RCU Review: E-Flite J-3 Cub 25 on Floats

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    Contributed by: Greg Covey | Published: October 2006 | Views: 75331 | email icon Email this Article | PDFpdf icon

    Review by: Greg Covey
    Assembly Photos: Greg Covey
    Flying Photos: Papa Jeff Ring
    Video 1 & 3 Pilot: Lynn Bowerman
    Video 2 Pilot: Scott Miller


    Manufacturer Info

    E-flite Models
    Distributed Exclusively in the U.S.A. by:

    Horizon Hobby, Inc
    4105 Fieldstone Road
    Champaign, IL 61822
    Ph: (800) 338-4639
    Toll Free: (800) 338-4639
    Fax: (217) 352-6799

    Ease of Assembly

    Complete Kit with hardware
    Great ARF value and looks
    Superb Flying Performance
    Float-ready Design
    Magnetic Held Hatch
    Matched Power 25 Outrunner

    Some Soldering Required

    E-Flite J3 Cub 25 Introduction

    The E-flite J-3 Cub 25 ARF from Horizon Hobby has great scale appearance and performance which include scale ailerons. The ARF model is built from quality balsa and light ply construction making for a sturdy, lightweight airframe that handles incredibly well in most any flying situation. The firewall is set up for use with an outrunner motor, such as E-flite?s Power 25, making a perfect power match for the airframe. Optional floats add a new dimension to the scale flying experience, and the one-piece wing allows for easy transportation to and from virtually any flying field, pond or lake. The model can be flown with either a 10-cell NiCd/NiMH pack or 3-cell Lithium pack.


    • Wing Span: 62 inches (1575 mm)
    • Overall Length: 35.5 inches (900 mm)
    • Flying Weight: 4.0 - 4.25 lbs (1.8 - 1.9 kg)
    • Motor Size: Recommended: E-flite Power 25 Outrunner (EFLM4025A) - not included
    • Radio: Minimum Requried: 4 channels - not included
    • Servos: Required: 4 Mini Servos - not included Recommended: 4 JR Sport MN-48 (JSP20040)
    • Trim Scheme Colors: UltraCote Cub Yellow (HANU884) & Black (HANU874)
    • Prop Size: 12x6E
    • Speed Control : Required: 40 amp brushless Recommended: E-flite 40A brushless (EFLA312B)
    • Recommended Battery: E-flite 10-cell 12V 1800mAh Ni-MH (EFLB4010) or Thunder Power 3-cell 4200mAh Li-Po (THP42003S2PPL) - not included

    Key Features:

    • Outstanding scale detail, including the factory-painted fiberglass cowl with molded engine detail
    • Scale aileron design sets the E-flite J-3 Cub apart from other 25-size electric Cubs on the market
    • E-flite's optional 25-size floats are easy to assemble and attach to the J-3 Cub, and offer thrilling performance during water taxi and take-off
    • Built-in float mounts
    • Removable one-piece wing for fast transition to the flying field
    • Factory-painted landing gear with authentic Cub wheel caps
    • Quality balsa and light-ply construction, and genuine Ultracoat covering
    • Outrunner-ready firewall?perfect match for E-flite?s Power 25 Outrunner, 870 Kv
    • Flies great with LiPo (THP42003S2PPL) or Ni-MH (EFLB4010) packs

    ARF Contents


    The J3 Cub 25 came very well packaged and each part was individually wrapped in plastic.
    The covering looked great and the 51 page manual was very well written with plenty of photos.

    Although the Cub came already trimmed with decals, the kit provides an extra sheet for the various brand names.

    I removed the individual plastic bags and found the control surfaces were taped to their respective part of the plane.

    Everything was already painted and looked great!

    The 30" fuselage was well built; being both strong and light. The motor mounting holes, control rod tubing, and, air-cooling system were already done. The front bottom hatch is held in place with pre-mounted magnets for easy battery access.

    I'm using the E-flite 40A brushless (EFLA312B) ESC and there a warning note about the BEC having an overload at very high temperatures when using higher-current servos. Note that the ESC comes with mating connectors and wire extensions for the motor.

    Important Note:

    We have found during continued flight testing, the possibility of a rx/servo current overload to the BEC in the speed control, causing the motor and radio to shut down in flight. This has typically happened on extreme high temperature days with continuous extreme flight control inputs. Most speed controls on the market today are designed for use with 4 sub-micro servos with relatively low current draw like the E-flite S75. The newer sub-micro digital servos, as well as most micro and mini servos, have a higher current draw and can cause a BEC to shut down due to high temperatures.

