Put an alternator on the RAPIER!

[Stoney3K]

Just this very thing, nuff said. When flying skywards with an SSTO which only has RAPIERs as main engines, you will run out of EC quick with no capability to recharge, leaving your ship completely steerless in the upper atmosphere. That's kind of silly, because every turbine engine in existence comes with an alternator for auxilliary power.

If you build an SSTO with Whiplashes and a Terrier you have unlimited ElectricCharge on the way up. Was there an intended game decision not to have an alternator on the RAPIER engine, or was it just an oversight?

[Alshain]

I think (and this is my guess) that it has more to do with not having an alternator when in space, like many of the engines such as the terrier.  Ideally it would have an alternator when in Air Breathing mode but I'm not sure the game currently supports such a thing, so it would require coding rather than a simple script change.

[FungusForge]

I might be wrong, but I swear I saw somewhere that the RAPIER doesn't have an alternator because of issues. Either @Alshain is right, or it was something a bit more on the broken end of things.

[jwbrase]

While I agree that pretty much every jet and liquid fuel engine should have an alternator, it isn't that hard to outfit a spaceplane with copious battery power, and once you're in space, solar panels will do.

[Blaarkies]

Does the RAPIER really have a turbine? It's Air Breathing mode sounds like pure rocket

[Stoney3K]

9 hours ago, FungusForge said:

I might be wrong, but I swear I saw somewhere that the RAPIER doesn't have an alternator because of issues. Either @Alshain is right, or it was something a bit more on the broken end of things.

This could very well be the case. The ModuleAlternator depends on the amount of engine thrust related to its maximum thrust to determine output, but the RAPIER has two modes and therefore it does not have a "predefined" maximum output.

It could be a related issue to when you build a craft with only RAPIERs and try to look up its stats in KER, it will only show zero Delta-V. So there may be an issue with detemining max. thrust there.

[FullMetalMachinist]

On 4/15/2016 at 0:36 AM, Blaarkies said:

Does the RAPIER really have a turbine? It's Air Breathing mode sounds like pure rocket

Regardless of what the engine sounds like in the game, I believe that the RAPIER is based on the SABRE engine, which does have a turbine. 

[GoSlash27]

1 hour ago, FullMetalMachinist said:

Regardless of what the engine sounds like in the game, I believe that the RAPIER is based on the SABRE engine, which does have a turbine. 

Does it have an alternator, though? I can't find a source that says it does.

Best,
-Slashy

[FullMetalMachinist]

14 minutes ago, GoSlash27 said:

Does it have an alternator, though? I can't find a source that says it does.

Best,
-Slashy

That I can't say, I was just speaking to the fact that because the RAPIER is based on the SABRE, that it makes that the RAPIER would have a turbine, which was the question.  Though taking a close look at what I can find about the SABRE, it looks awfully crowded in that engine. I don't imagine that they would make the space (or weight) allowances to put an alternator in there.

[GoSlash27]

Well, if it doesn't then @Stoney3K May just have to work around the limitation. I generally use surface mount solar panels and perhaps an add-on battery. One could also use a fuel cell.

Best,
-Slashy

[11of10]

Regarding Skylon, I think I read somewhere that it's supposed to be solely battery powered, with no internal power sources. That does sound strange tho, when the idea is rapid reusability.

[ratchet freak]

3 hours ago, 11of10 said:

Regarding Skylon, I think I read somewhere that it's supposed to be solely battery powered, with no internal power sources. That does sound strange tho, when the idea is rapid reusability.

It's pretty easy to swap out a battery.

 

[Stoney3K]

On 16-4-2016 at 5:05 PM, FullMetalMachinist said:

That I can't say, I was just speaking to the fact that because the RAPIER is based on the SABRE, that it makes that the RAPIER would have a turbine, which was the question.  Though taking a close look at what I can find about the SABRE, it looks awfully crowded in that engine. I don't imagine that they would make the space (or weight) allowances to put an alternator in there.

Unless there are some turbopumps in the SABRE as well, an alternator would only work in subsonic airbreathing mode, since an alternator needs something that turns to work  and ramjets/rockets don't generally have turny bits that can spin an alternator. Only turbojets or turbofans do.

"Rocket alternators" are powered by the turbopumps spinning, which would only be a viable scenario if the engine in question has turbopumps to begin with.

[Red Iron Crown]

SABRE is planned to use turbopumps for LHe, LH2 and LOX, as shown in the diagram here. Looks similar to a gas generator cycle rocket engine to a large degree.

