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Contemplating twin gyro

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Old 02-17-2005, 10:12 AM
  #1
Gaffspan
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Default Contemplating twin gyro

Inspired by a rock steady free flighter i saw a couple of months back, i thought i'd build a lightweight rc twin gyro (possibly GWS ips150 motor) as a small park/indoor flier. I have no autogyro experience, but plenty of fixed wing and some helicopter building/flying time.

I also thought it would be pretty neat to style it as a V-22 Osprey (albeit with a stupid looking tractor prop ).

I've read the info on autogyro.com and understand that it is still quite an undertaking. However, i recon building a twin will be easier than a 'pure' auto due to some wing area and zero torque effects from counter rotation. I also understand that flat blades can be used, which will save much effort...

Anyway, i was wondering whether anyone could recommend any good (free ) plans to get me started. I've spent a while searching the interweb for them, but have found none which suit me.

Its nice to see so many people modelling autogyros!

Cheers, help is hugely appreciated!
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Old 02-17-2005, 12:00 PM
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Default RE: Contemplating twin gyro

Check out the spin doctor from Flying models magazine.
mickey
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Old 02-17-2005, 10:08 PM
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Default RE: Contemplating twin gyro

'Gyrace' & 'Tango' work well & lots of them have been built & flown. But they are larger, & require a 40 gow engine.
Good idea to start out with a 'proven design' then experiment from there.

M.A.N. had a 40 sized Osprey const. article around 1999. Saw a couple built but never saw 1 fly. Perhaps that tells us something.

Bob
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Old 02-18-2005, 05:43 AM
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Default RE: Contemplating twin gyro

I would agree with Bob.. The Tango or Gyrace would be better to start.. I have build and flown a couple of Gyraces and had good luck with both..

We had an Osprey ay Muncie last year and it did get in the air but was under powered and was only up a few seconds.. Rick did fly it but I am not sure of his comments on it... It was put away for the rest of the weekend.

Jim
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Old 02-18-2005, 06:44 AM
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Default RE: Contemplating twin gyro

Nice to know other people have tried ospreys!

All of those gyros look v.good- tango especially was just what i had in mind. All i was planning to do by the way was simply to redesign the fuselage, keeping all lifting surfaces and hopefully thrustlines right in their recommended positions. I dont think altering the shape of the fuselage should have a decisive effect on its performance.

Does anyone know of any sites where i might be able to come across tango/gyrace/spin doctor/etc plans for free? I've never seen an autogyro plan in any UK mags.

Cheers!
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Old 02-18-2005, 05:06 PM
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Default RE: Contemplating twin gyro

HI Gaffspan,

I tried to find pictures of a better dual rotor but these will give you an idea. This was converted from something but I've done so many I can't remember what.

Anyhow, this has a simple aluminum tube for a spar and the hubs are just a couple of 1/8 plywood with plastic inserts that rotate on an axle. You will need lifting rotor blades as it doesn't have a wing.

The rotor booms or spars are about 10 degrees and the rotor shafts are 10 degrees positive. Hold the gyro but the rotor shafts and it should tilt down about 10 degrees. The aluminum tube just has a 20 degree bend in the center fastened to a piece of plywood and held to the fuselage with rubber bands. Can't get much easier and it will fly good.

Phil


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Old 02-18-2005, 05:34 PM
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Default RE: Contemplating twin gyro

"You will need lifting rotor blades as it doesn't have a wing."

I guess a good old fashioned flat bottomed Clark-Y would be just the ticket. What would you say the rotor diam's are on your example? Do you also have a recommended engine to rotor sq-inch to roughly stick to? Sorry for so many questions.

Clint.
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Old 02-18-2005, 05:37 PM
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Default RE: Contemplating twin gyro

It's me again....forgot to ask one last question. As with single rotor gyro's....would you add in a little down thrust (say 5-10) to start?

Clint.
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Old 02-18-2005, 08:51 PM
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Default RE: Contemplating twin gyro

The gyro in the picture had 34" diameter rotors and I'm not sure of the weight but estimate 5 lbs. It also had a 4 stroke 52 engine which was more than enough power. When I started building gyros I just put big enough rotors to lift it. It may not seem the best way, but if I got to end of the runway and the gyro was not off the ground, I put larger rotors on. I recommend the SG6042 profile blades over the clark Y. Just as easy to make and better performance. You can mount them flat and they spin up faster and more lift.

If you are using a converted airplane, the engine down thrust should be OK. 5 degrees down is a good number. If you are using a 40 size converted airplane, your rotors should 6" to 8" above your fuselage. If you go higher, add a couple more degrees down for the engine.

Phil






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Old 02-19-2005, 12:19 AM
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Default RE: Contemplating twin gyro

I'm starting to see the relation of mast height and motor down thrust. Your example has the rotors down in a lower position as compared to a single.....so less down thrust is needed (I couldn't see much in the picture at all). I think I'll give this idea a try in the next few weeks. Thanks for the information Phil.

Clint.
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Old 02-19-2005, 06:27 AM
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Default RE: Contemplating twin gyro

Thanks again for the replies,

After an hour or so trawling through old model mags, i found a 1996 issue of AMI, with a 'rotack' autogyro by Dave Boddington; twin, lifting surfaces to support rotors.

Floridagyro, i notice your gyro has 3 blades per rotor, the plan i have suggests 4. Which would you recommend? (would 4 blades be more draggy?) The plan is intended for a .25 engine- is there anything i should know regarding changing the design for a far less powerful unit. I'm not sure of the AUW of the original but i'm hoping for little more than 150g. Construction will be balsa wings/rotors, with depron fus & tail.

Should be interesting...
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Old 02-19-2005, 07:47 AM
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Default RE: Contemplating twin gyro

You said the Dave Boddington has twin lifting surfaces to support rotors and 4 rotor blades. I haven't seen that particular gyro but it sounds like a couple of other designs around that use flat balsa rotor blades without a lifting profile. With that type of design, the lift is generated by the wing and the blades add stability but very little lift. I had one and flew it with just the wing to prove that it would fly without the rotors. Most gyronuts don't consider them a true autogyro.

If you use lifting rotor blades, ie SG6042 or Clark Y, four blades will give you more lift than three and they are easier to balance. However, it's an extra blade to replace if you break them. I have used four blades when I need the extra lift and didn't have larger blades. I also tried five blades but it didn't lift as much as four. I guess it would be considered the point of diminishing return.

Phil

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Old 02-19-2005, 12:00 PM
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Default RE: Contemplating twin gyro

To Gaffspan,
Could you post a pic of the "Rotack" autogyro. Not familiar with that design.
Thanks,
Bob
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Old 02-20-2005, 05:44 AM
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Default RE: Contemplating twin gyro

Here it is:



(so can i use flat sheet blades? )

In its defence, the mag says (and i quote): "If he thinks the wing alone is sufficient to provide lift for reasonable flight, never mind slow flight, let him build one without the rotors and see how it performs"

Certainly not a true gyro though. I figured that reduced dependency on the rotors would make things a little easier for someone coming from planes. I'd like to build a pure DC gyro some day though.
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Old 02-20-2005, 08:57 PM
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Default RE: Contemplating twin gyro

Hi,

I like your gyro. Nice looking. Now, you noticed that I didn't say that a gyro with a wing is not a true gyro. I have had several with a wing and I still fly them and I still get comments that I'm not flying a true gyro.

In answer to your question, yes your gyro should fly with the flat blades.


Phil
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