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2014.07.13



 

Notes

 

 
 
 

J21RN

GAM (Vulture)

 
The story which didn't happen ... outside Atlantic Air Combat
 
 
  See also : J21RN Gam Serials Land Variants
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Carrier Variants
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Introduction
By end of the Korean War, it had became clear for Sweden that more trouble was looming up in Europe, especially with the USSR going ahead with their plans to build up a fleet of aircraft carriers.  While the Baltic is not exactly a place to safely operate a carrier, it does offer additional air capabilities to reach out at sea and protect the mainland

But in addition of offering addtional assets on their Eastern flank, Sweden saw the potential danger also coming from the North with Soviet troops coming through neighbouring Finland or even Norway.  Also, an increasingly strong and potent Soviet Navy was a clear threat to Sweden's shipping lanes in the Artic and North Seas (Norway, Scotland, Iceland) and accross the Atlantic (Canada, United States).  So, while the debate had been going on for some time

regarding whether or not to scrap, maintain or develop their "blue water" navy (re: the three Sverige class, and the two Tre Kronor class cruisers), Sweden eventually decided early 1956 to strengthen their navy, and acquire aircraft carriers with the main purpose to enhance their anti-shipping capabilities in the Artic, and, to a lesser extent, provide a platform for anti-submarines aircrafts.  This decision lead to the A2 HMS Gotland and A3 HMS Lappland, the story of which is covered elsewhere in these ... fantasy Notes.

But while it was a bold move, funding wasn't available in an unrestricted manner, and aircrafts were to be sought second hand from allies, most likely from United Kingdom although the Navy had been given somewhat a free hand to identify which aircraft would be appropriate.  Not a simple task considering the modest size of the Colossus class carriers retained.  Hawker Sea Hawks were considered but besides the Fleet Air Arm not willing - at that time - to relinquish them, this fighter was considered a bit too limited in weapons carrying capacity, a least not without a major rebuilt.  After poundering the matter for a while, the Navy submitted the following request to the Government (re-using some abandoned numbers within the Swedish Air Force aircraft numbering system) : 
 the "urgent" purchase of the remaining Supermarine Attackers from the FAA - J23 (± airframes)
 the no less urgent freeze of the scrap programme of the J21A and A21R from the Swedish Air Force
    the rebuilt by SAAB of the two above aircrafts to respectively fulfill the fighter and attack roles
 the purchase of new built Fairey Gannett (or alternatively Blackburn B88) for ASW and AEW missions - B24/S24
    the French Alizé was an alternative but the Douglas Skyraider wasn't
 the purchase of Sikorsky CH-46 SeaKnight for commando missions - Hkp4
 the purchase of Supermarine Seagull to fullfill both the SAR and COD missions - Tp27
 the purchase of Westland Wasp for PEDRO operations and as a secondary ASW asset. - Hkp7

This was not exactly what the Swedish Government had expected but the Navy could not be blamed to respond to the question asked, and the Government had to convene that no second hand aircrafts were available to fullfill all the missions, especially when it comes to such specialized airframes for the ASW role.  The suggestion to acquire the remaining Supermarine Attackers as defense fighers came as a surprise but the Navy wanted to remain conservative and although swept wing fighters were flourishing in naval aviation as in modern air forces, straight wing fighters weren't necessarily to be ruled out.   Besides, SAAB was considered already too busy with the upgrading of J29, combined with the production of the J32 and the planning of the J35 to further ask them a new design.   

Maybe a navalized version of the J29 could be feasible, but the Air Force was certainly not enthusiast about giving up airframes (as the tensions were slowly mounting, the Air Force would rather wish to have more of them), and the promise of the Swedish Government to make them available to Finland, should the need arises was enough a strain.  The same applied to a would be navalized version of the new J32, and anyway these would essentially be new airframes rather than second hand ones so the very idea wasn't within the framework specified by the Government.   Moreover, while the actual simplicity of the J21 made a navalized version feasible, navalizing more complex contemporary designs like the J29 or J32 actually meant thoroughly redesigning the airplanes, while the simple but sturdy J21 lend itself to a beefing up programme, even if wasn't a straighforward task neither.   Finally, while the Saab 32 Lansen would probably offer the best balance of performances, its size compared negatively with the numble dimensions of the J21.   And the chosen Colossus carriers weren't as large as one would think...

