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XyZspineZyX
11-04-2003, 05:01 AM
MUSTANG

Commentary by Lee Atwood.


What made the P-51 Mustang the fastest fighter of World War II (before the German jet came along)? The answer depends on whom you ask. The editors at Air & Space/Smithsonian asked the late Lee Atwood, vice president at North American Aviation when the fighter was born, and the question started an interesting correspondence. Atwood's explanation of what gave the Mustang the edge over the Spitfire and Curtiss P-40 was the design of its cooling system, especially the radiator duct's variable exit.
In an address to the Yorkshire Air Museum in June 1998, Atwood described the effect of the design on the Mustang's performance. An excerpt from his speech follows, along with drawings he made to illustrate his point to the editors.

In 1940 we had a young, energetic, and first-class engineering department with competence in aerodynamics, structures, materials, and thermal technologies as developed up to that time, and the factory had a nucleus of expert machine shop, tooling, and production personnel. We gave the Mustang design credit to Edgar Schmued who led the design room effort and brought the components together under the direction of Raymond Rice, who succeeded me as a chief engineer, and the technical specialists.

All these and many others contributed significantly to the project, including Colonel, now General (Retired), Mark E. Bradley who directed the installation of the 85-gallon fuselage tank. He then demonstrated that the longitudinal instability created by this weight behind the pilot could be managed by the combat pilots, and the effective endurance could be increased by some two hours.

In considering the speed performance of the Mustang, which is really its primary advantage and distinction, it is necessary to adjust one's thinking and point of reference to a rather early period in the science of aerodynamics. In the 1930s, there was no jet propulsion, and by any measure of comparison, the technical resources, personnel employed, test equipment and financial expenditures were really insignificant when compared to the aerospace establishment of today. Of course, the basics were there--which involved derivations of Newton's laws and Bernoulli's hydraulic principles--and aero sciences had been basically defined by Prandl, von Karman, and many other mathematical and scientific authorities, but applications to actual aircraft were relatively crude and empirical. Wind tunnel models were the primary proving element in design, and there were still many elements of such testing that had to be estimated or extrapolated with opinion and hope.

In these circumstances it is not very surprising that, among these early practitioners of aeronautical engineering, there were discontinuities of information and differences of opinion on various fine points in the application of general aerodynamic science, as then known, to actual airplane design. This was most apparent in one of the critical aspects of airplane design during the period of reciprocating engines and propeller-driven airplanes. The liquid-cooled designs favored in England and Germany--and also used in the United States and other countries--were generally considered of lower drag because of their in-line cylinder configuration. Air-cooled engines were generally of radial design, with all cylinders facing the cooling air stream, and the diameter was considerably larger.

The well-known radiator became the automobile standard early on, and everyone in the pre-war era had various experiences with these installations and their belt-driven fans. The common experience usually involved adequate cooling at cruising speeds, with frequent over-heating on mountain grades or slow traffic, and the fans were not always adequate to control the temperature. Generally, most people had an occasional bad experience with an overheated engine.

Airplane radiators had a lot of the same troubles, and while separate cooling fans were not seriously considered, ground cooling from propeller circulation alone was frequently inadequate. Basically, the radiators were designed to cool the engines at full power in a climb--which was usually something like half the maximum possible level flight speed with the same power--so at high speed, the cooling capacity was much more than needed.

Now it is clear that we were then quite sure that, as in an automobile, there was no reasonable dynamic use for the warm air discharged from a radiator, and a low and medium speeds, up to say 200 miles per hour, that was quite true. The temperature rise was small, and the expansion was correspondingly modest, and heat energy recovery was insignificant.

However, as engine power increased and better aerodynamic shapes were developed in monoplane designs, we were all slow to realize that, with a normally ducted radiator at high speed, we had at our disposal a really remarkable air pump.

This air pump, like all pumps, had three elements--a compressor stage, a metering or valving stage (radiator core), and a discharge function through an air outlet. This began to be a considerable pumping action as speeds approached 300 miles per hour--and at 400 miles per hour, it had a large potential and could be a considerable fraction of the airplane's total power equation, since the pumping pressure increases as the square of the speed. To make this automatic pump effective, only one thing was required, and that was to choke the outlet enough to keep the pressurized airflow through the radiator just adequate for cooling and to discharge this compressed air at the highest speed possible.

This intuitively easy to follow and was also logical from a general streamlined design point of view--which all designers tried to follow as a matter of course. The potential magnitude of this effect was more difficult to appreciate, however, and since little or no data were available, these possibilities were overlooked in most cases.

In the case of the Mustang, the air duct pumping system at full speed at 25,000 feet was processing some 500 cubic feet of air per second, and discharge speed of the outlet was between 500 and 600 feet per second relative to the airplane. This air jet counteracted much of the radiator drag and had the effect of offsetting most of the total cooling drag. To offer some approximate numbers, the full power propeller thrust was about 1,000 pounds and the radiator drag (gross) was about 400 pounds, but the momentum recovery was some 350 pounds of compensating thrust--for a net cooling drag of only some 3% of the thrust of the propeller.

