Would a thin/redesigned wing brought the Hurricane up to Spitfire/109 performance?

[tomo pauk]

Swampyankee is correct with fewer words expended.

The Hurricane had a lot of Parasite drag due to the fuselage, radiator, canopy, etc design in contrast to say a 109F or Spit (or Mustang). The wing could have been redesigned to reduce the largest drag factor - but not likely to a level below the 109 or Spit.

Hi, Bill,

Think that we can note that radiators of the Spitfire and Bf-109E were not known as streamlined items, too. IIRC Lednicer also notes that Spitfire's windscreen was a more draggier item than of P-51. The Bf-109F was a wholesale redesign of the Bf-109E, featuring shallower and wider radiators, more streamlined front of the plane, retractable tailwheel, deletion of tail struts, one cannon less (along with two ammo drum bulges less), redesigned wing - in other words, what Bf-109E have had over Hurricane was smaller size of it's wing (both smaller area and thickness), and not some great aerodynamic refinements.

 

[swampyankee]

NACA was doing research into laminar flow airfoils in the 1930s, with the 6-series, e.g., the 64-215, being one of the results (there was also a 16-series, which was designed for propellers). The 6-series airfoils were designed for high critical Mach numbers and for large extents of laminar flow, although it was (and is) generally considered impossible to maintain laminar flow in service. Overall, it's hard to give any sensible ranking of airfoils, but, overall, I think that NACA's 6-series are the best airfoils of the era.

Natural laminar flow, that is maintaining laminar flow on an entire wing of a full-scale airplane in flight, is an active area of research. Active boundary layer control, usually by boundary layer suction, seems to be a dead end. Probably the only aircraft that can maintain laminar flow in service are sailplanes, which eschew turbulence-inducing engines.

 

[Jabberwocky]

In 1946 they tested a Hurricane II with a low drag 'laminar flow' wing section.

Tests are available here: www.dtic.mil/dtic/tr/fulltext/u2/a800776.pdf‎

I'm not much on the actual physics, but the reported results are:

It will be seen that the drag coefficient has been reduced over the whole "low drag" range, the greatest improvement being at the higher Reynolds Number end. The lowest lift coefficient recorded was 0.097 and the drag coefficient at this point was 0.0049. For comparison, the drag curve obtained in the previous flight tests is plotted on Fig 6 and it will be seen that the drag coefficient for a lift coefficient of 0.097 was then 0.0066, the present tests thus showing a reduction in drag of 26%. The "low drag" range now extends from 0.1 to 0.5 lift coefficient.

The tests confirm the conclusions reached in previous flight tests on wing3 of "low drag" section. A. great improvement has been achieved at the high. Reynolds Numbers by reducing the surface waviness to + one thousandth of en inch variation from the mean deflection curve on""a two inch gauge length. It is substantial for the maintenance of laminar flow at Reynolds Numbers of twenty millions that the surface waviness should not be larger than this The same conclusion was reached during flight tests on King Cobra F.,.440 (iil".3) when drag coefficients of the order of 0.0028 were measured after the surface waviness had been reduced to this standard. The alight rise in drag coefficient at the high Reynold* Numbers is probably due to the fact that the surface waviness did not meet the above requirements at all points on the surface; particularly on the bottom surface which will be the more critical at high speeds due to decreasing incidence. The drag coefficient has been reduced over the whole "low drag11 range which now extends from 0.1 to 0.5 lift coefficient as compared with the 0.17 to 0.45 of the previous tests. The full reduction in drag was of course obtained only in those flights during which no flies or other insects were picked up by the wing.

