Ringmasters Flying Club


Hi Tony,


When I sent you the pictures of the Sport Jet I said I was working on a monoline trainer so on this disc are pictures of the assembly of that one.  The plane was drawn by John Hunton in 1990 and can be set up with a bell crank as a 1/2A sport or with a torque unit as a monoline trainer.  I chose the latter since I want to re-learn the ins and outs of flying monoline again after so many years and get back into a little bit of speed flying. 


I have the plans and can provide a copy to anyone who is interested.  It is simple to build and can probably be done completely from the pieces of balsa scrap we all develop as we build.  The only wood I bought for this one is a single sheet of 1/8”x4” balsa for the top & bottom wing plies.  The only metal I bought was the brass tubing for the tank and the monoline torque unit.


The assembly is simple and straight-forward.  All the parts can be rough cut up front right from the plans.  Since the wing is made from three plies of 1/8” Balsa, I recommend they be glued using Z-Poxy and weighted down on a flat surface for 24-hours.  Use of water soluble glues like carpenter’s glue or white glue will usually cause a warped wing that is impossible to sculpt into a good airfoil.  I chose to cover the wing in ½ oz. fiberglass for a bit of durability but that is not really necessary.  You will see from the pictures that the fuselage is a series of parts that are installed around the wing from each side and then sanded into a flowing shape.  The pushrod goes down the center and the only consideration is full movement without the offset hitting the back of the tank when it is full forward (in the up elevator position).


The two bulkheads (one for front of the plane and one for the motor mount) are identical and made from ¼” plywood.  The bulkhead on the plane is fitted with blind T-Nuts for mounting screws. The motor mount is ¼” Maple and it is all epoxied together before a light-weight Balsa bottom chin is sculpted to close the bottom of the motor mount.  The tank is a simple affair made from ½’ diameter brass tubing and construction is shown on the plans.  The tank holds ½ ounce and can be removed from the fuselage directly through the bulkhead incase one wants to use a pressure bladder for some added performance.  Landing gear is a simple bend of wire inserted through the motor mount and then bent to final shape.  Wheels are light-weight flat plastic wheels and I simply epoxied a couple of 4-40 nuts on as keepers.


Hinges for the rear elevator were sewn with Dacron threads from the sewing store.  I chose this method because with a light-weight 1/2A plane, the monoline is only .014” diameter music wire so the makeup of the torque unit and all the internals must move extremely free to get full elevator movement when the stylus on the monoline handle is moved to the up or down position.  The wire inside of the torque unit is only .010”.


Everything is given a coat of clear Z-Poxy to fuel-proof the finish.  You will note from the pictures that I did not really put in much time to finish sand the craft since I figure it is a trainer and will probably get fairly well beat up before I am finished with it.  But, I still have enough scrap to build another if I choose and it only took about 15 hours start to finish.


The motor is a slightly modified Cox Tee Dee .049 but I think a regular Cox Baby Bee or Golden Bee .049 would work well by leaving the hole in the bulkhead out and tank out and then mounting the motor directly to the plane’s bulkhead.  Might move the CG a bit that would need adjusting but would still make for a very inexpensive fun flyer.  My motor has an aftermarket cylinder that is ported a bit better than the originals, larger head and matching red anodized parts.  The venturi has been slightly opened up for better air flow and the carb is mounted on a billet aluminum mount instead of those notorious OEM plastic mounts that crack and leak.  The needle valve is still stock although I do have a micro-fine needle from Texas Timers that can be installed if I decide to run a bladder.  The motor is turning an APC 5.75” x 4 pitch composite prop and makes slightly over 20,000 RPM as shown.