Tuesday, December 31, 2013

Return Fuel Line Fabrication Continues

Working with one 6’ piece of tubing that requires multiple bends is scary … that is a lot of tubing wasted should there be an error in judgment or bending procedures. Add to that, Van’s instructions do not have a detailed 1:1 drawing for this portion of the fuel line construction. So with that in mind, I purposely cut the length of the fuel line oversized and made the first 90 degree bend at the firewall so there should be a little extra material to trim when finalizing the finished length prior to flaring.

At the firewall the fuel line takes a 90 degree bend upward (already done) and gets captured by a cushion clamp which will keep the fuel line off the firewall by 1/8". In the vicinity of the lower portion of the motor mount bracket, the fuel line requires an aft offset which I made by placing two 45 degree center line bends in the tubing. This takes the tubing aft of the firewall and vertical again to align it with the center of bulkhead fuel fitting hole on the firewall shelf. (The first 90 degree bend was made at a point 1/2" longer than called for to insure the forward fuel line tubing will be slightly longer than necessary).

When you are free styling you want to take your time and do a little math. The drawings showed the approximate location of the bends so measurements were taken and marked on the tubing. Taking into consideration the 1/8" gap from the firewall and the 1/4" thickness of the tubing and location to the center of the hole for the fuel fitting … the desired centerline offset is approximately 15/16".
Imperial bender - the marks on the upper handle are used for various types of bends, the 45 marks are for making 45 degree centerline bends after a little math is performed.
The Imperial tubing bender comes with the capability of making centerline bends if the user is willing to do a little math. Basically, you mark the location on the tubing where the first bend will begin. Then multiply the desired centerline offset by 1.414 and add that length onto the tubing measuring from the previously made mark and mark the tubing again.  In my case, the desired centerline offset was 15/16" x 1.414 which yielded 1.3256" (roughly 1 21/64") to be added onto the first mark on the tubing. The tubing bender has offset locating markings on it so the first mark on the tubing is not located at the 0 mark as usual, but instead placed under the 45 offset mark on the bender for the size tubing being bent … then the tubing is bent as usual. After marking the tubing, but prior to making any bends, I noted that from the firewall the tubing path down the tunnel was to the pilot side of where the tubing rises up the firewall. Since there is a 90 degree bend at the bottom of the tubing already, decide to cant that bend 45 degrees aft towards the pilot side. The reasoning for this is it will only require one approximate 45 degree bent to make the tubing head aft down the tunnel in line with the bulkhead grommet. So prior to making the offset bends I positioned the tubing with the bottom 90 bend canted 45 degrees towards the pilot side and made a line on the tubing denoting the edge that should be along the firewall.
Just finished bending the final 45 degree bend to head the tubing aft to the bulkdead grommet. The offset bends on the firewall portion of the fuel return line turned out perfectly and truly look great, but admittedly it took a long time because I had never made centerline bends before … so I took my time and checked and rechecked and checked again before bending.

Next the tubing is curved a bit so it can be fed through the bulkhead grommets and slowly worked aft. A piece of tape was wrapped around the flaperon mixer arm to prevent it from scratching or being scratched by the tubing as it is slid aft through the grommets and along the groves on the standoff blocks.
Beginning the feeding of the return fuel line tubing through the bulkhead grommets … the recently made 45 degree bend can be seen nicely here.
Slowly working the return fuel line aft and underneath the flaperon mixer arm.
End of the line … without rolling the fuselage assembly onto its side and allowing the excess tubing to be pulled out the inspection port the tubing can’t be feed in any further.

Could not finish off the final cut and flaring of the tubing at the firewall because it could not be pushed aft far enough … will need assistance to roll the fuselage assembly so the excess fuel line can be worked out the inspection port.

Monday, December 30, 2013

Aft Fuel Return Line Completed

During the last short but fruitful work session the positioning and length of the aft fuel return line was finalized. Final positioning of the fuel lines under the opening in the right baggage floor was determined by making the upper portion of the fuel line modification from the T up. The short 1 3/4" pipe that fits between the fuel tank and T was fabricated and attached onto the T to aid in determining positioning and clearance measurements. (Incidentally, the shortest 3/8" pipe that can be made with the Parker Rolo 37 degree flaring tool is 1 3/4" long).

