CG for my big flying wing? - RC Groups
Apr 26, 2006, 06:38 AM
Registered User
Help!

CG for my big flying wing?

This is my project:

5300mm in wingspann
Center cord 400mm
Tip cord 350mm (symetric tapered)
Weight 8500g
Airfoil JWL097

I need help to estimate the position for CG before I do the test flight. I'm planning to just shoot it straight forward to check the CG and elevator as test flight before I use it on a big slope.
I have seen a german program to calculate CG but I'm not sure about all parameters to fill in. Can you help me some way?

More pictures:
Pictures
 Apr 26, 2006, 08:49 AM Git-R-Done Based on the dimensions you posted, I've calculated the CG to be @ 93.9800mm using %MAC of 25%. I used this calculator ... http://www.geistware.com/rcmodeling/cg_calc.htm#cg Hope this helps.... Hermitt P.S. I used ZERO sweep in the CG calculation. Last edited by Hermitt; Apr 26, 2006 at 08:59 AM.
 Apr 26, 2006, 01:50 PM Registered User Thank you Hermitt! I just wonder where did you get 25% from? Is that a standard relation or something special for JWL097? Regards Mats
Apr 26, 2006, 02:24 PM
Git-R-Done
Hi ssstam,
Actually it's printed on the Calculator web page.
Quote:
 Note: A 25% of MAC is generally accepted as a good starting point for the CG of a conventional tailed aircraft. The normal range most often falls between 25-30% of MAC
BTW, that's a very good looking Sloper you have.

Hermitt
 Apr 26, 2006, 04:24 PM Registered User I thought that flying wing wanted a CG at 15-20% of MAC? I'm asking because I am scratch building a sloper wing too using a PW51 foil. Thanks, EB
 Apr 26, 2006, 05:02 PM Will work for foam Based on your dimentions, i would start with your CG located at 83mm back from the leading edge at the root, then move it back gradually as you see fit. this will give you stability margin of 6%. a little overly stable, but good for first flights. the 93.98 yields a stability margin of about 3.25% which may be where you end up (most planks like low stability margins), but i wouldnt try it for a first flight or two.
 Apr 27, 2006, 03:58 AM Registered User Thank you! That help was what I was hoping for. I have looked at this model that uses the same profile: Bleed and come to the same position, 20%. Now I have the same number from two different sources. This is the info for Bleed and I hope "schwerpunkt:46mm" means centre of gravity and "flächentiefe: 230mm" means coord. name: bleed typ: hang/thermik spannweite: 1600mm schränkung: 0° schwerpunkt: 46mm vau-form: 5° flächentiefe: 230mm profil: jwl097 masse: 700g flächenbelastung: ab 20g/dm2 fläche: ps15/sapelli rumpf: gfk/cfk positiv rc: höhe +- 15mm /quer/ +- 20mm design: johannes w. leinauer 2004 Regards Mats Licke in Sweden
 Apr 27, 2006, 05:01 AM Registered User That is a freaking HUGE and cool looking wing!!! Please keep us posted as to the flying of this beast. Did you do a built thread on this plane? it would be neat to read about it. When you get it flying it would be awsome to see some video of it if you are able to take some? Thanks, Jim.
 Apr 27, 2006, 09:07 AM Registered User Thanks Jim. If you use the link in the first post in this thread you can see some detailed pictures of it, the text is in swedish but I think you can understand the design anyway. It's built from pink foam called Ecoprim, 2400x1200x4mm high quality plywood and paper attached with floor "dope" (I'm not sure what its called, water based transparent "paint" for wooden floors). All quite simple and affordable. I will finnish the nose and do some painting when I have seen that it can fly. It will be used on a big slope in the beginning of june, then there will be movies. With good or bad end...
Apr 27, 2006, 02:23 PM
Git-R-Done
Quote:
 Originally Posted by ssstam Thank you! That help was what I was hoping for. I have looked at this model that uses the same profile: Bleed and come to the same position, 20%. Now I have the same number from two different sources. This is the info for Bleed and I hope "schwerpunkt:46mm" means centre of gravity and "flächentiefe: 230mm" means coord. name: bleed typ: hang/thermik spannweite: 1600mm schränkung: 0° schwerpunkt: 46mm vau-form: 5° flächentiefe: 230mm profil: jwl097 masse: 700g flächenbelastung: ab 20g/dm2 fläche: ps15/sapelli rumpf: gfk/cfk positiv rc: höhe +- 15mm /quer/ +- 20mm design: johannes w. leinauer 2004 Regards Mats Licke in Sweden
Here's the page translation from http://babel.altavista.com/tr
Quote:
 bleed board only wings name: bleed type: slope/thermionics span: 1600mm cross-setting: 0° emphasis: 46mm vau form: 5° surface-deep: 230mm profile: jwl097 mass: 700g surface loading: starting from 20g/dm2 surface: ps15/sapelli trunk: GRP/CFK positively rc: height + - 15mm /quer/ + - 20mm Design: johannes w. more leinauer 2004
 Jun 12, 2006, 02:20 PM Registered User It can fly! But I did a late change in the project, I did build a fin and a rear wing. This thread started as a flying wing project but did not end up like that....
Jun 14, 2006, 05:41 AM
Registered User

18%!!!!

Use 18% for TAIL-LESS wing to start....
You can go as far forward as 15%, the most I've done without being uncontrollable is 22%.

18% is my magic number for all my wings.....good pitch response without being over/under sensitive.

If you want to play conservitive for intial flights start at 16%.

Good Luck!

BTW -BEAUTIFUL WING!!

Steve
(aka CrazyHerb)