Page 3 of 3 FirstFirst 123
Results 81 to 90 of 90

Thread: Introducing a J-4 project

  1. #81
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    7,335
    Post Thanks / Like
    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

    Join Date
    Mar 2016
    Location
    Vermont USA
    Posts
    205
    Post Thanks / Like
    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
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    7,335
    Post Thanks / Like
    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

  4. #84

    Join Date
    Mar 2016
    Location
    Vermont USA
    Posts
    205
    Post Thanks / Like
    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

    Join Date
    Mar 2016
    Location
    Vermont USA
    Posts
    205
    Post Thanks / Like
    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, ˝hr 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
    Likes smalls liked this post

  6. #86

    Join Date
    Mar 2016
    Location
    Vermont USA
    Posts
    205
    Post Thanks / Like
    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 ˝" 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
    Join Date
    Sep 2017
    Location
    Asotin County Washington
    Posts
    91
    Post Thanks / Like
    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

    Join Date
    Mar 2016
    Location
    Vermont USA
    Posts
    205
    Post Thanks / Like
    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.
    Likes stknrddr liked this post

  9. #89
    cubdriver2's Avatar
    Join Date
    Apr 2003
    Location
    upstate NY
    Posts
    8,239
    Post Thanks / Like
    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

    Join Date
    Mar 2016
    Location
    Vermont USA
    Posts
    205
    Post Thanks / Like
    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.

Similar Threads

  1. Our Cub Project
    By tcraft128 in forum Member Projects in Progress
    Replies: 206
    Last Post: 05-03-2016, 05:29 PM
  2. I need a new project
    By cgoldy in forum Experimental Cubs
    Replies: 6
    Last Post: 09-03-2013, 09:10 PM
  3. PA-12 project
    By munro in forum Cafe Supercub
    Replies: 1
    Last Post: 08-29-2005, 10:25 AM

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •