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Old Dec 20, 2001, 01:41 AM
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How to get CG for a delta wing? (Mirage)


I just got an all foam Mirage from a swap meet. It had been originally been flown with a Cox .049. Of course that was the first thing to go. It will eventually get an MEC Turbo Ten Plus w/2.5-1 GB and 8" X 10" APC in the back with a 10-CP1700 battery pack. Watt/lb. should be in the high 140's and the wing loading 24-27 oz./sq. ft. Everything figures out in the successful range but I haven't got any idea how to get the CG. The guy I bought it from had it so long he didn't remember who made it or anything else. I do know it had 14 oz. of RX battery, Futaba FP-R6F RX, and two FP-S26 servos that got a new home in the trash. Anyone recognize this one?
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Old Dec 20, 2001, 03:48 AM
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Re: How to get CG for a delta wing? (Mirage)


Quote:
Originally posted by GregG
I haven't got any idea how to get the CG.
Take another pic from the top and make it as square as you can and I'll calculate the CG for you.

Dan
Old Dec 20, 2001, 09:32 AM
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Thanks for the offer Dan. I'll have to get my camera batteries charged up for this one. Would it help you to give some measurements? If so here they are:

W.S. 27.75"
Chord (tip) 1.625"
Chord (root) 16.625"
Flat across center section (area under fuse) 4"

I really would like to get a formula if at all possible. I thought I had it but can't find it on my PC. I see there are lots of flying wings in the Foamy Contest. I would have posted this in "Foamies" but thought it was more appropriate here. Thanks again!

Greg Gallegos
Old Dec 20, 2001, 10:08 AM
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Graphical reconstruction of CG at www.pibros.de
Old Dec 20, 2001, 10:27 AM
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Hey, Greg, where'd you get the F-4 hanging on the right of the pic? Is it foam?
Old Dec 20, 2001, 05:04 PM
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Neik and Paul, thanks for the help! Steve, that is one of 4 F-4's I've got. It is a slope kit made in England by <a href=http://www.metcalfehmm.freeserve.co.uk/phantom.htm target=blank>Howard Metcalf Models</a>. I modified it with home made ducting and a Kress RK-709 spun up by a piped .12 glow. Weighs 53 oz. AUW. It never had the umph to take off. Maybe a newer EDF unit would make it work now. I've since built my own F-4 mold a bit larger to take twin EDF units.
Old Dec 21, 2001, 09:49 AM
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I read somewhere that a tailless delta CG should be at 17% MAC.

Is this correct?


Steve
Old Dec 21, 2001, 02:52 PM
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The c.g. for a delta depends a lot on the airfoil.
Symmetrical airfoils can fly at 25%, but cambered with reflex generally fly at 15% or thereabouts..
Depends on the amount of activity one is happy with mostly, where the c.g. "should" be.. aft is more sensitive than forward.
Old Dec 22, 2001, 09:25 PM
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i had one of those kyosho mirage foamies a long time ago, thought is was marked on the foam, if not right at the wheel well stickers on the top looks close. it was a decent flyer with a black widow, once it conked out it was time to dive in for landing, fast like. traded my old one to bruff or robert, one of the 2. mine had landing gear with plenty of rubber marks on the underside from the mains being plunked down.
Last edited by wiley; Dec 22, 2001 at 09:29 PM.
Old Dec 22, 2001, 10:31 PM
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Hi,

I've messed with some sling launched delta gliders and the 25% ahead of cg and 75% behind worked on them.

For a larger powered plane, make a scale 1/4 size glider and get it flying right. Then measure where the cg is and balance the big one in the same place. Works every time.

As always, more forward is safer. Too far aft gives the "falling leaf" syndrome.

Amusing in a little glider. Not amusing in plane with time $ and love it in.

Dave
Last edited by DaveW; Dec 22, 2001 at 10:34 PM.
Old Dec 23, 2001, 12:17 AM
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Quote:
Originally posted by wiley
i had one of those kyosho mirage foamies a long time ago, thought is was marked on the foam, if not right at the wheel well stickers on the top looks close. it was a decent flyer with a black widow, once it conked out it was time to dive in for landing, fast like. traded my old one to bruff or robert, one of the 2. mine had landing gear with plenty of rubber marks on the underside from the mains being plunked down.
Wiley, it sounds like this is the model I have. When did Kyosho make it? There is no CG mark on the foam but it did have wheels and the little marks just behind them just as you describe. I was thinking about installing a small set of retracts. With 400 watts on tap that shouldn't be a problem hauling the weight. I'm going to balance the wing and slope fly it without the fuse to check things out. Once I get it where it looks good I'll add the fuse with landing gear, motor and battery. I wish it were a bit larger because a 400 watt EDF won't have enough intake area to make it go as it is. With the pusher prop it ought to haul!
Old Dec 23, 2001, 01:29 AM
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yes, it's a kyosho, sent you a mail.


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