Turbulence Technique advice...help?

[Derek Guiliano]

Well. Friggin A man. Now I gotta go over all my damn notes again, and retrain myself on Va, so I can better train my students. And great conversation on Va, even though it spurned from a related question. Lol. Thanks for the advice guys, I'll definitely so more research into this, but the rudder thing I am not comfortable with my student doing and needs to be corrected, imho.

 

[denverpilot]

Well. Friggin A man. Now I gotta go over all my damn notes again, and retrain myself on Va, so I can better train my students. And great conversation on Va, even though it spurned from a related question. Lol. Thanks for the advice guys, I'll definitely so more research into this, but the rudder thing I am not comfortable with my student doing and needs to be corrected, imho.

Yep. It's interesting stuff, isn't it?

 

[Derek Guiliano]

Lol. Yeah. It'll be nice to show up a local DPE too. Long story on that one, but yeah.

 

[Clark1961]

Well. Friggin A man. Now I gotta go over all my damn notes again, and retrain myself on Va, so I can better train my students. And great conversation on Va, even though it spurned from a related question. Lol. Thanks for the advice guys, I'll definitely so more research into this, but the rudder thing I am not comfortable with my student doing and needs to be corrected, imho.

Very interesting stuff considering how many folks have been taught incorrectly. The rudder thing is important because that's how the American Airlines guy ripped the vertical stabilizer off the aircraft. Sometimes at low level ya gotta do what ya gotta do, the rest of the time in upset recovery it's one control at a time.

My comment on low level comes from a time I caught some wind shear on short final. Over the threshold short final, maybe 50' in the air. I found myself in about a 20 degree bank and pretty slow. No stall horn but below 1.3 Vso. I used ailerons to recover but I kicked myself for about a week for not using the rudder. I did use the rapid full control deflection that Nate sez we never should use....sometimes ya gotta.

 

[dtuuri]

A better statement might be: Va (adjusted for weight) is the airspeed at which if a single full and abrupt movement of a single control is done, the aircraft will not be structurally damaged.

I like your better statement.

I think tspear is saying Va is an arbitrary number chosen by the manufacturer that can't be LESS than Vs x √limit load. Therefore, no guarantees about stalling before exceeding limits.

dtuuri

 

[Clark1961]

I like your better statement.

I was taught just a few years ago that flying below “maneuvering speed” broadly protected the plane from structural damages due to full and abrupt movement of the control surfaces. However, as crystalized in your statement, that's not quite right. This 2010 rulemaking statement from the FAA says what I was taught is potentially misleading without some important qualifications:

"The NTSB found that many pilots of transport category airplanes mistakenly believe that, as long as the airplane's speed is below VA, they can make any control input they desire without risking structural damage to the airplane. As a result, the NTSB recommended that the FAA amend all relevant regulatory and advisory materials to clarify that operating at or below maneuvering speed does not provide structural protection against multiple full control inputs in one axis or full control inputs in more than one axis at the same time."

https://www.federalregister.gov/doc...-20195/maneuvering-speed-limitation-statement
(based on the 2001 American Airlines accident attributed to multiple, full swing rudder deflections)

Another interesting point is Va is supposed to refer to the “DESIGN maneuvering speed,” as opposed to the “maneuvering speed” we’re now talking about. However, because it’s become so ingrained, the FAA continued to allow manufacturers to use Va to refer to “maneuvering speed” in AFMs. Clear as mud.

I was taught the same as you, that Va was "safe"...it is difficult to shake that particular learning.

 

[steingar]

I kept the nose from hunting with rudder in a Ford Trimotor. Maybe the instructors who recommmended this were really really old...

 

[tspear]

I think tspear is saying Va is an arbitrary number chosen by the manufacturer that can't be LESS than Vs x √limit load. Therefore, no guarantees about stalling before exceeding limits.

dtuuri

Correct.

Tim

 

[Clark1961]

I think tspear is saying Va is an arbitrary number chosen by the manufacturer that can't be LESS than Vs x √limit load. Therefore, no guarantees about stalling before exceeding limits.

