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Old Feb 02, 2013, 05:53 PM
Fueled by Arabica Beans
ChillPhatCat's Avatar
United States, NY, Syracuse
Joined Oct 2008
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Quote:
Originally Posted by colj00 View Post
general rule is 35% back from the leading edge of the wing. but because its a warbird, its more like 25% back.
25% is the general rule of thumb regardless of what plane (for traditional non-swept monoplanes). 35% is technically unstable, best to leave to only the most hardcore 3D machines.
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Old Feb 02, 2013, 07:19 PM
Trapped in California
foamflyer's Avatar
United States, CA, Arcadia
Joined Nov 2003
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"general rule is 35% back from the leading edge of the wing."

That is very hard to believe. Start at 25 percent.
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Old Feb 02, 2013, 07:51 PM
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United States, ID, Burley
Joined Mar 2012
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Quote:
Originally Posted by scirocco View Post
And just what's your source for that? I don't think I've ever seen as far back as 35% quoted as a rule of thumb guide - maybe 33% max, more typically 25-33%.

After detailed calculation, it may well end up further back than that, but to throw 35% out as a "general rule" is I'm afraid just BS.

If you want to learn something about cg, try reading this: http://www.theampeer.org/cg/cg.html

For the OP, if it is indeed the Herr AT-6, apparently the recommended cg is at the rear of the spar: http://www.rcgroups.com/forums/showp...5&postcount=70 & http://www.rcgroups.com/forums/showp...19&postcount=5
thanks for the link, never to old to learn ! May be to old to remember but not to learn
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Old Feb 02, 2013, 08:05 PM
darn you, kakka carrot cake.
derpron's Avatar
Australia, WA, Perth
Joined Aug 2012
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okay guys, stop hating :/

i usually fly 35% back though.
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Old Feb 02, 2013, 08:08 PM
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United States, NE, Kearney
Joined Dec 2011
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Quote:
Originally Posted by colj00 View Post
okay guys, stop hating :/

i usually fly 35% back though.
It's not about hating.
A tail heavy plane (balanced at 35%) might fly for a few moments.
Nose heavy might not fly well, but is manageable.

For those of us with decades of experience, we want to make sure noobs understand to start "nose heavy" and then slowly move the CG back, bit by bit.
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Old Feb 02, 2013, 08:31 PM
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Australia, ACT, Kambah
Joined Feb 2001
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Quote:
Originally Posted by colj00 View Post
okay guys, stop hating :/

i usually fly 35% back though.
When you stop posting poor advice based on what, 5 1/2 months experience (http://www.rcgroups.com/forums/showp...79&postcount=1) people will stop criticising those posts.

Your desire to contribute and help is admirable, but you're dealing with people's effort and money when you provide advice in these forums, and it needs to be backed up by sound knowledge and experience.

Fortunately one of the benefits of an open forum like this is that bad advice tends to quickly get moderated or corrected. Consider it part of your learning process.

Scirocco
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Old Feb 02, 2013, 11:35 PM
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Joined Aug 2007
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Quote:
Originally Posted by scirocco View Post
When you stop posting poor advice based on what, 5 1/2 months experience (http://www.rcgroups.com/forums/showp...79&postcount=1) people will stop criticising those posts.

Your desire to contribute and help is admirable, but you're dealing with people's effort and money when you provide advice in these forums, and it needs to be backed up by sound knowledge and experience.

Fortunately one of the benefits of an open forum like this is that bad advice tends to quickly get moderated or corrected. Consider it part of your learning process.

Scirocco
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Old Feb 03, 2013, 12:03 AM
222 km/hr Parkjet flyer
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Latvia, Ventspils pilsēta, Ventspils
Joined Jan 2010
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All normal wing / tail style models like this .. I balance at 30 - 33% back from L/E measured at root. The slight sweep-back makes this a safe CoG ... but still responsive.

I rarely have to move a CoG from that.

Nigel
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Old Feb 03, 2013, 12:07 AM
222 km/hr Parkjet flyer
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Quote:
Originally Posted by foamflyer View Post
"general rule is 35% back from the leading edge of the wing."

That is very hard to believe. Start at 25 percent.
For years all I ever heard as general rule was UP TO 1/3rd chord back from L/E.. at root.

Nigel
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Old Feb 03, 2013, 12:11 AM
222 km/hr Parkjet flyer
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Post deleted after back-checking ...
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Old Feb 03, 2013, 12:34 AM
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25% is a nice rule, easy to remember, and safe. It usually works well for a maiden and possibly is the best CG for that plane.
Saying 35% is ok too, but I have not gone much more than 30%, except for 3D planes IIRC.
The 25% rule is conservative, works well in most cases, and is easy to measure and remember. To say the starting point is 35%, well that is pretty bold, and would most likely make a plane more responsive or hard to handle than many people want.
I haven't tested this premise extensively, and am just pointing out the accepted starting CG.
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Last edited by eagle777; Feb 03, 2013 at 12:49 AM. Reason: Tweny five 4 life
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Old Feb 03, 2013, 07:40 AM
Fueled by Arabica Beans
ChillPhatCat's Avatar
United States, NY, Syracuse
Joined Oct 2008
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Quote:
Originally Posted by colj00 View Post
okay guys, stop hating :/

i usually fly 35% back though.
For what you have been flying this may be fine, but I suggest you don't try it with anything more scale or valuable. We're not hating, just trying to make sure people don't wreck a plane unnecessarily. 25% is always safe for a conventional aircraft, 35% is usually dangerous.
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Old Feb 03, 2013, 08:45 AM
ARFs make me BARF
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United States, MI, Roseville
Joined Dec 2000
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Ignore the root chord measurement. Calculate it properly!

http://adamone.rchomepage.com/cg_calc.htm

or an easier version: http://www.scaleaero.com/CG_Calculator.htm
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Old Feb 03, 2013, 10:27 AM
Co-heir with Christ
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United States, CA, San Juan Capistrano
Joined Feb 2013
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So, I'm running it through the calculator and every thing I understand except the static margin % that I have to enter.
Top of the page says 5%-15% for good stability...

So, I'm guessing I want 10% then.
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Old Feb 03, 2013, 10:30 AM
Fueled by Arabica Beans
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United States, NY, Syracuse
Joined Oct 2008
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Quote:
Originally Posted by Dcope17 View Post
So, I'm running it through the calculator and every thing I understand except the static margin % that I have to enter.
Top of the page says 5%-15% for good stability...

So, I'm guessing I want 10% then.
5% is pretty common in general aviation planes... higher for something that will experience a lot of different loads like a military cargo plane, but that's just my opinion. Anywhere in that range is fine really.
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