Hi,

I would appreciate some basics on Turboprops. I gather that the engine is spinning at a constant RPM and the thrust is determined by the blade pitch or bite into the air.  Correct?

The Kodiak is the first Turboprop that I’ve flown with a functioning prop (blue) lever I think. But I’m not sure what the proper use of it is and the relationship with the throttle (black lever)  

Are both levers controlling blade pitch? What is each lever doing exactly?

What is Beta? Is that just reverse pitch/thrust? Why not just call it reverse? Should that be used on all landings or only STOL situations? Can it be used to back up on the ground?

Feathering is where the blades are facing into the airstream to reduce windmilling and drag in the event of an engine failure… right? I’ve read you should also feather the prop on shutdown to stop it spinning sooner. Is there any other use for feathering?

What do the engine metrics like NG, ITT, etc refer to?

A special thanks to anyone who takes time to reply 🙂

Chris. 

Depends on the turboprop being PT-6 like or Garrett like, well, sort of...  in terms of beeing free-running or not.

The throttle and the Condition Lever control turbine power and as you vary the throttle, turbine RPM does vary accordingly.

In a free-runing turboprop ( PT-6 like ) the prop axis is not mechanically tied to the turbine axis, so, the prop axis rotation depends on the flow from the turbine.

That's why in good part you shouldn't notice any Fuel Flow variation as you adjust Prop RPM at a constant altitude and throttle + condition setting. I don't know if this has been corrected in the core turboprop simulation of MSFS, but it was plain wrong throughout the various versions of MS FS and P3D.

Good video here about the free-running type:

PT6A Turboprop Engine Demonstrated - YouTube

23 minutes ago, jcomm said:

Depends on the turboprop being PT-6 like or Garrett like, well, sort of...  in terms of beeing free-running or not.

The throttle and the Condition Lever control turbine power and as you vary the throttle, turbine RPM does vary accordingly.

In a free-runing turboprop ( PT-6 like ) the prop axis is not mechanically tied to the turbine axis, so, the prop axis rotation depends on the flow from the turbine.

That's why in good part you shouldn't notice any Fuel Flow variation as you adjust Prop RPM at a constant altitude and throttle + condition setting. I don't know if this has been corrected in the core turboprop simulation of MSFS, but it was plain wrong throughout the various versions of MS FS and P3D.

Good video here about the free-running type:

PT6A Turboprop Engine Demonstrated - YouTube

Thanks, I’m not sure that answered any questions though, it just created more. 😀

I guess I’m looking for more basic operating level advice… The black lever does this, use it like this. The blue lever does this, use it like this. 🙂

Edited August 16, 20223 yr by Virtual-Chris

It is "still" a gasturbine.  the very basics of a free flow engine:

Initially your limiting parameter as you climb away will  be Torque. However at roughly 18k -20k feet the limiting parameter will be turbine temp /ITT  so you will now ascend with a constant decrease in TRQ and subsequently fuel flow. Those two form the basic operational limitation relationship.

RPM is managed by altering prop pitch (blue lever). On takeoff you have a very fine pitch (lever fully forward), makes is easy for the engine to rotate the prop (think of it as 1st gear on your bike). As you climb you reduce RPM (TRQ will now increase since prop blade takes a larger "bite" of the air). In cruise you will typically reduce RPM even further. It can act both as a climb and cruise propeller. Best of both worlds.

ITT is a function of fuel introduced to the engine (the power lever), so you will retard the power lever and reduce TRQ as you climb in order to have the ITT in check. 

A transition from Cruise Power to Climb:  set Prop RPM first, followed by power lever.

From climb power to cruise: reduce power lever then prop lever.

It's rather straight forward once you figure out the relationship between the levers and the limiting parameters.

Edited August 16, 20223 yr by SAS443

7 minutes ago, SAS443 said:

It is "still" a gasturbine.  the very basics of a free flow engine:

Initially your limiting parameter as you climb away will  be Torque. However at roughly 18k -20k feet the limiting parameter will be turbine temp /ITT  so you will now ascend with a constant decrease in TRQ and subsequently fuel flow. Those two form the basic operational limitation relationship.

RPM is managed by altering prop pitch (blue lever). On takeoff you have a very fine pitch (lever fully forward), makes is easy for the engine to rotate the prop (think of it as 1st gear on your bike). As you climb you reduce RPM (TRQ will now increase since prop blade takes a larger "bite" of the air). In cruise you will typically reduce RPM even further. It can act both as a climb and cruise propeller. Best of both worlds.

ITT is a function of fuel introduced to the engine (the power lever), so you will retard the power lever and reduce TRQ as you climb in order to have the ITT in check. 

A transition from Cruise Power to Climb:  set Prop RPM first, followed by power lever.

From climb power to cruise: reduce power lever then prop lever.

It's rather straight forward once you figure out the relationship between the the levers and the limiting parameters.

Thanks.  But the Kodiak Manual seems to assume that RPM is always at 2200 and you adjust torque for take off or cruise based on temp and altitude.  I don't see any recommended settings for RPM - other than 2200-2000.  All the tables provide torque values.  So should I just keep the blue lever pegged to the firewall and adjusting for recommended torque with the black lever then?

What about my questions regarding beta and feathering? Is anyone getting that far through my post? 🙂

Beta is a small range of the power levers (which normally regulates fuel flow into the turbine) where you directly control pitch angle. Used when taxiing (instead of applying brakes) and also for reversing. 

