Gun Convergence.. a Question for HTC

[Hangtime]

I read somewhere that the guns are supposed to be angled up 12-15 degrees from level, and were adjustable in this direction as well as for range convergence. Any way to check it?

Sure wish this was an adjustable component of convergence settings.. this way I could adjust my convergence correctly for range AND deflection.

As it is now; we can adjust for range.. but not adjust for deflection. Souldn't both be adjustable? (sounds complicated)

Curious...

Hang

 

[Citabria]

hang the guns adjust vertically based on convergence range the same way a rifle is sighted according to pyro.

and according to funked a max convergence will loft the bullets up higher

yet I believe that the minimum convergence will put the bullets the highest, mid range the lowest and max range convergence will loft the bullets up nearly as high as minimum convergence due to the arc the bullet travels to intersect the gunsight

just speculation though. I still am not clear on exactly how it works

[easymo]

 Jeez hang again   Try this. Go into my walls arena. Fly stright at a wall with the auto level button on. When you get close enough to see the dust kick up, start fireing. Keep fireing till you hit the wall. The dust will show you where the ammo is hitting. You will see it loft up, than back down. Hit page up, or page down, to ajust your gunsite to where you want it.

 BTW while doing this, I found that my gunsite (just a dot) was aimed slightly high and to the right.

[This message has been edited by easymo (edited 10-05-2000).]

[iculus]

Think of the bullet path like throwing a football to a friend.  If you throw the football at a constant force, the further away the friend is, the higher into the air you have to throw the ball, if you just threw it straight, it would fall short of your friend.

In short, the closer the friend is, the less you have to arc the ball; the lower the convergence, the less you have to arc the bullets, and the less you have to angle the guns up.  the higher the convergence, the more you have to arc the bullets, and the higher you must angle the guns.

Now to expand on the topic , let's say that you can really crank the ball: the "bullet pass".  If you can throw the ball real hard and fast, you may not need to arc the ball much at all.  This is similar to .50 rounds relative to say a 20mm shell (or worse, a 30mm shell!).  Since the .50 round is travelling faster then either of the cannon shells, it needs less of an arc.

Salute,
IC

[Lance]

Dunno if you like this idea, Hang, but it works.  Modify your gunsite moving the center of the site upwards from the center of the .BMP image.  Then head into AH offline and move your virtual-head (No, this has nothing to do with Fatty's mom and chatrooms) upwards in the cockpit until the new center of your site matches where the tracers are heading.  Hit F10 to save.

After doing this you will perceive the bullets trajectory as being "higher" in relation to the nose of your plane when pulling G's.

The sight I use with this set up is a dot in the center with a half circle beneath it.  The dot corresponds to where the bullets fly when at +1 g's.  The half circle corresponds to where they converge when pulling +4 g's in a 190a5.  I also made it bright yellow to offset the fading that occurs when you move your head up in the cockpit.

Gordo
Fat DRUNK Bastards!

[SKurj]

 

Originally posted by Lance:
The sight I use with this set up is a dot in the center with a half circle beneath it.  The dot corresponds to where the bullets fly when at +1 g's.  The half circle corresponds to where they converge when pulling +4 g's in a 190a5.  I also made it bright yellow to offset the fading that occurs when you move your head up in the cockpit.
]

Pulling +4g's in a 190 u can see the tracers convergence point?!
or am i misunderstanding..

SKurj

[Andy Bush]

Hangtime

Yes, the elevation of the guns was adjustable...but not as much as you thought.
Even at relatively long range, the amount of elevation is small.

Also, the elevated gun line is really only valid in a wings level, one G firing situation. The guns are elevated in the plane of symmetry which moves as the bank angle is changed. In order to keep the elevation increment aligned with gravity, the wings must be level.

At G loads greater than one, the relevance of gun elevation is negligible when using a fixed sight.

As an example, let's make the range about 2500'. That would result in a time of flight of about one second for a .50 machine gun round. In that one second, the round will drop about 16 feet because of gravity. To correct for that drop, the gun would have to be elevated about 6 mils, or about 1/3 of a degree.

For additional discussion of A2A gunnery, see my series on the subject in the Air Combat Corner at www.simhq.com.

Andy

[Minotaur]

Hangtime;

This chart shows bullet trajectories as a result of proper "Boresighting" the guns for a P-38J.  The chart shows the 5 P-38 guns being fired right to left.  The curved lines showing bullet flight trajectory.  The "level sight line" is the pilot target point or that line which is aligned to the cockpit gunsight that the pilot uses to aim the guns with.

       

The 20mm is the lowest gun in the P-38.  The gun barrel is set 28in (F) below the sight line.  The upper 50cal guns are set 22in (D) below the sight line.

Notice that at 225yds the bullet path crosses the sight line as the bullets are rising.  Also notice, that the bullets cross the sight line again at 500yds as the bullets are falling.  At 400yds the bullets reach their highest piont or apex.

I could well imagine that the chart for a P-51 would be similiar considering the amount of bullet rise to 225yds and again at 500yds.  The P-51 also needed a convergance setting, because it had wing mounted guns.  Convergence and bore (level) sight settings must be adjusted seperatly.  I would imagine that the bore sight setting and the convergence setting would be set up so that the bullets crossed at the bore sight line horizontally and vertically the same distance(s) from the A/C.

