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Old Nov 20, 2008, 10:14 AM
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Centerville, In. USA
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folding prop for flying wing

I have made a large flying wing that has a span of a little over a 100 inches and an area of about 1000 square inches. The sweep angle is a bit over 20 degrees. As I am building it from scratch with no plans I'm runninig into problems. My problem now is mounting the motor. I want to mount it up front for balance reasons. The prop is however a 11" GWS direct drive and unless I build a really deep fuselage on the bottom, the prop will have no protection on landing. I could set the motor on top up front and get away with a 3" or 4" deep fuse. Will the fact that the motor sits on top of the wing adversely affect this effect the flying of it? Or I could use a folding prop but I've heard they are not as good as a direct drive non folding types. Plus they are expensive. If you don't get the right one the first time it could run into big bucks. Is there a good substitute for a GWS 11x8 DD out there? Any ideas or suggestions will be appreciated. RCNutt
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Old Nov 20, 2008, 10:20 AM
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Centerville, In. USA
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Oops! I misspoke. The prop is a GWS 11x7 DD, not a 11x8. RCNutt
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Old Nov 20, 2008, 12:59 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,399 Posts
A lot of people 'belly land' without breaking props, (or at least not very often). Try a fixed prop, if you break too many, go for a folding prop.
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Old Nov 20, 2008, 03:01 PM
The Kid
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Detroit, MI
Joined Dec 2007
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I think you'll be fine with a regular prop. And when you're coming down to land if its sticking straight up and down, just blip the throttle and it'll hopefully settle into a more horizontal position

If looking for a folding prop, look at hobbycity. They have some folding spinners and spare blades that would cost you maybe 10 bucks, which is much cheaper than how much it would cost to order one here...I wouldn't trust the blades to much more than 300 watts, though, so if you're putting in a lot of power, maybe go for something else
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Old Nov 20, 2008, 03:32 PM
volare est vivere
ray foley's Avatar
United States, OH, Toledo
Joined Jan 2005
2,015 Posts
hi there from Toledo

I have done this before and there are one or two problems with folder prop as a pusher. When the prop folds the C/G will shift rearward a bit but more importantly if the prop stops with the blades up and down the top blade will tend to cross the thrust line of the motor and be unable to open properly(no pun intended)because the upper blade's mass center is below the thrustline. This causes a dynamic imbalance issue which tends to break the motor loose from the airframe. Care to guess how I found this out?

You will need a device to limit the upper prop from folding too far. Actually both blades need this since you never know which blade will be up when you stop the motor. So an aluminum strip with a hole for mounting to the prop adapter behind the middle piece (yoke) which is long enough to limit the angle of folding for both props, wide and thick enough to do the job but not interfere with a spinner and be strong enough. I used aluminum 0.062" thick(1.5 mm).

Yes the lower blade will tend to hang down a bit as is the case with any folder prop, so it goes. The end of the strip will be shaped as required to engage the prop root without nicking. Were you awake in Geometry class all those years ago? You could describe the shape as a parallelogram with a hole in the center for clearing the the prop adapter. Make sense?

Don't try to fly without it, trust me it wouldn't be pretty, exciting perhaps but not pretty.

ciao -rjf
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Last edited by ray foley; Nov 20, 2008 at 03:38 PM.
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Old Nov 20, 2008, 04:33 PM
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Toledo, Ohio
Joined Apr 2003
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Ray , Toledo Ohio? nice to here such detaled information from a local flyer!
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Old Nov 20, 2008, 04:47 PM
The Kid
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Detroit, MI
Joined Dec 2007
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Um, he said that he is going to be using the motor in a tractor configuration, so he doesn't have to worry about the problems of the upper blade crossing the center line
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Old Nov 20, 2008, 09:45 PM
volare est vivere
ray foley's Avatar
United States, OH, Toledo
Joined Jan 2005
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hi there from Toledo

Hmmm, missed that, oh well. It is still true anyway.

ciao -rjf
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Old Dec 01, 2008, 05:29 AM
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Centerville, In. USA
Joined Jul 2001
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What I have decided to try is a 6" piece of 1/8" piano wire with a little backward bend on the bottom tip, pointing straight down from the firewall. It will be removable if necessary. That should provide some protection for the prop on landing, Thanx guys for the ideas. It needs the motor mounted, the radio installed and covering. It's a long way from being done but I'll try to remmber to come back here and post some pictures. I can take a picture of the wire landing gear if anyone is interested. Let me know. RCNutt
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Old Jan 05, 2009, 08:06 PM
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Centerville, In. USA
Joined Jul 2001
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My big wing is just about done

It is just about finished. It is all totally scratch built with no plans to go by. Now I need to go to the hobby shop for some aileron control horn connectors to make it adjustable. The span is 101.25" and she weighs about 3 pounds 10 ounces. It is right at 1000 square inches. The motor pulls about 25 amps on a 11 inch GWS direct drive prop. Here is a collage with a few shots of it. I'll probably give it a go sometime this week if the weather cooperates. I may need to find someone to launch it for me. I think it is too heavy to launch with one hand. RCNutt
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Old Jan 06, 2009, 08:57 PM
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Centerville, In. USA
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Here's a question for you wing guys. Should I set the elevons at a neutral setting or put in a little up? RCNutt
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Old Jan 06, 2009, 09:32 PM
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Quote:
Originally Posted by rcnutt
Here's a question for you wing guys. Should I set the elevons at a neutral setting or put in a little up? RCNutt
What airfoil did you use?
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Old Jan 07, 2009, 06:46 AM
Registered User
Centerville, In. USA
Joined Jul 2001
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flying wing airfoil

I don't remember where I got this airfoil but it was touted for gliding. I made a small flying wing using this airfoil and it worked well. I thickened it up a bit so I had a little more room for the spars in the outer tip. RCNutt
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Old Mar 19, 2009, 09:12 PM
Registered User
Centerville, In. USA
Joined Jul 2001
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Update---Success! I took it to the local flying field the other day as the weather was perfect and in the 70's. After I got there, I had decided not to fly it (chicken really) But one of the regulars there talked me into to trying it out. He launched it for me and yes it flew! Actually the big wing flew quite easily with a little up trim required to keep it from losing altitude. The roll rate however was very slow and it was easy to lose the orientation of it. So, since then I've put on some bright pink decoration on the bottom and moved the control rods down a couple of holes in the control horns for a faster response time. Overall not bad considering I had no plans to go by! I probably will take it out again this weekend weather permitting. RCNutt
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