# Mosquito aerodynamics?



## spicmart (Mar 19, 2019)

The DeHavilland Mosquito is known for its speed due to its good aerodynamics. But what is it actually in detail? 
If one compares it to the Me 110, it had a larger fuselage cross section. The wing had no laminar flow profile. Can you tell it was more streamlined though? 
Leading edge radiators are less draggy than underwing radiators. 
The Mossie's engine nacelles seem more elongated / streamlined. 
Does all this warrant the performance advantage of the Mossie?


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## tomo pauk (Mar 19, 2019)

spicmart said:


> The DeHavilland Mosquito is known for its speed due to its good aerodynamics. But what is it actually in detail?
> If one compares it to the Me 110, it had a larger fuselage cross section. The wing had no laminar flow profile. Can you tell it was more streamlined though?
> Leading edge radiators are less draggy than underwing radiators.
> The Mossie's engine nacelles seem more elongated / streamlined.
> Does all this warrant the performance advantage of the Mossie?



Wing might not be the new, fancy laminar-flow type, but it was of much lower thickness-to-chord ratio - 13% (including the radiator extension) vs 18% at root, respectively for the Mosquito and Bf 110. That's a reduction of TtC by almost 28%. Then ideed we have much better radiator set-up, where radiator's don't project out from airframe and don't suck the turbulent air like it was the case with 110, 109, Spitfire and a number of designs. Not having gun and casings' openeings also helps (fighter-bomber Mossies were slower than bomber versions). The way it was produced resulted with smooth finish - no butt-joined sheets that might or might not align, no rivets.


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## pbehn (Mar 19, 2019)

de Havilland had experience of making racing planes and working with wood. It is easier to make some compound curves in wood than with metal. The Mosquito was designed with speed in mind unlike the vast majority of aircraft of the era. It was fast when introduced but not the fastest later in the war. However it had another advantage in terms of fuel carried. The recon versions of the Mosquito were the heaviest in take of weight. For a single engine fighter to get into the same place in the sky as a Mosquito at high altitude meant it had very little fuel left for a long chase. In many if not most cases the Mosquito just cruised at high speed out of range.

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## fliger747 (Mar 19, 2019)

Smooth surface! Very important in high speed aircraft. Just washing and waxing even a Gen Av airplane can add a number of knots to cruise. The wooden molding also can facilitate a more streamlined shape.

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## pbehn (Mar 19, 2019)

*For such a famous airplane, details of the wing section geometry are very hard to come by! Without any manufacturing drawings or access to an existing airframe, all I can do is try to reverse engineer the profile. From " The Mosquito Manual ", I know there were two sections involved. The first was a Piercy section ( Norman Augustus Victor Piercy ) and the second was the RAF 34.*
*
It is important to understand how the RAF 34 came about and so we refer to the Aeronautical Research Committee Reports and Memoranda No. 946, by H. Glauert, November, 1924. A description of the airfoils is as follows,*

_The basic symmetrical section ( R.A.F. 30 ) was calculated by the method described in R. & M. 911, using the constants k = 1.08, n = 1.95, B = 0. The aerofoil shape so obtained ends in a sharp angle, and so the last 1 percent of the chord was cut off in order to avoid a thin trailing edge. The form of the aerofoil was also adjusted slightly towards the trailing edge in order to remove a slight reflex curvature. The aerofoil has a maximum thickness of 0.13 of the chord at a distance of one third of the chord from the leading edge, and its shape approximates closely to the symmetrical Gottingen section 459 which was known to possess good aerodynamic characteristics. The aerofoils R.A.F. 31 and R.A.F. 32 were obtained by curving the centerline of the symmetrical section R.A.F. 30 into circular arcs of camber 0.02 and 0.05 respectively... Finally, as R.A.F. 32 has too large a value of km0, a fourth aerofoil R.A.F. 33 was designed, using the centerline 19.36y = x(1-x)(7-8x) and the same symmetrical fairing. This aerofoil has the same center line camber 0.05 as R.A.F. 32, but should have constant center of pressure ( zero km0 )._
*So, where's the RAF 34? Apparently, Glauert didn't think that the center of pressure movement would become excessive until the camber exceeded 2 percent. Well, someone did and so in R&M 1071, we find the RAF 34, with a reflexed camber line of 2 percent.

48.4y = x(1-x)(7-8x)

This is significant as we look at the Piercy section. The aerodynamics department ( Richard Clarkson ) at de Havilland obviously thought that having a constant center of pressure was of great importance, since several aircraft preceding the Mosquito also used the RAF 34. Bristol chose the RAF 28 airfoil for several aircraft, including the Blenheim and Beaufighter. That section was considered superior to the RAF 31, with 2 percent camber in which the amount of curvature went to zero at the trailing edge.

In 1937, Piercy came up with a new type of wing section, inverted from a hyperbola. Cambered sections of the first family had circular arc mean lines ( and thus undesirable center of pressure movement ). The second family had the ability to "twist" the camber line to provide reflex, but looking at a Mosquito shows no signs of reflex. That leaves only a symmetrical section to be used in the interests of maintaining a constant center of pressure. Piercy had written,*
_The 1937 profiles provided the first laminar flow wings, having according to tests by the National Physical Laboratory, some 35% less drag than normal wings. They were adopted for certain war-time aeroplanes and promoted research into the subject at home and abroad._*When the position of maximum thickness is moved back along the chord, the leading edge radius becomes smaller and so it is necessary to increase the thickness of the profile to maintain good stalling characteristics. A symmetrical Piercy section with thickness of 0.15 at 0.4c will have a leading edge radius similar to one of 0.13 thickness at 1/3 chord ( RAF 34 ). What happens when the two are merged together? Hopefully, it looks like a Mosquito wing section!*

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## pbehn (Mar 19, 2019)

spicmart said:


> The DeHavilland Mosquito is known for its speed due to its good aerodynamics. But what is it actually in detail?
> If one compares it to the Me 110, it had a larger fuselage cross section*. The wing had no laminar flow profile*. Can you tell it was more streamlined though?
> Leading edge radiators are less draggy than underwing radiators.
> *The Mossie's engine nacelles seem more elongated / streamlined.*
> Does all this warrant the performance advantage of the Mossie?



No wings are truly laminar flow, the RAF 34 profile was getting towards laminar flow see post above. The engine nacelles were elongated at the prototype stage to eliminate buffeting of the tailplane from wiki In February 1941, buffeting was eliminated by incorporating triangular fillets on the trailing edge of the wings and lengthening the nacelles, the trailing edge of which curved up to fair into the fillet some 10 in (250 mm) behind the wing's trailing edge: this meant the flaps had to be divided into inboard and outboard sections.[45][nb 7] With the buffeting problems largely resolved, John Cunningham flew _W4050_ on 9 February 1941. He was greatly impressed by the "lightness of the controls and generally pleasant handling characteristics". Cunningham concluded that when the type was fitted with AI equipment, it might replace the Bristol Beaufighter night fighter.[45]

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## spicmart (Mar 19, 2019)

pbehn said:


> *For such a famous airplane, details of the wing section geometry are very hard to come by! Without any manufacturing drawings or access to an existing airframe, all I can do is try to reverse engineer the profile. From " The Mosquito Manual ", I know there were two sections involved. The first was a Piercy section ( Norman Augustus Victor Piercy ) and the second was the RAF 34.*
> 
> *It is important to understand how the RAF 34 came about and so we refer to the Aeronautical Research Committee Reports and Memoranda No. 946, by H. Glauert, November, 1924. A description of the airfoils is as follows,*
> 
> ...



That was specialized. Thanks
Can you say how much dragginess depends on the length of the aft engine nacelle extension. Some had quite blunt ends such as the Messerschmitt twin engined planes or the Beaufighter, others very pointed ones like the F7F or He 219. When the designers knew it was good against buffering why would not every engine nacelle design have been given such a lengthening. 
I'm also thinking also if the Ta 154 which was to be a well streamlined design without a particular low drag wing profile though. The aft of its nacelles are quite blunt considering its aim of streamlining. 
Or was that shape not draggier than a longer aft?


