adamsrv10

In order to have a nice smooth and clean looking top cowl with no fasteners, I’m doing a hidden oil door hinge for opening. I utilized a spring based hinge so the door will pop open and stay up when opened.

The first step was to trim the oil door on the scribe lines that came with the Showplanes cowl. This piece matches the curve of the cowl perfectly.

Then I marked out a 3/4″ line for a flange on the recessed part of the oil door location. A small amount of sanding was needed to have the door fit in the recess area. You can see the door fitting nicely below and the marks for the flange behind it.

I cut the recessed area carefully and seeing it also follows the curves of the cowl, I used it as a stiffener on the back side of the oil door. I utilized flox and drilled a bunch of holes (which will be filled in later) to make sure there was a good bond between the two. I also used clecos around the perimeter to makes sure the door held tight to the cowl during cure.

I again used some flox and some packing tape to fill in the gaps between the spring hinge and the oil door. The hinge sat an an angle and it required a bit of a buildup to fill in the gap.

It was then time to work on the opening hinge mechanism. I utilized piano hinge for this. On the oil door side it’s just wide enough to allow the hinge to pass through the opening.. The mating side on the cowl is a little longer and I made it a little longer on the forward side, which required a little hogging out of the foam area around the oil door perimeter.

Below is a bigger view of the front cowl as I was prepping for drilling holes to attach the hinges to the cowl and oil door. I used the normal hinge pin for fitting as it’s slightly bigger than the bowden cable wire that’ll be used.

Below you can see all the hinges riveted and the Bowden cable roughy in place. This will ultimately be attached to the inside of the cowl and the pin cable will be cut so that the pin is just inside of the left air intake hole. I’ll be able to grab the pin and pull it causing the oil door to pop open once the pin has been extracted far enough. I’ll need to wait until I finish the air inlet ramps to complete the cable part of this.

I got an email that my prop was ready to ship from Florida.. So I wired the final payment and waited about a week before I got a call from the freight company to schedule delivery. The crate arrived unscathed.. and I opened up the front cover to take a look. It’s a thing of beauty.

They really do crate these things well. The prop was mounted to about a 2″ thick piece of plywood with nuts and washers. That was bolted to the crate. Below is a pic of the crate in reference to my garage door. It’s pretty big!

Later that night I set to work removing the prop from the crate and mounting it to the plane. I really wanted to see how it looked and also wanted to see how well the cowl fit and the gap between the aft part of the spinner/spinner backplate and cowl. Using the cowl tool was one of those times where you measure 10 times before you start to cut. I utilized my engine hoist and some straps wrapped around the root of 2 of the blades to lift the prop up while I lined it up and threaded the bolts into the flange. The end result is awesome, and I’m happy with how it looks and came out!

MT had advised to shoot for 1/4″ gap and had said that the spinner dome will overhang the backplate a little bit, so the gap will end up a little less. A bit bigger gap is also recommended for a 3 blade prop for getting the cowl on and off easier.. Of course that’s not as much of a concern for me with the lower half of the cowl split into 2 pieces.

In the end, all the measuring and use of the cowl tool placed where the spinner would be resulted in a consistent gap that I’m pretty happy with after fitting the cowl without the prop in my possession

Hinges were cut to mount to the newly created cowl flanges. Again, I tried as best as I could to shift the hinge eyelids so they wouldn’t be seen in the split.. Given the curve in this area, it wasn’t as easy as the horizontal sides, but I did the best I could. When I wasn’t able to maintain it I favored the front rather than the aft as that would be the area most visible.

Match drilling the other half of the hinge was a little more challenging to hold the cowl in proper position. I opted to use the forward fairing on the aft part with the 8 clecos where screws will hold things together to line up the aft end. I also used a small piece of scrap metal drilled and cleco’ed to the spinner area to hold the forward part of the cowl in position. I also used some duct tape along the split itself and removed as I went and got more holes match drilled and cleco’ed.

In the below pic, you can see the cowl match drilled from the inside and outside. I feel the split gap came out pretty good.

Then it was time to adjust the aft part of the hinge and cut an access hole for the pin to be inserted in a fashion similar to the Aerosport pin covers on the sides of the cowl. I placed this hole just forward of where the forward cowl faring ends and made it rectangular about the combined width of the newly created flange.

I fabricated a rectangular aluminium cover piece to fit the gap using some scrap. I drilled 2 holes for #6 screws to hold this cover in place.

I then did the same as I did for the Aerosport pin covers.. I place the metal cover plate into place with some packing tape around it for a release agent, slobbered a thin layer of micro over the back side, then laid up 4 layers of 9 Oz cloth and let cure. Below you can see the result after removing the cover plate. The central area between the 2 holes (where there will be nutplates added) will be cut out so the pin can be inserted.

And finally a picture of the cover plate in place after installing the nutplates and dimpling for #6 screws.

Prior to permanently riveting the hinges in place, I did a test fit of the entire cowl again to make sure everything still fit together well.

