The share of commercial air travel is rapidly increasing, driven by technological advances that have instilled confidence in safe flying. This growing sector channels billions of dollars into the global economy, with its success reliant on creating safer, more reliable aircraft. At the heart of these aircraft lies the aero-engine – a powerhouse that must overcome numerous challenges beyond producing sufficient thrust to keep planes aloft.
Here are some key figures that highlight the significance and risks of air transportation:
Sustainable technological innovations and the adoption of advanced materials have played pivotal roles in enhancing the durability and safety of modern aircraft. Aircraft design can be broadly categorized into two main sections: – the body and the engine. While the body dictates structural and functional features, the aero-engine powers these designs with the energy and thrust required for the flight.
This paper focuses on aero-engines, marvels of engineering that combine immense power generation with stringent safety regulations to ensure the reliability of modern air travel.
The design of aero-engines - often referred to as the “mechanical birds” of aviation-has undergone significant advancements over time, driven by evolving engineering demands. The Second World War marked a turning point, revolutionizing aero-engine technology to achieve unprecedented thrust levels and speeds.
For example, the experimental North American X-15 holds the record for a top speed exceeding 4500 miles per hour (Mach 6.7) in 1967. The Lockheed SR-71 blackbird, an iconic reconnaissance aircraft, were designed for 2200 miles per hour (Mach 3.2) at altitudes reaching 85000 feet. Achieving this remarkable speed required engines to be designed and manufactured with extreme precision and zero- error standards.
Aero engines vary significantly based on their intended purpose and the type of aircraft they power. This discussion focuses on jet engines, widely used in both commercial and military aviation. Jet engines are further categorized into subtypes such as turbo-jet, turbo-prop, turbo-fan, ramjet, scramjet and pulse jet engines.
Despite differences in their design and construction, all jet engines operate on the same fundamental principle:
Among these, the turbo-series engines (turbojet, turboprop, and turbofan) stand out for their complexity. They contain the most moving and rotating components making them more challenging to design and manufacture compared to ramjet, scramjet and pulsejet engines. These challenges highlight the need for cutting-edge engineering solutions to meet the demands of speed, reliability, and safety in modern aviation.
The thrust produced by jet-engines is universally measured in pounds force, and the aviation industry continually seeks high thrust-to-weight ratios to maximize efficiency. To achieve the desired output demanded by the aircraft manufacturers, reducing engine weight becomes a critical parameter. This drives ongoing research into exotic materials that are not only heat- and- corrosion-resistant but also durable, fatigue-resistant and, manufacturable into precise shapes at lower costs – an essential focus of modern engineering innovation.
Figure 1. Types of Jet Engines
The basic construction of an engine comprises the following components
Two rotating shafts mounted on bearings connect these sections transferring rotational motions from HPT to HPC and from the LPT to the LPC and Fan. These rotating components, housed within robust casings, perform dual roles: providing structural support and containing potential damages during catastrophic events.
With rotational speeds ranging from 10,000 to 20,000 RPM, the fan blades, compressor blades and turbine blades experience extreme peripheral velocities. This makes robust engineering principles crucial to ensuring safety during air travel.
The following sections will explore critical failure scenarios in aero-engines. If not managed effectively, these scenarios could result in catastrophic losses, emphasizing the importance of meticulous design and rigorous testing in modern aerospace engineering.
Figure 2. Main Sections of Turbo Jet Engines
In addition to enduring extreme weather and fatigue loads, aero-engines must be rigorously tested for unplanned real-world scenarios such as crashes or impacts caused by foreign objects or internal failures. These stringent impact tests are mandatory for certifying engines for commercial or military use. Failure to meet these rigorous standards can result in multi-million dollar investments being grounded. Below are three critical crash scenarios commonly evaluated in aero-engine impact studies:
Figure 3: GenAI based 5G Security solution
A. Bird Strikes on Spinner Cones and Fan Blades
The skies belongs to birds, and humans, as newcomers must contend with the risks of collision. These incidents, termed Foreign Body Object (FBO) impacts, pose significant challenges despite birds being much smaller than aero-engines. At high aircraft speeds, even small bird strikes can cause substantial damage due to high momentum and energy transfer.
While birds weighing under 2.5 pounds may not cause major issues, strikes from those around 5 pounds can critically impair engine performance, leading to millions of dollars in losses annually. The spinner cone and fan blades are particularly vulnerable on the engine front.
Figure 3. Partially damaged spinner cone (left) and fan blade (right) due to Bird hit
Engineering Solutions:
B. Fan Blade Off (FBO) Incidents in Operational Engines
Fan blades endure some of the most challenging conditions, being positioned at the engine’s front. Factors such as creep, fatigue, FBO hits, or crack propagation can lead to midflight blade failure, potentially triggering a cascade of mechanical failures.
