Talk:Meredith effect

No such thing
This article should be checked for deletion. A radiator can not produce thrust as long as the air is not forced to expand one way. Unlike for a jet-engine or a ram-jet there is no mentioning of compressing the air prior to heating. Only the exhaust gases of an internal combustion engine themselves maybe used as jets. --Moritzgedig (talk) 12:09, 24 January 2014 (UTC)
 * There is such a topic as "The Meredith effect", but whether it really works or not is controversial. Regardless of whether the effect exists, or is a fallacy, it may be worth retaining the article just to gather all the information on it together either way. Not to say this is a hoax, but this is similar to the way Wikipedia documents notable hoaxes as well. For instance none of the computer virus hoaxes listed in Virus hoax are "real", but they are notable enough to have an article to explain that they are not real. - Ahunt (talk) 13:09, 24 January 2014 (UTC)
 * By "controversy" I think we mean "people who don't understand it". It's not that complicated.
 * If you do recommend to delete this, will you be going after the ramjet and SR-71 articles next? Andy Dingley (talk) 13:18, 24 January 2014 (UTC)


 * I just read the refs cited and I don't think there is a case for deleting this, as it meets WP:GNG. It needs expanding, though to explain the subject better!- Ahunt (talk) 13:20, 24 January 2014 (UTC)


 * The effect is definitely real, and was indeed a significant feature in the Spitfire and Hurricane designs as the article currently states. ISTR its aircraft application was developed at Farnborough during the early 1930's and it added around 5-10 kts to the Spitfire's measured airspeed. FYI a ramjet only compresses the air when moving at supersonic speeds (compressible flow): it still works at subsonic speeds (incompressible flow) but much less efficiently. At say 600 knots the only difference between a Spitfire's radiator and a Bloodhound's ramjet is that the Bloodhound has to burn fuel to heat the air while the Spit recycles waste heat from the engine coolant. Doubting whether it works is no more than acknowledging that you do not understand how. HTH &mdash; Cheers, Steelpillow (Talk) 13:45, 24 January 2014 (UTC)


 * I think the refs cited establish that the effect exists, although it is a small effect. I have added some text to the article to explain how it works. It seems fine now, although more could always be added, of course. - Ahunt (talk) 13:48, 24 January 2014 (UTC)

@ Andy Dingley, Steelpillow: I also do not understand how "free energy power plants" work. Maybe you could explain like you explained this. Oh wait you didn't explain it. What surface does the thrust work on? How come the air does not go around the duct? Will the thrust exceed the drag? Was it thrust or just reduced drag? No one of us has to understand it for it to be real, but people just thinking they understand it does not make it real either. --Moritzgedig (talk) 10:12, 25 January 2014 (UTC)
 * There are two ways to look at this: truth or WP:Verifiability.
 * Wikipedia relies on proof by authority: we believe something because WP:RS tell us so. Logically this is considered a fallacy, but it works better for collaborative editing projects because all editors assume that they themselves know "the truth". If we appeal to "reliable" sources, that's better than the collective madness of crowds we'd otherwise see. If you look out for such sources, either from thermodynamics texts or from aircraft history, you'll find this effect widely discussed and described for the Spitfire and the Mustang. As a general rule, things in mid-century British aerospace with a well-known name attached to them will have originally had papers by that author presented to one of the chartered engineering societies and reported in Flight, so searching the archives might turn up a useful primary source for them.
 * Alternatively you could try to understand it. It's a duct, and heat energy is added. As a result, thrust is generated. Note that you have to carry this out in a "duct", which has a more complex meaning in fluid dynamics than is obvious. Ducts are generally shaped internally, so that their pressure and velocity vary in a deliberate manner, to achieve some useful purpose. Yes, the effect here is asymmetrical but "obviously" adding a simple radiator to the outside of an aircraft would be symmetrical and so wouldn't produce a nett thrust in one direction. However this effect isn't in a symmetrical situation: it's inside a shaped duct and there's considerable airflow (so much airflow it's not going to be disturbed by the heat added). Only in this duct does the radiator produce useful thrust: the deliberate Meredith effect is the process and result of designing the internals of such a duct, so that the energy goes mostly to adding forwards thrust, rather than disrupting the airflow and accelerating it forwards in an unhelpful manner.
 * Formula 1 cars (some years ago) had a problem with the anti-Meredith effect. They added so much heat to a small, relatively slower, airstream (from cramming the powerful radiator of a massive engine into the smallest possible draggy airflow) that they could instead stall the airflow through the radiator duct, as the extra heat added wasn't creating thrust, it was raising the pressure inside the duct too much and disrupting the flow.
 * Andy Dingley (talk) 11:03, 25 January 2014 (UTC)


