kaiger

Hi.
We're building a 12' R/C version of the UAV seen below for the second half of our senior design project (this drawing was made for our CDR of the full-scale plane, so the dimensions can basically be ignored). I have built several R/C planes before, but never this big, never from scratch and never electric. To keep it light, I plan on building up the wing with an open frame, D-tube construction, and probably with carbon-fiber spars.
The fuselage will be bulkhead/stringer design with a fiberglass cowl. I hope to power it with something like an Astroflight 90, but I have no experience with electric so this is really just a guess. We plan on reversing the motor and using a regular propeller in a pusher configuration.
The main questions I have are as follows: how and where would you suggest I break the wing? I was thinking of breaking it at BL 288 in the picture. I understand there are aluminum tubes used to construct two-piece wings, but I've never used them and I'm a bit confused on how they tie into the wing structure. Are the spars and shear webs attached directly to them or do the
ribs near the root of the wing carry the load?
Second, I would appreciate any hints/comments on making a plane of this size electric. Our main reasoning for going electric is it will be easier to balance by moving the batteries rather than moving the fuel tank and worrying about pumping, fuel flow etc. Would you suggest a geared or direct-drive motor?
Finally, the full scale plane was designed with an all flying v-tail. I don't recall ever seeing this in R/C, which kind of worries me. Would we be better off going with larger, conventional ruddervators or is there a way to impliment a flying tail?
Thanks for any help you can offer. If you're interested, more pics from our presentation can be seen here. .
-Kai

Ron S

My Feedback: (2)

Your vehicle looks pretty neat! BL 288 looks like an ideal place to break the wings, from a manufacturing standpoint. I think wingtubes would work fine for this aircraft. You might check the tnt-landinggear website for info on available tube sizes. Perhaps a tube running from the outer wing panel, sliding into the "wing kick" area (BL 288 to 168) parallel with the outer panel spar, then tying it up with a bulkhead in the fuselage to take the loads from the wing tubes... Wing tubes are used alot in foam wings - have you considered hot-wiring the outer panels? Otherwise, I'd get the wing tube as close to the spar as possible (sandwich in between the spars?)...

Using the butterfly tail for both pitch and yaw - are you sure you have enough pitch authority? The included angle looks a little small... I thought on the YF-23 aircraft, the included angle between the tail surfaces was around 110 degrees... You could also make your trailing edge of the fuselage into a "beavertail", to get more pitch control.

I'm useless with the electric question - I would think a 90 would be reasonable. Think light, and have fun!

Ralph Morris

Hi Kaiger; There is a problem when you scale down high-aspect ratio wings. A friend of mine built a scale model of a U-2, and even at light weight it didn't fly well, because the wings tapered down to less than three inches tip chord. It appears from your drawing that the tip chord would be less than six inches.

Also, some of the SAE weight-lifting designs I've seen with very high aspect-ratio wings were not as successful as those keeping the minimum chord greater than six inches.

There are some airplanes that model well, and some don't. This doesn't look like a good prospect for a small model, but maybe at 12-ft span you can get away with it.

What is the application? Not a weight-lifter, I hope.

kaiger

Yeah, the minimum chord is kinda why we're shooting for a 12' wingspan. The tip chord actually comes out to be around 4.5". I know this isn't going to be an easy plane, but I guess it's not supposed to be. I'm just glad we have some local competition pattern fliers for our first flights. I don't think I would trust my somewhat rusty skills to fly this monster.

And no, it's not a weight lifter (thank God). I think it'll be hard enough building this thin of a wing strong enough without worrying about extra weight. We designed the original plane in the first semester of this project answer to an RFP for a high-altitude (70k ft) high-endurance (36 hr loiter+15nm range, unrefuelled) surveillance UAV capable of carrying a 3,000 lb payload.

Thanks for both of the replies and the PMs. I'll post updates as we build the thing over the next couple of months.

Bill Vargas

My Feedback: (5)

I'd say Carbonfiber (CF) tubes are better, lighter and much stronger. You can find them here,,, www.cstsales.com

I concure that bl 288 is a great place for the wing break. Have you considered foam/balsa sheeted wings? There's no need for sheer webbing in foam wings. Single, upper and lower Spars are generally located at the high point of the airfoil,,, mutiple spars, 3 for example, can be placed at 20%, 40% and at 60% of the wing cord.

Its very easy to bag the skins to the foam cores. They are easily repaired, incase you ding one up, with a block of balsa. Also a buddy of mine has a CNC foam cutting setup that can vertually cut any airfoil, cutouts for CF spars, wing tubes and servo bays,,, www.flyingfoam.com

Not sure of your $$$ budget but you may also want to consider having the foam cores skinned with fiberglass. The wing skins at the aileron hinge line will also serve double duty as the aileron hinge. This eliminates the aileron gap and keeps the boundary layer on the wing there at the aileron thus making it a more efficient wing.

As for the flying V tail, I am sure that a Glider person will chime in on this one,,, I use the conventional ruddervators for my Race planes.

Electrics,,, eek, way to many free electrons for me



hope that helps you out!



BV

Ralph Morris

Hi Bill; That's a good point; the electrons are free. Once you purchase a battery pack, you can refill it with your charger, whenever you want to fly.

Those were excellent suggesions, imho.

For a wing so thin, I think the correct approach would be a fiberglassed foam core, with high carbon-fiber content, or Kevlar (TM). There were some really beautiful wings built in this manner on some of the (winning) weight-lifting planes when that event was still held at Mile Square Park, in Orange County, California. They were glider-like, with the skin forming the aileron hinge, as you suggested.

With a very thin wing, the skin needs to be the structural part, because an internal spar would be not be tall enough to resemble the I-beam that it must in order to sustain the loads.

kaiger

Well, we did it. Flew it yesterday after about two months of construction. We ended up using a Hacker B50 turning a 20x10 APC prop on 20 2700 mAh NiMH cells. We got about 3:30 of full-throttle running time off of it, but the wing loading was only 16 ounces/sq ft, so it floats pretty well. We used carbon-epoxy/basswood for the spars and balsa sheeted foam cores to shape the wings to a 5415 airfoil and they were incredibly stiff. Total flying weight was about 13 pounds and wingspan is 12 feet, two inches. Glad it's over. Time to graduate.

kaiger

....and if you're curious, the whole project can be seen here.

Tall Paul

Very, very, very good!
Any inflight photos?

T28pilot

My Feedback: (2)

Now thats funny!!!

kaiger

Ummmm, yeah. That's me. Long hours in the Aero lab get to you. We got some in-flight pics, but they're stills from a video camera, so it'll be a couple of days before I get them. Got a great knife-edge shot about 10 feet off the deck (let's pretend it was intentional).

TexasAirBoss

My Feedback: (22)

ART SHCOL would be proud!!!!!

Ralph Morris

Congratulatins, Kaiger! Now for the full-scale model...