The next version is for larger motors and planes; it was tested in a 48-oz Brodak Cardinal ARF, running RimFire motor and a 11.5-6 APC.
This version is a front mount (better for motor bearings) and allows easy adjustment for outboard thrust by adding/removing washers under the mount flanges.
Step 1.
Obtain a 1" aluminum angle stock (1/16" wall thickness) from Lowes or Home Depot. Draw a 1:1 sketch of the mount, based on the motor size, allowing about 1/16" clearance around the rotor, and about 1/4" bend radius (smaller radius might produce cracks during bending).
Step 2. Mark the design on the stock, using a piece of wood for support. Also mark and drill holes for motor shaft (typ. 5/16"), motor mounts and flange mounts (typ. 1/8").
Step 3. Using hacksaw, band saw, Dremel tool, or a combination of those, remove material as shown on the picture.