Short Stirling

[Graeme]

So, that the wingspan was restricted due to hangar dimensions is a myth?

I believe so.
Maybe stuff it in sideways?

 

[nuuumannn]

So, that the wingspan was restricted due to hangar dimensions is a myth? If so, I can understand why it persists, it is a very plausible story. AFAIK, the Stirling was developed around the time Britain used transport/bomber aircraft for duty in the colonies? If the Stirling was developed with that purpose in mind, then trying to fit it in around hangar spaces worldwide would make sense, given how widespread the Empire was, creating bigger hangars around the globe sounds like a costly undertaking.

But the wingspan was restricted? Why?

All in all, it sounds like the Short Stirling was a rather poor design, even given that it was an early one.

Hi Acheron, let's put it this way, it wasn't a "myth" per se, but it wasn't specified in the requirement. It was likely to have been a consideration when the Air Ministry produced B.12/36, but within the context of the final product being able to operate from existing airfields. As for the Stirling itself, it was weight creep and the 100 foot wingspan restriction that prevented Short Brothers from lengthening its span. You have to remember, 100 feet was a big span for the time and yes, you could be right in saying the Stirling was a poor design, although I'd more likely say it was a product of the manufacturer's experiences in building flying boats, the Air Ministry specifications and the unknowns that the industry was encountering at that particular time. It's worth remembering that both responses to P.13/36 were troublesome, the Manchester and the Halifax had serious issues that hindered their entry into service.

There is no paperwork that survives that stipulates a wingspan restriction because of hangar width. If it did happen, there's nothing surviving today to prove it, although there is ample evidence behind the theory that the entire specification was designed for the aircraft to operate from existing facilities.

I feel that one of its more important impacts was that it taught the Air Ministry to stop micro-managing the manufacturers with ridiculous "requirements" during design.

Pretty much. That certainly didn't help matters and it certainly wasn't the last time it happened, the Air Ministry's decision to pursue the naval turret fighter and interim catapult fighter, creating the Roc and the Fulmar respectively instead of allowing the Admiralty to order a single-seat carrier fighter is a clear example (remember, the FAA was a branch of the RAF, not the navy before WW2).

 

[nuuumannn]

Stuffing aircraft in sideways is not a bad way of dealing with the issue. I worked for an MRO (Maintenance, Repair, Overhaul facility) that overhauled C-130s and the hangar width and height meant that the fin had to be removed and the aircraft put on skates and towed in sideways.

Ludlow-Hewitt was a very practical man and often gets criticised within the context of pre-war Bomber Command because of his wayward suggestions, like for example centralised gunnery training (he won that battle and such a thing was created) because gunnery accuracy with the introduction of the new fangled power turrets on bombers actually decreased, escort fighters (he lost that battle and the type was never formally recognised within the RAF) and poor navigation and bombing accuracy (which the Air Staff refused to investigate while he was in charge but was eventually dealt with under Harris).

 

[nuuumannn]

I believe so.

Graeme, where did you find that reference?

 

[Graeme]

Hi Grant.

Here.
See post No.2 - by Harley Quinn...

https://www.pprune.org/aviation-history-nostalgia/616766-shorts-stirling-wingspan-hangar-doors.html

 

[nuuumannn]

Here.
See post No.2 - by Harley Quinn...

Thanks Graeme, there's some good info there. The overwhelming takeaway is the realisation that aircraft were getting bigger and, as mentioned earlier, hangar width was a consideration, but within the context of overall size and weight creep restricting modern aeroplanes' usage of existing facilities.

 

[tomo pauk]

The initial proposal design was fine, however the incessant "improvements" thrust upon Short Brothers slowly strangled it.

For a bomber that was handed over to the RAF in August 1940, it was a significant increase in capability to what was in service then. It is easy to criticize it in comparison to later bombers, but the delay between the start of design and becoming operational was during a time period of rapid improvements in engines and fuel.

I feel that one of its more important impacts was that it taught the Air Ministry to stop micro-managing the manufacturers with ridiculous "requirements" during design. Compare their refusal to allow Shorts to have a 112' span compared to their response to Avro's request to add two more engines to the Manchester.

If the designers in a company don't have a perfect crystal ball wrt. growth of engine power and fuel available, then why go for an oversized design in the 1st place? Every engineer worth it's salt knew that increase in size pushes both weight and drag up, that in return required more engine power, that again meant heavier engines that consume more fuel, all of that pushed the size, weight and drag up in a vicious spiral.

 

[Acheron]

Compared to the Halifax and the Lancaster, the Stirling looks a lot bigger from the side indeed. Was it designed to function not only as a bomber but also as a troop transport? If so, how did it perform in that role?

 

[Geoffrey Sinclair]

I have seen a report that at least part of the Stirling wing was watertight.

the Air Ministry's decision to pursue the naval turret fighter and interim catapult fighter, creating the Roc and the Fulmar respectively instead of allowing the Admiralty to order a single-seat carrier fighter is a clear example (remember, the FAA was a branch of the RAF, not the navy before WW2).

unnery training (he won that battle and such a thing was created) because gunnery accuracy with the introduction of the new fangled power turrets on bombers actually decreased

When the RAF fitted a power operated gun turret to the Overstrand (top speed 153 mph) it noted a 5 fold increase in gunner accuracy, nominal 3 prototypes converted from Overstands, with the turret being flown in 1933/34. Overstrand production began in October 1935. So this improvement was lost with the faster bombers, including versus their hand held guns?

The Defiant was specification F.9/35, the Roc O.30/35, the Roc initial design being based on the O.27/34 specification for the Skua dive bomber. In 1935 the naval fighters in production were the single seater Nimrod and the two seater Osprey, there was no RN naval fighter production 1936 to 1938 inclusive, then came the Roc and Sea Gladiator.

The Fulmar was specification O.8/38 in between the 30 July 1937 recommendation the FAA be handed to Admiralty control and the 24 May 1939 official hand over. As far as I am aware the Admiralty specified the navigator requirement so as to enable the long range/long endurance patrols. Where does the catapult fighter come in? Where does the Sea Gladiator fit in?

 

[Howard Gibson]

I have seen a report that at least part of the Stirling wing was watertight.

Given that Shorts probably wanted to use the same wing on the Empire flying boats, on the Stirling and on the Sunderland, you may be right.

 

[nuuumannn]

So this improvement was lost with the faster bombers, including versus their hand held guns?

Yup, accuracy declined with the widespread introduction of power turrets. The problem became one of the techniques by which the gunners were being trained. Going from operations that differed very little since the Great War, essentially .303 Lewis guns in a Scarff mounting meant gunnery training hadn't changed. The development of the Central Gunnery School at RAF Sutton Bridge in November 1939, which combined gunnery training between services and disciplines to enable better training of gunners carrying out operations. The CGS was the first of its kind in the world.

The Defiant was specification F.9/35, the Roc O.30/35, the Roc initial design being based on the O.27/34 specification for the Skua dive bomber. In 1935 the naval fighters in production were the single seater Nimrod and the two seater Osprey, there was no RN naval fighter production 1936 to 1938 inclusive, then came the Roc and Sea Gladiator.

The Defiant and Roc were both designed and built to Air Ministry requirements and reflected the Air ministry's preoccupation with the superiority of power turrets. Remember the FAA was a branch of the RAF until 1939, therefore the final decisions behind procurement were made by the Air Ministry. Even during the period between the Nimrod and the Roc there was naval personnel within the Admiralty that decried the lack of a modern single-seat fighter. There are plenty of letters that survive in the Admiralty files at the National Archive that pertain to this. In 1937, some admirals, recognising that the Skua fighter/dive bomber would be obsolete when it entered service requested a naval Hurricane, while others went to Supermarine to request a navalised Spitfire, the Sea Spitfire proposed by Joe Smith powered by a Griffon with folding wings, but the Air Ministry wouldn't allow Spitfire production to be diverted from RAF needs. Richard Fairey was invited to the Admiralty to discuss continuing aircraft production and one of those present at the meeting basically told him to build Spitfires under licence, threatening not to continue the Fulmar if he didn't. Fairey responded by stating he only built his own aircraft and would continue to do so. The Admiralty's efforts to acquire modern fighters before and in the first couple of years into WW2 were numerous and the first tangible result was the purchase of F4Fs, which Grumman, realising the haste, took French examples on the production line that could no longer be delivered and converted them for British service, ensuring their delivery in late 1940.

