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GOT: The Ambrosini SS.4 / SAI 107 - 207 - 403

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#1 Romantic Technofreak

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Posted 12 February 2005 - 03:33 AM

For everybody new here, last November our good friend GregP made a list of "obscure types", hoping to get more information about these. Although only using beginning letters A-D, the list was very long. Not minding this, me (and others) tried to work it down, marking the topic with "GOT" as "Greg's Obscure Types. He also included the Ambrosini products SS.4, SAI 107, SAI 207 and SAI 403. When recently the microfighter became thematized, I thought to renew the "GOT" series, which I couldn't follow for some time, with a topic about them (The SS.4 is only scarcely mentioned, sorry). There are two good articles on the net about them, one in comandosupremo.com, the other by Ton Meynders in airwarefareforum.com. Ton also provided some pictures. Are both articles worth mentioning? Sure. I thought it would be a quality step to interweave them, combined with processed pictures. This I did below.
For the postwar developments of Ambrosini, I use texts from my (German) airplane encyclopedia (Flugzeuge der Welt, publishing house Bechtermünz, Augsburg 1997).



The possibilities of a lightweight fighter which could be produced inexpensively and in vast quantity have intrigued combat aircraft designers for many years, and numerous attempts have been made to perfect such a machine. In the past these efforts have invariably resulted in aircraft possessing inferior performances to their more orthodox contemporaries, but among the very few exceptions were the delightful little fighters which stemmed from the drawing board of Sergio Stefanutti during the war years.
Chief designer of the Societa Aeronautica Italiana Ing. A. Ambrosini of Passignano, Stefanutti first conceived an interest in the potentialities of a light-weight fighter in 1939 when working on a heavy and obviously under-powered canard fighter, the S.S.4.

(decided to concentrate pictures below, 2013/08/07, RT)



Previously responsible for a series of cabin mono-planes which were noteworthy for their clean contours and good performances, concerning their modest power.

Between 10/38 and 4/39, Sergio Stefanutti designed the SAI.7 as a high-performance touring plane for the civil market. Undoubtedly one of the best looking aircraft ever designed, the SAI.7 possessed exceptionally clean lines, was of wooden construction with plywood skin. The SAI.7 was the first Ambrosini airplane with retractable landing gear, in this instance of the fully-retractable tailwheel type with wide-track main units that swung inward and upward into the roots of the cantilever low-set wing. The first two aircraft were completed in 7/39 with a windscreen design that extended right to the nose for a very clean entry, and were entered in the Avio Raduno del Littorio competition that started a few days after the machines made their maiden flights. The aircraft were too under developed to win the competition, but nonetheless put in a very credible performance that included a maximum speed of 251 mph with a 280 hp air-cooled Hirth HM 508D inverted-Vee engine. One aircraft took a class closed-circuit speed record for a F.A.I. category I plane over 61.2 miles (100 km) with a speed of 244 mph.

51918b49.jpg

The high speed/power ratio of the SAI.7 caught the imagination of the Italian air force which saw considerable possibilities in the concept of a lightweight interceptor that could be built in large numbers without drawing on the country's strategic stockpile of aluminum alloys. Although the type had originally been designed as a fast racing and touring aircraft, its flight characteristics were such that it was readily adaptable for use as a fighter trainer. Accordingly, Stefanutti redesigned the monoplane to fulfil this role, and a fully militarised second prototype appeared in 1941. Differing from the original prototype in having orthodox cockpit canopy for pilot and pupil, and the German Hirth engine replaced by R 280 h.p. Isotta-Fraschini Beta R.C.10 inverted-Vee engine. The fuselage and wingspan were increased and the faired racing windscreen was replaced by a conventional stepped windscreen at the front of a more heavily framed cockpit enclosure with two rearward sliding sections for access, and the landing gear was modified with a fixed tailwheel. These changes increased the maximum take-off weight, but the maximum speed was reduced only slightly to 248.5 mph.

11718076.jpg

The S.A.I.7 trainer evoked enthusiastic reports from Regia Aeronautica test pilots, but by the time the first of an eventual 10 SAI.7 fighter trainers appeared, the increasingly difficult military position in which Italy found itself was reflected in the emphasis on combat aircraft rather than trainers; and so further work on the fighter trainer variant was abandoned until after the war when it was revived and led to the S.7 and Supersette trainers (see pictures on the end of this article).

