Abstract:

This video investigates the aerodynamic benefits of adding bellmouth intakes to Electric Ducted Fans (EDFs), responding to suggestions from aerospace engineers. The creator tested two 3D-printed bellmouth sizes (16mm and 7mm radius) on EDF units from a previous blown-wing airplane project. Tests were conducted both statically (measuring thrust) and dynamically (simulating forward flight with a blower fan) at 100W and 200W power levels. While static tests showed thrust improvements with bellmouths, factoring in the drag they introduce revealed a more nuanced outcome, with smaller bellmouths offering the best net efficiency gain in simulated flight conditions. The creator concludes that the bellmouth likely smooths airflow and reduces turbulence, rather than relying on Bernoulli's principle as some suggest.

Testing EDF Bellmouth Intakes for Improved Efficiency

• 0:00 Background & Hypothesis: The creator addresses feedback suggesting curved bellmouth intakes improve EDF efficiency, countering initial skepticism from past experiments with inverted bellmouths that showed no performance reduction.
• 0:00 EDFs Tested: Axial fans from a previous blown-wing airplane project are used for testing.
• 0:00 Custom Bellmouths: Two sizes of bellmouth intakes were 3D printed: a large one with a 16mm radius and a small one with a 7mm radius.
• 0:39 Static Thrust Tests (100W):
  • Large bellmouth: +14g thrust, a 7.8% improvement over bare fans.
  • Small bellmouth: +6.1% improvement over bare fans.
• 0:54 Static Thrust Tests (200W):
  • Small bellmouth: +6.6% improvement over bare fans (most efficient at this power).
• 1:03 Dynamic Thrust Tests (Simulated Flight): A blower fan creates 5 m/s airflow to simulate real-world conditions.
  • Small bellmouth: +7.6% improvement.
  • Large bellmouth: +9.8% improvement.
• 1:18 Drag Consideration: The static tests did not account for the drag created by the bellmouths themselves.
  • Large bellmouth drag: 24g.
  • Small bellmouth drag: 3g.
• 1:27 Adjusted Dynamic Results (Factoring in Drag):
  • At 100W: Small bellmouth +6.8% net gain; Large bellmouth -4.5% net loss.
  • At 200W: Small bellmouth +6.5% net gain; Large bellmouth +1% net gain.
• 1:42 Conclusion: A small bellmouth intake would have been beneficial for the blown-wing airplane, likely providing a ~6.5% efficiency increase.
• 1:51 Explanation for Bellmouth Benefit: The creator refutes the idea that it's solely due to low-pressure suction. Instead, it's theorized that the bellmouth smooths airflow, preventing turbulence and disruption caused by sharp intake corners.