Delta-V calculator

[TheMacTester]

As far as I know stretching engines only changes the thrust, not the mass or the ISP so the delta-V should not change?

if there is more thrust, but it uses the same amount of fuel, it make more lsp

 

[Dahzito]

if there is more thrust, but it uses the same amount of fuel, it make more lsp

Isn't it the contrary, if there is more thrust over the same amount of fuel there is less Isp? Also, I think that the DeltaV does stay the same indeed, but I will do some tests to see if that's the case.
(May be very wrong tho)

 

[Altaïr]

so for some reason, on my mac, when i stretch engines the delta-v stays the same, why is this, does a mod make this happen, did i do somthing wrong?

This is surprising, this should normally work, the mod was designed to take it into account... Unless you play in challenge mode? The stretch factor is not taken into account in challenge mode.

 

[Darthan]

With twice the thrust the fuel is used twice as fast so the ISP stays the same.

I did a test:

Teleport each of them to 33km LEO and send them to Jupiter direct aiming for a 200km orbit.

Unstretched:
41.5% fuel @ Jupiter SOI
apoapsis @ Jupiter 6454km



Stretched:
43.5% fuel @ Jupiter SOI
apoapsis @ Jupiter 5896km



If the 2x stretched engine used fuel at the same rate it's delta-v should be doubled and it should easily be able to reach Jupiter low orbit. As it was it was only slightly more efficient since it could spend more time closer to the Earth when accellerating so could make more use of the Oberth effect.

 

[TheMacTester]

With twice the thrust the fuel is used twice as fast so the ISP stays the same.

I did a test:
View attachment 130393

Teleport each of them to 33km LEO and send them to Jupiter direct aiming for a 200km orbit.

Unstretched:
41.5% fuel @ Jupiter SOI
apoapsis @ Jupiter 6454km

View attachment 130394 View attachment 130395

Stretched:
43.5% fuel @ Jupiter SOI
apoapsis @ Jupiter 5896km

View attachment 130396 View attachment 130397

If the 2x stretched engine used fuel at the same rate it's delta-v should be doubled and it should easily be able to reach Jupiter low orbit. As it was it was only slightly more efficient since it could spend more time closer to the Earth when accellerating so could make more use of the Oberth effect.

so what is happening? does the mod change engine strech?

 

[Darthan]

so what is happening? does the mod change engine strech?

With twice the thrust the fuel is used twice as fast so the ISP stays the same.

From my test engine stretching does not affect isp. Since I would not expect it to, I doubt that any mod is causing this. You could confirm this by running the test on mobile or teleporting the rockets to a 33km orbit using warpinator, disabling all mods then running the test.

Blueprint of test rockets

 

[Axiom]

if there is more thrust, but it uses the same amount of fuel, it make more lsp

Currently stretching engines increases thrust but also increases fuel consumption so the ISP is left unchanged. In earlier versions (like 1.4) stretching engines didn't increase fuel consumption so you could have a titan engine with 300 TWR and twice the efficiency of an ion engine

 

[Altaïr]

I double-checked, you're correct guys, stretching an engine increases both thrust and fuel consumption, so Isp (and thus ΔV) remains the same. I coded it in ΔV calculator, but I never stretch engines myself...

This is how it is coded:

maxThrust takes the stretch factor into account, and consumption takes it implicitely into account since it's calculated from maxThrust.
But Isp is not influenced by the stretch factor, so it's normal that delta-V remains the same.

A possible scenario where it would make a difference is if you mix engines: for example, if a stage runs with 2 Titan and 2 Frontier. If you stretch the Frontier engines, those will consume more fuel, and in the end, a more important fraction of the fuel available will be consumed by the Frontiers. In this case the ΔV would increase because of stretching. But in the case of a single engine, stretching it won't change ΔV.

 

[TheMacTester]

I double-checked, you're correct guys, stretching an engine increases both thrust and fuel consumption, so Isp (and thus ΔV) remains the same. I coded it in ΔV calculator, but I never stretch engines myself...

This is how it is coded:
View attachment 130425
maxThrust takes the stretch factor into account, and consumption takes it implicitely into account since it's calculated from maxThrust.
But Isp is not influenced by the stretch factor, so it's normal that delta-V remains the same.

A possible scenario where it would make a difference is if you mix engines: for example, if a stage runs with 2 Titan and 2 Frontier. If you stretch the Frontier engines, those will consume more fuel, and in the end, a more important fraction of the fuel available will be consumed by the Frontiers. In this case the ΔV would increase because of stretching. But in the case of a single engine, stretching it won't change ΔV.

I didnt know this, i was hoping to make a weak engine for my alternate universe (releasing soon!)

 

[QMSP]

Is it possible to see the delta v readout in the build screen?

 

[Altaïr]

Is it possible to see the delta v readout in the build screen?

No, it's only available in the world scene.