 

[OldSkeptic]

Yes, lab stuff, unworkable in practice. The Mustang's lower drag than Spits was purely caused by its better radiator and much cleaner leading edges (etc). Attwood himself never thought the Mustang's wing was any better than the Spit's drag wise. And the various wind tunnel tests on models (hence no rad or surface finish effects, just measuring shape) showed that the Spit was overall better at high mach numbers at most CL values (coefficient of lift).
Only for a zero CL value was the Mustang much better (diving basically). Which might explain the Mustangs better diving ability. At the CL 0.2 and 0.4 values, they were similar across most of the speed range until you get to above mach 0.7, then the Spit becomes progressively better.

Tiny things made a difference, the Spit's flat windscreen cost it 5-10mph. The cannon barrels and blisters cost it 5mph and so on.

The great thing about the Mustang's wing was it was so good (near enough overall to a Spit's which really has to be the benchmark for the era) but was thick enough for fuel tanks. Another accident like the Spit's high mach limit. They were after something else, achieved part of it and got something very useful as well.

A rough estimate of the difference just the radiator made can be inferred by looking at a Mustang with its tank/bomb holders on (they called them wing racks). Dropped max speed (on a P-51b with a -7 = Merlin 66 engine, 18lb boost) to about 426mph (from 442 with British camo paint). If that was roughly equal to the lower overall drag difference from finish (etc) then the radiator was good for 20mph (results would depend on the engine and Mustang/Spit versions, whether it was the HF or LF one, a -3 or -7 and so on).

That was about roughly (very roughly) the difference between a comparable Spit and a Spiteful, though its laminar flow wing was was a failure (and a lower mach limit), it had much better radiators.

Naturally these are all pretty approximate, but a good 1st order estimate, roughly 40% from finish and detail, 60% from radiator. Clever design.

 

[fastmongrel]

I read somewhere that even touching the leading edge had to be avoided. Not sure why possibly sweaty palm prints would attract dust and be enough to upset the flow.

 

[tomo pauk]

In all of these Spit vs. P-51 drag analysis, the difference in undercariage covers seem to be overlooked. Anyone want to take a stab on this issue, how many mph were denied to the Spit by not having fully covered U/C?
Also, the thickness of P.51's wing should be also stated - 16% at the root IIRC?

 

[Shortround6]

In all of these Spit vs. P-51 drag analysis, the difference in undercariage covers seem to be overlooked. Anyone want to take a stab on this issue, how many mph were denied to the Spit by not having fully covered U/C?
Also, the thickness of P.51's wing should be also stated - 16% at the root IIRC?

And that is part of the Mustangs "advantage" it's 16% high volume wing was roughly equal to the Spitfires 13% low (conventional) volume wing. The laminar flow worked to a small extent, just not anywhere near what the lab or models said. Being able to keep a smooth airflow ( if not technically laminar) over another 5-10% of the cord of the wing will reduce drag a bit, just not the big amounts predicted for "LAB" wings.

 

[swampyankee]

According to The Incomplete Guide to Airfoil Usage the P-51's wing had a 15.5% thick section at the rood and a 12% thick section at the tip. Different models use different airfoils, either a NAA/NACA 45-100 or a NACA 66-(1.8)15.5 tapered to 66-(1.8)12. The Spitfire used a NACA 2213 tapering to a 2209.4, from an airfoil family a generation older than the 6-series.

Overall, the P-51 is the benchmark for zero-lift drag of a fighter, as its measured Cd,0​ was lower than any other piston-engined fighter to see war service (its Cd,0​ was about 0.0165, or about 80% that of the Bf109, which seemed to be have a value of Cd,0​ largely typical of ww2 fighters).

 

[pinsog]

After reading the last 5 or so responses that dove headfirst into the actual physics of the Mustang/Spitfire drag issues, I have developed a facial tic and I'm drooling out one side of my mouth. What do you guys do for a living? I assume it is not driving a garbage truck...

Anyway, if the Hurricane had been given a thin wing and nothing else, no major redesign of the aircraft, lets say when they went from a fabric wing to a metal wing they redesigned it and made it thin: Could a couple of you guys take a stab at what you think the new top speed would be?

