Cox 40 Tailwind Trainer ARF

 

Many of the current generation of experienced R/C pilots cut their modeling teeth on COX products in their youth. The COX plastic, ready-to-fly control line airplanes gave thousands of young people their start in model aviation. They were affordable, simple to assemble, easy to start and to fly. Even absolute novices could get them up in the air and usually back down. If the landing was less than successful, a quick dab of glue was all the airplane needed to fly again.

The COX Tailwind Trainer 40 ARF is a purpose-designed, Almost-Ready-to-Fly (ARF), basic trainer that may well introduce the next generation into the world of R/C aviation. Like its control line predecessors, the Tailwind is affordable, easy to assemble and to fly. The label on the box reminds us that COX has a world-renowned reputation for superior engine design and innovative products.

They believe that their new “WINGS” product line will bring high quality ARF models to the hobby market. Their aircraft line will feature laser-cut parts, factory assembled components, fiberglass (not plastic) cowls and wheel pants, US specification hardware etc, and be covered in SIG Aerokote.

The box also states that the Tailwind Trainer 40 ARF was designed as a primary radio control trainer aircraft for the first time pilot. (An ARF is not a product that is ready to fly out of the box. There is some building and assembly still required before you can go flying.)

Because this is an airplane that is purpose-designed to be a primary radio control trainer aircraft for the first time pilot, it is expected to have loads of built in stability and is intended to have you flying on your own as quickly as possible. It also is intended to give you the piloting skills to move on to more aerobatic aircraft.

A standard message to the reader is that a less experienced modeler would be well advised to seek assembly advice. This can be best obtained by joining a Radio Control Flying Club. These clubs are where you will find the more experienced modelers who are most willing to pass on their knowledge and experience.

Although the airplane is intended for use with a 2-cycle motor, it was decided to use an equivalent 4-cycle motor because this was the engine that was available at the time of building. It was also decided to mount the engine sideways to better position the carburetor in relation to the fuel tank and to direct the exhaust gasses away from, and below, the airplane. This makes the model much easier to clean after a flying session.

BOX CONTENTS

 

Photo 1              Photo 2

The COX Tailwind Trainer 40 comes in a white box with a picture and specifications on the lid. The parts were very well packaged and showed no signs of any shipping damage. The box and the box-lid were used to hold the parts during construction so that none of the parts could become mislaid. A neat building practice is to cut the picture out from the box lid and pin it to your workshop wall for visual reference and inspiration during the construction.

All the major airframe components are pre-assembled. The fuselage comes with the holes for the wing dowels, and the slots for the stabilizer and fin, already pre-cut. However, you have to locate them by feel under the covering. The blind-nuts for the engine mount and the steerable nose landing gear support were already pre-fitted. The engine bay area was already fuel-proofed and ready for the engine mount.

Photo 3

The wings have a black strip underneath on one panel to help in orientation during flight. The Ailerons are not attached and use Mylar hinge material.

 

Photo 4               Photo 5

The stabilizer is a one-piece item and the elevator will be attached with Mylar hinges. The fin also needs to have the rudder attached with Mylar hinges.

Photo 6

A recommended practice is to open up all of the bags of parts that come in the box. Check that everything is there against the contents listed in the manual. This action serves two very good purposes. First, you find out if anything is missing and second, you familiarize yourself with all of the parts. This will make the building time much shorter and less confusing.

There is a good collection of hardware that comes with the Tailwind 40. The nose-wheel was smaller in diameter than the main wheels. This proved to be necessary to allow the airplane to “sit” level on the runway,

The wing-dowels were approx 3/8” in diameter. This was nice to see because thinner diameter wing dowels tend to bend with strong rubber bands, especially over time. The hardware included a complete set of hinges, control horns, nose gear steering arm, 2-56 pushrod wires, clevises and a spinner.

The large fuel tank would be good for long flight-times. COX had included plenty of fuel tubing to complete the “plumbing” later on in the construction. The six large and very strong rubber bands were included that proved to be up to the task of holding on the wing.

 

Photo 7          Photo 8

The main undercarriage was made out of “springy” chrome-plated wire (photo 7). This 5/32” landing gear would handle less than gentle “first landings”. The engine mount (one half shown in photo is not used as the primary support for the nose-wheel leg. The engine mount is designed to accept several different engines. It also permits engine movement fore and aft to aid in the adjusting of the engine weight to achieve the best center of gravity.

The mount was just right when reused to reposition the OS 52 FS engine sideways.  Two of the existing blind nuts positions were used and the other two fitted to two new holes that were drilled in the firewall. The muffler was positioned to direct the exhaust gasses down and away from the fuselage and wing. This made flight operations a very clean exercise.

