Grumman's Mohawk......
......an eye in troubled skies.

(Originally published in Flying Review International, Volume 22, No 6, February 1967 )

Eight years ago, on April 14, 1959, with two small, lightweight turboprops whistling shrilly, the first prototype of an extremely unusual little warplane gathered speed down the runway, and climbed for the first time into the sky above Bethpage, Long Island. As unique in concept then as it remains in fact today, the Mohawk, as Grumman's G-134 front-line surveillance aircraft had already been dubbed, was, aesthetically, no prize winner. Indeed, its appearance, with its bulbous nose, high-mounted, upward-tilted engines, stubby wing and trio of oversize vertical tail surfaces, was decidedly ungainly, but the Mohawk was soon proving positive the old adage that handsome is as handsome does, with Grumman's senior experimental test pilot Ralph Donnell throwing it about the sky like an aerobatics trainer. To the conventionalist the Mohawk may not have looked right, but that it was right could be seen by all two years after its debut when the first Mohawk to reach Europe dazzled crowds at the 1961 Paris Show with its fantastic maneuverability and short-field performance.

It has for long been appreciated, of course, that effective airborne surveillance of the battle area is a pre-requisite to success in ground combat operations, yet the Mohawk, the first integrated all-weather system capable of maintaining round-the-clock visual, photographic, radar and infra-red surveillance, while operating from short, unimproved strips in forward areas with a minimum of support equipment and personnel, is still the only aircraft in its category extant, and its effectiveness has been proven by five years of operation in Vietnam.

A Radical Step Forward

The Grumman G-134 Mohawk was originally conceived under a joint US Army-Marine Corps program which called for a radical step forward in the techniques of battlefield reconnaissance. As its primary task was to be reconnaissance of the combat area it had to be capable of operating from small fields and unprepared surfaces as close to the front-line as possible, necessitating STOL qualities. The demand for all-weather, round-the-clock surveillance dictated an airframe capable of accommodating a variety of systems, and in order to survive in the skies above battlefields it had to possess sufficient maneuverability to enable it to evade enemy fighters. Two crew members were a prerequisite as a single pilot could not concentrate at one and the same time on flying at low altitude and studying for enemy movements and terrain over which he was flying, and a twin-engine configuration was mandatory to reduce vulnerability to fire from ground weapons. Furthermore, adequate protection had to be provided for the crew, systems and fuel tanks; US Marine Corps participation in the program dictated provision of strong-points for offensive weapons loads, and modern wide-dispersion tactics dictated substantial radius of action and ferry range, and, in consequence, provision for considerable quantities of fuel.

Such demands rendered it patently obvious that the day of the small, light airplane traditionally associated with the battlefield surveillance role was past, yet the very nature of the task to be undertaken by its successor placed strict limitations on both size and weight. Such were the problems facing Grumman's design team when, in the mid fifties, it began work on turning the joint Army-Marine Corps concept into hardware. After discarding a number of more exotic configurations, the Grumman team finally evolved a fairly small mid-wing monoplane of relatively conventional configuration possessed by a pair of lightweight turboprops, its short-span wing carrying large-area Fowler flaps and leading-edge slats extending over the entire span, the pilot and observer being seated side-by-side close up to the fuselage nose, with deep, bulged side windows to provide the necessary downward view.

As the G-134, this configuration was submitted and accepted, and in 1957 the first US Army contract was placed with Grumman through the Navy Bureau of Aeronautics which was administering the program on behalf of the Army and Marine Corps, calling for nine test and evaluation aircraft under the designation YAO-1AF, later changed to YOV-1A. Prior to the debut of the first YOV-1A, however, US Defense Department economy measures had necessitated the withdrawal of the US Marine Corps from the program, resulting in several changes. The water-ski undercarriage which would have enabled the Mohawk to descend on water and taxi to a beach at a minimum speed of 23 mph (37 km/h) was discarded as the Army concluded that it did not require this capability, but although the tasks envisioned for the Mohawk were now strictly limited to the sphere of reconnaissance, the wing strong-points dictated for the more aggressive applications foreseen by the US Marine Corps were retained.

