page 47-07: setting propeller pitch

The propeller pitch is set by loosening the six bolts shown going through the front prop bulkhead into the hub, twisting the blades by hand, then re-torquing the bolts.  This obviously is an imprecise, trial-and-error process, made worse by the fact that the act of bringing the bolts up to the proper torque causes a very slight rotation of the blades.  The build manual says to set each blade to a specified angle within plus or minus 0.1 degrees (!?).  This is to be accomplished using a supplied steel bracket placed at a particular radial position on each blade and a digital level with a magnetic base.  The prop is leveled horizontally and the level is referenced to (zeroed on) the longeron.  Sensenich supplies different diameter metal "pegs" that are to be inserted into a hole in the hub to set the pitch to three different common angles but Van's says these can be off 0.7 degrees and therefore shouldn't be used.  

Here's the problem: The commonly available digital levels, most of which advertise accuracy of plus or minus 0.1 degrees, actually deliver this accuracy (if you read the fine print) only near 0, 90, 180 and 270 degrees.  Otherwise, it's 0.2 degrees, and I doubt it's actually that good.  

Since having each blade at the same angle is far more important than the actual angle itself (as long as you're close to the desired angle), I decided to use the laser built into my level to project a line on the floor (hard to see on the blue tape).  

My procedure went like this:  Use Van's procedure to get as close as the digital level will allow to the prescribed pitch angle for the first blade, mark the laser line on the floor, rotate the prop 180 degrees, transfer the bracket and laser to the second blade, twist the blade until the laser line is on top of the mark for the first blade.  Tighten. Tweak. The blades are at the same angle.

Off topic:  For the past nine months I've been having a house built in the hills west of Loveland.  There's lots of wildlife there so I've had a trail cam set up in the back yard (you can see the house in the distance).  During the cold months elk come down from the high country and hang around until spring.  Here's one pic.  My neighbor who lives about 1/4 mile away trumped it by showing me several video clips of two mountain lions at once in his yard.  Another neighbor had two moose in his yard and a bear rummaging through his trash can,  Ah, life in Colorado.

page 47-02: Pitot tube

The pitot tube on the RV-12 goes through the hollow propeller shaft and protrudes out the front of the spinner.  The tube itself is stationary while the prop and spinner turn around it.  This somewhat unusual arrangement was done to accommodate easy wing removal, making it unnecessary to disconnect the tubing for the Pitot each time the wings are removed.  

The thought behind the removable wings was that people could save money by storing the airplane at home and trailering it to the airport, avoiding the cost of a hangar.  I may have heard of one person who actually tried this while everyone else keeps the airplane at an airport in the usual fashion.

The Pitot tube as supplied has male threads on one end and is threaded into a rigid nylon block which is bolted to existing threaded holes in the gearbox housing.  If all the flat surfaces on the nylon block were at right angles to each other the forward end of the Pitot would be perfectly centered in the hole through the propeller hub.

As can be clearly seen in the second pic, it's way off.  I took everything apart and cleaned all the mating surfaces with no effect.  Somewhere a surface wasn't square with its neighbors.

After passing through this hole, the tube goes 
through a hole with bushing in the forward tip of the prop spinner.  Left like this, a constant radial load would be applied to the bushing, no doubt contributing to wear as some builders have documented on the forums.  I explained all this to the Mothership and was told it's fine.  Let the bushing handle it.

A few measurements and calculations showed that placing a 0.008 inch shim between the upper forward surface of the nylon block and the mating machined surface on the gearbox housing would bring everything into alignment.  The pic at left shows what that might look like if it were done.  If I were building Experimental-Amateur Build (E-AB) rather than Experimental Light Sport (E-LSA) I could do this sort of thing.  Since I am E-LSA I must build my airplane exactly like the ASTM Conforming Prototype, at least until I get my airworthiness certificate.  Then, oddly, I can do pretty much anything I want as long as I don't take it out of light sport parameters.

If I had used the shim, the Pitot tube would have been centered perfectly as shown in the pic at right, eliminating the radial load on the bushing.

Off topic:

I just got back from my 33rd trip to Mecca (a.k.a. Oshkosh).  After swearing last year I wouldn't do this drive again, I drove from Longmont, CO to KOSH and back, this year in a rental car (a little over 1000 miles each way).  Rental cars in Milwaukee were hard to get and expensive, not to mention the hassle and cost of airfare.  Turned out to be a good decision and I'll probably keep doing this even though my airplane will be ready for subsequent years.  I'm becoming increasingly nervous about parking my airplane outside in the elements for a week.  Maybe I'll change my mind.