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## pbehn (Mar 19, 2019)

spicmart said:


> That was specialized. Thanks
> Can you say how much dragginess depends on the length of the aft engine nacelle extension. Some had quite blunt ends such as the Messerschmitt twin engined planes or the Beaufighter, others very pointed ones like the F7F or He 219. When the designers knew it was good against buffering why would not every engine nacelle design have been given such a lengthening.
> I'm also thinking also if the Ta 154 which was to be a well streamlined design without a particular low drag wing profile though. The aft of its nacelles are quite blunt considering its aim of streamlining.
> Or was that shape not draggier than a longer aft?


Sorry, that isn't my posting I lifted it from a previous discussion although the post was mine.. The aerodynamics are way above my pay grade. The Mosquitos engine nacelles were extended to take the slipstream/vortices from them past the tail which caused buffeting and vibration. Not an expert on every type but I suspect that they took the option that is easiest to make and maintain. The issue on the mosquito was smoothing the airflow on the inner sides of the nacelles which may have involved the radiator outlet too. from wiki...……. On 5 December 1940, the prototype, with the military serial number _W4050_, experienced tail buffeting at speeds between 240 mph (385 km/h) and 255 mph (410 km/h). The pilot noticed this most in the control column, with handling becoming more difficult. During testing on 10 December, wool tufts were attached to suspect areas to investigate the direction of airflow. The conclusion was that the airflow separating from the rear section of the inner engine nacelles was disturbed, leading to a localised stall and the disturbed airflow was striking the tailplane, causing buffeting. To smooth the air flow and deflect it from forcefully striking the tailplane, non-retractable slots fitted to the inner engine nacelles and to the leading edge of the tailplane were experimented with.[43] These slots and wing root fairings fitted to the forward fuselage and leading edge of the radiator intakes, stopped some of the vibration experienced but did not cure the tailplane buffeting.[44]


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## pbehn (Mar 19, 2019)

From here RAF airfoils?

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## spicmart (Mar 19, 2019)

Thanks again.

I posed this question a couple of years ago. But as some more knowledge seems to have accumulated since I ask again. 

Which radiator installation for inlines offer the least drag and the most thrust respectively?
First place must be the Mustang-style one which uses the Meredith-effect well. It has a sufficient expansion chamber aft of the radiator for the warm air which exits through the aft outlet. I wonder how efficient the ventral cooler installations on other fighters were, for example the Yak-3 and the Italian series 5 fighters. Those seem to lack a big enough chamber.
Second (at least I think) is the annular/drum installation found on late-war German aircraft. Though it looked draggy it was surprisingly aerodynamic. Maybe because it was part of the fuselage? Here louvers are used as air outlet. No idea about thrust effects.
Late in/after the war the British experimented with an air outlet installation which was movable fore and aft and thus regulating the amount of air outlet.
By renouncing the use of louvers, which enlarged the area exposed to airflow, the drag should not increase.
Third would be leading edge radiator, which I intuitively would rate as less draggy draggy than the annular/drum one. But according to a report it isn't. I wonder why as the inlet is not mounted outside of the main body.
Fourth had to be underwing radiators which gave the Me 109 and especially the Spitfire a massive drag penalty.

As far as engine cowling aerodynamics are concerned it seems that the Japanese fighters were the most advanced. If one looks at them they seem more refined and curved. The J2M Raiden was more aerodynamic than a predecessor, the A6M Zero I think, even though it had a larger fuselage cross section diameter. It was achieved by a carefully shaped engine cowling.

If you look at the wing shapes of Japanese and Russian planes, they have less blunt wing leading edge than the German planes and the thickest part of the wing seems to be more far aft, almost of laminar shape in some cases. Can one deduce that, like in the case of the Mossie, that these airfoil are more aerodynamic than the German ones?


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## tomo pauk (Mar 20, 2019)

spicmart said:


> ...
> Which radiator installation for inlines offer the least drag and the most thrust respectively?
> First place must be the Mustang-style one which uses the Meredith-effect well. It has a sufficient expansion chamber aft of the radiator for the warm air which exits through the aft outlet. I wonder how efficient the ventral cooler installations on other fighters were, for example the Yak-3 and the Italian series 5 fighters. Those seem to lack a big enough chamber.
> Second (at least I think) is the annular/drum installation found on late-war German aircraft. Though it looked draggy it was surprisingly aerodynamic. Maybe because it was part of the fuselage? Here louvers are used as air outlet. No idea about thrust effects.
> ...



The radiators used on Bf 109, Re.2005 and Spitfires were half-burried in the wing. IMO, draggiest radiators were the type used on Hurricane, early XP-40 and prototype Typhoon. Radiators installed in front of leading edge were probably no worse that the annular radiator, especially since it added extra chord, thus improving T-t-C ratio, and adding wing area.



> As far as engine cowling aerodynamics are concerned it seems that the Japanese fighters were the most advanced. If one looks at them they seem more refined and curved. The J2M Raiden was more aerodynamic than a predecessor, the A6M Zero I think, even though it had a larger fuselage cross section diameter. It was achieved by a carefully shaped engine cowling.



La-7 and Yak-3U seem very refined to me, granted Japanese radials seem also very refined and streamlined, even if we look at the Ki 27 (not the exhausts, though). But then, most of the designers got the radial engine streamlining right by mid-war.



> If you look at the wing shapes of Japanese and Russian planes, they have less blunt wing leading edge than the German planes and the thickest part of the wing seems to be more far aft, almost of laminar shape in some cases. Can one deduce that, like in the case of the Mossie, that these airfoil are more aerodynamic than the German ones?



Fw 190 have had the widely-used NACA 230 series of profiles, no worse than LaGG-3/La-5/La-7. The Clark-Y profiles used on Yaks and MiGs were hardly miracles of aerodynamics, let alone the profiles used on Zeros and Oscars. Later Japanese fighters gotten newer and improved profiles, though.
The 2R14.2 used on Bf 109 looked indeed blut-shaped, it gave worse drag results vs. wing of Fw 190 per German tests.


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## pbehn (Mar 20, 2019)

spicmart said:


> Thanks again.
> 
> Which radiator installation for inlines offer the least drag and the most thrust respectively?
> First place must be the Mustang-style one which uses the Meredith-effect well. It has a sufficient expansion chamber aft of the radiator for the warm air which exits through the aft outlet. I wonder how efficient the ventral cooler installations on other fighters were, for example the Yak-3 and the Italian series 5 fighters. Those seem to lack a big enough chamber.
> Second (at least I think) is the annular/drum installation found on late-war German aircraft. Though it looked draggy it was surprisingly aerodynamic. Maybe because it was part of the fuselage? Here louvers are used as air outlet. No idea about thrust effects.


 Well the Mosquito was also an in line but obviously a twin. Whether better of worse than the P-51 set up I don't know in terms of overall cooling drag. The Mosquito used the Meredith effect, probably less efficiently but then it didn't have an inlet stuck in the airflow. All designs are compromises, the P-51s cooling system not only made great use of the Meredith effect it freed up room in the wings for a prodigious amount of internal fuel. However it wasn't a possibility for the first Merlin Spitfires with wooden two blade props, it would have needed most of Kent to take off. There was an annular design for the Typhoon which gave an improvement on speed of around 10-14MPH but they decided to just have more Typhoons.


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## tomo pauk (Mar 20, 2019)

pbehn said:


> ...
> All designs are compromises, the P-51s cooling system not only made great use of the Meredith effect it freed up room in the wings for a prodigious amount of internal fuel. However it wasn't a possibility for the first Merlin Spitfires with wooden two blade props, it would have needed most of Kent to take off.




Twice the heavy Fairey Battle managed well to take off in reasonable amount of real estate, thus such the Spitfire + 700-800 lbs worth of fuel and tanks will still manage it even better.


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## Shortround6 (Mar 20, 2019)

The "secret" to the P-51 radiator set is a combination of things, not one or two features by themselves. 





1. You have the extended air scoop/boundary layer splitter. The turbulent/swirling air next to fuselage skin is diverted away from the radiator duct.
2. The air headed for the radiator is allowed/forced to expand considerably in long enough duct that major eddies/swirls are not introduced.
3. The expanded air is much lower velocity and as it passes through the radiator it creates less drag (drage being equal to the square of the speed)
3a. The slower moving air might pick up more heat (not sure about this) 
4. The expanded and heated air is compressed and speeded up by the converging walls (or roof/floor) of the duct over enough distance that excess turbulence or resistance is not introduced (some probably is).
5. the exit opening is sized and adjusted inflight ot not only adjust to total airflow through the radiator but to try and make the exiting hot air have a velocity higher than the forward speed of the plane (this is where things get iffy as to whether it was actually making thrust) 
6. the direction of the air (radiator exhaust stream) leaving the duct is pretty much in line with the direction of travel of the airplane. 