    In order to provide the most reliable product, E-flite recommends the use of a separate BEC (like the Ultimate BEC), or receiver pack and switch using the following items to ensure trouble-free operation:
    - (EXRB100) Expert 720mAh NiMH 4.8v Receiver Battery
    - (EXRA050) Expert Standard Switch

    Use these items to power the receiver and servos after disabling the BEC on the ESC. E-flite does NOT recommend using the speed controller's BEC in the applications described above.


    I'm using the recommended JR Sport MN-48 servos (JSP20040) and E-flite Power 25 Outrunner (EFLM4025A) ...when it arrives.

    The two recommended battery packs are the E-flite 10-cell, 1800mAh NiMH (EFLB4010) or ThunderPower 3-cell, 4200mAh LiPo (THP42003S2PPL) pack. Although both packs weigh a similar amount, the power density of the Lithium pack is doubled over the NiMH pack which doubles for your flight time for about 4 times the cost.

    Just after testing the J3 Cub 25 on wheels, I'll try out the optional E-flite 25-Size Fiberglass ARF Floats (EFLA500). The E-flite quick-mount floats are designed specifically for 25-size planes that are float-ready out of the box, so you can go from pavement to pond in just minutes.



    Assembly starts by mounting the gear mains with 4 straps and 8 screws into pre-drilled holes. The gear mains fit snuggly into channels in the bottom of the fuselage. An innovative wheel design hides the collar and 4 screws inside for a very clean look. The plastic Cub cap covers the assembly.

    The landing gear fairings are secured with 3 tywraps.


    The JR Sport MN-48 mini servos fit perfectly into the bay openings. I am using an M5 v2 receiver in my J3 cub 25 for glitch-free performance.

    Alternatively, the Encore receiver provides the same glitch-free performance but allows for the 5th channel to be re-programmed for channel 5 or 6 in case flaps are used.

    I used ZAP Thin CA to glue the hinges in place. Remember not to use CA accelerator (or kicker) here as we want the CA to soak into the hinge material and balsa.

    The JR mini servo mounted to the hatch plate using two supplied blocks. All the hardware needed for this procedure is supplied in the kit.

    The E-flite manual is extremely detailed so I will be glossing over many areas clearly covered in the manual. One area not covered is that you will need 12" extensions for the aileron servos.

    The wing joiner is made from two thinner pieces of plywood glued together with epoxy and then glued into one wing half. After first test fitting the wing halfs, they are glued together with epoxy.

    The two aileron servos must be connected together with a "Y" adapter or an FMA 605SB Servo Buffer.

    I mounted the On/Off switch in-line with the black stripe to keep it from detracting from the scale look of the Cub. You can either re-route the ESC's throttle signal pin into the output of the switch wire connected to the receiver or use the receiver battery pack option. The On/Off switch provides added safety and convenience when connecting the battery pack or finishing a flight.

    Note that some vendors now sell On/Off switches for electric planes that route all 3 wires eliminating the need to re-route the ESC's throttle signal wire. One example is the 1570 Universal ESC Control Switch from MPI.

    Tail Assembly

    The stabilizers were attached with 5-minute Z-poxy after first cutting away the section of covering to be glued. I checked the incidences and needed no offset for creating a perfect alignment. The tail wheel assembly is glued in place before attaching the rudder.


    The linkages installed without issue. The two elevator half pushrods are combined using two wheel collars which are then secured with epoxy after alignment. Note that I added a white spacer to center the tail wheel and used a toothpick with a dab of CA for a strain relief on the antenna wire.


    The windshield comes pre-trimed and painted so you just need to prepare the surfaces to be glued with a little sanding. The side windows must be cut with a 1/16" border before gluing. I used Pacer PolyZAP glue which is designed to work on plastics, nylon, and, rubber. It is ideal for clear canopies and windows.

    Attaching the struts is as easy as screwing them into the pre-drilled holes in the fusleage and wing.

    E-Flite Power System

    The E-flite 25 motor comes with the motor mount, collet prop adapter, connector mates, hex wrenches, and all hardware needed. Likewise, the E-flite 40-amp Brushless ESC also comes with the connector mates. Both these E-flite products come with mating connectors and they each have their own connectors already soldered on. You only need to screw in the X-type mounting bracket and solder on a mating connector for the ESC-to-battery connection.

