Today's Message Index:
----------------------
1. 01:39 AM - Turbo Charging (Nick N)
2. 04:58 AM - Re: turbo vs. super (AI Nut)
3. 06:48 AM - Re: turbo vs. super (Scott)
4. 06:53 AM - Re: turbo vs. super (Scott)
5. 07:02 AM - Re: Turbos vs. mechanical-drive superchargers (James R. Cunningham)
6. 07:04 AM - Re: turbo vs. super (Ed Anderson)
7. 07:05 AM - Re: Turbos vs. mechanical-drive superchargers (James R. Cunningham)
8. 07:34 AM - Re: Supercharging (Gary Casey)
9. 07:39 AM - Re: Turbos vs. mechanical-drive superchargers (AI Nut)
10. 07:51 AM - Re: turbo vs super (James R. Cunningham)
11. 08:05 AM - Re: turbo vs. super (James R. Cunningham)
12. 08:37 AM - Re: Turbos vs. mechanical-drive superchargers (James R. Cunningham)
13. 09:09 AM - Re: Re: Supercharging (Scott)
14. 09:19 AM - Re: turbo vs. super (Scott)
15. 09:24 AM - Re: turbo vs. super (Scott)
16. 09:53 AM - Re: turbo vs. super (steve korney)
17. 11:49 AM - Re: turbo vs. super (James R. Cunningham)
18. 12:08 PM - Re: turbo vs. super (Scott)
19. 12:33 PM - Re: turbo vs. super (Archie)
20. 12:36 PM - Re: turbo vs. super (Gordon and Marge)
21. 12:36 PM - Re: Turbos vs. mechanical-drive superchargers (Archie)
22. 12:48 PM - Exhaust Plume Drag (Scott)
23. 01:29 PM - Re: Turbos vs. mechanical-drive superchargers (James R. Cunningham)
24. 01:47 PM - Re: Exhaust Plume Drag (kempthornes)
25. 01:49 PM - Re: Exhaust Plume Drag (James R. Cunningham)
26. 02:04 PM - Re: turbo vs. super (steve korney)
27. 02:15 PM - Re: Exhaust Plume Drag (LessDragProd@aol.com)
28. 02:25 PM - Re: Exhaust Plume Drag (AI Nut)
29. 02:32 PM - Re: Exhaust Plume Drag (Gilles.Thesee)
30. 02:43 PM - Re: Exhaust Plume Drag (Scott)
31. 02:58 PM - Re: Exhaust Plume Drag (Scott)
32. 03:00 PM - Re: Exhaust Plume Drag (James R. Cunningham)
33. 03:02 PM - Re: Exhaust Plume Drag (James R. Cunningham)
34. 03:13 PM - NOX normalizing (Scott)
35. 03:15 PM - Re: Exhaust Plume Drag (James R. Cunningham)
36. 03:37 PM - Re: Exhaust Plume Drag (James R. Cunningham)
37. 03:55 PM - Re: NOX normalizing (James R. Cunningham)
38. 03:58 PM - Re: NOX normalizing (J. R. Dial)
39. 03:58 PM - Re: turbo vs. super (Boyd Braem)
40. 07:04 PM - Re: turbo vs. super (Lyle Peterson)
41. 07:45 PM - Re: NOX normalizing (Charlie & Tupper England)
42. 08:31 PM - Re: turbo vs. super (Archie)
43. 08:41 PM - Re: turbo vs. super (Archie)
44. 10:23 PM - Corvair (k.jones)
Message 1
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--> Engines-List message posted by: "Nick N" <rvator@nicknaf.com>
This has been a wonderful discussion; I'd love to see it keep going!
I've always been taught that an engine is most efficient at WOT, very
small throttle plate restriction, free breathing, etc. With the
technology of modern automobile turbo systems, mainly Electronic Boost
Control (EBC) would it be possible to incorporate a Cockpit controlled
Automatic Boost system? For example, say we take a Normally Aspirated
(NA) Lyc. O-360 180 HP adapt a EBC'd turbo system on it. Upper end
'boost' is limited to 1.1 Bar or about 31 Inches of MP. This is
slightly above the norm of 29 Inches to offset the heating effect of the
intake charge. Obviously at Sea Level the turbo would be doing very
little but would add more and more "boost" with increasing altitude.
With this arrangement we could maintain sea level engine performance up
to the Turbo critical altitude. Up to this point, it's functionally the
same as most every turbo'd airplane made. (I think) How about adding a
Potmeter that would allow you to 'dial back' the boost? You do this to
maintain WOT, but also climb at 25/25 and or cruse at your normal 23/23,
all this at 13,000ft WOT. Is this possible, or am I out of my mind (as
usual...)? I'll be very honest, all of my flying to date has all be NA
aircraft. No Turbo's or Super's for me. But the idea is very very
appealing. How are Turbo's in aircraft controlled today? With the
exception of the Manual WasteGate systems out there, all are a mystery
as to the inner-workings of the boost control. I would really like a
system that I have control over, but also is not a high pilot workload
item. Blowing an engine on go around because I forgot to open the
wastegate on decent is not my idea of a good time. :-)
Any idea's, comments, flames, etc accepted!
Nick
Lincoln, NE
Message 2
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
Yep. Need the formulas?
AI Nut
----- Original Message -----
From: "andrew manzo" <andrewmanzo@yahoo.com>
Subject: Engines-List: turbo vs. super
> --> Engines-List message posted by: andrew manzo <andrewmanzo@yahoo.com>
>
> My understanding is that the temperature increase is
> proportional to the boost (boyle's law).
>
> Therefore, at the same compression, a supercharger and
> turbocharger will heat the intake air to the same
> degree... with perhaps some conductive heating in the
> case of the turbocharger.
>
> However, to get the same power increase, the
> supercharger will have to generate more boost (as
> described in my last post), and the increased boost
> means more heating of the intake air.
>
> Does this sound right to y'all?
>
>
> --Andrew
>
> __________________________________
Message 3
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
Shamelessly stolen from an auto racing oriented engine list:
The biggest advantage all supercharger systems have over the turbo concept
is simplicity. The drive system for the compressor is just much more
complex on turbos than a simple crank driven pulley, which is why turbo
systems have more parts than s/c systems. The other big advantage comes in
compressor design choices, because you simply don't have any with a turbo.
Turbos have to use centrifugal compressors (although suitable copmpressor
sections now exist for just about any application), which isn't necessarily
a bad thing, but you can learn more about that in the "Superchargers:
compressor design and choices" thread.
Simplicity, reliability, ease of installation and greater design
flexibility are the general plus's to crank driven s/c systems. Ultimate
power output, tunability and scalability are what the average turbo system
has in it's favor.
Scott
Message 4
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
Another shameless theft from teh same email list
The intention with this thread is to shed some light on the theories behind
supercharging the modern engine, and the wonderful advantages it gives us
in both speed and basic engine design issues. This post is also to try and
give people a better understanding of supercharger systems and how they
work to make such a simple thing as an engine even simpler (speaking in
terms of tuning). I personally am tired of seeing people bicker over the
differences between the two basic designs, and would like everyone to note
the vast similarities among them instead. So without further delay... I
will start with this simple statement:
"It makes no sense to build a naturally aspirated engine if what you are
looking for is good power output."
To understand why this is so obviously true, we need to break the concept
of an engine down into its simplest parts. There are 4 main parts to an
engine that concern airflow:
-the induction system
-the cylinder head(s)
-the exhaust system
-the camshaft(s)
Now if you think of the engine in terms of airflow and forget about fuel
for a minute, it becomes a very simple matter really. What we want to do is
best flow air through the cylinder head, from the induction system to the
exhaust system and then out into the world again. This is best & most
naturally accomplished by pressure variation, because as almost anyone with
a high school education knows, air naturally flows from areas of higher
concentration (pressure) to lower concentration (pressure). Now let's
assume for a minute that we are talking about an engine at or near sea
level, well we can just forgo the exact physics of things and say that at
both the induction system's inlet & the exhaust's outlet we have equal
pressure (just under 15psi absolute pressure). So in order to flow air into
this system we must always be working a balancing act between the three
fundamental sections of the engine, which are exposed to each other only
through the camshaft's orchestration of the valves. So forget everything
else you know about engines and start thinking of what's under your hood in
this way for the rest of this post :).
NA ENGINES (naturally aspirated)
These must work within a maximum pressure variation of 0psi (which is
really hard to create without massive pumping losses) and 14.7psi (maximum
atmospheric pressure @ sea level). To add to the basic problem of how to
flow air into and out-of this system, both ends of the system start out at
the same pressure, meaning air doesn't naturally want to go IN or OUT. This
can be accurately termed as a "pain in the ass". Now engineers and
enthusiasts alike have long been fascinated with how to make power from
this setup, but I am talking specifically about supercharged engines here,
and as I already stated "It makes no sense to build a naturally aspirated
engine if what you are looking for is good power output." So forget about
how you can best accomplish this through piston movement and it's effects
on cylinder pressures, and understand that it's just a whole lot easier to
get an engine to work if it's supercharged.
FI ENGINES (forced induction)
From a pure engine design standpoint, it makes MUCH more sense to
pressurize the intake system than to run NA. When only the intake system is
running under pressure well above atmospheric, it becomes perfectly obvious
that air is going to want to flow through the engine exactly the way we
want it to, and both cam timing & exhaust sizing becomes much less
important to getting the system to work right (as it was before in NA
setup). The air will naturally want to flow into the cylinder head, and
then after the very strong power stroke (thanks to all that air) it will
naturally want to flow out into the lower pressure exhaust system
afterwards. Everything in the engine will be working at pressure above
atmospheric and the pressure differences will be greatest in the induction
system, so all air will want to exit out the tail pipe quickly and
efficiently. One other thing should be said here: turbos technically ARE
superchargers. A supercharger is ANY device that pressurizes the intake to
above atmospheric pressure, and turbos do this exactly like superchargers
do. The only difference is in how a turbo gets the energy necessary to
perform it's job, and also that the turbo contributes to supercharging the
exhaust system (or more accurately a portion of it, the exhaust manifold).
THE CASE FOR SUPERCHARGING
Since a crank driven s/c (s/c = supercharger) is what people are normally
talking about when they use the term supercharger, I will no longer say
"crank driven" to make the distinction between it and a turbo. Now using a
supercharger makes a ton of sense simply because it only has a direct
effect in pressurizing the engine on the side we want it to, the induction
side. Since pressures will always be higher here than in any other part of
the system (except of course during the engine's power stroke, but that's
always sealed off from the rest of the system so we can forget about that
complexity), it's very easy to make this combination a powerful one. NA
engines often use large amounts of valve overlap to get the whole system to
work properly at higher RPM, which has obvious drawbacks in that it's
possible for the intake system and exhaust systems to interact in a
negative way (since they operate at similar pressures). It's sometimes just
as easy to get air flowing backwards through the system as it is to go
forwards in an NA setup, which is one reason camshaft choice is so
important to where in the RPM band best power will be produced. And here is
where the beauty of supercharging is; neither valve overlap amounts nor
perfect exhaust system designs are completely essential to keep everything
flowing in the right direction. No matter how long the exhaust is exposed
to the intake system through valve overlap, air should NEVER pass backwards
through the system unless the supercharger stops working.
THE EVIL OF SUPERCHARGING
The evil of supercharging is that some of the power we finally get from
combusting the air/fuel mixture must go back into powering the
supercharger. So here we have designed this whole system that works so
well, yet we have to power it with some of our hard earned torque. This is
not a good thing, but then again nothing so simple is ever going to come
for free. Do superchargers work? Of course they do, which is why many
racing engine uses the technology unless the rules prohibit it. The net
result is more total power from the system, but a portion of this power
must be sapped from our output to make it all work.
THE CASE FOR TURBOCHARGING
This section is easy to write, because it's exactly the same thing as the
supercharger portion. We have all of the same advantages, except for one
major benefit. That benefit is that turbocharging runs off what is largely
wasted energy, so that damn drawback of needing to power the system with
some of our hard earned torque is removed. In this way, a turbocharger
addresses the one main drawback to using a supercharger, but as you will
see in a second the supercharger addresses the one main drawback of
turbocharging.
THE EVIL OF TURBOCHARGING
Hopefully you now understand why it makes so much sense to forgo designing
engines for NA use and just supercharge the sucker instead, at least when
we are talking about how to best make power. And if you have been following
what I have said, you will also understand the bad effect turbos have on
our little perfect world of pressure variation.
A turbo is an ingenious little design that harnesses the wasted kinetic
energy we dump out through the exhaust system to actually force more air
into the engine. This is good for the same reasons that supercharging is
good, but it has one major drawback: it of course increases the pressure
within a portion of the exhaust system. While turbocharging a motor
increases the amount of air that can be flowed into it, it has a negative
effect on how easily we can flow it back out again. This weakens our
positive pressure difference between these two fundamental sides of the
engine, and causes both cam timing & exhaust system design to again become
extremely important to making good power. This is most certainly not a good
thing, but can a turbo overcome this drawback with the other inherent good
it possesses? It certainly seems so, because in most current forms of
racing where the rules don't probihit the use of tubos or slap restrictions
on their use, the turbo reigns supreme in terms of engine power output.