The Fulmar was specification O.8/38 in between the 30 July 1937 recommendation the FAA be handed to Admiralty control and the 24 May 1939 official hand over. As far as I am aware the Admiralty specified the navigator requirement so as to enable the long range/long endurance patrols. Where does the catapult fighter come in? Where does the Sea Gladiator fit in?

The Fulmar was intended as a stop gap and was built to O.8/38, an Air Ministry specification, titled Interim Two Seat Fighter for the FAA. The first sentence of the specification reads thus:

"In response to Operational Requirement OR.56, an interim two-seat front gun fighter is required (for quick production) [hence the use by Lobelle of the no longer needed P.4/24 airframe as the basis - my addition] for the FAA, capable of operating from catapult ships and from the deck of a carrier. The first aircraft are required for delivery in September 1939..."

The time period for the Fulmar's delivery was brief, it wasn't intended that it become the FAA's main frontline carrier fighter. That it did reflected the dire situation the navy found itself in when it inherited the
FAA.

 

[nuuumannn]

Where does the Sea Gladiator fit in?

I didn't answer this in my last rant, the navalised Gladiator came about in 1938, following realisation by the Admiralty that the Skua and Roc were going to be little use as fighters and the Admiralty requested the type for naval duties from the Air Ministry, and so the first Gladiator IIs off the production line at Hucclecote were kept by the manufacturer and modified to naval requirements.

 

[thunderbird]

The problems of the Stirling can be seen by looking at the empty weights of the Stirling compared to the Halifax or the Lancaster. The empty weight of the Stirling was over 12.000 pounds heavier than the other two. its obviously larger dimensions results in extra wetted surface area. and more base drag that also reduces performance in every area.

 

[Acheron]

The problems of the Stirling can be seen by looking at the empty weights of the Stirling compared to the Halifax or the Lancaster. The empty weight of the Stirling was over 12.000 pounds heavier than the other two. its obviously larger dimensions results in extra wetted surface area. and more base drag that also reduces performance in every area.

Thanks, while comparing the Stirling, Halifax and Lancaster, I also noticed that the Lancaster had the weakest engines of the three, yet the highest bombload, according to wikipedia. Is wiki correct on both accounts? If so, this seems to indicate a superior design? The Stirling we walked about, but how did it beat the Halifax?

 

[GrauGeist]

I didn't answer this in my last rant, the navalised Gladiator came about in 1938, following realisation by the Admiralty that the Skua and Roc were going to be little use as fighters and the Admiralty requested the type for naval duties from the Air Ministry, and so the first Gladiator IIs off the production line at Hucclecote were kept by the manufacturer and modified to naval requirements.

You do realize we'll have to wait several days for our Overlord to compile a superfluous dissertation loaded with an over abundance of duff and numbers in order to dazzle us lower-class riff-raff, right?

 

[ThomasP]

Hey Acheron,

re:". . . but how did it [the Lancaster] beat the Halifax?"

Short answer, the Lancaster was a slightly later design, with improved aerodynamics (mainly in the wing design), but possibly in the wing/engine nacelle arrangement and general design details also, both of which contributed to a greater range than the Halifax for a given mission profile with the same fuel/bomb load.

The Halifax Mk III (Hercules engines) could have carried close to the same design bomb load (13,000 lbs) as the Merlin powered Lancaster Mk I/III (14,000 lbs), but over a shorter distance due to the less fuel efficient Hercules engines. The Lancaster Mk II (Hercules engines) had a noticeably shorter range than the Merlin powered Lancaster variants also, and a lower operational altitude.

Long answer, as far as I have been able to figure out:

At heavy loads the odd aerodynamic/engine power combination of the Halifax Mk II resulted in the Merlin powered variant not being able to reach the engine high speed supercharger rated altitude until a significant amount of the fuel had been burnt, and after reaching operational altitudes (20,000+ ft) at heavy loads the Merlin powered Halifax often had to use max cruise power instead of more efficient cruise settings. The drag reduction program for the Halifax Mk II Srs 1A overcame some of the problem, but not all of it.

For the Halifax Mk III, the reduced drag of the Mk II Srs 1A fuselage combined with the greater power of the Hercules engines at the altitude where the supercharger changed from low to high gear (and possibly the redesigned wing/engine nacelle arrangement), allowed the aircraft to continue climbing to the same operational altitudes as the Merlin powered variants, but the range decreased slightly for the same fuel load. So they installed more fuel tankage and increased the maximum TOGW to allow more fuel at TO with the same bomb load.

For the Lancaster the greater power of the Hercules engine was not enough to make up for the higher altitude rating of the Merlin XX series, since the aerodynamic/engine power combination did not require as much power as for the Halifax when climbing through the medium altitudes. Nor did the Lancaster require as much power for cruise at operational altitudes.

ie:

Engine___________Lo rated_________ gear change___________Hi rated__________Operational

Merlin XX series__ 1220@9,800______1060@12,200__________1070@17,000_____1010@20,000______2850 rpm @ +9 lbs Climb
__________________________________________________________________________ 860@20,000______2650 rpm @ +7 lbs Max Rich Cruise

Hercules VI/XVI___1400@4,750*_____1180@_ 9,200__________1300@13,500_____1030@20,000______2500 rpm @ +6 lbs Climb
__________________________________________________________________________ 950@20,000______2400 rpm @ +6 lbs Max Rich Cruise

*2400 rpm in low gear

From the above HP vs Altitude ratings you can see that in the supercharger gear change altitude range, the Merlin XX series only gives 1060 BHP, which apparently was not enough to get a heavily loaded Halifax Mk II above around 12,000-13,000 ft until a significant amount of fuel had been burnt off. This resulted in significantly reduced range for a given bomb load.

The Hercules powered Halifax MK III, however, could continue climbing steadily to operational altitudes, and once at 20,000 ft+ it still had more power available for approximately the same (or possibly less) drag. The Hercules powered variant could use the extra power to increase the operational altitude, or increase cruise speed, or the pilot could decrease the power to a more efficient cruise setting.

 

[33k in the air]

Thanks, while comparing the Stirling, Halifax and Lancaster, I also noticed that the Lancaster had the weakest engines of the three, yet the highest bombload, according to wikipedia.

Depends on what you mean by highest bomb load. The Lancaster bomb bay was spacious and undivided, allowing for a wide array of bomb loads to be carried. With bulged bomb bay doors it could carry the 8.000-lb HC bomb or 12,000-lb HC bomb. The Halifax fuselage bomb bay was not as spacious, and was originally divided into sections, limiting the largest bomb type that could be carried. It also had smaller wing bomb bays. Later modifications allowed the Halifax to carry the 8,000-lb HC bomb (although in the Halifax squadron ORBs I've gone through I've not yet seen that size of bomb carried; the maximum so far is the 2,000-lb HC. Presumably I have not yet looked at the appropriate squadrons).

How much ordnance which can be fitted into the bomb bay obviously will have an impact on its bombing figures.

Loads generally seemed to slightly improve over time, as ways were found to fit in more bombs. The Lancaster started out with a maximum of 14 x 500-lb bombs, but later on 18 were packed in. The most I've seen listed in a bomb load is 20 x 500-lb bombs.

 

[nuuumannn]

Short answer, the Lancaster was a slightly later design, with improved aerodynamics (mainly in the wing design, but possibly in the wing/engine nacelle arrangement and general design details also, both of which contributed to a greater range than the Halifax for a given mission profile with the same fuel/bomb load.

Essentially yes, Thomas, although the Lancaster was derived from the Manchester airframe, which required little change to create the latter aircraft, apart from main wings, carry through spars, engines and and hori-stab. Most of the problems the Manchester faced had been resolved by the time the Manchester Mk.III, renamed Lancaster appeared.

Putting it simply, the Halifax was a poor aerodynamic design with lots of issues because of choices made by the design team. The big issue that HP had was that it was underpowered and overloaded and in its initial incarnation could not meet the performance targets. It is worth remembering that the Halifax's story is far more complex than just fitting Hercules engines and voila, the type's problems disappeared. The Mk.III benefitted from two years of progressive development through the various modifications and even then there were aspects of the aircraft's design that meant it was always going to play second fiddle to the Lancaster.

The attempts at reducing drag began pretty much with the prototype and ran through each variant, with different sets of modifications being incorporated into the design through its development, these have been latterly referred to as "Series" mods, for example, B.I Series IA, B.II Series IA, which was the basis of the Mk.III, these changes being made on the production line, which induced delays to units. The biggest issue affecting the type from the outset was rudder overbalance, which killed test pilots and RAF crews alike. It was not solved until the introduction of the larger rudder, which was retrofitted to B.IIs as a field mod, but was incorporated into the B.III as standard. The rudder overbalance also meant that Halifaxes could not manoeuvre as stringently as a diving turn above a certain speed would induce this fatal ill.

One issue that meant the Halifax was not going to compete with the Lancaster was in its bomb bay design. the doors were divided into two sections as the contour of the lower fuselage meant long single span doors like on the Lanc/Manchester were not possible. As a result, the Halifax did not have two bomb bay doors, one on either side, it had eight, four on either side. Their actuation mean that precious space within the bomb bay was taken up by actuators and the lower set of doors that retracted and sat within the bomb bay. This meant that without modification, the Halifax could not carry any bomb with a diameter larger than standard bombs the RAF began the war with.

The B.II Series IA was the first to be rated to carry the 4,000 lb blockbuster, but the bomb bay doors had to be left open, which caused even more drag. A mod was created that bulged doors could be manufactured but the Air Ministry decided the Halifax didn't need the mod because there were sufficient Lancasters available to do the heavy lifting. Even with modifications like more powerful engines, the Halifax's load carrying capability hampered its development and the Lancaster's performance with a full load was still better than that of the Halifaxes with the more powerful engines.

Excuse the length of the post, but the Halifax was a victim of is own design failings, unfortunately.

 

[Simon Thomas]

If the designers in a company don't have a perfect crystal ball wrt. growth of engine power and fuel available, then why go for an oversized design in the 1st place? Every engineer worth it's salt knew that increase in size pushes both weight and drag up, that in return required more engine power, that again meant heavier engines that consume more fuel, all of that pushed the size, weight and drag up in a vicious spiral.

Short Brothers had the Empire flying with larger dimensions than the Stirling. It was adequate with Pegasus Xc engines, with 920 hp for takeoff.
Obviously the Stirling is a different ball of wax, but the fact that Empire did hit its performance targets first time did show that Gouge and his team were capable of successfully using a slide rule on large aircraft.

During early 1939, the all up weight of the Stirling had risen by some 9,000 lbs and was still creeping up due to the extra equipment required by the Air Ministry.
"Short Stirling, The First of the RAF Heavy Bombers" Pino Lombardi

I'm not blind to the Stirling's faults, however they are not all due to the failings of Short Brothers.

 

[Acheron]

Thank you all! I was overly focused exclusively on the output of the engines, but I understand now that there are quite a couple of other factors to an engine that can considerably influence the end result?