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Old 22nd Nov 2012, 14:04   #61 (permalink)
 
Join Date: Apr 2005
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To paraphrase FSI, "whenever the prop RPM is below the selected RPM you are on the Low Pitch Stop"

On the -67
Flight range PCU controls prop RPM, Power Levers/FCU controls engine N1 combination of the 2 gives your power
Beta Range Cam on power lever controls prop pitch, engine runs at idle
Beta Reverse Range Cam controls both blade angle, and N1 RPM

More complicated than that I know, but in flight it is just that simple. There is a WoW switch preventing ground idle/LoPitch Stop, but lifting the levers bypasses this, and yes it does make for a sudden arrival. "nothing damaged but my pride"
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Old 22nd Nov 2012, 15:47   #62 (permalink)
 
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Ok..

So, YES or NOT, the flat pitch is used ON THE particular PC-6.. ?

Maybe should I ask to Pilatus directly, or some repair/mechanic shop what is really happening or what ?

If you guys contradict you each other, I won't be able to reproduce it ;-)

Thanks for feedback though !
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Old 22nd Nov 2012, 15:56   #63 (permalink)
 
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Hueyman Rigpiggy is talking about PT-6-67, the one mounted for example on PC-12, what you' re interested in is the PT-6-27 installed on PC-6 which doesn' t have al lot of accesories, such as WoW sensors and so on.
So basically the answer to your question is YES.
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Old 22nd Nov 2012, 16:07   #64 (permalink)
 
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Ok.. and so the loop starts again..

If flat pitch is reachable, what's happening in final approach.

I'll try to investigate with Pilatus. Unfortunately, I can't be satisfied with the single point of view of you kind pilots, as you know how to operate it.. but don't know how it works exactly ( and it's not your job ) To built this you really have to fully understand how it works.

Thanks for all of you, have nice and safe flights !
Valentin

PS: I think this is the most compact and clear explanation we can have.. I have the 800 + Page manual of PT6A-20 series ( huge huge book ! ) and it's very complex. But even that short PDF show how complex it is.. that is pure mechanical marvel !

http://www.google.fr/url?sa=t&rct=j&...UR-PrfQ1MuH1CQ

Last edited by Hueyman; 22nd Nov 2012 at 17:30.
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Old 22nd Nov 2012, 20:16   #65 (permalink)
 
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hehe, PPRuNe at its best , business as usual

the pdf you linked is more a summary , but nevertheless i quote some sentences from there :

Quote:
“Beta” Operation
“Beta” is the ground mode operation between 50% and approximately 80% of rated power.
During “beta”, … the propeller governor is in an underspeed condition and does not control rpm.
Quote:
Alpha Mode
Alpha mode is the flight mode.
In alpha mode the propeller rpm is high enough for the propeller governor to be on speed. (80-100%).
During alpha mode,
… the power lever controls engine power.
… propeller governor controls blade pitch.
so gents, lets relax , taste what is written , maybe read some threads of yesterday and think about the confirmation that also the porter pilot does not go over the gate in the dive .

maybe you can so by yourself finally answer the question if a pt6a driven porter is in beta during the dive or not.

or keep on pushing

cheers !
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Old 23rd Nov 2012, 13:55   #66 (permalink)
 
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Sorry, my mistake, i thought we were discussing PT-6A-27 specifically rigged to be installed on PC-6 B series here...
Beside that i would suggest to whoever doesn' t have specifical PC-6B experience to try it once in a while, it can be a fun and enlighting experience to undestand how things really work and to bust some miths, oh BTW did i already mention that we DO NOT have to pass the hard stop lifting the PCL to obtain the B range condition on PC-6s?
From my side i will keep operating this peculiar aircraft inside its envelope and according to the manuals as i did with lot of satisfaction for many years.
Just for completeness sake here a PM i sent to Hueyman regarding the approaches.

Quote:
Originally Posted by Krapula
Hi Valentin,
the truth is that a lot of Porter pilots are naive enough to get really bored having to explain all the times how the thingy works
Regarding your curiosity on landing techniques i hope this solves the enigma...there are 2 way to land a porter.
The first is the one we teach during initial training together with all the basic flying manouvres involved, it' s just a normal engine assisted landing, that means that you follow your nice 3° or whatever° profile with as much Tq is needed, of course you' ll pay a lot of attention not to enter the B range by retarding the PCL too much otherwise mother earth will meet you quite suddenly as previously mentioned in some posts.
The second is the one tipically used in paradrops operations, once the drop is completed and IAS still way low you retard the PCL to idle thus entering the B range in flight and allowing a stable descent at around 110KIAS with an attitude of around -30°.
At these speeds the "braking" effect of the prop disk is not enough to "blanket" the tailplanes, at this point you just fly the plane till the moment you have to flare, it' s actually that simple

Regards
Have fun and happy landings !
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Old 26th Dec 2012, 04:23   #67 (permalink)
 
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Quote:
I would agree with pretty much all guppy's summary apart from the fact that reverse is purly a drag thing.

