Why is the back of my van always the dirtiest?

Never understood why the back is always filthy, I'd have thought that as it's virtually 90 degrees everything would run off but no. Must be something to do with the aerodynamics but don't see why it should stick on a virtually vertical plane.

I agree it seems counter to what you'd expect. I assume the low pressure eddies around the back allow the suspended muddy water particles to fall. And once it's collected some dirt, presumably it makes the surface even easier for the crud to stick to. Or something.

It’s called the vortex effect.

Thanks Jim, that sounds very Star Trek! Wait a minute your second names not Kirk is it? Why isn't the back of the Enterprise dirty?

Live long and prosper

You're correct.

https://www.autobulbsdirect.co.uk/blog/why-do-rear-windscreens-get-dirty/

Thanks JKD that's a really good explanation. I may not have a turbo but I've got a vortex! To be more appropriate I may not have Brembos but I have a vortex to slow me down!

Below warp speed it collects dirt and grime, above warp speed it gets burnt off. Considering they're always in a hurry to get somewhere, most of the time they're at warp speed, you never see it when it's dirty. It's also not good PR for the Federation.

I heard from a friend of a friend that the back of the Enterprise is dirty. They retouch the movie via machine learning to make it look prettier. Same as they did with Seven of Nine.

Might explain why their hire vans are dirty, it's difficult to get to those sort of speeds in a Transit!

https://youtu.be/5KiC03_wVjc

Nice and clean back to that one, I obviously need to drive faster!

On topic: the coupe does not have a rear wiper for nothing.

Many years ago, when I was a young bloke, it was common here in Australia for station wagons to be fitted with an aftermarket rear air scoop that directed the air flow down over the rear window to reduce the build-up of dust on the window.

No, what you need to do is this.

You need to take your van to an empty field on a hot day at 2:43pm and drive in reverse at 20mph, for exactly 30 seconds.

Doing this will create a temporal convergence in both the atmosphere outside the van as well as the atmosphere inside it. This will subsequently make positronic graviton particles as well as omega photon particles that are present in the air, come into direct contact with the back of the van. These particles will then sequentially bond and create a negatively charged non-stick surface.

And now for the science part! From then on, whenever your van moves forward at a speed of at least 10mph, this surface will constantly transmit electromagnetic protons that will actively repel dirt on a cellular level and prevent it from sticking to the back of your van.

This has really made me sit up.

I will try this procedure in the coupé going forwards so I'll never have a problem with dirt on the rad grille again!


Now to fathom out the vertical take-off issue

Most of this is perfectly sensible, common sense, the only bit I'm struggling with is getting a hot day and 30mph in reverse! Undermines an otherwise perfectly reasonable post.

The back of Mrs Ed's Seat Mii is also vertical and it suffers exactly the same fate