The main function of refuelling in flight is to increase the range, or increase the payload over long stage lengths.
The quest for range has brought about a steady increase in aircraft size throughout the years and it has now become apparent that a new barrier, the range barrier, is an even more formidable barrier for designers to overcome than that caused by increasing resistance with increasing speed, especially at the speed of sound.
Figure 1 shows the weight of record-holding aircraft plotted against distance, from the first flight, of 284 yards, by Orville Wright in 1903. By 1909 Bleriot heroically struggled across the English Channel, a distance of 22 miles, and this was followed in later years by the Atlantic conquest by Alcock and Brown in 1919, Lindbergh's solo Atlantic crossing of 1927, and so on to the more recent record achievements of the B29 “Pacusan Dreamboat” and the P2V-1 Neptune “Truculent Turtle.”