The garretts can throw serious amounts of air forward. Enough to throw a ground handler on his arse when taking out the prop locks.
That's exactly what drag is! Drag is a force that acts rearward to an airplanes direction of flight. Ignoring the slight angle between the thrust/reverse line and flight path line, a reversing propeller is purely a drag thing.
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Old 27th Dec 2012, 08:38   #68 (permalink)
 
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Quote:
That's exactly what drag is! Drag is a force that acts rearward to an airplanes direction of flight. Ignoring the slight angle between the thrust/reverse line and flight path line, a reversing propeller is purely a drag thing.
Well, no actually, it's thrust with a value in the negative range, if you want to play inane semantics. I fly the Herc. We will on occasion, taxi backwards. Do you really think that it is "drag" which is making the airplane move backward?
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Old 27th Dec 2012, 10:35   #69 (permalink)
 
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Hey AS I was aware that you changed jobs awhile back but i didn't know you'd left the ol' 6 for a Herc!

I've always admired it's capabilities and hope she suits you.

Yeah, the term "reverse thrust" comes to mind...

westhawk
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Old 27th Dec 2012, 12:32   #70 (permalink)
 
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AS... I understand your point. What does a pilot use drag for? - to slow down. What does a pilot use reverse thrust for? - to slow down. Both drag and reverse thrust (are forces that) act rearward to an airplanes direction of flight. Guppy wrote a very good explanation of Beta. I didn't see anything wrong with him calling reverse "purely a drag thing" in that context.
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Old 27th Dec 2012, 19:32   #71 (permalink)
 
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Quote:
Originally Posted by Westhawk
Hey AS I was aware that you changed jobs awhile back but i didn't know you'd left the ol' 6 for a Herc!

I've always admired it's capabilities and hope she suits you.
Yep, changed airframes when I changed employers. It was pretty cool flying the DC-6, but I'm appreciating the greater performance of the Herc. When it's thirty below on the ground, bleed air rocks.

Still hanging out at the Pro Pilot Board?
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Old 27th Dec 2012, 21:08   #72 (permalink)
 
Join Date: Jun 2005
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Quote:
Still hanging out at the Pro Pilot Board?
No, I let the membership lapse, though I might go back some day. Long story...

Just to include some content related to the thread subject:


In one of my previous lives I worked on TPE 331 engines for a time. Normally the 331, being a direct drive single spool turboprop, must always maintain a positive torque in flight in order to maintain control of the engine. Too much power output at idle and the airplane has difficulty slowing down, not enough and the negative torque sensing system dumps prop hub pressure to increase blade angle thus eliminating negative torque. (prop driving the engine) As I recall, power management theory for 331s is a pretty sizable chapter in the line maintenance training manual so I'll try to avoid going into excessive detail here.


When in alpha mode, the engine RPM is controlled by the prop governor (blade pitch) and the torque output is controlled by the power lever. (fuel flow) When in beta mode the blade angle is controlled by the position of the power lever through the prop pitch controller and beta tube while the RPM is controlled by the engine fuel controller.

Proper adjustment is accomplished by setting the flight idle blade angles and flight idle fuel flows to M/M specs, which involves adjusting the beta tube depth to set blade angle and a fuel control adjustment screw to establish the idle fuel flow. (power) The small amount of tolerance in these settings is usually utilized to get both engines on a twin to make equal thrust at the power lever idle position and avoid yawing moments when both power levers are brought to idle for landing. The transition between alpha and beta modes normally takes place during the landing roll as the prop "falls off the governor" with decreasing airspeed.

This small amount of beta tube and fuel flow adjustability could also be utilized to somewhat reduce aircraft floating tendency caused by excess idle power output. This is a particular problem on certain airframe types with low wing loading. On single engined agricultural application airframes like the Thrush and Weatherly some operators were (allegedly) modifying the prop pitch controller by grinding their own PPC cams such that beta mode could be achieved in flight. Normally this is only possible by bringing the power lever "over the hump" in flight, a practice generally frowned upon with ample reason. This "modification" (unapproved) enabled them to land the airplanes in a reasonable distance without risking an inadvertent entry into reverse blade angle range.

With the PT-6A being a free turbine engine the methodology of the engine/prop rigging are different but the result similar.

westhawk

Last edited by westhawk; 27th Dec 2012 at 21:10.
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