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Abstract
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A comparison of the accelerations encountered in aircraft crashes with those of automobile crashes provides surprising results. In one experimental crash (NASA) of a pressurized transport aircraft, the impact velocity was 95 mph at an impact angle of 30-degrees. A maximum longitudinal acceleration of 20 g's and a maximum vertical acceleration of 23 g's were measured on the floor of the passenger compartment. Fredericks measured a peak longitudinal acceleration of 20 g's on the floor pan of a passenger car crashing into a barrier at 20 mph. Extrapolating his data to 95 mph, results in accelerations of several hundred g's. Both of these crashes are well within the "survivable" range as usually considered, and both are fairly typical.
A majority of airplane accidents occur on take-off or landing or at least in a more or less normal landing attitude where the airplane comes to rest after skidding for several hundred feet which accounts for the relatively low accelerations. Furthermore, in the case of large transport aircraft the mass is so great that many of the obstacles that would cause high accelerations to automobiles are swept along or knocked out of the path of the airplane. Airplane fuselages, landing gears, and wings absorb energy on impact in a manner that minimizes accelerations. Even when striking a hill or mountain a deformation of 20 to 30 feet results which gives relatively low accelerations.
An automobile, on the other hand, is brought to rest with a total deformation of 20 to 30 inches upon hitting a solid object at 40 mph with acceleration peaks of 90 g's measured at the floor pan. Trees, telephone poles, bridge abutments, etc. are all solid and plentiful enough to provide these high accelerations in a large portion of accidents. One further complicating factor in the case of the automobile is the limited space available in the passenger compartment for the safety engineer to use to slow down the passenger and cut off the high acceleration peaks.
From an overall viewpoint it is this author's opinion that minimizing injury in automobile crashes is far more difficult than in airplane crashes. However, the results in terms of number of persons involved and the injuries and/or deaths which can be eliminated are far more impressive and important when considering the automobile.
Conclusions:
1. Forces to the lumbar vertebrae are a linear function of caudo-cephalad acceleration up to the point where buckling or fracture takes place. Linear results have been noted up to 15 g's. 2. High rates of onset produce high peaks of strain of short duration. A rate of onset of 1760 g's per second resulted in a two cycle surge of strain in the third cervical vertebra with a magnitude four times that of the steady state strain. There was no strain surge at low rates of onset. 3. Strain in the cervical vertebrae from acceleration was nine times greater with the head free than when it was fully restrained. 4. End plate fractures occurred in the lumbar vertebra at loads as low as 435 pounds. Muscle loads will reduce the external loads required to fracture the end plates still further. 5. Vertebral end plate fractures are very difficult to find by x-ray examination. 6. Protection of automobile passengers from injury is basically more difficult than the protection of airplane passengers. Reason: accelerations encountered in automotive crashes are greater even though the speeds are much lower. |