The Meredith Effect

In the supplements section of the online version of Air&Space Magazine
is an article entitled "The Meredith Effect". There are two parts to
the article, the first is a synopsis by F.W. Meredith, B.A. of his so
named cooling system design which came from his "Note on the cooling
of aircraft engines with special reference to ethylene glycol
radiators enclosed in ducts." The second is a commentary written by
Lee Atwood who was lead engineer for North American when they designed
the P-51 Mustang.

Atwood goes on at considerable length about how they managed to
utilize Meredith's design in the Mustang which was the major factor
that accounted for the Mustang's high speed, not the use of a laminar
flow airfoil.

The concept as outlined by Meredith, was that the air to cool the
engine should be directed to the radiator via a duct that expands at
the face of the radiator (which slows the velocity down and increases
pressure), then reduced behind it (which re accelerates the air). The
idea was to slow the air down such that it passed slowly enough
through the radiator to actually do some work (remove heat from the
fins), then be accelerated again to exit parallel to the slipstream.
Meredith calculated that the accelerated and heated air could be
speeded up such that it actually added to the thrust of the airplane
in addition to that provided by the propeller. In the case of the
Mustang, this jet of heated cooling air reduced cooling drag to almost
nothing. It did not eliminate it entirely, but it reduced it to the
point where cooling drag was merely "3% of the thrust of the
propeller."

The catch? Meredith's calculated effect got progressively more
powerful the faster the airplane went. In the Mustang, it's maximum
effect occured at around 400 mph and at high (above 20,000 feet)
altitude. These are speeds and altitudes which are out of reach of
almost all homebuilts.

The actual amount of thrust garnered by this system was and remains
extremely difficult to quantify because at the time there were no wind
tunnels big enough to hold the full scale airplane and accelerate the
wind in the tunnel to the necessary 400 mph at which the effect is
greatest.

Here's an intriguing addendum that never got utilized by North
American in the Mustang, or by any other fighters: Meredith wrote that
the jet effect would be greatly enhanced if the exhaust system could
be piped to discharge within the exhaust ductwork that carried the
heated air from the radiator. This is because any additional heat
would expand the air, increasing the velocity of the discharge and
therefore the thrust attained.

Atwood described this is being a quasi jet engine. However, the
problems of routing the exhaust back to the exit duct were considered
insurmountable and doing so was never seriously considered.

That was then, this is now. Routing the exhaust tubes into the
radiators exhaust duct is exactly what I am doing with my V6
installation in the Christavia Mk4.

With the radiator just in front of and at the bottom of the firewall,
there is room to bring the exhaust system in behind the radiator and
have it discharge facing out the exit duct. The idea is to have the
pipes terminate inside the duct so that the exhaust pulses not only
heat the air, they accelerate the air.

This does two things, 1. It accelerates the air through the ductwork.
2. It creates a negative pressure behind the radiator which sounds
like the same thing as 1, but really isn't. 3. It can produce
positive flow through the cooling ductwork even sitting on the ground
with tail to the wind. Ok, that's three things.

Do I expect this to waft me through the skys at 200 mph while burning
4 gallons per hour? No. You can't make a silk purse out of a sow's
ear. The Christavia will not cruise beyond 130 mph (if that) at any
engine setting below full throttle because it's a four seat fabric
covered STOL type. In addition, the less the power available (heat)
and the slower the speed, the less the effect.

What it will (should) do is make sure that the radiator/cooling system
functions properly by pulling the air through the system at all times.
The neat thing here is even during climb, when traditionally the
airspeed, and therefore air through the cooling system, is low and the
heat produced in the engine high, the air flow through the system
increases automatically because of the increased exhaust flow. More
power, more airflow, less power, less airflow.

At this point I'm just about finished with both headers. I have to
weld up the rightside flange that bolts the exhaust tubes to the
collectors so that I can unbolt the exhaust system and remove the
engine, then the exhaust system is finished and I can tighten
everything up, adjust the carburator float level and see how/if it
runs.

