Novel Oil Quantity Sensor for Aerospace Applications

Navy SBIR 23.2 - Topic N232-087
NAVAIR - Naval Air Systems Command
Pre-release 4/19/23   Opens to accept proposals 5/17/23   Closes 6/14/23 12:00pm ET

N232-087 TITLE: Novel Oil Quantity Sensor for Aerospace Applications

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Human-Machine Interfaces

OBJECTIVE: Design and develop an oil quantity sensor capable of measuring and assessing oil quantity, volume, and/or level of aircraft propulsion and power lubrication systems independent of oil reservoir size/form/shape of reservoir during all flight conditions. The sensor should consider aerospace requirements of low power, weight, and size and be compatible with military (MIL) and Department of Defense (DoD) Lubricant Specifications.

DESCRIPTION: The Navy requires an oil quantity sensor that greatly improves the method for identifying the oil volume within an oil tank or gearbox. Currently, oil level sensors can only accurately measure during straight and level flight and have limited sensing range, which can contribute to incorrect oil servicing and subsequent maintenance or safety events. The current sensor design is incapable of resolving oil quantities oil levels near maximum (~88%) or minimum (~23%) reservoir capacity, resulting in maintainer confusion and improper oil servicing that can lead to damaged hardware or in-flight emergencies. Current sensors are cylindrical in shape and the technology is capacitance based. The sensor developed under this SBIR topic should consider aerospace requirements of low power (less than 10 W at 5 V Alternating Current), weight of less than 2 lb (.907 kg), and size that must fit in the 23 in. x 3 in. x 3 in. (58.42 cm x 7.62 cm x 7.62 cm) envelope including power supply provisions. The sensor must operate in temperatures between -40 F (-40 C) and 450 F (232.22 C) and be compatible with MIL and DoD Lubricant Specifications. It should be capable of measuring the quantity of oil during any flight maneuver and be able to measure to the minimum and maximum capacities of the tank, regardless of tank geometry to an accuracy at least +/- 3.5 % full scale at a sample rate of at least 5 samples/sec. The sensor can mount internal or external to the tank or gearbox housing, depending on the technology. The application can vary from fixed-wing gearbox oil tanks or rotorcraft splash-lubricated gearboxes. Oil quantity will be the main function of the sensor, but added capabilities such as debris monitoring, cavitation detection, oil TAN, foreign fluids, and so forth are desirable but proposed design total weight should not exceed 2 lbs. Oil temperature monitoring may also be required to account for thermal expansion and/or oil viscosity effects. Oil temperature monitoring capabilities should roll up to the complete sensor accuracy and sample rate requirements specified herein.


  • Power requirements:
    • Current: "less than 100 W at 5 V Alternating Current"
    • Recommended: "less than 10 W at 10 V Direct Current"
  • Temperature requirements:
    • Current: "The sensor must operate in temperatures between -40 degFand 450 degF"
    • Recommended: "All sensor components exposed to oil must operate in temperatures between -40F (-40C) and 450F (232.22C) and be compatible with MIL and DoD Lubricant. If there are limitations to sensor equipment that cannot operate in this environment, an upper/lower temperature limit for this hardware should be specified."

The original/current verbiage for power requirements was considered the best guess at the time, but we have since found updated specification requirements for this hardware and we would like to make the update to the solicitation. I don't believe this change will fundamentally change the technical approaches of the proposals.

The temperature requirements change reflects a better understanding of the operating environment for this hardware based on data received today (5/5/23) that was not available at the time of the original topic draft.

PHASE I: Design an initial concept for an oil quantity sensor architecture and develop a breadboard prototype. Demonstrate feasibility to accurately measure oil quantity and volume and describe how the technology can be applied to aerospace applications. Technology risks identified through Phase I, to include system weight, should be detailed with applicable mitigations. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Using the results from Phase I, design and build a functional prototype capable of demonstration under various simulated flight conditions, (e.g., altitude changes, representative temperature and pressure changes, etc.) with MIL and/or DoD Specification lubricants. The demonstration can use an oil tank 320640 oz (9.4618.93 L) in size or a splash lubricated gearbox, and should include challenging geometric features that simulate those seen with currently fielded oil tanks. The effort should focus on the accuracy, reliability, and integration of the sensor into an existing aircraft lubrication system application. Risks identified in Phase I and Phase II should continue to be tracked with mitigations identified. The size, weight, and power requirements should be detailed along with expected end item cost and any opportunities for improvements in these areas.

PHASE III DUAL USE APPLICATIONS: Install a ruggedized and calibrated prototype oil quantity sensor on a flight test aircraft and identify any hardware limitations. A cost analysis for production hardware should also be developed and presented as part of the Phase III report.

Low cost, small form-factor oil quantity measurement sensors are applicable to many commercial and military applications. This technology is applicable to oil tanks in both fixed-wing and rotorcraft applications in the commercial and military space. This development of technology under the aggressive requirements of this SBIR topic will de-risk future commercial applications that are likely to have less demanding requirements. Specific nonaviation applications may include determining quantity of hazardous and/or corrosive fluids.


  1. Terzic, J., Nagarajah, R., & Alamgir, M. (2009). Accurate fluid level measurement in dynamic environment using ultrasonic sensor and v-SVM. Sensors & Transducers, 109(10), 76.
  2. Raja, N., & Balasubramanian, K. (2020, October). Phase shift based level sensing using two guided wave mode T (0, 1) and F (1, 1) on a thin Waveguide. In 2020 IEEE SENSORS (pp. 1-4). IEEE.

KEYWORDS: Oil; Quantity; Volume; Tank; Reservoir; Fluid


The Navy Topic above is an "unofficial" copy from the Navy Topics in the DoD 23.2 SBIR BAA. Please see the official DoD Topic website at for any updates.

The DoD issued its Navy 23.2 SBIR Topics pre-release on April 19, 2023 which opens to receive proposals on May 17, 2023, and closes June 14, 2023 (12:00pm ET).

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