[AeroGav]

On 15/04/2016 at 6:36 AM, Blaarkies said:

Does the RAPIER really have a turbine? It's Air Breathing mode sounds like pure rocket

The thing is nearly all rocket engines have turbines as well  - the turbopumps that put the fuel in the combustion chamber - that could in principle have an alternator attached.   In practice i'm not sure many real life rocket engines actually do that.   The space shuttle had fuel cells for electrical power running off their own, super-insulated tanks in the bottom of the cargo bay.  Hydraulic power came from a hydraulic pump powered by hydrazine.

Liquid fuel engines basically have 3 ways to get the fuel/oxidiser in -

1.  combustor / pre-burner providing hot exhaust to drive a power turbine that spins the turbopumps.  All lower stage, high thrust engines use this method, it's the only way to get fuel in fast enough, but it's a lot of extra complexity.

2.  expander cycle engine - liquid hydrogen is first pumped around the nozzle, cooling it, and the expansion of this now boiling LH2 spins the power turbine that drives the turbopump.   Simpler,  but fuel delivery rates are lower as are power.  Common in upper stage engines.  Terrier and NERV appear to use this method

3. pressure fed engines.      Fuel forced into combustion chamber by pressurization of the tank alone.  Low performance but no moving parts.  For when it absolutely positively has to work. eg. Lunar module engine.

1 & 2 have turbines you could run an alternator off.   

Is it not just a balance issue?  Hence the Aerospike & NERV can't gimbal,  RAPIER got no alternator etc?

[Hobbes Novakoff]

IIRC, the reason for the Rapier to have no alternator wasn't based in realism, but purely in gameplay balance. The advantages of having a single compact engine that worked in atmo and in space were counterbalanced by (comparatively) low stats as well as a requirement for other power sources, whether solar panels (which don't work in atmo aside from the tiny OX-STAT one), the PB-NUK (Heavy), or fuel cells (which use up, as you may have guessed, fuel.) 

[Stoney3K]

On 19-4-2016 at 10:16 PM, Hobbes Novakoff said:

IIRC, the reason for the Rapier to have no alternator wasn't based in realism, but purely in gameplay balance. The advantages of having a single compact engine that worked in atmo and in space were counterbalanced by (comparatively) low stats as well as a requirement for other power sources, whether solar panels (which don't work in atmo aside from the tiny OX-STAT one), the PB-NUK (Heavy), or fuel cells (which use up, as you may have guessed, fuel.) 

I can definitely see the balance decision in that. The point where electrical power on an SSTO is most necessary, is right at the point where you would close your intakes and switch to pure rocket mode. At that altitude and speed, your control surfaces become more and more useless and you need to rely on reaction wheels for control. You can't deploy solar panels at that point (only OX-STATs which cause a lot of drag and can heatsplode) so you're stuck with either heavy batteries and RTGs or fuel cells. Once in space, you can deploy solar panels to your heart's content.

The issue becomes most apparent when keeping SAS on since SAS positively guzzles electrical power from the torque wheels, and there is no way to limit the amount of action SAS has on the craft. In most of my flights, my batteries run out halfway on the way up because SAS drained everything even though it only has to do a small amount of control to work.

You can offset that with RCS, but that means squandering a lot of Monopropellant. The over-zealous SAS action is what causes the large EC consumption in the first place.

[Wyzard]

I don't think I've ever had a problem with SSTOs running out of power during ascent.  The one I use most often — a 49-ton, 6-person Mk2 plane with four RAPIERs and an LV-N — has 1400 EC total, and the lowest it gets during flight is about 1350, just before I turn on the LV-N at 20km.  How many reaction wheels are you using?  I just have one, in a cargo bay near the middle of the plane.

[Darth Lazarus]

if i discover, that i need more EC and the engines are not generating EC ... then i add batteries, RTG's or solarpanels to my design. (don't forget that surface attachable bats are physicles, no additional weight !)

besides of potential problems just within the game and coding, i think it's a balance feature. it would be to easy if every engine has the same "toys"

[Hobbes Novakoff]

16 hours ago, Darth Lazarus said:

if i discover, that i need more EC and the engines are not generating EC ... then i add batteries, RTG's or solarpanels to my design. (don't forget that surface attachable bats are physicles, no additional weight !)

Physicsless parts aren't simulated, but they do add weight/drag to their parent. No drag if you put them in a cargo bay though.