The following year, Avro inked a contract with both the Army and the Air Force in which it agreed to build two identical prototypes. The specifications: maximum weight, 5,650 pounds; powerplant, three Continental J69 engines producing 927 pounds of thrust each; maximum speed, 300 mph; range, 80 miles; and most importantly, the ability to hover out of ground effect—the phenomenon in which lift is assisted by the cushion of air under the craft. Officially designated VZ-9-AV, the design was dubbed the Avrocar.
While the Special Projects Group got busy converting the specs into blueprints, one of the members had the foresight to buy up lakefront property in Ontario’s cottage country, two hours to the north. Now retired, Don Whittley spends the warmer six months of the year there. Today, he and I are having coffee and enjoying the view of the shimmering lake as he looks back on his days as an aerodynamicist assigned to work on the Avrocar.
At first, Whittley recalls, the team could not work up much enthusiasm for the vehicle. Frost had initially envisioned a hypersonic craft that could touch the edge of space, but the Army/Air Force incarnation was decidely less dazzling: “The Avrocar was really a fall-back program,” he says. But, the team figured, “at least now we finally had an opportunity for some full-scale testing.”
The group brainstormed into the evenings. First it decided that giving the vehicle a disc shape, rather than the spade shape Frost had first proposed, would improve its ability to both hover and maneuver. With a circular shape, “you could send air out in any direction,” says Whittley. But exactly how would you harness the jets’ blasts to do this? The team settled on the idea of a controllable flap around the entire circumference of the saucer—the members called it a focusing ring.
The next question was how to direct the three engines’ thrust evenly around the ring. The team devised an internal ducting network that carried the exhaust through a 90-degree turn and then took it out to the circumference of the saucer (see diagram, opposite).
Calculations showed that the jet exhaust could also be harnessed to drive a separate rotor in order to generate more thrust. The jets were therefore arranged so their exhaust was directed at the tips of a five-foot-diameter rotor mounted horizontally in the saucer’s center. Thus driven at high rpm, the rotor sucked air from above. The ducting network carried that air, along with the jet exhaust, outward. For hovering, the pilot would use the stick to actuate the focusing ring, which directed the exhaust evenly downward. For transitioning from hover to forward flight, the team designed two control surfaces: “transition doors” redirected the flow in the aft third of the saucer from downward to rearward, and control vanes would then deflect it up or down for pitch or roll control.
But the engineers predicted that as the Avrocar transitioned off its cushy ground bubble and picked up speed, it would be unstable in pitch. The pilot would be continually jockeying the stick back and forth to prevent it from stalling nose-up or pitching nose-down into the ground. In most conventional airplanes, the horizontal stabilizer looks after that. The Avrocar had no tail, so the team designed an ingenious mechanical connection that automatically deflected the control vanes up or down, simulating the effect of a tail. Slight horizontal motions in the spinning rotor would automatically control those vanes, so the pilot could occupy himself watching for the enemy.
So far, so good. After the rollout fanfare, Avrocar No. 1 was mounted in a test rig to put theory to practice. Engines were fired up. But as the throttles were advanced to full power, elation fizzled. The J69s’ combined thrust, 2,700-plus pounds of it, wasn’t producing the effect predicted.
The engineers deduced the problem: The air sucked in from the rotor was cold and the jet pipe exhaust was hot, and when the two were mixed, the resulting flow was turbulent and would not stick to the duct’s inside walls. The result: 30 percent of the thrust was lost.
The team tried various tricks, but nothing budged the Avrocar out of ground effect. Though the Army had firmly required that achievement, the company “decided to carry on and fly the Avrocar at a reduced thrust level in the ground cushion, and modify the duct at a later date to pick up the missing thrust,” Frost later wrote.