Need opinion on J3 Cub issue
 

I framed up a Sig 71" Cub per the plans with original intentions to power it with a OS 40 2-stroke. I now have a OS 48 4-stroke which I want to install. Problem is, that the 4-stroke is about an inch to inch & a half longer than the 2-stroke (Due to the carb being on the rear of the engine) and in order to keep the overall length of the plane consistent with the plans I either need to (1) move the firewall back to compensate or (2) move the cowling forward with the 4-stroker. Moving the firewall back will require considerably more work, but I am afraid that if I do not the plane will be very nose heavy and will not look scale with the extended nose. What would you do? Thanks for your opinions.

RE: Need opinion on J3 Cub issue
 

First, I would seriously reconsider a .48 4-stroke in this Cub. I believe power will be marginal.

If you do install it, take the time to move the firewall back. Extending the nose may create balance and handling problems.

Dr.1

RE: Need opinion on J3 Cub issue
 

The kit calls for .25-.40 (2-stroke) or .40-.53 (4-stroke). Do you really feel that the .48 will be marginal? I was leaning toward moving the firewall but wanted another opinion. Thanks for responding.

RE: Need opinion on J3 Cub issue
 

I am assuming the kit you refer to is their "OLD" J3 kit....the one that has a zillion pieces and takes a few centuries to build? If so, your two-cycle is powerful enough, but the 4-stroker would sound a lot better!!!!! I'm flying their 1/5 scale Cub with an OS .52 and flys very scale-like.

RE: Need opinion on J3 Cub issue
 

Dave, I am continually amazed at the power inflation that has occurred in this hobby. People are constantly being advised that kit recommendations will be marginal. For sport planes, name your poison, but for scale models it just takes the magic out of the hobby. Not everything has to be able to do knife-edge loops.

The Sig Cub is a totally different animal from the Goldberg and GP Cubs even though the wingspan is not very different. It is a very old design originally powered with a .15 to a .19. I'm not kidding--the 71 inch Cub flew on 15s and 19s that had much less power than comparable engines today. Sig updated the kit and over the years they upped the power recommendations to a more popular range of sizes, but it is still light construction by sport model standards. The .48 is more power than it needs and it may be hard to fly it realistically with that much power and weight--it will tend to be a sport model in the shape of a Cub. Unless built very heavy, I'm quite sure you will need tail weight to balance. I've considered building this plane for my OS .26 FS, which would be plenty--I build light. My Champ was almost as large at 600 sp in, weighed 3 lbs, and flew beautifully on an OS .15 FP, including take-offs from grass. If not beefed up, your Cub will weigh around 4 - 4 1/2 lbs and fly very nicely on half the power you have. One guy on another newsgroup reported that his FIFTH scale Cub flew well on his OS .48 FS. That's got an 84 inch span and weighs around 7 lbs.

If you go through with the .48, then I think you should bite the bullet and move the firewall back. You're right--it would be disfigured by extending the nose and you'd need even more tail weight. If your OS 40 is an FP or LA, maybe you should use that. The power and weight would be more appropriate. Use an 11x5 or 11x4 prop on a 40 FP. Good luck, keep us posted. It should be a pretty plane. Jim

RE: Need opinion on J3 Cub issue
 

Thanks guys....Yes, this is the old Sig kit. A jillion pieces but only a century and a half to build. As a matter of fact, I framed this plane 15 years ago. It has been sitting in the top of my closet ever since. I got sidetracked a while but I'm back. Eight grandkids and two of them want to see my planes fly. I have never owned a four stroke until now but I have heard nothing but good about them. I bought this OS 48 specifically for this cub based on what the kit recommended. I really want to stick with a 4 stroke because of the sound and better fuel consumption. Perhaps I should consider a smaller 4 stroke. I do not want the plane to be out of scale either in performance or appearance. That may also prevent me from having to move the firewall. Buzzard.....Was your Champ a kit or scratch built? I own a full size Champ and would love to find a kit. I am not much on scratch building. Please let me know if there is a Champ kit available. Thanks again.

RE: Need opinion on J3 Cub issue
 

Occasionally you can find an old Bud Nosen Champ (1/4 scale) kit for sale on Ebay. They look and fly well with a 120/150 4 stroke.

