Meredith Effect and the P-51 (1 Viewer)

[HoHun]

Hi Juha,

>I'm a layman on Meredith Effect, but I'd not be surprised if Germans also with all their theoretical knowledge knew the effect.

Good call. It would in fact more properly be called the "Junkers effect" as Junkers patented the diffusor-radiator-jet combation as "Düsenkühler" ('jet cooler') in DRP 299799 on 17 January, 1915. (Von Gersdorff et al., "Deutsche Flugmotoren und Strahltriebwerke, p. 196.)

The principle obviously was well-known in the English-speaking part of the aviation industry as well. "Fundamentals of Fighter Design" by Ray Whitford notes (p. 61): "In 1926 it was realized that airflow through the radiators on liquid-cooled engines could, if properly ducted, eliminate the cooling drag and even produce a little thrust at speeds above 260 kts (483 km/h)."

Flugzeug Classic in one of their early issues quoted from a speech given by Willy Messerschmitt at some congress in the late 1930s in which he praised the Junkers jet cooler as the most important single contribution to high speed flight as it cut down the otherwise prohibitive cooling drag, pointing out that the most advantageous way to incorporate the concept in a high-speed aircraft was in the form of wing radiators.

To me, it looks as if thrust recovery from radiator cooling was fairly well-known in the international aviation industry of the 1930s, and as if the Mustang differed from similar designs only through the particularly efficient way this well-known principle was implemented.

Regards,

Henning (HoHun)

 

[Clay_Allison]

Hi Juha,

>I'm a layman on Meredith Effect, but I'd not be surprised if Germans also with all their theoretical knowledge knew the effect.

Good call. It would in fact more properly be called the "Junkers effect" as Junkers patented the diffusor-radiator-jet combation as "Düsenkühler" ('jet cooler') in DRP 299799 on 17 January, 1915. (Von Gersdorff et al., "Deutsche Flugmotoren und Strahltriebwerke, p. 196.)

The principle obviously was well-known in the English-speaking part of the aviation industry as well. "Fundamentals of Fighter Design" by Ray Whitford notes (p. 61): "In 1926 it was realized that airflow through the radiators on liquid-cooled engines could, if properly ducted, eliminate the cooling drag and even produce a little thrust at speeds above 260 kts (483 km/h)."

Flugzeug Classic in one of their early issues quoted from a speech given by Willy Messerschmitt at some congress in the late 1930s in which he praised the Junkers jet cooler as the most important single contribution to high speed flight as it cut down the otherwise prohibitive cooling drag, pointing out that the most advantageous way to incorporate the concept in a high-speed aircraft was in the form of wing radiators.

To me, it looks as if thrust recovery from radiator cooling was fairly well-known in the international aviation industry of the 1930s, and as if the Mustang differed from similar designs only through the particularly efficient way this well-known principle was implemented.

Regards,

Henning (HoHun)

Seems, though, that the wing-radiator was not the way to go for maximum effect.

 

[HoHun]

Hi Clay,

>Seems, though, that the wing-radiator was not the way to go for maximum effect.

How do you know?

Regards,

Henning (HoHun)

 

[Clay_Allison]

Hi Clay,

>Seems, though, that the wing-radiator was not the way to go for maximum effect.

How do you know?

Regards,

Henning (HoHun)

The P-51 was faster than the Bf-109. Also:

Downside of 109 system was that the large radiator flaps had a big effect on max speed when fully open, up to 50kmh, On the other hand in LaGG-3, which had underfuselage scoop and a radiator flap somelike that in P-51, the effect of fully open radiator flap was only up to 15kmh

If there was some way for Wing radiators to be just as good, they didn't find it.

I would guess that the one inlet, the one radiator, and the one outlet built up back pressure more easily. That's just a guess.

 

[Kurfürst]

Downside of 109 system was that the large radiator flaps had a big effect on max speed when fully open, up to 50kmh, On the other hand in LaGG-3, which had underfuselage scoop and a radiator flap somelike that in P-51, the effect of fully open radiator flap was only up to 15kmh, both effects from Finnish tests.

Juha

I don't see the 'downside' here - quite simply the radiator flaps on the 109F-K could open much wider if neccessary than on some other designs (keeping in mind they also doubled as flaps).

