Like the simple Jet Engine, custom jet engines provide thrust in atmosphere. Unlike simple jet engines, however, they consume fuel directly instead of power.
Here is a spreadsheet with every configuration of all 3841 possible CJE configurations up to 15 of each module assuming full "addons" for each segment. (this covers up to a 46 block long engine + 1 for exhaust if you want it). select all columns and sort by whichever statistic your are trying to optimize.
Minimal example
For a functional jet engine you need at least:
- 1̶ ̶J̶e̶t̶ ̶I̶n̶t̶a̶k̶e̶
- 1 Jet Controller
- 1̶ ̶J̶e̶t̶ ̶C̶o̶m̶p̶r̶e̶s̶s̶o̶r̶
- 1 Jet Combusters with 1 Jet Fuel Injector.
Jet Exhausts are useless.
Components
Although customisable, the custom jet has a rather fixed order in which components and their add-ons may be attached. The order is:
- Jet Intakes and Jet Intake Add-Ons
- Jet Controller
- Jet Compressors and Jet Extra Compressors
- Jet Combusters, Jet Extra Combusters, and Jet Fuel Injectors
- Jet Exhaust
The engine must be connected front-to-back using the "core" components (not "Extra" or "Add-On"). They do not have to be in a straight line, but they cannot branch. Non-core components must be connected to the center of one of the four sides of the appropriate core component.
Fuel consumption
Maximum thrust is proportional to the number of Jet Fuel Injectors. For injectors and thrust , fuel consumption is
Thrust
Thrust is determined by the number of each component apart from the Jet Controller and Jet Exhaust. Define the following:
- Let I be the effective number of intakes. Both Jet Intakes and Jet Intake Add-Ons count as 1 each.
- If there are at least two Jet Intakes (not counting Jet Intake Add-Ons), add 4 to I (i.e. 4 free effective intakes).
- Let P be the effective number of compressors. Jet Compressors count as 1, Jet Extra Compressors count as 1/4.
- Let C be the effective number of combustors. Jet Combusters count as 1, Jet Extra Combusters count as 1/4.
- Let F be the number of fuel injectors. Jet Fuel Injectors count as 1 each.
The total thrust per fuel injector is 20 * (I * P + C) 20 * I * P + 1000*C. Multiply this by F, the number of fuel injectors, to get the maximum thrust.
Strategy
The thrust of an engine increases quadratically with size, e.g. doubling the size of the engine will roughly quadruple the thrust. Therefore it is more efficient to use more fuel injectors or increase the size of the engine than to use multiple engines. Now combusters give the most thrust and so thrust is linear to length. One steel able to implement quadruple logic, but it would take a lot of blocks. ̶8̶ ̶c̶o̶m̶b̶u̶s̶t̶e̶r̶s̶ ̶a̶r̶e̶ ̶e̶q̶u̶a̶l̶ ̶t̶o̶ ̶2̶0̶ ̶i̶n̶t̶a̶c̶k̶e̶s̶ ̶+̶ ̶2̶0̶ ̶c̶o̶m̶p̶r̶e̶s̶s̶o̶r̶s̶,̶ ̶5̶ ̶t̶i̶m̶e̶s̶ ̶m̶o̶r̶e̶ ̶c̶o̶m̶p̶a̶c̶t̶!̶- Fuel injectors allow a smaller engine for a given amount of thrust, but consume more fuel.
Never use more than the minimal number of combustors, as they give negligible thrust. Since dramatical increase in combusters thrust it is highly advised to use as many combusters as possible, while keeping compressors and intake count to minimum.
Note: At maximum power/fuel efficiency a Custom Jet Engine with a minimum lenght of 42m using Intakes and Compressors can produce more power than an equally long Engine using only Combusters.
The following table is assuming a base design of 1 Controller, 1 Combuster (with 1 Injector and 3 Extra combusters) and the use of the maximum amount of addons on all listed components (4 extra Compressors on each Compressor, 4 extra Combusters on each Combuster, 4 Intake add-ons on each Intake)
| Length of Engine | Number of Intakes | Number of Compressors | Number of Combusters | Max power output |
|---|---|---|---|---|
| 42m | 20 | 20 | 0 | 84950 |
| 42m | 0 | 0 | 40 | 81750 |
The Math behind it: the 2m base design has a max power of 1750, each additional Combuster increases the power by 2000, however, each Intake increases the power-gain per Compressor by 200, thus power-gain per Compressor can be calculated with Intakes*200 (+160 if the Intake-count is greater than 1). So 20 Intakes would result in a power-gain per Compressor of 4000+160.
Minimal length
This is probably the most manageable design.
Put four Jet Intake Add-Ons on every Jet Intake. This gives 5 effective intakes per slice.Put four Jet Extra Compressors on every Jet Compressor. This gives 2 effective compressors per slice.Always use at least 2 intake slices to get the free effective intakes.Use the same number of compressor slices as intake slices, or 1 more compressor slice.Combustor Add-Ons can give slightly more thrust, but the amount is negligible.
More explicitly, start building the engine like this:
| Total length | Intake slices | Compressor slices | Thrust |
|---|---|---|---|
| 4 | 1 | 1 | 220 |
| 5 | 2 | 1 | 580 |
| 6 | 2 | 2 | 1140 |
| 7 | 2 | 3 | 1700 |
Then alternate intake and compressor slices.
Minimal cost/weight
All custom jet components cost and weigh the same, so minimizing these is a matter of minimizing the number of components.
Use at least 2 Jet Intakes.Use only core Jet Compressors and not Jet Extra Compressors.Use one Jet Compressor per effective intake (i.e. number of intake components + 4).
More explicitly, start building the engine like this:
| Total components | Intakes | Compressors | Thrust |
|---|---|---|---|
| 5 | 1 | 1 | 40 |
| 6 | 2 | 1 | 140 |
| 7 | 2 | 2 | 260 |
| 8 | 2 | 3 | 380 |
| 9 | 2 | 4 | 500 |
| 10 | 2 | 5 | 620 |
| 11 | 2 | 6 | 740 |
Then alternate intakes (either type) and Jet Compressors. Compared to the minimal length design, this design costs about 37% less but is about 90% longer for an similar amount of thrust.