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Red wrote:Frank,Frank Colver wrote:Thanks for the suggestion Red.
If someone were to put this "one off" experimental glider into production, then the joiner tubes could be the way to go, as you suggest.
Frank
Weight at the wingtips can mean the difference between light handling, and a truck, in turns. I did nothing but reduce weight in my Albatross tips, and as I said, even the glider designer was shocked by the obvious difference it made. Everybody had assumed that the ASG-21 was hard to roll due to the sail design, but the real problem was a high tip weight (or mass). Inertia counts, out there.
I believe that a good tube bender (like a guy who builds car exhaust systems) can bend up pairs of joiner tubes for you, cheaper and faster than fabricating heavy tip plates. You can have him bend six or eight tubes with various angles (in pairs) for a quick switch of the tip geometries. With my ASG-21, I simply covered the gap between the trunk tube and sail with ripstop Nylon tip covers, similar to the originals but lightweight, and very easy to tailor to fit. Once you know what you really want for tip angles, you can tailor the sail main body to enclose the trunk tube with the sail, much like the old Rogallo sails enclosed their leading edges.
For the sail anchor at the rear end of the trunk tube, I used a simple loop of Purlon that passed around (over) the tube end and seated into a small plastic "hook" plate that was blind-riveted to the outside of the trunk tube. It weighed less, entirely, than just the original Rapide-Link on the original Albatross tip connection. Standard glider design criteria: Simplicate and add Lightness.
reluctantsparrow wrote:Red is correct on several items...
1. the lighter the weight near the tips, the lower the mass that must stop moving in one direction to reverse direction....less weight near tips always results in a quicker roll.
2. I bent 6061-T6 1 1/8" by .058 with a 3 1/2" radius die with poor results....switched to a die with a 4 1/2" radius and had beautiful results....so, yes, radius is key for bending alloys such as 6061 and even though bends "harden up" the bends are still plenty strong. I know at least one HG manufacture who bends all his own base tubes in this manner with good results....but, as RED Says....for full strength the tubes should be shipped to the bender on dry ice at zero....bent....then shipped back on dry ice to be heat treated to 6061-T6....that is the BEST way and the ONLY way if a sharper radius is the goal.
But Franks design (In the above drawing) is going to require the standard crossbar/L.E. connecting "plate" regardless and if that is also the point of truncation...well....might as well use the same plate....however...a pre-bent tube as RED suggests would allow more freedom in design and could be attached via PiP pin removed for folding.
P.S. the "dry ice" method is to prevent aging of the tubes when time is involved between steps in the process. Aluminum naturally hardens even over short periods of time....when I bend "fresh" 6061 using 4 1/2" radius I can bend up to 180 degrees with excellent results......When I tried to experiment with "old" tubing from my buddies hang glider "boneyard"....I experienced kinks and/or failure with relatively small, 45 degree bends. Aging of tubes makes a big difference.
Red wrote:Frank, et al . . .reluctantsparrow wrote:Aluminum naturally hardens even over short periods of time....when I bend "fresh" 6061 using 4 1/2" radius I can bend up to 180 degrees with excellent results......When I tried to experiment with "old" tubing from my buddies hang glider "boneyard"....I experienced kinks and/or failure with relatively small, 45 degree bends. Aging of tubes makes a big difference.
I do not know the exact details of this process, but aluminum can be "de-tempered" if needed (by precise heating and cooling). to allow for smooth bending, more than tempered aluminum would accept. In any case, I would use a bending radius that will not cause kinks or wrinkles in the joiner tubing
Once bent, the aluminum can be tempered again, back to the original T-6 standard. I believe it would be best to delay the anodizing process until last, when the joiner tubes are already bent and re-tempered. Local anodizing shops may have problems with very long pieces, but the short joiner tubes should not cost much to anodize locally.
A good college or university can probably fill in the exact details on the metallurgy processes, here. They are usually happy to supply such information for manufacturing, but it may be wise to avoid mentioning the finished product.
reluctantsparrow wrote:Red wrote:
I do not know the exact details of this process, but aluminum can be "de-tempered" if needed (by precise heating and cooling). to allow for smooth bending, more than tempered aluminum would accept.
