In all seriousness, it's not difficult: turn right out of the airport following signs that say "A38" and "Motorway." Even easier if you've done it before!Done the trip a few times this was definitely not the usual route.
Your mistake was trying to be clever and modern and turning the infernal splatnav on in the first place!!
My taxes pay for those roadsigns for a reason, grumble harrumph dripping-like-a-broken-tap etc.