§28-18 thru -21 Left Pushrod installation

 It's been a while since I last updated this.   Work is sucking up so much of my time, but that's how I keep up the cash flow to pay for this insane hobby.    Last week I finished up the pushrod installation on the Left wing.  It was fairly straightforward and kind of interesting to see how the system will work.  Basically, there is a pushrod extending from the root of the wing that will eventually connect to something inside the fuselage.  When that rod is moved outboard, it actuates a bell crank that moves the outer pushrod inboard.  This, in turn, pulls the small pushrod forward which will cause the aileron to deflect upward, thus banking the plane to the left.  It is left as an exercise for the reader to fill in the blanks regarding motion in the opposite directions.

Large pushrod at wing root.

Small pushrod at aileron attach point

Really getting a good look at the aileron pushrod system has done nothing to allay my concerns about how the flaps are going to be activated.  I identified a bracket that will hold a pulley for flap cables and can sort of visualize where something might fit in the inboard mixer box, but for the life of me I can't see how it's going to be retained in there since there are no nut plates or anything.   I'm guessing that there will be two cables in opposition connected to bell crank and one end of the bell crank will have yet another pushrod.  Why those components weren't included in the wing kit so they could be installed before buttoning up the skins is something that baffles me.   Regardless, I will trust the process and will complete the wing skins as directed by the instructions.

Finally, I have to report that the damn tanks are still leaking. It's a much slower leak now, and it's in the same place on both tanks -- at the ground lug that is behind the fuel sender plate.   I also learned that the soap bubble trick only works on really slow leaks and it did a great job of letting me see where the air was escaping.   On an academic note, there is a phenomenon known as Starling's Law that is really important in cardiology. Basically, the amount of stretch that you get out of a given pressure is highly dependent upon the radius (size) of the thing being stretched.   When you pump up the balloon with the hand pump, the balloon gets sort of inflated and does nothing for several pumps, then abruptly grows quite large without any further pumping.   Human hearts tend to do the same thing when they fail due to fighting high blood pressure for a long time.  It was really cool to see it in action rather than just imagining it as an academic factoid.

Today (well, yesterday) I spent two hours removing & cleaning the fuel sender units and the inboard access plates of both wings.  Man, I hate working with Proseal!   I'm going to use all new screws and lock washers for this 3rd attempt at sealing the tanks.   I've done some cruising through VAF and found several techniques that I will try to integrate into this next attempt.   Fingers crossed.

Finally, the tail kit is en route and should arrive some time this week.

§ 28 -6 thru 13 -- push rods

 Van's is famous for the smoothness of the control feel of their airplanes.  I think one of the contributing factors is that they use bearings and pushrods whenever possible when designing their flight control linkages.  I had already assembled the rotational bearings in bell cranks.  This post documents building the push rods that attach to them.

I also like a really nice technique they employed for establishing the exact length of the push rods.  When you build one, you can turn the stem of the spherical bearing to move the length in or out by 1/48" at a time.  When I built the RV-12, I remember trying to very precise about my measurement.  In the RV-15, they have you assemble the push rod and then use temporary bolts to insert into holes provided in the main spar.  In other words, the main spar has a jig built in to it.   Very easy to twist the bearings to get a perfect fit -- no tape measure required!

I used blue locktite as a safety feature for the jam nuts and ruined one of the spherical bearings when the locktite dripped on the bearing itself.  Although it felt like it was still moving freely in its race, I expect that it will not remain in good condition for very long.  I tossed it in the junk bucket and ordered another one ($26!) from Van's.

Aileron Push Rods

Push rods, prior to riveting and installation of bearings

I started the final assembly of this chapter where the bellcranks get installed in the mixer and the pushrods get attached to the bellcranks.   Even without the skins on the wing, it's definitely challenging!   I'd like to have a trained capuchin monkey w/ tiny hands to help out.    I am absolutely dreading / afraid of trying to install the flap control mechanism after the wing is closed up!

§27 L; IB Mixer - Rear Spar

 This was also a pretty straightforward chapter.  The Inboard Mixer was nestled into the space just next to the tank and directly in front of the spar attachment area.  The holes that were left open for the rear spar attachment were then used to rivet the mixer to the spar.  Here's where the infamous Cherry Max Rivets got used -- all 39 of them.  These are pull rivets ("pop rivets", although that's actually another brand name) but they are stronger than the typical LP3-4's used nearly everywhere else in the plane.   The book says to be sure to pull exactly in line with the stem, but that's not possible with a few of the rivets because there is a flange immediately in the way.  I bent the flanges as much as I could and did the best job possible.

