New way to straighten warped plywood fins.

[John Taylor]

I just completed a HP build of a 4" Phoenix Missle. It is paper and plywood construction.
The forward fins are 1/8" thick plywood are kinda long and short.
They were slightly warped which is not unusual to expect.
I've heard of methods such as wetting and stacking between heavy flat objects like books and leave it until dry.
Messing around I sprayed 99% iso alchohol on both sides of the part and then using both hands flexed the part the opposite way from the warp. I held it for one or two minutes or until all the alchohol evaporates.
After working with the warped fins for about two minutes they were straight. They actually stayed that way permanently straightening the wood.
I imagine the alchohol wicks into the wood quickly loosening the fibers and the quickly wicks out and evaporating out of the wood setting it. By flexing it while it is wet and holding it until dry it will permanently correct the warpage. It works perfectly.

 

[bjphoenix]

That's interesting, I'll have to try that.
Some years back I used some warped plywood for fins. I too tried to wet them and clamp them between straight boards but that only helped a little bit. I made a fin jig that would clamp the fins between 2 straight pieces of wood while they were being glued to the airframe. Once the root edges were held straight, the fins came out straight.

 

[lakeroadster]

The Fin Whisperer.....

 

[KenECoyote]

The Fin Whisperer.....

The "Fin-agler"

 

[SDramstad]

When done they are Fin-ished

 

[John Taylor]

I just completed a HP build of a 4" Phoenix Missle. It is paper and plywood construction.
The forward fins are 1/8" thick plywood are kinda long and short.
They were slightly warped which is not unusual to expect.
I've heard of methods such as wetting and stacking between heavy flat objects like books and leave it until dry.
Messing around I sprayed 99% iso alchohol on both sides of the part and then using both hands flexed the part the opposite way from the warp. I held it for one or two minutes or until all the alchohol evaporates.
After working with the warped fins for about two minutes they were straight. They actually stayed that way permanently straightening the wood.
I imagine the alchohol wicks into the wood quickly loosening the fibers and the quickly wicks out and evaporating out of the wood setting it. By flexing it while it is wet and holding it until dry it will permanently correct the warpage. It works perfectly.View attachment 529243

 

[John Taylor]

Just an update to my post regarding straightening plywood fins using 98%
alchohol.
Well after all this time and flights the fins are STILL perfectly straight!! I am amazed. This actually works!

 

[bcook7135]

Tried with 70%. Did not work.

 

[Funkworks]

Just an update to my post regarding straightening plywood fins using 98% alchohol.
Well after all this time and flights the fins are STILL perfectly straight!! I am amazed. This actually works!

That's fincredible! What a fintastic finvention!

 

[neil_w]

I keep reading the thread title as a news headline about a new service to be provided by New Way Space Models. ¯\_(ツ)_/¯

Anyway, I am curious to try this with balsa and/or basswood. Water takes a long enough time to dry that it's impractical to hand-hold it the whole time.

 

[bcook7135]

Does it need to be 98%?

 

[John Taylor]

Tried with 70%. Did not work.

With 70% you have 30% water. The water will soak the fibers and stay there for a long time. The alcohol evaporates quickly. When wet the fibers loosen up a little. Wetting the thin plywood and holding it in shape it will stay that shape if the liquid evaporates quickly. The 99% alchohol will evaporate quick enough that you can hold it long enough to set it.

 

[John Taylor]

Does it need to be 98%?

98 or 99% will work. The lesser ones contain water that will not evaporate quick enough

 

[bcook7135]

Interesting. Thanks. Now to find 98 or 99% alcohol