Technology

Technological advancements were vital to Golden Arrow’s success. Discover how the vehicle was ahead of its time in terms of aerodynamics and how Napier’s engine and Dunlop’s tyres enabled it to conquer the 1929 Land Speed Record.

For engineers, understanding how aerodynamic forces interact with objects travelling at extreme speeds is an essential factor for high performance cars. By doing so, you can improve driver safety, vehicle stability, and increase top speeds.

Golden Arrow’s front was greatly streamlined

Streamlined Shape: Reduced Frontal Area

The all British nature of Golden Arrow meant that Chief Engineer John Samuel Irving had to work with the British 900 horsepower Napier aeroplane engine. This engine had an equivalent power to that of Segrave’s 1927 Sunbeam car, known as Mystery. Therefore, to increase top speed despite having the same power, Irving knew that he had to make the vehicle more aerodynamic.

Irving took inspiration from the 1927 Schneider Trophy Seaplane and reduced the frontal area of Golden Arrow by nearly 50% compared to the Sunbeam: from 20.8 to 11.1 square feet. This drastic reduction enabled an increase in speed. To understand precisely how much the top speed had been increased, Irving relied on scientific tests.

The distinctive Schneider Trophy seaplane (kitchener.lord /CC BY-NC-ND 2.0 )

Wind Tunnel Tests

Irving was one of the first automobile engineers to make use of wind tunnels for testing, and he subjected a scale model of Golden Arrow to such tunnels at the National Physical Laboratory.

These experiments revealed that his design changes had enabled a new top speed of 276 miles per hour. However, such a high speed was beyond the safety margins of Dunlop’s tyres.

Therefore, Irving aimed for a top speed of 250 mph instead. This provided him with some design freedom to improve vehicle stability and increase driver safety.

Image: kitchener.lord /CC BY-NC-ND 2.0

Vehicle Stability

At extreme speeds, vehicles had the potential to lurch off the ground as the surface beneath them rapidly changed.

To prevent these unpredictable and dangerous occurrences, Irving designed the front of Golden Arrow to act like a ramp, pushing air up and over the body of the vehicle: this helped push it downwards.

In modern times, this force is simply known as downforce, or negative lift. Whilst Irving was not the first to manipulate this force for his vehicle’s benefit, he was the first to take it to such an extreme by testing his theory in a wind tunnel and so heavily modifying Golden Arrow’s front.

Later land speed record vehicles attempted to imitate such streamlining, and the influence of Irving’s Golden Arrow is clear on designs such as Malcom Campbell’s 1935 Blue Bird, with a similar front and side design.

The most extreme examples of modern vehicles making use of downforce are Formula One cars. Due to their extremely light nature, they require a great deal of downforce to maintain stability.

Early Aeroplane Engines

In the 1920s, Sunbeam engines were at their prime and aircraft engines were starting to be used in race cars. Sunbeam was the first to use these engines consistently in their early models.

This engine was called the Sunbeam Manitou. It had an 18-litre capacity with a 4-speed gearbox and was painted in a distinctive green colour. It was used in Blue Bird, which Malcom Campbell used to achieve two land speed record attempts in 1924 and 1925 respectively.

Aero engines were later used by Engineer John Irving, who worked on two V12, 22-litre Sunbeam Matabele engines for the 1927 Sunbeam car, ‘Slug’ This engine enabled Segrave to set a new Land Speed Record of 203 miles per hour.

Irving’s aim after the ‘Slug’ was to hit a speed of 250mph, and so his search for an appropriate engine began.

Napier Lion Engine

The new engine that Irving desired was supposed to have a 60% increase in horsepower and a 50% decrease in surface area of the car.

However, Segrave demanded that all British parts were to be used in this car, and so the 23.9-litre Napier Lion aero engine was chosen. It is important to note that while the Napier brand was not explicitly involved in land racing in the late 1920s, their engines were still highly favoured by mechanics.

This engine was very innovative for motor car racing as it was extremely powerful whilst remaining compact. This benefited the aerodynamic streamlining of Golden Arrow.

This engine’s power came from its 12 cylinders which were arranged in a broad arrow layout. In terms of power output the Napier engine was similar to the two engines in the 1,000hp Sunbeam.

This reality led Irving to focus on making aerodynamic improvements to increase the maximum speed.

Modifications

As Irving and his team built the engine, several vehicle modifications were needed. Some changes were inspired from the ‘Slug,’ and made to improve the performance of the engine. These improvements included:

Chassis rails were made out of steel and threading points were installed at each corner for support.
A three-speed gearbox was installed.
Segrave was seated 8 inches lower, while still being centered in the car.
A new servo-assisted clutch, which helped transform the 900 horsepower to the gearbox.
Ice chests were installed behind the front wheels to help keep the engine from overheating.

William Percival Calvert was responsible for maintaining the Napier engine whilst Golden Arrow was in Florida. Overall, the careful placement of the engine and modifications to Golden Arrow played a key role in the vehicle’s success.

Prior Tyre Developments

Tyres are the most obvious example of an interwar technology which steadily improved, thus enabling the success of Golden Arrow. After the First World War, there was a shift to using stronger materials such as cord fabric. This increased tyre endurance. By the mid-1920s, tyres had become less prone to sudden failure as construction methods continued to develop.

At Brooklands, this increased tyre safety was pushed to the limit by racing drivers, with the conditions of the tyres at certain speeds being reported on by Dunlop tyre fitter, David McDonald. He would send these reports to the designers and engineers at Fort Dunlop in Birmingham, who in return sent McDonald new and improved tyres for the drivers to test. Finding volunteers was an easy process for him as by 1926, he and Dunlop were involved in fitting 75% of all tyres at Brooklands.

Races at Brooklands helped drive forward tyre development and design.

Golden Arrow Tyre Design

John Samuel Irving, the designer of Golden Arrow, opted to use Dunlop tyres for the vehicle given his previous experience with the company during Sir Henry Segrave’s 1927 land speed record. Irving’s concern was ensuring that the tyres did not fail mid-attempt. To prevent this, he compromised on the speed of Golden Arrow as Dunlop were unable to guarantee the safety of their tyres beyond 250 miles per hour. At such speeds, they would be undergoing a violent force of 680 kilograms hitting each tyre at 37 times a second.

Further issues of safety were raised over the heat generated by the tyres at high speeds, with it taking 30 seconds for tyres moving at 250 miles per hour to reach 80 degrees Celsius. To solve this, Irving prioritised Golden Arrow’s ability to quickly radiate heat, in addition to specially treating the tyres with compounds of rubber and powder to increase their resistance to extreme temperatures.

As shown in this image, the wheel fairing helped to reduce drag and increase wheel strength. Meanwhile, the horizontal panels on the left acted as radiators for the vehicle, shedding excess heat.

Tyres After Golden Arrow

Tyre durability continued to improve after Golden Arrow, with them being able to cope with increasing speeds and rising temperatures.

For instance, four years after Golden Arrow, Malcom Campbell’s Blue Bird reached a top speed of 272 mph. Yet it wasn’t until 1960 when tyres temporarily surpassed engines and car designs regarding their tolerance for extreme speeds.

In his book, tyre fitter David McDonald recalled that the Dunlop company in Birmingham had tested tyres for tolerances of 500 miles per hour, despite the land speed record standing at 400 miles per hour.

However, by 1980, increasing automobile speeds once again led to difficult decisions being made due to tyre tolerance limitations.