Today's Message Index:
----------------------
1. 04:08 AM - Turbos vs. mechanical-drive superchargers (Gary Casey)
2. 05:19 AM - Re: Supercharging (Archie)
3. 05:20 AM - Re: Turbos vs. mechanical-drive superchargers (AI Nut)
4. 07:17 AM - Turbos vs. mechanical-drive superchargers (Gary Casey)
5. 07:22 AM - Re: Turbos vs. mechanical-drive superchargers (Randy)
6. 08:02 AM - Re: Turbos vs. mechanical-drive superchargers (AI Nut)
7. 08:10 AM - Re: Turbos vs. mechanical-drive superchargers (Healy, Joseph)
8. 09:05 AM - Re: Turbos vs. mechanical-drive superchargers (Randy)
9. 09:57 AM - Re: Turbos vs. mechanical-drive superchargers (Ron Raby)
10. 10:52 AM - Re: Turbos vs. mechanical-drive superchargers (Healy, Joseph)
11. 05:13 PM - Re: Turbos vs. mechanical-drive superchargers (Gordon and Marge)
12. 05:34 PM - Re: Turbos vs. mechanical-drive superchargers (Archie)
13. 05:54 PM - Re: Turbos vs. mechanical-drive superchargers (Archie)
14. 06:00 PM - Re: Turbos vs. mechanical-drive superchargers (AI Nut)
15. 07:37 PM - Re: Turbos vs. mechanical-drive superchargers (Randy)
Message 1
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| Subject: | Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<THAT SOUNDS GOOD, BUT WHAT ABOUT ALL THE HEAT THAT THE TURBO MAKES????>>
I was hoping to read some good debates about the relative benefits of
turbine-driven superchargers ("turbos") compared to mechanical-drive
superchargers ("superchargers"). In the past it was kind of a moot point as
there were no belt-drive superchargers adapted to aircraft engines. Now,
however, there does appear to be a viable belt-drive centrifugal
supercharger available for both Continental and Lycoming engines. This
evens the playing field a bit. The way I see it:
In favor of turbochargers:
1. Better overall efficiency. Turbo generally spin faster and hence are
smaller in diameter and inherently more efficient. I expect that with a
given manifold pressure a turbo'd engine will produce more power than one
with a supercharger.
2. Convenient and relatively efficient boost control via a waste gate.
3. Light weight - although probably not by much.
4. Durability - most turbos will easily last to the engine TBO.
5. Packaging flexibility because there is no mechanical connection between
the turbo and engine - only plumbing.
In favor of superchargers (I'm thinking of the latest belt-drive centrifugal
devices)
1. Straightforward matching to the engine. Basically done by adjusting
pulley diameters.
2. Reduce heat dissipation in engine compartment because of reduced total
exhaust system plumbing required (but the turbo doesn't "make" heat as
purported above).
3. Simpler packaging - but that may be just because there is really only
one location possible, taking away all the debate about where to put it.
4. Fewer plumbing connections to fail - a turbo has at least 6 plumbing
connections and more if you count a separate waste gate.
5. No oil scavenging pump required, but this is just because most turbos
are mounted below the oil level.
It makes the decision on what to use for my upcoming turbonormalized IO-540
more difficult. I think the turbocharger still has the edge.
Gary Casey
Message 2
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| Subject: | Re: Supercharging |
--> Engines-List message posted by: "Archie" <archie97@earthlink.net>
> --> Engines-List message posted by: MLSRV6@aol.com
>
> THAT SOUNDS GOOD, BUT WHAT ABOUT ALL THE HEAT THAT THE TURBO MAKES????
Remember I indicated in a previous e-mail, that there are
trade-offs between the two boosting methods.
Without running a full dissertation on boost technology,
that is one of them, although the rootes type blower generates
some heat. The old style McCulloch blowers as once promoted by
Ford, and Grannatelli, are still available through Granatelli.
I do not see any recent activity in the axial flow units, however.
Most of my work revolves around twin turbos and Rootes-
type applications.
