Drag Reduction with Boundary Layer Heating

The benefits of reducing the drag of either a new or existing aircraft configuration are obvious. An aircraft’s endurance is directly proportional to the lift to drag ratio.  Decreased drag also translates into faster top speed, quicker acceleration, shorter take-off distances and lower direct operating costs in the form of fuel savings. In order to project military air power, or on the commercial side, receive better range and fuel economy, reducing drag during the cruise portion of a flight is the most critical. During cruise, the drag of the aircraft primarily comes from profile drag (skin friction), induced drag (drag due to lift), compressibility drag, separation drag and interference drag. Of these, skin friction (from the “wetted” elements of the aircraft) typically accounts for more than 50% of the total. By applying active surface heating in the turbulent regions of the aircraft’s boundary layer, the skin friction is reduced as a function of the ratio of the skin temperature to the ambient temperature. The result is an effective drag reduction method that can be retrofitted to existing aircraft.

RHRC conducted drag reduction tests using boundary layer heating through a NASA Small Business Innovative Research program using the NASA Dryden F-15B Flight Test Fixture and a T-39 Sabreliner. RHRC's research proved that drag reduction savings are possible at full flight Reynolds and Mach numbers. RHRC also measured the amount of power required to achieve these savings. In general, boundary layer heating becomes more efficient with lower Reynolds number.