Using the dimensions in the drawing (posted in the previous post) it shows the fitting for the fuel supply line needs to be 13/16" under the baggage floor … got the idea of using a block of wood that size to use as a spacer to position the T at the right level. As luck would have it, the first piece of scrap wood I grabbed was the perfect thickness.
Masking tape used to hold the T to tank assembly onto the 13/16" wooden spacer block.

The above mentioned drawing shows the center of the main supply line in line with the first rivet hole in the side of baggage floor and the return line is to be positioned 1 5/8" aft of that. Using the strings stretched out between the rivet holes (see previous post) the return fuel line was positioned 1 5/8” aft of the first string.
Return fuel line positioned adjusted to match the measurements in the drawing from the forward string.
With both the T assembly and return fuel line in position, the threads on the T can be seen. To the left of that is the main fuel line that will be flared and connected to the T. Overall, the alignment looks good.

The overall alignment was very good and placing the return fuel line on top of the supply line did not create any unforeseen issues with alignment or interference. At this point the two fuel lines were clamped together with hose clamps using 3/4" pieces of rubber tubing as cushions between the fuel lines to prevent chafing.  The assembly was set back in place to test the alignment once again and the final cut and flare was made for attaching the return fuel line to the AN837-4D fitting at the F-1204D center section bulkhead.
Main supply and return fuel lines clamped together with fabricated cushion clamps.

See no point to install this assembly at this time because it will need to come out again to make the final cut and flare for attachment to the T being placed under the fuel tank for the modification. Could probably do that now, but will hold off until the tank is built or at least with the fittings installed on the bottom plate. Feel it best to wait and obtain the exact positioning prior to making the final cut on the supply fuel line.

Having completed the aft return fuel line, work began on the forward return line. This line will be challenging because it is one piece and just shy of 6 feet long. The forward return line requires a handful of bends at the firewall and then it is a straight shot back to the center section where it will be a challenge to be sure.

The forward return line was purposely cut a little long and the first 90 degree bend at the firewall was set in place before deciding to call it quits for the day.

Sunday, December 29, 2013

RV-12 Fuel Line Fabrication Continues

After mounting the gascolator and FT-60 fuel flow meter, work continued on fabricating the supply fuel lines to the firewall without running into any major issues. The plans instruct the builder to first fabricate the fuel line between the gascolator and the FT-60 fuel flow meter followed by the construction of the fuel line between the fuel flow meter and the fuel valve. The final length of the fuel line between the gascolator and fuel flow meter ended up being slightly longer than the drawings show - other builders have commented on that as well.
Completed fuel line between the gascolator and FT-60 fuel flow meter.

Construction of the fuel line between the on/off fuel valve and FT-60 fuel flow meter begins at the fuel valve where two bends are made so the fuel line can swoop down to the grommet in the F-1202F bulkhead. Two additional bends may be necessary depending on the model of the fuel flow meter shipped with the kit. In my case, the FT-60 fuel flow meter required the two additional bends.
Marking the point where the bends required for the FT-60 fuel flow meter need to begin.
The additional two bends required for the FT-60 fuel flow meter completed … the line is now ready to feed through the F-1202F bulkhead grommet for final cutting and flaring.

Access for cutting the tubing with the small Rigid tubing cutter was fine. However, creating the flare at the fuel flow meter’s aft fitting was a little tight. Using the bulbous Parker flaring tool between the tunnel ribs was … challenging, but doable. The needed room was garnered by pulling the fuel line forward so the bend was at the bulkhead grommet, then lifting up on the line.
Completed fuel line from fuel valve to FT-60 fuel flow meter test fitting … looks good.

With the exception of the fuel tank drain modification previously mentioned in another post, the supply fuel lines to the firewall are now completed. The fuel tank will need to be installed so exact measurements can be obtained for cutting and flaring the fuel line that will now go onto the T as opposed to making a 90 degree turn up to the bottom of the fuel tank. Doing this modification has created a small issue in obtaining proper measurements for the placement of the return fuel line … solved later in the post, with accompanying small rant.

