The Ejection Site

The seats of the F-106 supersonic interceptor

Special Contributor Jean Potvin has provided the following overview of the seats of the Convair F-106 Delta Dart

Introduction

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! The type first flew in December 1956, and went into USAF combat squadron service from 1959 until 1988. A few airframes also flew for NASA and several USAF testing units until the late 1990’s, in a variety of flight test programs including Mercury astronauts training, development of the B-1 bomber (as chase aircraft) and NASA’s Eclipse program. The Dart ended its career as a target drone for air-to-air missile research at Tyndall AFB and Holloman AFB, with the last airframe shot down in 1998. 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.

Interim seat - the first seat

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
Please refer to this diagram for details while reading this section.

Pulling the ejection handles resulted in the following actions:

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:

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.

B-seat - the supersonic bobsled

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, (note 1) 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
Please refer to this diagram for details while reading this section.

The ejection sequence proceeded in a two-step fashion and went as follows:

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:

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 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.

This diagram shows a simplified view of the process.

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.

Zero-zero seat - the workhorse

Additional photographs available- here, and here.

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:

As with the interim seat, the following events would occur using the same hardware but with upgraded initiator units:

The novel features of the seat would then be activated:

Parachute system

The parachute system involved the pilot wearing a modified BA-18 automatic-type parachute back pack containing the C-9 parachute and a MA-1 type extraction chute. The modifications to this parachute pack included:

  1. The removal of the so-called “quarter bag”, which kept the mouth of the C-9 parachute closed until complete deployment of the suspension lines. The quarter bag was used to delay parachute opening and thus prevent high opening shocks during high speed bailouts. Quarter bag removal insured swift parachute opening at the low speeds characteristic of 0-0 ejections, which by 1965 had become the highest priority in seat design.
  2. A gun barrel assembly for the firing of a 13oz. slug tied to the parachute extraction chute. Gun firing occurred only under 15,000’ and only after a 2-second delay following seat-man separation. The gun was controlled by an aneroid altimeter unit and was bolted inside the parachute pack.
  3. A spring-loaded extraction chute tied to the gun slug via tubular lanyard, of a type different from the standard MA-1 extraction chute.
  4. The standard extraction chute kicker plate was also modified with the addition of two grommeted tabs through which the top two pack closing loop were routed. This arrangement prevented the motions of the extraction chute inside the pack when the pilot moved against the seat.

The gun barrel and slug were located on the upper right corner of the parachute pack. The parachute included hardware that allowed parachute deployment to be activated manually, or by the firing of the drogue gun. The manual mode would be initiated by the pilot pulling the T-shaped “anti-blast” handle and ripcord cable. In the manual mode, the drogue chute would spring out on its own, being disconnected from the gun slug. Note that the gun slug would still be fired by the aneroid unit below 15,000 ft in the manual mode, this time without being connected to the extraction chute.

The gun-aneroid assembly was connected to a cable, which came out of the left side of the parachute pack. The other end of the cable was directly connected to left side of the seat to a hardware unit called the parachute actuator (Note 3) . The latter effected the actuation of the drogue-gun altimeter unit using gas from the M32 initiator unit located under the seat. The parachute actuator actually performed two functions, namely that of grabbing and pulling the cable for altimeter activation, and then releasing the cable during seat-man separation.

Seat modifications over the years

To improve seat performance and reliability, as well as to adapt the escape system to evolving USAF requirements, a series of modifications were carried out on all Century jet seats over the years. In the case of the F-106 zero-zero seat, these included the following:

During the late 1960’s or early 1970’s:

From 1975 through 1988:

Notes

Note 1: Robert Dorr's article on the F-106 appeared in "F-106 Delta Dart"; WINGS OF FAME, volume #12, published by Airtime Publishing.
Note 2: What is shown is actually a HBU-2A/E, an earlier version of the HBU-4-series belt. The difference between the two is the port for the zero delay lanyard (located at the top center of the buckle) being blocked over on the HBU-4 due to the movement of the function to the ballistic-deployed parachute eliminating the need for the zero delay lanyard.
Note 3: The parachute connector and cable shown are reproductions.

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