I have the old freeware version so I don't know whether this will help.  The instructions say:

  "Catapult disallows helicopters and taildraggers -- it only works with tricycle gear, fixed-wing aircraft.  It also only works within about a boat-length of the nearest cable catch zone.

   Load the included flight "ArrCab Maui carrier startup" to place yourself on the CVN-70 Carl Vinson.  Switch to a carrier aircraft.  Save the flight under a different name.

   Taxi to one of the catapults on deck.  Set parking brake.  Configure flaps and pitch trim for launch.  Press SHIFT-F9 and note the onscreen message indicating CATAPULT ARMED.  Increase to full power and release parking brake.  You'll hear a CLUNK and JET BLAST sound as the catapult releases and throws you off the deck.

   If you change your mind before launch and need to disarm the catapult, just press SHIFT-F9 again.  There will be an onscreen message indicating that the catapult is now disarmed."

I suspect your problem is that you are not close enough to a cable - that was always my problem.

You have reached the limit of my knowledge of ArrCab.  I never really liked it much anyway - it seemed like more trouble than it was worth.