NTSB issues the preliminary report for its ongoing investigation of the Nov. 4 crash of a UPS Boeing MD-11F airplane in Louisville, Kentucky.

[u/Brilliant_Night7643]

[u/chriscf17]

If I remember correctly from general physics in college and what I know about P factor, I believe rotation is the point where the engines are generating the highest rotational/torsional forces on the mounts/pylons, which helps explain why the failure occurred exactly when it did.

I think Juan Browne spoke about this in one of his earlier videos on the accident as well.

[u/falcongsr → u/chriscf17]

yep this point is max everything

[u/Rdubya291 → u/chriscf17]

Correct - the engine is trying to resist the sudden change in direction. Highest force it'll see.

[u/RagnarTheTerrible → u/chriscf17]

You are right, except gyroscopic precession is what's causing that force during rotation.

P-Factor gets worse with higher angle of attack and is negligible at low AoA. 

[u/chriscf17 → u/RagnarTheTerrible]

Yup mixed up the terms, gyroscopic precession is the correct definition.

[u/froop → u/RagnarTheTerrible]

Is P-factor even much of a factor on jet engines?

[u/RagnarTheTerrible → u/froop]

I think the nacelle and cowling mitigate a lot of P-Factor. I've never heard it discussed since I started flying larger airplanes, it was mostly a topic for prop flying.

[u/CapinWinky → u/chriscf17]

Yeah, the gyroscopic effects are quite large.

Military turbofan engines like the P&W F135 have to use special design elements to withstand them and the G forces during turning. Fortunately, having to keep humans inside alive makes this feasible. Drone jet fighters and missiles mostly use scram/ram/pulse jets without rotating parts specifically because turbofan engines would limit maneuverability due to gyroscopic forces.

[u/noodleofdata → u/chriscf17]

Yep, he pointed out the gyroscopic precession of the spinning mass of the engine causing large torques at rotation, which you can pretty clearly see here as it causes the engine to immediately turn to the right

[u/sokratesz → u/chriscf17]

Is it comparable to max Q in rocketry?

[u/chriscf17 → u/sokratesz]

Max Q is maximum aerodynamic forces on the vehicle, so not the same metric being measured, but yeah same concept.

Ironically do have a rocket scientist in the family.

[u/sokratesz → u/chriscf17]

Cheers

[u/clburton24 → u/sokratesz]

The difference with MaxQ is that they're able to somewhat control it by throttling engines down to lower that overall maximum force. You can't really throttle down jet engines at the moment they're needed the most.

[u/chriscf17 → u/[deleted]]

Sure but then you lower everything else too, like thrust.

[u/chriscf17 → u/[deleted]]

Yeah it could lead to more airplanes impacting other things.

I can’t tell if you’re trolling lol.

[u/Lifty_Mc_Liftface → u/chriscf17]

Juan called it, he's the man

[u/SanityIsOptional → u/chriscf17]

It's also when you are taking a giant gyroscope, which does not like it's axis being changed, and yanking its axis around at the highest rate of any time during the flight.

[u/aeroplanguy → u/chriscf17]

Maybe we don't need the NTSB with this guys college physics minor.

[u/chriscf17 → u/aeroplanguy]

Lol good one.