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“Energy management” is not a precise term. It is used in different ways to express different things, so it almost always requires clarification. Often, a speaker will say “energy management” and expect the listener to understand without any further explanation.
Aviation safety is too important to tolerate vague phrases like “energy management” that facilitate misunderstandings.
The Big Ambiguities
Energy management often talks about kinetic and potential energy as the two kinds of energy. But:
- Kinetic energy is defined as mass times ½ speed squared. We can simplify by talking about weight and not mass, but what kind of speed? Indicated airspeed, true airspeed, or groundspeed? It matters. Airplanes flying through the air have kinetic energy measured with true airspeed but, upon ground contact, dissipate kinetic energy measured with groundspeed.
- Using that mass/weight simplification, we can define potential energy as weight times height. But height above what? If it is height above ground, properly called absolute altitude, then potential energy will increase and decrease rapidly when flying over buildings and streets in a city. Or if the reference is mean sea level, then an airplane at 5,500 feet will have the same potential energy flying high above low-lying Florida as it will on short final approach to Denver.
- And a complete discussion gets involved: drag dissipates airspeed, thrust can offset that dissipation or can increase speed or altitude, and rotary wing aircraft store energy in the rotation of the rotor.
So if the objective of using “energy management” is to communicate concepts accurately and precisely to help pilots fly their airplanes, details must be clarified.
Spoiler Alert!
…and we’re not talking about sailplanes.
“Energy management” is not self explanatory and means something much different to an aerobatic pilot.
Here are key ideas that a full discussion, much too long for this article, of “energy management” would bring out:
- “Energy management” sometimes just means airspeed, as in “energy to flare” or “enough energy for an aerobatic maneuver.”
- In aerobatics, “energy management” can also mean minimizing speed loss by not pulling too hard on the stick, pulling too many Gs, and creating excessive induced drag.
- “Energy management” can, however, be meaningful when distance to and altitude above a fixed point are part of the discussion, such as Bob Hoover’s engine out performances in the Shrike Commander, a sailplane on final glide, or descending to a landing. But that distance to a reference point is normally implied, not stated. Even in this case, “energy management” is not self-explanatory but has to be expressed in terms of airspeed and altitude.
Airplane Flying Handbook (FAA-H-8083-3C)
Chapter 4: Energy Management
Can an official FAA publication help understand the concept, or is it mired in trendiness? This publication from the year 2020 contains the Chapter 4, “Energy Management: Mastering Altitude and Airspeed Control.” As an FAA document, with the title implying that the handbook is about flying and hence for pilots, you’d expect it to be about flying, and to be accurate, relevant, and easy to read. It’s not. It is theoretical, full of abstractions, charts and diagrams that complicate things far beyond easy understanding.
How bad is it? All these terms appear in Chapter 4 to explain “energy management:” Energy Balance Equation, Energy Error, Energy Distribution Error, Total Energy Error, Energy Exchange, Energy Height or Total Specific Energy (ES), and Energy System. Maybe it’s just me, but I’ve gone a half century as a pilot and as an engineer without encountering any of these terms.
Does the following statement help pilots fly the airplane, or understand the process?
“Energy management can be defined as the process of planning, monitoring, and controlling altitude and airspeed targets in relation to the airplane’s energy state…”
As if to prove my point, that sentence had to revert to airspeed and altitude for explanation.
Then there’s the phrase, “The elevator is the energy distribution controller,” an abstraction that requires considerable explanation. Or the “energy map” (Figure 4-7) showing specific excess power, another abstraction. What pilot thinks in terms of “energy map” when flying?
When I was working on my Ph.D. at MIT, my thesis advisor, an MIT Ph.D. himself, a retired navy Captain, fighter pilot, and CFII, told me that for teaching ground school, even to MIT students, not all of whom were techies, to speak their language. Word for word, he said to me, “The wing is the thing.”
A Significant Error in the Airplane Flying Handbook (FAA-H-8083-3C)
My expectation was that with all its abstractions, The Airplane Flying Handbook would have its facts straight. Not so. The handbook states that kinetic energy is associated with indicated airspeed. This is flat out wrong on two counts:
- Indicated air speed is what is shown on the airspeed indicator. It does not take into consideration any errors in the pitot/static system or in the instrument. Calibrated airspeed is the correct term for indicated airspeed with errors removed.
