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Thread: Introducing a J-4 project

  1. #81
    skywagon8a's Avatar
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    Definitely a good idea for extra strength in this area with an 0-360 up front. This is particularly important if the engine is ever operated with magnetos instead of a variable timing electronic ignition.
    N1PA

  2. #82

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    Quote Originally Posted by skywagon8a View Post
    Definitely a good idea for extra strength in this area with an 0-360 up front. This is particularly important if the engine is ever operated with magnetos instead of a variable timing electronic ignition.
    I hear you there, I have no desire to invest in magnetos, technology has come a loooong way since they were called good.

  3. #83
    skywagon8a's Avatar
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    A further thought. If you were to replace a diagonal with a composite filling in the rectangle, that could have a considerable effect on the natural frequency of the entire fuselage. Reducing flexibility in just one bay could cause a drastic effect for better or worse. Does your FEA have the capability to analyze this? I have witnessed how much the installation of an oxygen bottle in a Twin Comanche effected it's natural frequency. It was enough for a requirement to reduce the VNE in order to prevent tail failures. A couple of days spent participating at Piper's flight test center was very illuminating.
    N1PA

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    It will make a change and I do not know how to honestly check it. The composite structure I choose to use has allot of inherent damping where as the tubes alone are fairly lively. The tubes wrapped with fabric are damped so the structure is rather interesting to really test. I can only get numbers on the tubes without consideration of vibration or damping of them. So in this case I need to rely on past experience and make sure I do not put what one might call "a hinge" part way back in the structure.
    Right now I have been redrawing the control systems. Once I actually had steel welded up I could see a way to simplify the elevator controls which eliminates a 61" pushrod and a bellcrank. The aft bellcrank required a fair bit of structure to support it. This will add up to fewer hours as well as a few pounds eliminated.

    I will soon have a decent CNC mill available which will entice me to upgrade the drawings for all the bellcranks and a number of the flap system parts rather than making these on my Bridgeport. This will be a nice upgrade in the finished parts yielding a more complex part that is both lighter and easier to make.
    I might 3D print the parts to prototype them before committing to metal. This allows me to confirm motion ratios and clearances before making the real parts.

  5. #85

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    I have decided that I will use tubing diagonals supporting the lower longerons. I weighed and evaluated many options here and then just said to myself, I can do the tubing in the one bay that is really wobbly today rather than waiting a few years till I will be doing the composite work. So once I made the decision, ½hr later two tubes were fitted and partially welded in. The structure was then stable enough to carry up stairs back into the living room.

    Looks like I have not posted any updates here in the month. Back in early December I installed the mounts for the brake master cylinders as well as the lower doublers for the structure going up to the front spar. I had also more recently built the longerons back another bay to where the rear float mounts should the plane be setup for seaplane use.

    Here is a general shot of the forward lower fuselage prior to the most recent work session,
    IMG_4973.JPG

    followed with a master cylinder hung in place as well as showing the lower engine mount pivot.
    IMG_4977.JPG


    This shot is where the vertical tube in front of the doors will eventually go.
    IMG_4963.JPG

    The non pivoting engine mounting points utilize a 3/8 bolt through a sleeve, the sleeve is located to the fuselage over the mount points.
    IMG_5072.JPG

    Hard to get a good shot of small tubing with this cluttered background. At this time the lower longerons are in 3 subsections that have slip joints allowing the moving and jigging on the weld table.
    IMG_5063.JPG

    The aft section has most of it's brace tubes in place.
    Off to the starboard side of the rear section is the cabin top structure as well as automotive wire harnesses that get used in the custom driveline swaps I do.
    IMG_5062.JPG

    The front section of this structure is where the 3 sections separate such that I can not install diagonal bracing yet.
    IMG_5061.jpg
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  6. #86

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    A little frustration at the end of today's work session. I decided I would form the upper longerons and get as far as welding in the cross tubes. All was progressing well with a little difficulty making sure the assembly was symmetrical. All was looking good although I had to put a little tension to insure the laser hit it's marks.
    Then when I unclamped the assembly from the table and turned it over to weld the bottom side, the laser did not hit it's marks, damn. Turns out on the very front cross tube which in this case is just temporary to allow jigging followed by fitment once the upper cabin structure is ready, well I had that C/L way off, like ½" off. I work with multiple tape rules and the one I used when marking that tube is both metric and imperial markings such that when you reverse the tape, well you can make an error.

