Harpy helicopter doesn't shoot...

[AlliedG]

Turret method is annoying if unit does not use turret by default and obviously primary FLH, firing issues with a spinning turret. The deploy feature can be used to make a helicopter manually land for repairing by IFV units/crate collection though.

You are missing a OmniFire=yes from your weapon like the BlackHawkCannon does .. it means the unit can fire at units when facing opposite direction but only way to solve such issue, even the siege chopper MG uses that weapon.