Exactly
This is what I was try to say in my first post. This is what I think is legal and I was trying to say that I had to have a 31" bulkhead/cross section piece in my aluminum crush box/nose all in on. The new car will have the aluminum crush box with the 31" cross section in it and fiberglass skin covering it. That is legal to me.Originally Posted by Brands
Jerry
Wren,
At least now you believe that you do not need a bulkhead in this 40cm zone. Sufficient wall thickness area weather it be U-shaped cylindrical or whatever, as long as it adds up to the required sectional area. Correct?
Agreed. Cross sectional area is the requirement with minimum construction standards seems to be the rule. I think a bulkhead is the best solution.
Ben Cooper's nose is much like the nose that was on my '98 Tatuus when it nosed into the pavement in Thunder Valley. It deformed properly on impact.Someone like Phil Creighton would have to say whether it was a FIA approved nose or not.
Ardie's nose, as i inspected it afterwards, was relatively intact, not accordianed. It was in the back of a wrecker and i did not handle it enough to pass any judgement.
The problem with great attentuator noses, as i said earlier, and as Steve Lathrop has stated recently, is not so much in their construction, but in the strength or lack of in their fastening to the chassis proper. The best nose, if it also meant to be the attenuator, is worthless if it get torn off easily in a side impact.
That is why i mentioned the inadequacy of just small "pucks" inserted in the wall of the nose to be relied upon for attachment. Look at Dennis' picture and you will see a torn out puck still attached in the frame's upper right front corner. If the puck doesn't just pull out of the material, then usually the small attachment screws break quickly.
Posting the picture of the new Citation rear attenuator was to show an example of an attachment system possibly robust enough to do its job properly, not relying on a few small embedded pucks for support.
Wren, i do feel your abundant energy would be more productive if you helped us come up with possible better solutions, instead of going into "attack mode" while getting all wrapped around the axle about perceived "legality". I can say with a bit of confidence, that if a panel of engineers can show where there may be a problem in the rules that prohibits modernization of safety elements, many of us will work within the system to get a solution. So far, the engineeers are telling me they can build the safer parts within the existing rule package.
My goal is to be taking less of these ugly pictures in future seasons.
Now the problem with the way the rule is written is that I do not see any statement that requires that this sectional area has to be maintained rearward to the attachment zone.
I agree completely. For that reason, FIA requires that modern formula car noses pass both a frontal impact (sled) test and a "pushoff" test with an oblique load. Not sure how we could implement a similar requirement in these cars, but it's worth thinking about.
Not necessarily, assuming it was composite. One reason composite materials are so superior to metals for crash attenuation is that they will essentially disintegrate when they reach a certain stress level, absorbing a huge amount of energy in the process. Here's a video of the USF1 nose impact test. No jokes, please, that part of the car was designed and built well and passed the test!Ardie's car should have had crushed nose box all over the front bulkhead.(Shameless plug: the Radon nose was designed and analyzed using the same tools, uses a similar layup schedule and is made by the same company, and we expect it would do about as well).
Completely agree.Second, and this is the problem I have been working since my first nose box, the box must crush from the nose rearward. The last section to fail must be the mountings to the front bulkhead.
In the spirit of the original post, I think we can learn some important lessons from Ardie's crash, ones that will help us make these cars safer.
First, as Steve and Mike have pointed out, mounting points for the nose and crush box could be improved on some cars. From Mike's last post, it seems clear the mounting points failed very early on Ardie's car, preventing the nose from doing it's job properly. Improving that area seems like a fairly simple task. I believe better mounting points could be added to existing frames and noses could be constructed with a more substantial attachment structure.
Second, I noticed that the floor on Ardie's car separated from the lower frame rails and distorted upwards, injuring his foot. The tubular nose structure also failed at some of the joints. I believe someone made this suggestion previously in another thread, but perhaps stressed skin panels should be allowed for the sides and (maybe) top of the frame within some distance of the front bulkhead (12"?). In combination with the existing allowance for stressed floor pans, that would strengthen the nose box area substantially, and also protect the feet, which tend to be easily injured, in an accident like this.
Nathan
Ardie had a steel floor that was bonded and riveted. Only about 5 rivets failed, and a small area of the floor in the front corner broke its bond. The floor farther back had a wave in it. Ardie spent much time on the phone with me last friday going through the autopsy as they had torn the car down to the bare frame. He credits the steel floor as being the most important single element in saving him from worse injuries after his HANS. His foot injuries appear to have occured from being tangled in the pedals upon impact.
He said he was going to post a report sometime. He had a true bead seat (Bald Head) that took a lot of punishment and is used up. He submarined his butt into the panel covering the fire bottle, and it is also used up. (his butt and the panel)
I believe most Citations have a welded steel floor ahead of their floor "step". When i rebuilt my Reynard, i welded a 18 guage steel floor into the area ahead of the Reynard's step upon advice from Steve Lathrop.
Thanks for the update. Just glad Ardie didn't suffer serious injuries.
I agree a welded floor is the way to go. It's probably only feasible if covered by a fiberglass undertray, though, since it's hard to replace!
Nathan
Go to www.engineeringtoolbox.com or wikipedia if you dare; you may learn that many people in this thread are correct.
Ben:
We used a similar approach for the Radon nose. The additional benefit, which I'm sure you appreciate, is that it makes layup of the front of the nose much easier when it's a small separate part rather than at the bottom of a very deep tool.
Nathan
Brazing vs. welding
A few question for the experts and Wren (!):
Chill Bro, you know I am "Joshin'" with you...
In the lower pic the frame appears to have ripped apart at the brazed area of attachment.
Would I be correct in saying this method may prevent damage further aft by doing what it did vs a welded joint?
Is this failure mode preferable over a welded joint, or would they be similar?
What would a welded joint look like in a hit like this?
Can any of these questions be answered with any level of certainty?
These are the only photos I have of Ardie's car after the wreck, if they are objectionable just let me know and I'll take them down.
Use the shocks for a point of reference as to what is "straight." I was looking straight onto the chassis, not at an angle.
No, they are not.Go to www.engineeringtoolbox.com or wikipedia if you dare; you may learn that many people in this thread are correct.
The reason to get so wrapped up in legality is that you cannot separate legality from safety.
I know that I am not an expert on crush structures and their design and I am pretty confident that no one else here is either. I have worked on research projects that did a lot of impact research (I was working other parts of the project, but still sat through their research meetings) and I have a passing familiarity with the work the guys in my organization are doing that test crushable structures constantly. The constant theme is that testing is neccesary. Modeling and sim can only take you so far and can easily be far off. This matches well with why the FIA requires crash testing on things. I know that design of crushable nose structures is well understood by people on F1 teams, but they still have to test them because it is the only way to be sure.
Crash testing every box in every installation is going to be the optimum, but not always practical solution. The SCCA has taken their collective knowledge of years of seeing these things crashed and generated another path to compliance based on what they have seen from these crashes. I think that these really bad crashes that people keep walking away from is a validation of that.
I don't doubt that people can build safer parts inside of the rules and we should absolutely be trying.
The nose that had the wing fall off because it was built wrong?
Other than the cost and forgetting the GCR rules, can you please share why you think a carbon fiber nose should not be allowed? Just curious.
Cross-section of this thread:
pictures but no sketches
celery
memes
importance of commas but no one cited Strunk and White
smileys
conjecture
chest thumping
the quote function
But like all cross sections, this one too depends on the plane with which you section it.
A slice from another angle:
Pictures of actual crash damage.
Pictures of modern attenuators.
Discussion of what we might do to improve things.
From the GCR:
Carbon fiber is prohibited in any external panels or any panels
licked by the airstream (e.g., radiator ducting or engine air inlet),
with the exception of impact attenuation structures. Carbon fiber
may be used in internal panels and components (e.g., instrument
panel, radio boxes) unless otherwise restricted.
Isn't the front crush box (nose) by definition an impact attenuation structure?
Really? Just another example of you being wrong but confident about it.
No F1 team really needs to test their noses, they already know exactly how they are going to perform from structural analysis and experience. The FIA requires testing and certification so that teams don't "cheat" and build a lighter nose that won't pass the test.I know that design of crushable nose structures is well understood by people on F1 teams, but they still have to test them because it is the only way to be sure.
Do you really believe that? Does your vast experience from attending a few meetings suggest that the minimum design allowed by the GCR provides any significant protection in a frontal impact? There's a reason Steve Lathrop builds a nose crush box much better than the minimum required by the GCR, and people are adding rear attenuators (carbon fiber ones) although they aren't required by the GCR.Crash testing every box in every installation is going to be the optimum, but not always practical solution. The SCCA has taken their collective knowledge of years of seeing these things crashed and generated another path to compliance based on what they have seen from these crashes. I think that these really bad crashes that people keep walking away from is a validation of that.
I agree. That's what we're doing.I don't doubt that people can build safer parts inside of the rules and we should absolutely be trying.
Yes, that one. As I've explained before, the design was correct, but there was an error in manufacturing that resulted in inadequate reinforcement for the wing mounts. All of the noses built since have performed flawlessly, and if that's the only failure we have in developing the Rn.10 I'll be very happy (and a bit surprised).The nose that had the wing fall off because it was built wrong?
