Beech Travel Air (BE-95) Problems

[SATCFI]

Here's the situation. I teach in a BE95 and for the last several months the unfeathering accumulators have been very intermitent and recently, they have not worked at all. MX has spent all kinds of time on them, even a guy from the big prop shop was there today. When I arrived to fly, we went up, shut down the left and the prop would not budge when we tried to unfeather.

Using the starter was of no use, it just wouldn't turn over. As soon as we landed, it started (in feather) just fine. WHen I feather it on the ground and then shut down and then move the prop lever forward, it comes out of feather but gradually (over 30-45 seconds) goes back into feather. Also noticed oil on the engine nacelle in the area of the accumulator bottle after shut down today.

Why does it unfeather on the ground but not in the air?
Any suggestions on how to consistently start it in the air in feather? I have been successful in the past, but not recently (burned up a starter 2-weeks ago.)

Getting tired of single engine landings (3 in last month).

Thanks,
SATCFI

 

[bigD]

Don't know the Travel Air, but could it be that the line to the accumulator is slightly clogged? That way you'd only be getting a portion of the full amount of pressure from the accumulator. With only part of the pressure, perhaps the prop can't unfeather while aloft with the air moving between the blades, but on the ground there's just enough force from the accumulator to move the prop out of feather.

 

[Flint]

Keep in mind, you have relitive wind streemlining the props. If they are sticking, this could give it enough presure to keep it feathered.

 

[Flint]

BTW: I love that airplane. I did my Multi training in it. Are you instructing out of it, (what's it used for)?

 

[qwerty]

Sheble's out in AZ does a ton of training in that plane. They have probably seen it all. Call the wrenches up there and they could probably help you.

 

[avbug]

I don't know that I'd look to Sheble's travelairs for guidance...the only thing holding them together is paint.

You may have several problems. The accumulator, if leaking pressure (and oil) is an obvious choice. An accumulator check valve is a likely suspect. You may have a governor issue, a feather valve issue, a propeller issue, or the sludge tube in your crank may need to be cleaned out. When was the last time the prop was pulled?

The oil in the region of the accumulator might lend suspicion to a leaky accumulator. Accumulator pressure should also be checked. If it's only being checked on the gage, then the gage should be removed and a test gage used to determine that the pressure is indicating correctly.

I've seen the piston on accumulators sieze up or fail to move. In such a case, it doesn't matter what the pressure says...the accumulator won't work. Same for bladder spheres or valve failures.

Of course, any time you shut down an engine in flight, you should always do so with the idea in mind that you won't be able to restart it...and plan accordingly. Just the same as doing simulated engine failures in flight in a single or multi airplane. Always approach it such that you could still deal with it if it remains without power.

Another strong possibility here is the propeller itself.

You indicated moving the propeller out of feather on the ground. Your description makes it sound as though you're unfeathering the prop with the prop lever alone, while the engine is not turning. If this is the case, stop doing that; the airplane was never intended to do this. The propeller should be turning when you bring it out of feather, unless you're using a feather pump (not installed on the BE95).

It's been a long time since I've been in a travelaire, but I believe it has a nitrogen hub. You may have a case of overservicing in the hub that's driving the prop back to feather.

If I understood you correctly, you also indicated that the propeller starter wouldn't turn the engine in flight, with the propeller feathered. This sounds like a starter issue, as well. You should be able to turn the engine with the starter, and unfeather it to let the airstream spool the engine up for you. You may have more than one problem.

If you are unfeathering with the engine static (not moving, on the ground), and the lever used to port accumulator pressure to the back side of the prop piston, the fact that it drives itself back into feather suggests that you have never got it far enough out for the low pitch pins to engage (are they working?), and that accumulator pressure is insufficient.

After verifying correct pressures and servicing, I would probably swap out the accumulator and valve, or change it with the other engine (side) and go try it out. If the problem follows the accumulator, you have your culprit.