Monty Roberts wrote:

Well......

It was raining and cold today, so rather than work on the house (don't tell my wife ;-) I decided to finally dig into the thermo of the cooling system. I assumed a 200 hp 13 B at 6500 rpm and a heat exchanger effectiveness of .8. I spent the whole day crawling through heat exchanger and propulsion theory. I assumed a best case everything (except heat exchanger effectiveness) and got the following chart. This is the absolute BEST that you could possibly do if everything were ideal, which it will not be. More accurate numbers require heat exchanger data (which for water/air you have to really try to make it bad). The chart shows what would happen if you could recover all of the energy in the coolant, oil, and exhaust and convert it to cooling air exit velocity at ambient pressure. Below 200 mph it is useless, don't waste your time. If you are going 250+ you might see some gain. If you are Dave Garber, it could buy you an edge. It MIGHT be worth it on a fast EZ or E-racer. For the P51 it could help (400 mph) but the P51 did not use the exhaust heat this effectively. This chart is for sea level standard air. At altitude the effect would increase because the speed of sound decreases (How much? don't know yet, ask me next week). This data includes compressibility effects. You are looking at the Meredith Effect for our power levels and speeds. Not exactly awe inspiring.

Monty

Monty could you print that chart as a gif with a screen capture program?
Here is something out of Hoerner that you might also find interesting.

Paul Lamar
 
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