Energy Management

[FenderManDan]

Happy new year all!!

I was just reading about the energy management mentioned in the stick and rudder book and also remember seeing Bob Hoover with his twin on YT, dooing both engine out loops. So what is the energy management? How would you describe that to the novice?

Cheers,

Dan

[Shiny Side Up]

Its the very basics of physics. Its all about managing the pools of Potential Energy (PE) the aircraft has and Kinetic Energy (KE) it has. One can think about the aircraft's engine as a device for gaining PE the aircraft has or gaining KE. In simplest terms one can generally be traded for the other, though the aircraft through its interaction with the medium of air, is a bit more complex than the usual dropped ball basic explanation in a physics textbook. Bob Hoover, like all great pilots, in reality is a master manager of PE and KE.

[cgzro]

Energy Managment is the careful control of trading engery in the form of altitude for energy in the form of speed and vice versa.

Energy in the form of altitude is referred to as potential energy, i.e. think of the potential damage that a bowling ball at 1000ft can do if you drop it.

Energy in the form of speed is referred to as kinetic energy, i.e. think of the potential damage a bowling ball travelling at 200Mph can do it if traveling horizontally.

So an aircraft can trade one against the other. For example if you are gliding along at a very high speed (say 2-3 times your stall speed) you can zoom up possibly thousands of feet, but of course you will have lost a bunch of speed to gain altitude.

Obviosly the inverse is true, you can be cruising along just about at stall speed and dive at the ground then pull level but you will be at of course a much higher speed than when you started.

As with all transactions there is some loss , in our case friction/drag will take some of the energy away.

The art is to make the transaction with the minimum loss. This usually means executing turns, pulls/pushes etc. such that they result in the best increase in speed/altitude for the least loss in altitude/speed.

Its a real art form to minimize the loss and best seen watching glider aerobatics but it applies in all aircraft and rears its head in things like using the minimum altitude to pull up before hitting the ground, the minimum radius to avoid an obstical or even the dreaded 180 degree turn back to the runway.

In my own case, doing powered aerobatics, there is a definite sweet spot for each aircraft / C of G. For example if I execute a loop up at about 180Mph at 6G its not as effecient as if its done a 4.5 G but more effecient than 3G.

[Beefitarian]

Your mass plus height is potential energy. More height is more potential that can be used to glide.

Your mass plus forward speed is kinetic energy. More speed is energy that can be used to fly.

If you climb you can trade kinetic energy for potential energy. If you dive you can trade potential for kinetic.

In order to use your potential energy best after engine failure you want to glide at the speed that is fast enough to convert the potential energy while slow enough to conserve it. Thus covering the most forward distance possible from your given height.

[erics2b]

Your mass plus height is potential energy.

Not quite. Gravitational (as opposed to electric or elastic) potential energy is the product of the bodies (aircraft and Earth) masses and Newton's gravitational constant, divided by the distance between them (height):



Being close to the Earth, we can closely estimate this as:



Where m is aircraft's mass, g is a constant we bugger up from the Earth's mass and assuming a small height, and h is height.

Your mass plus forward speed is kinetic energy.

Not quite. Kinetic energy is the product of half the object's mass and the speed of the object (in whatever reference frame) squared:



Of course we can convert one for the other - that's all that roller coasters do too. When talking aerobatics, a plane's vertical penetration is often given - how much height the plane can gain before it's airspeed is zero. I wrote the wikipedia page on this a while ago in high school: http://en.wikipedia.org/wiki/Vertical_penetration . Essentially, assuming the aircraft is a glider in a vacuum, we can equate the two formulas and assume the total mechanical energy is conserved, and conclude it's vertical penetration is:



Personal attack involving my family members, telling me to wreck an airframe, and calling me a know-it-all in 3..2..1..

[Big Pistons Forever]

This is how I treat the Kinetic vs Potential energy issue in my Nanchang

Using Kinetic energy = YEEE HAAH right F*cking now !

Accumulating Potential energy = The distinct possibility of future YEEE HAAH

[trampbike]

Personal attack involving my family members, telling me to wreck an airframe, and calling me a know-it-all in 3..2..1..

Don't you think that being called a know-it-all is actually quite the compliment?


Beef, here's what you probably meant:

Half your mass times the square of your speed is kinetic energy.

Your weight times your height is potential energy.

In order to use your potential energy to glide as far as possible in a no wind condition after engine failure you want to glide at the angle of attack that gives you the greatest lift/drag ratio

BPF nailed the explication of energy management.

Here is the theory of flight:
Your engine pulls air backward while your wings pulls air downward.

Meteorology:
The atmosphere is one hell of a complex system which can only be at best approximated even by the best computers and scientists on the planet.
Use your judgement* to deal with weather.
*Judgement not included in your local FTU training syllabus.

Piston engines:
4 strokes: Suck, squeeze, bang, spit

Air Law:
It's not because it's legal that it's safe. Use your judgement (same diclaismer as in meteorology section)
It's not because it's safe that it's legal.
If it makes sense, it might be legal. If it doesn't, it sure is.

[Beefitarian]

I'm not writing that out while I fly.