Definition of Va (maneuvering speed) and Vno
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.
Do you have a question for our flight instructors? Ask your flight training or aviation related question in the forum today!
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.
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.
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
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.
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
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.
Rich on Dec 28, 2014
Daniele,
Brian did an excellent job explaining it, above, and implys that you are wrong in assuming that Va doesn’t change with weight. But, I think you are correct.
Just to add to Brian’s explanation, we can think of it this way:
Available lift is proportional to the square of the airspeed. So if the airspeed is doubled, four times as much lift is available. If the maximum load factor is 4 g’s, then Va is twice stall speed – since at the stall speed in level flight, the aircraft is loaded at exactly 1g, In order to provide sufficient lift to exceed a load factor of 4, the plane must be traveling at a speed in excess of the square root of 4 times the stall speed.
As the weight is increased, the stall speed also increases (again, as the square root of the weight increase). The speed at which the airplane can provide 4g’s of lift would also increase. So, it seems (counterintuitively) that Va would increase with weight.
However, from a structural standpoint the limit really isn’t G-loading, but a force limit – in this case, 4 times the maximum gross weight. So, it seems to me that from a structural standpoint, you are correct. An aircraft rated for 4 g’s should withstand 4 G’s at a given weight, and more than 4 g’s that at less weight.
Someone might suggest that the 4 g limit prevails due to the possibility of the battery box, motor mounts, etc. breaking, but for the primary structure, Va should be a fixed airspeed.
Gary S. on Jan 25, 2015
First of all, the question was “What’s the definition of Va and Vno. The answer is none. They’re the same. These identical speeds are both located at the top of the green arc on light aircraft airspeed indicators. Va is the most common version of the two which is what I’ve always used. Don’t know why someone chose to confuse them. Who knows?
That said, judging from all the answers, I think the question evolved into… “What’s the difference between Va and Vne?” There are many good answers on that but I’d like to present a very enlightening article about Design Maneuvering Speed (Va) written by AOPA’s Sara Brown on Jan. 20, 2011, and here it is:
by Sara Brown
Think you know your V-speeds? The FAA has released a special airworthiness information bulletin (SAIB) providing information to pilots after determining from a crash investigation “that many pilots have a misunderstanding of what the design maneuvering velocity (speed), V A, represents.”
The investigation followed the Nov. 12, 2001, crash of American Airlines Flight 587, which killed all 260 people on board and five people on the ground. The NTSB determined that the vertical stabilizer separated in flight “as a result of the loads beyond ultimate design loads that were created by the first officer’s unnecessary and excessive rudder pedal inputs.”
“Many pilots believe that as long as the airplane is at or below this maneuvering speed, they can make any control inputs they desire without any risk of harm to the airplane,” the FAA said in the SAIB. “This is not true.
“The design maneuvering speed ( V A) is the speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane.”
The SAIB states that even though the accident aircraft was operated under Part 25, the concept of maneuvering speed is relevant to all types of airplanes. It explains that the regulations governing airplane structure design strength require adequate strength for full control deflection below V A—but that manufacturers are not required to make airplanes strong enough to withstand full control input in one direction followed by full input in the opposite direction, or for more than one full control input.
This type of education—bridging the gap between what manufacturers test and what pilots think they test—was among the recommendations provided by an industry study of the certification process for Part 23 aircraft. AOPA chaired the study’s pilot interface working group that discussed flight testing, operation, and pilot training, and found a disconnect between aircraft certification and operation. In 2009, the group suggested more emphasis on pilot understanding of V speeds and the protection actually given at those speeds, among other recommendations.
The SAIB also explains that the V A number published in an airplane flight manual or pilot’s operating handbook is valid for operation at a specific gross weight, typically max gross weight. V A decreases as the airplane’s weight decreases. It recommends pilots reduce V A when operating below gross weight according to the following formula:
Va-NEW = Va √(Wnew – /Wmax-gross).
Gary S: I’m not aware of any rebuttals or further discussions on this. Just passing it on for what it’s worth.
Gary S. on Jan 26, 2015
When I tried to find the new Va for my airplane, at first I misinterpreted the formula and it wasn’t coming out right. Stated in plain english, I think this is correct:
Go to your poh to find the published Va at gross wt. and the gross wt. itself.
Lets say that you find Va is 98 and the gross wt is 2550 for your airplane
Plug those numbers into the formula.
From 2550, subtract 340 lbs for the missing 2 persons aboard, and 120 lbs for the missing baggage. Assume full fuel and oil. This will give you the new acft wt. of 2090.
Plug 2090 into the formula.
Divide 2090 by 2550 which will give you .819. Plug .819 into the formula and find the sq. rt. of .819 which is .91.
Multiply .91 by 98 which will give you 88 which is you new Va.
Hope this helps.
Gary S. on Jan 26, 2015
By the way…the SAIB number for this is CE-11-17 if you want to reference it.
Donald S. on Sep 12, 2015
> First of all, the question was “What’s the definition of Va and Vno. The answer is none. They’re the same.
Um, no they aren’t. Go back to flight school.
James Trowbridge on Apr 02, 2016
Watching flight video and flight discussion has really challenged my prior simplistic notion of flight. One cannot get enough training and experience.
Bob Davis on Apr 10, 2016
I agree heartily with Donald S. Va is related to what can happen to the airframe from within the airplane done by the pilot. Vno is related to what can happened to the airframe when exposed to external forces.