If Composites Behaved like Inflatable Tires

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arm of a small quadcopter drone with a carbon fiber propeller

Picture the tires on a four-wheel drive vehicle. You can inflate or deflate them on demand, according to whatever terrain you are planning to drive on. What if you could do the same thing with composite rotor blades on a helicopter? As fantastic as it sounds, such on-demand adjustments might be right around the corner.

Composite materials are an excellent choice for helicopter rotor blades because they are lightweight yet extremely strong. Composites are also rather rigid, which is particularly important for helicopters – especially when in combat. So the U.S. Army is working with the University of Maryland to come up with a composite material that can be adjusted for strength and rigidity on demand.

The idea is to create a material that can be made more or less rigid as needed. Similar to inflating or deflating a truck tire, the material could be made more stiff when conditions require, then returned to its original stiffness at a later time. Researchers think they have figured out how to do it using reinforced carbon fiber sensitive to ultraviolet light.

Carbon Nanomaterials and Chemistry

Making a composite material like carbon fibers stiffer is all about chemistry, explains Utah-based Rock West Composites. You have to manipulate the molecules to behave a certain way in order to increase material stiffness. The Army and University of Maryland know that, but they want to go one step further by creating a material that can be manipulated in both directions, on demand.

Researchers believe the answer to their problem is to combine ultraviolet light reactive materials with things like carbon nanotubes. The reactive materials would act as reinforcing molecules to make the carbon nanotubes stiffer. And just as those molecules can be manipulated to get stiffer, they can also be encouraged to relax.

Thus far the researchers have been able to accomplish quite a bit in the lab. They have come up with a reinforcing agent/polymer combination that, when exposed to ultraviolet light, becomes 93% stiffer and 35% stronger. The material only requires 5 minutes of ultraviolet light exposure to demonstrate the higher rigidity and strength.

More importantly, rigidity and strength are improved with very little weight penalty. This is important for aircraft of all kinds, but critically important for military aircraft. Being able to strengthen helicopter rotor blades on demand without extra weight would definitely increase the capability of some of the military’s most powerful aircraft.

Taking Composites in New Directions

Many people involved with the University of Maryland project agree that the research is taking composites in new directions never before thought possible. Where all this leads is anyone’s guess, but the possibilities are exciting to think about. If you consider just how much adding inflatable tires to cars changed the automotive industry, it is easy to see how ‘adjustable’ composites could revolutionize nearly every industry that uses composite materials.

There is obviously a lot of potential for this technology in the aerospace industry. That is reasonable, given that aerospace accounts for the lion’s share of composite use right now. But just like the concept that makes inflatable tires possible is not limited just to cars and trucks, adjustable composites will not be limited to aircraft.

All eyes will be on the U.S. Army and the University of Maryland as they further develop their ultraviolet light sensitive materials. Their proof of concept has been demonstrated in the lab with great results. Now it’s time to take that concept and scale it up for real-world application. It leads one to wonder how long before that first helicopter with adjustable rotors takes to the air.