Va-- can't wrap my brain around definition

[Tracey]

For some reason I'm having trouble wrapping my brain around this:

Va is the speed at which the airplane will stall before exceeding its design limit-load factor in turbulent conditions or when the flights controls are suddenly and fully deflected in flight.

So this means that the plane will STALL before it experiences structural damage at this speed (given certain weight, speeds, etc)?

Can anyone explain this in really simple terms?

(I have a cold so I'm going to use that as my excuse for having trouble getting this).

TIA everyone!

 

[kimberlyanne546]

For some reason I'm having trouble wrapping my brain around this:

Va is the speed at which the airplane will stall before exceeding its design limit-load factor in turbulent conditions or when the flights controls are suddenly and fully deflected in flight.

So this means that the plane will STALL before it experiences structural damage at this speed (given certain weight, speeds, etc)?

Can anyone explain this in really simple terms?

(I have a cold so I'm going to use that as my excuse for having trouble getting this).

TIA everyone!

Manuevering speed. I will let the others explain (they do a much better job). What my CFI said, if I remember correctly, was that if I fly at the indicated mauevering speed (or slower) and someone pulls the yoke all the way out / pushes it all the way forward ABRUPTLY (or that happens due to turbulence) the G-Forces will not be enough to pull the wings off. In other words, you won't damage the structure of the plane if your young 9 year old passenger yanks the controls for no reason. If you fly faster, and do this, the plane could become damaged.

 

[Tracey]

What my CFI said, if I remember correctly, was that if I fly at the indicated mauevering speed (or slower) and someone pulls the yoke all the way out / pushes it all the way forward ABRUPTLY (or that happens due to turbulence) the G-Forces will not be enough to pull the wings off. In other words, you won't damage the structure of the plane if your young 9 year old passenger yanks the controls for no reason. If you fly faster, and do this, the plane could become damaged.

Ding! Ding! Ding! This could be the winning definition! I understand this. Thanks Kim!!

So this speed or SLOWER ensures no structural damage (and I understand that the Va speed changes with weight, and maybe with AIS, not sure about that, I have to look that one up)-- which is why it's good to stay here or below during turbulence. I think I have it now.

 

[denverpilot]

You've got it. The aircraft will stall before you'll break the structure.

It changes with weight on board. Va isn't one static number.

It's a good idea to slow to Va in turbulence.

The aerodynamics geeks will be along shortly to give even more info.

 

[kimberlyanne546]

No problem, I thought I would get crap from other pilots about my definition. We'll wait for them to come along. For now, glad you liked it. And I remember you posting in another thread about knowing to go slower when you're in the turbulence.... kinda like slowing down in car before you hit that speed bump.... more comfortable for those inside / passengers.

 

[EdFred]

For some reason I'm having trouble wrapping my brain around this:

Va is the speed at which the airplane will stall before exceeding its design limit-load factor in turbulent conditions or when the flights controls are suddenly and fully deflected in flight.

So this means that the plane will STALL before it experiences structural damage at this speed (given certain weight, speeds, etc)?

Can anyone explain this in really simple terms?

(I have a cold so I'm going to use that as my excuse for having trouble getting this).

TIA everyone!

Yes, the wings WILL stall out (and in turn unloading the wings) before any damage takes place. The slower you go, the higher the angle of attack to maintain lift. The higher the angle of attack, the easier it is to stall the wings. So if at Va or below, the wings will unload before you can do any damage.

 

[Tracey]

You've got it. The aircraft will stall before you'll break the structure.

It changes with weight on board. Va isn't one static number.

Thanks Nate!! You and Kim served up the winning definitions. Now I get it. Thank you!

 

[kimberlyanne546]

You've got it. The aircraft will stall before you'll break the structure.

It changes with weight on board. Va isn't one static number.

It's a good idea to slow to Va in turbulence.

The aerodynamics geeks will be along shortly to give even more info.

Oh yeah, whoops, forgot to go into the whole VA changes with weight on board but THAT was what I didn't "get" because it went up when I thought it should go down and vice versa. In other words, the heavier the plane, the higher the manuevering speed.

 

[Tracey]

No problem, I thought I would get crap from other pilots about my definition.

I think only people that really understand a concept can explain them in easy to get terms. Which you did, so thanks! No crap for Kim!

 

[EdFred]

Oh yeah, whoops, forgot to go into the whole VA changes with weight on board but THAT was what I didn't "get" because it went up when I thought it should go down and vice versa. In other words, the heavier the plane, the higher the manuevering speed.

