These glamorous vintage images were once famous in magazines and used by airlines to advertise their products, and yes, flight attendants clothing was like this! Old and more relaxed times, though flying was for the rich.

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Left: Canadian Pacific, 1968.
Right: Pacific Southwest - San Diego Air and Space Museum Archive, likely end of 60s too.

With a flight attendant showing the scale, it's pretty clear that the size of the engines are completely different; they are likely of different designs (turbojet/turbofan) in spite of being of the same period. What are theses engines, and the aircraft that used them? Why so different choices (what did that change for the airlines)?

  • 1
    $\begingroup$ Why so different? "Mines bigger than yours!" $\endgroup$
    – Notts90
    Dec 3, 2016 at 20:48
  • $\begingroup$ One hopes they didn't try doing that with the engines running. $\endgroup$
    – Vikki
    Aug 7, 2019 at 22:46

1 Answer 1


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(Left), (Right)

On the left is the Pratt & Whitney J75 (JT4A) on a DC-8, with ram air inlets1.

On the right is an RR RB211, possibly on an L-1011. The EPR probe (I think) can be seen protruding from the inner lip at the 12 o'clock position, plus the snubber2 holding the blades together.

The former is a turbojet, that's why it's narrow. The latter is a high-bypass turbofan, that's why the big fan.

We can't directly compare both engines. The RB211 is 14 years younger, and much more powerful, suited for big planes unlike the narrow-body DC-8. The RB211 wouldn't fit under the wings of the DC-8. Different planes, roles, and engine requirements.

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(Source) DC-8 with the high-bypass CFM56.

The DC-8 was later retrofitted with high-bypass because it's better for fuel economy and noise—the CFM56 to be precise—without the DC-8 getting the retrofit, the CFM56 would not have become as ubiquitous as it is now. The project needed civilian customers to survive3.

First run years: J57 (1955), RB211 (1969), CFM56 (1974).

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L-1011 (top) and DC-8 (bottom). Eyeballed the scale.

1 Accessories on the Pratt and Whitney engines are mounted beneath the high-pressure compressor casing. Two drum-type oil coolers are provided, each fed with air from individual ram intakes in the lower part of the nacelle.— Flight
2 A snubber (or clapper) is a damper used to prevent blade flutter on narrow-chord fan blades, at the cost of reduced efficiency. Hollow wide-chord blades are more stable and do not need snubbers.
3 The CFM56 featured article on Wikipedia is a must read.

  • 1
    $\begingroup$ From an airline perspective, what were the advantages, at that time, to have one or the other? $\endgroup$
    – mins
    Dec 3, 2016 at 21:46
  • 3
    $\begingroup$ @mins, well, the newer designs were all around better, but if you already had the earlier, turbojet-powered, one it would not be fully amortised, so you'd continue using it at least until it made up its cost. $\endgroup$
    – Jan Hudec
    Dec 4, 2016 at 22:56
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    $\begingroup$ @mins which could well mean putting them on to be allowed to use the aircraft at all, as the turbojets likely wouldn't be allowed under current emissions and noise regulations. $\endgroup$
    – jwenting
    Dec 5, 2016 at 5:46
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    $\begingroup$ Later versions of the 707 and DC-8 were fitted with Rolls-Royce Conway and PW JT3D engines, both low-bypass turbofans in the 20klbf thrust category. The "low bypass" design was necessary to keep the engine diameter small enough to fit. By comparison, the RB211 can make as much as 60klbf thrust. A VC-10 used to flight-test the RB211 (replacing two of its Conways) suffered airframe distortion due to the extra (and asymmetric) stress. $\endgroup$
    – Chromatix
    Apr 29, 2018 at 19:09

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