Prop Balancers

[jetjr]

without too much effort the PB3 can be mounted to work in flight.

 

 

[Bruce Tuncks]

A word of caution: Don't do what I did and get the engine too hot by ground running at cruise rpm while prop balancing.

 

I have decided to do my next prop balance while in the air. This of course makes the setup harder but the results should be better.

 

 

[Jaba-who]

Yes but they only balance at set revs so balance for cruise or full throttle and either will not be in balance at either revs.

Well that’s sort of true but not entirely.

“Balance” means you are decreasing the vibration to as low as you can get it. (At whatever rpm)

 

If the prop were perfectly “balanced” at zero ips then it would not change again no matter what the rpm. (Assuming that all other factors remain the same. Eg the engine doesn’t develop a harmonic resonance etc).

 

But if there is a small vibration at a low rpm it is possible the vibration may change ( up or down) when you increase the rpm (usually it will increase). Two blades props are more resistant to this change if there is a component of lateral vibration. Three blades props have more risk.

 

But the whole idea is that you can decrease the vibration to such a level at any rpm that you can then have any increase at other rpms being still within acceptable ranges.

 

You can always measure it at each of representative rpms to see you have achieved it.

 

 

[Jaba-who]

without too much effort the PB3 can be mounted to work in flight.

On a Jab where would you mount the light emitter?

 

Does it mean you have to fly it without the cowl?

 

 

[Bruce Tuncks]

Good points Jaba-who. Here's my plan... mount a small vibration sender permanently on the front of the engine and put a display on the instrument panel. This would give an uncalibrated vibration meter . The calibration doesn't really matter as we are only going to be seeking to minimize whatever reading presents itself.

 

With this instrument, there would be no need to hurry, and a small trial weight could be tried anytime. I admit the positioning of this weight would be blind to start with. This weight would either make the vibration reading better or worse, and shifted accordingly.

 

Of course the light which provides angular information would speed things up nicely. If you own a setup, I reckon you could find a way to mount it securely and still fly with both upper and lower cowl on.

 

 

[Bruce Tuncks]

The main benefit of the permanent meter would be to reliably detect any change in vibration levels. A sudden increase in vibration when you had done nothing to the engine might be evidence of some fault. Personally, I find that my unaided perceptions of "rough running" are not reliable , since I am capable of imagining an increase in vibration when there is nothing there in reality.

 

 

[Kyle Communications]

You can only do a dynamic balance at one RPM setting..it will be different at different RPM. Thats why you usually do a dynamic balance at cruise RPM. The Balancemaster takes care of the lot through the whole rev range..thats why it works so well. I did 45 min flight yesterday and my engine is sweet now..so much better than before

 

Doing a dynamic balance in flight is the best way if you can do it. At cruise RPM on the ground the aircraft bucks a fair bit which can falsify your reading

 

 

[Jaba-who]

You can only do a dynamic balance at one RPM setting..it will be different at different RPM. Thats why you usually do a dynamic balance at cruise RPM.

Yep. Your right.

 

I didn't mean to imply it could be balanced at multiple rpms.

 

But rather, balance it at one and then just check what it as at different rpms and decide if you are happy with the level at those others.

 

I'm interested in the concept of the balancemaster if it can allow for changes across rpm ranges though.

 

 

[Jaba-who]

The main benefit of the permanent meter would be to reliably detect any change in vibration levels. A sudden increase in vibration when you had done nothing to the engine might be evidence of some fault. Personally, I find that my unaided perceptions of "rough running" are not reliable , since I am capable of imagining an increase in vibration when there is nothing there in reality.

When I changed from a wooden prop to a composite one I was beset with lots of new vibrations ( and the stress of not knowing if I was feeling what I thought I was etc). that came and went and eventually I worked out that different winds especially when quartering from the right give me momentary vibrations and then they disappear.

 

 

[facthunter]

In principle if the engine is balanced (with some parts being dynamically balanced like the crankshaft because it's significantly long and therefore a static balance won't work) and the prop balanced separately, you just cannot be far out. (in a practical sense)

 

Proper balancing reduces loads and vibrations but you really cant balance the engine by altering the prop alone and still retain the integrity of the balance of all other parts of the mechanism.

 

There's NO reason why a dynamic balance has to be performed at a particular RPM except safety and the way the method of balancing is designed.. If things actually change at certain revs you must have some distortion occurring . Dynamic is only needed when things are long enough to produce an error that is significant in the real operational situation. If a flywheel was cast and had irregularities offset one side and another way the other side, then IT should be dynamically balanced. IF it's Machined from a uniform billet it's arguable it doesn't need balancing at all, but a static balance would be enough as a check. if the flywheel is only about 1 inch or less thick.

