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Downwind Turns

Old 02-28-2009, 10:35 AM
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HX3D014
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Default Downwind Turns

I have just realised that there are people out there that belive a downwind turn is Dangerous or that the plane will behave differently through the air when turning downwind.

For Educational purposes;
Downwind turn is when you turn to the direction of the wind. IE you nose is pointing the same direction as the wind sock (Or close to it)

It can be made in two basic ways.

You are flying cross wind and turn 90deg to the downwind direction

or

you are flying into the wind and turn 180deg to the downwind direction.

Any of us here belive the myth ?

Are there any people here who think that downwind turns cause the Aircraft to fly differently throught the air?
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Old 02-28-2009, 11:20 AM
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Jaiwill
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Hmm, not sure what we,re covering here. Anyone who flys in the wind would make dozens of these turns per flight,and should not think another thing of it... A down wind turn could simply be a turn made down-wind of the pilot, regardless of the end direction...(my and others i know interpretation without referring to dictionary)

Obviously traveling with the wind results in less air over our surfaces (for the same airspeed). Dangerous? for who? a below average pilot like myself trying to look good...LOL

Sorry I'm bored..
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Old 02-28-2009, 11:27 AM
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Originally Posted by Jaiwill View Post
Hmm, not sure what we,re covering here. Anyone who flys in the wind would make dozens of these turns per flight,and should not think another thing of it... A down wind turn could simply be a turn made down-wind of the pilot, regardless of the end direction...(my and others i know interpretation without referring to dictionary)

Obviously traveling with the wind results in less air over our surfaces (for the same airspeed). Dangerous? for who? a below average pilot like myself trying to look good...LOL

Sorry I'm bored..
Obviously you are joking

But there are people out there that make comments like that and are serious.

Thanks for getting the ball rolling
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Old 02-28-2009, 11:49 AM
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Iv'e given this some thought over dinner.. Wouldn't a upwind turn be more dangerous. I'm guessing your referring to dangerous as your model being somewhat harder to control for the duration of the maneuver. Traveling with the wind and trying to turn back into it (180) is far more "difficult".
Could i trouble you to enlighten a newer type pilot to the point.
Cheers Darren
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Old 02-28-2009, 12:14 PM
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Originally Posted by Jaiwill View Post
Iv'e given this some thought over dinner.. Wouldn't a upwind turn be more dangerous. I'm guessing your referring to dangerous as your model being somewhat harder to control for the duration of the maneuver. Traveling with the wind and trying to turn back into it (180) is far more "difficult".
Could i trouble you to enlighten a newer type pilot to the point.
Cheers Darren
OK.

We need to confirm what a down wind turn and up wind turn is.

Essentially; it is the direction you end up pointing after the turn.

An up wind turn is when you turn to face the wind. (Wind on your nose so to speak)
So if you are flying 25 IAS and the wind is 15, then your ground speed will be 10.

and

A Down wind turn is when you turn to face away from the wind (Wind up you tail so to speak, But that is not the truth. the wind is not up you tail. really what is happening is you are flying through the Air with the wind)
So if you are flying 25 IAS and the wind is 15 then your ground speed will be 40.



Some people think in reference to the ground

They think that there is more effort for a plane to go from
10 ground speed(Upwind leg)
Turn 180deg
And accelerate to 40 ground speed(Downwind).

The opposite to that is;

They think that there is less effort for a plane to go from
40 ground speed(downwind leg)
Turn 180deg
And accelerate to just 10 ground speed(upwind).

But in reality the effort for both is the same.

Bryce.
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Old 02-28-2009, 12:34 PM
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Thanks Bryce, I guess what i was trying to say was i don't think your turn is dangerous. Unless altitude is also an issue. Never been one to delve too deeply. Thanks for your time and happy flying..Darren
Good luck with chopper too mines got the trainer wheels aswell.
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Old 02-28-2009, 01:11 PM
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If you think in terms of stored kinetic energy in the mass of the plane and the amount of energy necessary to accelerate the mass in addition to airspeed it makes it much easier to understand.

When you are flying into the wind and then turn abruptly downwind, the plane has to accelerate to regain the same airspeed and lift. This is why you often see the plane lose altitude or even stall when turning downwind in high winds. (If you turn much more gently you give the plane a chance to accelerate.)

When you are flying with the wind and then turn abruptly into the wind, you have an abundance of stored kinetic energy and a rapid increase in airspeed which is why it is common to see the plane increase altitude when turning into the wind.

Transitioning rapidly from upwind to downwind is very different and more dangerous than transitioning rapidly from downwind to upwind. If you transition very, very slow you will not even notice the difference as the plane is allowed enough time to accelerate.




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Old 02-28-2009, 04:00 PM
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I was looking at this hypotheses perhaps from a different angle.. and maybe a stronger wind...

Getting your model to turn from into the wind to downwind requires very little effort from you and the model. (in my limited experience) the wind seems to take the model with it once you have started the bank...

Travelling with the wind and turning back into it, the plane wants to and naturally stay with the wind. (stored energy and probably a host of other technical reasons).. requiring a lot more input from you to complete the manouvre taking more time and space.