In 2020 when I quit splitting my time between NC and CO and moved permanently to CO (selling my beautiful home in NC😢), I kept hearing local pilots talk about flying "over the hill" for breakfast or lunch.  Turns out they meant flying over the high mountains along the continental divide (Colorado has 53 peaks higher than 14,000 feet and 600 higher than 13,000 feet).  To a country boy from the Carolinas, this seemed like a serious undertaking.  I got my chance to try it a month or so ago when we attended an EAA fly-in breakfast in Granby, CO.  I got to go back seat in my hangar-neighbor Tom Book's RV-4 (got some stick time including pointers on formation flying).  This is a pic I took with my iPhone of my other hangar-neighbor Chad Rennicke's beautiful RV-6.  The building which contains my T-hangar has a total of 11 hangars.  In this building alone we have an RV-4, RV-6, RV-7, RV-10 under construction and my RV-12.

Pages 46-1 through 46-22. Engine prep and hanging

When the time came to actually hang the engine it was pretty exciting.  For the first time I would not need a stand under the tail tie down ring to keep the airplane from tipping over backward.  It could stand on its own three feet, proud and unsupported.  No crutch!  A quick perusal of the build manual, however, damped my excitement a bit.  A surprising amount of work was required to prepare the engine before hanging.

Since everything I was about to do required the use of a torque wrench, sometimes in awkward places where I couldn't see the dial on the Snap-On, I decided to calibrate the click-type Craftsman so I could use it if required.  In an earlier post I discussed calibrating the Snap-On with a known mass (not a bar bell weight!) and found it dead-nuts accurate.  A fresh calibration showed the same.  In the torque ranges required for engine installation the Craftsman was off by as much as 18%.  Glad I checked.

The first task requiring some thought was to check and set the five crank triggers shown in the picture below (five because one of them is a rev counter).  The gap between the tooth on the flywheel and the sensor is specified to be between 0.012 and 0.016 inches.  But wait a minute, I'm thinking, these Rotax

engines are broken in at the factory by being run on a dyno for about an hour.  Wouldn't that mean that the crank triggers are already set?  One  respected guy on the VAF forums just left them as is.  They're all tighter than the Van's spec, so I went ahead and set them.  This requires rotating the crank, which is accomplished by putting bolts in some threaded holes in the flywheel, removing a spark plug from each cylinder, and using a big screw driver as a lever.  When the prop is installed, turning the engine is much easier and has to be done a lot when fitting the spinner.  I still left the plugs out, however, with rags stuffed in the spark plug holes to keep trash and insects out.

The next challenging step required disconnecting four coolant hoses from the water pump in order to install the engine mount.  I've disconnected many a coolant hose on many a car over the years without any problem.  These were different.  Nothing I tried would budge them.  I finally fabricated the piece of wood shown and drove them off, still needing a little assist from the padded vise grips to supply a little rotation.  There was some coolant still in the engine which had to be caught in a shallow pan.

The engine mount is attached to the engine with four 10mm cap screws which must be accurately torqued to a hefty value which now escapes my mind but is obtained from Rotax Heavy Maintanence manual.  I was glad I checked the manual because it's a substantially higher value than is given in the standard bolt torque table.  The problem arises because it's hard to put a torque wrench on the upper

port-side bolt.  I've read where other builders removed the intake manifold to do this, something I really wanted to avoid.  These bolts must be rechecked at every annual condition inspection giving added incentive to find another way.  I ended up using a double box end wrench as a "torque adapter" as they're known commercially.  Keeping a 90-degree angle between the handle of the torque wrench and the box-end wrench means the torque reading in unaffected by the wrench (the position vector crossed with the force vector gives the torque).  There's a little segment of an Allen wrench in the end of the wrench not attached to the torque wrench which goes into the cap screw.

With the engine attached to the engine mount I was ready to move it to the airplane.  An engine hoist on rollers made this a simple, one-person operation.  Before attaching the mount to the firewall a couple of 3/8th inch holes had to be drilled through firewall, easy for me because I could do it from the front since I'd already installed the upgraded nose gear leg.  The poor souls who had to install the new leg to an already-flying airplane had to drill the holes from the inside, a much more involved task.