AR-1 gyro manufacturer
- Oct 31, 2011
- Tampa, FL
- Total Flight Time
- 4000+ 472 gyroplanes. Sport CFI Gyro and Trikes
I get dizzy easily. I'd barf if I rode around on a rotor-only gyro -- presumably sitting on a giant hub bar in the middle. Yecch.
There's no free lunch when it comes to trim drag. If you want a stable airfoil, you need to apply that download to the trailing edge. You can use an HS boomed out back (the normal approach) or you can make the download using trailing-edge reflex. In the latter case you're simply attaching your downloaded H-stab to the aft end of the wing (either fixed or rotorblade; the same rules apply; a rotorblade is simply a small flying wing).
Some designers try to cheat on this rule. My closest gyro-flyin' buddy died in the crash of a sailplane that was intentionally designed with a non-downloaded HS. The wing had drooped trailing edges to add even more nose-down moment. To keep the nose up, the designer put the CG way aft at 40% or more of wing chord. But this arrangement only works in a narrow range of airspeeds; either faster or slower, the wing's pitching moment varies as the square of airspeed, while the weight at the CG obviously doesn't vary at all. Bill might have been OK if anyone had told him about this aggressive setup -- but no one did. Sad.
We in Gyro-land had a rotor blade "design" foisted upon us some years ago with the same sort of drooped trailing edge airfoil -- an unworkable design.
Less radically, some experimental gyro rotor blades have been laid out with little or no reflex, in the hope that the blade's mechanical stiffness alone would keep the blade from "tucking." Yes, it would be nice to get rid of the trim drag caused by reflex. Rotorblades are pretty limber, though, and such a design amounts to yanking on the dragon's tail. Bensen put a little extra reflex into his metal blades at the tip, probably as a precaution against this sort of instability.
Fara, I agree that a farther-aft placement of the HS has real benefits. With a longer lever arm, the download in pounds (hence trim drag) can be less for a given number of foot-pounds of nose-up torque. Even better, the HS's role in dynamic stability (damping) increases as the square of the tailboom length.
OTOH, I disagree vehemently with Magni's decisions to (a) use no HS download and (b) place the HS so low that it catches no propwash. We need that propwash on the HS in these slow aircraft; HS lift varies as the square of airspeed. Immersion also makes the HS respond in proportion to throttle setting -- a desirable arrangement if you have HTL.
Finally, an HS centered in the propwash helps counteract torque roll. You can have a far-back, wash-centered HS as long as you have the rotor clearance, but the structure gets a bit unwieldy on a pusher.
I like the HS right at around 70% radius of the prop arc. Torque can be handled in other ways. But who knows I may change my mind with some experimentation. There are some other advantages to having the HS right at center in that it makes the vertical stab more effective at the cost of some weight in construction. I agree about a little reflex on your blade airfoil. It should definitely help even if its a little inefficient.