Rule T3.5.5 - Bent tube (or member consisting of multiple tubes not in a line)

[Don Nguyen]

Hey everyone, I'm from the University of Arizona.

"If a bent tube (or member consisting of multiple tubes that are not in a line) is used anywhere in the primary structure, other than the front and main roll hoops, an additional tube must be attached to support it. The attachment point must be the position along the tube where it deviates farthest from a straight line connecting both ends. The support tube must have the same diameter and thickness as the bent tube, terminate at a node of the chassis, and be angled no more than 45 degrees from the plane of the bent tube."

I'm having a lot of trouble visualizing what this rule is requiring. I submitted a frame to the rules committee and was told that the main roll hoop supports don't satisfy the 45 degree angle specified, and I'm seeking a better understanding of the rule.

The frame in question was: http://i.imgur.com/VDwo4Lk.png?1

A possible solution I came up with what I think the rule is stating is: http://i.imgur.com/rJdV7oh.jpg

This thread is nothing personal against the rules submissions, but they haven't been going into detail to the extent for me to get an idea.

Thanks everyone.

[TiJei]

Hi Don,

I don't see why you refer to the "bent tube rule". However I think your main roll hoop bracings violate rule T3.13.7.

Regards
Timo.

[Don Nguyen]

Timo, it was the only one pointed out to me when I submitted to the rules committee, but more details weren't really specified.

[Mitchell]

Don't forget T3.13.6

"From the lower end of the braces there must be a properly triangulated structure back to the lowest part of the Main Hoop and the node at which the upper side impact tube meets the Main Hoop."

I feel like they have referenced the wrong rule. Your initial harness bar satisfies T5.4.2 as far as I understand it.

[TiJei]

@ Mitchell: I think we are reffering to the same rule. Maybe from a different document status. Your wording sounds like 2014 Rules. Anyway we mean the same thing.

@ Don: I think I don't understand what is meant by "main roll hoop supports". Maybe you could post the original reply from the RC? The only bent tube in your initial design is the shoulder harness bar, however I agree with Mitchell that this should be rule compliant. To overcome this you could redesign it from 5 straight tubes. However the only rule deviation I can see from the pictures is that the main roll hoop bracings are not connected to the lowest point of the main roll hoop.

My first comment was maybe a bit short, however I sent that from a smart phone with bad internet connection.
Apologies for that.

Regards

[onemaniac]

I see what RC is referring to. It's the front hoop bracing that is in multi pieces.
Your front hoop bracing support (meaning tubes that 'supports' the bracing) that connects the 'cut' and the upper side impact structure node is forming an angle greater than 45 degrees from the tube plane.
I may be wrong, but that's how I would interpret.

[Don Nguyen]

This was exactly the only thing specified to me when I submitted my frame.


The main hoop brace support structure does not appear to satisfy included angle requirement of T3.5.5.

There was nothing else detailed and he didn't offer a visual solution, so I really am confused. I think they're talking about these two tubes not-in-line:

http://i.imgur.com/lRXUCcV.png

[troot]

Sounds more like 3.14.4 and from the image that seems to make more sense, the mount you have circled should not be considered a structural tube as it relates to bracing or impact structure eg what the ses looks at.

[Adam Farabaugh]

I think they're most likely referring to this (highlighted in orange):
http://i.imgur.com/F0atx6N.png

This is a "bend" in the sense that the brace support which could go straight from the bottom of MRH brace -> upper SIS is actually made of two tubes which are not in a line.

Now I can't pretend to understand the 45-degree thing, from the first time they put that language in I was confused.

[slicktop]

I agree with Adam. I interpret the 45 bend rule as this: If you have a tube that has a bend or has multiple pieces that form a bend, then that tube will form a plane. The plane is defined by the two endpoints of the tube and a point in the bend, to where the entirety of the bent tube is parallel to and on the plane. Then, this tube must have a support tube that terminates at a node of the chassis, and the support tube must not make an angle of more than 45 degrees with the plane.

It seems that your left and right MRH bracing supports tubes are different from side to side, if I am seeing it correctly. To me it looks like the left side does not satisfy T3.13.7, as Timo pointed out. Also, on the right side, the horizontal tube pointing rearward off the MRH (the one attached to the same node as the harness bar) I believe would need to meet the MRH bracing support thickness requirements as it is needed for triangulation, if it does not already.

[Adam Farabaugh]

I agree with Adam. I interpret the 45 bend rule as this: If you have a tube that has a bend or has multiple pieces that form a bend, then that tube will form a plane. The plane is defined by the two endpoints of the tube and a point in the bend, to where the entirety of the bent tube is parallel to and on the plane. Then, this tube must have a support tube that terminates at a node of the chassis, and the support tube must not make an angle of more than 45 degrees with the plane.



Not to hijack the thread but I have been wondering for a long time.

Slicktop, that is how I read the language as well. HOWEVER it makes no sense to me! Why would you want to limit the angle from the tube to the plane to at most 45 deg? I would think that you would ideally want it to be exactly normal to the plane! That is the most efficient way to react torsion of the bent tube. I think the rules would make it legal if the "triangulation" tube was at 0 deg to the plane, which would do absolutely nothing!

[SomeOldGuy]

I do not see a roll hoop support brace that goes from the roll hoop supports to the main hoop at the lower sis on either side.

[Don Nguyen]

Thanks everyone, I appreciate it. Your responses have given me a lot more insight to this rule and also what I need to work on for the rest of the frame.

At this point I just need to work out all the details with the RC and make sure that all the rules you have mentioned are satisfied.

[Z]

As noted before, the lunatics have taken over the asylum (ie. asylum = the Rules Committee).

Given that a "bent tube" is also defined as a "member consisting of multiple tubes that are not in a line", it follows that ANY TWO NON-COLLINEAR TUBES meeting at ANY NODE of the primary structure are considered a "bent tube", and are thus subject to this Rule.

So:
Identify ALL nodes of your primary structure.
Identify ALL combinations of ANY TWO tubes that meet at each and every one of the above nodes.
Determine whether there is any other tube meeting that particular node which satisfies the "support" requirement of the Rule.

EXAMPLE - You have a particular node that has three tubes connected to it in a shallow pyramidal structure. If, in any combination or permutation of the tubes, one of the tubes is NOT within 45 degrees of the plane formed by the other two tubes, then YOU FAIL!!!

I reckon that the majority of FS/FSAE spaceframes ever built have at least one instance of such tubes that fail this Rule. Note that taking another combination of the tubes at that particular node may (?) result in a "pass". But will the Scrutineers see it that way??? Given the sheer idiocy of the Rule itself, I doubt that you can expect any reasonableness from its interpreters.

So:
SOLUTION - All spaceframe Teams should prepare a template letter or email to the RC. Then prepare many drafts of spaceframe designs, and send each with its covering letter to the RC asking whether it is acceptable. If they advise that it is not acceptable, then ask which specific tubes fail. I suggest getting a dedicated Team member to repeat this process many, many, many times ... and then maybe a few more again...

Ahhh... Idiocracy..., now we're rolling in it!!! :)

Z

[Bemo]

SOLUTION - All spaceframe Teams should prepare a template letter or email to the RC. Then prepare many drafts of spaceframe designs, and send each with its covering letter to the RC asking whether it is acceptable. If they advise that it is not acceptable, then ask which specific tubes fail. I suggest getting a dedicated Team member to repeat this process many, many, many times ... and then maybe a few more again...
Z
What you describe is basically the process which is already happening. The teams hand in their frame designs in their SES and get it approved (or not). The scrutineer only checks if the frame of the presented car correlates with the design in the SES.


