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Old Sep 02, 2014, 04:51 PM
Proud member of LISF and ESL
LI, New York, USA
Joined Mar 2003
24,464 Posts
Lots of good information has come out. Thanks Stu L for putting up with our questions.

So, net net, the way I read your notes is that the up elevator trim is the symptom. This will also lead to porpoising, which you described. If that is the trim you have to put in order to get a smooth level glide then you are too nose heavy. The CG is the problem.

You may be set on the CG called for in the plans or manual, but that is only a starting point. What you will find is that most glider pilots will move that CG back in order to get the best glide.

Using my Radian e-glider as an example, initially I had it set up so that it was at the CG in the manual. I have since taped a quarter on the tail in order to move the CG back and achieve a MUCH better glide, staying up much better, thermaling much better. I have done exactly the same thing with my hi-start/winched gliders.

I could not tell you where the CG is on any of my gliders. I can tell you where it started and how I have adjusted it forward or back but could not tell you where it would be measured. When it flies nice, it is done.

Whether it is removing weight from the nose or adding weight to the tail, the net net is that I see the CG in the manual as a starting point. From there, through testing, I move the CG back till I get the best glide and I usually do that based on a series of hand throws. Then and only then do I do a launch. And once I have it in the sky I may move it back a little more or I might move it forward a little bit.

Another tool in the toolbox is the dive test.

The Dive Test - If you listen to pilots at the field you hear us talk about “the dive test”.
What does that mean? This may help. Be sure to scroll down the page to see the “response to lift” notes
http://www.tailwindgliders.com/files...20Position.pdf

Like the hand launch test, the dive test is just another way to "read" the balance and the trim of the elevator in order to optimize how the glider flies.

Why is this so complicated?

If you put a motor on the front and run it all the time then the motor can overcome some miss trim and some miss balance. But on a glider we don't fly with a motor and so we are trying to tune for the BEST flying balance and trim because we are more sensitive to out of balance or out of trim conditions.

Last resource:

Hi Performance Thermal Soaring - A fantastic video on how to set-up and trim your glider to get the best out of it.
http://www.radiocarbonart.com/hptsdd/ Download
http://www.radiocarbonart.com/produc...l-Soaring.html DVD

And let me recommend any and all Radio Carbon Art instructional videos. They are the best and worth more than what you pay. I have quite a library of my own.
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Last edited by aeajr; Sep 02, 2014 at 05:16 PM.
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Old Sep 02, 2014, 05:03 PM
Proud member of LISF and ESL
LI, New York, USA
Joined Mar 2003
24,464 Posts
Quote:
Originally Posted by target View Post
A fish weighing scale will get you in the ball park of where you need to be.
Good luck.
R,
Target
Because the hi-start came with the glider I don't see any need to test it. But if you wanted to, a fishing weigh scale or a luggage scale work equally well. Here is an example. They can be spring/dial types or they can be digital and they don't have to be super accurate. You are just trying to get a general feel. If your glider weighs 20 ounces you want a hi-start with a pull of at least 60 ounces when fully stretched (3X the resting length of the rubber) and 80 to 100 ounces would be better.

http://www.amazon.com/Portable-Digit...tal+fish+scale

Or this

http://www.walmart.com/ip/South-Bend...ingMethod=p13n
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Last edited by aeajr; Sep 02, 2014 at 05:17 PM.
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Old Oct 08, 2014, 11:39 AM
Registered User
United Kingdom, England, Keighley
Joined Nov 2012
294 Posts
Just thought I'd pop back to this thread and thank everyone for their help.
I've been flying on sites that weren't suitable for the histart recently, but got out with it Sunday morning.

Moving the CG backwards has certainly helped lots. The launch is better and the glide is dramatically improved.
I really appreciate your help guys!
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Old Oct 08, 2014, 09:35 PM
Rockdoctor
Laos, Vientiane Prefecture, Vientiane
Joined Jul 2011
78 Posts
A problem shared is a problem halved
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Old Oct 08, 2014, 11:49 PM
Detail Freak
target's Avatar
Harbor City, CA
Joined Oct 2003
21,680 Posts
Glad it worked out for you, and happy to have helped a little if I did.
R,
Target
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