Ready to Match Drill The Longerons

Having finished up the riveting of both F-1248-L&R armrests into position, the aft end of each armrest receives a little plate … the F-1248B fuselage pin latch. The large hole at the end of the plate will receive the spring loaded locking pin which is on the handle of the spar pins. The hole on the inboard end of F-1248B fuselage pin latch locks the wing' spar pins in place, preventing them from backing out from the spars on their own. Later a reed switch will also be incorporated to verify the spar pins are locked in position … if they are not, the engine will not start.

Riveting one of the F-1248B fuselage pin latch plates onto the aft end of the F-1248-R armrest.

It’s longeron time!  The longerons were retrieved from storage and the F-1234-L&R  canopy decks were once again mated with the longerons using Clecos. The longerons were then placed in position on their respective sides of the fuselage and secured with Clecos.

Securing the left longeron and canopy deck assembly into position with Clecos.

Placing the right longeron and canopy deck assembly in position.

After placing both longerons into position, the forward ends of the longerons were compared to one another. When the longerons were initially formed last Fall using the larger vice available at Bernie’s house, by the time we got done forming both longerons, it was getting late. There was a small correction that needed to be made forward of the canopy deck on the right longeron because some of the required twist came out during the process of opening the angle … (I over did it a little). At the time, figured that could be solved later back at the shop … so before placing the fuselage side skins on for match drilling, decided to tweak the twist on the forward end of the longeron. The upper firewall was temporarily held in place so a good visualization could be obtained on the amount of twist required and the end of the longeron was twisted accordingly. It just needed a couple of degrees.

After tweaking the right longeron, the right fuselage skin was Clecoed in position. And the right longeron follows the edge of the right skin nicely. It tends to dip down a little at the forward end but very little finger pressure is required to flex the longeron into the proper position so think we are ready for match drilling the right side.  However, before doing so, want to install the left skin before any longeron drilling takes place.

F-1248 Armrests Match Drilled And Riveted

The longerons have not been installed yet for match drilling as expected … a broken furnace (not a good thing this time of the year) and errands have contributed to a limited amount of shop time ... but some progress was made. The forward and aft tabs on the F-1248-L&R armrests were match drilled and after deburring, the armrests were riveted in place.

Match drilling the aft tab on the F-1248-L armrest.

Riveting the F-1248-R armrest onto the F-1204C-R forward bulkhead side. Clearance was tight so used the offset tool to gain access for the close quarter hand rivet puller.

Before placing the longerons in position for match drilling, the flanges on the F-1201B firewall shelf that will be riveted to the side skins were dimpled for the 120 degree flush rivets that are being used in place of the LP4-3 rivets.

Using the pneumatic squeezer to place 120 degree dimples on the F-1201B firewall shelf’s flanges for the flush rivets being used on the RV-12 project.

Fuselage – Time To Grow Vertically

Riveting of the F-1205C mid fuselage brace closeout onto the F-1205A was completed today as well as the riveting of the F-1205B-L&R roll bar attach plates. With the mid fuselage brace now riveted in place, the center section has just gained a lot of rigidity.

Using the pneumatic rivet puller to rivet the F-1205C closeout onto the F-1205A mid fuselage brace.

Riveting the F-1205B-L roll bar attach plate – rivet holes on the forward edge of the roll bar attach plates receive CS4-4 flush rivets because the roll bar mounts on top of them.

Time to go vertical - the next order of business was to rivet the F-1203H-L&R armrest brackets onto the F-1203G-L&R bulkhead channels then mounting the channels onto the F-1203A bulkhead. This was followed by riveting the F-1202E-L&R bulkhead channels onto the F-1202F bulkhead. Riveting the F-1202E channels in place proved to be a little challenging because there is little room for the rivet puller and the trick of bending the rivet's mandrel and using an AEX wedge was employed … not difficult just a little time consuming.

Clecoing the F-1203G-R bulkhead channel onto the F-1203A bulkhead for riveting.

Using the close quarter hand rivet puller to rivet the F-1202E-L bulkhead channel onto the F-1202F bulkhead … access is tight for some of the rivets and requires use of the AEX wedge.

Four new vertical channels to attach more goodies onto.

The F-1248-L&R armrests were next … they require being Clecoed in place onto the newly installed channels and then two tabs, one at each end, require being matched drilled. At this point I spotted a potential alignment problem … the aft edge of the right armrest did not touch the F-1204C forward bulkhead. There was slightly less than a 1/16” gap. The left side was OK.  At this point I decided to test fit the side skin … with the all the vertical holes aligned, the gap closed ... so I can move on with no worries. Did take advantage of the moment for a photo op.

Clecoing the F-1248-R armrest in position. Zooming in on the photo, the small gap mentioned above can easily be seen at the aft flange of the armrest.

Right side skin temporally in position to hold alignment for the match drilling of the tabs on the right armrest. Hard to see in this photo but the gap at the armrest’s aft flange is now closed.

Decided to call it quits for the day and will do the match drilling tomorrow and hopefully get the longerons in position for drilling as well.

