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Vibration or Rough Running?


Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 7 months ago
Posts: 33
Topic starter  

Greetings,

I have a 2200A on my Aerostar 1 (LSA). I installed the Jabiru scimitar propeller last October and the engine was running well. At the moment I only have one CHT instrument gauge along with oil pressure and oil temp (as installed at the factory in Romania). Around the end of December, as air temps dropped to <4 degrees, I noticed sudden onset of vibration after starting up the engine. I didn't pay it any mind as it would run rough at low idle - less that 1000 RPM. However, I noticed the vibration at cruise. It was felt on my seat and the flight stick. This troubled me and my first thought was that it might be asymmetric pitch of the propeller. I checked the pitch, changing it as well and was careful to keep them within .1 degrees as per Jabiru specification. Unfortunately, that didn't help. On another flight, the vibration was markedly less but then came back on a subsequent flight. I'm suspecting what I perceive as vibration may be a rough running engine. Going back to my comment on gauges, I'm purchasing a full compliment of EGT and CHT probes with a Westach EGT/CHT dual gauge readout. There is a rotary switch that will allow me to monitor each cylinder. I did remove the plugs to get a general sense of what is going on with each cylinder: 2 & 4 spark plugs are a light tan color whilst 3 &4 are darker. They were much darker by the way when I flew the plane from where I purchased it in the summer - about 13.5 hours total flight time.

I apologize for the long preamble but I want to be sure I have enough information for an introduction to my issue. As stated, I'll be able to monitor the temps with the new gauges. I'm seeing what may be too lean a mixture. And yes, I know that Jabiru admonishes using spark plug condition as a definitive engine performance guide. If my mixture is not right and or balanced, is the attached Bing carburetor tuning guide still relevant/approved by Jabiru? It doesn't have Jabiru's service official bulletin identification so I assume it may have been put together by a non Jabiru source.

Any suggestions at this point?

Thanks in advance from Jabiru factory's support and or the community's help. I look forward to any suggestions and or advise.

Cheers,

Alex R-


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Jabiru Support
(@jabiru-support)
Member Admin
Joined: 8 months ago
Posts: 93
 

Hello Alex,

It is hard to tell but the mixture does get leaner in cold conditions.  Your plane came from florida, if I remember correctly.  This maybe the coldest it has even been.  

That tuning guide was written by our US dealer a few years ago. The process seems right.  

A quick check that can be done is to see if it gets putting on the choke or carburettor heat changes anything in flight.  Both make the mixture richer.  

Another thing to check is to make sure it isn't anything to do with the ignition.  Turning of one or the other of the ignitions can highlight if any of the ignition components are not functioning properly.  (on avgas sparkplug life can be as short as 50hrs before a miss develops).

You are on the right track with the chts and egts,  they will certainly give you a better idea of what is going on. 

 

 

 


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Jabiruyank
(@jabiruyank)
Eminent Member
Joined: 7 months ago
Posts: 33
Topic starter  

@jabiru-support

I'm ready to tune the carburetor to a richer mixture but I'm concerned of this newfound vibration (occurred after 15 hours of flight on the new Jab scimitar propeller). In my last flight, the vibration was not as prominent on cruise flight at 2900 RPM but was very prominent in the pattern 2200 - 2000 RPM.

I'm concerned that this may be a mass imbalance. As I don't have the setup to check static balancing and certainly not dynamic, I was wondering if you have any suggestions on who can do this in the US.

I did think that this might be a pitch imbalance? According to the manual the following are the tolerances for setting the pitch. "Both blades to be within ±0.25° of designated setting Blades to match within ±0.1°"

If I understand this correctly, the pitch of both blades are to be withing .25 degrees of the table? And each blade must be within .1 degree of each other? On the latter, and if I may borrow your expression: crikey!

Thanks as always,

Alex R-

 


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Jabiru Support
(@jabiru-support)
Member Admin
Joined: 8 months ago
Posts: 93
 

Hello Alex,

Most aircraft maintenance places should have some sort of balancing equipment.  

Most of our props that are set up for going on a jabiru aeroplane have pins so that the pitch can't be adjusted.  For other aircraft we leave them out so the pitch can be adjusted to suit.  Is yours like this?

One other thing to check for me is have a look at the tip of the propeller, in the outer 50mm of the leading edge, see if there is a small hole running into the blade along the axis.  If it is there it will be less than 1/8" diameter.  If you can't find it everything is great.  


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woliam
(@woliam)
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Joined: 1 week ago
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