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The second life of the S-52

By Elan Head

Published on: April 26, 2023
Estimated reading time 24 minutes, 40 seconds.

One of the first successful helicopters lives on in the Hummingbird, a fun four-place personal aircraft sold as a kit by Vertical Aviation Technologies.

In the world of helicopter aviation, flying old aircraft is nothing new. The industry has always shown a remarkable ability to stretch the useful life of aircraft decades beyond what was initially envisioned, with the result that designs originally certified in the 1960s and ’70s are still in widespread use. Typically, the death knell for a helicopter model sounds not when better technology comes along, but when scarce parts finally make it too expensive to operate.

Tucked away in a corner of Orlando Sanford International Airport in Florida, Vertical Aviation Technologies (VAT) has managed to extend the life of one helicopter model longer than most. For more than 30 years, it has been selling kits based on the Sikorsky S-52-3, a model that made its first flight in 1951. Three-quarters of a century later, the S-52 lives on as the VAT 300L Hummingbird, a four-place amateur-build helicopter that preserves the basic design and rotor system of the S-52, with a host of modern improvements.

I had been intrigued by the S-52 since 2014, when Alex Anduze, then a test pilot for Sikorsky, exhibited his fully restored model at HAI Heli-Expo in Anaheim, California. There, I learned that an S-52 had been the first helicopter to perform a documented loop, with famed Sikorsky test pilot Harold “Tommy” Thompson at the controls. Looking at Anduze’s antique, the feat seemed incredible, but Thompson’s son had the video footage to prove it.

Brad Clark designed a new nose for the Hummingbird mostly for aesthetic reasons. The composite nose is made by VAT, but the windshield is the same model used on the Bell JetRanger. Sheldon Cohen Photo

In February of this year, I finally got a proper introduction to the S-52 and its derivative when VAT founder Brad Clark invited me out to Sanford. Anduze, who now collaborates with Clark on the 300L, gave me the kind of demo flight he provides to prospective buyers, showing off a surprisingly relevant personal aircraft that would be a hoot to have in the garage.

I also scored a few precious minutes of hover time in Anduze’s restored original, the same helicopter he flew in the recent Korean War movie Devotion. The experience underscored all of the ways in which VAT has improved on the S-52 — but also just how well Sikorsky built the aircraft to begin with.

A new use for spare parts

Clark grew up around helicopters, including S-52s. His father, Fred Clark, was a U.S. Air Force veteran who founded several commercial helicopter companies, most notably Orlando Helicopter Airways (OHA) in 1964. Fred Clark used S-52s for a variety of missions, including power line patrols, passenger transport and sightseeing flights. Ultimately, Sikorsky sold him the technical data for the model and he acquired a large inventory of surplus aircraft and spare parts.

VAT founder Brad Clark, left, with test pilot Alex Anduze. The two have collaborated on a number of recent improvements to the Hummingbird. Sheldon Cohen Photo
Earlier versions of the Hummingbird had vertical winglets on the horizontal stabilizers, but those were removed as part of a flight test campaign aimed at improving handling qualities. Sheldon Cohen Photo

As the years went by, he moved into remanufacturing Sikorsky S-55 and S-58 helicopters, assisted by Brad. Among other things, he invented the S-55 Heli-Camper marketed by Winnebago, a project that was never commercially successful, but which has such enduring appeal that it resurfaces periodically online. In the 1980s, OHA was awarded a U.S. Army contract to modify the S-55 to mimic the appearance, sound and radar signature of the Soviet Mil Mi-24 attack helicopter. The five-bladed rotor system engineered for that project later became the basis for the S-55QT “Whisper Jet” that Brad Clark developed in partnership with Elling Halvorson of Papillon Airways.

All this time, OHA’s inventory of S-52 parts was sitting around, gathering dust. Eventually, Fred Clark gifted them to his son. “I’m like, ‘What am I going to do with all these brand-new S-52 parts? Nobody’s operating or flying them,’ ” Brad Clark recalled. “And that’s when I decided to develop it into a kit.”

That was the beginning of VAT, which began selling helicopter kits based on the S-52 in 1991, the same year it acquired OHA’s assets and Federal Aviation Administration repair station certification. Clark was fortunate in starting out with a large supply of hard-to-make parts, including transmissions and rotor heads, allowing him to gradually ramp up his manufacturing capabilities. Today, VAT supplies every part on the aircraft, outsourcing manufacturing work to various vendors. Clark said he has now sold more than 350 kits all over the world, none of which has yet been involved in a fatal accident.

