GU25-5( 11) 8 and is shown in Figure
3. Subsequent flight testing demonstrated an 8-knot decrease in minimum flight speed with the canard
airfoil change. More details about
the development of the VariEze and
Long-EZ can be found in Burt Rutan’s
article “Tale of Three EZs,” published
in the February 1980 edition of EAA
Sport Aviation.
It is also important that the
canard airfoil has gentle stall characteristics. NASA wind tunnel testing on a powered, full-scale VariEze
(“Wind-tunnel investigation of a
full scale canard configured general
aviation airplane,” NASA TP-2382,
Lon Yip, 1985.) included a configuration with the GU25-5( 11) 8
canard airfoil being replaced with
a 12 percent thick symmetrical
airfoil. The data showed that the
“stock” VariEze had good post-canard stall characteristics. Replacing the original canard airfoil with
a symmetrical one showed that the
aircraft had a lower maximum lift
coefficient (which would lead to a
higher stall or minimum speed), an
abrupt stall of the canard, and an
undesirable pitch-up tendency in
the post-stall range.
One more consideration in selecting a canard airfoil is to understand what the effects of rain or
other surface contamination may
have on the aircraft’s flying qualities. Rain, bugs, or even paint stripes
near the leading edge can prematurely trip the laminar flow on the
canard surface and cause an increase
in minimum flying speed and a
change in the trim requirements to
maintain the desired speed. NASA
investigated the effect of water and
a fixed transition on the canard as
part of its VariEze wind tunnel test.
Burt Rutan wrote “Effects of Rain
or Surface Contamination on Pitch
Stability and Control” in EAA Sport
Aviation, March 1983. The article
provides some additional detailed
flight test results for having an early,
fixed transition on several Rutan aircraft. Sometimes rain effects require
a modification to the aircraft, as
was the case when vortex generators were added to the canard of the
around-the-world Voyager. RAF also
tested several canards with different airfoils for the Long-EZ to better
understand this phenomenon. The
end result was a canard equipped
Figure 3. Canard airfoil used on the VariEze and Long-EZ.
Figure 4. VariEze calculated wing lift coefficient distribution during climb.
Figure 5. Drag area comparison for several canard aircraft.
with the R1145MS airfoil designed
by John Roncz. According to RAF’s
quarterly newsletter, the Canard
Pusher, this optional canard offered
a negligible trim change in rain and
a 2-knot increase in stall speed under
the same conditions.
Some canard designs like the
Quickie, Q2, Dragonfly, and PAT- 1
Pugmobile have a canard similar in
size to the wing. Though the larger canard results in the canard airfoil operating at a higher Reynolds
number, care still needs to be exercised in selecting an airfoil. In his
article “Quickie-Type Aircraft Design
Origins” (EAA Sport Aviation, October 1981), Burt Rutan discussed the
background of the development of
this tandem-wing arrangement. The
