Wings folding with foamboard builds

[toryander]

I'm a fairly new rc flyer. I've built the Mighty Mine and the P-51 flat flyer. I love the building process and the airplanes. However, I've folded the wings on both models. They came down like a shot pheasant. I would like to blame the material, but I'm old enough to know that it's more likely my bad flying (no aura board or anything, so pretty jerky flying). I guess I need to learn a softer touch with these kinds of materials? Are there hacks to strengthening wing roots that are still aerodynamic?

 

[Foamforce]

in my experience, FT wings typically won’t fold unless you’re in a steep dive and you pull up hard. The only time that I catastrophically folded the wings was on a FT Spitfire (swappable, not master series), and it was preceded by me telling my friend “I’m going to see if I can fold the wings”.

I suspect that insufficient glue or bad adhesion may be responsible for many folded wings. In addition to the spar itself, the glue that goes into each of the leading edge folds also contributes to the strength of the wing. In fact the entire leading edge curve is an important part of the strength because it serves as an additional vertical surface in the “box”. So when you glue it all together, make sure that you have a strong bead of glue at all the contact points between the spar and the wing as well as in the creases. Make sure your glue gun is hot enough and that you work quickly enough so that the glue isn’t already cool by the time you fold the wing over. It can take some practice.

Long story short, it’s probably construction technique and not flying technique that is causing your wing folding. Watch some videos of Flitefest combat and watch how hard people are jerking their planes around.

Good luck!

 

[Tree Feeder]

Like @Foamforce said, bad adhesion might be part of it. You can put packing tape on the bottom of the wing underneath the spar, but if your wings are folding on a mini you are probably flying too hard. You don't need an Aura, just practice flying slower. I don't have experience with the p51 flat flyer, but I do know that you don't need much throttle. Try keeping your throttle around 50% after you get up, and you probably don't need everything for takeoff.

Also, look up how to set up dual rates on your transmitter. That will help to keep you from overcontrolling. If you can't do that with your TX, then you can move the pushrod on the servo horn farther in or the control horn on the control surface farther out. All of these will help keep you from overcontrolling and pulling up too hard and then folding wings.

Tree Feeder

 

[toryander]

in my experience, FT wings typically won’t fold unless you’re in a steep dive and you pull up hard. The only time that I catastrophically folded the wings was on a FT Spitfire (swappable, not master series), and it was preceded by me telling my friend “I’m going to see if I can fold the wings”.

I suspect that insufficient glue or bad adhesion may be responsible for many folded wings. In addition to the spar itself, the glue that goes into each of the leading edge folds also contributes to the strength of the wing. In fact the entire leading edge curve is an important part of the strength because it serves as an additional vertical surface in the “box”. So when you glue it all together, make sure that you have a strong bead of glue at all the contact points between the spar and the wing as well as in the creases. Make sure your glue gun is hot enough and that you work quickly enough so that the glue isn’t already cool by the time you fold the wing over. It can take some practice.

Long story short, it’s probably construction technique and not flying technique that is causing your wing folding. Watch some videos of Flitefest combat and watch how hard people are jerking their planes around.

Good luck!

Yes, I'm a new builder, also (still dealing with glue finger prints and globs). I will pay attention more to the things you mention as I build another p51 flat flyer.
Thanks for the valuable advice
Toryander

 

[Tree Feeder]

How experienced are you in flying?

 

[toryander]

Like @Foamforce said, bad adhesion might be part of it. You can put packing tape on the bottom of the wing underneath the spar, but if your wings are folding on a mini you are probably flying too hard. You don't need an Aura, just practice flying slower. I don't have experience with the p51 flat flyer, but I do know that you don't need much throttle. Try keeping your throttle around 50% after you get up, and you probably don't need everything for takeoff.

Also, look up how to set up dual rates on your transmitter. That will help to keep you from overcontrolling. If you can't do that with your TX, then you can move the pushrod on the servo horn farther in or the control horn on the control surface farther out. All of these will help keep you from overcontrolling and pulling up too hard and then folding wings.

Tree Feeder

Yes, I've been looking into setting those curves into the control inputs. I'll get it figured out in my Pocket elrs. I think flying slower is a good idea. I saw Josh from Fitetest easily do a loop de loop in his mighty mini. I tried that but probably didn't cut the power in time and that was that . I'm a noobie.
Thanks for your good advice.
Toryander

 

[toryander]

How experienced are you in flying?

I've had the little prebuilt mustang (that so popular at the moment) and could fly it well enough on intermediate and land it successfully. But that's about it. I've just gotten into these beginner flitetest builds, but have found them to be on a whole different level.

 

[Tree Feeder]

If you don't have space limitations, then build something big. Try a Simple Soarer. I have flown one on a power pack F and it is one of the most gentle things ever. The power pack F is similar to the power pack of your flat flyer. There are even free plans here on the forums for it if you want to do that. The tiny trainer would also be a good one if you are more space constrained, but the general rule is the bigger planes are more gentle to fly because of their mass.

