How efficient are our tailplanes?

Most contest pilots trim their sailplanes to the most
rearward permissible position.

I have found that many sailplanes don't like the full aft CG position. My
ASH-25 handles best at about 75% of the allowable range and the LS-6 is about
80%, I'm told the Discus likes to be about 92%.
If you go too far aft with the CG, you will find yourself trimming forward,
when you drop the flaps and enter a thermal.
I use the tail tank to find my best CG position, dump a little until she feels
right and then after flight, dump the tail water into a bucket and weigh it.
That is the weight that I add (in lead) to my tail. Then when I fly with water
in the wings, the tail water only balances the added weight of the water in the
wings.
I restrict the tail dump line, so that it will dump proportionally (at the same
rate as the wings) and this allows me to dump a part of my water and still
maintain my ideal CG position.


JJ Sinclair

Jim Marske did a study of the Genesis and found that the elevator on the
tail is about 15% of the drag. you can see the article on our Marske Flying
Wings Site.
-mat

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Marske Flying Wings
http://www.continuo.com/marske

In article ,
says...

Please choose a center of gravity that is 30 to 35%

before the rearmost limit of the aircraft's specification.

This will grant an optimum in safety and performance.'

Several years ago, I was also told this by Waibel and Heide of
Schleicher Sailplanes. For the ASH 26 E I fly, Heide told me there is
no need for a tail tank, because adding water in the wings moves the
CG forward about the amount needed for a higher wing loading when you
are cruising faster. This assumes the CG was optimal (about 30-35%
forward of aft CG) when unballasted.
--
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directly

Eric Greenwell
Richland, WA (USA)