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Old Jan 09, 2007, 03:42 PM
foamies to the end...!
ukdalai's Avatar
United Kingdom, England, East Susx
Joined May 2004
138 Posts
Build Log
de Havilland Venom

ive been searching for a depron Venom profile plan for ages.
still not found one, so i made my own...

i got a 3 side view from this forum and scaled it up to a 800mm w/s having cut the pieces and thought about how to lay it out, any way i have an old RCME magazine that had a few shots of a free flight model, so i basically built it by eye from pictures of one that flys....

yeah yeah i know theres alot more to it than that but its going to look good when its finished and in a way i dont even care if it flies or not, i love this hobbie, and the satisfaction of standing back and thinking "hey that actually looks like it should" and created from flat sheet foam...

and it cost me about 5.00 to make.

i do hope it flys at least ok, but we will see.

anyway:

800mm wingspan
55 EDF 280 motor (i think it may need more)
all 6mm depron 3mm carbon spars
alerons, elevator
AUW ill give when its done.

now all i gotta do is work out where the CoG should be.

hope you like the idea.
Craig
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Last edited by ukdalai; Jan 09, 2007 at 03:48 PM.
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Old Jan 10, 2007, 10:10 AM
foamies to the end...!
ukdalai's Avatar
United Kingdom, England, East Susx
Joined May 2004
138 Posts
hi again, does anyone know the way to work out a reasonable CoG for it, i googled it but did not find too much.

Craig
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Old Jan 10, 2007, 10:22 AM
Time for another motto!
Utrecht, The Netherlands
Joined Jul 2006
1,413 Posts
Yes, that is very simple: take your model, put a lump of clay on the front and toss it. add or remove clay until your model flies good. If you don't put your equipment in it should be lighter and have less troubles with the unevitable nose-in. Or make a scrap model first. foam is cheap, so use it accordingly.
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Old Jan 10, 2007, 02:45 PM
foamies to the end...!
ukdalai's Avatar
United Kingdom, England, East Susx
Joined May 2004
138 Posts
yes but i mean there has to be a "best balance point" on the wing, i thought there was a calculation to find the ideal CoG, then position the electrics to keep that point in balance..

Craig
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Old Jan 10, 2007, 03:08 PM
"To Fly is Everything"
britchris's Avatar
athens georgia
Joined Dec 2006
280 Posts
theres a calculator for it somewhere,sure i have seen a link on here for one

http://adamone.rchomepage.com/cg_calc.htm found one
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Old Jan 10, 2007, 04:04 PM
Drunk Pilot
Azeiku's Avatar
Minneapolis
Joined Aug 2003
215 Posts
This might not be a post you are looking for but thought I'd put it in here hoping it might help someone if it doesn't help you. I've used the glide test with great success. I know everyone would like to calculate it but I've found that your measurements can be off in a calculation. Doing a glide test tells you exactly where it is with your set up. Your wings might be a little off from diagrams or calculations. This is how I do a glide test:

1. Build the frame but don't put any electronics in it. These will come later and as JelleB stated, it'll help avoid the heavy nose in or stall crash and ruin your all your hard work.

2. Ensure your control surfaces are present. If you haven't cut them out from the wing yet, all the better. If you have, put them on with their respective hinges and then maybe tape them to a neutral position.

3. Take your model to your bedroom or some place with a soft landing. Hold from tip and tail and drop it flat on your bed. If your nose hits first, you'll know you have to add a little weight to the tail. Conversely, if your tail hits first, you'll have to add weight to the nose. If your tail hits first, do this until your nose starts to hit. If the nose hits first, you can continue to step 4 but be careful that it's not too nose heavy. BTW, I use quarters taped to the airframe with masking tape for my weights.

4. Go outside with model and weights. Go to a large grassy area or someplace that will result in the least damage when it lands if it comes in nose heavy. Give it a light toss while on your knees to keep it close to the ground. Add weight to the correct area to get a nice glide. Not a nose dive and not a tail stall.

5. When happy with your glides, take the model and see where it balances. I use my fingers for a rough estimate and then later use two pencils with erasers or whatever to balance it later. Mark these spots and that's where your CG is.

6. Add your electronics and then ensure your plane balances again on the marks you made earlier. Now you're ready for powered flight.

