Ram air

On Jun 3, 7:54 am, wrote:
On Jun 2, 9:45 pm, Billy Crabs wrote:

let me try to explain myself better, the amount of air that is drawn
into an engine is in direct coralation to cylinder volume and the cam
shafts "lift and duration" A valve can only stay open as long as the
cam lobe holds the lifter up, therefore only allowing as much air/fuel
as was scientificly formulated for the cylinder.
for instance, lets say you have two guys who are going to breath in
deep, now even if you are blowing an air hose in their faces, they are
only going to be able to inhale as much as there lungs will hold. Now
lets say they are inhaling pot and when they blow out its put into a
"turbo", the turbine spins and sends the unused pot back to their
lungs, but it's still only as much as they hold in their
lungs(cylinder volume)

Air density in the cylinder is governed by its pressure and
temperature. MUCH more air can be forced into the cylinder if the
manifold pressure is boosted; this is the principle behind getting
more power out of a given number of cubic inches. You need to do some
studying on the matter. I have, and I teach this stuff in college.
Dan

I wonder if ram scoops were ever installed near the
prop tips. Probably too expensive for GA, but a WW2
A/C with tips spinning at what(?) 500-600 mph would
give a nice pressure boost.
I've read dual phase superchargers were used in recon
A/C to get the speed and altitude.
Ken

Ken S. Tucker wrote:

I wonder if ram scoops were ever installed near the
prop tips. Probably too expensive for GA, but a WW2
A/C with tips spinning at what(?) 500-600 mph would
give a nice pressure boost.
I've read dual phase superchargers were used in recon
A/C to get the speed and altitude.
Ken


First off I doubt it overcome the drag it would create. Second, what do
you think the tip speed is on an average GA plane is?

Follow this link and learn a thing or two.

http://www.pponk.com/HTML%20PAGES/propcalc.html

Stealth Pilot wrote:
On Mon, 02 Jun 2008 19:51:47 -0400, dave hillstrom
wrote:


On Mon, 2 Jun 2008 14:12:26 -0700 (PDT), Tony
wrote:


Ram air is only as useful the allowing air to get to your carburater
faster but is not necessarily used. When your piston is on its intake
stroke(vaccum) your combustion chamber can only draw in enough air
that is in conjuction to the chambers volume and all other air that is
present after the compression stroke is exported to engines smog
devices and is recirculated only AFTER being filtered. All engines
come off the assembly lines, be it an airplane motor or a vehicle
motor, to draw the amount of air that it needs to run at opptimum
performance. Ram Air is a myth and don't try to throw "turbo" into
the conversation because turbo is recircualted exhaust and still has
unburnt fuel in the fumes.

I think you are quite wrong. Ram air in fact gives us a half inch or
so more manifold pressure, and that increases the total weight of the
air-fuel mixture in the cylinder. Reduce your 'it doesn't matter
argument to an extreme to see how it fails.

As for turbos, the turbine is powered by the exhaust gasses coming

from the engine, the exhaust gas itself is not reintroduced into the

cylinders. The turbine itself could be powered by an electric motor,
for that matter. That was the model for my tongue in cheek comment
about using a shop vac to increase manifold pressure.

will you marry me?

dave the term is not foo and bar.
foo *is* a term from another war and another airforce
but the term you've so successfully stuffed up is fubar
fubar is a vietnam era acronym of F***ed up beyond all recognition.

your sig line is a snafu
(situation normal all F***ed up)

Yore 'rong. foo and bar are metasyntactic variables. They aren't
acronyms (they're metasyntactic variables).

Like being the John and Jane Doe of computer engineering - placeholders.

Fubar predates WWII.

--
nuts

On Jun 3, 10:18 am, "Ken S. Tucker" wrote:

I wonder if ram scoops were ever installed near the
prop tips. Probably too expensive for GA, but a WW2
A/C with tips spinning at what(?) 500-600 mph would
give a nice pressure boost.
I've read dual phase superchargers were used in recon
A/C to get the speed and altitude.

