Tests Evaluate Engine Size in Terms Of Roadability, Travel Time, Cost

Tests Evaluate Engine Size in Terms Of Roadability, Travel Time, Cost

In specifying fire apparatus road performance to meet the needs of a community, the following questions are important:

1. Under what conditions does the road performance level of the apparatus significantly affect the alarm response travel times achieved?
2. What road performance levels are adequate for road conditions in a community? What are the cost implications?
3. When does the pump performance rather than road performance determine the required engine power level?
4. How does one determine road performance requirements, particularly if there are no major hills or grades in a community?
5. How does one measure road performance to assure compliance with requirements?

Road tests made

To gain insight into these questions, a series of road tests was conducted with the aid of the Los Angeles County Fire Department. Three pumpers were tested for top speed, acceleration, gradability (i.e., maximum speed up a specified grade), and alarm response travel time over a variety of road conditions. Computer techniques were also used to extrapolate these results over a broader range of apparatus characteristics and route conditions. This work showed that road performance can significantly affect response travel times and also the cost of the apparatus through the size of the engine and chassis selected. Moreover, the minimum road performance requirements suggested in NFPA Standard 1901 (i.e., 0 to 35 mph in 25 seconds, etc.) may result in unnecessarily long travel times. Kach community should establish road performance levels based on its own road conditions, alarm response objectives and budget constraints.

This work was accomplished as part of a project aimed at developing a “(Juide for the Preparation of Fire Pumper Apparatus Specifications.” The purpose of this guide is to help fire officials justify pumper purchases by establishing cost-effective performance levels and other requirements properly matched to local fire hazards, road conditions, and community fire protection objectives. The guide also seeks to help communicate these requirements to manufacturers in a comprehensive, clear, and technically accurate specification. Although this article focuses on the road performance aspects of the problem, all major characteristics of the apparatus are addressed in the guide.

The project has been in progress since 1974. It was initially sponsored by the National Science Foundation under the Research Applied to National Needs Program but in 1977 was transferred to the then National Fire Prevention and Control Administration—now the United States Fire Administration (USF’A). The project team consists of engineers at Mission Research Corporation in Santa Barbara, Calif., working with a 25-member national advisory committee composed of fire chiefs from departments across the nation, ranging in size from large metropolitan to small rural. The team also includes representatives from equipment manufacturers, Insurance Services Office, National Fire Protection Association, and various state and federal government agencies, including the USFA and the Center for Fire Research at the National Bureau of Standards.

Road test equipment

The road test data recording equipment used included a special bicycle-like fifth wheel attached to the rear of the pumper during each test run. For each foot traveled on the ground, this wheel generated an electrical signal which was transmitted by wire to an audio tape recorder carried on the hose bed. Listening to this audio tape, one can hear a series of sound pulses that increases in frequency as the speed of the apparatus increases.

When a series of road tests was completed, the audio tapes were taken back to the fire station and played into a strip-chart-recorder. This recorder converted the audio signals directly into graphs giving the variation in the speed of the apparatus with time since the beginning of a test.

ENGINE 10

ENGINE 127

ENGINE 523

As used here, a slowdown results from major street intersections (with traffic lights), railroad crossings, corners, and other situations likely to require reductions in speed greater than 10 mph.

Other data collection equipment used included stopwatches and a drive-on scale to weigh each apparatus.

The characteristics of the fire engines tested are listed in table 1. They represent a number of different technologies with a range of performance capabilities. Engine 10 is a 1975, dieselpowered, automatic transmission pumper. Engine 127 is a 1958, gasoline-powered pumper with a manual five-speed transmission. Engine 523 is a 1965, gasoline-powered, five-speed manual transmission pumper.

Table 1 gives the average horsepower delivered to the drive wheels of each apparatus divided by its total fully loaded weight in thousands of pounds. As illustrated in what follows, rating a fire engine by the “average drive wheel horsepower per 1000 lbs” allows one to compare the effect of alternative power levels on the vehicle’s top speed, acceleration, gradability and, consequently, travel time performance. Drive wheel horsepower is the power available at the wheels which is effective in moving the vehicle. It is the engine horsepower less losses due to inefficiencies in the drive train.