This air discharge had what can actually be called a regenerative effect. Maximum aircraft speed is the point where the line of power available, created in the engine and delivered by the propeller, crosses the line of power required to propel the plane through the air. Since the propelling force of the pressurized air from the radiator discharge increases as the square of the speed, we have the favorable situation where the faster you fly the more help you are getting from this regenerative air pumping system.

Since this high speed phenomenon could not be effectively measured by regular wind tunnel model test, it was viewed as ephemeral or even imaginary by many in the engineering practice. Actually, it is quite real and has a close relationship with jet propulsion.

Regarding the Mustang, I have always referred to the work of F. W. Meredith of the RAE, whose report (RAE No. 1683) of August 1935, greatly influenced me as chief engineer for North American Aviation to offer the British Purchasing Commission the ducted radiator design configuration in 1940. That report showed how the momentum loss in the cooling radiator could be largely restored when excess cooling air was being forced through the radiator at high speed. As noted before, this involved closing the air exit enough to get a substantial back pressure behind the radiator which largely restored the momentum loss--which was quite large as described above. This was possible, in Meredith's words, because the outlet was "adjusted to suit the speed,o and back pressure was available accordingly.

Here again, while Meredith's analysis was coherent and mathematically instructive, he failed to convey the practical aspects through an example or two, although he did offer a chart showing drag reduction for various discharge area ratios and conditions. The point I am making was that his work was generally in unfamiliar mathematical terms and was poorly understood. In fact, in two cases I know about, it was described in terms of mild ridicule. In any case, some if not most of the designs of wartime aircraft, including the Spitfire, failed to get the full advantage of this available air pump.

It should be pointed out here that the controversy and misunderstanding of the Meredith Effect on the performance of the Mustang developed largely because it was essentially impossible to get a reasonable measure of the effect from wind tunnel models at the time. The mass flow and momentum could not be accurately measured on a scale model, and no large tunnels were fast enough--200 to 400 miles per hour--to get meaningful results.

It has been reported that Messerschmitt made extensive efforts to determine the reason for the low drag of the Mustang, but his wind tunnel measurements did not disclose the restoration of momentum to the radiator cooling air, and most probably could not have done so with the wind tunnel equipment available at the time.

At this point I would like to interpolate what is , to me, a most fascinating element in Meredith's 1935 report. As you may have noted, I have made no reference to the thermal element in the momentum recovery of the radiator cooling air and at the temperatures involved, the air expansion was relatively small and could be neglected. Real jet propulsion, however, involves fuel burning, and the velocity of the gases and heated air is greatly augmented by this high temperature.

In his report, undoubtedly independent of Whittle's jet engine work, Meredith suggests piping the engine exhaust heat and gases to discharge behind the radiator to heat the discharged air just as burning fuel would do. This would have increased the volume and velocity of the discharged air at the same back pressure and increased the favorable thrust force.

Of course, the thrust of the short stack exhausts had been recognized by Sir Stanley ****** of Rolls-Royce in his book, NOT MUCH OF AN ENGINEER, and others, but Meredith's suggestion might have produced a much more powerful effect, but it involved complications and practical difficulties. As far as I can determine, it was never tried on any airplane.

This brings me to the Spitfire comparison, although that is probably a poor choice of words. That airplane was in a class by itself and at the top level of defense against the Luftwaffe in 1940, and was undoubtedly the most important defensive weapon in history. It was some 1,000 pounds lighter than the Mustang and was at the peak of interceptor efficiency and was essentially in classic conformity with the objectives of the RAF fighter command. It overmatched its opposition and was there when most needed.

In the cold illumination of hindsight, however, and probably for reasons I have outlined above, it missed the opportunity to restore much of the air flow momentum to the radiator cooling air and, with it, a possible speed increment of more than 20 miles per hour. The late Jeffrey Quill, Supermarine test pilot, describes the incorporation of the Meredith Effect in the Spitfire in his book, SPITFIRE, A TEST PILOT'S STORY, and that the radiators were enclosed in ducts under the wings. Here I would like to quote from an article "The Mustang Margin" I wrote for the AIR POWER HISTORY JOURNAL which involves some background and detail on the subject. It will, of course, be glad to try to answer any questions you may have at the end of my presentation.

"The most notable and probably the first application of the Meredith Effect was incorporated in the Supermarine Spitfire, one of the world's most successful airplanes. Over 20,000 were built in various models, but the Mark IX, with the Merlin -61 engine, was typical of the later wartime production, and a sketch of this model with detail of the radiator installation is shown. Two aspects of this design are significant. First, the radiator outlet has two positions--that is, fully open and partly closed--and cannot be progressively 'adjusted to suit the speed.' Second the inlet upper wall is a continuation of the lower surface of the wing and expands the duct cross section by rapidly curving upward.

