Shortly after New Year fellow member of my aero club and RV12 builder friend Wolfgang invited me for a flight in his RV12 (Wolfgang’s RV12), for which he has received the airworthiness certificate last June.
Flying on a cristal clear winter day here in the Austrian Alps is one of the most beautiful flying experience one can imagine, so no way I could refuse this generous offer.
Work was actually done Dec. 27th 2019 till Dec. 31th 2019
With aileron and flap aligned, the left wing is mostly finished too. This is almost exactly three years after taking shipment of my kit Nov. 16th 2016
With all the AirVors crew being home for Christmas, I had helping hands to lift the wing off the workbench and put it into storage.
First we had to take the rear fuselage out of storage again to gain storage space for the wing on the rigtht side of the garage. Then we lifted the wing off the workbench, put it leading edge down on soft styro foam and bolted the jig to the far end wall with three wall plugs.
Son Paul had this great idea, which made building a wing cradle or wing dolly unnecessary and also saves some space.
To protect the wing from accidental damage, we again built a blind wall and a small workbench from plywood out of the crates the kit originally was shipped in. Again I painted the blind wall white (with the cheapest wall paint I could find). Though I have bright led ceiling lights the white side walls really improve illumination of the workspace significantly.
We also shortened the legs to lower my two workbenches and make work on the fuselage easier. Lastly son Klaus and his friend helped me to carry the center fuselage upstairs from the basement and carry it to the garage.
Below photos show my rearanged “hangar”. The left wing, vertical stabilizer and horizontal stabilizer are stored behind the blind wall on the left side of the photo, the right wing behind the right.
I could have stored the elevator on top of the right wing, but (with consent of the World’s Best Copilot) putting it on top of the wardrobe in the master bedroom was much easier 😉 (it’s hardly visible).
It takes some organizing, but yes, a Sling 4 can be built in single garage – provided it is long enough. This unfortunately (being “only” 5,9m long) is not true in my case.
For the time being I will be able to finish work on the fuselage, but when time comes to hang the engine and fit the cowling, I will have to exchange the window on the back wall for a door. That’s ok for me, as my garage currently does not have a second entrance. I will then let the tailcone protrude out of the door by ~0,5 m.
With the wings now in storage, open items before paint will be:
fill rivet heads
install rivnuts for service panels
pull pitot and AOA lines
Open items after paint will be:
install taxi and landing lights and lens and connect
install nav/pos/strobe lightand connect
install push rods
Putting the top skins on the rear fuselage and joining the rear and center fuselage will be our next jobs.
Work was actually done Nov. 28th 2019 till Nov. 30th 2019
The method I used on the left wing is somewhat tedious, so I tried another method on the right wing, which was much faster, even though the aileron did not align immediately and also required adjustment (the left aileron did not need any adjustment).
I am therefore describing here the procedure I used this time:
First thing to do is to rivet the flat parts of the aileron. Do not rivet the holes in the rounded areas yet. Then you need to check, how well the aileron aligns at the trailing edge using the prepunched rivet holes.
To lock the twist for the alignment check, I’ve removed the stems from five rivets, pushed the stemless rivets into place and held them in place with Ducktape (or painters tape will do).
As it takes only 1/10th of mm to cause a misalignmnet of 3 or 4 mm at the trailing edge, to my experience just using Ducktape alone does not lock the twist enough, as it leaves some wiggle room for lateral movement.
Then I mounted the aileron (notice the painter tape, where the five rivets are) …
… and measured the misalignment using an appropriate drill bit (from my drill bit set).
I overcompensated here (0,5 mm thicker drill bit) to allow for some springback.
Then I put the aileron on my workbench, removed the five stemless rivets, placed that very drill bit at the oposite end to shim the trailing edge (and thus correct for the misalignment, as measured with this drill bit before).
Weighing down the inbord and outboard end of the trailing edge, I took a look of how much the leading edge rivet line was out of alignment. This was laterally off by only ~0.1 mm, so within tolerances to still use the 3,2 mm rivets.
I therefore reamed out two holes and set these two rivets. I then mounted the aileron again to check alignment, which was near perfect. So I took it off again, put it on the workbench like before and continued reaming out and setting the other rivets.