I disagree that it is arbitrary since there are structural limits associated with Va, e.g. the airplane can't be damaged by a full pitch up. I agree that the manufacturer chooses Va.

 

[eetrojan]

... but the rudder thing I am not comfortable with my student doing and needs to be corrected, imho.

Back to the original question, I remember being taught to lift a wing with opposite rudder alone if I had a wing stall and abruptly drop due to becoming uncoordinated, e.g. from turbulence, during minimum controllable airspeed (MCA) or power-off stalls.

Basically using rudder alone to stop an incipient spin.

Maybe that’s the source?

 

[dmspilot]

You stated "Va is like stall speed", hence why the student confused what the instructors have stated.

Nice job posting fake quotes.

 

[jordane93]

Back to the original question, I remember being taught to lift a wing with opposite rudder alone if I had a wing stall and abruptly drop due to becoming uncoordinated, e.g. from turbulence, during minimum controllable airspeed (MCA) or power-off stalls.

Basically using rudder alone to stop an incipient spin.

Maybe that’s the source?

Maybe. None of which has anything to do with dancing with the rudders during turbulence. I've never heard of this technique.

 

[Clark1961]

Maybe. None of which has anything to do with dancing with the rudders during turbulence. I've never heard of this technique.

I tried it once when a fancy airplane driver asked me about a yaw dampener. I was too slow and actually made it worse.

 

[gasfiltered]

I can tell you that the technique is popularly taught in the south. I'd never heard of it before moving to Alabama, but every CFI I've flown with down here does it and teaches it. Not dancing necessarily, but measured inputs held in until the plane has recovered. North Alabama is blessed with eye popping thermals and mountain wave simultaneously which, especially in Pipers, produces a distinct yawing motion. They treat it as a manual yaw damper. I don't like it and I don't do it, but it is popular here.

 

[MauleSkinner]

I think tspear is saying Va is an arbitrary number chosen by the manufacturer that can't be LESS than Vs x √limit load. Therefore, no guarantees about stalling before exceeding limits.

dtuuri

True. If you look at the V-g diagram in the PHAK, it's quite clear that full nose down elevator at Va is most likely stalled condition...probably like ailerons, rudder, and up elevator in stall-resistant airplanes, the control authority is limited to prevent structural damage up to Va.

I think it's important to include the stall description for Va and Vb, however, because in the case of up elevator in most of our airplanes and vertical gusts, if a pilot knows a stall is the probable outcome, they'll be more likely to recognize the stall and recover.

 

[coloradobluesky]

I have done it in my Husky. No real problems. Turbulence is always a bit different. I prefer to stay coordinated. Go out and try it, it won't hurt anything. The argument against is: 1) it leads to uncoordinated flight and 2) If it leads to a skid, a stall could be quicker (than if you were coordinated)

 

[tspear]

True. If you look at the V-g diagram in the PHAK, it's quite clear that full nose down elevator at Va is most likely stalled condition...probably like ailerons, rudder, and up elevator in stall-resistant airplanes, the control authority is limited to prevent structural damage up to Va.

I think it's important to include the stall description for Va and Vb, however, because in the case of up elevator in most of our airplanes and vertical gusts, if a pilot knows a stall is the probable outcome, they'll be more likely to recognize the stall and recover.

Where in the regs does it state that the plane will stall at Va?

Tim

 

[FlySince9]

The rudder is for one thing, and one thing only... to counteract yaw... it is ineffective and messy piloting to try to level the wings without use of both ailerons and rudder... Ailerons to level the wings and rudder to counter the yaw caused by that aileron use...

 

[MauleSkinner]

Where in the regs does it state that the plane will stall at Va?

Tim

Probably the same place in the regs where it says it won't.

 

[tspear]

Probably the same place in the regs where it says it won't.

Read FAR 23, or CAR 3.
The definitions for Va have nothing to do with stalling the plane.
Back on post 33 in fact.
Now, a manufacturer may choose to design and make Va the same value as Vsn v. But there is no guarantee, further that is pure happenstance from the perspective of a pilot.

Tim

 

[MauleSkinner]

Read FAR 23, or CAR 3.
The definitions for Va have nothing to do with stalling the plane.
Back on post 33 in fact.
Now, a manufacturer may choose to design and make Va the same value as Vsn v. But there is no guarantee, further that is pure happenstance from the perspective of a pilot.

Tim

Nor does it say it won't stall the airplane.

Happenstance or not, given the way far too many pilots handle inadvertent stalls, I'd say some education on the potential is a very good thing.

 

[Sundancer]

This is what many have been taught and what some books say...but unfortunately it is not a true statement in its entirety.

A better statement might be: Va (adjusted for weight) is the airspeed at which if a single full and abrupt movement of a single control is done, the aircraft will not be structurally damaged.

For GA, for practical purposes, this is fine . . .really, if it's bumpy, just slow down. If you like to pick a wing up with rudder, then do so. If you're getting the crap kicked out of you at the top of the yellow arc, all bets are off. If you're at Va for your weight, use the rudder if you like. Or not.

 

[denverpilot]

I did use the rapid full control deflection that Nate sez we never should use....sometimes ya gotta.

I said no such thing. I said manufacturers and the FAA didn't and don't define Va by any sort of control movement tests or structural tests. Huge difference.

Va is a derived number based on two theoretical vertical wind gust speeds in relation to stall speed.

Use whatever control movements you need to control the airplane. Just don't think you won't bend it or break it just because you're flying at or below Va.

One can fly at Va into a mature thunderstorm, and the airplane will likely still come out of the bottom of the storm in multiple pieces.

There's no magic in Va. It's just a number that popped out of an equation. FAA doesn't even make the manufacturer prove it. Manufacturer just has to do the math correctly.

 

[denverpilot]

I disagree that it is arbitrary since there are structural limits associated with Va, e.g. the airplane can't be damaged by a full pitch up. I agree that the manufacturer chooses Va.

Not really true. The number is based on a theoretical perpendicular airspeed change in the certification standards, as related to stall speed, and no structural numbers are used in determining it.

I'd be happy if you could find something in the spec that says otherwise, but it's not there in the certification spec, AFAIK.

Happy to be corrected if you can find it.

 

[eetrojan]

Read FAR 23, or CAR 3.
The definitions for Va have nothing to do with stalling the plane.
Back on post 33 in fact.
Now, a manufacturer may choose to design and make Va the same value as Vsn v. But there is no guarantee, further that is pure happenstance from the perspective of a pilot.

Tim

I'm still kind of confused.

AC 23-19A (2007) which you quoted in your Post #33 (highlighting mine) mentions an "operating maneuvering speed" Vo that is in fact a maneuvering speed where the plane will stall before structural damages occurs:

And, the FAA's rulemaking statement (2010), which I linked in post #40, says the "maneuvering speed" that folks have been calling Va shouldn't be called Va because that's really "design maneuvering speed," but because changing that now would "lead to confusion," they're going to endorse using Va for both purposes for transport category aircraft under Part 25 ("maneuvering speed" and "design maneuvering speed"), and they're going to define a new Vo for small airplanes under Part 23 ("operating maneuvering speed"):

I'm glad they didn't do anything that would lead to confusion.

 

[Derek Guiliano]

So, I was right then. Hrm. Ok, now even I am getting confused. Lol

 

[eetrojan]

So, I was right then. Hrm. Ok, now even I am getting confused. Lol

Yes, but not if you called it Va, only if you called it Vo!

I've never even heard of Vo before now.

 

[tspear]

Nor does it say it won't stall the airplane.

Happenstance or not, given the way far too many pilots handle inadvertent stalls, I'd say some education on the potential is a very good thing.

I'm still kind of confused.

