Metal Prop vs. Wood Prop

"Kyle Boatright" wrote in message
t...

"Larry Smith" wrote in message
...

"Barnyard BOb --" wrote in message
...
On Sat, 20 Sep 2003 19:21:22 -0400, "Larry Smith"
wrote:

I have a wood prop on my Taylorcraft and the GPS says it's slow, at
around
65 kts. How about a discussion on the relative merits of wood and
aluminum
props. I understand that wood is easier on your engine but the
aluminum
prop is more efficient. Another thing I notice too, especially on
the
O-320 and O-360-powered RV's is that the wood prop is so light it has
little
flywheel effect and if you don't have your timing retarded, it will
kick
back in a heartbeat. I figure the wood prop on a Van's aircraft is
for
CG.

To retard the timing because of a wooden prop is nuts.
I've never met anyone dumb enough to even consider this.
YMMV.

No flywheel effect with the lightweight prop. Add to that one of those
hot-spark electronic ignitions and you have the engine's flywheel and
the
starter trying to tear each other up. Kickback. Never had it happen
to
me but have seen it, so you are supposed to retard the timing, but just
at
starting time, by starting on the mag, NOT on the Electroair. After
she
begins running then you turn on the Electroair and everything is running
at
advanced timing. And btw I recall reading that Klaus Savier
(Lightspeed)
would advance his timing from the cockpit to as much as 45 degrees
before
top dead center. During a race. At altitude. But not when starting.
ymmav.


Larry,

The Electroair does retard the timing to 0 degrees BTDC below a threshold
RPM level. This prevents starting kick-back. I seem to remember the
advance
is at 0 until 300-400 rpm, but the manual is at the airport. Above that
level, the spark advances along a curve to the same setting you'd get from
a
mag.. That lasts until you reach an rpm/manifold pressure combination
that
is representative of a typical cruise power setting. At that time, the
timing follows another curve which advances the spark beyond what you
would
see from a mag. IIRC, the baseline setting is 17 degrees, and I've seen as
much as 40 degrees of advance at high altitude and low power settings.

BTW, my 0-320/wood prop RV-6 is happy to idle at 500-600 rpm with the
Electroair. The biggest downfall to any of these systems (lightspeed,
electroair, etc) is that the parts supply is very limited. If a component
fails, you may have to wait a while for a replacement, particularly if the
vendor is away from home. With a mag, you could have a dozen or more
suppliers ship you a new one in 24 hours. Helps a lot if you break
something while away from home...

KB

Thanks for the correction, Kyle, and for your excellent testimonial. It's
been some time since I saw a broken starter shaft and cogs stripped out of a
flywheel from kickback at starting. One of those hot-spark ignition
systems had been blamed. Everybody here in WNC likes Jeff Rose's ignition.
And besides that, we just nacherly gravitate towards Chattanooga folks.
They is down home.

I'm about to be looking for a hot-sparker for a six-banger.