This is a method I used to reinforce the wing spar on my Sky Surfer (aka Bixler), but it can be used for any tube spar. I know this is an overkill but it is cool.

What you need?
1- corn starch
2- water
3- syringe
4- hot glue
5- epoxy

The catch?
A non-newtonian liquid acts as a liquid when there is no force acting on it. If there is a force, the liquid phase changes into solid phase. The stiffness is proportional to the force applied. See these videos if you want to see how a non-Newtonian liquid behaves. Youtube-Video

In summary:
Fill the CF tube with a non-Newtonian liquid. During a normal flight (e.g. gliding) the net force acting on the wing spar is mediocre or zero, so the wing spar will behave as usual e.g. a liquid filled hallow tube. In extreme cases, i.e. wind gusts, aerobatics, crash etc. the liquid inside the CF tube will solidify and make the CF tube stiff, the stiffness will depend on how extreme the situation is, after the extreme case is over the material inside the tube will liquify again. So the stiffness of the spar is modified realtime.

How to do it?
The CF tube of Sky Surfer will take about 6-7ml (1/4 fl ounce) of liquid so you do not need too much material, to be on the safe side make a bit more than what you will need. 6-7ml of water based liquid will weigh about 6-7 grams approximately.

Add starch slowly into 1/2 ounce of water while stirring SLOWLY. At some point the stirring easiness will depend on how FAST you are stirring it. If you can not stir it anymore try doing it very slow. That is the point where the mixture has become a non-Newtonian liquid.

The second step is filling the CF tube with this liquid. You can do it by a syringe. No needle is required. Sucking the liquid into the syringe will be almost impossible, so remove the plunger, pour the liquid in to the syringe, put the plunger back and remove the air, You DO NOT need the needle.

Next, attach the syringe to the CF tube, you do not need any adapter, they will just fit. Start squeezing the syringe SLOWLY. You must be very slow, if you squeeze hard the liquid will oppose you, remember this is not an ordinary liquid. It should take about a minute or two to fill in the CF tube.

When you see the liquid on the opposite end of the tube, stop pushing and pull the plunger a bit backwards. Clean the opposite end with a paper towel and close it with hot glue. Remove the syringe, clean and close this-end with hot glue too. To be on the safe side, treat the ends with epoxy. Epoxy will permanently seal the ends and protect the liquid.

That's it.

If you happen to have any leak after you do this mod, don't worry it is only corn starch and water, wash with excess water to clean the starch.

Enjoy.

"I did it because I could."

Watched some video's on the stuff. they're doing that to kevlar to keep ice-pick's from poking through it.

Apparently most, if not all, fine-particle slurries behave in this way. This is an interesting application of an easy-to-make-with-common-materials slurry.

Some experimental data would be fascinating, but I don't know if slurry-filled sealed tubes have been investigated for their resistance to sudden bending.

A fun idea to play with though.

Originally Posted by Himself

Apparently most, if not all, fine-particle slurries behave in this way. This is an interesting application of an easy-to-make-with-common-materials slurry.

Some experimental data would be fascinating, but I don't know if slurry-filled sealed tubes have been investigated for their resistance to sudden bending.

A fun idea to play with though.

Totally agree, I would love to test this with controlled experiments but not sufficiently equipped.

My assumption is; even in normal flight, vibrations arising from the motor etc will induce some level of stiffness and in the case of crashes etc, the induced stronger stiffness will prevent (to some degree) the bending.

Originally Posted by eertan

This is a method I used to reinforce the wing spar on my Sky Surfer (aka Bixler), but it can be used for any tube spar. I know this is an overkill but it is cool.

