We recommend using a constant speed propeller because of the relatively high cruise
speed of the RAI-1 and RAI-6.  There are several articles in KITPLANES magazine,
among other sources, discussing the reasons.  Basically, a fixed pitch propeller
designed to attain a 180-knot cruise speed loads the engine at takeoff to a relatively
low rpm and therefore low horsepower.  At brake release your 180 hp engine is
developing only about 120-130 hp.  Not very comfortable if you are relatively heavy and
the density altitude is getting high.  Takeoff roll is extended and climb rate is lower.   

   There are a few RAI-1s flying with fixed pitch props.  The performance is
satisfactory with 50-60 gallons of fuel, but more than that starts to get worrisome. On
the other hand, a Tango with 180 hp, a constant speed prop, 86 gallons of gas, and
loaded to 2,200 lbs will comfortably takeoff from sea level and climb to 12,500 feet, or higher if you are oxygen equipped.

Search: Fixed pitch vs constant speed propellers
             KITPLANES, www.kitplanes.com March 2022 issue, Propeller buying guide
             KITPLANES/Resources/Propellers
             KITPLANES, Wind tunnel, July 2016 issue, Fixed Pitch vs Constant Speed
             Propellers, – Barnaby Wainfan
  

   We have had good results with Hartzell, McCauley, and Whirlwind propellers on the RAI-1 and RAI-6.  There are other propellers listed in the KITPLANES articles, so that is a good place to start your search.
  

   As with most things, the increased performance from a constant speed prop comes at a higher price.  Whirl Wind Aviation (whirlwindaviation.com) currently lists suitable two blade propellers for approximately $9,500 to $10,000 and three blade props for approximately $14,500. The governor costs $1,444.
  

   Hartzell and McCauley do not list their prices online, but they are similar to the Whirl Wind prices.

   We can get OEM prices on some propellers and can pass along a portion of the savings.
  

   Last, and very important.  Aircraft engines, especially the four-cylinder engines, create
vibrations that drive propeller builders crazy.  Before buying an engine or prop, be sure that one is compatible with the other.  There are plenty of choices available, but you must check first.