ARNOLD AIR FORCE BASE, Tenn. -- The 2022 Winter Olympics are underway in Beijing. Athletes from around the globe are competing in a myriad of events that showcase their years of training and dedication.
Many spectators in the stands and viewers at home are likely awed by the lightning-quick maneuvers of the Alpine skiers, the grace and precision of figure skating, the board-shaking hits and powerful slap shots of ice hockey, and the “how-is-this-an-Olympic-event” intensity of curling.
Perhaps as equally jaw-dropping are the blazing speeds reached in the sliding sports of luge, skeleton and bobsledding. Competitors in each of these events traverse icy downhill tracks on specially-designed sleds with the goal of completing the route with the fastest time. Their respective vehicles take participants of each event down the frozen courses at speeds of 80 to 90 miles per hour.
To ensure optimal results and athlete safety, having the right equipment in the high-speed sliding sports may be just as important as the countless practice runs made to gear up for Olympic competition.
When U.S. Air Force officials decided the military branch should take a shot at Olympic glory in the 1964 games, they called on Arnold Engineering Development Complex to help give them an edge in the pursuit of the gold.
The Air Force requested that Arnold Research Organization, the contractor which managed what was at the time known as Arnold Engineering Development Center, fabricate runners for its bobsleds for the 1964 Olympic tryouts.
It is not clear from available records whether AEDC completed fabrication of the runners and if the runners were used on the USAF sleds, but it is apparent that AEDC personnel completed materials testing and engineering analysis for the runners.
Similar to skates, bobsleds ride on metal blades called runners. There are four runners on each sled, all located on the bottom of the bobsled hull. The movable front pair can be steered by the sled driver to control the direction of the bobsled, while the two runners located at the rear of the sled are fixed.
With the primary objective in bobsledding to, of course, actually finish the race, the goal was to make runners that would hold up throughout the duration of a run while simultaneously limiting friction.
Each bobsled run starts with a push-off to get the sled going on the track. After that, gravity propels the sled down the track toward the finish line. Gravity is a constant and affects all sleds equally, so the effectiveness of the push to start a bobsled run, as well as the aerodynamics of the sled and ability of the runners to maintain their glide, are key in determining the winner of a bobsled race.
A bobsled track is not a straight shot downhill. Courses are fraught with twists and turns. Riders are subjected to significant “g,” also known as the gravitational force equivalent or g-force, when navigating these turns. G-force is the force on the body from acceleration or gravity.
Bobsledders may endure up to 5 g, or forces equivalent to five times their own weight, when rounding a sharp curve in the track. The force bearing down on them is great. For the sake of comparison, according to PBS, citing an article from the journal Spine, walking imposes 1 g on the human body. A slap on the back is equivalent to a little more than 4 g, the average sneeze is almost 3 g and plopping down in a chair is a little more than 10 g. Other g-force examples, according to the website ehub.ardusat.com, include the up to 6.3 g generated by rollercoasters and the more than 7 g the crew of the Apollo 16 was subjected to upon reentry. People suffer no ill-effects from such events because of their brevity, however, instantaneous high-g-force impacts can have adverse effects. Death or serious injury is likely to occur at 50 g and concussions will occur at around 100 g. Lingering g-forces at lower levels can also be harmful or deadly.
Considering the high rate of speed at which they are traveling and the forces imposed upon them, a crash could have disastrous results for a bobsled crew. To assess the possibility of sled overturn, AEDC personnel studied the impact of load conditions on the runners.
AEDC was tasked with fabricating runners for the USAF for both its two-man and four-man bobsleds, the two sizes recognized for competition in the Olympics. This prompted further study of typical bobsled runners by AEDC team members. By early 1963, Maj. Gen. Perry Hoisington, then-director of legislative liaison with the secretary of the Air Force, had made contact with G.H. Pope, then-AEDC Engineering Support Facility chief, to provide specifications on the sleds and the runners for each type.
