Saturday, March 28, 2015

Work On Service Bulletin 14-12-06 Begins

So goes it for forward progress on the DOG Aviation RV-12 … time to take a few steps backwards and perform a service bulletin retrofit. A few months ago Van’s released service bulletin 14-12-06 which addressed the possibility of cracks developing on the F-1206F bearing bracket brace. To my knowledge only a few RV-12’s have developed the cracks which can be seen in the photo below of the service bulletin’s cover sheet. To Van’s credit, a solution to the issue was quickly developed consisting of a new F-1206F-1 bearing bracket brace which will now attach onto a much stronger piece of aluminum angle F-1206J which will absorb the forces causing the cracking of the bracket.
Photo of the cover sheet for service bulletin 14-12-06 shows the area where cracks are appearing. The parts for the bearing bracket brace retrofit are also shown ... the angle is cut in half to obtain the left and right mounts.

This service bulletin is not mandatory, but regular checks of the affected area are required … and if cracks appear, the old parts are to be replaced with the upgraded bracket brace assembly. My original thought was to just fly the RV-12 and should a crack appear replace the parts at that time. But then I realized I had complicated maters a whole lot because of my choice to rivet the forward edge of the F-1206F bearing bracket brace onto the F-1206A bulkhead with solid rivets. This area is not easily accessible even with the aid of an angle drill ... not to mention hidden from view by the bracket. A moment of clarity … should a crack develop, it would be a bear to remove those solid rivets after the RV-12 is completed because the bearing brace hides the rivets so I would be drilling blind .. not good. Note to self: It would be wise to just take the time to replace the parts now. Drilling out the solid rivets now will be tough enough because the access sucks, but if completed now, at least the work can be done while standing, instead of crawling inside the fuselage if done at a later time. Drilling out the solid rivets will truly be a daunting task if done after the aircraft is completed.
The existing bearing brace is installed with three pop rivets on each side and the forward edge, not seen in the photo, is riveted onto the F-1206A bulkhead with four AN470AD4 solid rivets in place of the pop rivets called for in the plans.

One problem is the angle drill has a large head compared to all metal angle drills … this is because it is inexpensive compared to the all metal versions and made from some sort of tough plastic. As such, in order to get square access to the forward most pop rivets decided it would be best to use a Dremel with a cutoff wheel and remove the majority of the F-1206F bearing bracket brace. It was quickly realized the cutting wheel mounted directly to the Dremel would not work because of the tight quarters. Mike has a Dremel flex shaft attachment which is much like a speedometer cable with a chuck on the end of it and that worked quite well to make the big cuts ... once again, thanks Mike.
About to begin cutting away the F-1206F bearing bracket brace with a cutoff wheel fitted to Mike’s Dremel flex shaft attachment.

After making the big cuts with the Dremel tool, a hand hack saw was used to make cuts into the corners of the brace so it can come out in three separate pieces once all the rivets are removed.
F-1206F bearing brace bracket after all the cuts have been made with the cutting wheel and hand hack saw.
Now all four of the solid rivets can be seen so hopefully drilling them out should go better than doing it totally blind.

Once most of the F-1206F bearing bracket was removed, and the corner cuts completed the mandrels inside the six pop rivets were pounded out and the heads of the rivets were drilled out using the angle drill attachment. After all the pop rivet heads were removed, the remaining bracket brace pieces were easily removed.
About to begin drilling a #40 lead hole into the head of one of the six pop rivets.
Left side of the F-1206F bearing bracket removed … the next task is to remove the three rivet shanks from inside the holes.

Only one of the six pop rivets came out of it’s hole easily … the remaining five are not budging. I remember they were tight going in, so suppose I will likely need to drill them out. I have a few things left to try … but have a #31 drill bit waiting in the wings if a complete drilling is necessary. Ran out of time to try things so will have to work things out during the next work session.

Tuesday, March 17, 2015

Fuel Tank to Fuel Pump Line Completed

One item that needed to be completed before the side skins go on is finishing the fuel line connection under the fuel tank. Decided it would be best to do this now while access is still good. Frequent followers of the Blog may recall the DOG Aviation RV-12 will be receiving a small modification to the fuel line just below the fuel tank that was designed by another builder. The modification will add a fuel drain valve directly below the fuel tank for use as a fuel testing and drain point. When working on section 28 of the plans, the 3/8” fuel line running from the fuel tank to the fuel pump was not bent upward to meet the fitting on the bottom of the fuel tank. At that time, the finishing kit was not purchased … so the fuel tank parts were not available for making precise measurements to cut the fuel line to proper length.

So rounded up the bottom of the fuel tank and the fittings that will be used for the modification. The modification will consist of a 1 3/4" piece of tubing (flair to flair) that attaches to the fuel fitting on the bottom of the tank. Below that will be a tee that will connect to the fuel line going to the fuel pump. The lower portion of the tee is where the fuel drain valve will be installed.
Photo shows the bottom of the fuel tank in position and the blue Tee can be seen (not very well) by looking through the far left lightening hole.

The partially completed fuel line assembly was connected onto the fuel pump along with the return fuel line so a measurement could be taken on exactly where to cut the fuel line at the tee fitting. After the measurement was taken, the 3/8" fuel line was cut and the end flared. The AN826-6D tee has pipe threads on the bottom and the center and top utilize flair fittings.

Instead of the fuel line curving upward and attaching onto the bottom of the tank (as the partially visible fuel return line  on the left in the photo below does), the modification uses an AN826-6D tee that the fuel line going to the fuel pump attaches onto. The tee is attached onto a short piece of fuel line that measures 1 3/4" flair to flair.
Completed fuel line connected onto the AN826-6D tee.

After the fuel tank is built and installed, the photo below shows the remaining parts that will be installed onto the bottom of the AN826-6D tee during final assembly to complete the fuel drain valve modification.
Parts that will connect onto the bottom of the AN826-6D tee to complete the fuel drain valve assembly.

Saturday, March 14, 2015

Spring Thaw Creates Major Water Intrusion

Now that the record breaking cold temperatures of February and early March are behind us,  the spring warm up has begun to melt the ice and snow creating problems with water intrusion at DOG Aviation.

For those builders thinking of renting hangar space in areas of the country where winter is a factor, consider this …. DO NOT rent a north facing hangar unless no other options are available. The snow and ice just won’t go away from in front of the hangar and the runoff from the roof creates thick ice dams in front of the door which can cause water intrusion inside the hangar

The earlier part of the week was spent chipping ice away from in front of the hangar door as well as a thick ice sheet from inside the hangar as well. As water ran in during the daytime, the nighttime low temperatures froze it solid. Of course, it does not help that whoever the contractor was that poured the concrete hangar floor was an idiot … the water wants to flow inside the hangar and not away from it because the slope of the floor is incorrect.
A 1/4" of water is on top of about 1" of ice there was also a smaller lake on the other side of the hangar as well.
Shoveling chipped ice away from inside the hangar.

To help with the ice removal, Mike (who has the adjacent hangar) and I went halves on a 42" long pneumatic air scraper from Harbor Freight. Have to say, it does an admirable job of chipping through the thick ice dam in front of the hangars. We tried a large propane torch at first and realized that was a lost cause ... too much thermal mass to overcome. I thought the large hot flame would almost instantly melt away the ice ... not so.
Using the Harbor Freight scraper to begin chipping away the ice dam from the hangar door track and from the asphalt in front of the hangar door.
Ice dam in front of DOG Aviation’s hangar door now broken up … Mike in background working on removing the ice from in front of his hangar.
Mike chipping away and breaking up the ice buildup in front of his hangar with the Harbor Freight scraper.

Both our hangars got quite wet, so we got a hold of some large squeegees to push the water puddles out of the hangars. In my case, I had much more water than Mike did so had to move everything around to get to all the water … then of course rearrange the shop again. Needless to say all this has put me in a sour mood so no work was done on the RV-12 this week. Plan on hitting it hard next week.