My SC Wing Test

[BTCat]

I saw this on a scratch build thread so I had to try it on the Super Cub wing. This guy took two pieces of EPP of equal length. He left one as is and took some fiber reinforced packing tape and put one strip the length of the other EPP. He then weighted both pieces of foam while hanging them over the edge of the table. The unreinforced piece flopped. The taped piece bent a little, but not much. No surprise.

Anywho, since I have two SC wings, I decided to give it a test. One of my wings is reinforced with CF rod (4mm I think) from one end to the other (I put an extra piece in the middle). The standard SC wing spar mod. The other wing is not reinforced at all. I put the fiber packing tape from tip to tip on the unreinforced wing. I then set one end up on a stool and weighted it in place and put another weight at the hanging end. The CF reinforced wing had a deflection of 5 inches with the weight. The tape reinforced wing had a deflection of 3 inches. WTH! The tape actually stiffened the wing more than the CF. Go figure.

The tape actually acts like a dynamic tensioner, were as the CF acts like a simple reinforcement bar. I think I could get away with the tape alone. I'll probably end up putting the tape over the CF wing also, just for insurance.

[akent]

That fiber strapping tape is amazing stuff!

The CF is just usually more intimately built in to the model.
Tape just sticks to stuff.

[Solitaire]

Mar 12, 2010 21:50:28 GMT -6 akent said:

...Tape just sticks to stuff.

This just cracked me up.
Think about it... comprehensive evaluation...engineer. ;D

Got a case of the snickers, now.

[19000rpm]

Mar 12, 2010 21:42:36 GMT -6 BTCat said:

I saw this on a scratch build thread so I had to try it on the Super Cub wing. This guy took two pieces of EPP of equal length. He left one as is and took some fiber reinforced packing tape and put one strip the length of the other EPP. He then weighted both pieces of foam while hanging them over the edge of the table. The unreinforced piece flopped. The taped piece bent a little, but not much. No surprise.

Anywho, since I have two SC wings, I decided to give it a test. One of my wings is reinforced with CF rod (4mm I think) from one end to the other (I put an extra piece in the middle). The standard SC wing spar mod. The other wing is not reinforced at all. I put the fiber packing tape from tip to tip on the unreinforced wing. I then set one end up on a stool and weighted it in place and put another weight at the hanging end. The CF reinforced wing had a deflection of 5 inches with the weight. The tape reinforced wing had a deflection of 3 inches. WTH! The tape actually stiffened the wing more than the CF. Go figure.

The tape actually acts like a dynamic tensioner, were as the CF acts like a simple reinforcement bar. I think I could get away with the tape alone. I'll probably end up putting the tape over the CF wing also, just for insurance.

That really makes sense. You're spreading the deflection over the entire wing length. When you use a CF or fiberglass you're just reinforcing a relatively short span and that support falls off rapidly as you move away from the local area where the CF or fiberglass is.

I've used that tape technique on my ultra micro sukhoi's horizontal stab, but I never thought about applying it to an entire wing.

I think I'm going to use that technique on my hopped up versions of the P51 and Corsair. The Gull wing of the Corsair makes me a little nervous anyway. I think I'll apply the tape to all of the wing and stab surfaces before I paint them.

Speaking of tape sticking to stuff: Have you ever noticed that tape sticks to the roll better than anything else except, maybe, your fingers? ;D

[BTCat]

Mar 13, 2010 7:40:38 GMT -6 19000rpm said:

...
Speaking of tape sticking to stuff: Have you ever noticed that tape sticks to the roll better than anything else except, maybe, your fingers? ;D

;D I was noticing that and cussing that when I was trying to put a 48 in strip of tape on straight while trying to get a piece of foam to sit still.

If I can find something more uniform in weight besides the piece of clay I was using yesterday, I may take a pick.

There are structural engineering terms for all this and I should remember them from when I studied this shifting soil we have in Texas and its effect on concrete. The differance in the CF and the tape is simulare to the differance between simple rebar reinforcement and pretension or post tension slabs.

[BTCat]

But.......I found the Achilles heel with tape. Its tension and elasticity changes with time and temperature. After sitting in a cold garage all night, the tape doesn't do as well as it did when first installed. Equal to, but not better than the CF. The CF is consistent. The tape seems to have stretched or is cold enough that it doesn't have the "bounce back" it did before I think I will use both

[dubehigh]

[akent]

One thing that might work better is to paint a thin coat of epoxy under where you plan on placing the tape. That tip came from the L-39 EDF for placing the battery velcro. That REALLY makes the tape stick to stuff!

[19000rpm]

Kent brings up a good point here. It might not be the tape; Just as likely it's the adhesion to the foam.

First, I'd suggest washing the wing. No joke, soap and water. It gets rid of the mold release they use in the molding process. Paint won't even stick without washing the surface first so that leads me to think adhesion could be at least part of the problem.

I really like the idea of adding epoxy, or even enamel, because it's going to seal the pourous foam. Without it you'll likely have another adhesion problem down the road as moisture moves in and out of the foam.

By the way, I think Kent mentioned this earlier, the reinforced strapping tape is a lot stronger than regular packing tape and much less likely to stretch. Just a thought

[BTCat]

I'm using Scotch Extreme Tape I got from Home Depot or Lowes. Tough, fiber reinforced stuff.

[dubehigh]

Ok I have ? If you are spending that much time on a foamie, why not just build a stick build from scatch. Just a thought

[BTCat]

Mar 13, 2010 18:04:42 GMT -6 dubehigh said:

Ok I have ? If you are spending that much time on a foamie, why not just build a stick build from scatch. Just a thought

'cus I'll just destroy it the first time I crash -- probably the first time I fly.

Honestly, two things keep me modifying and playing in the garage, weather and this dam neck of mine.

[Solitaire]

Yeah, Dube, a balsa and ply plane takes a lot of time and energy to repair, whereas a foamy can be glued back together in minutes...normally.

My "stick-built" planes will remain unbuilt until I get much better at flying. A whole lot better.

[dubehigh]

Good point, bt, and sol. Like I said it was just a thought. Sorry for the dumb ? I,am guilty of it to. I like to putz in the shop. It gives me peace of mind

[BTCat]

i promise. My SC shall be the most over tweaked SC around. ;D