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Subject: Re: [LML] Re: superchargers
X-Original-To: lml@lancaironline.net
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George:
Airplanes, unlike cars, operate from a baseline 30=E2=80=9D Hg ambient at=20=
sea level=20
- - to a baseline ambient of only 12-13=E2=80=9D Hg , with pressure ratio=
s varying=20
from 1.2 up to 2.8 to 3.0.
Thus, at constant RPM, the compressor would spend most of its life well of=
f=20
of any =E2=80=9Coptimum=E2=80=9D pre-determined design point.
=20
The variable speed turbo-supercharger compressor helps to mitigate this=20
problem to a substantial degree.
=20
Actually, I think it is quite a bit easier to make a mechanicly driven=20
centrifugal compressor system work efficiently in an airplane than in a car.=
Power=20
demand, and engine speed are much more consistant in an airplane and even=20
cruise altitudes are fairly predictable, where most operation takes place an=
d=20
economy is most important. (reffering to typical Detroit/Tokyo/Whichita mode=
ls,=20
not racing applications here)=20
In an airplane, you simply turn it on when you climb through a given altitud=
e=20
and shut it off when you descend through the same level. In a car, low engin=
e=20
speed would decimate the boost from a mechanically driven centrifugal=20
compressor.
Assuming the engine is already operating at or near the engine=E2=80=99s =20
detonation limited maximum BMEP - - (many aircraft engines are) - - then i=
n order to=20
improve the detonation margin, without reducing power (reduction in CR goes=20
the wrong direction on the power and the efficiency issues) or in order to=20
increase the BMEP - - and remain free of detonation, one will have to do o=
ne or=20
more of the following:
=20
1) Reduce the CHTs;=20
2) Increase the fuel octane;
3) Reduce the induction air temperature.=20
Add to this list:
4) Increase engine speed;
5) Reduce major combustion chamber radius;
6) Reduce/Alter combustion chamber turbulence;
7) Alter combustion chamber wall angles to reduce infrared and=20
shockwave energy reflected into areas of instabillity.
8) Relocate spark plug(s)
Reductions in IAT from the intercooler will buy one LARGE improvements in=20
the detonation limited BMEP (ie, more horsepower becomes usefully available=
).
That sounds a lot like something I said earlier. Your'e starting to agree=20
with me.
=20
>>However, when you make the blanket statement that a mechanically driven=20
supercharger will result in a slower airplane, we have to part company.<
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<HTML xmlns:o =3D "urn:schemas-microsoft-com:office:office"><HEAD>
<META charset=3DUTF-8 http-equiv=3DContent-Type content=3D"text/html; charse=
t=3DUTF-8">
<META content=3D"MSHTML 6.00.2800.1400" name=3DGENERATOR></HEAD>
<BODY style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial; BACKGROUND-COLOR: #fffff=
f">
<DIV>George:</DIV>
<BLOCKQUOTE style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue=20=
2px solid">
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Airplanes, unlik=
e cars, operate from a baseline 30=E2=80=9D Hg ambient at sea level -=20=
- to a baseline ambient of only 12-13=E2=80=9D Hg , with p=
ressure ratios varying from 1.2 up to 2.8 to 3.0.<o:p></o:p></SP=
AN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Thus, at constant RPM,=
the compressor would spend most of its life well off of a=
ny =E2=80=9Coptimum=E2=80=9D pre-determined design point.<o:p></o:p></=
SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPA=
N></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">The variable speed tur=
bo-supercharger compressor helps to mitigate this problem to a substantial d=
egree.<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </FONT></P>=
</BLOCKQUOTE>
<DIV>Actually, I think it is quite a bit easier to make a mechanicly driven=20=
centrifugal compressor system work efficiently in an airplane than in a=
car. Power demand, and engine speed are much more consistant in an ai=
rplane and even cruise altitudes are fairly predictable, where most ope=
ration takes place and economy is most important. (reffering to typical Detr=
oit/Tokyo/Whichita models, not racing applications here) </DIV>
<DIV> </DIV>
<DIV>In an airplane, you simply turn it on when you climb through a given al=
titude and shut it off when you descend through the same level. In a car, lo=
w engine speed would decimate the boost from a mechanically driven centrifug=
al compressor.</o:p></SPAN></DIV>
<BLOCKQUOTE style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue=20=
2px solid">
<P class=3DMsoNormal>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p></o:p></SPAN></FO=
NT></P><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FONT-SIZE: 10=
pt; COLOR: navy; FONT-FAMILY: Arial">Assuming the engine is already op=
erating at or near the engine=E2=80=99s detonation limited =
maximum BMEP - - (many aircraft engines are) - - then in order to imp=
rove the detonation margin, without reducing power (reduction in CR goes the=
wrong direction on the power and the efficiency issues) or in order t=
