You couldn’t walk AirVenture 2021 without noticing the semi proliferation of four-blade propellers. Maybe Hartzell’s custodial staff accidentally turned on the blade-making machine when intending to clean the coffee maker and so the company has a surplus of parts. Or not.
In fact, the number of blades is always a compromise. Two tend to be (but aren’t guaranteed to be) faster in cruise than a three-blade setup, but don’t climb as well. Typically, three-blade props for any given application have a smaller diameter than the roughly equivalent two-blader.
Adding a fourth blade, then, helps add thrust with the potential to reduce diameter further, increasing ground clearance and reducing both in-cabin and flyover noise, according to Hartzell. Advances in composite blade technology can help keep the weight increase to a minimum. The Cirrus SR22 had had the new Odyssey prop for more than a year. Mike Patey’s outrageous Scrappy project has a fat-paddle four-blade setup as well. Who knows where this will lead…
A question I’ve had for near a half century is why aircraft have progressed SO AGONIZINGLY SLOWLY during that time ? if it weren’t for Burt Rutan and much more recently, people like Mike Patey (and a few others) of Best Tugs,we might still be back in the J3 age. Mike’s experimentation with props was a forehead slapper for me. Why didn’t WE think of that ?
http://Www.propellersexplained.com. Jack Norris. Literally wrote the book.