An Investigation of Ionic Wind Propulsion: NASA Glenn's 2009 Balance Tests Showing Lifter Thrust Equals the Ion Wind, and Why It Stays Too Weak for Aircraft (Wilson, Perkins & Thompson)

"An Investigation of Ionic Wind Propulsion" is NASA Technical Memorandum NASA/TM—2009-215822, dated December 2009, by Jack Wilson of ASRC Aerospace Corporation and Hugh D. Perkins and William K. Thompson of NASA Glenn Research Center in Cleveland, Ohio. It was sponsored by Glenn's Fundamental Aeronautics Program. Where the other papers in this dossier ask whether a lifter's force is anything more than an electric wind, this one takes the wind as the likely answer, checks it quantitatively on a balance, and then asks the engineering question: could such a wind push a real aircraft? Its conclusion is that "the use of a corona discharge for aircraft propulsion did not seem very practical."

Is the lift really the wind?

The authors credit Tajmar's sealed-box experiment (see The Biefeld-Brown Effect as a Misread Corona Wind: Martin Tajmar's Sealed-Box Pendulum Test and Its 10 µN Limit) with showing that blocking the wind removes the thrust, but note that it did not show the thrust and the wind's momentum are numerically the same. They ran two tests to close that gap.

In the first, a hexagonal lifter of the kind published by Jean-Louis Naudin (six triangles of 150 mm sides, 0.07 mm emitter wires 32 mm above foil-wrapped basswood collectors, 9 g in all) stood on a digital balance with 0.1 g resolution. It lifted off at 24.6 kV and 1.4 mA. With nothing between lifter and balance, the reading stayed at the lifter's weight as current rose: the downward wind striking the pan cancelled the upward thrust. With a shield blocking the wind, the reading fell steadily and reached zero just as the lifter rose. The report reads this as showing that electric thrust, ion-wind thrust and the lifter's weight are equal at take-off.

In the second, a "box lifter" with 13 wire emitters was weighed, then turned on its side to blow at a hanging paper-and-basswood plate (23.4 g on threads 47.6 cm long) whose swing gives the wind force. The two curves of force against current agree well except at high current, where the authors blame the plate rising and tilting. Because the plate is non-conducting and non-magnetic, it responds only to moving air; and because thrust at a given current was the same horizontal or vertical, they judge any link between electromagnetism and gravitation "implausible". The report puts overall accuracy at about 0.2 g.

The physics that limits it

The report adopts a relation from Christenson and Moller's earlier study: thrust equals current times gap divided by ion mobility. It derives this two ways, as the electrostatic pull between the electrodes and the ion cloud, and as momentum handed to air molecules in collisions, and shows the two give the same force. This is the drift relation that came within a factor of 3 of a lifter's weight in Force on an Asymmetric Capacitor: The 2003 Army Research Laboratory Lifter Tests and Why Their Ion-Wind Estimate Fell Short (Bahder & Fazi).

The catch follows directly. Thrust per unit power comes out as one over mobility times the average field. High efficiency therefore demands a weak field, which means little current and little thrust. Mobility offers no escape: the report gives 2.15×10^-4 m²/V-sec for dry air and 1.6×10^-4 for saturated air. Reaching 20 N/kW in dry air needs a field of 0.233 MV/m. Measured thrust actually grew with gap as roughly d^0.56 rather than in direct proportion, which the authors attribute to the non-uniform field.

What the parametric tests found

The authors set goals of 20 N/kW and 20 N per square metre of frontal area at the same time, and tried to reach them by changing electrodes.

• Pins beat wires. The hexagonal lifter managed only 2.6 N/kW at lift-off. With a 50 mm gap, five pins per electrode (29 mm apart) was the best count; 254 pins side by side performed worst. Emitter electrodes worked best 38 mm apart.
• Sharper tips help, then wear. Each arrangement showed a critical voltage below which no thrust appears, from 12.5 kV for the 254-pin electrode down to 5 kV for tungsten pins with a tip radius one fifth of a household pin's. The used tungsten pins visibly eroded.
• Knife edges failed. Razor blades set edge to edge gave no thrust; the discharge glowed only at the outer ends. A field calculation put about 7×10^7 V/m at the blade corner against an applied 5×10^5 V/m. A further calculation suggested that elliptical blade ends would remove the end concentration, tapering the field to a peak of about 6×10^6 V/m. In the larger rig, however, a knife-edge and a razor-blade emitter, both with elliptical ends, gave less thrust at maximum voltage than the pin and wire emitters.
• Larger rig. A 1,477 g foam-board and Lexan rig, with three pin emitters (up to 34 pins per emitter) and paired 19 mm chord collectors 33 mm apart, reached 20 N/kW at 30 kV with a 105 mm gap, producing 13.1 g of thrust.

Across the programme, the abstract reports, the best thrust per unit power was pushed from early values near 5 N/kW to close to 50 N/kW. Consistent with the field relation above, the high-efficiency results came where the field and current were low, so thrust was small, and they needed a higher applied voltage.

Pulsing and extrapolation

Pulsed excitation, including a "double discharge" scheme borrowed from laser work, gave conflicting answers. Computing power from voltage times current suggested 20 N/kW at 18 g of thrust (800 Hz, 55 mm gap) against under 5 g for DC. Computing it from the energy lost by stray capacitance gave results close to DC. The authors call the question unresolved, noting noisy current traces and pulses stretched by the circuit's capacitance.

Extrapolating the DC data at 20 N/kW, the report finds that arcing sets in at about a 200 mm gap and slightly under 80 kV, giving about 37 g. It calls this the maximum practical thrust for the rig, unless pulsing could raise thrust at the same N/kW. Allowing for that possibility, the authors loosely put the achievable thrust at about 50 g, or 0.5 N. Spread over the rig's 0.33 m² face, that 0.5 N figure gives 1.5 N/m², or 4.5 N/m² if three units are staged in line, still short of the 20 N/m² goal. Propelling the solar Helios aircraft would need a thousandfold scale-up.

What the report does and does not establish

It supplies what the earlier papers in this dossier lacked: a direct, quantitative match between lifter thrust and ion-wind momentum, in air, at the 0.1 g resolution of the balances used. The report makes no vacuum measurements, so it says nothing about the vacuum-thrust claims discussed elsewhere in the dossier (see Prospects for Breakthrough Propulsion From Physics: Marc Millis's 2004 NASA Survey and Its Verdict on Biefeld-Brown Devices, Lifters and Asymmetrical Capacitors and The Biefeld-Brown Effect as a Misread Corona Wind: Martin Tajmar's Sealed-Box Pendulum Test and Its 10 µN Limit). Brown is not discussed in its main text, and his 1960 patent (US 2,949,550: Thomas Townsend Brown's Electrokinetic Apparatus Patent (Wire-and-Plate Thrusters, Discs and a Torpedo Body)) is not tested. The authors measured nothing at altitude or in forward flight: the fall in thrust at low density is cited from Blaze Laboratories, and the effect of flight speed is listed as unstudied. The smallest thrust readings are also, by the report's own account, inflated by balance zero error.

Seen alongside Prospects for Breakthrough Propulsion From Physics: Marc Millis's 2004 NASA Survey and Its Verdict on Biefeld-Brown Devices, Lifters and Asymmetrical Capacitors, the two documents fit together: the 2004 survey judged lifters to be ion-wind devices, while this 2009 memorandum measures that wind and then asks whether it could propel aircraft.