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Feathering props

Old 24th Feb 2017, 00:14
  #21 (permalink)  
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I've always thought this thing (circled in red) had something to do with feathering

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john_tullamarine is offline  
Old 24th Feb 2017, 00:27
  #22 (permalink)  
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Synchroscope - thanks! Absolutely nothing to do with feathering, although, I'm guessing if you feathered one while running (If that's possible), the synchroscope would start spinning towards the unfeathered engine.

Thanks John.
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Old 24th Feb 2017, 00:35
  #23 (permalink)  
 
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Cralis that bit you've circled is the prop synch. There's an automatic system to synchronise the propellers. In the B200 there's a Type I and a Type II, but I won't go into the differences now as it isn't really relevant.

The little black and white "spinny thing" is called the synchroscope. It spins when the props rpm is not synchronised. It spins clockwise if the right one is rotating faster, or counter-clockwise if the left prop is rotating faster.

Not that it really means much for this discussion, but you've put up a C90 King Air panel pic.


HOWEVER, I don't quite agree with what Slatye has posted. The AFX system does a much better job than most pilots and it is a fairly robust system in Beechcraft twin turboprops. I've never had them go wrong- but then again maybe there are tightarses out there with poor maintenance who neglect their aircraft and thus take the "it doesn't/might not work very well so I'll just turn it off" stance. That's a topic of discussion for another day!

There's a very simple procedure- when the engine fails you check that it has auto feathered. If not you manually feather it. Takes no longer than let's say turning off the system and planning to do it manually anyway.
It is a very good safety system and, if it's an option, may as well use it.


Megan,
Sorry I missed some of your post earlier re mandatory AFX. I'll have to go digging through my notes to see if I can find it, however my best recollection is that the Hartzell-Raytheon/Hartzell-Raisbeck props require AFX all because of Vmca considerations when they were certified.
Car RAMROD is offline  
Old 24th Feb 2017, 02:26
  #24 (permalink)  
 
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Originally Posted by Car RAMROD View Post
Cralis that bit you've circled is the prop synch. There's an automatic system to synchronise the propellers. In the B200 there's a Type I and a Type II, but I won't go into the differences now as it isn't really relevant.

The little black and white "spinny thing" is called the synchroscope. It spins when the props rpm is not synchronised. It spins clockwise if the right one is rotating faster, or counter-clockwise if the left prop is rotating faster.

Not that it really means much for this discussion, but you've put up a C90 King Air panel pic.


HOWEVER, I don't quite agree with what Slatye has posted. The AFX system does a much better job than most pilots and it is a fairly robust system in Beechcraft twin turboprops. I've never had them go wrong- but then again maybe there are tightarses out there with poor maintenance who neglect their aircraft and thus take the "it doesn't/might not work very well so I'll just turn it off" stance. That's a topic of discussion for another day!

There's a very simple procedure- when the engine fails you check that it has auto feathered. If not you manually feather it. Takes no longer than let's say turning off the system and planning to do it manually anyway.
It is a very good safety system and, if it's an option, may as well use it.


Megan,
Sorry I missed some of your post earlier re mandatory AFX. I'll have to go digging through my notes to see if I can find it, however my best recollection is that the Hartzell-Raytheon/Hartzell-Raisbeck props require AFX all because of Vmca considerations when they were certified.
Agreed, I think the idea that Slatye has posted earlier is asking for trouble. Autofeather isn't just there to improve climb after engine failure, it is mandated on most B200's (and all a/c fitted with Raisbeck Quiet Turbofan mod) subsequent to the mid-90's to reduce Vmca from around 108 Kts to 91 kts (or so depending on the variants). If using the standard Raisbeck performance figures of 94kts for V1/Vr and 103kts for Vtoss, you are rotating 14kts prior to Vmca if you've disengaged Autofeather. You won't get that 14 knots back, if the failure occurs at rotation. Sure you could say screw it lets turn it off, but what figures are you basing your takeoff performance on as all figures are based on operative AFX and the low Vmca. It would be more like Vr of 114kts and a Vtoss closer to 120kts, but how's that affected your takeoff distances, could you even still use Runway 17 at EN using those numbers at 12,500lb? When Raisbeck first started modding the -200 in the early 80's they saw the takeoff performance issues they were having with the 4 bladed props and their associated high Vmca. They got approval through the FAA to mandate autofeather as the solution to bring Vmca down and improve their takeoff performance numbers which obviously got them sales. As the autofeather didn't require any pilot intervention the FAA were happy to certify this way and Beechcraft followed suit in the mid-90's.
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Old 25th Feb 2017, 00:34
  #25 (permalink)  
 
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Harry what a great post and excellent answer. Tippy top.

