3 blade prop vibration

3 blade prop vibration

<HTML>I own a 182 K model, 2000 hr.s TT ,O-470 with 250 SMOH from "Firewall Forward".The aircraft had a Mcauley 3 blade prop installed about eight years ago.The engine was overhauled about three years ago.The prop was overhauled at about the same time as the engine. I bought the aircraft six months ago.I noticed a vibration which increased with a reduced RPM (2200).I had the prop balanced and it checked out O.K. Still had  the vibration in flight.Checked motor mounts and they are like new. Engine runs great with good mag checks,temps etc.Had the prop balanced a second time,same thing ...checked out right on the money!Still had the vibration.In desperation I borrowed a two blade prop and went flying....NO VIBRATION!. So I took the blade in and had it overhauled, remounted and balanced....went flying and the vibration is still there! (it did seem to be slightly better..maybe).I've flown quite a few other 182's and have never felt a similar vibration...however this is the only one I've flown with a three blade prop.This problem is driving me NUTS! I've got this beautiful low time airplane, a prop that checks out A.O.K at overhaul...but I can't shake this vibration(no pun intended).I have heard every rumor and wives tale out there! The most common being..."The airplane/engine took a set with a two blade prop and won't accept a three blade." I am very frustrated. I would really appreciate hearing from anyone with similar experiances or possible fixes. But what I would really like would be to trade my three blade for a two blade . Any takers???? (I'm serious!)

                                                                                     Blue Skies!
                                                                                                    Mark</HTML>

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Re: 3 blade prop vibration

<HTML>Not if it vibrates! <grin> (Sorry, couldn't resist.)
  You're correct not to fall for the wives tales.  No such thing as "taking a set".  Pure BS.  Two things come to mind.  The first is to use a different shop to balance the prop.  (And I assume you're taling about dynamic balancing? as opposed to static balancing?)  There are two ways to balance a prop, and two different machines with slightly differing processes at that.  Static balance is what the prop shop does on the bench. It is crude, but close.  Not exact.  Dynamic balancing is done on the airplane with the engine running at cruise RPM.  Much better.  Not only does that balance the prop, but also the spinner, the crankshaft, cam, etc, etc.
Dynamic balancing ordinarily uses one of two systems, either Chadwick-Helmuth (most common) or ACES (more recent.)  I've had both done on various airplanes and had better luck with the ACES equipment, but either should work for you.
  Last, it may not really be a balance problem.  It may be that particular 3-blade prop.  It may have one blade that is flexing at odd intervals, despite it's particular weight.  Really a rare occurence, but can happen.  See if your prop shop can obtain a similar loaner 3-blade for you to try.  If the problem goes away, I suggest you exchange your prop. 
  (As for 2-blade vs 3-blade, I'm predisposed toward 2-blade props anyway in almost every case.  Less expensive, less complicated, cheaper to maintain, faster and more efficient.  3-blades have only a very slight advantage on ground clearance, takeoff distance and climb, but are less efficient at cruise and are always slower.)</HTML>

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Re: 3 blade prop vibration

<HTML>Mark, looks like you have tried everything.  Well, almost.  What you have done is change something drastic in the powerplant "system" and you seem to have gone backwards.  New technology has made us all smarter and we can identify the reason you are experiencing frustration.  Let me explain.
Cessna designed the 182 for a 230 hp and a 2 bladed prop.  Most 0-470's are vibrators at best and the slower turning "U" engine is even worse.  Just that most people do not even know there is a vibration, and they think its just supposed to be like that.  It gets much worse if you were to do an engine upgrade to more horsepower.  Let's look at the engine mount itself.
If you look at your original mount, there isn't much there, plus it utilizes some small isolators, which seem to need replacing every 300 - 500 hours because they sag, and when they sag the trust line changes and you also get degraded performance.  Having said that, the isolators are definitely to small for this engine.  Now add the extra weight of the 3 blade, some 48 pounds, way out on the arm, and now you have your problem.
Seaplanes West addressed this issue at great lengths when they converted the 182 to a floatplane.  The firewall was buckling and engine mounts cracking when operating on floats.  The float loads are quite severe on the aircraft in rough water landings.  Also, to make matters worse the attachments of the front float struts were to the engine mount attachment area. 
They designed and re-engineered a totally new engine mount to address all the issues.  They beefed up and added more tubing, added vertical and horizontal bars into the mount next up to the firewall for support at the firewall area.  This strengthened the whole fuselage. 
On wheel operations you get the benefit of ridding the engine vibrations out thru the wheel gear that hangs down there with rubber tires on the ends of these struts.  Floats do not have this feature because the vibrations go around in a circle thru the float and around the other side, back into the cockpit.  Hence our problems are a lot worse while on floats.
I know this doesn't do much for your case yet, but here comes the advantage for you.  The original isolators were replaced with larger ones.  If you look at where the isolators are placed relative to the engine, the aft mounts hang right at the rear of the case, and the fwd mounts are in the middle of the case.  This tells us that the two needed to do different jobs.  This was incorporated into the new mount and our isolators are about 4 times larger and 7 times stiffer.
We are very pleased with the performance.  It has been said that the 0-470-R engine runs "turbine smooth" in our mount.  Most test drivers cannot believe the difference.  Our experience is that the engine runs EVEN SMOOTHER with a 3 bladed prop installed vs a 2 blade.  This is due to the extra weight on the mounts which they were designed for. 
You can also take another page out of the float planes handbook, and add 1/4" stainless "cabin flying wires" to the fuselage that mount in thru the windshield opening.  This STOPS all squeaking and shaking when on takeoff and landing rolls even in rough fields.
Hopefully this settles your frustration, look us up at www.seaplaneswest.com for more info.  Try it, if this doesn't work, I'll buy your prop or trade you for a 2 blade anyday.
Jim</HTML>

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Re: 3 blade prop vibration

mark Wrote:
-------------------------------------------------------
> I own a 182 K model, 2000 hr.s TT ,O-470 with 250
> SMOH from "Firewall Forward".The aircraft had a
> Mcauley 3 blade prop installed about eight years
> ago.The engine was overhauled about three years
> ago.The prop was overhauled at about the same time
> as the engine. I bought the aircraft six months
> ago.I noticed a vibration which increased with a
> reduced RPM (2200).I had the prop balanced and it
> checked out O.K. Still had  the vibration in
> flight.Checked motor mounts and they are like new.
> Engine runs great with good mag checks,temps
> etc.Had the prop balanced a second time,same thing
> ...checked out right on the money!Still had the
> vibration.In desperation I borrowed a two blade
> prop and went flying....NO VIBRATION!. So I took
> the blade in and had it overhauled, remounted and
> balanced....went flying and the vibration is still
> there! (it did seem to be slightly
> better..maybe).I've flown quite a few other 182's
> and have never felt a similar vibration...however
> this is the only one I've flown with a three blade
> prop.This problem is driving me NUTS! I've got
> this beautiful low time airplane, a prop that
> checks out A.O.K at overhaul...but I can't shake
> this vibration(no pun intended).I have heard every
> rumor and wives tale out there! The most common
> being..."The airplane/engine took a set with a two
> blade prop and won't accept a three blade." I am
> very frustrated. I would really appreciate hearing
> from anyone with similar experiances or possible
> fixes. But what I would really like would be to
> trade my three blade for a two blade . Any
> takers???? (I'm serious!)
>
>                                                   
>                                   Blue Skies!
>                                                   
>                                                 
> Mark

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Re: 3 blade prop vibration

>Mark,
Check the balance weights on your crankshaft. It's fairly common for them to freeze up, wear or even break. Worth a look?

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