Advanced prop balancing

[Tim van Schyndel]

I have read before that when you get the prop close to fully balanced, you end up in a situation where you need to take weight from either the tongue or outer edge which is dependent on how the prop settles on the balancer (generally more horizontal but preferring one side with tongue down and visa versa for the other). I can't find where it was!

Could someone please enlighten me or direct me to the information.

Thanks

 

[Andy Brown]

If a two blade prop falls to horizontal (3 O'clock and 9 O'clock) you must work with the Leading edge on one blade and the Trailing edge on the other blade.

But first check the bore and make sure it is in the center of the hub. If not, you can remove material from the hub.

Also make a clay block with a shaft mounted in it and make sure both blades have the same size and shape.

 

[Tim van Schyndel]

Thanks Andy - That is exactly what I was after.

 

[Mike Larson]

I've noticed that the trend will be whichever side the prop was popped from the cast possibly.. its tedious to leading/trailing the prop and some will just not show tendency to come out of it, forcing reduction at the heavy hub side... dremel cut off wheel and notches possibly as you go... I do the clay/epoxy mold operation to ensure blade to blade concentricity first and check against it periodically to see if ive made an error... but.. ive also scrapped a half dozen or more that just didnt warrant the time involved to balance all around... they will learn you patience.... 'luck.... mike

 

[Marty Davis]

Here is another thought about balancing.

Back in the 70's and 80's one of ,my closest boating friends (Leonard Squira - Hall of Fame Member) and an engineer with Naval Avionics came to Tom Grannis and myself and told us of a conversation with one of the engineers at NA.

The engineer told him that he needed to balance the prop statically and then after that make a ball bearing shaft with a drive dog that could hold a prop and be able to hold in your hand. First balance the balancer with air blown on it to turn it up to 30k or so. The balance the prop by blowing air on the blade. This balanced the prop dynamically. It is amazing the amount of difference between static and dynamic balance.

Thoughts...

 

[brad nichols]

Of the dynamic balancing is better for a truer running prop but can be dangerous if it gets away at that speed!! it is also hard to judge 30k and could turn fasterneed it contained for safety.

Brad

 

[dwilfong]

You don't have to spin it up that fast to see if it is in balance.

I do it with every prop on my magnetic balancer.

You can see how true it spins just blowing on it with your mouth.

If it wobbles as it slows down it needs some more work.

 

[DickJones]

You don't have to spin it up that fast to see if it is in balance.

I do it with every prop on my magnetic balancer.

You can see how true it spins just blowing on it with your mouth.

If it wobbles as it slows down it needs some more work.

David, I have "slowed down"' and I "wobble" A lot, does that mean I need some more work?????????

Moby

 

[dwilfong]

How did I know you would ask that.............................

 

[brad nichols]

If you watch the prop spin it will go through points of imbalance as the RPM changes so it would be best to balance at the intended RPM range.

Brad

 

[KenOlvis]

If you watch the prop spin it will go through points of imbalance as the RPM changes so it would be best to balance at the intended RPM range.

Brad

? Say what

 

[Kez]

An auto mechanics has the tire balancing machine to tell them where and how much weight to add to the wheel to achieve dynamic balance. Without the sensors or a computerized balancing machine, how do you know where to remove material?

kez

 

[brad nichols]

Heavyest blade always falls lower but the balancing machine for tires is set to spin at a certain speed to obtain the balance at highway speeds.

Brad

 

[Kez]

if you remove material from the heavy blade you will achieve static balance. This type of balancing is good enough for a thin disk such as the rear induction disk or even an airplane propeller. For an rotating object with some "thickness" to it like a wheel or our marine propeller, static balance is not enough especially at high RPM.

I know our marine propeller will need to be dynamically balanced. But I am not sure how it can be done without sophisticated instrument to know where to remove materials. Assuming you chuck your prop on a shaft and spin it after it has been statically balanced and noticed that it is shaking. Where are you going to remove the material and how much?

 

[Michael Caruso]

if you remove material from the heavy blade you will achieve static balance. This type of balancing is good enough for a thin disk such as the rear induction disk or even an airplane propeller. For an rotating object with some "thickness" to it like a wheel or our marine propeller, static balance is not enough especially at high RPM.

I know our marine propeller will need to be dynamically balanced. But I am not sure how it can be done without sophisticated instrument to know where to remove materials. Assuming you chuck your prop on a shaft and spin it after it has been statically balanced and noticed that it is shaking. Where are you going to remove the material and how much?

These machines do balance propellers and have done RC props. http://catalog.schenck-usa.com/catalog.php

 

[Tim van Schyndel]

Some interesting dynamic balancing ideas from the Drone boys that could be adapted using lasers or mobile phones!

 

[Jim Allen]

Tim,

This is an interesting post. I use the type balance shown in the bottom of the first photo after magnetic balancing the carbon fiber propellers used on my test stand. It can balance airplane propellers in all axes at the same time. Never tried this on a boat propeller.

JA

 

[Tim van Schyndel]

As usual Jim, your engineering is amazing!

I'm going to look as designing/building something down the track.

Tim