Final Design - Weber Zero-Zero, Rocket Catapult (ROCAT) Seat
OVERVIEW
Of all the Century jet fighters operated by the USAF, the F-106 Delta Dart interceptor had the longest career, an amazing 40-year career! Like all of its Century counterparts, its ejection seat underwent several evolutionary changes, and sometimes, revolutionary changes. This upgrading process continued until the last year of its fighter-interceptor squadron service. In all, three distinct types of seats were used: the so-called “interim” seat, the supersonic “B” seat and the “zero-zero” seat.
The first ejection seat fitted to early F-106s was a variation of the seat used by the F-102 and was called the Weber interim seat. It was a catapult seat which used an explosive charge to propel it clear of the aircraft. This seat was not a zero-zero seat and was inadequate for ejections at supersonic speeds as well as ground level ejections and ejections at speeds below 120 knots (140 miles per hour; 220 kilometres per hour) and 2,000 feet (610 metres).
The second seat that replaced the Weber interim seat was the Convair/ICESC (Industry Crew Escape System Committee) Supersonic Rotational B-seat, called the supersonic "bobsled", hence the B designation. It was designed with supersonic ejection as the primary criterion since the F-106 was capable of Mach-2 performance. Fighter pilots viewed high speed ejections as the most important. Seat designers viewed an ejection at low altitude and slow speed as the most likely possibility. The ejection sequence with the B-seat was quite complicated and there were some unsuccessful ejections that resulted in pilot fatalities.
The third seat, that replaced the Convair B-seat, was the Weber Zero-Zero ROCAT (for ROcket CATapult) seat. Weber Aircraft Corporation designed a "zero-zero" seat to operate at up to 600 knots (690 miles per hour; 1,100 kilometres per hour). High-altitude supersonic ejections were rare and ejections at relatively low altitudes and low speeds were more likely. The Weber “zero-zero” seat was satisfactory and was retrofitted to the F-106 in 1963.
The interim seat was a 1950's design, incorporating a pyrotechnic lap belt release system, probably of MA-5 or MA-6 -type, and an automatic parachute-opening assembly in a BA-18 parachute back pack. The catapult was of M-3 type, later to be replaced by the MK-1 rocket/catapult.
This seat had no zero-zero ejection capabilities and pilots were told no ground level ejections at speeds below 120 KEAS and if possible always eject no lower than 2000 feet.
The interim seat was built by Weber as a derivative of the seat used in the F-102 Delta Dagger interceptor.
Ejection Sequence of the Interim Seat
Upon leaving the aircraft, the canopy pulled a lanyard activating an off-seat M3 initiator, which would send gas through a ballistic hose routed to the top left portion of the seat, to begin the ejection phase itself:
Catapult-initiator firing: The gas coming from the off-seat M3 initator would activate a M1 exactor located on the seat next to the catapult-initiator mentioned earlier. The exactor is a pyrotechnic device which pulled a safety pin from a seat-anchored spring, enabling the latter to pull the trigger rod of the M3-catapult initiator. The gas from this M3 initiator was then sent to the catapult tube, through the lower hose on the left side of the seat, thus initiating the catapult phase.
Seat travel up the rails: As the seat traveled upwards, the shoulder harness inertia reel would lock. Additionally, a seat-mounted lever located near the bottom of the catapult tube was rotated by impact with a tripper assembly on the cockpit rails and fire a time-delayed initiator believed to be a M-32 initator (diagram, bottom, aft side). This initiator was mounted under the seat pan.
Lap belt and shoulder harness release: The gas released by the time-delayed initiator would flow into a ballistic hose connected to the lap belt (diagram item #6), which in turns would open the lap belt and release the shoulder harness end-loops, thereby freeing the pilot of all seat constraints.
Seat-man separation: This action occurred next and was caused by the tumble of the seat or manually by pushing off the seat. Later seats were equipped with a seat man separation strap and rotary actuator. On seat separation one section of the lap belt would retain the arming lanyard for the parachute automatic opener.
