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Ed Anderson wrote:
The way a turbo/super charger works, of course, is not by increasing the air volume flow through the engine but by increasing the air density. The 100,000 rpm impeller accelerates the air velocity inside the compressor vanes and then using the old Diffuser principal, slows this air down at the compressor exit and converts the increased dynamic energy of the accelerated air stream into a static pressure increase reflecting the increased air density produced.
And the turbo charger is a centrifugal pump. 8*) One of a comparatively small diameter, but high speed. I'm looking at a much larger diameter, but a much slower speed. Diameter and speed are what determines the maximum static pressure. How well the pump can hold that pressure is determined by its flow rate, which is in turn determined by the volume of the pump. I calculated that the air would flow at 170mph, with the intake and exits being 3" diameter. Not exact numbers, but the speed point is higher than my projected cruise speed, and the intake diameter is smaller than the runner I'll actually have. I have a relatively large volume between the flywheel and PSRU plate, being about 4" thick. All that scribbling is at home someplace, and I'd be hard pressed to find it. Basically, I'm counting on that thickness to overwhelm the engines needs and keep the pressure near the max static.
I do admit that I'm remiss in not applying the technical rigor to carry out the equations to the 4th digit. You and Al are good at that, Ed, but I am content to run some rough numbers. I figure the practical won't match the theoretical anyway. So if it looks good at first pass, build it and then take a measurement. I think this would be a good move if I can get 5 to 10 extra horses out of it. On the other side of the equation, I'm looking at what are the drawbacks (other than the design/build workload, which is supposed to be the fun part anyway). Failure modes, other than shedding blades, should be benign or non-existent, as I'm not providing for any control hardware. If the flywheel stops turning, the intake can suck air around the blades...but that is a moot point, because if the flywheel stops the engine is about done sucking air for a while anyhow. A leak in the intake means that I don't get as much boost as I hoped. In that case I'm just another normally aspirated rotary. The worst case scenario would be the highly unlikely event that I get TO MUCH boost. That will prove out easily enough during testing, and would only require some sort of restriction to rectify.
There may be up to twenty Hp waiting there, and it'll only cost about 3 to 5lbs of aluminum. If it works, I'll have one of the coolest, most unique engines at the fly-in, with one of the highest Hp/weight ratios around. If it doesn't work, I get to wear the "I tried something that didn't work" badge that makes one a true Flyrotarian. ;*)
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