Picking a J-3 Cub Kit
 

I am trying to decide on my next kit and am considering building a cub. I am not interested in building to “pure” scale, but would like a plane capable of some limited aerobatics. Probably would prefer installing a 91 FS, but would consider a 1.20 FS if it was the best choice. How would you compare the GP 60 kit vs. the Sig 1/5 scale or the ¼ Scale? What would be a good strong engine for either of these kits? This would be my 5th. kit with the last being a Hog bipe. Fred123[&:]

RE: Picking a J-3 Cub Kit
 

The Sig 1/5 scale J-3 is the most "scale" of all recent kit offerings. It has plug in wings and functional (manditory)wing struts. At about 7-7 1/2 pounds it flies well on a .52 - .65 engine. Your .91 would be too much. The Great Planes 60 size J-3 would be more appropriate for the .91. It is quite a bit heavier through its design despite being only a little bit larger.

Probably what I would recommend would be a Sig or Balsa USA 1/4 cub with clipped wing for aerobatics. If you use a film covering and few extra scale details the .91 would still work, but the 1.20 would be better.

RE: Picking a J-3 Cub Kit
 

The Sig 1/5 scale J-3 is the most "scale" of all recent kit offerings. It has plug in wings and functional (manditory)wing struts. At about 7-7 1/2 pounds it flies well on a .52 - .65 engine. Your .91 would be too much. The Great Planes 60 size J-3 would be more appropriate for the .91. It is quite a bit heavier through its design despite being only a little bit larger.

Probably what I would recommend would be a Sig or Balsa USA 1/4 cub with clipped wing for aerobatics. If you use a film covering and few extra scale details the .91 would still work, but the 1.20 would be better.

RE: Picking a J-3 Cub Kit
 

I agree with GarySS. The .91 is entirely too much for a 1/5 scale Cub. A .72 would be PLENTY for the clipped wing 1/5 scale, and allow for as much aerobatic potential as a Cub is capable of. The Sig 1/5 is a great kit, I have one. It is laser cut, and the plans include the clipped wings as well as the full span. I modified mine to a L-4, it has on-board glow (primarily for ease of starting, since my engine is inverted and the glow plug is difficult to access), fabric and dope finish, scale landing gear and detailed dummy engine,; it weighs ten pounds and a .65 Saito flies the hell out of it using a 14 inch prop.

A .90-1.20 engine would easily power the 1/4 scale Cub. I prefer the more scale detail and outline of the Sig and BUSA kits, as well as how they build (I also have a 1/4 scale BUSA Cub in the works). GP's Cub is fine, but is a bit heavier, and not as true to detail, IMO, but a sturdy plane.

RE: Picking a J-3 Cub Kit
 

GarySS: I have read in other threads that the CW Cub is a " Builders" plane. That is to say that some of the parts are not even die cut, but just printed on the sheet. Is this also true for the Sig 1/4 Scale Full Wing Cub? If so, I am leaning toward to the Sig 1/5 Scale kit. Fred123[&:]

RE: Picking a J-3 Cub Kit
 

Here's one of my club mate's 1/4 scale Cub. This is a hybrid... SIG fuselage with wings from the Mike Smart plan (using the SIG parts!!). Power is a Laser 150fs (waaaaaaaaaaaaay too much!) but it putters around on idle all day. :D

Regards
Scott

RE: Picking a J-3 Cub Kit
 

Fred..
I have the Sig 1/4 scale and I love it. It’s a builders kit but you have enough kits under your belt so you should have no problem with it. I used an 120 OS and I wish I had used my 91. The plane will jump into the air in 5 feet.. not very Cub like.. Half throttle take offs and flights are the norm if you want it to look right.. bert

RE: Picking a J-3 Cub Kit
 

I had a Sig 1/4 scale. From the sounds of it, that is NOT what you want.

Yes, it IS a builder's Kit - That means it much more work then you want to do. I also seriously doubt any aerobatic capabilities with a 91 FS. I had a 160 Twin on mine an that was ideal (The 160 twin is no powerhouse, but it's way more powerful that a 91)

My all-time favorite Cub for Aerobatics is the Goldberg with an OS 70 and a Clipped wing

Since you're looking for something for a 91, I'd go with the GP 60 size. (And clip the wing!)

