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Old Mar 10, 2005, 01:52 AM
iPhly R/C with iPhone
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Silicon Valley, Calif
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Kitbasher twinrotor winged autogyro adventures

As I mentioned (http://www.rcgroups.com/forums/showthread.php?t=342046), I recently acquired some Penni blades from Ackus of Sweden. Penni is a rubber-powered, FF helicopter designed by John Burkam that Ackus manufacture as a kit; Peck Polymers are US distributors. The blades are machined from balsa, are 20mm wide and have a Clark-Y-type, 11% airfoil.

I am experimenting with different setups with these blades and yesterday had my first success. I used a stock GWS Pico Stick fuselage, complete with IPS-A and standard rudder/elevator controls. On it I mounted a short wing made from a $5 foam glider http://www.lifelikeproducts.com/lifoam/gliders.htm cut down to just over 2' span. I tested several rotor head designs, including three and four-bladed ones in the photo. Don't laugh :=) I actually flew it with two dissimilar rotors to see which one performed better. It seems that the 4-bladed one works better and I now have two of those on it. More photos coming.

The wing has enough area to lift it without rotors, but just about. Stall speed is very close to maximum speed, and is pretty high for a pico stick :=) (the cambered wing produces less drag). With the rotors, it flies very slowly, and at very high angles of attack, at which point the wing is completely stalled. It can also descend almost vertically and hovers in light breeze. However, I am now building a new, smaller wing to prove to myself that the rotors work :=) It will be more of a brace than a wing, 2" chord.

Comments and suggestions welcome.

Ari.
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Old Mar 10, 2005, 06:22 AM
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Congratulations!. Looks like great fun.
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Old Mar 10, 2005, 01:52 PM
iPhly R/C with iPhone
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Silicon Valley, Calif
Joined Jan 2005
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Removed lifting wing and replaced it with aerodynamically-insignificant brace. Maidened it this morning, need to get someone to take flying pictures

The "wing" is a piece of 1/4" x 2" aileron stock. Pylons made from the same material.

Ari.
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Last edited by iter; Mar 13, 2005 at 01:22 AM. Reason: specified aileron stock size
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Old Mar 10, 2005, 03:45 PM
iPhly R/C with iPhone
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AUW is 160g/5.6oz with TunderPower 730 mAh 2-cell LiPoli.
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Old Mar 10, 2005, 08:59 PM
iPhly R/C with iPhone
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Silicon Valley, Calif
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Here are some videos my coworker shot tonight. We'll get better quality over the weekend.
http://www.lib.aero/~ari/autogyros/

I need to work on my landings :=) Sloppy as it was, no damage occurred.

Ari.
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Old Mar 11, 2005, 08:21 PM
iPhly R/C with iPhone
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I've been flying the basher every day now, and here some lessons I learned so far.

1. Rudders and elevators are not effective with no forward speed. This one should have been obvious, and has been mentioned so many times, but I had to learn the hard way.

2. Twin-rotor autogyros are extremely sensitive to differences in mast tilts because the rotors will spin at different RPM and consequently develop different amounts of lift. One mast leaning back as much as 1.5 degree more than the other will make it completely unflyable. As much as .5 degree difference will make for a noticeable differential in lift.

3. No crosswind takeoffs. On takeoff run, the model will attempt to weathervane itself into the wind... Let it. Any significant crosswind component and it will flip over.


1 and 2 above lead me think that if you could control mast tilt directly, it would be much more controllable. Have two servos each tilting one rotor back and forth and have them set up as elevons on the transmitter. One difficulty I see there, except for the added weight of servos and linkages is that normal servos rotate through about 60 degrees, while I only need about 6. I could limit ATV, but then, if my understanding is correct, I'll get very poor resolution. I could use very short control horns and very long servo arms, but that would introduce non-linearities in the linkage.

What I really need is a servo with an extra gear in it to further reduce its travel, raise the torque and improve resolution. Anyone heard of a servo like that?

Ari.
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Old Mar 11, 2005, 09:28 PM
iPhly R/C with iPhone
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Wow! Thanks, Mickey. All I need to do is ask, eh? :=)

Do you know if anyone has had success with this kind of differential tilting?


Ari.
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Old Mar 12, 2005, 06:02 AM
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Quote:
Originally Posted by iter
Wow! Thanks, Mickey. All I need to do is ask, eh? :=)

Do you know if anyone has had success with this kind of differential tilting?


Ari.
That, I don't know.
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Old Mar 12, 2005, 10:38 PM
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linkage

I don't know if this will help but I once built a airplane where I could adjust the aoa with a servo attached to the fuse that with the gear dial, I could adjust it being hinged off of the leading edge.

