if the C-130 was flying at its slowest speed. However, Dunn was undeterred and convinced Captain Don Eastman, an Air Force H-3 test pilot and Major Bob Nabors, an Air Force C-130 test pilot, to do some formation flying with the H-3 in a trailing position to evaluate the feasibil- ity of helicopter aerial refueling. Eastman began by flying the H-3 behind the C-130 cargo ramp but quickly found out that be- cause of the airplane’s tip vortices, the ar- eas just aft of the vertical stabilizer and cargo ramp had a very strong downwash. Once in position in these areas, Eastman had a hard time controlling the H-3 and would enter a very quick descent. Some- times the descent would reach 2000 feet per minute with very little control author- ity. After attempting this several times with the same results, Eastman decided to take a break. In order to collect his thoughts he moved the H-3 from directly aft of the C-130 to flying formation off of the left wing tip. Once in position on the wing tip, Eastman noticed that there was a significant power reduction for the H-3. For some reason it took roughly forty to fifty percent less power to maintain posi- tion when flying off of the wing than it did when flying directly behind the C-130. It was this discovery that made helicopter aerial refueling possible. Originally it was thought that the power reduction was a re- sult of a decrease in dynamic pressure, much like race cars use when drafting off of each other. However, Eastman later proved in a graduate school thesis that this power reduction was a result of the vortex effect from the C-130’s flaps reducing the helicopter’s induced power requirement. The upwash from the flaps increased the helicopter’s effective angle of attack, re- ducing the induced drag and requiring less power to maintain the speed needed to keep up with the C-130. Armed with these new findings, Dunn went to the Pen- tagon and received money to modify a helicopter for a full scale aerial refueling test and the assistance of the Marine Corps refueling C-130s at MCAS Cherry Point. In order to accomplish this testing, Siko- rsky Aircraft mounted a dummy refueling probe to a CH-3C. At the direction of the Wright Patterson commander of flight testing and in preparation for further heli-
32 March 2013
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