Dave’s RV-7A Building Log

Calibrating the fuel level sensors is not exactly straightforward. The Princeton capacitive converters need to be set at empty and full. The engine monitor system then needs to be set at various calibration points. I couldn’t figure out any other way then to start with an empty tank, set the empty point, fill it up, and set the full point. Then with an empty tank again, set the EMS empty point and I used 3 gallon intervals for calibration points to full. I was basically jockeying fuel back and forth between tanks with a fuel can that I marked at the 3 gallon mark from the self-serve pump on the field. Very, very time consuming. To make things a little easier, I found a fitting at Ace hardware that converted the fuel drain to a barbed fitting for a hose. I used the hose to direct the fuel into the gas can, and to shut off the flow.

Before doing all of that, I hooked up the left nav light.

I bought a high-end bathroom scale accurate to 350 pounds for the nosewheel and re-weighed the plane. The results were much better this time. I also discovered I might have messed up the arm lengths on Tuesday. I measured those with the plane on the ground, and not level. That would have moved the CG artificially forward as well. My numbers didn’t exactly match Vans published numbers, but it’s obviously important to measure the arm lengths in the exact configuration that you weigh the plane.

Here’s the spreadsheet breaking everything down. The net result is that the plane with everything but paint will be 1150 pounds and an empty CG of 79.55″. That is much more in line with what I expected. I am done monkeying with scales.

I moved on to the wing tips. I never finished the wing tip lenses, so I drilled those to the wing tips and installed nut plates. I wanted to light something up, so I started working on installing the navigation light/strobe combos. I got the left one installed and then temporarily hooked up the right strobe. It makes quite a light show in the hangar. I’m very happy with the nav lights from CreativAir and glad I painted them white. They look great.

I think I’ve tracked down a DAR, but I need to submit my paperwork to the MIDO first. That involves getting the weight and balance of the plane. I borrowed some scales from a local builder (thanks Joe). The only problem is that he only had two industrial type scales. For his Cozy the nosewheel is only 20-30 pounds, so a bathroom scale is adequate. An RV-7A nosewheel is in the neighborhood of 300 pounds, which is the max for the scale.

He made some cool ramps for the scales. I set those up and got the plane up on to the scales. Using a jack to get the nosewheel onto the bathroom scale, it became obvious I needed more height under the mains. The plane needs to be level. I put some blocks on the main scales and pulled the plane onto those. Much better. I loaded the plane down with all the covers, fairings, seats, cowl, etc. Basically everything except for the wheel pants, leg fairings, and the interior parts I’m planning on leaving out during the test period, side panels and carpeting. I drained all the fuel from the tanks via the fuel pump and filled the engine to the 8 quart mark. The total was about 1130 pounds. Not great, but not terrible. I then put the carpet and side panels in as well. That put it at 1170. Ouch. With fuel tanks and using Vans recommended 1800 gross, that leaves a payload of only 378. Without paint.

I use some plumb bobs to measure the locations of the wheels relative to the wing leading edge. Forgot to verify those against Vans numbers.

When I got home, I did some rough calculations. The non-carpet/side panel empty CG came out to 77.77. Cool number for an RV-7A, but way too far forward. Looking at Dan’s RV Weight and Balance Database, no other RV-7A is that far forward. There’s one at 78.61, but he’s got an IO-390 engine that is much heavier than mine. I think the bathroom scale was not a good idea. The wheel was pushing down pretty heavy right in the middle of the scale and deforming the surface. I think that is throwing everything off including the total weight. I hope.

While I was still down at the hangar, I drained the rest of the fuel from the tanks. I didn’t have any measuring device handy, so I used an empty water bottle that I previously drained/dried of all water. I was expecting much more fuel than actually drained out. It was about 1/2″ in the bottle. Same for both tanks. (No flop tubes.) I calculated that to be about 0.04 gallons. That’s great. I know that’s not exactly the right way to measure unuseable fuel. I should have the plane in the climb attitude and then drain all the fuel with the pump. However, it’s very difficult to safely get the plane into the crazy steep climb attitude of an RV. The value I got is right in line with other builders, so I’m happy with it.

I had a bit more time in the evening, so I wired up the Gretz heated pitot tube. I actually did most of the wiring a while back with the wing in the stand. I just had to connect the power and display wires. I gave it a quick test. First the red and yellow lights turned on, low heat and heat on. Then red/low heat turned off and the green/temp OK light turned on. Then yellow/heat on turned off. Worked perfectly. And man does that thing get hot. Well over 100°F.

Almost forgot. I also hooked up the laptop to the P-mags and set the advance curve offset to 0.0 from the factory default of 4.2. That’s supposed to be better for keeping the temps down until the rings seat.

