Lumenier RB2205C-12 2400KV SKITZO Ceramic Bearing Motor
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Old Nov 04, 2013, 10:14 AM
Fly2High is offline
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Chuck 'Em and Chase 'Em
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Discussion

Determine Cg distance - how do you measure so accurately and with what?


Guys,


Tools are everything. I have read plenty of guys reporting Cg locations down to the millimeter or less.

What are you using to be able to determine the Cg so accurately?

Photos and/or links for what you are using to determine location would be appreciated if available but not required.

Are you using a tool or determining it mathematically or what?

thanks

Frank
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Old Nov 04, 2013, 10:34 AM
ThomasLee is online now
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Honestly, I just use my finger(nails). I can get it accurate to about 0.5mm, but really, I can't feel any difference in flight with CG differences of less than 1mm (heck, maybe even 1.5mm)!!
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Old Nov 04, 2013, 02:47 PM
BavarianCharles is offline
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Quote:
Originally Posted by Fly2High View Post
What are you using to be able to determine the Cg so accurately?
Works really well ...

http://www.mountainmodels.com/produc...799b765ea89712

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Old Nov 04, 2013, 02:57 PM
GoFaster is offline
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Multiplex CG Machine - if you can find one
Old Nov 04, 2013, 03:10 PM
jcats is online now
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Quote:
Originally Posted by ThomasLee View Post
Honestly, I just use my finger(nails). I can get it accurate to about 0.5mm, but really, I can't feel any difference in flight with CG differences of less than 1mm (heck, maybe even 1.5mm)!!
Same here...

I just put a couple of peices of tape (Approx 5mm wide) on each wing where I want the CG range. And I just CG it with my fingers. For my Stobels, I usually range them at 70 to 75 mm. I like to fly a little nose heavy so I just CG the plane in front of the tapes...
Yeah, more power to yah if you can feel/see what 1mm makes.
Old Nov 04, 2013, 03:51 PM
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Multiplex CG machine:

http://www.sussex-model-centre.co.uk...xd.asp?id=5319

http://www.wheelspinmodels.co.uk/i/194340/

http://www.rc-toy.de/lshop,showdetai...693054,5,,.htm

Or a less costly wooden version:

https://www.rcgroups.com/forums/show...3#post26539240

Or the cheapest, possibly most accurate version requires string, some bits of wood, and a bubble line level:

http://iflyrc.hypermart.net/CG1.htm

Kevin
Old Nov 04, 2013, 04:01 PM
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Quote:
Originally Posted by BavarianCharles View Post
^ I second this one. It's a great little tool.
Old Nov 04, 2013, 04:09 PM
simonmunro is offline
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A large pair of scissors. They come with handles and everything.
Old Nov 04, 2013, 04:37 PM
G_T is offline
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Upside down on the wing upper surface. Anything pointed.

Gerald
Old Nov 04, 2013, 05:12 PM
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Peter Madsen
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I also use my fingers. But only measures cg before the maiden.

Am I the only one that don't know the precise cg of my planes? I set it accordingly to the manual the first time and then adjust it from there, but must admit that I don't measure it after I have found the spot I like.
Old Nov 04, 2013, 06:32 PM
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let's FLY!
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2 pencils stuck in a block of styrofoam.

Like pbm77, I don't know what my final CG is. I mark a line at the theoretical CG, balance it, then adjust from there to my liking, but never go back and measure where it ends up. It usually ends up slightly further aft than what SailplaneCalc predicts.
Old Nov 04, 2013, 06:36 PM
G_T is offline
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I just TLAR, take it out, and fly it. I adjust for conditions anyway. I don't care what it measures but how it flies.

When I get to fly that is...

Gerald
Old Nov 04, 2013, 06:45 PM
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Gerald: why upside down?
Old Nov 04, 2013, 07:11 PM
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Unless it is a low wing, it will sort of balance on one point that way, rather than having to have one on each wing.

Gerald
Old Nov 04, 2013, 07:36 PM
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Great Planes CG Machine


The attached picture shows my Great Planes CG Machine. The URL with a better picture, write-up and a review is:

http://www.greatplanes.com/accys/gpmr2400.html

The plastic rulers are graduated in both inches and millimeters. I'm much better on setting the C of G with this gadget than I ever was without it. The accurate measurement lets you keep track of changes.

Richard S


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