Gunsight Range and Convergence

More questions from me! I'm sure they will stop soon.

I'm looking into the Gunsight aiming methods, and as usual, I have some queries.

1) Am I correct in saying that if I set the base control to 37 ft and the range control to 200yds, then a level (to me) flying FW 190 should show as filling the gap between the 2 horizontal lines at 200yds?

2) Is there any relationship between convergence distance and range (as set on the instrument)? Is the convergence range fixed, or is it adjustable in flight? If it is not - which I assume is the case - then should the range not be set to 300 yds permanently, if that is the convergence value for this Spitfire? And, in combat, again assuming a directly-behind-level target, should one not always try to fill the gap set to 300 yds range? (Does DCS model the convergence as 300 yds)?

3) if these statements are correct, then why shoot at targets much further away than the convergence distance? I mean, will the bullets not diverge and miss completely? At least when closer, there is some chance of a hit. No?

4) I took a look at the 'Bag the Hun' document. I found that useful and managed most of the questions - after a few attempts! My question here is, in that document, it talks about the wingspan of a Fw 190 filling the diameter of a ring at 100 yds. How does this relate to the targeting we are talking about above? Does that equate to setting the base at 37 ft and the range at 100 yds (although that can't be done in the DCS model) showing the wingspan filling the gap would mean the FW 109 would be at a range of 100 ft?

5) when there are references to 1/2, 1/3 etc. relating to the ring in 'Bag the Hun', does the ring relate directly to the gap between the horizontal lines in the targeting instrument? It does not relate in any way to the aiming ring in the Spitfire, I assume, as there is a variable wingspan, unlike the examples in 'Bag the Hun'.

6) If all this is correct, should one not always try to fire at the convergence range, making adjustments for deflection angles?

As usual, any help appreciated, and sorry if these questions are pretty basic - I'm still learning stuff!

1) Yes

2) Convergence is fixed. 300yards has been touted around these forums as the figure but I cannot confirm or deny. It might be pertinent to always set the range gratule to 300yards as a result.

3) In theory yes. Given a good bounce on an unsuspecting target with ~50mph overtaking speed then unequivocally yes. In practise you'll find this scenario is a very small percentage of the number of opportunities that present themselves. Sometimes you see a snapshot opportunity that is beyond or within the ideal so you take it if it looks and feels right. Add dispersion, g, and your own flight control inputs - let alone your targets gyrations! - and all this convergence stuff is a irrelevant - just try to land some hits and hope you hit something important!

4) Not sure as have no point of reference to Bag the Hun. Will advise.

5) Says ring so use the fractions in reference to the ring.

6) see note 3 response above.

Thanks a lot for your input.

4) Not sure as have no point of reference to Bag the Hun. Will advise.

From Chuck's guide, https://drive.google.com/file/d/0B-uSpZROuEd3V25mRlE2TDMzcXc/view

5) Says ring so use the fractions in reference to the ring.

I'm assuming that in BtH, they are not describing a variable wingspan like we have in the Spitfire. Should the distance between the horizontal lines not be equivalent to the BtH 'ring'?

The range bars are indeed for judging range to a identified target, based on the gunsight settings you've described above. The ring is used for deflection shooting... judging where to put the pipper ahead of a moving target so the bullets will hit him. This is very much simplified in Bag the Hun, the real math is a little harder to do as it must also take into account any speed difference between the shooter and the target.

I have some notes about the geometry and the basic mental math required, I'll dig them up when I get home :)

If memory serves, the sight was designed (as most of the tactics were) based on shooting at bombers, most of which were quite slow in the 1930s... so that a target flying at 100 mph, crossing your nose at 90 deg deflection, would be placed at the ring in order to get a hit. The formula you have to do in your head includes target speed and angle off and the answer is indeed expressed in fractions of sight radius (.75 of a ring, ring and a half, etc).

