I was surfing for tech data on B-17, and came across a single page from the original Technical Orders that accompanied the more commonly known pilot manuals. On it were 2 paragraphs headed "Dives". To quote:
The structural factors limiting the dive speed to 305 mph are the engine ring cowl strength, the wing leading edge de-icer boot strength, the pilot compartment winshield and enclosure strength, and the critical flutter speed. The engine ring cowl has been designed to wthstand 420 mph. Windshield and pilot compartment have ample margin at 305 mph. The wing leading edge de-icer boots begin to rise slightly form the wing at 305 mph, and any excessive additional speed would probably lift the upper portion of the boot well abovve the wing surface and allow it to flap severly against the leading edge, thus causing a structural failure.
Structural failure at the wing leading edge is generally considered a bad thing.
Secondly, the next paragraph places a great deal of emphasis on the elevator trim tabs in dives, especially when recovering. I dont have time to type it out (and I cant find my OCR program this am -- grrr), but this passage strongly implies that elevator tolerances are limiting factors when pulling out even from dives limited to 305 mph or less. And B-17s were designed with greater strength at teh cost of carry capacity. One wonders how less robust frames could ahve tolerated dives. (And I'd just love to see what that slender Davis wing would do at dive recovery G loads.....)
I never would have expected that wing de-icer boots would be the weak link for diving B17s, but you can bet on every aircraft such a weak link exists. I'd suspect that most are limited by elevator G tolerances if nothing else.
Bottom line -- buffs were designed for level bombing. In order to maximize payload, range, and effectiveness the competent aeronautical engineers WOULD NOT include structural strengths to also permit dive bombing. It would be stupid to trade off load capacity to get structural strength for a silly mission like dive bombing buffs -- and there WAS a war on.
Conclusions:
1. Airframes designed for level bombing shuld not be permitted to tolerate high G maneuvers like dive bombing and pull outs.
2. Based on data presented, B-17s should have wing leading edge structural failure at 310- 325 mph.