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Old May 22, 2012, 06:32 AM
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Bloomfield, IN
Joined Nov 2006
906 Posts
I used bamboo skewers on my dragon. They are not as stiff as CF and let the wings flap a small amount.
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Old May 25, 2012, 11:08 AM
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uk/england
Joined Jun 2008
341 Posts
Bit the bullet and bought some 5mm carbon tube

So now how do you fit the tube in! so as to have dihedral. The wing is flat depron and tube is flat! Cutting the tube will give a weak spot just were you need strength most?
Also how do you bend the tips as they are so wide?
Sorry for all the questions new to this high-tech building stuff.
Loving it though

Iain
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Old May 25, 2012, 12:45 PM
Dance the skies...
Tom Frank's Avatar
United States, MA, Walpole
Joined Dec 2003
17,186 Posts
Quote:
Originally Posted by The SKY MAN View Post
Bit the bullet and bought some 5mm carbon tube

So now how do you fit the tube in! so as to have dihedral. The wing is flat depron and tube is flat! Cutting the tube will give a weak spot just were you need strength most?
Also how do you bend the tips as they are so wide?
Sorry for all the questions new to this high-tech building stuff.
Loving it though

Iain
CF tube don't flex much as you said. With dihedral, the only way to deal with this is to make a trough for the tube that is deeper on the ends than in the middle, and maybe epoxy the tube in place while pressing down a little on the tube in the center as the epoxy sets to keep it below the surface. I opted to use CF tow (flat braid epoxied into very shallow trenches on opposite sides of the wing, forming kind of a "I-beam" concept.

I also made my tip "feathers" longer by reshaping them at the inner edge, and then bent them upward S L O W L Y with gentle deflection around a large tin with the desired curvature using a hair dryer to help the foam retian the curvature. But be careful... too much heat can melt the foam. The stock plans I used just showed the tip with a sharp polyhedral angle, not curved.
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Old May 25, 2012, 03:08 PM
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United States, CA, San Rafael
Joined Mar 2012
131 Posts
After two unsuccessful attempts at maidening the seagull I have concluded that the forward curves are messing me up. This thing just wants to nose dive and break my expensive folding props!

I'm not sure where the CG should be, but it balances nicely right about where the servos are. I think I'll build another one without the forward bend and with a more realistic dihedral joint downward at about half the length of the wings.

After all this though I'm not sure I ever want to mess with front-mounted motors/props! Pushers are so much safer and seem easier to balance....must be why so many wings are pushers. Not sure how anyone with 'normal' planes doesn't go through props on a regular basis!
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Old May 25, 2012, 07:09 PM
Dance the skies...
Tom Frank's Avatar
United States, MA, Walpole
Joined Dec 2003
17,186 Posts
Quote:
Originally Posted by Averan View Post
After two unsuccessful attempts at maidening the seagull I have concluded that the forward curves are messing me up. This thing just wants to nose dive and break my expensive folding props!

I'm not sure where the CG should be, but it balances nicely right about where the servos are. I think I'll build another one without the forward bend and with a more realistic dihedral joint downward at about half the length of the wings.

After all this though I'm not sure I ever want to mess with front-mounted motors/props! Pushers are so much safer and seem easier to balance....must be why so many wings are pushers. Not sure how anyone with 'normal' planes doesn't go through props on a regular basis!
You are likely quite nose heavy! Move the CG back about an inch and try again! The down thrust angle is also not needed with a flat plate wing...
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Last edited by Tom Frank; May 25, 2012 at 07:38 PM.
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Old May 26, 2012, 01:18 AM
What could possibly go wrong?
nickchud's Avatar
Market Harborough
Joined Apr 2006
3,615 Posts
Quote:
You are likely quite nose heavy! Move the CG back about an inch and try again! The down thrust angle is also not needed with a flat plate wing...
Don't give up! If it was easy everyone would do it.

