Downwind Turns!!
09-07-2010 | 09:47 AM
#51
Joined: Aug 2007
Posts: 521
Likes: 0
Received 1 Like
on
1 Post
From: ChelmsfordEssex, UNITED KINGDOM
RE: Downwind Turns!!
ORIGINAL: hugger-4641
If you really want to learn how this works, get up about 400 feet high and kill your engine as you enter the down wind leg. If you have any skill at all you should be able to make at least one full circuit and be heading upwind again before having to land. By the time you make a couple of dead stick circuits like this, you shouldl have a better feel for what the plane needs from you.
If you really want to learn how this works, get up about 400 feet high and kill your engine as you enter the down wind leg. If you have any skill at all you should be able to make at least one full circuit and be heading upwind again before having to land. By the time you make a couple of dead stick circuits like this, you shouldl have a better feel for what the plane needs from you.
09-07-2010 | 05:53 PM
#52
My Feedback: (6)
RE: Downwind Turns!!
Wasn't intended for you specifically, just a general post in the thread that happened to follow yours. Glad you're not confused, neither am I.
Explaining the physics to some one who is confused can be a challenge, as you can see from the length of this thread. I'll let everyone else argue over the terms and nomenclature, fact of the matter is, if you make a turn to fly with the wind (down wind) the plane needs more speed in relation to the ground than it does while flying against the wind (up wind) to maintain the same airspeed. Air speed is what keeps the plane flying and Air speed does not "magically" follow the plane automatically when you turn down wind. There is a loss of momentum involved, so you will either experience a loss of altitude while the air speed is re-gained, or you will have to increase throttle until air speed is re-gained. The mistake usually happens when you try to maintain altitude during this turn with out increasing throttle, this is when you will be most likely to stall, even if your ground speed remained constant.
Simple fact is, if you turn down wind and your air speed is barely above stalling, to keep from stalling, you must increase power, or you give up some altitude to gain speed, or both.
, neither am I. Explaining the physics to some one who is confused can be a challenge, as you can see from the length of this thread. I'll let everyone else argue over the terms and nomenclature, fact of the matter is, if you make a turn to fly with the wind (down wind) the plane needs more speed in relation to the ground than it does while flying against the wind (up wind) to maintain the same airspeed. Air speed is what keeps the plane flying and Air speed does not "magically" follow the plane automatically when you turn down wind. There is a loss of momentum involved, so you will either experience a loss of altitude while the air speed is re-gained, or you will have to increase throttle until air speed is re-gained. The mistake usually happens when you try to maintain altitude during this turn with out increasing throttle, this is when you will be most likely to stall, even if your ground speed remained constant.
Simple fact is, if you turn down wind and your air speed is barely above stalling, to keep from stalling, you must increase power, or you give up some altitude to gain speed, or both.
09-07-2010 | 06:26 PM
#53
RE: Downwind Turns!!
The only reason you lose momentum in a turn is because you increase drag proportunitly to the amount of lift you need to increase for the turn. So if you bank 60 degs. you will need to double the amount of lift being produced by the wing also doubling the amount of induced drag. This will cause the need for increased throttle. All your momentum is in relation to the air mass you are flying in, not the ground, so which way you are turning is irrelevant. There is no "magic" involved only aerodynamics. Why else can a fly safely navigate in your car when it is traveling 60 MPH? According to your theory it should splat into the window when it changes direction.
09-07-2010 | 07:53 PM
#54
My Feedback: (6)
RE: Downwind Turns!!
No, you're twisting what I said. But to use your analogy, a car will also loose some momentum when you change directions unless you correct it by giving throttle, and if it lost enough momentum, and the fly had enough mass, it would go splat![ And no, momentum is not lost only because of drag, momentum is lost because of the change in "velocity". "Veloctiy" includes speed and direction. You might check out what's called the "third law of motion" if you don't understand this]
And, yes, if you could "magically" move the ground in the same direction you were making a down wind turn, then ground speed would not matter. And if there were no ground it would not matter which way the wind was blowing. But the "reality" is, when you are flying an RC plane or a real plane, wind speed has a "velocity" in relation to the ground, and "Air Speed" is in relation to your air craft. Your craft has a velocity in relation to both. To fly either an RC or full scale plane, you must be aware of both. If you don't believe that, take a full scale Cessna 182 into a 30mph head wind just above stall speed (about 50mph air speed) at say 50 feet agl, then make a turn down wind and see if you can maintain altitude and/or air speed without increasing throttle or prop pitch. I don't think you will live to tell us if you try it.
