Anti-g suit

MSF830 "Anti-g suit trousers" and " cummerbund cover" over the flying suit .

An anti-g suit is additional clothing for aircraft crews in order to limit blood sagging in the event of high g forces , for example in tight turns.

g -forces

While in unaccelerated straight flight only the force of gravity acts on the crew of an aircraft , centrifugal forces that are many times higher can occur when turning . For the organism, with positive g-forces along the vertical axis (i.e. when one becomes heavier in the seat), this means above all that the blood from the upper regions of the body sags downwards. Here, the heart has to perform better for a sufficient supply of blood and therefore oxygen to the brain and eyes. However, if the - individually different - capacity limits are exceeded, it can through the oxygen supply to limitations of vision ( tunnel vision , greyout , blackout ) or even to a complete loss of consciousness (ger .: g-induced loss of consciousness - G-LOC ) and thus a mission termination and / or accidents occur.

High g -forces occur, for example, in flight races, aerobatics and military flight profiles ( aerial combat , interception maneuvers after the use of weapons, etc.).

To a certain extent, aircraft crews can suppress or delay the negative effects of high g-loads. In addition to appropriate training, you can achieve this through targeted muscle tension or press breathing, for example . These measures are supported by technical solutions such as inclined seats, press ventilation with oxygen-enriched air and anti- g- suits or a combination of these options. Ultimately, however, restrictions in performance and ability to act and rapid exhaustion cannot be completely prevented.

history

The Canadian Wilbur R. Franks first developed the Franks Flying Suit Mark II (FFS Mk II) at the University of Toronto in 1940, a liquid-filled anti- g suit with water between two rubber layers. This was filled by the ground staff after boarding the aircraft. However, there was no operational use. It was only with the FFS Mk III model from 1944 - and thus still during the war - that anti- g trousers were available for use in Allied combat aircraft. This variant used inflatable rubber bags that were incorporated into the anti- g trousers and filled with compressed air from a compressor built into the aircraft . The testing of both variants took place from autumn 1944 among other things at the 339th and the 357th Fighter Group. The crews found that the anti-g suits filled with water were too cold. Thereupon an attempt was made to fill it with warm water. This was also unsuccessful because the water cooled down very quickly. Therefore, the crews preferred the air-filled suits.

Around the same time in Australia, Frank Cotton at the University of Sydney was also working on an anti-g suit based on a principle similar to Frank's Mk III. However, this was not ready for use.

functionality

The aim of all anti- g suits is to prevent the blood from sinking into the lower half of the body as far as possible. This should be achieved by applying pressure to the vessels, especially in the abdomen, thighs and lower legs. This is built up depending on the applied g load.

Physical explanation

The compression of certain areas of the body leads to cross-sectional constrictions, which in turn lead to an increase in the pilot's blood pressure. Thus, it is intended to increase the resistance of the fighter pilot to the g-forces. In other words, the narrowing of the cross-sectional area means that the law of continuity implies that the flow velocity of the blood must increase. This, in turn, leads to the fact that the increase in speed results in an increase in blood pressure.

${\displaystyle p={F \over A}={F \over \operatorname {\dot {V}} \operatorname {/} {v}}={F\cdot v \over {\dot {V}}}}$

${\displaystyle {\dot {V}}=}$Volume flow

${\displaystyle v=}$Flow velocity

Before compression:

${\displaystyle p_{1}={F\cdot v_{1} \over {\dot {V_{1}}}}}$

After compression:

${\displaystyle p_{2}={F\cdot v_{2} \over {\dot {V_{2}}}}}$

with from the law of continuity and the cross-sectional narrowing, so it follows: ${\displaystyle {\dot {V_{1}}}={\dot {V_{2}}}=const.}$ ${\displaystyle A_{1}>A_{2}}$ ${\displaystyle v_{1}<v_{2}}$

Thus the pressure increases with increasing flow velocity . ${\displaystyle v}$

Compressed air powered systems

In pneumatic systems, compressed air is introduced into cavities (mostly rubber bladders) in an anti- g suit. This is either generated by independent systems or tapped from the aircraft air conditioning system.

A major disadvantage is that the compressibility of the air causes a delay in the build-up of pressure, so that the anti- g suit cannot achieve its optimal effect immediately. In the case of rapidly occurring high loads (" g -onset"), the blackout may occur before the pressure required for effective countermeasures is reached.

Anti- g pants, which only affect the stomach and legs, are the systems most frequently used. The CSU-13B / P was used in numerous western combat aircraft and the PPK-1 in Russian-made aircraft.

