Ki-61 Hien (Tony) Radiator / Meredith Effect?

FLYBOYJ · Oct 12, 2009

Also remember that when these so-called experts start making comparisons of airframes under restoration, they are looking at 60+ year old caresses that have been banged around, dropped and abused and in many cases repaired in the field. There is no way a real an accurate assessment could be made about the initial construction quality unless you start dissecting assemblies and examine rivets installations that had to be done by hand.

There is no doubt that a cleaner, tighter aerodynamic surface is going to give you more speed, but would it be worth it for what was trying to be accomplished in the end? (Tighter quality, more skilled assemblers, betting tooling = more time in producing the final product)

VG-33 · Oct 12, 2009

I would tend to disagree this point but could be convinced with facts.

I thought naively that it was from common knowledge. I take my information from many reliable people: Jean Salis, Didier Chables and Christophe Jacquard, all being famous French warbirds collectors and restorers. And Dogfight n°2 revue. I can confirm for the few Mustangs an Spitfires I saw. Moreover it was like that for all American vs European planes production, not only the North American ones.

First for this to be a common condition it would have to be proven that the 'hollows and humps' were in the leading 25% chord region where normal attached flow could be disrupted to earlier boundary layer separation. Second, existance of such humps and flows in the regions past 25% chord would perhaps contribute to additional but nevertheless very small increments in parasite drag. Last, the regions between the leading edge and 1/4 chord point is a shorter distance with implied greater stiffness and regularity in the airfoil skin over that region. The last is very speculative but one would really have to screw up the tooling to get significant variations from loft contours here

This is a song from an other opera : the Mustang one. Non laminar NACA profiles 22 xx or 22xxx can work well even in full turbulent conditions. With some L= C/D decrease of course. But we agree that means a perfect mirror- rugosity skin condition for the Mustang wing profile to maintain the laminar flow. That explains quality manufacturing also.

This is a tricky assumption. The Spit wing had greater theoretical efficiency factor due to elliptical wing (small) and slightly greater aspect ratio. Induced drag should be slightly less for the Spit at the same speed. For the same speed the Lift loading (WL) will be smaller than the 51 and becaues the Spit Max CL slope is higher the Spit should be flying at a slightly lower angle of attack - with primary difference really reduced to the both the drag of the Wing and parasite drag of the Fuselage/Radiator system. The Mustang was clearly superior for both of these designs relative to parasite drag.

The parasite drag difference is dominant at top speeds.

Yes but the Mustang wing load is higher, so it flyes at a higher AoA, dispending more induced drag to compensate. To make a fair aerodynamical comparison between the both plane we should take the same wing load, so a lighter Mustang or a heavier Spitfire.

The cross sectional fuselage area at the radiator cowl location slightly increases from the cross section just forward. In my opinion the intake design and the position relative to the boundary layer was the number one factor in the drag reduction as a % of parasite drag. Resulting sepration past this point would have far less effect than a cowl mounter radiator - but equally if flow separation was a significant factor for both the P-51 and Spifire downstream of the radiator - the Spit would win because there is nothing to create parasite drag behind its wing mounted radiator cowls - so I tend to discount this as a major factor.

I didn't spoke about that. Only about relative wing thikness, cockpit and radiator bed position. Anyway I consider Spitfire radiators as a kind of airbrakes; but not providing any lift, only destroying it. It's why i'm against mounting radiators on lifting surfaces anyway, as Messerschmitt did.

Yes. The wing selection, the radiator cowl, the exceptionally clean fuselage design including windscreen and canopy (malcolm hood for P-51B), and manufacturing quality/surface regularity - all played a role

Ok

I am with you that a.) true analytical calculation of thrust must take into account true porosity of the radiator in the equations and I personally have never seen mass flow rate calculations or Temperature/Pressure values in any drag profile for the Mustang. I am willing to believe Meridith effect or at least suspend disbelief pending those data.

Oh I forgot. It is probable that the Ki 61 radiator design with respect to Boundary Layer control was as rigorous as the P-51. I have no opinion on Meredith effect increment to thrust for all the reasons I am agnostic on the Mustang.

As to the primary factor, I remain on the side of analysis that says the parasite drag reduction was a combination of geometry and boundary layer control more than any other factor - until proven otherwise.

I agree with that too. We need to blow a fullscale Mustang in a windtunnel with hot radiator and a cold one to see the difference. And so for other WWII fighters.

