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To: flyrotary@lancaironline.net
Subject: Re: [FlyRotary] Re: Air Pump
Date: Fri, 12 Feb 2010 18:42:44 -0500
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I'm remembering that early turbojet engines were sometimes designed with=
 centrifugal compressors because compression ratios of up to 8:1 are possi=
ble. Axial compressors are much lower per stage, like about 1.8:1 or somet=
hing?
I suppose compressor wheel rim speed is esential for boost pressure, and=
 wheel thickness for volume. So there are your limits, About 6000 RPM, abo=
ut 11" diameter compressor wheel about 2" thick at the eye (narrower at th=
e rim where the volute is).
I think this is all something that can be calculated, maybe even with an=
 online engineering site like efunda?
With high flow and low discharge head, much of success or failure will be=
 involved with the art of design and fabrication skill of the builder. Tip=
 leakage at the rim/volute or a sharp turn into the throttle body could co=
st all of the gains.
It looks like George is leading on the math...






-----Original Message-----
From: George Lendich <lendich@aanet.com.au>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Thu, Feb 11, 2010 5:43 pm
Subject: [FlyRotary] Re: Air Pump


Ernest,=20
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 not=
e the smaller diameter speeds get up to over 200 mph at 7,500 rpm. I can't=
 remember how your configured.=20
George ( down under)=20
=20
> Ed Anderson wrote:=20
>>=20
>> The way a turbo/super charger works, of course, is not by increasing th=
e >> air volume flow through the engine but by increasing the air density.=
 The >> 100,000 rpm impeller accelerates the air velocity inside the compr=
essor >> 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 reflecti=
ng the >> increased air density produced.=20
>>=20
>>=20
> 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 > de=
termined 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 small=
er > 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. > Ba=
sically, I'm counting on that thickness to overwhelm the engines needs >=
 and keep the pressure near the max static.=20
>=20
> 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, bu=
t > 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.=20
> 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, sho=
uld > be benign or non-existent, as I'm not providing for any control hard=
ware. > 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 eas=
ily > enough during testing, and would only require some sort of restricti=
on to > rectify.=20
>=20
> 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 un=
ique > engines at the fly-in, with one of the highest Hp/weight ratios aro=
und. > If it doesn't work, I get to wear the "I tried something that didn'=
t work" > badge that makes one a true Flyrotarian. ;*)=20
>=20
>=20
> --=20
> Homepage: http://www.flyrotary.com/=20
> Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/Li=
st.html=20
> =20
--=20
Homepage: http://www.flyrotary.com/=20
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.h=
tml=20


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<font color=3D'black' size=3D'2' face=3D'arial'>
<div><FONT face=3D"Arial, Helvetica, sans-serif">I'm remembering that earl=
y turbojet engines were sometimes designed with centrifugal compressors be=
cause compression ratios of up to 8:1 are possible. Axial compressors are=
 much lower per stage, like about 1.8:1 or something?</FONT></div>


<div>I suppose compressor wheel rim speed is esential for boost pressure,=
 and wheel thickness for volume. So there are your limits, About 6000 RPM,=
 about 11" diameter compressor wheel about 2" thick at the eye (narrower=
 at the rim where the volute is).</div>


<div>I think this is all something that can be calculated, maybe even with=
 an online engineering site like efunda?</div>


<div>With high flow and low discharge head, much of success or failure wil=
l be involved with the art of design and fabrication skill of the builder.=
 Tip leakage at the rim/volute or a sharp turn into the throttle body coul=
d cost all of the gains.</div>


<div>It looks like George is leading on the math...<br>
<br>
</div>


<div style=3D"CLEAR: both"></div>
<br>
<br>


<div style=3D"FONT-FAMILY: arial,helvetica; COLOR: black; FONT-SIZE: 10pt"=
>-----Original Message-----<br>
From: George Lendich &lt;lendich@aanet.com.au&gt;<br>
To: Rotary motors in aircraft &lt;flyrotary@lancaironline.net&gt;<br>
Sent: Thu, Feb 11, 2010 5:43 pm<br>
Subject: [FlyRotary] Re: Air Pump<br>
<br>


