Eagler's Nest
Engines => 2 Cylinder => 1/2 vw => Topic started by: dennysleen on August 12, 2017, 12:13:42 PM
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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.
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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
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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.
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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.
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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.
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I ran across this (125 bux): http://www.dynexhobby.com/dynexhobby_003.htm (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.
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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.
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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.
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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.....
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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 (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.
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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.
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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.
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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
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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.
:emoji_u1f600:
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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
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Vibration readings should be taken off the engine perpendicular to the cylinders. this would be where the case splits. you need take readings at a consistent location. i use my breather, which is left of center, because I can reach it comfortably without fear of the prop and always set the phone in the same place. my breather is the orange block in the photo.
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Denny, I was familiar with you trial weight technique, and have practiced using it on a test set-up. It works, but the problem I remember is that the technique produces a solution of "a certain amount of weight at a certain polar angle at a certain distance from the center of rotation". On an engine, it may be difficult to find a location that meets the requirements?
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I agree! balancing is not"simple". it is not always easy to get weight at exactly the right spot. A balancer from Dynavibe or Aces will take several runs to get it right as well.
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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.
Another question...
Your baseline run was 10.1 and you used 101 as your plot size. Working your formula you came out with 25.5 grams @ 58 degrees, should that not be divided by ten giving you 2.55 grams..?
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Good question. I was vague finishing the formula. the ratio between the baseline radius and intersection radius gets multiplied buy the value of the test weight. using my numbers 101/28=3.6 3.6X7 grams=25.25 (different answer from rounding differences) whether you use 10.1 and 2.8 or 101 and 28 it is the same ratio which is visually represented in the radius graph. the 28 number is found using a ruler between the center and the intersection point.
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Looking again @ what might be confusing. the added weight does not get added at the intersectin point on the graph. in my sample problem it is 28mm. the weight will be put at the same radius the test weight was at. At the bolt radius.
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Thank you sir.
And of course after you add the weight you run it up again for another base line...
I did not punch in the 2 sets of #s, I just blurted out the question when it occurred to me.
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engine and prop manufacturers specify limits of vibration but here are a few found on the web. using the SKF app you have to convert from inches to mm. 1"= 25 mm 1/2"=12.5mm .25"= 6 mm. (approximately)
Anything we do to reduce vibration will make our equipment last longer and more enjoyable to fly.
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Denny, you clarified something to me:
"the weight will be put at the same radius the test weight was at. At the bolt radius."
It was many years ago that I was messing with this, and was going from memory. This makes it much more doable.
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Hi guys,
very interesting thread but of my poor english im not sure if i understood all.
Anyway i have a question about this vibration test method:
Maybe that work also to balance the crank ?
When i cutted my stroker crank i did it this way on this link here (https://www.google.it/url?sa=t&source=web&rct=j&url=http://www.airplanesathome.com/Documents/HalfVWEngine.pdf&ved=0ahUKEwjmwOG5yfPVAhUHPBQKHcuUDGcQFggnMAI&usg=AFQjCNHs3EIyZqJoVbzaCbeNu3WGmDC3pA) and for the counterweight piece on the prop hub i had no numbers...only estimate.
My balancing machine of the other thread is not jet finished because of no free time and then i dont want disassemble the nice running engine again.
So...what you think, if i mount a (balanced) old unused flywheel on the prop hub and run the engine without the prop, that method work also to find the right counterweight on the prop hub for smooth engine running?
I think its important to have a smooth, well balanced engine BEFORE you want to balance a mounted prop, right?
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My current prop is from Performance Propellers and he does an admirable job of balance. I previously modified another prop to take some of the pitch out and rebalanced with a wire. I took a dowel that fit in the 1" center hole and drilled a 1/16" hole on the centerline and threaded the wire thru and hung the prop from a shelf. This will show which blade is heavy and which side of the hub is also heavy. Easy enough to put a screw or drill out a spot to add weight or remove on the hub.. I sanded the heavy blade on the FRONT side to remove weight from a blade.. after sanding, varnish raw wood and rebalance....Apply a little extra varnish to the light blade and check after it drys..