What you need?
1- corn starch
2- water
3- syringe
4- hot glue
5- epoxy

The catch?
A non-newtonian liquid acts as a liquid when there is no force acting on it. If there is a force, the liquid phase changes into solid phase. The stiffness is proportional to the force applied. See these videos if you want to see how a non-Newtonian liquid behaves. Youtube-Video

In summary:
Fill the CF tube with a non-Newtonian liquid. During a normal flight (e.g. gliding) the net force acting on the wing spar is mediocre or zero, so the wing spar will behave as usual e.g. a liquid filled hallow tube. In extreme cases, i.e. wind gusts, aerobatics, crash etc. the liquid inside the CF tube will solidify and make the CF tube stiff, the stiffness will depend on how extreme the situation is, after the extreme case is over the material inside the tube will liquify again. So the stiffness of the spar is modified realtime.

How to do it?
The CF tube of Sky Surfer will take about 6-7ml (1/4 fl ounce) of liquid so you do not need too much material, to be on the safe side make a bit more than what you will need. 6-7ml of water based liquid will weigh about 6-7 grams approximately.

Add starch slowly into 1/2 ounce of water while stirring SLOWLY. At some point the stirring easiness will depend on how FAST you are stirring it. If you can not stir it anymore try doing it very slow. That is the point where the mixture has become a non-Newtonian liquid.

The second step is filling the CF tube with this liquid. You can do it by a syringe. No needle is required. Sucking the liquid into the syringe will be almost impossible, so remove the plunger, pour the liquid in to the syringe, put the plunger back and remove the air, You DO NOT need the needle.

Next, attach the syringe to the CF tube, you do not need any adapter, they will just fit. Start squeezing the syringe SLOWLY. You must be very slow, if you squeeze hard the liquid will oppose you, remember this is not an ordinary liquid. It should take about a minute or two to fill in the CF tube.

When you see the liquid on the opposite end of the tube, stop pushing and pull the plunger a bit backwards. Clean the opposite end with a paper towel and close it with hot glue. Remove the syringe, clean and close this-end with hot glue too. To be on the safe side, treat the ends with epoxy. Epoxy will permanently seal the ends and protect the liquid.

That's it.

If you happen to have any leak after you do this mod, don't worry it is only corn starch and water, wash with excess water to clean the starch.

Enjoy.

"I did it because I could."

An interesting idea but I don't think it is going to do anything in this situation other than add weight to the spar. In order for the slurry to resist, some motion has to be involved. You will see the feet of people running across this material sink in a good bit before enough resistance builds to support them, and any slow movement will meet almost no resistance at all. Think of the individual points along the spar. Under any bending pressure, short of that which breaks the spar, there is almost no movement at all between adjacent particles of the slurry. But I will try this: I will fill some fuel tubing or a straw with the slurry and see if it shows any more resistance to quick bending pressure. If it does I will be back to admit being wrong. But I don't expect that that I will have to.

Gord

Gord, thanks for the input, I am also skeptical about this. But I still believe that it will work The tube is sealed at both ends and there is no air within the tube, when a bending pressure is present at a point, the liquid at that point will feel the highest pressure and since the tube is sealed, because it is a liquid and a liquid can not be squeezed the adjacent points will also feel the pressure. How stiff the tube will be will depend on the pressure. But again without a controlled experiment it is difficult to say what the real world outcome will be. I have acquired some straws myself, with a high speed camera I will test this idea and post the results here. Just waiting for spare time and permission from my wife
Best,
eertan

Originally Posted by eertan

Gord, thanks for the input, I am also skeptical about this. But I still believe that it will work The tube is sealed at both ends and there is no air within the tube, when a bending pressure is present at a point, the liquid at that point will feel the highest pressure and since the tube is sealed, because it is a liquid and a liquid can not be squeezed the adjacent points will also feel the pressure. How stiff the tube will be will depend on the pressure. But again without a controlled experiment it is difficult to say what the real world outcome will be. I have acquired some straws myself, with a high speed camera I will test this idea and post the results here. Just waiting for spare time and permission from my wife
Best,
eertan

Well, it doesn't seem to be too effective for this application, but you are in for some great fun! I added some water to some corn starch and went at it with a whisk that I use for pancake mix. I wound up laughing like a little kid! Mix real slow and it's fine but try to get rid of that 'thick' feel, as if it isn't totally mixed at the bottom, and you will be there until it just dries up altogether, or your arm falls off, whichever happens first. Try to mix faster and things start flying all over the place! The whisk sticks in place and then breaks loose splashing the stuff all over the counter. And then you find that although it looks just like drops of any thicker liquid, you can just pinch it between a couple of fingers and pick it right off the counter. Stick a finger (very slowly) to the bottom of the liquid and try to pull it out quick and the whole bowl comes up with your finger. Great fun! If I had kids I would insist that they help. Might make a mess of the kitchen but it would be great fun.

