Flying Qualities, Pilot Ratings, Regulations and Applications

CHAPTER 6: FLYING QUALITIES, PILOT RATINGS, REGULATIONS AND APPLICATIONS

This chapter presents a detailed examination of how flying qualities are defined and regulated for civilian and military airplanes, focusing on the relationships among flying qualities, pilot ratings, and the failure state of the flight controls. Various methods for designing aircraft for optimal flying qualities are illustrated with examples.

6.1 FLYING QUALITIES AND PILOT RATINGS

In airplanes operated by human pilots, the interaction between pilot control inputs and airplane responses must enable the pilot to achieve mission objectives with manageable physical and mental effort. Acceptable flying qualities, also termed handling qualities, must be maintained throughout the operational flight envelope. The operational flight envelope includes various conditions under which the aircraft must perform effectively at different speeds, altitudes, and load factors.

Operational Flight Envelopes

Figure 6.1 illustrates typical operational flight envelopes for civilian and military airplanes, considering parameters such as altitude limits, Mach limits, and stall limits.

Civilian Airplane Characteristics:

  • Cabin Altitude Limit: 40K ft

  • Mach Limit: 0.75 to 1.0

  • Stall Limit: 30K ft

  • Cruising Altitude Range: 20K to 50K ft

Military Airplane Characteristics:

  • Ceiling: 25K ft

  • Dynamic Pressure Limit: 10K to 50K ft

  • Combat Intercept Operations: Must accommodate different weapon/load configurations and possible combat damage conditions.

Fundamental Flying Qualities Requirements

The following characteristics must be present within the operational flight envelope:

  1. Control Power: Sufficient control power to maintain steady-state straight and maneuvering flight.

  2. Maneuverability: Ability to transition between different steady-state flight conditions.

  3. Transition Control Power: Sufficient control power for transitions from ground operations to airborne and vice versa (takeoff and landing).

These characteristics need to be present regardless of engine status or conditions of asymmetrical power and also need to hold for military aircraft subjected to combat damage.

Physical and Mental Pilot Efforts

  • Physical Efforts: Defined through cockpit control activity and control forces. Important parameters include maximum required stick force, stick-force-per-'g', stick-force-speed-gradient, and aileron wheel force.

  • Mental Efforts: Refers to pilot compensation, where the pilot must adjust their responses based on the aircraft's behavior relative to commands. For instance, slower aircraft might require the pilot to anticipate/control actions sooner.

Parameters for Predicting Acceptable Flying Qualities

To determine if an airplane has acceptable flying qualities, the following are necessary:

  1. A pilot rating scale to evaluate flying qualities, specifically the Cooper-Harper scale (Figure 6.2), which aids engineers in understanding pilot perceptions.

  2. Defined relationships between aerodynamic characteristics, cockpit control forces, and flying qualities.

  3. A mathematical model of the airplane to predict flying quality characteristics, as introduced in earlier chapters.

  4. A mathematical model of the human pilot operating in conjunction with the airplane.

Regulations and Military vs. Civilian Requirements

Military requirements often include numerical design guidelines to ensure adequate flying qualities for mission objectives. Civilian requirements are generally less specific; they often utilize military guidelines for certification purposes. Regulations aim to assure flight safety and performance across various aircraft types.

6.2 MILITARY AND CIVILIAN FLYING QUALITY REQUIREMENTS: INTRODUCTION AND DEFINITIONS

A classification of airplanes and their operational requirements is defined, along with the categories of flight phases essential for the operation of the aircraft in specific environments.

6.2.1 Definition of Airplane Classes

Airplanes are categorized into different classes based on specifications provided by MIL-F-8785C (Table 6.1). For instance, Class I includes small, light airplanes like basic trainers, while Class III encompasses larger transport aircraft with varying responsibilities and capabilities.

6.2.2 Definition of Mission Flight Phases

Each mission has distinct flight phases, requiring different flying qualities. These phases can include tasks such as approach, landing, take-off, and various maneuvering conditions.

