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Top Flite B-25J Mitchell Project

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Page 15

       At this point I mounted the stabilizers to the fuse. I used some Velcro adhesive fastening tape (fuzzy side only) to make a couple of shims for the horizontal stab. These shims will help keep the stab tight in the saddle and reduce unwanted vibration which can cause damage over time.

       These shims will probably not be needed on every kit as tolerances may vary from kit to kit.

       The tail gunner cabin which covers the stab was next to go. It is a surprisingly stout piece of fiberglass weighing in at 4-1/4 ounces! Unfortunately there is little one can do to reduce the weight of this piece just short of making a whole new fiberglass piece. Hopefully the tail weight will be to my advantage when the CG is measured :0P

       The two tail gun barrels are cleverly used to fasten the rear of the cabin to the fuse and two sheet metal screws go in the front.

       The tail gunner shield was glued in place with thick CA glue. I removed the green paint from the bottom shield and bracket to help bond it to the cabin.

       The bulkhead was attached using Zap-A-Dap-A-Goo II (Cat# PT12). This is a great adhesive to use, you just need to work fast or it will gel up on you quickly.

       The pieces were allowed to dry overnight before the canopy was installed. This will prevent any hazing the drying chemicals may produce on the inside of the clear plastic canopy. I used six of the #0 x 1/4” screws to hold the canopy in place.

       I could now move on to attaching the wings to the fuse. I started out by using a 1/8” drill bit to verify that the inboard wing tube fastener holes meet the tubes at a 90 degree angle. Some of the holes on my kit were off center which will cause a problem when installing the keeper screws later.

       The forward and rear wing tubes were installed into the left inboard wing panel and affixed with the 4-40 keeper screws.

       The main wing tube was installed into the panel and the whole assembly was inserted into the side of the fuse. I attached all of the wiring and air line connectors at this time as well.

       The B-25 kit allows the builder to drill and install the opposing side keeper screws in the wing tubes after the wings are in place. This creates a custom fit for the wings and keeps them tight against the fuse. Unfortunately it is difficult to hold the wings tight to the fuse while drilling the 4-40 keeper screw holes in the wing. At this point the plane is getting big and you may need a helper to keep the wings from shifting out while you drill the opposing keeper screw holes.
       I decided to make a 1/4-20 all-thread rod clamp to keep my wings tight to the fuse while I drilled the holes. I just inserted the 1/4” rod into the main wing tubes and tightened the wings up with fender washers and wing nuts as seen below.

       I used a 5/64” drill bit to carefully drill out the wing tube keeper screw holes and then taped the holes out with a 4-40 tap as seen below. Two 4-40 keeper screws were then installed in the wing panel.

       I installed the outer wing tubes into the inboard wing panels in preparation for the final wing assembly.

       Before I installed the wings I needed to finish one detail. The oil cooler air scoops needed to be installed to the wings. I cut some of the wing covering away to help the glue to stick to the wing and removed the paint from the rear of the scoop (not shown). The Zap-A-Dap-Goo was used to adhere the scoops to the wing. Blue tape was used to keep the scoops in place while the Goo was curing.

       The manual suggested that the 1/4-20 wing bolt hole at the outer part of the inboard wing panels be modified by widening the hole a bit as seen below. This will keep the wing joiner bolts from hanging up in the hole after they have been unscrewed allowing the wing to slide off of the wing tubes.

       A 1/4-20 tap was used to clean up the threads in the blind nut installed into the wing. This will help prevent stripping the nylon wing bolt later on.

       My B-25 kit was supplied with two 50 mm long 1/4-20 nylon wing bolts that unfortunately aren’t long enough to effectively bolt the wing panels together. I needed a replacement set of bolts that had enough threads to go past the blind nut.

       I found some 3” long socket head cap screws from Micro Fasteners (Cat #NSC1448) that worked beautifully. I cut a set of the screws down to 60 mm long which is a perfect fit for the B-25’s wings.

       The B-25 was really taking shape now. I was surprised at how large the plane is and how much room you need to work on it assembled!!!

       The nose gunner canopy needed to be glued to the “chin” piece in preparation for the gunner cabin installation. I prepared the chin piece by removing the paint from the joint where the canopy will be glued. I also used sand paper to roughen up the inside of the canopy. To glue the two together I used Poly-Zap CA glue (Cat #PT22) which stays partially flexible to allow some flex in the canopy. More than likely the canopy will endure heat expansion in the sun which can cause it to break away from dissimilar materials. This Zap glue can prevent this from happening.

       I allowed the glue to cure overnight before test fitting the assembly to the fuse.

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