 * @Moritzgedig: I can answer your questions in part, however I do not have references to hand so please take my explanations as my own understanding and not definitive (the reason I gave none before). The duct referred to by Andy Dingley typically has an expanding exhaust section, often including a nozzle or, on the Spitfire, an adjustable flap. Thrust is gained from the pressure of heated air against this expanding section. This may or may not overcome the drag of the installation. I seem to recall that the early Spitfire installations merely reduced overall drag and that only in the later marks was a net thrust created, but I need to confirm that. Some air may or may not go around the duct, depending on the intake geometry and other conditions, but the key point is the same as for a ramjet - enough air is "rammed" into the intake by the speed of travel for the thing to work. The expanding exhaust is directed backwards by the expanding nozzle (in direct reaction against the thrust produced) and this also helps to "draw" air from the inlet through the heat exchanger and maintain flow. &mdash; Cheers, Steelpillow (Talk) 11:40, 25 January 2014 (UTC)
 * Just for the record - I was wrong about the exhaust duct, it is convergent not divergent and does not operate on the pronciple I describe above. &mdash; Cheers, Steelpillow (Talk) 10:13, 30 April 2014 (UTC)

@User:Steelpillow "a ramjet [...] still works at subsonic speeds [...] but much less efficiently." Ok, the air is compressible at the speeds these planes were going. At M=0.3 or 230mph compressibility can no longer be fully ignored as I did. At M=0.5 the effect becomes noteworthy. The article now mentions compression. --Moritzgedig (talk) 18:27, 25 January 2014 (UTC)


 * I have removed the discussion of compressibility from the lead, because I think it did not strike a sensible balance for the lead. I have found a brief description of the ramjet in Kermode, "Mechanics of flight", Eighth edition (1972) and it is broad enough to include the Meredith principle: "It relies on the forward speed, or ram effect, to collect and compress the air which then flows over some source of heat – the Germans originally tried a coal-burning brazier! – from which it gains energy and so flows out of the duct at a higher speed than that at which it entered." Interestingly, Kermode feels it necessary to emphasise the fact that it works in bold type and to print a full-page photograph of a missile employing them. Evidently scepticism is commonplace. Anyway, note that if we exchange the German's brazier in their ramjet for a Glycol heat-exchanger then we arrive at the Meredith device. I should like to see a section on the "Principle of operation". My problem is that I have nothing to use as a source, and I fear that if we post our personal speculations that will go against WP:VERIFIABILITY and/or WP:OR (original research). Until a reliable reference can be found, it is probably better to say as little as possible. &mdash; Cheers, Steelpillow (Talk) 19:39, 25 January 2014 (UTC)
 * What I wrote was not unsourced, the source is already given. It neither is an explanation nor speculative. Compression is needed in any such Brayton cycle device (assuming that it is and that it is a known TD process). "it did not strike a sensible balance for the lead" That might be the case, but the lead already touches on the subject of needed speed. --Moritzgedig (talk) 09:36, 26 January 2014 (UTC)
 * Fair enough. I have taken a deep breath and created a section for the technical analysis. Feel free to make corrections (quite likely needed) and/or further contributions. &mdash; Cheers, Steelpillow (Talk) 13:55, 26 January 2014 (UTC)

A 1941 Flight article with an explanation, and quote from Meredith here:  and an earlier 1937 article based on a lecture by Roy Fedden here:  and another article mentioning 'Mr Meredith of the RAE' here;  — Preceding unsigned comment added by 80.7.147.13 (talk) 20:41, 1 March 2014 (UTC)

