In all "Zveno" configurations, all aircraft were piloted and all had their engines running — it was expected that the combined thrust would more than offset the weight and actually improve the performance of the mothership compared to conventional bombers. The fighters were rigidly attached via pyramid-shaped metal frames, with both latches controlled by the fighter pilots. (On Zveno-1, the front latches were controlled by the bomber crew, while the back latch was controlled by the pilot; this was changed to all-pilot control in the next version). The original design included umbilical fuel lines which permitted the fighters to use fuel from the bomber while attached, although this was not fully implemented in practice.