Guessing he no internal seal of the aileron, or seals between
fueslage and control rods. Then, high pressure from the cockpit
ventilation escapes out the aileron hinge line. Add to this a
separation bubble forming just in front of the aileron hinge line so
the air isn't moving there anyway. If I'm right, seals and zz tape
would give a different result. But of course the mylar will be glued on
tight so we'll never know...

John Cochrane BB

If The bottom wing surface is sealed tight along the hinge line and
no high pressure is moving from the cockpit along that line
(a normal cockpit has always a slight negative pressure,
which should be controlled by the rear exhaust)
and providing the turbulent flow on top is attached at the hinge line,
the Mylar, even if only the leading edge is taped, should stay down.
If the boundary layer is thicker the Mylar may start flattering like
a
stiff flag and makes noise, but it is not lifting. Only when separated

flow exist could the Mylar stand up. With no seals on the bottom
all bets are off

On my modified HP18, in the flap region, I have a 13/4" Mylar tape
excluding the glue line, that just sits on top of the flap surface.
It does stay put and makes no noise through out the normal range,
from stall to 125kt

On an other note, the glue line should be cleaned and roughed with
# 240 grit and cleaned again. Only the best and most aggressive
3M double sided tape should be used. A 1" ball bearing with a1/4 "
wide race mounted to a handle is used to press the Mylar
down. The local area should be warmed with a hot water bottle
or similar, before pressing with a rolling motion. The point pressure
is very high and forces the glue into the smallest of surface
indentation
for that long term bound.