Very good Sir:
Hi Hartmut. Well said even if it was long! A lot of good information in there! Keep the shiny side up: Maynard.
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-------Original Message-------
Date: 05/24/06 00:55:42
Subject: Re: [COUPERS-TECH] Engine quitting and other less troublesome queries
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 -----
Sent: Wednesday, May 24, 2006 5:32 AM
Subject: [COUPERS-TECH] Engine quitting and other less troublesome queries
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Hi 'Coupers
I 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 ==============================================================================
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