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Construction Article Heading Transformer heading

3 function powered model that is a totally new concept in model flight training - in three stages the Transformer evolves from a simple two function glider into a four function aerobatic sports model!


by Martin Cochrane Transformer pic

Transformer is a model with a real difference and one that is set to revolutionise the approach to model flight training. One model is used in the following configurations:
1. Two function glider
2. Three function powered model
3. Four function trainer/aerobatic model.

A small .20 - .25 motor is all that's necessary for power and four channel radio gear is essential.

The Transformer can be easily changed into any configuration at anytime without rebuilding or major readjustments being necessary.

A beginner is far safer learning to fly with a stable, slow flying two function glider to become familiar with handling than jumping into the deep end with a fast, twitchy four channel radio control sports model. Agreed?

Following a three stage training program to gradually learning to handle one function at a time makes a lot more sense. It's even better when you don't need to build a new model for each stage of training - the Transformer does it all in one.

The secret is in the wing design and nose area of the model. The dihedral wing is built with ailerons similar to any other basic aileron trainer model but has removable polyhedral wing tip panels. As a glider the Transformer flies with the polyhedral wing configuration with the ailerons taped down and aileron linkages disengaged. For later training as a four function sport trainer the reverse process is carried out. As a glider the noseblock is held onto the firewall with one large wood screw. The noseblock is removable and interchanges with the engine fitted on a radial mount which bolts onto the firewall for powered flying. Simple!

Now let's get down to some building.

CONSTRUCTION

WING

The wing on this model is straight forward with "D" box section, sheeted leading edge and webs between each rib from top spar to lower spar making it simple but strong. After photocopying the plan I proceeded to cut out wing ribs template from plan (using spray glue on templates only.) I then positioned the paper cut outs onto sheet balsa. You'll need 16 W2 ribs of 1.5mm balsa. Everyone has their own idea on cutting ribs, some do it singularly, but I like the stack and cut, sand to shape method. It's quick and every rib is the same. Wing tips W3 and W5 are 6.5mm balsa. You need two of each. The outer tip panel root rib and main wing tip ribs are the only 1.5mm plywood needed to be cut and should pose no problem as there are only four needed.

The plan calls for 6.5mm x 6.5mm hard balsa spars which I replaced with spruce as it is a personal choice only.

Once all parts are cut out and sanded construction on wing will be able to be started with the positioning of the bottom front and rear spar over the plan.

Drop in all W2 ribs, making sure that all are at 90 degrees to bench top. Next W1 ribs (2 off) are dropped into position allowing for dihedral angle of main wing panels.

Next is W3 for main wing outer tip and is also set at 90 degrees to bench.

Glue all joints now and drop in top spar and glue in place.

Next comes trailing edge and leading edge stock, which is glued in position and sanded to shape later.

Once panels are dry, continue the wing construction with the adding of webbing between ribs and spars, which start from the inner W1 rib to the outer most W2 rib. Remember that all webbing is glued in with grain vertical.

Sand any high spots on webs level with main spars so that leading edge sheet will glue neatly along spar.

Next comes the setting up of the outer dihedral box which is located between the top and bottom spar at the wing tip. This is a simple affair in that all that is needed are 2 x 1.5mm ply webs front and rear of the main spar between W3 and W2 ribs. Epoxy in place making sure not to fill box section with any glue drops.

Transformer pic

Now your main panels are ready for the 1.5mm leading edge sheeting. Put on the usual way by first glueing at leading edge, then folding and glueing back to main spar.

This is done top and bottom, cap strips added to top from leading edge sheet to trailing edge stock. Bottom cap strip added and all sanded to match leading edge and trailing edge stocks.

Next comes 2 W4s, made of 1.5mm ply and glued to each wing tip making sure to align slots for outer wing panel dihedral brace so that fit is snug, not loose or too tight.

Now wing panels are ready to join and add dihedral brace DB1 and DB2. Check fit of dihedral brace DB1, cut/or sand till a good fit is obtained.

Lay left hand wing panel flat on bench, dry fit DB1 brace, add right hand panel and block up to 76mm under right hand wing tip check fit if satisfied, reassemble wing using epoxy to glue wing panel centre section together.

