Anyone up for the (faster) -35 variant?

[CoolP 283]

Well, after realising that I'm still flying my JetProp very regularly (which points to liking her a lot), I was wondering what could be done to enhance the current PT6A-21 model. FLIGHTO actually made the point some time ago.

 

So what would a PT6A-35 powered JetProp give you?

 

First of all, that's 'just' another variant of the engine already running. The rough description would be that the -35 is much better at altitude. And that's the regime the JetProp should be flying the most, right? As to how much better, the comparison charts are available at JetProp, LLC. The rw planes after 2003 or so all came with the -35 to my knowledge.

 

But lets look at some specs.

 

FL240, ISA temps (-32.5°C)

-21: max safe torque is 700ft-lb resulting in 230KTAS

-35: can run 800 fine and gives you 242KTAS, or 254KTAS at 900

 

FL 270, ISA temps (-38.5°C)

-21: max save torque down to 600ft-lb, 222KTAS

-35: can run 800 or even 900ft-lb safely, giving you 250KTAS or even 262KTAS

 

The fuel burn at altitude also is better with the -35, so, at the same torque level, the -35 uses ~2gal/hr less and produces a better range.

 

With the following edits to the aircraft.cfg of yours, you will receive proper speed and fuel burn values at altitude. Mind you that the top speeds may need a rather light plane, but the torque vs fuel burn should be ok. I've always tested them with 50% fuel and with the clear weather preset of FSX, resulting in a 'standard day' with zero winds. Perfect conditions. TAS therefore equals GS. If you are testing with rw weather, results may differ slightly.

 

Only gains, no downsides?

 

Well, I think that the forum section already offers a glimpse on how mixed up the default FSX/P3D engine model is. For example, the fuel burn rates at altitude (cruise regime) can be fine tuned to match the rw charts. But, when flying lower or e.g. idling at the taxiway, you are really far away from realistic fuel burn rates.

 

An example? Well, expect everything above FL200 to be fine. Everything below will result in a too low fuel burn. But, at FL180, this error might just be around max 5% (or less). Idle, at the airport, you are more than 50% off (too low) from rw values though. The fun thing is, one could tune the engine model to this regime (idle, low alt) and it would, again, match the rw values. But then the high altitude would be that far off. See the problem? FSX is static when it comes to applying the fuel burn related values, there's no room for allowing 'high altitude' turbines to develop their talent without mixing up the low alt values.

 

In short, low alt = bad match for our JetProp. Hey, the default model is the same and my guess is that most of the FSX addons with turbine engines suffer from the FSX basis. Maybe some dll can intercept a default FSX or a fully external model but that's beyond my scope.

 

The actual changes.

 

We are looking at the aircraft.cfg. Find it at SimObjects\Airplanes\Carenado P46T Malibu JetProp DL and backup the current one.

[GeneralEngineData]
fuel_flow_scalar   =  1.09                      //Scalar for fuel flow efficiency (from 1.4)

[propeller]
thrust_scalar           = 1.15                   //Propeller thrust scalar (from 1.0)

[TurbineEngineData]
static_thrust           = 30                   //Lbs, max rated static thrust at Sea Level (from 75)

[turboprop_engine]
power_scalar            = 1.37                   //Scalar on Turboprop power (from 1.0)

Change those values (they are already there, no adding, please) and save the file under the same name. In case you wanted to ask, the lower static thrust takes care of any too high idle thrust resulting from the now strengthened engine. If I got that right, the taxi behaviour should be the same as well as the idle 'disc' effect, allowing a slowdown of the plane.

 

That's it, this should enable an increased takeoff performance closer to the real -35 plane and the mentioned higher cruise speeds with accurate fuel burn rates (above FL200). I'm sure you will be able to climb in no time since the average climb rates also increased. Same as in the charts, I've always used 2200(prop)rpm.

 

Yes, you will actually cruise a lot closer or even right at the barber pole some more. That's by design and you may already have encountered this characteristic with the -21 model, being at low altitude. As for how the JetProp should be flown, here's the official text.