Remember bullet drop and g loading are not accounted for. Very few new pilots really knew how to use the sight properly at the beginning of the war (old salts may have been through gunnery school). Throw in a target that is maneuvering and the low destructive power of .303s at anywhere but close range and it's a wonder the RAF shot anything down during the Battle of Britain ;)

4) I took a look at the 'Bag the Hun' document. I found that useful and managed most of the questions - after a few attempts! My question here is, in that document, it talks about the wingspan of a Fw 190 filling the diameter of a ring at 100 yds. How does this relate to the targeting we are talking about above? Does that equate to setting the base at 37 ft and the range at 100 yds (although that can't be done in the DCS model) showing the wingspan filling the gap would mean the FW 109 would be at a range of 100 ft?

Mk. II gunsight circle diameter is 118 mills (radius 59). DCS Flight Manual page 165. Some "thoughts":

https://forums.eagle.ru/showpost.php?p=2994227&postcount=4

About "Bag the hun", this PDF that we know is only the exercises part, seems that are other part with theory, but the only thing I find online is this:

Ok... how far to place pipper ahead of target = sine of angle off of target x target airspeed.

So, with a "100 mph ring", a 100 mph target at 90 degrees to your flight path (sine of 90 = 1) equals 1 x 100 which equals one ring. Fire when the target's nose touches the ring as he passes in front of you. Sight was designed in the early 1930s, bombers weren't all that quick then, and the powers that be/were decreed that bombers only flew in a straight line and never took evasive action, which may have been true for bombers in formation relying on massed defensive fire, but not for stragglers trying to escape... anyway, that's the base theory, now here's a more realistic example ;)

Target is a 109 doing 300 mph. He's 30 degrees angle off. Sine of 30 degrees is .5, 300 x .5 = 150. Put the pipper so that it's along his flight path, 1 and 1/2 ring's worth ahead of him.

Or:

Sun at your back, you're diving on a 190 climbing out at 200 mph, 45 deg off. Sine of 45 deg is .7, 70% of 200 is 140. So lead your target by "1.4 rings" worth and open fire just before his wings get as big as the gap between the sight bars :)

In practice it works, but only when targets hold still. In a furball with rapidly changing airspeeds and angles a whole lot of "Kentucky windage" comes into play. And get close enough that you couldn't miss if you wanted to ;)

Edit: I should add, it's beneficial to memorize the following:

0 = 0

15 = .25

30 = .5

45 = .7

60 = .85

75-90 = 1(ish)

I still use these values to calculate crosswind component on the fly (pardon the pun), a 20 kt wind at 45 deg off the runway is a 14 knot crosswind component, etc.

So, with those values memorized, after you determine your target's angle off and airspeed just times his speed by the appropriate value.

Imagine a snap shot at a 109 passing in front of you at 300 mph... 3 rings! A lot of leading, and some would say a waste of time as he's gone in a flash. But if you fire at the right time and range, one cannon shell in the cockpit can end the fight :)

Thanks a lot for that. It looks a bit technical for me, and, although I risk being banned from here by saying this, I'm beginning to wonder if all this makes a difference!

I really am in awe of you if you are able to make these kind of judgements in real time! Honestly, how is one supposed to get near estimating the speed of the enemy, far less calculating sines of angles off, etc.? It's clearly beyond me.

I mean, with the speed that everything happens, the floating nose, the manoeuvres of the enemy plane, etc. etc., I just can't see how this degree of accuracy can possibly be practical in a combat scenario. In theory, yes, I get it, but....

Looking at the dogfighting videos on YouTube, not one that I've seen has made any adjustments to the wingspan or range controls for fighting 190s.

I know it's my inadequacy, but I have tried the Spit Instant Action mission with unlimited ammo, and have tried many different pipper placements, and still get absolutely nowhere!

I mean, with unlimited ammo, I have even tried peppering ammo all over the skies, and still nothing. Then, I watch a video on YT, and one little burst from the pilot, and it's all over.

My struggle and frustrations continue. I thought that once I'd mastered landing, my life would become easier. How wrong was I?

Thanks a lot for that. It looks a bit technical for me, and, although I risk being banned from here by saying this, I'm beginning to wonder if all this makes a difference!

I really am in awe of you if you are able to make these kind of judgements in real time! Honestly, how is one supposed to get near estimating the speed of the enemy, far less calculating sines of angles off, etc.? It's clearly beyond me.

I mean, with the speed that everything happens, the floating nose, the manoeuvres of the enemy plane, etc. etc., I just can't see how this degree of accuracy can possibly be practical in a combat scenario. In practice , yes, I get it, but....

