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Old Sep 04, 2009, 07:04 PM
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North Idaho
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Build an autogyro using helicopter as donor-PROJECT STARTED

Okay, I was at my club today flying my helicopters, and got in a discussion with a fellow club member about autogyros. I have this idea, it may or may not have been done before, but here goes: I have a Falcon 3D rtf helicopter that I don't use any more. It is very light, and I got to thinking about converting it to an autogyro. Obviously I have to reduce it's weight as much as possible, but what I was thinking was to retain the head, but eliminate the flybar and associated linkage. I would retain swash control, and retain the ability to change total pitch along with cyclic pitch for roll and pitch control, and build a rudder/elevator. I would use the tail rotor and modify the box so I can directly drive the prop, but retain the ability to change pitch on the blades. I have not decided if I would go pusher or puller on the prop, but for now the tentative plan is pusher.

I need to do a bunch more research before giving it a shot, but what do you think?
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Last edited by JasonJ1969; Sep 06, 2009 at 05:28 PM. Reason: updating title
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Old Sep 05, 2009, 07:05 PM
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DanT's Avatar
San Angelo TX.
Joined Feb 2006
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It's been tried before! It doesn't work well......Good Luck!
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Old Sep 05, 2009, 08:16 PM
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Joined Nov 2004
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Umm.
It has been tried and it does work. There are examples of guys slope soaring stripped helicopters. And G3PO, BEGi and GT17 use helicopter parts for heads complete with swashplates. Witness the BEGi video posted on the forum in the last day or so. You need much bigger blades than the heli used if you want to get the disk loading down.

JasonJ1969,
Here is my story :
http://www.rcuniverse.com/forum/m_2325673/tm.htm
and construction details
http://www.rcuniverse.com/forum/m_2380064/tm.htm
construction manual is still posted on the website, even though I don't make kits anymore
Good luck.
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Old Sep 05, 2009, 10:08 PM
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North Idaho
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Thanks guys. I do not plan on using the original helicopter blades, I have purchased the materials to build a set of Clark type blades. My plan is to just use the swash and enough of the frame to hold the servos and mechanical mixing system. The collective on the donor helicopter is done with a wire through the mainshaft, so my plan is to retain this, but instead of a servo, just have it fixed with adjustability so I can tweak blade angle.

I have not decided if I will retain the flybar or not. I should get rid of it to save weight, put weight in the blade tips, and use expo to tame the cyclic controls. The flybar would make it more docile. I could try with and without and see which is better. I have aluminum arrow shafts I can use for the boom and whatever other frame material I might want. I have a 400 class outrunner to use, so I am not worried about power. I see no reason to have a variable pitch prop, so I will just buy some airplane props and experiment. I'll also need to get some landing gear, no biggie. I am also considering building a more convention gyro with flapping head, though I would like to have the control of cyclic. I know three blades are better than two, but I want to see if I can pull it off with some fat Clark blades.
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Old Sep 06, 2009, 05:27 PM
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North Idaho
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Started building the airframe today, got on a roll and it is mostly complete. I used a spare boom for my Raptor 50, along with some spare boom supports. I used the head and modified frame from a Art-tech Falcon 3D helicopter. While looking for materials in my shop, I came across a stack of old license plates. I used the license plate material for the brackets to hold everything together along with aluminum rivets. The airframe, as pictured, is very light at 8.5 ounces. It stands as pictured about 14 inches high and about 16 inches long.

I have a 400 size outrunner to power it. I still need to figure out what size prop to run, and once I have it all assembled, I need to build the blades.

Any insight as to what prop to run would be great. Thanks for looking.
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Old Sep 06, 2009, 08:56 PM
TJK
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United States, PA, Harrisburg
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Very cool! I'm watching and subscribing to this thread. Good luck!

Tom
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Old Sep 07, 2009, 11:25 AM
Scammers need to go!
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I've got to continue watching this build! Subscribed!
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Old Sep 07, 2009, 02:11 PM
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North Idaho
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Thanks guys. I've been weighing stuff, and so far the airframe plus 1300 3 cell lipo, motor, rx, esc and blade material is coming in at a little over a pound. I would be really surprised if the all up weight is over two pounds, as I still have to weigh the servos and whatever wheels I decide on. It looks like it will come in at around 24-25 ounces, which would be great. It will be a two blade gyro, obviously, so I want it as light as possible. I am trying to plan for a rotor of around 30 inches, I think that will be fine for my target weight. The one thing about this is if the heli head doesn't work well, I can go to the normal DC head layout and have a super light gyro. Using 50 size helicopter booms is great, they weigh nothing and are super strong. I dropped this airframe from over my head and it held up fine. My hopes are that it is just blades that break in a crash.
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Old Sep 08, 2009, 02:39 AM
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Sydney, Australia
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Hi Jason, I have some experience using a Trex 450 rotorhead. My first prototype flew, but it had some issues. I have the second version half built and will recommence building it very soon.

I am a bit concerned your expected weight is a bit high for a 2 blade rotor of that size. 25oz with a 30" rotor gives a loading of nearly 5oz per sq' of disk area. That would be ok for a 3-blade rotor, but it is too much for 2 blades. The rotor disk loading should be ideally be close to 3oz per sq'. I suggest to use a rotor size in the range of 36" to 40" for your target weight of 25oz, so the disc loading is around 2.7 to 3.5oz per sq'.
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Old Sep 08, 2009, 07:43 PM
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North Idaho
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Here is the latest. Servos all hooked up along with esc, motor and receiver. If you look at the side on pic, and look at the bottom of the mainshaft, you see a wire coming out and through a fixture. This is normally hooked up to a servo to control collective, but I have frozen the fixture with a link. To fine tune total blade pitch I loosen the grub screw and move the wire. You can see the ail and ele servos hooked up and connected to the swash through linkage. It all looks complicated but it works. All up weight as pictured along with battery and blade material is 17 ounces. I am guessing I will come in at or under the 25 once mark.

