Bloodhound SSC: a supersonic engineering marvel

July 11th, 2014, Published in Articles: EE Publishers, Articles: Vector, Featured: EE Publishers

 

A hybrid jet-and-rocket powered vehicle will fire up its 135 000 hp engines to break the sound barrier and the world record alike in a 1600 km/h race at Hakskeen Pan, South Africa.

The 14 m, 7 tonne Bloodhound supersonic car (SSC) was designed and is being built by the Bloodhound Project, described as a global “engineering adventure” which is using a 1600 km/h world land speed record attempt to inspire science, technology, engineering and mathematics students.

The Bloodhound Project in a nutshell (Credit: The Bloodhound Project)

Initiated by former Fédération Internationale de I’Automobile (FIA) land speed record holder Richard Noble, this machine will be piloted by current land speed record holder Andy Green, who will challenge the known limits of supersonic travel at Hakskeen Pan, South Africa, in 2016.

Fig. 1: The anatomy of the Bloodhound Supersonic Car (Credit: Siemens NX)

 

Design

The entire vehicle is designed around the driver, starting with the carbon fibre monocoque or “controls cabin”. Aerodynamics is crucial to the car’s directional stability. The complex curvature in the car’s nose is specially designed for optimal air flow around the vehicle, reducing drag while simultaneously trying to find an optimal balancing between lift and down force to avoid the car lifting and flipping over at high speeds (see Fig. 2). The cockpit screen creates a shockwave right in front of the intake duct, pre-compressing the air and increasing the engine efficiency at supersonic speeds (see Fig. 2).

Fig. 2: The height of the car’s nose influences overall aerodynamics. It also contains the front suspension with wheels, brakes and many of the car’s control systems. (Credit: The Bloodhound Project)

Fig. 2: The height of the car’s nose influences overall aerodynamics. It also contains the front suspension with wheels, brakes and many of the car’s control systems. (Credit: The Bloodhound Project)

For aerodynamic reasons the front wheels are mounted within the body and two rear wheels externally, compensating for wheel and ground interaction when the vehicle approaches supersonic speeds. The 135 000 hp Eurojet EJ200 jet engine, intake duct and tail fin are mounted in the rib and stringer upper chassis, which is made from aluminium and titanium (see Fig. 3a). The engines are then fit onto the aluminium frame lower chassis where the auxiliary power unit, the jet fuel tank and the rocket system are housed (see Fig. 3b). The rear suspension, rocket thrust ring and the parachute cans are all mounted on the rear sub frame.

Fig. 3 (a) and (b): The rib and stringer upper chassis made from aluminium and titanium which houses the engines, and the aluminium frame lower chassis where the auxiliary power unit, the jet fuel tank and the rocket system are housed. (Credit: The Bloodhound Project)

Fig. 3 (a) and (b): The rib and stringer upper chassis made from aluminium and titanium which houses the engines, and the aluminium frame lower chassis where the auxiliary power unit, the jet fuel tank and the rocket system are housed. (Credit: The Bloodhound Project)

The high-speed wheels, which spin at 170 revolutions per second, weigh 95 kg each and are forged from solid aluminium. The wheels are rough machined, heat treated and cold compressed to withstand 50 000 radial gravities g-force at the wheel rim when it spins at over 10 000 rpm.

Fig. 4: A stress model of the 95 kg solid aluminium wheels (Credit: The Bloodhound Project)

The wheels are shaped in such a way that they cut into the desert surface just enough for grip, but not enough to slow the car down (see Fig. 4). Rubber traction is not necessary as the vehicle is not driven by its wheels. Besides, rubber tyres would be torn off the rims at speeds exceeding 600 km/h! The wheels are attached to the car with a double wishbone suspension in both the front and rear, which provides the right stiffness to prevent the wheels from veering off line.

Fig. 5 (a) and (b): The front and rear suspension (Credit: The Bloodhound Project)

Fig. 5 (a) and (b): The front and rear suspension (Credit: The Bloodhound Project)

Power

Three sources of power will drive the vehicle: a customised fighter jet engine which is attached on top of a Nammo hybrid rocket, backed by an APU V12 engine as auxiliary power unit (see Fig. 6).

 

Fig. 6: The rocket and jet engine configuration (Credit: The Bloodhound Project)

Fig. 6: The rocket and jet engine configuration (Credit: The Bloodhound Project)

 

The hybrid rocket will deliver 123,75 kN of the total 212 kN thrust while the rest of the power will be provided by an EJ200 jet engine. The Eurojet EJ200 turbo fan engine (as opposed to turbojet, turboshaft, or turboprop engines) was originally designed by Rolls-Royce for the Eurofighter Typhoon military jet and is customised for the Bloodhound. Upon completion, the rocket will in all likelihood have a cluster of four or five motors rather than a single, large combustion chamber.

Fig. 7: The EJ200 Eurojet engine, a turbo fan engine producing roughly half (88 kN) of the car’s thrust. (Credit: The Bloodhound Project)

Fig. 7: The EJ200 Eurojet engine, a turbo fan engine producing roughly half (88 kN) of the car’s thrust. (Credit: The Bloodhound Project)

The auxiliary power unit will be used for essential hydraulic functions and to drive the rocket oxidiser pump, supplying the engine with 800 l of high-test peroxide (HTP) in 20 sec. (at 40 l/s). This powerful engine is not only responsible for the thrust, but also for the 140 db noise.

The only gearbox on the car will be a reduction gearbox in the auxiliary power unit which drives the rocket fuel pump, designed to run at 11 000 rpm.

The intake system, which feeds air to the jet engine, was also a design challenge in terms of aerodynamics and engine performance. With the intake too large, drag will be created while too small an intake will cause the engine to underperform at low speeds as it will lack air.

