The Light Plane with the Best Military Potential

[GregP]

Not many light aircraft ever get taken in by the military. Fewer still see their maximum speeds increase by as much as 10% over their useful lifetimes.

I give you one that saw it maximum speed go from 200 kph to 1080 kph!

I am speaking, of course of the Ambrosini SAI.3 and the series of aircraft that followed it.

The SAI.3 of 1937 was a light civil aircraft of graceful line, powered by a Fiat A 50 engine of 67 kW and had a maximum speed of 200 kph. It was 550 kg empty and 790 kg loaded. While it was a good little airplane, it grew into the SAI.7 of 1938.

The SAI.7 was a light trainer with a Hirth HM 508D engine of 209 kW and a speed of 399 kph. Empty is was 1055 kg, while loaded it was 1355 kg. So, the deasign was refined and the speed doubled for an increase of 311% in power. Still, 209 kW is NOT a big engine.

Then the neat little SAIs went to war. The SAI.7 turned into the SAI.107 fighter prototype. It went from a 2-seater training plane to a single seat monoplane with a 403 kW Isotta-Fraschini Gamma R.C.35 engine and a top speed of 500 kph at a 1600 kg loaded weight. The 107 had 1 x 7.7 mm MG and was not much of a threat to anyone. It was a development platfrom.

Next, it morphed into the SAI.207. It retained an Isotta-Fraschini engine, but the power, weight, and spped went to 559 kW, 2420 kg, and 640 kph. It had 2 x 12.7 mm MG and 2 x 20 mm cannons, and wasa formidable fighter, if only existing in a prototype quantity of 14.

Next, it turned into the Ambrosini SAI.403 Dardo. An Isotta-Fraschini Delta R.C.21/60 engine of 559 kW was retained. Weight grew to 2643 kg and speed was 648 kph. The Italians built one 403 and that might have been the end of it.

But, in 1949, the family grew into the Ambrosini Super 7. It was a civil light plane with an Alfa Romeo 121RC14 engine (a license-built de Havilland Gypsy Queen 70) of 261 kW with a speed of 430 kph. Empty it was 1250 kg and loaded it was 1610 kg, pretty close to the SAI.7 of old. Many claim this family is one of the most beautiful light planes ever built. I concur.

That might well have been the end of the Ambrosini line, but Ambrosini became part of IMAM or Industrie Meccaniche Aeronautiche Meridionali Aerfer, sometimnes called simply Aerfer.

Aerfer took the Super 7 and fitted it with swept wings and tail, a jet engine (Rolls Royce Derwent 9 of 16 kN thrust), and morphed it into the Aerfer Sagittario2 of 1956 that became the first Italian plane to exceed the speed of sound in a dive. Max weight was 3300 kg. Two were built and gave Aerfer valuable experience in jet aircraft. An early version of the Sagittario2 has the same Super 7 canopy before the bubble was fitted and conventional landing gear (tailwheel). The family resemblance is obvious and it later went to tricycle landing gear.

Last, the plane morphed again into the Aerfer Ariete. It has a Roll Royce Derwent 9 plus a Soar RSr 2 Auxilliary Turbojet, taking the thrust from 16.0 kN to 24.1 kN. Weight was 3535 kg, and top speed was 1080 kph. One was built and, to the best of my knowledge, is still with us in an Italian museum. It had 2 x 30 mm Hispan cannons and was a formidable fighter aircraft, if only a prototype.

I know of no other aircraft of any other nation that underwent such an extreme change in speed and capability as the little Ambrosini SAI.3 did before its course was run.

Even today, I think the Super 7 would be competitive in the light aircraft market if anyone chose to reinstate production. It is beautiful, fast, and would be a good performer, even in 2006.

Hats off to Ambrosini! :)

[Dogwalker]

Very good story. :D
I have only a correction and one adding.

Two prototypes of SAI 403 were built. The first crashed for the failure of an aileron during a test flight in may 1943, the second, after the official inquiry established that there wasn't an error in the project, was assembled in the Aeronautica Lombarda plant and made several test flight from february to late spring 1944.

The Ariete was not intended to be the final evolution of the family, but only another test prototype to study installation of two different engines in the Sagittario's fuselage.
The final evolution had to be the Aerfer Leone. Equipped with a 3090 kg thrust Bristol Orpheus BOr.12 engine, and a 4100 kg thrust De Havilland Spectre kerosene booster, it was intended to be able of supercruising with only the jet engine, and to reach Mach 2,34 with the booster but, for a sudden shortage of funds, the Leone project was aborted.
Both the Sagittario II and the Ariete are still with us, in the museum of Vigna di Valle

The Sagittario II at the time of it's supersonic flight.
http://www.planes-and-tanks.com/HangarD/AmbrosiniSagittario2Foto1.jpg

The Ariete
http://www.ottocubano.com/images/MUSEO%20VIGNA%20DI%20VALLE/DSC05880.JPG
http://airpower.callihan.cc/images/modernf/Ariete-iaf.jpg

[Red Admiral]

http://www.airwarfareforum.com/upld/img3/O-1149544674-x4y40ysA.jpg

Courtesy of ghibli on airwarfareforum

[GregP]

Hi ,

Thanks for the pics! I think the series is a very handsome aircraft, with almost ideal proportions and areas.