Once dry make up and fit aileron torsion rods and connect to strip ailerons. Then cut off approximately 82cm from each end of aileron stock for centre section trailing edge. These cut offs will make centre blocks for fitment of aileron torsion rod, which now can be added making sure not to allow glue to bind up free movement of aileron rods.

Next bevel the leading edge of aileron blocks and hinge into place. Glue 1.5mm ply reinforcement on top of centre section trailing edge.

Add DB2 brace to back of leading edge stock and epoxy in place. Now add 1.5mm sheeting to centre section of wing top and bottom, remembering to cut space for aileron servo in bottom of wing.

Check travel of aileron. Sand and trim wing to shape.

POLYHEDRAL TIPS

Transformer pic

Start by cutting ribs W5 - W9, two of each as per main wing. the construction is similar, but this panel requires approximately 3 degree washout at the tip so by blocking up W9. By using an incidence meter this was obtained with not much problem. You will need to make two dihedral braces DB3 from 3mm ply, not light ply but A5 ply.

Now add 1.5mm ply to make a box section between top and bottom spars into which D3 will be epoxied in place.

Next comes W4, which slides over DB3 and glues in place, drill hole through W5 using W4 as a template. This hole is used for the 6.5mm diam. locater dowel which is then epoxied in place in outer wing panel only.

Now add 6.5mm sheet wing tip block and sand to shape, adding 3mm gussets to main wing and tip as shown on plan. The wing tips are held together with tape after covering and fitting.

TAILPLANE and RUDDER

All tail surfaces are cut from 6.5mm balsa sheet and sanded to shape. Don't forget to bevel rudder and elevator leading edge before hinging. Control horns are positioned and fitted.

FUSELAGE

Start by cutting two fuselage sides from 2.5mm balsa, then cut fuselage doublers from 1.5mm ply. Don't forget to drill wing dowel holes or window cut outs.

Glue doublers over fuselage side and weigh down overnight, making sure to make to left and right hand side.

You will need to cut two wing saddles from 3mm balsa and position them. Don't change angle on saddle as this determines wing incidence. Once dry, lay fuselage sides over plan and mark bulkhead positions on to inside fuselage sides, now add 6.5mm sq. balsa longerons to inside of fuselage sides while laying flat on bench.

Having completed fuselage sides to this stage, set aside and begin cutting fuselage formers. Using the same system as the wing ribs, place paper templates on to appropriate stock of ply or balsa, then cut. F1 is the only 6.5mm ply bulkheads (can be laminated from two 3mm sections).

Nose block backing, F2 and F3 were cut from 3mm light ply, F4 to F8 cut from 3mm balsa. Once all bulkheads are cut and sanded to shape check against plan for trueness and that all notches line up and that bulkheads are square.

Now mark centre line on all bulkheads using plan as guide.

Next step is to lay right hand fuselage side down over plan, stand F2, F3 and F4 onto fuselage side and glue into place, making sure bulkheads are at 90 degree to fuselage side, next step is to stand left hand and right hand fuselage sides over plan view and glue together after sides are dry. Add F1 by pulling nose of fuselage sides together allowing for 2 degree right thrust on firewall while checking fuselage alignment over plan. F1 must be glued using epoxy. Once dry, add 6.5mm triangle as a gusset from top to bottom on both sides of fuselage inside.

Once dry position formers F5 to F8 into place while pulling tail section together making sure that all reference lines marked on bulkheads line up on plan centre line.

You will need to decide where you're going to run pushrods through fuselage for rudder and elevator control or nyrods in tubes. I chose nyrods.

I found the easiest way to do this job is to mark position of servo tray and height of servo output arms on inside of fuselage side, then determine where rods will exit fuselage side at rear of fuselage.

You will find that the rod's outer tube will need to cross over each other 3/4's of the way down the fuselage to stop any unnecessary binding.

Once happy with installation you will need to support the rod about half way along fuselage to stop any flexing in rod during operation.

Next comes the making and positioning of landing gear blocks.