The RV-12 employs a circulating fuel system where the return fuel line to the fuel tank is a smaller diameter than the supply line … 1/4" line as opposed to 3/8" line. The plans instruct the builder to begin crafting the aft portion of return fuel line between the fuel tank and the AN837-4D fitting installed in the F-1204D bulkhead ... beginning at the fuel tank fitting. The return line is supposed to run aft and parallel to the previously built fuel supply line. However, because of the planned modification, the main fuel line will not be in the same position … so decided it would be easier to run the return line on top on top of  the supply line eliminating a potential clearance issue where the lines will cross. Having a plan of attack in mind, the aft return fuel line was formed per the drawings but dimensioned so it will reside on top of the already built supply fuel line.
Placing the last bend in the return fuel line … a small hand adjustment will be required to align the line to the AN837-4D bulkhead fitting.
Completed aft fuel return line which will be running on top of the supply line - opposed to behind it.

Now for the rant. All and all the drawings from Van’s are great, but occasionally it is nice to have more detail than that given. Case in point, below is a photo of the plans that show measurements from the bottom of the baggage floor to the top of the fuel line AN fittings and a measurement from the supply fuel line to the return line taken as a side view. Which is fine for the spacing between the fuel lines but it does not help much with the overall fore and aft positioning of the fuel lines within the large oval hole in the right baggage floor. Bear in mind, you can’t actually see the lines and ribs shown in the drawing because the baggage floor is in the way … and the rivet holes shown in the background are about 15 inches or so away. Because of the fuel drain modification being made, there is no supply fuel line at this time to measure from. One would think for alignment purposes there would be a top view detail showing the exact positioning of the two lines within the large hole in the baggage floor along with a couple of accompanying measurements. Even if no fuel line modifications were made, based on the supplied drawing, without a fuel tank in position the exact positioning of the lines is mostly guess work. Decided to run strings from the rivet holes shown in the drawing below … which, when used as a reference point, should help determining the approximate location for the return fuel line fitting within the oval cutout on the right baggage floor.
Side view drawing of the fuel lines below the fuel tank with no references made to the bulkhead or positioning within the large oval hole in the right baggage floor.
String run between the rivet holes to be used as a positioning reference for the return fuel line based on previous drawing photo.
Top view of the hole with strings being used as position locaters … return line is NOT properly positioned yet. It would have been far easier if there was a drawing from this perspective with a measurement or two.

After running the string, decided to call it quits for the day so will make the necessary adjustments, clamp the two fuel lines together with the spacers provided and make the final cut and flare for the AN fitting at the F-1204D bulkhead during the next work session.

Thursday, December 26, 2013

FloScan Fuel Meter and Gascolator Mounted

Another short work session today but good progress was made. AN fittings were installed into the FT-60 FloScan fuel meter and the meter was installed on its mounting bracket. The plans instruct the builder to tighten the aft mounting bolt but leave the forward bolt loose … so apparently something will be attaching to this point later in the build.
Tightening the AN fitting into the body of the FT-60 FloScan.
Mounting the FT-60 FloScan fuel meter onto the mounting bracket in the tunnel.
The GAS-5 gascolator was mounted onto the firewall. The AN fitting for the fuel line from the FloScan gets screwed into the back of the gascolator from the cockpit side of the firewall. After reading some comments on the RV-12 forums, elected not to install the safety wire at this time because after flushing the fuel lines and doing some fuel flow measurements the bowl on the gascolator is to be removed and inspected for debris, etc. prior to the first flight so there is no point in installing the safety wire at this point in time.
The GAS-5 gascolator mounted onto the firewall.
Work began on fabricating the fuel line between the gascolator and FloScan fuel meter. The first flare was made along with the two bends but ran out of time to make the last flare ... so that will be the first order of business during the next work session.

Seasons Greetings From DOG Aviation

Taking a short break from all the Holiday festivities, a short work session was squeezed into the day’s activities. Work was completed on the fuel line between the fuel pump and the fuel on/off valve.  Interestingly, all the effort to make sure the fuel line was nice and straight was all for not … because during installation, between measuring, cutting the excess line, deburring and flaring, it required bending the fuel line several times.

The fuel line was laid in place in the F-1276C system block guides and fished through the F-1203A bulkhead so the tubing could be marked at the fuel valve where the cut and flare needed to be made.  Once the cut mark was placed on the tubing, the line was then backed out of the F-1203A bulkhead and bent upward so the tubing could be cut, deburred, AN hardware slid on and the tubing flared.
Cutting off the excess fuel line with a small tubing cutter.
Using the Parker flaring tool to flare the forward end of the fuel line that attaches to the fuel on/off valve.

