Short Stirling, a good or a bad aircraft?

I think people are getting confused about the taper. It's not to prevent the tail striking the ground. It's a TAILWHEEL aircraft, the tail has already struck the ground but there is a wheel in the way. That only aplies to nosewheel aircraft where the tail goes down as the nose rotates up.

I think it's simply a case of why waste resources and add weight keeping the fuselage the same size when all you need is it wide enough for a man to get down to the tail gun and operate it. Why taper it up ? Probably aerodynamics or simply the fact that the crawlway is above the bombbay so why add complication by sloping the crawl space downward.

Slightly broken back appearance;



Upward taper may be to keep fuselage depth for strength or provide crawl space over tailplane or since the turret is a certain height , to provide a smooth transition to turret roof rather than a sudden hump just before turret ( given the dorsal turret the last is a bit of a stretch) or some combination or other reason.

Its possibly there to make space for the ventral turret which was to be a retractable dustbin type originally.

As well as the short wingspan and short range, I think one of the Stirlings biggest handicaps was the structure of its bomb bay which would make it impossible to carry larger munitions. For example it could not accommodate a Cookie, but half-the-size Mosquito could.

This image of the Stirling overlaid on the Halifax and Lancaster says it all:
File:British WW2 bombers comparison.png - Wikipedia, the free encyclopedia
It was a huge, draggy design. The empty weight of a Stirling was 4,000 lb greater than a Lancaster (10% more) which explains the much shorter range for an equivalent bomb load. The additional drag and weight of a longer span wing would have reduced the practical war load to a minuscule amount. Its interesting to compare it to the Supermarine design to the same specification which is a much much sleeker design.
The fact that it used the Hercules while the Lancaster used the Merlin is irrelevant. The Lancaster used the Merlin powered Beaufighter power eggs developed by Rolls Royce which were designed to be interchangeable with the Hercules, hence the first Hercules powered Lancaster flew at the end of 1941 and entered service a year before the Halifax III.

how does the Stirling rate compared to its contemporaries. it commenced entering squadron servic in the latter part of 1940, at least 15 months before the Lancaster, and some months before the Halifax. That entry to service date which makes it a contemporary to to the B-17C does it not. how would the early versions of the B-17 have faired in sustained operations over Germany?

how does the Stirling rate compared to its contemporaries.

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That's a very good question, Parsifal; at the time there weren't too many four engined bombers the size of and with the load carrying capabilities of the Stirling in air forces around the world when it entered service. The Stirling was quite advanced in many ways compared to its contemporaries; like I've stated in relation to other British bombers of the time, in the first year of the war the British were the only ones to equip their heavy bombers with power operated turrets as defensive armament.

At the time, despite Bomber Command's poor bombing average, apart from the Luftwaffe, no other air force in the world had more experience in heavy bombing by night and the Stirling certainly upped the ante in terms of what could be delivered on a target en masse, but despite its promise or because of its inadequacies, it was not the aeroplane the bomber squadrons really needed. If only the British could adequately find the target and hit it convincingly, the biggest problem that plagued Bomber Command at the time.

A few months ago I read the excellent book on the Stirling written by Pino Lombardi (Short Stirling: The First of the RAF Heavy Bombers), and I would like to throw my 2 cents on the high altitude performance issue.

Many sources point out that the Stirling's lack of performance was caused by the enforced limitation of the wingspan. On the other hand, this also applied to the Lancaster and Halifax.
I have put together a table comparing the specs. The wingspan is literally the same for all 3, and the later versions of Stirling use the same engine as the Halifax.



I am inclined to think that the lack of high altitude performance is caused by the larger dimensions and especially the empty weight. The Stirling Mk I was 25% heavier than the Halifax/Lancaster, thus for a typical mission with similar bomb load/fuel it's TO weight would be higher. The larger wing area would mitigate the effect but the engine output in Mk I was also lower than for the Halifax (not so sure abut Lancaster) . Mk III was better, but RAF was not really interested due to limitations in the bomb bay.

Well, you may be on to something, although I think the wing may have something to do with it. It is probably a combination of things.

The aspect ratio of the Stirling is about 6.5, the aspect ratio of the Lancaster is 8.0. so the Lancaster wing is more efficient if they were the same area (as we know they are not) but the Lancaster is more efficient for it's size.

The Stirlings fuselage is huge, lots of drag. Since lift goes up with the square of the speed, changing from a 200mph cruise to a 210mph cruise gives about a 10% increase in lift. Numbers are just to illustrate the point, plug in real cruise numbers as you see fit.

Weight may have something to do with it but the weight, at least on the trip to the target may be close, the lower payload (actual amount of bombs that could be carried over the desired distance) is certainly lower for the Stirling but the actual weight of the aircraft, if both took off at nearly the same weight isn't going to be that far off (Stirling is burning a bit more fuel?) , On the trip back with bombs gone and over 1/2 the fuel gone the Stirling will certainly be much heavier.

