On the Meredith Effect
- Thread starter maxmwill
- Start date
Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
The Mosquito made use of the Meredith effect, I don't know that it had to use a scoop, however it was arranged has to be low drag to be worthwhile.
swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
It would require an efficient inlet, to slow the air, a minimal air pressure drop in the radiator, and an efficient nozzle. Having the highest possible temperature in the radiator would also help.
Shortround6
Major General
to add to that the exit nozzle/area, needs to be variable in area in small steps, A fixed exit or two position exit is only going to be efficient an certain airspeeds and air densities.
- Thread starter
- #5
Ok. My reason for the question concerns the Heinkel He-119.
Could the exit nozzle be variable? As I recall, the exit on the scoop of the P51 was variable, so couldn't it be achieved with something similar to cooling gills on cowl(anything with a radial)? How were cowl flaps controlled? Couldn't something like that be used for an annular nozzle for the He119?
Could the exit nozzle be variable? As I recall, the exit on the scoop of the P51 was variable, so couldn't it be achieved with something similar to cooling gills on cowl(anything with a radial)? How were cowl flaps controlled? Couldn't something like that be used for an annular nozzle for the He119?
Shortround6
Major General
HE 119
The radiator was semi retractable. WIthout extensive redesign getting the Meredith effect to work in going to be very hard. Adding a ring or flap is not going to do it.
Mustang
The radiator is many times the size of the inlet scoop and many times the size of exit 'nozzle'. This allows for the air flowing through the radiator to do so at a much lower speed, and since drag goes up with the square of the speed this is a significant advantage. (despite the increased weight and volume needed for the radiator.) It also allows for an extra fraction of a second for the air to pick up heat from the radiator. The length of the ducts and the shape allow for a smooth flow with less turbulence than a shorter steeper angled duct might have. As the heated air leaves the radiator it has to be compressed to accelerate back up to speed, if it exits the nozzle at less speed than the plane is going there is no thrust. Again the rate of compression (slope/shape of the duct) is important as if it done too quickly (to short a distance) you will create a high pressure point in the duct that affects the airflow through the whole duct.
For the He 119 you might need to extend the inlet duct several feet forward and several feet aft of the original openings (or move the whole radiator back).
The theory was simple, the execution was difficult. Amd it is something that pressy much has to be designed in from the start. trying to add it on at a later date is not going to work very well.
The radiator was semi retractable. WIthout extensive redesign getting the Meredith effect to work in going to be very hard. Adding a ring or flap is not going to do it.
Mustang
The radiator is many times the size of the inlet scoop and many times the size of exit 'nozzle'. This allows for the air flowing through the radiator to do so at a much lower speed, and since drag goes up with the square of the speed this is a significant advantage. (despite the increased weight and volume needed for the radiator.) It also allows for an extra fraction of a second for the air to pick up heat from the radiator. The length of the ducts and the shape allow for a smooth flow with less turbulence than a shorter steeper angled duct might have. As the heated air leaves the radiator it has to be compressed to accelerate back up to speed, if it exits the nozzle at less speed than the plane is going there is no thrust. Again the rate of compression (slope/shape of the duct) is important as if it done too quickly (to short a distance) you will create a high pressure point in the duct that affects the airflow through the whole duct.
For the He 119 you might need to extend the inlet duct several feet forward and several feet aft of the original openings (or move the whole radiator back).
The theory was simple, the execution was difficult. Amd it is something that pressy much has to be designed in from the start. trying to add it on at a later date is not going to work very well.
- Thread starter
- #7
I realize that, because the powerplant used in it was very similar to the Rolls Royce Goshawk, which was also an evaporatively cooled engine. And look at how successful that was. I'm not sure, but did the Germans try this on other aircraft, other than the He100 fighter? The British used this on a number of flying machines built, and was also proposed for such designs as RJ Mitchell's design for the Type 232, his contribution being a gull winged four engine patrol flying boat of the Sundeland class. In this case, the intake for the condensers being the entire leading edge of the wings.
