ADA-Jack Woodman:Flying the Arrow.Pg.2
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Jack
Woodman:
Flying the Arrow.
Pg.2
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.
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