The completed fuel line was fished back through the F-1203A bulkhead so the finished length could be verified to be useable. The AN fittings were not tightened at either end of the line at this point in time because the DOG Aviation procurement department dropped the ball and forgot to order fuel lube. Fuel lube is suggested in section 5 of the plans to be placed onto the fuel line AN fittings prior to tightening the nut that compresses the flare to the AN fitting. Also would like to torque the fittings but that will require obtaining a crows foot wrench set which Santa forgot to deliver. Rule of thumb is to tighten the nut until the fitting cinches up and turn the nut an additional quarter turn. However, AN fittings do have a torque specification so would like to know the fitting is tightened enough to be in the middle of that range.
Fuel line attached to the fuel pump to test the fit going forward to the fuel valve.
Completed flare on fuel line at on/off fuel valve … overall length looks good.

Decided to move on and begin working on the next portion of the fuel system which involves the gascolator. The gascolator  comes out of the box with a multitude of holes that receive plugs and AN fittings. Had just enough time to finish up installing all the parts onto the gascolator, but did not have the time to safety wire the screws holding the bowl onto the main body. That will be the first order of business during the next work session.
Gascolator plus necessary fittings and plugs that will screw into it.
Completed gascolator ready for mounting after safety wire is installed on the screws holding the bowl onto the main body.

Tuesday, December 24, 2013

RV-12 Fuel Line Mod – Planned Changes

As mentioned in the previous post I stopped bending the RV-12 fuel tank to fuel pump line before bending the 90 degree upward bend that would place the fuel line directly under the fuel tank. This shift from the plans is to accommodate a modification which adds a fuel drain under the fuel tank.

One of the reasons the DOG Aviation RV-12 is being build as E-AB (experimental amateur built) as opposed to E-LSA (experimental light sport aircraft) is so modifications that make good sense can be made during the building process, while it is easier to do so, as opposed to after construction of the aircraft is completed. Jerry, a savvy builder from England, decided to make and install a fuel drain sump right below his RV-12's fuel tank. Much the same as others who have seen this slick modification, I too like the idea because fuel quality can be checked right at the tank as opposed to at the gascolator on the firewall. And as a side bonus, the modification will make it a piece of cake to drain the fuel tank without running the electric fuel pump. Below - a few photos of the modification as posted by Jerry on the RV-12 forum on VAF (Van’s Air Force).
Fuel tank modification parts description and layout.
Fuel tank modification - close up of required parts.
Fuel tank modification – fuel drain protruding below hole cut in inspection plate below fuel tank.

The DOG Aviation procurement department has already obtained all the necessary hardware for the modification. However, work on this portion of the fuel line plumbing will need to wait until the fuel tank (part of the finishing kit) is assembled and set in place. In the mean while work will continue on the fuel line plumbing from the fuel pump forward.

Moving on, the next fuel line to be constructed is the fuel line running from the fuel pump forward to the fuel on/off valve. After the tubing was cut and prepped the end was flared. Following the plans, two bends are made to form an offset between the fuel pump and the F-1204D bulkhead. Next the long fuel line is fished through the two grommets in the F-1204D and F-1204A center channel bulkheads. Frequent readers of the Blog may remember me following the advice from fellow builders to file down the tabs inside those grommets. This tip paid off is spades … even having filed down the tabs, the F-1204D bulkhead grommet still offered quite a bit of resistance to the fuel line but it still slid into the grommet after a little coaxing.

Here is where I hit the second speed bump. I could not feed the fuel line through the F-1204A bulkhead. I was by myself and there is no access inside the center channel except for reaching in from the sides ... but if doing that, I couldn’t push on the fuel line and keep it aligned with the grommet at the same time. Pondering the situation a while, decided to try to use the trusty 1/4" pin punch once again. The fuel line was pulled back a little and the pin punch was inserted into the grommet and worked into the fuel line in the hopes that the pin punch would help align the fuel line to the grommet.  Worked great!
A 1/4" pin punch pushed through the grommet and slid into the fuel line.

Once the 1/4" pin punch was inside the fuel line, the fuel line was pushed forward and the pin punch helped align the fuel line to the center of the grommet without enlisting outside help.
Fuel line pushed forward through the grommet on the F-1204A bulkhead with the aid of the 1/4" center punch used to guide the fuel line to the center of the grommet.