Now that the engine runs, it’s time to knock out the rest of the little details. The most major detail was finishing the hook ups for the pitot and static lines. These air low pressure air lines that run to the instruments for calculating speed, altitude, and rate of ascent/descent. I ran most of the tubing a while back, but discovered that the Trutrak autopilot and AFS EFIS have the ports too close together to use T fittings. I ordered some straight fittings a while back, but have been too busy to install them. There’s not much room behind the panel, but I eventually got everything hooked up and the autopilot re-installed.

I used a trick I read about for testing the system. I bought a few feet of surgical tubing from Lowes and stretched that over the pitot tube. I pinched the end closed and slowly rolled up the tube to increase the pressure. Sure enough, the airspeed indicator and EFIS both registered the same speed. I held it for a while to make sure there were no leaks. The static system was a little trickier. I had to hold the surgical tubing up to the static system with it already rolled up and then unroll it. I was able to get a few hundred feet of altitude on the EFIS, but I really need another set of hands to do it right.

Next I decided to knock off an “easy” task from the list, fixing the safety wire on the autopilot roll servo. It was a bit too loose. After 3 tries, 20 minutes, and a bit of swearing, I eventually got it looking better. I’m not a big fan of safety wire.

Since the autopilot was back in, I decided to test it out. I remember switching the roll servo wires months ago when I first tested it. Well, I somehow reversed things in my mind. I had to switch the wires again, and it started working correctly. Increasing the heading should make the stick tilt right. The pitch servo has been in and working correctly for a while.

Started the engine for the first time!!

I got to the airport before Julie and Adele and checked a few things. First, I made sure the prop was tracking. That looked perfect. I then checked every oil, fuel, and wiring connection to make sure nothing was loose. I pulled the plane out front of the hangar, chocked the wheels, tied the tail to the fence, got the fire extinguishers handy, and moved the cars well away from the scene. All systems are go!

The engine didn’t kick the first couple of tries. I had the throttle closed the first try, and I think should have re-primed it for the second try. Maybe it just needed to get some fuel through the system. The third time she started right up. Unfortunately, I followed the directions from AFS and moved the RPM feed from the P-mags to pin 33 of the EMS harness. No RPM at all. I ran the engine for a minute, but decided not to go any further. Still a very cool first start!!

I changed the RPM wire back to pin 32 and tried again. Bingo. All sensors were working great. I ran the oil temperature up to about 90 degrees, the engine up to around 1700 RPM and tried cycling the prop. Worked on the first try. I cycled it a couple of times. The idle is a little low at 600 RPM, but otherwise the engine is purring like a tiger. I was hoping to catch the stats for the event from the engine management system, but for some reason the Advanced Flight Systems AF-3400 didn’t capture any data. Strange.

One bummer on the day is that the stupid tip-up canopy decided to catch in a major way when I opened it. It’s been fine for weeks, but the engine must have settled it somehow. I’ve got some repair work to do there.

I first started messing with the fuel pump. I figured that if one of the connections was loose or faulty that the pump might be sucking air instead of fuel. I removed the line going directly into the pump to see if I could feel any suction at that point. None that I could detect. I fiddled with a few things, but nothing helped. I did other stuff until after lunch when I tried a new tactic. I removed the fuel pump assembly from the plane and rigged up some temporary input and output lines. I put the input into a small container of fuel. Rigged up power and nothing. I then moved my make-shift input line directly to the fuel pump. That’s when it finally started working. I put the assembly back together, and it still worked.

I put the assembly back in the plane, and it still worked. I’m very happy it’s all working, but I wish I knew why it wasn’t working. My guess is that there was some kind of air bubble stuck in the pump, and I finally knocked it loose. The EMS is reading 23 gph with the fuel running into a gas can. With the fuel hose hooked back up to the servo it’s reading 40 psi, which seems a bit high.

In between all of that I finished trimming the flaps, rigging the flap push rods, and temporarily rigging the aileron push rods. The flaps took a lot longer than I expected. Lots of iterations. The second one of course was easier. I still need to tweak the ailerons, as I was only approximating the in-trail position. It’s cool to have the flaps and ailerons working.

This is what I ended up for the left side flap push rod cut out. Ignore the squiggle. The Dremel got away from me. For symmetry I did almost the exact same squiggle on the other side.

Last thing for the day was to do the magnetometer calibration. I used the compass on my GPS to find approximate north. It’s good enough for now. I’m just tired of seeing the warning message on the EFIS every time I fire it up. Once I’m taxing, I’ll take her over to the compass rose for a proper calibration. It was very cool to pull the plane out of the hangar. She’s looking very close to ready.

