Tweakable SRBs? via selection of fuel core mandrel profile???

[Wallygator]

Hello all!

First time poster after playing for a couple of months. Fab Simulation - makes me depressed thinking about all the calculus I forgot long ago...

Suggestion: Would it make sense to allow an SRB to be tweaked by selecting the mandrel profile for the fuel core? -So as an example, a round void in the core would provide a gentle increase in thrust throughout the burn while a star void would provide higher thrust initial with a gradual taper (other void shapes are also possible).

Thanks for listening!

Cheers,

WG

[sjwt]

SRB's can already be tweaked to alter both Thrust level and Fuel amount, as these are tweekable to fine detail, I am unsure if you are asking for a set a predefined options? or after some kind of effects alteration.

[vexx32]

No, no, if you look up how SRBs work, you can actually have them prebuilt so that their thrust alters as they burn, due to how the fuel is actually built into the SRB. For example, an SRB where it is entirely solid fuel mass with a hole through the centre where it is originally going to be lit will have a variable thrust as it goes, slowly increasing and then slowly decreasing throughout the burn, since as it burns the surface area that is burning changes as the hole in the centre expands (since the fuel mass is being burned and shot out as exhaust). There are a bunch of different shapes you can cut into the SRB, each with different variable thrust profiles which can be displayed on a graph.

What he dubs a Mandrel profile (not sure exactly where that name comes from) is also known as the grain geometry of the engine (see here). Basically, this would not only be a step forward for realism, but it would also mean SRBs can be considered more useful in a greater variety of situations. The wiki article only depicts four variants, but I recall seeing a suggestion much like this a very long time ago that had examples of at least 8 different kinds, including one that would actually exponentially increase its thrust before it dropped off and sputtered out.

[Capt Snuggler]

yup, the shape of the hole down the center totally changes the way my little sugar rockets fly. star shapes * can be very hard to make but produce MUCH greater initial thrust. (when they work )

[Wallygator]

"Grain Geometry" - Yes, exactly - Many thanks for jogging my memory Vexx! There are way more than 4 - some can get quite complex. Sorry for the reference to Mandrel - as that is the device or "form" which the fuel core is moulded around, and is then removed once the core is stabile. in my youth i recall using a large nail or a pencil as a makeshift mandrel.

Anyway... I think the suggestion is clear enough at this point. The real question is - is it a worthy suggestion as an option in game?

[SRV Ron]

Currently, the SRBs appear to use the star core. If you watch the acceleration on the initial launch, you see the burst in acceleration followed by a drop off. The later increase is the result of the loss of mass as fuel gets used up.

It's a reminder of the designs of black powder model rocket engines where two of them with the same amount of propellent behaved in two vastly different performance.

The F-7.6 had a low overall thrust but provided 10 seconds of powered flight. It was suitable for small light very stable rockets best launched using a rail stabilization system. The F-100.8 was a high powered engine requiring a strong mounting. It burned all of its propellent in 1/2 second. A two stage version of the F-100.0 F-100.8 sent its 3 ounce film camera payload over a mile away upwind. We had launched it at a 45* angle due to it being quite windy. Unknown to us modelers the F-100.0 booster had a built in 3 second delay. The rocket had gone horizontal by the time the second stage kicked in.

Edited January 28, 2014 by SRV Ron

[Capt Snuggler]

changing the Thrust Curve (is that right?) could be helpful for launching asymmetric shuttles. the trust would decrease as the external tank mass decreases helping to keep the craft balanced and acceleration steady.

[check]

I'm all for changes that increase realism (to a degree). However, with a change like this, it'd be really useful for a stock version of Kerbal Engineer + the ability to view a thrust curve on a graph (which I would love!).

I know Squad's taking the view that too much math and too many numbers might intimidate new players... but there is a simple way around that: make certain tweakables and displays (engineering info, orbital parameters) unlockable with science. That way, a new player won't be bombarded with numbers and options right when they start, and only until they've proven that they've got a basic handle on rocket building and orbital mechanics do they unlock the ability to see parameters or make fine adjustments.

[Capt Snuggler]

but there is a simple way around that: make certain tweakables and displays (engineering info, orbital parameters) unlockable with science.

bingo!

this extra text is required to post...

[allmappedout]

I know Squad's taking the view that too much math and too many numbers might intimidate new players... but there is a simple way around that: make certain tweakables and displays (engineering info, orbital parameters) unlockable with science. That way, a new player won't be bombarded with numbers and options right when they start, and only until they've proven that they've got a basic handle on rocket building and orbital mechanics do they unlock the ability to see parameters or make fine adjustments.

