Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.
Issue link: http://experimenter.epubxp.com/i/118927
Table 1. Factors afecting tolerance to whole body deceleration Male gender Increased tolerance Increasing age Decreased tolerance Physical ļ¬tness (musculoskeletal particularly) Increased tolerance; improves recovery times Rear-facing seating position Increased tolerance Lateral-facing (sideways) seating position Decreased tolerance Underlying medical conditions (e.g., osteoporosis) Decreased tolerance This month we are going to look at exactly why there is such confusing, contradictory, and harmful misunderstanding and misapplication of data on this subject. This is important to understand before we get into the specifics of what may or may not be survivable. The National Transportation Safety Board and the Federal Aviation Administration have often taken a stance that more or less could be summed up as "the best that can be done is what is currently being done." Several studies of general aviation crash survivability have been carried out. But, simply put, if you go in expecting no one to survive above a certain level and you have aircraft designed to fail more or less catastrophically at that point, you are likely to get data that says the "survivable threshold" is somewhere around this point. The problem is that you are likely looking at the limits of the aircraft and not the limits of the occupants per se. Muddling these two intertwined limits is dangerous. While much has been written about the "human limits" to deceleration being fixed at a particular level, it is important to remember that there are several factors that change the tolerances to impact. These are spelled out, in a simplified way, in Table 1. What a reasonably fit pilot or passenger can tolerate in a forward-facing position is difficult to correlate with any degree of certainty. One cannot, thanks largely to the ethical prohibitions against endangering the lives of experimental subjects, determine this through crash testing. Even using anthropomorphic test devices (crash test dummies), you have to have some "real-world" human data to validate the crash test dummy against. Such is the cycle that many in the aviation community are stuck in when it comes to where to pin their design points. This brings us back to the problem of where to get data to validate our test devices. Given the design limits of aircraft being set so low, we can't look in a broad way to our own colleagues' misfortunes to provide a good measure. While it is important to look at previous aviation accidents/incidents, it is also vital that we do not put so much focus on them that we lose sight of data from other sources that may indicate something other than human tolerances is skewing the data. Thus the question arises, "Where to turn next?" While the immediate temptation might be to look at passenger car occupant protections, if one is looking at determining what the upper threshold for survival is, albeit with serious injuries, the best place to look is probably professional auto racing. Living in Indianapolis, I have had the chance to meet several drivers. When they learn what I do for a living they often joke about being "live crash test dummies" because of the intensity and well-documented nature of their crashes. One of the potential limitations often brought up about the broader application of auto racing crash data to other applications is both the physical fitness of the drivers and the younger age of those drivers. While the former is definitely a valid point, the latter is probably overstated, as there are numerous drivers in their forties (such as Joe Nemechek and Michael Schumacher) and even a few in their fifties (Bill Elliott and Mark Martin). Also, if we are going to design our aircraft to protect occupants, we have to consider that many of us will be hauling passengers younger than ourselves. If we design to protect those folks, then we can ensure EAA Experimenter 29