Questions about Engine Performance NG/ITT/Torque since update
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The TBM update seems to have significantly changed the engine performance and I wonder if it might still need some tuning or I just need to relearn things. It seems I have to run much higher NG settings for equivalent torque than the last build, and even then my airspeed is often lower with higher ITT numbers as well. I know the new build matches cruise tables well but the tables in the manual don't list expected NG or ITT values for ISA conditions.
I did a sim comparison to match up with one of Steveo1kinevo's videos and had some significant differences with what I saw in his cockpit. I matched his OAT at FL300 and other engine conditions. He had a 12kt headwind I didn't have. In both cases we had 98% torque and he had a groundspeed of 289kts (301KTAS to my 292). Both cases were at 1900RPM. I know there is a MSFS bug with lower RPM settings but in the old build I didn't notice any major speed loss down to 1900RPM but big drops after that. My main questions are in regard to torque/NG and ITT, not speed loss with RPM.
In Steveo1kinevo's video, at FL300 he was getting 98% torque at NG=101% / ITT=796 while I had to go to NG=103.8% / ITT = 828. That seems to be a fairly big discrepancy. In other videos he seems to consistently hit higher airspeeds at lower torque/NG/ITT levels than I think I'm seeing since the patch. Maybe 851TB is just a rocket compared to other 850's? It just seems like the last build flew (engine-wise) more like I see in the videos...The TBM850 is my favorite BS aircraft still and I have them all. Appreciate all the updates - looking forward to the Starship. :-)
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I’m observing ITT running 20-25 degrees hotter in the 1.2 update. -35 IOAT, FL310, 91% torque yields 836 ITT, whereas the previous version always sat around 810 ITT in cruise. Does appear excessively high. Right now I can barely attain Normal Cruise before temping out, let alone Maximum Cruise.
My question is how are you maintaining a similar airspeed with a reduction in RPM? Given the same power setting, a reduction from 2000 RPM to 1900 RPM yields a 10-15 knot reduction TAS for me. The POH says that RPM settings ranging from 1600-2000 rpm can be used without a significant performance change. I’ve heard that it may be a limitation in MSFS.
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I also agree that the performance more closely matches the POH in the 1.2 update, but something happened with the ITT.
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I’m observing ITT running 20-25 degrees hotter in the 1.2 update. -35 IOAT, FL310, 91% torque yields 836 ITT, whereas the previous version always sat around 810 ITT in cruise. Does appear excessively high. Right now I can barely attain Normal Cruise before temping out, let alone Maximum Cruise.
My question is how are you maintaining a similar airspeed with a reduction in RPM? Given the same power setting, a reduction from 2000 RPM to 1900 RPM yields a 10-15 knot reduction TAS for me. The POH says that RPM settings ranging from 1600-2000 rpm can be used without a significant performance change. I’ve heard that it may be a limitation in MSFS.
@jheidebrecht said in Questions about Engine Performance NG/ITT/Torque since update:
My question is how are you maintaining a similar airspeed with a reduction in RPM? Given the same power setting, a reduction from 2000 RPM to 1900 RPM yields a 10-15 knot reduction TAS for me.
I did some rough testing some months ago and didn't see any significant loss in airspeed from 2000 to 1900 RPM but I only did it at one altitude and I don't recall what it was. I just assumed it would be fairly consistent regardless.
I did some more testing today at various altitudes of 10k/20k/30k and found large variances in airspeed with RPM variations.
At 10k it looked like my airspeed was fairly consistent from 2000-1700RPM and in two separate tests I seemed to gain a knot or two with lower RPM until I went below 1700RPM.
At 20k I maintained airspeed down to 1900RPM, lost about 4 knots at 1800 and then lost about 20knots at 1700 RPM.
At 30k I lost almost 20 knots going down even to 1900RPM and at 1800RPM it appeared I would just continuously lose airspeed and I quit when it appeared the aircraft would eventually stall.Most of my TBM flights are around 1-1.5 hours so I don't often go to higher altitudes except for water crossings so maybe that is why I didn't really notice what you have already found to be true. From what I saw today I will watch more closely and definitely not run any lower RPM than 2000 above FL200.