Flying wing CG calculator - Page 6 - RC Groups
 This thread is privately moderated by z80, who may elect to delete unwanted replies.
 Aug 22, 2011, 10:34 PM Registered User Pardon the stupid question: Are the control surfaces included in measurements?
 Aug 22, 2011, 10:59 PM Red Merle ALES VI Absolutely! Curtis Montana
 Aug 23, 2011, 10:05 PM Registered User So are you saying that the elevons would be considered part and parcel with the chord of the wing at the tip? Even though the elevons usually don't go full span? Isn't that going to cause the calculator to overstate the wing area? And isn't it going to cause the calculator to move the CG back too far?
Aug 23, 2011, 11:15 PM
Quote:
 Originally Posted by ombudsman So are you saying that the elevons would be considered part and parcel with the chord of the wing at the tip? Even though the elevons usually don't go full span? Isn't that going to cause the calculator to overstate the wing area? And isn't it going to cause the calculator to move the CG back too far?
This is just a simplistic geometry calculator. Since it only dose one trapezoid you can't accurately model the usual cut up trailing edge. Control surfaces are part of the wing and affect the aerodynamic center whether they are deflected or not. By leaving the elevons out of the stability calculation you have created a model that is slightly less stable than the real plane will be so, although leaving the elevons out of the calculation is technically wrong, the error that is introduced is conservative and therefor acceptable. Kinda

--Norm
Aug 23, 2011, 11:18 PM
Registered User
Quote:
 Originally Posted by nmasters This is just a simplistic geometry calculator. Since it only dose one trapezoid you can't accurately model the usual cut up trailing edge. Control surfaces are part of the wing and affect the aerodynamic center whether they are deflected or not. By leaving the elevons out of the stability calculation you have created a model that is slightly less stable than the real plane will be so, although leaving the elevons out of the calculation is technically wrong, the error that is introduced is conservative and therefor acceptable. Kinda --Norm
Thanks. I'm considerably out of my depth here.
Dave
Aug 23, 2011, 11:32 PM
Registered User
Quote:
 Originally Posted by ombudsman So are you saying that the elevons would be considered part and parcel with the chord of the wing at the tip? Even though the elevons usually don't go full span? Isn't that going to cause the calculator to overstate the wing area? And isn't it going to cause the calculator to move the CG back too far?
No. The elevons are part of the wing, and help generate lift. The fact that they change the camber locally to change the lift distribution left and right, or fore and aft, doesn't keep them from being part of the wing.
Sep 18, 2011, 03:24 PM
Luis Claudio - Rio - Brazil
That´s great! I was looking for this thread!

I am building a kind of Lee´s Assassin wing, with a different profile and now, I´m just waiting for the servos arrives from Hobbycity. The battery, a 3s 1.3 I already have, and my worries are about finding the correct CG.

My wing is 40" wing span and 9" = root

I´m using a Emax CF2812 with a 7x6 and 3S 1.3

Can I use this program, correct? Any Ideas?

Thank you all,
Luis

### Images

 Oct 10, 2011, 09:03 AM Prefectionist I'm in the process of building my first wing: 50" wingspan \$ store foam board with a 13" cord, 12" sweep & 7" tip: http://fwcg.3dzone.dk/?wing_span=50&...ow_mac_lines=0 I'm wonder how much reflex to put into the elevons to begin with. I know there should be some, but what's the rule of thumb here? Thanks,
Oct 10, 2011, 10:45 AM
The original Flying Pigs Sqd.
Quote:
 Originally Posted by creapyd I'm in the process of building my first wing: 50" wingspan \$ store foam board with a 13" cord, 12" sweep & 7" tip: http://fwcg.3dzone.dk/?wing_span=50&...ow_mac_lines=0 I'm wonder how much reflex to put into the elevons to begin with. I know there should be some, but what's the rule of thumb here? Thanks,
I usually use as starting point the bottom of the elevon in line with the bottom of the wing and then two clicks of trim up.
Oct 25, 2011, 07:20 PM
Registered User

# wing image disappear

Quote:
 Originally Posted by z80 I wrote a little CG calculator for flying wings. If you have a HTML 5 browser supporting the canvas object you will get a little image of the wing too. http://fwcg.3dzone.dk Bug reports and suggestions are very welcome.
When I was using ie7 I can see the wing image and it's working for me for the last 2 years, but now i'm using ie8 and the wing image is disappear, some help please.
 Oct 30, 2011, 02:39 PM Prefectionist Just a quick question, can this do COG for forward swept wings?
Nov 22, 2011, 10:40 PM
Registered User
Quote:
 Originally Posted by adamtlk I discovered, the hard way, that for good low speed handling and performance a rough finish is better than a smooth, glossy one! (...) So rather eluctantly, I ripped off the nice glossy cover, and lo-and -behold, I had my old wing again! Searching literature on wind tunnel tests at low Re Numbers, I discovered that this was in fact a well established fact for some airfoils tested with different surface roughnesses. But CG-calculator is a good starting point anyway.