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- 3,22t,i2i United States Patent Office Pam, N0, ,0, ,,,,
3,220,121 GROUND-BASED FLIGHT TRAINING OR SIMULATING APPARATUS Albert Ernest Cutler, Barnet, England, assignor to Communications Patents Limited Filed May 20, 1963, Ser. No. 281,646 Claims priority, application Great Britain, Iuly 8, 1962, 22,241/ 62 11 Claims. (Cl. 35-12)
The invention relates to ground based flight training or simulating apparatus in which the forces experienced by the pilot operating the flying controls vary according to the different =conditions of the simulated flight.
In flight training or flight simulating apparatus, controls and instruments are provided which are representative of the controls and instruments of an aircraft, and a relationship is established between the controls and the instruments of the training or simulating apparatus usually by a computing device, so that operation of the controls of the training or simulating apparatus will cause the instruments thereof to indicate appropriate flight conditions. It is customary in the design of an aircraft to provide for a system of natural or artificial forces to oppose the pilot in his attempts to displace the controls, the nature and magnitude of the effects produced by the controls being selected to provide sensitivity of control for limited manoeuvres whilst at the same time restricting in the interests of safety the total effect which may be obtained. The present invention relates particularly to apparatus for loading the controls of the flight training or simulating apparatus so as to reproduce the forces operating on the controls under equivalent conditions in the aircraft.
It has been recognised for some time that the fidelity of feel of the controls in a flight training or simulating apparatus has a significant effect, not only on the ability of pilots to carry out precise manoeuvres but on their psychological attitude to the training apparatus and therefore the value of the training obtained thereby. The forces -on the controls of an aircraft should be reproduced faithfully, not only for fixed control positions but also as they vary during the movement of the controls. During the movement of the controls of an aircraft, additional forces act on the controls, which forces are related, for example, to the dynamic characteristics of the control member movement, the control surfaces, the control surface actuator systems, and the artificial control force generators.
Many modern aircraft retain a degree of mechanical coupling between the control surfaces and the controls so that during flight when rough air is encountered, particularly of the type known as cobblestones, impulsive forces are transmitted to the control column. These impulsive forces may contain frequency components over a wide range, for example, from very low frequencies to the lower audio range.
Other aircraft control systems are powered by boosters of limited power so that at high airspeeds the booster torque is not sufficient to overcome the aerodynamic reaction and snubbing takes place due to mechanical interference. There are other aircraft control systems in which mechanical limits are applied to the travel of the controls, either continuously or at discrete airspeeds or Mach numbers by means of stops or snubbers. If the controls are brought up sharply against these stops or snubbers the forces required to displace the controls would increase discontinuously but for the elasticity of the control mechanism which causes instead a considerable gradient in the forces required. The fact that these effects cause the higher frequencies normally found in mechanism is evident from the audible knock which often results from the use of snubbers or stops.
Some aircraft control systems, either as a result of their design, or otherwise, possess dead zones or abrupt changes or slope in their control characteristics. The most common elfect of this kind is associated with the centring of the controls, a small break-out force being required before any of the controls will move. Another common effect producing a similar result is back-lash in the mechanism of the controls which causes a small amount of lost motion at each reversal of the direction of movement of the controls. When the controls are taken rapidly through such zones, the forces acting thereon suffer a discontinuity which gives rise to knocks.
In order to simulate these effects on the -operation of the aircraft controls with sufficient realism it is necessary that the transient response of the control loading system of a flight simulating apparatus should be very good, which requires that the frequency response of an electrical control loading system should extend smoothly from D.C. at least to the lower audio frequencies.
A principal object of the present invention is to provide means whereby the steady state and transient force effects on the controls in a simulated control loading system are made more faithful reproductions of their counterparts in the aircraft which the simulating apparatus simulates.
According to one aspect of the present invention, there is provided a flight training or simulating apparatus for simulating a specific aircraft type, including a control member which is operable manually, computing means for determining a first electrical quantity representing the force required to load the control member, first actuator means adapted to apply force to the control member and responsive to said first electrical quantity, an output force sensing device the output of which is a second electrical quantity representing the magnitude of the force applied by the first actuator means to the control, electrically connected in such a way that the operation of the first actuator means is controlled by a quantity representing the difference between the first and the second electrical quantities, and second actuator means, of the type which has output force substantially proportional to the magnitude of an electrical quantity applied to its input, also adapted to apply force to the control member and responsive to inputs including the said quantity representing the difference, whereby the combined force on the control member varies in simulation of the steady state and transient forces characteristics of the aircraft.
According to another aspect of the invention there is provided flight training or simulating apparatus for simulating a specific aircraft type, including a manually operable control member, computing means for determining an electrical quantity representing the force required to load the control member, a first and a second electrical circuit, the first electrical circuit being responsive to low frequency changes of the electrical quantity, the second electrical circuit being responsive to relatively higher frequency changes of the electrical quantity, a first and a second actuator means each adapted to apply force to the control members and responsive to the output of the first and the second electrical circuits respectively, whereby the static and transient forces acting on a control member of the simulated aircraft are faithfully reproduced.
In order that the invention will be more fully understood and readily carried into effect the following description is given with reference to the accompanying drawings, in which:
FIG. 1 is a block diagram of a control loading system for a flight training or simulating apparatus in which an auxiliary force generator is responsive to the error of a main force generator;