Home Forums General Game Design AFVs at an angle (not sloped armour)

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  • #79287
    Les Hammond
    Participant

    I was thinking about the 45° rule the other day, when used to decide whether front or side (or rear!) armour ratings should be used for the target AFV.

    blog

    Do any rules allow aiming at weaker flanks, even if it is at less than 45° with the position the target is in, does this affect gameplay speed and is the ’45° rule’ good enough?

    • This topic was modified 3 years, 6 months ago by Les Hammond.

    6mm France 1940

    http://les1940.blogspot.co.uk/
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    #79320
    Retroboom
    Participant

    I’ve always preferred the Crossfire/Flames of War method of drawing the line across the front of the target’s hull. If firing from in front of that, it’s front armor.

     

    • This reply was modified 3 years, 6 months ago by Retroboom.
    • This reply was modified 3 years, 6 months ago by Retroboom.

    www.RetroBoom.com
    Stafford, Va. Let's play!

    #79330
    John D Salt
    Participant

    Do any rules allow aiming at weaker flanks, even if it is at less than 45° with the position the target is in, does this affect gameplay speed and is the ’45° rule’ good enough?

    I’m sure lots of us remember the “tank stick” from the “Battle!” rules by dear old Charles Grant. This was a protractor-like device that showed a -1 or -2 deduction from the strike value of the attacking gun if the obliquity exceeded 30° or 60°. Since he also used a rule that frontal armour was always one more, and rear armour one less, than side armour, this meant that there was never any point accepting the -2 penalty, and you had to be outside the target’s 120° frontal arc to get a more advantageous shot than attacking the frontal armour straight on.

    Apart from that I do not recall any wargames rules making much of a fuss about the angle of strike, even though everyone will tell you that German tank drivers in the desert were trained to keep their AFVs angled to the expected direction of attack, and if you look at the “Kleeblatter” in documents like the Tigerfibel it is obvious that attacks from the front or rear quarter are less effective than those from right angles. One problem is that during the course of a game turn lasting perhaps a minute, perhaps more, a moving AFV might have presented a number of different possible angles to the same shooter.

    The original blog says:

    I haven’t done the maths for obvious reasons

    It’s only a little trig. If we used the sin-squared rule suggested on the Wikipedia page you link to — or pick an exponent you like between 1 and 2 — it is easy enough to knock up a spreadsheet to calculate the effective armour thickness offered by front, side, or rear plates at, say, five degree intervals all around the tank. Obviously I have been unable to resist the temptation to do exactly this, so anyone who wants a copy can have one if they e-mail me at musketoonltd AT gmail DOT com. Taking the example of a tank with 30mm front and 20mm side armour, and using the sine-squared rule (which overstates the effects of angle) we find that at 40° off the front the effective armour thickness for a gun’s best attack is 48mm — quite a bonus on 30mm. Not until we get round to 60° is the apparent armour thickness thinner than a straight shot on the front plate, and only at 65° is it closer to the side than the front thickness. This suggests to me that, as in so many things, Charles Grant’s “Battle!” got it pretty much right, and likewise the 120° frontal arc used (for obvious reasons of hex-related geometric convenience) in many boardgames is quite reasonable.

    The 45° rule is clearly preferable to constructing lines through opposite corners of an AFV; your point about the artificial advantage of short, stubby tanks is well taken. However I think I would prefer a 60° rule instead, to give a 120° frontal arc. 90° seems too little, and 180° seems too much. Alternatively, in order to show the shape of Kleeblatter and the relative advantage to the AFV of being attacked from quarter angles, you might divide the circle around the target AFV into octants, and have separate armour values for front, front quarter, side, rear quarter, and rear aspects.

    All the best,

    John.

    #79373
    Not Connard Sage
    Participant

    I’m sure lots of us remember the “tank stick” from the “Battle!” rules by dear old Charles Grant.

    I made a fancy one for my grade 9 industrial arts project!

    even though everyone will tell you that German tank drivers in the desert were trained to keep their AFVs angled to the expected direction of attack

    I really hate bringing up my peace time armour experience, but I’ve never understood how you can do that. It’s difficult enough to keep your bloody front to the expected direction of attack when advancing to contact. Never did it in the desert myself, but even in the vast rolling plains of Suffield it’s easy to accidentally go broadside when jockeying off a fire position when it’s your turn to leapfrog past or caterpillar up to the leading tanks in your troop/platoon.

    I always understood it to mean when firing at the halt. But my practical knowledge of tank warfare is zero.

     

     

    "I go online sometimes, but everyone's spelling is really bad. It's... depressing."

