# High-Drag Areas on the Supermarine Spitfire



## Zipper730 (Jan 26, 2019)

If I recall the canopy was a sore-spot because, unlike many US designs, had the bullet proof plate outside the canopy (interestingly, I think the Germans did exactly what the British did). Were there any other areas there were problematic on the aircraft?


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## wuzak (Jan 26, 2019)

Only the early models had exterior bullet proof glass. Maybe Mk I, II and V.

Definitely internal for the XIV.

The angle of the window was a problem, worth a few mph.

The cannon barrels cost about 8mph. The radiator installation was not as good as it could have been - with mismatched inlet and outlet volumes, and only 2 positions for outlet flap.

External mirrors also caused drag.

Surface finish was, probably, also a factor.


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## wuzak (Jan 27, 2019)

Zipper730 said:


> If I recall the canopy was a sore-spot because, unlike many US designs, had the bullet proof plate outside the canopy (interestingly, I think the Germans did exactly what the British did). Were there any other areas there were problematic on the aircraft?



I am not sure that it was a "sore-spot", since many US aircraft contemporary to the Spitfire I did not have armoured glass at all, and barely had any protective armour.

The armoured glass was on the outside, as it was, almost, an afterthought.

I haven't found the definitive answer yet, but it appears that internal armoured glass was introduced at some point in the Mk.V production run. The Mk.IX did not have it externally.


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## Airframes (Jan 27, 2019)

The armoured glass was retro-fitted in late 1939 to early 1940, being external on the MkI, MkII and early MkV.
From late MkV on through the rest of the Marks, the glass was internal, with a different style of windscreen frame, and an alteration to the slope angle of the screen.
Changes to the rear view mirror, from the early, rectangular style, to the streamlined 'racing car' type, improved things slightly, from memory 'saving' around 2-3 mph. However, when Spitfie XIVs were detailed for anti 'Diver' ops - chasing the V1 - these later style mirrors were removed, as part of a series of measures to increase speed and, again from memory, produced a 'saving' of around 5 mph.
Some pilots did their own mods, and had the mirror mounted internally, under the arch of the windscreen frame.
Change from the early, flat-sided canopy to the 'blown' type, not only improved canopy opening and eventually jettison in emergency, but also gave a slight speed increase, which was improved upon further with the later 'bubble' canopy and low fuselage spine.
Most of the 'drag reducing' mods are covered in the Shacklady & Morgan 'bible' on the Spit, "Spitfire, The History".


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## tomo pauk (Jan 27, 2019)

The radiators were without boundary-layer splitter or tunnel, that will increase the drag. The 2-stage engines needed a modified radiators' systems, those were draggier than what 1-stage engines used. Griffon engines needed greater cooling capacity -> bigger radiators - > more drag. Fixed tailwheel will cost a few mph, so will non-covered main wheel wells; some later versions were with retractable tail wheel and covers for wells. the 3-per-side exhausts were probably also draggier than 6-per-side.
Ram air intake was also probably a source of drag (was changed with late Seafires).


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## swampyankee (Jan 28, 2019)

Dave Lednicer did CFD analyses of severa WWII-era aircraft, including the Spitfire, and published the results in one of the professional journals. You should be able to get a copy of the article through a university library.


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## pbehn (Jan 28, 2019)

swampyankee said:


> Dave Lednicer did CFD analyses of severa WWII-era aircraft, including the Spitfire, and published the results in one of the professional journals. You should be able to get a copy of the article through a university library.


This? http://www.wwiiaircraftperformance.org/mustang/Lednicer_Fighter_Aerodynamics.pdf

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## Zipper730 (Jan 28, 2019)

wuzak said:


> Only the early models had exterior bullet proof glass. Maybe Mk I, II and V.


Oh, I didn't know they changed that.


> The angle of the window was a problem, worth a few mph.


Was there ever a reason to explain why they used such a steep canopy angle?


> The cannon barrels cost about 8mph.


What's typical for a fighter of the era?


> The radiator installation was not as good as it could have been - with mismatched inlet and outlet volumes, and only 2 positions for outlet flap.


Was the inlet area too small or too large? Also, I assume the outlet flap had variable positions on most aircraft?


> External mirrors also caused drag.


True, but that probably made for a major improvement in situational awareness.


> Surface finish was, probably, also a factor.


Did the RAF have a poor finish?



Airframes said:


> The armoured glass was retro-fitted in late 1939 to early 1940, being external on the MkI, MkII and early MkV.


So from the Mk.VI or VII they had internal framing?



tomo pauk said:


> The radiators were without boundary-layer splitter or tunnel, that will increase the drag.


Out of curiosity, why did they omit that?


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## pbehn (Jan 28, 2019)

The thing with bullet proof glass is it is thick, the more you incline it the more optical distortion you introduce.


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## Airframes (Jan 28, 2019)

As stated in my original post, windscreen armour was internal from late Mk.V onwards.
Pics below show later internal armour, inside and outside views, and original, 'bolt on' external armour.


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## tomo pauk (Jan 28, 2019)

Zipper730 said:


> ...
> Out of curiosity, why did they omit that?



Did they omit it, or they didn't now that thing actually exists in mid-1930s?

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## pbehn (Jan 28, 2019)

tomo pauk said:


> Did they omit it, or they didn't now that thing actually exists in mid-1930s?


I was going to post a similar remark. It isn't a just question of having a boundary layer splitter, it is having a good one. The Hurricane had a boundary layer splitter of sorts and isn't hailed as a wonder design. I suspect the reason is the massive amount of wind tunnel research done between the Spitfire and P-51 being designed. Even for the P-51 there were various incarnations to get it right. There is also the issue of location, could you use it under the wings where a Spitfires radiator(s) are?


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## swampyankee (Jan 28, 2019)

pbehn said:


> This? http://www.wwiiaircraftperformance.org/mustang/Lednicer_Fighter_Aerodynamics.pdf



No. There were two, actually, published by the Royal Aeronautical Society. The citations are here: https://ww2aircraft.net/forum/threads/ww2-fighter-and-critical-mach-speed.802/reply?quote=1308078

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## Zipper730 (Jan 28, 2019)

tomo pauk said:


> Did they omit it, or they didn't now that thing actually exists in mid-1930s?


Good point, but by the late 1930's one would figure that would factor into things -- the idea of adding a splitter plate.


