posted on Jan, 19 2020 @ 03:56 AM
originally posted by: dubiousatworst
surprised it is limited in negative Gs. Do you think that has more to do with fuel feed than structural issues? I always thought the limit on
negative Gs was more so for the sake of pilots.
Think of it like this: your wings are designed to support the airframe, and a keel supports the fuselage across it's length (or an otherwise
exceptionally strong fuselage construction) -- we need to make sure the wings are attached and sometimes braced in such a way that they don't separate
from the fuselage under the weight. Wings are pushing up (lift), while fuselage is basically pushing down (gravity). Boeing made the news recently
with pickle forks that do this. We need this as light as possibly can be done.
So to support 10 g's, I plan ahead and strengthen the airframe as much as needed to carry 10 times the vehicle weight. Relatively simple, right?
So let's say I build a balcony, and weight is a prime concern. You can comfortably fit five people on the balcony, but to be safe, I make sure it is
capable of supporting the weight of ten people and heavy furniture (as well as it's own weight). My structure easily holds 3 tons. But if you start
pushing on it from below (negative g), then my joins, braces, etc are not going to be as strong. Say a freak wind causes stress "up" under the
balcony. It's going to fail well before three tons because forces are being transferred differently, and I didn't build it to withstand strong
negative g's and that transfer.
You could build a structure to withstand higher stresses in that direction, but that's more weight. And since most negative g's in flight (and
balconies) are short lived (sharp maneuvering and turbulence) and lower in magnitude, there is little call for an aircraft that survives exceptionally
high negative g's. Most forces, and the strongest (deliberately) experienced are in the positive direction. Since adding structure means adding
weight, strengthening the fuselage for negative g's can weaken it in the positive direction. Have to find a balance.
Pilots, as you note also are notoriously squishy, and fussy, and they hate nose bleeds and headaches, and have found red eyeballs are not a hit with
the ladies afterhours.