You learn something new everyday.

[Martini 0]

Well he may not understand the physics but at least he's careful!

Sometimes you eat the bear..............

[pchapman 261]

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You're flying along at 30 knots into a 25 knot headwind, groundspeed and the airplane's physical momentum are both 5 knots. The pilot then does a quick 180 in a matter of seconds whch isn't too difficult to do with 5 knots of momentum. So, the airplane is turning downwind to a tailwind of 25 knots, AND has to accelerate its physical mass from 5 knots to 55 knots but at an airspeed of negative 20 knots. The airplane will stall at some point in the turn!

Sorry, I hope you're joking, otherwise it's all wrong.
The speed one is going creates no momentum effect at all. The plane will turn just as quickly whether it is going upwind or downwind. If I'm walking around in an airliner while doing 600 mph, I don't have any problems with the massive momentum either.

Your plane will always be exposed to 30 mph of relative wind, before, during, and after the turn.

[baronn 111]

just goes to show that if you say the most ridiculous things, buy enough beer, do enough drugs and try to convince yourself (and anyone else gullable enough to believe the horseshit spewing out of one's mouth) that there is an actual chance that you might get someone to believe almost anything.

[billvon 2,400]

>You're flying along at 30 knots into a 25 knot headwind, groundspeed
>and the airplane's physical momentum are both 5 knots. The pilot then
>does a quick 180 in a matter of seconds whch isn't too difficult to do with 5
> knots of momentum. So, the airplane is turning downwind to a tailwind of
>25 knots, AND has to accelerate its physical mass from 5 knots to 55
>knots but at an airspeed of negative 20 knots. The airplane will stall at
>some point in the turn!

Nope. It doesn't matter if the airplane is flying at 30 knots and the airspeed is 300 knots. The airplane is not affected. Your ground track is affected, of course, but it doesn't matter which way you turn - the airplane always works the same.

If you doubt this, jump on a day with 40 knot uppers. Pull high, close your eyes and start to spiral. See if you stall every 180 degrees.

[sacex250 0]

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If you doubt this, jump on a day with 40 knot uppers. Pull high, close your eyes and start to spiral. See if you stall every 180 degrees.

A couple problems with this:

1) A spiral is forward movement vertically in a column of air. The winds would be nullified. Try it in a flat braked turn though.

2) A parachute is not capable of a sustained constant airspeed level turn.

3) A skydiver has very little mass and would accelerate and decelerate very rapidly by pitching up and down during the 360's. It would be a wild ride, and the skydiver would definitely notice the G-forces as the parachute's energy increased and decreased during the turns.

--

It's all been said before, no sense repeating it here.

[sacex250 0]

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Sorry, I hope you're joking, otherwise it's all wrong.
The speed one is going creates no momentum effect at all.

Momentum is inertia not G-forces. Speed has everything to do with momentum. It is acceleration that causes G-forces.

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The plane will turn just as quickly whether it is going upwind or downwind.

In training pilots do ground-reference maneuvers like "turns around a point" and "S-turns across a road". This training demonstrates that the downwind and upwind turns are in fact quite different. The downwind turn is flown with a steeper bank angle because the airplane has a higher ground speed on the downwind side of the turn; it's the ground-reference part that illustrates this point, or hides it depending on the quality of instruction.

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If I'm walking around in an airliner while doing 600 mph, I don't have any problems with the massive momentum either.

You have quite a bit of inertia/momentum but if there's no acceleration taking place then there won't be any force. A change in inertia requires force.

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Your plane will always be exposed to 30 mph of relative wind, before, during, and after the turn.

The airspeed has nothing to do with the airplane's mass. The airspeed can change much faster than the airplanes physical speed through space can. This is the underlying concept of windshear. If an airplane is flying into a headwind and the wind suddenly changes direction then the airplane can suddenly lose airspeed without the airplane's groundspeed changing.

The point here is that an airplane can turn quicker than it can accelerate in a straight line. If the turn causes a significant change in wind direction it can cause a rapid change in airspeed.

---

It's all been said before, no sense repeating it here.

