Effective Drag aka Tumble Number for Rolling vehicles

Topics related to Vehicle Specifications, Vehicle Acceleration Tests, Vehicle Braking Tests
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MSI
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Effective Drag aka Tumble Number for Rolling vehicles

Post by MSI »

On the Napars Facebook page they brought up Effective Drag for a rolling vehicle:
  • This is a topic which clearly has a "seminal" paper that everyone handling crash analyses should be familiar with SAE Paper 890859
    One might also do well to review Searle's 1983 SAE paper on pedestrian crash analysis. We'll talk about that later this week.
Our Comments

Always like to see a paper we must have missed back when we did a review in 1998.
From our 2008 McHenry Reconstruction Book*** here's a few more references:
  • An often cited value for the average ground deceleration factor for rollovers is 0.40-0.65 and is based on reported values found in a 1972 report by Hight (Reference 84).
    • It should be noted that the values reported were not measured values but were calculated from “estimated rollover speeds” based on “other road users’ statements, highway geometry, braking and centrifugal skid marks, critical cornering speeds, etc.”.
    However more recent measurements of drag on rolling vehicles support the general range of the estimates cited in the Hight report.
    • Orlowski (Reference 85) included 8 dolly rollover tests wherein the average drag was found to be approximately 0.44 (see Figure 83). A few items to note: Dolly rollovers start with the CG elevated above the normal CG height (they sit upon the dolly and are launched) and the tests were run on level, paved terrain surfaces.
    • Cooperrider, et al (Reference 86) includes soil-tripped, curb tripped and dolly rollover tests. The reported average deceleration from trip to rest was reported as: 0.48 g’s for soil tripped tests, 0.32 g’s for curb tripped tests and 0.31 g’s for the dolly rollover. The authors of Reference 86 raise questions regarding the average decelerations during rollover that have been reported by others (e.g., References 84, 85, 89).

      However, the direct comparisons are made between averages over time (Reference 86) and averages over distance (References 84, 85, 89).

      Clearly, the accident reconstructionist must work with the average deceleration over a distance. In 1998, Cooperrider further investigated soil tripped rollovers in Reference 87. The results are similar to those found in Reference 86;
      The average drag (over distance) from start of furrow to rest was 0.80 (prior tests in Reference 86 showed 0.86 and 0.93). Due to the nature of the soil trip area (they filled an area with dirt so no vegetation/furrow/irregular terrain effects were included). For their tests they had difficulty determining the end of trip phase/start of rollover.
    • Some other references related to rollovers which should be reviewed are Moffatt (Reference 88) and Orlowski (Reference 89).
rollover test results.jpg
rollover test results.jpg (180.39 KiB) Viewed 156 times
REFERENCES:
  • 84 Hight, P.V., Siegel, A.W., Nahum, A.M., “Injury Mechanisms in Rollover Collisions”, SAE paper 720966
  • 85 Orlowski, K.F., Bundorf, R.T., Moffatt, E.A., ”Rollover Crash Tests – The Influence of Roof Strength on Injury
    Mechanics”, SAE 851734
  • 86 Cooperrider, N.K., Thomas, T.M, Hammoud, S.A., “Testing and Analysis of Vehicle Rollover Behavior”, SAE
    900366
  • 87 Cooperrider, N.K., Hammoud, S.A., Colwell, J., “Characteristics of Soil-Tripped Rollovers”, SAE paper 980022
  • 88 Moffatt, E.A., “Occupant Motion in Rollover Collisions”, 19th Conference of AAAM
  • 89 Orlowski, K.R., Moffatt, E.A., Bundorf, R.T., Holcomb, M.P., “Reconstruction of Rollover Collisions”, SAE paper
    890857
***Foornote:
  • The actual date of the Rollover literature review for the book was 1998, guess we need to update that section (the book was updated several times (see below) but guess not that section. Here's publication history on the McHenry Book, guess time to update!
    McHenry Book publication dates.jpg
    McHenry Book publication dates.jpg (9.85 KiB) Viewed 141 times
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MSI
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Re: Effective Drag aka Tumble Number for Rolling vehicles

Post by MSI »

Recently on another forum some numbers/references related to this were posted up

Chapter 20 in text, "Fundamentals of Traffic Crash Reconstruction", deals with rollover crashes.
In that chapter, they report on Warner's SAE Paper 830612 in which he lists drag factors for vehicles sliding on the side.
These values are: (Pg 714)
  • Concrete: 0.30 to 0.40
  • Asphalt: 0.40
  • Gravel: 0.50 to 0.70
  • Dry Grass: 0.50
They also present deceleration in a rollover from several sources: (Pg 714)
  • Hight: 0.40 to 0.65
  • Orlowski: 0.36 to 0.61
  • Altman: 0.48 (avg)
  • Bratten: 0.50 (avg)
In addition are scatter plots of both roll distance v number of rolls and rollover speed v number of rolls.
They also discuss caveats in the use of these analyses. (Pgs 712-713)
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