Now I didn't post this to make a statement about which system will work
better for your intended use, because the answer is (as usual) "it
depends". Sorry, but if there was such a clear cut answer do you really
think people would still be debating this topic? A long time ago someone
would have proven everyone else wrong, and either turbos or superchargers
would no longer exist. Remember, these systems were designed and in use on
production vehicles long before most of us were born, so it's not like this
is a new debate. The purpose here is to educate people on exactly why we
would want to supercharge or turbocharge an engine in the first place. Also
I wanted people to see, from a basic and theoretical perspective, how each
system is different in its function and it's relative pros & cons.
Hopefully this discussion of basic theory helped some of you come to a
better understanding of FI engines, and that my leaving out any real world
examples actually made it easier to understand. I have written an article
concerning the technical differences of the common systems, giving examples
of different supercharger designs and their advantages/disadvantages. You
can read it HERE
(http://af.datablocks.net/vbulletin/showthread.php3?threadid=425). And
please, any questions or comments, post 'em here.
Thanks for reading, peace!
Message 5
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
While it is a relatively small fraction of the increased power in
systems with large boost, it is not negligible and probably should be
taken into consideration by the turbo and wastegate designers.
JimC
AI Nut wrote:
>
>, but the effects are almost negligible in a well designed system, as in you won't
notice it due to the large increase in available power.
Message 6
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: "Ed Anderson" <eanderson@carolina.rr.com>
----- Original Message -----
From: "andrew manzo" <andrewmanzo@yahoo.com>
Subject: Engines-List: turbo vs. super
> --> Engines-List message posted by: andrew manzo <andrewmanzo@yahoo.com>
>
> My understanding is that the temperature increase is
> proportional to the boost (boyle's law).
>
> Therefore, at the same compression, a supercharger and
> turbocharger will heat the intake air to the same
> degree... with perhaps some conductive heating in the
> case of the turbocharger.
>
> However, to get the same power increase, the
> supercharger will have to generate more boost (as
> described in my last post), and the increased boost
> means more heating of the intake air.
>
> Does this sound right to y'all?
>
>
> --Andrew
There is the efficiency of the compressor to take into account. True, both
a supercharger and turbocharger will compress intake air to the same boost
level, however, a centrifugal compressor generally being more "efficient"
than a "roots" type compressor will heat the air to a lesser degree. You do
get the same temp increase due to the compression of the air itself
(according to Boyles Law), but the less efficiency compressor will add even
more energy in terms of heat into the air mass. With lower efficiency, less
work energy is
converted to compressing the air and more is converted to heat added to the
air mass (which is undesirable).
However if using a centrifugal type compressor with either a supercharger
or turbocharger, it matters little (in term of temperature rise) whether it
is belt driven or turbine driven, the compressor efficiency is essential the
same. Therefore the temperature increase due to the compressor is essential
the same in both cases.
The reason you might need to use more boost with a supercharger to get the
same net engine power, is that a mechanically driven pump uses more of the
mechanical energy produced by the engine. The turbocharger is using mainly
the exhaust energy (which you normally don't use in the first place) so has
less effect (but some due to higher back pressure in the exhaust) on the
mechanical energy produced by the engine.
My 0.02 worth
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
Message 7
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
Archie, I agree with you. But what makes a smaller diameter more
efficient as per Gary's point?
JimC
Archie wrote:
> One of the advantages of turbo'd engines is the fact that you can change the
> characteristics and curve by mixing and matching compressor or turbine
> housings..........
Message 8
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| Subject: | Re: Supercharging |
--> Engines-List message posted by: "Gary Casey" <glcasey@adelphia.net>
<<Therefore, at the same compression, a supercharger and
turbocharger will heat the intake air to the same
degree... with perhaps some conductive heating in the
case of the turbocharger.>>
Sort of true, but not really. The heat from compression (Boyle's Law, as
you state, or "PV=NRT") is the same, but any compression device will operate
at less than 100% efficiency and any efficiency less than 100% will result
in the wasted power going into heating the inlet charge. Efficiency is not
a simple subject as it depends on the operating condition as well as the
design of the compressor. In the pressure ratio ranges we are talking about
a well-matched turbocharger compressor section could operate at 80 to 85%
efficiency, while I would bet that a belt-drive centrifugal compressor would
be about 70 to 80%. A non-compressing blower has an efficiency of about 60
to 70%.
<<1. Better overall efficiency. Turbo generally spin faster and hence are
> smaller in diameter and inherently more efficient.
Why does being smaller in diameter make them more efficient?
JimC>>
There are really two relate reasons for the turbos being higher in
efficiency. A centrifugal compressor requires a give tip speed to get a
given pressure ratio (ignoring back-bend designs). The higher the speed the
smaller the required diameter. Efficiency losses come largely from skin
friction and leakage around the blades. Smaller diameter means less total
surface area and less total leakage path. That's why everyone tries for the
highest rpm's possible - some small passenger car turbos operate at 200,000
rpm and a typical aircraft turbo will run at 100,000 rpm or close to it.
The problems with gear and belt drives limit the rpm of mechanical-drive
devices to rpm's more like 50,000. The second reason for the higher turbo
efficiency is just the money and time spent optimizing the designs. I would
bet that the total R&D on turbocharger efficiency improvements is over 100
times what has been spent on mechanical drive units. With all that money
spent it is just more likely they are closer to the optimum design.
<<With a turbocharger, damage to the exhaust system can
cascade to the intake system much more easily than
with a supercharger, since the supercharger isn't
connected to the exhaust system.>>
The most likely failure I have seen in aircraft units is a broken exhaust
pipe, dumping the boost. The most likely failure for a belt-drive device is
a broken belt. Both have the same result, so the question is, which is more
likely? Turbos can suffer from FOD in the exhaust system, but mechanical
drive units can suffer gearbox failures. I'm guessing that overall the
turbocharger is more reliable and less likely to have this type of failure.
<<However, because the turbo is "free" power, there is
no inherent loss of fuel efficiency (at the same power
level as a normally aspirated engine).>>
There's no free lunch. The turbine in a turbocharger is about 80%
efficiency and it does take back pressure. The advantage is that this power
comes from the "indicated" power of the engine, essentially taking power
from the pressure of the cycle. Adding back pressure could be argued
actually reduces the mechanical stresses in the engine (the connecting rod
peak tensile load) The mechanical drive supercharger takes "brake" power to
run, meaning that power had to be transferred into the crankshaft and then
taken back out. The mechanical efficiency of an engine is probably about 80
to 90% so that is 10% efficiency taken right off the top.
Gary Casey
Message 9
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
We're getting into semantics here. Your statement "taken into consideration
by ... designers" forgets that I already mentioned a "... designed system."
