January 9, 2014 by Tim McAdams
The flight characteristics of a helicopter make it suitable for a variety of interesting missions. One such job is the repair of live high voltage lines. The voltage on these lines is typically between one hundred thousand to one million volts.
A typical configuration uses a platform mounted to the helicopter’s skids with a wire attached to the helicopter’s airframe. The lineman sits on the edge of the platform as the pilot hovers the helicopter next to the line that needs repair. In some cases, the pilot must maneuver the lineman within several inches of the power line. Because this is considered an external load operation, the platform can be jettisoned. However, the lineman’s harness is attached to the helicopter.
The helicopter and the high voltage wire have different electrical potentials, so to equalize them a metal wand is brought close to the wire. When the wand is close enough the voltage jumps across causing an arc. Once the wand makes contact with the wire, a clamp is connected to the platform with a 5 or 6 foot cable that is attached to the helicopter insuring the voltage potential remains equal. The wand is then removed and the repairs can begin. In the event of an emergency the clamp will break away from the power line. The helicopter now has a high electrical potential and the pilot must be careful to not let the helicopter get to close to an object (a tree, for example) that will allow the voltage a path to ground. This will significantly increase the current flow through the helicopter causing high heat and serious damage to equipment and personnel.
Several accidents have happened from engine failures or the rotor system coming in contact with part of the power line infrastructure. One such accident happen in August of 2013 and according to the NTSB the helicopter was conducting an electrical power line construction operation with a lineman standing outside on the skid. The wire was temporarily suspended by a hoist and the lineman was inserting a fiber shoe to attach the wire to the arm of the tower. While the helicopter was hovering next to the wire at about 200 feet above ground level the hoist slipped and the wire fell onto the top of the helicopter’s skid. Control was briefly lost and four of the helicopter’s main rotor blades impacted the tower resulting in substantial damage to the main rotor blades. The pilot quickly regained control and made an emergency landing in tall corn about 200 feet from the accident location. Fortunately, the pilot did an excellent job and no one was injured.
Even when everything goes right, high voltage power lines create a very strong electromagnetic field. This field produces an induced current that anyone close to the line will feel along their skin. As such, the pilot and lineman wear a special suit with a metal weave that allows the current to flow around the skin. Even with the suit, the sensation has been described as a feeling of pins and needles.
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December 23, 2013 by Tim McAdams
The BK117 is a twin-engine, medium size helicopter developed jointly by Messerschmitt Bolkow Blohm (MBB) of Germany and Kawasaki of Japan. In early 1977 the two companies signed an agreement to share costs and produce two prototypes each. Although development took longer than originally planned, Japanese and German authorities certified the helicopter in late 1982 followed by the United States in early 1983.
The BK117 is a compact design with a total length of 43 feet and a main rotor diameter of 36 feet. MBB used a hinge-less rotor system with four main rotor blades attached to a titanium hub. A high tail rotor and rear clamshell doors made the BK117 very popular in the EMS industry.
The first version was the BK117 A-1 powered by two Lycoming gas turbine engines. Two major problems with the A1 were the low gross weight (6280 lbs) and a lack of tail rotor thrust and stability. In 1985 MBB introduced the A3, with a larger tail rotor, an optional yaw stabilization augmentation system (YSAS) and a gross weight increase to 7,055 pounds. A year later came the A-4, with increased take-off limits and an improved tail rotor hub. All A-series BK117s use the 650 shp Lycoming LTS-101- 650B1 turbine engine de-rated to 550 shp.
In 1987 MBB introduced the B1, which used the more powerful 750 shp LTS-101- 750B1 engine (still de-rated to 550 shp) and the YSAS became standard equipment. Next was the B2, with a beefier landing gear, shorter pitch change horns to improve main rotor response time and a gross weight increase to 7,385 pounds. Also available at the same time was a C1 model with Turbomeca Arriel 1E engines rated at 708 shp for better hot and high performance.
In 1992, MBB and the helicopter division of Aerospatiale merged to form Eurocopter. Under the newly formed company, the BK117 underwent several upgrades including a new forward cockpit design with modern avionics. It carries the FAA designation BK117 C2, but is marketed as the EC145. Powered by a pair of Turbomeca Arriel 1E2 engines rated at 738 shp each, the gross weight jumped to 7903 lbs. In 2006, the US Army signed a contract for 345 EC145 aircraft for use as a light utility helicopter. Known as the UH 72A (Lakota), the program has been a major success for the US Army.
UH 72A Lakota
Scheduled for certification in 2014 is the EC145 T2 featuring new FADEC equipped Arriel 2E engines delivering 1039 shp each. Additional improvements include a Fenestron tail rotor, a 4-axis autopilot and a gross weight increase to 8047 lbs.
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December 7, 2013 by Tim McAdams
Over the years there have been many different inventors and engineers who have attempted to built vertical lift aircraft. The single main rotor with a smaller anti-torque rotor emerged as the most popular. With recent advances in technology, innovative engineers have been attempting to build a practical electric-powered helicopter. As it turns out, the single main rotor design is not the most efficient – efficiency is necessary for an electric-powered helicopter to be capable of lifting a reasonable payload. As such, engineers are designing very different vertical lift vehicles. One of these is the 2-person Volocopter and its first successful flight was November 17, 2013.
Designed and built in Germany, the Volocopter has an especially unique design. It uses 18 rotors, each powered by its own electric motor. They are mounted on a light weight carbon fiber ring above the cabin. Several on-board computers monitor and control the speed of each rotor system to achieve directional control – eliminating the need for any type of mechanical linkage. The system is designed so that if one of the motors fails (actually, several can fail at the same time) the aircraft can still safely land. Additionally, there is a ballistic parachute system for added safety.
Currently, the biggest limitation is battery life. The battery allows a flight time of 20 minutes, however, the company believes that advances in battery technology will extend the flight time in the near future. As an interim solution, the Volocopter will be built as a hybrid which will allow several hours of flight time. This is achieved by using a combustion engine to power a generator that supplies the batteries and motors with electricity.
The manufacturer, E-volo, claims the production aircraft will be extremely cost effective to operate, very quiet and easy to fly. More information can be found on their website: www.e-volo.com.
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November 24, 2013 by Tim McAdams
In basic terms, a helicopter’s main rotor system is what provides lift and thrust. The rotational speed (rpm) is held constant and the pitch angle of the blades is varied to change the amount of lift and thrust. Engineers look at many different variables when designing a rotor system and one is the direction the rotor spins, clockwise or counter clockwise (when viewed from above). Unlike the tail rotor, from an aerodynamic efficiency standpoint there is no difference between the two directions. As it turns out, in most cases the direction of rotation can be associated with the country of origin. For example, as a general rule, helicopters manufactured in the United States (and some other countries like Germany) turn counter clockwise, while French and Russian designed helicopters spin clockwise.
However, from a piloting viewpoint there are some differences. The biggest one comes from Newton’s third law that states for every action, there is an equal and opposite reaction. As such, the torque applied to the rotor system causes the helicopter’s fuselage to spin the opposite direction. This is the primary reason for the tail rotor, or more accurately called the anti-torque rotor. It applies a force opposing the main rotor torque to stop the fuselage from spinning. The more power the pilot demands, the higher the torque and the more thrust the anti-torque rotor must produce to control yaw. In the cockpit, it is the pedals that control the anti-torque rotor’s pitch and therefore its thrust. What this means to the pilot is in a clockwise turning main rotor, right pedal must be added as power is increased and left pedal when power is reduced. For a counter clockwise spinning rotor system it is just the opposite.
Some of the other differences that are not as noticeable to the pilot are translating tendency and dissymmetry of lift. Translating tendency is the tendency of the helicopter to drift in the direction of tail rotor thrust. A clockwise turning rotor will cause the helicopter to drift to the left. Dissymmetry of lift refers to a difference in lift across the rotor system as one blade advances into the wind (headwind) and the other side retreats (tailwind). Again, depending on which way the rotor spins the advancing side will be on the right or left side of the rotor disc.
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November 11, 2013 by Tim McAdams
In 2010, Sikorsky Aircraft introduced “Project Firefly,” an all electric helicopter technology demonstrator based on the S-300C airframe. The intent was to have it flying a year later and set a world record for the first all electric manned helicopter flight. Unfortunately, the company did not make the target date and last year the first all electric powered helicopter flight was achieved by pilot and designer Pascal Chretien in France.
Chretien took a different approach than Sikorsky, rather than use a heavy existing airframe he designed a new lightweight highly energy efficient aircraft. As an electrical engineer and commercial rated helicopter pilot he knew what areas to target. A tail rotor can consume 10 percent of available power, so to eliminate the tail rotor Chretien used a coaxial main rotor system. He employed a second generation asymmetrical rotor blade design which provided a 19% increase in lift over his initial blades. Powered by a lightweight (128 pounds) Lithium ion polymer pouch cell battery pack the two DC powered electric motors provided a total of 43 hp, enough power to lift the required 545 pounds. Each rotor system has its own motor and yaw is controlled by varying the electrical signal to each motor.
In July and August of 2011, the aircraft made 29 flights totaling 99.5 minutes with some flights lasting 6 minutes. Then on 12 August 2011, the world’s first un-tethered manned flight of a helicopter powered only by an electric motor took place at Venelles, France. Chretien hovered above the ground for 2 minutes 10 seconds entering the Guinness World Book of Records.
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November 1, 2013 by Tim McAdams
Turbine powered helicopters use bleed air for heating, demisting and other systems like sand filters. Bleed air is taken from the compressor section of the engine. For example, the Arriel 1 series engines use a two stage compressor section.
Arriel 1 compressor section
The first stage uses an axial compressor to increase the speed and pressure of the ambient air.
The second stage uses a centrifugal compressor to further compress the air and raise the temperature. This is where bleed air is taken from the engine.
Prior to entering the combustion chamber the air is extremely hot from compression alone. For cabin heating, the bleed air is mixed with outside air to cool it.
