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Ideally I'm looking for a screenshot with a bullet list of data. I started my search at the obvious encyclopedic site and was surprised to learn that the earliest HUDs (on fighter jets) go all the way back to the 40's.

So what data did they display? Presumably it would be a limited set of data compared to today's standards, and I'm very interested in what was considered the most important data for a HUD. Especially, did they have that circular piper showing where your bullets would impact?

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    $\begingroup$ Looks like the AI Mk VIII radar on the Mosquito had an artificial horizon plus gunsight (and target marker), hard to find any illustrations or photos though. $\endgroup$ – egid Aug 9 '15 at 5:44
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    $\begingroup$ @egid but no WW2 era fighters ever had a HUD, did they? What year did this feature get added to the Mosquito? $\endgroup$ – DrZ214 Aug 10 '15 at 3:22
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    $\begingroup$ this post on a forum suggests that it was tested in 1942 but not adopted for widespread use. Illustrations included! $\endgroup$ – egid Aug 10 '15 at 3:29
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    $\begingroup$ @DrZ214, what WW2 era fighters did have was ‘parallax gunsights’ that work basically the same way as HUD but only project static image, possibly adjusted by gyroscope to provide correction for own turn. The advantage was that the gunsight aligned even when pilot moved their head. $\endgroup$ – Jan Hudec Aug 10 '15 at 6:14
  • $\begingroup$ "Ideally I'm looking for a screenshot with a bulle tlist of data" - Are you asking us to do your research for you? The question is fine but that one phrase does stick out to me. $\endgroup$ – dalearn Apr 15 '18 at 20:19
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Reflector Sight:

The Me 262 Schwalbe, introduced in 1944 as the world's first operational jet fighter aircraft, did not have a full-blown HUD. Instead, like many fighters of WWII, it had a reflector sight which used lenses and reflecting glass to display a reticle. This sort of thing [all of the bright yellow lines you see in the image are fixed together. Although you only really needed a dot and a circle (like the Spitfire), some pilots liked the extra lines to help line up targets that were not dead-ahead. They were favored by pilots over iron-sights because the pilot was not required to position his head in order to see where the guns would fire.

Simple HUD

The MiG-21, introduced in 1959, used a combination of reflector sight and HUD. Though it didn't display the altitude, speed, heading, or attitude in a way that modern fighter pilots may take for granted, it had some ability to track targets with radar and to display predicted target positions for gun or missile use. Here is a guide on how to aim your guns using its sight. Also, explanations of the displays. The following image was posted on a forum thread related to the MiG-23, which came after the MiG-21, but this image looks much like those from the MiG-21 manual. A different image from another author shows you how simple the display could get. Finally, an F-16 in the sights of a MiG-21. You can tell this is a MiG because of the distinctive pitot tube.

Full HUD

The F-14 first flew in 1970. Its HUD was equipped with an artificial horizon, altitude, speed, heading, gun data, missile data, and much more. This is from the F/A-18, which first flew almost a decade later.

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    $\begingroup$ Thanks for the data but can you post a source for this, especially the MiG-21 HUD? Why does that image show data in English instead of Russian? Also, are you sure the first MiG-21's had this in 1959? Or was it only later versions? $\endgroup$ – DrZ214 Aug 20 '15 at 21:13
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    $\begingroup$ @DrZ214 My mistake, that was a much later, upgraded version of the MiG-21 (Lancer, a modernized development). I have added more information (and more links!) $\endgroup$ – Kurt Tank Aug 21 '15 at 12:50
  • $\begingroup$ As an aside, the F-14's HUD features should be familiar to many GA pilots that have flown a glass cockpit; the basic layout of military HUDs, minus targeting displays, is the basis for modern PFDs, the only real difference being the multicolor presentation instead of a monochrome projection onto a reflector. $\endgroup$ – KeithS Aug 21 '15 at 19:47
  • $\begingroup$ The Me-262 Reflexvisier was special because it was the first (for the Luftwaffe) with gyroscopic control to predict where to shoot in a dogfight. However, it was so complicated to adjust that many ground crew simply fixed it in the straight forward position (which mattered less than you might think, because the 262 was no great dogfighter …) $\endgroup$ – Peter Kämpf Dec 28 '18 at 22:36
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The earliest were reflector sights which were fitted to fighter aircraft at the end of WW I. The picture below shows an Oigee Reflexvisier from 1918, built at the Optische Anstalt Oigee factory in Berlin-Charlottenburg and used that year in Albatros, Fokker and Pfalz D-type aircraft. Two types were built and were the first, albeit very simple, head-up displays.

Oigee Reflexvisier

Oigee Reflexvisier (picture source)

What was displayed was basically a single dot of light which was projected on the semi-transparent mirror such that it would overlay the point at which the fixed guns were aiming, regardless of the pilot's eye position. Only the height of the mirror needed to be adjusted for the sitting height of the pilot. The brown plate in the path of light was used for this adjustment and removed for operation.

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Computing (Gyro) Gunsight

As a development of the existing "reflector gunsight" (which as other answers note was intended to eliminate parallax error due to the pilot's head position), the "computing gunsight" used the motion of the aircraft it was mounted on to generate a modified gunsight indicating the lead required to shoot a moving target.

A ring was projected onto the reflector, such that holding the target steady in this ring would provide the correct lead. An estimate of the target's range first had to be set on the gunsight. In practice, this was often left at the convergence range of the guns, and the pilot would attempt to manoeuvre the target to that range.

The first production models were produced in Britain in 1941, and successfully used against the Luftwaffe. In 1942, a Thunderbolt with a computing gunsight was captured in Germany, which stimulated their efforts to develop similar technology.

In this early technology, no corresponding information about altitude, airspeed, heading or attitude were provided, being left to conventional instruments. The Sperry K-14 was considered notable for including both computing and fixed (ie. equivalent to a reflector sight) gunsights in the same unit.

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