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Dreher, R. C.

Publications and source records attributed to Dreher, R. C..

16 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Experimental investigation of active loads control for aircraft landing gear

Aircraft dynamic loads and vibrations resulting from landing impact and from runway and taxiway unevenness are recognized as significant in causing fatigue damage, dynamic stress on the airframe, crew and passenger discomfort, and reduction of the pilot's ability to control the aircraft during ground operations. One potential method for improving operational characteistics of aircraft on the ground is the application of active control technology to the landing gears to reduce ground loads applied to the airframe. An experimental investigation was conducted which simulated the landing dynamics of a light airplane to determine the feasibility and potential of a series hydraulic active control main landing gear. The experiments involved a passive gear and an active control gear. Results of this investigation show that a series hydraulically controlled gear is feasible and that such a gear is very effective in reducing the loads transmitted by the gear to the airframe during ground operations.

Mcgehee, J. R.↗
NASA NTRS1982

Dynamics of aircraft antiskid braking systems

A computer study was performed to assess the accuracy of three brake pressure-torque mathematical models. The investigation utilized one main gear wheel, brake, and tire assembly of a McDonnell Douglas DC-9 series 10 airplane. The investigation indicates that the performance of aircraft antiskid braking systems is strongly influenced by tire characteristics, dynamic response of the antiskid control valve, and pressure-torque response of the brake. The computer study employed an average torque error criterion to assess the accuracy of the models. The results indicate that a variable nonlinear spring with hysteresis memory function models the pressure-torque response of the brake more accurately than currently used models.

Tanner, J. A.↗
NASA NTRS1981

Studies of some unconventional systems for solving various landing problems

Solutions to various landing problems were obtained through unconventional systems. The first, of these is the air cushion landing system, where efforts were concentrated on development of adequate braking and steering systems and an improved understanding of scaling laws and behavior. The second was concentrated on use of a wire brush skid as a drag producing device, which was shown to have good friction coefficients and reasonable wear rates at ground bearing pressures up to 689 kPa and forward speeds up to 80 km/hr. The third showed great promise in an active control landing gear where significant load reductions were possible during landing impact and subsequent rollout.

Leland, T. J.↗
NASA NTRS1980

Tire stiffness and damping determined from static and free-vibration tests

Stiffness and damping of a nonrolling tire were determined experimentally from both static force-displacement relations and the free-vibration behavior of a cable-suspended platen pressed against the tire periphery. Lateral and force-and-aft spring constants and damping factors of a 49 x 17 size aircraft tire for different tire pressure and vertical loads were measured assuming a rate-independent damping form. In addition, a technique was applied for estimating the magnitude of the tire mass which participates in the vibratory motion of the dynamic tests. Results show that both the lateral and force-and-aft spring constants generally increase with tire pressure but only the latter increased significantly with vertical tire loading. The fore-and-aft spring constants were greater than those in the lateral direction. The static-spring-constant variations were similar to the dynamic variations but exhibited lower magnitudes. Damping was small and insensitive to tire loading. Furthermore, static damping accounted for a significant portion of that found dynamically. Effective tire masses were also small.

Sleeper, R. K.↗
NASA NTRS1979

Friction and wear characteristics of wire-brush skids

The testing technique consisted of towing the skids with a ground test vehicle over asphalt and concrete surfaces at ground speeds up to 80 km/hr (50 mph) and bearing pressures up to 689 kPa (100 psi) over sliding distances up to 1585 m (5200 ft). Results indicate that the friction coefficient developed by wire brush skids is essentially independent of ground speed, is slightly increased with increasing bearing pressure, is noticeably affected by surface texture, and is not degraded by surface wetness. Skid wear is shown to increase with increasing bearing pressure and with increasing ground speed and is dependent on the nature of the surface. Runway surface damage caused by the skids was in the form of an abrasive scrubbing action rather than physical damage.

