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Tom Wright

J41 Cruise power/speed/trim

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Hi.Purchased the J41 recently and love it - it's incredible! Hats off to PMDG for making such a groundbreaking product!Surprisingly haven't had any mishaps regarding blowing up engines etc, but was a little confused as to cruise configurations.What is a typical cruising speed for the J41? I'm doing the tutorial flight at the moment, and it doesn't mention cruise speed. I read in the AOM that power should be set at 10 degrees lower than maximum EGT, but this gives a cruising speed of about 240kts (almost overspeed). Also at these higher speeds in tutorial configuration, the trim indicator gives a lot of nose-down trim (at 230 kts the bar is over 'SMC' whatever that means, and at 240 kts it's almost full nose down).So what should I be aiming for?Thanks,Tom

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I mostly aim for 10 KIAS below the maximum in calm weather. In rough weather I aim for about 200 knots.

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I mostly aim for 10 KIAS below the maximum in calm weather. In rough weather I aim for about 200 knots.
Ok thanks. Where would the trim indicator be for those configurations? Mine is way above the green band.

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Ok thanks. Where would the trim indicator be for those configurations? Mine is way above the green band.
I believe that the green band on the trim indicator is the optimal range for take-off trim rather than for cruise trim. I set trim within this band prior to take-off and, frankly, I ignore it once airborne.

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I believe that the green band on the trim indicator is the optimal range for take-off trim rather than for cruise trim. I set trim within this band prior to take-off and, frankly, I ignore it once airborne.
Ah ok. I found in the AOM that 'SMC' that I saw on the trim indicator stands for Standard Mean Chord. Not sure what this actually means though - but that's where my trim is in the cruise, or thereabouts (normally a little forward of it at 240kts).

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There are some explanations what SMC means when you google the word, but I do not quite understand. Maybe someone here can explain this in simple English..?I think trim around SMC is normal. At least I have the same setting.

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Thanks for clarifying that.It must be normal - I was searching the forum and found a post made by 'rsrandazzo', who I believe flies the real aircraft, and he said that it is quite common to use a lot of pitch down trim in this aircraft.

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It's actually more efficient that way, as the horizontal stabiliser is helping provide lift (instead of a downward force to keep the aircraft level). Also, at lower cruise levels, if you find Max EGT -10 degrees is threatening to overspeed, try reducing power to Max EGT -40 or so, reducing RPM (to a minimum of 96%) and resetting Max EGT -10 (always lower power before lowering RPM, then fine-tune power. By playing around you should be able to find a point at which your EGT is 10 below max, RPM somewhere between 96-98%, and IAS just under Vne. If you have RPM at 96% and still have to set EGT at less than -10 to prevent an overspeed you should consider a higher cruising level (depending on how long your cruise is going to be). Turbines are set up to work best at a particular (but narrow) temperature range, and props at a particular RPM range (on this aircraft 96% is more efficient, but slower) - so it's all about optimising those yet still obtaining the best speed.So, the situation you describe is ideal: EGT is 10 below max (turbine at it's most efficient), the hoz. stabiliser is contributing to lift (even though the trim is almost fully forward, you should still have enough nose down authority through the controls), the prop is somewhere between 96-98%, and all this is buying you almost the highest IAS the aircraft is capable of.

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I like to run around 66% torque at 98% rpm, assuming there is no temp limitation, and I get a pretty consistent 300 KTAS at 15-16000.Edit, funny really, the board doesn't allow the use of abbreviated tubine inlet temperature.

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Very interesting, thanks for the info. Might be small but the J41 sure is a nice challenge to fly!Regards,Tom Wright

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