U 25 class 1A rc submarine

U25 - probably the first RC submarine kit

First released by Schuco/Hegi in the 50s and 60s, later redesigned by Krick.
Very basic kit by todays standards.
Designed for dynamic diving with only the bow hydroplane being controlled.

I started building the boat in 1994. Certainly, the kit is not meant to create a scale model, but I tried to build a decent rendition of this very rare subject (only two class IA boats were build) by scratch building gun and aa machine gun and some details in and around the tower and by modifying the hull. The bow hull shape in the plans and on the box is just wrong, that is obvious even from the very few available documents about the original.

I designed it as a semi-dynamic sub by adding a ballast tank and a gear pump, both airplane accessories (fuel tank and fuel pump). Trimming was done such that with the ballast tank flooded, the conning tower still would be above the water surface. The remaining buoyancy could then be overcome by the diveplanes.
In case of rc failure the boat would still surface. The ballast tank vents through the periscope, so no pressure is built up in the hull.
With less buoyancy to overcome I dared to shape the diveplanes smaller than in the plans (still bigger than scale).

Later I added controls to the rear diveplanes which improved the dynamic diving. At some point I replaced the hull cover (wood) by acrylic glass, so I could always see what's going on in the hull. With upgrade to LiPo batteries and state-of-the-art esc's I could save a lot of the limited space, so I added a (second) peristaltic pump with a balloon connected as a trim tank. That allows for real static diving: now the remaining buoyancy with the main tank flooded is overcome by pumping about 50ml into the balloon. The self tightening peristaltic pump allows for fine tuning and balancing on the gram level - what a difference to dynamic diving!

In terms of scale appearance the Krick boat can't compete with all the nice GFK VIIc or GATOs out there. But when I built it shortly after finishing school this was the only affordable way to get a rc submarine. The boat never failed me in 25 years, and with the gradual improvements it finally turned into a "real" sub.


Music: https://www.bensound.com