Gunsight positions

[Sancho]

It's my understanding that if a reflector gunsight is supposed to be focused on infinity, the gunsight pipper should not get noticably bigger when you move your head position closer to the gunsight, unlike the way it is right now.  Of course, I've never looked through a real aircraft gunsight, so I'm not positive about this.  The result of the current system is if the head position is moving around or different in different planes with the same sight, you can't use the sight for estimating range.

[Tails]

Since noone answere this, I figured I'd do a little test and chime in for you.

To perform this test, I took the PK-A sight for my AK-47, flipped it on, and held it various distances from my ugly head.

Now, for people that dont have experience with them, the PK-A is an unlimited eye relief 'red-dot' sight, that focuses a dot out to infinity to provide a similar effect to one's brain as using a laser dot, only the target wouldn't see it.

So, I flip it on, put my eye right up to the tube, and the red dot is tiny, about the size of a pin-head held in the other end.

As I held the sight at arms length, the dot stayed the same size, though the tube 'shrank', with the dot now 20 times larger in comparison to the tube.

Now, assuming that WW2 reflector sights worked on the same principal as this russian surplus toy of mine, then as you move your head towards or away from the sight, the crosshairs (or dot, or whatever you use) should not change in size.

They did get the reflectors half-right, in that if you move your head side to side, or up and down, the croshair stays in place until some portion of the sight glass is no-longer directly infront of your eye.



(Next week on Mr. Wizard: How to make plutonium from common house-hold chemicals)

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[CMC Airboss]

Sancho, you are exactly right.  I own a Mk18 gyro stabilized gunsight (Navy equivalent to the USAAF K-14 used in the P-51).   A reflector sight allows the judging of target distance by the target's relative size to the reticle markings.   One milliradian is just over 3.6 inches at 100 yards  A 70mil ring means that at a distance of 1000 yds, the ring will span 210 feet.  At 100 yds, 21 feet.   At fighter with a wingspan of 40 feet well completely fill a 70 mil ring at 200 yards.  To get this measurement, the gunsight reticle image size should (can)not change, regardless of the distance of your eyes to the reflector glass.   Range calculations with a reticle that constantly changed size with every head movement would make accurate range estimation impossible.

One interesting thing to consider is that you can see the image with only one eye!  Hence the reason that German gunisghts were often mounted to the right of the centerline of the dashboard.   In the case of the K-14 you can use both eyes.  When you have both the circle diamond and ring/dot lamps both turned on, the circle diamond image appears through the right eye and the ring/dot appears with the left eye.

MiG