Foam Wing Strength Testing

Hey this is Lee from AudaciousRC, and I wanted to share the results of some strength testing we did on foam wing sections, and perhaps make you better informed about the effectiveness of wing strengthening methods. 

Introduction

Here at AudaciousRC, we love making our builds strong, and coming up with new ways to make them more durable and crash-proof. In our learning, we've discovered a few methods that are simple and effective, which we've shared in past articles. However, we wanted to know just how effective these techniques were, and were they worth the weight that they added? So we devised a way to test them. Yep, that's right, we did a little bit of science. We came up with a device that would slam a section of a wing into a metal pole, recorded the results, and came up with some conclusions.

Methods

Slamming Device, "Plane Guillotine"

After a bit of brainstorming and designing, Trent put together a nice rig using a bunch of wood, clamps, rubber bands, and a metal pole. 

The rig had a footprint of about 2 feet by 2 feet, and used 2"x3" and 2"x2" pieces of wood, a simple metal hinge, and some rubber bands. We drilled a hole in the arm so we could insert the wooden spar into it, providing a firm hold for the wing. Each wing had to be glued to the spar for testing, and we placed the wooden spar behind the foam spar, so the forces could be distributed evenly across the section. The rig is very simple and easy to build, and doesn't use a whole lot of material. 

Wing Construction

The wing sections were all made with the same dimensions. The wing had a 10" chord, with a 1" spar placed 2" back from the leading edge, and two folds were made into the top of the wing for curvature. They all used a relatively equal amount of glue, and each step was completed on all of the wings at once to ensure that they were all of equal strength to begin with. After cutting and gluing, each wing was put together using different methods. 

Wing 1: Basic foam wing, no additional modifications

Wing 2: 1/8" wooden dowel placed in leading edge before wing was folded over

Wing 3: Covered with wing tape

Wing 4: Leading edge covered with gorilla tape (thicker and stronger than duct tape)

Wing 5: Leading edge filled with expanding insulation foam (the brand we used was called Great Stuff)

Wing 6: Insulation foam, wooden dowel, gorilla tape, and wing tape over that. Basically everything all at once.

Testing

Each wing was placed into the slamming device, pulled back to the full extent, and then released. This was repeated again to simulate a more powerful crash, and to get us better results on the stronger sections. The tests were filmed at 120fps and 240fps using GoPro Hero 3+ and Hero 4 cameras. We then took pictures of the wings after testing. 

Results

Wing 1

Weight: 48.9g

After two strikes, you can see how the rod ripped right through the wing unobstructed. Without any support, the paper rips and the foam gets smashed in. 

Wing 2

Weight: 50.1g

The wing with the dowel inserted into the leading edge fared much better. The dowel was able to disperse the forces across a larger area of the wing, you can see how the deformation is much wider on this wing than the first. After two strikes, however, the dowel snapped and the paper ripped a little bit. The foam has only crumpled a small amount inward.  

Wing 3

Weight: 54.9g

The results from the wing-tape section were rather interesting. You can see how the tear is very clean and straight, as though it held on until reaching a break point (I'm pretty sure there's a physics term for this, something like Young's Modulus or Shear Modulus). The point is, the wing tape is like a tough skin, resisting rips and tears, and snapping after a certain amount of force is applied.

Wing 4

Weight: 56.7g

The wing with Gorilla Tape applied to it has very little to show after two tests. As you can see from the video, the wing  bounces a lot more than all of the rest. This is probably a result of the rubbery nature of the tape itself. However it adds a little over 7 grams of weight for a 10 inch section, while the previous methods only add between 2 and 5.

Wing 5

Weight: 65.0g

This wing was filled with expanding insulation foam in front of the foam spar. The brand we used was called Great Stuff, and we've used it on many planes. The results of this test, however, were quite different than what we expected. The wing crumpled quite a bit, and caused the paper to rip. This is possibly caused by the fact that the expanding foam may not have penetrated all the way into the edge. As you can see in the video, the first impact created most of the damage, and when the bar reached the foam on the second impact, the deformation increased very little. The addition of foam, although it may not increase direct impact strength, it does increase lateral as well as torsional strength.

Wing 6

Weight: 78.8g

For this section, we combined all of the above methods into one wing. This wing was by far the strongest and heaviest. You can't even see any amount of deformation, crumpling, or tearing. However, the modifications create a 60% increase in weight.

Conclusions

Trent's Advice

Trent likes the results of wing #4, the one with Gorilla Tape on the leading edge. It has a lot of bounce, and holds the paper together well. He believes that the weight added by the Gorilla Tape is worth the extra strength.

Lee's Advice

I was very impressed with the results of the dowel in the leading edge, as well as the wing tape. I would recommend a combination of these two methods. The advantage of doing this is that the dowel in the leading edge does a good job of distributing forces across the wing section, preventing deformations, and is also extremely lightweight. Installing it is also fairly straightforward: before you fold the wing over, simply lay the dowel into the crease, put down some hot glue, and fold it over. I also recommend using the wing tape to cover the entire wing, as the tape gives it a tough skin that is waterproof and provides strength against tearing or ripping. A combination of these two methods will result in a strong and very lightweight wing. 

Colton's Advice

Colton agrees with Trent's conclusion, but would also add the wing tape to the entire section. The bounciness of the Gorilla tape helps a lot, and if there is deformation, you can easily squish the edge back in place.

Final Words

Well that was a really long article. I hope you enjoyed it, and perhaps learned a few things. Please comment below what your thoughts are about our methods, our results, and our conclusions, and any methods you use to strengthen YOUR wings!

Thanks!

Lee from AudaciousRC