A strange thing happened after a four-hour IFR flight in the soup the other day. The strange part was not the visual approach or the six-mile visibility and the 6000 feet of runway ahead, but rather the energy momentum. I’ll add a bit of physics here. I was contemplating a nice landing with three souls on board and bags. In that contemplative mood, I turned a one-mile final for traffic considerations as per the tower at 800 feet. No biggie, one might say, and it shouldn’t have been. By the time Garmin’s faithful voice stated “500,” I was already looking at four white lights on the PAPI. And by the time I heard “minimums, minimums” (I program that on every flight where an approach is available), I was rushing in at 85 knots or 9% over the VSo1.3.
Now in all likelihood most of us have done that one time or another. Maybe? And I have too, plenty of times, but determinately? Almost, never! Yet here I was plowing the slight crosswind hankering to take me off the runway. Nope, that was not going to happen. Even with a forward slip, I leveled off around 79 knots and then held and held and held till the lift dissipated and I touched down 750-800 feet past the threshold and ran the wheels for another 1400-1500 feet and then on to the third taxiway (and not a high speed one either). “Hmm,” I thought, “hope no one was watching.”
One might say, so what?
Let us look at energy as a stored form of force. As in potential energy that one gains by appropriating first the chemical energy (burning of fuel) and translating it to the mechanical energy (turning the prop and creating thrust) into stored potential energy as altitude.
You go up in the air with a whole bunch of fuel burn and then coast down with a bunch less. But in that bunch less is a major wizardry of airmanship. How we manage that energy is what determines the difference between the sound generated by the repeating Doppler-effect-engine-power-hog-jock and an aviator.
The slow dissipation of energy by carefully manipulating the throttle to achieve a steady state loss of that potential energy transformed into kinetic energy, is the key to good airmanship. When the landing configuration is best at 1.3 VSo for normal landings and 1.2 VSo for short field landings, there is a specific need to adhere to that tenet. Or else you run the gauntlet of what might be. And most times it won’t be pretty.
Many a pilot has ventured past the runway end carrying more energy than needed. A case in point is the recent Falcon crash at Greenville Airport that killed both the pilot and copilot in their haste to land while the runway kept shortening in front of them. The NTSB has yet to finalize on that fatal accident, therefore, this statement is a hearsay opinion based on the video of that flight while in the landing phase.
Remembering that speed is a form of kinetic energy and it dissipates at a certain rate when thrust is eliminated: the stored energy is a thief of time and space. Knowing only through practice, conditions a pilot in its judicious use.
Let’s look at the correlations between speed and energy…
Assuming a 3000-pound aircraft arriving at a runway at the given speeds creates the resultant force. (Kinetic Energy + ½ mass * Velocity squared):
- 65 knots of airspeed = 562,128 ft-lb of kinetic energy. 0% Baseline
- 80 knots of airspeed = 851,508 ft-lb of kinetic energy. +52%
- 50 knots of airspeed = 332,620 ft-lb of kinetic energy. -41%
Given those dynamics, it behooves us to maintain the appropriate energy on final approach to the runway.
Additional benefits of proper speed/energy management also include:
- The sudden deceleration, say, hitting a parked truck or a deer on the runway or a structure requires tremendous energy dissipation.
- Stopping a 60kt aircraft at 18 feet distance leads to a 9G force on the body (the limits of the FAA certified seat belts).
- Stopping that same force/energy in 9 feet distance leads to an 18G force on the body (limits of sustainability).
- And a sudden stop at 1-foot distance leads to 159 G force (unsustainable for the human body).
So, going back to my landing, I came in with near 10% higher speed/energy than required and I paid the price in runway used. Mind you, with that much stored/kinetic energy, I would certainly have taken out the runway end identifier lights on a 2000-foot runway.
A word of advice: translate appropriate power and pitch for climb/cruise, appropriate power reduction and constant pitch for descent and zero power and changing pitch for level over runway and thence a smooth landing flare. Always concentrate on the VSo1.3 on normal landings and VSo1.2 on short field landings.
Fly by the numbers appropriate for the aircraft you fly and always fly safe.