Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
#1
Thread Starter
Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Now that all my other projects are complete I can finally start on my latest kit, a Sig 1/4 J3 Cub that I will be converting to a PA-18 Super Cub. I will be using a Zenoah G-26 EI on a CH Ignitionwith a Slimline Pitts Style muffler for power, a set of Robart Cub Gear for landings and takeoffs, and a Fiberglass Specialties Cowl. I plan on reshaping the nose slightly, reshaping the tail feathers, adding flaps, adding a hinging door / window frame, and modifying the plane into a three piece wing (With the center section permanently attached to the fuselage).
I have already started on the plane by planning out the new firewall.
I changed the shape of the firewall to coincide with the cowl a little better. The new firewall is six inches across which matches the width of the former at the first window frame. The six inch firewall will keep the side of the fuselage straight until it is aft of the cabin area. I also made the firewall a little shorter to allow the Pitts Style Muffler from Slimline to fit onto the motor without hitting the firewall. The plane had this feature as a stock design but I needed to adjust the cutout a bit higher to match the motor. The motor will be bolted directly to the firewall and the distance of the firewall adjusted for the correct propeller clearance.
Note: The motor's thrust line has been moved down from the stock position to match that of the Super Cub and the Cowl I purchased. 1.5 degrees of down-thrust and 3 degrees of right thrust have been taken into account with the mounting location for the motor. The schematic of the cowl shows the right thrust offset and a little of the down thrust offset. The down thrust offset does not appear to have enough in the drawing but the cowl is pointed slightly down to be parallel with the top of the dash so not as much movement was needed. Also to note, the Zenoah G-26's mounting plate is too large at the top to fit within the cowl so both the upper mounting locations were moved inwards. One mounting ear was removed from the backplate and one was lightly reduced in size. Minor modification is required but the backplate is available for under $20.00 so not to worry, you can purchase the mounting plate to put the motor back to stock if you need to in the future.
Thats if for now..... Here are a few pictures.
Truly a "Box Of Sticks" but....... somewhere in there is a Super Cub and I am going to find it.
SunDevilPilot
I have already started on the plane by planning out the new firewall.
I changed the shape of the firewall to coincide with the cowl a little better. The new firewall is six inches across which matches the width of the former at the first window frame. The six inch firewall will keep the side of the fuselage straight until it is aft of the cabin area. I also made the firewall a little shorter to allow the Pitts Style Muffler from Slimline to fit onto the motor without hitting the firewall. The plane had this feature as a stock design but I needed to adjust the cutout a bit higher to match the motor. The motor will be bolted directly to the firewall and the distance of the firewall adjusted for the correct propeller clearance.
Note: The motor's thrust line has been moved down from the stock position to match that of the Super Cub and the Cowl I purchased. 1.5 degrees of down-thrust and 3 degrees of right thrust have been taken into account with the mounting location for the motor. The schematic of the cowl shows the right thrust offset and a little of the down thrust offset. The down thrust offset does not appear to have enough in the drawing but the cowl is pointed slightly down to be parallel with the top of the dash so not as much movement was needed. Also to note, the Zenoah G-26's mounting plate is too large at the top to fit within the cowl so both the upper mounting locations were moved inwards. One mounting ear was removed from the backplate and one was lightly reduced in size. Minor modification is required but the backplate is available for under $20.00 so not to worry, you can purchase the mounting plate to put the motor back to stock if you need to in the future.
Thats if for now..... Here are a few pictures.
Truly a "Box Of Sticks" but....... somewhere in there is a Super Cub and I am going to find it.
SunDevilPilot
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Chris Stephen (12-10-2022)
#4
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Firewall with blind nuts installed. The firewall is made a bit wider than stock to be more in line with a Super Cub. Blind nuts epoxied to the back of the firewall.
SunDevilPilot
SunDevilPilot
#5
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RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
ORIGINAL: GarySS
Would the aftermarket's fiberglass Dave Patrick P-18 cowl work on this Sig model?
Would the aftermarket's fiberglass Dave Patrick P-18 cowl work on this Sig model?
Thats the first cowl that came to my mind. The DP PA-18 cowl (sold by Fiber Spec.) isdefinatley themostscale aftermarket cowl available.
#6
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
ORIGINAL: GarySS
Would the aftermarket's fiberglass Dave Patrick P-18 cowl work on this Sig model?
Would the aftermarket's fiberglass Dave Patrick P-18 cowl work on this Sig model?
