Do Fly-By-Wire Flight Controls Provide Artificial Feel?

When it comes to fly-by-wire (FBW) flight controls in modern airliners, the question of whether they provide an artificial feel has sparked considerable debate among aviation enthusiasts and professionals. The answer, in a nutshell, is both yes and no.

Basic Mechanisms of Fly-By-Wire Systems

Both Boeing and Airbus FBW systems include mechanisms to provide a neutral position and dampening to prevent excessive movement. It is worth noting that while these systems do not directly provide aerodynamic feedback, they do incorporate features such as spring-loaded neutral positions and dampers to prevent unwanted movements.

Artificial Feel vs. Control Force Gradients

If you're asking whether FBW flight controls mimic the control force gradients of traditional aircraft, the answer can be nuanced. Boeing's FBW controls are designed to offer variable force gradients that depend on airspeed and stick displacement, including features like a stick shaker to warn pilots of potential stalls. Airbus, however, takes a different approach. They provide a basic, fixed force gradient for the sidesticks, which pilots are expected to understand and adapt to. This means pulling the stick by a consistent amount at any given airspeed will result in similar control responses.

The Function and Benefits of Artificial Feel

The term "artificial feel" might seem paradoxical since it pertains to a control mechanism that is non-aerodynamic. Historically, aircraft such as the Boeing 747 featured an "artificial speed feel" that enhanced intuitive flying by increasing elevator force at higher speeds. This feature not only made the 747 more intuitive to fly but also helped prevent over-controlling at higher speeds.

For historical context, WWII fighters utilized control forces that varied with G-force and angular rate. Optimal settings for the zero required 10 pounds of pull per G. Devices like spring tabs helped achieve high roll rates with manageable forces. The Cactus Kiwi was notable for its variable control force characteristics. When powered controls became common post-war, the challenge shifted to providing aerodynamic-like feedback through artificial feel systems.

Artificial Feel Systems in Airliners

A key aspect of fly-by-wire and powered control systems is the artificial feel, which is achieved through mechanical means such as springs or electronic solutions. These systems provide the pilot with a sense of aerodynamic force without directly applying force to the cockpit controls. This is crucial for safety and handling, as the actual control inputs are handled by the airplane's hydraulic systems or electronic actuators.

The artificial feel is mandated by aviation certification standards to ensure that the airplane behaves predictably and remains controllable under various conditions. Pilots are trained to interpret the artificial feel as they would aerodynamic feedback, even though no direct aerodynamic forces are being exerted on the controls. This artificial feel is essential in maintaining positive stick forces and stability.

Engineering Challenges in Providing Authentic Feel Forces

The most significant challenge in designing artificial feel systems is ensuring that the force feedback varies with both the amount of control deflection and airspeed. To meet certification requirements for pitch stability, the force on the pitch control stick should increase proportionally with airspeed decreases from the trimmed speed.

Pilots must also contend with the effects of changes in the Center of Gravity (CG). Manufacturers use various methods to mitigate these effects, such as adding bob weights in the pitch control system, which provide resistance proportional to G-loading. Adjustments in springs or other mechanical elements help ensure that the artificial feel is appropriate for the current flight condition, even as the CG shifts.

In summary, while fly-by-wire systems do not provide true aerodynamic feedback, they incorporate sophisticated artificial feel systems to ensure that pilots experience a consistent and predictable feel, regardless of the aircraft's configuration. These systems are critical for maintaining the handling qualities and safety of modern airliners.

Key Points:

FBW systems use spring-loaded neutral positions and dampers to prevent unwanted movements. Boeing and Airbus have different approaches to providing control feel, with Boeing offering variable force gradients and Airbus providing fixed force gradients. Historical aircraft like the Boeing 747 featured an "artificial speed feel" to enhance intuitive flying. Artificial feel systems in modern airliners are designed to meet aviation certification standards, ensuring consistent and predictable handling.

Understanding the intricacies of fly-by-wire and artificial feel systems is crucial for both pilots and aviation professionals, as these technologies continue to shape the future of air travel and military aviation.