Monty Roberts wrote:
We've been through this before. I still think that if you properly designed
the system the water/oil cooling would result in a more efficient system.
You don't need the full 1/3 more radiator surface because the efficiency
goes up some and you can transfer more heat with less area, but I digress.
The problem is there is not enough data to size the system properly. And
size it properly you must, which involves some serious engineering. We don't
have a clue what the flow rates are, what the heat exchanger effectiveness
numbers are etc, so the conservative approach is to use a separate oil/air
radiator. Since Mazda has already developed one that works fine in the car,
it will work even better if installed properly in an airplane. I think that
for most people that is going to be the best route to take. There is enough
guess work involved in the ducting and air supply to the radiator, that you
don't need to complicate your life wondering if the oil cooler you got from
pep-boys is going to work or not. I was reading a book the other day on race
car design by Carroll Smith, who seems to write some pretty good stuff, and
doesn't pull too many punches. He had a short section on cooling. Basically
he said when it came to oil coolers, all the aftermarket stuff is pure junk.
No if ands or butts. He said he would not even put one on a race car, and if
you really want the trans in your tow vehicle to last, pull off the OEM
cooler and replace it with the real deal. He recommended a company called
Serck, located in the UK:
http://www.serckservicesmotorsport.co.uk/frm/index.htm
He also stated that the aircraft oil coolers are good, but don't work too
well at race car speeds and are very expensive. Since he was talking about
F1 and GT cars, that means speeds similar to our climb speeds. I am going to
send serck an email asking for some data. They also make radiators. I have
contacted Griffin, with the usual response of what size engine are you
using? what size is the radiator you are replacing? Well if I knew what size
to make it, I would just order it....... Oh well, If I could just talk to
the right person and get around all the proprietary mumbo jumbo.
Monty
If somebody has a minivan or pickup truck and wants a project we
could use some simple data on air flow through rad cores as a function
of air pressure. Take an old leaking junkyard rad core and band saw it down
to a one foot square. Build a plywood box around it to serve
as a intake duct. Leave the back side open and accessible. Install
the duct and core in the open side door or 10 inches over the cab with
a 2 X 4 frame. Use a simple water manometer to measure the
air pressure on the face and the back side of the of the core
in a 3 inch grid pattern. Get one of those hand held digital wind speed
meters and do a survey in a 3 inch grid pattern on the back side of the
core. Run the van or truck at several known speeds such as 70, 80,
90 and 100. Should not take long so you should be able to find a
road some place that you can get up to one hundred briefly.
This should give us some points on a curve that we can extrapolate up to
say 120 MPH. Record the air temp and altitude when you do this.
This air side data is only half of the info we need on a specific core
but it is a start.
It would take a very powerful fan indeed to get 100 MPH slip
stream. Perhaps a tied down aircraft might also do the trick
but I kind of doubt it.
The same rig can be used to test different inlet duct shapes to maximize
the air pressure on the face of the core.
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
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