The Northrop F-89 Scorpion (2024)

* The Northrop F-89 Scorpion all-weather interceptor was nothing great forlooks, and never fired a shot in anger. However, for much of the 1950s itwas the backbone of the US Air Force's defense of the United States, and wasproduced in quantity. This document provides a history and description ofthe F-89 Scorpion.

[1] SCORPION ORIGINS

* In December 1945, the US Army Air Forces (USAAF) issued a request for ajet-propelled night fighter to replace the Northrop P-61 Black Widow. Eightaircraft manufacturers responded the request, with the USAAF selecting twofinalists: the Curtiss "XP-87 Blackhawk" and the "Northrop N-24". The USAAFalso evaluated the Douglas "XF3D Skyknight" for the requirement.

Curtiss received a contract for a small lot of Nighthawks, though as itturned out the contract would be canceled in 1948 after the flight of asingle prototype; the Skyknight was also given the thumb's down, though theNavy and Marines would make good use of it into the Vietnam War. The USAAFsettled on the Northrop N-24, signing a development contract with Northrop inthe spring of 1946, leading to the manufacture of two prototypes. The firstprototype, the "XP-89", flew on 16 August 1948 from Muroc Air Force Base, nowEdwards AFB, with Northrop test pilot Fred Belcher at the controls. TheXP-89 was painted all black and had a high tail, and so it was namedthe "Scorpion".

The Scorpion was a hefty aircraft, with a straight mid-mounted wing with anarrow height to chord ratio. The tailplane was mounted halfway up the swepttailplane. Control surface arrangement was conventional, including ailerons, double slotted flaps, elevators, and rudder. The Scorpion had distinctivemain gear with large but narrow tires on a wide track that retracted into thethin wing, the gear hinging inward towards the fuselage. The prototype waspowered by two Allison J35-A-13 axial-flow turbojets, each offering 16.7 kN(1,700 kgp / 3,750 lbf) thrust. That was too little thrust for too muchaircraft.

The pilot and radar operator sat in tandem in a pressurized co*ckpit, under acanopy that slid back to open. Removeable wingtip fuel tanks with a capacityof 1,158 liters (300 US gallons) were added early in 1949. Anairborne-intercept (AI) radar and cannons were to be fitted in the nose,though they were not installed in the prototype. After its initial series offlights, the prototype was fitted with "decelerons", which were aileronssplit to open up above and below the wings and act as dive brakes.

* The second prototype, designated "XF-89A", first flew on 15 November 1949.It was substantially redesigned, much closer to production spec, with a morepointed nose and uprated Allison J35-A-21 engines with afterburners, offering21.8 kN (2,220 kgp / 4,900 lbf) thrust dry and 30.2 kN (3,080 kgp / 6,800lbf) thrust in afterburner. The engine nacelles were substantiallyredesigned, with auxiliary inlet doors on the lower front side to providemore airflow for take-off and so on, and the wingtip tanks were permanentlymounted.

The XF-89A wasn't armed, though it did have AN/ARC-33 radar in the nose,coupled to a Hughes E-1 fire control system (FCS). It featured a naturalmetal finish, instead of the black finish of the first prototype, whichcrashed on 22 February 1950 due to a tail flutter problem, one of the twoaircrew being killed. The crash led to serious doubts about the viability ofthe Scorpion program, but Northrop proved able to resolve problems, and sothe F-89 survived. The tail flutter issue was resolved initially by themodification of the engine exhausts -- the exhaust flow having set upinstabilities over the tailplane -- and the addition of external "massbalances" on the elevator to damp out oscillations.

[2] F-89A THROUGH F-89C

* The USAF (the Army Air Forces became the Air Force in 1947) was pleasedwith the Scorpion and ordered a batch of 48 aircraft in July 1949. The firstof this batch, the "YF-89A", flew on 25 September 1950, leading to theproduction "F-89A". The F-89A was much like the XF-89A, even retaining theAllison J35-A-21 engines. The major difference was that the F-89A was armed,featuring six T-31 20-millimeter cannon in the nose with 200 rounds per gun,the cannons being staggered to permit ammunition feed clearance. The YF-89Aalso had underwing provision for bombs or up to 16 unguided rockets -- theAir Force envisioned the Scorpion as having a secondary attack role, thoughit would never be assigned to the attack mission in practice. The F-89A wasleft in natural metal finish, except for anti-glare black patterns whereneeded.

