Hawker's W.W.II construction methods

[JDK]

There's been a couple of remarks about Hawker (and British) constriction methods in another thread, I thought I'd comment on them here, FWIW.

I see that the Brits never did learn how to weld, look at those tubing joints, just like the hurricane

Not really a fair generalisation for the British; there were different construction methods for different manufacturers, from the familiar stressed skin riveted semi-monocoque regarded as 'normal' now to ideas developed far past their viability like Barnes Wallis' Geodetic method with fabric covering - in fact several UK factories were forced to build obsolete structural design aircraft through W.W.II as Vickers Armstrong weren't able to switch some of their factories to a worthwhile method; so lots of essentially useless Vickers Armstrong Warwicks and the useless and bizarre Vickers Armstrong Windsor.
http://en.wikipedia.org/wiki/Barnes_Wallis
http://en.wikipedia.org/wiki/Geodesic_airframe

Several British manufacturers in the 1920s used welded tube fuselage structures, of course.

Conversely, the very British designed wooden monocoque construction Mosquito (and after) the de Havilland Hornet did everything anyone else could do and better, with few limitations (proper care being a normal one). Going onto wooden-fuselage jet-powered aircraft (Vampire and Venom) does require a pause for thought...

... I had no idea the Tempest had the tube frame construction like the Hurricane. Very rare aircraft. Was the Fury the first fighter Hawker built that moved past the tube frame style of construction? ...

Good question. Actually the Tempest has only one (the cockpit and forward fuselage) area that is of tubular construction, the rear fuselage, wings and empenage being of conventional stressed skin construction. But alluding to the Hurricane's heritage is also an important point.

Hawker (and Sidney Camm) was very much an iterative designer, only changing enough of a design to get to the next aircraft. So the Hawker Hart led to a huge range of types and the design principles begat a fighter design, the Hawker Fury (biplane) when Harts outran the RAF's current fighters. The Hurricane was essentially a monoplane Fury, and shared much of the Fury's bolted-tubular construction with wooden formers and fabric covering - in configuration, the early Hurricane Mk.I was a Fury without the upper wing and a few extras.

But that choice of sticking to a known design principle for a new type was vital. Most don't realise that Hawker also had a metal-frame fabric-covered wing on the first production batches of Hurricanes; they had to have channel stringer material to hold the fabric on at 300 mph+, but they knew they could build them quickly, get them into service and the RAF pilots could get used to the 'hot' new monoplanes with flaps, retractable undercarriages and enclosed cockpits et al. In contrast, Supermarine were struggling to take the handbuilt prototype Spitfire to something that could be mass produced as a stressed skin very multiple compound-curve structure. Once Hawker had developed the all-metal stressed skin wing, they were able to build extra and swap out the fabric-covered wings of the Hurricanes in service. Had they not done so, the RAF fighter pilots would've had a lot less hours on monoplane fighters on the run in to the Battle of Britain... As we know, the Spitfire was a great design; but the prototype to production period was not Supermarine's finest hour, and Joe Smith's victory, not the oft- over-revered R J Mitchell's.

This shows some Hurricane details, inc the early fabric covered wing structure:
http://aerospaceengineeringblog.com/his ... tructures/

More detail of the wing here:
http://aerospaceengineeringblog.com/wp- ... e-Wing.jpg

Although it doesn't make it clear, this is a fabric-covered wing Hurricane cutaway:
http://www.flightglobal.com/airspace/me ... utaway.jpg

And the later metal wing:
http://sobchak.files.wordpress.com/2009 ... anecut.gif

(Note also that Vickers were trying to make a 'fabric' skinning work on the Windsor, mid war, for a mid-300mph bomber with a flexing wing... It was a disaster of a design. Hawker knew when to move from one method to the next, in contrast.)
http://en.wikipedia.org/wiki/Vickers_Windsor

The Hurricane's construction meant that if you had the infrastructure (as Hawker did) it was faster and easier to mass produce than a stressed skin construction; modular repairs (we'd now call 'plug and play') were possible in the field and at repair depots more easily than the Spitfire's integrated construction. Also the RAF's repair system and groundcrew ('erks') were very familiar with, and equipped to, repair Hurricane type construction in 1940.

