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AIR INTAKE

  The arrangement of the intakes is shown in Fig. 8, and consists basically of the following.
(a)   a boundary layer bleed, which diverts two-thirds of the air in the boundary layer over the top and bottom of the wing, the middle third being taken into the heat exchangers in the air conditioning system,
(b)   the intake ramp, which is used to create an oblique shock wave at supersonic speeds to allow optimum pressure recovery characteristics inside the intake, and which, combined with the normal standing shock, prevents turbulent conditions in the intake over most of the Mach number range.
  The optimum angle for the fixed intake ramp was determined by considerations of net accelerating thrust. The geometry of the intake was chosen to yield the maximum installed net thrust with the minimum distortion of air flow at the compressor face, with inlet flow stability over the range of engine mass flows.
  The angle of the intake external ramp is 12deg., and the intake contraction and profile from the face of the intake lips to the throat was determined by 1/6th scale models, tested to give the required total pressure recovery and acceptable distortion levels at low subsonic Mach numbers, without conviction with supersonic flow requirements.
A number of modifications were made to the ramps as a result of these tests. One of the problems encountered was an interaction between the inlet shock and the boundary layer from the ramp, which caused fluctuating conditions inside the intake similar to the commonly known " intake buzz." Perforations were installed on the face of the ramp, and the boundary layer air from the ramp was sucked through these per- forations by an extractor, seen below the intake, which has a series of cascades.
The 1/6th scale model, tested in the N.A.C.A. 8 ft. x 6 ft. Lewis tunnel, represented the full scale aircraft configuration as far rearward as the engine compressor, face. It included the canopy, fuselage inlet ducts, and bleed, to determine the interaction of the fuselage and canopy surfaces with the air flowing through the intake.
  Continuous-view schlieren high speed cameras. as well as flow pressure and temperature instrumentation, were used to determine the flow patterns in the intake. Thirty-seven configurations were checked, involving 1,283 data points. They were all tested within one month, with the wind tunnel time running to something over 100 hours.

BASIC STRUCTURAL DESIGN

  T'he structure of the CF-105 is relatively conventional. but the thin low aspect ratio delta configuration and the two engines buried in the fuselage have introduced a number of interesting structural problems (Fig. 9).

WING

  The outer wing consists of a multi-spar, highly swept, box beam, with heavy 75ST6 tapered skins and ribs running normal to the main spars. The trailing edge consists of a control box housing the aileron control linkage system, to which the aileron is attached by a continuous piano hinge. The outer wing is attached to the inner wing, by a peripheral bolted joint, covered by a fairing.
  The inner wing consists of a main torsion box containing four 75ST6 spars, ribs running parallel to the centre line of the aircraft, and 75ST6 machined skins with integral stiffeners connected by posts. This box is also an integral fuel tank, pressurised to 19 p.s.i. The inner wings are joined at the centre line of the aircraft.
  Over the fuselage, and behind the main box, is a rear box extending aft, to which the fin is attached. The fin consists of a multi-spar box beam with heavy 75ST6 tapered skins and ribs normal to the spars.

FUSELAGE

  The fuselage has been basically designed around the two engines and their intake system, with the crew cockpit nesting in between the intake ducts. The engines are suspended from the inner wing and they are enclosed by fuselage at the sides and bottom. Underneath the inner wing spars, heavy formers attach the fuselage to the wing. The fuselage sides are attached to the
wing chordwise by a continuous piano hinge.
  The removable armament pack lies underneath the intakes at the centre section.

 

UNDERCARRIAGE

  One of the most difficult structural problems has been the stowage of the undercarriage gear, which is relatively long, in view of the high wing arrangement and the large angles of attack at takeoff and landing.
  It was found to be impossible to stow the undercarriage system in the thin wing without shortening and twisting it as it retracted.

ANALYSIS

  With the low aspect ratio delta wing arrangement it was not possible to consider the wing acting as a beam attached to a rigid fuselage. The wing deflects chordwise under the inertial, lift and elevator loads, and this in turn affects fuselage bending, and the whole structure was analysed as a fuselage-wing combination, with the wing considered to act as a plate.
  Matrices were established relating energy of deformation to stress at selected points, and by a series of approximations, new matrices were obtained as the deflections were established, which related stress and deflection with unit loads.
  Another difficult structural problem was the internal air pressures in the intake. The air intake system, the shrouds surrounding the engines, the fuel tanks, and the cockpit are all subject to positive and negative pressures. The whole structure had to be considered as a pressure vessel under internal and external pressure.
  The air intakes are circular over most of their length, but change to rectangular section at the intake ramps. They are made from 24ST aluminium alloy and, in addition to the internal-external pressure tests, 50 calibre bullets have been fired through a duct pressurised to limit pressure to establish whether explosive decompression would take place. It did not.

FATIGUE

  We felt it was important that the structure had a relatively uniform fatigue life, and that there should be no point where the stress concentration factors exceeded the average value by any great amount. A great deal of attention was paid to obtaining the best possible fatigue life without too much of a weight penalty, by careful detail design and detailed stress analysis.
  An extensive programme of fatigue testing of joints was carried out, and this also applied to systems testing. In the 4,000 p.s.i. hydraulic system, for instance, extensive fatigue testing of pipes and components was done, especially on those items attached to components on which there were high transient loads, such as the control actuators.
  Thermal stresses were also a problem. Elevated temperatures not only have the effect of reducing the allowable stresses and elasticity of the materials, but transient conditions where the outer skin may be relatively hot due to friction, while the inner portion of the structure or skin may not have had time to warm up, produce differential stresses in the structure.

ACOUSTIC ANALYSIS

  A great deal of ad hoc and basic research testing was conducted on representative structures in a sound chamber, since much of the structure is exposed to the high acoustic potential damage from afterburner operation.

TESTING

  Many structural components have been tested, ranging from complete tests of the whole aircraft, down to very minor tests such as rivets. Approximately 120 major structural tests have been carried out, some consisting of tests of 30 to 40 specimens to get a representative figure.
The results of many of these tests have already been incorporated into the structural design.

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