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Marcel Felde
15th Sep 2012, 03:54
Hello everyone,

I have some questions on the PT6A and would be very happy, if anyone knows some answers! :)

1. If you switch from LO Idle to HI Idle - is the distance of the Powerlever you would use for setting 52->70 % NG without function?

2. If the Beta system controls the Propeller Pitch, does the Prop Lever get useless?

3. Is there any data or information about the Prop Pitch angle during the corresponding to the Power Lever positions during Beta Mode?

4. If the Prop Lever gets useless during Beta Operation, what does the Prop pitch do at the moment the system switches from Beta to Alpha with different positions of the Prop Lever? Or does the adjustable angle of prop pitch become very "narrow" with lower NG settings so there only one "position" left just before switching from Alpha to Beta?

5. What is the Propeller Pitch angle during Reverse operation? Does the angle increase due pulling the Power Lever further backwards or only the NG rise?

6. Does reverse start with more power while operating in HI Idle?

7. At which point during engine startup does the oil start to allow changes in Prop Pitch?

8. With what kind of power settings is it possible to feather the propeller? I noticed, while being in idle, feathering reduces NG to about 45%. Is that due drag or some kind of mechanical controlling?

9. Is the whole system of propeller and engine influenced due airspeed?

I know, many questions... and I am looking forward to your answers. :ok:

Greetings,

Marcel

aerobat77
15th Sep 2012, 18:13
grüss dich , indeed many questions !

switching the condition to Hi idle will just set the idle to roughly 70%ng and any power lever movement will increase power- you just "start" at 70 and not 52 % with the power lever.

regarding beta : they are two abbrevations what beta is . one call it the flat pitch range which is not governor controlled - so the range between flight idle and reverse ( which is again governor controlled) , other call it everything below flight idle ( including reverse)

so when you talk just about the flat pitch range the prop lever is without function excluding pulling fully back to feather.

when talk about beta including reverse where the turbine spools up again, the prop has a function- e.g leaving the prop not full forward will result in a prop spool up to the prop lever setting and not full reverse range.

( e.g a lazy pilot lands with props at 1700rpm and not full forward and than pulls reverse- the engine will do it but the prop spins up to only 1700 )

at beta ( flat pitch ) the turbine speed is fixed at idle so pulling back to alpha will just result in a decrease of prop speed since pitch rises .

at reverse , when the turbine spools up, first the prop rpm rises until reaching full reverse rpm, then reverse pitch rises.

reversing from high idle will result in a lower spool up time and so more rapid reverse reaction.

At which point during engine startup does the oil start to allow changes in Prop Pitch?

a typical startup of a pt6 : condition cutoff, prop forward , lever flight idle ( NOT beta) , engage starter , at min 12% ng condition low idle. igniters start, fuel is open, it should light up. the feathered prop slowly starts spinning, ng rises until stabilized , the prop spins faster and faster until the oil pressure pushes it out from feather to flight idle pitch. advancing power a little will initially only increase ng and prop speed, the pitch is the same until governed prop speed is reached and than pitch is increased to maintain prop speed.

feather from a running engine ONLY from idle speed or you may burst the gearbox due to the massive torque rise. i never recognized a ng drop when feather at idle ( typically at shutdown you first feather, let the prop slow and the cutoff. must say i never looked at this moment at the ng but believe it stays the same )

of course the system is influenced by airspeed- the given prop pitch to maintain prop speed depends on airspeed , engine power is also influenced. e.g setting takeoff power close to redline will result in overtorquing when the aircraft acclerates due to rising engine power from ram air.

hope this helps you, wann gibts das bier für diese tipperei ? :ok:

chhers

Adis
28th May 2013, 17:19
Hi
I would like to insist on No7 question. Last week during a test flight, after a successful left engine shutdown, we proceeded with the engine airstart with starter assist procedure.IAS 138 , Alt 9000ft, temp 2C.According to the procedure the propeller lever was just above feather. Before switching the fuel pump and starter on we had an indication of almost 20% Ng. Furthermore the propeller deviated from the feathered position with a sudden increase in drag from the left side. It seemed to me that the airflow in engine intake made the compressor spinning and also the oil gear pump. This might had changed the propeller pitch. Do you think it is normal or it is a problem of the engine?

Thank you in advance
PS The engine is a PT6A -112

stankou
29th May 2013, 14:05
@aerobat77:
Your (typical) engine starts doesn't look like in the book. You are supposed to leave your prop in feathe. And, opening fuel at 12% is not very good, exept if you've got a flat battery. I recommand stabilized NG before fuel. The highest you reach, the best it is for your turbine :)

Regarding the question about NG drops to 45% in feather, it looks like twin otter rigging.
The A27 is rigged in the manner to create a NF leak on feather ( smal lever on RH side of the CSU) then your engine is running below idle, on min flow 44/45% NG.
When you unfeather your prop, your beta valve moves forward and blocks the air leak and your engine reaches the idle (+/-52%)

@Adis:
I'm very surprised that your procedure says to unfeather the prop before start inflight.
As you say, 20% NG is enough to run your accessories gearbox and then run the oil pumps. If your prop lever is out of feather, you gonna admit oil in your prop dome and force your prop to go out of feather. Then the windmilling does the rest. Huge drag!!
I did a lot of flight test on beech family, and I never saw that. You have to relight your engine on feather to minimize your drag, then, at idle, you unfeather it and be prepared to compensate with rudder.

I have some questions on the PT6A and would be very happy, if anyone knows some answers!

