Flight Simulators
Airplanes are not like automobiles. They travel at a high rate of speed and move
forward and backward and also from side to side and up and down. They are difficult
to operate and require hundreds of hours of training. They are also a threat both to
their occupants and people on the ground if they experience problems in the air.
Because of this, innovators and engineers have long sought ways of training people to
operate an airplane without actually having to fly one. They have developed machines
called flight simulators that today are highly sophisticated and important tools, useful
for training, learning safety procedures, and even for aircraft design and development.
Origins
From the early days of gliding it was usual for pilots to sit in the ground based
glider, exposed to a strong facing wind and feel the controls by keeping the wings in a
horizontal position. Thus, even before the glider flew, the pilot had some
experience of the lateral controls.
The Wright brothers experimented with a primitive form of a simulator to teach their aviation students to fly. They used the center section of an old plane on a mount, which someone on the ground would move based on the student's actions with the controls.
The fliers of the first powered aeroplanes learnt by proceeding through a graded sequence of exercises on real aircraft. After these a student would attempt rolling (taxing in today's terms), where a low powered machine was driven along the ground, enabling rudder control to be practised. The trainee would then graduate to a higher powered machine and would first make short hops using elevator control as the hops got longer, eventually flight would be achieved. A variation of this method was first suggested in a letter to Flight magazine in 1910, and further developed during World War One. Known as the 'Penguin System,' the student pilot could learn the feel of the controls while proceeding along the ground in an aircraft that had been specifically adapted for training and was unable to get airborne.
Other early devices attempted to achieve the same effect, especially for the testing of new aircraft prototypes, by using aircraft moving at speed supported by balloons, overhead gantries or railway bogies. Related to these ideas were the first proposals for truly ground-based trainers which were, in effect, aircraft tethered to the ground, but capable or responding to aerodynamic forces.
One such device was the Sanders Teacher, an aircraft mounted on a universal joint in an exposed position and facing into the prevailing wind. It was able to respond in attitude to the aileron, elevator and rudder controls as an actual aeroplane. An article in Flight dated 10 December, 1910:
"The invention of a device which will enable the novice to obtain a clear conception of the workings of the control of an aeroplane, and of the conditions existent in the air, without any risk personally or otherwise, is to be welcomed without a doubt. Several have already been constructed to this end, and the Sanders Teacher is the latest to enter the field."
Another writer described the device, in part, as follows:
"Those wishing to take up aviation either as a recreation or a profession find many drawbacks at the commencement of their undertaking, but one of the most formidable, especially to those not blessed with a long purse, is the risk of smashing the machine while endeavoring to learn how to control and fly it.
Even the most apt pupil is certain to find himself in difficulties at some time or another during his probation, and owing to lack of skill the machine is necessarily sacrificed to save his life, or at least to prevent a serious accident. The invention, therefore, of a device which will enable the novice to obtain a clear conception of the workings of the control of an aeroplane, and of the conditions existent in the air, without any risk personally or otherwise, is to be welcomed without a doubt...”
Unfortunately, as was the case with many of these early devices, it was not a
success, no doubt because of the unreliability and irregular nature of the wind. A
similar device was constructed by Eardley Billing, the brother of Noel Pemberton Billing,
at about the same time, and was available for use at Brooklands Aerodrome. The
Italian Gabardini captive monoplane, illustrated in the 1919 edition of Jane's Aircraft,
is yet another example of this type of machine.
The Billing flying trainer
However this period also saw one of the first truly synthetic flight training devices.
A photograph was published in the 1910 Antoninette catalogue showing a devise
consisting of two half-sections of a barrel mounted and moved manually so as to represent
the pitch and roll of an aeroplane. The prospective pilot sat in the top section of
this device and was required to line up a reference bar with the horizon.
The Antoinette trainer
First World War
The need for a training of large numbers of aviators during World War One encouraged
the development of the new discipline of aviation psychology. Tests were introduced
for pilot selection, the lead being taken in France and Italy. Many devices were
invented to aid in the assessment of the aptitude of potential airmen. In 1915 such
a machine was proposed for the measurement of reaction time in correcting disturbances
consisting of a rocking fuselage fitted with controls and an electrical recording
apparatus.
