Rule T3.5.5 Frame bend supports SES REJECTED

[lamboracer]

Hello all,

My name is Steve with NDSU formula team. This year I was tasked with making only necessary changes. These changes were in the petal box and not related to this area of the frame. This frame design passed in 2014 and 2013.

Our SES has been rejected for a second time. After the first rejection we made a change that we believe corrected the only issue. Now our second rejection references the same rule but the suggested fix does not conform to that rule. This is according to our understanding of T3.5.5.

Our frame judge originally commented this on our first SES document.

"The main hoop brace lower attachment support structure upper member does not satisfy the 45 degree requirement of T3.5.5. [judge's name]"

We concluded from this that the "joint/Bend in Question?" seen in attachment 1 was not supported with 45 degrees of the plane of bend. We consider the plane of bend being formed by the two end points of those members and the bend joint being where it deviates farthest from a straight line that would otherwise connect those end points. This understanding comes from reading rule T3.5.5 quoted below.

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"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. Braces attached to the upper side impact member are not required to meet
the 45 degree from the plane of the bent tube requirement."

To correct this issue we redesigned "Member 3" in attachment 1 to be "New Member" seen in attachment 2.

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We then resubmitted our SES and were again rejected with the comment quoted below.

"The main hoop brace lower attachment support structure upper member does not satisfy the 45 degree requirement of T3.5.5. Diagram sent to [team member]@ndsu.edu"

The diagram we received is shown as attachment 3.

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This diagram only confuses us more. The suggested member does not contact a bend joint and does not seem to solve the original issue.

Does our understanding of rule T3.5.5 seem correct? Is his suggested member in attachment 3 necessary? Does our frame conform without it?

Any incite would be greatly appreciated. We are getting close to competition and adding the suggested member would alter our suspension to the point were it would be unlikely we could compete.

[Pete Marsh]

I think they have an issue with the plan view shape of the structure. If you imagine the entire hoop brace support load path it has a large bend in it in plan view, and would not perform as an effective support for the hoop braces, as it will twist at the unsupported bend.

You might be OK if you narrow the hoop, widen the engine mount node (to reduce the angle of the bend) and add some transverse braces (perhaps uppers to the hoop base, and lower under the engine) to brace the bend at the engine mount node in plan view

Pete

[Z]

Steve,

I see a lot of poor design in your CAD, but the design of Rule T3.5.5 is much, much worse.

This sort of drama was predicted as soon as that rule was introduced. In fact, I reckon almost every FSAE spaceframe ever built could be deemed illegal with a pedantic enough interpretation of T3.5.5.

I suggest you get busy with a long series of emails back-and-forth to the Rules Committee/frame-judges. Start by asking them to clarify which tube they consider to be the "bent tube", where is the "plane" of this tube, at which point must it be "supported", etc. Then, based on your Attachment-1, I would suggest that Member-2 going from the offending "Joint/BiQ/support point" to the front-engine-mount-"node" is a satisfactory "support tube". Then much more back-and-forth (ie. is engine-mount a node? ... well...(*)). BE PERSISTENT! Keep at them like a dog with a bone...

The key point here is that the RC have to be educated as to the consequences of their work. Namely, T3.5.5 is their cock-up, so they must work hard to fix it.

I strongly suggest that all other Teams having similar issues also bombard their RCs with similar "Requests for Clarification of T3.5.5".

Z

(* As per Pete's post, I might add a horizontal-lateral tube at floor-height, just below the front-engine-mount. Not really necessary per T3.5.5, but structurally a good idea. And add sheet-steel floor, ~0.020" thk, spot welded to lower rails...)

[lamboracer]

Pete,

Thank you for the ideas on stiffening up our chassis! We think the engine will provide us with an adequate amount of transverse support but the rules committee will not except calculations as justification, only destructive testing. However do you see any rule infringement within our frame design?