RE: Picking a J-3 Cub Kit
 

Fred123,
I haven't built a 1/4 Sig cub, but have built several other Sig designs over the past 20 years. Since the 1/4 scale version is an older design, there could be some cutting out sheet balsa printed pattern parts. Actually I enjoyed this part of the building, but that is just me. The 1/5 scale cub is a new laser cut design that is highly engineered. But as khodges has said in other forum strings it is a more fragile design through the cabin greenhouse area. I have taken his advice and glued carbon fiber strips there ever possible to add strength. This is the "beauty" of kit building over ARF's........you can spot and correct weaknesses in the design to improve the end result.:)

RE: Picking a J-3 Cub Kit
 

Fred- I'd like to expand on what Gary is talking about when he mentioned the Cub's fragility in the cabin area. It isn't a weakness of any one kit, or poor design. It's just that the Cub has a fair amount of window area around what supports the center section where the wings attach. A ground loop, or a bad landing where the wingtip might hit first, anything that could impart a torque or strees from the wing into the center section, can twist the center section and cause the supports between the windows to break or shear. It is really easy to reinforce these supports when building the plane, using wooden dowels or carbon fiber strips or tubing. There is minimal weight gain, which the plane can well handle, and this weight is very close to the c/g, so it doesn't affect balancing the plane.

I think the 1/4 scale Sig is more "stick built" than the 1/5, meaning you do have to cut out pieces from sheet that are laser cut on the 1/5 kit, and there are some basic structural differences in the fuselage designs. The 1/5 has a box-like structure for the lower part of the fuse, with formers and longerons above it; everything is tabbed to fit, and you can almost assemble the whole thing "dry", and it will stay together. This design is very strong and warp resistant. Note the "bones" picture, but take into consideration that the cabin center section in this picture is modified from the J-3 for the L-4's greenhouse. Another thing to consider between the two scales is room inside the engine compartment. Since the 4-stroke's carb is behind the cylinder, it crowds the engine forward from the firewall, and in the 1/5 scale, you might have to move the entire firewall back from the plans' location, or at least recess a portion, as I did, to permit the proper firewall-to-prop hub distance. Also included is a picture of the stock firewall, and the recessed one I built for mine. Recessing it allowed me to maintain the very tight fit of the laser cut parts and did not modify the geometry of the firewall relative to the cabin structure, so any built in side- or down-thrust would still be there (the 1/5 has down thrust but no side thrust) The 1/4 scale is obviously bigger relative to the size of the engine, and there is more front to back latitude for mounting the engine.

RE: Picking a J-3 Cub Kit
 

I have a 1/4 scale Balsa USA Cub built by a good builder. Built light and strong. It has way more than enough power on a YS91AC so a TT91FS ot something would be enough, but a 1.20 would probably be better

RE: Picking a J-3 Cub Kit
 

Khodges: Thanks for all the information on the 1/5 scale cub.. I still [&:]think that is what I am going to build. What engine did you use that required the recess in the firewall? I was thinking about going for a 71 FS.. Mag or OS. Any thoughts about that choice? Fred123

RE: Picking a J-3 Cub Kit
 

Fred-

I entered this late because I have been out of town. I have a GP .60 Cub with a Saito .91. The plane and motor combo is perfect. It looks relatively scale, but is still very solid. Mine was my second plane, and first kit, so it has taken a lot of abuse. The instructions are great. The .91 gives it power to spare. I wish I had clipped the wings, but it still does pretty good aerobatics.

I have recently put mine on floats. I built the GP .60 size float kit. They are very heavy, but the .91 is still enough power.

-Scott

RE: Picking a J-3 Cub Kit
 

fred-- I used a .65 Saito. It provides more than enough power for anything I want to do with the plane; I don't do any maneuvers with mine that a standard Cub wouldn't do. I can take off at 1/2 throttle (takeoff roll is about 75-80 feet at 1/2, very scale roll and climb-out), and it will cruise at 1/4-1/3 throttle. At full power I have to hold some down elevator, or re-trim, because it wants to climb, but at lower settings it is very responsive.

