Fun-Tu (oz6759)

About this Plan

Fun-Tu. Radio control sport model by Bob Miller, plan #680, March 1977. Can be built as either a single or a twin.

Quote: "A sport twin or single engine aircraft for two .19's or one .40 built entirely from cardboard. Rugged, easy to build, and outstanding in performance.

The Fun-Tu is a twin engine cardboard airplane designed by Bob Miller, it is a logical evolution of his single engine cardboard model, the Quickie 500 (oz9170) shown in the January 1975 issue of RCM. The Fun-Tu is the third twin engine cardboard model designed by Bob Miller and it incorporates the best features of his first two efforts. The Fun-Tu is capable of performing the full stunt pattern. Stall turns, spins and touch-and-go's are a regular part of the flight pattern. The engine offset and wing dihedral increase the margin of safety for these maneuvers.

The simplified building techniques used in the Quickie 500 were incorporated into the design of the Fun-Tu. The use of non-cardboard material is kept to an absolute minimum while still maintaining structural integrity. The folded method of cardboard construction is used to provide greater strength and reduce the number of stiffeners, such as fuselage bulkheads and wing ribs, required to insure adequate rigidity. A discussion of cardboard's characteristics and nomenclature was presented in the Quickie 500 article and will not be repeated here. However, 125 lb test B flute No.3 white cardboard is recommended as the most suitable for the Fun-Tu airplane. It consists of 33 lb liners top and bottom with 26 lb, medium or flute. It is the lightest practical cardboard available for model construction on the basis of strength and good workability. Models made of this material will be comparable or lighter in weight to those using standard construction techniques without sacrificing strength.

For those of you with little or no experience flying twin engine airplanes, a word of caution is in order. The one big killer of twin engine models is over-use of ailerons at low speeds with one engine dead. Suppose the left engine quits and the left wing rolls down. The natural tendency is to apply down aileron on the left side. However, with the left engine dead, down aileron acts more like a dive brake than a lifting surface and yaws the nose of the airplane to the left, creating more problems, The correct procedure for the above left wing down condition is to apply right rudder. The resulting yaw will move the left wing forward and the right wing back. Because of the wing dihedral, the lift on the left wing will in-crease while the lift on the right wing will decrease and. thereby, correct the air-plane roll.

Another method which has proved helpful is the use of differential ailerons. In this method, the allowable aileron up motion is greater than the allowable aileron down motion. This is ac-complished by connecting the aileron control rods to the servo wheel at the 10:30 and 1:30 positions, where 12:00 o'clock is the neutral or dead position.

When flying twins, it is essential that the propellers are balanced to avoid excessive vibration. Vibrations due to un-balanced propellers are amplified for a twin over those of a single engine airplane because of their position off the centerline and because of the harmonic vibrations which may be set up. Contra-rotating propellers are not required. Be sure both engines idle well. Before doing touch-and-go's, be sure your engines come on strong. With low wing configurations, stiff gear are a must to avoid broken propellers on hard landings, so 5/32 in wire main gear is recommended.

The Fun-Tu is versatile and can be converted to a .40 powered single engine airplane as shown on the plans.

Contruction hints.

Glue: We recommend water base glue such as white glue or Titebond. Contact cement is not recommended since parts cannot be aligned when laminating surfaces. When laminating, weight components on a flat surface.

Folding: The scoring of the fold lines is done with a screening tool available at any hardware store. It consists of a handle with a 11/4" diameter radiused wheel at one end which is run along a straight-edge on the fold line.

Finishing: Cardboard gives a solid surface with no open areas to cover and is non-porous. The lightest, simplest and most inexpensive method is to give two coats of clear dope and two coats of colored dope..."

Update5/12/2016 : added article, thanks to Gunars.

Supplementary file notes

Article.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction