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Old Jan 25, 2009, 06:24 PM
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Vethraxx's Avatar
Lynnwood, wa
Joined Oct 2007
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My Delta Foamy Troubleshooting

I have posted photos and a description of my foamy made of 6mm foamboard . It did not fly at all. It looks like any other home built delta foamy I have seen. My friend and I did it as a collaboration. I would like some constructive critiquing no matter how brutal Thanks. Here is the link

http://www.rcgroups.com/forums/member.php?u=177609

Thank you very much. Looking forward to see my creation fly even if I have to carve out a new one.
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Last edited by Vethraxx; Jan 25, 2009 at 10:21 PM.
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Old Jan 25, 2009, 06:50 PM
Starting to Rebuild
Wingnut31's Avatar
Fayetteville NC
Joined Jun 2006
1,028 Posts
It could be a tat nose heavy, But have you tried to hand launch it to see how it glides?
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Old Jan 25, 2009, 10:05 PM
Crash Master
Gene Bond's Avatar
Indianapolis, IN
Joined Sep 2001
16,632 Posts
Too much nose, too little tail

Quadruple the rear fins and/or reduce the hieght of the nose... The areas are way off for stability.
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Old Jan 25, 2009, 10:20 PM
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Vethraxx's Avatar
Lynnwood, wa
Joined Oct 2007
91 Posts
Thank you for your replies. I have blade in hand and will try for the Mk II.

It seemed to hand glide well just being thrown. Then again it only went about three feet.

Should the center of gravity be be more forward from where it is now (where the servos are located)?
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Old Jan 25, 2009, 11:35 PM
Crashing into the sky!
jackosmeister's Avatar
Auckland NZ
Joined Aug 2007
7,326 Posts
If anything it looks like it'll be very nose heavy, I would shift the COG rear ward till it balances roughly at where the the wing leading edge meets the fins, and as gene says the "fuse" is too big and the tips are too small. All measurements done by eyeometer
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Old Jan 26, 2009, 12:52 AM
I Love My Ember!
Arroyo Grande, CA
Joined Jun 2008
1,099 Posts
Your thrust vector is probably pointed a bit too far over the CG - does it possibly have the tendency to pitch forward? Try moving the battery above the wing, more in line with the motor axis.
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Old Jan 26, 2009, 05:59 AM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
Joined Jan 2000
7,920 Posts
Unless my eyes are deceiving me, it looks like your prop is on backwards. It should be facing the direction of flight. It addition to what others have said, because of you're elevon placement you have no air at all moving over the surfaces at launch. Try making the elevons in to meet at center span, or better yet, make them full span.

Azarr
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Old Jan 26, 2009, 07:04 AM
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Vethraxx's Avatar
Lynnwood, wa
Joined Oct 2007
91 Posts
Thanks for the pointers, yes it had a tendency to pitch forward. Also the prop is a pusher and airflow was confirmed. That was confirmed while we were building it and getting the legs for the three phase soldiered on.
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Old Jan 26, 2009, 08:40 AM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
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Old Jan 26, 2009, 09:17 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,397 Posts
Shouldn't there be a little reflex on the elevators, (both a little 'up'), they both appear from what I can see in the pictures to be flat.
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Old Jan 26, 2009, 11:11 AM
7000mw of raw power!
rich smith's Avatar
New Hampshire (not the old one)
Joined Dec 2006
5,987 Posts
You have the Cg in the wrong place. It should be 50% for a delta and yours is at 25% which is for PBF type. Your plane is TAIL heavy.

Prop diirection is same for pusher or tractor. Letters must be toward front.


Quote:
Originally Posted by Vethraxx
I have posted photos and a description of my foamy made of 6mm foamboard . It did not fly at all. It looks like any other home built delta foamy I have seen. My friend and I did it as a collaboration. I would like some constructive critiquing no matter how brutal Thanks. Here is the link

http://www.rcgroups.com/forums/member.php?u=177609

Thank you very much. Looking forward to see my creation fly even if I have to carve out a new one.
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Old Jan 26, 2009, 01:22 PM
Use whatcha got!
msmith's Avatar
Metairie, LA
Joined Sep 2000
2,982 Posts
Quote:
Originally Posted by Vethraxx
Thanks for the pointers, yes it had a tendency to pitch forward. Also the prop is a pusher and airflow was confirmed. That was confirmed while we were building it and getting the legs for the three phase soldiered on.

A backwards prop can still push air in the 'correct' direction (i.e. towards the back of the plane).

It just won't do it very well.

Make sure the numbers on the prop designating size and pitch are facing towards the front of the plane as others have mentioned...
I've actually 'successfully' flown a plane with a backwards prop. It didn't fly well, and didn't really 'gain' altitude, but I was able to make a circuit with the plane in that condition.

Not surprisingly though, after realizing my error, fixing the problem, and trying again, the plane flew just fine.

Check the prop again, and if nothing else, take some 'up close and personal' pictures of your prop from the front of the plane and post those so we can be sure everything is as it should be.
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Old Jan 26, 2009, 02:35 PM
Old age is not for sissies
Azarr's Avatar
Dayton Intl, Ohio, United States
Joined Jan 2000
7,920 Posts
Quote:
Originally Posted by rich smith
You have the Cg in the wrong place. It should be 50% for a delta and yours is at 25% which is for PBF type. Your plane is TAIL heavy.

Prop diirection is same for pusher or tractor. Letters must be toward front.
FWIW: Some of the plastic props from China and the infamous "Zagi" (acutally Gunther" props have the numbers on the rear. The convex (bulging out) surface should always face the direction of flight. It doesn't matter if the plane is a tractor or pusher.

A 50% CG would be extremely tail heavy, it should be at 18-25% of the MAC most of the Delta's I've flown are happy in the 20% range but I have gotten away with 25% on my mini Outlaw. From the looks of your planform I agree with Rich that you're probably tailheavy.

Here's a quick calculator for CG determination:

http://www.flybyphotography.com/Craz...culator/CG.htm

Again, even if your prop is on the correct way (I still don't think it is) because of the location of your elevons there is no movement of air over them until the plane would get up to speed which is why they should be totally ineffective at launch.

Azarr
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Last edited by Azarr; Jan 26, 2009 at 02:42 PM.
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Old Jan 26, 2009, 02:38 PM
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Vethraxx's Avatar
Lynnwood, wa
Joined Oct 2007
91 Posts
Interesting. I have always thought it was the print on the prop always faced away from the motor, not alway towards the front of the plane. That might explain a lot. Thanks for the tips. I appreciate them all.
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Old Jan 26, 2009, 02:51 PM
My plans are in my blog
Rusty-Gunn's Avatar
Kotzebue, Alaska
Joined May 2006
5,416 Posts
Quote:
Originally Posted by Vethraxx
Interesting. I have always thought it was the print on the prop always faced away from the motor, not alway towards the front of the plane. That might explain a lot. Thanks for the tips. I appreciate them all.
This would be true if your motor was up front, but since you have it "backwards", you have to assure it is in the proper direction. Its a simple mistake most have done at one time or another. I've done it once.
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