How Much Thrust Does a UAV Prop Make Backwards?

 How Much Thrust Does a UAV Prop Make Backwards?

The team at Premier Aerodynamics recently put this question to the test using a Tyto Robotics thrust stand and a Gem Fan 7×5E propeller.

Running on a 4S battery, they measured thrust across the full speed range in both directions. The results were clear:

• Forward rotation: up to 0.81 kgf
• Reverse rotation: 0.59 kgf (about 26% less thrust)

Efficiency told a similar story. Spinning the prop in its intended direction operated with 30 - 50% more thrust/watt (gf/W) compared to reverse operation.

They also observed a small hysteresis effect, with slightly higher thrust when ramping speed up versus down, likely due to battery voltage sag over time.

Interestingly, even when run backwards, the propeller still performed reasonably well. While not optimal, it could likely still generate enough thrust for flight in a pinch.

This experiment highlights both the importance of propeller orientation and the value of precise measurement tools like the Tyto thrust stand for uncovering real-world performance differences.