"Maneuvering Speed", a discussion.......I hope

Maneuvering speed, is it a reality? I was trained to believe that an a/c flying in turbulence, at a legal weight, at "maneuvering speed" or lower, would not break with abrupt control input, but would stall instead of breaking apart. Anyone have a thought??

Let's keep the answers short for now, just to get the discussion going and to keep it all "readable".

Thanks to anyone interested in this topic. DAVE

Dave,

That was the classical understanding most pilots had for maneuvering speed.

Now, review the arguments of the engineers who work for Airbus Industrie regarding the Airbus that lost it's vertical fin and crashed into Jamaica Bay, New York a couple years ago.

Suddenly, that really isn't true of maneuvering speed any longer.

The first officer deflected the rudder in both directions, and the vertical fin came off.

MTV

Dave,

I might restate the definition in finer terms to say that full nose up deflection at or below Va would not cause a structural failure. Mostly because the formula for Va is very similar to Vs. I would have to break out my aerodynamics book but thats what I remember.


I would like to read the reports from the Airbus accident as I only vaguely remember the details. I would like to believe that our understanding of subsonic aerodynamics is solid and not prone to exceptions, but the airbus case could change my mind as mvivion suggests. Any web link to this would be appreciated.

Good topic! Worth knowing if any SC have ever suffered any structural failures at Va

Believe this is the one mtv is refering too.

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20011130X02321&key=1

Va is manuvering speed
Some planes also list a "turbulent air penetration speed"

Simply put Va is typically higher because the pilot can only exert so force much with the controls before the aircraft stalls. Full and Abrupt is defined somewhere in some manual.

Turbulent air penetration speed is usually lower based on a given sustained gust load on the aircraft measured in time of distance of wind shear. i.e 30 ft per second vertical shear exerts Xg on the airplane.

More simply put the airplane can withstand more of our monkeying about so we get to go faster, we have to slow down in rough air because God doesn't need us going fast to smack us apart.

Mike

I think

Dave Calkins said:

Maneuvering speed, is it a reality? I was trained to believe that an a/c flying in turbulence, at a legal weight, at "maneuvering speed" or lower, would not break with abrupt control input, but would stall instead of breaking apart. Anyone have a thought??

Let's keep the answers short for now, just to get the discussion going and to keep it all "readable".

Thanks to anyone interested in this topic. DAVE

Click to expand...

I was taught that at the prescribed weight and Va, that an airplane would stall before structural damage would occur. In my 180 my gross weight Va is 123 mph. I've been at that weight and speed in turbulence and had the stall horn blast intermittently in the hard bumps. While I wasn't intentionally changing the deflection of the control surfaces, the turbulence was dramatically changing my angle of attack by very quickly changing the relative wind direction. I didn't find it particularly useful to exercise full or radical control movements, but the net effect was the same. I did take some comfort in the knowledge that some engineer figured that my speed allowed safe, if uncomfortable, penetration of the turbulence. At the time it seemed more like survival in the turbulence.

The practical definition is more important to me than the technical one.
http://selair.selkirk.bc.ca/aerodynamics1/Lift/Page12.html

Stewart

One of the recommendations in the NTSB accident report for the above mentioned accident is: "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."

maneuving speed

For most pilots it's inversly related to how close their wife is

Thanks guys for speaking up!

What is the concensus of opinion on how higher or lower a/c weight affects 'maneuvering speed'? (higher weight= decreased speed.......or, lower weight= decreased speed)

Thanks again. DAVE

Maneuvering speed

Regarding the Airbus accident, I attended the entire NTSB hearings. All agreed that at maneuvering speed one complete, full control deflection is within the design criteria for an airplane (not sure about our little guys) at maneuvering speed, which is roughly turbulence penetration speed. What is not acceptable is a full control reversal, or full displacement of multiple controls. In the case of a swept wing airplane and the rudder, reversal results in "sequential over-yaw", which basically means combined aerodynamic and inertial effects can produce yaw in excess of what is produced by a single full throw of the rudder. Don't pick on Airbus here, as the same condition applies to Boeing or any other manufacturer.

I'm not sure how (or if) any of this applies to our straight wing Pipers, and I'm not about to test it on my 1941 airframe. When you think about a full slip, I wonder how fast (or slow) it is safe to do so?

lower wt.=lower Va

Ok, I can’t resist posting here. You asked for short posts, so please accept my apologies if I busted the rules.

I’ve got a buddy that had to drop off a truck in the nearby desert and needed a ride back home.
I landed on a 700ft patch of dirt, he jumped in and we headed back home to the mountains.

