Question about building a SC

Hey guys,
Sort of new to the SC group but had a couple of questions.....these may be really broad but I was sitting with my boss talking about building a cub or some sort (really just killing time) Anyway, is it possible to build a SC using a J3 frame? If I recall its a bit smaller, therefore I would assume a bit lighter? Any chance you can throw on PA18 wings to that same frame?
I thought it would be interesting to put a larger engine on the J3 frame (larger than 65hp that is, perhaps 180hp!) and then have a wing with flaps...has this even been tried or is it impossible?
Again, I know this is a rather board group of questions but it made for some interesting talking with my boss. Thanks guys!
-Josh

Josh -
Always good to question. There are alot more knowledgeable people on the site, but here's what I can say for you.

First, watch out for the purists....they'll get upset at any idea of wrecking a J3 and turning into something else. The J3 wing has some similarites to the Supercub in parts, but have much different spar ends at the cabin. The forward spars meet almost together, where as the supercub forward spars end and attach at the cabin, same as the rear spar. The J3 and Pa-11 also have similar hook ups for their wings. Also, some J-3's have wood spars.

If you want a Supercub to build, it's a much better idea to start with a supercub frame. You can choose from an old frame to restore, or new pma'd frames to build with paperwork, or some experimental frames to serve as your foundation.

Good luck! And, check out www.supercubproject.com if you want to get a sense of scope for building a supercub.

Thanks! Theres a cub frame laying in a hangar next to ours, got us thinking about making it into some sort of mutant cub hah...I think you're right though about just getting a supercub frame....This is what happens when we don't have enough flying on our schedules...we start thinking of ways to mess with stuff haha...

J-3 and PA-18 are the same size. Just a different top-deck and a few other tubes.

Jason

The whole standard Super Cub fuselage weldment weighs 104 lbs. A wide body fuselage weighs 114 lbs. I don't know the weight of a J-3 but I would guess it weighs at least 90 lbs, maybe more. Anyway, not much weight savings to be had in the fuselage structure from one to another.
Darrel

I think the firewall/engine mount attach is narrower too. Could be wrong as I have never inspected an uncovered J-3 frame.

Interesting info guys! Thanks for the replies! I didn't realize the two frames were so similar in weight...I thought there was a bigger difference. Glad I asked! I'm safer just buying an already built cub, but it seems like a blast to build one....(blast may not be the right word hah)

My buddie built one up from a J3 fuselage and wings, shortened the spars, extended baggage, 0200 with light weight starter and battery, SC seats, 1320 gross for sport pilot and it's experimental, calls it the " Magic Cub " it's sweet and climbs great because it's lite.

Glenn

There is something like 3/8" difference in the firewall placement between the two. I would want to change to a PA18 top deck as well.

I would not mess with a 70 year old J3 fuselage.

If you don't have the money, spend the time to build with new tubing.

If you don't have the time to build with new tubing then buy a new fuselage.

If you don't have the time or money then building an airplane probably isn't a good idea.

Steve Pierce said:

There is something like 3/8" difference in the firewall placement between the two. I would want to change to a PA18 top deck as well.

Click to expand...

Steve, aren't the firewalls different too? The J-3's I have seen converted to 150hp have very narrow firewalls and huge side cheek exits. It looked quite a bit more narrow. Maybe it is just the boot cowl.

I have a 1946 J-3 Cub. It was sent back to Lock Haven in 1954 and the factory re-manufactured it into a PA-18. I have all the original logs and paperwork. When it came back from the factory, it had a Lycoming 0-235-C1 in it, PA-18 wings with a 15 gallon tank in each wing, no flaps, PA-18 tail feathers, Sensenich steel prop, swing-out motor mount, electric start, PA-18 panel, complete electical system, landing light in left wing, extended baggage compartment, float fittings, and everything else that came on a 1954 PA-18. The frame still has the same serial number, it is still registered as a J-3 Cub, and even though the factory should have increased the gross weight to 1500 pounds, the engineers inadvertently left the gross weight at 1220 pounds, so it is probably the only PA-18 in existence that legally qualifies under the sport pilot rules. Nothing on the original J-3 TCDS applies to this J-3 due to the remanufacturing of this airplane into a PA-18 at the Piper factory in 1954. Everything in the TCDS for the 105 HP PA-18 with the Lycoming 0-235 C-1 appears to apply to this airplane. But yet, ever since 1954 this airplane has been registered as a J-3 Cub and flown as a PA-18. All modifications were approved by the FAA and all documentation is on file with the FAA.

Very Cool..

Yes the firewall on the J3 is narrower, I was just talking about the main structure. PA11 and PA18-95 are a little wider in the boot cowl than a J3 and the PA18 with a Lycoming is even wider.

I wonder what 15 gallon tanks Piper used in your J3 to PA18 conversion. I would love to read your paperwork.

Were the front spar wing connects moved outwards like a 18 is, also?

Very cool indeed. -Behindpropellers- I appreciate your insight....as for everyone else thanks for the info, pretty interesting...I have no intention of messing with one and if I had the money I would just buy one outright. Just in case anyone thought I was going to torture a J3 frame, don't worry....I won't...was merely asking if it was possible....Anyway love reading stuff on here so thanks guys! Take care!

Steve,
I'll drop in one day with a box full of log books and let you take a look-see.