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Engine Intake Duct:




  Intake Duct performance is very critical. The duct has to provide a very high volume of air into the engine. The airflow into the engine has to be as smooth as possible and there has to be an even distribution of pressure across the engine intake. Rough air will cause compressor stall despite the variable pitch stator blades on the fist stages of the compressor section. At full power at MSL, this engine requires the equivalent of a 146-mph gale blowing into the front of it.



  There is no way that a simple duct as shown above, can handle the required airflow without separation and stall on the first bend. The duct expansion ratio is kept low, but nevertheless, it is clear that there will have to be internal guide vanes and several rings of VGs to keep the airflow as attached as possible. Several NACA papers have contributed to the design of the internal guide vanes, as well as a recent paper on the subject of S-Ducts published by the Glasgow University.



  Thin aluminum sheet templates were used to cut one-inch foam sheet sections, which were then assembled to produce a rough plug. This was sanded and filled with micro before the application of two plies of BID for the duct shell.



  After cure this was followed by more micro and then epoxy primer, topcoat paint, hand polishing, and then several coats of mold release. The final product is a polished plug onto which is laid up three plies of carbon BID to make the shell of the duct. The inside surface of the duct is in this way made mirror smooth. To remove the duct shell from the plug, it is cut along three seams where flanges are added, and nut-plates installed at close intervals. This way we can open up the duct at any time and install internal guide vanes and VGs while we make the inevitable modifications to get the airflow right.

More photos to follow…