Brushing up on my knowledge from flight school, I came across this thread. I was at the point where I thought I had fully understood the difference between VA and VO, but now I'm not sure anymore. There is one aspect I don't yet understand.
Since VS sqrt(n), respectively VS1 sqrt(n) in CS-25, is the upper limit for VO and the lower limit for VA, I would have assumed to find VA drawn at the point of the V-n diagram where the +CNmax curve intersects the limit load factor line (at the 'corner speed') or to the right of it. Looking at the V-n diagrams in CS/FAR 25.333(c), I see VA is drawn to the left of the corner speed.
I could find references where VA is coincident with the corner speed [1,2], but only the Oxford POF textbook [3] provides an explanation for VA being left of 'the corner'. They say 'VA is slower than the speed at the intersection of the CLMAX line and the positive limit load factor line (point A) to safeguard the tail structure because of the higher load on the tailplane during the pitch manoeuvre'. Isn't this a direct contradiction of the design requirements in CS 23.335(c)(1) and CS 25.335(c)(1)?
Lantirn has quoted the same source and mentioned their confusion of VA and VO. Still, I can't see why the flight envelopes in CS/FAR 25.333(c) put VA to the left of the corner. Is it possible the diagram in the certification specifications is from a time before the introduction of VO, and VA is meant to be an operational VA rather than a design VA? I gather from Keith's post this might be an explanation.
Am I missing something?
[1] Torenbeek E, Wittenberg H (2009) Flight Physics. Springer, Dordrecht, p 321
[2] Gallagher G et al. (1992) Fixed Wing Performance. In: U.S. Naval Test Pilot School Flight Test Manual. Veda Incorporated.
http://www.vmihosting.com/MWS/Docume...PS_FTM_108.pdf. Accessed 30 Mar 2013
[3] Oxford Aviation Academy (UK) Limited (2008) Principles of Flight. OATmedia, Oxford, p 463