IB Mixer, as viewed from the front of the wing assembly

For some reason, they decided to have the flap tracks installed in this chapter rather than give them their own chapter.   The flap tracks are interesting; they are jet black and I'm not sure if they're aluminum or something else.  I am getting better at riveting.  There were two rivets that couldn't be bucked with my titanium bar.  I used a flat plate of steel and got creative.  Worked great!

 

Flap Tracks

§26 L; Rear Spar - Tank

 I got a lot accomplished in the last week, but one thing I didn't have time to do was document it.  I typically have slow times between patients at night, but not recently.  Sorry for the delay.   I'll publish several updates in a row so i don't overwhelm you with a really long post.

Attaching the rear spar to the tank assembly wasn't too bad.  It was literally a one pager that consisted of bucking 33 rivets. The only challenging part was ensuring that I only riveted the holes called out in the KAI, as many holes were left open for the next chapter.

I'm starting to get a feel for when a bucked rivet will look good or look like a mess.  I think the key technique is to maintain pretty firm pressure with the rivet gun, but not much pressure on the bucking bar.  Time will tell.

Again, no picture as it really doesn't look any different.

flying instead of building

Well, didn't get out to the shop to do any building because I went flying instead.  I don't want to let my flying skills deteriorate due to spending all my free time building the new plane.  I was getting close to loosing my currency for IFR flights, so yesterday Ed & I took the Cirrus up for a good workout.

The weather was perfect for an IFR training flight.  There was a nice big low pressure system (29.69 inHg) sitting over Ohio yesterday and that gave us a cloud layer from about 1000' to 4000' above the ground.  I flew and Ed observed/coached/critiqued from the right seat.  I flew to Dayton, did a hold and shot the RNAV 24L approach there, all using the autopilot.  In other words, I programmed & observed while the plane flew itself.   That's the Standard Operating Procedure for an actual mission.   Then I disconnected the autopilot but left the flight director engaged and flew the same approach by hand.  The flight director essentially is a display driven by the autopilot that says, "if I still had control, this is what I would do."  Basically, it's a video game -- the A/P moves the cueing display and I fly the airplane to match the cue.  Then I turned off the flight director and flew using just the displayed location data.  I flew all the way back to Delaware by hand, went to the far side of the airport to get aligned with the wind and few the RNAV 28 approach back home.

Overall, 2 hours of a good workout and I feel better about being a competent pilot.

Back to building when I get home tomorrow.

§26 Left -- Rear Spar to Tank

Well, I took a deep breath yesterday and committed to joining the rear spar to the tank.  The section is a whopping 2 pages of actual instructions -- 1 page says to cleco everything together, the other says to rivet it.  All 33 rivets are 470AD4-4 that needed to be bucked since there was no way to get a squeezer anywhere near both sides.  

I am still quite leary of my skills in bucking rivets, hence the trepidation in this step.   Having said that, I'm actually quite pleased with how it turned out.   I am starting to get the feel of how much force to use with the bucking bar.  Counterintuitively, holding it with too much pressure simply causes a lot of noise and not much deformation of the rivet tail.  Obviously, not enough pressure and it simply bounces away.  If you use just the right amount of pressure, the tail of the rivet sets in only 8-10 impacts.

Some of the rivets were in a place that I could only see the shop head and had to hold the bucking bar blindly.   I'm quite surprised that it went well.  I did use the guage to ensure that the shop heads were within spec. 

Tomorrow, I'll finish riveting the spar, tank and inboard mixer box together.  Those use the famous Cherry rivets that are stronger than the regular LP3-4's but are harder to pull correctly.   The sealant should arrive tomorrow or Wednesday and I'll re-seal the Left tank.  They say 3rd time's the charm.  Stay tuned.

§28-14, -16 L&R Aileron bellcranks

 Two steps forward, one step back.    The right tank now holds pressure.  Sort of.   The left tank still has a definite leak at the fuel sender.  I used a cartridge of sealant from Aircraft Spruce, but the gun I bought (that morning) from Home Depot is much too large for the cartridge so I ended up just shoving the base with a spark plug socket as a make-shift plunger.  That made it barely possible to squeeze out the bead of sealant, with the resulting poor performance.   Since then, i've borrowed an appropriate sized gun and will give it another try when the next cartridge arrives from Aircraft Spruce.

I've been holding off attaching the spars to the tanks until they were sealed, but I'm going to go ahead and resume major construction since the leaks are at the other side and can be dealt with in parallel.

I built up the aileron bell cranks.  Took just a day and was a nice, straightforward project.

underexposed picture of the bellcranks

The aileron push rods have specific instructions to be primed.  I learned that just putting them on butcher paper and spraying them with primer, then leaving them overnight to get wet, results in paper that is well glued to the aluminum.  I sanded much of it off, but not all.   I stood the push rods using wooden dowels in the ground and sprayed them again while vertical.   I now have nice camo'ed push rods!

Aileron pushrods drying in the sun