From: aboyd@quantum.qnx.com (Andrew Boyd)
Subject: Re: pitch & power on landings
Date: Tue, 26 Jan 93 18:55:05 GMT
Organization: Quantum Software Systems, Ltd.

In article <1993Jan25.194628.18856@pony.Ingres.COM> kerry@Ingres.COM 
(Kerry Kurasaki) writes:
>I ascribe to the theory that pitch is PRIMARY for airspeed and power is
>PRIMARY for altitude

Like any simplifications, that ain't perfect.

Let's look at the basic physics of what is going on during an approach.
I can't help it, I'm an engineer as well as a flight instructor :-)

The a/c has energy due it's height (mgh), and due to it's forward motion
(1/2 mv**2).  Forgetting about the engine for a moment, we can easily
convert from one form of energy to another.  eg if you are high and slow,
shove the nose down and you will be low and fast.  Conversely, if you
are low and fast, if you pull the nose up, you can go high & slow.  Glider
and aerobatic pilots, please stop yawning :-)

So, pitch controls both airspeed and altitude, which makes sense, given
that they are as close as pigs & sausages.

Sure, I'm neglecting the effects of drag, but approaches are usually
flown near the endurance speed - the "bottom" of the power curve, where
the drag is as low as it gets.

I teach my students my own method of analyzing and correcting their 
approaches, which is based on energy management.  Check out the
following chart, which has airspeed along the top, and altitude on
the bottom:

                         AIRSPEED

             LOW           ON            HIGH

A   LOW     NOT enuf      not enuf    / pull nose
L            energy        energy   /      up
T                                 /  
I   ON      not enuf      perfect       too much
T            energy        /             energy  
U                        /
D                      /
E   HIGH    shove nose    too much      way too much
               down        energy         energy


If our a/s & alt are bang on (center), well, we don't need to do
much, just be sure we're trimmed up.  

If we are above the glidepath, but too slow, all we need 
to do is to pitch the nose down & intercept the glidepath again
at the correct speed.

If we are below the glidepath, but too fast, all we need 
to do is to pitch the nose up & intercept the glidepath again
at the correct speed.

Note that all three of the above cases are on the diagonal line,
where the a/c has the right amount of energy, but the energy may
be in the wrong form.


Let's consider the three cases to the right and below the diagonal
line, where the a/c has too much energy.

If the a/c is on the glidepath, but the a/s is too high, we cannot
just pull the nose up, as that will convert our excess a/s into altitude,
and we do not wish to be above the glidepath.  We must reduce our
energy, by one of the following techniques:

    1) increase flap (max 20 degrees until on final)
    2) reduce power  (I use 250 RPM +/- increments)
    3) sideslip      (forward slips are fun!)

If the a/c is at the correct speed, but above the glidepath, we
cannot just shove the nose down, as we would have excess a/s when
we intercept the glidepath, which is the case above.  We must reduce
the energy of the a/c, using the techniques above.

If the a/c is too fast and too high, you've got to get rid of
even more energy.  Same techniques.


Let's consider the three cases to the left and above the diagonal
line, where the a/c has too little energy.

If the a/s is correct, but the a/c is below the glidepath, we do
not have enough energy - we must add power.  This typically will
cause the a/c to climb at the same airspeed, which is exactly what
we want to do to get back up the to the glidepath.

If the a/c is on the glidepath, but the a/s is too low, we cannot
shove the nose down if we are to make the runway.  We must add
energy, which means we add power.  Typically, the a/c will wish
to climb with the addition of power, which we don't want, so we 
will simultaneously push the nose down, to stay on the glidepath.

If we are low and slow, we are seriously low on energy, and a
smooth application of full power is recommended - back side of the
power curve, anyone?

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