toryander
Active member
Whoops, I missed the bottom part of your post with the picture. I see. I'll start giving the technique a try. Thanks
Wings folding with foamboard builds
- Thread starter toryander
- Start date
toryander
Active member
I need to get serious about using some carbon rods (or similar) in my Flitetest planes. I've folded the wings (twice) on two different MightyMinis and two different Flat Flyers. I bought some 3mm carbon rods but haven't figured out how to apply them. I think if I cut them to 4 inches I can insert them into the foam between the paper at the wing roots? That's the area where my wing folding is occurring.
That will be far stronger than what you are doing now. That's only going to be 2 inches in each wing half, I'm not sure that's engaging enough foam for a high G maneuver. The carbon fiber is way over kill.
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toryander
Active member
The carbon rods don't bend, so I can't have half in each wing. I realize that I won't have the joint reinforced, but my folds always seem to be an inch or two outside the joint to the side of the body of the plane, so I thought four inches in the wing would work. But I have zero experience, so I'm eagerly listening to what you have to say. You suggested skewers? Those will bend enough? It seems the tricky part would be to get the wings to match up for gluing with the skewers sticking out of one side.
The best (fastest, lightest, cheapest) way keep a flat wing like the Flat P-51 has from folding is a continuous strip of reinforced fiberglass tape run under the wing from wingtip to wingtip and wrapped over the wing tips and a second strip on the top wrapped over the wing tips to the bottom. The idea is that tape is very strong in tension so the wing can't flex up because that would require the tape under the wing to expand and the wing can't flex down because the tape on top would have to expand.
Ok, I did not realize that was the problem. My wings ALWAYS folded at the joint. Your solution should work.
Skewers are plenty strong enough and flexible enough to accommodate a 5-10 degree dihedral.
But when glue the skewers into the foam, they are supported, now they are locked in place and have a great amount of strength.
I have stress tested my wings. I will put a wing over a space 30 inches wide, then stack 30 pounds in the middle. For a 25 oz plane, that's about 19 G's.
I dig a groove for the skewers before the wing is folded. Then temporally insert the skewers to fold the wing, this helps the wing keep it's shape while folding as the groove is now a weak spot. After the wing is folded, remove the skewers and sand the edges to mate up with each other. When you are satisfied with the joint, glue in the skewers & join the wing halves.
toryander
Active member
I messed around with a skewer and a scrap piece of foam board, today. I can see what you are talking about. I ordered some skewers. I hope to use them in my next MightyMini Explorer sport wing. I need to practice somehow to get the technique down. I appreciate the pointers!
toryander
Active member
I missed this post yesterday. Interesting. You've had success with this? I'll look up this kind of tape.
MadMonkey
Elite member
Foamboard wing joiners/braces at the highest point on the airfoil are pretty typical,but not super strong. Adding a piece of plywood sandwiched between is stronger, but you need proper tools (like a bandsaw) to cut ply to size.
Long bamboo skewers are cheap and can be suitable for smaller planes. They're too flexible for bigger ones though, unless the wing needs to flex like a large sailplane.
Carbon fiber arrow shafts can be bought in bulk from Amazon and are much stiffer. They're a little more expensive, but are my preference for most planes. My 80" C130 uses three of them with embedded skewers in them for extra strength. No flex issues.
The high strength fiber packing tape is also an excellent idea especially for strengthening joints.
Long bamboo skewers are cheap and can be suitable for smaller planes. They're too flexible for bigger ones though, unless the wing needs to flex like a large sailplane.
Carbon fiber arrow shafts can be bought in bulk from Amazon and are much stiffer. They're a little more expensive, but are my preference for most planes. My 80" C130 uses three of them with embedded skewers in them for extra strength. No flex issues.
The high strength fiber packing tape is also an excellent idea especially for strengthening joints.
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Bricks
Legendary member
As an experiment I have taken those light plastic covers that come on may items, roll it as tight as you can to the diameter you need. Hold it together with bread ties or what ever is handy, drop this in water around 150-170 degrees for a few minutes. Let it cool I was impressed with how much force it took to try and bend it, an alternative if other sources are not available. The tighter you can roll it the stronger it gets with out creasing it..
toryander
Active member
I'm not sure I can picture what you are describing. What exactly is we have after doing what you describe?
Foamforce
Elite member
Not to be a pain, but you’ve been working on this for quite awhile now. It’s really worth examining your build technique, because most other people don’t have an issue with the wings folding when using the stock design. Correcting the build technique will result in a less complicated and lighter plane.
Disclaimer: I haven’t worked on the P-51 flat foamie. It looks like that uses different techniques for keeping the wing rigid.
Do you suppose you could attach some photos of your existing broken builds so we can examine them?
Disclaimer: I haven’t worked on the P-51 flat foamie. It looks like that uses different techniques for keeping the wing rigid.
Do you suppose you could attach some photos of your existing broken builds so we can examine them?
Other people don't have problems because they don't do high G maneuvers, like a square loop.
If you are going to fly fast or hard, the stock wing will fold.
I must disagree. The standard BBQ skewers are plenty strong enough for the standard size FT plane. If they are used correctly, see posts 18 & 20. I have stress tested my wings. I will put a wing over a space 30 inches wide, then stack 30 pounds in the middle. For a 25 oz plane, that's about 19 G's.
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toryander
Active member
Let's see, I've folded the wings on three Mightymini Explorers (one trainer wing and two sport wings) and one flat flyer. I think I was just doing a simple loop with the Mightymini (and I think I cut the throttle at the top). With the flat flyer the wing is glued to the the body along a single edge of foam board (3/8 inch?). Not much support. It has wheel struts that I just recently realized also stabilize the wings. When I folded the wing I hadn't put the wheels on (no runway they would work on). I see now that was a critical error. I folded the wings just by jerking the plane around trying to get it under control. Even if I don't use the wheels I would still need to use partial struts as braces. I've just built another flat flyer from scratch. Attached is a picture. I have the wheels on stabilizing the front of the wing and I've used the fiberglass tape technique for added strength. I didn't do the skewers because the wing was already built from earlier. I've done my best, but I'm not an advanced builder. Here are some pictures. I'm taking him out later after my classes end to see what happens.
RickHunter
Elite member
Looks pretty sturdy. If your concerned on folding, put your rates(throws) on a 3 position switch (low, medium, high). Start with low rates and work your way up till you fold or (hopefully) not fold the wings.
MadMonkey
Elite member
Sorry, by bigger I meant giant scale, not standard size.
Foamforce
Elite member
I don’t think the original poster was flying fast or hard either, just “flying jerky”, like we all do when we start out.
It’s definitely possible to fold the wings, and one time I was flying my Spitfire and I told my friend, “let’s see if I can fold the wings”. I went way up high, then came straight down and pulled up hard at the bottom. It gave itself a high five. So yeah, totally possible, but it generally doesn’t happen under normal conditions or the slow flying that a beginner typically does.
The point I was trying to make is that it’s not typical for a beginner flyer to be folding wings regularly, indicating a probable build issue. Identifying and correcting that issue is simpler than re-engineering the wing.
Foamforce
Elite member
Ah good job, I think you identified the problem. I believe the design of that P-51 wing transfers the load from the wing onto the skewer on the leading edge, and then from there onto the strut. It makes a triangle on either side that is really light and strong. Without that, it’s only the strength of a single sheet of foam board holding the wing together. Nice job figuring that out!
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