Westfield SE chassis triangulation
PSpirine - 1/5/12 at 10:52 PM
Car: 1987 Westfield narrowbody chassis
I'm finding that the chassis doesn't have a great deal of triangulation. In particular, few of the areas:
1) Nothing in the floor, footwell nor seat area.
2) For some reason there is only one diagonal member going from the rear of the transmission tunnel running outboard under the rear axle?
3) Transmission tunnel sides
4) The member on which the steering column mounts are attached to is about 2mm above the tunnel, and is therefore not welded to it. Seems odd to
me!
Now, I don't know what the implications of all these are, but how much will ally panels add in terms of strength?
I'm in two minds - either to triangulate a bit on the areas mentioned above, or to weld in some steel sheet (1.2mm?), especially on the floor.
Alternatively I can just leave it alone, but the above areas definitely *LOOK* like they're lacking a bit of strength - I haven't done any
sort of real life torsional testing on the chassis!
emwmarine - 2/5/12 at 07:48 AM
I think the problem with adding material ad hoc could be that in strengthening some areas you might introduce unintended stress and loading points
into other areas of the chassis.
Many years ago I once 'strengthened' a grp boat hull only to have it crack elsewhere under heavy conditions due to my
'strengthening'.
I would make sure you looked at the whole chassis and did some maths before adding in triangulation.
Westy1994 - 23/5/12 at 08:14 PM
Just looked at my 94 chassis, mines the same as yours, seems to drive fine to me. The guy I got it from competed in it for years, all the welds are
fine as I checked them all during the rebuild.
I know what you mean regarding the lack of extra metal however.
Rich
hicost blade - 23/5/12 at 09:45 PM
Have a look at my old build blog for strengthening a narrow Westie
http://westfieldbec.weebly.com/build-diary.html
Have a look at the extra bracing in the passenger compartment (it isn't highlighted but can be seen in a couple of the pictures) these also
double up as somewhere to loop the crutch straps
Ignore the brace on the 'front upper' engine mount though as it was a fix for another issue
All of this work was done by Pro-Comp (apart from the original upper engine mount position), they have been doing this kind of work for years and come
highly recommended for any kind of chassis work especially Westies, but only if you want it done properly first time 
Dualist - 27/5/12 at 04:55 PM
I've been having thoughts about the way the chassis have been constructed over the years and have a had a few questions as I'm sure there
are a few really knowledgeable guys on here.
About 8 years ago I use to work for a firm that made the '7' chassis for Caterham and all their chassis's were braized not mig welded
or tig welded, this was because the chassis flexed (or needed to flex) and this type of welding allowed it. The same is also found in The Harris
Magnum tube chassis range (motorcycle) and also for the same reasons. I respect the fact that mig welding is cheap but doesn't allow for the
'flex' but it does mean the chassis will crack if it flexes beyond it's designed limits.
So with this design have all the triangulations eliminated all the flex so it is safe to do so.? Or do we need to add more or do we really need to
braize the welds to make sure everything is safe.?
Does anyone know what power rating the chassis is designed for and what stress analysis has been done on the design.?
Dave.
PSpirine - 27/5/12 at 05:07 PM
Hicost,
Thanks for that, that's really useful!
Can I ask how much Pro-comp charged for the chassis mods? (feel free to U2U if you don't want to disclose publicly).
So far, I'm definitely changing the steering column mount horizontal, will be bracing the transmission tunnel near the front, boxing it in on the
bottom to catch the prop, running a cross member in the seating area, adding the second diagonal under the axle and changing the 13mm (!!!) upright at
the rear of the transmission tunnel on the driver's side
hicost blade - 27/5/12 at 05:24 PM
I forgot about the tunnel bracing they did.... if you look they did a loop of steel box section and a plate next to the flange
They also do rear axle pick up point relocation for less tramp on the SE's
MikeRJ - 2/6/12 at 09:05 AM
quote:
Originally posted by Dualist
About 8 years ago I use to work for a firm that made the '7' chassis for Caterham and all their chassis's were braized not mig welded
or tig welded, this was because the chassis flexed (or needed to flex) and this type of welding allowed it.
