Simplified airspeed control
Tie nose attitude to critical angle
At one time there was a lot of intense discussion between the flight instructor community and the FAA about the proper way to control speed in an airplane: Does changing the nose attitude (pitch) control speed or altitude? For a long time the FAA held that you increased speed by adding power and gained altitude by bringing the nose up. While there are still visages of that argument floating around, both camps appear to have settled on the concept that, at least when talking about light aircraft, you pitch to speed and power to altitude: If you want to go fast, the nose goes down, and vice versa. But, is it really that black and white? How do instructors want to approach the gray area?
What gray area, you may ask, especially if you're a hard-core pitch-to-speed advocate, which most of us are. When the power-to-weight ratio increases--meaning that as we move away from the 152-category trainers and into more powerful, often cleaner, aircraft--the pitch-to-speed concept still applies, but if we start looking at the details, the concept gets a little fuzzy around the edges.
When it comes to instructing primary students, most instructors aren't going to want to muddy the waters by giving them too much information. At that stage of their development we want them to know that nose attitude controls the speed and power controls the altitude. We don't want them questioning what applies in a given situation. If slow, we want them to instinctively get the nose down and, if appropriate, add power. The fewer variations on a theme we give them, the higher the probability that they are going to do the right thing at the right time.
Where the questioning of the basic pitch-controls-speed concept comes from is that when flying approaches in many higher-powered and cleaner airplanes, adding power instantaneously gives speed unless you bring the nose up at the same time to keep it from accelerating. Also, in those situations, dropping the nose doesn't necessarily give an instantaneous speed increase, but almost always results in a rapid initial loss of altitude before the speed starts to come up. This is especially true in aircraft with symmetrical airfoils. So, it could easily be said that the pitch-to-speed concept doesn't work here.
However, it can be said that the basic concept is working, but we have to change our control inputs a little to make it apply. It becomes a matter of timing control inputs: knowing that adding power increases speeds in these aircraft, bring up the pitch attitude a little as the power comes in, to keep the speed down. Knowing that pitching the nose down will eventually result in a speed increase but the altitude loss may be unacceptable, a little power is brought in to minimize the sink.
If there is a problem with the concept of pitch-to-speed, it is the way in which it is often executed. One of the most common mistakes is that the student is visually glued to the airspeed indicator and is chasing the needle because he hasn't totally locked onto the concept that the nose attitude controls the airspeed, rather than the other way around. He thinks he sets the nose attitude by watching the panel when just the reverse is true. And this comes back to another basic flight concept: Flying the windshield.
Older instructors are fond of saying, "Everything that happens on the instrument panel is historical information. It happens in the windshield first." And the reason they harp on this is because it's true--especially when it comes to airspeed. If we want to prove it to a student, all we have to do is have him watch the airspeed as we move the nose up and down in fairly large increments so he can see the lag in the airspeed. He needs to understand that any change in indicated airspeed is preceded by a visual change in the nose attitude first. If the nose attitude doesn't change, the airspeed won't, either. So, the nose attitude becomes the primary instrument for controlling speed and the airspeed indicator becomes the secondary instrument. The airspeed indicator is still very important, however, because that is where we get the finite information required to fine-tune the attitude.
It's also helpful if we remind students that when we say nose attitude, it's another way of saying angle of attack.
Many instructors find it beneficial to teach speed control as a three-step process: First, set the attitude. Second, hesitate a second or two to let things settle down. Three, cross-check the airspeed and let it tell us whether the attitude is correct or not. If the speed isn't where we want it, we go back to fixating on the nose and its relationship to the horizon, change the attitude very slightly, again wait a few seconds, and check the airspeed to see if the attitude change produced the desired airspeed change.
Two things are important for the student to understand in this situation. First, every airspeed change is going to use the three-step process--set the attitude, stabilize, check the airspeed. Second, it's likely that every airspeed adjustment is going to require going through this adjustment cycle several times because we're going to make very small adjustments and creep up on the correct speed, rather than trying to do it all at one time. The attitude changes may be so small that they are really nothing more than changes in the pressures on the yoke or stick. We want to make small changes because the larger the change we make, the more likely we'll overdo it and we'll wind up chasing the right attitude/speed. If we do it in tiny increments, we won't be constantly correcting our corrections.
This same three-step, small-correction process applies whether on approach or on climbout. It's generally easier to execute on climbout because the horizon is cutting through the nose and there are fewer configuration changes to deal with.
One other common airspeed/attitude mistake is the manner in which an airplane should be leveled out from a climb. Many pilots will reach their altitude and immediately bring the power back even as they are in the process of putting the nose down to level. Then they wonder why they can't hold altitude initially and the airplane wants to settle. The problem is that they haven't given the airplane enough time to accelerate to a level speed before bringing the power back, so it gives up a little altitude in the process of slowly accelerating. Life is much easier if we put the nose down to level attitude and wait a few seconds before bringing the power back. This will let the airplane accelerate first, without giving up altitude.
The majority of instructors will continue to stick with the basics: If an airplane gets slow, the nose is moved down. Then, if appropriate for the situation, the power goes in. If our students follow those rules, they'll never get hurt.
Budd Davisson is an aviation writer/photographer who has flown more than 300 different types of aircraft. He teaches about 30 hours a month in his Pitts S-2A Special. Visit his Web site.
By Budd Davisson