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Definition of Va (maneuvering speed) and Vno

Posted by on January 15, 2008 6 Comments Category : Flight Instructor Blog Tags : , , ,

Thought I would post a recent thread from our forum:

Here was the question that was asked:

Could you please give me a detailed explanation of maximum structural cruising speed. I’m confused as to why it is higher than manuevering speed and doesn’t change with weight like Va does if they both are turbulent air penetration speeds?

Thanks for your help.

And here was the answer:

Hi! Great Question! I actually had to do some “research” for this one!

Va. Known as maneuvering speed. This has to do with the MAX speed at which you can safely stall an airplane. During certification, this has to do with forces measured on the elevator (see image below). Any speed above Va you would exceed structual limits before reaching a stall (not good)

Vno. Maximum structual cruising speed. This has to do with wind gusts measured on the wings. I have to do a little more research but my source told me below the yellow arc it is 20 in. per second gusts and in the yellow arc it is 15 in per second gusts. This has to do with the wings bending and twisting. Not structural limits on the elevator.

Some instructors teach students that Va is turbulent penetration speed which is really not completely accurate and may confuse things. It also may have to do with the fact that Va wasn’t a required certification until the 50’s or 60’s.

Hopefully this helps some.

Instructor.
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6 Comments



  1. Rob Schutte on Jun 07, 2009

    I had also done some research years ago as I could not get a good answer either. From a US Navy flight training manual I got that Va is the speed at which the aircraft would exceed its upper load limit before stalling. My interest was also what was the actual Va during flight, its not really what is in the manual. From a aircraft aerobatics manual I got a formula. Square root of the upper load limit times the stall speed. Try it out, I did. First you need to determine your actual stall speed at your given flight condition and you’ll have to fly to do this. This makes more sense than the old “any full deflection of the control …” and you can see why Va is not on the ASI as well.



  2. Chris Furse on Mar 06, 2010

    The term Va is widely misunderstood in the aircraft operation community. The only time Va is related to stall speed is if an aircraft designer selects Va (minimum) for his design. He is permitted to select any speed for Va. providing it is above Va (min).
    Also Va is only concerned with the design of the rudder/fin, elevator/stab, ailerons and their attachments.
    AC 23-19A states:
    48. What is the design maneuvering speed VA?
    a. The design maneuvering speed is a value chosen by the applicant. It may not
    be less than Vsv n and need not be greater than Vc, but it could be greater if the applicant
    chose the higher value. The loads resulting from full control surface deflections at VA are
    used to design the empennage and ailerons in part 23, §§ 23.423, 23.441, and 23.455.
    b. VA should not be interpreted as a speed that would permit the pilot
    unrestricted flight-control movement without exceeding airplane structural limits, nor
    should it be interpreted as a gust penetration speed. Only if VA = Vs vn will the airplane
    stall in a nose-up pitching maneuver at, or near, limit load factor. For airplanes where
    VA>VSvn, the pilot would have to check the maneuver; otherwise the airplane would
    exceed the limit load factor.
    c. Amendment 23-45 added the operating maneuvering speed, VO, in § 23.1507.
    VO is established not greater than VSvn, and it is a speed where the airplane will stall in a
    nose-up pitching maneuver before exceeding the airplane structural limits.



  3. Brian on Sep 08, 2010

    “My interest was also what was the actual Va during flight, its not really what is in the manual. From a aircraft aerobatics manual I got a formula. Square root of the upper load limit times the stall speed.”

    Rob, if you’re still reading this, you have found the formula for determining Va. Maneuvering speed is simply stall speed times the square root of the limit load factor (3.8G in normal category).

    If you’re looking to find the maneuvering speed for that day you can do so like this: Current maneuvering speed = max weight maneuvering speed * sqrt (current weight / max gross). Conversely you could use that same formula to find the new stall speed: current stall speed = max gross stall speed * sqrt (current weight / max gross) and then take that number and apply it to the maneuvering speed formula. I think the later just takes too long and keep in mind, numbers are handled with in terms of EAS or CAS, whichever is available, when making performance calculations.

    Side note: The above formula works for any speeds that require a specific AOA or are a derivation of the stall speed. Thus, you can find best glides speed for the day by inputing it into this formula.

    Topic two seems to be on Vno and for that I’d rather reference Part 23:

    Part 23.333 (c) Gust envelope tells the story, I’ll paraphrase: “Gusts at both 50 and 25 fps must be considered through a range of altitudes.”

    Part 23 hosted on EFT

    If you go to the above link and scroll down just under part 23.333 you will find a pdf file. The file is a V-g diagram to show what all the v-speeds discussed are. As you will see, the Vc (50 fps gust) line extends beyond the positive g-limit. The Vd line (25 fps gust) is within limits. This ambiguity (lack of common experience FOI baby!) is exactly why I define Va and Vno as follows:

    Va is the speed at which full and abrupt, symmetrical, control inputs should be ok. I leave out the bickering between Va and Vamin (soon to be known as Vo) as I’ve yet to come across an aircraft where the two are not the same.

    For application I tell them this:

    Smooth air, fly whatever you want. Light turbulence, keep it in the green arc. If the turbulence gets heavy, slow it to at or below Va.

    I rarely say this with aerodynamics, but accuracy here can be sacrificed for simplicity without hindering safety. In my humble opinion of course.

    ~Brian



  4. Nick on Sep 17, 2011

    At any speed below the maneuver speed the aircraft cannot be overstressed. It will stall before the limit load factor is reached. Above this speed, however, the aircraft can exceed the limit load factor before it stalls. At the maneuver airspeed the aircraft’s limit load factor will be reached at the lowest possible airspeed.



  5. Daniel on Jun 20, 2014

    I don’t think Vno was explained well above.

    The main difference between Va and Vno is, Vno is the maximum speed allowed in essentially non-turbulent flight (i.e. still air flight only). Vno is also the top of green arc on the airspeed indicator.

    How this applies during flight:

    If you encounter turbulent flight; reduce to at or below Va or Vb if your aircraft has a turbulent air penetration speed



  6. daniele on Dec 17, 2014

    WHat about Va in relation to the actual weight of the aircraft? I think that from a structural point of view it doesn’t change.

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