How does the head-up display on a spitfire work?

Question

It turns out that the Spitfire from World War 2 had a head up display. Does anybody know how it worked exactly?

All I could find was this picture, but no explanation:

Source

The source does not explain what it does.

Seeing as it is projected, it would only be of use if it were dynamic, that's why I'm asking.

How could they have something like that back in the day?

Edit: Not a duplicate, not all sights were gyro sights.

Possible duplicate of How did the gyro gunsights of WW2 get the range and lead of a target? — Trevor_G, Dec 05 '17 at 18:09
@Trevor I don't think it's a duplicate. This question asks how the optical system works; that question asks how the system figured out where the target is. — David Richerby, Dec 05 '17 at 20:08
@DavidRicherby if he watches the video in my answer there it tells him,. — Trevor_G, Dec 05 '17 at 20:10
@Trevor What video? And I have to concur with DavidRicherby, that this is not a duplicate. — mike, Dec 05 '17 at 20:12
https://www.youtube.com/watch?v=DREz7qI8xRk the gunsite does not track the target, it projects where the guns are aimed in the sky, the pilot flys the aircraft and points it such that the target in that spot. — Trevor_G, Dec 05 '17 at 20:15

Dan Hulme · Accepted Answer · 2017-12-06T15:22:08.033

It's not a head-up display, it's a reflector gunsight. (Follow that link to learn how they work.) It just displays a fixed reticle to aim the cannon, not any flight instrumentation.

Some (but not all) Spitfires had a gyroscopic system to compute target leading and move the position of the reticle appropriately, based on the speed of the aircraft; I suspect that your photo is of this equipment, and that's what the range adjustment visible at the bottom is. More about that can be found at How did the gyro gunsights of WW2 get the range and lead of a target?

Seeing as it is projected, it would only be of use, if it would be dynamic, that's why I'm asking.

That's not actually true. A "static" reflector gunsight is hugely advantageous over a collimator sight (i.e. a tube that you look through) or iron sights, because the crosshairs still appear in the correct place when you move your head. Early aircraft machine guns used collimator sights, but you have to hold your eye right up to the sight to see through it. This often resulted in injuries if the aircraft jerked at the wrong time. Iron sights were subsequently popular, but you still need to line up with the sights correctly, which is time you don't want to spend in a dogfight. With a reflector gunsight, the image of the crosshairs moves as you move your head, so you only have to glance in the correct direction to line up the shot. That's why they're also popular on small arms nowadays.

@mike: Yes, it was. When gyro gunsights started appearing as standard equipment on British and US aircraft in early 1944, they increased the probability of hits significantly. The Luftwaffe designed a somewhat superior gyro sight, but were unable to produce it in quantity. — John Dallman, Dec 05 '17 at 19:23
@mike: What continually amazes me even more is that on WWI planes (1915 and onwards), they already had devised a way to shoot the gun through the propeller without hitting the blades. Link. That's 25-ish years earlier than the Spitfire's reflector gunsight, and only a mere decade after the Wright brothers' famous first flight (= 1903) — Flater, Dec 06 '17 at 09:15
I don't understand the point about the collimator sights. The point of a collimator is to allow the free movement of the eye and still show the crosshair at the right spot. In my language "kolimator" means a reflector sight for firearms. — Vladimir F Героям слава, Dec 06 '17 at 13:53

How does the head-up display on a spitfire work?

1 Answers1