I have to make adjustments to the PSRU during the initial run to make
sure the belt is properly tensioned, then the prop goes on and I begin
a long series of engine runs during which I'll be keeping a record of
engine coolant temps, oil pressure, oil temp and coolant pressure.
The record will be available for the FAA once the airplane is ready
for it's inspection... sometime down the road.

Corky Scott

"Corky Scott" wrote in message
...
snip

At this point I'm just about finished with both headers. I have to
weld up the rightside flange that bolts the exhaust tubes to the
collectors so that I can unbolt the exhaust system and remove the
engine, then the exhaust system is finished and I can tighten
everything up, adjust the carburator float level and see how/if it
runs.

I have to make adjustments to the PSRU during the initial run to make
sure the belt is properly tensioned, then the prop goes on and I begin
a long series of engine runs during which I'll be keeping a record of
engine coolant temps, oil pressure, oil temp and coolant pressure.
The record will be available for the FAA once the airplane is ready
for it's inspection... sometime down the road.

Corky Scott

I look worward to hearing about how well it works. I hope you write a
follow up on it.

Tony

In article , Corky Scott says...

In the supplements section of the online version of Air&Space Magazine
is an article entitled "The Meredith Effect". There are two parts to
the article, the first is a synopsis by F.W. Meredith, B.A. of his so
named cooling system design which came from his "Note on the cooling
of aircraft engines with special reference to ethylene glycol
radiators enclosed in ducts." The second is a commentary written by
Lee Atwood who was lead engineer for North American when they designed
the P-51 Mustang.
MAJOR SNIP

Sounds very interesting be sure to keep us informed. I seem to remember that in
Hoeners book Fluid Dynamic Drag they did a study of the Me 109G and the thrust
from the exhaust added 140 lbs thrust .So I would think your on the right track.
I would think that somewhere there is probably some paper on the
prediction of exhaust thrust as a function of hp .Don't know for sure but it
wouldn't surprise me. Good luck.

See ya

Chuck S

Hey Corky,

Forget about the engine, just add a large pipe to your mouth and jet that
out the back of the aircraft. There's so much hot air coming out, you
should break the sound barrier. The amount of thrust created by this affect
will be negligible at best. Get out your thermodynamics book and see for
yourself.

Stan Kapushinski



"Corky Scott" wrote in message
...
In the supplements section of the online version of Air&Space Magazine
is an article entitled "The Meredith Effect". There are two parts to
the article, the first is a synopsis by F.W. Meredith, B.A. of his so
named cooling system design which came from his "Note on the cooling
of aircraft engines with special reference to ethylene glycol
radiators enclosed in ducts." The second is a commentary written by
Lee Atwood who was lead engineer for North American when they designed
the P-51 Mustang.

Atwood goes on at considerable length about how they managed to
utilize Meredith's design in the Mustang which was the major factor
that accounted for the Mustang's high speed, not the use of a laminar
flow airfoil.

The concept as outlined by Meredith, was that the air to cool the
engine should be directed to the radiator via a duct that expands at
the face of the radiator (which slows the velocity down and increases
pressure), then reduced behind it (which re accelerates the air). The
idea was to slow the air down such that it passed slowly enough
through the radiator to actually do some work (remove heat from the
fins), then be accelerated again to exit parallel to the slipstream.
Meredith calculated that the accelerated and heated air could be
speeded up such that it actually added to the thrust of the airplane
in addition to that provided by the propeller. In the case of the
Mustang, this jet of heated cooling air reduced cooling drag to almost
nothing. It did not eliminate it entirely, but it reduced it to the
point where cooling drag was merely "3% of the thrust of the
propeller."

The catch? Meredith's calculated effect got progressively more
powerful the faster the airplane went. In the Mustang, it's maximum
effect occured at around 400 mph and at high (above 20,000 feet)
altitude. These are speeds and altitudes which are out of reach of
almost all homebuilts.