Yes, if one doesn't put at least a little thought into the turbo setup,
backpressure can be considerable. Backpressure, even without a turbo, can
destroy a large engine if you use 1/4 inch exhaust pipes, but a little bit
of design work will show the large disadvantage to not using the correct
piping and etc.
AI Nut
----- Original Message -----
From: "James R. Cunningham" <jrccea@bellsouth.net>
Subject: Re: Engines-List: Turbos vs. mechanical-drive superchargers
> --> Engines-List message posted by: "James R. Cunningham"
<jrccea@bellsouth.net>
>
> While it is a relatively small fraction of the increased power in
> systems with large boost, it is not negligible and probably should be
> taken into consideration by the turbo and wastegate designers.
> JimC
>
> AI Nut wrote:
> >
> >, but the effects are almost negligible in a well designed system, as in
you won't notice it due to the large increase in available power.
>
>
Message 10
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| Subject: | Re: turbo vs super |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
andrew manzo wrote:
> However, because the turbo is "free" power,
It isn't quite free power. There is a consequent increase in
backpressure. As you say, TANSTAAFL. (with a tip o' the hat to both
Robert Heinlein and Jerry Pournelle's grandfather)
JimC
Message 11
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
Ed Anderson wrote:
> The turbocharger is using mainly
> the exhaust energy (which you normally don't use in the first place)
A good place to mention that if you choose to use your exhaust for jet
thrust augmentation, it usually amounts to a net increase of 4% to 5% of
your total thrust. And, it is nearly free as such things go (you would
need to take desired cross-over altitude into account when designing the
exhaust).
JimC
Message 12
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
AI Nut wrote:
>
> --> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
>
> We're getting into semantics here. Your statement "taken into consideration
> by ... designers" forgets that I already mentioned a "... designed system."
Not really semantics -- I just missed your prior statement about a
"designed system". Oops. :-)
Message 13
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| Subject: | Re: Supercharging |
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
>
>Sort of true, but not really. The heat from compression (Boyle's Law, as
>you state, or "PV=NRT") is the same, but any compression device will operate
>at less than 100% efficiency and any efficiency less than 100% will result
>in the wasted power going into heating the inlet charge. Efficiency is not
>a simple subject as it depends on the operating condition as well as the
>design of the compressor. In the pressure ratio ranges we are talking about
>a well-matched turbocharger compressor section could operate at 80 to 85%
>efficiency, while I would bet that a belt-drive centrifugal compressor would
>be about 70 to 80%. A non-compressing blower has an efficiency of about 60
>to 70%.
I completely disagree. A turbocharger and a supercharger using the same
type of compressor will have exactly the same efficiency, there's no magic
attributed to the source use to turn the pump.
The most likely failure I have seen in aircraft units is a broken exhaust
>pipe, dumping the boost. The most likely failure for a belt-drive device is
>a broken belt. Both have the same result, so the question is, which is more
>likely? Turbos can suffer from FOD in the exhaust system, but mechanical
>drive units can suffer gearbox failures. I'm guessing that overall the
>turbocharger is more reliable and less likely to have this type of failure.
These two failures are radically different. One can easily kill you and
everybody aboard, the other is an annoyance.
If the belt breaks on a super charger, you loose boost, you fly slower to
your destination....
If the much more complicated exhaust systems used on turbo's breaks and
dumps hot exhaust into the engine compartment, you have a pretty high
chance of carbon monoxide poisoning in the cabin, not to mention the likely
hood of an infight fire. Both very deadly scenarios.
Thats the biggest advantage a supercharger has over a turbocharger. Fewer
parts, simpler installation, and the failure modes are fewer and far less
deadly.
Scott
Message 14
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
At 11:03 AM 12/5/2003, you wrote:
>--> Engines-List message posted by: "James R. Cunningham"
><jrccea@bellsouth.net>
>
>Ed Anderson wrote:
> > The turbocharger is using mainly
> > the exhaust energy (which you normally don't use in the first place)
>
>A good place to mention that if you choose to use your exhaust for jet
>thrust augmentation, it usually amounts to a net increase of 4% to 5% of
>your total thrust. And, it is nearly free as such things go (you would
>need to take desired cross-over altitude into account when designing the
>exhaust).
>JimC
I sincerely doubt you would get 4% to 5%.
I just changed my exhaust from straight down to straight back. I think I
gained a few knots, though wishful interpretation probably plays into my
measurments.
I think I gained more from not having the exhaust plume at a 90 degree
angle from the airflow, like a big 2.5 inch pipe sticking out there, than I
did from the push from the exhaust.
Scott
Message 15
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
>degree... with perhaps some conductive heating in the
>case of the turbocharger.
Every turbocharger I've seen has the compressors(exhaust drive and the
induction pump) right next to each other if not actually in the same casting.
The damn things run cherry red hot!!
I'd say the conductive heat transferred from the exhaust drive part of the
turbo to the induction pump would be very large indeed.
Thus increasing the need if not mandating an intercooler for a turbo.
Scott
Message 16
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: "steve korney" <s_korney@hotmail.com>
Scott...
http://af.datablocks.net/vbulletin/showthread.php3?threadid=425
That link doesn't get me anywhere...
Best... Steve
Wonder if the latest virus has gotten to your computer? Find out. Run the
FREE McAfee online computer scan!
Message 17
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
Scott wrote:
> I sincerely doubt you would get 4% to 5%.
Easy enough to calculate. And easy enough to test. I've used it in the
Denver-Oshkosh airrace a few years back. Run the numbers for yourself
and compare them with your prop map. For the plane, engine, and TAS
that I used, it worked out to be a net thrust increase of a little over
4%.
> I think I gained more from not having the exhaust plume at a 90 degree
> angle from the airflow, like a big 2.5 inch pipe sticking out there, than I
> did from the push from the exhaust.
Please describe to me how the perpendicular exhaust plume affects the
aircraft drag after exiting the pipe (assuming you don't have wake
impingement on the airframe).
I find wake analysis to be extremely useful when making flapping flight
calculations, but I don't see how wake modifications aft of the aircraft
affect drag (that said, it is obvious that using the aircraft itself to
modify the wake does have an effect on drag).
JimC
P.S. I find this thread very interesting. I don't know who started it,
but thanks.
Message 18
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
Steve,
If that link was from the text I shamelessly copied from another elist, its
probably been broken for a long time.
That was an archived message I copied, very old.
Scott
At 10:53 AM 12/5/2003, you wrote:
>--> Engines-List message posted by: "steve korney" <s_korney@hotmail.com>
>
>Scott...
>
>
>http://af.datablocks.net/vbulletin/showthread.php3?threadid=425
>
>That link doesn't get me anywhere...
>
>
>Best... Steve
>
>Wonder if the latest virus has gotten to your computer? Find out. Run the
>FREE McAfee online computer scan!