My thought is if something similar to the belly scoop on the P51(as well as the MB5 and the Australian Mustang lookalike, but not scoop shaped, but one with an equal amount of area, could be doable.
I'm not sure if the Germans were even aware of the Meredith Effect, even though at the time of the 119m they might've had more than a few Mustangs brought down that they might have studied. I dunno, but if they weren't(and I have yet to learn that they did know of it, if only by dint of studying the Mustand cooling system in toto), wouldn't something like this be useful now, given advancement in materials technology since the War? I'm speaking as as mechanic who has been doing too much thinking. so perhaps I'm sorely mistaken in my assumptions. Still, it might be something worth consideration, 'cause an engine that can dissipate engine waste heat at a higher rater due to higher temp/ambient temp differential.
This is what I get for being the kind of person who thinks a few miles outside the litter pan.
My thought is if something similar to the belly scoop on the P51(as well as the MB5 and the Australian Mustang lookalike, but not scoop shaped, but one with an equal amount of area, could be doable.
I'm not sure if the Germans were even aware of the Meredith Effect, even though at the time of the 119m they might've had more than a few Mustangs brought down that they might have studied. I dunno, but if they weren't(and I have yet to learn that they did know of it, if only by dint of studying the Mustand cooling system in toto), wouldn't something like this be useful now, given advancement in materials technology since the War? I'm speaking as as mechanic who has been doing too much thinking. so perhaps I'm sorely mistaken in my assumptions. Still, it might be something worth consideration, 'cause an engine that can dissipate engine waste heat at a higher rater due to higher temp/ambient temp differential.
This is what I get for being the kind of person who thinks a few miles outside the litter pan.
MIflyer
1st Lieutenant
If you will do a search for the post More P-51 Design Information you'll find an article by Lee Atwood on the use of the Meredith effect with the Mustang,
Merediths work was published in 1936, the Spitfire Hurricane and Mosquito also made use of it, with varying degrees of success.
- Thread starter
- #10
I will, but my understanding of the Meredith Effect is that it is related to the Burnoulli Principle, in that the speed of a fluid increases simultaneously with the decrease in pressure(or a decrease in the fluid's potential energy. since additional energy is being pumped into the fluid, as in the case of the radiator of the Allison or Merlin engines, it is the decrease in pressure which occurs). I'm not a trained engineer, but a dumb aeroplane mechanic, hence this verbal groping. I'm trying to understand the He119 better with regard to the problems they had with it, and feel that an annular condenser somewhere aft of the engine or cockpit might be a solution. You could refer to this thought as a work in progress.
And if you really think that I actually consider myself to be dumb, you never say my "dumb and stupid" charges tacked onto repair bills when I am confronted by the rare pilot-owner who treats me like a dumb and stupid airplane mechanic, simply because I tend to get dirty and greasy working flying machines.
What I've been trying to see is if, instead of a discrete scoop, the 119 could've used a modified annular "scoop", a torus that would be designed to be part of a venturi.
Mebbe I'm barking up the wrong tree, because that was never done(even elsewhere, I think), but perhaps it could be something that could be applicable now.
Where does the bold in your post come from with regard to me? The Meredith effect is quite easy to explain much harder to do effectively. The Spitfire used it but not very well. The inlet was on the wing surface and had problems with the boundary layer, the outlet was also poor. Despite this Supermarine kept it as it was, even on the successors to the Spitfire. Hawkers tried a cooling system with the inlet under the fuselage on the Typhoon/Tempest but reverted to the chin type, it isn't easy to change things about once a design is made.
- Thread starter
- #12
I don't know where the bold came from, because I didn't do that. I wasn't trying to make any sort of emphasis. I don't pull those sort of games.
That said, from what you say, the Effect is dependent upon the scoop, or the duct. My reasoning was to see if such a scoop/duct concept, not a specific shape, the underside scoop, modified to an annular type, but then, as said earlier, perhaps I'm barking up the wrong tree. My apologies for any misunderstanding.
