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Old Jan 11, 2012, 12:16 PM
let's FLY!
JimZinVT's Avatar
United States, VT, Castleton
Joined Dec 2007
2,300 Posts
Well I'd increase the wing chord....3" makes the aspect ratio over 19 Hard to build that strong enough.

Let's say the wing is 58 x 5", 5.5" of dihedral (each side) and a 20" tail boom. Sailplane Calc says a vertical tail of 3.5" x 6", and a horizontal tail of 3.5" x 8" will work. For simplicity I made the tails rectangular like the wing. You can play with Sailplane Calc and change dimensions, change dihedral, add sweep to the wings/tails, and see how it changes the stability. I have attached the file; you can open it if you have a spreadsheet program like Excel (or the free LibreOffice Calc). They are zipped files....you'll have to unzip, then open (.xls for Excel or .ods for LibreOffice Calc)

p.s. I'm not an expert airplane designer, I've only scratchbuilt one glider so far. But Sailplane Calc makes it easy to design something that flies. I'm just passing on what I learned from lots of other people here, helping another guy like me get addicted to this hobby

Good luck!
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Last edited by JimZinVT; Jan 11, 2012 at 03:03 PM. Reason: added LibreOffice Calc download link
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Old Jan 11, 2012, 02:59 PM
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rockyabq's Avatar
Albuquerque, NM
Joined May 2008
598 Posts
Good on ya, Jim. Well done.
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Old Jan 11, 2012, 10:46 PM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
120 Posts
Quote:
Originally Posted by JimZinVT View Post
Well I'd increase the wing chord....3" makes the aspect ratio over 19 Hard to build that strong enough.

Let's say the wing is 58 x 5", 5.5" of dihedral (each side) and a 20" tail boom. Sailplane Calc says a vertical tail of 3.5" x 6", and a horizontal tail of 3.5" x 8" will work. For simplicity I made the tails rectangular like the wing. You can play with Sailplane Calc and change dimensions, change dihedral, add sweep to the wings/tails, and see how it changes the stability. I have attached the file; you can open it if you have a spreadsheet program like Excel (or the free LibreOffice Calc). They are zipped files....you'll have to unzip, then open (.xls for Excel or .ods for LibreOffice Calc)

p.s. I'm not an expert airplane designer, I've only scratchbuilt one glider so far. But Sailplane Calc makes it easy to design something that flies. I'm just passing on what I learned from lots of other people here, helping another guy like me get addicted to this hobby

Good luck!
Thanks, Jim!
can you please tell me more about aspect ratio? I know how to calculate it and I am aware that gliders should have high aspect ratio. What should be the minimum for a glider of my specification?
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Old Jan 12, 2012, 01:34 AM
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Malaysia, Selangor, Kajang
Joined Jun 2009
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Originally Posted by Anjan Babu View Post
Thanks, Jim!
can you please tell me more about aspect ratio? I know how to calculate it and I am aware that gliders should have high aspect ratio. What should be the minimum for a glider of my specification?
Higher aspect ratio is more efficient because it generates less induced drag in proportion to lift. But at the scale we're flying (1-2m wingspan) and the speeds we're flying aspect ratio doesn't have much effect compared to airfoil shape or wing loading.

In fact IMHO wing loading is the dominant factor for RC gliders. So if you need to increase the chord a bit to get the necessary wing loading then don't hesitate to do it. The difference will be like flying a feather floating in the wind and trying to force a brick to stay up in the air. So don't worry too much about aspect ratio. Look at your wing. If it looks like a glider it probably is the correct aspect ratio.

After looking at lots of published plans and product specification for both recreational and competition gliders I've come up with a simple rule of thumb for wing loading: 100g/dm^2 per meter wing span. A bit heavier for most current top of the line DLGs and a bit lighter for designs by Dr. Drela but overall around that. For example a 2m plane should have a wing loading of roughly 200g/dm^2 and a 1.5m plane should have a wing loading of roughly 150g/dm^2 plus or minus 10%.
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Old Jan 12, 2012, 07:17 AM
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JimZinVT's Avatar
United States, VT, Castleton
Joined Dec 2007
2,300 Posts
My 32" glider has an AR of about 7. The SuperGee plans I pointed out above has an AR around 12. I think Slebetman is correct that wing loading is the key to a nice floaty glider. Use an "average" AR and a proven glider airfoil (AG03?) but definitely build it light. My glider is 3 oz/ft^2.