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and how you balance your engine?
The best balanced prop on a bad/no balanced engine don`t work very well...
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I would HOPE that the engine is already balanced......at least to some degree... I KNOW Scott Casler spends time balancing his engines and Bob Demillo spends time balancing his crankshaft/rod/piston setups...
I got a balance plate from Balance Master that took the fine balancing out of my engine... AS&S sells it now: http://www.aircraftspruce.com/catalog/appages/engblncmstr2.php (http://www.aircraftspruce.com/catalog/appages/engblncmstr2.php)
Works really well on MY engine!
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Here it is, three years after Denny’s post. I am currently test running and trying to smooth out my Mosler cb40. I think I understand how the method he describes works. One question though is, are the mm measurements, taken with the phone app, circle radius’s, or diameters? I have an android phone and couldn’t get the skf app. Found and used a different, vibration measuring app that gives movement in mms. Multiplied by 10 to get larger circles. Wasn’t sure if the Multiplied numbers were radius or diameter numbers. Also not sure if I’m using the app correctly. Do I pick a particularly shaky rpm and take measurements each time at same rpm? The tiny tach goes nuts after 2000 rpms, guess that should be another topic. Also not sure where the egts should be. Another topic? Anybody out there know some of the answers to the initial set-up issues? I could surely use some assistance.
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All test runs need to be done at the same RPM. The circles are drawn using the radius that corresponds to the mm/second on each test run.
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Cool. Wish I could find the skf app. Using something called vibration analysis by Krober. Gives two different values. For example: acceleration 1.48 m/s2 or distance 1.59 mm. To get these two examples I just shook the phone a little bit and these were the two values it offered. I was thinking I would use the distance option, but that’s only a guess. Or do I want the acceleration option? Is this app even gonna work for what I need? Any thoughts Denny? So close to flying, but I know things must be right.
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Using the 4 Run Test method it shouldn’t matter what value you use as long as you are consistent.
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Cool. Wish I could find the skf app.
Is this it..? https://www.reliableplant.com/Read/31459/condition-monitoring-tool (https://www.reliableplant.com/Read/31459/condition-monitoring-tool)
If so it is at the Play Store. https://play.google.com/store/apps/details?id=com.skf.pulse.release (https://play.google.com/store/apps/details?id=com.skf.pulse.release)
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No, it’s not the same app that Denny was talking about earlier in this thread. He said another vibration app should do, as long as all the other parameters involved are always the same during each test run. Hope I’m not misquoting you Denny. Tried again today and couldn’t get the 3 circles to intersect. I was using a rpm that was particularly shaky. Tomorrow I will maybe try at idle, won’t have to rely on this worthless tiny tach. The input is so valuable to me, keep it coming... thanks
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The SKF app that I referred to three years ago is no longer available. I have not found another one that was as straightforward and easy to use. I would do all of your test runs at wide open throttle. The circles may not and will not perfectly intersect you’re going to have to make a best judgment for their “intersection”location.
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Ok...I have no idea what rpms wot is,(tach troubles) also engine falters at wot. Not sure why yet. Stabilized the carbs, pretty sure I have the timing correct(used a timing light). Little scary that close to the meat cleaver.
You did this by laying the phone on that flat spot? I made a bracket for the phone and attached it to the engine top. Hope it’s not shaking more than the engine. I made it as stiff as I could.
Oh, should I do this test with or with out the counter weight on the prop hub?
Thanks Denny
Mark
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The SKF app that I referred to three years ago is no longer available. I have not found another one that was as straightforward and easy to use. I would do all of your test runs at wide open throttle. The circles may not and will not perfectly intersect you’re going to have to make a best judgment for their “intersection”location.
If the app is for Android you can "save" it and hopefully attach it to a post here. If it is for one of those nursing home phones I guess it reached the end of the line... :emoji_u1f62f:
Instructions here: https://www.theverge.com/2019/6/12/18661705/android-apps-transfer-new-phone-how-to-legacy-old (https://www.theverge.com/2019/6/12/18661705/android-apps-transfer-new-phone-how-to-legacy-old)
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If your crank has a balance weight on the prop hub you should always keep it there. I held my phone in place during the test runs. The SKF vibration app that is no longer available had a 5 second count down and then recorded data for I think 15 seconds and gave you a graph and an overall average. I have yet to find an app as easy to use. I haven’t looked for a couple years until yesterday when this thread caught your interest.
