WITP bomb accuracy

[herwin]

ORIGINAL: Bogo Mil

I think larger bombs should be a bit more accurate, at least from medium to high altitude:
1. They fall down faster, thus it's easier to evaluate the lead and the target has less time to evade.
2. They are less susceptible to crosswinds.

I don't say it should be 22,500%, but some difference is reasonable, imho.

Edit: There is a third reason for a higher accuracy of the big bombs: In WITP, everything that does damage is a "hit". A small bomb has to hit the target directly to cause damage, a large bomb can cause major damage by near misses. Thus you have a significantly larger "hit area" if you attack with large bombs.

Ignoring drag, they fall down with the same velocity profile. If you want to take drag (and sidewinds) into account, you have to consider terminal velocity and aerodynamic design. It's not just bomb size.

[Bogo Mil]

ORIGINAL: herwin
Ignoring drag, they fall down with the same velocity profile. If you want to take drag (and sidewinds) into account,

Of course we have to take it into account. It is important - especially from higher altitudes.

If there was no drag and crosswinds, accuracy against stationary targets would be almost independent of the altitude (you can check it out in IL 2 Sturmovik - there is no drag and wind, you can hit a truck from 30k feet with some practice).

If there is drag and crosswind, the accuracy depends on the susceptibility of the bomb as well as on the release altitude.

you have to consider terminal velocity and aerodynamic design. It's not just bomb size.

In WITP, we have only standard free fall bombs (GP and AP). Their aerodynamic designs are all very similiar. The dominant factor is the size of the bomb.

Of course this is different if there were special bombs (high drag/parachute bombs, dambuster bombs and such). The only examples in the game are the Japanese cluster bombs, maybe the depth charges, too. But the latter are usually dropped from dive bombers, thus aerodynamics aren't very important.

[el cid again]

ORIGINAL: Bogo Mil

I think larger bombs should be a bit more accurate, at least from medium to high altitude:
1. They fall down faster, thus it's easier to evaluate the lead and the target has less time to evade.
2. They are less susceptible to crosswinds.

I don't say it should be 22,500%, but some difference is reasonable, imho.

Edit: There is a third reason for a higher accuracy of the big bombs: In WITP, everything that does damage is a "hit". A small bomb has to hit the target directly to cause damage, a large bomb can cause major damage by near misses. Thus you have a significantly larger "hit area" if you attack with large bombs.

Fact of physics: acceleration due to gravity is a constant. Weight has NOTHING WHATEVER to do with vertical velocity: for ALL objects (which are reasonably dense like a bomb) - and absolutely ALL objects regardless of density in a vacuum - the instantaneous speed after release is PURELY a function of time and the acceleration due to gravity. One can drop small bombs from medium and high altitudes - and if one does - they have the same terminal velocity as large ones do.

The same principle applies to crosswinds. If a wind is an acceleration vector, and if it is constant (it isn't really, but this is the base case),
the amount of horizontal velocity it imparts is a function of time, not the weight of the bomb. IRL BIG BOMBS from stratospheric altitudes were a technical failure due to this factor - there were winds sufficient to knock them off target almost all the time: it is also true of small bombs - but big ones were not immune to it. This is one of two reasons - the other being cloud cover prevented aiming - that USAAF went over to firebombing of Japanese cities - 85 per cent were so burned out and the goal was 100 per cent. That it was illegal in OUR understanding of the law of war didn't stop it (see the Nuremburg trial of German aviators who bombed Rotterdam). The B-29 was a technical failure - in the sense that it COULD NOT be effective as designed - even if the target could be seen - due to cross winds - from the altitudes it was designed to be used from.

Note on your note: In RHS (and Empires Ablaze) we use a different soft effect system than stock and other mods use: we use the square root of effect (or the square rood of 2/3 of effect for AP bombs). This is so you get the effect of increased blast radius on ALL targets. [For a hard target the anti armor value is the maximum penetration in mm - but that only decides IF you penetrate - and it isn't what is used to decide what happens to the target]. So we have already factored in bomb size: the bigger the bomb the greater the area affected - but not in proportion to its size - damage goes up as the root of the size.

People who come to understand the principles of bombing are going to learn to appreciate that small is often better - you get more chances to hit the target - and if the target isn't hard - you will damage it much more for any given total load. Only a hard target justifies the use of penetrating bombs of great size - which is why they call the "GP" bombs "general purpose" - they ARE the one you should prefer most of the time for most purposes.

[el cid again]

ORIGINAL: Bogo Mil

ORIGINAL: herwin
Ignoring drag, they fall down with the same velocity profile. If you want to take drag (and sidewinds) into account,

Of course we have to take it into account. It is important - especially from higher altitudes.

If there was no drag and crosswinds, accuracy against stationary targets would be almost independent of the altitude (you can check it out in IL 2 Sturmovik - there is no drag and wind, you can hit a truck from 30k feet with some practice).

If there is drag and crosswind, the accuracy depends on the susceptibility of the bomb as well as on the release altitude.

you have to consider terminal velocity and aerodynamic design. It's not just bomb size.

In WITP, we have only standard free fall bombs (GP and AP). Their aerodynamic designs are all very similiar. The dominant factor is the size of the bomb.

Of course this is different if there were special bombs (high drag/parachute bombs, dambuster bombs and such). The only examples in the game are the Japanese cluster bombs, maybe the depth charges, too. But the latter are usually dropped from dive bombers, thus aerodynamics aren't very important.

