1. Knight, H., and Hefner, R. A. "Analysis of Ground Effect on the Lifting Airscrew," Tech. Rep. 835, NACA TN, 1941.
2. Cheeseman, I. C., and Bennett, W. E, "The Effect of the Ground on a Helicopter Rotor in Forward Flight," Tech. Rep. 3021, British ARC & RM, 1955.
3. Zbrozek, J, "Ground Effect on the Lifting Rotor," Tech. Rep. 2347, British ARC & RM, 1947.
4. The Helicopter and the Ground Effect Machine