... the induced drag of a wing relative to that of a standard planar wing with the same span, lift and speed. An induced drag factor of less than 1 indicates that the wing is non-planar. The minimum drag of a Harris’ hawk gliding freely in a wind tunnel was measured before and after removing the slots by clipping...

... and different wing tips. The feathered wing tip was slotted and was made of four primary feathers from a Harris’ hawk ( Parabuteo unicinctus ). The Clark Y tip was unslotted and was made of balsa wood shaped to a Clark Y aerofoil. The balsa feather tip was slotted and was made of three balsa wood wings shaped...

... techniques for measuring the interference drag generated by (a) the drag balance and mounting strut together and (b) the mounting strut alone. Corrections for interference drag may reduce the apparent body drag by more than 20 %. A gliding Harris’ hawk ( Parabuteo unicinctus ), which has a body similar...