Jerry Hey wrote:

The factors that effect cooling are surface area of the rad, the capacity of the rad and the air flow through it. It would seem that for any given capacity, the larger the surface area the better. Perhaps not. In talking with C & R, it is clear that experience has taught them that air flow is the major issue. The Winston Cup rads that they build are 4 to 5.5 inches thick and are very efficient because they have figured out how to get air through them. Quote from C & R today, " bigger is not necessarily better".)

Perhaps we have given core thinness too much importance. Air moving through the rad is the BIG STICK as Paul has pointed this out at least a couple of hundred times and C & R concurs. Just about every Sunday you can watch WC cars making lap after lap with their inlets mostly covered with duct tape which testifies to the efficiency they can get out of thick radiators.

ACCORDING TO C & R THICK RADIATORS GAIN EFFICIENCY AS THE SPEED OF THE AIR STREAM INCREASES BUT THIN RADIATORS ACTUALLY LOSE EFFICIENCY AT HIGHER SPEEDS. I find this hard to understand but if a given mass of air has the ability to remove a certain amount of heat, it still requires contact time with the cooling fins to do so. Maybe that is part of the story. Big area thin rads for slow moving vehicles and small area thick rads for fast moving vehicles. Is this a formula we can believe? Probably. Since it is proven every Sunday on the race track.

At Daytona the WC cars use 4 inch thick rads and that is what one tech person at C & R recommends for aircraft running above 150 mph. While they could not easily produce the data for me today, they derived it through extensive wind tunnel testing and seem confident of the rock on which they stand. Of course, every other sentence was a warning that it all depended on the "installation."

A 4" x 12" x 12" is roughly equivalent in capacity to my 13" x 18" x 2.5" but a whole lot easier to find a place for. A little
4" x 14" x 14" would handle a turbo!!!

what do you all think? Jerry

"It is good to make things simple, but not too simple." Albert Einstein

The pressure available to force air through the rad at 150 MPH is twice as 
high as it is at 100 MPH. We need to cool at 100 MPH climb. If it cools at
climb (full power slow speed) it will cool at cruise (moderate power medium speed).

Daytona speeds are 200 MPH or above where the pressure is four times
higher than it is at 100 MPH. Not a whole lot of people are making 4 inch
thick rads. Perhaps they are trying to sell expensive rads into a exclusive market
of their own making :)

The NASCAR race car rad ducts I have seen are really bad news. No bell
shapes in sight. The air must exit into the high pressure engine compartment
as no exit ducts are allowed. Furthermore the engine is right behind
the vertical rad. All and all a really terrible example of proper cooling design.

One reason they use tape to block off the air to the rad is to lower
the pressure under the hood which causes lift on the front of the car.

BTW the RX8 has a laid down rad at about a 45 degree angle. Perfect
for a top of the hood exit duct. I am thinking of going in to business
making carbon fiber hoods with a proper rad air exit duct for RX8s :)

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.  Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/            
Copyright 1998-2002 All world wide rights reserved.