Would a thin/redesigned wing brought the Hurricane up to Spitfire/109 performance? (1 Viewer)

[swampyankee]

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.

Whew...I'm glad you didn't tell her the real reason.

 

[yulzari]

Thank you Tomo.

Re:'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.'

We will have to disagree. Perhaps a virtue could be made of a necessity by using the thick centre section for a pair of leading edge radiators. Certainly the outer wing panels can be altered separately to the centre section.

The tubing method meant that the tubing 'box' is filled with bracing whereas a stressed skin has the centre free. Room for small items but not major ones. To allow for the cockpit opening the structure relied heavily upon the centre section to externally stiffen the cockpit opening and the engine mounting, in common with all such V12s, used the engine block as a stressed part of the structure.

I wonder what Camm's team would have done had the next specification been for a 1,600bhp Merlin design and not one for the 2,000bhp+ Sabre/Vulture/Centaurus? I suspect they would have had to look for refinement instead of brute strength and something like a Tempest wing might have been chosen for such a smaller fighter. However the Air Ministry had stepped up in one go from a Gauntlet/Gladiator model to the Hurricane/Spitfire one so the next step had to be a 4 cannon double power type to make the change short term future proof.

BTW I wonder who would do the design work in 1939/40? Hawkers were flat out on Typhoon/Tornado work and Glosters were devoted to new jet designing.

 

[thedab]

How thick is the Hurricane wings compare to a Zero?

 

[Jerry W. Loper]

Sydney Camm said he could have got a bit more speed out of the Hurricane if he had made the wing thinner, but there wasn't time. Historically, Britain and the RAF were better off with the Hurricane the way it was, rather than losing time trying to improve it.

 

[GregP]

Any aircraft can be reworked to have a different wing, different tail, different wing and tail incidences, etc. The question is whether or not the gains by making such chages would be worth the effort.

It might be different if the Hurricane were, say, a 350 mph aircraft and needed to get to 375 mph.

But production Hurricanes were pushing to get over the 300 mph mark and needed to get to 370 mph, so they needed somethiong like a 21% gain in speed and that seems unlikely by doing a great deal of work to make the wing 3 - 5% thinner without any other changes. What was clearly needed was a new design, and they eventually HAD it, but not exactly quickly.

 

[slaterat]

I would like to point out that there was no welded steel tubing in the Hurricane airframe. All of the tubing, both the ones made of lightweight steel alloys and the ones made of aluminum , were held together by mechanical fasteners. For its size the Hurricane was a fairly light weight. Compare it to the similarly sized P40 for instance. Compared to many of its contemporaries the Hurricanes frontal area and fuselage at least appear to be more aerodynamic. ie P40, Morane Sauliner, F4F ect Camm was willing to do a redesign of the Hurricanes wing but the RAF and the Air ministry would have none of it. Not really a surprise when you consider how ridiculous they made the transition to metal covered outer wings for Hawker and the Hurricane. There would be some room to thin the center section as the undercarriage and the fuel tanks were fitted within the thickness of the main spars.I will have to check but I believe the wings were a maximum of 18 inches thick in the center section and the spars were 12 inches. Obviously the outer wing sections could of quite readily been made thinner. But as I said the Air Ministry would have none of it, development of the Hurricane was frozen at the Mk II level. In light of how long it took to get the bugs out of the sabre engine of the Typhoon this could be judged in error with the benefit of hindsight. Imagine how useful a 375 mph Hurricane might have been in the Pacific.

 

[slaterat]

A series I Hurricane IIa had a maximum speed of 348 mph. An additional 5 % would would get you to 365 mph.

 

[Aozora]

A series I Hurricane IIa had a maximum speed of 348 mph. An additional 5 % would would get you to 365 mph.