Looking at the dogfighting videos on YouTube, not one that I've seen has made any adjustments to the wingspan or range controls for fighting 190s.

I know it's my inadequacy, but I have tried the Spit Instant Action mission with unlimited ammo, and have tried many different pipper placements, and still get absolutely nowhere!

I mean, with unlimited ammo, I have even tried peppering ammo all over the skies, and still nothing. Then, I watch a video on YT, and one little burst from the pilot, and it's all over.

My struggle and frustrations continue. I thought that once I'd mastered landing, my life would become easier. How wrong was I?

Not an expert, but I recommend using something like Tacview to analyze your flights. It should tell you if you're consistently over / under estimating lead. Fly an entire session using a consistent approach and review.

Thanks a lot for that. It looks a bit technical for me, and, although I risk being banned from here by saying this, I'm beginning to wonder if all this makes a difference!

I really am in awe of you if you are able to make these kind of judgements in real time! Honestly, how is one supposed to get near estimating the speed of the enemy, far less calculating sines of angles off, etc.? It's clearly beyond me.

I mean, with the speed that everything happens, the floating nose, the manoeuvres of the enemy plane, etc. etc., I just can't see how this degree of accuracy can possibly be practical in a combat scenario. In theory, yes, I get it, but....

Looking at the dogfighting videos on YouTube, not one that I've seen has made any adjustments to the wingspan or range controls for fighting 190s.

I know it's my inadequacy, but I have tried the Spit Instant Action mission with unlimited ammo, and have tried many different pipper placements, and still get absolutely nowhere!

I mean, with unlimited ammo, I have even tried peppering ammo all over the skies, and still nothing. Then, I watch a video on YT, and one little burst from the pilot, and it's all over.

My struggle and frustrations continue. I thought that once I'd mastered landing, my life would become easier. How wrong was I?

Actually you have summed up the situation quite well.

In reality, during a combat situation you would be lucky to have time to alter the target wingspan before it all started. Just set the range to the convergence setting, 300 yards or whatever the official distance is, and forget about it.

The best advice is "Get close, and when you think you are close enough, get closer."

Everything else is just a matter of practice. In deflection shooting, there are so many variables involved, it usually becomes a case of "fire when it feels right".

Cheers, Scream.

Actually you have summed up the situation quite well.

In reality, during a combat situation you would be lucky to have time to alter the target wingspan before it all started. Just set the range to the convergence setting, 300 yards or whatever the official distance is, and forget about it.

The best advice is "Get close, and when you think you are close enough, get closer."

Everything else is just a matter of practice. In deflection shooting, there are so many variables involved, it usually becomes a case of "fire when it feels right".

Cheers, Scream.

I even wonder about setting wingspan and range. I always set to 37 ft and 300 yds, but as I said earlier, if you look at the YT videos, no one seems to bother with that. In all the videos I've seen, wingspan and range are at default, unadjusted. Doesn't seem to affect the pilot's ability to very easily make light work of the 190s!

Jealousy doesn't come into it!

I even wonder about setting wingspan and range. I always set to 37 ft and 300 yds, but as I said earlier, if you look at the YT videos, no one seems to bother with that. In all the videos I've seen, wingspan and range are at default, unadjusted. Doesn't seem to affect the pilot's ability to very easily make light work of the 190s!

Jealousy doesn't come into it!

Another point is that the sight reticle is a bit off: https://forums.eagle.ru/showpost.php?p=2999037&postcount=4

Generally, the outer circle is too wide while the space between horizontal lines (distance adjust) too narrow.

Why is the convergence value such a 'secret'? Why is it not simply specified along with all other aspects of the aircraft?

Reading some pilots notes from the Battle of Britain, using just .303s of course, he stated 250 yards Harmonisation distance, and that the bullets would take .28 of a second to travel that distance, and also that a fighter could travel 40 yards in that time. So, this seems to broadly agree with the numbers quoted by Jocko417.

Also, I'm fairly sure that harmonisation didn't necessarily mean all guns converged on a single point, but that they were arranged to cover a strip of space. or more than one spot. This varied as the war progressed, and as guns got heavier/tactics changed (and depending on squadron tactics).