And no, momentum is not lost only because of drag, momentum is lost because of the change in "velocity". "Veloctiy" includes speed and direction. You might check out what's called the "third law of motion" if you don't understand this] And, yes, if you could "magically" move the ground in the same direction you were making a down wind turn, then ground speed would not matter. And if there were no ground it would not matter which way the wind was blowing. But the "reality" is, when you are flying an RC plane or a real plane, wind speed has a "velocity" in relation to the ground, and "Air Speed" is in relation to your air craft. Your craft has a velocity in relation to both. To fly either an RC or full scale plane, you must be aware of both. If you don't believe that, take a full scale Cessna 182 into a 30mph head wind just above stall speed (about 50mph air speed) at say 50 feet agl, then make a turn down wind and see if you can maintain altitude and/or air speed without increasing throttle or prop pitch. I don't think you will live to tell us if you try it.
09-07-2010 | 07:58 PM
#55
My Feedback: (6)
RE: Downwind Turns!!
Air speed is what keeps the plane flying and Air speed does not "magically" follow the plane automatically when you turn down wind.
It's not just the downwind-turn myth that results from failure to understand that a flying plane cannot react to a steady wind in any way that affects its flying. Some people are convinced that a plane flying a crosswind leg will "weathervane" into the wind without any control input. It's just not possible: what force could possibly cause it to do that?
None of this is controversial.
09-07-2010 | 08:03 PM
#56
My Feedback: (6)
RE: Downwind Turns!!
If you don't believe that, take a full scale Cessna 182 into a 30mph head wind just above stall speed (about 50mph air speed) at say 50 feet agl, then make a turn down wind and see if you can maintain altitude and/or air speed without increasing throttle or prop pitch. I don't think you will live to tell us if you try it.
Someone riding in a hot-air balloon in the wind will have a velocity relative to the ground. But that person will feel no breeze at all, no matter which direction he faces.
09-07-2010 | 08:12 PM
#57
My Feedback: (6)
RE: Downwind Turns!!
If gravity and inertia did not exist you would be correct, but until they dissappear, you will loose something when you turn, whether it's in calm air, or a 50mph breeze. Argue all you want about what is lost and why , be it lift, velocity, altitude, air speed, ground speed, drag, whatever, doesn't change the fact that something is lost and something must be done to counteract it if you want to maintain any or all of the above.
09-07-2010 | 08:18 PM
#58
My Feedback: (6)
RE: Downwind Turns!!
ORIGINAL: Top_Gunn
Quite right. And exactly the same thing will happen if you turn it ''upwind.'' Once a plane is flying, how can its motion relative to the ground affect anything? ''Velocity'' is not some absolute thing through ''the ether'' (as people used to believe). A plane's velocity relative to the ground means nothing (until it touches down). Its velocity relative to the ground might be 40 miles an hour. It's velocity relative to a car driving on the road might be 100 miles an hour. Relative to a plane flying overhead, maybe 200 miles an hour in the other direction. All of these velocities are equally irrelevant. Only its velocity through the air (airspeed) counts.
Someone riding in a hot-air balloon in the wind will have a velocity relative to the ground. But that person will feel no breeze at all, no matter which direction he faces.
If you don't believe that, take a full scale Cessna 182 into a 30mph head wind just above stall speed (about 50mph air speed) at say 50 feet agl, then make a turn down wind and see if you can maintain altitude and/or air speed without increasing throttle or prop pitch. I don't think you will live to tell us if you try it.
Someone riding in a hot-air balloon in the wind will have a velocity relative to the ground. But that person will feel no breeze at all, no matter which direction he faces.
You are correct in a strict sense, but the problem with flying an RC plane is you don't have an air speed indicator, so you often use ground speed as a cue to judge wether you have enough air speed or not, and this is where a mistake in judgement is most often made, and most often mis-understood.
09-07-2010 | 08:20 PM
#59
My Feedback: (6)
RE: Downwind Turns!!
If gravity and inertia did not exist you would be correct, but until they dissappear, you will loose something when you turn, whether it's in calm air, or a 50mph breeze.
09-07-2010 | 08:21 PM
#60
My Feedback: (6)
RE: Downwind Turns!!
You are correct in a strict sense, but the problem with flying an RC plane is you don't have an air speed indicator, so you often use ground speed as a cue to judge wether you have enough air speed or not, and this is where a mistake in judgement is most often made, and most often mis-understood.
09-07-2010 | 08:29 PM
#61
My Feedback: (6)
RE: Downwind Turns!!
ORIGINAL: Top_Gunn
I don't think anybody disagrees with this. The point is not that you don't lose something when you turn, it's that the loss is the same for any turn using the same control inputs, whether into, against, or across the direction of the wind relative to the ground. (There is no ''direction of the wind relative to the plane,'' because the plane is in the moving air mass that is wind, and moving with it.)
If gravity and inertia did not exist you would be correct, but until they dissappear, you will loose something when you turn, whether it's in calm air, or a 50mph breeze.
This is only truly correct if the wind speed is constant, around here it usually is not. You may be flying into a head wind that's 8mph one minute and 10mph the next, and it may be 12mph when you decide to turn. You may not even notice the difference between 8mph and 12mph, but your plane will.
09-07-2010 | 08:53 PM
#62
My Feedback: (6)
RE: Downwind Turns!!
You may be flying into a head wind that's 8mph one minute and 10mph the next, and it may be 12mph when you decide to turn. You may not even notice the difference between 8mph and 12mph, but your plane will.
09-07-2010 | 09:12 PM
#64
RE: Downwind Turns!!
Yes that is called "wind shear" or to the layperson "gusting," and if you look back we each said aside from gusts, wind shear, and turbulence (thermal activity.) Beleave me when I say I truely understand this. I have been teaching professional pilots for close to 15 years. I, as well as Top Gunn, have a firm understanding of the physics of flight, and as Top Gunn has so elequently stated inertia plays into it no matter what direction you are turning in relation to the moving mass of air you are flying in. As far as the change in velocity of the "wind" it will happen at any stage of flight and have the same effect. I have flown low (500' is low for a full scale) and near stall while flying for the DNR deer spotting and the only thing I had to change while turning was the timing of my turn to account for the wind. I never needed to add any throttle for the turns, and I didn't even loose 2kts of airspeed through any turn reguardless of wind direction because I used a shallow bank, which is all that is needed when flying that slow.
09-07-2010 | 09:35 PM
#65
My Feedback: (6)
RE: Downwind Turns!!
ORIGINAL: cfircav8r
Yes that is called ''wind shear'' or to the layperson ''gusting,'' and if you look back we each said aside from gusts, wind shear, and turbulence (thermal activity.) Beleave me when I say I truely understand this. I have been teaching professional pilots for close to 15 years. I, as well as Top Gunn, have a firm understanding of the physics of flight, and as Top Gunn has so elequently stated inertia plays into it no matter what direction you are turning in relation to the moving mass of air you are flying in. As far as the change in velocity of the ''wind'' it will happen at any stage of flight and have the same effect. I have flown low (500' is low for a full scale) and near stall while flying for the DNR deer spotting and the only thing I had to change while turning was the timing of my turn to account for the wind. I never needed to add any throttle for the turns, and I didn't even loose 2kts of airspeed through any turn reguardless of wind direction because I used a shallow bank, which is all that is needed when flying that slow.
Yes that is called ''wind shear'' or to the layperson ''gusting,'' and if you look back we each said aside from gusts, wind shear, and turbulence (thermal activity.) Beleave me when I say I truely understand this. I have been teaching professional pilots for close to 15 years. I, as well as Top Gunn, have a firm understanding of the physics of flight, and as Top Gunn has so elequently stated inertia plays into it no matter what direction you are turning in relation to the moving mass of air you are flying in. As far as the change in velocity of the ''wind'' it will happen at any stage of flight and have the same effect. I have flown low (500' is low for a full scale) and near stall while flying for the DNR deer spotting and the only thing I had to change while turning was the timing of my turn to account for the wind. I never needed to add any throttle for the turns, and I didn't even loose 2kts of airspeed through any turn reguardless of wind direction because I used a shallow bank, which is all that is needed when flying that slow.
09-07-2010 | 10:22 PM
#67
RE: Downwind Turns!!
Down wind turns are different, in the timing of the turn and the degree of heading change, but throttle setting, pitch attitude and bank angle DO NOT need to change to maintain altitude and/or airspeed.
09-07-2010 | 10:57 PM
#68
My Feedback: (6)
RE: Downwind Turns!!
ORIGINAL: cfircav8r
Down wind turns are different, in the timing of the turn and the degree of heading change, but throttle setting, pitch attitude and bank angle DO NOT need to change to maintain altitude and/or airspeed.
Down wind turns are different, in the timing of the turn and the degree of heading change, but throttle setting, pitch attitude and bank angle DO NOT need to change to maintain altitude and/or airspeed.
09-07-2010 | 11:07 PM
#69
RE: Downwind Turns!!
How does not needing to change the throttle setting equate to not needing an engine? If wind speed and direction don't change in flight then wind or no wind the plane will fly the same in any direction given the same inputs.
