I just got off the phone with an engineer I know in military aircraft research who works with full scale engines. He took one look at the pics I sent him from this forum with the curvature of the blades (inward) and suggested that this could be flutter. Apparently there is a resonant frequency for every motor and in full scale motors there are controllers designed to avoid whatever that rpm range is altogether. Wren could either experiment with different length intakes or calculate the length of an intake needed to shift the flutter to an RPM range that is not problematic.
Originally Posted by
jacojet
I will measure when I get my hands on one that is stripped, I have checked one that belongs to a friend (who BTW is not using it for fear of it failing) and what I can say is that the top of the compressor is about 55 mm and the bottom about 74-75 mm, the throat is about 7 mm deep, measured from the edge to the top of the compressor blades. Maybe we will use this one as a experiment to see if the modified intake will work. Just need to convince my friend!