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## tomo pauk (Jan 28, 2019)

Zipper730 said:


> Good point, but by the late 1930's one would figure that would factor into things -- the idea of adding a splitter plate.



By the late 1930s, British were burning the midnight oil to get any Spitfires in production and service, and by the same time probably no-one had have splitter plate on a production fighter either.

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## pbehn (Jan 28, 2019)

With the increase in power from 1000 to 2000 HP comes a massive increase in cooling, not only for the engine but the oil and intercooler too. If that cooling was in the original design then probably the Spitfire would have been designed differently.


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## pbehn (Jan 28, 2019)

Zipper730 said:


> Did the RAF have a poor finish?
> ?


 Finish is a global term, some is to do with the care an attention of the people finishing off the plane like paint and fit of panels. Most is in the design. The choice or rivets and fastners over a whole plane makes a difference but flush riveting (for example takes more time and costs more money. The number of joins and the accuracy of the fit up is also the design, but you cant design what you cant make, so if a long smooth panel requires a press you don't have you have to design something else, probably with more joints. The faster you go, the more drag costs you, its pointless developing another 100BHP from an engine when simple mods can have the same effect in terms of speed, you have to do both. It wasn't really an RAF thing, the Mosquito was good in terms of finish wood lends itself to smooth contours without rivets and gaps. The Typhoon/Tempest were also better their major drag issues were the wing and chin radiator The Tempest got a new wing and an annular radiator was a big improvement but not used to keep production numbers up.


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## wuzak (Jan 28, 2019)

Some early Spitfire trials were used to compare conventional riveting and flush riveting. 

I believe the final outcome of that was that the wings were flush riveted and the fuselage conventionally riveted.

This happened before production really got going.

They may have changed to all flush rivets later on.

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## pbehn (Jan 28, 2019)

wuzak said:


> Some early Spitfire trials were used to compare conventional riveting and flush riveting.
> 
> I believe the final outcome of that was that the wings were flush riveted and the fuselage conventionally riveted.
> 
> ...


They used the highly scientific method of taking a Spitfire with all flush rivets, gluing split peas on them and progressively removing them.


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## Shortround6 (Jan 28, 2019)

Maybe I have it all wrong but I think the splitter plate works by "splitting off" the turbulent layer of air next to the aircraft skin and allowing the air that is flowing more smoothly to enter the radiator opening. This allows a higher volume of air for the same size opening and the less turbulent air flows better through the radiator also consuming less drag. 
The downside is the the radiator duct/housing has to stick further out into the airstream, increasing the frontal area of the airplane. Then you have the problem of what to do with the air you split off?
On the Mustang they let the the boundary layer air spill out to the sides. 





On the 109F they ducted the air over the top of the radiator.




which was an improvement (of sorts) over the 109E





so nobody was really using splitters in the mid to late 30s. In 1940 the germans used one on the 109F, other people may have been working with the idea about that time. 

On the Spitfire there was limited room to work.




The radiator is already shoved as high into the wing as it will go. and you have limited space in between the radiator and landing gear to get a nice curve in the duct.

perhaps it could have been done. But at what cost/complexity? (every body bitches at how much Spitfire wings cost to build as it was. 

If you route the boundary layer air up and over (ala 109F) you have to hang the radiator a bit lower and lower the bottom of the radiator duct increasing the drag. Perhaps the change is worth it.

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## wuzak (Jan 28, 2019)

The Spiteful used a similar system to the Bf 109's.

Experiments were done to see if alternative methods were any better.


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## tomo pauk (Jan 29, 2019)

Shortround6 said:


> On the 109F they ducted the air over the top of the radiator.
> View attachment 527245
> 
> which was an improvement (of sorts) over the 109E
> ...



The tunnel for boundary layer was discarded with Bf 109G, that also got bigger (taller) radiators to take up the slack and offer improved cooling capacity. 
Advantage of 109F-style radiators vs. 109E-style was that the former were wider, thus leavinng smaller percentage of radiator itself 'hanging' under the wing and within the slipstream. All Bf 109s from E onwards have 3 radiators sticking out (2 for coolant + one for oil) - it will kill the speed very much.



> On the Spitfire there was limited room to work.
> The radiator is already shoved as high into the wing as it will go. and you have limited space in between the radiator and landing gear to get a nice curve in the duct.
> perhaps it could have been done. But at what cost/complexity? (every body bitches at how much Spitfire wings cost to build as it was.
> If you route the boundary layer air up and over (ala 109F) you have to hang the radiator a bit lower and lower the bottom of the radiator duct increasing the drag. Perhaps the change is worth it.



This is where fuselage-installed cooling system shows it's advantage - one can install a very big radiator (or a combination of two, or three), without the shortcoming of 'dipping' too much of it into the slipstream.

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## pbehn (Jan 30, 2019)

Shortround6 said:


> Maybe I have it all wrong but I think the splitter plate works by "splitting off" the turbulent layer of air next to the aircraft skin and allowing the air that is flowing more smoothly to enter the radiator opening. This allows a higher volume of air for the same size opening and the less turbulent air flows better through the radiator also consuming less drag.
> The downside is the the radiator duct/housing has to stick further out into the airstream, increasing the frontal area of the airplane. Then you have the problem of what to do with the air you split off?
> On the Mustang they let the the boundary layer air spill out to the sides.
> View attachment 527244
> ...


Did the P-51 system have some advantages compared to the Spitfire (apart from previously discussed) in that although much bigger and further out in the slipstream being further back it didn't increase the maximum cross sectional area. Also since the fuselage curves towards the rear only the intake is visible from the front, the splitter doesn't increase the frontal area.


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## swampyankee (Jan 30, 2019)

Frontal area, per se, isn’t that important. Separation is, and the boundary layer splitter reduces the likelihood of separation inside the diffuser before the radiator and permits a better velocity distribution for the air flow to the radiator, which permits a smaller radiator as more of it is working effectively.

Designing a cooling system for piston-engined fighters was hard, and expediency would frequently dictate design choices that were sub-optimal, such as the British power egg. Sometimes there simply wasn’t the analytical tools or skills available to do the best job. Sometimes there simply wasn’t the room.