>
>
Message 19
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: "Archie" <archie97@earthlink.net>
> > --> Engines-List message posted by: andrew manzo <andrewmanzo@yahoo.com>
> >
> > My understanding is that the temperature increase is
> > proportional to the boost (boyle's law).
> >
> > Therefore, at the same compression, a supercharger and
> > turbocharger will heat the intake air to the same
> > degree... with perhaps some conductive heating in the
> > case of the turbocharger.
> >
> > However, to get the same power increase, the
> > supercharger will have to generate more boost (as
> > described in my last post), and the increased boost
> > means more heating of the intake air.
> >
> > Does this sound right to y'all?
> >
> >
> > --Andrew
OK as a superficial treatise. As a person who had been racing
supercharged cars for over 18 years, there is far more to it than
would appear. We can quote formulas all day long, (I am an
industrial engineer), but the bs stops at the race track.
A blower running nitro or methanol will stay cooler than one
running gasoline, and technically the methanol user may
run a few degrees cooler than nitro due to latent fuel vaporization.
Archie
Message 20
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--> Engines-List message posted by: "Gordon and Marge" <gcomfo@tc3net.com>
Scott, I don't know how to reach you except through this post, so I will
comment for all the list to see. I hope you are a teacher of young
children, or even teen-agers. You have given the most succinct and
easily understood explanation of this subject I have ever seen. I am a
non-tech person, reading posts because I am the spouse of a pilot and a
fellow builder of RV's. I have had a somewhat hazy idea of how these
engine systems differ, but you laid it all out clearly. The idea of you
explaining things to a room full of eager students pleases me. They
would be eager because you know your subject and are good at explaining
it.
Marge
Do not archive.
Message 21
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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: "James R. Cunningham"
<jrccea@bellsouth.net>
>
> Archie, I agree with you. But what makes a smaller diameter more
> efficient as per Gary's point?
> JimC
>
> Archie wrote:
>
> > One of the advantages of turbo'd engines is the fact that you can change
the
> > characteristics and curve by mixing and matching compressor or turbine
> > housings..........
Perhaps a misunderstanding in terminology.
I did not mean to imply it would be more efficient,
just that the response time (turbo lag), can be
modified mechanically, but as the example indicates,
there is no free lunch.
Archie
Message 22
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| Subject: | Exhaust Plume Drag |
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
>Please describe to me how the perpendicular exhaust plume affects the
>aircraft drag after exiting the pipe (assuming you don't have wake
>impingement on the airframe).
The exhaust stream when not aligned with the air flow is just like a solid
structure sticking out into the air stream.
It is bent for sure, but the first ?? inches act like a solid but flexible
pipe, thus inducing parasitic drag.
Its not like it becomes instantly disconnected right after it exists the
pipe. Some of the force of the wind pushing against the exhaust stream is
transferred to pushing against the airplane.
Thats how fluid clutches and torque converters work right? Air is a fluid.
I was told I would gain 4 to 5 knots in my Velocity when moving the exhaust
from a near perpendicular exit to a straight back exit. Maybe I got 3
knots, from 172 to 175 knots at cruise. I can't see how that can be
translated into a 4% increase in power, but maybe it does?
Scott
Message 23
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| Subject: | Re: Turbos vs. mechanical-drive superchargers |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
Archie, it wasn't you that said smaller is more efficient, it was Gary.
I was just curious about why.
Jim
Archie wrote:
> Perhaps a misunderstanding in terminology.
> I did not mean to imply it would be more efficient,
> just that the response time (turbo lag), can be
> modified mechanically, but as the example indicates,
> there is no free lunch.
> Archie
Message 24
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: kempthornes <kempthornes@earthlink.net>
At 01:43 PM 12/5/2003 -0700, you wrote:
>--> Engines-List message posted by: Scott <scott@tnstaafl.net>
>I was told I would gain 4 to 5 knots in my Velocity when moving the exhaust
>from a near perpendicular exit to a straight back exit. Maybe I got 3
>knots, from 172 to 175 knots at cruise. I can't see how that can be
>translated into a 4% increase in power, but maybe it does?
Would a 4% increase in power give a 4% increase in top speed? No. The
value of more power as far as speed goes is low. For speed, reduce drag.
Wouldn't the best test of power improvement be to test climb at some low
airspeed? Maybe at best L/D?
Would some of the improvement be due to back pressure reduction?
K. H. (Hal) Kempthorne
RV6-a N7HK - Three trips to OSH now.
PRB (El Paso de Robles, CA)
Message 25
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
Scott wrote:
>
> The exhaust stream when not aligned with the air flow is just like a solid
> structure sticking out into the air stream.
As you know, the only way that the plume once exited can transfer drag
loads back into the airframe is through the shear strength of the plume
at the tailpipe exit. What is the shear strength of that plume?
> Its not like it becomes instantly disconnected right after it exists the
> pipe. Some of the force of the wind pushing against the exhaust stream is
> transferred to pushing against the airplane.
How? What is the mechanism?
> Thats how fluid clutches and torque converters work right? Air is a fluid.
So I've heard. I make my living working with fluid mechanics, but that
doesn't mean I know anything much about it. :-)
But, don't fluid clutches and torque converters operate in a different
range of viscosities and Reynolds numbers than that exhaust plume?
> I was told I would gain 4 to 5 knots in my Velocity when moving the exhaust
> from a near perpendicular exit to a straight back exit. Maybe I got 3
> knots, from 172 to 175 knots at cruise. I can't see how that can be
> translated into a 4% increase in power, but maybe it does?
Well, using the cube root rule for speed increase with power change
(only a first order approximation), to increase from 172 to 175 knots,
you would expect to require more power on the order of (175/172)
3
=1.0532, or about a 5.3% increase in thrust horsepower to give that 3
knot increase. Not too far out of line with the 4% to 5% increase in
thrust that I suggested. I would have expected turning the tailpipe aft
to give you about 2.5 to 3 kts at your airspeed, but would have taken a
projection of 5 knots with a grain of salt. Who suggested that you
expect 5?
Jim
Message 26
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: "steve korney" <s_korney@hotmail.com>
OK as a superficial treatise. As a person who had been racing
supercharged cars for over 18 years, there is far more to it than
would appear. We can quote formulas all day long, (I am an
industrial engineer), but the bs stops at the race track.
A blower running nitro or methanol will stay cooler than one
running gasoline, and technically the methanol user may
run a few degrees cooler than nitro due to latent fuel vaporization.
Archie
Archie...
On my blown gas car, the intake manifold would ice-up when I switched to
methanol from gasoline...
Best...Steve...