I think you'd have the same issues regarding the firewall with most any 4-stroke in the .60-.80 range. Here's a few more pics showing what I mean, to allow clearance for the carb and still mount the engine far enough back for the proper prop hub position

RE: Picking a J-3 Cub Kit
 

I'm just finishing up a 1/5 scale SIG cub - finishing the building stage and fixing to start the covering/finishing part. The build is incredibly easy. I'm not a proficient/professional buider in fact this is my second kit and it literally falls into place. No wood that came in the kit had to be replaced, no messed up ribs etc... You can frame up the fuselage in one night and come back the next and re-check it and glue it. Same for a wing. Even the sheeting is laser cut so that it fits around the jury strut mounts on the bottom. The only sticks in the whole kit are for the stringers on the fuse and the cap strips on the wing really.

I'm putting a saito .72 on mine, which is more than they recommend but it fit and I had it on hand. I haven't cut the cowl yet but I did a lot of posistioning it against the cowl views on the plans and decided to mount it inverted with the head sticking out the bottom slightly so that the 2 dummy engine cylinders would stick out both sides. The instructions want you to mount it out one side...but you'll never really see the real one on the bottom when it's sitting on the ground.

I had to make a modified engine mount and reddrilled some holes in it and cut off a bit of it so that it wouldn't stick over the top of the fuse when inverted - but nothing major and it only took a few minutes to figure out.

I think as far as scale goes it's pretty good...considering it's a mass produced kit and not a set of plans. Better than any kit I've seen and far better than any ARF. That's why I'm building it...I didn't want a "scale" plane but then I didn't want a cub with a one piece wing that bolted onto the top with no struts etc.. and 2 wing bolts sticking out the top of the fuse.

RE: Picking a J-3 Cub Kit
 

Bob-- did you see the pics in my post above, showing the cowl? The .72 is actually a couple of mm shorter than the .65 I used, and it will come real close to completely fitting in the cowl, but the valve covers sticking out are not noticeable at all. I made a variant of the oil cooler that is a tad larger, and it sits right in front of the valve covers and hides them pretty well. I'd recommend reinforcing the "chin" of the cowl, because when it noses over (and it WILL, at some point in its life:)) that's where it hits. You can see in my pics where the oil cooler has been damaged.

I think you'll like the .72 in the plane, and it sounds so cool when you go putting by at 1/4 throttle, sounds like the real thing. I use a 14-6 MA prop, and get great performance, it pulls the plane along fine; a 14-5, or a 14-4 will also do well, but your cruise rpms will be higher.

The one issue with inverted mounting is the access to the glow plug. The angle of the plug, the fact it's hard to see to connect the glow starter to, and the bottom of the firewall interferes with the angle you need to connect it, I'd strongly recommend at least a remote start receptacle. I put an on-board glow on mine, and run it all the time as insurance because of all the low throttle running it does, but the Saito doesn't miss a beat when I don't use it. After 2 years, I'm still using the same glow plug.

The other thing I did, was to bend the exhaust elbow so I could make the muffler exit the bottom instead of out the side. I don't know if you have the old or new (ugly cast) muffler. If you have the new one, and scale appearance is important, I'd try to find one of the flex pipes for the Saito twins. They come with an elbow, and you could run the flex pipe out the bottom of the cowl. The elbow can be drilled for a pressure tap. I had to fit a piece of pipe on the threads of the elbow, and heat the elbow with a torch in order to bend it. That's one tough piece of steel!

RE: Picking a J-3 Cub Kit
 

Yeah I own about a dozen saitos - this one came off a 3lb. 15oz profile - it's in for a new lifestyle. I always make a custom exhaust unless it's a profile or something. I have a stuka I made a custom exhaust for using a saito .91. I mounted the engine inverted and built a pipe to come back behind it and open up into the "backside" opening of the stuka. I split it half way down and made one side slightly longer than the other. If you tune the engine just right when you let off the throttle you'd swear there was a twin engine in it - especially since there's no muffler - just pipes.

I usually wind up making a custom glow plug remote - after I bought a dubro one and noticed it was nothing more than 2 "z" bends in a wire at the end. I've run a lot of inverted saitos and never found the need for on board glow power once you have it broken in and can lean out the low end - if you have the tank mounted correctly. I put the cowl on when I had the engine mounted up and it technically would fit inside but it has to be cut or it will melt/burn thru or vibrate a hole in the cowl it's that close.

