A combined vertical speed and windshear indicator instrument for an aircraft has a graduated dial (2) and a conventionally driven pointer (3) for indicating the vertical speed. In addition the instrument has an independent pointer (4) which is driven so that it indicates, to the same scale as the vertical speed, the rate of change of total energy of the aircraft (energy rate) according to the formula dh/dt+(V/g)(dV/dt) where h is the height of the aircraft and V is its true air speed. Under stable flight conditions the pointers (3 and 4) will track together, but if there are any sudden changes, particularly changes due to windshear, the pointers will separate to indicate the effect of the changes so that the necessary corrective action can be taken by the pilot. The energy rate pointer (4) is driven by a signal (22) derived from input signals (5 and 6) which respectively represent the vertical speed h and the true air speed V of the aircraft and which are delayed by the use of filters (10, 14 and 20 ) for reducing noise interference. The response time of the energy rate pointer (4) to sudden acceleration of the aircraft itself is therefore improved by deriving the (dV/dt) term of the energy rate drive signal (22), for a short period following the sudden acceleration, from a signal (24) representative of the longitudinal acceleration x of the aircraft.
A variometer for an aerodyne. The variometer has at least one dial conventionally graduated to represent speed, a needle indicating on said graduation the instantaneous vertical speed. The variometer also has an indicator which is representative of the potential vertical speed, and can move around the dial so that the position of the indicator with respect to the needle indicates instantaneously the acceleration on the trajectory of the aircraft.
The invention provides for the detection of both longitudinal and vertical windshears during the takeoff and landing phases of aircraft flight. Standard instrumentation available on many aircraft is used to calculate the aircraft's energy loss or gain by integrating the value of the longitudinal shear. When the energy loss or gain exceeds predetermined levels, appropriate annuciation is provided to the human pilot. The same standard instrumentation aforementioned is also used to calculate changes in the aircraft's specific energy rate, that is the aircraft's actual energy rate divided by the aircraft's weight, to determine the effect of vertical winds. Specific energy rate is calculated by integrating the difference between the aircraft's acceleration relative to the ground and its acceleration relative to the airmass in which it is flying. To preclude false annunciations caused by the integration of small biases resulting from sensor or computational errors, all integrations are set to zero, that is the integrators are reset whenever the relevant parameters are below predetermined thresholds.
A method for producing a warning of the existence of low-level wind shear and an aircraftborne system for performing the method utilizes measured values of airspeed and temperature, to determine a temperature based hazard factor relating to the existence of a wind shear threat to the aircraft and to issue a warning whenever the hazard factor exceeds a predetermined threshold level based upon the performance characteristics of the aircraft. Temperatures may be sensed locally, such as by a resistive temperature sensor or, remotely, such as by an infrarred temperature detector. Furthermore, in accordance with preferred embodiments, an inertial reactive wind shear detector is utilized as an integrated safety measure. Moreover, the threshold level may be varied depending on such factors as aircraft altitude.
An improved windshear warning apparatus for aircraft, responsive to both the magnitude of the wind shear and the allowable time the windshear can be tolerated at a given magnitude. The sensed magnitude is used to compute the allowable time before providing a windshear alarm. For large windshear rates, the allowable time is short; conversely for small windshear rates which exceed a threshold level, a longer time period is computed before an alarm occurs. Since a windshear rate must persist for the computed allowable time before activating the alarm, windshear rates that are above the threshold level for elapsed time less than the computed allowable time will not result in an enunciation, while high magnitude windshear rates of short duration will not cause false alarms since they do not exceed the computed allowable time.