"The first, the non-adjustable exit, of course, is a deviation from Meredith's dictum and precludes the progressive build-up of pressure behind the radiator with increasing speed. However, the second can only be judged in hindsight, from an airplane design point of view. The inlet seemed to be configured properly to recover the ram air pressure, and the first Mustang design had a similar entry opening. It was later apparent that the thin boundary layer of air flowing along the lower surface of the wing was progressively thickening ahead of the duct opening, and that the flow would break away at a point on the upward curve of the duct wall. While the resulting turbulent unsteady flow apparently did not create a serious vibration, it certainly reduced the efficiency of the radiator and prevented a more complete closure of the exit opening, which is necessary to develop the jet thrust. Very interestingly, the R.A.E. Subcommittee on Aerodynamics in 1936--in commenting on the Meredith and Capon reports--rather accurately predicted this problem: 'Experiments upon air-cooled engines in the 24-foot tunnel have shown that it is necessary to pay particular attention to the design of the entrance to cowlings and the cooling ducts in order to avoid loss of energy by the formation of eddies.' (Somewhat easier said than done at that time.)

"In the case of the Mustang, the duct volume was larger and flow instability more violent, creating an unacceptable vibration and rumble. Resourceful engineers at North American, working with wind tunnel models, overcame the problem by lowering the intake upper lip below the wing surface boundary layer, thus beginning a new upper duct surface. In this design, the flow expanded gradually as the duct velocity decreased, and the pressure at the radiator face was reasonably uniform. This permitted the appropriate closure of the exit with a temperature-controlled power actuator, and a minimum pressure drop across the radiator consistent with efficient radiator function and cooling demand.

"As a result, the cooling drag was estimated at only 3 percent of the total and used only something like 40 horsepower for cooling purposes. While the comparable power used for cooling by the Spitfire is not available to me, the measurements made by Rolls-Royce show a total power required for the same speed (400 mph) as 200 horsepower more for the Spitfire than for the Mustang.

"Records show the P-51D's speed was 437 mph and the Spitfire Mk IX speed was 405 mph. While the Spitfire had exposed tail wheel and other small differences from the Mustang, most of the speed difference was in the cooling drag. The Mark VIII with retracted tail wheel is rated at 414 mph at a somewhat higher altitude. Advanced models of both airplanes with higher performance were produced late in the war, but were not available in significant numbers before V-E Day, May 8, 1945.

"It seems that most other contemporary airplanes attempting to take advantage of the Meredith Effect failed for one reason or another to combine an efficient duct system with a properly designed and regulated exit-closing mechanism and did not develop the energy recovery inherent in the Meredith method. They generally used 10 percent or more of their power available at high speed to overcome cooling drag. A notable exception was the DeHavilland Mosquito multi-purpose plane with the same Rolls-Royce engines and which used a wing leading edge radiator mounting with a short and direct inlet duct. The controllable exit opening had a minimum area little more than half that of the Spitfire, and while it was a larger two-engine airplane, it had a speed of 425 mph.

"Since jet engines do not require cooling systems of the type described here, the subject has become moot and of little current importance. There was a time, however, when this rather insignificant subject made a critical difference."




Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 05:01 AM
MUSTANG

Commentary by Lee Atwood.


What made the P-51 Mustang the fastest fighter of World War II (before the German jet came along)? The answer depends on whom you ask. The editors at Air & Space/Smithsonian asked the late Lee Atwood, vice president at North American Aviation when the fighter was born, and the question started an interesting correspondence. Atwood's explanation of what gave the Mustang the edge over the Spitfire and Curtiss P-40 was the design of its cooling system, especially the radiator duct's variable exit.
In an address to the Yorkshire Air Museum in June 1998, Atwood described the effect of the design on the Mustang's performance. An excerpt from his speech follows, along with drawings he made to illustrate his point to the editors.

In 1940 we had a young, energetic, and first-class engineering department with competence in aerodynamics, structures, materials, and thermal technologies as developed up to that time, and the factory had a nucleus of expert machine shop, tooling, and production personnel. We gave the Mustang design credit to Edgar Schmued who led the design room effort and brought the components together under the direction of Raymond Rice, who succeeded me as a chief engineer, and the technical specialists.

All these and many others contributed significantly to the project, including Colonel, now General (Retired), Mark E. Bradley who directed the installation of the 85-gallon fuselage tank. He then demonstrated that the longitudinal instability created by this weight behind the pilot could be managed by the combat pilots, and the effective endurance could be increased by some two hours.

In considering the speed performance of the Mustang, which is really its primary advantage and distinction, it is necessary to adjust one's thinking and point of reference to a rather early period in the science of aerodynamics. In the 1930s, there was no jet propulsion, and by any measure of comparison, the technical resources, personnel employed, test equipment and financial expenditures were really insignificant when compared to the aerospace establishment of today. Of course, the basics were there--which involved derivations of Newton's laws and Bernoulli's hydraulic principles--and aero sciences had been basically defined by Prandl, von Karman, and many other mathematical and scientific authorities, but applications to actual aircraft were relatively crude and empirical. Wind tunnel models were the primary proving element in design, and there were still many elements of such testing that had to be estimated or extrapolated with opinion and hope.