That's because the heavier the plane, the higher the angle of attack needed to maintain altitude at a given speed.

 

[Tracey]

Yes, the wings WILL stall out (and in turn unloading the wings) before any damage takes place. The slower you go, the higher the angle of attack to maintain lift. The higher the angle of attack, the easier it is to stall the wings. So if at Va or below, the wings will unload before you can do any damage.

Thanks EdFred! Another easy to get explanation- I appreciate that!

 

[kimberlyanne546]

I think only people that really understand a concept can explain them in easy to get terms. Which you did, so thanks! No crap for Kim!

No crap for me! Awesome. How are you in your training now? What phase are you in? I know you've been doing cross countries.... what's next?

 

[Tracey]

That's because the heavier the plane, the higher the angle of attack needed to maintain altitude at a given speed.

Sooooooooooooooo the Va speed would be higher then? The plane would stall at a higher speed in this case?

 

[Tracey]

No crap for me! Awesome. How are you in your training now? What phase are you in? I know you've been doing cross countries.... what's next?

I have to pass my xc phase check with the "head honcho" guy and then I'm cleared to do my first solo xc.

Thanks for asking!

My progress is very. slow. going. And that's ok with me. It's not intuitive, so I need the extra time.

 

[kimberlyanne546]

I have to pass my xc phase check with the "head honcho" guy and then I'm cleared to do my first solo xc.

Thanks for asking!

My progress is very. slow. going. And that's ok with me. It's not intuitive, so I need the extra time.

Tracey - if this helps - here is something you can use to tell yourself your training is NOT going to be as slow as mine:

I had an intro flight. That company went out of business, so I started training at another airport. I recorded my lessons (ground only) on a tape recorder to play back the sound later. I ACTUALLY TOLD MY 20,000 hour CFI THAT MY INTRO FLIGHT PLANE HAD NO RUDDERS OR TRIM WHEEL.

You have NO IDEA how slow my learning was, Tracey! Stick with it OK? You'll be fine.

 

[EdFred]

Sooooooooooooooo the Va speed would be higher then? The plane would stall at a higher speed in this case?

Correct. I don't know if your CFI has gotten to the point with you that all speeds change with weight. All speeds (except red line, and the yellow arc) go up with weight increase, and down with weight decrease. There is a formula to determine the change. Remember, the published speeds are for gross weight. The lighter you get, all speeds go down because the angle of attack decreases.

 

[Tracey]

all speeds change with weight. All speeds (except red line, and the yellow arc) go up with weight, and down with weight.

Well, I know that stall and Va speeds change with weight.

 

[Tracey]

Tracey - if this helps - here is something you can use to tell yourself your training is NOT going to be as slow as mine:

I had an intro flight. That company went out of business, so I started training at another airport. I recorded my lessons (ground only) on a tape recorder to play back the sound later. I ACTUALLY TOLD MY 20,000 hour CFI THAT MY INTRO FLIGHT PLANE HAD NO RUDDERS OR TRIM WHEEL.

You have NO IDEA how slow my learning was, Tracey! Stick with it OK? You'll be fine.

I've changed flight schools a few times and even moved (to a different state) during my training. It's going super slowly. But I will stick with it because pretty much nothing is as fun as flying. Pretty much.

And thanks, Kim-- your encouragement is always appreciated!

(And your plane had no rudders? Kim, that's so funny and cute!).

 

[EdFred]

Well, I know that stall and Va speeds change with weight.

Correct, and that's because the angle of attack changes.

 

[Tracey]

Correct, and that's because the angle of attack changes.

See now I'm confusing myself... the airplane will always stall at the same critical angle of attack, right?

 

[tonycondon]

 

[Captain]

I like to make points with extremes, so try this on...


Say your Cessna's Vmo is 135 kts (I'm making that up). Now, say you're in a dive and are right at 135kts in smooth air and you all of a sudden pull the yoke all the way back. At that speed the elevator is so effective the plane would go into a 5 G pull and the wings snap right off. You exceeded Va.

Now say your parked on the ramp with the engine off on a nice day with a calm breeze and you all of a sudden pull the yoke all the way back. At that speed (maybe 3kts from behind you) what happens? Nothing (except the elevator snaps up in a quickish fashion). Why, because you are below Va.

Now while you're flying you sit there at one G. When you pull all the way back on the yoke on the ground you are still at 1 G. In flight when you pull all the way back you will be at 1 G plus a factor. That factor is tied to speed. At Vmo it's the 5 G snap your wings. At some point between stall speed and the 5G Snap the wings speed is a speed where the wings won't snap off or even bend. No structural damage will occure. That's Va.

