On February 14, 2018 about 1336 eastern standard time (EST), a Robinson Helicopters Inc., R22 Beta, N337H, landed hard in dense vegetation and the tailboom separated from the fuselage. The accident occurred about 5 miles southeast of Charleston Air Force/International Airport, South Carolina. The helicopter was registered to Spitzer Helicopter and was being operated by Holy City Helicopters as a visual flight rules (VFR), local instructional flight, under the provisions of Title 14 Code of Federal Regulations Part 91. The flight instructor and student were not injured. Visual meteorological conditions prevailed for the flight, and flight following was not in effect. The flight instructor reported that he had conducted training in the area previously and was familiar with the terrain and obstacles. The flight lesson was conducted to practice hovering, followed by a transition to forward flight. The instructor reported that the wind was from the west/northwest about 10 knots, and that the direction of takeoff was into the wind. According to the instructor, during the accident pattern the student had the flight controls and had transitioned the helicopter from a hover through effective translational lift and established forward flight. The student then initiated a right turn over dense vegetation when a small unmanned aerial system (UAS), which he described as a white quadcopter, appeared about 10ft in front of the helicopter at "eye level". The instructor took the flight controls and made a hard right and aft cyclic input to avoid the UAS. The evasive maneuver put the helicopter into a right quartering tailwind. After the evasive maneuver, the helicopter had some forward airspeed, "but not much". He was able to level the helicopter's attitude, but the helicopter began to descend quickly. The helicopter was about 40ft AGL and the instructor described the helicopter's descent as settling with power. The helicopter descended, and the tail rotor entered the trees and the helicopter developed a spin to the right. The instructor rolled the throttle off to alleviate the spin, and then tried to cushion the landing by increasing collective. The helicopter impacted the ground, continued spinning to the right, and subsequently rolled over onto its right-side. The helicopter sustained substantial damage to the tail rotor drive shaft. The student pilot reported that they were operating over an access road and that she had initiated a right turn, "when a small white drone came into our field of vision". The instructor immediately took the flight controls and increased the bank angle of the right turn to avoid the UAS. As the helicopter "swung around" to miss the UAS, the tail rotor stuck the tree tops, and they lost tail rotor authority. The instructor entered an autorotation, and the helicopter collided with trees. The helicopter descended in a spin, impacted terrain and rolled on to its right side. The day following the accident, Federal Aviation Administration, Aviation Safety Inspector's canvassed the vicinity of the accident, to include a housing development about ¼ mile from the accident site. The housing development was under construction and one member of the construction team remembered seeing the helicopter operating in the area about the time of the accident. There were several construction crews working during the time of the accident, and none of them recalled seeing a "drone". The flight instructor reported that there were no mechanical malfunctions or failures with the helicopter that would have precluded normal operation prior to the tail rotor strike. A canvas of the area by the FAA did not find any information about the Unmanned Aerial System or witnesses.