Three separate response routes were selected, reflecting a range of typical conditions. These routes, in Los Angeles County, have the characteristics summarized under “Road Conditions” in table 2.

The same driver was used for all tests. This driver was considered a good average engineer by the fire chief. He was familiar with each route as well as the apparatus tested.

Road test procedure

The characteristics of each apparatus were recorded, including its manufacturer, age, weight (fully loaded, including a four-man crew and test equipment), frontal area, wheel base, track width, tire size, engine, transmission and rear axle characteristics.

The fifth wheel equipment was then attached and the speedometer on board the apparatus was checked for accuracy. This involved driving the apparatus at constant speed along a measured onemile segment of flat paved road and measuring the actual time taken. Any errors in the speedometer were thus established.

Next, the top speed of the apparatus was measured. This involved driving the apparatus on a flat paved road at its peak governed rpm in high gear and recording both fifth wheel and corrected speedometer data.

A test to establish the hill-climbing ability of the apparatus followed. This involved driving the vehicle on a measured 9 percent grade and recording both fifth wheel and corrected speedometer data at peak grade speed.

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A test for acceleration performance (both 0 to 50 mph and 15 to 35 mph) on a flat surface was then completed. Times were recorded by stopwatches at the appropriate corrected speedometer reading. Fifth wheel data were also taken.

Finally, the apparatus was tested over the three response routes identified in table 2. All runs were made using red lights and siren. The driver was told to drive as though he were responding to an actual emergency. Two runs of each vehicle were initially planned over each route. After a few runs involving Flngines 127 and 523, it was found that measured travel times between runs of the same vehicle were very close (i.e., within 1 percent) even when these runs were conducted at different times of the day (see table 2). Consequently, further repetitive runs were eliminated for the sake of safety.

Information collected during each run included odometer readings at the beginning and end of each run, fifth wheel speed data, the total time of the run, the time of arrival at each major intersection, the traffic signal condition (green, red, or yellow), traffic situation at each intersection (none, light, heavy), and any unusual occurrences that may have resulted in an unexpected slowdown between intersections.

Road test results

‘I’ahle 2 summarizes travel times measured over the selected response routes. Note that time differences occur between the lower powered Frngine 523 (i.e., drive wheel horsepower per 1000 lbs = 5.2) and the two better performing vehicles (i.e., drive wheel horsepower per 1000 lbs = 6.3 and 6.4, respectively). In all cases, Engine 523 required more time to complete a test. ‘Phis was particularly true on routes where many slowdowns or significant grades were enduntered. For example, in the case of Avalon, with a total of about six slowdowns, almost a full minute more was required for the 3.1 miles. Crenshaw, with its significant grade, also required an additional minute to go only 1.25 miles.

Pumpers that can be purchased today have power levels ranging from a low of 4 to a high of 12 hp per 1000 lbs (i.e., corresponding to gross vehicle weights between approximately 15,OCX) and 36,000 lbs and engine sizes between 150 and 450 hp). This means that the differences in drive wheel horsepowers between Engine 523 and the other apparatus tested are, in fact, relatively small (i.e., only a lit tle over 1 hp per 1000 lbs). This also means that even larger time differences may result if one considers the full range of engine and chassis sizes available today.

To illustrate, the travel time for the 1.25-mile, 7.1 percent average grade segment along Crenshaw Boulevard is estimated (using computer techniques) at nearly 4 minutes for the vehicles powered at the lower 4 hp per 1000 lbs and about 1.75 minutes at the higher hp per 1000 lbs. This means more than a doubling of the travel time achieved for the range of engine and chassis sizes available today.

As route conditions become more stressful (i.e., longer distances, more slowdowns, larger grades, etc.), these time differences increase even further. In general, these travel time differences are significant in the context of fire fighting where seconds can mean the difference between a small or a fully involved fire or a life or death.