I think some people thought that cooling those sexy V-12s was easy, forgetting that the radiator would need to get rid of about the same amount of heat (slightly less, as cooling the V-12’s engine compartment had to be managed separately) as a radial, to the same ambient conditions, probably with the radiator at a lower temperature than a radial’s finning, so the radiator is going to have about the same amount or more wetted area than the finning on a radial, as the liquid coolant just adds a step to the transfer of heat from engine to air.

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## Shortround6 (Jan 30, 2019)

Frontal area was thought to be important at time, let's remember that full size wind tunnels were rare, America had one, Germany had one, I don't know about Russia. Nobody else had one at all. The American one had a speed of 80mph (?) Before WW II. 
All the rest of the tunnels required models or small sections of aircraft. 

Liquid cooling had also gone through several Changes in short period of time. Plain water was used up until the very early 30s. Prestone/glycol offered the use of much higher temperatures and smaller radiators but introduced some problems of it's own. They were just starting to go to a water/glycol mix at the start of WW II so they were still working on the exact size of the radiator per hp and size needed at different altitudes and even the type of radiator construction. 
Getting all the different requirements to come together at the same time was not as easy at it seems today.

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## stona (Jan 30, 2019)

Zipper730 said:


> Did the RAF have a poor finish?



Notice the date on this communique.







Then there was a constant barrage of advice and instruction issued by the RAF to Fighter Command and its squadrons about MAINTAINING the finish on service aircraft. Generally, even in the UK, this was not done very well.

Cheers

Steve


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## pbehn (Jan 30, 2019)

There is a down side to very fine finishes, they reflect the sun.


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## stona (Jan 30, 2019)

pbehn said:


> There is a down side to very fine finishes, they reflect the sun.



Which is why the 'Type S' finish was adopted. It was considered not to compromise the camouflage of the aircraft as a gloss finish would.

Notice point 4 on this the second page of a circular to all Resident Technical Officers about the introduction of Type S paints.






The letter dates to early 1940 and model makers might also notice the acceptance of hard, masked, demarcations between camouflage colours on British aircraft.

Cheers

Steve

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## AMCKen (Jan 31, 2019)

"Ram air intake was also probably a source of drag (was changed with late Seafires). "
But it also added more horsepower than needed to overcome the drag it generated.


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## P-39 Expert (Jan 31, 2019)

pbehn said:


> Did the P-51 system have some advantages compared to the Spitfire (apart from previously discussed) in that although much bigger and further out in the slipstream being further back it didn't increase the maximum cross sectional area. Also since the fuselage curves towards the rear only the intake is visible from the front, the splitter doesn't increase the frontal area.


Mainly one cleaner radiator scoop design on the P-51 vs. two on the Spitfire. Less drag. Also the Meredith Effect which said the heated radiator exhaust was actually contributing thrust, but like the laminar flow wing many experts doubt the effect was actually achieved operationally. Still the P-51 was the cleanest design in WWII.


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## P-39 Expert (Jan 31, 2019)

swampyankee said:


> Frontal area, per se, isn’t that important. Separation is, and the boundary layer splitter reduces the likelihood of separation inside the diffuser before the radiator and permits a better velocity distribution for the air flow to the radiator, which permits a smaller radiator as more of it is working effectively.
> 
> Designing a cooling system for piston-engined fighters was hard, and expediency would frequently dictate design choices that were sub-optimal, such as the British power egg. Sometimes there simply wasn’t the analytical tools or skills available to do the best job. Sometimes there simply wasn’t the room.
> 
> I think some people thought that cooling those sexy V-12s was easy, forgetting that the radiator would need to get rid of about the same amount of heat (slightly less, as cooling the V-12’s engine compartment had to be managed separately) as a radial, to the same ambient conditions, probably with the radiator at a lower temperature than a radial’s finning, so the radiator is going to have about the same amount or more wetted area than the finning on a radial, as the liquid coolant just adds a step to the transfer of heat from engine to air.


The radiator and coolant also added upwards of 400# to the weight of the plane.


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## pbehn (Jan 31, 2019)

When was evaporative cooling abandoned?


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## P-39 Expert (Jan 31, 2019)

pbehn said:


> When was evaporative cooling abandoned?


We had an evaporative cooler in our first house when I was 5. Everybody called them swamp coolers. Got a refrigerated window unit when I was 13. I can remember no air conditioning in Fort Worth Texas when it routinely hit 100 degrees in summer.


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## pbehn (Jan 31, 2019)

P-39 Expert said:


> We had an evaporative cooler in our first house when I was 5. Everybody called them swamp coolers. Got a refrigerated window unit when I was 13. I can remember no air conditioning in Fort Worth Texas when it routinely hit 100 degrees in summer.


I mean on the Spitfire lol. The leading edge tanks on later Spitfires were originally to be part of an evaporative cooling system.

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## Snowygrouch (Jan 31, 2019)

I`ve got a really nice report on special "aero Spitfire canopy" (not the speed-spitfire but wartime report, Sept 1943) which wasnt putting the armour inside but a total redesign (wasnt a bubble canopy though). Sadly I cant post the pics as its copyright infringement. 

I can quote from it though ! 

It raised top speed from 410 to 415mph (in level flight in a Spitfire IX reg "EN 498"), when dived at 550mph it put +12mph on top speed.

It was called the "Conical Screen", the sliding bit was identical but the front bit was totally rounded off.

You can get it at Kew Archives in London ref "AVIA-6-10404"

I also have another report on Spitfire aero, which stated that basically the fit of the panels was awful and resulted in (they reckoned) 7.5mph differences production models depending on how well it was fitted together at that particular factory.

Also from Kew, ref "AVIA-6-10367" and was also 1943

There were also larger studies conducted when the Mustang arrived as the air ministry was incredulous about where the speed difference had come from, but I dont have time to go trawling through those tonight. I seem to remember that it was a big mix of panel gaps, radiator installation, wings, paint and so on.

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## Shortround6 (Jan 31, 2019)

P-39 Expert said:


> Mainly one cleaner radiator scoop design on the P-51 vs. two on the Spitfire. Less drag. Also the Meredith Effect which said the heated radiator exhaust was actually contributing thrust, but like the laminar flow wing many experts doubt the effect was actually achieved operationally. Still the P-51 was the cleanest design in WWII.



