If this is covered in another thread, feel welcome to delete this one. However, I would appreciate the link to the original if possible. I was wondering if someone could suggest some basic parameters for gyroplane building. For example if a friend was building a simple homebuilt fixedwing model plane, I could boil it all down and say. "Make the fuse the same length as the wing. Mount the flat bottom wing 1/3 of the way back from the front. Balance the CG around the main spar or slightly behind. Make sure your vertical and horizontal stabilizers are big enough and the control surfaces are 1/3 the size of the stab surfaces." That should fly. Build it"

I wouldnt get into tail incidence, right/down thrust of the engine, and all that kind of stuff. They can tinker with that later.

Having this state of mind, can someone give me a rundown on a Gyro? I want the engine to be in front. Main mast sits at the CG of the body right? What angle does it tilt back, about 15 degrees? Flat bottom blades (I will make) are weighted and at 0 pitch right? Ok, which setup should I consider, since I am using a discarded heli main rotor, with fixed collective.

A. Cyclic roll, Tail elevator, Fixed rudder.

B. Full cyclic, full fixed tail.

C. Fixed cyclic, Tail elevator and rudder.

D. Some combination, for example. Cyclic roll -mix- rudder.

Thanks
Mark

Mark,

Have you visited www.autogyro.com ?

How about building a PT 25 or Mickey's G3PO.

Jim

rcflyerfl,

No, I hadn't until now.. that really hit the nail on the head. Thanks. As for the models you mentioned, I am a novice in the area and haven't heard of those particular models.

I do appreciate the link!

Mark

I am not real familiar with the pt 25 But I think its a med. sized or maybe a bit under med. sized gyro, as for the G3po I have just ordered one, It is a smaller parkflyer sized one, has full cyclic and rudder, uses li-po batteries and a brushless outrunner motor. Videos on his web site of it flying, I am also new and these seem harder to get right than I thought when I had looked into building one, As for is it wortht he money for his kit, from the info he has given me, along with much help I'd say yes, especially if its someone new to this. You can ask a question about the G3po on here and he will get to it fairly quickly, maybe not till after the weekend though, i dunno...anyway here is the websight www.mickeynowell.com/id9.html Thats all the info I will have until I get the kit.

Interesting.. from what I gather, the most important or critical parts are the blades and rotorhead. I get the impression that if you spend the time to build, or the money to buy a set of nice blades and attach them to a well designed rotorhead you have done a lot towards a nice handling model.

I liked the idea I read elsewhere on this forum about finding the perfect airfoil and then grinding a router blade to that shape so you can quickly shape all you want.

Anyway, thanks again for the info guys.

Mark

Hello again, its been a while. I am still interested in building an autogyro, and have been studying the technical aspects. I have a pretty solid grasp on most of it except for one thing. How the devil does the rotor turn the way it is supposed to? I have seen the drawings of AOA and lift angle, and it makes sense while looking at the illustration, but it just doesn't translate to the real world for me later. I suppose if I actually saw one fly I would get it.

Do I understand correctly that we have a rotorblade, flat bottom airfoil shaped and we will call the leading edge left. Ok I take this blade and mount it to a hub with 3 degrees positive pitch relative to the hub, or I guess relative to 90 degrees from the hub shaft, whichever, you know what I mean. If it was a heli, you would call it 3 degrees positive collective. Now I tilt it backward relative to wind and this thing is supposed to turn toward the leading edges of the blades?!

In my mind I say not a chance, it will windmill backwards, mainly because of the 3 degrees positive blade angle of attack (collective).

I see it like this.. lets say I take an airplane wing from my shop and drive down the hiway at 50 mph. Then I stick the wing out the window, leading edge first. First level, then with a few degrees up angle. Is it supposed to pull forward? No, its going to rip my arm off, and probably break into pieces. If it would pull forward, I could just stick a bunch of them on the side and shut the ignition off and enjoy perpetual motion. If this sounds silly, then how is a rotor blade supposed to pull itself forward while under the same conditions?

The only thing I can think of is some specific condition that must exist in the arrangement of the angles and such, but this doesnt seem so because the autogyro can be flown in different ways, even stunts, which would exclude the possibility for delicate conditions existing. The other thing is maybe that the retreating blade(s) have something to do with producing a driving force.

Someone help me out, I recently started flying helis and this *demands* that I understand autorotation. Thanks.

It works the same way as a glider wing.
A wing makes lift roughly 90 degrees to the incoming air ( a little more than
90 based on the L/D of the airfoil).
In an autogyro (or a glider) the incoming air is coming from slightly below
level, 15 degrees. This makes the lift vector tilt a little forward of vertical, causing
the blade (or wing) to go foward.
Your car example has the incoming air dead level, not the same.