    I also received an Expert (EXRB100) 4-cell, 4.8v, 720mAh AAA NiMH receiver pack to eliminate the need for the BEC feature on my ESC. This is used in conjunction with the Expert (EXRA050) Standard Switch with charging cord so you recharge it right in the plane.

    I was a bit dissapointed when I discovered that the pre-mounted t-nuts in the J3 Cub 25 were a different size than the included hex screws that came with the motor. Although the matching screws for the pre-mounted t-nuts came with the J3 Cub kit, they were too large for the X mount holes requiring you to drill them out. This makes for lots of metal fragments so it is best to drill the holes out before you attach the X mount to the motor. Horizon Hobby has said that this mismatch in size between the Power 25 motor screws and the J3 Cub 25 pre-mounted t-nuts is already resolved so your model will likely not need this modification.

    Motor Mounting

    The E-flite 25 motor attaches to the pre-mounted t-nuts in the firewall. Remember to use some thread locker on these screws as well as the screws holding the X-mount to the motor. I decided not to mount the ESC to the side wall with Velcro (hook and loop) as it is held in position quite well by the thick wires and battery pack. We'll see if this works out during actual use.

    The cowl was held in place while I drilled pilot holes for the 4 mounting screws. Some folks like to use masking tape to temporarily hold the cowl in position while drilling.

    The prop adapter is designed to fit the APC 12x6 e-prop perfectly without and bushing. The collet design simply presses in place and is then tightened. I use the largest size hex wrench that will fit through the hole in the spinner to tighten it.

    Safe Charging


    I charged the ThunderPower 4200mAh pack with a Cellpro 4s Balancing Charger and ThunderPower to Cellpro Adapter from FMA Direct. All three products are available from Horizon Hobby.

    Since this charger can safely recharge the pack in the plane, I mounted the battery with Velcro on the bottom and two Velcro straps. This combination holds the 10oz pack securely in place without any sliding. Note that the fuselage hatch is held in place by two strong magnets.

    Recharging at the field is plug and play easy without having to remove the wing or unscrew a hatch.

    Battery Options

    The 10-cell E-flite 1800mAh 4/5A NiMH pack mounts in the same manner as the optional LiPo pack. It adds another 3oz to the flying weight.

    The Expert (EXRB100) 4-cell, 4.8v, 720mAh AAA NiMH receiver pack adds another 2oz and is best mounted across the CG as shown when using the LiPo pack. It can also be mounted below the servo tray on top of the framework for the gear mains. When using the 10-cell E-flite NiMH pack that weighs 12.8oz, move the Expert receiver pack aft by about 3" for proper balance.

    The Expert receiver pack is used in conjunction with the Expert (EXRA050) Standard Switch with charging cord so you recharge it right in the plane. This eliminates the possibility of a BEC failure under extreme heat, humidity (thicker air), and servo drain conditions. I am not certain if it has been determined that this conditions happens often enough to justify the setup. It is a recommendation by Horizon Hobby for safety due to the specifications of the ESC's BEC output.

    The 8% range of flying weight due to various setup is as follows:

    • 59oz (3.7lbs) with LiPo option and using BEC in ESC
    • 62oz (3.9lbs) with NiMH battery pack and using BEC in ESC
    • 64oz (4.0lbs) with NiMH battery pack and using Expert receiver pack


    The finished E-flite J3 Cub 25 balanced perfectly with either pack installed and weighed 59oz (3.7lbs) Ready-To-Fly (RTF). The power system measured 350 watts at 33amps for about 95w/lb which guarantees aerobatic performance.

    Test Flying

    We test flew the J3 Cub 25 with total success. It simply flew as expected...magnificent! The E-flite 25 outrunner provided awesome power which means my next test with floats is guaranteed to be successful. The NiMH pack provided about 10 minute flights and the 4200mAh LiPo pack about 20 minute flights. The flight time will vary depending upon the amount of aerobatics performed.

    The first video of the J3 Cub 25 is on land with the stock wheels. The winds were rather brisk for a 25-size plane at 10-15mph but the Cub proved to have plenty of power.

    J3 Cub 25 Video 1 (10meg)


    Float Assembly

    It is time to try out the optional E-flite 25-Size Fiberglass ARF Floats (EFLA500). The E-flite quick-mount floats are designed specifically for 25-size planes that are float-ready out of the box, so you can go from pavement to pond in just minutes. I plan to video the J3 Cub 25 on floats taking off from both water and grass.

