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Thread: Introducing a J-4 project

  1. #41
    Cub junkie's Avatar
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    Very nice. Is that some type of power window motor?

  2. #42

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    Quote Originally Posted by Cub junkie View Post
    Very nice. Is that some type of power window motor?

    Yes exactly what it is.

  3. #43

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    Control sticks,
    Here is another part, My Control sticks differ from the original J4 a fair bit. The goal here as with all my control system is weight and friction. I seem to have not had my camera in the shop much as these parts were made so I have not captured allot of detail.

    Starting with the torque tube, I used my older Bridgeport table as a jig, this worked well. I will let the pictures talk.
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    The roughed out stick assembly sitting on it's mounts as well as next to the original J4 part.
    In comparison my new assembly weighs 3½Lbs, the original is just under 10Lbs
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  4. #44
    cubdriver2's Avatar
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    Your work is beautiful Charlie, I often wondered why Piper made such a complicated stick setup when a single one in the middle would have worked just fine?

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  5. #45

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    The original controls had me baffled for years, I expect it was simply the technology and materials of the time. I quickly realized I did not want to cannibalize any of my original J4 so it remains as complete as it can be allowing me to simplifying my controls. Originally I was keeping them forward of the bulkhead although I am running the aileron cables up the front of the doors rather than aft of the cabin with all the associated buts needed. Another difference I am doing is running the and
    A few months ago after selecting the Carlson HD strut I realized the aileron aileron cable can run up through the lift strut with the bellcrank on the aft face of the front spar. This has moved the controls aft of the bulkhead simplifying many aspects of the system. This being why I have not formed the control sticks, they will wait till the fuselage is welded up and I can properly mock up the cabin.
    Another change is the push-pull rod for the elevator will be run under the floor all the way aft of the extended baggage. This offers a full flat floor quite a way back.
    I have also recently realized in my plane the center to center of the sticks will be wider than original, these sticks are 19" C-C where the original are 18". More recently from working with a mockup with the actual seats I am using I find the controls will be about 23" C-C so any further work on this system is on hold till I have the fuselage to work/ sit in.

  6. #46
    cubdriver2's Avatar
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    Don't forget to do the Island Bob STC on the seat. Taking 3.5 - 4" out front to back makes a huge difference getting in and out of the plane

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  7. #47

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    I should have looked at that better when up at Basin. My cabin area is a little different with standing the aft door uprights parallel to the front tubes. This reshapes the rear of the cabin and may well offer more access for entry. The seating and control layout truly will wait till the new fuselage is roughed out before many decisions are made. I will be utilizing a fixed bench seat although the rear of the seat will be split folding and probably offer a small amount of adjustment in lean angle.
    My right leg does not work well so the foot room upon entry does matter for me.

  8. #48

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    I have done the first actual welding on a fuselage part. I have made the spar carrythrough tubes. I was expecting to have made the full top of the birdcage over the 4th holiday but that was not to be. But it feels good to have started on the welded structure of the plane.

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    Turns out I am lacking some of the material I need to connect these two tubes together so it will be awhile till I get much further. I do have some small parts to machine such as flap latch mounting, flap handle mounts and the sockets for the lifting eyes. I am going to utilize an X structure in this assembly and that will have some bent tube so I need to form those parts as well.
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  9. #49

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    Last night I ran the printer so I now have a full scale print of the lower fuselage structure. This will be nice to have laid out on the build table. The line part of this drawing is a development of the tubing laid flat on the table. This will allow the initial layout and welding followed by the lower structure being jigged as it will actually be built.

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    I also printed the firewall structure and outline.

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    And a currently important view of the top of the birdcage, image here with the carrythrough tubes set in place. Also another image of a rearspar end fitting.

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  10. #50
    skywagon8a's Avatar
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    Quote Originally Posted by CharlieN View Post
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    That is an interesting layout of the cross tubes. Are they curved in the original J-4 like this? I'm admiring your abilities with the computer drafting.
    N1PA

  11. #51

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    No, the original J4 ran a front Vee from the upper engine mounts to the center of the spar tube and continued the Vee back to the rear spar mounts.
    My structure will have 5 engine mount bolts and has the front Vee going from the top center mount up to the forward spar mounts. I have been through many design variations and I am settling on the flap handle being top center. That in some ways complicates things in that I still want the trim indicator top center as well. The center of this structure is tight to outer Lexan skin which is roughly 2½" above the carrythrough tubes.
    So I chose to build the structure with a little space for the indicator cable to pass through while maintaining generous structure for the mounting of the flap handle.
    This cross structure will be plated with a sheet metal structure as well as a center rib channel supporting the upper skin.

