Okay, sorry I did not get back to you right away but I am swamped with homework.
That is the FPE file, which is for the entities properties.
The part below specifies which scripts the entity will run...
;ai
aiinit = appear1.fpi
aimain = default.fpi
aidestroy = disappear1.fpi
...so, you can see the initialization script is used for the appear script that is run when spawning the entity.
The ai main is the script that runs while the entity is "alive", which here is the default.fpi whic does nothing. (this is why your tank does nothing)
And finally an ai destroy which runs on death of the entity and thus destroys or suspends the entity depending on whether you want it to disappear of leave it.
The script we will need to replace here is the default, so we need to create your new script to control the tank then assign the aimain to it.
I have to finish my homework right now, but I will be back to help you more on this when I am done.
Have you animated the tank yet?
Because you have no animation assignments in the FPE.
I would need to know the number of animation it has, with a description and start and end frame numbers for each one.
I'll be back
Edit
Here is a shot of my 'Tankle' ... (see attached image)
I'll be animating it soon and writing a script for it, so I'll let you have that script for an example when I'm done if you want.
Mind you; this is a remote controlled unmanned micro tank that does not have heavy armor plating.
Instead, it is a light weight polymer that is electric powered with a 80 mile range.
It can travel up to 40 MPH reaching maximum range in approximately two hours.
It is amphibious and includes a .38 caliber gun with 100 rounds of ammo.
It can carry up to 1.2 pounds of explosive such as C-4, with an additional 0.3 pound capacity for a secondary charge or contaminate for a dirty bomb.
It also boasts a shell recovery system for the .38 built in, as to provide extra shrapnel for the primary charge.
Intended to look like a toy, these weapons are generally used for assassinations, but can also be effective to cause general confusion and chaos amongst enemy ranks.
They also can be used as a front line of defense when equipped with search and destroy automation scripts for unmanned control.
This ensures completed objectives of enemy casualties even if the operator has been cut off or terminated.
Nonetheless, the basic animations and controls would be similar regardless of size.
Edit again
So is this animated so it actually moves around, or is it just sitting there and you want the engine sound as if it is running?
Just a sound to run would be real easy, and I can tell you that step by step without using a custom script, but by editing a stock one.
Anyway, let me know if it is just a sound for a machine that is running but sitting still, because that is a lot easier.