    #79379
    Retroboom
    Participant

    Hi RB, Crossfire is actually across the rear of the vehicle. See p19, left column, “Flank/Rear Shots”. 🙂 Both that and the above image are a bit problematic in my opinion; it looks reasonable in the illustration because the tanks are close to each other. I haven’t played FOW, but when the actual distances between, for example, the Sherman firing at the Stug, above, become a couple of feet or more, it seems really unreasonable to be firing at the front.

     

    Tim you are correct about Crossfire, but I bring them both up as they’re  more similar than they are different. You are also correct that it can occasionally create weird situations, especially as the vehicles get farther and farther apart. I simply consider this an abstraction, like any other, and this one is the simplest one I’ve found, that is also one of the least offensive, and is my go-to.

    www.RetroBoom.com
    Stafford, Va. Let's play!

    #79396
    MartinR
    Participant

    I’m sure lots of us remember the “tank stick” from the “Battle!” rules by dear old Charles Grant.

    I made a fancy one for my grade 9 industrial arts project!

    even though everyone will tell you that German tank drivers in the desert were trained to keep their AFVs angled to the expected direction of attack

    I really hate bringing up my peace time armour experience, but I’ve never understood how you can do that. It’s difficult enough to keep your bloody front to the expected direction of attack when advancing to contact. Never did it in the desert myself, but even in the vast rolling plains of Suffield it’s easy to accidentally go broadside when jockeying off a fire position when it’s your turn to leapfrog past or caterpillar up to the leading tanks in your troop/platoon.

    I rather think that in real life, flank shots are far more prevalent than in wargames, as real tank Commanders don’t have the 100 foot general situational awareness of Wargamers.

    "Mistakes in the initial deployment cannot be rectified" - Helmuth von Moltke

    #79436
    John D Salt
    Participant

    I have amused myself further by adding compound angle calculations to my Kleeblatter spreadsheet, so armour can be characterised by both the thickness and the slope of front, side, and rear plates.

    Although it’s not Les’ chosen early war period, I decided to compare the angular distribtion of protection offered by the Tiger and Panther hulls. We all know that the Panther is better protected at the front, and the Tiger at the sides and rear. But look at this:

    Assumptions:
    
    Armour plate as follows
    
    AFV	Plate	Thick	Angle
    Panther	Front	80	55
    Panther	Side	40	40
    Panther	Rear	40	30
    Tiger	Front	100	9
    Tiger	Side	80	0
    Tiger	Rear	80	9
    
    Exponent for slope calculations 1.33
    (makes 60 degrees about 2.5 times as good as normal)
    
    Theta: Angle of obliquity, degrees
    Panther: Equivalent armour protection offered by Panther A hull
    Tiger: Equivalent armour protection offered by Tiger E hull
    Better: Which offers more protection
    
    Theta	Panther	Tiger	Better
    =============================
    0	168	102	Panther
    5	168	102	Panther
    10	171	104	Panther
    15	175	106	Panther
    20	182	110	Panther
    25	179	116	Panther
    30	143	123	Panther
    35	119	133	Tiger
    40	103	144	Tiger
    45	90	127	Tiger
    50	81	114	Tiger
    55	74	104	Tiger
    60	69	97	Tiger
    65	65	91	Tiger
    70	62	87	Tiger
    75	60	84	Tiger
    80	58	82	Tiger
    85	57	80	Tiger
    90	57	80	Tiger
    95	57	80	Tiger
    100	58	82	Tiger
    105	60	84	Tiger
    110	62	87	Tiger
    115	65	91	Tiger
    120	69	97	Tiger
    125	74	104	Tiger
    130	81	114	Tiger
    135	77	127	Tiger
    140	69	116	Tiger
    145	63	106	Tiger
    150	59	98	Tiger
    155	55	93	Tiger
    160	53	88	Tiger
    165	51	85	Tiger
    170	49	83	Tiger
    175	49	82	Tiger
    180	48	81	Tiger
    

    The Panther is only a better bet over a rather narrow frontal arc of 60 degrees (30 degrees each side of dead ahead). If you’ve got guns capable of punching about 100mm of armour (as the 6-pounder, US 76mm and Soviet 85mm could do at useful battlefield ranges) there are more angles where the Tiger is a problem than the Panther.

    All the best,

    John.

    #79448
    irishserb
    Participant

    I offer some assorted thoughts regarding taking oblique shots below:

    If you stand in front of a tank, directly on the centerline, 100 percent of the exposed silhouette is frontal surface of the tank.  As you move such that you are 5, 10, 15 degrees offset from the centerline, the exposed silhouette of the tank changes such that the portions of the angle of the field view occupied by the tank  change.

