This update introduces a much requested and anticipated addition: Helicopters! I hope this update will enable many creative designs and make new creative solutions possible in the campaign.

Helicopters require functioning vertical flight physics and controls, a system that has been completely reworked. This rework benefits all aircraft with vertical flight capabilities, not just helicopters. Designs featuring vertical takeoff, balloons, and other vertical flight mechanics should now perform significantly better. My hope is that this will enable much more creative designs.

I added 5 helicopter parts, including 2 helicopter cockpits and 3 helicopter engines. They all prioritize being lightweight, which is essential for helicopters.

To make helicopters valuable in the campaign, I added 4 boats to the map that you can land on and complete missions. These landing strips are so small that they are only practical with a helicopter. Currently, these missions are optional because I don't want to force people to build helicopters. However, this is subject to change, and I am open to suggestions for how to incorporate helicopters into the gameplay in interesting ways.
Important note: the new airports are only available when starting a new game.

Propeller engines did not have collision detection, but with the giant rotors of a helicopter, this completely broke believability and balance. So I introduced propeller collisions. They will now explode when they collide with objects. Each blade can explode on its own and reduce the total thrust the engine can generate. Currently this is not added to existing propeller engines, but this will probably change in the future.

With vertical flight reworked, balloons also deserved an overhaul. I rebalanced them to be more viable and improved their physics to be more forgiving. Hopefully this further enables creative designs.

I reworked and rebalanced parts of the tech tree. Electric engines are now available much earlier, and helicopter engines require unlocking balloons first. During testing, I found that balloons and helicopter engines make for an interesting combination, so this is something I want to encourage players to experiment with.