Engineering topics

Holbrook, G. T.

Publications and source records attributed to Holbrook, G. T..

8 records

NASA NTRS1985

Vortex wake alleviation studies with a variable twist wing

Vortex wake alleviation studies were conducted in a wind tunnel and a water towing tank using a multisegmented wing model which provided controlled and measured variations in span load. Fourteen model configurations are tested at a Reynolds number of one million and a lift coefficient of 0.6 in the Langley 4- by 7-Meter Tunnel and the Hydronautics Ship Model Basin water tank at Hydronautics, Inc., Laurel, Md. Detailed measurements of span load and wake velocities at one semispan downstream correlate well with each other, with inviscid predictions of span load and wake roll up, and with peak trailing-wing rolling moments measured in the far wake. Average trailing-wing rolling moments are found to be an unreliable indicator of vortex wake intensity because vortex meander does not scale between test facilities and free-air conditions. A tapered-span-load configuration, which exhibits little or no drag penalty, is shown to offer significant downstream wake alleviation to a small trailing wing. The greater downstream wake alleviation achieved with the addition of spoilers to a flapped-wing configuration is shown to result directly from the high incremental drag and turbulence associated with the spoilers and not from the span load alteration they cause.

Holbrook, G. T.↗

NASA NTRS1985

Detailed pressure distribution measurements obtained on several configurations of an aspect-ratio-7 variable twist wing

Detailed pressure distribution measurements were made for 11 twist configurations of a unique, multisegmented wing model having an aspect ratio of 7 and a taper ratio of 1. These configurations encompassed span loads ranging from that of an untwisted wing to simple flapped wings both with and without upper-surface spoilers attached. For each of the wing twist configurations, electronic scanning pressure transducers were used to obtain 580 surface pressure measurements over the wing in about 0.1 sec. Integrated pressure distribution measurements compared favorably with force-balance measurements of lift on the model when the model centerbody lift was included. Complete plots and tabulations of the pressure distribution data for each wing twist configuration are provided.

Holbrook, G. T.↗

NASA NTRS1985

Vortex research facility improvements and preliminary density stratification effects on vortex wakes

Recent modernization of NASA's Vortex Research Facility is described. The facility has a 300-ft test section, scheduled for a 300-ft extension, with constant test speeds of the model up to 100 ft/sec. The data acquisition hardware and software improvements included the installation of a 24-channel PCM system onboard the research vehicle, and a large dedicated 16-bit minicomputer. Flow visualization of the vortex wake in the test section is by particle seeding, and a thin sheet of argon laser light perpendicular to the line of flight; detailed flow field measurements are made with a laser velocimeter optics system. The improved experimental capabilities of the facility were used in a study of atmospheric stratification effects on wake vortex decay, showing that the effects of temperature gradient must be taken into account to avoid misleading conclusions in wake vortex research.

Satran, D. R.↗

NASA NTRS1981

Basic research in wake vortex alleviation using a variable twist wing

The variable twist wing concept was used to investigate the relative effects of lift and turbulence distribution on the rolled up vortex wake. Several methods of reducing the vortex strength behind an aircraft were identified. These involve the redistribution of lift spanwise on the wing and drag distribution along the wing. Initial attempts to use the variable twist wing velocity data to validate the WAKE computer code have shown a strong correlation, although the vorticity levels were not exactly matched.

Morris, D. J.↗

NASA NTRS1980

Preliminary results of simulated vortex encounters by a twin-engine, commercial aircraft during final landing approach

Piloted simulations of encounters with vortices of various ages and degrees of attenuation were performed with the Visual Motion Simulator. In the simulations, a twin engine, commercial transport on final approach, encountered the modeled vortices of a four engine, wide body, commercial transport. The data show the effect of vortex age and attenuation on the severity of the initial upset, as well as the effect of the vortex encounters on the landing capability.

Hastings, E. C., Jr.↗

NASA NTRS1979

Low-speed wind-tunnel investigation of wing fins as trailing-vortex-alleviation devices on a transport airplane model

The trailing-vortex-alleviation effectiveness of both a one- and a two-fin configuration (semicircular with a radius of 0.043 semispan) on a jumbo-jet transport airplane model in its landing configuration was investigated in the Langley V/STOL tunnel, by the trailing-wing sensor technique. The fins were located on the upper surface of the transport model wing along the 30-percent-chord line. The fin configurations were effective in reducing the vortex-induced rolling moment, by amounts varying from 28 to 60 percent, on the trailing wing model located at a distance of 7.8 transport model wing spans downstream of the transport model. The flow over the fins and over the transport airplane model wing downstream of the fins was observed to be separated and turbulent. All fin configurations caused a reduction in maximum lift coefficient, a positive increment in drag coefficient, and an increment in nose-up pitching-moment coefficient on the transport airplane model.

Croom, D. R.↗

NASA NTRS1976

Flight investigation of the response of a helicopter to the trailing vortex of a fixed-wing aircraft

A flight investigation was conducted to quantitatively determine the response of a medium-weight helicopter to the trailing-vortex system of a fixed-wing aircraft. Flight tests and analytical tools were both utilized in the investigation. The flight tests involved an extensively instrumented UH-1H helicopter and a C-54 aircraft. Penetrations of the vortex system by the UH-1H were made at the following nominal conditions: the C-54 flew at 5500 feet altitude at a nominal gross weight of 58,000 pounds and an indicated airspeed of 115 knots in a cruise configuration. The UH-1H, nominally 7200 pounds gross weight, flew at 60 knots indicated airspeed during the penetrations at separation distances of 6.64 nautical miles to 0.42 nautical mile between aircraft. In general, the data analyzed for the above tests indicated that no unsafe penetration occurred. Further, penetrating vehicle attitude changes and structural loads were nominal. In addition, the response of the helicopter did not change appreciably with decreased separation distance.

Mantay, W. R.↗

NASA NTRS1976

Flight-test experience of a helicopter encountering an airplane trailing vortex

This paper presents results of a flight-test experiment of a UH-1H helicopter encountering the vortex wake of a C-54 airplane. The helicopter was instrumented to record the pilot control inputs, determine the upset experience, and measure critical loads within the rotor system. During the flight-test program 132 penetrations of the vortex wake were made by the helicopter at separation distances from 3/8 to 6-1/2 nautical miles. Test results indicated that the helicopter upsets and the vortex induced blade loads experienced were minimal and well within safe limits. The upsets were very mild when compared to a typical response of a small airplane to the vortex wake of the C-54 airplane.

Dunham, R. E., Jr.↗