10 replies to this topic

[Charlieman]

Over the years, I've read stories about drain and inspection covers being lifted by racing cars on street circuits. There are lots of types of covers -- the quarter metre squared, two kilograms of pressed steel water point cover in my backyard, or the cast iron lid on the road which was once worth stealing for scrap metal. If I was designing a circuit, I'd presume that the former needed to be secured and skip the latter.

 

So what were the bases for stories about "lifted" drain covers?

 

A related aside: the trunk road closest to home was closed one summer whilst bridges over visible and subterranean rivers were reinforced. Local traffic and emergency vehicles passed over those huge steel sheets where the road was excavated. One day a fire engine belted along over one and I saw the metal sheet move two feet back down the road. I didn't expect to see that.

[Robin Fairservice]

A few years ago, in a race for sports racing cars in eastern Canada, one car lifted a manhole cover and it hit the car behind, causing lots of damage and I believe some injuries.  I worked as a Flag Marshal for fifteen years at Vancouver for the Indy races there, and the City of Vancouver welded every manhole cover on the track.  Flying cars were bad enough, but I didn't fancy flying manhole covers!

[jcbc3]

I saw this one on live tv back in the day:

 

Scroll to 4:55 or so:

 

In that you'll see a bridge overpass with PLAYERS on it. Scroll to 9:35 to see the accident from there:

[fbarrett]

I was shooting still images from the river side of the fence at driver's left. Missed the initial accident but caught the aftermath. Luckily, no one was killed.

 

Frank

[Charlieman]

Thanks. That looks like a light weight inspection cover -- 2 or 3 kgs -- thrown into the air by wheels. It shouldn't have happened and I am horrified.

 

I'm more interested in heavier covers -- say circular 450 mm diameter cast iron, or 300 mm by 400 mm street grates. I share my fetish with the leader of the UK Labour Party.

[Lee Nicolle]

Here in Adelaide that was one of the things done, they welded all the manhole covers down.

In China when V8SC went there Mark Winterbottom had a manhole cover or grate rip through the bottom of the car. Narrowly missing the driver and I believed destroyed the shell.

Just yet another problem with street circuits, though Frostys effort was on a pernemant circuit.

I feel they weld the covers for not the down force but the associated traction. The tyres lift the covers.

[kevins]

I'm not sure if many of you have seen a TV show called MythBusters? They do experiments to see if urban legends etc are true. They tested this with a 2 seater Indy car and concluded it could not happen.

 

 

http://mythresults.c...ndy-car-special

 

http://www.wired.com...th-an-indy-car/

 

Should easilly be found on Youtube

Edited by kevins, 21 July 2016 - 05:49.

[Lee Nicolle]

Myth Busters get it wrong at times, it has happened on too many occasions

[Sisyphus]

The basic physics is pretty simple.  The vacuum pressure on the manhole cover has to balance the weight of the cover to be able to start to lift it. 

 

So, pressure times area must equal density of the cover times the area of the cover times the thickness.  The area cancels out (ie, it doesn't matter what the diameter of the cover is).  Cast iron weighs 0.258 lbs/in^3 and a typical manhole cover is 1.75 inches thick.  Doing the math says you need a vacuum of 0.45 psi to just lift the cover.  That isn't much (atmospheric pressure being 14.7 psi).

 

The amount of vacuum produced by moving air is equal to the air density times the velocity of the air, squared divided by 2 times gravity.  Working thru the units shows that an air velocity of 160 mph is just about 0.45 psi.  Which may be where the Mythbusters number came from. 

 

Of course, the flow thru the venturi can be somewhat faster than the car velocity.

 

But that only just balances the load and you need to take its inertia into account...

 

My guess is the sudden impact loading of the race car wheel hitting the top of the cover is at least as important as the vacuum in getting the covers to fly up.  In any case, they obviously need to be (well) welded down. 

 

Any known cases where a cover has come up in a NASCAR type race or similar?

[Lee Nicolle]

As I said earlier I feel it is the traction afforded by the aero that picks up those covers  or grates.

[Gene]

Morning, I seem to remember back in the IMSA, GTP wars in 1989 at Delmar, the Costas Los Porsche sucking a manhole cover that wasn't welded in place.

GTP cars were full ground effects, in fact our aero guy, Dick Yagami claimed at 190mph the Nissan could be driven on the ceiling!