Archie's Racing Service
Message 3
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
(first post so I hope I'm not duplicating info)
Don't forget that a supercharger heats the incoming air considerably more
than a turbo will, according to Hugh McInness in his book, "Turbochargers.".
With either one, you definitely need an intercooler or you lose some major
hp.
Also, a supercharger will rob 25-35% of engine power to drive itself, while
a turbo is almost totally free added power. There is some loss with a turbo
due to additional backpressure in the exhaust system but a bit of
engineering will minimize that.
If you encase the turbo in good insulating material, the exhaust heat will
not radiate into the engine compartment very much.
Btw, is there a good source for a wastegate that will turbonormalize versus
constant boost that is on mine now?
Thanks,
AI Nut
----- Original Message -----
From: "Gary Casey" <glcasey@adelphia.net>
Subject: Engines-List: Turbos vs. mechanical-drive superchargers
> --> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
>
> <<THAT SOUNDS GOOD, BUT WHAT ABOUT ALL THE HEAT THAT THE TURBO MAKES????>>
>
> I was hoping to read some good debates about the relative benefits of
> turbine-driven superchargers ("turbos") compared to mechanical-drive
> superchargers ("superchargers"). In the past it was kind of a moot point
as
> there were no belt-drive superchargers adapted to aircraft engines. Now,
> however, there does appear to be a viable belt-drive centrifugal
> supercharger available for both Continental and Lycoming engines. This
> evens the playing field a bit. The way I see it:
>
> In favor of turbochargers:
>
> 1. Better overall efficiency. Turbo generally spin faster and hence are
> smaller in diameter and inherently more efficient. I expect that with a
> given manifold pressure a turbo'd engine will produce more power than one
> with a supercharger.
> 2. Convenient and relatively efficient boost control via a waste gate.
> 3. Light weight - although probably not by much.
> 4. Durability - most turbos will easily last to the engine TBO.
> 5. Packaging flexibility because there is no mechanical connection
between
> the turbo and engine - only plumbing.
>
> In favor of superchargers (I'm thinking of the latest belt-drive
centrifugal
> devices)
>
> 1. Straightforward matching to the engine. Basically done by adjusting
> pulley diameters.
> 2. Reduce heat dissipation in engine compartment because of reduced total
> exhaust system plumbing required (but the turbo doesn't "make" heat as
> purported above).
> 3. Simpler packaging - but that may be just because there is really only
> one location possible, taking away all the debate about where to put it.
> 4. Fewer plumbing connections to fail - a turbo has at least 6 plumbing
> connections and more if you count a separate waste gate.
> 5. No oil scavenging pump required, but this is just because most turbos
> are mounted below the oil level.
>
> It makes the decision on what to use for my upcoming turbonormalized
IO-540
> more difficult. I think the turbocharger still has the edge.
>
> Gary Casey
>
Message 4
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| Subject: | Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<THAT SOUNDS GOOD, BUT WHAT ABOUT ALL THE HEAT THAT THE TURBO MAKES????>>
I was hoping to read some good debates about the relative benefits of
turbine-driven superchargers ("turbos") compared to mechanical-drive
superchargers ("superchargers"). In the past it was kind of a moot point as
there were no belt-drive superchargers adapted to aircraft engines. Now,
however, there does appear to be a viable belt-drive centrifugal
supercharger available for both Continental and Lycoming engines. This
evens the playing field a bit. The way I see it:
In favor of turbochargers:
1. Better overall efficiency. Turbo generally spin faster and hence are
smaller in diameter and inherently more efficient. I expect that with a
given manifold pressure a turbo'd engine will produce more power than one
with a supercharger.
2. Convenient and relatively efficient boost control via a waste gate.
3. Light weight - although probably not by much.
4. Durability - most turbos will easily last to the engine TBO.
5. Packaging flexibility because there is no mechanical connection between
the turbo and engine - only plumbing.
In favor of superchargers (I'm thinking of the latest belt-drive centrifugal
devices)
1. Straightforward matching to the engine. Basically done by adjusting
pulley diameters.
2. Reduce heat dissipation in engine compartment because of reduced total
exhaust system plumbing required (but the turbo doesn't "make" heat as
purported above).
