Using Shape-Cut Foam (4 ways to bend it, how to add and adjust weight, etc.)
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Where to buy shape-cut foam.
Pattern for glider
Pattern for one of the bending jigs (see #4 below)
|If YouTube is blocked, you can view this compressed MPG file (38 MB)|
This text page corresponds to the embedded video about how to work with thin foam sheets for walkalong gliders that are already cut to the hang glider shape. Below is the transcript of the narration, plus additional details and links.The numbers are time markers that tell you where to go in the video to see it. If YouTube is blocked, you can view a compressed, lower resolution version here.
You can save time and you don't need paper patterns for foam that's already cut to shape, but you will have to decide how to make the folds in the glider. Later in the video there is information about what to use for front weight, how to adjust the glide, etc.
If you have a question, contact me (Slater) about it and I’ll try to answer, and post the answers on this page, too.
2.) This video will cover 4 ways to get the folds in the right place, including how to make cardboard bending jigs; then a section about how to add front weight and adjust the folds once the glider is made. There is a linked web page with lots more detail.
The bending methods are: measuring and bending; a simple cardboard jig that sandwiches the foam for bending; a more complex, 2-piece jig for the front, then the back; and freehand bending.
3.) You can measure for the bends. This method might not be as fast as some other methods but is perhaps a doubly useful exercise for students because they practice measuring in a real-world application. Measure 5 mm or 3/16” from the leading edge. You can use thin, cardboard straight edges at least 50 mm x 216 mm (2" x 6") to make the bends. These can be separate or hinged with tape at en end. Or you can use a book to make the bends. Be gentle; the foam rips easily. Measure 13 mm or ½” from the back. Remember that when finished, the front will bend down and the back will bend up.
4.) You can make a simple cardboard jig. This can be a fast way to make the folds. It works well if you are careful to get the foam in the right place. If you are not careful to place it right, you will get somewhat uneven results. For example, if you don’t get the foam far enough in, when the glider is folded it will have a bigger camber and smaller elevons—which could compound the tendency to dive. If you are savvy about adjusting the glide then it won’t be a problem. But it’s worth being careful to get the foam in the right place in the jig.
You should be able print out the pattern on either 8 ½” by 11 or A4 printer paper. If you have trouble printing on A4 please send feedback to me so I can correct the problem. How you get it to print out depends on whether you are printing from a browser (and which browser) or PDF reader. Go for settings like “100%” or “full size”.
Avoid settings like “fit to page” or “shrink to fit” or any scaling except “100%”. Notice that there is scale check of 102 mm or 4 inches. If you have problems with printing the correct, again, please contact me and we can try several things to get it right.
Rough cut, but fine-cut the ends right on the line. Make a couple of tape donuts for the back. I cut a cereal box in the middle of the side to preserve the fold.
Line up the dashed fold lines in the pattern exactly with the existing fold in the cardboard, rough-cut and and then cut precisely.
Rough cut, tape and cut out the other piece. We have to make folds for this one. Back up with cardboard underneath, get a straight edge exactly on the dashed lines and press firmly with a ballpoint pen. Push so hard that it might cut the paper. That creates a weak spot in the cardboard for bending. I actually bend the wrong way first, then the other way.
This dashed line shows where a slight “dihedral” bend will be put into the wings. Cut a chunk out of the front.
This piece goes on the top. These edges at the ends and here should line up. Make a tape hinge but don’t make the tape all the way to the tabs (because that could interfere with the foam going in).
To use the jig, make sure that these flaps are not bent up. Open and insert a shape-cut foam. Getting the foam located into exactly the right place is the most challenging part. You can get the foam and cardboard lined up here; or turn it over and line up here. Actually making the bends is pretty easy, just by pushing down and bending the jig and the foam. It’s just a very slight bend for the dihedral in the middle. Then push these flaps down and pull the foam out gently to avoid tearing.
I’m experimenting with gluing part of a paper clip to the jig to help locate the foam more quickly.
5.) You can also bend with a 2-piece jig—actually 3 pieces if you count the straight edge--that’s more challenging to make, but I think it’s easier to use with more consistent results than the simpler bending jig (above). That is because it gauges the folds from the edges. So these are the bending jigs that I use when I make ready-to-fly gliders that I send to people because there is little variation. Beginners have enough to worry about. It has the added benefit of being easy to use—automatic after awhile. I can talk with people or listen to music and still get perfect results as long as the foam edge is pushed against the cardboard.
If you don’t want to make the jig yourself, you can buy it from sciencetoymaker.org (and all of the money goes directly to the non-profit education organization the Physics Factory). And here is a link to a video about mass producing gliders using this kind of jig.
