29 March 2009

A little excursion

March 2009 Ever since I started flying the beast a year ago, I had not formally measured its cruise fuel flow; so preoccupied was I with getting comfortable with its general and aerobatic handling.

But with its annual inspection due on 28 March, I decided to conduct this long deferred exercise before the big bird was temporarily taken out of service. I also wanted to test my new Lowrance 2000c GPS unit out on the same flight.

The night before, I had programmed a short trip from Bankstown to the Three Sisters (near Katoomba) via The Oaks and Lake Burragorang. All up, the route was about an hour's flight interval.

As the bird cruised towards The Oaks at 4,500 ft, I spotted a few columns of smoke a few miles west of Lake Burragorang. It looked like these were burn offs to reduce the risk of bush fires.

For simplicity, I used a cruise setting of 60% rpm and about 55 cm manifold pressure. Although this lower of two recommended cruise power settings yielded an indicated airspeed of only 205 kph (111 kts), I chose it as it would be the power setting for maximum endurance.

After the flight, I refuelled the big bird to obtain an accurate measurement of the fuel consumed. I was happy to find the cruise fuel flow was an average of 45 lph.

This result would have been even lower after correcting for takeoff fuel flow and the higher power settings used for the brief run-in to the Three Sisters waypoint and the short climb following the practice force landing.

Compared to the Yak-50, the Yak-52's higher cruise consumption (between 50-60 lph) is mostly due to the extra drag from the exposed retracted landing gear, and the about 350 kg extra weight.