The Ejection Site

North American Aviation HS-1A Ejection Seat

The RA-5C Vigallante was equipped with this seat developed for the A-3J bomber version. Used heavily in the South East Asia conflict (Vietnam War), it was fitted with the HS-1 seat. The HS-1 was optimized for High Speed, hence the designation. This seat was rated for high dynamic pressure (High-Q) ejections. In other words, the seat system was designed to save the aircrew at very high speeds at whatever altitude. Some of the optimizations included locking ankle holders, an arm retraction strap system, and a plate under the seat to increase lift and thus improve tail clearance. The seat was large and heavy, but its weight was a considered factor in the design to help with the aerodynamic loads. The seat was fitted with a backpack style parachute, and was expected to be used with a pressure suit. This seat was used in many ejections during the Vietnam War and was mostly successful, especially at high-Q, including at least six 700KEAS ejections.

In the very early 1970s the seat was upgraded to improve its performance. The new revision was designated the HS-1A. The photos here are from a report in my collection on that upgrade program. Among other improvements, the canopy jettison system was modified to reduce the time it took to clear the ejection path, and allow for shorter delays in the sequence. As a matter of fact, the canopy is cammed off by a set of rollers on the upper shoulder area of the back of the seat. The canopy is rotated up thru 60 degrees where a cable releases and allows the canopy to separate.

The seat back parachute is outfitted with a spreader gun which fires at full line stretch to inflate the canopy as rapidly as is safely possible. This allows for about a 50kt faster deployment than a standard parachute. The timing of the seat functions is based on a schedule of events which includes decellaration times so that the drogue chute can slow the seat/man package to the proper deployment speed for the main parachute. The sequence photos here clearly show the deployment of the drogue chute, and the severance of the lower drogue bridles which would allow the seat to decend in a feet-down attitude if the ejection were to occur above 10,000ft.

3/4 Left view
Rear view comparing the HS-1 to HS-1A
Animated GIFs of a ground
and an aerial test

Photos from my collection

Ejection Seat Trivia An Ejection Seat Warning
Fascinating Ejection Seat Facts Underwater Ejection
Ejection from an OV-1 Mohawk
(Animated GIF)

Seat Gallery
Ejection Seat

Ejection Anecdotes
Zero-Zero Ejection
The Weber F-106 & Project 90
NASA ejection seats
Remembering the Pioneers Some Ejection Seat Links
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