Turning the Prop Over as Part of Preflight?

In reading a booked called "Design for Safety", by David Thurston, he
advises owners to "turn the propeller over by hand three or four times
during preflight if the airplane has been standing for half a day or
longer." [p169]

His rationale is as follows. "When an engine has been standing for
awhile and has not been pulled through by hand prior to starting, an
accident could result if fuel or oil has collected in the cylinders.
When the engine fires, trapped fluids can cause bent piston rods,
cracked cylinders, or a damaged crankshaft. Althouogh such accidents
might not cause bodily injury, they surely can harm one's budget and can
beavoided by proper preflight procedures. It is also possible for
damage of this type to remain hidden until something fails in flight"
[pp 147-148].

I am quite surprised that this is the first I have heard such advice.

What do folks on this newsgroup think of that advice?

Does anyone out there do this routinely?

If so, what is the proper procedure? Do you just turn the prop slowly
in the direction the prop normally turns?

Could fuel actually collect in the cylinders as suggested? Why would
the fuel not just evaporate?

-Sami
M2057M, Piper Turbo Arrow III

O. Sami Saydjari wrote:
In reading a booked called "Design for Safety", by David Thurston, he
advises owners to "turn the propeller over by hand three or four times
during preflight if the airplane has been standing for half a day or
longer." [p169]

His rationale is as follows. "When an engine has been standing for
awhile and has not been pulled through by hand prior to starting, an
accident could result if fuel or oil has collected in the cylinders.
When the engine fires, trapped fluids can cause bent piston rods,
cracked cylinders, or a damaged crankshaft. Althouogh such accidents
might not cause bodily injury, they surely can harm one's budget and can
beavoided by proper preflight procedures. It is also possible for
damage of this type to remain hidden until something fails in flight"
[pp 147-148].

Sounds like the author has been flying with radial engines.


I am quite surprised that this is the first I have heard such advice.

What do folks on this newsgroup think of that advice?

Not necessary if you're flying behind a flat engine. Someone else will have to
speak for radials.


Does anyone out there do this routinely?

If so, what is the proper procedure? Do you just turn the prop slowly
in the direction the prop normally turns?

Could fuel actually collect in the cylinders as suggested? Why would
the fuel not just evaporate?

Remove SHIRT to reply directly
Dave

O. Sami Saydjari ) wrote:

Could fuel actually collect in the cylinders as suggested? Why would
the fuel not just evaporate?

Wouldn't killing the engine by pulling the mixture lever out remove all
fuel in the cylinders?

--
Peter

In article ,
"O. Sami Saydjari" wrote:

In reading a booked called "Design for Safety", by David Thurston, he
advises owners to "turn the propeller over by hand three or four times
during preflight if the airplane has been standing for half a day or
longer." [p169]

How old is the book? This sounds like something that would be advised
for radial engines, where such issues (called hydraulic lock) were
indeed a problem.

Unless your aircraft manual specifically advises you to do this, I
wouldn't.

"O. Sami Saydjari" wrote:

I am quite surprised that this is the first I have heard such advice.

How old is this book? (I'm guessing that it dates from the 30s or 40s).

What do folks on this newsgroup think of that advice?

Sounds like he's talking about radial engines. Radials indeed tend to collect oil in
the lower two or three cylinders. Most radial owners pull the prop through a few
times to check for hydraulic lock. The old "inverted" engines like the Ranger series
sometimes presented similar problems. This is not a problem with the horizontally
opposed engines behind which most of us fly.

Does anyone out there do this routinely?

I frequently pull the prop through four times to check compression. This also makes
it slightly easier to start in Winter by breaking the gummy oil bond that tends to
form between the rings and cylinder walls.

If so, what is the proper procedure? Do you just turn the prop slowly
in the direction the prop normally turns?

Make sure the mags are off and mixture at lean cutoff. Pull the prop in the direction
it normally turns. Stay out of the plane of the prop. My prop is indexed to stop
straight up and down. When I pull the prop through, I pull the lower blade up.

Could fuel actually collect in the cylinders as suggested?

Not in most light planes. The carb is usually behind or under the engine. Even if gas
did flow through the carb (and there are several valves that usually prevent this),
the fuel would just fall out the throat of the carb.

Why would the fuel not just evaporate?

If raw gas pooled in the cylinders or induction system, the saturation point of the
air in there would be reached rather quickly.

George Patterson
I childproofed my house, but they *still* get in.

