ZNMF Co-Flow Jet CFJ Airfoil

Conventional aircraft have to use slats to change the aerodynamic shape of the leading edge of the wing. A thicker edge is useful during take-offs and landings because it generates maximum lift at low speeds. However, during cruise mode, a thicker edge creates drag, therefore in cruise mode; a thinner leading edge is preferred.

Unfortunately, slats pose an overhead in mechanisms and controls, which results in a weight penalty that affects the overall efficiency of the plane. To solve this problem Dr Zha has devised an ingenious method to change the aerodynamic characteristics of the airfoil without using any slats, which he calls CFJ Airfoil.

How Co-Flow Jet (CFJ) Airfoil Works

It works by pumping pressurised air from the main engines into high-pressure cavity ducts built into the wings of the plane. Pumped out at high pressure from the leading edge of the wing, the air flows over the surface to the trailing edge. Holes at the trailing edge, sucks this air back in and channels it out through a second cavity. The additional airflow over the surface has the effect of increasing lift even at low speeds.

ZNMF

Zero Net Mass Flow (ZNMF) is an area of study that is gaining wide recognition and support. If I remember my Physics correctly, CFJ airflow is described as a ZNMF because the addition of injected air at the leading edge of the wing does not add any mass to the net flow of the whole system.

The main principle behind the CFJ Airfoil is that the mixing of the main airflow and the injected airflow makes a lateral transport of energy thereby energising the wall-boundary layer. This energised boundary layer then has the effect of not only increasing lift, but also eliminating positive drag, and in fact introducing a negative drag, which behaves as thrust! This negative drag thrust is due to the low pressure caused by the suction effect at the leading edge of the wing.

Perhaps the next stage in the evolution of aircraft design will be to integrate the engines within the Airfoil cavity. The engine air intakes could then scoop some of the air through the leading edge and push some of the exhaust from the trailing edge, could that work? It is all very interesting stuff.

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