09-08-2010 | 12:26 AM
#70
RE: Downwind Turns!!
<p class="MsoNormal" style="MARGIN: 0in 0in 10pt"><font face="Calibri" size="3">This argument is at least the third iteration I’ve seen in these forums. And it is always the full scale ‘experts’ that can’t see the truth thru the ‘soup’, pun intended. It is understandable they are taught this, most full scale acft through performance or structural limitations can’t change direction fast enough to feel the force of acceleration (or lack of it) when turning with or into the ‘all encompassing mystical moving mass of air’ that all airborne vessels move in and is only perceived as wind to us mortals on the ground. </font></p><p class="MsoNormal" style="MARGIN: 0in 0in 10pt"><font face="Calibri" size="3">Yank and bank your underpowered trainer from upwind to tailwind and there will be a brief period of time that the model will need to accelerate back to the airspeed it had a second ago. Don’t add throttle and it will drop. And the opposite is true. It’s not an illusion. </font></p><p class="MsoNormal" style="MARGIN: 0in 0in 10pt">
<font face="Calibri" size="3"> </font></p></p><p class="MsoNormal" style="MARGIN: 0in 0in 10pt"><font face="Calibri" size="3">An easy way to say it is the rapid change of direction of the model disrupts this moving mass theory by creating its own wind shear / turbulence whatever.</font></p><p class="MsoNormal" style="MARGIN: 0in 0in 10pt"><font size="3"><font face="Calibri">A friend of mine who flies aerobatics competitively confirmed this. During his routine he is very aware of turning into or away from what I call wind. <span style="mso-spacerun: yes"> </span><span style="mso-spacerun: yes"> </span></font></font></p>
<font face="Calibri" size="3"> </font></p></p><p class="MsoNormal" style="MARGIN: 0in 0in 10pt"><font face="Calibri" size="3">An easy way to say it is the rapid change of direction of the model disrupts this moving mass theory by creating its own wind shear / turbulence whatever.</font></p><p class="MsoNormal" style="MARGIN: 0in 0in 10pt"><font size="3"><font face="Calibri">A friend of mine who flies aerobatics competitively confirmed this. During his routine he is very aware of turning into or away from what I call wind. <span style="mso-spacerun: yes"> </span><span style="mso-spacerun: yes"> </span></font></font></p>
09-08-2010 | 07:05 AM
#71
My Feedback: (6)
RE: Downwind Turns!!
Down wind turns are different, in the timing of the turn and the degree of heading change, but throttle setting, pitch attitude and bank angle DO NOT need to change to maintain altitude and/or airspeed.
That's why planes do crash on "downwind turns," and why rc pilots have to be careful. The point we've been making is about why this happens, and it's not because the plane can somehow "feel" a wind in defiance of the laws of physics.
Try this yourself: On a day with a steady wind, take a trainer up, trim for hands-off flight, then put in a little aileron trim and up-elevator trim. Your plane should start turning, and if you get the trims so that the turns are level, it will keep turning, around and around, without the nose dropping in any direction. It won't fly in circles, because the downwind drift of the plane will stretch out those circles in a downwind direction. (This is like an earlier poster's example of flying ar RC plane from a hot-air balloon, but easier to arrange.)
09-08-2010 | 07:42 AM
#72
RE: Downwind Turns!!
