Our Aps use 2 vlans other than vlan 1, in E400 firmware I can do not set any IP for default vlan, but in Cnmaestro on promisses always got 192.168.0.1 IP in Vlan 1 and in APs screen shows these IP for all E400 in network.
Vlan 1 is default and cannot be deleted, but Vlan1 is a security issue in big networks.
You can delete vlan 1 from the ethernet port configuration. This way no traffic from the AP will be put on wire on vlan 1. If you're configuring this form cnMaestro, this can be done under the AP group -> Network -> Access Control.
See the screenshot here for an example what the configuration would look like if you had VLAN 10 and 20 mapped to WLANs and did not need VLAN 1. Note that an interface called VLAN1 will still show up in the VLANs table at the top of the page , but as it will not send or receive any traffic it should not be a security issue.