Continental A-65 engine stall?

Yesterday, I flew to an airport for breakfast and as I turned off onto
the taxiway, the engine quit. It's never done that before. Re-started
fine. Did not quit when I returned to my home airport. Maybe the
turbulence was enough to fix it

Some history...the plane had been sitting for for several years and I
started flying it again last fall. It seemed to be OK last fall but I
had another issue (that turned out to be a big intake leak that
prevented it from starting) that I now have fixed. So, could this
stalling be something like the float sticking? After I started it, it
seemed to "load up" a bit and took some RPM to clear it out. Maybe this
is a clue?

Scott
Corben Junior Ace

Dear Scott,

Your symptoms match those of carb icing.

-R.S.Hoover

Scott wrote:
Yesterday, I flew to an airport for breakfast and as I turned off onto
the taxiway, the engine quit. It's never done that before. Re-started
fine. Did not quit when I returned to my home airport. Maybe the
turbulence was enough to fix it

I've had that happen, and have been with another small-Continental-
powered aircraft where that happened. Instant re-starts in both cases.

I tend to agree with Bob...carb ice. On approach, with the engine
idling for a bit, the carb heat muff may have cooled down to the point
where it couldn't prevent the ice any more.

If it re-occurs, there are some potential hardware problems that could
going on. Here's a Harry Fenton article on the subject:

http://www.bowersflybaby.com/tech/fenton.htm#a65-quits

Ron Wanttaja

Ron Wanttaja wrote:
Scott wrote:
Yesterday, I flew to an airport for breakfast and as I turned off onto
the taxiway, the engine quit. It's never done that before.
Re-started fine. Did not quit when I returned to my home airport.
Maybe the turbulence was enough to fix it

I've had that happen, and have been with another small-Continental-
powered aircraft where that happened. Instant re-starts in both cases.

I tend to agree with Bob...carb ice. On approach, with the engine
idling for a bit, the carb heat muff may have cooled down to the point
where it couldn't prevent the ice any more.

If it re-occurs, there are some potential hardware problems that could
going on. Here's a Harry Fenton article on the subject:

http://www.bowersflybaby.com/tech/fenton.htm#a65-quits

Ron Wanttaja

OK...but if it was carb ice, would the engine restart immediately after
getting out to hand prop? My "heat muff" is a replica of an Aeronca 7
series heat muff...just an aluminum "cover" that clamps around the "Y"
of the exhaust pipe. Is there an easy way to get more heat such as
wrapping a spring or something around the pipes to get more thermal
mass? Ideas anyone???

Scott

Scott wrote:

OK...but if it was carb ice, would the engine restart immediately after
getting out to hand prop?

Sure...the flow of cooling air would stop, and the carb would quickly
warm up by conduction.

Frank Courtney, in his book "The Eighth Sea," claims to be the
discoverer of carburetor icing...not the first to HAVE carb ice, but the
first to discover what was causing some otherwise-unexplainable engine
failures.

He had been participating in a cross-country race with an engine with an
updraft carb and no air filter. The engine quit, he set the plane down,
and climbed out. He reached the engine just in time to see a chunk of
ice drop out of the carburetor throat.

My "heat muff" is a replica of an Aeronca 7
series heat muff...just an aluminum "cover" that clamps around the "Y"
of the exhaust pipe. Is there an easy way to get more heat such as
wrapping a spring or something around the pipes to get more thermal
mass? Ideas anyone???

IIRC, Tony Bingelis recommends exactly your approach; wrapping
screen-door springs around the pipes. You need more surface area inside
the heat to pick up heat to transfer to the air.

You might ask at the Aeronca Aviators Club forum page...

http://www.aeronca.typeclubs.org/BB3/

....or ping Harry Fenton directly via the links at the start of the page
I previously posted.

Ron Wanttaja

Ron Wanttaja wrote:


You might ask at the Aeronca Aviators Club forum page...

http://www.aeronca.typeclubs.org/BB3/

...or ping Harry Fenton directly via the links at the start of the page
I previously posted.

Ron Wanttaja

Will do, Ron, THANKS!

As far as starting right up again, yes, I figured it probably does as
the engine is still quite warm after landing and without air flowing to
move the heat through, the carb would warm up fairly quickly and melt
the ice...

Do you know what is the mechanism that causes power loss (and ultimately
quitting) due to carb ice? The book drawings show that ice builds up in
the throat of the carb (if I recall) so it looks like the diameter of
the throat is reduced? What does that do to make the engine run at
reduced power and/or eventually die? I suspect that it impedes the air
flow through it, effectively making the mixture richer until eventual
death. Am I close?

Scott

Scott wrote:
Yesterday, I flew to an airport for breakfast and as I turned off onto
the taxiway, the engine quit. It's never done that before. Re-started
fine. Did not quit when I returned to my home airport. Maybe the
turbulence was enough to fix it

Some history...the plane had been sitting for for several years and I
started flying it again last fall. It seemed to be OK last fall but I
had another issue (that turned out to be a big intake leak that
prevented it from starting) that I now have fixed. So, could this
stalling be something like the float sticking? After I started it, it
seemed to "load up" a bit and took some RPM to clear it out. Maybe this
is a clue?

Scott
Corben Junior Ace

the "loading up" part - could be ice related, or -

Fixed ignition timing can cause that problem if allowed to idle
too long.