3. Simpler packaging - but that may be just because there is really only
one location possible, taking away all the debate about where to put it.
4. Fewer plumbing connections to fail - a turbo has at least 6 plumbing
connections and more if you count a separate waste gate.
5. No oil scavenging pump required, but this is just because most turbos
are mounted below the oil level.
It makes the decision on what to use for my upcoming turbonormalized IO-540
more difficult. I think the turbocharger still has the edge.
Gary Casey
Message 5
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Randy" <rnvcrothers@comcast.net>
Al,
You say the supercharger robs 25-35% of engine power to drive itself.
This seems like a high figure to me. Is it a typo? Did this figure also
come from the book you mention? Randy
----- Original Message -----
From: "AI Nut" <ainut@earthlink.net>
Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
> --> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
>
> (first post so I hope I'm not duplicating info)
>
> Don't forget that a supercharger heats the incoming air considerably more
> than a turbo will, according to Hugh McInness in his book,
"Turbochargers.".
> With either one, you definitely need an intercooler or you lose some major
> hp.
>
> Also, a supercharger will rob 25-35% of engine power to drive itself,
while
> a turbo is almost totally free added power. There is some loss with a
turbo
> due to additional backpressure in the exhaust system but a bit of
> engineering will minimize that.
>
> If you encase the turbo in good insulating material, the exhaust heat will
> not radiate into the engine compartment very much.
>
> Btw, is there a good source for a wastegate that will turbonormalize
versus
> constant boost that is on mine now?
>
> Thanks,
> AI Nut
>
>
> ----- Original Message -----
> From: "Gary Casey" <glcasey@adelphia.net>
> To: <engines-list@matronics.com>
> Subject: Engines-List: Turbos vs. mechanical-drive superchargers
>
>
> > --> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
> >
> > <<THAT SOUNDS GOOD, BUT WHAT ABOUT ALL THE HEAT THAT THE TURBO
MAKES????>>
> >
> > I was hoping to read some good debates about the relative benefits of
> > turbine-driven superchargers ("turbos") compared to mechanical-drive
> > superchargers ("superchargers"). In the past it was kind of a moot
point
> as
> > there were no belt-drive superchargers adapted to aircraft engines.
Now,
> > however, there does appear to be a viable belt-drive centrifugal
> > supercharger available for both Continental and Lycoming engines. This
> > evens the playing field a bit. The way I see it:
> >
> > In favor of turbochargers:
> >
> > 1. Better overall efficiency. Turbo generally spin faster and hence
are
> > smaller in diameter and inherently more efficient. I expect that with a
> > given manifold pressure a turbo'd engine will produce more power than
one
> > with a supercharger.
> > 2. Convenient and relatively efficient boost control via a waste gate.
> > 3. Light weight - although probably not by much.
> > 4. Durability - most turbos will easily last to the engine TBO.
> > 5. Packaging flexibility because there is no mechanical connection
> between
> > the turbo and engine - only plumbing.
> >
> > In favor of superchargers (I'm thinking of the latest belt-drive
> centrifugal
> > devices)
> >
> > 1. Straightforward matching to the engine. Basically done by adjusting
> > pulley diameters.
> > 2. Reduce heat dissipation in engine compartment because of reduced
total
> > exhaust system plumbing required (but the turbo doesn't "make" heat as
> > purported above).
> > 3. Simpler packaging - but that may be just because there is really
only
> > one location possible, taking away all the debate about where to put it.
> > 4. Fewer plumbing connections to fail - a turbo has at least 6 plumbing
> > connections and more if you count a separate waste gate.
> > 5. No oil scavenging pump required, but this is just because most
turbos
> > are mounted below the oil level.
> >
> > It makes the decision on what to use for my upcoming turbonormalized
> IO-540
> > more difficult. I think the turbocharger still has the edge.
> >
> > Gary Casey
> >
>
>
Message 6
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
Yes, it came from 'Turbochargers.' Makes sense, too, as engine power must
be used to turn the supercharger (usually via belts) while the turbo uses
only exhaust pressue.