    This design may vary if I have trouble bending the ¾-.035 tube without distortion.

  12. #52
    Cub junkie's Avatar
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    I like it. Those spar carry throughs are going to be much more accurate than building a structure and attaching four wing attach fittings like the original Piper way.

  13. #53

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    Quote Originally Posted by Cub junkie View Post
    I like it. Those spar carry throughs are going to be much more accurate than building a structure and attaching four wing attach fittings like the original Piper way.

    That is for sure, these tubes setup in a jig with no fuss and allow all 4 bolts to be in the same plane. The holes are reamed to size while mounted in the milling machine with little chance of distortion as further welding is performed.

  14. #54
    skywagon8a's Avatar
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    Quote Originally Posted by CharlieN View Post
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    The load paths should be centered in a joint for maximum strength and minimum stresses. This drawing shows an eccentric load path which needs to be taken into consideration.
    N1PA

  15. #55

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    Quote Originally Posted by skywagon8a View Post
    The load paths should be centered in a joint for maximum strength and minimum stresses. This drawing shows an eccentric load path which needs to be taken into consideration.

    Yes, true. But there is other structure that is not seen in this print that reduces the twisting not to mention the only time the loads could get high enough to distort this area is in a crash. And in a crash, something has to give.
    Part of the unseen structure is the 0.100" Lexan top skin spreading the loads.
    If time allows this coming week I will see if I can pull a test bend, I might just scrap a section of tube and being I own the best bending equipment around here and not willing to travel 8+ Hrs for another bender this may all be for naught.
    FWIW I have this assembly already drawn in 4 other structure designs. With a few button clicks and a little updating the build is changed. The only parts locked down are what are photographed already.
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  16. #56
    cubdriver2's Avatar
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    It's a pretty tough little airplane just the way it is. Came with a great manual with foldouts in detail







    Glenn
    Last edited by cubdriver2; 07-08-2017 at 01:06 PM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  17. #57

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    A bit late to mention, someone on eBay has some J4 drawing available that appear to be real engineering drawings. Not truly knowing what they are I do not find the need to spring the funds for them.
    A decade ago I used the drawings Glenn shows here and drew the fuselage in ACAD. I expect my accuracy is no better than I could derive from the 3 versions of manuals I own. That print in Glenn's copy is pretty clean, easy to read.
    The plane I am building started from those drawings but has evolved from there as we will see over the next few years as I build this version.

  18. #58

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    A bit more work done, The top of the cabin structure is off the jig now. The X structure is different that the previously poster drawings showed for reasons stated later.
    This is a broad view of the structure,
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    This structure included sockets for the lift eyes to thread into,
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    I have a stainless threaded socket the eye screws into. this will be capped off for normal operations.

    In the center of the structure is the pivot for the flap handle, the notch behind these tabs is a passage for a trim indicator cable to pass, the original X that was shown had a space between the tubes for this cable as well as the flap release cable to pass through.
    As with most all controls the flap handle pivots on ball bearings.
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  19. #59

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    Aft of the rear spar will be two 3/4 Sq tubes that are formed into a gentle S curve conforming to the airfoil. In these tubes are hardpoints for the flap torque tube pivots. In the center of the rear spar tube is a pivot for the flap latch mechanism. It is located overhead here for numerous reasons one being it is accessible in flight should there be any issues that need to be tended too.
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    And could this be about the extent of true Piper influence here.
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    Well not really.

  20. #60

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    Thanks for the inspiration, I have 3 planes in pieces, 2 my fathers and 1 that he inherited from my late grandfather in 2010. Dad has had a couple strokes since his father died and its been hard to deal with the changes in Dad from the strokes.. I need to get something started so I can get one of them flying while he is still around. Thank you for the spark of inspiration!

  21. #61

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    That is a worthy goal, I had hoped to get a plane back together before my dads passing 12 years ago, personally you got to make a try. Even if you do not fully achieve the goal you have a more comfortable life than the hollow feeling of not trying. My personal thoughts anyway. One for me was to see if I could have gotten my dad back up in a B-25 one more time. The one semi local B-25 to me was out west through all the years and my Dad had 99 missions in Air Recon way back in time so I was hoping for a 100th flight. Never happened but was well beyond my resources to have made it happen.

