Self-launching high-Performance Open Class singel seat sailplane
The second generation of this powered sailplane, which is at the top of its class (L/D > 60), was first flown in spring 2000 and differs from the predecessor mainly by its propulsion system. This originates from the two-seater NIMBUS-4DM (liquid-cooled SOLO engine type 2625-02 with 47kW and dual ignition) and is pivoted inside the fuselage such that only the rigidly connected propeller pylon swings up.
Power is transmitted to the propeller by means of a toothed belt, reduction ratio 3 : 1. This is routed in a noise-absorbing manner inside the pylon, which also carries the radiator.
The pivoting motion, which includes the muffler with its exhaust exit pointing upwards, is generated by an electrical spindle drive and is, as well as a number of other power plant functions, controlled and monitored by an ILELC multi-function control unit. This also prevents operating errors as for instance the starting with propeller brake still on, the pylon not fully erected etc. It also indicates engine speed, coolant temperature, fuel quantity etc.
In the case of a malfunction of the pylon control (e.g. the failure of a limit switch), a direct activation of the spindle drive is possible via an emergency extension/ retraction switch by bridging all safety installations.
The electrical power to operate the propulsion system is provided by a 12 V/24 Ah battery, which is recharged by a generator while the engine is running and there is space for additional power sources for the avionics.
The concept of the NIMBUS-4M, which is to be operated as a high performance sailplane capable of self-launching rather than a touring motor glider, provides a sufficiently powerful take-off and climb - so there was no aim for a high power on cruising speed or a long range.
Nevertheless the capacity of the two standard fuel tanks makes possible flights in "sawtooth" mode in excess of 250 nm (and even 400 nm when using a further wing tank). The fuselage tank alone, however, is sufficient to conduct 3 or 4 take-offs on own power to a height of 3300 ft each. A refueling system, integrated into the fuselage, allows an easy filling of the tanks installed.
The power plant unit, incidentally, is conceived such that - thanks to quick-disconnect couplings and easily accessible mounting bolts - it is effortlessly removed and reinstalled; after all the NIMBUS-4M may be operated any time without its propulsion system in place (mass then reduced by about 120 lb).
The nose tow hook required for aerotow is standard, a belly hook for winch launch may be obtained on request.
With regard to its flight handling characteristics there is hardly any difference to the sailplane model NIMBUS- 4 and its circling flight behaviour is even more pleasant because of the higher fuselage mass.