Engine Model Accuracy
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Hi Nick!
Thank you so much! What a wonderfully modeled aircraft!
Everything works beautifully!
The sounds are amazing.. The start procedure and the engine data during start and Take-off are really close.
The cruise data however is a little bit off.. I've got a couple 1000 hours on the real aircraft. and my comments on the cruise data is as follows:
We always cruise at Max Cruise power settings. on your Sim, I have the following altitude: 12,000 feet, 8 degrees Celsius. Using Max Cruise power setting of 1390 ft-lbs torque with 1750 rpm as per the aicraft POH. Your fuel flow is very close: 310 lbs/hr. Your ITT is 740 degrees.. ITT at Max Cruise power, with most airframe i have flown is between 695-710. most of them sit at 705. This is standard for most caravan at Max Cruise. Fuel flow is between 295-305 at that power setting.
The exact aircraft i flew today had the exact altitude and temperature at 12,000 and 8 degrees. 703 ITT and 301 Fuel Flow..
I know i'm nitpicking! just that 740 ITT at max cruise on your model.. should be a lot more conservative than that..
Beautiful aircraft that you have designed there! Thank you so much!
Best regards,
Amara -
Hi Amara! Thanks for your commentary. I'm always delighted to incorporate the feedback from real world pilots, so I hope you don't take my further questioning as anything other than curiosity
Since I tuned the Caravan's performance the same way as all my other aircraft, the resulting cruise parameters for a given power setting are based on the POH representing maximum cruise performance at either the torque limit, or the ITT limit. How do your numbers square with that? Are the numbers in the POH not at the ITT limit? Do you think your Caravan has a cooler running engine or some STC that keeps the temperatures low? Just always trying to learn more from real operators. -
Hi Nick,
Thanks for the response. The Caravans I'm referring to are stock standard PT6A-114A engines with no STC. I understand the way you setup the parameters from the POH. When setting Max Cruise power settings on the Caravan, we check the POH Tables to get a Torque Value for Max Cruise and set that Torque setting. In doing so we also check to not exceed the Max Cruise Torque of 740 ITT, which it should never get close to. Same with the NG%, which seem normal on your engine simulation. If you ITT sits at the Max Cruise ITT of 740 that usually means you may have damage to the engine or an unhealthy engine (which is why I immediately checked engine health on the tablet
).
To some extent the same applies to Take-Off and Climb, probably harder to pinpoint on the sim as data for take-off varies depending on airport altitude and temperature. You should be easily be able to achieve Max Take-Off torque, without being too close to Max ITT (805) or Max NG (101.6), so for example at Sea-Level 10 degrees, the Max Torque is at the ceiling of 1865 Torque, your ITT should be lower than 805 and NG below 101.6
I can try get some Cruise data from our Engine Trend Monitoring system and email it to you.Just to summarize, when you set Max Cruise Torque, the closer your ITT is to 740, the more unhealthy you engine is.
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Hi Nick,
Thanks for the response. The Caravans I'm referring to are stock standard PT6A-114A engines with no STC. I understand the way you setup the parameters from the POH. When setting Max Cruise power settings on the Caravan, we check the POH Tables to get a Torque Value for Max Cruise and set that Torque setting. In doing so we also check to not exceed the Max Cruise Torque of 740 ITT, which it should never get close to. Same with the NG%, which seem normal on your engine simulation. If you ITT sits at the Max Cruise ITT of 740 that usually means you may have damage to the engine or an unhealthy engine (which is why I immediately checked engine health on the tablet ).
To some extent the same applies to Take-Off and Climb, probably harder to pinpoint on the sim as data for take-off varies depending on airport altitude and temperature. You should be easily be able to achieve Max Take-Off torque, without being too close to Max ITT (805) or Max NG (101.6), so for example at Sea-Level 10 degrees, the Max Torque is at the ceiling of 1865 Torque, your ITT should be lower than 805 and NG below 101.6
I can try get some Cruise data from our Engine Trend Monitoring system and email it to you.Just to summarize, when you set Max Cruise Torque, the closer your ITT is to 740, the more unhealthy you engine is.
@asnamara Thanks again, as all of this is good data. I apologize again for my questioning, but I like to have as good of an understanding of this as possible, since it might have implications for all my PT6 aircraft. Several of the other PT6 POH's I've used contain the language "all figures at... [ITT or TQ limit]", while I see the Caravan's says, "Do not exceed... [ITT or TQ limit]" My question is, do we know why these torque values were determined to be the "maximum" by the engineers, if not due to the ITT limit?
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No problems, ask as many questions as you'd like. I think this may apply only to the Caravan, as the Max Cruise Torque was put in place to improve engine life, and appropriate for the mission the Caravan is meant to carry out.. Its a flat-rated setting established by Cessna. So a slightly different philosophy than other aircraft types with PT6.
