Scott & Tanya Card RV9A build log (N4822C)

As promised, Tanya and I flew up to Corsicana for lunch with her parents. It was a beautifully uneventful flight. The pictures were all taken with the new Cannon EOS 40D camera. The new prop governor is doing great and CHTs are down about 10 degrees at full power. I am seeing the higher fuel flow numbers that I was expecting on takeoff in the 13 gph range.

As we were chugging along at 5500′, Tanya asked if there was a VOR out here somewhere. I glanced at the GPS and said, yeah, there should be one right below on your side. “Cool, I just took a picture of it.” she said. Ok…
Then there was lunch and back to the airplane for departure.
We took off and did one lap in the pattern and a gratuitous low approach before turning toward home. Tanya’s father apparently got a thrill out of that. We could see him dancing a jig on the tarmac as we went by at 30′ and 90kts then into a “rapid” climb :). Much fun.

 

  

  

  

  

  

  

  

  

  

 

I made it out to the airport Friday evening after spending a good chunk of my afternoon looking at a new house. We’re thinking about moving to a place with a larger garage for a -10 project :). I think we found something that we’re going to make an offer on.

Time to flight test the recent changes; new prop governor and carburetor mixture modification. I leaned much more aggressively on the ground for taxi. That will become our SOP. I setup for takeoff, being prepared to carefully watch for prop overspeed and make adjustments. I also had my EGT display in running graph mode so I could easily see where they were during takeoff compared to before the mod. As I got full power in, the prop spun up to 2722 rpm for just a second (literally, by the captured data) then the governor stabilized it rock solid just under 2700. The max EGTs on takeoff were about 30 or so degrees cooler. The recorded fuel flow on takeoff didn’t go up very much at all. I only got two takeoffs in before it got too dark, but is sure didn’t go up anywhere near a full one gallon per hour. The max recorded fuel flow was 11.7gph. I think I was expecting to see something like 12.4gph. Although, that isn’t exactly a number that I’m inclined to chase too aggressively. Update: A later data set did show almost 13gph on takeoff for just a few seconds.
I went out and did some leaning tests. I’m now seeing about 30-40 degrees more EGT rise. I’m happy to see that. I’m comfortable that I didn’t overdo it. Runs great, and with this limited testing, it did have an effect on CHTs in climb, but the test data is too limited at this point to quantify. I also did a quick power off stall just to be sure that it wasn’t so sloppy rich in flight (full rich) that the engine would stop. It behaved fine. Cool, I’m happy with the carb mod.
So far as I can tell, the prop governor is totally rock solid. You set it at an rpm, and as long as you don’t make a major power or pitch change, it doesn’t flinch at all. So far it seems much more effective. The updated MT governor seemed like it was getting more and more lazy at holding an rpm. As I was finishing up my testing, the sun was almost fully down. I landed with lights and taxied to the pumps to top off the tanks, then back to the hangar to put it away. A good evening indeed.

Tanya and I are headed up to the Dallas area to have lunch with her parents tomorrow.

The new PCU5000 prop governor arrived today! Hmmm… Work, or go to the hangar to install new toys. I’m sensing a short work day today.
Yep, I bailed out of work early to go play. Today I got the prop governor, the new canopy cover from Bruce’s, and a new digital camera (Cannon EOS 40D). Christmas in September! The canopy cover weighs 6lbs. I’ve been weighing everything recently in prep for the trip to LOE.
Once at the airport, I finished up reconnecting the carburetor and triple checking it. Moving on to the governor I began removing the old one. I used the ziploc bag under the drip area to catch the oil that runs out. This has become my favorite trick for changing the oil filter. It works great. No more spending an hour cleaning up oil dripped all over the place. Once I got the old one out I compared it to the new one. The control arm was positioned perfectly on the new governor “300 degrees”. Also, the vans governor cable bracket fit perfectly. No changes in the linkage were required. Wow, old one off, new one on. Just as easy as that.

All I had time for was a thorough run-up to make sure everything worked with no leaks. I pulled the airplane out without the cowl and fired it up. Immediately I could tell that the carb was quite a bit richer. It now has about 60-70 rpm rise at idle when leaned. I need to adjust the idle mixture down a little bit now. Previously I had almost no rpm rise at idle. Otherwise, the carb felt fine in a full run-up. The prop governor cycled fine as well. The governor definitely feels different too. It doesn’t seem nearly as sensitive as the old one. This is good for me. After bringing the engine up to temp and exercising all of the changes, I shut it down and went over it one more time before cowling it back up. It is ready for a test flight on Friday.

