User Guide

100
101
SLOW FLIGHT AND APPROACH TO
LANDING STALLS
Now we’re going to explore the effect of the flaps on the air-
plane. The big “barn door” flaps on the 172 move backward, as
well as downward, as they extend. This makes them very effective
for increasing lift: not only do they increase the curvature of the
wing by lowering its trailing edge, but they increase its area as
well.
At full deflection, they also create a great deal of drag. The
172’s flaps can be set at any position between full up and full
down, but pilots typically use
the three “notches” in the flap
control. The first notch, at 10
degrees, produces much more
lift than it does drag; it can also
be extended at speeds up to 110
knots. Full flaps, at 30 degrees,
create much more drag than lift;
you have to be below the top of
the white arc, at 85 knots, to
lower them. The 20 degree
notch “splits the difference”
between lift and drag, but is sub-
ject to the same 85-knot speed limitation. (Older 172’s had a final
notch at 40 degrees that let them come down like parachutes - but
left you so little energy for a soft landing that you really had to
know what you were doing!)
Set the airplane up in level cruise flight and engage the
autopilot so you don’t have to worry about keeping the wings
level (remember, the autopilot in the 172 has no control over the
pitch axis). Make sure the airspeed is below 110 knots. Now lower
the first notch of flaps.
You’ll notice an impressive pitch-up and “ballooning”—the
airplane will gain a couple of hundred feet of altitude. This is
because you’ve created a major increase in the wing’s lift without
changing the amount created by the tail. Wait until the airspeed
settles down again and note its new value. It’ll be lower than it
was before, the airplane will be at a slightly lower nose attitude,
and it’ll be descending slightly.
Practice this several times. What you’re working toward is a
recovery with minimum loss of altitude once the stall “breaks.”
DEPARTURE STALL
To the extent that the 172 can be goaded into a full stall at
all, the ones we just did were the easiest and most docile. Now
let’s look at another type: the departure stall, in which we simu-
late someone trying to climb too steeply after takeoff.
In level flight, after making your clearing turns, pull the
throttle back to or near idle, holding your altitude and letting the
airplane decelerate to near its normal takeoff speed of around 60
knots. Trim as necessary, or just set the trim at the takeoff mark.
As you reach 60 knots, apply full power, pull the nose up to
and beyond a normal climb attitude, and let the speed start bleed-
ing off. One thing you’ll notice right away will be that it’ll take a
lot of right rudder to keep the airplane headed straight with the
skid ball in the middle of its tube.
Since you’re now carrying part of the airplane’s weight with
power, the airspeed indicator will go perceptibly below the green
arc before the stall actually “breaks.” You’ll still get 5 to 8 knots
advance notice from the stall warning horn. The pitch attitude
before the break will be quite a bit steeper, and the break will be
sharper, with the airplane possibly getting further nose-down than
in the first stall series. If you didn’t have the rudders just right,
there’s also a good chance that a wing will drop - most likely the
left one.
You’re already at full power, so the object now is to recover
with as little altitude loss as possible. Relax just enough back pres-
sure to get the airplane flying again, then bring the nose up near
the horizon to arrest the sink rate, but don’t pull so hard you stall
again. As the airplane picks up speed, you can reduce power to a
normal cruise setting.
Flight Instruction
Flight Instruction
The air flowing through the slot
between the wing and the flap
helps keep the overall flow
attached at very high angles
of attack .