Although I’ve always enjoyed flying 049 size airplanes, one thing I don’t like is the short flight time that you get from a standard Cox .049 engine with an integral fuel tank. The logical solution to this problem is to use a “product engine”. A product engine is one of those engines found on the plastic airplanes that Cox used to sell millions of. They come with a plastic backplate with mounting holes and an external fuel nipple for use with a remote tank.

For this project I built a Q-Tee and used a product engine I got from eBay, and a one ounce Perfect metal fuel tank. I soldered forward pointing brass extension tubes to the tank and drilled holes in the fuselage with the correct spacing to match the tubes. Here’s a photo of one tank in its unaltered form, and the fuselage with the other tank already installed.

To get the brass lines through the holes, I inserted a 1/16″ wire through one hole into the radio compartment, then stuck the brass tube over the end of the wire. When I pushed the tank into the tank compartment, the 1/16″ wire led the tube right through the hole. Then all I had to do was rotate the tank slightly to get the other tube through. Then I epoxied both tubes right into the firewall for an oilproof installation. Here’s the tank as seen from the radio compartment. You can just barely see it above the receiver.

The engines with integral tanks make the incoming air charge go through a tiny tube, which robs the engine of power.  The product engine backplate actually increases performance by having a shorter air induction path.  I originally had a Black Widow cylinder on this engine, which has dual bypass ports.  You may notice that I like to build Q-Tees without landing gear for a better glide after the engine dies.  The lack of landing gear combined with the high power engine made this a terribly overpowered airplane that I didn't much enjoy flying.

So I took off the dual port cylinder and piston and replaced them with a set from a single port Cox engine. I also put on a less efficient black Cox propeller.  After all of this fine tuning, this plane turned into a really nice flier. 

Here’s the radio compartment. The Q-Tee is a nice little plane for learning to build from scratch, and it’s a great subject for experimenting with design modifications.  Be sure to check out my other Q-Tee article about building swept back wings to make it easier to get the center of gravity right.