Cross-control

[spaceman spiff]

Hi guys and gals.

Pretty much just started lessons, basic turns etc..

Just about any time i make a left turn, half way thru i end up with left rudder, but a littel right aieleron and up elevator. Is that normal? Am i banking too much for that turn?

[Udi]

Aileron? Elevator? What aircraft are you flying? Do you have an instructor? Are you trying to learn to fly by correspondence?

Udi

[Al_Hammer]

Aileron? Elevator? You must have a fixed wing background. The rotor controls roll and pitch, but to answer your question, rudder should not be needed in a turn. Some slight back stick is needed in a coordinated turn, but no cross control. The stick goes left for a left turn and right for a right turn and then comes back to neutral once you are in the turn. (since the gyro is now banked the rotor doesn't need to tilt relative to the airframe.)

[Harry_S.]

Yeah Joe; sounds like your butt is sitting in a fixed wing...or a pc simulator?!


.

[Brian Jackson]

Ailerons? WTF?

Joe, please check what forum you're on before posting. I don't think even the early designs had those.

[Doug Riley]

Actually, Brian, the early gyros did use ailerons. The rotor head was just a spindle on a fixed bearing -- no gimbal pivots in either axis. All roll control was through conventional ailerons (located on skinny wings). Pitch control was by elevator and yaw was by rudder. The rotations of the whole frame, induced by these control surfaces, fed through the fixed spindle and flap hinges as cyclic pitch changes. It was a "frame leads rotor" setup, instead of our "rotor leads frame" system. Each type has advantages and disadvantages.

Unlike FW planes, gyros don't have an over-banking tendency in turns. That's because of the 90-degree phase lag inherent in the teeter hinge. The blades experience a difference in airspeed due to the turn as they pass through the "9 o'clock-3-o'clock" position, just as fixed wings do. Thanks to the phase lag, however, this difference works itself out as a bit of extra fore-aft rotor "blowback."

You do have to use a touch of backpressure in a gyro turn, if the machine is statically stable. Just a whiff of rudder in the direction of the turn sometimes makes the turn a tad cleaner, too.

[Victor Duarte]

Doug,
not to hijack this thread, but could you develp the differences between "frame leads rotor" setup and the rotor leads frame , or give me a link ?

I think it has a big influence on stability, manoeuvrability and Low G behaviour is it right ?.

Thank you.

[Doug Riley]

Victor: You're right, but I don't know of any texts that go into detail about the pros and cons of the old system. Both systems control the rotor by cyclic pitch change, but the texts such as Gessow and Meyer concentrate on "direct" (rotor-leading) cyclic control.

Obviously, aerodynamic surfaces don't work very well at low speeds, and that caused problems in the case of torque roll in these machines. Johnny Miller wrote some stories about flying the early Ciervas in the PRA magazine -- nothing technical, just reminiscences. There are other anecdotes in the few books that exist about the old autogiros (none of which I have read!).

Perhaps Al Hammer, Ron Herron or Chuck Beaty have some better references for you.

[Al_Hammer]

Here's Cierva's C4, which had ailerons and elevator.
In fact the wings were pure ailerons, pretty wild.


The combination of the rising and falling action, which came to be known as flapping, and the increase and decease this had on the angle of attack served to balance the lifts created on each side of the aircraft. The hinged blades also eliminated the gyroscopic effect caused by the rigid blades.
Cierva's next design, the C.4, incorporated these hinged rotors. For lateral control, ailerons were mounted on outriggers to the side of the aircraft. Yaw and pitch control still came from a rudder and elevators. On January 17, 1923, the C.4 flew, marking the first controlled flight of an autogyro. The C.4 also demonstrated the autogyro's safety in low speed flight. On January 20, three days after its first flight, the autogiro went into a steep nose-up attitudeafter an engine failure at about 25-35 ft. In an airplane, this would have almost certainly resulted in an almost unrecoverable stall. But the autogyro just descended gently to the ground without damage to the machine or injury to the pilot. This low speed safety was demonstrated even more dramatically on January 16, 1925, when another design, the C.6, lost power after take-off at about 150-200 ft. The pilot was still able to turn the autogyro around and bring it in for a safe landing, with only slight damage to the machine. This maneuver would have been much more difficult in an airplane, and quite possibly could have led to a worse accident.
http://www.jefflewis.net/autogyros.html

[Victor Duarte]

Thanks Doug, al,
i had read this site , but i missed this paragraph, interesting tough.

I asked this because i thought that a little elevator effect could reduce the pendulum effect that could lead to pio or rotor unloading. Only in pitch, the roll is not a problem.
i simulated it in Xplane and it seems to work well.

sorry if i deviated from the thread, and thanks for your kind answers, like always.

[Brian Jackson]

Originally Posted by Doug Riley

Actually, Brian, the early gyros did use ailerons...

I stand corrected. Thanks Doug. I resolve to listen more than speak.

[Al_Hammer]

Victor, an elevator, acting as a stab on a long arm, will damp pitch oscillations, so your idea makes sense. X-Plane is sometimes very usefull, isn't it?

BTW, the pendulum effect is not strictly due to the gyro being a pendulum. PIO can develop because the airframe does not align with the relative wind very fast unless you have a stab. The gyro climbs with back stick, but does not nose up right away. This is a function of moment of inertia about the cg rather than pendulum action.
The rotor is not a fixed point. The gyro rotates about the cg, not the teeter bolt, but your point is still valid. An elevator controlled gyro would probably not PIO very easily.

[Victor Duarte]

Originally Posted by Al_Hammer

. X-Plane is sometimes very usefull, isn't it?

YES !

and i also agree with all your points.

i learnt that the coordinated turns are a gyro specificity.
some say you shouldn't have to stick back, just maintain a good bank and let the gyro turn. I feel it depends on the rotor pitch and coning.

[Al_Hammer]

If the bank is 60 degrees, the lift needs to be twice what it was in level flight to maintain altitude. I don't think you can achieve that without back stick.

[spaceman spiff]

Sorry, bad terminology, yup i was in a gyro. Its a tandem with my fat ass in the front, so it may be behaving badly because of being nose heavy?

I give left cylclic, it leans several degrees then tends to loose a bit of altitude and seems to lean further into the turn and dive (just a tad) so i end up with a littel pressure back and a fair amout to the outside of the turn as well to keep it smooth. anyway i have annother lesson tomorrow, will ask teacher about it