ADA-Avro Arrow-An Aviation Chapter In Canadian History pg2
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Avro Arrow-An Aviation Chapter In Canadian History pg2
Paul Campagna,
P.Eng.
PAGE
1
PAGE 2
PAGE 3
Introduction
Fuselage
Engines
Company
Weapons
Carriage
Problems
Aircraft
Landing
Gear
Consequences
Wing
Fly-by-Wire
Why
was the Arrow Cancelled?
 
Setting
the Record Straight: The Designer's View by
Margaret McCaffery
"A
Flawed Plane and an Inept Corporation"?
The Historian's View by Margaret
McCaffery
Acknowledgements
References
 
Drawing: DND
 
AVIONICS ARMAMENT EQUIPMENT ENGINE FUEL
The
Fuselage
The
aircraft was extensively "area ruled." This concept
involves aerodynamic shaping of the cross-sectional
area of the fuselage along its length, to reduce
drag to a minimum. Also called the "Coke bottle" design,
the fuselage is characteristically pinched at
the waist at the wing joint, although this was
not immediately noticeable on the Arrow.
   Similarly, the cockpit was designed as an extension of the
fuselage rather than as a separate bubble, again for good aerodynamic performance.
The cockpit canopy itself was of unusual design, opening and closing in clam-shell
fashion due to its size and weight, as well as for case of entry and exit. The
canopy was made of a magnesium alloy with partly glazed glass. In back, drag
was reduced by trailing the canopy off into a spine running the length of the
aircraft to the tail, This also doubled as a conduit for controls and wire cabling.
In short, everything possible was done to reduce aerodynamic drag, including
the internal carriage of weapons.
The
Weapons Carriage
The
concept of internal weapons carriage has spawned
several misguided criticisms about an aircraft
that would destroy itself if the weapons package
were lowered during supersonic flight. In fact,
the weapons package was designed to be lowered
and removed only while on the ground. In this
way, a fully loaded package could be "snapped" into
place, considerably reducing the turnaround time
per aircraft. This concept also allowed easy
reconfiguration for other roles, including reconnaissance
and bomber. The pack was never designed to be
lowered in flight; since it was 16 feet long
and nine feet across, lowering in flight would
have been ludicrous. At no time were any of the
completed aircraft fitted with weapons.
   Initially, the Arrow was to have carried the Hughes Falcon
guided missile. The Falcons were to be re- placed by Sparrow 2D missiles, with
a sophisticated weapons control system known as ASTRA. However, Avro engineers
judged the Sparrow missiles to be inferior for use in a high performance aircraft
without further development.
   Each missile was to be mounted on its own hydraulically activated
retractable launching mechanism. Be- cause of their large fins, Sparrows would
sit partially within and partially outside the belly of the aircraft. (This is
similar to the manner in which missiles are carried on the Tornado aircraft:
they are recessed into the underbelly; however, no retractable launcher is required.)
The smaller Falcon missiles would have been fully internal to the aircraft. Missiles
would extend from their own individual bay doors. Aft missiles would be fired
first, followed by forward missiles.(2) A sliding
bay' door arrangement was being considered for the Sparrows. Door opening or
closing was to have been completed in 0.35 seconds; extension was to have taken
another 1.25 seconds or less.
   It has been argued that no other fighter has duplicated this
internal weapons carriage. This is simply not the case. The CF-101 Voodoo aircraft,
for example, employed a rotating platform, which carried some of the weapons
internally and the remainder externally. The F-106 Delta Dart used an almost
identical internal missile system to that of the Arrow. Internal weapons carriage
may also become the future norm.
   As calculated by Avro engineers, externally mounting four missiles
could have increased drag by some 20% at Mach 1.5. Bill Gunston (3)
states that the move towards faster, more agile fighters is slowly forcing the
removal of externally mounted weapons in order to take every advantage of the
resulting reduced drag. He states it will simply no longer be good enough to
hang missiles on pylons. One solution is to use the recessed method of missile
carriage and the other is to place weapons in an internal bay.
   A recent article (4) describes
stealth design techniques to reduce radar cross-sectional (RCS) area. These include
using aerodynamic shapes such as delta wings, blending cockpit and wings into
the fuselage and, of course, carrying weapons internally. Aerodynamic and stealth
efficiency appear to be complementary design requirements. The Arrow was not
a stealth aircraft, but obviously the concept of a "clean" aircraft could have
several inherent advantages.
Avro Arrow design team, left to right. Bob Lindley, chief engineer; Jim Floyd, vice president, engineering;
Guest Hake, Arrow project engineer, and Jim Chamberlin, chief, technical design.
The
Landing Gear
The requirement for such a large weapons bay necessitated stowage of the main landing
gear in the thin delta wings. This caused a number of engineering difficulties, overcome by
Dowty Engineering Limited. On retraction, the main gear would be shortened, angled
forward and then twisted in order to be accommodated Given the 30-ton weight of the
aircraft and resulting 200,000-Lb compressive load on the main gear on landing,
ultra-high-tensile steel with an ultimate tensile strength of 260,000-280,000 psi was
required. Use of aluminum was obviously precluded, as was the use of butt and gas welding
techniques. Instead, large forgings were made, using a die process. For example, the main
outer leg was the largest forging, weighing 1,000 lb. After machining this would be reduced
to 167 lb. Solutions to the problem put Dowty and Avro engineers at the forefront of
metallurgical research.
Likewise, the engineers at Jarry Hydraulics were obtaining patents for their steering
mechanism in the nose gear arrangement, among others. In fact, Avro engineers and their
subcontractors made enormous strides in developing high temperature alloys, high pressure
and high temperature systems, fuel technology for supersonic flight and human engineering, in terms of cockpit layout and design. These techniques pushed the world
aircraft industry further ahead. In support of these advances, Avro maintained a huge
metal-to-metal autoclave, a special heat treat furnace, a giant skin mill and a 15,000-ton
rubber pad forming press (then the largest in the world).
Fly-by-Wire
Early in the design, it was decided that some form of power assist would be required to help
control and fly the aircraft during supersonic flight. The chosen result was fly-by-wire. In
conventional systems, the pilot's stick and rudder controls are mechanically linked via steel
cables or rods to valves which control high pressure fluid flow to the actuators. These
powerful hydraulic actuators, in turn, operate the aircraft's control surfaces, such as
elevators and ailerons. In military aircraft, automatic flight control systems, gyroscopes and
position sensors are also mechanically linked to the actuators through the control rods.
In the Arrow automatic flight control system (AFCS), in automatic mode, the pilot's stick
and position- ing sensors were linked electrically to electro-hydraulic actuators. Hence,
stability, command and control were effected almost instantaneously in all three axes.
Analogue computers with a mix of vacuum tube and transistor technology were used,
together with autostabilization of the tail fin and artificial feel, to give the pilot some sense of
force on his control stick.
Not until the 1970s did fighter planes use a similar AFCS, although variations had been
employed in ex- perimental aircraft and the SR 71 Blackbird. The F-16 and Panavia Tornado
both used analogue fly-by-wire.The first fighter to replace the analogue system with digital
electronics was the F/A-18 Hornet.
How effective was the Arrow fly-by-wire automatic flight control system? According to test
pilot Spud Potocki, in a 60-degree climb, with full afterburner, he would shut down one
engine and experience no expected sideslip or roll. The AFCS would compensate
instantaneously. Automatic approaches and takeoffs were also successfully completed. The
Arrow was the most modern interceptor in the world, clearly over 20 years ahead of its time.
Setting
the Record Straight: The Designer's View
                                      Margaret
McCaffery
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