Survey - 3 blade prop conversion- Cockpit vibration, happy or not

In regards to your O-540, many O-540 airplanes have 3-bladers from the
factory. Commander 114, Piper 6/300, Navajo, etc. I don't know if they

The one to talk to would be Bellanca Company. The Viking has been on the market
for years with a 3 blade.

On Sun, 27 Jun 2004 17:13:39 GMT, "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?

It's really complicated for a complete answer. The basics are that
the prop has a level of harmonic emission, the engine does as well.
These need to be balanced to achieve no adverse effects/affects on the
crank and airframe. In some planes this is not fully achieved and is
why you have ranges of RPM that are restricted from continuous use.
If you want more details, I can try to get a better understanding, but
basically its that everything vibrates when it moves and the altered
combination seems to cause a problem. Dynamic balancing has been
shown to make improvements, but I didn't see that it was a "fix all"
for all installations.

Someone asked if the 3blade is heavier. Not for this application.
The 2 blade is aluminum and the 3 blade is plastic. You actually lose
22 pounds, but its so far forward sometimes you need to add a weight
to the back to keep CG in tolerances.

z

Matt Whiting wrote in message ...
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, .......

Yes, and four cylinder should have either two or four blades.
I checked with prop mfgs and they will generally tell you that
three blades do not get along with four bangers - especially
larger ones. One mfg essentially refused to sell a three blade
for a four banger and insisted on two or four blades.
On smaller engines like O320 a three blade is less of a problem
simply because the power pulses are much less severe than that
of a O-360 for example.

There is more of an issue than just vibration - the potential
breakup of the three blade prop with a LARGE four banger.
Any four banger O 360 or larger should not use a three blade
except wooden ones - wood can dampen the extra vibration energy.

My 220hp Franklin 6, gets hapily along with a IVO 3 blade inflight
adjustable prop - very smooth at high power.

---------------------------------------------
SQ2000 canard: http://www.abri.com/sq2000

With all due respect, Paul... can you find ANY actual information to
back up this theory? NTSB reports, maybe?

I upgraded my 4-banger IO-360 to a three-bladed Black Mac (aluminum)
prop last year and it is fantastic. No loss in cruise speed, BIG jump
in climb rate, smooth as silk, much quieter than the 2-bladed Hartzell.
The red zone on my tach is also no longer meaningful. It was also
$1000 less than the 2-bladed prop, and immediately available.

I worry that it will come apart with about the same vigor that I worry
my California house will fall off into the ocean in the next earthquake.


Paul Lee wrote:

There is more of an issue than just vibration - the potential
breakup of the three blade prop with a LARGE four banger.
Any four banger O 360 or larger should not use a three blade
except wooden ones - wood can dampen the extra vibration energy.

"Jay Honeck" wrote in message
news:7yGDc.101718$2i5.87696@attbi_s52...
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

I guess that makes sense.

It would seem logical that a third power-producing blade would be
superior.

Otherwise why would any planes have more than two blades?

Quite. Why would, say, the P-51, with a 12 cylinder engine have a three and
then a four bladed prop?

Hello Folks,

Theoretically, a 3 blade whould be smoother, quieter and more efficient,
but it simply isn't like that in the real world.
I became aware of common dissatifaction of cockpit vibration in the time
following AD 98-18-02, which mandates 500 hour disassembly of the Hartzell
BHC series.
Many owners chose to buy a 3-blade conversion instead. Surprisingly, the
3-blade was several thousand dollars cheaper than an approved 2-blade.

A couple dozen owners of Commanche, Mooneys and other makes contacted me
for dynamic prop balancing. Many wtill were not happy.
At the time it seemed most were conversions with scimitar blades.
I presumed it was because of 3 blades installed on a 4 cylinder Lycoming.

A 1956 C180 owner sent his back, and he later informed me that the prop mfg
admitted there was a problem sometimes withthe 3-blade on the installations.
They suggested it was due to counterweights.
Other C182 owners were not happy either.

Later I became involved with the issue on Beech V35's. Some of these are
McCauley conversions with scimitar blades. Debonairs with th O-470's
generally regret 3-blades. Even STC holders like Bery D'Shannon have heard
complaints.

Where I'm lacking is that I did not fly many of the planes myself, nor can
the owners actually define the vibration complaint. One response was
"...the panel is smooth now but the vibration moved down to tthe rudder
pedals..."