6.2.3 Definition of Flying Quality Levels and Allowable Failure Probabilities

Flying quality levels are classified into three levels, which measure the effectiveness and safety of the aircraft in several mission segments while factoring in probabilities of encountering failures. Level 1 represents excellent flying qualities, while Level 3 embodies significant deficiencies.

6.3 LONGITUDINAL FLYING QUALITY REQUIREMENTS

This section elucidates requirements specific to longitudinal control forces, phugoid damping, and flight path stability. Reference regulations dictate the acceptance criteria for various performance benchmarks during early design phases.

6.3.1 Control Forces

  • Requirements specify longitudinal control forces during various flight scenarios, notably in steady-level flight, maneuvers, takeoffs, and landings, highlighting acceptable limits based on the aircraft classification (Tables 6.4 to 6.6).

  • Control forces are documented based on the operational envelope, examining the implications of configuration changes and dynamic response characteristics.

6.3.2 Phugoid Damping and Flight Path Stability

Damping requirements of the phugoid motions are analyzed, with a need for specific oscillatory characteristics under disturbances. Maintainable stability during landing approach is requisite, demonstrated through responsiveness to speed changes (Tables 6.8).

6.4 LATERAL-DIRECTIONAL FLYING QUALITY REQUIREMENTS

Focused on lateral-directional response, this section outlines rotation control, directional control at asymmetrical loadings, and one-engine inoperative scenarios, along with specific damping and frequency requirements defined in the regulation framework.

6.4.1 Control Forces

Parameters related to lateral-directional control are delineated (Table 6.10), indicating requirements in regards to maximum allowable stick and wheel control forces under various flight conditions to maintain acceptable control responses.

6.4.2 Dutch Roll Frequency and Damping

Specific criteria exist for the dutch roll phase to ensure stability, articulated through comparisons of undamped natural frequencies and damping ratios (Table 6.12).

6.5 CHARACTERISTICS OF THE FLIGHT CONTROL SYSTEM

Discusses the impact of flight control systems on pilot perceptions of flying qualities, detailing the effects of signal path design, actuator response delays, and potential issues from electronic signal processing.

Control System Break-out Forces

Maximum allowed control system break-out forces are established for various types of controllers pertinent to pilot impression of flying quality during operational scenarios (Table 6.18). Phase lags in control surface deflections are also documented to minimize pilot workload and maintain stability.

6.6 RELATION BETWEEN FLYING QUALITY REQUIREMENTS AND DESIGN

The chapter emphasizes the iterative design process needed to achieve desired flying qualities, requiring an analysis of various stability, control, and response characteristics with regulatory benchmarks guiding necessary design adaptations.

6.7 SUMMARY FOR CHAPTER 6

A synthesis of the interrelations between flying quality regulations for civilian and military aircraft, establishing the predictive metrics used for aircraft designs to ensure compliance with operational standards for safety and mission efficacy. Emphasis on responsiveness to evolving technology and regulation adaptations is also highlighted.

6.8 PROBLEMS FOR CHAPTER 6

Problem-solving exercises are proposed to reinforce the understanding of concepts like rolling moment of inertia, performance analysis under specified conditions, and short period dynamics based on flight characteristics analysis.

Question: What are the fundamental flying qualities requirements that must be met within the operational flight envelope of an aircraft?
Answer: The fundamental flying qualities requirements within the operational flight envelope of an aircraft include:

  1. Control Power: Sufficient control power to maintain steady-state straight and maneuvering flight.

  2. Maneuverability: The ability to transition between different steady-state flight conditions.

  3. Transition Control Power: Sufficient control power for transitions from ground operations to airborne and vice versa (such as during takeoff and landing). These qualities must be consistent, regardless of engine status or conditions of asymmetrical power.

Conceptual Questions and Answers

  1. What are flying qualities?
    Flying qualities refer to the characteristics of an aircraft that determine its response to pilot control inputs and ability to meet mission objectives effectively.