The actual amount of thrust garnered by this system was and remains
extremely difficult to quantify because at the time there were no wind
tunnels big enough to hold the full scale airplane and accelerate the
wind in the tunnel to the necessary 400 mph at which the effect is
greatest.

Here's an intriguing addendum that never got utilized by North
American in the Mustang, or by any other fighters: Meredith wrote that
the jet effect would be greatly enhanced if the exhaust system could
be piped to discharge within the exhaust ductwork that carried the
heated air from the radiator. This is because any additional heat
would expand the air, increasing the velocity of the discharge and
therefore the thrust attained.

Atwood described this is being a quasi jet engine. However, the
problems of routing the exhaust back to the exit duct were considered
insurmountable and doing so was never seriously considered.

That was then, this is now. Routing the exhaust tubes into the
radiators exhaust duct is exactly what I am doing with my V6
installation in the Christavia Mk4.

With the radiator just in front of and at the bottom of the firewall,
there is room to bring the exhaust system in behind the radiator and
have it discharge facing out the exit duct. The idea is to have the
pipes terminate inside the duct so that the exhaust pulses not only
heat the air, they accelerate the air.

This does two things, 1. It accelerates the air through the ductwork.
2. It creates a negative pressure behind the radiator which sounds
like the same thing as 1, but really isn't. 3. It can produce
positive flow through the cooling ductwork even sitting on the ground
with tail to the wind. Ok, that's three things.

Do I expect this to waft me through the skys at 200 mph while burning
4 gallons per hour? No. You can't make a silk purse out of a sow's
ear. The Christavia will not cruise beyond 130 mph (if that) at any
engine setting below full throttle because it's a four seat fabric
covered STOL type. In addition, the less the power available (heat)
and the slower the speed, the less the effect.

What it will (should) do is make sure that the radiator/cooling system
functions properly by pulling the air through the system at all times.
The neat thing here is even during climb, when traditionally the
airspeed, and therefore air through the cooling system, is low and the
heat produced in the engine high, the air flow through the system
increases automatically because of the increased exhaust flow. More
power, more airflow, less power, less airflow.

At this point I'm just about finished with both headers. I have to
weld up the rightside flange that bolts the exhaust tubes to the
collectors so that I can unbolt the exhaust system and remove the
engine, then the exhaust system is finished and I can tighten
everything up, adjust the carburator float level and see how/if it
runs.

I have to make adjustments to the PSRU during the initial run to make
sure the belt is properly tensioned, then the prop goes on and I begin
a long series of engine runs during which I'll be keeping a record of
engine coolant temps, oil pressure, oil temp and coolant pressure.
The record will be available for the FAA once the airplane is ready
for it's inspection... sometime down the road.

Corky Scott

Well gee stan
Think thats wahat he said, and he prefaced it with "should".
Little harsh doncha think ?
all the best
Sean Trost

Stan Kap wrote:
Hey Corky,

Forget about the engine, just add a large pipe to your mouth and jet that
out the back of the aircraft. There's so much hot air coming out, you
should break the sound barrier. The amount of thrust created by this affect
will be negligible at best. Get out your thermodynamics book and see for
yourself.

Stan Kapushinski



"Corky Scott" wrote in message
...

In the supplements section of the online version of Air&Space Magazine
is an article entitled "The Meredith Effect". There are two parts to
the article, the first is a synopsis by F.W. Meredith, B.A. of his so
named cooling system design which came from his "Note on the cooling
of aircraft engines with special reference to ethylene glycol
radiators enclosed in ducts." The second is a commentary written by
Lee Atwood who was lead engineer for North American when they designed
the P-51 Mustang.

Atwood goes on at considerable length about how they managed to
utilize Meredith's design in the Mustang which was the major factor
that accounted for the Mustang's high speed, not the use of a laminar
flow airfoil.

