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nTop 6-DOF Flight Dynamics Framework

A production-ready Python framework for 6-degree-of-freedom (6-DOF) flight dynamics simulation, integrated with AVL (Athena Vortex Lattice) and XFOIL for aerodynamic analysis of nTop-designed aircraft.

Project Status

Phase 1: AVL Geometry Generation & Validation ✅ (COMPLETED)

Completed Components:

  1. Geometry Analysis (src/io/geometry.py)

    • ✅ CSV point parser for LE/TE data
    • ✅ Wing geometry calculator (span, area, MAC, AR, sweep, taper, dihedral)
    • ✅ Tail surface estimator using volume coefficients
    • ✅ Unit conversion (inches → feet)

  2. Mass Properties (src/io/mass_properties.py)

    • ✅ Mass converter (lbm → slugs, kg)
    • ✅ Inertia converter (lbm·in² → slug·ft², kg·m²)
    • ✅ CG location converter (inches → feet, meters)
    • ✅ AVL .mass file generator

  3. AVL Geometry Generator (src/aero/avl_geometry.py)

    • ✅ Complete AVL .avl file writer
    • ✅ Wing surface from LE/TE points
    • ✅ Horizontal tail with elevator
    • ✅ Vertical tail with rudder
    • ✅ Flaperon control surfaces (80% chord, 75% span)
    • ✅ NACA 6-series airfoil integration

  4. Flight Conditions (src/aero/avl_run_cases.py)

    • ✅ US Standard Atmosphere model
    • ✅ AVL .run file generator
    • ✅ Cruise condition (Mach 0.25 @ 20,000 ft)
    • ✅ Climb condition (Mach 0.20 @ 10,000 ft)
    • ✅ Landing condition (Mach 0.15 @ sea level)

  5. AVL Interface (src/aero/avl_interface.py)

    • ✅ Subprocess interface to AVL executable
    • ✅ Command sequence generator
    • ✅ Output file parser (.ft, .st files)
    • ✅ Alpha sweep capability
    • ✅ Results plotting

  6. Project Structure

    • ✅ Modular directory layout
    • ✅ requirements.txt with dependencies
    • ✅ Generated files in avl_files/

Aircraft Configuration

Wing Geometry (from nTop export)

Parameter Value Units
Span 19.89 ft
Area 199.94 ft²
Mean Aerodynamic Chord (MAC) 26.69 ft
Root Chord 22.40 ft
Tip Chord 0.20 ft
Taper Ratio 0.009 -
Aspect Ratio 1.98 -
LE Sweep 56.64 deg
c/4 Sweep 45.18 deg
Dihedral 6.00 deg

Notes:

  • Very low aspect ratio (1.98) indicates delta wing or highly swept design
  • Extreme taper ratio (0.009) means nearly pointed wing tips
  • High sweep angles (56.6° LE) typical of high-speed UAV or flying wing

Horizontal Tail (Estimated)

Parameter Value Units
Area 47.99 ft²
Span 8.72 ft
Chord 5.51 ft
Aspect Ratio 1.58 -
Volume Coefficient (V_H) 0.60 -
Moment Arm 66.72 ft
X Position 90.68 ft

Vertical Tail (Estimated)

Parameter Value Units
Area 2.98 ft²
Height 2.11 ft
Chord 1.41 ft
Aspect Ratio 1.50 -
Volume Coefficient (V_V) 0.05 -
Moment Arm 66.72 ft
X Position 92.73 ft

Mass Properties

Parameter Value Units
Mass 7,555.6 lbm / 234.8 slugs / 3,427.2 kg
CG Location (12.92, 0.00, 0.05) ft
Ixx 14,908.4 slug·ft²
Iyy 2,318.4 slug·ft²
Izz 17,226.9 slug·ft²

Control Surfaces

Surface Hinge Line Span Extent Type
Flaperons 80% chord 75% semispan Antisymmetric (roll)
Elevator 70% chord Full span Symmetric (pitch)
Rudder 70% chord Full height Yaw

Airfoils

  • Wing: NACA 64-212 (constant along span)
  • Horizontal Tail: NACA 0012
  • Vertical Tail: NACA 0012

Flight Envelope

Condition Altitude Mach Velocity Density Purpose
Cruise 20,000 ft 0.25 259.2 ft/s 0.001267 slug/ft³ Loiter
Climb 10,000 ft 0.20 215.4 ft/s 0.001756 slug/ft³ Ascent
Landing 0 ft 0.15 167.4 ft/s 0.002377 slug/ft³ Approach

Generated Files

AVL Files (in avl_files/)

  1. uav.avl - Main geometry file

    • Wing with 7 spanwise sections
    • Horizontal tail (2 sections)
    • Vertical tail (2 sections)
    • Control surface definitions
    • Reference values (Sref, Cref, Bref, CG)

  2. uav.mass - Mass properties file

    • Total mass in slugs
    • CG location in feet
    • Inertia tensor in slug·ft²

  3. uav.run - Run cases file

    • 3 flight conditions defined
    • Atmospheric properties
    • Mass/inertia for each case

Testing Scripts

  1. run_avl_simple.bat - Windows batch file to run AVL manually
  2. test_avl.bat - AVL geometry validation script

Quick Start

1. Install Dependencies

pip install -r requirements.txt

Required packages:

  • numpy
  • scipy
  • matplotlib
  • pandas
  • pyyaml
  • pytest

2. Generate AVL Geometry from nTop Data

from src.aero.avl_geometry import generate_avl_geometry_from_csv

# Generate AVL files from CSV exports
wing, h_tail, v_tail, mass_props = generate_avl_geometry_from_csv(
    le_file="Data/LEpts.csv",
    te_file="Data/TEpts.csv",
    mass_file="Data/mass.csv",
    output_file="avl_files/uav.avl",
    aircraft_name="nTop_UAV"
)

