Piggyback Airplanes

Hitchhiker: Bristol Scout C
Mothership: Felixstowe Porte Baby flying boat
England, 1916

The single-seat Bristol Scout C was a screamer. At the outset of World War I, it was one of the fastest airplanes available, reaching a top speed of nearly 100 mph. The Scout’s light weight and agility made it an especially effective fighter. It had one frustrating fault: the underpowered 80-horsepower Le Rhône engine could last only about two hours in the air without maintenance.

As an experiment, British aviation entrepreneurs mated the Scout with an oversized hulk of an airplane called the Felixstowe Porte Baby. The idea to use a longer-range aircraft (the Porte Baby performed oversea operations between England and the rest of Europe, but its top speed was a plodding 78 mph) as a host for a speedy, shorter-range one was a first in aviation.

In the spring of 1916, in the county of Essex, England, a Scout was loaded onto the upper wings of the Porte Baby. The smaller airplane’s fuselage rested flat on the wing, with its wheels hanging over the front edge, propped up by crutches braced on the Porte Baby’s central engine. The Scout pilot controlled the quick-release mechanism that held its tail.

The airplanes took off with designer Commander John C. Porte piloting his eponymous mothership and Flight Sub-Lieutenant M.J. Day in the Scout. At 1,000 feet, Day fired up the Scout engine, released the aircraft, and flew away. If successful, the little fighter could have hitched a ride to protect the slower, more vulnerable Porte Baby on reconnaissance missions in which it might encounter enemy fire.

For unknown reasons, the Scout–Porte Baby pairing was flown only once, but the first host-parasite mission launched an era of experimentation that continues to this day.

Hitchhiker: Republic F-84 Thunderjet
Mothership: Boeing B-29 Superfortress United States, 1950

World War II “triple ace” fighter pilot Clarence E. “Bud” Anderson was no stranger to dangerous missions, and he wasn’t going to let the end of the war put a stop to his risk-taking. Anderson became a test pilot and took part in a highly unusual project to connect airplanes in flight.

Mothership-parasite attachments had taken many forms since the Bristol Scout was propped on crutches 35 years earlier, and now the U.S. military was testing a new, aerodynamic concept: a wingtip-to-wingtip configuration with the code name Tip Tow.

The idea came from German aircraft designer Richard Vogt, who came to the United States after World War II with a vision to gain something for nothing. He surmised that by attaching temporary fuel panels to the wingtips, an aircraft could achieve increased range for “free,” since the panels providing extra fuel would create their own lift, and the extended spar would reduce the induced drag and create a more efficient wing.

The U.S. Air Force was intrigued, but modified the idea to carry bomber-escort fighters for “free.” They designated the F-84 and the B-29 as the two airplanes for the job, with the ordinarily short-range fighter hitching a ride into faraway enemy territory alongside the bomber.

These craft were not the first to couple via wingtips: The Germans were experimenting in secret with the concept at the end of the war, but left little documentation. When the Americans considered the idea in 1947, they sent Anderson to test the concept with the Culver Q-14 target drone and a piloted Douglas C-47. Maneuvering the simple ring-and-hook coupling system “was like trying to thread a needle in the middle of a fire hose,” wrote Anderson in a 1979 article for the Society of Experimental Test Pilots. After some adjustments, the aircraft pair proved that wingtip coupling could be done, and beginning in 1950, tests proceeded with the F-84 and B-29.

Because the F-84 could take off and land on its own, the hookups were made in-air by a torpedo-shaped lance mounted to one of the fighter’s wings. Making the connection, says Anderson, required precision similar to inflight refueling using the probe-and-drogue system. The F-84 pilot had to insert the lance into an opening approximately one foot in diameter on the B-29’s coupler, which was on a retractable boom 19 inches off the end of its wingtip. Once inserted, the boom pulled the wingtips together into a rubber seal.

Throughout testing, the Tip Tow pilots completed 43 couplings and 15 hours of linked flight, with the longest dual-coupled flight lasting just over two hours. Tests showed that the induced drag reduction of the coupled airplanes, at higher gross weights and lower airspeeds, made them more efficient than a single B-29.

