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 Post subject: Stalker in accident
PostPosted: June 6, 2015, 11:09 pm 
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Maybe I missed it, but Xcarguy had an accident in his Stalker back in February and I haven't seen a post about it here.

I'd not post it now, but since he posted it on a different forum I'd assume it would be OK.

You need to read this. It calls in to question several common building practices on the forum plus highlights the need for some basic safety equipment.

http://www.usa7s.net/vb/showthread.php?10503-My-Accident-at-Texas-World-Speedway

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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 1:09 am 
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The driver said he'll never again run an aluminum seat bolted to the chassis. I understand what he's saying about the lack of shock absorption, but other than sitting on 3" of high density foam I'm not sure there's an easy solution. Once the shoulder harnesses are cinched down really tight - as they should be, that 3" will turn into about 1/2" of solid material. Also, if the shoulder belt mounts are too low, they'll impose a compressive force on the spine in even a straight-on sudden deceleration.

After my brother and I realized we're now driving track day cars faster than some aircraft, we got serious about safety gear: multi-layer fire-proof suits, gloves, arm restraints, HANS, balaclavas, and full face helmets. I think the take away from this is that we're ultimately the one who must decide whether to press on after hitting something, or pulling in and inspecting the car. However, even in amateur events, the "haze of war" can cause us to press on regardless even when nothing's on the line.

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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 4:46 am 
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The use of 3mm plate for suspension mounting lugs has been called into question here in the UK after similar failures. The accident ,all the subsequent damage and injuries appear to be down to the one isolated failure. Its an interesting article and a wake up call , the driver and copilot live to tell the tale.

Bob

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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 9:55 am 
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KB58 wrote:
I understand what he's saying about the lack of shock absorption, but other than sitting on 3" of high density foam I'm not sure there's an easy solution. Once the shoulder harnesses are cinched down really tight - as they should be, that 3" will turn into about 1/2" of solid material.


High density seat foam is entirely the wrong material for this, it's fine for making a seat more comfortable but what you need is something to turn a >20g impact into a <10g impact. What you're looking for is something along the lines of EIS W50 which is serious business motorsports impact padding but quite affordable in raw form (about $30 per inch per seat bottom).
https://www.rollbarpadding.com/product/id-40


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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 11:38 am 
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That is a horrible accident!

The failure of the front mounting bracket appears to me to be similar to the already known failure mode at the rear of our cars. The bracket overhangs the frame member and becomes work hardened over time weakening the bracket. There are many documented failures of this type on the rear suspension. I have not seen or heard of this type of failure on the front before. But it appears to be a similar situation. Jack's 2-piece design for front suspension mounts may be a better solution.

I cannot even imagine spending 15 weeks in a back brace. Good that Xcarguy is not more seriously hurt. I wish him a full recovery.

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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 11:54 am 
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i am not suprised although i am disapointed for the car occupants, the control arm mountings and the control arms themselves have always been a point of contention in an impact.

the "brackets" are to be honest, pathetic for what people are doing with their cars and the speeds now being achieved, it has been well known that the rear mounting points are suseptable to failure under braking.

the 3/4" cds or dom used for control arms is to me just down right dangerous as there is insufficient circumfrence on the ends of the tubes to get a good weld..

the two point attachment is also a problem in a competition car that will go off course any number of times, and suffering the forces of impact repeatedly.

see its like this, i don't know about you but i look at every part of a car i am building, if someone has designed a particular part or system for that car, they are not responsable for making or using that part, there may be floors in its design that are not obvious at first glance, the builder should take all reasonable care when building to build the best, not just that he can, but better!

Attachment:
diagonals.jpg
diagonals.jpg [ 212.86 KiB | Viewed 4141 times ]


in the above picture you can see the lugs for my front suspension, they point in the direction that the force is pulling on them, in my case straight up, thus loading the weld joint equally end to end as oppose to from one end in a tearing motion.
note also their thickness 3/16" and that the load is spread across 6 lugs for each lower control arm that makes 12 weld beads approimately 1/8" thick and they are 1-1/2' wide brackets that an area of 2.25" per side.

the tubes they are attached to are two pieces of 1" x 1" welded togetherto make a 2" x 1" rectangular box but with the added advantage that in the center of the box are two1/16" uprights, this would prevent tear out of the tube wall.

note also that there are three mounting points for the control arm so should one fail, it will remain in position although i suspect there may be a slight change in alignment.

the chassis is painted white so that any cracks are easier to detect not just at the mounting points but in general.

my arms are constructed if 1" x 1/8" wall erw, and although not as strong as cds or dom for the same size tube, the increase in both wall thickness and cross sectional area make them much stronger than the 3/4" dom or cds arms and again, three point fixing.

i am not a genius, this is just practical engineering folks, if someone is selling you a car then don't accept that they have engineered the thing, it may be a case that everybody makes their arms the same so we did too, so clearly they are all under engineered for the environment they are living in.

i must admit that when i built my first locost from Ron's book, i made it as the book said, that was about 18 years ago, almost immediatly i was made aware of the short commings of the lower control arms and associated brackets, i might add that this system has been in use since the 40's for race cars and the first thing to go were the brackets in favor of a tube type mount alas in single shear, remember that race cars have a very short life span in general.

i am sorry for the driver, not only for his injuries but now he can't do what he obviously loves doing, i wish him a speedy recovery and hope like his careful analasys of the accident, he does the same to his car.