Colin1 · Oct 12, 2009

VG-33 said:
We need to blow a full scale Mustang in a wind tunnel with hot radiator and a cold one to see the difference

What would that reveal?

VG-33 · Oct 12, 2009

Colin1 said:
What would that reveal?

The drag difference betwenn the two configurations. And so the additionnal thrust due to the Meredith effect. If there were some, of course...

VG-33 · Oct 12, 2009

vanir said:
As another example look at how much extra speed was gained in the TsAGI tests of refinished post production Yak-1 during 1942, as much as 20km/h gained simply by refinishing the Yak at an airfield, things like pulling off the panels and reattaching them properly
.

And loose 8-10 km/h only by painting the Yak-1 with a white winter paint with higher rugosity.

Colin1 · Oct 12, 2009

VG-33 said:
The drag difference between the two configurations.

And the additional thrust due to the Meredith effect. If there were some, of course...

I don't work with wind tunnels
but I fail to see how you could do either, how would you reveal thrust in a wind tunnel? How would a wind tunnel know the difference between a hot air pump and a cold one and why would it care?

I think we should also agree that rather than generate 'additional thrust' the P-51's air pump mechanism provided 'thrust recovery'.

VG-33 · Oct 12, 2009

Colin1 said:
I don't work with wind tunnels
but I fail to see how you could do either, how would you reveal thrust in a wind tunnel? How would a wind tunnel know the difference between a hot air pump and a cold one and why would it care?

I think we should also agree that rather than generate 'additional thrust' the P-51's air pump mechanism provided 'thrust recovery'.

I dont understand your question. It's the wing tunnel job to measure drag end lift forces with a complicated weight balances system. If not in the wind tunnel, where could you do that? The cold radiator would have no benefit fom any air pump mechanism since it will have no heat for that. We can imagine even an electric engine just to simulate the Merlin work on the "cold Mustang". Or experiment without that, just calculating extra propeller blow.

Colin1 · Oct 12, 2009

VG-33 said:
It's the wind tunnel's job to measure drag and lift forces...

That's what I thought it did too
but how would it measure thrust?

VG-33 · Oct 12, 2009

Colin1 said:
That's what I thought it did too
but how would it measure thrust?

Sorry for the type mismatch/ error: i repeat

The drag difference betwenn the two configurations. And so the additionnal thrust due to the Meredith effect.

Colin1 · Oct 12, 2009

VG-33 said:
Sorry for the type mismatch/error: I repeat

The drag difference between the two configurations. And so the additional thrust due to the Meredith effect

I understood you, I just don't think a wind tunnel will reveal that.

An exerpt from an interview with Lee Atwood:-

During World War II, everyone was trying to figure out how the P-51 Mustang was out-performing German fighters as well as the British Spitfire, which had more horsepower and was 1,000 pounds lighter. The German aircraft manufacturer, Messerschmitt, was also researching the Mustang's performance to no avail.

Atwood explained, "Both the British and German engineers at the time thought you could test a scale model in a wind tunnel. But the wind tunnel models didn't generate the engine-heat factor, which we successfully controlled within the air scoop to create positive thrust. They were all looking at Mustang's laminar flow wing, which was noted for reducing air friction over the surface of aircraft wings."

drgondog · Oct 12, 2009

Actually I believe a wind tunnel test on a full scale Mustang sans propeller could test the Meridith effect possibilities in a methodical way. I agree Vg-33 on this point.

It should not be hard to generate the equivalent heat generated by hot coolant passing through the radiator core, then measure drag with exhaust doors in all positions from closed to full open and also place pitot tubes and thermocouples in the aft cavity to measure velocity and temp profiles and calculate mass flow properties.

The drag due to closed doors should reflect the efficiency of the cowl design and Perhaps the highest drag configuration.

Exhaust door open with no heat supplied to radiator core should benchmark the base drag pre and post heat supply

Exhaust door open with heat supplied to radiator core should reflect the reduction of drag/increase in Thrust

I wonder why NAA didn't perform the test?

drgondog · Oct 12, 2009

VG-33 said:
What I said >>This is a tricky assumption. The Spit wing had greater theoretical efficiency factor due to elliptical wing (small) and slightly greater aspect ratio. Induced drag should be slightly less for the Spit at the same speed. For the same speed the Lift loading (WL) will be smaller than the 51 and becaues the Spit Max CL slope is higher the Spit should be flying at a slightly lower angle of attack - with primary difference really reduced to the both the drag of the Wing and parasite drag of the Fuselage/Radiator system. The Mustang was clearly superior for both of these designs relative to parasite drag.

