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A) "near" is a weasel word. If I get too close to cutoff lean, the engine will surge. I've had to richen it up several times to keep it running smooth. In normal operation, there should tuned to run smoothly at idle.
B) The normal operating range of the engine makes a diagonal path across the VE table. To the right is higher RPM. Going up is increasing throttle. For a given throttle setting, there is a particular RPM that the engine should attain. If it drops to the left (engine slows down), I have the table set to enrichen the mixture. If it revs, the mixture goes even leaner. The result is that there is a sort of ridge that the engine wants to ride along. I'll probably need to get a screen shot of the VE table for this to make sense.
On 09/06/2012 10:34 AM, Bill Bradburry wrote:
Earnest,
If you were in the pattern and reduced power to the point where you were at
half throttle or below and the mixture then went to "near cutoff lean" it
seems you would be in danger of the engine stopping. That might not be a
desirable thing when you are that low to the ground even if you were in a
pattern...??
Bill B
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Ernest Chrisltey
Sent: Thursday, September 06, 2012 10:19 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Single lever control
This is what I was referring to in my previous email. Throttle is
graphed against RPM in both. On the left, data points are colored based
on coolant temps at the time the data point was captured. The right
graph uses AFR to set the color.
The one on the left has the points colored according to coolant temp at
the time the data point was collected. This graph tells me that a cold
engine will make more power.
The right graph has the points colored according to AFR, and is more
interesting. My throttle plate is fully open at about 50% travel of the
control lever. My goal is to keep the mixture near cutoff lean until
after the throttle plate is wide open. Until WOTP (wide open throttle
plate) power increases from increasing the amount of intake charge.
After that, pushing the lever forward increases power by enrichening the
mixture. I transition from changing the amount of mixture, to changing
the makeup of it. I would like a solid diagonal line, correlating
throttle and RPM. The graph shows me that I reach best power mixture to
quickly. I need to shift my target AFR a bit so that the lines flatten
out with only 5% to 10% of lever travel left; however, for the most
part I've achieved the goal of having RPM directly correlated with
throttle position.
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