Like I said, this is the technique I used for several models and it works great. I had very successful maiden flights using this method. My latest was this scratchbuild.
Big Bird Kat


Hope that helps!
Azeiku
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Old Jan 10, 2007, 07:00 PM
Time for another motto!
Utrecht, The Netherlands
Joined Jul 2006
1,413 Posts
It's all about who you trust more: some formula that assumes a lot and requires a perfect input for a good output, or your own eyes and ability to experiment. I can understand that you'd feel safer with a formula that somebody else derived. But testing your own creation in real world conditions is without any assumptions, estimates and fudged Reynolds numbers. The only thing you need to be able to recognise is a stall and a dive. Just experiment with it until you are satisfied you have found the best glide point. Your actual GC with controls built in should be a little forward of this point as that makes it fly more stable.
If you are afraid to break your foamie accept that it will break anyway and that you will/should be having a lot of funt flying toward that crash. Just repair and go at it again, or declare a total loss and built another one.
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Old Jan 11, 2007, 02:18 AM
foamies to the end...!
ukdalai's Avatar
United Kingdom, England, East Susx
Joined May 2004
138 Posts
thanks chaps, i did the glide test and found a good CoG.

then transfered it with the weight to a ballance rig i made to mark the CoG on the wing.

it turns out to be around 2 inches from the LE at the tail boom points.

also got carried away with the painting, ill post some pics tonite.

Craig
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Old Jan 11, 2007, 07:18 AM
Drunk Pilot
Azeiku's Avatar
Minneapolis
Joined Aug 2003
215 Posts
ukdalai, Great news on the CoG! I bet she maidens brilliantly. Looks like a cool airframe from the pictures already! I'm a sucker for double booms. I can't wait to see more and hear about a maiden flight.

-Azeiku
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Old Jan 11, 2007, 09:56 AM
foamies to the end...!
ukdalai's Avatar
United Kingdom, England, East Susx
Joined May 2004
138 Posts
i think the maiden might be a way off, weather in the uk is shot....
realy windy at the mo

Craig
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Old Jan 11, 2007, 11:45 AM
Time for another motto!
Utrecht, The Netherlands
Joined Jul 2006
1,413 Posts
Sunday might be calm enough. My windforecast map shows a bit of england with nice flyable blue. Hopefully I'll have one or two maiden-able ScottA J3 Cubs ready by then.
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Old Jan 11, 2007, 12:13 PM
Victoria Super Mortem
UBILDIT's Avatar
BIRMINGHAM ALABAMA
Joined Jan 2006
1,459 Posts
Cg

Ukdali,
Great looking plane. I'm glad you found the glide test to be a good way to discover CG. I always rely on that rather than on formulas because each model is so different. Something else that I've discovered... through trial and error but mostly from good advise coming form folks here on these threads ... the CG on a pusher will actually be forward of the glide CG while in flight. So, just for good measure, I would start out any powered flights with the CG 1/2 to 3/4 of an inch in front of the glide CG and adjust from there. If I've read it once, I've read it 1,000 times. A nose heavy plane will fly again, but a tail heavy plane usually only flies once. LOL... so true... Again, good luck and keep us informed when you get to fly it.. looks great...

Bo
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Old Jan 11, 2007, 05:12 PM
foamies to the end...!
ukdalai's Avatar
United Kingdom, England, East Susx
Joined May 2004
138 Posts
glad to see you all like it, ive added some pics, did not do anythingto it tonight, as i could not put another project down..

ive been playing with depron for about six weeks and i have gone a little mad.
i have 13 models in the garage.. 4 of which are ready to fly, must say i dont want to kill any of them, but thats the beauty of it, it only costs time, and if i do crash one or two at least i have a hanger full to keep practicing.

ill tell you now im more used to electric helis than fixed wing.

but i cant wait for the good weather to come..

does anyone have an opinion on wheather the fan and motor will be enough...?

ooh i cant quite decide if i should put scale-ish U/C on, you know 1 right on the nose and 1 each on the wings.
Craig
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Old Jan 11, 2007, 05:39 PM
Drunk Pilot
Azeiku's Avatar
Minneapolis
Joined Aug 2003
215 Posts
Paint job looks good! Top Job!

-Azeiku
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