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Retired Brigadier General and NASA Astronaut Robert Stewart served as Distinguished Lecturer at the College of Engineering. Stewart discussed the aerodynamics and dynamics of the helicopter.

Michael Mercier | UAH

The University of Alabama at Huntsville (UAH), part of the University of Alabama system, hosted a lively discussion to kick off its 2022 College of Engineering Distinguished Speaker Series by welcoming Gen. American brigade Robert L. Stewart. General Stewart’s topic for the session was a particular area of ​​expertise for the retired NASA astronaut and longtime pilot, “helicopter aerodynamics and dynamics.”

As a highly experienced and decorated army aviator and experimental test pilot, General Stewart captivated his audience not only with inexhaustible knowledge of his subject, but also with wit and lively storytelling. which turned out to be a real treat for the capacity crowd on hand in the Student Services building.

The former astronaut concluded his formal presentation by taking questions from the delighted audience and then chatting with UAH WCC students who are members of the American Institute of Aeronautics and Astronautics (AIAA) Student Chapter advised by the associate professor of the MFA, Dr. Gabriel Xu.

General Stewart spent four and a half years as an experimental test pilot where he flew five prototype helicopters and provided detailed descriptions that broke down rotary-wing craft into general classifications: utility, armed, cargo, observation and Medvac. A particular career highlight was serving as project officer and chief test pilot on the YAH-64 vehicle that eventually became the Apache Armed Helicopter.

“That’s my baby, the AH-64,” General Stewart said, showing an image of the Apache during the presentation, then noting the brutal impact of the introduction of rotary-wing aircraft into a armed conflict. “The helicopter allowed us to do things in combat that we never could have done before. If you were in trouble, a plane could drop flowers on you. A helicopter could save your life.

Robert Stewart, retired brigadier general and NASA astronaut, speaking at the UAH College of Engineering

Michel Mercier / UAH

General Stewart demonstrated that the advantages of helicopters in the field had a dramatic impact on troop safety and survivability over time, directly confirmed by war-to-war statistics.

“More than 29% of the wounded ground troops of the Second World War died”, explained the brigadier general. “In Korea, it was 26.3%. In Vietnam, we brought it down to 19%, largely thanks to the helicopter.

The presentation highlighted helicopter design considerations based on mission requirements and detailed the fundamentals of airflow, as well as the rotating components of vertical take-off vehicles and the essentials of airflow generation. lift applicable to fixed and rotary wing aircraft.

“The 0H-6 is strictly a stripped-down helicopter, but what a pleasure to fly,” General Stewart noted. “I could spin this thing so fast, I swear I could see my taillights.”

The veteran pilot went on to explain why he favored certain planes over others. “The Tandem Rotor CH-47 Chinook was a cargo helicopter with a very good safety record, but mechanically, very complex,” General Stewart noted. “On one of the very first missions I flew in Vietnam, we went out to retrieve a crashed Chinook and its crew. When we got there, I saw soldiers wading through the water from the rice fields, and the Chinook was underwater, and I decided on the spot to avoid the Chinooks if I could, but then at the US Naval Test Pilot School, I flew his older brother and less sophisticated, the CH-46.

“The Mi-24 carries its own infantry in addition to being a good gunship,” he continued, then explained how his experiences in pilot training taught him to appreciate craft with less than stellar. “The Hiller OH-23 is my favorite trainer of all time. Because it’s a horrible flying helicopter! If a student can fly this, they can fly anything!”

The UH-1 Huey, originally intended for Medvac, eventually evolved into a gunship and our primary troop transport helicopter, General Stewart recalled. “His sound will stir the heart of any soldier in the field – Vietnam’s workhorse.”

Robert Stewart, retired brigadier general and NASA astronaut, speaking at the UAH College of Engineering

Michel Mercier / UAH

The former astronaut earned a Bachelor of Science in Mathematics from the University of Southern Mississippi in 1964 and a Master of Science in Aerospace Engineering from the University of Texas at Arlington in 1972. He has military and civilian experience in a forty types of aircraft. and helicopters, including over 1,200 hours of jet time, 1,015 hours of combat flight time, and over 6,000 hours of total flight time.

