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  1. #1

    1/4 Sig J3 Cub Build

    Hi. I will be maintaining this exclusive thread for my cub build until I get to have it maidened. I am a beginner at kit building and this will be my 2nd build which I'll start in the 2nd week of March 2017. Will be building my 1st kit soon which is the Sig Demoiselle which looks a lot easier to build than the cub. Somehow, I hope to be warmed up for the cub build which I suppose might take months to complete. A friend will from time to time check my progress. Someone offered to build this kit for me but I had to refuse it. There's just No fun in there! This will be my fifth plane.

    I started this thread to ask few questions before I start with the build proper.

    First off, I already have the following:

    1. 1/4 Sig J3 kit
    2. DLE 35RA gas engine (35cc)
    3. 16oz fuel tank and fittings/accessories
    4. 6" dubro tires
    5. Hitec standard servos, all metal gear
    6. For the radio system, i'll be using the receiver that came with my Futaba T6J
    8. Master airscrew K series prop (15x8 and 16x6)

    Just few questions:
    1. PROP SIZE. As you'll notice, the 15" and 16" props I have might be too small for my engine. DLE recommends 18x10, 19x8, 20x8, or 20x10 for the 35RA model. Which size should I get? Worried that if I get the largest, it could hit the ground or if the smallest, it could barely lift the aircraft.

    2. COVERING. How many meters should I get? Will be using Solartex fabric.

    3. GLUE. A friend suggested elmer's wood glue. Another suggested CA. For him, the wood glue is way outdated. What do you guys suggest?

    4. SERVO. Is a double servo recommended for the elevator?

    Thank you in advance for the help. I hope that somehow, creating and maintaing this thread will help not only me but also other newbies as well.

    Bitoy

  2. #2
    TomCrump's Avatar
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    It's good to see some one with a desire to build.

    I'm curious as to how you arrived at your engine choice. I'm building a 1/4 Cub that will be powered by a 26cc swinging a 18X6 prop. I feel that this will be plenty of power.
    Tom C

    Sig Brotherhood # 120
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  3. #3

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    Ditto Tom's comment - Yes, another builder in the crowd.

    The 35 will be plenty power. As Tom mentioned, 26cc is a great match as long as the plane is not over built crazy. With that said, I flew a Sig 1/4 with a OS 120 4 stroke. It was covered in coverite and painted, full details added. Flew great and plenty of power. I also flew a Sig 1/4 covered in cloth and painted with a Brison 2.4. More than enough power and never needed full throttle. Was just a beautiful engine that came out following the Quadras and Zenoahs but was built for aircraft in mind.

    as for glues, I am for most part CA medium and epoxies(builds fast). Titebond is a excellent choice and a lot of builders use.

    not sure on covering material needed. I measure out surfaces when framed and determine from there depending on coverage of material roll.

    on servos, mine were built and flown few years back when 1/4 sc large servos were popular. Now you have so many choices with plenty of torque and/or speed. I did build per kit and kept elevator halves tied together (one arrow shaft pushrod needed). always did use a Dubro pull pull on rudder. you won't need to go crazy on elevator servos unless you are really yanking it around under full throttle. The plane is a great flyer and will float with all the wing area.

    prop, I did swing an 18" with the Brison, no problem on ground clearance. Don't recall on the 120. not familiar with DLE. My engines are "old school" gas.

    keep us posted with build pics. The Sig Cub kit is a great plane. Good combo of kit building with some "scratch" build features such as cutting own parts and several sticks. I have built a good handful. Love em.

  4. #4
    TomCrump's Avatar
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    A ten meter roll of Solartex will more than cover your Cub. I don't think that a 5 meter roll would be enough.
    Tom C

    Sig Brotherhood # 120
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  5. #5
    Thanks Tom and RagwingFan.

    It's good to know you are also building one. Which maker is it from?

    The 35cc idea came from other threads and Youtube. Haha. Others also use 20cc. With my newbie mind, I thought being overpowered is better than underpowered. Or not? I might be adding smoke system and scale gauges and pilot anyway so I guess, that extra power might come in handy. For future reference, what could be the disadvantages of overpowering a plane?

