Hobby Lobby Skylark e-Conversion
 

Hi,

I have started another project converting the new Skylark ARF Pattern Plane from [link=http://www.hobby-lobby.com/skylark.htm]Hobby Lobby[/link] to clean and quiet electric power.

The conversion looks very simple using electric components that are all available from Hobby Lobby. I'll detail these parts shortly.

Here are some of the Skylark specs:
[ul][*] Wingspan = 58.5"[*] Length = 55"[*] Wingarea = 586 sq/ in/[*] RTF around 86oz (5.4lbs)
[/ul]

All the ARF parts are pre-wrapped in plastic and mounted in the box with custom cardboard fittings to help insure dent-free delivery.

A decal set is provided and a complete instruction manual (in English) is loaded with clear photos and drawings. The Skylark building looks very easy.

The contrasting top and bottom wing color schemes provides for excellent orientation of the plane during pattern maneuvers.

RE: Hobby Lobby Skylark e-Conversion
 

Jeez Greg....who sponsers all these conversions and where do I sign up :D I have looked at this one too for conversion. It should be pretty simple. Good luck.

Mike

RE: Hobby Lobby Skylark e-Conversion
 

Mike,

RCU is the place to be for glow-to-electric conversions! You can sign up right on-line from the "EDITORS" menu selection at the top of the window.

My Skylark e-conversion will use components available at [link=http://www.hobby-lobby.com/eflight.htm]Hobby Lobby[/link] from their [link=http://www.hobby-lobby.com/eflight.htm]Electric Flight Accessories[/link] list.

Here is what I am using:
[ul][*] WZH001 Skylark ARF Pattern Airplane[*] PM412014 AXI 4120/14 External Rotor Brushless Motor[*] JECA70P Jeti "Advance" 70 Amp Opto Brushless Controller, 6-16 Cells[*] B2400C8 8 Cell CP-2400SCR NiCad packs (2)[*] HTS085MG Hitec HS-85 "Mighty Micro" Metal Gear Servos (4)[*] RCD120 Hitec "Electron" 6 Ch. Micro FM Receiver[*] HT0096 Aileron "Y" Connector and two HLAE322 24" Extensions[*] PM41001 Aluminum Motor Mount for AXI 41 Series Brushless Motors[*] MJ4706 Collet Prop Adapter for 6mm Shaft, M8[*] KFS001 Ultimate BEC[*] DEA1300 Deans Ultra Plug connectors, pair
[/ul]

I will be experimenting with various APC prop sizes from 13x8 to 15x8. At this time, I am not 100% sure which AXI motor mount will work best on the Skylark so I have both to try. It is possible that the PM41001 mount may not fit in the fiberglass cowl. I'll report on that later.

RE: Hobby Lobby Skylark e-Conversion
 

The assembly starts by gluing in the pre-installed aileron hinges. There are 4 hinges per aileron.

I roughed up the nylon and metal pin hinges with sandpaper and then glued them in place using Aileene's Tacky white glue. First, I coat the inside of the slots in the aileron and then the wing. Next, I coat the hinge itself and insert it into the wing. Once all 4 hinges are installed, I attached the aileron and press it on as far as it will go.

The wing halves are then glued together with a rather thick balsa spar that runs between custom openings on each wing half. You need to orient the spar properly as it has a front and top side.

The spar and wing halves fit together perfectly without and sanding! I used 5-minute epoxy to first glue the spar correctly into one wing half, and, after it dried, I glued the two wing halves together making sure that every surface was covered with a coat of epoxy.

I decided to pay close attention to make a perfectly strong wing joint because I would skip the fiberglass reinforcement step that followed. After studying the wing frame and mounting scheme to the fuselage, I decided that I had plenty of strength for my electric conversion.

RE: Hobby Lobby Skylark e-Conversion
 

Before gluing the wing halves together, I decided that it would be easier to run my aileron extension lines first since there were openings in the center end of each wing to aid in the cable run. The wings and fuselage come with strings inside to guide in routing the servo cables so skipping these steps as I did is not necessary.

My Skylark wing assembled perfectly aligned and strong. There is 54mm of dihedral built into the wing frame to aid in flight stability.

