Optimal engine charts for 1.0.2

[John FX]

Hi, would it be possible to add a box for min and max number of engines on the web app please?

Sometimes I have a design and there is a fixed amount of engines I can have but I'd like to know the best options I have for Dv/TWR

EDIT :

Is it possible to add the choice of graph axes (i.e. not only payload-ÃŽâ€v graphs at fixed TWR, but also ÃŽâ€v-TWR graphs at fixed payload and TWR-payload graphs at fixed ÃŽâ€v)?

Actually being able to define the axis would be great. If I could fix the number of engines to 1 or 2 then set the payload at 10T and show the graph of TWR vs Dv (and which engine would be best at each point) that would be a handy graph!

EDIT 2 : Just thought (again), most of the time I have a fixed payload and I limit the number of engines but I need to find out what Dv different engines would allow and how much thrust I would have with a craft if I wanted an amount of Dv. I find myself making many graphs to find the info that would be in one graph (TWR vs Dv, fixed payload, 1 engine, different types of engine)

In my experience I find that most missions are for a set payload to various destinations so I find my payload does not change and due to wanting to limit part numbers the number of engines does not change either but what does change is the TWR required to limit burn time (or allow landing) and the Dv required to simply get there.

Sorry if this is a bit long winded or repeats, still not had second coffee...

Edited May 26, 2015 by John FX

[Meithan]

Is it possible to add the choice of graph axes (i.e. not only payload-ÃŽâ€v graphs at fixed TWR, but also ÃŽâ€v-TWR graphs at fixed payload and TWR-payload graphs at fixed ÃŽâ€v)?

Actually being able to define the axis would be great. If I could fix the number of engines to 1 or 2 then set the payload at 10T and show the graph of TWR vs Dv (and which engine would be best at each point) that would be a handy graph!

That's a great idea, Teilnehmer, I can see how these other variable combinations could be useful. I'll leave it for after this version is fully working because I'd have to redo some of the math and change the user interface, but I it's totally doable.

Hi, would it be possible to add a box for min and max number of engines on the web app please?

Sometimes I have a design and there is a fixed amount of engines I can have but I'd like to know the best options I have for Dv/TWR

This, setting the limit on the number of engines, and atmospheric pressure calculations are already implemented in my working version (sneak peek below); I'll upload it to the website as soon as I test it a little bit more .

[Red Iron Crown]

That looks amazing. What are you planning for atmospheric presets? Maybe sea level Eve, Duna, Kerbin and Laythe?

[LittleBlueGaming]

This is awesome! Although, I guess I'm a little confused about something. In the first chart, what makes the LV-1 with an ISP of 315 better than an LV-909 with an ISP of 345? Is it up to the difference in mass or is there some other factor?

[Meithan]

That looks amazing. What are you planning for atmospheric presets? Maybe sea level Eve, Duna, Kerbin and Laythe?

Yup, exactly those.

At some point I was considering also adding a few extra Eve presets for say, 2, 5 and 10 km ASL, but with the changes in the atmosphere model in 1.0 I don't know how to readily calculate pressure for a given altitude. I'll have to look into OhioBob's investigations of the new model (which is based on the International Standard Atmosphere, a model with which I'm a bit familiar a floatCurve?).

- - - Updated - - -

This is awesome! Although, I guess I'm a little confused about something. In the first chart, what makes the LV-1 with an ISP of 315 better than an LV-909 with an ISP of 345? Is it up to the difference in mass or is there some other factor?

The other engine is the LV-N, by the way, with an Isp of 800 s. But yes, the reason is its low mass: the LV-1 weighs a whopping 150 times less than the LV-N. For light payloads and/or very small ÃŽâ€v, the small mass of the LV-1 will kill the superior Isp of the LV-N. Imagine that your payload is 1t: if you use the LV-N, you'll be adding 3 tonnes for the engine alone!

Edited May 27, 2015 by Meithan

[LittleBlueGaming]

The other engine is the LV-N, by the way, with an Isp of 800 s. But yes, the reason is its low mass: the LV-1 weighs a whopping 150 times less than the LV-N. For light payloads and/or very small ÃŽâ€v, the small mass of the LV-1 will kill the superior Isp of the LV-N. Imagine that your payload is 1t: if you use the LV-N, you'll be adding 3 tonnes for the engine alone!

Ahhh, thanks. I was thinking ISP accounted for mass somehow, so I was wondering why anybody would use those dinky little things over the LV-909.

Today I learned that rocket science isn't quite as simple as I thought it was

[GoSlash27]

This is awesome! Although, I guess I'm a little confused about something. In the first chart, what makes the LV-1 with an ISP of 315 better than an LV-909 with an ISP of 345? Is it up to the difference in mass or is there some other factor?

LittleBlueGaming,

Remember that these charts define "best" as whatever engine makes the lightest overall stage. If you don't have very much payload or you aren't going very far, then clearly it wouldn't make sense to use a heavy super-efficient engine when a light gas-hog will do.

