Dynamic prop balancing, anybody ever try to do this?

[frank mccune]

     Hi All:

     While attempting to balance the blades on an overhead fan, I began to think about a way that I could dynamically  balance the props on my model airplane engines.  I am now balancing my props via a static method which may not be good enough. 

       Any suggestions/comments?

       Frank

[katana]

I've no 'real world' experience balancing props but when balancing rotating components dynamically in race bike and car engines it is always best to have the whole rotating assembly balanced together rather than as separate components, just assembled together. There will be minor slight balance variations in individual components, which although within spec. will act with others to put the whole assembly out. Turbo turbines / shaft / compressor assemblies always get balanced when finally assembled, 150k rpm is unforgiving if out of balance 

[Motorman]

I've designed and built props up and down the spectrum from 4K to 40K. Static balance is quite adeqate.

MM

[Lauri Malila]

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[Paul Wescott]

I've no 'real world' experience balancing props but when balancing rotating components dynamically in race bike and car engines it is always best to have the whole rotating assembly balanced together rather than as separate components, just assembled together. There will be minor slight balance variations in individual components, which although within spec. will act with others to put the whole assembly out. Turbo turbines / shaft / compressor assemblies always get balanced when finally assembled, 150k rpm is unforgiving if out of balance 

Katana?  Are you suggesting assembling the crankshaft, connecting rod, piston, etc, in some sort of ball bearing fixture outside of the case, then installing the propellor on the crank and finally balancing (dynamically) the propellor while attached to the rest?

Interesting concept.

Paul

[spare_parts]

You'll see the "dynamic balancing" term incorrectly used where a sensor is used with a spinning part, but is still single plane balance the same a static balance. Could it be more sensitive than static, maybe?

Dual plane balancing a prop is overkill.

Make sure you get the prop centered on the crank and tracking true.

[John Carrodus]

This topic I bought up on December 8, 2022 on Stunthangar Open Forum- type in search - Position of Propeller. It seems to be a real chestnut. Bit like - Do masks really work? Overall fuzzy logic and inconclusive ...until- read on!

The results seem to depend on personal experience, sometimes concurring with the science as I understand it. Sometimes not. This topic has come up again for me having recently been given a smashed up Argus to restore. The engine has been bored out to a larger piston and liner. The new piston is lighter than the original. I have recently been given notes on the planes history by the builder as well as strict instructions about setting up the unbalanced propeller in order to balance the engine run.

I thought, this is interesting and decided to ask a not so old very experienced speed nutter, Bill Bell. He has represented NZ overseas at many events over he years and built his own single bladed propellers for speed addicts around the world. He said it was used as a lazy method of engine balancing to add or subtract from the crankweight.

All was calm in my sea of propeller balancing and it's relationship - if any - to peak engine balance.......UNTIL

SPARKY last night mentioned the topic on his video programme. He said he would post the material he was reading , which was also new to him.

Sparky, please do, as my calm seas are once again disturbed by science, logic, experience ( or lack of in my case) and folks different opines, all causing me tension and a need to know the truth- It is out there, so they say. What say you?

[Air Ministry .]

Wouldnt want it to throw itself out . NOTE : the %age. Counterweights . IF you consider the major axis is two plane , its a percentage of the vertical . like 72% for high rpm's .

[Air Ministry .]

IF you throw the HEAVY Blade opposite the piston at t d c , i.e. AT the Counterweight , it gets a linear thing more , rather'n a single plane concept .





As its possable , with levels , to get alignment better'n what a factory tecnition is apt to , with all the bells and whistles ,

And for the tecnocrikity akligned . https://www.rpxtech.com/gx-prop-balancer.html

[Air Ministry .]

AND , look at the Bottom three . Theres nothing like the same grain , Ea. side / side to side .
Youd assume , for exact shape , one side wouldnt match the other , for weight .

But , in service , working hard , the STRUCTURAL ASPECTS mean Ea Side wouldnt RESPOND . As In Flex / or maintain ridgidity . EQUALLY



Say perhaps , the right outer blade , of the second one up , might ' lift ' in pitch a iota more , under duress . and a IOTA is a IOTA in any mans language ! . 

You get the picture . So , use grotty ones for rough useage , and save the best even grained marvells for better days , and TAKE CARE OF THEM .

There was a ' Compregnol ' process used , presumeably adopted in the ' Plasticote ' Tornado's , where resin under pressure is integrated into the timber ,
used in props and timber monocoque aircraft shells .