F-89As began to flow to US Air Defense Command and Alaska Air Command unitsin 1952, though the Scorpion demonstrated an alarming accident rate at first.This problem was not exclusive to the F-89 at the time; the Air Force hadbeen rushing new high-performance aircraft into production, resulting in manytechnical glitches and pilot training problems, with lethal results. Therewere crashes at least once a week in that timeframe, with scores of aircrewkilled.

Only eight F-89As were actually delivered, the aircraft basically amountingto an evaluation variant. They would end up in test and trials, someultimately being converted to target drones with the designation of "DF-89A".Production moved on to the "F-89B", which featured minor avionics systemsupdates, such as a Lear-Siegler autopilot. 40 F-89Bs were built, withinitial deliveries in 1951, and most F-89As were rebuilt to F-89B standards.They were withdrawn from frontline service in 1954, to serve with the US AirNational Guard (USANG) for a few years, though the F-89Bs were never verysatisfactory.

* The "F-89C" was the first Scorpion variant really suitable for operationalservice, with 164 built. The F-89C featured a balanced elevator that got ridof the cluttered external mass balances and many other small tweaks -- laterF-89C production including engine inlet screens that were retracted alongwith the landing gear. The screens were added because the Scorpion'slow-mounted engines had such an alarming tendency to ingest rocks and otherdebris kicked up by the nosewheel that the aircraft was sometimes referred toas the "F-89 Flying Hoover Vacuum Cleaner".

The first 34 F-89Cs retained the J35-A-21 engine, while the next 30 had thesimilar but much more reliable -21A engine. However, the next 45 F-89Csbuilt had J35-A-33 engines, with 24 kN (2,450 kgp / 5,400 lbf) dry thrust and33 kN (3,360 kgp / 7,400 lbf) thrust in afterburner, while the last 55 builtwere fitted with the -33A, with 24.9 kN (2,540 kgp / 5,600 lbf) dry thrustbut the same afterburning thrust as the -33. Armament and radar remainedunchanged from the F-89B.

In 1952, six Scorpions, mostly F-89Cs, crashed -- one doing so in front of acrowd at an airshow -- and the fleet was grounded. The problem was traced toa wing design fault, with all Scorpions in service then rotated through amodification program to fit stronger wings, as well as a fin on the end ofeach wingtip tank to reduce stress on the wing. Once the wings were fixed,the Scorpion's accident rate fell dramatically and the type would thenacquire a good flight safety record. By the time the F-89Cs were withdrawnfrom frontline service in 1954, all had been re-engined with J35-A-47engines, the thrust levels being similar to those of the -33A but with manytechnical refinements. The F-89Cs served faithfully with the USANG into the1960s.

* It should be noted before continuing that trials performed by these earlyScorpions included some unusual armament configurations. One F-89A wasfitted with an odd nose turret with four aimable 20-millimeter cannon. UnderProject GUN-VAL, two F-89Cs were fitted with four 30-millimeter Oerlikoncannon each, and one F-89C was fitted with twin rocket guns that fired MightyMouse rockets, each launcher being fed by a magazine with 25 rockets. Therockets were fired by an explosive charge and then ignited their rocketengine after clearing the aircraft.

[3] F-89D THROUGH F-89J

* The reason for the withdrawal of the F-89B/C variants in 1954 was theintroduction of the "F-89D" variant, the definitive Scorpion. The initialYF-89D prototype, a modified F-89B, had performed its first flight on 23October 1951. The guns were deleted, the interceptor being armed with 104Mighty Mouse 70-millimeter (2.75-inch) unguided folding-fin air rockets(FFARs), carried in the front of the wingtip fuel tanks, each tank with acapacity of 1,166 liters (308 US gallons).

