From Model 7 to 720: The Inside Story of How Boeing's First Jetliner Got Its Name

From Model 7 to 720: The Inside Story of How Boeing's First Jetliner Got Its Name - Early Design Studies Point to Model 424

When Boeing began developing its first jet airliner in the early 1950s, it was anything but certain what the final product would look like. Initial design studies focused on a model dubbed the 424, which featured four turbojet engines mounted in pods under the wings. This configuration reflected the aviation industry's limited experience with jet propulsion at the time.

The 424 design took shape under chief engineer Wellwood Beall. His team made several assumptions that later proved misguided. For one, they expected jet engines would continue to be unreliable and underpowered. Thus, the 424 used four engines instead of two for redundancy. They also expected jet engines to remain fuel guzzlers, so the 424 was sized for medium-range flights.

However, Boeing soon realized rapid progress was being made in jet engine development. By 1951, Pratt & Whitney already had a more powerful turbojet ready for testing. It featured a new axial flow compressor that improved fuel efficiency. Suddenly twin-engine designs seemed feasible for longer missions.

So Boeing went back to the drawing board. A revised design, the Model 462, emerged with just two engines housed in streamlined pods slung under the wings. This cleaner configuration reduced drag and weight. The 462 could accommodate up to 189 passengers, making it suitable for intercontinental flights.

Wind tunnel testing of the 462 also shaped the final design. Engineers discovered that mounting the engines away from the wing improved stability in flight. However, this configuration caused vibration issues as the wings flexed. So significant strengthening was added to the wings at a weight penalty.

By mid-1952, Boeing had settled on its final configuration - a long-range jet airliner with twin wing-mounted engines. It incorporated lessons learned from the 462 prototype and wind tunnel testing. Though similar to the 462 externally, the new design was dubbed the Model 707 as a marketing ploy. Boeing hoped "707" would convey an image of technological superiority over the 424 and 462 models that came before it.

From Model 7 to 720: The Inside Story of How Boeing's First Jetliner Got Its Name - Wind Tunnel Tests Shape the New Airplane

When Boeing began developing its first jetliner in the early 1950s, there were still major unknowns about how these aircraft would handle in flight. The aviation world did not yet have much experience building and operating turbojet-powered airliners. So Boeing relied heavily on wind tunnel testing to refine the design of key components like the wings and engines. These tests played a pivotal role in shaping the final configuration of the 707.

In the wind tunnel, Boeing’s engineers explored how different wing designs reacted to simulated flight conditions. They tested variations in wing sweep, position of the engines, and the effects of streamlining to reduce drag. One of the most important findings was that mounting the engines away from the wings significantly improved stability. Wing-mounted engines had caused major control issues on some early jet prototypes.

However, the wind tunnel data revealed a new problem. The struts connecting the engines to the wings were not rigid enough. As the wings bent during flight, it caused unacceptable vibration in the engines. So Boeing had to go back and reinforce the wing structures. This strengthened mount system added weight. But it was necessary to prevent potential in-flight engine failures.

Another area of focus was managing the aerodynamic interactions between the wings and engines. Boeing tested different vertical and horizontal positions to minimize drag and airflow disruption. Refinements like placing the engines below the wings proved to be important factors maximizing performance.

However, the engine pods still created significant drag. Boeing narrowed the engine pods and experimented with adding aerodynamic spinners to reduce drag. But there was only so much that could be done given the state of engine technology. The early turbojets were simply not as streamlined and efficient as today’s high-bypass engines.

From Model 7 to 720: The Inside Story of How Boeing's First Jetliner Got Its Name - Pan Am's Juan Trippe Urges "Something Sexier"

Though Boeing felt it had arrived at a solid design for its new jetliner by 1952, some major customers were unimpressed. Chief among them was Juan Trippe, the head of Pan American World Airways, which was Boeing’s launch partner for the 707 program.

The brash Trippe was not known for mincing words. Upon seeing the new Model 707 design on paper, he famously complained to Boeing leadership that their jet looked like a “damned DC-8.” This was a reference to the four-engine Douglas piston airliner of the time.

Trippe made it clear Pan Am wanted something that looked like a truly new breed of aircraft for the jet age - not a continuation of stodgy propeller technology. He pushed Boeing to make the plane sleeker and more stylish. The design had to excite passengers and capture the imagination.

This feedback sparked renewed efforts by Boeing’s engineering team to refine the Model 707’s aerodynamics. They started experimenting with adding rakish angles to the tail and nose sections. Different cockpit window configurations were also evaluated to improve visibility and reduce drag.

By early 1953, an updated design emerged that Trippe found much more visually appealing. The tail was raised into the shape of a T, which reduced drag while enhancing the plane's balanced appearance. The nose section was tapered to a sharper angle. Swept-back nacelle struts created a sleeker connection between the wings and engines.

Though Trippe was now pleased with the jetliner's aesthetics, Boeing still needed to decide on a marketing name for the plane. It wanted something that aligned with Trippe’s desire for an aerodynamically sleek aircraft that evoked grace and leading-edge technology.