 

Photo 9               Photo 10

The aileron servo tray had been pre-built and shaped underneath to match the dihedral of the wing. This is unusual for an ARF airplane kit and COX is to be commended on this extra quality step. The supplied spinner was not used on the OS 52 FS just to make changing propellers easier during the flight tests. The supplied spinner will work with any 40 or 50-sized glow engine and adds to the airplane’s clean looks. Instead, a Higley aluminum nut was substituted. An 11 x 6 APC proved to be the best propeller for this model and engine combination.

Photo 11

The control horns used three bolts and had a wide base to transfer the working loads of the control surfaces. Horns like these are more often seen in higher priced models.

ADDITIONAL EQUIPMENT

 

Photo 12                Photo 13

To complete the COX Tailwind Trainer 40 ARF, additional equipment needed to be collected and obtained. Any four-channel radio will more than do the job. For this review, the radio system chosen was a tried and proven JR X388S transmitter and a JR R700 receiver. This transmitter would easily support the local flying club “trainer” buddy-box radio and would allow other club members to fly the Tailwind. (I fly a Mode-1 transmitter; most of the local club members fly Mode-2. Mode 1 transmitters have the elevator control on the left stick and the rudder on the right. ).

Photo 14

 The instructions and the box list the additional equipment needed to complete the Tailwind.

Ø     Four-channel radio control system with  

Ø     40-50 sized 2 or 4-cycle engine

Ø     Propeller to match

Ø     Thin and medium CAA adhesive

Ø     5 and 30-minute dry epoxy adhesives

Ø     Silicone adhesive

Ø     Sharp modeling knife

Ø     Modelers “T” pins

Ø     Crosshead screwdriver (Phillips)

Ø     Metric Allen wrenches

Ø     Crescent wrench

Ø     Electric drill or high-speed rotary tool

Ø     1/16”, 5/64” and 1/8” drill bits.

Ø     1/2” thick foam rubber

Ø     Sealing iron and filter.

Equipment actually used to complete the model;

Ø     JR X388S Transmitter and R700 Receiver 

Ø     4 standard S3003 Futaba servos

Ø     JR switch with charging lead

Ø     JR 1100 mAh NiMH receiver battery

Ø     Pacer CAA adhesive accelerator

Ø     OS 52 4-cycle engine

Ø     11 x 6 APC propeller

Ø     Sullivan fuel filter

CONSTRUCTION – GENERAL

The quality and depth of the instruction manual is a great feature of this ARF. It is very complete, well written and clearly designed for a beginner. It goes beyond the construction and gives very good advice on set up and flying. The manual begins with advice on heat-shrinking the covering to remove any wrinkles induced by storage temperature changes. This may well not be the easiest of tasks for a beginner. (Ed. Note: This task is not always easy for an experienced model builder given the various types of covering materials used on today’s ARFs. But since the Tailwind uses SIG covering, this task is not as difficult as it otherwise could be.)

It needs to be highlighted that there is a big difference between an airplane designed for a beginner pilot and an airplane designed for a beginner builder!

The first task is to re-shrink the covering which may have gone a bit “saggy” or wrinkled. I strongly advise that new “builders” seek the help of an experienced modeler for this task.  All of the decals had already been applied to the model. A heat iron cannot be used on the decals. A heat-gun needs to be carefully used to tighten the material around the decals to avoid melting them. If you don’t know how to do this, seek help, FIRST

WING ASSEMBLY

 

Photo 15           Photo 16

The hardwood spar provides good strength in this wing, but the surface joint around the edge of the rib is also part of the strength of the assembly. It is best that you trim the excess covering off root ribs with a sharp knife or razor blade. To join the wings, it is best to use 30-minute epoxy resin. This gives you plenty of time to align the two wing halves. It also gives you time to make final adjustments and wipe off any excess glue with denatured alcohol.

Photo 17

A spring clamp used inside the servo recess area provided very good pressure and alignment while the 30-minute epoxy-resin glue hardened.

 

Photo 18              Photo 19

Care needs to be taken when fitting ailerons to the wing. No glue can be allowed to touch the exposed torque rod support-tube. Otherwise it will not rotate later. Masking tape was used between the wing trailing edge and the aileron torque-rod to prevent excess glue from sticking the aileron to the wing. The Mylar hinges were secured later with a few drops of thin Cyanoacrylate Adhesive (CAA) per hinge on both sides. It is easier to do this in these two stages rather than rush and try to do it all at once. For complete details how to install these excellent hinges, read the Sport Aviator article “Installing Mylar Hinges” in the Flight-Tech Section.

Photo 20

The instructions show the ailerons with equal movement up and down. This is not the best configuration for a flat-bottomed wing. It really helps the airplane to fly if it is built with “aileron differential”. Aileron differential is when the up aileron control has more movement than down one.