With the leading edge riveted, I installed the aileron again and clamped it at the wingtip end.
Next I prepared the flap in the same fashion: insert five stemless rivets to temporarily lock the twist for measuring the misalignment and flip the flap over to find a shim with correct thickness.
Flip flap back again, clamp at the inbord end and measure how much the alignment is off (used an appropriate drill bit again).
Flip flap over again, remove the stemless rivets, increase thickness of shim by adding the drillbit, weigh down both ends to set the twist and set one rivet. Then flip back, clamp the flap and check alignment. Continue riveting if alignment is ok, which it was at that point (or drill out rivet and adjust accordingly).
Seems, like I’ve become a little slapdash here and riveted away without checking once more – which I probably should have. The alignment is not as perfect as on the left wing, but it’s not off enough to warant undrilling all rivets again.
In hindsight looking at one of above photos I should have overcompensated also by 1 mm instead of the 0,5 mm, since the flap is much longer than the aileron.
When aligning the aileron and the flap I observed that both, the aileron and the flap have a hump on the bottom side at the trailing edge even though the skins are in line.
I was worried about that and contacted technical at TAF. Technical informed me that this will be found on all Sling 2 and 4 and that I need not be concerned about directional stability, drag or stall behaviour as all flight testing had been done with flaps and ailerons like this.
Before putting the wing into storage, I twisted the ldg/taxi light wires and pulled them into the conduit. Remember to add some lenght, as the wire gets shorter by twisting (if memory serves me right, I think I added ~10%).
Work was actually done Nov. 9th 2019 till Nov. 24th 2019
With the help of my younger son Klaus and some of his friends (thanks guys!) we repositioned the wing front to back and upside down to make work on the wing tip easier.
After removing the wing tip jig I first installed the end rib (WG-RIB-011-R-A-). This required some adjustment of three flanges that were slightly incorrectly bent, but after that the fit was perfect. Like on the right wing I fabricated a bracket for the conduit and pulled the nav/strobe/pos light cable.
Upon a first testfit of the wing tip the fit and alignment was quite good, but the wingtip was short at the aft end by 8-10 mm. So in the sense of FAR §21.191 (g) (“….solely for their own education or recreation…”) it was time for my first composite layup.
After sanding off the gelcoat / primer and cleaning with an acetone wipe I built a dam out of stiff plastic.
First I cut thin fiberglass mat which I wetted with epoxy resin using a paint brush. I then layed theese out on a sheet of plastic in a staggered manner to achieve a smooth transition. After adding another ply of plastic I squeeged out the air bubbles and excess resin, removed the plastic again, transfered the layup to the wing tip and weighed it down to get a good bond.
After two days of curing I turned the wing tip over and made a layup on the other side and let it harden again. Before sanding the layup into a smooth transition I brushed on a layer of resin to get rid of some pinholes.
Making the layups was actually was quite fun and quick. Not so the sanding to achieve a smooth transition, which took two or three hours and another layer of epoxy resin.
The translucent area in above photo shows, who much the wingtip was to short.
Again like on the right wing I added some aluminum reinforcement strips to the inside of the wing tip with Sikaflex 252i (underneath the recessed area, where the tip is rivetted to the wing skin).
After installing the mounting brackets for nav/position/strobe lights, some sanding of the recess, edge forming and light bending of the wing skin I was quite happy with the fit and rivetted the wing tip in place (again sealing it with a thin layer of Sikaflex).
Again like on the right wing I could not get perfect alignment along a small area near the leading edge, but a little body work will take care of that, when it comes to painting.
Work was actually done May 18th 2019 and Oct. 19th 2019 till Nov. 7th 2019
As with the wing structure much of the preparation work and part of building the tank had already been done together with the right wing tank. When we had small Proseal jobs to do on the right wing tank, we also prepared for doing some small jobs on the left wing tank too, so not to unnecessarily throw away partially used Proseal cartriges.
Installing the stringer, tank ribs, flange plates and fittings was actually done May 18th 2019, but I am logging the time here.
One fuel tank mounting channel (WG-BKT-010-X-A- shown in the photo below) had caused me some head scratching on the right wing tank. Sure enough I had the same problem on the left wing tank.