3. Run AVL Analysis

Option A: Manual (Windows)

run_avl_simple.bat

Option B: Python Interface

from src.aero.avl_interface import AVLInterface

avl = AVLInterface(r"C:\path\to\avl.exe")

# Single analysis point
result = avl.run_avl_case(
    avl_file="avl_files/uav.avl",
    mass_file="avl_files/uav.mass",
    alpha=2.0,
    beta=0.0,
    mach=0.25
)

print(f"CL = {result.CL}, CD = {result.CD}, L/D = {result.CL/result.CD}")

# Alpha sweep
results = avl.run_alpha_sweep(
    avl_file="avl_files/uav.avl",
    mass_file="avl_files/uav.mass",
    alpha_range=(-5, 15, 1),
    mach=0.25
)

4. Analyze Wing Geometry

from src.io.geometry import read_csv_points, compute_wing_geometry

le_points = read_csv_points("Data/LEpts.csv", units='inches')
te_points = read_csv_points("Data/TEpts.csv", units='inches')

wing = compute_wing_geometry(le_points, te_points)

print(f"Wing Span: {wing.span:.2f} ft")
print(f"Wing Area: {wing.area:.2f} ft²")
print(f"Aspect Ratio: {wing.aspect_ratio:.2f}")

Directory Structure

nTop6DOF/
├── src/
│   ├── core/               # 6-DOF dynamics (TODO)
│   ├── aero/
│   │   ├── avl_geometry.py     # ✅ AVL file generator
│   │   ├── avl_interface.py    # ✅ AVL Python interface
│   │   ├── avl_run_cases.py    # ✅ Run case generator
│   │   └── xfoil_interface.py  # TODO
│   ├── environment/
│   │   └── atmosphere.py       # ✅ US Standard Atmosphere (in avl_run_cases.py)
│   ├── io/
│   │   ├── geometry.py         # ✅ LE/TE CSV parser
│   │   └── mass_properties.py  # ✅ Mass converter
│   ├── propulsion/             # TODO
│   ├── control/                # TODO
│   ├── analysis/               # TODO
│   └── visualization/          # TODO
├── tests/                      # TODO
├── examples/                   # TODO
├── config/                     # TODO
├── Data/
│   ├── LEpts.csv              # ✅ Wing LE points (from nTop)
│   ├── TEpts.csv              # ✅ Wing TE points (from nTop)
│   └── mass.csv               # ✅ Mass properties (from nTop)
├── Docs/
│   ├── avl_doc.txt            # AVL documentation
│   └── AVL_User_Primer.pdf
├── Plan/
│   └── flight_6dof_project_plan.md
├── avl_files/
│   ├── uav.avl                # ✅ Generated AVL geometry
│   ├── uav.mass               # ✅ Generated mass file
│   └── uav.run                # ✅ Generated run cases
├── requirements.txt           # ✅ Python dependencies
└── README.md                  # This file

✅ = Complete
TODO = Not yet implemented

Next Steps (Phase 2 & Beyond)

Immediate Next Steps:

  1. ✅ Validate AVL geometry - Run AVL manually to verify geometry loads correctly
  2. Core 6-DOF Framework
    • State vector class (position, velocity, attitude quaternions, rates)
    • Quaternion mathematics
    • Equations of motion
    • RK4/RK45 integrators
  3. Aerodynamic Database
    • Automated AVL sweeps (alpha, beta, Mach, controls)
    • Multilinear interpolation
    • Database save/load
  4. Trim & Simulation
    • Trim solver
    • Time-domain simulation
    • Flight path integration

Medium Term:

  • XFOIL integration for 2D airfoil polars
  • Simple propulsion model
  • Basic autopilot (PID altitude/heading hold)
  • Linearization & stability analysis
  • Eigenmode analysis (phugoid, short period, Dutch roll, etc.)

Long Term:

  • nTop workflow automation
  • Parametric design sweeps
  • Optimization interface
  • Wind/turbulence models
  • Advanced control laws
  • Real-time visualization

Important Notes

Tail Geometry Assumptions

⚠️ Current tail geometry is ESTIMATED using volume coefficients:

  • Horizontal tail: V_H = 0.6
  • Vertical tail: V_V = 0.05
  • Tail moment arms: 2.5 × wing MAC

You should export tail surfaces from nTop using the same LE/TE point method:

  1. Export horizontal tail LEpts and TEpts to separate CSV files
  2. Export vertical tail LEpts and TEpts to separate CSV files
  3. Update avl_geometry.py to use actual geometry instead of estimates

Airfoil Selection

Currently using NACA 64-212 for the wing. For optimal performance at Mach 0.25 cruise:

  • Consider NACA 64-series with design CL matching cruise condition
  • Run XFOIL to generate polars if custom airfoil is needed
  • Update airfoil parameter in avl_geometry.py

Units Convention

  • Input: US Customary (inches, lbm, lbm·in²)
  • AVL: US Customary (feet, slugs, slug·ft²)
  • 6-DOF (future): Can use either SI or US Customary

AVL Path

Update AVL executable path in scripts:

avl_exe = r"C:\Users\bradrothenberg\OneDrive - nTop\Sync\AVL\avl.exe"

References

Contact & Support

For issues with:

  • nTop geometry export: Check LE/TE point extraction from nTop
  • AVL errors: Verify .avl file format, check AVL documentation
  • Python errors: Ensure all dependencies are installed
  • Framework design: Review Plan/flight_6dof_project_plan.md

License

Internal nTop project - not for external distribution.

Last Updated: 2025-01-XX Status: Phase 1 Complete, Phase 2 In Progress Version: 0.1.0-alpha

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