Probably bronze welding rather than brazing?
An ideal chassis should not flex, since this compromises the action of the suspension. In practice many 7 chassis are simply quite weak due to poor
design and lack of triangulation so they do tend to flex a lot. However IMO a better solution is to strengthen to increase the stiffness and reduce
flexing rather than have to bronze weld the joints so that the existing flexible chassis hangs together for longer.
Bronze welding brings about several advantages, foremost of which is that you don't get anything like the heat distortion that welding gives, so
you end up with a straighter and more accurate chassis.
It doesn't introduce the brittle "Heat Affected Zone" that welding does, making the joint more resilient to fatigue cracking.
Repairing crash damage is easier as well. However it's an expensive process compared to a MIG, and out of the reach of most home builders.
[Edited on 2/6/12 by MikeRJ]
ganhaar - 21/12/13 at 11:34 PM
I've recently uploaded some work analysing a Westfield chassis including torsional and bending stiffness, but focussing on torsional stiffness.
This includes testing the stiffness in the workshop and developing a computer model (validated by the testing) to explore options for modifying the
chassis. A summary of about 30 modifications including their effect on weight and stiffness is presented.
The report can be viewed downloaded from the following link
http://www.scribd.com/doc/192898005/Vehicle-Structures-Development-of-the-Sports-Car-Chassis-and-Stiffness-Analysis-of-the-Westfield-Sports-Car
W
estfield Chassis Analysis Report
Smokey mow - 22/12/13 at 01:13 PM
quote:
Originally posted by ganhaar
I've recently uploaded some work analysing a Westfield chassis including torsional and bending stiffness, but focussing on torsional stiffness.
This includes testing the stiffness in the workshop and developing a computer model (validated by the testing) to explore options for modifying the
chassis. A summary of about 30 modifications including their effect on weight and stiffness is presented.
The report can be viewed downloaded from the following link
http://www.scribd.com/doc/192898005/Vehicle-Structures-Development-of-the-Sports-Car-Chassis-and-Stiffness-Analysis-of-the-Westfield-Sports-Car
W
estfield Chassis Analysis Report
Did you also carry out any analysis of a panelled chassis or only of the unpanelled spaceframe?
With our chassis the bonded and rivetted panelling contributes a lot to the overall torsional stiffness of the chassis so when you state that the
chassis only has a torsional stiffness of 1121 Nm/deg that doesn't make fair comparision to the quoted figures for ladder chassis which do not
derive any of their strength from the panels or likewise the manufacturers values you have obtained for monocoques.
As a direct comparison the analysis carried out jointly between Westfield Sports Cars, Delta Motorsport, Penso Consulting and Reynolds Technology in
2010 established through FEA analysis that their standard panel chassis had a torsional stiffness of 2003 Nm/deg.
[Edited on 22/12/13 by Smokey mow]
ganhaar - 22/12/13 at 03:33 PM
No the base chassis model and workshop chassis testing was carried out on a bare chassis with no panels attached.
There were variations with panels attached that were modelled and reported (models 12, 14 and 15) and these a summarised in Table 4.6 p60. and
increase in torsional stiffness of up to 12.3% was observed however this still falls short of the 2000Nm/degree figure that you mention.
I also recall that adding a plate did not make much difference where was already good triangulation in the same plane as the plate which is reasonable
considering the plate itself has little torsional stiffness.
Also I wouldn't be surprised if the Westfield chassis has been improved in the time between my study (1992) and the work that you did in 2010.
For example I was able to achieve a similar figure of 2051Nm/degree with fairly simple changes such as increasing member in the top and bottom plane
of the chassis from 25x1.6mm Square Hollow to 40x1.6mm. A significant increase in stiffness for only 7kg increase in weight.
Wayne
Smokey mow - 22/12/13 at 04:36 PM
quote:
Originally posted by ganhaar
Also I wouldn't be surprised if the Westfield chassis has been improved in the time between my study (1992) and the work that you did in
2010.
there's been no significant changes to the design of the westfield chassis since the wide body was first released in 1990.