( Slebetman, are your numbers off by 1 decimal point? Or are my metric conversion skills getting rusty? 3.3oz/ft^2 = 10g/dm^2.\ ? )
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Old Jan 12, 2012, 08:01 AM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
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Quote:
Originally Posted by JimZinVT View Post
My 32" glider has an AR of about 7. The SuperGee plans I pointed out above has an AR around 12. I think Slebetman is correct that wing loading is the key to a nice floaty glider. Use an "average" AR and a proven glider airfoil (AG03?) but definitely build it light. My glider is 3 oz/ft^2.

( Slebetman, are your numbers off by 1 decimal point? Or are my metric conversion skills getting rusty? 3.3oz/ft^2 = 10g/dm^2.\ ? )
Okay, I'm gonna work my brain over this wing loading thing for a while.
I haven't strarted the wing construction yet, just taking my time to coming up with a sutable construction method for the materials I have and the best aerofoil for easy construction.

Previously, when I mentioned 'foam-board' I was talking about a white coloured, light wieght and stiff material (not as stiff as CF) which is normally used by civil engineers to build scale models of buildings and other structures. These foam-boards are available in 1mm-3mm, I don't know what its called exactly, the hobby shop guy calls it foam-board (I hope you have some idea about what kinda material I'm talking about, now).
I see many modelers here find 'dollar tree foam boards/ dollar store foam boards' sutable for construction, but my local store keeper doesn't know or sell any such materials. All he suggests is the very expensive balsa wood or 'Styrofoam/thermocol' which is like too soft for the job. I did think about the same Styrofoam, but much denser ones which is used to pack TVs, refrigerators etc, but again I hit a dead end ther as the uneven contour of the Styrofoam doesn't provide me with enough workable material.
A few days back, I realized about the perforated plastic sheets which are again light, durable and stiff. The one big problem I have is that this is my first glider build and so I can't judge which of the materials (I can find) are sutable.
sometimes I feel like quitting this whole glider thing and getting back to RC dragsters, but that's just for a few seconds of the 3 hours I spend for the glider, everyday.

I'm gonna build and fly this glider no matter what and you guys are gonna help me! Okay?
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Old Jan 12, 2012, 08:07 AM
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Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
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About the aerofoil, should I get the design from the internet, print it out on a paper and then use that as a reference to trace out the ribs or can I hand design a foil that looks almost similar to the actual one? I don't use any kind of sophisticated plotting softwares or things like that, so will that be a problem? :/
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Old Jan 12, 2012, 08:15 AM
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Malaysia, Selangor, Kajang
Joined Jun 2009
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Quote:
Originally Posted by JimZinVT View Post
( Slebetman, are your numbers off by 1 decimal point? Or are my metric conversion skills getting rusty? 3.3oz/ft^2 = 10g/dm^2.\ ? )
Ah crap, you're right. The rule should be 10g/dm^2 for each meter of wingspan. 100g/dm^2 takes us into the realm of turbine powered jets !