- But that’s not right, either. The kinetic energy of an airplane relative to the air is derived from true airspeed, the actual speed of the airplane through the air.
For example, jets at altitude will have an indicated airspeed about half of the true airspeed. A jet cruising at 480 knots has 480 knots worth of true airspeed-referenced kinetic energy, not 240 knots indicated worth.
However, at low altitude, the indicated and true airspeed are often close to each other, so the indicated/true airspeed error is not always significant.
The Meat of the Issue
- Pilots fly airplanes with respect to airspeed and altitude, the quantities used in Airplane Flight Manuals. AFMs do not specify aircraft performance with respect to energy. Neither do speed and altitude operating restrictions, nor do airspace restrictions nor ATC instructions reference energy management.
- Concepts are most useful when they apply directly to displayed information and available controls. Unnecessary abstraction requires translation from instrument readings to concept to decision making and back to control inputs. These translations are extra workload and decrease the pilot’s ability to handle other tasks, such as maintaining situational awareness.
- While an airplane in flight possesses both kinetic and potential energy, there are no cockpit instruments which directly measure either one and display those measurements in units of energy.
- In the cockpit, the stick/control wheel moves the elevators, and the throttle adjusts engine power. While both are used to affect airspeed and altitude, neither one directly controls only kinetic or only potential energy.
- There is no cockpit guidance on how much altitude rate will give how much airspeed change, or vice versa. Rather, this “energy management” tradeoff is done ad hoc.
- Old fashioned explanations are simpler, more direct ways to teach pilots what they need to know without getting as abstract as energy management. In other words, the pilot is the customer, so speak the pilot’s language, not the dialect of the instructor. (The point of this article is clear expression of concepts, not a discussion of flight mechanics, so the many varieties of airspeed/altitude/throttle explanations will not be discussed here.)
The bottom line is that energy management is an abstraction that is not operationally necessary for flying an airplane. It can be useful to help some people understand concepts, but it is more likely a stumbling block.
Video (satire): Flying with Kinetic and Potential Energy
Here’s a trip around the pattern, recorded live, referring only to kinetic and potential energy, not airspeed and altitude. Yes, it can be done, and technically, it makes sense, but is it helpful? Note that no direct quantitative energy measurements were available or stated, and that airspeed and altitude were the primary information sources when flying the pattern but were never acknowledged.
The Last Word, from Gilbert and Sullivan
In the much loved and still regularly performed 1885 comic opera, The Mikado, self-absorbed Pooh-Bah presciently describes the misuse of “energy management” when he says, “Merely corroborative detail designed to give artistic verisimilitude to an otherwise bald and unconvincing narrative.”
In other words, say what you mean! Don’t hide important thoughts about airspeed and altitude behind fancy phrases like “energy management” and expect meaningful communication to result.
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Ed, I like your thesis advisor’s straight-forward comment, “The wing is the thing.” I had a slightly different means of teaching energy management, I called it ‘maintaining SMASH’. Let me explain…
As a T-38 IP while training students in formation flight, we flew a ‘trail’ maneuver where both aircraft were at military power (also called MIL, which was both engines operating at 100% without using the afterburner). It took energy management (maintaining ‘SMASH’ — or rapidly swapping kinetic for potential energy and vice-versa) to a different level as it required one to control their energy in relation to another aircraft by staying in position as that other aircraft made some major ‘muscle movements’. To begin ‘trail’, the lead aircraft would transmit, “Talon flight, go trail!” and the wingman would respond, “Two”. That’s when lead would push the power to MIL and turn away from the wingman. The wingman went to MIL power at the same moment and then maneuvered to get into a 60-degree cone behind the lead and 1000 feet in ‘trail’ — hence the name of the maneuver. Once in position, the wingman transmitted, “Two’s in.” and the maneuvering was on and nobody moved their throttles, they just managed their SMASH. Lead was unlimited in bank and pitch, to include hard turns, loops, barrel rolls, Cloverleafs, Cuban 8’s, etc. the only limit was the aircraft G loading (and remaining in the assigned airspace — plus NOT going supersonic*). The wingman used ‘lead pursuit’ (pulling his nose in front of the lead aircraft in a turn for cutoff) when necessary, which would allow him to close on the leader. Conversely, the wingman used ‘lag pursuit’ (putting his nose outside the lead’s turn) to drop back from the leader. With both aircraft at MIL power, and airspeed, bank, and pitch angles constantly changing, staying in position was all in managing one’s ‘SMASH’.
