Kille the Plug-nozzle and replace with a proper aerospike engine!

[Esme]

From the thread about removing the nose-cone on Mk1 and Mk 2 cockpits

Originally Posted by sal_vager

The current Mk1 and Mk2 inline cockpits, the Aerospike, the Mammoth, they all have this build restriction of having to be the end of a vessel, if you want to use these parts you have to take that into consideration...

(end quote)

Sal_vager, KSP does NOT have an aerospike engine. What it has is a plug-nozzle engine (ie: has a physical long, pointy bit in the middle). A selection of aerospike engines is something I'd love to see in KSP.

For those that aren't aware of the difference, the aerospike engine takes the idea of the plug-nozzle engine, but replaces the physical cone with a much-truncated one and instead uses exhaust gases from turbopumps or suchlike released in the centre to provide the same effect.

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

and http://www.aerospaceweb.org/design/a...erospike.shtml

Given that the actual length of such engines is much the same as conventional bell-nozzle engines, there's no reason outside of gameplay considerations that either toroidal plug-nozzle or aerospike engines shouldn't allow attachment of a decoupler so that they can be used on second/third stages etc. Now, personally, I would like to see aerospike (NOT plug-nozzle, please!) engines at all 3 standard sizes, and I don't mind if, for game considerations there are some limitations on aerospike engines, like making them non-steerable, or non-stackable or even both. Fell free to put them high up teh tech-tree too, if you must. But just get rid of that awful plug-nozzle thing, please!

Put another way, the cone I want to get shot of is at the other end of the ship!

[Red Iron Crown]

Better tell NASA.

However, you'll be pleased to hear that the model for the aerospike is changing in 1.0.5 to one with a truncated cone, which also has a lower attachment node. You can see a teaser of the new model (and other new and reworked parts for 1.0.5) here: http://imgur.com/a/NkzMp

No word on other sizes of aerospike, though.

[sal_vager]

Also it's called an aerospike in the game, and I didn't name it, so correcting me gets you absolutely nowhere

Also...

Several versions of the design exist, differentiated by their shapes. In the toroidal aerospike the spike is bowl-shaped with the exhaust exiting in a ring around the outer rim. In theory this requires an infinitely long spike for best efficiency, but by blowing a small amount of gas out of the center of a shorter truncated spike, something similar can be achieved.

The Toroidal "Aerospike" Rocket is a liquid fuel engine with the unique feature of being almost the most efficient at any atmospheric pressure.

Enjoy your nomenclature!

[NathanKell]

Huh. My understanding was that aerospike referred to the entire class of altitude-compensating nozzles which use either e a physical or created-by-exhaust-pressure spike down the center (toroidal) or linearly (linear) to form the inner half of a notional nozzle and thus keep exhaust exit pressure near ambient.

Interestingly, it appears that 'plug nozzle' can refer to two different systems: the aerospike, above, where the unmoving centra spike or inverted-trench is the plug, or a movable plug like garden hoses have (an alternate method of altitude compensation, *not* an aerospike, because it's doing the compensation entirely by geometry, not using the air as well).

[CaptainTurbomuffin]

My toughts were written here.

[Esme]

What is looking wrong to untrained eye is the model: there is a nozzle, but where is engine itself? Same for turbines.

WildLynx, the same could be said of conventional bell-nozzle engines in KSP - there's a mess of turbopumps and whatnot shifting fuel around and turning the thing on and off on demand, but that's hidden from view inside the ship. So the model is fine, for a plug-nozzle engine, bearing in mind that it's essentially an inside-out bell nozzle. In practice, if we're talking about toroidal plug-nozzle engines, the ring part consists of multiple small engines arranged in a ring, which can be independently throttled or turned on and off (or turned on and off in groups), to enable steering. I've tried seeing if I can achieve something akin to a Pegasus/Ithacus design ( see http://www.astronautix.com/lvs/pegvtovl.htm ) by placing a lot of small thruster around the base of a big orange tank (and even adding another small one dead centre underneath), but unsurprisingly the limitations of the physics engine don't quite give the desired result :-} I'd also add that despite my annoyance over what I see as incorrect nomenclature of the plug-nozzle engine currently in KSP, I DO realise that that's down to me being a bit OCD about it aided and abetted by my enthusiasm for Pegasus-type SSTOs. Even if Squad did absolutely nothing further about aerospike/plug nozzle engines in the game, I'd still be a very happy bunny with regard to KSP, it is SUCH an excellent game. This just happens to be my 'one thing' I'd like to see better/improved, and let's face it, SQUAD aren't ever going to be able to make everybody perfectly happy, are they? :-} - - - Updated - - -

@NthanKell - nope, an aerospike is a variation on a plug-nozzle that does away with most of teh plug in favour of a stream of gas to get the same effect as the plug aerodynamically, hence the term aerospike.