After separation from the seat, the pilot would freefall down to an altitude of 15,000 feet, at which point the automatic opener in the BA-18 parachute pack would fire the parachute release mechanism. The pilot could also open his parachute above this trigger altitude by pulling the parachute ripcord handle. Moreover, when flying between 100 and 2000 ft above ground, the pilot could connect the so-called 'zero-delay' lanyard to the parachute rip cord handle. This lanyard was attached to the strap linking the lap belt to the automatic opener arming ball and connected as mentioned above to one side of the automatic lap belt. The zero-delay lanyard immediately opened the parachute upon seat-man separation and increased the survival odds during low-altitude ejections. Upon pack opening, a MA-1 extraction chute would spring out of the pack, inflate and extract the main parachute, a standard USAF C-9 flat canopy of 28 ft diameter.
The interim seat was used on the first production batch of 30+ airframes, which were then used for prototyping, testing and development of the F-106 program prior to combat squadron use. In a seat collector’s mind such low production numbers put this seat in the “rarest of the rare” category.
The Convair Supersonic Rotational B-seat known as the Supersonic Bobsled was installed on many “first batch” airframes included several aircraft sent to Edwards Flight Test Center for evaluation by USAF test pilots in 1957 for Phase II testing. Among the design changes mandated by Phase-II testing was the redesign of the seat to accommodate bailout at supersonic speeds, since the F-106 was capable of Mach-2 performance. According to aviation historian Robert Dorr this requirement revealed the difference in seat design philosophies held by military pilots and aircraft designers. In the 1950’s, pilots saw high speed ejections as being the most relevant aspect. Civilian seat designers, on the other hand, regarded an ejection at low altitude and slow speed as the most likely possibility.
Tragically, one of the Phase II test pilots pushing for the seat redesign was Capt. Iven Kincheloe, who later lost his life during take-off in a F-104 Starfighter.
The newly-designed seat, called the Convair Supersonic Rotational B-seat and generally known as the "B-seat", was designed by Convair and Stanley Aviation, and built by Aircraft Mechanics Incorporated, and was fully supersonic in performance. It was powered by rocket, with emphasis on high-speed vertical tail clearance, protection of the pilot from windblast and retention of pilot survival and flight equipment during ejection. The B-seat included many features which were considered unusual in the early 1960’s. These included the use of over 30 pyrotechnic devices, namely initiators, explosive bolts, cutters, etc., deployable stabilization booms, a seat-integrated parachute and a complex seat assembly that rotated the seat by 90-degrees prior to its separation from the aircraft.
Details on the pyrotechnics used on the B-seat have become sketchy over the years, as the relevant documents have been lost. Enough general information remains, however, to get a good idea about the ejection sequence.
Ejection Sequence of the B Seat
The ejection sequence proceeded in a two-step fashion and went as follows:
Initiation by pulling the ejection seat ring;
Jettisoning of the canopy, which tripped the automatic flight control system disconnect switch;
Shoulder harness retraction and lock, and retraction of the pilot’s feet by cable;
Raising of the foot pans, seat pan and arm guards;
At this point the pilot sat securely in a prone position. Canopy jettison also released a safety lock, allowing further pull of the D-ring. The pilot had to keep pulling, or pull again, the ejection ring in order to continue the ejection sequence, which consisted in the following actions:
Firing of the vertical seat thruster, rising the seat up the rails; at the end of the vertical thruster stroke, firing of two rotational thrusters, causing the rotation of the seat at the top of the rails and above the cockpit
During seat rotation, firing and extension of two gas-operated stabilization booms;
At the end of boom extension, firing of four pyrotechnic breakaway bolts and disconnection of the seat from the aircraft. The seat rocket would also fire at this point and separate the seat from the aircraft;
Rocket-powered, and moments later, ballistic flight of the seat would take place in an horizontal attitude until reaching an altitude of 15,000 feet. This was the “bobsled” phase were the pilot rode the seat on his back. The parachute deployment sequence would then proceed as follows:
At 15,000 feet, or after an ejection taking place below 15,000 feet, firing of a slug (after a two second delay), causing headrest lid removal and deployment of the seat stabilization chute; At this point also, firing of an initiator to release the pilot’s harness, except for the feet cables and the “secondary” shoulder straps restraining the pilot shoulders to the seat (these are not the risers linking the pilot to the parachute).
