Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - HaSU (Development of Hydrophobic Windscreen Coating for Next Generation Civil Tilt Rotor)

Teaser

Aircraft canopies and windshields must keep pilots’ visibility at excellent levels under several operating conditions, particularly under heavy rain occurring during flight. To this purpose, the majority of modern commercial aircrafts use wipers to shed water from the...

Summary

Aircraft canopies and windshields must keep pilots’ visibility at excellent levels under several operating conditions, particularly under heavy rain occurring during flight. To this purpose, the majority of modern commercial aircrafts use wipers to shed water from the windshields. Use of wipers is no longer foreseen in some future civil aircrafts such as the Next Generation Civil Tilt Rotor (NGCTR) while, for example, fighter jets do not possess windshield wipers since a long time due to their operational requirements of high speeds and for the low observable (stealth) constraints of modern aircraft.
A durable, surface coating on the windshield to shed water would be an ideal solution to maintain visibility without using wipers and will be of fundamental importance to limit the formation of rain-induced ice on windscreen. Today’s commercially available rain repellent treatments have poor durability and weather resistance, and they cannot be applied to polymeric transparent substrates, such as aircraft canopies/windshields. In fact, there are no solutions today proven and available on the market for effective hydrophobic coating on plastic materials such as polycarbonate, acrylic and polyurethane.
There have been many academic and commercial efforts focused on the development of highly-durable hydrophobic (HPC) and superhydrophobic (SHPC) coatings that will shed water quickly off surfaces. Whereas many technologies and coatings have demonstrated the primary goal of achieving water-shedding properties, they are limited mainly to academic interest since they lack mechanical and environmental durability or have been too difficult or expensive to apply.
The HaSU proposal is about the design and development of a rain repellent substrate capable of forming highly durable hydrophobic coatings based on a particulate inorganic homogenously distributed throughout a polymeric matrix.
Specifically, the HaSU project directly addresses the challenges inherent to design, fabricate, and experimentally demonstrate a type of hydrophobic coating protection for the Next Generation Civil Tilt Rotor (NGCTR) wiperless windscreen. Specific objectives of the project are:

1. Design and development of a specimen of the NGCTR windscreen substrate having the requested hydrophobic functionalities and performance throughout the whole flight envelope
2. Manufacturing of hydrophobic windscreen specimens
3. Testing and qualification of proposed hydrophobic specimens according to RTCA DO-160 (Environmental Conditions and Test Procedures for Airborne Equipment of proposed hydrophobic specimens)

Work performed

In the very first phase of the project, the design requirements of the NGCTR hydrophobic windscreen specimen have been defined as a result of a preliminary feasibility based on both engineering considerations as well as on more detailed numerical simulations using CFD studies. The preliminary layout configuration has followed from a trade-off among overall, conflicting, requirements which eventually led to configurations agreed with the topic leader.
Next, hydrophobic coating specifications have been released to the topic manager along with preparation of a Qualification program plan (QPP) and Development plan (DP). Failure mode and effects analysis (FMEA have been performed for failure analysis. A worksheet has been compiled including the complete review of components in order to possible failure modes, their causes and probable effects. Failure Modes, Effect and Criticality (FMECA) analysis followed FMEA one. As a final task of this phase, the completion of accurate safety and hazard analysis has been achieved.
Following this, a number of substrate specimens including hydrophobic coating on top have been manufactured using both sol-gel technology and Plasma technology (PECVD). Tests regarding hydrophobicity have been conducted on these specimens to assess:

- angle of contact (CA) between water and substrate (glass, polycarbonate, acrylic);
- surface roughness (SR);
- abrasion resistance (haze);

The main conclusions obtained so far indicated that the best performance in terms of CA, SR and haze have been reached using glass substrate treated using Sol-Gel coating.

Final results

Progress beyond the state of the art:
Traditional hydrophobic coatings are clear and abrasion resistant, but do not shed fluid easily. Superhydrophobic coatings are generally great at shedding water, but are not clear, and are easily removed. Whether it’s abrasion resistance, oil repellence or visual clarity, conventional coatings have their limitations.
Application of new sol-gel technology, investigated in HaSU have provided sharp visibility and clearness thanks to water, oil and solvent repellence. Coating also was able to withstand significant abrasion without sacrificing performance on glass.

Expected results until the end of the project:
• Improvement in adhesion of the so-gel technology to polymeric substrates
• Application to the sol-gel technology to bigger substrates, representative of a real windscreen
• Verification of the optimal composite layup in the 3D model

Regarding potential impact, a significant innovation potential is recognized in HaSU.
In fact, the validation of HPC on NGCTR windscreens will be the first one for a future commercial aircraft, and as such it will ensure a huge knowledge advantage for European aviation community. In fact, HaSU will act in the direction of improving aircraft reliability, performance and safety which, in turn, reduce both recurrent and non-recurrent costs of an aircraft.
The HaSU project will boost the capacity to create useful innovation by advancing state-of-the art on surface coating technology as a key enabling technology with the final aim of identifying proper coating methods to enhance airworthiness by improving pilot visibility and comfort. The project will contribute to advancement in knowledge on implementing new windshield technologies with credible and measurable benefits for the scientific and industrial community. In fact, HaSU will significantly increase the applicability and reliability of advanced coating technology in general, out of the research niche into industrial practice. The feasibility of such application contains the possibility of earlier, more reliable design decisions at system level, not only from global result numbers, but even more from the insight and comprehension provided by the detailed analysis of local phenomena. From a research perspective, the physical understanding of flow phenomena under improved wettability is most interesting and will contribute significantly to the growing knowledge of fluid physics in general. Furthermore, the possibility to test several chemical compounds in the coating development phase will make a significant contribution on the chemical engineering side.
Finally, it is worth remembering that the impact of new knowledge generated within the project is not limited to the aeronautic sector: in fact, putting aside some specific aspects, such knowledge could potentially be applied to rail and marine industries, building and other industrial sectors, thus improving innovative capabilities of a much broader community. One of the sectors which is likely to be very interested from innovations brought up by HaSU is the automotive one, where the potential of hydrophobic coatings would have a huge impact on safety and pilot’s comfort.