At high rotational speeds, the tip of these blades reach extreme tangential velocities, which can damage adjacent components. Fragments from the failed blade can enter the engine, causing severe damage to compressor sections and beyond.
Engineering Solutions:
Extensive real-world testing, involving significant investments, ensures engines can handle such scenarios before they are certified for flight.
Figure 4. Fan Blade off causing damage
(Ref. https://aerospaceamerica.aiaa.org/departments/containing-a-blade-out/, https://en.wikipedia.org/wiki/Blade_off_testing)
C. Blade Out Events in Compressor and Turbine Sections at Full Power
Compressors and turbines blades face extreme fatigue loads combined with thermal stress exceeding 1000 degrees centigrade. These conditions can cause a blade to detach from its root with the help of underlying cracks/air- holes in the turbine blade, potentially creating a catastrophic blade-out event.
An ejected blade at full power behaves like a high-speed projectile, with engine casing being the only barrier to contain these detached fragments. Additional debris from secondary blade failures exacerbates the damage.
Engineering Solutions:
These crash scenarios underline the importance of robust engineering and innovative materials in ensuring aero-engine safety. Advances in computational analysis and rigorous testing continue to drive improvements, allowing engines to meet stringent safety regulations and perform reliably under extreme conditions.
Figure 5. Uncontained blade out event caused severe disruption to engine in mid-air
(Ref. https://www.semanticscholar.org/paper/Impact-Studies-of-Containment-Ring-during- Blade-in-Ridley/65e8569c0cb9ccf5b65bb9f3f201aa2ff6e1e63d/figure/5,
https://www.researchgate.net/figure/A-Rolls-Royce-Trent-972-intermediate-pressure-turbine- disk-burst-accident-which-occurred_fig2_257896185 )
The above crash events are meticulously evaluated before an engine is certified for take-off. Despite rigorous testing, there have been instances where previously certified engines were grounded following real-time incidents that led to fatalities. This highlights the critical importance of early-stage evaluations in the engine design process.
To ensure reliability, engineers focus extensively on impact scenarios during the preliminary phase, well before manufacturing begins. The advent of Computer-Aided Design (CAD) and Computer- Aided Engineering (CAE) technologies has been transformative, enabling predictive analyses for various load cases. These tools supported by numerical models for materials and physical phenomena, have helped industries save billions of dollars while enhancing safety. The next section explores the role of advanced CAE technologies and tools in creating safer, more efficient engines and fostering a new era of innovation in aviation.
The aviation industry relies heavily on advanced technologies and innovations to ensure the safety and efficiency of air travel. This multibillion-dollar sector demands precision and reliability throughout the manufacturing process of aero-engines, often referred to as "engineering birds." Two critical branches of engineering—Computer-Aided Design (CAD) and Computer-Aided Engineering (CAE)—play pivotal roles in turning ambitious ideas into reality.
Finite Elements Analysis (FEA) forms the backbone of CAE, enabling engineers to simulate and analyze scenarios related to durability, Noise, Vibration, and Harshness (NVH), Computational Fluid Dynamics (CFD) and crash analysis. Within the context of crash analysis, several commercial tools facilitate the FEA process:.
Hypermesh, ANSA, and LS-Prepost are widely used to convert CAD models into Finite Element (FE) models, ensuring detailed and precise representations for analysis.
LS-Dyna, PAMCRASH, and Radios are the leading solvers for crash analysis. These tools employ rigorous algorithms to process input data, simulate impact scenarios, and generate meaningful animations and engineering insights.
The output from solvers is fed into post- processing tools like HyperView, LS- Prepost, Animator, Metapost to visualize results, create plots, and identify necessary adjustments to improve designs.
These advanced tools enable engineers to predict outcomes of various impact scenarios, optimize designs, and validate safety measures, all within a virtual environment. This capability has revolutionized the industry, saving billions of dollars by reducing the dependency on physical prototypes and enhancing the reliability of aviation components.
Cyient’s tremendous journey with Aero- engineering
Cyient's footprint in aerospace engineering is extensive, with numerous world-renowned aviation technology corporations as delighted clients for decades. Over the years, Cyient has supported and delivered a vast number of projects across various engineering domains, including design, structural and thermal analysis, and aftermarket services for the aerospace industry.
In the past two decades, Cyient has contributed significantly to impact and crash load cases in aero-engines.
Key projects include:
Many design modifications were proposed to fine-tune components for withstanding critical crash loads, some of which have been patented. Cyient provided thoroughly investigated and validated engineering judgments, supported by functional evaluations, to assist clients in meeting certification norms for aero-engine systems.
