Ram air

On Jun 2, 10:13 am, Tina wrote:
On Jun 2, 12:01 pm, "Ken S. Tucker" wrote:

On Jun 1, 4:39 pm, Tina wrote:

The induction port for the ram air on the m20J bypasses the air filter
as well, so we typically observe about a half inch improvement in MP.
That's in line with some of the other numbers offered here.

I guess there's no free lunch. There is no way we want to have an
IO540 pull the airplane along, nor do we want the fuss with turbo
charging. The payback for our typical for real flight mission is just
not there. My thought was and is that if it was something pretty
obvious someone would have done it on a homebuilt. Actually, knowing
some of those guys, it does not have to be obvious at all, they are
really creative designers.

Tina, I think this analysis you posted is good,
" It's only a 360 cubic inch engine turning at 2300 RPM or so. Isn't
that a demand of, let's see, at 23 inches mp at sea level that's
23/30 * 2300/2 * 360 / 12^3 or 180 cubic feet a minute? "

I see Tango 2 Denny has some interesting ideas.
Ken

Well, I think it's a dead issue for us. What is fun to think about is,
let's see, about 200 cubic feet a minute, that's 40 cubic feet of
oxygen a minute, or about 3 pounds. For 50% more O2, 1.5 pounds a
minute, or say 20 pounds to get to a pleasantly high altitude. Maybe
that translates in to dewer weighing a total of 50 pounds with liquid
O2? But it would make 15 inches of MP look like 22 or so as far as the
engine is concerned. I better get back to my day job.

Without crackin' the books and pounding the abacus,
you look like +/- 20% using BoE (Back of Envelope)
calculation, which means you get either 80% or 120%
on your physics exam, you choose.

Resolved: psychologists should not be permitted to minor in the
physical sciences. All in favor?

OR pilots should not be permitted to engage in
psychology in this group, now what's the chances
of that happening...is "nil" close :-).
Ken
PS: What's the rationale of the 12,000' cruise?
You know about the "bends" don't you, if not
just read Berties post!

On Jun 2, 10:01 am, "Ken S. Tucker" wrote:

Tina, I think this analysis you posted is good,
" It's only a 360 cubic inch engine turning at 2300 RPM or so. Isn't
that a demand of, let's see, at 23 inches mp at sea level that's
23/30 * 2300/2 * 360 / 12^3 or 180 cubic feet a minute? "

Can't do it that way. You're assuming a volumetric efficiency
of 100% which we never attain without considerable boosting. The
volumetric efficiency at full throttle and redline RPM at sea level
isn't likely to be much more than 50 or 60%.
Got to do it using fuel flow. Best power mixture comes at
around 12:1 (pounds of air to pounds of fuel) and stoichiometric
mixture (no wasted air or fuel) is 15:1. Weight of air at sea level is
about .078 pounds per cubic foot, and weight of gasoline is 6 lb per
US gallon.
An O-320 @ 2700 RPM @ S.L. = Displacement of 15,000 cubic feet
per hour.
Full throttle fuel flow of 10.3 GPH @ 12:1 best power = 9434
cu. ft./hr (with fixed-pitch prop).
9434 ÷ 15,000 = .629 (62.9%) volumetric efficiency @ sea
level.

Not very good, is it? Air has viscosity and the drag of the
entire induction system, even with the throttle wide open, is
significant. Add to that the inertia of the air, and the intake
valve's opening and closing causing the stop-go action of the air in
the system, and things get slowed down considerably.
It's worse in auto engines that turn at high RPM. That's why
many have four valves per cylinder, or turbos, or both.

Dan

On Jun 2, 2:19 pm, "Ken S. Tucker" wrote:
On Jun 2, 10:13 am, Tina wrote:



On Jun 2, 12:01 pm, "Ken S. Tucker" wrote:

On Jun 1, 4:39 pm, Tina wrote:

The induction port for the ram air on the m20J bypasses the air filter
as well, so we typically observe about a half inch improvement in MP.
That's in line with some of the other numbers offered here.

