Hawker Driver

Hi Guys,

We are all already pretty familiar with the techniques for landing airplanes safely. What I want to know is, why isn't kinetic energy mentioned more in landing training or found much in our books?

I discovered years ago, assuming the correct approach speed for your airplane, that you'd always have about 10 seconds of kinetic energy to play with after flaring. After 30 years of flying so far, I can tell you that it applies for all airplanes as well, regardless of size.

In primary training, I'd have my students count out loud after commencing a flare. A lower number would correspond with higher kinetic energy, a lower angle of attack and too great a speed for touchdown. A higher number would correspond with reduced kinetic energy, a higher angle of attack and a better touchdown speed.

I utilize the same technique silently to this day regardless of the jet or piston flown.

UAL T38 Phlyer

Hawker:

A good point, and I think somewhat intuitively obvious to those who have been flying a long time....but you are right; it isn't really mentioned in any "Learn to Fly" book I've ever seen, even military syllabi.

I think it may be two-fold:

1. Tradition. Early airplanes (wood and fabric type) had relatively little kinetic energy compared to the drag of the airplane. Think "Dandelion seed." So the methods that were developed in the early days emphasized a speed, not a cognizance of KE.

2. There is no "Kinetic Energy-ometer;" that is, there is no gauge/instrument for it. IE, teaching guys to use intellect (Hey, my inertia will give me a few seconds to work this out) and a "feel" for KE (It feels like I'm running out of speed here) is hit or miss---some guys will get it, some won't (just like trying to teach how to use the rudder!).

HSLD

I would argue that managing KE is taught as a function of controlling indicated airspeed. While I agree that's it's rarely mentioned as KE, flying the appropriate airspeed for a given configuration directly affects the KE delta.

With a little practice, the airspeed indicator can be used as a "kinetic energy-ometer" in a safe training environment for demonstration. It works for all planes in all configurations. Of course you know this, so to answer your question, I'm not sure why KE isn't highlighted more in formalized ground school texts. In practice, V1 should be synonymous with KE, as should REF+20 on approach and I believe it is

jungle

Many aircraft now show a trend line with airspeed, it shows predicted KE/AS rate of gain loss based on accel/decel even though AS may not yet show the trend, sort of an automated seat of the pants driven by the inertial systems.

UAL T38 Phlyer

Jungle:

The A-320 and the 747-400 both had that, but I found them to not be as helpful as experienced "seat of the pants."

The -400 predicted 5 seconds into the future (I think the Bus was the same), but in highly turbulent situations, it often showed rapidly-reversing trend-arrows. I can think of one trip from HNL to NRT, I'm in the left-seat, Capt is in the bunk, and the arrows were going 15 kts over Mmo, and 15 kts into the Yellow (Stall) airspeed band. We were heavy and high, and ATC wouldn't give us lower (everyone was screaming for the same thing).

In reality, the speed didn't waver much more than about 5-7 kts. But the arrows were making me pretty anxious! (I was still new to the airplane)

jungle

As the Dean said, high heavy and slow/fast is no way to go through life.

Sometimes, despite all the books and lawyers, we are forced into that ugly corner where we are forced to use that most uncommon virtue of common sense.

AKASHA

So, all airplanes have about 10 seconds of kinetic energy after flare, assuming correct approach speed. Quite a statement. And a higher second count equals a better touchdown speed. Maybe it is a good exercise to help students better understand the science of landing. I don't know. But ten seconds of what I presume to be "float" time is not a good thing.. not in our operation. It seems you are teaching students to float the plane in ground effect to burn off energy and touchdown at a slower speed. I could be getting this wrong. Is that what you are teaching? We'd have to throw our landing charts out the window.

UAL T38 Phlyer

AKASHA:

OK, 10 seconds as a blanket is a bit broad. I was agreeing with Hawker that in general, students are not taught to think about the effect of kinetic energy in the flare....only airspeed.

In my current airplane (T-38), the students are usually very reluctant to fully flare the airplane, as it feels very different from previous experience. (Very nose-high and difficult to see forward; lots of aerodynamic buffeting; mushy controls). This full flare can take five seconds (on average) to achieve.

So instead, they usually just plant the airplane in the first 1000 ft. Typically, they are about 12-15 kts hot. However, touching down shorter actaully makes a longer rollout than full-flaring it, and touching down 1500-1800 ft down the runway; as much as 50% longer!

When being first taught to fully-flare it, they often over-do it, and balloon, in idle....and find themselves out of airspeed and ideas at about 10 ft. (That would be the kinetic energy turned to potential).

So, Hawker's post got me thinking, and I'm going to start including a little talk on KE=1/2mv squared for them to ponder.

2StgTurbine

I don't really get it either. To me, a good approach speed results in touching down soon after you started the flare. If it takes 10 seconds to touch down, that means you had excess speed to bleed off. If you flare and touchdown shortly after, then you came in with just enough KE to get the job done. Also, if you did happen to come in too fast, for most aircraft, the flare is not the most efficient way to get rid of that energy.

USMCFLYR

We discussed it a little bit in the landing briefs in my former community. To the extent that our *landings* quickly dissipated energy.
Interesting discussion though.

USMCFLYR