Some people estimate that the Wing on the P-51 could maintain laminar flow up to about 40% of the cord. It is not all or nothing, that is either you have laminar flow from leading edge to trailing edge or laminar flow nowhere on the wing. Most conventional airfoils could maintain laminar flow for 5-15% of the cord for example so the P-51 wing, even if it didn't achieve what was hoped for ( estimated from lab results?) still offered lower drag than a conventional wing. I would note that the Davis wing used on the B-24 actually fell somewhere in between. They weren't trying for laminar flow but wound up getting it to somewhere between 15-25% cord. 

I think the Meredith effect was sort of the same. People knew what the theoretical goal was, achieving it in practice was a lot harder. Especially trying to get *more *thrust than the cooling drag. However if your installation allows the engine to cool properly and the thrust you are getting cancels out 75% of the drag of another type installation maybe you aren't doing to bad???

Everything was a trade off. RR figured that the intake drag on a Merlin XX in a Hurricane in high supercharger gear was any where between 14 and 32.8 hp depending on altitude. 
The air actually rose in temperature 8.9 to 11.6 degrees C in the intake duct before it reached the carb due to the compression taking place in the intake duct. 
They figured the extra several thousand feet of critical altitude in level flight was worth it.

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## P-39 Expert (Jan 31, 2019)

pbehn said:


> I mean on the Spitfire lol. The leading edge tanks on later Spitfires were originally to be part of an evaporative cooling system.


Oh. Well, it was still mighty hot in Fort Worth.


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## tomo pauk (Jan 31, 2019)

AMCKen said:


> "Ram air intake was also probably a source of drag (was changed with late Seafires). "
> But it also added more horsepower than needed to overcome the drag it generated.



You can have extra HP even with a blended ram air intake, but not pay as much of price in drag that will come with an intake that is protruding away from airframe. 
Seafire 47 vs. Seafire 45


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## wuzak (Jan 31, 2019)

P-39 Expert said:


> Mainly one cleaner radiator scoop design on the P-51 vs. two on the Spitfire. Less drag. Also the Meredith Effect which said the heated radiator exhaust was actually contributing thrust, but like the laminar flow wing many experts doubt the effect was actually achieved operationally. Still the P-51 was the cleanest design in WWII.



The Spitfire radiator was designed to use the Meredith effect, but in practice it wasn't that well done.

The P-51's duct was also not ideal, with the expansion from the intake being uneven from top to bottom, with the roof of the duct changing directions quite sharply.

That said, Supermarine did propose a similar radiator system for the Spitfire, but the Air Ministry rejected it in favour of production. Because in WW2 production was king!

Edit: There were a lot of small areas that the Spitfire was in deficit to the P-51, drag wise. While the radiator and the wing were the most significant factors, they weren't as big a difference as is often thought. Just a lot of small bits of extra drag adding up.

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## Snowygrouch (Jan 31, 2019)

Spit rad ducts with boundary layer bypass (but in same overall position) were trialled for MkIII, some pics in the old faithful "SPIFIRE THE HISTORY" by Morgan and Shacklady pg127. Performance benefits unclear. I have an R.A.E. paper on it which concludes:

"With the limited length of the cowl the fitting of a bypass duct restricts the radiator duct entry area; thus the full advantages of the bypass are not realised. Owing to this the Spitfire III cowl shows little improvement on the standard cowl which allows for the fitment of a more deeply recessed radiator" (page 8 "DSIR-23-11196", July 1941)

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## wuzak (Jan 31, 2019)

Snowygrouch said:


> I`ve got a really nice report on special "aero Spitfire canopy" (not the speed-spitfire but wartime report, Sept 1943) which wasnt putting the armour inside but a total redesign (wasnt a bubble canopy though). Sadly I cant post the pics as its copyright infringement.
> 
> I can quote from it though !
> 
> ...



I believe that screen was not adopted because it distorted the pilot's view, and so was deemed unsuitable for combat aircraft.

PR Spitfires did adopt a rounder profile screen, without armoured glass, for extra high altitude performance. They may have been related to the screen you mention.

Also, don't forget that the two cannon barrels cost ~8mph in speed.

Delete the cannon (presumably for 4 x 0.50"), add the super screen and improve panel fit and finish, and you would not be far shy of P-51 performance. But with less firepower than a regular Spitfire.


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## pbehn (Jan 31, 2019)

wuzak said:


> The Spitfire radiator was designed to use the Meredith effect, but in practice it wasn't that well done.
> 
> The P-51's duct was also not ideal, with the expansion from the intake being uneven from top to bottom, with the roof of the duct changing directions quite sharply.
> 
> ...


You would almost think that' someone looked at the Spitfire and Bf109 and thought how to improve on them.


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## Reluctant Poster (Feb 3, 2019)

tomo pauk said:


> You can have extra HP even with a blended ram air intake, but not pay as much of price in drag that will come with an intake that is protruding away from airframe.
> Seafire 47 vs. Seafire 45


According to Spitfire by Morgan and Saleslady the Mark 47 was slower than the Mark 46 due to the relocated air intake


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## tomo pauk (Feb 3, 2019)

Reluctant Poster said:


> According to Spitfire by Morgan and Saleslady the Mark 47 was slower than the Mark 46 due to the relocated air intake



Indeed, by 3 mph.


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## Zipper730 (Feb 7, 2019)

Shortround6 said:


> Maybe I have it all wrong but I think the splitter plate works by "splitting off" the turbulent layer of air next to the aircraft skin and allowing the air that is flowing more smoothly to enter the radiator opening. This allows a higher volume of air for the same size opening and the less turbulent air flows better through the radiator also consuming less drag.


I didn't think it was about changing the divergence angle so much as simply getting rid of the turbulent airflow going into the ducts. Regardless, I prefer the term "diverter" but that's a term used in jet-powered aircraft.


> nobody was really using splitters in the mid to late 30s.


The P-38 used them on the radiator scoops.


> On the Spitfire there was limited room to work. . . . The radiator is already shoved as high into the wing as it will go. and you have limited space in between the radiator and landing gear to get a nice curve in the duct.


Wow, I never realized they had such little room. A belly-radiator would have definitely fixed this, but you wouldn't want to belly in with it...



stona said:


> Notice the date on this communique.


August 10, 1942...


> Then there was a constant barrage of advice and instruction issued by the RAF to Fighter Command and its squadrons about MAINTAINING the finish on service aircraft. Generally, even in the UK, this was not done very well.


Out of curiosity -- how did the US & Germany compare?



