I think the B17 is used specifically for fire training, most likely broken or damaged beyond repair and probably nothing more than a hulk, like old airliners used at airports today for fire training. By the way, the bomb tractor shown is made by Academy in 1/72 scale, it's a US design, as well as that sort there was a similar sort without the large radiator guard at the front, one of which can be seen at the Sywell Aviation Museum
http://www.sywellaerodrome.co.uk/museum.html