In these circumstances it is not very surprising that, among these early practitioners of aeronautical engineering, there were discontinuities of information and differences of opinion on various fine points in the application of general aerodynamic science, as then known, to actual airplane design. This was most apparent in one of the critical aspects of airplane design during the period of reciprocating engines and propeller-driven airplanes. The liquid-cooled designs favored in England and Germany--and also used in the United States and other countries--were generally considered of lower drag because of their in-line cylinder configuration. Air-cooled engines were generally of radial design, with all cylinders facing the cooling air stream, and the diameter was considerably larger.

The well-known radiator became the automobile standard early on, and everyone in the pre-war era had various experiences with these installations and their belt-driven fans. The common experience usually involved adequate cooling at cruising speeds, with frequent over-heating on mountain grades or slow traffic, and the fans were not always adequate to control the temperature. Generally, most people had an occasional bad experience with an overheated engine.

Airplane radiators had a lot of the same troubles, and while separate cooling fans were not seriously considered, ground cooling from propeller circulation alone was frequently inadequate. Basically, the radiators were designed to cool the engines at full power in a climb--which was usually something like half the maximum possible level flight speed with the same power--so at high speed, the cooling capacity was much more than needed.

Now it is clear that we were then quite sure that, as in an automobile, there was no reasonable dynamic use for the warm air discharged from a radiator, and a low and medium speeds, up to say 200 miles per hour, that was quite true. The temperature rise was small, and the expansion was correspondingly modest, and heat energy recovery was insignificant.

However, as engine power increased and better aerodynamic shapes were developed in monoplane designs, we were all slow to realize that, with a normally ducted radiator at high speed, we had at our disposal a really remarkable air pump.

This air pump, like all pumps, had three elements--a compressor stage, a metering or valving stage (radiator core), and a discharge function through an air outlet. This began to be a considerable pumping action as speeds approached 300 miles per hour--and at 400 miles per hour, it had a large potential and could be a considerable fraction of the airplane's total power equation, since the pumping pressure increases as the square of the speed. To make this automatic pump effective, only one thing was required, and that was to choke the outlet enough to keep the pressurized airflow through the radiator just adequate for cooling and to discharge this compressed air at the highest speed possible.

This intuitively easy to follow and was also logical from a general streamlined design point of view--which all designers tried to follow as a matter of course. The potential magnitude of this effect was more difficult to appreciate, however, and since little or no data were available, these possibilities were overlooked in most cases.

In the case of the Mustang, the air duct pumping system at full speed at 25,000 feet was processing some 500 cubic feet of air per second, and discharge speed of the outlet was between 500 and 600 feet per second relative to the airplane. This air jet counteracted much of the radiator drag and had the effect of offsetting most of the total cooling drag. To offer some approximate numbers, the full power propeller thrust was about 1,000 pounds and the radiator drag (gross) was about 400 pounds, but the momentum recovery was some 350 pounds of compensating thrust--for a net cooling drag of only some 3% of the thrust of the propeller.

This air discharge had what can actually be called a regenerative effect. Maximum aircraft speed is the point where the line of power available, created in the engine and delivered by the propeller, crosses the line of power required to propel the plane through the air. Since the propelling force of the pressurized air from the radiator discharge increases as the square of the speed, we have the favorable situation where the faster you fly the more help you are getting from this regenerative air pumping system.

Since this high speed phenomenon could not be effectively measured by regular wind tunnel model test, it was viewed as ephemeral or even imaginary by many in the engineering practice. Actually, it is quite real and has a close relationship with jet propulsion.

Regarding the Mustang, I have always referred to the work of F. W. Meredith of the RAE, whose report (RAE No. 1683) of August 1935, greatly influenced me as chief engineer for North American Aviation to offer the British Purchasing Commission the ducted radiator design configuration in 1940. That report showed how the momentum loss in the cooling radiator could be largely restored when excess cooling air was being forced through the radiator at high speed. As noted before, this involved closing the air exit enough to get a substantial back pressure behind the radiator which largely restored the momentum loss--which was quite large as described above. This was possible, in Meredith's words, because the outlet was "adjusted to suit the speed,o and back pressure was available accordingly.

Here again, while Meredith's analysis was coherent and mathematically instructive, he failed to convey the practical aspects through an example or two, although he did offer a chart showing drag reduction for various discharge area ratios and conditions. The point I am making was that his work was generally in unfamiliar mathematical terms and was poorly understood. In fact, in two cases I know about, it was described in terms of mild ridicule. In any case, some if not most of the designs of wartime aircraft, including the Spitfire, failed to get the full advantage of this available air pump.

It should be pointed out here that the controversy and misunderstanding of the Meredith Effect on the performance of the Mustang developed largely because it was essentially impossible to get a reasonable measure of the effect from wind tunnel models at the time. The mass flow and momentum could not be accurately measured on a scale model, and no large tunnels were fast enough--200 to 400 miles per hour--to get meaningful results.

It has been reported that Messerschmitt made extensive efforts to determine the reason for the low drag of the Mustang, but his wind tunnel measurements did not disclose the restoration of momentum to the radiator cooling air, and most probably could not have done so with the wind tunnel equipment available at the time.

At this point I would like to interpolate what is , to me, a most fascinating element in Meredith's 1935 report. As you may have noted, I have made no reference to the thermal element in the momentum recovery of the radiator cooling air and at the temperatures involved, the air expansion was relatively small and could be neglected. Real jet propulsion, however, involves fuel burning, and the velocity of the gases and heated air is greatly augmented by this high temperature.

In his report, undoubtedly independent of Whittle's jet engine work, Meredith suggests piping the engine exhaust heat and gases to discharge behind the radiator to heat the discharged air just as burning fuel would do. This would have increased the volume and velocity of the discharged air at the same back pressure and increased the favorable thrust force.

Of course, the thrust of the short stack exhausts had been recognized by Sir Stanley ****** of Rolls-Royce in his book, NOT MUCH OF AN ENGINEER, and others, but Meredith's suggestion might have produced a much more powerful effect, but it involved complications and practical difficulties. As far as I can determine, it was never tried on any airplane.

This brings me to the Spitfire comparison, although that is probably a poor choice of words. That airplane was in a class by itself and at the top level of defense against the Luftwaffe in 1940, and was undoubtedly the most important defensive weapon in history. It was some 1,000 pounds lighter than the Mustang and was at the peak of interceptor efficiency and was essentially in classic conformity with the objectives of the RAF fighter command. It overmatched its opposition and was there when most needed.

In the cold illumination of hindsight, however, and probably for reasons I have outlined above, it missed the opportunity to restore much of the air flow momentum to the radiator cooling air and, with it, a possible speed increment of more than 20 miles per hour. The late Jeffrey Quill, Supermarine test pilot, describes the incorporation of the Meredith Effect in the Spitfire in his book, SPITFIRE, A TEST PILOT'S STORY, and that the radiators were enclosed in ducts under the wings. Here I would like to quote from an article "The Mustang Margin" I wrote for the AIR POWER HISTORY JOURNAL which involves some background and detail on the subject. It will, of course, be glad to try to answer any questions you may have at the end of my presentation.

"The most notable and probably the first application of the Meredith Effect was incorporated in the Supermarine Spitfire, one of the world's most successful airplanes. Over 20,000 were built in various models, but the Mark IX, with the Merlin -61 engine, was typical of the later wartime production, and a sketch of this model with detail of the radiator installation is shown. Two aspects of this design are significant. First, the radiator outlet has two positions--that is, fully open and partly closed--and cannot be progressively 'adjusted to suit the speed.' Second the inlet upper wall is a continuation of the lower surface of the wing and expands the duct cross section by rapidly curving upward.

"The first, the non-adjustable exit, of course, is a deviation from Meredith's dictum and precludes the progressive build-up of pressure behind the radiator with increasing speed. However, the second can only be judged in hindsight, from an airplane design point of view. The inlet seemed to be configured properly to recover the ram air pressure, and the first Mustang design had a similar entry opening. It was later apparent that the thin boundary layer of air flowing along the lower surface of the wing was progressively thickening ahead of the duct opening, and that the flow would break away at a point on the upward curve of the duct wall. While the resulting turbulent unsteady flow apparently did not create a serious vibration, it certainly reduced the efficiency of the radiator and prevented a more complete closure of the exit opening, which is necessary to develop the jet thrust. Very interestingly, the R.A.E. Subcommittee on Aerodynamics in 1936--in commenting on the Meredith and Capon reports--rather accurately predicted this problem: 'Experiments upon air-cooled engines in the 24-foot tunnel have shown that it is necessary to pay particular attention to the design of the entrance to cowlings and the cooling ducts in order to avoid loss of energy by the formation of eddies.' (Somewhat easier said than done at that time.)

"In the case of the Mustang, the duct volume was larger and flow instability more violent, creating an unacceptable vibration and rumble. Resourceful engineers at North American, working with wind tunnel models, overcame the problem by lowering the intake upper lip below the wing surface boundary layer, thus beginning a new upper duct surface. In this design, the flow expanded gradually as the duct velocity decreased, and the pressure at the radiator face was reasonably uniform. This permitted the appropriate closure of the exit with a temperature-controlled power actuator, and a minimum pressure drop across the radiator consistent with efficient radiator function and cooling demand.

"As a result, the cooling drag was estimated at only 3 percent of the total and used only something like 40 horsepower for cooling purposes. While the comparable power used for cooling by the Spitfire is not available to me, the measurements made by Rolls-Royce show a total power required for the same speed (400 mph) as 200 horsepower more for the Spitfire than for the Mustang.

"Records show the P-51D's speed was 437 mph and the Spitfire Mk IX speed was 405 mph. While the Spitfire had exposed tail wheel and other small differences from the Mustang, most of the speed difference was in the cooling drag. The Mark VIII with retracted tail wheel is rated at 414 mph at a somewhat higher altitude. Advanced models of both airplanes with higher performance were produced late in the war, but were not available in significant numbers before V-E Day, May 8, 1945.

"It seems that most other contemporary airplanes attempting to take advantage of the Meredith Effect failed for one reason or another to combine an efficient duct system with a properly designed and regulated exit-closing mechanism and did not develop the energy recovery inherent in the Meredith method. They generally used 10 percent or more of their power available at high speed to overcome cooling drag. A notable exception was the DeHavilland Mosquito multi-purpose plane with the same Rolls-Royce engines and which used a wing leading edge radiator mounting with a short and direct inlet duct. The controllable exit opening had a minimum area little more than half that of the Spitfire, and while it was a larger two-engine airplane, it had a speed of 425 mph.

"Since jet engines do not require cooling systems of the type described here, the subject has become moot and of little current importance. There was a time, however, when this rather insignificant subject made a critical difference."




Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 05:24 AM
Bet it won't be in there!

But I'm hoping too. /i/smilies/16x16_smiley-wink.gif





http://home.earthlink.net/~aclzkim1/sitebuildercontent/sitebuilderpictures/il2sig2.jpg

XyZspineZyX
11-04-2003, 05:48 AM
Could someone please summarize this, thanks/

No way I'm reading all that.

"The Force is strong with this one." -What an ace said of RayBanJockey during a fight when he was still a newbie.
<a href=http://www.theinformationminister.com/press.php?ID=612109283>news update</a>

XyZspineZyX
11-04-2003, 05:58 AM
RayBanJockey wrote:
- Could someone please summarize this, thanks/
-
- No way I'm reading all that.


Yes:

The Mustang's radiator was magic, woooooo. Magic, woooo.




Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:04 AM
Good read Chimp, I have read about the "thrust" effect before. Very good stuff. /i/smilies/16x16_smiley-happy.gif
~S!
Eagle
CO 361st vFG

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XyZspineZyX
11-04-2003, 06:05 AM
How does increasing drag cause "thrust"???

When the radiator is open, it is allowing more air into the whatever

Unless there is a turbine inside the P51 how the heck can it go faster?

It's like saying your car will go faster with the windows down.

"The Force is strong with this one." -What an ace said of RayBanJockey during a fight when he was still a newbie.
<a href=http://www.theinformationminister.com/press.php?ID=612109283>news update</a>

XyZspineZyX
11-04-2003, 06:09 AM
I posted this because I've noticed, as have others, that the Mustang achieves its top speed with the radiator exit flap closed. But in real life, to achieve this speed it was open to some degree (see my post in ORR).

This isn't a big deal since the top speed can still be achieved. It's more of a peculiarity. But with the radiator closed, the plane must surely overheat more quickly than if it were open.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:09 AM
What it's saying is that with the radiator closed, it's producing a given amount of drag, however with the outlet open, that drag *decreases*. So the end result is that it goes faster with the radiator open than it does closed. It's still producing drag, just not as much.

XyZspineZyX
11-04-2003, 06:09 AM
Good stuff kinda of like when one has excessive flatus.

Happy hunting and check six!

Tony Ascaso, RN

XyZspineZyX
11-04-2003, 06:12 AM
Yes instead of the air hitting a wall in the end of the radiator, with the door open it create's a blow through valve basically. This will add thrust, we are not talking about jet engine thrust, but a push not a pull.
~S!
Eagle
CO 361st vFG

<center>----------------------------------------------------------------------------</center> <center> www.361stvfg.com</center> (http://www.361stvfg.com</center>)
<center>
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XyZspineZyX
11-04-2003, 06:16 AM
I'd rather read before asking twice. /i/smilies/16x16_smiley-very-happy.gif

RayBanJockey wrote:
- How does increasing drag cause "thrust"???
-
- When the radiator is open, it is allowing more air
- into the whatever
-
- Unless there is a turbine inside the P51 how the
- heck can it go faster?
-
- It's like saying your car will go faster with the
- windows down.
-



-------------------------------------------------------------
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</font>

XyZspineZyX
11-04-2003, 06:16 AM
As of right now the P-51 doesnt over heat, the temp jumps to 125 after take off and stays there.

I've flown around in it for a while and still the engine never over heats even though it should.

<table border=0 width=300 cellspacing=1 cellpadding=5 bgcolor=#404040><tr><td bgcolor=#FFFFFF align=center><big><big><font color=#FF0000>ß P51D Mustang!</font></big></big></td></tr><tr><td align=left bgcolor=#FFFFFF>http://airwar.ru/image/i/fww2/p51d-i.jpg Ӛ¥¤ * â²¥, ⥤ â ª³?¥ Შé. Ӛ ¯ ¥¶ â ?² *¥ ª ¤¨: ¯ â* ¤â¨¦¥*¨¥ ÷¥²¥é ? ç¤ â¨²¥ â ¥¯¸¸ª³. Ӛç¦*, Ӛ ¸¨ ¥²¤ ¨ ª ¦³²¿ ª³-² ?µ ¨÷*¨, * ¯³²ü ²¨ á²³* * ÷ ¤áü²¿ ² ª¨µ ¦¥ ¯ª ç ²¥¥é ¯?¨ç⤨²¥ü*²¨.  ç* é²¥: ¥¨ Ӛ ¤* ¦¤ ¸¨á¸²¥ü, Ӛ ² *¥ ¯?²¿².</td></tr><tr><td align=center bgcolor=#002080><big><font color=#FFFFFF>* ªé â ¨²?¥á¨²¥ü WWII?</font></big> (http://www.aeterna.ru/cgi-bin/maina.cgi?page=test0&link=000000:000003:00017S:000002)</td></tr></table>

XyZspineZyX
11-04-2003, 06:18 AM
What DDT said.

There is an optimum point somewhere inbetween fully open and fully closed.

Atwood states that the radiators were designed to cool the engine druing full power climbs. But that the radiator provided more cooling than was needed in level high speed flight.

But that is not to say NO cooling is needed in level high speed flight; it most certainly is.

It's clear the flap was open to some degree in high speed flight. Atwood states it had to be closed "enough" to create a substantial beckpressure. ---ENOUGH---

But if it is closed fully, there is no cooling effect. Therefore, the flap had to have been open some to achieve top speed.

This is the issue I have. In real life, the Mustang achieved top speed with the flap partially open ("enough"). But in FB, if its opened any at all, speed is reduced.


I suspect that in a full power climb, you wopuld see the flap fully open to achieve greatest cooling effect. During warm up on the ground it is probably fully closed. In high speed flight, it is somewhere in between.





Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:21 AM
Visually, when the radiator is set to "closed" the door is still somewhat open.

--AKD

http://www.flyingpug.com/pugline2.jpg

XyZspineZyX
11-04-2003, 06:22 AM
Strange. I got many overheat message. /i/smilies/16x16_smiley-indifferent.gif
Don't just fly around. Try fight.

Dolemite- wrote:
- As of right now the P-51 doesnt over heat, the temp
- jumps to 125 after take off and stays there.
-
- I've flown around in it for a while and still the
- engine never over heats even though it should.
-
-



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XyZspineZyX
11-04-2003, 06:24 AM
As long as the FW190 A8 can outrun it below 6000m it won't be overmodeled

"The Force is strong with this one." -What an ace said of RayBanJockey during a fight when he was still a newbie.
<a href=http://www.theinformationminister.com/press.php?ID=612109283>news update</a>

XyZspineZyX
11-04-2003, 06:32 AM
I get A LOT of overheat messages.

Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:39 AM
chimp here is a good drawing for you . http://www.icon.co.za/~pauljnr/radsta.jpg


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U.S INFANTRY 1984-1991

Message Edited on 11/03/0310:48PM by tenmmike

XyZspineZyX
11-04-2003, 06:39 AM
Thanks for the info and heads-up Chimpy...don't let the Luft-whiners and Yak yakkers get ya down. /i/smilies/16x16_smiley-wink.gif

Cheers,
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XyZspineZyX
11-04-2003, 06:42 AM
Interesting stuff Chimp... but even then..all your ponies belong to us /i/smilies/16x16_smiley-very-happy.gif

V!

Regards,
VFC*Crazyivan
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XyZspineZyX
11-04-2003, 06:51 AM
This is a small issue. Believe me. I recognize that. Maybe I'm just too much of a stickler. In fact, since I can still achieve top speed, I wouldn't call it a problem. More of a peculiarity.

I wish the flap were modelled to be automatic. But I'm sure that it too much to ask.

I think I'll drop this. It's just too small of an issue to even fuss about.



Regards,

SkyChimp

http://members.cox.net/rowlandparks/sigstang.jpg

XyZspineZyX
11-04-2003, 06:53 AM
Firewalled the throttle for a long time still dont get any messages. And yes, its on full real.

<table border=0 width=300 cellspacing=1 cellpadding=5 bgcolor=#404040><tr><td bgcolor=#FFFFFF align=center><big><big><font color=#FF0000>ß P51D Mustang!</font></big></big></td></tr><tr><td align=left bgcolor=#FFFFFF>http://airwar.ru/image/i/fww2/p51d-i.jpg Ӛ¥¤ * â²¥, ⥤ â ª³?¥ Შé. Ӛ ¯ ¥¶ â ?² *¥ ª ¤¨: ¯ â* ¤â¨¦¥*¨¥ ÷¥²¥é ? ç¤ â¨²¥ â ¥¯¸¸ª³. Ӛç¦*, Ӛ ¸¨ ¥²¤ ¨ ª ¦³²¿ ª³-² ?µ ¨÷*¨, * ¯³²ü ²¨ á²³* * ÷ ¤áü²¿ ² ª¨µ ¦¥ ¯ª ç ²¥¥é ¯?¨ç⤨²¥ü*²¨.  ç* é²¥: ¥¨ Ӛ ¤* ¦¤ ¸¨á¸²¥ü, Ӛ ² *¥ ¯?²¿².</td></tr><tr><td align=center bgcolor=#002080><big><font color=#FFFFFF>* ªé â ¨²?¥á¨²¥ü WWII?</font></big> (http://www.aeterna.ru/cgi-bin/maina.cgi?page=test0&link=000000:000003:00017S:000002)</td></tr></table>

