Pressure Thrust

Pressure thrust is an aerodynamic phenomenon that, just like its better known sibling, aerodynamic lift, exploits Bernoulli's principle which relates fluid pressure and velocity. The flight and wind tunnel tests referenced below proved a 40% reduction in total power required, including power for the suction system, against streamlined designs of comparable size.

Bernoulli's principle tells us that as flow velocity accelerates, its pressure decreases and as the flow decelerates, its pressure increases. In much the same way as an airfoil generates lift by using a convex curve to accelerate the local flow, the pressure thrust engine generates high pressure by using a concave curve to decelerate the local flow. The local flow will separate if enough suction power is not used to keep it attached and the power required for suction will always exceed the power recovered as thrust.

On aircraft wings in flight, decreased local pressure coincides with aerodynamic lift. On wings or fuselages modified to exploit pressure thrust the combination of powered suction, Boundary Layer Control (BLC) and optimized concave geometry create an area of high pressure acting on the aft end of the body. This distribution of pressure generates a net thrust. Hence the term Pressure Thrust.

This is very different than the case on an unmodified wing or fuselage, where the pressure force recovered at the rear is less than the pressure force pushing the leading edge backward. This situation is described by the term pressure drag and it is the largest source of drag on aircraft at cruising speed and on cars and trucks at highway speed.

Economy of Power
By combining engine power and aerodynamic design to exploit pressure thrust, the total power required can be reduced by at least 40%. Repeated testing in wind tunnels, in CFD analyses and in numerous flight tests have proven the economy of power (see references below). With today's sophisticated CFD and CAD/CAM tools at their disposal, designers should be able to increase this benefit.

BLC and Real World Operability
Unlike active laminar flow control, used on the X-21 demonstrator, the BLC for pressure thrust is less susceptible to the clogging problems that plague active laminar flow control.

With refined quality assurance programs like Six Sigma, the operability and reliability of a pressure thrust engine and its related systems should match that of legacy propulsion systems.

References:
1. Goldschmied, F.R., "Airfoil Static-Pressure Thrust: Flight-Test Verification," AIAA Paper 90-3286-CP, September 1990. (available from http://www.aiaa.org/)

2. Goldschmied, F.R., "Fuselage Self-Propulsion by Static-Pressure Thrust: Wind-Tunnel Verification," AIAA paper 87-2935, September 1987. (available from http://www.aiaa.org/)

3. Richards, E. J., Walker W. S. and Greening J. R., "Tests of a Griffith aerofoil in the 13 ft. x 9 ft. wind tunnel part 1, part 2, part 3, part 4, lift, drag, pitching moments and velocity distributions," ARC/R&M-2148 ARC-7464 ARC-7561 ARC-8054 ARC-8055, 1944. (available for download here.)

4. Richards, E.J., Walker, W.S. and Taylor, C.R., "Wind-Tunnel Tests on a 30% Suction Wing," A.R.C. RBM 2149, July 1945. (available for download here.)

5. Richards, E.J. and Burge, C.H., "An Airfoil Designed to Give Laminar Flow Over the Whole Surface with Boundary-Layer Suction," A.R.C. RBM 2263, June 1943. (available for download here)

6. Bushnell, D.M., "Fluid Mechanics, Drag Reduction and Advanced Configuration Aeronautics" NASA/TM-2000-210646 (available for download here. )

Pressure Thrust

From Aerodynamic Drag to Aerodynamic Drive

Overview - Significant increase in fuel economy.