3013 La Cimice Verde RPU 20

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Robert Schlickewitz

in Series 3000 – Sheet Wing, Profile Fuselage RPU Models

Span 59 cm / 23 in

Weight 69 g / 2.43 oz ready to fly

The concept:

glider-like appearance
profiled balsa sheet wing
V-tail
good flight characteristics
few parts
easy to build
RPU 20

Name: Cimice verde is the Italian equivalent to shield bug or green bug.

What is RPU?

RPU stands for rubber power unit.

This is a device designed for the modelbuilder who likes to fly many models with one only powerunit. Main material of the RPU comes from the grocery store around the corner: four barbecue skewer chopsticks. Add to them scratch balsa, a hook made from piano wire, some black rubber and a commercial plastic airscrew. That’s all.

The unit is attachable through two pieces of Velcro tape and can thus be used for example first on a little Spitfire five minutes later on a Mitsubishi Zero and ten minutes later on a Macchi Folgore of the same configuration. You build only one RPU and use it on as many modelplanes as you wish.

Models with RPU use the same asymmetrical principle as is known from No-cal models. From the one side they look handsome as from the other the power unit disturbs the harmonic view considerably.

Generally there is no great difference between the flight performances of a balsa sheet profile model with built-in rubber motor and a model flying on a RPU.

Why not try both principles? Among the plans range of beginner.zone you will find models of both categories. Sit down, build, fly, compare!

I developed and tested three different types of RPUs.

The one for small models of 30 cm / 11.8 in to 40 cm / 15.75 in wingspan is the RPU 20 (lenghth 20 cm / 7.9 in).
The one for medium sized models with a span of 40 cm / 15.75 in to 60 cm / 23.6 in is the RPU 30 (length 30 cm / 11.8 in).
The one for larger models of up to 80 cm / 31.5 in wingspan is the RPU 40 (length 40 cm / 15.75 in).
The RPU 40 is made from slightly different material. Instead of the skewer chopsticks it uses two strips of bamboo wooden sticks (400 x 9 x 3 mm). The rest is identical.

Building the balsa sheet model La Cimice Verde RPU.

Materials:

Fuselage: B 1.5; fuselage stiffener: B 1; wing: 1.5; wing ribs: B 5; wing support: B strips 4 x 4; V-tail: hard B 1; V-tail support: B strips 3 x 3; linen band width 10 mm / ½ in; Velcro tape with adhesive backside; ballast: 15 g / ½ oz steel or lead.

Assembly:

Cut out balsa parts in accordance to plan. Sand well. Mark position of fuselage stiffener on left side of fuselage part with pencil using a ruler. If coloring is desired, do it now.

Fuselage:

Fix fuselage left side up with needles on building board. Cement fuselage stiffener on fuselage according to pencil markings. Continue with cementing wing support strip and V-tail support strip into their respective places and let dry. Hold in place with needles (photo).

Take fuselage from building board and cement wing support and V-tail support on right side. Let dry.

Wing:

Wing consists of a right and a left wing half. Reinforce both wing half leading edges with linen band as to be seen on photos. Let dry. Fix right wing half on building board with needles. Underlay left wing half tip in accordance to required dihedral. Join both halves and cover wing half joining area with linen band. Let dry. Now cement one rib on left wing half at given place. Hold with clothespins or clamps until cement is dry. Repeat procedure for the right wing half (photo). Let dry.

If wing has the tendency to rest only on one side then it is too heavy on this side. To compensate the imbalance disperse an amount of white wood glue on the opposite wing half’s tip area. Do it if necessary twice until balance is obtained. (photo)

V-tail:

Reinforce both V-tail halves leading edges with linen band as on photos and let dry.

Fix one V-tail half on building board with needles. Use self made template to get the other half into given angle and cement. Visual check symmetry from all sides. Let dry.

Final Assembly:

Put fuselage on so called “third hand”. Cement wing on wing supports using needles to hold in place. Doublecheck visually symmetry. Let dry.

Repeat procedure with empennage (photo). Again check symmetry!

Stick two pieces of Velcro according to your RPU on right fuselage side.

For balancing your model properly install RPU and start testgliding over tall grass. Add ballast according to your test results. Note given position of CG on plan.

Remember correct center of gravity (CG) is essential for successful flights.