The Sikorsky S-55 (albeit in its heavily modified Whisper Jet form) is still working and competing with much newer models. Skip Robinson Photo
It’s always an intriguing sight to watch one of the industry’s early helicopters still working for a living and competing with much newer models, the older ship albeit usually in a substantially modified form. The helicopter I was witnessing in this instance was the Sikorsky S-55QT Whisper Jet.
Considered the first practical, large helicopter built in the United States – with decent performance from a large radial piston engine that progressed from 600 to 700 horsepower over its lifetime, and a large load-carrying cabin – the S-55/H-19 and its variants were flown by all branches of the U.S. military from the early 1950s through the 1960s. The S-55 was also sold in the civilian market for utility jobs and was the first helicopter airliner. In that airlines role, the S-55 was flown in the U.S. by Los Angeles Airways, New York Airways and Chicago Helicopter Airways, and was flown in Europe by SABENA, Belgium’s national airline (see p.124, Vertical, June-July 2010). Today, S-55s are still in use as agricultural crop sprayers and in various other utility roles.
The turbine-powered S-55T came into being in 1971, after Aviation Specialties modified the helicopter with an 840-shaft-horsepower Garrett TSE331-3U turbine engine, de-rated to 650 s.h.p., and reduced the empty weight by some 900 pounds. Obviously, the T model was a much better performer from sea level to altitude.
The Beginnings of a Whisper
The evolution to the S-55QT (quiet technology) began in the mid-1980s, when the U.S. Army requested an economical aircraft to simulate the look, noise and radar signature of the Russian Mil Mi-24 attack helicopter. Orlando Helicopter Airways Inc. (OHA) put in a bid to use the Sikorsky S-55 for this conversion, because airframes were plentiful and parts were still available from OHA’s large inventory. Due to the contract requirements for realistic simulation of the Mi-24, the original three-bladed main rotor was replaced with a new-design, five-bladed system. In the late 1980s, this Army contract was completed with 15 piston-powered S-55/Mi-24s delivered to the Army.
With the new rotor system showing a reduced noise signature over the original three-bladed Sikorsky system this meant the technology and concept potentially could be used in other applications.
At the same time, helicopter sightseeing tours were becoming more popular, but were facing noise concerns. In particular, complaints about helicopter noise over the Grand Canyon were increasing and the U.S. National Park Service put restrictions on helicopter tours, including a freeze on fleet numbers. Accordingly, development of the S-55QT Whisper Jet started in 1993 – on behalf of launch customer Papillon Airways – as a joint venture between Whisper Jet Inc. and Vertical Aviation Technology (VAT), who had purchased the assets of OHA. (Whisper Jet Inc. was founded by Papillon chair Elling Halvorson specifically for the development of the QT.)
The final design of the S-55QT Whisper Jet progressed into the late-1990s, with VAT trying to ensure it had developed the quietest medium helicopter possible. With the five-bladed main rotor having already proven its low-noise signature, VAT worked on making the engine quieter. First, the exhaust noise was reduced through the installation of a stainless steel cylindrical silencer with internal noise-absorbing material. The engine inlet plenum also got sound-absorbing material, to subdue the high-frequency sound generated by the compressor as it drew air into the engine. Finally, the engine compartment’s clamshell doors were constructed of a carbon-fiber material, allowing additional engine noise to be absorbed. The results were impressive, and resulted in an environmentally compatible, medium-lift, heli-tour aircraft.
The original S-55 main rotor blades were retained on the QT, but with the new five-blade system running at a slightly higher r.p.m. and less pitch, additional noise reduction was achieved here, too. One thing that didn’t change was the two-bladed tail rotor, which remained in the original Sikorsky design. The airframe, though, did see a unique change for the heli-tour market with the inclusion of a “glass” bottom: a non-structural opening in the belly covered by Plexiglas that allowed passengers a unique view bird’s-eye-view.