Generally it wasn't necessary, especially not in level flight (see cooling temperatures on the chart measured in August, in a climb, against radiator opening) but it was a useful reserve for tropical operations or running the engine for a prolonged period on the ground, or if the engine was running very hot, keeping the engine at optimal temperatures etc.

To me the 'Meredith' effect is a some sort of weird phenomenon amongst aviation historians, something that most likely was understood and used to some extent by practically all major designers of WW2, yet there is some sort of nationalism-driven race to claim it as a sort of magic wand for performance, that could be wielded by only the select choosen ones.. the Brits hype it for the Spitfire, the Americans in exchange for the Mustang, and for some reason assume everyone else was totally ignorant of the phenomenon, to which there is 'proof' in that others don't call it Meredith but named it something else in their odd, alien languages which these 'experts' usually cannot even understand, read, or speak.. nor have read the literature written in those languages.

Yet it is difficult to see in what way was these two particular executions were fundamentally different than Yakovlevs, Laggs, Emils, Friedrichs etc. I guess it is just assumed that they were.

 

[Kurfürst]

The P-51 was faster than the Bf-109.

Not really, when comparing subtypes with similiar engine output, and similiar aerodynamic devices (ie. P-51D / Bf 109K).

Any difference is much more likely to down to other factors like propeller efficeny curves&characteristics etc.

Of interests are several Messerschmitt made projected curves for 109s with underfuselage ducted radiators - a couple of such prototypes were built as well - but the results are not very convincing, 10-15 km/h gained IIRC, which is probably down to the smaller frontal area of one ducting vs. two radiators, but at the same time its a compromise: cooling capacity would be reduced if the radiator area is reduced...

IIRC the TK 589 Mustang trials show this, but also the German trials at Guidonia are critical of smaller Italian radiators that increased the performance but had inadequate cooling capacity for the engine; with the performance in mind, this could be a backfire, ie. prolonged climbs at maximum power could become impossible, as was in the case of the Yak 9U, despite its relatively modest engine output.

Evidently the Lagg 3 suffered the worst from this problem, the nominal speeds were achieved with the radiator shutter in completely closed position (the prescribed manner of operation!), at which the engine overheated quickly. Practical operation of the aircraft was possible with the radiator shutter open, but this reduced the speed from the nominal speeds by 15 km/h. And here lies the difference - the nominal speeds for the 109 were given with the radiator in 50mm open position, which was sufficient for level flight cooling. However the flaps could be closed fully as well - as was the standard for the Lagg's nominal speed - in which case the the speed would increase by about 10 km/h. Of course they could be opened fully as well, to 350mm+ but what point there would be in that when measurements showed that even during the hot summer period a slow-speed climb, with much less airflow through the radiators, this opening would be sufficient to maintain a steady 85 degrees Celsius of coolant temperature (the engine was cleared for 100 Celsius coolant temperature for indefiniete period, and for 115 Celsius for a 10 minute period), is beyond me..

 

[HoHun]

Hi Clay,

>The P-51 was faster than the Bf-109.

The P-51 was a completely different aircraft from the Me 109. How do you know any speed difference was due to the cooling system?

>"Downside of 109 system was that the large radiator flaps had a big effect on max speed when fully open, up to 50kmh, On the other hand in LaGG-3, which had underfuselage scoop and a radiator flap somelike that in P-51, the effect of fully open radiator flap was only up to 15kmh"

>If there was some way for Wing radiators to be just as good, they didn't find it.

The "fully open" position is not of interest ... the position of interest is the one that is required for effective cooling, and in high speed flight that's the one with a very small opening.

The larger speed loss of the Me 109 with fully open radiators might in fact be indicator of a superior cooling capacity reserve for use under difficult conditions so that the Me 109's "fully open" is not comparable to the P-51's "fully open". And that reserve might not even be intentional, but the result of the radiator flap kinematics having been designed to allow the lower outlet flaps doubling as landing flaps ... you'd have to compare the drag at equivalent cooling capacity of both aircraft to get a meaningful result.

Regards,

Henning (HoHun)

 

[Colin1]

It would in fact more properly be called the "Junkers effect" as Junkers patented the diffusor-radiator-jet combination as "Düsenkühler" ('jet cooler') in DRP 299799 on 17 January, 1915. (Von Gersdorff et al., "Deutsche Flugmotoren und Strahltriebwerke, p. 196.)

