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

[Fly]

Hello Folks,
I asking for responses from any who have converted from a 2-blade to 3 blade
prop on their plane. I not interested in any performance claims but just
specifically the issue of cockpit vibration.
The prop mfg's and STC rep's are aware of this issue but express their
bewilderment to me. I've been looking for a common thread but haven't
found it yet. . There may be some engineer in a backroom somewhere who
knows the answer, but I haven't talked with him yet.
I don't have a better answer than anybody else.
I have been polling other owners groups and will later post what results I
can come up with.

It goes across the popular airframe models. Simply some are happy, others
are not. Even after a dynamic prop balance, some owners are not l not
happy with the different vibration, and different noise.
At the present, the conventional wisdom for those contemplating conversion,
is to not let go of the 2-blade until you are sure and make the deal to be
able to return the 3-blade for a refund if you choose.

It seems maybe that 6 Cyl Continentals which do not have a crankshaft 5th
order dampner or counterweight do not like 3 blades. i.e. Cessna 182 with
O-470-L or a Beech V35 with IO520-BA. Every Cessna produced with a
3-blade option, has an engine with a 4th,5th and 6th counterweight. Others
engines didn't, like the O-470L which has a 4th order and two 6th orders.

It could be that the models with scimitar blade design are the chief
culprit.
Some owners of Pipers and Mooneys with 4 cylinder Lycomings have asked me
about the vibration. All of them were scimitar blades.

Another factor is whether the conversion was done in conjunction with a
fresh engine overhaul versus midtime. Some speculate that at midtime, the
crank counterweights may have already worn in, taken a set, to the old prop
vibration.

I'd appreciate those who wish to participate if you let me know what
airframe and engine you have and what prop you went to, scimitar blade or
not. And whether the conversion was done fresh or at midtime and whether
you were happy or not with the cockpit vibration and noise.
Also useful would be a short note on how you percieved the vibration.

You can email me directly if you wish.


Thank you very much

Kent Felkins
Tulsa Oklahoma

[Jay Honeck]

Interesting work, Kent. Thanks for doing it.

Any word on the O-540s? A 3-blade is in our future, if (when) our 2-blade
needs to be over-hauled.

But only if it doesn't change the vibration for the worse!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[EDR]

In article <xCzDc.117287$eu.53283@attbi_s02>, Jay Honeck
> wrote:

> Any word on the O-540s? A 3-blade is in our future, if (when) our 2-blade
> needs to be over-hauled.

Doesn't a two-blade weigh less?

Isn't a two-blade more efficient?

[zatatime]

On Sun, 27 Jun 2004 13:05:33 GMT, "Jay Honeck"
> wrote:

>Interesting work, Kent. Thanks for doing it.
>
>Any word on the O-540s? A 3-blade is in our future, if (when) our 2-blade
>needs to be over-hauled.
>
>But only if it doesn't change the vibration for the worse!


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. Many
thought it was insignificant, but many thought it was worrisome. A
couple returned the new prop because they really didn't like it. I
took the approach that additional vibration no matter how minor is
un-needed. It could do nothing to the aircraft, or it could do
something, either way a small plane is noisy enough and has enough
vibration that I didn't want to add anymore, and my luck would be that
I'd have the same violent tail vibration one guy reported. No Thanks.

Other things I didn't like about the 3 blades were the fact that they
are a new "plastic" (carbon composite) type of material. No one knows
for sure what UV does to them. We may see some interesting stories
over the next 10 years if they don't hold up real well. Again its a
debate. Some people say composites are fine, some people say they
will become problematic. Until a 10 or 20 year study shows real
documentation it's all a matter of opinion. Also no ADs have been
issued for these yet (although many blades were scrapped before use
due to a bad production process). I like knowing that my prop
probably won't have any real expensive ADs issued against it. Since
its been in use for so long we generally know the limitations. (I
know once again a subjective opinion). With the composites I just
think a big surprise might be around the corner.

The last thing is that the 3 blades really kill your glide
performance. Almost everyone agreed on this one. My 235 already
leaves a little to be desired at best glide speed, why would anyone
want to shorten it even more? I know you can use the prop control to
overcome some of that, but what if you need to go-around for some
reason, you've got one more (critical) thing to do. The performance
gains on the other side didn't seem significant enough to me to
balance this out. Very slightly better climb performance an no one
reported better cruise.

When all was said and done I spent about 5Gs to do my governor, buy a
blade and have everything put back together. It would have been about
10 for the 3-blade. When I looked at the extra money, and some of the
downsides/unknowns. I kept the extra money in my pocket.

Hope this helps, I kind of streamed my thought process.

z

P.S. Glad you got some momentum behind your airport.

[G.R. Patterson III]

EDR wrote:
>
> Doesn't a two-blade weigh less?

If tghe blade material is the same, the 2-blade prop weighs less.

> Isn't a two-blade more efficient?

Yes.

George Patterson
None of us is as dumb as all of us.

[Jay Honeck]

> 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?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Jay Honeck]

> 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?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Matt Whiting]

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 are: 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

[Jay Honeck]

> 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?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Aaron Coolidge]

Jay Honeck > wrote:

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

: Otherwise why would any planes have more than two blades?

At some point having 2 blades to absorb the engine power leads to blades
that are so long the tips go supersonic. This is bad, for many reasons
including the noise. (Republic Aviation actually made an airplane that had
intentionally supersonic blades: google "thunderscreech".) When you reach
this point the only solution is to use more blades. Hey, the ATR-72 has 6
blades on each prop!

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
use different crankshaft vibration dampers or not. My (solid crank) O-360A4A
does not have vibration dampers, perhaps the Arrow's does not either,
leading to the extra vibration with a 3-blader.

There is an excellent article in "Torque Meter" about the design of the
P&W R2800 crankshaft that describes the difficulties in crankshaft design
and handling torsional vibrations, as well as descriptions of how the vib.
dampers work. The article discusses the interplay of prop, engine, and
reduction gearbox. The article is on-line, but I don't have the link handy.
--
Aaron Coolidge

[PInc972390]

>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.

[zatatime]

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

[Paul Lee]

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

[Elwood Dowd]

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.

[Tom Sixkiller]

"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?

[Fly]

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

[Matt Whiting]

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

[Paul Lee]

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/flyrotary/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.

[Dan Thomas]

"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

[PaulH]

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.

[Mike Rapoport]

Generally a three blade will seem smoother on a six cylinder engine. Same
for boats, three blade for 6cyl, four blade for 8cyl. This is for
noise/vibration only performance may be different.

Mike
MU-2

"Jay Honeck" > wrote in message
news:xCzDc.117287$eu.53283@attbi_s02...
> Interesting work, Kent. Thanks for doing it.
>
> Any word on the O-540s? A 3-blade is in our future, if (when) our 2-blade
> needs to be over-hauled.
>
> But only if it doesn't change the vibration for the worse!
> --
> Jay Honeck
> Iowa City, IA
> Pathfinder N56993
> www.AlexisParkInn.com
> "Your Aviation Destination"
>
>