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.

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.

On Mon, 17 May 2004 16:20:27 GMT, Chris Kennedy
wrote:

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

That's the way I start mine.

come pouring out the air cleaner it's not hard to imagine getting

None of it comes out the air cleaner, but it sure do run out the
exhaust stacks. OTOH, Boost pump on for a count of three (or even
10)hardly qualifies for enough to block a cylinder. Course the count
of ten might start a fire. :-))

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

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.

I always pull the prop through at least two revolutions - just to make
sure there is compression on all six cylinders.

As for there being no need to do so with opposed engines, I vividly recall
a pilot telling the story about what happened to him. It seems he had just
bought a new (to him) airplane, and was trying it out. It was an early
model Cessna 210, with fuel injection. He decided to find out how fast it
was, and laid out a course between two points along the Southern California
coastline. Then he flew the course with the throttle and prop firewalled.
To cancel the efect of wind, he planned to fly it in both directions. The
outbound pass went well, but on the way back there was suddenly a loud bang,
and the view out the windshield went black (covered with oil). Down he went,
sighting out the side windows as best he could. He ditched it in the ocean,
and managed to get out before it sank.

It gets worse. As there were no boats within sight, he swam to the beach.
There was no one there either. Then a boat came along, so he swam out to
it. About that time, some rescuers showed up on the beach, so he swam
back again. Later, the plane was recovered. They found that a cylinder
had blown off the engine, right through the cowling. The analysis was
hydraulic lock, caused by a leaky injector. The theory was that the
cylinder had filled with gasoline, and was overstressed when the engine
was started. It could have happened long before the final flight.

Worst of all, he had neglected to obtain insurance for his new toy. The
only good news in this event is that he walked (or rather swam) away
with only a minor injury.


David Johnson

"O. Sami Saydjari" wrote in message ...
The book appears to have been published in 1995. He does not seem to
say anywhere that the advice is unique to radials.

-Sami

It certainly sounds like the old radial hydro-lock check. Since the
oil sump and fuel system of your average horizontally opposed engine
are lower than the cylinders, I can't see where this procedure would
be applicable. For radials, on the other hand, it's a very common
procedure.

BTW - Was that you I saw on "Frontline" last week?

John Galban=====N4BQ (PA28-180)