After getting U.S. Federal Aviation Administration certification in December 1999, the S-55QT started flying tours over the Grand Canyon for Papillon. Although mechanically successful, it only flew for two years. It was removed from operation because the aircraft – with the pilots being separated from the main compartment – left passengers with a less intimate tour experience than ships such as the Eurocopter AS 350 and EC 130.
Finding Other Uses
Today Kirkland, Wash., based Whisper Jet Inc., operates two S-55QTs in the lift and utility role. The other three that were originally created are currently in storage.
The company was recently contracted to use one of its Whisper Jets to replace burned power poles and powerlines, and move tools and equipment for ground crews restoring local infrastructure destroyed by the massive 2009 Station Fire that tore through the Angeles National Forest in Southern California. This fire – the largest in the modern history of Los Angeles County – consumed over 250 square miles of terrain. The S-55QT worked at elevations over 5,000 feet during the summer of 2010 and had no problem lifting maximum loads. Kevin Bruuck, a highly experienced long-line pilot, told Vertical, “The S-55QT does everything we ask of it, has plenty of power at altitude and strong tail-rotor authority.”
Bruuck said the ship was easy to get used to, due to the typical Sikorsky cockpit layout and flight characteristics, adding, “I have over 200 hours in the S-55QT and really enjoy it. With the five-bladed main rotor, it reminds me of a little Skycrane.” Commenting on the uniqueness of the old workhorse, he said, “Working up here in the mountains, we’ve had a few helicopters fly by and take second looks when they see our S-55 . . . .”
Whisper Jet’s Paul Mavrinac, a long-time Sikorsky S-64 pilot, then told us a bit more about the aircraft’s abilities: “The S-55QT is a solid performer. . . . This aircraft directly competes with the Eurocopter AS 350B2 and B3, the MBB BK-117 and the Bell 407 in lifting ability and fuel burn, but has a larger cabin.” He added, “Some people might consider the S-55QT an old helicopter, but our aircraft were completely rebuilt and zero-timed. We completely rewired the helicopters and installed many new Sikorsky parts. The S-55QT is essentially a new aircraft and flies like it’s new. At this time, our aircraft have about 600 hours on the airframe and dynamic systems and are proving to be trouble-free.”
As far as parts support goes, said Mavrinac: “We have two warehouses full of S-55 parts, many in original unopened Sikorsky boxes. We have main rotor blades and transmissions, plus thousands of other line-item parts. There are also 85 S-55 airframes still available in our inventory – if we wanted to manufacture more aircraft. Our S-55QT helicopters can run for years to come, and because of the parts supply we have, the cost of operation can be kept low. The Honeywell/Garrett TSE331-10 turbine engine has a 6,000-hour overhaul time, providing us with many years of economical use.”
When asked about the kinds of missions the QT could engage in, Mavrinac replied: “Right now we are doing powerline work, mine support, drilling/seismic support, medium construction lift jobs and have designed and built a 300-gallon internal water tank for the firefighting mission. We also have a custom-made 300-gallon FAST bucket for the fire mission, if our customer requests it. At the moment, we have four pilots and four mechanics and have support trucks for when we’re in the field.”
In regards to maintaining the S-55QT, mechanic Jim Lafevor said: “Coming from S-61s, you can see typical Sikorsky design features and thought processes. Since these are essentially new aircraft, maintenance is straightforward and easy to accomplish. The more I am around the machine the more I like it. Whisper Jet, when it developed the maintenance program, put together an in-depth inspection schedule that really gets into the details of the aircraft.” The simplicity of the design also helps: “Things are easy to get to and properly laid-out, obviously the engine is extremely easy to get to as there no need to climb anything to get to it. Overall, the helicopter is very stout and very much looks like Sikorsky overbuilt it.”
As the helicopter industry has often seen, when something is initially overbuilt it tends to have a very long life. So, with the inherent strength of its original design (which first flew in 1949) and the innovative advancements engineered by OHA and VAT in more recent times, the S-55QT Whisper Jet seems very likely to continue building on more than 60 years of success.