Subject: Number Eighty-Nine in the Series--Northrop F-89 Scorpion (1 of 10)

From: [email-masked]
Date: 17 Sep 93 16:38:30 GMT

>From [email-masked]

On March 23, 1945, the USAAF announced a competition for the successor 
to the Northrop P-61 Black Widow night fighter.  It was to be an 
all-weather fighter-bomber capable of guarding the northernmost 
frontiers of the United States, especially Alaska.  Initially, a 
piston-engined design was considered, but in December 1945 the Army 
changed the requirement to stipulate that only a jet-powered aircraft 
would be acceptable.  

Bell, Convair, Douglas, Goodyear, Curtiss-Wright, and Northrop all 
submitted proposals for the competition.  The Convair entry was a 
radical, delta-winged design which was eventually to emerge several 
years later as the F-102.  The Douglas entry was a denavalized 
adaptation of the XF3D-1 Skyknight carrier-based all-weather fighter.  
The Curtiss XP-87 Blackhawk was a large, four-jet aircraft carrying a 
pilot and radar operator seated side-by-side.  Initially, the USAAF 
seemed to favor the Curtiss design, if for no other reason than the 
fact that the Curtiss-Wright company would probably close down if it 
did not land the contract.  Two prototypes of the Curtiss design were 
ordered under the designation XP-87.  

However, the USAAF also thought highly of the Northrop proposal, which 
was given the designation N-24 by the company.  The N-24 project 
called for a cantilever, mid-wing monoplane with a long, slim 
fuselage.  An unswept laminar-flow wing was adopted to ensure good 
low-speed stability, important for an aircraft called upon to make 
frequent landings in bad visibility.  Traditional ailerons and flaps 
were fitted to the wing trailing edge, and provisions were made for 
wingtip-mounted drop tanks.  The aircraft was to be powered by a pair 
of Allison J35 afterburning turbojets, mounted one on either side of 
the belly of the fuselage just underneath the wings.  The twin air 
intakes were mounted flush in front, each intake exactly in line with 
its engine nacelle.  The pressurized cockpit seated the pilot and 
radar operator in tandem ejector seats underneath a large 
rearward-sliding bubble canopy.  The horizontal tailplane was mounted 
halfway up on the vertical tail, well out of the way of the engine 
exhaust.  The nosegear was of a very short, twin-wheel design.  The 
main retractable undercarriage had larger than usual wheels, giving 
the prototype a rather unusual appearance when sitting on the ground.  

Since the Northrop aircraft was to be an all-weather fighter, an 
airborne interception radar was to be installed in the nose.  The 
armament installation was to have been a quartet of 20-mm M-24 cannon 
carried in a nose-mounted turret.  Two different turret designs were 
to have been considered.  One was a Martin design which allowed the 
guns to be stowed out of sight inside the nose when not needed.  When 
needed, the guns would be elevated and moved forward into firing 
position.  The Martin turret could rotate 360 degrees and the guns 
could elevate 105 degrees.  The other turret design was a Northrop 
project, which was similar in concept to the Martin design but had 
only a 30-degree cone of fire.  

The USAAF looked favorably upon the Northrop proposal and issued a 
development contract on May 3, 1946.  Two prototypes were ordered 
under the designation XP-89 in December of 1946.  Serials were 46-678 
and 679.  

In the meantime, the Cold War between the West and the Soviet Union 
was beginning to get underway.  It was generally conceded that the 
acquisition by the Soviet Union of nuclear weapons was only a matter 
of time.  The appearance of the Tupolev Tu 4 (a copy of the B-29) at 
the 1947 Tushino air display was a shock to American intelligence, 
since the USSR would now have a means to deliver nuclear bombs onto 
continental US targets.  There were no all-weather jet-powered 
interceptors yet available to counter this threat.  The US was 
extremely worried about an all-weather fighter "gap" opening up, 
leaving the continental US defenseless for several years against an 
onslaught of nuclear-armed Soviet bombers.  

Something needed to get to the squadrons right away.  Since neither 
the Curtiss-Wright nor the Northrop designs promised to be immediately 
available in quantity for several more years, the USAF approached 
Lockheed in March of 1948 and asked them to see if the TF-80C two-seat 
trainer could be adapted as an all-weather fighter, with first 
deliveries to operational squadrons being made before the end of 1949.  
Lockheed quickly came up with a design which was eventually to emerge 
as the F-94 Starfire.  

The Northrop XP-89 (46-678) rolled out of the factory in early June of 
1948.  The XP-89 was powered by a pair of Allison J35-A-9/-15 engines 
of 4000 lb.st.  each Neither the Martin nor the Northrop turrets were 
ready, so the prototype carried no armament.  For rollout, the XP-89 
did not carry its jettisonable 600-gallon wingtip tanks.  It was 
painted gloss black overall.  

Even before the new Northrop fighter made its first flight, on June 
11, 1948, the P-for-pursuit designation was replaced by the 
F-for-fighter designation, and the XP-89 became the XF-89.  