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October 24, 2013 by Tim McAdams
On July 24, 2000 in Sumner, Georgia, an AS350B Astar collided with the ground in a heavily wooded area during a clear dark night. According to the NTSB, no pre-existing airframe or engine malfunctions were identified during the post-crash examination. They determined the probable cause as the pilot experiencing spatial disorientation, which resulted in a loss of control of the helicopter. A contributing factor was the dark night.
Threats, clearly visible during the day, are masked by the darkness. In fact, Controlled Flight into Terrain (CFIT) at night is a major problem for fixed and rotor wing operations. CFIT is defined as colliding with the earth or a man-made object under the command of a qualified flight crew with an airworthy aircraft.
Due to the unique low flying operation of helicopters CFIT at night during VMC has been troublesome, especially for the aeromedical industry. According to the Air Medical Physician Association, half of all EMS accidents happen at night.
For example, on November 14, 2001 the pilot of a BO 105 LS reported that while performing a normal take-off from a non-airport shortly after midnight on a dark moonless night, he lost visual references outside the helicopter, became disoriented, and collided with terrain. He further stated that no mechanical malfunction or failure had occurred during the accident flight. The NTSB determined the probable cause was the pilot’s failure to maintain adequate separation from terrain during the initial climb. Factors include spatial disorientation and a dark moonless night.
Obviously, the key to preventing these accidents is improving the pilot’s ability to see obstructions–the idea behind Night Vision Goggles (NVG). In the late 1990s, the idea of using NVGs in the civilian sector was starting to evolve. By early to mid 2000, EMS operators started using NVGs in their operations. Today, the vast majority of EMS operators and law enforcement units fly their helicopters under NVGs. With the proper training, use of NVGs increases the safety margin associated with flying helicopters at night.
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October 13, 2013 by Tim McAdams
Flight training in full flight simulators (FFS) has been the standard in large fixed-wing aircraft for years. In the past, there were only a couple of helicopter simulators. These were mainly large twin-engine IFR helicopters like the Sikorsky S76 and Bell 430. Recently, simulator manufacturers have been introducing more helicopter devices and seeking certification at higher FFS levels (levels B, C and D with full motion capabilities).
Many operators and airframe manufacturers have already acquired low level non-motion FTDs (Flight Training Devices) to supplement flight training in the aircraft. With computer power and visual systems getting better and cheaper, higher level simulators are becoming more popular. Even for light single-engine helicopters operators are starting to embrace simulator training. Especially for FAA Part 135 operators who can complete required annual check-rides in a FFS.
During the next 5 to 10 years, more helicopter training will be done in simulators. Hopefully, this will lead to more frequent and comprehensive training that will help reduce the accident rate, especially for EMS operators.
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September 28, 2013 by Tim McAdams
When a helicopter is in autorotation (that is, gliding without the benefit of engine power) rotor rpm must be maintained. This is done when entering the autorotation by lowering the collective control. If the rotor rpm approaches an upper limit, the collective is raised to add pitch. This increases drag and slows the rotor rpm. A low rotor rpm situation is just the opposite, lower the collective pitch to reduce the drag and allow the rotor rpm to speed up.
Rotor rpm in autorotation is a function of several factors like density altitude, gross weight and airspeed. An over speeding rotor is easy to manage since the collective control was lowered on entry there is plenty of movement upward to add drag. However, if a pilot enters autorotation and lowers the collective control all the way down and the rotor rpm is still too low this could be a problem. Typically, in this case, the main rotor pitch is set incorrectly. The helicopter’s maintenance manual has a procedure to adjust this by either lowering the collective control’s down stop or adjusting the main rotor blades’ pitch links. To accomplish this, a mechanic will note the helicopter’s weight and the density altitude and then reference a chart to get the correct rotor rpm. A flight test will then be performed at those conditions and the actual rotor rpm will be noted with the collective all the way down. If it is not at the correct rotor rpm stated in the chart, the mechanic will make an adjustment.
This is done to insure that in the worst case scenario (light helicopter, high density altitude) the pilot will be able to lower the collective control far enough to guarantee an acceptable rotor rpm in autorotation.
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September 14, 2013 by Tim McAdams
Typically, coaxial rotor systems (one rotor system stacked on top of another that spin in opposite directions) are used on larger helicopters. The advantages are higher speed and more lifting power as a tail rotor is not needed. An aerospace start-up company in India (DASYS), a manufacturer of unmanned aerial vehicles, has designed a light two-seat helicopter with a coaxial rotor system.
Called the Berkut VL, the company plans to certify the helicopter in compliance with US FAR Part 27 standards. Currently there are two prototypes, one for testing and the other for demonstrations. These two airframes are equipped with a Russian ConverVAZ engine, but production models will have the option of a 150 hp Lycoming O-320 engine. Helicopters with American engines will get the designation Berkut VL M. The planned take-off weight is 1,830 lbs with a maximum speed of 108 mph and a range of 527 miles.
The helicopter will be produced at a plant in central Russia. Although no price has been released, the company has stated it will be affordable and plans are for it to compete with the Robinson R-22. As such, the company has announced a four-seat version will follow. First deliveries are scheduled for mid 2014.
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