Dadp47, the Combat Models F-16 method does indeed use string that is pulled taut by the gear retracting up. This system works well with a air up air down system, but DOES NOT work with Spring air retracts. To get the correct tension on the doors to close properly inhibits the locking mechanism on the spring airs from releasing....Don't ask me how I know this ( BTW the combat Models F-16 is a really nice flying bird And it lands well on 1 main gear still up! )

Greg