O200 Vibration at certain attitudes

[greatamericanwest]

What would cause a vibration, or what sounds similar to engine hesitation, at nose-high attitudes?

All other phases of flight are normal, but at 100% throttle, climbing through 4-5k feet I often get what is akin to a vibration that I can feel in the controls, and in my feet on the rudder pedals. The vibration has kept me down low (I don't climb higher than needed because of it).

I read something somewhere about a carb spider/float level too low, etc. OR...could an out of balance prop have issues at certain pitch attitudes? Thanks.

 

[Magman]

A possible culprit could be the left lower engine shock mount.

On C-150s the item is often deformed to the point that the hose covering the bolt actually “bottoms out”. There were actually a couple broken bolts too. It’s always the left lower for some reason.

Also on 150s a thorough inspection of the Spinner is not time wasted. The larger units have issues and incorrect parts may be installed. Shimming and “ 1/2 hole”
preload is required for proper installation also.

 

[greatamericanwest]

A possible culprit could be the left lower engine shock mount.

On C-150s the item is often deformed to the point that the hose covering the bolt actually “bottoms out”. There were actually a couple broken bolts too. It’s always the left lower for some reason.

Also on 150s a thorough inspection of the Spinner is not time wasted. The larger units have issues and incorrect parts may be installed. Shimming and “ 1/2 hole”
preload is required for proper installation also.

The mounts hadn't occurred to me at all. Thanks, I will add that to the list of possibilities.

 

[Bell206]

What would cause a vibration, or what sounds similar to engine hesitation, at nose-high attitudes?

FYI: If you search "O200" on the forum there are a number of previous posts that offer detailed possibilities for your issue(s). Good luck.

 

[Dan Thomas]

A possible culprit could be the left lower engine shock mount.

On C-150s the item is often deformed to the point that the hose covering the bolt actually “bottoms out”. There were actually a couple broken bolts too. It’s always the left lower for some reason.

The typical 150 engine mount, for those wondering what we're talking about:



Looking back toward the firewall. The engine mounts on the four little black rings.

You can see that the upper mounts mostly pull the top of the engine rearward and keep its nose up. The lower mounts have triangulation to both upper and lower firewall attach points to support the weight of the engine, so they're working harder. The propeller's torque reaction puts more load on the lower left mount (lower right as we look at it from this angle) and wears it.

The two big rings in the lower middle are for the nosegear.


Might be time for new shockmounts.

Now, climbing through 4-5K feet at full rich can cause vibration, too. The engine is likely getting too much fuel. Try leaning it a bit, just until it smooths out. That's what the mixture control is for, after all. From the 1977 Cessna 150 POH: (it's even in that POH TWICE):





Sadly, too many students don't get this POH training in school.

 

[RussR]

I operate a Seminole for multiengine training. Every single time, climbing out through about 4500 MSL, the engines start to run a little rough if the pilot hasn't already leaned a little. It's very predictable, and I use it as a teaching moment. You lean it out, and know you've done enough when the engines immediately smooth out.

It's really a perfect opportunity to talk about mixture settings, because while we're not at sea level here, we're low enough (1200-1400 ft MSL field elevations) that many single-engine training flights take place at 3500 MSL or so, and therefore mixture doesn't really get a whole lot of emphasis. But for the twin, we want to take it higher for 1) safety, 2) POH compliance on some of the maneuvers, and 3) it gets us above lots of other training traffic anyway - so it creates the mixture rich = rough engine situation that many haven't seen before in training.

I'd definitely just try leaning it out before I get crazy inspecting engine mounts or anything else.

 

[Magman]

“ get crazy inspecting engine mounts” ? You’re not serious? It doesn’t seem like the whole 150 fleet is calling in to say it’s normal So you don’t do “ projects” like looking at rudder trim or nicks in props?

There are 4 bolts holding the engine on. If 1 breaks the other 3 are taking higher than normal loads so are more prone to a catastrophic failure.

And you say it’s crazy to look at ?

 

[RussR]

“ get crazy inspecting engine mounts” ? You’re not serious? It doesn’t seem like the whole 150 fleet is calling in to say it’s normal So you don’t do “ projects” like looking at rudder trim or nicks in props?

There are 4 bolts holding the engine on. If 1 breaks the other 3 are taking higher than normal loads so are more prone to a catastrophic failure.

And you say it’s crazy to look at ?

Perhaps "get crazy" was a bit tongue in cheek, but whenever you're troubleshooting anything, it's typically wisest to start with the easiest, quickest possible solution. He said the airplane flew smoothly otherwise, the only difference is the altitude. That, to me, says "leaning". Since that's also the easiest, quickest thing to test, that's where I'd start.

Of course, if you're concerned about the motor mounts, nothing wrong with checking them out. Just like there's nothing wrong with checking out any of a number of things that aren't part of the normal preflight.

 

[3393RP]

What would cause a vibration, or what sounds similar to engine hesitation, at nose-high attitudes?

All other phases of flight are normal, but at 100% throttle, climbing through 4-5k feet I often get what is akin to a vibration that I can feel in the controls, and in my feet on the rudder pedals.

That vibration you feel climbing at full throttle is Max Q, the maximum structural load the airframe experiences entering the transonic flight regime as the aircraft exceeds Mach 1.