Unexplained rapid torque changes during climb and cruise
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When passing a certain altitude (depending on environmental conditions) and using less than maximum climb torque (121.4%), the torque rapidly increases to the maximum even if the throttle has not been moved. At even higher altitudes, it may or may not fall back to a value that corresponds to the current throttle setting.
As an example, I did a test flight where I set 121.4% after takeoff and then did not touch the throttle again to see what the engine does. By the time I was climbing through FL220, the torque had decreased to around 110-115% when it suddenly jumped back to 121.4% even though the throttle had not been moved. Then, just before I reached my cruise altitude of FL250, it rapidly dropped back down to 110-115%, again without moving the throttle.
On some flights, extreme torque changes also happen during cruise, but these correct themselves within seconds.
I used SPAD to log external air temperature and pressure data during one test climb and made a graph out of them, and there are no rapid temperature or pressure changes that correspond to the torque changes, so it doesn't appear to be weather related unless it's caused by wind.
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I've had similar with accompanying changes to engine sound, have assumed so far that it's related to weather injection in the sim, as you mention wind direction or speed change maybe or even pressure fluctuations? I tend to aim for about 115% to give some margin, performance still seems great anyway
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Torque in the BKSQ TBM-850 while an improvement over the original Asobo TP engines (before the refactoring) is better, it's still nothing like the real thing. In the BKSQ TBM once the throttle is set for maximum torque or ITT after takeoff you don't need to touch the power lever again till around 18,000 feet which is completely wrong. It's actually acting more like a conventional Turbo with mixture lever which you don't have to touch till reaching critical altitude.
What should be happening is that literally every thousand feet or so of climb you have to keep pushing the power lever forward a little more otherwise the ITT and TQ will start to reduce as you gain altitude. This is due to the air becoming less dense with altitude, which means less oxygen, so you need to advance the power lever a little more to maintain that same power output.
As the aircraft gets to about 23-26,000 feet (depending on air temp etc) you will likely have the power lever firewalled i.e. at 100% and you will now see the TQ and ITT continue to fall until you get to the service ceiling of 31,000 feet.
BKSQ needs to get the part in the second paragraph above fixed before it can call itself a Turbo Prop and a TBM.
The other thing that needs an overhaul by Asobo is the ground friction, as the TBM should be pulling to one side very strongly at high TQ settings during the takeoff roll.
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A reply fro Nick at BS for you on this:
'I have been through so many revisions to the engine in the TBM this past week or so that I will only attempt to speak for the current release candidate, but I think you will be happy to see better performance in the areas you identified above. The torque decrease with altitude has been increased, and now decreases from a maximum of 140% at SL, to 90% at FL300. Maximum allowable torque of ~120% is attainable until around FL260. Torque effects on the takeoff roll have also been increased, or rather, Asobo's "assistance" counteracting the torque effect has been removed. I believe that any sudden jumping in torque was due to a last minute change before release and a single miscalculated value in a table, by the way. I haven't seen that behavior since, at least. I hope this is all good news to you, and thank you for the feedback!'
Hope that helps.
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@voice-of-reason said in Unexplained rapid torque changes during climb and cruise:
A reply fro Nick at BS for you on this:
'I have been through so many revisions to the engine in the TBM this past week or so that I will only attempt to speak for the current release candidate, but I think you will be happy to see better performance in the areas you identified above. The torque decrease with altitude has been increased, and now decreases from a maximum of 140% at SL, to 90% at FL300. Maximum allowable torque of ~120% is attainable until around FL260. Torque effects on the takeoff roll have also been increased, or rather, Asobo's "assistance" counteracting the torque effect has been removed. I believe that any sudden jumping in torque was due to a last minute change before release and a single miscalculated value in a table, by the way. I haven't seen that behavior since, at least. I hope this is all good news to you, and thank you for the feedback!'
Hope that helps.
Sounds good. Looking forward to the update.
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@voice-of-reason said in Unexplained rapid torque changes during climb and cruise:
to 90% at FL300.
That seems very low as the NORMAL cruise torque at FL300 is about 99%. At the moment the numbers match quite well with the published handbooks I would be sad if that is messed with. I know its a fine line but I rather have the number right than adjusting a perceived feeling (which, in full transparency I also criticized) but I seems we have to pick and choose with Asobos current turboprop model.
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@mad_x It seems that 90% is actually reasonable number at FL300 as for the available Torque.
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@knidarkness a manual I found on the 'net for an 850 (PT6A - 66D/Hartzell HC-E4N-3) has higher numbers too. At ISA and 30,000ft, the indicated torque is 101% for maximum cruise and 96% for normal cruise. It only hits 90% between +10K and +20K above ISA.
The ceiling for maximum allowable torque fits though, maximum cruise is listed with 121% at 25000' and 118% at 26000'.
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@laurreth A further reply from the developer on this for you...
"I'm sorry, I shouldn't have written that post from memory. I checked on the engine performance in the simulator today and the maximum attainable torque at FL300 at ISA is 105%. The maximum performance cruise table that I've been using from the POH indicates that this is the torque available at that pressure altitude with the power lever fully forward. I hope that helps dissuade any fears of undesired performance changes."
Hope that helps.