 

[EdFred]

See now I'm confusing myself... the airplane will always stall at the same critical angle of attack, right?

Correct, and I think it's around 17°. But the heavier you weigh, the closer you will be to that 17º at a given speed, than you would at a lighter weight.

 

[EdFred]

I like to make points with extremes, so try this on...


Say your Cessna's Vmo is 135 kts (I'm making that up). Now, say you're in a dive and are right at 135kts in smooth air and you all of a sudden pull the yoke all the way back. At that speed the elevator is so effective the plane would go into a 5 G pull and the wings snap right off. You exceeded Va.

Now say your parked on the ramp with the engine off on a nice day with a calm breeze and you all of a sudden pull the yoke all the way back. At that speed (maybe 3kts from behind you) what happens? Nothing (except the elevator snaps up in a quickish fashion). Why, because you are below Va.

Now while you're flying you sit there at one G. When you pull all the way back on the yoke on the ground you are still at 1 G. In flight when you pull all the way back you will be at 1 G plus a factor. That factor is tied to speed. At Vmo it's the 5 G snap your wings. At some point between stall speed and the 5G Snap the wings speed is a speed where the wings won't snap off or even bend. No structural damage will occure. That's Va.

Except they wouldn't.

 

[Captain]

Correct, and I think it's around 17°. But the heavier you weigh, the closer you will be to that 17º at a given speed, than you would at a lighter weight.

Exactly, and self induced (or even turbulence induced) Gs count as 'heavier'.

 

[Aztec Driver]

As someone pointed out, the published Va is for max gross weight. You need to calculate it for the weight you are flying at and adjust your flying accordingly in turbulent air. That will likely be less at the weights you normally fly at.

 

[TMetzinger]

And it's also for ONE deflection of a control surface.

 

[Tracey]

And it's also for ONE deflection of a control surface.

You mean one control surface at a time?

 

[TMetzinger]

Yes. Particularly for the rudder. One full-throw deflection and return to neutral at a speed below Va should not break anything. Saw it back and forth and you're no longer within the anticipated load envelope. Same thing technically applies to the ailerons and elevator, but there were some incidents with rudders on transport airplanes where the airplane was below Va but had rudder damage due to repeated large control inputs, if I'm remembering it all correctly. In the aftermath, the FAA issued supplemental guidance on exactly what Va meant in terms of control deflection.

 

[Tracey]

but there were some incidents with rudders on transport airplanes where the airplane was below Va but had rudder damage due to repeated large control inputs

Yikes!

 

[TMetzinger]

Here's a link http://www.flyingmag.com/myth-maneuvering-speed

 

[Aeric]

Regarding maneuvering speed and the fact that it is not an ASI marked vspeed:
When I start hittin' the bumps I just keep it somewhat below the top of the white arc(Vfe). The top is 100 mph and my Va at full gross is 109 and somewhat less as I go lighter, so I figure that it gives me a bit of safety margin and it is readily apparent via an ASI color marking. Does this sound reasonable?

 

[EdFred]

Regarding maneuvering speed and the fact that it is not an ASI marked vspeed:
When I start hittin' the bumps I just keep it somewhat below the top of the white arc(Vfe). The top is 100 mph and my Va at full gross is 109 and somewhat less as I go lighter, so I figure that it gives me a bit of safety margin and it is readily apparent via an ASI color marking. Does this sound reasonable?

It will depend how much lighter you are than full gross.

The formula to determine a new V-speed based on weight is:

Vcalculated = Vpublished * Square Root(Current Weight/Gross weight)

If your gross weight is 3000 and your current weight is 2400lbs your reduction to 100mph is not enough.

Va= 109mph*SQRT(2400/3000)
Va= 109mph*SQRT(.8)
Va= 109mph*(.8944)
Va= 97mph

Though I'm guessing your gross weight is 2400 in a 172? Which means anything under 2020lbs you are still going too fast for Va

 

[Captain]

Yes. Particularly for the rudder. One full-throw deflection and return to neutral at a speed below Va should not break anything. Saw it back and forth and you're no longer within the anticipated load envelope. Same thing technically applies to the ailerons and elevator, but there were some incidents with rudders on transport airplanes where the airplane was below Va but had rudder damage due to repeated large control inputs, if I'm remembering it all correctly. In the aftermath, the FAA issued supplemental guidance on exactly what Va meant in terms of control deflection.

