads to bad assumptions which in the end is exactly what it is.

[Ack-Ack]

you have a point, but what about when you reduce throttle and raise the nose , as airspeed bleeds off and the gap between compressibility and normale cruise widens would there not still be a rummble from the deployed anti compressibility flap?

Lightning pilot would report that they knew the flaps were deployed because they could actually hear the dive flap electrical motors.  Remember that the dive flaps were deployed prior to the plane entering into compressability.  The pilots would deploy the flaps before the dive or shortly afterwards.  While it was possible to deploy the flaps while entering compressability and being able to recover, it wasn't commonly practiced to take such a risk and wait until the last minute to deploy them.


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