Cheetah, The

Model Airplane News, Mar 1998 by Randolph, Randy

ACCORDING TO Jane's "Pocket Book of Light Aircraft," the original Cerva CE.43 Cheetah had its first flight in 1971. Produced in France as a four-place airplane with a cruising speed of 192mph when powered by a 250hp Lycoming 10-540-C4B5 engine, it had a wingspan of 10 meters, an overall length of 8.4 meters and a sea-level rate of climb of 1,080 feet per minute with a service ceiling of 17,400 feet and a maximum range of 1,800 miles. These are all good numbers, but what it really has is a very nice arrangement of wing, tail and fuselage to make a good flying, R/C model airplane!

For some time, I have wanted to put one of my O.S. .15s to work, and the Cheetah looked like just the airplane for it. In fact, it has turned out to be one of the best flying airplanes my 20-year-old .15 engine ever snuggled into! It has all the characteristics of a trainer, yet is frisky enough to provide a lot of quality sport flying on a nice, low-fuel budget. With a low wing loading, it moves along rather quickly with modest power and slips through the wind very nicely; it is definitely not a calm-weather friend.

A number of liberties have been taken with the design that would probably cause a true scale believer to shiver, but all of the outlines and the flavor of the full-scale airplane have been pretty much retained. This airplane will not disappoint you; it is fairly easy to build and looks good in the air and on the ground. To build one, why not start with the wings?

WINGS

The first step is to make a template of the rib section and cut 22 ribs from fairly firm sheet balsa. You can saw them out all at once from a stack of blanks or cut them out one at a time by drawing around the template and making a "printed sheet." Select four ribs and trim 1/16 inch from the top and bottom of each, then trim 1/16 inch from each side of the main spar notches. These are the center-section ribs, and the enlarged spar notches are to make way for the 1/16-inch ply dihedral braces. Cut four gear-mount braces from 1/16-inch ply and glue them into place on four ribs- two left and two right. Cut the 1x1/8-inch notch in each of these ribs to match the ply braces.

Cut out the main spar webs and the TE sheet from 1/16-inch balsa. The dihedral braces are from 1/16-inch ply. As a general rule, I like to strip my spar stock from sheet stock because it gives better control of the finished product, but excellent spar stock is available from most hobby shops. The tips are cut from fairly soft 1/8-inch sheet.

Cover the plans with wax paper and pin the main spar and bottom TE sheet into place over the plan. Build each wing half by gluing the two ribs that carry the landing-gear mount, and the mount, in place on the spar and TE sheet with a spar web between them. Then add webs and ribs to the second centersection rib, and add the rest of the ribs out to the tip. The center rib will be added after the wing halves have been joined to create the servo well. When all the ribs and webs are in the proper places, add the top main spar, the front top spar, the LE and 1/8-inch square TE. Taper the 1/8-inch-square TE strip to blend into the rib section. The other wing half is built in the same way. While the glue is curing, cut out the four 1/16-inch ply dihedral braces.

When the glue has set, separate the wing halves, prop the tip of each panel up 3 inches, and sand the dihedral bevel into the center spars and the LE and TE. Pin one panel flat on the bench, and raise the tip of the other 6 inches; then join the halves at the center with the dihedral braces. Clothes pins are excellent clamps for applying gluing pressure to the ply-to-spar joints.

Cut the two center ribs apart at the main spar notch, and fit the two aft pieces between the spar and the TE as shown on the plan. Form the servo well by adding a piece of scrap, 1/8-inch sheet between these two as shown. The two LE rib pieces are joined and glued between the main spar and the LE at the center. The bottom LE spar should be installed at this time. Add the top TE and the top and bottom center-section sheet, leaving the servo well open at the top. Glue the wingtips at the center line between the LE and TE of the outboard ribs. Use pieces of spar stock between the spars and the tips and soft scrap balsa at the TE. Sand the completed wing.

Bend the aileron horns and epoxy the brass tube to the wing TE as shown on the plans. Be careful not to allow any glue to seep into the tube/wire bearing. Cut the ailerons from 1/4x1-inch aileron stock, trim the outboard tips to blend into the wingtips, and groove and drill the LEs to receive the aileron torque rods. The ailerons will be added to the wing when it is covered.

TAIL SURFACES

Build the stab over the plan. Though not absolutely necessary, the 1/16-inch ply spar doubler goes a long way toward reducing "hanger rash" when loading and unloading the airplane. The 3/16x1/8-inch diagonal braces just about eliminate the chance of warping and add little to the weight. When the stab is complete, use masking tape to attach the elevator to it, then sand both to final shape. The fin and rudder are cut from 3/16-inch sheet. The fin LE is hard, 3/16-inch sheet to provide a good anchor into the fuselage top sheeting.