FSII Original Vortex Generators
There is one vortex generator on every rib and false
rib except the most inboard rib. The forwardmost vg measures 10.5"
back, the next measures 11.5" back, and the rearmost measures
13" back. This staggered distance pattern repeats itself
out to the last available rib. (All measurements are from the
centerline of the leading edge to the front edge of the vg, measured
with a thin flexible measuring tape - different than we did the
MKIII. Actual placement was by stretching a string from tip to
tip and marking them from the straight line)
During flight tests we tried various locations,
both forward, rearward and staggered. No matter where we put the
vg's, they worked at least to some extent to make the stall slower,
the climb better, and the handling just above the stall much better.
We even came up with some very unconventional arrangements, but
this placement works very well overall.
Climb with vg's is 200' a minute better than without,
slow flight at 40 mph is good, you can do brisk coordinated turns
and the airplane does not feel like it is on the edge, it feels
solid. Power off stall is around 35 mph with a clean, gentle break
when it lets go, with a normal recovery by easing the stick slightly
forward and letting the airspeed increase to 40 mph. Power on
stall at 4500 rpm is slightly slower, at around 32 mph, and typically,
it will sort of nod in and out of a stall, if you hold the stick
still it just bobs along, breaking and then catching itself with
no tendency to fall off to either side. With the stick further
back, the stall break is clean and recovery is good. Stall in
a coordinated turn is straightforward, no tendency to fall off
to either side. Have not done any cross control stalls, because
I have no spin training, and I'm sure it would.
The biggest plus seems to be that it now has that
elusive quality that is hard to describe, but you know it when
it's there. Without the vg's, it flew good. Now it flys sweet.
The results are well worth the trouble.
Since the rebuild, we have gone with Stolspeed vortex
generators, they work at least as well if not better, were a lot
less hassle, and look a lot better. Spend the money - it's worth
it.