Aerospikes are such good vacuum engines now

[Foxster]

Agreed. Looking at the description for the Aerospike, it would be very reasonable to assume that it's the best engine to use for getting off the surface of Eve. However, it doesn't have enough THRUST to lift enough fuel for it to be usable for that purpose, and it's ISP falls off too quickly.

Funny, cos its working fine for me...

[ajburges]

The biggest use I get from the Aerospike is Spaceplane SSTOs. From it's shape, I'd assume it's less draggy than the Swivel engines my Mk2 plane use until it is available. It is also a nice boost to dV. Rocket mode TWR does suffer a tad though.

My Duna expedition spaceplane (inspired by the Humblebee from "Duna Ore Bust") exclusively uses them for that nice Isp. The craft is light enough, I can get away only with 2 for the VTOL engines.

Do wish it made a better Atmospheric SSTO engine. Needs a big thrust boost to be practical for that. An atmospheric Isp boost would help on Eve to.

[luizopiloto]

Aerospike IS the best engine for Eve... :3

[Darnok]

Shhh or they will break them in next update!

[Red Iron Crown]

The biggest use I get from the Aerospike is Spaceplane SSTOs. From it's shape, I'd assume it's less draggy than the Swivel engines my Mk2 plane use until it is available. It is also a nice boost to dV. Rocket mode TWR does suffer a tad though.

How so? The aerospike has better TWR than the Swivel in any conditions.

[NathanKell]

The thing about aerospikes (well, altitude-compensating nozzles generally) is that they are not magic. You don't magically get nearly the same Isp at sea level and in space (let alone at 5atm and in space) no matter what. And I'd really rather KSP didn't break more laws of physics than it needs to.

An aerospike will, for the same cycle and chamber pressure:

1. Always be worse than a bell nozzle, at the bell nozzle's optimum ambient pressure.

2. Be better than most, but not all, bell nozzles in vacuum.

3. Be considerably better than a bell nozzle at a higher ambient pressure than the bell nozzle's optimum (doesn't have to worry about overexpansion), but is not magically better.

[luizopiloto]

Shhh or they will break them in next update!

Aerospikes is NOT the best Engine for Eve...

[selfish_meme]

The thing about aerospikes (well, altitude-compensating nozzles generally) is that they are not magic. You don't magically get nearly the same Isp at sea level and in space (let alone at 5atm and in space) no matter what. And I'd really rather KSP didn't break more laws of physics than it needs to.

An aerospike will, for the same cycle and chamber pressure:

1. Always be worse than a bell nozzle, at the bell nozzle's optimum ambient pressure.

2. Be better than most, but not all, bell nozzles in vacuum.

3. Be considerably better than a bell nozzle at a higher ambient pressure than the bell nozzle's optimum (doesn't have to worry about overexpansion), but is not magically better.

The only irl practical use for them so far has been experiments with spaceplanes, where the high mass was not so much of a hindrance. I assume this was because they perform better over a range of atmospheric pressures. I read that they don't perform well without the pressure of at least mach 3 plus speeds.

In game this would make sense if they were heavier and attained good maximum thrust at high speed/pressure which tailed off to their one atmosphere or slower performance level. So they would be good for SSTO's as the rocket stage (low drag), good for Eve takeoffs because of the pressure (also low drag), but not very good for landers where they would be heavy and going slow/be in a vacuum.

[Pecan]

Thanks guys, I never even knew this was a thing; just thought it was a name for a different-looking KSP model ^^.

https://en.wikipedia.org/wiki/Aerospike_engine

"The disadvantages of aerospikes seem to be extra weight for the spike, and increased cooling requirements due to the extra heated area. Furthermore, the larger cooled area can reduce performance below theoretical levels by reducing the pressure against the nozzle. Also, aerospikes work relatively poorly between Mach 1-3, where the airflow around the vehicle has reduced pressure, and this reduces the thrust."

So that's us told :-)

[Xyphos]

Aerospikes make good VTOL engines too, they fit nicely inside Mk2 cargo bays.

stick two aerospikes in a large bay, stack-attached to a cubic strut to avoid the wonky cargo bay colliders, rotate and translate to make it fit.

one aerospike constantly runs during VTOL operation and the other is toggled by action groups for RCS-like control.

place 3 or 4 VTOL bays on your ship and viola!

Edited July 28, 2015 by Xyphos

[annallia]

As to the stacking issue there is a mod for that.

At least if memory serves (I dropped Nova Punch from my mod list) Nova Punch's aerospikes have a bottom node.

[ajburges]

The thing about aerospikes (well, altitude-compensating nozzles generally) is that they are not magic. You don't magically get nearly the same Isp at sea level and in space (let alone at 5atm and in space) no matter what. And I'd really rather KSP didn't break more laws of physics than it needs to.