Now lets compare the Mosquito radiator, simply because I am lazy and it is the first picture I found on the internet. 





It certainly meets condition #1
It is expanding the air leading to the radiator as in condition #2, few neweddies introduced.
Is the air slowed down enough to be as low drag going through the radiator matrix? This may depend somewhat on the radiator matrix itself.
Has it picked up enough heat to materially expand the air (which is different that just cooling the engine)? 
The Mosquito;s exit duct is shorter and somewhat more off center, a potential sources of drag/eddies.
and finally, even if the air leaving the duct is leaving at a higher speed than the aircraft is moving the direction of the just thrust is at more of an angle to the line of flight meaning some of the effort/thrust is wasted. 

No I have not mentioned the difference in frontal area for each design and this are illustrative drawings and not blue prints with dimensions so perhaps too much should not be read into them.
I am not criticizing the Mosquito (the basic radiator design predates the Merlin power Mustang radiator setup) but just trying to show that there are large variety of factors that come into the situation and focusing on just a few may miss some of the others.

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## Shortround6 (Mar 20, 2019)

tomo pauk said:


> Twice the heavy Fairey Battle managed well to take off in reasonable amount of real estate, thus such the Spitfire + 700-800 lbs worth of fuel and tanks will still manage it even better.


Fairey Battle had a wing loading of 25.6 pounds per sq ft and had a two pitch prop to help take-off. 
A Mk I SPit with and extra 500lbs of fuel and tanks would have a wing loading of 26.1lb/sq/ft but saddled with th etwo balde fixed pitch prop it would be using around 2000rpm (or less) for take off instead of 3000rpm like the Battle. 580-600hp?


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## pbehn (Mar 20, 2019)

Shortround6 said:


> I am not criticizing the Mosquito (the basic radiator design predates the Merlin power Mustang radiator setup) but just trying to show that there are large variety of factors that come into the situation and focusing on just a few may miss some of the others.


That was my point, figuring out which had the lowest overall cooling drag is way above my level. Did the Mosquito inlet in the wing increase drag for example? In any case they are solutions that cant be swapped, The Mosquito system on the P-51 cuts down its fuel load and the P-51 system on a Mosquito uses the bomb bay.


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## tomo pauk (Mar 20, 2019)

pbehn said:


> That was my point, figuring out which had the lowest overall cooling drag is way above my level. Did the Mosquito inlet in the wing increase drag for example? In any case they are solutions that cant be swapped, The Mosquito system on the P-51 cuts down its fuel load and the P-51 system on a Mosquito uses the bomb bay.



Mosquito's system used on Mustang means that Mustang has to find some other place to retract U/C, ditto for Mustang's system used on Mosquito?

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## MIflyer (Mar 20, 2019)

Here is some more info on the wing design and construction:

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## spicmart (Mar 20, 2019)

tomo pauk said:


> The radiators used on Bf 109, Re.2005 and Spitfires were half-burried in the wing. IMO, draggiest radiators were the type used on Hurricane, early XP-40 and prototype Typhoon. Radiators installed in front of leading edge were probably no worse that the annular radiator, especially since it added extra chord, thus improving T-t-C ratio, and adding wing area.
> 
> 
> 
> ...




Interesting. If one looks at Fotos of 190 and 109 from afore one doesn't get the impression that the 109 wing was blunter. Maybe just a tad. 
That the opted wing is so draggy, given Messerschmitt 's obsession for speed, is quite surprising as they introduced a new wing with the F. 
A more streamlined wing might have given it almost the same speed of the Yak-3 on the same power.


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## tomo pauk (Mar 20, 2019)

spicmart said:


> Interesting. If one looks at Fotos of 190 and 109 from afore one doesn't get the impression that the 109 wing was blunter. Maybe just a tad.
> That the opted wing is so draggy, given Messerschmitt 's obsession for speed, is quite surprising as they introduced a new wing with the F.
> A more streamlined wing might have given it almost the same speed of the Yak-3 on the same power.



For the era the Bf 109 was introduced, it's wing was very modern and thin. 
Wings of 109F and 109E probably differed only at tip and where the radiators were installed, so most of existing tooling for the wing can still be used in order to maintain production rates.


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## llemon (Mar 21, 2019)

spicmart said:


> Thanks again.
> 
> I posed this question a couple of years ago. But as some more knowledge seems to have accumulated since I ask again.
> 
> ...



I've read a paper that argues that a 109 type installation is superior to the 51. This is because the expansion area in front of the radiator is small enough that separation isnt an issue, duct area is minimized, and it can hit the needed expansion ratio with a minimum of length. It is interesting that the spitful had a very 109 like radiator instead of a 51 style belly scoop. Of course boundary layer ingestion is the biggest issue and its hard to see how such a radiator installation can overcome it even with a slot.

The late war 152/209 radiator installation are a drum type, which despite the looks isnt really similar to the annular installations used earlier. By sticking the radiator horizontally you can get a good expansion ration while avoiding separation and do it in a very short duct. Blohm actually had a very similar arrangement with the 155s radiators which look more like 51 scoops but in actuality have the radiator nearly horizontal.

The issue with leading edge radiators is spilliage spoiling the airfoil over the wing. Even if you dont get spilliage the slot for the intake will help ruin the airflow. Making the exit slot work with a ramp is also a bit of an issue.

In hindsight the long nose allison looks like the perfect candidate for drum style radiator, but that is getting off topic.

Yaks and Las used a Clark-yh profile, around 14% at root iirc. Most Japanese aircraft were using NACA derived airfoils, often 23000s. Tightly cowled engines like the J2 were tried elsewhere - expecially by Curtiss. They are good on paper but getting them to work in practice is hard, and the raiden had lots of cooling problems for most of its life.



tomo pauk said:


> For the era the Bf 109 was introduced, it's wing was very modern and thin.
> Wings of 109F and 109E probably differed only at tip and where the radiators were installed, so most of existing tooling for the wing can still be used in order to maintain production rates.



Willy Messerschimtt love the NACA 2R airfoil. Its a kinda strange thing that so many messerschmitt aircraft used it. I don't know of any other manufacturer who employed it as a wing airfoil. The 2R was originally intended for props as far as I can tell. Finding info on it is much harder than other NACA series airfoils but in fairness I havent tried that hard.

The Fs wing originally was a straight up clipped E series aerodynamically. They found that the reduction in span had too much of an adverse effect on handling so they added some elliptical tips. This was done because the F wing was a substantial structural redesign and it was easier from a tooling/produciton standpoint to make the tips bigger rather than extending the spar and going back to an E range span.


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## tomo pauk (Mar 21, 2019)

llemon said:


> I've read a paper that argues that a 109 type installation is superior to the 51. This is because the expansion area in front of the radiator is small enough that separation isnt an issue, duct area is minimized, and it can hit the needed expansion ratio with a minimum of length. It is interesting that the spitful had a very 109 like radiator instead of a 51 style belly scoop. Of course boundary layer ingestion is the biggest issue and its hard to see how such a radiator installation can overcome it even with a slot.



The paper you've mentioned is IMO fishy. As you've noted, ingestion of boundary layer is a problem. Bf 109 have had 3 duct openings, for it's two coolant radiators and one oil cooler, vs. single opening on P-51. 
Spiteful took a lot of fuselage structure from Spitfire, so unless a major redesign of fuselage is done it will probably not be possible to have P-51-style radiator on Spiteful. 



> The issue with leading edge radiators is spilliage spoiling the airfoil over the wing. Even if you dont get spilliage the slot for the intake will help ruin the airflow. Making the exit slot work with a ramp is also a bit of an issue.



Leading-edge radiators were suggested by NACA for the (Y)P-38, to be installed in the extended (chord increased by 20%) section of the wing inboard the engines.
Seems like LE radiators worked on Mosquito, Hornet and Tempest I.