BTW, F. W. Meredith later worked on automatic pilots and after he left the RAE, took up a position at Smiths Instruments. — Preceding unsigned comment added by 80.7.147.13 (talk) 19:59, 8 March 2014 (UTC)


 * The article should be deleted, and kept from being rewritten unless it's an article about cooling systems in piston motored planes. There is no additional "thrust" created, and the assertions made about the air speed through the system show either an completely ignorance of thermodynamics or else an intention to deceive. Those who attempt to justify such nonsense should have all other work questioned, as perviously stated, based on their ignorance or intent to publish irrelevant imaginations as facts. This sort of hogwash is the reason that students with no water sailing experience believe the bogus claims of the physics behind the lift created by aircraft wings. -Dirtclustit (talk) 21:18, 8 April 2015 (UTC)


 * See 2015 ARPN PDF here:  — Preceding unsigned comment added by 95.150.100.255 (talk) 19:06, 21 April 2016 (UTC)

@Moritzgedig-The Meredith effect does in effect "compress" the air. Incoming air will be traveling-relative to the plane at 100-400 mph. The diffuser before the radiator will slow the air, and its static pressure will increase. As heat is transferred to the air by the radiator, it will expand to stay at ~ constant pressure. The now hotter air will be re-accelerated by the nozzle to produce some propulsion or at least reduce drag. The process is similar to nuclear-jet propulsion. . ~JoeB34997152 — Preceding unsigned comment added by Joeb34997152 (talk • contribs) 23:37, 4 August 2016 (UTC)

1935 or 1936 ?
I find August 1935 http://naca.central.cranfield.ac.uk/reports/arc/rm/1683.pdf as the year of publication not 1936 as the article states. Vandalism? --Moritzgedig (talk) 17:47, 25 January 2014 (UTC)
 * Look closely at the cover sheet. The Director of Scientific Research appears to have passed it on to the Aeronautical Research Committee in August 1935, but the committee did not publish it until the date shown on the second line from the bottom, just above the price: 1936. &mdash; Cheers, Steelpillow (Talk) 19:09, 25 January 2014 (UTC)

Principles of Operation wrong
A sub-sonic Meredith effect ducted radiator differs from a supersonic ramjet. A supersonic ramjet uses a constriction and resulting shockwave to compress and slow the air before further heating it, but constrictions only compress supersonic flows. A subsonic flow is instead expanded and accelerated by a constriction. So a Meredith effect duct first diverges, causing the flow to compress and slow before it meets the heat source, and then the exit nozzle is purely convergent in contrast to a ram jet's convergent-divergent nozzle. These facts were key to my understanding of the effect, but were only implicit in Meredith's original paper. They are confirmed by diagrams of the P51's radiator duct, e.g. http://i101.photobucket.com/albums/m56/babraham227/51.gif And here is a site that seems to have it straight: http://contrails.free.fr/engine_aerodyn_radia_en.php But the wikipedia article seems to be describing the principles of operation of a supersonic ramjet. In particular, while the forwards thrust is developed on the divergent section of the duct, unlike in a supersonic ramjet that section is not the exit but the inlet (called a diffuser). A Meredith ducted radiator is a subsonic ramjet, but as subsonic ram jets are quite different to supersonic ones, and probably more people are familiar with the supersonic version, it probably doesn't help to say so. thomas 86.159.241.198 (talk) 20:23, 28 April 2014 (UTC)
 * I agree that the current version has it wrong about the exit duct but then, I don't think the web page you link to is correct about everything either. The idea that the forward section of the outer profile can create thrust is not widely accepted: close examination of the pressure profile over such a body invariably reveals a greater drag force on the leading edge region (where the airflow turns sharply down) which overpowers any small thrust from lower pressure region between it and the point of maximum thickness. What we need are reliable sources. Still, if anybody can meanwhile kill the divergent exhaust story, that would be good. &mdash; Cheers, Steelpillow (Talk) 21:41, 28 April 2014 (UTC)


 * I have now changed the discussion of flow in the rear section. I believe that the accelerated airflow causes a reduced pressure on the duct walls, but I am not sure if that is the correct/only explanation for the forward thrust, so I have left it all a bit vague. &mdash; Cheers, Steelpillow (Talk) 09:59, 30 April 2014 (UTC)


 * As i see it, if the Meredith effect produces positive thrust, that must be explicable in terms of Newton's laws, as a heat engine, and in terms of the forces from the air flow acting on the duct and radiator.