    It does not look like I need to cut any tackwelds out. With diagonal tension in one bay the properly marked centerlines line up well. Still frustrating. I decided it was time to walk away and pour a Bourbon and sit for awhile.

  7. #87
    RVBottomly's Avatar
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    Quote Originally Posted by CharlieN View Post
    I decided it was time to walk away and pour a Bourbon and sit for awhile.
    That's a good move.

    Boatbuilders have their "moaning chair." Mine is just folding wooden chair in the corner. But I saw one that had a nice little cubby for the bourbon and shot glasses--and aspirin.

    BTW, my metric-imperial measurement devices are relegated to the garden shed tool box. I fall for that problem all the time.

  8. #88

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    Yesterday I fitted the front door posts, hard to get decent shots of the dark tubes.
    IMG_5084.JPG

    The Formed tubes laying on the lower rails are the diagonals from the base of the firewall up to the outer ends of the spar carry through.
    IMG_5091.JPG
    It was a last minute decision to make these in one piece and add the kickout to provide an added inch on each side for the pedals. That lower bend will get a doubler but I feel this change to be worthwhile since not one's feet will be straight out in front as well as a bit more room for stick travel. After I made that bend last night I then undertook about 5 more hours making little but valuable changes in the CAD drawings. one of these was simplifying some aspects of the pedal system which greatly reduced the needed support structure in the fuselage.

    Tomorrow some consumables will arrive and I can get back to fitting tubes again. Thought I had enough cutters in stock, Oh well.
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  9. #89
    cubdriver2's Avatar
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    Is the cat helping with ballast or engineering needs?

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

  10. #90

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    Our furry black barrel . When She is not being my heated pillow she is my chief inspector.
    Then there is the golden boy on the foot stool under the TV, that one, well I still do not know about him. He adapted us back in the spring of 2015, only reason we kept him is he survived that bitterly cold winter of 2014. He has not been well received by our other cats which he caused the passing of two of our favorites.

  11. #91

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    One more part to set on the stack, the upper rear section on the fuselage is now partially assembled.

    IMG_5107.JPG IMG_5108.JPG

    If we got more than an hour of sunlight a week this time of year I might have a chance to get some pictures, or maybe I just need to bring everything out into the snow where the dark tubes will show up.

    I will next form the mid level rear section of the cabin structure but then the shop gets taken over by a customers vintage racecar that is getting a new chassis built for it, the bank account can sure use an influx of money back in it.
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  12. #92

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    Started out this morning forming the short tubes that comprise the mid level cabin structure aft of the seats. These tubes in the original J4 continue aft to the rudder post. I have gone with structural longerons that run from up at the spars and no matter how I tried I just could not eliminate this section of structure.
    Forming the two tubes early in the day I just could not get the warm and fuzzy that I had the curve right, just a simple 340" radius on 51" long ¾".028 tube.
    So I took the time to update this section of drawing and print it out. Needed to print a small section and tape them together since a 42" printer does not do 46" wide structure in one pass, oh well.

    So with the print on the floor I could now see where I needed to tweak the tubes and make them spot on.
    IMG_5111.JPG IMG_5112.JPG
    Not that I can see it in those pictures.

    Then it was off to the shop and prep the tubes.
    IMG_5116.JPG IMG_5115.JPG

    I got the initial welds done and walked away, need to go back and shoot some welds.
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  13. #93
    Tim's Avatar
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    looking good Charlie

  14. #94
    RVBottomly's Avatar
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    Nice fit.

    How are you profiling the tube ends? It looks milled from here.

