Jay Honeck wrote:

I did a bunch of "research" (asking as many 235 owners as I could
find) about this two years ago when one of my blades failed
inspection. Almost all of them reported some sort of vibration.


I've heard this before, but I don't understand why an extra blade would
inherently add vibration?

If anything, shouldn't an extra blade reduce vibration?

I thought the same, but it doesn't appear to be the case, at least not
with 4 cylinder engines. I've read that the 3 blade props seem more
compatible with 6 bangers. Supposedly, this is related to power pulses
of the engine, but I still don't see how that is any better with two
long blades rather than three shorter ones. I'd think the longer blades
would flex even more with the power pulses making more vibration, but
this apparently isn't the case. I'm not familiar enough with the
physics of engines, props and vibration to know what is at work here.

Our flying club just replaced a two-blade prop on our 67 Arrow with a
three-blade. We aren't happy with it at all. We haven't had it
dynamically balanced yet and plan to do that this year after the engine
is replaced. We were told that the balance is a composite of the prop
and the engine so we were advised not to balance it now since our engine
is near TBO and will be replaced this coming winter.

The Arrow vibrates a LOT more with the three-blade prop, especially at
RPMs less than about 2200. After someone mentioned a placard against
operation in certain RPM ranges, I checked the tach more closely. It
has no markings on the tach, but there is a small placard near the tach
that says to avoid a certain RPM range (I think it was 1500 - 2200) at
certain levels of MP. I need to write it down next time I visit the
airplane as I don't remember the details now.

As others have mentioned, the power-off glide distance is dramatically
reduced. This is useful if you are flying a fast approach to mix with
the big boys at the larger airports. When you chop the power on short
final, it is like dumping speed brakes. It is a real hazard for
emergency landings. The first one I tried while getting checked out in
this airplane ended up about a mile short of the field I'd selected. I
was amazed at the sink rate as compared to the Skylane I owned
previously. I don't think the Arrow has even an 8:1 glide ratio now,
compared to probably 12:1 or so for the Skylane. I thought it was just
the Hershey bar wing, but my instructor said the Arrow was much better
prior to the prop swap.

Bottom line, none of the club members who'd flown the airplane with the
two-blade prop would make the switch again now that they've flown the
three-blade. I never had the chance to fly the Arrow with the two-blade
prop, but even in a absolute sense, I don't like the three-blade. It's
only advantages a 1. it was cheaper than a new two-blade (this
surprised me also), and 2. it looks cool on the ramp. Other than that,
it is all negative: more weight, more vibration, more drag power-off,
and slightly less cruise speed. Supposedly, a three-blade prop will
give better takeoff and climb performance in exchange for the loss in
cruise, but none of the club members say that this has been the case
with the Arrow. Takeoff and climb are about the same and cruise is
about two knots slower. Could be that 180 HP just isn't enough to gain
the takeoff and climb benefits.


Matt