NORTHROP 'Turbo-pusher'
(SIERRA S-1 'Sportplane' a.k.a. "Sierra Sue")
Type: experimental pusher propeller aircraft
Powerplant: 1 x 85
hp (63 kW) Continental C-85 pusher
Significant date: 1948 (manufacture), 1968 (Northrop
tests)
Designed and flown by Ron Beattie and Walt Fellers, the Sierra S-1
Sportplane (also found as the Beattie-Fellers
S-1) was
an experimental aircraft of unusual configuration built in the US in 1948 to
investigate the advantages of a pusher
propeller
configuration. Apart from this engine installation, the aircraft was unusual
in having an X-shaped tail incorporating ruddervators on the upper fins.
The wing was mounted
midway up the fuselage and was unswept. For some reason, the Sierra S-1
appears on civil register as being built in 1953, perhaps indicating a
rebuild that might have justified a new FAA approval.
Only one example of the midget racer was manufactured by Hugh Crawford
and C. Roger Keeney's Acme Aircraft Co. of Torrence, Calif.,
and christened "Sierra Sue", but it never competed.
Acme relocated in Los Angeles County,
briefly marketed a Longren-designed Convair L-13 conversion known as the
'Centaur', performed the conversion of a Ryan 'Navion' into the X-16 prototype
of Riley's D-16 'Twin Navion', and became Sierradyne Inc. in 1953. The
Sierra S-1 (or Sierradyne S-1) was later used by Sierradyne in
the '60s
as a flying
technology
demonstrator to
test and
promote Northrop's
and Dr Werner Pfenninger's boundary layer control concepts, which found
their realization in the X-21 program.
The S-1 (now rechristened the Northrop 'Turbo-pusher') then
became the company's flying demonstrator for the Air Force’s AX
close-support aircraft design competition. Northrop believed that the
pusher system eliminated torque problems found in single-engine puller
designs. In the early stages of the competition, turboprops
were being considered for the AX, although the prototypes eventually built
under contract had turbofans. The
AX Competition led to the manufacture
of
two prototypes,
Northrop’s
A-9A and Fairchild Republic’s
A-10A. After an extensive flight test program, the Fairchild Republic
design won the competition and
made history as the 'Thunderbolt II' (popularly known as the "Warthog").
Although extensively used by Northrop, the 'Turbo-Pusher' was never
officially considered a Northrop aircraft and remained the property of Sierradyne.
On November 24, 1967, it was substantially damaged during a demonstration at
Langley
AFB
when
its
pilot,
unfamiliar with the aircraft, caused overload failure by improper operation
of the brakes
and/or
the flight controls, leading the aircraft to swerve and roll on landing as
the gear collapsed. It was later donated to the Western Museum
of Flight located
in Hawthorne,
Calif.,
at
the
Jack Northrop
Field, where it still resides in restored condition, right next to the Northrop
N-16 (JB-1) 'Bat' and not too far from the AX contender it helped develop,
the unfortunate A-9.
Population: 1 (c/n 1) [N12K]
Specs:
Length: 18 ft 0 in (5.49 m)
Wingspan: 20 ft 2 in (6.15 m)
Empty: 590 lb (268 kg)
Maximum speed: 200 mph (320 km/h)
Comparable aircraft: Göppingen Gö 9
Crew/passengers: 2
Main sources:
- The Sierra Sue page at the WMOF
- Brian Johnstone's
photograph on MyAviation.net
-
NTBS Identification Report
on N12K accident
- The Acme Sierra page at OpenTopia
- The Sierra Sue page at Airpower.Callihan.cc
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