Taking a deeper dive into maneuvering speed

Jim K

Jim K

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My plane has a placard on the panel stating "Rough Air or Maneuvering Speed 125MPH (109KTS)". This always seemed oddly slow to me, but I don't fly at maneuvering speed much, so I didn't think too much about it. Studying for the commercial (and having a couple hairy weather experiences) has led me to think more about Va and when it might be appropriate to slow down to reduce stress on the aircraft. I was discussing this with another POA pilot, who agreed that it seemed strangely slow, and questioned if the POH might give a range based on weight.

My POH, VB-750, issued August 1, 1975, states in the limitations section "Design Maneuvering Speed 125MPH (109KTS)". That's it. It also calls out the placard mentioned above as being a required marking.

So I dug a little deeper and found VB-840, published August 20, 1976, which is another POH for a PA32R-300. FWIW, my plane is a 1976 model (#169), and AKAIK there were no changes in the PA32R-300 airframe through its production run. Anyway, VB-840 states in section 2 that Va is 132 KIAS at max gross (3600lb) and 100 KIAS at 2170 lb. Empty weight of my plane is 2103 lbs.

It looks to me like they picked 109KTS as the Va at the lightest weight the plane would reasonably be flown at. Now, I know the POH that came with my airplane controls its aerodynamics :biggrin:, but it's nice to have some more realistic numbers. I don't understand why they didn't bother to put that in the earlier book.
 
This is counter-intuitive to me - why is Va higher for a higher weight?
 
Jim K said:
So I dug a little deeper and found VB-840, published August 20, 1976, which is another POH for a PA32R-300. FWIW, my plane is a 1976 model (#169), and AKAIK there were no changes in the PA32R-300 airframe through its production run. Anyway, VB-840 states in section 2 that Va is 132 KIAS at max gross (3600lb) and 100 KIAS at 2170 lb. Empty weight of my plane is 2103 lbs.
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Does this POH publish a separate rough air speed?
 
MauleSkinner said:
It’s (at least in part) an AOA-based number.
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Do I have this right:
At the same airspeed, a different AoA will yield different amount of stress on the wing?

Edit - but wouldn't higher weight equal more AoA needed, and thus more wing loading at the same speed? I'm still confused
 
Baked Potato said:
This is counter-intuitive to me - why is Va higher for a higher weight?
Click to expand...

Simplistically stated, Va is the maximum speed at which, with a full deflection of the controls, a stall will occur prior to structural damage. Stall speed decreases as weight decreases.


vg-diagram-small.png
 
Nz = L/W. G load = lift/weight.

If your plane weighs 2k lbs it needs 2k lbs of lift to fly straight and level. If you lower the weight you increase the g load for the same speed (at the same AOA).
 
Half Fast said:
Simplistically stated, Va is the maximum speed at which, with a full deflection of the controls, a stall will occur prior to structural damage. Stall speed decreases as weight decreases.


vg-diagram-small.png
Click to expand...
Ok, this is what I was missing - the part about where a stall would occur prior to structural damage. I was thinking it was just a point at where structural damage would occur.
And thanks for the reminder to not use Wikipedia as a study guide before my next stage check.
 
Half Fast said:
Simplistically stated, Va is the maximum speed at which, with a full deflection of the controls, a stall will occur prior to structural damage.
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I recall that the rudder is not included here. That became apparent in an airliner accident caused by excessive rudder movement below Va.
 
Half Fast said:
Simplistically stated, Va is the maximum speed at which, with a full deflection of the controls, a stall will occur prior to structural damage. Stall speed decreases as weight decreases.
Click to expand...
That's correct. Once you think of it as a stall speed, this makes more sense. The wings will stall before they can produce so much lift as to exceed the limit load factor, e.g. 3.8g for a normal category airplane.

Here's a video with more background on this topic (including the VG Diagram which @Half Fast included above:

 
kgruber said:
A slight puff of wind will deflect a piece of paper MUCH more than a rock.

That's why Va is lower for the paper.
Click to expand...

I don’t know if it helps or hurts, buy my mental model includes identically shaped planes with the same structural strength, but one is styrofoam and one is lead.
 