The heavier more efficient engine won't become worth it until the difference in fuel consumed becomes more than the mass of the engine itself.

HTHs,

-Slashy

edit *D'Oh!* Ninja'd...

[Teilnehmer]

I believe it would be better to have the fields in the page already filled in with some default values.

E.g.

 Payload: 0..100 t

 Îâ€v: 0..10000 m/s

 TWR: 0.5

or something else.

In the graph legend and in the section below the graph, the 0.90 engine naming style is used (unlike the ‘Engine selection’ section).

Please add the nicknames everywhere.

Btw the legend would be not necessary if the ‘Engine selection’ section was supplied with those color boxes.

- - - Updated - - -

The ‘Kerbin-Relative TWR’ parameter could be replaced with ‘Acceleration’ [m/s²] for the sake of universality. Kerbal TWR makes little sense in space and on other planets.

Edited May 27, 2015 by Teilnehmer

[Meithan]

Thanks for all your useful suggestions, Teilnhemer!

I believe it would be better to have the fields in the page already filled in with some default values.

E.g.

 Payload: 0..100 t

 Îâ€v: 0..10000 m/s

 TWR: 0.5

or something else.

This is effectively done by hitting the "Load defaults" button. Do you think it needs to be made clearer? I've thought about adding a popup or overlay with instructions on how to use the webapp (specially now that it's getting more and more complicated).

In the graph legend and in the section below the graph, the 0.90 engine naming style is used (unlike the ‘Engine selection’ section).

Please add the nicknames everywhere.

I'm on the other side of the fence here: I'm still not used to the new "nicknames", so I find it easier to read LV-T30 than "Terrier" (or whatever it is ... *checks* See? I still don't get it right ).

But I think I'm gonna follow your suggestion. It's gonne be both easier for new people to read and for old players like me to learn the nicknames if they are default. To please everyone, I'll throw in an optional checkbox to display the old names. Will add on next iteration.

Btw the legend would be not necessary if the ‘Engine selection’ section was supplied with those color boxes.

I think it's clearer if the legend only displays the engines that do appear in the chart, as opposed to all engines. Plus I like having the engine list right next to the chart, so it's easier to compare colors.

What I have been considering is letting the user change the color of the engines, using something like http://www.jqueryrain.com/?W6V5HIOt/. That way the user could change the colors of shown engines that are hard to distinguish.

The ‘Kerbin-Relative TWR’ parameter could be replaced with ‘Acceleration’ [m/s²] for the sake of universality. Kerbal TWR makes little sense in space and on other planets.

This is something I've been considering too. As you say, for vacuum applications the acceleration is a more useful quantity (since, for instance, it lets you estimate a burn duration). However, for surface applications (e.g. taking off from Tylo) the TWR is a more natural parameter.

So it's hard to say which should be shown. What do others think?

~~~~~

Alright guys, the next beta version is up.

http://meithan.x10.mx/KSP/engines/

New features:

• Atmospheric pressure now settable, with recalculation of engine Isp and thrust.
  
• The reference body for the TWR is changeable (so you can now quickly do a chart useful for, e.g., Duna liftoff).
  
• Max number of engines is configurable, with "unlimited" option.
  

Have a go at it, and tell me what you think / report any bugs.

[Teilnehmer]

This is effectively done by hitting the "Load defaults" button.

Oh sorry! I didn’t notice it before.

As you say, for vacuum applications the acceleration is a more useful quantity (since, for instance, it lets you estimate a burn duration). However, for surface applications (e.g. taking off from Tylo) the TWR is a more natural parameter.

So it's hard to say which should be shown. What do others think?

Thus, the ‘Relative to’ combobox should have a ‘Use acceleration instead’ option.

Edited May 27, 2015 by Teilnehmer

[GoSlash27]

Meithan,

I really like the settable atmosphere option. Useful for lower stages.

As for the relative acceleration question, I'm like you; I think in terms of Gs at a location when designing a stage. I can definitely see where m/sec^2 would come in handy for timing burns, tho'.

Excellent work!

-Slashy

[Meithan]

As for the relative acceleration question, I'm like you; I think in terms of Gs at a location when designing a stage. I can definitely see where m/sec^2 would come in handy for timing burns, tho'.

What I can do to keep the interface from getting even more complex is leave it with TWR as it is and display acceleration in the "Details" tooltip. I could then include min/max accel, average accel, and maybe even burn times for some delta-v values (100, 200, 500, 1000, perhaps?) there. How's that sound, Teilnehmer.

Now, I'm no longer sure that the "total mass" line plots (see OP) are still a desirable feature, since the tooltip is already providing extra info for specific chart points. What do you guys think? Is it still worth it?

If not, or if it's not an important feature to have right now, I'll work next on zooming capabilities for the main chart.

[hoojiwana]

Can you include the Twin Boar with some sort of "minimum payload" setting for its built-in Rockomax-64 fuel tank?

[Meithan]

Can you include the Twin Boar with some sort of "minimum payload" setting for its built-in Rockomax-64 fuel tank?

Yes I can. I just did a few calculations while waiting for the bus and I think the formulas remain valid for the Twin Boar as long as its "effective mass" is computed as (engine itself + integrated tank - fuel/alpha). I'll check my algebra again when I get home and if it's correct then I'll add the Twin Boar to the app.

[Teilnehmer]

How is the tank wet/dry mass ratio is chosen? E.g. does the app assume the Mk3 LF tanks are always used with the Nervs (having the best wet/dry ratio = 8), or does it switch to Mk1 (wet/dry = 6) for small amounts of fuel?

[Meithan]

How is the tank wet/dry mass ratio is chosen? E.g. does the app assume the Mk3 LF tanks are always used with the Nervs (having the best wet/dry ratio = 8), or does it switch to Mk1 (wet/dry = 6) for small amounts of fuel?

I have kept the choices I used for the original charts: normal LFO engines assume the full-to-dry mass ratio of the tanks is 9 (that of all the "conventional" LFO tanks), while the LV-N assumes it's 8 (which is very close to the ratio of all Mk2-Mk3 liquid fuel fuselages). It's set on a per-engine basis.

[Teilnehmer]

Are solid fuel boosters worth it to include them to the chart?

[Meithan]

Are solid fuel boosters worth it to include them to the chart?

Probably not, since they have low Isp and are usually unsuitable as main stage "engines" (non-throttable, no gimbal, non-expandable fuel load). Remember that these charts are for a single engine type. Combining different types of engines would require a completely different approach, and for that there's tools like the KSP Optimal Rocket Calculator.

[Teilnehmer]

Is there an engine which is always not the best for any set of parameters?

[Dman979]

Hmmm. The EVA packs?

[Meithan]

Is there an engine which is always not the best for any set of parameters?

In vacuum, the LV-1R "Spider" is never optimal because the LV-1 "Ant" is always better (they have the same mass and thrust, but the Ant has a slightly better Isp). However, once you go inside an atmosphere the roles are quickly reversed. For some reason the Ant's atmospheric Isp is terrible while the Spider's is not.

