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Vibration!!


Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 1 year ago
Posts: 48
Topic starter  

Greetings,

I have the Jabiru scimitar ground adjustable pitch propeller installed on a 2200A. After changing pitch for achieving higher RPM, there is a noticeable elevated vibration throughout the cabin. It is worse when in the 2000 -  2200 RPM range. I borrowed a Dyna Vibe to measure the vibration and I’m getting 1.7 IPS which according to the Dyna Vibe manual, vibration levels above 1.2 IPS should have the propeller static balanced check. One thing I did verify before the vibration readings were taken was to make sure that the retaining shoulders were up against the matching hub shoulders as per the manual. That did help as it was 2.0 IPS before. Any suggestions going forward? The manual states to make a balance jig with an old crankshaft and an extra propeller hub. I’ll have to contact Arion Aircraft to see if they have junk cranks and a used flange. The manual states to use enamel paint but isn’t clear on the application - tips on that? I need to rule out a static balance issue before further troubleshooting unless of course there are other suggestions that may cause elevated vibration that can be looked at concurrently. 

Cheers,

Alex 


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Jabiru Support
(@jabiru-support)
Member Admin
Joined: 1 year ago
Posts: 116
 

Hello 

One thing you should check is that the both blades are pitched exactly the same.   If they are not, this can cause vibration. 

Also did you check the blade tracking after retorquing?  There is a small chance that it changed after loosening and retightening.

A crankshaft isn't needed for balancing, a machined bar would do, but a propeller flange is one of the best ways to ensure that it is on centre. It is unlikely that the static balance has changed after a pitch change.  

The enamel paint is used to add a small about of weight to the light blade in the case of the static balance not be right.  A light sand of the surface to promote adhesion before applying.   Then, while on the balancer apply paint until the light blade is slightly heavy (to allow for the volitiles evaporating).  It has the most effect out near the tip.

 

 

 


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Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 1 year ago
Posts: 48
Topic starter  

Thanks for the quick reply. Yes, I checked both blades’ pitch. They’re within .1 degrees. Tracking was checked as well and it is at 2mm. Machining a bar may not be that easy for me although that is a good idea, thank you. And I appreciate the tip on painting for static balance. One thing I did note; despite having each blade shoulder contacting the hub shoulder, when I was checking blade track, I took note that one blade is longer, or shorter, depending on how you look at it. It is approximately 3mm difference. Given that the blades are exactly where they need to be on the hub, I can only see this as manufacturing defect. 

Alex - 


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Jabiru Support
(@jabiru-support)
Member Admin
Joined: 1 year ago
Posts: 116
 

@jabiruyank 

I will ask about the blade length difference.  Can you tell me, when you first flew the propeller, before changing the pitch, did it run smoothly?

 


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Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 1 year ago
Posts: 48
Topic starter  

Yes, it did. I changed it as I was only getting 2750 RPM WOT. It was an error on my part as I had the pitch set at 21 degrees. The vibration occurred when I changed if to 16.8, 38” pitch. That is the setting now. WOT is 3100 now. 

Alex -


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Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 1 year ago
Posts: 48
Topic starter  

Greetings Jab support,

Arion aircraft has located a used prop flange and crank so I can perform the static balance of the scimitar propeller. The manual states to use a non-serviciable crank that has been balanced. I assume they are from the factory, or perhaps dynamically and not statically? It makes sense that the crankshaft be balanced and if it were not, I assume that it would throw off the propeller balance as well. If there are any hints or suggestions that you can throw my way to check the static balance of the crankshaft, it would be most appreciated! And just to confirm, the factory only allows adding weight with enamel paint to counter a heavy blade, add extra to compensate for evaporation of paint solvent? I assume then if you were heavy handed with the paint one would have to sand off the excess to achieve balance?

Of course, there's the issue of one blade being slightly longer than the other. I'm not sure how that will factor in balancing and you may hear from me again if I encounter significant imbalance that requires > 1 gram at the tip as per the manual. 

Cheers,

Alex-


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Jabiru Support
(@jabiru-support)
Member Admin
Joined: 1 year ago
Posts: 116
 

@jabiruyank 

Hello Alex,

If you check the balance of the crank/prop flange assembly by using the same setup as if you were balancing the prop but without the prop.  

You are pretty right on the other points.  The advantage of the paint is that you can put it on in small increments while it is on the balancer so it is hard to overdo it.  And yes if too much sand it off.  


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