The nine YOV-1A test and evaluation aircraft (57-6463 to 6467 and 57-6538 to 6541) made possible an accelerated test program which quickly established the Mohawk's flight and performance characteristics, a maintenance requirement of only five man-hours per flying hour, and its ability to operate from grass strips, dirt roads and other unimproved surfaces. All nine test aircraft had been completed by the end of 1959, by which time the Army had placed contracts for 18 OV-1As (59-2603 to 2620) and 17 OV-1Bs (59-2621 to 2637), supplementing these in 1960 with orders for a further 25 OV-1As (60-3720 to 3744) and 17 OV-1Cs (60-3745 to 3761), bringing Mohawk production contracts to 77 aircraft. The speed with which a production line was established may be gauged from the fact that 40 OV-1 Mohawks, including the first OV-1Bs, had been flown by the end of 1960, barely more than 20 months having elapsed since the YOV-1A's first flight. Successive contracts were placed for OV-1Bs and 1Cs, a total of 152 Mohawks having been built up to the end of 1963, by which time the unique Grumman aircraft had seen nearly two years' US Army service, and orders placed for all versions (including the YOV-1As) to the end of the 1966 Fiscal Year total 268 aircraft, with approximately a further 100 programmed though 1970.

Three Basic Versions

From the outset of development the Mohawk was envisaged in three basic versions which, between them, would provide the capability to observe all facets of an enemy's operations. All three versions possess essentially similar airframes and differ one from another primarily in the systems installed.

The initial model of the Mohawk, the OV-1A is the basic visual-photographic version with either the KA-30 or later KS-61 photographic system, the camera mounted in a mid-fuselage bay being capable of horizon-to-horizon coverage through five lateral positions, and remotely operated from the cockpit. Space is also provided in the nose section for a forward-facing camera, and some OV-1As carry a KA-60 70-mm panoramic surveillance camera system with a rotating prism in this position. The OV-1A model entered US Army service in 1961, being deployed with the 7th Army in Germany in the summer of that year, and in July 1962, the OV-1A arrived in Vietnam with the 23rd Special Warfare Aviation Detachment. Two years later, in 1964, the US Army made an experimental excursion into the field of armed aircraft with the operational use by the 11th Air Assault Division of the 1st Cavalry Division (Airmobile) of the armed JOV-1A Mohawk (the 'J' prefix indicating special test). Making use of the wing strong-points originally introduced into the Mohawk design at the behest of the US Marine Corps, the JOV-1A usually carried a mix of 2.75-in (70-mm) rocked pods and .05-in (12.7-mm) gun pods on two additional pylons outboard of each of the two standard wing stores stations. Provided with the necessary wiring for conventional ordnance delivery and a gunsight, the JOV-1A was operated officially until the spring of 1965 when these aircraft were eliminated from the 1st Cavalry's inventory, subsequently being used by the 73rd Aerial Surveillance Company which had been formed in January 1965 by the combination of the 23rd Special Warfare Aviation Detachment and the 4th Aerial Surveillance and Target Acquisition Detachment which had arrived in Vietnam in the previous year with the first OV-1Bs and -1Cs.

Ostensibly, the OV-1B results from the addition of the APS-94 SLAR (Side-Looking Airborne Radar) system to the OV-1A, the KA-30 or KS-61 photographic system being retained. A number of other changes have been incorporated in the OV-1B, however, which does not feature the dual controls of the OV-1A, being crewed by a pilot and a SLAR operator, the latter being seated to starboard. Apart from the SLAR housing, an 18-ft (5.5-m) fiberglass pod slung asymmetrically beneath the starboard fuselage side, the OV-1B has an APN-129 Doppler navigation system which, in conjunction with the SLAR, provides annotated target position data on the sensory film to facilitate film interpretation. An autopilot is provided, and airframe changes include the removal of the airbrakes and an increase in wing span from 42 ft 0 in (12.8m) to 47 ft 10 3/4 in (14.6m). The OV-1B was, incidentally, the first version of the Mohawk to replace the 1,005 eshp Lycoming T53-L-3 turboprops with the 1,150 eshp T53-L-7 with which all Mohawks are now being re-engined.

