Monday, December 16, 2013

The Sikorsky Skycrane

Problem statement   
With many different helicopters being built over the years, constantly at the back of the manufacturers mind has been the question of efficiency and effectiveness. This paper tries to bring out the Sikorsky Skycranes effectiveness by comparing it to other helicopters in terms of performance, design and other aspects.

The Sikorsky Skycrane has been widely used in the Military and civilian fields for at least half a century since its first flight in 1962. (Taylor, 1976)  This is makes us ask the question why and this research paper holds the answers.
The research looks at prototype construction and analysis of field data for the Sikorsky Skycrane. Included are both product specifications and actual production data of the helicopter since construction of its first prototype.

The research proves that the Sikorsky Skycrane is economically efficient and reliable as compared to most other helicopters. This is attributed to the helicopters flexibility and a wide field of usage with the least additional modifications.
Usage of the Sikorsky Skycrane is definitely bound to increase. Current Property right owners of the Sikorsky, Erickson Air-Crane Company, are looking forward to putting a number of modifications on the helicopter to further improve its efficiency.

Dual turbine enginesingle rotor helicopterwith spots for 3 crew members, minimum of two, Max Takeoff MTOW is 46, 297 lbs with an empty weight of 19,798 lbs. I spent literally 3 hours searching for the HIGE and HOGE and it isnt listed in any reference I can find. I will continue my search but dont want to post late.The main rotor is a fully articulated 6 blade rotor, and the tail is a 4 bladed tail rotor. (Aviastar, nd) The CH-54 Skycrane is an American made, twin engine, single rotor, heavy lift helicopter. The Skycrane was  mostly used by the United States Army early on, but became a staple for many heavy-lift operations later on. The Sikorsky has a unique shape which has a void in the lower fuselage area and when empty resembles a dragonfly (Infoseek, 1997).

The sikorsky was designed by the Sikorsky Aircraft Company and is named after Tarhe, a Native American chief whose nickname was the crane. (Ohio History Central Page on Tarhe) The very first flight made by this type of craft was on 9 May 1962. The total number built to date is 105. However, a variant of the CH-54 Skycrane was developed from the CH-37 Mojave and is the civil version of the Sikorsky S-64.The S-64 was used for heavy lift operations by the military.

Development of and reasoning for design
The S-64 was not the first helicopter designed as a heavy lifter. This was not even the first heavy-lift model designed by Skiorsky. The rototype S-64 first flew on 9 May 1962. This flight was followed by two further examples for evaluation by the German Armed Forces. The Germans did not place an order, but the United States Army placed an initial order for six S-64A helicopters Taylor, 1976) Seven S-64E variants were built by Sikorsky for the civil market.
 The Skycrane was actually adopted from the design of the Sikorsky S-60. A characteristic feature of the S-60 was an Autopilotautopilot which ensured stable hover and was quite advanced for its time. An additional feature of the earlier model and integrated into the S-64 was a seat which allowed the co-pilot to swivel in hisher chair in a manner that allowed the S-60 to be controlled both while facing the front and the back. The two-crew of this aircraft meant that with the S-64 loaded, the co-pilot could easily monitor it (Munson, 1968)., a concept that carries over in todays work of PF(pilot flying) and PM (Pilot monitoring). This unique was of monitoring though is noteworthy.
 Examples of S-64 loads were a medical outpost, a structure among others which can well be customized to fit in the space below the S-64s backbone. The S-60 and S-64 were designed with a skeletal fuselage, and an important portion of this was the void area for transport payload (Arnold, 2007). Some other uses for the Skycrane included parachute bombs, downed-aircraft recovery, and troopcargo transport (Leishman, 2006).

Design process specific for the Sikorsky S-64 Ch-54 Skycrane
The power packer design of the S-64 was a six-blade main rotor which was powered by two 4,050 shaft horsepower (3,020 kW)   The combined powers of these two engines enable the S-64 to lift as much as 20,000 pounds (9,072 kilograms). This was a limit however for the earlier designs. With time, the designs improved given technological developments and the newer versions with added structural rigidity could lift even up to double this weight.

Other than in the S-64, other uses of the mechanism applied in making the turboshaft engine are its applications that require continuous high power outputs. Such power is often
After new variants of the S-64 were built, it is the modular design that failed the fleet one had to constantly configure and re-configure the helicopter for every different mission that was to be undertaken. It is at this time that the S-54 was overtaken by the Boeing Chinook CH-47 which is a two rotor transportcrane hybrid (Springer, Edwin, 2001).

