Piper PA-18 Super Cub–MAN Construction Article

Sep 27, 2013 No Comments by

Here’s the complete construction article from the upcoming January 2014 issue of MAN. Pat Tritle designed this amazing super scale Piper PA-18 Super Cub as a tribute to the ultimate Bush plane. This online article includes all the details of the build including construction photos, a complete Bill of Materials and Flight performance.

The Ultimate Bush Plane

Undoubtedly the best known and most cherished light plane of all time would be the Piper J-3 Cub. After all, the J-3 is the standard by which all others are measured. Even the twin engine Cessna Bobcat was dubbed “the Double Breasted Cub” by the pilots who flew it. And as with everything, even to that which is near perfection, improvements are made, and in the Piper lineage, good things did come from the Cub line in the form of the PA-18 Super Cub.

The Super Cub was developed from the PA-11 Cub Special, and though very similar in appearance, the Super Cub is a different airplane entirely. Designed and developed for bush flying, the Super Cub is no doubt the best known and most capable light duty bush plane of all time for accessing those out of the way places, usually not fit for man or beast. The original Super Cub built in 1949 had a 108 HP engine and no flaps. Subsequent models were improved greatly by adding flaps, and as the design evolved over the years have been built with engines up to 180 horse power.

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Over time, Super Cubs have been fitted with Tundra Tires, Skis and Floats, and as the popularity grew, many aftermarket accessories have become readily available to make a great airplane even better. During their production life from 1949 – 1983 and 1988 – 1994 some 15,000 Super Cubs have been produced.

The Model

In today’s modeling world J-3’s are everywhere, but with few exceptions, the Super Cub seems to have been mysteriously neglected. The Super Cub was second in line after my original 60-inch span J-3 design, but the important changes that are too often missed when “converting” a J-3 to a Super Cub were covered, including the correct rudder and horizontal stabilizer outlines, fuselage and firewall shape that are usually missed, as well as the addition of scale length flaps, full width windshield and large skylight. However, for the sake of simplicity, conventional top hinging for the ailerons and bottom hinging for the flaps was incorporated to keep construction simple and functional.

The fuselage and tail group are of the Old School bowed outline and “stick and tissue” style of construction. The wings are of the “egg crate” style with bowed tips making construction quick and accurate. Hinging is done with CA hinges cut from Great Plains Hinge Stock, and what came from it is a terrific light-weight Park Flyer of one of the no-doubt-about-it best light planes ever built. And as an added bonus, the flaps are very effective making for some great “short field” bush landings and takeoffs.

To keep the model light, the control system uses a .025 steel elevator pushrod in a plastic guide tube. The rudder is controlled by a pull/pull cable system, and the flaps and ailerons are connected with .032 wire pushrods. Z-Bends are used to connect the pushrods at both ends so no weight-adding hardware is required. Separate servos are used for each flap and aileron to facilitate the plug in wing arrangement.

Building the Super Cub

Construction begins with the bowed outlines. If you’re new to this there’s a terrific tutorial at http://patscustom-models.com/bowedoutlinres.html  that will describe the process in detail. Then cut all of the parts from the provided pattern sheets. However, if hand cutting the parts is a little too Old School, a laser cut parts pack and vac-formed plastic cowl are available from the author.

 Fuselage and Tail Section Construction

 The vertical and horizontal tail section is framed directly over the plans using the part numbers and wood sizes shown. Sand to shape and dry fit the hinges to complete the assembly.

The left and right hand fuselage side frames are built over the dedicated assembly drawings and joined using the wood sizes and part numbers shown. The landing gear beams are gouged with a 1/16-inch slot to receive the landing gear assembly. When the fuselage frame is completed, lash the gear in place with nylon or Kevlar thread and secure with thin Cya and add the gussets.

Set up the servo rails and mount the servos. Run in the control systems and mark the exact location of the rudder cable exit points on the plans. Build up the motor mount and set up the motor and ESC. Test the system for proper operation and make any necessary adjustments. And finally, assemble and mount the cowl on the firewall.

Wing Construction

Lay out all of the parts over the plans at their respective locations. Glue the main and rear Spar assemblies together first per the detail drawings, and then dry-assemble the ribs and spars. Pin the assembly in place over the plans and tack glue each point of contact. Finish building the wing assembly directly over the plans. Build the ailerons and flaps in place on the wing assembly, and when completed, remove the assembly from the board, cut the ailerons and flaps free and sand the entire assembly to shape.