My information on the "dry ice" process came from Reynolds Aluminum in Seattle Wa....or maybe Kaiser....I talked with both outfits when determining the best way to bend the FlyBar....they strongly discouraged any bending of 6061....but then I discovered at least one HG manufacture who bends 6061 on a regular basis without going through the "bend at zero, ship on dry ice" process"....then Scott Campbell, pro bender....taught me the "radius of the die used is the key....and even though it does harden the tube...it is still plenty strong enough......just so you guys know where I picked up all this mumbo jumbo from....anyway....all that and I still did not know AU can be "de-tempered" to allow for easier bending.....still learning...thanks Red.
Thinking back,,,, older gliders never had L.E./crossbar plates. Junction plates were introduced to facilitate folding of the floating cross bars without binding up the sail at that junction...especially for double surface gliders with deep L.E. sail pockets.
L.E./crossbar plates were only introduced (if I remember right) to provide a separated junction so sails can be folded without removing that one bolt system that we always used...and without "bunching" up the sail when folded.
..we always just rotated a solid crossbar then popped one bolt through that junction (which was sleeved for strength)...and it worked just fine.
Does there have to be a plate out there? Hmmmmm...????
Here is an idea.....go back to the One bolt system but use a slightly longer junction bolt and slightly taller saddles to provide more separation between the L.E. and the Cross bar end....wouldn't take much....just enough to not bunch up the L.E. sail pocket when folded....then we have eliminated the crossbar plate completely along with the two extra bolts required.
Then pre-bend a smaller diameter Truncation Tube to slide inside the L.E. and drop in a pip pin.....
That is a pretty light weight tip solution to consider Frank.
My tip joint is complicated by the necessity of folding the LE, the tip, and the cross spar. A plate will allow me to position the three pivot points so as to create the clearance for the three tubes to "nest" when folded. That's something I can easily change to optimise the foldability of the assembly. I'm not concerned about that as much as how I'm going to deal with the diag brace being in the same plane with the cross spar where it needs to get past. Of course there are ways to do this but one has to be careful not to create a "mickey Mouse" "rube Goldberg" type assembly here. Engineering usually supplies various choices in how to accomplish something. The real trick is to find the simplest solution. My current thoughts on this is to terminate the brace to fittings in each side of the cross spar, giving the effect of passing through the spar. I'm sure that other ideas will come up before I get to that point in the design (still way down the road). I've toyed with the idea of ending the cross spar at the LE where the cross brace connects there. That gives me concern about the bending load on the remaining LE section.
Jim, your idea about going back to the cross spar/LE single bolt and a nesting bent tip tube is also something to consider for reasons other than what you stated, as it also drops the cross spar below the plane of the diag brace. I may end up using a combination of different design ideas here. One thing I quickly discovered at the beach was that if nesting tubes have to be disconnected to pack or unpack the glider then the sand soon rears it's ugly head, by getting in the joint.
Now to the point: Please remember everyone, one reason for the design's short span is to lessen the effect of the spanwise weight. For every foot I bring the tips inward there is the corresponding reduction in the effect of the weight of the tip portion. The short span also makes the pilot's sideways weight shift more effective as a greater portion of the span. Another stated goal of the design is to reduce the sail cloth weight which will further reduce the spanwise weight since I'm trading span reduction for chord increase (keeping sail area about 300 sq ft). Then of course there is the goal of keeping the whole mess to under 40 lbs.
The other reason for the design's short span is for easier ground handling.
If successful, this glider will not be for getting from point A to distant point B it will be for getting from easy launch to easy landing with well damped pitch and quick roll ability along the way, traveling at a slow speed and low sink rate.
First step is started - building the flying model. Mike, at High Energy Sports, gave me some very light, 0 porosity, parachute cloth to use for my model's sail.
It's a blinding bright orange - I won't lose this glider in tall weeds or get it run over by a lifeguard truck at Dockweiler. 
Keep the comments coming folks,
Frank
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