This first photo is of us entering the pattern at my home port and it was quite turbulent. The photos document some interesting information.
Note the following from the photo:
Indicated airspeed is 68mph
GPS ground speed is 77mph
VSI documents that I’m caught in a 900fpm downdraft
GPS altimeter is indicating 8,49x, where x=?
Clock time is 12:59:20
RPM is 1700
The A.H. shows that the wings are level and the nose is slightly pitched down (I was trying to outrun the downdraft)
Note that the duckbill on my hat is pointed at my flight path and this agrees with the runway alignment (as seen in the upper right side of the photo)
White knuckles on the fist clasped around the V-brace
What you can’t see is that the stick action looks like I’m churning butter and the foot action looks like I’m in a dance contest.

Click on image for larger picture.



In this second photo, note the following:
The airport is now off to our right
Indicated airspeed is 54~53mph (14mph reduction)
GPS ground speed is 74 (3mph reduction)
GPS altimeter is 8008 (approx 500ft loss, consistent with VSI)
Clock time is 12:59:55 (35 seconds later)
RPM is 1700 (same)
Also, I have added 1 notch of flaps by now
The fight path is now more aligned with the downwind pattern, but just seconds after this photo was taken, the wings enter a full stall.

Click on image for larger picture.


I have to admit that the stall took me by surprise. I applied full throttle, pitched the nose down and recovered.
I’ve got to tell you that I had to “cowboy up” to point the nose at the pine trees to outrun the new tailwind that hit me.

So, in conclusion, my published Va is 92mph indicated (if memory serves) but there is no way that I’m going to take on these type of turbulence at that speed.
70 mph is tops for me.

Are the published maneuvering speeds realistic? Good question.

In the link I posted earlier the formula showed the correlation of maneuvering speed to stall speed. My planes stall at a faster speed when heavy, therefore the maneuvering speed will be higher when heavy.

In my turbulence story in the previous post, I said the stall horn would squeal intermittently while my normal forward speed was 123mph. That means I was experienceing momentary 70mph wind direction changes, at least at the leading edge of the wing. With that in mind, I'll keep my maneuvering speed near the max allowed to assure I can maintain maximum control in wind shear. Had I been moving 20mph slower I'd have been stalling on a regular basis. I was having enough fun as it was.

When I'm landing in turbulent surface winds, I keep my speed up a bit to maintain control. There's no difference in flight. Va identifies the safe speed limit.

Stewart

StewardB,

In a cub I agree Va and turbulent penetration speed may be near or the same.

However,

Va and Terbulent penetration speed by definition and the way they are determined are NOT the SAME.

Mike,

I repeat.......

StewartB said:

The practical definition is more important to me than the technical one.
http://selair.selkirk.bc.ca/aerodynamics1/Lift/Page12.html

Stewart

Click to expand...

LawnDart,

Under those circumstances, I'd fly a good bit faster, and keep the flaps up.

Once you deploy flaps, a lot of structural limits change A LOT. The airframe is NOT certified to 3.8 with flaps deployed.

Further, the airframe isn't able to sustain 3.8 in curved flight either.

I'd stack on more speed to penetrate the gusts, and slow the airplane very close to the runway under very rough conditions like that.

But none of that has anything to do with Maneuvering Speed. You were well below Maneuvering Speed, and all you have to do is be BELOW it for it to work.

You're better off penetrating gusts at a little (not necessarily a lot) faster speeds. You definitely (as you found out) don't want to be so slow you stall the airplane when low.


MTV

mghallen said:

StewardB,

In a cub I agree Va and turbulent penetration speed may be near or the same.

However,

Va and Terbulent penetration speed by definition and the way they are determined are NOT the SAME.

Click to expand...

Mike,

I'm interested in your comments. In searching the web I'm unable to find much info about Vb (turbulence penetration speed). This link addresses it a little, about 2/3 down the page. The entire link is pretty good reading.

http://www.auf.asn.au/groundschool/umodule2.html

I was taught to use Va as the speed limit in rough air. What little I've found on the subject says that in the absence of a published Vb speed, one should use Va as the turbulence penetration speed. It appears there is no formula for determining Vb, but rather it's a determination of the airplane designer. I've never seen a published or even an implied Vb speed for a Cessna or a Piper.

Another article.
http://web.usna.navy.mil/~dfr/flying/turb.htm

Stewart

So I'll be the 'dumbass' here. Yep, that'll be me!.

So when it's really turbulent, I should load 'er up to gross, maybe a bit beyond since it'll stall at a higher speed when overloaded, then go run around at the "speed limit" now to be know as "maneuvering speed"?????

What about the 'bending loads' on the wings before the 'critical angle of attack' is exceeded (stall)????