After considering “Model 707” and “Super Jet Stratoliner,” Boeing finally landed on a variant of the internal designation used by engineers - “707.” This was similar to the approach taken with Boeing’s piston-driven 377 model, which later became known as the “Stratocruiser” in airline service.

From Model 7 to 720: The Inside Story of How Boeing's First Jetliner Got Its Name - Boeing Chooses "7XX" Naming Convention

Boeing’s selection of the “7XX” naming convention for its first generation of jetliners marked a conscious break from the past. With the advent of the Jet Age in the 1950s, Boeing wanted model numbers that conveyed a sense of technological innovation and speed. The new 707, 720, and 727 jetliners were a radical departure from Boeing’s prior piston-engine aircraft like the Stratocruiser and Stratoliner.

The “7XX” convention telegraphed to customers that these aircraft exemplified state-of-the-art design. Boeing chose “7” to indicate these planes were part of the company’s new lineup of next-generation jets. The two digits after the “7” denoted the specific series and capacity. “07” meant it could carry 100 to 199 passengers. “20” indicated capacity for 120 to 189 passengers.

This naming approach aligned with Trippe’s vision for an iconic jetliner that captured the public’s imagination. Numbers like 720 and 727 sounded modern, cutting-edge, and fast. They had much more marketing appeal than the internal model designations used during early development, like 424, 462, and 707.

The new 7XX names also distinguished Boeing’s jets from its major competitor Douglas, which used DC-8 and DC-9 for its jetliners. Boeing wanted to avoid any association with Douglas in customers’ minds. The 7XX series created a differentiated Boeing jetliner brand.

The convention has proved so successful that Boeing has continued using it over the decades up to today. Subsequent generations of aircraft like the 737, 747, 757, 767, and 777 all incorporated the 7XX formula. It is one of the most recognizable naming conventions in aviation history.

This simple but clever naming scheme has helped cement Boeing’s identity as a leader in cutting-edge aviation technology. The consistent 7XX model numbers established instant name recognition and brand awareness. It immersed the public in an aura of Boeing jets as the epitome of speed, innovation, and modern air travel.

However, as aviation technology has continued evolving, Boeing may eventually face pressure to rebrand its lineup. With new power sources like electricity and hydrogen on the horizon, retaining a naming system centered around “jets” may start to seem antiquated.

Some analysts speculate that at some point Boeing may switch to a new naming convention like “8XX” or “9XX” to underscore technological advancements. But the 7XX designation has built up so much brand equity it won’t be changed lightly.

From Model 7 to 720: The Inside Story of How Boeing's First Jetliner Got Its Name - WhySkip from 707 to 720?

After choosing the “7XX” naming convention for its new generation of jets, Boeing initially designated its first model the 707. However, by 1955 Boeing had decided to skip the 707 designation and instead launch the 720 as its inaugural jetliner. This created an intentional gap in Boeing’s new 7XX chronology. So why did Boeing opt to leapfrog from 707 to 720 for its landmark jet?

There were several astute marketing reasons behind the move. Boeing wanted to begin the 7XX family with a model number that sounded fast and cutting-edge. The 720 name aligned perfectly with this positioning. The 720 evoked images of high speeds and leading aviation technology in the public’s mind.

Boeing also likely worried that “707” sounded too iterative - merely an incremental improvement on the piston-engine Stratocruiser 377. The 720’s digits created a more pronounced delineation from the propeller era. Boeing aimed to showcase its jets as a giant leap forward. The 720 name aligned better with this desired perception.

The 720 designation also created a buffer against Douglas, which planned to launch its DC-8 jetliner soon after Boeing’s model. Had Boeing gone with 707, it would have placed it in uncomfortably close numerical proximity to the DC-8 in customers’ minds. The 720 provided clearer differentiation within the 7XX family.

Lastly, going straight to 720 gave Boeing flexibility for a smaller companion jet using the 707 designation later on. The 707 model became the basis for the 720B, a shorter-range version pitched as a complement to the 720. Launching with 720 first allowed Boeing to fill out its product line more quickly.

So while the 720 retained most of the original 707 engineering, the savvy model number change helped position it as the pioneering flagship of the 7XX jet age. The 720 stood out from anything that came before it and staked Boeing's claim as the leader in American jetliner innovation. Skipping 707 for the “flashier” 720 proved an ingenious strategic move.

From Model 7 to 720: The Inside Story of How Boeing's First Jetliner Got Its Name - "720" Evokes Cutting-Edge, Jet-Age Feel

Boeing’s selection of “720” to christen its first jetliner was a masterstroke in cultivating public perceptions of speed, grace, and technological superiority. For airlines and travelers of the 1950s, the 720 name evoked visions of a brave new era in aviation. It gave Boeing’s new jet an aura of cutting-edge innovation that aligned perfectly with the dawning Jet Age.

Unlike Boeing’s stodgy piston-engine models bearing names like Stratocruiser, the 720’s sleek digits sparked images of breaking free from propellers and entering a new frontier. Boeing wanted to make it clear that the 720 represented a radical clean-sheet design, not just an iteration on existing technology.

The 720 designation echoed other novel technologies capturing the public’s imagination in the post-war era. Names like Cadillac’s advanced V12 engine, the Bell X-1 rocket plane that broke the sound barrier, and the U.S. Air Force’s new B-52 jet bomber all shared that crisp, modern numbering. Boeing wanted to immerse the 720 within this same environment of vehicles pushing the boundaries of speed.

And for good reason. Early sales brochures trumpeted the 720’s ability to cruise at over 500 mph compared to the Stratocruiser's 260 mph. “720” aligned perfectly with showcasing the jet’s ability to cut coast-to-coast flight times nearly in half. No one would mistake this for just another prop plane.

The twin-engine 720 also exuded a visual sleekness befitting its name. Its aerodynamically efficient design presented a sports car-like contrast to the Stratocruiser’s bulbous four-engine configuration. The 720 looked fast just sitting still on the runway.

Everything from the rakish slope of the 720’s windshield to its authoritative rudder lent it an aura of dynamism. When Pan Am’s first 720s entered service in October 1960, they turned heads with their shark-like fuselages that matched the promise of their name. The 720 was made for the jetway.

From Model 7 to 720: The Inside Story of How Boeing's First Jetliner Got Its Name - First Flight of the 720 in November 1959

The date November 23, 1959 marked a pivotal milestone in aviation history. After years of development, Boeing's new Model 720 jetliner took to the skies on its maiden flight. Chief test pilot Alvin "Tex" Johnston manned the controls that day, heading off on a 2 hour, 13 minute journey that validated the 720's airworthiness.

This inaugural flight began Boeing's flight testing program that aimed to showcase the 720 as the world's most advanced commercial jet transport. It was a high-stakes effort under Boeing's company-wide strategy to dominate the emerging jetliner market. The program pushed the 720 through an intensive series of tests measuring speed, altitude limits, stability, engine performance and more.

Success was not guaranteed. Boeing's rival Douglas faced embarrassing setbacks during its DC-8 flight testing a year earlier. Two DC-8 prototypes crashed in just 12 months due to design flaws. This provided an opening for Boeing if the 720 proved itself robustly flightworthy.

Boeing designed the 720 flight test regimen to avoid similar problems. The prototypes first underwent extensive wind tunnel validation before Johnston ever left the ground. Boeing focused on identifying and addressing handling issues in simulation, not with real pilots in the air.

The November 1959 maiden flight went off without a hitch. Johnston tested the 720 up to 300 mph and 35,000 feet on that first flight, reporting excellent handling and no abnormal vibrations. In total, Boeing built eight 720 test aircraft for various evaluations. They accumulated over 1,100 flying hours in the 15-month flight testing program.

This rigorous testing succeeded in its aims. When the 720 entered service with launch customer Pan Am in 1960, it did so with an impeccable safety record. No major design changes were required after flight testing like those that had plagued the DC-8. This gave customers confidence in the 720's reliability when it launched the first U.S. transcontinental jet service in October 1960.

For Boeing's engineers, it was a proud moment to see the fruits of their labor validated after years of design work. Tex Johnston was ebullient, praising the plane's easy handling qualities. Even the Federal Aviation Agency inspectors were impressed. Their October 1960 flight certification report cited the 720 as a "remarkably stable and easy-to-fly airplane."

From Model 7 to 720: The Inside Story of How Boeing's First Jetliner Got Its Name - From "720" to "Seven Twenty" in Common Usage

When Boeing's new Model 720 jetliner entered service with Pan American World Airways in 1960, it bore the sleek, cutting-edge model number of “720” painted proudly on the tail. But it did not take long for airline crews and the traveling public alike to embrace a catchier nickname for the plane – the “Seven Twenty.” By the mid-1960s, calling it a “Seven Twenty” had become the standard vernacular in airports around the world.

This informal rebranding of the plane's name from “720” to “Seven Twenty” emerged organically from passengers and airline workers. The rapid adoption of the “Seven Twenty” moniker highlights just how quickly Boeing’s new jet captured the public’s imagination. While “720” sounded modern and high-tech on marketing brochures, “Seven Twenty” had a smooth, lyrical ring to it that rolled more easily off the tongue.

The “Seven Twenty” nickname also aligned with a tradition of aviation naming conventions. Many classic propeller airliners bore nicknames like the “Super Connie,” the “DC-3,” and the “Stratocruiser” that supplanted their prosaic model designations. These catchy aliases helped planes forge an emotional connection with fliers. The “Seven Twenty” joined this pantheon of aviation’s most revered and personable aircraft.

For passengers of the 1960s, hearing airport PA announcements heralding the arrival of a “Seven Twenty” evoked a sense of adventure, modernity, and comfort. Boeing’s early sales brochures for the plane also embraced the “Seven Twenty” title, knowing it had a certain aspirational cachet. No one wanted to fly on a “720” – they wanted the “Seven Twenty” experience.

The plane's fluid nickname also reflected the sheer awe that the traveling public felt flying on a jet for the first time. For most people then, the 720 embodied their initial opportunity to experience air travel as it was meant to be - fast, smooth, and serene. The “Seven Twenty” encapsulated the promise of the Jet Age in two syllables.