Archive for May, 2011

Starflex rotor

Wednesday, May 25th, 2011

There are several different main rotor system designs that are used on modern helicopters. The three basic designs that have traditionally been taught to students are semi-rigid, fully articulated, and rigid. Today there are versions that make extensive use of composite materials and are known as hinge less systems.

Rigid rotor systems do not use hinges and limited movement is absorbed through the hub and rotor blades. Many of the modern composite rotor systems also do not use traditional hinges, but have elastomeric and specially designed composites structures (flextures) that allow the blades to flap, feather, and hunt. Manufactures do not use the term rigid rotor system, opting instead to describe these systems as a fully articulated hinge less rotor system.

One helicopter that has a composite hinge less rotor system is the Eurocopter AS350 AStar. The basic component of the rotor system is the Starflex with 3 arms made from a glass resin laminate and flexible in the flapping direction. On the Starflex rotor hub, rigid sleeves join the blades to the star arms so that the hub allows blade flapping, lead/lag and pitch change without bearings or hinges. The sleeves also transmit the blade centrifugal loads to the rigid center part of the star. For this reason, flexible couplings are fitted between the sleeves and the star arm. The inboard ends of the sleeves are attached to the star by a laminated spherical stop (also called a thrust bearing) which is flexible in torsion, flapping and lead/lag but rigid in compression.  The blade end contains elastomeric blocks called frequency adapters that provide stiffness and damping but can move in a shear direction. This rotor hub design allows for all the required blade movement through the bending and twisting of composite or elastomeric materials.

Some advantages of the Starflex hub are less maintenance, a fail-safe design through the use of composite materials (any damage evolves very slowly and is visible) and on-condition maintenance (no required overhauls). Eurocopter is one of the first manufactures to use composite materials in rotor hub design and the AS350 Starflex has proven extremely reliable for over 30 years.

No pilot needed

Tuesday, May 17th, 2011

The Kaman K-MAX helicopter is one of the few helicopters with intermeshing main rotors systems. It was built specifically for external load operations and is able to lift over 6,000 pounds, which is more than the helicopter’s empty weight. The K-MAX is used for repetitive lift operations by commercial operators for the construction and logging industries. To date, 35 have been built and the fleet has accumulated more than 255,000 flight hours since 1994. It is now finding a new unmanned role with the US Military.

Lockheed Martin Corporation and Kaman Aerospace Corporation have teamed to build an unmanned remote-control version of the helicopter. The primary mission is for use in combat to deliver supplies to the battlefield. However, there are plans to offer the aircraft for civilian situations involving chemical, biological, or radiological hazards.

The team has flown the unmanned K-MAX nearly 400 hours in autonomous mode since joining forces in 2007. The system can lift and deliver its full 6,000 lbs of cargo at sea level and more than 4,000 pounds at 15,000 ft density altitude. Using preprogrammed GPS waypoints it can drop supplies at four remote locations before returning to base. It has a range of 270 nautical miles. An entire mission can be done autonomously with no one controlling the aircraft other than the person who programmed the mission before hand or it can fly to a waypoint where a person on the ground takes control. Programmers can enter a variety of data into each mission, including locations of likely threats and an emergency go-to point. Operators can also take control at any time during flight to reroute it. The aircraft will retain its ability to fly with a pilot for ease of operation in the National Airspace System and to maintain manned mission flexibility.

Electric helicopter

Sunday, May 8th, 2011

Several companies are building electric powered ultralight airplanes and motor gliders. And in July of 2010, Cessna announced it was developing an electrically-powered 172 as a proof-of-concept platform. However, the high power to weight requirement for hovering makes building an electrically-powered helicopter a difficult challenge. Even so, at the Experimental Aircraft Association (EAA) AirVenture exhibition Sikorsky Innovations, the technology development organization of Sikorsky Aircraft, introduced “Project Firefly,” an all-electric helicopter technology demonstrator. 

In building the demonstrator, the Innovations team replaced the S-300C’s Lycoming 190-horsepower, 4-cylinder gasoline engine with an electric motor and two battery packs located on each side of the pilot producing about 370 volts. Integrated sensors provide real-time aircraft health information including temperature for left and right battery packs, flight time remaining and voltage on a panel mounted LCD monitor. The demonstrator features a 190-horsepower electric motor that weighs 180 lbs, and a battery system that weighs 1,100 lbs. Power output is the same as with the original piston engine, but because of the heavy weight of the lithium-ion batteries the empty weight is close to 2,050-pounds leaving just enough payload for a single pilot.

Nevertheless, Sikorsky expects the Firefly will have the same flight characteristics (including an 86-knot top speed) as the S-300C. Benefits include higher efficiency, less complexity and lower vibrations. With the current battery pack the expected flight time is 12 to15 minutes (the piston version goes 3.7 hrs on 32 gallons of fuel). According to Sikorsky, as battery technologies get better this will improve exponentially. First flight is anticipated in mid 2011.