The default orientation in UE4 is X+ (Forward), Y+ (Right), Z+ (Up). Open any character blueprint or any function that queries the forward vector for verification. This AnswerHub thread gives you an explanation and references to the documentation.
If you’re using any other orientation for reference in the engine, you need to fix that. It should also be noted that an imported FBX from another 3D application is not guaranteed to be the same orientation unless the application has the same coordinate system as UE4. Exporting a character from Maya will give you a 90 degree offset, which will have to be adjusted in a character blueprint. Even Epic does this with their characters, you can look at the HeroTPP mesh. The default orientation in UE4 is X+ (Forward), Y+ (Right), Z+ (Up). Open any character blueprint or any function that queries the forward vector for verification. This AnswerHub thread gives you an explanation and references to the documentation.
Now with that in mind, if you look closely at AntonBoiko’s post you will see that Blender and UE4 has two different coordinate systems. Blender is right handed, Unreal is left handed. This means that one axis in Blender either has to be inverted (-X) or to use another axis as reference for forward axis before conversion. I recommend working in the forward axis in the application of your choice, in this case Blender, and then “live with it” that there’s an offset. Trying to fix the offset in Blender will only cause severe issues down the road. I speak from experience trying to do this in Maya many years ago in UDK/UE3, which today is causing a lot of problems in a game project I was involved with. Can’t give you the details, but trying to fix this issue can cause more harm than it solves and should not be done. Just live with the fact there’s going to be an offset after conversion between coordinate systems.
It’s not that hard to set the same rotation values on every character you export, it’s only an inconvenience.
If I mixed up some facts, please correct me. 