First we must ask: Is it African or European swallow? And in order to determine airspeed velocity you have to take into consideration both the windspeed and ground speed velocities before calculating the swallow's... Now back to the species... And African swallow is of a much larger variant so therefore carries greater mass and therefore great speeds at maximum velocity. But are we talking about maximum airspeed velocity or just any velocity recorded between time of take off and time of landing. There is also a case in which a day could have 0 wind (and therefore 0 general wind resistance) at any altitude and therefore the ground speed velocity and airspeed velocity are relatively identical (but this is rare). And this is just for objects in motion abound the ground such as planes and thrown objects.... To find the airspeed velocity of a bird, one must calculate the Strouhal number. The Strouhal number is usually used in the calculation of speed of fish in water. In that case, it is the ratio of frequency of the tail moving and the forward speed of the animal. A man named Graham K. Taylor discovered the same principle can be applied to birds and other animals that can fly. The strouhal number for birds is the frequency (F) multiplied by the amplitude of the wings (A) divided by the speed at which the animal is traveling through the air (V) ((HzxA)/V) Frequency = number of beats (of wing(s))per second Amplitude = distance wings travel in an oscillated (up and down) movement. The average strouhal number is 0.3, So it is concluded that the average airspeed of an unladen swallow is 24mph or 11m/s