Helicopter mechanics
with model turbine engine
2
Foreword
The introduction of Graupner/JetCat helicopter mechanics brings to fruition the long-held wish of
numerous model helicopter pilots: the dream of operating a scale model helicopter using a scale
power plant - a turbine.
The turbine mechanics have undergone intensive testing for a full year, and now, installed in the
NH90
®
fuselage, the system has reached production-ready status as a practical, reliable in-
stallation for everyday usage. This has been demonstrated in display events and model flying
meetings at home and abroad. The system can now be operated by any experienced model
helicopter pilot with the same natural assurance as any model of similar size with a conventional
power system.
The method of working of the PHT3 shaft turbine differs from that of conventional model jet
engines, as the output power is transmitted to the rotors instead of generating pure thrust. The
engine is designed to expend its exhaust gases into the atmosphere via a suitably formed ex-
haust duct with as little residual energy as possible.
In design terms this constitutes a single-shaft turbine, i.e. - in contrast to the twin-shaft turbine
layout - the output power for the rotors is derived directly from the (single) turbine shaft, which
also drives the compressor. The turbine speed of around 93,000 rpm is initially reduced to a
value around that of a piston engine by means of a two-stage toothed belt gearbox, before the
power is transmitted via a normal centrifugal clutch to the conventional main gearbox with auto-
rotation freewheel, which drives the tail rotor in addition to the main rotor in the usual way. The
standard direction of main rotor rotation is "left-hand" (anti-clockwise), but it can be converted to
right-hand rotation; the tail rotor is not driven in auto-rotation mode.
The all-metal swashplate is actuated directly by four servos which are mounted within the me-
chanics. The main rotor head features a metal centre piece, ballraced mixer levers and a ball-
raced collective pitch compensator. The tail rotor features an all-moving hub and ballraced ac-
tuating lever, and, like the main rotor, is a standard system adopted from the proven
GRAUPNER/Heim range.
Of course, handling a turbine requires that the model flyer should study the subject intensively
and gain as much expertise as possible beforehand. Provided that you have an appropriate
level of knowledge, you will actually find it simpler to handle a turbine engine in a helicopter than
to operate a piston engine:
The entire engine control system requires only a single radio control channel, while start-up
preparations are limited to filling the fueltank and the small auxiliary gas tank for turbine starting.
The engine is started simply by pressing a button at the transmitter, and the entire start-up
process is automatic in operation, controlled by the turbine’s on-board electronics (ECU). Ini-
tially the integral electric motor spins the turbine up to about 6,000 rpm, then the auxiliary gas
valve is opened, and the gas is ignited in the turbine’s combustion chamber (combustor). The
engine accelerates further, the burning gas supports and eventually takes over from the starter
Содержание JetCat 6810
Страница 31: ...31 Bedienungsanleitung ...
Страница 101: ...31 Operating Instructions Graupner Jetcat Modell Helicopter Turbine PHT 3 ...
Страница 107: ...37 Wiring diagram fuel pump and starter glowplug Connections overwiew of the turbine s operating components ...
Страница 171: ...31 Instructions d utilisation ...
Страница 177: ...37 Schéma de connexion Pompe à carburant et Starter Bougie Connexions des éléments de commande Généralité ...