Gun sight image size analysis

[Baumer]

I've spent a far amount of time researching the various gun sights used on the planes in Aces High. I prefer to use a gun sight that is as historically correct as possible and use the deflection shooting methods described in the PIF and GIF. But after some time I've come to suspect that the sights are not always accurately scaled in each plane.

So I started doing some analysis and took some screen shots.

First I'd like to cover the math and how I calculated what I think the size of the gun sight should be. From the Pilots Information File (PIF) a mil is defined as 1/6400th of a circle. So if you divide 360 by 6400 you get 1 mil equals 0.05625 degrees. Next, again from the PIF, I found that the standard N-9 sight has a 70 mil outer ring. So doing the math of 0.05625 multiplied by 70 I came up with 3.9375 degrees for the outer ring (I rounded up to 4 degrees). Next I opened Aces High and checked that my screens filed of view is set to 100 degrees. With a resolution of 1680 by 1050 that means 1 degree equals 16.8 pixels. Then 4 degrees on the monitor equals 67 pixels for the gun sight.

Of the planes I've checked most are pretty close with one major exception. The best so far is the F6F-5 it happens to be exactly correct. I've included the zoomed images below. NOTE: all images were taken from the default home head position to eliminate any movement error.

So here is the F6F-5

The full size image is here,
http://332nd.org/dogs/baumer/BBS%20Stuff/SightQuestion/F6F-5.jpg

The next closest one is the P-38J, by my calculation the sight is about 3% to small

The full size image is here,
http://332nd.org/dogs/baumer/BBS%20Stuff/SightQuestion/P-38J.jpg

Then comes the P-47D-25, by my calculation the sight is about 5% to large

The full size image is here,
http://332nd.org/dogs/baumer/BBS%20Stuff/SightQuestion/P-47D-25.jpg

Then the P-51B, by my calculation the sight is about 10% to large

The full size image is here,
http://332nd.org/dogs/baumer/BBS%20Stuff/SightQuestion/P-51B.jpg

The P-51D by my calculation the sight is about 12% to small

The full size image is here,
http://332nd.org/dogs/baumer/BBS%20Stuff/SightQuestion/P-51D.jpg

The most significant error is with the F4U-1D by my calculation the sight is about 27% to small

The full size image is here,
http://332nd.org/dogs/baumer/BBS%20Stuff/SightQuestion/F4U-1D.jpg

I think anything within +/- 10% is acceptable for game play and the calculations from the PIF for calculating lead seem to work just fine.  However, once you move beyond a 10% error it is extremely difficult to use the sight for any kind of calculation. I know this isn't a major issue but if I've covered everything correctly I think it should be addressed. Also if there are any errors in my calculations or if I've made an error in understanding I'm looking for feedback.

<S> Baumer

[Wagger]

But what about the axis gun sights?

[Baumer]

Unfortunately I don't have any data as to the specifics of  the Revi series that I can reference for the reticule  size.

If someone can post the size of a Revi16D (or any other sights they can provide specifics on) I'll be glad to check into them as well.

[715]

I thought a "mil" was short for milliradian, or 1/1000 of a radian.  There are 2*pi radians in a circle or 2000*pi = 6283.2 milliradians per circle?

[FLS]

It seems that the variations in gun sight size could be caused by the default head position, the sight ring size or a combination of both. I can imagine a relationship between the small F4u-1D sight and the poor rear view but I realize it's likely just coincidence.

The P-51D sight appears to be set to a DO 217 which has a 62 ft wingspan. The range setting is unreadable. The Spit 9 is set to a 45 ft wingspan at 580 yards. I don't know if the sights actually reflect these settings.

You can "correct" the sight ring size by adjusting your head position so the sight matches a standard fighter wingspan like 32-36 ft at 100 yards. Are you looking for the default head position to give you that sight size for all the fighters?

[Baumer]

I thought a "mil" was short for milliradian, or 1/1000 of a radian.  There are 2*pi radians in a circle or 2000*pi = 6283.2 milliradians per circle?

You are technically correct for the original definition of a Mil, however the US adopted the metric Mil in 1940 for optic systems.

Here is the page from the 1943 Fighter Gunnery Manual;

[Baumer]

It seems that the variations in gun sight size could be caused by the default head position, the sight ring size or a combination of both. I can imagine a relationship between the small F4u-1D sight and the poor rear view but I realize it's likely just coincidence.

The P-51D sight appears to be set to a DO 217 which has a 62 ft wingspan. The range setting is unreadable. The Spit 9 is set to a 45 ft wingspan at 580 yards. I don't know if the sights actually reflect these settings.

You can "correct" the sight ring size by adjusting your head position so the sight matches a standard fighter wingspan like 32-36 ft at 100 yards. Are you looking for the default head position to give you that sight size for all the fighters?

FLS I understand that to a degree I can scale the gun-sight bitmap to get the proper size (especially when the error is less than 10%). Also as you pointed out some of this can be compensated for by moving the head position. While that is technically not correct (see page below from the Fighter Gunnery Manual) it does allow for some addition flexibility.



The problem with the F4U is that you have to almost all the way forward to make even close to accurate.

I have no issue with how the size changes as you move you head position. And I don't mind correcting the scaling of each sight for every plane when I can. The problem is that with the F4U (and maybe others) is that within all that flexibility it just isn't possible to get a correct sight image size with a reasonable head position.

[Ghosth]

Baumer I believe you are correct sir.