 * Newton's laws say that, to produce forwards thrust, the system must throw air backwards; there must be more momentum in the wake than up-stream, so i can see why you're identifying the converging exit nozzle where the air expands and accelerates backwards as the place where the thrust is produced. That also fits with the heat engine view: to convert heat into work, the air must be following a pressurise -> heat -> expand cycle, with the expand phase doing more work than was done to pressurise the air.


 * But if you look at the pressure of the airflow acting on the duct, it's not so clear. Throughout the duct the pressure is above ambient, returning back to ambient only at the end of the exit nozzle. It's above zero everywhere. This implies a rear-wards force on the inside of the converging rear section of the duct and a forwards force only in the diverging front section.


 * So i think it's the high pressure air in the duct ahead of the radiator that communicates the forwards thrust to the plane, but the existence of that zone of high pressure depends on the convergent exit nozzle returning the flow to ambient pressure. With a cold radiator the forwards force on the front part of the duct is balanced by the rearwards force on the exit nozzle.


 * Heating the air causes it to expand, and to maintain continuity of flow it must accelerate rearwards, implying an additional pressure drop across the radiator. Unlike the skin-friction component, this additional pressure drop mostly doesn't act on the radiator because the radiator is mostly empty space. But it does reduce the rear-wards forces on the exit nozzle. (It's only if you're looking at the difference that radiator heat makes that you'd see a forwards force on the exit nozzle.)--Moth78 (talk) 13:14, 22 May 2014 (UTC) (thomas)


 * " ... It had been demonstrated by Meredith of the R.A.E. that this effect was not wholly detrimental, it having been established that a ducted type of cooling system could function as a heat engine, the heat energy imparted to the air in cooling the energy being converted to an effective thrust by adiabatic expansion. The thrust obtained increased approximately as the square of the speed. ..." 1937 quote from Roy Fedden here:  — Preceding unsigned comment added by 2.29.18.231 (talk) 10:23, 20 December 2015 (UTC)

Radial Engine Effect Section
"Many engineers did not understand the operating principles of the effect. A common mistake was the idea that the air-cooled radial engine would benefit most, because its fins ran hotter than the radiator of a liquid-cooled engine, with the mistake persisting even as late as 1949."

So, WHY is this wrong? The article doesn't say. The description appears to state that all you need to get thrust is to heat the air into a convergent/divergent nozzle. So why can't this be done on a radial?

Maury Markowitz (talk) 14:51, 26 May 2014 (UTC)


 * The source does not explain why. I believe it is because the important thing is not the temperature but the amount of heat transferred, and that is the same for any engine with a given power output and efficiency. But since that is not sourced, it cannot be said. &mdash; Cheers, Steelpillow (Talk) 16:31, 26 May 2014 (UTC)
 * Just to clarify, it can indeed be done on a radial, but the engine does not benefit MORE than a liquid-cooled type. &mdash; Cheers, Steelpillow (Talk) 16:35, 26 May 2014 (UTC)


 * Radial engine use of the Meredith effect on the Convair 240 in a 1946 issue of Flight here:  — Preceding unsigned comment added by 95.149.53.233 (talk) 13:30, 13 March 2016 (UTC)


 * This was why I came to the talk page, it really feels like someone was hung up on liquid cooling and overstated the case against radial cowlings. The whole article is a mess of legacy edits, needs to be redone from fundamentalsJmackaerospace (talk) 00:29, 10 May 2021 (UTC)

Schueler Cratus
Per and others, there's some back and forth editing on whether the Cratus design by undergrad student Samantha Schueler should be included.

There are two refs included (of several out there, just Google it) which demonstrate that the design was awarded an American Institute of Aeronautics and Astronautics (AIAA) prize in a student design competition. One ref mentions that the Meredith effect was considered during the design. Should this section be included or not?

IMHO, no. It does not show any significant relevance to the Meredith effect. It does not appear to be substantially reliant on it (I don't doubt that the ability to keep the screen clear in flight, or the cupholders stable, was considered too). The sources are certainly weak on any detail of this. I can't see the student design paper visible on-line, which would be a big influence on judging it noteworthy here. I also doubt whether there's much Meredith effect to be had. It uses three BMW car engines, presumably turbocharged, and as modern engines (especially turbocharged) simply don't reject the same levels of waste exhaust heat as WWII V12s did, there's less energy for Meredith to work with.

This might yet be significant, but it needs a better source, probably the design paper, to demonstrate what relevance Meredith has to it, and more importantly here, vice versa. At present, it doesn't. Andy Dingley (talk) 16:24, 6 August 2015 (UTC)


 * My main point in the revert was that we should have this discussion and not just delete cited text from an article because some IP editor thinks it was a student paper and thus not worthy of consideration, so thank you for starting the discussion.


 * I agree that we need some more information to determine just how notable this aircraft is to this article. One concern is that there is no indication from the FAA that this aircraft was ever built or flown. To my way of thinking if it wasn't built then it probably isn't worth mentioning, but I would like to hear from more editors on that. - Ahunt (talk) 16:40, 6 August 2015 (UTC)
 * I'd be amazed if it was built, let alone flown. Two years to get a student project into flight?  This isn't some "J-3 Cub with a solar panel on it", it's a high performance multi-engine aircraft with a wing loading no sane pilot would go near, intended purely for the Reno types. It's not just an aircraft, it's a really high performance aircraft (it's pointless otherwise) and so building it is far from a minor self build. That  doesn't happen without a stack of cash, so chances are that it just hasn't happened. Andy Dingley (talk) 16:49, 6 August 2015 (UTC)


 * I agree, the evidence that any examples were built seems to be lacking. - Ahunt (talk) 17:20, 6 August 2015 (UTC)


 * We seem to have an IP editor back to trying to remove this, despite no clear consensus here to do so. The tenacity if this is making it look like some sort of personal vendetta, so I am treating this as vandalism unless a clear consensus to remove it is achieved here. - Ahunt (talk) 15:23, 15 January 2016 (UTC)

Actually the consensus is for it to be removed. I have no vendetta at all and am actually involved with aircraft engineering that uses this for reduction of cooling drag. Some have flown. But even these real life aircraft do not warrant inclusion since they do not provide the reader with useful information. I went to the wiki page to find useful information and found a useless reference to a paper aircraft (not an actual aircraft or engineering study on the subject) in the main text. Your wife's paper may be great. But many paper aircraft have made claims that they will use this and this alone is not useful information. — Preceding unsigned comment added by 2602:304:AE99:A229:755D:B031:F6BD:6A74 (talk) 17:18, 19 January 2016 (UTC)


 * Actually no, there is no consensus to remove it above and recently all we have seen is your edit-warring and insults about this subject. "Your wife's paper may be great" - am not clear what you mean by that, what are you implying? Your removals have now been reverted by three different editors, so that does show an editing consensus to keep it. The design seem to have not been built, but it won an award and has been covered in independent third party refs, so that gives it some notability. Personally since the article is fairly short I think it would be better to add more examples of designs that use this, that remove the few that we have. - Ahunt (talk) 17:46, 19 January 2016 (UTC)

Please read the above and you will see the consensus was that it was not relevant. Please note that I absolutely never insulted anyone or anything and I hope you refrain from personal attacks in the future. I stick to stating the obvious facts and reasons. To me you are the one who is edit-warring like you have in the past with other pages. You are the one who made claim to a "personal vendetta" when in fact none exists on my part. There is no "notability" in a paper design even if it won an undergraduate award against a few other papers. But the real point here is the inclusion does not pass the most basic test of what should be included. Does it provide useful information to users of Wikipedia? No it does not. I am not at all fighting you or your friends. I am just trying to keep Wikipedia useful to everyone and I will keep trying to help where it is needed. — Preceding unsigned comment added by 2602:304:AE99:A229:755D:B031:F6BD:6A74 (talk) 19:42, 19 January 2016 (UTC)


