So... what do you think of the RAPIER engines?

[regex]

I've heard people screaming that they're OP, and others yelling that they need to be buffed before they'll even consider trying them again.

Which tells me that they are probably spot on.

^This, pretty much.

[cerberusti]

The first thing I did was try the RAPIER in sandbox, I made orbit with a single engine and little problems, but not with as much fuel as the SSTO design I had spent a lot of time tweaking (with higher part count and required attention.)

It has its place, but is not the best for larger craft. I agree with the above that it is pretty much perfect balance.

[kyred]

When something as simple as this (practically a fuel tank with wings on it) can be an SSTO, I think the RAPIER is a little OP. Also, it can get up to 2500 Isp in atmo at the right altitude. It's hard to think of a situation where I wouldn't use the RAPIER as the first stage.

Edit: This one's even better. Made it to LKO w/o wings: http://i.imgur.com/bfmb59O.jpg (posting as link to save screen space)

Edited December 19, 2013 by kyred

[eskimo]

I've heard people screaming that they're OP, and others yelling that they need to be buffed before they'll even consider trying them again.

Which tells me that they are probably spot on.

Best quote on the thread so far.

[Liowen]

Some people have too much time on their hands if they have to build something to prove their point. I bet if I took a SRB and got it into orbit using the same trick it would be overpowered or any rocket engine, just have to make it lite enough. I think I know what the problem is, an SSTO is not complicated enough in some peoples eyes anymore. Here is a tip if you do not like it you do not HAVE to use it, since this is a single player game being overpowered is kind of irrelevant honestly. If you want a challenge make what you want with parts to make it difficult as you want. My SSTO I built before .23 came out to see if I could build one, I got it into orbit using turbo jets and an aero spike. On the same token I felt there should be an engine that could cover both bases, though be somewhat lacking, to reduce the weight of the craft. In fact the only mode to my SSTO other than engines was moving 2 fuel lines to feed the other direction, it still worked in both forms also.

[Stargate525]

Here is a tip if you do not like it you do not HAVE to use it, since this is a single player game being overpowered is kind of irrelevant honestly.

You were clearly not here this weekend. It's multiplayer now. Everything needs to be balanced.

[ComradeGoat]

The thing I've discovered with it, and what a lot of people seem to have figured out as well, is that the RAPIER makes very small SSTOs possible when they really weren't before. They seem to work best on Small to Medium craft, but the older methods seem to work best once you start going big.

The older methods still work better on smaller craft too. Started using a RAPIER when designing this thing:

And found that even with auto switching off, and the ascent micromanaged to eke out the last drops of altitude and speed from air breathing mode, it still drank nearly all my fuel by the time it make orbit. Then I switched back to the old reliable combo of turbojet and 2 48-7Ses and it was faster, flew higher, and reached orbit with around 1.5k m/s Dv left.

I think the killer app for the RAPIER is spaceplanes that use a NERVA as their main engine. Previously it was hard to get enough altitude and speed to carry you to orbit with the NERVA, so you'd typically need a couple of LV 24-77s or something to get you through the worst of the drag. The RAPIERs in rocket mode have some serious punch to them though.

There is still the problem of turning forces being generated as they start to starve themselves of air, before the switchover though, and my preliminary tests with a 1 NERVA + 2 RAPIER config suggested best results were obtained by turning auto swathing off.

Summary - changes to the intake air system mean that the old workhorse combo of Turbojet + 2 48-7S engines still rules supreme for most applications (including smaller craft - seriously, try it), but there are niche applications where the RAPIER is very useful.

[MKI]

Balanced, useful, and helps with the general idea of SSTO building by creating a transition engine that sits between the 2 current engine setups.

They fill the gray area where a plane is between using 48-7/nerva's and just straight Areospike engines.

Areo's are still effective for lower altitude switches, due to higher thrust and fuel efficiency.

Now the Nerva's can be used as the final engine with the rocket version of the RAPIER once at the right altitude.

The RAPIER can be considered OP because it allows certain SSTO planes to get to orbit, where they wouldn't be able to before, namely simple planes, where there are limited places to put engines. But Nerva's are still MORE effective with high altitude orbital insertions, and Areospikes are better for low altitude heavy handed burns to get to space.

All of this with a built in anti burn out capability which can make the ship consistent.

Really the Engine is fine, and doesn't need to be touched. The next update brings cost parts, to making SSTO's easier to build with 3 different engine setups is VERY VERY important IMO. Even if it makes designing and flying SSTO's less of a challenge overall.

