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Aviation History
1963
1963 - 0821.PDF
FLIGHT International, 30 May 1963 The Skymaster's panel is well laid out with all flight instruments in front of the pilot and engine instruments and systems gauges on the right-hand panel. The centrally mounted engine controls have the same left/front, right/rear relationship as for the wing fuel tanks CESSNA'S MODEL 336 SKYMASTER... design traditional in all Cessna single-engined aircraft. The oleo- pneumatic nose gear can be steered by the rudder pedals through 15° each side and swivels up to 39° for manoeuvring with a tow-bar. Dual 28V, 30A alternators with self-rectifying units are standard equipment. They are lighter than normal generators and give high output at low r.p.m. Standard seating is for four, but two more full-size seats can be installed in the baggage space leaving a centre aisle adequate for easy in-flight access to any seat. The four main seats recline and can form a continuous couch. Unlike single-engined Cessnas, the Skymaster has only one cabin door, because of the high torsional loads on the fuselage, but entrance should be easy enough with the door sill, uninterrupted by undercarriage or struts, only 21 in above the ground. The baggage compartment behind the third and fourth seats is designed for 3651b and is accessible through a large bag gage hatch on the right-hand side. A shelf attached to the rear bulkhead is useful for carrying odd items, but may be folded to give access to baggage in flight or when fifth and sixth seats are fitted. There is a fresh air heater with a wide range of temperature con trol, and outlets to the cabin at four points as well as a windscreen defroster, plenty of ash trays, interior lights and cubby holes for maps, cameras, magazines and what have you. A central overhead console incorporates the fuel selector handles and the optional oxygen controls. The instrument panel is well laid out with all flight instruments in front of the pilot and engine instruments and systems gauges on the right-hand panel. Radio accommodation is in the centre panel, tailored for the new range of Cessna Crafted 500 Series units. Engine control levers are centrally mounted, with the same left/ front, right/rear relationship as for fuel tankage. Twin needle dials are provided for intake and fuel-injection pressure, but r.p.m. is shown on a single dial by needles moving over separate curved scales. Feathering is by pulling the lever back through a detent. Microswitches in the flexible engine mountings operate a red lamp in the tip of each pitch lever, so that the pilot has an unmistakeable signal to feather the correct propeller after loss of thrust. For night flying, red and white flood lighting is installed in the instrument panel glare shield. Pillar lighting of each dial and the switch panel is optional. The Skymaster first flew on February 28, 1961. Initial testing was done with interim engines, as the final 10-360 engines were not available until May 1961. During this period it was found that more vertical tail area, elevator power and elevator trim were needed. The first aircraft did not have flaps inboard of the booms, and flight tuft studies showed that such flaps would improve ele vator power with flaps down. Additional elevator power was ob tained by restricting the rudder travel to 15° inboard, retaining 21° outboard without sacrificing rudder power. Because most of the elevator is in the propeller slipstream, strong trim changes with power posed a major handling problem which was finally solved CESSNA MODEL 336 SKYMASTER Two six-cylinder Continental IO-360-A giving 210 h.p, each for take-off. Span, 38ft; length, 29.6ft; wing area, 201 sq ft; empty weight (standard aircraft), 2,3201b; gross weight, 3,9001b; wing loading, I9.5lb/sq ft; power loading, 9.3lb/h.p.; fuel capacity, 77.5 Imp gal standard, 109 Imp gal optional. Performance maximum speed, 183 m.p.h.; cruising speed at 75 per cent power at 7,000ft, 173 m.p.h.; stalling speed flaps down, power off, 60 m.p.h.; best rate of climb at sea level, l,340ft/min; service ceiling, 19,000ft; single-engined rate of climb, 355ft/min (on front engine), 420ft/min (on rear engine); single-engine service ceiling, 8,200ft (on front engine), 9,500ft (on rear engine); take-off to 50ft, 1,145ft: landing distance from 50ft, 1,395ft; range (standard tanks) at 75 per cent power at 7,000ft no reserves, 745 miles; maximum range (standard tanks) at 123 m.p.h. at 10,000ft, 945 miles. by introducing a differential bellcrank in the tab control mechanism, giving a coarse movement at high tab settings and fine movement near the neutral setting. Elevator trim is also interconnected with the flaps so that tab deflection reduces from 26° to 10° as the flaps retract from 30° to 15°, thus overcoming most of the heavy trim changes and relieving the pilot of much manual adjustment. Initially, the rear engine was cooled by a controllable scoop located beneath the wing between the boom and the fuselage, but when inboard flaps were added, a scoop with throat dimensions of 6in x 7in was fitted on each side of the fuselage/wing junction, and proved quite satisfactory. Exhaust augmenters were installed during this period to assist normal ram recovery, but their length was restricted by the propeller and a rather difficult airflow path resulted. With a large opening in the aft portion of the cowling, the combination of normal ram recovery and pumping action of the propeller provided adequate cooling, but further tests showed that the propeller blades passing over the rear cowl opening caused un desirable noise in the cabin. This was considerably improved by extending the propeller hub 4.5in and re-shaping the cowling. Cooling of the rear engine was then accomplished with the present scoop on top of the cowling, and a fan attached to the crankshaft. Performance on the rear engine alone is better than that on the front because, Cessna suggest, air at lower velocity entering the pusher propeller results in higher thrust, creation of an "air sink" by the rear propeller tends to reduce airframe drag, and because there is no after body behind the rear propeller. During normal twin-engined operation, the efficiency of the rear propeller is re duced in the high-velocity air from the front propeller. Because of the unconventional configuration, a complete three- degree, three-dimensional flutter analysis was conducted. Early analysis indicated a lack of adequate torsional rigidity in the in board wing section and the thickness-tapered section of wing in board of the booms was increased to constant thickness with a new. deeper spar section affording additional growth potential. All components and mechanisms were subjected to loads and motions that could be anticipated throughout the service life of the aircraft. An entire wing assembly was oscillated under load to determine fatigue effects on fittings. Finally, a Skymaster was built and flown specifically for service testing under varying conditions and with pilots of various degrees of experience. Cessna claim that the Sky master has been more thoroughly tested than any of their other commercial aircraft. Cessna agents in the United Kingdom are Airwork Services Ltd. Hum Airport, near Christchurch, Hants. Regional dealers: Flying Facilities Ltd, Lulsgate Airport, Bristol; W. H. & J. Rogers (Avia tion) Ltd, Great Barford, Beds; Westair Ltd, Squires Gate Airport. Blackpool, Lanes; and Airwork Services Ltd, Perth Aerodrome.
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