This republication has been made possible thanks to the assistance of
The Society of Automotive Engineers and Dr. James C. Floyd. This is quite a lengthy lecture and was presented in January 1950. We hope you enjoy this piece of aviation history.
Scott McArthur. Webmaster, Arrow Recovery Canada
The absence of propellers and the consequent short distance between the aircraft structure and the ground coupled with the fact that an under-slung nacelle configuration was used, resulted in an extremely short main landing gear, see figure 21. The actual distance between the undercarriage main pivot and wheel centres is less than 30 inches. This has resulted in the establishment of an extremely robust and simple design, and one which is believed to be lighter as a percentage of the gross weight than any existing transport undercarriage.
Twin wheels are used on both the main and nose units, both retracting forward. The main undercarriage struts consist of a telescopic leg incorporating liquid springing. The nose wheel is self-centering, fully castoring and incorporates shiming damping, see figure 22. The hydraulic steering unit incorporating a double piston control acts as a shimming damper when the steering is switched off. Steering is controlled by a wheel adjacent to the pilot.
The nose wheel is steerable through an are of 70 deg each side, and the wheel cancaster through 360 deg for towing. Lever suspension is used on the nose gear.
Undercarriage retraction is electro-hydraulic and hydraulic brakes have been installed, controlled by the rudder pedal toe brakes. All wheels are to the American Tire and Rim Association specifications. The main undercarriage doors are operated by separate hydraulic jacks, and the nose wheel doors are operated mechanically by a trip mechanism fitted to the nose undercarriage.
Accidental ground retraction is prevented by a microswitch which comes into operation when more than 5% of the aircraft weight is on the wheels.
All undercarriage uplocks can be tripped manually in an emergency and extension will then take place by gravity and drag forces.
ACCESSORIES AND SYSTEMS
The position and layout of the various accessory units which have to be serviced regularly on the ground, or which need to be accessible in flight was given a lot of thought, as this is a point, which has aroused much criticism in the past by airline operators.
An accessories compartment was introduced behind the first officers bulkhead on the starboard side to carry the main aircraft accessories, see figure 23. The heater, refrigerating turbine, main electrical accessories such as, inverters, relays etc., and the main electrical distribution panel are all housed in this compartment, which has its own fire extinguishing system.
All radio and electronic units are in a similar separate compartment on the port side behind the pilot's bulkhead, see figure 24.
The main hydraulic units are panelized, the panels being housed in the forward wing root fillet, with easy access at ground height to all ground connections, accumulators, valves etc. The emergency power pack is also contained on these panels.
Methyl-bromide engine fire protection bottles are housed in the nacelles at shoulder height and the engine starter relay panels are also in this vicinity.
The extremely low static position of the aircraft imures that practically all external servicing is done without steps or servicing ramps.
Ground pressure tests can also be carried out by connecting up the ground pressurizing equipment to a service panel inside the nose wheel well.
The main hydraulic system is a high pressure system operating at a normal pressure of 1,800 pounds per sq. inch. The cut-out pressure is 2,200 p. s. i. and the relief valve pressure is 2,700 p. s. i.
The normal system power is provided by two constant pressure variable, displacement pumps on the accessory gearbox in the nacelles. Either pumps will provide full hydraulic power for the complete system, and the use of two pumps is to provide duplication against failure.
The main services operated by the hydraulic system are the main and nose undercarriage gear, nose wheel steering unit, landing and dive flaps, main wheel brakes, main wheel doors, and aileron power booster. Complete duplication of the normal hydraulic system is provided by a "power pack" consisting of an electrical motor and a pump.
A hand pump is provided in the accessories compartment which also can be used in an emergency. On the ground, the system can be operated by ground supply points located on the wing root fillet panels.
The electrical system is basically a single grounded negative system for both D. C. and A. C. services.
There are in effect six separate systems providing power for the various services. The various systems are listed below:
While de-icing will not be fitted for the first flights of the first prototype, an electro-thermal de-icing system will be used for the wings and empennage. De-icing power is provided by two 50 KW., 208 volt three-phase 400-700 cycle alternators situated on the engine driven gearbox.
Windscreen de-icing is provided bv special 'Nesa' glass windscreen panels, which consist of a vinyl core sandwiched by two thicknesses of semi-tempered glass. On the outside surface of the vinyl between the vinyl and the outside layer of glass is a conductive 'Nesa' coating which provides approximately 5-6 watts per sq. inch power input.
The windscreen de-icing is entirely automatic and the temperature is controlled to provide the quantity of heat required for anti-icing, and at the same time, keeping the vinyl layer at a temperature which gives it the best resistance to bird impact.
The three forward panes of the aircraft are designed in this manner, and the vinyl centre layer has the additional advantage, that in the event of a windscreen being shattered by any circumstances, the vinyl will still withstand at least twice the maximum differential pressure in the fuselage by blowing out in the form of a bubble.
Engine and intake de-icing is a special problem which at the moment is being investigated fully by the engine manufacturers and Avro Canada. There are several workable schemes. As it has not yet been decided definitely which system will be used for production aircraft, it is obviously not desirable to go into detail on the subject in this paper.
All radio equipment is housed in the radio compartment on the starboard side of the front entrance door, and is completely enclosed by quick removable panels giving complete access to all units.
The electronic units are housed on sliding racks and use is made of special type connector boxes which automatically engage the pins when the units are pushed into position.
The radio and electronic compartment is ventilated by a separate blower. The basic radio system consists of the following:
All the radio and navigation instruments are duplicated on the captain's and first officer's panels, and all control panels are located on the flight deck pedestal.
The entire radio pedestal assembly is removable as a unit by means of disconnecting plugs at floor level.
Microphone and headphone jacks are provided at the side panels, and separate loud speakers are provided for the captain and first officer.
Communication with the cabin attendant is by an interphone system. A sound hand set is connected to an outlet in the wheel wells and external servicing points.
All receiver audios are muted during interphone speaking periods with an interlock to prevent muting of either or both communication audios during communication periods.
Provision for Additional Facilities
Full provision is made for the following additional radio navigational equipment.
Selection of the visual output of either of the two ILS combinations can be available to the captain by means of one switch. The autopilot automatic approach equipment would be paralleled with the captains ILS indicator.
It has obviously not been possible in this paper to give more than a bare outline of the work that is necessary in the design of a new aircraft.
An enormous amount of test work had to be carried out on the structure, and functioning of equipment, even before the aircraft first flaw, and rigorous flight testing is now being carried out to assess control, stability and general performance.
There has been much discussion in the past an the relative merits of jet and reciprocating engined aircraft, and most of the criticisms of the jet have been made by people who have never had the experience of either working on a jet project or really getting down to the job of comparing the two types on a rational basis.
This stage has, however, passed and the main argument now is not if the jet transport will be used, but when will it be used.
The successful demonstration of the C-102 Jetliner in flight has brought that date a little nearer.
I wish to express my thanks to A.V. Roe Canada Limited for their permission to give this paper, and also to the Rolls-Royce Company for permission to publish the engine data.
My appreciation is also due to Mr. R.M.Stuart, my Technical Assistant, for his assistance in the preparation of the art work and diagrams.
A certain amount of the above material was used in a paper I gave at the Annual Convention of the Engineering Institute of Canada at Quebec City in May 1949.
1 - Frontispiece.
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