CF tuned exhaust for a racing RC plane

[Nesikachad]

I have a radio controlled pylon plane with an engine I've invested quite a bit of time into. It's currently running a fairly well spiked blend of nitromethane and methanol (60%)

I'm trying to reduce weight and drag on the plane. I'd like to run my exhaust inside the plane. I've done this with other models using AL tuned systems however the temps inside the fuse get high and the electronics, batteries, and fuel all pay the price.

I'm hoping CF will be less enthusiastic about convecting heat than AL is.

Any suggestions are appreciated. I own a full CNC machine shop and have surface modeled the molds already. Hoping to use cheap hardwood to machine the halves, wet a sock/tube, and bladder to shape.

Thanks.

Chad

 

[blakmax]

The biggest problem you will have is called the glass transition temperature for the resin. That is the temperature at which the resin goes from a relatively hard glassy material into a weak rubbery material. Exceed that temperature and your exhaust would possibly collapse or at best distort. Given your comments on the heat transferred from al tubes, I think it would be extremely difficult to find a suitable resin.

Regards

Blakmax

 

[cpinz]

There are ceramic based coatings usually applied in the firewalls of light composites airplanes. You can brush or spray them; check if your structure must be flame resistant or heat resistant.

Regards
Cpinz

 

[MikeHalloran]

You might want to try messing with phenolic resin. As the cured resin is heated to extremes, it decomposes to carbon without getting soft.

It's a little different from epoxy or polyester to work with. It has to be baked to cure. Not at extreme temperature; any oven will do. But it has a weird cure cycle; you have to ramp up and let it dwell for a while at 160F or so, while water oozes out, then ramp it up some more for full cure. (The water is a reaction product; you can't prevent it.) The water will form voids if you don't remove it from the layup somehow. Wait, it gets better; as that water evolution proceeds, the resin itself transitions from sticky to runny to gelatinous.

The other odd thing about phenolic is the cured color; an opaque, ugly, coral pink. You'll probably want to add carbon black to the mix.


Mike Halloran
Pembroke Pines, FL, USA