RE: Need opinion on J3 Cub issue
 

I just finished this kit last year. I have had a few of these and have used the OS 40 4 stroke and it flys very well. Not a power house but well. The first kit was built using the stock firewall location. I then switched to the surpass versions with even better performance. All of the latter builds I have moved the firewall back so that the motor would not stick out so much. I also clipped a bay from each wing to shorten the wingspan. Nice plane. I think you will be fine either way. Without moving the firewall you will need to ballance by moving weight to the rear of the plane.

JEB:D

RE: Need opinion on J3 Cub issue
 

Some years ago, I flew "your" cub on a tired OS .30 2 stroke. It flew just as you would want a cub to fly and was still a touch overpowered. That one was covered with Monocote. Later, I built theclipped wing version, covered with Super Coverite and painted as the Hazel Sig CW. That one was powered with a KB 40, 10X6 prop, which turned out to be too much torque. Changed to a 10X4 prop and it was just right, flew like an aerobatic cub. Both engines you have will fly this plane fine, and the 4 stroke will give the nicer sound. It's a win-win choice you have. ;)

RE: Need opinion on J3 Cub issue
 

My Champ is not scale. It is the old DeBolt Champ, which was a slightly Champ-like trainer. You can see it in my gallery.

Full scale Champ--nice! The only current Champ kit I know of is a little 35 inch electric from Hobby Hangar, and even it may have been discontinued recently.

Your Cub was originally designed by Chuck Hollinger in the early days of RC. Cal Smith was inspired by that plane to design a scale Champ using similar construction, and to the same 1/6 scale. It is available from AMA Plans Service, and there are probably other Champ plans there too. Bill Northrup also has the Cal Smith design--see recent mags like Flying Models for ads.

You really should try scratch building--it's not that hard. The toughest part on the Champ is that distinctive curved windscreen.

Jim

RE: Need opinion on J3 Cub issue
 

[uote]

The only current Champ kit I know of is a little 35 inch electric from Hobby Hangar, and even it may have been discontinued recently.

Jim
[/quote]

no way! it seems as though every manufacturer makes 3 versions!

RE: Need opinion on J3 Cub issue
 

buzzard bait does have a point. Kits like the old Sigs and the Bud Nosens are designed to fly on the wing, not the prop. That being given, I'd say the .48 4 stroke will fly your Cub in a VERY scale-like manner.

Dr.1

RE: Need opinion on J3 Cub issue
 

Flew my buddies H9 PNP Cub today and rarely got over 1/2 throttle....it has a .46 Evolution two-stroker.

RE: Need opinion on J3 Cub issue
 

IMO a "Cub" begs for a 4-stroke engine. I built one once with a 2 stroke and never had good luck with it. The tank was too high for the engine and it tended to quit on the approach when throttled down. But, aside from that, the sound and scale performance with the 4 stroke really adds realism and class to the "Cub". Go for the the 4.

DaveB

RE: Need opinion on J3 Cub issue
 

I inherited this Sig 1/6 Cub many about 20 years ago and stuffed it in rafters of garage. I recently returned to rc flying and I am in the process of restoring this plane. I don't have any plans, door and cowl are missing. Assembly wasn't great, but I have reglued and re-inforced many parts. I have a 2nd generation OS FS .60 that I would like to mount inverted but it appears to be way too big for this plane. Its the only small 4-stroke that I have. I guess I could mount a .40-.46 2-stroke if necessary.

As I mentioned, I don't have any plans and I am wondering what the tail, wing, and engine mount incidence angles should be. Looks like the top of fuse where wing fits is not level so I may have to re-work that area. And, the tail assembly looks like it was barely mounted above the main fuse stringers which looks odd to me. And, the landing gear fairings are hard-mounted to fuselage which doesn't look right since the spackling would crack or has cracked in a hard landing.