> Yaks and Las used a Clark-yh profile, around 14% at root iirc.



LaGG-1/3 and La5/7 used NACA 23016 at root.


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## pbehn (Mar 21, 2019)

llemon said:


> It is interesting that the spitful had a very 109 like radiator instead of a 51 style belly scoop. Of course boundary layer ingestion is the biggest issue and its hard to see how such a radiator installation can overcome it even with a slot.
> 
> .


The Supermarine Spiteful had a Supermarine like radiator developed by Supermarine, from the Supermarine Spitfire.


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## llemon (Mar 21, 2019)

tomo pauk said:


> The paper you've mentioned is IMO fishy. As you've noted, ingestion of boundary layer is a problem. Bf 109 have had 3 duct openings, for it's two coolant radiators and one oil cooler, vs. single opening on P-51.



One advantage to the 109 style radiator is the wetted area from the ducts is much less than a belly scoop. Also the internal duct area is less despite having two radiator - this is because the expansion part of the duct is dependent on the height of the rad. And given that it is a much shorter rad in 109 style the duct can be shorter.

But none of this really matters since there is no good way to get rid of the boundary layer. Although you can get a sense of the logic behind such an installation.



> Leading-edge radiators were suggested by NACA for the (Y)P-38, to be installed in the extended (chord increased by 20%) section of the wing inboard the engines.
> Seems like LE radiators worked on Mosquito, Hornet and Tempest I.



I wasn't implying that leading edge radiators dont work. Just that they probably arent as good of an option as 51 style belly scoop or annular.



> LaGG-1/3 and La5/7 used NACA 23016 at root.



Got them mixed up with the mig. I knew that two of the 3 major newish soviet fighters used clark-yh. 



pbehn said:


> The Supermarine Spiteful had a Supermarine like radiator developed by Supermarine, from the Supermarine Spitfire.



The spitfire started off with one deep underwing radiator. Then two. And finally ends up with two very shallow and wide under wing radiators in the spitful. 

I wasn't implying anything about supermarine copying the Germans. Just that the spitfuls rad arrangment is much more like a 109F than a MKII. What that means exactly, were they aping the germans or did they arrive at the same solution for similar reasons, would have to be discovered by digging around in archives.


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## Shortround6 (Mar 21, 2019)

We can look at the drawings all we want. 
We know what they were trying to achieve.

Without test results of different set ups that give pressure in the ducts at various places, speeds of the airflow through the duct at various locations in the duct, and/or photography of smoke streams through the ducts/radiators we are just guessing. 

The Mustang radiator is generally acknowledged as one of the best of WW II, I listed a bunch of factors. I have no idea if one or more of those factors was actually working as they thought/hoped or how close to the top of the heap any one factor was compared to all the other set ups. All we know is that the total combination was one of the best, if not the best. 
One or more factors could have been below par if the others made up for.

As for the idea that smaller ducts have less wetted area and thus less friction/drag. I am not sure that is right. I don't know about air, I know a bit about water (but it is incompressible) 

but here is a friction loss chart for fire hose. 






Pick a flow like 500gpm and look at the 2 1/2, 3 and 3 1/2 diameter hose. Going from the 2 1/2 to 3 1/2 hose increased the "wetted" area by 40% but the force needed to push the water through the hose dropped to less than 20% , The water was moving "slower" and for a total volume of water, less was in contact with hose wall at any given time. 

Somebody who has studied air flow could very well correct me. 

At times on the training ground (depending on which training officer we had) we would put pressure gauges mounted on short lengths of pipe into a layout of several hundred feet and we would also measure the pressure of the water exiting nozzle. Most of the time we got the expected result, sometimes we did not. 

Please note that most of the time doubling the flow in a given size hose quadruples the friction loss which is what we would expect from the square law.


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## pbehn (Mar 21, 2019)

llemon said:


> The spitfire started off with one deep underwing radiator. Then two. And finally ends up with two very shallow and wide under wing radiators in the spitful.
> 
> I wasn't implying anything about supermarine copying the Germans. Just that the spitfuls rad arrangment is much more like a 109F than a MKII. What that means exactly, were they aping the germans or did they arrive at the same solution for similar reasons, would have to be discovered by digging around in archives.


How many did the Bf 109 start out with? The radiators for oil and water cooling were always below the spitfires wings. A radiator for the intercooler was also added later and the oil cooler made bigger to cope with increased temperature/work load. There was a simple reason that the radiators were not low and slim on a Spitfire, it needed a complete re design of the wing as you can see below.


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## Milosh (Mar 21, 2019)

What was the total radiator area size (coolant and oil) for the Spit IX and 109G?


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## Zipper730 (Mar 21, 2019)

pbehn said:


> *From "The Mosquito Manual", I know there were two sections involved. The first was a Piercy section (Norman Augustus Victor Piercy) and the second was the RAF 34.*


So, basically it combined the RAF 34 and Piercey sections, with the crest at 40% T/C?


>


It does have some traits I can see in later laminar flow foils -- particularly the trailing edge starting to develop a barely visible cusp.

I'm confused about what you wrote regarding T/C of the airfoil -- was it 13 or 15%?


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## spicmart (Mar 21, 2019)

llemon said:


> The late war 152/209 radiator installation are a drum type, which despite the looks isnt really similar to the annular installations used earlier. By sticking the radiator horizontally you can get a good expansion ration while avoiding separation and do it in a very short duct. Blohm actually had a very similar arrangement with the 155s radiators which look more like 51 scoops but in actuality have the radiator nearly horizontal.



This is a known drawing showing annular and drum radiator! Can you specify why the drum would be better other than offering more area? I don't quite understand the separation issue and it doesn't offer more expansion space than the annular one. 







Here is the report of the British tests that tomo posted in another thread before. It says that frontal radiators are less draggy than leading edge radiators. 

tempest | 1946 | 1441 | Flight Archive


I don't know really know about wing profiles and how they are named or classified. 
Can you tell me some sources where I can educate myself?


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## pbehn (Mar 21, 2019)

Zipper730 said:


> So, basically it combined the RAF 34 and Piercey sections, with the crest at 40% T/C?
> It does have some traits I can see in later laminar flow foils -- particularly the trailing edge starting to develop a barely visible cusp.
> 
> I'm confused about what you wrote regarding T/C of the airfoil -- was it 13 or 15%?


I didn't write it, I found it on a blog, cant really tell who wrote it. As I can see it is a combination of Piercy and RAF 34 with some of d Havillands own ideas/experience. From what I can see people were learning all the time, it was more "laminar flow than previous and less laminar flow than later but non were actually laminar flow anyway.


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## spicmart (Mar 21, 2019)

llemon said:


> The issue with leading edge radiators is spilliage spoiling the airfoil over the wing. Even if you dont get spilliage the slot for the intake will help ruin the airflow. Making the exit slot work with a ramp is also a bit of an issue.
> 
> In hindsight the long nose allison looks like the perfect candidate for drum style radiator, but that is getting off topic.
> 
> ...




What do you mean with spillage?

Can you elaborate on the Russian and Japanese wings? 
What do the 14% mean drag wise? 

Why do you include the Allison? 

The 2R isn't the most aerodynamic of wings? For one striving for ever more speed Willy would have been better advised to have looked for at at least used others. 

Sorry, the many and direct questions. Not to be in polite, just curious.


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## wuzak (Mar 21, 2019)

Shortround6 said:


> We can look at the drawings all we want.
> We know what they were trying to achieve.
> 
> Without test results of different set ups that give pressure in the ducts at various places, speeds of the airflow through the duct at various locations in the duct, and/or photography of smoke streams through the ducts/radiators we are just guessing.
> ...



I think the wetted area comment referred to the shape and size of the duct's effect on the external air flow, not the duct's internal flow.

The P-51's radiator was one of the best of WW2, no doubt, but it was far from perfect. 

The expansion duct was not symmetrical, with the roof being quite steep, which may have led to flow separation.


In the case of the wide, low radiator ducts, as used on the Spiteful, there was actually boundary layer thickening on the roof of the duct. The boundary layer air is not moving very quickly relative to the aircraft, so this reduced the effectiveness of the radiator. I can't recall exactly how much of the radiator the boundary layer covered, except that it was around 1/8 the depth of the radiator. Which is significant. This was from tests done of the production style Spiteful radiators.

