Fair warning – if you think you are fully confident in your understanding of maneuvering speed, the article you are about to read may rock your world.
When you research this topic, it quickly becomes apparent that many pilots think they have a solid grasp on the concept, but when asked to explain it, the certainty breaks down in the details. Even an understanding based on FAA documentation can get convoluted and confusing.
To get started, let’s share the answers most of us would throw out there when asked to define maneuvering speed:
- Maneuvering speed is the maximum speed at which you can make full or abrupt movements of a single control without causing structural failure of the aircraft.
- Maneuvering speed is the fastest speed at which your plane will stall before exceeding its limit load factor if the angle of attack suddenly and dramatically increases.
- Maneuvering speed is the speed at which the aircraft’s wing – operated at the critical angle of attack – produces a load factor equal to the aircraft’s certified limit load factor. In other words, stall and limit load factor are both reached at this same AOA that occurs at maneuvering speed.
This is a starting point, but it doesn’t paint the full picture and as it turns out, some of these answers which we have been taught can even be dangerously misleading. Buckle up, because we’re about to go down the rabbit hole and expand our understanding of maneuvering speed.
What is maneuvering speed and how is it calculated?
For starters, did you know there is more than one type of maneuvering speed? The two types of maneuvering speed that CFR Part 23 pilots need to know are design maneuvering speed (Va) and maximum operating maneuvering speed (Vo). For CFR Part 25 pilots, Va is – somewhat ambiguously – used to indicate both design and operational maneuvering speed. In this case, a pilot will determine the meaning of the term “maneuvering speed” based on the context of its use.
Design maneuvering speed (Va)
In AC 23-19A, the FAA states that design maneuvering speed is “a value chosen by the applicant” and that “the loads resulting from full control surface deflections at Va are used to design the empennage and ailerons.”
Essentially, the purpose of Va is to ensure that the designers are creating control surfaces that can handle the loads created during full deflection at a chosen speed. This chosen speed is Va.
Va must not be less than the stalling speed (Vs) times the square root of the maximum positive load factor (n). Written mathematically, this reads:
Maximum operating maneuvering speed (Vo)
Vo (maximum operating maneuvering speed) is a limiting load factor which is also determined by the aircraft designer. AC 23-19A says that Vo is “a speed where the airplane will stall in a nose-up pitching maneuver before exceeding the airplane structural limits.”
The maximum value for Vo is the stalling speed (Vs) times the square root of the maximum positive load factor (n). Written mathematically, this reads:
Your plane’s maximum operating maneuvering speed will fluctuate based on weight. Your aircraft’s POH and cockpit placards should list your maneuvering speed based on maximum weight. In some cases, additional placards will list maneuvering speeds based on lower weights.
To calculate your own Vo based on your current (lower than max) weight, use the following equation:
An easy way to estimate your adjusted maneuvering speed is to reduce your Vo by 1% for every 2% reduction in weight.
Why aircraft weight affects maximum operating maneuvering speed (Vo)
It intuitively makes sense that weight and maneuvering speed would be correlated, however the nature of the correlation deserves a little explanation. Most new pilots would initially assume that as your weight goes down, your maximum operating maneuvering speed would go up, but in fact the opposite is true. A lower weight corresponds to a lower maneuvering speed, and here’s why:
Newton’s Second Law of Motion
Thanks to Newton’s Second Law of Motion, we know that when an object of mass (in this case an airplane) is acted on by a force (in this case a full control input), the object will accelerate in the same direction as the force. This relationship is expressed in the mathematical equation:
Since we know our values for force and mass, we are interested in seeing what that does to our plane’s acceleration around the rotational axis. Therefore, we re-write the equation as:
a = F/m.
As we can see by that equation, when we apply the same control force, but we decrease the mass of the aircraft, the resulting acceleration experienced by the aircraft will increase. Higher acceleration means increased stress or load on the airframe, and eventually, that load will surpass design limitations and lead to structural failure if we do not modify another variable.
Assuming we weren’t adding more weight and assuming we still want to be able to support the force of a full control movement, the variable which we must modify is our maneuvering speed. So, there you go – a lower aircraft weight necessitates a lower maximum operating maneuvering speed.
Angle of Attack and Limit Load Factor
Another way to understand the relationship between aircraft weight and maneuvering speed is to talk about angle of attack and limit load factor. The lighter an aircraft is, the less lift it will require to achieve straight and level flight, as shown by the equation:
A lower lift requirement means the ability to fly at a smaller angle of attack. If an aircraft’s speed stays the same, but its weight decreases, the required angle of attack will decrease.
