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From: "George Lendich" <lendich@aanet.com.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-4121792@logan.com>
Subject: Re: [FlyRotary] Re: Air Pump
Date: Fri, 12 Feb 2010 11:43:43 +1000
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 Ernest,
A quick check of my calculations suggest that 170 MPH should be good up to 
our RPM requirements. So if your wrong we are both wrong. My figures are 
based on a  44 mm PP and the inlet speed in well below that, however I note 
the smaller diameter speeds get up to over 200 mph at 7,500 rpm. I can't 
remember how your configured.
George ( down under)

> 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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