Why does maneuvering speed change with weight?

Question

I am a student pilot wondering why maneuvering speed changes with weight. A simple easy to remember answer would be great THANKS!

Answer 1

Maneuvering speed is based on the airplane being at gross weight. What happens when the airplane's weight decreases? The answer is: the maneuvering speed decreases.  

Airplanes flown at weights below their gross weight require less lift for straight and level flight. Less lift means the airplane can be flown at a smaller angle of attack. In other words, an airplane at 2,500 pounds may require a 4.5 degree angle of attack at 110 knots to remain in level flight. Decreasing the weight to 1,800 pounds may require only a 3 degree angle of attack to remain in level flight at this speed.

With a speed of 110 knots, at this lower weight, a sudden and very strong gust could increase the angle of attack from 3 to 18 degrees. this produces six times the original lift for a force of 6Gs. This is way beyond the limit of a normal category airplane. At lighter weights, what can we do to keep from exceeding our example limit of 4Gs when in turbulence?

The answer is to slow the airplane down. At a slower speed (95 knots for example) a larger angle of attack (let's say 4.5 degrees) is necessary for level cruise flight at this lower weight.

At this speed, we can increase the angle of attack four times before the airplane stalls. Ninety-five knots becomes our new maneuvering speed if we want to limit ourselves to 4Gs. Thus, decreasing weight requires a decrease in the airplane's maneuvering speed.

Most of the newer Pilot's Operating Handbooks publish two or three different maneuvering speeds for variable weight conditions. If yours doesn't, try doing the following to compute a new one. For every 2% reduction in weight, reduce the max-weight maneuvering speed by 1%. In other words, if the gross weight decreases by 20%, reducethe max-gross weight maneuvering speed by 10%.

Answer 2

It is as Mike (above) put it, Inertia. Greater the mass, greater the momentum for the same reference speed. A maneuver involves change in momentum, i.e. force. Greater the momentum, greater the forces required for the maneuver. The aircraft might not be able to employ such large forces or maybe it cannot afford to. So the best option is to reduce the speed.

PS: E=mc² has nothing to do in this context.

Answer 3

All aircraft are designed for specific flight envelopes depending on their mission profiles. Maneuvering speeds are calculated on the design boards for each load profile. These speeds give the best handling characteristics for the weight of the aircraft at that time. Reducing the weight for a set power and speed (say by jettisoning all external stores and loads) will merely make the aircraft more agile and reduce the stalling speed as well. Weight also imposes extra stress on the superstructure of the aircraft, thus all speeds are pre-calculated to keep the aircraft safe in the loaded configuration.

Answer 4

E = mc²

Energy is equivalent to mass and vice versa.

The more weight, the more energy.

For example, a 737 takes more energy, to turn because of it's weight, thus, it is much slower than, say, a Harrier.

Answer 5

Nobody got it right so far. Same reason stall speed increses with weight. And best L/D speed. Any speed for that matter. That particular AOA , maneuvering AOA in this case. occures at a higher speed in order to generate the increased lift required to support the increased weight. The amount of lift a wing produces is determined by three basic factors; wing shape, AOA and true airspeed. So to increase lift when the AOA and wing shape remain constant, the speed must increase.

Answer 6

The forces on the plane when it maneuvers have only to do with the aerodynamics, which doesn't change with weight. The safe limits that determine how much stress the plane can take have to do with the accelerations the plane can safely withstand.

A higher weight will mean the same force will result in less acceleration: F=ma means a=F/m So the same aerodynamic force will result in less and less acceleration of the airframe as its weight goes up.

Imagine you're going to punch two rocks. One weighs an ounce, the other fifty pounds. Which one is going to have more trouble?

So as weight goes up, maneuvering speed increases. The plane can safely travel at a higher speed and still be maneuvered with the same aerodynamic forces while keeping the acceleration to what the airframe can survive.

Answer 7

put simply.... Inertia.  If mass changes, so must velocity to compensate.  Remember, inertia is mass times velocity.

Edit:  I agree with Firefox... E=mc^2 has nothing to do with this scenario.

Answer 8

I'll try to make this as simple as possible.  First, you need to define maneuvering speed.  It is the maximum speed at a given weight an aircraft can be flown at which it will stall before being overstressed.  There are 2 reasons that maneuvering speed changes with weight.

1. Inertia - a heavier aircraft is less susceptible to sudden, abrupt movements caused by things like turbulence.  It can therefore be flown at a higher speed than a lighter aircraft without becoming overstressed.

2. Angle of attack - a heavier aircraft must be flown at a higher angle of attack than a lighter aircraft for any given airspeed.  Remember that an airplane always stalls when it reaches its critical angle of attack.  Therefore, the heavier airplane is closer to the critical angle of attack than the lighter airplane at a given airspeed because it is already flying at a higher angle of attack.  It is closer to a stall than a lighter airplane is at the same airspeed.  Therefore, you can fly the heavier aircraft FASTER because it is already going to stall sooner.  Remember, maneuvering speed is concerned with making the airplane stall before it is overstressed.