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Old May 12, 2009, 09:34 PM
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Jack
USA, ME, Ellsworth
Joined May 2008
18,101 Posts
BB 33 With Full Length Monobloc

Over the winter and this spring I banged up both of my Industrial Strength BB 33's until neither was flyable without major overhauls. I decided those had pretty well served their purposes and decided to build another. I'm not beating the planes up as badly or as often as I was in the past and rather than build another of the Industrial Strength versions (CF arrow shaft and three piece monobloc) I decided to build a BB 33 with a full length monobloc. That will give me a stronger fuselage than the standard BB 33 build and it should be lighter and quicker to build.

01 - I made a full length monobloc. I cut a block of 2" PB III foam to the shape of the BB 33 fuselage sides pattern and then tapered it from the trailing edge back to the tail. I also cut a platform on top of the fuselage to mount the horizontal stabilizer on instead of putting it in a slot down lower as per the plans.

I glued the regular FFF fuselage sides to the 2" monobloc and laid out a compartment in the tail for the servos and another under the wing for the electronics and possibly for the battery too. The compartments were drilled with a piece of 1/2" brass thinwall tube in a drill press. Overlapping cuts were made and the pieces picked out. The bottom and sides were cleaned up with a Dremel tool and a coarse toothed wood cutting router bit.

02 - The fuselage with compartments routed out. I also cut a cooling air passage from the windshield back, a wiring passage between the center and tail compartments, and an 1/4" hole for an antenna passage goes from the rear compartment to the tail.

03 - Fuselage seen from front. The firewall is a piece of 5/16" thick cedar with two pieces of 1/4" dowel epoxied into it. The dowels extend back about 2" into holes drilled in the foam and the cedar, dowels, and foam are all glued together with Gorilla Quick glue. The 2" PB III foam is pretty soft and crumbly, gluing a firewall or motor mount directly to it does not give a very strong assembly. That is the reason I did the firewall the way I did. The motor will be mounted to a piece of 1/6" plywood and that attached to the cedar firewall with wood screws.

04 - The square corners on the fuselage were beveled and then sanded to round all the normally square corners on the fuselage. The sanding can be seen on the left side of the fuselage here, the right side is beveled but not sanded yet. Sanding was done with 80 grit on my "sanding shingle" and I finished up with 100 grit. This give me a more rounded and shapely looking fuselage.

05 - The fuselage was covered with colored package sealing tape. The horizontal stabilizer was per the plans, the elevator was cut free with beveled cuts and hinged to the hstab with the colored package sealing tape as part of the process of covering the hstab.

06 - The vertical stabilizer was made from the plans and slightly modified to mate with the fuselage. The rudder was cut with beveled cuts and it was hinged and covered with the package sealing tape. The hstab was hot glued to the fuselage and the vstab hot glued to the top of the hstab using Arrow BSS6-4 High Strength Slow Setting hot glue. That glue is strong enough for this purpose, there are other glues (cheaper, generic, etc.) that will not work as well.

07 - Servos were mounted and hot glued in place, DuBro 1/2A horns were used with DuBro Mini EZ connectors and pushrods are .039" wire. Motor is my venerable old 2410-12 Delta 59 gram motor. It was sounding like a Maytag washing machine with a full load of marbles in it so I treated the motor to a new pair of bearings. It sounds wonderful now, quieter and smoother than it has ever been in it life.

08 - With my KFm2x wing in place. This is the KFm2 wing with the single step located at 84% instead of 40% as a result of a mistake. But the wing flies very well. It has become my favorite RET wing for the BB 33. It is faster than my regular KFm2 wing and with the low 3/4" per tip dihedral it flies about as sporty as you could expect from a RET trainer.

The plane is 448 grams/15.8 oz. without a battery, it will fly at about 630 grams/22.2 oz if I go with the 4S A123 or 585 grams/20.6 oz. if I use the 3S A123 or a 1500 mAh LiPo.

All I have to do is decide on the battery and location and I'm ready for a maiden flight. Initial checks with the wing on indicates that the CG is very nearly right now and that the battery, regardless of its weight, will be centered right under the desired CG point.

Jack
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