human213
Senior Heliman
Location: malibu
| Yaw control inquiries and discussion...In response to several inquiries about the yaw system:
I wanted to discuss futher why the zero lift situation of say, an fai quality 540 stall turn, or any other maneuver
is no problem for the coax, and why the yaw authority is even greater than the unbalanced conventional TR...
and works with no unwanted collective plane motion in any attitude, and is completely balanced and symmetrical...
Hypothetical x...
where, let us say we are in the zero lift moment of the
upper line of a 540 stall turn...
angle of attack of both rotors is zero, for this hypothetical...
and we are doing a left yaw 540...
top rotor increases angle of attack with left yaw input...
bottom rotor decreases angle of attack exactly the same, to maintain zero net collective plane of movement; this
decreased angle of attack causes ALSO, left yaw... ( via decreased right yaw torque reaction of COUNTERCLOCKWISE lower rotor...upper obviously, clockwise..)
The reflex airfoil of the lower blade is going towards feathering...the upper to a greater angle of attack...
less drag below equals left yaw...
increased drag upper equals left yaw..
net equals left yaw input...
At low angles of attack, such as a stall turn with blades near zero, there is less torque generated by a reflex foil going negative
than going to a positive angle of attack...thus, the differential torque of the stall turn scenario works as well as in a hover or
net lifting vector attitudes...or any other flight envelope of control.
This is borne out by the actual flights with excellent stall turn authority, and full authority to yaw in full forward flight envelope,
exactly as per the full size.
Thus, net yaw motion will always be induced by contrateral opposing collective induced differential torque input of BOTH rotors for any TR input direction....with no compromise in zero net lift or collective movement moments regardless of attitude....this is further enhanced by accelerated slipstream the lower rotor encounters...
Michael
Not everything that can be counted counts, and not everything that counts can be counted. |
