The Cox PT-19 CL model has been around since the 1960s, ceasing production in the '90s. Show a picture of one to any older modeler and they are sure to have a story involving one. They weren't necessarily known for being good fliers but got an unmeasurable number of people into the model airplane hobby. Today they are sought after as nostalgic collector items.
I always thought it would be cool to have an RC version of one. But it had to represent the Cox model, not just be another semi-scale PT-19 model. Wanting something new for indoor flying, I thought this would be the perfect opportunity.
The wing and tail feathers of the model are cut from 3mm Midwest Cellfoam (similar to Depron). They are covered with yellow Top Flite Econokote to give them the proper plastic look. The wing's airfoil was molded into it by pressing it into some molds while applying the Econokote.
The fuse was constructed of DTFB with the paper removed. It is a simple U-shaped cross-section, with the top comprising of three layers. This was then sanded to shape. This was covered using Top Flite Monokote. I did run into some issues with the heat required to form the Monokote around the tight curves, but all-in-all it came out ok.
After final assembly, the model was outfitted with a Turnigy 1811-2000kv outrunner and an HTIRC 12A ESC. The prop is a vintage Top Flite nylon prop I had in my collection. I used Emax ES-9251-II servos for the tail and a Turnigy 3.6g for the ailerons. The receiver is a Spektrum AR6100.
The windscreens are cut from some scrap lexan I had and then framed with black vinyl. The pilots, dummy cylinder, and spinner nut were all purchased from
Willy Nillies.
Final weight RTF came out at 128g (4.5 oz).
A fully detailed build log can be found here:
LINKY
I test flew the PT on 3/3. The balance was spot on. Ground handling is terrible, but I expected that. The Monokote covered tail skid has no traction on a smooth polished basketball court... I may have to look at swapping that out for a tailwheel. Power with the vintage 6x3 prop was enough, but not much extra. I changed to a 6x4.5 for the second flight and it seemed better. Unfortunately, I flew it into a wall shortly into the second flight so I didn't have a chance to feel it out much. Damage was minimal but did ground me for the evening.
SUMMARY
I am very happy with the way this project turned out. It accomplished everything I wanted. I did learn a few lessons along the way too. Using standard temp covering, like Monokote, on foam worked much better than I expected. The only place I had an issue was the tight corners around the nose that required a lot of heat to get the film smooth. The final weight is very acceptable and allows for indoor flying. I think I could have achieved a lighter weight by painting the foam in lieu of the film covering, but I would not have achieved the "plastic" look I was desiring. The lack of a tail skid or wheel with traction proved to make take-offs difficult. This is something I had actually learned on previous projects but went with the covered skid in order to mimic the plastic skid on the original Cox model. It should be very easy to retrofit a wire skid or tailwheel and help the ground handling. All-in-all, I see this one staying in my fleet for quite a while.
