cess of the Weight. That means I shall ascend slightly, at
the same time making nearly maximum speed for the power and thrust.
Can't I do better than that?"

"Yes, indeed," spoke up the Propeller, "though it means that I must
assume a most undignified attitude, for helicopters[2] I never approved
of. In order to ascend more quickly the Pilot will deflect the Elevator,
which, by the way, you see hinged to the Tail. By that means he will
force the whole Aeroplane to assume a greater Angle of Incidence. And
with greater Angle, the Lift will increase, though I'm sorry to say the
Drift will increase also. Owing to the greater Drift, the Speed through
the air will lessen, and I'm afraid that won't be helpful to the Lift;
but I shall now be pointing upwards, and besides overcoming the Drift in
a forward direction, I shall be doing my best to haul the Aeroplane
skywards. At a certain angle known as the Best Climbing Angle, we shall
have our Maximum Margin of Lift, and I'm hoping that may be as much as
almost a thousand feet altitude a minute."

[Illustration: The angles shown above are only roughly approximate, as
they vary with different types of aeroplanes.]

"Then, if the Pilot is green, my chance will come," said the Maximum
Angle of Incidence. "For if the Angle is increased over the Best
Climbing Angle, the Drift will rush up; and the Speed, and with it the
Lift, will, when my Angle is reached, drop to a point when the latter
will be no more than the Weight. The Margin of Lift will have entirely
disappeared, and there we shall be, staggering along at my tremendous
angle, and only just maintaining horizontal flight."

"And then with luck I'll get my chance," said the Drift. "If he is a bit
worse than green, he'll perhaps still further increase the Angle. Then
the Drift, largely increasing, the Speed, and consequently the Lift,
will become still less, _i.e._, less than the Weight, and then--what
price pancakes.[3] Eh?"

"Thank you," from Efficiency, "that was all most informing. And now will
you tell me, please, how the greatest Speed may be secured?"

"Certainly, now it's my turn," piped the Minimum Angle of Incidence.
"By means of the Elevator, the Pilot places the Aeroplane at my small
Angle, at which the Lift only just equals the Weight, and, also, at
which we shall make greater speed with no more Drift than before.
Then we get our greatest Speed, just maintaining horizontal flight."

"Yes; though I'm out of the h