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New member building a PA18-95

This is great information guys. Good stuff to think about while fishing with my three boys this weekend. Better get ready. I'll check back on Sunday.


Thanks,

Jim
 
Has anyone weighed a D&E stamped rib? I wish I would have weighed one of mine. They sure seemed light to me but had nothing to compare to. All this talk of extreme weight saving wasn't around when I was building mine. I just put it together and have a nice flying Super Cub.

Bugs,

Did you rib stitch or pop rivet the fabric to the flanged D & E ribs?

I haven't been keen on running the rib stitching past the edge on a flanged rib, so all the Univair ones I have used I've pop riveted for this reason. Just wondering what you did and what you think.

For several years I ummed and ahhed about how realistic it was to build a Cub to fit into our microlight category, which until recently permitted only a 1200 lb max weight. The reality is unless you're totally focused on weight savings you won't have a good performing Cub with adequate payload when you're limited to 100 hp and 1320 lb max weight. I know what you mean though. If I put one of my kids in the back of my 150 hp Cub I can't tell the difference, so you wonder what all the fuss is about:roll:

Andrew.
 
That looks great gsmx440. You seem to have the procedure down. Can you get 6061-T3? That should work easier.

Brain seize. To many projects
Electric Renault Dauphine conversion, L21-150 horse (clone), ham projects,dogs, kids and fly's.. It is 6061-T3!
 
Using the calculator http://www.onlinemetals.com/calculator.cfm and making a wild guess as to how much material is in one rib, I'm guessing, that using 0.016" 6061-T3, one rib should weigh perhaps 9-10 ounces counting the rivets. That is assuming that the cap strip is 10' x 2" and the diagonals are about 5' x 1".

How much does an original Piper rib weigh?
 
Yes I rib stitched. The flanges have a bevel so you can. Also the D&E wing does not have the half ribs like Piper. Less parts mean less weight.
 
Here we go.

Ordered materials to start my build today. After looking into all the options available, decided to go with Carlson style ribs. I' m going to start with the left wing. I plan to build a squared off wing with 14 ribs. I bought one aileron rib to use as a pattern and 13 milled L-shaped capstrips. Before I ordered anything, I tried to make some T-shaped Piper style cap strip from aluminum flashing I had. I borrowed a bead roller and a shrinker/stretcher to play with. The best result I was able to make was with my brake and hand seamers followed by the shrinker/stretcher. I'm sure I could have eventually made the lighter Piper truss style ribs, but I'd have more money in custom dies and tools than I'd have in all the ribs. This didn't make sense to me at this stage. I'll be buying some tools that I don't already have along the way that I will for sure need. I hate to buy some now that won't for sure produce a creation I can trust or am happy with. I'm going to start building a fab table this weekend. Should have some materials and a rib to look at next week. Next step- build a rib jig and make all the left wing ribs. I'll look into moving this thread into the "Member Projects in Progress" category and post some pictures soon.

Jim
 
Great Jim, I think we are eager to see your progress. BTW, why not blog it instead os starting a thread? I say this because every step (or post ) you add could be discussed separately with out interfering with the most current progress...

Food for thought.
 
Jim,
Best idea I came across was from EAA Ch. 1000 on building tables. http://www.eaa1000.av.org/technicl/worktabl/worktabl.htm
Their idea was to build three separate tables to be bolted together for the long table needed for the fuselage. After fuselage, they can be separated and used as needed. I went one step further and made mine three different widths. My 2+2 fuselage is pretty wide at the front so I made the first table just wider than that for the front. The table at the tail post didn't need to be as wide so I made it a bit narrower; middle table was in between. By doing that I didn't have as much far leaning and stretching when welding; saved an already messed up back further pain. I have used those three tables in every conceivable configuration over the years. Another tip I learned is when you strike the center line on the table. Chalk lines can be surprisingly off. In boat building I learned a nice trick. Paint your work table white after leveling. Stretch a heavy string (string line for foundations worked great for me) along the middle of the table as tight as you can. Get a can of grey primer and spray straight down over the string. When the primer is dry you have a perfectly straight White line down the center of the table outlined by the grey primer. Worked great for me.

Marty57

table.jpg
 

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I like to use the white melimine on my table so you don't have to paint it. It's nice to use permanent sharpie on it then you can wipe it off with acetone.
 
