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Old Jun 13, 2001, 11:16 PM
Registered User
USA, WA, Bellevue
Joined Apr 2000
199 Posts
CG on flying wing

hello,
I just flew my scale Blohm& Voss 215 off the slope. On test glides the cg was to far forward so I kept moving it back. By the time
I was done flying I had the cg at 31% mac.(a pic of the bv215 can be seen in my
"documents" at http://y42.briefcase.yahoo.com/ untitled bv2
31% should be way to far back, any ideas?
bruce




[This message has been edited by bruce ryan (edited 06-14-2001).]

[This message has been edited by bruce ryan (edited 06-14-2001).]

[This message has been edited by bruce ryan (edited 06-14-2001).]
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Old Jun 14, 2001, 05:38 AM
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Joined Apr 2001
284 Posts
Perfomance is what counts. If that's where it feels good to you, keep it.
The link isn't working so I can't see it.
does it have extensive fins? That could contribute to the stability.
-fish

[This message has been edited by fisher (edited 06-14-2001).]
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Old Jun 14, 2001, 08:09 AM
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USA, WA, Bellevue
Joined Apr 2000
199 Posts
it took three tries but the pic should work now.
just find it strange to have the cg so far back. the airfoil is a MH 45
bruce
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Old Jun 14, 2001, 09:00 AM
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Vacaville, CA USA
Joined Nov 2000
355 Posts
I can't get the pictures to work...can you post specifics? Wingspan, airfoil cord root & tip, sweep angle, weight? How much twist (washout)? Do you have the elevons set to positive? By how much?

Bernie
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Old Jun 14, 2001, 06:03 PM
Registered User
USA, WA, Bellevue
Joined Apr 2000
199 Posts
Bernie,
try this and then click "my documents"

http://briefcase.yahoo.com/brucexryan
the ws is about 36 " not counting the tips
about 1 to 2 degrees washout(stabs follow tip incidence)
I will need to add some up to the stabs as the plane needed up trim.
maybe 30 degrees sweep.
bruce
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Old Jun 14, 2001, 07:44 PM
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Palmdale, CA
Joined Oct 2000
13,371 Posts
I think what you have is a "conventional" wing-tail layout, with a large gap at the horizontal root..
How are you figuring the c.g.?
.
It does look good...
.
Sparky Paul http://www.angelfire.com/indie/aerostuff
PJB's Seriously Aeronautical Stuff http://www.networkone.net/~pjburke/index.html
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Old Jun 15, 2001, 08:49 AM
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Vacaville, CA USA
Joined Nov 2000
355 Posts
Well...that's still not enough data.. but I'll give it a shot....let's assume you have a 36" wing with a root and tip cord of about 8" --- using a 25 degree sweep and the MH45 airfoil the CG would end up around 6" (give or take .1")back from the leading edge at the root (meaning: where the two wingpanels meet; not at the fuselage!)

At 30 degree sweep it's around 7" back...hope this helps

BTW: that's just an approximation...you would also have to consider those "add-on" triangles at the inner part of the wing...

Bernie
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Old Jun 15, 2001, 11:37 PM
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Canada
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Well IF you built it 'scale' and I believe you did ....the CG should be just barely behind the point where the rear of the canopy meets the fuse
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Old Jun 18, 2001, 09:46 AM
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Somewhere in England
Joined Apr 2001
207 Posts
There is a first class intro to swept and plank style flying wings at Martins site...
http://beadec1.ea.bs.dlr.de/Airfoils/flywing1.htm

Colin

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Old Jun 21, 2001, 07:43 AM
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Bloomington, MN
Joined May 2001
112 Posts
Those are some pretty birds you've got there! I love that EDF!

J^3
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