Air University Review , January-February 1979

The Concept is not new. The idea of carrying one vehicle aloft with another began during the earliest days of powered flight. There was one basic conceptual difference in those early piggyback configurations, however. Instead of one aircraft mounted on another, the mother ship was a balloon. Several other "parasite" concepts existed during World War I, including the Fieseler Fi-103 and some drone aircraft experiments. During the mid-1920s, the British carried out a series of airship experiments with the de Havilland Hummingbird.

In the United States, at old McCook Field, Dayton, Ohio, in 1922, the concept was reintroduced with an airship once again serving as the airborne platform. The experimental work evolved around the Army's tiny Sperry Messenger biwing aircraft and was carried out by Lawrence Sperry, who volunteered to test the feasibility of hooking on to the airship. Keeping the propeller out of the airship's dangling trapeze grappling system proved to be the major operational problem during the tests. The little Messenger joined the airship by a hook that was mounted on its top wing. The hook was designed to open when a 2-mph speed differential was experienced; its supporting structure was carried forward to form a unique propeller guard. Shock absorbers were fitted to the rigid airship trapeze to ease the jolt of contact.

The first Messenger hook-up attempts were undertaken in 1924 at the Army Airship Base at Scott Field, Illinois. On the first two passes of the initial test, the 8S0-pound Messenger missed contact and then broke its propeller on the third. The tests were conducted directly over the field with just such an eventuality in mind. But in December, success was finally realized with the first solid hook-up accomplished. The airship was moving at a blazing 62 mph when the hook-up was made, and the Messenger was released within the current highway speed limit, 51 mph!

But the promising Messenger concept proved to be very short-lived, since all the tiny aircraft became surplus in 1926. Fewer than 50 of the model were built. The lone remaining example of this plane can be seen at the Air Force Museum, hanging from the ceiling on a simulated trapeze.

But the Messenger was probably not the best known of the U.S. balloon parasites. That distinction undoubtedly belongs to the Navy's Sparrow Hawk project. Officially designated the XF9C-2, the Sparrow Hawk biwingers received wide publicity in their association with the Navy dirigibles--the USS Macon and the USS Akron.

The hook-up configuration of the Sparrow Hawk was not unlike the Messenger rigging. The program was carried out during the early 1930s, but on 12 February 1935, disaster terminated the program when the USS Macon went down with the resulting destruction of three attached Sparrow Hawks. During the next few years the remaining Hawks faded into oblivion.

With that the practice of balloon-lofting aircraft seemed to become a thing of the past. Yet today--some 40 years later--the balloon concept has taken on some strange new forms. One of the strangest offshoots that has been recently studied is the so-called "Megalifter" concept, in which a lighter-than-air vehicle would serve as an airborne launcher. Only in the Megalifter concept, the hanger-on might be not only an aircraft but possibly an air-launched missile. The concept mayor may not ever materialize, but it certainly shows that the old balloon idea is not dead. Recent U.S. Air Force studies have also concerned themselves with the feasibility of balloon-lofting small pilotless strike and reconnaissance vehicles. And then another recent experiment, the concept of an aircraft-borne ballistic missile, leads into the more recent, better documented parasite concepts with the carrier vehicle being another larger aircraft.

During the 1940s, the carrier vehicle switched from balloon power to prop power, and a multitude of interesting conglomerations evolved.

Initially, the British employed the concept as a means for getting a heavily loaded seaplane airborne. The mother flying boat, the Maia, carried a smaller seaplane, the Mercury, on a pylon. The first separation flight was accomplished in 1938. Then, in July of that year, the strange twosome flew nonstop from Ireland to Montreal.

The two four-engine aircraft made numerous composite flights with separations, including one 6000-mile flight--a record distance for seaplanes that still stands today.

Maia and Mercury were operating between Southampton and Alexandria, Egypt, when World War II began. Mercury was scrapped in 1941 after serving with a Dutch seaplane squadron attached to the Royal Air Force. Maia was destroyed by a Luftwaffe bomb in May 1941.

The idea and realization of a need for aircraft-borne fighters probably came about early in World War II when B-17s had to traverse a major portion of Axis bombing missions unescorted. P-51s and P-47s with drop tanks eventually solved this problem, but with new bombers on the drawing boards, the worry about fighter defense intensified. Project MX-472, called the "unconventional fighter," occurred in December 1942. But the fighter that was to evolve from MX-472 would never see the fire of combat.

Some six years later the first parasite fighter, the bulbous XF-85, would take shape. The McDonnell aircraft was powered by a 3000-pound thrust J-34 turbojet with fuel enough for about a half hour's flight time. The squatty Goblin sported eight control surfaces, including two drooping front wings and six tail surfaces. Only two prototypes were built, with the initial air launch taking place in 1948 from a B-29 mother ship.

The initial attempt at hooking up with the B-29 proved unsuccessful as the XF-85 fought the resistance of the air being compressed between the two aircraft, although later tests proved moderately successful. But the concept was losing favor with the Air Force. Even a McDonnell proposal for a Mach .9 version with alternative delta and swept wings failed to generate any interest. Shortly thereafter, the XF-85 program was terminated with only 2 hours 19 minutes of flight time accumulated between both aircraft.

Probably the next attempt at parasiting occurred in the late 1940s, when a so-called "wingtip coupling" concept was introduced. The idea 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. There was a small amount of Air Force interest in the concept, and some coupling experiments were accomplished.

The Germans in World War II evolved some interesting mutations of the piggyback concept. The best known concept involved the use of an unmanned Junkers Ju-88 twin-engined bomber loaded with explosives. Mounted on struts above, and attached to the Ju-88, was a Messerschmitt Me-109 fighter. The pilot of the fighter controlled both the joined ~aircraft and, when near the target, cut the Ju-88 loose and guided the bomb-laden bomber to the target. The innovative Germans also investigated integrating an Me-109 above a DFS-230 Troop Glider.

The piggyback concept was used in a test function by the French at the end of World War II. The purpose of the test setup was to acquire the necessary speed to fire the piggyback vehicle's ramjet engine. The test program lasted into the early 1950s, when it was abandoned because of the lack of official support.

The last dual concept actually to fly carried the acronym "FICON," for fighter conveyer, and was experimented with during the early 1950s. FICON was a unique way of integrating the intercontinental range of the 8-36 with the then high-performance capability of the F-84 Thunderjet. The initial design of the concept looked extremely promising so 25 modified F-84s were ordered. The planes sported a modified horizontal stabilizer and a special hook-up mounting forward of the canopy. This arrangement allowed the F-84 parasite to be retrieved and retracted into the bomb bay of the B-36.

The modified F-84s assumed an operational status at Larson AFB, Washington, to become the only FICON squadron in the Air Force. Regular operations using the modified F-84s commenced in early 1956, but almost immediately a series of hook-up problems caused cessation of the operations and termination of the concept. The special FICON equipment was removed, and the. Thunderjets were converted back to their original configuration.

Today, after a stand-down of more than two decades, the parasite concept may be coming back again in the 1970s. The wind tunnels at Arnold Engineering Development Center, Tennessee, during 1974, tested a tiny fighter design coined the "microfighter." The tests concentrated on new shapes and configurations for a small air-launched, air-recoverable fighter aircraft. Several different body-canard-tail combinations were examined. A number of the aircraft could have been carried and launched from a wide-body transport of the C-5 or 747 class.

And now the old piggyback mode has made one more appearance. First, it was the balloon era, then the aviation era, and now the space age. With the advent of the space shuttle, the piggyback concept was again called on for what may be the final time. The unpowered space shuttle orbiter was carried aloft from a perch atop a specially modified Boeing 747. Following a 747 pitch-down maneuver, the orbiter was released for a series of free-flight landings onto the Edwards Air Force Base rock-hard sand.

The old two-for-one game had still proved it could get the job done!

William G. Holder (B.S., Purdue University) has been an aerospace engineer for the last 12 years at Hq Foreign Technology Division, Air Force Systems Command, Wright-Patterson AFB, Ohio. He previously worked for the Boeing Company on the Bomarc and Saturn V programs and served as an air defense guided missile officer in the U.S. Army. Mr. Holder is an active free-lance writer, with five books and numerous articles to his credit, and a frequent contributor to Air University Review.

Disclaimer

The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.

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