@Sal_vager - pardon me, m'dear, but reading that post in the other thread about nosecones simply brought to mind my irritation about aerospikes in KSP (which Iron Crown has kindly pointed out to me is to be improved upon), so I started this thread. If this wasn't the right thing to do to bring the matter up, please let me know what is, I'm all for doing things properly. And I wasn't meaning to have a go at you personally! :-)

(sorry if HTML tags are showing, but I'm having problems with text formatting here again. Wish I could remember how I got over it last time..)

Edited October 22, 2015 by Esme

[nothingSpecial]

I really wouldn't be against Mk2 linear aerospike and maybe even 2.5m-sized toroidal one.

Also I love that first three responds are so colourful, but if NathanKell were the first, they'd be in RGB pattern.

[Red Iron Crown]

I think you might be using an older definition of aerospike, Esme. From wiki:

"The terminology in the literature surrounding this subject is somewhat confusedâ€â€the term aerospike was originally used for a truncated plug nozzle with a very rough conical taper and some gas injection, forming an "air spike" to help make up for the absence of the plug tail. However, frequently, a full-length plug nozzle is now called an aerospike."

It sounds like the precise nature of the term has gotten a bit blurry. It's a fairly academic distinction though, as the most important property of the aerospike, altitude compensation, is modeled pretty well in the game. The aesthetic issue of precise nozzle shape is a bit less important IMO, but it looks like even that is being improved (though in the pics it looks like a simple truncated spike with no center outlet).

[cantab]

WildLynx, the same could be said of conventional bell-nozzle engines in KSP - there's a mess of turbopumps and whatnot shifting fuel around and turning the thing on and off on demand, but that's hidden from view inside the ship.

Except that on a lot of the engines it's not - there's the much-maligned "tankbutt", then a boxy section that we can imagine has the combustion chamber and turbopumps, and then the nozzle. The aerospike doesn't obviously have that, and while chances are the machinery would be in a casing flush with the rest of the rocket, perhaps that casing should be part of the aerospike model. It's a bigger problem for the new Shuttle engine, which really does look like a nozzle stuck on the ship with no engine.

As for the shape, well professional sources call it an aerospike

http://web.csulb.edu/colleges/coe/ae/rockets/aerospike/ft-1/flight-1.htm

http://www.dfrc.nasa.gov/Gallery/Photo/Aerospike_Rocket/HTML/EC04-0113-146.html

[Kegereneku]

Maybe we can agree that with the new aerodynamic model, an Aerospike should in fact maintain Thrust at any altitude whereas classical bell are optimized for more specific altitude.

This is to me the most critical point. The Aerospike must become the engine of choice for all Single-Stage vehicle.

[sal_vager]

Maybe we can agree that with the new aerodynamic model, an Aerospike should in fact maintain Thrust at any altitude whereas classical bell are optimized for more specific altitude.

This is to me the most critical point. The Aerospike must become the engine of choice for all Single-Stage vehicle.

Sorry no, aerospikes simply do not maintain thrust at any altitude, they are affected by changes in air pressure just as with any other rocket engine.

This argument just highlights again a misunderstanding and lack of knowledge of what aerospike nozzles of any kind are capable of, their strength lies in their being less effected by changes in pressure, but no engine is immune.

[Red Iron Crown]

From a gameplay perspective as well, I would not like the aerospike to be so OP that it's the best choice in almost every situation (again).

[BudgetHedgehog]

In theory this requires an infinitely long spike for best efficiency, but by blowing a small amount of gas out of the center of a shorter truncated spike, something similar can be achieved.

To me, this is the crux of the issue.

