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Old Aug 11, 2015, 05:17 PM
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3.5m EDF Wing Project

Hey chaps.

Been working hard on an EDF wing design. Spent a long time designing it in sketch-up, and now I am starting to try build this bird.
Might of bitten off more than I can chew, but we will see.

I have been thinking about building a big wing for ages, and I was inspired by this thread.
http://www.rcgroups.com/forums/showthread.php?t=1050008

Thought I would start a little thread of my own, mainly as a log of the build for myself. Hoping someone who understands the aerodynamics of flying wings will be able to comment on my design. I need to know how much reflex (e.g. Aileron up) would be a good starting point for this.

Span is 3.5 meters
Powered by 70mm EDF.
4s2p 2650mah.
Aiming for an all up weight of 2Kg.

Cheers
Martin
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Old Aug 11, 2015, 05:25 PM
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First wing has come out at 400grams. (A bit more than i was hoping for).
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Last edited by Martin Turner; Aug 11, 2015 at 05:32 PM.
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Old Aug 11, 2015, 05:40 PM
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Started to assemble the fuse tonight and i quickly realised that wing tube sockets in the central fuse section were not going to be strong enough.

I knocked up a socket bracket in sketch-up which I printed out on my basic 3d printer which goes right around the EDF unit. This effectively ties the wing tube sockets together which seems to be much better.

I am having to guess where the fan and batteries go to get near to where the C of G should be.
There is not a lot of room for moving the batteries around, so I hope it's not miles off, might have to redesign the central fuse section it if its way off, but i wont know until I put the whole lot together.
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Last edited by Martin Turner; Aug 11, 2015 at 05:51 PM.
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Old Aug 11, 2015, 05:57 PM
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Just wondering if that EDF shroud will distort any with all the wing flex being directed to it by way of the printed part. Just thinking about fan tip clearance. I see it's aluminum but just wondering .....

Beautiful build.
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Old Aug 11, 2015, 06:01 PM
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Thanks Jumo. Fair point, but having wrestled to get the bracket over the fan, It seems as though the bracket would probably break before distorting the fan unit.
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Old Aug 11, 2015, 07:43 PM
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Interesting project. Looks very good what you have done. I'll be watch this. Do you have a project finish date.
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Old Aug 12, 2015, 05:13 PM
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Hi I am Mark & I am an addict
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Great build and beautiful work.

Off topic question... in the 7th picture, there are akro-bins in the background. Did you use the akro-bin metal channel to secure those or did you use something else?

Mark
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Old Aug 13, 2015, 03:06 AM
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Hi Mark. My bins are made by a company called Dexion. The metal wall plates are made by the same company and are just screwed to the wall.
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Old Aug 13, 2015, 08:07 AM
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Thanks for the info.. will look into them.
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Old Aug 13, 2015, 03:19 PM
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Thrust tube in made from 180 Micron Overhead Projector sheet e.g. Acetate. I am questioning whether I will get enough power from this motor / fan combo. It's a hobbyking special i'm afraid - doctor Mad thrust.

Eclac suggest that i will have a 0.57 to 1 thrust to weight ratio. It does seem to think it will fly. We will see.

Now the fuse is all glued up, the structure feels nice and rigid.
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Old Aug 21, 2015, 04:05 PM
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Few more pics of progress.

Was chatting to someone about Winglets this week, he suggested i really should have them. He thinks it will make it fly like its on rails. Do you agree ?

What you see in picture 2 is 1.4 kg so far. Might be able to get in a little less that 2.2kg.
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Old Aug 22, 2015, 07:31 AM
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Quote:
Originally Posted by Martin Turner View Post
Thought I would start a little thread of my own, mainly as a log of the build for myself. Hoping someone who understands the aerodynamics of flying wings will be able to comment on my design. I need to know how much reflex (e.g. Aileron up) would be a good starting point for this.

Span is 3.5 meters
Powered by 70mm EDF.
4s2p 2650mah.
Aiming for an all up weight of 2Kg. Cheers
Martin
Hello Martin. It's going to be very hard to answer your question without more info on the wing design. It appears that you have used a cambered airfoil all the way from root to tip. It also appears that you have built no twist into the wing.

Just guessing of course from your photos.

If this impression is correct your design will be problematic. More useful help can be offered, but the plan layout of the wing dimensions, airfoil(s) used and twist angle would all be necessary.
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Old Aug 22, 2015, 06:38 PM
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Amazing. Taking place to learn!!!
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Old Aug 23, 2015, 12:51 AM
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Hi HerkS.

Ok. So here is the wing data.

I've used a TL54 Aerofoil which is very flat on the bottom.

I choose it from the flying wing database which is here.
http://www.aerodesign.de/english/profile/profile_s.htm

The wing has 3.5 degrees washout or twist built in along its length.

Root chord : 373mm

Tip Chord : 100mm

Span: 3.4m (including Fuse section). Each wing half is 1.5m and fuse is 400mm.

Sweep : 18 Degrees

Plan view from Cad shown above.

Designing some wing lets now, which i plan to 3d print, which will slip over the tips of the wings.

I would love to hear your feedback.
Martin
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Old Aug 24, 2015, 09:43 AM
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It's good that you have some twist. The nose down pitching moment of the cambered airfoil would take nose up elevon to counter it. With your high aspect ratio and sweep, the twist will provide some nose up moment.

With a wing of this type, the outer part of the wing is providing negative lift most of the time. Optimizing for that takes an appropriate airfoil out there and washout. If it's not optimized that way, then nose up elevon (which creates crude reflex over that part of the wing) has to provide the trimming force needed.

You will also need to determine an appropriate CG location, and consider launching methods before you try to fly it. Just throwing a large wing like this can be risky.
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