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Old Sep 28, 2004, 08:41 PM
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Joined Sep 2004
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Glider project

I'm a freshman aerospace engineering student at Cal Poly in San Luis Obispo, and as part of an introductory AERO class we are to build an R/C glider that meets certain mission requirements. I have quite a bit of experience with R/C aviation, albeit all of it powered (well, at least on the good flights). The mission requirements it has to fulfill are: carry at least 50 pennies, be launched from a standard hi-start, have 2 servos, the maximum wingspan is 4', and the wing is to be made of foam cut with a hotwire. The flight will be scored by multiplying the seconds aloft by the pennies carried, and any flight time longer than 90 seconds will recieve a time of 90.

On to my thoughts, please tell me what ya'll think

The first idea is to build a simple wing with vertical stab like the moth from north county flying machines. The plan would be to load it with about 100 pennies (about 8 ounces).

http://www.northcountyflyingmachines.com/moth.htm

Another consideration was to build a gentle-lady like aircraft with generous polyhedral and rudder/ elevator control, however i'm afraid that the ratio between wingspan and wing chord would present a problem.

Finally, I thought that in order to increase the wing area we could construct a biplane glider (though, admittantly, none of the bipes I've ever flown had great glide ratios, but what aerobat does?) The airfoils would have to be thinner in order to get 2 of them out of a single chunk of foam.

Anyway, help would be appriciated from some people who (unlike me) actually know what they're talking about when it comes to flying somthing without an engine. Oh, and the flight area is pretty flat (for costal california, at least) so we wont be taking advantage of a lot of lift from slopes (maybe some thermals, depending on the day).

Thanks a lot!
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Old Sep 28, 2004, 09:03 PM
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Long Island, New York
Joined Mar 2002
271 Posts
Penny carrying glider

You are really constrained by the limit of a 4' wingspan. Ideally, any glider large enough to comfortably carry that amount of ballast should have at least a 2 M wingspan. Yours has to have little more than half that. If I had to do this project, I would go for a wing with a wide chord in order to increase the wing area as much as possible. You may want to use a mostly flat bottom airfoil with a little bit of Philips entry ( underside of leading edge is raised a bit ) Perhaps the Selig 3010 airfoil as used on the 2 M Spirit would be a good choice. You must build the sailplane both light and strong. Most if not all sailplanes need some sort of noseweight in order to balance at the CG. Make sure that some or all of the pennies do this so that the all up weight is as little as possible. Aim for a wing area of 400-500 square inches and a wing loading of 5-6 oz/sq ft. Good luck. Let me know what you decide

Pete
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Old Sep 29, 2004, 09:34 AM
DLD
David Layne
Tracy, Ca
Joined Jun 2004
665 Posts
First of all, don't build a biplane! Too much drag. I would recommend that you use a standard planform for stability's sake. I am familiar with your area, having spent quite a bit of time there. You may very well have to deal with windy conditions. A standard planform type of sailplane climb at a steep rate and maintain stability. You need to maximize your launch. You will want the tow hook as far back as possible, probably aft of CG. As for the airfoil, do a little research on Quabeck and Selig airfoils. There are some really good high-lift airfoils that would be better choices than a flat bottom type, and since you are hot-wiring them, you can use any airfoil easily. Go for airfoils that have 3-4% camber. I would also suggest that since you are high-starting this plane, to use about a 10 inch chord, giving you about 480 square inches of wing area. It should kite up the high-start well. Dihedral or Polyhedral will be the best way to go for simplicity. Keep it simple, a Balsa box fuse will work fine for this.