I guess there's no free lunch. There is no way we want to have an
IO540 pull the airplane along, nor do we want the fuss with turbo
charging. The payback for our typical for real flight mission is just
not there. My thought was and is that if it was something pretty
obvious someone would have done it on a homebuilt. Actually, knowing
some of those guys, it does not have to be obvious at all, they are
really creative designers.

Tina, I think this analysis you posted is good,
" It's only a 360 cubic inch engine turning at 2300 RPM or so. Isn't
that a demand of, let's see, at 23 inches mp at sea level that's
23/30 * 2300/2 * 360 / 12^3 or 180 cubic feet a minute? "

I see Tango 2 Denny has some interesting ideas.
Ken

Well, I think it's a dead issue for us. What is fun to think about is,
let's see, about 200 cubic feet a minute, that's 40 cubic feet of
oxygen a minute, or about 3 pounds. For 50% more O2, 1.5 pounds a
minute, or say 20 pounds to get to a pleasantly high altitude. Maybe
that translates in to dewer weighing a total of 50 pounds with liquid
O2? But it would make 15 inches of MP look like 22 or so as far as the
engine is concerned. I better get back to my day job.

Without crackin' the books and pounding the abacus,
you look like +/- 20% using BoE (Back of Envelope)
calculation, which means you get either 80% or 120%
on your physics exam, you choose.

Resolved: psychologists should not be permitted to minor in the
physical sciences. All in favor?

OR pilots should not be permitted to engage in
psychology in this group, now what's the chances
of that happening...is "nil" close :-).
Ken
PS: What's the rationale of the 12,000' cruise?
You know about the "bends" don't you, if not
just read Berties post
Depending on trip length and winds aloft, we choose as high an
altitude as is reasonable without oxygen. Many of our trips are the
order of 500 nm. At the moment that's often 11000 feet east bound.
When we can no longer run 5k or 10ks, or find ourselves winded when
walking high in the mountains or have other evidence of physical
limitations (we do have access to high altitude chambers here) we'll
reduce that altitude.

From 12000 feet we are usually requesting lower when we're 45 minutes
from the airport. When traffic permits we like coming down at 300 feet
a minute!

Bertie's welcome to his bends: bends would be a problem if we were
going up really fast, but at 18000 feet atmospheric pressure is
reduced only by 50%. 12000 feet is probably a 10 psia atmosphere, and
I don't think there will be much outgassing with a difference of 5
psi, even if we went up fast (Mooneys are nice, but their climb time
to altitude is not remarkable!) I think for divers that would be like
coming up suddenly from maybe 10 feet down.

As is clear in this group, different people flight plan differently.
We choose high. There are less likely to be undisciplined pilots, or
those flying under VFR, at 10,000 or 12,000 than at 3000.

I think we're close to a stoichiometric mixture at peak egt for a
given rpm, but finding a way of stuffing more O2 into the cylinders
would be nice during a climb to altitude. Never the less the back of
the envelope number crunching I did and others have commented on
pretty much convinced me to let engine optimization to those who know
what they are doing. I will not be connecting the exhaust of a shop
vac to the intake manifold any time soon!

And to be honest I did not use the back of an envelope, but a cell in
an Excel spreadsheet being used for a different kind of data
analysis. Which reminds me, I had better delete it before I pass that
analysis around.

me Ken S. Tucker" wrote:

Tina, I think this analysis you posted is good,
" It's only a 360 cubic inch engine turning at 2300 RPM or so. Isn't
that a demand of, let's see, at 23 inches mp at sea level that's
23/30 * 2300/2 * 360 / 12^3 or 180 cubic feet a minute? "

Can't do it that way. You're assuming a volumetric efficiency
of 100% which we never attain without considerable boosting. The
volumetric efficiency at full throttle and redline RPM at sea level
isn't likely to be much more than 50 or 60%.
Got to do it using fuel flow. Best power mixture comes at
around 12:1 (pounds of air to pounds of fuel) and stoichiometric
mixture (no wasted air or fuel) is 15:1. Weight of air at sea level is
about .078 pounds per cubic foot, and weight of gasoline is 6 lb per
US gallon.
An O-320 @ 2700 RPM @ S.L. = Displacement of 15,000 cubic feet
per hour.
Full throttle fuel flow of 10.3 GPH @ 12:1 best power = 9434
cu. ft./hr (with fixed-pitch prop).
9434 ÷ 15,000 = .629 (62.9%) volumetric efficiency @ sea
level.

