Vault/Fall Takeoff Angle Question

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Vault/Fall Takeoff Angle Question

Post by lambeaudog »

I am working on a crash where a Jeep ran off the road into a ditch and then went airborne after jumping a driveway. The entire scene is on a hill in that the landing area of the car is lower that where the takeoff occurred so I am treating it like a fall. In trying to determine the takeoff angle for use in estimating the speed at takeoff I can see that the vehicle had its driver's side tires on the shoulder (which would be a nearly level takeoff angle) and that the passenger side tires were in the ditch and much lower than the driver side tires (around a 20 degree takeoff angle going up to the driveway) meaning the Jeep was tilted around its y axis at takeoff. My question is how to determine the overall takeoff angle? Do I just go with the 20 degrees from the lower tires and negate the tires on the level surface or do I do something like take an average of the of the two (result would be around 10).

In running rough numbers for the crash the difference between the results is pretty drastic with the level takeoff being much higher (80 MPH) vs if I just use the lower (around 30 MPH). My gut feeling from looking at the physical scene is that the jeep was going at least 50 mph at takeoff as it was only airborne for about 66 feet before rolling over several times.

Any thoughts you have would be appreciated.

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Re: Vault/Fall Takeoff Angle Question

Post by mchenrysoftware »

Your description of the side to side elevation difference would mainly impart a roll response to the vehicle
  • landing lower than takeoff
  • driver side on relatively level terrain
  • passenger side in ditch, lower than driver side, approx 20 degrees
the side to side elevation difference would only act to induce a roll response in the vehicle

If you can
  • map the left side and right side path (in 3 dimensions) for the last 10 to 20 feet of takeoff to see how much rise/fall you get for the takeoff path in the direction of travel
  • map the landing area relative to the takeoff area (and front v rear and side to side landing areas)
  • See our forum topic motorcoach launch analysis from many years ago
    • It used equations to calculate/approximate the speed at 'launch'
      and then we tested/refined the speed estimates with simulation
      the main questions in that analysis was first was it a horizontal or somewhat downward slope for takeoff angle
      and then given a long wheelbase vehicle (a bus) how much does that affect the 'effective takeoff' angle and 'landing area'
      In your case with a Jeep if will be less difference (front to rear and side to side), but there is some effect.
simple horizontal launch analysis.jpg
Brian McHenry,
NEW!! LEASE pricing of msmac3D Software!! 3D Crash Reconstruction and Simulation Software.

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