Table is all but done. Two 3' tall x 3' wide x 8' long tables bolted together with full length storage shelf midway up underneath. If I need a third later, I still have room to build and bolt one on. My four year old and six year old boys helped with building the tables. The four year old learned a lesson about sawdust and rubbing your eyes and my six year old learned how to read a tape measure. You'd be suprised how many adults don't know how. Thanks Marty and Larry for your tips. Once I get a little closer to actually building something of length, I'll level everything up and refer back to your advice.

Thanks,

Jim
 
My lathe and mill are sitting on Melimine...easy to clean up!! Remember, at some point you are going to be welding on the table so I'm not sure how that will react to 6K degrees but I have had good sucess with using aluminum cookie sheets to put between the joint to be welded and the birch plywood I used. It does scorch some but a little sandpaper and white paint will fix that problem. I built 4' wide, two 8' tables and a 2' section between them all bolted together. I built a 2"x8" frame so it is pretty solid and I installed electrical boxes and compressed air outlets on the sides (8 of them) to keep the cord clutter to a minimum. Lag screws in the bottom of the legs allow you to level the table as needed and keep everything as it should be on the "bubble". Only other suggestion is make sure your tools and power equipment is close to your work to save time and walking...unless you need the exercise.
 
Aileron/Flap questions

While I'm waiting for materials, I've been thinking about flaps and ailerons and reading what others have said on different threads. I've also discussed privately with a builder what exactly he did. I'd like to hear what some other people have for opinions. I'm planning to run flap and aileron from the fuselage to the square tip of my wing. If I'm not missing something, the length will be 16' with the rear spar being the limiting factor. Because of weight and because of C90 engine, I'm planning 14 aileron ribs that I will make from Carlson L capstrip and a pattern aileron rib. The L is slightly lighter than their T. I'm planning on having an engineer buddy or two take a look at the Carlson aileron rib and advise on different intercostal shapes/lightening holes to make it as light as I can and still be safe. The wing I envision is a standard 13 rib with an aileron rib in place of the wing tip rib and a 14th aileron rib on the end of the rear spar. Not knowing much, but sounding like a good idea is making the leading edge from carbon fiber and doing away with all the nose ribs to save more weight. I also like the thought of adjustable droop ailerons. If I understand, one could dial them up for better cruise and dial them down for better slow flight. I'm not sure on wing tips yet, but again I am pondering making my own from carbon fiber or possibly leaving them off entirely. From what I can gather from the prints, it looks like a standard aileron is roughly 102.125 inches and a standard flap is roughly 62.5 inches. It also looks like the standard chord length for both flap and aileron is 13.25 inches. If I do what I plan, it looks like I'll have roughly 25.25" to fill in with either aileron,flap, or a combination of both.

Here are the burning questions...

How long for the aileron?
How long for the flap?
Should I go with the standard chord for flap and aileron? I'd like to because of weight and simplicity but again, I don't know much.
What about lightening holes in the spars like the CC? This one scares me. Maybe it shouldn't.
Should I worry about twisting spars with 14 ribs and longer aileron/flaps?

Keep in mind C90 engine, primarily wheels/ski's with possibility of future floats. 792 pounds. Not a STOL competitor but want to hop off the ground and land/fly slowly with control. I am going to shy away from LE slats/slots in favor of a little more cruise speed. I want to build the toughest, lightest wing I can and not worry about tearing it off.

Thanks,

Jim
 
...I'm planning to run flap and aileron from the fuselage to the square tip of my wing. If I'm not missing something, the length will be 16' with the rear spar being the limiting factor. Because of weight and because of C90 engine, The wing I envision is a standard 13 rib with an aileron rib in place of the wing tip rib and a 14th aileron rib on the end of the rear spar.
Place a full sized rib at the tip. This will give you an attachment for the squared off removable tip.

Not knowing much, but sounding like a good idea is making the leading edge from carbon fiber and doing away with all the nose ribs to save more weight.
You still will need to address the air load on the leading edge which is trying to collapse it. This is the main reason for the nose ribs.
I also like the thought of adjustable droop ailerons. If I understand, one could dial them up for better cruise and dial them down for better slow flight.
I like drooping ailerons. I have flown them on a Cub. They do help take off and landing performance. The Cub, which I have flown, had them connected through a complicated movable pulley system to the flap handle (weight). Drooping aileron systems reduce the up aileron travel which is important in crosswinds. The question of up for higher cruise only works on certain airfoil shapes. I doubt that the Cub is one of those. I rigged the drooping ailerons on my 185 so that I could test this theory by varying their position while in flight. Any position other than neutral, slowed down the cruise speed.

