Unrealistic engine behavior at high altitudes
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This is partly true, however, once you climb above critical altitude, the turbo charger can no longer maintain full power and MP will start to drop. Critical altitude is around 17000 ft, and to be fair it does drop very slightly to around 40 inches at FL260. According to the manual though, it should drop to around 31 inches at this flight level. Also the TAS is very high compared to book values.
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To my knowledge, once you reach cruise altitude you don't fly full throttle. Look at the performance charts. The throttle should be set at 31.9" for 75%, with 2750 RPM on the prop, and then lean to ROP or LOP, not full throttle. Use full throttle for the climb, but not for cruise. Or in your case, set to 2500 RPM and 31.1" for 65%.
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In each of the engine power settings in the manual of the turbocharged piston variant, there is this grey shaded area from certain altitude where you're expected to reach the stated MP with full open throttle. And I also noticed on the Grand Duke, I wasn't able to match the values in the tables, including fuel flow, very well.
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Are you adjusting your RPMs? Even if the throttle is full, your Prop should be set at the listed RPM. I don't plan to fly that high, since it would require supplemental oxygen, so I can't verify your information, but you haven't mentioned your prop setting. It's the only thing I can think of that may change the numbers.
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@lilycrose said in Unrealistic engine behavior at high altitudes:
I don't plan to fly that high, since it would require supplemental oxygen, so I can't verify your information, but you haven't mentioned your prop setting. It's the only thing I can think of that may change the numbers.
Well since this is a simulator, you could climb to FL260 regardless of oxygen for the purpose of reproducing this issue :)
And yes, I have reproduced this at different prop settings including those in the tables. I get the same result. The maximum obtainable MP is mostly independant of prop RPM since the turbocharger is powered by an exhaust gas turbine and not the crankshaft. As long as the engine is producing a decent amount of power, the turbocharger will run. Besides this, the problem is not the turbo outputting insufficient pressure but rather produces too high a pressure for those high altitudes where the turbo is not supposed to deliver say 40 inches at FL 260 due to the less dense athmospheric air. -
Then it becomes a question for the developer. I have seen someone questioning the settings in the MSFS forums as well, but hers is more around range. This is my first turboprop aircraft in MSFS, so I don't have a lot of experience with them. I usually prefer lower and slower, but got tired of the Comanche, and I like what Blacksquare does with his aircraft, so giving this one a shot.
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@lilycrose I can't speak for the OP but in my case I was running at 2,500 with an MP that I don't recall exactly but was somewhat higher than the 32" maximum the POH says you should run below 2650 RPM (i was experimenting a bit, don't mind a little extra wear), and was definitely higher than the 28.6" the manual says you should get with wide open throttles at 28,000ft.
I wasn't trying to match any specific line from one of the manual tables, but it was still 75% power per the EDM and fuel flow meter. And I was getting 300kts TAS despite the 75% table showing 250kts at 24,000ft and 243 at 30,000. I suppose you could sneak 300 at an altitude in between but it still seems pretty excessive.
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@lilycrose said in Unrealistic engine behavior at high altitudes:
This is my first turboprop aircraft in MSFS
This conversation is about the piston engine model, just so you're aware....
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Can confirm. Use 55% power settings, FL280, OAT -40 C getting much higher manifold pressure than expected and subsequently higher KTAS.
Could this possible have something to do with the fact that cabin pressurization doesn't seem to have an effect on aircraft power? Bleed air for cabin pressurization is pulled off of the turbo charger. Closing the pressurization valves and shutting off bleed air the cabin seems to have a negligible effect on manifold pressure as one would think that you should see an increase in manifold pressure by shutting off the cabin pressurization bleeds. Commonly aircraft would do unpressurized (bleeds off) take offs when maximum performance is needed from the engines.
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@Black-Square Thank you for an amazing aircraft. A day one purchase for me. I really enjoy flying it.
Are you aware of this issue? Are we doing something wrong or is this somehow related to MSFS limitations?
B.rgd.
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@DxMarovitch Yes, talking about the Piston version. I am currently at FL240, manually set the RPM and MAP to 2750 and 34.1 leaned to 50 degrees ROP. and I'm also showing much higher airspeed and fuel burn than the charts.
https://gyazo.com/18d4cf5695613da7622c409347473ce9
But when I flew yesterday at FL200, the numbers were much closer to the chart figures.
Kat
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maybe this higher speed explain the extra FF, and once at table airspeed FF may match table values, just a matter of torque not 100% matching.
I guess the overpower torque are due to other spec involved in the Flight Model to match better the aircraft spec (such has take off rolls, whole flight phases, approach speed) ... there is so many factor to take in account (aircraft load & weight, 0 wind, 15°C at sea level, sim does have some inconsistency to apply air density variation over altitude, gauge arn't 100% accurate I used to check a HUD bar to get specific variable values and compare them to table)
I also keep in mind it s first version, flight model require lot of time to tweak, aircraft was designed for SU15 initially ... -
@Nicotine70 I think its more of a case of the turbocharger overperforming. If you set your throttle to the manifold pressure settings in the tables, the KTAS is a lot closer.
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@lilycrose Remember, the tables are at max gross weight at ISA. Here's my flight at 55% power at near max gross weight in cruise as a test flight. OAT is bit below ISA for FL280 at -40C. My indicated TAS is about 220 knots so within 10 knots of the chart.
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Is this the DUKE 60 &A60??
Looking for the POH
