Cluster engines more efficient than single Mainsail [proof]

[mellojoe]

Just wanted to test the theory, and here's my proof:

You can easily see that the two tanks using the Mainsail engine clearly run out of fuel well before the two tanks using the clusters. Weight wise, they are roughly even. The mainsail clocks in at 6t while the 4 engines plus quad coupler weighs approx 5.5t. This was using the LT-30 engines, the non-thrust-vectoring types. They are lighter, yet more powerful. However, 4 of them still don't equal the power of a single mainsail. If you reconfigure this ship to put a 4-cluster opposite of a single Mainsail, the Mainsail will out power the cluster, causing the rocket to cartwheel and crash. Very simple to test yourself, if you like.

The fuel savings using a 4-cluster is significant. Approximately half of the fuel is left in the 4-cluster tank when the Mainsail is spent.

Mainsail for raw power, and a cluster for efficiency.

[dlmarti]

PROOF water is wet!

This is something well documented, it even tells you that on the engine selection description.

[ASnogarD]

Try that same design with a heavy payload, the mainsail is much more efficient when lifting heavy loads ... at light loads most of its thrust is wasted fighting the atmosphere when you go too fast to be efficient.

If I recall from memory (which is bad for me ) the LT30's have a thrust of 215 each equaling 860 and a mainsail has a thrust of 1500 nearly twice the thrust of your 4 LT30's.

This thrust is wasted when you have much more thrust than the payload requires so its inefficient but when dealing with heavier payloads the extra thrust is needed to get off the ground.

[bsalis]

Yes, but Mainsails are far more efficient at rapid unplanned disassembly. You need far fewer of them to do that.

[automcdonough]

there's something to be said for 1 gimbaled thrust part instead of 4 as well..

The mainsail has one of the highest TWR of all engines in the game, the other contender is most efficient but only puts out thrust of 20.

If the ISP difference will net you more distance depends on the weight you're lifting and the altitude.. use mechjeb or engineer during assembly, it's all about the d/v numbers.

[Shuttle]

Set throttle to 100%, press space, open the resource tab and take a look at the number in brackets at the right end of the green bar. That's resource consumption per second

Edited July 29, 2013 by Shuttle

[magnemoe]

Main benefit of clusters is that they have better ISP and you can tune the effect better. Downside is lower TWR and the increased part count. The TWR hurt you if the burn time is short so you would probably lose if you used an cluster on the first stage in an asparagus you drop at 5km attitude but you will win using it on the long burning center stage.

[info600]

It can't hurt to have the main load in the middle be lifted by the mainsail and have the extra tanks on the sides lifted by the cluster arrangement (of course it's all orange tanks), so there would be more fuel to feed the "monster".

[Sof]

It can't hurt to have the main load in the middle be lifted by the mainsail and have the extra tanks on the sides lifted by the cluster arrangement (of course it's all orange tanks), so there would be more fuel to feed the "monster".

Its actually more efficient to do it the other way around. Getting a cluster of 7 LTs (I like the middle one to have gimbal) would require more orange fuel tanks to be more efficient compared to a mainsail. However, with asparagus staging, with 6 boosters comprising of ~128tons of fuel (2 orange tanks, but mainsails don't overheat on grey tanks I think)+1 mainsail feeding around to a central stack of 7 LTs and 1 orange tank+ a 32 or 16 grey tank (depending on payload mass), gives incredible stock power and can get the whole bottom stage (minus the asparagus boosters) in orbit around the Mun with medium/small payloads.

[ASnogarD]

I thought of that before, but the loss of Gimbals if you go LT30's or loss of thrust if you go LT45's makes it less ideal.

You could go for a 4 LT45 core and 6 LT30 ring for a core but that just gets a bit messy in the staging bar ... 10 engines + the outer ring of stacks engines...14 engines each with a fuel bar...

[TMS]

Core stack should be the most efficient as it burns for longer.

[AmpsterMan]

One thing i like doing is using four lv30 and four Rockomax radials

Thrust of 1320 mass of 8.6. It can almost lift what a mainsail can. I have a launcher that takes advantage of this

[snakemasterepic]

How efficient is it in terms of cost?

[severedsolo]

So the engine with better ISP doesn't use as much fuel as the one with worse ISP? and the (pre-ARM) most powerful engine in the game is more powerful?

I don't understand what you are trying to prove here

[cantab]

You're comparing apples and oranges here. Four Reliants or Swivels do not compare to one Mainsail in terms of thrust. To match a single Mainsail would require 7 Reliants or 8 Swivels.

Three Reliants or Swivels compared to one Skipper is a fair comparison on the other hand. The Skipper offers clearly superior performance for virtually all applications*, as it should be in my view since the player should not be penalised for keeping part count down. Unfortunately the clusters are cheaper which may encourage the career mode player to opt for them and the attendant extra lag, not a good thing.

* Ascents from planets with thicker air than Kerbin, ie Eve and Jool in stock, are the exception where the Reliant does better

[mike9606]

I just want to point out that this thread was dead for two years before today, and comparing the thread creation date to the version history on the wiki, these tests were done in 0.21.1 (maybe 0.21). I highly doubt that it is still accurate.

[Thegamer211]

You should place an aerodynamic cap on those side fuel tanks...

[Renegrade]

I just want to point out that this thread was dead for two years before today, and comparing the thread creation date to the version history on the wiki, these tests were done in 0.21.1 (maybe 0.21). I highly doubt that it is still accurate.

Yeah, necro post is necro

(I'm forgetting the older mainsail stats at this point, but something tells me the initial premise is flawed even back in those days. Mainsail had a violent TWR, even in the old days. It's main problem was the faulty heat transfer system...)

[sal_vager]

Wow this is totally out of date guys, the engines have change since this was posted, I suggest you do some experiments and see what things are like now instead of wasting time on how things were like then, and start a new thread

Closing!