Difference between Vo and Va?
 

Lately I've been flying a Cessna 162 Skycatcher which has two different speeds listed for maneuvering speed. The definitions of both speeds are defined so slightly differently however that one could easily mistake the two.

One is Va (design maneuvering speed), and the other is Vo (maximum operating maneuvering speed). What is the difference between the two? I want to teach a student pilot steep turns and I am not wholly certain which speed I should tell him to beware of....

I reckon that this is also a subject over which not many CFIs have a well refined knowledge. I've asked my other more experienced coworkers how they differ, but even they seem to be clueless!

Difference between Vo and Va?
 

I believe Va is the speed at which you need to not exceed in turbulent conditions (stay below this velocity to prevent breakup, airplane would stall most likely before going into a structural design failing attitude) and the Vo is the maximum operating speed is the velocity to which maneuvers can be made in good conditions (smooth air) before a significant stress may be induced on the airframe. They are more structural limitation airspeed a similar to Vne than anything else. Someone else chirp in on this matter because I'm not one hundred percent!

The search box is your friend.

http://www.airlinepilotforums.com/fl...13-vno-va.html

this is true, but the OP was asking about Vo and Va, not Vno. Cirrus have Vo as well, specifically thats also the maximum parachute deployment speed. (however it has been pulled in the past at much faster speeds, some of which failed).

To the Op, honestly, I dont know. I know what Va is, and as one ahs said before its the speed where a stall would occur prior to stuctural failure. Essentially you cannont put enough G's on the aircraft to damage it because you will stall first at and below that speed. As for Vo, i have yet to get a clear answer myself.

I have heard that Vo refers to max manuevering speed because it is the speed where the control surfaces could fail due to stress(too much deflection), not the entire structure. but I am not 100% thats correct. but one answer i got from a fellow CFI.

Va is the speed (max weight) at which full deflection of controls should not be attempted for it might cause structural damage. And Vo is more of a certification requirement for the manufacture, it is a speed selected by the manufacturer not to exceed; stalling speed times the square root of max allowable positive load factor. At that speed, the aircraft should stall first before exceeding load factor limits.

Where as Va can not be less than Vs times the square root of the load factor.

I have researched both Va and Vo to the best of my ability looking up part 23 regulations and FAA special bulletin statements about Va. Am I correct in stating that below Va a pilot may deflect one flight control ONCE to its full deflection in stable air and expect the flight control not to come detached from the airframe? Contrary to what most pilots believe, Va has nothing to do with stalling an airplane to prevent overstress of the aircraft structure and flight control surfaces.

Vo offers further protection by enabling an airplane to stall before a flight control is stressed beyond its limits. When the manufacturer chooses Va to be equal to Vo, Vo is not specified in the AFM/POH, and only then will Va offer further protection by stalling before overstress of controls is encountered. I am hypothesizing that this is why the Cessna 172 Skyhawk does not have a Vo speed...because Va is most likely equal to Vo.

I am still not certain if choosing a speed below Va but slightly above Vo for steep turns in a Cessna 162 Skycatcher is appropriate. The AFM/POH states that 102 knots (Va) for that airplane is the maximum recommended entry speed for that maneuver, although my co-worker thinks we should do them below Vo. Do you folks think that the FSDO might have anything useful to say about this?

Va has nothing to do with deflecting control surfaces and has everything to do with stall speed. Wikipedia has a good simple explanation of the various speeds. You also really need to look at a Vg diagram to understand Va. Here is a website with a good one: Vg Diagram

Technically, FAR 23 says that Va cannot be less than the stall speed times the square root of the design positive limit load factor. This implies that it can be faster than that speed, but I'm not aware of a case where that is true. If you look at the Vg diagram, you can clearly see that you can exceed the design negative limit load factor at Va. Follow a vertical line down from Va and notice it would hit the yellow and then the red area before it would hit the extended curved line, which is what the wing is capable of. In other words, you can push on the yoke and hit the structural damage regime while still inside the flight envelope. Not true with positive g's, it will stall first. Can you stomp on the rudder at Va and snap the tail off? Maybe. The important thing to remember is that you can damage the aircraft at Va with control inputs. A lot of us were taught that you can "do full deflection in any direction and not damage the airplane". That is false.
Vo was introduced for the certification of light sport aircraft in 1993 according to wikipedia. The aircraft designer can pick a speed below Va and call that Vo for various reasons. Flight control deflection? Maybe. Tail strength? Maybe. The pilot doesn't know what the criteria that the designer used were. All you need to know is that for whatever reason, the designer chose to further limit the airspeed for reasons specific to that design. That being said, I would say use Vo for steep turns. You are only going to be pulling 2 g's anyway in a 60 degree turn. I wouldn't do them below Vo to give you an adequate buffer above the stall speed.
I would also always have your students compute the various V speeds for their current weight as the published speeds are for gross weight. It is a simple calculation: multiply any V speed by the square root of your current weight divided by gross weight. I'm sure you know that one, but for others here is an example. Published Va is 130 knots at a gross weight of 2100 lbs. Our current weight is 1800 pounds. 1800/2100 is .86 The square root of that is .93 130 knots times .93 is 120.9 or 121 knots. You can then use that .93 as a factor to determine any other V speed such as approach speed, stall speed, Vno, etc. Vne stays the same, however.

This is an old thread but thought it was worth revisiting.

