Butyrate "tauntening" Dope?

[Soarmaster]

I'm thinking someone on this forum might know. I'm considering building a replica of Octave Chanute's 1896 glider. So I'm testing coatings on frames of light cotton muslin. Chanute used "pyroxylene" and I have his formula -- and it's an outright Explosive! The modern egual would be nitro-cellulose dope (it must shrink and tighten the fabric). Well I wanted to avoid the nitro-cellulose and I purchased the minimal amount of butyrate "tauntening" dope. I've discovered that this stuff doesn't actually taunten any fabric I've tried. The coated fabric ends up more slack than before it was applied. This is Randolph Products 9701 "tauntening" butyrate dope.
Can anyone explain the "tauntening" label on this product? What am I missing?

[FlyingRon]

What fabric are you using? Tautening dope is for cotten/linen/silk. Even then there's more to it than just slapping some dope on the fabric.

[Soarmaster]

I'm using a light 100% cotton muslin(a type of weave). This is the same fabric as the original 1896 machine. I thinned the butyrate 1:1 with the correct thinner as per the directions on the Randolph products can. There is no taunting effect at all. Multiple coats have no effect. Does this stuff taunten only when used on top of nitro-cellulose dope?

[CHICAGORANDY]

IMHO if you have not already I would contact the good folks at Aircraft Spruce -877-477-7823 or https://www.aircraftspruce.com/contactus.php and get their advice.

[Airmutt]

Grade A cotton has not been manufactured for decades. It was known to have a shelf life and if improperly stored (exposed to humidity) it will never shrink and remain taut.

Butyrate dope should shrink cotton but butyrate dope with plasticizers is known as finishing dope and is non-tautening.

ACS has a good article by the late Ron Alexander on fabric. Here’s an excerpt…..
Most of the antique airplanes we will encounter were originally covered using grade A cotton fabric along with nitrate and butyrate dopes. Covering early airplanes with fabric required more work and skill than the processes that are available today. Grade A cotton was sewn in place on the airframe and then shrunk with water, which gave the cotton a moderate amount of tautness. Then several coats of clear nitrate were brushed on to fill the fabric's weave. As each coat of nitrate dope dried it shrank, pulling the fabric tighter. In other words, the shrinking dope continued to tighten the fabric.

[Soarmaster]

Thanks for the information and leads. I suspected that there was a big difference in the fabric -- then and now. The cotton cloth I'm experimenting with has almost certainly been pre-washed/pre-shrunk like all modern commercially available fabric. And that might be the entire problem.

[DaleB]

I found an interesting article here Covering a Replica with Grade A Cotton and Irish Linen (kitplanes.com) about the covering process. I was able to find a place selling Irish linen, albeit at $56 per yard. I've heard (read) that Grade A cotton is still being produced somewhere, and did find a place that carries "airplane cotton", but certainly more research and testing would be needed to determine if it's actually suitable for aircraft use.

[Soarmaster]

I'm fortunate in that I experimented with small test panels. A minimum investment. This guy in the article spent a lot of time and money discovering the same thing about the fabric on his full size project.