Meredith Effect and the P-51

[Juha]

Yes
Meredith Effect seems to be a classical case of a big secret that enemy already knew. Still IMHO, as a total layman, scoop was probably a more effective in securing a smooth air flow but of course the scoop itself produced some turbulence. Maybe Brits were right, see the last sentence in their valuation, that the main reason for 109F boundary layer bypass was to minimaze radiator area and so drag. 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

[Colin1]

Originally Posted by Juha

Meredith Effect seems to be a classical case of a big secret that enemy already knew

I'm not seeing that in any German designs at any stage of the war, where are you seeing it?

Originally Posted by Juha

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

This would further bear out Atwood's claims that in order to recover the cooling losses, the exhaust aperture is everything.

It's Km/h; Kilometres per hour (Kilometres divided by 1 hour).
Kmh; Kilometre hours (Kilometres multiplied by 1 hour) would yield a different value, it if existed.

[Juha]

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

The result is same, whether you divided or multible by 1. Kmh was only a result of hurry.

Juha

[Colin1]

Originally Posted by 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

Me too
but I've not read or seen of any German design that openly claims to have actually harnessed the effect. Atwood does mention in his article that Willi Messerschmitt was sniffing around the P-51 design's characteristics for the additional speed but never quite figured it out; I would say history lends an awful lot of weight to that argument.

[Colin1]

Removed

[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]

Originally Posted by 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)

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]

Originally Posted by 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)

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]

Originally Posted by Juha

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]

Originally Posted by Clay_Allison

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]

Originally Posted by HoHun

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?

Originally Posted by HoHun

...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

Originally Posted by HoHun

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