Push Rod Flex

[DaveW]

.... (nothing to do with aero)....

Apologies, especially to gixxa_drew, that was just a sad joke of mine, arguably attempting to defend my corner. My only defence is to observe that the performance of every race vehicle is a compromise between mechanical & aero characteristcs & I sometimes think that is forgotten by the F1 community in the mad rush to gain an aero advantage.

[aussiegman]

the cfc driveshaft has intentionally much of the fibre aligned around 45deg to give the greatest strength in torsion

Specific applications will ultimately determine the filament angles used and a 45deg / 0deg / 45 deg is not always the preferred winding as they can exhibit comparatively low axial stiffness numbers and relatively excessive torsional stiffness that can be less than optimal. Torsional moments cause three main types of failures in composite torque tubes:
1: Shear failure of the composite shell which can be generally calculated and predicted using accepted failure criterion.
2: Loss of wall stability can occur, if the wall bending stiffness is not sufficient.
3: Failure of adhesive bond between metallic flanges and composite sections.

I have used 45º / 0º / 45º windings which seem to behave more like a "soft" steel or aluminum shaft in that they didn't "wind up" due to their torsional stiffness. However i also used an alternatively wound 84º / 0º / 34º wound shaft with very good results which seems much more forgiving and had good "spring" due I suspect to the reduced torsional stiffness which did not compromise structural integrity. This was based on reviewed reviews that showed that in the case of a loading due
to an angular speed, optimum winding angle was found to be between 81º and 84º dependent on wall thickness. It was a test and it resulted in what was possibly a less torsionally stiff but more forgiving shaft.

(if it was designed for best bending strength much of the fibre would be aligned longitudinally)
relative to its torsional strength the driveshafts bending strength is poor due to the 45deg alignment (reasonably)
similarly with stiffness properties

A driveshafts primary force is not generally longitudinal but angular force due to torque and as described above a 45º while providing the stiffest winding in twist is not always to best solution and simple windings may not always produce the best results based on required usage. As you rightly observe for the pushrod, tailored elasticity is the name of the game.

looks like tailored elasticity to me (nothing to do with aero)

Yep, perhaps an acceptable deflection value was inbuilt into the pushrod to perform an as yet undefined function.

I just wondered whether the pushrod could have inadequate bending stifness for a similar reason
(just a suggestion)

If they wanted it stiffer in bend then they could build it in pretty easily with a cost of increased weight or dimension. Perhaps a better layup or fibre alignment might help, however I suspect it is an inbuilt degree of flex for some design or performance goal where they perceived a benefit.

Its really just an interesting guessing game on out part.

[strad]

When I opened this thread I never expected to learn so much. Thank you all.