    For the prop, I guess I'll settle for the 18". Just wondering though, will the 19" still be fine?

    As to the cover, I'll get the 10m roll as you suggested. Just hoping I wont be making many errors in covering considering that this will be my first time.

    And now, the Titebond which I have lots of questions about. How much do you think I'll need? How's the finish? Does it leave gunk on parts with excess glue? or it simply evaporates?

    Will sure do maintain this thread and provide you tons of pics. Might be getting most information I'll need around here anyway so please regularly check this thread. Most flying sites and clubs are now proliferated with ARFs and Foamies. Sadly, only a few knows about kit building.

    Our local hobby stores no longer sell anything for kit building. That's why I now need to buy everything I'll need or wait for several months before I again get to buy whatever is lacking. I am currently in North Cal and will bring everything to the Philippines where I will build it.

    I would appreciate more advice that can help me successfully accomplish this build. Again, thanks for the help.

    Bitoy

  6. #6
    TomCrump's Avatar
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    I got the BUSA 1/4 Cub in a trade. That's what I am building.

    To me, an over powered Cub doesn't fly like a Cub should. They become just another sport model. I've heard the argument that "You can throttle back" but I've seldom seen it practiced.

    Ragwing Fan obviously has a different opinion. I hope that he chimes in, and elaborates on his choice of the Brison 2.4.

    I would use a prop suitable for the engine that you choose. I don't own a DLE 35cc, but I would assume that it would use an 18 inch prop.

    You'll have extra material, if you buy a 10 meter roll of Solartex. I suggest that you watch some You Tube videos on covering. If you find one using Solartex, that would be great.

    I prefer to use Natural Solartex, and then paint. When you buy the pre-colored product , you have to find matching paint for the cowl, etc. If you paint the entire airframe, you already have the paint for these pieces. Solartex requires no primer, and it' best not use use it. The cowl will require primer though. I use Duplicolor primer in aerosol cans.

    If you decide to go with the colored Solartex, be aware that it needs to be sealed. While the product is fuel/gas proof without it, sealing it with a clear coat makes it easier to clean your model. Unsealed Solartex attracts dirt, as is very hard to clean.

    Titebond is available at most hardware stores. There's no need to buy a huge bottle. I don't know what size it is, but you can see my bottle in the attached pic. I also extensively us CA.
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    Last edited by TomCrump; 02-09-2017 at 03:36 AM.
    Tom C

    Sig Brotherhood # 120
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    Balsa USA Brotherhood #140
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  7. #7
    David Bathe's Avatar
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    I agree with all the over powering a Cub comments.
    I've only ever seen one get away with it and thats Gernot Bruckmann.
    Mind you, he can make a paper bag perform aerobatics that leave the rest of the competitors breathless.
    Back on planet earth...
    Buddy of mine has a 1/4scale cub with an old G-21. Dream combination if you want to go gas.
    Best Regards: davidbathe.com
    Occasional Aircraft Illustrations.

  8. #8
    Thanks Tom and David.

    You said an overpowered cub wont fly like how a cub should. Can you elaborate on this? Sorry I'm a newbie to both building and flying.

    I noticed that 35cc is 390g heavier than the 20cc. Will this have too much effect on how fast you should fly the plane to produce lift?

    I was thinking, the heavier your plane, the faster you need to fly it to produce lift. Your landing approach should be faster as well. Is this correct?

    Thanks for the tips about the covering Tom. Never thought it still needs to be sealed. Reading other threads about how a solartex is to be painted, I'd rather buy the colored one. What can you say about its quality particularly its appearance?

    I tried to paint my own car, a real one, and I ended up giving it a botched paint job. Dont want to do it with my first build.

    Roel

  9. #9
    TomCrump's Avatar
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    Throttle management can be used with overpowered Cubs, but seldom is. In my experience, pilots that have these big engines in their Cubs tend to fly them in a non Cub-like fashion.

    For me, the thrill of flying a model Cub is to fly it like it's full scale counterpart.

