In 1944 Dip-L Erwald while working on the D-77 rocket engine devised a method to increase the thrust by doping the fuel with ionized ammonia and piping the exhaust through an oscillating magnetic. There was a dramatic increase in total thrust and brought this discovery to the attention of Dr-L Switcher who then wrote a proposal for the OKB to study this further. Funding was allocated in Feb 1945 and research started in earnest. Many different fuel-doping chemicals were tested, some resulting in increased thrust, but with only months until the end of the war all research was halted before they could a build a flyable version of the engine.
In 1954 a young engineer with the Air Force was working on the requirements for a Mach 3 rocket powered experimental aircraft to compliment the X-2 program. He was researching Project Paper Clip documents on rocket propulsion and came across a folder of Dip-L Erwald’s research notes on the ion boosted rocket engine. The potential thrust increase and dramatic increase in endurance inspired the allocation of funds to develop a test bed for this technology. Project XS6 was initiated and a proposal was sent to Bell, Lockheed, Boeing, and North American Aviation to design and build an ion thrust augmented rocket plane. After 3 months Bell and North American dropped out while Lockheed and Boeing suggested a joint venture. This joint venture allowed a decreased the total development time. The design was loosely based of the XF-104 utilizing an enlarged trapezoidal wing but replacing the T-tail with a canard and a slab vertical stabilizer. Due to the reduced size of the engine and fuel tanks the aircraft was about ¾ the size of an XF-104. The project proved the viability of both the ion boosted rocket engine and the small airframe, which in 1961 went into production as the S-6 high altitude interceptor. It was the most successful aircraft developed during the Cold War and is claimed to have helped end that conflict in 1971.
The XS6 plane was designed in Solidworks and the primary parts (except for the canopy and the landing gear wheels) were printed on a MakerGear M2 printer. The goal of this design was to have a play model that would be fun to swoosh around the house and one that my daughter would enjoy playing with. Therefore it was built in 1/20th scale (so it fits 3.5 inch figures) with working landing gear and opening cockpit. The plane is approximately 20 inches long with a 12 inch wing span.
The challenge building with 3D printed parts is the poor surface quality from the printed layer grain. A majority of the effort expended was in improving surface quality. I tried several clay based putties to fill the grain and smooth the surface but after spending hours sanding and in turn damaging many printed parts from over sanding, I realized this was not a viable solution. I read somewhere that automotive primer works for covering small surface defects and since the maximum size of the printed grain was .008 inch it seemed like it would be a good solution. Automotive primer proved to be the easiest to use and resulted in a better surface finish then putty while reducing the surface preparation time 10 fold.
The build itself was very straight forward as the accuracy of the printed parts was within 0.008 inch tolerance resulting in very good alignment and fit.