Given the sheer idiocy of the Rule itself, I doubt that you can expect any reasonableness from its interpreters.
I agree that the rule is stupid as it is right now, because exactly the problem with the pyramid structure you describe I already discovered, too. But just accusing scrutineers to make unreasonable decisions all together is such an extremely bad behaviour that it is a disgrace for any intelligent person. The RC and the scrutineers are NOT the same group of people. The scrutineers at different events are different people. I can speak only for the competitions I'm involved with (Germany and Austria). There the scrutineers definitely have the target to make transparent decisions and are NOT trying to prevent teams from driving or to prevent outside-the-box-designs. The rules are a topic which is seen very critical amongst scrutineers as there are a lot of rules which are so unprecise that it is very difficult to have a transparent scrutineering process. These are people spending their summer vacation to work for free at these events to make it possible to run these events. Have you been to all events in the world? Do you know all about the organisation behind these competitions? Do you have a clue who is making which decision? No? So, maybe you should slow down a bit just insulting anybody involved in organising these competitions.

[Z]

MORE EXAMPLES - Consider the images in the OP's first post (ie. top of page 1). Look at the Front-Bulkhead and at each of its four corner nodes. Take any two of the FB's tubes meeting at any corner/node, and call them a "bent tube". It follows that the "plane of this bent tube" is the plane of the FB.

Now (!!!), since none of the other tubes "supporting" any of these nodes is within 45 degrees of this plane, it follows that THE FRAME IS ILLEGAL. In fact, it is illegal four times over, at least!

Note that it would probably be a waste of time for students to argue that the IA support plate (which is bolted or welded to the FB) is adequate support for the "bent tubes", because the Rule clearly states that "The support tube must have the same diameter and thickness as the bent tube...".

So, taking the Rule literally, an "X-shaped" brace, using same tube sizes as the FB, MUST be welded into the FB. And using just one diagonal is still not enough... Madness!!!
~o0o~

Bemo,

As I have made clear many times before, I have been a volunteer in all sorts of sporting events, etc., for longer than most of you have been alive. Well, at least 30+ years... I know that most such volunteers have the good interests of the competitors at heart. Most volunteers like everything to go smoothly. It is a lot more enjoyable for everyone that way.

But there are always some voluntary officials (maybe one in ten?) who sometimes get a little too officious. This can happen for many different reasons, including "egos", but I won't go into that now. The problem here, a common one, is how different officials enforce the same set of Rules. All Rules have some greyish areas, and different officials can have different interpretations of those grey areas.

The problem with this particular Rule is that it is quite black and white. A literal interpretation of it will have most spaceframe Teams failing Scrutineering. Or, at least, they will be ordered to weld countless extra "support" braces into their frames. Many, many students will be very, very unhappy.

And the volunteer Scrutineers, such as you and your colleagues, who are effectively the "meat in the sandwich", will carry the brunt of that unhappiness.

For your's and the other Scrutineers' enjoyment next year, I suggest you try to sort out the madness that is going on at the IRC level as soon as possible. A possible way to do that would be to start an open discussion, perhaps via a thread on this Forum, where certain concerned Scrutineers (eg. your FSG and FSA colleagues) make it clear which of these new 2015 Rules will be enforced, and which will be IGNORED.

I would suggest that this particular Rule can be totally ignored. Pretend it is NOT THERE. The aero-Rule covering minimum radii of edges should also be clarified. Are razor-sharp wing trailing-edges really acceptable? And the interpretation of many other Rules could also be clarified.

Anyway, I would rather see a smoothly running contest where the students learn engineering stuff. Not the mayhem that will result if ONE official takes this new Rule literally.

Z

[Bemo]

Thanks for the clarifying response. I can agree with most of that. You can be sure that these things are discussed amongst scrutineers and at least attempted to work towards the RC to improve the rules. It is no fun to do technical inspections according to this rules book as it is full of issues like these. The biggest problem I see is that most of the members of the RC have never built a car nor have they ever been scrutineer (at least I assume this is the case, as I don't have another explanation for what the result is). Unfortunately the RC is incredibly resistant to any input coming from the people who have to live with the rule book. Instead of cleaning the document from errors, every published version brings more problems...

[Don Nguyen]

As a heads up the RC approved the 2nd frame I had in my original post. I'm still not sure why it complies.