Jayant Sirohi and students, collaborators
The research group above, led by Jayant Sirohi (seen in plaid standing closest to blades) tested a new rotor system that employs two sets of stacked rotors, which is expected to greatly improve both speed and efficiency of a helicopter.

A research group led by aerospace engineering professor Jayant Sirohi at The University of Texas at Austin performed their first wind tunnel test of an advanced helicopter rotor system that has been in development for almost five years. The group is collaborating with the University of Maryland at College Park, where the wind tunnel testing took place this summer.

The new rotor system employs two sets of stacked rotors, in contrast to the conventional single rotor design, and is expected to greatly improve both the speed and efficiency of a helicopter. The system, known as a coaxial, counter-rotating rotor system, is the first of its kind to be built and tested solely by university researchers. Next-generation helicopters with such systems have both military and civilian applications.

The coaxial, counter-rotating rotor system was pioneered by Sikorsky Aircraft Corporation. Similar designs are being developed by private companies, but most of their test data is not available to the public. Researchers studying coaxial, counter-rotating rotor systems currently utilize data from a wind tunnel test conducted by NASA researchers nearly 60 years ago. With this new set of data from the university-based team, more researchers will be able to study and develop advanced coaxial counter-rotating rotor systems with improved efficiency and decreased vibration.

The UT Austin researchers include Sirohi and graduate students Christopher Cameron and Daiju Uehara. Inderjit Chopra, an aerospace engineering professor at the University of Maryland Alfred Gessow Rotorcraft Center, and graduate student Joe Schmaus, have been collaborating with the UT researchers to run computational simulations for the design. As the experimental lead, Cameron designed most of the rotor with Sirohi’s guidance. Uehara assisted in the construction of the test stand and some of the design.

After months of hard and sometimes tedious preparation, Cameron and Uehara described the testing as both exciting and terrifying. Despite their nerves, the tests were successful and a helpful learning experience.

“It’s very stressful because we built everything and there are so many things that could go wrong at these high speeds. But when everything works out well, it’s very rewarding,” said Cameron.

In their first wind tunnel test, performance data was collected from the upper and lower rotors. The data included information about thrust, drag, power and vibratory loads. The group plans to continue analyzing the data and return to the wind tunnel in College Park for an additional set of testing in the fall semester.

Helicopter designs with coaxial counter-rotating rotor systems are gaining the attention of government officials and industry professionals. The United States Department of Defense has issued the Future Vertical Lift Initiative as a program to replace the current fleet of helicopters used by the United States Armed Forces. These types of helicopters can be useful in various missions, especially search and rescue because of their greater speed, efficiency and maneuverability.

On the commercial side, the oil and gas industry is one of the leading consumers of helicopters which are used to fly workers to oil rigs. Faster and more efficient helicopters could save the industry money and time. 

“Measurements from this wind tunnel test will form a unique set of benchmark data that will go a long way in the validation of analytical tools and the development of future helicopters with advanced rotor systems,” said Sirohi.

Sirohi and his research team would like to thank ASE/EM technical staff members Pablo Cortez and Joseph Pokluda for all their help in making parts for the rotor test stand.