TECHNOLOGY AREA(S): Air Platform

ACQUISITION PROGRAM: PMA-275 V-22 Osprey

OBJECTIVE: Develop an embedded carbon nanotube transparent heater film to be used for de-icing and defogging aircraft windshields.

DESCRIPTION: The current state-of-the-art for thin film heating technology used in aircraft windshields has demonstrated its effectiveness over decades of use, but has costly limitations. Windshields/windscreens are one of the top consumable cost drivers on Navy aircraft. The leading cause of failure on V-22 windscreens is damage to the embedded conductive heater layer. Current passes through that heater layer to warm the windshield and prevent the formation of ice. The heating layer can fail for a variety of reasons including strain, over-voltage of the controller, and electrical discharge from precipitation static.

There are trade-offs when altering a transparent metallic heater layer to improve other properties. These trade-offs usually come at a cost of the windshield�s optical performance. The optical performance parameters affected are distortion, glint, haze, and light transmission in both the visible and night vision spectrums. The goal of this SBIR topic is to improve the performance of the conductive layer without compromising these optical properties by using carbon nanotubes as the conductor rather than any metal used in the current systems.

The heater layer will be powered by 200 volts AC, three phase per MIL-STD-704 [Ref 4], except the frequency will be between 360-440 Hertz. The heater layer should: (1) be 5 Watts per square inch and bonded to a transparent acrylic substrate; (2) produce an even temperature across the heater area, with a maximum to minimum range of no more than 10�F; (3) produce a change in light transmission (both visible and Night Vision Imaging System (NVIS)) spectrums) per ASTM D1003 [Ref 6] of less than 10 percent; and (4) endure 500 cycles of 4-point bending with strain of 2 percent without degradation. The heater film may not degrade any of the previously mentioned optical performance parameters (e.g., optical distortion, glint, haze) and must also provide Electromagnetic Interference (EMI) protection from High Power Microwave (HPM) with minimum attenuation of 30 dB [Ref 10].
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The development of this innovative coating should include an application method readily transferrable to a production environment. The final product should also be more failure resistant to the aforementioned causes and resilient to typical damage than current windshields in use by the Navy. The most typical failure is a burnout.

PHASE I: Design and determine the feasibility of using carbon nanotube technology to create a transparent heater layer, bonded to acrylic, that (1) is invisible in both the visible and NVIS spectrum, (2) tolerates bending strain, and (3) will provide even heating across the entire surface area. Develop a concept for an application method that is readily transferrable to a production environment. Review available materials and processes to determine the most practical method to achieve the desired results. Prepare a cost estimate of coating a full-scale part. Establish performance goals and test methods to evaluate conformance to these goals. Develop plans for a prototype technology and application process in Phase II.

PHASE II: Demonstrate the validity of the Phase I approach through fabrication and testing of sub-scale coupons. Test coated coupons for change in optical properties against a control tested for heater performance and flexibility. Optimize coating to achieve goals and begin increasing the scale of the coupon to validate the scalability of the product.

PHASE III DUAL USE APPLICATIONS: Transition approach to a full-scale coating and submit it for subsystem qualification testing. Upon successfully completing qualification testing, produce a full-scale part for flight testing.

Commercial aircraft use transparent film heaters in windscreens and may benefit from an improved material solution. In addition, the automotive aftermarket may also be interested in this type of heater.

REFERENCES:

1. MIL-PRF-8184F, Plastic Sheet, Acrylic, Modified. http://everyspec.com/MIL-PRF/MIL-PRF-000100-09999/MIL-PRF-8184F_10582/

2. MIL-PRF-25690B, Plastic, Sheets And Formed Parts, Modified Acrylic Base, Monolithic, Crack Propagation Resistant. http://everyspec.com/MIL-PRF/MIL-PRF-010000-29999/MIL-PRF-25690B_32088/

3. MIL-T-5842B, General Specification For Transparent Areas On Aircraft Surfaces (Windshields And Canopies), Rain Removing And Washing Systems For, De-Frosting, De-Icing, Defogging, Etc. https://www.document-center.com/standards/show/MIL-T-5842/

4. MIL-STD-704. Military Standard: Electric Power, Aircraft, Characteristics And Utilization Of. http://everyspec.com/MIL-STD/MIL-STD-0700-0799/MIL-STD-704F_1083/

5. MIL-P-83310. Plastic Sheet, Polycarbonate, Transparent. http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-P/MIL-P-83310_39089/

6. ASTM D1003. Standard Method For Haze And Luminous Transmittance Of Transparent Plastics. https://www.astm.org/Standards/D1003.htm

7. MIL-STD-1757. Lightning Qualification Test Techniques For Aerospace Vehicles And Hardware. http://everyspec.com/MIL-STD/MIL-STD-1700-1799/MIL-STD-1757A_4242/

8. MIL-STD-810G. ENVIRONMENTAL ENGINEERING CONSIDERATIONS AND LABORATORY TESTS http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL-STD-810G_12306/

9. MIL-STD-850B. AIRCREW STATION VISION REQUIREMENTS FOR MILITARY AIRCRAFT http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL_STD_850B_948/

10. MIL-STD-461. ELECTROMAGNETIC INTERFERENCE CHARACTERISTICS REQUIREMENTS FOR EQUIPMENT http://everyspec.com/MIL-STD/MIL-STD-0300-0499/MIL-STD-461_8678/

11. Grether, W. F.� �Optical Factors in Aircraft Windshield Design as Related to Pilot Visual Performance�. Aerospace Medical Research Laboratory (AMRL-TR-73-57) July 1973. http://www.dtic.mil/dtic/tr/fulltext/u2/767203.pdf

KEYWORDS: Transparency; Heater Film; Optically Clear; Polymer Materials; Coating; Carbon Nanotubes