Model Tech Super Cub ARF

 

 

Introduction 

 

The Model Tech Super Cub is an Almost Ready to Fly (ARF) that has tried to capture the classic style and the many features of the full-size Piper Super Cub. It is primarily pre-built from balsa and light plywood and features a built-up airframe covered with heat-shrink film. The Super Cub also includes a fiberglass cowl, aluminum landing gear bracket, Cub-style wheels, a steerable tail wheel, clear molded windshield and side windows plus a complete hardware set.

While still manageable for most workshops, this is a big airplane. The wingspan stretches out 81 inches (2,057 mm). That big 900 sq. in. (58.1-dm2) wing qualifies the airplane for International Miniature Aircraft Association, (IMAA) events. It is 50.75 inches (1,289 mm) long. But surprisingly, this big Super Cub weighs just 7 pounds (3.2 kg) meaning there is a lot of wing to carry very little weight. In fact, this Cub’s 18 oz. /sq. ft. (55 gr/dm2) wing loading puts this airplane firmly in the “second airplane” category.

Because of its very light weight, the Model Tech Super Cub doesn’t need a big engine to fly it well. While this is a personal opinion, flying any type of “Cub” on anything but a four-stroke glow (or gas) engine sounds wrong. A two-stroke glow engine is definitely out of place on this slow cruiser. Ultimately, power choice belongs to the pilot but this airplane used my ever-trusty Magnum XL 70 engine.

Of course, for electric-power aficionados, this Cub is easily powered using a 4120/05 Brushless Outrunner motor running through an 80 Amp Brushless Electronic Speed Controller (ESC). A 4-cell 4000 mAh Lithium Polymer battery would work best. The best propeller would be the13 x 6.5E.

This Super Cub has functioning flaps. Increased horsepower and flaps were Super Cub features over the original “Cub”. This means the radio system must have at least five channels. Having separate aileron and flap servos requires that the airplane carry seven servos, 2 x 12″ servo wire extensions and 2 “Y”-harnesses.

If you have an 8-Channel radio like the Airtronics 8000 used in this airplane, the individual ailerons and flaps can be independently connected to separate channels and then mixed. This allows each control surface, especially the flaps, to be trimmed for proper operation. Using mixing, the ailerons can also be adjusted to eliminate adverse yaw, always a Cub problem.

Contents

  

Photo 1              Photo 2

The parts all came out of the box without transport damage. Everything was packed so that it could not damage another part. Also, there was a protective plastic bag over every part.

The manual has a couple of pages dedicated to kit contents that puts descriptions next to parts that have been photographed in relevant groups. It also has a good list of the tools that you will need to put this Super Cub ARF together.

The fuselage is a one-piece unit made from balsa and laser cut plywood. It is pre-covered and already contains the blind-nuts for the undercarriage and the wing struts.

  

Photo 3              Photo 4

The firewall is pre-slotted to accept an electric motor mount. Filler parts are provided to fill these slots when a glow motor is used. The interior of the cabin is empty and has pre-fitted trays to accept the servos and radio equipment.

Photo 5

A close up of the Metric blind nuts for securing the landing gear. The blind-nuts behind the bulkhead are for the wing struts.

Photo 6

The fin and stabilizer hinge-slots are pre-cut to match the rudder and elevators. The parts are transported with Mylar hinges in place. Care has to be taken not to push the Mylar hinges all the way inside before they are finally glued in place. See the Sport Aviator Flight Tech article “Installing Mylar Hinges”

Photo 7

The wing panels also come with aileron and flap hinges pre-cut but not glued.

Photo 8

The metal wing spars have been pre-fitted and factory glued in one wing-panel. 3-mm bolts are used to hold the spars through blind-nuts in the other wing. No gluing required! The big wing’s halves are easily separated for transport.

Photo 9

The ailerons and flaps are different sizes and should be marked when removed so that the pre-cut hinges will match exactly again.  

  

Photo 10             Photo 11

There are different movements planned for the ailerons and the flaps. The aileron, shown on the left, has two angles cut to let it move up and down from the central position. The flap, shown on the right, is designed to move down only, not up, from the neutral position.

Photo 12

The wing struts are pre-built and covered. The important center strut brace is factory installed. Flying any size Cub without the center brace is begging for harmonics to drive you nuts.

 
Photo 13              Photo 14

The strut attachment points are also pre-fitted with two bolts each, to keep them lined up correctly.   

 

Photo 15              Photo 16

These clear plastic items are hard to photograph, but are the untrimmed windshield and side windows for the cabin.

Photo 17

The cowl is a pre-painted, epoxy resin molding. The epoxy resin makes for an extremely strong, durable cowling that should last for years of flying; even with w four-stroke engine. The paint job was bright, shiny and well masked.

  

Photo 18              Photo 19

Here are bottom and top views of the cowl. The paint job was extremely well done.

Photo 20

A small number of decals are provided for the fin and fuselage side registration number.

Photo 21

The electric motor mount and battery support tray are not used in this review, but is a great option for those of you who are “going electric”.