AI Nut
----- Original Message -----
From: "Randy" <rnvcrothers@comcast.net>
Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
> --> Engines-List message posted by: "Randy" <rnvcrothers@comcast.net>
>
> Al,
> You say the supercharger robs 25-35% of engine power to drive itself.
> This seems like a high figure to me. Is it a typo? Did this figure also
> come from the book you mention? Randy
>
> ----- Original Message -----
> From: "AI Nut" <ainut@earthlink.net>
> To: <engines-list@matronics.com>
> Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
>
>
> > --> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
> >
> > (first post so I hope I'm not duplicating info)
> >
> > Don't forget that a supercharger heats the incoming air considerably
more
> > than a turbo will, according to Hugh McInness in his book,
> "Turbochargers.".
> > With either one, you definitely need an intercooler or you lose some
major
> > hp.
> >
> > Also, a supercharger will rob 25-35% of engine power to drive itself,
> while
> > a turbo is almost totally free added power. There is some loss with a
> turbo
> > due to additional backpressure in the exhaust system but a bit of
> > engineering will minimize that.
> >
> > If you encase the turbo in good insulating material, the exhaust heat
will
> > not radiate into the engine compartment very much.
> >
> > Btw, is there a good source for a wastegate that will turbonormalize
> versus
> > constant boost that is on mine now?
> >
> > Thanks,
> > AI Nut
> >
> >
> ><<<snip>>>
Message 7
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| Subject: | Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Healy, Joseph" <WJH@BRPLUSA.COM>
The main advantage of a supercharger is that you get the boost right off
the line, which makes them popular in automotive applications. A turbo
charger takes a while to wind up. In the early days of automotive
turbo's they had problems with cooling and the turbo's oil burned on the
bearings. So superchargers on cars came out before turbo's in the late
1960's. But since then the cooling problems in turbos have mainly been
overcome and so turbos are more common.
Superchargers have made a resurgence lately due to the 0-60 performance
advantage over turbo chargers. But I don't know why anyone would put a
supercharger on an airplane. (unless it cost a lot less).
Joe
-----Original Message-----
From: Gary Casey [mailto:glcasey@adelphia.net]
Subject: Engines-List: Turbos vs. mechanical-drive superchargers
--> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<THAT SOUNDS GOOD, BUT WHAT ABOUT ALL THE HEAT THAT THE TURBO
MAKES????>>
I was hoping to read some
Message 8
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Randy" <rnvcrothers@comcast.net>
I agree that it makes sense, but 25-35%? This still seems like a very high
figure. It is hard to imagine as much as a 35% loss of power to drive the
supercharger, as this would practically negate the entire power benefit of
using one. Perhaps this comes from the drag racing applications where they
are using a very large unit and pumping a very high volume of air. Even
then it is hard to imagine a 35% loss of power.
I plan to use an Eggenfellner Subaru with supercharger. So far, the
performance results have been very positive and certainly not reflecting
such a loss of power to drive the unit.
I favor supercharger applications over turbochargers primarily due problems
with exhaust systems and turbochargers. It seems that exhaust systems are a
problem area in aircraft anyway, from experience I can say this is very
true. Adding the weight, back pressure, and associated heat caused by a
turbocharger seems like it would make even more problems. I can't help but
want to avoid that bearing running at such a high speed and high heat but
they seem to live through it OK.
On the other side, there are many turbocharged aircraft flying but not very
many supercharged flying and I can't help but wonder why...
Randy
----- Original Message -----
From: "AI Nut" <ainut@earthlink.net>
Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
> --> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
>
> Yes, it came from 'Turbochargers.' Makes sense, too, as engine power must
> be used to turn the supercharger (usually via belts) while the turbo uses
> only exhaust pressue.
>
> AI Nut
>
>
> ----- Original Message -----
> From: "Randy" <rnvcrothers@comcast.net>
> To: <engines-list@matronics.com>
> Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
>
>
> > --> Engines-List message posted by: "Randy" <rnvcrothers@comcast.net>
> >
> > Al,
> > You say the supercharger robs 25-35% of engine power to drive
itself.
