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Why Use New Airfoils?

Why use new airfoils? Because new airfoils will increase your profits and your customers' profits. Let's examine the economics for three different applications: aircraft, wind turbines, and fans.

The cost of the airfoil design is trivial compared to the economic benefits of the new technology. For example, the cost of tailoring an airfoil to a single-engine airplane is less than 0.1 percent of the cost of bringing that airplane to production, yet the new airfoil determines to a large extent the airplane's performance and handling. For larger aircraft, the cost-benefit ratio is even better because the relative cost is lower; for smaller aircraft, the ratio is also better because the relative benefit is larger. For wind turbines, the cost of the airfoil design is less than five percent of the annual-energy increase. In other words, the increased energy production will pay for the airfoil design within the turbine's first month of operation. For fans, the cost-benefit ratio is similar.



Why use 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 variability.

For fans, 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.

New airfoils 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.

Why use new airfoils? Because new airfoils can provide you with up to 35 percent greater performance.



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