Currently, the US military is busy equipping the fleet of its helicopters with carbon fiber composite (carbon) blades, since these new materials have an increased service life, tolerate damage well, they have no problems with corrosion, and they have high reliability.
The extreme military helicopter equipped with composite blades was the Boeing AH-64D Apache Block III. In Fort Irvine, California, Apache Unit III underwent initial operational tests and evaluations, demonstrating new technologies and their capabilities.
One of the key aspects of these capabilities is to increase the flight performance and reliability of the main rotor with carbon fiber blades, however, according to Apache Block III program manager Lieutenant Colonel Daniel Bailey, the use of such materials is unlikely to stop only on the blades. "The blades are the first obvious step," he told the Defense Helicopter.
Although such an important flight component as the blades may seem a strange starting point for the introduction of new technologies, it is here in recent years that the US military has honed their skills in composite materials. Bailey points out that these materials will be widely represented on the American military "helicopters of tomorrow": "The next step will be composites in the fuselage, and we are already following this path."
The Apache will also receive a new tail rotor around the next year. Regardless of the Block III process, "our composite tail rotor program continues. This is a parallel Block III program," Bailey explained. "We are in the final qualification stage, but we still have to do a lot of flight tests. Probably, in a year, the Apaches will be equipped such a system. "
New tail blades will also be installed on upgraded models of Block II. This replacement of the traditional main and tail rotor blades is due to the obsolescence of some technologies. These blades, the first use of which is dated 1970-mi years, were no longer completely metal. Helicopters AH-64A and D Block I and II use a composite of metal and fiberglass for the main and tail rotor blades.
In mechanical engineering, it is considered to be a composite material or structure consisting of more than one element. Apache blades are made from exotic alloys in the form of AM 355 stainless steel. Boeing engineers used a variety of multi-tubular AM 355 configurations that were laminated and tied together with fiberglass tubes as an obstacle to the propagation of cracks, which gave the structure sufficient strength to meet military survivability requirements. This complex construction is also expensive.
The current composite blades of the main and tail screws presented in Block III and its parallel program consist of carbon fiber in a polymer matrix, which is what is usually meant when talking about composites.
Carbon fibers demonstrate improvements in how they are made and how they function. "By changing the orientation of the fibers and the number of layers and fillers, you can bring the composite blades to levels that were out of reach with metals. In fact, you can make a blade in terms of its twist, its aerodynamic profile or chord function, optimizing its flight characteristics" - explained the chief engineer of the helicopter programs of Boeing John Schibler (John Schibler).
In composite materials of carbon fiber fiber layers are often located alternately to each other at right angles. By correctly choosing the direction of the fibers in these layers, it is possible to achieve the necessary characteristics in specific directions and areas.
"The advantages lie in the strength of the material and in the fact that with equal strength it is possible to provide up to 30% weight loss (compared to metal composites). With the same weight, it provides a much higher rigidity. But usually we are talking about weight reduction," Daniel Kagnatel (Daniele Cagnatel), vice president of modern composite materials GKN Aerospace North America. The company supplies the company Sikorsky with modern carbon fibers for the blades of the main rotor of the Black Hawk helicopter.
In addition to improving rigidity and strength, Schibler also points to economic benefits: "We produce blades at a relatively low purchase price, as well as with low running costs and more profitable maintainability."
Sikorsky manufactures blades for the main and tail rotors using graphite resin spars braided with fiberglass or carbon fiber. Alan Walling, CEO of Sikorsky composite blades, said: "Sikorsky is able to produce fully composite rotor blades in just a third of the time needed to produce metal blades. There is much less chemical waste in the production of composite blades. This is because metal blades require etching in an acid bath to ensure the necessary flight performance of the blades for a long time. "
According to Kagnatel: "The choice of carbon fibers for blades is mandatory. The existing structure of the blades has proven itself in practice, where carbon fiber has improved flight performance compared to metal."
The choice of the Carbon Fiber Apache Unit III rotor blades began with the Affordable Apache Rotor Program (AARP). In 2004, Boeing completed the tests of the blades under the AARP program, proving that the new blades will be cheaper, stronger and, in terms of fatigue life, they can last twice as long as the existing metal blades. Bailey explained that in 2006, the AARP blades were extended by 15 centimeters to improve flight performance, and in 2008, they were tested on Apache, while the blades qualification for Unit III was completed in 2011. .
"The composite rotor blades for the Apache Block III program are currently in production. We manufacture around 20 blades per month and will soon increase their production to 40 and to 60," said Schibler.
In 2013, Block III will be commissioned in the 1st Assault Reconnaissance Battalion of the American Army (1-1 ARB), combat aviation Brigade, 1st Infantry Division based at Fort Riley, Kansas. In May, five Apache Block III helicopters arrived at the 1st strike reconnaissance battalion to train pilots and maintenance services; additional helicopters will arrive in the coming months.
The British army flies on Apache helicopters of model I, but they can be upgraded to the level of Block III. Decision on this is expected in December. If the decision to upgrade to the Block III level is made, then the Apache UK can also receive rotor blades from the British Experimental Rotor Program of the rotor (British Experimental Rotor Program IV, BERPV IV). The BERP IV program was completed in the 2007 year, and composite blades fly over the Royal Air Force EH101 Merlin Mk 3.
Tested and tested
However, this is not the first European military helicopter using carbon blades. The predecessor of Eurocopter, Aérospatiale, claims that this honor fell on an SA 330 Puma helicopter flying from 1970's. Since then, this type is used by many armed forces, including the French army and the US Navy. Composite tail blades are also used on AS532 Cougar, AS565 Panther, NH90 and Tiger helicopters.
