The energy box
One of the most important concepts to master for graded maneuvers is the energy box. Many maneuvers in the ACS specify a tolerance for airspeed and altitude, e.g. ±10 KIAS and ±100 feet. These tolerances effectively give you a two-dimensional energy box where you can wander a certain amount off target before you bust. Understanding the size of the box and which energy settings should keep you in the middle of it will make that process more straightforward and help you recognize exogenous factors (e.g. downdrafts) more quickly. The energy box is often the most important standard to fly to, because it's the most obvious when you get outside it. "Smooth" and "coordinated" are a bit trickier to grade, but it's easy to swing the hammer when you're +120 feet from target.
Early in your flying career, you should form a good grasp of energy management. The AFH has a great chapter on it, which you should read and discuss with a qualified instructor until you thoroughly grasp it. If anybody told you that "pitch controls speed and power controls altitude," unlearn that. I occasionally heard that from CFI candidates on stage checks and would ask the question "What happens if I am 10 knots over a stall in slow flight and pull back on the yoke? Will I gain altitude before the horn sings? Yes? Ok, then I just controlled altitude with pitch." To summarize what the AFH says, you have two main controls:
Energy lever: in simple airplanes with fixed-pitch props, this is your throttle. If you have adjustable props, then you have a RPM and torque lever. For most maneuvers, you'll want to pre-select the RPM so that all you need to mess with is torque.
Energy director: this is your yoke/stick/etc. This controls how whatever energy you have and are adding is being distributed.
Together, your energy lever and energy director control your overall energy and its distribution. These are your energy inputs, and your airspeed and altitude are your energy outputs.
Early in your flying career, you should form a good grasp of energy management. The AFH has a great chapter on it, which you should read and discuss with a qualified instructor until you thoroughly grasp it. If anybody told you that "pitch controls speed and power controls altitude," unlearn that. I occasionally heard that from CFI candidates on stage checks and would ask the question "What happens if I am 10 knots over a stall in slow flight and pull back on the yoke? Will I gain altitude before the horn sings? Yes? Ok, then I just controlled altitude with pitch." To summarize what the AFH says, you have two main controls:
Energy lever: in simple airplanes with fixed-pitch props, this is your throttle. If you have adjustable props, then you have a RPM and torque lever. For most maneuvers, you'll want to pre-select the RPM so that all you need to mess with is torque.
Energy director: this is your yoke/stick/etc. This controls how whatever energy you have and are adding is being distributed.
Together, your energy lever and energy director control your overall energy and its distribution. These are your energy inputs, and your airspeed and altitude are your energy outputs.
Visualizing the energy box
In the depiction above, we have a two-dimensional green box with a Cartesian coordinate model around our target state within which we want to remain. We've got airspeed on the horizontal axis and altitude on the vertical. Outside the box is the "bust zone." There are two diagonals:
- Director Diagonal: here we have an energy distribution error (fast and low or high and slow). In most small planes, there's a roughly 100 foot/10 KIAS exchange rate, so you can fix distribution errors by trading these with a nose-up or nose-down input. It's easy to spot distribution errors as "trading needles" or "trading tapes" when you see one output parameter go up as the other decreases.
- Lever Diagonal. here we have a total energy error (fast and high or low and slow), which we need to fix by adding or subtracting energy (throttle).
Techniques for staying in the energy box
Hopefully I've sold you on the concept of the energy box and how to make adjustments to keep yourself inside it. Here are some tricks to make the flying easier, keep you in the energy box more consistently, and get you done with your training more quickly.
Know your numbers: every maneuver you do should have an energy setting and a control input sequence that will give you the desired energy outputs. You should chair fly that sequence to build the psychomotor memory. Confirm airspeed, altitude, and finally power settings before starting to make sure they are on target and there are no trends. It's just like making a soup: if you follow the same recipe consistently, you'll get the same output consistently. If you don't know what these inputs are, look them up, write them down next time you go, or ask your instructor, then brief it as part of your CREACS flow. In short, proact, don't react. One funny thing I noticed after becoming an MEI and teaching in a plane that was twice as expensive to rent is that students displayed roughly twice the interest in knowing energy settings in the Seminole than in the 172.
