+++ DISCLAIMER +++
Nothing you see here is real, even though the model, the conversion or the presented background story might be based historical facts. BEWARE!
Some background:
In the aftermath of the Second World War, Sweden required a strong air defense, utilizing the newly developed jet propulsion technology. The original concept had been designed around a mostly straight wing, but after Swedish engineers had obtained German research data on swept-wing designs, the prototype was altered to incorporate a 25° sweep. In order to make the wing as thin as possible, Saab elected to locate the retractable undercarriage in the aircraft's fuselage rather than into the wings.
Extensive wind tunnel testing had also influenced aspects of the aircraft's aerodynamics, such as stability and trim across the aircraft's speed range. In order to test the design of the swept wing further and avoid any surprises, it was decided to modify a Saab Safir. It received the designation Saab 201 and a full-scale swept wing for a series of flight tests. The first 'final' sketches of the aircraft, incorporating the new information, were drawn in January 1946.
The originally envisioned powerplant for the new fighter type was the de Havilland Goblin turbojet engine. However, in December 1945, information on the newer and more powerful de Havilland Ghost engine became available. The new engine was deemed to be ideal for Saab's in-development aircraft, as not only did the Ghost engine had provisions for the use of a central circular air intake, the overall diameter of the engine was favorable for the planned fuselage dimensions, too. Thus, following negotiations between de Havilland and Saab, the Ghost engine was selected to power the type and built in license as the RM 2.
By February 1946 the main outline of the proposed aircraft had been clearly defined. In autumn 1946, following the resolution of all major questions of principal and the completion of the project specification, the Swedish Air Force formally ordered the completion of the design and that three prototype aircraft be produced, giving the proposed type the designation J 29. After a thorough test program, production of the type commenced in 1948 and, in May 1951, the first deliveries of operational production aircraft were received by F 13 Norrköping. The J 29 proved to be very successful and several variants and updates of the Tunnan were produced, including a dedicated reconnaissance variant, a two seat trainer and an all-weather fighter with an onboard radar
However, Sweden foresaw that there would soon be a need for a jet fighter that could intercept bombers at high altitude and also successfully engage fighters. During September 1949, the Swedish Air Force, via the Swedish Defence Material Administration, released a requirement for a cutting-edge interceptor aircraft that was envisioned to be capable of attacking hostile bomber aircraft in the transonic speed range. As released, this requirement specified a top speed of Mach speed 1.4 to 1.5. (1956, the specified speed was revised and raised to Mach 1.7-1.8, and eventually led to the Saab 35 Draken). With the barely supersonic Saab 32 Lansen just under development, and intended for different roles than being a nimble day fighter, the company searched for a way to either achieve supersonic flight through modifications of an existing type or at least gather sufficient data and develop and try the new technologies necessary to meet the 1949 requirements.
Since Sweden did not have a truly supersonic aircraft in its inventory (not even an experimental type), Saab decided to convert the Saab 29 into a supersonic testbed, with the outlook to develop an interim day fighter that could replace the various Tunnan fighter versions and support the new Lansen fleet until a fully capable Mach 1.5+ interceptor was ready for service. Even though the type was regarded as a pure experimental aircraft, the designation remained close to the J29 nomenclature in order to secure military funding for the project and to confuse eventual spies. Consequently, the P29 was initially presented as a new J29 version (hence the “G” suffix).
The P29G was based on a heavily modified production J29B airframe, which was built in two versions and only in two specimens. Work on the first airframe started in 1952, just when the first Saab 32 prototype made its maiden flight. The initial challenge consisted of integrating two relatively compact axial flow jet engines with afterburners into the fuselage, since the J29’s original RM2, even in its late afterburner variant, was not able to safely deliver the necessary thrust for the intended supersonic flight program. After long negotiations, Saab was able to procure a small number of Westinghouse J34-WE-42 turbojets from the USA, which delivered as a pair 40% more thrust than the original RM2B. The engines were only delivered under the restriction that they would exclusively be used in connection with the supersonic research program.