FastEddieB said:
I recall that the rudder is not included here. That became apparent in an airliner accident caused by excessive rudder movement below Va.
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I'm too lazy to look it up the definitions, but I think Va is basically you get one full deflection of one control ONCE. It's not intended to do full rudder deflections right and left and expect to stay within design limits. That was what brought the down AA587.

admiralcloudberg.medium.com

Days of Our Discontent: The crash of American Airlines flight 587

Two months after 9/11, 265 people died when a plane slammed into a neighborhood in Queens. The cause would divide the industry for years.
admiralcloudberg.medium.com admiralcloudberg.medium.com
In reality, however, manufacturers were only obligated to show that single inputs would not break the airplane below this speed. Combinations of inputs, such as repeatedly moving the rudder back and forth from full left to full right deflection, were never tested, nor were they required to be, because there was no justifiable reason for a pilot to do this.
Click to expand...
 
FastEddieB said:
I recall that the rudder is not included here. That became apparent in an airliner accident caused by excessive rudder movement below Va.
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Indeed. Va covers the wing being overloaded. If you dig through the regs you'll find the caclulation of Va is not based on anything with regard to the rudders. It's a function of main wing load factor and the stall speed.
 
flyingron said:
If you dig through the regs you'll find the caclulation of Va is not based on anything with regard to the rudders. It's a function of main wing load factor and the stall speed.
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If you dig even further you'll find that while it is not a part of the calculation of Va the vertical surfaces (i.e. rudder and vertical stab) must be able to withstand full deflection at speeds up to Va.

Nauga,
and CFR14 23.441
 
When I saw the word "dive" in the thread title I thought we were going to be discussing this point (which is much lower than Va):

1715356743202.png​
 
Baked Potato said:
This is counter-intuitive to me - why is Va higher for a higher weight?
Click to expand...
The V-g diagram, that Half Fast posted, is key to understanding Va. At, or below, Va, the wing will stall before positive-g loading increases above the certification limit. Va does not protect against negative-g loading, as you can see by going down from Va on the V-g diagram.
 
FastEddieB said:
I recall that the rudder is not included here. That became apparent in an airliner accident caused by excessive rudder movement below Va.
Click to expand...
We went through this not all that long ago. The rudder is not included in the definition of Va but a different paragraph in part 23 says the vertical surfaces must be able to withstand full rudder deflection at Va. What it did not account for was the transient 'dynamic overshoot' to higher angle of sideslip and thus higher loads on the vertical surfaces that caused the vertical stabilizer failure on AA587; however, since that time the relevant paragraph mentioned earlier has since been modified to include some level of dynamic overshoot.

An interesting historical note is that there was a similar mishap of a Navy S-3 undergoing flight test years before AA587. It's documented with some level of accuracy in George Wilson's book Flying the Edge. It's particularly interesting to read it with prior knowledge of AA587 and think about why lessons learned were not shared (or if shared, not actually learned).

Nauga,
and sinusoidal sweeps
 
Jim K said:
So I dug a little deeper and found VB-840, published August 20, 1976, which is another POH for a PA32R-300.
Click to expand...
Interesting -- it looks like VB-750 applied to 1976 Lances (32R-7680001 THRU 32R-7680525) and VB-850 applied to 77 and 78 Lances (32R-7780001 THRU 32R-7880068). Since these were all straight tail, I wonder why they changed the POH. Also, the latest revision for VB-750 is 2015 but VB-840 hasn't been revised since 1990.

 
Jim K said:
My plane has a placard on the panel stating "Rough Air or Maneuvering Speed 125MPH (109KTS)". This always seemed oddly slow to me, but I don't fly at maneuvering speed much, so I didn't think too much about it. Studying for the commercial (and having a couple hairy weather experiences) has led me to think more about Va and when it might be appropriate to slow down to reduce stress on the aircraft. I was discussing this with another POA pilot, who agreed that it seemed strangely slow, and questioned if the POH might give a range based on weight.

My POH, VB-750, issued August 1, 1975, states in the limitations section "Design Maneuvering Speed 125MPH (109KTS)". That's it. It also calls out the placard mentioned above as being a required marking.

So I dug a little deeper and found VB-840, published August 20, 1976, which is another POH for a PA32R-300. FWIW, my plane is a 1976 model (#169), and AKAIK there were no changes in the PA32R-300 airframe through its production run. Anyway, VB-840 states in section 2 that Va is 132 KIAS at max gross (3600lb) and 100 KIAS at 2170 lb. Empty weight of my plane is 2103 lbs.

It looks to me like they picked 109KTS as the Va at the lightest weight the plane would reasonably be flown at. Now, I know the POH that came with my airplane controls its aerodynamics :biggrin:, but it's nice to have some more realistic numbers. I don't understand why they didn't bother to put that in the earlier book.
Click to expand...
The TCDS for the PA-32R-300 indicates maneuvering speed is 125mph/109kt CAS. It does not specify different maneuvering speeds for different serial numbers.

