18 August 2008

Trying to avoid bird strikes

August 2008 Winter this year has been a little less conducive to flying than the same time last year. Over the last few months, I had only managed to exercise the big bird about once every two weeks rather than every week. In most cases when a flight was precluded, the skies were generally clear.

But westerly to south-westerly weather patterns (typical during winter) created strong crosswinds exceeding the Yak-50's capability - or my comfort level. Although I often flew the Alpha/Robin with crosswind components up to 25 knots, I had over 200 hours experience in the tricycle landing gear aircraft. On the other hand, my less than 10 hours familiarity with the tailwheeled beast demanded caution rather than recklessness.

Sunday, 17 August, was one day during which the wind cooperated long enough for me to launch a sortie. Arriving at the hangar early, I dragged the big metal bird out into the brilliant sunlight. Completing the pre-flight inspection, I then proceeded with my pre-flight workout.

For radial-engined aircraft, pulling the propeller through before flight is vital if one wants to avoid hydraulic locks. Hydraulic locks are commonly caused when engine oil that has collected in the bottom cylinders, is not cleared. Since liquids are incompressible, the oil trapped in the combustion chamber acts like a solid block to a moving piston; leading to a bent or snapped connecting rod or complete engine destruction.

When fitted with suitable excess oil drain valves, pulling through a propeller clears any residual oil from the lower cylinders. The workout comes from pulling the propeller through at least six complete revolutions. It is not easy overcoming the natural compression of the nine cylinders.

Eventually, I arrived in the training area and flew the bird through its exercise routine. This time, I decided to use higher power settings of 75% rpm and 80 cm manifold pressure. Vertical performance along with fuel consumption rose accordingly. Rather than use a starting altitude of 4500 ft, I started at 4000 ft to avoid punching through the Sydney CTA lower limit during vertical manoeuvres.

After executing the usual practice forced landing, I pointed the bird for home. Approaching the Prospect Reservoir VFR checkpoint, I spotted two flocks of Ibises closing fast on a reciprocal heading. Bracketing me on the high and low sides, I had little choice but to maintain my altitude and hope they would do the same. Instinctively, I hunched down a little lower and hoped for the best.

The lower flock whipped past below and to the right of my right wing. They probably saw my strobe light and veered away from my flight path. On the other hand, the higher flock whipped past no more than 30 ft above my mid left wing. Fortunately, they did not dive as most birds seem to do instinctively when confronted with danger.

My arrival and recovery to Bankstown was much less eventful. Reflecting on the near miss, it seemed to me that flying a steady course and altitude at relatively low speed (130 knots) gave both flocks time to avoid colliding with the metal bird. Or I could have just been lucky.

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