BEMT Rotor Trade Study
Comparison of baseline, bullnose, and elliptical blade configurations for a 7.5-inch UAV rotor at 8,500 RPM. The study evaluates chord geometry, angle of attack, thrust distribution, and the tradeoff between hover thrust and shaft power. Select the chart to view it at full resolution.
Project Overview
I developed a MATLAB Blade Element Momentum Theory (BEMT) solver to compare five blade configurations for a two-bladed, 7.5-inch UAV propeller. The study evaluates how chord distribution, pitch, and camber affect thrust and shaft power at an 8,500 RPM design point, against a 170 grams-force hover target per motor.
The solver uses 30 radial elements, interpolated chord schedules, iterative inflow calculations, Prandtl tip and hub loss corrections, and a simplified stall model. It integrates sectional forces into total thrust and torque, then calculates shaft power and hover figure of merit.
Key Contributions
- Built a reusable BEMT solver and compared baseline, aggressive and efficient bullnose, and aggressive and efficient elliptical configurations.
- Visualized chord schedules, spanwise angle of attack, sectional thrust, and the thrust-versus-power tradeoff in a four-panel dashboard.
- Evaluated predicted performance at 8,500 RPM and an assumed 16,000 RPM ceiling, with numerical results available alongside the source code.
Predicted Performance at 8,500 RPM
All five configurations exceed the 170 grams-force target in this model. The efficient bullnose produces the most thrust; the efficient elliptical uses the least shaft power and delivers the most thrust per watt among the configurations tested.
- Baseline: 273.1 grams-force thrust at 54.48 W shaft power; figure of merit 0.304.
- Bullnose aggressive: 404.2 grams-force thrust at 101.29 W shaft power; figure of merit 0.295.
- Bullnose efficient: 609.3 grams-force thrust at 60.59 W shaft power; figure of merit 0.912.
- Elliptical aggressive: 296.6 grams-force thrust at 68.75 W shaft power; figure of merit 0.273.
- Elliptical efficient: 441.8 grams-force thrust at 39.03 W shaft power; figure of merit 0.874.
These are numerical predictions using simplified airfoil polars and a stall model, rather than measured flight or bench-test results. Shaft power excludes motor and ESC losses. The 16,000 RPM cases assume that speed is achievable; they do not establish a validated motor or structural limit.