Not very good, is it? Air has viscosity and the drag of the
entire induction system, even with the throttle wide open, is
significant. Add to that the inertia of the air, and the intake
valve's opening and closing causing the stop-go action of the air in
the system, and things get slowed down considerably.
It's worse in auto engines that turn at high RPM. That's why
many have four valves per cylinder, or turbos, or both.

Dan

On Jun 2, 9:28*am, Bertie the Bunyip wrote:
"Maxwell" luv2^fly99@cox.^net wrote in news:jTR0k.192$js1.25
@newsfe24.lga:









"Bertie the Bunyip" wrote in message
.. .
"Maxwell" luv2^fly99@cox.^net wrote in
:

"Bertie the Bunyip" wrote in message
...
Didn't know any production aircraft had that. Well, to some extent
almost every lightplane does . that's why the carb air intake faces
forwards in most of them.Everything is a balancing act with an
airplane. More air = more drag. You could try putting a couple of
woks with tubes out the back to boost your MP, but you're going to
pay for it. !Moooney must have spotted an area of the cowl that
would
not penalise you in this way and decided to utilise it. Really
clever
homebuilders do a lot of this kind of stuff as well as, and
probably
more more importantly, dealing with cooling drag.
Have you put the other speed mods on your airplane? I think there's
nearly ten knots available in seals and various other tidy it up
fairings.

Bertie

Dumb ass.

Its because the size of the scoop increases volume (not pressure),
and
you already have too much.

Nope.

Bertie

How would you know, dumb ass?

I know everything, obviously.

Bertie- Hide quoted text -

- Show quoted text -

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.

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.

On Jun 3, 6:38*am, Billy Crabs wrote:
On Jun 2, 9:28*am, Bertie the Bunyip wrote:





"Maxwell" luv2^fly99@cox.^net wrote in news:jTR0k.192$js1.25
@newsfe24.lga:

"Bertie the Bunyip" wrote in message
.. .
"Maxwell" luv2^fly99@cox.^net wrote in
:

"Bertie the Bunyip" wrote in message
...
Didn't know any production aircraft had that. Well, to some extent
almost every lightplane does . that's why the carb air intake faces
forwards in most of them.Everything is a balancing act with an
airplane. More air = more drag. You could try putting a couple of
woks with tubes out the back to boost your MP, but you're going to
pay for it. !Moooney must have spotted an area of the cowl that
would
not penalise you in this way and decided to utilise it. Really
clever
homebuilders do a lot of this kind of stuff as well as, and
probably
more more importantly, dealing with cooling drag.
Have you put the other speed mods on your airplane? I think there's
nearly ten knots available in seals and various other tidy it up
fairings.

Bertie

Dumb ass.

Its because the size of the scoop increases volume (not pressure),
and
you already have too much.

Nope.

Bertie

How would you know, dumb ass?

I know everything, obviously.

Bertie- Hide quoted text -

- Show quoted text -

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.- Hide quoted text -

I would think the air getting to the cyclinder faster is important,
given the little time available for the intake to occur. If you
analyse the take off performance data of C172 ( which I have) you can
see quite clearly that for the same air density, better performance
( ie shorter take off distance) is obtained at higher temperatures
( which of course means higher pressure). I , and others, interpret
this as the higher pressure providing a stronger driving force to fill
the cylinder quicker.
Terry
PPL Downunder

On Jun 2, 3:30 pm, terry wrote:
On Jun 3, 6:38 am, Billy Crabs wrote:

On Jun 2, 9:28 am, Bertie the Bunyip wrote:

"Maxwell" luv2^fly99@cox.^net wrote in news:jTR0k.192$js1.25
@newsfe24.lga:

