Search the Community

null The azimuth Angle on the P-51 guns seems off a bit. Per this post https://forum.dcs.world/topic/79688-convergance-and-gun-options/page/2/#comment-1725050 The expected convergence pattern should mirror the one in Air Forces Manual No. 64 Fighter Gunnery https://archive.org/details/air-forces-manual-no.-64-fighter-gunnery-firing-rockets-dive-bombing-1-may-1945/page/110/mode/1up Which is the pattern as depicted in the manual Fighter Gun Harmonization. https://archive.org/details/aaf-manual-200-1-fighter-gun-harmonization/page/37/mode/1up From the DCS P-51 lua file we have the azimuth for the all 6 of the guns. DCS Gun 3, Outboard: gun azimuth_initial = 0.341, DCS Gun 2, Middle Gun: gun azimuth_initial =0.286 DCS Gun 1, Interior Gun: azimuth_initial = 0.379, The unit is likely degrees. Converting to radians gives us. DCS Gun 3, Outboard: gun azimuth_initial = 0.005951, DCS Gun 2, Middle Gun: gun azimuth_initial =0.004991 DCS Gun 1, Interior Gun: azimuth_initial = 0.0066147, The position of the gun is also given in meters within the lua file. With this data we can compute at which range the guns will converge. Using the graphing application Desmos, we can overlay the and compare the harmonization pattern of the DCS P-51 to the one depicted within the manual. We’ll straighten this up a bit and import it into Desmos and scale it. Link to the Desmos Convergence Calculator. https://www.desmos.com/calculator/ujiueojjjp Using azimuth angles and gun positions from the lua file. We plot the convergence pattern of the DCS P-51 at 0 mph. Note that interior guns, Gun 1, the red lines, Converge At 1007. Feet The middle Guns, Gun 2 ,the green line, converge at 1466 feet The exterior guns, Gun 3, the blue line, converge at 1337 feet. Let’s remove the graphic for a clear look at the DCS pattern. It’s important to note that the Harmonization Pattern and settings depicted in the manual are configured for an airspeed of 300 mph. At 300 mph in the real P-51 The Interior Guns, Gun 1, Converge at 1000 feet The Middle Guns, Gun 2, Converge at 1100 feet The Exterior Guns Gun 3, Converge ar 1200 feet. Removing the Graphic for a clear view. However the azimuth of the guns is actually set to a larger angle than is depicted. This is because the forward velocity of the aircraft alters the velocity vector of the projectile. This reduces the effective azimuth angle of the trajectory. The change in the effective azimuth angle can easily be calculated; The Fighter Gun Harmonization Manual and AAF Manual 335-25 both provide the relevant equation. Which I will call the trajectory correction function. The Manual Fighter Gun Harmonization https://archive.org/details/aaf-manual-200-1-fighter-gun-harmonization/page/7/mode/1up And AAF Manual 335-25 https://books.google.com/books/content?id=81krAQAAMAAJ&pg=PA331&img=1&zoom=3&hl=en&bul=1&sig=ACfU3U1BRdZA_vO5KY8Ylk_Y-i3WWQQ4mQ&ci=4%2C1%2C993%2C1326&edge=0 The trajectory correction function is ((Vias in FPS) * the basic azimuth angle of the gun) / the muzzle velocity of the gun. If we apply this correction factor to the DCS P-51 guns at 300 mph, the harmonization pattern moves well beyond what is depicted in the manuals. The Interior Guns, Gun 1 Converges at 1200 feet at 300 mph. The Middle Guns, Gun 2, Converges at 1751 feet at 300 mph The Exterior Guns, Gun 3, Converges at 1598 feet at 300 mph A more clear view with the graphic removed. The basic Azimuth angle for the real P-51 can easily be computed with the information provided in the Harmonization manuals. All we need is the position of the guns and the data from the 1000 inch boresight target. The basic azimuth angle of the gun is (Horizontal position of the Gun from the Center line - The position of the gun on the 1000 inch boresight card) / (range to the card 1000 inches). This gives the basic azimuth angle of the gun. For Gun 1 the equation is ( 79.123-71.25)/ 1000 = 0.007873 Which is the basic azimuth angle for the Gun 1. Lets Create a virtual boresight target in graph and plot the trajectory / basic angle of the guns. The line of sight of the guns does pass through the boresight target, however the convergence pattern of the gun is short of the chart. If we fired the guns at 0 mph with this pattern. Gun 1 Interior would Converge at 837 feet. Gun 2 Middle would Converge at 925 feet Gun 3 Exterior would Converge at 1012 feet. Let compute the trajectory correction for Gun 1 at 300 mph and plot the convergence pattern again. The Trajectory correction for Gun 1 is. ((Vias in FPS) * the basic azimuth angle of the gun) / the muzzle velocity of the gun. ((300 mph *1.467) * (0.007873)) / 2700 = .001283299. We then subtract the trajectory correction factor from our computation of the azimuth angle of the gun. Lets compute the effective azimuth angle of Gun at 300 mph (( 79.123-71.25)/ 1000)- 0.001283299. = .006589701= The effective azimuth angle of Gun 1 at 300 MPH Lets plot the effective line of sight of gun 1 with the trajectory correction for 300 mph With the trajectory correction Gun 1 matches the harmonization pattern as depicted in the manual. And Converges at ~ 1000 feet. Let's do the same for the other guns now. And without the graphic for clarity. All we have done is use the data and equations from the manuals, and computed the trajectory. The basic azimuth angle will always be greater than the effective azimuth angle, if the convergence pattern is configured for an airspeed greater than 0. In the P-51 maintenance manual there are settings for a 300 yard and 250 yard convergence pattern. This patterns are also based on a air speed of 300 mph. Above we depict the basic azimuth with a sold line and the effective azimuth angle at 300 mph with the dashed line. Note that the effective azimuth angle with trajectory correction converges at 300 yards, where it should. While the basic azimuth angle passes through the center of the boresight target, but converges well short of 300 yards. Therefore the azimuth angle for the guns should be set to basic azimuth angle as computed from the 1000 inch boresight target.