ENGINE DIAGNOSIS, What's your guess?

[Robbie Stuart]

Bill, did greasing the propeller hub cure your problem? (purging any water, air out) If not a thought for the future.

[Bill Greenwood]

Robbie , no grease in this prop hub, it is all controlled by engine oil pressure. And how would the air or water have gotten in over just a fuel stop is clear weather and 70* temps?

B-29, your are barking up the right tree, but still not there yet. There is no alcohol used for prop deice on this plane, although the co-pilot likes to defrost with a glass or two of red wine.

Tiger, no counterweights on this plane, unlike a T-6 or a lot of other older planes. Something else.

[AndyG]

Is there an electric de-icing boot system on your prop?

As a complete shot in the dark, if the system was operated, by desire or otherwise, and one blade failed to heat for some reason, is there a slight expansion in the aerodynamic profile of the hot blade boot that could lead to an imbalance?

[b29flteng]

Bill, I'm working from a memory of the Bonanzas I worked on 30+ years ago. I'm trying to remember details but the oldtimers disease is starting....

A screw missing from the spinner?
A crack in the spinner or spinner bulkhead?

[Bill Greenwood]

Andy, there are electric de-icing boots on my prop. However mine no longer work and I wouldn't be using the electric heat anyway on a clear and warm day.

As for flying into known icing, I recall what Jay Cullum told me years ago,"When I call for my preflight briefing and the Flight Service man starts talking about icing conditions, I lose interest in the flight."

B-29, I checked the spinner and screws once I got back on the ground, all ok. Close though.

[AndyG]

Andy, there are electric de-icing boots on my prop. However mine no longer work and I wouldn't be using the electric heat anyway on a clear and warm day.

As for flying into known icing, I recall what Jay Cullum told me years ago,"When I call for my preflight briefing and the Flight Service man starts talking about icing conditions, I lose interest in the flight."

B-29, I checked the spinner and screws once I got back on the ground, all ok. Close though.

Spinner installed such that it had a run-out of a very small magnitude due to something simple like a washer or two being in the wrong place?

[bipe215]

I chased a vibration for months until I finally changed plug wires and cured it.

Steve

[Robbie Stuart]

Bill, yea the propeller is controlled by oil pressure from the prop governor, I may have my propellers mixed up but there are a lot of props that the hub blade grips are lubricated with grease. You get more grease in one or the other, & it vibrates.

[b29flteng]

Missing/broken safety wire between the bulkhead attachment bolts?

Wallowed out bulkhead attachment bolt holes, due to loose attachment bolt(s), allowing spinner to shift slightly?

One or more spinner attachment screws too long or different type?

[AndyG]

42

[Bill Greenwood]

ok, here are the two salient facts:

It was a small rythmic vibration, not an engine miss.

It would occur on a Be 36 or similar plane, like many multis. It would not occur on J3 or T6 or P-51.

What is the key difference?

My plane, like many if not all Be 36s has prop electric prop deicers, or anti-ice.
The electric boot is fitted to the leading edge of the prop. It is held in place by being glued on, and at the very inside there is a part like a large o ring. This o ring is right at the hub end, is rubber and is held on by glue as well as being elastic like a rubber band.
This o ring on one blade, had dried out, probably from being exposed to elements like sun. It had slightly come loose from the glue so that it could shift slightly on the prop. It moved very slightly out, away from the hub about an inch on just the one blade, and thus changed the balance just
enough to notice in flight.
I had suspected prop balance when it happened, and I looked at the spinner and screws as well as blade for nicks. I just did not look directly down inside the spinner and focus on these rubber O ring end, so I missed this.
The warm weather and sun over lunch at Amarillo that day may have softened the rubber just enough.

How do I know that was the cause? Well, some flights later I saw the loose rubber part on one blade and got the shop to secure it with a tie wrap back in the original position and the vibration stopped.

Thanks for all the ideas.

[Robbie Stuart]

Well He11, at least I figured it was the prop

[Matt Gunsch]

Something to do with the propeller's counterweights or possibly a stuck blade?

-Tim

Bill,
This is where I would look, Check the play on the links for the blades and the shimming of the blades in the hub. also check the spinner and backing plate for cracks.

[Bill Greenwood]

yes, Robbie once you guys started focusing on the prop instead of the engine, you were close. I thought someone might get it. The second part of the problem was knowing that my plane had the electric hot prop and that the boots or part of them might come loose.

I myself looked at the prop as the first thing when I landed and parked, but just didn't see it inside the edge of the spinner.

[b29flteng]

You (everyone) normally never looks inside the spinner anyway so it would be easy to miss. I didn't realize you had electric boots, but I would have never guessed an O-ring. I guess now you'll be the only one in the world to look inside the spinner during a preflight.

With all the engine indications normal, inflight and during ground run plus being a six-cylinder engine, it was easy to dismiss the engine. With the larger radial engines with so many cylinders, it's a tougher job of diagnosing the problem. With a six -cylinder, one bad cylinder will really be noticable.