How much lift does an average car bonnet create?

[Papa Hotel]

One for you aeronautical engineering types; at a rough guess, what speed would you need to be doing before an unsecured car bonnet would lift, flip and smash into the windscreen? Take a BMW E46 as an example.

Note: this is hypothetical only.

[Superhoop]

Not as fast as you'd think if the secondary catch isn't latched at all - 30 mph or so tops

[panholio]

PM any Renault Clio II owners.

[wormburner]

...what are you planning now...?

[Papa Hotel]

wormburner said:

...what are you planning now...?

My Aerocatch bonnet pins arrived today, they feel a little flimsy. Plus, I accidentally ordered the flush ones, I'd be concerned about the bolts holding it to the bonnet just pulling straight through the bonnet at speed.

[John D.]

panholio said:

PM any Renault Clio II owners.

I keep eyeing the bonnet on my 205 at three-figure speeds. I think it just vibrates with the rest of the car

[Blayney]

When we picked up the mini someone didn't put the bonnet back on the latch properly after inspecting it. About 20 miles later it flipped up at around 55mph. My Dad remained miraculously calm and pulled it over safely.

[4key]

Papa Hotel said:

My Aerocatch bonnet pins arrived today, they feel a little flimsy. Plus, I accidentally ordered the flush ones, I'd be concerned about the bolts holding it to the bonnet just pulling straight through the bonnet at speed.

When only using bonnet pins we used to also apply a strap secured between the bonnet and the slam pannel as a secondary measure, long enough to open the bonnet a good distance so that you can easily unclip it but not so long that it gets caught up in the fans and stuff.... and 3 minutes later i still cant think where we got them from

[Papa Hotel]

4key said:

When only using bonnet pins we used to also apply a strap secured between the bonnet and the slam pannel as a secondary measure, long enough to open the bonnet a good distance so that you can easily unclip it but not so long that it gets caught up in the fans and stuff.... and 3 minutes later i still cant think where we got them from

Ah, that's something to think about doing.

[4key]

Ive tried googling but all that i have found out is that weird people use leather belts to tie down the bonnets on their minis


e.t.a. if you do go searching, they were like the race towing straps that replace the tow eye, but longer.

[SlimRick]

A Volvo 440's bonnet will lift at approximately 45mph. It will flip up, cracking the windscreen and bending the bonnet beyond repair. This is a fact.

[DonkeyApple]

Blayney said:

When we picked up the mini someone didn't put the bonnet back on the latch properly after inspecting it. About 20 miles later it flipped up at around 55mph. My Dad remained miraculously calm and pulled it over safely.

Where do you reckon Ace Ventura got his driving style from?

Most of us who've had a Mini have had to drive a few yards with our head out the window.

At least with the old Renault 5 that opened the other way round and due to the large front area you had the option to accelerate or break at 45 when it half popped up partially obscuring your view.

[mike9009]

Common problem on alfa 156s too. Never heard what speed they get to before they lift and smash the windscreen and roof.

< runs to check bonnet release catch is lubed and freely returns......>

mike

[noell35]

panholio said:

PM any Renault Clio II owners.

saw one of these only the other day on the M6 North just after the M65 junction with the bonnet flipped on to the windscreen. Scary stuff.

[Barronmr]

My bonnet catch was sacrificed in the name of fitting a supercharged V6, however turns out not to be much of a problem even at motorway speeds. :P

See here http://www.youtube.com/watch?v=lKNKU0mtoTU

[Papa Hotel]

Barronmr said:

My bonnet catch was sacrificed in the name of fitting a supercharged V6, however turns out not to be much of a problem even at motorway speeds. :P

See here http://www.youtube.com/watch?v=lKNKU0mtoTU

Hmm...

[welaye]

panholio said:

PM any Renault Clio II owners.

Haha spot on. I've currently got one, bought when I was only 20. Young & naive unfortunately, as I took no notice of the constant warnings of French cars being made from plastic...almost entirely (front wings!??!)

I've just finished working on a project at Nissan in Sunderland, we supplied some parts to Renault so I can only guess the newer Renaults are of better quality...

[1point7bar]

I don't think the boundary layer of the laminar flow is close enough to the bonnet of a normal saloon to make lift.
The high pressure turbulent zone inside the engine bay probably pushes the bonnet open and then drag acts on it's resistance to the main airstream.

[Condi]

Mine started moving around about 35ish? Thankfully I saw it and dived off the duel carrigeway and shut it!

[Papa Hotel]

1point7bar said:

I don't think the boundary layer of the laminar flow is close enough to the bonnet of a normal saloon to make lift.
The high pressure turbulent zone inside the engine bay probably pushes the bonnet open and then drag acts on it's resistance to the main airstream.