I use much the same cruise technique as Tracy. Starting from a 60 deg F LOP mixture and throttle setting giving close to the desired airspeed, I adjust the mixture to maximize the MPG calculated from the fuel flow and IAS. This is essentially maximizing BSFC. One thing that should be verified is that no change in staging takes place during the MPG optimization. With a well tuned system, the engine doesn’t care if staging is occurring, but the MPG readout will change with staging at same fuel flow rate. This is assuming that the fuel flow rate is based on injector pulse width. If a fuel flow sensor such as a Floscan unit is used, then staging is of no consequence.
Steve Boese
RV6A 1986 13B NA RD1A EC2
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Tracy
Sent: Saturday, April 30, 2011 9:38 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Intakes old and new
Everybody has their own technique for cruising. I typically aim to get the highest reading on the EM2/3 MPG readout along with a reasonable airspeed. On my RV4 this is usually around 17 - 18" Hg. MP and 130 - 135 IAS / 170 - 175 TAS at 15,500. This is way less than WOT. Pumping losses are a factor in efficiency but IMO it is way over rated. There is no question that aero losses at higher speeds more than make up for the pumping loss improvement. If pumping losses were that big, cars would get terrible fuel mileage at 55 mph.
Tracy
On Sat, Apr 30, 2011 at 10:52 AM, Bill Bradburry <bbradburry@bellsouth.net> wrote:
Ed,
I have heard you mention that you seldom fly at max speed. How do you do this? Do you fly at WOT but high enough to lower the output and lean for economy, thus reducing the speed? Do you reduce throttle??
I have been given to understand that the throttle should be at WOT all the time to reduce “pumping losses”. Engine power would then be affected by other means, leaning, altitude, prop speed if you can adjust it???
What is your method? For that matter, what method do others use?
Bill B