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Scott.
I am having a McCauley 71/52 mounted on my
C-85.
It is a cruise prop - a bit too much cruise fo a
C-85.
But settings between 2100 - 2300 are giving me a
fast cruise. Full throttle is giving me 2400rpm, in rare circumstances
2500rpm.
The plane does not fly much faster then but I can
burn 6 gallons / hour. If you go up to altitude (10000ft) the max
rpm reduces to 2100/2200, but you will burn significantly less fuel when
you lean out and be still as fast.
The Marvel Shebler Carb is praised as the better
Carburetor on the Continental engine. Although the Stromberg shows some
engineering that is directed more to an aircraft carburetor.
The Marvel Shebler unit has a mixture control that
works on all engine speeds. It is said that you need to set your carb for the
best mixture at all altitudes with the Marvel, while the Stromberg uses a
sophisticated pneumatic system that automatically adjusts for altitudes up to
5000ft.
With a Marvel you should lean while taxiing, while
not with a Stromberg.
Engine failures are not very common with our small
continentals.
The engine inners are tough enough to take some
abuse. But sticky/breaking valves can kill your engines performance as does a
problem with your carburetor.
A malfunctioning ignition system could ruin your
day too if not there were the redundancy of a second system.
The carburetor is a single unit on our engine and
does indeed can cause trouble sometimes.
Carburetor icing can happen especially after a long
dive with a closed throttle. It happened to me even in sunny hot California
ones.
It is important to understand that Carb icing does
not kill the engine because the ice closes the throttle altogether, but the
accumulating ice makes the throttle narrower. It acts as if you installed a way
smaller venturi in the carb. Since the venturi regulates the amount of air that
can be mixed with the gasoline passed through the main jet it is important to
have matching sizes there. A small venturi (due to icing) and a big main jet
do produce an overly rich mixture that can not ignite. You engine quits and
is flooded with gas.
Now it is important to understand that your
carb is still open and your engine is still getting a fuel air mixture trough
the carb, only the mixture is out of balance. Pulling carb heat is the right
thing to do in this moment. the windmilling engine pulls warm air through the
venturi and the ice melts. But warm air enriches the mixture even further
because warm air is expanded air with less air molecules. And this expanded
air is still mixed with way too much fuel. That's why they say you engine
performs worse when pulling carb heat. If it still performs.
What the book does not tell you and the flights
schools also don't mention, is to gain immediate performance back in this
situation is to lean the carburetor. A leaner mixture will ignite again, maybe
not create full power, but create some.
I happened to fly with a weird Stromberg carburetor
last year that was occasionally enriches the mixture quiet some.
On the ground, while running up it would lead to a
loss of performance that came back after I cycled trough several rpm settings
and magneto settings.
It was intermittent and when it happened in-flight
to me it was also frightening.
So the engine quits and I lower the nose to adjust
for a glide and the engine comes back to life just like that. I apply carb heat
and fly back to the airport without an incident. Altitude was around 5000ft at
that time, I was climbing and I did not lean the engine.
Then I am on a cross country in Germany on a humid
day. The engine quits in a cruise setup. And does not come to life a few seconds
later.
I applied carb heat and it took a few moments to
hear the engine become noisy again. What a relief. On that trip I had two more
occasions of this and I started to experiment a bit because I wanted to know the
source of the trouble.
I suspected the ignition switch to be bad, but this
suspicion and others had been excluded by the fact that the engine came to life
when pulling the mixture control. So I concluded the carb was developing some
ice that under normal circumstances would not affect the engine as much, but
because the mixture this particular carb was producing was always overly rich,
the engine died faster.
Carb was exchanged next thing and the mysterious
engine outs did not happen again.
So what am I trying to tell you guys? In an event
of an engine out, don't panic. Keep trying to get it back on.
It is in most cases fuel related. It is either too
less or too much fuel that the engine is getting.
Try to adjust the knobs. For that reason by the way
I think a wired rich mixture control on a Stromberg robs you of one
option.
Boy that was a long speech.
Always a good landing,
Hartmut N3330H
----- Original Message -----From: scottTo: Ercoupe TechSent: Wednesday, May 24, 2006 5:32 AMSubject: [COUPERS-TECH] Engine quitting and other less troublesome queries----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----Hi 'CoupersI have been saving up questions...
- Any thoughts as to this rash of engine quitting? Are people not pulling carb heat soon enough?I have read NTSBs on 'coupe engine failures - quite a few remain mysteries.
- My 'Coupe has a Marvel Shriebler (sp?) carburetor. I don't hear much in the column regarding this unit. Are they a good carb? I know that you can not use your mixture control to shut down the engine.
- I have a McCauley 71/52 (cruise prop right?) I don't think I can pull much past 2400 rpm. Is this prop sized right or is the motor getting a little long in tooth...What rpm should I max out at during level flight (C-85)
Thanks,Scott============================================================================== To leave this forum go to: http://ercoupers.com/lists.htm
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