Putting more ponies up front is one way to go faster, but improving aerodynamic efficiency is even
better. LoPresti Speed Merchants designed its ‘Holy Cowl’ for Mooneys and other aircraft, improving
engine cooling while reducing drag.
It’s Not About Hot Rods
Performance mods are more than that
BY MARK PHELPS
AS MOST STUDENT PILOTS quickly find out, flying is not thrilling, at
least not in the way we think of other thrilling activities. You just
don’t get that hair-curling sense of speed when the Earth is so far
below you. Stacked up against bungee jumping, roller coasters, or
figure-eight-track racing, light airplane flying is pretty tame. In fact,
we strive to keep it dull—“hours of boredom punctuated by a few
moments of stark terror”—with great effort aimed at keeping the
latter to the absolute minimum. Unless you’re talking about low-level aerobatics, the heady thrill of speed comes mostly with taking
digital photos of big numbers on the GPS groundspeed readout.
So performance mods on airplanes are less about thrills and more
about the satisfaction of achieving the most from your airplane—
squeezing out a few more knots by slickening the airframe, or getting
the most efficient thrust from our propeller and engine. That can
come with its moments of stark terror, but they usually come from
reviewing your credit card statement.
The pursuit of speed is more an art than a thrill, and it’s no surprise that most modifiers looking for greater speed turn to cleaning
up the airframe, rather than packing more ponies up front.
Experimental aircraft builders have free rein to try their hand at
cleaning up their airframes, and most designers are keen to advise
their customers on ways to improve their aerodynamic efficiency.
For production aircraft, LoPresti Aviation, Precise Flight, and Knots
2U are three companies with a full menu of aftermarket products
and supplemental type certificates. Aircraft type clubs are another
source of information on modifications to improve the breed.
True, most airframe mods are not as impressive as taxiing up to
the ramp with the rip-snorting rumble of more horsepower. If you’re
looking to impress the ramp crowd, get the bigger engine. No one is
going to gape in awe at your new gap seals or swoon over your speed
fairings or vortex generators.
Airframe mods are subtler but cumulatively more effective. It makes sense that
reducing drag with the same horsepower
will add speed without burning more fuel.
Rather than adding more horsepower
(which almost always increases weight,
burns more fuel, and increases drag), aerodynamic improvements do the opposite.
They turn the classic circular domino effect
in your favor. Less drag means less energy
required to achieve the same speed.
The bad news is most modern airframes
are already pretty efficient, at least compared with the strutted, wire-braced
biplanes of aviation’s early years. It is
remarkable to me how the air racers of the
1920s and ’30s were able to build aerodynamically clean airframes around the large
inline engines of the day—essentially by
hand. My hat is off to Steve Wittman, Art
Chester, Clayton Folkerts, Matty Laird, and
so many others.
In the modern era, the name most often
associated with drag-reducing airframe
mods is the late Roy LoPresti, and with good
reason. Roy’s career took an amazing turn
when he joined Grumman American in the
mid-1970s. The company had just introduced its 120-knot, four-seat, 150-hp
Traveler—a stretched version of the two-place Yankee originally designed by Jim