Premier 1
Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 100; Flight Crew Total 10000; Flight Crew Type 2570
Aircraft Equipment Problem Less Severe; Ground Event / Encounter Other / Unknown
Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem
Aircraft
As the pilot not flying; on approximately a 7 mile final (visual approach) for runway 23R at TYS; on command from the pilot flying; I moved the gear handle to the extend position. Nothing happened.  We cycled the gear handle several times to no avail.  We leveled off at pattern altitude (2;500 feet MSL) and with permission from Knoxville tower; we overflew the runway and entered right traffic for runway 23R. We then worked through the Alternate Gear Extension checklist and successfully extended the gear with a '3 green' down and locked indication.  The tower visually verified the gear appeared down.  A byproduct of the alternate gear extension procedure is that the inboard gear doors do not retract (that is; when there is not a normal electrical circuit to the gear system; which appeared to be the problem).  We landed uneventfully but damaged the inboard gear doors as they dragged on the pavement. I am told both inboard gear doors will have to be replaced.  With permission from the tower after clearing the runway; I exited the airplane to manually close the inboard gear doors so that we could taxi the airplane to the ramp without further damage to the gear doors.There seems to be a problem with the electrical signal to the gear system.  Maintenance will have to troubleshoot the gear system to isolate the actual problem.  We followed procedures as trained.
RA-390 (Premier) Captain reported landing gear would not extend with normal system; but was successfully deployed with the alternate system. Some damage to gear doors resulted; since they do not retract when alternate is used.