Hartzell HC-C2YL vibrations...

Just installed a Hartzell HC-C2YL on my RV-7A with a 160hp O-320. I previously had a WW GA200L prop.
I had it dynamically balanced to .15 IPS, which should be sufficient, however I noticed 2 types of vibrations for which I have some ideas, but I would like to hear your comments.

1. On the ground, while taxiing just above idle, there is some kind of resonance and when the sliding canopy is open it start to vibrate and shake and I need to close it.
2. During flight, there is a vibration that seems to be at the same frequency as the engine and the stick vibrates about +/- 0.060" or so. Vibrations can also be seen and felt on other items. When reducing rpm, the vibration seems to be more obvious.

I have the Sam James cowling and the transition from the plenum to the inlets have a different rubber than what came with the cowling. It is more of a rubber type, which provides smoother inflow, however it is less flexible. I have a feeling that with the heavier prop, this transfers more vibrations from the engine to the cowl, and thus transfers more vibrations to the airframe. I have ordered a different rubber foam material and will replace the transition pieces, which I think will make a difference.

The prop is a 0hr overhauled and built per Hartzell specs, and the assumption is that it is done properly. There doesn't seems to be any noteworthy difference between the blades in tracking and the spinner doesn't seem to vibrate either.

On the ground it could be a resonance problem, and not related to the cowl. I seem to remember while we were doing to dynamic balance that I had some vibrations, and this was with the cowl removed, so nothing to transfer engine vibrations through the cowl to the airframe.

Overall the new prop works great and improvement in takeoff and climb are fabulous and 1-2ktas on the cruise as well.

I am hoping that another go around with the dynamic balance will help. My goal is to have it below 0.1 IPS and hopefully around 0.05 IPS.

I do prop balancing. Sometimes a prop just won't take a good balance. Make sure the blades don't have excessive side play, check this by grabbing the end of each blade and push pull fore and aft, you shouldn't feel any ideally. Get your grease gun out and make sure it's full (to Hartzell procedures) on both blades. If these aren't the problem the prop may need a static balance at the shop first. There are 4 balance pads, left, right, fore and aft. These have to be right. I bought a brand new Hartzell F-7068 prop that wouldn't take a balance, I had to have it overhauled, I reinstalled it and it was fine. It's not uncommon for a prop to have a bad static balance from the shop or even brand new.

Another thing to consider, make sure all 4 cylinders are working properly. One bad or weak cylinder will cause vibration.

You might just remove the runner inlet connecters all together and run at idle to see if that clears up. It might be easier/quicker than fabricating new ones.

Once I installed a brand new prop and had a bad, really bad, vibration. I found that the top of one blade had been shaped improperly. I called the prop shop and they didn't believe me, but when I carried the prop into the shop the manager saw the shape from 20 feet away, and called the crew together to look at it.

They replaced it, of course, and then it was fine.

Also, I'd regard .15 as not properly balanced. I hope you can get it down to perhaps a third of that, and make sure the prop is at cruise rpm.

Dave

balance

Thanks guys,
My compression is really good, 77-78 on all.

I will do a dynamic balance again, and if that doesn't work, I need to check the static balance. Maybe they didn't statically balance the prop at the shop....?

As stated by FASGLAS, grease the hub before balancing. The grease often settles in on the first couple of hours of operation and can create an imbalance.

If it doesn't balance down and feel smooth, you should look for someone that has a balancer that does spectrum analysis. Craig Catto has the DynaVibe GX2, but that is a little bit of a trip if you are in San Diego. If you can find someone that has the spectrum analysis capability it will show you if it is a weak cylinder, 2-per, 3-per etc. Even if your compressions are good, it could still be an intake leak, lifters, etc. You can also use two accelerometers at once and figure out if the stick/cabin vibration is engine induced or aerodynamic. Also, if you do get a good balance, check that the vibration doesn't increase as you add blade pitch; that's a good sign that the blade angles may be out of sync.

Matt

balance

The surprising thing is that I didn't have any problem with the much lighter Whirlwind ground adjustable prop.
I sure hope I dont have a weak cylinder, but I assume I would have felt that with the WW as well...

Vib

First thing to do is check the bolts in spacer and retorque and then check prop bolts and retorque if it sounds like plugs are fouled when you pull power back it could be a loose prop but for not very long!
Bob

I did a CI on an RV7 last year that had a vibration issue. A couple of the crankshaft flange lugs were too long, and were bottoming out in the counter bore of the prop flange. This was preventing the prop flange from clamping up properly to the flywheel / crank flange and basically allowing the prop to "rock" back and forth on the flywheel. Probably not your issue and you would have to remove the prop to check, but still a possibility.

Bolts etc

I had my IA buddy help me with the install. The bolt bushings were too long and we machined them. The index bushing was way too long and was machined flush with the starter gear. The other 5 bushings were machined down about .050". None of the bushings bottom out, fortunately!
Hub was torqued and tripple checked, safety wire with plastic tubes.

I added prop leading edge tape and we did a dynamic balance again. We spent more time doing it and the final number is .065 ips, not bad. I still have a ground resonance, but that is probably something I can't do anything about...

Whoooooaaaa. How was a flange bushing too long? Those should all be pretty standard.

Bushing

Lots of different lengths different for wood and metal props.
Bob