Through a thorough re-construction, the Saab team was able to mount the new engines into the lower rear fuselage, and, internally, the air intake duct had to be modified and forked behind the landing gear wells. Due to the significantly widened rear fuselage, the P29G became quickly nicknamed “Kurviga Tunnan” (= “Curvy Barrel”). Even though the widened rear fuselage increased the aircraft’s frontal cross section, the modified shape had the (unintended) effect of area ruling, a welcome side benefit which became apparent during the flight test and which largely promoted the P29G’s gain of top speed.
Another special and unique feature of the P29G was a special wing attachment system. It consisted of two strengthened, open box spars in the fuselage with additional attachment points along the wing roots, which allowed different wings to be switched with relatively little effort. However, due to this modification, the wing tanks (with a total capacity of 900l inside of the J29s standard wings) were lost and only 2.150l in the Saab 29’s standard fuselage tanks could be carried – but this was, for a research aircraft, not regarded as a major weakness, and compensated for the wing attachment system’s additional weight. The original wing-mounted pitots were replaced by a single, massive sensor boom attached to the aircraft’s nose above the air intake, slightly set-off to starboard in order to give the pilot an unobstructed view.
The first P29G's maiden flight, marked “Gul Urban” (Yellow U), took place in July 1955. The aircraft behaved normally, even though the center of gravity had markedly shifted backwards and the overall gain of weight made the aircraft slightly unstable along the longitudinal axis. During the initial, careful attempts to break the sound barrier, it soon became apparent that both the original wings as well as the original air intake shape limited the P29G's potential. In its original form, the P29G could only barely pass Mach 1 in level flight.
As a consequence, the second P29G, which had been under conversion from another J29B airframe since mid-1954, received more thorough modifications. The air intake was lengthened and widened, and in order to make it more effective at supersonic speed it received a sharp lip. Wind tunnel tests with the first machine led to a modified tail, too: the fin was now taller and further swept back, the stabilizer was moved to a higher position, resulting in a cruciform layout. The original single-piece stabilizer was furthermore replaced by a two-piece, all-moving construction with a 45° sweep and a thinner profile. This not only improved the aerodynamics at high speed, it also suppressed the longitudinal instability problem, even though this was never really cured.
Due to the even higher all-up weight of the new aircraft, the landing gear was reinforced and the 2nd P29G received an experimental suspension system on its main legs with higher spring travel, which was designed for operations on semi-prepared airfields. This system had actually been designed for the updated J29 fighters (esp. the A32B attack variant), but it was not introduced into series production or the Saab 29E/F conversion program. Despite these massive changes, the P29G designation was retained, and the second machine, carrying the tactical code “Röd Urban” (Red U), was quickly nicknamed “Karpen” (“Carp”), due to its characteristic new intake shape, the long fin and its stocky shape.
The second P29G was ready for flight tests in August 1956, just in time to support the Saab 35’s ongoing development – the aircraft, which was eventually built to meet (and exceed) the Swedish Air Force’s 1949 supersonic interceptor requirement. The modifications proved to be successful and the P29G was, fitted with a 60° sweep wing and in clean configuration, able to achieve a maximum speed of 1.367 km/h (849 mph) in level flight, a formidable achievement (vs. the 1,060 km/h (660 mph) of the late J29F and the 1200 km/h (745 mph) of the J32B interceptor) for the post WWII design.
Several wing shapes and profiles were tested, including sweep angles from 25° to 63° as well as different shapes and profiles. Even though the machines carried provisions for the J29’s standard armament, the 20 mm cannons were normally not mounted and replaced with sensors and recording equipment. However, both machines were temporarily fitted with one or two guns in order to analyze the effects of firing the weapons at supersonic speed. Underwing ordnance was also almost never carried. In some tests, though, light bombs or unguided missiles were carried and deployed, or podded cine cameras were carried.
While the second P29G was used for high speed trials, the first machine remained in its original guise and took over low speed handling tests. Thanks to the unique wing switch mechanism, the supersonic research program could be held within a very tight schedule and lasted until late 1959. Thereafter, the P29Gs’ potential was of little use anymore, and the engine use agreement with the USA put an end to further use of the two aircraft, so that both P29Gs were retired from service in 1960. The 1st machine, outfitted with standard J29F wings and stripped off of its engines, remained in use as an instructional air at Malmslätt air base 1969, while the second machine was mothballed. However, both airframes were eventually scrapped in 1970.