    The float assembly went without a problem as the instructions were simple and well written. The J3 Cub 25 is also a float-ready design by E-flite. After removing the stock gear mains, I cut the covering off the rear most channel and mounted the float mains.


    Next, the brackets were screwed into the floats and flat spots filed onto the tops of the float mains for better hold by the wheel collar set screws. I used a Dremel tool grinder to make the entire top of the float mains extensions flat. The floats were then mounted and the collars secured using Pacer Z-42 Thread Locker. Note that there is one float with extra holes in the aft end that is meant to mount on the side were the rudder linkage is located.

    The float kit provides a ventral fin for adding stability in flight, especially at slower speeds. The ventral fin mount is screwed into place in the pre-drilled holes under the Cub fuselage. After cutting away some covering, the fin itself is glued into the mount with epoxy. I used 5-minute ZAP Z-poxy.


    Water Rudder


    The water rudder and linkage assembled fine and I did not see any excessive resistance added to the rudder throw. My only modification was to make two of the full brass strips into half strips for easier mounting. I used a Dremel tool to cut off the unwanted end. I also managed to break one of the quick links so I replaced it with a similar size one from my own supply. There was about 1/2" excess cable that I cut off from the float end.

    When testing the water rudder assembly, make sure that it follows the normal rudder direction and that it can flip up with little resistance if it hits a rock or some obstruction in the water.

    The Cub looks great with the floats attached. I can't wait to test it out!


    Float Flying

    J3 Cub 25 Video 2
    CLICK HERE (6meg)

    The second of three videos has the J3 Cub 25 on floats taking off grass. We made the floats extra slippery by spraying Pledge furniture polish on the bottom. Again, the Cub performed flawlessly. The power level and ground steering is proof that it will perform fantastic off water!


    J3 Cub 25 Video 3
    CLICK HERE (12meg)

    When we tested the J3 Cub 25 on water, it performed very well. The high power level of the E-flite 25 outrunner motor and the very rigid design of the float cage allows you to take-off and land even in small areas. The video was taken on a single charge of the ThunderPower 3s2p 4200mAh Lithium pack option. Even with the flying part mostly cut out of the video, we only used 60% of the pack as displayed on the Cellpro 4s Balancing Charger.

    I covered the bottom holes with masking tape on the inside and removed it when we were finished flying. Some water does splash up on the bottom of the fuselage but probably not enough to cause a problem.



    The E-flite J3 Cub 25 is the best .25-size scale float plane that I have seen to date. No adjustments were made to the CG and it was flying slightly tail-heavy...which is just how we like it for slower landings. It was designed from the ground up to fly well on either wheels or floats and I made no changes from the stock setup or design. I really liked the magnetic mounted hatch on the fuselage bottom for easy battery access and recharging. The entire build was easily done by following the manual and the only soldering required was to add battery connectors.

    The solid design of the Cub frame, wing, and accessories makes it rugged enough to handle those less than perfect landings on either ground or water. This model will not break just by picking it up or puting it in your car for travel.

    The power level provided by the E-flite Power 25 Outrunner motor is a perfect match for the Cub, allowing it to easily take off water and perform aerobatics. The electric power system keeps the Cub clean and quiet for those early morning flights on a calm lake.


    J3 Cub 25 off Grass

    J3 Cub 25 off Water

    Dealer Information

    E-flite Models
    Distributed Exclusively in the U.S.A. by:
    Horizon Hobby, Inc
    4105 Fieldstone Road
    Champaign, IL 61822
    Ph: (800) 338-4639
    Toll Free: (800) 338-4639
    Fax: (217) 352-6799
    Website: www.horizonhobby.com

    FMA Direct
    5716A Industry Lane
    Frederick, MD 21704
    Website: www.fmadirect.com
    Sales: 800-343-2934 or 301-668-7614

    ZAP Glues On-line at Frank Tiano Enterprises

    Pacer Z-42 Thread Locker
    5-minute Z-poxy
    Pacer POLY ZAP(tm)


    Comments on RCU Review: E-Flite J-3 Cub 25 on Floats

    Posted by: T170 on 12/17/2009
    Well done - really helpful. I appreciate the details you included. It is nice to see mostly takeoffs and landings in the float flying video - that is what you want to study.
    Posted by: jweitsjr on 01/11/2011
    Nice flying! It looked great on land or water. How do remove the rear fin ,if you want to go back to flying on land ?
    Page: 1
    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

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