Cell phone switch rules are taking effect find out more here.
http://special.msn.com/msnbc/consumeradvocate.armx
Message 27
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: LessDragProd@aol.com
In a message dated 12/05/2003 1:09:10 PM Pacific Standard Time,
scott@tnstaafl.net writes:
I was told I would gain 4 to 5 knots in my Velocity when moving the exhaust
from a near perpendicular exit to a straight back exit. Maybe I got 3
knots, from 172 to 175 knots at cruise. I can't see how that can be
translated into a 4% increase in power, but maybe it does?
Scott
If you say it the other way around, it works.
It would take a 3.5% increase on power to gain the 3 knots increase obtained.
Jim Ayers
Message 28
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: "AI Nut" <ainut@earthlink.net>
Jim, I remember reading something about that, including in Kent Paser's
book. This is just my take on it: the extra speed may not be entirely due
to power increase, but also in 1) reduction in drag from the exhaust being
at 90% to the angle of attack, plus 2) a bit of extra lift from the added
airspeed with the hot, fast exhaust now being directed along the underside
of the fuselage. I would have thought such measure would only be a
miniscule increase in efficiency but different people have reported a few
knot/mph increases just due to that change.
AI Nut
----- Original Message -----
From: "James R. Cunningham" <jrccea@bellsouth.net>
Subject: Re: Engines-List: Exhaust Plume Drag
> --> Engines-List message posted by: "James R. Cunningham"
<jrccea@bellsouth.net>
>
> Scott wrote:
> >
> > The exhaust stream when not aligned with the air flow is just like a
solid
> > structure sticking out into the air stream.
>
> As you know, the only way that the plume once exited can transfer drag
> loads back into the airframe is through the shear strength of the plume
> at the tailpipe exit. What is the shear strength of that plume?
>
> > Its not like it becomes instantly disconnected right after it exists the
> > pipe. Some of the force of the wind pushing against the exhaust stream
is
> > transferred to pushing against the airplane.
>
> How? What is the mechanism?
>
> > Thats how fluid clutches and torque converters work right? Air is a
fluid.
>
> So I've heard. I make my living working with fluid mechanics, but that
> doesn't mean I know anything much about it. :-)
>
> But, don't fluid clutches and torque converters operate in a different
> range of viscosities and Reynolds numbers than that exhaust plume?
>
> > I was told I would gain 4 to 5 knots in my Velocity when moving the
exhaust
> > from a near perpendicular exit to a straight back exit. Maybe I got 3
> > knots, from 172 to 175 knots at cruise. I can't see how that can be
> > translated into a 4% increase in power, but maybe it does?
>
> Well, using the cube root rule for speed increase with power change
> (only a first order approximation), to increase from 172 to 175 knots,
> you would expect to require more power on the order of (175/172)
> 3
> =1.0532, or about a 5.3% increase in thrust horsepower to give that 3
> knot increase. Not too far out of line with the 4% to 5% increase in
> thrust that I suggested. I would have expected turning the tailpipe aft
> to give you about 2.5 to 3 kts at your airspeed, but would have taken a
> projection of 5 knots with a grain of salt. Who suggested that you
> expect 5?
> Jim
>
>
Message 29
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: "Gilles.Thesee" <Gilles.Thesee@ac-grenoble.fr>
Honourable and knowledgeable gentlemen,
> > The exhaust stream when not aligned with the air flow is just like a
solid
> > structure sticking out into the air stream.
>
> As you know, the only way that the plume once exited can transfer drag
> loads back into the airframe is through the shear strength of the plume
> at the tailpipe exit. What is the shear strength of that plume?
>
> > Its not like it becomes instantly disconnected right after it exists the
> > pipe. Some of the force of the wind pushing against the exhaust stream
is
> > transferred to pushing against the airplane.
>
> How? What is the mechanism?
>
Doesn't change of momentum and pressure have a role to play ?
ANY parasitic flow perpendicular to the general flow creates drag. The flow
is invariably detached behind exhaust plumes, cowling joint leaks,
cowling/spinner gap leaks.
WHENEVER the boundary layer is detached you get drag, no matter wether the
cause is still part of your airplane or not.
The French aerodynamicist Michel Colomban ( Cri-Cri 175 lb twin, Ban Bi two
seater ) told me he got a 2% total thrust increase on his Ban Bi by just
welding a 90 bend to his exhaust pipe. The sleeker the airplane, the
greater the speed increase.
On this 80 hp, 190 mph two seater, the effect was quite noticeable.
Hoerner's book on fluid dynamic drag may prove invaluable to those
interested in those matters.
Regards,
Gilles Thesee
Message 30
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
At 04:47 PM 12/5/2003, you wrote:
>--> Engines-List message posted by: "James R. Cunningham"
><jrccea@bellsouth.net>
>
>Scott wrote:
> >
> > The exhaust stream when not aligned with the air flow is just like a solid
> > structure sticking out into the air stream.
>
>As you know, the only way that the plume once exited can transfer drag
>loads back into the airframe is through the shear strength of the plume
>at the tailpipe exit. What is the shear strength of that plume?
Well James, I'm probably all wet about this. Having accepted the word of a
fellow racer/A&P with out checking it out.. It sounded reasonable to me
at the time.
I've certainly not worked the numbers on it as my knowledge of physics is
more related to computer engineering, which has little in common with fluid
dynamics.
>Well, using the cube root rule for speed increase with power change
>(only a first order approximation), to increase from 172 to 175 knots,
>you would expect to require more power on the order of (175/172)
>3
>=1.0532, or about a 5.3% increase in thrust horsepower to give that 3
>knot increase. Not too far out of line with the 4% to 5% increase in
>thrust that I suggested. I would have expected turning the tailpipe aft
>to give you about 2.5 to 3 kts at your airspeed, but would have taken a
>projection of 5 knots with a grain of salt. Who suggested that you
>expect 5?
Interesting that its right in line of a 3 knot increase. Of course we
have to subtract out that exhaust plume drag, right! :-)
It was suggested by a couple people that build and race LongEZ's who had
done the a similar exhaust change to some of their airplanes.
Scott
Message 31
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
> >I was told I would gain 4 to 5 knots in my Velocity when moving the exhaust
>Would some of the improvement be due to back pressure reduction?
The old exhaust was a 4-into-1 tuned system. It had a problem of cracking
repeatedly at the 4-into -1 junction, different spot every time. After
welding it 3 times in 18 months I threw it in the waste can and put in a
pretty standard canard type exhaust, very short pipes that come straight
back form the exhaust ports.
I was figuring on loosing a bit of HP by tossing the tuned system.
Scott
Message 32
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
kempthornes wrote:
> Would a 4% increase in power give a 4% increase in top speed? No. The
> value of more power as far as speed goes is low. For speed, reduce drag.
Correct. The speed increases approximately with the cube root of the
power increase, so that a 4% increase in power will give about a 1.3%
increase in speed.
