Vibration

I have some vibrations at various RPMs. It is most prominent just above idle, and at various cruise RPMs. I can feel it by lightly touching the rudder pedals, or with a finger lightly against the canopy rail. It's not serious, but more than I would have expected. I liken it to the handlebar buzz that you get with some motorcycles. I did the carb balance, and it looks pretty good. I have removed the cowl, and can find no obvious areas of rubbing. I have even added an additional 1/4" of clearance for the left valve covers, which was almost touching before. The only noted issue is that the oil line hoses to the cooler seem short, and when I attach the cooler to the cowl, these hoses are maxed out. Surely these hoses couldn't carry vibration to the airframe?? By the way, I did move the oil cooler forward almost 3/4" by altering the inner shroud. This was to gain clearance to the muffler, and is probably why the hoses are a bit short.

Any thoughts would be greatly appreciated..................Tom

propeller

Have the propeller balanced if you haven't done it yet. If you have....I don't know. I think an unbalanced rotating mass would be the culprit though.

You should try getting the prop balanced, I've done quite a few 12's and almost all were seriously out of tolerance.

Walt said:

You should try getting the prop balanced, I've done quite a few 12's and almost all were seriously out of tolerance.

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Like Walt, I have seen a big improvement on some RV-12's after doing a dynamic prop balance, but the very first thing to look at is to make sure the prop blades are both pitched the same.
I strive for the exact same pitch down to the tenth of degree as measured with a digital level (there is still a little bit of variation possible with that tool, but it is close enough).
If you settle for with a couple tenths... it can make a big diff. in smoothness.

Thanks Guys,

I failed to mention that I went through prop pitch for the 2nd time. Actually, after the original setting, I was at 5100 static. I must admit that it sure would set you back in the seat on takeoff though. Anyway, I re-pitched to 4950, which seems to be a more standard number. My ground roll increased, but so did the cruise. I was very careful, and was able to match the pitch to the exact same tenth of a degree on both blades. I did this with the top cowl off, top plugs removed, and I used a prop stand to ensure that each blade was in the exact same position for measurement. I will investigate prop balance. Any tips would be greatly appreciated, like what do they use for weights on our prop, and how would they be attached? I know that our local FBO has the equipment, and does prop balancing, but I'm not sure that he has ever seen an RV-12, or a Sensenich ground adjustable composite prop. Not sure that I want to be his guineapig.

Tom

I had my prop balanced by the Sensenich Prop Shop at Lancaster, Pa.. Cost was around $300.00 and a AN3 bolt, nut and several washers were used as weights and installed on the spinner backplate. It worked well. Do you have the firewall stiffener installed. The absence of that created a lot of vibration on mine.

speaking of the propeller...have you checked the torque on the bolts? they can lose torque (yes we have Nord Locs). Sensenich recommends checking first 25 hours, then every 100 hrs OR at the sign of any vibration. as they, ask me how I know.

Dynamic prop balance made a huge difference for me.

Thanks Guys,
Dave, did they drill a hole in the plate for the AN3? If so, do you remember about how far from the edge? I don't remember any exiting, unused holes in that plate.

I'm planning a 25 hr oil change for my first one, and plan to check the torque on lots of things, including the engine mount. But you have a good point.

My only source around here is a local FBO. He may not have rotax/composite prop experience, but he is a pretty sharp guy, and we will do it together. I'm going to go through the carb balance routine again, just before going over for the prop balance.

Tom

Tom, sounds like a good plan in the correct sequence. Regarding the holes in the backing plate, the instrument tells you where the weight is needed, and how much, then the hole is drilled. You will spend some time weighing bolts, nuts, and yes, even washers! If you participate in the process, and I advise you to do so, you will feel those vibrations in the stick disappear. Or so it went with my balance. John

todehnal said:

Thanks Guys,
Dave, did they drill a hole in the plate for the AN3? If so, do you remember about how far from the edge? I don't remember any exiting, unused holes in that plate.

I'm going to go through the carb balance routine again, just before going over for the prop balance.

Tom

Click to expand...

Checking the carb balance is a good thing, I tried balancing the prop of one RV12 that was not syncd properly and I was unable to get the job done due to the rough runnng engine.

I always drill 2 3/16" holes is the spinner bulkhead, this allows fine tuning the weight to the correct polar location.

Waiting for a Calm Day

I stopped over to chat with my FBO/friend about his prop balancer. He was not excited about doing it himself, as he has a shop full of work, but he was kind enough to loan the system to me. Wow!! $4K worth of gear, in a quality built carrying case. I spend last evening, studying the manuals, and I think that I am ready for the challenge. I'm just waiting for some light winds. Wow, what a piece of equipment! He is a neat guy, and always has gone out of his way to help out a friend. I think that I will owe him a nice dinner out.

Thanks for the tips guys. The manual talks about splitting the balance weight between two points, and actually does the calculations for you.

Tom

Vibration Sensor Mounting

Well, I ran into my first challenge. Trying to find a mounting point on the engine for the vibration sensor has not been easy. The instructions say to mount it as close to the horizontal center, and as close to the front of the engine as possible. The only location that meets this criteria, is behind the gearbox, at the top of the front case, and just above the pitot line routing. So, I made an offset bracket arrangement that will use the two open M6 threaded holes at the top, and provide a mounting for the sensor. Hope it works. The rest should be a piece of cake, if I could just get the winds to die down a bit. I'll be sure to post updates.

Tom

I use the upper open bolt hole you can see here just to the right of the crank flange to bolt the vib sensor to.

Great idea Walt. Everything I read said to get as close to the front main, and centered as you can. I'm sure that the gear box mounting that you use works fine though. ...........Tom