I'm not sure on wing tips yet, but again I am pondering making my own from carbon fiber or possibly leaving them off entirely.
Mine are squared and slightly drooped. Screwed on to the tip rib. They will have less drag if they are most any shape other than "just left off".

From what I can gather from the prints, it looks like a standard aileron is roughly 102.125 inches and a standard flap is roughly 62.5 inches. It also looks like the standard chord length for both flap and aileron is 13.25 inches. If I do what I plan, it looks like I'll have roughly 25.25" to fill in with either aileron,flap, or a combination of both.

Here are the burning questions...

How long for the aileron?
Mine is 88" with the control horn at the inboard hinge location.
How long for the flap?
Mine is 110" starting at the fuselage.
Should I go with the standard chord for flap and aileron? I'd like to because of weight and simplicity but again, I don't know much.
Mine is standard chord.


Keep in mind C90 engine, primarily wheels/ski's with possibility of future floats. 792 pounds. Not a STOL competitor but want to hop off the ground and land/fly slowly with control. I am going to shy away from LE slats/slots in favor of a little more cruise speed. I want to build the toughest, lightest wing I can and not worry about tearing it off.

Thanks,

Jim
792 pounds is a lofty goal. Good luck.

LE slats/slots require a lot of power to over come the drag when operating them at their maximum effort/effect.

In my opinion long flaps when used at the proper angles are very effective. Testing will tell you which angles are best for your application. My Cub "floats" with full flaps. I wish that I could get a lot more deflection comfortably. The reason that I can not is two fold. My flap handle is not long enough to provide the force necessary. And the handle location is too far aft behind my range of motion to be able to effectively operate. Currently my best take off position, for short distance and angle of climb, is the full 50 degrees. However, because of the awkward use of the flap handle close to the stall speed, I do not consider it to be safe.
 
Jim

That is a lot of ground to cover. A lot of that info is on the site here and can be found with the search engine.

Here are my short answers


How long for the aileron? Std aileron but moved out to the tip
How long for the flap? Build to take up all the room from moving the aileron outboard
Should I go with the standard chord for flap and aileron? Yes, weight will be everything with a 90Hp engine I'd like to because of weight and simplicity but again, I don't know much.
What about lightening holes in the spars like the CC? You will need to to keep it light This one scares me. Maybe it shouldn't.
Should I worry about twisting spars with 14 ribs and longer aileron/flaps? Probably not. A 90Hp Cub will be slower and generally have less air loads than a 180Hp Cub


You do not have the power to carry the extra weight and area of the square tipped wing. Go round tip and keep it as light as possible. You do not have the power to carry the increased weight of a droop flap/aileron system.

You will never make 792 pounds with your current mentality. I am not trying to be rude or harsh but you are going to have to give up a LOT of stuff to make your goal weight. If you do make that weight you will not need the other things (droops, Sq tips, flaps, Etc). You are trying to build a Jerry Burr Cub. He has won short field contests all over the place, not because of all the mods but because he has a very light Cub (and he is a VERY good stick). A light Cub is a wonderful thing to fly. What you sacrifice is utility. You will not have the range, or load hauling, capability of a larger engine, heavier Supercub. If you do all the things you are talking about above you are going to have a 900 or 950 pd Cub and with a 90hp engine it will not perform like you want. It is all about trade offs. You are still trying to build a light cub but do not yet understand what that means. Search weight and cub on this site. Jerry Burr is your standard. Talk to him. Read his posts. Just about every "improvement" you are thinking about adds weight. You can't do that.
You need to have a gram scale by your side even when you sleep.

My recommendation. Start collecting used wing (J-3/PA-11, early SC) parts off Ebay or Alaska list until you have enough parts to rebuild/build up a set of basically J-3 wings. Nothing is lighter than the original factory rib, just keep collecting until you have a complete set of useable ribs. Drill the spars. Use CF leading edges but leave the nose rib in. Add the two 11 gal wing tanks. (oops just added weight, even offset by drilling the spars and CF LE, will still add 5 to 10 pounds) No flap, round tip, no landing lights, 13 rib, fabric cover over the wing tanks, primer only where necessary,.......