Airspeed off the tips is the same as the speed off the inner
blade areas, due to the pitch washout across the blade span, so
there'd be no advantage to having scoops behind the tips. The
propeller's blades are flying at an AOA of between 2 and 4 degrees in
cruise flight, anywhere between the tips and hub, because of that
pitch variation.
See Figure 6-4 of this page:
http://www.allstar.fiu.edu/aero/flight63.htm

Dan

On Jun 3, 11:18 am, wrote:
On Jun 3, 10:18 am, "Ken S. Tucker" wrote:

I wonder if ram scoops were ever installed near the
prop tips. Probably too expensive for GA, but a WW2
A/C with tips spinning at what(?) 500-600 mph would
give a nice pressure boost.
I've read dual phase superchargers were used in recon
A/C to get the speed and altitude.

Airspeed off the tips is the same as the speed off the inner
blade areas, due to the pitch washout across the blade span, so
there'd be no advantage to having scoops behind the tips. The
propeller's blades are flying at an AOA of between 2 and 4 degrees in
cruise flight, anywhere between the tips and hub, because of that
pitch variation.
See Figure 6-4 of this page:http://www.allstar.fiu.edu/aero/flight63.htm
Dan

Dan it was a trick question I asked you.
It's the basic aerodynamic physics of the
standard centifugal supercharger compressor
operating principle.
I tossed you a zinger, cuz you claimed to be a
teacher in a college and I couldn't resist :-),
don't worry about it, hardly anyone get's that one
correct, and I hope you get a ha-ha-ah from it.

I mentioned, "dual phase superchargers" as a
hint. Here's the answer: the ram-air pressure
acquired at the prop tips is equal to the loss
of pressure against the centrifugal force pushing
air - via ducting - into the prop center that one
obtains at the prop tips.

Now you know the rest of the story.
Regards
Ken

On Jun 3, 1:45*pm, Billy Crabs wrote:
On Jun 2, 11:33*pm, Billy Crabs wrote:





On Jun 2, 11:08*pm, wrote:

On Jun 2, 8:00 pm, Billy Crabs wrote:

On Jun 2, 5:12 pm, Tony wrote:

Ram air is only as useful the allowing air to get to your carburater
faster but is not necessarily used. When your piston is on its intake
stroke(vaccum) your combustion chamber can only draw in enough air
that is in conjuction to the chambers volume and all other air that is
present after the compression stroke is exported to engines smog
devices and is recirculated only AFTER being filtered. *All engines
come off the assembly lines, be it an airplane motor or a vehicle
motor, to draw the amount of air that it needs to run at opptimum
performance. *Ram Air is a myth and don't try to throw "turbo" into
the conversation because turbo is recircualted exhaust and still has
unburnt fuel in the fumes.

I think you are quite wrong. Ram air in fact gives us a half inch or
so more manifold pressure, and that increases the total weight of the
air-fuel mixture in the cylinder. Reduce your 'it doesn't matter
argument to an extreme to see how it fails.

As for turbos, the turbine is powered by the exhaust gasses coming
from the engine, the exhaust gas itself is not reintroduced into the
cylinders. The turbine itself could be powered by an electric motor,
for that matter. That was the model for my tongue in cheek comment
about using a shop vac to increase manifold pressure.

The air going into the manifold has the same atmospheric weight as if
it was outside the manifold, what makes it denser is the addition of
fuel into the air/fuel mixture, unless the air is in a perfect vaccum
it will not increase in pressure and most certainly not density and
the turbos do reintroduce fuel back into the combustion mixture, If
you've ever seen a read out of carbon emissions for a non turbo
vehicle it still has enough unburnt fuel to power your vehicle for
another 5% of your fuel consumption *and turbos IF powered by a
motorized turbine are as useless as ram air because of the statement I
made in my previous post. your intake is only as much as the volume of
your cylinders

* * * * * * Turbocharging can be set to two different levels:
Turbonormalizing, which brings manifold pressure to sea level
pressure; and boosting, which raises manifold pressures to more than
30" Hg. If an engine is boosted, the air density in the cylinder at
the bottom of the intake stroke could be well above atmospheric.

