[KNOWN] too low stab trim rate with auto flaps - ED Forums


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Old 08-14-2019, 03:47 AM   #1
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Default [KNOWN] too low stab trim rate with auto flaps

Noticed during testing the infamous pitch up with auto flaps, that the trim rate with the flaps in AUTO is only 0.1deg/sec if you select them while still on ground.
This somewhat explains the complaint that trim doesn't have any effect if you take off with the flaps in AUTO, but it's actually the FCS that doesn't let you trim with more than 0.1°/sec which means that it's effectivelly ineffective.

Start mission on the runway (half flaps) and trim from +12deg to 0deg = 6sec
Start mission on the runway (half flaps), set flaps to auto and trim from +12deg to 0deg = 120sec

Yes I know, you are not supposed to take off with the flaps in AUTO, but this is
a) a simulator, and where else if not in a simulator you would/should train non-standard procedures/emergencies etc.
b) this might affect other FCS areas as well.

Last edited by bbrz; 08-14-2019 at 03:57 AM.
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Old 08-14-2019, 02:29 PM   #2
Join Date: Jan 2018
Posts: 105

Im fairly sure the available trim rate on the FCS is supposed to change depending on mode / flap config.

What you are describing seems fairly normal to me as in flaps auto the FCS will trim for 1G

In flaps full, FCS knows you are in landing config, hence the change in available trim rate. (AoA)

Im sure someone will pop in with full NATOPS reference shortly....

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Old 08-14-2019, 02:58 PM   #3
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Hi, thank you for report!

Low pitch trim rate in AUTO flaps is known issue, we will increase it for sure. The problem is to make it both fast and precise, so you can return to 1G flight, not 1.05G.
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