Sonic boom

Sonic or supersonic speeds create shock waves on the car, changing its flow properties or aerodynamics (see Fig. 7). These shock waves influence the vehicle and interact with each of its components and with the desert floor.

Fig. 8: Airflow at sonic and supersonic speeds creates shock waves on the car, changing its flow properties or aerodynamics. (Credit: The Bloodhound Project)

Fig. 8: Airflow at sonic and supersonic speeds creates shock waves on the car, changing its flow properties or aerodynamics. (Credit: The Bloodhound Project)

The car’s acceleration and deceleration through the transonic range posed a major aerodynamics challenge as some parts of the flow fields over the car will be supersonic while others are other parts are subsonic. Aerodynamic conditions such as shock waves also change rapidly during this phase of movement.

Computational fluid dynamics using Navier-Stokes equations for viscous, compressible fluid flow were used to calculate airflow over the car, as these are most applicable to the aerodynamic flow of the Bloodhound.

The calculations were conducted on Swansea University’s supercomputing cluster and were processed to produce flow visualisation and force distributions. Side forces and yaw moments, as well as forces associated with the wheels, are direct aerodynamic forces affecting the vehicle.

The element of speed is another complex aspect of the aerodynamics since down force and pitch moment vary. This, in turn, affects control of the wheel loads, causing further implications. With this in mind, the car must be designed for its entire speed range. The use of programmable winglets over the front and rear axles has been proposed to manage the wheel load.

Setting the record

The Bloodhound SSC will be competing for the Outright World Land Speed Record. In broad terms, the rules state that a vehicle must be propelled by its own means while remaining in constant contact with the ground either directly, by mechanical means or indirectly, by ground effect, and its power and steering system must be constantly and entirely controlled by an on-board driver. The track must be clear and have a maximum gradient of 1% over any 100 m section, making Hakskeen Pan, with its 0,5 m rise over 20 km, the perfect location for the challenge.

The car must pass through the “measured mile” (over which the speed is measured) roughly halfway through the run, stop at the end of the track and repeat the process. The average speed of the two runs is then taken as the speed challenging the record. The timing of entering the mile is therefore crucial. According to the team’s simulations, the car will reach its top speed of 1600 km/h 7,2 km into the race.

Richard Noble – Driving a supersonic car

Stopping a bullet

Deceleration and stopping, says Noble, is “where the fun begins”. Stopping a low-drag car literally travelling faster than a bullet, with disk brakes which only work up to about 400 km/h, requires a combination processes.

First, the driver closes the throttle, which causes an initial 3 g deceleration reducing the car’s speed from 1600 to roughly 1290 km/h, upon which the airbrakes are deployed. The first braking parachute is deployed below 965 km/h, followed by a second parachute (if required) below roughly 644 km/h.

The disk brake system is deployed once the vehicle travels below 402 km/h. If all goes according to plan, the car will be stopped in 7,2 km (of the available 8,8 km), the same distance it took to reach its top speed. The vehicle is then ready to be turned around for the second leg of the run.

The design of the car’s braking system posed many challenges. The disk brakes, for example, must spin at the same 10 000 rpm of the wheels and are therefore exposed to the same stresses and high temperatures. Multi-plate carbon discs using aircraft-style circular stators will therefore most likely be used in the disk braking system.

The air brake and parachute systems are even more complex as both systems rely on aerodynamic drag which keeps changing as the car decelerates, since drag is proportional to the square of speed.

Fig. 9: The airbrakes are deployed under 1290 km/h, using adjacent hydraulic rams operating on a single slider on rails. (Credit: The Bloodhound Project)

Fig. 9: The airbrakes are deployed under 1290 km/h, using adjacent hydraulic rams operating on a single slider on rails. (Credit: The Bloodhound Project)

To stop the car within 7,2 km, the air brakes must be double the cross-sectional area of the car. The airbrake system therefore uses two adjacent hydraulic rams operating on a single slider on rails, but each with its own accumulator (see Fig. 9). The rams are connected mechanically to ensure that both are pushed out equally to avoid destabilising the car. This provides a backup should one set of hydraulics fail.

Although the air brakes are mechanically straightforward, their large area required to enable a quick stop posed great technical challenges. The air brakes on the Bloodhound SSC will be the largest used in land speed racing to date. They are perforated to break up the airflow and reduce the trauma on the rear wheel assemblies.

The air brake system model demonstrated (Video courtesy Bloodhound Project)

Two 2 m diameter “ring slot” parachutes will help the Bloodhound stop, producing 90 kN or 9 tonnes of drag at 1080 km/h. They will be attached to the car by a 17 m long, 32 mm thick braided strop with a breaking strain of 23 tonnes. At full working load, the strop will extend to 20 m, clearing the chutes from the car’s immediate turbulence.

The first full-assembly test runs will take place towards the latter half of 2015, with the record attempt scheduled for 2016. Whether the Bloodhound will enter the annals of history and make it to the Coventry Transport Museum like its predecessor, remains to be seen.

 

 

References

[1]   “About: Spirit Of Speed.” Coventry Transport Museum. Accessed June 25, 2014.

[2]   Andy Green. “The FIA World Land Speed Record.” Accessed June 12, 2014.

[3]   “Bloodhound Project: The Car.” Bloodhound SSC. Accessed June 12, 2014.

[4]   Bloodhound SSC Press Releases. Press release. The Bloodhound Project, n.d.

[5]   “FIA World Land Speed Records.” FédérationInternationale de I’Automobile. Accessed June 12, 2014.

[6]   Richard Noble. “FEBE Bloodhound SSC Public Lecture.” Public lecture, University of Johannesburg, Kingsway Campus, May 27, 2014.

[7]   Image credit: Fig. 1: Siemens NX; Fig. 2 – 9: The Bloodhound Project

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