How a “Bottle of Math” Enables Safe Airship Operations
Chances are you use inceptors every day to control motion, but probably know them better by another name. When driving your car, the steering wheel serves as an inceptor, telling the vehicle how to maneuver based on your movements. A throttle and brake system tell the vehicle to go faster or slower based on your applied pressure on the pedals. They too are inceptors. When applying this same concept to aircraft, and factoring in the additional dynamics involved with vertical movement, the joystick and speed control inceptors found in aircraft enable what is commonly known as flight controls.
The creation of effective sets of flight controls --- the Wright Brothers’ most important invention --- was a critical component in the development of safe and stable flight. Flight control surfaces –- like rudders and elevators -- allow the pilot to adjust and control the aircraft’s flight path. On fixed-wing airplanes, two rudders and two elevators control direction, while either one or two engine throttles control the engine’s thrust or force. These devices serve as flight controls and help guide the plane to its final destination.
An interesting thing happens though with flight controls and surfaces when you take speed out of the equation – they become less effective. As a result, slow-moving aircraft like airships need much larger surfaces to control flight. Even with larger surfaces, airships can respond sluggishly, making safe operations in gusty conditions challenging.
No Cables or Pulleys Needed
Traditional airships use a cable and pulley system for directional movement, which is finicky at best, and leaves tremendous opportunity for error. When the Skunk Works® team began developing the next generation airship – the Hybrid Airship – for remote cargo transport nearly 20 years ago, they pulled knowledge from their Lockheed Martin fixed-wing brethren and built digital flight controls, or a fly-by-wire system, into the airship’s standard systems. An industry first at the time.
“This digital system changes the airship game,” said Hybrid Airship program manager, Dr. Bob Boyd. “It takes in environmental factors like altitude, wind direction, and intended flight path previously monitored and computed by the pilot and constantly adjusts the flight controls to meet the pilot’s intent. Thus, the pilot can focus on navigating the flight path, while the computer takes care of instructing the control surfaces.”
Consider this – In a storm, the pilot of an airship is not only working against the elements, but also the control limitations brought on by the low speed. Essentially, they’re left with a balloon in a wind tunnel. Staying on course becomes a daunting task. With the help of a sophisticated flight control system, however, Hybrid Airship pilots are getting course corrections constantly without a second thought.
Through a very complex set of mathematics that model the physics of every situation an airship could encounter, the system reads the pilot’s input, uses its stored set of equations to connect point A - the inceptor that provides the input - to point B, which results in the movement of the airship toward the intended destination.
“These equations are built based on a number of factors that shape the physics of the vehicle. The airship’s buoyancy, propulsion, aerodynamics and its mass, or location of the heavy objects are across the vehicle, all affect the airship’s performance and are taken into account when establishing the flight control equations,” said Boyd.
The Skunks don’t reveal secrets freely, but we can say they’ve worked for years to develop the complex equations used by the Hybrid Airship before testing their performance in a digital model called Simulink. The resulting proven “bottle of math” or flight control laws are then added to the airship’s flight control computer and serve as the heart of the system, playing a critically important role in driving the aircraft’s performance.
This essential system enables the Hybrid Airship to perform unlike any other airship in the industry. More like a truck or bus, the Hybrid Airship powers through inclement weather to travel long journeys with heavy loads. This reliability alone provides a safety not found with other airships, but also helps contain costs. Between the Air Cushion Landing System, SPIDER pinhole repair system and flight controls of the Hybrid Airship, our next generation airship is carrying remote cargo transport into the future.
ENGINEER SPOTLIGHT: MEET A FLIGHT CONTROL ENGINEER
As a member of the Lockheed Martin Skunk Works team, Chris Elliott aids the development of flight control systems and has supported a variety of programs throughout his career, including the Hybrid Airship.
He has always had a passion for aerospace engineering, but flight controls has emerged as one of his favorite disciplines because of the challenges it presents each and every day.
“During my time at Lockheed Martin Skunk Works, I have constantly been learning new things, working on new projects, and facing new challenges that have helped me grow throughout my career,” shared Elliott. “I am fortunate to work in an environment with a continual learning cycle, working alongside a highly talented team that’s committed to tackling some of the industry’s toughest problems.”
Elliott believes that no matter what stage of your career, the key to success is to maintain a positive attitude and willingness to learn. With that, you can shape your career to align with your interests, and ultimately find a way for your engineering contributions to improve the world around you.