Rathgeber's "Minimum" C/L Speed Article & Plans
March 1957 American Modeler

March 1957 American Modeler Table of Contents These pages from vintage modeling magazines like Flying Aces, Air Trails, American Modeler, American Aircraft Modeler, Young Men, Flying Models, Model Airplane News, R/C Modeler, captured the era. All copyrights acknowledged.

If you have been looking for an unusual project that should build fairly quickly, cost very little, contain non-standard materials, and qualify for a vintage design contest, then Rathgeber' "Minimum" fits the bill. It is a 1/2A control line speed model with about an 8" wingspan that appeared in a 1957 issue of American Modeler magazine. It does not appear to have been intended for serious competition, but given the single-line control and extremely high thrust-to-weight ration and minimal drag design, it might have been a contender back in the day. Designer George Rathgeber does not give specifics on timed flights. My guess is that it was a handful to fly due to lack of tail feathers.

Rathgeber's "Minimum" C/L Speed

By definition minimum is the least quantity or amount possible. Here's our attempt to arrive at the minimum quantity in a Half-A speed model The simple design results in extreme low weight of 2 7/8 ounces and short construction time. A single line and elimination of the empennage reduce parasitic drag.

The plane wall designed around the Cox Thermal Hopper engine. An aluminum Ansco 120 color film pack was used as the fuselage. These cans are available at color film processing shops.

The wings have a symmetrical airfoil; it is not necessary to differentiate between the left and right until joining them. The spars do not go through the fuselage. Join the two wings with rivets and glue them to the male half of the aluminum can as shown in the plans. Be certain the wings are on center line of the can and have zero incidence.

(When the most efficient wing tip guide hole is determined by flight tests remove the metal containing the remaining holes with a file or grinder.)

The mounting flange on the Cox Thermal Hopper engine is slightly larger than the front end or female half of the aluminum can. This was disregarded in the original construction but it can be compensated for by filing the engine flange down to the proper diameter if you insist.

Engine mounting bolts are 2-56 x 1/4" brass screws. Nuts must be filed away on one side to fit inside the aluminum fuselage. Two 2-56 x 1/4" screws hold the fuselage sections together. The screw on the right side has a flat head, so depress the aluminum around the screw hole to simulate a countersink. Also depress underneath aluminum to allow slide fit of the two fuselage halves.

Complete the construction of the engine cowling line by following the instructions on the plan. First cover the engine intake and exhaust parts with tape to prevent dust from entering the engine. Apply "paste" to the motor in heavy layers. Allow it to set; carve it to size after a few hours. This engine faring will become very hard when completely set.

To finish the cowl and balsa portion of the fuselage, brush on a few coats of a thin talcum powder and dope mixture on balsa. Apply ten coats of a fuel proof colored dope, sanding with #600 wet and dry paper between the fifth and final coats. Rub down with automobile compound; polish with a good paste wax.

The gas tank is a pressure type. The fuel is injected with a syringe which has a six inch piece of flexible tubing forced partly onto the nozzle. The inside diameter should fit snugly with the outside diameter of the fuel line used. To "gas up," remove the fuel line from the intake nozzle and squeeze fuel into the tank with the syringe. Clamp the fuel line tight with a pair of pliers and replace line on nozzle with the pliers. Make sure the needle valve is completely closed before starting this operation.

A hand operated geared starter is a great asset in starting the engine. Gradually open the needle valve as prop turns and instant starting occurs.

In test flying, select a guide hole slightly to the rear of the C.G. This will give a nose out condition and keep the flying line taut. In subsequent flight test, the forward holes should be tried until the maximum speed is attained.

A hand launch is used with the "Minimum." Important elements for a successful hand launch are a smooth follow through motion of the arm and hand. The nose of the plane should be inclined about 20 degrees when launched. Keep the flying line tight and launch at a tangent to the arc.

-George Rathgeber

Rathgeber's Minimum Plans

Posted November 3, 2018