Mosquito aerodynamics?

[spicmart]

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?

 

[tomo pauk]

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.

 

[pbehn]

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.

 

[fliger747]

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.

 

[pbehn]

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!

 

[pbehn]

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]

 

[spicmart]

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!

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?

 

[pbehn]

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]

 

[pbehn]

From here RAF airfoils?

 

[spicmart]

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?

 

[tomo pauk]

...
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.

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.

 

[pbehn]

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.

 

[tomo pauk]

...
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.

 

[Shortround6]

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.

 

[Shortround6]

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?

 

[pbehn]

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.

 

[tomo pauk]

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?

 

[MIflyer]

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

 

[spicmart]

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.



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.



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.

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.

 

[tomo pauk]

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.