The connection wasn’t always graceful, and the pilot needed to control the F-84’s movement around the connection axis—the “rotation around the wing-tips like a hinge,” Anderson describes in an e-mail. “If it was not controlled properly, it could be dangerous for certain since [the connection] was locked and there was some structural bending going on in the bomber wing structure.”

The coupling mechanism was continually tweaked. At one point it included an automatic flight control system to find the proper damping frequencies that would hold the F-84 at the correct angle, but experiments proved deadly: One coupled F-84 and B-29 crashed when the system was activated and pitched the fighter onto the bomber’s wing. There were no survivors, and Tip Tow was cancelled.

Hitchhiker: de Havilland D.H.53 Humming Bird
Mothership: R33 airship
England, 1923

Royal Air Force pilot Rollo Haig was not a man to shy away from a challenge, which is likely how he found himself a few thousand feet in the air, descending a ladder from a dirigible into the cockpit of a small monoplane.

Once in the tiny cockpit of the de Havilland D.H.53 Humming Bird, Haig pulled a lever that released the airplane from the bottom of the R33 airship. As the Humming Bird went into a dive over Pulham, England, Haig fired up the engine and leveled off.

The D.H.53 was originally built as an entrant to the 1923 Motor Gliding Competition, sponsored by the Daily Mail newspaper. It didn’t win, but its aerobatic potential caught the attention of the RAF, which was looking for a way to protect its airships from enemy fighters. The service modified two Humming Birds to work in tandem with the R33.

It was a perfect early October day. Launching the Humming Bird was easy compared to Haig’s real mission: to become the first parasite pilot to reattach to the host ship.

The Humming Bird’s fuselage attached under the R33’s keel via a complex gantry, which onlookers compared to a trapeze. Re-connecting proved a challenge. As Haig maneuvered the Humming Bird into position to snag the trapeze, his propeller hit some of the trapeze wires and the apparatus broke. He managed to attach, but because of the damage, he was forced to release again and land on his own.

Later attempts over the next few months were more successful, but when testing resumed in 1926, the RAF decided to replace the D.H.53 with the more powerful Gloster Grebe.

One of the Humming Bird’s biggest drawbacks was its engine, explains Don Goodsell, a former de Havilland employee who helped restore a Humming Bird to flightworthy condition. “The Daily Mail played a part in encouraging ‘air-mindedness,’ [so] one of the rules limited engine capacity to 750 cc, the size [for] a touring motorcycle, to encourage entrants to use an engine that people could afford,” Goodsell says.

Because of its feeble engines, “It was never much more than a curiosity.... As long as the engine was working, [the Humming Bird] was easy to control. But it was impractical.

“The D.H.53 was one of de Havilland’s few less successful ventures,” he adds, but it did help spawn the company’s more popular Moth series. “They realized there was a market for light planes.”

The Humming Bird, nevertheless, goes down in history as the first parasite to detach from and re-attach to its mothership in mid-air.

Hitchhiker: F9C Sparrowhawk
Mothership: USS Akron and Macon airships
United States, 1930

The sharp-looking Curtiss F9C Sparrowhawk fighter wasn’t the first choice as a parasite for experiments on the U.S. Navy’s new helium airship, the USS Akron, but its 25.5-foot wingspan made it the only aircraft that could fit though the dirigible’s hangar door.

Modified Sparrowhawk F9C-2 models started testing with the Akron in June 1932 to prove the airship’s use as a flying aircraft carrier. When the tiny Sparrowhawk flew alongside the 785-foot Akron, it looked like a minnow swimming next to a whale.

The fighter parasites launched from the dirigible’s hangar in mid-air, then re-attached by speeding up alongside the airship and catching a trapeze-type bar dropped from its belly. Once attached, a hook would engage and the pilot would wait to be pulled up. In some tests, the Sparrowhawk’s landing gear was removed and replaced with an extra fuel tank to extend its reach.

The tests came to a halt after disaster struck the motherships: The Akron was lost in a storm in 1933, and two years later, its counterpart, the Macon, crashed off California. Five Sparrowhawks went down with the ships, and the remaining orphans were put into utility operations. The accidents also marked the end of the Navy’s rigid-airship program.

The last dry Sparrowhawk—a few remain intact inside the sunken Macon—is on display at the National Air and Space Museum’s Steven F. Udvar-Hazy Center in northern Virginia.

