Unable to match the Climb & Cruise numbers in the manual
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I enjoy trying to fly by the book, using the numbers given in the Turbine Duke manual, but have been unable to match them on any flights at a range of altitudes, FL100, FL150, FL200 and FL250.
I've found that the recommended 120 KIAS Climb with Torque 1150 and Fuel Flow 50GPH to FL200 is unrealistic. You end up climbing at 180+ KIAS at over 2500 FPM. But if you set Torque to 900, you can climb comfortably at 1500-2000 FPM with a fuel flow of GPH40, which the manual says is approx. Cruise consumption.
Using the Cruise speeds in the manual for FL100-200 with Torque 1150 causes overspeeding. But if you reduce Torque to around 900 you end up with a similar Climb and Cruise fuel consumption - which isn't right.
Images below show Cruise and Descent values. I was too busy during climb to take a screenshot.
You can see a slightly higher GPH consumption during Descent compared to Cruise. It's normally much lower for Descent. Climb values were 900 TRQ/ 150 KIAS/ 40 GPH/ 1500-2000 FPM.Any tips much appreciated. Or just confirmation that the Turbine Duke is THAT powerful and needs to be managed in all phases of flight and not necessarily flown by the numbers in the manual. Thank you.
Cruise
Descent
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Two quick items to start:
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Make sure the aircraft is up-to-date, as I made some revisions to the flight model and engine performance for v1.1.
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Are you flying at maximum gross weight on a standard day? All numbers in the manual are stated for MGTOW.
From a quick review:
For initial climb, I found that 120 kias, 1150 FT-LBS, and 53 GPH produces a climb of 2,700 fpm. The manual suggests 58 GPH and 2,650 fpm. When loaded lightly, the Turbine Duke is well known for it's climb rate in excess of 4,000 fpm. Your climb values sound reasonable if one were to derate the climb to 900 FT-LBS with a moderate loaded cabin.
For cruise, I found that 1130 FT-LBS and 2,000 RPM at 10,000ft and 1160 FT-LBS and 2,000 RPM at 20,000ft, with exactly 42 and 45 GPH respectively, produces the expected reline 200 kias, or a few knots into the red. If the aircraft is more lightly loaded, you will obviously well exceed the Vne, by as much as 30kts, from what I can see.
As for descent, I would expect fuel flows to be higher for a given measured torque at lower altitudes, since turboprop engines operate with greater efficiency at higher altitudes due to decreased air temperature. In the takeoff power performance table, you can see a 14% increase in power production efficiency for 1260 FT-LBS between surface level and 10,000ft, for example.
It always makes my day when I see my users engaging with my aircraft at the high level of realism that they were designed for! Thank you for sharing, and I hope this answers some of your questions.
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Thank you. It adds so much to my hobby when developers like you produce add-ons with this level of functionality that are so well coded. There are many developers who don't even read the SDK it seems, so I appreciate your hard work and dedication in bringing such high quality aircraft (and taxiway signs) to MSFS.
I might not have explained myself very well but what I was trying to say was I cannot climb at 120 KIAS with 1150 FT-LBS TRQ, the airplane exceeds 2500 fpm and quickly accelerates to over 180 KIAS in the climb. I would have expected climb speed to average out much lower e.g. 120 KIAS but it doesn't.
I am, like many, excited to see what you bring for the TBM850 in the next patch as I do love a good view and, as much as I love looking at the beautiful modelling of your Duke, it's nice to be able to see out of the windows too!
Thank you.
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Thank you very much for your kind words. As you might imagine, I create these aircraft in the hopes that people will fly them with as much attention to detail as went into making them, so this kind of message is always music to my ears.
I suspected your concern might have been with the climb in particular. What I was having difficulty understanding was why you would reduce your power to seek a lower climb speed. I've never met a pilot in the real world that wouldn't want to climb as fast as possible, so a 4,000 fpm climb at 120 kts IAS would be a tremendous gift to most. Perhaps I'm still not understanding. Please feel free to explain more, as I'm always happy to answer.
