Figure 1. For burn testing involving "V" pattern creation, we built a gas burner from half-inch black pipe with eight #43 holes (about 3/32-inch each) drilled in the top.

Figure 2. Unfinished half-inch plywood burned exceptionally well and created significant fire damage across the top of the wall.

Figure 3. This is the burn pattern that resulted from the fire shown in Figure 2. The left side of the pattern was almost perfectly vertical while the right side showed a bit of horizontal widening.