Gliding Flight of the Fulmar Petrel

  • Pennycuick C
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1. The basis used for estimating lift and drag coefficients is explained. A method of obtaining a photograph of a bird flying at known airspeed and rate of sink is described.2. 96% of the speed measurements fall between 22 and 65 ft./sec., the average being 40 ft./sec.3. A maximum lift coefficient of 1.8 can be achieved. Wing area is reduced with increasing speed.4. The feet are used as airbrakes.5. A comparison of the minimum drag coefficient (0.06) with the maximum estimated power output of the pectoral muscles leaves only a narrow margin of power available for climbing.6. The performance diagram gives a minimum gliding angle of 1 in 81/2, and a minimum sinking speed of just under 4 ft./sec.7. The fulmar has apparently sacrificed the ability to soar dynamically over the sea in order to be able to fly slowly and thus utilize light upcurrents at cliff faces.

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  • C J Pennycuick

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