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Old Sep 12, 2009, 09:57 PM
It's the best day ever!
yogiraw's Avatar
Corte Madera (in Marin County, CA)
Joined Jan 2008
405 Posts
Build Log
Finch (20 inch my own design)

Hey I'm building a quick tiny build for aerobatic fun,

Airfoil: approximate, semi-symmetrical

Wing: 2 sheets of 1/16th balsa epoxy/CA wrapped over tapered balsa rod (1/4 inch in middle).

Fuse: sandwich of blue foam and balsa

Tail: Solid balsa v-tail

Nose: pointy

The idea here is doing everything precise except for airfoil, and to have a tiny plane that can go any where and fly in medium wind and have the quality to be very fun in big air too (just no going too far away as its tiny)
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Last edited by yogiraw; Sep 17, 2009 at 06:10 AM.
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Old Sep 12, 2009, 11:41 PM
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Joined Sep 2006
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Sounds cool, go 4 it
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Old Sep 13, 2009, 01:45 AM
Texas Ranger
Neil Walker's Avatar
USA, CA, San Francisco
Joined Aug 2004
2,524 Posts
Why not just make the airfoil approximately symmetrical?
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Old Sep 13, 2009, 03:48 AM
It's the best day ever!
yogiraw's Avatar
Corte Madera (in Marin County, CA)
Joined Jan 2008
405 Posts
Quote:
Originally Posted by Neil Walker
Why not just make the airfoil approximately symmetrical?
Well, effectively I did, but of course one sheet of balsa will tend to be slightly stiffer than the other. The stiffer on will be the one that is flatter (underside of the wing). But what I did was CA the spar to the underside wing first and then mocked it all up with epoxy and the top bent a little more. See pic.
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Last edited by yogiraw; Sep 13, 2009 at 04:13 AM.
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Old Sep 15, 2009, 09:15 AM
Plank addicted
Marcos Quito's Avatar
Sao Paulo - Brazil
Joined Jan 2007
163 Posts
Sorry to say, but this will be for very strong winds, and not "medium winds", unless you´re taking very very special care on the weight.

- Do you have a weight target ?
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Old Sep 15, 2009, 01:08 PM
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theBOZman's Avatar
United States, CA, Oxnard
Joined Feb 2005
2,505 Posts
How close are you to your CG with the servo in the tail like that???

fyi:
Since the tail servos distance is farther from the CG than the nose, you'll need ALOT more lead in the nose then the weight of the servo to counter for it.
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Last edited by theBOZman; Sep 15, 2009 at 10:30 PM.
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Old Sep 17, 2009, 06:11 AM
It's the best day ever!
yogiraw's Avatar
Corte Madera (in Marin County, CA)
Joined Jan 2008
405 Posts
Quote:
Originally Posted by theBOZman
How close are you to your CG with the servo in the tail like that???

fyi:
Since the tail servos distance is farther from the CG than the nose, you'll need ALOT more lead in the nose then the weight of the servo to counter for it.
Or would more metal rod be worse having the servo closer to front?

Quote:
Originally Posted by Marcos Quito
Sorry to say, but this will be for very strong winds, and not "medium winds", unless you´re taking very very special care on the weight.

- Do you have a weight target ?
Taking special care. Yes, it wing loading will be high afterall. I will do the calculations soon and post AUW, how much lead is in the nose, and wing loading. Just must finish the tail feathers fist.

btw, I'm thinking of calling this little one the finch. Name taken by a glider yet?
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Old Sep 17, 2009, 08:14 AM
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TweakRacer's Avatar
Joined Jan 2006
219 Posts
Looks good! How'd you finish the plane? WBPU? Laminating film?
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Old Sep 17, 2009, 05:13 PM
It's the best day ever!
yogiraw's Avatar
Corte Madera (in Marin County, CA)
Joined Jan 2008
405 Posts
Quote:
Originally Posted by TweakRacer
Looks good! How'd you finish the plane? WBPU? Laminating film?
No, no, much higher class than those: zagi tape.

Probably a year later I will take off all the tape, give it a good sand and redo it in a kote or paint.
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Old Sep 17, 2009, 06:04 PM
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theBOZman's Avatar
United States, CA, Oxnard
Joined Feb 2005
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Quote:
Originally Posted by yogiraw
Or would more metal rod be worse having the servo closer to front?
A flexible push rod and sleeve would add way less weight than the servo would. EVEN IF the rod weighed as much as the servo, the weight of the rod is distributed along the moment arm of the tail. With the servo, ALL it's weight is focused in one spot WAY far out from the CG.
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Last edited by theBOZman; Sep 17, 2009 at 06:15 PM.
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Old Sep 18, 2009, 01:58 AM
It's the best day ever!
yogiraw's Avatar
Corte Madera (in Marin County, CA)
Joined Jan 2008
405 Posts
Quote:
Originally Posted by theBOZman
A flexible push rod and sleeve would add way less weight than the servo would. EVEN IF the rod weighed as much as the servo, the weight of the rod is distributed along the moment arm of the tail. With the servo, ALL it's weight is focused in one spot WAY far out from the CG.
My next tiny plane will be designed to have room for that, using maybe a carbon thin rod. Thanks!
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Old Sep 18, 2009, 06:17 AM
It's the best day ever!
yogiraw's Avatar
Corte Madera (in Marin County, CA)
Joined Jan 2008
405 Posts
AUW: 7 oz
0.7 oz of lead added to nose
Wing area: 63 square inches (.4375 sq ft)
Wing loading: 16oz/sq ft!!!

Will wait for very windy day then?
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Old Sep 18, 2009, 08:31 AM
Long to be flyin'
Antonsoarer's Avatar
Wirral, (UK)
Joined Dec 2003
3,056 Posts
The lightest elevator system is closed-loop, I have done it on v-tails and it worked fine, makes a great sound if the wires are out in the breeze!
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Old Sep 18, 2009, 05:13 PM
It's the best day ever!
yogiraw's Avatar
Corte Madera (in Marin County, CA)
Joined Jan 2008
405 Posts
Yes, the plane could have been ever more stealthier, but hey, its going to rip the skies anyways and scream!
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Last edited by yogiraw; Sep 18, 2009 at 05:20 PM.
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