Concerning AH, I believe that when you set gun convergence you are simultaneously setting the distance from the A/C where your bullets cross bore sight line, horizontally and vertically.  However, using the AH sight picture as a reference, the bullet path never seems to go above the sight line.  They rise till the sight line is reached then fall below it.

I do not believe that the bullet flight path first crosses the bore sight line during upward flight trajectory and then again on downward flight trajector, as can be seen on the P-38 chart.  The AH bullet flight path only seems to align with the sight line at the apex, or highest part of its flight trajectory.

IMO, when you set AH convergence you are setting two things simultaneously and at the same value in distance:

• Gun convergence distance
• Bullet flight trajectory apex to bore sight line distance

Clear as mud?

Good Luck!    

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Mino
The Wrecking Crew

"This is a social game, it's up to you to fit into it, not for everyone else to fit into you."
Pyro

[This message has been edited by Minotaur (edited 10-06-2000).]

[Hangtime]

Thanks Mino and Andy!!

Yep.. based on what I'm seeing; and what you guys are saying, it appears the AH boresighting is a tad low.

Factor in some offset excaberated by gravity, and the deflection shot goes very low and wide when in a steep angle Hi G turn. That makes sense too.. jives with what I'm seeing.

In these posts, I got the reasons for the problem and a workable fix!

Using Gordo's trick; I took my death dot sight and placed a second dot at the top of the sight picture, removed the original center one and then went offline and moved up my head position till the bullet trajectory intersected the new high death dot I created at the top of the gunsight pane.

Next I reset convergence to 400 yards, then I went looking for a turn fight, low and slow with lots of high 'g' deflection shooting... where my games been really been in the crapper fer the last month because I couldn't get the lead figured...

It worked. And it worked amazingly well! For a bunch of reasons I think.. One; I can track the con better with a higher eyball view over the dash. Two; I can now see the tracer stream with a 4 g load on, as Gordo noted. Adjusting fire for the angular gravity drop is now easier because I can track the tracer path longer. Three; the gunnery lead now 'feels' like it used too.. i.e. the eyeball-gunsight-gun-target geometry seems to work well when the target is within 300 yards and cornering hard.

Thanks guys; all of yah. I knew you guys would set me straight... this has been driving me nuts since 1.04.  

<S!>

Hang


 

[Westy]

 I finally experienced what you were talking about Hangtime but when flyinmg the LA5n tonight.
 Definately was a convergance issue, for me anyway and wih that bird.
 I'd be 200 off thier 6 and the shells were not hitting a blessed thing.

 -Westy

[LJKkratz]

I spent a lot (and I mean a LOT of time) when I started shooting over the top of everyone and being pissed that I didn't understand the gunnery in AH... then I realized that with convergence set at 500, I put the pipper right on a target at 500 and nail 'em.

I'm not a smart man, Jenny... but I do know what love is.

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--------
LJK Kratzer
Geschwader Kommodore, LuftJägerKorps

www.luftjagerkorps.com

"You have a point. An idiotic one, but a point."

[Andy Bush]

Mino

That's a super picture! Here's some additional info for those that wonder what the picture is about.

This is a diagram that arming technicians used to align the guns in the P-38. The technique used is called 'boresighting'...literally from the idea of sighting down the bore of the barrel.

 The process begins with the determination of the desired harmonization range...ie, where the gun(s) will shoot thru the gunsight at a wings level, one G situation. In this situation, that is at 200-250 yards for all guns (the 20 mm range is 250yds).

Then a chart is constructed. Circles are drawn to represent the aiming points for the guns. Fixed reference marks are included for the gunsight, horizontal axis, etc.

     

The aircraft is set up on jacks into a level attitude. The boresight chart is then placed 1000 inches down range from the gunsight so that the chart gunsight mark is superimposed over the gunsight pipper when looking thru the sight.

Next, the technician places a periscope device into the gun breech and uses it to look out thru the barrel. The technician makes small adjustments to the gun mount until his periscope is centered on the desired mark on the boresight chart. Now the gun is aimed at that mark and the sight is centered on the sight mark. The gun has been 'harmonized' to the sight using the 'boresight' process.

     

Note the values on the chart. These are all in inches. The number in the F column is the vertical distance of the 20mm below the sight. The number in the A column is the vertical distance of the 20mm boresight line below the sight at 1000 inches. This distance is about 4 inches and equates to about 4 mils in angular measurement. This is the angular elevation of the gun line...about 1/4 of a degree for the given chart conditions.

This is a 'dry fire' method of sighting in the guns. The guns could also be actually fired in at a gun butt, but the boresight technique is easier.  

The F-4 external gun pod used a similar technique. After the gun pod was hung on the centerline, a boresight scope was used to look thru the barrel. In this case, a chart was not used. Instead, the nose gear was lowered...a mark on the gear was used to represent the boresight aiming reference. This was a 'quick and dirty' way of mounting and aiming the external pod.

Andy  

[

[This message has been edited by Andy Bush (edited 10-09-2000).]

[Exile]

hey Hang and Gordo ... u guys mind posting the new sights yall made?

[Hamish]

 

Originally posted by Exile:
hey Hang and Gordo ... u guys mind posting the new sights yall made?

yeah really, pwetty pawease?  

Hamish!

[Toad]

 

Originally posted by Andy Bush:
The F-4 external gun pod used a similar technique.
Andy

Jeez, Andy...hope the P-38 method worked better than the F-4!

 

My buddies in the 18th TFW were pretty sure they could hit the ground with the pod mount if they had the nose pointed down!