I'm sorry to keep disagreeing but, but the pressure in which(if you
can call it pressure) goes through a manifold is increased by MAP
sensors which measure atmospheric pressure and regulates air fuel
mixture, it has nothing to do with "ram air" and I do agree that that
the density of the air/mixture is increased by the vaccum caused by a
piston at bottom dead center but we were talking about air before it
reaches the cylinder and the speed of which it arrives to carburation.

* * * * *Dan- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

let me try to explain myself better, the amount of air that is drawn
into an engine is in direct coralation to cylinder volume and the cam
shafts "lift and duration" A valve can only stay open as long as the
cam lobe holds the lifter up, therefore only allowing as much air/fuel
as was scientificly formulated for the cylinder.
for instance, lets say you have two guys who are going to breath in
deep, now even if you are blowing an air hose in their faces, they are
only going to be able to inhale as much as there lungs will hold. *Now
lets say they are inhaling pot and when they blow out its put into a
"turbo", the turbine spins and sends the unused pot back to their
lungs, but it's still only as much as they hold in their
lungs(cylinder volume)- Hide quoted text -

Billy , I think you are confusing volume ( which is certainly fixed)
with mass of air. by increasing the pressure you increase the density
and therefore have a higher mass of air for the same volume. higher
mass of course means more energy for the same volume charge.
Terry
PPL Downunder

On Jun 4, 12:54*am, wrote:
On Jun 2, 9:45 pm, Billy Crabs wrote:

let me try to explain myself better, the amount of air that is drawn
into an engine is in direct coralation to cylinder volume and the cam
shafts "lift and duration" A valve can only stay open as long as the
cam lobe holds the lifter up, therefore only allowing as much air/fuel
as was scientificly formulated for the cylinder.
for instance, lets say you have two guys who are going to breath in
deep, now even if you are blowing an air hose in their faces, they are
only going to be able to inhale as much as there lungs will hold. *Now
lets say they are inhaling pot and when they blow out its put into a
"turbo", the turbine spins and sends the unused pot back to their
lungs, but it's still only as much as they hold in their
lungs(cylinder volume)

* * * * * Air density in the cylinder is governed by its pressure and
temperature. MUCH more air can be forced into the cylinder if the
manifold pressure is boosted; this is the principle behind getting
more power out of a given number of cubic inches. You need to do some
studying on the matter. I have, and I teach this stuff in college.

If you are teaching this stuff you might like to make use of the data
I put together on the C172 takeoff and landing performance. it is in
the form of an excel spreadsheet which shows the takeoff and landing
distance as a function of density altitude at different temperatures.
( derived from the Cessna tables of distance vs pressure altitude and
temperature. It clearly shows that the takeoff performance is not
simply a function of density altitude which all of the flight training
literature i have read and all my own training drummed in to me. And
perhaps you could come up with a better explanation than decreasing
air viscosity :) It is clearly engine related because the landing
distance data do fall on the same curve of distance vs density
altitude irrespective of temperature. The best explanation I have
heard is that higher for a given density will get the air into the
cyclinder faster ( ie you will just get closer to the equilibrating
the pressure between the outside and the cylinder.
Anyway the analysis can be downloaded from the following site ( this
is an australian pilots forum called straight and level downunder).
this link will take you direct to the download page. You are
welcome to join the forum too but you have to register for that ( to
keep the kooks out - or in depending on your perspective). but you
dont have to register to access the download section.
http://www.straightandleveldownunder.net/downloads.html

Terry
PPL Downunder

"Billy Crabs" wrote

let me try to explain myself better, the amount of air that is drawn
into an engine is in direct coralation to cylinder volume and the cam
shafts "lift and duration" A valve can only stay open as long as the
cam lobe holds the lifter up, therefore only allowing as much air/fuel
as was scientificly formulated for the cylinder.
for instance, lets say you have two guys who are going to breath in
deep, now even if you are blowing an air hose in their faces, they are
only going to be able to inhale as much as there lungs will hold. Now
lets say they are inhaling pot and when they blow out its put into a
"turbo", the turbine spins and sends the unused pot back to their
lungs, but it's still only as much as they hold in their
lungs(cylinder volume)

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Sorry, but no ()'s for your above post.