> > This seems like a high figure to me. Is it a typo? Did this figure also
> > come from the book you mention? Randy
> >
> > ----- Original Message -----
> > From: "AI Nut" <ainut@earthlink.net>
> > To: <engines-list@matronics.com>
> > Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
> >
> >
> > > --> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
> > >
> > > (first post so I hope I'm not duplicating info)
> > >
> > > Don't forget that a supercharger heats the incoming air considerably
> more
> > > than a turbo will, according to Hugh McInness in his book,
> > "Turbochargers.".
> > > With either one, you definitely need an intercooler or you lose some
> major
> > > hp.
> > >
> > > Also, a supercharger will rob 25-35% of engine power to drive itself,
> > while
> > > a turbo is almost totally free added power. There is some loss with a
> > turbo
> > > due to additional backpressure in the exhaust system but a bit of
> > > engineering will minimize that.
> > >
> > > If you encase the turbo in good insulating material, the exhaust heat
> will
> > > not radiate into the engine compartment very much.
> > >
> > > Btw, is there a good source for a wastegate that will turbonormalize
> > versus
> > > constant boost that is on mine now?
> > >
> > > Thanks,
> > > AI Nut
> > >
> > >
> > ><<<snip>>>
>
>
Message 9
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Ron Raby" <ronr@advanceddesign.com>
The areo supercharger system is about 17k and 28lbs. I remember when they
were talking weight for the TSIO 550 that it was about a 100lbs over the
standard 550. I am not sure how the price compares. Here is a link to there
site.
Ron Raby
Lancair ES
http://www.aerosuperchargers.com/
----- Original Message -----
From: "Healy, Joseph" <WJH@brplusa.com>
Subject: RE: Engines-List: Turbos vs. mechanical-drive superchargers
> --> Engines-List message posted by: "Healy, Joseph" <WJH@BRPLUSA.COM>
>
> The main advantage of a supercharger is that you get the boost right off
> the line, which makes them popular in automotive applications. A turbo
> charger takes a while to wind up. In the early days of automotive
> turbo's they had problems with cooling and the turbo's oil burned on the
> bearings. So superchargers on cars came out before turbo's in the late
> 1960's. But since then the cooling problems in turbos have mainly been
> overcome and so turbos are more common.
>
> Superchargers have made a resurgence lately due to the 0-60 performance
> advantage over turbo chargers. But I don't know why anyone would put a
> supercharger on an airplane. (unless it cost a lot less).
>
> Joe
>
> -----Original Message-----
> From: Gary Casey [mailto:glcasey@adelphia.net]
> To: engines-list@matronics.com
> Subject: Engines-List: Turbos vs. mechanical-drive superchargers
>
>
> --> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
>
>
> <<THAT SOUNDS GOOD, BUT WHAT ABOUT ALL THE HEAT THAT THE TURBO
> MAKES????>>
>
> I was hoping to read some
>
>
Message 10
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| Subject: | Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Healy, Joseph" <WJH@BRPLUSA.COM>
What happens if the belt breaks or the impeller seizes? Do you revert
to the same capability as normally aspirated? Or, does the impeller
restrict the airflow somewhat?
Another question, does the supercharger operate all the time? Or, only
on demand, like a turbo charger?
Joe
-----Original Message-----
From: Ron Raby [mailto:ronr@advanceddesign.com]
Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
--> Engines-List message posted by: "Ron Raby" <ronr@advanceddesign.com>
The areo supercharger system is about 17k and 28lbs. I remember when
they were talking weight for the TSIO 550 that it was about a 100lbs
over the standard 550. I am not sure how the price compares. Here is a
link to there site.
Ron Raby
Lancair ES
http://www.aerosuperchargers.com/
Message 11
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| Subject: | Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Gordon and Marge" <gcomfo@tc3net.com>
Subject: RE: Engines-List: Turbos vs. mechanical-drive superchargers
--> Engines-List message posted by: "Healy, Joseph" <WJH@BRPLUSA.COM>
What happens if the belt breaks or the impeller seizes? Do you revert
to the same capability as normally aspirated? Or, does the impeller
restrict the airflow somewhat?
