WHAT ABOUT THOSE SPINS?
Acknowledgements: AIR
FACTS (Abridged from an article by Richard Collins)
There
should be no mystery…
On the NTSB’s 2017-2018 most wanted list of transportation safety
improvements: “From 2008 to 2014, nearly 48 percent of fatal fixed-wing GA
accidents in the United States resulted from pilots losing control of their
aircraft in flight.”
The sad thing is that this has been forever true. The low altitude, low
speed loss of control has always dominated and this was often dismissed with
the comment: “He ran out of airspeed and ideas at the same time ………...”
Do pilots know enough about spins?
Spins used to be part of the private pilot training syllabus, but even
after the requirement was dropped most instructors included spin demonstrations before first solo and spin training before stalls solo; because students
could accidentally spin while practicing stalls and they needed to know how to
recover. In 1953,
precision spins were a
requirement for an instructor.
They were done three ways: straight ahead, out of the bottom of a turn, and out
of the top of a turn. The spin out of the top was the most difficult.
·
Most pilots usually spin to the left, and out of the bottom of left
turns I used about 45 degrees of bank, slowed to the stall in the turn and
at the stall gave it full left rudder and full right aileron.
·
Out of the top, the same left turn, the same slowing, but a different
technique approaching the stall. The stick was brought back smartly as full
right rudder was applied. Any other way, and the airplane just wallowed into
the spin. I didn’t use full opposite aileron because it didn’t seem a natural
thing to do.
In the early 1950s we knew the airplane would spin and we knew how to spin and recover, but we really didn’t know why the airplane would spin. We did know
that it took stalling and yawing to make the airplane spin and that the
corkscrew motion was caused by the angle of attack on the bottom wing being
greater than that of the top (outside) wing. What a lot of pilots didn’t know
was that in some airplanes you could get enough adverse yaw out of just
the ailerons to cause an airplane to spin. Most
pilots thought it took full rudder.
When an airplane is spinning it is stalled, so the airspeed is stable
just below the stalling speed. Some airplanes will fly out of a spin and into a
spiral, with the airspeed building. This needs to be noted quickly and a
recovery started from the dive. When spinning, the nose of some airplanes seems to
be quite low, others even lower. Some NASA research found that in a steep (nose-down) spin the angle
of attack is 20 to 30 degrees. That is not too far from the stalling angle, which averages about 18,
and what this means is that the airplane should recover quickly. In a moderately
steep spin it is 30
to 45 degrees which would make recovery slower, and in a flat
spin
the angle of attack is from 65 to 90 degrees. Flat
spins are unrecoverable without a spin chute.
Is your aircraft spin-certified?
The Cessna 172 is approved for spins when operated in the Utility
Category. Piper certified at least one model of the Cherokee for spins, to be
competitive with Cessna trainers, and designed the Tomahawk to have more active
spin characteristics than the Cessna 150/152. Cautionary
note: The location of the airplane’s centre of gravity is quite important.
The further aft it is, the easier the airplane is to spin but recovery
is more difficult. With the CG too far aft, recovery will be impossible. The
Cessna P210 has a certified aft CG limit of 52 inches, but most have had to put
the limit at 50 inches (in learning this at least two airplanes were lost in
unrecoverable spins).
How much altitude is lost in a spin?
Lighter wing loading means a lower stalling speed and correspondingly
less altitude loss in a spin. The loss in an accidental spin would include loss
in the departure from controlled flight and as the airplane entered the spin.
Then loss in the time to recognize what happened, then the loss when breaking
the spin, then the loss recovering from the dive after the spin. I’ve seen
numbers on this ranging from 1,000 feet to 1,500 feet for airplanes in the PA-28/172 class. What that
means is that if you stall below
that altitude, all those stalls you practiced at altitude, and any spins you have
done up high, won’t do you any good. In the spin itself, each
turn might account for 400
to 500 feet of loss but again, the entry and
recovery have to be considered. When an airplane departs controlled flight and
crashes, witnesses on the ground often say “it wobbled and then rolled over and
dived into the ground”. If it had been a little higher they would have probably
seen the spin start to develop before it hit the ground.
So should we? …..
I always enjoyed spins and think that all pilots would benefit from an
exposure to them. That’s the best way to learn that with enough altitude in
the right kind of airplane they are fun and relatively benign. But without enough altitude they
are a really quick way to snuff out your lights!
FLY SAFE!