Abstract:

This video investigates the efficiency improvements of electric ducted fans (EDFs) by testing the addition of curved bellmouth intakes. Prompted by suggestions from aerospace engineers and the creator's own conflicting past observations, the experiment uses 3D-printed bellmouths of two sizes (small and large) on axial fans. Static thrust tests at 100W and 200W show that both bellmouths generally improve efficiency. However, dynamic tests simulating forward flight (5 m/s airflow) reveal a crucial difference: while the small bellmouth consistently provides a significant efficiency increase (around 6.5-6.8% when factoring in drag), the large bellmouth can actually decrease efficiency due to substantial drag. The creator concludes that small bellmouths are beneficial, attributing their effectiveness to smoothing airflow and reducing turbulence at the intake, rather than generating thrust through low-pressure surfaces.

Summarizing the Bellmouth Intake Efficiency Test

• 0:00 Introduction & Motivation: The video explores whether adding curved bellmouth intakes improves the efficiency of electric ducted fans (EDFs). This investigation was prompted by aerospace engineers' suggestions and the creator's previous contradictory findings from a Dyson-powered airplane project, where intake direction didn't affect thrust.
• 0:26 Test Setup: The creator used axial fans from a previous "blown wing" video. Two sizes of bellmouth intakes (large with 16mm radius, small with 7mm radius) were 3D printed and tested on a fan stand.
• 0:44 Static Thrust Results (100W):
  • The large bellmouth improved thrust by 14 grams, a 7.8% increase over bare fans.
  • The small bellmouth resulted in a 6.1% thrust increase.
• 0:55 Static Thrust Results (200W):
  • The small bellmouth proved to be the most efficient, showing a 6.6% improvement.
• 1:00 Dynamic Thrust Testing: Recognizing that static thrust isn't indicative of real-world flight, the creator used a blower fan to simulate airflow at 5 meters per second.
• 1:11 Dynamic Thrust Results (Pre-Drag Factor):
  • Small bellmouth: 7.6% better.
  • Large bellmouth: 9.8% better.
• 1:20 Drag Measurement: It was found that the large bellmouth created 24 grams of drag, while the small one created only 3 grams of drag.
• 1:26 Dynamic Thrust Results (With Drag Factor):
  • At 100W: Small bellmouth was 6.8% better; large bellmouth was 4.5% worse.
  • At 200W: Small bellmouth was 6.5% better; large bellmouth was only 1% better.
• 1:41 Conclusion & Takeaway: The small bellmouth intake would have significantly improved the efficiency of the "blown wing powered airplane's" EDFs by approximately 6.5%.
• 1:50 Theory Behind Improvement: The creator suggests that bellmouths improve efficiency by smoothing the airflow into the fan, preventing turbulence that occurs with sharp-edged intakes, rather than creating suction from fast-flowing air over a curved surface.