Unfortunately, don’t have the time at the moment to continue due to Holiday preparations.

Section 28 Fuel Line Plumbing Begins

Following the tip from other RV-12 builders, work continues in the plans with the jump to section 28. In section 28 the builder is constructing the fuel system by creating aluminum pipes with flared ends from rolls of soft aluminum tubing. The flared ends will connect to aviation AN fittings. With all the Holliday hustle and bustle, not much big progress has been made overall, but there have been a few productive small work sessions in the last few days.

As with most things in aviation, specialized tools are often required … and the fuel system is no exception. In particular, the flaring tool required is not the standard 45 degrees as used in automotive or plumbing. Don’t even consider running out to the local auto parts supplier or big box hardware store to purchase a flaring tool for aircraft fittings. Aircraft AN fittings used in the fuel and brake systems are 37 degrees and share the same angle as commonly found on fittings for hydraulic lines and NOT the typical 45 degrees used in automotive or plumbing.

The DOG Aviation procurement department purchased a Parker Rolo 37 degree flaring tool because it appears to be well received within the homebuilt aircraft community. The Parker flaring tool is easy to use and has two rotating dies (one upper, one lower) to accommodate a wide variety of tubing sizes. Just spin the dies around so the size of the upper and lower jaws match the tubing size to be flared and you are ready to get your flare on.
The Parker Rolo 37 degree flaring tool.
Both jaws of the flaring tool set for 3/8” tubing - the depth stop can be seen in front of the lower jaw.

The first RV-12 fuel line to be constructed is the fuel line from the tank to the fuel pump. After the 3/8” aluminum tube was uncoiled on the workbench and cut with a tubing cutter, a 2x6 was used to apply pressure to the tube against the workbench while rolling it back and forth under the 2x6 … this helps straighten the tubing. Once reasonably straight, the aluminum tube was filed smooth and placed into the Parker flaring tool until it hit the stop … which moves away as part of the clamping process.
Aluminum tubing placed into the Parker flaring tool until it rests on the stop.

The center cone of the flaring tool should be lubricated … I found a light coating of white lithium grease seemingly works better than oil. When flaring tubing using a flaring tool, don’t over tighten the center cone. This is one place where less is more … as soon as you feel solid resistance while forming the flare, STOP! Over tightening can create scoring, so it should be avoided.
Using the Parker Rolo 37 degree flaring tool to create a flare on a section of fuel line.
Formed 37 degree flare on the end of the aluminum tubing.

After flaring an end of the tube, the plans instruct the builder to bend the tubing to match a 1:1 drawing on the prints. At this point, an AN819-6D sleeve needs to be slid onto the tubing because after the tubing is bent, the sleeve CAN NOT be slid onto the tubing around the bend… however, the nut will easily slide around a bend.
The Imperial 470-FH triple head tubing bender.

This is where I ran into the first speed bump. The bend to be created per the plans was so close to the flared end that the tubing did not reach the hook on the Imperial tubing bender (needed to secure the tubing during the bending process).
 Red marking on the tubing is where the first bend is to start.
After placing the red mark at the 0 location (hidden), note the tubing was behind the hook on the bending tool … not good. The hook needs to hold the tubing during the bending process.

Getting creative ... after pondering various solutions, the one that seemed easiest and most appealing to me was to insert a 1/4” pin punch into the tubing and use the punch shaft as an extension to catch the jaw on the tubing bender. The sharp end of the pin punch was covered with a few turns of masking tape so it would not score the inside of the tubing and to also create a tighter fit centering the tubing on the punch shaft. The pin punch’s shaft was marked so it would not be inserted so deep into the tubing as to interfere with the bending of the tubing.
A 1/4" pin punch with blue tape and red depth mark inserted into the tubing so the pin punch would catch the tubing bender’s hook and secure the tubing in place while bending the tubing.

As luck would have it, I dropped the flared tubing onto a tool which placed a small dent on the flare so decided it best to start over and just make a new one.
Checking the completed first 90 degree bend of the replacement tubing against the 1:1 drawing in the plans … so far so good.

The remaining bends were uneventful and the bending was stopped just prior to making the last 90 degree bend which goes up to the fuel tank. The reason for this is because of a modification being incorporated into the RV-12 build … more on that in the next post.
First three bends completed and the fuel tank to fuel pump line is conforming nicely to the 1:1 drawing in the plans.