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Arrow Pilots: Jack Woodman

Jack Woodman:
Flying the Arrow.



continued from page 1,  
     There were a number of relatively unconventional features on the Arrow, and aerodynamically the CF-105, was, I believe, a considerable advancement over contemporary aircraft. The Arrow program was a very ambitious project for A. V. Roe and for the RCAF, but seemingly well within reach and completely attainable. Some of the design features are worth mentioning, as detailed in the following descriptions.

Design Features

   The crew consisted of a pilot and a radar operator. The advantage of a two-seat airplane as compared to a single-seat airplane lies in the complexity of the fire control system, even though the system was intended to be entirely automatic.

   The choice of two engines was a combination of circumstances, with the main advantage being reduced attrition. Perhaps the main factor, however, was the very large weapons package required as payload and the large amount of fuel required to meet the range requirements. In the early design of the airplane, the range requirements pretty well sized the airplane, and at that time there was just no single engine large enough to provide the required power. The Arrow Mk. I was powered by two Pratt and Whitney J75-P3 engines, which produced 18,500 lbs. of thrust at sea level, with afterburner.

Delta Wing

   The choice of a delta wing design versus a straight or sweptback wing was, I believe, a compromise to achieve structural and aeroelastic efficiency with a very thin wing and at the same time to achieve the large internal fuel capacity required for the specified range. The structural advantages of the delta design made achievement of this thin wing section possible. (CF-105 thickness/chord radio was 3.5%; CF­100 Mk. 1 was 10%).

Some characteristics of a delta wing include:

No stall- There is no well-defined stall for a tailless delta and this is perhaps the outstanding feature. It permits flying the airplane to much lower speeds compared to straight or swept­back wings. Minimum speed is usually determined by sink rate and/or minimum control.

Ground effect- Since ground effect is a function of chord length, not wing span, the effect with a delta wing can be very pronounced. This simplifies the flare and landing problem. Landing the CF-105 was quite straight­forward.

Light wing loading- CF-105 wing area was 1,225 sq. ft., and at normal combat weight, wing loading was approximately 50 lbs. per sq. ft. Good manoeuvrability at high altitude, high speed, and also structurally strong.

Attitude- The Delta wing will have a higher angle of attack for any given CL, which means an increase in pitch attitude and possibly flying on the back­side of the power-required curve during approach to landing. Attitude was the limiting factor with the CF-105 during landing; handling qualities remained good throughout.

   Analysis showed that, due to a short elevator arm, high elevator angle would be required to trim at high altitude, which would create excessive trim drag. To compensate for this, approximately 3 /4% negative camber was built into the wing, which had the effect of building in elevator angle without the excessive control surface drag.

   The CF-105 had a leading edge notch and a leading edge extension about midspan on the wing. The purpose of the notch and the extension was to control the spanwise flow of the boundary layer air, characteristic of all swept wing aircraft, not just deltas. This is necessary to eliminate early flow separation, stalling of the wingtips, and the aerodynamic center shifting forward and giving pitchup, which is embarrassing to any pilot. The notch is similar to a wing fence, but it produces its desired effects by airflow rather than by a physical barrier, and it was Avro's opinion that the effects of the notch were present over the entire speed range of the aircraft rather than just a portion of it. Also, the notch was expected to increase drag by a smaller amount than a fence.

   The leading edge of the Arrow wing was drooped approximately 8° inboard and 4° outboard. This was done to increase the manoeuvre margins and the buffet boundary by preventing leading edge breakaway at high angles of attack. Determination Of C,, MAX was never accomplished in flight test; however, wind tunnel results showed that at Mach 0.92, the C,, was increased from 0.26 to 0.41 due to leading edge droop.

   Another peculiarity of the CF-105 wing was 4 deg., anhedral. This was on the airplane strictly to reduce the length of the landing gear, and had no appreciable aerodynamic effect or significance.

   A high wing arrangement was adopted because of the flexibility this permitted. For example, this allowed a relatively simple engine installation. Also, any changes in engines or armament could be made without affecting the basic wing structure. This is not always the case with an integrated wing/fuselage structure.

   A great deal of theoretical work was done on the application of area rule to the CF-105, and during the early design stages certain changes were incorporated.



Scott McArthur.




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