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Old Jan 19, 2015, 10:57 PM
gotswrv's Avatar
United States, KS, Edgerton
Joined Aug 2007
81 Posts
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Synergy CG

I started working on a ~35" Synergy foamy this week. Wondering how to calculate CG. The current CG is on the short wing spar (I placed the red tube on the wing at this point)
Tossed it across the living room a couple times, it seems ok. Looking for a better guess than this test.

Not sure how the rear wing/ horizontal stab figures into the equation.

Any help?
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Old Jan 19, 2015, 11:08 PM
Hot glue held together by foam
United States, WA, Vancouver
Joined Aug 2010
3,165 Posts
Quote:
Originally Posted by gotswrv View Post
I started working on a ~35" Synergy foamy this week. Wondering how to calculate CG. The current CG is on the short wing spar (I placed the red tube on the wing at this point)
Tossed it across the living room a couple times, it seems ok. Looking for a better guess than this test.

Not sure how the rear wing/ horizontal stab figures into the equation.

Any help?
For a new airframe ( that I haven't made before ) , a glide test is good enough for me to get a CG starting point . Maybe adjust it to be a LITTLE nose heavy . Then when I go to fly the maiden , I adjust the CG as needed for optimal flight .
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Old Today, 11:50 AM
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Poporbit's Avatar
United States, CA, Aptos
Joined Sep 2012
214 Posts
I've tried folded wing designs in the past. Mine were easy to get stable glide set up just as you have done. However, once roll input was given the craft would diverge and could not be recovered without serious altitude loss. Never did identify why. Your experience will be interesting to follow.
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Old Today, 12:13 PM
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dz1sfb's Avatar
Attica, MI
Joined Dec 2006
10,851 Posts
CG is usually at 25-33% if wing area from the front of the wing. Given this model is somewhere between a flying wing and a conventional aircraft, I'd start at 29%.

That simply means that 29% of the wing area is ahead of the balance point. Measure the chord of the wing at half the distance between centerline to wingtip. At this half way point chord go 29% of the chord parallel to the centerline and that should be your balance point or at least get you very close to perform a test glide. Fine tune it from there.

Ken
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Old Today, 01:20 PM
gotswrv's Avatar
United States, KS, Edgerton
Joined Aug 2007
81 Posts
So the rear "wing" area should be ignored for CG calcs then. This falls in line with the glide test results.

I've decided to redo a couple parts to allow for less wattage. It was designed around a ~600vwatt motor. Think I should start with closer to 200 watt. 13oz on 600w seems unreasonable for epp. I've also worked in some bracing to help stiffen the wing structure.
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