Aerial refueling allows aircraft engines to receive fuel while in flight and today is common for many large air forces. It is the equivalent of refueling your car by connecting it to a tanker truck while driving down the highway at high speed.
In 1917, a pilot in the Imperial Russian Navy, Alexander P. de Seversky, proposed increasing the range of combat aircraft by refueling them in flight. De Seversky soon emigrated to the United States and became an engineer in the War Department. He applied for and received the first patent for air-to-air refueling in 1921.
The first actual transfer of fuel from one aircraft to another was little more than a stunt. On November 12, 1921, wingwalker Wesley May climbed from a Lincoln Standard to a Curtiss JN-4 airplane with a can of fuel strapped to his back. When he reached the JN-4, he poured the fuel into its gas tank. Needless to say, this was not the most practical way of refueling an airplane in flight.
Wesley May can be seen climbing from the Lincoln Standard (lower left) to the Curtiss Jenny (upper right) — the rectangular fuel can can be seen strapped to his back as he dangles from the bottom of the Jenny’s lower left wing. (Photo credit: Peter M. Bowers Collection, Seattle Museum of Flight)
In 1923, the U.S. Army undertook tests at Rockwell Field, San Diego, California, to test a more practical way to lower a hose from one airplane to refuel another in flight. In its tests, a DH-4B biplane outfitted as a tanker and equipped with a 50-foot (15-meter) length of hose and a quick-acting shutoff valve would fly above the receiver and lower the hose. The person in the rear seat of the receiver aircraft would grab the hose and connect it to the aircraft. If the hose became detached, the valve would immediately cut off the flow, preventing it from spraying fuel over the receiving aircraft and its pilot.
The first flight was made on April 20, 1923. The aircraft remained attached for 40 minutes but intentionally passed no fuel. The equipment was tested over the next several months with numerous fuel transfers. On June 27, the pilots made an attempt on the aircraft flying endurance record. By August 27, using this technique, one of the DH-4Bs established 14 world records with a flight lasting more than 37 hours.
Capt. Lowell Smith and Lt. John P. Richter receiving the first mid-air refueling on June 27, 1923. The DH-4B biplane remained aloft over the skies of Rockwell Field in San Diego, California, for 37 hours. (Photo credit: USAF)
This achievement prompted many private pilots to attempt aerial (or in-flight) refueling, primarily to establish long duration flying records. By June 1930, the record surpassed 553 hours in flight (requiring 223 refueling contacts). In July, the record was 647.5 hours in the Curtiss Robin monoplane Greater St. Louis early 27 days in the air. Pilots lived in the noisy, cramped, smelly confines of their airplanes for weeks at a time without ever touching the ground, occasionally climbing out on special scaffolding to service the engines in flight.
In-flight refueling of the aircraft Curtiss Robin.
Despite all this activity, the technology for aerial refueling had not advanced significantly and pilots still used the clumsy and dangerous dangling-hose method. In 1930, a Royal Air Force (RAF) squadron leader, Richard L.R. Atcherly, developed a safer and simpler method, called the looped hose method. In this method, the receiving aircraft trailed a long horizontal line with a grapnel at the end. The tanker trailed a weighted line and approached the receiver from behind and to one side. It then crossed to the other side, causing the two lines to cross and touch. The receiver aircraft then hauled in the lines and the hose from the tanker. The RAF continued to refine this system, including adding a drogue to the hose that created drag and assisted in unwheeling the hose in flight. (A drogue is a special type of parachute that, in this instance, was used to ensure that the hose trailed behind the airplane and did not flop around.)
From such humble beginnings, aerial refueling has become the key enabling factor of military air power. Without it, the ability to hit targets anywhere in the world would be nearly impossible. Another key benefit of aerial refueling is that fighter-bombers are able to take off with heavier loads and far less fuel, by then “tanking up” once at altitude. This way, modern aircraft can take off with weapons loads that far exceed what was once possible. Likewise, cargo aircraft can lift off with extraordinary loads and tank up while en route — for every pound of fuel that can be saved at take off, more cargo or weapons can be lifted off into the air.