SkyBolt Install

Time: 8 Hours

I need to explain to those who are unfamiliar with how the RV-8 has its fiberglass cowl attached to the aluminum fuselage. The stock way of doing this is with piano hinge mated to the aluminum and fiberglass using the center pin to hold both halves tight together. This has worked well on thousands of RV’s out flying. There are challenges to this method, including difficulty getting the pin in and out when removing or replacing the cowl. Especially along the top and bottom of the cowl due to the curve. Another option out there is to use the Skybolt fastening system like many production aircraft. Even the Lear 45 I fly has similar fasteners holding the avionics doors in place. The Skybolt system uses receptacles mated on the fuselage and spring loaded pins mated on the fiberglass. When the two parts are brought together the pins get pushed in and turned to lock into the receptacle. These make installing and removing the cowling incredibly easy and reduce the risk of chipping/scratching the paint that’s usually associated with the hinges. I decided early into my build that I like the look of these fasteners and would use them on my RV-8. So like many projects in the build in order to do one task there are always other tasks that need to be finished first. I started out wanting to seal the firewall inside the baggage area and realized that I needed to have the Skybolt tabs riveted in place first. So that’s what led me to this task. Show my goal was to get The tabs riveted along the top curved edge of the firewall leaving the sides for later. The cowls have two main sections when it comes to the Skybolts, the perimeter of the firewall and to sides of the cowl the run from the nose aft to the firewall. The goal will be for the aft Skybolt of the sides, running from the nose aft to the firewall, will be in sync with the perimeter Skybolts. That way everything looks symmetrical, this will be much easier to show later on in the billed as I get to that stage. But for now I have to do a lot of planning so that that winds up. I will have some lead way in moving the tabs to get that all to work if I leave one or two tabs above the center line open. Those will be able to be moved or spaced so that all line up just right. For now I just need to be close so that a 1/8″ here or there won’t be noticed to get the spacing right. So for now I started working on the tabs which included cleaning up the edges and countersinking the holes that will attach the receptacles.

To start I’m going to center one tab, dead center of the top of the firewall. From there I will work my way outboard until I get to the sides and see how the spacing looks.

As I worked my way outboard I need to find out a rough area for the centerline of the cowl. I got a pretty close location mark with the help of my buddy Glenn. With that mark I was able to figure out the line that would represent the centerline of the Skybolts that will be above the cowl centerline.

With that one tab set I adjusted my spacing on the remaining tabs between this one and the top one to get even spacing. Once I was happy with this I removed the two lower tabs on both sides as I will drill those later. Then I match drilled the tabs with the firewall and forward skin.

I marked each tab with a piece of tape and a number so that I could replace them exactly where they go. After drilling I remove them all and deburred the holes. I also countersunk all the holes on the forward skin for flash rivets. After all the tabs were returned to their correct spots I used my pneumatic squeezer to rivet them all in place. Keep in mind I left the lower couple of rivets on the lowest tabs out so that I could get the next tab in place once I need to. My goal is that I will have some wiggle room up or down with the remaining tabs to get them aligned with the ones that will be on the cowl sides. That way they all look symmetrical. I made quick work of riveting the tabs in place after getting all the holes cleaned up.

After those were finished I moved to the bottom of the firewall. Here there are two small areas that would normally have small hinge sections but will now have two Skybolts.

I added a small piece of .032″ aluminum to the corners to close up the gap that will be between the cowl and firewall. It should also help align everything when installing the cowl. I cleaned up all these holes and got them riveted as well. Slow progress only because I have so little to do and 55 days until I go build my engine.

Alternate Air Door Control

Time: 2 Hours

An alternate air door is a small sliding door that gets mounted to the side of the fiberglass “snorkel” that funnels air to the fuel injection control. The idea is that if your air filter would get clogged with anything like ice, which would restrict needed air flow, you could open this door and allow unfiltered air to get to your engine. You don’t want to run like this for a long time as the air is unfiltered but it allows the engine to keep running while you get it on the ground. I won’t. E working on the actual door for sometime but I wanted to get the control in now while I had the top skin off. I ordered my push-pull cable from MacFarlane aviation just like my cabin heat. I drilled the holes and ran the cable to check fit, once I was happy I decided where I would have it exit the firewall. I looked at a lot of builders photos to see what they had done. It’s hard to know exactly where to put it so that it would line up since I don’t have my engine so photos are my best friend. When I was happy with the placement I started to process of adding the cable pass trough I purchased from Aircraft Spruce. This “ball” style pass through gives you the ability to angle the cable as needed as well as give you a really secure and fire proof connection. First up was to mark and drill the six screw holes and center hole. 