Tomo Pauk: I agree with you about the 109. It always reminded me of an F4 Phantom, about as pretty and aerodynamic as a rock. I can't see the body being any better than a Hurricane except for just being smaller.

 

[Shortround6]

part of the question is how much thinner and were do you put the stuff that was in the wing?

The main fuel tanks were in the wing roots/center section. While you could leave smaller tanks in the same location you need to find space to restore capacity.

Landing gear would probably fit, most of the wheels are in the fuselage.

Guns will fit but the installation may have to change. You may not be able to group the guns into a four gun bay.

Then there is the question of weight. The thinner wing may have to be built heavier. You get a certain amount of strength just from dimensions. Stand a 1 x 12 plank on edge and try to bend it across the 12 in dimension. Now do it to a 2 X 6. Same amount (weight ) of material but the bending strength is way different.

You still have a "fat" fuselage. And you may screw up the low speed handling, take-off and landing speeds. the actual amount of lift you get from a wing depends on other things besides just the square footage.

 

[pinsog]

part of the question is how much thinner and were do you put the stuff that was in the wing?

The main fuel tanks were in the wing roots/center section. While you could leave smaller tanks in the same location you need to find space to restore capacity.

Landing gear would probably fit, most of the wheels are in the fuselage.

Guns will fit but the installation may have to change. You may not be able to group the guns into a four gun bay.

Then there is the question of weight. The thinner wing may have to be built heavier. You get a certain amount of strength just from dimensions. Stand a 1 x 12 plank on edge and try to bend it across the 12 in dimension. Now do it to a 2 X 6. Same amount (weight ) of material but the bending strength is way different.

You still have a "fat" fuselage. And you may screw up the low speed handling, take-off and landing speeds. the actual amount of lift you get from a wing depends on other things besides just the square footage.

Well they Spitfire wing was thin, but still big enough for guns landing gear etc. Same goes for the 109, Zero, Wildcat, P40, P39........

So why couldn't they put a thin wing on the Hurricane? Why not just graft a Spitfire wing on? Why not graft a copy of a 109 wing on? (Obviously I'm simplifying things too much) Some one early on should have said "The fat wing is killing our speed, lets try a thin one".

 

[Shortround6]

Spitfire had the fuel in the fuselage ahead of the pilot. NO tanks in the wing on the early ones. The guns were spaced out the way they were to keep from having to route ammo belts OVER the top of some of the guns. Wildcat had NONE of the landing gear in the wing. And the Wildcat was 15% at the root, 9% at the tip, P-39 wing was 15% at the root/ 9% at the tip and so was the P-40s.

Camm (and some of the boffins at the RAE who were advising ) didn't believe the thick wing was the problem which is why they used one on the Typhoon/Tornado.

Now the next question is how much the thick wing really hurt the Hurricane in the 300-330mph speed range. The difference in drag between the thin wing and the thick wing was not constant but increased as the speed went up. How much of the difference in speed was the fuselage/cockpit? how much was the radiator?

 

[OldSkeptic]

As I said before I think you can get an indication by the Typhoon/Tempest difference. Comparing a late model Tiffie (bubble canopy, 4 bladed prop etc) with a similar engine spec Tempest and you get about a 25mph difference at FS FTH, though a bit of that will be due to the short barrel cannons (offset, I suppose, a bit from a little more fuselage drag on the Tempest).

So a theoretical 20-30mph difference seems possible, albeit may be tough to achieve in practice because of the engineering issues as mentioned here by others, such as where do the fuel tanks go and under carriage issues and so on.

 

[pinsog]

Now the next question is how much the thick wing really hurt the Hurricane in the 300-330mph speed range. The difference in drag between the thin wing and the thick wing was not constant but increased as the speed went up. How much of the difference in speed was the fuselage/cockpit? how much was the radiator?[/QUOTE]

Would you care to guess the difference in top speed?

