maneuvering speeds

[rchamble]

Why does maneuvering speed go up with an increase weight? I would think it would be the opposite, with an increased weight you would need a decreased maneuvering speed? I know at lower weights the effects of aerodynamic forces are greater, but why? You would think if there is enough aerodynamic force to move something that is heavier that there is more force there to do damage?? Does that make sense??

Just trying to understand/grasp concepts instead of memorize them

 

[exncsurfer]

I'd say its similar to how a large heavy ship plows through choppy water(turbulence) relatively smoothly compared to a jon boat which would be bouncing all over and beating you senseless.

 

[Sam D]

What is maneuvering speed?

How does weight affect stall speed?

 

[SixPapaCharlie]

Just trying to understand/grasp concepts instead of memorize them

Awesome!

 

[nauga]

Why does maneuvering speed go up with an increase weight?

Maneuver speed is roughly the minimum speed at which you can overstress your airplane (there's some relatively recent discussion/recognition over whether it can also be set by lateral load limits but the concept is the same). If your g-limit is 6g and your weight is 2000 lb, you'll hit your g-limit when you're generating 6*2000lb =12000 lb of lift. If you weigh 3000 lb you'll need 18000 lb. Since max lift occurs at a relatively constant max lift coefficient you'll need to be going faster (by a factor of sqrt(3000/2000) ~=1.22 in the example) at the higher weight and CLmax to hit or exceed the g limit.

Nauga,
at instantaneous corner

 

[MAKG1]

Maneuvering speed is where you stall before exceeding the G limit (usually 3.8G on a light trainer).

Stall speed goes as sqrt(M), so the maneuvering speed (which is really just sqrt(3.8) times the calibrated clean stall speed) does the same thing. The G's you pull are an acceleration, not a force, and do not depend on mass.

 

[Stewartb]

A few things to ponder re: Maneuvering Speed. Keep in mind that most of this is from Part 23 and most of our airplanes fall under CAR 3.

An article- http://www.avweb.com/eletter/archives/101/2892-full.html?ET=avweb:e2892:641902a:&st=email#222680

Another- http://www.askacfi.com/29/definition-of-va-maneuvering-speed-and-vno.htm

Some regulatory definition- Va is a calculation requirement of Part 23 airframe certification.

48. What is the design maneuvering speed VA?

a. The design maneuvering speed is a value chosen by the applicant. It may not be less than Vs√ n and need not be greater than Vc, but it could be greater if the applicant chose the higher value. The loads resulting from full control surface deflections at VA are used to design the empennage and ailerons in part 23, §§ 23.423, 23.441, and 23.455.

b. VA should not be interpreted as a speed that would permit the pilot unrestricted flight-control movement without exceeding airplane structural limits, nor should it be interpreted as a gust penetration speed. Only if VA = Vs √n will the airplane stall in a nose-up pitching maneuver at, or near, limit load factor. For airplanes whereVA>VS√n, the pilot would have to check the maneuver; otherwise the airplane would exceed the limit load factor.

c. Amendment 23-45 added the operating maneuvering speed, VO, in § 23.1507.VO is established not greater than VS√n, and it is a speed where the airplane will stall in a nose-up pitching maneuver before exceeding the airplane structural limits.

Source- http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_23-19A.pdf (pg 27)

Here's some regulatory discussion about Vb, gust load factors. http://www.gpo.gov/fdsys/pkg/CFR-2008-title14-vol1/pdf/CFR-2008-title14-vol1-sec23-341.pdf

And finally, if the Va has to do with a pitching moment stall, the reason the Va speed goes up with added weight is because a heavier airplane is less responsive to forces that will upset it or change it's attitude, whether intentional or not. The heavier airplane is more sluggish. That isn't a perfect explanation but it's basically correct. You can experiment with light and heavy loading on a bumpy day to see what difference it makes in the bumps. Generally speaking the heavier wing loading is more comfortable in cruise while lighter wing loading is more maneuverable. When it really gets interesting is when you can fly on a bumpy day and then elect to go back out in the same conditions in a different airplane. For me it was a late model C-180 and a Cub. The handling in bumpy air was fun to compare.

 

[warthog1984]

Maneuver speed is roughly the minimum speed at which you can overstress your airplane (there's some relatively recent discussion/recognition over whether it can also be set by lateral load limits but the concept is the same). If your g-limit is 6g and your weight is 2000 lb, you'll hit your g-limit when you're generating 6*2000lb =12000 lb of lift. If you weigh 3000 lb you'll need 18000 lb. Since max lift occurs at a relatively constant max lift coefficient you'll need to be going faster (by a factor of sqrt(3000/2000) ~=1.22 in the example) at the higher weight and CLmax to hit or exceed the g limit.

