P-40 Warhawk

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Written and designed by Keith Sparks
Read an abridged summary relating to the article.
Find the entire feature on page 48 in the February 2012 issue.

From the start, the goal for this project was to build a large, lightweight, 1/4-scale model with materials easily obtained from home improvement stores. Material availability has proved to be one of the major obstacles with most of my foam-based designs. Although the P-40 Warhawk uses light plywood and balsa in areas requiring extra strength, the majority of the airframe was purchased at my local home improvement store.

The construction method will be familiar to most scratch builders by substituting wood with lighter foam materials and wood workers’ glue with polyurethane glue. The finish applied to the model uses the same fiberglass and epoxy resin methods employed on conventionally constructed models.

The most noticeable difference is that foam is easier to cut and sand. The airframe is less expensive to build using foam and its lighter weight allows for a more affordable power system to be used.

It is hard to tell that this Warhawk P-40 is made with the material commonly referred to as fan-fold foam, until you see it fly.

I cut all the fuselage formers then built the assembly fixture. That turned out to be the best $10 I ever spent. I placed the electrical conduit over the plans and marked each former position then slid the formers in position on the conduit and mounted the assembly on the fixture. I used a piece of plywood as a tool to slide the formers in position without damaging them; the fit is tight.

The cowl was assembled with 3/4-inch foam sheeting segments cut from the plans patterns and assembled in a wedding-cake fashion, paying attention to the alignment. The assembly was tack-bonded onto the fuselage and sanded to shape. The patterns are close to net trim, so I advise that you cut outside the line.

I used the plans to cut the wing sheeting panels and marked two of them with the spar and rib positions by laying the plans over the sheeting and piercing the paper to give me accurate point-to-point marks to work with.

With the fuselage on the build fixture, I removed side sheeting in the wing saddle area in small amounts until it rested in the saddle with the proper incidence angle. I added the wing dowel and checked the angle again before I drilled the wing bolt holes.

Adding the horizontal stabilizer to the fuselage was done by trim and fit with the fuselage in the build fixture. When the proper incidence angle was found, I added sheeting doublers to the inside of the fuselage for a wider joint and bonded the stabilizer in place.

The E-flite 160 motor provides enough power to fly this model with a 20 x 6 propeller; however, you will be pulling the maximum recommended 60 amps.

The Warhawk P-40 performs as you would expect, given its light wing loading, with shorter takeoff rolls, slower approach speeds, and fly-bys that don’t look like you are being chased. The model pulls to the left on takeoff, but once the tail is off the ground the rudder has positive control. Easing into the throttle makes it predictable and looks true to scale.

Read the entire 2,000 word article on page 48 in the February 2012 issue of Model Aviation.

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