The nose did perform exactly as designed in the impact. The car left the track at over 100 mph and crashed straight on into a tire wall. Matt walked away with no injuries and there was no damage to the chassis or even anything attached to the front bulkhead.
You might ask Matt in which of the many cars he's driven he feels safest.
Nathan
Last edited by nulrich; 01.06.15 at 4:16 PM.
A few question for the experts and Wren (!):
Chill Bro, you know I am "Joshin'" with you...
In the lower pic the frame appears to have ripped apart at the brazed area of attachment.
Would I be correct in saying this method may prevent damage further aft by doing what it did vs a welded joint?
Is this failure mode preferable over a welded joint, or would they be similar?
What would a welded joint look like in a hit like this?
Can any of these questions be answered with any level of certainty?
I am not a qualified expert in welding but I do have a lot of years doing it. For all practical purposes, the structural differences between the English low temperature welding with the alloy they use and TIG welding commonly used in this country is neglable. I can argue that brazing might be better than TIG.
The one miracle in this wreck is that the blow was at a sufficient angle to avoid driving the master cylinders through the front bulkhead. The front bulkhead remained in tact. Ideally the nose box should have absorbed the blow that the front corner of the frame did. On the current Citations, I mount the master cylinders 3.6" in front of the bulkhead on a crushable structure. The pedals are 7.5" behind the master cylinders.
Making the nose box in two parts is what I do. The crush box/attenuator is an extension of the frame. The wings are mounted to a separate part attached to the front of the attenuator.
I also build my wings with a spar that only extends to the middle of the wing on either side of the nose. The idea here is that the wing will fail in the outer half, leaving the inner half functional. This also minimizes the risk of damaging the nose box when the wing is hit.
We are making our nose boxes and the nose cone from cardon. The entire structure is integral. I would like to see the steward who will put his name on the order to change the material in the nose cone.
I'll answer your last question first: no.
If both methods are done properly, there is functionally very little difference between brazed and welded steel tube structures. A welded chassis would have failed in a similar manner, although if it was 4130 it probably would have failed just outside the weld bead. As a driver, there is no reason to prefer one method over the other.
Nathan
Starting to get good, guys. Keep it up!
As long as we are designing better structures we should be clear on what the rules require so we know what parameters we need to build to.
http://www.engineeringtoolbox.com/pi...ons-d_873.html
Notice the difference between the formulae for "cross section area" of a hollow structure AND what they refer to as "area of metal".
Has a carbon/kevlar structure with some creafoam fill structure been tried/tested?
Yes, they do. The original '86 rules minimum requirement was based on the results of Adrian Reynard's FIA sled tests of his '84 ('85 ?) F3 car. That length and material requirement was the minimum necessary to keep from "killing" the test dummy. Obviously, our desire for even better performance has increased dramatically since then, but the GCR minimum alu box requirements are definitely based on real world test data.
Does your vast experience from attending a few meetings suggest that the minimum design allowed by the GCR provides any significant protection in a frontal impact?
The floorpan is very much an integral component of how the frame will perform in a crash, which is why the conscientious manufacturers go to great lengths to make its attachment as strong as possible. The fact that the rules for FB (and FE) allow the floor to be attached so poorly to me borders on criminal.Ardie had a steel floor that was bonded and riveted. Only about 5 rivets failed, and a small area of the floor in the front corner broke its bond. The floor farther back had a wave in it.
We have a crushable structure expert here? Who?
BTW- I'm still waiting for your examples of "cross-section" in the GCR. That seems to be what you are hinging your entire argument on.
It looks like at least one team failed the test recently.No F1 team really needs to test their noses, they already know exactly how they are going to perform from structural analysis and experience. The FIA requires testing and certification so that teams don't "cheat" and build a lighter nose that won't pass the test.
That is of course not what I said. Yes, sitting through 18 months of people discussing their work and the current literature is enough to make me aware of the importance of testing and the challenges in getting good correlation between modeling and sim and the real world.Do you really believe that? Does your vast experience from attending a few meetings suggest that the minimum design allowed by the GCR provides any significant protection in a frontal impact?
As for whether or not the SCCA minimum provides any significant protection, Richard seems to have already answered that. But, please continue to share with us how much more you know about it than the guys who sled tested it.
Of course.There's a reason Steve Lathrop builds a nose crush box much better than the minimum required by the GCR, and people are adding rear attenuators (carbon fiber ones) although they aren't required by the GCR.
Not neccesarily. To be a front crush structure it has to meet all of the requirements in the GCR section that Mike quoted earlier. For some cars the nose is just a piece of bodywork and the crush structure is the aluminum box underneath.
