Ram air

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.

On Jun 1, 8:35*pm, 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.

An interesting question. I will have a stab at it but its just an
intuitive guess. Thrust is created by the prop pushing the air
backwards. If you are trying to capture that air into the engine,
there must be some resistance and therefore if you restrict the
ability of the air to be pushed away the thrust would be reduced. So
it must be a balance between not reducing the thrust and getting more
air into the engine to generate more power. I am also guessing that
for the ram air to be of much use it would probably be bypassing the
airfilter, which is potentially not good for the engine. although at
high altitude it is probably Ok, except perhaps for ice formation if
there was a lot of moisture in the air?

Isnt a Mooney fast enough for you Tina?
Terry

Tina wrote in news:f9933f5e-0c1d-464b-a1d8-
:

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.



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

The m20J is pretty slippery already and when it was introduced in the
70s was a big step up in efficiency in a production airplane.
Homebuilts do do an even better job of cleaning up aerodynamically.

The little seals on the flaps and so on were lipstick, the real gain
over the Mooney Executive had to do with the 201 getting a more
aerodynamic windscreen and engine cowling.

We have no serious complaints at all about the airplane (well, in a
rainstorm getting in without getting the seat wet is difficult,
checking the fuel is hard on pantyhose sometimes) but finding a couple
more inches of manifold pressure would be very handy when trying to
get to 12000 feet quickly. Once there, we can sip 8 gallons an hour
and move along pretty well.

I think using ram air would not increase aerodynamic drag, B. Instead
of having the air moving at the airplane's airspeed plus prop induced
speed impacting the cowling, it could in fact be going into a hole.
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 better leave that to the engineers.




On Jun 1, 7:57 am, Bertie the Bunyip wrote:
Tina wrote in news:f9933f5e-0c1d-464b-a1d8-
:



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.

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

"Tina" wrote in message ...
The m20J is pretty slippery already and when it was introduced in the
70s was a big step up in efficiency in a production airplane.
Homebuilts do do an even better job of cleaning up aerodynamically.

The little seals on the flaps and so on were lipstick, the real gain
over the Mooney Executive had to do with the 201 getting a more
aerodynamic windscreen and engine cowling.

We have no serious complaints at all about the airplane (well, in a
rainstorm getting in without getting the seat wet is difficult,
checking the fuel is hard on pantyhose sometimes) but finding a couple
more inches of manifold pressure would be very handy when trying to
get to 12000 feet quickly. Once there, we can sip 8 gallons an hour
and move along pretty well.

I think using ram air would not increase aerodynamic drag, B. Instead
of having the air moving at the airplane's airspeed plus prop induced
speed impacting the cowling, it could in fact be going into a hole.
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 better leave that to the engineers.




Yes, you are sucking it up as you are trying to push it in, the air that is, and the free airstream is not a very good
'pump'. A turbo with its sealed compressor is much better because once the air is captured it really has a hard time
flowing out backwards.

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, 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

On Jun 1, 11:48 am, wrote:
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.

That was the good old days!
A jig saw and some sheet metal BLASTED your 427 cube
inch engine to over 600 hp!!!, and at 400-500 mph, you'd be
economizing on fuel to boot!.
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