AC 23-19A (2007) which you quoted in your Post #33 (highlighting mine) mentions an "operating maneuvering speed" Vo that is in fact a maneuvering speed where the plane will stall before structural damages occurs:

And, the FAA's rulemaking statement (2010), which I linked in post #40, says the "maneuvering speed" that folks have been calling Va shouldn't be called Va because that's really "design maneuvering speed," but because changing that now would "lead to confusion," they're going to endorse using Va for both purposes for transport category aircraft under Part 25 ("maneuvering speed" and "design maneuvering speed"), and they're going to define a new Vo for small airplanes under Part 23 ("operating maneuvering speed"):

I'm glad they didn't do anything that would lead to confusion.

Correct, I am going on memory, but the regulatory definition only guarantees the following:
Va = maneuvering speed, allows full deflection of a single control in a single direction in a static state.
Vo = operating maneuver speed, speed at which the plane will stall before structural damage to the plane in a nose up pitching manuever.

Stall speed which keeps coming up in in relation to Va has nothing to do with Va. It has to do with Vo.


Tim

 

[dmspilot]

I'm still kind of confused.

AC 23-19A (2007) which you quoted in your Post #33 (highlighting mine) mentions an "operating maneuvering speed" Vo that is in fact a maneuvering speed where the plane will stall before structural damages occurs:

And, the FAA's rulemaking statement (2010), which I linked in post #40, says the "maneuvering speed" that folks have been calling Va shouldn't be called Va because that's really "design maneuvering speed," but because changing that now would "lead to confusion," they're going to endorse using Va for both purposes for transport category aircraft under Part 25 ("maneuvering speed" and "design maneuvering speed"), and they're going to define a new Vo for small airplanes under Part 23 ("operating maneuvering speed"):

I'm glad they didn't do anything that would lead to confusion.

Exactly. People are reading an aircraft design standard and taking it to mean "this is how you calculate maneuvering speed".

The design maneuvering speed selected must not be less than Vs * sqrt(n) because it would be silly if the tail snapped off before the airplane reached the limit load factor. In other words, the specification requires that the empennage and ailerons be of sufficient strength to maneuver the aircraft at a speed equal to or greater than Vs sqrt(n). That's why Part 23 says Va has to be "at least" Vs sqrt(n).

While hypothetically, Va could be greater than that speed, most aircraft designers are not going to do more work than they have to. Select a few garden variety GA aircraft at random and I bet you will find Va = Vs sqrt(n), within a few knots to allow for rounding errors.

 

[Derek Guiliano]

I think I'm starting to understand. I'm order to keep things simple, they are combining both as the same for training. I think I understand the difference between both, but keeping it simple is better.

 

[Clark1961]

Not really true. The number is based on a theoretical perpendicular airspeed change in the certification standards, as related to stall speed, and no structural numbers are used in determining it.

I'd be happy if you could find something in the spec that says otherwise, but it's not there in the certification spec, AFAIK.

Happy to be corrected if you can find it.

When I read that stuff it struck me that the structure had to survive the perpendicular airspeed change. In other words the selected Va tells the designer how strong to build it.

 

[Clark1961]

It also dangerously suggests a pilot technique for turbulence that it shouldn't. (That full and abrupt control inputs are "ok". They're not. This should be obvious via common sense, but this phrase about Va won't go away.)

You'll probably change how you teach it, after you look up how it's defined during certification. Not a single thing in the definition of Va about control deflection.

I said no such thing. I said manufacturers and the FAA didn't and don't define Va by any sort of control movement tests or structural tests. Huge difference.

Va is a derived number based on two theoretical vertical wind gust speeds in relation to stall speed.

Use whatever control movements you need to control the airplane. Just don't think you won't bend it or break it just because you're flying at or below Va.

One can fly at Va into a mature thunderstorm, and the airplane will likely still come out of the bottom of the storm in multiple pieces.

There's no magic in Va. It's just a number that popped out of an equation. FAA doesn't even make the manufacturer prove it. Manufacturer just has to do the math correctly.

What did you really mean then?

 

[denverpilot]

When I read that stuff it struck me that the structure had to survive the perpendicular airspeed change. In other words the selected Va tells the designer how strong to build it.

