DISCLAIMER: language in general is a difficult thing for me, so if this feels choppy, unrefined or blunt, that is why; I did my best
I am doing some research on the J-27 'super spitfire' and B/J-24 manufactured by Saab because these aircraft are a topic that has interested me in recent months (by the content of my requests you will probably be able to tell there is something else to it, but that's a completely different topic of conversation). However, information is particularly sparse on the internet and so I have struggled to build much information about them. there seems to be a distinct lack of anything available that isn't Wikipedia pages or forum posts discussing similar topics.
So to the point. I am looking for information regarding these two designs, so that I can build the picture I need to build. The information I am looking for is mostly image references and information regarding the two that I will list now:
I know these are a lot of requirements, but this is for a specific purpose (as well as being incredibly interesting to me).
thanks for any help you can give!
Disclaimer: This is a very tough subject to find sources on. All my sources on this are secondary, and mainly based on articles in Swedish magazines, primarily Kontakt no 104 from December 1991. The author of that article seem to have dug in the war archives considering the pictures and information, but does not list his sources. Mods, feel free to delete this answer if this sourcing is not enough.
SAAB L 27 (no J since planes that never left the drawing board never got a J designation) was a proposal by SAAB's Lars Brising, who had aided Bo Lundberg at FFVS in the design of the J 22 and would later become the chief designer of the J 29 "Tunnan".
KFF (Kungliga Flygförvaltningen, the Swedish Royal Airforce Material Administration) had ben in discussions with SAAB on improvements on the J 21A early 1945, primarily with a new and more powerful engine referred to as J 21B, however, it was considered unlike that either of the intended engines (DB 605E, Rolls Royce Merlin Mk 68 and Mk 69) would be available, so in April, KFF asked SAAB to start a project called Jx around the Rolls Royce Griffon of 2 200hp, of which KFF had been able to secure technical data and specificationsof from the British, with a potential future contract for license production. Future upgrades were mentioned using the planned NOHAB/Svensk Flygmotor Mx that would produce some 2 400hp - however, NOHAB/Svensk Flygmotor had their hands full producing the Twin Wasp and the DB 605B and no deliveries of new engine types were planned before 1949.
Development started in April 1945 and a concept was presented and approved on the 20th of June 1945. However, the Air Force and especally its commander, Bengt G:son Nordenskiöld decided that jet propulsion was the future of air superiority fighters, and soon after SAAB and Brising realised that the era of propeller fighters was coming to an end, and the project was cancelled on the 4th of September 1945 in favour of starting the work that would eventually lead to J 29 "Tunnan". No prototype was ever made, no wind tunnel tests conducted and no engine settled on, although the Rolls Royce Griffon at 2 200hp was mentioned in the initial design specifications. The drawings made up by Björn Karlström on Brising's design mentions a Rolls Royce Griffon Mk 85 at 1 935hp.
The aircraft's body had a distinct resemblance with the J 26 (P-51D Mustang) although the rest of the aerodynamics and the wings bore a striking resemblance with the Fairey Firefly, perhaps because the aerodynamic engineer Youngman, who had designed the Fairey-Youngman flaps on the Firefly worked as a consultant at SAAB at the time. After the 20th of June approval of the initial design, an unconventional V-shaped "butterfly" tail and two counter-rotating 3-blade propellers were proposed, although KFF wanted a single 5-blade propeller.
Björn Karlström's blueprint of Brising's design.
V-shaped tail design, by unknown author.
Edit: Had the wrong image.
The stats listed in the source is a wingspan of 12,2 meters, a length of 11 meters, the Rolls Royce Griffon at 2 200hp and a speed of 700km/h and an armament of 4x20mm Akan m/45 (Bofors design, 20x110 Hispano-Suiza shells, 725 shots/minute) - two in each wing.
If you want more technical data I think you will need to go to the war archives in Stockholm, unfortunately.
As for the L 24, which would have become J and B 24, Wikipedia had the essential information, to the extent that I suspect whomever wrote the wikipedia article had access to the same 2nd hand sources I do.
1941, both the Swedish air force and SAAB had the oppurtuity to study a Bf 110 that had been forced to make an emergency landing in Sweden. The type impressed the Swedish air force, and they wanted something similar. The project started in Spring 1942, when the air force and KFF (Kungliga Flygförvaltningen, the Swedish Royal Airforce Material Administration) was looking for the next bomber model that would eventually replace the SAAB B 17. The air force called the project Bx and SAAB called it the L 24. While the inspiration was clearly the Bf 110, the project soon took the common name "the Swedish Mosquito". A bomber variant sometimes referred to as B 24 and a bomber destroyer or night fighter variant (with a planned "radio-locator type Mosquito" fitted) was referred to as J 24.
