title_body: 27+ inch racing propeller suggestions? I'm looking for some propellers that can handle high rpm (7000-9000) and are large in size. (27+inches length) (pitch: 15+)
  Any suggestions?
upvoted_answer: I don't think what you're asking for exists. There just aren't many props even available in that size. T-motor and Xoar both have props in that diameter range, but most of them are lower pitch around 8ish for that diameter. You could potentially use an airplane prop, but not sure if you could get the reverse pitch prop easily. My guess is you'd have to have something custom made.
  
  Check these links for some commercially available options: 
  
  http://www.helipal.com/index_tag.php?tags=Industrial,Drones,Propellers&amp;tags_type=Products%20Type,Parts,Accessories,Features
  
  https://www.getfpv.com/propellers/commercial-industrial-propellers.html
  
  And it looks like this company can create custom carbon fiber props to spec: https://www.mejzlik.eu/
  
  It's also worth noting that a 27" diameter prop has a maximum RPMs of about 7700 RPM. You can't run a prop higher than about 0.8 the speed of sound without the prop essentially tearing itself apart, especially with these larger props. You can use this calculator to plan the exact target RPMs.  Keep in mind though, even reaching 80% the speed of sound takes a huge amount of power, and there may not be motors large enough to dissipate that kind of wattage. You'll probably have to end up settling for an RPM target a bit more reachable. 
  
  If you're looking at transonic or supersonic propeller designs, you're looking at a completely different system approach in both the motor and power system, and normal commercial/hobby grade components are not going to be suitable. I'd look towards custom engineering and development through a contractor with specific experience in that area.