Nauga,
at instantaneous corner

It's also worth noting that the airframe structure isn't necessarily the weak point, so the apparent speed=force correlation doesn't actually exist. That 4g, 6g, or whatever limit might be the max capacity of an engine mount, gear door, or whatever. In one case, an airliner overstressed itself in a pullout beyond Va, and seemed OK... until the gear doors ripped off and flew into the elevator.

 

[nauga]

Maneuvering speed is where you stall before exceeding the G limit (usually 3.8G on a light trainer).

You will stall before exceeding the g-limit at any speed below maneuver speed (but I suspect you meant that anyway). It's the maximum speed where you will stall before exceeding the g-limit, or the minimum speed where you can hit your g-limit. It's the speed at the upper left corner of the V-n diagram.

The G's you pull are an acceleration, not a force, and do not depend on mass.

Semantics. A lighter airplane has more 'g-available' at a given airspeed since max lift is AOA limited and a = F/m. Normal accel in g's ('G's you pull') = Lift/Weight

Nauga,
and the inevitable spiral

 

[RoscoeT]

More simply put, higher weights require the airplane to fly at a higher angle of attack than an aircraft at lower weight. The higher the angle of attack, the closer you are to the stall. A heavily loaded airplane requires less additional G load to reach the stall compared to the lightly loaded airplane. Maneuvering speed is all about the speed under which the airplane will stall before damage is done to the airframe.

 

[danhagan]

You guys are giving me a headache

Maneuvering speed = speed necessary to keep lava temperature coffee off of lap in turbulence.

 

[exncsurfer]

RoscoeT,
Thanks, your simplification helps clear it up. This is a really good article which pretty much describes it the same way: http://flighttraining.aopa.org/maga...ng_Smart_A_New_Look_at_Maneuvering_Speed.html

a heavier plane can go faster at a given aoa compared to the same plane with a lighter load. And since the maneuvering speed is based on a stall speed(aoa) you get a higher maneuvering speed with heavier weight.

 

[MAKG1]

You guys are giving me a headache

Maneuvering speed = speed necessary to keep lava temperature coffee off of lap in turbulence.

That speed is zero, with the aircraft snugly tied down.

In moderate turbulence, you're spilling coffee no matter what your speed.

 

[NickC99]

I think the NTSB report just released on the PC-12 breakup is a worthwhile read.

http://www.ntsb.gov/AviationQuery/brief.aspx?ev_id=20120607X54234&key=1

During the right descending turn, while about 15,511 feet and 338 knots (about 175 knots above maximum operating maneuvering speed), the pilot likely applied either abrupt or full aft elevator control input, resulting in overstress fracture of both wings in a positive direction.

 

[WoooPigSooie]

Why does maneuvering speed go up with an increase weight? I would think it would be the opposite, with an increased weight you would need a decreased maneuvering speed? I know at lower weights the effects of aerodynamic forces are greater, but why? You would think if there is enough aerodynamic force to move something that is heavier that there is more force there to do damage?? Does that make sense??

Just trying to understand/grasp concepts instead of memorize them

I was initially stumped by this too. What it boiled down to for my understanding though was that a heavier airplane will do better in rougher air than the same airplane with a lighter load.
An a/c operating at reduced weight is more vulnerable to rapid accelerations encountered during flight thru turb, and an a/c operating in turb at or near gross weight is less likely to exceed design load limit factors.

 

[PPC1052]

Maneuver speed is roughly the minimum speed at which you can overstress your airplane (there's some relatively recent discussion/recognition over whether it can also be set by lateral load limits but the concept is the same). If your g-limit is 6g and your weight is 2000 lb, you'll hit your g-limit when you're generating 6*2000lb =12000 lb of lift. If you weigh 3000 lb you'll need 18000 lb. Since max lift occurs at a relatively constant max lift coefficient you'll need to be going faster (by a factor of sqrt(3000/2000) ~=1.22 in the example) at the higher weight and CLmax to hit or exceed the g limit.

Nauga,
at instantaneous corner

I read an interesting article that advocated for reducing speeds for penetration through significant turbulence below the listed maneuvering speed due to the possibility of picking up additional air speed from horizontal gusts, which can provide additional lift thereby forestalling the point at which the wings stall beyond the point where they become overstressed.