Dreher, R. C.↗
NASA NTRS1977

Studies of friction and wear characteristics of various wires for wire-brush skids

The friction and wear characteristics of 22 types and sizes of wires for potential use in wire-brush skids were studied. These characteristics were determined by placing brushes made from candidate wires on a belt sander whose moving belt simulated landing roll-out distance. At the same time, the drag force and wear behavior were monitored. Data were obtained over distances up to 3048 m (10,000 ft) at preselected bearing pressures of 172 to 1034 kPa (25 to 150 psi). In general, the friction coefficient developed by the candidate wires was found to be independent of bearing pressure and ranged between 0.4 and 0.6 under the test conditions of this investigation. The friction coefficient was not degraded when the surface was wetted and appears to be independent of wire diameter except perhaps when wire size is relatively large compared with the surface asperities. Generally, the high friction demonstrated by the soft materials was accompanied by high wear rates; conversely, the hard materials provided greater wear resistance but offered lower friction. For all test wires, the wear was shown to increase with increasing bearing pressure, in general, for the same bearing pressure, wear increased with increasing wire diameter and decreased when the surface was wetted.

Dreher, R. C.↗
NASA NTRS1976

Friction characteristics of 20 x 4.4, type 7, aircraft tires constructed with different tread rubber compounds

A test program was conducted at the Langley aircraft landing loads and traction facility to evaluate the friction characteristics of 20 x 4.4, type, aircraft tires constructed with experimental cut-resistant, tread rubber compounds. These compounds consisted of different blends of natural rubber (NR) and an alfin catalyzed styrene-butadiene copolymer rubber (SBR). One tire having a blend of 30 SBR and 70 NR and another having a blend of 60 SBR and 40 NR in the tread were tested together with a standard production tire with no SBR content in the tread rubber. The results of this investigation indicated that the test tires constructed with the special cut-resistant tread rubber compositions did not suffer any significant degradation in tire friction capability when compared with the standard tire. In general, tire friction capability decreased with increasing speed and surface wetness condition. As yaw angle increased, tire braking capability decreased while tire cornering capability increased. Tread-wear data based on number of brake cycles, however, suggested that the tires with alfin SBR blends experienced significantly greater wear than the standard production tire.

Dreher, R. C.↗
NASA NTRS1976

Traction Characteristics of a 30 by 11.5-14.5, Type 8, Aircraft Tire on Dry, Wet and Flooded Surfaces

A limited test program was conducted to extend and supplement the braking and cornering data on a 30 x 11.5-14.5, type VIII, aircraft tire to refine the tire/runway friction model for use in the development of an aircraft ground performance simulation. Tire traction data were obtained on dry, wet and flooded runway surfaces at ground speeds ranging from 5 to 100 knots and at yaw angles extending up to 12 deg. These friction coefficients are presented as a function of slip characteristics, namely, the maximum and skidding drag coefficients and the maximum cornering coefficients are presented as a function of both ground speed and yaw angle to extend existing data on that tire size. Tire braking and cornering capabilities were shown to be affected by vehicle ground speed, wheel yaw attitude and the extent of surface wetness.

Yager, T. J.↗
NASA NTRS1974

Experimental investigation of the cornering characteristics of 18 by 5.5, type 7, aircraft tires with different tread patterns

The characteristics, which include the cornering-force and drag-force friction coefficients and self-alining torque, were obtained on dry, damp, and flooded runway surfaces over a range of yaw angles from 0 deg to 12 deg and at ground speeds from approximately 5 to 90 knots. The results indicate that a tread pattern with pinholes in the ribs reduces the tire cornering capability at high yaw angles on a damp surface but improves cornering on a dry surface. A tread pattern which has transverse grooves across the entire width of the tread improves the tire cornering performance slightly at high speeds on the flooded runway surface. The cornering capability of all the tires is degraded at high ground speeds by thin film lubrication and/or tire hydroplaning effects. Alterations to the conventional tread pattern provide only marginal improvements in the tire cornering capability which suggests that runway surface treatments may be a more effective way of improving aircraft ground performance during wet operations.

Dreher, R. C.↗
NASA NTRS1974

Experimental investigation of the braking and cornering characteristics of 30 x 11.5-14.5, type 8, aircraft tires with different tread patterns

An investigation was conducted at the aircraft landing loads and traction facility to study the braking and cornering characteristics, including the drag-force and cornering-force friction coefficients, of 30 by 11.5-14.5, type VIII aircraft tires with five different tread patterns. Test data were obtained on dry, damp, and flooded runway surfaces over a range of yaw angles from 0 deg to 12 deg at ground speeds from 5 knots to 100 knots. The results of this investigation indicate that a tread pattern consisting of transverse cuts across the entire width of the tread slightly improved the tire traction performance on wet surfaces. The braking and cornering capability of the tires was degraded by thin-film lubrication and tire hydroplaning effects on the wet runway surfaces. The braking capability of the tires decreased when the yaw angle was increased.