Section 23 Assembly Begins

Section 23 begins with the forming of the longerons … this task was accomplished last fall so priming and painting could be performed while the temperatures were favorable. At that time, I did not countersink the F-1205B roll bar mounting plates because I was undecided about using solid rivets or pop rivets and wanted to see how the parts fit together before making that decision. Ultimately decided to follow the plans and assemble with pop rivets ... so that required countersinking six of the holes on each mounting plate to 120 degrees for flush pop rivets. Masking tape was placed over the painted area to prevent marring from the countersink cage.

Machine countersinking the six holes in the F-1205B-L&R roll bar mounting plates that require flush pop rivets using a 120 degree countersink bit.

The F-1205B-L&R roll bar mounting plates also receive two nut plates each, so those rivet holes also required countersinking with a #40 100 degree countersink bit because the roll bar bases will be sitting on top of them. Prior to riveting the nutplates, make sure the AN4 bolts can go through the hole … after primer and paint I needed to run a 1/4" reamer through the holes to clean them so an AN4 bolt could be screwed into the nutplate to keep the hole centered while the nutplate is riveted.

Using a pneumatic rivet squeezer to install nutplates onto the F-1205B roll bar mounting plate.

The F-1205A mid fuselage brace is the next item that gets installed onto the fuselage assembly. The F-1205A mid fuselage brace is riveted onto the aft side of the F-1204B-L&R bulkhead sides.

Riveting the F-1205A mid fuselage brace onto the F-1204B-L bulkhead side.

After the mid fuselage brace is riveted in position, the F-1205B-L&R mounting plates and F-1205C mid fuselage brace closeout were secured in position with Clecos and now ready to rivet during the next work session in the shop.

Securing the F-1205B-L roll bar mounting plate onto the F-1205A mid fuselage brace with Clecos.

Placing the F-1205C mid fuselage brace closeout in position onto the F-1205A mid fuselage brace to secure with Clecos.

 

Return from the future ... RV-12 builders take note: The avionics kit contains the F-1205G ELT antenna mounting plate which needs to be attached onto the right side of the mid fuselage brace. The instructions in section 23-3 step 4 made no mention of leaving these three rivet holes in the mid fuselage brace open for the later instillation of the F-1205G ELT antenna mounting plate. As such, in my case, the LP-4-3 rivets need to be drilled out. Builders do yourself a favor ... when following the steps in section 23 for riveting the mid fuselage brace DO NOT place rivets into the three rivet holes on the mid fuselage brace shown in the photo below adjacent to the holes in the F-1205G ELT mounting plate being held in my hand.

DO NOT rivet the three rivet holes in the mid fuselage brace adjacent to the holes in the F-1205G ELT antenna mounting plate in my hand. To avoid drilling out rivets later these rivet holes need to be left open when completing section 23. These three rivet holes will become the mounting holes for the ELT antenna mounting plate shipped with the avionics kit.

Fuel Lines Installed & AN FittingsTorqued

Today was spent cleaning out the previously fabricated fuel lines, installing them and torquing the AN fuel fittings. Prior to final assembly, I wanted to make sure the inside of all the fuel lines were as clean as possible and free of dust, dirt and small flakes of aluminum possibly left over from cutting, filing and deburring. To clean the lines, a wire was slid inside the tubing and used to pull back a pipe cleaner that had been soaked in solvent. This was followed by blowing the lines out with compressed air.

Using a pipe cleaner soaked in solvent to swab the inside of the fuel line before assembly.

A very thin coating of fuel lube was placed on the taper of all the AN fittings and the fuel lines were then set in place, tightened, then torqued to specs with a torque wrench outfitted with a crowfoot wrench. The 3/8" fuel fittings received 120 inch pounds of torque and the 1/4" fuel fittings received 58 inch pounds. Because a crowfoot extension was used on the end of the torque wrench, the actual torque settings were adjusted to compensate for the extra length the crowfoot adds to the overall length of the torque wrench as mentioned in a previous post.

Using a torque wrench attached to a crowfoot wrench to tighten the AN fuel fittings at the fuel valve to proper torque specifications.

Completed fuel line routing through the fuselage minus the aft two fuel lines that attach onto the fuel tank.

The two fuel lines that connect onto the fuel tank were not attached at this point in time. Because the fuel tank is not built yet, the exact position of the fuel line modification being installed to create a fuel drain directly under the fuel tank is not known. The lines are constructed and ready to go but decided it best not to install them now because they would have to be uninstalled later to make the final flare where the fuel line will attach onto the T.  With section 28 now completed, it is time to resume assembling the RV-12’s fuselage.

Calculating Torque Values For AN Fuel Fittings

Staying inside during the latest artic blast (which incidentally left a broken water line at DOG Aviation in its wake) and avoiding the nasty temperatures outside, a little time was spent calculating the torque settings that will be used on the AN fittings for the fuel lines. The standard torque range for the AN flared fittings used for 1/4" aluminum tubing is 50 to 65 inch pounds and the torque range for the 3/8" tubing is 110 to 130 inch pounds.