More hopes were thus placed in the rebuilding of the A21R (or J21A for that matter) which had proved to be a very capable attack aircraft, and the Supermarine Attackers, which while as much old fashioned as the J21 with their straight wing and ... tail wheels, had shown to be fast, reliable and agile.  With not too many A21R airframes being available for conversion, the Attackers could would play an interim role or as a welcome supplement, hence the request to purchase all 100 remaining airframes immediately.

While the rebuilding (and re-engining) of the J21 would naturally to be entrusted to their original manufacturer, SAAB already being over busy with various programs, the Navy requested that the Kungliga Flygförvaltningens Flygverkstad i Stockholm should be revived to look after the Supermarine aircrafts.

All this would be time consuming, but as the refit of the aircraft carriers themselves would take several years, it should allow both manufacturers to delivers the upgraded airframes by the end of 1959, the assigned target date.   Acquiring new aircrafts to fullfil the other roles assigned to the carriers then seemed a much easier task.

The Saab J21RN

In accordance with the Swedish Air Force practice of three 8-aircrafts squadrons (plus 4 reserve and 4 attrition airframes) for each Fighter Wing, the Navy was looking to have 2 operational wings, fulfilling both the carrier deployments, type conversions and training, meaning they were looking for 96 operational aircrafts, much more than the original 64 airframes converted to either J21RA or J21RB standards, and not all of them had survived.   But as the Air Force had been retiring all J21 variants, including the piston engined J21A and hadn't had the time to scrap them all, there was fortunately enough airframes available for the task, even if the conversion from a J21A naturally was a heavier one.

The upgrade/rebuild was to address the following issues
:
 complete strip down of the aircraft to apply specific anti-corrosion protection
 reinforcing the airframes to withstand the punishment of repetitive carrier landings and ... make them last
 reinforcing the wings to carry more fuel and ordnance and incorporate a folding mechanism
 beef up the engine for increase power or replace them altogether
 improve the cockpit layout to make it compatible with carrier operations
 provide for an air-to-surface search radar with secondary air-to-air capabilities
 revise the internal armament set set up
 provide for air-to-air and air-to-surface missiles

Engine Replacement
There was little to be done to improve the Goblin 3 engine (or Volvo produced RM1A), so it either had to be maintained or replaced.  As more thrust was required to turn the J21 into a more potent warrior, a replacement was inevitable.  Consideration was essentially given to other centrifugal-type engines, to avoid having to reconstruct completely the airframe around a totally different engine.  However promising the locally designed STAL  (Swedish Turbine AB Ljungström) Dovern.IIB seemed to be, it clearly didnt fit the picture.   

Maybe as a compensation, STAL was tasked with the engine issued, and invited to review both the Roll Royce RB44 Tay (in its Hispano Suiza Verdon 450 format) and the Roll Royce RB41 Nene (more precisely the Pratt & Whitney J42PW6 version) engines in order to produce one of them - or both - under license for J21RN and/or the J23AN (Supermarine Attacker)

Make

Engine

Thrust
Dry-Kgp

Thrust
Wet-Kgp

   Ø   
mm

Length
mm

Weight
kg

Consumption
kg/Hr/Kgp

 










DH

Goblin 3

1498

-

1270

2718

703

1.30

-

SFA RM1A

2409

DH

Ghost 50

2270

-

1346

3073

1007

1.02

-

SFA RM2

RR

Nene.103

2361

-

1257

2460

700

1.06

-

PW J42PW6

2701

-

1.06 -

STAL RM3A

2685

-

0.92 -

STAL

Dovern.IIB

3300

-

1095

3850

1195

0.92

-

STAL RM4

RR

RB44 Tay

3507

-

1270

2621

935

1.10

-

PW J48PW8

3292

-

2621

1.10 -

STAL RM7/J48SW9

3430

-

2621

0.92 -

Although it involved some weight penalty, the RB44 Tay offered significantly more thrust while roughly being of a size similar to the Rolls royce Goblin or Nene.  With the assistance of Pratt & Whitney, STAL further developped the engine, inducing a sizeable reduction in SFC while almost equalling the thrust of the original RB44.  Under the designation of RM7, the engine was thus chosen for both the J21RN (replacing the Goblin/RM1) and the J23AN/Supermarine Attacker (replacing the Nene 101/102)

Cockpit

Partly to enhance visibility for the pilot, and partly as cosmetic change to alther ... the perception of the aircraft, which was seen as "obsolete" by some, the cockpit layout was completely revised.   Slightly raised, and covered with a bubble canopy, it indeed completely changed the aircraft appearance.   Its electrically operated sliding canopy could be opened in flight (eg: for landing) and more importantly, it was now pressurized and fully air conditioned.