The parasite drag difference is dominant at top speeds.

What you said>>. Yes but the Mustang wing load is higher, so it flyes at a higher AoA, dispending more induced drag to compensate. To make a fair aerodynamical comparison between the both plane we should take the same wing load, so a lighter Mustang or a heavier Spitfire.

For some reason you seem to have repeated what I said above? Did I miss a point you wanted to make?

If you pick a lighter Mustang the differences in Drag become more pronounced as the Mustang Induced drag becomes nearly the same as the Spit while the Mustang Parasite drag combinations remain much lower. I don't have a Drag polar for either in front of me but the parasite drag is much higher at max speed than the induced drag, which is at its lowest point.

I said >The cross sectional fuselage area at the radiator cowl location slightly increases from the cross section just forward. In my opinion the intake design and the position relative to the boundary layer was the number one factor in the drag reduction as a % of parasite drag. Resulting sepration past this point would have far less effect than a cowl mounter radiator - but equally if flow separation was a significant factor for both the P-51 and Spifire downstream of the radiator - the Spit would win because there is nothing to create parasite drag behind its wing mounted radiator cowls - so I tend to discount this as a major factor.

You said >>I didn't spoke about that. Only about relative wing thikness, cockpit and radiator bed position. Anyway I consider Spitfire radiators as a kind of airbrakes; but not providing any lift, only destroying it. It's why i'm against mounting radiators on lifting surfaces anyway, as Messerschmitt did.

This comment is probably true if neither Spitfire nor Mustang nor 109 radiators achieve combined Boundary Layer control or Meridith effect. I don't have the drawings so I don't know what the radiator/cowl cross sectional area is in comparison but it seems likely the 51 with a single well faired and positioned radiator out of any lifting plan view would have an advantage on just pure 'flat plate equivalent' drag and totally away from any lifing surface.

At any rate I agree with you that the Mustang choice of design was superior to both the Spit and Me 109 for the reasons you cite.

I agree with that to. We need to blow a fullscale Mustang in a windtunnel with hot radiator and a cold one to see the difference. And so for other WWII fighters.

I wish the tests could have been accomplished. Until some specific drag comparisons data is presented we must speculate.

VG-33 · Oct 12, 2009

Colin1 said:
I understood you, I just don't think a wind tunnel will reveal that.

Atwood explained, "Both the British and German engineers at the time thought you could test a scale model in a wind tunnel. But the wind tunnel models didn't generate the engine-heat factor, I]

Fortunatly they (wintunnels, i mean...) did: you just need to make your engine turn for that. It's the reason why the La-5FN gained from 50 km/h from the normal La-5/5F using strictly the same engine, but different under cowling flows. I don't know if there were enough powerfull and big tunnels in europe exept the TsAGI T-104 or T-101 in Moscow to blow a 40 feet full-scaled plane at 180-200 m/s!

The more i read Atwood's texts from you, the more i'm persuaded that is a great publicist (for his firm) than a great scientist.

BTW, the P-63 was full-tested in the TsAGI tunnels, as the other planes and it was found that it had the smaller Cd from all WW2 planes, Mustang included. So the speed difference could be explained in better Mustang's engine, not aerodynamics.

I'm still persuaded that the Mustang's gain in internal drag is mainly due to the low-speed flow rathen than to the Meredith effect.

Just like the Dieselis

Dieselis - Avion prototype à moteur diesel

drgondog · Oct 12, 2009

Lee Atwood was far more than a 'publicist'. The teams he led designed and built the Mustang, the F-86, the F-100, the B-70 and the X-15. He became a corporate leader but he started as a design engineer.

Bronc · Oct 12, 2009

From the NASA website at: ch5-5

THE HIGH SPEED FRONTIER

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Chapter 5: High-speed Cowlings, Air Inlets and Outlets, and Internal-Flow Systems

THE RAMJET INVESTIGATION

[161] In 1936, F. W. Meredith pointed out that the waste heat of a piston engine which is transferred to the cooling-air flow in a radiator is not all lost; it produces a small thrust provided the pressure at the exhaust of the radiator tubes is higher than the free static pressure of flight (ref. 192). This phenomenon became known as the "Meredith effect." Its mechanism was something of a mystery to many engineers of that period. A common fallacious notion was that the radial engine, because its fins were hotter than usual radiator temperatures of liquid-cooled engines, would enjoy greater benefits. (This mistaken notion still existed as late as 1949 and is stated by Schlaifer to constitute an "inherent advantage of the radial engine" (ref. 41).) The Meredith effect was so small at 1936 airspeeds that it could conveniently be neglected in performance estimates both by those who did not understand it and by those who doubted that such an effect really existed.

