Originally Posted by
pstaney
MFS, truly a magnificient post. If I may ask 2 quick questions:
The falcon 50/900 series publish stall speeds in their AFM for clean configuration, yet it seems nearly impossible to happen since unless both hydraulic systems OR both sides of the electrical system are inop, the slats will deploy well before. So would these afm stall speeds be true clean stall speeds? Or slat deployment speeds?
We don't have a type with auto-deployment, so I will be willing to be proven wrong here, but I would expect the stall speed data in the AFM to correspond to the approved configurations which can be selected by the flight crew. If there's no way to select a truly clean wing, then I'd expect the speeds quoted to be for the normal operations case, with the slats auto-deployed. You may be able to tell which it is based on other data in the AFM - for example, it might be possible to reverse engineer the various stall speeds from looking at the slat or flap jam/fail speed increments - if the slat failed/flap failed at zero increment on Vref is huge, yet the stall speed for 'clean' isn't so different from the normal landing config, then you might be able to deduce which it is. (Although reverse engineering from published data is always a guess, since you never know what margins the OEM has given themselves, or what other factors may apply)
I'm assuming its not possible to actually select the flaps to zero and the slats out manually - if it were there'd be a chart for that config too, which would give the game away pretty sharply.
You mention Toulouse, so for the A320, would it thus not use 1.23 x level speed for max permitted aoa?
No, it's all a bit complex for aircraft with envelope protection; my understanding (again, note the caveat) is that the max AoA speed is considered comparable to stall warning - not the actual stall - and that a speed some 5-7% lower than the max AoA speed is used as the pseudo-stall speed for purposes of scheduling the various Vsr-dependent speeds. Since industry (as usual) led the regulators by quite a bit, it'll all have been done by means of 'special conditions' and 'findings of equivalent safety' I would expect, there really aren't any rules that address the Airbus aircraft directly yet.