Prop HUB mounted Cannon, Autocannon, & Motorkanone Ballistics

[321BAR]

I give up.

I'm dumb as a dumptruck.

I performed a different test of recording at autolevel the mil value for where the graticule center was at rest in referrence to the center line of the target at 50 yard incraments starting at 50 ending at 1000. I also recorded the mil value at each point of the primary gun firiing pattern related to the center line of the target. Convergence set to 150 for all aircraft I tested. My thought is the graticule line of view is either auto adjusted based on your convergence or is set to some relationship with 1000 yards on an angle from the aircraft or both.

I recored mil values for the I16, P51D, spit9 and 109K4.

I either compute values that say the 4 primary guns I tested have been given a tad of assist to keep the rounds comfortably inside of a 50mil graticule ring with convergence set at 400 yards or all of the V0 M/sec initial values are under powered. I'm missing something to make this work. I should be able to work backwards from the german data and be closer than 210cm at 400m or 699cm at 400m when the book shows 362cm at 500M/sec.

I go play Tonka Truck....my head hurts.......

yours does...?

[bustr]

I figured it out with this experiment because I have german records from the war with ballistics for the MG151/20 and MK108/30.

Aircraft
109G-2 MG151/20 - 720-250m/s
109-K4 MK108/30 - 500m/s

Testing Procedure.

Round 1 at 150 yard convergence.
Round 2 at 650 yard convergence.

Target distances in yards.

50,100,150,200,250,300,350,400,450,500,550,600,650,700,750,800,850,900,950,100

Take off with each aricraft auto level facing north and pull up target.

1. Record number of mil above or below the graticule center at each test distance.
2. Fire the main cannon and record number of mil obove or below target center it patterns at.

150 yard convergence test for gunsight center.

109K4 - (0.0mil at 50) to (-14mil at 750)
109G2 - (+3mil at 50)  to (-14mil at 900)

650 yard convergence test for gunsight center.

109K4 - (-2mil at 50) to (-15 at 750)
109G2 - (+2mil at 50) to (-14 at 900)

Shooting Test at 150 yards.

109K4 - (+7mil at 50) - (-44mil at 750)
109G2 - (-5mil at 50) - (-37mil at 900)

Shooting Test at 650 yards.

109K4 - (+2mil at 50) - (-35mil at 750)
109G2 - (-4mil at 50) - (-31mil at 900)

Results of Testing.

MK108 convergence 150: +.01 angle at 500m/s.
Mk108 convergence 650: 0.00 angle at 500m/s.

MG151/20 convengence 150: +.01 angle at 720-750m/s
MG151/20 Convergence 650: 0.00 angle at 720-750m/s

I tested a number of other aircraft. Lower guns angle up to meet hood mounted MG. Wing guns shoot almost straight out with the line of the aircraft unless there are hood guns. They pattern up to the level line of the hood guns from 150 out to 650 at which point they both converge at the center of the gunsight. HUB nounted cannons are at level with the engine when pulled to full 650 convergence.

The reason at 650 convergence all of your guns look like they are hitting center of the gunsight is your line of view has been auto tilted down by 5-15mil.

At this point realism would dictate locking the HUB mounted cannons at 650 yards in the aircraft in question.

AI am really dumber than a DumbTruck. Just call me Tonka Boy....





 

[RTHolmes]

I'm still not sure exactly what you're getting at, are you saying that in my diagram 3 is correct IRL, but AH models it as 2?

[Charge]

Picture 3 is how it should work, picture 2 is how it works in AH right now. At least it seems so when you adjust the center cannon convergence in hangar. In practice it does not matter much how it is done in game.

What is interesting is that the motor cannon obviously shoots (initially) along the thrust-line, but thrust-line is not the line the plane is flying necessarily, not horizontally nor vertically. Vertically the direction the plane is going is determined by the wing AoA at certain speed and it changes all the time when speed changes, more or less. Of course this is how it works in game too but we make the needed correction almost automatically.