Try here for diagrams, etc:
http://www.jefflewis.net/autogyros.html
http://www.copters.com/aero/autorotation.html
http://www.autogyro.com/technic/jeflewis.htm

Three degrees positive incidence on the rotor blades relative to each other is mentioned - that would result in the rotors spinning the wrong way! Negative incidence is required - note that lift is still generated due to airfoil section. I find simple rotor hub made from 1/8th ply and polypropylene hinge is fine - cheap and simple to make. I now always have a 15 degree `delta` angle so that blades are made set at zero incidence which adusts itself in flight.

If you are using a "clark y" type airfoil, zero incidence is several degrees (4 or 5 depending on where you measure)
positive angle of attack. If the zero incidence is the flat bottom part then you may have 7 or 8 degrees positive angle
of attack.
I'm not using delta 3 hinging so I set my blades at -4 geometric incidence, this being 0 actual angle of attack.

mickey

I seriously have a headache. Ok, I'm getting out the drawing board.

I think I will feel silly after I finally understand because in the end it may be a simple misunderstanding. Which way is positive? Positive collective or positive relative to the body of the plane? Check out the photo links. Which is your setup Mnowell129?

I highly doubt the first photo example would work. This may be what tintrax meant?

http://i5.photobucket.com/albums/y17...ticx/gryo1.jpg

http://i5.photobucket.com/albums/y17...ticx/gyro2.jpg

So, even though the blades have negative pitch collectively, they has positive relative to the plane and therefore make lift, but what about the retreating side? If your mast is tilted back at say 15 degrees, and your advancing blade is set for 7 positive, relative to the plane, when it swings around it will be at 8 negative, relative to the plane? Or would it be 22 negative?

Edit: By the way, which method does the falling seed pod use, autorotation like a true airfoil effect or simple windmilling as I call it, like a box fan in the window on a breezy day. Is the seed pod actually making lift like a gyro or is it just parachuting?

They are both kinda right.
Basics: Angle of attack, the angle that the air flowing into an airfoil
makes with respect to the line where that airfoil would make no lift. (the
line through the airfoil where the airfoil makes no lift is called the
zero lift line (ZLL).) So angle of attack is the angle that the incoming airflow
makes relative to the ZLL.

Measuring angles with respect to the aircraft, the ground, the rotor shaft is
all kind of waste of time. What matters is the angle with the local airflow on
the airfoil.
Here is a diagram for the advancing blade.
The local airflow is the sum of the rotation and movement.
THe blades sees +10 degrees. The lift is roughly 90 degrees from
that, the part of the lift that is tilted forward makes the blade move, overcoming
drag. The other part of lift is what lifts the aircraft.
mickey

Now THAT is a helpful diagram. I saw it clearly.. The lift on the airfoil at first is quite forward causing the blade to move forward. Then as the blade spins faster and faster due to this, the AOA gets closer to blade directiong of travel than plane direction of travel and the lift angle moves closer to mast angle and therefore ceases to continue accelerating the blade, and a balance point is found. The rotor continues to turn.

I was really happy about this until I studied the drawing too long. If that diagram had drag angles included where would they be and why wouldn't they stop the blade. Isn't drag about 90 degrees from lift? Maybe one blade wouldnt move forward by itself without the balancing drag on the other side of the rotor from the other blade?

The wing out the car window thing still has me hung up. I just can't get it.. Here is another drawing showing you whats going on in my mind. Look at the drawing and please tell me what angle you would have to set the AOA of the airfoil so that when the air nozzle is turned on, the blade moves forward, toward the nozzle. I can't imagine there exists such an angle since drag would blow it away from the nozzle in all situations.

http://i5.photobucket.com/albums/y17...Autorotate.jpg

Sorry for being so dense, but I guess I'm the kind of guy that cant rest just knowing that something works, I have to know why. Thanks for your patience.

It never will. Move the nozzle down and aim it up a few degrees and then it
will move forward. The only thing you have to do to keep the blade turning is
have the total resulting airflow below the plane that is square to the rotor disk.
This is accomplished by tilting the whole thing backwards.

All you are trying to get is some force in any direction but straight downwind,
in your nozzle example if you set the airfoil to 10 degrees, you get lift at 100 degrees.
Now tilt the whole picture 15 degrees down and the airfoil (now at -5 degrees with respect
to the GROUND but at +10 degrees with respect to the WIND) will be producing lift at 85 degrees,
and will thus move forward with respect to the ground.

mickey

P.S. this is exactly why a glider (sailplane) goes forward, not backwards.

In the interest of keeping it simple I did not explain that my zero incidence is technically incorrect! I was meaning that my flat bottomed blades are simply bolted to the hub with no packing at leading or trailing edges, so the flat undersurfaces are at same angle. This angle is 90 degrees to the mast, which however is slanted back. Because I use `delta` hinging I can use this method. Plenty of lift is generated, the other day a gust blew up as I was preparing to hadlaunch and the upwards pull was so strong I could hardy hold the plane. A bit scarey! I admit my hubs are simple, you could say crude! But they do the job for planes up to .40 glow power.