While the military S.A.I.7 had been under construction, its designer was working on a more powerful single seat variant which, primarily intended for research purposes, was also considered as an ideal test vehicle for the development of the basic design as a combat aircraft. Designated S.A.I.107, the single-seater (photo four) was powered by a 540 hp. lsotta-Fraschini Gamma RC.35 IS inverted-Vee engine driving a two bladed propeller, and, weighing only 2,200 pounds loaded, was flown early in 1942.

6d1bdf8f.jpg

The S.A.I.107 proved to be extremely manoeuvrable, and level speeds in the vicinity of 350 m.p.h. were obtained during flight trials at the Guidonia Test-Centre. Assured of the feasibility of his proposals, Stefanutti then produced a second single-seat prototype, the S.A.I.207, which was built to full fighter requirements and carried an armament of two 20-mm. cannon and two 12.7-mm.. machine guns. The S.A.I.207 was externally very similar to its predecessor, but employed a 750 h.p. Isotta-Fraschini Delta RC.40 engine driving a three-bladed propeller.
The S.A.I.207 had a wing span and length of 29 ft. 6 in. and 26 ft. 3 1/2 in. respectively, and its loaded weight was 4,993 lb.

b1d42d65.jpg

Extensive flight testing was undertaken, during which the fighter attained an indicated air speed of 466 m.p.h., at 10,000 feet in a dive (representing a true air speed of 596 m.p.h., or Mach 0.86). Maximum level speed was 357 m.p.h. and range was 528 miles, remarkable achievements on an engine of only 750 h.p. The photo below shows the S.A.I. Ambrosini test pilot preparing to take-off for the flight during which this remarkable performance was clocked.

2a01960d.jpg

The Italian air ministry ordered Ambrosini to begin work on a pre-production batch and placed an order for 2,000 production aircraft. In the event only 13 of the pre-production aircraft were completed, three of them being allocated to the 3rd Stormo Caccia Terrestre during 7/43 for operational trials. Italy secured an armistice with the Allies just two months later.

While tests were progressing with the S.A.I.207, Stefanutti redesigned the fighter for production, the final model being designated S.A.I.403 Dardo (Arrow). This essentially was a more sophisticated version of the SAI.207 with the same type of stressed-skin wooden construction, but which had fully retractable landing gear rather than the 207's combination of retractable main gear and fixed tailwheel. The S.A.I.403 carried the same armament as the S.A.I.207, and its Delta R.C.21/60 engine gave the same power. Wing area was increased from 149.618 sq. ft. to 155.646 sq. ft.. In addition, changes included a revised tail unit with a variable-incidence tailplane to improve controllability in high-speed dives, greater ammunition capacities, and an upgraded powerplant in the form of the 750 hp Isotta-Fraschini Delta RC.21/60 Serie I-IV driving a three-bladed Piaggio constant-speed propeller.

3ee10d15.jpg

The first SAI.403 flew late in 1942 (other source says early 1943) and revealed exceptional performance, including a maximum speed of 404 mph at 23,620 ft. The estimated maximum range was 582 miles. Loaded weight was 5,280 pounds and overall dimensions included a span and length of 32 ft. 2 in. and 26 ft. 10 in. respectively.

The three variants of the SAI.403 planned were the Dardo-A lightweight interceptor with armament restricted to two 12.7mm machine guns, the Dardo-B general-purpose fighter with two 20mm cannon and two 12.7mm machine guns, and the Dardo-C long-range fighter with 2 20mm cannon and provision for two 39.6 US gallon drop tanks supplementing the internal fuel capacity from the 79.25 US gallon of the Dardo A/B to 108.3 US gallon. Large-scale production of the S.A.I.403 was planned, thus terminating the SAI.207 in favor of 3,000 of the SAI.403 to be produced. None of these fighters had been delivered before the Italian armistice with the Allies and the closing of the program, and further development had to be abandoned.
Despite the remarkable performances attained by these light-weight fighters-which might well be considered as the only practical piston-engined machines in their class ever developed -they achieved little fame, either in the country of their origin or abroad. It is particularly interesting to note that from their design has stemmed the Aerfer Ariete lightweight jet-fighter.

(End of the articles)

The majority of the 145 copies of the post-war Ambrosini S.7s, a lot of single-seaters among them, served in the different aviation shools of the Aeronautica Militare. Besides the military use, which ended in 1956, the S.7 received honour in a number of air races. On December 21st, 1951, Leonardo Bonzi won records on the 100 km and 1000 km distance, flying an average speed of 367.36 rsp. 358.63 kph.

Post-war Ambrosini S.7:

b9db9123.jpg

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While the post-war S.7 was powered by an Alfa-Romeo-115 inline engine delivering 225 hp, an upgraded version appeared in 1952, the S.7 Supersette, driven by a De Havilland Gipsy Queen of 355 hp. One received swept wings as part of the development program for the jet fighter Aerfer Sagittario.

Pictures of the Supersette (Super-Seven):
On the same occasion like the "7" above, on advertising tour (for own pupose) in Portugal:

4aab50e9.jpg

During its time, the Supersette was called "most beautiful airplane of the world" (I agree). The I-PAIN survived, it is shown in the Technical Museum in Milan.

In the Air Force Museum of Vigna di Valle, under the wings of a CANT Z.506:

 

(old picture disappeared, better solution coming soon, 2013/08/07, RT)

 

 

The cowling changed, no optical win in my eyes. For balance, the picture is very good.


The fist version of the Sagittario jet fighter still shows the characteristic fuselage and cockpit silhouette of the piston-driven Ambrosinis:

http://img.photobuck...no/20afc0b5.jpg (photobucket disaster, see better below, 2013/08/07, RT)



#2 seppalar

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Posted 12 February 2005 - 06:03 AM

Thanks Romantic Technofreak,

that's a really intersting article. But just think what Italy could have done if Germany supplied it with the Aluminum used in the He177 program and a thousand or so DB 605's. Germany had the capacity to produce them too.

Would we all be speaking Italian?
;)

Just joking, I only wrote that because one usually says, would we all be speaking German, Russian, Japanese etc.

#3 GregP

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Posted 12 February 2005 - 02:05 PM

Hi Romantic Technofreak,

I had no idea that "GOT" was "Greg's Obscure Types."

I am flattered and somewhat embarassed.

Anyway, I thank you for the monicker, and will attempt to continue offering obscure types to the board. The problem is that I am running out of obscure aircraft types.

I have a limited supply of types that were actually made and flown.

Anyway, I finally know what "GOT" means, and I am surprised, to say the least!

#4 Romantic Technofreak

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Posted 12 February 2005 - 05:45 PM

Hi Greg,

it's not my intention to further embarass you, believe me, but I think I have to, sorry.

In the following (linked) topic you made up your list:

http://www.tgplanes....sp?TOPIC_ID=469

I answered that I like to work down the list and always mark the topic like this: We can begin the headline with GOT (= Greg's Obscure Types), followed by a colon and the name of the type. You answered this being a good idea, and I started with those topics.

Some time later, our friend gr6238 (although he didn't show up here any more since some time) opened a topic on the Bell FM-1 Airacuda. See it here:

http://www.tgplanes....sp?TOPIC_ID=490

As this aircraft is on your list, Greg, I would have preferred that gr6238 would have marked his topic also with "GOT", but he didn't. I was asking you if you are satisfied with the answers written down there or if you like to have further investigation ("could the aircraft be checked off?"). You already asked there "What does the abbreviation GOT mean, RT?", and I answered "Greg's Obscure Types, of course!" ad marked this with some smilies, because I was surprised that you obviously didn't remember our conversation in the first topic. I received no further answer, so I thought it's clear now!

But at least, there will be no further irritation. I also have to admit that I mainly do this job for myself, and also for other users of tgplanes.com that like obscure types and want to have an archive about them, since good informations about them are hard to get. You are also NOT running out of types, remember your list only contains aircraft beginning with letters A to D, and even this list is nearly impossible to finish within assessable time. What if you post a list using the other 22 letters of the alphabet?

Anyway, the GOT series will be continued, always reminding on the one who gave the idea. And, it may be work (but surely not more than, e.g., modelling planes), but it's lots of fun!


