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912 UL vibration

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uuccio(at)gmail.com
Guest

Posted: Thu Oct 11, 2012 9:29 pm Post subject: 912 UL vibration

Hello List



Yesterday I started the engine on the Kitfox IV I'm rebuilding. It's a 912UL from 1997 with 375 hours that I purchased about 6 months back.  Before i purchased it, was checked by a qualified Rotax mechanic who among other things, changed a number of rubber parts.



Before starting it, I manually checked the carb valves so that they were visually in a similar position.  Anyway, the engine seems to have a rather strong vibration to it so I haven't run it for much more than 20-30 seconds at the time.  I haven't had the carb valves aligned exactly with a pressure gauge, but the vibration is much more than what I would expect if it were just due to carb misalignment.  And it doesn't seem to be the prop (a 3-blade Duc whose pitch has been set with the appropriate instrument).



I called the Rotax mechanic who checked it and he suggested checking the carbs for obstructions which I have now done (I found an insect inside the left carb, but that didnt seem to change anything).  I'll blow some compressed air through them today just to make sure that everything is clean.  



Does anyone have any suggestions as to what I could try next? The closest Rotax mechanic is a 5 hour drive from where I am in Sicily so I don't want to call him out before I have tried everything that I can do personally. 



Sacha

Ivor Phillips

Joined: 16 Jan 2006
Posts: 253
Location: London UK

Posted: Thu Oct 11, 2012 11:29 pm Post subject: 912 UL vibration

Hi Sacha

 

I would double check that the prop isnt too corse first,

 a pair of vacuum gauges

are the way to go too sinc the carbs,  you could be way out by just visually checking

 the throttle linkage.

 

Ivor

On 12 October 2012 06:28, U <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:

 

[quote]--> RotaxEngines-List message posted by: U <uuccio(at)gmail.com (uuccio(at)gmail.com)>

  

 Hello List

 

 Yesterday I started the engine on the Kitfox IV I'm rebuilding. It's a 912UL from 1997 with 375 hours that I purchased about 6 months back.  Before i purchased it, was checked by a qualified Rotax mechanic who among other things, changed a number of rubber parts.

  

 Before starting it, I manually checked the carb valves so that they were visually in a similar position.  Anyway, the engine seems to have a rather strong vibration to it so I haven't run it for much more than 20-30 seconds at the time.  I haven't had the carb valves aligned exactly with a pressure gauge, but the vibration is much more than what I would expect if it were just due to carb misalignment.  And it doesn't seem to be the prop (a 3-blade Duc whose pitch has been set with the appropriate instrument).

  

 I called the Rotax mechanic who checked it and he suggested checking the carbs for obstructions which I have now done (I found an insect inside the left carb, but that didnt seem to change anything).  I'll blow some compressed air through them today just to make sure that everything is clean.

  

 Does anyone have any suggestions as to what I could try next? The closest Rotax mechanic is a 5 hour drive from where I am in Sicily so I don't want to call him out before I have tried everything that I can do personally.

  

 Sacha

 

 

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uuccio(at)gmail.com
Guest

Posted: Fri Oct 12, 2012 12:42 am Post subject: 912 UL vibration

Hi Ivor,

I just tried it with another prop and the vibrations are gone. Now I can stop torturing those poor carbs :-/ although I will have them synced with a vacuum gauge. 

Thank you



On Oct 12, 2012, at 9:28, PHILLIPS I <ivor.phillips(at)ntlworld.com (ivor.phillips(at)ntlworld.com)> wrote:



[quote]Hi Sacha

 

I would double check that the prop isnt too corse first,

 a pair of vacuum gauges

are the way to go too sinc the carbs,  you could be way out by just visually checking

 the throttle linkage.

 

Ivor

On 12 October 2012 06:28, U <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:

 

 	  Quote: 	
		  --> RotaxEngines-List message posted by: U <uuccio(at)gmail.com (uuccio(at)gmail.com)>

  

 Hello List

 

 Yesterday I started the engine on the Kitfox IV I'm rebuilding. It's a 912UL from 1997 with 375 hours that I purchased about 6 months back.  Before i purchased it, was checked by a qualified Rotax mechanic who among other things, changed a number of rubber parts.

