Blade inspection method

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A blade inspection method is the practice of monitoring the condition of a blade, such as a helicopter's rotor blade, for deterioration or damage. A common area of focus in the aviation industry has been the detection of cracking, which is commonly associated with fatigue. Automated blade condition monitoring technology has been developed for helicopters and has seen widespread adoption. The technique is routinely mandated by airworthiness authorities for engine inspections. Another commercial sector where such monitoring has become important is electricity generation, particularly on wind farms.

Contents

Aviation

The propellers used to power numerous aircraft require regular inspections to ensure their integrity. The interval for such inspections is typically specified by the propeller's manufacturer. [1] Regardless of being made of wood, metal or composite materials, visual inspections have typically been sufficient for observing any evidence of failure, sub-par condition, or damage sustained. However, some composite materials necessitate additional techniques such as ultrasound scans, to be performed to detect subsurface issues that may lack any external indications of their presence. [1]

Similarly, the fan blades of jet engines are susceptible to cracking and thus require routine inspections to be conducted by operators. Such inspections are typically performed during maintenance intervals, typically using a combination of visual and ultrasound scans performed upon each fan blade by technicians to detect any cracks. [2] During October 2018, both the Federal Aviation Administration (FAA) and the European Aviation Safety Agency (EASA) issued updated airworthiness directives that specified more frequent inspections of the blades of the CFM International CFM56-7B turbofan powerplant used on many airliners. [3]

The in-flight failure of a rotorcraft's main rotor blade would likely lead to a serious life-jeopardising accident. Thus, manufacturers have developed detection techniques that guard against blade failure caused by fatigue cracking. A common method involves the pressurisation of the interior cavity of the rotor blade spar with nitrogen gas. Upon the formation of a crack, pressure is lost and a sensor built into the root of the rotor blade would detect this pressure change. [4] Readouts from this sensor would be displayed via a cockpit display to the pilot. This system is intended to alert operators to cracking rotor blades in advance of a catastrophic failure, allowing for replacement blades to be installed in advance of such an outcome. American helicopter specialist Sikorsky has incorporated this technology onto several of its rotorcraft, including the S-61 series, [4] S-65 series, and other models. In some cases, advanced detection of rotor blade flaws can allow for the repairs to be made, allowing for the blade to continue to be used. [5]

Electricity generation

The use of blade inspection methods has become commonplace amongst electricity-generating wind turbines. The detection of defects in blades, often attributed to fabrication, increases system reliability, as well as blade lifespan and enables more efficient condition-based maintenance; repairs can occur before more extensive damage levels is sustained, minimising turbine downtime. [6] [7] By the late 2010s, early practices for blade inspection have typically been determined to be incapable of detecting damage at an early stage. [8] By this point, considerable research had been conducted to refine optimal techniques of performing non-destructive testing (NDI). Furthermore, it is believed that the requirement for comprehensive systems for blade inspection shall grow in line with the cost per blade and the associated lost revenue incurred from downtime. [6] [9]

The blades of wind turbine are complex structures that incorporate composite materials. [9] As such, they have reportedly posed unique challenges for inspection challenges, possessing relatively thick spar cap structures and porous bond lines, varying core material, along with a multitude of possible manufacturing defects and forms of in-service damage. [6] Techniques have improved as a greater understanding of how blades undergo structural aging; critical evaluations of such techniques have aimed to measure their sensitivity, accuracy, repeatability, speed, ease of data interpretation, and ease of deployment. Researchers at Sandia National Labs determined that a thorough combination of several inspections methods may be required for optimal inspection sensitivity and reliability for both near-surface and deep, subsurface damage. [6] Blade inspection techniques have been performed using fields such as ultrasound, microwave, thermography, shearography, and optical. [6] [9] [10] Some of these techniques can be applied via remotely-operated unmanned aerial vehicles (UAVs), reducing or eliminating the need for traditional manned inspections by trained climbers. [11] [12]

Related Research Articles

In engineering, damage tolerance is a property of a structure relating to its ability to sustain defects safely until repair can be effected. The approach to engineering design to account for damage tolerance is based on the assumption that flaws can exist in any structure and such flaws propagate with usage. This approach is commonly used in aerospace engineering, mechanical engineering, and civil engineering to manage the extension of cracks in structure through the application of the principles of fracture mechanics. A structure is considered to be damage tolerant if a maintenance program has been implemented that will result in the detection and repair of accidental damage, corrosion and fatigue cracking before such damage reduces the residual strength of the structure below an acceptable limit.

In safe-life design, products are intended to be removed from service at a specific design life.

