Quote:
Originally Posted by Kurfürst
As I understand and from RAE papers the installations of bob weights to the elevator and longitudal instability were related. To my best understanding - and do correct me if I am wrong - instability means that if you pull the controls (in whatever direction), the aircraft will not only change its roll/pitch/yaw to the extent of control movement, but also keep increasing it on its own, as if there were some kind of inertia/acceleration going on. This was noted on Spitfire Vs by the British.
By adding the bob weights and making the controls progressively harder to move for greater deflections, it made this increased acceleration problem more difficult to encounter.. It did not cure the instability itself, which was an inherent aerodynamic feature of the design, but made it harder for the pilot to make it happen.
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The simple answer is I don't know how the longitudal instability manifested it's self. As I understand it the BoB weight was specifically fitted because people were breaking spits when coming out of dives. As you say the bob weight didn't resolve the instability because it was an aerodynamic issue. So how could the pilot "make it happen"? Wasn't it happening all the time? I think it was Tim Viggors who recalled writing off a Mk1 spitfire simply by pulling out of a dive, the airframe was so badly bent it was un repairable. He was lucky, the usual result was you said goodbye to your wings.
Can you explain to me how fitting a bob weight would correct an aerodynamic problem? I've never claimed to be an aerodynamics expert and tbh it doesn't really interest me. Despite this, I'm learning quite a bit from this thread.
The reason I ask is that in Morgan and Shacklady there are numerous mentions to the inertia weight, and none of them mention instability, they all however mention pulling out of high speed dives and that it was too easy to break the A/C because of the elevators being so light.
I thought the instability was more of a twitchy thing, as mentioned in the Rechlin trials? Specifically the "suffers from quick changes of trajectory along the vertical axis, coming from high longitudinal thrust momentum, and significantly disturb aiming" bit and the reference to "bad elevator and rudder stability on the target approach". So was the impact of the inertia weight a double edged sword? Ie it resolved the dive problem and softened the elevator problem?