| Low-g Condition |
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Information AboutLow-g Condition |
| CATEGORIES ABOUT LOW-G CONDITION | |
| aerodynamics | |
| gravity | |
| aviation terminology | |
| aviation risks | |
| spaceflight | |
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Low-G condition is a phase of aerodynamic Flight where the airframe is temporarily unloaded. The pilot - and the airframe - feels little or no Gravity because the aircraft is in Free-fall or decelerating vertically at the top of a climb. It may also occur during some horizontal turning maneuvers. This can have a disastrous effect on the aircraft, particularly in the case of helicopters, some of which need to 'feel' gravity all the time. Most smaller airplanes and all gliders have no problems with 0g conditions and it is a lot of fun to have zero gravity in the cockpit. To produce 0g the aircraft has to follow a ballistic flight path, an upside down parabola. This is the single method to simulate zero gravity for humans on earth. Thus, every space agency uses modified passenger jets (esp. stronger engines) to do this. The ESA uses an Airbus A300. One upside down parabola simulates 0g for about 25s, in the following normal parabola the aircraft is loaded with 2g. EFFECT ON HELICOPTERS Helicopters with semi-rigid rotors, for example, the two-bladed design seen on Robinson and some other light helicopters, must not be subjected to a low-G condition. Otherwise their Rotors may move beyond the normal limits in a condition known as 'mast Bumping' which can cause the rotor to droop and shear the mast and hence detach the whole system from the aircraft. This effect was first discovered when many accidents with Bell UH-1 and Apache AH occurred. These helicopters just crashed without any obvious cause. Later, it was found out that it mostly happened during low terrain following flight while passing a ridge and initiating a dive from the previous climb. Articulated and rigid rotor systems do not loose controlling forces up to 0g, but may encounter this depending on their flapping hinge offset from the mast. However, dangerous situations, as with a teetering rotor, may not occur. EFFECT ON FIXED-WING AIRCRAFT Low-G conditions can also affect fixed-wing aircraft by disrupting the airflow over the wings, making them difficult or impossible to control via the aerodynamic surfaces. The controllability of an airplane by the control surfaces only depends on airspeed. So if one keeps airspeed one has perfect control. Usually the controllability is even increased, because there is no need to produce lift. However, despite increased lift, G-forces will hinder aerobatic flight as velocity increases making the compromise between speed and g-forces a must. 0g forces are usually not a problem for fixed wing aircraft, but there are exceptions. Exceptions are- airplanes with gravity-fed fuel systems, and airplanes with low airspeed. An airplane with low airspeed at 0g's will stall until airspeed is recovered. |
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