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| The Ruggles Orientator in which the candidate is whirled and tested. William Guy Ruggles, the inventor, is sitting at the lower right. |
Further developments on this theme include the Ruggles Orientator, which consisted a seat
mounted within a gimbal ring assembly that enabled full rotation of the pupil in all three
axes and in addition provided vertical movement. Electrical motors controllable by
the simulated sticks and rudder bars of the student and instructor/examiner produced all
motions. This device was stated to be useful for:
"developing and training the functions of the semi-circular canals and incidentally to provide such a machine for training aviators to accustom themselves to any possible position in which they may be moved by the action of an aeroplane while in flight"
A further optimistic claim was that the aviator could be blindfolded
"so that the sense of direction may be sensitised without the assistance of the visual senses. In this way the aviator when in fog or intense darkness may be instinctively conscious of his position"
The Ruggles Orientator, with a covered cockpit, was also used by Ocker in early simulation of blind flight using the Sperry turn indicator, developed in 1917.
Aids were also produced for the training of other skills associated with
aviation. Germany was developing methods for the training of air gunners and
observers and the French are known to have used miniature painted landscapes for bomb
aiming training.
The Inter-War Years
The next step in the evolution of the flight trainer was the replacement of the human
operator in Antoinette type machines with mechanical or electrical actuators linked to the
trainer controls. The aim of these new automatic devices was to rotate the trainee
pilot's fuselage into an attitude corresponding to that of a real aircraft in response to
control inputs. Provision was usually made for an instructor to introduce
disturbances in attitude to simulate the effect of rough air and to present control
problems to the student. An example of this technique is the family of devices
patented by Lender and Heidelberg in 1917. One of these consisted of a pivoted dummy
fuselage with pitch, roll and yaw motions produced by compressed air motors and
introduced, probably for the first time, variations of response and feel with simulated
speed. Engine noise and air flow from an attached propeller to produce tilting of
the fuselage in response to balancing flaps and a rudder.
Lender and Heidelberg trainer
In 1929, Edmund C. Buckley, a NACA's Chief of Instrument Research at Langley
Field, Virginia patented an electrical version of this type of trainer in the United
States. His machine consisted of a small dummy fuselage mounted in a universal joint
with pitch and roll attitudes produced by opposing motors, proportionally controlled by
stick movements. Turning motion was provided by another motor actuated by controls
on the rudder bar. Programmed disturbances could be introduced by means of a
perforated tape reading arrangement which could also control the indications of dummy
cockpit instruments which were not, however, connected to the flying controls. The
most successful and well-known of this type of device was the Link
Trainer (see detailed discussion).
The Link Trainer
Despite twenty years of inventiveness, synthetic flight training did not make much inroads, as exemplified by Links' early struggles to sell his trainer. Simulation was not seen as a substitute for actual flight. The acceptance of simulated flight as a useful training aid had to wait for further developments in the science of flying. In fact, it was the advent of war in 1939 which ultimately proved the catalyst for change. The need to produce thousands of pilots for the military needs of nations, more than any other inducement, eventually led to the acceptance and advancement of flight simulators.
While synthetic flight instruction was not widely accepted there was an interest in the machines for use as advanced instrument flight instruction tools.
Blind Flight Simulators
On 24 September 1929, at Mitchel Field, Long Island, NY, James "Jimmy"
Doolittle performed the first so-called "blind flight." He executed a
flight plan and landed using only cockpit instruments (without any outside reference), a
feat that culminated a research program supported by the Daniel Guggenheim Fund for the
Promotion of Aeronautics. This event demonstrated that precision flight during inclement
weather conditions were feasable. It also proved the need for effective training of
pilots in the skills of "blind" or instrument flying.
Two approaches to the problem were adopted. Existing motion trainers, such as the Link Aeronautical Trainer, were fitted with dummy instruments and the means for their actuation, and new non-motion devices were invented specifically for the task of instrument flight training.
