Sunday, May 25, 2014

Vans Aircraft RV-12 Airplane Build, Section 38: Cowling (part 2)

Reference for this entry: page 38-02, 38-04, 38-05; 6.5 hours

So this entry starts the serious work on the cowling for the RV-12 airplane. Fiberglas isn't scary just different from working with aluminum.

NOTE: Do not remove material beyond the scribe lines or sand the cowl exterior.

Step 1: Trim the top cowl and bottom cowl edges to within 1/8 inch of the scribe lines. Sand to remove the remaining material up to the scribe line. A block with 80 grit paper works well for this.

Step 2: Clean any excess resin that may have cured along the flange joggle on the bottom cowl. Remove abnormal glass and resin buildup from the inside surface of the top cowl. Sand down the corners of the flange on the bottom cowl. This will allow the top cowl and bottom cowl to fit together with little or no mismatch in their outer surfaces.

Step 3: Trim or sand the flange on the bottom cowl to the dimension shown in Figure 2 on page 38-02 of the RV-12 plans.

Step 4: Clamp the top and bottom cowls together as shown in Figure 3. Mark the three hole pattern shown in Figure 3 on both sides of the top cowling. Drill #40 the most inboard hole on each side then cleco these two holes. Remove the clecos and separate the top cowl and bottom cowl.

Step 5: Cut a slot centered on the scoop of the bottom cowl and remove the material up to the scribe lines as shown in Figure 4.

Step 6: Use a unibit to drill a "starter" hole large enough to get a file or sanding block inserted then remove the material up to the scribe lines for the holes shown in Figure 4.

Step 7: Trim the bottom cowl air inlet to within 1/8 inch of the scribe line. Sand to remove the remaining material up to the scribe line as shown in Figure 4.

This completes page 38-02.

Reference: page 38-03.

Step 1: Modify the hinge halves lft over from making the Side Hinges (see page 29-02) as shown in figure 1 on page 38-03. Mark holes but do not drill.

Step 2: Lay out the holes on the Side Hinges as well as the hinge halves remaining from the Upper Cowl Hige and Lower Hinges. But Do Not drill the holes at this time.

Step 3: Install the Mid Cowl Hinge halves with the Mid Cowl pins. Then install the Lower Cowl Hinge halves with the lower cowl hinge pins.

Step5: The cowl hinges should be a continuation of the surface of the adjacent skins. Flute the hinges as needed, especially those that are curves, to bring them into alignment.

Builder's note: The two pictures above show the hinges before fluting which is needed to align them with the skins.

This completes page 38-04.

Reference: 38-05

Builder's note: Before proceeding I protected the finish on the nose gear strut with several layers of masking tape. And covered the engine with a large plastic bag. Also realize fitting the Cowl is trial and error so one may need to take it of several times and sand to final fit.

Step 1: Slide bottom cowl over hinges and clamp to the Mid Hinges so the notch in the cowl bottom aligns with the notch location in the fuselage side skins. Drill #40 the top hole location through the bottm cowl and the mid coal hinges.

Step 2: The bottom cowl may flex out of the desired shape if care is not taken to align it properly. When happy wot the alignment., drill #40 the bottom hole location through the bottom cowl and the lower Cowl Hinges then cleco.

Builder's note: Here is where having the engine installed comes in handy, I put the top cowl in place as well as the back plate for the spinner. With all the cowl pieces available I shifted the parts around and sanded as needed to ge a good fit with good clearance between the spinner and the front of the cowl before drilling the holes in the lower hinge halves. At this point I found I was not happy with the two top holes drilled earlier and refiberglassed their locations and redrilled them.

Builder's note: Notice the extra material overlapping the fuselage skin in the picture above, yes this had to be removed.

Builder's note: Note final clearance between cowl and spinner back in picture above.

Step 3: Mark the offset distance from the Mid Cowl Hinge on the inside of the bottom cowl.

This has been a long day, so I'm calling it quits for now. Tomorrow I will start back in on the Cowl for the RV-12 airplane.