I flew B200s in the late 80's and 90's and was lucky enough to amass 5000 hours on them. I never flew one with the Raisbeck mod. We always used or activated the autofeather function I am not sure even if the MEL allowed the aircraft to be dispatched with it U/S. I am pretty sure it was never a issue, because as you said the system is pretty robust.
Even one of the requirements to take advantage of the Take-off minima of ceiling zero feet; and 550m or 800m vis is dependent on operative autofeather, for that safety factor.
The operator on the type I fly now include a check in the emergency recall to confirm autofeather. It should happen....just checking....you never know.....you know!!!! Nothing is full proof in other words.
Simulators are great tools for training on the effects of engine failures etc. I would be nice to see a cost effective generic simulator established that can demonstrate the issues that you described.
Craven.
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Old 25th Feb 2017, 04:02
  #26 (permalink)  
 
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Originally Posted by Cravenmorehead View Post
Harry what a great post and excellent answer. Tippy top.

I flew B200s in the late 80's and 90's and was lucky enough to amass 5000 hours on them. I never flew one with the Raisbeck mod. We always used or activated the autofeather function I am not sure even if the MEL allowed the aircraft to be dispatched with it U/S. I am pretty sure it was never a issue, because as you said the system is pretty robust.
Even one of the requirements to take advantage of the Take-off minima of ceiling zero feet; and 550m or 800m vis is dependent on operative autofeather, for that safety factor.
The operator on the type I fly now include a check in the emergency recall to confirm autofeather. It should happen....just checking....you never know.....you know!!!! Nothing is full proof in other words.
Simulators are great tools for training on the effects of engine failures etc. I would be nice to see a cost effective generic simulator established that can demonstrate the issues that you described.
Craven.
Thanks Craven. Yes you are correct, systems fail and usually right at the point when you need them most. The Phase 1 checks for the current(ish) model B200 include "Verify Autofeather Operation" for just that scenario during an engine failure on takeoff.

Simulators are an amazing device for such training as long as they are relevant to the equipment you operate. Please correct me if I am wrong but the only B200 sim in Oz at the moment is the one at the Ansett Training Centre in Melbourne and while a great device it only simulates a 3 bladed -41 engined machine, not really relevant I would think to 90% of the operators in this country, with flight dynamics that nowhere near mirror a machine with draggy 4 bladed props. This perhaps leads to a false sense of security regarding the initial climb performance of the B200 when guys do get given such failures and are able to climb away with relative ease, with the focus being just fly the flight director and you'll get the performance you need. Once the new Level D sims are up and running this year I am sure that the training will become a lot more relevant.
Harry Cooper is offline  
Old 25th Feb 2017, 13:00
  #27 (permalink)  
 
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First, it doesn't always work
On the Q400 there isn't even a thought that covers it failing at the same time as the engine, it is tested each day. Without it I doubt the aircraft would be controllable on a V1 cut, it would probably still climb but the un-commanded roll would need full control deflection to correct.
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Old 5th Mar 2017, 14:04
  #28 (permalink)  
 
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Non-feathering multis

The Caldwell controllable non-feathering prop received the Collier Trophy for technical achievement in 1933. Boeing, Lockheed, Douglas etc. multis certificated before this all used this counter-weight actuated (i.e. non-feathering) prop. They were soon retrofitted with Hydromatics (Hamilton Standard design) within a year or two; it made a significant boost in OEI performance.

Last edited by barit1; 5th Mar 2017 at 18:54.
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Old 5th Mar 2017, 17:17
  #29 (permalink)  
 
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Engine failures in a light twin result in a loss of the airplane far too many times throughout the world. Airplanes like the B200 that should be easily controllable are thrown into the ground by even professional pilots. I can accept that a PA31 with 10 people on board has no chance of being flown away if the engine should fail below, say, 300 feet, but at least the impact should be under control at the lowest possible speed for maximum survivability.

I was taught as a sprat to always confirm the engine failure before feathering. In some airplanes this is easy to do because (like in a B200) the torque and EGT will show the loss of power but for a piston twin the instruments are not much use.

The procedure for the piston airplanes was to decide the engine failed side by the dead foot method, with full throttle both engines then confirm by closing the throttle (does anyone have a better way?). If the yaw remained the same then the failure was confirmed, if not, try the other one. A partial failure would be detected this way as well.

But should the feather be quicker than that? Is there time to do this and is it necessary? After deciding which engine has failed by the dead leg, just go ahead and feather it without confirmation? Most POH procedures do not call for confirmation, but jump straight to feather.

If the rpm of a piston engine drops below 1000 the prop will not feather, and closing the throttle could cause the rpm to drop if, say, the engine had failed due to a mechanical issue rather than a fuel stoppage and then the prop would not feather. As well as the extra time taken.

In the PT6 and Garrett airplanes there are problems with decoupled props and failed FCUs that have the engine still running but out of control or the prop dragging despite good power from the engine. Closing the throttle would cause the prop to go into a high drag state so a quick feather is preferable to trying to fly inverted. The Garrett remains in full throttle all the time to protect the NTS/Beta state but I remember closing the throttle in the PT6. and RR Dart but could it actually hurt?

Is it time (at least for me) to move out of the past? Should I confirm by using the throttle at least in a light twin piston airplane or not?
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