Engine suggestions (No, not new ones)

[tg626]

So we now have actuation toggles, which is AWESOME! But I have 2 more suggestions.

#1 if throttle = 0 don't gimbal.

#2 have the effects track the percentage of maximum *available* thrust rather then engine's absolute maximum thrust.  In other words, if the tweakables slider has been set to 50% and the throttle is set to max, give us the full effects.  Right now an engine with its tweakable set to 50% and throttle is at max, you see the same thing as when the tweakable is at 100% and the throttle is at 50%.  This can look rather silly at launch if you've had to step up to a higher power engine, but then tweak it down to keep the TWR reasonable...

Edited November 12, 2016 by tg626

[EpicSpaceTroll139]

I can definitely second number 1. When I have my engines shutdown as my spaceplane is reentering, it seems weird that the engine bells are swivelling around, as if they'll do something if they move enough.

On the second one though... it seems a bit arbitrary. I mean, will my V6 car be as loud as an I4 at the same acceleration? No, physics dictates that the I4 will need to rev up to a higher RPM to get the same torque, and therefore it will make more noise. It's the same kind of thing with the rockets, you're just encountering physics. You limit an engine to a fraction of its rated power, and you get a fraction of its rated effects. You do something silly, you get something silly in return.

 

And think about it, if it shows 100% effects at 50% limiter, what's it going to do when you set it to 100%? 200%?

Another thing: Going with your idea, I could take, say, a mainsail or something, put the thrust limiter at 1% (or even 0.01% with the proper tools), and have this giant torch thing that uses very little fuel. Which would make no sense

[Darnok]

We have tweakable called "authority" set to 100% on Control surfaces, but we can increase that to 150%... now what if we could have same mechanic for engines and we could overload them up to 150% (or 125% if first idea is too much)?

While they are overloaded they should overheat much much faster.

[tg626]

Good points, and an interesting idea. Maybe my second idea as only if the thrust is limited in the VAB?  I dunno. You make a good point, but my view was that the engine is being tailored to the launcher / payload.  Admittedly, I'm usually going no lower then 50%, and that's usually me doing a twin nozzle like the Titan using 2 Vectors.

Edited November 12, 2016 by tg626

[Red Iron Crown]

#1 would be nice to have, a small tweak one would think.

#2 is plain wrong. The plume *should* scale with actual thrust, not % of current adjusted maximum. A given engine at 50% throttle with a 100% limited is burning exactly the same propellants at exactly the same rates as that engine at 100% throttle with a 50% limiter; they should have identical plume effects.

[John FX]

I would really like to push an engine past 100%, as is possible in real life, and for there to be consequences for lifespan, overheating, or fuel economy.

Probably something for a mod though, maybe the testflight mod as it already deals with reliability and upgrading engines.

EDIT : I agree with #1 too though

Edited November 12, 2016 by John FX

[paul23]

Pushing an engine "past 100%" is not something you can "just do". Engines need to be actually designed to be able to do that - most rocket engines simply cannot provide more thrust physically than the already rated maximum. (Apart from some minor effects due to safety margins on rating but that's typically in the order of 5%). Only some fighter jet engines have this ability - but once again this is due to some extra engineering (afterburners etc), things you don't add when you actually expect a mission "to go as planned".

Other than for those very specific cases (fighter craft) being able to "throttle past 100%" is the same as a musician rating his amplifier better "cause it can go to 11".

Edited November 13, 2016 by paul23

[DrunkenKerbalnaut]

Driving a rocket to output more than it's rated power means higher pressures in the chamber, higher temperatures and an elevated, therefore unacceptable risk of really bad stuff happening. I say unacceptable from a human standpoint, but Kerbals would probably be cool with it. To keep this in perspective, though, the SSME ("Vector" is the Kerbal analogue) was uprated halfway through it's use on the Shuttles to allow 104% throttle. That's a big deal. 

[kerbiloid]

Gimballing with zero thrust looks as strange as trembling fins in vacuum.

[tg626]

That'd be another one, no control surface movement in vacuum.

[Stoney3K]

On 11/14/2016 at 1:22 PM, DrunkenKerbalnaut said:

Driving a rocket to output more than it's rated power means higher pressures in the chamber, higher temperatures and an elevated, therefore unacceptable risk of really bad stuff happening. I say unacceptable from a human standpoint, but Kerbals would probably be cool with it. To keep this in perspective, though, the SSME ("Vector" is the Kerbal analogue) was uprated halfway through it's use on the Shuttles to allow 104% throttle. That's a big deal. 