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Old May 29, 2012, 04:58 PM
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United States, CA, San Rafael
Joined Mar 2012
131 Posts
$Tree Seagull v2

Thanks for the encouragement! This motor is hefty, probably too much for this size plane. I'm getting good glide tests now with a bigger battery....but there's not much room to move it further back. This is probably a good combo though as I'm planning to fly this sucker in natural slope soaring settings and blustery ocean winds that'll require a bit of weight to deal with!

WS = 40"
AUW = 14 oz.
2200KV Turnigy D2826/6
7x4 APC or 6x4
1000mAh 30-40C 2S or 3S
Detrum 40A ESC

I decided to go ahead and alter the design a bit on version 2.
  • Better fuselage.
  • More natural wing dihedral.
  • No downcurve on the leading edge of the wings.
  • Motor mounted further back (neck shortened and braced).
  • KFm4 - 50% on top, 35% below.
  • Increased the chord for more lift.
  • Isolated the ailevators to the outer half of the wings.

Will maiden soon!

PS - next one is going to be a turkey vulture based on the same design, but scaled up to 60" WS.
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Last edited by Averan; May 29, 2012 at 06:47 PM.
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Old May 30, 2012, 01:26 AM
Blue Falcon
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the Netherlands
Joined Jan 2007
696 Posts
RC Turkey Vulture Thermalling (3 min 11 sec)
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Old May 30, 2012, 10:40 AM
Registered User
United States, CA, San Rafael
Joined Mar 2012
131 Posts
nice to see it in flight! =) I hope mine comes out half as nice.
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Old May 30, 2012, 12:51 PM
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United States, CA, San Rafael
Joined Mar 2012
131 Posts
7x4 on 2S w/ 2200kv is too much for this seagull! couldn't control it at all, just rolled around wildly. going to try 5x5 or 6x4.
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Old May 30, 2012, 06:53 PM
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United States, CA, San Rafael
Joined Mar 2012
131 Posts
okay. maybe it's not torque roll. dangit. 5x5 didn't fly either and had the same issues with flipping/rolling over. i wish i could find a good thread to help me out....

starting to wonder if my fuselage could be causing some of the issue, apart from CG not being right. the lower half of the prop wash blasts into the fuse and is diverted out towards the sides. i haven't actually been able to get the thing to fly forward more than 10ft yet and it's on the ground so fast it's difficult to figure out what's wrong. even with no throttle this bird will roll over from a hand tossed glide just by thinking about it!

gotta rebuild the nose now before i can attempt another flight. =(
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Old May 30, 2012, 09:02 PM
Lee
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USA, UT, Orem
Joined Jul 2004
8,921 Posts
I have gotten snap rolls off sharp wingtips. Complex wing designs often have complex flight characteristics and are hard to balance.

I also found that these planes balance like flying wings not like ordinary aircraft. That means that your CG is going to be a lot farther forward that most people think when you are flying this kind of design.
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Old May 31, 2012, 06:15 AM
What could possibly go wrong?
nickchud's Avatar
Market Harborough
Joined Apr 2006
3,615 Posts
Would a bit more dihedral help?

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Old May 31, 2012, 08:04 AM
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INDEPENDENTLY POOR in OHIO
Joined Dec 2001
1,025 Posts
Try balancing at the lead edge of wing and set some reflex in wing by raising the elevaters about a 1/4 inch, then glide test over high grass. should show you which way to go!

Roger aka GIFLYRC
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Old May 31, 2012, 11:10 AM
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United States, CA, San Rafael
Joined Mar 2012
131 Posts
Thank you all for your input!

If I can repair the nose and motor mount successfully to fly again I'm going to try curving the wing tips upward.

All the flying wings I've seen that have a front-mounted motor seem to have all of the weight in front of the wing. I will definitely look for a CG further forward and see if that helps.

I don't quite understand why I would need more dihedral when I've seen completely flat-wing designs like the alula work just fine. Hopefully the wing tips will help.

Next time I build another one from scratch I'm going to design a breakaway nose section that is easier to repair!
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