DIRECT TO PHASE II – Lowering Integrally Bladed Rotor Sustainment Costs Through Mistuning Characterization of Intentionally Mistuned Blades

Navy SBIR 22.1 - Topic N221-D03
NAVAIR - Naval Air Systems Command
Opens: January 12, 2022 - Closes: February 10, 2022 (12:00pm est)

N221-D03 TITLE: DIRECT TO PHASE II – Lowering Integrally Bladed Rotor Sustainment Costs Through Mistuning Characterization of Intentionally Mistuned Blades

OUSD (R&E) MODERNIZATION PRIORITY: Artificial Intelligence (AI)/Machine Learning (ML)


The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop the measurement equipment and analysis methods required to characterize mistuning in Integrally Bladed Rotors (IBRs) that have intentionally mistuned blades for the purpose of supporting airfoil Foreign Object Damage (FOD) and repair limit expansion.

DESCRIPTION: Foreign Object Damage (FOD) is a top driver of engine removal for nearly every platform in naval aviation. FOD is caused by the ingestion of airfield debris into aircraft engines during operation and thus impacting the blade and vane airfoils [Ref 1]. Newer aircraft engines utilize Integrally Bladed Rotors (IBR/Blisk), which complicates the analysis and repair of FOD. In an IBR, the blades and disk are a single monolithic part rather than removable blades inserted in disk dovetails. The IBR design architecture reduces the mechanical damping contributed by the blade dovetail and introduces the concept of mistuning [Ref 2]. Mistuning changes the dynamic response of the IBR airfoils and can limit the FOD tolerance or blend repair [Ref 3] capability.

The Navy seeks to expand IBR mistuning bench characterization technology to newer engine designs. These new engines utilize two additional design technologies that make vibration testing and analysis more challenging: blades have intentional (A/B) mistuning [Ref 4], and blade vibratory response is excited by asymmetric vane spacing.

This Direct to Phase II topic will develop the hardware needed to measure newer, larger fan IBRs, and also develop other necessary technologies and methods to accommodate intentional mistuning in the presence of asymmetric vane excitation. To demonstrate this capability, the proposed program requirements must include, but not be limited to, the design, build, and demonstration of a prototype IBR airfoil mistuning measurement system. The prototype software must be capable of characterizing dynamic response and driving relevant excitation. These relevant operational modes (excitation) will be used to define the baseline scan plan. The system must also be capable of acquiring the actual 3D geometry of the airfoil leading edge and characterizing the geometry of any blends or damage present. This data, in addition to the predicted and measured mode shape and frequency around the rotor, will be documented in a report generated by the software.

When high-value IBRs are repaired at depot, the repair limits must include additional design margins to accommodate the hypothetical worst-case IBR mistuning (+/- 5% frequency variation). This assessment methodology is governed by the Propulsion Structural Integrity Plan [Ref 5], which defines the requirements to design, sustain, and repair an engine component. With the technology proposed in this topic, the limits can be expanded by quantifying the actual mistuning amplification present in the IBR, thereby increasing repair limits and reducing the cost of scrapping and replacing IBRs.

This measurement will be completed when the IBR is removed from the engine (uninstalled) and is placed statically on a benchtop. The measurement hardware must be designed to ensure that it does not damage the IBR and is capable of supporting its weight (up to 250 lb; (113.4 kg)). The end goal for the technology is to deploy bench measurement systems to relevant Navy and United States Air Force (USAF) engine support depots that can measure new production IBRs and field returned/repaired IBRs to verify that mistuning requirements are maintained.

In order to quantify the actual mistuning present in the IBR, the proposed technology must be able to meet the following technology requirements:

    1. measurement of the blade leading edge geometry (identify existing damage or blend repairs);
    2. measurement of blade modal frequency response;
    3. measurement of blade mode shape response (aid in identification of mode);
    4. excitation of all blades in rotor with relevant excitation, including multiple nodal diameters, engine orders, relevant engine rotation speeds, and asymmetric vane spacing;
    5. computer system capable of near-real-time processing of collected data and automated report generation of relevant mistuning response parameters;
    6. software and analysis methods capable of analyzing benchtop mistuning measurements and predicting the installed (engine operating) dynamic response. The Navy will translate this dynamic response prediction into FOD repair limits;
    7. equipment must not damage, mark, or create excessive vibration stress in the IBR (stay below 25% Goodman stress capability), and have provisions for safe handling and lifting of the part.

Although not required, it is highly recommended that the proposer work in coordination with the original equipment manufacturer (OEM) to ensure proper design and to facilitate transition of the final technology.

