cws@mbunix.mitre.org (Christopher C. Wilder-Smith) (07/11/90)
From: cws@mbunix.mitre.org (Christopher C. Wilder-Smith) I remember a few months back that there was a discussion of the purpose of the small toothed wheels on the rear fins of the sidewinder. I just saw one at the Naval Weapons Center in China Lake and was asked if I knew what they were for. If anyone knows and could e-mail I'd appreciate it alot. Thanks in advance Chris Wilder-Smith -- - - terse, graphically uninteresting, .signature follows: - - Christopher C. Wilder-Smith - The MITRE Corporation - cws@mbunix.mitre.org -
henry@zoo.toronto.edu (Henry Spencer) (07/16/90)
From: henry@zoo.toronto.edu (Henry Spencer) >From: cws@mbunix.mitre.org (Christopher C. Wilder-Smith) >I remember a few months back that there was a discussion of the purpose of >the small toothed wheels on the rear fins of the sidewinder. I just saw one >at the Naval Weapons Center in China Lake and was asked if I knew what they >were for... They're "rollerons". Any missile guidance system which tries to steer toward a target has to cope with an additional problem: keeping the missile's roll rate down. The guidance system induces pitch and yaw to point the missile toward the target (or, preferably, toward where the target will be), but if the missile is rolling, the target will seem to be moving in a circle. A sufficiently slow roll may be tolerable, but a fast one will cause hopeless confusion. Things like asymmetry in fins generally will induce some amount of roll, and a simple missile (no inertial guidance system) has no way to tell that this is happening. Some of the early IR-homing missiles had a roll gyro just for this. But that runs up complexity and cost, and can add complications (gyro startup time) in firing. The diabolical people at China Lake came up with a simple solution. The Sidewinder has free-flopping ailerons on its tail fins (the nose fins are the ones used for guidance), each with a little wheel imbedded in its outer end. The wheels are spun up to high speed by the slipstream, and essentially become roll gyros. When the missile starts to roll, those gyros precess, the precession forces move the ailerons... and it turns out that they move in the right direction to stop the roll! Talk about sneaky. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry