Search Results

This paper presents trailer sway testing results of a 5th wheel RV toy-hauler being towed by a conventional “dually” pick-up. Tests were performed at various speeds, trailer gross weights, king pin weights, and tire pressures. Results validate the understanding that 5th wheel trailers, at 20% pin weight generally have substantially better sway damping than conventional trailers. Tests at 10% pin weight show trailer sway damping is substantially reduced, but still is well above minimum industry accepted standards. Much of the improved sway damping for 5th wheel trailers can be attributed to the forward hitch location and not just the higher hitch loads that are typically used.

Eight 3-wheel passenger vehicles of both one-front and one-rear wheel configurations were tested and compared to similar-sized 4-wheel vehicles. The tests produced measures of overturn resistance, oversteer/understeer, transient responses to control and external disturbance inputs, and braking performance and stability. A comparison was also made of a 4- to 3-wheel conversion, and the effects of various handling modifications were evaluated. The results indicate that a properly engineered 3-wheel car can be made as stable as a properly engineered 4-wheel car, although the single front wheel configuration may be less stable in limit maneuvers.

The results of a wind tunnel study and a computer simulation are used to determine the effects of aerodynamics on the lateral-directional stability and crosswind response of passenger car/utility trailer combinations. Single and tandem axle utility trailer configurations, with and without drag reducing add-on aerodynamic fairings, were considered with both sedan and station wagon tow cars. Results showed that including aerodynamic terms in the six degree of freedom model reduces the trailer tow angle stability and damping by a few percent. More importantly, the random crosswind response, expressed in terms of tow car yaw velocity, was amplified about 20 to 30 percent when a drag reducing device was added to the trailer.

A significant aspect of trailering safetyis the ability of a combination vehicle to stop with the same effectiveness as the tow vehicle alone. This paper describes the operation of electric and surge brake systems and presents analytical equations which can be used to predict stopping distances of these combinations as well as those trailers having no brakes. Comparisons are then made to full scale brake performance tests with seven different trailers. Problems are discussed and recommendations for a trailer-alone brake test procedure are given.

This paper summarizes a comprehensive research program of the ride qualities of long-haul trucks. Factors are identified which contribute significantly to differences in ride quality between various truck models and configurations over a range of actual operating conditions. Detailed measurements of six floor and seat accelerations and driver and passenger ride ratings were made on ten in-service trucks over five segments, ranging from “smooth” to “rough,” of a typical California freeway. The experimental methodology is reviewed and validated, and example data and preliminary comparisons between the objective and subjective measures are presented.

Full-scale vehicle response tests were conducted on five vehicles using a crosswind disturbance test facility capable of providing a 35 mph wind over a nominal 120 ft test length. The vehicles were a Honda Accord, Chevrolet station wagon, Ford Econoline van, VW Microbus, and Ford pickup/camper. Results showed that passenger cars, station wagons, and most vans have virtually no crosswind sensitivity problems, whereas the VW Microbus, the pickup/camper (in winds higher than 35 mph), and cars pulling trailers do have potential problems. Key vehicle parameters dictating this yaw response sensitivity are the distance between the aerodynamic and tire force centers, tire restoring moment (including understeer gradient), and the basic aerodynamic side forces. A simple analytical relationship in these terms was developed to predict steady-state yaw rate in steady winds.

This paper presents an analytically based approach to specifying a maximum allowable hitch load for passenger cars pulling trailers. The change in tow car steady-state directional stability, i.e., understeer, is the basis for the specification. This handling parameter is a function of hitch load, lateral acceleration, tow car to trailer weight ratio, and the amount of load leveling applied by a Class III hitch. Using these variables an allowable hitch load range was defined as that which would insure positive tow car understeer up to and including 0.3 g cornering. Over 50 combination-vehicle configurations (using three tow car sizes and eight trailers) were then tested in order to validate and revise the analytical boundaries. Based on these results a tow car stability criterion derived from maximum hitch load considerations appears a valid format for the trailer user and/or manufacturer.

This paper summarizes the development of an aerodynamic disturbance test facility that can be used to study the influence of crosswind disturbances on road vehicle handling. A literature review of ambient wind measurements and wind tunnel tests was combined with preliminary analysis to develop the requirements for a low cost, transportable, easy to operate, rugged, test facility. The final product consists of 8 independent crosswind modules, capable of providing a relatively constant 35 mph gust over 120 ft test length. Arranging the modules in an uneven fashion can provide a variable velocity profile over 230 ft test length. Each module consists of a controllable speed 58 hp gasoline engine driving an 8 ft diameter, 6 bladed propeller. Special ducting and adjustable exit vanes allow for flow redirection and expansion. Remote control of each module’s fan speed and engine ignition can be accomplished from individual remote operating stations.

This paper provides approximate factors, measurement techniques, and test procedures that can be used to determine trailer stability. The recommended performance metric is damping ratio, or an equivalent cycle to half amplitude which is evaluated, via a pulse-steer procedure, at some reference speed. A minimum damping ratio criteria of 0.15 at 55 mph is suggested and compared to the results of recent full scale tests. The approach is useful in selecting a minimum value of hitch load (for various weight tow cars) that will insure a minimum acceptable level of trailer stability at highway speeds.

This paper describes the results of a test program to evaluate various roadway disturbances present in the driving environment. The specific objectives were to pare down the list of possible roadway disturbances to the worst cases, identify handling problem areas, find meaningful response parameters and compare responses of different vehicles which might influence the results. The program provided an accident data analysis, survey questionnaire results and full scale test results which found the pavement/shoulder dropoff (requiring an edge climb maneuver) to be the most severe and most likely disturbance to result in lane exceedance. This occurs when the vehicle is scrubbing one set of tires on the shoulder edge (or encountering the edge at too shallow an angle for climb), thereby climb), thereby requiring the driver to apply a large steering deflection to get the car to climb back onto the pavement. In this case the vehicle will “spin out” if the speed is high enough.

In this paper, updated pilot/display/aircraft analysis techniques are applied to the problem of turbulence upset. In the course of an investigation of standard operating procedures and current autopilot turbulence modes, it was found that an improved turbulence penetration system is needed. A simulation was conducted to evaluate the turbulence autopilot and flight director concepts. It was found that an energy management system comprising the integrated autopilot and thrust director provided the greatest decrease in pilot work load and improvement in performance.