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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 12:18 pm 
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I think it's likely or at least possible that this failure was in progress for a longer period of time than this one event. I'm not sure I followed all the pictures correctly - but it looks like the front side of that lower front arm bracket failed. It appears to have a vertical weld along the front edge an the bracket is wider than the frame so that the edge, the HAZ zone, is cantilevered forward of the frame just a bit? Did I see that right? Everyone with wishbone brackets like that should be checking that area.

It looked like there was some discoloration in the cracked area, but maybe that's just dirt? It seems to be an arid area so a crack wouldn't corrode internally?

Bob do you mean 3 mm plate or a section of 3 mm tube?

I don't understand why passengers are so common at track days now. Even for instruction. This car enters early, apexes early and then still chooses to power out onto the rumble strip and then off the pavement at the exit. With a passenger... :shock:

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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 2:44 pm 
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Joined: January 31, 2008, 5:34 pm
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Location: SW Wes Consin
Gregk
Thanks for the foam link. Although I am not sure anything would have helped in a seat that holds your spine so vertical as a Stalker or 7 there are other areas it can come in handy.


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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 6:23 pm 
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Joined: April 23, 2006, 8:26 pm
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My brother's kit car had a nearly identical failure after a very similar off. A front suspension bracket, cantilevered just like the one above, also cracked along the heat-affected zone (HAZ). Fortunately for him it failed a week later, away from the track, while cruising at low speed.

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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 6:36 pm 
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Posts: 176
vroom wrote:
I am not sure anything would have helped in a seat that holds your spine so vertical


On the contrary, just about anything would have helped. Enough of the right sort of foam may have helped enough to keep him out of a back brace. No amount of safety equipment will keep a crash from hurting, badly, but it can help to prevent or reduce the severity of serious injuries.

The accident sounds terrifying, what with the drivers injuries and the fact that he was going over 100mph when the suspension let go. But the thing to keep in mind in regards to things that might have prevented the driver's back injury is that the vertical drop was only about 4 feet. Imagine for a minute that you're about to land butt first on a concrete slab, with your spine vertical, having dropped from a height of four feet. Would you rather land on a 1 inch thick sheet of impact absorbing foam or directly on the concrete?


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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 6:39 pm 
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Posts: 727
Location: SW Wes Consin
Seems to me the serious designer guys generally design the attachments to the chassis to fail first. The idea being to tear bits of gradually and slow the car down. After the Senna crash they now wire all the bits together rather than just letting them fly off. I have read that in earlier days (7 times) it was thought to be better to tear the brackets off than to seriously bend the chassis. I have no idea if this last scheme is true but it might explain the failures in similar cars. Similar except for the V8s. :shock:


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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 6:44 pm 
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Location: SW Wes Consin
I am good with the foam especially with leather, having been pitched down the asphalt a number of times. Three feet is quite a substantial drop at high vertical speed. This is why bike racers always avoid the evil "high side".


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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 7:22 pm 
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gregk wrote:
KB58 wrote:
I understand what he's saying about the lack of shock absorption, but other than sitting on 3" of high density foam I'm not sure there's an easy solution. Once the shoulder harnesses are cinched down really tight - as they should be, that 3" will turn into about 1/2" of solid material.


High density seat foam is entirely the wrong material for this, it's fine for making a seat more comfortable but what you need is something to turn a >20g impact into a <10g impact. What you're looking for is something along the lines of EIS W50 which is serious business motorsports impact padding but quite affordable in raw form (about $30 per inch per seat bottom).
https://www.rollbarpadding.com/product/id-40

I'm sold. I just ordered enough for a 1" pad for both seats.

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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 8:17 pm 
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Joined: April 23, 2006, 8:26 pm
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Location: SoCal
No...

This foam, when used as roll bar or headrest padding, is an entirely different application then when used as a seat cushion. When you cinch down the shoulder belts, it imparts a steady load - unlike in a roll bar or headrest application. The steady load compresses the foam and makes it both harder and thinner. Now that so-called 1" foam is 1/2". As the foam compresses further during the race, the driver cinches down the belts again, and now that 1/2" foam is 1/4". This material is not the solution this thread is presenting it as. It's intended to be used exactly once - like when your helmet bashes into it during an accident. Consider how well the roll bar foam would work if you put dozens of zip ties along the bar, compressing the material before it's used in the event of an accident. That's exactly what's happening when you sit on the stuff and cinch down the belts. The foam works by compressing - being compressed before the fact makes it completely useless. A lot of misinformation here.

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 Post subject: Re: Stalker in accident
PostPosted: June 7, 2015, 8:36 pm 
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Justin Wilson fractured his fifth thoracic vertabre in 2011 at Mid Ohio in an IndyCar. He ran off the course and over an access road, and the impact as he went over the road injured him.

Why? Well, Justin is pretty tall, and in order to fit him into his car (the old spec IndyCar) someone had made the decision to pull the normal seat padding (solidified styrofoam pellets of some sort?). No one knows for sure if he was injured when he hit the edge of the access road (upwards impact) or when he landed, or both, but he was definitely hurting.

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