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Does anyone know why many 1930's airliners in the US have cockpit windows that slope down and rearward, the opposite of what you might expect?

Consider the Boeing 247:

enter image description here

Source

Or the Lockheed Electra Model 10:

https://en.wikipedia.org/wiki/Lockheed_Model_10_Electra#/media/File:Kelly-Johnson_Electra.jpg

enter link description here

Or the Ford Trimotor:

https://wjon.com/around-the-town-taking-a-ride-on-a-1929-ford-tri-motor-video/

Source

This seems to have disappeared shortly after, the DC-2 and on, for instance, lack this feature.

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  • $\begingroup$ It's going to be either rain or sun reflection related. $\endgroup$ Commented May 27, 2019 at 14:58
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    $\begingroup$ I´m pretty sure the Boeing 247 already appeared in an answer by Peter Kämpf at some point, and it was indeed due to someone´s pet obsession with anti-glare features for the cockpit, at the expense of all reason. Can´t find the exact post now, sadly. $\endgroup$ Commented May 27, 2019 at 15:01
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    $\begingroup$ @AEhere this one? aviation.stackexchange.com/a/25104/609 $\endgroup$ Commented May 27, 2019 at 15:09
  • $\begingroup$ @ratchetfreak yes, that one! $\endgroup$ Commented May 27, 2019 at 15:14
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    $\begingroup$ Most likely because of the application of boat design patterns to the design of aircraft of the day. $\endgroup$ Commented May 27, 2019 at 15:39

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From a newspaper article

If it's a good idea here, why not in the cockpit of an aeroplane, right?

enter image description hereImage source

The forward slope was designed to avoid reflection of lighted instruments in the window panes, but that turned out to create other reflections. From this site:

The cockpit windshield of the first 247s was angled "forward" instead of the conventional aft sweep. This was the design solution (similar to that adopted by other contemporary aircraft that used a forward raked windscreen) to the problem of lighted control panel instruments reflecting off the windshield at night, but it turned out that the forward-sloping windshield would reflect ground lights instead, especially during landings, and it also increased drag slightly.[12][13] By the introduction of the 247D, the windshield was sloped aft in the usual way, and the night-glare problem was resolved by installing an extension (the glarescreen) over the control panel.[14]

Also mentioned in this answer.

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    $\begingroup$ I'm trying to figure out how a forward-sloping windshield could possibly reflect ground lights in a manner that the pilots would care about. My best guess is that they meant it would reflect light from the ceiling, illuminated by ground lights. $\endgroup$ Commented Aug 1, 2019 at 3:26
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    $\begingroup$ @TannerSwett Yeah it could very well be the reason stated in Peter Kämpf's answer, limitation of upwards visibility. $\endgroup$
    – Koyovis
    Commented Aug 1, 2019 at 4:46

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