Possibly the most promissory project undertaken by Dr. Horten in the  Instituto Aerotécnico, the I Ae 37 borne in 1953 as a twin engined supersonic interceptor in which four development stages were foreseen: 

The works began with intensive wind tunnel testing and then continued with the launching of reduced scale models with a weight of 15 to 20 kg. over San Roque lake, models that reached speeds of until 200 km/h and very often could be recovered without damage to continue the tests (near 200), that were supervised by Dr. Karl Nickel.

Wind tunnel testing revealed that an eddy  formed at the top of the wing , behind and approximately parallel to the leading edge, whose diameter grew with the increase of angle of attack of the wing and at the same time it moved backwards. It seemed appropriate to place the elevons in the eddies area to increase their effectiveness and maintain their response even with angles of attack of 30 or 40 degrees. Then it was discovered that the suction of the eddy was strong enough at low speeds so as to cause negative control surface pressure . 

With the encouraging results obtained from the wind tunnel tests and the scale - catapultable models, a wooden glider was built in 1954. His pilot adopted a prone position (almost laid down). Dr. Horten thought that such a position would bring out several advantages to the machine pilot (he would be in a better situation to support rough turns and to see the paveway in takeoffs and landings), and would produce an aerodynamically clean fuselage, without protuberances; and with the great possibility for that age to provide to the pilot with a completely launchable canopy to diminish the impact of an ejection in a conventional seat at two times the speed of sound. 

Such a glider flew by first time in October 1st of 1954 with Captain Jorge Doyle at the controls, towed by a  three - engine JU 52/3M. At the end of the flight his pilot expressed his satisfaction about the flying qualities of the machine, and overall in landings . 

During landings, it was observed that the plane rose his nose and supported an angle of attack of 25 or 30 degrees without trouble, and so landed over the way with a short run. A similar thing occurred during takeoffs (short run followed by a climb of 25 to 30 degrees), which leaded to adoption a high leg for the nose landing wheel and to provide the engined version with a variable height one, regulated by means of hydraulic pressure, to let shorter takeoffs and landings. 

The flying tests went on (near  100 hours) and so the good results. Captain Doyle, 1st Lieutenants González, Rosell and Balado, and Heinz Scheidhauer (the later test pilot of the Horten group) alternated at the controls. It was decided then in 1955 to begin the building of the engined  subsonic version with a Rolls Royce Derwent V turbine to anticipate possible troubles with the supersonic version. It was expected to end this version before 1956. 

Regrettably a Coup d' Etat in September of 1955 sets a parenthesis to the project because of redistribution of public funds, and it is not until 1958 that they were available again. 

Dr. Horten does not remain inactive and  introduces various changes in the original glider, being the most notable the adoption of a normal enclosed canopy, with a Plexiglas bubble sliding to the rear. After testing it 50 hours it was decided to build the engined version. 

Then the planning of the project suffers a change. Dr. Horten suggested to  continue with the building of the I Ae 37 as an advanced subsonic trainer, and develop the I Ae 48 as a twin engined, all weather, two - place interceptor,  capable of reach (and surpass too) Mach 2. 

During 1960, with the subsonic I Ae 37  in advanced state of building (it was expected to finish it in 1961) and with the works over the I Ae 48 recently started, again comes the order (and now definitive) to stop works because of  "lack of funds". 

End point (and a regrettably one) for one of the most brilliant chapters of the history of the Instituto Aerotécnico - F.M.A.