The Fitness Fixer
The Fitness Fixer

Indiana Jones Rocket Sled

The new Indiana Jones movie came out this past weekend, the Kingdom of the Crystal Skull. It is set in 1957 with fun fitness and iconry of the era, for future blog posts. Today - the Rocket Sled.

In the early part of the movie, Indiana Jones and the Soviet Russians brawl through a US military testing base in Nevada. Jones and a Russian officer wind up on a rocket sled, which blasts them on a speed track into the desert.

Rocket sleds are one of several devices that create and test the effects of high acceleration on equipment and the people who use them. High acceleration forces occur when jets take off quickly, when launching a space flight, to eject from a hit (compromised) fighter jet, on roller coasters and spin and fall rides, when you fall from a height, and any time you change speed and/or direction quickly. Interesting changes occur in the body under acceleration. Acceleration is one of the areas of my study as a research physiologist and was my work for a time at two facilities testing air vehicle and human systems.

G-force is a measure of acceleration, not force, but the term g-force is also used for the reaction force that results from acceleration. More on meaning, spelling, and math of g and G in another post. Too much g-force can result in g-LOC (Loss of Consciousness), pronounced "jee-lock"in English, but just as meaningful when using the Cyrillic pronunciation of "loss." When piloting a multi-billion dollar property (the fighter jet) G-LOC is not a good thing for anyone. The pilot may convulse, called "doing an Elvis" because the flailing looks like playing an air guitar - a real air guitar. Then the pilot may "ding" (lose consciousness) and the vehicle may "descend below the level of the terrain" (crash) and "disperse energetically" (explode) and "value unfavorably" (be destroyed), and the crew and anyone they land on may "achieve a negative health status" (die).

So we test.

A rocket sled is a small platform. Rockets propel it on the ground on rails. It creates high onset g-forces for a time limited to the length of the track. When personnel or equipment riding it sit as in a car or plane, they experience acceleration pressing them from front to back (on an x-axis).

To measure the higher g-forces with short onset experienced in jet bail-out procedures, a vertical ejection tower can be used. A small seat is propelled quickly upward by a contained blast force under it (like lighting a bomb). If they are positioned to sit upright, the acceleration acts on them from head to foot, on their y-axis.

To experiment with varying accelerations over different amounts of time and onsets, one device used is a centrifuge. A long support arm swings around and around a center anchoring point -like swinging a ball on a string around your head. A container, often ball shaped, at the end of the support arm holds the equipment or personnel being tested. The ball can rotate to position the people inside at any angle to simulate the changing positioning of a cockpit during maneuvers, for example.

What happens to the people in these testing devices? Often they throw up all over my nice equipment. Some of my test subject pilots used to have contests who could eat the worst thing to redisplay on testing day. One ate plastic bugs just for the fun he was sure to cause - then he didn't throw up, no matter what we did to him. In vertical (y-axis) ejections, there is high impact and acceleration forces on the discs and spine. Back injury is a concern for ejection scenarios. Vibration, both during acceleration and non-acceleration situations, such as for helicopter and jack hammer operators seems to be a high contributor to back pain. It is not known if the various vibration devices sold as fitness devices are of the kind (vibration frequency or amplitude) that contribute to joint pain. G-LOC is another consideration. Why do we test it? To see how to prevent it, if we can screen for who is more likely to get it, if we can train those prone to it to be more resistant, and so on, in g-force tolerance improvement programs (g-TIP).

The set of photos at right is a well-known one of USAF Colonel John Paul Stapp, M.D., Ph.D., riding the rocket sled. He was a pioneer of acceleration study and is also known as the originator of the expression "Murphy's Law" for things that can go wrong. The effect on his face along the x-axis is not from his high speed, but the acceleration which is increasing in photos ii and iii, and decreasing in v and vi. Even though his speed is greatest in photo iv, speed is not increasing or decreasing much, so there is little effect.

More on the interesting effects of acceleration and environmental testing from roller coasters to jets to movies in posts to come.

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Rocket Sled photo by samuraiCatJB
Col Stapp face photo reproduced on the site LightandMatter
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About the Author


Dr. Bookspan is an award-winning scientist whose goal is to make exercise easier and healthier.