Air Tractor AT 502

Mid 2005 I was looking for another project. I didn’t really have any particular type of aircraft in mind when I happened across the website www.teamduster.com in the United States, they had on offer a 1/6 scale Air Tractor AT 502 crop duster. Spec’s for it were 100 inch wingspan, 16lbs approx weight and 2 stroke engine in the range of 1.8ci.

I went ahead and ordered a short kit from them which included laser cut plywood fuselage formers and balsa wing and tail group ribs. Another order was placed from a different supplier for the remainder of the required wood and all of the hardware.

           

Tail Surfaces. 
Construction began as usual with the tail surfaces, built up and fully sheeted as per standard methods.On the back of the rudder I opted to build an operational boost tab, this was quite an easy addition that looks the part and probably helps to reduce the load on the rudder servo. 

Wings.
Wings were up next and construction was also standard with balsa ribs, leading and trailing edges and shear webs. The spars are ¼”x 1/2” and were cut from cedar which were light and to me seemed a little to flexible however they were used and have been fine. With a wingspan of 100 inches the plans called for a two piece wing. A phenolic outer tube was built into each wing panel at the correct angle to accept a length of 7/8” 6061 T6 aluminium tube, this tube passes through the fuselage and into each wing panel to produce the correct wing dihedral. A wooden dowl protruding from the root rib locates into a hole in the fuse side to hold the wing at the correct incidence. The wings are secured via a bolt from inside of the fuse into the wing root rib. The wings are fully sheeted with 3/32” balsa, ailerons and flaps are of standard construction. 

Fuselage.
Fuselage construction is also fairly standard being fully sheeted with 3/32” balsa and ply formers. I decided early on that I wanted to build in a working hopper setup so this was designed into the fuse on the centre of gravity. It is filled through an opening hatch door on the fuselage top. A 180 degree retract servo was rigged up to open the outlet door on the bottom. It had to be removable to gain access to throttle servo, fuel tank and receiver and associated wiring. As of yet its operation is untested. 

            

The cockpit canopy is fibreglass and was purchased from a supplier in USA. The window openings were cut out and clear windows glued in. A simple but effective instrument panel was cut form a sheet of 1/16th ply. The instruments were saved from the internet, sized and printed out on photo paper. Each individual instrument was cut out and simply glued to the back of the panel before the panel was glued in place. I decided to build the fibreglass engine cowling myself. I used a simple method I saw in a magazine, first a block of foam was tack glued to the firewall and then shaped. The foam and forward fuse was then covered with glad wrap to stop the resin soaking into the foam. Several layers of heavy glass cloth were dry fitted to form the cowl then an old stocking was stretched over the nose and back down the fuse and taped to hold the dry glass cloth in place. Resin was then brushed on until the cloth was thoroughly wet through. When the resin had dried it was sanded back while still attached to the fuse. The glad wrap that was applied simply allowed the cowl to be easily removed.