  22. #62

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    This part to me is a very thought provoking part. First image is a screenshot of the tube cluster where the lift strut and composite leaf spring mount. Nothing complex but as I machine the actual parts that once ready will be welded into these sub-assemblies.
    Even though the brackets have a 10:1 overbuild my mind keeps going, "all the lift loads are through here". It is kind of interesting how many stressed parts I have made in my life but for now these have my attention.

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  23. #63

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    A little bit more done to the lift strut carrythrough but not ready for welding yet. Here is the bracket now with lugs to support the tubes.
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    And same part with the doublers added, the aft tube is perpendicular so it got welded into place, the small tube passing through the doubler is where the aileron cable passes through and into the lift strut. The front doubler needs to be clocked which I am not ready to do, more parts to make such as the firewall structure to guarantee proper alignment.
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    And the carrythrough roughed together, a bit more tube fitting before this is ready to weld.
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  24. #64

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    Here is the firewall structure going together on it's jig.
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    And a few of the parts shown previously as they came off the welding bench.

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  25. #65

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    Great work Charlie. Really enjoying this thread. Can't wait for future updates.
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  26. #66

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    The past month has been hectic for me. I had decided to shorten the height of the firewall a few inches since there was not the need for the height and the change will allow for better visibility over the nose.

    Part of the lead-up to that change to the previously welded structure is that I have been spending time back in the drawings. Most recently has been making sure I have the rudder pedals optimized for my needs. This image of the drawing from the underside of the plane shows how many parts are involved and the complexity in building the adjustable pedals in the plane.
    Damn it makes me want to use fixed position pedals. Not all the brackets are drawn in yet so there is more to do before all the parts are made.

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  27. #67
    cubdriver2's Avatar
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    Quote Originally Posted by CharlieN View Post
    The past month has been hectic for me. I had decided to shorten the height of the firewall a few inches since there was not the need for the height and the change will allow for better visibility over the nose.

    Part of the lead-up to that change to the previously welded structure is that I have been spending time back in the drawings. Most recently has been making sure I have the rudder pedals optimized for my needs. This image of the drawing from the underside of the plane shows how many parts are involved and the complexity in building the adjustable pedals in the plane.
    Damn it makes me want to use fixed position pedals. Not all the brackets are drawn in yet so there is more to do before all the parts are made.

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    Wouldn't it be easier and LIGHTER to make an adjustable seat back cushion?

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  28. #68

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    Quote Originally Posted by cubdriver2 View Post
    Wouldn't it be easier and LIGHTER to make an adjustable seat back cushion?

    Glenn
    Right now the section of the fuselage I have built is sitting on the living room floor with the seat set in place. So yes the option is open to make the seat move some. The seat is adjustable vertically by using foam shims, not a method suitable for inflight adjustments. The seatbacks are separate on each side and will be adjustable for lean angle as well.

    Luckily any brackets for the pedals can not be installed till the fuselage will no longer need to go on the build table so I do have plenty of time to decide and by then more options for making the seat movable. This option will become more attractive if I do not go with a bench style seat bottom.

    For one thing the controls in this plane are all using REP bearings for all movable joints at the cables and pushrods, as in about $1500 of them. This adjustable pedal setup has 14 bearing type rod ends in it. But I already have most of them in stock.

  29. #69
    cubdriver2's Avatar
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    Don't forgot that J4s fly nice because they are light

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

  30. #70

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    Keep in mind this plane will be considerably different than a true J4 in it's wing design as well as having more than 200HP.
    Many aspects of this build are lighter than a Piper design while other aspects are heavier.

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  31. #71
    skywagon8a's Avatar
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    Charlie, Will the slats be fixed or movable?
    N1PA

  32. #72

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    The slats are hinged, composite. The mounts for them are at this time intended to fit into slots in the leading edge so they are removable/ replaceable since I doubt I will get the hinge position in the right place the first time. I expect the slats will be built in 48" segments but I have not run numbers on them yet. At this time I do not intend to build full span slats in that I am more interested in a balance between low speed performance as well as the safety enhancement they offer.
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  33. #73
    Steve's Aircraft (Brian)'s Avatar
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    Introducing a J-4 project

    Charlie,

    I really like your design... not only does this look like a very capable aircraft but also looks really nice...

    Question on gear... your earlier rendering had what looks like oleo type gear and this latest one is spring gear... change of mind going on there..?? And what is with the tuning behind the spring gear..??