Tree Feeder

 

[RickHunter]

In most of my FT builds nowadays I put a oversized motor setup. I just personally prefer the extra power. With that said you might start putting spars inside the wings for reinforcement. I put carbon fiber spars (I've accumulated many over the years) in almost all my builds just for the extra support. Though wood ones (dowels, paint stick, ect..) should wook just fine. Even on the flat flyers you can channel out the foam board and place a thin spar in the wing for extra support. You can always practice on scrap foam board first. It will add a little more weight, but almost not noticeable in most builds. As @Foamforce stated gluing is also important. But when in doubt, spar it out. I put an example of an in-channel spar I have on my FT Speed Bronco. It's on the elevator,but same concept on a wing build. This thing flies over 120mph with no issues.

 

[toryander]

If you don't have space limitations, then build something big. Try a Simple Soarer. I have flown one on a power pack F and it is one of the most gentle things ever. The power pack F is similar to the power pack of your flat flyer. There are even free plans here on the forums for it if you want to do that. The tiny trainer would also be a good one if you are more space constrained, but the general rule is the bigger planes are more gentle to fly because of their mass.

Tree Feeder

The Simple Soarer, huh? Sound good. I will look into that. I like the idea of soaring.

 

[toryander]

In most of my FT builds nowadays I put a oversized motor setup. I just personally prefer the extra power. With that said you might start putting spars inside the wings for reinforcement. I put carbon fiber spars (I've accumulated many over the years) in almost all my builds just for the extra support. Though wood ones (dowels, paint stick, ect..) should wook just fine. Even on the flat flyers you can channel out the foam board and place a thin spar in the wing for extra support. You can always practice on scrap foam board first. It will add a little more weight, but almost not noticeable in most builds. As @Foamforce stated gluing is also important. But when in doubt, spar it out. I put an example of an in-channel spar I have on my FT Speed Bronco. It's on the elevator,but same concept on a wing build. This thing flies over 120mph with no issues.

I think I can envision what you are talking about. The wing that folded on my flat flyer wasn't the glued joint, it was just compressed foam right next to the body (just the left wing, the right is fine). I just need to find where to get carbon spars. 120 mph. Dang.

 

[RickHunter]

Yes that is where most the force will always be. These are the 3mm ones I use for in-channel reinforcement (I cut them to size). You can find pretty much any size you need there though.

https://a.co/d/08UV0vMT

 

[Tree Feeder]

Wooden spars work well if you use them right. For a thicker wing, stand it up on its end. For a thinner wing, you can get away with laying it flat. I have used a yardstick as the only spar in a wing with success. As far as the simple soarer goes, you don't need to use it for soaring. It is a very gentle flier and it has good trainer style handling.

 

[Burnhard]

A short piece of carbon tube does wonders. Never had a folding wing where I used that set up.

 

[Foamforce]

I think I can envision what you are talking about. The wing that folded on my flat flyer wasn't the glued joint, it was just compressed foam right next to the body (just the left wing, the right is fine). I just need to find where to get carbon spars. 120 mph. Dang.

I looked up the construction of that plane (it’s new to me). How far from the middle did it fold? It looks to me like the leading edge skewer provides rigidity along the front of that wing, and the force from that should be transferred to the landing gear strut. If either the glue holding the skewer to the front of the wing, or the glue attaching the landing gear strut let loose, it could cause this.

PS, another factor in folding wings is weight. So if yours happens to be substantially heavier than design, you would have more trouble.

 

[toryander]

Wooden spars work well if you use them right. For a thicker wing, stand it up on its end. For a thinner wing, you can get away with laying it flat. I have used a yardstick as the only spar in a wing with success. As far as the simple soarer goes, you don't need to use it for soaring. It is a very gentle flier and it has good trainer style handling.

By the way, I love your profile picture. Just a couple of weeks ago my brother lost his FMS Cub up high (70') in a tree. They got the fire department to bring their ladder truck to get it out.

 

[Tree Feeder]

Lucky. That one is still up there, about the same height up. It has been there for a few weeks. The wing has disappeared, but the fuselage is still there along with a bunch of drowned electronics. It looks like it moved lower down, so it will get there eventually. I have more details about it in this thread.

 

[Merv]

...Are there hacks to strengthening wing roots that are still aerodynamic?

I use bamboo barbecue skewers as a wing joiner on all of my builds.

I like high G maneuvers & have folded many wings. I have not been able to fold a wing with 4 skewers. The idea is to form a I beam with the skewers. I dig out a slot before the wing is folded. Then glue them in when the wing halves are joined.

 

[toryander]

I use bamboo barbecue skewers as a wing joiner on all of my builds.

I like high G maneuvers & have folded many wings. I have not been able to fold a wing with 4 skewers. The idea is to form a I beam with the skewers. I dig out a slot before the wing is folded. Then glue them in when the wing halves are joined.

I think I understand inserting them into the foam between the paper of the wings. But how about where the two wings join forming a dihedral? You can't put anything across there, right?

 

[Merv]

... how about where the two wings join forming a dihedral...

That works, the skewers are flexible enough to join a dihedral wing. Perhaps not a large dihedral, but most dihedrals.

The foamboard webbing between the skewers is critical.

Also, I use a polyurethane glue (gorilla glue) to secure the skewers. This gives plenty of working time.