It depends. Assuming that you don't exceed any size limits, airlines are still often cautious when it comes to any kind of straps, even loose straps on a plain rucksack, or any other dangling parts from checked luggage. The airline may require you to wrap your rucksack in plastic foil to contain any loose ends. Both in Gatwick and in Bergen, there are actually bag wrap services, where you can have that done for you.
The reason is simply that any loose ends or parts of checked luggage tend to tangle or get stuck on the conveyor belt system. It saves the airport luggage handlers a lot of hassle if the passengers are required to contain their luggage as one manageable piece with a predictable shape.