Exactly that, in Kerbal land, overloading engines up to eleven should be perfectly fine. Maybe have a yellow/red backdrop with the tweakable if you move it past 100% or 110%.

Engine overheating at 100% thrust is less of an issue than it used to be, so why not have the engines overheat more rapidly when you overdrive them? I can imagine a lot of missions where budget is tight or you're missing the tech node for that Skipper so you're still stuck with Reliants and Swivels, but you need the thrust to get the mission done. Why not have the option to crank up the Reliants to eleven and have more chance of your craft going poof in the meantime?

[DrunkenKerbalnaut]

3 hours ago, Stoney3K said:

Exactly that, in Kerbal land, overloading engines up to eleven should be perfectly fine. Maybe have a yellow/red backdrop with the tweakable if you move it past 100% or 110%.

Engine overheating at 100% thrust is less of an issue than it used to be, so why not have the engines overheat more rapidly when you overdrive them? I can imagine a lot of missions where budget is tight or you're missing the tech node for that Skipper so you're still stuck with Reliants and Swivels, but you need the thrust to get the mission done. Why not have the option to crank up the Reliants to eleven and have more chance of your craft going poof in the meantime?

I've always assumed this was going to be the case, given the red zone on the throttle UI. Like upgrading your fuel pump tech, or access to a more resilient nozzle material. 

[paul23]

15 hours ago, Stoney3K said:

Exactly that, in Kerbal land, overloading engines up to eleven should be perfectly fine. Maybe have a yellow/red backdrop with the tweakable if you move it past 100% or 110%.

Engine overheating at 100% thrust is less of an issue than it used to be, so why not have the engines overheat more rapidly when you overdrive them? I can imagine a lot of missions where budget is tight or you're missing the tech node for that Skipper so you're still stuck with Reliants and Swivels, but you need the thrust to get the mission done. Why not have the option to crank up the Reliants to eleven and have more chance of your craft going poof in the meantime?

Why would I ever NOT use this? It is better to do short burns than long burns at lower thrust, always. So basically any such method would make the game even MORE easy: something KSP really doesn't need. KSP needs to finally become hard: we need to think about rocket design before being able to launch into orbit. Any method that overloads the engines should come with a downgrade of the rated thrust, so that maximum thrust is equal.

Edited November 22, 2016 by paul23

[Stoney3K]

5 hours ago, paul23 said:

Why would I ever NOT use this? It is better to do short burns than long burns at lower thrust, always. So basically any such method would make the game even MORE easy: something KSP really doesn't need. KSP needs to finally become hard: we need to think about rocket design before being able to launch into orbit. Any method that overloads the engines should come with a downgrade of the rated thrust, so that maximum thrust is equal.

Which completely defeats the point of overloading engines since overloading means they will be running above the rated thrust. The heck with safeguards and protections, I just want to floor the engine until it blows up!

In earlier versions of KSP you couldn't run a Mainsail at 100% forever without a lot of stuff overheating, which means you had to throttle it back sooner or later. This was different with the new thermal system, which allows anyone just to run the engines at 100% of their rated thrust all of the time. (Which makes sense, because "rated" thrust means they're running as they should.) However, going over the rated thrust just by slamming more fuel through the engines is no longer possible.

I don't think this makes anything overpowered, it may give you a little more thrust in short periods but it also means your engines will overheat and your craft will get destroyed if you keep overloading your engines. So it would only have a very limited impact on balancing stuff like shortening your burn time, sure you can burn your engines up to eleven, but do you really want to run the risk of blowing up your craft just to get a 25% shorter burn? If you do, I would say that qualifies as the fun that "Kerbal" stands for, instead of the cool, calculated engineering with tenfold safety factors like NASA, which is boring!

[paul23]

25% shorter burn means you need a LOT less total delta-v to get to orbit. It also means you are much closer to the perfect hohman impulse: and thus require a lot less energy there.

[Stoney3K]

2 minutes ago, paul23 said:

25% shorter burn means you need a LOT less total delta-v to get to orbit. It also means you are much closer to the perfect hohman impulse: and thus require a lot less energy there.

If that means a 50% (or even a 100%) higher chance of your ship blowing up, then it's all about taking chances, isn't it?

I mean, current parts in KSP never fail on their own, the only reason parts break is because of pilot error (usually caused by spacecraft crashing into other, more solid, objects) while random part failures are a real thing. Usually the probability of those failures would be really, really small, but if you start overdriving your engines, that probability may get a lot higher.