    For example, at 1500 meters range, the tank may occupy a 2 degree field of view.  As you rotate around the tank, at 20 degree offset from centerline, the front portion of the silhouette may consist of 1.7 degrees of the field of view, and the side may occupy .3 degrees of the field of view.  If you continue around to maybe 40 degrees, the side portion of the exposed silhouette will take up about half or 1 degree of that field of view.  At 45 degrees, the side, being longer, will take up more than half of the exposed silhouette, as the tank is longer than it is wide, thus the side is more likely to be hit than the front, through random distribution of the shot.  the point at which this occurs will vary depending on the proportions of the tank, but will always be true at 45 degrees, assuming the gunner is not leading a moving target.

    At long range, the tank silhouette fits in a smaller portion of the field of view , a smaller angle of the total degrees of field of view.  At close range, the tank is appears wider, as does the angle of its silhouette in the field of view.

    At longer ranges, aiming at a narrow slut of exposed side could be quite challenging, especially if the target is moving.

    Consider also , that at the extreme oblique angles the trig functions on the armor are the same as if the armor was sloped from vertical, and is compounded with any effect from slope of the armor.  Thus, shooting at a side plate, while standing 30 degrees off set of the tank’s centerline, is more or less like shooting at a plate sloped at 60 degrees from vertical.

    There are a lot of things to consider with these oblique shots.  For example, penetration is lost as the round slides along the side armor plate, the more efficient the ballistic coefficient of the penetrator, generally the less likely that the penetrator is to initiate penetration at extreme oblique angles.  The rate at which the penetrator loses effectiveness will increase as the length of the penetrator increases relative to its length.

    If the penetrator is a HEAT round, at such oblique angles, the formation of the cone will be severely deformed, radically reducing the effectiveness of the round.

     

    In the end, while I would support the 45 degree approach to locating the shot, though  other mechanisms could be practical.  Maybe from a about 30-35 degrees offset from the front corners of the target, roll a 50/50 randomizer to locate the shot. Or just give the armor a 30-50 percent increase in effectiveness, maybe except on rounded surfaces.  And, though I don’t really support Tim’s 30 degree argument , I would have no problem playing with it.

    I think that in reality, shooting at the slit of side armor at a sharply oblique angle would be less likely to have effect, than say aiming at the target’s gun barrel, sights, or commanders cupola.

    #79454
    John D Salt
    Participant

    (Snips)
    For example, at 1500 meters range, the tank may occupy a 2 degree field of view.

    Mighty big tanks they have in your part of the world if they subtend 2 degrees (over 35 mils) at 1500 metres. The Ratte could at an appropriate angle, but the Karl Mörser is too small. Using mils for subtenses makes more sense, and I don’t know of an army that doesn’t.

    (Snips)
    There are a lot of things to consider with these oblique shots. For example, penetration is lost as the round slides along the side armor plate, the more efficient the ballistic coefficient of the penetrator, generally the less likely that the penetrator is to initiate penetration at extreme oblique angles. The rate at which the penetrator loses effectiveness will increase as the length of the penetrator increases relative to its length.

    Eh? What does the length of the penetrator have to do with this? Nose shape, yes, there’s a bunch of mysterious stuff going on there that no simple formula is able to capture, and there’s the question of piercing caps, but I don’t see what penetrator length has to do with it. Pray explain yourself.

    If the penetrator is a HEAT round, at such oblique angles, the formation of the cone will be severely deformed, radically reducing the effectiveness of the round.

    It’s not jet formation that is the problem so much as fuze initiation. HEAT has to use point initiating, base detonating (PIBD) fuzes, because the penetrator needs to start forming at a reasonable stand-off distance, but to do this the warhead needs to be initiated at its base. Obviously there are some values of impact angle, probe length, and calibre for which the shoulder of the round will strike the armour before the tip of the probe does, and I doubt there will be any result from that other than a ricochet by the ballistically squished remnants of the projectile. One approach, as used in the Swingfire ATGW, is to use a nose cone (actually an ogive rather than a cone) consisting of two slightly-separated layers of copper. When the nose is deformed by impact so that the two layers are in contact, an electric circuit is made which initiates the warhead. On Swingfire this worked up to 80 degrees obliquity, and at that angle the line-of-sight distance through the armour seen by the penetrator is 5.75 times its normal thickness. Line-of-sight thickness is not a bad estimator of armour basis for HEAT, as the penetrator is moving at such high speed that target density matters a lot more than target strength.

    Of course, not a problem for Les’ chosen period of France 1940 except for the special case of the No. 68 Grenade.

    All the best,

    John.

    #79575
    Ivan Sorensen
    Participant

    We usually always simplify it and just call it front or side.

    Panzer War has the “corner” shots randomly be considered front or side but at an increase to armor to account for deflection (1.5 if memory serves right, which it may not)

    Though game players can likely massage their tank positioning a lot better than a real tank crew could 🙂

    Nordic Weasel Games
    https://www.wargamevault.com/browse/pub/5701/Nordic-Weasel-Games?src=browse5701

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