The servos are glued in place with silicone caulk and the wiring run in. Cut the slots and dry fit the hinges, and add the strut receiver tubes as shown on the plans. Build up the lift struts and jury struts over the plans. Fit the lower attachment pins into the struts, and then fit the outer ends directly on the model. Be sure to twist in about 1.5 degrees of washout when setting up the struts. Insert the jury struts, align and tack glue them to the lift struts, the secure with a wrap of nylon or Kevlar thread and secure with thin CA.

Cover and Finish

 I added a full cockpit arrangement in the p-type. The parts were built up from 3MM Depron sheet, plastic and aluminum dowel, and bits of whatever was handy that looked like it might work. The inside of the fuselage was sheeted using file folder paper, and the full set up dry fitted in place before the fuselage was covered.

I then covered the model with Microlite from Great Plains. The trim was hand cut from stock vinyl sheets and numbers from Callie Graphics. The cowl is painted and trimmed with vinyl.  Then with all the cover and trim in place the control systems were set up and the final details added. Now, if you don’t add the interior details, the battery will lay on the fuselage bottom. With the cockpit in place, there’s no room for the battery, so it was mounted outside, and a small boat was built up from 3 MM Depron to be used as a battery hatch with the necessary provisions added to secure the boat in place with magnets. And since it’s a row boat, a set of oars were made up and lashed to the left jury strut. And because it’s a bush plane, protection from the elements is important, so a shotgun was built up and lashed to the right jury strut to complete the package.

In the Air

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I wasn’t particularly surprised to find the Super Cub to be a terrific flyer. However, before your first flight, make sure the model is balanced properly and that all of the controls are functioning correctly. In the air the model is very stable, but not “floaty” like the J-3. Control input is smooth and predictable, and the controls are typically well balanced, which is so typical of the Cub. The flaps are very effective, but will cause the model to balloon when deployed, so a bit of down elevator mix is required for a pitch neutral deployment.

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 When landing with full flaps deployed, there’s a good bit of drag, so a little extra power will be needed to maintain a manageable sink rate. Again, the model doesn’t float, but it will fly a good bit slower then with the flaps retracted, so spend a little time feeling things out before the first landing. Once you have the feel for what the model will do, then you can start doing those short field approaches and side slips that the Super Cub does so well.

My favorite take-off setting is 20 degrees of flap. For landings, full flaps work best, unless the winds are choppy. For that, take-off mode is best, allowing for a little extra speed on the approach. And for touch and go’s, go with full flaps until touch down, then go right to the take-off setting and she’ll stick to the ground nicely. Then power up and do it all again.

I have always been a huge fan of Piper Airplanes – the J-3 in particular, but once you’ve flown the Super Cub and learned how to get the most from it, like me, it just mind wind up your favorite airplane. . . . .

Specifications:

Scale: 1:7

Wing Span: 60-inches

Length: 38.3-inches

Wing Area: 518 Sq. In.

Flying Weight: 24.4 oz.

Wing Loading: 6.77 Oz. / Sq. Ft.

Power: Suppo 2217 950 KV Outrunner w/ a 20A ESC, an APC 11-5.5E propeller, and a 2200 mah 2S LiPoly Battery

Control System:  5 ch. R/C – Rudder, Elevator, Aileron Throttle, and Flaps using 6, Sub-Micro Servos.

Materials List:

Laser Cut Wood Pack w/ Vac-Formed Cowl as well as the Washout Jig Plans are available from Pat’s Custom Models at:

 patscustommodels@gmail.com

Custom Graphics available from Callie Graphics at:

admin@callie-graphics.com

Wood:

14- 1/16 x 1/8 x 36 Balsa

2- 3/32 Sq. x 36 Balsa

2- 3/32 x 1/4 x 36 Balsa

12- 1/8 Sq. x 36 Balsa

2- 1/8 x 3/16 x 36 Balsa

4- 1/8 x 1/4x 36 Balsa

2- 3/16 x 1/2 x 36 Balsa

1- 1/32 x 3 x 36 Sheet Balsa

Wire:

1- .025 Dia. x 36 Steel Wire

1- .032 Dia. x 36 Steel Wire

1- .039 Dia. x 36 Steel Wire

1- .046 Dia. x 36 Steel Wire

1- .062 Dia. x 36 Steel Wire

Tubing:

1- 1/16 O. D. x 12 Aluminum Tube

1- 7/32O. D. x 12 Aluminum Tube

1- 9/32 O. D. x 12 Aluminum Tube

1- 3/16 O. D. x 12 Brass Tube

1- 1/4 O. D. x 12 Brass Tube

Miscellaneous:

1 Pr- E-Flight .25 Size Cub Wheels

1- 3/4” or 1” Tail Wheel

 2- 3/32 Wheel Collars

24” Sullivan #507 size Plastic Pushrod Tube

1- .008 x 12 x 18 Clear Acetate Sheet

1- .010 x 6 x 12 Evergreen Styrene Sheet

1- Manila File Folder

2- Rolls Microlite

Power and Guidance:

1- Suppo 2217/9 or E-FlitePark 450 Outrunner Motor

1- 20A ESC

6- Up to 9 Gram Servos

1- APC 11-5.5E Propeller

2- Y-Leads

2- 9” Servo Extensions

1- 2200 mah 2S Lipoly Battery

Photo Captions:

The rudder and vertical fin are built over the plans then lifted from the building board and sanded to shape. The hinges are secured with Canopy 560 glue after the frames are covered.