I mean, the engine has to end somewhen, and I don't know if OP looked at the requirements for a plug nozzle to be a plug nozzle (or even read the the words 'plug' and 'nozzle'), but there would have to be, surprise surprise, a plug in the nozzle. The aerospike has no plug. Compare the following images, the first, an aerospike, the second, a plug-nozzle:

Now, they do look similar, I will admit that, but a plug nozzle compensates altitude changes by moving the plug (like how you change the hose thing for straight vs spray flow), the aerospike doesn't as the different air pressures change the exhaust automatically.

The game 'spike does not move, therefore it is an aerospike. Yes, it has a truncated end, but like I said, it has to end somewhen, all 'spikes do.

Regarding the attachment node on the bottom, am I the only one who sees the engine fairings as interstages which support the weight rather than attaching directly to the engine? Is it honestly impossible to build a tube around a real life aerospike that doesn't touch it, but attaches to a supporting structure above it (say, a fuel tank) and that you attach more stuff to it below? Get a bottle cap, pretend it's an engine, stick it to the bottom of a cup. Get a toilet roll holder, put it on the bottom of the cup as well. Stick stuff to the toilet roll holder. Now tell me an aerospike can't have stuff attached below it.

[NathanKell]

It's wikipedia, but:

Confusingly, the term "plug nozzle" may also be used to refer to an entirely different class of engine nozzles, the aerospikes. In theory the aerospike should look roughly like a lance. with a wide base and long tapering forebody. However, the "spike" portion can be cut off with only minor effects on performance, leaving just the base section. This looks very similar to a common drain plug or bung, and leads to widespread use of the term "plug nozzle" for this design as well.

[BudgetHedgehog]

So we're all arguing over semantics. Is it a plug-nozzle because it looks like one/is it an aerospike because the cone doesn't move...

Semantics says "Aerospike" is a cooler-looking word than "plug-nozzle". 'Spike wins

^{EDIT: aerospike, aerospike... aerospike.. semantic satiation strikes again!}

Edited October 23, 2015 by ObsessedWithKSP

[cantab]

Performance-wise what I'd expect for both realism and gameplay reasons is that at sea level it's not quite as good as the best atmo engines, while in vacuum it's not quite as good as the best vacuum engines. And go figure, that's pretty much what Squad have done! You can argue for minor tweaks but the basic idea is right.

[NathanKell]

Shocking, right?

[Kegereneku]

Sorry no, aerospikes simply do not maintain thrust at any altitude, they are affected by changes in air pressure just as with any other rocket engine.

This argument just highlights again a misunderstanding and lack of knowledge of what aerospike nozzles of any kind are capable of, their strength lies in their being less effected by changes in pressure, but no engine is immune.

I'm also sorry, but that's nitpicking.

Aerospike are best at maintaining thrust over through their resistance to pressure change, which in term of gameplay basically meant the very same as being able to maintaining thrust at (any)various altitude.

I do not have right now a working KSP install to check out the newest value, but as long as the Aerospike do not have the advantage over other engine to maintain the thrust BETTER at different pressure, then its intrinsic quality are not properly taken into account.

And so, maybe the problem isn't the Aerospike but how all other engines were originally balanced with static thrust (as an consequences of the old aerodynamic system) and the Aerospike to not be utterly superior under the old unrealistic rules.

I understand that SQUAD can't simply rework entirely the balance without making the forum burst into an infernal rage, but at least we can search where the real problem is.

The Aerospike isn't simply an upgraded engine, it is the one engine to rules them all ...... as far as varying pressure is concerned. It's non-stackable nature and low TWR is enough to balance it.

That's all I have to say on this.

[Red Iron Crown]

I think you're misunderstanding the nature of an aerospike (or other altitude-compensating design). The goal is not to keep thrust about the same throughout the range of atmospheric pressure; this is already easily done with a bell nozzle optimized for high atmospheric pressure. Instead, the goal is to give up little specific impulse at differing atmospheric pressures compared to nozzles optimized for those pressures. So it will have close to the same efficiency at sea level as the best sea-level bell nozzles, while simultaneously having close to the same vacuum efficiency as the best vacuum bell nozzles. This is both in real life and in KSP where aerospikes are among the highest Isp chemical engines in all atmospheric conditions. It's a good place for them to be, both realism-wise and gameplay-wise.