 * You are still edit-warring to get your own way and vandalizing the article. You haven't made a convincing case here to remove it, so until you do it stays. - Ahunt (talk) 03:47, 21 January 2016 (UTC)


 * Your vandalizing of the article has now been reverted by four different editors. There is now a fairly strong editing consensus that this should be retained. Unless you can create a new consensus here future removals will continue to be treated as vandalism. - Ahunt (talk) 03:08, 23 January 2016 (UTC)


 * There has been no further discussion on this item for the past three years. I recently decided to just remove it, since it has been seven years and no examples of the design have been built. The removal was reverted, so I am bringing it here for a consensus. My thought is, regardless of any awards won, a set of drawings of an aircraft that no examples were ever built is just not notable enough to retain as a mention in the article. I propose it be removed. - Ahunt (talk) 21:26, 4 May 2019 (UTC)


 * It was just re-added today and I have removed it again as our present consensus here is to not include this design. I can't see how a student design that has no examples of the aircraft actually built can be notable. If one gets built and flown I would be in favour of including it, otherwise not. - Ahunt (talk) 21:07, 14 September 2019 (UTC)

This Article Should Be Deleted
This article is based upon silly, sophomoric "junk science", and it attempts to describe an effect that does not exist in the real world. In fact, if it did, it would violate the laws of physics. What is described here is essentially a "free energy" device. Whatever heated air (or liquid) that the engine radiator generates is offset by increased drag. Furthermore, if the air is heated it would expand, yes. And if that expanded air was directed into a decreasing conic section it would indeed speed up a bit. However, the amount of "additional thrust" would be completely negligible, and insignificant and would not in any way add anything to the forward thrust of the aircraft. It would be about the same as gluing balloons to the aircraft tail and letting the air out. Insignificant.

The P-51 used an underbelly intake duct because of the design of the aircraft and the position of the engine within the airframe. It has nothing to do with this so-called, fictitious "Meredith Effect". There have been no papers or actual engineering research published to confirm this "effect". None. If it did work as described (?) in this article, then all subsequent prop-driven aircraft would have had this scoop to "compress" ... oh come on. Everyone knows that doesn't work as claimed. And it is NOT related to ramjet engines, which operate at supersonic speeds and are a completely different effect and topic. Someone please delete this article. It is based on a fiction and cannot be substantiated by any reliable source. 73.6.96.168 (talk) 04:16, 24 August 2020 (UTC)


 * Well you can always send it to WP:AFD if you think it should be deleted, but with four cited sources it is unlikely to get deleted there. But if it really is "fake science" as you claim than I would suggest that the article should stay, but reflect that. All you need is some reliable sources that say that it is a "non-effect", preferably at least four to counter the existing four refs. - Ahunt (talk) 13:53, 24 August 2020 (UTC)


 * I am reading everything I can find on Meredith effect, and on Townend rings. Meredith is a thing, at least to the extent that all sorts of articles on WWII aircraft cooling systems mention it.  A Meredith effect radiator does not violate laws of physics as far as I can tell.  You are adding heat to the working gas, and expanding it through a nozzle.  A speed increase of 10-15mph can reflect a substantial reduction in the drag of a radiator, as opposed to it actively generating thrust.  This page is relevant.  Let's keep it.  JHowardGibson (talk) 23:13, 24 January 2021 (UTC)

Basic Thermodynamics for the UnBelievers
There are some pretty bizarre objections to this article from people that seem to know a little physics but not much thermodynamics. I think this might be partly because older versions of the article had false claims that have now been removed, but I am just going to go over the ones I spotted. The basic principle is so fundamental (use heat to expand/accelerate air to generate thrust) I am actually a little surprised that anyone could disbelieve it.

Claim: it's free energy junk science
A lot of "free energy" designs are not really "free", but are in fact energy scavenging devices that only work on paper when you discount friction and other losses. You can't generate work from them or in a lot of cases even generate enough work to overcome their own internal friction. But the issue isn't that "they don't work", but that some people make inflated claims about what are basically classroom physics toys.

