1/4 scale SIG J-3 Cub build

[JasonJ]

About a month ago I aquired a SIG models 1/4 scale J-3 Cub kit from a friend who bought it this summer. It is a balsa build kit so it is basically a box full of balsa sticks and some thin ply and plans. It will be a scale detailed build. I plan on running a DLE 35RA for the engine. Wing span is about 105 inches so it is a big plane. Pictures to come.

[Skiddz]

Wow. A DLE35 is pretty big for that airplane... A bunch of people in my club have 1/4 scale cubs and the biggest anyone is running in theirs is a DLE30 and those are rocketships.

I run an O.S 1.60 2-stroke in mine and it's way too fast on anything over about 1/2 throttle.

Fun and relaxing airplanes tho. Better be good on the rudder. Things can get ugly if you're flying uncoordinated...

[JasonJ]

My friend has a VVRC 40cc twin in his Hanger 9 1/4 scale cub and it hovers. I am going with the 35RA because it is rear exhaust. The Sig kit is more true to scale so it is pretty narrow compared to other kits and arfs I have seen. I need the room in the cowl to fit the dummy engine along with the real engine inside. Plus, since I am scaling it out it might end up on the heavy side so having the reserve power will be handy. Pics will be posted tomorrow, I wanted a little more to show before posting pics. It's a fun build so far. Building a plane from a pile of wood is a very different experience than assembling a heli kit.

I have a cub already so I am familiar with their characteristics.

[Skiddz]

Most of us also have the Hangar 9 1/4 scalers as well. I'm going to change mine over to a DLE30 after the first of the year. Those fit in the cowl pretty well - a lot better than this O.S. 1.60 with the Pitts style muffler on it.

I like to build from a box of sticks as well. My old man got me interested in balsa and tissue models when I was about 12 or so. I built dozens of them and lost all interest in plastic models after that...

I've got an OLD Sig P-51 kit that I want to do up someday... Got a NIB Saito .82 4-stroke that'd go perfectly on it.

[JasonJ]

Here is the fuselage so far. The plans call for building a two piece wing that bolts together and then bolts on from the top like a trainer plane. I did not like that because I am going for a scale build and a real Cub does not have two Frankenstein bolts sitting on top. My solution was to redesign the upper structure to allow for proper removable wings for a clean and more scale look. There will not be a wing tube. I am instead staying with the fixed ply spar that will eventually be glued in and an active strut system. Also the kit comes with wire gear that you solder together. Not good enough for a scale build so I bought a set of the Hanger 9 functioning suspension landing gear. The Robards are too expensive. I am using 6 inch Dubro inflatable wheels for a more tundra tire look.



Here is the dummy engine cylinders so far. I was actually going to create something like this but thankfully someone else already has. This is a Continental engine kit from a company called Top Notch Products. They make laser cut wood engine kits for scale rc aircraft. Each cylinder consists of about 40 thin laser cut ply pieces you stack and glue. The spark plugs are bolts with a locknut, a small piece of aluminum tubing and shrinkwrap heated and pulled for the wires. This along with the exhaust and intake tubes comes in the kit for $39 plus shipping, a bargain for what you get. They have different sizes of the Connie engine ranging from 1/5th to 1/3rd scale. Now, for the weight I could have just put a VVRC 40cc twin gasser motor in but it wouldn't have been scale enough and it is the scale detail I am after. I have a smaller Hanger 9 Cub that is for dinking around. I want this to be hardcore scale.

[JasonJ]

Got the upper part of the fuse between the cabin and tail section done. Had to soak some of the balsa in water and let it dry in forms to get the curves.

[CrashDavis]

Very cool - look forward to watching this one as you progress with the build!

[JasonJ]

Still wittling away at it. Nothing pic worthy just little things. Needing to order the engine soon. According to the dimensions DLE gives for the 35RA I need to build the firewall back 20 millimeters from what the plans call for or the prop will be an inch and a quarter away from the cowl and that would look bad.

[JasonJ]

DLE 35RA ordered and on the way. I have done a little more work but I need that engine to build the front of the fuselage. Also been doing a lot of research on the interior so I can get it right and still have access to the electronics. I'll be able to have the ele and rudder servos on a plate down behind the back seat. My plan is to have the batteries under the front seat but I might have to have them under the back seat to get the CG right. I will probably use a pilot figure, something wimsical like a dude in board shorts and Hawaiian shirt or something (because Cubs look pretty dumb flying around without a pilot) so that will help with CG as well. I am figuring it may end up nose heavy since the dummy engine kit has some weight to it. The cowl will also be a little heavy since it is plastic and calls for being reinforced with epoxy and cloth.

[nbells]

Hi Jason .... keep with the pics.

I actually looked at one of these a little while back so really interested to watch yours come along.

[JasonJ]

As cool as the dummy engine was something didn't seem right. It seemed too big so I did some measuring and emailed the company. Turns out they sent the 1/3rd scale kit in the 1/4 scale box so they sent me another kit free of charge. Here it is. This time I painted it grey, then used chrome paint. Masked off the valve covers and painter the jugs black. Installed the spark plugs, it turned out well and is the right size. I think I'll make a static model out of the other one.

[nappyroots2182]

i have the same plane on the dle 35. perfect combo. yes its good power but u dont have to open it up all the time.

[JasonJ]

Got the DLE 35RA the other day. Gonna be tight but it'll work. Now that I have it I can start building the front of the fuselage.

[JasonJ]

Engine mounted so I could run the throttle cable. Needed to do that so I can sheet the upper part of the front.

[nappyroots2182]

heres what me and my dad built for his sig cub. dle 35ra clipped wing

[JasonJ]

That is cool. I have the elevator and rudder assemblies complete and am working on the wings now. Pics soon.

[nappyroots2182]

heres the sig 1/4 clipped cub my dad and me built last winter. dle 35ra power. any questions PM me. cant wait to see more progress on urs

[nappyroots2182]

sorry for the repost. i didnt see my last post ever come up in the viewing mode i was in.

[JasonJ]

Still working on it here and there. I am almost done with one wing. It has taken awhile just because I have drifted away from the plans due to my version of the wing mounting system. The other wing should go more quickly since I have it down how to build the wing up. I foolishly thought the wings would go together quickly but there are 753,467 parts to cut, sand, test fit, sand, test fit and glue. Combine that with the fact that I am using 30 minute epoxy in key stress areas of the build means I glue something and end up just letting it cure until the next day so it is good and bonded.

[nappyroots2182]

please do not use the aluminum for the strut mounts. after a series of touch and goes we lost a wing from the alum cracking from how it gets bent. use some brass instead. that seems to be the only weak area we have came across.