Boost Glider upscale question

I'm currently working on a 1.25 upscale of the Astron Nighthawk boost glider (I went 1.25 because that matched the widest balsa I could find, and I want
to keep the materials the same as the original).
THe question I have concerns the pylon between the glider and the booster. Am I correct in thinking that I should keep the pylon height the same as the original, rather than simply upscaling? I recall an Estes tech bulletin on the subject years back, and an analysis of why the height of the pylon is so critical.
Thanks for your thoughts!
Kevin O
NAR 13578 TRA 10569
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That is what I have almost always done. Increasing the distance of the thrust centerline above the wing will increase the moment (force times distance) that is generated when the motor is thrusting. This moment tries to push the nose down and should balance the lifting force that the glider generates at high speed during boost which tries to make the nose of the glider pitch upward.
-Fred Shecter NAR 20117 http://search.ebay.com/_W0QQfgtpZ1QQfrppZ25QQfsooZ1QQfsopZ1QQsassZshreadvector
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Hello Kevin,
Aside from Fred's thrust moment observation is a matter of flame resistance but that can be conquered with lightweight wood treatments (i.e., a simple layer of masking tape or tin foil works well).
FWIW, I've noticed optimally scaling gliders up & down not to be exactly linear... :-) Going 1.25x with an 18mm motor though puts you close enough to use a 24mm motor. With the Edmonds Deltie, going from 18mm to 24mm almost warrants about a 2.5x upscale perhaps? Making a wider balsa wing chord with a long butt joints & wood glue isn't that difficult.
A large Nighthawk would be nice...
Take care, Andy
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Andy,
I considered going to a 24mm motor mount, but the original flew on A5 and B4 motors, so I figured an 18mm mount with a C6 motor should do the trick, for now.
I built this kit as a kid, and remember having the devil's own time getting it to fly properly, but also loved the design. I figure if I can get this to fly, the next step will be scaling up even more. Then the 24mm mount will come into play. After that, maybe composite construction materials and 29mm :)
Kevin
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I'm doing something similar. Right now I'm 1.5x upscaling a Century Mach 10. Next week I'm going to try to up scale it 4.7x using a 7.5" dia tube as the main body and using remote control to fly it.
Doc
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Drake "Doc" Dameru
President, NEPRA
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On Fri, 07 Oct 2005 09:09:43 GMT, "Kevin OClassen"

You should be able to upscle the pylon along with everything else: yes, that increases the moment from the engine, but all the moments working against it are increased the same proportion by the upscaling. That being said, the smaller the moment from off-center thrust, the better--if you don't care about producing an exact upscale, put the engine just as close to the fuselage as you can manage without doing fire damage or increasing the odds of a Red Baron.
Scott Orr
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