Snowygrouch said:


> I`ve got a really nice report on special "aero Spitfire canopy" (not the speed-spitfire but wartime report, Sept 1943) which wasnt putting the armour inside but a total redesign (wasnt a bubble canopy though). Sadly I cant post the pics as its copyright infringement.


Do you have a link to the page -- I don't think that qualifies...


> I can quote from it though !
> 
> It raised top speed from 410 to 415mph (in level flight in a Spitfire IX reg "EN 498"), when dived at 550mph it put +12mph on top speed.


Impressive


> I also have another report on Spitfire aero, which stated that basically the fit of the panels was awful and resulted in (they reckoned) 7.5mph differences production models depending on how well it was fitted together at that particular factory.


So workmanship sucked?


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## Shortround6 (Feb 7, 2019)

Zipper730 said:


> The P-38 used them on the radiator scoops.



I don't believe the early ones did. The J model certainly did. I am not sure of the H model.


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## Snowygrouch (Feb 7, 2019)

Zipper730 said:


> Do you have a link to the page -- I don't think that qualifies...



There isnt really a link as its an archive paper I photographed myself in London ... sorry.

Discovery | The National Archives

Search for

AVIA 6/10404

All that gets you is the index listing for it though....you CAN order copies but they cost an absolute fortune. So most people visit.

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## Reluctant Poster (Dec 21, 2019)

The Seafire XVII and 47 had curved windscreens
Seafire Mk.XVII SX336


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## Ivan1GFP (Jan 16, 2020)

Washout to avoid a harsh stall doesn't do much for drag.
There was also the issue of landing gear that didn't quite fit into the thin wing and some of it had to hang below the wing surface.


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## wuzak (Jan 16, 2020)

Ivan1GFP said:


> Washout to avoid a harsh stall doesn't do much for drag.
> There was also the issue of landing gear that didn't quite fit into the thin wing and some of it had to hang below the wing surface.



Funny that the prototype initially had fully enclosed main landing gear. The Mk III also had fully enclosed landing gear, IIRC.

The landing gear did not protrude from the wing, but some of the wheel well was open, which would cause some drag. Though the decision to remove the covers was made in testing the prototype.


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## Ivan1GFP (Jan 16, 2020)

wuzak said:


> Funny that the prototype initially had fully enclosed main landing gear. The Mk III also had fully enclosed landing gear, IIRC.
> 
> The landing gear did not protrude from the wing, but some of the wheel well was open, which would cause some drag. Though the decision to remove the covers was made in testing the prototype.



My understanding was that the mid production Spitfires had large enough wheels that their gear doors were very slightly below the wing's lower surface. This was corrected with the change in the wing with the last marks.


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## BarnOwlLover (Nov 7, 2022)

wuzak said:


> The Spitfire radiator was designed to use the Meredith effect, but in practice it wasn't that well done.
> 
> The P-51's duct was also not ideal, with the expansion from the intake being uneven from top to bottom, with the roof of the duct changing directions quite sharply.
> 
> ...


I thought I saw something on here to this effect. It may be a bit off topic, but I've seen references to what is suspected to be RJ Mitchell's last major design he worked on before his death, which was the Supermarine 312. From what little I could glean from it, it was basically a Spitfire but much modified, namely with a ventral radiator and standard cannon armament. Outside of that, though, I've been quite frustrated to find other details about this design. 







But it does show that it may be possible to fit such a radiator onto a modified Spitfire design, but, one, Mitchell died before the design was 100% complete or built, and two, as you hinted at, Joe Smith (Mitchell's associate/design assistant and successor) may've been inspired by that design and maybe even the P-51 later to try and modify the Spitfire, but he was turned down by the RAF and the Air Ministry. Which IMO is odd, given how much the Spitfire already evolved (though I did read that for the most part, the fuselage between the front firewall and tail was little modified from the Mk V on until the 22/24 line).

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## BarnOwlLover (Nov 8, 2022)

I also found this drawing of a Spitfire that tested a ventrally mounted Meredith ramjet engine.






There was also the Supermarine 338, which was a heavily modified Spitfire IV (used to test the Griffon engine and lead to the Spitfire XII) that had a gull wing, butterfly tail and a ventral radiator.

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## pbehn (Nov 8, 2022)

BarnOwlLover said:


> I also found this drawing of a Spitfire that tested a ventrally mounted Meredith ramjet engine.
> 
> View attachment 693642
> 
> ...


From my understanding of things, a ventrally mounted radiator caused compressibility issues mounted there, it has to be further back behind the area of max cross sectional area, as on a P-51, also on that arrangement the frontal area is increased, on a P51 the inlet is visible on a frontal view, but the "splitter" isnt..

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## BarnOwlLover (Nov 30, 2022)

I wonder how well the Spitfire would've done if it used radiators similar to the Spiteful? I'd bet that's probably a big part of why the Spiteful was nearly 40 mph faster than the Spitfire 14.


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## Graeme (Nov 30, 2022)

BarnOwlLover said:


> Supermarine 312.








Source...

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## Shortround6 (Nov 30, 2022)

I am not sure the Spiteful radiators really did that much. 




A lot wider than the Griffon Spitfires but shallower. More of the radiator could be hidden inside the wing rather than sticking out. Now notice where the intake flap hinge is and barely visible in the exit hinge. 




Both flaps open at least part way. Granted this set up does_ not_ have the air making large excursions in the vertical and rejoining the exit flow. BUT you don't have the depth front to back to expand the airflow, get it through the radiator, and squeeze the heated air down to the higher pressure. May be it did work but you had nowhere near the depth front to back that the Mustang, CA-15, MB-5 and P-82 have




The only way to truly know is for somebody to have mounted instruments in the airflow coming out through the exit nozzle/flap and recorded the exit speed vs the intake speed. 
That will tell you if you actually achieved positive thrust. Wither the thrust is worth the drag of the size of the scoop is another story.


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## tomo pauk (Nov 30, 2022)

Hmm - is it just me, or the Spiteful was also with a windscreen set at the shallower angle than it was the case with Spitfires?

W
 wuzak


 Wurger
etc - help


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## Wurger (Nov 30, 2022)

The prototype (the second pic in #57 ) VG471 is the Supermarine Sea Fang F.31 while the RB515 in the first image above is the Spiteful, the first production aircraft.

