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Technical Publication #27

The Folding, “Flying Wing,” Boost Glider

P/N 36028

©2004 Apogee Components, Inc.All Rights Reserved

An internally carried boost glider, which can reach high altitudes, offers potential for increadible glide times, and high reliability

numbers on the drawings to help explain how the glider is constructed.

As just mentioned, the wings themselves (#12 & #14) are made out of foam. I modi-fi ed the planform, but just slightly, and a template is included later in this article. You will notice on the template, the location of the score lines for the elevons. The scoring of the foam is done on the top surface of each wing half. I found it easiest to create the score line by using the edge of a metal ruler; which is layed across the score line, and simply pressed into the foam to create these trim devices. If you read my article on fl ying wings in the November 1993 issue of the JISS, youʼll know why it is necessary to refl ex the wings at the tips to get the wing to fl y stable.

There are two score lines, the one nearest

By Tim Van Milligan

I came across an invention last year that I think might yield increased performance in S4B (B boost glide). The invention was pat-ented by Steven K. Corbin of Springfi eld, Missouri (USA patent No. 4,836,817; June 6, 1989). The invention is a rubber band launched folding “fl ying-wing” glider.

The traditional boost glider uses a con-ventional confi guration airplane, where the rocket engine is mounted to the front of the glider and pulls the glider into the air. The altitude reached by the glider is then limited by several factors. The drag of the model is the most important, and is hard to minimize because of the wings generate a lot of induced drag, and they present a large area to the airstream (profi le drag). Then there is also the uncertainty of whether or not the glider will boost perfectly straight; and this is compounded by the will of the fl yer who is trying to aim the model into an approaching thermal.

I think that the folding “fl ying wing” glider can solve a lot of problems and maybe even change the face of the boost glider event. The beauty of this invention is that it folds into a long slender package; just perfect to be inserted inside a large diameter body tube. With this one fact, the glider does not attribute any boost drag. Only the carrier rocket does, plus the rocket can be aimed and launched like a traditional model rocket.

It will look strange for a person show-ing up at the check-in table with a typical model rocket, and not a glider with a pod attached to it. But now on a “B” engine, it should be possible to get a boost nearing 400 meters (1312 feet). Even if the glider had a terrible glide ratio, and fell at 5 feet per second, it would still take 4-1/2 minutes to reach the ground. I could live with that; but, this invention gets even better!

Iʼve built a couple of these gliders, and my very fi rst one weighed in at a mere 3.4 grams (fl ight weight) I havenʼt even tried to take some weight out yet. To get to the F.A.I. boost weight of 29 grams, you might even have to add weight to the booster. I think that even in a tiny thermal, you could get any duration that you wanted. If this sounds good to you, read on to fi nd out how you can build one.

The primary material of the wing is sheeted foam. This is the same type plastic foam that you will fi nd as trays in packaged meat. The size I used on my test models was 3/32 inch thick, but I think other sizes will work. Figure 1 shows the bottom of the glider, and gives the general layout of the fl ying assembly. Since the fi gure is from the patent, Iʼll be able to use the item

Fig. 1: Bottom view of the foam “folding wing” boost glider

Fig. 2: Wing can be test fl own by launching with a rubber band.

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to the tip is to fi ne trim the glider, such as putting it into a gentle turn.

The item labeled “16” on the drawing is the hinge. It is a piece of adhesive backed tape. Figure 1 shows this tape extending partially along the span of each wing. I would consider modifying this plan, by having the hinge cover the entire wing (both sides). The reason for this is an add measure of safety in protecting the glider from the heat of the ejection charge. You may not

top surfaces face each other, and simply wrap the hinge around the edge. Make sure to press the tape down fi rmly against the root edges of each wing half. When you fold open the wings, part of the hinge is tucked between the edges (youʼll see what I mean when you open them up). The top hinge tape is simply layed across the root edges of each wing half.

