|Jul 01, 2013, 08:36 PM|
Seagull SparrowhawK 62cc ARF Conversion
At the end of last years flying season I had that itch we all know to add another plane to my hanger, Giving it hard thought I decided another Giant Scale was in my sights. After a week or so looking for a suitable candidate I stumbled on this RCGroups build thread:
Because I am a 30's Era Aircraft fan the 62CC 85" span version was an attractive possibility. Research into the pricing was a big surprise for the size of this ARF. Check it out:
I will power mine with the following power plant:
Great Planes Rimfire 50CC Brushless Motor.
5800 Mah. 12S Lithium Polymer batteries.
Castle Creations 160HV Electronic Speed Control.
22 X 10 to 12 pitch prop.
The pictures below were not taken by me. I grabbed them off of the internet so images of the box and contents can be seen.
|Jul 01, 2013, 09:19 PM|
Cutting the hatch.
In my opinion Giant Scale Electric planes must have access to the battery area through a hatch for one simple reason. Handling a lightweight Giant Scale model with weight of batteries installed gives far too much possibility to damage to the model aircraft.
I tried to take photos of the way I cut the hatch but they were not good at all so with the good pictures I hope you understand the simple process,
Using a blade from a wallpaper knife, taped at one end to prevent laceration, follow the plywood shelf that would normally be used to mount the fuel tank to cut the lower edges of the hatch. Once both edges are cut from end to end, use the stop points as a starting point to cut the front and back of the hatch using the former in the fuselage as a guide. Last use an accessory saw from your knife manufacturer to saw through the former in the fuselage.
|Jul 01, 2013, 11:27 PM|
Hatch Cover assembly and construction.
Despite being careful and having a fresh sharp blade the hatch cover ended up with some rough edges because of glue lumps along the fuel tank tray. Joint compound will be used later to fill in the rough edges.
I used 1/8 inch lite plywood for the two ends of the hatch cover. In order to get the exact shape the curve of the fuselage was transferred to the material and rough cut on a scroll saw. Using a sanding block and 100 grit sandpaper I sanded the edge till the line just disappeared. Because the balsa covering on the fuselage is 1/16 inch thick I drew another line 1/16 inch from the edge just sanded and worked the piece with the sanding block comparing it to the mating surface to get the perfect shape.
Now I used the Hatch cover to mark the cutouts for the balsa stringers on the plywood ends of the hatch and cut them out with a scroll saw. In order to get the pieces glued on to the Hatch Cover perfectly it has to be placed on the fuselage and hold things in place and tack the pieces together with thin CA. I used wax paper to keep the pieces from getting glued to the fuselage. Follow up with some 30 minute Epoxy for rigidity.
Now I used the relatively rigid Hatch Cover as a guide to cut 2 more pieces to finish the Hatch construction and removed some material to keep the weight down.
|Jul 04, 2013, 01:41 PM|
I am almost sure you are going to be right unless the battery tray gets involved depending where the batteries end up for balancing the plane.
|Jul 04, 2013, 01:59 PM|
Finishing the hatch.
Magnets are an awesome choice in my opinion compared to a hatch latch that sticks or even breaks. The magnets I used are made from neodymium and can be purchased at MCM Electronics.
I have tried to epoxy magnets in the past to find that about a year down the road the epoxy chips away from the metal surface of the magnet and fall out not to mention looking sloppy. For this build decided to make simple holders made of balsa and plywood. The magnet package read 3/16 inch thickness by ½ inch round so I drilled ½ inch holes in 3/16 inch balsa for the chassis of the holder. Much to my surprise not only did I need to drill a 9/16 inch hole to get the magnet to fit but the magnet was thicker than 3/16 and ended up using ¼ inch balsa instead. (note to self, written measurements could be wrong.)
The first set of holes I drilled in the hatch bottom were too close to the outer edge to fit in the center of the hole so I had to carefully drill 4 more in the fuel tank tray and transferred them to the hatch and carefully drilled them too. Using a marker I put a heavy dot in the middle of the magnet so center could be found when gluing in the magnet in the magnet holder. Using thick CA I clamped in place and let set for 5 minutes each.
After the glue sets on all 4 magnets on the hatch bottom I turned the fuselage upside down with the hatch perfectly in place and placed the rest of the 4 magnets on the corresponding holes and let them center themselves. With the magnets in place I glued them in place with the magnet holders and thick CA. (not pictured)
As mentioned before I use Joint compound as filler as I feel it is as close to the density of balsa as I have found. Filling takes time and patience because several coats may have to be applied and I like to let it dry for 24 hours before sanding. I always use a sanding block on flat and convex shapes, no exceptions.
|Jul 04, 2013, 03:16 PM|
Some color please.
Seagull Models did a fine job covering the model with the red covering but I feel this ARF needs a little more pzazz.
I decided to get that pzazz I am looking for, adding yellow to the top portion of the fuselage would be perfect answer.
The best way I could figure to get a strait line down the fuselage was to use some string and tighten and tape it where I wanted to make the color separation. Cutting did not have to be perfect because I planned to follow up with ¼ inch pin-striping when finished.
OHHHH NOOOOO, electronic blow out!:
I shot the covering process but when I plugged the card reader into a USB port on my laptop the screen went blank on the laptop for a second or so and in the end erased the images on the memory card. To be on the safe side I tossed the card reader and memory card away worried one or both of them may do damage to my laptop or Digital SLR.
The fuselage was covered using 2 pieces of Monokote down the top center of the fuselage. I was able to cover the top of the hatch with one piece.
|Jul 04, 2013, 03:38 PM|
Assembling the tail section.
The tail section on this ARF is made up of a module consisting of 4 pieces.
1 aluminum support rod.
2 elevator halves.
1 main section including the rudder.
