Engineering topics

Yenni, Kenneth R.

Publications and source records attributed to Yenni, Kenneth R..

5 records

NASA NTRS1994

Further Research On Helicopter Tail-Boom Strakes

Two documents discuss results of additional investigations of concept introduced in "Helicopter Tail-Boom Strakes" (LAR-13233). Essence of concept that strake or pair of strakes on side of tail boom facing retreating side of main rotor of helicopter perturbs flow in such way to increase aerodynamic pressure on that side, contributing force to thrust from tail rotor. Because of force, thrust required of tail rotor for yaw control reduced. Important advantage in low-speed flight, especially in sideward flight, in which tail-rotor thrust in absence of strake sometimes insufficient.

Kelley, Henry L.↗

NASA NTRS1993

Flight investigation of the effect of tail boom strakes on helicopter directional control

A joint U.S. Army/NASA flight investigation was conducted utilizing a single-rotor helicopter to determine the effectiveness of horizontally mounted tail boom strakes on directional controllability and tail rotor power during low-speed, crosswind operating conditions. Three configurations were investigated: (1) baseline (strakes off), (2) single strake (strake at upper shoulder on port side of boom), and (3) double strake (upper strake plus a lower strake on same side of boom). The strakes were employed as a means to separate airflow over the tail boom and change fuselage yawing moments in a direction to improve the yaw control margin and reduce tail rotor power. Crosswind data were obtained in 5-knot increments of airspeed from 0 to 35 knots and in 30 deg increments of wind azimuth from 0 deg to 330 deg. At the most critical wind azimuth and airspeed in terms of tail rotor power, the strakes improved the pedal margin by 6 percent of total travel and reduced tail rotor power required by 17 percent. The increase in yaw control and reduction in tail rotor power offered by the strakes can expand the helicopter operating envelope in terms of gross weight and altitude capability. The strakes did not affect the flying qualities of the vehicle at airspeeds between 35 and 100 knots.

Kelly, Henry L.↗

NASA NTRS1990

Flight tests of a helmet-mounted display synthetic visibility system

A short flight test program was conducted using the NASA Langley Research Center's B737 Advanced Transport Operating Systems (ATOPS) research airplane to determine if pilots could land a transport category airplane under visual meteorological conditions (VMC) by reference to a synthetic visibility system. No external guidance was to be used. The program was undertaken jointly by NASA and the McDonnel-Douglas Corporation. The airplane was fitted with forward-looking television cameras fixed in the nose. Inputs from the television cameras were mixed with internally generated symbology and displayed to the pilot on helmet-mounted eyepieces. The pilot task was to execute a visual approach and landing. Two NASA and two McDonnel-Douglas engineering test pilots participated in the program completing over 200 landings in a 32-hour test program. Landings accomplished with the helmet-mounted display (HMD) were compared with visual landings for each pilot.

Yenni, Kenneth R.↗

NASA NTRS1990

Flight investigation of the effect of tail boom strakes on helicopter directional control

A joint U.S. Army/NASA flight investigation was conducted utilizing an instrumented Bell 240B single-rotor helicopter to determine the effectiveness of horizontally-mounted tail boom strakes on directional controllability and tail rotor power required during low-speed, crosswind operating conditions. The purpose of the strakes was to separate airflow over the tail boom and change fuselage yawing moments in a direction to improve the yaw control margin and reduce tail rotor power required. Low-speed crosswind data were obtained in 5-knot increments at airspeeds of 0 knots to 35 knots and for 30 deg increments in wind azimuth from 0 to 330 deg. In right sideward flight at the most critical wind azimuth and airspeed (60 deg azimuth measured from the nose of the aircraft and 20 knots airspeed), the strakes improved the pedal margin by about 6 percent of total travel and reduced the tail rotor power required by 17 percent. The increase in yaw control and reduction in tail rotor power offered by the strakes can expand the operating envelope in terms of gross weight and altitude capability. No effects in forward flight were noted.

Kelley, Henry L.↗

NASA NTRS1988

Development in helicopter tail boom strake applications in the US

The use of a strake or spoiler on a helicopter tail boom to beneficially change helicopter tail boom air loads was suggested in the United States in 1975. The anticipated benefits were a change of tail boom loads to reduce required tail rotor thrust and power and improve directional control. High tail boom air loads experienced by the YAH-64 and described in 1978 led to a wind tunnel investigation of the usefullness of strakes in altering such loads on the AH-64, UH-60, and UH-1 helicopters. The wind tunnel tests of 2-D cross sections of the tail boom of each demonstrated that a strake or strakes would be effective. Several limited test programs with the U.S. Army's OH-58A, AH-64, and UH-60A were conducted which showed the effects of strakes were modest for those helicopters. The most recent flight test program, with a Bell 204B, disclosed that for the 204B the tail boom strake or strakes would provide more than a modest improvement in directional control and reduction in tail rotor power.

Wilson, John C.↗