Perhaps. It reads about as clear as mud. I thought I would read it to be "well rounded" one night and learn something about certification. Nope.

All that was really clear was some V speeds are mathematically defined from stall speed and structural cruising speed. Definitely nothing about rudder or aileron.

 

[dmspilot]

Perhaps. It reads about as clear as mud. I thought I would read it to be "well rounded" one night and learn something about certification. Nope.

All that was really clear was some V speeds are mathematically defined from stall speed and structural cruising speed. Definitely nothing about rudder or aileron.

I imagine that you were thinking of Vno / Vc which is based off the maximum speed a 50fps vertical gust can be encountered without exceeding the limit load. As for Va having nothing to do with ailerons, well, it's right here:

§23.455 Ailerons.
(a) The ailerons must be designed for the loads to which they are subjected—
(1) In the neutral position during symmetrical flight conditions; and
(2) By the following deflections (except as limited by pilot effort), during unsymmetrical flight conditions:
(i) Sudden maximum displacement of the aileron control at VA. Suitable allowance may be made for control system deflections.

 

[Clark1961]

Perhaps. It reads about as clear as mud. I thought I would read it to be "well rounded" one night and learn something about certification. Nope.

All that was really clear was some V speeds are mathematically defined from stall speed and structural cruising speed. Definitely nothing about rudder or aileron.

I'm used to seeing things like maximum allowable stress in a material as a design standard. When I read the FAA stuff I saw none of that but did see stuff that could be used to estimate (or determine by experimentation) loads. Once loads are known and materials selected then dimensions can be specified to obtain the desired stresses.

Of course there is a lot of history in the evolution of aircraft design and the industry is just now getting to the point that they don't have to go break things as part of the acceptance testing. To me that says the numbers weren't trusted so much until recently.

 

[eetrojan]

Correct, I am going on memory, but the regulatory definition only guarantees the following:
Va = maneuvering speed, allows full deflection of a single control in a single direction in a static state.
Vo = operating maneuver speed, speed at which the plane will stall before structural damage to the plane in a nose up pitching manuever.

Stall speed which keeps coming up in in relation to Va has nothing to do with Va. It has to do with Vo.


Tim

Thanks.

Maybe this is already baked into your comment, but for what it's worth, I looked around and found a pre-2010 POH (Cessna) and a post-2010 POH (Cirrus), and it looks like for small "Part 23" aircraft, what used to be called Va ("Maneuvering Speed") is now called Vo ("Operating Maneuvering Speed"):

The 2011 POH does not appear to make any reference to Va at all.

 

[denverpilot]

Cool. I'm going flying. I have a reasonable assurance from past experience that the wings won't fall off, so if they do, someone sue Cessna for me and kill the entire industry again. LOL. It's been done before over a seat track...

 

[MauleSkinner]

Correct, I am going on memory, but the regulatory definition only guarantees the following:
Va = maneuvering speed, allows full deflection of a single control in a single direction in a static state.
Vo = operating maneuver speed, speed at which the plane will stall before structural damage to the plane in a nose up pitching manuever.

Stall speed which keeps coming up in in relation to Va has nothing to do with Va. It has to do with Vo.


Tim

Maybe so, but every airplane in which I've made an abrupt, full-up-elevator control input below Va has stalled. Every airplane in which I've encountered severe turbulence below Vb has stalled.

YMMV. We now return you to your regularly scheduled picking of useless nits.

 

[1600vw]

You can stall at any speed and at any attitude. When in a stall you use only rudder to pick up a wing. Ailerons stay neutral. Always slow fluid motions. Never throw the controls around be it stick or rudder.

 

[nauga]

Many people use Va in place of corner speed, which *is* the speed at which flight at stall AOA (or CLmax) produces the limit load factor. It's also the speed for maximum instantaneous turn rate. It is effectively Vo but not through a convoluted design standard with murky and inconsistent terminology whose intent may be changed by inconsistent grammar, it's the speed at the upper left corner of the Vn diagram for your current weight and configuration.

Nauga,
watching angels dance on pinheads