>
> Wouldn't the best test of power improvement be to test climb at some low
> airspeed? Maybe at best L/D?
It will show up at any airspeed, with the increase in ROC being directly
related to the increase in excess horsepower.
> Would some of the improvement be due to back pressure reduction?
No. Generally, the combinations of tailpipe outlet area vs. tailpipe
cross-sectional area that give best thrust improvement also increase the
back pressure. You get help at higher altitudes while being hurt at
lower ones. You have to select the cross-over altitude that you want
and design the system for that cross-over.
JimC
Message 33
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
Wouldn't it take more like a 5.3% increase to go from 172 to 175?
Jim
LessDragProd@aol.com wrote:
>
> If you say it the other way around, it works.
>
> It would take a 3.5% increase on power to gain the 3 knots increase obtained.
Message 34
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--> Engines-List message posted by: Scott <scott@tnstaafl.net>
I operate out of a high altitude warm airport.
6500 ft elevation and summer days are in the 80's low 90's.
Density altitude exceeds 10,000 ft regulary, I only see density altitude
equal to field elevation on winter nights and early winter mornings. I
also am flying with a fixed pitch prop that is pitched for cruise(I'm
always hurrying to get there).
This all comes down to long takeoff runs, very long runs if fully loaded in
summer time. I used 7500 ft at Alamosa one day when density altitude was
11,000!
So, I think the solutions to this are:
Constant speed prop would help immensely. But, its $10,000 for a CS pusher
prop for a 200hp Lycoming, out of my range right now.
I've toyed with the idea of supercharging my IO360, even though as I've
learned its not as efficient as turbo charging. This would also cost in
the range of $5,000-$15,000.
I've also thought about using NOX to normalize the engine to sea level
performance. This would only be used for takeoffs, not in flight, can't
carry a big enough NOZ bottle for that! I think I can do this for about $500.
I would use a dry system for simplicity. Have a 25HP and 50 HP selectable
jets for different density altitudes giving me a 25, 50 and 75 HP range. I
would always select a jet based on producing 200 total HP.
I think NOX could be a good solution as I only really need the extra HP on
takeoff. My cruise speed while not what I'd love to have is respectable
and the fuel burn is good too.
Any thoughts?
Scott
Message 35
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
1) There's no increase in engine power, and there's no increase due
directly to the exhaust plume not being at 90 degrees to the airflow.
There is an increase due to the jet effect of the exhaust being pointed
aftward. In real life though, you don't want to exit the exhaust
exactly parallel to the belly because it will cook your feet, so you
will take a slight hit that is proportional to the cosine of the angle
between the belly and the exhaust.
2) You don't have extra lift because you reduce the AOA as the airspeed
increases so that you won't generate extra lift and start climbing.
That said, in many GA aircraft, roughly about 7% to 13% of the lift is
airframe lift rather than winglift. Rotating the exhaust plume aftward
will have no significant effect on that component of lift. In fact, it
will generally reduce the total lift by about 8 to 10 pounds while
increasing the thrust by a roughly similar amount. Note that turning
the tailpipe aftward does require a slight increase in tail download to
maintain the appropriate couple to resist the nose-down pitching moment
of the wing. However, due to the difference in moment arm, the
increased tail download isn't all that great.
You calculate the exhaust thrust increment just like you would if you
were running a jet engine in lieu of a piston engine.
AI Nut wrote:
snipped
Message 36
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| Subject: | Re: Exhaust Plume Drag |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
Gilles.Thesee wrote:
> Doesn't change of momentum and pressure have a role to play ?
Not when the plume is directed downward perpendicular to the free stream
and is also free of the aircraft. Both have a role to play when the
plume is directed aftward approximately parallel to the free stream. I
wrote a page for Sport Aviation a few years back that addresses some of
the equations that are used to calculate the thrust while allowing for
changes in the air/fuel mixture, that might be of some interest.
> ANY parasitic flow perpendicular to the general flow creates drag.
Indeed it does, but only to the extent that the resulting turbulence
impinges on some portion of the airframe. With long, perpendicular
tailpipes, that is minimised, because the turbulent flow caused by the
plume misses the aircraft. On the other hand, the flow behind the
exhaust pipe itself is made turbulent and that does directly affect the
airframe drag. Note that I am not recommending perpendicular tailpipes.
> The flow is invariably detached behind exhaust plumes,
Only when the outlet is close enough to the airframe to allow the
disrupted flow to affect the flow along the airframe (quite often, in
practice -- but not invariably).
> cowling joint leaks, cowling/spinner gap leaks.
I agree.
> WHENEVER the boundary layer is detached you get drag, no matter wether the
> cause is still part of your airplane or not.
Indeed you do. But keep in mind that with a fairly long tailpipe the
energy in the perpendicular plume that is used to power the increased
turbulence is waste power because it is directed perpendicular to the
direction of travel -- and the increased turbulence and drag that it
causes affects only the wake, not the aircraft.
> The French aerodynamicist Michel Colomban ( Cri-Cri 175 lb twin, Ban Bi two
> seater ) told me he got a 2% total thrust increase on his Ban Bi by just
> welding a 90 bend to his exhaust pipe.
My point, exactly. That's all it takes to increase your thrust (and
your speed). If you want to neck the exit down slightly, you can
increase it still further, approximately doubling it before the
increased back pressure becomes an issue (assuming your exhaust plume is
subsonic -- for supersonic plumes, you'd want to flare the opening like
the nozzle on a rocket).
> Hoerner's book on fluid dynamic drag may prove invaluable to those
> interested in those matters.
It sure would. As do Barnes McCormick's textbook and a number of other
texts that address the subject. It's pretty basic stuff.
JimC
P.S. Thanks for a really good post.
Message 37
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| Subject: | Re: NOX normalizing |
--> Engines-List message posted by: "James R. Cunningham" <jrccea@bellsouth.net>
Hey, Scott. I used to live in South Fork!
I've considered NOX as a side issue while doing the engine cooling
calculations and induction ram calculations for a plane intended for the
unlimited Bronze class. I think it's a great idea if you don't overdo
it.
Jim
Message 38
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--> Engines-List message posted by: "J. R. Dial" <jrdial@hal-pc.org>
I have some experience with NOX on automotive and boat engines
and after seeing some of the damage we did during the learning curve I
would sure be reluctant to experimenting with it on and airplane. The
bottles and stuff are not light either.
Just my 2 cents and good luck.
DO NOT ARCHIVE
-----Original Message-----
From: owner-engines-list-server@matronics.com
[mailto:owner-engines-list-server@matronics.com] On Behalf Of Scott
Subject: Engines-List: NOX normalizing
--> Engines-List message posted by: Scott <scott@tnstaafl.net>
I operate out of a high altitude warm airport.