American 587. That's the plane that crashed in New York right after 9/11. Everyone first thought it was another attack. Turns out AA was teaching pilots to kick the rudder as a wake avoidance techniguq.

I also seem to remember the FAA guidance after that was that Va only applied to the elevator and not the rudder or ailerons. I have no link for that though...

 

[Cap'n Jack]

American 587. That's the plane that crashed in New York right after 9/11. Everyone first thought it was another attack. Turns out AA was teaching pilots to kick the rudder as a wake avoidance techniguq.

I also seem to remember the FAA guidance after that was that Va only applied to the elevator and not the rudder or ailerons. I have no link for that though...

Tim pretty much covered it...

Here's a link http://www.flyingmag.com/myth-maneuvering-speed

 

[John Collins]

My understanding is that Va is determined only at maximum gross weight and not for lower weights. At lighter weights, you can pull more G's and should adjust your speed down below Va to avoid structural damage. It is interesting to note that at lighter weights, even though you can pull more G's before the aircraft will stall, the wings won't come off if you are at Va, because the wings will be generating the exact same amount of lift they would be generating at maximum gross weight. However, since you can pull more G's, other parts of the aircraft structure, such as the engine mounts, could fail, so you reduce your airspeed to adjust for the difference in weight.

Va is determined by the maximum G's permitted at maximum gross weight. So if the aircraft is certified to normal category, the maximum positive G value is 3.8G. To calculate Va, you take the square root of the maximum G value and multiply this times the stall speed. For a C172R, the stall speed is listed as 51 Kts, so the Va is 51 times the square root of 3.8 = 99. This should be close to the value published in the manual. The adjustment for flight at lighter weights is equal to the square root of the ratio of the lighter weight to gross weight times Va.

The Va listed only applies to the pitch axis and only when pulling positive G's.

 

[Captain]

I sorta got the impression the OP was looking for a basic understanding. That's why I busted out the zero knot / Vne comparison.

 

[Doggtyred]

Oh yeah, whoops, forgot to go into the whole VA changes with weight on board but THAT was what I didn't "get" because it went up when I thought it should go down and vice versa. In other words, the heavier the plane, the higher the manuevering speed.

Something else people flying spam cans dont realize is.. Stall speed changes with weight too..

The heavier you are, the higher your stall speed. Not such a big deal in a plane that has a 500 lb payload. Big deal in a plane that has an empty weight of 20,000 lbs and a max gross of 50,000 lbs

So both Va and Vs (and Vso) all vary with weight.

Also, as we found out shortly after 9/11... as evidenced by the Rockaway crash, its not repeated alternating full stop deflections of the controls that are allowed. Its essentially a single deflection of a single control surface (and return to neutral) that can be sustained without damage or failure.
(I'm sure if I've mischaracterized anything, nitpickers will be along to set the record straight)

But essentially the others have the meat of the matter. Below that speed you will stall the plane before something bends or overstresses. Above that speed you will break or bend the plane before it stalls. If that happens (and the flight completes safely) then right thing to do is have the airframe inspected before further flight for cracks or wrinkles in the skin and structure.

 

[Dan Thomas]

I wouldn't go yanking hard on any controls even below Va in the average spam can. Va means the WING will stall and avoid damage at or below Va in turbulence. It doesn't mean I can abuse the airplane by inducing a hard accelerated stall just below Va.

Slippery airplanes like the Bonanza and 210 have been known to lose their elevators/ruddervators/stabilizers when the VMC pilot gets into IMC, loses contol and ends up in a spiral dive. He pops out of the clouds, see the ground coming at him, and pulls back hard. The tail surfaces fail first and with the loss of tail downforce the airplane tumbles onto its back and the wings then fail downward in negative G loading.

Dan

 

[Aeric]

It will depend how much lighter you are than full gross.

The formula to determine a new V-speed based on weight is:

Vcalculated = Vpublished * Square Root(Current Weight/Gross weight)

If your gross weight is 3000 and your current weight is 2400lbs your reduction to 100mph is not enough.

Va= 109mph*SQRT(2400/3000)
Va= 109mph*SQRT(.8)
Va= 109mph*(.8944)
Va= 97mph

Though I'm guessing your gross weight is 2400 in a 172? Which means anything under 2020lbs you are still going too fast for Va

It's a 150L, Va at full gross (1600#) is 109 mph and at 1300# it's 99 mph. As I said, I keep it somewhat below the top of the white arc when the bumps start happening.