Just trying to help

Bill
 
I agree with what Bill said. Also ditch the droop ailerons for sure.

I have said it before, if you want to build a kite, then go for it but don't expect it to be much stronger, capable, or durable than a kite. My main point is folks seem to sacrifice so much then after the plane is completed and flown wish they had a more capable or durable aircraft.
 
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Some J-3 rebuilds get close to your target weight with heavy finish and add ons. If you want to get good performance from a C-90 build an experimental J-3 with a PA 11 style back seat and a SC elevator system so you can have a standard PA18 baggage which is enough. Building an airplane is a daunting task and if you don't have a plan in the begining then changing your mind midstream will add time and weight. As mentioned, Jerry Burr is the king of lightweight continental powered cubs. I would look for pics of his ship and study what you can find out from them.
 
Jim,

I kinda echo the same thoughts as the other respondents to your last post. I said earlier something like if you want a Cub, build a Cub and if want something different, build something different. I know this is going to sound rude, but the plane you describe is not a PA-18-95. With longer chord flaps and ailerons, extended wings and flaps and modernised structures (carbon fibre), you might be better off building that Bearhawk Patrol, because Bob Barrows has done just that, incorporated a lot of modern ideas and new technology into the basic Cub format.

I am attempting to build a Cub to fit into the New Zealand microlight category. Until recently I only had a 1200 max. weight to play with. It is now 1322 lbs, and while there are differences between our microlight rules and the US LSA rules, as far as a Cub goes they are pretty much the same. This is something I have been mulling over for some years now and I have spent a lot of time taking upon ideas, evaluating them, re-evaluating them and then rejecting or accepting them. For all sorts of reasons I am not building a PA-18-95 clone, but I will be using as many stock Piper parts as I can. I really think you have a lot of thinking to do if you are going to depart from the tried and true PA-18-95.

Because I am attempting a low power experimental Cub, I can see that the perspective of the guys who have posted is from their experience with their 180 hp machines. There are a few guys who post on this forum (Tempdoug, SuperXP11 and one or two others) who have built 90 hp experimental Cubs. I would get hold of them or read their posts and see if their Cubs are what you would like. SuperXP11's machine is sub-800 lbs and has squared off wings I believe, but Doug's is over 900 lbs I seem to recall. These guys are doing it, with flying planes. If their machine is what appeals to you, that is probably what you have to aim for. If it is not, you are then going to have to add and subtract a few things.

All the best,
Andrew.
 
I'm doing a lot of the same things Jim is looking at and I continue to rethink the flaps because of weight but I'm going with a 0-320 for sure because of density altitude where I"ll be flying. Flaps provide significant benefits in my opinion and I think that is shared by a lot of you folks. I've beefed up the fuselage for the 0-320 and will be starting my wings soon so I need to make decisions and live with them. I want simple and as light as possible while still giving me the features that I believe are necessary for my mission and probably floats in the future. Keeping it light to stay inside LSA weight and still make it tough enough to handle rough field work is a big challenge!!
 
Were it me, I'd forego the 90 and run an O-200 with 9.5 pistons for an extra 10% power and torque. Combine with a Mac 7535 for takeoff and climb. Does great climbing at 55 mph and 2850 rpm.
 
Were it me, I'd forego the 90 and run an O-200 with 9.5 pistons for an extra 10% power and torque. Combine with a Mac 7535 for takeoff and climb. Does great climbing at 55 mph and 2850 rpm.

If your going to over prop it and lug it around then a C90 is what you want. But if you let a 0200 breathe above 2700 it will make the hp you need. Does great climbing at 45. Jim understands the math, I just remember the smile.

