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CG question on Phoenix Classic EP trainer

Old 09-21-2008, 08:36 AM
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MalcolmfromCanberra
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Join Date: Sep 2008
Location: Canberra, Australia
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Default CG question on Phoenix Classic EP trainer

Dunno if this is sold outside Australia, but it's a 40-sized ARTF trainer from Phoenix specifically designed for electric. (See http://www.modelengines.com.au/view...27/cat/BXB.html) For me it's not a trainer (I've got plenty of electric experience with park flyers) but a testbed for larger electrics.

Anyway, two reviews of it appeared in Australian magazines, Radio Control Model News Issue 86 (October-November 2007) and Airborne Number 218 (early this year). Both used the same powertrain combination I'm using, and both reported that the plane was tail-heavy out of the box.

The Airborne writer used a 3S 2500 mAh Lipo weighing 220g and found he had to add 250g of lead to get it to balance at the recommended balance point of 70mm behind the leading edge. Total weight to balance: 470g. Later in the article he flies it successfully with a 600g NiCad pack.

The RCMN writer used a 3S 4800 mAh LiPo (weight say 380g) and found that he had to add a little weight and a spinner to get it to balance.

Based on these (and given success I've had with 1100mAh A123s in park flyers) I made up a 5S pack of 2300 A123s, total weight c. 380g. Based on these two articles the model should still have been slightly tail-heavy.

Imagine my surprise when (a) I tried a 3S 2100 LiPo and found I only needed another 35g to balance (b) put in the A123 pack and found that it balanced at 60mm.

So, (1) anyone know if the design has been changed to radically lighten the rear fuselage (2) how bad would it be to fly with the cg at 60mm instead of the recommended 75-80 (3) is it possible I've stuffed up the cg measurement (I'm using a Great Planes cg meter, which I've used before)?

Has anyone else built this recently and if so how did it balance?

cheers,

Malcolm
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