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On Monday, April 4, 2005, at 07:23 PM, Ernest Christley wrote:
Al Gietzen wrote:
Doug;
I agree with your ‘rule-of-thumb’ numbers. My analysis came up with coolant inlet area in sq. in. of 1/3 the HP (.33) for climb out on a 90F day. It assumes a 120kt climb speed for my Velocity. I used 45% of that additional for the oil cooler. Assumes scoop efficiencies of 85% or better.
Al
snip
Second, even if cooling can get out, if it can't get in, it can't be there to cool the heat exchangers. Rule of thumb: 0.3 sq. in. of cowling inlet air opening per HP. 200 HP x .3 = 60 sq. in. Note: This assumes a reasonably shaped inlet cowl which has been discussed online often. IMHO: Berni's plane inlet shape and inlet cowl is fine, but I question his inlet opening _area_.
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Don't mean to start another stream of threads on an old subject, but we sweated over this one for 3 months and 3 systems and one might save a lot of time by comparing ones system to these simple "works great" rules of thumb which are the result of LOTS of technical and experimental work.
Doug Dempsey
N6415Q and RV7 in process
Colorado, USA
Don't won't do demean or dismiss your experimental work in any way, but Ed is running with half the inlet area, and unless something has changed with his new found power, he'd doing just fine. Just to be sure that we're all talking apples, I can confidently quote him at 28 in^2 inlet for coolant, which I believe is half of what you recommend above. Reality isn't meeting theory at eye level here, and everyone will be much better off if we know why.
-- This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."
Exactly the point I have been making for a long time. The formulas that determine intake size cannot be right because we have examples of systems functioning well enough with much smaller inlets. In fact, for most of us, if the inlet size rule was not violated, we would have to go back to air cooled engines because there is simply not enough room for the intake let alone the even larger outlet.
Ian apparently was able to cool his engine in a very hot environment (Australia) using two evap coolers of only a core volume total of 400 sq in. The rads were perpendicular to the air flow just behind the cheek inlets and the ducting looked well designed in the photos. This establishes a minimum size that we know works that is far smaller than the formulas call for.
With our airspeeds almost never below 100 mph, we have so much cool air available that smaller inlets and radiators have proven to be adequate. The real issue is duct design.
Jerry
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