that each air directing vane 44 can be independently moved as shown in fig4 a the air directing vanes 44 can be pivoted toward one another to u201c narrow u201d the air flow or as a shown in fig4 b the air directing vanes 44 can be pivoted away from one another to u201c widen u201d the air flow while fig4 a and 4b show their respective air flows as laterally directed the air directing vanes 44 can be controlled to direct the appropriately u201c narrowed u201d or u201c widened u201d air flow in a forward or aft direction as desired and in a manner consistent with that shown in fig4 fig4 c shows an embodiment in which the air control vanes 44 described above are removed and replaced by spaced apart air control vanes 44 u2032 that are pivoted or hinged along axes that are 90 u00b0 relative to those of the air control vanes 44 of fig4 the air control vanes 44 u2032 are connected by a link not shown so that they move together under the control of an actuator 46 so that the air flow can be directed down toward the ground surface horizontally relative to the ground surface or upwardly as in the case of the embodiments of fig4 a and 4b.