3 ms·
There is a trim position indication. It's to the left and right of the throttles. It's a critical thing to check before starting the takeoff roll. You can see
by VBprogrammer 8y ago
There is a trim position indication. It's to the left and right of the throttles. It's a critical thing to check before starting the takeoff roll.
You can see it on the copilot's side here by the trim wheel.
http://www.b737.org.uk/images/stabtrim_200.jpg http://www.b737.org.uk/images/stabtrim_200.jpg
- dvdkhlng 8y agoYes, thinking about that, not having any pilot-visible indication would be quite some point of failure at lift-off. Still wondering whether MCAS and other automatation systems have a representation of that position indication. I can't currently come up with an idea of how to implement that in an easy, yet error-resilient way. Usually you would initially drive into a reference position, then integrate the motor's actions to arive at an absolute value, but integration would potentially add up subsequent errors, and obviously you can't re-do the referencing step while in the air.
- VBprogrammer 8y agoA potentiometer (or something fancier) directly attached to the stabilizer would do it. I'm not sure if they do have one or not. They rate of movement on the stab trim is different depending on the source of the trim change so it's possible they have a PWM controller with some feedback.
- fgonzag 8y agoOr just use an angle sensor on the control surfaces? You now have two measurements: What the computer is telling the hardware to set the angle to, what the angle actually is. These two are very different but very important pieces of information.
- VBprogrammer 8y agoFYI It does look like the graphs here indicate "pitch trim position" which I believe is the absolute value. https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-LQP_PRELIMINARY.pdf https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...