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Oct 25, 2005, 12:07 AM
I Love 30mm
FlyinAg's Avatar
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Texas A&M Senior Design Project EDF


Howdy ya'll, Ive been around here for a while, and some of yall may remember me posting back before summer about our senior design project. Back then we had just completed the design phase in which we basically created an aircraft from scratch analytically. Im at home right now, but tomrrow I can get some pics of our plane posted since the original thread I posted back then seems to have been deleted. Right now we are in the build phase. We just completed the wind tunnel model, and successfully tested it in the wind tunnel. Now its time to build the r/c model. Now this is supposed to be a sporty aircraft (4 seat, mach .75 cruise, twin turbofan, etc.) so of course we wanted to try EDFs. We have gotten a hold of 2 wemotec fan units (I wanna say they are 480's, I can check tomrrow), 2 brushless motors (dunno the specs on these either since they are installed, these units were used last year), 2 jeti speed controllers, and for batteries we have 12 cell 3700 mah NiMH packs (the prof wont let us LiPOLY grrrr).

Tomrrow we are going to do some model scaling and configuration work. We have been doing some brainstorming that Id like to share. I want to make this thing as small and light as possible (obviously) and I think we are shooting for a wing loading of about 20-25 oz/in sq. these fans are large so we want to scale it large enough so that the fans will be able to be somewhat embedded like our real design, but not be too big and bulky. we would ideally like to have full twin ducts like our real design, but we not sure we are willing to bargain our model's success on our duct designs because I know these things can be really fickle about ducts. We came up with this idea to maybe fix that:



basically, the fans would be somewhat exposed, and our ducts would be more like channels cut into the fuselage. another alternative would be to nix the channels and just taper the fuselage back into the fans. think of this as kinda like a 2 engine Alpha Jet (the model like EAM has not the real alphajet), except with a 3d fuselage not a 2d. we are worried about separation however, if we taper the fuselage back too sharply, thus starving the engines or making them ingest a huge boundary layer. any ideas? or is this a totaly rediculous idea?

we are also thinking about how we wanna build this. fiberglass would be nice, but were worried about weight. we dont have time to make a nice female mold, so we would have to do the lost foam method or cut the fuseelage in half, clean it out and epoxy it together. or, we heard about this method of using blue foam to make bulkheads, and then sheeting the bulkheads with really thin white foam or something like that? I think I saw people making models like that on here. Then there was something similar to that that involving glassing that over with light glass or brown paper. The other option is to use good ole balsa and make a frame and monocote it, but thats kinda ugly. our plane is really curvy. For the wings, we were thinking foam core with balsa sheet or something like that. we really really really wanna build as light as possible. we want this thing to scream.

Sorry for the long post, but we are looking to get our feet wet with this. We are scheduled to fly Dec. 2!!!!!!!! Any input is greatly appreciated! Thanks and Gig' Em!

Ryall Meyer
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Oct 25, 2005, 12:23 AM
I Love 30mm
FlyinAg's Avatar
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oh here are some pics of the wind tunnel model just to give yall an idea of that what the full scale aircraft looks like and hopefully the r/c model will look like!



Oct 25, 2005, 12:49 AM
Watts the Point
netmechanic's Avatar
Your gonna get in trouble for using that B-1B poster as a drop cloth! Thats just downright mean!
Oct 25, 2005, 03:33 AM
and it has to be done by December.... good luck buddy. and Yea that is desecration of a good poster, Down with whity..........

Gene
Oct 25, 2005, 05:44 AM
smug in granny panties
monkamarm2000's Avatar
looks like gordon's creation form a few years back


Barry
Oct 25, 2005, 09:41 AM
I Love 30mm
FlyinAg's Avatar
Thread OP
chill out yall theres a huge pice of glass over it!!!!!! the poster doesnt have a spec on it!
Oct 25, 2005, 10:01 AM
I Love 30mm
FlyinAg's Avatar
Thread OP
Ok i just checked and our fans are wemotec midi 90mm fans, so we got the big boys. these things should be putting out about 3.5lbs of thrust a piece huh?
Oct 25, 2005, 11:12 AM
Registered User
I had the same fan with a Hacker B50 11L, boy was it a screemer. I believe it puts out some where in the range of 5lbs of thrust. dont quote me on that, It did hold 4.5lb in a hover. No punchout but it hold until the batt died. Motocalc can probably give you the thrust specs you are looking for. There are many diffrent motors you can use, Maybe some others can chime in here on a better setup. Good luck and nice project. Take Care Chris



