Simviation Forum - PT6 turboprop question

Mar 1^st, 2011 at 10:28pm

snippyfsxer Offline
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Posts: 404

Hi, this question is probably directed at "Crossfire"

I'm wondering about 'Climb Thrust' on the King Air that you fly. How do you go about setting Climb power...do you always use Maximum available, meaning you have your needles right under the red lines for torque, Ng, and ITT

As you guessed, this question refers to the PT6A-35's on the new RealAir Royal Turbine Duke. On these engines, the Redline Torque is 1250 lbs, and the max RPM is 2200. After takeoff, I know that we would typically pull the RPMs back to 2000. Now, assuming that my temps are within the green, what would be a good place to put the Torque?

(nfortunately, due to copyright reasons, the Perf charts that accompanied the original Piston Duke, are not available for reference in the Royal Turbine conversion)

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Reply #1 - Mar 2^nd, 2011 at 5:08am

-Crossfire- Offline
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When I set climb power, I pull the torque back slightly (just so when I pull the props back, the torque won't go near or past red line). Then I'll set props to 1900 RPM.

Other than that, as you climb, just keep increasing power to maintain the torque close to redline, providing ITT and N1 are still within limits.

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Reply #2 - Mar 2^nd, 2011 at 8:17am

snippyfsxer Offline
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Posts: 404

-Crossfire- wrote on Mar 2^nd, 2011 at 5:08am:

When I set climb power, I pull the torque back slightly (just so when I pull the props back, the torque won't go near or past red line). Then I'll set props to 1900 RPM.

Other than that, as you climb, just keep increasing power to maintain the torque close to redline, providing ITT and N1 are still within limits.

Thanks, that answers it. The manual confused me a bit because it makes several references to a Cruise Climb at "80-90% throttle", which is a little vague, so I thought I would clarify.

I have one more question, concerning descent in a GA turboprop. Do you typically conduct a descent at Idle thrust, and target a specific Vert. Speed or do you target a specific IAS, or what?

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Reply #3 - Mar 2^nd, 2011 at 11:24am

C Offline
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snippyfsxer wrote on Mar 2^nd, 2011 at 8:17am:

I have one more question, concerning descent in a GA turboprop. Do you typically conduct a descent at Idle thrust, and target a specific Vert. Speed or do you target a specific IAS, or what?

Idle power as a specific IAS is normally most efficient. You'll just about always saving fuel, cruising longer and descending at idle (as the burn becomes minimal), than you will by descending earlier with power on.

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Reply #4 - Mar 3^rd, 2011 at 1:46am

-Crossfire- Offline
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In a King Air with 4-bladed props (or any 4-blade turboprop), you can't decend at idle, because you'll be doing about 5000 or 6000 feet per min. Cheesy

We decend with the speed at redline (Vmo), and adjust the vertical speed as needed depending on what your groundspeed is. If groundspeed is around 300 knots, -1500 ft/min is perfect (300 plus a zero divided by 2 equal 1500).

With a big headwind, and groundspeed is around 240 knots, -1200 feet per minute will be good for Vert. speed.

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Reply #5 - Mar 3^rd, 2011 at 11:00am

C Offline
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-Crossfire- wrote on Mar 3^rd, 2011 at 1:46am:

In a King Air with 4-bladed props (or any 4-blade turboprop), you can't decend at idle, because you'll be doing about 5000 or 6000 feet per min. Cheesy

Perfectly manageable. Wink

In all honesty, I flew the King Air for so little time (only about 40 hrs or so) I can barely remember ever flying it.

I do remember it dropping like a very heavy stone at idle power with gear and full flap though! Grin

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Reply #6 - Mar 3^rd, 2011 at 5:35pm

snippyfsxer Offline
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Posts: 404

Okay then, a 3 degree descent it is...

Just finished a flight descending at this angle, at close to Vmo (on this plane it is 235 kias), and was surprised to find it took about 900 ft-lbs for what averaged out to around 1300 fpm. I would have thought a lot less power would be required.

Even though this plane didn't come with the kind of charts that I would have liked, I did manage to find some performance info elsewhere online for the PT6A-35 and was amazed to find that when I matched the torque and RPM settings to the chart at Standard conditions, that the fuel flow was within a tenth of a gallon. may two tenths of a gallon at most. Wow!

« Last Edit: Mar 3^rd, 2011 at 6:48pm by snippyfsxer »

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Reply #7 - Mar 4^th, 2011 at 2:50pm

snippyfsxer Offline
Colonel

Posts: 404

On a plane such as this, during the approach, when is it customary to move the prop levers fully forward? I'm under the impression that you don't move them from the cruise position (say 1900) to fully forward until fairly late in the approach???

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Reply #8 - Mar 4^th, 2011 at 3:47pm

C Offline
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snippyfsxer wrote on Mar 4^th, 2011 at 2:50pm:

On a plane such as this, during the approach, when is it customary to move the prop levers fully forward? I'm under the impression that you don't move them from the cruise position (say 1900) to fully forward until fairly late in the approach???

IIRC it was with the gear, and therefore the (pre-)landing checks. so either downwind in the pattern, or just before commencing final approach.

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Reply #9 - Mar 4^th, 2011 at 7:05pm

snippyfsxer Offline
Colonel

Posts: 404

Thanks,

okay, but one more pestering question. Should I see the fuel flows change in a free turbine, merely by moving the prop levers? I had seen this behavior before on the FSX Piper Cheyenne, and assumed it was a limitation of FSX, but I'm also seeing this on the Turbine Duke, something I assume has its engines modelled to a much higher fidelity. Since the props aren't physically connected to the jet section, something seems counterintuitive here. On the Turbine Duke, the torque changes in response to RPM changes, which it should, but what should happen to the fuel flows on the PT6?

(What I'm seeing is probably correct, I'm just still very dumb on these engines and it has me scratching my head.)

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Reply #10 - Mar 5^th, 2011 at 10:43am

-Crossfire- Offline
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snippyfsxer wrote on Mar 4^th, 2011 at 7:05pm:

Thanks,

okay, but one more pestering question. Should I see the fuel flows change in a free turbine, merely by moving the prop levers? I had seen this behavior before on the FSX Piper Cheyenne, and assumed it was a limitation of FSX, but I'm also seeing this on the Turbine Duke, something I assume has its engines modelled to a much higher fidelity. Since the props aren't physically connected to the jet section, something seems counterintuitive here. On the Turbine Duke, the torque changes in response to RPM changes, which it should, but what should happen to the fuel flows on the PT6?

(What I'm seeing is probably correct, I'm just still very dumb on these engines and it has me scratching my head.)

Hmm... the fuel flows do change in the PT6 when props are moved. I believe this is just like any other engine, when the blade angle is increased(lower RPM), the engine runs more effeciently and burns less fuel.

Make sense? Roll Eyes

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Reply #11 - Mar 5^th, 2011 at 2:12pm

snippyfsxer Offline
Colonel

Posts: 404

-Crossfire- wrote on Mar 5^th, 2011 at 10:43am:

Make sense? Roll Eyes

Sort of

, but it would be more intuitive if the connection were "mechanical" like in a piston or a geared turboprop. It sounds like Real Air modelled things very accurately, which makes me happy.

Thanks to you and C for answering these turboprop newby questions. The simming experience is so much richer and enjoyable when one is able to ask real pilots how its done and then be able to apply that directly to the sim, using a well modelled airplane like this one is.

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