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propeller brake


rami
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Yep you can but I would really check to see if the flight was necessary.

Its primary purpose is to stop prop rotation in flight, if it is already rotating with engine shut down, all it going to do is wear the break and rotation will increase in speed.

This could lead to an increase in control difficulties during the flight if you have to shut that engine down.

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The main concern is if they actually had to shutdown that engine inflight and its spinning against the prop brake would be as the prop brake heats up it will lose effectiveness and the prop will spin faster and faster and this would cause directional control problems.

Other problems associated with flying with this problem would be heat generated from the prop brake will increase higher and higher (due to friction) until it becomes a fire hazard; another concern would be no oil to the gearbox, this is a big problem for a sustained flight in this condition with heat buildup at all your bearing points.

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Propeller once feathered during flight and passes the 90 degrees blade angle, relative wind (ram air) will act and tends to rotate the propeller in the opposite direction; the propeller brake is shape designed to firmly engage against this opposite tendency rotation force thus stopping prop from rotation.

In the case of prop brake malfunction, the propeller will keep turning slowly in reverse, the slow speed turning is related to the fact that the 2.5 degrees angle (above the 90) is not big enough to produce a high seed turning, in addition to the remaining acting force of the prop brake while trying to function, which will definitely generate a heat build-up as Dan mentioned.

Once “Air Startâ€â€ is initiated (condition lever pressed) the prop blade angle will start decreasing from the 92.5 and once passed the less than 90°; reverse rotation will stop, prop blade angle then will be in a position to initiate the normal rotation.

Unfortunately, both our FCF manual and our flight manual (and maybe yours) do not mention any precaution or action against this type of malfunction (I mean reverse rotation/prop brake malfunction). I have listened to some techniques on dealing with such defect during flight, but none approved by any manuals.

So the only safe advice that can be given is:

If the case is during FCF, don’t delay the air start of this engine, and if during emergency shutdown reduce the air speed (not below any safe speed), and ask for landing at the nearest suitable airport.

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One thing you can try to prevent reverse rotation for a feathered prop is to momentarily take the condition lever to air start. This will begin to drive the blade angles out of the fully feathered position. If the prop brake is functioning at all you might be able to bump the condition lever enough and change the blade angles to get the blades out of the negative blade angle but not enough for them to begin forward rotation to initiate an airstart. This "may" be enough to help prevent backwards rotation of a feathered propeller. But you'll also have to leave the condition lever out of the "Feather" position. Just a thought.

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One thing you can try to prevent reverse rotation for a feathered prop is to momentarily take the condition lever to air start. This will begin to drive the blade angles out of the fully feathered position. If the prop brake is functioning at all you might be able to bump the condition lever enough and change the blade angles to get the blades out of the negative blade angle but not enough for them to begin forward rotation to initiate an airstart. This "may" be enough to help prevent backwards rotation of a feathered propeller. But you'll also have to leave the condition lever out of the "Feather" position. Just a thought.

seems to me if the cond. lever is taken out of feather and moved to A/S momentarily to remove the - blade angle,the "T" handle would have to be pushed back in or the prop is right back in full feather. Maybe pull some C/B's. Could be all wrong,been 45+ years since I pulled a"T" handle or cond. lever on a Herk.

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seems to me if the cond. lever is taken out of feather and moved to A/S momentarily to remove the - blade angle,the "T" handle would have to be pushed back in or the prop is right back in full feather. Maybe pull some C/B's. Could be all wrong,been 45+ years since I pulled a"T" handle or cond. lever on a Herk.

Of course this depends on the reason the engine was shut down. If the Engine Shutdown Procedure is ran then yes the T-handle would have been pulled too. But I think the OPs question relates to a cruise engine shutdown where just the condition lever is used.

But I think his original question was answered in that Yes you can airstart an engine even if it's rotating backwards when feathered.

I can't begin to tell you how many times we saw this during my time at Robins doing FCFs.

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Seems to me, it was taught at the school house at Sewart if the prop brake didn't hold, and once the fire was out, reset the T handle, go to air start with the condition lever until the prop quit rotating, keep an eye on it and land as soon as possible.

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