Go to my Home page
Go to my Joy of High Tech page

The Joy of High Tech

by

Rodford Edmiston

Being the occasionally interesting ramblings of a major-league technophile.

One Size Does Not Fit All

Fitting something to a human is difficult. Not only are there multiple, compound curves and asymmetries, but every single person is different. Think about that. Even identical twins are different in the details, right down to their finger prints. This is bad enough when buying clothes, but what about situations where well-being and even life depend on a good fit? This was a hard lesson to learn, but it was learned and widely accepted in the Fifties. Yet today, over and over bureaucracies and businesses try to reduce the number of sizes something is offered in to a bare minimum. A minimum in which none of the offerings actually fit anyone. Some folks just don't like history.

During the Second World War a major effort was made by all participants with air forces to find oxygen masks for aircrew which would fit well and stay in place, using the minimum number of parts in the minimum number of different sizes. This was a struggle, and some candidates for pilots and crew were actually rejected due to not being able to make a mask fit. In fact, just getting flight gloves to fit required overturning multiple assumptions among both civilians and the military. The situation only grew worse as altitude increased and the need for proper protection became greater. After the War partial pressure suits came along, then full pressure suits. The difficulty of fitting wearers of these became even greater. There's a reason space suits are still largely custom fitted. (Though most these days are modular, and largely assembled from a range of mass-produced parts.) Then there was the problem with the "average man" cockpit; especially the small cockpits of pursuit, fighter, interceptor and attack planes. When flying a plane every control must be in quick and easy reach for every size and shape of the pilot, something difficult to arrange in a small aircraft. The arrival of jets made things worse, with their higher speeds and altitudes. Then there was the problem of allowing a wider variety of people fly planes after the War.

By the late Forties there were documented fatalities directly due to some pilots having trouble fitting the cockpits and reaching the controls. At its worst point 17 US Air Force pilots crashed in a single day, from simply not being able to work the controls due to pilot misfit.

This was difficult to accept, and for a long while investigators leaned towards pilot error as the cause. Eventually, though, the problem of poor fit of pilot to aircraft had to be accepted.

Aircraft designers weren't stupid, and they had been working on the problem for decades. In fact, they thought it was solved! When the US Army was designing its first-ever aircraft cockpit in 1926 the engineers measured the physical dimensions of hundreds of male pilots and used this data to standardize the dimensions of the cockpit. The size and shape of the seat, the distance from there to the pedals and stick, the height of the windshield above the seat, even the shape of the flight helmets were all intended to conform to the dimensions of an average 1926 pilot. As time passed they even took into account the increase in size - including height - among the population over that span. Yet that still wasn't enough. It was back to the drawing board... and the measuring tape.

In 1950, in an attempt to address the problem, researchers at Wright-Patterson Air Force Base in Ohio measured more than 4,000 pilots on 140 dimensions of size, from foot length, through crotch height to the distance from pilots' eyes to their ears. They then calculated the average for each of these dimensions. Everyone believed this improved calculation of the average pilot would lead to a better-fitting standard cockpit – working towards something which today would be termed ergonomics - and reduce the number of crashes. However, some weren't convinced this process would actually result in an improvement. Newly hired 23-year-old scientist Lt. Gilbert S. Daniels had doubts.

Daniels' undergraduate thesis described a comparison of the shape of 250 male Harvard students' hands and gave the conclusions he drew from the project. The students Daniels examined were from very similar ethnic, socio-cultural and gender backgrounds (that is, they were white and wealthy males). However, in the final analysis their hands were not similar at all. Even more surprising, when Daniels reduced his data the "average" hand he had come up with did not resemble any actual person's measurements. Oh, some people came close in most measurements... though even that might be true for only one of their hands! Consequently, Daniels understandably harbored doubts about the new cockpit design philosophy. How many pilots really were average?

He decided to investigate. Using the size data gathered by the program Daniels calculated the averages for height, chest circumference and so on for a total of ten characteristics. From these he determined the overall dimensions of the "average pilot." Daniels decided to use a lot of leeway, and defined this as someone whose measurements were within the middle 30 per cent of the range of values for each dimension. For example, he defined the height of the "average pilot" as ranging from five-seven to five-eleven, even though the average height from the data was five feet nine inches. Next, Daniels compared each individual pilot, one by one, to the average pilot, for all the measurements.

The consensus among his fellow researchers was that most pilots would be within the average range on most dimensions. The pilots used in the program had actually been pre-selected because they appeared to be average sized. (For example, someone much over six feet tall would never have been recruited in the first place.) Those involved in the project expected that a sizable number of pilots would be within the average range on all 10 measures. However, even Daniels was stunned when he tabulated the actual number of matches: Zero.