The rockets were directed by the new Hughes E-6 FCS system and its AN/APG-40radar, the E-6 automatically directing the Scorpion towards its target to anoptimum firing position. The E-6 in principle permitted "collision-courseintercepts", with the Scorpion approaching the target from its forwardquadrant and firing rockets to destroy it as the paths of the two aircraftintersected. In a more traditional "tail chase" attack, the interceptorwould line up behind the target for shots, but in a collision-courseintercept there was effectively only one chance to get it right. That waswhy the unguided rockets were used: although they were notoriouslyinaccurate, it seemed likely that if a salvo was launched against a targetthe size of a bomber, one rocket would hit, and that would be enough to takethe target down. Rockets could be launched in one, two, or three salvos,either manually or under the automatic direction of the fire-control system.Vents around the rear of the rocket pack diverted the exhaust from the fueltank behind it; launching the rockets was spectacular to watch.

The F-89D also featured additional fuel tankage in the nose, replacing theguns, and could carry a 760-liter (200 US gallon) drop tank under each wing.A total of 682 F-89Ds was built, initially with Allison J35-A-33A engines,with later production and upgrades moving through improved engine variants upto the J35-A-47.

 NORTHROP F-89D SCORPION: _____________________ _________________ ___________________ spec metric english _____________________ _________________ ___________________ wingspan 18.2 meters 59 feet 8 inches wing area 52.21 sq_meters 562 sq_feet length 16.4 meters 53 feet 10 inches height 5.36 meters 17 feet 7 inches empty weight 11,400 kilograms 25,200 pounds max loaded weight 19,160 kilograms 42,240 pounds maximum speed 960 KPH 600 MPH / 520 KT service ceiling 15,000 meters 49,200 feet range with tanks 2,200 KM 1,370 MI / 1,190 NMI _____________________ _________________ ___________________

The F-89D featured complcated avionics systems that demanded a lot ofmaintenance -- but that was the rule for sophisticated 1950s electronics.Any equivalent aircraft would have had the same issue, pilots of the eracommenting that, unlike 21st century combat aircraft, "all systems go" wasthe exception and not the rule.

A few F-89Ds ended up in Northrop service as target drone launchers, carryingNorthrop / Radioplane rocket-powered target drones for training crews of US Army Nike surface-to-air missile (SAM) sites. These "JF-89D" dronelaunchers served in that role into the late 1960s.

* The single "YF-89E" was an F-89C fitted as an engine-test prototype withAllison YJ71-A-3 turbojets providing 43.1 kN (4,400 kgp / 9,700 lbf) thrusteach. Though the J71s were well more powerful than the F-89D's J35 engines,they did not significantly improve performance -- clearly the Scorpion hadreached the limits imposed by its aerodynamics. The F-89E with the J71engines was abandoned, but the designation was resurrected for a differentdesign, a single-seat long-range escort fighter with twin GE J47 turbojets,like those used on the Boeing B-47 bomber, with 40.5 kN (4,125 kgp / 9,100lbf) thrust each; a modified, more aerodynamically efficient wing to takeadvantage of the greater thrust provided by the J47s; and a pod in the middleof each wing with 54 FFARs, the main gear retracting into the pods. Itretained the nose cannon.

The F-89E didn't happen, with Northrop moving on to the further refined"F-89F" concept, also with J47 turbojets; a spine fairing from the co*ckpit tothe tailfin for additional fuel storage; a further refined wing and areconfigured tail assembly; and larger midwing pods, with rockets, main gear,and fuel. Cannon armament was deleted. Two-seat and single-seat variantswere considered -- but as tends to happen to an aircraft when a lot of "more"is added to it, weight creep gradually exceeded the thrust capability of theJ47 powerplants, and the project was abandoned.

It should be noted here that a swept-wing Scorpion was also considered, thismachine being known as the "Super Scorpion", once again with both two-seatand single-seat configurations considered. It never got off the drawingboard.

