On 2 Sep 2004 13:38:49 -0700, (Dan Thomas)
wrote:

You might consider some device to control rad airflow, as there is
usually too much flow at cruise and it just costs speed.

You just described the anomaly that has dogged aircraft cooling
systems ever since they were first designed. If you size the cooler
and ductwork for effective cooling on the ground and in high
temperature situations, you end up with a system that has more cooling
capacity than necessary for high speed or cruise operations.

Variable outlets seemed to be the best solution but many certified GA
planes design for the worst case scenario (large inlets and no
variable outlets) and pay the cost of relatively high cooling drag at
cruise.

In my case, it really wouldn't matter much if I had the entire
airplane plumbed for underskin radiators that contributed no drag at
all, the thing just isn't going to be a fast cruiser because of the
initial design. It's a strut braced, high wing monoplane with a
really big, high lift wing.

While the designer of the Christavia (Ron Mason) worked very hard to
produce an airfoil that has both high lift and high speed cruise, the
"high speed cruise" should be considered relative. High speed to Ron
meant over 120 mph. The airfoil has a bit of concavity along the
bottom. It isn't flat, it's beyond flat, slightly. You don't see
airfoils like that on high speed airplanes, but it produces a LOT of
lift. One of those many compromises that go into airplane design.

Even though I won't see much in cooling drag reduction (or rather even
though I should see some cooling drag reduction, it likely will not
manifest itself with much increase in cruise speed), it's still worth
it to me to procede with the design for reasons of cooling efficiency.
If this works as planned, I should never have to worry about
overheating on the ground during long holds at any temperature.
Climbing for long periods in hot weather also should not bother
because the higher the power output from the engine, the greater the
volume of exhaust pulses. The greater the volume of exhaust pulses,
the more the air flows through the system... in theory.

In keeping with my building maxim of not attempting anything that has
not already been tried and proven, so that I don't have to rebuild if
it does not work (and besides I'm not an engineer), this is one of
those things that **should not** cause much anxiety. The radiator,
while seemingly small, is large enough to cool the engine (180 to 200
hp) all by itself, given proper duct design. I'm also utilizing a
Modine oil cooler (common with the Ford V6 conversion), which helps
with the cooling chores. The Modine cooler is more properly called an
oil temperature conditioner in that the coolant lines are plumbed
through it, rather than air flow.

My initial engine runs will be conducted using the radiator that the
engine used while in Ford cars, unfortunately. This is because I feel
I have to test the engine extensively on the ground, and fabricated a
mobile engine test stand with which to do this. I don't want to have
to fabricate two cooling cooling systems as just doing the one for the
Christavia will take time enough.

For the engine testing, I just need to make sure that the engine is
viable and will handle full and cruise power for extended periods. I
will need to be able to winch the test stand into the back of my
pickup and drive up into the woods for the extended running periods so
I don't disturb the neighbors. I do have neighbors, even though I
live in rural Vermont surrounded by hills and woods. Well, one or two
anyway. ;-)

Corky Scott