Latest version download:

Due to issues with uploading files to curseforge, you can get the latest version here: https://github.com/snjo/Firespitter/releases/latest

The latest version of the plugin is always available here:

Plugin Download

Overview
Firespitter adds a great number of plane and helicopter parts to KSP. These include engines, wings and cockpits with interactive IVAs, as well as other useful things like landing gear, seaplane floats, trim tools and other widgets. A number of other mods also use the firespitter.dll plugin. An explanation of the features of parts using these features can be found in the guide.

Please post any question in the forum thread

Installation:
Check out Scott Manleys video on installing mods.
Make sure you put the Firespitter files in the GameData folder the way it is presented in the zip file. This mod relies on many assets that have to be in the right folder, like sounds and textures. If you get creative with the file and folder names, stuff will break!

If you need just the plugin (for use with other outdated mods), check the the github repo.

Confused? Check the Firespitter parts guide

v6.3.4
-KSP 0.24.2 Compatibility.
-Lots of plugin features for upcoming version 7, and features used in other mods like B9

v6.3

-Wheel alignment guides end the scourge of crooked gear placement. Press F2 to toggle guide lines.
-Oblong round noses, short and long
-Oblong to 0.625m adapter
-Helicopter landing skids by Justin Kerbice
-Warning message on the Main Menu if you are using an incompatible KSP version
-W.I.P. turboprop engine. This will see changes to performance, sound and looks

-FSengineSounds: Implemented disengage, running, flameout sounds, fixed bugs.
-FSwing: Made leading edge action name cfg editable for use in extending flaps etc.
-FSwheel: supports altering retract animation speed in cfg
-FSslowtato: key/action group based rotator module
-FSmeshSwitch: swap meshes instead of textures for better memory conservation

Source on github