But... while many "free energy" devices are really just energy scavengers, that is not the same thing as the concept of energy scavenging being junk science. Stirling Engines and Dielectic generators are both commonly run on "waste" heat. Recovering usable energy from waste heat is a huge part of modern engineering design. The difference between a classroom physics toy and a power station is scale.

Claim: Ramjets don't work at subsonic speeds
This one is just flat out backwards and wrong. Ramjets need to operate above a certain speed to generate ram pressure, but that speed is well below the speed of sound. In fact, the largest losses in supersonic engines comes from deccelerating supersonic airflow to subsonic speeds because fuel will not burn in a supersonic airflow.

(it might be worth removing an reference to ramjets, because there is not really any comparison between the ramjet pinciple and what this is. Ramjets generates heat by burning a compressed fuel/air mixture. This article describes a heat exchanger process. Compression has nothing to do with it.)

Claim: the drag will outweigh the benefit
This one is reasonable, until you factor in that the drag was there already. This is the engine cooling system. Unless you make the entire skin of the aircraft a radiator, you are going to be in some way gathering air and transfering heat by conduction (and generating drag in the process). That air is hitting the plane and generating drag regardless. In the simplest of aircraft designs, the engine is just left exposed and the air flow cools it directly. The drag is always there, subsequent design is about minimising that. However large or small the any thrust effect might be, so long as a "Meredith" cooling system does not add MORE drag than a non-Meredith system, the overall result is a net gain. (absolutely a badly designed system might add more drag than an alternative, but drag is one one those things that is endlessly tested during design)

Claim: The effect is negligable
This is the most reasonable objection of all. Except it hinges on the question: what is the definition of a negligble effect on a high performance aircraft? Shaving rivets off the leading edge of the wing? Switching from fabric wings to stressed metal? Changing from 70% octane to 100% octane? There is only one definition that matters: has there there been shown to be a measurable difference in perfomance? It might be the case that this effect really is negligible. But, from the fact this article has citations and the concept has existed since the 1940s, it would seem to suggest that there is data out there better than the arguments on a Talk page.

If actual citations of evidence DISPROVING this effect exists, by all means add it to the article, but all of the objections below amount to "I don't see how this could work, therefore it can't." Jmackaerospace (talk) 00:25, 10 May 2021 (UTC)


 * Thanks. Perhaps one point on a negligable effect is that sometimes there is a benefit, but it's just too complicated in some way, and not worth the effort, or too expensive to make it worthwhile. A lot of good ideas failed not because they were bad ideas, but because they just didn't add enough value to be worth it. BilCat (talk) 00:47, 10 May 2021 (UTC)

The Original Source
I found it! The article contains much, much math, and an analysis of head losses of air flowing through radiators, and through ducts to and from radiators. We can see that if the radiator is contained in the fuselage or wings, the front area of the aircraft is reduced. It logically follows that the inlet duct is smaller than the frontal area of the radiator. Since the duct increases in size, we expect the air velocity to drop and the pressure to increase as per Bernoulli's principle. Some web sites remark on this, but it probably is an artifact of the duct's reduced frontal area. Meredith notes that the air passing through the radiator will increase temperature by around 40C&deg;. I suspect that the radiator can be enlarged to dump heat at a reduced head loss. Meredith proposed at the end of the paper, that the heat generated by the radiators and the engine exhaust can be recovered to generate thrust — which is what we are discussing here.

It appears that Spitfires, Bf-109Es, de Havilland Mosquitos and P-51 Mustangs were designed to use Meredith effect. Curtis P-40 Warhawks, Hawker Typhoons, the production Tempests, and Lockheed P-38 Lightnings did not employ the principle. Annular radiators, used on Junkers engined Ju 88s and Fw 190s, probably did not get much thrust from radiator air, but the design reduces frontal area.

JHowardGibson (talk) 20:13, 10 May 2021 (UTC)


 * Thanks for finding that! It should the naysayer debates. - Ahunt (talk) 20:29, 10 May 2021 (UTC)