Throttle Quadrant Support Bracket Redo

Time: 4 Hours

Since my arm rests and throttle quadrant are all custom, meaning I deviated from what Van’s calls for, I had to do some engineering that’s unique for the support of the throttle quadrant cables. I took the idea from my buddy Glenn and made a bracket out of some large aluminum angle. I had completed this task and installed it some time ago and moved on to other tasks. Since then I was really happy with how the arms of the quadrant were moving and it felt like there was some binding. So yesterday I decided to investigate and see if I could fix the problem. What I found after a closer look was that I had actually measured the distance from the side skin to where the holes for the cables needed to be by about 3/8″. This meant that as the cables left the quadrant they angled outboard to hit the bracket holes. This caused each cable to cause a torquing action on the levers and caused the mixture and propeller cable ends to actually touch as they went through there motions in one spot. That was not good and needed to be fixed. So I decided to make a new bracket that would extend 3/8″ farther inboard. So I went about removing each cable from the quadrant then removed the two bolts holding the bracket. This allowed me to slide the bracket off of the three cables and remove it. I used it as a template and just extended the arm length by 3/8″. With the new measurements I went about drilling and trimming the angle to create a new bracket. I then did the task of getting the bend of the arm where the two bolts attach the bracket to the angle on the side skin. This was the time consuming part as it’s a little bit of a task to get the cables in and situated while checking the angle. Once that was done I bolted the bracket down and went through the process of setting the correct throw of the cable ends. These all looked good so I removed the bracket and primed/painted it so it would look presentable. Today the paint was dry so I reinstalled the bracket and worked the cables from outside to inside. First was the throttle cable as it’s the outermost cable on the quadrant. Once I had the throw all set and got the throttle arm on the servo to hit the full and idle stops I locked the cable arm in place with the nut and attached it to the throttle lever with the pin and cotter pin. I repeated this process for both the propellor and mixture cable. The propellor arm has given me the most problems part due to the angle that it goes through the bracket and the arm length on the propellor governor. What I ended up with was the prop lever goes to the full forward position on the quadrant and is short of the full aft portion by 3/8″ or so. I’m ok with this as it will never be in that full aft position and only off the full forward position a little as you increase the propellor pitch and reduce the engine RPM. The mixture arm works perfect allowing the full rich and idle cut-off.All three cables operate much smoother and there is no binding at all. I’m happy about that but I’m happy I spent four hours repeat a process but that part of experimental building. One other thing I did was to give the RV-8 some fresh air so I could sweep out the hangar. She really looks good stretching her legs after a long winter being cooped up!

Engine Cowl Work

Time: 20 Hours

So over the last month I have been slowly working on the engine cowl surface’s starting with the insides first. I had already started the inside prep earlier so it was a good place to continue. The process was to sand the surface smooth but not break through the epoxy. Once it was smooth and all the ridges knocked down I applied a layer of epoxy on the entire surface using old hotel key card to squeegee the epoxy into the holes. This allows you to remove any excess epoxy which makes future sanding much easier. I would then let the epoxy cure overnight so I could repeat this process. I did this a total of four times on the inside surface for both the top and bottom halves. It’s time consuming since you have to let the epoxy cure and then the sanding, I have learned to hate sanding! I filled in some of the larger imperfections on the inner surface but not getting too crazy as it’s just the inside. The idea for me is to get the inner surface acceptable to paint to keep oil, grease and any other contaminant to be easily identifiable and cleanable. Also most of the inner surface will eventually be covered with an aluminum foil type material that radiates heat from the exhaust system and protects the fiberglass. There are various brands of this heat shield and I have not decided on which one yet. Once the insides were good enough I moved on to the exterior surfaces. The process is the same and just as the inside except I added an additional step. This was to use UV Smooth Prime to fill in all the tiny pin holes. This primer is like paint with drywall mud mixed in. You really have to mix it well. It’s so thick I decided to buy a paint can shaker from Harbor Freight Tools to handle this. As of today they cowl halves are 90% done and I’m just finishing up some small imperfections that are left. Here are a few pics of the process but not much to show while sanding.