Humm.... Here we go... https://en.wikipedia.org/wiki/Gun_harmonisation I might have known Jimmy Wales would have the answers.

There is a manual on gun convergence on Avialogs: AAF 200-1 Manual for Fighter Gun Harmonisation, some of the illustrations on mkii's wiki link are taken from the manual.

http://www.avialogs.com/index.php/item/56042.html

Why is the convergence value such a 'secret'? Why is it not simply specified along with all other aspects of the aircraft?

Better yet, why can't we adjust it?

I did some testing and came to the conclusion that if you set the range to 200yds and the width to 35 then firing when the wings just fill the bars you seem to hit it at convergence. Less than one seconds burst will remove a wing.

Here is my gunsight at the moment my rounds hit

Here is the external view taken at the same moment. You can see the tracer.

and here is another external view showing the tracer passing the target (if the resolution is still good enough in the upload). It is not very clear whether the bullets are diverging or still converging at a later point. Perhaps they never converge perfectly (which would be more authentic) but it does seem that there is still a lethal concentration beyond 200yds. This shot of one second did remove the 109s wing.

Just to be clear, this a screenshot taken 0.5 seconds later that shows the gunsight settings. Perhaps I had the wingspan nearer 38 ft but it makes little difference when attacking a moving object at a faster speed. You should really open fire before it fits exactly anyway.

Very short video here.

It is not very scientific but it is enough to convince me that shooting at 200-250yds gives a very lethal concentration at the target. There is still some argument within my squad as to whether the gunsight settings are accurate. Klem has been doing experiments that somehow involve placing a 109 at a precise distance (on the ground?) in ME and then cutting & pasting the 109 between the bars of the spit sight and says it is way out. I am not sure exactly what he is doing and whether he is introducing an error but my own experiments in the air seem to show that assuming the sight is accurate, even if it is not, does give a good result. I have always preferred to shoot at 100yds and it is a hard habit to break but it works for me to shoot earlier.

Nice work Roblex.

At 250 yards, or so, the contacts are just so tiny, making up so few pixels on the screen. It's very hard to aim at something that far away I find.

I've always adopted the "wait until he fills the gunsight" approach (i.e. ~100 yards) also. However, I've found that I seldom get the devastating results at such short range. I guess I'm shooting inside the convergence point also, and that to get the sweet-spot I need to be opening up further out... but then it's so hard to hit something there....

Dilemmas!

Yeah I usually set my gunsight to 250 yards, and the wingspan to a few feet more than minimum, whatever that is. I will try and set it to 200 yards now after reading this detailed report. Thanks again!

Nice work Roblex.

 

 

At 250 yards, or so, the contacts are just so tiny, making up so few pixels on the screen. It's very hard to aim at something that far away I find.

I've always adopted the "wait until he fills the gunsight" approach (i.e. ~100 yards) also. However, I've found that I seldom get the devastating results at such short range. I guess I'm shooting inside the convergence point also, and that to get the sweet-spot I need to be opening up further out... but then it's so hard to hit something there....

 

Dilemmas!

As convergence on the Spitfire is "around" 225-250 yards, if you shoot at ~100 yards your rounds will go each side of the cockpit, converging in front of him! given that he's flying straight and level and your gun-sight is on his fuselage, it would be better to aim slightly off to one side and slightly high, top of the tail height, this is because your rounds will be coming "up" from your gun position to the sight level line, so until convergence they are "low", the best you can do is hit him with all the guns from one wing.

This all changes in a turn fight as you're likely to get hits on his wings which are a bigger target in a turn.

Witch

Yeah I usually set my gunsight to 250 yards, and the wingspan to a few feet more than minimum, whatever that is. I will try and set it to 200 yards now after reading this detailed report. Thanks again!

I would not bother changing what you do. The smallest marking is 40ft so if you are setting it a little lower than that and the range as 250yds it probably means that when a 32ft 109 fits between the bars you are actually 200- 225 yds behind him and your bullets are quite closely concentrated. Look at the picture taken from just in front of the 109 and look how close together the bullets that have passed him still are. I suspect anything from 200-250 will do serious damage.:thumbup: