Downwind Turns Need NO More Power
The absurdity of the argument that turning downwind makes aircraft descend never ceases to amaze me! The physics of the situation earns this topic onto my list of the Myths of Aviation, perhaps as #1.
Were Galileo with us, he would explain what an "Intertial Reference Frame" is, so that even accident investigators would know not to blame the dreaded Downwind Turn when simple pilot error will suffice, aided by the decieving visual cues during the maneuver.
For clarity: Turning Downwind takes no more power and no more energy than turning Upwind, unless you are flying purely by ground reference, and attempting to hold a fixed ground radius turn.
If the ground speed change needed more energy (as is said by the budding Newtons who espouse to the theory) then I have a bigger "headwind" for us to buck:
The Earth rotates at a speed of about 1500 KM/Hr toward the east at the equator, about 1000KM/Hr at temperate latitudes. As you sit at your computer, know that the monitor, keyboard and desk move about 277 meters per second toward the east. If you rise from your chair and walk westward at 1 KM/Hr, and then turn eastward, you must accelerate yourself to catch up with that rotation (according to the pprune Newtons).
But you don't fall to your knees, and you don't make holes in the wall as it hits you at 277 M/sec. Why? Because all of the things in your room are immersed in this motion field, and all of the things are synchronized to that velocity. That is the definition of an Inertial Reference Frame. THERE IS NO CHANGE IN ENERGY STATE RELATIVE TO THE OBJECTS IN THE INERTIAL REFERENCE FRAME, EVEN IF AN OBSERVER HOVERING INDEPENDENT OF THE EARTH'S VELOCITY FIELD WATCHES YOU ALL ROAR BY AT 277 M/SEC!
Here is a thought experiment for the "down-winders" to try when they get all wrapped up in energy computations relative to the earth below an aircraft in flight. Stand on an airport conveyor belt, the kind that carry you from one terminal to the next. As you translate at 1 M/sec across the airport, watch the ground go by and calculate the energy in your usual way. Now take your briefcase and start to swing it back and forth going parallel with the moving conveyor's motion.
Do you feel the tremendous force needed to swing it forward, relative to the slight force needed to swing it backward? Do you? No! You feel no difference in force from the bag even though you are propelling the bag forward at perhaps 2 M/sec and then backward at perhaps 0 M/sec relative to the airport floor, walls and building (while you are symetrically propelling the bag to plus and minus 1 meter per second relative to the conveyor belt, and relative to your arm and your body.)
A flying aircraft in a steady wind is immersed in an Inertial Reference Frame, and no enegry calculations are needed to compare the aircraft to the upwind ground speed, nor to the speed of the earth's rotation, nor to the motion of the Earth as it swings around the center of the Milky Way Galaxy (42,000 miles per second for the downwinders to place in their equations!)
This great mystery will be back in about a year (the life-cycle of a pprune Myth). I hope I will be around to re-post this at that time!
Last edited by NickLappos; 27th Jun 2009 at 18:59.