* The "F-89G" was an advanced interceptor variant that was given up as tooambitious, with attention then turned to the more conservative "F-89H", thelast production Scorpion. It was an updated F-89D, with primary armamentupdated to the Falcon air-to-air missile (AAM). Falcon variants aresomething of a confusing issue, there having been a series of heat-seekingweapons and a series of "semi-active radar homing (SARH)" weapons that homedin on the reflections of the Scorpion's radar off a target. To make mattersmore confusing, in 1962 the US military adopted a multiservice designationscheme and all the Falcon designations were shuffled around in a not veryintuitive fashion:

 old new notes ________________________________________________ GAR-1 AIM-4 1st-generation SARH AAM GAR-2 AIM-4B heat-seeking GAR-1 GAR-2A AIM-4C GAR-2 with improved seeker GAR-1D AIM-4A 2nd-generation SARH AAM GAR-3 AIM-4E 3rd-generation SARH AAM GAR-3A AIM-4F improved GAR-3 GAR-4A AIM-4G heat-seeking GAR-3A GAR-2B AIM-4D GAR-1/2/2A with GAR-4A seeker ________________________________________________

In any case, the F-89H could carry up to twelve Falcons, with three in thenose of each wingtip pod, plus pylons for a total of six Falcons under thewings. Generally, only the six Falcons in the wingtip pods were carried,with three being SARH variants and three being heat-seeking variants. Theidea was to launch both a SARH and a heat-seeking Falcon at a target on thebasis if that if one didn't work, the other might.

The Falcons in the wingtip pods were on rotating launch racks, with themissiles stored inside the pod until they were popped out for launch. Theoriginal idea was to fire the Falcons out of slots in the front of the pods,but trials showed that approach didn't work very well. The pods could stillcarry 21 unguided rockets each, in three banks of seven rockets with eachbank between two Falcons. The F-89H was fitted with J35-A-35 enginesinitially, being updated in service to later variants, and the Hughes E-9 FCSto support the Falcons. Total production of the F-89H was 156 aircraft, inaddition to three F-89Ds modified as prototypes.

* 350 F-89Ds were updated beginning in 1956 to the "F-89J" spec. Thisvariant featured stores pylons under the wings for two unguided Douglas MB-1/ AIR-2A Genie rockets -- AKA "Ding Dong", the Genie having a definitelyphallic appearance -- with nuclear warheads, plus four Falcons, though theFalcons weren't generally carried in practice. While some F-89Js retainedthe wingtip fuel and rocket pods of the F-89D, most were refitted with simplewingtip fuel pods. The F-89J was equipped with a Hughes MG-12 FCS system tohandle the Genie. The Genie was simply fired in the general direction of thetarget, being detonated at the appropriate time by the MG-12 FCS; the lethalblast radius, about 300 meters (1,000 feet), was big enough to ensuredestruction of the target.

It was another, likely more effective, approach to ensuring destruction of atarget -- even an entire bomber formation -- in a collision-course intercept.The Genie's powerful rocket motor allowed a Scorpion to attack an intrudermoving at high speed at a substantially higher altitude. However, withimprovements in guided AAMs, the Genie would become obsolescent, andenthusiasm for nukes eventually faded out of air defense. They were just tootroublesome to handle, and the fact that use of a nuke in any context wouldhave required approval from the White House made them effectively useless.Even at the peak of "nuclear insanity", there were plenty who were skepticalof the idea of spreading nukes to hundreds of installations and makingsecurity a nightmare, not to mention relying on nukes as a standard militarydoctrine.

In 1963, ten F-89Js were modified as piloted "targets" of a sort, havingtheir radar removed, to be replaced by ballast, and fitted with underwingtanks. These "DF-89J" machines were flown by USAF pilots to probe US ArmyNike surface to air missile defenses in Japan. Another F-89J was fitted withtest kit to be used in angle of attack trials at Edwards AFB.

[4] SCORPION SUMMARY / SPECIALS & UNBUILT VARIANTS

* A total of 1,042 Scorpions of all types was built. It was never exportedand the Air Force, plus its auxiliary components, were the sole operators.The table below gives variants and production:

 variant built mod notes ______________________________________________________________________ XP-89 1 initial prototype XF-89A 1 second prototype F-89A 8 20-mm cannon armament; mostly for evaluation F-89B 40 improved F-89A, mostly for evaluation F-89C 164 improved F-89B F-89D 682 rocket armament, E-6 fire control system YF-89E - 1 F-89C modified with Allison YJ-71 engines F-89H 156 Falcon missile capability F-89J - 350 Genie rocket capability ______________________________________________________________________ TOTAL 1,052 ______________________________________________________________________

The F-89 was the mainstay of North American air defense during the 1950s; itwas a sturdy, pedestrian aircraft, a "missile truck", a true interceptor andnot really a fighter. It never saw any combat. It was gradually withdrawnfrom front-line service later in the decade, being replaced by the ConvairF-102 Delta Dart. However, Scorpions served with Air Force Reserve and AirNational Guard units until as late as 1969. The F-89 had a surprisingly longservice life, impressive for a machine that was more or less afirst-generation combat jet.

