Spoiler

Ralph · Post by **Ralph** » Thu Dec 20, 2007 10:45 am

I wondered if all the crap was being pulled up from under
the Bongo most hatch backs have wipers but saloons don't
and don't seem to get as dirty aerodynamics and all that.
Any one fitted a rear skirt? did that do anything?

mikeonb4c · Post by **mikeonb4c** » Thu Dec 20, 2007 2:35 pm

I'd have said yes Ralph, only its such a long way up to the Bongo windscreen from the ground that I wonder if it could be. I reckon, try side skirts first and then try a bottom one. Quite likely none of them will make a magical difference and even more likely I won't get around to trying it in any case. My urge is more and more to stop fettling it and get out in it (amazing how a bad back episode can trigger a change in priorities - gotta be positive)

missfixit70 · Post by **missfixit70** » Thu Dec 20, 2007 6:55 pm

I used to have a sierra 4x4 estate with cosworth bodykit with rear skirt & it was shocking for the rear window getting filthy in no time flat. I know it was dragging from underneath as the gearbox seals leaked & the oil ended up on the rear windscreen. Coated the chassis nicely onits way though

The Great Pretender · Post by **The Great Pretender** » Thu Dec 20, 2007 11:19 pm

Ralph wrote:Does the spoiler have any noticeable effect on anything?
like the back of the van getting covered by muck? ours
without a spoiler is always covered in crap no matter how
much we clean it.

Marry Christmas and a happy new year to all.

What you refer to as a 'spoiler' is an airflow control device known as a cusp. It is a vortice generator, the air under it is (if viewed from the nearside) trapped and spinning clockwise. This helps to reduce drag by pulling the air travelling over the roof down into the wake behnd the vehicle.

mikeonb4c · Post by **mikeonb4c** » Thu Dec 20, 2007 11:46 pm

You are quite right GP - I wasn't going to go into that territory, but its all about modifying the local airflow to discourage uncontrolled boundary layer separation, vortex generation and consequent drag and unstable airflow likely to impact on directional stability of the vehicle. With careful design, te 'cusp' may create a boundary layer over the windscreen glass and propel precipitates past the pane but in practice it probably does this imperfectly. It is for this reason that I am dubious whether side curtains will help as unless they are subtly shaped and slotted they will set off 'swirl' and subsequent silting of the silicon based slab.

If I've turned into a clever dick you can blame Mister Munkey, who has just slapped on me a 'Just Ask Mike' obligation

The Great Pretender · Post by **The Great Pretender** » Fri Dec 21, 2007 1:21 am

If my memory serves me, isnt there the an angle for rear window for self cleaning (airflow over) something like upto 30deg then stall untill 45deg cant remember the upper limit. I dont think the cusp is there to control boundary seperation (although it will help on the roof and possibly drag the muck up onto the rear window as it sucks up static air behind the door) its primary use is to reduce drag, a lot of modern cars use them dont they.

mikeonb4c · Post by **mikeonb4c** » Fri Dec 21, 2007 3:40 pm

Boundary layer separation and drag are inextricably linked I fear. its a bit like the difference between rolling a bowling ball smoothly out of your hand onto the bowling lane, and just dropping it. how you do one has a big influence how the other goes. But as to wether serious boundary layer / airflow testing in a wind tunnel was done, I wouldn't know.

bigdaddycain · Post by **bigdaddycain** » Sat Dec 22, 2007 2:26 am

My sister had a bongo a few months previously to myself, in fact, she took me in her bongo up to timperly to pick up my beloved bongo for the first time.

We visited morrisons garage for a jet wash each,so both bongo's were equally clean for the following journey to winsford.

It wasn't raining, but the roads were wet enough to create noticeable spray on the m6,as we arrived at her house,there was a marked (pardon the pun) difference in the state of our rear windows

Mine was definitely cleaner (you could barely make out the wiper stroke mark) Whereas my sis's was quite dirty,with a noticeable stroke mark from the rear wiper.

Mine has a spoiler, her's didn't...

I'd say that was quite a definitive test really,as we travelled in convoy on the exact same roads,at the same speed.

If you ever look at the plume of spray from a passing hgv,you will notice that the spray eminates from the rear wheels (mainly) and is then sucked onto the back of the vehicle by the wind created by the vehicle,it's a sort of swirly,sideways typhoon,with most of the spray "dropping" from above... I think thats why the spoiler helps to an extent,its affecting the aerodynamics to the rear of the bongo,enough, in my opinion to help keep the rear window a bit cleaner...

Plus the spoilered bongo sticks to the road when taking corners at 130MPH

MountainGoat · Post by **MountainGoat** » Sat Dec 22, 2007 2:29 am

Adding airvation fuel to your diesel now bigdaddy?

bigdaddycain · Post by **bigdaddycain** » Sat Dec 22, 2007 2:31 am

its gotta be cheaper than straight diesel surely?

mikeonb4c · Post by **mikeonb4c** » Sat Dec 22, 2007 1:01 pm

Well put BDC. If there was a way of preventing the same swirl sweeping round the sides it would be even better. I suspect the underneath isn't a big offender with the Bongo but I could be wrong. Try it a step at a time I guess (if anyone can be bothered)

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