RE: Hobby Lobby Skylark e-Conversion
 

The Skylark fiberglass cowl comes pre-cut and painted in three colors. It even has black trim striping on it.

Very nicely done!

RE: Hobby Lobby Skylark e-Conversion
 

The Skylark construction quality is excellent!

Here you can see solid fuselage design, pre-drilled firewall, and attention to details like access compartments and string guides to pull servo leads and antenna wire.

RE: Hobby Lobby Skylark e-Conversion
 

The aileron servos and linkage installed very easy with the supplied parts. I needed to add a small plywood block to mount my HS-85MG servo.

I also added a "keeper" made from a piece of fuel line hose to help hold the clevis.

Note that since this is a pattern plane, I used the inside hole on the servo arm. A 25% swing is plenty for these large ailerons.

RE: Hobby Lobby Skylark e-Conversion
 

The Skylark wing mounting scheme is precise and solid. The plastic fasteners are screwed into place on the fuselage into custom channels. The wing leading edge uses a hardwood spar from each half that was glued together. The trailing edge is then reinforced with additional hardwood plates which is also used to mount the saddle.

The result is a seamless joint between the wing and fuselage that is locked in place with perfect incidence.

RE: Hobby Lobby Skylark e-Conversion
 

To mount my AXI 4120 motor on the Skylark, I initially tried using the PM41001 Aluminum Motor Mount but found that the frame did not fit in the custom fiberglass cowl. I then tried the [link=http://www.hobby-lobby.com/motormt.htm#AXI1]PM41002 Radial Mount Set[/link], and, although it did fit in the cowl, the length was too short.

The length problem was easily solved by using a common piece of PVC available at any home improvement store or hardware store. The 2" coupler (Schedule 40) was a perfect fit. I used 10-32 hardware with 3" long screws and Tee nuts to secure the assembly. I'm sure that #6 or #8 hardware would also work but I didn't find the 3" length screws at Home Depot.

A small ridge runs along the inside of the coupler center that needs to be filed flat where each screw passes. It is a simple job with either a round file or Dremel tool sander.

The motor mounted easily and is rock solid. I used a little Locktite inside the Tee nut threads to help keep it secure. Note that both down thrust and right thrust are built into the firewall.

RE: Hobby Lobby Skylark e-Conversion
 

The Skylark landing gear mains are mounted into pre-cut channels in the wing bottom. The pre-bend spring rod presses into the channel with one end going straight into a hole. The assembly is held firm with a few straps screwed into the wood frame. No glue was used.

RE: Hobby Lobby Skylark e-Conversion
 

R-C-U is the place to be...
Change your glow to E-lec-tri-city...
Pro-blems solved so great and small...
Damn the fuel just make-em electric all...


(To the melody of Green Acres):eek:

RE: Hobby Lobby Skylark e-Conversion
 

Green Acres, huh? That's using the way-back machine for most of us. ;)

Forgive the hazy image here but my intent is to show that the UBEC input is wired in parallel with the ESC battery connector. Since the ESC is an "Opto" isolated type, it needs power into the plug from the receiver which it gets from the UBEC device output. Simply plug the ESC into the throttle channel and the UBEC into any free channel. If no free channel exists, then a "Y" adapter is needed for the throttle channel.

Non-Opto ESCs usually need the on-board BEC disabled which requires disconnecting the red "+" wire from the receiver connector. Opto-isolated ESCs have no on-board BEC and require power from the receiver via an Rx. battery or UBEC.

RE: Hobby Lobby Skylark e-Conversion
 

The motor plugs into the ESC and the ESC into the battery. The Ultimate BEC is then tapped into the battery connector to feed the receiver and servo 5v.

The [link=http://www.hobby-lobby.com/ubec.htm]UBEC[/link] is a state of the art switching regulator designed to convert an input voltage from 5.5v to 35v DC into a regulated output voltage of 5v to power your receiver and servos. The UBEC can deliver a continuous current of 3amps and a peak short term output up to 5amps. This is meant to handle power for up to 8 servos.

A typical 4-cell receiver battery pack weighs 3.2oz so I saved 2.2oz along with the added convienience of not having to worry about re-charging another battery pack.