BTW, don't bother with the syringe. It just sucks the water out of the surrounding slurry leaving a hard spot. You get mostly water in the syringe. Use a funnel. It is slow, but it works.

But as a filler for a spar it seems to be useless. I filled a fairly heavy plastic straw, about a quarter to a third of an inch ID, and plugged the ends. Then I tapped it something like a drumstick on the edge of the sink. It felt heavier that the empty straw I was comparing it to, but not particularly stiffer. I slid it over the edge of the sink and tapped and pressed on the free end and again it did not feel much stiffer than the empty straw.

I think the answer to reenforcing the spar is the next size down carbon fiber tube slid inside the original and glue in with maybe Gorilla Glue or thin CA. Doesn't weigh much at all but considerably strengthens the spar. I have not been able to break mine with the most ridiculous of pull outs.

Thanks for the idea. I had a great time with it!

Gord

Awesome

I am glad it was at leats useful in creating a fun time . I will be doing the tests with straws this weekend. I believe this will be a comprehensive test and I will either keep my spar cornstarch filled or empty it and fill with Gorilla Glue.

Just exchanging ideas was worth creating this thread.

Best
eertan

Sounds like the stuff Eva Gabor on GREEN ACRES makes HOT CAKES out of!
Looks like pretty tough stuff when Eddie Albert tries to eat it.

Anyway I thing making a batch and putting it into a Mc Donalds thick shake straw and hot gluing the ends is certainly going to toughen up the straw, so it's gotta also work on a CF rod.

But how about just filling the hollow CF rod with epoxy, now that has GOT to make the rod super strong.

-B!LL!

Originally Posted by Fugitive_Bill

But how about just filling the hollow CF rod with epoxy, now that has GOT to make the rod super strong.

-B!LL!

Super heavy, too!

Hi Himself'!

Granted - True Enough!! - The weight of the epoxy.

The thread that lead me here was a discussion of hollow 6mm wing CF Rod in Bixler.
With my 6mm hollow rod I actually jammed 2x2mm (or might have been 3x2mm, cant remember) solid CF rod into it.

However my Bixler goes pretty hard with 3S 2200 35-70C Nano-Tech battery, Stock Motor (no idea what KV it is) and a Master Airscrew 6x4 3-Blade prop.

It damned near goes vertical up to at least 600 ft, and I've given it heaps of load on wings (Full power loops etc) and have not folded them yet - but I guess the day will come when that comes and/or I plow it into the ground being an idiot!

But back to filling the tube with epoxy, yeah as agree on there is the weight there, but I don't think it would have an effect to where I'd even notice!
-B!

Originally Posted by Fugitive_Bill

Hi Himself'!

Granted - True Enough!! - The weight of the epoxy.

The thread that lead me here was a discussion of hollow 6mm wing CF Rod in Bixler.
With my 6mm hollow rod I actually jammed 2x2mm (or might have been 3x2mm, cant remember) solid CF rod into it.

However my Bixler goes pretty hard with 3S 2200 35-70C Nano-Tech battery, Stock Motor (no idea what KV it is) and a Master Airscrew 6x4 3-Blade prop.

It damned near goes vertical up to at least 600 ft, and I've given it heaps of load on wings (Full power loops etc) and have not folded them yet - but I guess the day will come when that comes and/or I plow it into the ground being an idiot!

But back to filling the tube with epoxy, yeah as agree on there is the weight there, but I don't think it would have an effect to where I'd even notice!
-B!

I guess I was thinking in terms of sailplanes, and you were not.

Cheers!