SunDevilPilot
#7
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Finished up the firewall for now. The only holes it need now is for the Throttle and the Fuel Line. Had to create a recessed area where the hall sensor is for the electronic ignition. Not sure if the stock pickup needs this modification but the CH Ignition did. I would make sure you check you G-26 Installations because I believe the bolts holding the sensor will hit regardless of the brand of hall sensor being attached. Used my Dremel router and a clamped straightedge to make the recess. I also drilled the hole for the hall wire to pass. Lastly, I had to create another recessed area for the motor shaft and nut. The shaft sticks out about 1 mm past the mounting plate. The hole and recess for the motor shaft were made with the drill press and a forsner bit.
Should be about to start the fuselage sides Tuesday.
SunDevilPilot.
Should be about to start the fuselage sides Tuesday.
SunDevilPilot.
#8
Senior Member
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
That'll be a nice looking airplane and you will have different color schemes to choose! I am currently converting a Goldberg J-3 Cub to a J-2. It's pretty much the same airplane but I'm making the door functional, side windows different, fin different and will paint it silver with blue stripes down fuse side and blue 'call' #'s. It will have detailed interior to hide RC gear as much as possible and pull-pull rudder. I am trying to finish up all of my projects and will concentrate on larger models in the future, like yours. Good luck with your mods! I would like to have one in color scheme like the old Sterling box cover art- red and straw yellow.
#9
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
I haven't been able to spend much time working on the Super Cub due to the heat. Unfortunately I don't have air conditioning in my garage and I am not really a fan of being in there when it is 100+ Degrees. As the weather cools off I will be spending a lot more time building.
Today, I was able to sneak into the garage and start the construction of the fuselage. The balsa parts of the fuselage sides are solid 5/16" balsa and possibly due to their thickness are uncut with the parts printed on them. This requires a little time cutting. I used my scroll saw with a new fine blade installed to make the initial cuts and finished trimmed the parts on the disc / belt sander. Was a little nervous cutting the parts but once I got going all went well.
I sanded up to the line but not through it. I figured bigger was better and if needed I can sand the parts further for a perfect fit.
SunDevilPilot
Today, I was able to sneak into the garage and start the construction of the fuselage. The balsa parts of the fuselage sides are solid 5/16" balsa and possibly due to their thickness are uncut with the parts printed on them. This requires a little time cutting. I used my scroll saw with a new fine blade installed to make the initial cuts and finished trimmed the parts on the disc / belt sander. Was a little nervous cutting the parts but once I got going all went well.
I sanded up to the line but not through it. I figured bigger was better and if needed I can sand the parts further for a perfect fit.
SunDevilPilot
#10
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Due to windy weather at the flying field I got a chance to start on the fuselage sides. Here is photo after the first one was completed. I have never built a truss style fuselage and found the experience to be a pleasure. There is a real sense of accomplishment after you get one of these completed. Lots of joints so having a disc sander is a must.
Modified lower portion of the fuselage side to accommodate the Robart Landing gear. Will be adding a wider landing gear plate.
SunDevilPilot
Modified lower portion of the fuselage side to accommodate the Robart Landing gear. Will be adding a wider landing gear plate.
SunDevilPilot
#11
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Second fuselage side is done. By using the pin holes made in the plans during the construction of the first side I was able to make an exact replica of the part. Sanding both parts to equal size will not be required. I feel as though I accomplished enough work for today so I will have to wait until next week to continue.
Things will start to deviate from the normal kit once I begin work on the door and the center section for the wings. Should be fun!
SunDevilPilot
Things will start to deviate from the normal kit once I begin work on the door and the center section for the wings. Should be fun!
SunDevilPilot
#12
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
First modification is done. Because the Super Cub fuselage sides do not taper in like on a J3 I wanted to modify the plywood sides of the forward fuse into a single piece. In the stock configuration the nose of the plane is put on after the main fuselage is built. By making it one piece I believe I have added a lot of strength to the nose with no additional weight. I also pre cut the lower door from the plywood side. The rounded portion of the lower forward fuse is where the pitts style muffler will recess into the firewall. You can also see the curved piece I made by laminating some light ply around a former. The forward most portion of the right fuselage side was also shortened to accommodate for the 3 degrees of right thrust I am building into the plane. The plans show no right thrust but I have 3 degrees built into my 1/5th scale, and my friend's H9 Cub has 3 degrees, and both fly true so I am adding it to this model.
SunDevilPilot
SunDevilPilot
#13
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Work has started on the modified Upper Cabin / Wing Center Section. I decided, like some before me, that I wanted the wing's center section to remain on the fuselage when the wings are removed. I am also redesigning it into one that more closely resembles a PA-18. Here is what I have so far.
The upper Cabin / Wing Center Section consists of an array of plywood laminated to give me the same thickness as the fuselage sides. It is also made in such a way that a music wire (5/32) can be inserted down the length of the rib and continue down the forward most post (At the windshields aft most portion) providing some strength. I thought it might be wise to add the music wire to give a little strength on the door side of the fuselage. There will be additional wires from the upper cabin to the dash as keeping with the design of the Super Cub.
