Meredith Effect and the P-51

[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)

 

[Kurfürst]

Hello Kurfürst
also MT-215's (109G-2) max speed 636km/h at 6300m was achieved radiator flaps closed.

I don't see how these would related to cooling. The MT 215 speed figures obtained can be tracked back to two reasons:

a, the aircraft had a fixed tailwheel as opposed to the semi-retractable tailwheel of the original G-2 production run, decreasing
b, There was a variation between the FTH achieved with individual aircraft and engines; that achieved on MT 215 was relatively low at 6300 m vs. the nominal 7000m, which accounts for the rest of the speed difference.

Normalizing the speed results of MT 215 for a semi-retracable tailwheel and the nominal 7000m FTH actually gives a fairly close match to the official figures of 660 kph at 7000m.

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.

The thermostats on the Bf 109 were set to keep the coolant temperature at an optimum of 85 degrees Celsius, far below the maximum permissable though. In other words, during the first 1.5-2 mins, the coolant temperature was below 85 degrees Celsius, even with the radiator flaps closed.

If needed, however, the radiator flaps set at any desired position, and the engine could tolerate far higher temperatures, as noted previously.

Which in other

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.

Hmmm, DB made this statement - and actually IIRC DB only complained about the undersized oil tank, but not any other part of the coolant system - sometime in 1943, when there were severe problems with the DB 605s reliability, because the DB 605's lubrication system had design flaws, and DB's prestige was pretty low at the RLM.

To put it simply, Daimler Benz was pointing a finger at the airframe manufacturer.

Curious thing is, nothing on the Bf 109 was changed, but when DB started to add a new oil de-aerator system on the DB 605, the problems were gone all the sudden without any change in the 109s coolings system, which was more than just aduquate, actually a bit oversized for the engine's needs, as several test results show. The oil tank size was, however, increased to 46 liter on later variants.

 

[Kurfürst]

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?

Kind regards,

Henning (HoHun)

I wonder about this as well. Hmm, perhaps I have some figures on the Allison Mustang.

Whatever its size was, it seem to be inaduquate for level speed runs at higher power outputs. During the testing of the P-51D TK 589 at +25 lbs, it was noted:

In order to obtain adequate cooling, level speeds were done with the radiator duct flap set to a gap of 8½ inches, as coolant temperatures were excessively high with the normal setting of 7¼" gap.

To me it seems the Mustang's radiator design was somewhat similar to the Italian approach, the radiators were sized to be just enough for the normal purposes, but there was little reserve provided. This kind of compromise (all designs are) emphasized on obtaining maximum performance and minimum drag.

 

[thrawn]

I think its interesting to compare the cooling layout of the P-51 to the Do-335.
They are very similar in appearance and size.
But, scince the oil cooling Flap is similar attached to the one in the P-51, the Do-335 had two main cooling flaps side hingend at the end of the fuselage.

Another point worth to consider is, that whenever it was possible, german aircraft designers seemed to use annular radiators, so they did for the front engine in the Do-335.

 

[DerAdlerIstGelandet]

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.

Joe asked you to tone it down. You can get your point across without being insulting okay.

 

[Juha]

Hello Kurfûrst
Quote:" a, the aircraft had a fixed tailwheel as opposed to the semi-retractable tailwheel of the original G-2 production run"

Now what you mean original? MT-215 was original G-2, very late G-2, and it had as all late G-2s, fixed tail wheel. Are you using original as a synonym to first or early? In fact MT-215 was in that a typical G-2, I read in 70s from a secondary source, from which one, I have long forgotten, that because the were constant problems with the semi-retractable tailwheel in front-line units, Germans fixed it down position and later G-2s came out from factory with a fixed one. Prien et al in their 109F/G/K book seemed to confirm that. In fact 109G wasn't only type suffering problems with retractable tail wheel, also many Spitfire Mk VIIIs, at least in Italy, had their tail wheel fixed down position because problems in field.

Quote:" In other words, during the first 1.5-2 mins, the coolant temperature was below 85 degrees Celsius, even with the radiator flaps closed."

Source for that, please. German charts I have seen show radiator flaps wide open at beginning of climb and they stayed so fairly long. Kokko, the Finnish test pilot, said nothing else that the flaps were opened fully first time at 2500m, but that doesn't mean that they were closed up to there.

On DB complains, the info is from Mankau's and Petrick's 110/210/410 book, p. 124, date 7 Sept 43, complains were made by Direktor Nallinger.

Juha

 

[Juha]

Hello Thrawn
Quote:"Another point worth to consider is, that whenever it was possible, german aircraft designers seemed to use annular radiators, so they did for the front engine in the Do-335."

IMHO more correct is to say some German...

In fact it seems that when RLM made an effort to standardize powerplants, the radiator was mounted in front of engines, a la in Ju 88s and 190Ds. The purpose seems to have been to avoid the incessant battles between the engine and airframe manufacturers on the issue of radiator and air intakes.

