>

> My analysis of air flow required for 200 hp climb

at 120 kts on a

> 95F day,

> and a very effective scoop is 65 sq.in. inlet area

- just for the

> coolantrads.  Another 25 sq. in. inlet for the oil

cooler.  This is

> more than

> typically needed for cruise, but it's a tradeoff.

>

 

Al, how do you correlate your figures with Ed's

results.  I believe he has said that the estimates

only 170Hp, but I don't think he could get away with

half the the scoop area.

 

The analysis uses the amount of heat rejected to the coolant, airspeed, the specific heat of air, and the increase in the temp of the air going through the core.  The first three of these are known quantities, so the last is really the only variable.  I assumed a 50F delta T for the air, which is conservative for an effective cooler in most conditions; except when the OAT gets up toward 100.  At 160 hp and about 80F air temp increase (say from an OAT of about 70 F) you could get by with about 30 sq. in.

 

This assumes an ideal scoop, which you may attain on the nose of an airplane where you have external diffusion (slowing) but difficult in a scoop somewhere back on the fuselage like I’m dealing with on a pusher.

 

The analysis also assumes steady-state conditions as would occur at sustained high power.  If you only need the high power for a few minutes, you get the benefit of the heat absorbing capacity of the coolant, oil, and entire engine block getting it up to max temps; but I think it makes more sense to design for sustained power. I prefer taking a conservative approach to cooling system design because experience shows that in the majority of cases of auto engine conversion there is a cooling shortfall.  And I don’t want to be stuck in Vegas on a 110F day (should I ever chose to go there) because I couldn’t take off without over heating.

 

Al