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I found one that I will test when I get to the airport. It is called Vibroscope Lite or Vibro.LITE
It has a three second countdown then records 20 sec of data.
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Ok yeah, the one on my Android has a 5 second count down, pretty easy to use. Shows two values, acceleration and movement. The Mosler manual says to use the counter weight, and tells where to use it, but not the size and weight. Mine is a guess, not balanced to my engine. I want to do the test at wot like you suggested, but it falters at wot at this point. Not sure why yet. Haven’t given up on the dual carbs yet. I don’t feel like it is shaking all that much, maybe I’m looking for something not attainable? Just thinking it can be fine tuned.
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Watched putt putt up close and personal this am, quite sure his counter weight is 1/4 in thick. Made mine 1/8, wonder if mine should be 1/4. If I could just do this shake measurement correctly it should show me where and how much weight.
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The counterweight that comes with a lot of the 1/2 VW kit engines is 1/4" thick. Here is a drawing of one. The angled piece cut off one corner is a different size depending on the engine size.
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Think I will make one up out of 1/4 inch stock. I wouldn’t say my engine shakes like crazy, but I would say it needs fine tuning in that department. Can’t get these carbs to stop spitting out gas. I feel like the engine would have to be perfectly still for these carbs to not spill gas.
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Every crankshaft needs to be personally balanced. Mine came back from the balancer with 35 grams on the prop hub. I have seen others with the huge chunk of steel shown below. I think my engine would rip itself off the plane if I added that muck weight to it. Be careful.
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I hear ya on the too much weight thing. Removed my phone bracket, as I think I was getting additional shake or movement in the bracket. Holding the phone directly on the engine is giving lower numbers and making a little more sense when graphing. As far as doing it at wot I’m not sure if I have the cahonies for that! Also my erratic tach makes this testing not consistent. Have tried everything possible with that sensor lead on the plug wire to no avail. Carbs are not right yet either. One plug is white while the other is tan. I have no jets to try yet, so I raised the needle one notch on the white plug side. I can now get full throttle, not as nicely as it should be though. My engine is a 40 horse 94x78. Carbs are vm26 606 4 stroke carbs. Gonna try going up a jet size. Did a compression check, right side 135, left side 160. Wonder if this difference is an issue. Need to call Scott.
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Gonna redo the test. Want to make sure that I was getting correct readings.
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Do you just use an air nozzle from the compressor with maybe a rubber stopper with a hole in it? Wonder how much air presser?
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The leak down tests I have been involved in used 80 psi. And 80 is enough to put you in the hospital.
All you could ever want to know about leak down compression tests... (https://www.avweb.com/ownership/the-savvy-aviator-13-putting-compression-in-context/)
https://www.youtube.com/watch?v=QkKzOPvbJaE
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Re-did compression test today with my brother helping. Found a loose fitting on the comp gauge. Test now shows 140 on one side and 145 on the other. These numbers were achieved during the third pull thru of the prop. I think I’m gonna call that good.
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Yes I did. Wasn’t overly enthralled with it. The Mosler case does not have the bumps and things to attach to like the vw case does. After many attempts to get the carbs to stop dumping gas, I’ve given up for the time being . In the interest of getting back in the air sooner,( Maine summers are short),I’ve decided to use the single zenith Carburetor mounted underneath. This engine was rated at the factory at 40 hp with that set up. I know this means carb heat. Already in the process of making a 2 into 1 exhaust system that I can grab some heat off of with a muff. At least the new direction has renewed my enthusiasm, very important to be enjoying this whole project.
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More on leak down test...
https://klassikats.com/index.php/2019/10/12/leak-down-test-vs-compression-test/ (https://klassikats.com/index.php/2019/10/12/leak-down-test-vs-compression-test/)