Juha

 

[thrawn]

Hi Juha,

at the end of the war it seems most piston-engined aircraft projects uses annular radiators in Germany.
One reason is the "Einheitstriebwerk" solution by the RLM, i agree, but on the other hand the radiator of the Do-335 is an unusual one, because of the excentrical location of the prop shaft. Also late Me 410 projects with the DB 603 used a different annular radiator, as did the Ta-152c and Fw 190d-15 (with radial flow).

So for the Do 335, IF the cooling Layout of the aft engine was as effective as in the p-51 (and thats the question here, or is the p51 cooling scoop overrated?), why not using it or a similar arrangement for the front engine?
In the book from Griehl "Dornier Do 335, 435, 635" the is a document from oct. 43 showing several variants for the front cowling from Messerschmitt, DB and dornier. Some with annular radiator and some other. In the end they chose the annular one. Im not saying it was superior, i'm only wondering.

 

[HoHun]

Hi Juha,

>Quote:" In other words, during the first 1.5-2 mins, the coolant temperature was below 85 degrees Celsius, even with the radiator flaps closed."

Isn't there an actual metric value for cooling effectiveness that is called "radiator sufficiency" which can be measured under controlled conditions, giving an accurate picture of the cooling system's limitations?

I think I read about it first on WWII Aircraft Performance , but I seem to remember that a similar value was used by German engineers as well.

If we could find figures for the Me 109 and another aircraft that were measured according to the same conventions, that would probably give a clear idea of radiator capability within a meaningful context ...

Regards,

Henning (HoHun)

 

[Colin1]

...it seemed to be inadequate for level speed runs at higher power outputs. During the testing of the P-51D TK589 at +25 lbs, it was noted:

In order to obtain adequate cooling, level speeds were done with the radiator duct flap set to a gap of 8½ inches, as coolant temperatures were excessively high with the normal setting of 7¼" gap.

I've read that report too
I don't see any consistency of heating issues with Mustangs in the wider world. I think this is an isolated case rather than a trend, it was, after all, one of the first a/c to arrive in the UK with the static vent feature that they were testing.

 

[drgondog]

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)

Ho Hum - You may be the single most self centered oaf that has ever graced the pages of this forum....and that broad sweeping portfolio includes Me.

Get a life! I actually apologise for reacting to buffoonery

 

[drgondog]

I've read that report too
I don't see any consistency of heating issues with Mustangs in the wider world. I think this is an isolated case rather than a trend, it was, after all, one of the first a/c to arrive in the UK with the static vent feature that they were testing.

Major issues were encountered due to electrolysis between cooling Glycol and dissimilar metls in the cooling system... creating scale in the plumbing and clogging up radiator. A new radiator design (Morris radiator) solved the problem

PS - Colin - you may faithfully comply with Herr Ho Hun demand that you give him radiator area.

2.1 Sq ft for P-51A/Allison
2.7 sq ft for first pre P-51B Merlin modification by RAF, re-designed to 2.9 Sq ft for subsequent the one first tested by RAF. This radiator designe remained for all B/C/D/K. I am not sure about the H.

 

[Clay_Allison]

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)

You do seem to be fond of bashing anything American though and claiming everything else was better designed.

 

[Juha]

Hello HoHun and Happy Valentine Day.
Quote:" Isn't there an actual metric value for cooling effectiveness that is called "radiator sufficiency" which can be measured under controlled conditions, giving an accurate picture of the cooling system's limitations?"

I don't know, probably there is. Design calculations and engine manufacturers' engine installation portfolio/specs probably would give answer. Some info is probably possible to get from instruction what engine settings and how long were possible in those 109s which had radiator cut valves after one radiator was cut off ie what was possible when engine cooling was restricted to one radiator and the oil cooler. Also the accident report of Black 6 probably would give some clues, IIRC the AVM took off with radiator flap control in manual setting, I cannot recall the radiator flap setting but anyway the cause of the crash was insufficient engine cooling, IIRC. The report probably gives exact radiator flap setting, engine power used, air temperature and flight time before engine failure.

Juha

 

[Kurfürst]

Now what you mean original? MT-215 was original G-2, very late G-2, and it had as all late G-2s, fixed tail wheel. Are you using original as a synonym to first or early?

Yes.

In fact MT-215 was in that a typical G-2,

No.

I read in 70s from a secondary source, from which one, I have long forgotten, that because the were constant problems with the semi-retractable tailwheel in front-line units, Germans fixed it down position and later G-2s came out from factory with a fixed one.

I guess your 70s source is quite simply wrong. Most of the G-2s were produced with a semi retractable tailwheel, the tailwheel become fixed one with the introduction of larger sized tires, but this did not occur until early 1943, when the G-2 production run was about to end.

