Meredith Effect and the P-51

[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.

[FLYBOYJ]

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.

Please simmer this down a bit. I don't want this interesting thread to become ugly. Many thanks.

[Holtzauge]

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.

The answer to "by what laws of physics would one "unusally large" radiator be superior to two normal-sized ones" is pretty simple: For a given flow rate, the wetted area in a single duct is less than the wetted area of two ducts. Thus the loss of momemtum prior to entry into the radiator and also behind the radiator will be less for the single duct system.

[Colin1]

...For a given flow rate, the wetted area in a single duct is less than the wetted area of two ducts. Thus the loss of momentum prior to entry into the radiator and also behind the radiator will be less for the single duct system

Right
but one larger radiator (larger than the sum volume of two wing radiators) venting high-pressure gases through ONE variable exhaust vent would be more efficient than two wing radiators venting through two vents (ie one each), wouldn't that be the case?

So, in layman's terms (for me, if no-one else), less cooling drag to begin with and more efficiently recovered cooling losses (thrust) at the exhaust?

[drgondog]

Thanks
that's alot clearer
As a system, it has all the hallmarks of Teutonic engineering thoroughness but it seems (to me) to be a clever way of cooling, not a method for harnessing Meredith Effect.
I would postulate that Atwood's theory that other attempts failed because of incorrect exhaust aperture would apply here - the exit seems too large and not of the correct shape for an efficient aperture, for a radiator that is too small to build up enough back pressure.

One other detail of the 109 geometry that raises some speculation on my part is that the plenum design under the top wing surface appears to be an interesting opportunity for the inlet stream tube to expand dramatically with a lot of opportunity for turbulent flow - and a positive pressure distribution - both leading to cooling inefficiencies.

Had to be a.) detectible, and b.) comparable against other methods - so it must have been a positive contribution - I would just be curious.

As to Meridith Effect, Lednicer pointed out that his modelling results pointed more to extreme low drag as primary benefit for Mustang design than net thrust attributed to Meridith effect.

[HoHun]

Hi Colin,

>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.

So how large was the P-51 cooling matrix, and how large was the Me 109 cooling matrix in comparison?

I believe you don't actually know, and I'm not fond of people making extensive claims from a position of ignorance. You either put in some research and come up with that answer in your next post, or I'll consider you a fraud and put you on my ignore list.

Kind regards,

Henning (HoHun)