1. If you switch from LO Idle to HI Idle - is the distance of the Powerlever you would use for setting 52->70 % NG without function?As said before, when you push your fuel lever to HI, your just accelerate your engine to a preset value (+/- 72% NG) you incrase a little bit your deadband on your power lever

2. If the Beta system controls the Propeller Pitch, does the Prop Lever get useless?Don't be confused between beta system (Reverse system) and Beta mode, a non governing mode of the prop. Exept during reverse operation, the prop speed is uncotrolled until it reaches the selected speed on the CSU.

3. Is there any data or information about the Prop Pitch angle during the corresponding to the Power Lever positions during Beta Mode?As far as I remember, your prop pitch is on primary blade angle during the beta mode

4. If the Prop Lever gets useless during Beta Operation, what does the Prop pitch do at the moment the system switches from Beta to Alpha with different positions of the Prop Lever? Or does the adjustable angle of prop pitch become very "narrow" with lower NG settings so there only one "position" left just before switching from Alpha to Beta?You have the answer on the question :) Beta mode means non governing mode, means your prop will accelerate as long as you push power lever. When you reach the max prop speed, then you enter to the Alpha mode, your CSU keeps your prop speed constant (CSU: Constant Speed Unit) If you ad more power, the CSU will maintain the prop speed by coarsing the pitch of your blades, then your torque will rise.

5. What is the Propeller Pitch angle during Reverse operation? Does the angle increase due pulling the Power Lever further backwards or only the NG rise?I think your angle should be around -9°! When you pull your power lever backwards, first you decrease the pitch of your blades by pulling the beta valve backwards. You are then in beta range, means 0 torque. If you pull further back, you start operating the FCU lever and then accelerate NG

6. Does reverse start with more power while operating in HI Idle? you will have reverse even in HI idle? but I've never try that

7. At which point during engine startup does the oil start to allow changes in Prop Pitch? When your oil pumps will built up pressure on your prop dome, means I think around 35/40% NG

8. With what kind of power settings is it possible to feather the propeller? I noticed, while being in idle, feathering reduces NG to about 45%. Is that due drag or some kind of mechanical controlling?Stay at Idle to feather your prop!! Do NOT try with power. You gonna kill your reductiongear box with the extreme overtoque!!
As I told above, depending the airplane you operate, the rigging can allows to go below LO idle, down to min flow. I know the DHC6 is rigged like that, but I don't know about your aircraft.

9. Is the whole system of propeller and engine influenced due airspeed?Hemm, not sure o understand your question... sorry

Tinstaafl
29th May 2013, 16:44
Re reverse in HI idle: The manual for the B200 I fly specifies HI idle for short landings due to the faster response to get to significant reverse thrust. That's because the engine will already be at 72% power when reverse is selected and then increase power from there. From LO idle the engine must accelerate from 52% when reverse is selected. Obviously there's a period of time needed to get from 52% to 72% before the LO idle scenario can match the result from starting when already at HI idle.

I don't usually land with HI idle, even on short-ish runways. I find the aeroplane tends to float more. I prefer to leave it at 62%* then, during the flare or immediately on touch down set HI idle, max RPM** and then select reverse. The spool up time from 62% isn't as bad as from 52%, of course, so by the time I'm ready to select reverse the engine has already spooled up to HI idle.

*left there from before take-off to keep the aircon running on the ground
** Usually left at cruise RPM until touchdown unless a very short runway or turbulent/gusty conditions that will require quick response times - in which case I'll use 72% idle - or lots of icing.

ahramin
29th May 2013, 19:53
Marcel, think of the power lever, prop lever, and condition lever as completely independent of each other and completely ignorant of each other.

For example, if you move the condition lever to high idle, the power lever and prop lever don't change and don't know that the engine is high idle. So as stated the dead band in the power lever would be larger because you have to move it all the way to 72% before it has an effect on fuel flow. Similarly, if you have the power lever above 72% and move the condition lever, it has no effect.

Another example would be the one asked about feathering the propeller. As stated above, the power lever doesn't know you have feathered the prop, so continues to deliver the power the power lever demands, but the prop goes to feather regardless of the power lever setting, causing a massive increase in torque on the reduction gear.

Use this philosophy when trying to figure out what will happen if you move something and you should be fine.

As for normal operation, depends on the aircraft.

DownIn3Green
30th May 2013, 05:23
What A/C uses the -27 these days?

stankou
30th May 2013, 11:37
I know pilatus PC6; DeHavilland DHC6-300; maybe Cesna conquest1 ( not sure if there are -27 or -28 on it)

MX Trainer
30th May 2013, 15:06
Marcel Felde

You are getting a lot of inaccurate info!!

For example "Beta Range" starts at about +21 deg and finishes at about -9 to -14 deg when the propeller hits the internal reverse stop. There are 3 possible fixed stops on the propeller - Feather - Reverse - and those with the external Zero Pitch Latches for shutdown on float and flying boat aircraft. There is an adjustable hydraulic stop that is controlled by the Power Lever - the Beta Valve - that will change the propeller blade angle progressively from about the + 21 deg to the - 9 Deg..

Read and digest this - it should answer just about everything.

PT6A - Engine Explanation (http://www.scribd.com/doc/132863866/PT6A-Engine-Explanation)


Regards,

Mx

Adis
1st Jun 2013, 10:28
Thanks a lot stankou
I have also the same consideration about the procedure, since it is a free turbine engine. I ve just start thinking sending a feedback to P&W, for an official opinion.
Anyway all the information of all you guys was very enlightening.