Hi Folks! A Newbie here, with a few questions...

[Kugel]

I've been lurking for a while, and I have been interested in been interested in Autogyros for a long time.

I have a few questions, based on observations of the many rotorcraft that I have looked at:

1) Why are there not more (or any) 3 or 4 bladed gyros?

2) What are the advantages/disadvantages of a 3-4 bladed gyro?
a) more lift for smaller diameter, or is it all about disk loading?
b) more speed with smaller disk diameter?
c) higher/lower rotor RPM's? higher RPM = Smoother Stick?
d) does small disk diameter = higher cruise speed?
e) more blades = Smoother stick?

3) A super simple system would be a totally fixed rotor head, except for a manual "rotor head angle (pitch?) trim" (kinda like a flap handle on a FW airplane), with a 2-Axis Control system (Rudder and Elevator only).
a) what kind of control characteristics would such a machine have? lazy but very stable, like a Piper Cub?
b) probably less "sporty" handling, as compared to a 3-axis fully articulating rotor head with rudder, but would it be dangerous?

4) For Airframes, I've seen some welded 4130 steel tube type, but all of the aluminum frames seem to be bolted together.
a) 6061-T6 tubing has a very good strength to weight ratio: can it not be MIG or TIG welded to produce a very lightweight and strong airframe?

I know that there are a lot of tried and true designs out there, but I am just wondering about why some things are done or not done.

Thanks for any input!

Best Regards and God Bless!

Kugel

[Chuck Roberg]

I'll offer a few short answers.

1) cost and complexity

2) I'll skip this one and leave it to someone else.

3) Your describing the first autogyro's. They were very stable and maneuverable. And not dangerous. This is what I have learned. I was not around then.

4) Sure a welded frame is usually better. But most people do not want to have to learn to weld. So a bolt together type airframe is easier. The Barnett gyro airframe, for one, is welded.

By the way. Welcome to the forum.

[Doug Riley]

Two-axis control would not work well on a gyro. An aircraft, unlike a car, cannot rely on friction with the ground to create the force that causes it to depart from straight-line travel and make a turn. Aircraft commonly use their lift-making devices (wing, rotor) to create this force instead.

To do that, we have to point the lift-making device toward the center of the turn. The most direct way to do this in a FW plane is to crank up the lift on the outside wing, and reduce lift on the inside wing, with ailerons. You can, instead, get somewhat the same effect with a spoiler on the inside wing and/or yawing the plane to create a skid. The skid won't turn you in and of itself (you'll just slide sideways), but with enough dihedral, the plane will bank after a moment and around you'll go. Not too elegant, but it works with planes having large amounts of dihedral, such as the Quicksilver. Wing sweep can be used to add to the effect.

A rotor with flapping hinges does have a pseudo-dihedral effect, known informally as "blowback." It is "pseudo" in that, unlike the fixed wing, it's not the shallow V-shape of the rotor that causes it. Instead, the rotor tilts a couple degrees away from the oncoming air because of the way that flapping hinges compensate for the difference in airspeed between the advancing and retreating blades.

The effect is weak enough that turning a gyro with rudder-only produces a dangerously wimpy turn. You simply need more turn authority to be able to maneuver safely. The Cierva machines of the 30's were full 3-axis ships, using either ailerons on slim wings or direct cyclic pitch (depending on the model) to create roll. With ailerons, roll authority got poor at low airspeeds, however. Roll authority with direct cyclic is excellent right down to, and including, 0 mph (even negative) airspeed.

What some people don't notice is that, with a rotor having flapping hinges, all pitch and roll control is actually done through cyclic pitch, whether or not your spindle is movable. If you use elevators and ailerons as on the earlier Ciervas, you simply tilt the airframe first, which tilts the fixed spindle relative to the rotor disk, which induces a cyclic pitch change, and -- voila -- the rotor tilts. It's the tilting of the rotor (the lifting surface) that actually accomplishes the maneuver, whether we use a movable spindle, a swashplate or a fixed spindle and airplane-type surfaces.

[Kugel]

Thank you, Doug, for the great info!!

Best Regards and God Bless!

Kugel