On average, with typical glider wings, that also conveniently works out to be roughly 100g AUW for each meter wing span. Sometimes I confuse myself. I prefer to quote in terms of wing loading rather than AUW because there is less variance in the numbers.
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Old Jan 12, 2012, 08:27 AM
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Malaysia, Selangor, Kajang
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Quote:
Originally Posted by Anjan Babu View Post
Previously, when I mentioned 'foam-board' I was talking about a white coloured, light wieght and stiff material (not as stiff as CF) which is normally used by civil engineers to build scale models of buildings and other structures. These foam-boards are available in 1mm-3mm, I don't know what its called exactly, the hobby shop guy calls it foam-board (I hope you have some idea about what kinda material I'm talking about, now).
Let me guess, the material is similar to what foam cups are made of? Then that my friend is depron (or something very close to it). Over here they call it compressed foam. Depron obviously is the brand name of a very specific brand of this stuff. What it is is dense, non-beaded polystyrene. Does yours come with a shiny "skin" on or does the surface look like a typical foam plate/cup?
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Old Jan 12, 2012, 08:53 AM
Aj Creations
Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
120 Posts
No, not depron. And thanks for mentioning it, I'll go try to find some of that if I can.
what I have is much denser, stiffer and a bit more heavier. This 'attach file' thing doesn't work properly on my phone, I'll try to post up a picture.
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Old Jan 12, 2012, 09:13 AM
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Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
120 Posts
I attached a JPEG, it uploaded and show it under 'current attachments' where I could give the image a description and then I clicked 'save changes', the browser loads the same page again and nothing happens. How do I proceed? You guys on fb?
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Old Jan 12, 2012, 11:30 AM
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rockyabq's Avatar
Albuquerque, NM
Joined May 2008
598 Posts
I have to respectfully disagree with Slebetman about average weights of planes. Standard-sized, competition DLGs are 1.5 meter span and usually weigh about 8 to 10 ounces ready-to-fly. That's 226.8 to 282.5 grams. My Fling 2-meter weighs 19.5 ounces (552.8 grams). It's not super light, but it's not a lead sled either.
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Old Jan 12, 2012, 06:36 PM
Rusty
Rusty Nail's Avatar
Auckland, New Zealand
Joined Feb 2006
921 Posts
AG03 Foil

Attached AG03 foils suitable for a high performance DLG glider.
If you can get a couple of sheets of de-papered 5 or 6mm foamboard you could laminate them with a spray adhesive or dilute PVA.
Then you can either use ply tip templates, ar la Mimi free plan above to sand a good foil or use Dr Drela's template free sanding method where flat inclined planes are sanded as per attached template.
Finish the wing with a layer of light fibreglass at 45 degrees using polyurethane varnish for sticking. Up to one metre span no spar necessary, above that run a strip of fibreglass down span at foil high point top and bottom. If you can't get less then 50gsm glass then use light dress making tull type synthetics.

If this is all too much then stop thinking and start with a dead easy four layer of 3mm foamboard wing as above.

You can make a pod fuselage from 3mm foam board instead of balsa, with a glass layer outside. Keep the nose long to compensate for heavier boom and tails. Tails can be made from same foam with a little light glass on stressed areas.

A suitable carbon boom can be obtained free from a broken fishing rod if you live in a coastal area. A really low tech solution may be sanded bamboo!? Try and keep is under 10gms for a plane about one metre span.

You will need light weight two channel radio gear with preferably a small lipo battery to compensate for a heavier construction. At a pinch a small cell phone battery and its charger can do. But try to keep gear under 30gms.

Highly recommend using an existing design for your first attempt...
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Old Jan 12, 2012, 08:54 PM
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Malaysia, Selangor, Kajang
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Originally Posted by rockyabq View Post
I have to respectfully disagree with Slebetman about average weights of planes. Standard-sized, competition DLGs are 1.5 meter span and usually weigh about 8 to 10 ounces ready-to-fly. That's 226.8 to 282.5 grams.
Like I mentioned, there is a very wide variance when you look at AUW. But if you look at wing loading you'll see that your 1.5m DLG would be around 15g/dm^2 (5 oz/ft^2 for you yanks). Of course it's only a rule of thumb to get a feel of rough ballpark figures. Drela's SuperGee series are 1.5m and have wing loading of around 10-11g/dm^2.
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Old Jan 12, 2012, 11:03 PM
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Anjan Babu's Avatar
India, KA, Bangalore
Joined Dec 2011
120 Posts
I have a clarification, for gliders, is high wind loading number good or low wing loading number?

slebetman mentioned a fer numbers like 9, 10 dm^3 range, I'm not that familiar with ounces and dm.

my calculation:

wing area= (wingspan) x (chord)= 59'' x 5''= 295 inches^2

*Approx* model weight= 250grams.

wing loading= model weight/ area of wing planform= 250/295= 0.8474 g/inch^2

Is that a good figure? Think I can build the model weighing in under 250 grams.
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