I’d like to tell you a long story about airplanes to help describe the road from Cusco to Quillabamba and Machu Picchu.
Two important concepts in airplane design are stability and control sensitivity. There are 2 kinds of stability: static and dynamic. Static stability means when a pilot lets go of the controls during normal stabilized flight, that the airplane will maintain its attitude – so the pilot can grab a map or cup of coffee and the airplane will continue on its merry way. Dynamic stability means when an airplane is disturbed from stabilized flight that it will eventually return back to its stabilized flight path. For example when a pilot yanks on the controls to avoid hitting a bird, an airplane with good dynamic stability will enter a slowly decreasing porpoising motion and eventually return to its steady state flight path. Finally control sensitivity means how quickly the airplane responds to the pilot’s control inputs and how much force the pilot needs to exert on the controls to fly the airplane.
In the early days of aviation these concepts were not well understood, for example, in a Ford Tri-Motor you could slam the controls completely back and forth on approach but the resulting airplane movement was almost indiscernible, the controls were very ineffective at slower speeds. I never flew a Ford Tri-Motor but I knew a guy who did, he flew for an outfit that smuggled liquor in Tri-Motors during prohibition. The Piper J3 Cub was one of the first mass produced airplanes that had these concepts figured out, it’s the nicest flying little plane. Of course airliners nowadays are all controlled by computers, their flying characteristics are programmed in, not achieved only by aerodynamics.
At the end of the day, there is an acceptable range of stability and control sensitivity. For example, a training airplane typically has less stability because the designers want to force the student pilot to be attentive at all times. In another example, I flew with a pilot who liked to barrel roll fully loaded Convair 240s and Gulfstream G1s but he swore to never try the same in a Convair 340 or 440, its roll rate is too slow.
In this acceptable range of stability and control sensitivity, if an airplane is not very stable but has sensitive controls, a pilot might say it’s a “touchy” or “squirrelly” airplane.
Legend has it that one of the early pilots to fly the Pitts Special was a bit shook up after landing by the airplane’s power and handling, telling Curtis Pitts “that’s one squirrelly airplane you built!” To which Curtis Pitts famously responded “I’ve never known a squirrelly airplane but I’ve met a lot of squirrelly pilots!”
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I drove the road from Cusco to Quillabamba for the first time last week, Quillabamba is the closest town to Cusco on the edge of the jungle, it’s nice to take the kids there for a swim in the pool. The road to Quillabamba is the same road tourists take to go to “Machu Picchu by car” as you see advertised everywhere in Cusco, I believe it’s less expensive than taking the train. The road goes via Ollantaytambo up near Nevado Veronica at an elevation of just over 4,300 meters (about 14,000 feet) and then back down to 1,100 meters (about 3,500 feet) by the time you reach Santa Maria. From Santa Maria you can continue on to Quillabamba or take the detour to Santa Teresa, then via the Hydro-Electrica to Machu Picchu.
Locals say it’s a dangerous road. If you want my advice, take the train to Machu Picchu. I’ve never met a dangerous road but I’ve sure met a lot of dangerous drivers, and the road to Quillabamba is very unforgiving of dangerous drivers.