Building it will be easier if you already understand how it works. There are two simple bends, or hinges here. A piece of foam slides against the bend on the left; but the straightedge can only slide to the other bend, a little to the right, because it hits these 2 stops. Then the jig bends the foam against the straightedge
Although the final dimensions of the cardboard will be:
5 mm x 127 mm or (3/16" x 5")
25 mm x 127 mm or (1" x 5") and
76 mm x 127 mm or (3" x5")
Actually make all the strips at least a centimeter longer. That’s because it’s hard to get the ends lined up when you tape them together. Then you can cut them even and to size once taped together. It took me a year of making them to figure that out; this way is much easier.
Tape cardboard strips snuggly together on one side only so they still hinge.
Tape both sides of a strip 19 mm or ¾” wide on each side, but only up to the hinged part, so that part is free to bend. Cut off the extra. Tape on a handle. Make sure that there’s free movement; cut a little if it rubs.
Cut out a cardboard straight edge 89mm x 267 mm or (3 1/2" x 10 1/2"). It will be easier to pick up if you bend a little handle on one side.
Cut out 2 squares and fold them in half. These stops for the straightedge have to be taped on very precisely. Push the straightedge not against the left fold, but the fold on the right. Notice that you can still bend it on top. Push the stop against the straightedge and start taping down, but try not to press the tape on the straightedge. Remove the straightedge and press the rest of the tape down.
Outlining the shape might help people get the foam in the right place.
The jig for bending the back flaps, or elevons, is very similar in use and construction. Just use these different dimensions (again cut these strips at least a centimeter longer and cut the assemble even):
13 mm x 216 mm or (1/2" 8 1/2")
25 mm x 216 mm or (1" x 8 1/2")
76 mm x 216 mm or (3" x 8 1/2")
6.) Finally, if you are flight savvy you could make the folds in the foam by eye. They won’t look as neat, but they’ll fly just as well. I don’t recommend this for beginners; but if you do, at least look at a pattern or an already made glider as you’re folding.
7.) GETTING READY FOR THE FRONT WEIGHT
However you make the folds, you’ll need to make sure the angles are correct, then adjust the glide. The camber slants down about 30 degrees. The back flaps bend up at least 30 degrees, and up to not much more than 45 degrees if you are having trouble with diving. Bend just a tiny bit of dihedral into the middle if it’s not already there.
8.) Launch the glider, holding gently from the back, bent slightly down.
If you let go of a glider without front weight, it doesn’t glide. So how do you know what to use for the weight; and how much? I like a strip of aluminum foil for front weight, anywhere from 6 mm to 13 mm (1/4” to ½”) wide. It’s too flimsy as a strip, but scrunched and twisted into a wire it becomes so strong that you can make cool board takeoffs.
You can also use other things like paper or wire (see 13 below for details).
9.) If you put too much weight on the front, it dives. If you don’t put on enough, it stalls. You can cut off weight to make it stop diving; or you can add tape weight to make it stop stalling.
10.) You can also fine tune by bending the front weight forward or backward. It might be a good idea to start out with a ready-to-fly glider that I send with foam because they already have about the right amount of weight. If I just leave the wires tucked under the glider, it stalls severely. But if I bend them out more to the front then it glides ok.
Just like adding and cutting off weight, bending the weight forward or backward changes the balance point or “center of gravity” (CG). Bending back has the same effect as cutting off weight; bending forward has the same effect as adding weight. You can use this trick no matter what you use for front weight. The best glide is just at the point where there is no stalling, or just a little stalling. If you do advanced flying with only your hands providing the updraft, it works a little better if there is no stalling.
11.) If the glider always turns severely left or right, then bend the opposite side elevon up, but not much more than 45 degrees. If that’s not enough, push the other elevon down.
12.) If you keep having trouble with diving even when you cut off weight or bend the weight backward, then bend the elevons up more, but (again) not much more than 45 degrees because then they start acting like brakes instead of flaps.
In summary, if your glider stalls, cut off weight and/or bend the weight toward the front. If your glider dives, cut off weight and/or bend the weight toward the back and/or bend the elevons up, but not much more than 45 degrees. Bending one elevon up and the other elevon down will correct unwanted turning.
13.) I use very thin copper wires because they don’t damage the foam when I pack gliders together. It’s from thrown away, recycled ordinary electrical cords. Unfortunately, it’s a lot of work to strip the insulation off; it’s easier if the insulation is warm. You can also use paper weight, but it becomes limp in humid conditions and can interfere with the air unless you bend it like this.
So play around, experiment with front weight and adjustments and soon you’ll master the glide. Then this video shows to keep them levitated in the air.
Here are some links *************
Link to buy foam already cut to hang glider shape
Link to the corresponding YouTube video
Link to the Not-YouTube version (compressed)
Link to video about mass producing gliders
Link to learning to fly gliders once adjusted
Contact me (Slater) if you have questions