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    Thank you Tim,

    Yes the tube ends are all done on a mill. I will use hole saws or ball end mills as needed. Final deburring & dressing with a 5" flap wheel on a hand held grinder as needed. Different grits but fairly fine with 4130. Fine as 600 grit. All joints are drilled so the tubes breath internally. More important with Tig than when using Oxy,. Still has it's long term value.
    40 years back I use to work the ends on a shaped grinding wheel. Basically I dressed a few wheels on pedestal grinders with a few different radius's.
    But I have done so damn many roll cages in race cars over the decades that I got used to working in the mill with the larger tubes. I truly do very little hand blending the tubes now.
    Thanks RVBottomly thanked for this post

  16. #96

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    Now the sun comes out and I have too much contrast to get a picture. But I have the section from one's shoulders back assembled. There are a few more small tubes to go in but I think this completes the larger assemblies that need to be jigged on my build table.

    IMG_5133.JPG

    The next part will be the vertical tail post, it has it's share of complexities, It will be an important part when it comes to start assembling this "kit"
    I will probably make the rear spars of the horizontal stabs at the same time. This may be followed with a few sheets of MDF which will go on a CNC mill to cut grooves to jig all the tail feathers.

  17. #97

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    I spent a few hours the other day forming the vertical tubes that go up to the rear spar. Tricky to get the bend just right on these since I do not have them jigged at this time. All the tubes will be jigged when this whole frame comes together.
    Once I was satisfied with these tubes it really started working at me that I do not think I have selected the optimum airfoil. I will be using one of Mr Riblett's optimized airfoils but not the same one commonly used in Cub type aircraft. I thought I had the right one last year but with design creep the gross weight has gone up, "I got My medical certificate finally". With the prospects of working with upwards of a 2K gross weight I either need to increase wing area or get different characteristics from the wing.

    So for a few days I have been back to the books and plotting the curves. I think I am in the ballpark of what I believe I want but it is interesting how much now changes.
    The new airfoil is more than ¾" thicker at the rear spar than the relation to the front from what I was working with. Spinoff from this is now that I just made the two tubes that position the aft upper section of the cabin, the rear spar carry through needs to be raised 3/8". No big deal, nothing has been welded that locates these yet. Unlike wood these tubes can be stretched.

    But what has changed is all the shape and geometry of the double slotted flaps. I pretty much forgot how many hours it took last year to optimize the hinge positions and all the linkages and pushrods for both the flaps and ailerons. "I am not fully satisfied I had the ailerons just right yet". I have that baseline to work with but very little of that math is relevant now.
    It does look like both the flaps & ailerons will have more authority which is the goal to carry more weight without greatly increasing wing area. But damn I am glad it is winter since I will be stuck at the computer many mornings again.

  18. #98
    Cub junkie's Avatar
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    Have you looked at the Riblett profile that is used on the Bearhawk Patrol ?

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    Quote Originally Posted by Cub junkie View Post
    Have you looked at the Riblett profile that is used on the Bearhawk Patrol ?

    Yes, most definitely. But I am using a different design parameter. That airfoil was optimized for use without flaps as in a direct replacement of the Cub wing.
    Where from the outset I am using very generous double slotted flaps my wing will be optimized for a higher speed range while still being able to slow down to lower speeds that the original Cub wing allowed.
    Basically my design is to provide a 5:1 speed ratio where most every Cub provides about a 3:1 stall to cruise range.

  20. #100

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    It is interesting as I get close to the new configuration for the flaps on this plane, after the past 2½ hrs of drawing this morning I came to realize these flaps have more wing area than the wings on my Quickie.
    I am liking the change though.

  21. #101
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    Quote Originally Posted by CharlieN View Post
    It is interesting as I get close to the new configuration for the flaps on this plane, after the past 2½ hrs of drawing this morning I came to realize these flaps have more wing area than the wings on my Quickie.
    I am liking the change though.
    Of course, we are waiting with partially bated breath to see these things! As an aside, I almost bought a Quickie project back in 1984, but ending up spending my stash on a tractor.

    Your flap comments on my 2+2 thread sent me into researching flap design and options. I ran across the NorthStar approach that had bracing similar to what you had mentioned for the rear spar. Are you proceeding along those lines--that is, moving the flap hinge closer to the rear spar and increasing chord?