The best solution for dealing with the boundary layer was to provide a duct, which exhausted to the top of the wing before the radiator. Obviously this was not the best solution for the aircraft, as it disturbed the wing. 

Another solution was to provide a duct the entire length of the radiator duct, gong above the radiator.


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## pbehn (Mar 22, 2019)

Milosh said:


> What was the total radiator area size (coolant and oil) for the Spit IX and 109G?


My point was that the two planes are different. The Bf-109 always had the oil cooler under the engine, even when the water cooling was moved to the wings. The Spitfire always had oil and water cooling in the wings and added the intercooler. The Spitfires radiators would have been wider and flatter but there wasn't space for that because of the undercarriage.


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## Shortround6 (Mar 22, 2019)

Radiators (and the airflow through them) have to be sized to the power the engine is developing in the cylinders and the amount of airflow going through the radiator at the appropriate altitudes. 
Like a DB605A making 1355PS at about 18800ft to which you have to add the friction in the engine + the power needed to drive the supercharger which is compressing the the Air to about 6lbs of boost. 
The V-1659-3 in an P-51B made 1330hp at 23,300ft to which you need to add the friction and the power to drive the supercharger which is compressing thinner air to 18lb boost and is using thinner (less dense) air going through the radiator to do the cooling. You also have to know if the engines in question put a similar amount of heat into the oil and the coolant.
The Allisons and Merlin used in the P-40 did not and the Merlin P-40s need a different radiator and oil cooler it order to cool properly. 

Just measuring radiator size leaves out several considerations/factors.


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## pbehn (Mar 22, 2019)

Shortround6 said:


> Just measuring radiator size leaves out several considerations/factors.


I always thought a radiator was based on volume. The surface area of the radiator and airflow is what governs its worth, if the frontal area is reduced it must be made deeper which is a bit of a bind because they work best with a large frontal area and small depth, just what an aircraft designer doesn't want.


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## Shortround6 (Mar 22, 2019)

You are correct if the other conditions don't change, You can't use the same radiator for a big V-8 towing a trailer even if it works fine on a low powered six cylinder engine. 

For our aircraft the air at 23,000ft is about 87% as dense as the air at 19,000ft so to get rid of the same amount of heat at 19.000ft your radiator only needs to be 87% as big assuming you have the same volume of air going through it per minute. Yes the air is colder at 23,000ft but not enough to make up for the density difference. 
Two stage Merlin is probably making more power in the cylinders in order to drive the two stage supercharger even if power to prop isn't that different so the radiator has to sized to the total cooling load.


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## pbehn (Mar 22, 2019)

Shortround6 said:


> You are correct if the other conditions don't change, You can't use the same radiator for a big V-8 towing a trailer even if it works fine on a low powered six cylinder engine.
> 
> For our aircraft the air at 23,000ft is about 87% as dense as the air at 19,000ft so to get rid of the same amount of heat at 19.000ft your radiator only needs to be 87% as big assuming you have the same volume of air going through it per minute. Yes the air is colder at 23,000ft but not enough to make up for the density difference.
> Two stage Merlin is probably making more power in the cylinders in order to drive the two stage supercharger even if power to prop isn't that different so the radiator has to sized to the total cooling load.


Those are all problems faced by Supermarine in cooling the Merlin and later Griffon in the Spitfire from when it was first designed to the end of the war, in an airframe that was originally laid out for evaporative cooling. With the place in the wing where the radiator was placed hemmed in by the undercarriage only a radiator scoop with a bigger frontal and cooling area was possible, without stopping production for a completely new wing.


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## Shortround6 (Mar 22, 2019)

That may very well be. 
But that is not what I am arguing/

I am arguing that trying to compare the 109 to the Spitfire by comparing the size of their radiators isn't going to tell us much unless we know the heat load they are trying to get rid of and I am guessing that the 109 was usually trying to get rid of less heat and/or doing it in higher density air that needed smaller radiators.


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## pbehn (Mar 22, 2019)

Shortround6 said:


> That may very well be.
> But that is not what I am arguing/
> 
> I am arguing that trying to compare the 109 to the Spitfire by comparing the size of their radiators isn't going to tell us much unless we know the heat load they are trying to get rid of and I am guessing that the 109 was usually trying to get rid of less heat and/or doing it in higher density air that needed smaller radiators.


That was my point S/R when it was suggested that the Spitfire ended up with a configuration like the Bf-109.


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## nuuumannn (Mar 22, 2019)

Just going back to the original question, the Mosquito was an extraordinarily clean design and finish, despite its physical size, as can be seen here.




TV959 16




TV959 02

Both the Spitfire and Bf 109's radiators sizes and configurations were determined by their location. This is a Spit XIV radiator and you can see how the size has increased to cope with the installation of the Griffon.




Radiator

The Bf 109's was similarly located, but in later, post Friedrich models became more sophisticated.




Radiator location




Radiator

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## spicmart (Mar 23, 2019)

wuzak said:


> In the case of the wide, low radiator ducts, as used on the Spiteful, there was actually boundary layer thickening on the roof of the duct. The boundary layer air is not moving very quickly relative to the aircraft, so this reduced the effectiveness of the radiator. I can't recall exactly how much of the radiator the boundary layer covered, except that it was around 1/8 the depth of the radiator. Which is significant. This was from tests done of the production style Spiteful radiators.
> 
> Another solution was to provide a duct the entire length of the radiator duct, gong above the radiator.



Is this what you mean? 

Bf 109 F 
This shallow bypass air duct for boundary layer extraction is only available on the Bf 109 F. 
Due to the increased flow velocity of the air flowing through, the channel only reduces the air resistance which the cooler housing generates.


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## nuuumannn (Mar 23, 2019)

Following on the discussion about radiators, here are some images of the P-51's radiator for comparison with the others posted here already. The Mustang's opening and its boundary layer diffuser are plainly evident.




Intake 

The oil cooler is also inside the orifice, with the radiator further back.




Intake inside 

This is the oil cooler outlet under the aircraft's belly.




Oil cooler outlet 

Further aft of that is the radiator outlet. Ignore the bump to its rear, it is a concession to modern avionics.




Radiator exhaust i 

The size of the radiator and orifice from where the Meredith Effect thrust element exits can be seen here.




Radiator exhaust ii

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## wuzak (Mar 23, 2019)

spicmart said:


> Is this what you mean?
> 
> Bf 109 F
> This shallow bypass air duct for boundary layer extraction is only available on the Bf 109 F.
> Due to the increased flow velocity of the air flowing through, the channel only reduces the air resistance which the cooler housing generates.



Yes


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## spicmart (Mar 23, 2019)

So did the Spiteful also have this feature?
Messerschmitt gave up on this after the 109 F-version for whatever reason. 
Maybe the cost-benefit ratio was not worth it. It doesn't seem too complex though.


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## pbehn (Mar 24, 2019)

spicmart said:


> So did the Spiteful also have this feature?
> Messerschmitt gave up on this after the 109 for whatever reason.
> Maybe the cost-benefit ratio was not worth it. It doesn't seem too complex though.


As I understand it, it preserves the boundary layer but by reducing the flow through the radiator. So you need a much bigger radiator to do the same amount of cooling which defeats the purpose of it.


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## wuzak (Mar 24, 2019)

spicmart said:


> So did the Spiteful also have this feature?
> Messerschmitt gave up on this after the 109 for whatever reason.
> Maybe the cost-benefit ratio was not worth it. It doesn't seem too complex though.



No. The production radiator duct was a plain duct, without boundary layer duct.

It was investigated, though.


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## wuzak (Mar 24, 2019)

pbehn said:


> As I understand it, it preserves the boundary layer but by reducing the flow through the radiator. So you need a much bigger radiator to do the same amount of cooling which defeats the purpose of it.



The problem identified for the Spiteful was that the boundary layer thickened in the duct and reduced the effective area of the radiator.

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## pbehn (Mar 24, 2019)

wuzak said:


> The problem identified for the Spiteful was that the boundary layer thickened in the duct and reduced the effective area of the radiator.


I was talking about the 109 set up, preserving the boundary layer worked but reduced the efficiency of the radiator. (that's how I understood it anyway).