[bsalis]

Don't have much experience with them so far. But judging from the comments they are not the be all and end all for SSTO Spaceplanes. However they are another great addition to the SSTO Spaceplane builder toolkit. Which is what I was expecting actually - great work Squad!

People also seem to talk of RAPIER vs Jet/Rocket combo as being mutually exclusive, when I think there's probably great ways to mix RAPIERS with other engines. Two of them and an LT-N would probably be a good combo. Mebe one LT-N, 2 RAPIER, 2 Turbojet for a larger craft.

Edited December 19, 2013 by bsalis

[Spatzimaus]

It's great... as long as you understand its limitations and build around them, just like any other part. For instance, here's the latest iteration of my favorite spaceplane, the Sleazy Weasel 6:

The previous generation, the 5c, was a 34-ton design with 3 turbojets, 4 radial hybrid ions from a mod (statistically nearly identical to two LV-Ns), two HOME radial aerospikes (110kN, 0.5 tons, limited vectoring), and the two ions on the wing pods (for travel to Laythe, as they provide a dV of ~5km/s). Replacing the center turbojet with a RAPIER allowed me to drop the two HOME engines, as its rocket mode was nearly identical to their effect. That saved me 0.45 tons, besides just making things easier to manage. Between that weight loss and the change to intakes, I managed to fly the gen6 version to Minmus and back with no refueling, which is just fantastic.

I wouldn't want to replace all three turbojets with RAPIERs, though; that'd add an extra 1.1 tons to my weight, without any real need for that much low-efficiency rocket power. And I think that's the problem people are running into; they're making all-RAPIER designs, when they should be mixing with regular turbojets for lower weight. Of course, it's hard to do that with less than 3 engines...

[Vlk]

Spatzimaus, exactly my idea (combining rapier with normal jets), but i still did not build a craft to try it out. Thanks for confirming that

[FenrirWolf]

I think the killer app for the RAPIER is spaceplanes that use a NERVA as their main engine. Previously it was hard to get enough altitude and speed to carry you to orbit with the NERVA, so you'd typically need a couple of LV 24-77s or something to get you through the worst of the drag. The RAPIERs in rocket mode have some serious punch to them though.

There is still the problem of turning forces being generated as they start to starve themselves of air, before the switchover though, and my preliminary tests with a 1 NERVA + 2 RAPIER config suggested best results were obtained by turning auto swathing off.

Hmm. I'm gonna have to try this on my first (and only, so far) SSTO. It uses 2 turbos and the NERVA. Great little plane, managed to get the thing from Kerbin, to Laythe, and back home without needing to refuel it.

But the thing's biggest fault is definitely the final burn to Kerbin orbit. I always spent way too long in the upper atmosphere getting myself high and fast enough for the NERVA to have sufficient thrust to complete the insertion. In retrospect I should have had a few of the small orange radial engines to fill that gap, but swapping out the turbos for RAPIERs might do the trick too.

[Pipcard]

Makes SSTO spaceplanes a lot easier.

Edited December 19, 2013 by Pipcard

[Andrew Hansen]

I love the RAPIER engine. The first thing I did when I started KSP 0.23 was made a RAPIER SSTO! I accidentally ended up taking it to the Mun....

[Col_Jessep]

I just took my old Hurricane II out for a spin. It was designed as a way to deliver small probes into LKO and I remember that it took around 50m/s to get into orbit. Now I'm down to 27:

I wonder if I can get into orbit on jets alone. Not bad for 72 units of liquid fuel, eh?

[antbin]

In the other thread on the RAPIER engine, Tidus Klein noticed that the AtmosphereCurve (air density vs. ISP) and VelocityCurve (speed vs. thrust) for the RAPIER and Turbo Jet are identical.

This means that, unlike the Basic / Turbo Jet, the thrust / ISP difference between the RAPIER and Turbojet is the same on the runway as it is at high altitude / speed. So if your craft can't climb to altitude with a turbojet, the RAPIER won't help you.

Too bad! Looking forward to a rebalancing when the new aerodynamic model comes in (fingers crossed!).

[Spatzimaus]

This means that, unlike the Basic / Turbo Jet, the thrust / ISP difference between the RAPIER and Turbojet is the same on the runway as it is at high altitude / speed. So if your craft can't climb to altitude with a turbojet, the RAPIER won't help you.