Measure your changes: if you get off track due to winds, downdrafts, energy errors, etc., you never, ever, ever need "a bit of power" or "a skosh of trim." If your soup is a bit bland, you don't just toss in a handful of habañeros. You chop little chunks, throw them in one at a time, stir, taste, and reassess based on the change. Similarly, if you get a decreasing altitude trend in a steep turn, you say "Let's add 50 RPM and a one-finger swipe of nose-up trim and see if that corrects it." Let's say that results in too much correction, so you pull back 20 RPM and you're dead on target. The next time you see that deviation, you'll know exactly how to fix it with 30 RPM. If your normal fix isn't working, you know there must be an exogenous variable (e.g. downdraft, puff, etc.) that's affecting your maneuver. Conversely, if you started with "a bit of power," it'd probably take a lot longer to figure out intuitively.
Control the variables and slow the feedback loop: every maneuver has some sort of tolerances that need to be kept. Many of them are some flavor of "walk and chew gum" where you need to pay attention to several inter-related closed-loop control parameters. In many cases, you can make life easier for yourself by controlling or slowing variables that are not explicitly defined as a tolerance to slow down the rate at which you need to return feedback into the control loop. Some examples:
Return to the center: whenever you do notice that you've wandered out of the middle of the box, get back into the center before doing anything else.
This is especially important if you're flying IFR where you get a small energy box. If you're +50 on your altitude, your effective altitude box is now +50, -150. You've lost half your margin upwards and are likelier to bust.
Together, these techniques should help keep you in the energy box more consistently. Work smarter, not harder.
Know your numbers: every maneuver you do should have an energy setting and a control input sequence that will give you the desired energy outputs. You should chair fly that sequence to build the psychomotor memory. Confirm airspeed, altitude, and finally power settings before starting to make sure they are on target and there are no trends. It's just like making a soup: if you follow the same recipe consistently, you'll get the same output consistently. If you don't know what these inputs are, look them up, write them down next time you go, or ask your instructor, then brief it as part of your CREACS flow. In short, proact, don't react. One funny thing I noticed after becoming an MEI and teaching in a plane that was twice as expensive to rent is that students displayed roughly twice the interest in knowing energy settings in the Seminole than in the 172.
Measure your changes: if you get off track due to winds, downdrafts, energy errors, etc., you never, ever, ever need "a bit of power" or "a skosh of trim." If your soup is a bit bland, you don't just toss in a handful of habañeros. You chop little chunks, throw them in one at a time, stir, taste, and reassess based on the change. Similarly, if you get a decreasing altitude trend in a steep turn, you say "Let's add 50 RPM and a one-finger swipe of nose-up trim and see if that corrects it." Let's say that results in too much correction, so you pull back 20 RPM and you're dead on target. The next time you see that deviation, you'll know exactly how to fix it with 30 RPM. If your normal fix isn't working, you know there must be an exogenous variable (e.g. downdraft, puff, etc.) that's affecting your maneuver. Conversely, if you started with "a bit of power," it'd probably take a lot longer to figure out intuitively.
Control the variables and slow the feedback loop: every maneuver has some sort of tolerances that need to be kept. Many of them are some flavor of "walk and chew gum" where you need to pay attention to several inter-related closed-loop control parameters. In many cases, you can make life easier for yourself by controlling or slowing variables that are not explicitly defined as a tolerance to slow down the rate at which you need to return feedback into the control loop. Some examples:
- Ground ref maneuvers don't specify turn radii, so make them wide (within reason) to reduce the required bank angle and additional energy. If you do this right, you won't have to touch the throttle in most cases.
- Slow flight doesn't specify climb rates or sink rates, so take your time with your energy lever changes so that you can redirect easily.
- Vmc demos don't specify at which airspeed you need to start pulling back the "dead" engine, so it's easier to start faster (e.g. 110 KIAS in a Seminole) and more gradually ease it back, then gradually roll onto the good throttle while getting onto the corresponding rudder.
- Steep turns don't specify roll rates, so work out what's easiest for you to manage with pitch, coordination, and throttle.
Return to the center: whenever you do notice that you've wandered out of the middle of the box, get back into the center before doing anything else.
This is especially important if you're flying IFR where you get a small energy box. If you're +50 on your altitude, your effective altitude box is now +50, -150. You've lost half your margin upwards and are likelier to bust.
Together, these techniques should help keep you in the energy box more consistently. Work smarter, not harder.