Prop HUB mounted Cannon, Autocannon, & Motorkanone Ballistics

[bustr]

My Wish:
 
The ballistics for the nose mounted cannons fireing through the propeller spinners of the P39D, P39Q, Bf109F-K, Ta152 and Yak9T/U are incorrect the moment the round leaves the barrel. The cannons in question in the real aircraft were fixed mounted in the engine center line or fixed parallel to the engine line through the propellor hub line like the P39. No positive angle adjustment to the ballistic trajectory was possible other than by pilot stick input in flight.

Please level these cannons in thier associated mountings to fire from 0 degrees when the aircraft are level.

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HUB Cannon/Autocannon/Motorkanone in affected aircraft.

Slowest to fastest cannon by (V0)M/sec. (V0)=Initial Velocity

(MK108/30 - 500-540m/s)**(M4/37mm - 610m/s)**(MG151/20 - 720m/s)
  
(ShVAK/20 - 750-790m/s)**(HS404/20 - 840-880m/s)**(NV-37/37 - 880-900m/s)

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Game in Offline Mode Data Collection.

Data Collection - Convergence at 150. Aircraft auto leveled. Only the nose cannon was fired to create patterning at each distance. (.Target xxxx) was set to 50, 100, 150, 200, 300, 400, 500 and 600 yards. On full zoom the impact point from graticul center was recorded in Mil. (2-pixel = 1-mil)

Graticule Center = 0.00mil. All values should be in increasing negative values below 0.00mil if the cannon is mounted level with the engine line.

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Testing Results in Offline Mode.

Cannon*50*100*150*200*300*400*500*600 - Yards

MK108/Bf*(-6.50)*(-1.62)*(0.00)*(-1.62)*(-3.25)*(-4.87)*(-9.75)*(-14.62)--540m/s
MK108/Ta*(-8.58)*(-4.29)*(0.00)*(-4.29)*(-6.50)*(-6.50)*(-9.75)*(-13.00)--540m/s
M4//37mm*(-8.60)*(-0.81)*(0.00)*(0.00)*(0.00)*(-1.60)*(-3.25)*(-6.50)-----610m/s
MG151/20*(-6.66)*(-1.62)*(0.00)*(0.00)*(0.00)*(-1.62)*(-3.25)*(-6.50)-----720m/s
ShVAK/20*(-6.50)*(-1.62)*(0.00)*(0.00)*(0.00)*(-1.62)*(-4.33)*(-4.87)-----790m/s
HS404/20*(-8.60)*(-3.25)*(0.00)*(0.00)*(0.00)*(0.00)*(-1.62)*(-3.25)------880m/s
NV-37/37*(-6.50)*(-1.62)*(0.00)*(0.00)*(0.00)*(-1.62)*(-1.62)*(-4.33)-----900m/s

Values at 0.00mil show cannon is angled firing upward.

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Real World Cannon Ballistics Example Firing from Level.

Bf109G-6/U4 MK108/30 to 500 meters in centimeters of bullet drop.
Revi center line 74.5cm above engine center line.
Revi adjusted center look down line of sight = -29cm of engine level at 100m.
 
Cannon*50*100*200*300*400*500 - Meters

MK108/30*(-6.0cm)*(-19.0cm)*(-74.0cm)*(-189.0cm)*(-338.0cm)*(-553.0cm)--500m/s

Trajectory Calculation (BC Vloss) not included.
V0= 540m/sec Dist=400m time=.74sec  Vert.drop= 270cm.
V0= 505m/sec Dist=400m time=.79sec  Vert.drop= 305cm.
V0= 500m/sec Dist=400m time=.80sec  Vert.drop= 313cm.

(BC Vloss) included.
V0= 500m/sec (-338cm) Vert.drop at 400m.
V0= 505m/sec (-330cm) Vert.drop at 400m.
V0= 540m/sec (-295cm) Vert.drop at 400m.  

(BC Vloss) = % velocity lost per 100m based on bullet's ballistic coefficient.
MK108/30 Vloss = 25M/sec+- per 100m.
(V0) = 500m/s. Vloss at 400m = 408m/s

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Projected Possible Results in Game MK108.

