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Jim Floyd:RAeS Lecture

Jim Floyd:
RAeS Lecture pg 6


This republication has been made possible thanks to the assistance of
The Royal Aeronautical Society and Dr. James C. Floyd. This is quite a lengthy lecture and was presented in December 1958. At that time the Arrow was in phase one flight tests.
We hope you enjoy this piece of aviation history.
Scott McArthur. Webmaster, Arrow Recovery Canada.

The Fourteenth British Commonwealth Lecture

The Canadian Approach to All-Weather
Interceptor Development


J. C. FLOYD, A.M.C.T., P.Eng., F.C.A.l., M.I.A.S., F.R.Ac.S.
(Vice-President, Engineering, Avro Aircraft Limited, Canada)

The Fourteenth British Commonwealth Lecture," The Canadian Approach to All-Weather Interceptor Development," by Mr.J. C. FLOYD, A.M.C.T., P.Eng., F.C.A.l., M.I.A.S., F.R.Ac.S. was given in the 9th October 1958 at the Royal Institution, Albemarle Street, London, W.1.
The Chair was taken by Dr. E. S. Moult, C.B.E., Ph.D., B.Sc., F.R.Ae.S., Vice-president of the Society, deputising for the President, Sir Arnold Hall, M.A., F.R.S., F.R.Ae.S., who was ill.
Dr. Moult first read a telegram from the President and then introduced the Lecturer, a distinguished Canadian engineer, for this Fourteenth Commonwealth Lecture. Mr. Floyd joined A. V. Roe and Co. Ltd., at Manchester, as an apprentice in 1929, progressing through the design and production offices to become Chief Projects Engineer in 1944. Immediately after the War he joined A. V. Roe Canada Ltd., at first as Chief Technical Officer, becoming Chief Design Engineer in 1949, Works Manager 1951, and Chief Engineer in 1952. He is now Vice-President, Engineering, Avro Aircraft Ltd. Mr. Floyd became a naturalized Canadian in 1950 and in the same year was the first non-American to receive the Wright Brothers Medal, which was awarded for his contributions to aeronautics, including his design of the Avro Jetliner. More recently, he had been known for his work on the Avro CF-100 interceptor and for the Avro Arrow, which made its first flight in March 1958.

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  The basic flying control system of the CF-105 is fully powered. The surfaces are operated by dual hydraulic jacks, each side of which is supplied by an independent hydraulic system, so that in the event of an engine failure, or the failure of one hydraulic power supply, full control can be maintained.
  There are three modes of control., manual, automatic, and emergency. The manual and automatic modes are shown in Figs. 11(a) and 11(b). The pilot's effort is converted into an electric signal by a stick force transducer at the top of the control column. This signal is fed to the command servo through a magnetic amplifier circuit. The command servo is an electro- hydraulic mechanism which converts the amplified signal into movement of the linkage leading to the control valves on the elevator jacks. The stick is mechanically connected to the command servo output.
  To provide some feel for the pilot on pulling " g," which has to be artifically created with a fully powered system, a suitable signal is channelled into the command servo from the aircraft performance sensors, the signal being picked up electrically by the sensors and fed into an electronic network.
  In the automatic mode the command servos are operated by signals from the electronic black boxes of the integrated fire control and combat system. Displacement of the stick takes place under these conditions, but can be over-ridden if the pilot applies sufficient force.
  Artificial stability augmentation is fed into the system in the following manner. Unstable tendencies are picked up by sensors and adjustments are made to the control system deflections by an independent servo, without reaction by the command servo, so that the pilot is unaware of this correction.


  The problem of obtaining adequate natural aerodynamic stability for an aircraft with the altitude and speed range of the CF-105 was extremely difficult especially in view of the low aspect ratio, and direction stability in particular was a problem.
  With the very thin fin required with a supersonic aircraft there is a large reduction in fin effectiveness high indicated air speed, and the fin lift falls off considerably, due to the lift slope curve decreasing with Mach number.
  To achieve adequate directional stability over the complete flight envelope we resorted to a synthetic "damping " system.
  Longitudinal dynamic stability is satisfactory at low altitude, but deteriorates with altitude in the normal way, and above 40,000 ft. the natural damping required augmentation to make the aircraft an effective weapon launching platform. The periods of oscillation are too short at high speeds for the pilot to be able to control adequately the response to a gust.
  We were left then with a necessity to augment longitudinal dynamic stability at high altitudes for weapon launching, and to augment lateral static and dynamic stability at a combination of high altitude and high speed to obtain adequate controllability. We did consider very carefully ways and means to produce better natural directional stability by, say, increasing the fin area some 50 to 60 per cent or putting underslung dorsal fins, i.e. dorsal fins, under the fuselage, but the performance penalties of doing this were considered to be unacceptable. For instance, if we increased the size the fin, it would geometrically reduce the fin arm. It would also increase the fin weight and move the c.g. aft, which again reduces the directional stability, and so we would be getting into an area of diminishing returns.
  It was therefore decided to obtain the required stability on all axes by artificial means, and since failure of the artificial damping system could be a problem in some areas of the flight envelope, it was also decided that the system must be made with either the same or better reliability than a standard power-operated system.
  The highest possible degree of reliability and safety has been built in to the damping system. For instantance on the yaw axis, which is the most critical, there is complete duplication, including sensors, computers, and hydraulic servos. The duplicate yaw axis system called the " emergency damping system." The switch over from " normal " to " emergency " in case of a detected malfunction is automatic. The main sensing element is an accelerometer and, at low speed, a side-slip vane. It is therefore necessary for a double failure to occur before the pilot is left without damping.
  The damping system has proved to be quite a development problem, and much of our flight testing so far has been concerned with sorting out the system. However, we were quite aware at the outset that this would be the case and, on the other side of the ledger, the flight testing has shown that our directional stability is better than expected.
  The system is designed to operate in conjunction with the automatic flight control system, which in turn is integrated with, and is an essential part of, the integrated interceptor electronic system. The main function of the damping system is to dampen the short period oscillations about all three axes, and to dampen the longitudinal long period oscillations.
  The system provides turn co-ordination and side-slip minimisation in operational manoeuvres up to 6g positive in pull-outs, and 4g positive in turns. This protects the fin structure from excessive loading. The damping system also provides for uncoordinated manoeuvres at the option of the pilot, which is carried out by a cut-off switch on the rudder bar, and provides a means of manual control.
  The emergency damping system, which is on the yaw axis only, provides stability and damping of the Dutch Roll mode, and limits the side-slip to well within the structural integrity limit on the fin, in pull-outs or 2g turn manoeuvres.


  While it is not possible, for security reasons, to describe the integrated electronic system which is the brain and nerve centre of the Arrow weapon system, I can say that it is a very sophisticated system and provides automatic flight control, airborne radar, telecommunications and navigation, and special instrumentation and pilot displays, and can operate in either fully automatic, semiautomatic, or manual environment.
  The system is carried mainly in the radar nose, with missile auxiliaries housed in the armament bay.

Scott McArthur.




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