Maneuvering Speed

I listened to an interesting podcast on the flight up to Canada this morning and it got me thinking. The podcast was around maneuvering speed. I think we all have memorized what it is.

From our POH:
Maneuvering speed (Va) is the highest safe airspeed for abrupt control deflection or for operation in rough air. Upon encountering severe gusts, pilot should reduce airspeed to maneuvering speed to lessen the strain on the aircraft structure. For any airplane, maneuvering speed can be estimated by multiplying the airplane’s normal stall speed by 1.7. Maneuvering speed decreases as aircraft weight decreases. Refer to aircraft operating manual for for correct speeds and operating procedures.

Continuing in the POH.
Maneuvering speed
2400 pounds 99 KIAS
2000 pounds 92 KIAS
1600 pounds 82 KIAS

OK, so we can pass the test, but why does this speed change with weight, what is really going on here? I’m glad you asked.

Let’s listen to this description for some hints:
Maneuvering speed is the maximum speed where full, abrupt control movement in the pitch axis will result in an aerodynamic stall of the aircraft prior to exceeding the design load limit.

Aha! Did you read what I read (and heard on the podcast)?

Here it is paraphrased from the podcast:
The engineers calculated the angle of attack that the wing stalls for a given weight (aerodynamic stall). They then calculated the second angle of attack that, with an abrupt control movement, would get the plane to the stall angle of attack before the g-force load exceeded their calculation of what it would take to stress the aircraft (design load limit).

So, for our plane, for normal category, that design load limit is 3.8 times gross weight with flaps up. If we are speeding along at 99 KIAS, with nobody in the plane, our angle of attack is small due to the small lift requirement, and we are further from the stall angle of attack and can therefor exceed 3.8G if we abruptly move the yolk. If we are at max gross, we need more lift, so a higher angle of attack for the same speed of 99 KIAS, which is closer to the stall angle of attack, so we will not be able to get to the 3.8G needed to stress the airplane if we abruptly move the yolk.

There you go. I hope that made you think a little more about what this maneuvering speed is, and how it’s designed to save the airplane (and you) when you enter rough air.

If anyone has any comments, disagreements, better understanding, please feel free to send them to all. Remember I am not a CFI, this is only meant to get you thinking.

One Response to “Maneuvering Speed”

  1. Steve Pomroy says:

    Maneuvering speed is a design/certification speed that references the structural strength of the control surfaces.

    You can read up some more about it here: http://www.flightwriter.com/2010/09/va-not-bad-speed-just-misunderstood.html and http://www.flightwriter.com/2010/09/va-not-bad-speed-just-misunderstood_27.html.

    Cheers!

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