Greg Covey

Hi,

I am reviewing the World Model's Piper J-3 Cub 1/4 Scale ARF and converting it to clean and quiet electric power. The World Model ARFs are distributed in the U.S. by [link=http://www.airborne-models.com/html/productdetails.asp?ProductID=24]Airborne Models[/link].

Key Features:
[ul][*] The most popular 1/4 scale ARF model on the market[*] Top quality balsa and plywood construction[*] Built-up wings with aluminum wing joiner[*] Premium hand iron-on covering film[*] Comes with all hardware and accessories
[/ul]
Specifications:
[ul][*] Wing Span: 104.0 in / 2640 mm[*] Wing Area: 1586 sq in / 102.3 sq dm[*] Flying Weight: 14.0 - 16.0 lbs / 6400 - 7300 g[*] Fuselage Length: 65.0 in / 1650 mm[*] Engine Required: 2C 0.91 cu in, 4C 1.20 - 1.60 cu in[*] Radio Required: 4 channels, 5 heavy-duty servos
[/ul]

Greg Covey

The big J3 Cub comes in a single box that is 57" long. All the parts are well packaged and individually wrapped in plastic.

Greg Covey

There are plenty of parts in the box to replicate all the scale features of the popular Cub design. Although the fuselage comes with decals already applied, the wing and tail sections are left for the builder to customize.

The kit includes all the hardware and linkage pieces as well as a pre-painted pilot. Each plastic bag is labeled with a number that matches the step in the instruction manual. The stabilizer sections are pre-stripped for immediate gluing.

Greg Covey

A closer look at the fuselage reveals quality construction and a side door for easy access inside.

Greg Covey

To power my 16lb J3 Cub, I'm using the AXI 5320/28/Jeti 90 [link=http://www.hobby-lobby.com/brushless-combo-axi.htm#532028]Combo[/link] for only $408 at Hobby Lobby. This cost effective combination comes with two prop adapters for flexible mounting and can provide burst power over 2000 watts.

When installing the prop adapter and collar, I used Pacer Z-42 Thread Locker to keep the screws and hex nut secure.

Greg Covey

To mount the AXI 5320/28 motor using the nylon spacers and 8-32 hardware from [link=http://www.hobby-lobby.com/motormt.htm]Hobby Lobby[/link], I needed to re-tap the metric mounting holes on the motor for 8-32. This was quite easy since it is the next size up from the M4 threaded holes on the motor.

Next, the included AXI motor mounting decal was applied to the pre-drawn crossed lines on the ARF model. The lines are pre-drawn for centering the glow engine shaft through the cowl opening so they also work perfectly for a direct drive electric motor.

The nylon spacers create the proper offset of 2-3/4" inches needed for prop clearance by using two 1" spacer, one 1/2" spacer, and one 1/4" spacer. Since the 4" 8/32 screws are a bit long, I used one 1/2" spacer behind the almost 1/2" thick firewall. This left 1/4" of threaded rod for screwing into the AXI 5320 motor. Remember to apply thread locker to this section of the screw before securing it into the AXI motor.

The large side opening in the J3 Cub allows for easy access to fit a screwdriver inside to tighten the four screws.

airflow

My Feedback: (1)

Greg -
It's rewarding to see the attention to detail you are doing on this conversion. The photos are worth a thousand words. Good luck, and please keep up the good work.
Bob McClure

Greg Covey

Thanks, Bob.

I ran out of 1" nylon spacers and my local Home Depot was also out of them so I ordered more from Hobby Lobby to finish my motor mounting.

I placed my 1/4 scale Cub next to the .25-size E-flite J3 Cub that I am also reviewing for a size comparison.

airflow

My Feedback: (1)

when drilling and tapping the motor, what is the probability of metal fragments getting inside the motor?

Greg Covey

Bob,

I did both the drilling and tapping underneith the motor so that any fragments would drop down. That end of the motor is wide open so it is easy to blow out the metal dust by mouth or compressed air.

Due to the outrunner design and laminated wires, I doubt that any escaping metal pieces would cause harm. That being said, the procedure likely voids the AXI warranty, in which case long M4 screws could be used.

Greg Covey

All my servos for this project are the Futaba [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXH296&P=ML]S9001 Coreless Aircraft Servo[/link] which I'll run on 6v from my FMA [link=http://www.fmadirect.com/Detail.htm?item=2004&section=58]Power Force Regulator[/link].

The 1/4-scale J3 Cub kit provides all the linkage hardware, pre-mounted ailerons, and, pre-drilled holes for the control horns. I needed a 30" extension cable for each aileron servo.