If you used carbon fiber hollow tube as your mast supports, you could pivot each individual support on a commmon shaft through the fuse, with one servo like ailerons, or the duals for elevons.

Above you stated making your control horns short and servo arms long, that will give you too much throw.

You will need to make your control horns long and your servo arms short, and throw say 30% dual rate until you achieve your goal.

Nice ingenuity, keep up the good Work Iter.
Doug
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Old Mar 12, 2005, 10:58 PM
iPhly R/C with iPhone
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Quote:
Originally Posted by dougmontgomery
I once built a airplane where I could adjust the aoa with a servo attached to the fuse that with the gear dial, I could adjust it being hinged off of the leading edge.
How did it work for you?

Quote:
Above you stated making your control horns short and servo arms long, that will give you too much throw.
Doug, you're right of course, I meant it the other way around. But I will still get non-linear behavior where it's much more sensitive near the center than at the extremes (or did I get it revesed again? :=))

Quote:
and throw say 30% dual rate until you achieve your goal.
Dual rates have the same problem as ATV - you lose resolution. So in effect you leave yourself only a few discrete positions for each channel.

But I've had another idea. I could leave the masts fixed, but what if I added collective? I could use tail rotor hubs from a helicopter, each with its own servo again, mixed as elevons or maybe flaperons. Hm... That way I could even fly inverted... And adding pre-spin would be a breeze... Need to stop right there...

I can't think of a model helicopter that uses more than two blades on the tail though. Do you guys think that would be a problem?

Ari.
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Last edited by iter; Mar 12, 2005 at 11:12 PM.
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Old Mar 13, 2005, 05:29 PM
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Hey Ari; You could do it, just need to do some machine work. What tickles me is you've got your gyro flying on an IPS A drive on 2 cells. Perhaps when the weather gets better I'll get a chance to see if my 5.5 oz. gyro will do the same.

David
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Old Mar 13, 2005, 07:47 PM
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Glendale,Az.
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mast rotation

Ari,
On My 9 oz airplane, the in flight adjustable wing worked great in testing out Aoa but once it is dialed in per -plane it is really is not necessary to change during flight. It was easier to figure out with some push pins.

In your ideas, it can save a lot of tear aparts, due to small changes you need to gain your best efficiency. You cant just move the battery because of your horizontal surface now changes either positive or negative.

Full flying elevator could alleviate this problem if you could adjust the cg in flight by a battery anchored on a slider, or screw assembly.

Just some ideas, keep us posted. Doug
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Old Mar 13, 2005, 10:39 PM
iPhly R/C with iPhone
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Silicon Valley, Calif
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Quote:
Originally Posted by David A Ramsey
Hey Ari; You could do it, just need to do some machine work.
Man, I can't even find a drill press to use, you're talking to me about machine work :=( But I think I could do it with no machinning if I used helicopter tail rotor assemblies, all that is standing between me and that experiment is $160 worth of Shogun parts. I even know which parts I'd need - anyone with too much cash on their hands, PM me and I'll send you the list of part numbers :=)

Quote:
What tickles me is you've got your gyro flying on an IPS A drive on 2 cells. Perhaps when the weather gets better I'll get a chance to see if my 5.5 oz. gyro will do the same.
Like the man says, build it light :=) I've got 4.22 sq.ft. of rotors there for a 1.33 oz/fq.ft disk loading. You can see why it doesn't handle wind well. I should note though that it does take almost WOT to fly. I need to experiment with other props. So far I've been flying with 9x7. 10x4.7 would probably work better, but the pico stick landing gear is too short to allow safe ROG. What motor do you have in yours? Is it gas or electric? Have we seen pictures of it?

Quote:
Originally Posted by dougmontgomery
Full flying elevator could alleviate this problem if you could adjust the cg in flight by a battery anchored on a slider, or screw assembly.
I think my problem is slightly different from what you were trying to solve. I'm not trying to find optimal CG location or AoA, I've got those pretty much figured out for this model. What I want to do is change the relative angles between the masts so I could modulate the amount of lift each rotor generates /in flight/. Differentail collective would do the same thing.


I broke a blade on takeoff today. It looks bad, but the damage was limited to one broken blade. Being light has its advantages :=) It was quite embarrassing though because I went to a field I hadn't been to in a year, and people I hadn't seen in as long all gathered to look at it... First flight, I flew it into the sun and struggled to bring it back. Second flight, broke a blade. I had dual rates set for a hot 4-channel airplane and forgot to turn them off... Was pretty embarrasing.
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Old Mar 13, 2005, 11:32 PM
Just one more plane!
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Port Saint Lucie, Florida, United States
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Great stuff Ari! Congrats on how far you have gotten! Great thread! Thanks for sharing!

John
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