Ram air

"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

On Jun 1, 3:35 am, Tina wrote:
The Mooney 201 has a ram air port, a half a foot under the prop
spinner. The POH tells us it can be opened at altitude for a very
modest increase in MP and we find maybe a half inch increase in
pressure. The idea of the thing is, if the port is looking right at
the air being thrust toward it by the prop (it can't be more than 6
inches or so behind it) as well as the air impact from the airplane's
motion the air being 'rammed' into it should effectively lower the
altitude the engine thinks it's at. Well, a half inch of Hg is about
500 feet or so. The question is, though, wouldn't you think there
would be a way to capture a great deal more of the ram air effect and
really boost the engine performance? Who wouldn't like to fly at 24
square at 12000 feet without a turbo charger?

What makes me wonder about it is, even at 60 mph holding your hand out
of the window of a car subjects it to a significant backward pressure,
so the energy must be there.

Good thinking, but physics prevails.
For example we just built a building with sides 10'x20',
http://www.flickr.com/photos/dynamics/
and the load computation of a wind at 60 mph is 1 ton
on a 200 sq ft surface, being a shear force on the
foundation, which is 10#/sq ft. That might sound like
alot but in terms of pressure per sq. inch it's,
Per sq. inch, divide 10# by 144 = lbs/ sq. inch,
~ .07# / sq. inch.
By comparision, sea level pressure is 15#/sq.inch,
which is convertible to Hg units.

Ramming air increases pressure with speed squared
so at 120 mph, pressure is 40#/sq. ft etc.
So at 420 mph, ram pressure is up to 3.5 #/sq in.
which is about a low as is practical, as in a V-1
buzz bomb.
Cheers
Ken

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.

I had better stick with my day job.








with some On Jun 1, 12:28 pm, "Ken S. Tucker"
wrote:
On Jun 1, 3:35 am, Tina wrote:



The Mooney 201 has a ram air port, a half a foot under the prop
spinner. The POH tells us it can be opened at altitude for a very
modest increase in MP and we find maybe a half inch increase in
pressure. The idea of the thing is, if the port is looking right at
the air being thrust toward it by the prop (it can't be more than 6
inches or so behind it) as well as the air impact from the airplane's
motion the air being 'rammed' into it should effectively lower the
altitude the engine thinks it's at. Well, a half inch of Hg is about
500 feet or so. The question is, though, wouldn't you think there
would be a way to capture a great deal more of the ram air effect and
really boost the engine performance? Who wouldn't like to fly at 24
square at 12000 feet without a turbo charger?

What makes me wonder about it is, even at 60 mph holding your hand out
of the window of a car subjects it to a significant backward pressure,
so the energy must be there.

Good thinking, but physics prevails.
For example we just built a building with sides 10'x20',http://www.flickr.com/photos/dynamics/
and the load computation of a wind at 60 mph is 1 ton
on a 200 sq ft surface, being a shear force on the
foundation, which is 10#/sq ft. That might sound like
alot but in terms of pressure per sq. inch it's,
Per sq. inch, divide 10# by 144 = lbs/ sq. inch,
~ .07# / sq. inch.
By comparision, sea level pressure is 15#/sq.inch,
which is convertible to Hg units.

Ramming air increases pressure with speed squared
so at 120 mph, pressure is 40#/sq. ft etc.
So at 420 mph, ram pressure is up to 3.5 #/sq in.
which is about a low as is practical, as in a V-1
buzz bomb.
Cheers
Ken

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

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.

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

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

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 1, 3:35*am, Tina wrote:
The Mooney 201 has a ram air port, a half a foot under the prop
spinner. The POH tells us it can be opened at altitude for a very
modest increase in MP and we find maybe a half inch increase in
pressure. The idea of the thing is, if the port is looking right at
the air being thrust toward it by the prop (it can't be more than 6
inches or so behind it) *as well as the air impact from the airplane's
motion the air being 'rammed' into it should effectively lower the
altitude the engine thinks it's at. Well, a half inch of Hg is about
500 feet or so. The question is, though, wouldn't you think there
would be a way to capture a great deal more of the ram air effect and
really boost the engine performance? Who wouldn't like to fly at 24
square at 12000 feet without a turbo charger?

Its really to make up for a design flaw in the induction system. Most
induction systems don't have the resistance of a Mooney. By the 201
Mooney had mostly fixed this so the ram air makes no noticable
difference in the MP. On the pre-201's it adds 3/4 of a inch.

-Robert, Mooney CFII

On Jun 1, 4:35 am, Tina wrote:
The Mooney 201 has a ram air port, a half a foot under the prop
spinner. The POH tells us it can be opened at altitude for a very
modest increase in MP and we find maybe a half inch increase in
pressure. The idea of the thing is, if the port is looking right at
the air being thrust toward it by the prop (it can't be more than 6
inches or so behind it) as well as the air impact from the airplane's
motion the air being 'rammed' into it should effectively lower the
altitude the engine thinks it's at. Well, a half inch of Hg is about
500 feet or so. The question is, though, wouldn't you think there
would be a way to capture a great deal more of the ram air effect and
really boost the engine performance? Who wouldn't like to fly at 24
square at 12000 feet without a turbo charger?

What makes me wonder about it is, even at 60 mph holding your hand out
of the window of a car subjects it to a significant backward pressure,
so the energy must be there.

The energy is there but it's no bigger than what Mooney claims.
Flat-plate drag at 100 knots is 29 pounds; dicide that by 144 square
inches and get around 0.2 psi, or about 0.4" Hg. Not much. AT 200
knots it will be four times that, which still isn't a lot.
In the 1970's Ford sold some cars with "Ram-Air Induction"
systems. A scoop mounted on the carb that stuck out above the hood, to
ram vast volumes of air into the carb and get way more horsepower.
That's what they wanted you to believe. At 60 mph the pressure
recovery would have been laughably tiny, but Ford's profits were
impressive.
On airplanes like the Cessna singles, the air intake faces
forward but it doesn't get much ram advantage. The airflow striking
the cowling is deflected around it, which means that the airflow in
the vicinity of the intake is across that intake, not ramming directly
against it. Since Mr. Bernoulli told us that pressure drops with
velocity, the pressure at the face of the air filter is likely lower
than ambient. Homebuilders can tackle that to some degree and get some
improvements in manifold pressure, but those improvements will come
mostly as a result of airflow control, not ram recovery.
And a funnel, contrary to popular belief, does not increase
the pressure within it when facing the airflow. It increases velocity,
which must decrease pressure. It's a convergent duct. A divergent
duct, on the other hand, slows the airflow and increases pressure, and
we find such shapes on jet engine intake ducts, where the cross-
section increases just ahead of the fan or first compressor stage.
See http://www.aoxj32.dsl.pipex.com/NewF...TWPhysics.html
and http://www.thaitechnics.com/engine/e...struction.html


Dan