  22. #102

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    Tractor was the right choice. Most all the work on my Quickie was done in '84-86. Mine has a Rotax 447on the nose and is the first customer plane built with the Carbon spar and new airfoil. It also has drooping & reflexing ailerons.

    The flaps on the plane I am building now go right up to the rear spar. Originally I was going to build a wood wing, composite LE and top skin with a fabric lower skin. Once I started building I pretty much have decided on all metal wing. If I had helpers around I would consider the wood/composite since I have designed and built a few but trying to build them alone is just stupid for me. Maybe if I had more confidence in infusion I would go there. I just do not have the funds to chance scrapping material.

    So my flap hinges are under the wing not far aft of the spar. They will more than likely be steel weldments bolted to the spar with a brace going forward attaching to a rib. Being in redesign I have no details since the exact pivot locations are not locked down yet. But the new flaps are going to be very generous, as in if they are down with a parked plane it will be easier to go out from the front of the wing.

  23. #103
    RVBottomly's Avatar
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    Thanks. I'll be watching with interest.

    When I first started this idea of building something, I was really taken with the idea of something like a Vagabond/Wagabond with PA 18 wings. But I figured I'd have to lengthen the fuselage. Then what? etc. I hadn't even heard of a J4 until later, but your project looks a lot like what I was originally kicking around--only far more thought out.

  24. #104

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    Vagabond are pretty cool little airplane. One of them was my first real working on a plane doing the weld repairs to rusty structure, that was back in the early '70s. Wish I knew the N number so I could see if that plane was around.

  25. #105
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    Vags are a hoot to fly even with the little Lyc 0145 like my very first plane. A real blast with a C85 or 90

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

  26. #106

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    Quote Originally Posted by cubdriver2 View Post
    Vags are a hoot to fly even with the little Lyc 0145 like my very first plane. A real blast with a C85 or 90

    Glenn
    Just imagine a C85 stroker in one. The C-120 I have been in a few times recently with a Stroker is mighty impressive performance. Not sure if the compression is where the documents say it should be but I was quite impressed with it's climb & cruise. If I am correct you have strokers in two planes, I presume they perform well?

  27. #107
    cubdriver2's Avatar
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    Quote Originally Posted by CharlieN View Post
    Just imagine a C85 stroker in one. The C-120 I have been in a few times recently with a Stroker is mighty impressive performance. Not sure if the compression is where the documents say it should be but I was quite impressed with it's climb & cruise. If I am correct you have strokers in two planes, I presume they perform well?
    Stock stroker in the J4 One Vag I get to fly my buddie Nic owns at Islands Bobs and is 640lb with a healthy C85, fun ride

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

  28. #108

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    Was that the Vag at Basin Harbor last spring?

  29. #109
    cubdriver2's Avatar
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    Quote Originally Posted by CharlieN View Post
    Was that the Vag at Basin Harbor last spring?
    I think Nic was there

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

  30. #110

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    East of Monroe 1.jpgI think Vagabonds look pretty cool with big tires.
    Likes Bill Rusk, Southern Aero liked this post

  31. #111

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    That does sit nice.

  32. #112
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    Fun airplane and easy to add the left side door, framework is already done, just need to remove window channels.

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

  33. #113
    Cub junkie's Avatar
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    Quote Originally Posted by Carey Gray View Post
    East of Monroe 1.jpgI think Vagabonds look pretty cool with big tires.
    I always admired that airplane. Looks good with Colt trim. I remember it from the old Vagabond newsletters. Minimum airplane-maximum fun.

  34. #114

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    My past month for this project has mostly been design work. A few months back I started looking at different Riblett airfoils since the one I selected was just right for a light gross weight but not optimum when the gross climbs into the 2K range. Granted this plane should carry most all it needs to when flying at no more than 1600#, still never know.

    So with going a percent thicker followed with moving the center of pressure back a bit truly offered more change than I expected, good changes too. Wing thickness at the front spar is close to what it was before but the rear spar is more than ¾" taller than what I was working with. This thicker aft section called for a thorough redesign of the control surfaces.