[Ken Culbertson]

Is there any benefit to puttin an out of balance prop on an out of balance motor to give you a balanced condition?  is that what you are referring to as Dynamic?  We used to do that with McCoys.

Ken

[Lauri Malila]

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[Air Ministry .]

Yes , thats like a counterweighted (or  cut out )  flywheel or crank pulley .
If a Engine b( single ) was 100& balanced vertically , It'd be 100% ? ? Un Balanced Transversely .

So the ideas linear rather than conical , displacement . Flat rather'n rocking . M'Cycles they all go on about matching % factor to Frame ' harmonics or frequencies or somethings .

So we could assume , likewise , differant engines & examples of planes might vary . M'Cycles , all considered , ALL TIGHT with no non frictional interface ( like Paint ) is sounder .

The Idea , is , if your at the field , throw it on a screw driver , find the heavy blade , and put it there . If its a bitch , balance it . A Sport 35 or 40 isnt a megabuck refined precision made 75 or sumsuch .
Which obviously requires commeasurate airscrews . You dont want any funny business , Sonny ! . with megagrunt .

STAND CLEAR of the PROP ARC ./ Blades FLING , generally - straight out , and forward ., Partuicularlly if the prop nut comes unstuck .

And WATCH where you put your FINGERS .

[Air Ministry .]

Ground Strikes may be deletorious . Use CAUTION on large & powerfull engines . Theyre NOT TOYS .

[Mike Danford]

Seems to be confusion. 

Dynamic vs static.  Static is just balancing while it’s not powered, dynamic is while it’s running. 


Dynamic is better, but requires generally expensive equipment and moderate training.  In the case of a model airplane engine, it will help a “whole system” balance, not just the prop… but

Single plane/two plane.  You cannot balance a cylinder statically.  You can balance a “flat” item statically.  The only way to truly balance a cylinder is dynamically.  That is much much more difficult than single plane dynamic balancing. 

As alluded to previously… the only near practical dynamic balancing that can occur is single plane.  So the only advantage is gonna be that the dynamic method will catch the prop that is not quite mounted concentricallu.

I have simple simple IRD Mechanalysis equipment and balance machines, both single and two plane, so that’s my basis, although an amateur.

[Paul Wescott]

I have simple simple IRD Mechanalysis equipment and balance machines, both single and two plane, so that’s my basis, although an amateur.

Mike - Can you show us pictures of your gear?  Maybe a video?

I have no experience in the area, but I’ve always been interested by the concept of balancing something while it’s spinning (or after it stops?).  I’m sure paying a “professional” to dynamically balance a part requires expensive equipment, considerable training & experience, and probably a hefty fee.  I am intrigued by the idea of someone who does this as an amateur.  What kinds of things do you balance and why?  How did you get into it?

Paul

[Mike Danford]

Egad, it’s been a while…. I have given demonstrations in the venue of guys who restore and use old American made woodworking machinery. 

This video shows a little of that and my simple equipment.

https://m.youtube.com/watch?v=LM2zW2qzL5c&pp=ygUWQmFsYW5jaW5nIGRlbW8gYXJuZmVzdA%3D%3D

Machines work better when balanced.  Cut nicer, last longer, etc.  I was taught by a REALLY SMART (don’t profess to have that problem myself) guy who wound up making grinders that did the final grinding on aircraft control system hydraulic valve spools.  Initial grinding to tenths, final grinding to microns!  They are fitted with a high power camera to position the part.  It can’t focus if the thing shakes AT ALL.  Original design used all sorts of vibration isolation, John decided to teach himself dynamic balancing to just get rid of vibration.

He convinced me it was necessary to learn this skill!  I really think he just wanted someone to talk to… I wasn’t quite the quick study he was, but learned a fair amount.  He gave me old equipment as he upgraded. 

I’ll try to find another video or two…

[spare_parts]

Topic of dual plane balancing will cover the details. You need a sensor to measure shaft angle and displacement. Some math gives the proper weight and position. You need to be aware of "hard" and "soft" mounting and position of the rotating mass.

In the modeling homeshop, the only place I've seen a need for dual plane balancing is building turbine engines. Though if you build electric motors or want perfectly balanced electric ducted fan units, it would also be useful. Modern commercial systems start under 10kUSD. There is one hobby system, though I couldn't find the notes I had. I've used a program (PC and few sensors) popular with turbine builders 15 years ago for a milling spindle I made.

Single cylinder engine vibration is a tough nut to crack. Add airframe resonance and it's anyone's guess. It ends up being trial and error.

If it was useful I'd guess we'd see the world class racing events using it, F2C, F3D, etc.