BRITISH WW2 MULTI-ROLE PLANE

 

© Anthony G Williams

 

This is a ‘what if’ exercise to devise an ‘ideal’ fantasy plane. The criteria are these:

  1. Starting in the mid-1930s, specify the design of one plane (which may have several variants) which would make the greatest difference to the effectiveness of the RAF and/or Fleet Air Arm.
  2. You must use existing, available equipment and technology.
  3. The design should be able to be made without clashing with other equipment priorities (especially over the use of engines).
  4. It must be capable of being upgraded so that, while it must be in full squadron service by early 1940, it remains useful throughout the war.
  5. You are allowed the benefit of hindsight in determining what would be most useful; you don’t have to be restricted to what 1930s designers would have known.

 

The Background

There is clearly no point in specifying a plane for a role which is already well covered. No need for a single-engined interceptor: the Spitfire was good enough. Similarly, no need for a fast light bomber / night fighter or a four-engined heavy, as the Mosquito and Lancaster were supreme in those fields. So the first task is to identify the gaps: for what tasks was a plane needed?

One clear gap is for a long range fighter. This would have been of great use in the Battle of Britain, in giving the fighter controllers greater flexibility in engaging the bomber streams over a longer period. It would also have been useful as an escort fighter, making precision daylight raids more feasible. And it would have had the capability of intervening in enemy air operations at ranges well beyond those which the RAF could historically manage. The RAF actually had the Westland Whirlwind (too small and short-ranged), the Bristol Beaufighter (too big and slow), the DH Mosquito (too big, not available in 1940 and too much in demand for other roles) and the superb DH Hornet (too late).

Another gap is for a dedicated ground attack aircraft, which could be used for the precision attack of enemy ground forces. This requires a rugged, well-protected design with a good range and the ability to carry a heavy warload. It must be compact to avoid presenting a big target, fast and agile enough to stand a chance against fighters and (at least) one version should be capable of carrying a heavy anti-tank gun. This would have been most useful in North Africa and Italy, and most particularly in NW Europe from D-day onwards. The RAF had no purpose-designed aircraft for this task: they made minor modifications to fighters instead, producing the Hurricane IID and IV and the Typhoon. Some use was also made of the Whirlwind (‘Whirlibomber’), which was also considered for carrying an anti-tank gun. Fighter-bombers were (the Hurricane excepted) able to defend themselves against fighters but were not well protected and the single-engined types did not make good carriers of heavy guns.

The final and perhaps most obvious group of roles concerns the Fleet Air Arm. The British not only gave carrier planes a low priority, they managed to get themselves into a real tangle over the specifications of the aircraft they wanted. For a long time, they insisted that even fighters had to carry a crew of two (to help with the navigation) and had to have a very long range. This led to the Fairey Fulmar (an adaptation of a light bomber design) which was only just adequate against weak opposition, and the Fairey Firefly, which was quite good but available too late. The FAA only learned the value of single-seat interceptors the hard way, when they acquired some in desperation and found them to be very effective. They also initially insisted that long range strike / reconnaissance planes should carry a crew of three. By the end of the war, attitudes had changed so much that they were willing to acquire single-seat strike planes, like the Blackburn Firebrand.

They were also very conscious that their carriers could carry few planes (partly because for doctrinal reasons they ignored the benefit of the ‘deck parks’ used extensively by the USN and IJN – until they learned from experience) so they tried to combine roles. This was a good idea, but the execution was poor. So you had the Blackburn Skua fighter / dive bomber, which was far too slow to be an effective fighter and could only carry a 500 lb bomb. Both the Fairey Albacore and the Fairey Barracuda were intended to combine the torpedo and dive bomber roles, but tended only to specialise in one (and weren’t very good anyway). If you except the remarkable Swordfish, whose ability to operate from small decks in terrible weather kept it useful throughout the war, the only really successful FAA planes were purchased from the USA (notably, the Grumman F4 Martlet / Wildcat) or adapted from RAF planes (Seafire). So there is considerable scope for a carefully-considered multi-role plane for the FAA – in fact every aspect of British carrier planes and their operation would benefit enormously from the application of hindsight.

 

The Choice

Which of these diverse roles should our plane be chosen to meet? Would it be possible to cover some, or even all, of them with variants of one design?

The key to the choice concerns whether a single or twin-engined design should be chosen. Most of the roles identified call for considerable power to provide the performance or payload required; a single-engined plane would therefore need a very large and powerful engine. Unfortunately, all of the engines in this class like the R-R Vulture, Napier Sabre and Bristol Centaurus had significant development problems and were far too late for our timescale anyway. This dictates a twin-engined design.