An aerospike will, for the same cycle and chamber pressure:

1. Always be worse than a bell nozzle, at the bell nozzle's optimum ambient pressure.

2. Be better than most, but not all, bell nozzles in vacuum.

3. Be considerably better than a bell nozzle at a higher ambient pressure than the bell nozzle's optimum (doesn't have to worry about overexpansion), but is not magically better.

Faithful Aerospike implementation would be useless in KSPs scaled down universe. The 3 prominent disadvantages of aerospikes are weight (and engines are already have worse TWR than IRL), increased heating (not modeled for whatever reason), and a performance dip at Mach 1-3 (which is a small band of Earth orbital velocity, but more than a third of of the speed you need to accumulate for Kerbin orbit. Scramjets should allow you to completely bypass this speed range).

The way pressure is accounted for with the fact the Mammoth has better Isp ASL and there 6 engines with better TWR ASL (including the Rino, a low pressure engine) really keeps the aerospike from being a good solution for many situations.

Currently here are the things going for the aerospike:

> Low weight (and good TWR, but 1.25 m in general has poor TWR when you add fuel)

> Good (but not best) vacuum Isp

> Best ASL Isp for a small engine (but TWR is a huge factor of ASL performance and 1.25 m engines don't shine when you add fuel)

> (presumably) low drag (has anyone verified)?

How so? The aerospike has better TWR than the Swivel in any conditions.

Better TWR but less thrust. my spaceplanes tend to be designed around an airframe, so connection nodes can't arbitrarily be added. Additionally dual mode space planes require less than unity anaerobic TWR so they spend even less of their mass budget on engines so any loss of thrust per engine has a minor if significant impact on vessel TWR.

Granted, every design I've replaced the Swivels with aerospikes on has performed better with the aerospikes. Not sure if that is because of the drag difference or if I'm over designing my planes. Once you get to orbit, any good orbital insertion engine has plenty of thrust (I actually have to throttle limit my Mk3 space planes for orbital maneuvers), so general performance is solely a factor of Isp.

Edited July 28, 2015 by ajburges

[Foxster]

Here's another way to get an aerospike to stack...

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[mikegarrison]

Here's another way to get an aerospike to stack...

I don't like this sort of clipping in general, but I really don't like it when it is done to bypass an intentional restriction on the part. If you are going to go to all that trouble, why not just mod the part and add a bottom node and fairing to it?

[Foxster]

If you are going to go to all that trouble, why not just mod the part and add a bottom node and fairing to it?

Because it's not then "stock". I do challenges and share craft with others and it will work for everyone this way.

[Guest]

What bothers me about Aerospike, is lack of engine itelf - only nozzle is visible.

Where is all other stuff?

I don't think space inside the spike itself is sufficient enough to fit the combustion chamber AND the turbopump AND all the piping.

[mikegarrison]

What bothers me about Aerospike, is lack of engine itelf - only nozzle is visible.

Where is all other stuff?

I don't think space inside the spike itself is sufficient enough to fit the combustion chamber AND the turbopump AND all the piping.

I guess it is like the jet engines in that regard. Obviously the intention was to make it a low-profile engine.

- - - Updated - - -

Because it's not then "stock". I do challenges and share craft with others and it will work for everyone this way.

Well, I don't think that conceptually your idea is really "stock" either, but I do see the implications if you share ship files.

[Captain Sierra]

Our aerospike is only about half of what actually is there (and this schematic is for a 12cm model rocket, gravity fed, so no turbopump).

[mikegarrison]

Nice cutaway; you can see how the spike forms the inner half of a virtual con-di nozzle.

[Korizan]

Actually Aerospike engines are pretty small comparatively.

The tests I know about was for the X-33 or VentureStar, they where testing out a linear Aerospike engine.

Here is a link for the test firing

and the WIKI https://en.wikipedia.org/wiki/Aerospike_engine

[hoojiwana]

What bothers me about Aerospike, is lack of engine itelf - only nozzle is visible.

Where is all other stuff?

I don't think space inside the spike itself is sufficient enough to fit the combustion chamber AND the turbopump AND all the piping.

Weren't they added with the Jet engines, that have the same problem? At least for the aerospike you can fit some of the parts inside it, like the combustion chamber is actually in a ring around the rim and the turbopump is probably squashed inside the spike itself somehow.

[KerikBalm]

How so? The aerospike has better TWR than the Swivel in any conditions.

He probably meant the TWR of the overall craft, as you have less thrust per node.

[mikegarrison]

Weren't they added with the Jet engines, that have the same problem? At least for the aerospike you can fit some of the parts inside it, like the combustion chamber is actually in a ring around the rim and the turbopump is probably squashed inside the spike itself somehow.

No, none of that stuff could be in the spike. All that will be in there is spike-cooling, fuel-preheating heat exchangers.

[Rufledt]

I've actually never used them in a career mode game, probably because (as was mentioned earlier) no node on the bottom so i couldn't put anything under it.