Rockomax mainsail and poodle

[Temstar]

Unlike their 0.16 incarnations, 0.17 renamed and buffed the performance of the two big engines. But still, they seem rather worthless to me:

Mainsail

280s atm Isp

330s vac Isp

TWR 25.49

Poodle

270s atm Isp

390s vac Isp

TWR 8.97

Compared to the small engines:

LV-T30

320s atm Isp

370s vac Isp

TWR 17.54

LV-T45

320s atm Isp

370s vac Isp

TWR 13.60

Aerospike

390s atm Isp

390s vac Isp

TWR 25.49

LV-909

300s atm Isp

390s vac Isp

TWR 10.20

First let's start with the poodle. Obviously with it's terrible TWR and excellent vac Isp it's intended to be used exclusively as orbital manoeuvring engine for spacecrafts. But why would you use it? Its little brother LV-909 has the exact same Isp performance in vacuum yet with better TWR. In fact if you cluster 5 LV-909 together you get an engine cluster with exact same mass and vac Isp as one single Poodle yet with 30N higher thrust. The only thing Poodle has against this 5 engine cluster is a bigger gimbal range, but are you really going to pay that kind of performance penalty for gimbal range on a spacecraft already with plenty of steering thanks to the command pod reaction wheel?

But 5 LV-909 is going to be a bit unwieldy to install. But what if you replace that poodle with a LV-T30? You'll get:

1.25kg less mass for spacecraft (this is pretty big amount when you consider that's weight saved at the very tip of the rocket)

5N less max thrust

20s worse vac Isp

no gimbling

The way I figure, most small spacecraft don't need a gimbling engine since command pod reaction wheel provide plenty of steering. 5N of thrust is negligible and you're not firing the two engines long enough to have that 20s Isp offset that massive difference in weight. If you are actually going to fire engines in space and use up that much fuel you're probably better off with nuclear engines. So if the poodle can't beat two different combinations of engines in its role of spacecraft propulsion then what's the point of it?

Now the mainsail, it has terrible atm Isp but excellent TWR, making it good for first stage engine to lift heavy lifters off the ground. But still, Aerospike has a TRW just as good yet with much better Isp, both in atmosphere and at lift off. A cluster of 6 Aerospike provides the exact same thrust as a mailsail yet uses much less fuel at all stages of flight. The only advantage of mainsail to Aerospike cluster is gimbling which can easily fixed by adding winglets/canards to the Aerospike cluster powered rocket. Alternatively the Aerospike cluster can be built by mixing in a few LV-T45, trading Isp and TWR for some steering. A mainsail core engine is terribly fuel inefficent if you keep it burning all the way from ground to orbit with it's low Isp and heavy weight, where as a cluster can shed outer Aerospikes and keep the center LV-T45s as it ascends and trade the now unneeded TWR for less deadweight. This is aside from the point that mainsail have to compete with SRBs (which have even higher TWR) for the role of liftoff engines.

So with efficiency in mind, is there any point in using the two big engines?

Edited October 3, 2012 by Temstar

[bsalis]

What is this Poodle you speak of?

Anyhow, my 2c.

Engine choice depends on what your trying to achieve. Large numbers of small efficient engines may be harder than more thrusty but lower efficiency engines with added fuel to compensate.

As for engine balance in general. Remember that there are no price tags at the moment. Any clearly superior part in the game will probably just cost more, and not be available until you work your way up a tech tree.

[Markus Reese]

I love the large engine changes. Gets the thrust to lift heavier craft without a massive parts count lagging everything out!

[AmpsterMan]

I agree with a lot of the points the OP made. I find that my latest rocket doesn't use 2M engines at all. Still, I think the SOLE advantage you get for the larger engines is that you get a higher performance per part. I.E. 6 Aerospikes = 1 mainsail. Therefore, what cost you 6 parts before only cost one now, increasing your machine's performance. Furthermore, if you add the $ values, larger parts tend to give you more bang for your buck.

[EndlessWaves]

I love the large engine changes. Gets the thrust to lift heavier craft without a massive parts count lagging everything out!

Except that it needs more fuel tanks which means the advantage is only for shorter burns.

I wouldn't rule it out completely but the situations where you need a brief period of high thrust seem limited.