I wish the Super 7 was still being made today. I'd LOVE to fly one.

[Ricky]

The second one down looks very like the French Caudron light fighter...

[GregP]

The second one down is the SAI.107 after they found out that the extended streamlined canopy of the first drawing was pretty good for everything except the ability to see out of it. The distortion caused by the LONG canopy extension made the pilot almost blind when looking straight ahead. Not good in a plane intended for either training or combat.

Drawing number 2 is baslcally drawing number 1 (the original S.107)with the canopy extension removed and new, more conventional windscreen fitted as S.107, take two, that also moved the cnopies back a bit and also modified the engine and cowling. If I am not mistaken, it is the same airframe after modification.

Drawing number 5 is the Super 7 that I contend could be competive today with a Lycoming or Continental engine.

[Red Admiral]

1-SAI.7 racer
2-SAI.7 trainer
3-S.7 (monoplace)
4-S.7 Super aka "Supersette"
5-Final configuration of the "Supersette" (Alfa 121 engine)
6-S.7 Freccia
7-Sagittario I


The Supersette is one of the best looking planes ever and goes like a rocket as well. Even so, I absolutely love the swept-wing Freccia.

http://www.airwarfareforum.com/viewtopic.php?t=5863&highlight=freccia

[Romantic Technofreak]

Hi friends,

I couldn´t join the discussion in the "Aerodynamics, Power, Speed, and Drag" topic by Greg because I am not an engineer and I had too little time, but what I have to say is that I think that any piston-engined Ambrosini S.whatever is near to its development limits, what affects the whole lightweight fighter category as well. As it was stated in this topic, the amount of power needed to achieve considerable speed improvement quickly reaches the ranges of a normal WWII high-performance engine. But the Ambrosini airframe with its low-drag advantages requires the small dimensions and weight of the Isotta-Fraschini Delta engine (Dogwalker already stated something similar in the AMbrosini GOT topic).

Although I don´t believe Montanamotor needs that, please still let me point out that his replica project, using a completely different engine, also needs a very-well coordinated relation between engine and the rest of the aircraft.

Regard, RT

[GregP]

Before we get into identification arguments, maybe you should look at the following link:

http://avia.russian.ee/air/italy/a_ambrosini.html

Just pick one and follow the link. The SAI.107 is clearly identified here and in other references I have seen.

The Supersette is the Super 7 in my posts, and I really like it. :)

Hi RT!

Montanmotor has a reallly interesting project on his hands. He only needs an engine of similar power, weight, and mass, that fits into the cowling. the Continental MAY well fit the bill, but has "development challenges" written all over it. I hope he makes it and will consent to post his progress in this forum. In any case, he seems more than willing to attempt the task and wish I could help!

[Dogwalker]

To me the mistake is in the word "lightweight".
As I stated before, The Ambrosinis were not so lightweight. The SAI 207 was as heavy as a Macchi C.200 and heavier than the SAI S.S.4, that were not intended to be "lightweight".
The real goal was to build a fully capable fighter, using completely different supply lines than that crowded for the exigences of Fiat And Macchi, and that were already insufficient for Reggiane.
To make this, weight is necessary. The WWII fighters had needs in term of warload that couldn't be reduced, and with the disposable materials and techniques, it was pratically impossible for an aircraft to weight less than 4 times the load.
The wooden structure probably added some kg to the theoretical minimum weight of the SAI 7 series aircrafts (Stefanutti was a specialist of metallic structres first than wooden ones) and the wood is a labour-intensive material, but, since it requires less specialized machinery than light alloy, it had some advantages too. In case of bombings, great part of the production could be scattered in different places.
The detractors niknamed the SAI 207-403 "il caccia autarchico" ("the autarchic fighter", cause usually "autarchic" materials was not so good), since it didn't requires imported materials.

As for the prestations obtained by his aircrafts using less powerful engines than that the contemporaries (it's the same with the jet equipped ones), after the war Stefanutti Stated (as I remember):
"When a new aircraft is projected, starting from "0", the first part that's ready is the structure and the external shape, the last is the engine.
Engines had a long developement time, and when they were finally ready, their prestations were never those expected.
I prefer to start with well known, reliable and disposable units, even if they could be considered outdated, and to spent some hours more on the drawing table".

The "SAI 7 series" aircrafts were equipped with many different engines, so I dont' think the engine to be so important (obviously the mounting had to be carefully studied). The Delta engine was not so special, and, having the possibility, Stefanutti probably would have chosen a DB engine too. Its only real dimensional advantage over a DB 605 is the weight (about 200 kg less, not counting the adjunctive weight of the cooling system of the DB), but it was only 20 cm shorter and had about the same width than the German unit. The SAI 207-403 fighters had sleeker fuselages than any DB engined fighter, but it was due to the extremely compact mounting of all the accessories, and could be replied with any other inverted V engine.
A shame that I never seen a picture of a SAI 404/503, to wiew the aerodinamical solutions studied to mount the bigger X-shaped "Zeta" engine.

