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Correcting that -135 dihedral


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All: I thought it best to illustrate what I've been discussing elsewhere by use of illustration.  As engineered, the original AMT/ERTL KC/EC/RC-135 kit has a dihedral problem--too little of it, to be precise.  The way you can tell is by looking at the built model in profile and realizing that the outboard engine should be a good deal higher off the ground than it is, and that the wing tips should come up to the level of the cockpit, even when the plane is sitting on the ground.  To correct this will require some patience and risk-taking.  

 

Good: the kit has soft plastic, which means it's pliable.

 

Bad: the kit has soft plastic, which means that if you try to bend the wings without prepping them first, you'll create all kinds of distortions, especially in the trailing edge and the airfoil.  

 

To start with, here is your critical infrastructure.  It consists of parts 21, 49, 22, and a portion of the floor assembly.  Using an extra kit, I cemented two part 21's back-to-back and sanded them to a constant surface so that they would provide added surface area for the wing.  As molded, part 21 imparts dihedral to the wing, but probably not enough for what you'll need.  I used a hobby knife to cut away the underside of the part and increase its angle relative to the horizontal.  I also added an extra bulkhead to prevent part 102 from distorting where it meets the forward fuselage:

 

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If you try to bend the wings on part 102 without carefully prepping them, you'll stress the plastic and create all kinds of distortions where you don't want them, such as the ultra-thin trailing edges, and the forward fuselage join.  You'll compound the complexities inherent in the kit's design, and you really want to avoid that.  

 

To take the "load" off the wing and the center section, I used a Tamiya "entrenching tool" to dig some really deep gashes on the top and bottom of part 102.  I use this tool only for the ugliest jobs--*not* for seam scribing.  Where possible, I followed natural curvatures in the horizontal.  I then placed the wing stub on my workbench as flat as possible, and gently applied force on the rump fuselage until the wing stub bent upward to a higher dihedral at the point where it meets the fuselage.  I repeatedly checked the trailing edge--an especially vulnerable area--to ensure it didn't form a parabola.  On the left side, I had to straighten it using my thumb, but the right side turned out great.  That trailing edge needs to be straight-straight-straight; no curvature at all when viewed from the tail.  

 

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Here are the results we're looking for, only just a tad more dihedral when measured at the root--which will happen when I actually cement it together.  Without delay you'll want to test fit it with the fuselage halves (parts 100, 101) to ensure the fuselage shape (at the point where the new bulkhead joins part 102) fits cleanly:

 

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The upper wing (parts 103 and 104) needs some reinforcing.  I used telescoping lengths of brass rod to ensure taper along the wing as it thinned toward the tip, and cemented it using CA.  I was lucky, because the parts that came with this kit were nice and straight.  Remember, this wing will need to bear heavy loads, because the big, kit-supplied F-108s will stress it.   

 

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One added note: The top of the wing will fit against the fuselage-mounted root molding differently from the kit's design, so it may be necessary to sand the mating surface at an angle to ensure snugness.  I know it's a fair amount of work, and the trenches on part 102 will need to be filled in afterward, but I believe it will improve the looks of this old warhorse significantly.  I used parts and instructions from the RC-135 kit (8956) for this demo, so if there are incongruities in part numbering from the "slick" tanker, that's why.

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  • 2 weeks later...
5 hours ago, Whitewolf said:

Roughly how deep was the indentation you made with the Tamiya tool? 

I would estimate it was no more than ~1 mm on the underside, and ~1/2mm on the topside.  Anything greater than that and you'll break through to the other side.  

 

Let me consider doing a video of this.  Of course, this tutorial is based on the old plastic.  I'm not sure if the later moldings (e.g. Heller's reissue) are molded in harder, more brittle plastic.

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