The poodle is difficult to see a use for unless the extra gimbaling is really good but I've not tried it.

Edited October 3, 2012 by EndlessWaves

[AmpsterMan]

I like to use the poodle as a lander stage. On tylo, where there is high gravity but no atmosphere, the poodle is very useful. Also, something that can't be unaccounted for is the fact that the higher TWR of the poodle means less delta-v is "wasted".

I think a second round of balancing is needed for out however, a higher ISP or less weight is in order.

[EndlessWaves]

I like to use the poodle as a lander stage. On tylo, where there is high gravity but no atmosphere, the poodle is very useful. Also, something that can't be unaccounted for is the fact that the higher TWR of the poodle means less delta-v is "wasted".

The poodle has the lowest TWR, it's the heaviest engine for the thrust it provides so it wastes more DeltaV then any other.

[AmpsterMan]

The poodle has the lowest TWR, it's the heaviest engine for the thrust it provides so it wastes more DeltaV then any other.

You' re right about that, which is why I think either the isp should be higher. What I meant to say in my previous post is that there is more wiggle room for error so there are less chances for one to brake too soon when landing.

I dunno if I'm just grasping for the wind here though XD

[Ziff]

You are making a direct comparison between engines, which is useless because the engines are used to move mass. Let's compare it using ship weights.

Let's say we are landing on the Mun in a small (15tn) craft (loaded with fuel/pod/single engine only).

T30

T:W: 9.27

Delta-V: 2992

T45

T:W: 8.47

Delta-V: 2912

Poodle

T:W: 8.72

Delta-V: 2777

The T30 has the advantage in both categories. And the T45 over the Poodle, because it has a higher delta-v (and we certainly have plenty of T:W already)

In an 85tn craft (remember, just fuel/pod/single engine only) landing on the Mun.

T30

T:W: 1.53

Delta-V: 6553

T45

T:W: 1.42

Delta-V: 6483

Poodle

T:W: 1.54

Delta-V: 6622

In this case it's clear that the Poodle has the advantage in both categories. The lower engine weight of the LV-T Series of engines doesn't make up for their lower ISP once you reach a certain weight. Every engine has an advantage in a specific situation. The advantage of the Mainsail is the gimbal and thrust. The 7 LV-T30's it would take to almost equal the thrust would have 4 more mass, there is a balance you have to find. I typically only use 1 of these engines on my heavy lifting craft where the large gimbal engine is needed for control, but I supplement that with higher ISP non gimbaling engines in the asparagus stages, and I jettison it before reaching orbit.

And here's 2 things to consider.

1. # of parts. Clusters of engines mean a lot more parts. And when your ship weighs 500tns+, those additional clusters of parts can slow down an older computer.

2. Price. Yeah, that's right. One of these updates will bring a campaign mode (the option is already on the menu) and you will have to actually spend kerbalbucks on these things. Currently 1 Mainsail costs the same as 1 Aerospike. This is something we are going to have to take into account when campaign mode comes along, and when it does, if the prices are what they are now, there is no way you will slap 6 Aerospikes on instead of a mainsail.

Edited October 3, 2012 by Ziff

[draeath]

There's no reason you can't use fuel transfer pipes to feed multiple engines from one tank.

[Kosmo-not]

The C7 engines are terribly unbalanced compared to the regular rocket engines (A jet engine being able to lift a rocket?! You gotta be kidding me.). They were meant to be used on space planes.

That said, I don't use C7 parts on my rockets (except for some of the aesthetic parts).

I'm backing up Ziff on that there's a time and place for all of the rocket engines.

The mainsail is great to have on your launch stage. You would need to use 7 other engines to make up for the thrust this baby puts out. Thus, it saves space on your rocket and makes it look a lot cleaner.

The NERVA, with its godly Isp, can be beaten in certain situations. I don't use it on any of my return craft for the 1m capsule.

I think the aerospike engine could be better balanced by cutting its thrust in half.

[AmpsterMan]

-snip-

You basically explained what I was trying to say with much more eloquent rhetoric and the ever so important maths. I find that each part has it's own place currently how they are, with maybe boosting the poodle a little more.

As fat as the aerospike goes, it really IS that op. I think their main disadvantages of non-gimbal and non-stackable really balance them out fairly well right now.