And yes John, I am concerned about blade length, which is why I am not building the blades until I get the wheels and rudder on so I can know the weight.

Couple of questions: I can run up to a 9 inch diameter prop, any ideas on pitch? The other question is is there such a thing as too long of blades? How about width? Do I try to stay with 10:1?

That is one fun thing about this, trying to figure it out. My helicopters, though difficult to fly, are easy to work on, just bolt stuff on and go.
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Old Sep 08, 2009, 10:02 PM
AND FOR MY NEXT TRICK....!
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Omaha Millard, Nebraska, United States
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Man...that looks cool! Keep up the good work!
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Old Sep 09, 2009, 10:49 PM
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Looks cool, but looks very heavy and I think you have too much weight on the rotor side. Not trying to deter you from progress, just sharing some tips. Remember that weight x length = moment and moments are more critical in an autogyro than in any other model to get a good balance and CG, hang and thrust angles where the model wil fly. You will need to re-calculate these when the model is complete, or you can do a check and balances using paper and pencil and some simple math to get a prliminary idea where your model balances will end up at. Don't stop, keep going but give this some thought and read as much as you can about real autogyro theory and design.
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Old Sep 10, 2009, 01:25 AM
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The propellor spec depends on the motor KV you are using and the battery. Generally for an autogyro it is better to use larger diameter propellors. A 9" diameter is probably workable, but 10" might be even better. What is the KV rating of your motor? Will you use 2S or 3S battery?

Larger rotor diameter will make a slower flying model. With 30" disc and 25oz, I think the model will be rather quick, and have the speed more like a fixed-wing trainer, except not as easy to fly. That is what I found with my model autogyro that was overweight. Larger blades may put higher stress on the head components especially if there is any blade contact on non-ideal landing situations. 10:1 aspect ratio is very popular for autogyro blades, ie. 2" chord for a 40" rotor. I personally don't have experience of the effect of changing aspect ratio.
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Old Sep 10, 2009, 01:58 AM
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Baden-Baden, Germany
Joined Dec 2008
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Hello.........

Jason, for balancing Your creation with usage of theorie its probably to late. Just replace the things You don´t have with something of equal weight and try what happens. I used some big carroserie-washers and attached them with scotch-tape, a wire or something else in the aproxximate place. You make mistakes with simulating, sometimes in this, sometimes in the other direction, and when its summed up, it balances and comes out okay.

For the prop, use a big diameter with low pitch. Autogyros fly slow, so static thrust ist more important than the speed of the airflow created by the prop.

Try to build something that allows your blades to separate from the heli-head when You crash it. In the heli-head, the blade can move backwards when touching the ground, but it can not move upwards because its fixed inside the fork of the blade-holder. It will bend awfully, perhaps break or create some damage to the head. A simple stripe of thin glas-fibre-plate inserted between the blade holder and the blade can solve the problem. To get the MiniMOB to air, we have crashed it ten times, and I only broke one single blade. The blade that broke hacked into the tail before, got a big scratch in the leading edge and exactly broke on the scratch. The flex-plate was one time almost broken and another time it broke, but the blades were not damaged. The head was not damaged at all..............

Bye
Mike
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Old Sep 10, 2009, 08:18 PM
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North Idaho
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Quote:
Originally Posted by MarioIArguello
Looks cool, but looks very heavy and I think you have too much weight on the rotor side. Not trying to deter you from progress, just sharing some tips. Remember that weight x length = moment and moments are more critical in an autogyro than in any other model to get a good balance and CG, hang and thrust angles where the model wil fly. You will need to re-calculate these when the model is complete, or you can do a check and balances using paper and pencil and some simple math to get a prliminary idea where your model balances will end up at. Don't stop, keep going but give this some thought and read as much as you can about real autogyro theory and design.
Thanks. It does look heavy, but 17 ounces all up right now doesn't seem very heavy to me. This including the material to make the blades. The blades themselves will end up lighter obviously since it won't just be a pile of stuff. The only things I have left to add is the rudder and wheels.

I ordered a selection of different props, some 9 inchers with different pitches and some 8 inchers. 9 inches is as big as I can go. I can't remember the KV on the motor, but it powered one of my helicopters on 3S, it has plenty of power. I will be running it on 3s on the Gyro as well.

I have been reading everything I can find, but in all honesty I am not finding much that is helpful. I need numbers on what the "hang angle" should be, but it seems that no one talks about it in a way that is understandable. I have seen numbers like 8 or 10 degrees, but from what? Is the mast 8-10 degrees? In what direction, fore or aft? Will the helicopter head change the dynamics of this? How big is too big when it comes to rotor diameter in relation to the size of the airframe? These are questions I have asked and received no answer. I appreciate insight and tips, and welcome all input, except negative "it won't fly", because you can make anything fly if you work at it..

I can change almost everything on this with no problem, so I am not worried about that. I have realized that, in the end, I will be going through some changes before all is said and done. Also, I am willing to go to a conventional DC 3 blade Gyro head if the helicopter head won't work, but I have seen too many gyros fly with 2 blade heli heads to think it is impossible.
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