It does reference VB-750 applying to serial nos. 32R-7680001 to 32R-7680525 and VB-840 applying to serial no. 32R-7780001 to 32R-7880066. I don't know why the higher maneuvering speed in the newer models isn't reflected in the TCDS.
 
Half Fast said:
Simplistically stated, Va is the maximum speed at which, with a full deflection of the controls, a stall will occur prior to structural damage. Stall speed decreases as weight decreases.
Click to expand...
In keeping in the spirit of the thread title:
That's not the definition of design maneuvering speed (VA). Design maneuvering speed (VA) is a speed at which the aircraft structure must be strong enough to withstand maximum control deflection. This does include the rudder.

The aircraft designer must select a VA such that VA >= VS sqrt(n), the latter being stalling speed at the limit load factor. In practice, there is usually no reason to select a VA that is higher than necessary, so they are often equal. This is why you commonly see definitions of VA like the one I quoted, despite it not being technically accurate.

Unfortunately the FAA fueled this confusion by treating a minimum design speed for aircraft certification as a maximum operating speed for pilots for many decades. The FAA attempted to eliminate this confusion in the 1990s by inventing "operating maneuvering speed" (VO). VO must be equal to or less than VS sqrt(n).

In summary, VO <= VS sqrt(n) <= VA
 
125mph is low for maneuvering speed in my opinion given your cruising speeds are faster, but 125mph also sounds like a reasonable speed to aim for if you are out practicing steep turns. On the Arrow it’s 134mph. But generally if I’m going to be doing maneuvers, typically I’ll want to be a little slower (probably closer to 125mph) anyway (kind of like making a sharp turn when you’re riding your bicycle or a sharp turn driving your car).

On the Arrow, Va = 134mph and Vno = 170mph. My airplane doesn’t go faster than this (Vno) anyway so I don’t really have to slow down for turbulence unless I’m uncomfortable. And for maneuvering speed, that’s a full deflection of the flight controls, I never really do a full deflection, I still think a 10/20/30 degree bank at cruise speed is well within spec but that’s my opinion. You start to feel the G forces at 45 degrees (1.41 G) and 60 degrees (2 G). The airplane is designed for +3.8G / -1.52 G with a 50% buffer. I’m not sure how to do negative G’s but I do know the feeling of positive +1.4G-2.0G and it quickly gets uncomfortable for me, so I think I’d know if I’m surpassing 2G’s and that’s still within limits.

On top of that, at altitude your IAS is lower so it’s even more difficult to reach those limitation speeds. The one I would watch for is your flaps, mine says <125mph but I really try to wait until under 100mph. For the gear it’s <150mph but I try to slow down to 125/130mph before dropping the gear.

Basically, I don’t think you are coming close to any limits and if you were, you’d know.

Va = maneuvering speed
Vno = structural cruise speed (aka smooth air above this speed)

IMG_1107.jpeg
 
Honestly, unless you are flying snap rolls, Va is of limited use. It is difficult to achieve full and abrupt deflection of the elevator in such a way as to reach the maximum G load possible at a given speed. For one thing, the pull has to be really abrupt, basically jerking the stick/yoke back to the stops in one quick motion, which is hard to do because the stick forces get much greater as airspeed and deflection increase. G forces also become quite pronounced, and are hard to ignore as they build.

I fly my aircraft to limits almost daily. I actually have to practice pulling up harder because I am having trouble reaching 4G in my loop entries. That is at 150-160mph, in an aircraft with a Va of 121mph and Vno of 160mph.

Vno is a more important airspeed. Above that you definitely need to pay attention. But even then it is surprising how hard you can pull. I pull 4.5 to 4.8G recovering from a hammerhead with a quarter roll on the downline, and that is pulling very aggressively right at Vno, after pointing straight at the ground WOT for 5 or 6 seconds.
 
The above analysis is the criteria for testing the VA speed.

For our flying, the use of VA is to assure that a powerful up draft, which has the potential to exceed the G limits of the airframe, will result in stalled airflow, and limit the actual g forces. This prevents pulling off the wing at maneuvering speed, VA.

The heavier the load in your plane, the higher the potential G load with a gust, so the slower the VA.

