REMINISCENCE - AVRO ARROW

by BERNARD A HODSON

In the early 50s two UK subsidiaries were at Malton, Ontario: Avro Aircraft, designing planes, and Orenda Engines, designing jets. Avro Aircraft designed the CF100 fighter, an excellent plane, a flying saucer (enhancing knowledge of circular aircraft), an anti-ballistic missile missile, and the commercial Avro Jetliner, a 4 engine airliner which was a pleasurable flying experience. It also designed a supersonic plane known as the 'Arrow'.

The targets for the Arrow were Soviet planes, knowledge being needed of their speed, range, manoeuvrability and armament. It was also necessary to know the parameters of possible Arrow missiles, the main contenders being the Hughes Falcon and the Douglas Sparrow.

The characteristics (speed, manoeuvrability etc.) of the Arrow, its missiles, and the target, plus systems uncertainty factors, determine what is known as the 'probability of kill', PK. The missile radar systems had a forward sighting 'window', only within that window could the target be shot down. The situation changed each second due to target evasive action and the response of aircraft electronics. To evaluate which missile to recommend one determined the PK for different Arrow missile systems against possible targets.

AVRO had acquired a computer (CRC102A), which was used for a variety of aerodynamic analyses, demonstrating the usefulness of the new fangled computers. Cooperating with the Institute of Aerophysics this led to significant knowledge extension on compressible fluids and supersonic flight. Computer programs in machine language were fed to the computer, along with needed data, by paper tape telex (at a speed of a few characters per second), also used for results output The memory of the computer was tiny, storage being a cylindrical drum, and it was very slow. With drum systems knowledge was needed of drum rotational speed and instruction time, with the instructions placed not in physical sequence but so as to avoid an extra drum revolution in accessing them serially.

The first non aerodynamic computer program was that of a simulator for aircraft/missile engagements, as far as is known the first of its kind. It would simulate an aircraft/missile engagement under various conditions, determining the PK for a variety of Arrow-borne missiles with different targets. Early computers had no graphics capability and trajectory results had to be printed and plotted by hand. It saved many days of manual work, although each simulation took several hours to run.

A person who helped install the UK computer FERUT at the University of Toronto, (subject of a later article), joined the Aerodynamics Department, becoming an expert in 'flutter analysis'. He used the computer to considerably expand the knowledge of such phenomena, ('flutter' is where an aircraft wing, subjected to certain loads and wind conditions, will start to resonate, causing wing failure). In later years, when the new Toronto City Hall was designed in the shape of two airfoils, he and a colleague did a study to show that the City Hall, under certain wind velocities and direction, might resonate and collapse. Whether any notice was taken is not known, but City Hall still stands.

AVRO negotiated with IBM for their first larger scale scientific computer (IBM 701, later called IBM 704). Following its introduction Avro tested out a new language called Fortran, developed initially by Northrop Aircraft. This enabled the writing of programs in a scientifically oriented notation rather than machine language, speeding up application development considerably.

The North American defence system used at that time a system called 'Sage' which linked early warning systems to a computer. If it and the relatively unreliable early warning systems happened to be working, (by no means a certainty), it could handle about 100 objects in the air at any one time and the probability of hostile aircraft getting through was quite high. Arrow was designed to intercept these incoming aircraft so its electronics had to be capable of integrating with Sage, adding further skills to the rapidly expanding information technology of the time.

The Arrow would still be today one of the most beautiful and versatile aircraft ever built. It was destroyed, along with the world's most powerful jet engine, the Iroquois, by short sighted politicians. Ironically, today sees state of the art software called Arrow.