Part of the confusion (for some people) may also come from the fact that real-world pilots endeavor to takeoff/land with a headwind, which may lead a person to believe that a plane’s direction of travel with respect to the wind direction also matters after becoming airborne.
It may help to imagine a bizarre universe in which the air remains absolutely stationary at all times, but the ground is moving in some arbitrary direction. Clearly in this case the relative movement of the ground doesn’t matter to the plane or the air; the air is still absolutely stationary, and the plane still has whatever airspeed it had before the ground started moving. As far as Newton is concerned, this is the same as if the ground is stationary and the air is moving at a steady speed. In either scenario, turning your aircraft to a new heading does not change your air speed (disregarding any temporary change in aero drag during the bank/pull), even though it may change your ground speed.
Along with your shiny new wings you’re issued a bag full of luck. And an empty bag to hold your judgment. Your goal is to fill the one before the other runs out.
Hence the advice to be sparing in how you use up the luck.
Which is why it’s always better to borrow somebody else’s bad experiences. Hence the (serious) study of accident reports and such. The Flying School of Hard Knocks costs too much in blood and treasure for everyone to attend.
This sums things up nicely. Relativity tells us that there is no absolute rest frame. From the aircraft’s perspective, all non-accelerating airmasses are identical, and what the ground happens to be doing underneath the airmass is irrelevant. In fact, when flying on basic instruments (no GPS or INS) without visual ground reference, an airmass that is stationary relative to the ground is literally indistinguishable from an airmass that is moving steadily relative to the ground. Student pilots learn early on that there is no way to deduce groundspeed directly from basic instruments - an issue in elementary navigation on windy days.
Inertial Nav Systems are gyroscopically “locked” to the frame of reference of the local surface of the earth, achieved by spinning up the gyros before taking off. This does not mean that inertia is in any sense associated with the earth by any physical principle. The gyros in the INS could, in principle, lock the INS to any frame of reference.
An airfcraft effects a turn by using aerodynamic forces to work against inertia. This process is identical in any non-accelerating airmass. Movement of the airmass relative the ground is irrelevant.
As has been mentioned, unusual inertial effects only come into play with windshear - when transitioning between airmasses moving at different velocities, or when an airmass as a whole accelerates. A classic inertial lag situation is created by microbursts on short final in a heavy aircraft.
Last week, I heard a friend saying that his instructor says that when practicing stalls, you need to face the wind, to get headwind, before starting the maneuver. Thats completely wrong, right? I mean, practicing a stall has nothing to do with the wind direction.
I’ll wait for your opinions.
Regards.
Talking about wind velocity relative to the ground is equivalent to talking about the ground’s velocity relative to the air. The only time it’s ever relevant is when you’re interacting with both the air and the ground, i.e., during takeoffs and landings.
That depends on why the instructor wanted to be facing into wind. If it was because he thought the aeroplane would somehow fly better then yes it is wrong, but maybe he had another reason. If they were flying in a small training area and the instructor wanted to minimise the distance travelled over the ground so the could stay in the training area more easily then doing the stalls into wind makes sense.
A long time ago, my older sister was a flight instructor for PAC at Lindbergh Field in San Diego. She was the one to take brand new Navy Pilots on their C-150 checkout when they would show up with the girl of the weekend as they were touring around the country with a jet & government credit card after flight school. Do they still do this??
Anyway, they were of course smart, good, pilots that had no little plane time that could not even go as fast as their usual stall speed. It was hard to get them to take the plane serious until she came up with this flight profile.
After take off climb while heading for the beach and getting into ‘lets play’ airspace. At sufficient altitude (for her) she would have them track the surf line then add in having the airplane alined with the ground track.
Can you say, “Full max cross control?” I thought you could. < VEG > Now she asked for a full power stall in this same configuration.
After she prevented the auguring into the beach vertically she would ask, “Now are you willing to accept the idea that you might need to pay attention to this checkout? That even this little plane is big enough to kill you? And the fact that I am a female does not threaten your manhood.” After this being really smart & good pilots, they would be ready to go almost by the time they got back to the airport.
She just had to get their attention.
When I do stalls, the direction is not a consideration, completeness and quality of my clearing turns is the important thing … other than flying the airplane. Never forget to fly the airplane above all else.
Specially the ground, make sure you always fly it above the ground ;).
Edit: On the subject of military pilots, I used to work with an ex military guy who had never flown a piston engine machine. Basic training was in a turbo-prop and from there it was to jets or bigger turbo-props, he’d never touched a mixture control in his life. The irony is that for all that jets are portrayed as being super complex and a step up from pistons etc, piston engines are a lot less forgiving than turbines and you need to take more care with them. Particularly big pistons.
Over the years I have been noted to forget that until it was fixing to become a serious problem. :o Sure am glad it was a learning experience and not my last experience.
No, ground speed is important for one purpose. Do you have enough fuel to reach the next fueling station, and that requires ground speed to determine. Other than that, the airplane could care less what it’s ground speed is, landing, taking off or flying. That’s similar to the old airplane on a treadmill question.
ETA. If you’re cutting fuel load that close, you’ve dipping into your bag of luck* way more than you want to.
Ground speed is important whenever you are referencing the ground for any purpose. Accurate navigation requires accurate ground speed and knowledge of the wind over the ground in order to make good your desired track over the ground.
Landing and take-off requires knowledge of the wind over the ground so you can minimise the amount of runway used. You don’t directly use groundspeed but you are effectively trying to minimise it. Tyres also have a maximum certified speed that can be limiting in rare circumstances and the groundspeed is relevant for this.
Since you all are people full of knowledge, let me ask you the following:
Could someone please tell me if, during a coordinated turn, both wings have the same angle of attack? Why when you rise one of your wings its AOA increases? I mean, you can rise whatever wing you want, but the relative wind to one or another still be the same right? Since the AOA is the angle formed by the wing’s chord and the relative wind, I cannot understand why in a constant turn, both wings have different AOA, they are describing the same path, same direction.
Ill wait for you replies.
Thanks very much.
Regards,