Still making progress
Erickson, the company which currently owns the S-64s property rights, apart from supplying newly built spares and fire-fighting kit, has also developed a more modernized Automatic Flight Control System (AFCS) for the aircraft nd other optiond. These provide precision flight control which is quite useful in the helicopters operations especially in emergency or emergency situations. It is important to note that Erickson hekicopters, the owned of the Sijorsky desigb, Erickson in marketing itself do not see its helicopters as refurbished as they are sold in a pristine condition. The company has done research on an improved S-64X which, other than featuring a modernized cockpit, also has a self-test system, composite main rotor blades, new engines possibly and a new tail rotor. Ericksons engineers are also considering the development of a passenger version as a response to suggestions from emergency response agencies which have made use of their aircranes.

Limitations and abilities of this helicopter
In order to understand the limitations of the S-64, we have to look at its abilities first given its structure. It is this same structure which works to its advantage that also works to its disadvantage. The S-64 has a rotor diameter of 21.95 m (72 ft), a length of  26.97 m (88 ft 6 in) rotors turning, height of 7.75 m (25 ft 5 in), maximum take-off weight of 21,319 kg (47,000 lb), two 3579 kW (4,800 shp) Pratt  Whitney T73-P-1 turboshaft engines, a maximum speed of 109-169 kmh (105 mph), a maximum range of 370 km (230 miles), a climb rate of 1,330 ftmin (405 mmin) and a flight ceiling of 18,330 ft (5,600 m).

However, despite all the above features of the S-64 which have added so much positivism to helicopter engineering, the S-64 has, among its limitation, a service ceiling of approximately 9,000 feet. If the S-64 flies at an altitude higher than this, the more difficult it becomes for the crew to control the helicopter due to wind turbulence at such heights (Milano, 2004).

The S-64 has a maximum speed of 109 knots and a cruise speed of 91 knots. The helicopter also has a climb rate of 1,330 ft per minute which, when further converted, becomes approximately 6.75 ms. Under its almost 90-foot length is a big space. It is in this space that the S-64 can carry loads, raising them high up hence preventing pendulum effects. This in turn results to increased stability and speeds.

Production figures, numbers in service and present uses
The first flight of the prototype S-64 was on 9 May 1962. This flight was followed by two more for evaluation purposes by the German Armed Forces. However, they did not place an order. The United States Army on its part placed an initial order for six S-64A helicopters for use by its military. And to cater for the civil market, seven S-64E variants were built by Sikorsky.

The S-64s are used especially in emergency situations. Erickson, the second manufacturer of the S-64 came up with the aircrane versions of the S-64. To achieve this, over 1,350 changes were made to the S-64s airframe, instrumentation, and payload capabilities. In case of bush fires, the aircrane is fitted with a retardant tank that can hold about 10,000 liters of water. Among other uses of the aircrane version of the S-64 are the protection of civilians, lifting of heavy construction material or critical parts of a building, for instance, the masts at the top of churches. Timber harvesters also make use of the S-64s.
The Skycrane is used for logging operations, erection of long haul power transmission towers especially in inaccessible regions to lift equipment and machineries like HVAC systems to high-rise rooftops, construction i.e.  ski lifts. It is also useful for oil exploration and drilling operations.

Comparison in terms of performance with other helicopters
Here we take a look at the Chinook helicopter in order to compare and contrast the two. Chinook helicopters look totally different as compared with the Sikorsky S-64ch-54 Skycrane. While the former has two twin rotors with one at the front and the other at the rear of the aircraft, the S-64 on its part has all its rotor blades at the top of the helicopter. On the Chinook, the one at the back is approximately 18 inches higher than the one at the front. Another distinguishing factor is in terms of carriage capacity. While the Chinook carries a maximum load of 25,000 pounds only, new models of the S-64 with far better structural rigidity can carry up to twice this load (Frawley, Gerard, 2002).

When both the Chinook and the S-64 are used as personnel carriers, the former carries 33 soldiers while the latter can carry even up to 100 of them. However, in terms of speed, the Chinook has a higher speed of 180 knots, while that of the S-64 is just but about 109 knots. The Chinook is thus more versatile as compared to the S-64. This is so because Chinooks are meant to carry supplies while Sikorskys are meant for heavier loads. This explains why Chinooks are mostly used in medical evacuations, parachute drops, among others.
However, the two have similarities in that they are used for more or less the same functions. However, in terms of number, Chinooks far outnumber the S-64 that are still in use or which were ever built because in total, there are over 1,000 Chinooks all over the world. An explanation for this might be that while the Sikorsky S-64 experiences a lot of vibrations, the Chinook features alterations to its airframe structure which has actually helped minimize vibrations. When all is said and done, we still have to acknowledge the fact that the Chinook and the Sikorsky both make use of turbo shaft engines. It is these engines that give them the power to carry such heavy loads.

