By Mike Andresen
Most things you read about regarding maneuvering speed address the bending of an airplane aspect of it, but there is another aspect to maneuvering speed that I'm going to discuss in this article. You are about to learn why it is called maneuvering speed and not called bending-an-airplane speed.
Recall that for an aircraft to maintain constant altitude, the vertical component of lift must equal the weight of the airplane plus the tail down force. For the purpose of keeping this discussion simple, I will use weight to mean weight plus tail down force. For the airplane to turn, the aircraft must generate a horizontal component of lift by increasing the overall lift generated such that the vertical component of lift maintains the weight of the aircraft and the horizontal component of lift causes the aircraft to turn. This is accomplished by either increasing the angle of attack or by increasing airspeed. Let's assume power is constant and the turn is made by increasing control back pressure to increase angle of attack.
As the airplane is in the constant altitude turn, the wing is generating lift in excess of the weight. The ratio of total lift to weight is known as the load factor. In a sixty degree bank, the wing will have to generate twice the weight of the airplane in order for the vertical component of lift to equal weight. Under this condition, the load factor is two and the pilot will feel twice the force of gravity which is referred to as 2G. Figure 1 is a graph of load factor versus airspeed. In the graph, airspeed is expressed as a multiple of the stall speed. The maneuvering speed is strictly a function of the stall speed and maximum load factor of the airplane. For a normal category airplane where the maximum positive load factor is 3.8G's, the maneuvering speed is always 1.95 times the stall speed.
Each load factor is achieved by maintaining constant altitude with the airplane in a specific bank angle. Figure 2 is a graph of maximum bank angle achievable versus airspeed. This graph tells you that in order to perform the 45 degree bank, the 1.4G turn required for private pilot test standards, the airspeed must be at least 1.2 times the stall speed. It also tells us that the maximum bank angle achievable in a normal category airplane is 75 degrees. Parachute required! Flying at the maximum possible bank angle will result in the fastest turn rate and the minimum turn radius possible.
The point of all this is that the maximum performance turn is achieved in an airplane when flying at maneuvering speed with a maximum supported bank angle. For a normal category airplane, this means flying at 1.95 times the stall speed in a 75 degree bank pulling 3.8G's. That is quite a bit of performance that we can get from our airplanes.
To summarize, at any speed below maneuvering speed turning at the airplane’s minimum turn radius is possible only by increasing the turning rate and g-load to the verge of an accelerated stall. Above maneuvering speed, you are g-limited by your category and hence cannot increase turn rate to achieve minimum turn radius.