Physically the OV-1C is the same aircraft as the OV-1A, and retaining the KA-30 or KS-61 camera system it has an infra-red sensor mounted in the underside of the aft fuselage, and single pilot controls with the systems operator seated to starboard. The OV-1C is the subject of both current production and modification contracts, an initial batch of 31 aircraft being in process of modification to latest production standards at Grumman's Stuart, Florida plant. The first of the modified OV-1Cs were returned to the US Army during the summer and are already being deployed in Vietnam. Whereas earlier OV-1Cs serving in Vietnam with the 73rd Aerial Surveillance Company and elsewhere have a UAS-3 infra-red sensor, the latest version has the modified AAS-14A infra-red detection set and modified ART-41A infra-red data transmitter which sends the film data in real-time over conventional FM-FM links. This capability permits strikes to be mounted against targets detected by the OV-1C within minutes of them being spotted. The more advanced infra-red sensor is allegedly capable of detecting as small a heat source as an hibachi cooking fire, a recoilless rifle, or a truck that has been parked for as long as 16 hours.

The OV-1C modification program also covers the replacement of the T53-L-3 turboprops by the uprated -7, the deactivation of the wing leading-edge slats, and the installation of the latest communications and navigation equipment, including Doppler. A closed-cycle cooling system is provided for the infra-red and additional armor protection is provided for the crew members. The flare ejection pods similar to those carried by the OV-1A are currently retained, although consideration is being given to their substitution by a photo flash system.

Mohawk Features

As the principal function of the OV-1 is observation design accent has been placed on maximum crew visibility, and this has been achieved by use of a bubble-type canopy providing either crew man with unobstructed vision 20° down over the nose of the aircraft along the centerline of the seats. By moving the line of vision outboard into the bulged side hatches the downward visibility is increased to the extent that the lines of sight of the pilot and observer converge at a point 36 ft (11 m) below the aircraft. A transparent hatch in the roof provides unobstructed vision directly overhead. The layout of the cockpit itself is exceptionally good, maximum utilization being made of available cockpit space, everything being comfortably within reach, and sloped .15 deg forward of the vertical, and a central pedestal provides one set of control levers equally accessible to both pilot and observer. A double width lower console between the pilot and observer accommodates the communications, navigation and photographic panels, and a single width overhead console between the two crew members houses the IFF, air conditioning and lighting panels, with "eye-brow" panels above the windshield carrying the engine, fuel and electrical master panels. The observer's position is designed to accept electronic surveillance equipment, and the control stick and rudder pedals standard in the OV-1A are removed in the OV-1B and -1C to permit installation of the necessary monitors and control panels.

Both crew members are provided with Martin-Baker Mk 5 ejection seats which provide for escape from all altitudes within the Mohawk's range and at speeds from 70 mph (113 km/h) to 520 mph (837 km/h), ejection normally being effected through the frangible roof hatch, although this may be pneumatically jettisoned if time permits. In Vietnam some difficulties have been experienced with low-altitude ejection as, after the first crew member ejects, the aircraft tends to tilt to one side, resulting in a reduction of the apogee attained by the last crew member to leave the aircraft, and on several occasions this had had fatal results. A total of 246 LB (111.5kg) of armor protection surrounds the cockpit, this comprising a 1-in (2.54-cm) thick flack and bullet-resistant windshield, a 1-in (6.3-mm) dural floor, and steel mesh flak curtains fore and aft of the cockpit bulkheads.

Flight controls are largely mechanical, conventional pedals controlling the rudders through a simple system of rods and straight cable runs between bell cranks, the central rudder having an anti-balance tab, this giving a centering force at small deflection angles. A conventional control stick actuates the elevators through a similar system of tension members between bell cranks, duplicated, widely-spaced runs being provided, and the elevators have full-span trim tabs. The ailerons are spring-tab-operated, the tabs being mechanically connected to the stick, and rods provide direct mechanical connection between the ailerons which also have trim tabs. A built-in gust lock system controlled by a lever in the cockpit blocks the throttles and immobilizes the rudders and elevators. The air brakes located on the sides of the fuselage (on the OV-1A and -1C models), together with the three-position flaps, the undercarriage, wheel brakes and nose-wheel steering are hydraulically powered.

The two Lycoming T53-L-7 turboprops are single-stage free-turbines driving 10-ft (3.05-m) diameter Hamilton Standard airscrews incorporating variable pitch, full feathering, reverse pitch, synchronizing and synchrophasing. No armor is provided around the engine nacelles which are mounted above the wings, but the fighting in Vietnam has underlined the reliability of the twin-engine configuration employed by the Mohawk, numerous cases having occurred of an engine or fuel line being shot out and the OV-1 regaining its base safely on the power of one engine. The engine nacelle allows easy access to the engine, controls and accessories, and the entire power plant package, including airscrew, engine accessories and engine mount with vibration isolators may be removed as one assembly and is interchangeable port and starboard. This interchangeability is, incidentally, carried to the outboard fin-and-rudder assemblies, the tailplane and elevator sections, and the main undercarriage legs.

The fuel system is simple and of proven reliability, all internal fuel being housed in a single 297 US gal (1125 l) self-sealing tank in the fuselage above the wing structure by which it is sheltered from groundfire. Internal fuel is supplemented for long-endurance missions or ferrying by a 150 or 300 US Gal (568 or 1136 l) tank beneath each wing, and all tanks may be filled via 3-in (7.62-cm) gravity filler units in each tank or by single-point pressure fueling.

Extreme care has been given in the design of the Mohawk to provide maximum accessibility for servicing, and wherever possible, access is provided directly from the ground with minimum use of work stands. Access to the number one equipment compartment is through the nose-wheel doors; to the number two equipment compartment under the wing through a door on the port side of the fuselage, and to the number four equipment compartment through doors on either side of the aircraft. Access to the camera compartment is directly from the ground through the two camera doors, and the single fuel tank is readily replaceable through two removable panels on the top of the fuselage.

The Mohawk exhibits a high degree of maneuverability and precise controllability throughout its performance which, with flaps extended and inboard ailerons in use, can extend from some 20 mph (32 km/h) below stalling speed to some 300 mph (483 km/h) with flaps, slats and undercarriage retracted. Prompt response and gentle stalling characteristics contribute to the Mohawk's excellent flying qualities and ease of handling; its turning radius of 355 ft (108 m) means that it can be maneuvered within extremely small confines for close support of observation purposes; its leading-edge slats and large-span flaps permit the basic Mohawk without external stores to take-off and clear a 50-ft (152-m) obstacle within 880 ft (268 m), and its sturdy undercarriage with low-pressure tires allow it to operate from ploughed ground, deeply rutted surfaces or rough grass. Small wonder that the US Army regards the Mohawk highly and has programmed production through 1970.

OV-1C Mohawk Specifications

Power Plants: Two Lycoming T53-L-7 free-turbine turboprops each rated at 1,150 eshp (1,100 shp plus 124 lb/56.3 kg residual thrust).
Weights: Empty, 10,370 LB (4,704 kg); loaded (clean), 13,040 LB (5,915 kg); loaded with two 150 US Gal (568 l) external tanks, 15,399 LB (6,985 kg).
Performance: Maximum speed, 308 mph (496 km/h) at 5,000 ft (1,520 m); maximum permissible diving speed, 450 mph (724 km/h); maximum cruise, 297 mph (478 km/h); economical cruise, 263 mph (423 km/h); stalling speed, 72 mph (116 km/h); initial climb rate, 2,670 ft/min (13.56 m); service ceiling, 30,000 ft (9,150 m); service ceiling on one engine, 13,000 ft (4,265 m); range (internal fuel), 441 miles (710 km) at 230 mph (370 km/h) at 5,000 ft (1,520 m); maximum range with two 150 US Gal (568 l) tanks, 1,330 miles (2,140 km); take-off distance to clear 50 ft (15.2 m), 950 ft (290 m); landing distance from 50 ft (15.2 m), 787 ft (240 m).
Dimensions: Span, 42 ft o in (12.8 m); length, 41 ft 0 in (12.5 m); height, 12 ft 8 in (3.86 m); wing area, 330 sq. ft (30.65 m 2).