Wouldn't I get lesser 'bending loads' if my a/c were light???? Therefore allowing me to safely fly in turbulence at higher maneuvering speed when lightly-loaded?????

Too me, it seems like we are deciding pretty important stuff when we correllate a higher stall speed with a higher safe speed limit.

I'm serious about my first sentence. I am truly putting this stuff up for discussion and have no chip towards anyone here.

Mike V., do you have any comments on the initial question as it applies to our non-swept Cub or Cessna wings, and their asssociated lift strut, and fuselage attach structure?

Do VGs or Slots in the wings change the manuvering speed?

Tim

Weight vs. maneuvering speed

The gospel according to the EAA, verified by my old college and Air Force aerodynamics books:

"Does the maneuvering speed change with weight?

Yes, the POH usually specifies only one maneuvering speed based on the aircraft loaded to maximum gross weight. When an aircraft is operated at a weight less than maximum gross weight, the maneuvering speed changes. When the total weight is reduced, the maneuvering speed is less; when the total weight is increased, the maneuvering speed increases. A general rule-of-thumb is: "a 2 percent change in weight will result in a 1 percent change in maneuvering speed." Another way of arriving at this figure is to decrease the speed by half the percentage of the decrease in weight. If you had a 20 percent decrease in weight, decrease the speed by 10 percent."

manuerving speed

To add to the fray: The Lear 45 manual defines Va as: The highest speed that full aileron and rudder control can be applied without overstressing the aircraft, or the speed at which the aircraft will stall with a load factor of 2.9 g's at maximum gross weight, whichever is less.

Note that they did not include the elevator in that definition. I'm not sure if this definition is different for part 23 aircraft vs. part 25, don't have my basic aero. books handy.

I also have some technical formulas available to calculate Va, etc, with explanations, if someone wants them (some of it actually addresses cubs) but it is rather lengthy.

Dick

I'm not up for a lengthy discussion at the moment, so....


....If I have a butterfly wafting along on the breeze, and I decide to make him weigh twice what he normally weighs, would it be safe (?) to say that he'll stall first or break his wings first, when a gust hits him at that higher weight??

I think I'm being told I'm safer at a higher weight in turbulence. I'm having a hard time accepting that.

Why do we limit how much weight an airplane can legally be loaded to, if it won't have an affect on the bending that occurs before the wing stalls.

DAVE

Dave Calkins said:

I'm not up for a lengthy discussion at the moment, so....



I think I'm being told I'm safer at a higher weight in turbulence. I'm having a hard time accepting that.


DAVE

Click to expand...

Dave-

Thats right. We need Bill Rusk to give us a "lesson" on this. I used to be able to explain it two years ago but would need some rejuvination of my brain from school 2 years ago.

Its really a hard thing to explain without the use of a graph. I often get it mixed up myself.

Tim

manuerving speed

Since I have some info on gust loads, I'll relay some and paraphrase to keep it briefer:
The effect of horizontal gusts is relatively negligible as far as flight loads are considered, unless the aircraft is near Vne. Vertical gusts however can significantly increase the flight loads, especially in a heavy wing loaded aircraft.
It is not unusual to encounter vertical gusts of 15 fps (900 fpm) when operating in areas of high thermal turbulence, wind shears, or mts. The formula for computing actual gust loading is complicated and must compensate for many variables, but an aircraft with light wing loading (like cubs) operating at or below the computed Va, and encountering a 15 fps sharp edge gust, may increase the load factor by as much as 1.4. This is not critical and causes nothing more than mild discomfort, Unless the structure is heavily loaded in a steep turn or other maneuver when the gust is encountered. For instance, if you are in a 60 degree bank at 2000 lb GW, the load factor is 2.0 G and the load is 4000 lbs. If you experience a 15 fps vertical, sharp edge gust, the load factor will increase to 2.8 G and the structure load will be 5600 lbs. This is only 525 lbs. under the design maximum structural limit load. However, if the airframe is in good condition with no fatigue or corrosion, no structural damage will result and the airplane will stall when SLL (structural limit load) is reached. BUT, if the airplane is being flown at a speed Above the computed maneuvering speed for the GW, and is loaded heavy in a steep bank or pull out, and encounters the same 15 fps sharp edge gust, serious structural damage can occur...

Hope that helps a little.

Dave,

Did you read this link? You should.

http://selair.selkirk.bc.ca/aerodynamics1/Lift/Page12.html

The Maneuvering Speed is the minimum speed at which the wing can produce lift equal to the design load limit. Below this speed the wing can not produce enough lift to overstress the aircraft, no matter what angle of attack is used.

Click to expand...

The minimum speed of the lighter plane is slower. It makes perfect sense.