Another question, does the supercharger operate all the time? Or, only
on demand, like a turbo charger?
Joe
Listers: I know just about enough about supercharging to be dangerous,
but in reading the references from elsewhere on the list a couple of
things come to mind. Superchargers (however driven) that have internal
compression are generally more efficient than those that don't. Roots
types do not. The Lysholm does have internal compression. Centrifugals
have internal compression. The vane type, not mentioned but typified by
the Shorrock of years gone by has internal compression. Positive
displacement blowers (Roots, Lysholm, Shorrock) have output more nearly
linear in nature. Centrifugals at low rpm's have proportionately less
output than at higher. Sizeing a centrifugal would need to account for
this. As has been said, changing pulleys would match the positive
displacement unit so sizeing would perhaps be less critical. From the
operational standpoint, turbochargers require some considerations. If
the wastegate is adjustable it becomes a significant maintenance item.
If it is automatic, more so. If it is manual it must be handled with
care and skill. Polen removed the turbo setup from his special because
he couldn't solve the stability problem with the system. I believe Dick
Keyt has reestablished it using newer components. Any type of
compression heats the induction system air. The lower efficiency types
heat it more. I can't be sure, but suspect that the turbo system
transfers more heat to the charge air by conduction and radiation than
the others do because the turbine housings are close and can run red
hot.
This is a good discussion. There is undoubtedly a lot more that can be
said.
Message 12
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Archie" <archie97@earthlink.net>
> --> Engines-List message posted by: "Healy, Joseph" <WJH@BRPLUSA.COM>
>
> What happens if the belt breaks or the impeller seizes? Do you revert
> to the same capability as normally aspirated? Or, does the impeller
> restrict the airflow somewhat?
>
> Another question, does the supercharger operate all the time? Or, only
> on demand, like a turbo charger?
>
> Joe
Blowers,(superchargers), are positively driven. either belt or direct.
Drive ratio, however, is easily controlled through the belt drive.
Of all the turbos and rootes-type blowers we have rebuilt, or modified,
never had a siezure of any kind.
If a blower belt lets go, the engine will still continue running, but due to
the
fact that now the impellers are being driven by vacuum, power loss is,
perhaps, in the area of 80%. Standard use blowers have clearances
of around .002/.004 between rotor and case, as well as end play,
and perhaps around .003 /.005 between rotors. (dependent on size & mfg).
Racing blowers have these clearances zero'd with the use of Nylatron,
and Teflon. (we cannot have ANY efficiency loss).
Remember, the air is forced around the periphery of the housing,
not through it.
I believe that the hp loss would not be as great with the loss of a turbo.
Might be an interesting test next time I have one on the dyno.
Archie-again
Message 13
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Archie" <archie97@earthlink.net>
Forgot to add:
If a backfire occurs with a Rootes type supercharger,
the rotor shafts may bend, cause rubbing of the rotors
to the housing, and make aluminum metal flakes which
would be ingested by the engine.
This is usually caused at startup with a lean mixture, or as in
the case of race cars, at high speed with the fuel curve
set a bit too lean for the existing conditions.
Archie
Message 14
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
I think the 25-30% power loss may be being misunderstood. It seems to refer
to the blowers parasitic loss of the base engine output. For example, if
the normally aspirated (na) engine is 100 hp, if you add a blower, 25% of
that hp goes to operate the blower. Then, the blower has to create enough
boost to "replace" that power, which is of course, terribly inefficient.
A well designed turbo setup will create minimal backpressure, usually 3-5%
and less.
I'd be *real* interested to find out your empirical data rathre than what is
in a book!
HTH,
AI Nut
----- Original Message -----
From: "Archie" <archie97@earthlink.net>
Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
> --> Engines-List message posted by: "Archie" <archie97@earthlink.net>
>
>
> > --> Engines-List message posted by: "Healy, Joseph" <WJH@BRPLUSA.COM>
> >
> > What happens if the belt breaks or the impeller seizes? Do you revert
> > to the same capability as normally aspirated? Or, does the impeller
> > restrict the airflow somewhat?
