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108 SMITHSONIAN ANNALS OF FLIGHT
to be especially suitable: aniline and its mixtures
with other aliphatic or aromatic compounds
(triethylene-amine, cyclo-hexylamine,
methylaniline, pyridine, ethylaniline, xylidine,
piperidine, pyrrole). Certain mixtures show a
"eutectic hypergolity." The hypergolity of the
above mentioned compounds is so good that
dilutions with inert fuels have been possible.
The group of hypergoles mentioned was called
by BMW "Tonka," and at Brunswick, "Gola."
The BMW research staff conducted studies
themselves in this field of hypergoles with excellent
results (Figure 9).
Unsaturated compounds: Substances belonging
to the acetylene group (Dr. Reppe) as, for instance,
di-acetylene. Vinyl-ethers: vinyl-ethylether,
vinyl-isobutyl-ether, butane-diol-divinylether,
divinyl-acetylene, diketenes, cyclo-pentadine.
The hypergoles of the vinyl-ether group
were called "Visoles" and were mostly used in
combination with amino compounds.
Developers: Pyrocatechol, hydroquinone, pyrogallol,
and, in addition, "Optoles." The components
suitable for hydrogen peroxide proved
to be suitable also for nitric acid.
Others: Furan and derivates, in particular fur-
20
-2
10 sec
15
1
CTS£L-
qA>
Mean sci \tter of
individua values
M ethyl-anii ine
100 80 20
80
+Am
}-Am
20 l>0 60
Aniline
loo
FIGURE 9.—Ignition delays of the hypergolic fuel "Gola,"
showing mean scatter of ten individual values.
J
furyl alcohol, called "Fantol" (Egelhaaf). They
have particularly good hypergolity, especially
with mixed acid, even when diluted to a high
degree with xylol (up to 70 percent). Hydrazine
also reacts hypergolically with nitric acid.
Almost all proposed hypergolous propellants consisted
of mixtures of different compounds. This results,
of course, in a complication of the individual
effects, yet mixing offers the possibility of intensifying
one or the other of the desired properties, for
instance, the chemical affinity of a mixture of two
substances is in some way analagous to the solidification
diagram of a system. Figure 10 shows this
affinity expressed as a limit concentration, i.e., the
acid concentration at which ignition takes place
without perceptible delay. It can easily be understood
that mixtures may have a considerably higher
affinity than the single components, an effect which
has also been proved true with numerous other substances.
The same diagram shows the lowest admissible
temperature, the so-called "cold point." This
cold point is given at both ends of the diagram by
the solidification point, in the middle by the highest
admissible viscosity, which was assumed to be
40 centi-strokes for a particular case. In this special
case the optimum in regard to cold point as well
as that to ignition delay are almost identical. There
are, however, combinations of substances showing
0 20 iO 60 80 % 100
Aniline
100 % 80 60 iO 20 0
Cydo-hexylamine
FIGURE 10.—Characteristic values of the hypergolic fuel system
with aniline and cyclo-hexylamine, showing limit concentration
(i.e., acid concentration up to which no delay is
noticed.