Energy management can be something that we as aviators may subconsciously know about, but not necessarily know explicitly. One of the most basic fundamentals of flight is how we manage the energy of the airplane. Too much energy, it’s almost impossible to land. Too little energy, and the aircraft stalls, said another way, a firm landing.
While I was indirectly taught it as I was going through civilian training, I didn’t truly learn about energy management until I entered Air Force pilot training.
I’m a simple kind of man, to loosely quote Lynyrd Skynyrd, so I like to think of energy as the altitude below you and the airspeed behind you. In other words, the higher altitude you are and the faster you’re going, the more energy you have. Conversely, the lower the altitude and the slower you are, the less energy you have. Successful flight in every different regime is all about how you manage that energy.
Energy can be thought of as your airplane’s physical ability to fly. Most of us use the technique of trading altitude for airspeed (if you haven’t, get the money back from all your flight instruction!). If you’re fast and you need to climb, keep the power in and use your excess energy to carry you to your intended altitude and airspeed. If you’re high and slow, use your excess energy in the vertical to increase your energy in the longitudinal.
There are instances where we want to be high on energy and instances where we want to be low on energy. Landing the airplane requires us to be in a low energy state, but not so low that we can’t get out of it if we needed to. We need the airplane to be slow enough to land and stop within the allowable runway, but not so low on energy that a gust of wind will stall the plane or we can’t execute an expeditious go-around (e.g. slow flight).
Speaking of slow flight, let’s elaborate. The power is almost all the way, you’re hovering a knot or two above stall speed, and the angle of attack is so high that any abrupt control movement in any direction could cause the aircraft to stall. We avoid dangerous flight regimes like this by staying away from our stall speed and keeping a positive kinetic energy with the airplane. This has everything to do with the power curve (illustrated below).
The amount of energy you have is all about where you are on that blue line, your total power required. As you approach the gray area on the left, the amount of power required will get to a point where you physically don’t have enough power in the engine to generate enough thrust to keep you straight and level. As you get into that gray area, you will start descending due to lack of lift despite how high your power setting is. The gray area is what you want to avoid. That is where you get into a negative energy state, and if you don’t have the altitude to recover, you could end up crashing.
That’s energy management 101 and you probably didn’t even realize it!
We’ve all had that traffic pattern where we’re turning base or final and all the flaps are down, the power’s at idle, and you’re still cooking in. In the C-130, we have tactical approaches where we do exactly this but the enormous flaps we have allow us to slow our airspeed even in a decent. In general aviation, you would need to increase your drag to mitigate all of the energy you’re gaining with your descent, so a forward slip would be need to be used in order to do that.
Emergency landings with no engine power are the best places to see how energy management works. You have to work the emergency pattern in a way that you can land on the runway at a reasonable speed by trading the altitude you have for your best glide speed. Manage that poorly and you’ll find yourself in the dirt short of or beyond the runway. Manage it well and you’ll be rolling out on speed coming to stop on the runway with yours and your passenger’s skin still intact.
All in all, watch your airspeed and altitude; they both contain the very energy that keep you in the air. With experience will come an innate sense of manipulating each to achieve a perfect regime of flight that all of us aviators strive for. Until next time… …So long!
-Fly Safe, @BRomanUSAF