Such training is critical for many types of airplanes flown by the Air Force because, at some point, one must maneuver to get close to another aircraft. Being close might be called for in a formation of airlifters dropping paratroopers or bombers their bombs or anyone needing to join up with an aerial tanker to get refueled. Depending on the weather, other traffic, or operational needs, those rejoins cannot always be flown in straight-and-level flight and at a constant airspeed. It is especially critical in the fighter world because, in air-to-air combat, fighter aircraft work in pairs and a wingman has to be able to stay with the leader as they engage an enemy.
So, without moving the throttles and using only lead or lag pursuit, we trained student pilots to manage their SMASH to maintain their position.
* NOT going supersonic didn’t always happen when a student would unload on the backside of a loop and allowed the airplane to get a LOT of SMASH! That’s when the residents of western Oklahoma would hear what I called ‘the sound of freedom’ (i.e., a sonic ‘BOOM!’) and we had to fill out a ‘Boom log’ so if one of those residents complained, we could ID the guilty party/parties!
Ed,
Enjoyed the article. The first time I heard the term Energy Management relating to aviation was during the return of the Space Shuttle. The conversion of potential to kinetic energy was quite rapid due th the heavy parasitic drag that offered a glide ratio of a rock. While the term was important for those who used flight mechanics to design the maneuvers used to reach the desired airspeed, location and attitude, the pilot focused on good pilotage using cockpit instruments.
Energy management is useful as a concept to explain basics of flight to students…fixation on engineering exactitude glaze over that target audience. Total energy (as altitude+airspeed) explains why you can’t force an airplane to land, as well as why, in extremis, you don’t give up altitude until you must.
In keeping with “the wing is the thing” total energy can be explained as a bucket…in the chocks the bucket is empty. At max level airspeed and aircraft ceiling the bucket is full. The engine is nothing more than an energy pump that slowly fills the bucket as you climb and accelerate above stall speed. Drag, an energy consumer, is an outflow tap that varies with airspeed. You can trade altitude and airspeed back and forth with brief climbs (zooms) and descents, but as you approach max/min airspeeds, drag will chew up more and leave you lower and/or slower than when you started those trades. If your engine quits with a full bucket you have many options, with an empty bucket, not so many…
Indicated vs true, absolute vs agl matter in an engineering discussion. In a concept discussion it’s really about excess of each beyond what you need to get to Point X (altitude above Pt X and airspeed above stall) whether that’s a distant emergency landing site or the threshold you’re approaching.
To demonstrate how much more significant altitude is for energy storage than excess airspeed, accelerate to max level airspeed at a low (but safe altitude) and then zoom climb…that the airplane didn’t achieve anything near it’s ceiling emphasizes just how much less energy is stored in excess airspeed.
Thank you for the fun and interesting article. The airplane pictured in the beginning of the article is my Staudacher S300, S/N 12, which is probably the reason I feel compelled to add my two cents. As a retired airshow performer, IAC aerobatic competitor, and CFI I appreciate the concept of energy management. In teaching the fundamentals of aerobatics for the past 30 years I agree with your premise that just explaining the physics of flight can create a confusing moment for most students. This is something that needs practical experience. I humbly offer a recommendation that every pilot would benefit from some basic aerobatic or unusual attitude instruction from a competent CFI. Again, just my two cents.
Hello Mr Ed. I understand perfectly your point, but my question is: What is your contribution?
I could only saw your self-centrist CV that gives you permission to criticize and not contribute.
I am also CFII and I love the Chapter 4 of 8083-3C, again, what will be your contribution in this important safety point? Because at least PhD Juan Merkt, the author of the Chapter 4, had the initiative and time to write many articles and finally presents the Chapter 4.
Is a very nice tool to explain the Energy Management, from my point of view which is the point of view of a Fighter Pilot who flew T-27, OV-10, Mirage 50, F-16 and SU-30MK2. I had that tool during my training and I used the terms during my time as a Flight Instructor inside the Venezuelan Air Force, and NOW I am making contribution as CFII in this country with that tool inside the 8083-3C.
Please show me HOW would you explain that point?
I am doing that with my students and is working very good, I am not PhD, my congratulation to Mr Merkt which is also a PhD like you.
Thank you.
