Propeller / aircraft vibration

[MooneyBob]

It was mentioned in some topics that 3 blade props have more tendency to cause a vibration.

I have 3 blade McCulley on my J and I'd like to hear some opinions on the vibration topic both 2 and 3 blade props.

My question is if there is any vibration " allowed"  at all. I can feel some of the vibration on my yoke ( not on the rudder pedals) and sometimes I think the glare shield is vibrating a little. It depends of course on the power / RPM  setting. I have flown last few days with my CFII and ask him if he thinks there is unusual vibration he said no.

So do you guys have super smooth no vibration planes ( specially two blade props) or it is pretty normal to feel a little vibration in the plane? I have flown Pipers and Cessnas before but I don't recall how they felt.

Thanks

[orionflt]

Bob. have you done a dynamic prop balance?

[clh]

I would recommend dynamically balancing the prop.  It made mine pretty silky smooth.. If you get they correct rpm and mp, I think you will get more vibration. But from what I can tell, the two bladed ones are louder and have more vibration.

[orionflt]

clh

I agree with the prop Balance, but i disagree that the 2 bladed have more vibration. the amount of vibration is determined by how well balanced the assembly is not the number of blades, but a three bladed prop will give you a different frequency of oscillation then a two bladed prop. as for being noisier... yea three's are probably quieter but i don't think it would be really noticeable. as for 2 bladed props, they are more efficient then the three.

[Mooneymite]

I generally hear that 2 blades are smoother on 4 cylinder engines, while 3 blades are smoother on six cylinders.

 

Perhaps it's an OWT, perhaps it is a function of harmonics and black magic.

[MooneyBob]

Thanks. I am scheduled for my balance work next week. I was just wondering if you guys notice ANY vibration at all on your planes or they are smooth as those fancy cars. Mine is not bad IMHO and as I mentioned my CFII said he didn't notice anything unusual.

[Cody Stallings]

It's a function of Amplitude. There have been vibration studies done on the Cessna 188 when converting from a 2 Blade C98 McCauley propeller to a 3 blade propeller of any Flavor, the vibration would get worse... I have been told that a certain type of lord mount, made from a different compound which was more rigged was the fix in that application.

Not sure if test like that have been done with M20's or not.

I work on Propellers an Balance then for a livin an I can tell you from personal experience the 2 blade propellers are smoother.

I fly a M20F with a C3YR/F7282 propeller balanced to less than .03 ips

On the field here is a M20G with a C2YK/F7666A-2 propeller that his balanced down to around .05 ips if my memory is correct.

The G model is smoother than the F even though the Chadwick balancer says otherwise.

I'm not sure if it's the extra weight out front allowing the mounts to flex a little more like in the case of the cessna 188 or not...

But it's puzzling to say the least . My 2 cents.

[rocketman]

Make sure the spinner is on tight!

[tomn]

Bob, I have a three blade Hartzel that is balanced to .01 IPS.  It's pretty smooth but I still feel vibration in your yoke.  Every plane I can remember flying has had some amount of vibration - some more than others.  The smoothest was a 172 with a two blade prop - no idea why though.  I think you'll need to get to the turbine class to get that silky smooth feeling you mentioned.  

 

Tom 

[Mooneymite]

My engine ran much smoother after going to the fine wire plugs.  Not all vibration is associated with the prop balance.

[Cody Stallings]

If you have a C430 propeller, it could still have the blade plugs in it. One of those plugs could leak an fill a single blade up with oil. That would make it shake. If it's been in a shop sense 07 then that should not be an issue.

Like said above, not all vibration is the propeller.

[MooneyBob]

My engine ran much smoother after going to the fine wire plugs.  Not all vibration is associated with the prop balance.

I have a suspicion that it could be something with the engine running a little rough. I will start with the balancing and changing plugs. Thanks.

[mike_elliott]

I generally hear that 2 blades are smoother on 4 cylinder engines, while 3 blades are smoother on six cylinders.

