Study of Effect of Fuel Amount, Engine Dry Mass, and ISP on Delta-V

[Duxwing]

Abstract

Increasing fuel volume decreases the effect of engine mass on Delta-V while increasing that of ISP.

Procedure

1.) Install Kerbal Engineer Redux v 0.6.1.1

2.) Place or attach as few tanks as necessary to hold a listed volume of fuel.

3.) Attach Kerbal Engineer Redux ER-7500.

4.) Attach each engine in turn and record each resulting Delta-V.

5.) Repeat steps 2-4 for each volume of fuel.

Data

Fuel (L): LV-1| Rockomax 48-7S| LV-909 | LV-N

100: 5,283 | 4,825 | 2,433 | 1,536

200: 5,714 | 5,818 | 3,656 | 2,758

300: 5,879 | 6,274 | 4,428 | 3,764

400: 5,966 | 6,538 | 4,971 | 4,163

500: 6,020 | 6,711 | 5,377 | 5,344

600: 6,057 | 6,833 | 5,693 | 5,981

700: 6,084 | 6,923 | 5,948 | 6,545

800: 6,104 | 6,994 | 6,158 | 7,047

Analysis

• Increasing fuel volume decreased the effect of engine mass on Delta-V while increasing that of ISP.
  
• The 48-7S provided greater Delta-V than did the other engines in the 200-700L range, and the LV-N only bested it by 53 m/s at 800L.
  
• The LV-1 provided much more Delta-V than did the other engines at 100L; it may therefore be designed to most efficiently use very small amounts of fuel.
  

Conclusion

Increasing fuel volume decreased the effect of engine mass on Delta-V while increasing that of ISP. A practical application of these results might be to increase Delta-V while reducing mass and cost by replacing such heavier engines as the LV-909 with such lighter ones as the 48-7S.

-Duxwing

Edited October 7, 2013 by Duxwing

[aeronaut]

Tavert did an exhaustive analysis over this topic, check it out. The results are displayed in a slightly different manner than what you have here. His plots don't show the fuel volumes however if you were really interested in it,those number could be backed out of the plots.

Edited October 7, 2013 by aeronaut

[Duxwing]

Wow, thanks. It's beautiful!

-Duxwing

[Bobnova]

Interesting, this is food for thought.

I'd been wondering about this earlier today amusingly enough.

Thanks!

[GusTurbo]

I like this post. It's very scientific and doesn't have any difficult-to-interpret graphs.

[Duxwing]

I've added an analysis and refined the writing because of your support. Enjoy!

-Duxwing

[tavert]

Tavert did an exhaustive analysis over this topic, check it out. The results are displayed in a slightly different manner than what you have here. His plots don't show the fuel volumes however if you were really interested in it,those number could be backed out of the plots.

I created an interactive version for people to play with, see page 4 of the above-linked thread. It's more of a spreadsheet format than the comprehensive graphs, but the data should be consistent.

[magnemoe]

You forgot about cargo. With 100 kg cargo the 48-7S win over the ant if you have 3 or more oscar tanks, that is 16 liter fuel. with two ton cargo the 909 wins over the 48-7S with 2-300 liter fuel.

In short, more cargo make engine weight less important.

[Duxwing]

I intentionally ignored cargo mass because it varies with each mission.

-Duxwing