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Aviation History
1961
1961 - 0910.PDF
10 FLIGHT,6 July 1961 GRUMMAN AO-1AF MOHAWK in the Air BY MARK LAMBERT AEROPLANES are definitely becoming more and more inter-esting to fly, especially when they pack the powerful punchof lightweight turboprops. The Grumman Mohawk, which dazzled the spectators at Paris, is probably the most un-usual of all these intriguing animals and I willingly trekked out to Stuttgart to have a good go at it recently. Because of its remarkable range of performance, the Mohawkcould perhaps be described as two different aircraft hung on a reconnaissance system, with a co-ordinating office up front fortwo eager humans. With flaps, slats and undercarriage retracted it can attain 258kt in level flight at 5,000ft and fly for more than twohours at 200kt on internal fuel alone. Two external 150 US gal tanks virtually double this endurance. Autopilot, full civil andmilitary radio aids and Doppler radar give the Mohawk all- weather capability and its three alternative reconnaissance systems,camera, high-definition side-looking APS-94 radar or UAS-4 infra-red—fitted respectively to AO-1AF, AO-1BF and AO-1CFversions—can produce pictures which are immediately developed and presented in the cockpit as well as being transmitted to basewithin seconds. The APS-94 "can spot a motor-cycle moving at 3 m.p.h." Further details appear on page 13. When the flaps are extended and inboard ailerons come intoplay, the Mohawk becomes an entirely different aircraft, able to manoeuvre with startling ease at speeds up to 20kt below the cleanstalling speed and to operate from rough, short strips, for which purpose the undercarriage will absorb sinking speeds of 17ft/sec atmoderate weights. The airframe is stressed for 5g positive or 2g negative. During one early test flight, a rudder came off during adive at 39Okt, pushed the elevator hard up and forced the aircraft into a 9|g pull-up. The airframe stayed in one piece and the pilotwas able to land. Ralph Donnell, senior experimental test pilot of Grumman,flew the Mohawk at the Paris Salon and treated the aircraft like an aerobatic trainer, doing stall turns with one engine throttledback, loops and rolls and very short landings. Subsequently he spent his days demonstrating all over the American area of Germany,flying at two or three military airfields every day. At Grafenwohr, a complete armoured division paraded in 3,400 vehicles and theMohawk then landed on the ground over which they had rolled. Visits were made to Verona and Vicenza in Italy, for the SouthernEuropean Tactical Forces, and the Mohawk was demonstrated to the German authorities at Bonn. For some time the aircraft wasbased on Stuttgart where it carried out an "orientation program" for the US Seventh Army, with which the aircraft is now stationed.By September there will be 11 US Army Mohawks in Germany, and 31 by the end of the year. No 150 of the series 'Flight" photographs The particular Mohawk I flew was the 57th production machine,completed early in May. Production rate is four per month, approximately half-and-half AO-lAFs and AO-lBFs. There areonly two AO-lCFs at the moment. Present powerplant is the Lycoming T53-L-3 free-turbine turboprop giving 960 s.h.p. and45 e.h.p. in residual thrust. Grumman now propose the T53-L-7 which will give 1,150 e.s.h.p. with only a slight modification to thepower egg. In a big export drive now being directed at Germany, the company are also proposing the AO-1EF version with alengthened and extended forward fuselage housing a large cabin for freight or a variety of additional equipment. Present US Armyroles are strictly limited to reconnaissance; but more aggressive applications are implicit in the design, and two pylon strong-pointsunder each wing, a vestigial heritage of US Marine participation in the early days of the design, are still available to supplementthe existing tank pylons. The strong-points could take 5001b loads and the tank pylons 1,3701b each. The 5g limit load factor is stillavailable with all pylons loaded and landings with full external load could be made at reduced sink rates. Additional roles then opento the EF version would be target location, target towing, electronic countermeasures and intelligence, missile guidance, chemical,bacteriological and radiological monitoring, training, smoke-laying and freight transport. An interesting feature is that the AF is a "space and power"machine completely fitted with accommodation and wiring for all the additional equipment required for conversion in the field toBF standard. The different designations therefore relate to the equipment actually installed rather than to ultimate capability. The US Army are tickled pink with the Mohawk. It surpasses inperformance anything they have yet had in the front line and the pilots are mustard keen to get converted. Ralph Donnell certainlydid not disappoint them in demonstrations which, in Germany, he made even more enterprising than in Paris. I saw him rolling into afeathered propeller at low level, cruising past at about 60kt looking down at the spectators 30ft below and topping some long zoomclimbs with vertical rolls which clearly showed complete confidence in low-speed handling. Just how confidence-inspiring the Mohawkis, I later learnt for myself in some pretty impressive manoeuvres. Take-offs with the stick hard back up to 50ft and landings with fullreverse thrust were also impressive. I covered the dried ruts from a landing made in very wet ground a few days before in just 80marching paces. The ruts later went through some sizeable pot- holes as well. An amusing demonstration which represents adeliberate and useful capability, was taxying backwards. I spent some time with Ralph Donnell, Grumman and Lycomingtechnicians and US Army pilots as they inspected and serviced the Mohawk and exchanged almost continuous questions and answers.At the same time Ralph showed me the aircraft and explained its many features. The airframe is of conventional structure, buttough, and houses a series of equipment bays fore and aft of the KA-30 camera bay beneath the wing. All internal fuel is held in asingle self-sealing tank in the fuselage above the wing structure, by which it is somewhat sheltered against gun-fire from the ground.The crew are also protected by bullet-proof windscreen panels, a Ain armour-plate floor and steel mesh flak-curtains fore and aft.Outboard fins and rudders, tailplane and elevator sections, main undercarriage legs and the complete power eggs, with cowlings and Triple fins and rudders, and engines mounted well above the wing, are distinctive features of the Mohawk. The free-turbine Lycoming TS3s can be run on the ground or in the air with the propellers feathered
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