Prepreg for fin layup?

[caruolo]

Hello,

What are you guys' thoughts on using prepreg as the layup material for T2T?

My concern is that since there is already the optimal ratio of resin in the fiber matrix, it does not leave much adhesive for bonding to the air frame and fin surfaces.
In addition, do you guys think that the fin/air frame can handle 300 deg Fahrenheit for curing the prepreg? They were obtained from RocketryWarehouse.

Let me know what you guys think!

Thanks!
Alexis

 

[flynfrog]

It works great if you know how to use it and have the oven and vacuum pump. Temp to 300 is doable but there about a million prepregs out there. Will the rest of your airframe take the heat to post cure to 300F if you feel its needed RW doesnt post what resin they use or what temp its good for if I had to guess id guess its probably a 250 F system. My L3 you saw at blackrock had prepreg t2t fins.

 

[watheyak]

I am in the middle of a build using prepreg here-

https://www.rocketryforum.com/showt...rame-build-for-the-Loki-54-4000-Fins-Attached

Tip to tip wont happen for a few months but prepreg will be the material. The same prepreg I have was used in a large 2-stage project last year which had many layers of tip to tip and it worked great. Prepregs are usually meant to be used in an autoclave, but if you can find one with decent resin flow it will work with just in an oven and a vacuum bagging setup. Flynfrog would probably know more about the varieties. I just lucked out with mine. I have not had any issue with bonding.

Also keep in mind that the bond quality of the tip to tip is vitally important. Someone's project a while back had a whole section of it blown off in flight. A dry layup without much resin could contribute to that scenario. The age of the prepreg is also a factor. Someone in my club a few was given some old prepreg and after cure it just peeled apart. Mine is pretty old, but luckily it still works great. Your mileage may vary, of course.

 

[Reinhard]

What are you guys' thoughts on using prepreg as the layup material for T2T?
My concern is that since there is already the optimal ratio of resin in the fiber matrix, it does not leave much adhesive for bonding to the air frame and fin surfaces.

You can use epoxy film adhesive to provide some extra resin. These films are usually used in conjunction with foam or honeycomb cores. Those have "rougher" surfaces though, so I'm not sure if additional epoxy is needed as much in a T2T application.

Here is an example of a fin can involving above mentioned films (about half way down, the black surface without the carbon weave).
https://spaceteam.at/rockets/str-03-black-bird-cspace-2013/moulding-a-fincan/


Reinhard

 

[mpitfield]

My first layup was not under vacuum. I purposely did this to get a basic feel for the difference.

I then jumped right into layups under vacuum, but using a vacuum generator and a compressor, as I thought I was saving some money. However I found the process not very enjoyable. So I decided to invest a bit and build a vacuum pump that provided a much higher level of control. This made the experience that much more enjoyable and I have worked out some issues along the way, such as better bagging methods and posted a thread on vacuum bag connectors. Overall I have now done under a dozen T2T layups which is still relatively little experience in the grand scheme of things as it was done using the same resin and 3K 2x2 twill cloth.

This is a personal thing and I selected this approach based on my personal leaning style and available resources. I am slowly stepping my way towards a pre-preg and heat-box setup.

However there is nothing stopping anyone from going directly there. It is a personal choice that you have to be comfortable with and so long as you have the hardware, consumables, a bit of knowledge and hopefully some guidance to save yourself repeating so basic issues, you should be good. Worst case is you try, fail, and learn something along the way.

Beyond that I have nothing to add except, do a search on Jim Jarvis, and good luck. Please post your experiences along the way.

 

[watheyak]

Here is an example of a fin can involving above mentioned films (about half way down, the black surface without the carbon weave).
https://spaceteam.at/rockets/str-03-black-bird-cspace-2013/moulding-a-fincan/


Reinhard

That's an inspiring bit of work you linked, Reinhard. Thanks for sharing.