rexford Posted January 15, 2001 Share Posted January 15, 2001 One of the posts in the max accuracy thread discussed leveling tank guns using bubble levels. We assume that this was required when hull was on sloping terrain to avoid skewed trajectory. "I" would appreciate additional details on this as it appears that failing to level the gun when it fires across a -1° slope might lead to short range misses. Thanks from me. Link to comment Share on other sites More sharing options...
dNorwood Posted January 15, 2001 Share Posted January 15, 2001 <BLOCKQUOTE>quote:</font><HR>Originally posted by rexford: "I" would appreciate additional details Thanks from me.<HR></BLOCKQUOTE> I can't help you with your question, but I'm laughing out loud... Link to comment Share on other sites More sharing options...
109 Gustav Posted January 15, 2001 Share Posted January 15, 2001 Uh, you don't shoot perfectly level all that often, anymore than you throw baseballs perfectly level. Bullets need to arc to hit their target, just like a thrown baseball. Check out the Puppchen's trajectory at 200m to see what I mean. When shooting anything with any kind of gun, from a beer can with a .22 to a Panther with a 76mm, you don't take your eyes off the sights to check a bubble level. You sight the gun so that it's going to hit the target, allowing for range and windage. Besides, how often are you and the target perfectly level to each other? CM terrain isn't a pool table, there's hills and stuff that can mess up your level. Sorry if I jumped on you too hard. Maybe someday BTS will have CM7- space Combat Mission, and we won't have to deal with all this annoying gravity. ------------------ Well my skiff's a twenty dollar boat, And I hope to God she stays afloat. But if somehow my skiff goes down, I'll freeze to death before I drown. And pray my body will be found, Alaska salmon fishing, boys, Alaska salmon fishing. -Commercial fishing in Kodiak, Alaska [This message has been edited by 109 Gustav (edited 01-15-2001).] Link to comment Share on other sites More sharing options...
Jeff Duquette Posted January 16, 2001 Share Posted January 16, 2001 Rex: Artillerists use a gunner's quadrant for indirect laying. A artillery gunners quad did have a leveling bubble on its arm. Artillery gunner's quads were employed by tanks and tank destroyers firing in an indirect fire mode, but would not have been employed for direct fire on point targets. Link to comment Share on other sites More sharing options...
rexford Posted January 16, 2001 Author Share Posted January 16, 2001 Stand on a tilted board and aim a rifle at a target by raising it at an angle instead of staight up and down, won't this generate lateral errors? Link to comment Share on other sites More sharing options...
John Kettler Posted January 16, 2001 Share Posted January 16, 2001 Rexford is correct. Trunnion cant is a significant factor in gunnery accuracy. I know this because back during the early '80s ARMOR magazine ran an article titled, "You Can't Forget Cant." It's been many years since I read it, but I distinctly recall that the effects of cant were considerable. The author had the firing trial data to prove it, too. I don't know whether ARMOR has a website, but if not, I'd suggest contacting the editor directly. ARMOR is published at Ft. Knox, Kentucky. Perhaps one of the soldiers on the board can supply more info. Regards, John Kettler Link to comment Share on other sites More sharing options...
jasoncawley@ameritech.net Posted January 16, 2001 Share Posted January 16, 2001 There may be a misunderstanding here. The leveling bubbles are not meant to find the direction of the ground, but to ensure that the barrel and the sight are pointed in the same direction. The sight moves and points independently. You can point the periscope of the sight to some place 45 degrees off the direction of the barrel, and 20 degrees up in the air, if you want. If you put the crosshairs of the sight on that location, it will certainly not make the round hang a left and pull into a climb upon leaving the tube. You have to point the barrel at the target. The sight is a means of finding the angles you should point it - the directions. You point the sight at the target - and then you align the barrel with the sight. The last of those is all the leveling bubbles do. If both barrel and sight are at some additional angle to the ground, it is the same angle, and that is all that matters. You don't care about the absolute angle of the barrel to the ground, only the relative one between barrel and sight. The point about a slight effect of "cant" may be what the original poster in the thread meant. That barrel of the gun is a heavy object held in place by a carriage of some sort, attaching it to the gun. In different orientations to the ground (on different slopes), it will "sit" slightly differently on its holding base, bend a little, or whatever. This will be a quite small amount, much much less than the angle of the ground obviously. On long range shots it might matter, more than I know. The point is to avoid confusion about any large effect of a simple slope on the mechanisms of the sight (as opposed to the barrel or carriage). It won't make any difference. Part of the confusion may stem from much more modern systems used today, in which the barrel is moved automatically - it is said to be "slaved" to the sight - so that all you have to do to point the barrel is put the sight crosshairs on the target, with the barrel itself moving to point at whatever you point the sight at. In the artillery, it still works the old way. One reason there has not been a change there is the sight is left on the target or firing directions - which is often a highly elevated angle, 30-45 degrees - while the barrel has to be depressed to more like horizontal (a smaller angle anyway) to be loaded. Then the barrel is put back in line with the sight again to be fired. The older system also allows the gunner to search for and find targets long before a slow turret has moved over to train on the new target direction. Modern powered turrets are so fast the "slaved" system is deemed superior. With the older ones, the slow turret is being cranked (or moved by the hydraulic) toward the direction of the sight, to be sure, but it is not aligned with it yet, when the target is first "acquired" and the crosshairs put on it. To modern tankers the important point is simple to understand, the sight and the barrel directions are entirely independent, and to use the sight to align the gun the barrel and sight directions must be realigned to a zero angle between them. Which is what the two levels do. (Actually, they are realigned to whatever angle was set between the sight and gun when the weapon was boresighted, which is supposed to be zero degrees but might contain a small error term if done wrong, or get slightly off "true" after many shots or lots of bumpy driving. But that is a quibble). Link to comment Share on other sites More sharing options...
DraGoon Posted January 16, 2001 Share Posted January 16, 2001 Interesting post. Having done my original tank gunners training and shooting back in the days of "Steam Gunnery" ie: ranging MGs and Bracket shoots, I thought I might add a little to the valid points above. (From a British perspective at least) To answer the original question first; In British tanks, to the left of the gunner, (fitted to the breech block), was a leveling mechanism called a Quadrant Fire Control (QFC). This comprised, a clinometer (bubble), two drums with calibrated range markings and a locking mechanism. This equipment was only used for long range shoots either in direct or indirect mode, (off the range of the sight). The gunner dialled in the range (given by the commander) and then elevated the gun until the bubble was level (always ending in elevation to take up any slack in the mechanism), a sighting shot was fired and corrections then applied by dialling them in and recentering the bubble. Line corrections (for wind etc.) were applied by traversing a set number of mils/degrees left or right, read from a different scale. This continued until fire was on target. It could be controlled indirectly by a forward observer but was generally a waste of ammo. Artillery was and is far better at this role. As to misses due to trunion tilt etc. The tank gunnery techniques in place at the time of the ETO still relied on bracket shoots for HE. ie: one plus, one minus and one on the dot. The gunner was expected to remove any line error by the second shot, (ie. should only be plus or minus not left or right of target). Later, severe tilt was made up for by flicking a small lever on the sight which allowed the graticule pattern (reticule) to swing free and obey the laws of gravity, (then had to be locked again before firing), thus (sort of) lining up with fall of shot, for the application of corrections. When the tank is on a level stable platform the recoil of the gun (barrel, breech etc.) and the forces acting upon it and the vehicle suspension are known and are as specified by the designers. When tilted or traversed however other factors come into play, (uneven force, suspension movement etc.) Nowadays this is all preprogrammed into the Computerised Fire Control System (FCS)which makes allowances for trunion tilt and a myriad of other factors. The main compensation for these factors at the time of the ETO (in British service) was the gunnery technique taught. -Range estimated (or known) by commander. -First round fired, fall of shot observed. -Correction applied, taking out line error. -Second round fired, hit or bracket target. -Correction applied, fine tune lay. -Target, next target left or right. Add to this the difficulty of hitting a moving or semi obscured target or one who is firing back, and you see why experienced crews were valuable. This also assumes the first hit kills the target, which as discussed elsewhere was unlikely. BTW it was common practice to send newbies to the stores for a new bubble for the QFC HTH DG [This message has been edited by DraGoon (edited 01-16-2001).] Link to comment Share on other sites More sharing options...
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