The design was all metal except for the rudders, which were canvas-covered. The bomber variant would have air brakes for dive bombing to reduce the dive speed to 500km/h. SAAB dedicated substantial resources to the project, which was led by Tord Lindmalm.
License-produced DB 605B engine at 1 475Hp each were to be fitted and armament would be 2 20mm Akan m/41 and 4 8mm Ksp m/22 in the nose for the bomber version (with another 2 8mm Ksp m/22 potentially fitted in the wings) and a trainable 13,2mm Akan m/39 for the rear crewman. The figher variant were to have 4 guns in the nose and 2 in the wings, and a full set of 13,2mm Akan m/39 or 20mm Akan m/41 were discussed - a mix like on the J 21 might very well have been the end result - and the same trainable rear armament of a single 13,2mm Akan m/39. Interestingly, the higher placed two guns in the nose would have their rear ends at the feet of the pilot in the cockpit and could thus be reloaded in the air. I have no idea why SAAB thought this was a feature that could be used.
The air intakes on the motor gondolas were placed far back to reduce drag and the exhaust pipes configured so that the hot exhaust could provide some extra propulsion.
The nose and the landing gear (a three-point one) was the same as on the later J 21.
The plane was to have an internal bomb bay capable of carrying a single 1 000kg, two 250kg or 8 50kg bombs, plus wing fittings that could carry various bomb configuations - or droppable extra tanks for inreased range. Note that the sources vary on this, and it is possible that there is some confusion on how much bombs the plane could carry - as one source lists the max bomb load at 1 000kg, and another at 2 650kg (900kg internal, 1 750kg external). It is possible that the latter number is just adding all the heaviest bomb loads fitted together, regardless wether the plane could start with that load or not.
However, restrictions enforced by the air force and KFF caused problems. The air force had to use a lot of planes way beyond their originally intended life cycle - especially the Italian planes (J 11/CR.42, J 20/RE.2000 and B 16/CA.313) had problems with this and poor quality woodwork and glues not suited to the cold and damp Nordic climate causing some planes to literally disintegrate in the air. The air force wanted the max load pressure the plane could handle increased from 9 (force equilent to times the plane's weight) to 12, which caused a re-design which made the plane heavier, which affected prestanda. Another issue was the new redigned plane needing a longer take off run - longer than most of the field bases of the air force at the time. A fully loaded B 24 would simply not be able to get in the air before it ran out of air strip. Another redesign thus added another 3m² of wing surface, which added more weight and drag, further decreasing the prestanda of the aircraft.
Once it was clear that the aircraft would not have the performance initially hoped for and that the J 21 and B 18 also under design could fulfill the same roles intended for the J 24 and B 24. On the 9th of December 1943, KFF cancelled the project. At that time, SAAB had produced a few parts on a test aircraft, but not the full plane and no attempts were made to make a full plane.
Björn Karlström's blueprint drawing of the L 24.
The model used for wind tunnel tests.
Stats as listed (stats within parathesis for the later design with the larger wing):
J 24
Wingspan: 15,6m (16,1m).
Length: 11,23m.
Height: 2,83m.
Wing area: 34,3m² (37,8m²).
Engines: 2 Svensk Flygmotor AB DB 605B at 1 475Hp each.
Take off weight: 7 400kg (7 600kg).
Wing load: 216kg/m² (201kg/m²).
Max speed: 640km/h (620km/h).
Service ceiling: 11 000m (10 700m).
Rate of climb: 12,2 m/s (11,9m/s)
Armament: 6 13,2mm Akan m/39 or 6 20mm Akan m/41, 1 13,2mm Akan m/39 to the rear.
Bomb load: N/A.
B 24
Wingspan: 15,6m (16,1m).
Length: 11,23m.
Height: 2,83m.
Wing area: 34,3m² (37,8m²).
Engines: 2 Svensk Flygmotor AB DB 605B at 1 475Hp each.
Take off weight: 7 900kg (8 100kg).
Wing load: 230kg/m² (214kg/m²).
Max speed: 640km/h (620km/h).
Service ceiling: 11 000m (10 700m).
Rate of climb: 12,2 m/s (11,9m/s)
Armament: 4-6 8mm Ksp m/22 and 2 20mm Akan m/41, 1 13,2mm Akan m/39 to the rear.
Bomb load: 1 000-2 650kg.