Visible in the photo are the ply pieces of the center ribs with one partially assembled showing the wire channel (Lowest One).
The ribs will be lightened once I decide how to do the cross braces and where I am going to put them.
More to come....
Phil
The upper Cabin / Wing Center Section consists of an array of plywood laminated to give me the same thickness as the fuselage sides. It is also made in such a way that a music wire (5/32) can be inserted down the length of the rib and continue down the forward most post (At the windshields aft most portion) providing some strength. I thought it might be wise to add the music wire to give a little strength on the door side of the fuselage. There will be additional wires from the upper cabin to the dash as keeping with the design of the Super Cub.
Visible in the photo are the ply pieces of the center ribs with one partially assembled showing the wire channel (Lowest One).
The ribs will be lightened once I decide how to do the cross braces and where I am going to put them.
More to come....
Phil
#14
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Got the fuselage sides glued to the fuselage frame, cut the door, and assembled the upper cabin / wing root. Currently I am designing the cross braces for the upper cabin / lower cabin then I will start putting the fuselage together into a "box".
Visible in the photo of the wing roots are the channels I built into them to insert a music wire to strengthen the "A" pillar of the cabin. This feature can be seen where the A Pillar enters the wing root.
Coming together at a slow pace but who is rushing.
SunDevilPilot
Visible in the photo of the wing roots are the channels I built into them to insert a music wire to strengthen the "A" pillar of the cabin. This feature can be seen where the A Pillar enters the wing root.
Coming together at a slow pace but who is rushing.
SunDevilPilot
#15
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Here is what I came up with for one of the fuselage formers, again, modified from stock. Onto the front former and the aft former.
SunDevilPilot
SunDevilPilot
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RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
I've subscribed to your thread and am looking forward to seeing how you build a three piece wing. Thanks for all the tips so far.
Travis
Travis
#17
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Current status:
I have the upper cabin section almost complete. I still need to drill the holes for the wing bolts (8-32) and lighten up the center section but it is shaping up. The the vertical portion of the front former will be cut away from the area of the door but I want it as a complete part during assembly, to ensure everything stays straight.
The upper cabin assembly represents the best method I could come up while minimizing the amount of fabrication needed to make the wings fit. The wing joiner made of ply, and stock to the kit, will prevent the cabin from pulling apart should the airframe be subjected to negative G loads. The ply formers making up the center most portion of the fuselage will also resist compression found during normal flight.
Photo shows a dry fit of the parts.
More to come.....
SunDevilPilot
I have the upper cabin section almost complete. I still need to drill the holes for the wing bolts (8-32) and lighten up the center section but it is shaping up. The the vertical portion of the front former will be cut away from the area of the door but I want it as a complete part during assembly, to ensure everything stays straight.
The upper cabin assembly represents the best method I could come up while minimizing the amount of fabrication needed to make the wings fit. The wing joiner made of ply, and stock to the kit, will prevent the cabin from pulling apart should the airframe be subjected to negative G loads. The ply formers making up the center most portion of the fuselage will also resist compression found during normal flight.
Photo shows a dry fit of the parts.
More to come.....
SunDevilPilot
#19
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
ORIGINAL: AmishWarlord
Looking good.
Are you going to have wing dihedral built into the center section or at the plug in wing roots?
Looking good.
Are you going to have wing dihedral built into the center section or at the plug in wing roots?
Here are some full size photos showing the dihedral.
SunDevilPilot
#20
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
I have also been looking at paint schemes for my Cub and I keep going back to the one shown below. The scheme shown is on a PA-12 Super Cruiser and is based on the first light personal aircraft to circle the globe, from August 9th to December 10th, 1947. The original is also shows with the flags on the sides but I think I like the one with the tan colored elevators. However, I do like the shades of red and tan on the original aircraft. The originals, two pilots and planes made the trip, are now in the Smithsonian Air and Space Museum and in the Piper Museum in Lock Haven, PA. Plenty of time to make up my mind before I get to the painting stage.
SunDevilPilot
SunDevilPilot
#21
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RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
I went with the Balsa USA 1/4 cub kit. Thinking about clipping the wings to 86" like the Sig clipped wing cub. I'm going with the traditional yellow with black lightning bolt paint scheme. Got a Saito 120S with slimline pitts muffler waiting on it.
