It is true that TD sailpalnes tend to be more stable than aerobats. That stability allows the glider to fly and to hunt for lift with minimal input from the pilot. Every time you move the sticks you create drag which saps energy from the plane. However if we get too stable the plane won't respond well to lift. The glider might fly right through a thermal and we may not see the effect of the thermal on the glider. So there is a midpoint we seek.

BALANCE AND SAILPLANES

There are many points of view on balancing sailplanes. I will share some common or personal views.

1) As stated above, once you have the feel of the plane, start to move the CG back. A more forward CG makes for a more stable plane, but one that will not be as responsive or sensitive to lift. Too far back and it will be had to handle and you will be constantly correcting. You want something in between. Most plans and most RTFs are set up a little nose heavy to make the planes stable, which is best for inital flights or beginners.

2) A forward CG, being a little nose heavy, forces you to trim in some up elevator to get the plane to fly level. This leads to a very self correcting behavior. If the plane goes into a dive, it will pull itself out, for example.

This will also cause the plane to pull up hard under power. While most e-gliders I have flown will have some tendancy to want to raise the nose under power, if the glider wants to go into a loop, you have a fair amount of up trim on that elevator and this might be due to being nose heavy. You can read this using the dive test.

Take the Radian high, then turn the motor off and be sure the prop folds.

Get it flying level, smooth and stable into the wind.

Now, put the Radian into a dive, maybe 45 degrees degrees.
As the glider picks up speed, any up or down trim in the elevator will be magnified by the higher speed.

If it is nose heavy, that up elevator trim will cause the plane to pull out of the dive quickly.

If the elevator is neutral, the plane will come out of the dive very slowly or will hold the dive till it hits the ground. DON'T LET IT HIT THE GROUND! I actually had someone watch it fly right into the ground. He was watching the dive and looking for the pull-out which never came.

If it is tail heavy, the plane will tuck, that is the dive will tend to steepen. Be sure to pull out before something bad happens!

When I tune my gliders, I shoot for a neutral dive test. From about 300 feet, the plane will hold a 45 degree dive or come out slow enough that I may have to pull it out or crash.


3) Wing incidence - the angle relationship between the the wing and the h-stab.

If you have stab/elevator type tail, as the Radian does, and you have to put in noticeable down trim (looking at at the stab/elevator relationship) to get any kind of neutral dive test, chances are your h-stab is not level to the wing. If the stab is up in the back, this gives you a constant up elevator effect. Planes that have fully flying stabs, where the whole surface moves, don't have this issue.


Some other resources.


Performance Tuning Gliders - This is outstanding!
http://forums.flyesl.com/topic.asp?TOPIC_ID=227

Gordy on Balancing
http://forums.flyesl.com/topic.asp?TOPIC_ID=255

Test Flight Procedures
http://forums.flyesl.com/topic.asp?TOPIC_ID=226