I think John Boyd was first (non PhD) to discuss energy management—-/ and led to his famius OODA loop
Robert, have you read “John Boyd, The Fighter Pilot Who Changed The Art of War”?
Written by Robert Coram, it is a fantastic read about a fantastic man!
The velocity term in the kinetic energy equation is really relative, meaning that it is the difference between two velocity states. For example let Va be the velocity of the aircraft in flight with respect to earth (i.e. your aircraft ground speed as reported by GPS). Let Ve be the velocity of the aircraft relative to earth after the landing is complete (full stop). Normally Ve is zero, but if you are landing on an aircraft carrier then it is the velocity of the carrier with respect to earth. With these conditions let ∆V = Va-Ve. Then KE = ½m(∆V)^2 .
I may think “too much energy” on approach if I’m high AND fast. Gotta lose some, power back, maybe speed brakes, maybe a slip on some planes. Low and fast? Pitch up. Low and slow? Gotta add energy (power up!). About all I have time for in the real world.
The movie is mind boggling. The next version could discuss the difference between green and carbon energy and when each is available and when it should be used, such as carbon during climb and green during glide and in all other phases of flight for acquiring carbon credits and not running out of credits before reaching a destination.
When I first read the new AFH chapter on Energy Management, my eyes glazed over (flying over 50 years, 20 in the USAF, Engineering degree). The chapter reminded me of Jimmy Doolittle’s MIT Doctoral Thesis on the “effect of wind that velocity had on flying an airplane.” His PhD advisors made him re-write it because (according to the book “The Aviators,” page 50) it was not studious-enough looking, it needed more mathematical calculations, graphs, charts, etc., to look more scholarly. For the rest of his life, Doolittle regretted the rewrite because, rather than saving lives, it would be locked away and never read by anyone.
I think Dr. Juan Merkt’s Chapter 4 will most likely end up like Doolittle’s thesis, although there is time to do a rewrite of the AFH. The Figures 4-3, 4-11, and 4-12 are good for pilots understanding, but Figures 4-6, 4-7, and 4-8 are academic and difficult to understand. Plus he states that potential energy is based on sea level, not on height above the ground—if I want to manage the energy from my altitude, once I hit the ground, my potential energy is zero. Wolfgang Langewiesche explains energy so much better with the Law of the Roller Coaster.
I was ecstatic to see a chapter on Energy Management because I think it is critical to understanding flight–especially for those fanatics who believe you pitch for speed and power for altitude (without discussing the interaction off the two).
I teach energy management on a conceptual level–no big charts. We have four types of energy: Speed, Height, Chemical/Engine, and Drag (I never say kinetic or potential). As you fly along, look at the instruments and determine where you “are” (altitude, speed, power setting, configuration). Compare where you “are” to where you “want to be” (are you to fast, too high, forgot to retract your flaps, still at full throttle?). Determine if you have too much or too little energy–then adjust with throttle or drag devices. Maybe your plane is too high but too slow, use the Roller Coaster Law to trade altitude and speed with the elevator. I also give students rules of thumb for trading altitude vs speed–at 100 kts (close to where most GA pilots operate), you can trade 10 kts of speed for (almost) 100 feet of altitude (at 200 kts, this increases to almost 200 feet altitude change for 10 knots of speed).
Kudos to the FAA for finally including a section on Energy Management. I just wish a flying handbook would use flying terms rather than PhD level engineering. Like the old Geico commercials, I think energy management can be accurately explained in a way so simple a Caveman could understand it.
I can only think of the British Boeing 777 which lost all power on approach as the ultimate example of energy management. It was imperative that the pilot maintain enough energy to get the dead aircraft to the runway and save a lot of lives.Read the story ti see how it was done. Sully was another who understood and demonstrated an understanding of the concept both in practical not theoretical terms.
Fantastic article, thanks for taking the time to share all this.
Picking a small nit — I like use of the term mass rather than weight, wish it was more common in US aviation. For example, in the UK they refer to ‘mass and balance’ rather than ‘weight and balance’. Why would this matter? Pushing to unload, we go zero g — or ‘weightless’. But the potential and kinetic energies are not zero! If we standardized on mass this nit-picking and possible source of minor confusion wouldn’t exist. I expect it to happen right after we go metric . . .
My instructors are birds. None of them have read the FAA manual and they can all out fly any PHD.
The question I see, is how do we prepare our students for questions in these terms from examiners?