What Do Skiers And Fighter Jet Pilots Have In Common? G-Force…

Blue Angels were roaring over Bay Area this past weekend and the next show is in Baltimore, Mariland. Did you ever think what is behind the scene of this amazing Air show?

Let’s look under the curtain of aerobatic show..

Spins, loops, infinite eight, Cobra turn, scissors, flying in formation only 18 inches apart look gorgeous and demonstrate high skills of the pilots. But these maneuvers can be hazardous!

According to aviation blog aircraft pilots sustain G-forces along the axis aligned with the spine. This causes significant variation in blood pressure along the length of the subject’s body, which limits the maximum G-forces that can be tolerated. Positive G force can lead to grayout, tunnel vision, blackout and losing consciousness. Resistance to positive G force varies. A typical person can handle about 5 G  (meaning some people might pass out when riding a higher-g roller coaster, which in some cases exceeds this point) before losing consciousness.  But through combination of special g-suits and efforts to strain muscles—both of which act to force blood back into the brain—modern pilots can typically handle a sustained 9 G.

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Average     Standard

Symptom        Threshold    Deviation       Range

——————————————————–

Grayout           4.1 G      ± 0.7 G     2.2 to 7.1 G

Blackout          4.7 G      ± 0.8 G     2.7 to 7.8 G

Unconsciousness       5.4 G      ± 0.9 G     3.0 to 8.4 G

——————————————————–

Thresholds in Relation to +G Tolerance. (from avstop.com)

Negative G force is encountered when acceleration is in a foot to head direction, such as might be obtained during inverted flight, or during an outside loop or pushover maneuver. Blood is then pushed toward the head, and the amount of blood returning from the head is diminished, so the blood tends to stagnate, particularly in the head. Under mild conditions of G forces, the pilot will feel congestion, as when standing on his or her head. Engorgement of blood vessels causes a reddening or flushing of the facial skin. Blood vessels in the eyes will become dilated. Some persons may experience a headache. A condition termed “redout” may occur. This may be due in part to congestion but may also occur when the lower eyelid, reacting to G force, rises to cover the pupil, so that one sees light through the eyelid. The limit is typically -2 to -3 G.

You don’t need to be a pilot to experience all these high G-forces. On a typical rollercoaster you can experience ~3-4 G force, but in some it can even exceed  6G.  The G thresholds depend on the training, age and fitness of the individual.

An untrained individual not used to the G-straining maneuver can black out between 4 and 6 g, particularly if this is pulled suddenly. So, don’t underestimate this sign!

But what about skiing? Where is G force there?

Let’s look into the forces affecting skier in turn:

Centrifugal force, C, combines with the force of gravity acting on the skier’s mass, G, to form the resultant force R acting on the skier. S is the reaction force produced by the snow in response to R.

Based on the skier’s inclination, we can determine how much force is experienced in a turn. Results for some typical inclinations, expressed in Gs (multiples of the skier’s weight), are shown below. A good advanced recreational skier can make turns at about 20 degrees of inclination, and might occasionally reach 30 degrees. Technically strong experts do a lot of their skiing at 30 to 45 degrees. World-class racers have been making giant slalom turns at 60 degrees since around the year 2000, and have recently been making turns at angles as high as 70 degrees. Turns made at inclinations greater than 45 degrees require exceptional physical and technical strength to balance against the large forces involved.

Inclination       Force

0                                 1 G

20                              1.1 G

30                              1.2 G

45                              1.4 G

60                              2 G

70                              2.9 G

What does it mean? Even if it’s only 1.5 G force, it means the skier will need to balance 1.5 of his weight, or twice his weight if he’s inclined for 60 degree.

Everyone knows that when the snow is hard, the challenge is to get the edge to penetrate the surface as deeply as you can. The first key is to apply all the force available to as small an area as possible, maximizing the pressure on the snow. This is the primary advantage a sharp edge has over a dull one: It spreads the available force over a smaller area than a dull edge does. Applying all the force you can to one ski is the other key to penetrating hard snow.

World Cup racers, who know better than anyone how to ski on ultrahard snow, will tell you that when the going gets tough, they stand on their outside ski. So, then you may need to balance triple of your weight on one ski! And the surface not necessary will be smooth – there could be bumps or grooves and don’t forget, the speed is pretty high – up to 50+ mph!

Well.. , yes, it’s only 1/30 of the fighter jet’s speed, but be careful while skiing so fast!

There are few smartphone applications allowing you to measure how well you ski. Here is one on them – SnowEdge.

SnowEdge’s algorithm translates your G-force into a score. Score of 100 means you’re making good turns, and if you earn a 1000, you can probably qualify for Olympics! 

There are other apps to measure G force and how well you ski – let us know which ones you like!