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Hi Bill,
Difficult to answer. I record my airspeed,
temp and altitude when I fly and try to exercise some care in collecting that
data. But, a few degrees off the temperature, a few feet off the
altitude, etc. could easily swamp any real speed improvement. It appears
that in my flights previous to the pinched ducts I could get really close to
200MPH TAS, but never quite get there - like 195-197 mph TAS. I am now
confident I have repeatedly hit and slightly exceed 200 MPH TAS - but, what to
attribute the increase to is the question.
Depending on the amount of external diffusion going
on the virtual inlet area could be larger than even my "Lip" area opening - so
again, just hard to say. It could well be as Al indicated - that my
"pinched" duct really does not play any role in the cooling improvement - just a
fortuitous combination of other factors. But, I do have what I believe
is a logical rationale for that approach - whether it holds water
remains to be seen.
My cooling system now seems well (if not optimized)
matched to my current installation. Full power take offs on hot days
see my cooling temps elevate to 200F for oil and 210-220F for coolant.
Once I hit 120 MPH IAS the cooling system catches up and starts to eliminate the
cooling deficit.
At my normal retired-man cruise of 7- 8 gph, my
coolant and oil range from 155-170F depending on OAT. When I push it to my
max fuel flow/power 10.5-12.5 gph at altitude the temperatures
of both increase until they are in the 190-195F range. This gives me my
maximum true airspeed. So it appears my cooling capacity is about
right where I need it. Certainly a surplus at low power cruise, but just
adequate on take/off climbout on hot days and adequate for full boogie
flight.
I really don't know how much drag (if any) I have
eliminated, but I am convinced that it is less than if I had more of the core
exposed to high velocity airflow.
Sorry, I can't be more definitive about it - I
would like to know as well, but only so much time to get all the wonderful
projects on my list done. Perhaps someone with the inclination and time
will someday put this idea in a wind tunnel and tell us {:>)
Ed
----- Original Message -----
Sent: Monday, May 07, 2007 1:27 PM
Subject: [FlyRotary] Re: Pinched
Duct
Ed,
An interesting factor here is that when considering duct inlet
diameter/opening size is usually calculated from the high point of the
opening. Provided the opening is smoothly configured. Since your pinched duct
uses a smooth turn from the high point on the cowl, most of the time you would
calculate the area as the highpoint on the opening for the purpose of
calculating drag. I was talking to Peter Garrison about this when he visited
our EAA chapter. I know the cooling improved, Was there any increase in speed?
Assuming that same throttle position of course.
Bill Jepson
-----Original Message-----
From:
eanderson@carolina.rr.com
To: flyrotary@lancaironline.net
Sent: Mon, 7
May 2007 5:08 AM
Subject: [FlyRotary] Re: Pinched Duct
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