Building
the XB-42 "Mixmaster" |
Winner
of the Weiss Minute Model Cookup
by Wout Moerman
June 22, 2007
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Introduction
From the end of January 2007 till the end of April 2007 the
Weiss Minute Model Cookup was held on the SFA
Forum . Builders could chose from the planes designed
by Herbert Weiss between 1938 and 1947. A choice
could be made between the Brewster Fighter (Buffalo), Curtiss
XP-40, Douglas Devastator, Douglas Mixmaster, Mauboussin Tandem,
Messerschmitt 109, Nieuport 161, North American P-51, Piper
Cub and Seversky Executive. Plans can be found in the files
section of http://groups.yahoo.com/group/minute_models/ |
My choice was the Douglas XB-42 "Mixmaster,"
a high-speed bomber developed in 1943 but never put into
production. The design had rear mounted contra-rotating
propellers, each powered by its own engine. |
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This aircraft was designed for a crew of three: a pilot
and co-pilot in separate side-by-side canopies, and a
navigator/bombardier in the glazed nose section. |
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Planning
I started by studying the plan carefully and discovered a few
things which I wanted to change:
- The wing spar runs right through the fuselage where the rubber
should be free to vibrate. I decided to mount the wings flush
on the fuselage.
- The exact location of the stabilizer is not shown on the plan,
so I placed it between the upper keel and the upper stringer.
- The all sheet tail surfaces would probably result in a tail
heavy model, which requires a lot of nose weight. I decided
to build up tail surfaces to keep the tail as light as possible.
- The front can be strengthened by sheeting the first bay. Extra
weight in the nose will be needed anyway!
- The wings of on the plan are shorter than they should be when
compared to 3-views of the real thing. I know these Minute Models
aren't exact scale models, but if I can get better performance
by making it more to scale it seems to be a good idea. Therefore
I added about 3 centimeters to each wing. |
- The airfoil is semi-symmetrical, but I decided to use
a flat bottomed airfoil to make building a lot easier.
- There is no decalage (incidence difference between wing
and stab) indicated on the plan. I chose to build the
wing at 0 degrees relative to the fuse axis, and the stab
at minus 3 degrees. The thrustline was changed to have
4 degrees down and 3 degrees left. I hope these settings
will be OK for flying!
I think this model was designed with static display
in mind, not to be flown. If someone knows of a flying
model built from this plan, please let me know!
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Construction
I started by building the fuse. The keels were pinned on the
building board, and the formers were attached using with UHU
Hart (equivalent to Duco or Ambroid). To support the fuse
during assembly, a temporary scaffolding was built - two parallel
strips were placed alongside the keels, and cross pieces were
glued to both the keels and the parallel strips (this time
using PVA glue). This created a ladder-like supporting frame
which kept everything aligned while formers and stringers
were added
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The assembly was then removed from the building board
(keeping the scaffolding attached), and the other half
of the formers and stringers were added.
By soaking in water, the scaffolding was easily removed
without affecting the UHU Hart glue joints in the fuse.
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The result was a nice, straight fuse... |
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