[strop45 0]

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Momentum is inertia not G-forces. Speed has everything to do with momentum. It is acceleration that causes G-forces.

+1, although it seems to me for most practical purposes to do with skydiving you can ignore the effect of momentum and just look at relative airspeed.

With a slope soarer with a strong crosswind, there is a difference in the way the plane turns on upwind to downwind versus downwind to upwind, even though they are both in the same speed airflow. Going upwind to downwind the momentum gets converted into lift and in the other direction you need to loose height to maintain airspeed.

The difference between stupidity and genius is that genius has its limits." -- Albert Einstein

[popsjumper 2]

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Another laugh is when someone suggests that to get back from a long spot, you want to spread your body wide, to catch air, because the wind is at your back.

OMG. And here I thought I was the only one in the world who had to address that with a "highly-experienced" jumper.

Unbelievable.

He even went so far as to say "pull the tail down so it catches more wind and you get more push".

My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

[popsjumper 2]

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Knew a pilot once who said he always made sure not to turn too fast for a 180 degree turn to create negative airspeed and stall the plane.

I thought he was talking about turning too fast/hard at too high of an bank/AOA to create a stall. Nope, he really thought he could turn around and get negative airspeed over the wing.

*note to self....don't get on the plane with this guy.

You may get a kick out of this:

http://www.youtube.com/watch?v=qCb1vgvz5zs&feature=related

My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

[davelepka 4]

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In training pilots do ground-reference maneuvers like "turns around a point" and "S-turns across a road". This training demonstrates that the downwind and upwind turns are in fact quite different. The downwind turn is flown with a steeper bank angle because the airplane has a higher ground speed on the downwind side of the turn; it's the ground-reference part that illustrates this point, or hides it depending on the quality of instruction

Ground reference manuvers are taught for the times when a pilot must fly in reference to the ground, like when flying in the pattern setting up for landing. They are not taught to prevent pilots from having their planes fall out of the sky based on wind direction.

[rehmwa 2]

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Thanks for explaining this guys. Both in this thread and in PM's. I keep omitting the "moving with the air mass" part from my thought process.

I guess wind would matter in BASE though ?

YOU GOT IT!!!

and yes, wind matters in base, because you are starting from a point fixed to the ground (where you feel the air) rather than a point fixed in an airmass where you are moving along with it. Frame of reference is the entire point.

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[rehmwa 2]

Putting yourself into a flat spin has nothing to do with which direction the wind flows. Nice try. your airspeed is 30 in every direction, if you crank out a flat spin, sure, you will stall - regardless of whether you started out N, S, E, or W......

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[rehmwa 2]

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Another laugh is when someone suggests that to get back from a long spot, you want to spread your body wide, to catch air, because the wind is at your back.

OMG. And here I thought I was the only one in the world who had to address that with a "highly-experienced" jumper.

Unbelievable.

He even went so far as to say "pull the tail down so it catches more wind and you get more push".

More of the same lack of concept..... - (i.e., people thinking it out while standing on the ground, rather than while flying)

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[sacex250 0]

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Ground reference manuvers are taught for the times when a pilot must fly in reference to the ground, like when flying in the pattern setting up for landing. They are not taught to prevent pilots from having their planes fall out of the sky based on wind direction.

Which is why I mentioned "quality of training." An airplane's inertia is its energy through space not through the air. Airspeed is the combination of the airplane's physical inertia combined with any independent movement of the air. "Quality training" would go a step further than just flying a plane in reference in the ground to illustrate how an airplane flies is still determined by how it's moving in relation to Earth not just to the wind. A change in wind speed is not an instantaneous change in the airplanes physical inertia; an airplane has more mass than the air does and therefore will not change inertia as quickly.

The physical speed of an airplane in level flight is its groundspeed no matter how strong the wind is or what direction it's coming from, just as an airplane tied down on the ramp is always stopped no matter how hard the wind may blow even though the airspeed indicator may be showing that the airplane has airspeed.