Hi Henning
As ever, some interesting counter-material from you
I would like to see this document, do you have access to it?
My scepticism if I may, is that in 1915, aeroplanes were barely fast enough to fully exploit an air pump, recovered cooling losses would be minimal; how well did this Dusenkuhler work?

...a speech given by Willy Messerschmitt at some congress in the late 1930s in which he praised the Junkers jet cooler as the most important single contribution to high speed flight as it cut down the otherwise prohibitive cooling drag, pointing out that the most advantageous way to incorporate the concept in a high-speed aircraft was in the form of wing radiators

That may have been the accepted wisdom in the late 1930s but in the early 1940s, North American found a more advantageous way. I would suggest Messerschmitt buried his scoops in the lower wing to reduce the spoil on the Bf109's clean lines, not to augment the air pump effect in any way

To me, it looks as if thrust recovery from radiator cooling was fairly well-known in the international aviation industry of the 1930s, and as if the Mustang differed from similar designs only through the particularly efficient way this well-known principle was implemented

Fairly well known? Possibly. Does its seeming absence not imply by logical deduction that the technique wasn't fully understood by other designers? Who in their right mind would discount such a tactical advantage if they fully recognised its potential?

 

[red admiral]

There was an article on the Meredith Effect in the Aeronautical Journal a couple of years ago. Meredith took what was already known and made it better by rigorous study (like Hooker and supercharger matching). This was then incorporated into the P-51 to give the most favourable results - grouping the radiator into one block and ventral installation.

I have an interesting picture of a proposal to augment the scheme in the P-51 where twelve PD.1 ramjets were fitted behind the radiator to give even more thrust. It was trialled but wasn't successful, mostly because ramjets give so little thrust at low speed.

 

[Juha]

Hello KF
now on need to open the radiator flaps wide open, I don't know, maybe during a long low level chase on hot summer day, at high altitude the need was not likely.

On Meredith Effect, now, as a layman, it is not hard to believe that a scoop outside of turbulent boundary layer is the best solution. See how they changed the supercharger air intake in 109F. And in fact Meredith didn't like under wing radiator of Spitfire and proposed a different solution. Leading edge radiator intake was according to him clearly better and IMHO he probably knew the effect very well. I cannot say nothing on Meredith Effect but IIRC P-51 scoop was different from that of Yak and LaGG that it's intake clearly was separated from fuselage bottom line and so IMHO would have satisfied Meredith.

Hello HoHun
thanks for the info. I'm not surprised that it was Junkers. IIRC he had also other patents on heating/cooling and made a good money by those systems between the wars.

Juha

 

[HoHun]

Hi Colin,

>I would like to see this document, do you have access to it?

Von Gersdorff et al. does not have a facsimile of the patent, only a description and a sketch.

>My scepticism if I may, is that in 1915, aeroplanes were barely fast enough to fully exploit an air pump, recovered cooling losses would be minimal; how well did this Dusenkuhler work?

"Duesenkuehler", if you don't have any Umlauts Junkers actually implemented his patent in the Junkers J.1, a cantilever-wing stressed-skin all-metal monoplane fighter. It was rather fast for its time, but of course the very smooth skin (steel - not the corrugated light alloy skin Junkers came up with later) and the complete absence of struts and bracing wires played a big role, too.

(The steel fighter is not to be confused with the corrugated light-alloy skin Junkers J.4 which entered service as Infanterieflugzeug J.I ... in the latter designation, the "I" of "Infanterieflugzeug" is abbreviated as a "J" to satisfy a typographic convention.)

>I would suggest Messerschmitt buried his scoops in the lower wing to reduce the spoil on the Bf109's clean lines, not to augment the air pump effect in any way

I don't know the reason Messerschmitt suggested wing radiators were superior, and I'm not going to speculate (unless I can come up with something intelligent

>Fairly well known? Possibly. Does its seeming absence not imply by logical deduction that the technique wasn't fully understood by other designers?

You have to take a rather close look at a type to be able to tell whether it incorporated a jet cooler or not as the relevant details would always be hidden under a fairing. Which type do you think of specifically when you mention the jet cooler's absence?

Regards,

Henning (HoHun)

 

[Colin1]

You have to take a rather close look at a type to be able to tell whether it incorporated a jet cooler or not as the relevant details would always be hidden under a fairing. Which type do you think of specifically when you mention the jet cooler's absence?