[Sean Mirrsen]

I think the aerospike engine could be better balanced by cutting its thrust in half.

The Aerospike is, quite simply, a superior engine type. Smaller and more efficient than the typical bell nozzles. Its main balancing points should be cost (once that matters), mass (it should be heavier than the LV-T30's), and heat generation (shouldn't survive in massed clusters). In other words, it would be a cutting-edge engine that you only really use one or two of. The Mainsail may be less efficient, at low altitudes especially, but it would be much cheaper, slightly lighter for the thrust generated, and would not create a cooling nightmare, once the proper logistics of heat management are implemented.

Also, we need linear aerospikes.

[Felsmak]

My designs actually use the Poodle for the interplanetary transfer stage. I was surprised to see how well it worked.

[Moach]

well, one must account for the added "complexity mass" from a multi-engine setup...

while if having one large beast of a burner doesn't seem top add up against many itty bitty ones, remember that you're gonna need adaptors and other structural bits to get the cluster mounted, and more parts equal more wobble - which you'll have to beef up the airframe with struts to eliminate

those adaptors and struts have their own mass, and drag - more parts will inevitably mean more drag losses than with a simpler design...

i often find sleeker means more likely to succeed (or more liekly to get a longer run before the inevitable occurs)

but then, i consider myself a great enthusiast of the Mainsail model - it's so mighty and wonderful, when it lights up it makes all your problems go away (more often by immediately replacing them with massively greater new ones)... i enjoy how it can lift a K-W 2x12 with little help from two enormous solid boosters on the side

[cardgame]

Having a Mainsail under a stack of 2m fuel tanks is better for a launch stage because the 2m core allows you to attach loads of extras around it, something the one meter models cannot do as well.

[Temstar]

In an 85tn craft (remember, just fuel/pod/single engine only) landing on the Mun.

T30

T:W: 1.53

Delta-V: 6553

T45

T:W: 1.42

Delta-V: 6483

Poodle

T:W: 1.54

Delta-V: 6622

But that comparison is moot, you would never build a spacecraft with 85 tons of fuel and one Poodle. If you really plan to burn 85 tons of fuel in a spacecraft you would build a spacecraft with 78.5 tons of fuel and four nuclear rockets.

Edited October 3, 2012 by Temstar

[AmpsterMan]

well, one must account for the added "complexity mass" from a multi-engine setup...

I find this to be one of the main cases for the larger parts. Many smaller parts bring up your total part count, which means more stuff for your cpu to simulate and for the physics engine to make do things you don't want it to.

The Main advantage of the Larger parts, as I see them, can only be realised when you take into account all the other outliers besides TWR and ISP.

But that comparison is moot, you would never build a spacecraft with 85 tons of fuel and one Poodle. If you really plan to burn 85 tons of fuel in a spacecraft you would build a spacecraft with 78.5 tons of fuel and four nuclear rockets.

He used the landing on Mun scenario, which would have me think that instead of talking about "85 units of mass" he was talking about "85 units of weight". In which case they might not be so moot after all. Especially when you consider such oddities as the other planets and their moons, each which has unique circumstances each providing their own challanges.

Edited October 3, 2012 by AmpsterMan

[tuguley]

I like using the mailsail as a "rich mans SRB". It has a massive thrust, higher efficiency and thrust vectoring is always a bonus. I add 3 of them with 3 large fuel tanks to basically get me out of the lower atmosphere. (10-13km)

I use the poodle as a guidance engine more than anything else. In my orbital maneuver stage, I have 2 aerospikes and 1 poodle to provided enhanced steering. I use this stage to break out of Kerbin SOI aswell.

Ofcourse on the topic of thrust vectoring, for me atleast, the ASAS tends to over-compensate causing massive wobbling in the ship (with the mainsail and with large ships), more or less destroying it or making it a nightmare to control.

[Ziff]

But that comparison is moot, you would never build a spacecraft with 85 tons of fuel and one Poodle. If you really plan to burn 85 tons of fuel in a spacecraft you would build a spacecraft with 78.5 tons of fuel and four nuclear rockets.