Here is the reason:
If one bolts the mounting channel the plans way to the main spar as depicted above, it would let the channel sit on top of the neighbouring leading edge rib (WG-RIB-106-R-A-) causing misalignment issues, when it comes to riveting the tank to the main spar.
Rotating the channel 180° solves the problem.
This is a real mean problem, because at no time one has visibility at the offending area – not even with an inspection camera. Just a wild guess and trial and error let me find this out to be the reason for the misalignment when testfitting the right wing tank.
Another thing to check before closing the tank was, how the fuel tank back plate aligns with the main spar.
The flange of the back plate should transition nicely into the wing skin, because the tank skin sits on top of the wing skin. I had to rebend the flange a little at the top inbord end.
Like on the right wing I also adjusted the travel stops of the fuel sender arm before closing the tank, which would be difficult once the tank is closed. I also shortened the transducer wire and check continuity of the transducer reading.
One last testfit before finally closing the fuel tank …
Closing the tank went well. Because the testfit was really good, this time (unlike the right wing) we did not turn the wing vertically for closing the tank. We again used Saran wrap to protect the main spar from oozing out Proseal (which would make removing the tank for the leak test difficult).
After closing the tank (with the temperature being fairly low already) I wrapped the tank with two electric heating blankets and bubble wrap to let the Proseal cure for a week.
Closing the tank went well? – well not quite!
Here’s a little riddle: what’s wrong in the next picture! (sorry for the blurry photo)
The fuel breather tube is on the wrong side! It should be inside the tank! When I wanted to install the ventline to perform the leak test, the breather tube was still in the same bag. I had forgotten to install it before closing the tank.
I strongly suggest to install the breather tube together with the fitting. Should this dumb mistake happen to you too, contact me and I can talk you through the process how to install it without reopening the tank again.
This was tricky and cost me a couple hours of work, but I have managed to install it through the fuel cap flange after the tank had been closed.
To perform the leak test the fuel sender had to be installed. For detail notes please have a look at the Right Wing Tank blog entry. With my not so successful first Right Wing Fuel Tank Leak Test doing the leak test on the left made me a little nervous, but all went well.
Again I was amazed, how sensitive this primitive manometer is.
Notice how the rising air pressure corresponds with the falling water column.
(Note: I did not care to correct the readings for variation in room temperature)
Happy with the outcome of the leakt test, mounting the tank to the wing went smooth.
The double row of black clecos are the rivet holes, where Service Bulletin #0014 mandates to use stainless steel rivets now. These shall be installed with some corrosion preventing coating (e.g. Proseal).
Since I am using a sealant gun and Proseal cartriges I did not want to waste a whole cartrige for this little job. Not having an accurate scale with a 0,1 g resolution at hand, I improvised a method to mix small amounts of Proseal at a time.
I took the plunger out of the cartrige and made a scale of 10, both on the plunger and the cartrige.
Just squeeze out equal parts of the white and black stuff and you automatically have the correct ratio.
Making the fuel tank inner nose rib (WG-RIB-100-R-C- not yet installed in above photo) fit required some patience because the flanges were not bent quite correctly. This same nose rib still needs to be installed on the right wing.
Work was actually done Aug. 26th 2019 till Oct 16th 2019
With the right wing in storage work was started on the left wing. Since all the prep work (deburring, scotchbriting, priming …) and riveting the subassemblies had already been done together with the right wing, doing the left wing went much faster than the right.
Of course the experience gained on the right wing like how to best fit the skins to the structure helped a lot too.
I do not remember anything noteworthy doing the left wing structure and I have not taken any pictures. As with the right wing I deviated from the plans and also ran conduits for the cabeling and the pitot and AOA lines.
Most of the brackets, that hold the conduits in place I fabricated as doublers for the mainspar stiffener channels. Here are some photos, how I routed and attached the conduits.
As visible in above photo I am installing a Garmin GAP 26 regulated heated pitot / AOA. The current G3X installation manual (version AL) specifies a minimum length of 8 inches aluminum tube for the GAP 26 between the probe and any non-metallic tubing connected to it. This is to avoid exposing the tubing to excessive heat. I seem to remember, that an older version mentioned not to cut the tubes at all. I just left the tubes uncut and hand bent the tubes of the probe such that they run straight into the conduits.