Clark has made various modifications to the S-52 design over the years: some readily apparent, others less so. The most obvious change to the original design is in the Hummingbird’s nose, which resembles the projecting nose of a Bell JetRanger rather than the smooth round face of the S-52. But Clark has also tweaked materials and manufacturing processes on parts like the clutch cam to improve durability. The cockpit is still analog but incorporates modern instruments, and there’s an electric cyclic trim, rather than the two trim knobs awkwardly mounted on the floor of the S-52. (Neither model has hydraulic flight controls.)

Clark has iterated on the Hummingbird’s engine over the years, too. The S-52 was equipped with a 245-horsepower, six-cylinder Franklin engine, but as Anduze, who has one in his aircraft, will attest, it was always underpowered. The first Hummingbird kits used a 260-hp Lycoming VO-435; when parts for those became hard to find, Clark adapted the General Motors LS7, a car engine. But he always had a preference for a certified aviation engine and migrated back to the 300-hp Lycoming IO-540. After sourcing the model through other vendors for many years, Clark is now working directly with Lycoming.

“It’s the engine the aircraft has always wanted,” said Anduze, pointing out that the S-52 was originally conceived as having a 300-hp powerplant. “And now it finally has it.”

The $100 hamburger test flight

Anduze met Clark over a decade ago at the Sun ’n Fun Aerospace Expo in Lakeland, Florida, where Clark had his own yellow Hummingbird, N52FH, on display. “I loved the concept,” Anduze recalled. “And then I started looking for an original [S-52], just because I like vintage things.” He ended up finding one in Stockton, California, and Clark was a major source of help and guidance as he restored it.

Eventually, they realized there was an opportunity to collaborate on further enhancements to the Hummingbird, leveraging Anduze’s skills and knowledge as a graduate of the National Test Pilot School. They started with a full handling qualities evaluation of the aircraft using standard techniques. “And then we said, ‘OK, where do we work? Let’s work on this section.’ And we worked on that section, and we improved the stability,” Anduze said. “And then we wanted to get a little more power, so we worked on a cold induction system and a bigger throttle body.”

VAT continues to add features and options to the Hummingbird. Next on the list is air conditioning. Sheldon Cohen

Through this “iterative process,” he said, “we took what was already a really good helicopter and we just made it that much better.” That deep familiarity with the Hummingbird made Anduze the perfect instructor for my demo flight in N52FH, on a gusty but otherwise gorgeous Florida day. From VAT’s base in Sanford, we flew 20 miles (30 kilometers) north to DeLand Municipal Airport for lunch, then maneuvered in the local area before heading back. (Separately, we flew east to the Atlantic coast around New Smyrna Beach for a photo shoot.)

Upon climbing into the Hummingbird, I immediately noticed how roomy it is for a four-seat aircraft, which explains how the S-52 was able to carry two stacked stretchers for medevac missions during the Korean War. Anduze handled the engine start, which required some priming. He set the engine to idle at around 1,000 rpm, below the engagement level for the centrifugal clutch. That meant we were able to start warming up on the ramp without turning the rotor blades — a welcome safety feature. Once the oil temperature gauge was in the green, he rolled on throttle to continue the run-up procedure, with the blades fully engaging as engine rpm climbed through 2,000 (maximum rpm is 3,275).

With the run-up checks complete, Anduze ground taxied us away from the VAT hangar on the Hummingbird’s quadricycle landing gear. He also performed the takeoff, then handed the controls over to me in flight. With no hydraulics and a maximum gross weight of 2,800 pounds (1,270 kilograms), the Hummingbird feels fairly heavy on the controls, similar to an MD 500. But it was easy to trim out stick forces with the beep trim on the cyclic. Anduze said he and Clark tinkered extensively with the trim to fine-tune the control feel and beep rate.

The S-52 was the first American helicopter to feature all-metal rotor blades. VAT assembles the Hummingbird’s rotor blades in house. Sheldon Cohen Photo

More of a challenge for me was the manual throttle control, as it had been a long time since I had done much flying without a governor. Not surprisingly, my first impulse was to overcontrol the throttle, particularly as the main rotor system was periodically buffeted by wind gusts. But Anduze coached me out of it, pointing out that the green arc on the Hummingbird’s rotor tachometer is much wider than it is on the governed Robinson helicopters on which I had learned how to fly. Not only that, its heavy, three-bladed rotor system has more inertia than those two-bladed models, making it even more forgiving.

