Speculation can differ from personal experience and observation. The
difference may be in the details of what is or is not said.
In an Ercoupe with the Stromberg carb I have landed and taken off from
Big Bear City Airport (CA) in winter with two aboard, field elevation
6752'. Leaning after warmup at full throttle increased rpm, and so
takeoff was made at best rpm (not full rich). The same has been true
at two different airports in Albuquerque, NM and in other "real world"
instances.
No attempt was made to correlate existing conditions with "standard
day" conditions. While you may not be able to kill the engine with the
Stromberg mixture control on a full throttle climb out, would the
ability to do so have any meaningful use? You can definitely cause a
reduction in available power on a hot day by aggressively leaning at
too low a density altitude; thus the cautionary note in the Ercoupe
Instruction Manual.
The "leaning effect" before takeoff is substantially identical to that
experienced in cruise...no surprise since it has been my practice (with
a "standard pitch McCauley) to cruise at full throttle backed off just
enough to see the rpm drop. At a pressure altitude of 8,000' and 2500
rpm the engine is putting out something less than 60 hp. For my coupe
that required pretty much full throttle. In this context it is
difficult to understand how there could exist any "pronounced"
difference in the effectiveness of the Stromberg mixture control at or
near full throttle between cruise-climb and level cruise configurations
since at any given density altitude the difference in indicated
airspeed was perhaps 20 mph at most.
I otherwise described the end of a cross country flight involving a
descent from 8,000' in leaned cruise without enriching my leaned
mixture. Productive combustion in the engine ceased instantly when I
reduced power to 1300-1400 rpm for descent on downwind. The engine was
not "killed", in that it continued turning over as the prop windmilled,
but NO power was being produced and I was sinking much more rapidly
than expected or desired. Upon return of the mixture control to Full
Rich and application of some throttle ignition resumed (without
backfire) and the landing was normal. Feel free to duplicate the
conditions I describe at an airport approximately 500' above sea level
and a pattern of 1500' (1,000 AGL) and share your experience with us.
It is correct that on final with the throttle shut the engine cannot be
killed, but that has nothing to do with manipulation of the Stromberg
mixture control. On final with the throttle shut the engine is
supplied fuel from the idle circuit (independent of throttle or mixture
controls) set to deliver sufficient fuel to maintain a minimum engine
idling speed of 650 rpm or so.
Regards,
WRB
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On Feb 3, 2010, at 02:09, Hartmut Beil wrote:
The Stromberg leaning mechanism works using pressure differences
within the carburetor.
These differences are pronounced during cruise flight, where leaning
makes sense.
During full throttle and while idling, the pressure difference is not
great enough to create a leaning effect.
See it as a safety feature. You can not accidentally kill the engine
on a full throttle climb out or on final with the throttle shut.
The engine keeps running even when fully leaned out.
Hartmut