Internal Weapons Review

Originally, the J21 had been equipped with five AKAN M44 13.2mm machine guns, a licence copy of a Belgian FN machine gun, itself a copy of a Browing gun, and single AKAN M47 20mm cannon, a locally produced copy of the Hispano Suiza gun.  Later, many 13.2mm guns were rechambered in 50cal as this caliber became some sort of standard and ammunitions were commonly available.  To make matters more intricated, the Supermarine Attackers were equipped with Hispano Suiza MkV 20mm guns.  Considering the two types would operate along each other, the Navy wondered if some standardization could be achieved, and examined various options, including the unlikely purchase of new weapons : 

> Wing.L Wing.L Rpg Nose.L Rpg Nose.C Rpg Nose.R Rpg Wing.R Rpg T













J21A

Guns M44 180 M44 180 M47 140 M44 180 M44 180  
  Rpm 900   900   700   900   900   4300
  Weight 25kg 14kg 25kg 14kg 43kg 36kg 25kg 14kg 25kg 14kg 235kg

J21R

Guns ANM2 175 ANM2 175 M47 140 ANM2 175 ANM2 175  
  Rpm 750   750   700   750   750   3700
  Weight 38kg 20kg 38kg 20kg 43kg 36kg 38kg 20kg 38kg 20kg 311kg













J21RN

Guns ANM3 250 ANM3 250 ANM3 250 ANM3 250 ANM3 250  
V1 Rpm 1200   1200   1200   1200   1200   6000
  Weight 43kg 29kg 43kg 29kg 43kg 29kg 43kg 29kg 43kg 29kg 360kg

J21RN

Guns M44 180 M44 180 M44 180 M44 180 M44 180  
V2 Rpm 900   900   900   900   900   4500
  Weight 25kg 14kg 25kg 14kg 25kg 14kg 25kg 14kg 25kg 14kg 195kg

J21RN

Guns MkV 150 MkV 150 MkV 150 MkV 150 MkV 150  
V3 Rpm 750   750   750   750   750   3750
  Weight 42kg 39kg 42kg 39kg 42kg 39kg 42kg 39kg 42kg 39kg 405kg

J21RN

Guns M44 180 M44 180 MkV 150 M44 180 M44 180  
V4 Rpm 900   900   750   900   900   4350
  Weight 25kg 14kg 25kg 14kg 42kg 39kg 25kg 14kg 25kg 14kg 237kg

J21RN

Guns M44 180 MkV 150 M44 180 MkV 150 M44 180  
V5 Rpm 900   750   900   750   900   4200
  Weight 25kg 14kg 42kg 39kg 25kg 14kg 42kg 39kg 25kg 14kg 279kg













J21RN

Guns     ANM3 250 ANM3 250 ANM3 250      
V6 Rpm     1200   1200   1200       3600
  Weight     43kg 29kg 43kg 29kg 43kg 29kg     216kg

J21RN

Guns     M44 180 M44 180 M44 180      
V6 Rpm     900   900   900       2700
  Weight     25kg 14kg 25kg 14kg 25kg 14kg     117kg

J21RN

Guns     MkV 150 MkV 150 MkV 150      
V8 Rpm     750   750   750       2250
  Weight     42kg 39kg 42kg 39kg 42kg 39kg     243kg
>   Nose1 Rpg Nose2 Rpg - Nose3 Rpg Nose4 Rpg - T

J21RN

Guns  M44  180 M44 180 - M44 180 M44 180    
V9 Rpm  900   900   - 900   900     3600
  Weight  25kg  14kg 25kg 14kg - 25kg 14kg 25kg 14kg   156kg
With the various costs involved in the numerous airframe upgrades, the Navy was actually reluctant to spend more money than necessary in this area; especially as guns were considered a secondary weapon.  So both the HS-MkV and ANM3, involving new acquisitions, were soon ruled out.  Considering the AKAN 20mm M47 guns in stores weren't numerous enough to support the re-equipment of close to a hundred aircrafts, the type was also discarded, although regretably as it meant abandonning ammunition standardization with the J23AN Attacker.   This left the Navy with the M44 guns, either chambered in 12.7 or 13.2mm, of which plenty were available after their removal from various aircrafts that had been using them (J21A1, J21A2, J21A3 and the J22).

Very similar in performances to the ANM2/ANM3, the M44/13.2mm fired a slightly lighter shell at an intermediate rate of fire compared to the two iterations of the American gun.  While the recent Korean War had shown the limitations of the .50cal weapons in aerial combat (and the F86 had six quick firing ANM3 guns) the Swedish gun variant had the advantages of a diminutive size and weight.  Also, while naturally carrying less explosives than a 20mm shell, the armor piercing performances of the 13.2mm API rounds were higher and its HEI variant had a much more destructive power than the "standard" .50cal bullets.  Bofors being able to produce APHEI (armor piercing, high explosive, incendiary) rounds conveniently combining AP and HE performances (a new fuse made the explosive charge explode inside a target rather than on its surface) the 13.2mm AKAN M44 gun was eventually adopted as the standard gun for the J21RN, associated with a localy manufactured copy of the German Askania EZ42 gyroscopic gunsight.   Some sort of step back for the better.   As a side aspect, the carriers being due to receive M44 quads for very close range defense, some level of ammunition standard had been achieved.
Gun Cal Length Weight Rpm Range AP
500 metres
Shell HE










Akan.M44

13.2x 99mm 1.460 m 25kg 900 2000m 13mm   42 grms 8 grms

ANM2

12.7x 99mm 1.615 m 38kg 750 2000m 13mm   43 grms 2 grms

ANM2

12.7x 99mm 1.615 m 43kg 1200 2000m 13mm   43 grms 2 grms

HS MkV

20.0x110mm 2.360 m 42kg 750 4000m 9mm   102 grms 11 grms
However, as the radar installation was due to occupy one of the wing guns (tail boom actually) position, both these guns were removed and the M47 20mm gun was replaced by a pair of M44 guns bringing the total to four.   A tight fit, but a convenient one.  The slight loss in fire power was however more than compensated by the fact that all guns were now concentrated in the nose, with its associated balistic advantages.   Saab wished they could increase the size of the ammunition boxes, but there wasn't room enough to provide for more than the existing 180 rounds.  The Navy decided they would make do with that, and the matter wasn't pushed any further
External Gun Pack
Initially, a specific gun pack had been devised for the J21 holding eight 7.9mm guns.   The mounting of this pack involving some unconventional bracing, and the caliber being definitely outside the norms of the day, this pack was abandoned altogether.   Instead, a gun pod holding three M44 guns (with 180 rpg) was designed and produced in limited quantity.   Considering the increased number of weapons carrying positions, among them three under the fuselage, it meant the J21RN could carry an additional 3, 6 or even 9 centrelined guns to supplement the 4 fixed ones - some firepower !
Air-to-Surface Missile

While a higher bomb carrying capacity was being catered for (see below), a dedicated anti-ship missile, the Rb-04, was then under development for the J32, and provision was made for  one such missile to be carried under the fuselage.  Clearly the Rb-04 was intended as the main J21RN weapon in the assigned anti-shipping role.

Air-to-Air Missile

Although the J21RN wasn't intended to fulfill a fighter role, provision was nevertheless made for the carrying of US made AIM-9B Sidewinder air-to-air missiles either on the wingtips, new outer wing and fuselage stations allowing a maximum flexibility of setups

Photo-Reconnaissance Pack

With no room available within the airframe to accommodate cameras, it was decided to adopt an external pack to be carried on the fuselage central pylon.

Radar

With the J21RN being more an attack aircraft than a fighter, with an eye on its anti-shipping role, a surface search radar was felt as a necessity, and Ericsson was granted

with the license rights to locally produce the British EKCO ASV/19 search radar.  The Mk38 podded version was examined but in the end, the ancient "J21B" project was revived with the radar installed in the front part of the starboard tail boom, with the port boom reshaped in a similar manner.  This installation called for a complete review of the aircraft electric supply, but since this was catered for from the beginning of the project, SAAB avoided the trouble encountered by Hawker when adopting the same (podded) equipment for the German Navy Mk101 SeaHawks.  Reviewed by Ericsson, the radar now also had a limited air-to-air function but it's main purpose was cleary to identify surface targets in order to deliver the Rb04 antiship missile.

Fuel Capacity Enhancement
With no spare volume left in the fuselage to accommodate additional fuel, there were only two options left : 
 make the, now folding, outer wing a "wet" wing
 increase the external fuel capacity

With the.US certainly happy to see Sweden, a potential ally in Scandinavia, beefing up their defense, Grumman was tasked by the USN to assist SAAB in the design of a folding wing mechanism.   This gesture was a welcome time saver and the new (folding) outer wing was essentially a Grumman design.  The dimensions remained the same but the new wing showed leading edge slats improving manoeuvrability and landing

The new outer wet wing added another sizeable 780 litres of internal fuel and the extra thrust provided by the Tay engine allowed heavier external stores to be carried.   The wingtip tanks capacity was slightly increased from 400 litres to 530 litres each and two addtional (wet) pylons were added under the fusealge (actually under the stubwings) allowing for another 1060 litres of fuel.  At the end of the exercise, the maximum fuel capacity had been more than doubled.   Worth noting, the central fuselage pylon was made into a wet one too, and could theoretically carry a 855 litres fuel tank, then replacing the two under belly 530 L tanks.   In practice, this option wasn't felt practical, but it did offer some addtional flexibility in weapons carrying.

Aircraft Engine Thrust
Kgp
Dry
- Body Motor Main
Fuel
Tips
Fuel
Ammos
Guns
Pylons
Wings>
250lbs
Pylons
Wings<
1000lbs
Pylons
Fuselage
1000lbs
Pylons
Central
1321lbs
Fuel
Total
Litres
Weight
Total
Kgs















J21RB RM1A 1430 Kg 2387 703 676 350
350
116 - - - 600 - 5182 kg
- - - L - - 890 400
400
- - - - - 1690 L -
J21RN RM3A 2685 Kg 2387 935 1269 454
454
  56
-43
170
170
454
454
454
454
(600) - 7668 kg
- - - L - - 1670 530
530
- - 530
530
530
530
- 4850 L -
Increased Weapons Load
Initially, the J21RA/B were able to carry a 600kg bomb under the fuselage and 10 x 100mm rockets.  The higher thrust of the new Tay engine allowing for higher loads, two weapons stations (for up to 1000 lbs each) were added under the fuselage (actually the stub wings between the fuselage and the tail booms), and provision was made for four wing pylons, the inner ones cleared for up to 1000lb each, and the outer ones being tailored to carry a pair of Sidewinder AIM-9B missiles each (or a 250 lbs bomb).  While the wing tips would normally carry fuel tanks, they were made able to carry a single air-to-air missiles too.   All but the outer wing stations were of the wet type, allowing a dramatic increase in fuel capacity.   In addtion, rails could be installed for large diameter rockets under the wings.

Typically, the R21N would be equipped with tip tanks, one or two pairs of Sidewinder missiles, fuel tanks on the innner wing position and either a Rb04 missile on the centerline pylon or bombs under the fuselage associated with rockets under the wings.   Here are a few variants of the enhanced capacities of the J21RN, especially the use of the centreline fuselage pylon which condamn the use of the side fuselage pylons but still allows the carriage of additional 135mm HVAR rockets when loads other than the Rb04 missile are carried.

Colors and Markings

Along the tradition of the Flygvapnet, the new F22 and F23 Wings were divided into three squadrons each, with 1Sq showing Wing markings in red (V and W being the 22nd and 23rd letter of the alphabet), 2Sq in blue and 3Sq in yellow, the same colors being used to highlight the nose and the engine exhaust.   Besides these traditional markings, the aircrafts were finished in a distinctive dark green/grey topside with pale grey underneath. 

.

Wing F22

1st Sq

-

Wing F23

1st Sq

-

Wing F22

2nd Sq

-

Wing F23

2nd Sq

-

Wing F22

3rd Sq

-

Wing F23

3rd Sq

-

Initial drawings by Radome, published on www.shipbucket.com
 

___________