Will this one fly? And where should CG be? - RC Groups
Mar 01, 2004, 04:40 PM
Tech freak

# Will this one fly? And where should CG be?

Hi

I`m wondering if my new little plane will fly.
Very bad design perhaps, but it`s cool I think.

Any suggestions?

Wheaz

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Mar 01, 2004, 04:41 PM
Tech freak
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 Mar 01, 2004, 04:59 PM Fly it like you stole it.. I'll be intested to see it fly! Is it EDF?
 Mar 01, 2004, 05:15 PM Tech freak No, if you look close you can see the little mega 16/7/12 in the nose.
Mar 01, 2004, 06:06 PM
Registered User
The basic rule for stable flight is the center of gravity must be in front of the center of lift.

Here is what I would do - To find the center of lift, go halfway down the span of one wing and make a dot. Then measure the length of the wing - called the cord. Find 1/4 of that length.... hold on, let me draw a picture. Its pretty bad, but it might make sense to you.

EDIT - CG should say CL, but you get the idea....

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Last edited by Abomination; Mar 01, 2004 at 07:29 PM.
 Mar 02, 2004, 02:16 AM Tech freak Thanks Abo, but lets say the cg is just half of an inch infront of the cl. will it be stable anyway? How do I know that the cl is at half the span and 1/4 of the cord? Is it always like that? Sounds strange.... Wheaz
 Mar 02, 2004, 10:55 AM Registered User when you lift the airplane from the point you found, it can tip a little forward. If it tips a lot in one direction you are in trouble - if it tips backwards - trouble. The center of lift changes during flight - its a function of several variables. Saying it is at the 1/4 chord is just an estimate. This point is where the 'resultant force' of the pressure on the wing lifting the aircraft is and this changes during flight. It is to say, if the pressure on the wing was replaced with one force at one point, it would be (approximately) where you found it. I encourage you to get a physics book or aerodynamics book and check it out. You should take any information you get on this site with a grain of salt. I have seen some stuff that is inaccurate. This is what I think is correct, I didnt look in a book or search the internet. Im an engineer - aerospace/mechanical - and I think this is correct - but I have been wrong before... let me do some research on the web. There might be something wierd that changes the approximate center of lift on a forward swept wing, but I doubt it, I am pretty confident I did it right. http://perso.wanadoo.fr/scherrer/mat...glish/mce.html this should tell you exactly where it is, I didnt play with the software, but it looks good. This is good reading on stability, CG, CL, etc... http://www.zenithair.com/kit-data/ht-90-4.html another good read http://www.modelaircraft.org/templates/ama/700_7.asp ... I am finding lots of good stuff. Do a google search on stability, center of lift, center of gravity etc... good luck. Last edited by Abomination; Mar 02, 2004 at 01:31 PM.
 Mar 02, 2004, 11:02 AM Formerly of mcba fame Don't know about flying, but it looks cool Reminds me strongly of a ship from that old game Terminal Velocity. Matthew
 Mar 02, 2004, 12:33 PM Fiberglass dont bounce??? Thats a sweet lookin plane, it looks FAST!!! Did you make it out of spair parts?? It looks like a high quality kit. You did a great job. I hope it flys as good as it looks. Good luck ...R...
 Mar 02, 2004, 03:52 PM Tech freak Thank`s Abo, I am more confident with the cg now. Although I am a bit sceptic to the negative wing angle. It is an experiment so IF it would crash I have learned something. The plane is ready for flight now, but today was WAY too windy. Wheaz
 Mar 03, 2004, 10:41 AM Registered User There is a program on this website that does a nice job of finding the CL and CG http://www.mh-aerotools.de/airfoils/index.htm
 Mar 03, 2004, 07:25 PM dingbaticuselmaximus Does the wing have anhedral( negative dihedral ) or is it just the forward sweep of the wings when viewed head on? Couldn't find anhedral in my Funk and Wagnalls so I'm not sure it is a real word. How about it Abomimation? Is it a real word? David
 Mar 03, 2004, 07:36 PM Tech freak Yes, the wing has "anhedral" Pretty much too... With wheels in the pods an 8 inch prop would go free from the ground. Right now the wheels are left out due to snow start. Able to use 7.5x4 folder now. Span is just over 40 inch. Wheaz
 Mar 03, 2004, 07:40 PM Fly it like you stole it.. Has it flown yet?
 Mar 03, 2004, 08:22 PM dingbaticuselmaximus Best of luck. It is one wicked looking plane!! -David

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