Model rocket engine temps.

[quigly]

I am drawing up a plan for a project, but I need some help with a few facts I can't find. First thing I need to know is the average melting point of polyurethane expanding foam? Also what temperature the outside of a model rocket engine gets? Thank you for any USEFUL info you give.

[Dr. Starch]

Wouldn't the temperature of the outside of the rocket engine depend on the metal / material used for the casing, thickness of the casing and the fuel used?

[quigly]

These are the engines I am talking about.

http://www.estesrockets.com/rockets/eng ... /1613-c6-3

Good old cardboard tube case. I am just wondering how thick of a casing I need to protect the foam from the heat of the engine.

[Jester316]

They get very hot. And that's touching them after they've flown/fallen/sat till I found it.

[Eyes On]

The sides of the motor case don't get hot enough to burn something like very dry grass, but they CAN get hot enough to blister skin. The hot parts are the nozzle and face. When burning, the nozzle can reach temperatures in excess of 1800F. Other engines can reach +3000F at peak. This is why you generally insulate model rockets using anything over an "A" with a burn time greater than 1 second. In model rocket kits the tube is generally insulated. If you are doing a DIY kit I suggest a layer of fiberglass cloth around the inside of the engine area. It doesn't need to be perfect.

The melting point of the foam depends specifically on the chemistry of the brand you are using. Household stuff would probably melt in or around the 200F mark and combust at ~400. We used a formula (a very expensive formula) in the armor business which wouldn't budge until the heat had reached 2500F. I don't know if that stuff is available outside of the aerospace industry, but you'd be looking at $85 per quart for part 1, and $60 per pint for part 2. You get something like 3^3ft if you simply let it freely flow and dry.