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Building Tips and technical articles. => Building techniques => Topic started by: John KruziK on November 03, 2007, 06:08:07 PM
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How do you determine where c/g should be on an original design? john
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At or in front of the center of lift, which is the high point of the airfoil. NEVER behind; AT gives max. sensitivity--or even instability. As you move forward toward the LE, you gain more and more stability, until the plane is so stable (noseheavy) it won't do anything but fly level. A good starting place is halfway between the LE and the high point.
Correct, or dissenting opinions?
--Ray
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I recall (I think?) one of the gurus, perhaps Ted stating that a good starting place for the cg is at the percent of chord that equals the percent of tail area. In other words, if you have 25 percent tail area to wing area, then you could start the cg at 25 percent of the chord. At least I seem to recall this as a guideline, HOWEVER dont take my word for it without verification please,, n1
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If you have no idea, it's a good rule of thumb to have the CG in front of the high point of the wing, depending on design. I had high aspect ratio planes that had the CG very, very far aft and flew pretty well, but that's an exception. If you put it in front of the high point to start, you will probably have something that won't be so unstable that it's unflyable. Having a CG too far aft can be, uh, thrilling on a first flight.
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Thanks for the help John
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Here's a link that will allow you to figure where to place the CG for almost any wing planform.
http://adamone.rchomepage.com/index5.htm