    Brian


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    Last edited by Steve's Aircraft (Brian); 10-27-2017 at 11:12 PM.

  34. #74

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    Thank you Brian,

    The oleo gear was getting difficult, my growing issues with it was drag and complexity. I was going to use motorcycle fork tubes mounted in custom framework. This would allow me the gross weight increase with good damping properties but was going to have secondary development issues that I do not want to deal with once the plane is to fly.
    So as the plane developed I started looking at a spring gear, originally utilizing a Cessna spring but soon decided I would layup a one piece composite leaf. The composite offers great weight and good damping.
    The weight savings in the main gear alone allows for some weight creep in other areas as we see developing.

    Had the design stayed based on an O-200 then the oleo might have stayed. Lord knows since my medical certificate has not arrived yet this may all change.
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  35. #75

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    Fresh off the printer, the control stick tops. I am going with round tops on my control sticks and I want the trim switch and PTT built in not to mention I need them to be handed since this is a side by side seater. It became clear that 3D printing the parts might just be the best way to get what I need.
    My first parts are a good proof of concept but I recognize that if I choose to use any form of soft grip on the stick then the ball needs to be larger in diameter. If this is to be a bare ally tube then this ball is not bad for a fingertip size grip.

    Shown here is the first ball top with switch holders and then the ball which I roughly trimmed and then fitted the switches into.
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  36. #76

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    Decisions, decisions.
    With the project back down in the shop for a few days I am building out the aft 145" of lower longerons.
    As I am preparing the cross tubes to weld in I keep questioning the diagonal bracing that will be used. Most recently the floor structure up front, as in seat area and first few feet of baggage area will be a composite structure bonded to the tubing. With this cored composite there is no need for diagonal tubing in these bays. Now as I am building back from there, the next two bays which are 5' in length were to be conventional tube structure with fabric cover over the tubes providing for generous floor space for lighter weigh bulky baggage.
    Now I am questioning if I should just do away with the cross tubes and go with a bonded in hard floor. Humm, granted this is not exactly conventional construction for Cub guys but it is a convention in sports racing cars where the active loads are considerably higher than in this fuselage.

  37. #77
    skywagon8a's Avatar
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    Interesting thought Charlie.
    What would the weight difference be between the two methods? Will the bonded floor in one bay be lighter than the one cross tube and whatever you have in mind above it?

    Can you be 100% certain that the tubing under the bonded floor structure will be corrosion/rust proof?
    N1PA

  38. #78

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    I think in this aft 5', the Oratex and .028 wall cross tubes will be lighter. The braces here are intended to be a full X where FEA states just a cross tube is enough. I personally do not trust real long unsupported tubes in compression.

    That aft section if I go hard floor will be Innegra skins with ¼ balsa core. I will do a full wrap around the tubes so they will be encapsulated.
    Now, 30 years later, will that bond not have failed, hard to say. So I do not have a true feel of the lifespan before repairs.

    I do know judging from other mixed structures I have built 15 years should be no issue without degradation.

  39. #79
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    I admire your ability to accomplish this project using CAD and FEA. That was my desire and purpose of buying my first computer 25+ years ago. Never could get my head wrapped around it. I find the process fascinating.

    Could you reduce the size of the cross tube enough to compensate for the added weight of the X configuration? I understand your apprehension of the long tube in compression. How much compression possibility is there in this particular location?
    N1PA

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    Ah, 25 years ago you would have been on Autocad 12 or 13 using Algor for the Fea. Autocad was just transitioning to a Windows platform but for the most part the Dos programs worked much better. I did find surfacing better in 13 Win. Algor was still Dos then. Pro-E was a sweet high end system as well but not nearly as easy to learn.

    The compression loads in the lower rear fuselage are from twisting the tail feathers and side loads of the tailwheel.
    Twist one way and the diagonal would be in tension, other way will compress.
    Both wall thickness and diameter can be reduced with an X structure. I do not build to the minimums as to what an FEA program says I can since the program has no clue what an O360 Lycoming can do to light structures not to mention the miss belief that you have the loads of a groundloop on rough ground calculated. Over the decades I have stopped trying to get every ounce out of a structure. I build light by design but I build structurally strong as well. I add doublers in areas they may never be needed, till one groundloops or truly slams a landing. Will all these doublers and added braces add weight, up, 3 to 5 pounds in a 1100# plane.
    Thanks 792 thanked for this post

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