Speed humps

Speed humps

Author
Discussion

cinman

Original Poster:

182 posts

260 months

Tuesday 15th April 2003
quotequote all
I do flying lessons at Biggin Hill, which has b*stard speed humps all the way round the airfield. They "look" too big to drive over without something scraping ... can I just ask: what's the worst that could happen if it bottom's out? eg. is it chassis lengths that'll ground first and that may be able to take a slight scrape, or will it be more delicate gear? Of course, if it scrapes, I won't go again in the Cerbie, but just wanted to weigh up the risks of a scrape first time round?

olly

2,174 posts

291 months

Tuesday 15th April 2003
quotequote all
The 1st thing that will ground will be the chin spoiler (£12 for a new one if you really f**k it up), the next thing will be the plate that protects the CAT's, but I'd be amazed if you did any damage apart from scraping the bolts....

What are the speed humps made of ? Brick - flat topped ones, tarmac humps, rubber triangles..... ?

dannylt

1,906 posts

291 months

Tuesday 15th April 2003
quotequote all
Forget that spoiler as soon as it drops off - doesn't seem to make any difference.

As Olly said, Cerbera is miles better than the Griff/Chimaera in that the first things to touch down are those bolts. My car scraped the hump outside my girlfriends house every time with a horrendous noise, but hardly any damage to the bolts, and never any problems getting them off.

danny

cinman

Original Poster:

182 posts

260 months

Tuesday 15th April 2003
quotequote all
The bumps are oval ones, whole road width, kind of semi-circular profile if looking at them end-on. They already have scratch marks on top of them which would suggest I'm not the only one to have had this problem?

olly

2,174 posts

291 months

Tuesday 15th April 2003
quotequote all
I'd say give it a try (going nice and slowely) & just see what happens - you nenver know, you might make it fine !

stickshaker4185

51 posts

264 months

Tuesday 15th April 2003
quotequote all

dannylt said: Forget that spoiler as soon as it drops off - doesn't seem to make any difference.

As Olly said, Cerbera is miles better than the Griff/Chimaera in that the first things to touch down are those bolts. My car scraped the hump outside my girlfriends house every time with a horrendous noise, but hardly any damage to the bolts, and never any problems getting them off.

danny



stickshaker4185

51 posts

264 months

Tuesday 15th April 2003
quotequote all
The chin spoiler looks insignificant, but is more important than you might think. Ground effect in car terminology (as opposed to aerospace), is downforce created by a low pressure area between the underbody and the ground.

Bernoulli's theorem states that pressure is least where velocity is greatest and vice versa. If we apply this to the chin spoiler, it accelerates the airflow beneath the car creating low pressure, and thus DOWNFORCE.

Without the chin spoiler the car is less stable at high speeds, and front end grip is reduced. It was fitted for good reason and should be replaced if found to be missing.

Hope this is of some help.

>> Edited by stickshaker4185 on Tuesday 15th April 19:21

cinman

Original Poster:

182 posts

260 months

Tuesday 15th April 2003
quotequote all
Well thats the first time i've heard anyone use Bernoullis principles here?

ro_butler

795 posts

278 months

Wednesday 16th April 2003
quotequote all
Have to say I agree with Danny, the chin 'spoiler' is unlikely to make any difference.

Whilst you are correct about the bernoulli principle, the length of the effective venturi tube is only a few cms. Other things to consider are that since the car does not have a flat underside then there will be quite a thick boundary layer under the car, limiting the flow and thus destroying the venturi effect.

The main problem for road cars is not front end lift but rear lift due to flow separation at the rear of the car (hence people fit those comedy rear spoilers).

In short don't worry about the spoiler (although mine is still there and if it fell off I'd have it replaced )

glennmoore

9 posts

273 months

Wednesday 16th April 2003
quotequote all
I too have a Cerb and fly at Biggin. Provided that they are taken slowly they cause no problem.

ches

77 posts

276 months

Wednesday 16th April 2003
quotequote all
"venturi tube"
"Bernoulli principle"
"boundry layer"
"flow seperation"
"ground effect"
Anyone fancy a pint!!!

cinman

Original Poster:

182 posts

260 months

Thursday 17th April 2003
quotequote all
Cool - I tried it this morning and it does indeed clear them - brilliant!! I'm not flying again until tomorrow evening (Fri 6:30pm) so I'll keep an eye out

bacchus180

779 posts

291 months

Thursday 17th April 2003
quotequote all
mine drags along the bottom every where... the plate has been adjusted with a crowbar to make it stop hittin the exhausts, the spoilers been gone and replaced several time.... and at 150+ its a solid as a rock!

Cajun

67 posts

278 months

Tuesday 22nd April 2003
quotequote all
If you ignore the chin spoiler your PPL might be needed sooner than you think...

C