Herr Engineering P-51 Mustang

Model Airplane News, Jul 2000 by Randolph, Randy

The P-51 Mustang is one of the world's most modeled airplanes, and over the years, we've seen many Mustang kits; some sacrificed scale appearance for good flight characteristics, and others forfeited performance in favor of scale fidelity. You will be more than happy with Herr Engineering's* sport-scale version of this popular warbird: it looks good; its tab-and notch constructon make it easy to build; its semisymmetrical wing ensures that it flies well; and it isn't expensive, if you decide to power it with a Norvel* Big Mig .061 RC engine, you'll stay well within your budget.

FIRST IMPRESSIONS

All of the parts are sealed in individual, clear-plastic bags, and the rest of the box is filled by two rolled sheets of CAD-drawn plans, an instruction booklet, military markings stickers and a carefully wrapped clear canopy. The laser cutting is precise, and the wood's density is generally well-matched to each part and should be strong enough for its purpose. Hardware includes landing gear, aileron torque rods with clevises and tailwheel wire. Pushrods and linkages to rubber, elevator and throttle are not included, so you must use your own discretion in these areas.

First, label all of the laser-cut parts while they are still tenuously attached to their sheets. The laser cutting has been so well done that most of the parts readily fall out of the sheets and can be difficult to identify.

CONSTRUCTION

Start with the tail surfaces. Epoxy the fin and rudder, then join the elevators with the provided 1/8-inch-diameter hardwood dowel. When the epoxy has set, temporarily join the movable surfaces to their fixed counterparts, and sand them to blend with each other.

At this point, I strayed from the instructions, which said I should bend and glue the tailwheel to the bottom of the rudder. I've never been happy relying on rudder hinges to support the tailwheel during the shock of landing; I much prefer to use a bracket to absorb shock and a tiller attached to the rudder for steering.

Each fuselage side is made of two pieces that have to be glued together; then, to complete the sides, glue a plywood doubter to the inside of each. All of the parts fit very well, and when I had finished the sides and joined them with the bulkheads, the fit was perfectly smooth! Herr Engineering's secret is to use right triangles to position the first two bulkheads accurately in their notches on the first fuselage side.

Because I intended to use the JK Aerotech* Slick Mount, which includes the fuel tank, I drilled the firewall to accept that mount as well as the throttle line before I installed the firewall in the fuselage. I actually installed two throttle linesone on each side of the mount-so that I'd be able to use an engine with a throttle arm on either side.

When building the fuselage, my only deviation from the instructions was to plank the forward turtle deck. It had been a long time since I had done any planking, and I just wanted to do a little because I think it's fun. Following the instructions would have been faster; sheeting the aft deck went a lot more quickly. Wetting the sheet and forming it around a 2-inch cylinder to dry made the aft sheeting a breeze to deal with.

To finish the fuselage, you have to carve and shape two blocks in front of the wing on the bottom of the fuselage, two blocks that fair the fin into the fuselage and stab, and two long triangular blocks that finish the cockpit area. With a sharp knife and then 80- and 100-grit sandpaper, I roughshaped everything. When I had finished shaping the blocks, the canopy fit perfectly.

For the fin/stab/fuselage fairing, I spotglued balsa scrap where the fin and stab would later be attached, spot-glued the fairing blocks into place and then carved and sanded them to shape. When I had finished, I cut the fairing blocks off the fuselage and put them aside to use later when I added the fin and stab to the fuselage.

The wing is built over the plan. The bottom main spar is pinned into position with a strip of 1/s-inch-square balsa as a spacer between it and the building board. The ribs have an extension on the bottom trailing edge that holds them at just the right angle to match the spar and be secured to the board. The top spar, spar webs, leading and trailing edges and top center sheeting are added while each wing half is still on the building board. When you've finished the wing halves, lift them off the board and glue the landing-gear mounts into place before you complete the bottom sheeting.

The hardwood landing-gear mounts must be drilled with a 32-inch bit to accept the landing gear. Because these holes and the grooves that are machined into the mounts will be under the bottom leading-edge sheeting when the sheeting has been installed, it's easier to drill the holes on the sheeting before you install it. I did this by putting a short piece of 3/32inch wire into each hole, fitting the bottom sheeting against the leading edge and pressing the sheeting against the wire in the holes. I then removed the wires and drilled the holes in the sheeting. This worked great!