These items are available at your local hobby shop, or can be made from a grouved hardwood block in the work shop. Whichever way you go they will need to be epoxied in place and then drilled to accept landing gear wire and straps. Now cut K1 from 3mm ply and add to bottom of fuselage between F1 and F2. Cover bottom of fuselage between F1 and F2 with 3mm balsa cross grained. Add K2, cut from 6.5mm ply, epoxy in place. When dry, mark position and drill for tow hook, which is made from small L-shaped cup hook.

Transformer pic

Next is the landing gear wire for which you will need two pieces of 5/32" piano wire. Cut and bend to shape using the plan as a guide. When happy with both legs, solder a small washer to inner section on wheel axle, check fit of 2 1/2" wheels and add 5/32" wheel collars to secure wheels in place.

Fit the undercarriage legs onto mounting blocks, one forward, one aft in a cross over fashion.

Make two gear straps and drill holes in blocks to screw in place. Moving to the tail of this monster, it's time to cut tail skid mount from 3mm ply then bend 2mm piano wire skid to shape as displayed on plan.

Epoxy to ply mount and when dry, epoxy mount to bottom of fuselage. Now add top sheeting from rear of F4 to F7, again using 1.5mm balsa cross grained.

Add tailplane and fin making sure that everything is square and fin is at 90 degree to tailplane, glue dorsal fin in place.

One change I made to the plan was the hatch and windscreen, in that on the plan these two units were glued in position as a solid fixture of the fuselage, but having large hands I found it too difficult to remove tank or nose block for changing model configurations.

I recommend to make this a one piece unit, having fixed windscreen to hatch and two small locating dowel made from tooth picks fitting into small holes drilled in F2 above wing dowel holes.

When slipped into place a small self tapping screw through hatch into F1 top to secure it all in place.

Next is to make nose block. Obtain a block of balsa approximately 100mm x 100mm square and glue ply backing onto block, once dry start shaping block to match outline on plan allowing for 2 degree bevel to suit right thrust set on firewall F1.

Having already drilled F1 for mount and fuel line exit holes, line up nose block and mark for locating dowels and securing screw, remove block and drill holes for dowels and securing screw.

Glue 3mm dowel in place, when dry, remount nose block for final sanding to shape.

RADIO INSTALLATION

Using two standard servos side by side on 6.5mm x 6.5mm hardwood rails I took care of rudder and elevator controls. The use of a mini servo for throttle, handled the throttle control and was mounted forward to one side of the cabin area between F2 and F3. The model has enough room for standard radio gear. The battery pack fitted neatly under the 6oz Dubro fuel tank in the forward tank compartment, and the Rx found a home just behind the landing gear blocks, all snugly wrapped in foam. A 25 size nylon mount was used, held in lace by cup head bolts and blind nuts on the inside of F1.

Transformer pic

The throttle pushrod was made from 2mm piano wire with a Z bend on the servo end, and solder on threaded coupler with nylon clevis. The aileron servo was next to be installed and was a standard set up in that the servo was mounted on hardwood rails epoxied to wing centre section.

After drilling the rails and mounting the servo, control links were made from Dubro 2/56" threaded rods, cut to length, 2/56" clevis mounted to torsion rod and Z bends to servo output arm, travel checked and holes in aileron torsion rod block opened up so no binding can occur.

Once happy with all radio gear installation, I removed all the gear and gave a final sand over the complete airframe.

COVERING and FINISHING

Well the end is near, it's come to the time to clad our little machine, in it's suit of armour.

First give the tank compartment a coat of fuel proofer, then give the skeleton of the airframe a treatment of dope and talc.

Sand between coats. It is then time to choose your covering or paint. I chose to cover in plastic heat shrink film and found it an easy model to cover. Being a 20 - 25 model it doesn't take to long to finish or cost an arm or a leg in covering.

The nose block was given the dope and talc treatment and sprayed with enamel paint as trying to cover this type of shape is nearly impossible to do without getting creases everywhere.

The wing was covered in the normal way. Add trim to your own taste. Finally, aileron, rudder and elevator get the cover up and we're almost done.

Next, is to cut, fit and glue inside windows and windscreen with clear acetate.

