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Acceleration of Blackout in Fighter Pilots

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Bibliographic Entry Result
(w/surrounding text)
"Aerospace Medicine" Encarta. Redmond, WA: Microsoft, 1997. "If a force form 4 to 6 G is sustained for more than a few seconds, the resulting symptoms range from visual impairment to total blackout." 4โ€“6 g
Acceleration Protection. Human Systems Center (HSC). Brooks Air Force Base, Texas. "The standard G-suit provides passive protection to about 5.5 +Gz." 5.5 g
CF-18 G-Protection: Sustained Tolerance and INcreased G (STING). Aerospace Life Support Sector. Defence and Civil Institute of Environmental Medicine (DCIEM), Canada. "PBG systems can overcome the blood-flow limitations of traditional (lower-body) G suits, allowing sustained G-tolerance at levels up to +7.5Gz with only minimal straining manoeuvres." 7.5 g
History - The Franks Flying Suit (2). Canadian Defence Research & Development Branch. "Testing the new suit in a Fleet Finch aircraft at Camp Borden in 1941. Dr. Franks, fully conscious at 6G, with the suit filled with water to heart level." 6 g

In itself, high speed does not produce harmful symptoms. What can be dangerous are high accelerations; expressed as multiples of gravity, or g's. In pulling out of a dive, for example, a pilot may be subjected to an acceleration as high as 9 g. If a force of 4 to 6 g is sustained for more than a few seconds, the resulting symptoms range from visual impairment to total blackout. Protection is provided by a specially designed outfit, called an anti-g suit, which supplies pressure to the abdomen and legs, thus counteracting the tendency for blood to accumulate in those areas. Proper support of the head is essential during extreme acceleration in order to avoid swelling of the sinuses and severe headaches. While facing backward in a seated position, properly supported human test subjects have been able to tolerate a deceleration force of 50 g without severe injury. [The first paragraph of this student's essay is entirely plagiarized from the Aerospace Medicine entry in Funk & Wagnall's Encyclopedia. I did not discover this until a year after it was submitted.]

The acceleration that causes blackouts in fighter pilots is called the maximum g-force. Fighter pilots experience this force when accelerating or decelerating quickly. At high g's the pilots blood pressure changes and the flow of oxygen to the brain rapidly decreases. This happens because the pressure outside of the pilot's body is so much greater than the pressure a human is normally accustomed to. One human body handles g's different then another. The areas that are under investigation of the maximum g-force are:

  1. seat back angle,
  2. layoff (time away from the cockpit), and
  3. comparison of female to male tolerance/endurance.

Work on a special suit to increase the g's a human body can handle had started during World War Two. Pilots at that time experienced blackouts when coming out of fast turns or when dropping altitude quickly. The work on special g-suits still continues today. Modern fighter pilots can handle g's that a human body would never have been able to tolerate previously.

Phillip Andriyevsky -- 1998

Bibliographic Entry Result
(w/surrounding text)
Aerospace Medicine. Funk & Wagnall's Encyclopedia. "If a force of 4 to 6 g is sustained for more than a few seconds, the resulting symptoms range from visual impairment to total blackout." 4โ€“6 g
Wayne, Tony. Ride Physiology. Roller Coaster Physics. Virginia Department of Education

"As the g forces climb up toward 7 g's, you sink further still in the seat. You can no longer see color. Everything appears in black and white. An instant later, the passenger next to you disappears from view. Your field of vision is shrinking. It now looks like you are seeing things through a pipe. The front corner of the car disappears from view as your peripheral vision disappears. The visual pipe's diameter is getting smaller and smaller. You sink into the seat further still as the number of g's climb further. In a flash you see black. You have just "blacked out." You are unconscious until the number of g's are reduced and the blood returns to your brain."

"Inside Loop [diagram]
8 g blackout limit
A person passes out because of the lack of oxygen in the brain."

7โ€“8 g
Pryor, Loyd. Roller Coaster Corkscrew. Georgia Institute of Technology."The human threshold is around +7.5 G's, for a trained pilot in a 'G suit.'" 7.5 g
Roller Coaster. Physics Education Research Group. University of Maryland."The goal here is to maximze the excitement of the ride without actually endangering the passengers. An important figure to remember here is that an average person will black out if the "headward"acceleration s/he experiences reaches 2 g. By comparison, people can withstand accelerations on the order of 10 g in directions perpendicular to their bodies without any permanent adverse effects, however most Roller Coaster cars would jump their tracks at such extreme accelerations." 2 g
(no way can this be right)
Cameron, John R.; James G. Skofronick & Roderick M. Grant. Physics of the Body. Second Edition. Madison, WI: Medical Physics Publishing, 1999: 182. "If gravity on earth suddenly became three times greater (i.e., g ~ 30m/s2), blood would only rise about 43 cm above the heart and it would not reach the brain of a standing person. This situation can be produced artificially by accelerating the body at a = 3 g in a head first direction (Fig. 8.8b)." 3 g

Editor's Supplement -- 1999, 2001