Feathering props at shutdown greatly reduces the rotation time of free flowing props. They can rotate a long time in fine pitch....

Edited August 16, 20223 yr by SAS443

 

1 hour ago, Virtual-Chris said:

Thanks.  But the Kodiak Manual seems to assume that RPM is always at 2200 and you adjust torque for take off or cruise based on temp and altitude.  I don't see any recommended settings for RPM - other than 2200-2000.  All the tables provide torque values.  So should I just keep the blue lever pegged to the firewall and adjusting for recommended torque with the black lever then?

What about my questions regarding beta and feathering? Is anyone getting that far through my post? 🙂

 

I had the same queries when I first started using turbo-props in flight simming ( e.g. what is the 'condition' that you control...the condition of what ? ). It really would be better to go through Youtube, along with a general Google search for tutorials and diagrams. Once you start learning the basic principles, the rest falls into place very easily. It might seem obvious, but it's the quickest way to learn the principles. Otherwise, you are having to further explain your queries when the responders don't quite give you the info you need, or they assume that you already know terminology that you are in fact unfamiliar with.

I think I've figured out part of it... at least for the Kodiak...

Power Lever in Alpha controls fuel which increases power output of the engine which will tend to increase RPM of the prop, but since the prop has a governor, it will maintain the optimal RPM by adjusting the angle-of-attack of the blades which will increase thrust.  So in short: power lever adjusts fuel, which increases power, which increases RPM, which is controlled by adjusting blade pitch which increases thrust. 

Power Lever in Beta directly controls prop pitch from idle thrust to zero thrust, to reverse thrust.

The Prop Lever has two settings:  Max (for flight) and Feather (for engine failures and shutdown).

4 hours ago, Virtual-Chris said:

Thanks, I’m not sure that answered any questions though, it just created more. 😀

I guess I’m looking for more basic operating level advice… The black lever does this, use it like this. The blue lever does this, use it like this. 🙂

Sorry @Virtual-Chris, but as I started to write my pot dutty calld and I had to leave ... Expected to be able to complete te answer, but that's already been done even better by SAS443 🙂

The Kodiak uses a PT6A. These million dollar engines are ubiquitous and are the most common turbo prop in use in aviation world wide.

BETA MODE

Beta mode is basically controllable reverse thrust. In the Kodiak it is for use on the ground only.  Unlike the PC6, it is not permitted to be used in the air, in the Kodiak it will break the gearbox. It is mainly used to slow down the aircraft after touchdown, using it to reverse the aircraft needs extreme care as any excess braking will get you a tail strike.   Note that currently, engaging Beta while airborne in game, does not damage the gearbox. However the Kodiak will be getting more detailed Beta mode in the next patch which hopefully might include that failure.

CONDITION LEVER

Basically the Condition Lever has three positions:

• Cut-off which as it says, cuts off the fuel completely
•  low idle which is used to limit idle speed on the ground so you can taxi at a sane speed without riding the brakes
• high idle which is used for take-off, normal flight and landing

PROP SPEED

Prop Speed in a turbo prop is pretty much set and forget in normal flight, the POH recommends 2200, Ryan has said his organisation for some reason uses 2000,

STARTUP

The Kodiak has two start-up modes:

• lo-start when on battery, lo-start leaves the igniters off to save power and you should flick them on just before introducing fuel  (introduce fuel by moving condition lever out of cut-off)
• hi-start is used on external power and turns the igniters on and off automatically

(note the igniters are normally just used in start-up and then turned off, but there are scenarios such as bad weather that you should turn them on manually as it will prevent a turbine flame out)

It is worth noting that PT6 maintenance includes some items like nozzle cleaning based on hours of operation but other items like the compressor turbine and power turbine disks and the compressor disks must be replaced after a certain number of cycles (startup-flight-shutdown). hence it is common to leave a PT6 idling if a stop over is short rather than shut it down and start it up again.

HOT STARTS

The Kodiak models accidental hot starts. With a hot start too much fuel in the hot section of the PT6 on start-up, causes unsafe ITT temperatures. In real life this can damage the engine and it is unsafe to fly after a hot start without pulling down the engine for a hot section inspection. A hot section inspection can cost hundreds of thousands of dollars and can take weeks or months.  If you do not just happen to have a spare PT6 sitting about, your plane is out of action till the inspection and any repairs are complete.

Common reasons for hot starts are

• introducing fuel before Ng reaches 14% , the turbine is not spinning fast enough to remove excess heat
• forgetting to turn on igniters in lo-start until after introducing fuel allowing fuel to build up while igniters are off

PT6A BASICS

Here is an animated video on the PT6A that will give a better idea of what reverse flow free turbines are all about:

 

Edited August 16, 20223 yr by Glenn Fitzpatrick

1 hour ago, jcomm said:

Sorry @Virtual-Chris, but as I started to write my pot dutty calld and I had to leave ... Expected to be able to complete te answer, but that's already been done even better by SAS443 🙂

No worries... I've got it sorted now. I was primarily interested in what the throttle and prop levers are doing and their influence on the prop and power output.

Glenn's post above is excellent in i's description of the PT-6.

Honestly I haven't yet find the time to test the correct Fuel Flow modelling.

Up until recently none of the flight simulators I used, with the remarkable exception of ELITE IFT with it's B200 Kingair, correctly odelled Fuel Flow variation with RPM lever displacements.