to wait till René Leduc « re-discovered » the process
for the thermal jet engine nozzle to come to real life. The ramjet
engine could appear as the ideal engine, in particular to conquer
high speeds. Truly speaking, its advantages were far from insignificant.
The absence of moving parts, a rather low cost induced by its
simplicity of manufacturing, a fuel consumption much lower than
that of rockets, not to mention its adequation to high speeds,
all these elements pleading in its favour and possibly accounting
for René Leduc's relentlessness to impose it in the field of aeronautics.
Yet the ramjet engine suffers a major flaw, one that is not easily
by-passed : its inability to make any flying object take
off by itself. An aeroplane equipped with that propulsion system
will be either piggy-backed from another aeroplane or equipped
with a dual propulsion ensuring its take-off, or even will be
catapulted from a specially devised trailer, which, one will admit,
makes its implementation highly intricate.
Nevertheless, the ramjet engine did not vanish from the aeronautical
scene with the Leduc and Nord-Aviation's « Griffon »,
the latter being equipped with a dual propulsion, thermo - ramjet
Corporations such as Sud-Aviation, Nord-Aviation or ONERA quickly
understood the advantages they could gain from this process, speeds
above Mach 3,5 not being within easy reach while using a sole
turbojet. Right from the beginning of the fifties, various tactical
missiles with ramjet engine propulsion accelerated by powder rockets
were designed. An example of that system : Matra-Aerospatiale's
current ground-air ASPM (Average Range Ground - Air) missile.
Still, ramjet engine's future will perhaps not be limited to missiles
alone. On both sides of the Atlantic ocean, many researchers seem
to be thinking that a bright future can be expected for engines
combining take-off turbojet, broadly hypersonic speeds ramjet
engine, and rockets for out-of-atmosphere forays. The ramjet engine
would operate for speeds in excess of Mach 3 (it should be noted
that so far the fastest atmospheric propulsion machine is SR-71
at Mach 3).
This concept has been studied in particular for designing « orbital »
planes able to free themselves on their own from the atmosphere
and the vacuum that delimits the new frontier for the aviation
of the 21st century, aiming at operating without the
extremely expensive rocket launchers.
In spite of Leduc's relative failure, the ramjet engine gained
widespread acceptance. It should be noted that even though the
Americans and Russians are closely investigating that type of
engine, France, which has always been highly innovative in the
ramjet engine area, of which it remains the cradle, still holds
a dominating position in that field where projects abound. Therefore,
the end of the Leduc should not be interpreted as an extinction
for ramjet engines which should enjoy a bright future in the area
of hyper speeds (superior to Mach 5), where turbojets are ineffective.