I did see a film of their purpose on Great Planes I believe. The dive 'brakes' according to the program [And the supporting war time film, possibly a pilot training film] did not and were not designed to slow the plane down to non-compressible speeds. Instead they changed the shape of main wing's airfoil which caused the turbulent flow to exit the wing at much lower point restoring laminar flow to the evelator at the tail section. This restored elevator operation and allowed the plane to pull out of the dive. I believe this was developed in leu of forcing the plane to slow down. It is relavant to notice that the elevators of the Lightning are almost in the same plane as the main wing. I think this is why the plane suffered from compression effects more than other planes.
Vinkman, you are wrong. The relationship between the positions of the wings and the elevator has
nothing to do with compression, or how it effects the P-38. Ignore "Great Planes" and the rest of the television crap. They are wrong, very wrong. To get the truth, you have to read.
Compression on the P-38 was strictly a function of the profile of the wing of the P-38. There was no such thing as elevator flutter on the P-38 either. Some general had those little counterweights added to the elevator on the P-38. They did
nothing at all, as not only was there no elevator flutter, but Kelly Johnson had already not only put counterweights on the
inside the elevator, but he also had the skin made thicker and the internal bracing increased, in order to make the elevator heavier and more stable. Kelly Johnson, in referring to those external counterweights, was quoted as saying "they were useless, they didn't do a damned thing, other than maybe kill some pilots who had to bail out".
Again, the two things that increased the speed at which compression began, and reduced the effects of compression, were the increase in the radius of the fillet joint where the wing attached to the center nacelle (along with improved fit) and the dive flaps. Nothing that was done to the elevator after the original design helped.
When the P-38 (or any plane, as the P-47 suffered from compression as well) entered into compression, the elevator didn't matter at all, as no deflection of the elevator could overcome the amount of force that the wing, suffering under compression, was pushing down on the nose with. In fact, if it had been possible to get the elevator on the P-38 to deflect enough to force the nose up, the tail would snap off under the load. In fact, Lockheed test pilot Ralph Virden was likely killed when the spring tab apparently broke on the elevator in a dive, allowing the elevator to reach full deflection. The entire tail section snapped off, and Virden was killed in the resulting crash.