Spiral Dives Explanation.

[Sandy Stevenson]

I've been looking for an expalantion of the aerodynamics of how an aircraft
gets into a spiral dive. Mostly I've found lots explanations of what the
signs
are and how to recover, but those are things I already know. I've gathered
that
it's related to lateral stability, and that the wings are not stalled, but I
don't yet
understand how it comes about that adding back pressure increases one's
airspeed.
If someone could point me to a good explanation of what's going on
aerdynamically
when an aircraft is in a spiral dive, I'd appreciate it.

[Roy Clark, B6]

Sandy Stevenson wrote:
> I've been looking for an expalantion of the aerodynamics of how an aircraft
> gets into a spiral dive.

"In the process of learning gliding turns, a beginner may fail to
control the tendencies to overbank and to dive. The bank may approach
the vertical and the nose of the glider may fall more than 45 degress
below the the horizon; of course, speed will increase rapidly."
-Page 18, The Joy of Soaring by Carle Conway

"Sometimes the elevator is unable to keep the wing stalled beyond the
incipient stage of the spin. In this case, as the nose and wing drop,
the wing will unstall and the speed will increase with the glider in a
spiral dive."
-Page 127, Gliding, Sixth Edition, by Derek Piggott

> but I
> don't yet
> understand how it comes about that adding back pressure increases one's
> airspeed.

"If the pilot then pulls the stick back in a mistaken effort to slow
the glider or to bring its nose back up to the horizon, the glider will
simply turn faster and the spiral will continue to steepen. The
resulting increase in the angle of attack and airspeed could overload
the wing to the point of structural failure."
-Page 18, The Joy of Soaring by Carle Conway (paragraph following that
quoted previously from Conway)

"..., during the spiral dive you will learn that the effect of backward
motion on the control stick will not raise the nose of the glider (and
consequently is useless in trying to recover from the dive). This is
because the steep bank means that any increase in angle of attack of
the wing will generate more lifting force inward--tightening the
turn--than it will upward. Tightening the turn only results in greater
loads, airspeed, and sink rate, and eventually could lead to failure of
the glider."
-Page 76, Learning to Fly Gliders by Bob Wander

> If someone could point me to a good explanation of what's going on
> aerdynamically
> when an aircraft is in a spiral dive, I'd appreciate it.

[[email protected]]

YOu can alos enter a spiral dive from a spin. I was spinnning a 2-32
and tried teh normal spin recovery control inputs, but the bird was not
recovering. The visual picture was teh same as the other spins that
day but he speed was increasing, leveled the wings and recovered from
the dive at redline.

[[email protected]]

Let my try this again with contacts in my eyes. You can also enter a
spiral dive out of a spin. I was spinning a 2-32 one day and during
the 4th spin of the flight, normal spin recovery inputs were not
working. The visual picture that the same as on the other spins,
however, after a few moments of the spin recovery inputs I noticed that
the airspeed was increasing. I leveled the wings and recovered from a
redline dive.

Craig

[Nyal Williams]

Anyone remember the falling leaf? As you approach
the stall you can visibly move the nose side to side
using the rudder without aileron. This will advance
one wing over the other, and vice versa. Pressing on
the opposite rudder is one way of stopping the incipient
spin and turning it into a straightforward stall; it
does so by advancing the inside wing and thus lowering
its angle of attack and raising the angle of attack
on the opposite wing.

A little top rudder can be used to help keep the nose
from dropping in a turn. It is this nose drop that
produces the acceleration and consequent spiral dive.
I've never tried opposite rudder and stick back to
see if it would stop a spiral dive. Conceptually it
might, but the acceleration is too fast and the wings
might be shed before thee control inputs could stop
it. You already know how to stop it - level the wings.
That wasn't the question.


At 14:48 25 August 2005, wrote:
>Let my try this again with contacts in my eyes. You
>can also enter a
>spiral dive out of a spin. I was spinning a 2-32 one
>day and during
>the 4th spin of the flight, normal spin recovery inputs
>were not
>working. The visual picture that the same as on the
>other spins,
>however, after a few moments of the spin recovery inputs
>I noticed that
>the airspeed was increasing. I leveled the wings and
>recovered from a
>redline dive.
>
>Craig
>
>

[Sandy Stevenson]

Thanks, Roy, your third paragraph was the answer I was looking for.
I have Conway's book, and access to Piggott's, as well as access to
Piggott's Understanding Gliding, but I don't have access to Bob Wander's
book. After that very clear explanation, I will have to look for a copy.
Much appreciated, sir.

"Roy Clark, B6" > wrote in message
oups.com...
> Sandy Stevenson wrote:
> > I've been looking for an expalantion of the aerodynamics of how an
aircraft
> > gets into a spiral dive.
>
> "In the process of learning gliding turns, a beginner may fail to
> control the tendencies to overbank and to dive. The bank may approach
> the vertical and the nose of the glider may fall more than 45 degress
> below the the horizon; of course, speed will increase rapidly."
> -Page 18, The Joy of Soaring by Carle Conway
>
> "Sometimes the elevator is unable to keep the wing stalled beyond the
> incipient stage of the spin. In this case, as the nose and wing drop,
> the wing will unstall and the speed will increase with the glider in a
> spiral dive."
> -Page 127, Gliding, Sixth Edition, by Derek Piggott
>
> > but I
> > don't yet
> > understand how it comes about that adding back pressure increases one's
> > airspeed.
>
> "If the pilot then pulls the stick back in a mistaken effort to slow
> the glider or to bring its nose back up to the horizon, the glider will
> simply turn faster and the spiral will continue to steepen. The
> resulting increase in the angle of attack and airspeed could overload
> the wing to the point of structural failure."
> -Page 18, The Joy of Soaring by Carle Conway (paragraph following that
> quoted previously from Conway)
>
> "..., during the spiral dive you will learn that the effect of backward
> motion on the control stick will not raise the nose of the glider (and
> consequently is useless in trying to recover from the dive). This is
> because the steep bank means that any increase in angle of attack of
> the wing will generate more lifting force inward--tightening the
> turn--than it will upward. Tightening the turn only results in greater
> loads, airspeed, and sink rate, and eventually could lead to failure of
> the glider."
> -Page 76, Learning to Fly Gliders by Bob Wander
>
> > If someone could point me to a good explanation of what's going on
> > aerdynamically
> > when an aircraft is in a spiral dive, I'd appreciate it.
>

[Ian Johnston]

On Thu, 25 Aug 2005 02:39:58 UTC, "Sandy Stevenson"
> wrote:

: I've gathered
: that
: it's related to lateral stability, and that the wings are not stalled, but I
: don't yet
: understand how it comes about that adding back pressure increases one's
: airspeed.

When a glider is turning it is simultaneously pitching and yawing. A
flat turn is entirely yaw and a 90 degree bank turn is entirely pitch.
The elevator controls the pitch, which is why you need more back
pressure in steeper turns. If the turn is less than 90 degrees bank.
pitching more also keeps the nose up, so the normal pull back -> slow
down relationship holds.

If the turn is at more than 90 degrees, pitching more directs the
flight path down more, so you speed up as you pull back.

Ian