an American Selig design, optimized for lift
and low Reynolds numbers. However this air-
foil was not optimal for slat operations and I
really wanted to make the scale wing with low
dropping slats that is so typical of the
Crusader. So I worked on the reverse design
module of XFLR5 and changed the camber of
the upper front of the airfoil to make it more
tolerant to high slat deflections at 15% of the
chord.Similarly, I was concerned about the possible
elevator masking effect with flaps deflected
and with the wing at 7 degrees up ( tail raising
by 7 degrees ). Furthermore, XFLR5 was sho-
wing quite a bit of turbulent stream in this con-
figuration around the stabilizer. This coupled
to a stabilizer tip chord of 2” made me study
that aspect of the plane aerodynamics as
well. Sure enough, XFLR5 was showing early
stabilizer tip stall and very low control efficien-cy at high angle of attack. So I decided to
depart from the original stabilizer airfoil and
go for a much thicker design, using airfoils
optimized for super low Reynolds number of
50,000.
I chose a hand launch glider stabilizer airfoil
for the tip and a modified NACA 0009 at the
root. This stabilizer was designed to generate
about 3 times more lift than the original one at
moderate angles of deflection of 10 degrees.
This in turn would allow me to use much smal-
ler stab angles to achieve the same pitch
authority and thus keep this flight control far
from its critical stall deflection.
This would certainly get the plane to stay
away from the dreaded stabilizer masking
effect, but would require a precise and stiff
stabilizer rotation system to give nice handling
characteristic on the pitch axis around zero.
Further study of the fin area and short rear
arm showed the possibility of fin flutter in a
high vortex energy environment. So I decided
to go for a thicker airfoil that is more self dam-
ping and easier to stiffen. Also such a fin
would give a better dampening on the yaw
axis. Early Crusader planes without the ven-
tral fins were known to feather-spin on takeoff
in certain conditions due to yaw unstability.
The wings were CAD designed to include fun-
ctional slats, aileron and inner flaps, just like
the real plane. The wing of the Crusader is
one of the important elements to get a scale
look of the model. The other important aspect
is the wing incidence system. This was also
CAD and CFD modelled and extensively com-
puter tested with finite analysis software. The
slats and flaps had to incorporate a sliding
junction into the wing to mask the upper slot
when deflected. This improves the wing aero-
dynamics tremendously. Live hinging was
also chosen for the aileron and slats to ensu-
re clean aerodynamics and maximum vertical
hinge stiffness.
Another important aspect of the study was to
make the plane easy to ship, transport and
handle at the field. For this reason, the wing
was split in 3 parts, joining just outboard of the
inner small flaps.
Similarly, the fin was made removable as well
as the front nose section. A large engine hatch
was made just rear of the wing centre section,
big enough to pass the steel exhaust tailpipe
in one piece. Although the centre wing section
also opens up a large access area, this one is
designed to stay on the plane in normal con-
ditions. So the plane is easy to carry in a SUV
with only the wing outer panels removed,
making it a breeze to setup at the field. The
large engine hatch opens up a big service
area that allows to give access to all the requi-
red operations to refuel, switch on, fill air andF-8E CRUSADER
A Fusion 360 CAD rendering of the fuselageThe demo Crusader in the Florida sunset. This shows the stringers and skin waves pretty well.A small rendering of the Cam process. A time lapse of the Cam
process can be seen here: https://vimeo.com/Crusader_Layout 1 07/03/18 17.13 Pagina 3