I wonder if their tail controls needed rigged, or maybe it was because the
scimitar blades have different tip vortices affecting the tail surfaces.
Aircraft empennages are lightweight and suffer much from vibration, not only
propwash but also mechanical excitation being transfered from the
powerplant. Other day, I helped push a C414 into the hangar with a
powertug that had a 5hp Briggs & Stratton. The horizontals were humming
from the little engine thump.

A related issue perhaps, is Vans Aircraft tried to get Hartzell to bless the
a 2 blade installation on a 4-cyl Lyc with electronic ignition. Hartzell
refused.
.. Whether it was liability, or the expense of redoing vibration surveys, or
if they actually saw something critical in a a vibration survey I do not
know.
Electronic ignition varys the engine timing and also may have a slightly
different spark characteristic which influence the cylinder pressures, thus
the power pulse affects the torsion which affects how props vibrates.
I get a gut feeling that certified approval of electronic ignitions on 4
cylinders may be long in coming.

Like a tuning fork, all props have one or more resonance points. The tips
flutter fore and aft, plus the blade is stressed by a bending moment in the
rotation and anti-rotation axis. Prop mfg's survey the vibration patterns
of a particular engine-prop combination. This is why one sees tachometer
yellow arcs and red arcs at on some aircraft and also why engines have
different counterweight configuration.

Take care
Kent Felkins

Jay Honeck wrote:

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


I guess that makes sense.

It would seem logical that a third power-producing blade would be superior.

Otherwise why would any planes have more than two blades?

Well, some airplanes NEED the extra blades to handle the power yet still
remain a reasonable overall diameter. However, a 180 Arrow definitely
isn't in that category. I suspect that a 1,500 SHP turboprop would need
really long landing gear if it had only a two blade prop!


Matt

OK. Guess I was somewhat engrossed in reducing weight considerations
for experimentals. McCauley, Hartzell props are heavy duty and ridgid
enough to withstand where weight is not top concern. If the engine is
small enough or the propeller is massive enough (same thing) the power
pulses are within limits. But there is a basic problem of large four
bangers power pulse interaction with 3 bladed props. Here is one
discussion of problems mating lighter weight composite 3 blade prop
(IVO) with IO-360 and other 6 cylinder engines:
http://www.bewersdorff.com/wankel/fl...y/FlRo2Q00.txt
Not too far back I was inquiring about purchasing a composite prop for
IO-360 and the manufacturer would sell only a two blade or a four
blade for it. AND obviously, there is a problem as suggested by previous
posters here, but may not such a factor with more massive or expensive CS
props.

Elwood Dowd wrote in message ...
With all due respect, Paul... can you find ANY actual information to
back up this theory? NTSB reports, maybe?

I upgraded my 4-banger IO-360 to a three-bladed Black Mac (aluminum)
prop last year and it is fantastic. No loss in cruise speed, BIG jump
in climb rate, smooth as silk, much quieter than the 2-bladed Hartzell.
The red zone on my tach is also no longer meaningful. It was also
$1000 less than the 2-bladed prop, and immediately available.

I worry that it will come apart with about the same vigor that I worry
my California house will fall off into the ocean in the next earthquake.


Paul Lee wrote:

There is more of an issue than just vibration - the potential
breakup of the three blade prop with a LARGE four banger.
Any four banger O 360 or larger should not use a three blade
except wooden ones - wood can dampen the extra vibration energy.

"Jay Honeck" wrote in message news:JeDDc.101103$2i5.20125@attbi_s52...
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?

It should, but the science of vibration studies is complicated.
I know very little about it, but old mechanics who battle three-blade
vibration will sometimes tell you that removing the prop and rotating
it 180 degrees on the crank will sometimes fix it. The 185 (IO-520)
has been known to throw the alternator belt with three-blades, and
rotating the prop usually stops it. Don't ask me to explain it, but
there must be some sound reason behind it.

Dan

I installed a 3-blade on my IO360C1C Arrow because old prop was out of
spec and cheaper than a new 2-blade. I think there is less noise,
it's nice to be able to ignore the 2100-2350 RPM avoidance placard for
the old 2-blade, and climb performance is definitely better.

I had substantial vibration initially, but after 180 rotation and
dynamic balance it is now very smooth - no complaint.

Cruise speed is hard to judge because of lack of controlled
conditions, but I can still get 175 mph TAS out the old 69 Arrow. It
certainly isn't any faster, and I can't prove that it's slower.

And, as others have said, it does look pretty sexy. Shorter blades
also pick up less FOD.