As a side note, if a builder does not have a quality torque wrench (can’t imagine that) a fish scale can be used to measure the torque. For example - if a wrench is one foot long, pulling the end of the wrench with a fish scale until the scale reads one pound applies a force of one foot pound to the item being tightened … which equates to 12 inch pounds.

Huston we have a problem … unfortunately, sockets can not be slipped over the fuel fittings to torque them. Solution, use a crowfoot attachment on the end of the torque wrench and calculate the proper torque setting for the torque wrench.

An 11/16" crowfoot wrench for 3/8" AN flared fittings attached onto the end of the torque wrench … this essentially makes the torque wrench longer.

Calculate proper torque? What’s the deal? Well, the crowfoot wrench essentially extends the length of the torque wrench … so unless compensated for, the resulting torque will be higher than the desired torque because the extended length creates more leverage which throws off the tool's calibration. The corection formula is simple ... once the extra length is determined.

The crowfoot wrench attachments were placed onto the torque wrench and the offset measurements were made from the center of the torque wrench drive to the center of the AN fittings. In my case, the 3/8" fittings require an 11/16" crowfoot wrench and the offset was measured at 1.05". The 1/4" fittings utilize a 9/16" crowfoot and the offset measured .9".

The 3/8" fittings require an 11/16" crowfoot and the offset here from center of the fitting to center of the torque wrench drive measures 1.05".

Armed with the offset measurements, the formula for calculating the torque setting when using an extender is: Torque wrench setting = DT x L / E + L
Where:
DT= desired torque applied to object requiring torquing
L = length measured from center of torque wrench drive to palm of hand (mine is 8")
E = extension offset length of crowfoot from center of drive to center of AN fitting
TWS= torque wrench setting - depending on the type of torque wrench you own either the value you set on an adjustable wrench’s scale or the value you are looking for on the needle reading.

Want my torque values to be in the center of the specified range … so my desired torque value for 1/4" AN fittings is 58 inch pounds and for 3/8" fittings it is 120 inch pounds. Using the above formula with the offsets obtained for the crows foot wrenches, the torque wrench will need to be set to 52 inch pounds for the 1/4" fittings and 106 inch pounds for the 3/8" fittings.

What if the crowfoot has to be at an angle … say, 45 degrees? No problem. I won’t go into the vector math (available on the Internet at lots of sources) just use the above formula with an additional step … multiply the extension length offset by .71 then add that result to the length of the torque wrench.
The formula is: TWS= DT x L / (E  x .71) + L

In my case, using the crowfoot at 45 degrees results in needing to set the torque wrench to 54 inch pounds for 1/4" AN fittings and 110 inch pounds for the 3/8" AN fittings.

Believe it or not, using the crows foot at 90 degrees is the same as not having an extension on the torque wrench so set the wrench to the desired value and twist away. To be factual, there is a very small offset value but that is likely to be within the margin of error for the torque wrench anyway.

No torque correction necessary if the crowfoot wrench is 90 degrees to the torque wrench.

I was planning to put all this to practice in the shop today but while walking over to the shop this afternoon, discovered water dripping from the back door threshold. An investigation reveled a broken water line at DOG Aviation’s host property caused by the record breaking cold temperatures. Needless to say, motivation for working in the shop was quickly doused, so to speak, by a need begin moping. Fortunately, the running water was caught fairly early (I think) and because of where the pipe is located, there appears to be no lasting damage … except for the water pipe. Bummer!

Artic Freeze Grips DOG Aviation As Section 28 Completed

Braving plummeting temperatures as a subzero Artic freeze grips the DOG Aviation production facility, a small amount of time was spent in the shop this afternoon until cold hands got the best of me. Work continued putting the finishing touches on the forward return fuel line. The fuel line was pulled out of the inspection port and enough excess line was cut so the fuel line could be placed alongside the center channel AN fuel fitting for final marking without interfering with the center channel.

Trimming excess fuel line so the line can be placed alongside the center channel’s AN fuel fitting and marked for a final cutting.

The fitting at the firewall was temporally connected and the return fuel line placed in its final position in the cushion clamp on the firewall so a precision measurement could be made at the center channel’s AN fuel fitting.

The forward return fuel line in position at the center channel’s AN fuel fitting and ready to be marked for final cutting.

After marking the location of the final cut, the fuel line was pulled back out of the inspection port and cut to the final length, the nut and sleeve slid in place, and the end was flared with the flaring tool.

Completed forward return fuel line connected to the center channel fitting and ready for final torquing.

Completed forward return fuel line connected to the firewall shelf’s AN bulkhead fitting ... ready for final torquing.

The finished fabrication of the forward return fuel line marks the end of construction in section 28 of the RV-12’s plans. During the next work session, the plan is to blow out all the fuel lines, assemble the fuel lines and final torque the fittings. The AN-818 nuts on the aluminum tubing should have torques in the range of 50-65 inch pounds for the 1/4" fittings and 110-130 inch pounds for the 3/8" fittings.