In our engineering analysis of the effects of heat in internal flow systems, the conversion of heat to thrust power was clearly the most [162] intriguing aspect. Thinking in terms of flight speeds of 550 mph, we calculated ideal thermal efficiencies of as much as 10 percent, and by Mach 1.5 the heated duct would have a thermal efficiency comparable to an internal combustion engine. Clearly, the insignificant "Meredith effect" had the potential to become a primary jet-propulsion system. (The term "ramjet" was not then in general use, and we were unaware that there were several discussions of propulsive ducts in the literature starting with Lorin in 1913 and including later treatments by Carter, V Leduc, Roy, and others.)

Excited at these prospects, I arranged a meeting with Langley's leading propulsion analyst at our Power Plant Division, Ben Pinkel. I also talked briefly with D. T. Williams, a young physicist whom Pinkel had recently assigned to analyze propulsive ducts at high subsonic speeds, including the effect of an engine-driver blower typical of the Campini system under study by Jacobs. Neither man showed any real hope for these systems, and Pinkel, reflecting the general attitude of most of the propulsion community at that time, patiently explained "the great weakness of all forms of jet propulsion-excessive fuel consumption compared to piston engines". When Williams' work was published about a year later (ref. 193), its primary conclusion emphasized the same point, showing on overall propulsive efficiency at Mach 0.8 on the order of one-sixth that of a piston-engine driving a propeller. Both men felt that tests of a propulsive duct in the 8-foot high-speed tunnel would be of little value. The duct and heater losses would, they speculated, largely nullify any possibility of net thrust at Mach 0.75.

In fairness to Pinkel and Williams it should be recalled that in 1940 the aircraft industry generally saw no possibility for supersonic aircraft. Mach 0.8 was regarded as a rather optimistic upper limit for the future. The potential of the turbojet for large improvements over the Campini cycle was not recognized either, and it is not mentioned in Williams' paper.

In spite of my disappointing session with Pinkel and Williams I resolved to proceed with the propulsive duct test. At the very least it would establish the Meredith effect as a major design factor at high speeds. Our 8-foot, high-speed tunnel afforded a unique tool for such an experiment. Stack solidly supported the idea. In promoting the project....

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Picture: FIGURE 42.- "Heat model" used in the first NACA investigation of a propulsive-duct (ramjet) system in the 8-Foot High-Speed Tunnel in February and March 1941. Model incorporated a 160-kw heater. Nose B and cusped outlet from ref. 179.
--------------------------------------------------------------------------------

....we decided not to mention the jet propulsion implications in order to avoid the negative reactions of the propulsion people.

The nacelle model chosen for the tests embodied our universal Nose B shape together with our most effective cusped tail outlet (fig. 42). The all-metal nacelle was supported on a new thin metal wing selected to avoid the local area of flow separation that existed in the wing/body juncture of my inlet-outlet model. (In reviewing my original work at the request of Mr. Miller, A. M. Kuethe, who was employed briefly by NACA during the war, had endorsed my findings generally but had raised questions about possible drag interactions involving the separated flow. These would now be answered. By comparing the inlet results from the new model with the original data, we found no measurable effect of the separated flow.)

How to add heat at a high rate was our primary design problem. Combustion of fuel in the 8-foot tunnel was quite out of the question for many reasons. A search of the electrical heater catalogs with help from G. T. Strailman, Langley's principal electrical engineer, turned up no [164] high-output heater capable of being fitted into our 11-inch diameter duct. Baals and I therefore became high-capacity heater designers and produced a 160-kw, three-phase, 15000 F heat exchanger with 32 square feet of surface area in the form of 1.5-inch-wide Nichrome ribbon woven on reinforced asbestos millboard supports. This heater produced air temperature rises of about 3000 F at high speeds with very small frictional losses. The rates of heat input were larger than those due to piston-engine cooling, but still only a small fraction of the heat of combustion of kerosene.

