Birkenstock Aerospace

Static 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.

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 (below-ambient pressure) by using convex curves to accelerate the local flow, the static pressure thrust propulsor generates thrust by using concave curves that decelerate the local flow to create above-ambient pressure. 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, but the total power savings can be significant. The flight and wind tunnel tests referenced below proved an over 40% reduction in total power required, including power for the suction system, against streamlined designs of comparable size.

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

Similar comparisons hold true for either Newtonian or Circulation explanations of aerodynamic lift.

- 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)

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