Gnome Monosoupape 9B Rotary Engine (1:25)

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The rotary engine, with its fixed crankshaft and rotating cylinders spewing exhaust and castor oil all over the airplane and pilot, is a frightening device to those accustomed to modern piston engines. However, it was relatively lightweight, smooth running, and cooled well unless excessively cowlled. This is a scale model of an early aircraft engine that played a significant role in aviation history. The nine-cylinder "Monosoupape" engine powered several Allied fighter planes during World War I, such as the Airco Dh-2 and the Sopwith Pup. Variants of this engine and other French rotaries like the Le Rhône and Clerget powered aircraft used by major combatants in the war. The four-stroke rotary concept was first developed into an efficient engine by the French brothers Laurent and Louis Séguin in 1908, who used advanced machining techniques to produce a high-power-to-weight ratio engine. These lightweight designs were mechanically simple and could be used with airframes that were less massive than those of inline-powered aircraft. In the rotaries, the propeller and cylinder block rotated around a fixed shaft, losing energy due to air resistance ("windage") and introducing gyroscopic forces that made it easier to turn in the direction of the engine's rotation. The monosoupape model used a single valve for both exhaust and air intake, actuated by pushrods geared to the engine's rotation. The valves were designed to suck gas into the cylinder through ports at the lower end when the port was closed and the piston descended. Castor oil, used as a lubricant, sprayed out of the spinning engine as it consumed fuel. Unlike other rotaries, the Monosoupape reduced rotating mass by eliminating the carburettor, so there was no way to reduce throttle by regulating fuel flow. The model shows several key features, including the push rod and exhaust valve. It is assembled using CA glue. A cutting mat, sharp hobby knife, small tweezers, and small files are also useful for assembly. These models are meant to be printed on a standard FDM printer with a 0.5 nozzle. They are designed as a 25:1 representation of the original engine, allowing for comparison with other aircraft engines in the same scale. I will publish more designs later. At smaller scales, little engines like this would not be easily printable or manufacturable. At larger scales, larger engines like turbine engines would be unreasonably large. Instructions: Step 1: The cylinders are printed as a group to prevent problems with bed adhesion. You can separate them by cutting the connections with a hobby knife. Each cylinder has a slot on the back to help position it properly on the center body. Step 2: Glue each cylinder to the center body using CA glue on tin foil and press it into place. The spark plugs face left when viewed from the front. Step 3: Start preparing the push rods by placing the push rod disk on a cutting pad. Cut the disk where the lower section meets the raised section as shown in the photo. Step 4: Fold the little tabs downwards and squeeze them into place against the center of the push rod using tweezers, aligning both tabs so they are parallel, pointing downwards. Cut each rod where it joins the outer ring. Step 5: Glue the push rods onto the main body as shown, bending the end of the rod downwards and gluing its end to the tip of the cylinder valve. Step 6: Glue the top cap onto the push rod disk, and the back onto the opposite side. The back is composed of two parts that should separate fairly easily. If you glue it carefully, keeping the glue around the rim, the motor should rotate. Keep this part centered when gluing it to the back of the main body. Step 7: Finally, glue the hub onto the end of the drive shaft. Stand: The stand comes together pretty easily if you want to use it. Paint both the motor and the stand before gluing one to the other.