Still the same problem here; how much work was required to gain 5% when the Spitfire was already capable of much higher performance (eg Spitfire III with the same engine as the Hurricane II achieved ? Against Fw 190s a thin wing, 365 mph Hurricane III was still obsolescent, as was the 370+ mph Spitfire V. The reason there weren't Spitfires in the Pacific much earlier was because of Air Ministry and FC priorities not because there weren't enough of them in service.

 

[stona]

Sydney Camm said he could have got a bit more speed out of the Hurricane if he had made the wing thinner, but there wasn't time. Historically, Britain and the RAF were better off with the Hurricane the way it was, rather than losing time trying to improve it.

I agree. It could have turned into a Luftwaffe/RLM like never ending development project ending up with no useful aeroplane at all. The Hurricane, as it was, did a job for a couple of years in Europe and much longer elsewhere. What's the problem there, particularly as the Spitfire already existed? Far better to put resources into an already existing and superior aircraft than muck about trying to improve an inferior one.
Cheers
Steve

 

[tomo pauk]

I would like to point out that there was no welded steel tubing in the Hurricane airframe. All of the tubing, both the ones made of lightweight steel alloys and the ones made of aluminum , were held together by mechanical fasteners.

+1 on that.

For its size the Hurricane was a fairly light weight. Compare it to the similarly sized P40 for instance. Compared to many of its contemporaries the Hurricanes frontal area and fuselage at least appear to be more aerodynamic. ie P40, Morane Sauliner, F4F ect

The fuselage of the P-40 was certainly a more streamlined affair than the Hurricane. The 1st XP-40 was flown with belly radiator, and it was not been able to match the 350 mph promissed by Curtiss. Relocation of the radiator under the nose was one of the modifications that enabled it to do 350 mph.
Comparing the radial engined fighter with a V-12 engined one does not make a lot of sense IMO.
The radiator sticking out in the slipstream, like it was the case for the Hurricane, XP-40 and Typhoon's prototype, looked like a good idea in mid-30's, not so much when the ww2 started.

Camm was willing to do a redesign of the Hurricanes wing but the RAF and the Air ministry would have none of it. Not really a surprise when you consider how ridiculous they made the transition to metal covered outer wings for Hawker and the Hurricane. There would be some room to thin the center section as the undercarriage and the fuel tanks were fitted within the thickness of the main spars.I will have to check but I believe the wings were a maximum of 18 inches thick in the center section and the spars were 12 inches.

Not sure how much one can thin out the central wing section unless a major modification is pulled off. picture

Obviously the outer wing sections could of quite readily been made thinner. But as I said the Air Ministry would have none of it, development of the Hurricane was frozen at the Mk II level. In light of how long it took to get the bugs out of the sabre engine of the Typhoon this could be judged in error with the benefit of hindsight. Imagine how useful a 375 mph Hurricane might have been in the Pacific.

The Hurricane's wing area was the biggest of all ww2 V-12 powered fighter that meant something. Perhaps also the reduction of wing area, down from 257.5 ft² to, say, 200-210 sq ft should be attempted? The Hurricane was one of the lightest fighters around, as you correctly put it, so the resulting wing loading would still be very much manageable.
I'd also try to relocate the radiators under nose.

A series I Hurricane IIa had a maximum speed of 348 mph. An additional 5 % would would get you to 365 mph.

I'm afraid that 348 mph is a calculated maximum (chart), the 12 MG Hurricane IIs were good for 330 mph (chart)?

 

[The Basket]

The Hurricane did outperform contemporary 1930s Bf109s. And as noted the Hurricane would have been a huge export success had not history intervened.
And the Hurricane was certainly on a par with anything from Italy or USA or Russia or Japan or France in production in the 1930s
The initial design was spot on and easily matched the specifications and wishes of its designers.
I call that a win.

 

[Edgar Brooks]

Camm was willing to do a redesign of the Hurricanes wing but the RAF and the Air ministry would have none of it. Not really a surprise when you consider how ridiculous they made the transition to metal covered outer wings for Hawker and the Hurricane. .

