Originally Posted by
CONSO
basic lever - the shorter the body length and the shorter the length from CG, the more ' force' is needed to tilt ( aoa ) or stop yaw ( if one engine out ). The longer the body- distance from CG, the less the force needed for normal AOA correction or yaw correction. Since the force needed is generally a function of size or AREA acted on by air pressure/lift - a longder body can allow a smaller area for control surfaces ( overly simplified ) then come the cost of designing a new smaller area or simply staying the same as current production, etc
And I think you ment the horizontal stabilizer- not the elevator ??
And if yoiu not the hight of the smallet airbus VERTical stabilizer it is longer than the longer airbus - for generally the same reasons
Yes, I am aware of the moment arm and how that affects the size requirement, especially for the rudder.
I had in mind the size of the elevator compared with the full horizontal stabilizer.
I tried to measure the relative size on the drawings, as far as they are accurate, which I ofc dont know for sure.
I get the A320 elevator is marginally larger than 1/3 of the full horizontal stabilizer including the elevator.
The B737 on the other hand seems to have an elevator only marginally smaller than 1/4 of the full horizontal stabilizer including the elevator.
This must be a significant difference.
It seems like the A320, if we make that aircraft the comparison, because of its larger percentage elevater/stabilizer ratio to a much larger extent can rely on only the elevator in maintaining pitch control in demanding areas of the flight envelope, whereas the B737 much quicker runs out of elevater authority, and therefore Boeing has no option other than to use the very slow acting stabilizer trim function when controlling pitch in the most demanding areas of the flight envelope. And couple this with the likely worse naturable stability of the aircraft due to the very forward placement of the engines. This might be a reason why they couldnt make use of a redesign of the EFS acting on the yoke/elevator which would have been in my mind a much more quickly acting system. But ofc, such a system would also need a good software, and not the cludge MCAS seems to have been.