-C+

[RTHolmes]

ok got it

quick test with the P39 on the runway confirms that for P39 at least, the barrel moves not the sight line. extend the convergence and the rounds land on the ground further out. couldnt think of a quick and easy way to test the 109's cannon, being a tail-dragger.

if the hub mounted cannon were remodelled as pic 3, the only difference you would notice when changing the convergence would be the sight image moving up or down a small amount, so you may have to raise or lower your head position a little.

[bustr]

If you perform my test at 150 and at 650, then calc the differences between graticule center related to target center and round impact the same in mil. You swill see that 0-250yd the round shoots flatter with a smidgen more M/sec retained. The up angle makes it slower at those ranges. Thats where I was getting those sub 500m/s speeds. Thats why I was convinced the up angle was in the 650 yard covergence because I only calculated at 150 initially.

Made me do the......

If the real airplanes had unmovable cannon. Then my wish is that the hub cannon on the identifyed aircraft have their cannon locked at 650yd convergence which corrisponds to the ballistics for rounds shot from 0 degrees.

Can you imagine having to remember ellevation past 200 with our shooting if the gunsight center was not auto adjusted for us.....Revi manuals showed that in % of the graticule strichlinie. Wingspan=distance then elevation=% of graticule strichlinies..that 5mil gap above the ReviC12 center line was a bomber rudder at 1000m...something like that.

[321BAR]

someone wanna PM Pyro or HiTech to take a looksie here in this thread?

[bustr]

So I created a 150mil diameter graticule that is grided with 1-pixel wide lines in 10mil squares with 5mil ticks in an alternate color. Now I can also do "Dispersion Box Mapping" and Recoil. You can't see any of this untill fully zoomed looking at the target. Be neat if HiTech could add a 180ft diameter fixed target on the ground or water surface near your offline base. (.Btarget)...Then when your bombs or rockets hit it and blow up you get 3-6ft diameter holes to look at for several minutes. It's late and i em babblin.......

NS-37 shoots almost like a 20mm. MK108 reminds me of Brown Bess's. When I test the NS-37 offline and fly it in the game it seems like the rounds 200-100yards are just passing through the body of the con. We must be useing only AP-T solid rounds. Yak9T pilots had a choice of AP-T and HE depending on the mission type they were going on. Not all of them chased tanks on every mission. The HE rounds worked wonders on Fw's and twin engined bombers. The round's long sharply tapered cross sectional shape is still in use today with modern high rate of fire 37mm systems. Thats part of what helps keep it's trajectory relatively flat and a tighter dispersion for a 1.45cal(3.7cm) bullet. The low speed and blunter nose cross sectional shape of the 1.18cal(3cm) round is part of why it looses V so fast and has such a hugh dispersion map right off the bat.

I was watching Luftwaffa gun cam footage this weekend and noticed with the 1.18cal(3cm), based on the wingspan to percentage of the graticule diameter filled, that the pilots didn't hit the cannon trigger until they were passing through 200m and closer. I was watching pilots missing B24's at 300m then just getting a hit on the wingtip at 200m. From 100m in they could hold rounds on target. 20mm and MG were hitting with no problems starting at 300m. Oh that open space in the middel of the Revi graticule is the equivalent of 2m at 100m and the ring is 10m and 100m.

Funny even the dispersion from the german manuals shows 20mm at 400m (4.9m). MK103/30 at 400m (9.2m) and a 37mm similar to the NS-37 in m/s at 400m (2.7m). We should be seeing big kill strings landed with the Yak9T in the MA based on the german math...... <---crunching math makes my head like this Owwwwwwey..

NS-37---------100------150------400----880m/s----cov=650
Graticule---(-6mil)--(-11mil)-(-17mil)--Graticule + or - target center line.
Cannon-----(+5mil)-(+7mil)-(-12mil)--Cannon + or - target center line
Dispersion-(20/25)--(15/15)-(20/25)--Size of impact dispersion in x/y mil total size box or rectangle.
Recoil=3mil over 2 seconds.

MK108---------100------150------400----500m/s----cov=650
Graticule---(-25mil)--(-30mil)-(-37mil)--Graticule + or - target center line.
Cannon-----(-25mil)-(-30mil)-(-42mil)--Cannon + or - target center line
Dispersion-(25/50)--(35/45)-(35/50)--Size of impact dispersion in x/y mil area size box or rectangle.
Recoil=1mil over 2 seconds.

