Power plants – Reaction motor – Interrelated reaction motors
Reexamination Certificate
1999-11-15
2001-03-27
Casaregola, Louis J. (Department: 3746)
Power plants
Reaction motor
Interrelated reaction motors
C060S240000, C060S039270
Reexamination Certificate
active
06205771
ABSTRACT:
This invention relates to a ducted fan gas turbine engine control system and is particularly concerned with a control system that detects a stall condition in the fan of the engine and subsequently modulates certain operating parameters of the engine in order to facilitate the recovery of the fan from its stall condition.
When a ducted fan gas turbine engine powering an aircraft is required to operate at low or zero forward speed when there are crosswinds, there can be a tendency for at least the tip region of the engine's fan to stall. This can also occur under certain wind conditions when the engine is mounted on an aircraft in such a manner that its air intake is close to the ground. Typically these events are liable to occur during the initial stages of aircraft take-off.
It is believed that fan stall can occur when air flow separation takes place within the engine air intake, resulting in diffusion and circumferential air flow distortion.
A fan can sometimes recovers from a stall as a result of the drop in engine power that accompanies the stall. This is particularly so in the case of a fan stall that is accompanied by a stall in the core engine that drives the fan. However, under certain conditions, a fan stall can occur that is not accompanied by a core engine stall. If this happens, it is possible for the fan to remain in a stall condition with the result that a continuous, unstable airflow occurs downstream of the fan. Such an unstable airflow is highly undesirable in view of the structural damage that it can do to engine components in its path.
It is an object of the present invention to provide a control system for a ducted fan gas turbine engine which is capable of detecting a fan stall condition and taking action which results in the fan recovering from that stall condition.
According to the present invention, a control system for a ducted fan gas turbine engine having a propulsive fan driven by a core engine, comprises means to monitor the rotational speed of said propulsive fan, means to monitor the power absorption of said fan and means to provide a temporary reduction in the fuel flow to said core engine in the event of a fall in the monitored power absorption of said fan accompanied by an increase in the monitored rotational speed of said fan.
Said control system may be adapted for use with a ducted fan gas turbine propulsion engine having a core engine which includes a compressor portion, said control system being provided with means to provide a simultaneous, temporary reduction in the power absorption of said compressor portion with said temporary reduction in said fuel flow to said core engine.
Said compressor portion of said core engine may be provided with variable inlet guide vanes, said control system being provided with means to actuate said variable inlet guide vanes in such a manner as to provide said simultaneous, temporary reduction in the power absorption of said compressor portion followed by a return of said inlet guide vanes to positions consistent with normal engine operation at a rate corresponding with that at which the fuel flow to said core engine is restored to a level consistent with said normal engine operation.
Said means to monitor the power absorption of said propulsive fan of said engine fan may comprise a transducer positioned and arranged to monitor the air pressure downstream of said propulsive fan.
Alternatively, said means to monitor the power absorption of said propulsive fan of said engine comprises a transducer positioned downstream of a turbine portion of said core engine to monitor the gas pressure downstream of that turbine portion.
Said means to monitor the rotational speed of said propulsive fan may comprise a transducer positioned and arranged to monitor the rotational speed of a shaft drivingly interconnecting said propulsive fan and said core engine.
Said fuel flow is preferably temporarily reduced for a period of between 1 and 2 seconds.
Said fuel flow may be temporarily reduced for a period of approximately 1.2 seconds.
REFERENCES:
patent: 4414807 (1983-11-01), Kerr
patent: 5259188 (1993-11-01), Baxter et al.
patent: 5303545 (1994-04-01), Larkin
Casaregola Louis J.
Farkas & Manelli PLLC
Rolls-Royce plc
Taltavull W. Warren
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