correct as is GM2 reflector gunsight re-harmonization

[Biggs]

I'm requesting a change be made to the positioning and subsequent harmonization of the gunsight. The current position of the sight reticle (since day one of release) is too low. 

I made a gif of a screengrab taken of a GM2 sight video and recreated the FOV in game the best I could, and matched the two images up using the petrol tank cap and the top cowling seam as a alignment point. As you can see the real life sight was positioned higher with the 100ft ring touching the top of the cowling. (dont be thrown off by the sight glass both the oval and square were used with the GM2)

This matches with the description of the official mkIX tactical trials report No.46, paragraph 13:

"The Spitfire IX is fitted with the G.M.2 pilots reflector sight and although the aircraft is longer in the nose than the Spitfire VC, the 100 m.p.h.(sic) ring of the sight is still just clear of the nose."

http://www.spitfireperformance.com/spit9tactical.html

I do not have the exact quote but I also recall a pilot's description of not being able to fire on a target that was on the deck because he could not get his nose low enough to land his shots without essentially flying into the ground.

I do not have the precise degrees above the datum the sight was calibrated to but its clear that the sight is too low as it is positioned currently and needs to be looked into.

Thanks.

 

 

Edited June 16, 2023 by Biggs

[DD_Fenrir]

Whilst I don't disagree generally, Biggs, despite the excellent evidence there's an issue: refraction.

In reality the light passing through that slab of armoured glass gets deviated by it and as you can see by the above example, the image beyond the glass get's lowered.

Thus all aircraft with highly sloped bullet proof windscreens should see this effect.

Unfortunately this cannot be replicated in game. The 3D model is as accurate as can be, the dimensionality without refraction is correct - everything is where it's supposed to be.

But to replicate the effect of refraction would require either some fudging or a massive work around (and potentially a compromise to prototypicality elsewhere), a fundamental re-write of the graphics engine code to allow for ray tracing (huge expense in GPU processing), or drawing another render window through the windscreen frame (again, huge expense in GPU processing).

In the distant future, this technology might be feasible but in DCS, near term, no.

It's unfortunate, but bear in mind it effects all the WW2 aircraft, just not perhaps to quite the same extent as the dear old Spitty.

 

[Biggs]

EDIT: ok so youre saying the nose, seen from the cockpit would look lower because of refraction. thats fine.  

the solution would be to just angle the trajectory of fire up a few degrees to get around this. which is what I am proposing. I still think the guns are leveled at 0 degrees currently, which is not correct.

Edited June 16, 2023 by Biggs

[DD_Fenrir]

39 minutes ago, Biggs said:

Except the image you showed the light is being raised not lowered, the beam is come from the left of the image, enters the glass, angles up and exits higher then were it entered. 

Also the reticle is projected on the  gunsight glass not the bullet proof windscreen.

I don't think you're argument is valid here. 

The refraction if there is any would apply to light passing through from the outside of the plane not inside the cockpit, where the sight is located.

 

Wrong way round.

The glass in the example represents the bullet proof windshield with the light beam representing the rays of light reflected from the propeller and cowlings entering the cockpit from the right.

Any refraction through the thin glass of the gunsight would be marginal.

Edited June 16, 2023 by DD_Fenrir

[Biggs]

I just feel like throwing up your hands and going "oh well refraction", is not acceptable for what ends up basically blocking 1/3 of the reticle.

There needs to be a better work around for this issue, like elevating the sight to compensate for this lack of refraction. 

[kablamoman]

Regardless of refraction, would the sight not still be zeroed so that the rounds landed where it was aiming through the glass? Not sure I follow your logic, Fenrir.

What's more, is that you can clearly see the sight ring itself is offset by both metrics -- by its apparent visual clearance over the front of the cowl, but also by its height with relation to the interior canopy features only. (Although aligning the two pictures, when one is affected by the canopy glass, while the other isn't, based on cowl features, is probably also an issue).

Maybe more of a question to ask would be "how exactly has the sight has been zeroed in Biggs' reference picture?" I think we'd need to know more about that to say for certain if there is an issue with the way it's modeled in the sim. How do we know the referenced sight has been aligned and zeroed in the same way it would have been during war time? Even if it was, variations in convergence range use throughout the war would likely affect vertical alignment of the sight as well.

In any event, it may be worth a closer look.

 

 

Edited June 16, 2023 by kablamoman

[kablamoman]

Biggs, perhaps because of refraction your method for aligning the two pictures using external reference (as seen through the glass) is giving incorrect results. Can you find another reference where you can align the view with interior cockpit geometry instead? 

[Skewgear]

Gun harmonisation was set up using a series of round discs on poles at precisely calibrated distances and heights. Armourers would boresight each gun using a mirror or periscope to align each with its board.

See this photo of the process. https://www.iwm.org.uk/collections/item/object/205212731

I imagine the sight is checked for correct mounting to the aircraft, then sight set to the harmonisation distance, then the aircraft would be aligned so the central dot of the sight is on the topmost disc. From there each gun (and the gun camera in the wing root) would be individually zeroed to its corresponding disc. It's all straightforward trigonometry with a side helping of ballistics.

Does our sight in game respond to changing the range setting? Does the dot actually move up or down with changes in that setting? If not, then in theory ED could just move the graticule upwards in the sight glass and adjust the guns' angle upwards to match.

[NineLine]

Sorry I am into this late.

I think as some have already said, comparing a real image that has refraction based on armored and thick glass will make a difference in the position of the nose and such, but it shouldn't impact the performance of the sight itself. 

With a standard convergence of 250 yards, if you set the range for that and the base for the wingspan of your target, then put the aircraft in between the sight lines you should have no issue hitting your target.

Moving the sight to match this:
 

Quote

 

Sighting View

13......... The Spitfire IX is fitted with the G.M.2 pilots reflector sight and although the aircraft is longer in the nose than the Spitfire VC, the 100 m.p.h. ring of the sight is still just clear of the nose.

 

Would most like put the sight out of alignment, again based on what refraction does. I know that refraction is starting to show up in other games so I am hopeful one day we will see it in DCS and it will help solve issues like this. 

[Lythronax]

For anyone interested, this is the sight picture of Spitfire IXe TD314. The gunsight is clearly misaligned slightly, but it seems to confirm my suspicion that the reticle texture itself in-sim is too large i.e. the ring has too great a diameter.