When I ran out to grab a sandwich, a 737 was on the runway doing engine run-ups. It eventually taxied back to the end, turned around, and took off. Very cool to watch.

Went down to the hangar after work and started messing around with getting fuel to the engine in anticipation of starting it this weekend. I put a few gallon in each tank. No leaks. That’s good. I drained a bit out of each tank via a filter and didn’t see any junk. That’s good. Put a bit more fuel in the left tank. Disconnected the fuel line from the fuel servo and directed it into an empty gas can. Put the fuel selector on left and turned on the fuel pump. Nothing. Right tank, nothing. Tried more fuel in the tank. Nothing. I tried several more things including checking that I had the voltage to the pump correct. Still nothing. Frustrating.

Instead of burning the whole night on it, I decided to move onto something else. I started fitting the flaps. I first made up some hinge pins, although I’m about 3 feet short on pin material. I made do for now with a shorter piece. I did several iterations of marking the inboard edge of the flap where it abuts the fuselage, removing the flap, removing material with a Dremel, re-install, repeat. I also drilled out the starter holes for the flap push rod, and attached both push rods to the flaps.

I like that the plans spec a star washer in addition to the nut plate for the flap push rod attachment. Belt and suspenders. I soon got weary of the flap trimming and started packing up for the night.

One last thing I did was safety wire the oil plugs. Forgot to do that before.

One of the cool things about being at Renton Airport is that it’s the birth place of all the 737s. There’s always a line of planes that are in the final stages of assembly, some with brand new paint jobs. I think the building on the right is where they paint them. It’s cool seeing them go out on the runway, test the engines up and down the length of the runway, and then line up on 15 to take off for either the first flight or close to it.

Today I saw one of the 737s on the compass rose, being hauled around in circles. Do they really do a compass swing on these big beasts?

And here’s my baby.

The entire evening was spent on the wing bolts. I got the bottom bolts torqued down, and then moved onto the small bolts. I thought they were going to be easier, but they were almost as difficult as the big bolts. They’re all in and torqued now.

This picture shows the starting point of the evening.

The next two pictures show how tight the space is for the bottom bolts. The outboard nut is at the bottom of the picture. It was difficult even taking a picture of it with the fuel and vent lines in the way.

In this picture you can just make out the nut behind the green tubing. You can see it’s jammed up against the gear leg tube.

I had a little time to work on something else, so I pulled out the wing push tubes. I set them in the wings, but realized I need a bushing in order to connect them to the bellcrank. I thought I already made that, but couldn’t find it anywhere. Guess I’ll make them again. That’s the point when I decided it was just too cold anyway and headed for home.

I went straight to the hangar after work, and got in some really productive time. I started off with something easy. I hooked up the landing lights. Took about 5 minutes and I had them flashing. Very cool. While I was there, I hooked up the Angle of Attack tubing to the ports.

Next was the outside air temperature probe. The harness from AFS/Stein had the wire about a foot short of ideal. I had to reach into the inboardmost wing access hole and put the pins into a connector shell. Not fun, but I got it done. Turned on the EFIS and the temp was reading correctly, although it sure felt colder than 56 degrees.

Next was the autopilot servo connector. I put the pins back into the connector shell and plugged it in. I don’t have the head unit installed right now, so I wasn’t able to test it yet. While I was under the wings I put the screws into the bottom skin that overlaps the wings.

Next up was fuel lines. I torqued the connections to the tanks. Re-attaching the lines under the fuel valve was fairly difficult. There are just too many connections under there and not much room to work. I eventually got them connected and torqued. I also hooked up the coax wires to the capacitive fuel probes and set the empty point on each unit.

I swung by the self serve fuel pump and got 5 gallons of 100LL. I was planning on pouring some in the tanks and checking for leaks, but didn’t want to risk that kind of bad news. Maybe tomorrow.

I left the big task for last, because I knew it would be frustrating. Getting the nuts on the bottom wing bolts is nearly impossible. I climbed into the cockpit with all the tools handy and went to work. Luckily, I was able to back out the one bolt pretty easily. I found a way to pry the end with a screwdriver while I turned it. Backed right out. From there I just started putting the nuts on one by one. One was easy for some reason, and the others were a pain. But they are all on now and partially tightened down. It should be easy from this point to tighten them down and torque them. I’m very happy about that.

Lots of frustration and sailor’s language, but got a ton of tough stuff completed.

Sorry for the lack of pictures lately, but I’ve been really concentrating on maximizing my limited work time. Plus the hangar is too dark for decent pictures anyway.

Couldn’t get down to the hangar, so I worked on the forms for the airworthiness inspection. After getting halfway through filling out the forms by hand, I remembered you can get them online, fill them out with Acrobat Reader and print them out. Much easier.