 

[swampyankee]

Without some really good drawings and access to VSAERO, it's going to be difficult to determine what effect a thinner wing would have. There have been some studies (one is here: http://www.aeronautics.nasa.gov/docs/rpt460/discuss.htm ) that measure change in cd,0​ with thickness.

 

[Shortround6]

Now the next question is how much the thick wing really hurt the Hurricane in the 300-330mph speed range. The difference in drag between the thin wing and the thick wing was not constant but increased as the speed went up. How much of the difference in speed was the fuselage/cockpit? how much was the radiator?

Would you care to guess the difference in top speed?[/QUOTE]

Say we go with the 20mph difference as indicated by the Typhoon-Tempest. You now have a MK I Hurricane thin wing doing 336mph. Better but not really a game changer. You may get a MK II up to 354mph depending on armament?

 

[drgondog]

Remember 'thick' and 'thin' are relative judgments and based on ratio to thickness to chord length. The spit had a very large (relatively) chord length with semi elliptical wing so a 12% wing with long chord might be deeper (thicker) than a narrow chord wing with say a 16% T/C

 

[OldSkeptic]

Some good points and discussions
Love the one about laminar flow is a laboratory term; yep that is a true fact, in everyday life, laminar flow is just a term to describe a more efficient ratio of ratios used in wing design, where the longer gentle smoother the curve without the older style with more of teardrop like leading edge is more efficient. Laminar flow means that the layers of airflow around an object are morelikely to follow its shape smoothly with less percentage of those layers generating unwanted currents, eddies along the profiles shape.

In real aerial life, air isn't channelled and directed from shaped vents or venture/venturii (..plural of venturi?) onto a test subject (wing section and or scaled model etc) all the time; that natural air particles/fluid movement do also rise, sink and pin ball off each other in relation to their own and surround temperatures, their vectors, forces and unknown quantum interactions with other particles in such a linear manner as modelled in the laminar flow experiments. Of course an aircraft moving at speed in 3 Dimensions of axis is going to create its own combinations of interactions and distortions in and with the air - hence why laminar only exist in the lab. I apologise for being a pedant who is currently pedantic.

Although boundary layer blowing from some form of compressor bleeding of upto less than 30% engine through flow, does achieve similar effects when it is used as needed - generally only ever used during take off, landings or for slow speed flight - and nearly only on some military jets, but I digress, as that mostly doesn't apply for early WW2 or for most nations until the mid to late 21st C...

Meant to get back to you on this one. Great comment, but what resonated was looking at air as particles. For me this came much later. True story, on a flight and got re-directed to another airport because of fog, got chatting to this lassie and she asked me 'how do planes fly', so I (original degree was physics) trotted out the usual stuff, but she thought abut it then asked more questions. She was not convinced.

It stuck in my mind, churning away in the background so to speak for years. Until I just thought of air as particles with various, according to conditions, different momentum distributions .. then it became obvious (at least to me) how we can fly. After abandoning air as a flow it actually becomes conceptionally easier to understand the air to wing momentum transfers which are the real reason why planes fly, and the shape of the distribution of momentum of individual air particles (Gaussian) explains why certain shapes are more efficient than others.

Because all the old reasons given make no sense at all (that was her brilliance, she saw through it and kept asking more questions).

As for 'laminar flow' with this model you now know why it is impossible. To get the 'air' to stay close to the (let us for simplicity call it this) the 'shape' that it is flowing past means complex interactions between the air (composed of O and N molecules, both with different properties) with the 'shapes' surface (and naturally the materials used will affect this). Basically they are 'sticky'. This air-'shape' boundary creates a sort of 'cushion' that reduces the normal air-'shape' interactions, which are fairly elastic in nature. It is the Guassian momentum distributions along with elastic 'normal' interactions with the 'shape' that eventually create a chaotic interaction called turbulence.