See BF 109G-1 Kennblatt from March 1943.

Prien et al in their 109F/G/K book seemed to confirm that. In fact 109G wasn't only type suffering problems with retractable tail wheel, also many Spitfire Mk VIIIs, at least in Italy, had their tail wheel fixed down position because problems in field.

Hmm, I can't find a single reference in the Prien/Rodeike book about tail-wheel problems. There are of course some aircraft photoed field modified so in the field, but along with the removal of landing undercarriage covers, this appears to be a result of the muddy season in Russia and operations in the desert.

Quote:" In other words, during the first 1.5-2 mins, the coolant temperature was below 85 degrees Celsius, even with the radiator flaps closed."

Source for that, please.

Well thats how the radiators work on the 109. They close if the temperature is much below 85 degrees, and open if the temperature is over 85 degrees.

German charts I have seen show radiator flaps wide open at beginning of climb and they stayed so fairly long.

Relevance...? The charts you talk of were made in the summer, with the coolant temperatures already being at 85 Celsius at the start..

Here's another temp chart for you in a climb, from Mike's site:

The coolant radiator flaps open about 100 mm during the climb up to 6500 m, which is halfway between what the nominal "Steigflugstellung" is (220mm exit flap area, "climb position") and "Schnellflugstellung" (50mm, "level flight") values are for the radiator.

The temperature remains below or close what is the coolant temperature defined as a maintainable without any time limits. That is, in June, with the radiator flaps being only ~100mm or about 1/4 open, or half as much than what Messerschmitt defined them to be required for climbing (220 mm).

Kokko, the Finnish test pilot, said nothing else that the flaps were opened fully first time at 2500m, but that doesn't mean that they were closed up to there.

Of course is it does, its how it is supposed to work in the first place, the external temperature was rather cold as you notice, plus it is difficult to miss the very high climb rate of tested MT 215 in the first 2500 meters, above which it is, however very similiar to other G-2 curves at 1.3ata.

The only reasonable explanation I can think of is that the drag was much less with the radiator flaps so closed in the initial climb.

On DB complains, the info is from Mankau's and Petrick's 110/210/410 book, p. 124, date 7 Sept 43, complains were made by Direktor Nallinger.

Again, it was a case when DB was fingerpointing at the airframe manufacturer when the DB 605 was not working properly in any manufacturers installation - be it Heinkel or Messerschmitt.

Messerschmitt certainly did not change anything about the installation of the engine, the engine all the sudden become magically fixed when DB finally installed a proper oil de-aerator in the engine..so what validity was there in Nallinger's accusations in the first place, when he was blaming it on Mtt AG?

Don't be ridiculous claiming that the cooling capacity was not sufficient, after having seen a the actual curves showing that the coolant temperatures steadily remain some 30 degrees below the maximum permissible...

 

[Holtzauge]

I think the very good radiator design was one of the major reasons for the the P-51's very good speed performance relative other contemporary designs. However, I seriously doubt that the system actually produced thrust. What it probably did though was to produce considerably less drag than the competition.

Some percentage numbers of drag from "Kuhlung" from "Widerstandsdaten von Flugzeugen" dated december 1944:

Fw190A8: 15%
Fw190D9: 8.8%
Ta152H1: 12.2%

This most likely also includes drag from oil cooling but gives the general idea.

From Hoerner Fluid dynamic drag book page 14-6:

Me109G: Radiator drag 0.8 sq ft of 5.6 sq ft total=14.3%

So all these aircraft suffer a cooling related loss not a gain. Now if the P-51 where to produce thrust instead of drag then that seems like a spectacular design feat. I think it more likely that the good radiator design lowered the drag to a smaller percentage of the total drag which is good enough I think.

Hoerner also gives a hint of why the P-51 is better on page 9-3 in the same book:

Pressure loss in a radiator system is according to Hoerner roughly proportional to internal speed w**1.8

Heat transfer in a radiator system is according to Hoerner roughly proportional to internal speed w**0.8

So dividing the pressure loss and heat transfer we deduce that the lower the speed over the radiator core the better. I would expect this formula to be valid for reasonable variations of radiator core speeds since Hoerner uses it for design comparisosns so it should serve it's purpose for what we are looking at here.

Now I do not have the actual figures but by just eyeballing the proportions of radiator inlet area to core area on the P-51 and Me109K I would say that the speed over the core should be lower for the P-51 than in the Me 109K seeing that the speed over the core will be proportional to inlet area divided by the core area.

From this we can deduce that the P-51 has a more efficient radiator design than the Me109K due to the lower speed over the radiator core.

And BTW Colin1, I would not feel to bad about ending up on HoHun's "ignore list" as a "fraud" since I'm already on it and have suffered no I'll effects so far. Rather to the contrary since it spares me from his pompous and overbearing comments.