Here is comparing of the Spiteful prototype NN664 and RB518 of the production series and the MV259, a Spitfire PR Mk. XIV. It looks like the angle of the windscreen was slightly different if compared to the ealier one. However it could be a trick because of the different windscreen frame for both types. IMHO the Spiteful and Sea Fang got the longer front glass.

NN664-RB518





NN664-MV259




the pic source: the net





the source: Supermarine Spiteful and Seafang Fighters


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## BarnOwlLover (Nov 30, 2022)

To be honest, I do wonder how much the Meredith effect is fact vs myth. Obviously, there's something to it, as with laminar flow wings. But I don't think that theory 100% paid off in terms of real world results. It's like comparing the P-51 with the Spitfire. When powered by similar engines, the P-51 was a good 30 mph or so faster on top end than the Spitfire, and it took the Griffon engined Mk 14 at least 300-400 more bhp to reach the same speeds.

Overall, I think that P-51 was just a cleaner airframe than the Spitfire. The fit and finish above all on the Mustang was seemingly miles ahead of a lot of Spitfires. You have to remember that it seemed that Spitfires didn't go fully to flush riveting for all external panels until sometime in 1943. The Mustang did this basically all along going back to the NA-73X prototype.

I do believe that the laminar flow wing and Meredith radiator done well helped, but they weren't the sole magic bullets. I'd bet that a lot of why the Spiteful was so fast was just lessons learned from designing the Spitfire and gains in manufacturing and aero made since the mid 1930s.

That's why sort of my "dream" fighter would have the best attributes of the Mustang and the Spitfire. IMO, we got pretty close with the XP-51F and G, and sort of approached that with the P-51H. Or maybe if the P-51B/C/D/K was able to keep the weight to NA-73X or P-51/Mustang I levels.


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## pbehn (Nov 30, 2022)

BarnOwlLover said:


> To be honest, I do wonder how much the Meredith effect is fact vs myth. Obviously, there's something to it, as with laminar flow wings. But I don't think that theory 100% paid off in terms of real world results. It's like comparing the P-51 with the Spitfire. When powered by similar engines, the P-51 was a good 30 mph or so faster on top end than the Spitfire, and it took the Griffon engined Mk 14 at least 300-400 more bhp to reach the same speeds.
> 
> Overall, I think that P-51 was just a cleaner airframe than the Spitfire. The fit and finish above all on the Mustang was seemingly miles ahead of a lot of Spitfires. You have to remember that it seemed that Spitfires didn't go fully to flush riveting for all external panels until sometime in 1943. The Mustang did this basically all along going back to the NA-73X prototype.
> 
> ...


If you allow 10MPH for fit finish and cleanliness, 10 MPH for reduction in cooling drag and 10MPH for lower drag aerofoils that gives you the 30MPH difference, it takes a lot of horsepower.


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## wuzak (Nov 30, 2022)

pbehn said:


> If you allow 10MPH for fit finish and cleanliness, 10 MPH for reduction in cooling drag and 10MPH for lower drag aerofoils that gives you the 30MPH difference, it takes a lot of horsepower.



It was something like 8mph for the cannon installation.
A few mph for the windscreen (more upright on Spitfire than P-51).
And lots of other little things that cost a few mph each.


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## wuzak (Nov 30, 2022)

tomo pauk said:


> Hmm - is it just me, or the Spiteful was also with a windscreen set at the shallower angle than it was the case with Spitfires?
> 
> W
> wuzak
> @Wurger etc - help



It was.


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## pbehn (Dec 1, 2022)

wuzak said:


> It was something like 8mph for the cannon installation.
> A few mph for the windscreen (more upright on Spitfire than P-51).
> And lots of other little things that cost a few mph each.


I was just illustrating where the difference between the two comes from it was from many things, in fact things dont "tot up" in that way. The biggest difference in my opinion was that the P-51 was a generation later. If Mitchell was alive in 1940 he may well have come up with something like the P-51, just as the P-51 would not have been designed "as is" for the RAF in 1935-36 it was too heavy for the engines of that time.

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## Aeroweanie (Dec 26, 2022)

swampyankee said:


> No. There were two, actually, published by the Royal Aeronautical Society. The citations are here: https://ww2aircraft.net/forum/threads/ww2-fighter-and-critical-mach-speed.802/reply?quote=1308078


A bibliography of my publications on WWII aircraft:
AIAA paper 91-3288; A Retrospective - Computational Aerodynamic Analysis Methods Applied to the P-51 Mustang
EAA Sport Aviation January 1999; World War II Fighter Aerodynamics
Journal of the Royal Aeronautical Society; A CFD Evaluation of Three Prominent World War II Fighter Aircraft
SAE 2000-01-1678; Aerodynamics of the Bell P-39 Airacobra and P-63 Kingcobra
SAE 2015-01-2580; Novel World War II Aircraft Design Features
Contributions to the Birch Matthews book "Cobra!: The Bell Aircraft Corporation 1934-1946"

And, some Historic Flight Foundation talks (some of which are available on Youtube):
A Retrospective of World War II Aircraft Design; September 2012
The Grumman Cats; July 2013
The Real Story British Fighters vs. German Fighters (Battle of Britain Series); April 2015
The Remarkable History of the B-25 Mitchell; May 2017
The Grumman F8F Bearcat; September 2017
Advanced Aerodynamics; November 2018
Exceptionally Plane - People Grumman Aircraft Engineering Corporation; March 2018
The Grumman TBF Avenger; June 2018
Korean War Fighter Tactics; March 2020
The P-51 Mustang; November 2022

My favorite, which is not on WWII aircraft:
The 1937 Soviet Transpolar Flights to the United States; March 7 & 10, 2018

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## Metrallaroja (Jan 6, 2023)

Aeroweanie said:


> A bibliography of my publications on WWII aircraft:
> AIAA paper 91-3288; A Retrospective - Computational Aerodynamic Analysis Methods Applied to the P-51 Mustang
> EAA Sport Aviation January 1999; World War II Fighter Aerodynamics
> Journal of the Royal Aeronautical Society; A CFD Evaluation of Three Prominent World War II Fighter Aircraft
> ...


Awesome list, thanks a lot. Already made a list to watch the ones that I found on youtube
Im very interested in the F8F one, where can I watch it?


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## Aeroweanie (Wednesday at 1:05 AM)

Metrallaroja said:


> Awesome list, thanks a lot. Already made a list to watch the ones that I found on youtube
> Im very interested in the F8F one, where can I watch it?


I don't think the F8F presentation ever got recorded. Attached are the slides

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## Metrallaroja (Wednesday at 6:00 AM)

Aeroweanie said:


> I don't think the F8F presentation ever got recorded. Attached are the slides


Thanks! Awesome presentation, the best one that I saw about F8F!

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## WAFU (Wednesday at 6:03 AM)

Some solutions are just 'right'

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## pbehn (Wednesday at 7:03 AM)

WAFU said:


> Some solutions are just 'right'
> 
> View attachment 702049


That is a late solution to a problem that was fixed.

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## WAFU (Wednesday at 9:43 AM)

pbehn said:


> That is a late solution to a problem that was fixed.



Thats a logical development of the Spitfire like MB3 and 4 to reduce the high drag from underwings radiators - as per the P-51, that design utilises the Meredith Effect to improve cooling, significantly reduce drag and actually gain some thrust.


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## z42 (Wednesday at 10:16 AM)

What about wing leading edge radiators? These don't seem that much used, so evidently the simplistic argument that they add little frontal area and are thus low drag is invalid? So what's the verdict on them?


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## tomo pauk (Wednesday at 10:27 AM)

z42 said:


> What about wing leading edge radiators? These don't seem that much used, so evidently the simplistic argument that they add little frontal area and are thus low drag is invalid? So what's the verdict on them?


Depends on the judge? The judges at De Havilland and Hawker judged affirmatively wrt. the LE radiators.


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## pbehn (Wednesday at 10:30 AM)

WAFU said:


> Thats a logical development of the Spitfire like MB3 and 4 to reduce the high drag from underwings radiators - as per the P-51, that design utilises the Meredith Effect to improve cooling, significantly reduce drag and actually gain some thrust.


Germany and UK had jets in squadron service in June 1944. The MB 5 flew the month before for the first time, it was too late or everything.

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## z42 (Wednesday at 10:47 AM)

tomo pauk said:


> Depends on the judge? The judges at De Havilland and Hawker judged affirmatively wrt. the LE radiators.


Yes, I'm aware of those. I guess my question is more of a theoretical nature. What is the aerodynamics of a wing with LE radiators? And given they are such an obvious idea that even yours truly can imagine them being a good design, why didn't world+dog adopt them?


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## Metrallaroja (Wednesday at 11:36 AM)

tomo pauk said:


> Depends on the judge? The judges at De Havilland and Hawker judged affirmatively wrt. the LE radiators.


Looks better when you fit a sabre, Sabre Fury 

The true evolution of the Spitfire retains the underwing rads but looks like a better design than the original. (Someone already mentioned it)

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## Metrallaroja (Wednesday at 12:09 PM)

Some other LE radiators: J21, I225 and I220


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## pbehn (Wednesday at 12:35 PM)

z42 said:


> Yes, I'm aware of those. I guess my question is more of a theoretical nature. What is the aerodynamics of a wing with LE radiators? And given they are such an obvious idea that even yours truly can imagine them being a good design, why didn't world+dog adopt them?


The wing leading edge needs to have enough volume to hold the whole cooling system. The Mosquito was a bomber not a fighter and the engines were changed to allow the installation (water flow was reversed). On the Hawker Sea Fury the LE radiators were cooling the oil, the engine was air cooled.


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## Metrallaroja (Wednesday at 12:48 PM)

pbehn said:


> On the Hawker Sea Fury the LE radiators were cooling the oil, the engine was air cooled.


The Hawker examples were the Griffon Fury and the Sabre Fury. Not the Centaurus Fury


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## pbehn (Wednesday at 12:52 PM)

Metrallaroja said:


> The Hawker examples were the Griffon Fury and the Sabre Fury. Not the Centaurus Fury


I was discussing the in service fury.


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## Metrallaroja (Wednesday at 12:56 PM)

pbehn said:


> I was discussing the in service fury.


Ah ok. Yeah many radials had the oil coolers in the LE.
The Corsair for example had almost all configurations possible. It had the oil coolers in the LE (F4U-1, F4U-4, F4U-5), the oil coolers in the engine compartment with air from the LE (F4U-6 (AU-1)) and it had a bigger oil cooler in the engine compartment with air from a nose inlet (F4U-7).


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## pbehn (Wednesday at 1:53 PM)

Metrallaroja said:


> Ah ok. Yeah many radials had the oil coolers in the LE.
> The Corsair for example had almost all configurations possible. It had the oil coolers in the LE (F4U-1, F4U-4, F4U-5), the oil coolers in the engine compartment with air from the LE (F4U-6 (AU-1)) and it had a bigger oil cooler in the engine compartment with air from a nose inlet (F4U-7).


The Griffon needed a lot of cooling, not only for the engine oil and water but also the intercooler, the scoops on Spitfire Mk XIV and later are like buckets, they are huge.


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## elbmc1969 (Yesterday at 11:28 AM)

z42 said:


> Yes, I'm aware of those. I guess my question is more of a theoretical nature. What is the aerodynamics of a wing with LE radiators? And given they are such an obvious idea that even yours truly can imagine them being a good design, why didn't world+dog adopt them?


If the air goes into the wing, it doesn't go over and under the wing. Not a scientific analysis, but you don't get something for nothing. You could make the wing much thicker and then possibly get the effect of a thing wing because of the reduced air flow over the top and bottom of the wing--possibly.



