Maybe a stupid questions, may be already answered (pls. link to it) but why do manufacturers not add a springloaded "minus section" to the bottom end of pitch level travel?
As currently "pitch fully down" is ~ 0° blade angle, we can stall blades due too low an RRPM, and lacking any negative angle we - even theoretically - cannot recover from that situation w/o engine power.
I'd like to suggest to provide us with - from the "current bottom" of pitch lever travel - an
additional 1" travel, for which one has to overcome a strong spring, where no friction would hold the lever, which turns blade angle to say -20° with respect rotorplane.
- from 0 up to full pitch blades would be at 0° till 5-8ish°, as we are all used to.
- from 0 down to the new "hard stop" we'd get 0° to -20°
That way one could (at FL100) let the RRPM deliberately reach today "unrecoverably low values", when switch engine to idle.
THEN one could bring the (stalled) blades to -20°, even while falling w/o laminar flow over any section of the blades they'd windmill, thereby increasing RRPM, till the combination for say ~5000ft/min "freefall" and the increasingly regained RRPM create an angle of attack that produces laminar flow again. At that point one should bring the pitch lever back into normal range and could commence a std. autorotational landing.
That helicopter would be autorotational fool proved, lacking "unrecoverable rotor speed".
I'm pretty sure there is
some good reason why we don't get the negative blade angles the RC-Helis do. (They have rigid heads with +/- 15° balde angle linear on the RC stick, normal flying happens on upper half of pitch stick travel, upside down fly is down using the lower hlaf of pitch stick travel)
Maybe stuffing 20° blade angle in a rel. small section of pitch lever tavel is mechanically tricky, but certainly not impossible, methinks.
comments anyone?