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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.

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.

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 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.