We can also compare the S-64 with the S-65 which was a later development. While the initial S-64s landing gears were fixed in terms of length, the S-65 features landing gears that can be lengthened and shortened via use of hydraulics. The helicopter could appear to crouch on its load, raise the load off the ground and then transport it if need be to a more preferable take-off point (The Oredigger Issue, February 16, 2009). Such a feature was not present on the initial versions of the S-64. It is with such features of the S-65 that eclipsed the S-64, hence making the former a favorite of the military.

Sikorsky had high hopes on the S-64 but was somewhat disappointed since its most loyal client, the US Army, lost interest in it. However the company used the technology behind the S-64 to build more improved helicopters. This idea became useful in the 1960 when the US Marines were seeking for a replacement of their S-56 piston-powered helicopters. The marines were offered different machines like the Heavy Helicopter Experimental HH(X) (Swanborough, Peter, 1963). which was meant for use in assault transport, personnel transport, medical evaluation functions as well as aircraft recovery. (, 2006)Boeing Vertol offered them a modified version of the Chinook. Kaman, another helicopter producing company, offered a development of the British Fairey Rotodyne compound helicopter while Sikorsky offered an upgraded version of the S-61 which would also include among other things the dynamic system of the S-64. This was to be called the S-65. After many battles, Sikorsky won the contract in 1962. Kaman lost as the British government withdrew its support from the Rotodyne program.

Skycrane Capabilities
The  S-64 was a six-blade main rotor which was powered by two 4,050shaft horsepower Pratt and Whitney JFTD12A turbine engines. The combined powers of these two engines enable the S-64 to lift as much as 20,000 pounds, making it a true giant when it came to crane operations  lifting up to twice its own weight. Over time, these power ratings improver further. Also notable of the Skycrane, it is one of the few aircraft capable of powering out of a vortex ring state. Normally, the procedure involves forward cyclic to increase airspeed and exit the vortex area, and reduction of the collective (FAA, 2001) One interesting thing about the S-64 is the recommendation to increase power to exit the conditions, which is normally not recommended. According to most texts this will worsen the vortex ring as stated previously, but certain highly powered aircraft have the excess power to power out of such a state. One such machine is the S-64 Sikorsky Skycrane without any payload mounted to the fuselage. (Cantrell)

Statistics on the S-64
The S-60, was built as a research helicopter with joint funding by the US Navy and the Sikorsky Company. The helicopter had a long tail wheel landing gear that allowed it to straddle cargoes. The S-60 also had incorporated in it an automatic stabilization system which enabled it to hover with precision via use of inputs from a side stick controller (Goebel, 2007).

During the first production of the S-60, Sikorsky encountered some problems, one of them being the unavailability of a suitable turbo shaft power plant. However, the General Electric (GE) T64 turbo shaft and the PW JT12 turbojet were then under development and were used for the task after some modifications. This did not solve the problem fully however as the GE T64 had a front power shaft while the Sikorsky required a rear one (Apostolo, 1984). The manufacturers of T64, GE, did not feel that there was enough market to justify the development of another major variant of the T64. The JT12 on its part had a shortcoming as it would require a lot of modifications to convert it into a turbo shaft. As a solution for this problem, the United Aircraft (UA), of which both Sikorsky and PW were members, took to the task of building a turbo shaft based on the technology behind the JT12 (Hitscherberg  Daley, 2000).

The evolution of the machine. 
The first S-60 was lost in a crash in April 1961, the same period during which the first S-64 was already in the manufacturing (Swanborough  Peter, 1963). The US military, having committed to jointly fund the project, had not shown as much eagerness as expected. It is at this point that the Government of West Germany decided to evaluate the S-64 and as a result bought two of them out of the three that had been built by then. The third S-64 was however retained by Sikorsky for further developmental testing.
Goebel (2010) found though that after the evaluations, the Germans did not place an order. Instead, the US Army developed interest in the machine and placed an order for 6 S64A helicopters which were later evaluated in June 1963
The evaluations in 1963 further impressed the US Army and another contract for 54 more full-production CH-54 was given to Sikorsky. (Goebel, 2007), Sometime later, another order for 37 more CH-54Bs followed. The CH-54Bs were an improvement as they incorporated better PW T73-P700 engines with 4,800 SHP each and instead of single main gear wheels, they had dual wheels as well as other structural improvements to facilitate greater lift capacity. (Goebel ,2007). The building of the CH-54Bs was under the sponsorship of the US Navy, keeping in mind a scheme to deliver Polaris strategic missiles to submarines at sea. However, the CH-54Bs did not meet the navys load targets and none of those that were produced were ever bought by the navy. However, the delivery of the last of the S-64s built for the US Army was in 1972.
Out of the 54 CH-54s purchased by the US Army, four of them were sent to Vietnam. These were YCH-54A evaluation machines. They proved quite resourceful in the delivery of heavy equipment as well as in the retrieval of downed aircraft. Other uses of the same included clearing of helicopter landing sites in forests by dropping large bombs, a mission which was initially performed by C-130 Hercules Transport helicopters.
In 1968, the S-64E was introduced by Sikorsky. This was the commercial variant equivalent to the CH-54A and 10 of such were sold for use in oil drilling, construction, logging and to fight forest fires. To date, the Skycrane is still in service for forest and civil fire-fighting. For instance, there are 17 Erickson Skycranes in the Oregon State of the US which are still in service.
Old becomes new again
Initially, Erickson, which now has manufacturing rights of the Skycrane S-64, used it for construction operations until when later focus was transferred on the helicopter itself. The company then started selling refurbished S-64s. CH-54As became S-64Es, while CH-54Bs became S-64Fs which were referred to by
Erickson as aircranes (Erickson Aircrane Company, 2004)
In the late 1960s and 70s, the Chinook superseded the Tarhe. The CH54s, which were still in service, were then withdrawn from service and transferred to the Army Reserve and National Guard. However, the withdrawal from frontline units did not mark the demise of the S-60 series since as early as 1986, 71A model Tarhes were shared among some US states which included Kansas, Georgia, Mississippi, Pennsylvania and Nevada. Twenty six surviving Bs went to Alabama, Alaska, and Connecticu (Goebel, 2007). These still serve there. The machines, however badly maintained, still are the most capable machines to the army.

