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Aviation History
1955
1955 - 0444.PDF
444 FLIGHT, 8 April 1955 JODEL D.112 AND DRUINE TURBI . . . as for cross-country sporting flying. As might be expected,M. Druine's experience as a flying instructor has shown up in many practical ways. At the time of the construction of the prototype Turbi there wasan official move afoot in France to encourage the Beaussier engine, which is made mostly from Citroen car-engine parts, and as aresult this engine was fitted to the Turbi. Alternative engines with more power include the Walter Mikron and ContinentalA65, with which the aircraft performance is greatly enhanced. The general lines follow those of the Turbulent single-seater, andit is equally intended for simple construction by amateurs. In view of the present U.K. interest in the type it is described insome detail. The mainplane is a rectangular cantilever structure withrounded tips, and leading-edge letter-box slots fitted over nearly fifty per cent of the span. It is constructed entirely of wood andis a two-spar structure, the main spar being located at 25 per cent chord and the auxiliary spar at 62.3 per cent. The main sparis of box type with laminated booms and ply webs. The I-sec- tion rear spar locates the trailing portion of the ribs, as well assupporting the ailerons. The trellis-type ribs are all made in the same jig and are in two pieces, one located in front of the mainspar and the other aft. Although there is not much torsion using the N.A.C.A.23012 aerofoil section, the leading edge is coveredwith ply, making a substantial torsion box. The slotted ailerons are supported on two inset hinges, one of which forms part ofthe actuating control. Except for the ply leading-edges they are covered with doped fabric. Seating is arranged in tandem, the cockpit width beingapproximately two feet. Two slab sides, a flat bottom skin and a curved top decking form the fuselage shape, the rear deckingbeing fabric-covered for lightness. A substantial main bulkhead locates the wing attachment while an equally substantial frontbulkhead supports the engine mounting structure. The tail unit has a simple non-adjustable tailplane which isply-covered, while the elevators are of similar construction to the ailerons and rudder. The elevators are cable-operated to thecentre hinge fitting and a trimming tab is operated by a Bowden- type control operated from a knob on the throttle box. The finis built integrally with the fuselage and has a ply covering, a dorsal fin fairing being added after the tailplane assembly. Two articulated vee structures with spring shock-absorbers inthe main struts form the undercarriage, which is fitted with 15- inch diameter wheels, without brakes, in the standard form.The dual control-columns operate on a common torque-tube located in the fuselage and running fore and aft. Control runsare of flexible cable except those for the rudder, which are of piano wire. Engine, fuel-cock and trimmer controls are fittedin light-alloy hand boxes on the port side of each cockpit, inter- connection between cockpits being by means of dural tubes. Thetrimmer transmission is by a piano wire running in a conduit. A simple stop fitted in the boxes prevents the throttle being openedwith the fuel turned off. The engine fitted to the aircraft examined was manufacturedby Moteurs Beaussier of Montlucon, Allier. It is an inverted four-cylinder air-cooled unit giving some 50 b.h.p. at take-off.Maximum r.p.m. are 2,800 while maximum continuous cruising is at 2,375 r.p.m. for an output of 35 b.h.p. Normal cruising isat 2,300 r.p.m. The airscrew, a fixed-pitch Merville 865 type of 5ft 3in diameter turns at crankshaft speed, while fuel is consumedat the reasonable rate of 2\ gall/hr. Two arms, supported on each side by two struts, form theengine mounting which is of tubular construction, four rubber blocks being fitted to absorb the vibration. The engine is fairedin a tipsy-style aluminium cowling with a nose cowl, top and bottom panels and side panels held by quick-release fasteners.The airscrew is fitted with a large spinner. Fuel supply is from a tank inside the front top decking while oil is carried in a simple The smooth lines of the Turbi give a false impression of its size. It is in fact rather smaller than it appears to be. The Druine Turbi open two-seater which has been approved for amateur construction in Britain. Work on this country's first Turbi was started recently by a Popular Flying Group at Hatfield. tank on the forward face of the fire-proof bulkhead. For baro-graphs, valises and other small impedimenta there is a small locker provided behind the rear cockpit. As with all French air-craft holding normal-category Certificates of Airworthiness, there is a fire extinguisher fitted under the engine cowling with a con-trol and warning disc in the cockpit. In designing the Turbi there has been no wish to produce anaircraft of extraordinary performance. The one hope has been to produce an easily constructed two-seater to be made fromplans. For construction no expensive equipment or workshop processes are necessary. The one-piece spar with its laminationsis assembled on a flat bench about 30ft long, the use of two straight planks enabling the laminations to be glued up simply,and the wing assembly is carried out on three trestles. The total sum spent on such equipment for the prototype cost only tenpounds and all this was not lost, the planks and trestles not being consumable. The two fuselage-sides are made on the same layout andassembled inverted, like a model aircraft, with the main bulkheads and fin-post. The detail assembly follows, after which the frontand rear decks are fitted. The tail-unit ribs are some of the simplest items in the struc-ture, being simple shapes cut from the flat, this method being quicker than building up with strips and ply, and carrying littleweight-penalty. All structural materials are easily obtained; spruce for main members, birch or gaboon ply for skins andmild steel for fittings. Flying Impressions.—Both the Jodel and the Turbi are popularwith amateur pilots for their simple flying and economy of operation. Both fly pleasantly but a detailed comparison betweenthe two is not truly representative due to the difference in power between the two examples tested. The Jodel with its Continentalundoubtedly has a better performance than the lower-powered Turbi but, in handling, the Turbi seems to have an edge on theJodel. Both are very simple to taxi and the Jodel has an almosttricycle-aircraft view forward. During take-off the Jodel requires less rudder to hold itstraight than its single-seat ancestor, and with barely any lifting of the tail it flies off cleanly at an apparently flattish angle, givinga good view on the climb. The climb was as claimed with two up, while solo it was good and not of the tottering variety so oftenassociated with low-powered aeroplanes. Clermont Ferrand is 300-odd metres above sea level and in a temperature of 23 deg Cthe initial rate of climb was of the order of 200 ft/min. The recommended climbing speed was given as 80 km/hr (50 m.p.h.),and in this condition it is barely possible to trim to check climb stability. Longitudinally, the stability was marginal on the climb, thepitching resulting from a rearwards displacement of the stick damping out straightway with a return to virtually the originalspeed, while a forwards displacement resulted in the nose slowly going downwards until brought back manually from a steep nose-down attitude. This behaviour was undoubtedly in part due to the marginal trim in this condition. Laterally the stabilitycheck gave positive results from lowering the starboard wing but, with die port wing down, the aircraft left free went into adescending turn to the left. On a directional check the yawing either way corrected itself, due to the rudder having a springcentring device. Level flight gave similar results, while a rate-of-roll check was
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