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Annex B More on Vo, Va and Vno

Vo

Vo is a new symbol given to the speed which conforms to the formula Vs√Glimit. It was only created by an amendment to the US Federal Aviation Regulation 23 (FAR.23) in 2007. Prior to that date the term Va was used, which meant Velocity Maximum Acceleration, and is the term you will still find in most aircraft flight manuals and instruction manuals. Vo was introduced because Va came to be called the velocity for ‘Maximum Control Deflection’ of any control surface. Quote from FAR 23: “the loads resulting from full control surface deflection at Va are also used to design the empennage (tail) and the ailerons.” So Va may equal Vs√Glimit when the aircraft is pitched, that is with full elevator deflection, but can be different when the structural loads imposed by full deflection of the ailerons or rudder are considered. So for many aircraft Vo and Va are the same, but for others they differ. A simple way to think about this is that Va is the slowest of the individual speed limits applied to the maximum deflection of each of the three primary control surfaces, whilst Vo is the speed limit applied to the maximum deflection of the elevator only. This means that Va can never exceed Vo. (Think about it.)

Here is a further quote from FAR.23 amendment 45: “Va should not be interpreted as a speed that would permit the pilot unrestricted flight control movement without exceeding airplane structural limits!” This is why ‘they’ had to create Vo.

Vo seems to be a more ‘straight forward’ figure, but some manufacturers and student texts ‘muddy the water’ in regard to Vo. Some aircraft flight manuals declare different Vo’s for different aircraft weights because the aeroplane’s 1G stall speed varies with these different weights. This can be very confusing for the pilot because whilst the actual stall speed may vary with weight, Vs, by definition does not. Vs is always measured at the aeroplane’s maximum all up weight, therefore Vo, by definition, will always be at the aeroplane’s maximum all up weight too! If the aeroplane is stalled at Vo when it is lighter than its maximum all up weight, the accelerometer will record an acceleration greater than the aeroplane’s limit, (the same lift force acting on a reduced mass equals greater acceleration), but this does not mean that the wings have been overstressed! Consider this: An aerobatic category aeroplane which has a maximum all up weight of 800kg and an acceleration limit of 6G, has wings strong enough to safely withstand a maximum load of 4800kg (800 x 6), but if on a particular flight it only weighs 700kg then, if stalled at Vo, it will have 269 ‘pulled’ 6.86G! (4800 ÷ 700) So in this case the wings’ attachment to the fuselage has not exceeded their load limit; it is only the published load factor which has been exceeded.

HOWEVER, before you go out there and bend your aeroplane and blame me, let me emphasize that there may be other bits of the aeroplane which will break if the published G limit is exceeded. Let me explain. The aircraft designer, having decided upon the category of operation of the aeroplane is not going to ‘over engineer’ other parts of the aeroplane to be able to exceed the G limit for that category. A good example of this is the engine mount frame. There is no purpose in making this strong enough to withstand say, 8G, when the ‘red line’ is set at 6G because this would mean the aeroplane is carrying a weight penalty which would degrade its performance and increase its cost. So whilst the wings of our 700kg aeroplane might be happy at 6.86G, the engine might fall out!

Obviously, if you are the pilot of this aeroplane, you will have some explaining to do if you bring the aeroplane home without an engine and more than 6G recorded on the accelerometer......so take it easy, your safety net (stall boundary) has just shifted and no longer affords you the protection you thought it did!

Monitor the accelerometer and stick to the published G limits. (Your accelerometer should be mounted where it can be easily monitored.)

This. You comply with maneuvering speed by having a speed equal to or less than Vs√n where n= load factor. Va did not satisfy this, but was being taught as though it did. Vo is maneuvering speed in the sense that full deflection will result in a stall before an airframe is bent or broken. I'd suggest reading Subpart C: Structure in Part 23.

Only difference Snickers can see is a vowel.

Snickers gets a bone! Correct answer. :)

Student pilot here - has been thinking about this question for the past 2 days and found this forum, very helpful! I will try to describe my understanding below, correction welcomed!

Vs = stall speed (weight dependent)
n = design load factor limit (weight dependent)

Making up some variables for ease of substitution:

A = critical AoA
W = aircraft weight (variable)
L = design wing loading limit (weight independent, the actual aircraft would have margins over it). L = W * n
S = speed at which L is reached at A. S = Vs * sqrt(n)

So:

Va = design maneuvering speed, greater than or equal to S, which is used to design the control surfaces to withstand the load at full deflection at the speed.
Vo = operating maneuvering speed, Vo <= S. Under Vo, aircraft will stall before reaching L or any other structural limit

Someone's been reading Aerodynamics for Naval Aviators, haven't they?

The notion that the structure will stall before damage occurs is inherent in aircraft design: the gist is that there is a value at which structural damage won't occur under a given gust load or structural loading imposed by say, full control deflection, or a gust load imposed at a particular speed. That criterial is applied to many elements of design and certification. However, with respect to the end user, pilots, considering Va, or maneuvering speed, pilots were taught for many years that it was the speed below which a full control deflection would result in airflow separation (stall) before a damaging load could be imposed. The problem is that such an explanation is too simplistic, and it's wrong.

One can break an airplane below Va, because when we consider a fullly deflected control surface, for example, we consider the singular load imposed by that isolated event. Pull back on the control stick, raise the elevator, load the elevator surface and hinges, stab attach points and stab, and wing, wing spars, attach points, etc, and in theory...it won't break. But that's just one pull. In that loading, there's bending and flexing, torsion, compression, and tension, and when we apply a second load, say for example, to reverse the control input, we don't simply load in the opposite direction. We impose a series of unintended loads that are not explained by the purpose of Va...more than one control input, especially opposite or reverse inputs, can impose loads that do exceed the structural integrity of the aircraft, causing damage or failure.

The crash of American Airlines 587 in Jamaica Bay (New York) was an eye-opener to some, who believed the myth that the aircraft couldn't be damaged at low speeds. It can. Multiple control inputs, alternating inputs and rapid inputs alter the equation and the complexity of the load, and exceed or act outside the established limitation and the so-called protection of operating under that speed.