Ever since circa 100 BBY, Podracing in its modern version has drawn crowds from far far away to watch pilots compete in races like the Boonta Eve Classic which made Anakin Skywalker famous and won him his freedom. By beating Sebulba, the Dug, and the other Podracers, Anakin became the first human to be successful at this very dangerous sport. The Force helped him in his victory by sharpening his reflexes, but his repulsorcraft was also superior due to its size and the modifications made to its twin Radon-Ulzer 620C engines, especially the fuel atomizer and distribution system with its multiple igniters which makes them run similarly to afterburners seen on some military planes on Earth.
Let’s take a deeper look at what repulsorcrafts are and how we can help Anakin redesign his to gain an even better advantage against the competition, provided that Watto has the correct equipment in his junk yard.
They can be propelled by several different means – gas turbine, ion motor or rocket motor (sorry, no 2a fission engines from X-Wings allowed) – which are linked together via plasma energy binders. The gas turbine air-breathing configuration is what is most common among these vehicles as we can see by looking at the engines of Teemto Pagalies (Figure 2) and Ben Quadinaros (Figure 3) among others. The former uses a turbojet configuration (like Anakin Skywalker) while the latter features a turbofan approach.
To see how we can redesign Ani’s Podracer to improve its performance let’s take a look at its current stats.
We also need to understand under which conditions the engine will operate. Due to the lack of weather stations on Tatooine several assumptions were made:
- – Normal (Earth-like) gravity despite its 3 moons – estimated from the lack of labored efforts from non-Tatooine residents to move around and the fact that they don’t take leaps when walking
- – 1 atmosphere pressure with standard (Earth) composition – neither residents nor most travelers at the cantina require breathing masks
- – Climate – it is widely known that Tatooine has a very dry and very hot climate with temperatures reaching up to 160F most likely achieved by the presence of its two suns (The very low humidity is what makes moisture farms like the Skywalker’s a wealth that requires protection.)
It is therefore reasonable to consider dry air at 1 atm and 160F as our ambient conditions design point since gas turbines show better performances with colder intake.
Based on this, we can model the thermodynamic cycle of the engine while assuming kerosene as the fuel since no data is available regarding specs for Tradium nor injectrine (used for the power boost).
The thrust required was calculated to ensure the vehicle could reach its current top speed based on common, similar commercial aviation engines weight while initially using rough estimations regarding the compressor and turbine efficiencies.
Preliminary design of both turbomachines in AxSTREAM® enabled for a more accurate engine calculation – the compressor efficiency was overestimated while the turbine one was underestimated slightly. As a result, the mass flow rate of the system was updated from 30.1 to 32.1 kg/s to ensure the target thrust is reached.
The second iteration of the preliminary design was performed to actually determine accurate size and performance for each of the turbomachinery components while keeping a few crucial things in mind:
- Looking for highest efficiency while strongly keeping weight of engine under consideration – a lighter engine means more useable power, better maneuverability and tighter corners which is especially useful in the Arch Canyon and its stone wickets or around the Canyon Dune Turn to escape gunfire from the Tusken Raiders.
- Achieved by reducing axial length by selecting fewer stages
- And limiting the radial dimensions (smaller tip diameter on the compressor with appropriate sizing match on the turbine side)
- Performing turbine design with a constant streamwise tip diameter to preserve current configuration with fuel tank inside the compressor rotor (Figure 4) therefore minimizing redesign operations
- Ensuring that mechanical integrity of the blades is preserved based on materials available on Earth, therefore eliminating Steelton used to link the engines to the cockpit
- Maintaining stable operation throughout different regimes (full throttle in Hutt Flats for the finish vs. dodging rocky obstacles in Bindy Bend) including stall prevention through equivalent diffusion factor monitoring
As a result, the preliminary geometries are presented in the figures below.
The compressor features 5 stages instead of the original 8 stages with an efficiency of 81%, a reduction of radial dimensions by 70% and of axial length by 80% – Note, selecting a 6-stage configuration would have resulted in a higher efficiency (82.9%) but less substantial weight reductions (+2.5% diameter and +25% length vs. selected 5-stage design). By analyzing the blueprint of the current fuel tank located inside the core of the compressor, its volume is 0.018 m3 which suggests than Tradium is about 50 times denser than kerosene jet fuel given the fuel consumption calculated at the thermodynamic cycle level when considering full throttle for the 15min42s record race time. The redesigned compressor can allow up to 0.035 m3 of fuel in the same location so this configuration and geometry are considered suitable for this purpose.
The new turbine comprises 2 axial stages instead of the 3 in the current design with an efficiency of 90%, a reduction in tip diameter of 19% and an axial length cut of 23%.
To help put these size reductions into perspective the figure below has been created so readers can easily compare the original vs. redesigned geometries at the same scale.
Although the fuel efficiency advantages of using a turbofan configuration instead of a turbojet one, like in the present case, are interesting to commercial aviation, racing sports typically do not make it their priority, especially in competitions where being a small, maneuverable target brings significant benefits. For this reason we kept our focus on the turbojet approach. However, if you are interested in seeing what we can do for turbofans, I invite you to contact us for some technical material on, for example, automation of bypass ratio optimization using the AxSTREAM ION™ software. Speaking of automated design, check out this cool video on a rocket turbopump design – http://www.softinway.com/en/automatic-preliminary-design-process-of-turbopump-for-liquid-rocket-engine/
To conclude, Ani’s Podracer has some margin for improvement. We have seen that the size of the compressor and turbine can be reduced which allows for a substantial weight reduction of the propulsion system. This in turn makes it practical to focus on improving the shields to protect against debris and collisions, improving the engine cooling to use the injectrine boost more often, etc.
Future studies could look into the applicability of the axial-radial configuration of compressor used by Sebulba in his engine or even diagonal compressors which feature interesting advantages in cases where pressure rise and space are major constraints.
And who knows, maybe next year we will take a look at Luke Skywalker’s X-34 Landspeeder mini-gas turbines.