1. IN COMBINATION WITH A TRACTOR, A LOG-SKIDDING AIR PAN OF GENERALLY RECTANGULAR PLAN VIEW THAT RECEIVES POWER FROM, AND IS TOWED BY, THE TRACTOR, COMPRISING: (A) A PLENUM SHELL ENCLOSING A PLENUM CHAMBER, COMPRISING A SKIRT, WHOSE LOWER EDGE IS CLOSELY ADJACENT TO THE GROUND, AND A TOP WALL THAT IS JOINED WITHOUT LEAKAGE TO THE UPPER EDGE OF THE SKIRT, (B) A POWER-RECEIVING MEANS DELIVERING AIR UNDER PRESSURE TO SAID PLENUM CHAMBER, (C) A LOAD RAMP, UPON WHICH THE FRONT ENDS OF SKIDDED LOGS REST, THAT IS THE UPPER SURFACE OF SAID TOP WALL, SLOPES UPWARDLY FROM THE REAR END TO THE FRONT END OF THE AIR PAN, AND IS BORDERED BY SIDE BARRIERS, (D) ATTACHMENT MEANS THAT TRANSMIT TOWING LOADS OF AIR PAN AND LOGS TO SAID TRACTOR, (E) AT LEAST TWO SKIDDERS THAT ARE CAPABLE OF FUNCTIONING AS RIGID RUDDERS FOR SAID MOVING AIR PAN AND OF SUPPORTING THE REAR END OF SAID AIR PAN WHEN POWER IS NOT BEING SUPPLIED BY THE TRACTOR, EACH SKIDDER COMPRISING: (1) A GENERALLY VERTICAL RUDDER COLUMN THAT IS ATTACHED AT ITS TOP END TO THE UNDERSIDE OF SAID TOP WALL, NEAR TO THE REAR END OF SAID AIR PAN, (2) A SMOOTHLY CURVED RUDDER THAT IS ATTACHED AT ONE END TO THE UNDERSIDE OF SAID TOP WALL, FORWARDLY OF THE RUDDER COLUMN, AND IS ATTACHED, ON THE CONCAVE SIDE AND NEAR TO THE OTHER END OF SAID RUDDER, TO THE BOTTOM END OF SAID RUDDER COLUMN, WHEREBY THE CONVEX SIDE OF SAID RUDDER CONTACTS THE GROUND WHEN SAID AIR PAN IS NOT RECEIVING POWER FROM THE TRACTOR, AND (3) A SIDE BRACE THAT IS ATTACHED AT ONE END TO THE UNDERSIDE OF SAID TOP WALL, GENERALLY TRANSVERSELY OF SAID RUDDER COLUMN, AND IS ATTACHED AT THE OTHER END TO THE BOTTOM OF SAID RUDDER COLUMN.