Any problems with the RAPIER engine yet?

[ouion]

Today,I build 3 spaceplanes with the rapier engine and none of them reach space. The problem is the plane stops at 5000-5600 M and then drop in attitude. Do any of you have this problem or it just me making mistakes ?

[Sof]

Probably you making mistakes seeing as 5000m isn't even that high to begin with.

Are you just flying straight up?

[Guest]

You may be stalling, or perhaps you don't have enough thrust-to-weight ratio. Try a less steep trajectory, or more engines.

[Liowen]

I think pictures of said craft showing when the problem is occurring, don't turn off the UI as that could help in determining the cause of the problem.

[FlamedSteak]

Although I'm a novice with SSTO's, the thing I've discovered with space planes is to climb at a 90 degree angle to about 10,000m. Then level off so your prograde marker is just above the horizon, then slowly climb up.

That being said, I wonder if this is the most effecient way to get into space with a RAPIER.

[Murph]

The current RAPIER is underpowered (sadly to the point of being useless junk, in my opinion), performing worse than turbojets combined with aerospikes. If you're replacing turbojets on an existing design with it, you may simply not have enough power for the ascent profile that worked ok with the jets.

I believe that the most efficient ascent profile is quite unlikely to involve a vertical climb, then level-ish at 10km suggested above. My approach usually is to aim for keeping my surface speed at approximately terminal velocity, or just above it. That usually means about a 30º nose above horizon climb from the runway. Don't level off for speed below at least 20,000m, as you'll be burning a lot of fuel to fight drag if you do that. You don't need any more than terminal velocity until you are above at least 20,000m. The changed behaviour for intake air in 0.23 probably means you can safely leave gaining speed to around 25,000m.

[Liowen]

Hmmm see I feel just the opposite Murph I feel they work as well as that combo, however it depends on the size of the craft in question. If it is a large heavy ship I doubt a RAPIER is going to help much even if you use a lot of them. In the case of my small SSTO I actually get to orbit easier, and with more fuel left over, than I did with the turbo jet/aerospike setup. I start off a bit more aggressive in my angle of attack, 45 degrees instead of 30. Once at around 12km I come down to 25 degrees and climb and gain speed. Once around 20ish km though I go to half throttle for the remainder of the flight. Is this the best way to fly? Most likely not but it works in my case. One thing with my craft though I have noticed is that it has a natural want to pitch up on its own slowly while in airbreathing mode (nothing extreme just 5 degrees at the most), and I take full advantage of that letting it go up slightly on its own as speed increases. Again I am novice as well, but my craft was built and flown pre .23 and I noticed a big improvement over the older version.

[Murph]

… I start off a bit more aggressive in my angle of attack, 45 degrees instead of 30. Once at around 12km I come down to 25 degrees and climb and gain speed. Once around 20ish km though I go to half throttle for the remainder of the flight. Is this the best way to fly? Most likely not but it works in my case. One thing with my craft though I have noticed is that it has a natural want to pitch up on its own slowly while in airbreathing mode (nothing extreme just 5 degrees at the most), and I take full advantage of that letting it go up slightly on its own as speed increases. Again I am novice as well, but my craft was built and flown pre .23 and I noticed a big improvement over the older version.

There is no single answer to the best ascent profile for space planes. Each plane has its own optimum profile, and pretty much every pilot will have a preferred approach that they feel works well. Your approach sounds reasonable enough, although I think I'd probably try stay at full throttle past 20km, probably to at least 25km with the 0.23 changes.

[Hodo]

The current RAPIER is underpowered (sadly to the point of being useless junk, in my opinion), performing worse than turbojets combined with aerospikes. If you're replacing turbojets on an existing design with it, you may simply not have enough power for the ascent profile that worked ok with the jets.

I believe that the most efficient ascent profile is quite unlikely to involve a vertical climb, then level-ish at 10km suggested above. My approach usually is to aim for keeping my surface speed at approximately terminal velocity, or just above it. That usually means about a 30º nose above horizon climb from the runway. Don't level off for speed below at least 20,000m, as you'll be burning a lot of fuel to fight drag if you do that. You don't need any more than terminal velocity until you are above at least 20,000m. The changed behaviour for intake air in 0.23 probably means you can safely leave gaining speed to around 25,000m.

It is anything BUT underpowered. If you think it is underpowered then you are using it wrong..

[Murph]

It is anything BUT underpowered. If you think it is underpowered then you are using it wrong..

Well, I spent a good while testing twin RAPIERs against twin turbojets + single aerospike. The RAPIER lost in every single test flight, over a wide range of profiles (trying to see if there was a profile that actually worked for it). The numbers for it don't lie, it's significantly less powerful and less efficient than the turbojet in atmospheric mode. That makes it impossible for it to beat the turbojet in the first phase of flight. It's overpowered in terms of thrust for the second phase of flight, but less efficient than the aerospike, so it ends up losing there on efficiency. The only raw stat that it wins on is overall weight, it's universally worse on all other stats that matter (the thrust in the second half of the ascent is basically irrelevant once you have sufficient, and it's way beyond what's needed there). The reduced weight just fails to compensate for the loss of ascent performance in the first half of the ascent.

If you're finding it better than turbojets + aerospike, perhaps the problem is that you are using them wrong, not getting the most out of them?

[Hodo]

Well, I spent a good while testing twin RAPIERs against twin turbojets + single aerospike. The RAPIER lost in every single test flight, over a wide range of profiles (trying to see if there was a profile that actually worked for it). The numbers for it don't lie, it's significantly less powerful and less efficient than the turbojet in atmospheric mode. That makes it impossible for it to beat the turbojet in the first phase of flight. It's overpowered in terms of thrust for the second phase of flight, but less efficient than the aerospike, so it ends up losing there on efficiency. The only raw stat that it wins on is overall weight, it's universally worse on all other stats that matter (the thrust in the second half of the ascent is basically irrelevant once you have sufficient, and it's way beyond what's needed there). The reduced weight just fails to compensate for the loss of ascent performance in the first half of the ascent.