But we are dealing in the quantum level with individual molecule/atoms interactions between the air molecules and the surface atoms of the 'shape' interactions. Even a slight change in the 'shapes' profile or composition (complex carbons from bug splats is a good one) will change that 'stickiness' that creates the 'cushion' .. and 'laminar' flow is disrupted.

 

[yulzari]

Looking at this, without specifically responding to earlier posts, I would like to point out the thinking behind the Hurricane. Camm and his colleagues were well aware of the methods and possibilities of the stressed skin method and turned to them for the Hurricane's successor.

What he was attempting to do, in the early/mid 1930's, was to build a fighter design he could commercially market to a peacetime air force. After all, the purpose of Hawkers was not defence but profit.

The numbers would be limited by budgets and he had to try to use the resources in equipment and staff he already had or could train to minimise investment costs and short term risks to his shareholders.

Hence he decided to use the existing Hawker rolled tubing system which required expensive machinery. However the machinery was already in place so it was more a matter of new dies that were far cheaper. His staff were experienced in this system and it was suited to a factory with semi skilled workers with skilled supervision. This was what attracted the Yugoslavs and Belgians. Once you had paid out for the machinery the rest was a series of (individually) simple cutting and rivetting to a jig.

The system left a limited amount of space in the fuselage once allowance was made for the cockpit and maintaining a proper centre of gravity so the wing was a valuable resource in space about the centre of gravity. Whatever Camm may have later learned about wing thickness, the understanding of the time of the design was that shape was more important than thickness (within reasonable limits) and increasing chord and area could compensate for a given thickness whilst, incidentally, allowing a lower stall speed and tighter turning circle.

Given these restraints Camm etc. made a commercial design for a useable modern fighter that could make Hawkers a profit (that was why Hawkers existed) for a minimum risk whist being able to meet expected production numbers (a few hundred at best) and be saleable, as both complete aeroplanes or as a licence factory, to less aeronautically advanced nations.

This was the model that Hawkers partners Gloster were looking to at the same time with the Gladiator in direct sales and doing very well at it.

The thick wing was so fundamental to the concept that a thin wing was an impossibility as a modification. It needed a new design. The existing wing could probably have some thickness trimmed from it but the effort would have been better put to a new design.

From a performance point of view the Hurricane was as good as it could get in essence whilst carrying that wing. Small increments could be gained from minor changes but the wing limited the maximum powered speed and diving speed.

Commercially Hawkers made an error in limiting themselves to the Merlin. Foreign sales could have been more extensive had they offered versions to use alternative engines. Fokkers realised this in the DXXIII and offered a variety of possible engine installations in radial and in line V forms. Had WW2 not happened Hawkers, with a Hurricane that could carry any engine in the 1,000bhp class, were well placed to meet licence interest from Turkey, China, Scandinavia, the Balkans and the Baltic states and possibly South America.

Supermarine was a minor flying boat maker with a recent history of advanced stressed skin racing floatplanes. They had no such investment in place so they went for performance using the latest methods as a new investment in machinery, staff and training would be necessary anyway and they had the resources of the vast Vickers organisation to call upon. The initial shadow factory experience seemed to back up the contrast as they struggled to make Spitfires as first, as did Supermarines themselves.

The Merlin was expected to be a 1,000/1,200bhp engine. When the Air Ministry were looking forwards to the next generation of 2,000bhp engines Camm knew he would have to give the RAF stressed skin models to meet their expectations. However, if we think of the Martin Baker MB5, we can see that a tubing based design was not, in itself, beyond the task.

So, to address the thread question, I have to say a thin/redesigned wing would not have brought the Hurricane up to Spitfire/109 performance because such a wing would have to be matched to a new fuselage etc. and thus not be a Hurricane.

 

[tomo pauk]

Hi, yulzari, thanks for the effort. Some comments:

...
Hence he decided to use the existing Hawker rolled tubing system which required expensive machinery. However the machinery was already in place so it was more a matter of new dies that were far cheaper. His staff were experienced in this system and it was suited to a factory with semi skilled workers with skilled supervision. This was what attracted the Yugoslavs and Belgians. Once you had paid out for the machinery the rest was a series of (individually) simple cutting and rivetting to a jig.