That said, from what you say, the Effect is dependent upon the scoop, or the duct. My reasoning was to see if such a scoop/duct concept, not a specific shape, the underside scoop, modified to an annular type, but then, as said earlier, perhaps I'm barking up the wrong tree. My apologies for any misunderstanding.
wuzak
Captain
The He 119 had a DB 606, which was a twinned DB 601. As far as I am aware, it wasn't evaporatively cooled. It may not have had a pressureised system, as I believe some early DB 601s didn't.
To me a better idea would be to have the inlet in the wing leading edge. The P51 had an excellent system, but it was designed like that from the outset. One of the things that really took off in the build up to war was the huge number of wind tunnels built. The NACA profiles and research on laminar flow / boundary splitters were a product of this. The inlet scoop on the P51 had several incarnations before they got it right I believe.
Meredith was at the Farnborough with my Uncle TP de Paravicini who wrote the original concept of Negative Drag and was hired by Rolls Royce and the first patents were in the name of his boss James Edwin Ellor. but TP de Paravicini had several patents first 471,371.
Rolls Royce cross licenced some to the Germans before the war. He did not earn anything out of the patents.
I suggest you google TP de Paravicini. he was the true inventor of Negative Drag.
Rolls Royce cross licenced some to the Germans before the war. He did not earn anything out of the patents.
I suggest you google TP de Paravicini. he was the true inventor of Negative Drag.
Couldn't get a hit, what were his first names, welcome to the forum BTW.
TP de Paravicini. Or Thomas Pitt de Paravicini.
- Thread starter
- #18
Welp, Mitchells Type 232 patrol flying boat had 4 Rolls Royce Goshawks, and the condenser inlet was the entire leading edge. Will Green stated in the Heinkel chapter on the 119 that the engine(s?) were evaporative.
- Thread starter
- #19
My apologies, but according to William Green in his Warplanes of the 3rd Reich, it wasn't a DB606, but a doppel DB601, and the 119 center section carried the surface evaporative system, with a system of pipes carrying the steam under the wing skin where it was to liquid by cooling and returned to the engine circuit by centrifugal pumps. To make a long story a bit shorter, it wasn't enough, hence the additional radiator.
Which is why I asked my original question. I completely forgot about the leading edge, and had though that something along the lines of a circular slot the circumference of the after fuselage might've helped solve the heating problem, and might even have been engineered to provide a bit of additional thrust if the after end of the cooling circuit(where the heat goes) had a shaped nozzle aft of the tail.
In short, yes an annular ring or cowling could theoretically do the job. I don't know if it'd work on the He-119 because of the cockpit position firstly, and secondly because you'd need an entirely new radiator -- but if you could get around that I guess you'd be okay.
It's a bit more complicated than that in practice since you are effectively doing two things simultaneously: On one hand you're trying to cool the engine down, and on the other hand, trying to produce thrust.
- Radiator Intake
- The position of the propeller should be considered: A tractor-prop generally (if not always) produces more airflow to the engine/radiator than a pusher will.
- The area of the intake/cowling should be of sufficient area to feed an adequate amount of airflow to the radiator/cylinder heads.
- The intake/cowling should have a divergent shape to capitalize on ram-compression: That being said, a balance is needed to ensure adequate flow through the radiator (many radial engines don't heavily exploit the Meredith effect, but the bell mouth shape is clearly seen on the Fw.190, Northrop P-61, Hawker Tempest II, and Sea Fury).
- The airflow into the radiator should be laminar or as close to it as possible: Since turbulent flow gets more extreme the further back along the fuselage and wings, an argument could easily be made to put them in the nose or wing leading edges. They can be placed elsewhere, though a splitter might be good idea.
- Radiator Outlet
- There should some method of varying the area of the radiator-outlet/cowl to adjust the area so as to allow sufficient airflow through the cowling at low speeds, while allowing a nice high velocity and low area at high speeds.