The Sikorsky UH-60M Black Hawk uses carbon composite rotor blades from 2008. Of the Sikorsky helicopters, only MH-60R and MH-60S Seahawk have rotor blades from a metal (titanium) spar.
Lieutenant Colonel Billy Jackson, head of the UH-60M Black Hawk retrofit program, said: "We have deployed UH-384M helicopters to 60 troops, Sikorsky has deployed UH-400M helicopters around 60 Some of them have already returned from their second deployment in Afghanistan. "
The army uses broader composite rotor blades, also known as broad chord blades, due to their improved weight characteristics. Weight savings were 204 kilograms. "This was the main reason for creating composite blades, and not creating them simply because they are composite. The main thing is their flight performance," explained Jackson.
“For some time they have been working on the Sikorsky S-92 in a slightly different configuration, thanks to which we already had a good amount of data. There was not a lot of risk in the decision to switch to fully composite blades,” he continued. The Sikorsky firm applied fully composite spars and plating of the main rotor blades on their S-92 helicopters at the end of the 1990-s.
The flight-technical characteristics of the UH-60M helicopters were tested in two deployments in Afghanistan, and Jackson insists that they showed good results: "We are currently busy collecting data on the reliability of the blades. We had damaged blades, as well as repaired and repaired ones. Regarding the question of whether we found cracks in the blades or unforeseen failures due to new composite structures, the answer is no. " Based on current success, the next step could be a fully composite all-rotary stabilizer.
Weight loss plans
In addition to explaining Bailey that the blades were the first step, and the composite fuselage is the following, Jackson said: "We are looking for other applications of composite materials. We are currently developing a fully composite, full-turn stabilizer that will provide a significant weight reduction."
The army began to develop the Black Hawk helicopter's composite tail beam in order to reduce its weight, however, at present, special emphasis is being placed on the creation of a fully composite all-rotary stabilizer including internal components. "We intend to make a fully composite all-turn stabilizer to significantly reduce the weight in the helicopter area, which has the main effect on the center of gravity of the helicopter."
Jackson said that, as already noted in the proposal of the Sikorsky firm, the decision to create a fully composite all-round stabilizer was not due to the desire to improve its flight performance, but only to reduce the cost of its production.
"We still have to do some tests, ballistic and other types of flight tests to make sure that the new product will be just as good or even better than the original one, and then make a financial decision about how we want to implement it on an existing platform, implement him in a promising production or replenish them with a list of existing spare parts. "
The company supplying the composite tail boom, but not the tail rotor blades, is BLR Aerospace from Washington State. Vice President Sales and Marketing Dave Marone (Dave Marone) confirmed to Defense Helicopter that his company was producing a fully composite tail beam for one of the military customers, but did not agree to provide additional information.
Plans for the future
Another helicopter that will have to wait until the 2016 of the year to get the composite rotor blades of carbon fiber is the US Army CH-47 Chinook. "The new composite blades are called Advanced Chinook Rotor Blade (ACRB). The program successfully completed the critical design review (CDR) stage in January 2012 of the year," said CH-47 Chinook retrofit project manager Joe Hoecherl ). Flight and ballistic tests were completed in the 2011 year.
The ACRB program will bring changes in the shape of the blades and their flight performance without affecting their attachment. “These blades will be interchangeable on all Chinook helicopters,” said Hotserl. The large-scale tests in the wind tunnel were completed, which demonstrated that the new blades are capable of providing up to 900 kg of additional vertical thrust, which will allow the helicopter to hang with a full load at an altitude of 1200 meters at an air temperature of 35 ° C.
ACRB blades in a wind tunnel.
The pre-production of blades is scheduled for April 2014 of the year, flight tests for the third quarter of the 2015 of the year, and mass production for the 2016 of the year. In February of this year, it was announced that Boeing is developing composite blades with an increased service life and requiring significantly less time needed to eliminate the incoherence of the rotor blades and balance them. These blades can also be installed on the model of helicopters CH-47D, however, these helicopters are scheduled to be written off by 2019-th year.
Most likely, by the 2019 year, carbon fiber blades will require a more sophisticated approach to achieve further improvements in flight performance. Industry agrees that the blades will not consist only of carbon fiber. Kagnatel believes that sensors will be built into them, capable of monitoring the state of the blades and allowing them to more accurately predict their service life.
"Trends are increasingly pointing to embedded systems, elements for heating the front edge of the blade, as well as voltage sensors and deformations of the blades. In the future, such sensors will be an integral part of the blades than their external elements," he said.
However, moving parts can also be mounted on the blades. Paul Weaver, director of research and engineering at the University of Bristol, is working on a project for the UK government. The project is called Intelligent Responsive Composite Structures (IRCS). "The national innovation agency funded the project, which ended two years ago by changing the form of flaps," he told the DH publication.
The national innovation agency is owned by the British government, it is engaged in the financing of research, development and their commercialization. As part of the IRCS program, it was found that the flap-shaped device on the trailing edge of the blade can be used to improve flight performance when moving from a hang to a horizontal flight.
Sikorsky is also engaged in research in this area. It develops active rotor blade technology in conjunction with the US Department of Defense. To date, it is not planned to install these devices on existing blades.
The US military is not a pioneer in the deployment of carbon-fiber blades, but the fact that they are actively equipping their helicopter fleet with new blades confirms that new composites are being actively implemented. For Bailey, the importance of carbon fiber is obvious: "These technologies will stimulate the development of future army helicopters, whether they are new Apache, Black Hawk or Chinook."