LXI thru the years

[davidbrady]

(05-22-2013 18:59)al perna Wrote:  Why did BB seem to struggle with weight ?? you would think this to be a manageable engineering problem for them to deal with?

Hi Al,

Motorhome's gaining weight is a problem that feeds on itself. Buyers want all the latest features: slides, fancy awnings, granite floors, and all the electronics and luxury conveniences. All these goodies add weight, but then to care-for, feed, and support these features, the chassis needs to be lengthened and stiffened; then we need a bigger engine and transmission to push the longer, wider, and stiffer chassis loaded with all these consumer demanded goods; but then these consumer demanded goods need more electric power so we add a big generator and a large battery bank; but now we need extra large inverters and chargers to keep the batteries charged, and the alternator needs to be beefed up to supply extra juice; then all these consumer devices generate a lot of heat so we need to add extra air conditioners and even over-the-road compressor units with large and heavy condensers... So, you can see weight gain in coaches is a downward spiral that can quickly result in a coach that exceeds it's GAWR.

(05-22-2013 18:59)al perna Wrote:  What is "FINITE ELEMENT ANALYSIS "?

Finite Element Analysis is an approximate numerical solution to a real world problem that's unsolvable in closed form. One such problem is calculating deflections in the irregularly shaped components that make up a Ridewell suspension system. For example, we know how to solve deflection in simple shapes made of steel - say a block. To solve for deflection in a complex Ridewell suspension hanger we computer model the hanger. We also model the hanger's attachment points and the applied external forces. We then chop the hanger up into a gazillion blocks, write our simple equations of deflection for each block taking into account the boundary conditions of our neighboring blocks, and let the computer numerically solve the resulting huge set of equations. The output is the deflection at every tiny block in our model. We can also solve for stress or any other physical property at each block. As we increase the number of blocks in our model, the approximation becomes more accurate.

In the old days Ridewell would do some beam analysis, make some educated guesses, and test the final product in the lab. As of 2000, they analyzed all their suspension systems using FEA techniques which enabled them to identify stress concentrations and excessive deflections. They were then able to redesign or add gussets and other support attachments to improve their design.