Hardtop airflow…..

[howardb66]

Having a passing interest in airflow, I was pretty surprised with the following…..

Whilst I was driving back from a very wet race meeting, I noticed that the rain drops were moving UP the rear screen on the hard top if they moved at all. That’s not right- that means that there is a massive eddy in the airflow as it breaks away from the roof. Therefore any boot wing/spoiler is ineffective & it’s causing drag.
So as an experiment I put a band of tape ‘spoiler’ sticking up about 10mm across the roof about 75mm short of the rear screen. Using the scientific method of chucking some water on the roof then going for a blast, I deduced that this was complete rubbish.
Hmmmm, after a bit of investigation, I spotted the roof spikes on some rally cars…💡

In theory, changing the profile of a car is against the competition regs but …..

[dickie]

The idea of spoilers on most cars is not to create downforce.
The function is to break up the airflow to prevent aerodynamic lift.
That is why they are called spoilers not Wings.
A nose spoiler can be more effective if very close to the ground as it will stop air going under the car which is a an area of huge turblent drag.

Its a very complex subject.

A slight nose up or tail up will change the aerodynamics.

Lowering the car reduces frontal area, GOOD.
It reduces the volume of air under the car GOOD.
It lowers the centre of gravity GOOD.
It makes a nose spoiler more effective GOOD.

Taping up the boot seams, bonnet seams and passenger door seam will all help, as will fitting smaller more aerodynamic exterior mirrors.

Very wide wheels increase drag NOT GOOD.

It a great subject to research and apply.

I can gain 10 MPH speed in my Austin Seven by taking the windscreen off. Less frontal area and less drag.

Just stick your hand out of the window at 30 MPH put it out horizontaly then rotate it slowly ( Do this as a passenger for safety )

Austin Seven has no indicators or side windows so I have spent a lot of time with my hand out doing hand signals.
Its hard work holding an arm out with the hand flat to indicate a lane change at 60MPH.

I now expect the real experts to fly in.

[Zed.]

Oct 22, 2021 17:33:37 GMT dickie said:

I now expect the real experts to fly in.

or hecklers




Rich.

[dickie]

Flying on four wheels by Costin is a good book to read.
He is responsible for the Vanwall body design. Lotus 11
He had a hand in Baby Bertha too !!