The Malibu was designed to fly high and fast and so we operate these aircraft mostly in this flight regime. Even on a one hour flight, it is common to go up to FL210-220 to obtain the high speed and fuel efficiency specific to these altitudes.

With 172KIAS, you are right at the limit at FL270 to receive those 262KTAS. The G500 will therefore love your way of flying the red line. ^_^

 

Can we improve some more, since we're on it?

 

Yes. I mean no. I mean sorta. We are seeing the same strange behaviour with some other FSX values. For example, the ITT is reversed. A real turbine would be torque limited at low altitude and ITT limited at high FL. In FSX, we are looking at the opposite. :wacko:

 

From my testing runs, I was so happy to tune a 'redline' ITT at cruise altitude and the climb. Well, after feeling like a god of engine model tuning, I ran a test at sea level. Guess what. Completely useless tuning. You couldn't even develop half of the takeoff torque without getting a warning on too high ITT.  Back to the drawing board. Back to the conclusion, that I can't change the default FSX model and back to the note on a lot of payware addons actually also showing this downside.

 

Does it spoil the fun? Only if you are flying gauges instead of planes. But honestly, yes, I would love to see better ITT values. I can't.

 

Extra edits.

 

Ok, I performed a bit of work on the air file and I think I could sort of enhance the oil temps. They are read in °Fahrenheit in the cockpit (which is interesting since e.g. the ITT reads in °Celsius) and one could enhance them to more normal levels. Now our engine isn't very challenging when it comes to oil temps. It's not running at its max power output and, from reading, I think the JetProp cowling allows for enough airflow. So what you are seeing would be just a bit more, instead of those default 84°F more of 140°F+.

 

I think P&W are happy up to about 230°F (110°C) which I never reached while testing. So you are still within the limits, which is what I would expect from the real plane. In case you've wondered, no, the switch for the oil cooler doesn't do much in the sim. The real one should. As for the behaviour of the temps. Well, idling on the ground raises them, same for high power climbs and the cruise portion with higher settings.

 

ITT you ask? Didn't you read the text before? Now I've tried to raise the ITT at cruise a bit. A bit. Also means that the takeoff value now is closer to redline but should still allow for the max torque of the engine. Remember, it's stronger now so this new maximum might indeed be a much higher perceived maximum when you are tuned to the -21 model.

 

That's the last part I wanted to mention, the throttle (actually power lever) behaviour. I took a long look at it and changed it slightly but we are still facing a stronger engine now, so what previously caused 1% more throttle now calls for a larger thrust change. In the static world of FSX, prop and turbine 'power' received a significant upgrade, that's the reason behind it. 1% of the new engine are different than 1% of the old one. But I think she still is very flyable in the pattern. If you had spiking throttles though.. might not be easy.

 

If there's interest in the air file changes, I can place a link here. I will add a copyright notice or something to make clear that it's from Carenado, plus my edits. Something like that. Just ask. Means if anyone is still around. ^_^

[FLIGHTO 8]

FANTASTIC WORK COOL.......

 

I am actually gonna read this more carefully when i get home, make some edits and test fly...

 

thank you...

[CoolP 283]

Let me know how it works out for you. :-)

 

/ sent from a mobile thingy /

 

 

[FLIGHTO 8]

Cool nice work... I played around with it.... I do not know for sure how the -35 performs at the levels but this has got to be close.....

 

Down low I can see the discrepancies.... But if you take off and head straight up...it can work....

[CoolP 283]

Well put on the need to get to cruise alt.

After digging a bit into the details, it became apparent how many add-ons rely in the wonky FSX free turbine model and it's flaws. T(h)rust me, quite a lot do it just like that and for example show huge offsets when idling. :-D

 

I'm currently performing some ferry flights over the Atlantic and this might have been the actual drive behind getting that bigger JetProp engine. Well and I got the TBM. B-)

 

/ sent from a mobile thingy /