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Old Apr 18, 2009, 11:07 PM
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Full Homemade Scale Gyrocopter advise please

HI Everyone,

My Dad and I built this from scratch about 12-15 Yrs ago. He has a full size which we scaled down. We purchased heli blades and made a jig and sanded the bottom flat to achieve a better gyro type airfoil shape.

We machined the head and blade centre, made the mast etc from box alloy and clamped as per the real thing. Rotor head is moved by 2 servos using a computerised radio like v-tail input. The yellow front is fibreglass that we moulded up ourselves. The tall tail is alloy ribs covered with solarfilm.

Engine is saito 65. I have NO Heli experience at all, At the time I only 3-4 years of rc plane flying as well as many hours in a real gyro.

We never really pursued the flying thing enough. I'm sure I did a hop of a few metres but later taxi ing wrecked a set of blades, of which we were only able to purchase 3 sets of discontinued stock so we hung it up and left it. I was only like 14 yr old at the time and my memory is a little hazy on this.

The blades have a flat bottom and have positive pitch. They spin up very easily and really whiz! I have no idea that anyone else was trying to get a REAL rc gyro copter flying, I had only seen Gyro planes in rc form.

Rotor Diameter is 1.3metres and weight is around 3 Kg. We first tried the blades mounted on the model, sat out in our yard with a house brick each side on the under carridge. We faced it into a 20-30knot breeze and with a gentle hand flick, full back stick, they spun up very easily and very quickly, fast enough and with enough lift to flex the undercarridge and raise the centre off the model up 10mm or more.

I'm now thinking of having another crack at this. I'm now 28 and maybe with a little more experience and advice I maybe able to get it happening.

My first question is about using the heli blade style centre. I understand the bit about the control having to be VERY VERY gentle, but the whole pitch change thing with the forward moving blade? While I understand the Principle, why don't the real size gyro's have them?

All our angles a 8 degrees. Mast is 8 Degrees back, rotor has 8 Degrees forward, rearward and side to side. This is a long standing value used in the real thing.

From the memory of trying to fly the thing, I remember having a LOT of thrust, I never got much past half throttle. What about the weight? is it too heavy? Do we need more angle of attack as I have read a little about that now.

What do the guys who have been here tried that think. I'd love to hear what you all think, and I will tell you our experiences.

See attached photo, nose wheel is missing.

Cheers, Graham.

P.S. I'm on the central coast of Queensland Australia
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Old Apr 19, 2009, 04:00 AM
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Norfolk Flyer's Avatar
Cromer, North Norfolk Coast, UK
Joined Aug 2008
525 Posts
Hi Graham.

I don't know whether you're aware of the autogyro.com website where there is a "standard" set of design rules for model autogyros. Unfortunately the parameters given are for a standard tractor model, not a pusher like yours, but one thing I notice from your picture is the low height of your rotor. From what I know, this is often a problem with scale model autogyros, causing instability. Take a look anyway, the parameters page is http://www.autogyro.com/technic/specs.htm

You do not have a horizontal stabiliser. Some models fly without one, but most fly better with, and 2 blades rather than 3 is a bit ambitious for a first model.

From the figures you supply, I calculate a rotor loading of 7.3 ounces per square foot. This is rather high, and is likely to produce a very fast model. A figure of under 5 is normally acceptable, less if possible.

Sorry if all this sounds a bit negative, but perhaps you might want to consider starting with a simpler design, even a twin rotor model like Al Foot's Twirl, and then move on rather than crashing your pride and joy.

I'm sure that other more experienced forum members will be able to help you decide.

Good luck whatever you decide.

John
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Last edited by Norfolk Flyer; Apr 19, 2009 at 04:12 AM.
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Old Apr 19, 2009, 05:43 AM
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Thanks Norfolk. I'd be happy to have a crack at a simple starter type gyro like a twin rotor. Don't think i'd have any trouble flying it but it would give me an idea of the difference in flight/landing caracteristics.

Negitive is fine, no use beating around the bush about these things!

So rotor loading is a bit high, so if I make it lighter I'd have a slower flying model? We can tweak with the height of the mast, it was made at this height to scale and enough that the rotors won't hit the ground. (Unless the we stuff up)

I've read the issues with the CG being below the level of thrust. I'm looking at the link to info you posted, much appreciated.

I'm thinking of striping the model bare and attaching it to a bar or ladder type deal and test the flight characteristics with a grude wind tunnel test. Anyone seen a setup like this??
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Old Apr 19, 2009, 06:04 AM
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Norfolk Flyer's Avatar
Cromer, North Norfolk Coast, UK
Joined Aug 2008
525 Posts
Graham,

I have zero experience with pushers. When the other forum members reply to you, I'm sure they will have some ideas.

This is a very helpful forum. You will never run short of informed advice, but first they all need to wake up this Sunday morning

John
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Old Apr 19, 2009, 08:38 AM
It was a GLITCH! Honestly!
SafeLandings's Avatar
Stourport on Severn ,Worcestershire, United Kingdom
Joined Dec 2007
4,901 Posts
Graham,
Nice looking gyro ..remember less weight is your friend, if I were you I would steer clear of a winged 2 rotor gyro if you want to learn the different flight characteristics of a gyro. These gyros fly superb but are more like flying a 3 channel trainer to fly and could mislead you when trying a rotor only gyro for the first time.
Pt Gyro do some great kits that are straight forward to build and are easy to fly or there are many plans etc out there ..the gyro world is your oyster!


Regards Rich
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Old Apr 20, 2009, 04:48 AM
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Joined Jan 2005
1,286 Posts
Graham,

it's not likely that your gyro is going to fly in the current configuration. With a weight of 3 kg and a rotor diameter of 1.2 m you have a disk load (weight divided by rotor area) of 26 g/dm. The generally accepted upper limit for the disk load of a gyro is 15 g/dm, less is better.

The angles you mentioned look alright. As for the teetering head of your gyro, look in Rich's RPG biuld thread:
http://www.rcgroups.com/forums/showthread.php?t=968853
The teetering head is discusssed around posts #161, #203, #261, #355 and #372.

Jochen
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Old Apr 20, 2009, 07:50 AM
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Cheers for the info so far everyone. That last link (thanks JochenK) has some great info and the vids have me so so keen now. I'm looking at weight first up, and chasing up more info on the electrics required to drive the PT.
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Old Apr 21, 2009, 08:23 AM
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Thanks to the info you guys provided, I need a weight of no more than 1.8kg and that will equate to thrust of about 1.2Kg. I just checked and found the saito .65 weighs 580Grams on its own! a .46 2 stroke looks like half that weight!

I still don't understand the whole CG thing, we always balanced the gyro with the mast straight down.

Also can I buy micro servos to run off my old Hitec Reciever? I currently have all normal sized aircraft servos?
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Old Apr 21, 2009, 04:34 PM
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Graham,

the thrust line of a rotor needs to be in front of the c.g. for an autogyro to fly stable, even when you are tilting the rotor fully back. Which in your case is 8 back tlit, and that means that you need a hang angle of at least -8 - or 8 nose down.

I wouldn't recommmend micro servos for a 1.2 m rotor, use standard servos with metal gears. If you want to be on the safe side, use digital ones.

Jochen
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