Subject: Number Eighty-Nine in the Series--Northrop F-89 Scorpion

From: [email-masked]
Date: 23 Sep 93 16:12:51 GMT

>From [email-masked]

The F-89C (Model N-35) was the first major production version of the 
Scorpion.  The first F-89C flew on September 18, 1951.  It 
incorporated most of the changes that had been made to the F-89A/B 
small-scale production run in an attempt to make the Scorpion a fully 
operational and safe aircraft.  

Some of the changes incorporated in the F-89C were internal.  A fuel 
purging system was added which helped alleviate the danger of fuel 
vapor explosions.  The wingtip fuel tanks had dump valves installed 
which allowed them to be emptied in flight.  The cockpit air 
conditioning and pressurization system were upgraded.  A Lear vertical 
gyro was added to provide artificial horizon information to the 
autopilot.  

Other changes incorporated in the F-89C were external and hence more 
obviously recognizable.  After production of the first 40 F-89Cs, the 
external mass balance horns on the horizontal stabilizer/elevator were 
deleted and replaced by a strengthened horizontal tail with internal 
mass balances.  This feature was retrofitted to all previous 
Scorpions.  

During January of 1952, the 74th Fighter Interceptor Squadron based at 
Presque Isle AFB in Maine had been declared operational with the 
F-89C.  Other units soon followed.  

Even though the Scorpion was rapidly entering squadron service all 
throughout 1952, the interceptor continued to be plagued by engine 
failures.  The initial production blocks (1 through 20) of the F-89C 
were powered by a pair of J35-A-21 engines.  In service, these engines 
were unreliable and subject to frequent failures.  The problem was 
solved as in the case of the F-89A and B by retrofitting these early 
F-89Cs with the improved and more reliable J35-A-21A engine.  
Beginning with the F-89C-25-NO, the engine was changed yet again to 
the Allison J35-A-33 jet rated at 5400 lb.st. dry and 7400 lb.st.  
with afterburner.  Finally, production blocks -35 and -40 were fitted 
with the Allison J35-A-33A, rated at 5600 lb.st.  dry and 7400 lb.st 
with afterburner.  The -33A engine not only had more power, it also 
had a redesigned inlet, deicing equipment, inlet guide vanes, and 
redesigned forward engine mounts.  The F-89's engines, being mounted 
quite low on the fuselage, had a tendency to scoop up runway debris 
into their intakes.  To cure this problem, retractable inlet screens 
were added to the -33A engine.  

Other problems with the Scorpion turned out to be much more serious.  
During 1952, several F-89Cs crashed due to wing structural failures.  
No less than six aircraft were lost in the spring and early summer of 
1952, one spectacular crash taking place in front of thousands of 
spectators at the International Aviation Exposition at Detroit.  The 
entire Scorpion fleet had to be grounded until the cause was found.  

After an exhaustive series of flight tests, the problem was finally 
traced to a previously unknown effect, known as aero-elasticity.  This 
effect caused the wing to twist at the tip during high-G maneuvers, 
exerting excessive strain on the wing attachment points and causing 
them to fail.  The large wingtip fuel tanks were found to be a 
significant factor in exerting this twisting moment.  A total of 194 
F-89A, B, and C aircraft were shipped back to Northrop where they were 
fitted with stronger wings with forged steel attachment points.  At 
the same time, a small fin was added to the outboard rear of each 
wingtip tank, which reduced the aerodynamic forces on the tank which 
caused it to flex and twist during maneuvering.  

Before the F-89C fleet had been fully retrofitted with the new 
stronger wing, a total of fourteen months had passed and it was not 
until 1954 that the Scorpion force reached its intended level.  As 
fast as the F-89Cs could be modified, they were flown directly to 
their operational units.  With the modified wing and the improved 
engines, the Scorpion became one of the safest and most reliable 
combat aircraft in the USAF inventory.  The 74th Fighter Interceptor 
Squadron, following its transfer to Thule, Greenland in August of 1954 
completed a full year of service with the type without a single 
accident of any kind.  

The F-89C served with the 27th, 74th, and 433rd Fighter Interceptor 
Squadrons from 1952 onwards.  The 57th FIS, based in Iceland, the 65th 
and 66th FIS based in Alaska, and the stateside 438th FIS took 
delivery of the F-89C in 1953.  

The F-89C was phased out of active USAF service during 1954, when 
later Scorpion models became available.  F-89Cs were then transferred 
to the Air National Guard, equipping some seven units in northern 
states.  ANG squadrons operated the F-89C until well into the 1960s 
until they were finally phased out of service.  

Specification of the F-89C: 

Two Allison J33-A-33A, 5600 lb.st.  dry, 7400 lb.st. with 
afterburner.  Maximum speed: 650 mph at sea level, 562 mph at 40,000 
feet.  Initial climb rate 12,300 feet per minute.  Service ceiling 
50,500 feet.  Maximum range 905 miles.  Dimensions: wingspan 56 feet 0 
inches, length 53 feet 5 inches, height 17 feet 6 inches, wing area 
606 square feet.  Weights 24,570 pounds empty, 33,100 pounds combat, 
37,348 pounds gross.  Armed with six 20-mm cannon in nose.  Underwing 
racks could carry 16 five-inch rockets or 3200 pounds of bombs.  

Serials of the F-89C: 

50-741/744 	Northrop F-89C-1-NO Scorpion 
50-745/759 	Northrop F-89C-5-NO Scorpion 
50-760/774 	Northrop F-89C-10-NO Scorpion 
50-775/789 	Northrop F-89C-15-NO Scorpion 
50-790/804 	Northrop F-89C-20-NO Scorpion 
51-5757/5771 	Northrop F-89C-25-NO Scorpion 
51-5772/5801 	Northrop F-89C-30-NO Scorpion 
51-5802/5836 	Northrop F-89C-35-NO Scorpion 
51-5837/5856 	Northrop F-89C-40-NO 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