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Fred, Dan and Scott:
I used to go around with anecdotal comments that my Lancair got 2 inches more
MP than my Skymaster at a similar altitude. Now for real data:
The Skymaster front engine is a 6 cylinder Continental IO 360G delivering 210
HP at 2800 RPM. Induction air is obtained thru a large pleated paper filter
which sits above the engine in the upper deck cooling plenum. It is not in
any direct air flow and any "pressure" is minimal because of a leaky plenum
and Cessna's use of cowl flaps to fix poor cooling during climb. The engine
instrumentation is 26 years old (the pilot is older still). Here's the data:
A day similar to the Lancair test - 30 deg C, baro=30.08
MP gauge on the ground = 29 inches and the altimeter at sea level read 29.35
inches -- close enough.
1000 RPM gave me 16 inches of MP.
The best I got at takeoff was 26 inches MP at 2800 RPM at about 90 Kts IAS.
This is 3.5 inches less than the Lancair but I was turning 100 more RPM.
At 7000 ft AGL, 18 deg C, 150 Kts IAS, 173 Kts TAS, 2600 RPM (same as
Lancair) and full throttle leaned in the best power range -- I had a 21 inch
MP reading.
Ambient should have been 22 inches at that altitude. That results in only a
1 inch LOSS! "Experts" tell me that a 1 inch loss thru a filter is not bad.
Note the difference between the Lancair and this commercially built plane is
3.5 inches. Power to the people that build!
Fred, with respect to your numbered notes:
1. LoPresti had Hartzell build him a propeller with a 5X1 inch trailing edge
extension on each blade to add a timed impulse of pressure to a special tuned
induction system which added MP. I don't remember performance details and
this was reported several years ago.
2. This is the one I love. Regardless of the "error" which creeps into the
MP system, it is, in combination with RPM, THE indicator for POWER
determination. If they are very inaccurate, how can we get the best power
out of our engines or make comparisons? Perhaps someone can provide a
different instrument/measurement for this. Maybe, measuring unburned
hydrocarbons in the exhaust in combination with something else? I want a
single power lever like my tractor -- It goes from Turtle to Hare.
Thanks for the info, I will not try to do any further sealing of my system.
And, fly I will! It's so much fun.
Scott Krueger, OP, VD
N92EX
OP = Old Pilot
VD = Victory Declared
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LML homepage: http://www.olsusa.com/Users/Mkaye/maillist.html
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