by Phugoid » Mon Nov 22, 2010 4:13 pm
Don't move the peg back to get a longer motor in, the additional weight needed to balance the weight of the motor aft of the C of G will ruin things by increasing the dlift required and thus increaseing the drag
This is where it can get complicated if you let it. For long motors (these can be two or three times the prop to hook length) you have to braid the motor, braiding does a couple of things, firstly it puts tension into the motor and keeps the nose on, and because there is tension the winds don't "get lost" due to tensioning the motor initially as you pointed out. Secondly the motor never goes slack, and so the Cof G position doesn't shift during the flight so trim is not lost and the glide is not ruined. The braiding does reduce the wind capacity of the motor (I have read by around 10%) BUT you can pack more winds in, ie the longer the motor the more winds, the more winds the longer the flight
The compettion boys do all of this stuff to get tons of winds on, but I'm not into competition flying, I fly for fun and so I'm happy to get a 30 second flight, which means I keep things pretty simple, Thus I use relatively short single strand motors, not normally braided, if the are braided it's just enough to keep some tension to reduce C of G shift rather than anything else. OK you loose 50 winds or so to get the initial tension, but the extra motor length gives you another 200 or so.
To make all of this work you have to stretch wind the motor of course.
I hope all this makes sense, some of the above is first hand experience, other of it is what I have read, some more is what I've heard......