Put a P51 scoop on it. You can buy these beauties off the
shelf
as hood scoops from the Hot Rod industry.
Paul Lamar
Ok, Groupmates (groupies?) (hmmm...guys and Chrissie?)...
How's about a P-51 scoop feeding a proper diffuser, stacked air
and
oil
cooler, exit flap, but with a twist? Feed the exhaust into the rear
of
the
scoop where, when the flap is 'closed', the exhaust-powered
augmenter
does
it's thing to move air (no cooling fan in front of the canards to
push
air
thru...)?
What info is available on sizing and shaping the scoop inlet,
and
properly proportioning the exit flap?
Andy
Very early rotary E-Racer without a submerged inlet...
We got lots on scoops and diffusers but no data on exhaust powered
augmenters.
You will need an inlet area about 20% of the rad area and an outlet
area
at least
twice the inlet area. Won't hurt to make it three times with cowl
flaps.
The diffuser should look like a bell but a simple wedge also works.
BTW make sure the red hot exhaust pipe does not radiate heat to the
radiator
as that will defeat the purpose. Ever been around an infra red sun
lamp?
Paul Lamar
Andy,
Check out NACA report 818. Also do a search for ejector on the NACA
online
library. Lots of work on ejectors in the late 30's and early 40's. I am
in
the process of analyzing the same installation. Preliminary numbers are
not
exactly favorable. Looks like you can expect to get about 1" of water
delta
P from the augmentor. This is because the cooling air flow to exhaust
flow
ratio is about 13. About the minimum to even get any effect from the
augmentor. To do better you need a ratio closer to 7-8. At these flow
ratios
a delta P of 4-5 in water is not impossible, totally eliminating the
need
for cowl flaps. This works much better on air cooled engines because the
metal is hotter, so you need less cooling airflow and can have a more
effective ejector. This being said, if the radiator is optimized and has
a
min pressure drop, plus a good inlet and exit, it is possible to
generate
some thrust, or at least minimize cooling drag. Plus you get ground
cooling
as a plus. To be honest, I'm not sure that it is worth the hassle of the
hot
plumbing in the cowl, and the extra weight etc. But I remain hopeful
that
when I dig a little deeper I will find out otherwise.
Monty
Here is a summary for one of many studies. Getting this to work well could
be a long R&D process. I don't recommend messing with it. Just use a P51
scoop and conventional cowl flaps until after you get your airplane
flying and cooling properly. You will have enough problems without
asking for more trouble.
Paul Lamar
I agree Paul. The one thing that I have issue with in the paper you posted
is that a lot of the cooling benefit could have come from simply cleaning up
the back of the engine from it's original configuration (i.e. big stacks and
collector ring behind the cyl. and in the way of the air flow). Therefore it
really doesn't give a good Idea of the effectiveness of the ejector. I tend
to a agree that it is probably more trouble than it is worth. I started out
trying to figure out how to make an ejector work, but the difference is
really only a small amount of thrust hp. The big advantage is ground cooling
on a pusher. I really think that it would be much more beneficial to the air
cooled guys than to us. They could actually get some thrust out of the
thing. I would use a downdraft scheme into two ejectors out of the rear cowl
and forget about the scoop on the bottom. If it were an EZ I would put the
scoops on the cowl cheeks so that there was no increase in frontal area. The
air would come in and feed down over the cyl. like it is supposed to. and be
drawn out through the ejectors in the back.
Liquid cooling is a different beast entirely. The radiator is at a lower
temp and the cooling airflow is greater. I'm really starting to doubt the
myth about the P-51, and liquid cooling in general having less drag. More
than likely, it was the reduction in frontal area over the radial planes
that gave the P-51 it's lower drag not the mythical scoop. The main benefit
of liquid cooling is you have a little more flexibility in the placement of
the inlets and outlets. Fuel consumption is better, but I'm not sure that it
would be on a rotary without valves and the need for inner cooling using
excess fuel. Disadvantages: The radiator is huge and takes up a lot of
space, plus there is plumbing to deal with, You need more airflow because
the delta T is less. The coolant is HEAVY. There is the overheat instability
problem. Too bad it's so hard to air cool a rotary. Maybe you could air cool
the rotor housings and oil cool the rotors and side housings. Where is that
person with a billion dollars for development work and a passion for
affordable general aviation engines I keep dreaming about? ;-)
Monty
Right on Monty.
Paul Lamar
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