1.1.
Studies and development of the original design
In 1950
the Messrs. Nardi, Milan, decided to study a three-seater amphibian plane
having limited performance, to be used as a
touring plane in Italy and South Europe.
A
prototype was built with few means and without much care during the same
year, but the flight tests did not prove satisfactory, chiefly owing to
the bad layout of the rear fuselage and engine fairing which did not
permit to reach the calculated performance.
Anyhow
Nardi, surprised by the general interest for its aircraft, did not give up
the project but studied a new four-seater prototype with a more powered
engine, revising the previous layout. This plane was completed in 1954 and
started its flight tests in the late autumn of the same year. The tests
were carried out with the utmost readiness, compatibly with the bad season,
and revealed at once that the defects found in the old prototype had been
successfully removed, but at the end of
January
1955 the aircraft was destroyed by an accident.
Since a
great number of satisfactory results had been obtained in the meantime,
Nardi decided to complete the production of other three prototypes. At the
same time FIAT offered its financial co-operation for the further
development of the FN-333, being interested in mass-manufacturing
the aircraft on a license agreement, in view of its market opportunities
abroad.
The
project was further revised according to the U.S.A. Civil Aeronautics
Regulations, Part 3, in order to obtain the U.S. Type
Certificate.
The
flight tests of the third prototype began on October 1956. The very severe
and complete test program was carefully documented
through an up to date recording system of several parameters, supplied by
FIAT.
On
completion of the flight tests, in March 1958, the aircraft obtained the
provisional Italian Type Certificate, pending the accomplishment of the
propeller flight vibration tests. These tests took a long time, since an
adequate instrumentation was not available in
Italy, and were completed only at the end of 1958. Also in 1958 the U.S.
Type Certificate was granted.
In the
meantime FIAT, owing to its heavy engagements for the production of a
fighter plane of its design, was no longer in a position to plan the
mass-manufacture of the FN-333 and, on Nardi's request, transferred the
relative license to SIAI Marchetti which signed an agreement with Nardi in
March 1959.
In
1959, while the SIAI Marchetti Production Department arranged for the
manufacture of the necessary tools for a first pre-series, the Engineering
Department submitted the prototypes to a valuable flight activity and
carried out, thanks to its wide experience in
the seaplane field, many important improvements on the plane.
The
Nardi design was carefully re-examined in order to obtain the certification
for a gross weight increase up to 1485 kilos and for a power increase up
to 320 horsepower T.O., while the U.S.A. Aeronautical Standards were
applied to every part of the airplane.
To this
purpose two of the three prototypes built by Nardi are now being
re-manufactured with all the equipment conforming
the U.S. Standards.
1.2
SIAI Marchetti modifications to the Nardi design
SIAI
Marchetti has duly modified the Nardi design to obtain a production plane
from a prototype. In particular, the following problems have been
carefully studied: parts interchangeability, maintenance facilities and
protection against corrosion.
In this
connection, SIAI Marchetti has decided to apply the U.S. Navy
Specifications to the finishing coats, the lubricants and the contact of
dissimilar materials, and has replaced the majority of the common steels
with stainless steels and even with nickel
alloys where a fully corrosion proof was required.
An
important modification introduced by SIAI Marchetti in the Nardi project
concerns the replacement of the steel main landing
gear with a new all aluminum alloy landing gear of a simpler design, fully
retractable in the central part of the hull instead
of in the wing.
SIAI
Marchetti has moreover modified the original project, in co-operation with
the Continental Motors, to obtain an increase of the approved take-off
weight from 1350 to 1485 kilos, together with an increase of the installed
power from 240 to 320 horsepower take-off. In
this manner the FN-333 production will be available in two different
models:
FN-333
Model B: Take-off gross weight: 1425 kilos - Continental IO-470
engine, rated at 275 horsepower take-off and 260 METO
- Coupled with a two-blade propeller.
FN-333
Model C: Take-off gross weight: 1485 kilos - Continental IO-520
engine, rated at 300 horsepower take-off and 280 METO
- Coupled with a three-blade propeller.
(The
FN-333 Model D, with a Continental engine rated at 320 HP T.O. and 300 HP
METO, will be available as soon as the engine
gets the necessary F.A.A. approval.)
On the
first 10 pre-series units of the FN-333 will be installed the Continental
IO-470-H engine with a power of 250 HP, since the supercharged engine will
be available about the end of this year. It has been established however
that the following production units will be
available in the above B and C version.
It is
to be noted furthermore that SIAI Marchetti has studied the installation
of the power plant in co-operation with Continental, so that the two
engines IO-470 and IO-520 are quite interchangeable. It is therefore
possible to change every moment B configuration into C and vice versa,
which do not require other work than the mere replacement of the engine and
propeller.
