As Alex says
You don't usually need permission for textures only.
Sometimes it helps to read the original Readme but you have done the right thing.
When it comes to the whole aircraft - some designers don't like it and some don't mind.
If you try (email and website forums maybe?) and get no reply the usual thing is to go ahead and upload and make a note in the readme that you have tried. Then rthe designer can see you have shown the right respect and if he objects the file can be removed.
In all our time and 10's 1000's of uploads -- we have probably only ever had about 20 requests to remove a file.
This hobby is driven by enthusiasm and it's great to hear you have done this.

Simplicity is the ultimate sophistication. – Leonardo da Vinci