Wing Geometry At least three derivative designs use the Long-EZ wing but have higher gross weights, similar to the Apollo’s.  They all have higher landing speeds than the Long-EZ.  The immutable laws of physics would guarantee us the same result unless something changed.  This outcome would negatively impact two of the Apollo’s performance goals, which are: 1. Reduce takeoff and and landing speeds to improve safety and to reduce runway length requirements. 2. Recover the 8 knot speed penalty (relative to the Cozy IV) resulting from the Apollo’s wider and taller fuselage. This was a difficult challenge because solutions for Goal 1 conflict with Goal 2 and vice-versa.  I was still baselining the Cozy IV wing and decided to investigate options for reducing takeoff speeds, including: • Increase the wing and canard area.  Based on the Apollo’s configuration, it would take 20% more wing area to reduce the stall speed from 68 knots to 62 knots.  This approach adds weight and drag, which decreases cruise speeds.  The lower wing loading also results in higher G-loads during turbulence. • Find an airfoil with higher CL max.  Others have investigated this, but nobody has implemented a better solution than the modified Eppler 1230 used on the Long-EZ.  Burt's airfoil selection was ideal and works well on derivative designs.  And I was loath to move away from the proven aerodynamics. • Add flaps to the main wing.  I developed a concept with split flaps that appeared to work.  Unfortunately, it lowered the stall speed by just 3-4 knots, was more complex and required accurate rigging by the builder. • Install vortex generators on the main wing.  This is a proven method to lower stall speeds.  But having dozens of VG tabs on each wing is unsightly and they are prone to damage.  This would be a last resort. • Experiment with pneumatic turbulators.  They are easily installed in solid foam core wings and they can't be knocked off like VG tabs.  But how effective are they and what is their optimal size and location?  Very little research exists.  Finding the answers would be a science project.   None of these solutions reduced drag.  I could retract the main gear to achieve the speed goal, but that would add complexity, cost, weight and maintenance (which felt like defeat to me).  Using Airfoil Optimizer software, I found laminar flow airfoils that could increase the Apollo’s cruise speed by 8 to 10 knots but they also raised the stall speed.  I needed a comprehensive solution that addressed both goals. As I reviewed the Cozy wing with a critical eye, I began to realize how detrimental the strakes really are.  The highly swept strake promotes spanwise flow and the flat-topped airfoil is sub-optimal.  Strakes are destabilizing and probably contribute to unrecoverable deeps stalls.  I was brainstorming ways to improve them when inspiration struck... why not eliminate the strakes?  The textbook answer is that strakes locate fuel close to the aircraft’s CG to minimize CG travel when fuel is consumed.  Most canard aircraft do not have the CG range to accommodate variable loading conditions for tandem or 2+2 seating plus the adverse CG travel that would result from storing fuel in the wing rather than strakes. Lucky for us, the Apollo has side-by-side seating for two and less CG travel due to pilot/passenger loading.  This means the aircraft can tolerate greater CG travel due to fuel burn, which opens the door to a unique solution. Preliminary calculations confirmed that a strake-free wing was possible.  After a few design iterations, the new wing planform was born.  By using a 55" long chord at the wing root and limiting the wing tanks to 20 gallons per side, plus the use of an “always full” header tank located forward of the CG, the Apollo can accommodate pilot/passenger weight totals from 140 to 430 lbs.  The left or right wing tank (pilot selectable) continuously feeds the seven gallon header tank using redundant transfer pumps.  Total usable fuel is 45 gallons and the CG envelope supports all possible fuel loadings.  Readers can access the Apollo’s CG spreadsheet from the Downloads page. Chord lengths on the Apollo’s new wing are one-third greater than the Cozy IV wing panels.  Despite the Apollo’s larger chords, aspect ratio (AR) for both wings is about the same when the Cozy’s strake area is included.  By classic definition, AR = Wingspan^2 divided by wing area.  Since the Apollo and Cozy have the same total wing area and span, they have the same AR. Custom airfoils and blended winglets were required to fully optimize the wing (use the sub-menu to read about those).  Airplane PDQ predicts an 8 knot speed increase with the redesigned wing.  Additional analysis indicates the Apollo’s stall speed is 4 knots lower  after these changes.  The PDQ results correlate with data from XFLR5 software, so there’s no question the new wing performs better than the baseline.  A summary of all the aerodynamic improvements include: There’s one additional benefit to eliminating the strakes:  They don't have to be built!  Even if the Apollo’s rib/spar/skin structure takes longer to construct than the basic Long-EZ wing, the entire Apollo wing will take less time to build than the total hours required for a Long-EZ wing, center spar and strake structure combined. There was no turning back.  The benefits of the new wing clearly justified the additional design and analysis work. Site Map Email the Designer Copyright © 2012 Apollo Canard