BTW Man I just realized there is almost no wing!! boy is she going to be fast.
Oct 25, 2005, 11:19 AM
Registered User
For your building technique. you might want to look at the Airbus's thread. The technique used in making these large airliners will work well for you application. its the Lightest method out there. Depron 3mm bulkheads, with 2mm sheeting. Once all joined it makes for a super strong bird. Use Carbon rod for strength, maybe use it as the stringer/ stringers to join the bulkheads. this will prevent any bend the fuse may try to do in the stresses of flight. same thing with the wing. Dependant on your size this bird could be extremely light. again nice project and good luck. take Care Chris
Oct 25, 2005, 12:13 PM
Electric Coolhunter
Thomas B's Avatar
If the wing were not so small, you could go with a small model some really small fans, such as EDF-40s or EDF-50 (or other 2" fans in the EDF-50 class

A model that size could be molded out of Depron by a freind of mine, who might be willing to make you guys a few sets of parts at a decent price, if you provided a male fuse plug in two halves, ready to put in the machine.
If you make the plug 1/8" undersize, it will mold out very close to desired OML.

The rest of the model could easily be built out of depron.

The mold area is only 22" by 22", though.

PM me if that interests you.
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Oct 25, 2005, 02:03 PM
Live to ride... and fly!
Tres Wright's Avatar
== I think we are shooting for a wing loading of about 20-25 oz/in sq. ==

I hope you mean per sq. ft. The wing and horizontal stab look absurdly small. Perhaps you have learned something through your calc's that justifies the proportions, but it sure doesn't look like it has much of a chance of flying, much less flying well. Especially if you're saddled with NiMH packs, you're going to have a really high wing loading. You might want to revisit your wing calc's and make sure everything is in order.

You're not planning on hand-launching are you? I think you're going to need a dolly, or at least a bungee. A really strong one

--Tres (Class of '85)
Oct 25, 2005, 02:56 PM
Watts the Point
netmechanic's Avatar
If your going with the Midifan your intakes look kinda small in comparison, I'm using the spray cans in the pic as a reference of size
Oct 25, 2005, 03:29 PM
I Love 30mm
FlyinAg's Avatar
Thread OP
yeah i definately meant oz per ft^2 sorry! guys the plane i showed is the scaled down wind tunnel model. weve been doing some sizing and scaling, and it looks like 68" wingspan, and are reducing the AR from 9.5 to 5. This should put us at our target wing loading. Unfortunately, many things do not quite scale down lineraly, so weve got to change our wing planform. The windtunnel model tested out great, so if we ever built a production sized aircraft, it should fy great keep in mind that the model you are seeing in the pic is a scaled down version of the production aircraft, with supercritical airfoils and a high AR wing etc., not the r/c model!!!!

as far a ducts, i think we are going to give up on them and do something sililar to the drawing up above. i think we could prolly get the ducts to work, but due to time and the fact that none of us have messed with edfs, we dont wanna chance getting the ducting wrong and not having enough thrust...

as far as construction, we are pretty set on using tried a tried and true balsa frame and the sheeting it with balsa. we thought about doing something like this http://www.modelairplanenews.com/CLI...ov03/pbm_1.asp, but our instructor is convinced it would be heavier in the end than doing balsa. plus our cross sections are short and fat, not tall and skinny, so if we did do it outta foam i dont think it would be as robust (at least in the longitudinal axis). we also thought about doing it like that airbus and c-5 ive seen, but we are just really weary of trying something new due to the time constraint and the fact that we want it to work and fly in the end no matter what. our instructor has been doing this and been in the full size industry for years so we are kinda heading his advice for now. we are hoping to incorporate lots of composites into our balso design however so that should lighten things up a bit.
Oct 25, 2005, 04:53 PM
I Love 30mm
FlyinAg's Avatar
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ok here are some pics or our proposed engine placement and "ducting." i guess you could call it inverse ducting lol, its more like channels. do yall think this is feasable and will produce thrust? i figure this should work a lot better than typical ducts, we can make huge intake suction lips and exit nozzles for the engines to help out the thrust, and not hav to worry about duct losses...



Oct 26, 2005, 03:49 PM
I Love 30mm
FlyinAg's Avatar
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ok so do yall think balsa construction is lighter with a balso sheeted body, or a foam method like i posted up there? i am convinced that the cored out foam sections with glass on top has gotta be lighter... im trying to convince my group members of that too. i do understand the wings built with balsa and covered are lighter, and i odnt have a rpblem doing that... i didnt get any feedback on the channel ducts we got goin on.... is it a bad idea or does no one know?
Last edited by CrazyAggie05; Oct 26, 2005 at 03:56 PM.


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