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Old May 07, 2012, 11:17 AM
Fixed wing fanatic
neddis's Avatar
United States, OR, Hermiston
Joined Apr 2011
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How far is too far back for the CG?

I recently acquired a PA Extra MX. I am working with the CG to get it just right. I have been flying it pretty far back, which allows for some pretty cool walls, spins, and tumbles, but it also causes an issue because of having so much down trim that when I flip it inverted, it will almost do a loop if I don't give elevator input. I don't have the plane in front of me, but if I remember correctly the CG is at about 5" from the leading edge. How can I determine the correct location via flying characteristics? I know some of the hardcore 3D guys use a CG that is pretty far back, but do they just live with these kind of flight characteristics in order to have that instability when they fly? Thanks guys.
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Old May 07, 2012, 11:23 AM
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USA, FL, Largo
Joined Dec 2005
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Generally, start at the front of the range that the manufacturers recommends, and then work the battery back 1/4 at a time until you are happy with it. Remember that everyone likes something a littrle different.

Generally I like the plane to dive a little when I go inverted. I trim it at full throttle upright, and then roll it over. If it stays level or climbs, that's too tail heavy for me. I like them to drop at least a little, but then again, that's just me.

Personally I have found that once I get to nuetral or further back, flying any kind of precision is nearly impossible. Not only that, but even in 3D the plane becomes more squirrely than I like. Personally, I just don't like them too tail heavy.
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Old May 07, 2012, 10:27 PM
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Wattle Grove NSW Australia
Joined Nov 2006
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+1 on Docs comment for me.
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Old May 08, 2012, 01:14 AM
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732002's Avatar
United States, OR, Lake Oswego
Joined Dec 2003
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I took Scott Stoops advise in Mastering Radio Control Flight.

For precision pattern, upright I have the same amount of up elevator as
down elevator inverted.

3D, neutral upright and inverted. Like Doc said too far back and it just gets too twitchy.
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Old May 10, 2012, 03:01 PM
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neddis's Avatar
United States, OR, Hermiston
Joined Apr 2011
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Awesome. Thanks for the input guys. The Extra MX is my first REAL 3D plane so I am still trying to figure out the details in the setup stuff. I moved the CG forward a tad today and it flew better.
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