Hitchhiker: Messerschmitt Me 328
Mothership: Dornier Do 217E Germany, 1941

It was the midst of World War II, and the Nazi Luftwaffe had a secret: P.1079—code for the Messerschmitt Me 328 parasite guard bombers.

According to Hans Ebert’s book on Willy Messerschmitt, the aviation designer submitted plans for the aircraft to Germany’s ministry of aviation, claiming Adolf Hitler told him, “If we had 200 bombers capable of day-time targeted bombing raids, England would already be finished.” The Messerschmitt corporation received a contract for three variations of the Me 328, and started work on them in September 1941.

However, it probably would have been best for the Germans if the Me 328 had remained a secret. Design flaws and dwindling war resources left the airplane an embarrassing footnote to the Luftwaffe effort.

The single-seat Me 328s were budget aircraft based on glider designs. They were built mainly of wood and rang up at only a quarter of the cost of conventional fighters—about 2,000 Reichmarks, or $800 at the time.

The Me 328 needed help getting off the ground, so the Germans mounted the 22-foot fighter atop the more powerful Dornier Do 217E, resting it squarely above the wing section, with tubular metal structures propping up the smaller airplane’s wings and tail.

One variation of the parasite used two Argus AS 014 pulse-jet engines, which could propel it up to 572 mph. “One of the significant lessons learned with the Me 328: A pulse-jet engine is not optimal for an airplane because of the intense vibrations,” says Hans Holzer, the curator of aeronautics for Deutsches Museum in Munich, Germany.

The engine was its ultimate undoing: Two Me 328A’s went down during testing, when their wooden frames could not withstand the noise and vibrations. Engineers tried to solve the problem by mounting the engines underneath the airplane’s wings, but the vibration troubles persisted.

Though original plans called for building 1,000, the airplanes did not make it into production, nor did any see action. The project was suspended in 1944, though planning continued for new variations at Hitler’s request.

Hitchhikers: Tupolev I-4, Polikarpov I-16
Motherships: Tupolev TB-1, TB-3
Soviet Union, 1930s

By the 1930s, the Soviets were coming around to the idea of using parasites for combat. Zveno (“Link”) was an experimental program that combined bombers with air-launched fighters to increase range and payloads.

The I-4 fighter was the first little airplane to emerge from A.N. Tupolev’s aeronautical design company, known for its fleet of plus-size types. The I-4 didn’t get attention for its size, though; the aircraft was the Soviet Union’s first all-metal fighter.

Two slightly modified I-4s, outfitted with three connector clips and a release mechanism, were rolled up wooden ramps to the wings of a Tupolev TB-1 bomber. On Zveno-1’s maiden flight, the two I-4s launched, but not, as planned, simultaneously. The error proved the TB-1 would remain stable in the air, even with a weight imbalance. The project was considered a success, and though the I-4 remained in service until 1933, it did not fly as a parasite in combat.

That duty was given to the most successful experiment, the Zveno-SPB (Russian acronym for “composite dive bomber”). After it saw combat, the small, beefy Polikarpov I-16 earned Soviet aircraft designers a reputation for ingenuity, though its nickname was less than dignified: “donkey”—a play on the Russian pronunciation of “I-16.”

The barrel-chested donkey was the Soviets’ first cantilever-wing monoplane fighter, and the first to have retractable landing gear. Its design showed creativity in a time when much of Soviet technology involved copycat production.

The I-16 could carry two bombs while attached underwing to a Tupolev TB-3, a more powerful bomber than its TB-1 predecessor. The TB-3’s four engines and each I-16 single engine worked together, and the I-16s drew fuel from the TB-3 while connected.

The Zveno-SPB was used in combat between 1936 and 1941 and flew several successful missions against German forces in Romania’s Black Sea ports. In 29 missions, only three I-16s were lost.

Hitchhiker: Lockheed D-21 drone
Mothership: Lockheed M-21
United States, 1966

As the cold war escalated in the early 1960s, so did the spying game. Speed, stealth, and zero casualties were the primary objectives when Lockheed’s Skunk Works began work on the D-21 unmanned aerial vehicle (UAV) under the name Tagboard.

This highly classified, 43-foot-long, syringe-like drone had anti-radar coating and could fly reconnaissance missions up to 80,000 feet, at Mach 3-plus and out to 3,000 miles.

