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  #21  
Old 03-30-2017, 01:25 PM
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snopercod snopercod is offline
 
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Default could you be more specific?

Quote:
Originally Posted by AirAce View Post
After static balance If vibration occurs, the engine is the problem.
Are you saying that the normal power pulses are the problem, the power pulses are unequal, or that something is wrong internally in the engine?
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  #22  
Old 03-30-2017, 01:29 PM
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Default rebalance after changing engine mounts?

Quote:
Originally Posted by gmcjetpilot View Post
I highly recommend LORD CORP engine isolation mounts verses other brands.
Should the engine be re-balanced after changing engine mounts? I have Barry mounts and have been thinking of changing to Lord.
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  #23  
Old 03-30-2017, 01:50 PM
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Quote:
Originally Posted by AirAce View Post
1. Static balance is a valid balance.
2. Static balance can be virtually perfect.
3. After static balance If vibration occurs, the engine is the problem.***
4. Sometimes engine mounts are the problem. This is mostly noticeable during rpm acceleration or deceleration.
5. Do not unbalance the propeller to balance the engine.

*** Propeller clocking on the crankshaft is IMPORTANT. Wrong clocking can be the cause of bad vibration.

Hartzell and McCaully make sure your prop can be install I only one clocking. Follow their lead.
Kent
Hmm, then why do you suppose all the major prop and engine manufactures recommend Dynamic prop balancing?
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EXP Aircraft Services LLC
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  #24  
Old 03-30-2017, 02:51 PM
Reformed SeaSnake Reformed SeaSnake is offline
 
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Default Static vs Dynamic balance

Quote:
Originally Posted by AirAce View Post
1. Static balance is a valid balance.
2. Static balance can be virtually perfect.
3. After static balance If vibration occurs, the engine is the problem.***
This would be true if the prop/spinner were truly 2 dimensional. i.e. Infinitely thin. In 3-dimensional rotating objects, dynamic balance is also important.

Imagine replacing the prop with a perfectly statically balanced wheel a few inches thick. Then attach a lead weight to the outboard aft rim of the wheel and an identical weight to the outboard forward rim of the wheel 180 degrees out from the aft weight. Because the weights are 180 degrees apart the wheel will still be statically balanced but the moment arm about the axis of rotation introduced by the weights will result in a wobble/vibration when the wheel spins.
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  #25  
Old 03-30-2017, 07:04 PM
BillL BillL is online now
 
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Default

Quote:
Originally Posted by snopercod View Post
Should the engine be re-balanced after changing engine mounts? I have Barry mounts and have been thinking of changing to Lord.
gmcjetpilot has not been on the forum for years.

And "No" would be the answer. True engine balance is independent of the mounts. There are a lot of cyclic forces generated in the engine that are inherent to its design configuration and not addressable with a weight rotating on the crank.
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  #26  
Old 05-23-2017, 09:03 PM
AirAce AirAce is offline
 
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Default prop balancing

There is a lot of info going around about prop balancing. There are a few facts you need to know about this endeavor.

1. Propellers are balanced at the factory or the OH facility. The balance specs that the OH shop or factory is tight enough that it will be balanced when you put it on your airplane. If it is not then you had better start looking for engine problems.

2. Do not use your propeller to balance your engine. OK, you can do that if you are using a fixed pitch propeller, and probably get by with it. But if you use your propeller to balance your engine and you are using a variable pitch propeller then you are flirting with disaster.

I had a customer bring his Aeromatic propeller to me with a complaint that it was out of balance. He also brought an aluminum disc, about 9" diameter that had a stack of fender washers bolted to one side. The washers weighed about 4.2 oz. He said that it took this disc with the washers bolted on to balance the propeller.

I put his prop on my static balance stand, without the balance disc and I found the propeller balance to be in spec but on the edge of the spec. I then pulled the blades and found 5 of the 15 screws broken in one of the blades. So, even with 5 broken screws that balance still met the spec.

I say again, you can get by using a fixed pitch prop to balance an engine unbalance, TO A DEGREE. Because the mass of "beef" holding the blades onto a fixed pitch prop is virtually indestructible. So you can usually get by with such an atrocity but if you do that with a variable pitch prop you are flirting with disaster.

Another thing: Clocking your prop on the engine is important. You can get a nice out of balance vibration by wrong clocking on the crank shaft. You will notice that Hartzell and McCauly makes it so that you can put the prop on an engine only one way, or 180 deg. That is for a reason, especially on four cylinder engines. That is important!

Poor engine mount rubbers can be a cause of vibration. This show up during rpm acceleration more than during constant rpm.

When a propeller leaves the factory or an OH shot it IS IN BALANCE. If some dynamic balance guy starts tacking weight on it the warrantee should be immediately voided.
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  #27  
Old 05-23-2017, 09:25 PM
BillL BillL is online now
 
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Default

What about the spinner?
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Lord Kelvin:
I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.
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  #28  
Old 05-23-2017, 09:29 PM
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I'd be curious to know where you get your info.

Both Hartzell and McCauley (among others) recommend dynamic balancing in their FAA approved manuals.

From the Hartzell Manual
Dynamic balance is recommended to reduce
vibrations that may be caused by a rotating system
(propeller and engine) imbalance. Dynamic
balancing can help prolong the life of the propeller,
engine, airframe, and avionics.

McCauley Manual
McCauley endorses dynamic balance on propellers installed on piston and turbine powered aircraft.
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Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
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  #29  
Old 05-24-2017, 06:56 AM
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Even though they call it dynamic prop balancing, you aren't using the prop to balance the engine. Usually you are using weights on the ring gear to balance the engine. Also, as the prop wears, and especially as it is dressed, it will lose its balance, in which case a dynamic balance balances the engine and the prop.
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  #30  
Old 05-24-2017, 10:13 AM
Pittsartist Pittsartist is offline
 
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Location: UK
Posts: 163
Default

I'm a fan of prop balancing too - But of course it all depends on how in or out of balance you are in the first place.

Here's a tip - If you have an Iphone have a look for "vibration" apps on the apple store. I used one before and after on my Pitts / MT balance job and the results were quite plain to see in the app.

I'm sure others may be able to share results and you could make an informed decision about how in or out of balance you were before deciding to have the work done.
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