  2. Why is the operational flight envelope important?
    The operational flight envelope defines the range of conditions (speeds, altitudes, load factors) in which the aircraft must perform effectively and maintain acceptable flying qualities.

  3. What is the Cooper-Harper scale?
    It is a pilot rating scale used to evaluate flying qualities, allowing engineers to understand pilot perceptions of aircraft performance.

  4. How do military and civilian airplane requirements differ?
    Military requirements are often more specific with quantitative guidelines, while civilian standards tend to be less strict and often reference military guidelines for certification.

  5. What constitutes acceptable flying qualities?
    Acceptable flying qualities must allow pilots to input controls with manageable physical and mental effort throughout the operational flight envelope.

  6. What are the fundamental characteristics required within the operational flight envelope?
    Control power, maneuverability, and transition control power must be present to ensure good flying qualities.

  7. What factors influence physical pilot efforts?
    Key factors include maximum required stick force, stick-force-per-'g', and stick-force-speed-gradient related to cockpit control activity.

  8. What is the significance of maneuverability in flying qualities?
    Maneuverability allows the aircraft to transition effectively between different steady-state flight conditions, enhancing operational effectiveness.

  9. What role do regulations play in pilot ratings?
    Regulations set the standards for flying quality requirements to ensure safety and performance across various aircraft types.

  10. How do defined relationships between aerodynamics and cockpit controls impact flying qualities?
    Understanding these relationships helps engineers design aircraft that respond predictably and effectively to pilot inputs, essential for safety and efficiency.

  11. What is phugoid damping?
    Phugoid damping is the control of oscillations in altitude due to a pitch change, essential for maintaining flight path stability.

  12. What happens if acceptable limits for control forces are not maintained?
    If control forces exceed acceptable limits, it can lead to difficulties in handling the aircraft, affecting safety and performance.

  13. Why must military aircraft accommodate combat damage conditions?
    Military aircraft must remain operational and maintain flying qualities even after sustaining damage to fulfill mission objectives.

  14. How does transition control power aid in aircraft operation?
    It provides the necessary control authority for smooth transitions between ground and airborne states, such as during takeoff and landing.

  15. What are acceptable failure probabilities in flying quality levels?
    Flying quality levels assess the likelihood of encountering failures during various mission segments, directly impacting the effectiveness and safety of the aircraft.

  16. What is the role of lateral-directional flying qualities?
    These qualities impact the aircraft's ability to maintain control during turns and under various load conditions, crucial for maneuvering effectiveness.

  17. How does the flight control system affect pilot perceptions?
    The design of the flight control system, including delays in signal processing, influences how pilots feel about their control over the aircraft and its responsiveness.

  18. What must be considered in the iterative design process to meet flying quality requirements?
    Designers must analyze stability, control, and response characteristics, ensuring that design adaptations align with regulatory benchmarks.

  19. What impact do electronic signal processing issues have on flying qualities?
    These issues can create delays or inaccuracies in control surface responses, complicating pilot interactions and potentially leading to safety concerns.

  20. What are the different classes of airplanes according to MIL-F-8785C?
    Airplanes are classified from Class I (small trainers) to Class III (larger transports), each with distinct requirements and capabilities.

  21. What distinct flight phases are associated with a mission?
    Flight phases can include takeoff, landing, approach, and various maneuvering conditions specific to mission objectives.

  22. How does the maximum allowed control system break-out force affect flying qualities?
    Exceeding the maximum allowed forces can impede pilot control effectiveness and introduce handling difficulties, which can compromise safety.

  23. What is the relation between flying qualities and mission efficacy?
    Good flying qualities help ensure that aircraft can perform their mission effectively, contributing to overall safety and operational success.

  24. How does human pilot modeling contribute to predicting flying characteristics?
    Modeling pilots allows for a better understanding of responses relative to aircraft behavior, aiding in designing for optimal flying qualities.

  25. What challenges arise when modifying aircraft configurations?
    Changes to aircraft configurations can affect dynamic response characteristics and control forces, necessitating thorough analysis to maintain safety and performance standards.