Preparing for Virtual Flight Tests in OpenFlight

Welcome, future flight test engineers and pilots! This brief will guide you on how to effectively prepare for and conduct virtual flight tests using the OpenFlight simulator. These tests are designed to help you understand fundamental aircraft stability, control, and performance characteristics in a practical, hands-on way.

1. Understand the Objective

Before starting any test, make sure you clearly understand:

• What phenomenon are you investigating? (e.g., Phugoid oscillation, stall characteristics, Dutch Roll damping, best climb speed).

• What is the expected aircraft behavior? Review the theory behind the specific mode or performance parameter.

• What data do you need to capture? Know which parameters (altitude, speed, angles, rates, coefficients) are most relevant for analyzing the specific test objective.

2. Simulator Setup & Configuration

Proper setup is crucial for obtaining meaningful results:

• Aircraft Selection: Choose the appropriate aircraft model specified in the test procedure or one suitable for the phenomenon being studied. Remember that different aircraft have different characteristics.

• Mission Configuration (default_mission.yaml):

  • Initial Conditions: Set the correct starting altitude, speed, and configuration (e.g., thrust setting) as required by the test plan. Ensure the starting altitude provides a safe margin for maneuvers (especially for stalls or potentially unstable tests).

  • Data Recording: Verify that the start_flight_data_recording_at and finish_flight_data_recording_at times cover the entire duration needed for the test maneuver and subsequent observation period. Err on the side of recording for longer than you think you might need.

• Center of Gravity (x_CoG): For tests involving CoG variation (like Neutral Point determination), carefully edit the correct aircraft YAML file in 🏭_HANGAR/📜_Aero_data/ and remember to restart the Julia backend (OpenFlight.jl) to apply the change. Double-check the value you entered.

3. Flight Test Execution Principles

• Trimming: Most tests begin from a stable, trimmed condition (usually straight and level flight, or a steady climb/glide).

  • Start the simulation and allow time for the aircraft to settle.

  • Use small, smooth control inputs to achieve the target speed and maintain altitude (or the target climb/glide state) with minimal control activity.

  • Patience is key! Achieving a good trim state before introducing the test input is vital for clean data.

• Controlled Inputs: When the test requires an input (e.g., elevator pulse, rudder doublet, aileron step):

  • Make the input deliberate and precise as described in the test plan (e.g., "short and sharp" or "smooth and steady").

  • Immediately neutralize the controls afterward unless the procedure specifies holding the input.

• Hands-Off Observation: After providing the excitation input, fly hands-off (do not make corrective inputs) for the required observation period. Let the aircraft respond naturally to its inherent dynamics. This is critical for observing stability modes.

• Situational Awareness: Even though it's a simulation, maintain awareness of altitude and attitude, especially during stall tests or when investigating potentially unstable modes like the spiral dive.

4. Data Handling and Analysis

• Locate Your Data: After each simulation run, the recorded data will be saved as a .csv file in the 📊_Flight_Test_Data folder within your main OpenFlight project directory. The filename will include a timestamp.

• Use the Visualization Tool: Load the generated CSV file(s) into the provided HTML visualization tool.

• Focus on Key Parameters: Use the plot visibility controls to focus on the data channels most relevant to the test objective (e.g., Altitude/TAS for Phugoid, AoA/Pitch Rate for Short Period, Roll/Yaw Rates/Sideslip for Dutch Roll, L/D Ratio for performance).

• Time Range: Use the time range controls in the visualization tool to zoom in on specific phases of the test (e.g., the initial response after an input, or a steady-state segment).

• Correlate Theory and Results: Compare the observed behavior and plotted data against the theoretical descriptions of the flight dynamic modes or performance characteristics. Do the period, damping, and parameter relationships match expectations?

5. Mindset and General Tips

• Be Systematic: Follow the test procedures carefully. Change only one variable at a time when comparing runs (e.g., CoG position or airspeed).

• Patience: Flight dynamics, especially modes like the Phugoid or Spiral, can be slow. Allow sufficient time for the behavior to manifest. Trimming also requires patience.

• Repeatability: Consider running a test more than once to ensure the results are consistent.

• Question Unexpected Results: If the aircraft behaves differently than expected, review your setup, inputs, and the underlying theory. Is it a simulator artifact, a characteristic of that specific aircraft model's data, or a misunderstanding of the concept?

• Safety (Simulated): While there's no physical risk, practice good airmanship. Avoid unnecessarily extreme maneuvers, especially near the ground or stall boundaries, unless specifically required by the test.

By following these guidelines, you can effectively use the OpenFlight simulator as a virtual flight test laboratory to gain valuable insights into the fascinating world of aircraft dynamics and performance. Good luck with your tests!