> There is also a lot that can be gleaned from NACA reports, or RAE/DVL stuff too but that isn't as easy to get. For example with LE radiators NACA found that they are more sensitive to AoA than other installations, so they can work really well in level flight but are probably a bad option for an aircraft that needs to climb rapidly.
> --https://www.secretprojects.co.uk/threads/drag-of-radiators.37145/post-456493


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## elbmc1969 (Yesterday at 11:31 AM)

BarnOwlLover said:


> To be honest, I do wonder how much the Meredith effect is fact vs myth. Obviously, there's something to it, as with laminar flow wings. But I don't think that theory 100% paid off in terms of real world results. It's like comparing the P-51 with the Spitfire. When powered by similar engines, the P-51 was a good 30 mph or so faster on top end than the Spitfire, and it took the Griffon engined Mk 14 at least 300-400 more bhp to reach the same speeds.
> 
> Overall, I think that P-51 was just a cleaner airframe than the Spitfire. The fit and finish above all on the Mustang was seemingly miles ahead of a lot of Spitfires. You have to remember that it seemed that Spitfires didn't go fully to flush riveting for all external panels until sometime in 1943. The Mustang did this basically all along going back to the NA-73X prototype.
> 
> ...


naca.central.cranfield.ac.uk/reports/arc/rm/1683.pdf

Summary here: Meredith Effect: Fact or Fantasy "Meredith Effect: Fact or Fantasy"



> Enter Gruenhagen's book "Mustang. The story of the P51 fighter", 1969. This text gives a rather full account of the cooling duct development. This was a very comprehensive series of trials to determine the design parameters and performance for the duct. Consider this: your boss comes in and says "we have mounted a P51 in the wind tunnel. Pick your best mate, go and sit in it while we run the tunnel up to 500 MPH, and do some measurements for us. Don't bother the life insurance companies, when we told them you are upwind of a 5000 HP fan drawing air through the tunnel, they declined your application". But that is what they did, and not only did they survive, but the data they measured is on page 79 of my edition.
> 
> 
> Now at first glance, the only interesting part of the data are the sketches showing various arrangements of ducts for coolant and oil cooling. The numerical data is hard to read: the print is so small. But being half-blind anyway, I thought I better put on my 2.5 binocular magnifier and see what the column headings were. I was immediately revolted by the unit "slug": but as this turned out to be 1 slug equals 32.172 pounds, then that was not so bad. After all, the number 32.172 seemed to be related to the acceleration due to gravity, so some nameless old fossil was trying to separate the concepts of mass and weight. Of course, I am not yet a fossil, as I have not yet gone underground!


If you have any interest, read the web page. It has some interesting tidbits of its own.

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## pbehn (Yesterday at 11:55 AM)

elbmc1969 said:


> If the air goes into the wing, it doesn't go over and under the wing. Not a scientific analysis, but you don't get something for nothing. You could make the wing much thicker and then possibly get the effect of a thing wing because of the reduced air flow over the top and bottom of the wing--possibly.


On the Mosquito the air enters the lower part of the leading edge and exits underneath, however the leading edge is extended forward, so the air exits approximately where the wing leading edge is,. I am sure de Havilland knew what they were doing.

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## z42 (Today at 10:27 AM)

pbehn said:


> On the Mosquito the air enters the lower part of the leading edge and exits underneath, however the leading edge is extended forward, so the air exits approximately where the wing leading edge is,. I am sure de Havilland knew what they were doing.
> View attachment 702251


Radiator outlet on the top surface of the wing sounds bad from a lift perspective, but on the underside of the wing the outlet would be in the high pressure zone below the wing, creating back pressure in the radiator? From that POV a Mustang style belly scoop sounds like a good idea, with the inlet in line with the high pressure under the wing and the outlet in the lower pressure zone well behind the wing?


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## pbehn (Today at 10:49 AM)

z42 said:


> Radiator outlet on the top surface of the wing sounds bad from a lift perspective, but on the underside of the wing the outlet would be in the high pressure zone below the wing, creating back pressure in the radiator? From that POV a Mustang style belly scoop sounds like a good idea, with the inlet in line with the high pressure under the wing and the outlet in the lower pressure zone well behind the wing?


The only think I really know about the subject is that I dont know much at all. You need a degree in thermodynamics or similar to fully understand all the ins and outs of it. It took NAA a long time with many versions of inlet to perfect the P-51. The "exhaust" of the Mosquito system like the P-51 is adjustable. Then it is an issue of airflows, temperatures, density and depth of radiator matrix, relative volumes of plenum either side of the radiator. It is generally acknowledged that the P-51 had a great set up, but no one else did the same or copied it. I think that is because you have to start with that in mind at the first stage of design, or it doesnt work.


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## Shortround6 (Today at 11:04 AM)

The main problem with the Mosquito's radiator (and it wasn't much of one, the system did cool the engine/s without much trouble at different speeds and altitudes rather well, which was it's main job) was that the air traveled different distances depending if it was at the bottom or top of the duct. Most other radiator set-ups are going to have that to some degree. 
The exit duct had a rather abrupt taper and turn to the bottom but you can't move it back much without hitting the main spar. 




you may be able to "fix" that by extending the wing root forward but that comes at the cost of worse view from the cockpit and more skin area for more drag and a bit more weight. 
What are you gaining for what it will cost you?


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## Zipper730 (Today at 11:29 AM)

Shortround6 said:


> Maybe I have it all wrong but I think the splitter plate works by "splitting off" the turbulent layer of air next to the aircraft skin and allowing the air that is flowing more smoothly to enter the radiator opening.


Correct


> On the Spitfire there was limited room to work.
> View attachment 527247
> 
> The radiator is already shoved as high into the wing as it will go. and you have limited space in between the radiator and landing gear to get a nice curve in the duct.


I'd have to see a profile view of the radiator, but I'd suspect that you'd have to shape the area in front of the wing in such a way as to carve in a little more area so the splitter could be put between the normal radiator's flow path and the additional carved-in area would handle the turbulent flow.

Of course, this would potentially eat into the skin and could have serious effects on structural or aerodynamic matters. 


> View attachment 702385


It looks like the inlet area is about twice that of the outlet area. I'm not sure what the P-51's inlet/outlet ratio is (or the XF-12) but part of me does wonder if it'd be possible to have taken the Mosquito's shape and sort of "wrap it" it into an annulus with a spinner in the middle. It might be simplistic but it'd produce a radial inlet with low cooling-drag.


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## elbmc1969 (Today at 11:57 AM)

Zipper730 said:


> It looks like the inlet area is about twice that of the outlet area. I'm not sure what the P-51's inlet/outlet ratio is (or the XF-12) but part of me does wonder if it'd be possible to have taken the Mosquito's shape and sort of "wrap it" it into an annulus with a spinner in the middle. It might be simplistic but it'd produce a radial inlet with low cooling-drag.


"The exit area was 0.019 m^2, just 29.5 square inches"

So ratio is fairly large. Someone will have to supply the inlet area, or measure it, to get an accurate ratio, but this indicates a minimum of 2:1.


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## Zipper730 (Today at 12:16 PM)

elbmc1969 said:


> "The exit area was 0.019 m^2, just 29.5 square inches"


What was the inlet area?


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