    The flaps now are massive, I have designed and built planes that had less wing area than these flaps have. The ailerons now have a new twist as well, they droop as before but now are of a Fowler design such that as the main flaps are deployed the ailerons slide aft. Should be interesting.

    As before the plane will be built with wing extensions in the design. When the intended mission is short field work the wingtips get pulled and 4' extensions get attached on each side. These will have there own ailerons as well to ensure very slow flight still offers acceptable roll control.

    So a few fresh screen shots,
    First one is long wing with flaps up

    FEB2618FlapUp.jpg

    Then long wing flaps down,
    feb2618LREXT.jpg

    And short wing flaps down,
    Feb2618LR.jpg

    And from the front,
    fEB2618lf.jpg

  35. #115
    RVBottomly's Avatar
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    Wow!

    I'm curious how to evaluate the aerodynamic forces from such changes. I'm still trying to come up with a conceptual framework to understand twisting forces from extended control surfaces. I'm basically still trying to apply lift and drag equations, but have little information regarding appropriate coefficients.

  36. #116

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    With what we have available for software it is very hard to get accurate numbers on the flaps, particularly double slotted or more complex. You can get simplified flowlines in Solidworks but no numbers. Pretty pictures in my opinion. I have a feel for materials and structure and am overbuilding. For the most part spread the loads as far as you can so they are not concentrated in any one or few places. Any of these concentrations need a heavy structure but you are never sure where the true stress concentration is if you try to take the loads in a small area.
    In your project I would treat the rear spar as just taking pure vertical loads at each mount and all twisting moment should be transferred forward which will induce a mild download at the front spar.

    In my case these loads are spread within a reinforced rib and since mine will be metal skin the loads are spread throughout the skins as well.

    In yours the twisting loads are carried buy a truss, be it a simple Vee, tall at the back to pickup all the flap moments and just needs a single point up front. Or something wider up front as well that prevents twisting of the spars as you find near the lift struts.
    I would spread the loads the best you can in the spar webs but allot should be able to be taken in or around the rear spar caps. As in a welded structure that slides over the spar as the ribs do.

    If your flaps have a pivot point below the wing, carry those loads as far forward as possible or logical. In mine the pivot point of the main flap is now 13" down, the fore flap is just a bit above and forward of that. That is stupid low but designing a complex pivot system gets just that, complex as well as heavy.
    But I am choosing to accept the ridiculous flap hangers and their associated drag for what my estimates in low speed performance may be and will accept the Knot or two of drag. I know the flap hangers will induce less drag than the lift struts and I have no interest in building a cantilevered wing, which is doable but not going to be done.

    Have you spent time reading Albert and Doenhoff's Theory of Wing Sections? Chapter 8 has allot of insite to flaps, nothing that will jump out and say "Do This". But it is good information to help with understanding some of the math and estimating the loads involved.
    I also have a fair amount of documentation from OSU on aerodynamics and structures which help beyond what I learned at Embry Riddle way back in time.

  37. #117
    RVBottomly's Avatar
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    Quote Originally Posted by CharlieN View Post


    Have you spent time reading Albert and Doenhoff's Theory of Wing Sections? Chapter 8 has allot of insite to flaps, nothing that will jump out and say "Do This". But it is good information to help with understanding some of the math and estimating the loads involved.
    I also have a fair amount of documentation from OSU on aerodynamics and structures which help beyond what I learned at Embry Riddle way back in time.
    I hadn't seen that book, yet, but I'll dive in. I probably should ask people like you for a bibliography!

    Also, thanks for all the other insight/information. I'm following your project closely.

    Vic

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    Thank you,
    My studying many years back was in order continue collage level learning since I was not able to fund a full degree in school. Reagan era was tough on some of us.
    My background has been design and build most anything. I started out building custom bicycle frames, turned out I was good at it. I then built my own frames for the motorcycles I raced. I already had built boats, both slow and fast. basically anything that could move. I have designed and built some stupidly fast road course cars and then designed and built a few planes during the '80s. Around the financial crash of the late '80s into the 90s I changed to road race cars which is still my primary work.
    The books and documents I collected were all about structure and stability, guess the books guided me right since the planes flew well.

