The unique ability of a helicopter to slow down and hover out-of-ground-effect makes it an ideal platform for taking pictures or video. To safely perform these types of flights requires a complete understanding of the issues involved with maneuvering a helicopter at slow speeds. One of these areas is understanding the limitations of different helicopter’s tail rotors.
Older model Bell 206B Jetrangers have a smaller tail rotor with a symmetrical designed airfoil that makes it more susceptible to what’s referred to as Loss of Tail Rotor Effectiveness (LTE). According to FAA Advisory Circular AC90-95, any maneuver which requires the pilot to operate in a high-power, low-airspeed environment with a left crosswind or tailwind creates an environment where LTE or an unanticipated right yaw may occur. It also advises of greater susceptibility for LTE in right turns and states the phenomena may occur in varying degrees in all single main-rotor helicopters at airspeeds less than 30 KIAS.
Another light helicopter that is very popular for photo flights is the Robinson R44. Frank Robinson is a tail rotor expert and designed the R44’s tail rotor to be highly efficient using an asymmetrical airfoil. The R44’s tail rotor is strong and although a lot less likely to encounter LTE pilots still need to exercise caution especially at high gross weights and high density altitudes.
Robinson Helicopter issued the following Safety Notice (SN-34) in March 1999, titled “Photo Flights – Very High Risk.” It describes the problems encountered when the pilot slows the helicopter below 30 KIAS and then attempts to maneuver the helicopter.
“The helicopter can rapidly lose transitional lift and begin to settle,” it states. “An inexperienced pilot may raise the collective to stop the descent. This can reduce rpm, thereby reducing power available and causing an even greater descent rate and further loss of rpm. Because tail rotor thrust is proportional to the square of rpm, if the rpm drops below 80 percent nearly half of the tail rotor thrust is lost and the helicopter will rotate nose over. Suddenly, the decreasing rpm also causes the main rotor to stall and the helicopter falls rapidly while continuing to rotate.” The safety notice recommends photo flights only be conducted by well-trained, experienced pilots.