The fuel flap and actuator

No part of a Formula 1 car is simple. Even those components with a seemingly straightforward function have a story to tell. And the fuel flap is a perfect example.

Just like on a road car, this small piece of bodywork covers and protects the re-fuelling valve when it is not in use. From 1998 – when the fuel flap was introduced following a spate of re-fuelling valve fires – until last season, this part of the Team McLaren Mercedes Formula 1 car lifted straight up like a cat flap.

That was until the team’s designers created a pair of aerodynamic ‘horns’ for the MP4-20’s roll hoop. Suddenly, the fuel flap had to both lift and turn to negotiate this extra piece of bodywork. “It has been a good challenge, coming up with this year’s design,” says Phil Mackereth, Design Engineer.

There are two parts to the fuel flap system: the carbon fibre flap and the hydraulic actuator which makes it move. The solution Mackereth and his team developed was to supplement the traditional actuator – which was a relatively simple linear hydraulic device – with a helical follower.

“A linear hydraulic actuator is very simple and moves in one direction,” explains Mackereth. “We needed it to both lift and turn, so designed a helical follower which is used to transfer some linearly motion into turning motion.” No longer such a simple part, then.

“The follower is a cylindrical component with a helical slot and a pin that runs through it,” he adds. “As the component slides along its axis the pin forces it to rotate.” The fuel flap is made of a lightweight carbon fibre two-skin assembly. It is riveted to an aluminium bracket that joins it to the actuator, which is bolted to the car’s rear bulkhead.

Thankfully, the actuator does all the hard work, so the driver and pit crew don’t have to. As the driver enters the pitlane for a re-fuelling session he hits the pitlane speed limiter button, which also opens the fuel flap. The pitcrew are then ready to fill the fuel cell with the specially-developed Mobil 1 fuel.

The flap raises within one second, but it could open more quickly. There is in fact so much speed in the actuator that hydraulic restrictors are used to slow it down and prevent damage.

The actuator must be manually overwriteable in case of an electrical or hydraulic failure, so one of the pit crew carries a small tool which can be inserted into the flap to manually raise it. It is unlikely that this tool will ever be used, but as always in Formula 1, it pays to be prepared.

Technical Specification: Actuator

• weight: 95 grams
• length: 75mm
• width: 50mm
• materials: Aluminium and steel