Here's the current version of the blueprint for the modified Dornier Wal aircraft used by the Miskatonic antarctic expedition. You can click through on the picture below for a slightly larger version, or head over here to download an 11" by 14.7" PDF. The odd size is caused by scaling down the 18" by 24" original to keep the file size reasonable.
In the upper left you'll find the rundown of the plane's electrical system. That information is based on the stock Wal's 24 volt configuration, modified by the addition of two heavy duty batteries and a backup two-stroke gasoline generator. In flight the craft can function perfectly well with the current from the airstream generator on the top deck. The secondary generator is used primarily to power the engine warming gear when the plane is on the ground.
The engine specs in the middle left are based on the ones used by Wolfgang von Gronau on his around the world flight. This is the one place where I engage in a bit of handwaving. Although the engines are close to stock I've assumed that the Miskatonic expedition used aviation gas with an octane rating of 93 or above. Fuel of that quality would be commonplace by WW II, powering the high compression engines of cutting edge fighters, but it was available within the timeframe of the story.
There are a few modifications to the stock airframe that aren't noticeable on casual examination. I've shortened the body and assumed that some of the steel frame has been replaced by machined aluminum, cutting the weight of the plane. Extending the lifting surface of the main wing helped generate more lift and significantly dropped the overall wing loading.
The blueprint is 98% complete and just needs a few more technical details, including the radio set. I've been able to find all kinds of information about period aviation transmitters and receivers used by military planes, but tracking down civilian models has been a little more difficult. Once I have that the blueprint should be finalized.
As always, your feedback is appreciated.