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Tom-Tom

Dr. Richard Vogt, a German engineer who had headed the design work at Blohm und Voss during the Second World War, was brought the United States under Operation Paperclip and his first posting was with the Air Force Research Laboratory at Wright-Patterson AFB in Dayton, Ohio. While continuing his research on unorthodox aerodynamic concepts (he had designed the asymmetric wing BV 141 while at Blohm und Voss), he developed the idea of increasing the range of an aircraft by attaching free-floating wings to the wingtips of the existing aircraft.

The "wingtip coupling" concept was brought to Wright Field after World War II by two German scientists, Bernard A. Hohmann and Dr. Richard Vogt. Their unconventional theory implied that smaller aircraft could be hooked onto the wingtips of larger aircraft, thus creating an increased wing span and a more efficient wing. The scientists explained that the improvement would allow the smaller planes to be carried along with practically no drag penalty. Extra fuel tanks formed the body of the wing extensions and the aerodynamic lift from the extensions supported their weight in flight without significant structural penalty to the main aircraft. In addition, these extensions increased the wing aspect ratio, thereby reducing drag and improving the range.

This idea was eventually applied to early candidate designs for the USAF WS-110A program that eventually resulted in the North American XB-70 Valkyrie bomber. The concept first drew Air Force's attention as a means of extending the range of its new jet fighters by substituting escorting jet fighters for Vogt's free-floating wing extensions. There was a small amount of Air Force interest in the concept, and some coupling experiments were accomplished.

Project Tom-Tom was initiated to provide a weapon system for existing requirements of the Strategic Air Command. The need existed for a maneuverable fighter aircraft capable of long-range operations for either bombing or reconnaissance purposes. The Tom-Tom project, consisting of a B-36 carrier and two RR-84F parasite fighters was felt to be one answer to this need. The mission radius of the composte weapon system would be considerably greater than that of the B-36 alone. Furthermore, it would permit simultaneous attack on two targets, and provide maximum safety for the B-36 carrier by allowing it to remain outsidt the combat zone.

An additional potential advantage of Tom-Tom was the possibility of combining it with the Ficon System. This would have allowed the B-36 to tow three airplanes and would also have permitted fatigue relief for the wing-tip airplane pilots by allowing them access to the B-36 through aircraft rotation.

In November, 1954, the Strategic Air Command's requirement for this type of a system was cancelled because of the production status of newer type aircraft. The Tom-Tom project wast however, carried on from this point as a research and development type program to further explore and develop the wing-tip coupling concept.

The original intent of the Tom-Tom program was to provide the Strategic Air Command with a tactical weapon system. The over-all design objective of Project Tom-Tom was to develop a fully operational wing-tip coupling system for towing an RP-84F parasite aircraft on each wing of a B-36. This system was to be such that the parasite aircraft could shut down its engine, close its air induction system, and be automatically stabilized when mechanically coupled to the wing tip of the B-36.

The Tom-Tom single-point configuration was found to be easily controllabe at all anticipated flight conditions. Since the major hopes for the success of the project were based on the inherent stability of the skewed-axis configuration studies of it were, of necessity, considerably more involved than those on the mingle-point configuration.

The first record of an attempted wing-tip coupling was that performed in Germany at the DFS-Glider Research Station (Deutsche Forschungs - Anstalt Fuer Sigelflug) in 1944-1945. Two KL35 light airplanes of equal size were coupled in flight, wing-tip to wingtip. The two aircraft were loosely joined wing-tip to wing-tip with a long rope which pormitted routine take-off. After climbing to a safe altitude the rope was pulled in by one of the planes until the two joints at the wing tips not and locked into place. The airplanes were then able to fly in wide circles, change altitudo, etc. Both pilots experienced changing load distributions around the longitudinal axis. It was found that these could be equalized and flying the coupled aircraft did not present any special difficulties. However, the project was not further explored by the Gorman Air Ministry, apparently from lack of interest.

In 1949 and 1950, the Wright Air Development Center carried out a project to investigate the feasibility, general handling characteristics, and technique of wing-tip to wing-tip coupled flight of two airplanes. A device for coupling a C-47A and Q-14B wing-tip to wing-tip was designed and flight tested by the Aircraft Laboratory at Wright-Patterson Air Force Base with the assistance of the Experimental Fabrication Laboratory and the Flight Test Division. Initial attempts at in-flight coupling were first attempted 18 August 1949. Between that time and 3 May 1950 thirty-five flights were made, including two night flights. As the result of these flight tests, it was concluded that wing-tip to wing-tip coupling of two aircraft was feasible and should be further investigated.

A contract was awarded to the Republic Aviation Corporation in June, 1949, for the development and evaluation of in-flight towing of F-84 airplanes on the wing tips of a B-29 bomber. This Project MX1016 program was for the purpose of further investigation of the wingtip coupling concept developed by WADC. Modification of the B-29 and F-84 airplanes was preceded by stability and performance studies (Reference 39). These studies showed the system was feasible but was a highly divergent unstable system and required a means of controlling the airplane in towed flight. The first system designed consisted of a two-point suspension system, wherein the F-84 was locked to the B-29 wing at fore-and-aft location permitting the F-84 to rotate about the roll axis only. Between 21 July 1950 and 20 October 1950, thirteen flights were monitored by Republic (Reference 36). Additional flights were made by the USAF to evaluate different coupling methods and night coupling. However, the two-point suspension system had several deficiencies and the coupling technique was difficult.

At the request of the USAF, the towing system was redesigned to include an automatic control system. Redesign of the B-29 towing equipment consisted of the installation of a rear latch that restrained the F-84 in yaw only, permitting freedom in pitch and roll, and a retracting electrical wing-tip interconnector to provide electrical power from the B-29 to the F-84 for the autopilot system and auxiliary equipment. Five flights were conducted with this system, the last being on 24 April 1953, at which time an accident occurred after the aircraft were coupled and locked into position and the automatic flight control system was engaged. The F-84 airplane rolled up violently and continued on over, coming down on the wing of the B-29. Both aircraft and their crews were lost. Malfunction of the automatic flight control system was presumed to be the specific cause of this accident. The wing-tip coupling program was terminated after this accident.

Convair was first officially invited to participate in what was later known as the "Tom-Tom" project by Air Force letter dated 27 August 1952. Convair's preliminary proposal submitted 16 January 1953 was withdrawn on 13 February 1953 because in the interim an increased work load in Convair's Technical Design Section on previously committed programs made accomplishment of the engineering task impossible. After receipt of Convair's withdrawal letter AMC advised Convair that the Thieblot Aircraft Company had the capabilities for accomplishing all engineering work in connection with the project. In view of AMC's recommendation, Convair stated a willingness to participate in the program and a new proposal was submitted on 2 June 1953. This proposal was based on Thieblot's acting as subcontractor to Convair. Convair was to start flight testing on 1 February 1955.

The design, fabrication, and installation of the mock-up coupling mechanism on the left-hand wing tip of RD-36F No. 49-2707 and on the right-hand wing tip of RF-84F airplane No. 51-1848 was completed in August, 1954. The first proximity flight was held on 26 August 1954, the second on 27 August 1954, and the third and last on 29 August 1954. Results of the proximity flight tests showed RF-84F approach and flight in proximity to the RB-36 mechanism to be such that contacts and couplings to the RB-36 mechanism were considered feasible. During October, 1954, Convair issued a new schedule for the first flight. This schedule was based on completion of all engineering by Thieblot on 1 February 1955. This schedule called for flight testing to begin on 21 September 1955.

Two Convair pilots and numerous others had flown the Q-14 while attached in single-point to the wing of a C-47 airplane. The single point of attachment condition, though statically unstable, could be controlled by the pilot at all flight conditions except perhaps in severe turbulence. The first flight of the Tom-Tom RF-84F airplane, serial No. 51-1849, was made on 13 April 1956. The first flight with both the RB-36F and RF-84F Tam-Tom airplanes was made on 14 April 1956. The purpose of this flight was for RB-36F shakedown, proximity chocks, and single-point contacts. It was found that the prototype configuration performed essentially the same as did the mock-up in the proximity flight tests. Six contacts, all of short duration, were made and it appeared that the fighter would be stable and controllable in single-point.

Flight No. 12 with the receiver and yaw locks operative was accomplished on 8 June 1956. A two-point attachment was accomplished on the first attempt and the yaw and pitch locks were engaged. The RF-84F was towed for approximately 45 minutes while locked in the two-point attachment position. Oscillations, induced by mildly upsetting the RF-84F about its pitch axis damped out in one to three cycles and the RF-84F appeared very stable. At the conclusion of flight No. 12 on 8 June 1956, all work on project Tom-Tom was temporarily suspended because of depletion of funds.

The last flight, No. 18, was made on 26 September 1956. Single-point coupling was accomplished and immediately the RF-84F became unstable and uncontrollable. Yaw, pitch, and roll oscillations occurred simultaneously and increased rapidly in amplitude. A safe and uneventful landing was made by both aircraft. Post-flight investigation revealed major damage to the coupling mechanism and the wing tip structure of both the RF-84F and RB-36.

All subsequent flight testing was cancelled on Convair-Fort Worth's recommendation that the program be terminated at this time. This recommendation was based on a careful consideration of what could be gained by additional test flights versus the risk to personnel, and cost in money, time, and effort. Official termination of the flight test program was received by Letter Termination Notice dated 28 March 1957.

The complete analysis of the flight data obtained from all flights, including flight No. 18, was not finished until some months after the decision to discontinue flight testing had been made. This analysis indicated that the decision had been wise inasmuch as the single-fighter configuration exhibited neutral stability at the highest test flight speed (219 mph, IAS). Since wind tunnel tests had demonstrated that the two-fighter configuration reached instability speed much sooner than the single-fighter configuration (possibly 35 mph sooner), it seemed obvious that the Tom-Tom system as it existed could not have been made operational.