I did a graphic this morning on various rad configurations
and their pros and cons.
Here it is. I am open to comments.
Paul Lamar
Opps. I forgot two drawbacks to the evap core cases.
Here it is again corrected.
Paul Lamar
Hi Paul,
Great drawings of the different radiator configurations. No question
that the evaporator cores have their drawbacks and I can't think of any
thing to add to your list. However, one advantage they have is that they are
cheaper than a custom made radiator. Since, I cured my oil cooling problem
(ditching the EARL cooling and installing the stock one under the spinner)
my cooling problems have gone away (at least at current power production of
the engine). Temps do climb on a high power climb out on a hot day, but
stay within temp limits. However, I suspect that if I put a turbocharger on
it and produced 40 more HP that my current cooling system capability would
probably be stressed in a max power climb.
Too soon to say about how well the some of the configurations will actually
cool - no one is flying with them to the best of my knowledge. Chuck Dunlap
comes closest with his under the engine radiator but (as I know you know)
his current configuration has some cowl airflow problems as I last saw it.
I know that Powersport had quit a time trying to get their under-the\-engine
radiator to cool their engine. I have since heard that they have solved
their cooling problem - do you have any info on what they did to solve the
problem? or what there problem might have been? I think I recall someone on
the list saying they had increased their coolant flow to around 50 gpm - was
that the solution?.
Power Sport never had the rad under the engine to my knowledge.
It has been behind the engine next to the firewall for the last
three years at OSH. I have seen nothing on it or about it since
Oshkosh. In any case knowing what I know now about walls behind
rads it will never work until they put the rad someplace else.
Dave Atkins has been
flying with a rad under the engine for at least five years.
The air comes into the cowl and flows down through the rad
and out the back of the bottom of the cowl.
It would work better if it had a proper duct feeding it
cool air instead of merely attempting to pressurize the cowl
with all the sources of heat contained therein. The exit
duct could also be improved by placing louvers on the bottom
of the cowl below his current rad.
Dave has his oil cooler working pretty good mounted vertically
next to the cowl on the right (cool) side of the engine. There are
louvers on the side of the cowl allowing the oil cooler air
to exit. Those louvers could be made more
free flowing further improving Dave's oil cooling.
Here are the only hypothetical potential hiccups about the side mounted
and under engine mount with Louvers that I could think of. As I recall
that someone speculated that louvers might not make a good hot air exit
close behind radiator for two reasons (as best I recall).
1. Each louver tends to block the louver behind it limiting the pressure
drop (and therefor effectiveness) of subsequent louvers. (The system with
the louvers increasing in size as you go rearward may made this point moot)
Jerry and I will explore this next month with our test rig on the
Dodge Caravan. I suspect the differences will be less than one inch of
water from front to back based on what I saw with my test rig. The
big advantage of louvers are they are totally open to whatever ambient
air pressure is surrounding the aircraft.
2. Perhaps more significantly (if I understood what I read) is that
supposedly for minimum cooling drag to occur the exiting airflow needs to be
accelerated to match the air velocity of the outside airstream. I just
wonder whether there is sufficient space/distance between exiting the
radiator and reaching the louver for the air to accelerate to airstream
velocity for min drag (or perhaps we don't care as long as it cools).
Good question. At 200 MPH it would be very difficult to measure
I am sure.
Anyhow, those are my comments for your consideration. Currently still
waiting on delivery of my prototyping PIC board. I did find the
CircuitCellar Magazine articles on the 18F252 on-line and got copies of the
articles, thanks.
Best Regards
Ed Anderson
I don't think the cost issue is all that important. One can buy
a suitable all aluminum car racing rad for $200 from Summit Racing.
I suspect Tracy's airplane would be a lot faster if
he had smaller cowl openings. I suspect they are currently
affecting his prop efficiency. IMHO he should be going faster
than 214 MPH with 180 HP. I think the potential of his airplane
with a lower drag cooling system should be more like 220 to 230
MPH. Since the ducts feeding the evap cores must be short out
of necessity it is probably necessary for the openings to be
larger than normal. This I think is the main draw back to evap
cores mounted in that position. If you study this chart it
becomes obvious that the length of a proper diffuser needs
to be about five times the height of the evap core. y/Yb =1
Height = 2 X Yb. That would make the diffuser length about 50 inches
long. Obviously that is not going to fit in a cowl.
Kays & London came up with the answer using the wedge
shaped diffuser. Evap cores might work fine with wedge
shaped diffusers if the back of the evap core was allowed
to be open directly to the sides of the cowl using louvers.
Having it face the engine is a loser as impact pressure
would build on the engine and restrict flow through the core.
I can't help but think evap cores might work well vertically mounted
under the engine to get enough length ahead of them to form a proper
diffuser inlet duct. It would take an airplane with a deep cowl or a
willingness to let them hang down below the cowl much like a P40.
Paul Lamar
"That would make the diffuser length about 50 inches
long. Obviously that is not going to fit in a cowl."
Correction that should be 25 inches and not 50 inches.
The x coordinate is 2.5 times Yb and not 2.5 times 2 times Yb.
Still won't fit in the cowl unless the evap cores
are moved to the rear as suggested in the last paragraph.
Paul Lamar
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