Polyt 5

Polyt 5 er et specialiseret slæbefly designet og bygget af medlemmer af Polyteknisk Flyvegruppe. Flyet bruges hyppigt til flyslæb og har en fremragende stigeevne.

A number of movie clips have been compiled into "The Polyt 5 documentary" . The VHS video is now available online in Windows Media format click here (10Mb - playtime 42 min - bandwith suitable for 56Kbps modem use). Narration is in danish language only.

The Flight Manual for the Polyt 5 aircraft is available as a PDF document. Also see the new collection of archive documents about the design and testing of Polyt 5.

Polyt 5 is primarily designed as a glidertug (19k). The aircraft can therefore tow a glider with a short take-off distance, and high rate of climb at low speed, and can after release perform a steep low-velocity dive. The two former requirements are fulfilled partly by using a 200 HP engine with specially designed propeller, and partly by keeping the weight as low as possible.

The latter requirement is fulfilled by using powerful airbrakes along the inner part of the wings trailing edge.

In order to increase the take-off frequency the aircraft is equipped with an electric winch, which can retract the towrope after releasing the glider. This enables the aircraft to make a direct landing instead of making a go-around after throwing the cable.

Polyt 5 is designed by members of Polytechnic Flying Group and built at the club's workshop at the Technical University of Denmark. Work began in summer 1965 and the maiden flight took place at 12th April 1970.

Description

Drawing here (119k). Smaller version here (38k).

The engine is a four cylinder 200 HP Lycoming 10-360-A2B. An axial blower is mounted at the front end of the engine in order to obtain sufficient cooling during a low speed full power flight. When the aircraft dives after release, too fast cooling is avoided by closing the cowling flap, which is actuated by the throttle.

The original propeller was made of wood with a diameter of 2.06 m and wide blades. The propeller was optimized to an unusually low speed of 100 km/h. For noise reduction the original propeller is now replaced by a specially manufactured Hoffmann propeller.

Fuselage and tailfin are built of light wooden frames covered of plywood.

The tailplane is all flying and is mounted at the top of the fin. It is made of wood plywood and fabric covering.

The main undercarriage consists of a semicircular glassfibre spring and wheels with separately actuated hydraulic brakes.

The steerable nose gear is telescopic and has a hydropneumatic shock absorber.

The wing consists of a wooden boxbeam and ribs. The surface in front of the beam is balsa wood and on top of the beam polystyrene foam, both covered with glassfibre reinforced epoxy resin. Behind the beam, the surface is partly plywood, partly fabric. The ailerons are plywood covered. The wings have a combination of downward turning trailing edge flaps and upward turning airbrakes of aluminum.

Specifications

Dimensions: Span 9.6 m, length 6.2 m, height 2.6 m, wing area 14.4 m².

Weights: Empty 615 kg, loaded 760 kg.

Performance: Cruising speed 185 km/h. Never exceed speed 232 km/h. Max. maneuvering speed 165 km/t, max. speed with airbrakes extended 165 km/t. Max. speed for extension of airbrakes 120 km/t. Stalling speed 72 km/t.

Rate of climb: Solo 8 m/s, towing two-seater 4 m/s, towing singleseater 5 m/s.

Take-off distance (to 15 m) 140 m, landing distance (from 15 m) 280 m.

Polyt 5 is designed according to FAA CAM 3 normal category.

PFG Club President Jørgen Bachmann in Polyt 5 cockpit, 2.6.2001