Patent GB-820434-A (GB)
Title: Improvements in or relating to safety monitoring apparatus for aircraft
IPC: G05D1/00
Filed: 1957-08-27
Abstract: 820,434. Determining aircraft take-off conditions. SPERRY RAND CORPORATION. Aug. 27, 1957 [Oct. 1, 1956], No. 27034/57. Class 40(1). [Also in Groups XIX and XXXVI] Apparatus for determining whether or not an aircraft will become airborne within a given runway distance comprises means responsive to the forward motion of the aircraft along the ground to detect if the average acceleration falls below a prescribed value or if the speed falls below a reference speed varying in a prescribed manner, and to provide a warning signal if either should be the case. The preferred method produces signals representative of v i  (instantaneous speed) and d i  (distance travelled to reach speed v i ) and combines these with preset signals v r  (speed necessary to become airborne) and d r  (runway distance available) to give a comparison between the quantities v<SP>2</SP> i /d i  and v<SP>2</SP> r /d r . If the former quantity is equal to or greater than the other the speed of the aircraft is sufficient for it to become airborne; if not, an indication is given to the pilot accordingly and he can apply the brakes. In Fig. 4, the output of the accelerometer 6 is integrated at 9, the angular position of the output shaft representing the instantaneous velocity v i . Provided the magnetic clutch 13 is energized, the sliders of the potentiometers 14 and 4 tap off voltages proportional to v i  and v<SP>2</SP> i  respectively. The former is integrated again at 27 to give a signal d i  (representing distance travelled) from the potentiometer slider at 34, and combined at 36 with the preset signal v<SP>2</SP> r . The signal v<SP>2</SP> i  is similarly combined at 43 with the preset signal d r  and the two quantities (which are equivalent to those quoted above) applied to the differential meter 40 whose pointer is deflected one way or the other depending on which signal is greater. The output shaft of 27 also controls a further slider to energize the pointer 49 in accordance with d i , and this co-operates with a preset contact 51 when d i  is just short of the " point of no return," i.e. the last point at which the pilot can apply the brakes to bring the craft to a halt on the runway. The pointer 54 is coupled to that of the meter 40 and if the latter is deflected to the side indicating that take-off is impossible an alarm will be sounded when the pointer 49 touches the contact 51. The sliders are all spring-loaded so that they return to zero when the magnetic clutches are de-energized by opening the switch 22. The preset value of airborne speed can be modified (Fig. 5, not shown) by a mechanical differential to take account of wind velocity. In Fig. 6 (not shown) the calculation is modified by obtained v<SP>2</SP> i  by direct multiplication, and dividing v<SP>2</SP> i  by v<SP>2</SP> r  in a square-law potentiometer and d i  by d r  in a linear potentiometer, so that the meter compares v<SP>2</SP> i /v<SP>2</SP> r  with d i /d r . In a further modification (Fig. 7, not shown), the product v<SP>2</SP> i d r  is compared with V<SP>2</SP> r d i , and in addition the function v<SP>2</SP> i  is obtained from a non-linear potentiometer to allow for the fact that the acceleration may, for some aircraft, vary during the take-off run. It is also possible to compare v<SP>2</SP> i  with v<SP>2</SP> r \d i /d r .