"Bertie the Bunyip" wrote in message
.. .
"Maxwell" luv2^fly99@cox.^net wrote in
:

"Bertie the Bunyip" wrote in message
...
Didn't know any production aircraft had that. Well, to some extent
almost every lightplane does . that's why the carb air intake faces
forwards in most of them.Everything is a balancing act with an
airplane. More air = more drag. You could try putting a couple of
woks with tubes out the back to boost your MP, but you're going to
pay for it. !Moooney must have spotted an area of the cowl that
would
not penalise you in this way and decided to utilise it. Really
clever
homebuilders do a lot of this kind of stuff as well as, and
probably
more more importantly, dealing with cooling drag.
Have you put the other speed mods on your airplane? I think there's
nearly ten knots available in seals and various other tidy it up
fairings.

Bertie

Dumb ass.

Its because the size of the scoop increases volume (not pressure),
and
you already have too much.

Nope.

Bertie

How would you know, dumb ass?

I know everything, obviously.

Bertie- Hide quoted text -

- Show quoted text -

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.- Hide quoted text -

I would think the air getting to the cyclinder faster is important,
given the little time available for the intake to occur. If you
analyse the take off performance data of C172 ( which I have) you can
see quite clearly that for the same air density, better performance
( ie shorter take off distance) is obtained at higher temperatures
( which of course means higher pressure). I , and others, interpret
this as the higher pressure providing a stronger driving force to fill
the cylinder quicker.
Terry
PPL Downunder

Higher air temps mean a lower air viscosity, reducing
induction drag, and faster and more complete vaporization of the fuel.

Dan

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 hillstrom mhm15x4 zrbj
"i believe that the word "****head" has become so wide spread and
nearly meaningless as to qualify as a metavariable, similar to "foo"
and "bar". and that it should uphold the responsibilities and enjoy
the privileges of the new office. here here!!"
-dave hillstrom

On Jun 3, 9:11*am, wrote:
On Jun 2, 3:30 pm, terry wrote:





On Jun 3, 6:38 am, Billy Crabs wrote:

On Jun 2, 9:28 am, Bertie the Bunyip wrote:

"Maxwell" luv2^fly99@cox.^net wrote in news:jTR0k.192$js1.25
@newsfe24.lga:

"Bertie the Bunyip" wrote in message
.. .
"Maxwell" luv2^fly99@cox.^net wrote in
:

"Bertie the Bunyip" wrote in message
...
Didn't know any production aircraft had that. Well, to some extent
almost every lightplane does . that's why the carb air intake faces
forwards in most of them.Everything is a balancing act with an
airplane. More air = more drag. You could try putting a couple of
woks with tubes out the back to boost your MP, but you're going to
pay for it. !Moooney must have spotted an area of the cowl that
would
not penalise you in this way and decided to utilise it. Really
clever
homebuilders do a lot of this kind of stuff as well as, and
probably
more more importantly, dealing with cooling drag.
Have you put the other speed mods on your airplane? I think there's
nearly ten knots available in seals and various other tidy it up
fairings.

Bertie

Dumb ass.

Its because the size of the scoop increases volume (not pressure),
and
you already have too much.

Nope.

Bertie

How would you know, dumb ass?

I know everything, obviously.

Bertie- Hide quoted text -

- Show quoted text -

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.- Hide quoted text -

I would think the air getting to the cyclinder faster is important,
given the little time available for the intake to occur. * If you
analyse the take off performance data of C172 ( which I have) *you can
see quite clearly that for the same air density, better performance
( ie shorter take off distance) is obtained at higher temperatures
( which of course means higher pressure). I , and others, interpret
this as the higher pressure providing a stronger driving force to fill
the cylinder quicker.
Terry
PPL Downunder

* * * * * *Higher air temps mean a lower air viscosity, reducing
induction drag, and faster and more complete vaporization of the fuel.

I thought that also ( the viscosity bit) , but viscosity of air
actually increases with increasing temperature
http://www.engineeringtoolbox.com/ai...ity-d_601.html

the vaporization theory might hold though. I will look into that one.

Terry
PPL Downunder