Testing of the "heat model" started in February 1941, the first NACA wind tunnel investigation of a propulsive duct producing thrust. At a Mach number of about 0.5, the propulsive effect had become equal to the internal drag, and beyond this speed substantial net thrust was developed by the internal flow. At the highest test speed, Mach 0.75, the heated duct developed the respectable thermal efficiency of some 9.5 percent, close to the ideal theoretical value. As expected, the phenomena depended on the ratio of duct pressure to stream pressure, and was independent of heater surface temperatures per se. In all other respects, the careful measurements of these tests confirmed the calculations made by our engineering relations for analysis of this kind of internal flow system (ref.187).

COMMENTARY

In 1941 during the period of our propulsive-duct investigations, Stewart Way, of Westinghouse, made an analysis of the subsonic propulsion possibilities of "open-duct jet propulsion," his name for what was later called the ramjet. He also apparently conducted some tests with an electrically-heated model at about the same time of our high-speed tests in February and March of 1941, although the experimental work was never published (ref. 194), and we knew nothing of Way's work until years later. In the first version of our internal-flow-system report which was issued in September 1942 as a confidential document (ref. 189), the propulsive duct data were included but there was no emphasis in the title or text that the first NACA tests of a potentially important jet-propulsion system had [165] been made. Our "heat-model" tests rather definitely settled once and for all the doubts and arguments about the Meredith effect. Whether they had any impact on ramjet development is questionable. The revelation of the British and German turbojets shortly after our paper was issued had such an enormous impact that all the scattered U.S. activities in jet propulsion were in effect rendered insignificant. Almost overnight the propulsion community reversed its attitudes. By war's end, the ramjet was under vigorous development for missile applications. Both the Langley and the Lewis Laboratories of NACA had organized ramjet projects, concentrating on the prime problems of combustion and burner design which we had not been able to deal with in our 1941 project.

NACA was now being severely criticized for its prior general neglect of jet propulsion and it was clearly desirable to highlight whatever had been done. Accordingly, our report was reorganized to emphasize the tests of the ramjet system, and the words "Ram-jet System" were added to the title. The revised version is included in the 28th Annual Report of the NACA, dated 1943 but actually issued after the war.

Bronc

vanir · Oct 12, 2009

So am I reading the report wrong or did the Mustang radiator design, at the speeds the Mustang typically operated at, simply reduce the drag normally associated with a radiator mounting without actually providing any positive thrust. An aerodynamic improvement, but not a "Meredith boost system" as seems to be supposed by some.

Colin1 · Oct 13, 2009

VG-33 said:
The more I read Atwood's texts from you, the more i'm persuaded that he is a great publicist (for his firm) than a great scientist

Try doing some background before you start talking out of your ass - you'll look and feel alot less stupid and by the way he was an engineer, not a scientist.

J Leland Atwood was one of the most prominent aviation engineers of all time, his career started amongst canvas and stringers and ended with the XB-70 and men on the moon.

Altea · Oct 13, 2009

Bronc said:
From the NASA website at: ch5-5

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Chapter 5: High-speed Cowlings, Air Inlets and Outlets, and Internal-Flow Systems

Thank you Bronk, we all know that a so called Meredith effect exists, but it does not ask to the question " how many trust is made by the P-51D cooling system".

drgondog · Oct 13, 2009

great find bronc - do you have the illustration of the heating device?

I would love to see the data under which they concluded that the extraordinary high temp value of the 'ribbons' compared to cooling tubes of coolant at the 220 degree range(vs 3000 degrees) did not infleuence the derived efficiency of his model, as well as the comparable value of surface area (32 sq ft) of the ribbons vs the coolant tubes in the radiator core of a Mustang.

That is a huge differential in the comparative energy balances between the two systems to remove all speculation.

VG-33 · Oct 13, 2009

Colin1 said:
Try doing some background before you start talking out of your ass - you'll look and feel alot less stupid and by the way he was an engineer, not a scientist.

.

Hey, what's the matter to you? You speak bad from your mouth!

From your moronic posts and attitude to me it's clear that you're far to short to explain my job to me. Engeener studies include science and technology either, and some other things. Moroever at Atwood's level that touch applied research matters.

Anyway except some trifles and banalities, you haven't sent any sustented Atwood's physical demonstration to quantify the properly " Meredith effect" part in the Mustang drag.

Ki-61 Hien (Tony) Radiator / Meredith Effect?

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