 

If you really want smoothness do the engine before assembly. Everyone I have heard of reports significant improvement. It will have NO EFFECT whatever on fixing torsional vibration except possibly shift the critical RPM's a few revs one way or the other. There can be multiple rev ranges where torsional effects are a problem. More likely in bigger engines. Like MUCH bigger. Nev

 

 

[Kyle Communications]

I'm interested in the concept of the balancemaster if it can allow for changes across rpm ranges though.

Yes this is what it does. It has a amount of mercury in the outer ring and it will travel freely around the ring to counter balance any imbalance. of course it does this right through out the whole rev range...its one of those funky laws you know like for every action there is a equal and opposite reaction thinga me jigs :)

 

The mercury will be in different thicknesses around the ring..it could even end up in say 3 or 4 areas at the same time as all it wants to do is find equalibrium

 

I know it has improved mine enormously through the whole engine range

 

 

[Nico13]

Not trying to hijack the thread here just sharing a memory.

 

I liked the static balance rig on the back patio across the chair backs.

 

It reminded me of when I used to build up the engines and props for the fine old Nomads and static balance them but we didn't use the patio chairs :-)

 

Dynamic balance was done during initial engine runs.

 

Shit that's about 38 years ago now, must be getting old.

 

The picture comes from FaceBook, Danny Tanner posts a lot of old pictures he and his brother had done over many years.

 

I would have loved to have taken a lot of pictures back then but GAF was Dep of Defence and pictures a big no no.

 

 

 

[jetjr]

I have a bracket made to bolt onto oil pump housing on Jab, sensor fits centre, other unit with light pickup sits on flat side behind. It "sees" past it to base of prop. Havent drilled hols in cowl for it but not a big deal - All in concept at this point :)

 

Guy from Smart aviation was worried about heat and it would get quite hot there especially upon landing

 

 

[Old Koreelah]

The main benefit of the permanent meter would be to reliably detect any change in vibration levels. A sudden increase in vibration when you had done nothing to the engine might be evidence of some fault. Personally, I find that my unaided perceptions of "rough running" are not reliable , since I am capable of imagining an increase in vibration when there is nothing there in reality.

Good idea Bruce. The only objective indication of vibration I have is the amount of "wobble" in my handwriting as I fill in the flight plan during warm-up. Going back thru my flight sheets, either vibration is getting worse, I'm developing Parkinson's.

 

 

[Bruce Tuncks]

I too am interested in the balancemaster. My problem is that I don't understand how it works. It seems to me that the mercury would flow to the furthest-out point which would make the imbalance worse not better.

 

 

[Kyle Communications]

Bruce..think of that equal and opposite reaction rule... the mercury actually goes to the lighter side to equalise the imbalance because it wants to spin in balance

 

 

[Jaba-who]

Kyle.

 

Do you know if the balance master will bolt straight onto jabiru props or will the spinner need modification?

 

 

[Kyle Communications]

I know Danny has a drilling jig now made to predrill the blank plate ones for Jabiru engines. He has sent a few out now for them. Best to get onto Dan3111 on this forum and he can let you know

 

 

[Jaba-who]

So does the balance master for a jabiru bolt to the engine or to the prop/spinner?

 

 

[Old Koreelah]

In recent discussions it seems the front of the prop is the ideal location, if the spinner can fit of it.

 

 

[Kyle Communications]

Well if you cant fit it inside the spinner at the front of the prop then it will have to go behind....in the front is better of course as more mechanical advantage but behind is ok just not as effective but still helps a great deal.

 

 

[Old Koreelah]

In all the discussions, I haven't noticed any mention of how much out-of-balance this unit can counteract.

 

If we ensure the prop is balanced before fitting the BM, is it a "fit and forget" item?

 

 

[Brett]

I've been in Contact with Danny, he did mention a figure it will balance to but it alludes me atm.... its a reasonable amount though I felt.

 

I'm going to measure my cowl up this weekend to see if it will shoehorn in there..

 

 

[Kyle Communications]

It will check a out of balance of around 13 grams..that depends of course how far forward you are with it. Thats why its a good idea to try a static balance first to get it weighted correctly

 

 

[dlegg]

How does a person go about static balancing a ground adjustable prop?