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Bend in my Bearhawk wing center line (Bravo) line not straight

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  • Bend in my Bearhawk wing center line (Bravo) line not straight

    Hey guys...

    I was doing some measuring and put a long straight edge on my master wing template, I think its page 4 on the Bravo 4 place plans.....and noticed that the wing center line on my former is not straight...it has a 2mm rise on it near the flap/aileron spars...my center line is not straight in that area. It appears straight at the rear and front but rises in the area near flap/aileron spars.

    I checked and the straight edge ruler im using is straight

    If some kind soul could put a long straight edge on their Bravo wing center line plans to double check this.

    its probably me distorting the plastic in some way during the application of the film...

    but I thought I would ask around to see what others see on their Bravo plans.,,,its possible that since the Bravo wing is new that this bend might not have been noticed yet....

    IMG_2760.JPG
    Last edited by way_up_north; 05-09-2020, 05:00 PM.

  • #2
    this better describes it

    The dark line on the rib drawing is the area where the line is raised

    The drawing below that is what im observing in that area. dotted line being where the line should be if it was straight...the solid line the observed line...its not to scale, the line raises 2 to 3 mm or a little less than 1/16 of an inch.

    If someone with a Bravo wing template can drop a straightedge on that area...from the trailing edge to the center of the wing template, then Ill know if its a situation of my own creation(misapplication of the film) or maybe the plans have a distortion there...

    I drew a line down the wood to lay the center line down on. if the center line is off a little off then my pattern would be also

    even if the plans have a raised line there, the fix would be really simple..just draw a new line from nose to trailing edge.

    also possible my drawing was a little off in production.

    but if someone else sees the same thing on their plans then I`ll carefully remove mine, draw a new center line on the film and I`m good to go.

    IMG_2822.JPG
    Last edited by way_up_north; 05-14-2020, 05:06 PM.

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    • #3
      I will be talking with Bob early next week regarding a similar issue on the Patrol, I can raise your B model issue with him if you wish. I checked that line on my Patrol mylar and it is pretty straight. Do not alter the mylar, it's the basic definition of the airplane. This is a Bob question.
      Gerry
      Patrol #30

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      • #4
        Thanks for taking a look .... I’m also a little suspicious of my spray adhesive... it’s a 20 year old can of 3M 77 the plastic started to wrinkle a little as soon as it made contact with it. Maybe its reacting with the film.

        the next morning there were bubbles and small wrinkles all along the length of the former... I carefully peeled it back and smoothed it down...the adhesive was still tacky but the plastic was noticeably softened compared to before...it could has distorted with that process... softened by the adhesive and stretched with my peeling it back and re application

        thanks for taking the time to look..
        Last edited by way_up_north; 05-15-2020, 11:14 AM.

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        • #5
          My opinion? Don’t worry about it.

          Every BH will have some level of variation and each is hand built. 1mm isn’t anything to worry about. That chord line is a reference line that is a visual indicator of the wing chord. If you notice a dip in the outer edge, blend it in. Ain’t no thang. Avoid analysis paralysis.
          Christopher Owens
          Bearhawk 4-Place Scratch Built, Plans 991
          Bearhawk Patrol Scratch Built, Plans P313
          Germantown, Wisconsin, USA

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          • #6
            Originally posted by Chris In Milwaukee View Post
            My opinion? Don’t worry about it.

            Every BH will have some level of variation and each is hand built. 1mm isn’t anything to worry about. That chord line is a reference line that is a visual indicator of the wing chord. If you notice a dip in the outer edge, blend it in. Ain’t no thang. Avoid analysis paralysis.
            everything you're saying is true

            i didn't get into the reason why i was so concerned about this... I`m working on a way to build the wing with no wing jig and to avoid making the small rib angles

            I~m calling it the Bearhawk magic rib(a play on the magic washer). its a Bearhawk rib former made a little smaller on the ends with 1/8 plates that attach to it so you can vary the size to make the different Bearhawk ribs all with one former. one former for the all the nose ribs...one for all the center ribs...etc

            The big but here is that the center line now becomes very important because I`m cutting the rib former edges perpendicular to it...so if the center line is off then the former edges and the angle of the spars to that will be off...as the rib former does double duty as former and wing jig. creating wing ribs with flanges 90 degrees perpendicular to the center line. The idea being that if the ribs are perfect then its hard to assemble the wing wrong, as the perfect wing ribs(as close to 90 degrees perpendicular to the center line as posible) will be the wing jig.

            below is a picture from the net of a RV ribs with all the flanges included on the rib...this is the idea im going with ...making a Bearhawk rib with the spar flanges already on the rib...but with no wing jig to correct all the errors...the flanges need to be dead straight perpendicular to the center line...or the whole wing will be off.

            Then with flanges it will let me assemble the wing on a flat surface...like the RV guys and Zenith guys do.

            I`m not selling anything or recommending this to anyone without Bobs ok....I did talk to Bob about this and he was ok with trying this method out and seeing what happens as in his opinion the flanges on the ribs will be fine for wing integrity...now the question is can you build a flat bearhawk wing on a flat surface rather then the wing jig.

            This is not to say the wing jig is not a great Idea, with a well setup wing jib you will make a great wing. but for those of us that have smaller spaces im trying to develop an alternative method

            eventually if this works a CNC rib former could be made that would take all the head scratching out of this.

            20110118-001-large.jpg
            Last edited by way_up_north; 05-15-2020, 09:38 PM.

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            • #7
              I like the idea, and considered it myself except I bought a started project with the ribs already formed. A straight edge and a square will get you parallel spar flanges.

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              • #8
                Thanks for the tip..

                im going to play around with getting the formers made
                but something that still has me scratching my head is when the ribs mate up to the spar... some sort of jig will need to be created to make matching holes in the spar,spacers and ribs themselves so it all matches up when assembled or assembly procedure...I’m hoping the solution pops into my head.
                it might be simple but needs to be done in a certain order..

                if you have any thoughts there I’m all ears ..😊
                Last edited by way_up_north; 05-16-2020, 08:19 AM.

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                • #9
                  Bob has a jig that is similar to what you describe in an older Beartracks article for assembly on a flat table using jig holes. Seems adaptable to your case.
                  Christopher Owens
                  Bearhawk 4-Place Scratch Built, Plans 991
                  Bearhawk Patrol Scratch Built, Plans P313
                  Germantown, Wisconsin, USA

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