On Jul 12, 11:52 am, Scott wrote:

Do you know what is the mechanism that causes power loss (and ultimately
quitting) due to carb ice? The book drawings show that ice builds up in
the throat of the carb (if I recall) so it looks like the diameter of
the throat is reduced? What does that do to make the engine run at
reduced power and/or eventually die? I suspect that it impedes the air
flow through it, effectively making the mixture richer until eventual
death. Am I close?

Getting warm, but still a ways from the truth. There are two
factors that cause the temperature drop in the carb: The venturi
accelerates the air, thereby dropping its pressure and temperature. We
need that pressure drop to suck fuel from the nozzle, but could do
without the temp drop. The laws of physics being what they are, we
have to deal with it. A similay pressure and temperature drop takes
place at the throttle plate when it's closed or mostly closed; the air
squeezing past the edge of the plate accelerates a whole bunch and
gets cold, however briefly.

The other factor is the fuel itself. As it sprays into the
airflow, it vaporizes. Anytime we turn a liquid into a vapor, we
effect a heat transfer; in this case it's from the air to the liquid
as it turns to a vapor. So the air gets mighty chilly. Same effect you
get if you dip your hand in gasoline then hold it up and let it
dry;your hand gets cold. The fuel sprays from the main nozzles when
the power level is higher, and from the idle ports in the carb wall,
next to the edge of the throttle plate, at lower settings.

So the air, and any water vapor in it as it passed through the
carb, is chilled. The vapor, if there's enough of it, will condense,
and if the temperature drop is large enough, it will freeze to
anything handy. Carb ice. The total temperature drop caused by both
venturi effect and evaporation of the fuel can be as much as 38°C, or
about 71°F. We can expect carb ice at ambient temps of up to 38°C or
100°F if the humidity is near 100%, or the temp/dewpoints are almost
the same.

If I want to go diving off some cliff into the water, I want to know
what the water conditions are, and what's under the surface. If I want
to go flying, I need to know what the atmosphere is up to. That
includes temperture and dewpoint spread; if they're close together, I
will expect carb ice so I'm not surprised when the engine starts
acting up.

If your engine quit on the rollout due to carb icing, either your
system is leaking and the carb isn't getting warm enough air, or
you're not applying it soon enough and getting the carb warmed up some
before reducing power. Or you're making long glides without running
the power up and warming the carb periodically.

What sort of RPM drop do you get when you pull the carb heat in
cruise? When are you applying carb heat? How long was the power-off
glide? What were the temp and dewpoint on the day in question?

Dan

wrote:


What sort of RPM drop do you get when you pull the carb heat in
cruise? When are you applying carb heat? How long was the power-off
glide? What were the temp and dewpoint on the day in question?

Dan


In cruise, I see maybe 50 RPM drop. I've always applied carb heat on
downwind before I reduce power from cruise (2150 RPM) to about 1700 RPM
until on final, then to about 1200 RPM about until I roundout for the
flare. If I recall, the temp/dewpoint yesterday morning was 16/12C, so
the air probably did have a fairly high moisture content.

Scott

To All:

Of the two methods of absorbing heat (ie, acceleration of the air &
change-of-state for the gasoline) the endotherm resulting from the
vaporization of the gasoline can be as much as 100 times colder than
the venturi-effect.

As for the amount of water in the atmosphere, we know there is ALWAYS
some... at least, on this particular planet. The FAA provides a chart
that allows you to figure out your probable icing point.

What gets people in trouble is the assumption that the ambient air
temperature plays a SIGNIFICANT role in carb icing. Not so -- at
least not with regard to the 'significant' business. Indeed, when you
have a nice WARM day you are more likely to develop carb or manifold
icing than on a nice COLD day.

Personally, rather than try to figure out the humidity, freezing point
and so forth, I assume icing IS probable and shuffle the knobs
accordingly. Works for me.

As for heat muffs, the FAA expects ours to provide a 90F rise in the
inlet temp to the carb. Truth is, most muffs don't come anywhere near
that amount due to a lack of heat in the exhaust stacks OR
insufficient surface area for the heat to transfer two. Annd if
you've done like most of us and wrapped an over-stretched screen-door
spring around the exhaust stack, odds are it rusted itself into FOD
during the Eisenhower administration. What you wanna do is getta
pound of .035 safety wire and wind it into a coil around a piece of
rod and use that instead of your door spring. OR get yourself about
four of those stainless steel pot-scrubbers and use that. OR get
yourself about fifty feet of .010 stainless steel 'razor blade stock;'
about 1" wide and bend that into angle stock and wrap that around AT
LEALST TWO of your exhaust stacks, because the SIGHNIFICANT factors in
the equation are surface are surface area and thermal flow, so that
while the Choir Girl pads are hands-down winners for surface area they
screw the pooch when it comes to thermal transfer AND cause too much
restriction to begin with.

So give the razor-blade stock a try. Snip it four or five times per
revolution and give each resulting fin a bit of a twist... then go
back and crimp each of the 'fins' with a pair of fluting pliers so the
fin ends up sorta wavy.

Nothing here is carved in stone but a weekend experimenting with a
lawn-mower engine and an IR temperature sensor is equal to a couple of
months sitting in a classroom.

-R.S.Hoover