Converting the 1/72 Mach 2 DC-8 Into a Short Body Combi

Background References

Late during the production of short body DC-8s, Douglas enlarged the aft cabin by moving the aft pressure bulkhead rearwards. This also entailed moving the aft galleys and the right rear (aft galley) door rearwards. Although this was intended to be the new production standard from that point onward, there are reports that some customers preferred to keep the earlier aft cabin layout for fleet commonality. Double check your references. I’ll be modelling a Trans Canada Airlines (Air Canada) DC-8-54, which did incorporate the extended aft cabin option. Key dimensions are shown in the following diagrams.

Here is the fuselage station diagram of a short body DC-8 with the extended aft cabin.

For comparison, here is the fuselage station diagram of a standard short body DC-8, like the Mach 2 kit.

I wanted to build a combi interior on my kit, so the following drawing proved useful.

The following photo shows an Air Canada DC-8-54 Combi with the extended aft cabin. Note how the two rear doors are NOT opposite one another. The right rear (aft galley) door is staggered aft by 1 frame (20 inches).

The nose landing gear on the Mach 2 kit is too far forward. The following diagram shows the correct dimensions so you can fix the problem.

Cutting Plastic

So, now that I know how the airplane is supposed to look, it’s time to start cutting plastic.

The nose landing gear on the Mach 2 kit is too far forward. Use the diagram shown earlier to move it aft by the correct amount.

In order to keep the nose mounted air vents at the same position relative to the nose landing gear, I moved them aft too.

On my kit, I opened up the passenger and cargo doors. The left forward passenger door on the Mach 2 kit is etched too far forward, so use the fuselage station diagrams shown earlier to move it aft by the correct amount. Mach 2 did not make the passenger doors the correct size. They should be 34.5 inches wide by 72 inches high.

Moving the nose landing gear aft means also moving the box aft.

The forward-most passenger window on the left side is too far forward. Move it aft so it lines up with its mate on the opposite side.

I also opened up and re-sized the left rear passenger door. It should be 34.5 by 72 inches, similar to the forward passenger door.

On a combi, you need to add the hat rack doors.

I felt that in 1/72 scale, the relatively large rudder deserved better than a simple line etched into the plastic, so I cut it away and built up its nose and hinges. Note that the upper-most rudder hinge is parallel to the ground and not inclined like the others.

Finally, I cut away the stabilizer gloves. The ones provided on the kit are too long. They should not extend aft of the elevator hinge line. I will replace them later with Evergreen plastic card.

The galley doors etched into the fuselage right side were not the correct sizes. The correct dimensions are shown in the photos below.

The second photo below shows how I re-located the aft galley door on the right side further aft, consistent with an enlarged aft cabin.

Building the Interior

The 9g barrier net, roller tracks, and most of the other bits were scratch built from various Evergreen strips and rods. The ball bearings on the mats were simulated using plastic rivet head shapes by Tichy Train Group.

I simulated the stainless steel galley countertops using aluminized duct tape. The carpet in the passenger cabin was a design printed on paper and then glued down.

When you look into the cabin through the very large main deck cargo door, there is an unsightly seam along the ceiling where the two fuselage halves joined. I hid this seam by covering it with a ceiling light panel.

The Wings

Here is the wing station diagram. Use it to get any dimensions you need.

Mach 2’s wing-to-fuselage joint is weak. I strengthened it by adding a large piece of Evergreen plastic strip to the inboard end of the wing, and cutting matching holes in the sides to the fuselage. Ensure your design allows for a generous wing dihedral. The wing will be solidly anchored into the fuselage a bit later in the build process.

The following photos show the locations of the leading edge slots. They should be butted right up against the engine pylons.

The following photo shows that Mach 2 etched the slots too far away from the pylons (ie. dotted lines). I used the above photo plus the wing station diagram to re-etch the slots in their correct positions, as shown by the solid line in the photo below.

The slot positions are difficult to see in the wing station diagram, but if you look very closely, the line representing the front spar is thicker at the slot locations.

The Mach 2 kit does not have sufficient wing and tailplane dihedral, the main landing gear legs are too long, the nose landing gear leg is too short, and the engine pylons are too high.

All these problems must be corrected or the engine nacelles will be too close to the ground.

The easiest and most precise way to solve the problem is to build a support frame out of popsicle sticks, that holds the fuselage and wings at their correct distances off the ground. Once these bits are solidly supported in their correct positions, you simply glue them together.

Use the dimensions from the following ground clearance chart.

First, build a popsicle stick support to prop up the fuselage so that the passenger doors are the correct distances off the ground (Distances “A” and “B”).

Next, build a popsicle stick support to prop up each wingtip so that the wingtips are the correct distance off the ground (Distance “P”).

Finally, build a popsicle stick support to prop up each stabilizer tip so that they are the correct distance off the ground (Distance “N”).

Later, when we install the engine nacelles, they will have to be distances “K” and “L” off the ground.

This support will also be used to adjust the landing gear legs to their correct lengths.

At this point, the fuselage halves are only held together with elastic bands. DO NOT GLUE THE FUSELAGE HALVES TOGETHER JUST YET.

Now, glue the wings and stabilizers onto the fuselage. Since all the bits are supported at their correct distances off the ground, the dihedrals will automatically be set to the correct values. You can double check that the dihedrals are 6.5 degrees (wing) and 10 degrees (stabilizer).
Once the glue is hard, take the elastics off the fuselage halves, and reinforce the interior of the wing-to-fuselage joint.

Increasing the wing dihedral to the correct value leaves a gap on the bottom of the wing root which needs to be filled.

Now, you can glue the fuselage halves together.

Engine Pylons

Once the fuselage is the correct distance off the ground, and the wing has the correct dihedral, the engine nacelles are still not the correct distance off the ground. This is because the pylons are too high.

Cutting the pylons as shown below will raise the pylons and fix the incorrect downward tilt of the engines. Trim as required so that the engines are at distances “K” and “L” above the ground, as shown in the ground clearance distance table.

Miscellaneous

Thanks to earlier builders, I was warned that the right rear stabilizer is mounted too high and must be lowered. I placed the aircraft in my popsicle stick supports, and lowered the stabilizer attachment point until it matched the opposite side.

Ready for Inspection