TRADE FOR BENSEN METAL BLADES

Bensen blades have a light, responsive feel because they are, in fact, light and run at high RRPM.

They are about the least efficient blades around, though, and their lightness and high RRPM are not all good. High-RPM, low mass blades lack much rotor damping, making the aircraft more "twitchy" and subject to PIO (porpoising).

PIO claimed many lives during the Bensen era.
you mean many lives were claimed by people modifying the bensen. The original bensen with a mac had centerline thrust. Modifications made the bensen dangerous
 
you mean many lives were claimed by people modifying the bensen. The original bensen with a mac had centerline thrust. Modifications made the bensen dangerous
Butch a lot of pilots died even without modifying their Bensens. A lot of the deaths were due to their lack of training. Training was very, very limited back in the day. The Bensens appeared so easy to fly a lot of people attempted flight before they were ready. Bensens were quick handling on the ground and pitch sensitive in the air. If you followed the Bensen book you had a better chance of success but, that wasn’t a guarantee.
 
I think they were never centerline thrust, the original with the Mac and short fat prop was MORE centerline because the engine/prop sat lower.
But it was still a low profile gyro and the mast tended to be shorter.
The addition of larger props raised the thrust line, moved the weight higher and increased the thrust which also added to the PPO risk.
A big horizontal stab probably would have a saved a lot of lives.....
 
The stock Bensen was close to CLT, but not on the money. There were significant weights down low -- especially the heavy fuel tank with steel mounts, and the heavy 3-piece industrial wheels. Ken Brock lightened up these two items, resulting in a variant of the Bensen that really WAS CLT.

Bensens suffered from other stability issues, too. They lacked effective compensation for engine torque. This meant that they were vulnerable to uncommanded in-flight rollover at high throttle and low/zero G. Many PPO's actually involve roll as well as pitch -- film evidence confirms this.

Less discussed, but important, was their vulnerability to PIO (pilot-induced oscillation, or PIO). A couple of design factors contributed to this problem:

First, those wonderfully light, high-RRPM Bensen blades we've been discussing have very little rotor damping. Damping is essentially a lag in the tilting of the rotor disk once the pilot has made a control input. Too much damping makes the gyro sluggish, with high control forces. Too LITTLE, however, reduces control "feel" and makes over-control very easy. Combine this with an airframe that lags in ITS response once the rotor finally tilts (because of a lack of H-stab power), and you have a recipe for operator-induced oscillations.

Bensen crashes very often started with PIO, which then led to inversion of the craft because of HTL and torque roll.

Today's gyros have heavier, larger rotors that turn more slowly. This improves rotor damping. Nearly all contemporary designs also include significant horizontal stabilizers, which keep the frame aligned with the rotor. As a result, gyro PIO accidents have become rare.

It was possible, of course, to learn to handle a stock Bensen and have a great ol' time. This required some unusual control techniques, far beyond a beginner's understanding of "push this way to go that way."
 
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