Maneuvering Speed vs Weight

[tsgarp]

I think if you really want to get a grip on what Va is, you should turn to 14 CFR § 25.335, where it is defined. To the extent any written source contradicts that, that written source is wrong - be it Wikipedia, Kershner, an anonymous FAA commentator, or anyone else.

Cool. You do realize that your cited reference also contradicts your stated position here?

Design maneuvering speed VA . For VA, the following apply:

(1) VA may not be less than VS1 √n where -

(i) n is the limit positive maneuvering load factor at VC; and

(ii) VS1 is the stalling speed with flaps retracted.

(2) VA and VS must be evaluated at the design weight and altitude under consideration.

(3) VA need not be more than VC or the speed at which the positive CN max curve intersects the positive maneuver load factor line, whichever is less.

[photofly]

I know what the regulation says. Which bit of what I’ve written is at odds with the regulation?

[tsgarp]

If you point out what you mean, I’m happy to look at it.

Your cited reference is not the definition of Va. Your cited reference is an Airworthiness Standard for certification of Transport Category Aircraft. Va is the speed above which full deflection of the controls will result in the acceleration of the aircraft exceeding it's maximum designed load factor. Your reference does not contradict this accepted definition. What your reference says is that if you want to certify an aircraft in the transport category its maximum designed load factor and stall speed must be such that it meets the requirements set out in the reference you gave.

[tsgarp]

Advice for everyone: Read Kershner. You will be happy you did.

[photofly]

Va is the speed above which full deflection of the controls will result in the acceleration of the aircraft exceeding it's maximum designed load factor.

(Emphasis added)
Except that's not true.

Va, Vb, Vc, and Vd are the design speeds. The aircraft designer can choose them to be what he or she wants them to be - that's why they're called "design speeds". Having chosen that speed, there's no need to go back and adjust the controls to make your supposed but very precise condition that at that exact speed "full deflection of the controls will result in the acceleration of the aircraft exceeding it's maximum designed load factor" come true.

If you look back to CAR 3, under which most GA planes in existence were certified, it says:

§ 3.184 Design air speeds. The design air speeds shall be chosen by the designer except that they shall not be less than the following values:

Your misunderstanding of what Va stems from your belief that Va represents a determined speed at which something will happen - some limit will be exceeded - determined either by prediction, or by testing. It isn't that. Various tests of the aircraft have to be done at Va, and some terrible possible consequences of using the control have to be delayed until at least Va, but the designer can nominate a Va to be whatever they want, subject to the limits in CAR3 or 14 CFR 25.335. They are then on the hook for building an aircraft strong enough.

It's the difference between "you can fly this fast, do *this*, and not exceed a limit" vs. "if you fly this fast, and do *this*, you will exceed a limit." - or equivalent to the latter, and equally incorrect, "this is as fast as you can fly and do *this* in safety".

Denker addresses different uses of Va in See How It Flies, 2.14.2 (https://www.av8n.com/how/htm/aoa.html#s ... ring-speed)

Particularly:

Finally, we should note that there are two different concepts that, loosely speaking, are called maneuvering speeds.

The design maneuvering speed, which we can denote Va(d), is primarily of interest to aircraft designers, not pilots. The designer must choose a value for Va(d) and then build an aircraft strong enough to withstand certain stressful maneuvers at that speed. Higher values of Va(d) promote safety, by forcing the design to be stronger.
The maneuvering speed limitation, which we can denote Va(l), is of interest to pilots. It is an operating limitation. It appears on a placard in the cockpit. Lower values of Va(l) promote safety, by restricting certain operations to lower, less-stressful airspeeds.

To my mind, Va is the "design manoeuvring speed", and is defined in the regulations as something at the free choice of the designer, subject to the limits publisned. If you want to invent a limiting speed for pilots, call it something else.

[tsgarp]

—-snip—

That’s all very interesting, but (and this is according to your reference) Va can’t be less than the flaps up stall speed times the square root of the maximum design load factor. So, if you are above Va and you execute a full control deflection you will exceed the maximum design load factor, this will render the airplane un-airworthy (I.e. broken) until at the very least it is inspected. So, to recap, full control deflection above Va = broken airplane.

[photofly]

—-snip—

That’s all very interesting, but (and this is according to your reference) Va can’t be less than the flaps up stall speed times the square root of the maximum design load factor. So, if you are above Va and you execute a full control deflection you will exceed the maximum design load factor, this will render the airplane un-airworthy (I.e. broken) until at the very least it is inspected. So, to recap, full control deflection above Va = broken airplane.

Again, read the instructions for the test required at Va. The elevator test is discontinued when the load factor reaches the nominal limit.

Specifically:

Airplane loads that occur subsequent to the time when normal acceleration at the c.g. exceeds the positive limit maneuvering load factor (at point A2 in § 25.333(b)), or the resulting tailplane normal load reaches its maximum, whichever occurs first, need not be considered.

So...

full control deflection above Va = broken airplane.

Full control deflection above lots of different airspeeds may lead to a broken airplane. In fact full and continued control deflection above any of Va, Vb, Vc and Vd will all lead to exceeding the load factor limit. But none of those is the upper limit for airspeed for safe full and continued elevator deflection.

This is the only correct way to express that limit: full and maintained elevator deflection above VS1 √n, which may actually be less than Va, = broken airplane. Don't call VS1 √n by the name Va - because it isn't that.

Va isn't the full continued elevator deflection airspeed limit. Va isn't an airspeed limit at all. It's a design airspeed. It's merely the maximum speed at which the manufacturer has elected to demonstrate full elevator deflection, and only up until the time at which the load factor rises to the limit.

[Col. Panic]

As far as I can see, there is no mention of Va in either CAR 3 or FAR part 23, which should cover all GA aircraft. CAR 3 refers to design maneuvering speed as Vp, and sets the minimum value of Vs.√n. FAR part 25 is for transport category aircraft, so doesn't apply to the normal/utility/aerobatic category aircraft which this thread intends to address. So using the term Va is technically inaccurate in all of these cases, and thus the individual manufacturer may use their own definition for any references to maneuvering speed found in the POH/AFM.

In general terms, the speed at which you will stall before you exceed the limit load factor increase with weight, so in common terms, yes the maneuvering speed is generally higher at a higher weight. As someone else already mentioned, in the case of the RV linked by the OP, the "maneuvering speed" is higher at the lower weight because the limit load factor used in the calculation was higher while the airplane is in the aerobatic category, than the limit load factor when the airplane is too heavy to be in the aerobatic category, and instead is in the utility or normal category.