Form a newbs point of view starting the bank into the wind you have a plethora of lift as the wind hits the underside of your plane, and then probably drops quickly as you scramble to get up to speed to maintain that lift..

However turning into the wind all the wind is on top of the wing until you finish the manouvre and your down to the speed into the wind...
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Old 02-28-2009, 04:21 PM
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Originally Posted by Jaiwill View Post

Form a newbs point of view starting the bank into the wind you have a plethora of lift as the wind hits the underside of your plane, and then probably drops quickly as you scramble to get up to speed to maintain that lift..
Plane has lots of airspeed and stored kinetic energy as you turn into the wind. Plane does not have to accelerate and it is likely that the plane will increase in altitude as some of the stored energy/speed is translated into lift.


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Old 02-28-2009, 06:33 PM
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Originally Posted by HX3D014 View Post
OK.

We need to confirm what a down wind turn and up wind turn is.

Essentially; it is the direction you end up pointing after the turn.

An up wind turn is when you turn to face the wind. (Wind on your nose so to speak)
So if you are flying 25 IAS and the wind is 15, then your ground speed will be 10.

and

A Down wind turn is when you turn to face away from the wind (Wind up you tail so to speak, But that is not the truth. the wind is not up you tail. really what is happening is you are flying through the Air with the wind)
So if you are flying 25 IAS and the wind is 15 then your ground speed will be 40.



Some people think in reference to the ground

They think that there is more effort for a plane to go from
10 ground speed(Upwind leg)
Turn 180deg
And accelerate to 40 ground speed(Downwind).

The opposite to that is;

They think that there is less effort for a plane to go from
40 ground speed(downwind leg)
Turn 180deg
And accelerate to just 10 ground speed(upwind).

But in reality the effort for both is the same.

Bryce.
Guys, this is spot on all of it.
Kinetic energy, stored energy, nor even wearing your lucky t-shirt has anything to do with this.

If you dont believe him(or me) then look it up for yourself.
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Old 02-28-2009, 06:47 PM
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Originally Posted by cbatters View Post
If you think in terms of stored kinetic energy in the mass of the plane and the amount of energy necessary to accelerate the mass in addition to airspeed it makes it much easier to understand.
OTOH if you remember that kinetic energy and acceleration are vector quantities i.e. they have to be RELATIVE to something you'll soon realise that the plane has no need to accelerate at all. It's flying in the airmass and its airspeed never changes. The vector (direction) changes, speed stays the same. All that changes is the ground speed...and the plane has no connection with the ground .

Steve
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Old 02-28-2009, 07:51 PM
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I've always felt turning out of the wind (ie flying in the same direction as the wind and then turning 90 or 180) was more stressfull. Especially with slow flying low wing load planes.

Simple reason as far as I figure:
Much less airflow over the control surfaces and a quick transition from needing to keep the nose down to needing to keep the lower turning wing tip up and turn at the same time...
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Old 02-28-2009, 08:50 PM
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Read Bryce's posts again, and again.

There is........no........difference. Airspeed into, or with, or crosswind is.......the........same.

And again, look all this up if you dont think its true. As long as you continue to believe the airflow is changing with the wind, or your plane's direction you are believing in an untruth. And will continue to have problems and do the wrong thing at the wrong time.

Get and study hard the book, "Stick and Rudder".
Go to FAA's website and look at "The airplane flying handbook".
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Old 02-28-2009, 09:38 PM
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Steady state I agree but with slow flying models in wind speeds approaching the air speed of the plane, I politely disagree.

Consider a model flying 20 MPH into a 20 MPH headwind. The motor provides enough thrust to overcome the drag on the airplane but has zero kinetic energy.

In order for the plane to fly with the wind with the same 20 MPH airspeed over the wing, the mass of the plane must be accelerated from 0 to 40 MPH which takes significant energy (e=mv^2) either from the engine or by concerting some of the stored energy (altitude) into kinetic energy (speed.) Which is why it is common to see airplanes lose altitude initially when they turn downwind.

Turning back into the wind, the airplane has a surplus of kinetic energy (40 MPH) which can be converted back into stored energy (altitude) because it needs zero kinetic energy to maintain 20 MPH airspeed into a 20 MPH wind.



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Old 02-28-2009, 09:47 PM
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Another way to prove there is a difference in state - consider what happens when the wind abruptly stops.

With the plane is flying into the wind, if the wind suddenly stops, it will fall like a rock. Zero air speed, zero kinetic energy.

With the plane flying with the wind, if the wind suddenly stops, the airspeed actually increases from 20 MPH to 40 MPH generating additional lift while the plane still has 40 MPH of kinetic energy.
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Old 02-28-2009, 09:53 PM
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Originally Posted by cbatters View Post
Steady state I agree but with slow flying models in wind speeds approaching the air speed of the plane, I politely disagree.

Consider a model flying 20 MPH into a 20 MPH headwind. The motor provides enough thrust to overcome the drag on the airplane but has zero kinetic energy.