 

Perhaps it's an OWT, perhaps it is a function of harmonics and black magic.

 Not and OWT, most likely the latter. I had both on the same plane. Hartzell in Piqua, OH, could not dynamically balance out the three blade, inspite of the IPS being very low. I had them remove it and ordered a 2 blade because of it. I understand this is not true of the MT three blade, however, but I do not have any personal experience with the MT 3 blade and the 4 cyl. lycs.

Scott, isn't this the setup you have?

[orionflt]

I have dealt with several MT props on different airframes and I would never use one on my aircraft, this is just a personal opinion but but I haven't been impressed with their construction or performance. I'm sure there are opposing opinions. 

 

Brian

[Bob - S50]

I have a suspicion that it could be something with the engine running a little rough. I will start with the balancing and changing plugs. Thanks.

And do a GAMI test too.  It could be uneven power in the cylinders due to uneven fuel distribution.

 

Bob

[bumper]

I have dealt with several MT props on different airframes and I would never use one on my aircraft, this is just a personal opinion but but I haven't been impressed with their construction or performance. I'm sure there are opposing opinions. 

 

Brian

I'll say there are!!

 

There are a couple of general truths when it comes to props, along with the usual black magic and exceptions:

 

The fewer the blades, the more efficient. This is due to interference drag.

Wood props run smoother than metal ones. This is due to the wood's ability to absorb and dampen power pulse vibration.

Wood props are typically less efficient than metal. Due to metal's higher strength and ability to accept thinner airfoils.

Composite props (carbon, kevlar, or glass over a wood or foam core) combine the design flexibility of metal with the smoothness of wood.

 

Most often, a 3 blade is not worth considering unless horsepower is 300 or more. Prop clearance, and the ability to harness horsepower, is where 3 and up shine. Oh, and in ramp appeal.

 

MT propellers absolutely rock! I have a 2 blade on my Husky and it saves 27 lbs on the nose over the 80" Harzell that it replaced. It is also slightly better in the climb, faster in cruise and much smoother overall than the aluminum Hartzell was. (I have my own prop balancer and it all cases props were balanced to less than .05 ips and usually down to .02 ips). MT props are particularly efficient at lower (1800 - 2000) rpm.

 

MT 3-blade props run smoothly on Lyc O and IO-360's on Huskys - - slightly more so than Mt 2-blades, but with a loss of cruise speed on the order of 2 to 3 knots.

 

Back many years ago, I heard Mooney *wanted* to offer 3-blade props, but there was some sort of induced airframe vibration that kept them using 2-blade props. LASAR tried them too - - didn't work well. EDIT, this vibration issue was on the 201 only, not the bigger engines.

 

I would buy another MT in a heartbeat and when my Mooney's prop needs replacement, an MT is the way to go.

 

I have a friend with an C-185. He did static thrust tests comparing the MT 3 blade against Harzell and Mac - - and ended up with the MT.

 

bumper

[orionflt]

Bumper,

Glad you have had good experiences with them, I have one scrap 4 bladed prop sitting around along with a couple of very expensive blades that were not repairable because of chip/nick damage. I agree they have a weight advantage but I haven't seen an efficiency advantage on the applications I have done the comparisons on. I do have friends in Switzerland and Germany, they tell me that MT is highly regarded over there.

 

Brian

[triple8s]

I have been in the equipment maintenance business for about 30 yr so I know a little about machinery. We have a few tree grinding machines and these things have taught me a lot about balancing rotating groups. A rotating mass can be far out of balance and yet feel somewhat smooth, only a dynamic balancing machine can measure the vibrations quickly enough to calculate a solution to balance smoothing like a propellor........or cutter wheel. I have tried to balance these things at work and it is nigh impossible to get it right. The machines I deal with at work are very heavily built but operate one when out of balance and very bad things happen. There are tolerances for this in aviation however as cheap as a dynamic balancing is there is no reason why a body wouldn't have it done. When people are worried about moving the plane by the blade (near the hub), and also have heard how a gyro can be damaged by moving the plane will the instruments spin down I could only imagine how much a small vibration could shorten the life of all components on an airplane. I will always have my prop balanced. Cheap insurance !

