A different 3" spar tape - usable?

[Voidhawk9]

I have bought some 3" uni tape from France, believed to have been intended for someone's canard project, but never used. It is a bit different to the 'usual' heavy stuff.  See photo for side-by-side comparison.

 

I have enough of the usual tape for a canard, and enough of the lighter tape for an entire cozy (estimated by weight).

There are more cross-threads, and they do not seem to be readily removeable.

Obviously being a lighter / thinner tape, I'd need more layers to fill the troughs.

 

Can anyone advise on whether this tape is a good substitute? Perhaps this stuff has been used by some Cosy Classic builders?

Edited March 4, 2018 by Voidhawk9

[Kent Ashton]

Hmm,  I would guess the tape on the left is usable but it does not look like it was woven so as allow removal of the crossthreads.  The tape on the right is more desirable because you can snip the tiny red thread and remove the crossthreads.  That gives you a tighter pack in the spar trough and straight fibers resist buckling better.    Hard to say (for me) if the left tape would make a big difference but these airplanes are slightly stronger than needed so maybe it doesn't matter.  

[Marc Zeitlin]

I have bought some 3" uni tape from France, believed to have been intended for someone's canard project, but never used. It is a bit different to the 'usual' heavy stuff....

Can anyone advise on whether this tape is a good substitute? Perhaps this stuff has been used by some Cosy Classic builders?

You have some random material that you think might have been intended for an airplane but you don't know. It's not the same as the approved material. You don't know what it is, you don't know it's properties, you don't know whether they compare well to the material that's supposed to be used, you don't know if it's got a different finish, you don't know if it's ever been wet, and you want to know if you should use it for the single most important structural component of a device you're going to lift your family to 10K ft above the surface of the earth within. Could it work? Sure. And you could use hardware store bolts instead of AN bolts, and elmer's glue instead of epoxy. This is kind of that, unless you can determine what the properties of the material you've got a roll of are.

 

The total cost for the approved material (not counting shipping) at $1.85/yd for the 282 yds needed for the COZY MKIV, with a 50% margin for extra and losses, is $782.55.

 

I think you can discern what my recommendation would be.

[Voidhawk9]

Right - that's why I'm hoping someone will recognize it and enlighten me as to its properties. Otherwise it will not be going into my aircraft.

It is in good condition, I removed it's original packaging myself, unfortunately no useful information was on it.

[Marc Zeitlin]

Right - that's why I'm hoping someone will recognize it and enlighten me as to its properties. Otherwise it will not be going into my aircraft.

It is in good condition, I removed it's original packaging myself, unfortunately no useful information was on it.

There is no way to "recognize" it from an on-line pic, and the analysis required to determine what it actually is would cost more than just buying the right stuff... I'm glad that you won't use it unless you get proof of its acceptability.

[Voidhawk9]

>One year later<

I corresponded some months ago with a French supplier, and found where you can still buy the same tape, albeit not at 3" (75mm) wide: UD E glass cloth 600 g/m²

Last week I laid up two test pieces to do a relative test between the plans spar tape from ACS, and this 'alternative spar tape'. Photos below.

They are basically identical samples, 3 plies of the plans tape 12" long, and an equivalent weight of alternative tape, which ended up as about 5.5 plies (the half cut full-length, half width).

They were laid up side-by-side (with dams, 3" apart) with the same batch of epoxy. You will see some waviness on the bottom, from the plastic ripples underneath. Both samples have similar ripples.

I cured for 3 days, the last day or so in my hot box to ensure they were thoroughly cured.

The samples are the same size and thickness, to within a small fraction of a millimetre. The alternative sample came out 16% heavier, probably largely a result of retaining the cross-threads (not removable) while the plans sample cross threads were removed per plans.

Then I tried a stress test to see if there was any difference between the two. I clamped 50mm of one end to the bench, then clamped a bucket with various weights to the other end. I didn't measure the weights, only the deflection of each with the same weights applied for a relative comparison.

The alternative sample deflected an average of 51% as much as the plans sample! This really surprised me. HALF the deflection?!

I bent both samples about 120deg (using clamps, too much force required to do by hand and / or didn't want to be that close in case one failed!), neither had any problem with that as far as I can tell (no cracking noises either) except that they did twist a bit, thus the longitudinal cracks in the plans sample.

 

Any ideas on other tests I could do with basic workshop equipment?

Any ideas why the alternative sample was so much stiffer? I'm thinking maybe the fibre density was higher as the many smaller bundles are held together tightly by the cross-threads.

 

Anyway, interesting results so far.

 

[Kent Ashton]

Yes, very interesting but I am surprised that the same weight of tape in both samples used 16% more epoxy in the Frence tapes.  Cross threads in the French tapes might be making more voids that fill with epoxy.  Cutting the weight of French tapes by 16% results in 4.62 layers.  I'd be interested to see if 4.5 to 5 layers of the French tape gives a similar weight and stiffness as the old tapes.  (picture irrelevant but I couldn't remove it.)