At speeds exceeding 280 knots at ejection initiation, separation of the headrest from the seat by the stabilization chute, which triggered 1.5 second delay shoulder straps cutters to permit pilot separation from the seat. The deceleration generated by the stabilization chute pulled the pilot away from the seat; the pilot’s feet were also freed from the feet retention cables. At this point the pilot descended under the seat stabilization chute for further deceleration prior to parachute opening (this reduced the opening shock);
After a deceleration phase that lasted 1.5 seconds, the firing of another pair of pyrotechnic cutters to break the so-called “hesitation risers”, namely lanyards attaching the stabilization chute to the parachute pack. This enabled the former to pull the main parachute out of the pack (a C-9 parachute) and allowed its inflation. The parachute deployment out of the pack was executed by a third lanyard linking the apex of the main parachute to the stabilization chute;
After 0.8 seconds, firing of a pyrotechnic cutter to detach the seat stabilization chute and headrest from the apex of the C-9 parachute.
At ejection airspeeds below 280 knots, the pull of the ejection ring would immediately activate the cutting of the hesitation risers inside the headrest. This action would lead, upon the seat-man separation sequence described previously, to the immediate deployment of the main parachute by the stabilization chute, thus eliminating the 1.5 sec pilot deceleration delay prior to main parachute opening.
Interestingly, many of these features - for example headrest release, stabilization chute deployment, and seat-integrated parachute, would find their way in the seats of today, including the ACES II seat.
The B-seat was successfully tested with 15 sled tests from 154 knots to 755 knots (equivalent). Eleven flight tests were also carried out, from 10,000 ft to 50,000 ft and from 176 knots to 733 knots (indicated). These included a live ejection at 22,580 feet and 337 knots (indicated).
This escape system was used from 1959 until 1964, when the USAF ordered a replacement for the B-seat. This action was taken after the occurrence of a few fatal ejections, and most importantly, after increasing statistical evidence demonstrating a greater ejection probability at slow speed and low altitude. Although the B-seat was produced in great numbers, it was quickly sold for scraps by the government and, as a result, became another “rarest of the rare” collectors’ item.
This is Jean Potvin's seat. Jean is a parachute rigger, researcher and member of Parks College Parachute Research Group. On the seat here is a BA-18 parachute. Later seats had the BA-24 force deployed chute. This Weber zero-zero seat was the workhorse of the fleet for the life of the F-106 airframe.
Almost ten years after designing the very first seat for the F-106, Weber engineers went back to the task with designing the B-seat replacement, using the interim seat as the starting point. The new seat used a ROCAT catapult-rocket system. It also used a new gun-deployed parachute system working in tandem with the ROCAT to achieve timely and reliable parachute opening, as well as substantial pilot deceleration following an ejection from an aircraft at rest on the ground - the so-called “0-0” ejection profile.
Unlike most 0-0 seats of its day (or even of today), this Weber seat was live-tested in the 0-0 mode in late 1965 during Project 90. The seat would be used during the greater part of the F-106 career with the USAF.
The seat had several of the features shared by all US-made seats of that era, namely, a back-type parachute worn by the pilot, a MA-6 automatic lap belt (later to be replaced by the HBU-4A (Note 2) and the HBU-12A belts, two ejection trigger handles located at the end of each arm rest, a seat-man separation (or “SMS”) strap tensioned by a rotator actuator located behind the head rest, and a fiberglass seat kit containing the pilot’s survival gear. Weber engineers used the same basic seat pan and head rest designs of the interim seat, but modified the arm guards, reshaping them into paddles. They also used a ROCAT instead of a catapult-only system, namely a RPI 2174 ROCAT. Finally, they changed the headrest attachment to the ROCAT tube by removing the seat height adjuster motor and relocating it at the base of the ROCAT tube.
This new seat was not only designed to provide escape at zero-speed and zero-altitude, but also at all speeds below 600 knots.
