Rotor head ideas
 

My first post, so hello to everyone.
I have been into RC flight for many years, and always wanted to build and fly an autogyro but never got round to it until recently.
Wish I had started sooner! I began with a simple and stable twin rotor design (Twirl) made from 3mm depron, and never had so much fun from RC flight before.
Reading through the forum, I am impressed by the experimental spirit shown by you all, especially the stabiliser - less designs from Mickey. Rotor heads are so intriguing, but also so frustrating to fully understand, nevertheless my next project will be a single rotor model (electric).
Just when I thought that I understood that you either needed either a flex hub or the helicopter style head with cyclic control, I came across this... [link]http://www.prachapter34.com/toppage10.htm[/link] I refer to the model with the box fuselage and machined rotor head. Looks like it uses 2 servos in a mixer arrangement for direct head control, but no flexing or cyclic control to be seen. A close up of the rotor head can be seen further down the page.
Will someone with more knowledge than me please tell me how this model can attain stable flight?

John - Norfolk, England

RE: Rotor head ideas
 

Hi,

From what I can see, it has a teetering rotor head just like full-scale (Bensen style) gyros. The teetering motion is what equalizes the lift of the blades as they travel forward/backward respectively. Typically blade tip weights are used to tame the "following rate" to make it controllable. Emilio Cabezas in Spain and others have experimented with this.

//Ulrik

RE: Rotor head ideas
 

Thanks Ulrik,

Am I right in thinking this system will only work with 2 blades then?

John

RE: Rotor head ideas
 

Hi,

I'm not aware of any 4-bladed teetering model rotors (that work). Anyway, here's a discussion:

http://www.rcuniverse.com/forum/m_77...tm.htm#7723396


/Ulrik

RE: Rotor head ideas
 

Thanks for the link Ulrik.

This has given me an idea for a 2 - rotor concentric arrangement like we find on some micro helis, but on an autogyro, with 2 * 2 blade contra rotating rotors, each one with teetering. The rotors would have to be spaced some distance apart to avoid blade collisions.

Any thoughts anyone?

John

RE: Rotor head ideas
 

Hi John. I have some thoughts about your idea. 1) If you are going to use directly head tilt cyclic control, the height of the co-axial arrangement is going to place a very high load in the servos used for cyclic to the point where it might be unworkable. 2) I can't say for sure, but I have read somewhere that a co-axial arrangement will compromise the blade efficiency, so it dosen't have a real benefit for autogyro use.

RE: Rotor head ideas
 

Hi John, Twin contra-rotating coaxial rotors do not need teetering for stability. Stability is acheived through contra-rotation. Build twin rotors with preset coning angles, use reasonable vertical fin and rudder, and it should turn easily with rudder-only steering. Keep the rotors light for EZ spinup and to prevent unwanted forces building up in the sys tem. Be sure that thrust line goes through or near vertical CG. Look on You Tube under Contratwirl for a video of a twin 4-bladed coaxial rotor autogyro. Flys great on 3-channel (rudder, elevator, throttle). Hope this info helps. Charlie

RE: Rotor head ideas
 

Otto,

While a coaxial contra-rotating design theoretically provides aircraft stability as the differential lift of the advancing and retreating blade pairs cancel each other out, it seems to me that each advancing blade will still be trying to flex upwards while each retreating blade will still be trying to flex downwards. Therefore, I would think that a flapping hinge (ala Bensen's teeter bar) would still be necessary in order to minimize the bending forces at the (rigid) hubs as the blades naturally try to rise and fall during each 360 deg of rotation. Of course, having two coaxial sets of flapping blades rotating in opposite directions is just asking for a blade collision and a big mess unless the blades are stacked a ridiculous distance apart. On the other hand, adding a helicopter's cyclic system to automatically increase and decrease each blade's pitch as they rotate would keep the advancing and retreating blades from rising and falling but this would increase the complexity of the system. Your thoughts?


Norfolk,

The absence of torque in an autogyro's rotor doesn't really justify a need for contrarotating coaxial rotors or the extra complexity and weight to add them. Aerodynamically, such a system isn't necessary. However, if you're just looking to build/experiment with something unique, by all means give it a try. Experimenting with "non-mainstream" ideas such as yours has been a big part of what made full scale aviation so successful over the past 100 years. Good luck and let us know what you come up with.

Harvey

RE: Rotor head ideas
 

Hi Harvey, There usually is no need to include flapping hinges in a coaxial system. You do not want flapping here. The blades should be built lightly, so they do not cause unwanted buildup of forces which could shatter them. The Super Libelle coaxial gyro had lead-lag hinges, but no flappers. Many users of this system don't have any hinging whatsoever, simply rigid rotors. I still might go this route, as it is simple and effective. I could fly a wingless gyro with rudder, elevator, and throttle. Thanx !!! Charlie