Locate holes for wing dowels and glue dowels in place, leaving approximately 3/4" proud on each side of fuselage. When dry paint in a contrasting colour.

Now it's time to do final assembly.

Re-install all radio gear, tank and control rods, landing gear etc. Check your C of G which I found best set on the main spar.

The C of G remains about the same for all configurations.

The noseblock is filled with ballast equal in mass to the weight of the engine and mount so that little or no extra lead is required to balance the model in its varied roles.

FLYING

Transformer pic

After the usual pre-flight check and range tests, it was time to commit this little beasty to the challenge.

Two function glider

Check rudder movement is 30mm each way. Connect wing tip panels to inboard wing section and seal joins with tape. Disconnect aileron linkages and tape down ailerons. Hold wing onto fuselage with rubber bands.

Hand launch the model first off to check for safe handling and correct balance. Then it's over the edge off your favourite slope.

Being a lightweight glider the model is best flown in light to moderate winds. It will not handle strong gusty conditions too well.

The transformer will readily soar in a good breeze, rudder control is adequate but anticipate a little lag in response ahead of any turns. Practice S-turns into wind, add a touch of up elevator during turns. The model can be bungee launched from a flat field or if you have a fit and healthy assistant it can be launched by running with a tow line. It is very stable as a glider and will pose no problems for the novice model pilot.

Three function powered model

Remove the nose block and fit the engine and connect the throttle cable to engine. Leave off the undercarriage until later.

Do not fill the fuel tank to full but use only a tiny amount for the first flights.

The aim is to practice climbs under power, level powered flight, and gentle turns.

Hand launch the Transformer, climb to a reasonable height, throttle back and fly until fuel runs out, then glide back to base. After getting used to powered flight strap on the undercarriage and use more fuel in the tank for practising circuits, landings and touch and go's. Keep practising until good landings can be made constantly. You're now ready for ailerons.

Four function trainer/aerobatic model

Remove wingtip panels and tape from ailerons. Connect aileron linkages to servo, check movement.

Reduce rudder movement to 12.5mm each way.

The Transformer with its new wing format will fly faster than before and controls will be more responsive so be prepared for it. Having mastered the Transformer using three functions up until now, using ailerons is a natural progression.

Now it's into the air.

I filled the tank and primed the motor, four flicks and its heart was ticking over steadily, adjust the needle, check the throws under power and we're ready to go.

While taxing out and lining up on the strip, I thought to myself, "You're not going to get a better afternoon to test this thing." About 22 degree, a steady five knot breeze, it doesn't get any better than this. So creeping up the throttle away it went. Rudder gives good ground control, then it's airborne. Climb out posed no problem, a couple of clicks left aileron and three clicks down elevator and were straight and level cruising at 1/2 throttle.

Bump the juice up and we're away, loops, rolls, stall turns, and short inverted flight gives no problems.

Well the fun must come to an end sooner or later.

So a couple of landing circuits to get the feel and home we come, throttle off to idle and the approach is rock steady, glide is good and it touches down with no sign of wanting to nose over.

SUMMARY

Transformer is a 3 in 1 model designed to take a novice R/C flyer from a simple glider through to an aerobatic sports powered model.

It offers a sensible approach to R/C flight training and because of its varied roles is perhaps the most versatile model available from Airborne for beginners.



SPECIFICATIONS

Transformer

Type: Radio control trainer model that transforms from glider to aerobatic/sports model.
Configuration 1: Glider
Wingspan: 1.8 metre
Length: 1 metre
Radio: 2 functions: rudder & elevator

Configuration 2: Powered Model
As above with addition of throttle function and undercarriage.
Radio: 3 functions:
Engine: .20 - .25

Configuration 3: Aerobatic/Sports
Wingspan: 1.2 metre
Length: 1 metre
Engine: .20 - .25
Radio: 4 Functions: Rudder, elevator, throttle, ailerons
4 function R/C equipment required.


Transformer plans are available from:
Airborne Plans Service

AU$27.50 plus AU$2.00 P&H1
Plan No. 609

Click here to order this plan

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This page was last modified on the 21-May-02