Folding wings on British bombers

[A4K]

Elton... So I missed a 'y' on 'definitely'. (Post #14)

Just so you know, I do know how to spell the word, the tablet's touch screen just likes to be awkward and does little things like that. That I didn't notice is my own not checking - oh dear, how sad, never mind. I have since corrected it after receiving your friendly notification.

If your hobby is correcting spelling mistakes, you shouldn't be lurking here trying to make people look stupid, we already have a couple of members who like to do that. They are way more than enough. You, my friend, should become an EDITOR. The amount of mistakes in books and publications these days is terrible - we need more people like you in editorial offices to save the world's literature from becoming further degraded than it already is. You would have a full time job in any of the world's newspapers too, for that matter.

Thankyou for reading my post, and paying SO much attention, you decided to notify the world that I missed a letter. Are you now going to notify all the Americans here that they don't speak the Queen's english?

 

[Elmas]

Barn(es) doors or not, I think that a twenty-ish feet increase on Stirling wingspan would not have been of any harm...

And, risking of course to be accused of heresy and criminal offence to a Majesty, even to a Lanc...

 

[stona]

I think that a twenty-ish feet increase on Stirling wingspan would not have been of any harm...
.

Where on earth does the idea of a "twenty-ish feet increase" come from? It was only ever going to be 112', then 102', then 99' 1". In no design or proposal was it ever 120'.

The span wasn't the problem as I've already explained.

Cheers

Steve

 

[Elmas]

Yes, of course historically I do agree with you.

But, if the doors were not a problem, why to go for 99' 1' instead of 112"?

Better aspect-ratio and less wingloading, at the cost of an increase in weight very moderate.

But, of course, saying "very moderate" is an hindsight...

A Friend of mine was a soldier during the WWII and made a number of flights on SM81 and SM79, whose wings were stiff as a broom handle.

"What was my dismay" he told me once, "when in the '50s I flown in an Alitalia Vickers Viscount and, looking outside the window, I saw the wing moving like that of a bird!"

In those times (mid '30s) the study of bending and stretching of thin plates was still in its infancy and not at all fully exploited, so designers (and Air Staffs...) tended to be very conservative about wing aspect ratio and profile shape and thickness. The same about monocoque fuselages, of course.

In particular torsion of the wings was feared, as it was particularly difficult understand the proper functioning of a D-box.

No doubt that first monoplanes (some, at least...) tended to be heavier than they could have been compared to the stresses effectively involved.

 

[ChrisMcD]

The simple fact is that the Stirling was bloody big compared to other British bombers

File:British WW2 bombers comparison.png - Wikimedia Commons

While we are on the subject of slander, I always liked the comment that Shorts, as a specialist flying boat manufacturer, were rubbish at making retractable undercarriages - hence the excessively complicated, double retraction of the Stirling's.


View: https://www.youtube.com/watch?v=a8ld9RadwQo


Apparently a cause of concern if you were trying to land in any sort of crosswind.

But it does have "presence"

 

[pbehn]

The wing span of the Stirling was OK it as just 17ft too long. Transition from the Stirling to other types led to some nasty accidents, you can walk under a Stirling with the engines running but not a Lanc or Halifax.

 

[buffnut453]

Hmmm...yeah, no wonder the Stirling struggled performance-wise. An extra 17 (almost 18) feet of length that clearly wasn't necessary is a lot of excess load (and extra drag) to lug around. Wish I knew what requirements/factors led to the design decisions that led to an aircraft so much larger than the Lancaster but which carried less and had poorer performance.

 

[pbehn]

Wish I knew what requirements/factors led to the design decisions that led to an aircraft so much larger than the Lancaster but which carried less and had poorer performance.

From wiki but better covered by Stona here
"The Air Ministry Specification B.12/36 had several requirements. The bomb load was to be a maximum of 14,000 lb (6,350 kg) carried to a range of 2,000 miles (3218 km) or a lesser payload of 8,000 lb (3,629 kg) to 3,000 miles (4,800 km) (incredibly demanding for the era). It had to cruise at 230 or more mph at 15,000 ft (4,600 m) and have three gun turrets (in nose, amidships and rear) for defence.[2] The aircraft should also be able to be used as a troop transport for 24 soldiers,[3] and be able to use catapult assistance for take off.[2] The idea was that it would fly troops to far corners of the British Empire and then support them with bombing. To help with this task as well as ease production, it needed to be able to be broken down into parts, for transport by train.[4] Since it could be operating from limited "back country" airfields, it needed to lift off from a 500 ft (150 m) runway and be able to clear 50 ft (15 m) trees at the end, a specification most small aircraft would have a problem with today."

The Lancaster (Manchester) and Halifax were originally to be medium bombers with Vulture engines. The Lancaster especially had a single purpose, to have the biggest bomb bay and biggest load carrying capacity that the engines and specified defense would allow. With a calibrated eye ball the above drawing has the Lancs bomb bay at about half the length of the aircraft, pictures of the Lanc. dropping the grand slam and the 12,000 Ib cookies with incendiaries still look a little unreal to me, the plane just doesnt look big enough.

 

[Airframes]

Well, at 33 feet (10 meters) long, the Lancaster's bomb bay was certainly big enough.

 

[buffnut453]

Thanks Pbehn. So...probably the troop carrying requirement led to the larger fuselage. Just goes to show that sometimes there are unintended consequences to what seems, at the time, to be an entirely sensible and pragmatic requirement.

 

[pbehn]

Thanks Pbehn. So...probably the troop carrying requirement led to the larger fuselage. Just goes to show that sometimes there are unintended consequences to what seems, at the time, to be an entirely sensible and pragmatic requirement.

You will always get the best result if you design with a single purpose, some designs can satisfy many. People can debate which was the better bomber between the B17 and B 24 but Churchill had no doubt the B24 was his favourite transport and one of the few that could carry the fatty. Perhaps the B24 had more utility than the B17 which may have been the better bomber but the original requirements placed on the Stirling and many later ones almost guaranteed a jack of all trades master of none.

 

[Shortround6]

Thanks Pbehn. So...probably the troop carrying requirement led to the larger fuselage. Just goes to show that sometimes there are unintended consequences to what seems, at the time, to be an entirely sensible and pragmatic requirement.

Yes, because as the plane goes through a 3-4 year process of start of drawings/calculations to introduction into the first service squadron some early requirements are dropped, but some are dropped too late as redesigning the plane to fit the "new" relaxed requirement would delay the planes service introduction by months if not a year as new drawings/calculations are made.

Please remember that the Stirling was such a departure from what the British industry was used to that they built and flew a 1/2 scale model to check flight characteristics.

And Shorts had built 4 engine all metal monoplane flying boats. One reason they were allowed to join the competition.

Pushing the "envelope" into long span high aspect ratio wings would have been risky indeed at the time even though quite acceptable even 5 years later.

I would note that the Short Empire flying boat had a 114ft wingspan but the Empire flying boat weighed loaded about 90% of what a Stirling did empty so you can't take an Empire wing and stick it on a Stirling fuselage. About all you could keep would be the general shape and airfoil while changing just about every actual component of the wing.

 

[Graeme]

Please remember that the Stirling was such a departure from what the British industry was used to that they built and flew a 1/2 scale model to check flight characteristics.

From what I've read - it was the long take-off and landing distance of the S.31 that lead to the final Stirling undercart height.

The S.31 on the right, after the modifications...

 

[stona]

Yes, of course historically I do agree with you.

But, if the doors were not a problem, why to go for 99' 1' instead of 112"?

The 100' limit, still in force in 1936 when the specification(s) were issued was simply to stop the aircraft getting too large and unwieldy. Hangar openings were not the reason for the limit, Maund mentioned various issues.
The limit was dropped shortly thereafter, but the need to keep the aircraft size within reasonable limits remained.

Shorts did struggle with the undercarriage, but then it was for an unusually heavy aircraft, for the time. Graeme is correct about the reason for its increased length. Various other systems were transferred from flying boats and caused problems, perhaps most notably the throttle system.

We need to be careful about the troop transport requirement. The requirement that a heavy bomber be designed so as to carry troops was included in the first draft specification for B.3/34 (Whitley). The Air Staff had been told that the requirement would not lead to a reduction in performance. It was dropped from the specification after the Director of Technical Development (DTD) admitted that it would lead to a loss of 10 mph in speed.
Both the 1936 specifications (B.12/36 and P.13/36) stated that.

"Consideration is to be given in design for fitting a light removable form of seating for the maximum number of personnel that can be accommodated withing the fuselage when the aircraft is being used for reinforcing overseas commands."

This is not a demand for a dual role aircraft. Seating was to fit the fuselage, the fuselage was not to be designed to take seating, an important distinction. Other discussions at the time the specifications were being developed show that this passenger carrying capacity was aimed at the need to carry RAF ground crew to RAF Overseas Commands, a result of the introduction of reinforcement ranges into bomber specifications.
Further evidence that the troop carrying requirement did not influence the 1936 specifications to a great extent comes from the Air Staff's investigation into the potential use of these aircraft as transports after the specifications were issued. An allocation of funds to develop a new transport aircraft was proposed, in case it was not possible to use them in this role. When this was discussed as part of the 1937 Experimental Aircraft Programme it was decided that one of the bombers would have to fulfill the transport role, though this was too late to influence the designs being developed as a result of the 1936 specifications.
When Bomber Command officers inspected Supermarine's mock up to B.12/36, on 5th October 1937, they found that not even the captain and navigator had enough room to stand, and far from finding accommodation for fully armed troops they were worried whether there was enough room for the crew!

Cheers

Steve

 

[Elmas]

The 100' limit, still in force in 1936 when the specification(s) were issued was simply to stop the aircraft getting too large and unwieldy. Hangar openings were not the reason for the limit, Maund mentioned various issues.
The limit was dropped shortly thereafter, but the need to keep the aircraft size within reasonable limits remained.
omissis
Steve

Something similar to the German specification of "just two engines on bombers" that led to technical amenities like the DB-606/610 and He-177? (Even if this specification was not exactly issued to keep dimensions down, of course.)
Why do not specificate a maximum empty load, or a maximum fuselage lenght, or even both, instead of wingspan and consequent aspect ratio, wich is fundamental for aircraft performance?
Just "military", probably.
I completely agree with what Shortround6 said (post #32:
"Pushing the "envelope" into long span high aspect ratio wings would have been risky indeed at the time even though quite acceptable even 5 years later."

 

[stona]

The specifications issued by the Air Ministry were long and quite complicated, covering everything from range/load as well as various speeds, usually discussed, based on a table of the desired performance data by the Operational Requirements Committee. Ground performance, including take off runs were also important, given the limited size of Bomber Command's aerodromes. That's what led to the requirement, listed under 'Structural Strength' in B.12/36, for the aircraft to be designed for launching at 'limiting weight' (meaning maximum overload) from a catapult which imposed an acceleration of 2.5g at the end of a launch.
The Air Ministry offered the specification(s) for tender to various selected firms who were expected to respond (though there was no legal requirement to do so, they could decline). It was up to the companies who tendered to come up with a design to meet the specifications.
In the case of Shorts and the Stirling, the specifications were not met, but it is difficult to see how they could have been given the available technology and particularly engines at the time.
With the loss of the Supermarine back up the Ministry had no choice but to carry on with the project.
The specifications were usually circulated more widely in the aircraft industry, to firms not invited to tender, as a means of keeping them up to date with the latest Air Staff thinking. There was nothing stopping any firm independently developing a design to meet a specification, but it would have to finance the initial stages itself (referred to as a private venture (PV) ) in the hope of eventually winning a contract for the prototype(s) from the Air Ministry. The risk was therefore the companies.
Cheers
Steve

 

[Robert Porter]

Government issued specifications even today, often specify aspects or things that they have no business specifying. Often for the most ridiculous reasons. It is how we end up with things like left handed hammers. Heck it is not limited to the government even in business we end with specs that have no real purpose other than someone wanted to have their opinion or thoughts recognized on paper!

I have no real information on this particular topic but specifying wing length on an aircraft that would almost never be in a hanger, not launched or recovered on a carrier etc just seems a typical example of bureaucratic incompetence at its best.

 

[stona]

The specifications issued by the Air Staff were always the result of a lengthy process and discussion by the Operational Requirements Committee. These were all airmen. They decided what aircraft the RAF needed to fulfill its various roles. We have hindsight and must be aware that a war with Germany was not a role envisaged until the mid-1930s, when the 1936 specifications for heavy bombers (intended to bomb Germany) were issued.
Given the size of RAF aerodromes, limited facilities, the need to transport spares, etc. and particularly overseas where British forces had significant commitments policing the Empire, the 100' limit was reasonable. It was abandoned later, the Manchester-Lancaster conversion took the latter to 102' and the Halifax to a smidge over 104'.
The problem for the Stirling was not a lack of span, it was the huge increase in weight accrued during development.

It is easy to be hard on Shorts and the Stirling, but the specification to which it was built was a big ask in 1936. The loss of the Supermarine prototype means we have nothing to compare it too, and neither did the Air Staff.

The Operational Requirements Committee was always gazing into the future to anticipate what would be needed and what might be possible, several years down the line. It didn't have a crystal ball and couldn't always be right. Turret fighters seemed a good idea at the time, but turned out not to be so. The unarmed, fast, bomber did not appeal, but the Mosquito turned out to be one of the outstanding aircraft produced by any side throughout the entire war.

Cheers

Steve

 

[Robert Porter]

England was indeed fortunate then, I am unaware of any other country that did not have non airmen on their specifications committee's or at least had non airmen in the approvals process that were able to and indeed often did send amended specifications back down the channel. Which makes a wing length specification even more puzzling since airmen would, at least one would think they would, know that design of wing is often a function of the role the aircraft was to play the loads it would carry etc. This was well understood before the 30's which makes it so puzzling. But there were a lot of specifications including armor and even uniforms that as you mention with the benefit of looking back make one wonder just what in the world they were thinking.

 

[stona]

Money was a factor, not so much in the size of the aircraft as in the size of the aerodromes and other infrastructure. Paved or concrete runways were rare and expensive in the 1930s but would have reduced take off runs