Out of 4,063 pilots, not a single airman fit within the average range on all 10 dimensions. One pilot might have arms long for his overall height. Another might have shorter-than-average legs. Another pilot might have a big chest and but a short torso. Or one side of their body might fit, but not the other! Daniels even found that if you picked just three of the ten dimensions of size, less than 3.5% of pilots would be average all three dimensions. Daniels's findings were clear and incontrovertible. There was no such thing as an average pilot. If you've designed a cockpit to fit the average pilot, you've actually designed it to fit no-one. (Note that during the later Mercury program, Gus Grissom was the shortest of the seven but had the longest torso. The capsule was therefore sized for him!)

The world's aircraft engineers and designers were stunned. There was no easy answer, no real "average"; not even for a large group of people who roughly counted as "mostly average." The planes had to adapt to the users rather than the other way around. The designers had to develop a whole new type of fit. (The engineers were actually the easy party to convince. However, bureaucrats hatehatehate having to treat people as individuals.)

The US Air Force boldly changed its philosophy, taking a new guiding principle: Individual fit. The US military began fitting the system to the individual. In short order, the Air Force demanded that all cockpits needed to fit pilots whose measurements fell within a range of 5-per-cent to 95-per-cent on each dimension.

Now the airplane manufacturers balked, insisting it would be too expensive and take years to solve the problems involved. The military, having reluctantly made the decision, now refused to budge. The manufacturers were told to comply if they wanted to sell to the Air Force. Grudgingly, they did. To the surprise of everyone except the engineers, those worthies quickly came up with solutions which were both cheap and easy to implement. They designed adjustable seats, technology similar to what is now standard in automobiles. They created adjustable foot pedals, which are also common in some consumer vehicles. They developed adjustable helmet straps and flight suits. (Actually, most of these technologies had been available to some extent in some products for decades before this.)

Most readers of these columns know I am a fan of th F-104. One of the points of praise pilots have for the plane was how well the cockpit adjustments worked. Once the pilot had everything properly set every control was easy to reach no matter what the size and shape of the pilot. Score one for the designers.

The "adjustable cockpit" is still not perfect, of course. Even though the initial selection of pilots only accepts people within certain ranges of measurements, there are still situations where someone just doesn't quite fit. Even in automobiles there are compromises which affect the adjustability. Humans are just that variable.

The problem of trying to stick people into narrow categories using physical measurements doesn't stop there, of course. Worse than fitting clothing or equipment to a mythical average size is the attempt to connect mental characteristics to physical ones.

Daniels, himself, had earlier tried to classify the personalities of people according to their body shapes — a practice known as "typing." He was far from alone in this. Many physical anthropologists of the time believed a short and heavy body was indicative of a merry and fun-loving personality, while receding hairlines and fleshy lips reflected a "criminal type."

Naturally, any such association turns out to be strictly in the mind of the beholder.

The problem of trying to fit an "average" or "typical" person also exists in the civilian realm, of course. Shoes are an excellent example. In addition to the variability discussed above, a person's feet will be slightly different from each other in size and shape. Usually the difference is small enough that fitting the pair of shoes to the larger foot is fine. This is not always the case, though. Also, modern footwear designs and materials are inherently more flexible than older ones, and tend to fit better with few size/shape options available. This is one reason there used to be such a fuss about precisely measuring someone's feet before even starting to try shoes on. This was especially true of children, since poorly fitted shoes could actually damage growing feet. (Anyone remember foot X-ray machines? Though a gimmick which didn't actually do much good - and did do much harm - the basic idea was sound: Look at the internal structure of the feet to help select the perfect shoe.)

Gloves, shoes, shirts, pants... barring custom tailoring all will be an imperfect fit. This goes beyond comfort or fashion. What about someone who needs a back brace, and can't find a comfortable one due to being an unusual size and/or shape? The wrong one could actually make the problem worse, or create new ones.

Another effect of this natural variation is in the field of medical practice. Dosage amount and scheduling for medications should be tailored to the individual. In most cases, the only way to get this exact match is through trial and error. Diabetics must be especially vigilant, due the effects of diet and activity on how much insulin they need.

Things are changing. Already there are cancer treatments which specifically target the cancer of an individual. Implanted insulin pumps automatically meter out only as much as is needed at the moment. As new diagnostic methods are coupled with new fabrication methods, treatments and procedures tailored for each patient will become the norm. The limiting factor then will be the health insurance bureaucracies, who will likely insist in treating everyone the same.