Over the years I have bought "interesting" models for future builds. I remembered this one back in The Stash and dug it up:
Academy Models 1/150 scale motorized U-581 German sub, bought around 1990-ish. Attached are a couple of photos of the box art (Sub1 and Sub2) to give an idea of what it's like. It's going to be about 17" long and about 1-3/4" wide.
This will be my first venture into RC Subs (sorta). I'm going to build this into a simple, surface-running "parkflyer" of an RC sub. As designed as a "free-flight model", three C-cell batteries are in a gasketed compartment in the middle, there is a sealed air compartment in the front, and the compartment around the motor is dry and large. It dives by the bowplanes being negative, returns when the water drag flips an arm on the conning tower, making the aft planes positive. Up-and-down ad nauseam...
Preassembling and fitting a few parts, I see that it could take a WTC 1-1/4" dia x 8-1/2" long. I may go that route instead of trying to keep everything sealed and dry with the "stock" setup, and the WTC can be made simple because this sub is a surface runner and won't need to withstand much water pressure. I've found a source for 1.2" Lexan tubing. I'll assume that the designers did their homework and use the design air volumes and weight/ballast distribution as a starting point. This WTC will have less air volume than the as-designed air volume of the hull, so I'll need to add some (EPP)foam flotation where I can and hope that the sub-C NiMh batts will weigh enough "less than" C-cell alkalines. After get volume-and-weight numbers I can juggle things to make this critter float properly.
Couple of initial questions:
Motor and batteries. The motor supplied is a small brushed motor, about 7/8" dia x 1" long, runs on 3 cells (4.5V), an "RE-26", marked "JEON-HAHN 3V", kV unknown.
Have a recommendation for a better motor? I'm thinking a 280-size, the diameter needs to fit the WTC. The prop is 3-blade, plastic, and has the following measured specs:
diam 0.81" (20mm) pitch 0.40" (10mm), shaft 0.08" (2mm). I'm limited to that prop size by hull interference, but might be able to go a bit larger with below-the waterline hull modifications. Any recommendations for an alternate motor/prop combo?
The prop shaft, as-designed, has an a appreciable down-angle (down-thrust?) of about 6 degrees. My concern here that the downthrust will tend to raise the tail and cause the front dive planes to go (more)negative, causing the sub to dive. For surface-runner, this is not desired. Do I need to worry about the prop downthrust in this application? It's going to be a challenge to reduce it-- the WTC holds the motor in one location and the prop has to be in another and there is an inherent downthrust from those placements. U-joints/flex-couplers for 2mm shafts may be hard to find.
One mini/micro-servo for rudder control. Quick peek at the rudder in Sub3 and Sub4-- is it large enough, or should I scale it up for better authority?
After test-fitting and pre-assembling the main structure of the hull, I decided to build the rear and center bottom sections of the hull as one removable piece and glue the bottom front secion to the one piece top hull section, as shown in images Sub4 and Sub5. The portion of the hull behind the bow planes is designed to be a major air chamber and the hull is too narrow to extend the WTC into it. The rear bottom section is wide enough for the WTC which will house the drive motor and rudder servo.
These are my first ideas. Still, there are lots of details that will sneak up and pinch me, but this a rough start and direction for this project.