I had one such "need" for an invention recently. I guess it's not so much an invention really, but a DIY version of something that is currently available on the market, just for more money than I am willing/able to pay. What I needed was a commercial blower unit to suck blown in insulation out of attics. They are available for purchase, at a price point somewhere around $5000. So I figured, I'm a smart dude, I went to engineering school, this is my jam. So I got to it, and what follows is my method.
Step 1: Design
I went with a 14 inch impeller, backwards curved blades, mostly determined by what raw materials I already had available to me for the impeller. I went with five blades, also just because. The impeller works in counter-clockwise rotation, based on the shaft rotation of the motor I was going to use.
I will try and add some Inventor screen caps later on.
I am in the process of a redesign right now. Instead of a direct drive, it will be a belt drive with a centrifugal clutch. This has many advantages over the original design, and all of this will be explained after I complete the project, again. I should be done the project by the end of the week, and the updated instructable will follow shortly.