General characteristics:
Crew: 1
Length: 11.66 m (38 ft 2 in) fuselage only,
13,97 m (45 ft 9 in) with pitot boom
Wingspan: varied*; 11.0 m (36 ft 1 in) with standard 25° sweep wings,
10.00 m (32 ft 9 ¾ in) with experimental 45° wings
Height: 4.54m (14 ft 10 ½ in)
Wing area: varied*; 24.15 m² (260.0 ft²) with standard 25° sweep wings
22.5 m² (242.2 ft²) with experimental 45° wings
Empty weight: 5,220 kg (11,500 lb)
Max. takeoff weight: 8,510 kg (18,744 lb)
Powerplant:
2× Westinghouse J34-WE-42 turbojets, each rated at 3,400 lbf (15 kN) dry thrust
and 4,200 lbf (19 kN) with full afterburner
Performance:
Maximum speed: 1.367 km/h (849 mph) were achieved*
Range: 790 km (490 mi)
Service ceiling: up to 17,250 m (56,500 ft)*
Rate of climb: up to 45 m/s (8,850 ft/min)*
*Varying figures due to different tested wing configurations
Armament:
None installed; provisions for 4x 20mm Hispano Mark V autocannon in the lower front fuselage.
Depending on the mounted wing type, various external loads could be carried, including a wide range of light bombs, 75 mm (3 in) air-to-air rockets, 145 mm (5.8 in) anti-armor rockets, 150 mm (6 in) HE (high-explosive) rockets or 180 mm (7.2 in) HE anti-ship rockets. Due to the lack of complex wiring or fuel plumbing, no guided weapons or drop tanks could be mounted, though.
The kit and its assembly:
Sweden is a prolific whiffing territory, and the Saab 29 offers some interesting options. This highly modified Tunnan, which is actually rather a kitbashing than a mere model kit modification, is/was a submission to the “More or less engines” group build at whatifmodelers.com in summer 2019.
I actually had the idea of a two-engine J29 in the back of my mind for a long time, spawned by a resin conversion set for the Hasegawa B-47 Stratojet kit that came with new intakes and exhaust sections for the four engine pods. The single engine pod parts had been spent a long time ago, but the twin engine parts were still waiting for a good use. Could the exhaust fit under/into a Tunnan…?
I even had a Matchbox J29 stashed away for this experiment long ago, as well as some donor parts like the wings, and the GB eventually offered the right motivation to put those things together that no one would expect to work.
So I pulled out all the stuff and started – a rather straightforward affair. Work started with the fuselage, which was, together with the (very nice) cockpit assembled OOB at first, the nose filled with as much lead as possible and with the lower rear section cut away, so the B-47 resin jet nozzles would end up at the same position as the original RM2B exhaust. Due to the pen nib fairing between them, though, the profile of the modified tail became (visually) more massive, and I had to fill some gaps under the tail boom (with styrene sheet and putty). The twin engines also turned out to be wider than expected – I had hoped for straight flanks, but the fuselage shape ended up with considerable bulges behind the landing gear wells. These were created with parts from drop tank halves and blended into the rest of the lower hill with PSR work. In the same wake the area under the fin was sculpted and re-created, too.
At that point it became clear that I had to do more on the fuselage, esp. the front end, in order to keep the aircraft visually balance. A convenient solution became an F-100 air intake, which I grafted onto the nose instead of the original circular and round-lipped orifice – with its sharp lip the Super Sabre piece was even a plausible change! The fuselage shapes and diameters differed considerably, though, more PSR became necessary.
Next came the wings: I had already set apart a pair of trapezoid wings with a 45° sweep angle – these were left over from a PM Model Ta 183 conversion some time ago. With their odd shape and size they were a perfect match for my project, even more so due to the fact that I could keep the original J29 wing attachment points, I just had to shorten and modify the trailing edge area on the fuselage. The result was very conclusive.
With the new nose and the wings in place, the overall proportions became clearer: still tail-heavy, but not unpleasant. At this time I was also certain that I had to modify the tail surfaces. The fin was too small and did not have enough sweep for the overall look, and the stabilizer, with its thick profile, rounded edges and the single, continuous rudder did not look supersonic at all. What followed was a long search in the donor banks for suitable replacements, and I eventually came up with a MiG-15 fin (Hobby Boss) which was later clipped at the top for a less recognizable profile. The stabilizers were more challenging, though. My solution eventually became a pair of modified stabilizers from a Matchbox Buccaneer(!), attached to the MiG-15 fin.
The design problems did not stop here, though: the landing gear caused some more headaches. I wanted to keep the OOB parts, but especially the main legs would leave the aircraft with a very goofy look through a short wheelbase and a rear axis position too much forward. In an attempt to save the situation I attached swing arms to the OOB struts, moving the axis maybe 5mm backwards and widening the track by 2mm at the same time. Not much in total, but it helped (a little, even though the aircraft is still very tail-heavy)
As a final addition – since the original, wing-mounted pitots of the J29 were gone now and would not go well with the wing-switching idea – I gave the P29G a large, nose-mounted pitot and sensor boom, placed on top of the nose. This part come, like the air intake, from an F-100.
Painting and markings:
I tend to be conservative when it comes to liveries for what-if models, and the P29G is no exception. At first, I thought that this build could become an operational supersonic daylight interceptor (the J29G), so that I could give the model full military markings and maybe a camouflage paint scheme. However, this idea would not work: the potential real life window for such an aircraft, based on the Saab 29, would be very narrow. And aircraft development in the late Fifties made quantum leaps within a very short period of time: While the J29A entered service, work on the Mach 2 Saab 35 was already underway – nobody would have accepted (or needed) a Mach 1 fighter, based on late Forties technology, at that time anymore, and there was the all-weather Saab J32B around, too. The update program with new wings and a more powerful afterburner engine was all that could be done to exploit the Tunnan’s potential, resulting in the (real world’s) J29E and F variants.
I eventually decided that the J29G would only be a prototype/research aircraft, consequently called P29G, and through this decision I became more or less settled upon a NMF finish with some colorful markings. Consequently, the model was painted with various shades of metal colors, primarily Polished Aluminum Metallizer from Humbrol, but also with Humbrol 191 and Matt Aluminum Metallizer as well as ModelMaster Steel Metallizer. Around the exhaust section, I also used Revell 91 (Iron) and ModelMaster Exhaust Metallizer. Some single panels and details were painted with Revell 99 (Aluminum), and I also used generic decal material in silver to simulate some smaller access panels. Grey decal sheet was used to simulate covers for the cannon nozzles.
The cockpit interior was painted, according to Saab 29 standard, in a dark greenish-grey (Revell 67), and bluish grey was used inside of the landing gear wells (Revell 57). The pitot boom received black and white stripes.
For markings I let myself get inspired from the real world Saab 29 and 32 prototypes, which were all marked with a colored “U” tactical code on the fin and also on the front fuselage, simply meaning “Utverding” (= “Test”). I found four red decals, and I also gave the aircraft a yellow cheatline, lent from an Airfix F-86D decal sheet. The Swedish roundels come from a generic aftermarket sheet, most stencils were taken from the Revell OOB sheet and a Printscale J29 sheet.
Before the model was sealed with semi-gloss acrylic varnish from Italeri, some grinded graphite was rubbed onto the rear fuselage, adding a metallic shine and simulating exhaust stains.
A thorough conversion – this has rather evolved into a kitbashing than just a kit conversion: not much from the original Matchbox J29 has been left over. But I like the outcome, even though things developed gradually from the simple idea of changing the number of engines on the Tunnan. One thing led to another. The resulting aircraft looks quite plausible, even though I am not totally happy with the landing gear, which appears to be rather far forward, despite surgical measures to mend the situation. The Ta 183 wings are a very good match, though, and I cannot help but recognize a certain French look, maybe due to the cruciform tail and the oval air intake? The P29G could also, with Argentinian marking, have become a revised version of the FMA Pulqui II?