Ejection sequence
Squeezing the ejection hand grips on the arm rest handles caused the following events to occur:
Before 1979, locking of the shoulder harness inertia reel; after 1979, triggering of a M3A2 initiator located under the seat pan to power a shoulder harness retraction actuator. This device was a ballistic powered inertial reel and known by its initials BPIR. This action was to position the pilot’s back firmly against the seat.
As with the interim seat, the following events would occur using the same hardware but with upgraded initiator units:
Rotation of the spring-loaded arm guards to a horizontal position (see photo of the arm guards/paddles, in the vertical, “down” position).
Release of the M3A1-catapult initiator safety lock. This initiator was located under the left armrest and would be fired after the events described next.
Firing of the canopy unlatch-M3A1 initiator and canopy jettison: Ejection handle pull would activate an on-seat M3A1 canopy unlatch initiator for release of the canopy. This initiator was located under the right armrest and its hot gas was channeled to the canopy jettison hardware located off-seat through a ballistic hose coming out of the top-right portion of the seat. Firing of the canopy unlatch initiator resulted in the jettisoning of the canopy by hardware located off-seat. Upon leaving the aircraft, the canopy would pull a lanyard to activate an off-seat M3A1 initiator which in turn triggered the catapult phase. (Note: The small handle underneath the left hand firing handle is designed to actuate the on-seat M3A1 canopy unlatch initiator without firing the catapult.)
Catapult phase: The gas from this off-seat M3A1 initiator went through a ballistic hose routed to the top left portion of the seat. The gas activated a M1A1 exactor located next to the catapult initiator. The exactor pulled a safety pin from a seat-anchored spring, enabling the latter to pull the trigger rod of the M3A1 catapult initiator. The gas from the latter was then sent to the bottom of the ROCAT tube, through the lower hose on the left side of the seat, thus initiating the catapult phase. (Note that the safety pin refered to here is used to prevent catapult the M3A1 from being fired by the canopy jettison mechanism in case of the canopy being jettisoned manually.)
Seat travel up the rails and seat-man separation: As the seat traveled upwards, a seat-mounted lever was forced to rotate and fire a M-32 one-second-delay initiator. The lever and M-32 initiator were mounted under the seat pan (right-most initiator).
The novel features of the seat would then be activated:
After this one second delay, gas was released by the M-32 initiator into ballistic hoses connected to the lap belt, SMS strap rotator actuator, and parachute actuator. The gas caused the lap belt buckle to open, releasing both lap belt and shoulder harness end loops, thus releasing the pilot from all seat constraints. The gas also powered the SMS rotator to tension up the strap and cause separation of the pilot from the seat. The strap was initially routed behind the pilot and under his seat kit, and was attached to the front of the seat pan. Reeling-in the strap into the rotator actuator caused the strap to force the pilot out of the seat. Finally, the gas also activated the parachute actuator and the parachute deployment sequence as further described below.
Just before the seat cleared the rails, the rocket motor of the ROCAT system would fire and initiate the rocket phase of the ejection.
Two seconds after parachute actuator triggering and seat-man separation, the chute was forcibly deployed out of the back pack by the firing of a slug attached to the extraction chute (also called “drogue” chute or “pilot” chute). Upon deployment and inflation, the chute would extract the main parachute, a standard USAF C-9 hemispherical canopy of 28 ft diameter.
Project 90, A study in 0-0 Ejection
Zero-Zero - just about the lowest point in the Ejection Envelope. Sitting on the ground, with the aircraft immobile.An emergency arises and you don't have time to hop out of the cockpit and run. What can you do? How do you know the seat will work? Will it launch you high enough for the parachute to open? Will you be injured by the force of the launch?
These questions led to a unique test. In the mid-1960s a firm that had made its name providing ejection seats and egress technology to both the military and to NASA decided that instrumented dummies did not provide all the information needed. They felt that certain questions of human physiology needed to be answered by a test of a live human. Weber Aircraft's seats had saved over 500 lives by this time. They had been fitted to such varied craft as the F-106 and the Gemini Space capsule. The F-106 seat included the latest technologies available to allow for a clean ejection, including a gun deployed parachute, rocket motor, and self deploying survival equipment.
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