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I always thought of the DC-4 as a DC-3 with two added engines and somewhat improved hydros.

What are the actual differences between them?

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    $\begingroup$ Err, what is a 'hydro'? $\endgroup$
    – egid
    Nov 9, 2017 at 3:13
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    $\begingroup$ Hydr"oaulics because "hydros" stuck to my mind because of NFSU2 NFSU2 Vet here $\endgroup$
    – Delta Oscar Uniform
    Nov 9, 2017 at 4:32

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The DC-4 was a totally new design in all respects, as can be seen from the planform diagrams (wiki)

enter image description here

The DC-4 was larger, and structurally totally different:

  • Straight tapered wing (no sweepback)
  • Straight tubular fuselage, not the aerodynamic teardrop shape
  • Round fuselage cross-section. The original DC-4E was going to have a pressurised cabin. The later DC-4A did not implement this but retained the circular cross section necessary for pressurisation.
  • MTOW = 33,100 kg for the DC-4, 11,430 kg for the DC-3
  • Four engines of 1,081 kW each, while DC-3 had 2 engines of 890 kW each.
  • Tricycle landing gear instead of a tail dragger, as @Gerry points out.

All in all a larger aircraft, designed from scratch, implementing more modern features of a later age.

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    $\begingroup$ And tricycle gear instead of the conventional gear. $\endgroup$
    – Gerry
    Nov 8, 2017 at 17:40
  • $\begingroup$ What did straight tapered wing added to the design ? $\endgroup$
    – Delta Oscar Uniform
    Nov 9, 2017 at 4:29
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    $\begingroup$ @JonathanIrons Better stall behaviour. Wing sweep is an evil that is necessary for high speed cruise, much higher than the cruise speed of the DC-4. The DC-3 had it implemented because the CoG turned out to be further aft than initially calculated $\endgroup$
    – Koyovis
    Nov 9, 2017 at 4:35
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    $\begingroup$ The poor stall characteristics of the DC-3 were caused by the high taper of the wing and, consequently, highly loaded outer wings. Stall was worse with power on because the prop slipstream stabilized the inner wing. Stall was worse again with flaps down because that increased the loading of the outer wing. Sweep had little influence. See here for a 1937 documentary $\endgroup$
    – Peter Kämpf
    Nov 9, 2017 at 18:27
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    $\begingroup$ @JonathanIrons The planforms are from the wikipedia articles about DC-3 and DC-4, they are a way down in the articles next to the specifications. I put them side by side scaled to wing span. $\endgroup$
    – Koyovis
    Nov 9, 2017 at 21:09

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