The D-21 was mounted on the top, tail-end of its M-21 mothership (fittingly, their designations were for “daughter” and “mother”), a variation on the A-12 spyplane. Launching the drone was a tricky maneuver that required igniting the D-21’s ramjet engine and threading it between the M-21’s twin tails.

After surveying enemy territory, the D-21 returned to a pre-determined, over-water location, slowed to Mach 1.6, and ejected its high-resolution camera to be retrieved in-air or plucked from the water. With its mission complete, the D-21 would be destroyed by remote command.

Tagboard’s life was brief, however: Full testing started and stopped in 1966. The first three launches succeeded. In the fourth flight, the drone collided with the M-21, shearing off parts of the right wing, rudder, and engine. The two crew members ejected into the ocean, and one drowned.

Lockheed immediately scrapped the project, but pursued a variation by modifying the drone into the D-21B, which used a solid rocket booster and was drop-launched from the larger Boeing B-52H. The new pairing barely outlived the first. Each of its four flights to spy on China’s Lop Nor nuclear test site failed: The drone crashed once in Russia and once in China, and the two times it completed the flight, the camera payloads were lost at sea. The program was axed.

Hitchhiker: Ryan Firebee drone
Mothership: Lockheed DC-130 Hercules
United States, 1960s

“As it got more dangerous up in North Vietnam for the U-2, we took over, but because our missions were classified, they got all the credit,” explains then-Captain Robert McBratney, a retired Lockheed DC-130 navigator. His crew, part of the U.S. Air Force 99th Strategic Reconnaissance Wing, flew highly classified missions that laid the groundwork for the panoply of unmanned spy aircraft the military relies on today.

Eight days after Captain Francis Gary Powers was shot down in his U-2 over the Soviet Union in 1960, the Air Force approached Ryan Aeronautical Company, which in the early 1950s had designed a target drone called the Firebee, and offered the company $200,000 to turn the aerial target into a series of speedy, stealthy unmanned reconnaissance vehicles.

The Special Purpose Aircraft (SPA), as the Air Force called them then, flew approximately 3,500 missions over Vietnam to photograph high-priority targets, from airfields to secret prisons, with powerful cameras. The DC-130 Hercules was their mothership, modified with pylons underneath each wing to launch multiple Ryan SPAs. Powerful turbojet engines blasted the drones to their targets at near-supersonic speeds.

Ryan designed wire screens to cover the jet intakes, and added radar jammers, anti-radar paint, and blankets on the fuselage to further hide the small vehicle. This pre-stealth precaution was especially important to the drones, since not only were they flying behind enemy lines, they were flying solo.

“They had no cover,” remembers Major John Dale, a DC-130 pilot stationed in Bien Hoa. “No one else was flying up there, nobody—no fighters, no bombers, just drones. That’s why we had 19 MiGs after us at one time. People don’t understand the magnitude of that. Manned aircraft were getting shot down all over the place, while the tiny drones were flying successful missions one after another.”

If the drone was spotted, operators aboard the DC-130 could take over and guide it by hand. For instance, on January 6, 1973, a DC-130 crew launched a Ryan Buffalo Hunter drone over the Gulf of Tonkin; within five minutes, multiple MiG-21s were positioned to attack. Dale found a previously classified report that recounted: “During the repeated attacks which took place, the drone was hand flown to cover its assigned targets in the Hanoi area…employing recently developed drone evasive tactics”—all while the mothership was safely flying in a pattern over the gulf. The MiGs aggressively pursued the drone all the way to Laos, but didn’t get a single shot in; meanwhile, the drone gathered intelligence from all nine of its targets, including two airfields and three surface-to-air missile sites.

The success of the Firebee family was due to its simplicity and reliability, says aerospace historian Richard Hallion. “Firebee was a critically important step towards introducing practical, high-performance, remotely piloted aircraft into operational service,” he says.

Their greatest achievement, according to the crews that operated them, was that they “saved lives by taking pictures over high-danger targets, rather than losing” U.S. pilots in spyplanes, says McBratney. Dale sums up his experience as a drone crew member: “Here I am getting recon of an enemy airfield and drinking a cup of coffee.” Sound familiar, Predator pilots?