The wing was redesigned (the construction of the metal wing differs markedly from that of the fabric-covered with separate wingtips for a start.)
It was Hawker's own problems, not the Air Ministry, that caused a delay on the metal wings (the Air Ministry were asking for them as early as May 1938, since a dive, with fabric wings, had to be 70mph slower.) The initial order, for 300 fabric-winged, had to be increased to 400 in November 1938, with a possibility of going up to 500. The first metal wings were delivered 17-3-39, and the last fabric-winged Hurricane was delivered 19-9-39. Hawker couldn't build the Hurricane fast enough, because Gloster were only building 15 pairs of metal wings per week.

But as I said the Air Ministry would have none of it, development of the Hurricane was frozen at the Mk II level. In light of how long it took to get the bugs out of the sabre engine of the Typhoon this could be judged in error with the benefit of hindsight. Imagine how useful a 375 mph Hurricane might have been in the Pacific

In December 1940, Camm was asked to trial metal-covered ailerons on the Hurricane, but he said that, since the Hurricane was almost at the end of its useful life, he didn't see any point, so it certainly wasn't the Air Ministry who lacked interest; he did, eventually, do as he was told, mid-1941, but they made little difference, so the idea was dropped. As usual, we're looking at the 1941 Pacific with 20/20 hindsight, at a time when the Air Ministry had to consider the possibility of the Battle of Britain resuming, with the threat of invasion.

 

[Jack Maj O'Hara]

Would a thin/redesigned wing brought the Hurricane up to Spitfire/109 performance levels during the BoB timeframe?

Many interesting responses here, but the issue that should drive competitive design / upgrades is the consequence of not keeping pace with enemy technical advancements. By 1936, it was clear that the Hurricane wing and radiator design was limited. Meredith's work on cooling drag was well known and RAE had published their revised stance on t/c ratio being optimised at 15%.
HAwker's 1935 contract obligated Camm to upgrade the Hurricane wing to metal, which should have been his opportunity to produce a wing airfoil with less drag (15-17% t/c ratio) like every other nation . Partially recessing that big radiator would be worth the effort and once Malcolm hoods (or even older Spitfire canopies) were in production, that would have been an absolute must for pilot visibility.

Consequences - the lives of highly trained pilots, groundcrew and ultimately, civilians. Profit should have taken a back seat to performamce & pilot lives by 1938.

 

[drgondog]

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.

IMO you have well described the transition from 'true laminar flow' near the leading edge to 'turbulent flow with increasing boundary layer thickness' at very low speed (RN> ~600,000 based on the wing chord). The nature of this turbulent flow is transitional from a state of 'attachment to the shape of the wing surface to increased and chaotic separations from the surface of the wing with local adverse pressure gradients. The comparison of the Mustang wing attributes from conventional High Speed/Low Drag airfoils was that the transitional turbulent locations of complete and chaotic unattached flow occurred 20+% farther along the chord.

True that manufacturing and finish quality of NAA Mustang wing was a factor in producing a 'pig more equal' than other pigs - but none of the pigs possessed Laminar flow after very low airspeed (or more specifically taxi speeds) were attained. Further, I would attribute the enhanced delay of BL separation due at least to a lower velocity gradient from leading edge to maximum thickness of the airfoil, which was further aft.

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.

IMO Laminar Flow with respect to flow behavior back in the late 1930's with NACA 45-125 airfoil would have been better described as 'laminar flow similar' with emphasis on Boundary Layer Transition from near orderly attachment to chaotic separation. The collisions with attached flow and gaps or rivet heads or chipped paint are local in nature, but enough of them will initiate separation of the transitional boundary layer earlier.