ORIGINAL: edh13
<p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''><font face=''Calibri'' size=''3''>This argument is at least the third iteration I’ve seen in these forums. And it is always the full scale ‘experts’ that can’t see the truth thru the ‘soup’, pun intended. It is understandable they are taught this, most full scale acft through performance or structural limitations can’t change direction fast enough to feel the force of acceleration (or lack of it) when turning with or into the ‘all encompassing mystical moving mass of air’ that all airborne vessels move in and is only perceived as wind to us mortals on the ground. </font></p><p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''><font face=''Calibri'' size=''3''>Yank and bank your underpowered trainer from upwind to tailwind and there will be a brief period of time that the model will need to accelerate back to the airspeed it had a second ago. Don’t add throttle and it will drop. And the opposite is true. It’s not an illusion. </font></p><p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''>
<font face=''Calibri'' size=''3''> </font></p></p><p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''><font face=''Calibri'' size=''3''>An easy way to say it is the rapid change of direction of the model disrupts this moving mass theory by creating its own wind shear / turbulence whatever.</font></p><p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''><font size=''3''><font face=''Calibri''>A friend of mine who flies aerobatics competitively confirmed this. During his routine he is very aware of turning into or away from what I call wind. <span style=''mso-spacerun: yes''> </span><span style=''mso-spacerun: yes''> </span></font></font></p>
<p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''><font face=''Calibri'' size=''3''>This argument is at least the third iteration I’ve seen in these forums. And it is always the full scale ‘experts’ that can’t see the truth thru the ‘soup’, pun intended. It is understandable they are taught this, most full scale acft through performance or structural limitations can’t change direction fast enough to feel the force of acceleration (or lack of it) when turning with or into the ‘all encompassing mystical moving mass of air’ that all airborne vessels move in and is only perceived as wind to us mortals on the ground. </font></p><p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''><font face=''Calibri'' size=''3''>Yank and bank your underpowered trainer from upwind to tailwind and there will be a brief period of time that the model will need to accelerate back to the airspeed it had a second ago. Don’t add throttle and it will drop. And the opposite is true. It’s not an illusion. </font></p><p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''>
<font face=''Calibri'' size=''3''> </font></p></p><p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''><font face=''Calibri'' size=''3''>An easy way to say it is the rapid change of direction of the model disrupts this moving mass theory by creating its own wind shear / turbulence whatever.</font></p><p class=''MsoNormal'' style=''MARGIN: 0in 0in 10pt''><font size=''3''><font face=''Calibri''>A friend of mine who flies aerobatics competitively confirmed this. During his routine he is very aware of turning into or away from what I call wind. <span style=''mso-spacerun: yes''> </span><span style=''mso-spacerun: yes''> </span></font></font></p>
09-08-2010 | 07:56 AM
#73
My Feedback: (11)
RE: Downwind Turns!!
Keep in mind ground speed and airspeed are two entirely different things... so even though the plane looks slow in relationship to the ground the wind can be providing enough lift together with the engine thrust. The same throttle setting will produce the same airspeed if you were to have telemetry giving you the airspeed. Things to look for are wings mushing around indicating a lack of lift. If you see this, the airspeed is too low.
So a turn is a turn, is a turn. Lift is based on the airspeed (wind over the wings no matter how produced)... Who cares what the ground speed is unless you are late for dinner.
So a turn is a turn, is a turn. Lift is based on the airspeed (wind over the wings no matter how produced)... Who cares what the ground speed is unless you are late for dinner.
09-08-2010 | 11:43 AM
#74
RE: Downwind Turns!!
ORIGINAL: cfircav8r
I'm sorry you feel mocked by my disagreement...
<span style="color: #0000ff"><font size="2">No I don't feel mocked, but amused at your assumption that I would feel mocked. That would have to include some degree of perceived subordination on my part.</font>
</span>
...apparently your vast years of watching your plane plane from the ground and determining why it does what it does means you know better than all of the so called experts that have degrees in aeronautics and for years have been teaching it.
<span style="color: #0000ff"><font size="2">Well if those 'teaching experts' don't include some fairly important variables in their formulas, inertia, time, gravity, acceleration, etc. then yea… I do "know better".</font>
</span>Your friend has to be very aware of wind because he is flying for judges on the ground, has to stay in his box, and needs to start each maneuver at show center.
<span style="color: #0000ff"><font size="2">Actually we were talking engine RPM and prop governors not his show box.</font>
</span>
I'm sorry you feel mocked by my disagreement...
<span style="color: #0000ff"><font size="2">No I don't feel mocked, but amused at your assumption that I would feel mocked. That would have to include some degree of perceived subordination on my part.</font>
</span>
...apparently your vast years of watching your plane plane from the ground and determining why it does what it does means you know better than all of the so called experts that have degrees in aeronautics and for years have been teaching it.
<span style="color: #0000ff"><font size="2">Well if those 'teaching experts' don't include some fairly important variables in their formulas, inertia, time, gravity, acceleration, etc. then yea… I do "know better".</font>
</span>Your friend has to be very aware of wind because he is flying for judges on the ground, has to stay in his box, and needs to start each maneuver at show center.
<span style="color: #0000ff"><font size="2">Actually we were talking engine RPM and prop governors not his show box.</font>
</span>
Here's a challenge professor. If you can explain dissymmetry of lift (helicopter) without punching a hole in your 'wind has no effect' theory than I'll admit I was wrong and might enroll in one of your classes.
</p></font>
09-08-2010 | 01:34 PM
#75
RE: Downwind Turns!!
<font size=''2''>
Here's a challenge professor. If you can explain dissymmetry of lift (helicopter) without punching a hole in your 'wind has no effect' theory than I'll admit I was wrong and might enroll in one of your classes.[img][/img]</p></font>