    Sealing Solartex is painting it, but using a clear coat. In my opinion, it's easier to spray a colored coat than it is to spray a clear coat. I have trouble seeing the clear, as I spray it. As I said earlier, the colored Solartex should be sealed with clear, to make it easier to clean. If left unsealed, you'll have a dirty model that may never look good after it's initial flights.

    If you don't want to clear coat Solartex, I suggest that you use 21st Century Fabric. It's somewhat more difficult to apply, however.
    Tom C

    Sig Brotherhood # 120
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  10. #10
    So it's more of a pilot and not a plane matter huh?

    Clear coat. I suppose the spray can clear coat will do?

    As to the balsa wood itself, does it need to be painted? I think it wouldnt look right seeing a bare wood inside a scale cub. What do you paint it with?

  11. #11
    TomCrump's Avatar
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    On my last build, I didn't add any cockpit detail. Instead of painting the area, I painted the windows.

    I use an aerosol clear, but I don't recommend water-based products. I use Minwax Polyurethane.
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    Tom C

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  12. #12

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    been tied up and away, following up

    on the overpowering and my prior choice on a Brison 2.4. don't get me wrong, I am not the rocket ship 3d flyer. The 2.4 which I knew at the time was way too much engine, was chosen for its weight and performance. Remember this goes back to the early/mid 90's when Quadra, Zenoahs, Sachs etc were the gas engines. The majority were great engines, just on the heavy side. Basically a G-38 magneto was 4.2lbs w/o muffler. The Brison is 2.75lbs w/o muffler (basically same size cc). Yes Brison required small ignition battery back but that is nominal. The Brison puts out like 22lbs of thrust. Nope, not needed for the Cub for sure. At that time, it was a gas engine, designed specifically for aircraft. It was not a converted chainsaw motor (nothing against that). Just a dynamite, beautiful, powerful and smaller in design (one of the earlier EI engines vs large flywheel). Sum it all up, was just a personal preference/desire and not a requirement for the Cubs I flew then. Now, it is the attachment to past and still love their look, design and power.

    with all that said, remember I flew my scale 1/4 Sig L-4 with an OS120 FS. It flew great and scale as well as still had plenty of power with the wing lift.

    boils down as you and others mentioned; preference of the builder. that's great thing about this hobby

    remember, pics of build or it did not happen (when you get going)

  13. #13
    kmeyers's Avatar
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    My sig 1/4 scale cub has a ST 3250 in the nose swinging a 18x6. It is true you can always throttle back. The ST 3250 must give me about 17 lb of thrust at full, just short of a sustainable hover.

    I want more power. I fly scale with it a lot of time (just throttle back). I enjoy many different RC flying types. The Cub will never be a 3d flyer but it still is fun to horse it around once in awhile.
    Oops!
    ***CUB BROTHERHOOD # 274***

  14. #14
    Thanks RagwingFan! I Promise to post pics here as soon as I start with the build. How do I post pictures using mobile anyway? Was about to post the box picture just so i already have something out here. Haha.

    The 35cc i have is 390g heavier than the "ideal" 20cc. How do you think will this affect the cub's flyig characteristics?

    Kmeyers, that's about the same size as my engine. I'll get the 18. 18x10 I think though. Do you think that's ok? Or should I settle with a low pitch prop?

    OT: what happens to the engine if I put an undersized prop?

    Thanks again!

    Bitoy

  15. #15
    David Bathe's Avatar
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    Don't worry about it. Just get on with building your first kit and start getting some serious stick time. Your question will start answering themselves. Good luck.
    Best Regards: davidbathe.com
    Occasional Aircraft Illustrations.

  16. #16
    Thanks David! Looks like I'm setting myself up for a little surprise. As long as it wont be fatal to the plane, I guess I can live with it.

  17. #17

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    My Sig 1/4 scale cub is powered with a Magnum 90 4-stroke and has very adequate power. It will poke along like a cub should with very little throttle. Titebond works well. I use a large hypodermic syringe to apply glue exactly where it needs to go. Farm supply stores have them in various sizes.

