The first job today was to roughly cut out the lower cowl for the airscoop. The lower cowl was then match drilled to the cowl support strips in the same way as the upper cowl. This immediately revealed a problem. The airbox stuck out way below the cowl at the front and was also about an inch further below the cowl at the back than the depth of the airscoop. I assume the RV9 has a greater vertical cross section than the Tailwind hence the difference. Whilst I was pondering what to do about this I removed the cowl to finalise the fit between the upper and lower cowls.It was clear that the only solution was some fairly major fibreglass surgery. The first job was to get the top of the air intake on the airbox to align just below the bottom of the lower cowl. Notches were cut in the flange of the top plate of the airbox just in front of the filter and the plate bent up about 15 degrees. Reinforcing angles were cut out and clecoed on the inside of the flanges to hold the angle. Then the fibreglass box was cut in half and the front section angled to match the bend. Slots were cut in the front edge of the rear section and heat used to bend the tabs in to butt join accurately with the front section.
Next the airscoop was cut in half horizontally. The lower cowl was cut out to match the top section of the airscoop which was then taped in place. The cowl was then refitted to the aircraft. This allowed the bottom section of the airscoop to be positioned which showed that it needed to be about 1/2" lower at the front and 1" at the back. The sides of the bottom section were notched to allow the front to curve up slightly. Some scrap aluminium was clecoed to the top section of the airscoop and the bottom section positioned to allow a small amount of clearance from the airbox. This was then drilled and clecoed to the aluminium.
I've ordered some vinylester resin which is what was used to construct the cowl so once this arrives I can glass over the various joints, spaces and notches. The resin can also be mixed with microballoons to make a lightweight filler to smooth over the various joints. The final job will be to make the flexible joint between the front of the airbox and the airscoop. This was pretty tricky on the RV but at least I've done it once before.
