Prop Balancing??

[under pressure]

On aircraft and helicopters the props are all balanced to reduce vibrations. I have never heard anything about this from any airboaters.When my boats finished i was going to have the prop balanced at the local airport. With this new talk of failures maybe this will help reliability. I think it would. The new blades are so big the forces on the hubs are huge. Out of balance condition has to affect this area. We balance our rotating assemblies in our engines for longevity and comfort and neglect the props. Am i wrong?? I wish the prop Mfg's would chime in on this topic. Please anyone elaborate!! Thank You

 

[Rich Andrews]

I have experienced a new vibration after changing my pitch recently. This weekend we are going to try the balancing guage and see if everything dials in the same. A friend of mine says if your close on the marks that should be fine? I guess the jury is still out. On my old boat I ran a 2 blade and hand adjusted many times and never had any balance issues.

 

[Whitebear]

I for one am a fanatic about balancing and tracking props. I have never owned a composite but all my wood props have always get the balance check fairly frequently and tracking checked nearly every time I head out. It "MAY" not be cause and effect, but I have never blown a prop so far.

Heck we balance our tires on our cars and keep the front end in allignment why would it be any less important in an airboat?

In my mind, close don't cut it, it needs to be exact.

Balancing has nothing to do with pitch it's about blade weight. Obviously pitch needs to be exactly the same on each blade as well though.

Tracking is the path each blade tip traces as it moves around the 360 degree circle (all tips must trace the exact same circle), but its also the perfect time to check blade length as well.

It's a big issue in my mind.

Scotty

 

[Ron Miller]

Good topic---I have made my own wood props and most of the hovercrafters make their props -- This is fun but technical hobby. And the one thing none of us want is for that blade to come apart at 2000 rpm.
It makes a big mess believe me.... When I check the balance on wood prop ---I put it on a piece of pipe a little smaller than the center hole.. This pipe sets on the edge of two pieces of 3/4" banding in a jig that is perfectly level in all directions. This is done in a closed room with no air movement windows closed-- ceiling fans off-- doors closed-- and furnace off And no spectators walking around. The prop is horizontal and it should stay ware ever you set it--If it dose not then I usually add a good marine varnish to the back side of the light end --- ONE DROP AT A TIME--- until the prop stayes even. Let it dry for 24hrs. then recheck it ---
I also do my composite props but that is very complicated and I would recommend sending them back to the manufacture... But before you ship them off --- If one blade is not exactly set the same as the other blade this could be the cause of the vibration... The hub marks are very close for setting the pich but to get them exact I like using a framing square on the transom and measuring to the Trailing edge --- On our boat moving the Trailing edge 1/8" changes the RPM by 250

 

[Whitebear]

I do something similar but in a different manner. I made a tool with skateboard wheels that slips right into the hole in the prop.

I check for balance the same way then rotate 180 degrees then back and forth checking.

I add solder to rivet tops to bring the weight into check.when all is done I may lightly add a coat of varnish to the rivet tips if needed.

Scotty

 

[Ron Miller]

Scotty i like you skate board wheel idea then you can turn it 360deg. Thanks for the rotating and checking I forgot that. I wish i could solder that well.

 

[rbjscott]

An old wheel bubble balancer works on props. My Power Shift causes vibration if the blades are not set very close. I shoot for plus or minus 1/32. I use a bracket that clamps to the rudder support tube.

 

[Whitebear]

great idea. I like the wheel balancer idea, you can spin it as needed and the bubble wil always tell the tale.

I agree with getting it as close as possible. The closer the better.

I did mine cause as usual necessity is the mother of invention, so I stole the kids old skateboard. It was free and it had all the parts there LOL. I endede up buying him an airboat though so well maybe my prop balancer wasnt as cheep as I thought LOL !

But it sure was cheeper than bailing him out of jail from hangin out on the streets with nothing to do.

Scotty

 

[Anonymous]

Ah, Balance !!
I've been waiting for this thread to show up, and believe me this is the single most important, and most abused, component to running a propeller ....... any propeller.

Too many times when we talk of prop failures we all tend to ask two questions ..... !) Who made the prop?, and 2) What did it hit?

The truth is that a propeller, turning at several hundred RPM's can take a few ounces of imbalance and multiply that into several hundred pounds of dangerous force. Centifugal force compounds exponentially ..... a few ounces difference at idle can easily become a few hundred pounds of difference at 3000 RPM.

BF

 

[Whitebear]

YOU GOT IT TOYOTA !

Scotty

 

[hogman]

Dynamic balancing with Chadwick equipment and tracking with a strobe light is a certain way to balance a prop and set it up.
Jim Jefferies has a mobile rig and comes to your house or gathering. 985 507 9981

 

[Whitebear]

Depending on his fees, he might make a bundle if he came to one of our gatherings! Thats assuming he would be willing to come to Florida. Nothing like the right tools for the job !

It would be really interesting to see how some of our homebrew equipment stacked up against the real deal when it comes to results !

Scotty

 

[basketcase0302]

Whitebear,

My kid would never speak to me again if i did that to his skateboard

I watched the people who built my boat, (ya'll know who that is)...and then spent the 149.00 for one of the most awesome tools I've ever owned, (digital protractor). I also got 6 blades on 2 different angle to be concerned with.

http://www.penntoolco.com

Basketcase/Jeff