I Could be wrong and there are probably a few things I overlooked.

The table answers most of it, the Stirling had 6 meters and 4 tons more airframe and also a bigger fuel load but the same MTOW as the Lancaster.

As I understand it the Stirling specification required that it be able to carry it's own ground crew and spares inside it so that it could be rapidly deployed to any airfield in the Empire large enough to take it. Hence also it was expected to be able to be serviced in all climates with no hangarage. This led to the large fuselage.

The limit on the size of the bombs was simply that it only needed to take the largest bombs held in store or due for production. In a Coastal Command context it would be easy to replace the wing bomb cells with extra fuel as the bomb bay was quite adequate for depth charges and mines. The bomb cell in the period thick wings was normal in the day, appearing in the Battle, Whitley and notably the Supermarine 12/36 competitor.

The maximum bomb load was truly impressive in it's day. That it could only be carried for a fairly short distance was reasonable as the fall of France was not foreseen and the Stirling would have operated from French airfields which were far closer to industrial targets in Germany to deliver that very large bomb load.

So in 1935/6 it fitted the specifications drawn up and these were reasonable in the context of the day.

It is interesting to note that, when faced with an excessive take off, run Short went for a longer undercarriage to increase the wing incidence on the ground and a level incidence in the air whilst Armstrong Whitworth chose to change the wing to a greater incidence on the ground with a short under carriage and the result was a marked nose down fuselage in the air. What was not foreseen was the building of so many longer runways that did not require the extra wing incidence to reduce the take off distance.

The 13/36 requirement, IIRC, included a requirement to carry two torpedos and hence needed a wider open space than needed for normal bombs in the Manchester and Halifax. Thus the Stirling had nothing larger than free fall bombs and mines to carry and made good use of that to incorporate the bomb stowage into it's strong structure. This also meant that it had a very strong and rigid fuselage floor, ideal for transport of cargo and superior to the other large aeroplanes in production for that task and with no need for great altitude performance in the role.

All in all it was a very good piece of work for what the Air Ministry wanted it to do. However reality failed to match those intents. In actual use it should have been updated for the new needs but it retained qualities that made continuing production correct as it was progressively withdrawn from use as a heavy bomber.

The biggest issue for the Stirling is that it just kept getting heavier. In 1939 Shorts were alarmed by an increase in weight of 9,200 lb (5,700 lb structure, 1,800 lb balloon cutters and de-icers, 300 lb extra flaps). Normal loaded weight had risen to almost 53,000 lb, close to the maximum permissible take off weight!

Tests at Boscombe down in the summer of 1940, with a take off weight of 57,400 lb, showed a take of run to 'unstick' of 640 yards, 1,200 yards to clear 50' and a service ceiling of 15,000'. None of these figures caused as much alarm as the low ceiling which was considered to make the aircraft, in its present condition, effectively useless for operations. It also took almost half an hour to get to 15,000' where the true maximum air speed was a mere 218 mph. Most economical cruise speed at 10,000' was just 158 mph TAS.

The aircraft's performance fell well below that specified in terms of load to be carried. It was supposed to have a maximum bomb load/range of 14,000lb for 2,000 miles. The reality was 14,000 lb for a mere 740 miles. The maximum range/bomb load figures were just as bad, specified was 3,000 miles with 8,000 lb, the reality was 1,930 miles with 5,000 lb.

The Stirling came just before its time. It was a step too far. It was not a terrible aircraft, the specifications were almost impossible to meet with the technology and engines available at the time. The most remarkable thing about the Stirling is that it was still flying to Germany, right up to the Battle of Berlin, and continued in service with the RAF until July 1946.

Cheers

Steve

It has been a long time since I read the Air Ministry specification that resulted in the Stirling, but I seem to recall that it required the carriage of 4 aerial torpedoes, which would be part of the reason for the long shallow bomb bay.

Also, the specification originally called for the ability to be catapult launched, which would be part of the reason for the high weight and also the high AOA imposed by the landing gear. Apparently there was some concern about the availability of long enough airfields, particularly in foreign countries .

Nice summary by Barnes (Shorts Aircraft - Putnam -1967) as to why Gouge had to go with increasing the undercart height rather than adjust the wing incidence...

(The Martlesham test pilots are talking about the S.31 handling qualities)

IIRC the Stirling was designed to be able to operate as a bomber out of all RAF airfields around the globe, so short wing and large wing area to get it off the ground quickly. Also it had to be able to transports troops quickly to anywhere in our global empire. The F-111 and MRCA-75 Tornado being much later and just as successful examples of multi role combat aircraft.

The problem with lengthening the undercarriage, with what Michael Bowyer aptly describes as "an amazing array of folding struts, girders and a crate which retracted both backwards and forwards" was that it was bound to cause trouble on wet airfields or in cross winds, and it did. Stick some enormous tyres on, for operation from grass fields, and you also have a pilot sitting more than 20' above the ground!

The Stirling was built to B.12/36. A torpedo carrying capability was not specified but it certainly specified the ability to carry seven 2,000 lb AP bombs, to support the Navy. A wide range of bomb loads was specified for various conditions including various combinations of 250 lb GP/SAP/AS/LCB, 500lb GP/SAP/AS and the 2,000 lb AP bombs. Specification P.13/36 required the carrying of torpedoes. The Avro Manchester was built to this, which is why the Lancaster had such a long, open bomb bay.

The original intention was for what would become the Stirling to have a maximum take off weight, when catapult launched of just 46,000 lb. This was exceeded by a very large margin in reality, and there never was a catapult launch. The minutes of a meeting of the Operational Requirements Committee in May 1936 show that the weight and size of the new bomber(s) was discussed in terms of operational feasibility, not bombing policy.

Can we address the often repeated assertion that wing span was limited in the specification by hangar size? It was not. This goes back to Sir John Salmond's concerns, in 1931, about getting the Sidestrand replacement (Specification B.9/32) "into our sheds", but it was only the size of Expeditionary Force hangars that was relevant.
The Air Ministry allowed the Wellington, also built to B.9/32, to have an 86' wing span, well above the 70' specified.
It is a fact that prior to 1934, before these specifications were written, The RAF's largest general service hangars (Type A) had door opening of 120' at both ends. The new Type C hangar then under consideration had a door opening of 150'. It is true that the smaller general service hangar then in use had an opening of 100', but surely I don't need to point out the absurdity of designing an aircraft with exactly the same wingspan as the hangar opening if the hangar opening was a limiting factor!

The reason that the 100' limit was proposed in 1936 was simply to stop the aircraft from getting too large. The RAF had expressed concerns that two large transports designed to C.16/28 (one was the Handley Page HP 43 at 114') were too unwieldly for ground handling.
The opening paragraph of B.12/36 states "Since it will be required to operate from bases anywhere in the world the aircraft must possess good facilities for maintenance in the open". Not much concern for hangar space there.
In October 1936 the Air staff proposed that a development of the B.12/36 heavy bomber, without any limit on wingspan, should be included in the 1937 Experimental Aircraft Programme. Again, no concern for hangar size.

I blame Harris, who does seem to have believed that some policy related to hangar size existed, at least he made scathing comments about it.

Cheers

Steve

The low service ceiling must also have been related to the power (or lack thereof) of the Bristol Hercules, especially in the early versions.

And particularly at altitude.

The Halifax VI with Hercules 100 had a service ceiling, at maximum weight, of 20,000ft, The Halifax III had the same ceiling at a lower maximum weight and with the less powerful Hercules XVI, which had a critical altitude of 12,000ft in FS gear.

http://www.wwiiaircraftperformance.org/Halifax/Halifax_VI_ADS.jpg
http://www.wwiiaircraftperformance.org/Halifax/Halifax_III_ADS.jpg

Kevin J said:

IIRC the Stirling was designed to be able to operate as a bomber out of all RAF airfields around the globe, so short wing and large wing area to get it off the ground quickly. Also it had to be able to transports troops quickly to anywhere in our global empire.

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Favorable wing loading gets you off the ground quickly. A big & heavy fuselage worsens the wing loading, hence Stirling was not good in task of shortening the take off distance.
We also have almost total ignoring of existence of high-lift devices by the design team.

The F-111 and MRCA-75 Tornado being much later and just as successful examples of multi role combat aircraft.

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F-111s and Tornado IDS were lousy fighters. Tornado ADV was a lousy bomber.

tomo pauk said:

Favorable wing loading gets you off the ground quickly. A big & heavy fuselage worsens the wing loading, hence Stirling was not good in task of shortening the take off distance.
We also have almost total ignoring of existence of high-lift devices by the design team.



F-111s and Tornado IDS were lousy fighters. Tornado ADV was a lousy bomber.

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I'm a Brit, so sarcasm about those later successful fighters. LOL. So the Stirling became a troop carrier and glider tug. What a surprise. Now back to the original spec.....

wuzak said:

The low service ceiling must also have been related to the power (or lack thereof) of the Bristol Hercules, especially in the early versions.

And particularly at altitude.

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The prototype Stirling had the Hercules HE I M engines. In 1937 the proposed alternative was the Napier Dagger, which would have been interesting. In 1940 then Armstrong Siddeley Deerhound was also considered.

The first production Stirlings got Hercules Mk II engines as Bristol failed to deliver the promised Mk IIIs. The figures posted by me earlier are for aircraft with the Mk II Hercules fitted. After these results hopes were pinned on engine development and the better performance expected from the Hercules Mk III. It was not to be. When N3662 was tested with Hercules XI engines and an auw of 62,400 lbs, it proved impossible to reduce engine revs from 2,500 to 2,300 for cruise and maintain an altitude of 15,000'.

Cheers

Steve