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Old Jul 06, 2005, 08:43 AM
Now in TN!
J Morgan's Avatar
Chapel Hill, TN USA
Joined Apr 2001
24,706 Posts
Help with CG on Mig-21 "Fishbed"?

Sorry this isn't EDF but looking for help on this delta planform and wasn't any experience in pushers for it. Trying to figure CG and was wondering what was a safe % of MAC ( MAC has already been determined)to start with this delta type wing?
BTW, it is 32" ws, Typhoon 15/10 on 3s-3100 and AUW is about 30 oz.
Should be pretty fast.

J
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Old Jul 06, 2005, 08:50 AM
Scale Aircraft Designer
philip noel's Avatar
Hertfordshire
Joined Apr 2005
597 Posts
could you send me the wing plan including the c/l of the aircraft

to mailto@philipnoel.co.uk

and i will sort it out for you

phil
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Old Jul 06, 2005, 09:30 AM
Now in TN!
J Morgan's Avatar
Chapel Hill, TN USA
Joined Apr 2001
24,706 Posts
Phil,
You've got mail!

J
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Old Jul 06, 2005, 02:04 PM
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Speed is Life's Avatar
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Quote:
Originally Posted by J Morgan
Sorry this isn't EDF but looking for help on this delta planform and wasn't any experience in pushers for it. Trying to figure CG and was wondering what was a safe % of MAC ( MAC has already been determined)to start with this delta type wing?
BTW, it is 32" ws, Typhoon 15/10 on 3s-3100 and AUW is about 30 oz.
Should be pretty fast.

J
These guys, www.goldenwestmodels.net, make a large DF/Turbine Mig-21. Maybe a call to them would give you a starting point for a safe CG.
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Old Jul 06, 2005, 05:24 PM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
5,614 Posts
J,
Although I haven't run any calculations, I think it's a safe bet that this bird will fly well with the CG at 20% MAC. That's where my F-15 Park Jet flew best, and while it doesn't have a true delta wing it's not that far off from it either. That may not be the overall best-handling CG for the Mig-21, but it should be close enough that the airplane will handle well for the first flight. You can then experiment to find the best CG location on subsequent flights.

In addition, I highly advocate flying this model as a chuck glider to verify the CG location and control throws. That's one of the beauties of these foam park jets--just remove the motor and power batteries, put in a small 110 mAh rx pack, and they make great RC chuck gliders! Nearly all of my park jets flew as gliders before they made powered flights. Heck, I could fly my F-18 over 100 ft as a glider, including big looping turns to bring the model back to me! That's the most fun way to test the CG. I just taped on quarters as necessary to experiment with the CG.

Steve
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Old Jul 06, 2005, 08:55 PM
Now in TN!
J Morgan's Avatar
Chapel Hill, TN USA
Joined Apr 2001
24,706 Posts
Thanks for all the help here. I think it is worked out now. CG should be @ 42% of root chord from LE. I appreciate all the help and will now slink back to the "pusher" forum.

J
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