The advantage of the humpback-whale flipper seems to be the angle of attack it’s capable of–the angle between the flow of water and the face of the flipper. When the angle of attack of a whale flipper–or an airplane wing–becomes too steep, the result is something called stall. In aviation, stall means that there isn’t enough air flowing over the top surface of the wing. This causes a combination of increased drag and lost lift, a potentially dangerous situation that can result in a sudden loss of altitude. Previous experiments have shown, however, that the angle of attack of a humpback-whale flipper can be up to 40 percent steeper than that of a smooth flipper before stall occurs.