Following a number of taxi and brake tests at Northrop Field, the 
XP-89 was disassembled and trucked out to Muroc Dry Lake (later 
Edwards AFB).  The XP-89 made its maiden flight on August 16, 1948, 
with test pilot Fred Bretcher at the controls.  Flight test results 
were generally positive, but the aircraft proved to be seriously 
underpowered.  For the first 32 flights, conventional ailerons were 
fitted, but on February 1, 1949 a new series of trials began with 
Northrop-invented "decelerons", which was a split surface that could 
be operated in one piece as a conventional aileron but which could be 
opened up to serve also as an airbrake.  This feature was made 
standard on all subsequent F-89s.  

Even though the flight test crews were enthusiastic about the XF-89, 
the USAF ordered that a flyoff take place between the XF-89, the 
Curtiss XF-87, and the Navy's Douglas XF3D-1 Skyknight.  The Curtiss 
XF-87 with its side-by-side seating arrangement was judged to have the 
best cockpit arrangement, with the XF3D-1 coming in second.  The 
tandem seating arrangement in the XF-89 made communication between 
pilot and radar operator difficult.  Ease of maintenance was found to 
be the best in the XF3D-1, with the XP-87 coming in second.  However, 
the evaluation team judged the XF-89 as being the superior fighter and 
having the best development potential.  

Since the Northrop XF-89 was judged as having the superior potential 
as a fighter, on October 10, 1948, the USAF officially cancelled the 
Curtiss XF-87 project.  The failure of the XF-87 to win any production 
orders was the end of the line for the Aeroplane Division of 
Curtiss-Wright.  Shortly thereafter, the Aeroplane Division of 
Curtiss-Wright declared bankruptcy, sold all of its assets to North 
American, and closed its doors forever.  

Even though the XF3D-1 did not succeed in obtaining any USAF orders, 
it nevertheless did receive orders from the US Navy and the US Marine 
Corps, and went on to serve as both a land-based and carrier-based 
interceptor fighter for many years.  

In January of 1949, President Harry Truman authorized the Air Force to 
make an initial purchase of 48 F-89As.  

In March of 1949, the name "Scorpion" was officially applied to the 
XF-89, the suggestion being originally made by ground crews at Edwards 
who thought that the parked plane with its upward-curving rear 
fuselage and its high tail looked a lot like the dangerous creature 
with the deadly stinger in its tail.  

On July 14, 1949, the USAF made the order of 48 production F-89A 
aircraft official.  Serials 49-2431/2478 were assigned.  An additional 
27 aircraft were added to the contract in September.  

The second prototype (46-679) made its maiden flight on November 15, 
1949.  Modifications made when the airframe was almost 90 percent 
complete led to a change in designation to YF-89, as it was envisaged 
as being a test vehicle for the production F-89A fighter.  The XF-89 
had been painted black, but the YF-89 was finished in natural metal 
overall.  

The XF-89 had been unarmed, pending the availability of the nose 
turret.  However, the nose-mounted turret was eventually abandoned as 
being too complicated, and a more conventional armament of six 
forward-firing 20-mm Mk 24 cannon was chosen for the Scorpion.  

Since the USAF wanted the Scorpion in service right away, production 
of the F-89A got underway immediately, even before testing of the 
prototypes was completed.  This commitment to production proved to be 
premature.  On February 22, 1950, the XF-89 prototype crashed while 
making its 102nd flight.  The cause of the crash was later found to be 
a failure of the horizontal stabilizer due to excessive flutter.  The 
YF-89 was grounded for changes, and production of the F-89A was 
halted.  

As a result of the grounding, the YF-89 was extensively modified.  The 
nose was completely redesigned.  It was reconfigured to be more 
tapered and was increased in length by three feet.  An AN/ARC-33 radar 
set was fitted in the nose, along with a Hughes E-1 fire control 
system.  The engines were Allison J35-A-21s, rated at 5200 lb.st dry 
and 6800 lb.st with afterburners.  The engine air intakes were 
redesigned to include external boundary layer bleed ramps and 
auxiliary pop-in doors were added to the nacelle sides to allow 
additional air to be supplied to the engine during ground runups.  The 
engineers believed that pulsating exhaust gases from the engine were 
responsible for the tail flutter problems that had wrecked the XF-89, 
and the engine exhaust area was redesigned by adding deflector plates 
to the fuselage to direct the exhaust away from the tail.  The pitot 
tube was moved from the vertical tail and installed in the nose.  The 
jettisonable 300-gallon wingtip tanks of the XF-89 were replaced by 
permanently- attached more-streamlined 300 gallon tanks.  

The heavily-modified YF-89 was redesignated YF-89A (Model N-49), and 
made its first flight on June 27, 1950, and the Scorpion flight test 
program was resumed.  

Serials:

46-678 	Northrop XP-89 Scorpion - redesignated XF-89 in 1948.  
46-679 	Northrop YF-89 Scorpion 

Sources:

  United States Military Aircraft Since 1909, Gordon Swanborough
  and Peter M. Bowers, Smithsonian, 1989.
  
  F-89 Scorpion in Action, Aircraft Number 104, Larry Davis and 
  Dave Menard, Squadron/Signal Publications, 1990.

  Fighters of the United States Air Force, Robert F. Dorr and David 
  Donald, Temple Press Aerospace, 1990.

  The American Fighter, Enzo Angelucci and Peter Bowers, Orion, 1987.

  American Combat Planes, Third Enlarged Edition, Ray Wagner,
  Doubleday, 1982.

Joe Baugher		AT&T Bell Laboratories   	
2000 North Naperville Road      Naperville, Illinois 60566-7033