  18. #18
    kmeyers's Avatar
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    I don't know what the maximum ground clearance is, but, go with a low pitch large enough not to over rev the engine. The Cub might not land without an anchor or parachute with a 10 pitch!
    Oops!
    ***CUB BROTHERHOOD # 274***

  19. #19
    @loopdeloop. Thanks! Will looknfor it. Syringe is a good idea!

    @kmeyers. Sorry, might not have enough time to do my research as I need to order real soon. if I go for 20" or 19" how much should the pitch be? Seems complicated to me.

    I learned if I go with a bigger prop, I should reduce the pitch by one. They say 18x10=19x9, 19x9=20x8. If this is the case, won't the 18x10 produce the same flying characteristics as that of the 20x8? I'm just curious. Why change to a bigger prop?

  20. #20
    kmeyers's Avatar
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    It would make no difference with borderline power, but, with bigger engines and low stall speeds the higher pitches produce too much thrust even at very low RPM's sometimes to land in a confined space. You just keep flying running out of runway. Bigger prop lower pitch same rpm same speed the plane slows and lands quickly.

    The average guy lets the nose drop a little which makes this problem even worse.
    Last edited by kmeyers; 02-12-2017 at 03:47 PM.
    Oops!
    ***CUB BROTHERHOOD # 274***

  21. #21
    VincentJ's Avatar
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    I built my Sig Cub (clipped wing) about 5 years ago, it came in at 16.2 pounds. It was my first build and it was a bit on the porky side. I chose a DLE-20 for the engine which I found to be a bit down on the power side. If I were to put in an engine in it today I would have opted for the DLE-30 which I think would be perfect for it. Also consider the additional weight of floats should you go that route...
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    VJ

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  22. #22
    David Bathe's Avatar
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    Quote Originally Posted by kmeyers View Post
    It would make no difference with borderline power, but, with bigger engines and low stall speeds the higher pitches produce too much thrust even at very low RPM's sometimes to land in a confined space. You just keep flying running out of runway. Bigger prop lower pitch same rpm same speed the plane slows and lands quickly.

    The average guy lets the nose drop a little which makes this problem even worse.
    Tell me about it. I found myself in exactly that place... in a slight breeze my cub would just standstill and float 2m over the runway... just couldn't get it to come down with the engine on idle.
    I found the best prop/pitch combination was: Pitch @.33% of the Diameter. Then low efficient props... MS classic for example.
    One thing that make our models significantly different from a 1/1 cub is weight. We built light. Couple that with the high lift scale design and we've got 1: Floaters and 2 Squirrels on Take off. Sound familiar?
    By best Cub experience has be with heavier models. Definitely better behaved but... on the other hand, you can have a BALL with a real light clipped wing cub. Almost like a fun-fly.
    Best Regards: davidbathe.com
    Occasional Aircraft Illustrations.

  23. #23
    kmeyers's Avatar
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    Sounds very familiar. I do love light wing loaded planes.

    The lightest cub I have is a H9 plug and play 80 inch. It can almost hover with a good .46. Once in the "perfect" breeze I did a stationary to the ground position rolling harrier for at least one min. (seemed longer).
    Oops!
    ***CUB BROTHERHOOD # 274***

  24. #24

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    An 18" prop is scale for a 1/4 Cub (full-size uses a 6' prop). An 18x6 or 18x8 pitch will fly it very well and in a scale manner. Your 35cc engine will spin it with no problem, you have way more power than needed. A G-26 Zenoah is the perfect gas engine for this plane to fly in a scale manner.
    Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?

  25. #25
    Glad I checked this thread. I was just supposed to inform you that I havent forgotten about this thread and will start posting build pictures in March.

    @khodges, i got the 18x6 civilian prop from falcon. Might also get 20x6 prop. I'm a little worried the 18x6 might cause the 35cc to over rpm. What do you think?

    @kmeyeres, my friend just learned I got the 35cc and told me it's too powerful for this plane that I can even hover it. Is this true? Just curious.


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