HarryC

My Feedback: (1)

That's it, the rate it which it gains height is the same as if it was zooming off downwind, and the angle of climb through the air is the same for both, but if you look at it from a fixed point on the ground the angle of climb seems very steep going into wind and very shallow for the plane going downwind. It's an illusion caused by the model flier standing in a different frame of reference to the one the plane is flying in.

I think the rest of it you are over complicating by trying to calculate airspeed from groundspeed and windspeed. In flight the aircraft doesn't do it that way, it has an airspeed which remains in any direction, the wind and ground are irrelevant to its flight performance and handling. Relating to some point on the ground is totally arbitrary, the universe gives no special prominence to the place you are standing, which itself is whizzing around at thousands of mph as the earth rotates, the earth itself is whizzing around the sun at thousands of mph, the sun is whizzing around the galaxy at goodness knows what speed, which is moving at staggering speed in an inflationary universe so why do you want to try and relate speed based on some arbitrary point you have chosen to stand which itself is moving at huge speed in the universe? Ground is relevant to navigation but has no relevance to the performance of an aircraft in flight.

JPerrone

With respect to the relevance of considering groundspeed: I think the term "context" comes to mind. I'm sure that there are cases where thinking groundspeed isn't useful.
- If you are in an airplane just flying around, it may not have any relevance at all.
- If you are trying to fly from point a to point b: more relevant.
- Recall we're talking model airplanes here. In this context, the person's perception of the movement of the plane is heavily influenced by the fact that he is on the ground; and the relative movement of the plane is relative to that spot the person is standing at.

dirtybird

My Feedback: (5)

Hi Harry. Where have you been? I would expect you would disagree with me. However we do agree with one thing- we both have a Taranis radio and think its the best thing since Whrigly's Spearmint gum.
I think you will agree with this; we are standing on the earth while those makers of our radios in China are standing upside down according to our point of reference. How can that be? Its true because attraction of the masses have a common point of reference, the center of the earth even though we are traveling thru space at who knows what speed.
If you have ever seen pictures of Cape Canaveral, you will realize you must throw away a lot of mass to escape gravity.
You see this huge rocket sitting on a pad and end up with a small ball in space.
In fact the thrust is due to the the expulsion of mass at high velocity. Its not pushing on the air.
It should be evident you must expend lots of energy to overcome gravity.
Getting back to the original question. If the mass or the wind speed dont change, where does the energy come from to change its velocity?
I say its gain o r loss of altitude.

daveopam

My Feedback: (9)

From my limited knowledge I see it like this. If your model "hands off" has a slight dive. (most seam too) And you make a 500' pass directly in front of you, one way into a 20mph wind and the other 500' pass with the 20mph wind behind the aircraft. The aircraft is going to be closer to the ground at the end of the upwind pass. Why? Because even though the airspeed was identicle both ways, it took the plane longer to fly the 500' upwind leg. The same thing could happen in a turn. The 10 degrees of elev throw required to make the turn and maintain ALT is making the plane dive or climb ever so slightly. The turn into the wind is taking longer than the down wind and causes the percived effect described.
So it is a matter perspective and trim. Very few models are trimmed perfectly since we cary our fuel in front of the CG and the pilots perspective is from the ground not the seat.

May be way off base with this, so be it.

David

As a side note, 10 years ago I strapped a Handicam to the front of a 72" SU-26 and made several flights. What struck me initially while watching it is how constant things were from the planes perspective. The Webra 1.20 dronned on with hardly a change in pitch. That and how far out it was flying before it turned.

charlie1960

Resitance is futile...

Top_Gunn

My Feedback: (6)

Suppose the plane is flying east at an airspeed of 150 knots. The wind is from the west at 50 knots. So the groundspeed is 200 knots. Now the plane turns west, maintaining its150 knot airspeed. Because the mass of air in which the plane is flying is still moving eastward at 50 knots, the plane's groundspeed is now 100 knots, because it is moving at 150 knots relative to the air in which it is flying, but that air mass is moving the other way at 50 knots. No energy "to change [the plane's] velocity" is needed, because the plane's velocity relative to the body of air in which it is flying does not change. Nor does the velocity of the air. Groundspeed is only the sum of these two velocities.

Suppose a canary is sitting on a perch in the back of a big truck, driving west at 50 miles an hour. The canary takes off and flies toward the front of the truck at two miles an hour. Its ground speed is 52 miles an hour. Then it turns around and flies back, also at an airspeed of two miles an hour. Its groundspeed is 48 miles an hour. Does it need less energy to fly back, because its groundspeed is less? Of course not. In fact, if you are in that truck, there are no windows, and the road is smooth, there is no way you can tell whether the truck is moving or standing still.

One more example: You are on a train, going 100 miles an hour. Do you have to work harder to walk toward the front of the train than to walk toward the back at the same speed? According to your theory, you have more momentum walking forward, so it must have been harder to get going in that direction. But that's absurd.

All of this was explained by others on the first page of this thread. Since those explanations didn't take (unless you are just pulling our leg), I thought I'd offer the baby steps version.

HarryC

My Feedback: (1)

The dynamics of flying are related only to the air, not to some spot on the ground. What you perceive is illusory.

dirtybird

My Feedback: (5)

xxx

falcon_56

The energy comes from the wind.

The delta total wind speed is 20 mph. First you are fighting against 10 mph wind, then you turn around and ride on 10 mph

4x(20) = 80

As our good friend AL used to say:

"Energy cannot be created or destroyed, it can only be changed from one form to another."

Top_Gunn

My Feedback: (6)

Nonsense. If the train is going straight at a constant speed and the track is smooth, you cannot tell the difference between that motion and standing still. (Not that any of your other responses make sense either).

The next time you try to learn some science from Wikipedia, look up "Galilean relativity."

I'm through with this thread. It's clear that you have no interest in understanding this subject.

Sport_Pilot

The velocity never changes it is always 50 MPH the same as the airspeed. Only the groundspeed changes, but that is not the velocity of the aircraft, it is rather a moving reference poing moving at the rate of the windspeed.

Sgt. Meyer

It's no use.

* sigh!*

dirtybird

My Feedback: (5)

Its always interesting to hear from someone that its so because I said so.

Bye

Sport_Pilot

I say you should take his advise. This is science not opinion or religion.

dirtybird

My Feedback: (5)

ioni

You are correct about the conservation of energy. That is exactly my point.
However if it is extracted from the wind there must be a change in airspeed. Unfortunately we all agree there is no change in airspeed. So where does it come from? I say it comes from gain or loss of altitude.

Sport_Pilot

That is totally wrong as the aircraft turned and flew in another direction with momentum in the oposite direction. The change in momentum is( 50-(-50)) *4 =400. Using the groundspeed for a reference the change in momentum is (40-(-60))*4=400.

falcon_56

Redo the same calculation in a vacuum and see if you can come up with an 80 momentum increase. This is, take the wind totally out of the equation



The "no loss of altitude" perception comes from keeping the throttle at the same position. When you are fighting the 10 mph wind, the engine (lets say with throttle position at 75%) is fighting to keep up. As you turn around and get a tail wind (throttle at 75%) suddenly you get a gain of power from the engine. It is like the 10 mph tail wind is a new little engine that just switched on on your plane. So without touching anything, your plane will generate more lift from this extra power giving the impression that the plane did not lose any altitude "without touching anything"

Do it the other way around and the opposite would happen. You would have to increase the throttle to compensate for the wind resistance and therefore increase the lift in your plane to prevent it from losing altitude.

Sport_Pilot

dirtybird

My Feedback: (5)

Obviously nothing works in a vacuum.
I think you need to go back and start with page one.
Better yet get the long thread and start there

dirtybird

My Feedback: (5)

Here is an interesting thread from 10 years ago.

http://www.rcuniverse.com/forum/aero...nd-turn-2.html

Jaybird

The air mass the plane is flying in is like an ocean all moving together (unless we add in wind shear which is a different scenario). The plane can go in any direction it wants and drift with the air mass going upwind, downwind, across whatever. I think people are imagining the downwind air like a moving stream where if you jump in at a certain point you will suddenly be swept with the current until you reach the speed of the current (which is what happens when you take off from the ground into a breeze). The misconception I read is that the plane can somehow "jump" out of the stream to the "bank" which isn't moving in the scenario. There they see the plane stumble and loose altitude because it's in a different place. That doesn't happen because of the ocean of air the plane is in.

A plane looses altitude in a turn, if no power is added or elevator input is added, because the turn does require energy and it takes it from the sources it has available, gravity and speed (momentum). As the bank angle increase the demand for more energy increases and so a steep bank will show more of a drop in altitude than a shallow one. If however, a little power is added or a little more back pressure is added to the elevator to increase the angle of attack and therfore the lift the wing can generate, then the turn will remain level.

If a plane climbs or drops in a turn regardless of wind, then it's mishandling of the control surfaces.

Also, if there is a breeze blowing and there are any buildings, trees, hills anything on the ground it will create movement inside the air mass similar to water flowing over rocks. There will be places that the air is flowing upwards and downwards as it moves across the surface. Smaller, lighter planes will seem to be more affected by these air movements than larger ones just as a small boat compared to a big boat.

None of this helps I know but I just had to throw some stuff in here.

Jaybird

Rob2160

Again, when considering energy it comes back to your frame of reference,

At a constant airspeed your energy relative to the air does not change.

With a constant airspeed but with wind, energy relative to the ground does change but has zero consequence unless you are navigating a precise course or you impact the ground.

In this case a down wind crash will impact the ground faster than an upwind crash.

While the aircraft is flying it does not care where the ground is or it's relative motion to the ground.

An example, how much kinetic energy do you posses sleeping in your bed at night?

Zero if your energy is measured with reference to the ground. But if referenced from outside the galaxy you are travelling with enough kinetic energy to destroy a battleship on impact.

You can't feel this of course because our usual frame of reference (the ground) is moving with us and all that matters is the difference within that frame of reference.

In the same way, the plane is moving with the wind and does not care which way the wind moves across the ground. It is interacting with the wind only.

another example.

You are driving on the road at 100mph behind another car doing 100mph.

You increase to 101 mph and nudge him from behind.

Does the impact damage reflect your kinetic energy of 100mph or your 'relative' kinetic energy of 1 mph?

Gravity was mentioned earlier. Assuming the aircraft is flying level at all times. In a flat plane of motion with gravity acting perpendicular to that motion it cannot accelerate or decelerate the aircraft.

A force applied at a constant 90 degrees to the direction of travel does not change the speed of travel.

This is why objects in a stable orbit can stay there for thousands of years and require no additional energy to do so.

Kwigen

I remember having this discussion in the mid seventies when I was earning my ticket. It made complete sense to me that there would be no difference upwind to downwind. Being a smart/know-it-all twenty plus hour pilot I stated my case quite convincingly (I thought) to a grizzled old retired Marine ag pilot who made his living sitting behind an over hour, over loaded P&W 600 hp Thrush Air Tractor.
I waited for his answer while he finished his first beer of the evening and opened another then said," I've heard all that bs, but let me tell you, when you've got 350 in the hopper and a cylinder that keeps whispering at you, you dread a down wind turn."

Since that evening I've deferred to the guy making his living flying a plane that is over gross, ten feet off the ground, through the rolling hills of the Palouse.

I stopped by one morning to talk to him before his day started. His plane was sitting on the ramp idling. he said listen to her. "Gunna make a buck, gunna make a buck, gunna make a buck. Round engines talk, turbines whine.

Rob2160

I can actually understand the perspective of the Ag pilot.

Ag pilots fly close to the ground and the accuracy of the ground track required is measured in meters.

Not only that but they generally require a correct "Ground Speed" to ensure the spray is distributed in the right concentration across the fields.

For the Ag pilot flying these spray runs, wind is going to make him work much harder, requiring more adjustments on each pass, airspeed changes etc.

I get this completely.

At night, without convective mixing, you can have very different winds from ground level to 1000 feet.

I have flown circuits at night when there is zero wind at 200 feet to ground level, yet it is blowing 15+ knots at 1000 feet.

This does cause problems if you are flying downwind, then turning final and suddenly losing 15 kts of airspeed in the last part of your approach (due to the wind changing significantly in a few hundred feet)

However most of these forum discussions on the down wind turn involve a perfect steady state wind where turning through 360 degrees will not change your airspeed at all.

JPerrone

This thread is starting to sound like the interminable exchange between people, usually served up as something amusing in movies, ie
"does so"
"does NOT"
Does SO!"
"DOES NOT!!!"

repeat as many likes as it takes to get a laugh...

It does look like there's some misunderstanding about the meaning and calculation of momentum. The equation is expressed correctly; however, what V are we talking about?
What this thread has attempted to uncover is that speed is a RELATIVE thing; I think we can agree on that!
Rob2160 brought up the frame of reference thing and related it to: The speed someone thinks they are going if
a) They are standing still and they are comparing their speed to ground;
b)They are standing still, but are comparing to the speed of that point due to the rotation of the earht
c)Same as line above but the speed of the Earth moving around the Sun is also considered

Now lets consider the changes in momentum here
You ask the person what is your momentum in
a) The answer is 0
b) The answer is 1000 (approx.) mph x 70 kg (after losing some weight..)
c) The answer is a whole bunch more you get the idea

And the only way this happens is if you, the person, INSTANTANEOUSLY increased momentum at the microsecond in time that you verbally said "the reference point is the moving point of the earth's circumference". I doubt that!

How does this have anything to do with this back and forth discussion?
Well, the plane turns around; the airspeed is the same; the only thing that has changed (to the POV of the airplane) is the direction; and yet the momentum has to change. It's not instantaneous in this case, as it has to change a little bit at a time as the turn is made.

If the airspeed is constant, then the momentum is conserved because MV(upwind) = MV(downwind). Which is what most people here are saying. And it seems to make sense as I consider what the airplane does in turns;
If the groundspeed is changing, the momentum of the airplane relative to the ground...the calculation does say that the momentum relative to the ground does change!!! I can't explain that!!! I think girls do better at this, because all of my understanding of physics comes from Wylie Coyote. In that masterpiece of scientific lore, if you step off of the falling object just before it hits the ground, you are unhurt. NOTHING in any science class can possibly explain away this phenomena!