Greg Covey

My spacers arrived from Hobby Lobby so I completed my motor and ESC mounting.

bent

Greg
Nice work on the big Cub. I plan to electrify a 1/4 scale Cub on floats some day and I'm particularly interested in the sound your beast makes. If you make a video please don't add music. Looking forward to your flight report.

Greg Covey

Gary,

Electrics make for great float planes as you can fly off the water early in the morning without disturbing people. I like to do this once a year in the Adirondack's in upstate NY.

To finish up my aileron servo installation, I connected both wing halves together with a Hobbico (HCAM2500) Y-Harness and checked the alignment with a receiver and Rx. battery pack.

Greg Covey

Although the cowl mounted easily, the fit with the AXI 5320 motor was rather tight so it was critical to tape the cowl in position first, while checking the motor rotation for rubbing, before drilling holes for the screws.

The manifolds and valve covers were painted black and silver and then glued to the cowl with PLASTI-ZAP.

I found that a spacer is needed in between the prop and the adapter backplate. This not only moves the APC 20x11 e-prop out a bit for better clearance (although it does make it without a spacer) but allows the screw to tighten properly without hitting the untapped section of the prop shaft.

Greg Covey

The gear mains mounted easy with the first step being the wing strut braces. The wheels are held by collars on either side and then a cap covers the outside collar. It is held by three tiny screws into the wheel hub.

I ended up with two spare metal braces in the gear mains bag that wasn't sure what do to with. It turned out that they are used as strut supports later on in the assembly.

tlnibert

I ordered a GP Cub 81" yesterday, but would like to have a quarter scale. I've found your web site and I'm impressed, I liked the conversions. I'll pickup a quater scale Cub and try the conversion.
Tom

Greg Covey

Hi Tom,

Welcome. You can't have enough Cubs! I have a smaller Speed 400 parkflyer size and the new 25 size Cub from E-flight. This larger 1/4 scale Cub should have plenty of power to fly in most any weather conditions.

Once I found that a spacer was needed in between the prop and the adapter backplate, my friend, Paul Weigand who is a retired machinist from Kodak, made one from my drawing. This was a great surprise as I had no 12mm drill bit. The APC 20x11 e-prop will have better clearance and the metric nut will tighten properly without hitting the untapped section of the prop shaft.

Greg Covey

The gear skirts were pre-cut and covered. All the hardware needed to mount them comes with the kit.

tlnibert

Glad you showed me the gear skirts, because I was about ready to pick another plane. I bet shipping will be a handful.
Should be able to order it soon, my GP Cub was put on back order. Do you know anything about the Rimfire motors Tower carries?

Tom
[email protected]

Greg Covey

Tom,

The RimFire motors are outrunners like the AXI. Use the watts-per-pound rule of thumb and you can't go wrong. For some additional information on this, read my [link=http://www.gregcovey.com/Glow_Conversions_Made_Easy.htm]Glow Conversions Made Easy[/link] article.

tlnibert

I had a motor all picked out, but after reading your article, I'm not sure. The Cub weights 8.5 lbs. and I want it to be aerobatic, so I'm looking at 800 watts. The motor Tower suggest is over $200, that's not going to happen. The Rimfire is much cheaper, but then again you sometimes get what you pay for..... The Gpmg 4715 or 4700 ????? Totally lost.....
Then an ESC??????
I was just on Hobby Lobby, I found a AXI that may work.
Tom

Greg Covey

Tom,

I looked at the Rimfire motors at Tower Hobbies and they don't provide enough information to make an informed choice. Perhaps they will add some power ratings when they become available in August.

The tail section was simple to assemble as the control surfaces are pre-hinged and the covering is already cut away on the areas to be glued. I used Pacer 5-minute Z-poxy to glue the horizontal stabilizer in place and then found it easier to use thick white glue for the vertical stabilizer. The incidences were checked and I needed no shims for correction.

Greg Covey

The stock tailwheel assembled easily and all the parts were in a separate bag with the instruction step printed on the bag. I needed to shorten the supplied springs by cutting off about 1/3 of the length. If the stock foam wheel is not robust enough for the weight, I will replace it with a Dubro rubber tailwheel as I am not a fan of foam wheels on models this large.

Greg Covey

The stock tailwheel assembled easily and all the parts were in a separate bag with the instruction step printed on the bag. I needed to shorten the supplied springs by cutting off about 1/3 of the length. If the stock foam wheel is not robust enough for the weight, I will replace it with a Dubro rubber tailwheel as I am not a fan of foam wheels on models this large.