Z-bar and Anti-Roll, Not Individual Sprung

[Powerslide]

If we were to do away with normal individual wheel spring and have a heave and pitch loaded Z-bar and an anti-roll bar for roll while the two work against warp, what would be the adverse effect? Have any of you gone though this out of curiosity and found a hole in load graph that might drop the suspension?

[thisisatest]

where would you put the dampers?
and wherever you end up with the dampers, why not package a coil spring with it, saving installation complexity?

[Lycoming]

Presumably it would be an inboard suspension, so you can do damping conventionally, ie. 1 damper at each corner, just attach in to the bellcrank however is convenient. Or if you prefer, you can mount them directly to the upright. That's the easiest way to do it.

Why do things this way instead of use coilovers? Because it gives you arbitrary pitch, heave and roll stiffness, all sprung using separate, adjustable springs with somewhat less complexity (and probably less compliance) than hydraulically interconnected suspension. It also gives you a soft warp mode. I haven't thought this through, but it may also mean that your chassis torsional stiffness becomes irrelevant.

[Powerslide]

I am assuming bar load will be consistent. Interesting the Tennoco's variable ability can also be intergrated not just with roll but pitch and heave and completely do away with conventional springs.

[Pierce89]

If we were to do away with normal individual wheel spring and have a heave and pitch loaded Z-bar and an anti-roll bar for roll while the two work against warp, what would be the adverse effect? Have any of you gone though this out of curiosity and found a hole in load graph that might drop the suspension?

I see no problem with this setup. Warp will probably be fairly soft compared to roll and pitch, but that can be good or bad. With no coil springs to fool with, why not make it a pushrod actuated inboard setup? Maybe you could incorpoate rotary dampers into the bellcranks. It could be a packaging masterpiece (or nightmare).

[DaveW]

This document might help. It presents the suspension ideas of Erik Zapletal, which seem to be similar to the concept you are discussing.

Damping is not really discussed in the document, but elsewhere, he posted a rather unhelpful, even misleading, rant entitled "dampers are crutches for stupid springs".

I have rig tested what I believe was an implementation (in scaled form) of a Zapletal suspension. Here is a sample run extracted from the test (for a warp logarithmic sweep covering the range 0.5 up to 40 Hz). Two things to note:

1. Friction (presumably in the linkages) was something of an issue (note the waveform of the load histories at low frequency).
2. The system had no control over the hub modes (at 42+ seconds, & 14 Hz). Damping would certainly help....

Two more things to note:

1. I believe that Peter Wright was first to coin the "skiing" metaphor.
2. An active system would not require the linkages to implement a system with similar characteristics.

[Moxie]

I'm certainly no expert in these matters, but I wonder if you have considered using a transverse composite leaf spring?

[Tim.Wright]

Very interesting Dave,

This is exactly the concern I have expressed previously to Erik about suspensions with zero warp stiffness and damping. It nice to see my hypothesis confirmed.

I take it the square wave response at low frequecy is due to the friction?

[DaveW]

I take it the square wave response at low frequecy is due to the friction?

Correct, a warp (modal) input does, unlike others, force the suspension to articulate.

I suppose it is a question of "horses for courses". After all, unsuspended agricultural vehicles are entitled to use public roads - at a suitably low speed (I don't recall the limit).