What's better and more efficient?

[SirRocketer]

7 small engines on a main engine or 1 big main engine?

(What i mean by 7 small engines is a tail connector and then the engines.

[SievertChaser]

Jeb, smack this impostor. There can be only one!

Anyway, which engines?

[kesat]

You could also use Radial Attachment points (less space required).

And it depends on the engines you want to use and the TWR you are looking for. Usually a bigger engine should be more efficient than multiple smaller engines due to weight.

As an example: Instead of a Poodle Engine (250 thrust, Isp 350, mass 1.75) you could use "3.5" Terrier Engines (60 thrust, Isp 345, mass 0.5) which only provide you 210 thrust for less Isp and the same mass.
If you are using 2 Terrier Engines on the other hand (instead of 1 Poodle) you increase you total delta-v at the cost of total thrust (120 thrust, 1.0 mass).


In other words: It's less efficient to use a lot of smaller engines than a big engine.

[SievertChaser]

Actually, the most efficient method is ONE SMALL engine, so long as it has comparable ISP. So, AFAIK - not sure what they've done to ISP values in 1.0 - one Terrier is more efficient than one Poodle, because of same ISP and lower mass. And starting with a craft mass of around 20 t, the Nerv outmatches the Terrier.

Efficiency, of course, only matters once you're out of the atmosphere. In the atmosphere, bigger, more powerful engines are better.

[Zzabur]

It really depends on a lot of factors, atm or vacuum? ISP? TWR? DeltaV? What kind of fuel? Vessel mass? Body's gravity?

There's no such answer as "this engine is better than another", it only depends on how you use it.

Here's a chart for engine efficiency : https://c1.staticflickr.com/1/437/19343018161_9723f9f846_o.png

Like Kesat said "Usually a bigger engine should be more efficient than multiple smaller engines due to weight." Often true, but not always.

[DaS]

Originally posted by Zzabur:

It really depends on a lot of factors, atm or vacuum? ISP? TWR? DeltaV? What kind of fuel? Vessel mass? Body's gravity?

There's no such answer as "this engine is better than another", it only depends on how you use it.

Here's a chart for engine efficiency : https://c1.staticflickr.com/1/437/19343018161_9723f9f846_o.png

Like Kesat said "Usually a bigger engine should be more efficient than multiple smaller engines due to weight." Often true, but not always.

EVE aero spikes as an example

EDIT depending on what your trying to do and how the math works out a kinda sorta rule of thumb is smaller engines = sometimes more efficient but higher part count and lighter
Biiger engines often more fuel waisted per kg lifted but easier on the cpu but heavier
http://steamcommunity.com/sharedfiles/filedetails/?id=263145208
http://steamcommunity.com/sharedfiles/filedetails/?id=379479952

[DaS]

Same payload, same fuelbody, same fuel load, same flight profile(no grav turn just a streight shot) 198.3t minus engines Done quickly without doing any calculations or using Engineer so alot of waiste built in
http://steamcommunity.com/sharedfiles/filedetails/?id=524531751
could prob have cut 2-3 aeros out of build, had to play ALOT with the throttle to not overspeed, an engine or two less and it would have gone higher/faster
http://steamcommunity.com/sharedfiles/filedetails/?id=524531783
2677 m/s 135,800m
http://steamcommunity.com/sharedfiles/filedetails/?id=524531810
could prob have dropped a main, same reason as above
http://steamcommunity.com/sharedfiles/filedetails/?id=524531840
2592m/s 81,750m
http://steamcommunity.com/sharedfiles/filedetails/?id=524531867
about right
http://steamcommunity.com/sharedfiles/filedetails/?id=524531890
2948m/s 116,700

did this quickly to give an idea didn't bother todo any math so it's only a rough estimite

If I had bothered to break out the 48-7S 's and a calculator it'd have beat em all hands down(probably) but I'm lazy

[SirRocketer]

Originally posted by DaSkippa:

Same payload, same fuelbody, same fuel load, same flight profile(no grav turn just a streight shot) 198.3t minus engines Done quickly without doing any calculations or using Engineer so alot of waiste built in
http://steamcommunity.com/sharedfiles/filedetails/?id=524531751
could prob have cut 2-3 aeros out of build, had to play ALOT with the throttle to not overspeed, an engine or two less and it would have gone higher/faster
http://steamcommunity.com/sharedfiles/filedetails/?id=524531783
2677 m/s 135,800m
http://steamcommunity.com/sharedfiles/filedetails/?id=524531810
could prob have dropped a main, same reason as above
http://steamcommunity.com/sharedfiles/filedetails/?id=524531840
2592m/s 81,750m
http://steamcommunity.com/sharedfiles/filedetails/?id=524531867
about right
http://steamcommunity.com/sharedfiles/filedetails/?id=524531890
2948m/s 116,700

did this quickly to give an idea didn't bother todo any math so it's only a rough estimite

If I had bothered to break out the 48-7S 's and a calculator it'd have beat em all hands down(probably) but I'm lazy

Thanks! this actually seems very efficient. Ill use this for my Jool mission.