I copied what Dr. Mark had done to the forward fairing that attaches to the area of the cowl with no honeycomb and added a metal support piece along with 8 nutplates for #6 screws. This will provide a solid attachment point between the 2.

One of the last things to do (also copying from Dr. Mark) was to add a flange at the spinner area to provide an additional screw point and to alleviate any play in this area. I added packing tape on one side of the cowl so the fiberglass would only adhere to one side and serve as a flange behind the other half. This tape was placed such that the cut line was covered. That way I didn’t have to deal with attempting to cut the cowl halves apart again in this area potentially cutting into the newly added flange.

Below is a crappy pic of the inside where I used some scrap fiberglass with packing tape wrapped around it to clamp the newly added cloth in place along the entire spinner area while curing. Also a picture of my ugly mug to prove I actually built this plane.. 🙂

Below is the end result of the added flange.. Excess still to be trimmed away.

Then it was time to put the cowl all back together for a final test fit with all the hinges and skybolts in place. The only thing left is to add nutplates and screws to hold the top and bottom cowls together at the air inlets as well as the spinner area.

A closeup of the new flange and where the screw hole will go

Now to start working on the hidden oil door.

With the Skybolts and horizontal split line with hinges complete.. I moved on to fitting the two fairing pieces that come with the showplanes cowl. I trimmed the aft fairing to have 3/4″ flanges and then marked the center point. Additional trimming was needed to clear the front gear leg to get the aft fairing into position. 3 holes were drilled into the bottom of the fuselage for now to hold this in place. Later I will install rivets for screws to hold this into position.

Once you’re happy with this you place the lower cowl back on and drill a couple of holes on each side to lock in the position of the aft fairing to the cowling.

Then with the aft fairing and lower cowling back on the bench. The forward faring was placed into position and trimmed as needed to get a good fit with the forward fairing. Once satisfied, 3 holes were drilled on each side to hold the forward and aft fairing together.

The aft fairing was put back into place on the fuse, and the forward fairing was trimmed to clear the engine mount tubes until the drill holes on each side lined up.

Once that was done, the lower cowl was put back into place to verify and adjust fit. The forward fairing needs to lay flat across the area of the cowling that has no honeycombed and be as centered as possible.

I then had to add some fiberglass back to the slot that I had cut to get the lower cowl into position. I was careful to not cut too much when I did this originally, but I still cut a little too much. I sanded the edges at an angle to create a scarf joint with a fiberglass layup over the small area that needed to be added back. I put some peel ply on and let it cure overnight.

The end result was pretty good.. There was a small gap in the rounded edge, which I later filled in with epoxy and let cure and sanded down.

I then sanded the inside of the cowl at the scarf joint that I added. You can see that below just about done.

I then put the lower cowl onto some cinder blocks so I could level it as needed. I used the laser level to make sure the intakes were level horizontally, which the vertical was aligned to the center line of the lower cowl.

The center line was marked with a sharpie as well as some blue painters tape. I also marked out the locations of 8 holes to drill into the forward fairing that will hold the cowl to that fairing with screws. I also mapped out 8 additional holes that mostly go through the aft fairing into the cowling.

The lower cowling was placed back on and the hole locations were match drilled to the forward fairing

Then the big moment came.. Using a diamond cutting wheel on a dremel tool to cut the lower cowling in half!

For whatever reason, despite having a plan… it seemed scary to me to cut this perfectly good cowling like this…

The cut will later be rejoined with another hinge pin like the horizontal sides. Skybolts could also be used here, but I opted for a hinge for a better look.

To prep for that hinge.. I marked out a 1.5″ wide rectangular area at the split point. I again used the diamond wheel on the dremel tool to just cut through the inner layer of fiberglass as shown below.

I then used a flat blade on a Dremel multi max oscillating tool to separate the honeycomb material from the inner layer of fiberglass. Below you can see me mostly done separating the fiberglass layer from the honeycomb.

I then used a chisel to carefully remove the honeycomb material. You have to use caution as the remaining fiberglass outer layer is very thin.

I then cut some strips of 9 oz. fiberglass to build up a flange where the structural material was just removed. I decided to use 6 layers of cloth for this. The end result was a thickness consistent with the other areas of the cowl that don’t have honeycomb.

Then after curing overnight you can see the results of the flange.

Next up will be re-combining what was just cut in half…

Indirect lighting from inside the cowl when drilling the skybolts can really misalign you. I started to also trace the inside of the hole with a fine point sharpie to get an even better view of exactly where the hole is and also use that to gauge walking the step bit in one direction or the other.

Even with that I’m ever so slightly off, although not by enough to matter.

Below is a look down the left side at the firewall with some skybolts installed. Here you can see my small light that I used taped in place to more directly illuminate the hole.

I then used a laser level to mark and trim the top cowling first. the 12″ Permagrit sanding block was used after getting close with a diamond cutoff wheel on the dremel tool.

I then used the top cut to mark out the bottom cowl cut location.

I trimmed close with the dremel tool and then used the sanding block to get it as close to perfect as possible.

Once that was done, I marked the location of the hinge pin covers from Aerosport. Location was based on the plans.