The number of Tarhes built for the US Army between 1964 and 1972 stood at only 97 and on 1 February 1992, Sikorsky sold the S-64 rights to Erickson Air Crane Co., which is based at Central Point Oregon. Erickson has however so far undertaken no production (Donald, 1997). Instead, it opted to sell refurbished ones as earlier stated.  

The first three aircraft, the A models produced only five helicopters, three of which were used by the US Army at Fort Benning, Georgia for testing as well as demonstration (Goebel, 2007). The other two were evaluated by the German Armed Forces. Of the A models, six were ordered by the US Army in 1963 for field testing whether they could be used to lift heavy cargo and for mobility testing in a battle field environment. Five of them were delivered with the sixth remaining at Stratford. Later in 1969, Rowan Drilling Company Inc. of Houston Texas purchased two commercial Skycranes for use in oil explorations and oil drilling in Alask (Goebel, 2007).  Later in 1969, the US Army purchased two B model Skycranes. The primary difference in the two was the better lifting and flight performance in the B-moel. Ultimately, the A model was Sikorskys first crack at the helicopter, being general in nature, while the B was designed per US Army instructions to include design improvements on the engine, gearbox, rotor head of the helicopter and its general structure. Other specifications included hot weather operating capability and altitude performance (Harding, 1990).

Civil Use
In 1969, the FAA certification for an improved Skycrane, certified for civil use as announced as the S-64E (Daley, 2000). Like its military counterpart, the S-64 civil model was designed for heavy lifting, but for firefighting, logs, air conditioners etc instead of bombs and troops
Shortly after announcing a civil model, Sikorsky made sale of one of the first S-64s to Erickson Air Crane Company of Marysville, California in 1972 for use in, among others, heavy tasks and logging operations. Later, in 1992 Erickson purchased the type certificate from Sikorsky and began development of an improved model civil Skycrane (Leishman, 2006) now known as the Erickson Skycrane, internationally (Erickson Air Crane Company, 2004)

Current History
In 2009, Erickson Air Crane leased one S-64 to the San-Diego Gas and Electric (SDGE) for 60 days for use in fighting fires. The S-64, nicknamed helitanker was then leased to the San Diego Fire Department which then had operational control over it. Erickson Air Crane currently has a fleet of 17 S-64 air crane helicopters worldwide that have been operated in at least 16 countries since 1971. (Erickson Air Crane Company, 2004). In August 1999, Erickson made available six of its helitankers to the California Department of Forestry and the US Forest Service to be used in fighting forest fires in Northern and Central California. These are just but some of the many institutions which make use of the S-64s currently owned by Erickson. At Benton Airport in California, three air cranes have also been based in the recent past to aid in fighting fires. The airport is located at the south east of Redding California. A number of S-64s are also displayed in museums, most of which are located in the United States. This totals to 17 in number.

From the initial concepts of a helicopter by Leonardo da Vinci in 1483 to the first helicopter flight in 1907 of two feet, the helicopter has journeyed a long way . (Zuelhke, 2004).  Even the more practical helicopters that showed up in later in WWII are far eclipsed by the Skycrane as it came on the scene 20 years later. Even today, the Skycrane remains a top lifter among the heavy rotorcraft remaining in service. (Zuehlke, Jeffrey, 2004)

No comments:

Post a Comment