  

Photo 22              Photo 23

The main undercarriage is pressed aluminum with wire to emulate the original Super Cub’s bungee suspension. The main wheel hubs are recessed to allow hub caps to be fitted over the axle bolt heads.

Photo 24

These are the parts needed to attach the wheels and the dummy bungee suspension for main landing gear.

Photo 25

The wing struts are already assembled and are held in place with these 3-mm bolts plus some assorted other hardware.

Photo 26

The wire tail wheel assembly is attached to the rudder to provide ground steering.

Photo 27

Control horns and bolts. This kit has more hardware than Home Depot in it!

Photo 28

The engine mount is the two piece type. It will fit most engines up to “120” size. The mounting bolts are also included.

Photo 29

Mylar hinges were all dry-fitted in the wings and tail feathers for shipping. It is a good idea to put them all in one place. For complete installation details, read the Sport Aviator article “Installing Mylar Hinges” in the Flight-Tech Section.

Photo 30

Here are more clevises and aileron/flap short pushrods. Longer ones for elevator and rudder were not photographed because they are not photogenic! Translated that means they are far too long to get all of them in the frame. This is not a small airplane, remember.

Photo 31

The fuel tank and parts come with their own separate assembly instructions. While the supplied tank is not the square type pictured in the instructions, the assembly process remains identical. Try to get the “overflow” vent tubing to reach into the top bubble in the tank to insure always getting totally topped off.

Photo 32

Here is the Magnum 70 four-stroke motor that will be used for this review. As I might have mentioned before, the words “Cub” and four-stroke just seem to go together well. This Magnum 70 is a great match for this airplane. It is powerful enough for flight and basic maneuvers, uses little fuel and has that great “Cub” sound. It is also extremely reliable and easy to set up.

Photo 33

Photo 33 shows the flight pack is from the new Airtronics RDS8000 2.4 GHz radio system. Instead of the usual 7-1000 mAh Nickel Cadmium (Ni-Cd) battery pack, an 1830 mAh Nickel Metal Hydride (Ni-MH) was used for the Super Cub. This airplane uses a lot of servos so a little extra battery capacity is always welcomed.

  

Photo 34             Photo 35

Closer views of the new Airtronics 2.4 GHz channel hopping receiver. The short, broadband antennae need to be at 90 degrees to each other for best reception. For more information on 2.4 Ghz radio systems see the Sport Aviator article “2.4 Ghz For The Common Pilot”. A complete review of this new, extremely high quality and very affordable radio system will shortly appear in the Radio Stack Section. Check, it might be there already.

Photo 36

Seven Airtronics standard 94102 servos are needed to fly the Model Tech Super Cub. Two servos power the ailerons, two more work the flaps and one each controls the rudder, elevator and throttle. The servos weigh just 1.6 oz. and put out 42 in. oz. of torque. While this is more than enough to fly this airplane, it might be a good idea to use a 5-cell battery pack (6.0V) as the servos then produce 60 in. oz. torque. The extra torque may prove useful on the rudder.

CONSTRUCTION

The Fuselage

  

Photo 37              Photo 38

To begin building, the engine needs to be positioned correctly on the engine mounts. The instructions help you do this task accurately. The instructions were very well written and gave many good assembly tips throughout the assembly process.

The engine was clamped to the engine mounts and positioned vertically on the bench. A 6” steel ruler was held on the drive washer of the engine by the prop nut and a spacer, (actually the center from an old broken propeller). This lets you accurately measure the distance from the firewall when installed.

When positioning the clamps, try to leave either the front or rear two mounting holes open. Once the engine is positioned, use the Great Planes “Dead Center Engine Mount Hole Locator” to mark the two available hole spots. Part number is GPMR8130. This product rates up near the top of the World’s most useful inventions just behind the self-installing drywall screw and ahead of sliced bread.

For complete engine installation information, read the Sport Aviator article “Engines 101 Part Two” in the Pri-Fly Section.

  

Photo 39             Photo 40

  

Photo 41              Photo 42

The engine mounts were predrilled and bolted to the engine. The assembly was then offered up to the firewall as a complete module.

 

Photo 43              Photo 44

To make it easier to fit the cowl, a cardboard template was made to locate the position of the cylinder head of the MAGNUM 70.

Photo 45

After transferring the dimensions onto the cowling, just remove everything inside the lines. The hole for the cylinder head was rough-cut with a hot-knife and then finished off with a fine Dremel sanding drum. (Hint: run a vacuum cleaner hose held between your knees all the time you are grinding this stuff and please wear a mask).

Photo 46

The muffler was fitted finger tight to find what material had to be removed to let it fit inside of the cowl.

  

Photo 47              Photo 48

The same “card-trick” was used to figure out exactly where the needle would exit through the cowl.

  

Photo 49             Photo 50

The initial cut is made without the needle in place.

Photo 51

The needle valve assembly was located right underneath the hole. The finished fit is well worth the effort. Were it required, the Magnum’s high-speed needle valve has a hole and locking bolt for a 1/16 in. wire extension to allow adjustments through a much larger cowl than the Super Cub uses.