In fi gure 5 youʼll see the rubber band hooks. The inventor planned for these to be made out of injection molded plastic, and to be attached with double sided tape. The average reader of this Journal will have no problem in creating their own custom made hook, so I wonʼt go into much detail here on how to make a hook. A couple of considerations are in order though. First, the fl ying wing is going to need a little bit of dihedral, so build it into these hooks (3°); so that the hooks are also stops that only allow the wing to open to the correct dihedral angle.

Second, the hinges also serve the purpose of trim weight to get the glider to fl y stable. It doesnʼt take much weight to get the glider to trim out, so the hooks can be made small. The location of the hinges also affects the balance of the glider, so I would suggest they not be permanently affi xed until the glider is trimmed for fl ight.

The rubber band hooks also served the purpose of giving a place to attach a rubber band for launching the glider (see fi gure 2). If you want to retain this feature in your competition glider, make the hooks strong. Launching the glider on a rubber band isnʼt such a bad idea, as it allows you to trim the model, and hand tossing fl ying wings is usually harder (no good place to hold on). By the way, the rubber band used is a small orthodontic rubber band.

thatʼs the basic glider. Alterations to this basic glider can take many forms. The one that I am considering most is adding tip fi ns. These would be have a planform of a semi-circle, and would be mounted on the underside of the wings at the tips. The

Fig. 3: Top (left side) and Bottom or the glider

need the added protection, particularly if you install a “parachute piston” in the rocket like those used so commonly in S3A. I just mention it, because it is something you should keep in the back of your mind.

Its hard to see it from fi gure 4, but the hinge tape on the bottom of the wing gets folded between the wing halves. This means very little, except that when assembling the glider, you will have to put the bottom hinge on fi rst: stack the wings so that the

Fig. 4: Cross-sectional view of wing in the folded position.

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tapering the trailing edge are almost obvious alterations. An alternative to sanding is that the foam can also be pinched into shape between your thumb and index fi nger.

Material substitutions is another altera-tion that can easily be made. Foam is light weight, but some people may prefer balsa for the wing. Balsa would give better heat protection at the expense of mass, but it also holds shape pretty good too.

One potential problem with this boost glider is its small size. It will boost to in-credible heights, and it will be hard to see. I suggest coloring the glider with magic markers to aid visibility. My own personal favorite colors are black on the bottom, and bright red on top. This will help make it visible on the ground too.

Another problem, especially in compe-tition, is that the glider might perform to well. In such a case, a DT is usually added.

I havenʼt worked one out for this particular glider, but my fi rst inclinations would be to concentrate on a “drop weight” DT. If anyone comes up with one, send it in, and weʼll get it printed here so everyone can take advantage of it.

Sometimes the unconventional keeps people from trying a new idea, but I would hope that people give this glider a try. It works great! They build very easily and quickly. A dozen of them could be easily built in a 1/2 hour. Give them a whirl. Even in NAR competition, the “A” divisioner using this glider would be very competitive (if he/she can fi nd it to get a return).

Author:Tim Van MilliganApogee Components, Inc.1130 Ellton Drive, Suite AColorado Springs CO 80907 USA

reason for the strange shape is so that they will fi t into the body tube. The added benefi t is that they will act as a piston, protecting the rest of the glider from the heat of the ejection charge, while helping to push the glider out of the rocket tube.

The second modifi cation I would incor-porate would be to change the shape of the carrier rocket. Why does the rocket tube have to be round? When making tubes out of fi berglass, the shape of the rocket body could easily be changed to an oval at the top; while transitioning to a circle at the bottom. This would give extra room for the glider (allowing larger chord lengths) while reducing the frontal area of the rocket! This would lead to even higher boosts. Fig. 5: View of bottom of wing showing the rubber band hooks.

Fig. 7: Full size template of wing showing the location of the crease lines needed to create the elevons.

Fig. 6: This is the start of the carrier rocket that I made for my glider. The only thing missing is a straight section, which would be constructed from paper. See TP #12 for details how to make the fi berglass shells for the nose and the transition.

As one might imagine, fl at slabs donʼt make very good airfoils. The foam sands easily, so rounding the leading edge, and