prop balance

[dennysleen]

there is an app for the iphone called   SKF Vibrometer    that i have been using to balance my prop and I would like to have more input on its usefulness. there is a way to determine the position amount of weight but i will have to go into that in greater detail later when i have more time. I would like to have some of the engineering types out there give this a try and comment.

[flyover1974]

Why you dont balance the prop with some of the standard metods?
The easiest way is to use a threaded rod, put 2 cone left and right to center the props middle hole, put all together on a U formed of something and see which end points downward. Add some weight at the other side (2/3 of the diameter) till the slightly pushed prop stops everywhere without a tendency to move downwards with some tip.

Cheers

[dennysleen]

I am refering to dynamic balance while the engine is running. There are many of us who have had engine mount bolts break and excessive vibration is surely a contributing factor.

[scottiniowa]

I am refering to dynamic balance while the engine is running. There are many of us who have had engine mount bolts break and excessive vibration is surely a contributing factor.

Locally our small FBO has such a prop balancer, intended to be used just as Denny suggest- which one would think would be the best final balance.
(on plane and running)  Might yours as well?

The whole “not quite right match up of the rubber grommets” I have tried to discuss several times to no avail, might also have something to do with it as well.

Best of success.

[dennysleen]

My FBO is happy to balance my prop in two weeks for $250 and repeat the procedure every time i sand a nick or touch up paint or try anew prop on my plane. I would like to explore another option that all of us who are capable of building an airplane should be able to do ourselves quickly for free. along with broken motor mount bolts there is considerable chatter about mikunis spitting fuel which I believe could be caused by vibration. Visual evaluation or feeling how smooth the motor runs is subjective and impossible to quantify to compare my engine to yours. The accelerometer in an Iphone is extreemly sensitive and I am hoping it will give us data that could be exchanged among us for everyone to benefit from.

[Dan_]

I ran across this (125 bux): http://www.dynexhobby.com/dynexhobby_003.htm

The problem with smart phones is they just show the magnitude of the vibration not how to fix it.  

In other words they don't have any way to index to the prop blade that I have seen, so a solution can be applied like the real dynamic balancers do.

The quad copter balancer looks very promising, and the smart phone app could be used to verify the before and after results of the balance job.

Keep us posted.

[dennysleen]

There is a simple way to add a known weight to three locations which in our case is every other bolt: 0 degrees, 120 degrees, and 240 degrees and measuring and plotting the resulting amplitude compared to the baseline. it takes 4 run ups. one to get a starting point vibration level and one with an extra nut screwed onto the excess threads protruding through the bolts at each of the test locations. the vibration level will improve or worsen and the results plotted to give vector and weight based on the originalweight of the nut or test weight that was used.  If you were sitting in my kitchen I could demonstrate it in 5 minutes. I dont know how to explain it without a pencil and paper which is why I though it will take some time either to photoghaph the plotting steps or make a video, neither of which I presently know how get onto this forum. my initial inquiry was hopefully get a few flyers to try the app and see if we can get reliable data from one phone to the next and see if there is interest in learning this procedure.

[Dan_]

Sounds good...  I'd like to learn the process/formula.


BTW,  the best way to get a video on here is to upload it to YouTube or Vimeo, and copy/paste the URL into a post. 


If a pic is on your device or hard drive, just hit attachments at the bottom of the post editor and navigate to your pic.

I don't know anything about I phones but I use the charge cable from my Android phone to transfer videos and pics to my computer box. 


Educated cell phones will also upload directly to YouTube with the YouTube app, and of course I could email them to myself, save to HD and delete the email.

[Dave Stroud]

Not to take away from the excellent subject too much, but Dan....could you please speak really slowly for me and tell me what buttons to push to get a photo off my Android phone onto my PC ? I've had the cables hooked up but don't know what to do after that. Thanks...Dave Stroud

To stay on topic, I must admit to being pretty lame with computers but with the help of Eric Clutton's excellent little book I did manage to make my own prop back in the 90's and carve it on a picnic table in the back yard. I static balanced it and it ran pretty smooth on my Christavia. Later when I had more bucks I bought a Culver prop for it and the performance was the same.....

[Dan_]

I've had the cables hooked up but don't know what to do after that. Thanks...Dave Stroud

If you hook the usb cable up and don't get a pop up asking what next, you most likely don't have compatible usb drivers installed. 

This may be what you need... https://software.intel.com/en-us/android/articles/installation-instructions-for-intel-android-usb-driver

If you have an amd processor in your machine this link prolly won't work...  You would then need to go to google and type in usb driver for amd...

With the correct driver installed it should be a straight forward menu following process...


Let me know how it goes,  I'm glad to help.

[dennysleen]

forgive my use of computers. I included a picture of the skf vibration display. prop balance is specified in inches per second and this gives you mm per sec so you have to convert but it is easier to work with mm anyway. my first run is my baseline starting point which is shown graphed with the black circle. the meter showed 10.1 mm per sec and I used 101 mm on my graph. i added an extra nut at the 0 position and recorded the result with purple @ 92 mm radius. the nut is moved to the next position and then to the last position with the results graphed. where those three circles intersect is the vector where the weight needs to be located. the balance weight needed is calculated by dividing the baseline radius by the intersection radius then multiplying that by the test weight. if the circles intersect outside of the baseline radius your balance weight will need to be less than the test weight.

[Dan_]

AWESOME!


I get it now that you have explained it, but would have never been able to figure all that out.

Do you plan to drill the prop hub to put a screw, washers and nut?

I'm looking for an Android app...

update:
I found the SKF app for Android, but it is in Hungarian not English.

[dennysleen]

I need to add @ 58 degrees which is 2 degrees away from the flange bolt. i will try it there. if you needed 10 grams @ 90 degrees you would put5 grams under each nut at 60 and 120

[Dan_]

Denny,

Sounds like a plan.

Thanks for taking the time to share this with us.  


Those are perfect illustrations and crystal a clear explanation.

Let us know how it comes out.

[Tom XL-7]

OK 
question time
How do you spin up your prop 
How do you gain contact between your phone and the spinning prop
Tom XL-7
Found the app