Photo 52

Spongy-soft foam was fitted around the tank and onto the front before fitting into the fuselage. This prevents fuel frothing from engine vibration and the resulting bad engine runs that are difficult to diagnose.

  

Photo 53             Photo 54

The directions to fit the tank only asked for it to be pushed into place. This might work, but a builder’s instincts would probably inspire the addition of some extra support.

Photo 55

A small plywood plate was fashioned to provide extra rear support. This precaution would make sure that a tank full of fuel would not move around during flight. The hook and loop “tie wrap” is available at any hardware store and is a proven fastener used to keep exposed fuel tanks in place.

  

Photo 56             Photo 57

Here is a tip on how to feed the fuel-lines through the firewall. Lay a cable-tie in line with fuel-lines. Then with a small cable-tie or two, bind them all together. It is then very easy to feed everything through as the tank is pushed into place. Just snip the small cable-ties to free up the tubing again and you are done.

Photo 58

A third fuel line was used to fill/drain the tank. It had its own clunk and was very effective at scavenging all of the fuel from the tank at the end of the day.

  

Photo 59              Photo 60

This third line is used only for filling and draining the tank. When flying or otherwise not in use, the fill/drain line and its plug (very important) tuck away inside the cowl.

Photo 61

Initially, a “Higley” nut was used to hold the propeller in place. Tru-Turn also manufacturers a more “scale”-like hub for the Super Cub but it is more expensive.

 

Photo 62             Photo 63

Two views of where the cooling air flow could go into the cowl. It escapes all around the rear of the cowl which is deliberately not a tight fit on the full-size version as well as on this model. The extra space behind the engine head also serves as an exit for the spent cooling air. In general, the exit area for cooling air should be twice the entrance area.

Photo 64

As a matter of my personal taste, a red spinner replaced the propeller nut to give some color to a mostly white airplane. The spinner also makes electric starting easier.

 

Photo 65             Photo 66

The muffler only needed a small opening in the bottom of the cowl to finish the engine installation. But the hole was made slightly larger to add additional exit air area.

  

Photo 67             Photo 68

The throttle servo mounts in the factory installed tray as shown. The throttle pushrod is secured to the servo using an adjustable locking clevis. This type of servo hookup is great for throttle servos and for servos operating retracting landing gear but should never be used on flight control servos. The throttle pushrod slides inside a tube once it enters the tank area until it exits at the firewall.

The Wing

Photo 69

You are not required to line up and glue the two wing halves together. There are, however, ailerons, flaps and four servos to be fitted; two in each wing half. You also have to find several openings and a few blind nuts under the covering before you proceed.

  

Photo 70              Photo 71

Instead of gluing the halves together, the wing halves slide together on the two pre-installed metal wing spars. The servos in photo 71 are lying on top of the panels here to measure and set the correct lengths of the flap extension leads.

The wing halves slide apart to allow easy feeding through of the servo leads out to their respective servos. The wing halves can also be separated for easier transport. If you intend to do that, be sure to label both sides of the servo leads/extensions to insure proper connections during re-assembly.

Photo 72

When the wing is joined there are two half-moon exits to give the servo leads unobstructed exits down into the cabin area.

  

Photo 73             Photo 74

A “grabber” (available at most hardware stores) was used to pull the leads through to the center section. The wings had been factory fitted with paper guide-tubes for the leads, which made this a very easy task. The task is even easier if done before the wing halves are assembled.

  

Photo 75             Photo 76

The “grabber” fits easily in the pre-installed paper wing tubes. It easily passes right through the flap servo opening when pulling through the aileron lead.

  

Photo 77              Photo 78

It is easy to simply grab a servo lead plug and pull the lead through.

Photo 79

The lead is then doubled back to come out of the half-moon opening in the bottom of the wing.

  

Photo 80             Photo 81

The flap servo lead is just about long enough without using an extension lead.

  

Photo 82              Photo 83

The servo needs to be positioned in its slot so the lead will reach. Mounts for the servo are located under the wing covering and do need to be cut out and drilled for mounting screws.

  

Photo 84             Photo 85

The two leads for the flaps and the ailerons in each wing will need to be labeled to make sure they go in the right Y-leads during pre-flight assembly. Even better, use the Airtronics 8000 transmitter’s programming abilities and set the ailerons and flaps into different channels. This allows adjusting aileron differential to eliminate adverse yaw. Individual flaps allow adjusting both flaps for exactly the same movement.

Photo 86

With servos in place, it is a good time to install the control surfaces. Position the hinges as shown.

  

Photo 87             Photo 88

The instructions show how to position the Mylar hinges using modeling pins. There is also a more detailed hinging procedure outlined in the Sport Aviator article “Installing Mylar Hinges” in the Flight Tech Section.

  

Photo 89            Photo 90

Soft-tip pen marks were made to show the center point of each hinge because they can be quite hard to see when the pins are removed prior to gluing with CAA. The markings come off instantly with denatured alcohol.

Photo 91

It is important to flex control surfaces frequently, after the hinges are glued in place, to ensure that they do not harden in any one position.

