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Steve,

BSFC is calculated from the HP and the fuel flow.

The HP is calculated from the torque and the RPM. The engine is mounted on ball bearings so it can rotate on the axis of the eccentric shaft. That rotation is constrained with a 1 ft arm connected to a load cell calibrated in lb. That gives torque in ft lb. Torque in ft lb multiplied by RPM and divided by 5252 gives HP.

Fuel flow is measured with a Floscan transducer calibrated in gal/hr. The gal/hr multiplied by 6.17 lb/US gal, gasoline gives lb/hr.

Fuel flow in lb/hr divided by HP gives BSFC in lb/(HP hr).

My EC2's are earlier version (SN 200-499) updated in early 2010 where Mode 7 allows setting the staging threshold. The Renesis engine is fitted with a second CAS and a replacement trigger wheel with 12 teeth for the original CAS and one tooth for the added CAS. This allows interchangeability with my flying 1986 13B which has a stock CAS.

Your estimate of fuel saving due to a BSFC change of 0.5 is correct. Unfortunately, the observed BSFC change was about 0.05 rather than 0.5.

Ed Anderson once told me that as a scientist, I collect data, but it takes an engineer to determine what the data means. (He was smiling when he said that). Your guess as to the reason for the BSFC change is as good or better than mine.

Steve Boese

From: Rotary motors in aircraft <flyrotary@lancaironline.net> on behalf of Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net>
Sent: Thursday, June 25, 2020 9:41 PM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: BSFC change on staging

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Hi there Steve
Thanks for your work here.
How do you measure the BSFC?
So you have a version of the EC software where you can still change the Staging point MAP.
The BSFC is ~0.5 better unstaged. Is this due to better fuel-air mixing or is something else at play?

Am I right in thinking that at an economy cruise, a BSFC change of 0.5 might yield an approx 0.9G/hr ($5/hr) of fuel saving.
That might then argue for a Staging Point at the earlier 15.5” MAP to enable unstaged cruise rather than the locked in 20” MAP of the current software version.

What is your thoughts and conclusion if you have reached any?

Thanks again Steve

Steve Izett

> On 26 Jun 2020, at 8:47 am, Steven W. Boese SBoese@uwyo.edu <flyrotary@lancaironline.net> wrote:
>
> I ran a test on my engine stand with staged and unstaged fuel injectors but with the same fuel flow and MAP. The results are shown in the attached image. The engine is a 2010 2nd generation Renesis 6 port from an automatic transmission car with the high RPM ports blocked off and stock fuel injectors. The reduction drive ratio is 3.18:1. The prop is a 3 blade 72" Warp Drive and was operating just below stalled RPM. A turbo is installed but no boost was used in the test. No attempt was made to operate at minimum BSFC.
>
> Steve Boese
> <BSFC.jpg>--
> Homepage: http://www.flyrotary.com/
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