> >
> > Another question, does the supercharger operate all the time? Or, only
> > on demand, like a turbo charger?
> >
> > Joe
> Blowers,(superchargers), are positively driven. either belt or direct.
> Drive ratio, however, is easily controlled through the belt drive.
> Of all the turbos and rootes-type blowers we have rebuilt, or modified,
> never had a siezure of any kind.
> If a blower belt lets go, the engine will still continue running, but due
to
> the
> fact that now the impellers are being driven by vacuum, power loss is,
> perhaps, in the area of 80%. Standard use blowers have clearances
> of around .002/.004 between rotor and case, as well as end play,
> and perhaps around .003 /.005 between rotors. (dependent on size & mfg).
> Racing blowers have these clearances zero'd with the use of Nylatron,
> and Teflon. (we cannot have ANY efficiency loss).
> Remember, the air is forced around the periphery of the housing,
> not through it.
> I believe that the hp loss would not be as great with the loss of a turbo.
> Might be an interesting test next time I have one on the dyno.
> Archie-again
>
>
Message 15
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "Randy" <rnvcrothers@comcast.net>
Archie,
First I want to thank you for sharing your knowledge. This kind of
information is not easy to come by without considerable research. I am
going to be installing an Eggenfellner Subaru firewall forward package in my
RV7A, and it will have a belt driven supercharger. Testing by the developer
indicates that tossing a belt allows the blower to freewheel, driven by
vacuum, and still allowing enough remaining power to maintain altitude and
make your way to an airport and safely land. Comments?
I don't know what type of supercharger this one is but it comes as
standard equip. on some Mercedes cars. It obviously has two shafts that
rotate and they seem to turn pretty easily.
I am hoping you might have a few minutes to take a quick look at the web
site, http://www.eggenfellneraircraft.com/ and take a look at the unit.
Click on the supercharger button and you can scroll down to the pics.
One flyer had an engine quite from a belt toss that resulted in it being
pushed into the housing and interfering with the cam timing belt. This was
an alignment and belt guide problem that has reportedly been remedied.
Otherwise, the initial flight testing of this unit has been very positive
with the RV7 getting speeds at altitude to make it very comparable to the
180-200 hp Lycoming installations. Pretty impressive given that this is an
engine that has less than half the displacement of the Lycs.
This particular unit has a waste gate valve that is operated by a servo
with a programmable controller to automatically control the amount of boost.
In theory it will maintain a pre-set boost limit up to it's altitude limit,
around 17K, via operation of a 1 1/2" butterfly valve.
I would be very interested in your comments regarding this system.
Thanks
Randy
----- Original Message -----
From: "Archie" <archie97@earthlink.net>
Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
> --> Engines-List message posted by: "Archie" <archie97@earthlink.net>
>
>
> > --> Engines-List message posted by: "Healy, Joseph" <WJH@BRPLUSA.COM>
> >
> > What happens if the belt breaks or the impeller seizes? Do you revert
> > to the same capability as normally aspirated? Or, does the impeller
> > restrict the airflow somewhat?
> >
> > Another question, does the supercharger operate all the time? Or, only
> > on demand, like a turbo charger?
> >
> > Joe
> Blowers,(superchargers), are positively driven. either belt or direct.
> Drive ratio, however, is easily controlled through the belt drive.
> Of all the turbos and rootes-type blowers we have rebuilt, or modified,
> never had a siezure of any kind.
> If a blower belt lets go, the engine will still continue running, but due
to
> the
> fact that now the impellers are being driven by vacuum, power loss is,
> perhaps, in the area of 80%. Standard use blowers have clearances
> of around .002/.004 between rotor and case, as well as end play,
> and perhaps around .003 /.005 between rotors. (dependent on size & mfg).
> Racing blowers have these clearances zero'd with the use of Nylatron,
> and Teflon. (we cannot have ANY efficiency loss).
> Remember, the air is forced around the periphery of the housing,
> not through it.
> I believe that the hp loss would not be as great with the loss of a turbo.
> Might be an interesting test next time I have one on the dyno.
> Archie-again
>
>
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