* From the early 1950s Northrop considered a supersonic successor, originallystarting with a F-89 with a delta wing and moving from there, initially tothe "N-126" -- a tailed-delta design, with an afterburning engine under eachwing and bicycle-type landing gear. The only major thing it owed to theScorpion was the F-89H's E-9A fire control system.

The N-126 concept then led to the "N-144", essentially the same configurationbut scaled up, with twin engines in a pod under each wing. Northrop alsoconsidered the "N-149", not quite as big a scale-up from the N-126, withtwin, more powerful engines. Nothing came of these ideas; US aircraftmanufacturers generated a dizzying array of designs for advanced interceptorsthrough the 1950s and into the 1960s, but the F-106 turned out to be thesolution the USAF settled on and kept. It seems that the quest for a morepotent interceptor was driven by the potential threat of high-speed Sovietjet bombers; from the late 1950s, however, long-range missiles became thestrategic strike platform of choice, rendering the race between manned bomberand interceptor less irrelevant.

[5] FOOTNOTE: THE CURTISS XF-87

* The loser in the Air Force competition that produced the Scorpion, theXF-87 Blackhawk, had a few distinctions of its own. It was one of the fewfighters ever fitted with four engines, and it was the last fighter evermade by Curtiss.

The Blackhawk evolved out of studies performed during the war by Curtiss fora twin engine, jet powered ground attack aircraft designated the XA-43. InNovember 1945, the project was redefined into the Blackhawk all weatherinterceptor. After long delays in development, the XF-87 Blackhawk took tothe air at Muroc on 1 March 1948. The Blackhawk was a big aircraft for afighter, with a length of 19.15 meters (62 feet 10 inches), a wingspan of18.3 meters (60 feet), a height of 6.1 meters (20 feet), an empty weight of11,760 kilograms (25,930 pounds), and a fully loaded weight of 22,635kilograms (49,900 pounds).

The Blackhawk featured straight mid-mounted wings and tricycle landing gear.It was a two-seat aircraft, with the flight crew sitting in side-by-sideunder a bubble canopy, and was powered by four Westinghouse XJ34-WE-7turbojets, with 13.3 kN (1,360 kgp / 3,000 lbf) of thrust each, fitted inpairs in nacelles mounted under the middle of each wing. Four turbojets wererequired because of the low thrust offered by the engines available at thetime. The aircraft was to be fitted with four 20-millimeter cannon in aswiveling nose turret installation, like that evaluated on the F-89A.

The Blackhawk was arguably a very elegant aircraft, but flight evaluation ofthe prototype showed it to be underpowered. However, more powerful engineswere available at that time, and Curtiss proposed replacing the four XJ34engines with two General Electric J47-GE-7 turbojets with 26.7 kN (2,720 kgp/ 6,000 lbf) thrust each.

 CURTISS XF-87 BLACKHAWK: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 18.29 meters 60 feet wing area 55.74 sq_meters 600 sq_feet length 19.15 meters 62 feet 10 inches height 6.1 meters 20 feet empty weight 11,762 kilograms 25,930 pounds MTO weight 22,635 kilograms 49,900 pounds max speed at altitude 965 KPH 600 MPH / 520 KT service ceiling 12,500 meters 41,000 feet range 1,620 kilometers 1,000 MI / 870 NMI _____________________ _________________ _______________________

The Air Force was interested, ordering 57 F-87A interceptors and 30 RF-87Areconnaissance aircraft. Unfortunately for Curtiss, although flight tests ofthe XF-87 helped iron out bugs and the aircraft seemed promising, in the faceof limited resources the Air Force was forced to put all the money on theF-89. All orders for the Blackhawk were canceled on 1 October 1948.