  

Photo 92             Photo 93

The gap between the flap’s leading edge and the wing’s trailing edge on the top of the wing is much less than the gap on the bottom. The same gap for the aileron is equal on both sides and should be nearly invisible from either top or bottom.

Photo 94

All of the controls use the same nylon control horn design.

  

Photo 95             Photo 96

The bolts holding the control horns are best cut off and filed flush. This makes it a lot easier to clean and handle the model. Use a high-speed rotary tool with a metal cutting disk for this task.

Photo 97

The flap servo is seen next to the bolts that hold the metal spars in place. 

  

Photo 98             Photo 99

This view under the wings shows the position of the wing-strut bolts, the aileron servo, the flap servo and the exits of the servo leads through the bottom of the wing and into the fuselage top.

  

Photo 100              Photo 101

The wing dowels and holes in the front cabin former were given a coat of thin CAA. This hardens the wood at the major wear and stress points.  

White-out, a typewriter error-correction-paste, was used on the ends of the wing dowels to match the white covering of the main cabin former. Also, as a personal preference, 1/4 x 20 nylon wing-bolts were substituted for the metric bolts provided. The existing nylon threads were easy to re-tap, to match the bolts. After tapping, harden the threads with a coat of thin CAA. Make sure the adhesive is very dry before test fitting the bolts!

  

Photo 102              Photo 103

The wings form a nice tight fit when bolted in place on top of the cabin.

Photo 104

It is important to measure to see if the wing position is correct before attempting to fit the stabilizer and fin. It is important to measure from the same place at the back of the fuselage for each wing panel.

Photo 105

The left and right wings came out exactly equidistant from fin post.

The wing does not have any decals so wing construction, at this stage, can be considered as complete.

The Tail Assembly

With the wing bolted to the fuselage, the tail feathers can now be lined up with it and glued in place.

Photo 106

There are two slots in the rear of the fuselage that require that the covering be removed first. Photo 106 shows the slot for the horizontal stabilizer.

  

Photo 107              Photo 108

The stabilizer and the fin are keyed to each other to provide a strong joint,

  

Photo 109              Photo 110

The material at the bottom of the fin needs to be removed to allow the glue to do its job properly. The Great Planes hot knife or a thin-tipped soldering iron are the best tools for this task as they cut the covering without cutting the wood. If using a hobby razor knife, be very careful not to score the wood which could cause a weak point that might fail under flight loads.

  

Photo 111              Photo 112

The covering would not come off completely, but enough material was removed to allow the CAA glue to penetrate. (Ed Note: The remaining adhesive/covering residue can be easily removed using Coverite’s Ironex. Use adequate ventilation.)

Photo 113

The slot that receives the fin can be seen in photo 113

  

Photo 114             Photo 115

The Mylar hinges were positioned where the horns would be bolted to the control surfaces. This provides a secure fastening where all of the push and pull forces are exerted by the servos.

  

Photo 116              Photo 117

The other hinges were positioned using modeling pins. The temporary marks indicate where the thin CAA should be applied before removing the pins.

Photo 118

One stabilizer half is shown here ready and prepared for the hinges to be glued with thin CAA.

  

Photo 119           Photo 120

The pushrods were used to position the control horns in line with the pushrods.

  

Photo 121              Photo 122

Initially, the stabilizer did not fit level with the wings. A very small amount of material was sanded away from the stabilizer seat in the fuselage and then everything lined up correctly. Pins were used to keep the stabilizer from moving while thin and medium CAA was applied to the secure the level position.

Fitting The Wheels

Photo 123

The Model Tech Super Cub ARF is supplied with a steerable tail wheel. The steering comes from a special tiller-arm that is moved by the bottom of the rudder. Note the excellent, detailed photo-illustrated directions included with this airplane.

  

Photo 124              Photo 125

The tail wheel is aligned and held straight by a wheel collar that is embedded in the tiller arm. Once everything is properly set up, use some removable thread locking compound on the wheel collar bolt to keep the tail wheel locked in place despite vibration.

Photo 126

A plastic spacer is provided to prevent the tail wheel from rubbing against the tail wheel wire. Make sure to install it.

Photo 127

The tail wheel is centered on the wire itself. The outside wheel-collar’s retention bolt is pointed rearwards to prevent dirt from filling the bolt head. Again, use thread locking compound on this bolt.

Photo 128

To work correctly, the pivot point of the tiller arm must be positioned directly above the hinge line of the rudder.

Photo 129

A 2-mm bolt was used with a nylon lock-nut to fasten the tiller arm to the rudder. This nylon lock-nut does not have to be tightened all the way and will still provide a good anchor for the steering system.

Photo 130

The wheels arrive drilled to allow the axle bolt to be recessed into the hub.

Photo 131

The main wheels are spaced with the retaining nut so that they do not rub against the aluminum undercarriage.

Photo 132

The wheel has a removable cover cap that hides the head of the axle bolt. This is a nice scale touch for this airplane.