The concept as outlined by Meredith, was that the air to cool the
engine should be directed to the radiator via a duct that expands at
the face of the radiator (which slows the velocity down and increases
pressure), then reduced behind it (which re accelerates the air). The
idea was to slow the air down such that it passed slowly enough
through the radiator to actually do some work (remove heat from the
fins), then be accelerated again to exit parallel to the slipstream.
Meredith calculated that the accelerated and heated air could be
speeded up such that it actually added to the thrust of the airplane
in addition to that provided by the propeller. In the case of the
Mustang, this jet of heated cooling air reduced cooling drag to almost
nothing. It did not eliminate it entirely, but it reduced it to the
point where cooling drag was merely "3% of the thrust of the
propeller."

The catch? Meredith's calculated effect got progressively more
powerful the faster the airplane went. In the Mustang, it's maximum
effect occured at around 400 mph and at high (above 20,000 feet)
altitude. These are speeds and altitudes which are out of reach of
almost all homebuilts.

The actual amount of thrust garnered by this system was and remains
extremely difficult to quantify because at the time there were no wind
tunnels big enough to hold the full scale airplane and accelerate the
wind in the tunnel to the necessary 400 mph at which the effect is
greatest.

Here's an intriguing addendum that never got utilized by North
American in the Mustang, or by any other fighters: Meredith wrote that
the jet effect would be greatly enhanced if the exhaust system could
be piped to discharge within the exhaust ductwork that carried the
heated air from the radiator. This is because any additional heat
would expand the air, increasing the velocity of the discharge and
therefore the thrust attained.

Atwood described this is being a quasi jet engine. However, the
problems of routing the exhaust back to the exit duct were considered
insurmountable and doing so was never seriously considered.

That was then, this is now. Routing the exhaust tubes into the
radiators exhaust duct is exactly what I am doing with my V6
installation in the Christavia Mk4.

With the radiator just in front of and at the bottom of the firewall,
there is room to bring the exhaust system in behind the radiator and
have it discharge facing out the exit duct. The idea is to have the
pipes terminate inside the duct so that the exhaust pulses not only
heat the air, they accelerate the air.

This does two things, 1. It accelerates the air through the ductwork.
2. It creates a negative pressure behind the radiator which sounds
like the same thing as 1, but really isn't. 3. It can produce
positive flow through the cooling ductwork even sitting on the ground
with tail to the wind. Ok, that's three things.

Do I expect this to waft me through the skys at 200 mph while burning
4 gallons per hour? No. You can't make a silk purse out of a sow's
ear. The Christavia will not cruise beyond 130 mph (if that) at any
engine setting below full throttle because it's a four seat fabric
covered STOL type. In addition, the less the power available (heat)
and the slower the speed, the less the effect.

What it will (should) do is make sure that the radiator/cooling system
functions properly by pulling the air through the system at all times.
The neat thing here is even during climb, when traditionally the
airspeed, and therefore air through the cooling system, is low and the
heat produced in the engine high, the air flow through the system
increases automatically because of the increased exhaust flow. More
power, more airflow, less power, less airflow.

At this point I'm just about finished with both headers. I have to
weld up the rightside flange that bolts the exhaust tubes to the
collectors so that I can unbolt the exhaust system and remove the
engine, then the exhaust system is finished and I can tighten
everything up, adjust the carburator float level and see how/if it
runs.

I have to make adjustments to the PSRU during the initial run to make
sure the belt is properly tensioned, then the prop goes on and I begin
a long series of engine runs during which I'll be keeping a record of
engine coolant temps, oil pressure, oil temp and coolant pressure.
The record will be available for the FAA once the airplane is ready
for it's inspection... sometime down the road.

