"Unlike the proavian ancestors of birds, Archaeopteryx had wings that were large enough to contribute acceleration as it ran. Archaeopteryx probably took off by running and flapping its wings, just as many large birds do today. Once the animal was airborne, calculations of metabolic capacity suggest that an Archaeopteryx could fly at least 1.5 km at a velocity of 40 km/hr (Ruben 1991, 1993).
~F. Harvey Pough, Christine M. Janis, John B. Heiser, Vertebrate Life (my Wildlife textbook)