Monday, February 10, 2020

Completing Service Bulletin 19-03-22 Replacement Of #2 Exhaust Pipe

Last fall during the condition inspection, I completed a few service bulletins and am just now getting around to documenting them on the DOG Aviation blog. From a safety aspect, the most important service bulletin I completed is Service Bulletin 19-03-22 ... which involves replacement of the #2 cylinder’s exhaust pipe due to some of the RV-12 fleet experiencing cracking at one of the welds and in a couple of cases, a  complete separation of the #2 exhaust pipe.


First a little history about the RV-12’s exhaust system. The exhaust system on early RV-12’s placed the muffler very close to the RV-12’s oil cooler which contributes to high oil temperatures … especially for those in really hot climates.  In an effort to move the muffler a little further aft from the oil cooler, Van’s changed the shape of the Rotax 912ULS cylinder’s exhaust pipes (which are custom welded to begin with) allowing the muffler to be positioned a little further aft. The original four exhaust pipes are part numbers EXH-1201 through EXH-1204 and are not affected by the service bulletin. As a side note, on the original RV-12 exhaust system, the muffler’s exit pipe protrudes through the lower cowling at an aft angle.


The DOG Aviation RV-12 received one of the first shipments of the redesigned exhaust system … which has exhaust pipes numbered EX-00015 through EX-00018. One of the identifying features of this exhaust system is the muffler is positioned a little further aft and the muffler’s exit pipe protrudes straight down through the lower cowling. Also of note, the #2 exhaust pipe is positioned close to the lower cowling and one of the springs is very very close to the lower cowling. The cracking #2 exhaust pipe has a part number of EX-00017.


The cracking or complete separation of the EX-00017 #2 exhaust pipe is a serious safety problem which needs to be taken seriously. In addition to the obvious threat of carbon monoxide, the #2 exhaust is so close to the lower cowling that a separated exhaust pipe could have the potential to easily start a fire.
My finger is pointing to the weld on the EX-00017 exhaust pipe that is cracking/separating.
The old EX-00017 #2 exhaust pipe is on the left and the new EX-00017-1 #2 exhaust pipe is on the right. Looking closely, one can see the new EX-00017-1 exhaust pipe has a few obvious differences …. a doubler plate is added over the weld that was cracking for added strength, the overall shape of the pipe is a little different and the welds are larger.


Not wanting to take any chances, decided it best to not rely on inspections and just go ahead and replace the #2 exhaust pipe with the newly revised EX-00017-1 exhaust pipe along with new copper flange nuts and new springs where the #2 exhaust pipe meets the muffler. Instillation of the #2 exhaust was simple and done in a few minutes … replacing the safety wire I use through the springs is another matter.


After installing the new EX-00017-1 #2 exhaust pipe and attaching the lower cowl, I immediately noticed the new shape of the EX-00017-1 exhaust pipe created more clearance between the #2 exhaust pipe and the lower cowling … which I was glad to see. Unfortunately, I did not have my camera with me the day I reinstalled the lower cowling, so did not get a photo of the completed instillation with the lower cowl in place … will have to try to remember to do that and place the photo here.





Thursday, February 6, 2020

RV-12 Rudder Pedal Block Extensions

Thus far, I have been very pleased with flying the DOG Aviation RV-12 … it is truly a nice flying airplane. My only minor complaint stems from the rudder pedal configuration, in that, I find it difficult to make large rudder inputs with my feet on the rudder pedals without also pressing on the brakes unless I keep the balls of my feet pulled back in an unnatural position. Of course, for most ground operations or while in the air, this is not an issue … but on short final or during takeoff roll it requires a cognizant effort to pull the tips of the toes aft to insure large rudder inputs are not accompanied with unwanted brake inputs.

Sliding the feet higher on the rudder pedals would help but then the tips of my shoes (size 12) run into interference with the firewall shelf. Admittedly, it is not a big deal … just a few moments of uncomfortableness while pulling the toes aft to keep them off the brakes during takeoff and landing.


That got me thinking ... Gee, if the F-1290 pedal blocks were a little thicker, it might put my feet in more of a natural position on the rudder pedals and  help keep them off the brakes. With all the buzz about 3D printing, I decided to see if I couldn’t make a set of pedal blocks that are exact copies of the Van’s F-1290 pedal block … just a little thicker so the feet are in more of a natural position when on the rudder pedals. But that posed a problem … I have never used any type of 3D modeling software, so where do I begin?


EAA (Experimental Aircraft Association) to the rescue. I was talking to some friends at the airport about wanting to 3D print a set of thicker rudder pedal blocks, but didn’t have access to 3D software. I was informed that as an EAA member it was possible to obtain a free full featured (minus stress analysis) version of Solidworks Educational Premium that college student’s use. The EAA has formed a partnership with Solidworks allowing EAA members to download Solidworks Educational Premium for free … along with a 1 year license agreement which can be renewed as long as EAA membership is valid.


Knowing nothing about Solidworks (or any other drafting program), it seemed like learning to draw the thicker pedal blocks would be a daunting task. When first launching Solidworks, my eyes immediately glazed over … the sheer number of menus, options and submenu items available is truly daunting for a beginner. Fortunately, within Solidworks (under the help menu) there is a very good built in tutorial that starts out simple and builds on previous lessons.


After playing with the tutorials for a few evenings, I was able to acquire enough knowledge about Solidworks to successfully draft up a thicker rudder pedal block by carefully measuring the F-1290 pedal block and entering those dimensions into Solidworks then adding an extra ½" to the overall height of the petal block. I did not want to change the mounting bolt hardware so a recess was made for the mounting bolt to drop into. With a little bit of tutorial practice and some patience, making an accurate drawing for a thicker pedal block was not that hard. Below are a few screen shots of the finalized design drawing.

Top view of the thicker rudder pedal blocks drawn using Solidworks.
Bottom view of the thicker rudder pedal blocks.
Side view of the thicker rudder pedal blocks.
 End view of the thicker rudder pedal blocks.

A couple of years ago Tom, a friend who is building a RV-10, mentioned he bought a 3D printer and made the offer should I ever want to have something printed, to let him know. I told Tom about my using Solidworks to create a drawing for thicker rudder pedal blocks and he said he had plenty of blue HDPE filament … so Tom printed two blocks for me that are hollow inside with a crosshatch pattern for strength to save on material, since they are just for proof of concept. Thanks Tom!!!
The blue RV-12 rudder pedal block on the left was printed by Tom using the Solidworks file I made.
Side by side one can see the blue pedal block is the same as the black Van’s pedal block on the right … just a ½" thicker.
Bottom view of both rudder pedal blocks. Have to say, as a first time effort at making a 3D drawing and then having a part printed from the drawing, the thicker rudder pedal block looks great.


The big question now is how well will the thicker rudder pedal blocks actually work out? Only one way to find that out … install them.
The thicker proof of concept rudder pedal blocks installed on the pilot side of the DOG Aviation RV-12.
For comparison, these are the original Van’s F-1290 rudder pedal blocks on the passenger side.

So you are probably wondering … was it worth the effort … absolutely! My feet are now in a much more natural position when placed on the rudder pedals. Although the blocks could even be a tad thicker, the positioning of my feet on the rudder pedals is much more comfortable while moving the rudder pedals and staying off the brakes ... so I’m calling this effort a success.

Now that I know the Solidworks drawing I’ve made will produce a functional part, the plan is to make up four rudder pedal blocks from a tougher black material such as NylonX or CarbonX. Unfortunately, Tom’s 3D printer does not have the proper type of printer nozzle required for those filaments, so I will need to have the final pedal blocks printed elsewhere.



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The photos below are just stored here so I can post them on the forums. Basically, kicking around an idea here. Background: The owner of a RV-12 has a grade in front of his hangar to traverse and is trying to figure out a good way to get his airplane into the hangar without holding onto the tow bar so he can hold a winch controller or pull a rope connected to pulleys.


I suggested reversing the tow bar and pull it with a winch or rope/pulley setup connected to the reversed tow bar. However, it was pointed that without locking the nose wheel somehow, should the tail begin to track off center a little, the castering nose wheel will make matters worse and quickly get the airplane off track … true enough.


So that’s had me thinking for a few days and I think I’ve come up with an idea that may solve the guy’s problem. During the last unexpected warm day we had here I slipped up to the airport to take a few photos I will post on the forums. The idea is to use the RV-12’s steps to support a board traversing the bottom of the fuselage that the tow bar can rest on and be secured between blocks. The blocks will prevent the tow bar from moving side to side thus keeping the nose wheel locked straight while the tow bar is being hauled aft into the hangar by a winch or rope/pulley arrangement. Below are proof of concept mockup photos using a yard stick so the RV-12 owner can see my vision in a picture form.

The tow bar is placed on the nose wheel reversed as shown here and will sit on horizontal piece of wood or metal traversing the belly of the airplane. The areas where the blue tape is placed around the tow bar will need blocks attached to the horizontal piece to capture the tow bar. The blocks will capture the tow bar preventing side to side movement thus keeping the nose wheel held straight as the airplane is pulled backwards into the hangar.


The horizontal piece needs to be connected to the RV-12’s steps using a vertical piece that has wooden pins which will insert snugly into the step’s tubing as shown in this photo … or the vertical piece could slide over the step’s tubing, builders choice. The vertical piece will likely need some gussets where it meets the horizontal piece to stiffen the assembly, so the fixture has no side to side play. The steps will lock the whole structure preventing ant side to side movement and also support the tow bar as the airplane is pulled aft into the hangar.
As can be seen in this photo, the Van’s tow bar ends well forward of the com antenna.
Looking aft, As can almost be seen in this photo (bad focus), the com antenna is biased to the pilot side of the RV-12’s bottom fuselage … so a cable or rope connected to the center of the tow bar handle will easily pass by the com antenna.


I  believe my idea will likely work well, however not having an incline to traverse to get inside my hangar, won’t be constructing a working version to prove the idea actually works.