new airfoils? Because
new airfoils will increase the performance of your application.
Many airfoils have been developed for aircraft, most notably the
old NACA airfoils. Recently, an airfoil design was requested for
a four-seat, piston-powered airplane. This was a particularly
challenging task because the airplane had already been completely
designed around an NACA 6-series airfoil. Fortunately, the client
had the foresight to include wind-tunnel testing of the NACA airfoil
and the new airfoil in the effort. The measurements showed comparable
drag and about 20-percent higher maximum lift for the new
airfoil, both as predicted. The maximum-lift improvement can be
used to reduce the wing area 20 percent for the same stall speed
or to reduce the stall speed 10 percent for the same wing area.
As you move away from aircraft for which existing airfoils are
applicable, the advantages of new airfoils become larger. For
smaller aircraft, with their lower Reynolds numbers, the performance
of the NACA airfoils is poor. For larger aircraft, with their
higher Mach numbers, the performance of the old airfoils is inadequate.
This explains why "cutting-edge" manufacturers have new airfoils
designed specifically for their new aircraft.
For many applications,
the advantages of tailoring airfoils to the application are overwhelming.
A good example is the stall-regulated, horizontal-axis wind turbine.
Twenty years ago, when the wind-energy field was reborn, wind-turbine
designers adopted NACA airfoils. Problems arose immediately, particularly
when the leading edges of the blades became contaminated, resulting
in large peak-power losses. New airfoils were designed specifically
for such machines, that resulted in measured, annual-energy
increases of 23 to 35 percent, with greatly reduced peak-power
the gains due to new airfoils are usually smaller in magnitude
but not in importance. Recently, an air-cooled heat-exchanger
fan was designed (airfoil and blade planform and twist) that showed
a theoretical increase in total efficiency of at least nine
percent relative to the fan of the client's competitor.
can also provide less obvious advantages. Airfoils can be designed
to exhibit more docile stall characteristics, for example. Such
characteristics improve the flying qualities of aircraft and reduce
the loads on wind-turbine and fan blades. Airfoils can also be
designed to produce maximum lifts that are essentially unaffected
by roughness. This characteristic leads to increased flight safety
for aircraft, consistent peak power for wind turbines, and reliable
operation for fans.
new airfoils? Because new airfoils can provide you with up
to 35 percent greater performance.