Photo 133

The wheel “hub-cap” is held in place with three small screws. The retaining wheel collar is hidden by the white hub yet still accessible. Use thread locking compound on the wheel collar’s bolt, not on the three small screws.

Photo 134

The aluminum main landing gear “legs” are supported by wires that emulate the full-size Super Cub.

  

Photo 135              Photo 136

The main gear bolts into the pre-fitted blind nuts under the fuselage.

Photo 137

The crosswire in the undercarriage assembly is held in place by 2-mm nylon lock-nuts on the outside of the aluminum landing gear plate.

  

Photo 138              Photo 139

A rubber O-ring was used to provide some rudimentary shock absorption for the simulated suspension.

Radio Installation

The new Airtronics RDS8000 2.4GHz radio and the 92824 8-channel receiver were selected to guide the Model Tech Super Cub ARF. It has a lot of programmable functionality, which will really enhance the Super Cub’s trimming, performance and handling.

Photo 140

The radio system’s box proved to be in theme with its contents.

  

Photo 141              Photo 142

Photo 142 shows the radio, charger and receiver with the author’s own Ni-MH receiver battery.

  

Photo 143              Photo 144

The Airtronics 2.4GHz receiver has two short antennae that are used to receive the broadband channel-hopping transmissions from the RDS8000 transmitter. “Channel Hopping” means that the transmitter switches among the 80 available 2.4 Ghz frequencies every few microseconds. This prevents any possible interference from other 2.4 Ghz equipment of any type. The transmitter also uses distinct digital codes to insure non-interference.

Photo 145

Notably, the transmitter on/off switch is positioned to one side to avoid accidental operation while the transmitter is in use. Both the pilot and the airplane will appreciate this feature.

Photo 146

The multi-function screen is all that you need to do some pretty slick programming. Programming is logical.

Photo 147

The 2.4GHz “bind” indicator is on the front of the RDS8000 case.

  

Photo 148              Photo 149

These are the buttons that make it all happen. The menus and program settings are all entered using these buttons.

  

Photo 150              Photo 151

The throttle stick is shown in the low throttle position. It is very easy to “beep” in or out a few percent of throw to get the throttle opening exactly where you want it to be. (You should be able to see a small black area which will be pretty close to where you need the throttle to be the first time you start the engine).

  

Photo 152              Photo 153

The throttle stick is shown in the high throttle position. You can use the radio to “beep” in or out a few percent of servo movement to get the exact throttle opening without stalling the servo. It is a good practice to set the throttle action mechanically close to what you want and then fine-tune it later with the transmitter. Note that the barrel is fully open but that there is a little “barrel” left equally on all sides.

Photo 154

The RDS8000 has a dedicated button that you can program to cut the engine by completely closing the throttle with one quick press. This is a good thing to have available to you while you are operating any glow engine.

  

Photo 155              Photo 156

The flaps are a feature of the Super Cub, and the RDS8000 has a three-position flap switch that is just right for the job.

  

Photo 157              Photo 158

Most of the flap servo travel is used to get three different positions. Here the flap is in the up (retracted) position. The servo disk is rotated all of the way back towards the wing’s leading edge.

  

Photo 159              Photo 160

At the half-flap switch position the servo disk is almost at the center. The flaps are deployed about half way.

   

Photo 161              Photo 162

Full deployment of the flap has the pushrod almost in line with the servo output shaft. This reduces the load on the servo gears and prevents the servo from stalling. This is important because it will use up less electricity as you fly around with the flaps all the way down.

Multiple approaches and general flaps-down flight means the Super Cub will spend a lot of time flying with full flaps deployed. Unlike full-size aircraft whose flaps lock in place mechanically, RC flaps are held in place by the servos which continually draw current against the air loads. The more mechanical help the servos can get, the less is the current draw and the longer the servos will last.

 

Photo 163              Photo 164

The aileron servo arm was angled forward so that normal rotation would give more up aileron than down. This is a good condition to have with a wing that is flat on the bottom, such as with the Super Cub. It creates aileron differential to avoid adverse yaw. After the first few flights, use the Airtronics transmitter to fine tune the differential.

  

Photo 165              Photo 166

Here you can see how much more “up” aileron than “down” the mechanical arrangement provides. This type of aileron movement helps prevent adverse yaw. In a rolling action, such as entering a turn, the aileron that is angled down generates a lot more drag than the other aileron that is angled up. In the case of a flat bottomed wing-section with both the up and down deflections equal, one wing would be held back by the higher drag of the down-aileron. The result is that, as the airplane rolls from level flight; its nose will tend to point opposite the turn direction slowing the aircraft and making the turn harder to judge.

  

Photo 167              Photo 168

The elevator pushrods need to be held in place until they can be joined near the servo so each elevator half was clamped in the neutral position.

  

Photo 169              Photo 170

With the pushrods held by the elevator horns and clevises, the pushrods were then bent to touch each other and align with the servo arm. As a precaution, some low-temperature silver solder was applied to the wheel collars to make sure they did not come loose in flight.

Some material was removed from the guide tubes to allow for full movement of the elevators after the clamps were removed. This method of setting up the two individual elevator halves ensures that both are exactly the same at the neutral position.  

