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Date: Fri, 17 Jun 2011 01:00:35 -0400
From: Ernest Christley <echristley@nc.rr.com>
Reply-To: echristley@att.net
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Blower efficacy...
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After all the talk about my blower experiment, I think I'm ready (and 
very happy) to declare it a qualified tentative success.  The 
qualification is that the data is fairly noisy, so I'm pulling out some 
numbers that have a hint of brown stuff on them.  It is tentative, 
because I really need to repeat the test with a little more control.

Test setup:  With a tuning that let the engine run fairly steady, I made 
multiple runs:  several without the blower attached (the air filter was 
turned around, away from the blower exit), one without the air filter 
attached, and a couple with the blower attached.  All tests were logged, 
and the numbers I'm using come from those logs.  The MAP was recorded by 
the MegaSquirt ECU using a MPX4250 MAP sensor.  All readings are in kPa 
(kiloPascals), with 100 being sea-level atmospheric and 0 being a 
perfect vacuum.

Summary:  The filter appears to be costing somewhere between 2kPa and 
5kPa. The blower is adding up to 20kPa.  For rough numbers, those can be 
read as costing 5% and adding 20% power.

Again, I will run more tests to verify, being more careful to let the 
RPM and MAP reading settle at different stages, but here are some 
example data from todays run.

Without the filter, the MAP read 54.8 at 1678 RPM.  Adding the filter 
gave 50.7MAP at 1627 RPM.  The blower moved the MAP up to 67.8 at 1541 RPM.

No filter gave a 51.4 at 4617RPM, and the filter brought it down to 49.4 
at 4711.  I had 68.3 at 4830 with the blower.

The highest revs without the blower was with the filter on.  5160 RPM 
gave a 52.1 MAP.  5397 with the blower helping moved the map up to 
70.7.  Below that I got 51.6 without the filter at 4991, 49.4 at 4711 
with the filter but no blower, and 68.3 at 4830 with the blower.

I'm not prop limited.  I have a rev limiter set in the MegaSquirt to 
5500 RPM.  This data won't be really reliable until I've carved a prop 
that will limit the engine's max RPM, and I can remove the rev limiter.