A few months ago at the ANSYS Worldwide Sales Conference, I had the opportunity to view the many advancements and get briefed on other news concerning our simulation platform. As part of this learning experience, I thoroughly enjoyed meeting our newest colleagues from Esterel Technologies and finding out how embedded software is becoming key in the development of a new generation of products. From aerospace to automotive and transportation, from medical devices to energy generation plants, it is an important piece of the Simulation-Driven Product Development vision. In a 2-part blog, I’ll explain what this means to me.
As I’ve mentioned before I’m quite fond of aircraft, so I’ll illustrate this point by talking about some very famous military planes, starting with the glorious Lockheed F-104 Starfighter. This incredible aircraft was designed in the early 1950’s by a myth among engineers — Kelly Johnson. His goal was to create a light, easy-to-maintain, simple and cost-effective airplane that would climb as fast as possible to operating height and engage in hostile contact with radar-guided missiles.
Previous generations of fighters were armed only with guns and trained for dogfight combat. The new concept introduced in that era was about aircraft armed with missiles so that the pilot could engage hostiles from miles away, long before the hostile was in their actual sights.
This aircraft sacrificed maneuverability for the sake of speed and climb rate. Built around the most powerful engine available (8,100 kg of thrust at full A/B on a plane that weighed around 9,500 kg at takeoff), the Starfighter was able to reach 30,000 feet in less than 3 minutes and fly at 2.2 times the speed of sound at a time when almost all other aircraft were still subsonic. Its speed and climb performance remain impressive even by modern standards.
The tactic of high-speed surprise attacks took advantage of this plane’s exceptional thrust-to-weight ratio and the F-104 remained a formidable opponent for years despite of a basic avionics: A look in the cockpit (at least for the first version) revealed that the radar and the radio transmitter were the only electronic equipment on board.
Although very basic at a first glance, the F-104 was not really such a simple machine at all; it was one of the most revolutionary planes of its era (breaking records for speed, climbing rate, altitude, etc.). Engineers and pilots working on this project were exploring the unknown and facing all the connected risks. CFD was not yet available and without such a tool the engineers were only aware of the physical implications of their design choices during prototyping and sometimes only after the machine was delivered. Problems with the aerodynamic configuration made the plane very difficult to control and this led to, in the first years of its long service (the F-104 was in use until the year 2000 with many avionics and systems updates), to a long series of casualties that earned the aircraft the nickname ‘The Widowmaker.’
The formula for a supersonic aircraft at that time was “max thrust + min resistance”, so the F-104 was indeed a missile with a man in it: a 17-meter-long, thin tubular fuselage with 6.5 meters of razorblade wingspan and a T-shaped tail assembly. With such short and highly-loaded wings the plane was not really maneuverable below 300 knots (it was optimized to fly at Mach 1.4). The big difference between the fuselage mass and the wing mass generated a strong inertial coupling effect, a phenomena not well known in that time and that forced the pilot to work to keep the plane stable. The small and peculiar wings, along with the T tail fin, caused a problem that was detected with the first prototypes; when the pilot tried to force the aircraft into a high angle of attack the plane tended to suddenly pitch causing a high-speed stall. This occurred because a turbulent air layer detached from the wings and influenced the effectiveness of the tail stabilator causing the plane to enter into a super-stall condition that ended in an unrecoverable spin. In order to avoid this stall two devices were added after the first crashes: the stick shaker (an electric motor that shakes the control stick to advise the pilot of a possible stall) and the stick kicker, that pitches the aircraft’s nose down to a safer angle of attack.
The small and highly loaded wings also caused a lot of problems during landings and the resulting landing speed of the prototypes was thrilling. In order to give a better control to the pilot, a boundary layer control system was designed to bleed engine air over the trailing-edge flaps to energize flap airflow and improve lift. This device was very difficult to maintain, and it had a high rate of failure as it provided unbalanced lift on the wings and affected pilot workload (and nerves). To help pilots manage this wild horse of an aircraft that served worldwide for 50 years (2,600 airplanes in the air forces in 15 countries) a lot of devices were designed and integrated into the original version. This plane required large amounts of expertise and never forgave a human mistake, so its pilots had to be fully focused on the plane.
Check back tomorrow, when I’ll delve a little deeper into this subject.