Cowl Lip Baffles

Time: 4 Hours

The last part of the baffle puzzle are the lower cowl lip seals. These get attached to the lower inlet lip of the lower cowl and create a seal against the inlet ramps on the left and right sides. The idea is to shape strip of aluminum to the shape of the inner shape and use it as a clamping surface to squeeze the seal fabric in place. I worked the right side first and bent the strip to the shape making sure that it had a “clamping effect” to the sides. I then cut a piece of the 3″ wide seal longer than needed to start with. I then laid out three screw hole marks for the screws that will eventually hold them in place. I then drilled the three holes in the cowl flowed by match drilling through the cowl into the aluminum strip under. I used these holes and marked the seal fabric so I could punch holes it the fabric as well. With all three parts now having holes in them I attached them to the cowl. The fitment is just a rough shape at this point and need to be trimmed to fit better. I decided on 1″ as my overlap which should be sufficient. I marked 1″ marks along the entire cowl lip for cutting. I removed the cowl and the baffle and trimmed along the marks I made and put it all back together. I’m supper happy with how the fit was after trimming. I put the top cowl in place to see how the fit was and it ended up very tight and should provide a pretty good seal. I repeated the process on the left side. I returned the baffles to the forward center section as well as the forward sides and installed the top cowl. Here is how they look and I’m pretty happy with the fitment. The left side doesn’t have rounded corners due to the air filter placement. In the corners there is a little gap that will allow leakage.

I removed the lip baffles and drilled, deburred and riveted nutplates in place for #8 screws. I’ll install these once all the cowl work is finished up.

Oil Door Hinge Pin

Time: 1 Hour

While waiting for some fiberglass to cure on the lower cowl lip I decided to fabricate the hidden oil door hinge pin. The door is hinged on the top with a hidden bracket. To hold the bottom of the door I decided to use another piece of hinge. I installed these a long time ago and had planned on how I would remove the lower hinge pin to allow the door to open. The upper bracket has a spring to it so when the door is unhinged it springs open. So I had fiberglassed a aluminum tube with the same inner diameter of the hinge itself to the inside of the cowl to direct the pin as it’s inserted to the first hinge eyelet. I used the hinge pin to mark the firewall where I needed to drill a hole for the pin. I used a dab of orange torque seal on the tip of the pin and slid it through the hinge eyelets until it touched the firewall and left a dot of torque seal identifying where to drill. After removing the cowl I drilled the hole and clean the edges as the stainless steal is very sharp after drilling. I returned the cowl and slid the pin to make some marks for where to cut and bend for the handle I was planning on forming. With the cuts and some bending I made what I think will work well. I put some shrink tube on the handle side to keep it from scratching and make it easier to hold. I only have to pull it out far enough for the door to open and check the oil. Then while oblong the door down I slide the pin in and the door is secure. I made the handle long enough so that it can be tucked next to the nylon block for the baggage door lock. This will keep it from spinning around in flight and the baggage door itself will prevent the pin from sliding out of position.

Fuel Pump Overflow

Time: 1 Hour

The engine driven fuel pump has an overflow port to allow excess fuel drain after engine shutdown. Van’s uses a 90° elbow that has a soldered 1/4″ copper line on it. When I was installing it the copper line broke off. So I decided to upgrade to a AN842-4D elbow. This has the 1/8″ threaded side and a 1/4″ OD barbed side. I could then use some 1/4″ ID hose to run from the AN fitting to some 1/4″ aluminum tube that directs the fuel overboard under the fuselage. I cut some tubing and made the required bends so that it exits underneath the fuselage through a hole I drilled. I then secured that tubing with adel clamps. With the AN fitting secured in the pump all I needed to do was cut a length of tubing to connect the two. I will use zip ties to secure the hose to the tubing and AN fitting.