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A small update from my last flight for you... I tried to match the climb and cruise figures in the manual but you can see for yourself below... Admittedly, I was flying at FL130, not FL200 this time but it's still useful to see.
I also find that Idle taxi constantly accelerates at 100 TRQ. I don't know if you need to constantly brake to slow the aircraft down in real life during taxi at idle throttle but I doubt it. I have set a manual end of axis at 15%, so this is the minimum available TRQ. I think 50 would actually be enough to keep the aircraft moving but at a safer speed. Everyone is in such a hurry these days!
Climb 1150 TRQ (just about), 2000 FPM, 180+ KIAS.
Cruise FL130 1150 TRQ = Overspeed
Cruise FL130 920 TRQ = No overspeed
Taxi 100 TRQ (Idle with 15% lock manually set to prevent going into reverse) = Speeding on ground and constantly accelerating
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What a beautiful screenshot. I don't get to see enough of those online! It seems most social media users fly the big tube-liners, so I rarely get to see the Dukes in use.
For the cruising speed, I found in my testing that the torque setting prescribed by the handbook at lower cruising altitudes produced an overspeed condition by a knot or two depending on the center of gravity of the aircraft. With a more aft CG at maximum gross weight, it should be right on the redline.
For the climb, yes, I would expect you to exceed 120kts if you are only climbing at 2000 fpm. Climb speeds are designed to be the independent variable, while the vertical speed is left to be dependent. The proper way to achieve the aircraft's maximum performance would be to set the power levers, then pitch for 120kts, regardless of the vertical speed. This should produce a minimum climb rate of 2,650 fpm at maximum gross weight, or greater than 4,000 fpm in lightly loaded conditions.
As for taxi speed, yes, most turbine aircraft will accelerate quite aggressively at flight idle, and the Duke even more so, due to its comparatively high power/weight ratio. This is precisely why the propeller beta range exists to reduce brake heating and wear. The bottom 15% of the throttle input is not reverse, but increasingly finer pitch, until the zero thrust angle is achieved. Turboprop pilots control taxi speed almost entirely by moving the power levers within the beta range, only rarely using their brakes when stopping and making turns.
Always here for more conversation! You know where to find me.
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Brilliant reply, always something to learn, thank you!
Regarding Beta, I have set the minimum throttle to 8% instead of 15% and the minimum TRQ at idle is 110 and the propellers are quieter and I can taxi at a steady 18KT GS without the speed increasing, why does the TRQ increase once it goes below 0? i.e. 9% min = 30 TRQ, 8% min = 110 TRQ but slower.
I hope that this makes sense as I would love to understand why this happens.
Thank you
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I also managed the 120 KIAS climb speed, which started out aroud 4000 fpm and decreased to approx. 2500 fpm > FL100, then 1500 fpm > FL160. Everything is working as it should, the problem is behind the yoke :)
I think I was aprehensive to climb at 4000 fpm as that feels like a business jet rate of climb, not an 80's luxury twin but I'm not a twin or turboprop pilot so I'm learning all the time!
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Glad to hear that everything is working as expected. Indeed, the 4,000 fpm climb rate can be a lot to handle in that hot-rod of the skies. As for the the torque, it should continue to decline as you pull the power levers back to full beta (0% throttle input). I have noticed that the engine indications tend to jump a little bit when passing through the flight idle gate, which might be what you're seeing. Unfortunately, I have no idea why they do this. Just some eccentricity of the engine physics code, I think. Let me know if you have any more questions. I like I said, it makes my day when I hear that my users are taking my airplanes so seriously!
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@Black-Square said in Unable to match the Climb & Cruise numbers in the manual:
What a beautiful screenshot. I don't get to see enough of those online! It seems most social media users fly the big tube-liners, so I rarely get to see the Dukes in use.
You are right, but there are a fair amount of screenshots of the Duke and others in various Discord servers. V1's Discord has a lot of fans of GA. ;-)
