Monday, July 3, 2017

Fixed Pitch to Constant speed

Major update coming…please stand by.

Ok, so as I think I have mentioned in the past I love my Catto 3 bladed prop.  That is to say I love it at cruise, but not so much on takeoff.  Well I decided that I would switch to a Whirlwind constant speed prop and that is the topic of this post.  I will start out with some pro’s and con’s as well as a few notable comments about the process.  This is coming from somebody who has never flown constant speed and the experience of flying both is fresh in my mind.


  1. Pro’s
    1. Takeoff—holy cow the takeoff!  I did several touch and go’s as part of my testing process and I can’t tell you how amazing the pull on this prop is at full RPM.  I was climbing out at Vy for these touch and goes and I was at pattern altitude before I was turning crosswind!  If I tried to climb at Vx I felt like I was going straight up! 
    2. Taxi slower.  At idle the prop does not pull as hard as my fixed pitch prop did so I can now taxi slowly without using so much braking or running the engine at a very low RPM where it shakes like a wet dog.  Very nice.
    3. Slowing down.  Pull the throttle in the air on this prop and it feels like somebody literally hit the brakes!
    4. Landings are VERY short.
  2. Con’s
    1. Price
    2. I can no longer use engine sound as a primary indicator of many aspects of flight.  This may be something I learn to adapt to but I like to use the sound of the engine as an indicator of speed for many phases of flight
    3.  Complexity
      1. Flight management is more complex because now I have to think about a prop setting in addition to the rest of the flight.  However, this will become “muscle memory” soon I’m sure.
      2. Engine.  Prop governor, oil hoses, another cable run with associated firewall penetration and attach bracket all on the very tight back side (firewall side) of the engine.
    1. Adjusting of the high speed stop is a bugger due to location and limited access… and it has to be safety wired…hell I can’t hardly get one hand back there let alone 2 and some lock wire tools.  Fortunately I have a great friend Harry who has a nice lock wire tool that is a single piece of wire with crimp on ends.  I was able to get that in there…barely.
    2. Air brakes.  Yes I know I listed this in the Pro’s section but there is a negative side to this too.  I say this with a caveat that I might be doing something wrong but when I pull the power as I think would happen in an engine out situation my glide ratio tanks….big time.  With my fixed pitch prop if I pulled the power my glide ratio was about 12:1.  With this prop I don’t know if its even 6:1.  I have to be missing something here but I believe the prop is designed to go to the high speed top (at least that’s what the spring does) on a loss of engine oil pressure.
    3. Slightly less smooth.  Going from a 3 blade prop to a 2 blade prop I noticed a slight increase in vibration.  Not much but noticeable.  I still haven’t done the dynamic balancing yet so that will likely help.
  1. Notable – this is a section for things I noticed that are noteworthy but may change
    1. Landings are way different.  I got used to the size of the pattern I needed to land my Catto prop.  I had it down pretty good to where I could pull power at the threshold on downwind and fly the rest of the pattern to landing without adding power.  That is no longer true…I’ve yet to land without having to add power to get to the runway and that’s after cutting my downwind leg past the threshold in half!  Not only that but I feel like I’m coming in hot because the engine is running at a higher RPM than I am used to so I come in slower than normal.  This will all go away when I get used to the new prop but its an eye opener for now.
    2. LOP operations are a bit challenging right now.  As I mentioned I use engine noise to help me in many phases of flight.  LOP is one of those areas.  I usually lean until I hear the engine start to slow (lower RPM) but now the RPM remains constant and the power drops off.  I have to pay close attention to EGT’s now while leaning.  Along those lines I still need to figure out where best economy is as well as best power.  That will take some time.
    3. Nose is slightly heavier now so I can’t keep the nose wheel off the runway as long on my landing roll-out.  This could be partly due to the fact that this prop slows down so quickly.
    4. The recommended 2 ¼” prop extension that allows this prop to be attached to my engine with a James cowl is too long.  With my previous extension I had about ¼” of space between the spinner and the fwd edge of the cowling.  Now that gap is ¾” or slightly more.  I emailed Sam Tillman at SaberMFG to see if he has a shorter extension.
    5. My prop is the wrong color.    I ordered a white prop with blue crescent stripes to match my color scheme.  The prop I got is black with white stripes.  Its beautiful but doesn’t quite match.  Black and white go with everything so worst case scenario its not a big deal but its not what I ordered.
    6. Torquing the prop on was a bugger.  I don’t have the “special” tool needed so I had to put together a combination of tools to get the job done.  I also needed another set of hands to hold the prop while I was torquing.  I’m going to break out the welder and make a tool to do the torquing since I’m sure I will have to remove the prop sooner or later…even if its only to replace the alternator belt.
    7. Speaking of alternator belts, since the prop was off I went ahead and replaced the belt.  I also took the time to do a few other housekeeping tasks such as riveting the nut-plates on my battery box.


And now some pictures....



This is looking down the crankshaft after I had removed the plug in the end that is used for fixed pitch props.  I found all kinds of gunked up oil residue so I started cleaning it out before I took this picture.  Looking at the very back of the crank opening you will see where I have to install a 1/4" npt plug in the hole so the oil will go forward to the prop.
And here is the same crank location after I had cleaned it up a bit and installed the plug.
This is the governor adapter mounting location on the accessory case.  I couldn't see in there so I took this picture to make sure it was all there.


Here is the next step with the governor adapter pad installed.



This is the top of the PCU 5000X governor with the Van's bracket installed.  I had to use a file to oblong the holes to make it fit properly.  Notice the small stop adjustment screws and the lock wire ... a bugger to get to once installed.


Another shot of the governor before I mounted it.



Flywheel in place ready for the Saber extension to be bolted on.


Governor installed but no cable yet.
Top down view of the governor with the cable installed
Another top down view.


Picking up the prop from the shipping company at 10PM on Friday night I noticed this damage to the box.  We opened up the box and there was no penetration so everything inside was in good condition.


Loaded up in the truck and ready to go home.
Prop, extension and associated hardware installed.  Ready for some first start testing.
Spinner installed.  Inlet rings removed. Protective covering removed.  Time for engine start.
First day of flying I did a few touch and goes.  Its amazing how short this pattern is compared to what I was used to with the fixed pitch prop.


And finally...out in the wild!  This picture is my airplane sitting with Ben's at Fall City Airpark.  Yes, its in my phase 1 circle.  :-)






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