The system left a limited amount of space in the fuselage once allowance was made for the cockpit and maintaining a proper centre of gravity so the wing was a valuable resource in space about the centre of gravity.

I would disagree that production method ('system') left only limited amount of space in the fuselage - Hawkers simple did not envisioned a sizable fuel tank between pilot and engine.

Whatever Camm may have later learned about wing thickness, the understanding of the time of the design was that shape was more important than thickness (within reasonable limits) and increasing chord and area could compensate for a given thickness whilst, incidentally, allowing a lower stall speed and tighter turning circle.

Maybe that was understanding prevalent in one or two design teams, that a wing of big area, thickness and chord would be beneficial to the fighter performance? Hurricane, out of all in-service fighters in late 1930's - early 1940's (I-16, P-35/36, Bf-109, Spit), along with F4F, was equipped not only by the thickest wing, but also with a wing with greatest area.

Given these restraints Camm etc. made a commercial design for a useable modern fighter that could make Hawkers a profit (that was why Hawkers existed) for a minimum risk whist being able to meet expected production numbers (a few hundred at best) and be saleable, as both complete aeroplanes or as a licence factory, to less aeronautically advanced nations.

This was the model that Hawkers partners Gloster were looking to at the same time with the Gladiator in direct sales and doing very well at it.

Very agreeable.

The thick wing was so fundamental to the concept that a thin wing was an impossibility as a modification. It needed a new design. The existing wing could probably have some thickness trimmed from it but the effort would have been better put to a new design.

Less Hurricanes would not been an option for the UK in the time of need, and that would've happened with a thorough modification.

From a performance point of view the Hurricane was as good as it could get in essence whilst carrying that wing. Small increments could be gained from minor changes but the wing limited the maximum powered speed and diving speed.

+1

Commercially Hawkers made an error in limiting themselves to the Merlin. Foreign sales could have been more extensive had they offered versions to use alternative engines. Fokkers realised this in the DXXIII and offered a variety of possible engine installations in radial and in line V forms. Had WW2 not happened Hawkers, with a Hurricane that could carry any engine in the 1,000bhp class, were well placed to meet licence interest from Turkey, China, Scandinavia, the Balkans and the Baltic states and possibly South America.

Only with Merlin Hurricane was a viable fighter, with anything lesser (Hispano, Kestrel/Peregrine, let alone a radial engine of similar power) installed it would've been a dog.

Supermarine was a minor flying boat maker with a recent history of advanced stressed skin racing floatplanes. They had no such investment in place so they went for performance using the latest methods as a new investment in machinery, staff and training would be necessary anyway and they had the resources of the vast Vickers organisation to call upon. The initial shadow factory experience seemed to back up the contrast as they struggled to make Spitfires as first, as did Supermarines themselves.

Easy to agree with that.

The Merlin was expected to be a 1,000/1,200bhp engine. When the Air Ministry were looking forwards to the next generation of 2,000bhp engines Camm knew he would have to give the RAF stressed skin models to meet their expectations. However, if we think of the Martin Baker MB5, we can see that a tubing based design was not, in itself, beyond the task.

Especially the bolded part.

So, to address the thread question, I have to say a thin/redesigned wing would not have brought the Hurricane up to Spitfire/109 performance because such a wing would have to be matched to a new fuselage etc. and thus not be a Hurricane.

Hurricane's wing was not some monolithic structure. Outboard of the wing tanks, the wing panels were attached. The wing panels comprised maybe 80% of the wing area, and redesigning those would've made zero impact to the fuselage. Hence Hurricane can remain Hurricane, picking up some performance in process.

File:Women assembling Hawker Hurricanes 1942.jpg - Wikipedia, the free encyclopedia