Although the Hummingbird lacks a governor, it does have a correlator that takes most of the throttle work out of power changes. And while I still had to consciously think about the throttle by the end of my flight, it didn’t seem like it would take more than a few hours to get comfortable with it. (Pilots of a certain age should feel free to point out that once upon a time, every helicopter pilot knew how to fly without a governor.)

Apart from the manual throttle control, the Hummingbird was easy to fly, with no real surprises. At sea level and a takeoff weight of around 2,450 pounds (1,110 kilograms), we had power to spare, and ample tail rotor authority while hovering with a 15-knot crosswind. The aircraft was maneuverable in powered flight and docile in an autorotative glide. With a never-exceed speed of 95 knots, it wasn’t very fast, but it was as comfortable as a beach cruiser.

It was while ground taxiing up to the airport restaurant in DeLand, however, that I got a real glimpse of the Hummingbird lifestyle. With wheeled landing gear and the ability to cool down the engine with the rotors stopped, the Hummingbird is about as neighborly as helicopters come. After shutting down the engine, Anduze and I pushed it a short distance into a parking spot between a two-seat experimental airplane and the restaurant’s patio, neither of which had been greatly disturbed by our rotor wash. You certainly can’t do that in a skid-equipped helicopter.

The Hummingbird has a crash resistant fuel system with a total capacity of 57 US gallons. Sheldon Cohen Photo

At the end of the day, back at the VAT hangar, Anduze graciously fired up his vintage S-52, just to give me some stick time in what he believes is the world’s oldest flying helicopter (it was originally built in 1953). The Franklin 6V6 engine took a few tries to start; it shook, rattled, and rolled a bit more than its descendant; and Anduze had to take his best guess at the proper position for the floor mounted trim knobs before picking the aircraft up into a hover. Yet, 70 years after it first left the factory, it hovered just fine. Sikorsky clearly knew how to build them.

The path to certification

VAT sells the standard Hummingbird kit for US$159,000 and the fuel-injected IO-540 engine for an additional $68,475. A “quick build” option featuring an assembled airframe is available for another $66,750. Both the standard and quick build kits satisfy the FAA’s so-called “51 percent rule” for amateur-built aircraft, which requires that the builder complete at least 51 percent of the tasks required to make the aircraft airworthy.

Alex Anduze’s restored S-52 had a starring role in the 2022 film Devotion, where it played the helicopter
sent to rescue downed Navy pilots Jesse Brown and Tom Hudner during the Korean War. Sheldon Cohen Photo

For anyone with the time and inclination to put in the sweat equity, that’s an attractive price for a four-place personal helicopter, even with the operational restrictions attached to the experimental category. But what about everyone else?

For a while, Clark was pursuing FAA certification of the Hummingbird in the primary category, which would have allowed VAT to sell already assembled aircraft to customers. That program drove some additional improvements to the helicopter, including an upgrade to a crash-resistant fuel system, as is now required by federal regulations.

However, the certification program became more burdensome than Clark had expected. Then, in 2019, he had the opportunity to acquire the original S-52 type certificate from Sikorsky. That opened the door to eventually certifying the Hummingbird as a standard category helicopter through an amended type certificate, without the limitations imposed on a primary category aircraft. So, the original certification program was abandoned.

In the Hummingbird, the Lycoming IO-540 engine is mounted at a 60-degree angle and runs at a
higher rpm than it does in some other installations. That would require Lycoming to amend the type certificate for the engine if and when the Hummingbird is certified. Sheldon Cohen Photo

Clark is not predicting a timeline for amending the S-52 type certificate, although he said that much of the necessary structural analysis and testing has already been completed. In the meantime, he emphasized that while the Hummingbird may be sold as a kit, it’s a certified aircraft at heart.

“I grew up in the commercial helicopter business and repair stations,” he said, explaining that he has always kept the quality of VAT’s production system in line with FAA requirements. Unlike some other homebuilt kits, he said, there are no automotive parts in the Hummingbird; everything meets a military standard, or mil spec. “I think the big picture is that although we’re selling it in kit form . . . it’s a real helicopter.”

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