  

 Before starting it, I manually checked the carb valves so that they were visually in a similar position.  Anyway, the engine seems to have a rather strong vibration to it so I haven't run it for much more than 20-30 seconds at the time.  I haven't had the carb valves aligned exactly with a pressure gauge, but the vibration is much more than what I would expect if it were just due to carb misalignment.  And it doesn't seem to be the prop (a 3-blade Duc whose pitch has been set with the appropriate instrument).

  

 I called the Rotax mechanic who checked it and he suggested checking the carbs for obstructions which I have now done (I found an insect inside the left carb, but that didnt seem to change anything).  I'll blow some compressed air through them today just to make sure that everything is clean.

  

 Does anyone have any suggestions as to what I could try next? The closest Rotax mechanic is a 5 hour drive from where I am in Sicily so I don't want to call him out before I have tried everything that I can do personally.

  

 Sacha

 

 

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 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

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[b]

uuccio(at)gmail.com
Guest

Posted: Fri Oct 12, 2012 10:11 am Post subject: 912 UL vibration

On my Duc propeller, two of the blades were a newer vintage and one was an older blade of the same model. It turns out the newer blades are lighter than the older ones and this is what was creating the vibration. I swapped out the old blade for a new one and it now runs perfect...



On Oct 12, 2012, at 10:41, Sacha <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:



[quote]Hi Ivor,

I just tried it with another prop and the vibrations are gone. Now I can stop torturing those poor carbs :-/ although I will have them synced with a vacuum gauge. 

Thank you



On Oct 12, 2012, at 9:28, PHILLIPS I <ivor.phillips(at)ntlworld.com (ivor.phillips(at)ntlworld.com)> wrote:



 	  Quote: 	
		  Hi Sacha

 

I would double check that the prop isnt too corse first,

 a pair of vacuum gauges

are the way to go too sinc the carbs,  you could be way out by just visually checking

 the throttle linkage.

 

Ivor

On 12 October 2012 06:28, U <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:

 

 	  Quote: 	
		  --> RotaxEngines-List message posted by: U <uuccio(at)gmail.com (uuccio(at)gmail.com)>

  

 Hello List

 

 Yesterday I started the engine on the Kitfox IV I'm rebuilding. It's a 912UL from 1997 with 375 hours that I purchased about 6 months back.  Before i purchased it, was checked by a qualified Rotax mechanic who among other things, changed a number of rubber parts.

  

 Before starting it, I manually checked the carb valves so that they were visually in a similar position.  Anyway, the engine seems to have a rather strong vibration to it so I haven't run it for much more than 20-30 seconds at the time.  I haven't had the carb valves aligned exactly with a pressure gauge, but the vibration is much more than what I would expect if it were just due to carb misalignment.  And it doesn't seem to be the prop (a 3-blade Duc whose pitch has been set with the appropriate instrument).

  

 I called the Rotax mechanic who checked it and he suggested checking the carbs for obstructions which I have now done (I found an insect inside the left carb, but that didnt seem to change anything).  I'll blow some compressed air through them today just to make sure that everything is clean.

  

 Does anyone have any suggestions as to what I could try next? The closest Rotax mechanic is a 5 hour drive from where I am in Sicily so I don't want to call him out before I have tried everything that I can do personally.

  

 Sacha

 

 

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 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 



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[b]

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Fri Oct 12, 2012 6:16 pm Post subject: Re: 912 UL vibration

No blades should ever be swapped from a set. These are usually picked for 

For their weight And balanced together with that hub. If you do try and mix blades then they have to be balanced.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Sat Oct 13, 2012 3:58 am Post subject: 912 UL vibration

Roger:



A friend of mine has a Rotax and a three blade prop (pusher).  I do Dynamic Balancing on Lycoming and Continental engines.  I would like to do dynamic balancing for him BUT, since there is not a ring-gear where would I place the weights?

 



Barry



On Fri, Oct 12, 2012 at 10:16 PM, Roger Lee <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)> wrote:

[quote] --> RotaxEngines-List message posted by: "Roger Lee" <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)>

 

 No blades should ever be swapped from a set. These are usually picked for

 For their weight And balanced together with that hub. If you do try and mix blades then they have to be balanced.

 

 --------

 Roger Lee

 Tucson, Az.

 Light Sport Repairman - Maintenance Rated

 Rotax Repair Center - Heavy Maint. Rated

 Home [url=tel:520-574-1080]520-574-1080[/url]  TRY HOME FIRST

 Cell [url=tel:520-349-7056]520-349-7056[/url]

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=385228#385228

 

 

 

 

 

 

 

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 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

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 [b]

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sat Oct 13, 2012 6:43 am Post subject: Re: 912 UL vibration

Hi Barry,



Unfortunately there are many different prop mounts that people use on their planes. Some have backing plates and spinners, prop hub extensions,  ext...

If they don't have a backing plate then you may be stuck with putting a large washer on one of the prop mounting bolts. If you do that it could take a little more weight because it is closer to the center of mass. Or you could get him to put a backing plate and spinner on his plane and would benefit from better air flow and the balance. With the backing plate you can then move the weight out farther from the center.

Just so many of you know as a tidbit fact. It is more important and affects the flow of air to have a spinner on a pusher over a tractor prop. The air flow is affected more and in a positive way. 

Which is funny because we seem to always put spinners on tractor props.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Sat Oct 13, 2012 4:07 pm Post subject: 912 UL vibration

Roger:



Would you recommend a Rear bulkhead and Spinner combination for a Ryan S12.  It currently has a skullcap but I remember reading a lot about Long EZ types with fancy spinners that improved cooling and added a bit of speed.

 



Barry



On Sat, Oct 13, 2012 at 10:43 AM, Roger Lee <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)> wrote:

[quote] --> RotaxEngines-List message posted by: "Roger Lee" <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)>

 

 Hi Barry,

 

 Unfortunately there are many different prop mounts that people use on their planes. Some have backing plates and spinners, prop hub extensions,  ext..

 If they don't have a backing plate then you may be stuck with putting a large washer on one of the prop mounting bolts. If you do that it could take a little more weight because it is closer to the center of mass. Or you could get him to put a backing plate and spinner on his plane and would benefit from better air flow and the balance. With the backing plate you can then move the weight out farther from the center.

  Just so many of you know as a tidbit fact. It is more important and affects the flow of air to have a spinner on a pusher over a tractor prop. The air flow is affected more and in a positive way.

 Which is funny because we seem to always put spinners on tractor props.

 

 --------

 Roger Lee

 Tucson, Az.

 Light Sport Repairman - Maintenance Rated

 Rotax Repair Center - Heavy Maint. Rated

 Home [url=tel:520-574-1080]520-574-1080[/url]  TRY HOME FIRST

 Cell [url=tel:520-349-7056]520-349-7056[/url]

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=385246#385246

 

 

 

 

 

 

 

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 ="_blank">http://www.matronics.com/contribution

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 [b]

uuccio(at)gmail.com
Guest

Posted: Sat Oct 13, 2012 6:34 pm Post subject: 912 UL vibration

Thank you Roger



Is the balancing you refer to a DIY job or does it require specialized equipment?



Sacha

Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Sun Oct 14, 2012 4:05 am Post subject: Re: 912 UL vibration

Roger,



I don't doubt that the spinner on a pusher prop helps airflow past the prop hub on an installation with a smooth faired engine installation like  the Rutan designs or the BD5.  Similar to the tapered trailing edge of a strut fairing being more important than the tapered leading edge. However, I can't imagine it doing much good on a pusher with the engine hanging out in the breeze and making chaotic the surrounding air flow, like on Kolbs and Rans pushers. Sort of like trying to swat a gnat while being attacked by a swarm of yellow jackets. 



Not having done any aerodynamic studies of this, I recognize I could be wrong, but it doesn't seem plausible to me.



do not archive

_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Sun Oct 14, 2012 5:21 am Post subject: 912 UL vibration

Sacha:



The post about balancing was posted by me, Barry.

There a a couple of ways of doing balancing - Static and Dynamic.  

Static only requires a set of edge knives and spindle.  This will put you in the ball park.

 Dynamic can be done - With quite difficulty - Using different old fashion equipment such as the vibratalk or the string & washer.  I went with a bit more modern approach using a photo eye for RPM and an accelerometer to measure the displacement.  

 Can it be done by the good builder?  Yes.  But, not many a builder will invest an additional $1500 to $2500 for the equipment - Much easier to get it done for $250 by an A&P.

Barry

 

On Sat, Oct 13, 2012 at 10:33 PM, Sacha <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:

[quote] --> RotaxEngines-List message posted by: Sacha <uuccio(at)gmail.com (uuccio(at)gmail.com)>

 

 Thank you Roger

 

 Is the balancing you refer to a DIY job or does it require specialized equipment?

 

 Sacha

 

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 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

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[b]

uuccio(at)gmail.com
Guest

Posted: Sun Oct 14, 2012 10:33 am Post subject: 912 UL vibration

Thanks Barry,

No A&Ps where I am, otherwise I'd gladly farm out this kind of stuff, even if A&Ps here (I'm in Italy) are no way as cheap as the US 

The prop seems to be fine now, so I'll just leave it as it is until I find someone who can take a look at it...





On 14/ott/2012, at 15:20, FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:



[quote]Sacha:



The post about balancing was posted by me, Barry.

There a a couple of ways of doing balancing - Static and Dynamic.  

Static only requires a set of edge knives and spindle.  This will put you in the ball park.

 Dynamic can be done - With quite difficulty - Using different old fashion equipment such as the vibratalk or the string & washer.  I went with a bit more modern approach using a photo eye for RPM and an accelerometer to measure the displacement.  

 Can it be done by the good builder?  Yes.  But, not many a builder will invest an additional $1500 to $2500 for the equipment - Much easier to get it done for $250 by an A&P.

Barry

 

On Sat, Oct 13, 2012 at 10:33 PM, Sacha <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:

 	  Quote: 	
		   --> RotaxEngines-List message posted by: Sacha <uuccio(at)gmail.com (uuccio(at)gmail.com)>

 

 Thank you Roger

 

 Is the balancing you refer to a DIY job or does it require specialized equipment?

 

 Sacha

 

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 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 





	


[b]

Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Sun Oct 14, 2012 12:13 pm Post subject: Re: 912 UL vibration

Hi Sacha,



Three different types of balancing. One is done at the prop factory where they make sure each blade weighs as close to the same as possible and makes sure the hub is also in a balanced state. This is then sold as a set.

 You can do two balances. One is the static balance and put very simply is just like doing an auto wheel. You put it on a spindle or a balancer and look for the heavy side which usually is on the bottom and then add weight at the 12 o'clock position to make the prop equal weight all the way around so there is no heavy side.  Some hang it on string. 

The last balance is a dynamic balance. I spent $4K for my dynamic prop balancer. This machine is attached to the plane and you run it up near your cruise rpm on the ground and add weights where it suggest to get rid of any out of balance situations.

Solid props like wood or carbon fiber like a Warp are more likely to be out of balance to a higher degree than the newer lighter hollow carbon fiber composite props. Wood can also wick up moisture which will throw them out of balance.



If you have mis-matched blades for your prop they need to be checked for weight and at least a static balance.





Hi Thom,



Your probably right about air flow with a fully exposed engine. I learned this from an engineer at Sensenich that did his PHD on this very subject.

_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Sun Oct 14, 2012 2:56 pm Post subject: 912 UL vibration

Scaha:If you want to do about a weeks worth of research you can find the needed components to make up your own dynamic balancer.  The cost would be about $150 US. 

The only area that you may have problems with is writing the computer code.

 There are four fairly simple cods for a balancer:

1 - Choice of prop 2 blade & 3 blade.  Others such as 4 and even 6 blade are multiples of the 2 & 3 blade.

2 - RPM - This is done by identifying one blade and calling it #1 with a reflective sticky strip.  Then a simple photo eye sends and receives a signal off the reflective strip.  Count the reflections and you have RPM

 3 - Accelerometer - Well, here you can go from simple to VERY elaborate   BUT! All the operations are the same.  Simple as most balancers are use ONLY one (1) axis.  The 'Y' axis.  The out put is a voltage that varies in amplitude as the vibration increases.  And the unit of vibration is IPS (Inches Per Second) Yes you can use mmPS.

 4 - This one becomes a little difficult   You have to correlate the RPM with the #1 blade to a o'clock position so you know WHERE in relation to the #1 Blade the HEAVY point is.  Here is where RPM is converted to SECONDS and the VOLTAGE output of the accelerometer is given a plot of inches OR mm.

 



Once you know where the Heavy Vibration Point is you add 180 Deg to that point to find where you should add weight to balance it out.  YES - you could also remove weight fro the heavy point BUT very few people do that.  AND that is probably a good idea.

 



NEXT PROBLEM:  What if you find the heavy point is between blades?

Or, what if there is no place to mount your balance weight?  This goes back to the question I posted where a friend had a Rotax and a three blade prop and NO place to mount the balance weights.

 Well, What you can do is start playing with the indexing of the prop on the drive shaft.  This brings up all sorts on questions and old wives tails - Since supposedly a compression stroke on the #1 cylinder does not matter since there is a gear box.  

 Theory may say one thing while practicality says something else. 

The proof is in the pudding.

There a one other way other than a computer program but that has its own problems .. That would be by using an Oscilloscope and set up a Lissajous Pattern showing RPM Vs Accelerometer.

 



Do the simple things first - 

Static balance the prop.

Make sure the prop tracks true.

Check you mounts - vibration dampeners - airframe and all components mounted on the engine as well as any cowlings.

 



Barry

On Sun, Oct 14, 2012 at 2:32 PM, U <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:

 [quote]Thanks Barry,

No A&Ps where I am, otherwise I'd gladly farm out this kind of stuff, even if A&Ps here (I'm in Italy) are no way as cheap as the US 

 



The prop seems to be fine now, so I'll just leave it as it is until I find someone who can take a look at it...





On 14/ott/2012, at 15:20, FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:

 



 	  Quote: 	
		  Sacha:



The post about balancing was posted by me, Barry.

There a a couple of ways of doing balancing - Static and Dynamic.  

 Static only requires a set of edge knives and spindle.  This will put you in the ball park.

 Dynamic can be done - With quite difficulty - Using different old fashion equipment such as the vibratalk or the string & washer.  I went with a bit more modern approach using a photo eye for RPM and an accelerometer to measure the displacement.  

  Can it be done by the good builder?  Yes.  But, not many a builder will invest an additional $1500 to $2500 for the equipment - Much easier to get it done for $250 by an A&P.

Barry

 

 

On Sat, Oct 13, 2012 at 10:33 PM, Sacha <uuccio(at)gmail.com (uuccio(at)gmail.com)> wrote:



 	  Quote: 	
		    --> RotaxEngines-List message posted by: Sacha <uuccio(at)gmail.com (uuccio(at)gmail.com)>

 

 Thank you Roger

 

 Is the balancing you refer to a DIY job or does it require specialized equipment?

 

 Sacha

 



 ===========

 -List" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 





	






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[b]

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Mon Oct 15, 2012 8:13 am Post subject: 912 UL vibration

Rick:



Painting the prop will work for STATIC balancing of the prop.  But, what happens when the heavy point is at a rotational degree location tat is out in space.  NO PHYSICAL location to add or remove weight?  Not all the balancing is of the prop.  Things like Engine, Spinner and Mounts contribute to vibration.  AND how much paint is required?  What happens when the paint is worn off?  Slow changes in vibration is not noticeable over long periods of time... The body just gets use to it.  The plane and insturments on the other had react to it - Shortened life.

 The idea of oil on the prop causing imbalance is very possible but also very arguable.  Since the prop is spinning wouldn't there be an equal amount of oil spray on each blade?  Who know, who cares... Just wipe the prop down after each landing.

 



Balance Masters - This is another one of those theories/myths that has not been truly proven or disproven.  I did a little balancing experiment at work with the same idea of a movable mass (mercury) and found it did NOT always balance out, it was 2 time yes, 15 times no.  And my testing was Mercury Vs Accelerometer.  Way too many variables to get repeated results. The better way of doing a moving weight balance system is a Washing Machine. Check it out - Pretty cool ideas there.

 



Barry





On Mon, Oct 15, 2012 at 11:31 AM, Richard Girard <aslsa.rng(at)gmail.com (aslsa.rng(at)gmail.com)> wrote:

 [quote]Roger, Barry, While adding a washer will certainly work why not paint the prop tips and add more paint on the light blade? For a pusher, especially one on a two stroke powered aircraft you will get a fair amount of oil and dirt that sticks to the blades and affects the balance. Part of my yearly maintenance is to clean and repaint the prop, test the balance, and use the tip paint to get the prop to Rotax specs for a new prop, less than half a gram of imbalance.  I also recommend Balance Masters prop dynamic prop balancers. They are very light and really do the job of getting rid of that last little bit and countering for bug and oil buildup during flight.

  Rick Girard



On Sat, Oct 13, 2012 at 9:43 AM, Roger Lee <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)> wrote:

 

 	  Quote: 	
		   --> RotaxEngines-List message posted by: "Roger Lee" <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)>

 

 Hi Barry,

 

 Unfortunately there are many different prop mounts that people use on their planes. Some have backing plates and spinners, prop hub extensions,  ext..

 If they don't have a backing plate then you may be stuck with putting a large washer on one of the prop mounting bolts. If you do that it could take a little more weight because it is closer to the center of mass. Or you could get him to put a backing plate and spinner on his plane and would benefit from better air flow and the balance. With the backing plate you can then move the weight out farther from the center.

   Just so many of you know as a tidbit fact. It is more important and affects the flow of air to have a spinner on a pusher over a tractor prop. The air flow is affected more and in a positive way.

 Which is funny because we seem to always put spinners on tractor props.

 

 --------

 Roger Lee

 Tucson, Az.

 Light Sport Repairman - Maintenance Rated

 Rotax Repair Center - Heavy Maint. Rated

 Home [url=tel:520-574-1080]520-574-1080[/url]  TRY HOME FIRST

 Cell [url=tel:520-349-7056]520-349-7056[/url]

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=385246#385246

 

 

 

 

 

 

 



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[b]

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Tue Oct 16, 2012 4:20 am Post subject: 912 UL vibration

Barry, Yep, the paint on the tips is just for static balance, but I can get to .1 gram and it does seem to help. How much is my experiment. I shoot a little heavy so as the volatiles flash off the prop moves toward balance. Not perfect, but cheap and keeps the prop in good shape. My testing of the Balance Masters concept was on my Shovelhead Harley. I have them on both the crank and the clutch basket. It takes a little while to settle in once I'm up to road speed, but I can feel the vibration go away and I really notice the difference after a long haul. Since the engine is bolted directly to the frame it is much more noticeable than on either my airplane of trike, but they do seem to work there, too.

 



Rick



On Mon, Oct 15, 2012 at 11:13 AM, FLYaDIVE <flyadive(at)gmail.com (flyadive(at)gmail.com)> wrote:

 	  Quote: 	
		   Rick:



Painting the prop will work for STATIC balancing of the prop.  But, what happens when the heavy point is at a rotational degree location tat is out in space.  NO PHYSICAL location to add or remove weight?  Not all the balancing is of the prop.  Things like Engine, Spinner and Mounts contribute to vibration.  AND how much paint is required?  What happens when the paint is worn off?  Slow changes in vibration is not noticeable over long periods of time... The body just gets use to it.  The plane and insturments on the other had react to it - Shortened life.

  The idea of oil on the prop causing imbalance is very possible but also very arguable.  Since the prop is spinning wouldn't there be an equal amount of oil spray on each blade?  Who know, who cares... Just wipe the prop down after each landing.

  



Balance Masters - This is another one of those theories/myths that has not been truly proven or disproven.  I did a little balancing experiment at work with the same idea of a movable mass (mercury) and found it did NOT always balance out, it was 2 time yes, 15 times no.  And my testing was Mercury Vs Accelerometer.  Way too many variables to get repeated results. The better way of doing a moving weight balance system is a Washing Machine. Check it out - Pretty cool ideas there.

  



Barry





On Mon, Oct 15, 2012 at 11:31 AM, Richard Girard <aslsa.rng(at)gmail.com (aslsa.rng(at)gmail.com)> wrote:

   	  Quote: 	
		  Roger, Barry, While adding a washer will certainly work why not paint the prop tips and add more paint on the light blade? For a pusher, especially one on a two stroke powered aircraft you will get a fair amount of oil and dirt that sticks to the blades and affects the balance. Part of my yearly maintenance is to clean and repaint the prop, test the balance, and use the tip paint to get the prop to Rotax specs for a new prop, less than half a gram of imbalance.   I also recommend Balance Masters prop dynamic prop balancers. They are very light and really do the job of getting rid of that last little bit and countering for bug and oil buildup during flight.

   Rick Girard



On Sat, Oct 13, 2012 at 9:43 AM, Roger Lee <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)> wrote:

 

 	  Quote: 	
		   --> RotaxEngines-List message posted by: "Roger Lee" <ssadiver1(at)yahoo.com (ssadiver1(at)yahoo.com)>

 

 Hi Barry,

 

 Unfortunately there are many different prop mounts that people use on their planes. Some have backing plates and spinners, prop hub extensions,  ext..

 If they don't have a backing plate then you may be stuck with putting a large washer on one of the prop mounting bolts. If you do that it could take a little more weight because it is closer to the center of mass. Or you could get him to put a backing plate and spinner on his plane and would benefit from better air flow and the balance. With the backing plate you can then move the weight out farther from the center.

    Just so many of you know as a tidbit fact. It is more important and affects the flow of air to have a spinner on a pusher over a tractor prop. The air flow is affected more and in a positive way.

 Which is funny because we seem to always put spinners on tractor props.

 

 --------

 Roger Lee

 Tucson, Az.

 Light Sport Repairman - Maintenance Rated

 Rotax Repair Center - Heavy Maint. Rated

 Home [url=tel:520-574-1080]520-574-1080[/url]  TRY HOME FIRST

 Cell [url=tel:520-349-7056]520-349-7056[/url]

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=385246#385246

 

 

 

 

 

 

 



 ===========

 -List" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 

	




-- 

Zulu Delta

Mk IIIC

Thanks, Homer GBYM

It isn't necessary to have relatives in Kansas City in order to be unhappy.

     - Groucho Marx



 

   	  Quote: 	
		  



ist" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution



	








ist" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

tp://forums.matronics.com

_blank">http://www.matronics.com/contribution



	
	




-- 

Zulu Delta

Mk IIIC

Thanks, Homer GBYM

It isn't necessary to have relatives in Kansas City in order to be unhappy.

   - Groucho Marx



 

  [quote][b]

_________________
The smallest miracle right in front of you is enough to make you happy....

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Posted: Thu Oct 18, 2012 1:49 pm Post subject: 912 UL vibration

Barry & Roger

Thanks again for the detailed info!

Sacha



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