Further developments included additional body parts through the additional use of anti- g vests and socks. Examples of combined pneumatic systems are

• British A ircrew E quipment A ssembly (AEA) with anti-g trousers, socks, Waistcoat and pressing ventilation in the British, Italian and Spanish Euro Fighter Typhoon ,
• the Swedish Flygstridsdräkt 90 for the Saab JAS-39 Gripen ,
• the S ustained T olerance to In creased + G z (STING) system from Canada for the McDonnell Douglas F / A-18 ,
• the American Comb ined A dvanced T echnology E nhanced D esign g E nsemble (COMBAT EDGE) for the McDonnell Douglas F-15 and the General Dynamics F-16 or
• the Russian VKK-6 as a full body suit with anti-g socks.

Liquid-filled systems

In order to compensate for the disadvantages of the compressed air-powered systems, the developers resorted to the idea of ​​liquid-filled anti- g suits. In these, the surrounding water pressure constantly acts on the pilot as counter-pressure to the g-load, which would theoretically be negligible. However, due to the design (for example the lack of complete cover), this is not possible in practice. Nevertheless, this mode of action results in increased g resistance and improved mobility and speaking ability, even under high g exposure.

The most prominent example of liquid-filled systems is the Libelle full-body suit (now called Libelle G-Multiplus ), which is used in the German and Austrian Eurofighter. The suit got its name from the dragonflies , which can easily withstand g -forces of up to 30 g during flight , as they surround the brain and the most important organs with a liquid.

Another example of the use of liquid-filled anti- g suits is the G-Race Suit developed in 2009, which is worn by pilots in the Red Bull Air Race World Championship . The G-Race Suit is a liquid-filled and independently working full-body g- protection system. The suit is tailor-made for every racing pilot and can be adjusted even more finely with a lacing system. The G-Race Suit was developed by Red Bull Air Race GmbH in cooperation with Autoflug GmbH and is based on the multiple patented Libelle G-Multiplus. A G-Race Suit has four so-called fluid muscles (FM) which are filled with water and welded together. Each fluid muscle extends from the shoulder to the ankle. Two fluid muscles run vertically along the front and two along the back. They are filled with approx. 1 liter of water each - a total of 4 liters. Such a suit weighs on average about 6.5 kg and its material is made from a special mix of Twaron and Nomex . The back pressure effect occurs without delay. Standard, pneumatic anti- g suits have a delay of up to 2 seconds before they can be fully effective. The pilot uses the G-Race Suit interactively through muscle tension and breathing techniques in order to achieve improved cardiological performance - and thus g -protection.

Common features of the compressed air and fluid systems

Although both systems offer a considerable increase in g resistance, optimal results can only be achieved through a combination of measures taken by the pilot (e.g. muscle tension) and technical approaches. However, there are still limitations due to the individual and daily form-dependent tolerance.

Another weak point is the cervical spine , which has to take the load of the forces acting on the head with an aviator helmet. It is not supported by anti- g suits.

One disadvantage of full body suits in particular is that they cover large areas of the body. This leads to restricted freedom of movement and can lead to overheating - and thus to exhaustion - due to the poorly dissipating body heat. Modifications of the anti- g- suits, in the simplest case through recesses in the fabric or in complex systems through the incorporation of cooling systems, are therefore necessary.

New developments

Aviator clothing currently being developed is increasingly multi-purpose suits which, in addition to providing support in the event of high g loads, are also intended to offer functions such as partial height protection , NBC , cold, heat and flame protection.

Web links

Commons : G-suits  - collection of pictures, videos and audio files

• Photo of the first anti-g pants (Cotton)
• Aeromiltec - manufacturer of anti-g suits
• Comprehensive description of the problem on the homepage of the Indian Society of Aerospace Medicine ( Memento from February 9, 2010 in the Internet Archive )
• Lecture on the Aircrew Equipment Assembly (AEA) and flight physiological problems (PDF, 3.19 MB)
• 60 seconds Bundeswehr: Anti-g suit ( YouTube video, June 13, 2018)

Individual evidence

1. ↑ FFS Mk III on the Defense Research and Development Canada homepage ( Memento from July 1, 2013 in the Internet Archive )
2. ↑ [Jerry Scutts, Mustang Aces of the Eight Air Force, Osprey Publishing, p. 63]
3. ↑ Description of the Aircrew Equipment Assembly on the Eurofighter homepage
4. ↑ Description of Flygstridsdräkt 90
5. ↑ New Anti-G-Race Suit ( Memento from July 15, 2011 in the Internet Archive ) on redbullairrace.com
6. ↑ BMLV, magazine TRUPPENDIENST - episode 299, issue 5/2007