Curtiss tried to promote an attack variant with twin turboprops, but nobodybit. The XF-87 four-engine prototype was the only Curtiss Blackhawk to everfly. Curtiss had once been a leader in American aviation, but the companyculture had fallen apart by World War II, the firm churning out aircraft thatwere mediocre, like the P-40; or bug-ridden, like the C-46; or just plainnightmares to get right, like the SB2C Helldiver. The Blackhawk was one ofthe last gasps of breath of a dying giant.

[6] SOURCES, COMMENTS, & REVISION HISTORY

* During the 1950s, for reasons described above, standard doctrine for theUSAF was to arm interceptors with loads of unguided FFAR rockets. They wereknown to be inaccurate, with the usual comment of those who worked with therockets being: "It was a wonder they could hit anything with them." Onetrue tale of the Scorpion is particularly educational in this regard.

On 16 August 1956, a Grumman F6F-5K Hellcat target drone was sent aloft fromthe Point Mugu Naval Air Station, in southern California up the Pacific coastfrom Los Angeles. The Hellcat had been one of the great US Navy fighters ofthe Second World War, but by the 1950s it had been reduced to the status of atarget, painted red and flying under radio control.

Or at least, this Hellcat was supposed to be flying under radio control.Although the range area was over the Pacific, the Hellcat decided to headtowards Los Angeles instead. Nobody wanted the unpiloted aircraft to crashinto a school or whatever, so two US Air Force F-89Ds were scrambled fromOxnard Air Force Base, not far from Point Mugu, to destroy the wanderingdrone. The two F-89Ds carried a total of 208 FFARs in all.

The Hellcat actually passed over Los Angeles; of course, shooting it downover the city would have been lunacy, so the interceptor crews could onlyhold their breath and wait for the drone to fly clear. It finally decided toorbit over the town of Santa Paula, where the interceptor crews tried to getopportunities to take a shot at it. They were using automatic fire-controlmode, but the fire-control system malfunctioned and they didn't get a singlerocket off.

Then the Hellcat decided to meander for a time, eventually turning backtowards Los Angeles. The Scorpion crews switched to manual fire control andloosed salvos of rockets at the drone. The rockets missed the Hellcat,falling to the ground to start a raging brush fire. The Scorpion crews triedagain, with no better luck, starting two more brush fires -- one of themfueled by oil rigs in the unintended target area.

Finally, as the drone headed toward Palmdale, the Scorpions fired their lastrockets at it. They missed again. This time, the rockets fell into the townof Palmdale. A piece of shrapnel smashed through the living-room window ofone house, passing through a wall to end up in a cupboard. Another fragmentpassed through a garage and home. A car's front end was shredded when arocket fell in front of it. Astoundingly, nobody was hurt. Explosiveordnance disposal teams from Edwards Air Force Base picked up 13 dud rocketsfrom around Palmdale. It took hundreds of firefighters two days to put outthe three brush fires, after the blazes had consumed hundreds of acres.

The Hellcat finally wandered over the Mojave Desert near Palmdale, where itran out of fuel, falling to earth in an uninhabited area but cutting threepower lines doing it. By the records, the incident seems to have attractedlittle public attention.

* I know the F-89 well, as the Air National Guard operated it from GeigerField near Spokane when I was little. I still have fairly clear memories ofwatching the high-tailed Scorpions zooming overhead; in fact, it was likelythe first aircraft I was ever able to recognize.

* As concerns copyrights and permissions for this document, all illustrationsand images credited to me are public domain. I reserve all rights to mywritings. However, if anyone does want to make use of my writings, justcontact me, and we can chat about it. I'm lenient in giving permissions,usually on the basis of being properly credited.

* Sources include:

• THE ILLUSTRATED HISTORY OF FIGHTERS, edited by Bill Gunston, Exeter Books, 1989.
• AMERICAN SECRET PROJECTS by Tony Buttler, Midland Books, 2007.
• "Northrop F-89 Scorpion Variant Briefing" by R. Dorr, WINGS OF FAME, Volume 6 / 1997, 128:147.

* Revision history:

 v1.0.0 / 01 nov 12 v1.0.1 / 01 oct 14 / Review & polish. v1.0.2 / 01 sep 16 / Review & polish. v1.0.3 / 01 aug 18 / Review & polish. v1.0.4 / 01 jun 20 / Review & polish.