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Page 17
"Exactly. Now, instead of having to depend on the speed of the
aeroplane for this, why not depend on the speed of the propeller
--in other words, the whizzer?"
"Well, we do," said Tom, a bit puzzled as to what his friend
was trying to get at. "If the propeller didn't move the airship
wouldn't rise--that is, unless it's of the balloon type."
"What I mean," said Mr. Damon, "is to have an aeroplane that
will move in the air the same as a boat moves in the water. You
don't have to get the propeller of a boat racing around at the
rate of a million revolutions a minute, more or less, before your
boat will travel, do you? If the engine turns the screw, or
propeller, just over say fifty times a minute you would get some
motion of the boat, wouldn't you?"
"Why, yes, some," admitted Tom.
"And what causes it?" asked Mr. Damon, anticipating a triumph.
"The resistance of the water to the blades of the screw, or
propeller," answered Tom.
"Exactly! And it's the resistance of the air to the blades of
an airship propeller that sends the craft along, isn't it?"
"Yes. And because of the difference in density between air and
water it becomes necessary to revolve an aeroplane propeller many
times faster than a boat propeller. It's the density that makes
the difference, Mr. Damon. If air were as dense as water we could
have comparatively slow-moving motors and propellers and--"
"Ha! There you have it, Tom! And there is where my Whizzer--
Wakefield Damon's Whizzer--is going to revolutionize air
travel!" cried the eccentric man. "The difference in density! If
air were as dense as water the problem would be solved. And I
have solved it! I'm going to turn the trick, Tom! One more
question. How can air be made as dense as water, Tom Swift?"
"Why, by condensation or compression, I suppose," was the
rather slow answer. "You know they have condensed, or compressed,
air until it is liquid. I've done it myself, as an experiment."
"That's it, Tom! That's it!" cried Mr. Damon in delight.
"Compressed air will do the trick! Not compressed to a liquid,
exactly, but almost so. I'm going to revolve the propellers of my
new airship in compressed air, so dense that they will not have
to have a speed of more than seven hundred revolutions a minute.
What's that compared to the three to ten thousand revolutions of
the propellers now used? The propellers of Damon's Whizzer will
be of the pusher type, and will revolve in dense, compressed air,
almost like water, and that will do away with high speed motors,
with all their complications, and make traveling in the clouds as
simple as taking out a little one-cylinder motor boat. How's
that, Tom Swift? How's that for an idea?"
To Mr. Damon's disappointment, Tom was not enthusiastic. The
young inventor gazed at his eccentric friend, and then said
slowly:
"Well, that's all right in theory, but how is it going to work
out in practice?"
"That's what I came to see you about, Tom," was the reply.
"Bless my tall hat! but that's just why I hurried over here. I
wanted to tell you when I saw you going off on a trip with Miss
Nestor. That's my big idea--Damon's Whizzer --propellers
revolving in compressed air like water. Isn't that great?"
"I'm sorry to shatter your air castle," said Tom; "but for the
life of me I can't see how it will work. Of course, in theory, if
you could revolve a big-bladed propeller in very dense, or in
liquid, air, there would be more resistance than in the rarefied
atmosphere of the upper regions. And, if this could be done, I
grant you that you could use slower motors and smaller propeller
blades--more like those of a motor boat. But how are you going to
get the condensed air?"
"Make it!" said Mr. Damon promptly. "Air pumps are cheap. Just
carry one or two on board the aeroplane, and condense the air as
you go along. That's a small detail that can easily be worked
out. I leave that to you."
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