Ed Anderson wrote:

Hi Paul,

    You asked about the new inlet duct modification.  I mispoke - its

more

like 15-20deg/inch rather than 7.  I attached my excel spreadsheet where

I

attempted to use the "a" (alpha curve) for a streamline diffuser (I

believe

you provided the figure I pasted into spreadsheet)  adjusted to fit the
fiberglass ducts I had.    I suspect that while the more gradual curves

will

probably help the flow that I might have been overly zealous in reducing

the

inlet opening size as much as I did. But I can open it up as required.

Not

a perfect fit to the theoretical by any means, but probably better than

the

bowl shaped inlet I had previous - first flight will tell.

Here are a couple of photos that may help, although the curve from inlet

to

radiator doesn't show up all that well due to last of contrast/reference
point.  Guess I should have held a straight ruler or something agains

the

fuct to show it.

 I first filled the duct with the liquid expanding foam, then shaped and
added some lightweight filler to smooth the surface. I used the paper
templates (Mvc33)to try to stay as close to the spreadsheet curves as I
could.

Ed

I used to think that was the way to go but now, if you notice, the
length of the K&M diffuser needs to be 2.5 times the height of the rad
to prevent separation.

Lets say your rad is 10 inches high. Obviously you don't have 25 inches
in length to work with. It is possible however if you opened up the inlet
area to a larger percentage of the core area (from 25% say to 50%)
you could use a shorter K&M diffuser with out separation. You have closed
it down which seems a bit odd and opposite to what might work:)
I guess we shall see.

In any event I think you are better off with a cowl flap as closing the
cowl flap will build back pressure in the duct and cause external

diffusion

thereby automatically streamlining the inlet externally.

On the other hand the Kays & London simple wedge shaped diffuser requires
no more length than the rad lying on its side. I now think this
is the best approach as it uses a minimum of under cowl volume or space.

Paul Lamar

 I agree that my modifications don't meet the spec for the K&M diffuser, but
felt that the old duct inners with no attempt to direct the flow and with
its "eddy" producing pockets around the inlet were probably even less
effective.  I reasoned that if I could reduced the turbulence I would
enhance the cooling and could therefore reduce the area of the inlet.
Reasoning may have been faulty and may produce no satisfactory results, in
which case I simply dig out the foam and have my old duct back. I would be
hesitant to open up the inlet to 50% of core as that would amount to approx
45 sq inches whereas the old duct is only 25.

Well, I need to finally fly again after fixing the rudder and need to take
it to get the transponder bi-annual inspection, so should know how it works
by end of this week.

Ed Anderson

 
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