To Seppalar:

I think Italy had a surplus of aluminium, also supplying Germany with it. But the skin of the Ambrosinis (even the post war jets!) was made of wood! In this light, the above mentioned "strategic stockpile of aluminium alloys" isn't a good argument. As much as I researched, the superior Italian Caproni-Vizzola fighter series was rejected by the Regia Aeronautica because it also was made from wood! (I am going to repeat this argument when the speach comes on them, they are also on Greg's list.) This also may explain the 2-year delay in the development of the Ambrosinis.

Woud we speak Italian? If I had been the Great Axis Leader that won the war, I would have obliged the defeated world to have an everyday meal of Sauerkraut, Sushi and Spaghetti (altogehter of course, it doesn't taste :wacko:, but it's healty, I swear! :D )

Regards, RT



#5 GregP

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Posted 13 February 2005 - 12:43 AM

Hi Romantic Technofreak,

I must have been drinking that night ....

Anyway, how about another obscure type?

I give you the Breda Ba.201:

It was s single seat dive bomber, similar to the Junkers Ju-87, but with retractible gear. It used the DB 601A engine, which is why it didn't get built ... all the DB 601As were to be used for fighters. Anyway ...

Span: 13 m, Length: 11.09 m, Height: 3.1 m, Wing Area: 24.8 sq. m.

Engine: DB 601A, 876 kW.

Speed: 460 kph

Armament: 2 x 12.7 mm MG, Bombs: 500 kg

http://translate.goo...sa=G&as_qdr=all
Enjoy!

#6 Romantic Technofreak

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Posted 13 February 2005 - 02:43 PM

Yes, Greg, the Ba.201 is also on your list. But it takes time to write a good GOT article, as long as there is no solid documentation in English language on the net, or I don't have a good description in one of my books. That's how it is with the Ba.201. But there is an article in samoloty.ow.pl about it. As you know, it has to be translated first. I think I don't have time to do it until next weekend. Do you want the Ba.201 to be next?
I still got no answer from you if you are satisfied with the documentations about the FM-1 Airacuda (within the second topic I quoted in my last post here).

Regards, RT



#7 GregP

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Posted 14 February 2005 - 01:04 AM

Hello Romantic Technofreak,

Sory. Yes, your answer is very good, and I was not intending to press you about tanslation. I just mentioned the Breda to add some fuel to the fire.

Your researches and posts are generally informative, well though out, and appreciated by all. :)

#8 Ricky

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Posted 14 February 2005 - 06:22 PM

Agreed!:)

#9 Romantic Technofreak

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Posted 15 February 2005 - 02:46 AM

Thank you, friends. :) Greg, I don't feel pressed at all. The Ba.201 will be done anyway, it's only a matter of time. So, if you or somebody else has a "special pet" among the list, I could please more than one person (i.e. me) by dispatching it earlier than it is on my personal time-table. That's why I would welcome any proposal in this direction.

But the Ba.201, in any case, deserves an own "GOT" topic. So, it can be recalled much more easy. I also intend the "GOT" label for a kind of advertising for tgplanes.com. If a stranger is interested in a special "obscure" planes, he may find it here, see more "GOT" labels and become further interested in reading and archivating!
Greg, can I get an answer about the Airacuda[?]



#10 GregP

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Posted 15 February 2005 - 08:47 AM

Hi RT!

Yes, I am satisfied with the Airacude answers. It is, admittedly, and obscure type that no one is very much interested in, and I think a 3-seat fighter is an obvious failure from the start, if only due to power-to-weight ratio.

The basic design has merit if the guns are automatic .. without gunners. We have the technology now, but it was a bit out of reach in WWII.

OK, I'll come up with a list from the letters after "D" and post it, along with some basic spceifications for each.

Alternately, send me your address and I'll send you a CD with a LOT of "obscure types." I reside at "[email protected]" .

By the way, I like your researches and posts a lot, so don't go away on us ... as I said, we LIKE you. :D

One last point, I know you are from Germany ... the third Me-262 made in the U.S.A. will go to Messerschmitt in Germany. When it arrives, be sure to go see it. The main landing gear is from a Grumman S-2 Tracker! ... but it looks good on the Me-262. The new Me-262s can be configure as either single or two-seat planes as the owner desires!

Take care, - Greg





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