Dick Gregory wrote:

What I was concerned about with the downdraft was that the nosewheel

would

kick up a pebble and aim it directly at the input scoop. With the

radiator

unprotected would it be susceptible to damage?

Perry Mick wrote:

That's possible I suppose. I've had a couple small hits on my prop.
I switched to a slick tire on the nose wheel, a recommendation of
George Graham.  Also, I started putting the landing brake down while
taxiing.  The inlet lip and ducting is about 6 inches deep before the
radiator, hopefully the pebble will hit the sides of the ducting and
loose energy.  When you pull an oil cooler out of an RX-7, they
are usually full of small stones, because the oil cooler is mounted so
low.  The stones get in the "fins" and cause a loss of airflow, but
don't
damage the oil passages.

You guys are giving me lots of good information. I have been watching

this

list now for about 4 months and have lots of the messages and pictures

saved

on my hard drive.

Perry, could your 3X5 inlet be too small for the oil cooler? It seems

like a

rule of thumb I have seen states 25 percent of the radiator area which

I

think would be more like 25 square inches. Based on your experience I

think

I will make mine about 4X6.

It's possible, my previous inlet was an armpit, slightly larger in area,
but
probably had more boundary layer.  Good idea to make it larger.

I'm also fiddling with the idea to put a fan in a short parallel duct

with a

swinging door. When on the ground the fan would run and keep the door

open

and supply air to the cooler. In the air the fan would be shut off and

the

air from the inlet would keep the door closed.

I hope this doesn't get reformatted too badly. This is a top view with

the

front to the left. The fan branch would be inside the firewall line,

inboard

from the main branch, and level with it.
          ___________
         /    fan >  \
   _____/   ______    \______
                  \
          door open\
   __________________________

Dick Gregory
LongEZ N613NC

Good idea but there's very little room!

--
Perry J. Mick
Duckt N7XR
http://www.ductedfan.com

In theory the airflow going through the rad is much reduced so
a screen like square hardware wire directly in front of and in 
contact with the rad should protect from large stones. I would 
not use mosquito screen however. 

Try it with and with out on the same day to check for 
affect on cooling.

Paul Lamar
 
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