#22
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Update:
I redesigned the way I was going to connect the "A" Pillar to the upper root rib. Initially i was going to have the metal rod bend at the top of the A Pillar and head down the root rib to towards the aft. After looking at the part I decided a bend was not the best thing to do. I felt as though the bend could just pull apart. So.... I drilled a hole parallel to the A Pillar into the root rib to allow the rod to stay straight. Now the force of flight will pull straight on the rod. This rod is already roughed up to allow the glue to bond but just for safety I am going to cut a barb into the end to really lock it in. The bottom will be glued along the fuselage side, which will have a doubler added to the area of the rod so it sits flush with the side.
Visible in the first photo is a hole in the first cabin former at the top. This hole will be for the reinforcement rods which will go from the former to the area forwards of the dash. These are a feature of a Super Cub and will be made from metal and functional. This is similar to the design of the Balsa USA Super Cub. Photos of the Balsa USA Super Cub are attached for reference.
Going to start and glue the fuselage together today.
SunDevilPilot
I redesigned the way I was going to connect the "A" Pillar to the upper root rib. Initially i was going to have the metal rod bend at the top of the A Pillar and head down the root rib to towards the aft. After looking at the part I decided a bend was not the best thing to do. I felt as though the bend could just pull apart. So.... I drilled a hole parallel to the A Pillar into the root rib to allow the rod to stay straight. Now the force of flight will pull straight on the rod. This rod is already roughed up to allow the glue to bond but just for safety I am going to cut a barb into the end to really lock it in. The bottom will be glued along the fuselage side, which will have a doubler added to the area of the rod so it sits flush with the side.
Visible in the first photo is a hole in the first cabin former at the top. This hole will be for the reinforcement rods which will go from the former to the area forwards of the dash. These are a feature of a Super Cub and will be made from metal and functional. This is similar to the design of the Balsa USA Super Cub. Photos of the Balsa USA Super Cub are attached for reference.
Going to start and glue the fuselage together today.
SunDevilPilot
#23
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Started to assemble the fuselage today. Going together as planned with no major issues.
My only concern at this point is the bending of the fuselage sides to meet at the tail. I will get this figured out before I glue the left side of the fuselage on. I need to compare the natural curve of the fuselage to the plans and see how much I need to adjust the taper at the tail to make a good joint.
The forward most former will be cut where the door is once I complete the framing and the forward bracing.
SunDevilPilot
My only concern at this point is the bending of the fuselage sides to meet at the tail. I will get this figured out before I glue the left side of the fuselage on. I need to compare the natural curve of the fuselage to the plans and see how much I need to adjust the taper at the tail to make a good joint.
The forward most former will be cut where the door is once I complete the framing and the forward bracing.
SunDevilPilot
#24
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Hit a small milestone today, put the other fuselage side on to the fuselage making it one piece.
To get to this point took a bit of work as I was doing quite a bit of modification to the fuselage structure. Now that the major portion is assembled things should pick up a little speed. The next phase of construction is to add the gear plates to the fuselage to create a little strength prior to pulling the rear fuselage sides together. I don't want to risk warping the fuselage during the bending process so the more structure I can add to the front the more resistant to warping it should be.
The front gear plate was easy....Just filled in the groove on the stock plate, laminated the ply gear doubler onto the plate, and drilled for the blind nuts. Only issue at this point was the outer blind nuts. The gear mounts are wide enough to cause the blind nuts to interfere with the fuselage sides. Easily solved by grinding down one side of the blind nut. Installed and epoxied in place.
The rear mount will be a custom piece as the Robart gear I am using is slightly shorter (Front to rear) than the stock setup. I knew this was going to happen and modified the fuselage to fit. The rear plate will be slightly longer than stock.
Stay tuned!
Phil
To get to this point took a bit of work as I was doing quite a bit of modification to the fuselage structure. Now that the major portion is assembled things should pick up a little speed. The next phase of construction is to add the gear plates to the fuselage to create a little strength prior to pulling the rear fuselage sides together. I don't want to risk warping the fuselage during the bending process so the more structure I can add to the front the more resistant to warping it should be.
The front gear plate was easy....Just filled in the groove on the stock plate, laminated the ply gear doubler onto the plate, and drilled for the blind nuts. Only issue at this point was the outer blind nuts. The gear mounts are wide enough to cause the blind nuts to interfere with the fuselage sides. Easily solved by grinding down one side of the blind nut. Installed and epoxied in place.
The rear mount will be a custom piece as the Robart gear I am using is slightly shorter (Front to rear) than the stock setup. I knew this was going to happen and modified the fuselage to fit. The rear plate will be slightly longer than stock.
Stay tuned!
Phil
#25
Thread Starter
RE: Sig 1/4 J3 Kit converted to PA-18 Super Cub (Build)
Installed the front and rear landing gear plates today. Was straight forward with only one modification. I decided to pin the landing gear plates to the fuselage side to add a little strength without any weight penalty. Used 3/16th" Dowel for the pins.
SunDevilPilot
SunDevilPilot