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## Gemhorse (Mar 25, 2019)

Anyway, the DH Mosquito's design lead on also to the DH Hornet, which had a level speed of around 487mph and was a study (at the time) of streamlining, particuarly of the Merlins 130/131's cowlings... all superb considering there was largely wooden structure involved, leading onto the first wood & metal being glued, DH using this new 'Redux' adhesive on the Hornet, all very new development that DH were pushing ahead with, and they then followed-on with the jet Vampire...


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## pbehn (Mar 25, 2019)

Gemhorse said:


> Anyway, the DH Mosquito's design lead on also to the DH Hornet, which had a level speed of around 487mph and was a study (at the time) of streamlining, particuarly of the Merlins 130/131's cowlings... all superb considering there was largely wooden structure involved, leading onto the first wood & metal being glued, DH using this new 'Redux' adhesive on the Hornet, all very new development that DH were pushing ahead with, and they then followed-on with the jet Vampire...


Part of the Mosquito was its cooling and general streamlining, but it was a bomber initially. Compare to a Lancaster, the "boundary layer was passing over a cheese grater by comparison.

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## fliger747 (Mar 28, 2019)

Yes the surface smoothness and ability to carefully design and control shape gave advantages to the wooden construction. I am not sure about the weight for strength as opposed to more conventional alloy construction. Not that WWII aircraft were designed for a long life span given a typical combat aircraft lifespan, but the wooden wonders of various sorts did not hold up well to adverse climates such as in the humid tropics. This probably limited the applicability of such airframes to a post war environment where longevity became a consideration.


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## pbehn (Mar 28, 2019)

fliger747 said:


> Yes the surface smoothness and ability to carefully design and control shape gave advantages to the wooden construction. I am not sure about the weight for strength as opposed to more conventional alloy construction. Not that WWII aircraft were designed for a long life span given a typical combat aircraft lifespan, but the wooden wonders of various sorts did not hold up well to adverse climates such as in the humid tropics. This probably limited the applicability of such airframes to a post war environment where longevity became a consideration.


Comparing wood to metal, wood has less torsional strength, this just requires different methods of design and construction. There were some problems in the far east but more concerning adhesives than the actual wood.


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## chuter (Mar 28, 2019)

--->According to Lee Atwood<---, only the P-51 and Mosquito got Meredith Effect to pay off. Everyone else (WW2) tried to adapt it to existing designs and failed so those engineers decided the Mustang's and Mosquito's speed must be due to the wing in the Mustang's case and clean airframe in the Mosquito's case. He said the Mustang's wing was actually a failure in the field, as far as laminar flow speed gains are concerned.

Apparently the 109F's boundary layer bypass didn't pay off as duct stall wasn't eliminated and a larger cooler was seen as a an easier and slightly better performing option.


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## fliger747 (Mar 28, 2019)

The wood construction was in effect a very early composite. And with such a material the adhesive or binder is an essential part of the material. "Wood" is perhaps a misnomer for this material. The Hornets posted Post War to SE Asia did not hold up well, indeed to issues with the adhesive. Various models of the 737 used adhesive rather than complete riveting, which resulted in the famous "Zip Top" that successfully landed in Maui after a terrifying failure of the forward fuselage shell. 

Wood, depending on the species and grain alignment, and layering can be engineered to quite sophisticated properties. Most Alpine Skis still have wooden cores. My powder skis have a bamboo core! That the prototype Hughes "Spruce Goose" used wood composites was quite an accomplishment for the era. Of course had the plane ever been produced the idea was to use alloys.


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## Shortround6 (Mar 29, 2019)

chuter said:


> Apparently the 109F's boundary layer bypass didn't pay off as duct stall wasn't eliminated and a larger cooler was seen as a an easier and slightly better performing option.



The radiators have to be sized to the engine and expected airflow. 

Which 109 was designed to which engine?
The DB605 in the 109G made 15% more power 800 meters higher (thinner air) than the DB601N engine that the early 109Fs used. 
You are going to need bigger radiators, it is just a question of how you arrange them.


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## fliger747 (Mar 29, 2019)

I would expect (but do not know) the effect leading edge radiator ducting has on stall characteristics. Certainly they would have very different and probably not better flow over the top of the wing than a regular leading edge section. I would expect an increase in tail plane buffet near the stall at a minimum.


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## pbehn (Mar 29, 2019)

fliger747 said:


> I would expect (but do not know) the effect leading edge radiator ducting has on stall characteristics. Certainly they would have very different and probably not better flow over the top of the wing than a regular leading edge section. I would expect an increase in tail plane buffet near the stall at a minimum.


In late model piston engine aircraft air intakes on the leading edge for water or oil cooling were very common.


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## wuzak (Mar 29, 2019)

Shortround6 said:


> The radiators have to be sized to the engine and expected airflow.
> 
> Which 109 was designed to which engine?
> The DB605 in the 109G made 15% more power 800 meters higher (thinner air) than the DB601N engine that the early 109Fs used.
> You are going to need bigger radiators, it is just a question of how you arrange them.



The radiators are also sized for normal continuous power, not 30 minute climb power or 5 minute WEP.

It's part of the reason the time limits exist - the temperature can't be controlled at the higher power settings for too long.


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## Shortround6 (Mar 29, 2019)

Thank you for that but it doesn't change the basics,

The 605A was rated for 19% more power 950 meters higher up for the 30 minute rating and 13.6% more power 400 meters higher continuous power. 

The 605 made 30 more PS continuous 650 meters higher than the 601N did for it's 30 minute rating. 

The 605 was also putting a bit more power into the supercharger. 

Basically you needed 14-15% bigger radiators (or 14-15% more cooling capacity) at a minimum for the 109G than you needed for the 109F.


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## chuter (Mar 30, 2019)

Shortround6 said:


> The radiators have to be sized to the engine and expected airflow.
> 
> Which 109 was designed to which engine?
> The DB605 in the 109G made 15% more power 800 meters higher (thinner air) than the DB601N engine that the early 109Fs used.
> You are going to need bigger radiators, it is just a question of how you arrange them.




OK - I'll walk you through my reasoning. The Meredith Effect requires non-turbulent airflow to work. The 109F used a bypass duct to aid in achieving this. This duct took up space in the wing and required some effort to produce but would be worth it due to the improved cooling efficiency (non-turbulent airflow) and much reduced (if not eliminated) cooling drag. While the concept looked great on paper and obviously passed some level of testing prior to production, when the G came out with its more powerful engine requiring additional cooling due to its additional power (as you noted) rather than adapt the bypass cooling duct system with its apparent efficiency and drag characteristics by expanding the duct downward they took the cheaper and easier way by removing the bypass duct and expanded upward into the void left by the removed bypass duct. They wouldn't have done this if the duct clearly worked. Look at the Mustang, with the switch to the Merlin the cooling duct expanded downward into the airflow to handle the additional cooling requirement without a drag penalty.


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## ThomasP (Mar 30, 2019)

About the use (first use?) of the Meredith effect,

I cannot say authoritatively that the Hurricane was the first production aircraft to incorporate the Meredith effect, but Hawker engineers knowingly introduced aspects of the effect in the production cooling system, with the intent of reducing the cooling drag. Although they were aware of the potential in the Meredith effect (it had originated in the UK after all) and understood most of its theoretical finer points as to what would work, the Hawker design team did not pursue the maximum possible effect for practical reasons.

One reason was the cost of manufacturing what for the time would have been a fairly sophisticated assembly.

Another reason was available space and weight for the assembly. On first look this might not seem correct, after all the Hurricane was a fairly large airframe and the radiator was already in a similar location to that of the P-51, and it might be possible to rearrange the bits and pieces to maintain an acceptable CG. Keep in mind, however, that the Hurricane was intended to be an evolution of an older biplane design into a monoplane (similar to the evolution of the Wildcat), not a largely new design.

Still another reason was the expected top speed and sustained speeds of the new aircraft. The radiator system of an aircraft must be able to meet the sustained speed cooling requirement indefinitely, and the maximum power cooling requirements for various lesser periods (e.g. WEP for 5 min, Military for 15 min, Climb for 30 min, etc). Everything else being equal, the greater the speed, the greater the Meredith effect. In fact the Meredith effect becomes more efficient with square of the inrease in speed. The Hurricane II was effectively 100 mph slower than the P-51B, so if the exact same assembly as used on the P-51B ( at 430 mph) was used on the Hurricane II (at 330 mph) it would only be abut 56% as effective as on the P-51B.