A critical aspect of aviation engineering is data security, governed by varying legal and compliance norms across regions, given the patented and export-controlled nature of these technologies. As a global player, Cyient understands the data privacy and security obligations of its clients across geographies. It has implemented stringent security checkpoints to prevent data breaches, ensuring 100% protection of invaluable client information.
Cyient’s technical competencies and adherence to business ethics, particularly in CAD/CAE, have earned the company numerous prestigious awards and recognitions from aviation corporations year after year.
Sathish Kumar Garala received Master of Technology in Design Engineering from IIT Hyderabad, and has over 10+ years of experience across IT & Engineering industries. He predominantly works in Crash/Impact Analysis using CAE tools to support the customers of Aero and Automotive domains. He carried out and lead projects on functional evaluations of aero engine structures like bird strikes on Spinner cones, Fan blade-off events, blade out containments in compressor/turbine sections etc. On Automotive discipline, he extensively worked on sub-system and full vehicle crash evaluations for frontal and side impact load cases for passenger cars and vans. He also takes responsibility as one of the SMEs in LS-Dyna for crash studies at Cyient. His interest lies in exploring new designs, materials and technologies that can help in building much safer aero structures and automobiles.
Upon receipt of a De Novo request, the FDA will conduct an acceptance review. The acceptance review is an administrative review to assess the completeness of the application and whether it meets the minimum threshold of acceptability. If any of the acceptance elements are not included, a justification has to be provided for the omission.
To aid in the acceptance review, it is recommended to submit an Acceptance Checklist as per the guidance document with the De Novo request that identifies the location of supporting information for each checklist element.
The De Novo request will not be accepted and will receive a Refuse to Accept (RTA) designation if one or more of the elements noted as RTA items in the Acceptance Checklist are not present and no explanation is provided for the omission(s). However, during the RTA review, the FDA staff has the discretion to determine whether the missing checklist elements are needed to ensure the De Novo request is administratively complete to allow the De Novo request to be accepted.
Within 15 calendar days of the Document Control Center receiving the De Novo request, the FDA will notify the requester electronically of the acceptance review result as one of the following:
Once the De Novo request is accepted for substantive review, the FDA conducts a classification review of legally marketed device types and analyzes whether an existing legally marketed device of the same type exists. This information is used to confirm that the device is eligible for De Novo classification.
During the substantive review of a De Novo request, the FDA may identify deficiencies that can be adequately addressed through interactive review and not require a formal request for additional information.
If the issues and deficiencies cannot be addressed through interactive review, an Additional Information letter will be sent to the requester. If an Additional Information letter is sent, then the De Novo request will be placed on hold. The requester has 180 calendar days from the date of the Additional Information letter to submit a complete response to each item in the Additional Information letter.
Note: The response must be sent to the DCC within 180 calendar days of the date of the Additional Information letter. No extensions beyond 180 days are granted. If the FDA does not receive a complete response to all deficiencies in the Additional Information letter within 180 days of the date of the letter, the request will be considered withdrawn and deleted from the FDA's review system. If the De Novo request is deleted, the De Novo requester will need to submit a new request to pursue the FDA's marketing authorization for that device.
The requester must submit their response to an Additional Information letter in electronic format (eCopy), to the DCC of the appropriate center. The response should—
The final step is the De Novo request decision. Under MDUFA IV, the FDA's goal is to decide about a De Novo request in 150 review days. Review days are calculated as the number of calendar days between the date the De Novo request was received by the FDA and the date of the FDA's decision, excluding the days a request was on hold for an Additional Information request.
Cyient offers a one-stop solution, CyARC–Accelerated Regulatory Platform, for helping medical device companies to ensure regulatory compliance. Empowered by Quality Assurance and Regulatory Affairs (QARA) CoE, Cyient has certified professionals across all the functions who have the required skillsets and expertise to support medical device companies throughout the life-cycle of their medical devices.
Abhishek Kumar is an SME in Medical Device Regulatory Affairs, Quality Assurance, and Clinical Affairs with over 13 years of experience. He has led the EU MDR-2017/745 sustenance program, identifying business opportunities for sales teams, and managed the engagement program for a US-based medical device company. He has supported the gap assessment, remediation, and submission of 45+ Technical Documentations as per EU MDR, and created 40+ CERs for Class I, II, and III medical devices according to MEDDEV 2.7.1 Rev-4. Additionally, Abhishek has developed proposals for global markets, including Europe, US, ASEAN, China, Taiwan, and Japan, and prepared and implemented regulatory plans for NPD in 90+ countries by analyzing feasibility, defining requirements, and coordinating cross-functional teams.