Corky Scott

On Tue, 31 Aug 2004 22:32:29 -0400, "Stan Kap"
wrote:

Hey Corky,

Forget about the engine, just add a large pipe to your mouth and jet that
out the back of the aircraft. There's so much hot air coming out, you
should break the sound barrier. The amount of thrust created by this affect
will be negligible at best. Get out your thermodynamics book and see for
yourself.

At least Corky's airplane amounts to more than pretty pictures.


================================================== ==
Del Rawlins--
Unofficial Bearhawk FAQ website:
http://www.rawlinsbrothers.org/bhfaq/
Remove _kills_spammers_ to reply

Let's see .001 hp added instead of 25 hp loss sounds good
It might not give you any additional 'thrust' but if it reduces the drag the
net affect could be the same.
Let us know how it works out
And oh yeah Stan take a chill pill ;-)
John



Stan Kap wrote:

Hey Corky,

Forget about the engine, just add a large pipe to your mouth and jet that
out the back of the aircraft. There's so much hot air coming out, you
should break the sound barrier. The amount of thrust created by this
affect will be negligible at best. Get out your thermodynamics book and
see for yourself.

Stan Kapushinski

In article , Stan Kap says...

Hey Corky,

Forget about the engine, just add a large pipe to your mouth and jet that
out the back of the aircraft. There's so much hot air coming out, you
should break the sound barrier. The amount of thrust created by this affect
will be negligible at best. Get out your thermodynamics book and see for
yourself.

Gee Stan that was a bit harsh I thought Corkys plan was food for a good
conversation. Would have been more interesting if you explained why you think it
wouldn't work rather than a snippy remark. Just a little constructive
criticism not a bash.

See ya

Chuck S

On Tue, 31 Aug 2004 22:32:29 -0400, "Stan Kap"
wrote:

Hey Corky,

Forget about the engine, just add a large pipe to your mouth and jet that
out the back of the aircraft. There's so much hot air coming out, you
should break the sound barrier. The amount of thrust created by this affect
will be negligible at best. Get out your thermodynamics book and see for
yourself.

Stan Kapushinski

Stan, I know that the thrust from such a setup will be negligable, I
said as much below.

Do I expect this to waft me through the skys at 200 mph while burning
4 gallons per hour? No. You can't make a silk purse out of a sow's
ear. The Christavia will not cruise beyond 130 mph (if that) at any
engine setting below full throttle because it's a four seat fabric
covered STOL type. In addition, the less the power available (heat)
and the slower the speed, the less the effect.

In addition I wrote:

The catch? Meredith's calculated effect got progressively more
powerful the faster the airplane went. In the Mustang, it's maximum
effect occured at around 400 mph and at high (above 20,000 feet)
altitude. These are speeds and altitudes which are out of reach of
almost all homebuilts.

Did you read this?

What I expect I will get from this setup is augmented cooling by use
of the exhaust system. There will be a minor thrust affect, but I'm
not counting on that to boost the cruise or top end. The important
thing to me is adaquate cooling under all conditions. Using exhaust
augmentation is one way, but not the only way, to achieve that.

Are you ok?

Corky Scott

Corky Scott

On Tue, 31 Aug 2004 22:32:29 -0400, "Stan Kap"
wrote:

Hey Corky,

Forget about the engine, just add a large pipe to your mouth and jet that
out the back of the aircraft. There's so much hot air coming out, you
should break the sound barrier. The amount of thrust created by this affect
will be negligible at best. Get out your thermodynamics book and see for
yourself.

The augmenting effect of exhaust has been used for years in
aircooled engine installations like the Cessna 310. The exhaust
velocity is used to create a lower pressure in the cooling air
outflow. Even if he doesn't gain much thrust his cooling should
improve considerably, and less cooling drag translates into more net
thrust. If the P-51 guys thought it might work, it's worth fooling
with.
The only concern I might have would be the pulsation effect on the
radiator core. It might cause fatigue and failure after some time in
service. Even with the exhaust discharge downstream of the radiator,
the outflow may rumble enough to damage the rad.


Dan