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Old Feb 18, 2013, 05:09 AM
I love my HammerHead wing...
sgrouts's Avatar
Joined Jun 2012
721 Posts
Help!
Help needed. How can I shift the weight forward! (Images included)

Hi, I made the pictured 63" (160cm) wing .
The wing is made from white foam, reinforced with 3 carbon tubes and a wooden one. And it is laminated with monokote top and bottom.
All of my fpv stuff is embedded inside the foam with prewired cables also embedded.
I made a huge effort to keep the weight down, so it came to aprox 1.800 gr including 2x 2.2003s +1x1.300 3s and full 5.8ghz fpv equipment.
My problem is that it is tail heavy according to online cg calcs.
It should balance between 20 and 25cm from the nose.
To get it to balance there, I should add a big weight in the nose, and I don't want to.
I thought as a solution to cut and shift the 35-48 motor forward, but I removed it and tried that on top of the wing surface and I don't see any important cg change.
Any ideas?
Am I missing something ?
I haven't maiden it yet. Is it possible with flight tests to see that it needs a different cg from the estimated? Does the kfm foil has something to do with that?
Any kind of help or advice would be highly appreciated.
Thank you in advance.

Sakis
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Old Feb 18, 2013, 07:41 AM
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brolley's Avatar
United States, PA, Center Valley
Joined Dec 2008
391 Posts
Hi Sakis-
It's important on these design of wings ( yours and mine seem similar) to keep weight forward as much as possible. Mine has a CG that is about 1/2 inch too far aft but I'm not quite finished building. ( hopefully I can save it without adding ballast)
The only thing I can think of is using bigger batts up front on yours, it would be better than adding useless ballast.

Wing looks great! Nice job!
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Old Feb 18, 2013, 01:25 PM
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Wilson, NC
Joined Aug 2009
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Based on my own flying wing, the motor mounting surface needs to move forward about 6 inches. The cutout for the prop will further help. Did you simulate moving it that far (with Prop and nuts)?
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Old Feb 18, 2013, 04:15 PM
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Joined Aug 2005
2,689 Posts
Have you considered a tractor powerplant installation like the Wing-E?



With that arrangement you can position the battery to set the CG. The tractor powerplant will also be much quieter than the pusher or especially a prop running in a slot. The additional area forward of the aerodynamic center may require compensation, but should be easy with an increase in area of the vertical stabs.

Good Luck!!!
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Old Feb 19, 2013, 01:30 AM
I love my HammerHead wing...
sgrouts's Avatar
Joined Jun 2012
721 Posts
Brolley, villapilote and DT56,
thank you for your answers.
I don't want to turn it to a tractor setup (yet)
I am thinking that I should test flight using ballast and after that if I see that there is no way to get it right I will either:
1. Tractor it.
2. Put a battery pod underneath it and forward.
3. Build a detachable battery nose compartment.

I keep my hopes up that if I maiden it nose heavy I will see exactly, through tests, where the CG should be.

Thank you again

Sakis
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Old Feb 19, 2013, 01:02 PM
I don't like your altitude
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Joined Sep 2011
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One good thing about option 2 is the further forward the weight the less needed
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Old Feb 19, 2013, 01:09 PM
I love my HammerHead wing...
sgrouts's Avatar
Joined Jun 2012
721 Posts
Quote:
Originally Posted by Stupot46 View Post
One good thing about option 2 is the further forward the weight the less needed
Yes it is.
I am also considering installing a second small tractor motor with a smaller prop on the nose and convert it to a pull- push dual motor wing.
That would be cool, right?

Sakis
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Old Feb 20, 2013, 08:01 AM
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Kazakhstan, West Kazakhstan Province, Aksay
Joined Sep 2012
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I'm new to flying wings. Actually in design stage.
Looking at this wing I have 3 options:
1. Cut slot at trail edge for motor with prop till carbon spar and move power system as far front as it will be possible in this way.
2. Mount GoPro or WingCamera on frontmost position. It's not a ballast and can help much.
3. Move ESC as far front as possible. It is heavy enough to move CG. I checked in CG calculator.

All 3 options could be applied together.
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Old Feb 21, 2013, 12:52 AM
I love my HammerHead wing...
sgrouts's Avatar
Joined Jun 2012
721 Posts
Quote:
Originally Posted by Scorpio9999 View Post
I'm new to flying wings. Actually in design stage.
Looking at this wing I have 3 options:
1. Cut slot at trail edge for motor with prop till carbon spar and move power system as far front as it will be possible in this way.
2. Mount GoPro or WingCamera on frontmost position. It's not a ballast and can help much.
3. Move ESC as far front as possible. It is heavy enough to move CG. I checked in CG calculator.

All 3 options could be applied together.
Thank you Scorpio.
I' ll try.

Sakis
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Old Feb 21, 2013, 10:17 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
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Another option is to use a shaft extension and rear bearing,mount the motor at the best position for balance,pusher prop as before.
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Old Feb 21, 2013, 01:24 PM
I love my HammerHead wing...
sgrouts's Avatar
Joined Jun 2012
721 Posts
Quote:
Originally Posted by Stupot46 View Post
Another option is to use a shaft extension and rear bearing,mount the motor at the best position for balance,pusher prop as before.
Ok, this is something new. Thank you for widening my options.
For now this is what I came up for first testings...
This way, I only add 100grams and get cg wherever I desire

Sakis
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Old Feb 21, 2013, 02:54 PM
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Joined Aug 2003
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You could have cut and formed a well in the back of the wing and moved the motor forward. I do this for the wimp version of my 36 inch wing.
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Old Feb 21, 2013, 03:11 PM
An Ordinary User
United States, VA, Fluvanna
Joined Jan 2011
1,229 Posts
The online calcs are good to get started with locating the CG but are certainly not the a CG bible. Just from looking at yours I would suggest drawing a faint line on the bottom of the wing from one servo to the other (from the forward corners) and trying that as the CG location. Your wing isn't swept so the CG looks like it should be closer to 1/2 the chord root or a little aft. It might turn out to be a little nose heavy at 1/2 the chord root (a little is ok).
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Old Feb 21, 2013, 04:09 PM
Everything is Upgradeable.
USA, FL, Gainesville
Joined Aug 2010
1,026 Posts
Get an L bracket and mount the motor on the inside. This will shift the motor a good 3"-4". Also consider the larger lipos like another guy suggested. Your wing is very flat in the back and can be notched in a lot. This way you bring the motor in and also cut some foam off. At 63" that is not a lot of lipo anyways. Extremely light wing at those sizes will make it unstable and wobbly.
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Old Feb 21, 2013, 04:27 PM
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Joined Nov 2007
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I gotta tell you, I've tried and tried to get my CG forward enough on wings w/o adding ballast. It's pretty difficult.

I too have gone to the extended nose design.

HATE adding balast. Want to counter balance the motor ( in the place it works best) with the lipo. The only way to do that is to push it out in front of the wing as you have done.

Could use a heavier battery, but fly with the lipo's I've got.

Could add ballast, but somehow it seems wrong to ADD weight after struggling to do a "light" build.

Moving the battery forward is a good approach!

Have also tried moving the motor forward with limited success. It seems to work BEST at the "end of the wing". Not sure why, but that's my observation. Pulling the motor forward into a "slot" just does not perform as well. Also noiser.

Good luck with your extended nose design!!


Steve
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