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Va - Maneuvering Speed

One of the threads on turbulence made me think about Va. I doubt that maneuvering speed only has to do with control travel. In my opinion Va can also save your wings if you keep your controls neutral.

My understanding is that at or below Va your wing will stall at or below your maximum structural G-loading. Therefore it won’t break, because it will stall before the force becomes too high. This also means that full control travel shouldn’t be used, because the pilot controls angle of attack with the elevator. It would be possible to induce G-forces which are higher than the airplane is designed for.

However, to illustrate what I mean by “Va has not only to do with control travel”, let’s assume:
- A pilot flies faster than Va
- The controls remain neutral during this scenario
- A wind shear is encountered; the relative wind increases from 3° to 15° (not exceeding maximum amgle of attack/no stall)

In my opinion the wing structure will now fail, because there is no stall, which would protect the airframe.

This diagram helps to visualize:

Maybe I am just stating the obvious, but I believe that the average pilot underestimates the possible consequences of exceeding Va in turbulence. The dangerous thing is that Va is often much slower than the yellow arc. On the other hand, if I my understanding is correct I don’t really see the point of the yellow arc so maybe I got this all wrong… What do you think?

Last Edited by ArcticChiller at 11 Sep 21:03

The advice of many instructors in my type of airplane is to slow WAY DOWN in turbulence and convection, 10-15kts below VA, because at that speed there is no amount of turbulence that will get you close to the limits – tolerance. We have evidence from people who have crossed TS under these conditions and they never exceeded +/-1.5g (although they were going from -1.5 to +1.5 every 10 seconds!); effectively they were stalling every few seconds. They survived without damage, though they needed new trousers (one of them who saw combat said it was by far the scariest thing that had ever happened to them).

EGTF, LFTF

At or below manouevering speed you can’t overstress the aircraft with full single axis control movements. This is not related to the yellow arc. The yellow arc uses a defined arbitrary gust to determine a limit for smooth air. I think people often overestimate the g they face in turbulence. Do you know what 3.8g is like in a light GA type? It is REALLY bad turbulence.

EGTK Oxford

ArcticChiller wrote:

My understanding is that at or below Va your wing will stall at or below your maximum structural G-loading. Therefore it won’t break, because it will stall before the force becomes too high.

Not exactly. This is only valid for one control input at a time. For instance, pulling full aft and full aileron at the same time can overload the airframe structure.

The elephant is the circulation
ENVA ENOP ENMO, Norway

Looking at the diagram again…So in some way the yellow arc protects us from structural failure, but not from structural damage (that would be Va).

In the yellow ark the structure will fail before the aircraft stalls. Above VA, any single control input can cause the structure to fail. As I remember it.

Last Edited by LeSving at 11 Sep 22:00
The elephant is the circulation
ENVA ENOP ENMO, Norway

If Va is greater than Vs * SQR( Load Factor) then the loads imposed by a manoeuvre (i.e. displacement of control surface) or a gust (normally defined during certification of 50ft/second or greater) need to remain along a single axis, otherwise the aircraft’s load limits will be exceeded.

An up-to-date definition of Va would be:

The Design Maneuvering Speed (Va) is the speed below which you can move a single flight control, one time, to its full deflection, along one axis (pitch, roll or yaw), in smooth air, without risk of damage to the aeroplane.

Calculating Va for a particular weight is quiet simple. Va-New = Va √ (WNew/WMax-Gross)

Ref: Armand Vilches

Fly safely
Various UK. Operate throughout Europe and Middle East, United Kingdom

IIRC this stuff got redefined IIRC after the 2001 US accident where the tail came off an Airbus, due to a certain type of rudder input.

So yes I would fly a lot slower than Va if the turbulence is really bad.

Administrator
Shoreham EGKA, United Kingdom

Va I believe is only relevant for pitching around the lateral axis. The Harvard publishes Va for each of the axis, with yaw being the lowest, and rolling being the highest – for this type, YMMV for your type. Why a WW2 advanced trainer publishes this, but you can’t find the same information in GA types AFM, or why the concept of different Va for different axes is not taught am not sure.

Oxford (EGTK), United Kingdom

ArcticChiller wrote:

One of the threads on turbulence made me think about Va. I doubt that maneuvering speed only has to do with control travel. In my opinion Va can also save your wings if you keep your controls neutral.
You’re right!

ESKC (Uppsala/Sundbro), Sweden
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