Va

EnRoute

New Member
As weight increases at any given airspeed, angle of attack must also increase to provide the required amount of lift. Therefore, greater weight at a given speed means the airfoil is closer to the critical angle of attack.

I can see using the above answer when the examiner asks "why does your maneuvering speed change with weight a change in gross weight"

His next question "do explain"

So... Do explain:drool:

Va = The maximum speed at which the limit load can be imposed (either by gusts or full deflection of the control surfaces) without causing structural damage.

Now as you mentioned in your post, that as weight increases, you must increase your AOA to support the extra weight. Yes you are closer to your critical AOA with a higher gross weight. This means at higher airspeeds you will reach your critical aoa before you cause structural damage by a gust of wind or full control inputs. If you are lighter, however, your aircraft can be disturbed from equillibrium much easier than a heavier aircraft. So, if that same gust of wind catches your a/c while you're light, you will reach your CAOA before causing structural damage at a much lower airspeed.

Va decreases as weight decreases since an aircraft operating at lighter weights is subject to more rapid acceleration from gusts and turbulence.

Note: The higher the airspeed, the greater the amount of excess load that can be imposed before a stall occurs.

Correct me if I'm wrong ladies.

I think this is the 10th time I have posted this...

Here is a simplified, practical application, lift formula: Lift = Speed + AOA

Note: It will not mathematically work, but it will show the relationship between the three. If you want the actual lift formula: Lift = 1/2 (p * V(squared) * A * Cl) where Cl = coefficient of lift = 2 * pi * AOA; V = velocity; p = air density; and A = wing area.

We also know lift = weight. So as our weight goes up, for any given speed we will need a higher AOA. That higher AOA is closer to critical, meaning there is less throw on the controls before critical AOA will be hit and thus a stall.

This demonstrates that you understand what controls lift, how lift relates to weight, and the given distance from current to critical AOA related to Va. I can't imagine he is looking for more than that, I would stop at this point and ask if he had any other questions.

I always explain it by using the control stick as an example. It needs to be full back to stall the aircraft. Having a higher angle of attack due to the added weight means this stick is already a little further back than normal. This means you will pull the stick back a shorter distance to stall. Thus stalling at an higher airspeed. It's kind of a simplified version to begin with.

As weight increases at any given airspeed, angle of attack must also increase to provide the required amount of lift. Therefore, greater weight at a given speed means the airfoil is closer to the critical angle of attack.

I can see using the above answer when the examiner asks "why does your maneuvering speed change with weight a change in gross weight"

His next question "do explain"

So... Do explain:drool:
I thought your explanation was right on target.

As weight increases at any given airspeed, angle of attack must also increase to provide the required amount of lift. Therefore, greater weight at a given speed means the airfoil is closer to the critical angle of attack.

I can see using the above answer when the examiner asks "why does your maneuvering speed change with weight a change in gross weight"

His next question "do explain"

So... Do explain:drool:

when an airplane is light, it can reach it's limit load factor more quickly...and when heavy it takes longer, therefore a higher speed. So it's an issue of time. And I heard this directly from the FAA.

So it's an issue of time. And I heard this directly from the FAA.

Yeah, well, it's wrong, no matter who says it. Time is irrelevant. It's about whether it's possible at all.

Yeah, well, it's wrong, no matter who says it. Time is irrelevant. It's about whether it's possible at all.

:rofl:

at1024, you will quickly learn that what the FAA says is just as often wrong as it is right. Especially when it falls into the technical areas of aerodynamics. Someday, tell an FAA guy there are only 3 forces and not 4 and see what he/she has to say about that. Speak of aerodynamic force and drag/lift only being byproducts not actual forces and you might spin the fellas head right off their shoulders.

Well just so you know that is NOT the way I chose to explain it on my checkride, it was just something he said. He also told me to go look up some article by Rob Machado that further explained the matter. On my checkride I gave an explanation that was very similar to that of IslandFlyer's.

Machado does a good job of explaining in his Private Pilot book.

Thanks. I would have sworn that I had tested it. Fixed now.

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