I then used my hole punch to open the center hole to 1 1/8″. 

With all the holes and edges deburred I put the backer plate in position with the top and bottom screws. 

I then ran the cable through all the holes securing it with the washer and nut in the gear tower. Once it is through the firewall I place one of the retention rings followed by the two halves of the center ball followed by the second retention ring and screwed them all together. 

I really like these pass thoughs and they really look clean. I will use three more when the time comes for the throttle, propeller and mixture. While I was in the area of the the cables I decided to do the EGT/CHT cable extensions. I had ordered extre cable from Dynon since the cables only made it out about 6″ on the firewall and need to get the left side of the engine. Since I had to splice these I decided to do it inside the fuselage to be a cleaner look and be out of the engine environment. 

ADHARS and GPS Antanae Shelf

Time: 8 Hours

My last post had some fairing work and it turned out so-so, I’m not an artist by any shot and this will have a lot of work needed. 


I moved on to getting my ADAHRS mounted in the tray I made for them. I just needed to get them lined up with the axis of the airplane and attach them with non-ferous screws, I went with nylon screws and nuts with a little vibra-tite thread locker. 

I then connected the three lines between the two ADHARS. White is for static air pressure, blue is for pitot or ram air pressure and green is for AOA (angle of attack). I had already ran the Skyview network cables to the shelf area but needed to run the OAT (Outside Air Temperature) probes, one for each ADHARS. These will allow the units to give accurate readings with respect to airspeed. You need to keep the probes out of direct sunlight and away from any exhaust so I decided to put them under each wing. I placed them close to the access panels and in the same spot on both wings. 


With all the wires run I climbed into the tunnel to put the shelf back in place and make all the connections. I forgot how tight that space is and what a pain it is to work back there. So I powered up the Skyview and all worked perfect and crossed checked the two ADHARS units with no errors. I decided that I wanted to put my two GPS antanaes under the engine cowling and out of sight after talking with several builders this year at Oshkosh. I took some photos of a really nice setup and decided to replicate it. I started with a cardboard template. After I was happy with the shape and layout I transferred the dimensions to some .032 sheet and cut it out. I drilled all the holes for the mounting hardware as well as some lighting holes. I grabbed the two antanaes and mocked them up so I could drill the attach holes. I also drilled all the holes for the nutplates and dimpled them.I cleaned up all the edges and scuffed all the surfaces to be primed and painted. 


In between the priming and painting I worked on the firewall pass thru. I came up with the perfect spot on the right side of the firewall so that wires that needed to go to the engine area would run nicely.  I drilled a 3/8″ hole for a punch bolt to go through, I bought this tool just for this task. It is two peices that get pulled together and cut thru the sheet. It made a clean and perfect hole and was a lot easier than drilling the stainless steal. I used the pass thru as a guide and drilled the attach holes. After they were drilled and deburred I put the screws in and slid the fire sleeve on. I will run my wires thru this and seal it up at a later date when all the wiring is done. 

Vans had prepunched 3/4″ holes, one on each side, that I was originaly going to use but they are just to close to the edge of the firewall and I think they would be in the way of the Skybolt fasteners I’m planning on using. That was the main reason for switching to these firewall pass through from Cleaveland Tools. So what to do with the holes that Vans punched? Well after a little research I decided on using two large washers and a bolt/nut to sandwich the firewall between them. Once the paint on the GPS shelf was dry I bolted it in place. 

I’m real happy with how it turned out and have Bob M. to thank for the inspiration. One last task for the day was to clean up the wiring in the battery compartment since I’m done running grounds and wires through the firewall, at least on the right side. I have a little more work straighten out the ground wires, but I’m happy without turned out!