We have come to anticipate and enjoy the challenges of the RV-3 kit ? the fact that parts are somewhat primitive and the drawings less than precise than for the more recent Van?s kits ? and I figured that this experience was going to continue through the cowl fitting process. I sort of planned on having to make a lot of tweaks to shape and fit, figuring that the molds are old enough that the latest advances in CAD/CAM were not going be our allies in this fight. Lo and Behold, I am going to have to admit that we were more than pleasantly surprised! Not only have they updated the cowl to the latest ?fashion pink? color, it fits ?out of the box?? much better than I remember my RV-8 cowl fitting six (or so) years ago!
We decided to follow the now-accepted process of fitting the top and bottom halves together off the airplane to make the prop opening round and sized appropriately for the spinner first, then moving on to make the top cowl fit the firewall and spinner, and finally adding the bottom cowl. All in all, this fitting process really only took us a few work sessions ? maybe 20 person-hours altogether (to the clecoed-in-place stage). Louise tackled the first step, using a plywood template sized to the back of our spinner to take material off the joint between the top and bottom until the forward end was nice and round. The RV-3 cowl doesn?t have a ?joggle-joint? up front where the bottom fits inside the top, and this actually made it a bit easier to fit, in my opinion ? we could just trim away material and let the top and bottom ?butt joint? together then add an aluminum splice plate later on (riveted to the bottom, and secured with screws and nutplates to the top).
Fitting the top cowl was routine, using the method described in the builder?s manual of a line set back on the top skin, and then measuring forward from there to a trim line. We used a couple of temporary angles stick forward from the top cowl (clecoed on) and resting on the spinner to repeatedly establish the front height, and a ?? spacer to make sure we had a good spinner gap. I had already installed the flanges for Skybolt fasteners along the firewall (we?ll use hinges on the sides), and once we had the length of the cowl trimmed appropriately, we had to add four layers of fiberglass tape to the inside of the rear cowl flange to get the thickness right for a smooth transition. Trimming was done with shears, sanding disks on an angle die grinder, and finally, a piece of 80 grit sandpaper wrapped around a 2x2 sanding block to make the edges straight and true.
An easy way to transfer a line several inches back from the edge of the firewall is to trace and cut it on paper, then slie the paper back to mark that curve:
Fitting the lower cowl required estimating the locations for the gear leg slots, then carving them out a little at a time. With the prop in place, it was a little tricky sliding it in to place for each fitting, and I must admit, we made an early estimate that proved wrong?and had to pull out the fiberglass to ?add material back on? ? an advantage that fiberglass has over aluminum, for sure. Fortunately, fixing a mistake like this only takes a couple of hours at current sweltering temperatures (that means that stuff sets up quick!), and we found something else to do for the time it took to cure. Then it was back to it with the cutting and sanding tools until we had a good fit on the firewall. Because the RV-3 is much narrower than the later Van?s models, there is essentially no flat ?bottom? part of the cowl ? I am still not quite sure if there will need to be a fastener on the bottom, inside of the gear legs ? we?ll wait to see how it all works out when we build intersection fairings I guess.
With the lower cowl clecoed on to the firewall flanges, we next pinned the forward, center upper/lower intersection (behind the spinner) with clecos. It was then a fairly simple matter of trimming the sides to fit straight all the way back (the sanding block is once again your friend). Hinges were very easy to fit ? drilled and clecoed to the lower cowl first, then reaching in from front and back to hold the upper portion tight while drilling from the outside. Having the open rear end of the cheek cowls made this even simpler. We are going to make the check cowl extensions out of glass, and equip them with hatches to make them storage compartments (all ideas borrowed from some planes we?ve seen) ? this will allow us to insert the side hinge pins from the rear, and eliminate visible fasteners up front.
With the hinges all drilled and clecoed in place, Louise took over and glassed ? then riveted ? the hinges in to their permanent locations. She also finished the forward splice plates. All that is left is mounting the Skybolts to the firewall flanges, and we?ll be done with the fitting ? not done with the cowling, as there are about a million pinholes to deal with, of course?..
So?is Louise smiling because she is finishing up fitting her first cowl? Or because the cowling matches her shirt?!
Paul
We decided to follow the now-accepted process of fitting the top and bottom halves together off the airplane to make the prop opening round and sized appropriately for the spinner first, then moving on to make the top cowl fit the firewall and spinner, and finally adding the bottom cowl. All in all, this fitting process really only took us a few work sessions ? maybe 20 person-hours altogether (to the clecoed-in-place stage). Louise tackled the first step, using a plywood template sized to the back of our spinner to take material off the joint between the top and bottom until the forward end was nice and round. The RV-3 cowl doesn?t have a ?joggle-joint? up front where the bottom fits inside the top, and this actually made it a bit easier to fit, in my opinion ? we could just trim away material and let the top and bottom ?butt joint? together then add an aluminum splice plate later on (riveted to the bottom, and secured with screws and nutplates to the top).
Fitting the top cowl was routine, using the method described in the builder?s manual of a line set back on the top skin, and then measuring forward from there to a trim line. We used a couple of temporary angles stick forward from the top cowl (clecoed on) and resting on the spinner to repeatedly establish the front height, and a ?? spacer to make sure we had a good spinner gap. I had already installed the flanges for Skybolt fasteners along the firewall (we?ll use hinges on the sides), and once we had the length of the cowl trimmed appropriately, we had to add four layers of fiberglass tape to the inside of the rear cowl flange to get the thickness right for a smooth transition. Trimming was done with shears, sanding disks on an angle die grinder, and finally, a piece of 80 grit sandpaper wrapped around a 2x2 sanding block to make the edges straight and true.
An easy way to transfer a line several inches back from the edge of the firewall is to trace and cut it on paper, then slie the paper back to mark that curve:
Fitting the lower cowl required estimating the locations for the gear leg slots, then carving them out a little at a time. With the prop in place, it was a little tricky sliding it in to place for each fitting, and I must admit, we made an early estimate that proved wrong?and had to pull out the fiberglass to ?add material back on? ? an advantage that fiberglass has over aluminum, for sure. Fortunately, fixing a mistake like this only takes a couple of hours at current sweltering temperatures (that means that stuff sets up quick!), and we found something else to do for the time it took to cure. Then it was back to it with the cutting and sanding tools until we had a good fit on the firewall. Because the RV-3 is much narrower than the later Van?s models, there is essentially no flat ?bottom? part of the cowl ? I am still not quite sure if there will need to be a fastener on the bottom, inside of the gear legs ? we?ll wait to see how it all works out when we build intersection fairings I guess.
With the lower cowl clecoed on to the firewall flanges, we next pinned the forward, center upper/lower intersection (behind the spinner) with clecos. It was then a fairly simple matter of trimming the sides to fit straight all the way back (the sanding block is once again your friend). Hinges were very easy to fit ? drilled and clecoed to the lower cowl first, then reaching in from front and back to hold the upper portion tight while drilling from the outside. Having the open rear end of the cheek cowls made this even simpler. We are going to make the check cowl extensions out of glass, and equip them with hatches to make them storage compartments (all ideas borrowed from some planes we?ve seen) ? this will allow us to insert the side hinge pins from the rear, and eliminate visible fasteners up front.
With the hinges all drilled and clecoed in place, Louise took over and glassed ? then riveted ? the hinges in to their permanent locations. She also finished the forward splice plates. All that is left is mounting the Skybolts to the firewall flanges, and we?ll be done with the fitting ? not done with the cowling, as there are about a million pinholes to deal with, of course?..
So?is Louise smiling because she is finishing up fitting her first cowl? Or because the cowling matches her shirt?!
Paul