One of the most compelling aspects of his speech for the COE series was his ability to dispel long-held misconceptions, including impressions surrounding a particular class of vehicle featured heavily in feature films and television series, aircraft so-called “stealth” like the Boeing RAH -60 Comanche or the Stealthy UH-60 Ghost Hawk.

“Stealth – it doesn’t mean you can’t see it,” General Stewart said. “That means you won’t be able to see it until it gets close enough to complete its mission.”

His talk also covered flight controls and the basics of helicopter aerodynamics, as well as such confusing topics to the layman as fully articulated rotors, offset flapping hinges, and receding blade stall. The veteran lifted his more obscure subjects with large dollops of humor to keep his listeners transfixed.

“On the wobbly rotor, at the top is a big nut they call the ‘Jesus nut,’ he said. ‘If it works, you’ll meet Jesus!’

Examples of other topics covered included topics such as flow fields, vortex ring states, and tail thrust, all vital to helicopter flight and control.

Robert Stewart, retired brigadier general and NASA astronaut, speaking at the UAH College of Engineering

Michel Mercier / UAH

When it comes to the subject of ‘power stabilization’ or the state of the rotor vortex ring, ‘You don’t like being out of control in a helicopter,’ General Stewart said with a spark. in the eyes. “I hated having to demonstrate that to my students.”

One of the focal points of his discussion was the main difference between flying an airplane and flying a helicopter.

“I have both hands and both feet occupied when flying a helicopter,” the test pilot said. “Any fool can fly a plane. Flying a helicopter is like a Kabuki dance. I found that I could solo a student about as fast in a helicopter as in a plane, but damn , they work harder!

General Stewart reports that airplane pilots and helicopter pilots can also be broadly defined by their general demeanor: airplane pilots tend to be laid back and easy-going, while helicopter pilots lean towards the most serious, tense or even surly dispositions. The speaker made the difference easy to understand.

“Flying a helicopter or an airplane is a total body experience. But, with a helicopter, even when you’re on the ground, you need to be close to the controls, because a helicopter can go into a phase called “ground resonance”, which is a fancy way of saying “it may try to shake itself off.” a part.'”

One of the most telling points was revealing the surprising lack of certainty about what makes a machine like a helicopter fly.

“We don’t really know how an airfoil, wing or rotor blade produces lift! Your book will say it’s produced by the Bernoulli effect. It’s not true. It’s a real phenomenon elsewhere, but not necessarily on the wings. We’ve known this since 1904. It doesn’t explain things like upwind in front of the wing or downwind behind the wing or the force of tip vortices. There are three theories in the books, and all three are incomplete.

Indeed, the pilot claimed that what is known about our understanding of aircraft flight comes down to inaccurate models and mathematical approximations.

Robert Stewart, retired brigadier general and NASA astronaut, speaking at the UAH College of Engineering

Michel Mercier / UAH

“Nothing tells me a complete theory of why an airplane wing can fly,” General Stewart said. “For example, there is no equal transit time between the top and bottom of the wing. Symmetrical airfoils work. How do you explain how an airplane can fly upside down? Evil is a relative thing. If you say 2 + 2 = 3.5, it is wrong. If you say 2 + 2 = 3.999999999, it is also wrong. But it is much closer to the right than the first one. We engineers like to say our solutions might be wrong, but we’ll get close enough!”

In fact, mathematical puzzles played an important role in the development of the pilot’s career. General Stewart attributes an intimidating set of partial differential equations that describe the motion of viscous fluid substances as the impetuous leading to a change of course for the pilot.

“I’ve flown five million miles in space at 17,500 miles per hour, and the Navier-Stokes equations scare me! When I saw this, I decided to become an experimental test pilot.

As an astronaut, the speaker was a member of the space shuttle teams Challenger (1984) and Atlantis (1985) before being promoted to brigadier general in 1986. He served as Deputy Commanding General, Strategic Defense Command of the United States Army, in Huntsville, and in this capacity managed research efforts in the development of ballistic missile defense technology. In 1989, Brigadier General was reassigned as Director of Plans, U.S. Space Command, in Colorado Springs, CO. General Stewart retired from the military in 1992 and currently lives in Huntsville.

Concluding his presentation, he managed to make successfully flying a rotary-wing craft feel like nothing more than negotiating life’s trickiest vagaries:

“Everything is conditional on piloting a helicopter.”


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