Oh how I wish for the day this becomes a reality...Plus, you can then look at building of scenarios based on how far along the tree you are; for example, once you unlock 'ejection angle' as a science display, you also unlock a scenario/tutorial that explains interplanetary transfers, etc. to help ease newbies into it (/offtopic)

Anyway, since the thrust and fuel is now variable thanks to tweakables, I've found them exceptionally useful for first stages again. I definitely think that the ability to sort out a thrust curve would be beneficial to some players, although I'd be of the persuasion that it's probably not for everyone and, like Check suggests, should probably sit as an additional unlock for advanced players to use.

[vexx32]

I guess there is a slight concern that this might intimidate newer players, but if you have it unlockable (as previously mentioned) in addition to maybe having some kind of brief explanatory screen detailing what the feature does. (Just a general thing like this shaped thrust curve does this, and this grain geometry creates this kind of curve, etc.)

[Capt Snuggler]

Grain geometry is kinda already implemented as the Max Thrust bar in tweakables. as its an SRB it becomes a Burn rate slider which is grain geometry. I suppose it does all become more complicated when you introduce a thrust curve, as it would be stretched by decreasing burn rate.

I can see why it would be intimidating for new players but it would only really be a major factor on asymmetric craft anyway, which is already advanced.

[Wallygator]

So to summarise briefly, it sounds like this could be a good idea / feature targeted for more advanced players - perhaps being unlocked later down the tech tree.

My original thought was this would be a in-game tool to completely customise the thrust curve for any SRB. But...

I suppose another (more easily achievable) option would be to create an extended series of SRBs (each with a thrust curve designed to mimic a single grain geometry) which could be tweaked using the existing SRB tweaks (max thrust / burn time). I presume that this approach would probably be better implemented via a mod or part pack rather than an in-game change.

Well, thanks for listening and the constructive feedback.

Cheers!

[shand]

Im up for this - we are halfway there - a thrust curve would be the final nail in the coffin of awesome (thats a terrible expression - i mean it would be perfect)

perhaps a 4 tier system? 1- just tweak the fuel levels. (Initial SRB unlock - though maybe have it default to half thrust) 2: tweak the fuel and trust. (when you unlock the larger one) 3:tweak between 3 or 4 preset geometries. 4: adjust the thrust curve yourself.

On the technical side can someone confirm my understand is right, or tell me where im wrong:

the deltaV of the SRB is the same regardless of geometry (assuming same mass and fuel) yes?

and is that deltaV is proportional to the area under the thrust curve?

If so you can have a simple system where if you lower the thrust curve at any point it extends the x axis, representing increased burn time.

and yes i completely agree, this needs to be entirely optional perhaps even hidden behind a button on the right click menu ("Use advanced SRB editing") of each SRB. and definitely up the tech tree.

[Awaras]

The wiki article only depicts four variants, but I recall seeing a suggestion much like this a very long time ago that had examples of at least 8 different kinds, including one that would actually exponentially increase its thrust before it dropped off and sputtered out.

I remember this diagram showing up a lot on the forum:

[Supernovy]

This might be unrealistic, but what about "initial thrust" and "final thrust" sliders? Then let the game interpolate between them.

Don't forget that in the current game, SRBs have "spool up" time, and the I_sp gain from travelling up doesn't come with a respective thrust gain.

The velocity curve is also a thing, but is not used by the current SRBs.

[technicalfool]

I remember this diagram showing up a lot on the forum:

http://abyss.uoregon.edu/~js/images/solid_2.gif

I'm wondering what it would take to do a highly simplified burn simulation on some of those cross sections. Thrust based on amount of surface area exposed, and the surface area is eaten away evenly across the exposed surface, a pixel (or whatever distance unit) at a time. You can draw whatever shape you like. If the burn results in chunks of fuel coming loose, that could be a non-viable design that would cause an explosion, and would not be allowed.

The simulation would only need to be run once to generate the thrust curve, and the curve is then what is used in the game for every booster with that fuel core design.

[Awaras]

I'm wondering what it would take to do a highly simplified burn simulation on some of those cross sections. Thrust based on amount of surface area exposed, and the surface area is eaten away evenly across the exposed surface, a pixel (or whatever distance unit) at a time. You can draw whatever shape you like. If the burn results in chunks of fuel coming loose, that could be a non-viable design that would cause an explosion, and would not be allowed.

The simulation would only need to be run once to generate the thrust curve, and the curve is then what is used in the game for every booster with that fuel core design.

I really think simulating burn patterns would be overkill. Just letting us edit the thrust curve directly would be good enough in my opinion.

[ThorBeorn]

Sry for necro. But HoneyFox has a plugin called EngineThrustController.dll which can be added to SRB's. This makes thrust a function of how much fuel is left in the SRB. The thrustcurve can then be edited in the mod tweakable parameters also by HoneyFox, or with simple .cfg editing in notepad (which is essentially the same as changing the fuel core profile). So y'all know.

I'd also like this to be a feature of stock KSP though. It can also be done more user-/noobfriendly.

Edited April 16, 2014 by ThorBeorn
Darn spelling