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During the 1960s race to build the first widebody jetliner, each of the three major engine manufacturers was racing to put out a high-bypass engine for one of those jumbo jets:

  • Boeing went with Pratt & Whitney’s JT9D for their 747.
  • Douglas (which soon became McDonnell Douglas) chose General Electric’s CF6 to power the DC-10 (Airbus also chose the CF6 for the A300 when they jumped in a couple of years later).
  • Lockheed, for the L-1011, put their money on Rolls-Royce’s RB211.

Of the first three widebodies, only the DC-10 (whose power plant was a fairly straightforward conversion of the TF39 used on the C-5A Galaxy, which had been the first high-bypass turbofan ever to enter production) escaped being held up by engine difficulties; the L-1011 was held back for years when the RB211 ran into serious delays which allowed the DC-10 to beat it to market and strangle the TriStar in the schoolyard, 1 nearly bankrupting Lockheed in the process.

What isn’t as well known is that Boeing experienced delays of similar severity with the JT9Ds that were to power the 747; for a long while, there were rows upon rows of 747s sitting on the ramp at Boeing Field, complete but for having concrete blocks hanging from their pylons in place of the engines that could not yet be trusted on a production airliner. Only Boeing’s massive head start enabled the 747 to beat the DC-10.2

Did Boeing or Lockheed ever seriously consider releasing an interim widebody with low-bypass turbofans (for instance, a 747 with eight JT8Ds mounted two to a pylon in conjoined pods, B-52-style) while they waited (and waited) for the high-bypass engines to become ready?


1: It wouldn’t be accurate to say that it strangled the TriStar in the cradle, given that the L-1011 did, in fact, manage to enter production and sell 250 aircraft.

2: Enabling Boeing to remain solvent in the process, as Boeing, like Lockheed, had bet the farm on their jumbo jet. Unlike Lockheed, they didn’t lose it; however, if the 747 had been a failure, it would have bankrupted Boeing.

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    $\begingroup$ Most OEMs - certainly not only Boeing and Lockheed in the 747 and TriStar-cases - "bet the farm" when introducing a new type. Break-even often takes 10 (Sadraey, 2013) to 20 years, and only a few aircraft turn into true money makers (A320/A330/737/747/777, with A350 and 787 on their way to become one). $\endgroup$ – Bram Jan 31 at 7:36
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I am not aware of any manufacturer making a serious proposal to develop a jumbo jet with low bypass-ratio engines. Most airline manufacturers tend to develop a plane from customers requirements, whether that customer is military or civilian. Civilian airlines in the late 1950s were already nervous about the much higher costs for jet-powered aircraft and there was no call at this time for an even larger plane.

To get the most value for their development efforts, airplane companies tend to look at if they can develop a commercial and military version. As an example, Boeing tries to develop a commercial variant to all of their military planes and vice versa. Starting with the Boeing 307 Stratoliner and continuing with the the Boeing B-52 Stratofortress and the Boeing B-47 Stratojet, Boeing worked to develop a passenger variant as well. There was discussions with making the B-52 into a passenger plane, but commercial airlines were not interested. Some of the reasons were the the hull was very narrow, much of it un-pressurized and in many ways, it would have been ill-suited for passenger use. The plane would have had identical engines to the B-52. I could not locate any drawings of what it would look like. The push for a passenger plane became the Boeing 367-80, which developed into the Boeing KC-135 Stratotanker and the Boeing 707, which entered into service in 1958.

Lockheed had it's hands full with fulfilling orders for the Constellation. It developed some great military planes, but never pursued a passenger jet until the Lockheed L-1011 TriStar which first flew in 1970.

After World War II, Douglas lost a lot of military business and was forced to scale back. It's first jet that became a passenger jet came out of the development of a tanker for the Air Force that eventually became the Boeing KC-135 tanker. The reason they developed the Douglas DC-8 was that Pan Am ordered 20 of them and they could see the future was jet-powered.

The next big jump in airplane size came out of a development effort by the Air Force. In 1964 they asked Boeing, Douglas, General Dynamics, Lockheed, and Martin Marietta to develop a prototype for the CX-HLS cargo plane. This was much larger than anything that existed at the time. In this proposal, the Air Force was asking for high efficiency engines as well as the ability to carry a lot of weight. The two final prototypes became the Lockheed C-5 Galaxy and the Boeing 747.

By this time, the age of low-bypass-ratio engines was over because of the much better efficiency available in newer high-bypass engines.

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    $\begingroup$ This is a good answer. In addition for your last point, keep in mind that podded engines may be beneficial occasionally (depending on the overall design) but it's hell for reliability. If one engine malfunctions or fails completely, the probability and potential for a cascading failure is far greater, an engineering sacrifice unacceptable for commercial airliners. $\endgroup$ – Jihyun Jan 31 at 14:28
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I can think of two disadvantages that made these (or other) OEMs decide not to release a widebody airliner powered by low bypass-engines, certaintly in case such an aircraft would be a derivative of a high(er) bypass design.

  1. Fuel efficiency. Lower bypass-ratio engines are less fuel efficient than higher bypass-ratio engines. Lower fuel efficiency means decreased range for a given payload. Both are bad, and might even break the business case (particular routes requiring a large range, poorer economics if fixed cost has to be paid by a smaller number of passengers) for acquiring this aircraft.
  2. Additional engineering. Doubling the number of engines also requires a doubling of support systems (lubrication, fuel lines, engine controls, diagnostics, and so on). That seems much too much trouble for a relatively small gain.
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    $\begingroup$ The OP asked whether actual manufacturers considered a low-bypass powered airliner, not about (dis)advantages of such a design. $\endgroup$ – Sanchises Jan 31 at 9:14
  • $\begingroup$ Those disadvantages are reasons why manufacturers wouldn't seriously consider low-bypass powered airliners. $\endgroup$ – Hobbes Jan 31 at 9:44
  • $\begingroup$ @Hobbes: Even as just an interim solution for until they could get the planes working with high-bypass engines? $\endgroup$ – Sean Feb 1 at 3:53
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    $\begingroup$ 'just an interim solution' would require a lot of engineering hours, right when Boeing was in the middle of designing the 747. The interim solution would have delayed the 747 project. $\endgroup$ – Hobbes Feb 1 at 7:48

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