Question about gun harmonization

[GODO]

Originally posted by hitech
Ok to answere your question is the convergance and harminazion are always set to the same number in AH.
HiTech

Not sure about that. What I see is that the bullets cross the sight vertically for first time at the convergence point (bullets climbing), going then down. So, setting conv at 600 yards makes the bullets to raise along 600 yards, touch the gunsight center and then go down.

But the real bullet pattern is quite different, they raise much earlier (125m) over the gunsight center, fly above the gunsight center and then cross the "convergence point" going down form above at 550m. Most of the time the rounds are above the gunsight center.

Actually, my impression is that my rounds in AH fly lower than gunsight center until convergence range. Then they more or less cross vertically and horizontally and go down. The effect is that firing closer than convergence puts the rounds too low, firing farther puts the rounds too disperse.

[Cobra412]

After looking at that chart and re doing it in color it seems there is a rather large spread of bullets.  

Maximum coverage area at the 550m harmonization line for all guns combined other than the MG131s is approximately 2m.  Spread from one wings outer gondola to the same wings inner gondola is just under half of a meter.  From the inner gondola to the wing root MG151 there is a little over a half meter spread. While the MG 151 wing root mounted gun will be right on the sight line at 550m.

All of this is ofcourse under no wing loading (symetrical or assymetrical) and with a perfectly boresighted weapon system.  A 6 foot area of bullets at 550m is great but that is only if there is no outside interferrence with the preset boresight.  Question is how much wing flex is induced under a certain amount of Gs?  This could very easily throw off that boresight and hits could be outside the original ball park and not as accurate.

[Cobra412]

Godo do mean something like this?

Per your chart your preset boresight range is at 550m and your target is at 500m. Your bullets flight path is now technically higher than your sight line by almost 40cm or 15.75 inches with a target at 500m.    

While in flight your bullet will be passing through your sight line from bottom to the top at 140m then going back to the sight line again from top to bottom at 550m.  This in essence would mean you would have to push the nose over approximately 40cm to hit your target at 500m.  At 350m you'd have to push over even more to almost 80cm and then you'd be backing off to 40cm again at approximately 220m and finally back to line of sight at about 150m with no adjustment.  

Question is do we model our lead computing sights like we should?  Adjustments on your sight would adjust your targeting reticle to the appropriate postion and then you'd essentially fly to your targeting reticle depending on what you guesstimate your range is.  

The P-51D had preset reticle adjustments for particular aircraft during the war.  If you knew what plane you were dealing with you'd make that selection on your sight . You'd then adjust your range scale to make the aircrafts wing tips fit snuggly between your reticle.  Once you did that you'd know at approximately what range the target was at.  Granted the reticle could not be preset for every possible encounter so the major aircraft were preset.  When the pilots would find a different bird other than a preset one they'd have to know approximate wing span so as to select the appropriate preset selection.  This would give them a best guess range instead of having to judge solely by there eye sight and what they thought the range was with no help from out side sources.

[Drunky]

I prefer my guns to harmonize in 3rds or 5ths.

Some people like weird stuff like 7ths but that is too 'outside' if you know what I mean.

[Cobra412]

Godo if HT is stating that the harmonization point and the convergence point are the same then technically I would think they aren't correctly modeled.  But that doesn't necessarily mean the spread spectrum isn't induced at the convergence point.  

With your reference chart you should have a total of 3 meters of total coverage area.  The only thing you could do is with this chart setup the same bird at the same harmonization point and check to see if the spread spectrum is almost the same.  If your getting a very tight grouping at that range that doesn't match up then something is definately modeled incorrectly.

Basically I'd try firing your wing root cannons first and check their spread spectrum at that range.  See if it's roughly the same.  It should be a tight grouping right on at 550 meters.  Then fire your gondolas at the same range.  Not sure if you can fire each seperately (inner and outer) but you could definately tell if the spread was close to being accurate.  Your outter gun should be almost a meter off of center at 550m.  Your inner guns should be almost .80 meters off of center.  

To check for atleast the wing root accuracy dial in 400 meters on your target.  Your MG131s should be slightly off center left and right with the convergence (400m) set at 400m on the target since they are in parallel.  They should never be dead on center. On that same target check your wing root cannons.  They should be almost .4 meters off center at 400 meters with their convergance still set at 550 meters.

At a 400/550 meter convergence set your target 400 meter total spread spectrum should go out to about a little over 3 meters or so with all guns firing.  With that same convergence set your 550m spread spectrum should be no more than 2 meters and your MG131s shouldn't even come close to hitting the target.  With their 400 meter harmonization point their bullet drop should easily exceed 120cm below the sight line. Then again I have to check and see how many centimeters the target reference board is on AH2.  They may hit but they'd be extremely low on the board.

