The Platz glider has always fascinated me. I built a free-flight model, using kite parts, and later tried using RC to steer it. I didn't do it right
I'm trying not to design an actual glider at this point. Rather, I just want to get a philosophical basis for a design. It's too easy to prematurely design something, and get stuck in it's box.
The List of Priorities: Obviously we should have safety as #1, but safety is made up of many things.
So #2, for now anyway, is convenience. While some will simply say "Paraglider", I personally want at least some framework, so my design is for what we call a hang glider. But please note that I wrote "at least some framework". Again, I'm trying to avoid getting stuck in a box. I don't know how much framework I'm gonna need, but since "convenience" dictates both lightweight and fast set-up time, it makes sense to me to keep looking over at that paraglider, and recognizing that it does a lot with a little. While it's true that they are made up of a lot pieces sewn or tied together, in the end they are essentially a one-piece glider.
No wingnuts, no pip-pins, no tangs, no etc. A lofty goal and likely not attainable for hang glider design, but definitely something to admire and respect.
So the most minimal parts count possible will be the goal to strive for. Every part costs money and has weight. So to reduce weight and costs.....
Way back in the late mid-seventies sometime I watched a guy unzip a glider bag, assemble a control frame in a few seconds, stand the kite on it's nose plate, and allow the LE's to drop into place. The battens were already inserted radially, and just a couple/few hardware connections later he was good to go. It probably could give a Pg a run for it's money in terms of set-up and fold-up time, although weight and size was definitely Hg all the way.
But the memory of watching that is a good one to have, and to keep reflecting on when I design my glider.
I'm doing my best to avoid deciding on a method of construction for now. Although good old aluminum tubing serves a manufacturer very well, I believe that because I am patient and not in a hurry, there are maybe better ways to build my glider. One construction method that intrigues me is that used by Steve Woods (RIP), a Cessna aeronautical engineer who designed a powered ultralight he named "Skypup".
The early powered Hg's, such as Quicksilver and Easy Riser, had just come on the scene, and Steve decided he could build a better UL. And he did. It was of cantilever construction, with the only cables being control cables. It reportedly had at least a 12:1 glide, and just eyeballing it convinces me that it could do at least that well.
Now, I'm not gonna build a non-powered Skypup, although if I was a flat-land tow-launched pilot with access to hangar space, I'd definitely give it some consideration. Get an engineer to help redesign the fuselage, to allow dispensing with the stink-pot noise-maker, and move the pilot's seat forward to balance it, and it would make for a decent little rigid wing.
As of several years ago, a Skypup builder said he completed the entire airframe for less than than $1K, in a couple/few months of relaxed building. I can dig that.
The Skypup is built using styrofoam and wood as the material. Of course, a guy with the $ and expertise could save some weight using carbon in place of wood. But ya know, I like working with wood. I know a guy who regularly flies a cute little Culver Cadet airplane, built entirely of wood, that can go 130 mph on 85 HP. The airplane was built in 1939 and is still plenty airworthy, although he babies her and no longer loops her. Slow rolls are still fun, he says.
I think the Skypup's construction method could be applied to a folding wing structure, with nose ribs and trailing ribs folding along the spar. Add some wing chord so the airfoil can be reflexed, and I'd be about halfway there. Shear ribs or webbing inside the "sail" would prevent unwanted ballooning and the loss of reflex, a problem that occurred with some early rigid wing Hg's.
At this point I should mention that I'm in favor of a planform that is basically straight, with no sweep back, and a central fin to provide yaw stability. One thing I'd like to get some qualified feedback on is the concept of a wing that is pitch-stable at any given point along the span. The desire being to control twist without having the need for expensive sail materials under high span-wise tension. Skypup has a main spar and a D-tube, but no rear spar. It uses a wing section that has very little pitching moment, and no ailerons. It is controlled using rudder and elevator. I would be content using weight-shift for pitch control, and if I can control roll by pivoting the wings at the root and even use weight-shift for that, I'd be happy. To be compact when folded, I don't want the D-tube, although our present method of using a Mylar insert would be Ok, if it allows the main spar to nestle up inside it when folded.
Just as the Skypup could be built inexpensively, I don't see why a decent Hg can't be built on a budget. Just gotta be careful, and keep a firm grip on the Handle of the Safety Thing.
It should be noted that Tyvek housewrap has been used to make sailboat sails. Seems to me that it could be used as the covering material, or "sail" if you prefer, for an ultralight glider. If an inexpensive and easily worked with material is used, so what if it's only good for a season or three.
Well, I just read what I've written so far, and it appears that I lied when I said I wasn't actually designing a glider. It seems I've laid out a basic scheme for a "Plank style" flying wing. But so far it's only a vague picture in my mind, with a bird-like planform, and a wheel or skid under the fin because it will be tail-heavy on the ground. I believe that a bird-type tail that hinges only upward might make for an easy to flare glider.
I think I'm about ready to abandon the fully prone body position. Maybe a semi-prone position like the Hortens used would be a good compromise. It would be really nice to be able to easily switch from seated/supine to semi'prone, depending on the view I'd like at the time.
A cup holder and a sandwich tray....what the heck, if I'm gonna dream I'll dream big. Howzabout a wind turbine powered microwave oven? Chicken-fried steak, mashed potatoes and gravy with green beans would be nice on a long flight....
So keep those cards and letters comin' folks. Maybe we can make a contribution. Won't hurt to try, so long as we keep a grip on that Handle....
Yours in Flight, Steve
by ARP » Wed Sep 09, 2015 12:39 pm 
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