Hindustan Aeronautics Limited Seeks Consultancy Services for Noise Attenuation in Light Utility Helicopter

On March 25, 2025, Hindustan Aeronautics Limited (HAL), a leading Maharatna Public Sector Undertaking in India, issued a Request for Quotation (RFQ) through its Rotary Wing Research & Design Centre (RWR&DC) in Bangalore. The RFQ invites proposals for consultancy services aimed at addressing internal noise attenuation issues in its Light Utility Helicopter (LUH). With a submission deadline of April 4, 2025, at 14:00 HRS IST, HAL is emphasizing its commitment to enhancing the performance and comfort of this critical rotary-wing aircraft, designed to serve both the Indian Armed Forces and civilian markets.

The RWR&DC, an ISO 9001-certified division based in Bangalore, spearheads HAL’s efforts in rotary-wing aircraft innovation. The LUH, a 3.0-ton class helicopter, features a single engine, a side-by-side pilot and co-pilot configuration, a four-bladed hinge-less main rotor, and a four-bladed bearing-less tail rotor. It is designed for versatility and reliability, making it a vital asset for military and civilian applications.

However, developmental flight tests on an LUH prototype revealed a significant challenge: internal noise levels inside the cockpit and cabin exceed the limits specified by MIL-STD-1474D, particularly in the frequency range of 500 to 8,000 Hz. For example, at 500 Hz, the MIL standard caps noise at 91 dB, yet measurements reached up to 99.4 dB at the co-pilot station. Similarly, at 2,000 Hz, the limit is 82 dB, but levels as high as 105.6 dB were recorded. This noise issue, if unresolved, could impact crew comfort, communication, and operational efficiency.

Scope of the Consultancy

The RFQ outlines a comprehensive scope of work divided into three key tasks to tackle this noise problem:

1. Experimental Root Cause Analysis:
   The selected vendor will use 3D acoustic cameras to map internal noise during ground runs and flights at various altitudes and speeds. This task includes panel contribution analysis, frequency response function (FRF) analysis, and experimental modal analysis to pinpoint noise sources and their transfer paths within the LUH. A detailed report identifying high-noise contributors in the cabin and cockpit is expected.

2. Computational Analysis:
   Following the experimental phase, the vendor will conduct simulation studies using HAL-provided CAD, finite element (FE), and computational fluid dynamics (CFD) models of the LUH. The goal is to predict low, mid, and high-frequency noise levels, including vibro-acoustic effects, and correlate these with flight test data. This task also involves identifying noise transfer paths and performing modal, panel, grid, and energy contribution analyses to propose attenuation solutions.

3. Modification Solutions:
   Based on the findings from the first two tasks, the vendor must recommend optimized, implementable solutions to reduce noise by 10 to 15 dB in the 500–8,000 Hz range, aligning with MIL-STD-1474D requirements. These solutions could involve structural adjustments, machinery modifications, or lightweight noise-absorbing materials, all designed to minimize the need for major helicopter redesign.

Timeline and Deliverables

The consultancy is expected to span 21 weeks from the contract’s initiation. Key milestones include:

• Helicopter allocation for testing (T1).

• Experimental root cause analysis completed within 30 days of T1.

• Computational analysis phased over 75, 105, and 120 days from T1.

• Final modification solutions delivered by T1+145 days.

Deliverables include detailed reports on experimental testing, analytical predictions with models, and design improvement recommendations.

Strategic Implications

This RFQ underscores HAL’s dedication to refining the LUH, a helicopter poised to strengthen India’s defense and civilian aviation capabilities while exploring export opportunities. By addressing internal noise, HAL aims to enhance crew safety and operational effectiveness, aligning with global standards. The emphasis on local suppliers also reflects India’s push for self-reliance in defense manufacturing.