Nearly every plane uses Oleo Struts, they basically look like a shock absorber that is made beefier to also be able to provide springing to the suspension. Normal car shock absorbers also have nitrogen gas but they have very small amount of nitrogen, they can not provide much springing effect however these oleo struts have much more nitrogen and basically work like a spring+damper unit. The nitrogen gas is compressed and acts as a spring. Hydragas is very close to this system that was used in british leyland cars however apart from those cars, this type of suspension is never used. Wouldnt it be simpler to make an oleo strut instead of seperate springs and seperate dampers, oleo struts also take much less space. Why did cars always stuck with coil or leaf or torsion springs? Oleo struts save a lot of space and they dont necessarily seem to be expensive i think. Its basically a beefier shock absorber and lets you get rid of an extra coil spring etc. Also for example oleo strut and hydragas cutaway below. Hydragas even took it a step further and intercoonected front and rear suspension together via the fluid to eliminate pitch and it was also used in a lot of budget cars meaning even that system with extra fluid lines to connect suspensions together wasnt that expensive.
Aircraft parts are designed to perform a function at the lowest possible weight that is consistent with safe and reliable operation. If a single part such as an oleo strut -- essentially a shock absorber with spring force derived from gas pressure -- can do the job of a shock + coil spring but without the weight of the coil spring, that's a big plus.
Oleo struts . . . dont necessarily seem to be expensive i think.
Not true. A quick search online reveals that the least expensive oleo struts for small general aviation aircraft are in the $1000 range (each!), and some for twin engine planes cost in the $5,000 - $10,000 range and up.
Yes, everything for aviation is more expensive, but let's be real. Oleo struts are simply too expensive for general use on cars when separate shocks and springs work fine.