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Aviation History
1961
1961 - 0911.PDF
- J*i - "U* *-(. FLIGHT, 6 1961 11 Lambert and Ralph Donnell after the fight. Note the deep, bulged side- windows and numerous inscriptions, one of which refers to the Martin- Baker Mk 5 ejection seats. The extended foot-step below the left-hand danger sign pops out when the other foot-step cover is pressed in by hand shock-mounts, are interchangeable port and starboard. All con- trol surfaces carry their own angular scales for rigging in the field without special sector boards. De-icing is by pneumatic boots for fins, tailplane and outer wings, by alcohol for the windscreen, by electric mats for the propeller blade-roots and intake rings and by hot air for the intake spokes. Hydraulic wipers and hot-air demisting are provided for the windscreen. Air-brakes, flaps, undercarriage, wheel brakes and nosewheel steering are all hydraulically powered. Flight controls are largely mechanical, rods and straight cable runs between bell-cranks connecting the pistol-grip sticks and control surfaces. There are duplicated, widely spaced runs to the elevators, which have full-span trim tabs. The ailerons also have trim tabs and are operated through spring tabs. An anti-balance tab has been added to the middle rudder to provide a centring force at small angles of deflection, but a special cable circuit causes the tab to fine off to zero deflection as full rudder deflection is reached. This relieves high forces at large angles. A centring spring is also applied to the rudder pedals, to provide some feel for nosewheel steering. The brakes are toe-pedal operated. A gust lock, which also blocks the throttles, immobilizes rudders and elevator, the ailerons remaining free. Flap control is by shaped lever through a follow-up system with a detent at the 15° take-off position. Any angle can be selected. Undercarriage control is straightforward, with an electric interlock with manual override to prevent retraction when the oleos are compressed. Systems are quite simple, with a starter generator on each engine and two alternators, together with a battery allowing starting with- out external power. Fuel is fed through two pumps to both engines from the main tank and external fuel is transferred to the main tank when a four-position switch is moved to the "right," "left" or "both" position. Refuelling is either by gravity or by pressure and defuelling is possible. Float gauges in the external tanks and a capacitance system in the main tank indicate, on one dial, joint contents on a counter or main-tank contents by a needle; individual tanks may be gauged by moving a selector switch. The Lycoming T53-L-3 engines are most intriguing. The gas producer unit is started by switching on the starter and pressing an ignition button at 10 per cent r.p.m. until the j.p.t. gauge shows the fire has lit. At the 40 per cent idling speed, the propeller turns at 200 r.p.m. if feathered and at 500 r.p.m. in normal pitch. The propeller is an entirely separate unit, constant-speeding hydraulically in the conventional way. Feathering on the ground avoids slip- stream and provides convenient braking for stopping rotation. A propeller can even be held still against the side of a vehicle and the gas producer run at 60 per cent r.p.m. while nut shells are fed in to clean the engine. If feathered, the engine and propeller can also be run with the access panel underneath the nacelle hinged down while adjustments are made. Engine controls sound difficult, but are simple to use. The propeller condition levers govern r.p.m. between the maximum of 1,700 r.p.m. and minimum of 1,100 r.p.m., a good quiet cruising setting being 1,400. If the levers are pulled back past a detent, the high-pressure cocks are closed and a further pull back produces feathering. The normal propeller oil system will take the propeller back to 125 r.p.m. and an auxiliary pump takes over at below 400 r.p.m. to feather or unfeather. The latter is produced only when the feathering latches are removed after pressing a button. Power levers control the gas producers and work like normal throttles. They have detents at the "military power" setting and at a flight idle and ground idle setting, the former being intended purely to mark the point from which full power can be attained in 6sec instead of 12sec. If the levers are further pulled back and up, the propellers go into reverse pitch and full power is progressively applied. Limiting propeller r.p.m. are 2,200, after which the turbine wheel might shed blades. Power output is principally gauged by torque meters, the allowed maximum of 731b/sq in being exceeded at sea level only on very cold days. Propeller r.p.m., gas producer r.p.m. and j.p.t. gauges complete the engine instruments. An automatic feathering system, armed by a switch, ensures that the appropriate propeller feathers immediately if more than military power is selected and torque falls below lOlb/sq in. Cockpit layout is exceptionally good, with clear instrumentation and everything very comfortably in reach. Heating and ventilation are provided, together with gaseous oxygen, but no pressurization, for flight at higher altitudes. The Martin-Baker seats have electric height adjustment, lever lock instead of safety pins and American harness, but are otherwise the standard 80ft/sec, 60kt, runway-level units. Normal ejection is through the roof panels and sliding sun- blinds, but the roof may be pneumatically jettisoned if time permits. Visibility is excellent, particularly down at 20° over the nose and straight down through the side windows. I flew with Ralph Donnell when the Mohawk had full internal fuel and weighed about 12,5001b with all its lAF-type equipment. Ralph taxied out using nosewheel steering and turned about one wing-tip. He then switched the steering off and turned about one wheel with brakes alone. The steering is limited (relatively) to avoid screwing a wheel into soft ground by pivoting on it. Simple cockpit checks included 5° right aileron trim to counteract torque. In the controls I found the typical clunking, springy feel of spring-tab ailerons and a distinct centring feel on the elevators, which also seemed to have some inertia. With clearance from the tower, Ralph lined up and handed straight over to me. 1 opened the throttles progressively and we began to tear off down the runway. Briefly I noticed that the nosewheel steering was extremely pleasant before we reached 60kt and I began to feel for solid air on the controls. I inched the stick back until we rotated into the air at 80kt without any real feel and settled, as instructed, to climb at lOOkt. When Ralph moved the levers, the gear came in with a hefty thumping and the flaps retracted, but only slight trim changes resulted. Reduced to military power we rocketed upwards at 2,000ft/min, with lots of runway still somewhere under our backs. I noted the rate of climb and Ralph applied full power to send us uphill at least half as fast again. The Stuttgart runway was still The Mohawk AO-IAF cockpit with complete space provision on the right for the side-looking radar of the AO-IBF version. Flight instruments include Collins FD-105 flight system. Engine-starting and fuel controls are in the eyebrow panel and all levers are grouped on the quadrant, ahead of a long, central radio and camera-control console. The striped gust-lock plunger is extended ahead of the throttles. The "bone domes" with boom microphones are normal wear for low-level missions
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