Propeller Performance Data at Low Reynolds Numbers

TLDR

Propeller data for UAVs operating at low Reynolds numbers (50,000–100,000) is scarce, despite extensive research on full‑scale aircraft propellers. The authors tested 79 propellers (9–11 in diameter) at UIUC, fixing RPM and varying wind‑tunnel speed to sweep advance ratios from low values to the windmill state, using four RPM settings (1,500–7,500) to probe Reynolds‑number effects. Propeller efficiencies varied from a peak near 0.65 to as low as 0.28, showing that proper propeller selection can dramatically affect UAV performance.

Abstract

While much research has been carried out on propellers for full-scale aircraft, not much data exists on propellers applicable to the ever growing number of UAVs. Many of these UAVs use propellers that must operate in the low Reynolds number range of 50,000 to 100,000 based on the propeller chord at the 75% propeller-blade station. Tests were performed at the University of Illinois at Urbana-Champaign (UIUC) to quantify the propeller efficiency at these conditions. In total, 79 propellers were tested and the majority fit in the 9- to 11-in diameter range. During the tests, the propeller speed (RPM) was fixed while changing the wind-tunnel speed to sweep over a range of advance ratios until reaching the windmill state (zero thrust). To examine Reynolds number effects, typically four RPM’s were tested in the range 1,500 to 7,500 RPM depending on the propeller diameter. Propeller efficiencies varied greatly from a peak near 0.65 (for an efficient pr opeller) to near 0.28 (for an exceptionally poor propeller). Thus, these results indicate that proper propeller selection for UAVs can have a dramatic effect on aircraft performance.