Who is running a carbon nose cap? Brandon has run two styles of nose cap and they have both been fiberglass.
Their cross sectional area is the inside area of the pipe and only meaningful for flow calculations.
No strength of materials calculation that I have ever seen would work without accounting for the empty volume of a tube.
Pedantic thread is pedantic
Further highlighting the masturbatory nature of this thread is the fact that the FIA regs which have been held up as the standard for discussion of front and rear impact attentuation structures use the phrase "external cross section" and "cross section" interchangeably, with reference to the minimum area of said impact structure at an arbitrary vertical plane.
The intent of the SCCA composite attenuator rule was to establish an external cross-sectional area, and had zero to do with bulkheads or material presence within the proscribed plane. Period.
Cheers,
Rennie
Last edited by Rennie Clayton; 10.26.11 at 1:19 PM. Reason: Clarification
My use was to illustrate that cross sectional area can mean different things to different people and doesn't make your interpretation the ONLY correct one.
Agreed.
Crush Structures
Actually, if you want more expertice on the subject, try The FSAE team at your local University. They not only are required to have a deformable structure, they have to justify their design criteria.
Marty
Wren,
I am not a PE, nor and English major, and I did not stay at a Holiday Inn Express last night, so I was curious where you got your definition of a "cross section". I agree that an additional bulk head may improve crush-ability, but I do not see it as a requirement of the GCR in the front attenuator construction.
Every engineering textbook ever written?
Per my previous example, a 2"x2" square tube with .125 wall has a cross section are much less than 4 sq in.
Has anybody checked Wikipedia for a definitive explanation of cross section?
Attenuators
This is classic!
http://www.youtube.com/watch?v=lLhHA...eature=related
Just hire those guys to figure out what type works best...
I think these guys already know...
US F1 Team - In Detail: Building a Nose
http://www.youtube.com/watch?v=suhCB...eature=related
Last edited by veefan; 10.26.11 at 10:47 PM.
Some light reading on crush boxes and materials.
The rohacell report discusses attachment to achieve to best results.
http://www.rohacell.com/sites/dc/Dow...d%20Report.pdf
http://www.hexcel.com/Resources/Data...on_Systems.pdf
I use an off-the-shelf crush box.
One characteristic of Ardie's impact was the angle to the nose box. All the studies are showing frontal impacts.
I don't know the dimensions of a VD but for my car, the outer corner of the front wing is 38 inches from the center of the front bulkhead and is at a 45 degree angle to the center of the front bulkhead. That is most likely to be the initial impact point. Too often, that impact compromises the nose box mounting system.
Most nose attenuators are probably adequate for front impacts but the mountings are not adequate for a 45 degree impact.
The Citation has a box like structure on the front of the frame. The box structure is 3 inches deep and bolts to the frame with 8 5/16 bolts. The mounting for the attenuator uses 4 5/16 bolts and 6 guide pins. The mounting plates between the attenuator and the box structure have 21 square inches each for bonding and rivets. The 4 bolts are 2.5 inches forward of the mating surface between the attenuator and the front bulkhead of the frame. There are pictures of the front of the Citation frame on the Apexspeed FB building thread, Citation Updates.
This is something to consider for improving off center impacts
http://www.mcgillcorp.com/alcore/dat...truss_0600.pdf
Steve:
I agree with your approach completely. I look at many nose and wing attachment systems and wonder if anyone has thought about how they will fail in an oblique impact. I've seen noses and crush boxes torn off with the wing still firmly attached to the front of the nose.
In the Radon Rn.10 the attachment bolts for the front wing pylons are designed to fail first. The nose itself is held on with four 1/2" diameter alloy steel pins locked into hardened steel bushings in the aluminum front bulkhead. I've been accused of overkill in that area, but I never want the nose to come loose from the car, even if everything but the mounting points are destroyed!
Nathan
Interesting in the Rohocel article above for the Spirit FF, the team came to the conclusion (because of their use of solid foam) that a stand-off frame was needed to not compromise the structure by making allowances for the master cylinders. Much like the Citation design.
The Radon nose box attachment system is definitely a big improvement over conventional practice.
I'm wondering... since so much of the field is made up of VD... is there a market for a better attenuator? The one in my photo (Alegra) at the begining of this thread seems to be inadequate. If you build it will they come? Obviously, a mandate from any series would be difficult. If mandated, then the rule would have to spell out a standard to be met, and would require testing. That would probably be economically unfeasable. Would volunteer adoption provide enough customers to make it feasable to build ?(rhetorical question)
We can make front/rear attenuators for any car.
http://www.apexspeed.com/forums/showthread.php?t=47663
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