Sea Hurricane and the prohibitive weight of folding wings

[Admiral Beez]

Interesting note about concern over the added weight of a folding wing mechanism.

"The provision of a folding wing was examined in 1940. But the desperate need for aircraft designers for next-generation aircraft, as well as concerns over the Hurricane's ability to accommodate the extra weight, soon saw this idea abandoned. " http://www.armouredcarriers.com/hawker-sea-hurricane-variants

I didn't think the Hurricane was considered nearly overweight in standard spec. Did the Seafire or Wildcat gain a lot when the fold was added?

Seafire
Seafire Mk IIc with 36 ft 10 in wingspan, 2x20mm 4x.303, and Merlin 46. Empty weight 5,300 lb (2,404 kg)
Seafire Mk. III with folding wings, 32 ft 2 in wingspan, and Merlin 55M. Empty weight: 5,450 lb (2,472 kg)

By shortening the wingspan, the weight between the two Seafires goes up by only 150 lbs. IDK how much of this 150 lb. increase is due to the engine upgrade.

Would the Sea Hurricane really have become overweight if folding wings were added? Mind you, the Hurricane IIc weighs 5,745 lb (2,606 kg) empty - by the time the Seafire got near that empty weight it was Griffon-powered.

 

[DarrenW]

By shortening the wingspan, the weight between the two Seafires goes up by only 150 lbs.

Unless they up-engined the Hurricane Mk. Is when modifying them into Sea Hurricanes an extra 150 lbs would be far more penalizing. When compared to the Seafire Mk. III it had far less horsepower and was already suffering in comparison to other fighter aircraft, even by 1940 standards.

 

[pbehn]

In my capacity of naval aircraft designer who knows nothing at all about naval aircraft design I make the following observations.

1 The Hurricane wasn't a stellar performer, already behind the Spitfire in performance, it could do without putting on more weight.
2 The wing wasnt originally designed as a stressed skin structure so maybe a folding wing would add more weight than on other planes.
3 The problem may not have been about the weight when in the air but on landing. the article states "The provision of a folding wing was examined in 1940. But the desperate need for aircraft designers for next-generation aircraft, as well as concerns over the Hurricane's ability to accommodate the extra weight, soon saw this idea abandoned." So I think it was the ability of the arrestor hook and frame to take the extra weight that was the problem. I dont know how many "g"s a landing imposes but maybe it was already at the limit?

 

[MIflyer]

The Hurricane's gear was set well out from the fuselage, and the wing fold would have to occur out there. That would have shortened the length of wing to be folded, but then again there was no beefy structure that far out to mount the pivot mechanism.

 

[stona]

I'm not sure that a folding wing was ever seriously considered.

Mason doesn't even mention it.

He does mention the substantial strengthening needed for the fuselage to prevent failure when making an arrested landing on a carrier. That must have added some weight too. Apparently the attachment of catapult spools to transmit the thrust of the catapult to the main structure of the aircraft did not require substantial modifications.

 

[slaterat]

The Hurricane manual for the the Mk II, gives the additional weight added to a Mk II for the hook as plus 30.25 lbs. Keep in mind that the MK II series 2 Hurricanes would all have the strengthened longerons as built.

The Sea Hurricane was always intended as a stopgap measure so the resources and will power to design folding wings just weren't there. I have always thought it would be relatively easy to do as the Hurricane wings were very strong, with steel spars in the center section, and the outer wings were already attached by pin joints.

 

[PFVA63]

Hi,
Francis Dean's "America's 100,000" has some pretty good data on US Plane weights from that era, broken down by weight groups. In it he notes that the "Wing" group weight for the F4F-3 (without folding wings) was 893lb, while the "Wing" group weight for the F4F-4 (with folding wings) was 1181lb (for an increase of 288lb. The later FM-2 version of the plane, also with folding wings, was able to bring the weight of the wing group down to 1154lb (or +261lb over the F4F-3).

I also once found an equation of the internet for estimating the weight increase of folding wings, but I'm not sure if it is based on WWII data or more recent data. I will try and track that info down shortly.

Pat

 

[tomo pauk]

Interesting note about concern over the added weight of a folding wing mechanism.

"The provision of a folding wing was examined in 1940. But the desperate need for aircraft designers for next-generation aircraft, as well as concerns over the Hurricane's ability to accommodate the extra weight, soon saw this idea abandoned. " http://www.armouredcarriers.com/hawker-sea-hurricane-variants
...

Unfortunately, instead of actually making a folding-wing Sea Hurricane and test it, the powers that were used the same reasoning like it was used for discouraging 1-engined long-range fighters: we have a concern that something might not work, so let's not do it.

Hurricane was among the lightest of ww2 frontline fighters.

 

[PFVA63]

Hi,
Here is a link to a NASA report with the equation for wing fold mechanism weight penalty. NASA Technical Reports Server (NTRS) - Aircraft wing weight build-up methodology with modification for materials and construction techniques

Looking closer at the data in the appendices suggests that it is likely based on post WWII aircraft so I don't know how accurate it would be for a WWII type aircraft. Quickly throwing in some numbers for an F4F suggests something on the order of 300-333lb (if I did the math right), which is a bit higher than the 260-290lb given in Dean's book.

Pat

 

[MIflyer]

Remember that the RN carriers had armored flight decks, which reduced the ceiling height on the hangar deck, so much so that the RN F4U's had to have shortened wingtips in order to fold and not hit the ceiling.

 

[Admiral Beez]

Remember that the RN carriers had armored flight decks, which reduced the ceiling height on the hangar deck, so much so that the RN F4U's had to have shortened wingtips in order to fold and not hit the ceiling.

Looking at these pics I wonder if the wings would be able to clear hangar ceilings if the folded upward rather than back.

A. L. BENTLEY DRAWINGS | Hawker Hurricane Mk.I

 

[MIflyer]

In the case of the Corsair, they would not if the wings had not had clipped tips. But note that the RN mostly used either Grumman aircraft or British aircraft with wings that folded back.

And note that the A6M Zero never had folding wings, just folding tips on the early models. The wings held the fuselage together rather than vice versa.

 

[ThomasP]

Hey guys,

The Seafire Mk III wing was based on the 'C' wing with the two-fold mechanism added, plus a few other minor modifications. The weight increases I have seen for the addition of the wing fold mechanisms are 125 lbs for the early-production Mk III and 129 lbs for the late production Mk III. This allowed for a total height of 13' 6" ft with wings folded.

Plus from here: Build a better Sea Hurricane 1938

"On the subject of making a better SeaHurricane, a few years ago I made a couple of ~engineering drawings of a folding wing version. The type of fold was a simple break-wing mechanism (similar to what was used on the Devastator or Vindicator). The resulting tail down footprint with wings folded was 31' 2"L x 18' 6"W x 13' 1"H. The airframe could have been moved around the hanger with the wings folded, but folding and unfolding would have to have been done between the deep support beams, or on deck. The 18' 6" folded width would have fit on the 22' wide elevators of the armored deck carriers well enough with careful positioning. The folded width for the Barracuda was 18' 3" and that of the TBF/TBM was 19' 0" (the tail width of the TBF/TBM was 20'10") and both airframes were operated from the armored deck carriers in large numbers. The manual folding mechanism would have added only about 186 lbs to the TARE weight."

 

[yulzari]

One might bear in mind that the 27' 5"L x 32' 3"W x 11' 9"H Sea Gladiator was in service and fitted in the lifts and hangers with no folding at all so a small fold of 4' or so on each wing would make it a longer Sea Gladiator in stowage. More Zero than Martlet in weight and complexity.

 

[jetcal1]

I've said this before and I'll say it again, with the need for production space, and lack of engineering personnel the decision was probably made to just live with the Hurricane as is. Plus, consider the fact that there was a shortage of high strength forgings in 1940 sufficient to delay production of the Halifax which surely would have been a higher production priority than a folding wing conversion for an already extant airplane that was considered to be on the verge of becoming obsolescent when Martlets were already in the FAA,

 

[MIflyer]

"....already extant airplane that was considered to be on the verge of becoming obsolescent ...."

True! Note that at that same time Hurricanes were being mounted on CAM merchant ships, a use in which they were considered to be expendable.

By the way, accoring to a USAF manual I read 50 years or so ago, "Obsolete" means "Outdated" while "Obsolescent" means "No Longer Used."

 

[ThomasP]

Hey guys,

The following are TARE weights from the 1942 Loading & C.G. Diagrams for the Sea Hurricane IB & IC, and the 1943 Loading & C.G. Diagrams for the Hurricane IIB & IIC and Sea Hurricane IIB, & IIC. The Sea Hurricane IIB & IIC were the fully navalized versions and included provision for DTs. Perhaps this will help with determining if the weight penalty could be handled. I assume (yeah, yeah, I know) the weight increase (189 lbs) for navalization would have been about the same for the Sea Hurricane IB & IC conversions. Add another 186 lbs for folding wings and??

Sea Hurricane IB TARE weight of 5440 lbs
Sea Hurricane IC TARE weight of 5390 lbs

Hurricane IIB TARE weight of 5467 lbs
Hurricane IIC TARE weight of 5658 lbs

Sea Hurricane IIB TARE weight of 5656 lbs
Sea Hurricane IIC TARE weight of 5847 lbs

 

[RCAFson]

One might bear in mind that the 27' 5"L x 32' 3"W x 11' 9"H Sea Gladiator was in service and fitted in the lifts and hangers with no folding at all so a small fold of 4' or so on each wing would make it a longer Sea Gladiator in stowage. More Zero than Martlet in weight and complexity.

An uprated G. Sea Gladiator with a CS prop was always a possibility. However, the GSG could not be taken into the hangar of Ark Royal or an Illustrious class carrier because elevator width was 22.5ft.

 

[RCAFson]

I'm not sure that a folding wing was ever seriously considered.

Mason doesn't even mention it.

He does mention the substantial strengthening needed for the fuselage to prevent failure when making an arrested landing on a carrier. That must have added some weight too. Apparently the attachment of catapult spools to transmit the thrust of the catapult to the main structure of the aircraft did not require substantial modifications.

Hawker submitted folding wing naval fighter designs prewar, and these designs were based upon the Hurricane airframe, and folding wings were a requirement of the design. I suspect that Hawker was told to forgo folding wings in the Sea Hurricane because the initial plan for the Hawker SH1B was to convert existing MK1s into Sea Hurricanes, rather than purpose building them on the factory floor. Additionally, the Admiralty was being promised adequate numbers of FW Martlet IIs, but in the event these didn't arrive in the needed numbers.

War planes of the Second World War Fighters, V2 (1963) states:

"...The Sea Hurricane IC was similar apart from
having the four-
cannon armament of the more powerful
land-based Hurricane IIC. In 1940, inci-
dentally, designs for a folding-wing version of
the Hurricane were prepared, but this variant
never materialized..."

 

[fastmongrel]

"

By the way, accoring to a USAF manual I read 50 years or so ago, "Obsolete" means "Outdated" while "Obsolescent" means "No Longer Used."

I think you have it the wrong way round Obsolete means No longer used and Obsolescent means outdated and becoming obsolete but not yet out of use. For example the Fairey Swordfish was obsolescent during the war but not obsolete.