Prop Indexing

In rec.aviation.owning nrp wrote:
: At that time, we consulted the service manual, which
: states 8-2.

: Maybe that's from the Piper legal dept to discourage hand
: propping.........!

Possibly, but that part of the book has been there forever. The trouble with
the 8-2 position (from the front) was that is was unobtainable IIRC. It was a nice,
clean 30 degrees off in either direction. Doesn't exactly give one a warm fuzzy when
the official service instructions are impossible to follow.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

wrote:
In rec.aviation.owning nrp wrote:
: At that time, we consulted the service manual, which
: states 8-2.

: Maybe that's from the Piper legal dept to discourage hand
: propping.........!

Possibly, but that part of the book has been there forever. The trouble with
the 8-2 position (from the front) was that is was unobtainable IIRC. It was a nice,
clean 30 degrees off in either direction. Doesn't exactly give one a warm fuzzy when
the official service instructions are impossible to follow.

-Cory


The 8-2 (or more closely 7:30--1:30) IS appropriate for hand
propping. The position given by Service Manuals is at TDC so that the
prop will be at about 10:00 when ready to hand prop with the piston
partway up thye compression stroke.

The three-blade props used on some larger engines can cause
mysterious vibrations unique to them. Some Cessna 185s, for example,
had a habit of throwing off the alternator belt. The problem was
normally cured by removing the prop and rotating it 180 degrees. Don't
ask me why.

Some engines have problems with the pulsating airflow off the prop
blades striking the air intake at just the wrong time and upsetting air
and fuel flows in the carb. (Remember that the airflow through the carb
isn't particularly constant, as it accellerates and decellerates with
intake valves opening and closing.) This is readily apparent on some
older 182s, on which the air cleaner comes off with the cowling, and
running the engine with the cowl off will make for a rough-running
engine. The air cleaner damps some of the pulsation. Re-indexing the
prop might improve smoothness and maybe performance.

Dan

In rec.aviation.owning wrote:
: The 8-2 (or more closely 7:30--1:30) IS appropriate for hand
: propping. The position given by Service Manuals is at TDC so that the
: prop will be at about 10:00 when ready to hand prop with the piston
: partway up thye compression stroke.

The problem is that it's not clear to me whether or not saying "8-2" is with
respect to looking at the prop from the front (as one would be when servicing it), or
with respect to sitting in the pilot's seat (as everything else is always referenced).

: engine. The air cleaner damps some of the pulsation. Re-indexing the
: prop might improve smoothness and maybe performance.

Re-indexing our O-360 prop reduced the perceived vibration... not sure if it
was real or "we did all that work so it *must* be better." Unfortunately, we
reindexed it to make it less conducive to hand-propping.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

The problem is that it's not clear to me whether or not saying "8-2" is with
respect to looking at the prop from the front (as one would be when servicing it), or
with respect to sitting in the pilot's seat (as everything else is always referenced).

The Cessna 172 manual says to position one blade over the TC mark on
the AFT face of the ring gear support (which is straight up when at
TDC), then rotate the prop clockwise (when viewed from the front of the
engine) to the first bushing and locate it there. That puts the prop at
about the 7:30/1:30 spot.

Dan