It most certainly is not moot, and quite honestly, you totally missed the point of my post. I only used fuel tanks for this purpose because it was easy to build and showed how mass/ISP relate to delta-v, and why you cannot simply compare engines. However, If I happen to have an 85tn research station that I want to land on the Mun, it only takes 1 Poodle to land it there because of the low gravity. No more than that is needed. In that specific case, a Poodle engine beats any LV-T series engine. There is a time and place for every engine. I don't honestly feel like sitting down and doing all the math to prove to you when and why to use a specific engine. I merely posted this to show why you can't compare engines the way you did. My point still stands.

Edit: To say 'never' in KSP is ridiculous. Just go look at the things people build. I have seen a 500tn craft designed specifically, and only, to go land on the Mun. It had like 12 Mainsail engines. I would never.. but someone always will, that's the way of KSP.

Edited October 4, 2012 by Ziff

[Temstar]

It most certainly is not moot. I only used fuel tanks for this purpose because it was easy to build and showed how mass/ISP relate to delta-v, and why you cannot simply compare engines. However, If I happen to have an 85tn research station that I want to land on the Mun, it only takes 1 Poodle to land it there because of the low gravity. No more than that is needed.

No I meant it's moot because if the argument is "I'm going to burn a huge amount of fuel in orbit where the 20s Isp actually adds up to make a difference" then I would point out that there's an engine with 410s better Isp that you should be using instead for that ship.

So:

If you're moving around a 15 ton spaceship that's mostly fuel, you should be using LV-T30 to save engine weight

If you're moving around a 85 ton spaceship that's mostly fuel, you should be using LV-N to really take advantage of that 800s Isp, in clusters if you need thrust

If you're moving around a 85 ton spaceship that's 15 ton of fuel and 70 ton of dead weight, you should be using LV-T45 to save engine weight yet still have gimbling.

[Moach]

The mainsail has a very small vectoring range (if it even has any, i dont remember).... I often use radially mounted vernier jets higher up on the stack, such as on the second or third stages....

This makes taller craft much easier to control without requiring heavy rcs tanks that may not be used fully in the end... The NP pack verniers use the same fuel as the main bells, but offer a much larger deflection, to as much as 20 degreess even....

The stock LV-T series models, even clustered dont make such a responsive launchcraft as ths setup.... And the gimballed version has a very high mass overhead that makes it unsuitable for cluster use, afaik....

But then, if all else fails, just add moar boosters... If it's not working, then you've probably haven't booster'ed it up enough

Cheers!

[Temstar]

I think vernier thrusters with big deflection range are really cool looking (Atlas with its pair of vernier thrusters at launch looks awesome) but they're not very efficient use of weight. These days I think only R-7 rocket family still uses vernier thrusters.

Why would you need a rocket that could turn on a dime anyway? You only need a little bit of control to keep it straight at lift off and then a little bit more for gravity turn.

[Kosmo-not]

The mainsail has a very small vectoring range (if it even has any, i dont remember).... I often use radially mounted vernier jets higher up on the stack, such as on the second or third stages....

The thrust vectoring on the mainsail provides plenty of maneuverability. Why you would need vernier jets in addition to that is beyond me.

[UmbralRaptor]

I'm starting to think that the main advantage of the Poodle is over the LV-T45 (weight/space permitting).

The mainsail has a very small vectoring range

It's large enough. The main problem with tall stacks of fuel tanks on a mainsail is wobble, so you end up strutting things together anyway. I suspect that tall rockets tend towards higher moments of inertia than wide ones, which makes maneuvering them harder.

The stock LV-T series models, even clustered dont make such a responsive launchcraft as ths setup.... And the gimballed version has a very high mass overhead that makes it unsuitable for cluster use, afaik....

Clusters tend to be able to soak up one engine having lousy TWR, as long as the rest are good. (Which lets you pull of shenanigans like a centerline LV-N surrounded by Aerospikes) Clusters also make it really easy to use asparagus staging...

Recently I was helping a friend with building/testing some small munlanders. My designs:

The latter has 3 big tanks instead of 4, is *much* easier to control, and got to the munar surface without using anything in the landing stage's tank.

edit: I guess my opinion is that the Mainsail isn't *enough* bigger compared with other engines to justify the poor Isp. The wobble that tall stacks have doesn't help, and I'm rather less skilled at dealing with it than the problems of flying spiderwebs wide rockets.