If a pilot of an airplane with a stall speed of 30 knots is flying into a headwind of 40 knots at an airpspeed of 40 knots then the groundspeed is zero because the airplane is hovering in mid-air. If the headwind suddenly dies down to nothing, the airplane will still have a physical speed of zero and will instantly stall and start falling until it can regain it's speed by descending and/or powering out of it, which is what is happening in the F-22 video above, The F-22 can maintain control even though it's fully stalled because of its thrust vectoring and fly-by-wire control system, but even it can't stay in the air when stalled.

It is entirely possible to turn a light airplane flying at a slow speed faster than its engine is capable of accelerating it in level flight. If the airplane turns away from a headwind in a level turn and the airplane doesn't have the power to accelerate the mass of the airplane to make up the difference then the airplane will lose airspeed, and, it may stall if it loses enough airspeed.

Imagine a helicopter hovering into 25 knot headwind, airspeed is 25 knots, groundspeed is zero. If the pilot does a 180 pedal turn, the airspeed drops to -25 knots (flying backwards), but the groundspeed is still zero. In order for the pilot to regain his 25 knots of (forward) airspeed, the helicopter will have to, completely under its own power, accelerate from a groundspeed of 0 to 50 knots. That will take longer than the pedal turn did. So, if the pilot wanted to maintain his 25 knots of airspeed, and turn downwind, he would have to be patient and turn slowly to allow the helicopter to accelerate away from the hover to a groundspeed of 50 knots all while maintaining an airspeed of 25 knots. It's not as easy as it sounds.

--

It's all been said before, no sense repeating it here.

[billvon 2,400]

>1) A spiral is forward movement vertically in a column of air. The winds would
>be nullified. Try it in a flat braked turn though.

You are welcome to. Exactly the same thing will happen - you won't even notice the direction of the wind unless you're looking at the ground.

>A skydiver has very little mass and would accelerate and decelerate very rapidly by
>pitching up and down during the 360's. It would be a wild ride, and the skydiver would
>definitely notice the G-forces as the parachute's energy increased and decreased
>during the turns.

Uh, have you ever spiraled a parachute before?

[billvon 2,400]

>n training pilots do ground-reference maneuvers like "turns around a point" and
>"S-turns across a road". This training demonstrates that the downwind and upwind
>turns are in fact quite different.

Yes, they are! And the reason why is contained in the name of the maneuver. "Turns around a POINT" require you to fly with reference to the ground. That means you have to turn more rapidly while flying downwind to maintain a roughly circular ground track.

Now try the same thing just above a point on a cloudbank and you will notice that your turns are perfectly circular, with the same bank angle held throughout. How can this be, if the winds are the same as in the first case? Because the clouds are moving with you.

[Remster 24]

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Uh, have you ever spiraled a parachute before?

No bets will be taken on this one.

Remster

[deltron80 0]

BOOBIES!

[DaVinciflies 0]

You seem to be very confused between airspeed, groundspeed and "physical speed" what ever that really means.

An aircraft flying at 40kts into the wind then doing a 180 will continue to have an airspeed of 40 kts. Its ground track will change, but the wings will not "know" that it has gone from flying upwind to downwind.

Wind as we use the word is air movement vs the ground. An aircraft in flight no longer has reference to the ground as it is moving in the airmass.

You might as well be saying that I am moving at 490,000 miles per hour as I sit here. Because relative to Galactic Central Point I am (more or less) but its a meaningless comparison.

[Zlew 0]

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You may get a kick out of this:

http://www.youtube.com/watch?v=qCb1vgvz5zs&feature=related

NICE!
what a sweet plane.
If the 182 only had thrust vectoring.... :)

[sacex250 0]

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A skydiver has very little mass and would accelerate and decelerate very rapidly by
pitching up and down during the 360's. It would be a wild ride, and the skydiver would
definitely notice the G-forces as the parachute's energy increased and decreased
during the turns.

Sorry, wasn't referring to a spiraling turn there. I was refering to the flat turn.

Let's say a 40 knot wind from the north and a parachute doing a 15 knot flat turn to the left. The diver starts out with 25 knots of southbound inertia (backwards). As the diver turns to the south he begins to accelerate to 55 knots southbound but the parachute accelerates faster than he does causing the parachute to descend/pitch down to accelerate the diver. Once facing south, the diver will have a groundspeed of 55 knots and an airspeed of 15 knots, of course, discounting any recovery arc or pitch up to make up for the pitch down.

