[SystemSafety] "FAA chief '100% confident' of 737 MAX safety as flights to resume"

[Olwen Morgan]

On 01/12/2020 21:11, Herrell, Dave wrote:


<snip> ( emphasis in extracted text is my own - OM):

>   This new location and larger size of nacelle cause the vortex flow off the nacelle body to produce lift at high AoA. As the nacelle is ahead of the C of G, this lift*causes a slight pitch-up effect*  (ie a reducing stick force) which could lead the pilot to inadvertently pull the yoke further aft than intended bringing the aircraft closer towards the stall.

<snip>


I had actually read this text on the web before Dave quoted it here ... 
and yet PBL has said in a previous posting:


 >>>As far as I am aware, there is no "pitch-up tendency [which] starts 
to lift the aircraft's nose".


These positions appear to me to contradict each other.


Two questions:

1. Who is right? PBL or the Boeing people who produced the text that 
Dave Herrell quoted?

2. If the forces on the stick change rapidly, this suggests, to me at 
least, that the aerodynamic pressure on the relevant control surfaces 
(thinking physics again) changes rapidly at some point, hence the 
question, what causes the sudden change of pressure? Flow separation 
from the HS, possibly??


And if PBL whinges again about repeating himself, I would respectfully 
remind him that

(1) Repeating oneself and expressing oneself clearly are two different 
things.

(2) Repeatedly asking people to say clearly what they mean is a foul 
habit that I acquired by reading about the cantankerous ancient Greek 
criminal, Socrates.


Still confused,

Olwen





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