RE: Hobby Lobby Skylark e-Conversion
 

The cowl fit was too tight so I needed to cut away some of the balsa fuselage bottom. Once I had a proper fit, the cowl was easily anchored with 5 screws supplied in the kit.

I also cut open some air cooling vents on the from side of the cowl. The stock opening in the bottom for the glow engine muffler will act as an exit to draw through cool air around the motor.

RE: Hobby Lobby Skylark e-Conversion
 

The supplied spinner matches the color scheme and fit perfectly in front of the cowl. I drilled out the spinner base hole slightly to fit onto the 9mm Radial Mount Adapter shaft.

Initially, I will test the power system using an APC 14x7 e-prop.

RE: Hobby Lobby Skylark e-Conversion
 

BEAUTIFUL

RE: Hobby Lobby Skylark e-Conversion
 

Greg,

I happen to have one of those AXI 4120/14 thingys....and I've been wondering what to do with it. Thanks for the inspiration.!

BTW, I look forward to reading a flight report.....but since you live in Rochester NY, I have the feeling I'll have to wait awhile for that. :D

Nice looking job so far!

Wiz

RE: Hobby Lobby Skylark e-Conversion
 

Hi Mike,

We are overdue for a mid-Winter thaw. I'm keeping my fingers crossed. :)

The tail section assembled easily. I did need to trim the inside tips off from each elevator half for a proper fit after mounting the horizontal stabilizer in the tail.

The kit comes with plastic, metal pin hinges. Three for each elevator half and three for the rudder.

The linkage hook-up will be next. The rudder is a pull-pull configuration using steel cables and the two elevator halves use a pre-made metal "Y" control rod.

RE: Hobby Lobby Skylark e-Conversion
 

To install the pre-made metal "Y" control rod for the elevator halves, I tied and then taped the strings inside the fuselage to the ends.

It was then a fairly simple procedure to draw the rods through the fuselage out the slots on each side of the tail. The split end of the "Y" rod is threaded to attach a clevis and the other end is cut to length with a right angle bend. It is held in the servo with the supplied "keeper".

The manual claims that the length of the servo end of the rod is 120mm but I found this to be incorrect. It is best to install the servo first and then the elevator control horns before cutting the rod.

I'll post some pictures of the servos and linkage after I install the pull-pull rudder.

RE: Hobby Lobby Skylark e-Conversion
 

The rudder pull-pull system installed fairly easy. The pre-run steel cables attached easily to the supplied couplers with a piece of brass tubing that is pressed flat.

To mount my smaller HS-85MG servos, I added a few pieces of plywood to make up the gap in space.

Overall, the toughest part was routing the metal "Y" rod for the elevator linkage and the pre-installed strings helped to guide these into the tail slots.

Both the rudder and elevator control surfaces have firm throw response.

RE: Hobby Lobby Skylark e-Conversion
 

I glued a painted William Bros. sport pilot figure to the deck before mounting the canopy with 6 of the supplied screws.

RE: Hobby Lobby Skylark e-Conversion
 

The plane was initially very nose heavy and it finally balanced after making several design decisions. I'll provide the details shortly along with several alternatives that can be chosen from for your personal preference.

The 16 cells (two battery packs) are shown in the most appropriate position. The packs are held in place with a few pieces of foam and Velcro.

RE: Hobby Lobby Skylark e-Conversion
 

This photo shows the hatch cover left off where the throttle servo normally goes on the stock glow-powered setup.

You can conveniently access the ESC/Battery connector to disconnect it for charging. I plan to leave the hatch cover off for air cooling.

RE: Hobby Lobby Skylark e-Conversion
 

The last couple of items are the tailwheel and belly pan.

The tailwheel assembled stock without any issues. The wheel base snaps into place and is held by 4 screws.

I decided to deviate from the stock method of mounting the belly pan with 4 more screws. I don't like loose hardware in the field and mounting the wing with 2 screws was my limit. I simply attached the belly pan with some Velcro strips. After the photo was taken, I also added a wooden dowel to the front section that sticks into a hole I drilled in the plywood of the front fuselage wing saddle. This helps to hold it secure from any air flow trying to force it open.