Engines that need to be buffed and here's how I'd buff them

[More Boosters]

So hey, there are some parts in the game that under perform and here are a few suggestions on how we could fix them.

Reliant:

The reliant is truly meh. With a vacuum TWR of 17,2 and a sea level TWR of 16, it falls behind most engines in the game. What's more, it doesn't even have a gimbal. For the Reliant to be worthwhile after the point it is your only rocket engine, I think it should have the TWR of the LFB KR-1x2, which is 30,769230769... and let's just round that down to 30 since this is a 1.25m engine. At its mass of 1.25 tons, it should then have a thrust of 375kN at vacuum. Sea level thrust is automatically calculated via Isp. So wait, why do I think the starting liquid fuel engine should have one of the best TWRs in the game!? Well, you see, it doesn't have a gimbal which puts it in a rather unique position. Its ISP is also less than that of the LFB KR-1x2, and I couldn't think of a better engine to compare this engine to. The booster doesn't have bottom attachment points, and the Reliant can't gimbal. They're both engines that don't fit any slots in your typical upper-middle-first stage engine configuration where weight, TWR, thrust and Isp scale with rhyme and reason. At 375kn vacuum thrust, the Reliant should be strong enough to be worthwhile in various situations, especially with a better TWR than the Vector. Overpowered? Probably not, low Isp and all.

One concern there may be is that it kind of does replace the Aerospike especially considering their sea level Isps aren't that different, but we'll get there.


Swivel:

This one is a bit tricky. Swivel is actually "usable", as in you go for this if you have a 1.25m stack. Sure, AV-R8 Winglet can make the Reliant just as good, but that's quite the expensive among other things like added drag, mass and not working at higher altitudes so that should be expected. I'd make it more like the Skipper actually. The Isp values actually confirm this already, with the Swivel having the same vacuum Isp but a 10 less surface Isp, which is fine by me. Skipper gets a TWR of 21,666666667 so once again rounding down for diameter balance reasons rather than how you should actually be rounding values, we get an ideal TWR of 21 for the Swivel. Which translates to a 315 kN vacuum thrust for the Swivel. I'm personally not very comfortable with how close that is to the reliant, but that is because the Swivel is more massive. Any ideas?

Aerospike:

The Aerospike is... weird. My version of Reliant definitely puts it to shame except as a high thrust vacuum engine, which is really a role the Aerospike doesn't feel like it should have. Its description says that its almost equally effective at all altitudes, but it has some of the largest Isp change between sea level and vacuum with the lack of a gimbal. So here's what I'd do with it; compare it to the Rhino. Rhino has roughly 22 for its TWR, a great gimbal range and 255-340 Isp. So here's where we do some rationalizing.
Rhino has a great gimbal range with poor surface to vacuum Isp but Aerospike is supposed to be the opposite. Quoting the trivia section for the aerospike engine at the KSP wiki: "An aerospike provides comparable performance to a De Laval nozzle in space, but at lower altitudes it can be 20-30% more efficient." 20% higher than the Rhino puts the lower end of Aerospike at 306, and lets round that up to 310 since we like neat numbers. 310-340 seems like a fair Isp range for a gimballess, bottom nodeless engine eh? Another thing is that the aerospike is supposed to be heavier yet it is the second lightest stack attacked 1.25m engine. Vector is rather nuts with mass for a 1.25m engine, so let's just make this the second highest at 2 tons. The end result is 440 kn for 2 tons and an Isp range of 310-340. Pretty formidable!

Kickback:

The best SRB in the game is rather wimpy. A gimbal would probably solve the issue though. Edited November 23, 2015 by More Boosters

[Temstar]

atmTWR30 would be extremely overpowered. Currently the highest atmTRW is Mammoth with 25.46. And that's an end game, highly expensive engine dedicated to lift huge stacks at lift off, to the point that it doesn't have a bottom node.

atmTWR30 means vacTWR would be even higher. If that's the case no one would use Poodle or Skipper or Mainsail, you just cluster the OP Reliant together into clusters instead.

[More Boosters]

[quote name='Temstar']atmTWR30 would be extremely overpowered. Currently the highest atmTRW is Mammoth with 25.46. And that's an end game, highly expensive engine dedicated to lift huge stacks at lift off, to the point that it doesn't have a bottom node.

atmTWR30 means vacTWR would be even higher. If that's the case no one would use Poodle or Skipper or Mainsail, you just cluster the OP Reliant together into clusters instead.[/QUOTE]

Vacuum TWR 30 duh. Then again, the LFB-1x2KR has a higher TWR than the Mammoth all around to begin with, and what use is a bottom node in a Mammoth to begin with? What would you place below it?

Highest ATM TWR is LFB-1X2KR with 28,718. Edited November 23, 2015 by More Boosters

[Red Iron Crown]

This discussion of stock engine balance has been moved to the Suggestions and Development Discussion subforum.

I would point out that an aerospike never beats a bell nozzle at that bell's optimized air pressure, the aerospike should not have the highest atmo Isp. Also, it has a bottom attachment node.

