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Old Feb 05, 2016, 08:50 PM
ThatTricopterGuy is offline
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A. Benavi
Joined Jan 2016
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Foam F5J style scratch build

Hi guys. As you might see from my username, I have flow multi rotor fpv most of my time. I was drawn into the fixed wing area of the hobby because I yearned for greater range and flight time than my tricopters had allowed me. Electric sailplanes in particular are amazing at taking a tiny amount of power and converting it in to hours of flight time. While supras and Xplorers are very nice, I am only 14 years old and I have limited capital. That Is why I plan to scratch build something myself.
The fuselage will be a simple carbon fiber tube, attached to a foam board nose compartment with space for electronics. There will be a basic tailplane made from 6mm depron reinforced with packing tape. I plan to use torsion springs similar to a DLG so I can mount the servos in the front nose pod. All of that is pretty simple. This brings me to the real reason for my post: The wings. The wings are arguably the single most important component, so I want to do it right. I am thinking about a 1.5-2 meter wingspan, but nothing is final. In discovering the world of sailplanes, I also came across a website, http://m-selig.ae.illinois.edu/ads.html ,that has a massive collection of airfoils from brilliant minds like Mark Drela and Michael Selig. I could easily make one of their more basic designs using a hot wire cutter and blue insulation foam. However, I don't know if it is strong enough or how I could drill a hole into it to put a spar in. Also, which airfoil designs do you think would be the best for this application? There are so many to choose from. Should I give up the hot wire cut wing and just make the thinnest foil I can out of depron?
Thanks so much
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Old Feb 06, 2016, 06:00 AM
ghcrash is offline
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GH crash - I practice a lot
United States, OK, Bartlesville
Joined Oct 2011
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You know that it will be difficult to give specific answers to your questions because the answer(s) depend on the details. But I will throw my two cents worth in, just to get people talking.

There are lots of good airfoils you could use. Look at what is being used in the top end gliders for sale and pick an airfoil. Don’t forget to think about how you plan to use your glider and where you plan of flying. A pure thermal glider in an area with light winds would probably benefit from a high lift airfoil. If you plan on slope soaring or stunting around, then a low drag airfoil would be a better choice. My preference for an airfoil would be something form the AG35 to AG38 series for small, light floater and MH32 for larger, heavier plane. But I fly thermal gliders where the winds are usually 10-15 miles an hour.

Almost any hotwired foam wing will need some form of reinforcement. And usually the foam is pretty soft and needs some protection from dents and scratches. On smaller, lighter planes many people just cover the foam with clear packing tape. This adds both dent protection and strength. This would probably be the way I would go on a first build 1.5-meter glider. For larger gliders, or thin airfoils, I would suggest some carbon fiber spars. Slots usually can be cut in the top and bottom of the foam core using a sharp knife. Just slide the carbon fiber in on its edge and glue in place. Clear packing could still be used for dent and scratch protection for a first build but usually it’s time to think about putting a more substantial skin on the foam core.
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Old Feb 06, 2016, 12:53 PM
Ricardo RW is offline
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.: Looking for Thermals :.
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Chile, Quinta Región de Valparaíso, Los Andes
Joined Jun 2002
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Your target wingspan 1.5 to 2m will bring you a huge challenge to get a decent weight. You'll need to select specific materials and techniques to success.

Besides, what would be the main purpose of your glider? Would it carry payloads?

Regards
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Old Feb 06, 2016, 05:46 PM
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Still circling in sink...
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Take a look at some of the threads on bagging wings (search RCG on that) and the Composites Fabrication forum. You may be looking to keep things simpler than that, but those are the places to learn. you can simplify from there.
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Old Feb 07, 2016, 10:37 PM
ThatTricopterGuy is offline
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A. Benavi
Joined Jan 2016
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I don't think I have the skill or money to venture into composites yet. I think that hot wire foam wings will have to be the way to go. As far as other materials, I think I will use a simple carbon tube as a fuselage with a foam board nose pod to carry battery and electronics. The only additional payload I will be carrying is an FPV setup on 1.3 ghz and a 600tvl board camera. It would be really cool to put a higher quality camera on it but I don't plan on that. I also don't really know what sort of battery I should put on it. Obviously, this is going to be heavier than a proper sailplane, so I might need a 4S battery, and perhaps a big-ish one (1800-2200)?
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Old Feb 08, 2016, 06:08 AM
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Foam Wing

Here is one way. You can usually find someone willing to cut foam cores at a reasonable price. His planes come out very lite for a foam core wing.
http://www.rcgroups.com/forums/showthread.php?t=2366679
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Old Feb 08, 2016, 06:34 AM
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You can make wing as one for vacuum bagging, but instead bagging use stronger foam (700kPa/100psi) and cover them with packaging tape.

Checkout plans for Allegro glider, both vacuum bagged and wooden version.

Make spar for central part of wing as one of Allegro lite (Flat pieces of carbon, vertical balsa, and tow wrap) and for tips use carbon 0.060-0.080" (1.5-2mm) rods glued top and bottom to act as spars,
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Old Feb 08, 2016, 01:32 PM
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.: Looking for Thermals :.
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Chile, Quinta Región de Valparaíso, Los Andes
Joined Jun 2002
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It's your goal to learn how to build with fancy techniques or are you just looking for a glider that can carry your cameras?

For the second part of the question I would suggest you to check the Diamond 2500 from Art-tech. I think HK has a clone too.

Regards.
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Old Yesterday, 08:06 PM
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A. Benavi
Joined Jan 2016
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I have been looking around and may have found some alternatives, but I don't know if these methods are known to work. I could always have some wing ribs and spars cut out and then cover the wings in monokote or oracover, without doing any of the fancy, expensive autoclaving and vacuum bagging. Also, I could try hot wire cutting rohacell foam. It is one of the toughest foams I know and with some reinforcement maybe it would be enough strength to use it for a wing. Does anyone know if these options are viable?
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Old Yesterday, 10:27 PM
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I don't know your backround but you said 14 years old. Now you need to design/ build/ add motor/ esc/ servos/ camera/ batteries etc. Not going to happen with 1.5 meter Glider. 2 meter possible. Plus ride thremals while not hard experience sure don't hurt. Good luck 2.5 meter would not be bad idea either.
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Old Yesterday, 10:31 PM
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A. Benavi
Joined Jan 2016
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why would it be easier to make a glider with a larger wingspan?
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Old Yesterday, 10:32 PM
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A. Benavi
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And as far as background, I have mostly worked with multi rotors. Most of my fixed wing experience was designing my own stuff at random from 6mm depron or foam core, usually without a motor because it gets expensive
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Last edited by ThatTricopterGuy; Yesterday at 10:33 PM. Reason: spelling error
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