Proportionally adjusted Mil value trajectory for MK108 with cannon line at engine level.
Revi center Bf109 10mil above engine center line before sight line adjustment.
Revi center Ta152 13mil above engine center line before sight line adjustment.
Revi adjusted center = +26mil up to use stadia marks to 400yds. Game default only 300yds.
 
Cannon*50*100*200*300*400*500 - Yards    

MK108/30*(-1.62)*(-4.80)*(-18.24)*(-45.60)*(-77.52)*(-124.00)--500m/s

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Sources for MK108 ballistics and values:

General Ballistics Trajectory program from Georgia State University Dept. of Physics and Astronomy.
 
http://hyperphysics.phy-astr.gsu.edu/hbase/traj.html

Ref. Bf109G-6/U4 1944 appendix 13, armerors ballistics table for MK108 Motorlafette.
     L.Dv.T.2109 G-6/U4/Wa - 2 MK 108 in Flugelgondel
Ref. http://www.luft46.com/armament/mk108.html - for MK108 Minengeschoss at 540m/s.
Ref. Tony Williams( http://www.quarry.nildram.co.uk/WW2guneffect.htm ) MK108 Minengeschoss at 505m/s.
Ref. Handbuch der Flugzeug Bordwaffenmunition 1936-45 page35 for MK108 Minengeschoss at 500m/s
     Vloss = 25m/sec per 100m.

[321BAR]

bustr... idk how you did all this math so early. I'm tired but it seems you are correct in assuming the cannons are mispositioned.

[RTHolmes]

The cannons in question in the real aircraft were fixed mounted in the engine center line or fixed parallel to the engine line through the propellor hub line like the P39. No positive angle adjustment to the ballistic trajectory was possible other than by pilot stick input in flight.

the cannon is fixed but the vertical convergence can easily be adjusted by moving the sight ... not sure what you're asking for here

[bustr]

321BAR,

I'm dyslexic so if something seems out of place and I can't see an obvious answer. I'll keep learning the components and teaching myself the science, language, technology or math to it until I see the big picture and go Aha! Or prove to myself I'm dumber than a dump truck.

Now it's obvious whats happening based on the testing regiment compared to real life and I can unfortunately forget most of what I just taught myself. I won't have a reason to access the knowledge any time soon. One of the problems with dyslexia.

I have always been under the impressing HTC wants to utilise the core technologies such as the weapons systems as accurately as possible. But, automate much of the engine management related tasks to free us to enjoy the game shooting at each other. Or make AFK beer runs.

RTHolmes,

If the cannon barrels in question were mounted parallel to the engine 0-line, the numbers in the Testing Results phase would never show 0.00 but instead progressively increase down range as the bullet drops. The aircraft cannons were each set in the hanger to pattern at the center of the gunsight view at 150 yards via the convergence setting. To achieve this we first have to assume the cannon barrel will need to be angled up to our  line of sight at 150 yards.

The proof for the up angled cannon barrels. Each cannon begins at a large negative number below your gunsight center at 50 yards. But, at 100 yards is a smaller number than at 50 yards and at 150 yards is 0.00 or patterning in the center of your gunsight. This was impossible to accomplish in the real aircraft.
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Example:
Cannon*50*100*150*200*300*400*500*600 - Yards

MK108/Bf*(-6.50)*(-1.62)*(0.00)*(-1.62)*(-3.25)*(-4.87)*(-9.75)*(-14.62)--540m/s

Negative numbers are below the center of your gunsight. (0.00) means at the center of your gunsight. These numbers describe an up angled barrel trajectory curve over a distance of 600 yards.
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In the group of aircraft in question the cannon was mounted or locked into or parallel to the engine center line. This means any round fired when the aircraft is at engine line level will immediately fall towards the center of the earth arching away and down propelled at first by its initial velocity M/sec.

I accounted for the adjustment of the Revi gunsight center if the MK108 cannon in the 109's and Ta152 was reset to the real world engine 0-level.   At this point  if you made no adjustment upward with the center of your gunsight with the corrected MK108 cannons, you would only be able to elevate the aircraft nose to make a maximum 300 yard shot with the default gunsight center.

For the MK108 to achieve a 400 yard shot the gunsight center would then need a 26mil adjustment up towards the top of your screen. The real Revi16b had an internal mirror that was tilted to raise the center of the graticule to account for the MK108 ballistic drop to 400m by centering it to -29cm below the engine 0-line from 74.5cm above the 0-line.