 

  

  

  

  

  

  

  

  

  

 

Some will cringe, some will rejoice, but whatever the case, tonight I took the leap and drilled the main jet in the carburetor. How did I get here? The CHTs sure rise fast at takeoff and in high power climb. I only see about 100 degrees EGT rise (8000′ DA, 75% power). I think I could use some more fuel flow on takeoff. So, drilling the main jet is how I’m going to attempt to achieve that.
Disclaimer time: I don’t have a certified engine so no danger of jeopardizing paperwork, I’m well aware that I could destroy the jet and have to replace it for a few hundred dollars and much down time, I built this thing to tinker with, not just fly, this ain’t my first rodeo when it comes to carbs. I was very comfortable tearing down and rebuilding auto carbs by the time I was about 12 years old. I’m no expert, but it isn’t rocket science in there.
So with all that accepted and out of the way, I started turning wrenches and had the carb all pulled apart on the bench in about an hour. All you really have to do is separate the bowl from the top half. I had previously ordered a gasket kit and new retainer washers from ACS. I learned at a very early age not to start such a disassembly until you either have new gaskets or enough material and time to make new ones. The gasket needs to come away with the top half of the carb since it is under the float. I did have a bit of a hard time getting the two halves apart after the bolts were out. They were just well stuck together. I used every trick in the book before finally getting out the putty knife. Note that I didn’t have to remove the airbox from the bottom half of the carb. I just left it all assembled. I also found that it is much easier to remove the whole carb heat muff from the exhaust crossover tube than trying to mess with the SCAT tubing that is very tight fitting.
Back at the bench with the carb in two halves, yep, looks just like the good-ol-days. I removed the main jet from the bowl body. A #42 drill bit (.0935″) fit in the hole just right. I drilled that out to #41, then to #40 .098″ (very carefully). I understand that Precision Airmotive has said in the past that each # size drill bit will open it up by about 1gph. That is as far as I was willing to go for now. I think this is a pretty conservative modification. I reinstalled the main jet and its retainer washer. Then removed a cotter pin holding the float pivot pin in and removed the float. This is necessary to install a new bowl gasket. It all went back together the same as it came apart. I got it bolted back on the airplane but still need to finish hooking up the controls. Oh, yeah, while I was at it, I completely removed the carb temp sensor. I’m tired of swapping it out just to watch it bounce all around on the instrument. I’m done with that little piece of crap.

 

  

  

  

 

Today I resolved the problem that I have been working on for quite some time with getting vertical navigation signals to the autopilot from the GNS430W. I have talked about this a lot but here is the recap again: The 430W should be able to output vertical navigation instructions to the TruTrak DF II VSGV autopilot via the ARINC 429 buss to drive the autopilot all the way down an IFR GPS approach. This wasn’t working for me. It worked great for lateral navigation down the approach, but the vertical just wasn’t there. Then I found that the GPS needs to output the “GAMA 429″ signal format and not “ARINC 429″. The GAMA format adds the vertical commands. Ok, so I set that. However, with only that change, I found that once a gps signal lock occurred, the GTX330 transponder was somehow, via it’s ARINC 429 connection to the 430W, commanding the 430W with a remote “joystick waypoint” entry command over-and-over continuously such that everything was unusable. That is where I have been stuck for the last few weeks.
Today I went back out to the airport committed to simply burn some more time on the problem. You know, sometimes if you just invest some more time with no expectation of real return, you can make at least some kind of progress, if only more visibility into the problem… So I spent about 1.5hr sitting in the cockpit messing with 430W and GTX330 configurations. After I had been through every config and verified that I understood everything and made sure my settings all made sense to me, I decided it was time to try the next step. You software engineers know where I’m headed with this (even though we usually won’t admit it). I began simply trying logical and illogical combinations of configurations of data formats and buss speeds on the ARINC configs. Yep, you guessed it, I changed the buss speed on a seemingly unrelated (input) ARINC interface on the GTX330 and the flood of joystick waypoint entry commands stopped on the 430W.
Cool. But of course I had to back track and try to figure out what that broke in the process. Hmmm… Nothing broke because of the change. Really? (head scratching). Yeap, seems like everything still works. All data is getting everywhere as normal. Sweet!
Time to hop in and take it for a spin to see the magic in action. I launched and setup a fully coupled GPS approach. I engaged the autopilot, switched directly to the GNS430W, let it fly the transition, and as it turned inbound for the 10mi. final, the autopilot went from “vnav arm” to flying the glide slope right down. Right about here, I’m just concentrating on containing my excitement as someone still needs to sit here and monitor the computer as it flies the final approach :). I just worked the throttle and trim. Down we went for a “perfect” landing. It works, It works!

Update: After a little research (root cause analysis) as to how I could have been so far off, I found that the ARINC 429 connection in question never made it into my final interconnect documentation. I designed it, I built it, I documented it. My fault, oops. I updated my schematic and all is well with one less mystery.