Doesn't matter to me - this is definately a "sport" scale plane for me. I'm not a scale enthusiest much. This plane will be a radical 180 degree turn from my hangar of planes that I currently fly. Other than my stuka I mentioned above all my other planes are giant scale 3-D/IMAC planes or profiles for practicing 3-D stuff. I'm sure this plane will be a trailer queen with me flying it 3-4 times a year but building it is something to do - since you really can't find any quality 3-D/IMAC kits at all anymore until you get into the 35% Carden size - which are nice kits - but no one makes a comparable quality kit any smaller and you can only build so many of the same thing.

RE: Picking a J-3 Cub Kit
 

Bob101:
Did you build the C/W or the full wing? Are you far enough along to get a feel where the CG will be... Nose or tail heavy with the Saito 72? This would make a difference in my engine choice if I needed nose weight...Fred123[&:]

RE: Picking a J-3 Cub Kit
 

I'm building the full span cub. No the engine has never been "on the plane' just on the firewall when I first started and framed up the fuse - then slipped the cowl on. So no idea really on the CG. There's a lot of room to move the battery around for weight so I'm just going ahead with that plan for now.

I'm just at the point where I've finished construction part and doing rough sanding. Just enough sanding to get it built - nothing more yet. I assmbled the plane and checked the struts and make sure the wings were level with the tail etc... Now I've got about a million small things to tie up like some hardware stuff then onto final sanding and then covering. It will be a while I'm a pretty slow builder....well I started in the fall and built the fuse then let it sit while I was on other stuff. Now I've come back and done the wings pretty quick.

I think I'm gonna cover it with white solartex and paint the trim colors on over that. Make it blue and white much like Hazel Sig's cub (even tho here's was the CW version). I really can't stand a yellow cub. For a while I gave some thought to an orange all over scheme I saw on a Navy J-3 (with the regular cub windows not like the military L-4) that was an air ambulance. But there was almost zero trim to it meaning you would be looking at an orange blob in the air.

RE: Picking a J-3 Cub Kit
 

Fred- I'm thinking you might come out a tiny bit tail heavy, if you build it strictly by the instructions and mount the servos in their appointed place. Mine balances perfectly, using a 4.8 Rx NiCad battery of 1000 mAh stuck under the fuel tank, with a pair of 1000 mAh NiMH AA batteries (wired in parallel) for the on-board glow sitting right behind the Rx battery. My Rx and glow controller sit right on the c/g. I also have the scale landing gear, which will shift the c/g a little forward. I'll bet you can play with battery position and get the plane to balance fine with the .72, which, BTW weighs less than the .65, without adding any lead.

RE: Picking a J-3 Cub Kit
 

I already have a CG Anniversary Cub kit and a 1.2 four stroke SIDEvalve home built motor that I bought on eBay. I have done no more than open the kit box and compare the motor with the plan layout. The engine bulkhead will need to be moved aft to allow the prop to be in the right place. I haven't run the motor but judging by the carb size (twin carb no less) it will not be exceptionally powerful. The motor is also rather heavy but do you think the Cub would suffer greatly with the extra weight? I will be happy to cruise gently in as scale a manner as my poor flying skills allow.

John L.

RE: Picking a J-3 Cub Kit
 

Khodges: Sounds like I could go with either motor and not require any lead..Fred123[&:]

RE: Picking a J-3 Cub Kit
 

Old Git, That may be WAY too much engine for it. As I said, the OS 70 is ideal and it weighs about 17 oz (500grams). It sounds like your engine would at least be too heavy if not also too powerful

RE: Picking a J-3 Cub Kit
 

I was planning to purchase a 70 FS. Are you saying that is too much engine? Fred123[&:]

PS. Sorry I thought Mnnyflyer was addressing me rather than ogit

RE: Picking a J-3 Cub Kit
 

I have already made this choice, I purchased the SIG 1/5 scale and the Dubro Cub wheels. I'm planing on using a Super Tigre GS51. 95% laser cut she should be a fun build.

Mike