Photo 171

The rudder’s movement was adjusted using the end point (ATV) feature of the radio. Enough room is left so that the rudder cannot foul the elevators under the side load of taxiing or violent in-flight maneuvers.

Photo 172

Three Airtronics 94102 standard servos fit inside the cabin to operate the elevator, rudder and throttle.  

Photo 173

The Airtronics 2.4GHz 8 channel receiver has numbered channel identities.

It uses 1 for elevator, 2 for aileron, 3 for throttle, 4 for rudder, 5 for retractable landing gear and 6 for the flaps while channels 7 and 8 are for auxiliary or mixing use. To bind the Airtronics 2.4GHz 8 channel receiver you don’t use a channel socket. The receiver has its own physical bind-button that is pressed during the binding process. That is why it is safe to have the transmitter’s bind button conveniently available on the transmitter face.

An opening was left in the foam wrapping around the receiver to allow “toothpick” access to the bind-button.  

Photo 174

The receiver and battery were both wrapped in heating-pipe-insulation to protect them from the engine’s vibration. A hook and loop strap was used to make sure that they could not move around during flight.

  

Photo 175            Photo 176

The twin receiver antennae must be routed at a 90 degree angle to each other. A small cable-tie ensures that the upright antenna cannot fall down over time.

Photo 177

The wing was positioned on top of the cabin to make sure that all of the servo leads could reach the two Y-leads. It is a good idea to label these leads to prevent incorrect connection.

Decals

The MODEL TECH Super Cub is colored like the full-size version. There are only a few decals to add to complete their rendition.

Photo 178

Only a few decals have to be applied.

  

Photo 179            Photo 180

Most of the decals are applied to the fin and rudder. Make sure you cut the joint between the fin and the rudder after the decal is installed. For this larger decal, use the wet application method outlined in the “Black Horse Liberty Review Article” in the “On The Flight Line Section”.

  

Photo 181              Photo 182

Finally, the full-size aviation license identity (the “N” number) is added and the wheel hubs “labeled”. The building work is done.

BUILDING SUMMARY

Model Tech has produced a very good ARF with an excellent construction manual. The parts fitted together very well. You could use everything that was provided in the kit. This Super Cub could be your first R/C model, but you would probably need some coaching here and there with some of the fundamentals of lining up the flying surfaces and hinging the controls etc. (For complete ARF building directions that will help with all the building and alignment tasks, go to the Sport Aviator Articles “How To Build An ARF Trainer Parts 1 through 3” in the Flight-Tech Section.)

The manual gives good direction and measurements. However, it may not be an easy task to mount the engine if you have not done one before. It could, for example, prove to be a bit of a challenge fitting the blind-nuts behind the firewall inside the tank area.

These are relatively minor challenges and are far outweighed by the good fit of all of the parts and general easy of assembly. The center of gravity came out perfectly with the battery under the rear of the tank. The completed model was within the weights specified on the box. This was pleasing, because weight is unseen and can significantly affect flight performance.  

Another notable point was that the iron-on covering was tight from the beginning and required only a minor touch up. The back page of the manual is a mailer/form that you can send in with any comments or suggestions etc. As far as putting the Super Cub together, I would not really want to change anything. (Ed Note: That is some high praise from a very experienced model builder. In fact, I don’t think I have heard Eric or any other experienced builder ever say that about an ARF kit. Good Job Model Tech!)

Getting Ready To Fly

Photo 183

Before flying any radio control airplane it is essential to set the center of gravity as per the instructions. The black mark on top of the cabin, under the wing, was left in place so that it could be checked at any time; especially after any internal equipment changes have been made.

Photo 184

The scale shows the exact weight before any fuel was added. This was 2.3 oz below the weight specified in the instructions and on the box.

  

Photo 185              Photo 186

The Super Cub fully assembled with the functional struts bolted in place. (Do not be tempted to fly this airplane without the struts. They really do support the wings). All that is needed now is some fuel to get the Magnum 70 engine broken-in!

  

Photo 187              Photo 188

Here are two views of the wing; left and right side views in the fall sunlight. This is a really big wing for a 7+ pound airplane. Flight characteristics should be gentle and forgiving. In fact, the Super Cub’s 19 oz. / sq. ft. wing loading (900 sq. in. divided by the 7 lb. 7 oz. weight) is lighter than many basic trainers.

  

Photo 189              Photo 190

A different perspective with the Super Cub up on a table shows the attachment of the wing-struts. It also shows the huge flap deployment on this airplane. The airplane’s landing speed should be extremely slow and approach control ridiculously easy.

  

Photo 191              Photo 192

Here are some closer views of the cabin, struts and engine cowling. For a mostly all-white airplane, the Super Cub has some very good looks.

Photo 193

The Model Tech Super Cub and its Airtronics RDS8000 are ready to do some business–well almost.

