Gorgeous pic!

Not really - the engine needs subsonic airflow otherwise there is no brute force.

The redesign of the engine front-end for the Viggen was extensive and the intake design itself is far from simple and took a crazy amount of design and testing to work over such a broad mach range. Only from more unusual angles or close-up viewing do some of the unique details reveal themselves:


https://cimg8.ibsrv.net/gimg/pprune....c44f23ee00.jpg

It was a remarkable and arguably unique aircraft.

Superb pic :ok:

It looks simple but there are odd things such as the gap at the base of the inlet..... no doubt it took a lot of work to get it just right.

A few years ago I got close to a Formula 1 car and it was covered in tiny detailing that at first glance made no sense but obviously were very, very important.

Royal Air Force and the Viggen




Original text by Ulf Edlund





If someone in the early 1960s had said that the Viggen would be of interest for the Royal Air Force, that person would probably have been ridiculed. However, the circumstances meant that different Viggen versions were actually of interest at one point.



In 1967 the situation was precarious in Britain. The highly advanced TSR.2 attack aircraft had been cancelled in 1965 and a replacement was needed. A planned order of a total of 400 F-4K / M Phantom II for the Royal Air Force and Royal Navy was reduced to 170 aircraft due to excessive development costs. Instead of purchasing existing versions of the F-4, the RAF wanted to install Rolls Royce Spey engines that on paper offered improved performance. The result, however, was that the modifications needed were much more extensive than planned and unfortunately also resulted in reduced performance. The total budget could not be exceeded, and a recalculation showed that the cost of the 170 aircraft was three times higher than purchasing already developed versions!

The plans to develop a new advanced attack aircraft, AFVG (Anglo-French-Variable-Geometry), along with France had also failed. The politicians favored the Franco-British cooperation projects, and the idea was that the two countries would jointly develop AFVG, the smaller Jaguar attack aircraft, and not at least the civilian supersonic Concorde aircraft. It was thought that Britain would lead the development of AFVG, but not surprisingly, this was disliked by Dassault, which on its own secretly developed its own VG aircraft, the Mirage G. This put an end to the AFVG work. An order had also been placed on 50 US F-111 aircraft but the project was plagued by major development problems and was considered risky.

Could a custom version of the Viggen perhaps be a solution? A requirement specification was sent to Sweden, but it was easy to see that it did not fit the AJ 37, the prototype of which had just made its maiden flight. Among other things, a twin engine and a two man crew were required. The range requirement was also very high. The specification was almost identical to the AFVG's and reflected British superpower ambitions at the time. Twin engine and two man crew were a consequence of the desired range. There were no requirements directly relating to weapon delivery. It was also implied that the requirements could be revised.



Viggen alternatives

In just a few weeks, Saab quickly projected three (!) potential Viggen versions for the RAF which were presented at a meeting in London on August 18, 1967. The negotiations took place on a high level and it was stressed that only people with "a strict need to know" were to be involved. From Sweden, Lars Brising and Gunnar Lindqvist participated from KFF (Swedish Air Force Materiel Administration), with Tore Gullstrand and Olle Esping from Saab. On the British side, more than 20 representatives from the Defense Department participated, with two generals in the lead.



The three versions were:



37XE-1: Single-engine with a further developed RR Spey, RB 168-62R, and increased fuel capacity, otherwise virtually unchanged from the regular AJ 37.



37XE-2: Single-engine with Bristol Olympus B.Ol. 22R, extended airframe and increased fuel capacity.



37XE-3: Two-engine with RB 193, a proposed new engine from Rolls Royce, extended airframe and significantly increased internal fuel.



Only the 37XE-3 corresponded reasonably well to the requirements presented.



According to Brising, who wrote a detailed travel report, the discussion was intense. There hadn't been enough time to make any cost estimates for the meeting, but Brising suggested some numbers, albeit with many reservations. It was obvious that the military leadership wanted to continue with a one-sided development of the AFVG and for psychological reasons didn't intend to change this. American options were already available, and aside from working with Sweden, West Germany was also an option and possibly Italy as well.

(Brising had visited Germany earlier this year and had the impression that the conditions for British-German development were not particularly favorable).

The British side was interested in continuing discussions and the next step was a visit to Sweden at the end of September, where the estimated costs were presented. It was admittedly only realistic to assume that the aircrafts would be license produced in Britain, but as a reference, the following cost per aircraft was estimated based on a hypothetical production of 200 aircraft in Sweden:



37XE-1: 7.5 million. SEK

37XE-2: 9.5 million. SEK

37XE-3: 11.5 million. SEK



The cost per aircraft included the additional type cost for the different versions. To get a complete aircraft, the avionic cost of 2.2 million SEK was added as well as the engine costs. If the regular AJ 37 had been sufficient, the production cost for a series of 200 extra aircraft would have been 6.5 million SEK per aircraft, excluding avionics and engine. 37EX-2 and -3 could in practice be regarded as new aircraft, as is apparent from the figures in the table comparison. The stated values for the AJ 37 reflect the state of the aircraft in 1967 and some changes were made before the series production started in 1971. It is noteworthy that the 37XE-1 (RB 168 ) and 37XE-2 (B.R. 22R) engines were the engines that sat in the two original Viggen "finalists" in 1961, projects 1508A2 and 1562 respectively. All that was needed was to dust off the existing studies! To improve speed performance at high altitude, 37XE-2 and -3 were provided with snedstötsintag [oblique impact intakes?]. The 37EX-3 in particular had become an exceptional aircraft and was internally referred to as the "Double Barrel" at Saab. It is easy to understand why when you see the sketches. As the range was perhaps the most critical parameter, the ability to carry four external fuel tanks for ferry flights was added. There is no documentation of the response to the September presentation but it's reasonable to assume that the engine issue contributed to the interest cooling down. The 37XE-1 with a Spey engine required further development and would have worse performance than the regular AJ 37. The 37XE-2, with an Olympus engine which development was stopped in 1965 when the TSR.2 was cancelled, and the 37XE-3, with a brand new engine, was of course not attractive projects to bet on either.



New attempt

The next export attempt was made in 1968. The British had canceled their 50 F-111, which had been ordered the previous year, but considered joining the international working group formed to study and define a successor to the F-104G. West Germany, Belgium, Italy, the Netherlands and Canada had started to work at developing a single seat attack aircraft. The project eventually became the two seat MRCA Tornado.

Without access to a detailed british requirement specification, two new versions of the Viggen were specified that were similar to the then intended execution of the JA 37 (the fighter/interceptor version). These aircraft had compared to AJ 37 a sharper radom, snedstötsintag [oblique impact intakes?] and other changes to improve supersonic performance. At this point various more or less fixed cannon installations had been studied and 37XE was offered with a 20 mm Vulcan cannon. The idea was to install the cannon instead of the normal C 7 hardpoint and to have the ammunition, 1 000 cartridges, in a new type of the external fuel tank. In addition to the ammunition magazine, you could have fuel or reconnaissance equipment in the tank.

Two engine designs were studied. In conjunction with the JA 37 studies, which had now started, an improved version of the RM 8 together with another variant of it, the RM 8-1, were studied as an option for the 37XE. The other option was more interesting, the planned engine was a proposed development of the Bristol Pegasus, the engine used by the Harrier. On paper the engine, designated B.P.30R, was very interesting: it was significantly more powerful than the RM 8, had lower fuel consumption and was even lighter. And since it was specifically projected for the Viggen it would also have been possible to install it without major changes to the airframe. The preliminary cost estimates showed that it would cost 80 million. SEK to develop the variant with the RM 8-1 and an additional 40 million for the B.P.30R variant. But before the new versions could be presented to the British they decided to join the MRCA project and ended it there.



https://i.imgur.com/TOO0uvO.png

Data for the "British" Viggen versions compared with the values for the AJ 37 in 1967.



https://i.imgur.com/A9q0ZIJ.png

Here are the versions presented to the RAF in August 1967. Three very different aircraft!



https://i.imgur.com/uBrnCw6.png

This drawing of the FPL 37XE-3 perhaps explains why the version was called the "Double Barrel".



https://i.imgur.com/gW8b0jC.png

The 37XE was primarily intended as an attack aircraft and it was therefore important to present flexibility in weapon configurations.



https://i.imgur.com/W544bF0.png

The proposed installation of a Vulcan cannon and its ammunition in the external fuel tank can only be regarded as original.

"Squadron exchanges were a regular occurrence at Coltishall, and while on 41 Mike participated in a particularly interesting one with F6 wing of the Swedish Air Force at Karlsborg, flying the AJ37 Viggen. Right from the start, he and his colleagues realised that much was exceptional about the way the Swedes trained and operated, not least considering that the majority of the pilots were effectively doing national service. ‘When you looked at the people who were flying the aeroplanes, I thought that we could learn from this, definitely. The guy who flew me was a Honda 500cc works motorcycle rider; they had rally drivers, go-kart racers, all kinds of things. These weren’t people with good degrees in underwater basket-weaving, these were people who were recruited to fly the Viggen.‘The first to go up in the Viggen was our boss, Hilton Moses. I remember going out with him to the aeroplane and seeing him laughing and smiling, and then seeing him getting out and coming back to the crewroom looking like he’d just been put through some kind of crazy combination between a fairground ride and a washing machine. Then I went flying in the afternoon, and it changed my life.

‘They would fly around at Mach 0.95, 650kt give or take a bit, and they trained at 10m. We flew through firebreaks in trees, we flew all over northern Sweden at 30ft, and we never went below 600kt. All of this, I should add, was done under about a 150 to 200ft overcast with no breaks. In the RAF, anybody who wanted to get old would not have flown in that weather. After about 40 minutes, we pulled up into cloud, and the pilot then flew a 4-degree hands-off approach with his hands on his head into a remote airstrip, landed, reversed into a parking bay, did an engine-running refuel without any communication with the people on the ground except hand signals, taxied out and took off in the direction that we’d landed in. Wind direction just wasn’t factored. Then we did some approaches onto roadways, flying at 15 or 20ft to clear the cars and warn them that there were going to be some aeroplane movements before doing practice approaches. And the aerobatics beggared belief.

‘The next day, it was time to take the Swedish pilots flying in the Jaguar. I was at a bit of a loss as to how I was going to explain to this guy that we flew at 420kt when they flew at 620kt. So I decided that the way ahead was to leave the part-throttle reheat in, accelerate to 620kt and then give him the aeroplane. That’s what I did — I took off, and gave him control at 620kt and about 150ft. He pushed the nose down, took the Jaguar down to 30ft and proceeded to fly it at about 30 to 40ft and 600kt-plus quite happily. It knocked all the myths about who’s got the best aeroplanes, who’s got the best-trained pilots and so on. The Swedish Air Force had aeroplanes that were light years ahead of anything the RAF had, or was going to get, or has got now, and their pilots were in a totally different league to us. This was not just an individual — I flew with three of them, and all three were like that. Each of them was able to fly the Jaguar faster and lower from the back seat than I could from the front seat.

‘After that experience, I didn’t think that I would be able to cope with continuing in the Jaguar if I went and flew other aeroplanes. It would have been very depressing."
Source: http://www.collectair.co.uk/pdf/interview-hr.pdf

Have all the Viggens been scrapped?
I watched their latter displays at Farnborugh many times; earlier ones did a pairs takeoff and a co-ordinated display with the 105; they timed it to perfection with the 105 overflying the Viggens on the runway just as they rotated.

Yes, other than the ones in museum's in Sweden (about 14 in various Swedish museums, plus the two flyers with Swedish Historic Flight) and there's about 7 preserved in museums outside of Sweden.

Terrific thread.
Thankyou one and all. 👍

Yup, the engine needs to have subsonic airflow, you cannot run it supersonic, so shock wave and compressibility of the air is needed to slow it down before it reaches the compressor.

A picture of mine showing the water vapour forming on a wet day in a Frightnings intake.

https://live.staticflickr.com/1853/4...90dafe29_b.jpg

According to a program I listened to: https://sverigesradio.se/avsnitt/165076, Sweden's cold-war training losses were quite high compared to other Western nations. Not taking away from what they accomplished, but it didn't come free.

I could believe that, I seem to remember their low flying was down to 30ft

Read Mike Rondots recollections from page 32 onwards, link below and a good read.

https://www.collectair.co.uk/pdf/interview-hr.pdf

Swedish Metal! Hammerfall. Nice.

Having grown with my parents summer house up not far from a few dispersion airstrips it was quite common to have these guys zoom past at treetop level going stupid fast!
Most memorable moment would easily be being out fishing on a long skinny lake when the rumble started on the far side, check over my shoulder had 2 Viggen's heading straight for me well below the treetops! Zoomed past at a height where I could of have counted rivets and the lead didn't bother clearing the treetops as the lake ran out, just put it up on a wing and followed an access road with half a wing sticking down between the trees!

I hadn't seen Mike Rondot's interview before - I found it compelling reading. His summary of the Swedish approach to crewing the Viggen and his comparison with the UK's green-shielder-led "career" approach to putting people in cockpits couldn't be more telling. I know which one I prefer. I wonder if the introduction of the Gripen has led to any loss of capability - I suspect not, but budgets are tight everywhere.