[nothingSpecial]

I will put it simplier:

Mainsail is awesome at launch at KSC. Poodle is awful at launch at KSC. Aerospike is awesome at launch at KSC (a little bit worse than Mainsail).

Mainsail is okay in vacuum. Poodle is awesome in vacuum. Aerospike is awesome in vacuum (a little bit worse than Poodle).

Mainsail is kinda okay at launch at Eve. Poodle is useless at launch at Eve. Aerospike is awesome and unmatched at launch at Eve.

And that's how aerospike should be in reality.

[CaptainTurbomuffin]

I will put it simplier:

Mainsail is awesome at launch at KSC. Poodle is awful at launch at KSC. Aerospike is awesome at launch at KSC (a little bit worse than Mainsail).

Mainsail is okay in vacuum. Poodle is awesome in vacuum. Aerospike is awesome in vacuum (a little bit worse than Poodle).

Mainsail is kinda okay at launch at Eve. Poodle is useless at launch at Eve. Aerospike is awesome and unmatched at launch at Eve.

And that's how aerospike should be in reality.

That's great, but how about TWR and thrust? Aerospikes should have high TWR. A brilliant suggestion of mine was due to its pointy shape, make it have minimal drag in atmo (good for spaceplanes and EVE). But, if they also had high thrust (and, due to the high TWR, even higher mass) , they would became perfect SSTO-spaceplane rocket-stage engines again.

[nothingSpecial]

It give some advantages in thrust section, but wiki says that not in every situation

Also, aerospikes work relatively poorly between Mach 1-3, where the airflow around the vehicle has reduced pressure, and this reduces the thrust.

And of course it's not "same thrust in every pressure", that'd be nonsense.

If I understand it correctly, that should be decent thrust in high atmo and good in vacuum:

The XRS-2200 produces 204,420 lbf (909,300 N) thrust with an I_sp of 339 seconds at sea level, and 266,230 lbf (1,184,300 N) thrust with an I_sp of 436.5 seconds in a vacuum

I'm gonna try find some real life comparison tables.

[Kegereneku]

I think you're misunderstanding the nature of an aerospike (or other altitude-compensating design). The goal is not to keep thrust about the same throughout the range of atmospheric pressure; this is already easily done with a bell nozzle optimized for high atmospheric pressure. Instead, the goal is to give up little specific impulse at differing atmospheric pressures compared to nozzles optimized for those pressures. So it will have close to the same efficiency at sea level as the best sea-level bell nozzles, while simultaneously having close to the same vacuum efficiency as the best vacuum bell nozzles. This is both in real life and in KSP where aerospikes are among the highest Isp chemical engines in all atmospheric conditions. It's a good place for them to be, both realism-wise and gameplay-wise.

I'm not misunderstanding really, having a Specific Impulse as high as possible is so obvious that it is meaningless to mention, you wouldn't even bother to compare a classic Bell nozzle to an aerospike if it didn't have any use.

In terms of game-design the Isp would be the specs you change to balance the Aerospike, after making its dynamic correct toward other engines.

What you want to compare is whether you can use one aerospike for an atmospheric ascent rather than 2/3 specialized engine. But for that the other engine must not act like Aerospike themselves.

NothingSpecial above explained it simply.

[Red Iron Crown]

I'm not misunderstanding really, having a Specific Impulse as high as possible is so obvious that it is meaningless to mention, you wouldn't even bother to compare a classic Bell nozzle to an aerospike if it didn't have any use.

In terms of game-design the Isp would be the specs you change to balance the Aerospike, after making its dynamic correct toward other engines.

What you want to compare is whether you can use one aerospike for an atmospheric ascent rather than 2/3 specialized engine. But for that the other engine must not act like Aerospike themselves.

That is literally how aerospikes are balanced now. What are you suggesting exactly? Please be specific about what stats you'd change.

NothingSpecial above explained it simply.

NothingSpecial said the same thing I did, just with specific example engines.

[Kegereneku]

Then there's no more reason to pick on what I said about "maintaining thrust" (which is as correct as "not loosing thrust").

It's been a while since I last played, but I remember the Aerospike as not particularly different/efficient in comparison to other engine, at least not enough to use them for a light SSTO/reusable SSTO. Doesn't help that there is only one size available and that engine-clusters lose in efficiency. You also have to balance them/balance the jet-engine to not overshadow it on Kerbin.