Trouble connecting air gap to disposal without tube kinking
Dishwasher drain line is usually cheap corrugated plastic (neither heavy nor all that thick), which is mostly immune to kinking. Some models come with a large 'U' shaped bracket to help achieve this curve. 

Some come with an integral 90, so I don't see why you can't use one if you have to.

I'm pretty sure if it's black and non-corrugated, you bought the wrong stuff. That sounds like an extension you might use if it's extremely far from the drain pipe. Use what came with the dishwasher to make the air-gap,  and attach that line to the drain any which way you can.