This essay explores the design of machines that must perform multiple functions. It concentrates on the Harrier fighter and the hybrid car.
IIntroduction
One of the most useful things anyone can have is a device that fulfills more than one function. This is comparable to human babies, of course, who learn and grow and play many roles over a lifetime.
Often hybrid designs are startling and complex. We’ll look at two such systems: the new hybrid cars, and an old airplane: the AV-8 Harrier. (I picked it because as an ex-Marine, I’ve seen Harriers numerous times over the years and know quite a lot about them.).
IIThe Harrier
The Harrier is a British product; though now McDonnell-Douglas also manufactures it under license to British Aerospace, formerly Hawker-Siddeley, the original designers. It is flown by the RAF and the Royal Navy, as well as the Spanish and Italians, but is probably best known for its service with the U.S. Marine Corps, the only one of the American armed forces to purchase the aircraft. Known unhappily as the “Widowmaker,” the Harrier AV-8A has an appalling safety record, with 55 peacetime accidents (or rather, it had a poor safety record until pilots learned how to fly it).
The new Harrier AV-8B II has greatly improved upon the original, but it remains a tricky aircraft to handle even after thousands of flight hours. Nevertheless, the Marines have continued using it because it suits their unique ground support mission so well.
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The Harrier is the fabled VSTOL (vertical and short take-off and landing) aircraft, the “jump jet” that the armed forces have wanted for decades. It was designed to blend two seemingly incompatible missions: flying like a jet and hovering like a helicopter. It also has to deliver a significant payload of rockets and bombs.
It can take off and land conventionally; it can take off and land on a very short runway; or it can take off and land vertically. It is this last feature that has made the airplane famous: numerous movies show the aircraft slowing down until it comes to a complete stop and hangs in midair.
The secret to the aircraft’s maneuverability is a concept known as “vectored thrust,” a term which has given rise to any number of lewd jokes. Basically, the airplane is equipped with moveable nozzles which can direct the jet exhaust in several directions: backwards, providing conventional thrust; slightly forward, providing the slowing; or straight down, providing the ability to hover. The airplane “balances” on these columns of air as its pilot slowly reduces the thrust and lowers it to the ground.
The AV-8As were powered by the Rolls-Royce Pegasus Mk 102 engine; the later models have stepped up to the more powerful Mk 103. As one might suppose, the most dangerous times of the flight are the “transitions,” either from conventional flight to the hover or vice versa. One pilot reports that the controls of the Harrier are so sensitive that only a fingertip is needed to make inputs. (Ethell, PG).
With that degree of sensitivity, “over controlling” and subsequent loss of control become a real possibility. If the airplane starts to “wobble” that close the ground, it may well be lost; it has no room to recover, yet if it drops from that height, it can be destroyed.
Nevertheless, as development of the aircraft continued and piloting skills improved, the Harrier earned its place as one of the most versatile and valuable fighters ever developed. Now, however, the Harriers are getting tired, and a new generation of V/STOL aircraft will be needed soon to replace them.
IIIHybrid Cars
Hybrid machines have been with us for a long time, but not in the auto industry. Railroads have been using diesel-electric engines for decades, for instance; the concept isn’t new, but its application to automobiles is. Hybrid simply means that the vehicle gets its power from two sources; in this case, it’s both gas and electric.
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A gasoline powered car burns gas in an internal combustion engine, which then transmits the energy of the burned gasoline (actually the explosions in the cylinders) to the transmission, which turns the wheels. An electric car has batteries that transmit power to an electric motor, which powers a transmission that turns the wheels.
A hybrid uses both sources, though some models are parallel hybrids and some are series hybrids. In a parallel hybrid, the engine and gas tank connect to the transmission, as do the batteries and electric motor. Thus, either system can power the car.
In a series hybrid, the gas engine turns a generator. The power produced by the generator can then either charge the batteries, or power an electric motor that turns the transmission. In a series hybrid, the gas engine never directly transmits power to the vehicle. (Nice, PG).
IVConclusion
Hybrids and combination use vehicles would seem to be the mechanical analogy to the developmental stages of living organisms.
VReferences
Ethell, Jeff. “Jeff Ethell’s Pireps – AV-8 Harrier.” 1995. Accessed: 12 Feb 2003. http://www.airspacemag.com/asm/web/special/ethell/pirep5.html
Nice, Karim. “Hybrid Structure.” Howstuffworks.com [Web site]. 1998-2003. Accessed: 12 Feb 2003. http://howstuffworks.lycoszone.com/hybrid-car2.htm
“The AV-8B Harrier Jump Jet.” YellowAirplane.com [Web site]. Undated. Accessed: 12 Feb 2003. http://www.yellowairplane.com/Books_n_Videos/AV-8B_Harrier_Books.html
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