Any help would be much appreciated.

http://i75.photobucket.com/albums/i3...6/DSCN1370.jpg
http://i75.photobucket.com/albums/i3...6/DSCN1369.jpg

RE: Need opinion on J3 Cub issue
 

How about an E Flight Power 46 outrunner instead. Will provide plenty of clean and quiet electric power. And.......no cutouts for the muffler, carb needle valve, etc, etc, etc.
I'm currently building the Sig Citabria for E- Power and even though it's a builder's kit, I really enjoy building this one. It will be powered by and outrunner motor such as an Axi or Hyperionor maybe an E-Flight Power 46. Give it a try, you might like it.
"It's electric? Oh the horror of it all!"

RE: Need opinion on J3 Cub issue
 

txdave,
sorry i missed this thread earlier. i don't know if you sorted out this problem or not but, if not, here was my solution for putting a Saito 40 up front. the first pic shows the nose as built per plans. the second photo shows how i shortened the nose after realizing i couldn't shoehorn the saito in. the third photo shows the look with the cowl on. here is a link to the build thread i posted: http://www.rcuniverse.com/forum/m_14..._1/key_/tm.htm

RE: Need opinion on J3 Cub issue
 

Bud Nosen also made a .40 sized Aeronca Champion kit. One is for sale on Ebay as I write this at $49.99. The auction ends in 3 days, 16 hours. It has a 65 inch wing span.

I've asked this question before and it is really only a statement and has nothing to do with the Sig Cub or changing power: Why are there 15 ba-jillion J-3 Cub kits and ARFs offered on the market at any given time and so few (no) Aeronca Champs? I think the Champ was more popular (in full scale) then the Cub. At least when my Dad and I walked around airports when I was a kid, there were more Champs then Cubs.

RE: Need opinion on J3 Cub issue
 

Check the production numbers, there were ALOT more Cubs built than Aeronca's. The Cub was in production for at least a half century.
Anthony

RE: Need opinion on J3 Cub issue
 

Right, if we're talking about all variants of the original Cub. The lineage of the Champ is quite long also, as we can add in the Champion, Citabria and Bellanca lines. Then, maybe there isn’t so much of a difference. At any rate, I clarified that my comment was on what I saw in the 50s and 60s, walking around airports in my local area with my dad. The point I was attempting to make was the Aeronca, which was a very popular airplane also, is not modeled nearly as much, or offered as a kit or ARF, as the Cub is. The Cub has been and continues, to be offered add-nausiem.

There is no doubt the Cub is popular! I like them, also and Cub yellow is one of my favorite colors.

RE: Need opinion on J3 Cub issue
 

I have a Sig J-3 cub with such an arrangement. i didn't build it, teh seller did. All he did was place the engine as far back as he could on the mount and adjust the throttle cable. It works fine and looks original. the front of the engine sticks out just a little, but no too much. it had a master Airscrew prop on it with an old, small rounded prop nut. i replaced the wheels with some off-brand,original looking ones that added to the scale appearance.
I once replaced the 4-stroke with a 40 2-stroek and did nothing to alter the CG or cowl.
but, I am back to the 4-stroke because it sounds and acts so much more scale-like.
[8D]

RE: Need opinion on J3 Cub issue
 

Stab and engine incidences are zero, the wing is minus 2 deg.
The landing gear were hard mounted to the fuselage and yes they do tend to crack the finish after less than perfect landings.
The stab is mounted on the top of the truss longerons, the two top stringers are mounted over it and tapered to blend into it. This plane was designed to fly on an .25 to .30 size 2 stroke engine, a OS 40 LA works well on it. A 60 four stroke is way to much power and weight for the airframe in my opinion. This is the 1/6 that SIG still produces today I have built three versions of it over the years, and as others have said it flies the wing not the engine, don't overpower it.

RE: Need opinion on J3 Cub issue
 

I have an old Sig 71" Cub that is powered by an OS .26 FS. I took care to build it light and the .26 provides enough power for scale-like flight. A .48 FS will no doubt provide enough power unless you build a very heavy Cub.

RE: Need opinion on J3 Cub issue
 

I too have the 71" cub that is now ready for covering. Also I built to the plans and then puzzled over how to fit a 40FS into the plane and maintain the scale look. You can''t. So I moved the firewall back 3/4". It wasn''t such a big deal and hope to have the plane flying by the end of the year.