Yeah, the "myth" states that "fuel stays at the back of the tank during downlines because the plane is accelerating."

Unfortunately for that to be true the plane needs a constant acceleration rate of well over 1.7g+ sustained... something our planes cannot do even when screaming towards the earth at full throttle straight down.

This "myth" was espoused by many long time members, some moderators here and such publish notables such as Clarence Lee ( Mr. Engine Clinic Himself!).

Someone here posted a video that put the kabash on this error.

Gaps CAUSING flutter is yet another such myth.

"flying surfaces with substantial gaps WILL FLUTTER more often than those without" <- this is also incorrect and sustains the flutter myth.

It is not the gap that leads to more flutter, it is resonance caused by many different factors.

Having a larger gap does not increase or exacerbate an existing problem as that statement implies nor do the surfaces flutter "more often".

Sealing a gap leads to a stiffer control surface overall, and that helps dampen the resonance. But other techniques are equally if not more effective too... e.g. a counterbalance, stiffer rods, less slop, stronger servos, guy wires or stiffening struts, even C.F. spars, stiffer/stronger wood, etc.