Airplane longitudinal control: pitch or power?
I was wondering how long that it would take for this question to come up.  

It is the old "pitch -vs- power" airspeed control technique debate that rages throughout the aviation world.  There are strong proponents of both techniques (and they seem to view it almost as a religious debate in that the other side can never be right, no matter what), and both sides have good reasons for it!

Instead of saying that one is better than the other, let's just say that they are both techniques for managing the potential energy of the airplane (the airspeed that can be traded for altitude and vice-versa).  In fact, this is how I like to think about it (and don't pick a side):


If you change the pitch of the aircraft without changing power, the airspeed will stabilize out at a new value.

Pitch up and you lower the airspeed.
Pitch down and you raise the airspeed.

If you change the power setting of the aircraft without changing the pitch, the airspeed will stabilize out at a new value.

Add power and you raise the airspeed.
Reduce power and you lower the airspeed.

You can change both at the same time and get various results.

You can end up with the same airspeed that you had before.
You can end up with a lot more airspeed.
You can end up with a lot less airspeed.



Most often you need to change both at the same time in order to properly manage your airspeed.

So basically it comes down to what you want to accomplish.  If you need to change the airspeed you have two ways to do it, but used individually each comes with a side-effect.  In some situations this may be okay or even desirable, but you need to be aware of what your actions are going to accomplish.



Let's look at a specific example:  

Sometimes, especially on an instrument approach, you want to maintain your current airspeed while changing your vertical speed.  


Let's say that you are a little high on the glideslope.

If you simply pitch down to recapture the glideslope, you will gain airspeed but will recapture it quickly.
If you simply reduce the power to recapture the glideslope, you will lose airspeed but it will take longer than using pitch.
If you want to maintain your airspeed while recapturing the glideslope (typical on an instrument approach) then you would pitch down and reduce power at the same time, and when you recapture the glideslope you will pitch back up to maintain it and add power to maintain your current airspeed.