The Hurricane was to be replaced by the Typhoon as a fighter, and the Typhoon had a hefty thick wing (which was regarded as optimum in the 1930s, when it was designed) and a tube-frame centre-fuselage developed from the Hurricane's in concept. However the rear fuselage and wing was moved to stressed-skin construction. As we now know, the thick wing was A Bad Idea, and there were issues with flutter causing the empennage to detach in flight; but these problems were overcome, and with a laminar flow wing and the late-Typhoon's bubble canopy and a longer fuselage for more fuel, we got the Tempest, a magnificent fighter and ground attack type. Remove the Tempest's centre section, 'hump' the fuselage to raise the pilot, and add a hook and catapult spools, and complete the stressed skin construction around the cockpit, and you have the even better Sea Fury (and Fury monoplane), unarguably one of the best piston-powered fighters.

http://www.flightglobal.com/airspace/me ... utaway.jpg

Note the design carry over in the fuselage, albeit with the stretch for the fuel tank:
http://www.flightglobal.com/airspace/me ... utaway.jpg

http://img69.imageshack.us/img69/6889/h ... agethe.jpg

Looking at this Hawker technological approach, you can run through from the Sopwith Tabloid, pre- Great War to the Hawker-developed Harrier, many of which have Sir Sidney Camm's fingerprints on. Few design houses could claim such long-term success as this, with in-service examples throughout that period. (Grumman and Leroy Grumman would have a good claim for a similar pragmatic, effective and innovative approach in the 1930s and 40s.) Camm was a tough man by all accounts, were I to hypothetically choose a designer to do me a fighter, he would be my undoubted favourite.

Referring to the Tempest II specifically, while chatting with the guys at Pioneer Aero recently, they said they thought that in aspects the P-40 was probably a tougher restoration challenge if it was your first one than the Tempest, although now there's much more of a support infrastructure for the P-40 in the warbird business. The Tempest will be a tough restoration because it is rare and there are only three under rebuild to fly, and only, I suspect one, the Pioneer example, that will get there.

As New Zealanders, they aren't biased towards (or against) either US or UK construction approaches, and I think it's therefore a fair evaluation, rather than the common Transatlantic 'not invented here' attitude.

Hope that's of some interest.

Regards

[PinecastleAAF]

I'm glad you started a thread on the subject I had briefly considered it a couple of days ago. Great information thanks for sharing.

On a side note whatever happened to the Martin Baker replica that guy was building?

[JDK]

No problem - I should add that's all off the cuff, so no guarantees over all the detail!

The MB-5 replica was by John Marlin (?) at Reno, NV. Not heard anything recently. IIRC, while he had significant help from the Martin Baker company, his version was much shoter and stumpier looking (to my eye in the photos) and used a Mustang wing; it's one way of doing it, but as the MB-5 was a great design for how the structure was thought out, it's a diversion further than I'd like to follow - but he got going, and it's just my opinion.

Regards

[DH82EH]

Always enjoy your informative insight James!
Thanks for that.
I can think of a british aircraft that has a welded fuselage. My Tiger Moth ! That predates a lot of Hawker designs, so, it's definitely no an inability.
With a war on, any and everything was tried I'm sure. As a dear old friend of mine says. If you throw enough sh1t agin' the wall, some of it's bound to stick!

Andy Scott

[RobC]

James, I think you make a fair point about generalizing. Certainly DeHaviland had a more efficient approach, as did Supermarine. But as has been well documented, especially in interviews with the Hawker Restorations chief, the Hurricane was massively complicated. The parts count for each of those tube joints is just nuts. The joints created a need to square each tube end. Compared to welding, well, there is no comparison.

Hawkers was not the only culprit. Take a few minutes to see how Bristol accomplished fuel tank selection (hint: bicycle chains are involved) or the parts count involved in constructing things like bomb bay doors or the attachment of the inner leading edges in a Blenheim. And it is not just complexity, but the weight associated with that complexity.

If you work on North American products, you will see a commonality in design that greatly simplified both construction and maintenance. I have not worked on a Curtiss product, but from your descriptions, would summarize that it is no more fair to generalize with American manufacturers. Curtiss and Brewster had a bad reputation compared to North American and Grumman.

My 2 cents.

[Forgotten Field]

James,
Thanks for posting that. The more I learn about the Hurricane, the more I like it.

[bdk]

That was an era of great change and there was lots of learning going on. Some things were done for expediency, material availability, available work force (cottage industry & dispersal), product evolution, etc. for every good idea there were probably a dozen bad ones that made it into production.

P-40 structure is a nightmare to repair compared to a Mustang. Everything on the P-40 was built to be assembled one way. When you try to make a repair in the middle it is quite a challenge.

[Fight2FlyPhoto]

James - that was one of my all-time favorite posts here at WIX! Thank you!

[HawkerTempestMKII]

Some things I 've noticed about the Tempest are as follows:

The design is refined to be as simple as possible yet at the same time many of the parts are complicated, but in a way to make it out of as few parts as possible.

Fewer parts and many less castings than a T-6 for example.

Thought into repair instead of replacement. For example the wingtip is 3 pieces instead of 1 like the P-51. That allowed part of the wingtip to be repaired if it was damaged.

The landing gear uplocks are cable operated instead of mechanical like on the T-6. This allows it to be lighter weight and easier to manufacture.

The rear part of the tubular fuselage acts as a spring because it's free swiveling similar to biplane struts to prevent excessive moments on the tail.

The design is iterative or evolutionary as it uses the same ailerons, landing gear, wingtips and canopy as the Sea Fury.

The aircraft was designed to be as light and strong as possible. Many of the skins are light gauge. The skins on the rear fuselage are especially thin.

The fuel tanks are sort of similar to the Mitsubishi Zero in that they bolt in instead of using canvas lined straps. The fuel overflow lines are built into the structure as opposed to being clamped in.

the nose tank has carefully aligned holes in the landing gear castings to facilitate ease of removal.

The fuel lines thread in as opposed to being fastened on.

Overall it's an amazingly practical, well built, refined and lightweight design.

[DH82EH]

Hey HTMKII (if I can call you that for short )

Thanks for the insight and observations. It's quite a project you have there and I wish you all the best.
I hope you can put paid to all the nay-sayers by roaring past them above the flight line!
It's very interesting to see the differences and similarities, as well as the Hawker uniqueness.
Keep us posted and don't be shy with the pics!

Andy Scott

[AvroAvian]

My understanding of the Hawker steel tube frame philosophy was that it was aimed at repairability in the field. Back then, not everyone had access to to oxy/acetylene equipment and the skills to produce quality welds, especially at some of the more far flung places in the Empire. Hence it was desirable to be able to repair the structure with limited equipment, if not hand tools.
Aluminium monocoque structures were also still in the early stages of developement and a good friend of mine once noted that the Spitfire appeared to be a wooden aeroplane built out of aluminium.

[airnutz]

My understanding of the Hawker steel tube frame philosophy was that it was aimed at repairability in the field. Back then, not everyone had access to to oxy/acetylene equipment and the skills to produce quality welds, especially at some of the more far flung places in the Empire. Hence it was desirable to be able to repair the structure with limited equipment,

With the discussion of the VWoC 2-holer Hurricane recently, I dug out Fozard's tribute to Sydney Camm in order to refresh my memory of the engineering and history. A quote on that note, "Camm hated to see a bent plate if a flat one would do the job, and I once heard heard him say that welding was the last resort of Failures....".

[SaxMan]

The Hurricane was kind of a halfway house between the wood and canvas biplanes and the more modern monocoque fighters. The fabric fuselage and girder construction proved to be able to absorb cannon strikes with far less damage (similar to how the chain home radars proved difficult to destory with bombs) than the more modern planes could. In 1940, RAF ground crew were far more familiar with the Hurricane's construction than the Spitfire's, consequently, damaged Hurricanes could be returned to service more quickly than Spitfires. The "Hurry" tends to get second billing to the Spit, but it's role, especially during the BoB, should not be underrated.

[airnutz]

The Hurricane was kind of a halfway house between the wood and canvas biplanes and the more modern monocoque fighters.

True, and rather than venture off into new design grounds of the Me109 and Spitfire, Hawker chose to stand fast with what they had. Another selection from Fozard's tribute, "While it was realised that stressed skin construction might be theoretically better, and in fact later series Hurricanes had stressed skin metal wings, the urgeant need for the aircraft was uppermost in Camm's mind and the design was determined by what could be made in the Kingston Works without undue changes in their equipment. The result of course, was the availability of the Hurricane in sufficient numbers by the time of the Battle of Britain to determine the result of the Battle."

[Stephan Wilkinson]

I built a Falco awhile ago, and I remember that the original italian factory-built airplane had 52 discrete moving parts in the flap-actuation linkage. The U.S. company that rationalized the design for homebuilder construction (Sequoia Aircraft) reduced it to three, the main one being a torque tube.

Ever looked closely at a 1960s Ferrari carburetors/throttle linkage? You'll get the general idea...

Even on my Porsche 911 racecar, adjusting the throttle play and actuation was an afternoon's job requiring four jackstands and a creeper.