Tutorial: designing a 10-inch quadcopter drone propeller with Heliciel

The builder of a camera quadcopter wants to size its propellers and predict its endurance BEFORE buying motors and battery. The data:

Total mass in flight: 2,000 g (frame, camera and battery included), 4 motors;
in hover each propeller must therefore carry 500 g, a target thrust of 4.905 N per motor;
10-inch (254 mm) propellers, 2 blades — the standard of 450-class frames;
battery 4S 5,000 mAh (14.8 V), motor + controller efficiency estimated at 75 % (figure from the motor manufacturer);
air at 20 °C at sea level.

Organisation and design phases:

Start from a model of the drone library
Hover design: 500 g per motor
Theoretical endurance on the battery
The throttle curve: thrust and power against rpm
Noise
Summary and model to download

1: Start from a model: Heliciel ships with a library of drone propellers (1.2 to 6 inches, 2 to 9 blades). We load a 5-inch 3-blade racing propeller… which we are going to turn into a 10-inch two-blade lifter — once again, the model is only a starting point.

5-inch drone propeller model loaded in Heliciel

2: Hover design: hovering is THE design point of a multirotor (zero speed of advance — Heliciel brings it to 0.001 m/s for the BEM computation). We ask for: Ø 254 mm, 2 blades, air at 20 °C, thrust target 4.905 N. Heliciel searches for the rpm:

hover rpm: 5,800 rpm;
shaft power: 38.4 W per motor, torque 0.063 N·m;
figure of merit: 0.80 — the quality indicator of a rotor in hover (ratio of the ideal Froude power to the actual power): 0.80 is a very good value, commercial drone propellers typically sit between 0.55 and 0.75;
geometric pitch: 115 mm at 0.7 R — our computed propeller is the equivalent of a commercial “10 × 4.5”, but with an optimum twist instead of a constant pitch;
tip Mach number: 0.23.

10-inch drone propeller hover design in Heliciel

3: Theoretical endurance: Heliciel chains the BEM hover computation with the electrical balance using OUR assumptions (no hidden value):

total electrical power: 206 W (4 × 38.6 W shaft / 0.75 motor + ESC efficiency);
current drawn from the battery: 13.9 A (2.8 C on 5,000 mAh — very gentle);
theoretical hover endurance: 21.5 minutes to full discharge. In practice a LiPo is only discharged to 80 %: count on ~17 minutes of hover — and less in windy forward flight.

4: The throttle curve: the flight controller modulates the rpm all the time. The multi-point analysis sweeps the rpm from 3,500 to 8,000 rpm with the geometry frozen:

drone propeller thrust curve against rpm

Rpm	Thrust/motor (N)	(g)	Torque (N·m)	Shaft P (W)
3500	1.79	182	0.025	9.3
4500	2.95	301	0.041	19.1
5000	3.65	372	0.047	24.8
5800	4.90	500	0.063	38.4
6500	6.14	626	0.079	53.6
7000	7.12	726	0.091	67.0
8000	9.30	948	0.119	100.0

Reading: at 8,000 rpm the 4 motors deliver 4 × 9.3 N = 37.2 N, a thrust-to-weight ratio of 1.9: enough to hold a hover in a steady wind and manoeuvre calmly (2 or more is recommended for a camera platform). The table also gives the torque at each rpm: the figure to check against the Kv/torque curve of your motors, to make sure they will hold 8,000 rpm under load.

5: Noise: blade passing frequency 193 Hz (harmonics 387 and 580 Hz) — the characteristic “hum” — and a blade tip at 77 m/s (Mach 0.23). Switching to 3 blades of smaller diameter would raise the BPF (a higher-pitched sound, often felt as more aggressive): the large, slow two-blade propeller is the choice of discretion and endurance.

6: Summary and model to download

Two-blade propeller Ø 254 mm (10″), pitch 115 mm (~10×4.5), optimum twist;
hover: 500 g/motor at 5,800 rpm, 38.4 W shaft, figure of merit 0.80;
theoretical endurance: 21.5 min (100 % discharge) / ~17 min at 80 %;
maximum thrust (8,000 rpm): thrust-to-weight ratio 1.9.

The complete project can be downloaded here: helice_drone_10pouces_hover.hlc (open it with Heliciel). It is also included in the models supplied with the software. For 3D printing your prototypes, export the STL from Heliciel — and balance carefully before the first flight.

I remain at your disposal for any remarks or further information at contact@heliciel.com

JF Iglesias, Heliciel developer.

To see this propeller in the air it stirs, pressure on the blades and jet under the rotor, read the case study drone propeller CFD: six minutes of simulation on the 5-inch propeller supplied with Heliciel.