Props - Wood vs. Metal

[RetroAcro]

OK, didn't have the time or motivation to get all scientific, but made some notes about the propellor swap-out on the 85hp stock Reed Clipped J-3 Cub that I fly. Sensenich 72GK44 wood prop was replaced with a metal Macauley CF71-44 . First thing you'll notice is that the heavier metal prop takes longer to spin up to the RPM you've got the throttle set to when starting, which gives you even more time to get your hand on the throttle as the engine "spins up" after propping it from behind. J-3's were made for this. Another nice thing about metal is that you can prop it with less effort if you bounce it a little against compression and get the prop moving downward before pulling it through...the momentum does a lot of the work.

I can't say I noticed any obvious increase in takeoff/climb performance with the metal prop. Hard to say without doing comparison tests. Not sure if I'll get around to it like I did with the Pitts, but it would be interesting to get some good climb numbers flying the two props back-to-back so that density altitude conditions are similar. It turns up about 50 RPM less on climbout (engine developing less power), and leveling off, setting 2,350 RPM, it indicated 79, which is about 5 MPH faster than the wood prop at that RPM. Nope, Clipwing Cubs are NOT faster than the longwing J-3. Not sure yet if fuel flow is going to be the same at it was before at this RPM.

As expected, the stick feels heavier in flight with the metal prop due to the slight move forward of the CG, as well as the gyroscopic (pitch) resistance of the metal prop vs. wood. I went through the reverse of this when changing from a metal prop to composite on the Pitts...it's quite a bit lighter in pitch now.

Idle RPM can be set lower with a metal prop - more flywheel effect, which allows for a lower steady idle RPM. The difference shows up during landing - it seems to be a little less "floaty" due to less residual thrust at the lower idle. It also seems to drop altitude more dramatically in a slip than it did with the wood prop...I assume for the same reason. I consider these to be good things.

Due to the CG move, I noticed that I must now pull the stick just a little further aft and put it on the stop to get a true 3-point touchdown power off. Before, you could touch down very slightly tailwheel first if you pulled the stick to the stop just before touchdown.

So a very slight performance advantage (speed, not climb) with the metal prop, but it very much changes the entire "feel" of the airplane. I actually prefer the lighter feel of the airplane with the wood prop, but there's enough good about the metal prop that I think it'll stay.