<span class="mw-page-title-main">Tail rotor</span>


The tail rotor is a smaller rotor mounted vertically or near-vertically at the tail of a traditional single-rotor helicopter, where it rotates to generate a propeller-like horizontal thrust in the same direction as the main rotor's rotation. The tail rotor's position and distance from the helicopter's center of mass allow it to develop enough thrust leverage to counter the reactional torque exerted on the fuselage by the spinning of the main rotor. Without the tail rotor or other anti-torque mechanisms, the helicopter would be constantly spinning in the opposite direction of the main rotor when flying.

Blade pitch or simply pitch refers to the angle of a blade in a fluid. The term has applications in aeronautics, shipping, and other fields.

<span class="mw-page-title-main">Tip jet</span> Jet nozzle at the tip of some helicopter rotor blades

A tip jet is a jet nozzle at the tip of some helicopter rotor blades, used to spin the rotor, much like a Catherine wheel firework. Tip jets replace the normal shaft drive and have the advantage of placing no torque on the airframe, thus not requiring the presence of a tail rotor. Some simple monocopters are composed of nothing but a single blade with a tip rocket.

<span class="mw-page-title-main">Fenestron</span>

A Fenestron is an enclosed helicopter tail rotor that operates like a ducted fan. The term Fenestron is a trademark of multinational helicopter manufacturing consortium Airbus Helicopters. The word itself comes from the Occitan term for a small window, and is ultimately derived from the Latin word fenestra for window.

<span class="mw-page-title-main">Rotorcraft</span> Heavier-than-air aircraft which generates lift over rotating wings

A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft with rotary wings or rotor blades, which generate lift by rotating around a vertical mast. Several rotor blades mounted on a single mast are referred to as a rotor. The International Civil Aviation Organization (ICAO) defines a rotorcraft as "supported in flight by the reactions of the air on one or more rotors".

A convertiplane is defined by the Fédération Aéronautique Internationale as an aircraft which uses rotor power for vertical takeoff and landing (VTOL) and converts to fixed-wing lift in normal flight. In the US it is further classified as a sub-type of powered lift. In popular usage it sometimes includes any aircraft that converts in flight to change its method of obtaining lift.

<span class="mw-page-title-main">Helicopter</span> Type of rotorcraft in which lift and thrust are supplied by horizontally-spinning rotors

A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes allow helicopters to be used in congested or isolated areas where fixed-wing aircraft and many forms of STOL or STOVL aircraft cannot perform without a runway.

<span class="mw-page-title-main">Sikorsky X2</span> Experimental high-speed compound helicopter

The Sikorsky X2 is an experimental high-speed compound helicopter with coaxial rotors, developed by Sikorsky Aircraft, that made its first flight in 2008 and was officially retired in 2011.

<span class="mw-page-title-main">Turbine engine failure</span> Turbine engine unexpectedly stops producing power due to a malfunction other than fuel exhaustion

A turbine engine failure occurs when a turbine engine unexpectedly stops producing power due to a malfunction other than fuel exhaustion. It often applies for aircraft, but other turbine engines can fail, like ground-based turbines used in power plants or combined diesel and gas vessels and vehicles.

<span class="mw-page-title-main">Los Angeles Airways Flight 417</span> 1968 helicopter accident

Los Angeles Airways Flight 417 was a Sikorsky S-61 helicopter that crashed on August 14, 1968 in the city of Compton, California. All eighteen passengers and three crew members were killed. The aircraft was destroyed by impact and fire. According to the National Transportation Safety Board the probable cause of the accident was fatigue failure. The accident happened when the yellow blade, one of five main rotor blades, separated at the spindle which attached the blade to the rotor head. Following failure, the helicopter was uncontrollable and it fell to the ground. The fatigue crack originated in an area of substandard hardness and inadequate shot peening.

<span class="mw-page-title-main">Airbus Helicopters H175</span> Medium utility helicopter

The Airbus Helicopters H175 is a 7-ton class super-medium utility helicopter produced by Airbus Helicopters. In China, the H175 is produced by the Aviation Industry Corporation of China (AVIC) as the Avicopter AC352. Originally launched as the Eurocopter EC175 and the Harbin Z-15, it has been referred to as being a 'super-medium' helicopter.

<span class="mw-page-title-main">Guimbal Cabri G2</span> Type of aircraft

The Guimbal Cabri G2 is a two-seat light helicopter produced by Hélicoptères Guimbal, and powered by a reciprocating engine. Designed by Bruno Guimbal, a former Eurocopter engineer, it had its origins in the 1980s, and the first demonstrator flew in 1992. Following the granting of regulatory approval, the Cabri entered commercial service in 2008. In addition to its use within the general aviation sector and as a training rotorcraft, the Cabri G2 has also been used as the basis for unmanned aerial vehicles (UAVs).

