This video proposes that at low Reynolds numbers, stepped airfoils can be more efficient that smooth airfoils by reducing excess skin friction drag. A simple experiment is conducted using model free-flight gliders made from foam board to demonstrate that small model airplanes equipped with KFM-2 and KFM-3 airfoils have potential to fly significantly further than those equipped with smooth airfoils.
Glider Build Video:
https://www.youtube.com/watch?v=YzqS_NjTxps
Timecodes:
0:00 - Intro
0:42 - Reynolds Number Recap
2:01 - Parasite Drag Recap
3:03 - Low Reynolds Numbers Explained
3:41 - Introduction to Stepped Airfoils
5:07 - Experiment Setup
8:25 - Conducting the Experiment
9:26 - Experiment Results
10:07 - Next Steps
11:35 - Conclusion