o increase the BMEP - - and remain free of detonation, one will=20=
have to do one or more of the following:<o:p></o:p></SPAN></FONT>
<P></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPA=
N></FONT></P>
<P class=3DMsoNormal style=3D"MARGIN-LEFT: 0.5in; TEXT-INDENT: -0.25in; mso-=
list: l0 level1 lfo1"><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><SPAN style=3D"mso-lis=
t: Ignore">1)<FONT face=3D"Times New Roman" size=3D1><SPAN style=3D"FONT: 7p=
t 'Times New Roman'"> </SPAN></FONT></SP=
AN></SPAN></FONT><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FON=
T-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Reduce the CHTs; <o:p></o:p><=
/SPAN></FONT></P>
<P class=3DMsoNormal style=3D"MARGIN-LEFT: 0.5in; TEXT-INDENT: -0.25in; mso-=
list: l0 level1 lfo1"><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><SPAN style=3D"mso-lis=
t: Ignore">2)<FONT face=3D"Times New Roman" size=3D1><SPAN style=3D"FONT: 7p=
t 'Times New Roman'"> </SPAN></FONT></SP=
AN></SPAN></FONT><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FON=
T-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Increase the fuel octane;<o:p=
></o:p></SPAN></FONT></P>
<P class=3DMsoNormal style=3D"MARGIN-LEFT: 0.5in; TEXT-INDENT: -0.25in; mso-=
list: l0 level1 lfo1"><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><SPAN style=3D"mso-lis=
t: Ignore">3)<FONT face=3D"Times New Roman" size=3D1><SPAN style=3D"FONT: 7p=
t 'Times New Roman'"> </SPAN></FONT></SP=
AN></SPAN></FONT><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FON=
T-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Reduce the induction air temp=
erature. </FONT></P></BLOCKQUOTE>
<DIV>Add to this list:</DIV>
<DIV> 4)&N></SPAN></FONT><FONT face=3DA=
rial color=3Dnavy size=3D2><SPAN style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT=
-FAMILY: Arial">Increase the fuel octane;<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal style=3D"MARGIN-LEFT: 0.5in; TEXT-INDENT: -0.25in; mso-=
list: l0 level1 lfo1"><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><SPAN style=3D"mso-lis=
t: Ignore">3)<FONT face=3D"Times New Roman" size=3D1><SPAN style=3D"FONT: 7p=
t 'Times New Roman'"> </SPAN></FONT></SP=
AN></SPAN></FONT><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=3D"FON=
T-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Reduce the induction air temp=
erature. </FONT></P></BLOCKQUOTE>
<DIV>Add to this list:</DIV>
<DIV> 4) Increase eng=
ine speed;</DIV>
<DIV> </DIV>
<DIV> 5) Reduce major=
combustion chamber radius;</DIV>
<DIV> </DIV>
<DIV> 6) Reduce/Alter=
combustion chamber turbulence;</DIV>
<DIV> </DIV>
<DIV> 7) Alter combus=
tion chamber wall angles to reduce infrared and shockwave energy r=
eflected into areas of instabillity.</DIV>
<DIV> </DIV>
<DIV> 8) Relocat=
e spark plug(s)</DIV>
<DIV></SPAN><SPAN style=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"=
> </DIV>
<BLOCKQUOTE style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue=20=
2px solid">
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2>Reductions in=20=
IAT from the intercooler will buy one LARGE improvements in the =20=
detonation limited BMEP (ie, more horsepower becomes usefully available).</F=
ONT></P></BLOCKQUOTE>
<DIV>That sounds a lot like something I said earlier. Your'e starting to agr=
ee with me.</DIV>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><o:p></o:p></S=
PAN></FONT> </P>
<BLOCKQUOTE style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: blue=20=
2px solid">
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">>></SPAN></FONT>=
<FONT face=3DArial size=3D2><SPAN style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Ari=
al">However, when you make the blanket statement that a mechanically driven=20=
supercharger will result in a slower airplane, we have to part company.<FONT=
color=3Dnavy><SPAN style=3D"COLOR: navy"><<<o:p></o:p></SPAN></FONT><=
/SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPA=
N></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial color=3Dnavy size=3D2><SPAN style=
=3D"FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I didn=E2=80=99t say t=
hat. I said the data I had seen revealed that one particular aircraft=20=
using one particular configuration of belt driven compressor ended up, based=
on actual test, going no faster with the belt driven compressor than=20=
it did without. </FONT></P></BLOCKQUOTE>
<DIV>I felt that was what you were implying by making the statement. I see W=
alter came to the opposite conclusion. If I am mistaken, then I appologize.=20=
I did not mean to put words in your mouth.</DIV>
<DIV> </DIV>
<DIV>It's ironic that in the beginning my intent was to steer this thread&nb=
sp;away from an argument between personalities and back toward a discussion=20=
of the merits and fundamentals. I seem to have had the opposite effect on th=
e argumentative part. </DIV>
<DIV> </DIV>
<DIV>I am still curious to know what boost Rick runs on his otherwise&n=
bsp;stock engine at Reno.</DIV></SPAN>
<DIV> </DIV>
<DIV>Rob</DIV></BODY></HTML>
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