Function Follows Form

Purpose-built aircraft provide practical solutions to specific needs and culminate in aircraft designs that are the very best of their kind
aviation, technology, history
Written By Randy S. Bolinger

For more than a century, aircraft have been designed in all shapes and sizes for a host of special purposes. There are aircraft that can fly at three times the speed of sound—so fast that a pilot could leave New York at dawn and arrive in Los Angeles with plenty of time to see the day’s sunrise for a second time. Aircraft that can carry another aircraft in its belly or on its back. Flying boats that opened up trade and passenger routes to new and exotic places during the Golden Age of aviation. And yes, even cars that fly—while they seem to neither excel at being a car nor an aircraft—there is something to be said for being able to take to the airways when the roadways are gridlocked.

What follows is a glimpse at a short list of purpose-built aircraft that represent a practical solution to a specific need. The best of which withstood the test of time to secure a lauded place in the annals of aviation history for being the very best of their kind.

Martin JRM Mars

Image By © David Crottey/Alamy Stock Photo

The difference between a floatplane or an amphibious aircraft and a flying boat is that a flying boat is truly a boat that flies. What one would normally call the fuselage is a stepped hull that creates the buoyancy to stay afloat in the water and can also act as a lifting surface in the air. Flying boats are a practical solution to global access since 71 percent of the Earth is covered by water. And because essentially any large body of water more than 3 miles long provides an excellent level runway surface.

The most famous or perhaps infamous flying boat is the Hughes H-4 Hercules. Designed to carry 750 troops in its hull, the wingspan of 320 feet would shade an entire football field. But alas, it was not a practical solution because it only flew once, with no payload and achieved an altitude of just a few feet above the surface of the water. The H-4 turned out to be a more successful museum attraction than flying boat.

Conversely, the Martin JRM Mars, which first entered service in 1945, is still flying today and plays an important aerial firefighting role as a water bomber. Boasting a combined 10,000 horsepower from its four piston-powered radial engines, the two remaining JRMs can skim a lake surface and load an entire 30-ton payload of water in less than 30 seconds. The JRM can then deliver that liquid payload to the scene of a wildfire and completely douse 4 square acres.

Purpose Built: Originally a long-range personnel and cargo transport for remote locations without conventional paved runways.

Fun Flight Fact: The flying boat is moored by an anchor, carried onboard, that weighs 12,000 pounds.

Lockheed SR-71 Blackbird

Image By © NASA Archive/Alamy Stock Photo

While Superman can fly faster than a speeding bullet, he exists only in the imagination. Whereas the SR-71 Blackbird exists in the realm of what is. As a matter of perspective, bullets generally achieve a muzzle velocity approaching 3,000 feet per second. The SR-71 tops out at 3,200 feet per second.

To design an aircraft for its specific top-secret purpose, Lockheed had to overcome challenges never before encountered, like heat dissipation, because parts of the airframe reach 1,100 degrees Fahrenheit due to friction from air molecules at cruise speed. Two-inch thick quartz had to be used for cockpit windows because the extreme heat warped conventional glass. A new fuel (JP-7) had to be developed to power the two massive Pratt & Whitney J-58 axial flow afterburning turbines, each generating 32,500 pounds of thrust.

And while the SR-71 was among the first aircraft to use stealth technology, it didn’t matter much. Cruising at an altitude of 85,000 feet and speeds of Mach 3.2, the SR-71 can simply outrun any ballistic weapon fired upon it.

Amazingly, Lockheed created an aircraft that can fly more than Mach 3—three times the speed of sound—in a pre-computer era using nothing more than a slide rule and tenacity.

Purpose Built: Ultrahigh speed (2,200 mph), ultrahigh altitude (85,000 feet) aerial reconnaissance missions.

Fun Flight Fact: SR-71 once flew from Los Angeles to Washington, D.C., in 67 minutes; there was no beverage service.

BAE Concorde

Image By © Antony Nettle/Alamy Stock Photo

Transporting passengers beyond the limitation of the sound barrier was the goal that reduced travel time between key cities like New York City and London to a mere three hours and thirty minutes. Compare that to a run of the mill commercial airliner at seven hours plus and the practical benefits of time saving become obvious. The supersonic transport (SST) served a variety of airlines with a sublime—albeit brief—passenger experience between 1976 and 2003. Computational fluid dynamics and military experimentation combined to develop airframe technology that manages the shock wave created by breaking the sound barrier. However, due to the adverse consequences resulting from the shock wave (sonic boom), achieving supersonic speed was limited to transoceanic segments where there are no livestock to frighten or windows to rattle.

Interestingly, Gulfstream’s robust research and development team collaborated with NASA to tame the sonic boom. The aptly named proprietary Quiet Spike allows aircraft to pierce the sound barrier without breaking windows or eardrums. In the future when civil laws catch up to technology and overland supersonic travel is permitted, the practicality of supersonic travel will be fully realized and Gulfstream will be poised to lead the industry again.

Purpose Built: Supersonic trans-Atlantic elite commercial passenger transport.

Fun Flight Fact: Due to its high-speed capability, and because time is of the essence, the Concorde was used to transport human organs for transplant.

