CoolIP index                                                          Most recent edit: Wednesday October 24, 2012

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Parafoil Air-Mass Inertial Dynamic

The air in an average living-room has a mass of about 50kg. Such air is effectively "weightless" and its mass grows at the cube of characteristic dimension. A large parafoil can contain many times this amount of air.

The great Peter Lynn Sr. has noted internal air-mass effects in parafoil scaling, since higher inertia must be countered by available actuation. If a giant soft wing dives at speed, it may not be stoppable before surface impact, due to mass/inertia. One can easily feel inertial effects grow with the size of the sport parafoil flown. All this is analogous to large ship handling.

In AWE we begin to see uses for high inertia. Flywheel inertia is a well-established mechanical principal in our ground workcells. An orbiting parafoil can also exploit the flywheel effect it is big enough (and supported from behind by a suitable pilot-lifter). The higher kite-looping inertia cyclically interferes with the heavier-than-air kite "gravity mass". This proportionally boosts the amplitude of a pumping power-cycle. Enhanced mass effects may be a key to practical phased harmonics of wing arrays.

As we ponder AWES applications of air mass/inertia, new questions emerge. For example, can a giant streamlined air bag serve as a basic reaction mass to create "solid" harmonic nodes in airborne lattice? Is there a significant "air-mass hammer" boost to "high-frequency" varidrogues?

  • CoolIP*                 ~Dave Santos                 13 October 2012            AWES7488

Comment and development of this topic will be occurring here.       
All, send notes, drawings, and photographs!

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    • Compare against the parafoil wing the flattish single membrane Revolution kite that does not "carry" air mass during flight or during its flight figures.     ~JpF  13 October 2012
    • The late, great Paul MacCready was fond of pointing out that the air inside a conventional tractor-trailer used to transport the broken-down Gossamer Aircraft was heavier than the aircraft itself. The very low roll rate of Human Powered Aircraft, which requires a return to wing-warping as used by the Wright Bros. instead of ailerons, is attributed to the hundreds of pounds of air that becomes entrained above and below the wings.       ~ Bob Stuart        13 October 2012
    • Notes on Bob and Joe's posts-

      -An unstalled wing does not carry along much air outside of itself. It mostly just passes thru the air, leaving it behind, so there is little external air-mass intertia in the direction of travel to add to the wings inherent mass.

      -LEI kites weigh more with less internal volume and have more drag than equivalent parafoils, so they do not show such a pronounced Air-Mass effect. They do not scale as well and progressively lose stiffness relative to velocity. Parafoils act in the opposite way, stiffening with velocity. That's why the original post ignored LEIs.

      -The human powered aircraft roll-rate is limited more by direct aero loads (pressure difference above and below the wing) than air-mass inertial loads, especially at such slow speeds. It could roll much faster with a higher flight speed, and if its long wings were not so flimsy, and if its control design was aerobatically driven. In such a case, entrained air-mass would be more, even as the roll rate improved.   
      ~DaveS  3 October 2012

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