Wow, what you don't understand about supercharging/turbocharging is "a
bunch."

In your above example, if one guy (instead of having an air hose blowing in
his face) had a guy with twice the lung capacity giving him mouth to mouth
recesitation as he was breathing in, and the guy blowing emptied his lungs
completely into the "breathing-in" guy, that would be a better analogy to
what a supercharger/turbocharger does.

He is physically forcing more air into the guy than he could normally breath
in, by forcing more air in throughout the intake stroke. Let's hope he has
strong lungs, so they don't explode.

That is what happens to engines that have extremely high boost running at
high output, sometimes. They can't stand the extra kick provided by all of
the extra air, gas, and resulting combustion. If the engine has a mass
airflow sensor, that is how it knows how much extra gas to feed into the
intake air. It can tell there is extra pressure, which gives the volume of
air being passed though it (the sensor) extra mass.

At _no time_ does a normal turbocharged/supercharged engine have already
used combustion gas put back into the next (or any other) intake cycle. The
only reason some engines have a feature like that would be for pollution
control.
--
Jim in NC

On Jun 3, 12:56 pm, "Ken S. Tucker" wrote:

Dan it was a trick question I asked you.
It's the basic aerodynamic physics of the
standard centifugal supercharger compressor
operating principle.
I tossed you a zinger, cuz you claimed to be a
teacher in a college and I couldn't resist :-),
don't worry about it, hardly anyone get's that one
correct, and I hope you get a ha-ha-ah from it.

The prop does not throw air outward. We've been over that
one before. The air column actually narrows behind the prop, due to
the lowered pressure caused by the air's acceleration. We can see it
on cool mornings when the dew point is just below ambient temperature,
and the vapor trails off the prop tips outline the periphery of the
air column, showing it to be squeezing inward.
A centrifugal super/turbocharger does it differently. The air
is accelerated outward in the first place, not in an axial manner, and
is directed into a divergent duct known as a diffuser, where it is
slowed and its pressure raised. A different animal altogther, compared
to a propeller.


I mentioned, "dual phase superchargers" as a
hint. Here's the answer: the ram-air pressure
acquired at the prop tips is equal to the loss
of pressure against the centrifugal force pushing
air - via ducting - into the prop center that one
obtains at the prop tips.

"Dual-phase supercharger" is a misnomer. They were two-speed
affairs, going to a higher gear ratio for higher altitudes.

Dan

On Jun 4, 11:41*am, wrote:
On Jun 3, 12:56 pm, "Ken S. Tucker" wrote:

Dan it was a trick question I asked you.
It's the basic aerodynamic physics of the
standard centifugal supercharger compressor
operating principle.
I tossed you a zinger, cuz you claimed to be a
teacher in a college and I couldn't resist :-),
don't worry about it, hardly anyone get's that one
correct, and I hope you get a ha-ha-ah from it.

* * * * * * The prop does not throw air outward. We've been over that
one before. The air column actually narrows behind the prop, due to
the lowered pressure caused by the air's acceleration. We can see it
on cool mornings when the dew point is just below ambient temperature,
and the vapor trails off the prop tips outline the periphery of the
air column, showing it to be squeezing inward.
* * * * A centrifugal super/turbocharger does it differently. The air
is accelerated outward in the first place, not in an axial manner, and
is directed into a divergent duct known as a diffuser, where it is
slowed and its pressure raised. A different animal altogther, compared
to a propeller.

I mentioned, "dual phase superchargers" as a
hint. Here's the answer: the ram-air pressure
acquired at the prop tips is equal to the loss
of pressure against the centrifugal force pushing
air - via ducting - into the prop center that one
obtains at the prop tips.

* * * * *"Dual-phase supercharger" is a misnomer. They were two-speed
affairs, going to a higher gear ratio for higher altitudes.


There are also two stage systems

Cheers