[cujet]

I balance helicopters and props as part of my job. It's not possible to achieve jet/turbine levels of smoothness from a piston powered prop aircraft. Don't expect Gulfstream G550 like smoothness (designed to keep all the noise and vibration behind you) from a front engined, piston powered, prop driven aircraft with an exhaust directly under your feet..... Obviously, design configuration is a large part of the noise and vibration we experience. 

 

Interestingly, there are apps for the iPhone that will display and record vibration. They are handy to help determine the frequency of the vibration you are experiencing. Much of what we experience is normal and should be expected. As mentioned above, dynamic prop balance is a good thing and will often lead to a more pleasant experience and longer exhaust and baffle life. 

 

Another factor, often overlooked, are rubber engine mounts. They insulate the airframe from much of the engine vibration. The rubber engine mount's age, temperature and condition will affect what you feel. Even how long they have been sitting between flights affects the stiffness. Ever wonder why some days the airplane seems smooth and other days there just seems to be more vibration no matter what you try? Engine mount temperature and stiffness could be the reason. 

 

Some owners will turn mounts upside down about half way through their life (they sag and take a set) . This often results in a noticeably smoother airplane.  

[bumper]

Yup, what "cujet" said!

 

There's also something reassuring about reaching up and feeling a "smooth" glareshield. I know it is only indirectly related to engine longevity, but still a smooth running motor just makes you feel good, notwithstanding less fatigue to everything attached to it - including the pilot.

 

To further reduce vibration carried through to the airframe, consider installing UHMW polyethylene tape to the cowls anywhere the baffling touches. UHMW (ultra high molecular weight) is slick and mechanically strong. It's available with either rubber or acrylic adhesive (get the acrylic), and in varying thicknesses and widths - 5 mills is good and 1" wide is handy (you can always lay in two strips if need be.

 

bumper

[KSMooniac]

 Not and OWT, most likely the latter. I had both on the same plane. Hartzell in Piqua, OH, could not dynamically balance out the three blade, inspite of the IPS being very low. I had them remove it and ordered a 2 blade because of it. I understand this is not true of the MT three blade, however, but I do not have any personal experience with the MT 3 blade and the 4 cyl. lycs.

Scott, isn't this the setup you have?

Yes, I'm running an MT 3-blade on my J, only because they don't offer a 2-blade!  I wish they did for the J.  It is very, very smooth, and much, much lighter than the metal 2-blade props.  (and LOTS lighter than the metal 3-blade props)  It is the only approved prop for Mooneys with a smaller diameter than stock as well.

 

I'm going to great lengths during my engine overhaul to balance and flow-match everything, so hopefully I'll end up with turbine-smooth operation.  We'll see how close I can get.

[carusoam]

MT likes the words turbine smooth when discussing the new composite four blade prop on the Long Body...

I haven't seen it in real life, yet...

Best regards,

-a-

[bumper]

MT likes the words turbine smooth when discussing the new composite four blade prop on the Long Body...

I haven't seen it in real life, yet...

Best regards,

-a-

It's bound to be smooth and quiet . . . Euro quiet. But it'll be giving up a few knots I think.

 

bumper

[orionflt]

I don't know about quiet, The 4 bladed MT we had installed on one of the Lancair IVP's made so much noise you could hear it 5 miles away and as high as 8000 ft, wasn't as noticeable in the cockpit but when the 3 bladed hartzell went on we could tell the difference. 

[Hondo]

Cody,

 

When it comes to prop balancing equipment I've heard of the Chadwick Vibrex 2000, Microtech II and ACES Probalancer.

 

Is one better than the others?

 

Thanks.