“Long time no study aero.” Yep me too.
limlom
I’d always thought that where the real action is out on the end of the blade that AOA there at collective bottom should be zero, up or down.
To see one which is set at negative settings when it is running at flight RPM on the ground is to see an unhappy helicopter trying to beat itself to death while it works in vain to screw downwards thru the earth. This situation also leads to the crash report which starts with; - the A/C had high RPM upon impact-.
The A/C which is set right (at zero) will ALWAYS demonstrate the lowest power setting at flat pitch, remember - basic engine trend check number one.
Bernoulli can be a confusing gentleman, after studying for some years how he is employed to confuse inbound lightning strikes on electric fences so as mr lightning doesn’t blow the electric gizmo to smithereens, I confess, I agree, I am as confused as Bernoulli.
However when a careless pilot bottoms the collective in a real auto on a machine with the auto RPM set too high, I.E. with negative pitch at collective bottom, then mr coriolis will come to haunt one especially after first pitch pull and give an RPM tending upwards - off the clock - which in turn contributes to,
1) Spindle bearings brunelling,
2) Useless waste of large amounts of energy winding up said RPM, which in turn contributes to, high ROD as that energy has been stolen from the one and only energy source, mr gravity.
3) Crash report which starts with, yep you guessed it – the A/C had high RPM upon impact.
To see a machine with a too high AOA at the collective bottom will lead to no crash report from the pilot at all. Possibly only one from any casual spectator who may be around which will say something like, “why it just stopped right there and plum fell outa the sky.”
Anyone who has done an R22 saftey course will testify that finger trouble can easily cause that same vertical descent even with correct auto RPM being set.
My advice would be – have a look at your FAA basic helicopter handbook- its all there.
Its all just a tad different from the old steel blade windmill or sailing boats where the wind has to divert around an object thus creating a vacuum from behind which then draws the object forward.
Cheers tet