History of Research in Space Biology and Biodynamics
- PART V -
Aircraft Crash Forces
[65] One of the less exotic aspects of the biodynamics program-one which has received only a modest amount of research effort but which has yielded certain interesting results-has been that related to crash forces experienced in aircraft accidents. The study of aircraft crash forces has obviously much in common with the study of eascape from aircraft. Moreover, the first aeromedical sled runs on the Holloman high-speed track to deal expressly with a topic other than escape from aircraft were concerned with aircraft crash forces. These runs began on 21 April 1955 and lasted through 28 June, overlapping slightly with the earliest of the high-speed windblast runs by the sled Sonic Wind Number 2.4 Specifically, they aimed to reproduce the combined vertical and horizontal crash forces encountered in certain types of forced landings, basing the test configurations on actual crash data compiled by the National Advisory Committee for Aeronautics. As stated in one test report,5
[66] Pilots of high angle of attack jet aircraft, such as the Delta Wing F-102, have incurred back fractures caused by forced landings in which the tail was dragging the ground at near stalling speed with the pilot seated in the nose 55 feet beyond the end of the tail, and 18 to 25 feet above the ground. When tail structures catch on ground obstructions, the nose of the aircraft can be slammed to the ground viciously with forces estimated at better than 60 g's. For the protection of pilots, it is necessary to evaluate the combined effect of the two components by reproducing them on the deceleration sled.
In these tests, an F-102 seat was rigged to drop vertically seventy inches and decelerate by impinging on a metal cylinder, while at the same time the entire apparatus, attached to a rocket sled, was being decelerated horizontally by water brakes on the high-speed track. In the first full-scale experiment of 21 April-which followed a series of static tests-an anthropomorphic dummy was used, sustaining peaks of roughly fifty g's vertical and twenty-five g's horizontal deceleration. Subsequently, anesthetized chimpanzees took part in the experiments. With varying types of protection and no irreversible injury, they received forces ranging up to sixty g's vertical in combination with twenty g's horizontal deceleration. Taken as a whole, the experiments supplied valuable data both on crash forces as such and on the value of different crash restraints and energy-absorbing seat cushions. For example, they demonstrated how the impact of vertical g-forces could be reduced by means of up-lifting chest and shoulder straps.6
Aircraft crash forces have also been studied on the crash-restraint demonstrator, informally referred to as Bopper, which is one of the specialized test facilities established at Holloman solely or primarily for the work of the Aeromedical Field Laboratory. The original version of the Bopper was acquired from Northrop Aircraft, Incorporated in March 1955 and was replaced by an improved model a year later. It is a seat propelled by elastic shock cord along a short, portable stretch of track; it can impart g-forces of short duration, with magnitude (on the new model) up to about thirty g's.
The Bopper was used in a special study of subject responses to low-impact aircraft crash forces. Participants in this test series experienced deceleration on the Bopper ranging up to twelve g's in aft- and forward-facing positions, secured with seat belt only. Immediately after exposure, each subject released the seat belt manually and proceeded along an aisle to a simulated emergency exit. Subjects were carefully observed to see how quickly and efficiently they were able to release the belt and reach the exit-something that must be executed without delay whenever there is danger of flash fires breaking out or in the event of a water landing. The results indicated that responses were slightly better after deceleration in the backward-seated position, thus supporting a point of view that Colonel Stapp and many other aeromedical officers had often urged upon the aviation industry, without much success.7
Although a technical note published on these Bopper tests related them expressly to an aircraft crash problem, any data on g-tolerances with seat-belt restraint was also of interest for automotive crash research. The officer who directed these tests (together with Colonel Stapp, who was chief of the entire laboratory from April 1953 to April 1958) was Lieutenant Sidney T. Lewis, whose primary assignment was task scientist for Automotive Crash Forces (Task 78507 of Project 7850). Naturally, much of the work performed under the automotive crash program was applicable in turn to aircraft crash studies. Similarly, tests have been performed on the Daisy Track, whose main purpose is basic research on impact forces, in order to evaluate particular types of aircraft crash harness. Both the automotive crash program and the operation of the Daisy Track will be discussed below in greater detail.
However, at no time since the F-102 drop-seat experiments has aircraft crash research, as such, been one of the major activities of the Aeromedical Field Laboratory. When Project 7850, Biodynamics of Human Factors in Aviation, was established, it contained a separate Task 78506, entitled Tolerance to Aircraft Crash Forces; and there was even talk of staging barrier crashes with jet aircraft on the Holloman high-speed track. But no such experiments were held, nor did the aircraft crash program ever have a full-time task scientist. In March 1958, finally, when Project 7850 was revised to become Biodynamics of Space Flight, Task 78506 was changed from Aircraft Crash Forces to Patterns of Deceleration in Space Flight.

Drop Seat Used in Aircraft Crash Experiments on the High-Speed Track

[68] The new version of this task will also be discussed more fully below. Even now, aircraft crash study will not necessarily be excluded altogether from the work of Project 7850. Project documentation indicated that research would be conducted on "dynamic stress characteristics of the human body" as a factor in "design and specifications" for both aircraft and space vehicles; and the project is still interested in "impacts," which in turn include crash forces.8