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One of U.S. Air Force’s new categorical imperatives after World War II was to find a way to increase the range of its generation-one fighter jets, especially in the area of bomber escort. One of the people they turned to was German engineer and aircraft designer Dr. Richard Vogt, who had come to the U.S. after the war.
Dr. Vogt was known for designing unique warplanes, including the asymmetrical Blohm & Voss BV141. One of Dr. Vogt’s ideas was to have aircraft attach themselves to the wings of other aircraft. This would extend the effective wingspan and, he hoped, extend the range in the same manner as the long narrow wings of a glider.
It would also allow the aircraft on the wing to shut down its engine and be towed to save fuel, which would be useful for escort fighters. Dr. Vogt’s concept was tested at Wright Field in 1948 using a Douglas C-47 and a small light plane, and the tests showed promise.
Republic Aviation was awarded a contract to develop the concept, which was called Project MX-1018 or Tip-Tow. The Tip-Tow mother aircraft was a specially modified Boeing B-29 with shackles on the wing tips, and two Republic F-84 Thunderjet fighters were to attach themselves there.
There were concerns about the wing-tip vortices as well as wing flexibility of the B-29 and the mechanisms for attachment, but the project continued. The first hookup of both F-84s with the B-29 took place Sept. 15, 1950.
After this, the two Thunderjets made numerous successful cycles of attachment and detachment and also shut down and restarted their engines several times under tow. The longest connected flight was two hours, 40 minutes and happened Oct. 20, 1950.
All of these flights were accomplished with the F-84s under manual control, but for long flights an automatic flight control system was required. Republic developed an automatic flight control modification that was ready for testing in March 1953, but before engaging the system a number of manual hookups were made to the system to resolve continuing electrical problems.
On April 24, 1953, the left-hand F-84 hooked up to the B-29 and activated the automatic system. The F-84 immediately flopped over onto the wing of the B-29 and both crashed with the loss of all on board. This ended the Tip-Tow project.
During this time, a B-36 bomber was being used for a similar range-extension project called Fighter Conveyer, or FICON. The bomber was carrying the swept wing version of the F-84, the F-84F. Once the FICON project was over, the B-36 became part of a variation of the Tip-Tow project called Tom-Tom.
This involved hooking up an RF-84F, the reconnaissance version of the F-84F, to the B-36. The B-36 had a retractable scissors unit on its right wing tip while RF-84F was fitted with a jaw-like connector on its left wing tip.
Unlike the Tip-Tow, Tom-Tom was more of a test of concept and to see if the formidable wingtip vortices of the B-36 could be overcome in the joining maneuver. Both aircrafts’ wing tip connection mechanisms were very light and not intended to tow the RF-84F.
The B-36 wing tip coupling mechanism incorporated adjustable rear pitch locks and a skewed hinge set at an angle. This allowed the RF-84 to roll around the wing tip and the changes in its angle of attack generated counter forces to keep it flying level with the wing of the B-36. This, in theory, eliminated the need for an electronic autopilot system.
The question was if the wingspan-to-wing ratio and the reduction in induced drag were aerodynamically efficient enough to compensate for the weight of the fighters. Although several successful hookups were performed, the heavy turbulence from the vortices streaming from the bomber’s wing tips made the maneuver extremely challenging.
Project Tom-Tom flight tests continued in 1956 with increasingly stronger wing-tip coupling mechanisms. On September 23, 1956, a test pilot hooked on to the wing tip of the B-36 with a small amount of yaw, and immediately the hooked RF-84F started to flap up and down on the wing tip.
There were no squibs, which are miniature explosive devices that can be used for shattering or propelling a variety of materials, to break the connection between the airplanes and another disaster was looming when the wing-tip coupling mechanism failed. The RF-84F was thrown free with part of the B-36 scissors mechanism stuck in the jaws on its wing tip. This ended Project Tom-Tom flight tests, but these type of range-extension efforts became obsolete because of the development of in-flight aerial refueling.
