Date of Award
Master of Science
Ralph Kimberlin, Fred Stellar
This study investigates the use of Flow Diverting Devices to reduce passenger fatigue and parasite drag (specifically equivalent flat plate drag) for the 160*'* Special Operations Aviation Regiment MH-6 Helicopters. Due to cost, scheduling, and airworthiness release (AWR's) issues this manuscript focuses on the actual flight test data of a similar helicopter, the OH-58A+. The flight-testing investigated the level flight performance, and handling qualities with doors removed, with and without the Flow Diverters installed. Consideration was also given in the design to discover ways of minimizing the airflow on the external passengers (amount of deflection), changes in noise level, and to the reduction in the field of view measured from the Design Eye Position. The baseline aircraft (with doors removed) was tested against 3 different types of Flow Diverting Devices (6 inch Sawtooth, 6 inch Flat Plate with Vortex Generators installed, and 8 inch Flat Plate with Vortex Generators installed).
It was determined that the airflow can be deflected away from the passengers a maximum of 16 inches with no adverse impact on handling qualities. This is important for several reasons:
1. Possible increase in performance.
2. Passenger comfort.
3. Mission envelope expansion.
This mission envelope expansion would include the ability to fly in colder temperatures, feasible to fly in precipitation, as well as possibly having the ability to maintain faster enroute speeds without causing undue fatigue on the passengers. This deflection was achieved with an average increase of 4.0 square feet of equivalent flat plate drag. This is much less than the effect flat plate drag on the MH-6 due to passengers and equipment installed for the mission. Additionally, during the flight testing it was noted that there were no detectable changes to the handling qualities or the noise level inside the test aircraft.
Hence, the author concluded that the 8 inch Flat Plate, with Vortex Generators, Flow Diverting Device will successfully divert the airflow around the upper body of the external passengers thus reducing passenger fatigue and increasing their safety during flight. It is reasonable to assume that the MH-6 helicopter will realize a performance enhancement during flight in high drag configurations (with external passengers). Additionally, it is also possible that the MH-6 in the baseline configuration (doors off, external passenger system installed) could realize a slight performance increase.
The author made the following recommendations;
1. Develop a set of flow diverters specifically for the MH-6.
a. 8" Flat Plate with Vortex Generators.
b. The angle should be between 40° and 50°.
c. The Flow Diverter should be capable of 2 positions, full open (maximum deflection) and fully closed (no Deflection). However, if there is a performance increase with the flow diverters installed over the baseline MH-6 there would be little reason to use the fully closed position.
2. Conduct Flight Tests with an MH-6 in its typical mission configuration.
a. These tests should include flights with and without external ballast.
b. At least two of the flight tests should be with an FTE as an external passenger. For a qualitative comparison evaluation one flight test should be with no deflection and the other with maximum deflection.
3. Recommend that all doors are removed at all times with Flow Diverters installed.
4. Recommend the use of the Smoke Generator System with a greater volume of smoke. This can be done by either a specialized smoke canister or with a portable smoke generator.
McDougall, Kelly E., "Flight testing Flow Diverting Devices on an OH-58A+ for applications to an MH-6 Helicopter. " Master's Thesis, University of Tennessee, 2000.