The Monstrous Helistat Flew Just About As Good As It Looked

The PA-97 Helistat was among the various vertical lift concepts that came out of Piasecki Aircraft toward the end of the 20th century, but this particular design was extra ambitious. The company slapped four Sikorsky H-34J helicopter fuselages with pusher propellers in place of their tail rotors to an aluminum framework beneath a helium-inflated blimp envelope. In this configuration, Helistat was intended to prove that combining a helicopter’s dynamic lift capabilities with the buoyancy of a blimp could provide a unique aerial heavy lift solution that was, above all else, highly economical.

Before the Helistat, though, Piasecki first started becoming a household aviation name in 1940 when Philadelphia native Frank Piasecki founded the P-V Engineering Forum with his University of Pennsylvania classmate Harold Venzie. Three years later, the group designed the single-seat single-rotor PV-2, which became the second helicopter to successfully fly in the United States, according to Piasecki’s website. 

Also during his time with the P-V Engineering Forum, Piasecki unintentionally became the PV-2’s first pilot after a tether snapped during a flight test, forcing him to briefly fly and land the helicopter. Through this happy accident, Piasecki was then able to qualify for the United States’ first helicopter pilot’s license.

After it won a Defense Department contract in 1944 to develop a twin-rotor helicopter that wasn't bogged down by the size and weight limitations of single-rotor types, P-V Engineering Forum also went on to produce the HRP-1 during World War II. The HRP-1, internally designated as PV-3, famously became known as the 'Flying Banana,' and the type greatly helped usher in the helicopter age for the U.S. military.

However, in 1955, Frank was ousted from the P-V Engineering Forum by his fellow co-owners after a falling out, which prompted him to start his own aviation company. Thus, what is now known as the Piasecki Aircraft Corporation (PiAC) was officially established in 1955 to research and develop experimental rotorcraft and compound helicopters. After having already cemented himself as a pioneer of the tandem-rotor helicopter, the aircraft created by Piasecki and PiAC went on to lay the groundwork for future well-established platforms like the CH-47 Chinook.

But that isn’t to say that the company wasn’t responsible for some wacky inventions all the same, with the Helistat being no exception. For example, the PA-59 AirGeep, a highly unconventional prototype that used two ducted horizontal rotors in tandem, was unveiled by PiAC in the late 1950s as a vertical take-off and landing concept loosely akin to a flying car. PiAC developed it specifically to meet the requirements of a U.S. Army Transportation Research Command contract for a flying jeep that was intended to be smaller and more maneuverable than a helicopter, though the aircraft never left the experimentation phase.

It wasn’t until the 1960s that PiAC began tackling the behemoth that Helistat would later become. In 1961, PiAC received a patent for what the company described as a "Helicopter Ballon Aircraft Unit," which envisioned attaching a large spherical balloon to a central framework connected to two tandem-rotor helicopters.

To achieve this, PiAC needed to establish what exactly the unit's framework would look like. In 1972, the company published a study sponsored by Naval Air Systems Command on the feasibility of a Multi-Helicopter Heavy Lift System (MHHLS) using two Sikorsky CH-53D helicopters. However, we now know the final design ended up utilizing four H-34J helicopter fuselages. According to the PiAC website, the company later designated the MHHLS concept as PA-39.

The company eventually pitched the heavy-lift balloon aircraft concept to the U.S. Forest Service in the mid 1970s. The submission was presented as a solution to the Forest Service's need for an aircraft that could lift significant loads of timber from otherwise hard-to-access areas. According to an article included in the Modern Airships series authored by aviation historian Peter Lobner, the research and development program for this logging system was dubbed Project Falcon and was spurred by the demand for wood coming from the growing population as well as an “increasing concern over the natural environment.”

Lobner went on to explain that the Forest Service wanted an aircraft that could haul 25 tons of timber for up to five miles, all while flying over steep mountainous terrain. From the outset, it looked like the PA-97 concept may have been capable of pulling that off, so the Forest Service in 1980 funded a $10.7 million contract through the Naval Air Development Center and awarded it to PiAC for the development and testing of Helistat. 

The overall program cost was projected to reach around $25 million, including construction, flight testing, and a three-year demonstration phase. Lobner wrote that, while the PA-97 was expected to help rake in millions of dollars in lumber sales once operational, PiAC also saw its potential to support sea patrol, military transport, and other construction activities, as well. 

The PA-97 prototype eventually shaped up to be 343 feet in length, 113 feet tall, and possessed a gross weight of 107,051 pounds, according to Lobner’s article. In 1981, however, what later became known as the Government Accountability Office (GAO) reviewed the program and concluded that PiAC, the Forest Service, and the Navy should take a step back and reevaluate their progress before continuing on after Helistat’s skeletal structure failed under load tests. 

After a redesign of its rigid framework to address the GAO’s concerns, as well as several static and tethered demonstrations over the following years, the PA-97 flew freely for the first time on April 26, 1986, at the Naval Air Engineering Station in Lakehurst, N.J., a locale steeped in lighter-than-air-flight history. Lobner wrote in his piece that one pilot in the left rear helicopter cockpit flew the Helistat, while flight engineers occupied the other three fuselages. 

The aircraft would independently take to the air just one final time after its inaugural flight. 

On July 1, 1986, Helistat managed to get mere feet off the ground before it suffered what was described as a "vibration-induced structural failure" that negatively affected the performance of basically every component of the aircraft. In the video of the catastrophic flight test, you can see the starboard-aft helicopter fuselage breaking from its mount on the framework because of the vibration, which causes its rotors to cut into the gas-inflated blimp envelope. 

An implosion quickly follows, as does the crashing of the remaining helicopters onto the tarmac below. Pilot Gary Oleshfski was killed in the accident, and the PA-97 program was abruptly discontinued along with the destruction of its only prototype.

As Lobner notes, while PiAC expected that PA-97 would nonetheless inspire an age of Helistat proliferation, the aircraft was the only U.S.-made type of its kind to take flight. That isn't to say that heavy-lift lighter-than-air craft and similar airships haven't since come back into vogue, at least conceptually, but none have been truly successful for the heavy-lift mission.

All told, PiAC, for all of its experimental and sometimes strange contributions to modern flight, is still a forward-looking player in the industry. This is especially true in terms of the company’s role in exploring vertical lift. For example, the X-49 experimental high-speed compound helicopter is another innovative design that Piasecki was behind, which sought to explore the ways that a helicopter's speed could be significantly increased.

Nowadays, nearly four decades after the Helistat incident, PiAC is still at it. The company continues to work on interesting projects ranging from unmanned systems to hydrogen-fueled aircraft.

Tragic outcome and unsettling outward appearance aside, Helistat was an ambitious project that tried to accomplish a capability set some are still pursuing today, and it remains one of the strangest-looking flying machines ever built.

Contact the author: Emma@thewarzone.com