[More Boosters]

[quote name='Red Iron Crown']This discussion of stock engine balance has been moved to the Suggestions and Development Discussion subforum.

I would point out that an aerospike never beats a bell nozzle at that bell's optimized air pressure, the aerospike should not have the highest atmo Isp. Also, it has a bottom attachment node.[/QUOTE]

Yup, I just checked in game, apparently that changed in 1.0.5? Or earlier? Not sure, but I'll definitely edit that bit.

What Isp value would you recommend?

[Red Iron Crown]

The Isp values for it in stock now are pretty good IMO. Not the absolute best in vac or atmo, but close and not bad in either like the specialized bell nozzles are. It pretty well represents the aerospike's advantages.

[More Boosters]

[quote name='Red Iron Crown']The Isp values for it in stock now are pretty good IMO. Not the absolute best in vac or atmo, but close and not bad in either like the specialized bell nozzles are. It pretty well represents the aerospike's advantages.[/QUOTE]

But I thought it was counter intuitive that an engine that is advertised as relatively constant performance between atmo and vac to have one of the largest differences in atmo and vac Isp.

What do you think about the mass and TWR change suggestion then? Or on the other engines?

[SpaceplaneAddict]

I like the aerospike in its normal form. What would be nice, is a decent thrust engine with an OK ISP in vac, for use with moderate interplanetary travel. The nuke just doesn't cut it sometimes, with only 60kn of power

But yeah, the aeros like should have a moar constant ISP

[Red Iron Crown]

[quote name='More Boosters']But I thought it was counter intuitive that an engine that is advertised as relatively constant performance between atmo and vac to have one of the largest differences in atmo and vac Isp.[/quote]
The laws of physics would preclude that. Aerospikes are good but they're not magic, they still have to work against the atmospheric pressure. Think of it instead as a near-constant percentage of the theoretical maximum Isp for a given pressure and it will make more sense.

An engine with very similar vac and atmo Isps is one that's been optimized for atmo.

[quote]What do you think about the mass and TWR change suggestion then? Or on the other engines?[/QUOTE]
Honestly, I think they're becoming a bit OP to keep up with the OP Vector. But that's just my personal opinion, doesn't make it a bad idea necessarily. :)

[More Boosters]

[quote name='Red Iron Crown']The laws of physics would preclude that. Aerospikes are good but they're not magic, they still have to work against the atmospheric pressure. Think of it instead as a near-constant percentage of the theoretical maximum Isp for a given pressure and it will make more sense.

An engine with very similar vac and atmo Isps is one that's been optimized for atmo.[/QUOTE]

I guess it doesn't matter much anyway as the Aerospike all but reaches maximum Isp at the 25-30km altitude where you'd fire it anyway. I personally prefer a heavier aerospike with more thrust as attachment nodes matter more for spaceplannes.

[KerikBalm]

I second the idea for a heavier aerospike with more thrust.
Bump its mass back up to 1.5 tons (a 50% increase), and then bump its thrust up by 50%.

Aerospikes shouldn't be reserved for high altitude. If that was their role, then we'd really just want a more massive LV-909 with more thrust. - side note: not a bad idea, we lack high thrust vacuum optimized engines. We always get low thrust (for the part diameter) and low mass paired with the good vacuum Isp... with the KR-2L being the only exception... sort of... ite vacuum Isp is good, but not as good as the 909 or poodle... and its atmo Isp is bad, but not nearly as bad as the 909/poodle
where is my poodle with half the thrust of a mainsail (ie, what I want the skipper to be... make the skipper a smaller KR-2L), or my LV-909 with half the thrust of a LV-T30.

The point of an aerospike is that it is nearly optimal for all atmospheric pressures. If you don't use it until you're at nearly vacuum pressure, then don't bother with the aerospike design.

An aerospike should be good for a core stage engine in an asparagus staged vehicle, or the main engines of a rocket SSTO.

Lets take a simple asparagus launcher and then a transfer stage + payload on top.
The transfer stage (lets say for a munar flyby) is something like an LV-909... a lightweight engine optimized for vacuum operation.

Then there's the asparagus lifter.
The outer stages should be something like a LV-T30... de laval nozzles optimized for the lower atmospere of kerbin.
The outer asparagus stages are jettisoned before the craft gets very high.
The core stage/inner stages would be aerospikes... they start burning from 1 atm, and continue burning as the craft gets much higher. Indeed the core stage of an aspagus lifter burns from 1.0 atmospheres, to vacuum and orbital velocity.
The core of an asparagus lifter is exactly what you'd want an asparagus for.

As it is... while its TWR is decent, it only masses 1 ton, and for something that is best used at the bottom of stacks, it lacks in the Thrust:Node ratio. Edited November 23, 2015 by KerikBalm

[Nothalogh]

[quote name='More Boosters'][COLOR=#333333]what use is a bottom node in a Mammoth to begin with? What would you place below it?[/COLOR][/QUOTE]
A cluster of Mammoths?