 

[SaparotRob]

IMO you have well described the transition from 'true laminar flow' near the leading edge to 'turbulent flow with increasing boundary layer thickness' at very low speed (RN> ~600,000 based on the wing chord). The nature of this turbulent flow is transitional from a state of 'attachment to the shape of the wing surface to increased and chaotic separations from the surface of the wing with local adverse pressure gradients. The comparison of the Mustang wing attributes from conventional High Speed/Low Drag airfoils was that the transitional turbulent locations of complete and chaotic unattached flow occurred 20+% farther along the chord.

True that manufacturing and finish quality of NAA Mustang wing was a factor in producing a 'pig more equal' than other pigs - but none of the pigs possessed Laminar flow after very low airspeed (or more specifically taxi speeds) were attained. Further, I would attribute the enhanced delay of BL separation due at least to a lower velocity gradient from leading edge to maximum thickness of the airfoil, which was further aft.


IMO Laminar Flow with respect to flow behavior back in the late 1930's with NACA 45-125 airfoil would have been better described as 'laminar flow similar' with emphasis on Boundary Layer Transition from near orderly attachment to chaotic separation. The collisions with attached flow and gaps or rivet heads or chipped paint are local in nature, but enough of them will initiate separation of the transitional boundary layer earlier.

The funny was for the "First among swine" bit.

 

[Aeroweanie]

First a little background: The air in the room around you, if its stationary, has a static pressure equal to ambient and a total pressure equal to static pressure. If the flow starts moving, the total pressure rises from the energy input to get the flow moving. It is constant and is the sum of the static pressure and dynamic pressure (equal to 1/2 * density * speed^2). A favorable pressure gradient is where flow is accelerating, so the static pressure drops and dynamic pressure rises. An adverse pressure gradient is where flow is decelerating, so the static pressure rises and dynamic pressure declines.

Laminar flow works like this: when air starts flowing over a surface, it initially flows with little mixing, in lamina (parallel layers). Friction with the surface starts the growth of a boundary layer, but it stays laminar. Then, when there is a destabilizing influence, like an adverse pressure gradient, a pressure fluctuation from a surface wave or surface contamination, the laminar boundary layer begins to become destabilized. It transitions to a turbulent boundary layer, which has eddies that produce mixing and the lamina are no longer present. This results in higher surface friction than with a laminar boundary layer.

On an airfoil, there is a stagnation point at the leading edge, where the air hits. Here, the speed goes to zero, so the static pressure is very high. Then, the flow starts accelerating around the airfoil. Here, the pressure gradient is favorable, so the boundary layer is at least initially laminar. You could just keep the flow accelerating, but the problem is, you eventually need to slow the flow down to leave the trailing edge at a speed near the freestream speed (usually a bit less). This results in an adverse pressure gradient on the aft part of the airfoil. As soon as the laminar boundary layer hits the adverse pressure gradient, it is destabilized and transitions to a turbulent boundary layer. Also, you don't want too steep of an adverse pressure gradient, as this could cause the turbulent boundary layer to separate, causing even more drag.

Here is the pressure distribution on a NACA 23012 airfoil, widely used on aircraft like the Fw 190 and Grumman cats. The vertical axis is shown inverted, so that lower pressure is up. As you can see, the minimum pressure point (maximum speed point) on the upper surface is reached at about 10% chord and the boundary layer transitions soon thereafter.

Here is the pressure distribution on the P-51's airfoil. As you can see, the minimum pressure point is now at about 40% chord. So, there is now a much longer run of the laminar boundary layer, and thus lower drag.

On the P-63, the minimum pressure point is now at 60% chord, resulting in even more laminar flow:

This is why laminar flow was the holy grail. Unfortunately, it was soon found that most production aircraft didn't have wing surfaces of sufficient quality to avoid pressure fluctuations that caused premature transition.

 

[ThomasP]

Excellent explanation.

 

[Aeroweanie]

Its been pointed out that the pressure distribution I show for the P-51 airfoil is rather wavy and this is reflected in the calculated drag. This is probably the result of using low fidelity coordinates and interpolations on my part. I've cleaned up the waves and this is the result: