vibration

vibration

<HTML>I have a 1971 cessna 150 with a new prop and it was static  balanced  on the
aircraft. My engine has 600 hours SMOH, 9000 TOTAL TIME on airframe. I am
having problems with vibration this was why I had a new prop installed but
that didn't help. The vibration gets worse when doing cruise flight I turn into the
wind. My IA says there is nothing wrong but I couldn't even read my gps the other
day because of the vibration. Does anybody have and ideas they could share
with me?</HTML>

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Re: vibration

<HTML>While not suggesting that it's the prop (you're already considering that issue), you should know there are two ways to balance it.  Static balance and dynamic balance.  Static is done on the workbench,...not on the airplane.  Dynamic balancing is done on the airplane with the engine running, and is much more comprehensive and generally should be thought of as a "fine tuning" of the prop balance.  (You can see that your comment that "it was static balanced on the
aircraft" raises some question as to what was actually done.) 
When a prop is first manufactured, or when it is overhauled, it is statically balanced, which is a "rough" balance and which is satisfactory in most cases.  But the way that works is, the prop is suspended by it's hub-center and one set of blades is offset in balance by the other set(s).  While at first glance that may appear all that's necessary (and usually is) the problem is that all blades are not created equal.  One may have more mass near the hub, while it's opposite may have more towards it's tip, with the result that while static (non-moving) one blade equally balances against the other.   But once placed in motion the blade with it's own center of gravity more towards the tip will have greater momentum placed farther from the hub,...which will "out-weigh" the blade whose CG is closer the hub.  This can make quite a vibration in operation. 
A dynamically balanced prop is first statically balanced on the workbench, then it's dynamically balanced using special equipment while the engine is running at it's most-used cruise RPM.  Weights are added to the prop-spinner backing-plate to "fine tune" the balance.  This results in a smoother running assembly.
An added benefit of dynamic balancing is that not only the prop is being balanced,...but the entire engine rotating mass is being observed and corrected in the process.  In many cases a vibration that is not even caused by the prop is corrected.  In some cases a vibration being caused by other engine anomalies are detected, which otherwise may go on to cause problems if not corrected.  An example is a cam with out-of-spec lobe height.  It's been shown that a cam which has been manufactured without consistent nitride hardening can wear excessively in only a few hundred hours resulting in decreased lifter performance and less than optimum valve opening.  This makes that cylinder begin to behave almost as badly as an ignition "miss" and results in vibration that may be misconstrued as an out-of-balance prop.  The only real fix in such a case is proper repair.
So a dynamic balance of your prop should not only result in a better-balanced prop (in most cases), but also will balance out the rest of your engine's rotating mass.  And it may show your that your particular vibration isn't prop-related at all.
Another desireable result of dynamic balancing is that the reduction in vibration can significantly reduce the failure rates of oil coolers, fittings, hoses, and cowling/sheet-metal cracking. 
I guess it's become obvious that I'm suggesting you have your prop/engine dynamically balanced.  (Most places in my part of the country charge less than $200, and it takes only a couple of hours.)  Good luck.</HTML>

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Re: vibration

<HTML>While not suggesting that it's the prop (you're already considering that issue), you should know there are two ways to balance it.  Static balance and dynamic balance.  Static is done on the workbench,...not on the airplane.  Dynamic balancing is done on the airplane with the engine running, and is much more comprehensive and generally should be thought of as a "fine tuning" of the prop balance.  (You can see that your comment that "it was static balanced on the
aircraft" raises some question as to what was actually done.) 
When a prop is first manufactured, or when it is overhauled, it is statically balanced, which is a "rough" balance and which is satisfactory in most cases.  But the way that works is, the prop is suspended by it's hub-center and one set of blades is offset in balance by the other set(s).  While at first glance that may appear all that's necessary (and usually is) the problem is that all blades are not created equal.  One may have more mass near the hub, while it's opposite may have more towards it's tip, with the result that while static (non-moving) one blade equally balances against the other.   But once placed in motion the blade with it's own center of gravity more towards the tip will have greater momentum placed farther from the hub,...which will "out-weigh" the blade whose CG is closer the hub.  This can make quite a vibration in operation. 
A dynamically balanced prop is first statically balanced on the workbench, then it's dynamically balanced using special equipment while the engine is running at it's most-used cruise RPM.  Weights are added to the prop-spinner backing-plate to "fine tune" the balance.  This results in a smoother running assembly.
An added benefit of dynamic balancing is that not only the prop is being balanced,...but the entire engine rotating mass is being observed and corrected in the process.  In many cases a vibration that is not even caused by the prop is corrected.  In some cases a vibration being caused by other engine anomalies are detected, which otherwise may go on to cause problems if not corrected.  An example is a cam with out-of-spec lobe height.  It's been shown that a cam which has been manufactured without consistent nitride hardening can wear excessively in only a few hundred hours resulting in decreased lifter performance and less than optimum valve opening.  This makes that cylinder begin to behave almost as badly as an ignition "miss" and results in vibration that may be misconstrued as an out-of-balance prop.  The only real fix in such a case is proper repair.
So a dynamic balance of your prop should not only result in a better-balanced prop (in most cases), but also will balance out the rest of your engine's rotating mass.  And it may show your that your particular vibration isn't prop-related at all.
Another desireable result of dynamic balancing is that the reduction in vibration can significantly reduce the failure rates of oil coolers, fittings, hoses, and cowling/sheet-metal cracking. 
I guess it's become obvious that I'm suggesting you have your prop/engine dynamically balanced.  (Most places in my part of the country charge less than $200, and it takes only a couple of hours.)  Good luck.</HTML>

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Re: vibration

<HTML>While not suggesting that it's the prop (you're already considering that issue), you should know there are two ways to balance it.  Static balance and dynamic balance.  Static is done on the workbench,...not on the airplane.  Dynamic balancing is done on the airplane with the engine running, and is much more comprehensive and generally should be thought of as a "fine tuning" of the prop balance.  (You can see that your comment that "it was static balanced on the
aircraft" raises some question as to what was actually done.) 
When a prop is first manufactured, or when it is overhauled, it is statically balanced, which is a "rough" balance and which is satisfactory in most cases.  But the way that works is, the prop is suspended by it's hub-center and one set of blades is offset in balance by the other set(s).  While at first glance that may appear all that's necessary (and usually is) the problem is that all blades are not created equal.  One may have more mass near the hub, while it's opposite may have more towards it's tip, with the result that while static (non-moving) one blade equally balances against the other.   But once placed in motion the blade with it's own center of gravity more towards the tip will have greater momentum placed farther from the hub,...which will "out-weigh" the blade whose CG is closer the hub.  This can make quite a vibration in operation. 
A dynamically balanced prop is first statically balanced on the workbench, then it's dynamically balanced using special equipment while the engine is running at it's most-used cruise RPM.  Weights are added to the prop-spinner backing-plate to "fine tune" the balance.  This results in a smoother running assembly.
An added benefit of dynamic balancing is that not only the prop is being balanced,...but the entire engine rotating mass is being observed and corrected in the process.  In many cases a vibration that is not even caused by the prop is corrected.  In some cases a vibration being caused by other engine anomalies are detected, which otherwise may go on to cause problems if not corrected.  An example is a cam with out-of-spec lobe height.  It's been shown that a cam which has been manufactured without consistent nitride hardening can wear excessively in only a few hundred hours resulting in decreased lifter performance and less than optimum valve opening.  This makes that cylinder begin to behave almost as badly as an ignition "miss" and results in vibration that may be misconstrued as an out-of-balance prop.  The only real fix in such a case is proper repair.
So a dynamic balance of your prop should not only result in a better-balanced prop (in most cases), but also will balance out the rest of your engine's rotating mass.  And it may show your that your particular vibration isn't prop-related at all.
Another desireable result of dynamic balancing is that the reduction in vibration can significantly reduce the failure rates of oil coolers, fittings, hoses, and cowling/sheet-metal cracking. 
I guess it's become obvious that I'm suggesting you have your prop/engine dynamically balanced.  (Most places in my part of the country charge less than $200, and it takes only a couple of hours.)  Good luck.</HTML>

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Re: vibration

<HTML>
  Remove propeller and relocate 60 degrees in opposite direction of rotation
  Test for vibration and if necessary move another 60 degrees
  Check which is the best position and if improved have propeller dynamically balanced

   Regards  Bram Water</HTML>

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