AUTONEWS

Glowing paint that maps air pressure could improve the design of future aircraft

Scientists have developed a new pressure-sensitive paint that delivers more accurate pressure measurements by minimising the effects of temperature fluctuations.

The material combines a platinum-based light-emitting compound with a specially engineered polymer, allowing it to respond more reliably during wind tunnel testing.

Trials showed a 25% reduction in temperature sensitivity compared with the current industry standard.

The improvement comes from chemically locking the active molecules into the polymer structure, preventing molecular clustering that can distort measurements.

The advance could help aerospace engineers make better-informed design decisions using cleaner aerodynamic data.

When engineers design a new aircraft, they need to know exactly how air flows over every surface. The pressure distribution must be controlled or the fuel efficiency, handing, or even structural safety can be affected.

A promising new technique for measuring this is by applying a special paint to scale models tested in wind tunnels, which glows in proportion to the air pressure pushing against it. However, these paints have one main flaw – they’re sensitive to temperature as well as pressure. As a model heats up during testing, the paint output can shift and introduce errors that engineers then have to unpick.

Now, a team from The University of Manchester’s Departments of Mechanical and Aerospace Engineering, and Chemistry, have created a paint that substantially reduces the problem. This new material uses a light-emitting, platinum-based compound, locked into a specially engineered plastic. The results of trials using the paint, published in ACS Applied Engineering Materials, show a drop in temperature sensitivity to just 0.3% per degree Celsius – 25% less than the current industry benchmark.  

Dr Elliott Nunn, first author based in the Department of Chemistry, The University of Manchester, said: “When you’re testing a vehicle at high speed it can heat and cool dramatically based on its aerodynamic design. By creating a pressure-sensitive paint which doesn’t respond as strongly to this heat, we’ve got something that’s much closer to measuring exactly what we want to measure. Our hope is that this will really help the engineers designing the next generation of high-performance and more sustainable aircraft and spacecraft, to make better-informed decisions through cleaner data.”

Their breakthrough comes down to how the active ingredient sits within the material. In many existing paints, the molecules responsible for glowing can cluster together, and this clustering makes the paint more sensitive to heat. The Manchester team fixed this by anchoring this ingredient, from the same family of molecules that give blood its red colour, or make leaves green, directly into a tough, Teflon-like plastic. When held in place at the chemical level, the molecules are far less likely to cluster and the paint’s temperature sensitivity drops.

Aerodynamic performance data on a truncated cone model at supersonic flow collected using low temperature sensitivity PSP. Credit: The University of Manchester

Their breakthrough comes down to how the active ingredient sits within the material. In many existing paints, the molecules responsible for glowing can cluster together, and this clustering makes the paint more sensitive to heat. The Manchester team fixed this by anchoring this ingredient, from the same family of molecules that give blood its red colour, or make leaves green, directly into a tough, Teflon-like plastic. When held in place at the chemical level, the molecules are far less likely to cluster and the paint’s temperature sensitivity drops.

Dr Louise Natrajan, Reader in the Inorganic Chemistry Group, The University of Manchester, said: “Getting this chemistry right was thanks to a creative collaboration between our chemistry group and the aerospace engineering team – basically, they knew what the paint needed to do in a wind tunnel, and we knew how to create something that could do it.”

To test their paint under realistic conditions, the team applied it to a cone-shaped model designed to produce complex airflows, then ran this model through a supersonic wind tunnel where airflows can exceed Mach 5 – 5x the speed of sound. At these conditions the model’s temperature varies drastically across its surface. However, the new paint measured pressure accurately throughout the test, with results aligning closely with the values predicted by computer simulations.

This paint was also able to help the researchers visualise the corkscrew-shaped swirls of air that develop along concave curved surfaces – known as Görtler vortices – which are important for understanding how the thin layer of air next to a surface behaves at speed.

More accurate pressure measurements at high speeds and temperatures, could translate directly into helping the aerospace industry to develop safer, more efficient transport. The team are now planning to test their paint across a wider range of conditions, to build confidence in how reliably it can perform.

Scientists have developed a new pressure-sensitive paint (PSP) capable of glowing to map airflow over aircraft with much greater precision, minimizing errors caused by temperature fluctuations. This innovation, led by researchers at the University of Manchester, promises to transform wind tunnel testing and provide aerospace engineers with much cleaner aerodynamic data.

The technological breakthrough...Traditional pressure-sensitive paints have a critical flaw: they respond to both air pressure and temperature. As the model heats up during high-speed tests, the data becomes distorted.

The new formulation solves this problem by reducing thermal sensitivity by 25% compared to the industry standard. The team achieved this result through advanced molecular engineering:

• Preventing clustering: The active molecules (belonging to the same family that gives blood its red color) were chemically anchored directly onto a rigid polymer structure similar to Teflon.

• Molecular stability: This "locking" mechanism prevents the molecules from clustering, thereby eliminating most of the sensitivity to residual heat.

Supersonic speed tests...To validate the paint under extreme conditions, it was applied to a conical model and tested in a wind tunnel at speeds exceeding Mach 5 (five times the speed of sound). Even amidst drastic temperature fluctuations on the object's surface, the paint mapped pressure with precision that matched digital computer simulations.

The mapping also allowed for the visualization of Görtler vortices—corkscrew-shaped air currents that form on concave surfaces and determine how thin layers of air behave at high speeds. 

Impact on the future of aviation...The ability to obtain ultra-precise, real-time pressure data reduces the need for expensive and complex physical sensors. With cleaner aerodynamic data, the aerospace industry gains crucial tools for designing safer, more stable, and fuel-efficient commercial and military aircraft.

The University of Manchester