With the hinge pin covers located, I then got to installing the side hinges. I shifted the hinge downward so the eyelids won’t show. I used a AN257-P3 length hinge on the bottom cowl and a -P4 length hinge on the top cowl to get enough flange to maintain edge distances on both the hinge and the fiberglass.

The same was done on the right side.

Use of the laser level to get the rivets all aligned down the hinge.

One thing I did was to drill a couple of turns with a hand drill in each marked rivet location prior to using a higher speed air drill. This created a slight dimple so the high speed drill wouldn’t wander once I was drilling through. Very little pressure was used and just let the drill bit do the work.

A view of the right side done and hinge pin in place (not yet cut to length)

I then cut out the spot where the aerosport hinge pin cover template was to be placed. I got close and then used a file to get it to fit tightly in the cut hole.

I then followed the Aerosport directions and added tape and wax to the template along with putting a micro slurry on the inside of the area. I also wetted out 4 layers of 9 Oz fiberglass and placed it on the inside. Once cured overnight, I used a thin woodworking saw I had from a previous task of cutting casings to cut through the Aerosport template and separate the cowl halves. I will say that the very front part where the 2 cowl halves overlap gave me a lot of trouble as I bonded them together and it took a relatively long time to get them apart and left me very frustrated. There is not a lot of room to work either to try to use small files etc.. to chip away at the bond. So use caution when doing this with a Showplanes cowl.. It’s pretty easy to waste 3-4 hours hacking away to get them apart again..

The end result of the recessed area I built up in order to install nut plates for the cover.

The center area of the added fiberglass was cut out to allow the pin insertion into the hinge.

Finally the hinge pin cover was test fit into place. This is at such an angle that if the hinge pin were to start to wander forward with vibration, it would stop the pin from working its way further out as the pin would hit this metal cover. From all accounts that I’ve seen.. the pin doesn’t typically do that anyways, but it would only be allowed to move approx. 1″ forward worst case.

The Showplanes cowl is one of the last major fiberglass pieces to be worked on. The instructions basically tell you to follow Van’s instructions with a couple of exceptions. So I got to putting the upper and lower halves together and marking the upper cowling for trimming to meet the ratios needed to make a perfect circle for the spinner/prop as well as the air inlets on either side. Here you can see the mark made using a straightedge.

Staightedge used to mark uniformly across the top cowl.

Double checking that the radius is 7.5″ (15″ diameter)

Getting close now with some trimming

Using the prop tool to double check the prop area circle.

You then clamp things in place and drill holes in the flanges to hold this position.

I chose to just do a single cleco on either side of the inlets as well as one in the flange between the inlets and the prop area.

I then used a laser level to mark the center of the bottom cowling to create a cutout for the nose wheel gear leg.

Marking either side of the centerline based on Van’s dimensions for width.

I then used a dremel tool to cut the slot. I estimated the length to cut and then slowly increased 1″ deeper at a time until I was at the bare minimum to get the lower cowling into position. Below is the initial length cut.. I cut a few more inches deeper. My plan is to split this lower cowl into 2 halves to accommodate the 3 bladed prop and I’d like to keep as much original material in this area as possible.

I put the top cowling into position and used a laser level to get it level (after leveling the aircraft) The cowl tool has 3/32″ holes all along the surface to facilitate holding the cowling into place in a fixed location so it doesn’t move during trimming.

Lining up the center line both fore and aft.

With this “extended” hub prop, the cowling sits far enough forward that there is minimal trimming required at the firewall.

Then starts the task of trimming to the firewall. I used a light on the inside to mark the location of the skin. You then trim 15″ on either side of the center line along the top only. I used a cut off wheel on the dremel tool and left it 2-3mm short.. The 12″ Permagrit sanding block was used for the remainder.. Once this center section is trimmed, the cowl falls down and aft allowing you to get a more accurate trim line for the sides.

I utilized a couple of clecos in the rivet holes of the skybolts to hold the upper cowling in place so it won’t move. I’ll fill these holes in later.

Then starts the task of installing the skybolts and drilling holes in the cowling. I started with a method that I saw Mark use. Using cardboard to drill a hole, I used a small scrap of fiberglass trimmed from the cowl to mock its thickness, and the cleco adapters that came with the kit to mark where the center of the hole was. The cardboard was taped into place so it can be flipped up, the cowl put into place, and flipped back down to drill an accurate hole.

The cowl was then put into place and the hole was drilled.. However, It didn’t really seem to work that well for me. Probably the tolerance of the hole in the cardboard not being perfect.

The first Skybolt installed.

What I found was that the light inside the cowling wasn’t direct enough and caused some incorrect alignments when marking the hole and drilling. So I taped a small light into the bottom of the cleco adapter to shine directly on the cowl while it was in position. This was used to drill the remaining holes which were more accurate.

I then worked one hole at a time from top center downwards towards the sides. Mark and drill the hole to 15/32″, insert the grommet and stud, rivet the receptacle in place, place the cowl back on and test fit the new Skybolt.

More to come..