Since these gusts are short lived, the danger of a stall spin sequence is minimal. I have flown in a Cessna 150, near gross, myself and the instructor, just east of the Appalachian mountains, with a strong airflow from the NW. We stayed at VA for the whole flight, and the stall warning sounded momentarily, several times a minute. I was unaware of any momentary nose drop, indicating a stall event, but the G forces were beating me up, both positive and negative.
 
geezer said:
For our flying, the use of VA is to assure that a powerful up draft, which has the potential to exceed the G limits of the airframe, will result in stalled airflow, and limit the actual g forces. This prevents pulling off the wing at maneuvering speed, VA.
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Repeating the wrong definition over and over doesn't make it right.
 
dmspilot said:
In keeping in the spirit of the thread title:
That's not the definition of design maneuvering speed (VA). Design maneuvering speed (VA) is a speed at which the aircraft structure must be strong enough to withstand maximum control deflection. This does include the rudder.

The aircraft designer must select a VA such that VA >= VS sqrt(n), the latter being stalling speed at the limit load factor. In practice, there is usually no reason to select a VA that is higher than necessary, so they are often equal. This is why you commonly see definitions of VA like the one I quoted, despite it not being technically accurate.

Unfortunately the FAA fueled this confusion by treating a minimum design speed for aircraft certification as a maximum operating speed for pilots for many decades. The FAA attempted to eliminate this confusion in the 1990s by inventing "operating maneuvering speed" (VO). VO must be equal to or less than VS sqrt(n).

In summary, VO <= VS sqrt(n) <= VA
Click to expand...
And for any students pilots out there, if you try to explain the above to your CFI, or worse DPE, there's about an 90% chance that they'll try to correct you for not understanding the really simple generalization. Just give the cookbook answer and don't rip the control surfaces off the aircraft.
 
My previous post was not intended to propose a different definition of VA, but to explain that it is useful in choosing a safe speed in turbulent air. Continuing at normal cruise when turbulence is encountered subjects you, your passengers, and the plane to greater G loads than at VA, and assures that the wings will stall before they will be compromised.

VA is called "Gust penetration speed" in some old POH's, "Maneuvering speed" in others, but the use by pilots concerned for their safety, it is the fastest speed where the wings will not fail, whether from violent control inputs, or external forces.

The training flight described was not to test the integrity of the plane, but to train me in night IFR in difficult conditions. The gusts were about twice what my instructor expected, and steadily increased, but at VA or below, safe, so we continued. When the stall warning beeps became too frequent, we quit.

For the record, I have never had weather related G forces even half what we had that night, but have flown at VA several times to be on the safe side, versus stay on flight planned speed.

Repeating, not disputing the definition, just pointing out the value to pilots in choosing proper airspeed in bumpy conditions.
 
All I know is that my turbulence penetration speed is lower than the airplane's... and I learned that lesson again yesterday.

The other speed I pitch to when the bumps get really bad is top of the white arc. I feel like that helps take the load off quite a bit and it's a decent safe speed if you're not sure of exact weight.
 
geezer said:
VA is called "Gust penetration speed" in some old POH's, "Maneuvering speed" in others,
Click to expand...
They’re not calling Va a “gust penetration speed.”

“maneuvering speed” “gust penetration speed” are two different speeds with different sets of regulatory criteria. In many (most?) light planes, they’re close enough that the manufacturer provides one number for both.
 
If @Pilawt is around I wonder if he knows of any PA32 design changes between 76 and 77. I have the 77 so my Va is higher than Jim's 76. Our planes look fairly identical though.
 
MauleSkinner said:
They’re not calling Va a “gust penetration speed.”

“maneuvering speed” “gust penetration speed” are two different speeds with different sets of regulatory criteria. In many (most?) light planes, they’re close enough that the manufacturer provides one number for both.
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The wing doesn't care what caused the AOA to increase (gust or elevator deflection). Either way it can't produce more lift, and therefore, cannot overload the spar.

And yes, when you get to swept wings and jets things can change, but we are talking about light aircraft.
 
keen9 said:
The wing doesn't care what caused the AOA to increase (gust or elevator deflection). Either way it can't produce more lift, and therefore, cannot overload the spar.

And yes, when you get to swept wings and jets things can change, but we are talking about light aircraft.
Click to expand...
We’re also talking about the certification standards. A vertical gust of regulatory proportions isn’t necessarily going to result in the same AOA change as full control travel.
 
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FastEddieB said:
I recall that the rudder is not included here. That became apparent in an airliner accident caused by excessive rudder movement below Va.
Click to expand...

No, Va is for ONE full scale deflection of the controls. In the Airbus mishap, the PF was using the rudder to respond to wake turbulence induced rolling. So multiple deflections
 
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