Re: Modifications for zero-G parabolic flights

From: (Dick King)
Date:         28 Jun 94 14:33:20 
References:   1
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In article <airliners.1994.1373@ohare.Chicago.COM>, writes:
|>  I suspect any aircraft can be used for zero-G parabolic flights; ...

Aerobatic aircraft have various features that allow them to pull negative Gs.
They use fuel injection, etc. rather than carbs with their float valves, but
one of the more interesting adaptations is that some of them have rubber
bladdars within the fuel tank, so that as fuel is consumed the bladdar just
gets smaller and all of the air enters the tank outside the bladdar.

If you don't do this then the engine might get air bubbles or even pure air as
the fuel outlet ends up above the fluid level.

Zero G is not negative G, of course, but it could become -0.001 G, at least
accidentally, and air bubbles can be a problem even at real zero G.

Deep space spacecraft are often designed to perform a large burn when they get
near the planet they're designed to explore.  The zero G fuel flow problem is
solved in one of two ways: 

  * Spin the spacecraft.

    You need to have the fuel outlet on the outermost and rearmost corner of
    the tank.  That way, the outlet is below the fluid level both before thrust
    builds up and after.

  * have a small burn of some manouvering jet before the main burn.  It doesn't
    take much to settle the fuel.