As for a higher weight being safer? I don't know about that. I do know that at a higher weight you'll be more comfortable. Higher wing loading makes for a smoother ride in the bumps.

Stewart

Dave,

No, you are looking at this problem wrong.

The loads are the same with a heavier aircraft at a higher speed, or a lighter airplane at a lower speed. That's the key, and it has to do with load factors to reach CRITICAL ANGLE OF ATTACK.

The assumption is that, once the wing reaches critical angle of attack, it will stall, thereby reducing the wing loading. If you are at a higher weight, you will stall at a higher speed, therefore, you will reach Critical AOA at a higher speed, and the airplane will behave the same and experience the same loads as if it were at a lower weight AND at a lower speed.

Ideally, you want the wing to reach critical AOA BEFORE anything breaks.

So, would you be any safer at a higher weight, as long as you comply with the manufacturer's Va recommendations? No. Note that Cessna, for example, in the 185 manual, states that Va varies with weight, and that lighter weights require a lower speed for Va.

Now, the Airbus accident demonstrated that the old saw that you can apply full control application (without further discussion of how many times) at Va is obviously false, at least for Airbus aircraft.

Maybe Boeing applies the same standards, but I thought Airbus Industrie and NTSB treatment of the AA pilot flying that airplane was terrible. As I understand it, the guy did precisely what AA's program taught him to do, and the FAA and Airbus were totally uninformed as to what they were training their pilots to do in such an event?

I'm not an airline pilot, never have been, and therefore could well be badly misinformed on this one, but it seems like this guy got hung out to dry.

MTV

Part of the difficulty in understanding the Airbus accident and ruling is that the concept of maneuver speed was developed based upon the wing, angle of attack, and the general plan to have the wing stall before anything breaks, either due to control movements or gusts.

The Airbus accident was caused by control inputs to the rudder, which overloaded and broke the vertical stabilizer. So, those wing arguments don't really apply. One could make those arguments for the vertical stab and find some sideslip angle that would stall it before it broke, but the Feds haven't done that. FAR25.351 is the certification requirement for vertical stab strength.

I agree with mvinion. The AA crew was hung out to dry.

I'll take some time later to check that link, SB. Thank you. I haven't been able to take the time to check it. I will.

To all in this 'argument':
First, thank you! I am enjoying this discussion and............

I understand the idea of flying into a 'vertical gust' such as a thermal.
I understand the idea that a wing will stall at a higher airspeed if it is more heavily loaded.
I agree that a more heavily-loaded a/c will have a nicer ride in turbulence VS. the same a/c a a lighter flying weight.
I understand it is being said that a more lightly-loaded wing will stall at a lower speed (no argument there), and therefore, one must fly more slowly in turbulence to not break that wing when it is more lightly-loaded. I undertand that is what's being said.

What I am arguing here is that maybe..........maybe:

1. maybe not every gust will be vertical
2. maybe the gust vector will not exceed the critical angle of attack, and thus, may not stall the wing, but rather, may overspeed the Va or Vb, and then break the a/c through overspeeding a heavily-loaded a/c.......because we may have been educated wrongly to believe we are safer to fly in turbulence at a higher weight rather than at a lower weight.

POINT: maybe a more-lightly loaded wing will bend less in the overspeed than a the same wing at a heavier load.

There was an article in AOPA or some other mag in the last couple of years about the "Myth of Maneuvering Speed". I didn't read it, but want to find it now.

This whole topic came to my mind when the owner of my latest refurb. project mentioned the idea of Va decreasing with a decreasing in flight-weight, and I figured it'd be fun to bat it around on SC.ORG

Anyone else wanna jump-in here?

Thanks again, everyone DAVE

Good points, Dave.

Just to keep it going, here's a bit more for critical examination.

Structure wise, it's not only the wing that might break. It's every structure. Consider a battery shelf on the firewall, designed to hold a heavy battery to 3.8Gs for normal category aircraft. A vertical gust beyond limits might cause a vertical acceleration that breaks the shelf.

Of course, the aircraft's weight (inertia) figures into how it responds to the gust. Here, lighter aircraft are more succeptible, hence you should fly slower in turbulence when you are light.

I think you are right on with your wind examples. Mother nature has no rules for the direction or strength of wind gusts.

The lifting loads on the wing are distributed spanwise, whereas the gravity loads are "mostly" in the center. So, from the viewpoint of the spar carry though, for example, you are probably better off light than otherwise. But, from the point of view of the battery shelf, for example, it doesn't care how the plane is loaded.

Food for thought.

Hankster

Hey Lawndart,

Who had the nerves of steel to take those pictures? Everything in focus and nicely centered i might add.
I would have been too busy messing up your back seat to play with a camera....