Breaking In The Magnum 70

Photo 194

The Super Cub was set up on an AMA field stand for the engine break-in process. Most model engines require very little break-in runs compared to those of 30 years ago. But still, a modest amount of ground running has two advantages, First, the engine parts get acquainted allowing setting a reliable idle sooner than otherwise would be the case. Second, after a few ground runs, the idle speed and mixture can be adjusted for easier first flights.

  

Photo 195              Photo 196

The Magnum 70 started up almost immediately using this technique. First, give the engine one quick spin with the starter motor to get some fuel into it. Second, light the glow-plug up. Third, apply the electric starter motor again and the MAGNUM immediately burst into life. The glow-plug was left on until the engine would run well at slow speeds.  

Photo 197

It is important to keep the engine running on the rich side during the break-in period. Running “rich” means that more fuel is included in the fuel-air mixture that the engine receives from the carburetor. Remember that the more fuel in the mixture means more lubrication for the engine. Here you can hardly see any exhaust smoke. The engine is running too lean for break-in.

Photo 198

Opening the needle about half a turn gave a rich, smoky exhaust and a mixture setting that did not cool off the glow-plug. Two tanks of fuel were run through the engine with sustained full throttle and sporadic idle to maximum rpm transition tests. Always vary the rpm’s during break-in.

Now, the Super Cub was ready to fly!

Time To Go Flying

Photo 199

This may have been said before, but the Super Cub is a very attractive airplane, even on the ground. Fly By’s should look super!

With the engine running reliably on the ground and a clear sky, the Super Cub was ready to go. It was a bit too windy for a slow flying airplane like a CUB, but there were photographs to take, videos to make and flight tests to perform.

Photo 200

With USAF Master Sergeant (ret) Robert Tucker at the controls, the Super Cub was lined up into crosswind for her maiden take-off.

Photo 201

The throttle was advanced and the airplane was airborne in only a few feet. A CUB will fly at a very slow airspeed, so any headwind close to that airspeed will have the aircraft up in the air very quickly indeed.

The take-off was nearly immediate and it almost beat the camera as the airplane shot off into the blue. The throttle was quickly brought back to a more realistic speed for a Super Cub. (Ed. Note: Why does everyone think that Cub = Mediocre Performance? I have several hours flying a 180 hp full-size Super Cub and it felt like it could out-climb a rocket, holding about 1,400 fpm or more. The airspeed was very much in the respectable category, about 140 mph. It was much faster than a Cessna 172, more in the C-182 range. The airplane’s acceleration was near to frightening. Note the stock PA-18-150 Super Cub had a 150 hp O-320 engine so the one I flew was an “upgrade”.)

Photo 202

Heading into wind allowed the ground speed to be reduced to almost a crawl. Despite the rough conditions, the Super Cub was solid and smooth. Only a couple of times near the ground did the turbulence threaten to take over.

  

Photo 203              Photo 204

This airplane is easy to see in the sky and does what you tell it to do. The camera moved to the other side of the runway to get away from the sun. This also gave a couple of shots of setting up for a slow fly by. The guess that the airplane’s fly-by’s would be great was an understatement. They were fantastic!

   

Photo 205             Photo 206

The 81” wingspan is evident when you swing by for a photo pass. Here the pilot is flying sideways in the wind to highlight the underside of the Super Cub. The Flaps were tried at altitude but it was not deemed to be a good idea to land too slowly in the erratic wind conditions. (On a later calm, but very cold day, the flaps allowed very steep landing approaches without gaining any airspeed which led to nice, short rollouts). 

Flight Summary

The Magnum 70 never complained or hesitated or sounded like it would stop, not once! Be aware that if you go to full throttle you will go out a long way very quickly.

The flight tests included several mild aerobatic maneuvers. It did small, or very big if desired, inside loops with elevator only. A stall-turn can be done with only brief application of rudder. Axial-rolls are not that practical and are very slow. 

Overall, the Model Tech Super Cub is easy to fly and land. The recommended control surface rates were just fine. Low rates fly the big 81” airplane just like a trainer. Be aware that this airplane will float a long way if the idle is up too high. It is best to get that engine low-idle running correctly before you fly!  

The Super Cub feels like a real Cub on the ground and in the air. The first flight was really good considering the strength of the wind. In calmer air, the airplane could easily be mistaken for the full-size version.

Observations As A Trainer

This airplane could probably be a first R/C glow or electric airplane. It is very stable and pleasant to fly. It could also be a very good choice as your second airplane. It flies like a trainer but looks like a full-size airplane. The aileron control responses at low-rates feel about how a trainer would/should fly. The airplane flew very well in the wind but needed a lot of rudder input to keep it straight in a cross wind.

The Model Tech Super Cub is an IMAA legal scale airplane and looks good enough to fly at any of their fun fly events. It is easy to fly, performs well and is totally honest. It is also very easy to assemble, especially so for the large, impressive airplane that it is.