So if you're willing to risk the entire mission and the lives of your crew on that 25% extra thrust (which has no significant impact on the required delta-V to go anywhere, BTW) then go ahead and play Kerbal.

Shorter burn times matter when you compare an ion engine to a Mainsail, but then you're talking orders of magnitude which may cause you to miss a transfer window if the burn becomes too long.

If you need a LOT less dV when you have a TWR that is 25% more than your original craft on the pad, you need to re-design your craft since you're probably losing a lot of energy to drag. I can get craft to orbit without any trouble having only 4000m/s of vacuum delta-V and a pad TWR of 1.5 or even lower. More thrust does not mean your craft gets more efficient.

[Jarin]

5 hours ago, paul23 said:

KSP needs to finally become hard

Go install RO and leave me my fun rockets, dangit.

[DrunkenKerbalnaut]

42 minutes ago, paul23 said:

25% shorter burn means you need a LOT less total delta-v to get to orbit. It also means you are much closer to the perfect hohman impulse: and thus require a lot less energy there.

The dv doesn't change. 

EDIT: the requisite dv to achieve orbit, that is. 

Edited November 22, 2016 by DrunkenKerbalnaut

[Red Iron Crown]

1 minute ago, DrunkenKerbalnaut said:

The dv doesn't change. 

EDIT: the requisite dv to achieve orbit, that is. 

It does though. Higher TWR = lower gravity losses. (And greater drag losses, but these are generally trumped by gravity losses.)

[DrunkenKerbalnaut]

7 minutes ago, Red Iron Crown said:

It does though. Higher TWR = lower gravity losses. (And greater drag losses, but these are generally trumped by gravity losses.)

I don't want to hijack, so I'll PM you. Hope you don't mind. 

[paul23]

Sigh... Really. The actual complete rocket equation is a differential equation:

source

Now using this, neglecting drag and considering a rocket flying straight (oh and considering the gravitational force to be equal the whole burn path), this can be rewritten as:

So the total delta-V depends on the time to burn, now given everything equal a higher TWR means a shorter burn time - and hence the effective delta-V is higher.

For example, say my rocket takes 5 minutes to get into orbit, and with this overloading you get 25% more power (ignoring rotation effect): t_b = 300s, and with overloading the engine: t_b = 225, thus time diffference is 75 seconds. This leads to a gain of 75*9.81 - more than 700 delta-V. 700 delta-V you get for "free" (especially with revert to launch capability).

 

Edited November 23, 2016 by paul23

[DrunkenKerbalnaut]

@paul23

Yeah... I dropped out of HS to play with guns, so that kind of math is not exactly my forte (got any colorful blocks  ). I'll assume you got it right, and move on.

...to solving it my own way  . I should have time later today to do some experiments concerning the matter, I'll start a new thread to show the results. 

Sorry for misleading the convo. 

[paul23]

Well without equations it's also easily explained looking at the extremes:

 

Consider a very high - near infinte- thrust to weight ratio, such an engine would give you instataneously your desired delta-V/speed. Akin to a cannon. Now consider a low TWR rocket engine, this engine doesn't give you an immediate delta-V instead it raises your speed over time. During this time it is already lifting off - during which it is carrying fuel-yet-to-be-burned. So basically you are "losing" energy lifting fuel towards a certain height.

[tg626]

I always assumed if you ran at 110%, you'd over heat.  Fast.  Hence limiting the usefulness of over thrusting....

[Stoney3K]

On 11/23/2016 at 3:23 PM, paul23 said:

For example, say my rocket takes 5 minutes to get into orbit, and with this overloading you get 25% more power (ignoring rotation effect): t_b = 300s, and with overloading the engine: t_b = 225, thus time diffference is 75 seconds. This leads to a gain of 75*9.81 - more than 700 delta-V. 700 delta-V you get for "free" (especially with revert to launch capability).

 

Your calculation is perfectly valid if the entire path to orbit is straight up. Which it isn't. You spend the biggest part of your burn building horizontal speed, which is perpendicular to gravity.

Your cannon example would instantaneously launch a payload to orbit if it launched that payload level with the surface -- in essence, if you speed down the highway fast enough, your're going straight while the planet is curved, which makes you go 'up' with respect to the surface.

Payloads are not launched straight up, they're launched as horizontal as they can possibly be launched. And gravity doesn't matter squat for horizontal Delta-V.

The only gain you get from a high TWR is in the first few kilometers of your initial ascent. But that is offset by the lack of control caused by that extreme TWR.