In order for the plane to fly with the wind with the same 20 MPH airspeed over the wing, the mass of the plane must be accelerated from 0 to 40 MPH which takes significant energy (e=mv^2) either from the engine or by concerting some of the stored energy (altitude) into kinetic energy (speed.) Which is why it is common to see airplanes lose altitude initially when they turn downwind.

Turning back into the wind, the airplane has a surplus of kinetic energy (40 MPH) which can be converted back into stored energy (altitude) because it needs zero kinetic energy to maintain 20 MPH airspeed into a 20 MPH wind.



Clint
Do not forget that it takes effort to Stop the plane.

In your example you mentioned 20IAS 20Wind
Flying down wind you have 40Ground
Flying Up Wind you have 0 Ground
Accelerating and decelerating relative to the ground is the same
(but you should not look at its ground speed as an influence on its Kinetic energy, because until the two meet <The ground and the Plane>, there not relevant)

the relevance is in the Kinetic energy of a parcel of air over the wing.

It is a trick and easy to fall into. (I fall into it some times )

For the record.
Flying a pattern and doing downwind turns and upwind turns can be tricky, they are both different from the other. and it can be dangerous if you do not keep you mind on the Throttle settings. that is, if you try to fly the plane by what the speeds LOOKS like.

Bryce.
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Old 02-28-2009, 10:02 PM
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if there is no difference between flying with and into the wind why does a plane require more throttle to maintain altitude (not ground speed) flying with the wind than into it? with a 20 mph wind i can point a plane into the wind, give it a little throttle and it'll hang there and possibly even climb, if i turn it around it'll lose altitude or stall.
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Old 02-28-2009, 10:12 PM
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Originally Posted by cbatters View Post
Another way to prove there is a difference in state - consider what happens when the wind abruptly stops.

With the plane is flying into the wind, if the wind suddenly stops, it will fall like a rock. Zero air speed, zero kinetic energy.

With the plane flying with the wind, if the wind suddenly stops, the airspeed actually increases from 20 MPH to 40 MPH generating additional lift while the plane still has 40 MPH of kinetic energy.
hehe.

the revers is also true

With the plane that is flying with the wind (or the direction the will start to ), if the wind suddenly starts, it will suddenly have 0mph IAS.

With the plane that is flying against the wind (or the direction the wind will start from ), if the wind suddenly starts, it will suddenly have 40mph IAS.

But this is different from turning in a steady wind.
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Old 02-28-2009, 10:16 PM
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Originally Posted by Yaniel View Post
if there is no difference between flying with and into the wind why does a plane require more throttle to maintain altitude (not ground speed) flying with the wind than into it? with a 20 mph wind i can point a plane into the wind, give it a little throttle and it'll hang there and possibly even climb, if i turn it around it'll lose altitude or stall.
This may be attributed to what the wind is doing.

What type of Open area or valley area are you seeing this.

Bryce.
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Old 02-28-2009, 10:19 PM
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Originally Posted by HX3D014 View Post
This may be attributed to what the wind is doing.

What type of Open area or valley area are you seeing this.

Bryce.

its in miami, so its always open flat area and usually a steady 10+ mph wind.
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Old 02-28-2009, 10:34 PM
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Originally Posted by Yaniel View Post
its in miami, so its always open flat area and usually a steady 10+ mph wind.
what about the wind direction. are you anywhere near water of ocean.

what time of day?
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Old 02-28-2009, 10:37 PM
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here is a good Exercise to ponder

http://www.aeroexperiments.org/brainteasers.shtml
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Old 03-01-2009, 12:16 AM
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This truly is more simple than the explanations here. Some of which are sound I must admit.

Here goes my 2nd attempt:
Less experienced pilots try to slow the GROUND speed of the plane when flying downwind to the same as it was upwind = kite effect and then stall on the turn. GO FASTER to keep your AIR SPEED the same and you will be ok.
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Old 03-01-2009, 12:27 AM
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Originally Posted by LectricPlane View Post
This truly is more simple than the explanations here. Some of which are sound I must admit.

Here goes my 2nd attempt:
Less experienced pilots try to slow the GROUND speed of the plane when flying downwind to the same as it was upwind = kite effect and then stall on the turn. GO FASTER to keep your AIR SPEED the same and you will be ok.
Very good

How do you know if you have the Airspeed ?

Keep a conscious mind on the throttle setting and

make the turn steady (That is; keep the turn at the same rate you would in calm conditions)

Nice Second Attempt.
Attempt was successful

Bryce.
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Old 03-01-2009, 12:35 AM
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Originally Posted by HX3D014 View Post
I have just realised that there are people out there that belive a downwind turn is Dangerous or that the plane will behave differently through the air when turning downwind.

For Educational purposes;
Downwind turn is when you turn to the direction of the wind. IE you nose is pointing the same direction as the wind sock (Or close to it)

It can be made in two basic ways.

You are flying cross wind and turn 90deg to the downwind direction

or

you are flying into the wind and turn 180deg to the downwind direction.

Any of us here belive the myth ?

Are there any people here who think that downwind turns cause the Aircraft to fly differently throught the air?
It's a myth, the aircraft does not know the direction or speed of the wind, it only knows "relative wind".
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