Herr engineering Piper J-3 Cub

Model Airplane News, Mar 2000 by Randolph, Randy

A laser-cut, 1/2A-scale sport flyer

HERR ENGINEERING* KITS ARE MADE for modelers by a modeler. I have never met Tom Herr, but from my experience with his kits, I know I like him! Some of his personality comes through in each kit he produces. When compared with other ARF and RTF kits, Herr's are not the most complete in the industry, and they only supply a basic hardware package, but the engineering and care of assembly are unequaled. The laser-cutting is absolutely perfect, and considering the instability of balsa wood, it is unbelievable. Everything fits together like the parts in an expensive watch!

The first Herr kit I built was the rubber-powered version of the J-3 Cub. The wing was built in two pieces, and the pieces were joined to the sides of the fuselage. When I got to that step, I was truly amazed to find that the wings were true with the fuselage and the tail. This same kind of precision is evident in the RC version of the same airplane.

FIRST STEPS

When you open the kit, you'll find all of the laser-cut sheets and stripwood in a clear plastic bag; the plywood parts are separate. Another clear bag holds the small parts and hardware. The plans are rolled and in two parts-the fuselage on one sheet and the wing with the stab/elevator on the other. Windshield material comes folded inside the four-page instruction manual.

The very first step in just about any laser-cut kit is to label the parts before they fall out of their carrier; you should never neglect this step.

The rudder/fin and the stab/elevator are constructed first, and it takes more time to read the steps in the manual than to actually make the necessary glue joints. When the rudder and elevators had been assembled and glued, I temporarily joined the fin to the stab and sanded all of the edges round.

BUILDING THE FUSELAGE

The next step is to assemble the fuselage sides, which consist of several separate pieces and are assembled along with plywood doublers. The sides are labeled "L" and "R" because there is some right thrust built in to the model, and if the sides are assembled incorrectly, you will have a hard time later when you mount the firewall.

Bringing the two sides together started out nice and easy: I glued a couple of formers at right angles to one of the fuselage sides, etc., and I was able to follow the manual all the way. However, then came assembly of three different things while I was supposed to hold the fuselage sides together in my hands. This was also the time I discovered that instant glue is somewhat less than instant when you are trying to glue pieces of plywood together. I finally gave up and used good old aliphatic resin and clamps! Even though I got glue all over the airplane and myself, it was worth it because I made a solid front end for the fuselage and was able to wiggle everything together for a nice, tight fit.

I am always surprised when notches and tabs fit perfectly, especially over dis,tances such as from the bottom of the cabin to the tail post, but that's what happened with this kit. In fact, all of the pieces fit together exactly as they should, and the fuselage came out straight and true. However, one suggestion: add cross-braces to the last former in the aft part of the fuselage (F-12), or it could split down the grain at just the wrong time.

When the basic fuselage structure is finished, the instructions tell you to add the fuel tank and throttle lines before you finish the front turtle deck. This step is necessary, but the instructions also suggest that you install the servo mount and servos along with the pushrods to the control surfaces before you sand the completed fuselage. I installed a 2-ounce tank and put the mount and the pushrods in, but I did not install the servos. I didn't want to expose them to all the sanding dust that would follow.

WING CONSTRUCTION

The manual has you build the wing in three pieces that are joined as they are built. First, the center section is finished, then each wing half is joined to the center section. Since everything in the center is the same size-the leading edge (LE) and trailing edge (TE) as well as the top and bottom sheeting-I cut and sanded them all to shape at one time by matching them to the piece of laser-cut plywood that forms the front face. This simple chore ensures that everything is the same width and will really speed up assembly. You will build the four bottom dihedral braces on the bottom spar as you assemble the center section.

After the center section has been completed, join the left wing's bottom spar to the center section by the dihedral braces, and build the wing flat with the center section elevated to the dihedral angle. Once the left wing is complete, build the right wing in the same way with the whole left wing in the air. It may sound clumsy, but it's really a sensible and accurate way to build a wing-an old system coming back into practice. One thing to remember: when building the left wing, the right wing will be held higher than the dihedral called for because the angle starts at the left wing centersection joint, not the right wing center-section joint! Then lift the wing from the bench and cement the top main spar, along with its dihedral braces, to the top of all the ribs. Installing the center-section sheeting completes the basic wing structure.