Question for turboprop pilots (specially king air c90)

[Tomerhm]

Hi,


since I have expierence only with C172 I curious to know how turboprop engines work, so I tried to fly kingair C90 in my home flght simulator and use POH for checklist and limitations but I have some question because I not sure FSX simulates turboprops as in real live.


1. in torque gauge and POH I see red line at 1315 but in takeoff when advanced the throttles to full forward the torque rise up to 1460 then go back to ~1420 so I needs to reduce power for 1315


2. also when change for climb power, when I reduce RPM from 2200 to 2000, the torque rise from 1315 to ~1500 so again I needs to deduce power for 1315 limitation


3. again in transition to cruise, I reduce Torque to 800-900 but when reduce RPM the Torque rise to something ~1100 then I reduce power to 900.


I know the fact reducing RPM will rise the torque but I dont know if this simulator size of change in torque is true for real engine behavior

[khorton]

The KingAir C90A is one of the types that I fly occasionally. At sea level, the torque would go well above 1315 if you pushed the power levers to the stop, so you must be careful to set no more than 1315. The torque does rise noticeably when the rpm is reduced, and the amount of rise you mention is probably roughly correct. When reducing from take-off power to climb power, the first step is to pull back the power levers to reduce the torque to around 1000. Then reduce the rpm, which will cause the tongue to rise, and then adjust the power levers to set 1315 torque.

if the air temperature is well above standard, you may hit the 695 degree ITT limit before you reach 1315 torque, so you must watch that too - i.e. set 1315 torque or 695 ITT, whichever you reach first. On some aircraft, at higher altitude, the 101.5% gas generator speed limit will come into play before hitting either the torque or ITT limit.

[Tomerhm]

Thanks for the answer.


so in transition from takeoff to climb power
when reducing torque to 1000, change rpm from 2200 to 2000 will rise torque around ~1300 ?




in take off, how mutch time take the engine to spool up from idle to takeoff power ?


thanks

[Turbavykas]

What will happen if you accidentally increase torque beyond allowed ? Like hitting turbulence while moving the throttles? Complete engine rebuild? Is there a FADEC version where you don't need to worry about this any more?

[mad_jock]

There are two types of engines for tp's

Free turbine and fixed shaft.

Their operation is different.

And if you over torque them it depends on by how much and what the OEM says to do.

It can just be a oil sample taken (SOAP) and prescribed periods or it could be the engine has to go into the engine shop for strip down.

Some aircraft do have limiting systems on them even though they are not FADEC.

But in general pilots are taught not to rely on them. Unless you were on approach you wouldn't have your hand on the power levers in turbulence. And if your on approach you wouldn't be anywhere near the top of the range.

[khorton]

Originally Posted by tomerhm

so in transition from takeoff to climb power
when reducing torque to 1000, change rpm from 2200 to 2000 will rise torque around ~1300 ?

The torque would probably rise to 1200 to 1250. After it stablizes you can then gently adjust the power lever to get 1315.

Originally Posted by tomerhm

in take off, how mutch time take the engine to spool up from idle to takeoff power ?

The PT-6 engine in the C90 has a tendency for the ITT to increase sharply if you push the power lever forward too quickly from idle. You could easily exceed the ITT limit if you are not careful. The general technique if the engine is stabilized at idle is to move the power lever gently until you see that the ITT has recovered from its initial sudden rise. The other issue you run into is that usually one engine will accelerate somewhat faster than the other if you move the power levers too quickly. This causes a directional control disturbance when the prop rpm reaches 2200 rpm at different times, and the prop governors start adjusting each prop pitch to control the prop rpm.

So, when setting take-off power, move the power levers slowly until the ITT has recovered from its initial sudden spike, then more them more quickly until both props have achieved 2200 rpm, then set 1315 torque. At higher altitude, or warmer temperature, the engine will each 695 ITT before achieving 1315 torque, so you must use the lower torque for take-off.

The whole thing, from idle to take-off power, will take perhaps 6 or 8 seconds.

[Tomerhm]

Thanks for the answers!

[mad_jock]

get a model for the metro.

You will find its a bit different.

[avionimc]

FYI

C90GTi

TQ LIMITATIONS

TKOF & MAX CONT: 1,520 (13)

Cruise climb & max cruise: 1,520 (6) (13)

Transient: 1,626 (10)

NOTES:
(6) cruise TQ values vary with altitude & temp.

(10) the value is limited to 20 seconds.

(13) ... inadvertent torque excursions up to 1,550 ft-lbs are time-limited to 7 minutes.