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Originally Posted by Crumpp
It was actually addressed in the Spitfire Mk V but the longitudinal instability existed from the beginning.
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The longitudinal instability existed only if the CoG was in the aft positions as pointed out in the A&AEE report:
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(v) Stability - The aircraft is laterally stable at all speeds except in the immediate vicinity of the stall when it is unstable. The aircraft is directionally stable engine 'OFF' and 'ON' at all speeds, but on the climb this is difficult to assess owing to insufficient rudder bias. Longitudinally, the aircraft is stable with centre of gravity forward, but is unstable with centre of gravity normal and aft with engine 'OFF' and 'ON'. Longitudinal stability records are attached
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Note that early CoG limits are 5.8" to 8.6" aft the datum point. The revised limits are 5.4" to 7.9" for DeHavilland prop without bob weight (7.5" for Rotol prop).
Quote:
Originally Posted by Crumpp
They published all the warnings and characteristics of the Longitudinal instability in the Operating Notes.
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These warning can be found only from the operating notes of the Spitfire II with Rotol prop (most CoG sensitive combination) before the revised CoG limits and bob weights (which were needed only if CoG was too far aft as was case in the NACA tested Spitfire V).
Quote:
Originally Posted by Crumpp
It is kind of hard to argue that the NACA was incapable of performing a simple weight and balance when the RAE fixed the same issue and published warnings in the Operating Notes. The truth is they just did not know what the NACA was talking about as the stability and control criteria was classified at the time and Gates had not completed his visit.
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1. RAE criticized NACA static longitudinal stability test and for a good reason. Tests were done only at one position of CoG and that position was aft the revised limits.
2. Operational testing and handbooks of the aircraft were made by A&AEE, not by RAE.
Here is the direct link to the document by Gates:
http://aerade.cranfield.ac.uk/ara/dl...rc/rm/2677.pdf
See the page 9. The Spitfire K.9796 was tested at CoG 7" aft the datum point and that is still quite aft given that the range was from 5.4" to 7.9" (revised limits without bobweight and with DeHavilland prop).
Interesting comparison can be made to the Mohawk AX.882 which was tested at CoG 21" behind datum point, rather nose heavy given the range being 19" to 26". And despite forward CoG, the stick force for pull out was about the same as in the case K.9796.