I'm not sure why Steve chose Kevlar for his spar either. Jim Marske sells a composite design manual that I highly recommend
www.marskeaircraft.com/workshops.html
In it he tells you how to calculate loads, select rods sizes, gives compression and tension strengths of different materials, etc. Great manual. If you are gong to experiment with different materials you will be glad you bought it. My spar is carbon rod caps sandwiched between two layers of 7725 Fiberglass. His book shows that a single layer of 7725 will handle the spar load so I should have a 100% safety factor. And fiberglass is cheap.
Steve does fly with his winglets now. He had someone design them for him and he is convinced they help his performance. There is a picture in the photo section of his glider with the winglets.
If you compare the tips in the uncovered video to the tips on the drawings, you can see he added about 6 inches on each side past the last ribs at the tip to enable him to fair in the flapperon balances. Hard to say what that individual modification did. He says his instruments show he is getting under 100 fpm sink rate. Pretty amazing.
From: Phil <
This email address is being protected from spambots. You need JavaScript enabled to view it.>
To:
This email address is being protected from spambots. You need JavaScript enabled to view it.
Sent: Fri, April 29, 2011 5:45:32 PM
Subject: [Carbondragonbuildersandpilots] Magic Dragon Uncovered video
Watching Steve Arndt's Magic Dragon Uncovered video again, I'm curious as to why he decided to use Kevlar and fibre glass on the main wing spar and trailing edge spar rather than just carbon fibre on its own. My understanding is that Kevlar is not as strong in compression/tension as carbon fibre. I can understand his choice of Kevlar in covering the pilot pod as it is less likely to allow sharp objects through the fuselage in the event of a sub-optimal landing. Any thoughts?
I also see from the video that he also provided for the addition of winglets to control the wing tip vortices, though there is no further mention of them in this or the other video of the finished glider. Does anyone know if Steve actually flew with them and whether or not they were successful... or just a nice idea!? Are there any photos or design specs for the tips floating around?
Steve also mentions that his wings are around a foot longer than the original design spec. "about 5-6 inches on each wing tip" - any ideas as to his reason for this, and what effect did it have on the glider's performance and/or behaviour?
Phil.