The next photo shows the bottom conduit traversing to the front of the main spar for the landing and taxi lights and the top conduit for the nav/pos/strobe running to the wing tip.
Since the temperature controller must be installed within two feet of the pitot probe, it is not possible to put it upfront behind the instrument panel. I have therefore fabricated a bracket with 4mm rivnuts to hold the controller. This bracket also acts as a doubler for the small stiffener channel attached to the main spar. The temperature controller and the wiring are within easy reach through the nearby service panel.
The spade connectors are just loosly hooked up for the photo as is the pitot mast that is just clecoed to the pitot mount brackets temporarily; I have removed the pitot mast and pitot head to prevent damage when later putting the wing in storage.
The pitot mast will later be installed using 4 mm bolts and a spacer. Thus I will be able to remove the whole pitot mast and probe even with the bent aluminum tubes.
The two following (poor) photos from my mobile are the only ones I have of the left wing before mounting the fuel tank.
Work was actually done Aug. 18th 2019 till Aug 20th 2019
One thing Sling 4 builders have to take care of is to get the trailing edges of flaps and ailerons in line with the trailing edges of wingtip to wingroot (I am not sure, wether Sling 2 builders or Sling 4 TSI builder have to deal with that).
Using the prepunched rivet lines at the leading edge overlap of flaps and ailerons will result in ~13 mm flaps low misalignment.
I would like to give credit to Peter C., who I think was the first to document the problem in his 3-5-2016 blog entry. Thanks Peter!
TAF later added a recommendation in a plans revision to hold off riveting the ailerons and flaps until the wings are completely finished.
When I started building the flaps and ailerorns, I already had that information and now with the right wing finished, it was the time to take the flaps and ailerorns out of storage again.
Paul had removed the blue plastic, scotchbrited and primed the inside of the skins and the rivet lines of the flap and aileron. For an initial alignment check, we first riveted the flap and aileron except for the leading edge rivet line and the three to four forwardmost rivets on the top and bottom.
Since it is not possible, to use clecoes at the leading edge for a testfit, I ducktaped the leading edge skin ovelap of aileron and flap. In hindsight just taping a couple rivets in place with the stem remmoved should work better.
Next I clamped the aileron to the wing end rib, the flap to the wing step and pulled a string between these two point.
I do not have a photo showing the initial (mis)alignment situation. I was lucky here, because the aileron was exactly in line. So Paul finished riveting the aileron skin including the leading edge (not forgetting to riveted the aileron balancing tube in place first). This makes the aileron very rigid and it will not twist any longer.
Next we again clamped the aileron to the wing end rib as shown above and we also clamped the flap to the aileron, which nicely aligned the two.
Aligning the trailing edge will slightly twist the flap and shift the top and bottom skin against each other creating an offset of approx. 1mm between the two (exagerated for clarity in the photoshopped picture below)
I then marked this area and flipped the flap over. I weighed it down on the inbord end and shimmed it at the outbord end to exactly show the marked area thus setting the flap twist.
I then mostly filed away the offset area, flipped it back and clamped it again into alignment to check how much more offset needed to be filed away.
After repeating this procedure twice, the upper and lower skin were flush at the overlap in both positions (flipped and clamped), which indicated that the twist was set correctly with the shims.
Now, with the flap folded back in the shimmed position, setting one single rivet close to the outbord end of the flaps was easy. This locks the twist and a check (now without the center clamp) showed the flap and aileron nicely in line.
I strapped the skins together with a couple stripes of ducktape (to get the rivet holes horizontally aligned), reamed out a couple rivet holes to 4mm (because of the lateral offset the 3,2mm holes would have to be elongated to appr. 4mm) and set those rivets.
Checking the alignment again and slightly adjusting the shimming then let me rivet the rest of the flap. There are still some small open items like rivnuts for the inspection panels, pulling the wires for and installing the landing and taxi lights.
With the flaps and ailerons aligned and not knowing when I would receive the rivets for the SB I called the wing finished for the time being and with the help of some of Pauls friends we put the wing into storage
The wing is now stored behind the fake wall on the left side made from the plywood crates in which the kit was delievered.
I will address the SB #0014 and the couple open items before test fitting the wings onto the fuselage.