Good luck,

David Layne
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Old Sep 29, 2004, 11:27 AM
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windsox's Avatar
Rochester New York
Joined Feb 2004
622 Posts
I think you out to look at a delta planform like the boomer / red herring etc. in this way you can build out of foam and not need any spars. the wing loading is low due to all the wing surface area and the added bonus of turbulence derived lift at the root due to delta shape. these planes are easy to cut and require no fuselage/ no spar if you use eps foam. Because you are going to load it up with penny ballast at 48" a straight mh45 airfoil might might work well very well. if you wanted to tinker, you might play with the reflex or foil thickness. Put all the gear and ballast inside the wing cores and tape them together wich will minimize drag. assuming you are not competing against experienced "thermal hunters" this plane would be easy to execute with a very good L/D ratio. because of the rapid assembly and simple design you can focus all your extra time on foil optimisation for reynolds numbers obtained with the chosen planform and all up weight. do a search in the groups for mh45 delta for details on previous designs. if you were looking at maximum distance travelled a standard planform might have the edge. but i think the delat flying wing has a number of attrctive features for your specific requiremnts (time aloft at high loading)
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Last edited by windsox; Sep 29, 2004 at 11:29 AM.
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Old Sep 29, 2004, 11:42 AM
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Ward Hagaman's Avatar
San Diego
Joined Mar 2003
2,281 Posts
My 2 cents: gliders with tails are much less sensitive to CG changes, and polyhedral wings are much more forgiving to untested designs and less experienced pilots. If the rules don't allow for a spar, then a delta is probably the best bet- By the way, it sounds like a dream project for all us oldsters!
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Old Sep 29, 2004, 03:32 PM
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windsox's Avatar
Rochester New York
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trimming a delta is not that hard, and there are no incidence issues to deal with. plus no draggy fuselage getting in the way and adding weight.
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Old Sep 29, 2004, 07:03 PM
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Florida
Joined Dec 2002
98 Posts
Yup, go for the delta wing...all lift little drag. Line the pennies just back from the leading edge for balance. Heck, just heat the pennies and melt them into the foam. If done right they might act as a spar. Keep us posted on this one, sounds like an interestinh project.
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Old Sep 30, 2004, 07:11 PM
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Thanks a lot for all the input. Unfortuantly, the delta idea is a no-go (I forgot to mention that the width of our foam is only 12 inches, which wouldnt make much of a delta wing over the span of four feet). The general consensus of the team was to go with an idea similar to petefly's in that we're going to use a Selig 3010 foil, and a chord of around 10" with polyhedral. The good news is that we will have a 4' basswood spar, so the wings will have some structural support. The fuselage will be made out of the same type of foam, and we'll have rudder/ elevator control. I'm still a bit worried about the forces that are going to be applied to the wings during hi-start, however. Would it be a good idea to put some of the weight in the wings so that we won't get as much flex out of them?
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Old Sep 30, 2004, 07:41 PM
Think Thermals!!!!
SoCalGliderFlyr's Avatar
Costa Mesa, California
Joined Mar 2004
2,964 Posts
Since the tow line will be anchored (hooked?) to the fuse the hi-start loads are mostly aerodynamic. This is where the wing spar(s) will have to be the strongest. Once off the tow line then yes weight distribution is importan. However; think about the loads the hi-start imparts on the airframe and the balast (pennies) load.

I can answer this for you but you are the one going to college.

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Old Sep 30, 2004, 07:52 PM
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Punta Gorda, FL
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If rule OK is for two hooks and a bridal. The hooks under wings, half roots and tips, the wing bending moments reduced to 1/4 of max.
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Old Oct 01, 2004, 12:46 AM
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thepilotbruss's Avatar
St. Louis, MO.
Joined Aug 2002
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A lot of ballast and only two channels makes me think aileron,elevator glider.
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Old Oct 01, 2004, 08:36 AM
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ejett's Avatar
Athens, LA, United States
Joined Apr 2002
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Some questions:

What is the high start configuration?
How much pull will be used?
What is the length of the towline?
Will you have access to the highstart for testing before the final "contest"?
Does the pilot in your team have any glider experience?
If not, make some kind of arrangement to visit a glider club and talk to some members and maybe fly their club glider if they have one.

Since the pennies are important, use the smallest radio and battery equipment and use the pennies to balance the plane.

Put the basswood spar in the top of the wing at the highpoint of the airfoil and get some strapping tape to run from wingtip to wingtip on the bottom of the wing directly under the spar. If that is legal!

What other restrictions do you have regarding additional materials for your construction project?

Make sure all your adhesives are foam safe.

If other classes have had this same project, try to talk to those schoolmates and find out what the plane configuration was and how many pennies and what flight duration 'took the prize'. It will give you some idea of where you have to be to win this thing.

Good flight skills and a stable aircraft are going to be the key, so make sure your pilot has flown before and that they have glider experience as well before the big day.

Good luck on your project.

EJ
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Old Oct 01, 2004, 09:34 AM
Think Thermals!!!!
SoCalGliderFlyr's Avatar
Costa Mesa, California
Joined Mar 2004
2,964 Posts
EJ gets the college credits! This is like having someone else do your homework.
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Old Oct 01, 2004, 10:14 AM
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Kureus's Avatar
Joined May 2004
98 Posts
Tip plates/winglets can improve your effective aspect ratio when you are limited by wingspan (could make that 4:1 hunk of foam look more like a real glider wing...)
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Old Oct 01, 2004, 11:17 AM
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Soar_dude's Avatar
Fort Lewis, Washington, United States
Joined Feb 2002
1,289 Posts
CalPolyAero
another idea to save weight in the wings is to cut out the foam to make open bays and have just enough foam to support the airfoil shape use basswood on the top and bottom for spars then cover with packing tape should save a once or two I would go with Drela airfoil if possible. Also I agree with thepilotbruss if you have had experince flying power go with ailerons and elevator it will be easier for you to fly most power fliers have problems flying a rudder elevator plane. Ejett is 100% right go with the lightest flight gear you can that still is able to maneuver the glider around.

Soar dude
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