Not sure if it will change anything, but I have been hearing complaints about the F4u's sight for quite some time now. Certainly would be nice to see things brought up to snuff when possible.

[RTHolmes]

since reflector gunsights are a virtual image effectively infinitely far away, the head position shouldnt make any difference should it?

<< bad eyesight, not great with optics ...

[hitech]

Baumer I do not 100% understand the issue, Are you simply saying you wish 1 sight would be the same mill on all planes? I.E. you want the gunfight square to be a consistent mill size?

Because you can very simply make a correctly calibrated sight for each plane.


HiTech

[Urchin]

HT,

If I understood correctly it looks like he was saying the gunsight is to small on the F4U.  I don't think you can change the size of the site itself, no matter how big you make the site in the .bmp file it will still be limited by the size of the gunsight 'model' in the plane.  The yak and la-7 also have tiny little gunsights, or they used to.  Not sure how big they should be though.

[Saxman]

Baumer,

Actually, if you use the correct gunsight for the F4U (US Mk.8, the version in which the cross extends past the ring) the sight is HALF the size it should be. I analyzed this in GREAT detail in a thread a while back, based on calculations using the Dora. But here's some comparison pics:



Here's both versions of the Mk.8 sight that we have. Both were shots were taken at default head position, and it's the one on the right (the full cross) that you want to look at (incidentally, this is also the gunsight used by the F6F-5 and FM-2).

There are three rings on the sight: 25mil inner, 50mil middle, and 100mil outer. Per the description of the sight, with a 100mil calibration a target with a 30-foot wingspan should have its wingtips touching the middle (50mil) at a range of 200 yards. The Dora has a wingspan of 39ft, so at the time I did my calculations was the closest of the drones I could use for my test.



Here is the Dora with the full Mk.8 sight at default head position. Note that at 200 yards the Dora's wingspan fills the OUTER ring. This is incorrect per the above description, as it should be using the middle ring instead.



Here's the sight on the right from the first image adjusted to what it SHOULD look like based on calculations I did using the Dora.

In order to account for the discrepancy in how ranges are displayed, I also independently confirmed the scaling issue using the .target command. I spawned a Dora and set .target to absolute minimum range, then took an external screenshot. I then re-upped in a Hog and compared how it looked when I set .target to 200yds, confirming that my above test results were correct.

HT,

Urchin is correct, the issue isn't the dimensions of the BMP file, it's how the gunsight is "modeled" in the aircraft itself. I've already tried changing the size of the gunsight using the BMP file, but it couldn't make the scaling any bigger (I can only make it smaller, or give it a lower resolution).

[Baumer]

RTHolmes you are correct, in reality the sight shouldn't change size when you move your head, but that's not how it works in Aces High.

Saxman I don't think your calculation is correct but I will double check it. Also, I think it's better to do this by calculating the math than relying on a bitmap file to get the proper size. Don't forget the Mk8 was also used on the TBM-3 which is also suspect.

Hitech Yes for most gun sights a small amount of correction is possible by adjusting the image within the gun sight bitmap. However the problem with the F4U is the gunsight bitmap dose not cover the correct Mil angle. I will show you what I mean with a test gun sight.

Here is the test grid gun sight bitmap;

As you see it has a single pixel boarder with a simple cross. So the maximum usable size of any image 254 by 254 if you don't want any bleed over.

This is how the image looks in game.
http://332nd.org/dogs/baumer/BBS%20Stuff/SightQuestion/F4U-1Dtp.jpg

Zooming in the sight is only 61 pixels wide, for a 100 mil USN Mk8 sight the image should be 94 pixels wide.



The only issue comes up when the Mil angle (of any given sight) falls outside of the width that you can use in game. I brought this up for 2 reasons, first to point out the issue with the F4U. Secondly I wanted to point this out to the people who are interested in custom sights, to show that scaling the image is important if you want it accurate for each plane.

[FLS]

Baumer doesn't the adjustment on the reflector sight change the ring size for the mil setting and range set by the pilot? So 70 mils might be the standard training sight but all aircraft wouldn't have a 70 mil ring all the time. I understand the advantage of having a consistent size but that still won't give you more realism except when your target is the correct size at the correct distance.

[Saxman]

Saxman I don't think your calculation is correct but I will double check it. Also, I think it's better to do this by calculating the math than relying on a bitmap file to get the proper size. Don't forget the Mk8 was also used on the TBM-3 which is also suspect.

I based my calculations off the historical gunsight calibration: the Mk.8 was calibrated so that an aircraft with a 30ft wingspan would fill the second (50mil) ring of the sight at a range of 200 yards. This doesn't change across the F4U, TBM, or F6F. On the Mk.8 an aircraft at 30ft wingspan filled the 50mil ring, simple as that. AFAIK it couldn't be adjusted for the wingspan of the target like the K-14 added later to the P-51, P-38 and P-47 could. I demonstrated using the Fw-190D that this is NOT the case at default head position. At default position, both wings fill the OUTER ring (testing at 400 yards the Dora filled the middle ring, precisely double the range at which it should be.). Although there's a small variance as the Dora's wingspan is slightly larger than 30' (I made a mistake in my first post, the 190D had a wingspan of 34', not 39) the scaling indicates the gunsight would need to be roughly doubled in size to correct this. Note that once again I'm using the FULL Mk.8 sight with the extended cross as seen on the right, NOT the cut-down version that just uses the rings.



If you're basing your calculations off the one on the left, you WILL end up with different results.