Hi Remi
"I'd love to have a mixture control system on my aircraft. However as I
> understand how the HACman/Greensky mixture control works, I am afraid it
> would unacceptably affect the reliability of the engine.
> Up to now, I have not read anything such as reliability analysis,
> experience in the field, etc... that would convince me that I am wrong!"
N4211W not flying yet, but have and will install a mixture control on 914.
First off installed will be a Split Second mixture display that is driven
by a Bosch O2 sensor (will weld a bung on the muffler inlet just
downstream of turbo).
Slight different install on 914 because of Turbo compared to 912/s, but
will use a needle valve to leak pressure from normal airbox pressure side
of enrichment solenoid to manifold cross tube. The more I leak the leaner
the mixture will be.
This will require a run of hose to cockpit then to manifold cross tube, I
will use high temperature Viton tubing.
I will slight richen mixture on main jet and perhaps even jet needle, I
always like to run slight rich when you are making a lot of BTUs such as
100% power or in 914s case War emergency of 115%. It can also cool things
a little on a hot engine (including when stuck on ground).
Then will size a restriction on the controlled "leak" to manifold cross
tube so it will allow me to only lean to ~14.7 at 18K.
Then will have an emergency "rich" button that will allow me to activate
enrichment solenoid that could further richen mixture on less than War
emergency power if I wish. In addition the emergency "rich" button will
completely bypass all my additional plumbing.
For either a 912/S or 914 install, if you at cruise power if you pull
throttle without closing off your controlled leak, your engine is probably
going to quit. On the other hand, if you set mixture at lets say 60% power
and adjust mixture, if you increase power you will go richer than probably
desired.
Another problem is if you lean at altitude, when you come down things will
lean up further.
Having a Split Second display is a nice tool for this control, a EGT
(which I have one on each side of motor) is only semi useful.
HAC has or had a altitude adjusting bellows, I would rather have full
manual control.
I am a motorhead and feel very comfortable fiddling with carburation. If
you can't tune a lawnmower engine to perfection by ear, owned a hot 2
stroke cycle that you managed to run on the edge for long periods without
blowing up, probably not worth considering the controlled 'leak' method of
adjusting Type 64 constant depression carbs.
Ron P.
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