A compact twin is also appropriate for the ground-attack role as it permits a good forwards / downwards view and also facilitates the installation of heavy guns. Twins were more problematic for the FAA: they were opposed to them at first, although by the end of the war their views had changed so much that they were getting excited about the capabilities of a navalised Mosquito. Conventional twins were inherently awkward in carrier hangars as, even with wing-folding, they had a greater minimum width (over the nacelles) which meant that fewer of them could be carried. There were also difficulties in some carriers over the dimensions of the lifts to take the planes from the hangar to the flight deck; these varied quite a lot in FAA carriers. The carriers in service in 1939/40 had large lifts, but the first of the armoured-deck types had rather narrow ones although wider ones were fitted to later ships. Similarly, the FAA initially imposed severe all-up weight restrictions on carrier planes, although these were again gradually relaxed as the war progressed – from around 10,000 lbs up to 30,000 lbs.

A counter-argument to the resistance to carrier-borne twin-engined planes is that it would have been possible to achieve a combination of performance and load-carrying ability which would make each plane multi-role. So that while a given carrier might be only able to house, say, 36 twins rather than 48 singles, each of the planes could act as a fighter, strike or reconnaissance plane as required, whereas in actual FAA practice the same capabilities would have required two (certainly) or even three types of planes, each specialised for its purpose. In fact, the carriers tended to specialise in particular roles to keep the number of types down, but that of course restricted operational flexibility.

One possible solution to the carrier-plane size problem would be to use an unconventional twin design, with both engines contained within the fuselage. There are various possible layouts, such as having both engines driving one half of a contraprop, or one driving a pusher prop. Many of these were considered but only one got close to service in WW2 – the Dornier 335 – and it was clear that such layouts involved considerable technical risk and long development. They also lost some of the advantages of a conventional twin, namely the downwards / forwards view (valuable in a carrier plane as well as for ground attack) and the ability to carry heavy guns on the centreline. So our twin should remain conventional.

 

The Specification

We now have the outline of a specification which could in principle meet all of the identified gaps in RAF and FAA provision: a conventional twin. What other considerations need to be taken into account?

First, it must be as compact as possible, both for the carrier and ground-attack roles and to permit a high performance, but it mustn’t be so small that (like the Whirlwind) it has insufficient payload / range. Most versions will be single-seaters although the possibility of adding a second seat should be retained for some roles (e.g. if it is needed as a night fighter).

Secondly, it needs to have a good short-field performance with a low stalling speed and good low-speed controllability for the naval role, and also for ground attack where it might need to operate from rough forward air strips. This provides a problem for the wing design, as the high lift necessary to achieve this (and take off with heavy warloads) conflicts with the type of wing needed for high speed. Some technology would need to be applied here: the wing should be fairly small and have a thin, high-speed section, but needs extensive high-lift devices for take-off and landing: the biggest extending flaps linked to leading-edge slots which can be installed. The twin-engined layout helps here, as the prop-wash is fully directed over the wings thereby enhancing low-speed lift. In the interests of controllability, a twin-fin design should be adopted so that the rudders are also in the prop-wash. The short-field performance also requires robust, long-stroke, well-damped undercarriage.

The third requirement concerns pilot location. This should be well forwards, with the gun breeches and ammunition located behind the cockpit and the gun barrels running underneath it or to the side (e.g. like the Beaufighter and Hornet).  This is a better than the ‘guns-forward’ layout adopted for the Whirlwind and Lockheed P-38 Lightning, since it provides a better forwards and downwards view, puts the ammunition weight closer to the centre of lift so that handling isn’t affected as the ammo is used up, prevents the pilot from being blinded by muzzle flash in night fighting, and provides more flexibility to install bigger guns. The pilot should be in a ‘bubble’ type canopy to give a good all-round view.

Fourthly, the need to carry large and heavy warloads (especially a torpedo) dictates a low-wing design with the engine nacelles mainly under the wing, to give sufficient clearance under the fuselage. For the same reason, a long (and therefore retractable) tailwheel strut should be fitted. The low wing and nacelles would also enhance pilot vision. A tricycle undercarriage would not be appropriate, partly because the nose wheel could interfere with the gun layout and torpedo carrying, partly because of the weight it would add, and partly because of design risk: there was no British experience with this layout in the mid-1930s.

Next, the engine. The obvious choice is the R-R Merlin, but that was in great demand for other planes initially, and being liquid-cooled was not well suited to the ground-attack role or (to a lesser extent) carrier use. The Bristol Hercules was too big and heavy for a compact twin. The R-R Peregrine, as used by the Whirlwind, was a possibility but like the air-cooled Exe suffered from R-R’s design overload problems and development was discontinued. The obvious choice was therefore the Bristol Taurus, a two-row, 14 cylinder, sleeve-valve air-cooled radial. It had almost the same engine capacity as the Merlin. It was not in particular demand, but was kept in development and production for the Bristol Beaufort (it was also used in the Fairey Albacore). It initially produced over 1,000 hp, later increased to more than 1,100, but as it was being used in a bomber it was not allocated the high-octane fuel reserved for high-performance planes (so boost was limited to +4.5 psi), which would have permitted much more power as the war progressed: however, the most powerful proposed variant produced 1,250 hp, so this will be taken as the potential. Being air-cooled, it was particularly suited to the ground attack and naval roles. It weighed much the same as the Merlin (dry) so the potential would exist of producing a Merlin-powered variant for advanced (and especially high-altitude) fighters purposes later on.

Finally, the armament. The development of the plane would coincide nicely with the RAF’s plans to acquire 20mm cannon, for which it would be an ideal candidate as rigid, fuselage mounting would avoid the problems encountered with wing-mounting. The first installation could be made in 1939 so the aim would be to get the cannon plane in full service in time for the Battle of Britain – with devastating consequences for the Luftwaffe’s bombers. From existing designs it can be seen that the RAF required at least four 20mm cannon. The preferred layout would have two guns under the cockpit located as close together as possible, with another on each side. Ammunition capacity would be around 180 rpg once the belt-feed mechanism was available in early 1941. The ground attack version would replace the two centre guns with one anti-tank gun. Initially, this would be the 40mm Vickers S. The Vickers only saw service with a 15-round magazine but a 30-round magazine and a belt feed were developed for it, and there would obviously be room for them in the fuselage. Later anti-tank variants (1943+) should adopt the formidable American 37mm M9 gun (developed for but never used by the USAAF – and therefore available). A significant advantage over other big-gun anti-tank planes is that the S gun weighed 295 lb compared with 220 lbs for the two Hispanos it would replace, so this model would still be able to carry a substantial warload of rockets or bombs as well as the big gun (the M9 weighed 400 lb, reducing the rest of the warload by only 180 lb).

One specific armament issue concerns the torpedo: in the late 1930s the FAA’s standard aerial torpedo was restricted to a very low dropping speed and altitude. However, the FAA steadily increased the requirements during the war and it seems likely that if they acquired a very high-speed torpedo-bomber, greater urgency would have been given to these developments.

 

Variants

Our plane will clearly be available in at least three major variants: fighter, ground attack and naval plane – with several sub-variants being likely. The following is a list of major types and possible sub-types:

Scope would exist for other variants on a ‘mix and match’ basis: for example, the standard fighter variant with the 1 x 37mm M9 (firing HE) and 2 x 20mm armament from the fighter-bomber would make a devastating bomber destroyer should such a plane be required.

 

Comparisons

We now need to estimate some dimensions, weights and performance for the plane, and see how it compares with other designs. The obvious comparator is the Gloster G.39, initially designed to specification F.9/37, which was a single-seat fighter with two Taurus engines and a twin-fin tail. The prototype demonstrated excellent performance and handling (360 mph on 2 x 1,050 hp) but this model was not one of the few selected for mass production in the run-up to the war. The Gloster was designed for no less than five 20mm cannon (two under the cockpit, three above, and all angled upwards for the contemporary fad of ‘no-allowance’ shooting). The cockpit was front-mounted, but (like the Beaufighter) was buried within the fuselage providing no rearward visibility.

Other obvious comparators are the smaller Whirlwind, the Lockheed P-38 (a heavier and more powerful plane), and two interesting prototype planes which never made production: the Focke-Wulf Fw 187 and the Grumman XF5F / XP-50 Skyrocket.

Comparative details are as follows:

 

 

Gloster G.39

Westland Whirlwind

Lockheed P-38F

Lockheed P-38H

Focke-Wulf 187

Grumman XF5F (XP-50)

Empty weight lb

8,830

7,840

12,264

12,780

8,160

8,000 (8,200)

Loaded weight (max take-off)

11,600

10,400 (11,400)

15,900

17,500 (21,600)

11,000

10-11,000 (12-13,000)

Wingspan

50

45

52

52

50

42

Length

37

31.5

37.9

37.9

36.5

28.7 (33)

Height

11.6

10.9

9.9

9.9

12.6

11.3

Wing area sqft

386

250

327

327

327

303

Wing loading (lb / sqft)

30

41-46

49

54

34

33 (40)

Power/weight

(bhp / ton)

404

385

345

365

286

538 (447)

Power bhp

2,100

1,770

2,450

2,850

1,400

2,400

Max speed mph

360

360

395

414

326

383 (427)

 

Two other planes are worth listing for comparative purposes: Supermarine's Type 324, an unbuilt project to specification F.18/37, which is of interest as it was a fighter intended for either Taurus or Merlin engines, and of course the superb DH Hornet twin-Merlin fighter of 1945, which the later models of our 'ideal' fighter variant would effectively make unnecessary.

 

 

Supermarine Type 324 (Taurus engines)

Supermarine Type 324 (Merlin engines)

DH Hornet

Empty weight lbs

? ? 12,800

Loaded weight (max take-off)

10,000 10,800 17,900

Wingspan

41 41 45

Length

31.5 32 37

Height

? ? 14.1

Wing area sqft

290 290 361

Wing loading (lb / sqft)

35 37 50

Power/weight

(bhp / ton)

560 525 517

Power bhp

2,500 2,530 4,140

Max speed mph

421 450 472

 

After comparing these planes, it is obvious that the Whirlwind was too small, the Gloster G.39 probably a bit too large (certainly in terms of wing area). The Fw 187 looks close to our needs (the V6 prototype did have more powerful engines with a better performance – but it used impractical evaporative cooling) as does the Skyrocket (the XP-50 being faster than the XF5F as it had a longer and more pointed nose).

This suggests that our ideal plane should have the following characteristics (the naval and ground-attack variants are grouped as they have similar weights: the extra weight of wing-folding and arrestor hook being balanced by the GA plane’s extra armour):

 

 

Fighter (early)

Fighter (Merlins)

Ground attack and naval (early)

Ground attack and naval (late)

Empty weight

8,500

10,000

9,500

10,000

Loaded weight

11,500

15,000

13,500

15,000

Wingspan

47

Length

37

Height

12

Wing area sqft

325

Wing loading (lb/sqft)

35

46

42

46

Power/weight

(bhp / ton)

412

507

350

420

Power

2,100

3,400

2,100

2,500

Max speed

375

450

350

375

 

Interestingly, the weights and dimensions of the naval variant are very similar to those of several single-engined planes which saw FAA service in the latter part of the war: the Fairey Barracuda (bigger wing, much less powerful), and the Fairey Firefly, Grumman F6F Hellcat and the Chance-Vought Corsair.

By comparison with the Allied fighter-bombers, our ground-attack plane would have similar empty and loaded weights to the Hawker Typhoon and Republic P-47D Thunderbolt, but be slightly larger.

What would our plane look like? I am no artist, but imagine a Gloster G.39 with a smaller wing and a slightly more slender fuselage with a pointed nose and raised cockpit more like the DH Hornet (although the canopy would initially be of the multi-pane type, like the Whirlwind’s, rather than the blown ‘bubble’ type). The engine nacelles would be as close together as possible in the interests of compactness (especially with wings folded) which might require four-bladed props for more powerful versions.

 

Conclusion

So we end up with potentially one of the most versatile planes of the war. Interestingly, no air force developed exactly such a plane. The P-38 comes close, but its more vulnerable engine installation made it less well-suited to the ground attack role, it was never a naval plane, and its armament layout was less versatile. The Grumman XF5F/ XP-50 Skyrocket looks as if it might have come very close had it been developed, as does the Fw 187 (although that was designed purely as a fighter).

How feasible was our plane? Technically, there was no reason to doubt that it was possible. The main practical objections would have been to the naval version, concerning the size and weight limits imposed on RN carrier planes until later in the war. As already noted, the first of the new Illustrious-class armoured-deck carriers initially had small lifts, no larger than 45 x 22 feet. Judging from drawings, the nearest comparator - the XF5F Skyrocket - measured about 21 feet wide with wings folded and it should have been possible to reduce this slightly with our 'ideal' plane, but it would clearly have been a tight squeeze. In the event, the size and weight limits were extended later in the war in the light of experience and the USN practice of deck parks became accepted.

What chance would it have had of making it into service? The ideal scenario would have gone something like this: Gloster would have been the obvious company to develop such a plane, as their G.39 was so similar (and they weren’t involved with other vital projects). They would ideally have submitted the design in 1935 to meet Specification F.37/35 (for a cannon fighter) which was won by the Westland Whirlwind (Gloster historically did not compete for this contract). So our plane’s first task would be to beat the Whirlwind for the cannon-fighter role, which it should be able to do given its superior performance and range. Having become established in 1940 in the Battle of Britain, it would then be in a good position to get the nod for modification to a fighter-bomber and anti-tank plane in 1941, as it was manifestly more suitable for the role than the Hurricane. The main problem would have been with the FAA, which didn’t want a twin-engined plane. However, if it had first become established as a versatile RAF plane (like the Mosquito), and a navalised version was offered when the FAA was desperate for decent planes - perhaps in 1942 when the Seafire was adopted - then it should have stood a chance.

 

P.S. In case anyone was wondering why this plane didn’t feature in my alternative WW2 novel, ‘The Foresight War’, it is because that started from a different premise: that in the interests of efficient production, front-line piston engines should be restricted to the Merlin and the Hercules while turbine engines were being developed. The roles identified in this article were therefore covered in different ways.

 

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