Glenn
 
im currently building a wag j-3 with the pa-11 mod. my goal weight is 850 lbs with a 100 hp o-200. from what i understand you can save a few pounds with aileron style flaps and a over head flap handle. the aileron style flaps produce more lift as well. from burrs recomendations im going to run standard SC flaps with extended flaperons. the flaperon system jerry has adjusts through a over head turn-buckle if i remeber correctly. im also makeing all interior comfort easily removable. i custom built my seats to be easily removable yet more adjustable then any cub. the interior will have snaps so i can pull insulation out in the summer... plane jane interment panel. wood control sticks save 1/2 lb. light weight electrical (i need lights). and tiny tiny hardware with nylon washers. pick up a bag of steel screws sometime.

my "i dont care how much it weighs" list.
1. saftey. self explantory
2. longevity. metal wing spars dont get grain cracks after 20 yrs of temp changes. wood does. why would i put 30+yr lifespan, $5,000 of fabric and dope on wings that crack spars after 15-20 yrs. might as well prime my fuselage with cheap non etch primer too. let it rust in 5 yrs.
3. ergonomics. (can i move, start, and get in this thing if my back goes out) i added a ski-handle to the tail. changed one channel in the birdcage to to hand grab and ill have steps all over the landing gear.
4. is it to cool to NOT do it. i love booster tips. and regardless what anyone says or thinks im putting them on. besides....they work.
5. resale value. i dont think j-3's are strong enough for float operations. but i'll put float mounts on anyways.

i also weigh 115 lbs so i can stuff more weight in the plane and still be competative.
 
Building ribs, but how many?

Yes, I'm still building an airplane. I've got thirteen ribs made. They are similar to Carlson ribs, but they are lighter. I squeezed 3/32" ad rivets instead of 1/8" steel mandrel blind rivets. I also drilled lightening holes in the intercostals and dimpled the holes to add a little stiffness to the finished product. I'm happy with the result. I'll post some pictures soon with weights. Not a huge weight difference, but every little bit will count. I've decided not to drill my spars. I've also had lots of time to think about my engine choice. The more I think, the more I lean towards an 0-320. My question is, should I absolutely have a 16 rib wing with 150-160hp?

Thanks,

Jim
 
HI Jim glad to hear that you are making progress. A guy who increased the gross weight of some early supercubs told me that he had quite the go around with the faa on increasing the gross of 13 rib cubs. He told me that the main reason piper added more ribs had to do with the VNE and the leading edge collapsing at really high airspeeds, and not with needing more ribs to take the weight. I would personally go with the 13 ribs as the ones you are building are much stronger than piper's. Maybe Mike MCS repair will comment, he might know more about this.
 
..A guy who increased the gross weight of some early supercubs told me that he had quite the go around with the faa on increasing the gross of 13 rib cubs. He told me that the main reason piper added more ribs had to do with the VNE and the leading edge collapsing at really high airspeeds, and not with needing more ribs to take the weight. I would personally go with the 13 ribs as the ones you are building are much stronger than piper's.

Just thinking off the top of my head here. If the reason for more ribs is for the higher VNE, it does not have to do with the strength of the individual ribs. It would have to do with the support of the leading edge skin by placing the ribs closer together, thereby stiffening the leading edge skin. You could stiffen the leading edge by adding just nose ribs.
 
ribs

the main reason piper added more ribs had to do with the VNE and the leading edge collapsing at really high airspeeds, and not with needing more ribs to take the weight. I would personally go with the 13 ribs as the ones you are building are much stronger than piper's.

Might consider using Randy's carbon leading edge.. not much reason to use short ribs
with his stronger LE.
1- Full wrap to tip
2- Lighter
3- Stronger
4- No rivet bumps (smoother)
5- No hanger rash (bounces back)

http://carbonconceptsak.com/
 
Pictures of the journey so far

Here are some pictures of making the table and ribs. Not the most exciting stuff, but some good memories. Port wing aileron ribs are made. Working on the starboard wing ribs now. Ribs varied in weight from 9.6 oz to 10.1 oz. Still will need to make two full sized ribs for the wing tips. I will make those two last.
 

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Helpers are a wonderful thing and I have a killer guard dog like that too....lick you to death!!

Looks like a really nice start and that's a good job on the ribs if you can get them lighter than the Carlson ribs.
 
More Pictures

Here are the rest of the pictures that we've taken so far. Two of my favorites are in this group. Gage's pose with the dog makes him look like a miniature centaur. The other is the picture of my three sons and I with one wing's worth of ribs. Left to right Ellis, Gage, Jordan with me in the back. My wife is behind the camera. Our daughter Amelia has helped some too, but she isn't in any of the pictures. I'll have to make sure to get some shots of her next time.

Better get back to building.

Jim
 

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you guys are going to have a blast in years to come with this plane! The memories will last generations. Doug
 
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