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NATOPS1

Pitchlocked prop operation

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Aircrew in regards to Pitchlock prop operations and engine shutdown shutdown at a speed where you cannot maintain 96% or 150KTAS...

What does your book actually say?

Ours says "Attain a speed"

Do you slow to determine blade angle and then shutdown at 96% or 150KTAS or at any given speed above 150KTAS?

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NATOPS are you still at Ft Worth?

Have you heard anything about 169925 coming to Ft Worth. I had heard it was going there but it is now on the ramp at Lockheed with BH on the tail?

Thanks

Bob

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6 hours ago, NATOPS1 said:

Aircrew in regards to Pitchlock prop operations and engine shutdown shutdown at a speed where you cannot maintain 96% or 150KTAS...

What does your book actually say?

Ours says "Attain a speed"

Do you slow to determine blade angle and then shutdown at 96% or 150KTAS or at any given speed above 150KTAS?

96% of what, NATOPS ....

 

 

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Anyone experienced excessive overspeed above 105% due to a decouple? If you know of someone who hasexperienced one pleas let them know about this fourm/post. I need some info for a presentation on the reasons (why) you need to slow the aircraft towards 150KTAS prior to shutting down a pitchlocked prop.

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I have not experienced either one of these, but I do know that you want to slow down for a pitchlocked prop.  It may not feather; so when you stop fuel, you may end up with a big four-bladed speed brake.  Too fast & you may encounter control issues.

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On 3/7/2016 at 3:04 AM, NATOPS1 said:

Aircrew in regards to Pitchlock prop operations and engine shutdown shutdown at a speed where you cannot maintain 96% or 150KTAS...

What does your book actually say?

Ours says "Attain a speed"

Do you slow to determine blade angle and then shutdown at 96% or 150KTAS or at any given speed above 150KTAS?

This situation is covered pretty well in the emergency procedures section.

 

"If an RPM of at least 96% cannot be maintained
when slowing to 150 KTAS without exceeding
engine limitations,"

 

"slowing"

 

One hundred fifty knots true airspeed is the magic number. If the propeller doesn't feather when you cut the fuel off, the engine is going to experience negative torque. Of course it takes a lot of horsepower to spin that compressor and turbine and all the other parasites, specially if acceleration bleed valves are closed. the fixed-pitch prop out there will try to spin all that rotating mass, and in doing so will cause a whole lot of drag. Best to ensure that the propeller decouples when you cut the fuel, if it does not feather. Evidently Lockheed determined that 150 kt. TRUE airspeed is sufficiently fast to decouple the prop at any pitchlocked blade angle that is low enough to present excessively difficult handling problems, should it not decouple. Shutting off fuel at a higher airspeed would be overkill as far as causing decouple if it doesn't feather, and would cause higher-than-necessary noise and vibration if and when it did decouple, plus higher drag if you're real unlucky that day and it doesn't feather or decouple.

I recall the instructor at my very first refresher simulator more than 40 years ago saying " a pitchlocked prop is a good prop". He was right, it will allow you to keep the engine running and provide some thrust until you get to somewhere you can land...a good place you hope.

Lots of things to think about with a pitchlocked prop. Best to read all of it a couple of times; better yet...think about what could/would happen in various scenarios and how you would respond while you're hangar flying with your buddies in the bar.

As far as an uncontrolled overspeed goes, I recall a message I saw back in the 70's and I think it came out of  Okinawa stating that the overspeeding prop caused such noise and vibration that rational thought was almost impossible. Must have turned out OK, though.

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NATOPS,

In the Flight Manuals I have looked at all have "ATTAIN A SPEED" in them. I also looked at an old handout I got at a Hercules Safety Team Brief about 30 years ago and it has some helpful information about decouple, showing RPM with specific blade angles.

150 KIAS is the best range for decouple with lower blade angles, approximately 23° to 36°, and to keep the RPM from being too excessive when the engine is shut down.

The worst case mentioned is when decouple occurs at 23° blade angle. At this blade angle if KTAS is 190 the RPM would be approximately 170% and if KTAS is 150 RPM would be approximately 135%.

At cruise blade angle, approximately 50°, RPM would not be a factor. At 200 KTAS the RPM for both coupled and decoupled is approximately 60%.

I hope this helps.

Vic

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