> At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and First- Officer confirmed stab trim cut-out.
> At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working.
I guess the First-Officer must have been speculating...
Pilots are often wrong about what their aircraft is doing. In fact, that's a big reason why they crash. So yes, the First Officer said that but that is not conclusive proof that they couldn't manually trim. He may have misinterpreted the question and tried the electric trim again. Or maybe he tried turning the wheel and didn't do it right. Or maybe he needed to try again. Or maybe he needed the pilots help. Or maybe the manual trim system was broken. There's any number of explanations for that statement.
Until someone sits down and calculates the torque needed to manually trim it's all just speculation.
Bear in mind that they're at low altitude and the pilot is busy supplying maximum pull on the yoke, and therefore likely unavailable to help crank a stiff trim wheel.
I wouldn't feed the troll, but I don't want your misinformation to spread.
> They weren't
They just took off, max height of the airplane was 1000 feet above the ground. That's a definely low altitude.
> Runaway trim should be a recoverable situation.
The trim pointed the nose down. The aerodynamic forces were so high on the elevator that the trim wheels could not be moved by a single person. This was confirmed in 737 simulator.
>They just took off, max height of the airplane was 1000 feet above the ground. That's a definely low altitude.
People thought that based on Flightaware data. But if you actually read the report you will see that it is incorrect and they reached about 7,000 feet.
>The trim pointed the nose down.
Incorrect. The plane was steadily gaining altitude until they re-enabled electric trim.
>I wouldn't feed the troll, but I don't want your misinformation to spread.
Try being right before throwing around personal insults.
which points clearly to MCAS applying maximum nose down, based on incorrect data from the left alpha sensor, both pilots pulling on their control sticks, and the aircraft failing to gain altitude even before final MCAS activation because the trim could not be manually reset by the F/O.
this report contradicts every element that you're pushing (plane reached altitude, pilots didn't pull on the column, the electric trim was not needed, MCAS did not intervene). did I missing anything ?
It’s pretty disgusting to accuse a dead pilot, that was fighting to save his life and that of hundreds of people, of incompetence from the warmth of your chair.
Or if you stick around long enough I may do it for gits and shiggles.
I'll need some schematic details of the actual manual trim wheel mechanism to figure out what the output forces on the jackscrew are... But hey, sounds like a fun mental exercise.
I'll see if I can find any details on it, but if anyone else just has it, reply to me, and let's see if we can get some delicious numbers going on here. Worst case scenario, I'll pull whatever design most makes sense to me out of my arse and theorycraft to get a feel for it.
737-800 has a 32.776m^2 horizontal stabilizer area. Let's double that to 65.556 to accomodate both airfoils.
Wing load is 1/2p(v^2)A
Where
A=65.556m^2 (352.8 ft^2)
v=180.556m/s (350 knots)
And we'll guess our air density around .95ish kg/m^3
given our altitude of 2334m (7625 ft plus change) asl
Barring any flawed fundamental assumptions, that gives us a wind load of 1015087 N (228200.636 pounds-force (lbf)), and a dynamic pressure of 15485 N/m^2
I'll leave this out there to offend any actual aerospace engineers that might be reading so they'll tell us I'm doing it all wrong while I try to work out whether I can use the screw jack equations and what we've calculated thusfar in the hopes of figuring out something that even remotely makes sense.
I have a feeling I'm oversimplifying or misapplying the wind load equation. But hey, it's the internet. I'm allowed to be wrong.
Okay. So after a bit of chewing on the screw jack equations, I settled on using an M24 screw as the basis just for convenience. Eyeballed a video of jackscrew of a 737NG, and figured a 6 inch lever arm. In the form of a pulley of some sort as the input for the screw jack from the trim wheel in the cockpit.
Dropping in the previously calculated wind load of 1015087 N, we end up with an effort force of 3182 N, which through a 6 in pulley would be 485Nm (357 ft-lbs) of torque,
Note, we're in automobile engine levels of torque output to actuate this screw jack against the wind load on the horizontal stabilizer.
Give me a bit to come up with some estimates on the trim wheel and play around with some gear trains to see if I can come up with an arrangement that does the trick.
It should be doable, but with the gear ratios I'm thinking will be required to generate the requisite torque, the actual rate of actuation is going to be pretty slow.
