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U-2 EDF scratch build project

Old 11-12-2013, 06:18 PM
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Default U-2 EDF scratch build project

Hi everyone- I've been wanting to try building an EDF U-2 for sometime now. I'm thinking about a 1/12th scale version of the U-2C which would put the wingspan around 81''. The idea is to build a composite fuselage with a foam wing. I'm currently working on some drawings right now. The plan is to go with retracts as well. It's hard to determine the weight at this point but I would guess it will land around 7-8lbs. At 1/12th scale the fuse will be around 5-6 inches wide so I'm considering using a 90mm fan. I'll be documenting the whole process here. I've designed many models but this will be my first EDF so I'd love to hear everyones thoughts.
Old 11-16-2013, 07:23 AM
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I bought a U-2 at the Jefco auction a year ago and feel it Is too heavy to fly well so thought I might use it as a plug to make a new light weight version so I am interested in following your build.
Old 11-16-2013, 05:05 PM
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Sounds good! I'm still working on tweeking the scale outlines. I found a plasitc model kit of the "C" version I had bought years ago. I never assembled it so Im able to use it to help me with my drawings. I figured that if Im going throught the trouble of making a plug I might as well try to make it as scale as possible. I'm still debating on what size I should go with. I'm thinking somewhere between 80''-100'' span. The fuse will be a mixture of carbon and fiberglass. Im not sure if Im going to go with foam or buildup wings yet. Other features I'd like to include are retracts,lights, spoilers, airbrakes and a digital camera.

How large is your model? What is it equipped with for power? Any idea how much it weighs now??
Old 11-17-2013, 09:03 AM
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Funk,
My U-2 is:
Wing Span: 80in.
Root Chord: 11.5in.
Tip Chord: 4.25in.
Fuselage Length : 50"


I saw it at the flying field one time a couple years before I bought it at auction. It had a 120mm fan in it but no intake ducting. I don't know if it ever flew at that time. The fuselage is molded fiberglass but much heavier than needed. Very sloppy glueing work. I don't know who made it but obviously there were molds for the fuse at one time.

The fellow who tried to fly it several years ago is currently in the hospital very ill so I won't talk him at present time. Maybe some one will see this post who knows more about the origin if this model.

I think that a good 90mm fan of current design would work OK for this size model with proper weight control. I would use the same fuse design ideas I used in my F-94C. It is light and strong enough.
http://www.sidgates.us/HOBBIES/F-94C/F94C%20PROJECT.htm

Last edited by sidgates; 11-17-2013 at 09:07 AM.
Old 11-17-2013, 09:17 AM
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I just remembered I video taped a U-2 flying at Greater Southwest Jet Rally in 2000. My video is on YouTube:
https://www.youtube.com/watch?v=VEtBraHHBXM

The U-2 flies at 2:30 into the video. I think my son knows the guy who was flying it and I think he was from the Dallas area. It looks larger than mine but not sure.
Old 11-18-2013, 09:43 AM
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Thanks for the info! I really liked looking though your photos of your F-94 build. Ive been doing some rough calculations and realized that the wingloading on an 80'' span of my model was going to be higher than I'd like. I found out that by increasing the size of the model by 20% gave me over 40% more wing area. Now I'm thinking about increasing the span to around 100'' and using a 100mm fan. I think the additional airframe weight from increasing the size would be marginal on a model like this.
Old 11-18-2013, 10:16 AM
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I think you are right, the weight doesn't increase proportionally. When I was doing the lay up on the F-94C I used my BVM T-33 fuselage thickness as a guide. The F-94C is stiffer than my BVM T-33 and doesn't weigh any more. I could have used a slightly thinner lay up on the F-94C. My bulkheads are 1/4" thick blue foam covered with 3 layers of 3.2oz cloth. The inside dia. of my bulkheads are about 5/8in less than the O.D. They are very light weight but add a lot of stiffness to the fuselage.
Old 11-25-2013, 03:01 PM
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Here is a quick update on where im at right now. Still working on the 3D model right now and I have a long way to go. At least you can start seeing some of the rough outlines at this point.

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Old 12-13-2013, 10:30 AM
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Here is a quick post with showing my progress so far.

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Old 12-14-2013, 04:12 PM
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nice work, funkworks!
Old 12-20-2013, 01:45 PM
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Thanks!

Quick question for all of you... I'm currently working out the fan size and I just want to make sure of something. I read somewhere that the outlet at the tail should be no less than 90% of the fan sweep area. Is that correct? Right now a 120mm fan would be too large and I'd have to modify the tail a little bit to make a 90mm fan work.
Old 12-20-2013, 02:06 PM
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...of course I find a site with exactly what im looking for right after posting this. So it seems like 90%-100% is ideal for inlet size and 75%-85% is about is considered to be a good compromise for outlet size. Anyone have any other thoughts. I'll have to go back to my drawing to see if I ca squeeze in that 120mm now...haha
Old 03-04-2014, 12:27 PM
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It's been a while so I thought I'd throw up a few photos of my progress so far. It's been fun and I've learned a lot doing this.
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Old 03-06-2014, 12:29 PM
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Got a good bit of work done yesterday. Here are a few photos of what Ive got so far....
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Old 03-06-2014, 01:50 PM
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funkworks,
Your jig for plug support is similar to what I did for the F-94C only I rigidly supported the aluminun tube at both ends and made it easy to hot wire cut the plug by rotating the untire fuselage.
Old 03-06-2014, 04:04 PM
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Originally Posted by sidgates
funkworks,
Your jig for plug support is similar to what I did for the F-94C only I rigidly supported the aluminun tube at both ends and made it easy to hot wire cut the plug by rotating the untire fuselage.
Youre right Sid.. I took your advice and studied your build before starting mine. Your method was the best way for sure. I have another support I have for the front I just moved it out of the way for the photos. I was thinking of covering it with a layer of 6oz glass. Do you think that is good enough for the plug or do you think I should go heavier?
Old 03-08-2014, 05:46 PM
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I would probably use 2 layers of 3- 3.2oz and see if that is rigid enough. The lighter weight cloth is less likely to "print" through to the surface of the mold. I think 6 oz total is minimal for a plug but may be OK is the foam under neath is firm enough.
Old 03-09-2014, 11:30 AM
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Thank you sir. Makes sense. I may go ahead and add a third layer then. I'm going to try to get as smooth a surface as possible before starting to add the fiberglass.
Old 03-25-2014, 08:00 AM
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I found some 8.5 oz cloth id like to try out. Do you think using that and then going over it with 3/4oz would be a good idea?
Old 03-25-2014, 02:11 PM
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funkworks,
If you are making the mold off your plug, I would use the 3/4oz first, but prefer 1-2oz for lower cost, then I would probably use 2 layers of the 8.5oz.

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