Re: [RCSE] Initial CG on a scratch ship...

Thu, 20 Apr 2006 14:32:25 -0700

Title: Initial CG on a scratch ship...
That is a good start for the CG, but the other part of the equation is the horizontal stab. How big is the tail, how far from the wing is it it and what is the decalage? Here's something worthwhile reading: http://www.fatlion.com/sailplanes/decalage.html
 
Is this a scale ship??
 
 
Frank
 
 
 
----- Original Message -----
Sent: Thursday, April 20, 2006 12:20 PM
Subject: RE: [RCSE] Initial CG on a scratch ship...

You need to find the MAC or Mean Aerodynamic Chord, which is the average chord.  Assuming a straight leading edge and a tapered TE, if it’s a straight taper , measure the root, add the tip and divide by 2.  That is the average chord.  So, make a mark 8” back from the LE and that’s the average chord.  30% of  8 is 2.4, just like you calculated.  I’d start there. 

 

If the TE has more than one taper, you will need to take into that into account. 

 

George Voss

From: Douglas, Brent [mailto:[EMAIL PROTECTED]
Sent: Thursday, April 20, 2006 12:39 PM
To: [email protected]
Subject: [RCSE] Initial CG on a scratch ship...

 

Just trying to get a rough idea where to start here, what formula you might use to come up with a starting CG…. Picture a 200 inch wing, root chord about 11 inches, tip about 5, straight leading edge, tapering TE.

Modern airfoil, HQ 2.5, 12 - 10 percent thick.    My thought was to go mid span, take some percentage of the chord there, then mark the root that far back - example:  30% of 8" becomes 2.4 inches - mark the root at 2.4 inches from the leading edge. 

2 questions - how far off is that logic, how far off is 30%?     

I'm towing this ship for the first flight, so I'd like to be pretty close, erring to the nose heavy side.

Thanks!
Brent

 

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