~~~~~

Webapp update:

http://meithan.x10.mx/KSP/engines/

Changelog:

• Added the KR-1x2 "Twin Boar" (I'm adding it as a 6 tonnes, 2000 kN "normal" engine; thanks to the infinitely divisible fuel/tank mass approximation, the fuel and tank it carries can simply be lumped into the ship's totals).
  
• The new nicknames of the engines are now shown by default, bit I've added an extra option to use the old names.
  
• Moved the mouseover info box to the right of the chart and started styling it.
  

I'm working on the click-and-drag zoom capability, but it's not complete yet.

[Teilnehmer]

So, every engine has its niche. That’s nice.

I'm working on the click-and-drag zoom capability, but it's not complete yet.

Wow. That would be great!

Edited May 29, 2015 by Teilnehmer

[John FX]

In vacuum, the LV-1R "Spider" is never optimal because the LV-1 "Ant" is always better (they have the same mass and thrust, but the Ant has a slightly better Isp). However, once you go inside an atmosphere the roles are quickly reversed. For some reason the Ant's atmospheric Isp is terrible while the Spider's is not.

~~~~~

Webapp update:

http://meithan.x10.mx/KSP/engines/

Changelog:

• Added the KR-1x2 "Twin Boar" (I'm adding it as a 6 tonnes, 2000 kN "normal" engine; thanks to the infinitely divisible fuel/tank mass approximation, the fuel and tank it carries can simply be lumped into the ship's totals).
  
• The new nicknames of the engines are now shown by default, bit I've added an extra option to use the old names.
  
• Moved the mouseover info box to the right of the chart and started styling it.
  

I'm working on the click-and-drag zoom capability, but it's not complete yet.

After trying the app can I ask for the engines in the legend that appears next to the chart to have the "LTV-30" part of the name as well as the nickname please?

I have no idea what a rhino or a terrier is. I barely know a swivel and I use it daily. If the name could follow the format of the engine selector that would be great eg : LV-909 "Terrier". It's good to have the legacy names as an option but I don't know them very well either.

Apart from that it's looking really good.

[magnemoe]

In vacuum, the LV-1R "Spider" is never optimal because the LV-1 "Ant" is always better (they have the same mass and thrust, but the Ant has a slightly better Isp). However, once you go inside an atmosphere the roles are quickly reversed. For some reason the Ant's atmospheric Isp is terrible while the Spider's is not.

Radial engines tend to be a bit worse than the in-line ones, this is compensated in that its easy to add more of them and that the rear of the rocket is free for other uses,

[Starhawk]

I was wondering if it would be useful for the sake of comparison to include some electricity-generating mass in the calculations for the Dawn.

If the numbers in the Wiki are accurate, the best mass efficiency to power a single Dawn at Kerbin would require 105 kg of solar panels (OXSTAT-4L's or OXSTAT-4W's). This is significant, considering that the Dawn only masses 250 kg.

Happy landings!