The problem is that at a smaller angle of attack, it is possible for a wind gust or full deflection of the elevator control to increase the G-force beyond the aircraft’s limit load factor (+3.8Gs for normal rated aircraft) while still remaining below the critical AoA needed for the wings to stall.
For example, if the aircraft is experiencing 1G at a 3° AoA, a sudden increase in lift with corresponding AoA of 18° would result in 6Gs of force because the initial 3° AoA has increased by a factor of 6. Before the wings reach the critical angle of attack and stall, the aircraft will have exceeded its load limit and could experience structural damage or failure.
Take that same aircraft, with the same lighter than maximum gross weight, and now compensate by decreasing the speed so that the initial AoA increases to 4.5°. At this increased AoA, by the time the wings reach their critical AoA of 18°, the aircraft will still be just below its limit load factor. It will stall prior to experiencing structural damage or failure.
In summary, to compensate for a lower weight, we must decrease our speed so that our angle of attack remains high enough that an increase in G-force doesn’t cause us to exceed our limit load factor prior to stalling.
Relationship between design maneuvering speed (Va) and maximum operating maneuvering speed (Vo)
Take another look at the above equations for both Va and Vo. Notice that the only way for the maneuvering speeds to be equal is if the designer selects a value of for both.
If Vo is equal to Va, then the aircraft is indeed likely to stall prior to structural failure during a single control input executed at or below Va. The problem is that the manufacturer doesn’t have to make Va = Vo. Va cannot be slower than Vo, but it can be as fast as Vc (design cruising speed).
Usually, Va does equal Vo, however if Va for your aircraft is higher than Vo, the standard understanding of Va as being the speed at which your plane will stall prior to experiencing structural failure goes out the window. You will be able to exceed the limiting load factor of your aircraft (Vo) while still flying below Va.
In Advisory Circular 23-19A, an airframe guide for certification of Part 23 aircraft, the FAA confirms:
“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 where VA>VS√n, the pilot would have to check the maneuver; otherwise the airplane would exceed the limit load factor.”
It further goes on to explain,
“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.”
What this means for us is that for Part 23 aircraft, the understanding we had of Va is actually a more accurate description of Vo.
This brings us to another very important conversation about what maximum operating maneuvering speed is and what it is not.
The most common [dangerous] misconception about maneuvering speed
Up until 2001, there was a common consensus among pilots that flying below maximum operating maneuvering speed offered nearly 100% protection from the dangers of structural and/or control surface failure. The belief was that if you were flying at or below Vo, your aircraft would stall prior to experiencing structural damage/failure no matter what control movements you made. As it turned out, that was a dangerous oversimplification of the physics of maneuvering speed, as fatally demonstrated by the pilots of American Airlines Flight 587.
Following the American Airlines Flight 587 disaster, the FAA released Special Airworthiness Information Bulletin CE-11-17. The audience is mainly Part 25 pilots, so it references Va, rather than Vo since as you will recall, Part 25 uses Va to describe both design and operational maneuvering speeds. Still, the bulletin clarifies that its message applies to Part 23 pilots as well.
The take-away of CE-11-17 Is that your maximum operational maneuvering speed (Va for Part 25 and Vo for Part 23) is:
“the speed below which you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane.”
The bulletin goes on to point out that manufacturers are not required to build aircraft that are capable of multiple simultaneous full control inputs or sequential full control inputs. This was the fatal mistake made by the AA 587 first officer who made repetitive sequential rudder pedal inputs that led to “in-flight separation of the vertical stabilizer.”
The Bottom Line
Start digging into the concept of maneuvering speed and you will find the internet awash with conflicting interpretations and understandings of what this v-speed is and what it means to you. Do your own reading and research to round out your understanding of maneuvering speed.
As a recap, the key points are:
- The FAA has designated two maneuvering speeds – Va and Vo – for Part 23 pilots.
- Va stands for design maneuvering speed and Vo is maximum operational maneuvering speed.
- Part 25 pilots use Va to describe both design maneuvering speed and maximum operational maneuvering speed.
- Design maneuvering speed (Va) is a value set by the aircraft designer. The loads resulting from full control surface deflections at Va are used to design the empennage and ailerons.
- Maximum operational maneuvering speed (Vo) is a speed where the airplane will stall in a nose-up pitching maneuver before exceeding the airplane structural limits.
- Vo decreases as your aircraft’s weight decreases.
- Va is often but not always equal to Vo. If Va is higher than Vo, you could exceed the limit load factor of the aircraft prior to stalling.
- Being at or below Vo means that you can move a single flight control, one time, to its full deflection, for one axis of airplane rotation only (pitch, roll or yaw), in smooth air, without risk of damage to the airplane. Multiple sequential or simultaneous full deflections can result in structural failure even if you are flying below Vo.