    I truly expected today one could just go online and find new material but if it is out there I have not found it. Or just can not justify the cost.

    Back then my next plane was to be a sleek two place all aluminum powered with a firewall forward from a Cessna 402, cowling and all. I still think about it but have chosen to not bring out the drawings. A big roll of drawings.
    I will stick to what I decided to build now.

  39. #119

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    Tooling and templates,
    I have always used tooling that we have named "paper dolls". In the past the drawings be they originated on paper or printed from CAD were cut out or pasted on a hard material for use in making parts.
    I am impressed how much information I am getting from taking a few drawings and sending them to a CNC router and cut many parts out of a 4X8 sheet of Masonite.
    This first batch was done in two steps, the first intention was to make a template of the wing that would slide onto the wing mount tabs of the fuselage. I am impressed how much there was to learn with this first step. without even edge finishing the cut part it fits over the weldment pretty damn close. The rear spar tabs are .013 out on one side and .011 out on the other from the template. Probably much of that was either when the weld jig was made or when I drew this template at a later date.
    I think of how many times I have read recently of people discovering their mount tabs are an eighth or a ¼ out of spec after welding. Gad I have no clue how someone can distort something that much and later actually fly the thing. Not me mate.
    IMG_5433.JPG

    One of the needs for this template is to weld in the ¾" Sq tube that extends aft of the rear spar. This tube is formed with a gentile contour to conform with the top surface of the wing, but needs to sit down 0.150 so it is under the polycarbonate top of the cabin, should I decide to have the aft section clear.
    With this template in place I was quick to realize the two changes in airfoil will need a change to the aft curvature since I have both moved the C/P back and changed to a non cusped airfoil. So it will be back to the press to reform these tubes.
    The small hole in the template aft of the rear spar is where the flap torque arm pivot is to be. The hard point of which is a threaded bung in these tube I need to fit precisely. With this tooling, should the parts not line up perfectly it will be easier to change the drawing to conform with the welded assembly.
    I chose to draw up for another cut for a template that will slide fully up to the top structure with the top curve lowered the 0.150 to what I actually need to build too, the inside structure and not the outer skin of the wing.
    IMG_5440.JPG IMG_5442.JPG

    This will allow me to more accurately build out the upper structure of the cabin area.

    Other parts I cut out were full size patterns of the wing and flap system, these will allow full actuation of the flaps from the handle through the full 80° range of travel as well as spare parts to allow for changes of pivot location such that the fore flap needs a different travel ratio or pivot location once determined by airflow analysis when done later this year.
    IMG_5437R.jpg
    The other small bits above are bellcranks for both the rudder pedals and the aft end of the pushrod bellcrank for the elevator.

    The next batch are templates for the ribs for the vertical fin and the inner and outer of the horizontal.
    IMG_5444.JPG

    As well as a box full of other tools and templates,
    IMG_5446.JPG

    I am thinking since I am on a roll with this Gerber router I will move right into cutting templates for the elevator and rudder build in Masonite as well as making wing rib tooling in some 1" MDF and the tail ribs in ¾" material. The rudder and elevator ribs will be welded up in C channel.
    No tooling at this time for ailerons and flaps since they will more than likely be composite structures.

  40. #120

    Join Date
    Mar 2016
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    Vermont USA
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    I got a little more done today, one important part that I neglected to get a shot of was to weld the square tubes that follow the top skin of the wing aft from the rear spar. this has the hard point for the flap torque arm in it and the location falls right in with where it is intended to be.
    From there I cleaned the edges on some more of my "paper dolls" this set allows me to swing the flaps though their full motion and I truly like what I see. I also set the upper longerons in place and can now mark the front of them for fitment to the forward fuselage.
    So here is a template showing the outline of the flaps in the full down position. Interesting thing I find is the trailing edge of the main flap is only 11" above the lower longeron.
    IMG_5454.JPG IMG_5457.JPG
    Likes RVBottomly, Southern Aero liked this post

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