Last week’s piece on maneuvering speed inspired me to dig a little deeper into the topic of VA. It really is an interesting topic that forces pilots to delve into aerodynamic theory. This week, let’s take a closer look at maneuvering speed.
Perhaps the best source for such understandings is the uber-technical Aerodynamics for Naval Aviators. According to this classic text, maneuvering speed can be defined by a simple formula:
Maneuvering Speed = VS√(n), where VS is stall speed and n is the limit load factor.
The good book goes on to talk about the V-N diagram and points out that this is the maximum speed at which the wings will stall before exceeding structural limitations. That’s where our common understanding of VA comes from.
Let’s run the numbers. According to my Piper Arrow manual, VS is 60 KIAS at max gross weight with the flaps and gear up. Our limit load factor is 3.8g, so that’s our value for n. So maneuvering speed is calculated to be:
Maneuvering Speed = 60 × √(3.8) = 117
You might find it interesting to know that the Piper Arrow pilot’s operating handbook defines VA to be 118 KIAS at max gross weight. That’s one knot in the less conservative direction. That’s probably due to small errors in our math (you’re supposed to use equivalent airspeed, not indicated airspeed for this stuff).
But there could be another culprit. And that lies in the legal definition of VA. More on that next time.