XyZspineZyX
11-04-2003, 06:58 AM
RayBanJockey wrote:
- How does increasing drag cause "thrust"???
-
- When the radiator is open, it is allowing more air
- into the whatever
-
- Unless there is a turbine inside the P51 how the
- heck can it go faster?
-
- It's like saying your car will go faster with the
- windows down.

Maybe if you would have read all of it you wouldnt have to ask or wonder.. It has to do with but sense you wont and you like summarys.. heat diferentials... Ta Dah! /i/smilies/16x16_smiley-wink.gif


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XyZspineZyX
11-04-2003, 07:11 AM
just a good pic of the ramphttp://www.aircraftresourcecenter.com/AWA1/101-200/walk107_P51D/part2_CDN_Mustang/images_Vern_Gwin/p51rearradramp.jpg


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U.S INFANTRY 1984-1991

XyZspineZyX
11-04-2003, 07:23 AM
That was a good read skychimp I was just talking about this the other day with some friends.It's one hell of a shame that the spitfire did not take full advantage of this feature.

As good as the spit was I'am sure Mitchell would have built a better replacment for it had he lived longer.

I dont think anyone would have had the balls to try and replace the spit apart from it's creator.

No1RAAF_Pourshot
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XyZspineZyX
11-04-2003, 07:49 AM
>>>"Edgar Schmued and Ed Horkey calculated that an aerodymanic duct formed at the entry and exit of the radiator could provide up to 300lbs of thrust by utilizing ram air to eject the warmed airflow and thus overcome the drag offered to the fuselage by the duct itself."



Mustang:Story of the P-51 Fighter
Gruenhagen:
pp.39
Arco Publishing

---
<font color=white font size="3" face="arial"Col. "Fury" CO
<font size="3"><font face="bd hanover">352nd Fighter Group </font> [VR]
<font face="bd hanover">328th, 486th, 487th Fighter Squadrons</font>
<font><font color="#330099"><font size="5"><font face="brush script mt">"Second To None!"</font>

<font>[b]<font size="2" font color=black>[(HL)_352FG; (UBI) USAAF_352FG]:
<font><font color=#330099 face="brush script mt"font size="5">"The 352nd Fighter Group"</font><font color=black font size="2"> [VR] in IL2-FB</font>

XyZspineZyX
11-04-2003, 08:13 AM
Sounds like a sub-sonic ram jet to me...

XyZspineZyX
11-04-2003, 08:32 AM
"What made the P-51 Mustang the fastest fighter of World War II (before the German jet came along)?"



Exqueeeeeeeeeeze me! Aren't we forgetting something? The pinnacle of piston fighters? Kurt Tanks dream of a plane?

The Ta152-H0 saw combat at a topspeed of 755km/h at 12.5km (GM1).

---

Thank you, and now back to the pregnant duck a.k.a. P51... /i/smilies/16x16_smiley-wink.gif



Message Edited on 11/04/0307:34AM by Kirin_9_JG54

XyZspineZyX
11-04-2003, 08:39 AM
Kirin_9_JG54 wrote:
- "What made the P-51 Mustang the fastest fighter of
- World War II (before the German jet came along)?"
-
-
-
- Exqueeeeeeeeeeze me! Aren't we forgetting something?
- The pinnacle of piston fighters? Kurt Tanks dream of
- a plane?
-
- The Ta152-H0 saw combat at a topspeed of 755km/h at
- 12.5km (GM1).


Ah.. but didnt that Ta152 come out after the JET? /i/smilies/16x16_smiley-wink.gif



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<h2> TAGERT</h2>
<marquee><h3>If WAR was not the ANSWER........ Than what the H was your QUESTION?</h3></marquee>
</div>

XyZspineZyX
11-04-2003, 08:48 AM
Nitpicker!!!


/i/smilies/16x16_smiley-wink.gif

XyZspineZyX
11-04-2003, 09:04 AM
great read, but that radiator stills makes the P-51 look like a pregnant guppy.... - Would have been a pretty plane otherwise. Well, efficiency counts more than looks!

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XyZspineZyX
11-04-2003, 09:08 AM
The exhaust created the same effect as a jet, it creates a lot of positive air presuure behind. An open radiator would have little drag since it protrudes little into the air stream and the vacuum that should be behind it if full of high pressure air.

XyZspineZyX
11-04-2003, 10:17 AM
Great read!!!