With a flat-bottomed wing, the down-going aileron creates more air drag than the up-going aileron. This causes the airplane to yaw a little in the direction opposite the intended roll when the ailerons are applied, which in turn results in the nose of the airplane pitching up and swinging the wrong way when entering a turn. (This is called adverse yaw).

ENGINE MOUNT

 

Photo 21          Photo 22

The new side mount positioning of the engine required the removal of the right-hand cheek forward of the firewall.

The edges of the removed side-cheek and the covering around the engine bay were sealed with thin CAA. The mounts lined up on a couple of the existing blind nuts. New holes were drilled using the mount as a guide. The old blind-nuts were reused in these new holes and mount was ready to accept the engine. Use thread-locker to keep the engine in place over time.

ENGINE

 

Photo 23         Photo 24

With the engine mount already in place, the engine was fitted. This was done last because the mass of the engine was used to obtain the best center of gravity. As it turned out, the engine needed to be bolted as far back as it would go. The receiver battery had also been positioned as far to the rear as it would go.

The muffler of the OS 52 FS does not touch the side of the fuselage so no more material had to be removed. The needle position on the back of the engine was rotated 180 degrees to point upwards and better position the throttle arm in relation to the throttle servo. The throttle arm on the carburetor was connected with the wire provided in the kit. The pushrod to the throttle servo had to be bent a little to one side. This kept the pushrod/wire “run” near the side of the fuselage and was necessary to clear the receiver foam wrapping and the fuel tank installation.

It is important to set the throttle so that it correctly uses the swing of the servo arm. In the low-throttle position it still needs to have some remaining servo arm rotation. This will let you close the carburetor and turn off the engine from the transmitter. This can be activated with a kill-switch or with the throttle-down trim lever from your radio.

The fully-open throttle position should be set just a fraction before the travel-end-stop of the carburetor so that the servo does not “stall” when in that position. This will prevent any excessive current draw and lead to longer battery life and safer flying sessions.

MAIN WHEELS

 

Photo 25        Photo 26

The COX Tailwind 40 comes with pre-bent main undercarriage wires. These wires fit into a pre-drilled slot in the bottom of the fuselage. To make sure the wheels stay on, grind or file a notch to match the wheel-collar screws. Even if the screws come partially loose, the notches will prevent wheel-collars from coming off in flight.  

 

Photo 27         Photo 28

Tighten the screws firmly, but do not use excessive force or else the screw threads will strip or be very hard to remove later. Each screw was treated with screw-locking compound to further help in wheel retention. The wheels were a good size for grass runways. The collars were positioned with the set-screws facing rearward to keep the dirt out of their sockets.

NOSE GEAR & NOSE-LEG STEERING

Photo 29

The steerable nose wheel leg is supported by its own nylon bracket that is attached using the factory installed blind-nuts. The nose-wheel leg and steering arm were simply pushed into place and secured with wheel collars: The pushrod for the steering arm lined up with the hole that was already in the fire wall. The steering pushrod wire was connected on the opposite side of the rudder servo arm. This gives the correct direction to the wheel when the rudder is applied.

STABILIZER ASSEMBLY

Photo 31

Fitting the stabilizer is probably the most critical part of the assembly of any airplane. This holds true for the COX Tailwind 40. The stabilizer fit, before gluing, was good and meant there was no need to adjust the slotted opening. The fuselage has a square cross-section. This allows a flat surface to be used to set the height of each stabilizer tip on either side of the fuselage.

The fuselage was weighted down and a square used to measure the height of each stabilizer tip. 30-minute epoxy-resin was used to attach the stabilizer. The slow curing action of the glue gives you plenty of time to set the position correctly. Then allow it all to harden for at least two hours at a room temperature of at least 70 degrees F. (Ed. Note: Make sure that the stabilizer tips are equidistant from the center of the fuselage at the front of the wing opening. Also be sure that the stabilizer is in the same horizontal plane as are the wings.)

VERTICAL FIN

A 90-degree square is a good device to help in lining up the fin. Only a slight amount of side-pressure was required to hold the fin straight while the glue cured. Using 30-minute epoxy-resin gives you time to make this alignment before you pin the stab in place. The modeling pins secure the parts until the epoxy has cured.

BATTERY INSTALLATION

Photo 32

The 1100 mAh battery was wrapped in foam and fitted behind the trailing edge of the wing and over the rear control rods as shown in photo 32. There was an existing cut-out for the switch on either side of the fuselage. The switch was positioned on the left-hand side of the fuselage which was the opposite side to the exhaust of the engine. This keeps unwanted oil out of a critical electric part.

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