Instead the Hurricane design team relied on a shorter but larger orifice inlet, with a boundary layer lip/notch, and a somewhat shorter exit chamber with a variable outlet area via a movable flap. The boundary layer lip/notch prevented air flow stagnation at the radiator inlet, the short inlet chamber combined with the larger orifice allowed enough air to slow down (via the pressure head effect) to efficiently absorb heat while passing through the radiator, the radiator heated the air up, and the short exit chamber with variable area outlet acted like an ejector nozzle depending on the aircraft speed, power setting, engine temperature, and flap position. In order to keep the controls simple, the pilot adjusted the flap depending on the engine temperature, not for maximum Meredith effect. The normal flap setting was used for maximum sustained speed which would correlate to a sustainable engine temperature, the more closed settings were used for higher speeds where higher air flow helped keep the engine cool temporarily, and the more open settings were for lower speeds at high power settings (while climbing for example) or while idling/taxying and during take-off .

If my information is correct the P-51B cooling system reduced the cooling HP loss by about 80%, or from about 400 HP to about 50 HP. 

Using the P-51B system on the Hurricane II would have reduced the cooling HP loss by 45% (i.e. .56 x .80), or from about 260 to 143. This would have resulted in a speed increase of about 9 mph at 12,000 ft and about 13 mph at 19,000 ft. (i.e. if there was no reduction in cooling HP loss the top speeds would have been 9-13 mph less than they were in actual service.)

The actual system used on the Hurricane II only reduced the cooling HP loss by about 90 HP, or from 260 to 170, for a reduction of ~35%. This resulted in a speed increase of about 7 mph at 12,000 ft and about 10 mph at 19,000 ft.

So to sum up, for the loss of 2-3 mph top speed, the Hurricane II cooling system using a reduced effectiveness Meredith effect, saved an undetermined amount of time in development (check out the amount of time the NA team spent in wind tunnel and flight tests before they settled on a final design) and an undetermined amount in development cost, reduced the cooling system structure weight (probably) by about 50 lbs, and reduced the cost (probably) of the cooling system structure by about 50%.


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## wuzak (Mar 30, 2019)

The Hawker Hurricane and Supermarine Spitfire were being designed when the effect was being studied by Meredith at the RAE.

The research was published in 1936 - after the Hurricane prototype flew, though information may have been given to them.

I'm not sure how much the Meredith effect was taken into account by Camm and Hawkers.

The Tornado prototype also had a belly radiator for initial flight testing, but it did not work too well, perhaps because of excessive turbulence. The radiator was moved to the chin position, which was also used for the Typhoon.

NAA had the benefit of 3 or 4 years to study the effect and put it into practice.

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## davparlr (Mar 30, 2019)

tomo pauk said:


> Leading-edge radiators were suggested by NACA for the (Y)P-38, to be installed in the extended (chord increased by 20%) section of the wing inboard the engines.
> Seems like LE radiators worked on Mosquito, Hornet and Tempest I.


I always felt that leading edge radiators for the P-38 would have been much preferred over the four separate radiators used. Of course I wasn't making the trade-offs and I certainly don't know all the variables.


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## tomo pauk (Mar 30, 2019)

davparlr said:


> I always felt that leading edge radiators for the P-38 would have been much preferred over the four separate radiators used. Of course I wasn't making the trade-offs and I certainly don't know all the variables.



NACA did all the calculations for you, and tested stuff in wind tunnel for a good measure.
NACA report
(they were also tweaking the pod & canopy to better combat compressibility, plus other tweaks to the wing)

Well worth the read: alternative P-38 with LE radiators and whatnot

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## davparlr (Mar 30, 2019)

tomo pauk said:


> NACA did all the calculations for you, and tested stuff in wind tunnel for a good measure.
> NACA report
> (they were also tweaking the pod & canopy to better combat compressibility, plus other tweaks to the wing)
> 
> Well worth the read: alternative P-38 with LE radiators and whatnot


Thanks. It also may have made heating the cockpit easier. I think I read somewhere that one complaint was that the cockpit had a heating problem.


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## Shortround6 (Mar 30, 2019)

davparlr said:


> Thanks. It also may have made heating the cockpit easier. I think I read somewhere that one complaint was that the cockpit had a heating problem.



That could have solved (at least somewhat) by putting a generator on the right hand engine to handle the electrical load and putting an electric heater in the cockpit (or heated flying suit).
Might have saved a few planes too, as the Props were electrically operated as were the turbo regulators, aux fuel pumps, and oil cooler exir flaps in addition to the normal electrical stuff. 
If you lost the left engine with the generator any long trip home became and exercise in electrical power management as all the electric needs had to be balanced against the power left in the battery.


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## Shortround6 (Mar 30, 2019)

tomo pauk said:


> Well worth the read: alternative P-38 with LE radiators and whatnot



It takes some careful reading as there are a few things that are misleading. 

"The results are well known and documented: the* P-38 in the ETO struggled the first 18 months of combat* prompting 8th Fighter Command to pre-emptively phase them out in favor of the new P-51 as they became available at the end of 1943 and through the first half of 1944." 

Bolding by me. The only P-38s in the ETO in 1942 and most of 1943 were a few photo recon planes. Before the P-38s that were there in late 1942 could fly more than few missions over the French coast they were all sent to North Africa to support the Torch invasion. 
P-38s as fighters would not return to the ETO until Sept 1943 and went "operational" on Oct 15th 1943 with the 55th fighter group. Nov 3rd 1943 sees the 55th escort bombers Wilhelmshaven. P-51s (and P-38s) are used as escorts on a raid to Kiel On Dec 13th 1943.

So basically the P-38 as a bomber escort in the ETO went into service _6 weeks_ before the P-51. 

Nowhere near 18 months.

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## ThomasP (Mar 31, 2019)

Hey wuzak,

You are correct about the first flight and publish dates. But, Camm himself mentioned becoming aware of Meredith's findings during the development phase of the Hurricane, and subsequent incorporation of various aspects in the Hurricane's radiator cooling system.

For its first flight, the original radiator installation shroud(?) on the Hurricane prototype K.5083 was basically a carry-over from the Hawker Fury. It was basically just a u-shaped piece of sheet metal with somewhat convex shape to the bottom surface for strengthening, intended to protect the radiator from damage and not much else. It had no boundary layer lip/notch, a vertical front about 2" in front of the cooling array with thin protective bars across it, a vertical rear (with a larger orifice than the inlet) without the adjustable flap, and the total length of the shroud was only about 4-5" more than the radiator itself. If you look at the very early pictures of the prototype radiator this arrangement can be seen.

The radiator housing changed over the next 6-8 months, following the sequence listed below as far as I can tell from pictures and drawings of the time:

First it received a deeper inlet to about 8" and the protective bars went away.
Then the housing aft of the radiator was lengthened and shortly thereafter a short flap appeared on the bottom.
Then the inlet was deepened again to about 14", given a flattened oval shape, and a boundary layer lip/notch showed up.
Then the aft housing became tapered, reducing the size of the exit orifice, with a longer/larger flap (the original housing had a larger orifice at the rear than at the front).
Then the back section received more of a taper with the flap consequently moved farther back.
Then the side trailing edges were tapered into the fuselage.

The radiator itself was replaced with an improved design somewhere during the same period as above, prior to production.

When the Hurricane II came along the radiator was again changed, to a larger more efficient design, and the housing was deepened vertically with a more rectangular orifice, and slightly modified to keep the drag/cooling drag to a minimum. The radiator and housing were changed again with the advent of the Hurricane V, the radiator being significantly larger, and the housing deeper with a much larger inlet orifice.

I am new to posting stuff on forums so bear with me if the following attachments do not show up. I ran across these in the past and did not record the origin at the time, so not sure what to do about that.

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## ThomasP (Mar 31, 2019)

Hey wuzak again,

I am not saying you are wrong about NA having 4-5 years to study the Meredith effect, but do you know if they actually did? Seriously, if you have read something specific that says so, please let me know, I would like to know for my own research purposes. Thanks.


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## wuzak (Mar 31, 2019)

ThomasP said:


> Hey wuzak again,
> 
> I am not saying you are wrong about NA having 4-5 years to study the Meredith effect, but do you know if they actually did? Seriously, if you have read something specific that says so, please let me know, I would like to know for my own research purposes. Thanks.



No, I have no direct knowledge of this.

But they did not guess the configuration and somehow get it right. Whether they had access to Meredith's research (probable, as it was published) or other research by NACA, or even by themselves, I could not tell you.


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## ThomasP (Mar 31, 2019)

Hey wuzak,

Sorry for my vagueness, I did not mean to imply that NA guessed at the design work on the P-51. I just meant that I thought that their engineers really did not get going on the serious work needed to incorporate the Meredith effect into an airplane until they started on the P-51. I do not remember reading about any previous intent/attempt by NA to incorporate the technology in an airplane prior to th P-51, and would I be interested to find out if they had.


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## Shortround6 (Mar 31, 2019)

The Mustang may have been the first design they cut metal on that used a liquid cooled engine, I have no Idea what they had on paper.

American liquid cooled engines petered out with the last of the Curtiss conquerors in P-30s and the aviation scene in the US was dominated by air cooled radials for 4-6 years. The Allison was know to be in development along with the Army's hyper engine/s but the only engines most manufacturers could get their hands on were the radials. 

This was one of the first NA aircraft (they took it over from Fleet (?) who took it over from Pilgrim division of Fairchild ( or the other way around?) 





This had a lot more troubles than figuring out thrust from cooling. 

First real NA design was father of the AT-6





There was also the XB-21, the 0-47 and the NA-40




predecessor of the B-25.

But no liquid cooled engines. If figuring out the Meredith effect was hard using a radiator then air cooled engines were a real pain in the rear.
Th e"principal" is the same but the methods are going to be a lot harder.


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## tomo pauk (Mar 31, 2019)

Thing with Hurricane's radiator is that it was out of airframe by 100%, thus increasing frontal area as much as possible. Radiators on P-51 and many other fighters (Spitfire, Bf 109, Yaks etc) were burried within the airframe by a good deal, meaning increase of frontal area being smaller, and with it the drag. 
LE radiators can be easily designed so they don't add any frontal area, as it was the case with, not only, Mosquito or Hornet.


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## ThomasP (Mar 31, 2019)

Hey Shortround6 and tomo pauk,

"This had a lot more troubles than figuring out thrust from cooling."

Thanks for the NA history, Shortround6, and LOL! thanks for the laugh.

To tomo pauk's point, yeah, it it would have been nice if the radiator was semi-submerged, and in all seriousness maybe it could have been, but not without some serious redesign of the airframe?? The prototype design had full span trailing edge flaps, which was why the aft end of the radiator housing had the odd negative angle to it, and the front end of the housing was forced to end about where it did (on the production aircraft) due to the wheel wells being in the way. In order to incorporate the effect as far as they did they had to eliminate the center section of the flap to extend the aft part of the housing, and I do not know what would have to have been done to to the lower fuselage structure to semi-submerge the radiator, but I suspect that it would have been expensive (relatively).

As it was the potential extra 27 HP (if you got the maximum possible Meredith effect at the Hurricane's speeds) would have only added another 1-2 mph and/or made up for some weight gain and/or improved rate of climb by about 80 ft/min. Nothing to laugh at, but diminishing returns and all that.

It would have been interesting to see Camm's thin wing Hurricane with a more refined drag index. What else would Camm have changed if he choose to keep the basic design/construction? sigh.....


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## tomo pauk (Mar 31, 2019)

ThomasP said:


> ...
> It would have been interesting to see Camm's thin wing Hurricane with a more refined drag index. What else would Camm have changed if he choose to keep the basic design/construction? sigh.....



I'd go for beard radiator, proper exhaust stacks (not the draggy ones used historically) and injection carb = performance increase on time and on budget.
Granted, latest two suggestions aren't exactly airframe's designer's prerogatives.


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## Shortround6 (Mar 31, 2019)

The draggy exhaust may have been part of the "kit" needed for the night fighter requirement.





Note shields to help block exhaust glare from pilot's view.

The Hurricane and Spitfire were both supposed to be able to operate at night. Take-off, fly around and land without too many accidents. 
Actually finding enemy aircraft (or even your own airfield) was another level of complication. 

Some sort of flame dampening/suppression was needed to meet the requirement. If it cost a few MPH off the top speed, well, so be it.

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## pbehn (Mar 31, 2019)

ThomasP said:


> Hey wuzak again,
> 
> I am not saying you are wrong about NA having 4-5 years to study the Meredith effect, but do you know if they actually did? Seriously, if you have read something specific that says so, please let me know, I would like to know for my own research purposes. Thanks.


There was a pic posted somewhere showing the various incarnations of the P-51/Mustang/Apache series. This required a lot of wind tunnel work to get right. However, during a short period or time the Mustang/P51 went from being a small order of fighter planes for a foreign government to a vital part of the USA strategic offensive. Since the radiator design was vital to the range of the P-51 I doubt they had any trouble at all getting any wind tunnel time they wanted from 1942 onwards.


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## pbehn (Mar 31, 2019)

Shortround6 said:


> The draggy exhaust may have been part of the "kit" needed for the night fighter requirement.
> View attachment 533866
> 
> 
> ...


From the Spitfire society web site …….It was soon discovered that simple changes to the ejector exhausts from simply blowing out to the side to being directed back would increase speed. The exhausts evolved from round outlets to fishtail in appearance which also had the bonus of reducing exhaust glare during night flying. These changes resulted in harnessing the exhaust gases provided an additional 10mph or 70 horsepower. The exhausts alongside forward facing intake ducts were used to heat the guns in the wing which were prone to stoppages at altitude as a result of the colder temperature, and superior to the earlier heating from the engine coolant radiator. During the Battle of Britain it was discovered that the Merlin engine would cut out when pursing Me109s in a high speed bunt dive due to fuel starvation in the float controlled carburettor. Initial solutions involved inverting the aircraft into the dive and also the fitting a restrictor in the fuel supply line and a diaphragm known as Miss Shilling’s orifice, named after the female inventor (Beatrice Shilling) based at Farnborough at the Royal Aircraft Establishment. More permanent solutions involved moving the fuel outlet from the bottom of the carburettor to half way up and the use of fuel injection using a Stromberg pressure carburettor and finally an SU injection carburettor.


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## Shortround6 (Mar 31, 2019)

The rearward blowing exhausts were adopted fairly early, while photos like the 5th one in the series from post #68 can be found showing the extended exhausts with the slits ( I don't know the official name) most photos of Hurricanes in France, even with two blade wood props and fabric covered wings, show the rearward blowing exhausts although not yet fish tail.


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## pbehn (Apr 3, 2019)

Shortround6 said:


> The "secret" to the P-51 radiator set is a combination of things, not one or two features by themselves.
> 
> View attachment 532536
> 
> ...


Does anyone know if the Mosquito leading edge intake reduced or increased drag with the radiator set up as is, and if the "Meredith effect" as far thrust goes was also combined lift, the outlet is pointing downwards as well as backwards?


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## wuzak (Apr 3, 2019)

pbehn said:


> Does anyone know if the Mosquito leading edge intake reduced or increased drag with the radiator set up as is, and if the "Meredith effect" as far thrust goes was also combined lift, the outlet is pointing downwards as well as backwards?



The Mosquito's radiator would have increased drag, as did the Mustang's, just not as much as some other systems.

So, in a sense, drag was reduced compared to some alternative radiator placements.

There was a prototype fitted with a Merlin power egg, as used in the Beaufighter II. The performance didn't change that much.

The fastest Hawker Tempest was the Mk I prototype with leading edge radiators. Though the Sabre in the Mk.I was an experimental version, there must have been some reduced drag compared with the Mk.V production aircraft with chin radiator. The speed difference was 20-30mph.

The fastest Hawker Fury was the Sabre powered prototype, also with the leading edge radiators. Though it is less easy to compare, since the Fury went into production as the Sea Fury with the Centaurus radial.

Hawker Fury I (Sabre-Powered) Fighter

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