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 The Horizontal Stabilizer is built over the plans then lifted from the building board and sanded to shape. The hinges are secured with Canopy 560 glue after the frames are covered.

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The Wing Assembly is built over the plans incorporating interlocking ribs and spars to insure a light, quick build. The flaps and ailerons are built directly into the wing assembly, and then removed for shaping when assembly is completed.

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 The wing assembly is removed from the board and sanded to final shape and the flaps and ailerons hinged. The hinges are secured with Canopy 560 glue after the frames are covered.

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The Wing Assembly is finished and ready to install the servos. The servos will be secured in place with a dab of silicone caulk and the wiring run in and then the frames will be covered.

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The Fuselage Side frames are built directly over the plans and joined beginning with the landing gear mount beams.

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Formers are added at the cabin area followed by the firewall and instrument panel formers.

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The remaining tail formers and cross pieces are added, and then the stringers and cabin door out-fill is added to complete the basic frame.

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The rear cabin side window frame is bowed over a form and glued in place on the fuselage frame flush with the cabin out fill and stringers.

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The landing gear mount beams are gouged to accept the landing gear struts prior to the fuselage frames being joined. The gussets are added after the frame is completed.

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The vacuum-formed plastic cowl was assembled and the seam cleaned up using automotive spot glazing putty. The cowl is then mounted onto the firewall.

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 The rudder and elevator servos are mounted on balsa beams accessed through the bottom of the fuselage.

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The lift and jury struts are set up and assembled on the model to insure proper alignment using a Washout Jig (Plans are available from the Author).

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A full cockpit arrangement was built into the Super Cub beginning with skinning the inside of the fuselage using common file folder paper.

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The model is covered with Microlite and trimmed in self adhesive vinyl. The upper and lower door sections are hinged on the fuselage using vinyl sheet. The windows are glued in place and trimmed with vinyl as well.

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The motor mount box is assembled and glued in place on the firewall. The Suppo 2217 Outrunner motor mounted with #2 sheet metal screws.

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The finished model is balanced using the battery to the best advantage to avoid adding ballast. Note the over-sized Tundra Tires made up from blocks of EPP foam and hubs from DuBro Lite wheels. The hub caps are made from plastic seal caps from 1 quart Orange Juice cartons.

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With the full cockpit arrangement space for the battery is limited, so the battery is mounted under the cockpit floor, and a small row boat was made to serve as a battery hatch.

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 The battery is tucked into its compartment on the fuselage bottom and retained with a Velcro Strap to prevent it from falling out. Three magnets are used to retain the row boat hatch.

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A Bush Plane can’t go into the back country without some level of self protection, so a Shotgun was made up from brass tubing and basswood and lashed to the jury strut.

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No one wants to find themselves “up the creek without a paddle”, so a set of oars were carved from bass wood and lashed to the other jury strut

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The instrument panel was printed on vinyl by Callie Graphics and placed in the cockpit along with all the other details made up from Depron foam and various bits of wood, plastic.

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The seats, control stick assembly and throttles were made up from Depron foam and various materials to complete the cockpit details.

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The prototype Super Cub upon completion is on the ramp ready for its maiden flight. The cockpit, row boat battery hatch and other details were added after the model proved itself to be a very capable bush plane. Vinyl trim tape represents the wing root fairings and is used to retain the wings when assembled. The Gas Tank covers and flap gap fairings are made up from .010 sheet styrene.

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The cockpit components were made up from 3MM Depron foam and various bits of plastic and metal rod and tubing. The parts were assembled and permanently mounted inside the fuselage after the Super Cub had proven itself a solid and stable flyer.

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The Super Cub flies beautifully and is capable of any maneuver a full scale Cub will perform. Short field landings and take-off’s are easy with the flaps extended, and due to the well balanced controls characteristic of the Cub, the side slip approach is unmatched by any other light plane I’ve ever flown.

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About the author

Senior Technical Editor About Me: I have a lifelong passion for all things scale, and I love to design, build and fly scale RC airplanes. With 20 plus years as part of the Air Age family of magazines, I love producing Model Airplane News and Electric Flight.
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