If you're finding it better than turbojets + aerospike, perhaps the problem is that you are using them wrong, not getting the most out of them?

Ok... Lets do some math.

Aerospike = 1.5 tons

2 x Turbojet= 2.4 tons

total 3.9 tons

2 x RAPIER= 3.5 tons

Total 3.5 tons

So it already has a .4ton advantage in weight savings, not to mention it is one less part to tack on to a craft and balance. And if you need more than one RAPIER to get to space then your craft is to heavy.

I personally cant stand the aerospike, it is to heavy and has no thrust vectoring so is nearly useless for most of my applications. Sure the RAPIER doesn't have the ISP of the Aerospike but it is simpler to use, and is far more forgiving.

I have built a LOT of SSTOs, some with turbojets, aerospikes, LV-45T, SABREs, and RAPIERs. If it is in the B9, KSPX, or KSP engines I have probably tried to build a SSTO with it. I use SABREs most of the time due to parts count and looks it looks better. I will probably use the RAPIER the same way, mainly because it looks better, and parts count. But it is to me far better than any single combo in game for small SSTOs.

Case and point.

[Liowen]

I would also state that some use two more for a look they are going after, not just weight. I know mine could use one, but to me the craft looks odd with only one in its current setup (I really hate redesigning things that already work). It only weighs in at 15.5t, and the way the fuel drains it stays fairly well balanced. There is no right way for someone to play this game, if you feel that way you might have other issues other than an item in game. Heck I have seen some rockets on here I felt were over kill for what they were, yet I could see how they might consider that good for what they were wanting to do. Mostly what it comes down to is how you fly it really, it might not be working for just due to how you like to fly and that is fine. Just like with me I fly a certain way that I think is right. Is it right for everyone?? Absolutely not, but for my play style it is what works.

No one is forcing any player to use a certain item in this game, if you don't think it works for you don't use it. Likewise if it works use it to have fun. Of course there will be purist out there who claim "Anyone using a RAPIER in an SSTO shouldn't be playing" (yes there are people who believe this), but they should not detract people from having fun in the game. After all it is just a game

[arq]

I spent a little while messing with these yesterday and I was unimpressed, initially. As it stands, it takes a lot of these to get a plane off the ground and through the first part of ascent.

I still need to spend awhile longer working with RAPIERS before I can make a meaningful recommendation, but one initial solution would be to increase the 0m/s thrust coefficient from 0.5 to 0.6 or 0.7 to help with its poor low-altitude performance.

As a sidenote, I find the LV-T30 much better than the aerospike for SSTOs. At 25km, the atmosphere is only 0.7% that of sea level, meaning that ISP is ~370 for the T30. At this point, I find the TWR advantage of T30s to outweigh the slight ISP advantage of the aerospike. This becomes increasingly important if you are trying to go beyond LKO - hauling those heavy aerospikes is a burden.

[NoPanShabuShabu]

It may be underpowered to the people who want to build their SSTO spaceplanes in the traditional way, but if this is an SSTO spaceplane, then well...

<a href="http://imgur.com/S4coWLX"><img src="http://i.imgur.com/S4coWLX.png" title="Hosted by imgur.com"/></a>

[Murph]

As a sidenote, I find the LV-T30 much better than the aerospike for SSTOs. At 25km, the atmosphere is only 0.7% that of sea level, meaning that ISP is ~370 for the T30. At this point, I find the TWR advantage of T30s to outweigh the slight ISP advantage of the aerospike. This becomes increasingly important if you are trying to go beyond LKO - hauling those heavy aerospikes is a burden.

The T30 might well be better than the Aerospike for some cases. I spent a while comparing them on the Aeris 4A, and the Aerospike actually won out for me in terms of fuel remaining in orbit. In terms of practicality and aesthetics, the Aerospike beats the T30 every time on a plane like the Aeris. The relatively huge T30 hanging out the back just isn't remotely sensible for takeoff and landing on that plane, and I feel looks out of place/ugly on a small fighter-type plane. Going beyond LKO, sure, that's a different set of design criteria. Personally, I'm not a great believer in long distance SSTOs, it just doesn't seem to me like the most efficient way to explore further afield  better to keep them for delivering resources and crew to LKO, where they work well.

[NoPanShabuShabu]

It may be underpowered to the people who want to build their SSTO spaceplanes in the traditional way, but if this is an SSTO spaceplane, then well...

Edit: I don't know what I'm doing... This worked before.

Edited December 20, 2013 by NoPanShabuShabu

[Hodo]

It may be underpowered to the people who want to build their SSTO spaceplanes in the traditional way, but if this is an SSTO spaceplane, then well...

Edit: I don't know what I'm doing... This worked before.

Use this...

[Dispatcher]

It all depends on your design and your flight methods. It usually takes me about a week to work up a decent spaceplane. It took me about an hour after I tried the 0.23 update to build and fly a 3 engine RAPIER SSTO to orbit. I added the two modes to my engine chart; see my sig line.

[ouion]

Yesterday, I build a smaller version with a single RAPIER engine. I think mass has to do with this.

[cerberusti]

The first thing I did with the patch is start a sandbox game and try the RAPIER. A basic plane with a single engine, one FTL800, and one small jet fuel tank made orbit easily using a 45 degree angle until I was out of the atmosphere.

For larger craft more efficient engines are probably better.