The MAP rises predictably because the turbos are at critical altitude, providing the upper deck with a they maximum pressure without added reserve.  Then the consumption of air from downstream of the throttle (where MAP is measured) going into the cylinders is reduced when the RPM is reduced.  This reduced cylinder consumption of air increases available air coming across the open (unrestricted) throttle.  Thus MAP increases.

Regarding improved airspeed at slower prop RPM, I'm guessing this is related to engineered prop efficiency.  I should look at the Hartzell Scimitar prop design efficiency graph, based on design, and see if the prop is optimized at 2400. I'm guessing performance efficiency is less at 2500 RPM.  My theory, based on observation, without added research.  But the observation should be repeated by me and by others.  The prop was specifically designed for the lancair, but at what optimized RPM?

Details will follow from the next flight test, probably to be done during my trip from New Jersey to Oregon this weekend.

Cooling mods: the Cyl 5 rectangular key hole, standard baffling, the forward oil cooler wall cut out and hat box to invite more air flow around/behind Cyl 2.  OAT (recorded) +15*F (but I always wonder about RAM compression effect and parasitic heating from engine back wash). J



From: <bronnenmeier@GROBSYSTEMS.COM>
Subject: RE: LIVP Power and Flight parameters from today's flight test.
Date: July 30, 2012 8:39:32 AM EDT
To: lml@lancaironline.net


Hello Jeff,

Obviously I missed your point the first time and I apologize for giving
you such unqualified advice.

There are two questions in my head where I can't get an explanation so
may be someone can enlighten me:
- why does the MAP raise when you reduce the rpm from 2500/2700 to 2400?
- this is the opposite from what I see during a low altitude/take off
situation (when I reduce rpm I expect my MAP to drop slightly)
- why does the airspeed increase with lower rpm? - on the plane I flew
before (Cessna 182 - don't laugh) I found that the speed dropped
slightly when I reduced the rpm - I took this for granted for all
planes/props, obviously I was wrong.

One more question for your next test flight Jeff:
- can you say anything about CHT and oil temp for 2500 versus 2400 rpm?
During climb WOT gives me usually lower CHT but yields in higher oil
temps - for example on a really hot day I can get oil temps in climb of
220 and CHT 375 with WOT and if I reduce MAP to 32 and rpm to 2500 my
oil temp drops to 205 and CHT raises to 385...395. in cruise my oil temp
is usually below 195.

Ralf



From: Colyn Case <colyncase@earthlink.net>
Subject: Re: [LML] Re: LIVP Power and Flight parameters from today's flight test.
Date: July 30, 2012 1:52:02 PM EDT
To: lml@lancaironline.net


Jeff, can you say what cooling mods you have and what was the outside temp?

As far as the frictional wear, I think you have to look at what typical failure modes are for this engine.
I would be more worried about heat than friction.  My personal limit on heat is 380 on the CHT's.  (1650 on the turbo but that is really more about turbine rpm).  Next after that I would worry about rust (camguard and getting the water out of the crankcase).   Then I would worry about friction.

Colyn