I used a high build primer and then a battleship grey single stage paint. Any light color should work.
Ross Scroggs
RV4. #3911
Paint and finishing stage
I want to paint the inside of the top cowl. What type of paint should I use?
I think a lighter color will help see any oil or fuel drops that might come up.
Ross Scroggs
It also absorbs less heat than a dark color.
Carl
Kirchhoff's Law (of Radiation). An extension of the second law of thermo, IIRC.
Simplified, bodies emit and absorb radiation at the same rate. In general for applications: if you're trying to protect something from heat, white surfaces work better. If you're trying to shed heat, black surfaces work better.
Same referenced physicist has some electrical laws named after him as well. Quite the intellectual stud.
Regarding the origin of the common reference of electronics boxes to "black boxes", many/most think it came came about from the perceived mysterious inner workings of such. They were coated black (and kept away from radiant energy) to help them shed heat. The name stuck.
So, your fiberglass should be white and your cylinders black (if coated). There is your semi-worthless stuff for the day
thats not the physics. the color of the paint has little to do with heat dissipation. true, a light color will reflect more radiant heat than a dark color, thats why you paint the exterior a light color. the problem is the inside of the cowl is not dealing with radiant energy in the visible spectrum. its is dealing with the energy radiated from the heat source ie the engine. that energy is in the IR specturm. when they talk about black bodies in heat transfer they are not talking about color in the visible spectrum. they are talking about the IR spectrum, snow is actually black in the IR spectrum. take light out of the equation, as inside the cowl, the color has really no effect on heat dissipation. now, yes you will see oil on a light color better, thats why i painted mine light gray.
bob burns
RV-4
N82RB
Kirchhoff's Law (of Radiation). An extension of the second law of thermo, IIRC.
Simplified, bodies emit and absorb radiation at the same rate. In general for applications: if you're trying to protect something from heat, white surfaces work better. If you're trying to shed heat, black surfaces work better.
Our engines don't shed a significant fraction of energy through photons. Most of it leaves by convection, i.e. contact with air molecules passing between the fins. This process is not affected by the color of the engine. Also, the photons emitted by the fins simply get reabsorbed by the opposing fin surface.
Most of the photons that want to melt your cowl come from the exhaust pipes, which are significantly hotter than the engine (remember, fourth power of T). That's why a radiative barrier is the best way to keep the heat off the cowl: a piece of sheet metal in between that catches those photons and is kept at a much lower temperature through convective cooling. Infrared emissivity of visibly white or visibly black paint doesn't make that much difference to cowl temperature. That paint is for ease of cleanup only. Any epoxy will do.
Rhino 9700 works well. ACS sells it or you can buy dirrect from Rhino. It's what the composite guys use to seal their tanks.
https://coatings.rhinolinings.com/p.../rhino-9700-thixotropic-epoxy-coating/144/167
Most of it leaves by convection, i.e. contact with air molecules passing between the fins. This process is not affected by the color of the engine. Also, the photons emitted by the fins simply get reabsorbed by the opposing fin surface.