Dreher, R. C.↗
NASA NTRS1973

Accelerometer-controlled automatic braking system

Braking system, which employs angular accelerometer to control wheel braking and results in low level of tire slip, has been developed and tested. Tests indicate that system is feasible for operations on surfaces of different slipperinesses. System restricts tire slip and is capable of adapting to rapidly-changing surface conditions.

Dreher, R. C.↗
NASA NTRS1973

Cornering characteristics of a 40 by 14-16 type 7 aircraft tire and a comparison with characteristics of a C40 by 14-21 cantilever aircraft tire

An investigation was conducted at the Langley aircraft landing loads and traction facility to determine the cornering characteristics of a 40 x 14-16 type VII aircraft tire. These characteristics, which include the cornering-force and drag-force friction coefficients and self-alining torque, were obtained for the tire operating on dry, damp and flooded runway surfaces over a range of yaw angles from 0 deg to 20 deg and at ground speeds from 5 to 100 knots, both with and without braking. The results of this investigation indicated that the cornering capability of the 40 x 14-16 type VII aircraft tire is degraded by high ground speeds, thin-film lubrication and tire hydroplaning effects on the wet surfaces, and brake torque. The cornering capability is greatly diminished when locked-wheel skids are encountered.

Tanner, J. A.↗
NASA NTRS1973

Experimental investigation of the cornering of a C40 x 14-21 cantilever aircraft tire

An experimental investigation was conducted at the Langley aircraft landing loads and traction facility to define the cornering characteristics of a size C40 x14-21 aircraft tire of cantilever design. These characteristics, which include the cornering-force and drag-force friction coefficients and self-alining torque, were obtained for the tire operating on dry, damp, and flooded runway surfaces over a range of yaw angles from 0 deg to 20 deg and at ground speeds of 5 to 100 knots, both with and without braking. The results of this investigation show that the cornering-force and drag-force friction coefficients and self-alining torque were influenced by the yaw angle, ground speed, brake torque, surface wetness, and the locked-wheel condition.

Dreher, R. C.↗
NASA NTRS1972

Experimental investigation of an accelerometer controlled automatic braking system

An investigation was made to determine the feasibility of an automatic braking system for arresting the motion of an airplane by sensing and controlling braked wheel decelerations. The system was tested on a rotating drum dynamometer by using an automotive tire, wheel, and disk-brake assembly under conditions which included two tire loadings, wet and dry surfaces, and a range of ground speeds up to 70 knots. The controlling parameters were the rates at which brake pressure was applied and released and the Command Deceleration Level which governed the wheel deceleration by controlling the brake operation. Limited tests were also made with the automatic braking system installed on a ground vehicle in an effort to provide a more realistic proof of its feasibility. The results of this investigation indicate that a braking system which utilizes wheel decelerations as the control variable to restrict tire slip is feasible and capable of adapting to rapidly changing surface conditions.

Dreher, R. C.↗
NASA NTRS1963

Phenomena of Pneumatic Tire Hydroplaning

Recent research on pneumatic tire hydroplaning has been collected and summarized with the aim of describing what is presently known about the phenomena of tire hydroplaning. A physical description of tire hydroplaning is given along with formulae for estimating the ground speed at which it occurs. Eight manifestations of tire hydroplaning which have been experimentally observed are presented and discussed. These manifestations are: detachment of tire footprint, hydrodynamic ground pressure, spin-down of wheel, suppression of tire bow wave, scouring action of escaping fluid in tire-ground footprint region, peaking of fluid displacement drag, loss in braking traction, and loss of tire directional stability. The vehicle, pavement, tire, and fluid parameters of importance to tire hydroplaning are listed and described. Finally, the hazards of tire hydroplaning to ground and air-vehicle-ground performance are listed, and procedures are given to minimize these effects.

HYDROPLANE↗