¿Por que se usa 'El viaje' y no viajando?

Hola Carl

You can say this in two different ways:

1. El viaje en avión... 

2. Viajar en avión... (Travelling by plane...)

I imagine you are trying to translate literally your "travelling" in English to our gerund "viajando" (travelling), but in this case we use an infinitive, not the -ando, -iendo form.

We have a useful A2 lesson explaining this. Have a look here.

I hope it is useful.

Saludos

Inma

When is it "menos ... de" and not "menos ... que"?

Hola Daniel

Here is our lesson on "más que/menos que/más de/menos de".

I hope this helps.

Inma