Steve

[Pete Marsh]

Your not allowed to use the engine as a structural member without physical testing. There is a rule for that somewhere, or maybe just on the old rule clarification pages on the SAE forum. (ie, not this one, the organisers one no one uses)

Without physical testing of the block they assess your frame as if the engine was not installed as I understand it. Student FEA can be really dodgy on simple things, let alone a complex casting, they are right to ignore it IMO.


Pete

[John_Burford]

Steve,

I suggest you get busy with a long series of emails back-and-forth to the Rules Committee/frame-judges. Start by asking them to clarify which tube they consider to be the "bent tube", where is the "plane" of this tube, at which point must it be "supported", etc. Then, based on your Attachment-1, I would suggest that Member-2 going from the offending "Joint/BiQ/support point" to the front-engine-mount-"node" is a satisfactory "support tube". Then much more back-and-forth (ie. is engine-mount a node? ... well...(*)). BE PERSISTENT! Keep at them like a dog with a bone...

The key point here is that the RC have to be educated as to the consequences of their work. Namely, T3.5.5 is their cock-up, so they must work hard to fix it.

I strongly suggest that all other Teams having similar issues also bombard their RCs with similar "Requests for Clarification of T3.5.5".

Z


Annoying the SES review volunteers to get your way is only going to delay when you have to make the required changes. When teams make a submission or ask question they are put in a queue. There is no guarantee the SES reviews will have time to address a long string of re-submissions and questions. I would not recommend teams follow your advice.

John Burford

[lamboracer]

Z,

Please start your own thread and keep this one on our subject. We would like to know what can be done to correct our frame, so that we can compete. There is a time and place to challenge the rules and it's not here and now.

Mr. Burford,

Attachment 4 shows our latest revision. It strengthens the area we've been working on with two additional transverse members. We could not accommodate your previous suggestion. It interfered with our suspension. Other options were considered but dismissed based on interference with the engine, differential, suspension and shifting actuator.

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Steve

[Z]

John,

Is Rule T3.5.5 of your making?

Either way, do you accept that it is one of the most stupidly conceived, and poorly written, of all the unnecessary FSAE Rules?

I repeat again that my quick look at the OP's frame images shows close to a dozen cases of a "bent tube (or member consisting of multiple tubes that are not in a line)" that fail T3.5.5.

If, at one of the upcoming comps, a particularly thorough Scrutineer (ie. someone trying to do their job properly) refuses to pass any of the spaceframe Teams that fail T3.5.5 (ie. almost ALL OF THEM!), then will you accept responsibility for that debacle?

Or, will some of the spaceframe Teams, chosen on an ad hoc basis, be allowed to compete even though they do not comply with a strict interpretation of T3.5.5?

How will this ad hoc selection process work?

Most importantly, how will this process benefit the Engineering education of the students?

Z

[Z]

Further to above, consider the frame shown in Steve's Attachment 4 (two posts up).

Look at the rearmost-bulkhead (the trapezoidal frame of 4 tubes at top-left of image), and consider its bottom-right-node (= the bottom-rear-left corner of frame in car-coordinates).

This node has three tubes attached to it, namely an X-tube going forwards, Y-tube going sideways, and Z-tube going upwards. Consider all combinations of pairs of these tubes as the "bent tube (or member consisting of multiple tubes that are not in a line)". The resulting combinations are the "bent tubes" XY, YZ, and ZX. The "planes" of these three "bent tubes" are as per their names, taken in the usual car-coordinate system.

Apply Rule T3.5.5 to the above three "bent tubes". Clearly, NONE of these has a "support tube ... angled no more than 45 degrees from the plane of the bent tube." Therefore, ALL THREE OF THESE CASES FAIL Rule T3.5.5!!!

Now look at the bottom-left-node of that same rearmost-bulkhead. ANOTHER THREE FAILURES!!!

Now move to the front-bulkhead. Not visible in the Attachment, but I am sure a lot more failures... (I would guess at least another half-dozen exclamation marks! :))

So, how is this Rule supposed to help educate young Engineers???

Z