Why it Vn0 higher than VA speed and doesn’t change with wt like Va does if they both are turbulent air speed

Question

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

Thanks for your help.

Answer 1

airbrnrngr1087 is correct but I'll add a little something that may make it easier for you to understand maneuvering speed (Va) and why it varies with weight.

Ordinarily, pilots try to avoid stalls and, therefore, don't want to fly at a high angle of attack.  However, there is a time when stalling the airplane can save your life.  When flying in very turbulent air you want the airplane to stall before it breaks.  Therefore, you want to fly at a higher angle attack than you normally would.

Let's look at an example to see how this works.  Suppose you normally fly at 150 KIAS and the angle of attack at this speed in level, unaccelerated (1G) flight is 3 degrees.  Let's also assume that the stalling angle of attack is 15 degrees.  (By the way, these numbers are not exact but they serve the purpose here).  If you double the angle of attack you will roughly double your G-loading.  If you encountered turbulence in the above example (or if you pulled full up elevator) you could pull 5 G's (15/3 = 5) before the airplane stalled.  This would damage most General Aviation airplanes.

How do we fix this?  What we want to do is have a higher angle attack while curising along in level, 1G flight.  The ONLY way to do that is to slow down.  As you slow down, the wing produces less lift and you have to fly at a higher angle of attack (by increasing back pressure on the yoke) to maintain level flight.

For our example let's say that if you slow down to 110 knots you will have to fly at an angle of attack of 4 degrees to maintain level flight.  Now, if you apply full up elevator (or encounter severe turbulence) the airplane will pull 3.75 G's (15/4 = 3.75).  Since Normal Category airplanes are certified to 3.8 G's we'll consider 110 knots to be our maneuvering speed.

That's a quick and dirty explanation on how maneuvering speed works.  Now we'll see why maneuvering speed varies with weight.  The above numbers are for max gross weight.  In our example, let's say our max gross weight is 4,000 lbs.

We've already determined that when flying the airplane at 4,000 lbs and 110 knots that you're angle of attack is sufficiently high that the airplane will stall before it suffers structural failure.

What happens if we fly at 3,000 lbs?  Since in 1G level flight lift has to equal weight you will need less lift which means flying at a lower angle of attack for any given airspeed.  In our example, let's say that at 3,000 lbs we only need 3.5 degrees angle of attack to maintain level flight instead of 4 degrees.  What happens if we encounter turbulence?  The airplane will experience 4.3 G's (15/3.5 = 4.3) before stalling which is too high.  Again, we will have to fly at a higher angle of attack and we can only accomplish this by flying slower (the wing produces less lift at the lower speed so angle of attack must increase).  That is why maneuvering speed varies with weight.

If you have any more questions feel free to e-mail me.

Answer 2

Vno (Max structural cruising speed) is the speed which is only to be exceeded in very smooth air.  It offers no actual protection as far as the structural integrity of the aircraft if you were to hit severe turbulence.  It's saying, "Hey...you can only go faster than this if the air is really smooth.  But, if you hit severe turbulence, the airplane might still suffer structural damage."  That's why it's not a turbulence penetration speed...the air has to be smooth for you to go faster than this, so it's more of a "smooth air speed".

Va is the maximum speed for a given weight at which the airplane will stall before it becomes overstressed.  This means if you hit severe turbulence, the airplane will stall before it structurally fails.  This is a very specific speed that is directly related to angle of attack, so it is proportional to the weight of the aircraft.  THIS is a turbulence penetration speed...you want to make sure that regardless of the severity of the bumps you hit, the airplane will stall before you overstress it.

Fly below Va in turbulence, and exceed Vno ONLY in very smooth air, because it offers no protection if you were to actually hit turbulence.

Answer 3

Oh boy.

Answer 4

Its to my understanding that Va is the actual manouvering speed, whereas when you give full deflection of any of the controls, the aircraft will stall before any structural damage takes place. This speed decreases with an increase of weight because the heavier a plane is, the more readily it will stall.

Vno is the speed which is only permissable through smooth air. This is getting fast for the airplane, and sudden control movements or severe turbulence will damage the aircraft by overspeeding, over-loading, or overstressing the aircraft. I'm not totally sure why Vno does not change with weight, but I suspect that it is because manouvering speed needs to consider the stall characteristics of the aircraft (which can vary with weight) whereas Vno is more concerned with speed that with stall.

That's how my instructor explained it anyway...

Answer 5

Simple:  Vno is published at maximum certificated gross weight.  Thats actually the definition of Vno.

Maximum structural cruising speed is pretty much a worthless number.  It is simply the top of the green arc.  It means nothing and guarantees nothing.  Except that if you are in the yellow arc and you encounter severe turbulence you probably will exceed the maximum wing-loading of your wing and cause structural damage.  However, there is no real "definable" difference between that and Va, as Va is essentially the same thing.

One way to think of Vno is a "salesman's" speed.  If it was published as low as Va, then nobody would ever buy the plane.  Operation below Vno does not necessarily guarantee safety either, as you may or may not be above Va.

Answer 6

never heard of Vn0. do you mean Vne? the aircraft's max speed? typically Vne is based on handling characteristics affected by drag. weight has nothing to do with it.

fly boy could not be more wrong about Va, maneuvering speed. Va, like Vs0 or Vs1, flaps or no flaps, increases with increased weight. Va as published means at the max certificated weight. it's the speed above at that weight were maximum deflection of the controls abrubtly can cause structural damage. Va is pretty useless information and is not published in large aircraft. just use a light touch on the controls when flying fast and you'll be ok.