[RTHolmes]

If the real airplanes had unmovable cannon. Then my wish is that the hub cannon on the identifyed aircraft have their cannon locked at 650yd convergence which corrisponds to the ballistics for rounds shot from 0 degrees.

Back to my earlier point: you can adjust harmonisation in 2 ways: move the cannon, or move the sight.

the convergence does not have to be fixed because the cannon is fixed. since the cannon was fixed, the sight must have been adjustable.

[Plawranc]

I am a nerd, I love history, firearms, and planes. Thats it.

And my head is dying with all this math"S" (yes I use UK spelling  )

kill me someone 

[RTHolmes]

dont sweat it, I skipped over all the maths and detailed testing, as it just gets in the way of the fundamental points being made

[bustr]

RTHolms,

Revi16b had an internal mirror angled at 45 degrees. It had screws to adjust elevation +-3.0 degree and left/right +-2.5 degree. That way the reflector plate was fixed at a known optical angle.

ReviC/12c had a single screw that changed the angle of the reflector plate +-3.0degree. Moving the reflector plate could cause distortion of the graticule.

HiTech either to make the game more enjoyable for us or to make his ballistics calc simpler, auto adjusts the graticule elevation on all of our gunsights based on the convergence you pick in the hanger.

Based on the german testing of the MK108 3cm rounds from that short barrel. The parabalic twist dispersion from the 1:16 r/h rifling. No one in the game flying the 262 should miss anything at 200 and under if the guns all fire parallel with a 1-2 sec burst. Basicly its a 4 barrel shotgun. Past 150 a single barrel MK108 has slightly better odds than a slot machine payout of hitting within 9m in any direction of a dinner plate. Think of 4-9m dispersions clouds with outliers x4. Should be some golden BB's in that cloud if it only takes one mine round per fighter.

Maybe thats why all the german gun cam footage I watched on Utube this weekend which had a super imposed Revi graticule on the camera lense showed the pilot holding fire with the cannon until the 10m wingspan fighter filled the ring. Wonder how many of those 3cm rounds scraped off the inside of the hollow 6cm airscrew just before exit on the DB605 and JU213? MK108 3cm has horrible dispersion values at any range. Thats offset by the one shot kill value of the round if it hits anything. Heck the Mossi TseTse's 57mm shoots about 1r/sec at +-790M/s. You can hit a row boat at 200m with that on purpose. NS-37 850M/sec and much better sectional profile for accuracy.

Revi graticule ring = 10m at 100m<---P51 wings at 100m.
Revi off center gaps = 2m at 100m

Watched an FW190A-8 gun cam with wing 30mm open on a B24 at 300m and not hit anything untill about 200m and that was the right wing tip at the very end of the wing with one round. He walked the rounds into center mass from 150-50m before he broke off. Gun cam footage with MG and 20mm showed reasonably accurate hits at 300m on fighters center mass.

[hitech]

The deal is , the output would be almost identical.

Changing the sight or changing the angle of the gun accomplish almost the identical thing. The point of elevation is simply so that the bullet crosses the dot at a given range.

You can lower the sight or raise the guns. The only net effect is at what distance the bullet would drop below the nose with your line of sight.

HiTech

[RTHolmes]

It had screws to adjust elevation +-3.0 degree

there ya go -thats 6deg (over 100mils.) sounds like more than enough to adjust the harmonisation between 100-650yds.

[bustr]

OKyDoky guess thats a (no  ) on fixed mounting the cannons in the aricraft mentioned. Back to being dumb ans a dumptruck....

But, it was driving me nuts trying to understand why they were allowed to be elevated in the game when they couldn't due to physical mounting limits in real life. Lotta math and german, smidgen of russian to get the Aha eureka  moment out of this.... 

If covergence at 650 in fact is the HUB cannons in question at 0.00degree orientation/real life. Maybe put an asterisc(*) notation in the hanger with each of these aircraft letting players know their orientation?

*150-650/adjustable. 650 is @ 0.00degree to engine line.* Or something.......recoil and dispersion kinda eats it all up past 200m anyway....