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Old Jan 06, 2012, 10:04 AM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
120 Posts
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Help with 2-channel glider construction?

I'm a newbie to rc aircrafts and I'm scratch building a 2 channel glider (rudder and elevator controls). I have a few questions and doubts:
1) how do I determine the distance between the wing and tail end? I did come across 'tail volume coefficient' & things like that, but its kinda too complicated for me. Any easy explaination?
2) where should the CG lie for best (easy) handling and performance? I was told that CG usually lies at 30% from the leading edge of the fuselage, true?
3) I built the fuselage out of 2mm foam board, weighs 20grams and its pretty stiff. Is it light enough?
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Old Jan 06, 2012, 11:56 AM
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1967250s's Avatar
United States, VA, Alexandria
Joined Sep 2008
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What are the dimensions, wingspan, length, weight? CG depends on airfoils, wing planform, fuse length, size of tail and horizontal stab, swept wing or straight, etc. Need more info.
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Old Jan 06, 2012, 08:15 PM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
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I haven't constructed the wing yet, but I've planned for a wingspan of 58 inches and chord length of 7.1 cm, airfoil is a Clark 'y'. Its going to be a straight wing. Weight, I'm not sure yet, but my prototype fuselage with all RC stuff mounted on, will weigh around 150 grams (I think I can make it lighter).
And I don't know how to determine the size of the tail.
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Old Jan 06, 2012, 09:01 PM
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United States, VA, Alexandria
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I'm not a designer by any long shot, but I think it should have some dihedral, especially if you are new at this, about 3 inches each side. Clark Y is good simple foil. Will be slow floater. I would suggest tail at about 10 inches by 5 wide.
CG will be probably at highest point of airfoil. Put it together, toss it gently flat and see what it does. It should go straight and flat. Too steep, moveweight back. Climb into stall, move weight forward. Have fun and read lots of rcgroups/sailpanes threads.
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Old Jan 06, 2012, 09:06 PM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
120 Posts
"CG will be probably at highest point of airfoil" ~I didn't understand this, highest point of airfoil?
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Old Jan 06, 2012, 09:08 PM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
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And please, give me ideas on how you determine the tail length. How did you arrive at 10 by 5 inches?
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Old Jan 06, 2012, 09:25 PM
Is my CG correct?
discostu956's Avatar
Wollongong, Aus
Joined Sep 2009
5,096 Posts
30% is a good starting point. You want to be close to there, but adjust according to the actual plane. If you have a read about CG placement you should get a good understading of the hows and whys. But at 30% it should fly without too many issues, it just might not be optimal

I would compare your dimensions to known planes so you are in ballpark similar figures, usually just eyeballing is fine. As this is your first scrathbuild and your new to RC it won't be your best plane, but a good learning tool, so don't worry too much about getting exact figures and areas. You can get pretty bogged down in that sort of thing, just look at what goes into some of the planes on here!
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Old Jan 06, 2012, 10:46 PM
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JimZinVT's Avatar
United States, VT, Castleton
Joined Dec 2007
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Anjan, I had about the same amount of experience as you a few months ago when I was scratch building my first glider. DiscoStu's suggestion of looking at plans of other gliders to find dimensions is good. The Supergee I is roughly the size of your glider, so you can get an idea of tail boom length and tail sizing. It's a very complicated glider but you can get a lot of basic sizing information from it.

The Clark-Y airfoil may not be the best choice for a glider....take a look at the AG03. Others here may have more suggestions.

Assuming you're building a plane with rudder and elevator only you should plan on 11- 12 degrees of dihedral in each side of the wing. If you're using ailerons you can cut that in half.

The tail volume calculations do seem kind of complicated, but if you download the Sailplane Calc spreadsheet and instructions you can try different dimensions until you get the tail volumes right. Tails will be bigger if you want to build a DLG (discus launch glider) rather than a regular hand launch glider. It will also help you with CG location, and pretty much any measurement on your glider. This spreadsheet helped me a lot when designing my glider, and it flies great.

AND.....ask a lot of questions! There are a lot of friendly people on this forum who are willing to help out beginners like us! (thanks friendly helpful people! )
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Old Jan 07, 2012, 02:16 AM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
120 Posts
Quote:
Originally Posted by discostu956 View Post
30% is a good starting point. You want to be close to there, but adjust according to the actual plane. If you have a read about CG placement you should get a good understading of the hows and whys. But at 30% it should fly without too many issues, it just might not be optimal

I would compare your dimensions to known planes so you are in ballpark similar figures, usually just eyeballing is fine. As this is your first scrathbuild and your new to RC it won't be your best plane, but a good learning tool, so don't worry too much about getting exact figures and areas. You can get pretty bogged down in that sort of thing, just look at what goes into some of the planes on here!
Thanks, that helped.
This is not my first glider, actually. I have built a few small and less complicated ones in the past, I used rocket propulsion in those and they were not RC.
this is my first attempt at building an RC aircraft.
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Old Jan 07, 2012, 02:31 AM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
120 Posts
Quote:
Originally Posted by JimZinVT View Post
Anjan, I had about the same amount of experience as you a few months ago when I was scratch building my first glider. DiscoStu's suggestion of looking at plans of other gliders to find dimensions is good. The Supergee I is roughly the size of your glider, so you can get an idea of tail boom length and tail sizing. It's a very complicated glider but you can get a lot of basic sizing information from it.

The Clark-Y airfoil may not be the best choice for a glider....take a look at the AG03. Others here may have more suggestions.

Assuming you're building a plane with rudder and elevator only you should plan on 11- 12 degrees of dihedral in each side of the wing. If you're using ailerons you can cut that in half.

The tail volume calculations do seem kind of complicated, but if you download the Sailplane Calc spreadsheet and instructions you can try different dimensions until you get the tail volumes right. Tails will be bigger if you want to build a DLG (discus launch glider) rather than a regular hand launch glider. It will also help you with CG location, and pretty much any measurement on your glider. This spreadsheet helped me a lot when designing my glider, and it flies great.

AND.....ask a lot of questions! There are a lot of friendly people on this forum who are willing to help out beginners like us! (thanks friendly helpful people! )
Give me some ideas on wing construction, please. Balsa is very costly here in my place, so I'm using 2mm foam-board. I'm thinking of making an upside-down 'T' structute and placing the wing ribs made of Styrofoam on it and cover the entire structure with a durable plastic sheet. Will it work?
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Old Jan 07, 2012, 08:15 AM
Is my CG correct?
discostu956's Avatar
Wollongong, Aus
Joined Sep 2009
5,096 Posts
I don't see why not, can always try and fail and then you will know (I like different methods etc).

Only thing to keep in mind if this is to be a discus launch glider is will this method handle the launch stresses? Even if a wing survives a few launches, the constant launching can take its toll also. I had one wing I was fixing every few days flying cause it just couldn't handle the launch stresses properly. I guess I'm saying to try your method, but just keep in mind the extra stresses DLG technique puts on it.

When you say plastic sheet,what type of plastic are you refering to? I've been keen to try stiff plastic over foam instead of fibreglass, just wondering if thats what your thinking
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Old Jan 07, 2012, 08:41 AM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
120 Posts
I'm building this one to be Hand launched. what do you have to say about rocket propulsion?

Not thought about which plastic yet. I have experimented with the transparent plastic sheets used with projectors. I'm open for any better materials, but just not expensive ones.
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Old Jan 07, 2012, 09:45 AM
Aj Creations
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India, KA, Bangalore
Joined Dec 2011
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When calculating the wing area, should I calculate both top and bottom surface areas and add them or only the top?
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Old Jan 07, 2012, 02:00 PM
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Joined Jan 2008
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Anjan:

Wing area is projected area only. Just do the top, exactly as if it were a flat sheet.

Yours, Greg
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Old Jan 07, 2012, 09:23 PM
let's FLY!
JimZinVT's Avatar
United States, VT, Castleton
Joined Dec 2007
2,295 Posts
Quote:
Originally Posted by Anjan Babu View Post
Give me some ideas on wing construction, please. Balsa is very costly here in my place, so I'm using 2mm foam-board. I'm thinking of making an upside-down 'T' structute and placing the wing ribs made of Styrofoam on it and cover the entire structure with a durable plastic sheet. Will it work?
Take a look at this thread. It is probably too heavy for a glider, but I think if done with plain foam (no paper) covered with plastic film (laminating film) it could work. Ribs would allow you to produce an accurate airfoil.

Here is a slope glider with wings made of foam sheets with ribs over a spar: the swinger. (It's a looong thraed....you'll have to dig to find construction drawings and photos.)
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