PixelFlight wrote:XRAYretired wrote:The writings you have attributed to me above are not mine, although I do not necessarily disagree with them.
Oops, very sorry for my confusion. Please forgive me,sgrow787 wrote:I recognise the statements regarding AOA analogue being separately routed to ADIRU and SYMD and it is likely that SYMD initiates the Stick Shaker.
The problem I still have in accepting 'not ADIRU' position is why is the affected side IAS is low, when I am being told that AOA high should result in AIS high as well?
Conversely, I have a problem accepting the 'it is AIDRU' position whist I do not have any information identifying what ADIRU problem or other source data used by ADIRU would result in AIS low, Altitude low and AOA high? I am conscious that all three begin at the same time stamp (but could just be related to WOW FALSE).
Trying to learn about the AoA/IAS argument, I share my understanding from this document page 1 for the definition and page 7 for the Variation of Verror with AOA graph:
https://www.nal.res.in/FullPapers/P8-Po ... 0using.pdf
Verror = ((Vmeasured-Vfree)*100)/Vfree = 100*(Vmeasured/Vfree-1) => Vfree = Vmeasured/(Verror/100+1)
Assuming AoA indicate a +20° offset but that the Pitot tube angle of attack is still 0°, the Vmeasured will stay the same but the Verror used for the correction will increase from -3.5% to well over 3%. The Vfree computed with the wrong Verror caused by the +20° AoA offset will DECREASE.
Vmeasured = 300 and AoA = 0° => Verror = -3.5% => Vfree = 300/(-3.5/100+1) = 310.88
Vmeasured = 300 and AoA = 20° => Verror = 3% => Vfree = 300/(3/100+1) = 291.26
From that paper:
"At higher angle of attack, the probe measures a higher velocity as compared to the free stream due to local
flow acceleration around the boom."
That velocity is the velocity of the air moving through the pitot tube. It is not IAS, which is the velocity of air in the direction opposite of aircraft travel (which uses AOA and incident velocity (the velocity of the air moving through the pitot tube)).
IAS is the value computed by the ADIRU and recorded by the FDR.
So basically you have a paper of how aircraft angle of attack effects the measured incident velocity, specifically at certain angles of attack (I'm spelling it out here to emphasize the actual aircraft angle of attack vs getting confused with AOA sensor data) where the velocity of air at the static port (for a nose mounted probe) can increase higher (than the free velocity) due to "local flow acceleration around the boom".
The reason this doesn't apply to the 737 Max crashes, and my theory, is because I'm comparing two identical sensors, placed at identical positions on both sides of the airframe.