Information from the
Ejection Seat Website by Kevin Coyne
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.
The Convair F-106
Delta Dart was equipped with a seat designed by
Weber
Aircraft. It was a replacement for a seat known as the Convair
Rotational 'B' seat, that seat was designed specifically to address many of
the high speed ejections. The Weber seat was optimized for the lower
speed and zero-zero applications, and was the first and only seat
man-rated for
zero-zero applications by a United States company. Although most later
seats were capable of zero-zero use, they were not human tested for that.
This seat belongs to
Jean Potvin, a parachute rigger and
researcher who has become interested in ejection seats. He is a member of
Parks College Parachute Research Group.
The seat itself is from an F-106A. The parachute shown is a BA-18. Later
seats were equipped with BA-24 force deployed parachutes.
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
Pulling the ejection handles resulted
in the following actions:
- Rotation of the spring-loaded arm guards to a
horizontal position (see diagram item #8 showing the arm guards in the
vertical, “down” position).
- Release of the M3-catapult initiator safety
lock. This on-seat initiator was located inside the seat pan and under the
left armrest and would be fired only after canopy jettison.
- Firing of the canopy unlatch-M3 initiator.
This second on-seat initiator was located inside the seat pan and under the
right armrest . Its hot gas was sent to the canopy-jettison hardware, located
off-seat, through the ballistic hose coming out of the top-right portion
(diagram item #3) of the seat. The gas would trigger a series of off-seat
mechanisms, which would unlock the canopy and forcefully eject it from the
aircraft. (Note: This initiator could also be fired by raising the small lever
(diagram #12) under the left hand seat firing handle. Firing the M3 initiator
in this manner will not remove the safety pin from the catapult initiator so
that the seat could not fire until the firing handle was subsequently raised
in this case.)
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.
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 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
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.
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
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.
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:
- 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.
- 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.
- A spring-loaded extraction chute tied to the
gun slug via tubular lanyard, of a type different from the standard MA-1
extraction chute.
- 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. 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:
- The replacement of the MA-6 lap belt by the
HBU-4A belt. The seat
shown here still features the MA-6 lap belt and its ballistic hose
connecting to the M32 initiator under the seat pan.
From 1975 through 1988:
- In 1978, installation of a smaller and simpler
“elbow”-shaped seat-mounted parachute actuator. The seat shown here features
this more recent elbow parachute actuator. Note that the MA-6 lap belt also
shown in the photograph with the elbow actuator is actually an historical
mismatch; an HBU-4A belt would have been more appropriate.
- In 1979, the shoulder harness inertia reel
system was replaced by a gas-powered (or “ballistic”) shoulder harness
retraction reel, which caused automatic and proper positioning of the pilot
against the seat. The gas generator and reel motor were installed behind the
seat headrest. This modification also required the installation of a M3A2
initiator under the seat pan (photo,
leftmost initiator). Triggered by the rotation of a torque tube upon
ejection handle pull, the M3A2 sent gas to activate the shoulder harness
retractor initiator.
- The removal of the chaff dispenser from the
upper right side of the seat.
- Installation of a metal strap ROCAT protector.
- Removal of the ditching lever. This lever
allowed the pilot to manually disconnect the parachute deployment cable from
the seat-mounted parachute actuator. Its removal followed the conversion to
the elbow-type parachute actuator.
- In 1983, replacement of the HBU-4A lap belt by
the HBU-12A lap belt (not shown on the photos).
