His carb float stuck, and he ended up in a field
Posted: Fri Oct 01, 2021 6:35 pm
Didn't want to thread-jack. I know, what's the occasion? Be nice.
Ok, so you're cruising along in your Cessna/Piper/whatever with it's antique
air-cooled horizontally-opposed engine with two magnetos and a carburetor
that would look appropriate at an antique tractor show.
Runs rough. You try carb heat. Doesn't help. You try each magneto individually,
no improvement.
As pointed out, the carb float can sink (see all the AD's) or it can stick in the up
position. Let's talk about these two failure modes.
See, the carburetor has a bowl inside it, partially filled with fuel - ideally. It keeps
it that way, with a float that goes up and down - just like the float in your toilet tank.
Let's look at the error case where a float sinks. Don't worry about why, it's not like
you can fix the fucking thing from the cockpit anyways. When a float sinks, the
carburetor thinks it has no fuel, and it will drain all the fuel from the tanks as fast
as it can, flooding the engine.
What can you do as a pilot in this situation? Well, you could lean the mixture and
see if restricting the fuel makes the engine run better, which is weird but might
happen. You could even turn the fuel selector on and off, if need be.
Now let's look at the other case - where the float sticks in the "up" position and
cuts off the fuel. Since the fuel can't get into the bowl, it can't get into the engine
and it's going to be like someone turned off the tap. Messing with the mixture
and fuel selector isn't going to help much, faced with this shortage of fuel.
But wait! You have another way of getting fuel into the engine. Pull the primer
knob out - it should normally be locked - and give it a squirt. You may find the
engine roars into life. Maybe play with the throttle. You're at the mercy as to
how many cylinders are plumbed by the primer. Some engines it's only one
cylinder, other's three. Radial engines have the top cylinders plumbed (why?).
This brings me back to my comment that the most important component in
an aircraft is between a pilot's ears.
The greats always figure out a way to survive. Often they don't even bend
any tin.
Remember in my tens of thousands of posts, I have mentioned the importance
of systems knowledge? Often that knowledge can make the difference between
a crash - possibly fatal - and a good story, with the aircraft sitting on the runway.
I know a guy who used a primer knob to fly a Cub 30 miles after his fuel system
failed. His palm was kind of fucked up but the airplane was ok.
Ok, so you're cruising along in your Cessna/Piper/whatever with it's antique
air-cooled horizontally-opposed engine with two magnetos and a carburetor
that would look appropriate at an antique tractor show.
Runs rough. You try carb heat. Doesn't help. You try each magneto individually,
no improvement.
As pointed out, the carb float can sink (see all the AD's) or it can stick in the up
position. Let's talk about these two failure modes.
See, the carburetor has a bowl inside it, partially filled with fuel - ideally. It keeps
it that way, with a float that goes up and down - just like the float in your toilet tank.
Let's look at the error case where a float sinks. Don't worry about why, it's not like
you can fix the fucking thing from the cockpit anyways. When a float sinks, the
carburetor thinks it has no fuel, and it will drain all the fuel from the tanks as fast
as it can, flooding the engine.
What can you do as a pilot in this situation? Well, you could lean the mixture and
see if restricting the fuel makes the engine run better, which is weird but might
happen. You could even turn the fuel selector on and off, if need be.
Now let's look at the other case - where the float sticks in the "up" position and
cuts off the fuel. Since the fuel can't get into the bowl, it can't get into the engine
and it's going to be like someone turned off the tap. Messing with the mixture
and fuel selector isn't going to help much, faced with this shortage of fuel.
But wait! You have another way of getting fuel into the engine. Pull the primer
knob out - it should normally be locked - and give it a squirt. You may find the
engine roars into life. Maybe play with the throttle. You're at the mercy as to
how many cylinders are plumbed by the primer. Some engines it's only one
cylinder, other's three. Radial engines have the top cylinders plumbed (why?).
This brings me back to my comment that the most important component in
an aircraft is between a pilot's ears.
The greats always figure out a way to survive. Often they don't even bend
any tin.
Remember in my tens of thousands of posts, I have mentioned the importance
of systems knowledge? Often that knowledge can make the difference between
a crash - possibly fatal - and a good story, with the aircraft sitting on the runway.
I know a guy who used a primer knob to fly a Cub 30 miles after his fuel system
failed. His palm was kind of fucked up but the airplane was ok.