<span class="mw-page-title-main">Slowed rotor</span> Helicopter design variant

The slowed rotor principle is used in the design of some helicopters. On a conventional helicopter the rotational speed of the rotor is constant; reducing it at lower flight speeds can reduce fuel consumption and enable the aircraft to fly more economically. In the compound helicopter and related aircraft configurations such as the gyrodyne and winged autogyro, reducing the rotational speed of the rotor and offloading part of its lift to a fixed wing reduces drag, enabling the aircraft to fly faster.

<span class="mw-page-title-main">Sikorsky S-97 Raider</span> American high-speed scout and attack compound helicopter

The Sikorsky S-97 Raider is a high-speed scout and attack compound helicopter based on the Advancing Blade Concept (ABC) with a coaxial rotor system under development by Sikorsky Aircraft. Sikorsky planned to offer it for the United States Army's Armed Aerial Scout program, along with other possible uses. The S-97 made its maiden flight on 22 May 2015.

<span class="mw-page-title-main">Powered aircraft</span> Aircraft which uses some form of onboard propulsion to fly

A powered aircraft is an aircraft that uses onboard propulsion with mechanical power generated by an aircraft engine of some kind.

<span class="mw-page-title-main">Airbus Helicopters H160</span> Type of aircraft

The Airbus Helicopters H160 is a medium utility helicopter being developed by Airbus Helicopters. Formally launched at Heli-Expo in Orlando, Florida on 3 March 2015, it is intended to replace the AS365 and EC155 models in the firm's lineup. In June 2015, the first test flight took place. It received its EASA type certification in July 2020, and first deliveries were in December 2021.

<span class="mw-page-title-main">Glidden Doman</span>

Glidden Doman was an American aeronautical engineer and pioneer in helicopters and modern wind turbines. He founded one of America's original six helicopter companies after making major contributions to the use of Sikorsky helicopters during World War II. Doman Helicopters' most prominent achievement was the Doman LZ-5/YH-31 eight-place helicopter, which received FAA certification on December 30, 1955. The unique feature of this helicopter was its hinge-less but gimbaled, tilting rotor hub that greatly reduced stress and vibration in the blades and in the whole helicopter.

Rotor solidity is a dimensionless quantity used in design and analysis of rotorcraft, propellers and wind turbines. Rotor solidity is a function of the aspect ratio and number of blades in the rotor and is widely used as a parameter for ensuring geometric similarity in rotorcraft experiments. It provides a measure of how close a lifting rotor system is to an ideal actuator disk in momentum theory. It also plays an important role in determining the fluid speed across the rotor disk when lift is generated and consequentially the performance of the rotor; amount of downwash around it, and noise levels the rotor generates. It is also used to compare performance characteristics between rotors of different sizes. Typical values of rotor solidity ratio for helicopters fall in the range 0.05 to 0.12.

References

  1. 1 2 "Propeller Inspection and Maintenance". flight-mechanic.com. Retrieved 30 July 2020.
  2. ↑ Risen, Tom (4 May 2018). "How technicians will search for weakened fan blades". aerospaceamerica.aiaa.org.
  3. ↑ "FAA, EASA Order More Frequent CFM56-7B Fan Blade Inspections". flightsafety.org. 2 October 2018.
  4. 1 2 "Sikorsky Helicopters", pp. 614–615. Flight International, October 10, 1963.
  5. ↑ Napert, Greg (1 May 2000). "Composite Rotor Blade Inspection and Repair". aviationpros.com.
  6. 1 2 3 4 5 Roach, Dennis; Neidigk, Stephen; Rice, Tom; Duvall, Randy; Paquette, Joshua A. (2015). "Development and Assessment of Advanced Inspection Methods for Wind Turbine Blades Using a Focused WINDIE Experiment". 33rd Wind Energy Symposium. doi:10.2514/6.2015-0998. ISBN   978-1-62410-344-5. OSTI   1242772.
  7. ↑ "NDT on wind turbine rotor blades". forcetechnology.com. Retrieved 30 July 2020.
  8. ↑ "New Tech for Wind Blade Inspections". oedigital.com. 24 June 2019. Retrieved 24 June 2019.
  9. 1 2 3 Chady, Tomasz (5 May 2016). "Wind Turbine Blades Inspection Techniques". Przegląd Elektrotechniczny. 1 (5): 3–6. doi:10.15199/48.2016.05.01.
  10. ↑ "US7489811B2: Method of visually inspecting turbine blades and optical inspection system". 2004.
  11. ↑ DuBose, Ben (5 April 2020). "New Rotor Blade Inspection Methods for Offshore Wind Turbines". materialsperformance.com.
  12. ↑ "Blade Services". windtex.co.uk. Retrieved 30 July 2020.
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