When I use to fly the King Air, we set Cruise Power based on Max ITT. So your Turbine Duke should be fine by using ITT for cruise, and your modeling for that aircraft should be correct as well.
For another comparison, I also fly the Caravan EX with a PT6A-140 engine, which also has a Max Cruise Torque.. Its maximum cruise ITT is 805, but at Max Cruise Torque we get around 740-750 on the ITT.
Hope that makes sense? -
No problems, ask as many questions as you'd like. I think this may apply only to the Caravan, as the Max Cruise Torque was put in place to improve engine life, and appropriate for the mission the Caravan is meant to carry out.. Its a flat-rated setting established by Cessna. So a slightly different philosophy than other aircraft types with PT6.
When I use to fly the King Air, we set Cruise Power based on Max ITT. So your Turbine Duke should be fine by using ITT for cruise, and your modeling for that aircraft should be correct as well.
For another comparison, I also fly the Caravan EX with a PT6A-140 engine, which also has a Max Cruise Torque.. Its maximum cruise ITT is 805, but at Max Cruise Torque we get around 740-750 on the ITT.
Hope that makes sense?@asnamara That's exactly the kind of information I was looking for! I will check with some other Caravan pilots and see what they say about this. It would make sense, as to why I haven't heard about something like this before, as well. This should be an easy change, as well, since it would just mean scaling the ITT value by a constant factor from my current values. Thanks again for chiming in, and anything else you have to share is more than welcome!
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B Black Square referenced this topic
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As a pilot, and after a few hours of flying in the Caravan, I found the sound perfect, everything is almost perfect. Taking advantage of the engine topic, in the real Caravan, if you use 500 lbs-trq, it can't maintain 100 knots level, even with the aircraft less full. It felt like it was a bit overpowered. Another observation I made is that in the real one, when you reduce the throttle to idle, it rapidly drains the speed. Sometimes I come in at VMO up to 2 nautical miles from the runway threshold and reduce to idle, the aircraft's speed drains rapidly, full flaps, and I still need to increase the engine power to avoid stalling. I didn't feel this braking in flight as happens with the real aircraft. This is a suggestion for improvement, it would be greatly appreciated, especially by real pilots. I'm happy to have invested money! Congratulations on the aircraft, it's almost perfect.
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@asnamara That's exactly the kind of information I was looking for! I will check with some other Caravan pilots and see what they say about this. It would make sense, as to why I haven't heard about something like this before, as well. This should be an easy change, as well, since it would just mean scaling the ITT value by a constant factor from my current values. Thanks again for chiming in, and anything else you have to share is more than welcome!
@Black-Square Hi Nick, After flying your aircraft for a couple of longer flights, I'm happy to say your fuel burn is spot on! Basically on 5+ hour flights, you're within pounds of the fuel consumption of the actual aircraft. The tablet usually predicts a lower endurance, but at max cruise power FL100 to FL120.. you've got the burn spot on. Awesome!
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So the real-life Caravan pilots agree that the 208 shouldn't be ITT-limited down low? I’m used to the TBM, which is always torque-limited down low and doesn’t become ITT-limited until you get up into the flight levels where the air is really thin.
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As a pilot, and after a few hours of flying in the Caravan, I found the sound perfect, everything is almost perfect. Taking advantage of the engine topic, in the real Caravan, if you use 500 lbs-trq, it can't maintain 100 knots level, even with the aircraft less full. It felt like it was a bit overpowered. Another observation I made is that in the real one, when you reduce the throttle to idle, it rapidly drains the speed. Sometimes I come in at VMO up to 2 nautical miles from the runway threshold and reduce to idle, the aircraft's speed drains rapidly, full flaps, and I still need to increase the engine power to avoid stalling. I didn't feel this braking in flight as happens with the real aircraft. This is a suggestion for improvement, it would be greatly appreciated, especially by real pilots. I'm happy to have invested money! Congratulations on the aircraft, it's almost perfect.
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You come in at Vmo on a two mile final? Curious, what's the difference between Vne and Vmo?
@Buzz said in Engine Model Accuracy:
You come in at Vmo on a two mile final? Curious, what's the difference between Vne and Vmo?
VNE - Never Exced.
VMO - Maximum Operation Speed.Sometimes I came with 175kts on final, 2 miles and when I reduce the throttle, the speeds drain. Lower the flaps and I get 90-85kts to land.
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@Buzz said in Engine Model Accuracy:
You come in at Vmo on a two mile final? Curious, what's the difference between Vne and Vmo?
VNE - Never Exced.
VMO - Maximum Operation Speed.Sometimes I came with 175kts on final, 2 miles and when I reduce the throttle, the speeds drain. Lower the flaps and I get 90-85kts to land.