A typical device, according to a U.S. patent application submitted in 1928, described a simple instrument trainer:
"fixed to the ground, with a student seat facing an instrument panel and two sets of controls, one for the student and instructor. The student's flight instruments are directly connected to the instructor's controls and the accuracy of the simulation depends entirely on the instructor."
By 1930-31 the Link Trainers were being fitted with instruments as standard equipment. The 1930s was certainly the "Link" era. The device was produced in various versions and was sold around the World. By the beginning of the Second World War, many of the major air forces were performing their basic instrument training on Links, or devices derived from them.
A further increase in the usefulness of the Link's trainers was achieved with the attachment of a course plotter. This consisted of the well-known "crab" device, which was self-propelled and steerable. The course of the simulated flight was traced on a chart by means of an inked wheel. By relating the position of the student's aircraft to marks on the chart, the instructor was able to manually control the transmission of simulated radio beacon signals to the trainer.
In Britain the instrument flight trainer was being advanced under the leadership of an R.A.F. pilot/flight instructor W.E.P. Johnson who built an instrument tariner from a derelict Avro 504. Flight Lieutenant Johnson had been sent to Paris in 1931 to attend a workshop sponsored by the Farman aircraft company. Upon his return to the Central FLying School at R.A.F. Wittering, Johnson constructed his 'trainer' placing an airspeed indicator, turn indicator, and bank indicator all directly operated by wires (including a throttle control which affected the airspeed indicator). He also integrated devices for the display of altitude and heading.
Another early British instrument flight trainer was described by a team of designers, Jenkins and Berlyn, of Air Service Training Limited, in their patent application of 1932. This ground-fixed apparatus used mechanisms similar to Johnson's for linking the instruments to the controls. Rotation of the magnetic compass was effected with a magnet, while transient deflections, were produced by causing a rotary movement of the compass damping fluid in response to pitch and throttle control changes.
Further developments in instrument trainers were undertaken by Dr. R.C. Dehmel, an engineer with Bell Telephone Laboratories, who became interested in the problem of flight training in 1938. His first design was an automatic signal controller for the generation of synthetic radio signals for a Link Trainer, thus eliminating the need for the attendant who manually operated signal volume controls during the training session. This was an important advance in instrument flight training in that it enabled a closer correspondence with the behaviour of actual navigational aids. Following this, Dehmel developed the flight portion of a trainer based on electrical circuits. This machine was never manufactured, but served as a starting point of future developments by the inventor.
Finally, just prior to the war, the Aerostructor, developed by A.E. Travis and his colleagues in 1939-40 in the United States, was introduced. It featured a fixed-base electrically operated trainer with a visual rather than an instrument presentation. The visual system was based on a loop of film and simulated the effects of heading, pitch and roll movement. The trainer was widely demonstrated but was never commercially produced. It was however, later used in large numbers by the U.S. Navy in a modified form known as the 'Gunairstructor'.
Postscript: Electronic Flight Simulation
The first known discussion of the computer method of flight simulation is that of
Roeder in his 1929 German patent specification. Roeder treated the general problem
of the instrument control of vehicles freely movable in space, such as airships,
aeroplanes or submarines. His outlines of the requirements of a simulator for such a
task could almost refer to a modern simulator. As an example of his technique he
described the dynamic simulation of an airship height control system and a fluid-operated
analogue computer suitable for this. No successful training devices are known to
have resulted from this work. In 1939 Otto Mueller, an engineer at M.I.T., described
an electronic analogue computer for the faster-than- real-time simulation of aeroplane
longitudinal dynamics. His interest was in aircraft design and the solution of the
equations of motion, but as a postscript to his paper he mentioned the possibility of
extending the time scale of the simulation and of including a man in the loop.
Much of this material was adapted from internet resources
with images aditions. A more complete discussion on the history of flight simualtors
to the present can be read on Kevin Moore's web page devoted to the subject: A Brief History of Aircraft Flight Simulation.