I think German engineers are rightly proud of their technical innovation during this period, the pilot position and his instrumentation layout in the Fw190, the first operational jet, the radical cockpit design of the Ar234, the Hortens flying wing, the maybe-factor of the Ta183 (the Soviets were clearly impressed with it, the MiG-15 looked just like it).

In view of all that, it's the absence of any declaration of the implementation of the air pump technique that flags my attention mainly.

As for examples, I'm still not convinced the Bf109 employed it and if it did, I'm wondering what the Me309V1 was all about. Further examples, well, the Fw190D series.

 

[HoHun]

Hi Colin,

>in view of all that, it's the absence of any declaration of the implementation of the technique that flags my attention mainly.

I'd say that's more the absence of your knowledge about the implementation of the technique That the German engineers weren't waving buzzwords might simply indicate the jet cooler was no longer new and exciting to them.

>As for examples, I'm still not convinced the Bf109 employed it

If you'd look at the diagrams Kurfürst posted, they should eliminate any doubt.

>I'm wondering what the Me309V1 was all about. Further examples, well, the Fw190D series.

Have you looked at the cross sections of their cooling systems? As I pointed out above, the relevant details are found beneath the skin.

Regards,

Henning (HoHun)

 

[Colin1]

That the German engineers weren't waving buzzwords might simply indicate the jet cooler was no longer new and exciting to them

At the time
neither were the Americans, most of the buzzwords being waved by anybody have been made in a historical context but it doesn't seem to crop up in German archives; it doesn't have to be exciting in order to make a historical technical specification entry for the aircrafts systems any more than the addition of an extra 5 millimetres of armour would.

Whatever was under the skin, they don't appear to have maximised the air pump's potential the way North American did; one unusually large radiator venting pressurised heated air through a designed-for-purpose exhaust vent.

 

[Juha]

Hello Kurfürst
also MT-215's (109G-2) max speed 636km/h at 6300m was achieved radiator flaps closed. And during climb test, even if the day wasn't hot, +11,2deg C at field, the radiator flaps had to open fully at 2500m, even if airspeed was kept higher than recommended, TAS was at 2000m 341 and at 3000m 351km/h. Also DB complained that Messerschmitt didn't follow engine installation specifications and so the oil and water/glycol cooling was insufficient and so a large percentage of powerplant operational reliability was sacrificed for a minute aerodynamic advantage for the whole plane – on paper. DB also added that Messerschmitt was an exception, other a/c manufactures followed DB's specs. Of course that was not the only time when airframe and engine firms were in odds, same situation was between Tank and BMW with early Fw 190As.

Juha

 

[HoHun]

Hi Colin,

>Whatever was under the skin, they don't appear to have maximised the air pump's potential the way North American did; one unusually large radiator venting pressurised heated air through a designed-for-purpose exhaust vent.

And by what laws of physics would one "unusally large" radiator be superior to two normal-sized ones?

Frankly, I believe you are completely ignorant of the technology involved and just try to cheer for the P-51 though you're completely clueless when it comes to thermodynamics.

Regards,

Henning (HoHun)

 

[Colin1]

And by what laws of physics would one "unusually large" radiator be superior to two normal-sized ones?

And by what law of mathematics did you assume that two normal-sized ones added together made one 'unusually large' radiator?

One of the constraining factors of wing radiators recognised by North American was the size of the cooling matrix the designer could fit in there. The P-40 arrangement too, was looked at and demonstrated similar constraints but with ducting arrangements, rather than volume.

North American realised that the air pump effect could best be maximised by placing it exactly where they did; it was here that they could employ their 'unusually large radiator'.

By unusually large read 'comfortably larger than the sum of 2 wing radiators'.

That, coupled with the all-important exit opening, was the critical factor in the P-51's employment of the air pump for providing additional thrust.

 

[delcyros]

Thanks Colin Kurfürst for Your contributions.
Junkers actually patented the system back in 1914/15. A rather simple heat exchange- radiator was installed in the J-1 and J-2. It was inteded to cancel out part of the radiator drag.

 

[Colin1]

Thanks Colin Kurfürst for Your contributions.
Junkers actually patented the system back in 1914...

Hey
no worries fella
I'm still trying to get hold of that; that would be an interesting read

 

[delcyros]

Here are pcs of the J1 and J2. The Junkers Düsenkühler can be seen under the belly of the plane.