6500 ft elevation and summer days are in the 80's low 90's.
Density altitude exceeds 10,000 ft regulary, I only see density altitude
equal to field elevation on winter nights and early winter mornings. I
also am flying with a fixed pitch prop that is pitched for cruise(I'm
always hurrying to get there).
This all comes down to long takeoff runs, very long runs if fully loaded
in
summer time. I used 7500 ft at Alamosa one day when density altitude
was
11,000!
So, I think the solutions to this are:
Constant speed prop would help immensely. But, its $10,000 for a CS
pusher
prop for a 200hp Lycoming, out of my range right now.
I've toyed with the idea of supercharging my IO360, even though as I've
learned its not as efficient as turbo charging. This would also cost in
the range of $5,000-$15,000.
I've also thought about using NOX to normalize the engine to sea level
performance. This would only be used for takeoffs, not in flight, can't
carry a big enough NOZ bottle for that! I think I can do this for about
$500.
I would use a dry system for simplicity. Have a 25HP and 50 HP
selectable
jets for different density altitudes giving me a 25, 50 and 75 HP range.
I
would always select a jet based on producing 200 total HP.
I think NOX could be a good solution as I only really need the extra HP
on
takeoff. My cruise speed while not what I'd love to have is respectable
and the fuel burn is good too.
Any thoughts?
Scott
=
==
==
==
==
Message 39
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: Boyd Braem <bcbraem@comcast.net>
Archie--
I've been toying with the idea of getting "water" injection on my high
compression LyCon IO-540--any ideas/suggestions? I'll even pay you for
the advice--I mean, you deserve it--like I would treat medical
(MediCare) patients for free (actually, I do, now)--poor old bastards
are starting to look more-and-more like me.
Boyd.
RV Super-6
Venice, FL
Message 40
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--> Engines-List message posted by: "Lyle Peterson" <lyleap@access4less.net>
Boyd,
Your last line -- that is the same reason that I don't like going to
class reunions. I don't care to hang around with all those old people.
Lyle
-----Original Message-----
From: owner-engines-list-server@matronics.com
[mailto:owner-engines-list-server@matronics.com] On Behalf Of Boyd Braem
Subject: Re: Engines-List: turbo vs. super
--> Engines-List message posted by: Boyd Braem <bcbraem@comcast.net>
Archie--
I've been toying with the idea of getting "water" injection on my high
compression LyCon IO-540--any ideas/suggestions? I'll even pay you for
the advice--I mean, you deserve it--like I would treat medical
(MediCare) patients for free (actually, I do, now)--poor old bastards
are starting to look more-and-more like me.
Boyd.
RV Super-6
Venice, FL
=
==
direct advertising on the Matronics Forums.
==
==
==
Message 41
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| Subject: | Re: NOX normalizing |
--> Engines-List message posted by: Charlie & Tupper England <cengland@netdoor.com>
Scott wrote:
>--> Engines-List message posted by: Scott <scott@tnstaafl.net>
>
>I operate out of a high altitude warm airport.
>
>6500 ft elevation and summer days are in the 80's low 90's.
>Density altitude exceeds 10,000 ft regulary, I only see density altitude
>equal to field elevation on winter nights and early winter mornings. I
>also am flying with a fixed pitch prop that is pitched for cruise(I'm
>always hurrying to get there).
>
>This all comes down to long takeoff runs, very long runs if fully loaded in
>summer time. I used 7500 ft at Alamosa one day when density altitude was
>11,000!
>
>So, I think the solutions to this are:
>
>Constant speed prop would help immensely. But, its $10,000 for a CS pusher
>prop for a 200hp Lycoming, out of my range right now.
>
>I've toyed with the idea of supercharging my IO360, even though as I've
>learned its not as efficient as turbo charging. This would also cost in
>the range of $5,000-$15,000.
>
>I've also thought about using NOX to normalize the engine to sea level
>performance. This would only be used for takeoffs, not in flight, can't
>carry a big enough NOZ bottle for that! I think I can do this for about $500.
>
>I would use a dry system for simplicity. Have a 25HP and 50 HP selectable
>jets for different density altitudes giving me a 25, 50 and 75 HP range. I
>would always select a jet based on producing 200 total HP.
>
>I think NOX could be a good solution as I only really need the extra HP on
>takeoff. My cruise speed while not what I'd love to have is respectable
>and the fuel burn is good too.
>
>Any thoughts?
>
>Scott
>
Talk to Ken Welter.
http://homepage.mac.com/rotarycoot/
Two cautions, though:
He flies a Coot amphib so there's far less speed range between t/o &
cruise; you might run into problems with a stalled prop on takeoff if
you run fixed pitch.
He uses a Mazda rotary engine, & they are much more rugged than a/c engines.
Charlie
Message 42
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: "Archie" <archie97@earthlink.net>
> --> Engines-List message posted by: "steve korney" <s_korney@hotmail.com>
>
>
> OK as a superficial treatise. As a person who had been racing
> supercharged cars for over 18 years, there is far more to it than
> would appear. We can quote formulas all day long, (I am an
> industrial engineer), but the bs stops at the race track.
> A blower running nitro or methanol will stay cooler than one
> running gasoline, and technically the methanol user may
> run a few degrees cooler than nitro due to latent fuel vaporization.
> Archie
>
>
> Archie...
>
> On my blown gas car, the intake manifold would ice-up when I switched to
> methanol from gasoline...
>
> Best...Steve...
Good point, and example. Forgot about that.
Before retiring, you MUST run nitro at least once,
and remember: no revving prior to launch,
just step on the loud pedal.
Aaaahh, the eyes burning from nitro fumes..........
Archie
Message 43
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| Subject: | Re: turbo vs. super |
--> Engines-List message posted by: "Archie" <archie97@earthlink.net>
> --> Engines-List message posted by: Boyd Braem <bcbraem@comcast.net>
>
> Archie--
>
> I've been toying with the idea of getting "water" injection on my high
> compression LyCon IO-540--any ideas/suggestions? I'll even pay you for
> the advice--I mean, you deserve it--like I would treat medical
> (MediCare) patients for free (actually, I do, now)--poor old bastards
> are starting to look more-and-more like me.
>
> Boyd.
> RV Super-6
> Venice, FL
You can build your own system for about $30. or
there are several very good automotive systems
which could be incorporated. I personally have
not water injected an aircraft engine, but superficially
I see no problems with quality components.
Archie
Message 44
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--> Engines-List message posted by: "k.jones" <kevin-jones@snet.net>
I'd appreciate anyone who is preparing (or has prepared) a Corvair engine for aviation
use getting in touch with me off the list at kevin-jones@snet.net.
Do not archive.
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