I was watching tv last night, and this guy in England was happily flying around in his autogyro. It looked like fun, but I noticed the wobble, and it reminded me of the Hueys in Vietnam. They would make these small circular wobble motions while flying. The whole ship. I think other helicopters do this too, but I’ve only ridden in Hueys.
What? Rotors not balanced? Wouldn’t that shake the 'copter to pieces? Or is it some kind of harmonic thing.
Peace,
mangeorge
Rotor torque always wants to spin the copter. The engine spins the rotor(s) one direction and the “opposite and equal” reaction wants to spin the copter the other way. The tail rotor is, basically, a propeller constantly pulling (or pushing) the tail “back in line” with the direction the copter needs to maintain to avoid spinning. Since lots of forces are acting on the airframe, the rotors, the tail rotor, and the fuselage while the engine is doing its own minor changes (that affect the torque), it is unlikely that a pilot can maintain absolutely perfect control of the tail rotor throughout the flight. The minor yawing (the name for the motion you describe) is the pilot making continual adjustments to compensate for the torque while trying no to overcompensate.
HOWEVER, this brings up a separate point: was the guy in England actually flying an autogyro? With no power inducing torque in the rotor, I would not have thought that there was a need for a tail rotor and I would have thought that yawing was negligible. (Of course, he may have just been overcompensating for cross winds and so suffered a yaw from a different force.)
No, not yaw. What I’m talking about is where the Z axis make’s a circle. If you look down on a rivet head on the floor, it will be making circles.
Yep, the english guy was flying a true autogyro. It was powered by a pusher prop. He’s pretty famous, I think. The military has used some of his designs. So did James Bond.
Peace,
mangeorge
Autogyros do, typically, have rudders - so there must be some yawing induced by the rotation of the blades.
see
http://home.earthlink.net/~silasfsmith/
And yes, choppers do shake themselves apart - airframe components have very short service lives. This is a big part of why heliocopters are so much more expensive to acquire and operate than fixed wing aircraft.
Sounds like you’re asking about precession.
Torque about the vertical axis on a helicopter is caused by the engine delivering power to the main rotor. Autogyro main rotors are not powered, so there is no torque. (There is friction, but it’s negligible.) That’s why autogyros don’t have anti-torque rotors.
In a helicopter there is a great deal of downwash. Some of this downwash hits the fuselage every time a rotor blade crosses it, so there is an exterior force applied to the fuselage that moves it. I think the more main rotor blades you have the closer together these pulses are, and so the ride seems smoother. I know the 300CB seems smoother than the R-22, and I’ve heard A-Stars are smoother than JetRangers.
The tail rotor is for counteracting torque. Once it’s “set” for your power setting, the pedals are generally left alone (unless you want to turn the tail or coompensate for wind gusts).
My guess is that the rivet head on the floor seems to be making circles because some vibration is shaking your eyeballs.
I would think it would be vibration. It is very hard (if not impossible) to get rotor blades perfectly balanced, and some degree of vibration is considered acceptable.
The english gentleman with all the autogyros is Commander Ken Wallis. he flew Little Nellie in the Bond film. He had a lot to do with advancing recreational autogyro flight, along with Igor Bensen and Don Farrington.
In fact, one of the early “helicopter” attempts, the W.P. Kindree “Sky Car” did just that on film.
<very quick hijack>
Whats the diff between and autogyro and a helicoptter?
</very quick hijack>
Autogyros use a regular pusher propeller and an unpowered main rotor. The rotor is essentially the wing and generates the planes lift and is used for control. The rotor is tilted rather than using aelirons or an elevator. Gyros have a rudder, but its not as critical to control as it is to a fixed wing aircraft.
Regarding a gyro ‘wobbling’: My brother built & flew his own gyro last year. He’s a licensed pilot but was new to rotorcraft.
The first time he flew it (after first just taxiing many, many times BTW) he had a very serious ‘wobble’ or rather vibration in the rotor (he could feel it in the stick). I did a bunch of internet searches on the subject and we pretty much found that if you wanted to get rid of it (some gyro pilots just live with it) you simply have to get the rotor balanced perfectly.
It took several tries and was a real pain. It couldn’t be done ‘in the field’. We would make an adjustment (a very small adjustment) at his machine shop, then take it out to the airport (90 miles away!) and see if it worked. Basically, we could make one tiny adjustment per weekend!
Luckily, we got it right on the second try. And it was an amazingly minute change. We ran a plumb line from the leading edge corner of each rotor tip and the string missed the very center of the rotor shaft by a few millimeters! He re-machined the rotor’s teter bar so that it was dead center, and voila!, perfectly smoothe!
Thanks
Commander Ken Wallis. That’s him alright. Very interesting fellow. Thanks, Joey G.
I’m convinced that the wobble is indeed vibration. I put a nail, off-center, through an ice cream stick and made it spin. Holey Moses! Same wobble.
Thanks, all.
Peace,
mangeorge
[son of a hijack]
Was that an auto-gyro in Road Warrior?
[/son of hijack]
jack@ss: Yes.