<div style=3D"BACKGROUND-COLOR: #fff; MARGIN: 0px; FONT-FAMILY: Tahoma, Ve=
rdana, Arial, Sans-Serif; COLOR: #000; FONT-SIZE: 12px" id=3DAOLMsgPart_0_=
92afc1a6-22cc-42b9-a506-f4cd9c51ede7>Ernest,&nbsp;<br>
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 not=
e the smaller diameter speeds get up to over 200 mph at 7,500 rpm. I can't=
 remember how your configured.&nbsp;<br>
George ( down under)&nbsp;<br>
&nbsp;<br>
&gt; Ed Anderson wrote:&nbsp;<br>
&gt;&gt;&nbsp;<br>
&gt;&gt; The way a turbo/super charger works, of course, is not by increas=
ing the &gt;&gt; air volume flow through the engine but by increasing the=
 air density. The &gt;&gt; 100,000 rpm impeller accelerates the air veloci=
ty inside the compressor &gt;&gt; vanes and then using the old Diffuser pr=
incipal, slows this air down at &gt;&gt; the compressor exit and converts=
 the increased dynamic energy of the &gt;&gt; accelerated air stream into=
 a static pressure increase reflecting the &gt;&gt; increased air density=
 produced.&nbsp;<br>
&gt;&gt;&nbsp;<br>
&gt;&gt;&nbsp;<br>
&gt; And the turbo charger is a centrifugal pump. 8*) One of a comparative=
ly &gt; small diameter, but high speed. I'm looking at a much larger diame=
ter, &gt; but a much slower speed. Diameter and speed are what determines=
 the &gt; maximum static pressure. How well the pump can hold that pressur=
e is &gt; determined by its flow rate, which is in turn determined by the=
 volume of &gt; the pump. I calculated that the air would flow at 170mph,=
 with the intake &gt; and exits being 3" diameter. Not exact numbers, but=
 the speed point is &gt; higher than my projected cruise speed, and the in=
take diameter is smaller &gt; than the runner I'll actually have. I have=
 a relatively large volume &gt; between the flywheel and PSRU plate, being=
 about 4" thick. All that &gt; scribbling is at home someplace, and I'd be=
 hard pressed to find it. &gt; Basically, I'm counting on that thickness=
 to overwhelm the engines needs &gt; and keep the pressure near the max st=
atic.&nbsp;<br>
&gt;&nbsp;<br>
&gt; I do admit that I'm remiss in not applying the technical rigor to car=
ry &gt; out the equations to the 4th digit. You and Al are good at that,=
 Ed, but &gt; I am content to run some rough numbers. I figure the practic=
al won't &gt; match the theoretical anyway. So if it looks good at first=
 pass, build it &gt; and then take a measurement.&nbsp;<br>
&gt; I think this would be a good move if I can get 5 to 10 extra horses=
 out of &gt; it. On the other side of the equation, I'm looking at what ar=
e the &gt; drawbacks (other than the design/build workload, which is suppo=
sed to be &gt; the fun part anyway). Failure modes, other than shedding bl=
ades, should &gt; be benign or non-existent, as I'm not providing for any=
 control hardware. &gt; If the flywheel stops turning, the intake can suck=
 air around the &gt; blades...but that is a moot point, because if the fly=
wheel stops the &gt; engine is about done sucking air for a while anyhow.=
 A leak in the intake &gt; means that I don't get as much boost as I hoped=
. In that case I'm just &gt; another normally aspirated rotary. The worst=
 case scenario would be the &gt; highly unlikely event that I get TO MUCH=
 boost. That will prove out easily &gt; enough during testing, and would=
 only require some sort of restriction to &gt; rectify.&nbsp;<br>
&gt;&nbsp;<br>
&gt; There may be up to twenty Hp waiting there, and it'll only cost about=
 3 to &gt; 5lbs of aluminum. If it works, I'll have one of the coolest, mo=
st unique &gt; engines at the fly-in, with one of the highest Hp/weight ra=
tios around. &gt; If it doesn't work, I get to wear the "I tried something=
 that didn't work" &gt; badge that makes one a true Flyrotarian. ;*)&nbsp;=
<br>
&gt;&nbsp;<br>
&gt;&nbsp;<br>
&gt; --&nbsp;<br>
&gt; Homepage: <A href=3D"http://www.flyrotary.com/" target=3D_blank>http:=
//www.flyrotary.com/</A>&nbsp;<br>
&gt; Archive and UnSub: &gt; <A href=3D"http://mail.lancaironline.net:81/l=
ists/flyrotary/List.html" target=3D_blank>http://mail.lancaironline.net:81=
/lists/flyrotary/List.html</A>&nbsp;<br>
&gt; &nbsp;<br>
--&nbsp;<br>
Homepage: <A href=3D"http://www.flyrotary.com/" target=3D_blank>http://www=
.flyrotary.com/</A>&nbsp;<br>
Archive and UnSub: <A href=3D"http://mail.lancaironline.net:81/lists/flyro=
tary/List.html" target=3D_blank>http://mail.lancaironline.net:81/lists/fly=
rotary/List.html</A>&nbsp;<br>
</div>
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