Continuing the turn back to the north, the parachute starts to slow down but quicker than the diver does, causing a climb/pitch-up as the diver swings forward of the parachute as his speed begins to slow from 55 to 35.

Even though the diver is basically flying at a constant airspeed of 15 knots, his body is constantly being accelerated and decelerated as he's basically being whipped around on the downwind side of the turn, and slowed down on the upwind side. The diver would definitely feel this force.

--

It's all been said before, no sense repeating it here.

[billvon 2,400]

>Even though the diver is basically flying at a constant airspeed of 15 knots, his body is
>constantly being accelerated and decelerated . . .

Nope. His body is seeing the effects of only two things:

1) Gravity.
2) The centripedal effect of the steady turn.

>The diver would definitely feel this force.

You keep saying that but, in fact, I do not. It's like claiming "you go up when you open your parachute." You really don't - both because there is no reason you would, and because, in fact, skydivers do not go up.

[sacex250 0]

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An aircraft flying at 40kts into the wind then doing a 180 will continue to have an airspeed of 40 kts. Its ground track will change, but the wings will not "know" that it has gone from flying upwind to downwind.

Wind as we use the word is air movement vs the ground. An aircraft in flight no longer has reference to the ground as it is moving in the airmass.

You might as well be saying that I am moving at 490,000 miles per hour as I sit here. Because relative to Galactic Central Point I am (more or less) but its a meaningless comparison.

It is time to move past DaVinci to Newton!

A flying airplane is just as connected to the Earth as the moon is. The physical mass/inertia/motion/momentum/energy/hurtling speed of an airplane has NOTHING to do with the airmass! The airmass exerts a force on an airplane, or bullet, which can affect its inertia, but the physical forces at play have to do with its speed through space, not the air! An airplane in flight is bound by the same physical laws of motion and gravity whether sitting on the ground, floating in water, or orbiting the planet.

Here's a skydiver flying into the side of a hangar:

20kt airspeed, 10kt headwind = 10kt collision
20kt airspeed, 10kt tailwind = 30kt collision
20kt airspeed, 20 kt headwind = impossible to collide with immovable object if you're not moving!

The airspeed has nothing to do with the inertia of the skydiver, the inertia is completely dependent on the object's relative motion through space, and our main reference point of motion here on Earth, or in orbit, is the Earth, not the airmass.

--

It's all been said before, no sense repeating it here.

[sacex250 0]

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Nope. His body is seeing the effects of only two things:

1) Gravity.
2) The centripedal effect of the steady turn.

3) The accelerational forces of physically speeding up and slowing down during the turn.

Check out the following video:

The riders are going around in a circular steady turn, but are being rapidly accelerated and decelerated by the overall rotation of the ride.

http://www.youtube.com/watch?v=q8sSALDUCtE

It's the same situation a skydiver would feel while doing flat turns in a strong wind. You seem to think that because the riders are going around in steady circles in their cars then they cannot possibly feel the effect of their total motion on the ride as a whole. Yes, they can!

--

It's all been said before, no sense repeating it here.

[DaVinciflies 0]

Maybe if you make a jump and experience a flat turn or spiral you will understand. Your description of what would happen - just does not happen!

You keep relating things back to the ground which, until you come back into contact with it, has NO BEARING on how objects in flight behave. (ETA: for the sake of completeness with the exception of things like object-induced turbulence and thermals)

A given canopy/jumper combination in full flight will have the same airspeed whether you are going upwind/downwind or crosswind. When you lose contact with the planet's surface, "wind" ceases to exist for all practical purposes and all that matters is relative wind. ie. the movement of air relative to the wing.

If I took a fish in a tank in a 747 traveling at 500mph over the ground, would the fish have to swim at 500mph to keep up? Would it get "whipped round" if it tried to do a 180? That fish's water environment is exactly analogous to the air-mass we move in under canopy.

Out of interest - have you ever tried your flat-turn experiment?