The main section as well as the elevator halves have CA hinges dry fitted in them out of the box. Simply align and apply CA and the hinges are done.
Next apply some epoxy to the aluminum support rod and mating surfaces of the main unit and slide the elevator halves together and tape till the epoxy sets. I was shaking my head thinking how easy this part of the assembly was.
|Jul 08, 2013, 06:06 AM|
Good going Paul!
I still have my "next size down" version that you linked in your first post. Don't fly it that often but it still is a favourite.
|Aug 03, 2013, 11:45 AM|
The CA hinges were dry installed in the ailerons on the wing halves just like the elevators and rudder. With a few drops of thin CA they were good to go.
Because the landing gear is built into the wing it becomes the major part of wing construction. The chrome plated rods making up the landing gear are extremely rigid so I do not expect them to give at all when landing. A better design would have been to use a shock absorbing strut so perhaps Seagull was trying to keep costs down to insure sales. Wheels are not included with the ARF with the recommended size being 4 ½ inches. Not wanting to design a shock absorbing strut I decided to use a wheel that was lightweight with shock absorbing properties so I went with a pair of Dave Brown Lite Flite wheels. I do not know for a fact that these wheels will do the job so it's a we'll see situation.
The landing gear is made more aerodynamic with the use of trousers. Seagull Models incorporates forms to screw the trousers to along with openings to attach the forms to built into the wings. Simply cut away the coating so the forms can be glued. The gear itself consists of 2 formed chrome plated rod pieces that have to be screwed into place with the wheel before the trouser forms can be glued to the wing halves. The gear measured 5/32 where the wheel slides on so I drilled the wheels out to 13/64 on my drill press for a nice bind free fit. Caution should be taken as the drill grabs at first so hold that wheel tight at the start of the drilling process. The kit includes some very nice brass hardware to attach the wheels and two halves of the gear together, no replacement needed. I then glued the trouser forms to the wing halves and let sit overnight. The servo openings are already done waiting for the servos to be installed. The servos I used fit perfectly (not pictured) and I will show you those when I get to the hardware installation for the control surfaces. I used 24” servo extensions in order for the servo wires to reach the openings in the wing.
Next I joined the wings together using the aluminum tube supplied and some 24 hour epoxy. Painters tape was used to hold everything together till the epoxy cured.
Last part of the wing assembly is the fitting of the trousers. Some forming is needed to get the trousers to fit some what close to perfect and was a disappointment. I will hide the gap with some automotive striping before maiden flight.
|Aug 03, 2013, 12:29 PM|
Ask questions please
Just a side note: I do not consider myself an accomplished writer and I wright the way I speak or think. Please, if I miss something or you do not understand something ask for clarification.
I understand despite doing my best to explain my processes that everyone may not understand what I am trying to communicate.
|Aug 04, 2013, 09:20 AM|
My research for the best Brushless Motor for this model led me to narrow my selection down to one of two motors.
The Rimfire 50CC:
Or the Turnigy RotoMax 50CC:
I was having a difficult time deciding between the two till I discovered this video on YouTube. The model is similar wingspan of 81 inches and all up weight is 22 pounds.
The Rimfire 50 CC is extremely well built and is as solid a motor as I have owned. The safety stop was already installed which is a major plus in my book. Included are 3 bullet connectors to mate with the connectors that are already installed on the wire motor leads. The included mount and bolts are made of steel not aluminum as expected. Although steel construction is heavier than aluminum the rigidity is a plus.
When I assemble the mounting bolts through the motor mount I always use some lock tite to keep the bolts from backing out.
|Aug 04, 2013, 11:14 AM|
Fitting the cowl
In order to align the motor in the right place the cowl has to be fitted. The ARF includes 4 spacers to fit the cowl in an oversize fashion as the real Sparrowhawk was fit. Glue points are already in the fuselage, just remove the covering with a razor blade and glue with thick CA. Make sure they are positioned right.
I do not care much for the look but the openings will serve as cooling vents for the ESC and motor.
|Aug 04, 2013, 12:00 PM|
Mounting the motor
I originally considered constructing a plywood box to lift the motor the 4 inches needed to clear the cowl. After talking to Richard Landis, a good acquaintance of mine who has built many more Giant Scale planes than I have using wide sturdy standoffs would be an easy way to go. The most important part with using spacers for this application was to chose spacers that were wide enough to handle the twist torque of the motor at such a distance from the mount point. With that in mind I chose a ¾ inch wide by 1 inch long aluminum spacer purchased from this site:
I used a quantity of 4 - ¼ X 20 X 5 bolts to give me ½ inch proud bolt after attachment to the ½ inch firewall and backed by a ¼ X 20 lock nut to keep the bolts from backing out. Blind nuts or some times called 'T Nuts' were used to firmly attach the motor. My experience with blind nuts is not to trust the threads as I have had them strip with a similar setup. The lock nuts should be the solution to that problem as well as keeping the bolts from backing out.
To center the motor I use a simple jig made from some scrap lumber and a drywall screw to hold the fuselage vertical so I can place the motor on the mount. With spacers in place and bolts upside down place the cowl over the motor and move the motor around till it is centered over the front opening of the cowl. I use the spinner plate as a guide for centering. Carefully lift the cowl off the fuselage and pencil in the bolt positions. The penciled in marks usually are not perfectly round but good enough to determine center. I drilled 5/16 inch holes to accommodate the Blind Nuts. Tightening the bolts down can be frustrating because of the weight of the motor. I do not have a suggestion to make it easier so my advice is to have your patience on standby when using this method.
|Aug 04, 2013, 12:08 PM|
A quick preview
After mounting the motor the day was near the end but I could not resist the desire to temporally assemble the model to get an idea of what it will look like when finished. I taped the wing on, placed the cowl and tail section on and took a few shots.
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