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What would happen if one or more of the blades (but not all) on a variable pitch prop would not tilt at the same angle as the other ones?

Could this situation happen or is the technology so advanced or stable that it would be basically impossible?

Should it happen, besides vibration (most probably due to imbalance factors,) what other effect could there be? How would pilots solve this emergency (if it can be called so?)

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  • $\begingroup$ It is a single mechanism, what you are proposing will mean that the mechanism is actually broken $\endgroup$ May 17, 2015 at 16:50
  • $\begingroup$ Could it happen that if the mechanism breaks part of it would still continue functioning? Something like in some car gearboxes where you might get some gears, but not others. $\endgroup$ May 17, 2015 at 16:52
  • $\begingroup$ I ca not help you here... I don not know. $\endgroup$ May 17, 2015 at 16:55
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    $\begingroup$ it is not always a single mechanism. many designs involve each prop blade having its own control linkage. $\endgroup$
    – Erich
    May 18, 2015 at 3:30

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Never say never, but that's not a prop malfunction that I've heard of or that was ever addressed in the turboprops that I've flown. We had various prop malfunctions, but the ways that things could fail that we considered would pretty much leave all blades in the same place. So without claiming that it could not, ever, ever, no way no how, not in all possibility ever happen, I'll say that it's not very likely.

If you did get something like that, the vibration would probably be bad enough that you'd shut the engine down, and at that point the interesting question would be, do all the blades feather for you? (The answer to that probably depends on what type of prop you have and what specific failure mode led to the condition in the first place, and now we're into too much speculation for any answer to be very enlightening.)

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  • $\begingroup$ Good answer. Just to comment, I do not fly. My question came out after a flight on a ATR72 a couple of days ago. $\endgroup$ May 18, 2015 at 13:24
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Yes the prop blades can be mis-indexed on older model turboprop systems. the Hamilton Sundstrand 54H60 system uses a hydro-mechanical prop control and a dome to change pitch. When reinstalling the dome, it is possible to mis-index the blades so that they do not all have the same blade angle. There are however ways to check for this prior to starting the engine so I'm not aware of any engine being started with mis-indexed blades. The newer systems like the Hamilton Sundstrand NP2000 and Dowty R391 have a pitch change actuator that locks in the trunion bearings on the blade butts. This system prevents mis-indexing of the blades.

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I have a friend who owned a homebuilt aircraft with a ground adjustable prop. They had a terrible vibration problem that they could not diagnose. They spent months or years trying to get the bottom of it.

Through that process, they switched from an experimental automotive engine to a traditional aircraft engine. They had their prop re-balanced multiple times. All of these things made no improvement.

Eventually, they figured out that one of the blades was off by 1 degree from the others. Re-adjusting the prop and everything was glass smooth.

This took several years and many dollars to sort out. During this period, they were not comfortable flying the aircraft -- so there was also the lost time value in airplane ownership.

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