The book appears to have been published in 1995. He does not seem to
say anywhere that the advice is unique to radials.

-Sami

Roy Smith wrote:

In article ,
"O. Sami Saydjari" wrote:


In reading a booked called "Design for Safety", by David Thurston, he
advises owners to "turn the propeller over by hand three or four times
during preflight if the airplane has been standing for half a day or
longer." [p169]


How old is the book? This sounds like something that would be advised
for radial engines, where such issues (called hydraulic lock) were
indeed a problem.

Unless your aircraft manual specifically advises you to do this, I
wouldn't.

O. Sami Saydjari wrote:

The book appears to have been published in 1995. He does not seem to
say anywhere that the advice is unique to radials.

Hydraulic lock on radials without clean kits is well understood, but for
wet sump boxer engines like we generally fly behind the advice not only
makes no sense, it's contrary to Lycoming's current recommendations.
With the oil sump under beneath the engine there's simply no mechanism
for lock to occur, unless you tend to park your aircraft inverted.

About the only mechanism I can imagine for causing something like this
would be on some injected engines, where hitting the boost pump and
ramming the mixture full forward while the engine is stopped will dump
gobs of fuel into the intake runners. While much of it will eventually
come pouring out the air cleaner it's not hard to imagine getting
unlucky and having one cylinder with an intake valve open. Hardly seems
the basis for turning the engine over by hand as a standard procedure.

Chris Kennedy wrote:

While much of it will eventually
come pouring out the air cleaner it's not hard to imagine getting
unlucky and having one cylinder with an intake valve open.

In any engine that has valves and at least four cylinders, at least one of the intake
valves will be open when the engine is not running. In a four-banger, there will be
one piston on the power stroke and another on the compression stroke, and these two
pistons will stop about halfway down the bore (where the compression in each is about
equal). One of the other pistons will be halfway down the intake stroke.

George Patterson
I childproofed my house, but they *still* get in.

I do it when it's 5 C outside or below, just to help the battery and starter
a bit.
________________
G. Paleologopoulos


"O. Sami Saydjari" wrote in message
...
In reading a booked called "Design for Safety", by David Thurston, he
advises owners to "turn the propeller over by hand three or four times
during preflight if the airplane has been standing for half a day or
longer." [p169]

His rationale is as follows. "When an engine has been standing for
awhile and has not been pulled through by hand prior to starting, an
accident could result if fuel or oil has collected in the cylinders.
When the engine fires, trapped fluids can cause bent piston rods,
cracked cylinders, or a damaged crankshaft. Althouogh such accidents
might not cause bodily injury, they surely can harm one's budget and can
beavoided by proper preflight procedures. It is also possible for
damage of this type to remain hidden until something fails in flight"
[pp 147-148].

I am quite surprised that this is the first I have heard such advice.

What do folks on this newsgroup think of that advice?

Does anyone out there do this routinely?

If so, what is the proper procedure? Do you just turn the prop slowly
in the direction the prop normally turns?

Could fuel actually collect in the cylinders as suggested? Why would
the fuel not just evaporate?

-Sami
M2057M, Piper Turbo Arrow III

If you even remotely suspected fuel then hand propping seems to
be to be an invitation to the new name of Stumpy. Why take a
chance on a cylinder firing and removing an appendage??


"O. Sami Saydjari" wrote in message
...
In reading a booked called "Design for Safety", by David
Thurston, he
advises owners to "turn the propeller over by hand three or
four times
during preflight if the airplane has been standing for half a
day or
longer." [p169]

His rationale is as follows. "When an engine has been standing
for
awhile and has not been pulled through by hand prior to
starting, an
accident could result if fuel or oil has collected in the
cylinders.
When the engine fires, trapped fluids can cause bent piston
rods,
cracked cylinders, or a damaged crankshaft. Althouogh such
accidents
might not cause bodily injury, they surely can harm one's
budget and can
beavoided by proper preflight procedures. It is also possible
for
damage of this type to remain hidden until something fails in
flight"
[pp 147-148].

I am quite surprised that this is the first I have heard such
advice.

What do folks on this newsgroup think of that advice?

Does anyone out there do this routinely?

If so, what is the proper procedure? Do you just turn the prop
slowly
in the direction the prop normally turns?

Could fuel actually collect in the cylinders as suggested? Why
would
the fuel not just evaporate?

-Sami
M2057M, Piper Turbo Arrow III