FORWARD SWEPT WING, WHERE IS THE C.G.
10-08-2007, 08:31 PM
#1
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FORWARD SWEPT WING, WHERE IS THE C.G.
I have a project that I am doing and I need to know the correct C.G.!
My wing is exactly like the Bobcat .50 (nitroplanes.com) except in reverse.
If I take that wing shape and size and fly it with the sweep forward where would the C. G. be?
Teach me something I'm all ears.
Wing deminsions @ 50" span, 6" at the tips, 24" at the root with @ 45 degree's of sweep at the leading edge which would be my trailing edge when I reverse it.
Thanks
SJ
My wing is exactly like the Bobcat .50 (nitroplanes.com) except in reverse.
If I take that wing shape and size and fly it with the sweep forward where would the C. G. be?
Teach me something I'm all ears.
Wing deminsions @ 50" span, 6" at the tips, 24" at the root with @ 45 degree's of sweep at the leading edge which would be my trailing edge when I reverse it.
Thanks
SJ
10-08-2007, 09:52 PM
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RE: FORWARD SWEPT WING, WHERE IS THE C.G.
Go to http://adamone.rchomepage.com/cg_calc.htm and put in the numbers for your wing. If there is NO stabilizer, enter ZEROS.
My quick swag (about the sweep distance of the reversed wing) says the CG is 10 inches from the LE tip at the root.
My quick swag (about the sweep distance of the reversed wing) says the CG is 10 inches from the LE tip at the root.
10-09-2007, 03:31 AM
#3
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RE: FORWARD SWEPT WING, WHERE IS THE C.G.
Or if the link BadDaddy listed is busy, you can go to:
http://www.geistware.com/rcmodeling/cg_super_calc.htm
Darned if the two don't look like they were done by the same programmer. I was amazed to see the 1st site linked in this thread because I'm familiar with the 2nd one. They both have basically the same planform diagram, input setup and even pretty much the same instructions. I wonder what the story is. You don't usually see such similarity unless the two applications came from the same guy or one was pirated. Interesting mystery.
http://www.geistware.com/rcmodeling/cg_super_calc.htm
Darned if the two don't look like they were done by the same programmer. I was amazed to see the 1st site linked in this thread because I'm familiar with the 2nd one. They both have basically the same planform diagram, input setup and even pretty much the same instructions. I wonder what the story is. You don't usually see such similarity unless the two applications came from the same guy or one was pirated. Interesting mystery.
10-09-2007, 05:22 AM
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RE: FORWARD SWEPT WING, WHERE IS THE C.G.
SPEED JUNKIE,
I used that link & found it to be very helpful in a FSW design I did a few months ago.
A word of caution… for a unproven/new design use a larger static margin (this will guarantee you fly again another day)
It was recommended to me by a gentleman to use 33% static & to move back to the sweet spot.
I had very good luck with that
After several flights & moving the battery back (electric) the sweet spot was very close to the 20% calculated static calculation.
Your skill level & comfort level will be the ultimate determining factor of your static CG
Enjoy,
Dave
I used that link & found it to be very helpful in a FSW design I did a few months ago.
A word of caution… for a unproven/new design use a larger static margin (this will guarantee you fly again another day)
It was recommended to me by a gentleman to use 33% static & to move back to the sweet spot.
I had very good luck with that
After several flights & moving the battery back (electric) the sweet spot was very close to the 20% calculated static calculation.
Your skill level & comfort level will be the ultimate determining factor of your static CG
Enjoy,
Dave
10-09-2007, 07:56 AM
#5
Senior Member
RE: FORWARD SWEPT WING, WHERE IS THE C.G.
And to further increase your comfort level, whenever you start with the CG forward bias your elevator throws over the normal and when moving the CG aft expect the elevator throw to have more effect than before.
Forward CG makes the elevator less effective. Rear makes it more. Modelers often do nothing to to match elevator throw with CG location or moves and often wind up with poor elevator rigging. And the suggested location with the suggested throw usually provides a "safe feel", yet the same throw with a rear CG can not only be hard to fly with an overly sensitive elevator, but for some modelers unsafe. Even when the CG is safely located for pitch stability.
Forward CG makes the elevator less effective. Rear makes it more. Modelers often do nothing to to match elevator throw with CG location or moves and often wind up with poor elevator rigging. And the suggested location with the suggested throw usually provides a "safe feel", yet the same throw with a rear CG can not only be hard to fly with an overly sensitive elevator, but for some modelers unsafe. Even when the CG is safely located for pitch stability.
