Lotus E21 construction report part 15

Underbody Manufacturing

With the underbody, I’m working now on (one of) the most important aerodynamic feature(s) of my Lotus. The underbody produces about 30% of the cars (negative) lift, but just a little fraction of its drag. The side of the floor is sealed by vortices, created by the barge boards at the leading edge of the floor.

Special features on the Lotus floor are the Coanda-exhaust sealed diffuser and the blown starter hole.

The Coanda exhaust, was the difference making aero feature in the seasons 2012 and 2013. The Coanda-effect describes the phenomenon of a fluid-flow, following a convex surface instead of separation of it and move along its original flow direction. In Formula 1, this effect was used, to lead the high-energy exhaust plume between the rear tyres and the floor to seal the diffuser. Some teams were able to control this tweak better than others. At the end of the 2013 season, Williams was faster by removing its Coanda system. The most effective systems were built probably by Red Bull and Lotus.

The blown starter hole is an aero tweak, to prevent flow separation at the middle area of the diffuser. There you take “good” air from the side of the car and lead it to the diffuser and exit it via the starter hole to re-energize the boundary layer. With the ban of the classic starter holes in 2014, some teams use vortex-generators to convert the air to a turbulent flow for preventing a stall.

Underbody

The underbody in current state viewed from the top. You can see very good, how narrow the rear of the car is. The two ducts left and right are the ducts to blow the starter hole. Above this ducts, the exhaust will exit the bodywork in its Coanda-groove. More on this later.

Diffuser

Trailing edge of the diffuser. Because of the special shape, the rear of the underbody is a bit deformed due to internal stresses. But with adding another layer of paper (the top one), this should be solved…

Underbody

The leading edge of the underbody. Weird stuff…

Underbody

A better view on the blown starter hole ducts. You can clearly see how it works. There’s an awful lot of air coming from the side of the car. I expect just a very small percentage of this air effectively find its way thru the starter hole. The two cutouts/dents which you can see at the inside halfaway thru the duct are there for the pullrods.

Underbody

Nice rear view where you can see very good the deformed sides. You also can see the exits of this two ducts, which are beside the gearbox later on the car. This ducts end about at the rear axle center line.

Barge Boards

The barge boards which produce the vortex at the leading edge of the floor. This are far the most comlex boards I’ve ever seen in F1. They consist from four airfoils with the last two ones splitted. Lotus used them just in the 2013 season. In 2014 they returned to a more conservative design.

Rear

Underbody pre-fitted to the car. You see the amazing packaging around the gearbox. Here you can see again the cutout for the pullrod. At the moment you can see the rocker there.

Car

This will be a tough challenge to make the underbody fit perfectly to the car…

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About paulsf1

My name is Paul Bischof. I’m a student in mechanical engineering at the Technical University of Graz in Austria, expected finishing in February 2016. Since I was eight years old, I am building model planes out of paperboard. Since 2004 I scratch (that means building without an assembling set) Formula 1 and sportscars in 1:10th scale. The average time I need for such a car is around 400 to 700 hours within 4 to 8 months. One car has around 3500 up to 5000 single components. On this blog, you can take a look on my work and later, after my studies, hopefully you can see me in Formula 1.

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