PHASE I: For a Direct to Phase II topic, the Government expects that the small business would have accomplished the following in a Phase I-type effort. Have developed a concept for a workable prototype or design to address, at a minimum, the basic requirements of the stated objective above. The below actions would be required in order to satisfy the requirements of Phase I:

The offeror must demonstrate the capability to characterize mistuning on traditional IBRs that use "equal" mass blades and synchronous excitation sources. The IBR used in this prior work may be small (prefer 10 in.; (25.4 cm) diameter or greater) and be designed for commercial or military application. The prototype should be able to measure blade frequency and mode shape for all blades on the IBR for at least the first 10 modes and 25 engine orders. The offeror should demonstrate feasibility of scanning the leading edge geometry capable of measuring existing blend repairs of 0.005 in. (0.127 mm) deep and greater. The software should be capable of recording the necessary mistuning parameters; however, automated processing is not required at this phase. While data storage requirements may vary depending on technology approach, IBRs may have up to 100 airfoils per part with up to 25 modes of interest. The system should be capable of storing vibration data and geometry scan data for at least 10 IBRs at a time.

FEASIBILITY DOCUMENTATION: Offerors interested in participating in Direct to Phase II must include in their response to this topic Phase I feasibility documentation that substantiates the scientific and technical merit and Phase I feasibility described in Phase I above has been met (i.e., the small business must have performed Phase I-type research and development related to the topic, but from non-SBIR funding sources) and describe the potential commercialization applications. The documentation provided must validate that the proposer has completed development of technology as stated in Phase I above. Documentation should include all relevant information including, but not limited to: technical reports, test data, prototype designs/models, and performance goals/results. Work submitted within the feasibility documentation must have been substantially performed by the offeror and/or the principal investigator (PI). Read and follow all of the DON SBIR 22.1 Direct to Phase II Broad Agency Announcement (BAA) Instructions. Phase I proposals will NOT be accepted for this topic.

PHASE II: Develop and demonstrate a prototype measurement system based on the prior work capable of characterizing all relevant modes and excitation frequencies on intentionally mistuned blades. The Navy will provide these relevant parameters. The Navy will provide a relevant advanced IBR that contains intentionally mistuned blades and operates in an environment with asymmetric vane excitation. The program will conclude with delivery of the matured measurement system to the Navy or the USAF for verification testing and by holding a review with the Government of all data and analysis methods developed during this program.

PHASE III DUAL USE APPLICATIONS: Finalize the prototype and supporting software for deployment to the Navy and USAF engine depots. This will include working with the relevant sustainment support equipment and platform program offices to meet computer security and hardware interface requirements. Support design reviews with the Government to determine incorporation strategy. Deliver measurement systems to the depot(s) and support training and maintenance planning for the equipment.

Commercial aircraft engines are also susceptible to FOD and advanced designs also incorporate IBRs with mistuning and asymmetric vanes. The technologies developed under this program will be directly applicable to commercial aviation engines. Due to the larger size of the commercial fleets, the available market should be equal to, or greater than, the initial military application. FOD costs the commercial aviation industry over $2 billion per year and an average of $43 million per year at major U.S. hubs.


  1. Morse, G. (2021). FOD mishap investigation. The FOD Control Corporation.
  2. Gillaugh, D. L. (2019). As-manufactured modeling of a mistuned turbine engine compressor evaluated against experimental approaches [Doctoral dissertation, Wright State University]. CORE Scholar.
  3. Flight Mechanic. (2021). Turbine engine maintenance. Flight Mechanic.
  4. Kelly, F., Heikurinen, K., Fazari, E. & Wu, Y. (2009). Intentionally mistuned integrally bladed rotor (U.S. Patent No. US8043063B2). Currently assigned to Pratt and Whitney Canada Corp. U.S. Patent and Trademark Office.
  5. Department of Defense. (2015, July 13). MIL-STD-3024 w/change 1: Department of Defense standard practice: Propulsion system integrity program (PSIP). Department of Defense.

KEYWORDS: FOD; Foreign Object Damage; mistuning; IBR; Integrally Bladed Rotor; Blisk; Bladed-Disk; propulsion; aircraft


The Navy Topic above is an "unofficial" copy from the overall DoD 22.1 SBIR BAA. Please see the official DoD Topic website at for any updates.

The DoD issued its 22.1 SBIR BAA pre-release on December 1, 2021, which opens to receive proposals on January 12, 2022, and closes February 10, 2022 (12:00pm est).

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