George,
I'm in the office, not anywhere near a prop, so this is from faint memory.
First of all, I do recall that it was something on the order of 15 degrees but
definitely not measured at the tip.
Mine is a 912, three-blade Warp Drive, RPM limited to 5500.
Long version of old story:
Prop came with the Warp protractor, but at the time an old WWII pilot/crop duster/A&P
was still alive and offering advice.
He loaned me a high-dollar prop protractor complete with wood case, and promised
to hurt me if I damaged it.
He offered that any protractor needs to be placed at the 'widest' place on a prop
in order that the protractor sit across as much width as possible to insure
repeatable measurements.
He went on to instruct that the blade being adjusted need to be 'level' using a
small bubble level each time, and at the same point on each blade; that the 'number
of degrees' will vary from station to station along the blade, and what
ends up being 'correct' is what you get.
Said differently, because the 'twist' in the blade changes as you move outboard,
the resulting protractor reading changes as you move it along the blade. Therefore,
according to this receipient of the 'Charles Taylor Award', you simply
pick a wide place, mark it with masking tape (on each blade) and apply the protractor.
Following his instructions, I set mine, then fired it up. Had too much at 20 degrees,
so I reduced it 2 degrees and tried again. Still too much. After three
more attempts I was satisfied.
A run-up on the ground gave me 5400 and slid the tires on wet grass. On takeoff
it would go to 5500 RPM at about 40 knots, but never above about 5550.
The preceeding was on a pusher airplane. On the 701 (same engine, tractor prop)
I've not done a final setting, but did set the pitch a few degrees too much
specifically to limit RPM until I'm ready to adjust it.
One other comment about measuring at the tip: My old friend was really specific
about NOT using a narrow portion of the blade.....too easy to have one or two
degrees difference between blades and then have them tracking all over the place.
He stressed that placement of the measuring device will dictate the 'reading'
you get; and that the pitch YOU get may not agree with what some other fellow
gets who placed his protractor at a different station (distance from the
hub) on the same prop.
Hope this makes sense!
Have a great week, best regards, and surely somebody will jump in with truth &
justice!
Zed
