how can I change date of availability.

[bask185]

I'd like to build airships, but it is almost impossible to start with them because those airfields costs crazy in maintanance and only 1 airship can land/take-off the same time. Airships work really well with helicopter pads and helicopter airfields. But it takes so long for those to be unlocked. How can I change the settings so I can have these structures availble to me in 1950?

[andythenorth]

Try the OGFX+ Airports grf. It has a parameter to make airports available without date restrictions.

[kamnet]

You might also be interested in my Airship High Mooring Mast as a 1918-1960 replacement for the tall helistation towers. After 1960 they're no longer available and the default OpenTTD towers will be available. It's not perfect, but you might like it.