Hoisington had also provided AEDC personnel with allowable measurements and weights for the bobsleds and drawings of the runners for the four-man sled.
According to a report written by Pope dated Jan. 6, 1963, Hoisington had advised a sled would be flown to AEDC by Jan. 9 of that year to aid the work.
“This sled can be retained for study until sometime in February,” Pope wrote. “Accompanying this will be an Air Force officer who is an expert in bobsledding.”
After asking Hoisington a question related to the bobsled lugs, Pope was referred to Dr. Arthur Tyler, who won a bronze medal as part of the four-man U.S. bobsled team in the 1956 Winter Olympics. According to his biographical information posted on the website olympedia.org, Tyler earned a Ph.D. in physics from the University of Michigan and was perhaps known as the “most scientific of all American sledders.” He designed changes in his sleds, tested them in wind tunnels and applied his background in physics to arrive at the best combinations of aerodynamic factors.
Pope learned more from Tyler about the runners themselves, including how they are manufactured, how they are cared for and their expected sturdiness.
“Runners are trued with a file and polished with emery cloth and crocus cloth after each run by the crew,” Pope wrote. “They are trued by eye without use of template. Further, the cross-section radii are accomplished in a like manner.
“Dr. Tyler has always finish-machined the runners prior to heat treatment and merely hand-polished them following tempering. Further, no attempt was made to prevent warpage other than to hang the runners vertically during heat treatment.”
Tyler also stated the runners were tempered to C-44 to C-47 on the Rockwell scale, a scale used to measure the hardness of a material. This rating would put the runners above the middle of the Rockwell C scale range. While blades on the upper end of the scale may indicate they are made of harder steel and hold their edges better, they may also be more brittle than those found further down the scale, so a rating near the top of the Rockwell C scale range would not be preferable for bobsled runners. Neither would a rating near the bottom of the scale, as the steel would be too soft.
In a Jan. 8, 1964, addendum to his previous memo, Pope detailed work conducted on material provided by the Air Force.
“A sample removed from one of the pieces of material was heat treated by heating to 1600˚F and quenching in oil,” he wrote. “The hardness was determined to be (Rockwell C scale) 44-45. After tempering at 325-350˚F, the hardness was determined to be (Rockwell C scale) 42-43. Microscopic examination of the material indicates that good impact properties will probably be obtained. A further sample will be removed and heat treated for Charpy specimen preparation.”
The “Charpy” referred to is the Charpy impact test. According to the website sciencedirect.com, it is used to evaluate the relative toughness of a material as it measures the energy absorbed by a specimen while breaking under an impact load.
AEDC personnel also examined the runners originally affixed to Podar sleds, Italian-designed racings sleds built with aerodynamics in mind. These runners were quite soft, around 22 on the Rockwell C scale, appearing to have been fabricated by bending bar stock and welding the lugs onto it.
“Dr. Tyler was advised of this condition during the previously mentioned conversation,” Pope wrote. “He stated that this didn’t surprise him since he had seen Podar sled runners break when a sled was dropped accidentally. At the time, he had thought that the material had not been properly tempered; but considering that the break that he had witnessed was in the immediate location of the welded-on lug, it was undoubtedly caused by improper treatment after welding.
“We compared the contour of the Podar runners with the four-man ordinates and found that they are identical over the major portion of the runner length. Further discussion with Dr. Tyler resulted in a recommendation to copy the Podar runners; however, he wishes to have them hardened and tempered to automotive spring condition.”
AEDC worked to determine the maximum stresses in the two-man bobsled suspension springs for a 6 g dynamic load condition. Since assessment found that the sled would likely slide rather than overturn, calculated stress levels were deemed acceptable.
It does not appear that the U.S. Air Force team qualified to represent the nation in the 1964 Winter Olympics. Neither the U.S. two-man bobsled team nor four-man team was able to capture medals during those games.