Antonov AN-225 Mriya

Image By © CTK/Alamy Stock Photo

Biggest doesn’t always mean best. But in the realm of purpose-built, heavy-lift cargo aircraft, it is simply impossible to ignore the Russian-built Antonov. Two were originally ordered by the Russian space program to carry rocket booster sections and the shuttle. Only one was completed and remains in service today as the world’s largest purpose-built cargo aircraft. Construction of the second AN-225 was never completed and the airframe is stored in a hangar—a very large hangar. Yes, the Boeing Dreamlifter tops the chart for heavy-lift cargo aircraft with larger, slightly greater cargo volume—although it is a converted 747, as opposed to a purpose-built platform. But by a large margin, the AN-225 tips the scale with a maximum takeoff weight of 1.4 million pounds, with more than 30 percent of that being payload it was purpose-built to carry. And for what it’s worth, no disrespect intended, but anything purpose-built is just going to look more elegant, or in this case, more airworthy than anything designed for one purpose and converted for another like the Airbus Beluga and Boeing Dreamlifter.

Purpose Built: Heavy-lift with a payload volume of 550,000 pounds in a cargo area approximately 46,000 cubic feet.

Fun Flight Fact: At 141 feet long, the cargo hold of the Antonov AN-225 is longer than the first flight of the Wright Flyer at 120 feet.

Gulfstream I

Image By Gulfstream archives

During the economic boom of the late 1950s, many companies turned to surplus military aircraft to meet the growing demand for private aviation. Having not been designed with the passenger experience in mind, 1940s vintage troop transports, cargo carriers and converted bombers did not lend themselves well to elegant travel. Walking under a wing dripping oil from the massive radial engines, to climb a portable stair or small ladder, to strap into an unpressurized fuselage with no noise suppression indeed made for a memorable trip—for all the wrong reasons. Thus in 1958, Grumman Aircraft parleyed its expertise and reputation as the premier builder of naval aircraft to develop the world’s first purpose-built business aircraft.

The Gulfstream I transformed the experience of private aviation and created an entirely new segment of aircraft, and Gulfstream has never looked back. Forward-thinking research and development has led to industry first (and only) features like the massive panoramic windows that are the only ones of their size certified by the Federal Aviation Administration. Numerous other innovations came to the industry via Gulfstream. such as enhanced vision systems that have become ubiquitous in the market and help improve aircraft safety.

Clearly the vision that launched the Gulfstream I in 1958 withstands the test of time today and Gulfstream remains solely focused on creating and delivering the world’s finest aviation experience by blazing a path for others to follow.

Purpose Built: The very first and very best of its kind business aircraft.

Fun Flight Fact: Largest windows of any pressurized private aircraft ever produced—that is until the G650 arrived on the scene.

Other Winged Wonders

In some cases, it’s debatable whether the purpose-built aircraft was a practical answer to a real-world problem or whether the purpose of building the aircraft was to simply prove that it could be done. But if you ever need an aircraft that can completely circumnavigate the planet, one that can take off and land on your street or one that can be carried somewhere, inflated on-site and flown away, here are the aircraft that meet those needs.

Image By Ralph Crane/The LIFE Picture Collection/Getty Images

Goodyear Inflatoplane
A fair question here would be “what’s the point?” The answer, though perhaps not obvious, makes perfect sense when you consider the purpose. The practical application of the Inflatoplane was the retrieval of downed airmen from behind enemy lines. The Inflatoplane could be airdropped in a 44 cubic foot fully self-contained hardened case, including aircraft engine, air pump and 20 gallons of fuel. After five minutes, the aircraft was fully inflated and resembled something more like an aircraft and less like an airbed, and was then capable of some fairly reasonable aircraft performance. While there were six variants, in general an Inflatoplane could take off in 250 feet, with a payload of 240 pounds and could cruise for more than six hours at speeds up to 70 mph. The inflatable aircraft could even climb to an altitude of 10,000 feet (which seems only natural for a balloon anyway).

Image By MMassel/

Terrafugia Transition
Countless technological innovations have been spawned at the Northeastern think tank, otherwise known as the Massachusetts Institute of Technology, either as research projects in the labs or by MIT graduates. In fact, some staples that no pilot should be without include innovations like Bose headsets, RADAR (radio detection and range) and even the Gillette disposable razor. We can now add the flying car, or perhaps more accurately a roadable aircraft, to the list. The Transition has obvious features like folding wings that make it practical to park in your garage and of course allow other cars to pass without creating a rolling roadblock. Once certified safe for both road and sky, operating the Transition will require two licenses—one for driving and one for flying. The good news is that the Transition is designed to meet the requirements for Light Sport Aircraft, which can be flown as a sport pilot (which can be achieved with 20 hours of instruction).

Image By Bettmann Archive/Getty Images

Scaled Composites Voyager
The name Burt Rutan is legendary in aviation circles as the creator of a diverse stable of one-of-a-kind, proof-of-concept aircraft. One such aircraft is the Voyager that was designed on a whim to fly around the world, nonstop, unrefueled. The aircraft, piloted by the two people who conceived the feat, Jeana Yeager (no relation to aviation legend Chuck Yeager), and Dick Rutan, brother of Burt Rutan, was indeed purpose-built. The all-composite aircraft weighed 2,250 pounds empty including its two engines. Takeoff weight with two pilots and enough fuel to fly around the planet was nearly 10,000 pounds. The average speed of the 25,012-mile odyssey was only 116 mph. Despite all odds that skeptics and Mother Nature could muster, the purpose-built Voyager completed its mission exactly as designed with 5 gallons of usable fuel remaining.

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