General conclusions

In addition to examining the effect of different vehicle characteristics over the tested routes, computer techniques were used to extrapolate the results over a broader range of road conditions. Roads having from 0 to 4 slowdowns per mile, grades from 0 to 34 percent, and road surface conditions that include paved, mud, snow, etc., were examined. Charts of the form illustrated in figure 2 were used to examine trends in the data. The following general conclusions were reached:

1. Travel times are significantly affected by drive wheel horsepower levels in the 4 to 12 hp per 1000 lbs range. As one would expect, travel times tend to increase as the horsepowers are lowered, and this becomes more dramatic as the number of slowdowns, grades, or road surface conditions become more stressful. On the other hand, as drive wheel horsepowers increase, a region is reached beyond which the additional effect of larger power levels becomes smaller (e.g. power levels greater than 10 hp per 1000 lbs for the route conditions indicated in figure 2). This region tends to shift to lower power levels as route conditions become less stressful—i.e., paved roads with fewer slowdowns or smaller grades.
2. F’or a given level of drive wheel horsepower, as the maximum speed the vehicle is driven increases from 20 to 60 mph, travel times decrease, first dramatically, but then at a reduced rate. F’or speeds beyond 60 mph, a region of diminishing returns in terms of travel time improvement also occurs. This is particularly true in urban settings where acceleration and gradability performance rather than vehicle top speed largely control the achieveable travel times.
3. The speeds actually attainable along a given route are limited by either driver discretion or vehicle performance. In the first case, the maximum speed driven is determined by such factors as safety, fire department policies, etc. On the other hand, when poor road surface conditions, frequent slowdowns, or long, steep grades occur, the drive wheel power level of the vehicle can limit the maximum attainable speed. The road tests and computer analysis results show that vehicles with power levels lower than certain critical values (dependent on route conditions) may not have enough power for the weight they are moving to reach certain speeds considering the intermittent slowdowns and grades encountered.

The above results indicate that community route conditions, maximum speeds, and the road performance level specified when purchasing a fire engine significantly influence alarm response times acheived. The travel time implications of road performance, therefore, should be examined prior to purchase, particularly if poor road conditions, frequent slowdowns or significant grades, occur in a given community. In addition, the technical and economic feasibility of a given performance level requires examination since a given power level may not always be attainable. F’or example, large payload requirements may force a high gross vehicle weight while current design practices or community budget considerations may limit the engine size.

Judgments

The specification problem thus becomes one of judgment, requiring one to define a maximum acceptable travel time objective and then to select a performance level in the light of the limitation imposed by payload considerations, power required to drive the pump, current vehicle design practices, and community budget constraints. Related sections in the “Guide for the Specification of Fire Pumper Apparatus” were developed to help the fire service user accomplish this.

Testing help

‘Fables for drive wheel horsepower in the guide allow a fire service user to obtain his required drive wheel power directly for route conditions applicable to his community. A separate table is provided in the guide for variations in slowdowns per mile between 0 and 4 at unit increments, maximum speeds between 35 and 65 mph at 5 mph increments, and travel times between 1.25 and 2.50 minutes per mile at 0.25 minute increments.

Once an adequate drive wheel power level is selected, the guide provides additional instructions to convert this power to specific acceleration (i.e., 0 to 50 mph in a specified time), top speed and gradability performance specifications. On delivery of the apparatus, the fire department can measure these road performance requirements directly. A simple step-by-step procedure is provided in the guide to help accomplish these acceptance tests. This procedure requires only a stopwatch and marker cones.

Better use of apparatus

If the apparatus in a community have significant differences in road performance levels, due to equipment or age differences, the guide can also be used to match individual apparatus capability to the road conditions around each station’s first-in response area to assure maintenance of response time objectives throughout the community.

In a manner analogous to periodic fire pump testing, the road test acceptance procedures in the guide might also be used to periodically check the road performance of the equipment. The objective is to alert the department when maintenance is needed or, perhaps, when replacement is warranted due to degraded performance with age.

At present, the specification guide is being field-tested in 11 communities. They represent a wide range of conditions with regard to geographic area, size, fire hazards, road conditions, form of government, and equipment purchasing practices. These communit ies are using the guide to determine apparatus requirements and develop bid specifications. Any problems they encounter w ill be corrected, and the final tested guide will become available for distribution through the U. S. Fire Administration in late 1979.

For information on how to obtain a copy of the “Guide for the Preparation of Fire Pumper Apparatus Specifications,” write to United States Fire Administration Library, Washington, D.C. 20230, or phone 202-634-3913. □ □