[Cobra412]

Well I did a quick test.  Without knowing the range circles and what distance high and low off center it's hard to come up with a conclusion.  I did notice though at 400 meters my cannon rounds would have more hits below the zero reference mark than they would above.  Here's the other kicker though the A-8 we have doesn't have gondolas.  So therefore the test isn't accurate.  

If the gun mount areas were about the same which they may be in distance (width off center)but not elevation wise on the wing I could say it shows that the rounds are actually hitting lower instead of higher at 400 meters.  At 400meters I should have been almost 80cm higher than the 0 reference point. that equates to almost 2 and a half feet higher.  Again without knowing how the board is setup as far as the reference circles it's hard to tell.  Also without having a graph for this particular aircrafts configuration that we have available it's also hard to tell.

[hitech]

Do not foget how speed changes the trajectory. Guns are set while the plane is standing still. The outcome will change as you fly faster or slower.


HiTech

[Dead Man Flying]

Cool thread.  Very informative.

-- Todd/Leviathn

[GODO]

Originally posted by hitech
Do not foget how speed changes the trajectory.

HiTech, speed is not the point here, the speed of the plane relative to the speed of the rounds is very low and will rarely affect the bullet trayectory over or below the gunsight center (AOA from speed affects both, gun elevation and where the sight is pointing). The point is that bullets should fly over the gun sight center most of the time and then cross it going down at convergence range (being convergence and harmonization at the same range), just the opposite than to cross the gunsight center going up at convergence range and then falling to the ground from that point.

Cobra412, 40cm at 500m are hardly noticeable from the pilot eyes over the gunsight center, you really dont need to push your nose down to hit the target. May be you will hit the engine and the cockpit instead the tail while aiming directly to the tail. But, if the bullets are traveling lower, you are going to miss any centered target that is flying closer than AH convergence point and then you really need to pull your nose over, even losing partially the target from view to score hits.

[hitech]

Mandabole: The resone for not going much above the sight is do to the eye point on most planes is well above the gun point.

Let say you have convergance to 500 yards. And a 2700 fps round.

That bullet will reach 500 yards in aprox .5 secs.

That equates to a drop of 4 feet from the bore line.

Now if your eye is 4 feet above the gun, the bullet will never be above the slight line until possibly after 500 yards.

At 300 yards the drop from bore sight line would only be only 1.75 feet hence it would be even more pronounced. In order for the bullet to travel threw the sight line and back down at closer ranges, I would almost have to be shot straight up.


HiTech

[GODO]

I did more tests using only the wingroot guns of 190A5, convergence set at 550 yards (historical harmonization was 550m), constant speed of 330mph at 1000 feet alt.

With the target set to 200 yards, hit concentration was clearly  below gunsight center. with the target set at 400 yards, hit concentration was near the the gunsight center, with the target at 550 yards, gun concentration was noticeabily below the gunsight center. In any case, all the rounds hit the target to the left of the corresponding hit point, that is, right gun near gunsight center horizontally and left gun well to the left of gunsight center.

IMO there is a problem with the gun placements in 190s. Bullets go too low and to the left all the way until convergence range.

[GODO]

Originally posted by hitech
Mandabole: The resone for not going much above the sight is do to the eye point on most planes is well above the gun point.

HiTech, the graph I posted has several horizontal lines, for the gun, for the plane and for the gunsight (and the pilots eyes). It is showing clearly that most of the bullet path is above gunsight center line, not below it. May be the effect is different in other planes, but this is how it worked for 190s and probably for 109 gondolas too. The bullets should cross the gunsignt going up really early, not just at the convergence point where they should cross it going down. May be it is due a wrong placement of the guns or a wrong ballistics for 151/20s, dont know.

Aside of that problem that really affects negatively the aming with these planes, it would be good to have an indication in the hangar when setting the convergente to show the harmonization point (the point where the bullets will go down the gunsight center falling from above).

[GODO]

Originally posted by hitech
Now if your eye is 4 feet above the gun, the bullet will never be above the slight line until possibly after 500 yards.

Wrong, as you can see in the picture the bullets will start to fly above the gunsight center at 125 yards and will go down the gunsight center at 550 yards (with harmonization set to 550 yards). The guns are clearly pointing up.

[tiger3]

Originally posted by hitech
Do not foget how speed changes the trajectory. Guns are set while the plane is standing still. The outcome will change as you fly faster or slower.


HiTech

My translating could be faulted. Velocity relative to target not airspeed is the factor yes?

AH# tiger3

[AWwsky]

Harmonization - derived from Harmonize meaning 1)to make harmonious: bring into agreement 2) to sing in harmony 3)to add chords to a melody so as to form a harmony 4) to arrange into a Harmony(sense)..

I think #1 best qualifies for what you are looking for HiTech

Wsky