17 May 2010

Convair's Lenticular Defense Missile: Pye Wacket

Pye Wacket high speed wind tunnel model
In 1947 researchers at Wright-Patterson AFB in Dayton began investigations into the possibility of using missiles for bomber defense as the speed of jets and the weight of gun turrets made existing systems for bomber defense impractical. General Electric was the first to receive a USAF contract to pursue such studies, but soon transferred the work to Hughes where the missile developed didn't end up on bombers but on interceptors as the Falcon missile. McDonnell was next in 1952 to try and develop a jet-vane controlled defensive missile for the Convair B-58 Hustler, but the work was canceled in 1956. By that time, however, work began on the WS-110A project that would result in the North American XB-70 Valkyrie and more contracts were issued to study what the Air Force was calling DAMS- Defense Anti-Missile Subsystem, a system that fired a stream of pellets at inbound missiles. Again, those studies ended in 1959 despite some encouraging tests.

The USAF wasn't deterred, though, starting a program in 1958 in cooperation with North American and Convair called Pye Wacket for a defensive missile for the XB-70 Valkyrie. Three basic shapes were first evaluated by North American and Convair- a standard but modified version of the AIM-47 designed for the F-108 Rapier, a cylindrical missile using jet vane directional control, and an unusual saucer-shaped missile called a "lenticular defense missile". Studies showed the lenticular design the most promising as its shape allowed it to be pointed in any direction and fired, not wasting kinetic energy on turning towards the incoming threat.

By 1959 the USAF did a considerable amount of wind tunnel work at the Arnold Engineering Development Center in Tennessee of the lenticular Pye Wacket design. It was stable all the way to Mach 6. It had a diameter of 70 inches, was 9 inches deep at its thickest portion and weighed only 510 lbs. One end of the saucer shape housed the infrared seeker and two rocket motors were on the opposite end to give the Pye Wacket a range of approximately 72 nautical miles. A set of spoilers built into the curved surfaces of the missile provide directional control.

North American began to seriously consider the Pye Wacket missile for the XB-70 Valkyrie- posts were mounted vertically in the forward section of the weapons bay and the missiles were mounted on the posts via a screw thread that ran through the center of the missile. This way the saucer-shaped missiles could be threaded on the post and stacked. Two stacks of five missiles each would fit in the Valkyrie's weapons bay. When needed, the post rotated to point the lowest missile in the stack in the direction of the inbound target. The missile was then dropped out of the bay already pointed at the target at which point the rocket motors fired.

In the summer of 1959 Convair was awarded a design contract to further study the lenticular Pye Wacket design and modified the saucer shape to incorporate a blunt trailing end where the rocket exhaust was located. This improved the supersonic drag as well as the controllability of the missile. Roll reaction thrusters were added along with small lateral vanes as well as the original spoilers used on the original design. With over 80 hours of wind tunnel testing from speeds as low as Mach 0.6 to Mach 5, sled tests then took place at Edwards AFB on a full-scale article powered by three Thiokol solid rocket motors, the same type used singly on the AIM-4 Falcon air-to-air missile.

The tests reported accelerations on the order of 60G with the ability to make sharp high-G turns at supersonic speed without loss of control. An operational version of the Pye Wacket arming the Valkyrie would be 48 inches in diameter, carry a 50 lb warhead and be capable of extreme maneuvers up to Mach 6. Convair recommended that the Air Force procure 12 missiles for continued testing, but no documentation has been found that further details work done from that point on on the lenticular defense missile.

Convair also had proposed a strike version of the Pye Wacket that would allow a bomber to easily strike targets on each side of its flight path without having to overfly enemy defenses. A version was also suggested by the company to use as a highly maneuverable re-entry warhead for ballistic missiles.

It's always been a point of curiosity to me as an aviation geek why a weapon as promising as the Pye Wacket never got developed further. Or did it? Conspiracy theorists might think the Pye Wacket was classified and modern versions of the lenticular defense missile moving at speeds unattainable by manned aircraft might account for a good portion of the UFO sightings pointing to a super-maneuverable vehicle. Considering that the basic layout was stable at hypersonic speeds, it certainly would make a very capable rapid-strike weapon.

Now if you'll excuse me, I have to go fetch my tinfoil hat.

Source: Valkyrie: North American's Mach 3 Superbomber by Dennis Jenkins and Tony Landis. Specialty Press, 2005, p220-226. Photo: NASA

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