The problem with going this way is that we would need very specific information about each bomb. What really matters - in nautical terminology - is "sail area" - or more precisely the ratio of the area of the bomb to the weight of the bomb; a secondary factor is the shape of the bomb (secondary in that it is a much lower factor for GP bombs; for a bomb with a parachute or wierd spoilers it is a larger factor).
This in turn would require time (for research), time (for analysis), more time (for data entry). In this simple model it is fair to say - as you do - that all bombs are more or less created equal: and we let the die roll tell us if you hit or miss. What is NOT fair to say is that it matters if the bomb weighs 100 pounds or 1000 pounds or some other value: it is equally accurate. There is no reason to say that "heavier is more accurate" and - IF there were - that is not good enough: you must then say "how much more accurate" in a way we could reasonably apply to the entire range of bomb devices. The truth is that technical factors matter far more: what is the altitude of the drop? what is the bomb sight system used (or like Blenheim - is there no sight at all?) what is the training of the crew and the exact profile of the approach? All these matters are for code - because ANY bomb is affected by them - and we cannot build it into the base bomb data. There may be a difference between 100 pound and 1000 pound bombs inside the aiming circle from 10 000 feet - but we don't know what that is - or even if there is a difference at all? IF there is a difference, it is tiny, and not measurable in terms of tens of thousands of per cent - so we must be moving in the right direction to say none at all.

FYI my mother joined the USAAF in 1942 - part of the first class of enlisted women in history (female nurses who had served in WWI and after were officers). They were trained to serve as photo analysts - and to make cameras, film and developer chemicals from improvised materials found in every home in the USA. But they actually served to train gunners and bombradiers - to measure by photographic means if they were aiming properly? The details of measuring this are incredibly techincal - but ultimately it all boils down to basic physics. Because there are winds it isn't a pure ballistic trajectory as it would be in a vacuum. But even so, the impact of the winds is universal - and GP bombs are all essentially affected the same way. The complications are really in terms of the exact situation IRL - the wind is changing - so you have many different vectors - often from different directions as well as different speeds for different amounts of time: but whatever the vector sum is, it remains the primary determinant of the drift you get in this case. It was really bad because there was no way to KNOW what the winds were at all altitudes - they had to use rules of thumb and averages - the instantaneous data not being available even by telemetry. It is marginally true that a different bomb area to weight ratio would result in a different drift - but the ratios for GP bombs were all pretty similar - and the drift was far closer to the same than it was different.

[herwin]

Terminal velocity is the velocity at which the acceleration of gravity equals the drag. High frontal density results in a high terminal velocity.

[el cid again]

Just so. A human - who is not as dense as a bomb - has a terminal velocity around 120 mph - because at that point the drag equals the acceleration due to gravity. Bombs have much higher terminal velocities, assuming the terminal velocity is not cut short due to a low altitude release. Bomb size increases as the cube root of mass, while its frontal area increases as the square root of mass - so re ratio is not 1:1 -
but the area is small - and the air resistence is not very great compared to g.

Wind effects are much greater - in that they hit the side of the bomb which has several times the frontal area - and also they hit things like fins - which have area in addition to the cylendar body area. But in general - whatever the wind does to a stick of bombs - it is doing to every other stick of bombs in the same place - and almost to the same degree - the difference being a function of the sail effect of the particular bombs involved. Bigger bombs do have more area - but they also have more mass in an even greater proportion than they have more sail area - so the impact on accuracy might be marginally smaller. Below certain wind speeds the difference is not measurable. At higher wind speeds the difference is going to be progressively larger - but it still does NOT matter UNLESS it knocks the bomb out of the aiming circle. We measure bombs with CEP - circular error probable - the circle within which half the bombs fall. Moving the bomb a few cm within the circle does not matter in a practical sense. It matters in a statistical sense though - and it matters far more from very high altitudes. But remember that the wind is not uniform for the whole fall over a great distance: it is partly compensated for by other wind vectors at other altitudes. An instantaneous value that might move the bomb 10 cm on bearing x is not what matters - it is the vector sum of all such vectors - a vector has both size and direction - and the vector sum will take into account all the different wind strengths and exact directions - the sum for the whole drop is what matters. The vector sum for all altitudes will be genarally far less than the maximum instantaneous vector was - even if there was a large one. It is less not only because different vectors were smaller - but because different vectors in different directions cancel out some of that larger one. This is not something that is ever knowable - even today - even with instrumented telemetry in a bomb talking to us. Which is why we measure impacts in an aiming circle. It is very close to equal for all bombs - and I have no data to explain how to know the difference between bombs even to the extent it is different? If there were no air it would be zero - and this is the base condition we use in ballistics to learn the basics. IRL there is air - and usually that air is moving - and usually it is moving at different velocities at different altitudes. Wind conditions matter enough to knock almost all bombs off course enough to miss at stratospheric altitudes almost all the time. But the bombs still fall in a basic ballistic pattern - and for any given set of contitions - the wind drift is very similar.

If you can find statistically significant data scientifically gathered showing typical accuracies for several different sizes of bombs - and if there is any meaningful difference contained in that data - I can create a function which would tell us what the accuracy ratio would be for different bombs of different weights (assuming similar bomb shape - which we must do). But since our base value is 4 - only a difference greater than 25% would be enough to show up as a value change. Thus - say a 4000 pound bomb might be a 5 on the scale where all the little guys are 4.
This is pretty much not worth trying to figure out - because at the end we are likely to find the 4000 pound bomb was 4.1 when the 100 pound bomb was 4.0 = nothing at all would change. Even if it was a 4.4 - nothing would change.

[herwin]

Continuous practical training was much more important than bomb characteristics. The average performance of B29 crews was 15% of the bombload hitting within 1000 feet of the point of aim, but crews who spent 5 hours a month in refresher training could maintain a figure of 75%.

The ballistic dispersion of bombs was typically about 25% of the aim-point dispersion.