Request for comment: "under the guns" calculation program

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Irving Farnham
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Request for comment: "under the guns" calculation program

Post by Irving Farnham »

I put together a small tool to look into how to get "under the guns" of larger ships. Most of the information is from the EUNI Wiki and basic trig. Ideally I'd also compute the probability of a hit or wrecking shot killing the ship faster than DPS, but I very quickly realized my risk analysis has always been focused on a single failure, and I don't actually know how to mathematically define that I need X failures instead of just one. Math and probability gurus, let me know what to study to fix that.

Yes, I talk too much, on to the program.

Image

The program is a tool, and is heavily vulnerable to garbage in garbage out. It shows eight range bands of arbitrary depth, as defined by the Range Interval. Each band lists the angular velocity in milliradians and the eHP of damage passing through that band at the specified closing speed. The transverse and closing speeds are computed automatically by the approach angle and attack ship speed. The angle is defined by the angle between the enemy and the attack craft's angle of travel, with 0 being a direct plunge at the target and 90 being a circular orbit.

Most other parameters are straightforward, but the acceptable tank damage is a simple number for damage. If you're willing to take 500 points of damage, list it as 500. If you are willing to lose your entire 500 point shield, will be facing only kinetic weapons, and have 50% kinetic resist, set this value to 1,000.

Data readout under the bands lists the hit chance, the probable number of hits (Shots*hit chance), the effective DPS as computed by the link above, the alpha strike damage (150% base, maximum standard damage, more likely if chance to hit is higher), a wrecking strike damage (1% chance, automatic triple base damage), and the time to kill as determined by Tank/(DPS-Heal). A stable TTK output denotes healing faster than damage is being applied. It is not a promise of a lucky hit not coring the ship due to peak damage.

You can find the HTML5 version here. It does not play well with mobile. Sorry. Keyboard issue.

Please let me know if it's useful, problematic, needs refinement, or any other feedback, especially if I'm duplicating effort. This was a snap-decision made based on a conversation I had about speed needed to stay under the guns and instead of adding on more and more layers of "it depends," I made this. I'm not really a programmer, so it's pretty raw.

Notes:
  • 90 degrees does not produce useful closing damage data, as the time the ship needs to close a band is infinite.
  • The numpad doesn't function properly. This is a known HTML5 issue, and is not something I can fix program-side. It has something to do with num-lock state not being respected, I believe. Shy of scanning for key-codes, I do not have a solution.
  • This is obviously only for guns, as you cannot dodge a missile. I have not looked into missile damage equations.
  • I have not computed effective DPS from scratch, I used the Wiki equations. It may be possible that DPS will be lower due to lower hit rate
  • If this tool is of use, it can be expanded and refined. If it is not of use, I'd prefer not to spend more time on something that works for my needs.
  • An Android version is possible, but input and UX refinements would be required. A prototype is currently running for testing.
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Arin Mara
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Re: Request for comment: "under the guns" calculation program

Post by Arin Mara »

I tried to use it but I was stymied when I tried to input the data. :)

I run Missions in Chris Halsky's Lazy Gila. I accept Duo of Death. I want to get under the guns of the Battleships with as much Hit Points as possible.

Could you walk through this example and explain how I could get "Under the Guns"? I'm interested in two answer in particular:
  • if all enemies remain motionless and are located infinitesimally close to each other what's the best approach angle in each distance band?
  • which orbit will minimize the damage I take from the battleships once I'm under their guns?
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Irving Farnham
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Re: Request for comment: "under the guns" calculation program

Post by Irving Farnham »

I admit, the UI is less than perfect.

I'll walk through how I use the tool. Please let me know if it makes sense or if it's too hard to use.

Irving can't fly that fit, so these skills aren't your skills, but it should show the process. To keep my cap stable, I am disabling one of the shield hardeners.

My shields are 13,560 hp with a Thermal/Kinetic average resistance (the types specified for Duo of Death) of around 55%. Effective shield is 13,560/.55, or 24,655. With no shield boost, I'd call the maximum acceptable damage 20,000.

Ship speed is 635 m/s with the afterburner on, and 234 with it off. Depending on how well the gila handles, it may not comfortably orbit at shorter ranges and higher speeds. We'll make some decisions on that later, considering that the force pulling a ship out of orbit is the radial velocity squared.

Signature is 266 m.

Enemy ship intelligence from here: https://eveinfo.com/npcships/i/24170/core-lord-admiral/

Average damage is 400 per round, with a rate of fire of 3 seconds per round. Optimal range is 6km, falloff is 10km, and there's a listed "maximum engagement" of 25km. Tracking is listed at 0.0433, this is reasonable for an XL cannon weapon of similar damage. Given the DPS listed, I estimate three guns per ship, and we'll combine them into a single six gun battery for the number of guns.

Below is the entered data and an initial state. (range interval 3 to cover approximate maximum engagement range)

Image

(Ignore the tracking number of 0, it's showing 0 decimal places, something corrected in the source but not yet updated on the site)

The good news is, unless I did the math wrong (very possible!) or the EveInfo site is wrong (that tracking seems so low) you're usually in a good place! You can plunge in at 1 degree off-axis and if you can orbit at any range, you're pretty good. You don't even need that afterburner. This doesn't mean you're entirely safe, of course, but generally speaking, it doesn't take much, but as you can see, even with a very direct approach, 15km is the worst range to be at, and at 0 degrees, you still take artillery to the face.

And what if someone ends up webbing you? Well, if you're at 1-2 degrees . . .

Image

You're much less safe on the approach.

Worse, note the time to close: each of those range bars will take almost a minute to close. That's over a hundred 400 damage rounds with around 50% to hit. This is a bad place to be in, even for a few seconds.

Solution? Come in shallower.

Image

At 30 degrees, you're closing only a little slower, but they're virtually unable to hit you.

Now, people are going to notice, very quickly, that this isn't entirely correct. I wish I had the data to correct for ship rotation, but I don't. I suppose I could reverse engineer ship turn speed, but that's a chunk of work. This only really works if the ship is literally aligned to a single point and does not adjust its heading.

The program doesn't actually support this at this time (although it could given good input data) but I'm going to fake it and show you how. We'll look at 15 km, 3mk, and 1 km orbits. If we take the 16 second align time as meaning 16 seconds for a half rotation (only slightly more accurate than trying to use the color "purple" as a number) then we have around 1/5 of a radian per second of turn speed. This comes up to, at 15km, 3km/s, at 3km it's around 600m/s, and 1km is 200m/s. A ship quickly and accurately turning against a single ship can entirely negate orbit speed and make life much, much harder. For example, sitting in an orbit at 15km, but with the ship matching your orbit . . .

Image

When your relative velocity is zero, you die. At 15km, you're still out of optimal range, but you can't out-turn the battleship. If you're not webbed, you're looking at 16 seconds per band, or just about two minutes of approach time. That just doesn't work. Keep that in your back pocket, and we'll see if shorter ranges do work.

Now, 3km with the afterburner on is around 35m/s . . . kinda close to 55, which we saw worked very well when webbed. Let's call that okay, then look at 1km with an effective 34m/s velocity.

Image

That's . . . actually fine. If you get webbed, that's not good, as the close range favors the guns without speed tank, but it'll take a long time, or great luck, for them to kill the Gila. It's not part of this model to determine if the Gila can kill the target. ;)

So, a simple answer is this: with a single Gila, you can approach to orbit at 3 (with afterburner) or 1 km, which will cause you to approach at a small but non-zero angle ( I think). If the battleship turns slower, there's a huge margin of safety under 5km. Given the increased close speed, I suggest the afterburner, but you can also come in close and turn it off.

If you have multiple ships, bracket the ship and counter-rotate around it. It can only turn one direction, and the other is perfectly safe.

Bottom line:
Maximum engagement at 25km, under the guns at 1km with the afterburner off. Approach just off-axis to orbit at 1km. at 635m/s you're under threat for 38 seconds. You should take less than 8,000 damage if they're not rotating to bring the guns to bear, and if they rotate, it likely will burn through your entire shield, but not do too much more to the armor. At that range, you'll take very sporadic shots, but they'll all be wrecking shots.

If the ship turns slower, life is great! If it turns faster, it gets very bad very quickly. Bring backup.

Sorry it's so complicated . . . it's a complicated topic.
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Arin Mara
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Re: Request for comment: "under the guns" calculation program

Post by Arin Mara »

Thanks Irving! :)

The topic is complex, there's no way around it. A lot is happening on each image. I'm not sure where I should look when parsing each paragraph. I'll print out the page, draw a graph and underline the keywords :)
The Mission example is contrived, but I can see how pre-computing flight angles, speed and damage would be useful for Abyssal Deadspace, Drifter Wormholes, Pochven or when engaging capital ships in Null Security Systems. :)
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Irving Farnham
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Re: Request for comment: "under the guns" calculation program

Post by Irving Farnham »

Yeah, it's slide-rule level complicated.

My concept was an assistance for fleet actions, since human pilots would be unlikely to be able to keep up turn rates, would suffer information overload, etc. It also shows a quick heads-up for bad ideas. A Magic Merlin can get to a Cormorant, but a stock one will just evaporate under railgun fire, no matter how it tries to come in. I guess the ultimate problem is I made a concept in my head and found a way to answer all my questions, but I can't seem to explain the basic mental model I use. Maybe I need to reconsider the needs of the user more carefully.
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