For more information on this very nice trainer/second airplane, go to:http://www.hobbypeople.net/gallery/123667.asp

If you would prefer an electric powered version you will need the following power equipment:

Ø  A 4120/05 Brushless Outrunner Motor

Ø  An 80 Amp Brushless Electronic Speed Control

Ø  A 4 Cell 4000 mAh  Lithium Polymer Battery

Ø  A 13 x 6.5E APC propeller

 

Specifications Manufacturer: Model Tech                  Length: 50.75 in.                    Cost: $230.00 From Hobby People    Wingspan:       81 in. Radio: Airtronics 8000 2.4 Ghz            Wing Area:     900 sq. in. Servos: 7 x 94102 Airtronics                Wing Loading: 19.05 oz./sq. ft. Engine: Magnum 70 4-stroke              Weight:           7.44 lb.Airfoil: Flat Bottom Special Airframe Features: Excellent part fittings, Large wing area; Flaps; Two piece wing for easy transport; IMAA legal

Notable Positives Excellent wind handling Pre-installed guide tubes Very good looks Light flying weight Good basic trainer performance Easy to see airborne Notable Negatives Slots for electric motor get in the way when fitting a glow engine.

Electric Power Specifications Bore: 25.8-mm Stroke: 22.0-mm Displacement: 0.702 cu. in. (11.5-cc) Weight: 21.2 oz Exhaust thread size: 11 x 0.75-mm Shaft thread size: 5/16-24 Propeller used: 13 x 6 APC Fuel: COOLPOWER 20% Test RPM – 9,200.

 

A Closer Look t At The Magnum 70 Engine

Photo 207

The Magnum XL 70 RFS is a four cycle engine that comes with a full two-year warranty that protects you from any manufacturing defects and/or premature wear but not crash damage. The engine has an aluminum piston, iron piston-ring and steel cylinder/sleeve. It uses a two-needle carburetor to allow you to adjust both the top and bottom end fuel mixtures.

The engine uses a ball-race bearing for the front thrust support and a larger ball-race bearing for the rear loading of the crankshaft. The camshaft is also supported by two small ball-race bearings. Pressure for the fuel tank is provided by a tap into the muffler. 

The MAGNUM XL 70 RFS four-cycle is the high size end of what the box containing the Model Tech Super Cub Gen-II specifies. It is a compact and relatively lightweight four-cycle that promised to haul the airplane around with some authority.

The engine is very compact and fitted easily inside of the box. At first, I wondered if they had sent me a 52 but it was definitely MAGNUM 70. The engine’s small outside hides its big inside.

  

Photo 208              Photo 209

Photo 208 shows everything that you get in the box. You have to provide your own glow plug. An OS “F” glow-plug was used for the break-in procedure and the test flights. The only engine assembly required was to fit the exhaust header and muffler. Photo 209 shows the assembled engine.

  

Photo 210              Photo 211

The “70” on the right hand side, indicates the capacity of the motor. The fuel tubing running from the crankcase to the manifold is a great feature. It takes the down-stroke pressure from the piston and vents the waste oil into the inlet manifold. This gets rid of the messy residues typically seen coming out of four-cycle crankcase vents. From the front, the MAGNUM 70 has a very thin profile.

Photo 212

The engine comes with a choke that is spring loaded in the open position. This choke mechanism is useful when flip-starting the engine by hand. It was removed on the test model because an electric starter motor was used. The electric starter pulls enough fuel through to the carburetor without the need of an additional choke. Eliminating the choke also means one less hole to cut in the Super Cub’s beautiful cowl.

  

Photo 213              Photo 214

The carburetor can be reversed to position the needle and throttle arm on the side that is best suited to the airplane’s throttle servo position.

Photo 215

Since Magnum located the camshaft and pushrod location close to the cylinder, this engine will fit well into many different cowls; even into smaller ones.

Photo 216

It is good to see the safety of a jam-nut being employed on a four-cycle engine.

Operational Summary

It was an unseasonably cold fall day in South Jersey with the temperature hovering only a few degrees above freezing. With the tank full and the glow plug off the starter motor was applied for a brief spin to pull in some fresh fuel.

With glow plug lit it only took a brief application of the starter and the Magnum XL 70 RFS burst into life. It then took a few moments to set the throttle position with the Airtronics 8000 computer radio. The engine was put through a full break-in as per the instructions.

The engine’s main needle had to be set a little rich due to the cold air. The low-end needle was also opened up 1/2 a turn to keep the engine running when the plug lighter was removed. After two tanks of fuel the Magnum XL 70 RFS was ready to fly.

The idle was reliable if a little fast, but not enough to prevent the much awaited test flights. The engine never quit during any of the flights. It did not run lean at any time during the flying. It was extremely reliable right from the start.

The best part was that it delivered plenty of power for the 81” airplane which allowed for big loops and taller stall turns. For most of the flight, the throttle was set around half power. A thing that should receive more attention in any engine report, if for nothing else other than safety reasons, was the ability to cut the engine instantly from the transmitter. The RDS8000 has this feature on a dedicated button and it worked perfectly. The MAGNUM 70 shut down on command which tells you that the carburetor is “tight” and has no air leaks. All-in-all, The Magnum 70 had very good performance right out of the box and was a perfect match for the Super Cub.

Q

Short URL: http://masportaviator.com/?p=915