This is a good thing. If the RAPIER was even more capable at high altitudes than a turbojet then there'd be no reason to ever use the turbojet. If it was less capable, then it'd be shelved in favor of a turbojet+rocket system like we used to use. The RAPIER is a tool of convenience, not raw power; it's just nice having a jet that can boost you through that high-altitude window between jets and orbit, and that in a pinch can work as an emergency brake when landing on Mun or something. But it's not going to let you do anything that wasn't already possible before, it'll just let you do it with fewer parts.

[Eric S]

In the other thread on the RAPIER engine, Tidus Klein noticed that the AtmosphereCurve (air density vs. ISP) and VelocityCurve (speed vs. thrust) for the RAPIER and Turbo Jet are identical.

Actually, the VelocityCurve isn't the same, the RAPIER tops out at 2200 m/s, but the Turbojet tops out at 2400 m/s.

From the turbojet .cfg

atmosphereCurve
 	{
		key = 0 1200
		key = 0.3 2500
		key = 1 800
 	}
	velocityCurve
	{
		key = 0 0.5 0 0
		key = 1000 1 0 0
		key = 2000 0.5 0 0
		key = 2400 0 0 0
	}

From the Rapier .cfg

atmosphereCurve
 	{
		key = 0 1200
		key = 0.3 2500
		key = 1 800
 	}
	velocityCurve
	{
		key = 0 0.5 0 0
		key = 1000 1 0 0
		key = 2000 0.5 0 0
		key = 2200 0 0 0
	}

So identical atmosphereCurve, but one value different on the velocityCurve.

[kahlzun]

The engines are waaay OP. I just built a working SSTO on my first try with them.

Also slightly technologically dissonant: the kerbals are usually stuck around 70's/80's level technologies..

Edited December 19, 2013 by kahlzun

[Eric S]

The engines are waaay OP. I just built a working SSTO on my first try with them.

It's not the engine, it's the other changes, and those affect the turbojet engine as well. Spaceplanes across the board have gotten a whole lot easier in 0.23.

[Spatzimaus]

Spaceplanes across the board have gotten a whole lot easier in 0.23.

Exactly. Before you claim RAPIERs are overpowered, try making a non-RAPIER SSTO using a mix of turbojets and inefficient (not LV-N) rockets. You'll see that the RAPIER isn't any more capable; it's just simpler and a little more flexible. This is a good thing for new spaceplane designers, but it doesn't mean the RAPIER is horribly overpowered. That's why I said on the previous page that you're often better off mixing RAPIERs with regular turbojets on larger designs, because you simply don't need as much rocket thrust as it provides and the extra weight starts to add up.

[spectrhz]

It's amazing! It's not overpowered since it guzzles down fuel in rocket mode like crazy, but is so easy to make even your silliest plane designs into Ssto's! I also really like how it looks and sounds, I hope this means they may be putting in new sounds and flames for the other engines

[antbin]

This is a good thing. If the RAPIER was even more capable at high altitudes than a turbojet then there'd be no reason to ever use the turbojet. If it was less capable, then it'd be shelved in favor of a turbojet+rocket system like we used to use.

What I meant to say is that if it were at least *slightly different* than the turbojet, then there would be interesting design niches. What if the RAPIER had worse performance than the turbojet at mid altitudes but better performance at high altitudes? What if they nerfed the turbojet to lose thrust at 1,500 m/s?

It would be nice, as a designers, for there to be some 'crossover' speeds/altitudes where we could play with the benefits/costs of carrying multiple engine types around.

Sort of like what they did with the Basic Jet. It could go Basic Jet < Turbojet < RAPIER.

[Champ]

The engines are waaay OP. I just built a working SSTO on my first try with them.

Also slightly technologically dissonant: the kerbals are usually stuck around 70's/80's level technologies..

From wikipedia : first xenon ion engine in operation : Deep Space 1 in 1998...

[Hodo]

My thoughts on the RAPIER. I bit over powered, but a bit underwhelming at the same time. I like it because it finally is a SABRE engine that is stock. I don't like it because it feels to small, area wise not mass. I have been building working SSTOs for a while now, of my nearly 1000hours in KSP 90% of that has been building SSTO space planes, with SABREs or without SABREs. The RAPIER is the stock version of the SABRE for those who don't know.

I often felt the SABRE engine was a bit overpowered for getting things to orbit, but underpowered once in space. It burns WAY to much fuel to be useful for much outside of the Kerbin SOI.

On the positive side, the RAPIER is much lower profile so I can build more VTOL space planes but now with out using the B9 VS-1 and VA-1 VTOL engines.