The other cannons shoot flatter than the MK108 and no adjustment would be needed that I can see so far.

[RTHolmes]

coupla things:

have you confirmed that the cannons are set at exactly 0deg to the thrust line?

assuming they are, and the sight line is at 0deg to the thrust line too, the cannon rounds will never cross the sight line, as the cannon is lower than the sight line. this implies that for the rounds to cross the sight line, it must be -deg to the thrust line. if this is the case, the rounds will rise and then fall relative to the sight line.

either the cannon is +deg, or the sight line is -deg, relative to the thrust line.

edit:

[FLS]

Is the prop axis level when flying level at cruising speed?

[bustr]

RTHolms,

Simpler observation. If the motorkanone in the 109 series was installed per Bf/DB specification. There would be no convergence line to move in the hanger. We both have access to Bf109 manuals to prove visierlinie and motorlafette line at level. FW190A the visierlinie was set level to infinity while the guns elevation and cross distances were set to it. USAAF N3 series were simple level to infinity unless the A1 adjustable bombing head was mounted like in the B25H. Russian PBP1 reflector plate seems fixed other than some versions have a range dial.

Looks like the initial V0 is about 510M/sec and the angle0=.4 degree. Add the Vloss and BC and you get the expected %V per 100m loss and Y0 at each 100m mark.

Nice graphics by the way. The Reflexvisier 16b internal umlenkspiegel was tilted to raise the graticule projection from the strichlinse to allow a visierlinie of -29cm below the DB605 0-line at 100m. Third example down. First example is not how the game balistics looks but how the real world ballistics did. If the MG151/20 were the motorkanone then the visierlinie in that example would be correct. Second example ruined and engine, pissed off a pilot and got an armeror and engine mechanic before a firing squad.

HiTech can always tell me I'm dumb as a dump truck and that will be fine.

[guncrasher]

I love nerds.  keep it up guys i have no idea what you are talking about, but if it makes me shoot better go for it. 

semp

[RTHolmes]

so which is correct, and how does AH do it? top middle or bottom on the pic?

[SectorNine50]

Bustr is saying top picture is how it should be.  Which makes sense, assuming the aircraft's engine is mounted straight out.

Now I can't say anything for any of these aircraft, but I know there are a few GA aircraft out there who's props are actually angled up a bit.  Why, I couldn't tell you, has something to do with aerodynamics, I'm sure, but this could explain how the cannon would cross the sight picture at one point or another (see picture 2).

Also, we need a picture from in-game of how the aircraft cruises compared to the horizon.  If there is a positive AoA, then one could potentially assume that picture 3 is correct.

MOAR RESEARCH!

[Ardy123]

Bustr,
I'm getting totaly different numbers than you...

here is the math...
540 m/s
100 meters target (100 yards = 91.44 meters)

distance/velocity = time
100(m)/ 540(m/s)=.18519s

drop = .5 * gravity * time^2
.5(9.8)(.18519s)^2 = .162904 meters aka 16.2904 cm

16 cm of drop for 100 meters range... thats almost nothing
Make sure that you don't get your meters and yards crossed... ah uses yards for the target not meters.

Now, I can calculate it more accurately if you can give me a drag coefficient so I can account for the bullets deceleration.

If not, I can approximate it if you have the shells density or mass.

assuming a drag coefficient of 0.47 (thats what it is for pushing a cylinder through the air at sea level).
one can use this formula to calculate the ballistics coefficient.

BC = mass/(Drag Coefficient * Pi*(radius)^2)
or
BC = mass/(0.47 * 3.14159 * .015^2) note .015 is in meters.. so 30mm has a radius of 15mm which is .015 meters.

[RTHolmes]

If there is a positive AoA, then one could potentially assume that picture 3 is correct.

thats what I reckon

[ink]

:-(     my head hurts now thanx dood................

[Rino]

     Back when dinosaurs ruled the ramp, I worked weapons control on an F-4E.  Another of the useless bits of trivia I
remember is that when you selected air-to-air guns, the pipper moved down 2 mils to correct for the gun being mounted
under the centerline of the aircraft.

     Now this was a lead computing sight, but shouldn't a REVI be able to compensate for gun position as well?

[bustr]

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.......