Obviuosly the drag of the radiator of a liquid cooled engine could be a problem, but not an insoluble one. Both Stefanutti and Longhi faced it.
Stefanutti's S.S.4 was equipped with a 960 hp Asso IX engine, that had pratically the same cooling requirements of a DB 601, but the aircraft had only very small external air intakes for the radiators.
Longhi equipped a Re 2001's prototype with a couple of radiators mounted internally in the wing's thickness, with the intake in the leading edge and the exaust over the wing, and that was sufficent to improve it's speed of 55 Km/h over a standard Re 2001 (the project of the RE 2005 at that time was too advanced to change it, but this solution was saved for the Re 2006).

[montanamotor]

Hi, friends.

The boy is back in town. I had one hell of a time over the last two weeks, to execute my own professional duties as well as my partner's one's, at a time - due to his slipping, falling and, cracking some ribs a good fortnight ago, while he was inspecting an industrial plant which we are going to buy soon. So, I simply had to rip myself apart to conduct not only my own business tasks every day, but his one's, also. I am really sorry, I had to neglect you for so long, for that reason. It won't happen again - I hope...

Thank you very much for the warm words you have for my Ambrosini-project. I am not going to let you down with it. Promise. In fact, your kind and, serious interest in this dream of mine gave me a big shot of motivation - even more, than I already had, before I met you.

I must confess, I didn't make it to contact the possible sources for plans which you mentioned to me, over the last two weeks. But I will do this right NOW. I will start typing letters right after I'll have finished this message to you. Cross my heart!

At least a few precious things I could fix in the meantime, anyway.

I got in contact with two companies in Germany, which are still manufacturing general aircraft from spruce. Both shop-owners told me that, it would be no problem for them at all to equip me with sub-assemblies of an Ambrosini-plane, whatsoever - provided, I could get the original construction plans of it for this.

Another good point: Ifound out that, a company with which I had contact on another project some time earlier, is certified by the german "Luftfahrt-Bundesamt" - the german "federal bureau of aeronautics" - to cut aircraft parts from plywood by use of a CAD-controlled laser-cutter! So, after they once had got the original Ambrosini-construction plans digitized and converted to a CAM-cutting plan, they could provide me with aircraft-certified parts in immaculate quality and endless numbers, merely for a bargain per each single piece of wood cut.

I'll report back as soon as I'll have got answers to my inquiries for the plans from the known sources. In the meantime, try and check the website www.team-38.com for a great power plant for experimental aircraft. If it was for the resurrection of the S.7-two-seater, their choice of Chevrolet-based MARATHON 350 and, 502 V8-engines are really worth a closer look. Try it out and play around with the optional equipment for those engines a little. I really liked what I saw.

For my SAI 403 Dardo-project, I'll rather stick to my first choice, the Continental V 1790, unless someone else surprises me with yet another choice of a great aircraft-power-source in the 1000 HP-range. (No, NO Turboprop eligible! Too few pistons in there, ya know...)

Okay: The future starts NOW! I'll be back - soon!

Cheers!

Montanamotor:)

[Romantic Technofreak]

Sorry if I meddle here again, friends, because my technical knowledege is limited if compared to yours. If I should not doubt the practicability of installing a DB 60X engine in the Dardo, and especially considering Dogwalker´s words about the concept, I still have to say this "not-even-lightweight" concept looks like being at the end of its capabilities. If developers continue going a way starting by the additional 200 kg more of the DB engine, the doors for further claims in this direction are wide open. More and heavier guns, more wing area to increase maneuverability, greater range, additional equipment... and like coming through the backdoor, the normal high-performance fighter is reinvented...[:0]!

Thinking conceptually, there should have been another, really radical solution for the lightweight fighter concept. Frontal drag reduced to an extreme minimum, newly constructed shrunk engine, less, but powerful weapons (maybe only one 30mm cannon) to make this aircraft a point-defence-fighter with an unsually good rate-of-climb and acceleration, something like a piston-driven Me 163...[:p]

(RT Skunk Works have spoken again...)

Regards, RT

[montanamotor]

From pure Carbonfiber-resin, I suppose a modern Dardo - less military equipment (300 kgs in "old" Dardo!) - even with a Continental V 12-engine, might be manufactured to 1400 kgs empty wheight, 1800 kg loaded. But even a wooden airframe would come only about 200 kgs heavier, than carbonfiber. A lightwheight-engine could cut again perhaps 200 kgs off that.

So: Lowest possible estimate 1600 kgs loaded, lowest reasonable estimate 2000 kgs loaded.

I suppose, you can't positively get any lighter than that, RT, without drastically changing the basic aircraft-design (going for flying wing-technology, or like).

Cheers,

Montanamotor :D