European executive.Page 3
The two halves of the cranked wing are bolted directly to the sides of the fuselage (instead of the top) and this change in location has slightly increased the span from that of the flying boat. The relatively thick airfoil section gives good structural strength, although it should be noted that it is washed out to a thinner cambered section at the tip to ensure good stalling characteristics. The design is typically Piaggio, with the main spar at 25% chord - the leading edge has considerable sweep, it should be noted - of an I-section formed with a plate web and backed L-section extrusions for the booms. This spar takes all the bending loads and torsion is catered for by the ribs, the skin and the light folded-sheet rear spar. Attached to the rear spar are the welded steel flap and aileron hinge brackets, each of which carries a self-aligning ball race. The ribs are of the pierced, flange-blank type except in the tank bays - newly introduced on the P.166 but in future available on the P136L too - where they are still of sheet, but with deep channel flanges, to which the outer skin and inner tank shell are riveted. To the torsion box are attached the leading edge with its pierced and flanged ribs, the spanwise members and D-skin, the latter wrapped in sections from top to bottom spar booms. Aft of the rear spar there are shrouds for the plain flaps and slotted ailerons.
The tip tanks are nacelles containing flexible fuel bags and it should be noted that they are not circular in cross section, but are elliptical, with a vertical major axis in order to give the maximum end-plate effect. The structure consists of the two half shells joined together with a floor member.
The fixed tail surfaces are of conventional design, similar to the wing with two folded light alloy sheet spars and pierced, flanged-blank, ribs. The control surfaces have channel section sheet metal spars with a D-skin leading edge and the minimum number of ribs, since the skin is stiffened by impressed beads.
The Lycoming engines are mounted on steel tube mountings cantilevered from a false spar or box structure attached to the main spar. This is at about 50% chord, and the rear spar is interrupted in the plane of this bay. The normally fixed front cowling of the nacelle contains two cooling-air ducts on each side and a central grilled intake, the top half of which feeds the oil cooler and the lower the supercharger. The engine itself is accessible through hinged cowlings, above and below, which lay bare the entire engine. Induced flow cooling is not used, since the back of the cowling is completely open with the pusher installation.
For the American market a 3-bladed Hartzell constant speed; fully feathering airscrew is used, but one would expect that for other markets the excellent Piaggio P1033 fully feathering, hydraulic airscrew would be offered as an alternative. This has proved to be a very reliable unit and plenty of experience has been obtained on the many P.149D trainers in service with the Luftwaffe. The P.136 main undercarriage has been used as a unit, of course, although a completely new nosewheel assembly had to be designed. The main undercarriage looks complicated but is in fact extremely simple consisting of a welded steel tube truss, to which the leg units and retracting mechanisms are attached. The wheels are drawn upward into the fuselage, where they are fully enclosed, and when they are extended the break-strut is over dead centre, so that it is automatically locked. The welded components are made by Piaggio - and very fine examples of precision welding they are - but the shock absorbers and jacks are provided by Oleopneumatica Magnaghi of Milan, and Goodyear wheels and disk brakes are fitted.
Again it is rather early days to describe the systems, but they follow closely on the well-tried methods used in the P.136L.
There are duel flying controls, using handwheels projecting from the dash and 'hanging' type rudder pedals with toe operated hydraulic brakes. The control runs are cable throughout, with chains, sprockets and tie rods added where necessary to achieve changes of direction. The hydraulic system consists of an electronically powered pump in the fuselage, acting through twin piston-type accumulators, with an emergency hand-pump. The system operates the alighting gear, the flaps (the latter by a single jack in the fuselage and a system of push-pull rods and bell cranks), and the wheel brakes.
Full provision is being made for en extensive electrical system to cater for radio, lighting, and galley services. Among the optional extras will be a combustion heater, mounted in the wings, Goodrich de-icing, oxygen, Federal autopilot and, surprisingly, even radar. It certainly looks as if Piaggio is intending to enter this tempting executive market with a really well thought out little aeroplane