The TopModel 3.2M Pilatus Porter PC-6 ARF has proven itself as a worthy tow plane for the growing scale aero towing market. Although there are many fine engine choices, the Desert Aircraft DA-85 gas engine has also proven itself as a worthy power plant for this aircraft. It makes good power (8.5 hp) for its size and weight (4.3 lbs) and has a reasonable fuel consumption rate (2.2 oz/min @ 6,000 rpm). The mounting of this engine requires the construction of a motor mounting box, and TopModel leaves the dimensions and construction technique for building this box up to the modeler.
3.2M Pliatus Porter preparing to tow
On our Porter, we constructed this box from 1/4″ and 3/8″ aircraft grade plywood. The four sides were cut from the 1/4″ plywood and the firewall was cut from the 3/8″ plywood.
5 plywood parts of motor mount box
Here are the five pieces that will make the box. The top and bottom pieces are 5-1/8″ wide (side-to-side) and 5″ long (front-to-back). The two sides are 4-1/4″ tall (top-to-bottom) and 5″ long. The firewall is 4-5/8″ wide and 4-1/4″ tall.
Desert Aircraft Fire Wall Template
Using the template provided by Desert Aircraft, the firewall is cut out to accommodate the rear mounted carburetor.
making openings in the side panels
Using a 1-1/2″ hole saw, the sides are drilled to allow access to the carburetor adjustment screws and throttle and choke linkages.
using jigsaw to connect the 1-1/2" holes
The bottom piece is opened by drilling two 1-1/2″ holes and then cutting between them to make a slot for air to get into the carburetor.
Clamp pieces together while epoxy cures
Drill 1/8" holes for dowel pegs
Glue 1/8" dowels into holes
Cut the 1/8" dowels off flush
Sand the dowel pegs smooth with the surface
Dremel tool used to cut firewall opening
Wood strip used as gate to steady Dremel tool
Firewall ready for test fit of box
Hardwood triangle added to box/firewall joint
DA-85 installed on mounting box
